This is the Tenth Edition, of Debugging with gdb: the gnu Source-Level Debugger for gdb (GDB) Version Momonga (7.3.1-1m.mo8).
Copyright © 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being “Free Software” and “Free Software Needs Free Documentation”, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below.
(a) The FSF's Back-Cover Text is: “You are free to copy and modify this GNU Manual. Buying copies from GNU Press supports the FSF in developing GNU and promoting software freedom.”
This file describes gdb, the gnu symbolic debugger.
This is the Tenth Edition, for gdb (GDB) Version Momonga (7.3.1-1m.mo8).
Copyright (C) 1988-2010 Free Software Foundation, Inc.
This edition of the GDB manual is dedicated to the memory of Fred Fish. Fred was a long-standing contributor to GDB and to Free software in general. We will miss him.
The purpose of a debugger such as gdb is to allow you to see what is going on “inside” another program while it executes—or what another program was doing at the moment it crashed.
gdb can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act:
You can use gdb to debug programs written in C and C++. For more information, see Supported Languages. For more information, see C and C++.
Support for D is partial. For information on D, see D.
Support for Modula-2 is partial. For information on Modula-2, see Modula-2.
Support for OpenCL C is partial. For information on OpenCL C, see OpenCL C.
Debugging Pascal programs which use sets, subranges, file variables, or nested functions does not currently work. gdb does not support entering expressions, printing values, or similar features using Pascal syntax.
gdb can be used to debug programs written in Fortran, although it may be necessary to refer to some variables with a trailing underscore.
gdb can be used to debug programs written in Objective-C, using either the Apple/NeXT or the GNU Objective-C runtime.
gdb is free software, protected by the gnu General Public License (GPL). The GPL gives you the freedom to copy or adapt a licensed program—but every person getting a copy also gets with it the freedom to modify that copy (which means that they must get access to the source code), and the freedom to distribute further copies. Typical software companies use copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve these freedoms.
Fundamentally, the General Public License is a license which says that you have these freedoms and that you cannot take these freedoms away from anyone else.
The biggest deficiency in the free software community today is not in the software—it is the lack of good free documentation that we can include with the free software. Many of our most important programs do not come with free reference manuals and free introductory texts. Documentation is an essential part of any software package; when an important free software package does not come with a free manual and a free tutorial, that is a major gap. We have many such gaps today.
Consider Perl, for instance. The tutorial manuals that people normally use are non-free. How did this come about? Because the authors of those manuals published them with restrictive terms—no copying, no modification, source files not available—which exclude them from the free software world.
That wasn't the first time this sort of thing happened, and it was far from the last. Many times we have heard a GNU user eagerly describe a manual that he is writing, his intended contribution to the community, only to learn that he had ruined everything by signing a publication contract to make it non-free.
Free documentation, like free software, is a matter of freedom, not price. The problem with the non-free manual is not that publishers charge a price for printed copies—that in itself is fine. (The Free Software Foundation sells printed copies of manuals, too.) The problem is the restrictions on the use of the manual. Free manuals are available in source code form, and give you permission to copy and modify. Non-free manuals do not allow this.
The criteria of freedom for a free manual are roughly the same as for free software. Redistribution (including the normal kinds of commercial redistribution) must be permitted, so that the manual can accompany every copy of the program, both on-line and on paper.
Permission for modification of the technical content is crucial too. When people modify the software, adding or changing features, if they are conscientious they will change the manual too—so they can provide accurate and clear documentation for the modified program. A manual that leaves you no choice but to write a new manual to document a changed version of the program is not really available to our community.
Some kinds of limits on the way modification is handled are acceptable. For example, requirements to preserve the original author's copyright notice, the distribution terms, or the list of authors, are ok. It is also no problem to require modified versions to include notice that they were modified. Even entire sections that may not be deleted or changed are acceptable, as long as they deal with nontechnical topics (like this one). These kinds of restrictions are acceptable because they don't obstruct the community's normal use of the manual.
However, it must be possible to modify all the technical content of the manual, and then distribute the result in all the usual media, through all the usual channels. Otherwise, the restrictions obstruct the use of the manual, it is not free, and we need another manual to replace it.
Please spread the word about this issue. Our community continues to lose manuals to proprietary publishing. If we spread the word that free software needs free reference manuals and free tutorials, perhaps the next person who wants to contribute by writing documentation will realize, before it is too late, that only free manuals contribute to the free software community.
If you are writing documentation, please insist on publishing it under the GNU Free Documentation License or another free documentation license. Remember that this decision requires your approval—you don't have to let the publisher decide. Some commercial publishers will use a free license if you insist, but they will not propose the option; it is up to you to raise the issue and say firmly that this is what you want. If the publisher you are dealing with refuses, please try other publishers. If you're not sure whether a proposed license is free, write to licensing@gnu.org.
You can encourage commercial publishers to sell more free, copylefted manuals and tutorials by buying them, and particularly by buying copies from the publishers that paid for their writing or for major improvements. Meanwhile, try to avoid buying non-free documentation at all. Check the distribution terms of a manual before you buy it, and insist that whoever seeks your business must respect your freedom. Check the history of the book, and try to reward the publishers that have paid or pay the authors to work on it.
The Free Software Foundation maintains a list of free documentation published by other publishers, at http://www.fsf.org/doc/other-free-books.html.
Richard Stallman was the original author of gdb, and of many other gnu programs. Many others have contributed to its development. This section attempts to credit major contributors. One of the virtues of free software is that everyone is free to contribute to it; with regret, we cannot actually acknowledge everyone here. The file ChangeLog in the gdb distribution approximates a blow-by-blow account.
Changes much prior to version 2.0 are lost in the mists of time.
Plea: Additions to this section are particularly welcome. If you or your friends (or enemies, to be evenhanded) have been unfairly omitted from this list, we would like to add your names!
So that they may not regard their many labors as thankless, we particularly thank those who shepherded gdb through major releases: Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0); Jim Blandy (release 4.18); Jason Molenda (release 4.17); Stan Shebs (release 4.14); Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9); Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4); John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4, and 3.3); and Randy Smith (releases 3.2, 3.1, and 3.0).
Richard Stallman, assisted at various times by Peter TerMaat, Chris Hanson, and Richard Mlynarik, handled releases through 2.8.
Michael Tiemann is the author of most of the gnu C++ support in gdb, with significant additional contributions from Per Bothner and Daniel Berlin. James Clark wrote the gnu C++ demangler. Early work on C++ was by Peter TerMaat (who also did much general update work leading to release 3.0).
gdb uses the BFD subroutine library to examine multiple object-file formats; BFD was a joint project of David V. Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
David Johnson wrote the original COFF support; Pace Willison did the original support for encapsulated COFF.
Brent Benson of Harris Computer Systems contributed DWARF 2 support.
Adam de Boor and Bradley Davis contributed the ISI Optimum V support. Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS support. Jean-Daniel Fekete contributed Sun 386i support. Chris Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support. David Johnson contributed Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support. Jeff Law contributed HP PA and SOM support. Keith Packard contributed NS32K support. Doug Rabson contributed Acorn Risc Machine support. Bob Rusk contributed Harris Nighthawk CX-UX support. Chris Smith contributed Convex support (and Fortran debugging). Jonathan Stone contributed Pyramid support. Michael Tiemann contributed SPARC support. Tim Tucker contributed support for the Gould NP1 and Gould Powernode. Pace Willison contributed Intel 386 support. Jay Vosburgh contributed Symmetry support. Marko Mlinar contributed OpenRISC 1000 support.
Andreas Schwab contributed M68K gnu/Linux support.
Rich Schaefer and Peter Schauer helped with support of SunOS shared libraries.
Jay Fenlason and Roland McGrath ensured that gdb and GAS agree about several machine instruction sets.
Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM contributed remote debugging modules for the i960, VxWorks, A29K UDI, and RDI targets, respectively.
Brian Fox is the author of the readline libraries providing command-line editing and command history.
Andrew Beers of SUNY Buffalo wrote the language-switching code, the Modula-2 support, and contributed the Languages chapter of this manual.
Fred Fish wrote most of the support for Unix System Vr4. He also enhanced the command-completion support to cover C++ overloaded symbols.
Hitachi America (now Renesas America), Ltd. sponsored the support for H8/300, H8/500, and Super-H processors.
NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D processors.
Toshiba sponsored the support for the TX39 Mips processor.
Matsushita sponsored the support for the MN10200 and MN10300 processors.
Fujitsu sponsored the support for SPARClite and FR30 processors.
Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware watchpoints.
Michael Snyder added support for tracepoints.
Stu Grossman wrote gdbserver.
Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made nearly innumerable bug fixes and cleanups throughout gdb.
The following people at the Hewlett-Packard Company contributed support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0 (narrow mode), HP's implementation of kernel threads, HP's aC++ compiler, and the Text User Interface (nee Terminal User Interface): Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific information in this manual.
DJ Delorie ported gdb to MS-DOS, for the DJGPP project. Robert Hoehne made significant contributions to the DJGPP port.
Cygnus Solutions has sponsored gdb maintenance and much of its development since 1991. Cygnus engineers who have worked on gdb fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler, Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton, JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner, Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David Zuhn have made contributions both large and small.
Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for Cygnus Solutions, implemented the original gdb/mi interface.
Jim Blandy added support for preprocessor macros, while working for Red Hat.
Andrew Cagney designed gdb's architecture vector. Many people including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick Duffek, Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei Sakamoto, Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason Thorpe, Corinna Vinschen, Ulrich Weigand, and Elena Zannoni, helped with the migration of old architectures to this new framework.
Andrew Cagney completely re-designed and re-implemented gdb's unwinder framework, this consisting of a fresh new design featuring frame IDs, independent frame sniffers, and the sentinel frame. Mark Kettenis implemented the dwarf 2 unwinder, Jeff Johnston the libunwind unwinder, and Andrew Cagney the dummy, sentinel, tramp, and trad unwinders. The architecture-specific changes, each involving a complete rewrite of the architecture's frame code, were carried out by Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich Weigand.
Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from Tensilica, Inc. contributed support for Xtensa processors. Others who have worked on the Xtensa port of gdb in the past include Steve Tjiang, John Newlin, and Scott Foehner.
Michael Eager and staff of Xilinx, Inc., contributed support for the Xilinx MicroBlaze architecture.
You can use this manual at your leisure to read all about gdb. However, a handful of commands are enough to get started using the debugger. This chapter illustrates those commands.
One of the preliminary versions of gnu m4
(a generic macro
processor) exhibits the following bug: sometimes, when we change its
quote strings from the default, the commands used to capture one macro
definition within another stop working. In the following short m4
session, we define a macro foo
which expands to 0000
; we
then use the m4
built-in defn
to define bar
as the
same thing. However, when we change the open quote string to
<QUOTE>
and the close quote string to <UNQUOTE>
, the same
procedure fails to define a new synonym baz
:
$ cd gnu/m4 $ ./m4 define(foo,0000) foo 0000 define(bar,defn(`foo')) bar 0000 changequote(<QUOTE>,<UNQUOTE>) define(baz,defn(<QUOTE>foo<UNQUOTE>)) baz Ctrl-d m4: End of input: 0: fatal error: EOF in string
Let us use gdb to try to see what is going on.
$ gdb m4 gdb is free software and you are welcome to distribute copies of it under certain conditions; type "show copying" to see the conditions. There is absolutely no warranty for gdb; type "show warranty" for details. gdb Momonga (7.3.1-1m.mo8), Copyright 1999 Free Software Foundation, Inc... (gdb)
gdb reads only enough symbol data to know where to find the rest when needed; as a result, the first prompt comes up very quickly. We now tell gdb to use a narrower display width than usual, so that examples fit in this manual.
(gdb) set width 70
We need to see how the m4
built-in changequote
works.
Having looked at the source, we know the relevant subroutine is
m4_changequote
, so we set a breakpoint there with the gdb
break
command.
(gdb) break m4_changequote Breakpoint 1 at 0x62f4: file builtin.c, line 879.
Using the run
command, we start m4
running under gdb
control; as long as control does not reach the m4_changequote
subroutine, the program runs as usual:
(gdb) run Starting program: /work/Editorial/gdb/gnu/m4/m4 define(foo,0000) foo 0000
To trigger the breakpoint, we call changequote
. gdb
suspends execution of m4
, displaying information about the
context where it stops.
changequote(<QUOTE>,<UNQUOTE>) Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) at builtin.c:879 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
Now we use the command n
(next
) to advance execution to
the next line of the current function.
(gdb) n 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\ : nil,
set_quotes
looks like a promising subroutine. We can go into it
by using the command s
(step
) instead of next
.
step
goes to the next line to be executed in any
subroutine, so it steps into set_quotes
.
(gdb) s set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") at input.c:530 530 if (lquote != def_lquote)
The display that shows the subroutine where m4
is now
suspended (and its arguments) is called a stack frame display. It
shows a summary of the stack. We can use the backtrace
command (which can also be spelled bt
), to see where we are
in the stack as a whole: the backtrace
command displays a
stack frame for each active subroutine.
(gdb) bt #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") at input.c:530 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70) at builtin.c:882 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30) at macro.c:71 #4 0x79dc in expand_input () at macro.c:40 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
We step through a few more lines to see what happens. The first two
times, we can use ‘s’; the next two times we use n
to avoid
falling into the xstrdup
subroutine.
(gdb) s 0x3b5c 532 if (rquote != def_rquote) (gdb) s 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \ def_lquote : xstrdup(lq); (gdb) n 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ : xstrdup(rq); (gdb) n 538 len_lquote = strlen(rquote);
The last line displayed looks a little odd; we can examine the variables
lquote
and rquote
to see if they are in fact the new left
and right quotes we specified. We use the command p
(print
) to see their values.
(gdb) p lquote $1 = 0x35d40 "<QUOTE>" (gdb) p rquote $2 = 0x35d50 "<UNQUOTE>"
lquote
and rquote
are indeed the new left and right quotes.
To look at some context, we can display ten lines of source
surrounding the current line with the l
(list
) command.
(gdb) l 533 xfree(rquote); 534 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\ : xstrdup (lq); 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ : xstrdup (rq); 537 538 len_lquote = strlen(rquote); 539 len_rquote = strlen(lquote); 540 } 541 542 void
Let us step past the two lines that set len_lquote
and
len_rquote
, and then examine the values of those variables.
(gdb) n 539 len_rquote = strlen(lquote); (gdb) n 540 } (gdb) p len_lquote $3 = 9 (gdb) p len_rquote $4 = 7
That certainly looks wrong, assuming len_lquote
and
len_rquote
are meant to be the lengths of lquote
and
rquote
respectively. We can set them to better values using
the p
command, since it can print the value of
any expression—and that expression can include subroutine calls and
assignments.
(gdb) p len_lquote=strlen(lquote) $5 = 7 (gdb) p len_rquote=strlen(rquote) $6 = 9
Is that enough to fix the problem of using the new quotes with the
m4
built-in defn
? We can allow m4
to continue
executing with the c
(continue
) command, and then try the
example that caused trouble initially:
(gdb) c Continuing. define(baz,defn(<QUOTE>foo<UNQUOTE>)) baz 0000
Success! The new quotes now work just as well as the default ones. The
problem seems to have been just the two typos defining the wrong
lengths. We allow m4
exit by giving it an EOF as input:
Ctrl-d Program exited normally.
The message ‘Program exited normally.’ is from gdb; it
indicates m4
has finished executing. We can end our gdb
session with the gdb quit
command.
(gdb) quit
This chapter discusses how to start gdb, and how to get out of it. The essentials are:
Invoke gdb by running the program gdb
. Once started,
gdb reads commands from the terminal until you tell it to exit.
You can also run gdb
with a variety of arguments and options,
to specify more of your debugging environment at the outset.
The command-line options described here are designed to cover a variety of situations; in some environments, some of these options may effectively be unavailable.
The most usual way to start gdb is with one argument, specifying an executable program:
gdb program
You can also start with both an executable program and a core file specified:
gdb program core
You can, instead, specify a process ID as a second argument, if you want to debug a running process:
gdb program 1234
would attach gdb to process 1234
(unless you also have a file
named 1234; gdb does check for a core file first).
Taking advantage of the second command-line argument requires a fairly complete operating system; when you use gdb as a remote debugger attached to a bare board, there may not be any notion of “process”, and there is often no way to get a core dump. gdb will warn you if it is unable to attach or to read core dumps.
You can optionally have gdb
pass any arguments after the
executable file to the inferior using --args
. This option stops
option processing.
gdb --args gcc -O2 -c foo.c
This will cause gdb
to debug gcc
, and to set
gcc
's command-line arguments (see Arguments) to ‘-O2 -c foo.c’.
You can run gdb
without printing the front material, which describes
gdb's non-warranty, by specifying -silent
:
gdb -silent
You can further control how gdb starts up by using command-line options. gdb itself can remind you of the options available.
Type
gdb -help
to display all available options and briefly describe their use (‘gdb -h’ is a shorter equivalent).
All options and command line arguments you give are processed in sequential order. The order makes a difference when the ‘-x’ option is used.
When gdb starts, it reads any arguments other than options as specifying an executable file and core file (or process ID). This is the same as if the arguments were specified by the ‘-se’ and ‘-c’ (or ‘-p’) options respectively. (gdb reads the first argument that does not have an associated option flag as equivalent to the ‘-se’ option followed by that argument; and the second argument that does not have an associated option flag, if any, as equivalent to the ‘-c’/‘-p’ option followed by that argument.) If the second argument begins with a decimal digit, gdb will first attempt to attach to it as a process, and if that fails, attempt to open it as a corefile. If you have a corefile whose name begins with a digit, you can prevent gdb from treating it as a pid by prefixing it with ./, e.g. ./12345.
If gdb has not been configured to included core file support, such as for most embedded targets, then it will complain about a second argument and ignore it.
Many options have both long and short forms; both are shown in the following list. gdb also recognizes the long forms if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with ‘--’ rather than ‘-’, though we illustrate the more usual convention.)
-symbols
file-s
file-exec
file-e
file-se
file-core
file-c
file-pid
number-p
numberattach
command.
-command
file-x
filesource
command would.
See Command files.
-eval-command
command-ex
commandThis option may be used multiple times to call multiple commands. It may also be interleaved with ‘-command’ as required.
gdb -ex 'target sim' -ex 'load' \ -x setbreakpoints -ex 'run' a.out
-directory
directory-d
directory-r
-readnow
--readnever
You can run gdb in various alternative modes—for example, in batch mode or quiet mode.
-nx
-n
-quiet
-silent
-q
-batch
0
after processing all the
command files specified with ‘-x’ (and all commands from
initialization files, if not inhibited with ‘-n’). Exit with
nonzero status if an error occurs in executing the gdb commands
in the command files. Batch mode also disables pagination, sets unlimited
terminal width and height see Screen Size, and acts as if set confirm
off were in effect (see Messages/Warnings).
Batch mode may be useful for running gdb as a filter, for example to download and run a program on another computer; in order to make this more useful, the message
Program exited normally.
(which is ordinarily issued whenever a program running under
gdb control terminates) is not issued when running in batch
mode.
-batch-silent
stdout
is prevented (stderr
is
unaffected). This is much quieter than ‘-silent’ and would be useless
for an interactive session.
This is particularly useful when using targets that give ‘Loading section’ messages, for example.
Note that targets that give their output via gdb, as opposed to
writing directly to stdout
, will also be made silent.
-return-child-result
This option is useful in conjunction with ‘-batch’ or ‘-batch-silent’,
when gdb is being used as a remote program loader or simulator
interface.
-nowindows
-nw
-windows
-w
-cd
directory-data-directory
directory-fullname
-f
-epoch
-annotate
levelThe annotation mechanism has largely been superseded by gdb/mi
(see GDB/MI).
--args
-baud
bps-b
bps-l
timeout-tty
device-t
device-P
--python
sys.argv
. This option is only available if Python
scripting support was enabled when gdb was configured.
-tui
-interpreter
interp‘--interpreter=mi’ (or ‘--interpreter=mi2’) causes
gdb to use the gdb/mi interface (see The gdb/mi Interface) included since gdb version 6.0. The
previous gdb/mi interface, included in gdb version 5.3 and
selected with ‘--interpreter=mi1’, is deprecated. Earlier
gdb/mi interfaces are no longer supported.
-write
-statistics
-version
Here's the description of what gdb does during session startup:
If you wish to disable the auto-loading during startup, you must do something like the following:
$ gdb -ex "set auto-load-scripts off" -ex "file myprogram"
The following does not work because the auto-loading is turned off too late:
$ gdb -ex "set auto-load-scripts off" myprogram
Init files use the same syntax as command files (see Command Files) and are processed by gdb in the same way. The init file in your home directory can set options (such as ‘set complaints’) that affect subsequent processing of command line options and operands. Init files are not executed if you use the ‘-nx’ option (see Choosing Modes).
To display the list of init files loaded by gdb at startup, you can use gdb --help.
The gdb init files are normally called .gdbinit. The DJGPP port of gdb uses the name gdb.ini, due to the limitations of file names imposed by DOS filesystems. The Windows ports of gdb use the standard name, but if they find a gdb.ini file, they warn you about that and suggest to rename the file to the standard name.
quit
[expression]q
quit
command (abbreviated
q
), or type an end-of-file character (usually Ctrl-d). If you
do not supply expression, gdb will terminate normally;
otherwise it will terminate using the result of expression as the
error code.
An interrupt (often Ctrl-c) does not exit from gdb, but rather terminates the action of any gdb command that is in progress and returns to gdb command level. It is safe to type the interrupt character at any time because gdb does not allow it to take effect until a time when it is safe.
If you have been using gdb to control an attached process or
device, you can release it with the detach
command
(see Debugging an Already-running Process).
If you need to execute occasional shell commands during your
debugging session, there is no need to leave or suspend gdb; you can
just use the shell
command.
shell
command stringSHELL
determines which
shell to run. Otherwise gdb uses the default shell
(/bin/sh on Unix systems, COMMAND.COM on MS-DOS, etc.).
The utility make
is often needed in development environments.
You do not have to use the shell
command for this purpose in
gdb:
make
make-argsmake
program with the specified
arguments. This is equivalent to ‘shell make make-args’.
You may want to save the output of gdb commands to a file. There are several commands to control gdb's logging.
set logging on
set logging off
set logging file
fileset logging overwrite [on|off]
overwrite
if
you want set logging on
to overwrite the logfile instead.
set logging redirect [on|off]
redirect
if you want output to go only to the log file.
show logging
You can abbreviate a gdb command to the first few letters of the command name, if that abbreviation is unambiguous; and you can repeat certain gdb commands by typing just <RET>. You can also use the <TAB> key to get gdb to fill out the rest of a word in a command (or to show you the alternatives available, if there is more than one possibility).
A gdb command is a single line of input. There is no limit on
how long it can be. It starts with a command name, which is followed by
arguments whose meaning depends on the command name. For example, the
command step
accepts an argument which is the number of times to
step, as in ‘step 5’. You can also use the step
command
with no arguments. Some commands do not allow any arguments.
gdb command names may always be truncated if that abbreviation is
unambiguous. Other possible command abbreviations are listed in the
documentation for individual commands. In some cases, even ambiguous
abbreviations are allowed; for example, s
is specially defined as
equivalent to step
even though there are other commands whose
names start with s
. You can test abbreviations by using them as
arguments to the help
command.
A blank line as input to gdb (typing just <RET>) means to
repeat the previous command. Certain commands (for example, run
)
will not repeat this way; these are commands whose unintentional
repetition might cause trouble and which you are unlikely to want to
repeat. User-defined commands can disable this feature; see
dont-repeat.
The list
and x
commands, when you repeat them with
<RET>, construct new arguments rather than repeating
exactly as typed. This permits easy scanning of source or memory.
gdb can also use <RET> in another way: to partition lengthy
output, in a way similar to the common utility more
(see Screen Size). Since it is easy to press one
<RET> too many in this situation, gdb disables command
repetition after any command that generates this sort of display.
Any text from a # to the end of the line is a comment; it does nothing. This is useful mainly in command files (see Command Files).
The Ctrl-o binding is useful for repeating a complex sequence of commands. This command accepts the current line, like <RET>, and then fetches the next line relative to the current line from the history for editing.
gdb can fill in the rest of a word in a command for you, if there is only one possibility; it can also show you what the valid possibilities are for the next word in a command, at any time. This works for gdb commands, gdb subcommands, and the names of symbols in your program.
Press the <TAB> key whenever you want gdb to fill out the rest of a word. If there is only one possibility, gdb fills in the word, and waits for you to finish the command (or press <RET> to enter it). For example, if you type
(gdb) info bre <TAB>
gdb fills in the rest of the word ‘breakpoints’, since that is
the only info
subcommand beginning with ‘bre’:
(gdb) info breakpoints
You can either press <RET> at this point, to run the info
breakpoints
command, or backspace and enter something else, if
‘breakpoints’ does not look like the command you expected. (If you
were sure you wanted info breakpoints
in the first place, you
might as well just type <RET> immediately after ‘info bre’,
to exploit command abbreviations rather than command completion).
If there is more than one possibility for the next word when you press <TAB>, gdb sounds a bell. You can either supply more characters and try again, or just press <TAB> a second time; gdb displays all the possible completions for that word. For example, you might want to set a breakpoint on a subroutine whose name begins with ‘make_’, but when you type b make_<TAB> gdb just sounds the bell. Typing <TAB> again displays all the function names in your program that begin with those characters, for example:
(gdb) b make_ <TAB>
gdb sounds bell; press <TAB> again, to see:
make_a_section_from_file make_environ make_abs_section make_function_type make_blockvector make_pointer_type make_cleanup make_reference_type make_command make_symbol_completion_list (gdb) b make_
After displaying the available possibilities, gdb copies your partial input (‘b make_’ in the example) so you can finish the command.
If you just want to see the list of alternatives in the first place, you can press M-? rather than pressing <TAB> twice. M-? means <META> ?. You can type this either by holding down a key designated as the <META> shift on your keyboard (if there is one) while typing ?, or as <ESC> followed by ?.
Sometimes the string you need, while logically a “word”, may contain
parentheses or other characters that gdb normally excludes from
its notion of a word. To permit word completion to work in this
situation, you may enclose words in '
(single quote marks) in
gdb commands.
The most likely situation where you might need this is in typing the
name of a C++ function. This is because C++ allows function
overloading (multiple definitions of the same function, distinguished
by argument type). For example, when you want to set a breakpoint you
may need to distinguish whether you mean the version of name
that takes an int
parameter, name(int)
, or the version
that takes a float
parameter, name(float)
. To use the
word-completion facilities in this situation, type a single quote
'
at the beginning of the function name. This alerts
gdb that it may need to consider more information than usual
when you press <TAB> or M-? to request word completion:
(gdb) b 'bubble( M-? bubble(double,double) bubble(int,int) (gdb) b 'bubble(
In some cases, gdb can tell that completing a name requires using quotes. When this happens, gdb inserts the quote for you (while completing as much as it can) if you do not type the quote in the first place:
(gdb) b bub <TAB>
gdb alters your input line to the following, and rings a bell:
(gdb) b 'bubble(
In general, gdb can tell that a quote is needed (and inserts it) if you have not yet started typing the argument list when you ask for completion on an overloaded symbol.
For more information about overloaded functions, see C++ Expressions. You can use the command set
overload-resolution off
to disable overload resolution;
see gdb Features for C++.
When completing in an expression which looks up a field in a structure, gdb also tries2 to limit completions to the field names available in the type of the left-hand-side:
(gdb) p gdb_stdout.M-? magic to_delete to_fputs to_put to_rewind to_data to_flush to_isatty to_read to_write
This is because the gdb_stdout
is a variable of the type
struct ui_file
that is defined in gdb sources as
follows:
struct ui_file { int *magic; ui_file_flush_ftype *to_flush; ui_file_write_ftype *to_write; ui_file_fputs_ftype *to_fputs; ui_file_read_ftype *to_read; ui_file_delete_ftype *to_delete; ui_file_isatty_ftype *to_isatty; ui_file_rewind_ftype *to_rewind; ui_file_put_ftype *to_put; void *to_data; }
You can always ask gdb itself for information on its commands,
using the command help
.
help
h
help
(abbreviated h
) with no arguments to
display a short list of named classes of commands:
(gdb) help List of classes of commands: aliases -- Aliases of other commands breakpoints -- Making program stop at certain points data -- Examining data files -- Specifying and examining files internals -- Maintenance commands obscure -- Obscure features running -- Running the program stack -- Examining the stack status -- Status inquiries support -- Support facilities tracepoints -- Tracing of program execution without stopping the program user-defined -- User-defined commands Type "help" followed by a class name for a list of commands in that class. Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (gdb)
help
classstatus
:
(gdb) help status Status inquiries. List of commands: info -- Generic command for showing things about the program being debugged show -- Generic command for showing things about the debugger Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (gdb)
help
commandhelp
argument, gdb displays a
short paragraph on how to use that command.
apropos
argsapropos
command searches through all of the gdb
commands, and their documentation, for the regular expression specified in
args. It prints out all matches found. For example:
apropos reload
results in:
set symbol-reloading -- Set dynamic symbol table reloading multiple times in one run show symbol-reloading -- Show dynamic symbol table reloading multiple times in one run
complete
argscomplete
args command lists all the possible completions
for the beginning of a command. Use args to specify the beginning of the
command you want completed. For example:
complete i
results in:
if ignore info inspect
This is intended for use by gnu Emacs.
In addition to help
, you can use the gdb commands info
and show
to inquire about the state of your program, or the state
of gdb itself. Each command supports many topics of inquiry; this
manual introduces each of them in the appropriate context. The listings
under info
and under show
in the Index point to
all the sub-commands. See Index.
info
i
) is for describing the state of your
program. For example, you can show the arguments passed to a function
with info args
, list the registers currently in use with info
registers
, or list the breakpoints you have set with info breakpoints
.
You can get a complete list of the info
sub-commands with
help info
.
set
set
. For example, you can set the gdb prompt to a $-sign with
set prompt $
.
show
info
, show
is for describing the state of
gdb itself.
You can change most of the things you can show
, by using the
related command set
; for example, you can control what number
system is used for displays with set radix
, or simply inquire
which is currently in use with show radix
.
To display all the settable parameters and their current
values, you can use show
with no arguments; you may also use
info set
. Both commands produce the same display.
Here are three miscellaneous show
subcommands, all of which are
exceptional in lacking corresponding set
commands:
show version
show copying
info copying
show warranty
info warranty
When you run a program under gdb, you must first generate debugging information when you compile it.
You may start gdb with its arguments, if any, in an environment of your choice. If you are doing native debugging, you may redirect your program's input and output, debug an already running process, or kill a child process.
In order to debug a program effectively, you need to generate debugging information when you compile it. This debugging information is stored in the object file; it describes the data type of each variable or function and the correspondence between source line numbers and addresses in the executable code.
To request debugging information, specify the ‘-g’ option when you run the compiler.
Programs that are to be shipped to your customers are compiled with optimizations, using the ‘-O’ compiler option. However, some compilers are unable to handle the ‘-g’ and ‘-O’ options together. Using those compilers, you cannot generate optimized executables containing debugging information.
gcc, the gnu C/C++ compiler, supports ‘-g’ with or without ‘-O’, making it possible to debug optimized code. We recommend that you always use ‘-g’ whenever you compile a program. You may think your program is correct, but there is no sense in pushing your luck. For more information, see Optimized Code.
Older versions of the gnu C compiler permitted a variant option ‘-gg’ for debugging information. gdb no longer supports this format; if your gnu C compiler has this option, do not use it.
gdb knows about preprocessor macros and can show you their expansion (see Macros). Most compilers do not include information about preprocessor macros in the debugging information if you specify the -g flag alone, because this information is rather large. Version 3.1 and later of gcc, the gnu C compiler, provides macro information if you specify the options -gdwarf-2 and -g3; the former option requests debugging information in the Dwarf 2 format, and the latter requests “extra information”. In the future, we hope to find more compact ways to represent macro information, so that it can be included with -g alone.
run
r
run
command to start your program under gdb.
You must first specify the program name (except on VxWorks) with an
argument to gdb (see Getting In and Out of gdb), or by using the file
or exec-file
command
(see Commands to Specify Files).
If you are running your program in an execution environment that
supports processes, run
creates an inferior process and makes
that process run your program. In some environments without processes,
run
jumps to the start of your program. Other targets,
like ‘remote’, are always running. If you get an error
message like this one:
The "remote" target does not support "run". Try "help target" or "continue".
then use continue
to run your program. You may need load
first (see load).
The execution of a program is affected by certain information it receives from its superior. gdb provides ways to specify this information, which you must do before starting your program. (You can change it after starting your program, but such changes only affect your program the next time you start it.) This information may be divided into four categories:
run
command. If a shell is available on your target, the shell
is used to pass the arguments, so that you may use normal conventions
(such as wildcard expansion or variable substitution) in describing
the arguments.
In Unix systems, you can control which shell is used with the
SHELL
environment variable.
See Your Program's Arguments.
set environment
and unset
environment
to change parts of the environment that affect
your program. See Your Program's Environment.
cd
command in gdb.
See Your Program's Working Directory.
run
command line, or you can use the tty
command to
set a different device for your program.
See Your Program's Input and Output.
Warning: While input and output redirection work, you cannot use pipes to pass the output of the program you are debugging to another program; if you attempt this, gdb is likely to wind up debugging the wrong program.
When you issue the run
command, your program begins to execute
immediately. See Stopping and Continuing, for discussion
of how to arrange for your program to stop. Once your program has
stopped, you may call functions in your program, using the print
or call
commands. See Examining Data.
If the modification time of your symbol file has changed since the last time gdb read its symbols, gdb discards its symbol table, and reads it again. When it does this, gdb tries to retain your current breakpoints.
start
main
, but
other languages such as Ada do not require a specific name for their
main procedure. The debugger provides a convenient way to start the
execution of the program and to stop at the beginning of the main
procedure, depending on the language used.
The ‘start’ command does the equivalent of setting a temporary breakpoint at the beginning of the main procedure and then invoking the ‘run’ command.
Some programs contain an elaboration phase where some startup code is
executed before the main procedure is called. This depends on the
languages used to write your program. In C++, for instance,
constructors for static and global objects are executed before
main
is called. It is therefore possible that the debugger stops
before reaching the main procedure. However, the temporary breakpoint
will remain to halt execution.
Specify the arguments to give to your program as arguments to the ‘start’ command. These arguments will be given verbatim to the underlying ‘run’ command. Note that the same arguments will be reused if no argument is provided during subsequent calls to ‘start’ or ‘run’.
It is sometimes necessary to debug the program during elaboration. In
these cases, using the start
command would stop the execution of
your program too late, as the program would have already completed the
elaboration phase. Under these circumstances, insert breakpoints in your
elaboration code before running your program.
set exec-wrapper
wrappershow exec-wrapper
unset exec-wrapper
You can use any program that eventually calls execve
with
its arguments as a wrapper. Several standard Unix utilities do
this, e.g. env
and nohup
. Any Unix shell script ending
with exec "$@"
will also work.
For example, you can use env
to pass an environment variable to
the debugged program, without setting the variable in your shell's
environment:
(gdb) set exec-wrapper env 'LD_PRELOAD=libtest.so' (gdb) run
This command is available when debugging locally on most targets, excluding djgpp, Cygwin, MS Windows, and QNX Neutrino.
set disable-randomization
set disable-randomization on
This feature is implemented only on gnu/Linux. You can get the same behavior using
(gdb) set exec-wrapper setarch `uname -m` -R
set disable-randomization off
The virtual address space randomization is implemented only on gnu/Linux. It protects the programs against some kinds of security attacks. In these cases the attacker needs to know the exact location of a concrete executable code. Randomizing its location makes it impossible to inject jumps misusing a code at its expected addresses.
Prelinking shared libraries provides a startup performance advantage but it makes addresses in these libraries predictable for privileged processes by having just unprivileged access at the target system. Reading the shared library binary gives enough information for assembling the malicious code misusing it. Still even a prelinked shared library can get loaded at a new random address just requiring the regular relocation process during the startup. Shared libraries not already prelinked are always loaded at a randomly chosen address.
Position independent executables (PIE) contain position independent code similar to the shared libraries and therefore such executables get loaded at a randomly chosen address upon startup. PIE executables always load even already prelinked shared libraries at a random address. You can build such executable using gcc -fPIE -pie.
Heap (malloc storage), stack and custom mmap areas are always placed randomly
(as long as the randomization is enabled).
show disable-randomization
The arguments to your program can be specified by the arguments of the
run
command.
They are passed to a shell, which expands wildcard characters and
performs redirection of I/O, and thence to your program. Your
SHELL
environment variable (if it exists) specifies what shell
gdb uses. If you do not define SHELL
, gdb uses
the default shell (/bin/sh on Unix).
On non-Unix systems, the program is usually invoked directly by gdb, which emulates I/O redirection via the appropriate system calls, and the wildcard characters are expanded by the startup code of the program, not by the shell.
run
with no arguments uses the same arguments used by the previous
run
, or those set by the set args
command.
set args
set args
has no arguments, run
executes your program
with no arguments. Once you have run your program with arguments,
using set args
before the next run
is the only way to run
it again without arguments.
show args
The environment consists of a set of environment variables and their values. Environment variables conventionally record such things as your user name, your home directory, your terminal type, and your search path for programs to run. Usually you set up environment variables with the shell and they are inherited by all the other programs you run. When debugging, it can be useful to try running your program with a modified environment without having to start gdb over again.
path
directoryPATH
environment variable
(the search path for executables) that will be passed to your program.
The value of PATH
used by gdb does not change.
You may specify several directory names, separated by whitespace or by a
system-dependent separator character (‘:’ on Unix, ‘;’ on
MS-DOS and MS-Windows). If directory is already in the path, it
is moved to the front, so it is searched sooner.
You can use the string ‘$cwd’ to refer to whatever is the current
working directory at the time gdb searches the path. If you
use ‘.’ instead, it refers to the directory where you executed the
path
command. gdb replaces ‘.’ in the
directory argument (with the current path) before adding
directory to the search path.
show paths
PATH
environment variable).
show environment
[varname]environment
as env
.
set environment
varname [=
value]For example, this command:
set env USER = foo
tells the debugged program, when subsequently run, that its user is named ‘foo’. (The spaces around ‘=’ are used for clarity here; they are not actually required.)
unset environment
varnameunset environment
removes the variable from the environment,
rather than assigning it an empty value.
Warning: On Unix systems, gdb runs your program using
the shell indicated
by your SHELL
environment variable if it exists (or
/bin/sh
if not). If your SHELL
variable names a shell
that runs an initialization file—such as .cshrc for C-shell, or
.bashrc for BASH—any variables you set in that file affect
your program. You may wish to move setting of environment variables to
files that are only run when you sign on, such as .login or
.profile.
Each time you start your program with run
, it inherits its
working directory from the current working directory of gdb.
The gdb working directory is initially whatever it inherited
from its parent process (typically the shell), but you can specify a new
working directory in gdb with the cd
command.
The gdb working directory also serves as a default for the commands that specify files for gdb to operate on. See Commands to Specify Files.
It is generally impossible to find the current working directory of
the process being debugged (since a program can change its directory
during its run). If you work on a system where gdb is
configured with the /proc support, you can use the info
proc
command (see SVR4 Process Information) to find out the
current working directory of the debuggee.
By default, the program you run under gdb does input and output to the same terminal that gdb uses. gdb switches the terminal to its own terminal modes to interact with you, but it records the terminal modes your program was using and switches back to them when you continue running your program.
info terminal
You can redirect your program's input and/or output using shell
redirection with the run
command. For example,
run > outfile
starts your program, diverting its output to the file outfile.
Another way to specify where your program should do input and output is
with the tty
command. This command accepts a file name as
argument, and causes this file to be the default for future run
commands. It also resets the controlling terminal for the child
process, for future run
commands. For example,
tty /dev/ttyb
directs that processes started with subsequent run
commands
default to do input and output on the terminal /dev/ttyb and have
that as their controlling terminal.
An explicit redirection in run
overrides the tty
command's
effect on the input/output device, but not its effect on the controlling
terminal.
When you use the tty
command or redirect input in the run
command, only the input for your program is affected. The input
for gdb still comes from your terminal. tty
is an alias
for set inferior-tty
.
You can use the show inferior-tty
command to tell gdb to
display the name of the terminal that will be used for future runs of your
program.
set inferior-tty /dev/ttyb
show inferior-tty
attach
process-idinfo files
shows your active
targets.) The command takes as argument a process ID. The usual way to
find out the process-id of a Unix process is with the ps
utility,
or with the ‘jobs -l’ shell command.
attach
does not repeat if you press <RET> a second time after
executing the command.
To use attach
, your program must be running in an environment
which supports processes; for example, attach
does not work for
programs on bare-board targets that lack an operating system. You must
also have permission to send the process a signal.
When you use attach
, the debugger finds the program running in
the process first by looking in the current working directory, then (if
the program is not found) by using the source file search path
(see Specifying Source Directories). You can also use
the file
command to load the program. See Commands to Specify Files.
The first thing gdb does after arranging to debug the specified
process is to stop it. You can examine and modify an attached process
with all the gdb commands that are ordinarily available when
you start processes with run
. You can insert breakpoints; you
can step and continue; you can modify storage. If you would rather the
process continue running, you may use the continue
command after
attaching gdb to the process.
detach
detach
command to release it from gdb control. Detaching
the process continues its execution. After the detach
command,
that process and gdb become completely independent once more, and you
are ready to attach
another process or start one with run
.
detach
does not repeat if you press <RET> again after
executing the command.
If you exit gdb while you have an attached process, you detach
that process. If you use the run
command, you kill that process.
By default, gdb asks for confirmation if you try to do either of these
things; you can control whether or not you need to confirm by using the
set confirm
command (see Optional Warnings and Messages).
kill
This command is useful if you wish to debug a core dump instead of a running process. gdb ignores any core dump file while your program is running.
On some operating systems, a program cannot be executed outside gdb
while you have breakpoints set on it inside gdb. You can use the
kill
command in this situation to permit running your program
outside the debugger.
The kill
command is also useful if you wish to recompile and
relink your program, since on many systems it is impossible to modify an
executable file while it is running in a process. In this case, when you
next type run
, gdb notices that the file has changed, and
reads the symbol table again (while trying to preserve your current
breakpoint settings).
gdb lets you run and debug multiple programs in a single session. In addition, gdb on some systems may let you run several programs simultaneously (otherwise you have to exit from one before starting another). In the most general case, you can have multiple threads of execution in each of multiple processes, launched from multiple executables.
gdb represents the state of each program execution with an object called an inferior. An inferior typically corresponds to a process, but is more general and applies also to targets that do not have processes. Inferiors may be created before a process runs, and may be retained after a process exits. Inferiors have unique identifiers that are different from process ids. Usually each inferior will also have its own distinct address space, although some embedded targets may have several inferiors running in different parts of a single address space. Each inferior may in turn have multiple threads running in it.
To find out what inferiors exist at any moment, use info inferiors
:
info inferiors
gdb displays for each inferior (in this order):
An asterisk ‘*’ preceding the gdb inferior number indicates the current inferior.
For example,
(gdb) info inferiors Num Description Executable 2 process 2307 hello * 1 process 3401 goodbye
To switch focus between inferiors, use the inferior
command:
inferior
infnoYou can get multiple executables into a debugging session via the
add-inferior
and clone-inferior
commands. On some
systems gdb can add inferiors to the debug session
automatically by following calls to fork
and exec
. To
remove inferiors from the debugging session use the
remove-inferiors
command.
add-inferior [ -copies
n ] [ -exec
executable ]
file
command with the executable name as its argument.
clone-inferior [ -copies
n ] [
infno ]
(gdb) info inferiors Num Description Executable * 1 process 29964 helloworld (gdb) clone-inferior Added inferior 2. 1 inferiors added. (gdb) info inferiors Num Description Executable 2 <null> helloworld * 1 process 29964 helloworld
You can now simply switch focus to inferior 2 and run it.
remove-inferiors
infno...
kill
or detach
command first.
To quit debugging one of the running inferiors that is not the current
inferior, you can either detach from it by using the detach inferior
command (allowing it to run independently), or kill it
using the kill inferiors
command:
detach inferior
infno...
info inferiors
,
but its Description will show ‘<null>’.
kill inferiors
infno...
info inferiors
, but its
Description will show ‘<null>’.
After the successful completion of a command such as detach
,
detach inferiors
, kill
or kill inferiors
, or after
a normal process exit, the inferior is still valid and listed with
info inferiors
, ready to be restarted.
To be notified when inferiors are started or exit under gdb's
control use set print inferior-events
:
set print inferior-events
set print inferior-events on
set print inferior-events off
set print inferior-events
command allows you to enable or
disable printing of messages when gdb notices that new
inferiors have started or that inferiors have exited or have been
detached. By default, these messages will not be printed.
show print inferior-events
Many commands will work the same with multiple programs as with a
single program: e.g., print myglobal
will simply display the
value of myglobal
in the current inferior.
Occasionaly, when debugging gdb itself, it may be useful to
get more info about the relationship of inferiors, programs, address
spaces in a debug session. You can do that with the maint info program-spaces
command.
maint info program-spaces
gdb displays for each program space (in this order):
file
command.
An asterisk ‘*’ preceding the gdb program space number indicates the current program space.
In addition, below each program space line, gdb prints extra information that isn't suitable to display in tabular form. For example, the list of inferiors bound to the program space.
(gdb) maint info program-spaces Id Executable 2 goodbye Bound inferiors: ID 1 (process 21561) * 1 hello
Here we can see that no inferior is running the program hello
,
while process 21561
is running the program goodbye
. On
some targets, it is possible that multiple inferiors are bound to the
same program space. The most common example is that of debugging both
the parent and child processes of a vfork
call. For example,
(gdb) maint info program-spaces Id Executable * 1 vfork-test Bound inferiors: ID 2 (process 18050), ID 1 (process 18045)
Here, both inferior 2 and inferior 1 are running in the same program
space as a result of inferior 1 having executed a vfork
call.
In some operating systems, such as HP-UX and Solaris, a single program may have more than one thread of execution. The precise semantics of threads differ from one operating system to another, but in general the threads of a single program are akin to multiple processes—except that they share one address space (that is, they can all examine and modify the same variables). On the other hand, each thread has its own registers and execution stack, and perhaps private memory.
gdb provides these facilities for debugging multi-thread programs:
libthread_db
to use if the default choice
isn't compatible with the program.
Warning: These facilities are not yet available on every gdb configuration where the operating system supports threads. If your gdb does not support threads, these commands have no effect. For example, a system without thread support shows no output from ‘info threads’, and always rejects thethread
command, like this:(gdb) info threads (gdb) thread 1 Thread ID 1 not known. Use the "info threads" command to see the IDs of currently known threads.
The gdb thread debugging facility allows you to observe all threads while your program runs—but whenever gdb takes control, one thread in particular is always the focus of debugging. This thread is called the current thread. Debugging commands show program information from the perspective of the current thread.
Whenever gdb detects a new thread in your program, it displays the target system's identification for the thread with a message in the form ‘[New systag]’. systag is a thread identifier whose form varies depending on the particular system. For example, on gnu/Linux, you might see
[New Thread 0x41e02940 (LWP 25582)]
when gdb notices a new thread. In contrast, on an SGI system, the systag is simply something like ‘process 368’, with no further qualifier.
For debugging purposes, gdb associates its own thread number—always a single integer—with each thread in your program.
info threads
[id...
]thread name
, below), or, in some cases, by the
program itself.
An asterisk ‘*’ to the left of the gdb thread number indicates the current thread.
For example,
(gdb) info threads Id Target Id Frame 3 process 35 thread 27 0x34e5 in sigpause () 2 process 35 thread 23 0x34e5 in sigpause () * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8) at threadtest.c:68
On Solaris, you can display more information about user threads with a Solaris-specific command:
maint info sol-threads
thread
threadno(gdb) thread 2 [Switching to thread 2 (Thread 0xb7fdab70 (LWP 12747))] #0 some_function (ignore=0x0) at example.c:8 8 printf ("hello\n");
As with the ‘[New ...]’ message, the form of the text after ‘Switching to’ depends on your system's conventions for identifying threads.
The debugger convenience variable ‘$_thread’ contains the number of the current thread. You may find this useful in writing breakpoint conditional expressions, command scripts, and so forth. See See Convenience Variables, for general information on convenience variables.
thread apply [
threadno | all]
commandthread apply
command allows you to apply the named
command to one or more threads. Specify the numbers of the
threads that you want affected with the command argument
threadno. It can be a single thread number, one of the numbers
shown in the first field of the ‘info threads’ display; or it
could be a range of thread numbers, as in 2-4
. To apply a
command to all threads, type thread apply all command.
thread name [
name]
On some systems, such as gnu/Linux, gdb is able to determine the name of the thread as given by the OS. On these systems, a name specified with ‘thread name’ will override the system-give name, and removing the user-specified name will cause gdb to once again display the system-specified name.
thread find [
regexp]
As well as being the complement to the ‘thread name’ command, this command also allows you to identify a thread by its target systag. For instance, on gnu/Linux, the target systag is the LWP id.
(gdb) thread find 26688 Thread 4 has target id 'Thread 0x41e02940 (LWP 26688)' (gdb) info thread 4 Id Target Id Frame 4 Thread 0x41e02940 (LWP 26688) 0x00000031ca6cd372 in select ()
set print thread-events
set print thread-events on
set print thread-events off
set print thread-events
command allows you to enable or
disable printing of messages when gdb notices that new threads have
started or that threads have exited. By default, these messages will
be printed if detection of these events is supported by the target.
Note that these messages cannot be disabled on all targets.
show print thread-events
See Stopping and Starting Multi-thread Programs, for more information about how gdb behaves when you stop and start programs with multiple threads.
See Setting Watchpoints, for information about watchpoints in programs with multiple threads.
set libthread-db-search-path
[path]libthread_db
.
If you omit path, ‘libthread-db-search-path’ will be reset to
an empty list.
On gnu/Linux and Solaris systems, gdb uses a “helper”
libthread_db
library to obtain information about threads in the
inferior process. gdb will use ‘libthread-db-search-path’
to find libthread_db
. If that fails, gdb will continue
with default system shared library directories, and finally the directory
from which libpthread
was loaded in the inferior process.
For any libthread_db
library gdb finds in above directories,
gdb attempts to initialize it with the current inferior process.
If this initialization fails (which could happen because of a version
mismatch between libthread_db
and libpthread
), gdb
will unload libthread_db
, and continue with the next directory.
If none of libthread_db
libraries initialize successfully,
gdb will issue a warning and thread debugging will be disabled.
Setting libthread-db-search-path
is currently implemented
only on some platforms.
show libthread-db-search-path
set debug libthread-db
show debug libthread-db
libthread_db
-related events.
Use 1
to enable, 0
to disable.
On most systems, gdb has no special support for debugging
programs which create additional processes using the fork
function. When a program forks, gdb will continue to debug the
parent process and the child process will run unimpeded. If you have
set a breakpoint in any code which the child then executes, the child
will get a SIGTRAP
signal which (unless it catches the signal)
will cause it to terminate.
However, if you want to debug the child process there is a workaround
which isn't too painful. Put a call to sleep
in the code which
the child process executes after the fork. It may be useful to sleep
only if a certain environment variable is set, or a certain file exists,
so that the delay need not occur when you don't want to run gdb
on the child. While the child is sleeping, use the ps
program to
get its process ID. Then tell gdb (a new invocation of
gdb if you are also debugging the parent process) to attach to
the child process (see Attach). From that point on you can debug
the child process just like any other process which you attached to.
On some systems, gdb provides support for debugging programs that
create additional processes using the fork
or vfork
functions.
Currently, the only platforms with this feature are HP-UX (11.x and later
only?) and gnu/Linux (kernel version 2.5.60 and later).
By default, when a program forks, gdb will continue to debug the parent process and the child process will run unimpeded.
If you want to follow the child process instead of the parent process,
use the command set follow-fork-mode
.
set follow-fork-mode
modefork
or
vfork
. A call to fork
or vfork
creates a new
process. The mode argument can be:
parent
child
show follow-fork-mode
fork
or vfork
call.
On Linux, if you want to debug both the parent and child processes, use the
command set detach-on-fork
.
set detach-on-fork
modeon
follow-fork-mode
) will be detached and allowed to run
independently. This is the default.
off
follow-fork-mode
) is debugged as usual, while the other
is held suspended.
show detach-on-fork
If you choose to set ‘detach-on-fork’ mode off, then gdb
will retain control of all forked processes (including nested forks).
You can list the forked processes under the control of gdb by
using the info inferiors
command, and switch from one fork
to another by using the inferior
command (see Debugging Multiple Inferiors and Programs).
To quit debugging one of the forked processes, you can either detach
from it by using the detach inferiors
command (allowing it
to run independently), or kill it using the kill inferiors
command. See Debugging Multiple Inferiors and Programs.
If you ask to debug a child process and a vfork
is followed by an
exec
, gdb executes the new target up to the first
breakpoint in the new target. If you have a breakpoint set on
main
in your original program, the breakpoint will also be set on
the child process's main
.
On some systems, when a child process is spawned by vfork
, you
cannot debug the child or parent until an exec
call completes.
If you issue a run
command to gdb after an exec
call executes, the new target restarts. To restart the parent
process, use the file
command with the parent executable name
as its argument. By default, after an exec
call executes,
gdb discards the symbols of the previous executable image.
You can change this behaviour with the set follow-exec-mode
command.
set follow-exec-mode
modeexec
. An
exec
call replaces the program image of a process.
follow-exec-mode
can be:
new
exec
call can be restarted afterwards by restarting the
original inferior.
For example:
(gdb) info inferiors (gdb) info inferior Id Description Executable * 1 <null> prog1 (gdb) run process 12020 is executing new program: prog2 Program exited normally. (gdb) info inferiors Id Description Executable * 2 <null> prog2 1 <null> prog1
same
exec
call, with
e.g., the run
command, restarts the executable the process was
running after the exec
call. This is the default mode.
For example:
(gdb) info inferiors Id Description Executable * 1 <null> prog1 (gdb) run process 12020 is executing new program: prog2 Program exited normally. (gdb) info inferiors Id Description Executable * 1 <null> prog2
You can use the catch
command to make gdb stop whenever
a fork
, vfork
, or exec
call is made. See Setting Catchpoints.
On certain operating systems3, gdb is able to save a snapshot of a program's state, called a checkpoint, and come back to it later.
Returning to a checkpoint effectively undoes everything that has
happened in the program since the checkpoint
was saved. This
includes changes in memory, registers, and even (within some limits)
system state. Effectively, it is like going back in time to the
moment when the checkpoint was saved.
Thus, if you're stepping thru a program and you think you're getting close to the point where things go wrong, you can save a checkpoint. Then, if you accidentally go too far and miss the critical statement, instead of having to restart your program from the beginning, you can just go back to the checkpoint and start again from there.
This can be especially useful if it takes a lot of time or steps to reach the point where you think the bug occurs.
To use the checkpoint
/restart
method of debugging:
checkpoint
checkpoint
command takes no arguments, but each checkpoint
is assigned a small integer id, similar to a breakpoint id.
info checkpoints
Checkpoint ID
Process ID
Code Address
Source line, or label
restart
checkpoint-idNote that breakpoints, gdb variables, command history etc. are not affected by restoring a checkpoint. In general, a checkpoint only restores things that reside in the program being debugged, not in the debugger.
delete checkpoint
checkpoint-idReturning to a previously saved checkpoint will restore the user state of the program being debugged, plus a significant subset of the system (OS) state, including file pointers. It won't “un-write” data from a file, but it will rewind the file pointer to the previous location, so that the previously written data can be overwritten. For files opened in read mode, the pointer will also be restored so that the previously read data can be read again.
Of course, characters that have been sent to a printer (or other external device) cannot be “snatched back”, and characters received from eg. a serial device can be removed from internal program buffers, but they cannot be “pushed back” into the serial pipeline, ready to be received again. Similarly, the actual contents of files that have been changed cannot be restored (at this time).
However, within those constraints, you actually can “rewind” your program to a previously saved point in time, and begin debugging it again — and you can change the course of events so as to debug a different execution path this time.
Finally, there is one bit of internal program state that will be different when you return to a checkpoint — the program's process id. Each checkpoint will have a unique process id (or pid), and each will be different from the program's original pid. If your program has saved a local copy of its process id, this could potentially pose a problem.
On some systems such as gnu/Linux, address space randomization is performed on new processes for security reasons. This makes it difficult or impossible to set a breakpoint, or watchpoint, on an absolute address if you have to restart the program, since the absolute location of a symbol will change from one execution to the next.
A checkpoint, however, is an identical copy of a process. Therefore if you create a checkpoint at (eg.) the start of main, and simply return to that checkpoint instead of restarting the process, you can avoid the effects of address randomization and your symbols will all stay in the same place.
The principal purposes of using a debugger are so that you can stop your program before it terminates; or so that, if your program runs into trouble, you can investigate and find out why.
Inside gdb, your program may stop for any of several reasons,
such as a signal, a breakpoint, or reaching a new line after a
gdb command such as step
. You may then examine and
change variables, set new breakpoints or remove old ones, and then
continue execution. Usually, the messages shown by gdb provide
ample explanation of the status of your program—but you can also
explicitly request this information at any time.
info program
A breakpoint makes your program stop whenever a certain point in
the program is reached. For each breakpoint, you can add conditions to
control in finer detail whether your program stops. You can set
breakpoints with the break
command and its variants (see Setting Breakpoints), to specify the place where your program
should stop by line number, function name or exact address in the
program.
On some systems, you can set breakpoints in shared libraries before
the executable is run. There is a minor limitation on HP-UX systems:
you must wait until the executable is run in order to set breakpoints
in shared library routines that are not called directly by the program
(for example, routines that are arguments in a pthread_create
call).
A watchpoint is a special breakpoint that stops your program when the value of an expression changes. The expression may be a value of a variable, or it could involve values of one or more variables combined by operators, such as ‘a + b’. This is sometimes called data breakpoints. You must use a different command to set watchpoints (see Setting Watchpoints), but aside from that, you can manage a watchpoint like any other breakpoint: you enable, disable, and delete both breakpoints and watchpoints using the same commands.
You can arrange to have values from your program displayed automatically whenever gdb stops at a breakpoint. See Automatic Display.
A catchpoint is another special breakpoint that stops your program
when a certain kind of event occurs, such as the throwing of a C++
exception or the loading of a library. As with watchpoints, you use a
different command to set a catchpoint (see Setting Catchpoints), but aside from that, you can manage a catchpoint like any
other breakpoint. (To stop when your program receives a signal, use the
handle
command; see Signals.)
gdb assigns a number to each breakpoint, watchpoint, or catchpoint when you create it; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be enabled or disabled; if disabled, it has no effect on your program until you enable it again.
Some gdb commands accept a range of breakpoints on which to operate. A breakpoint range is either a single breakpoint number, like ‘5’, or two such numbers, in increasing order, separated by a hyphen, like ‘5-7’. When a breakpoint range is given to a command, all breakpoints in that range are operated on.
Breakpoints are set with the break
command (abbreviated
b
). The debugger convenience variable ‘$bpnum’ records the
number of the breakpoint you've set most recently; see Convenience Variables, for a discussion of what you can do with
convenience variables.
break
locationWhen using source languages that permit overloading of symbols, such as C++, a function name may refer to more than one possible place to break. See Ambiguous Expressions, for a discussion of that situation.
It is also possible to insert a breakpoint that will stop the program
only if a specific thread (see Thread-Specific Breakpoints)
or a specific task (see Ada Tasks) hits that breakpoint.
break
break
sets a breakpoint at
the next instruction to be executed in the selected stack frame
(see Examining the Stack). In any selected frame but the
innermost, this makes your program stop as soon as control
returns to that frame. This is similar to the effect of a
finish
command in the frame inside the selected frame—except
that finish
does not leave an active breakpoint. If you use
break
without an argument in the innermost frame, gdb stops
the next time it reaches the current location; this may be useful
inside loops.
gdb normally ignores breakpoints when it resumes execution, until at
least one instruction has been executed. If it did not do this, you
would be unable to proceed past a breakpoint without first disabling the
breakpoint. This rule applies whether or not the breakpoint already
existed when your program stopped.
break ... if
condtbreak
argsbreak
command, and the breakpoint is set in the same
way, but the breakpoint is automatically deleted after the first time your
program stops there. See Disabling Breakpoints.
hbreak
argsbreak
command and the breakpoint is set in the same way, but the
breakpoint requires hardware support and some target hardware may not
have this support. The main purpose of this is EPROM/ROM code
debugging, so you can set a breakpoint at an instruction without
changing the instruction. This can be used with the new trap-generation
provided by SPARClite DSU and most x86-based targets. These targets
will generate traps when a program accesses some data or instruction
address that is assigned to the debug registers. However the hardware
breakpoint registers can take a limited number of breakpoints. For
example, on the DSU, only two data breakpoints can be set at a time, and
gdb will reject this command if more than two are used. Delete
or disable unused hardware breakpoints before setting new ones
(see Disabling Breakpoints).
See Break Conditions.
For remote targets, you can restrict the number of hardware
breakpoints gdb will use, see set remote hardware-breakpoint-limit.
thbreak
argshbreak
command and the breakpoint is set in
the same way. However, like the tbreak
command,
the breakpoint is automatically deleted after the
first time your program stops there. Also, like the hbreak
command, the breakpoint requires hardware support and some target hardware
may not have this support. See Disabling Breakpoints.
See also Break Conditions.
rbreak
regexbreak
command. You can delete them, disable them, or make
them conditional the same way as any other breakpoint.
The syntax of the regular expression is the standard one used with tools
like grep. Note that this is different from the syntax used by
shells, so for instance foo*
matches all functions that include
an fo
followed by zero or more o
s. There is an implicit
.*
leading and trailing the regular expression you supply, so to
match only functions that begin with foo
, use ^foo
.
When debugging C++ programs, rbreak
is useful for setting
breakpoints on overloaded functions that are not members of any special
classes.
The rbreak
command can be used to set breakpoints in
all the functions in a program, like this:
(gdb) rbreak .
rbreak
file:
regexrbreak
is called with a filename qualification, it limits
the search for functions matching the given regular expression to the
specified file. This can be used, for example, to set breakpoints on
every function in a given file:
(gdb) rbreak file.c:.
The colon separating the filename qualifier from the regex may optionally be surrounded by spaces.
info breakpoints
[n...
]info break
[n...
]If a breakpoint is conditional, info break
shows the condition on
the line following the affected breakpoint; breakpoint commands, if any,
are listed after that. A pending breakpoint is allowed to have a condition
specified for it. The condition is not parsed for validity until a shared
library is loaded that allows the pending breakpoint to resolve to a
valid location.
info break
with a breakpoint
number n as argument lists only that breakpoint. The
convenience variable $_
and the default examining-address for
the x
command are set to the address of the last breakpoint
listed (see Examining Memory).
info break
displays a count of the number of times the breakpoint
has been hit. This is especially useful in conjunction with the
ignore
command. You can ignore a large number of breakpoint
hits, look at the breakpoint info to see how many times the breakpoint
was hit, and then run again, ignoring one less than that number. This
will get you quickly to the last hit of that breakpoint.
gdb allows you to set any number of breakpoints at the same place in your program. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (see Break Conditions).
It is possible that a breakpoint corresponds to several locations in your program. Examples of this situation are:
In all those cases, gdb will insert a breakpoint at all the relevant locations4.
A breakpoint with multiple locations is displayed in the breakpoint table using several rows—one header row, followed by one row for each breakpoint location. The header row has ‘<MULTIPLE>’ in the address column. The rows for individual locations contain the actual addresses for locations, and show the functions to which those locations belong. The number column for a location is of the form breakpoint-number.location-number.
For example:
Num Type Disp Enb Address What 1 breakpoint keep y <MULTIPLE> stop only if i==1 breakpoint already hit 1 time 1.1 y 0x080486a2 in void foo<int>() at t.cc:8 1.2 y 0x080486ca in void foo<double>() at t.cc:8
Each location can be individually enabled or disabled by passing
breakpoint-number.location-number as argument to the
enable
and disable
commands. Note that you cannot
delete the individual locations from the list, you can only delete the
entire list of locations that belong to their parent breakpoint (with
the delete num command, where num is the number of
the parent breakpoint, 1 in the above example). Disabling or enabling
the parent breakpoint (see Disabling) affects all of the locations
that belong to that breakpoint.
It's quite common to have a breakpoint inside a shared library. Shared libraries can be loaded and unloaded explicitly, and possibly repeatedly, as the program is executed. To support this use case, gdb updates breakpoint locations whenever any shared library is loaded or unloaded. Typically, you would set a breakpoint in a shared library at the beginning of your debugging session, when the library is not loaded, and when the symbols from the library are not available. When you try to set breakpoint, gdb will ask you if you want to set a so called pending breakpoint—breakpoint whose address is not yet resolved.
After the program is run, whenever a new shared library is loaded, gdb reevaluates all the breakpoints. When a newly loaded shared library contains the symbol or line referred to by some pending breakpoint, that breakpoint is resolved and becomes an ordinary breakpoint. When a library is unloaded, all breakpoints that refer to its symbols or source lines become pending again.
This logic works for breakpoints with multiple locations, too. For example, if you have a breakpoint in a C++ template function, and a newly loaded shared library has an instantiation of that template, a new location is added to the list of locations for the breakpoint.
Except for having unresolved address, pending breakpoints do not differ from regular breakpoints. You can set conditions or commands, enable and disable them and perform other breakpoint operations.
gdb provides some additional commands for controlling what happens when the ‘break’ command cannot resolve breakpoint address specification to an address:
set breakpoint pending auto
set breakpoint pending on
set breakpoint pending off
show breakpoint pending
The settings above only affect the break
command and its
variants. Once breakpoint is set, it will be automatically updated
as shared libraries are loaded and unloaded.
For some targets, gdb can automatically decide if hardware or
software breakpoints should be used, depending on whether the
breakpoint address is read-only or read-write. This applies to
breakpoints set with the break
command as well as to internal
breakpoints set by commands like next
and finish
. For
breakpoints set with hbreak
, gdb will always use hardware
breakpoints.
You can control this automatic behaviour with the following commands::
set breakpoint auto-hw on
set breakpoint auto-hw off
gdb normally implements breakpoints by replacing the program code at the breakpoint address with a special instruction, which, when executed, given control to the debugger. By default, the program code is so modified only when the program is resumed. As soon as the program stops, gdb restores the original instructions. This behaviour guards against leaving breakpoints inserted in the target should gdb abrubptly disconnect. However, with slow remote targets, inserting and removing breakpoint can reduce the performance. This behavior can be controlled with the following commands::
set breakpoint always-inserted off
set breakpoint always-inserted on
set breakpoint always-inserted auto
breakpoint always-inserted
mode is on. If gdb is
controlling the inferior in all-stop mode, gdb behaves as if
breakpoint always-inserted
mode is off.
gdb itself sometimes sets breakpoints in your program for
special purposes, such as proper handling of longjmp
(in C
programs). These internal breakpoints are assigned negative numbers,
starting with -1
; ‘info breakpoints’ does not display them.
You can see these breakpoints with the gdb maintenance command
‘maint info breakpoints’ (see maint info breakpoints).
You can use a watchpoint to stop execution whenever the value of an expression changes, without having to predict a particular place where this may happen. (This is sometimes called a data breakpoint.) The expression may be as simple as the value of a single variable, or as complex as many variables combined by operators. Examples include:
int
occupies 4 bytes).
You can set a watchpoint on an expression even if the expression can
not be evaluated yet. For instance, you can set a watchpoint on
‘*global_ptr’ before ‘global_ptr’ is initialized.
gdb will stop when your program sets ‘global_ptr’ and
the expression produces a valid value. If the expression becomes
valid in some other way than changing a variable (e.g. if the memory
pointed to by ‘*global_ptr’ becomes readable as the result of a
malloc
call), gdb may not stop until the next time
the expression changes.
Depending on your system, watchpoints may be implemented in software or hardware. gdb does software watchpointing by single-stepping your program and testing the variable's value each time, which is hundreds of times slower than normal execution. (But this may still be worth it, to catch errors where you have no clue what part of your program is the culprit.)
On some systems, such as HP-UX, PowerPC, gnu/Linux and most other x86-based targets, gdb includes support for hardware watchpoints, which do not slow down the running of your program.
watch
[-l
|-location
] expr [thread
threadnum](gdb) watch foo
If the command includes a [thread
threadnum]
clause, gdb breaks only when the thread identified by
threadnum changes the value of expr. If any other threads
change the value of expr, gdb will not break. Note
that watchpoints restricted to a single thread in this way only work
with Hardware Watchpoints.
Ordinarily a watchpoint respects the scope of variables in expr
(see below). The -location
argument tells gdb to
instead watch the memory referred to by expr. In this case,
gdb will evaluate expr, take the address of the result,
and watch the memory at that address. The type of the result is used
to determine the size of the watched memory. If the expression's
result does not have an address, then gdb will print an
error.
rwatch
[-l
|-location
] expr [thread
threadnum]awatch
[-l
|-location
] expr [thread
threadnum]info watchpoints
[n...
]info break
(see Set Breaks).
If you watch for a change in a numerically entered address you need to dereference it, as the address itself is just a constant number which will never change. gdb refuses to create a watchpoint that watches a never-changing value:
(gdb) watch 0x600850 Cannot watch constant value 0x600850. (gdb) watch *(int *) 0x600850 Watchpoint 1: *(int *) 6293584
gdb sets a hardware watchpoint if possible. Hardware watchpoints execute very quickly, and the debugger reports a change in value at the exact instruction where the change occurs. If gdb cannot set a hardware watchpoint, it sets a software watchpoint, which executes more slowly and reports the change in value at the next statement, not the instruction, after the change occurs.
You can force gdb to use only software watchpoints with the
set can-use-hw-watchpoints 0 command. With this variable set to
zero, gdb will never try to use hardware watchpoints, even if
the underlying system supports them. (Note that hardware-assisted
watchpoints that were set before setting
can-use-hw-watchpoints
to zero will still use the hardware
mechanism of watching expression values.)
set can-use-hw-watchpoints
show can-use-hw-watchpoints
For remote targets, you can restrict the number of hardware watchpoints gdb will use, see set remote hardware-breakpoint-limit.
When you issue the watch
command, gdb reports
Hardware watchpoint num: expr
if it was able to set a hardware watchpoint.
Currently, the awatch
and rwatch
commands can only set
hardware watchpoints, because accesses to data that don't change the
value of the watched expression cannot be detected without examining
every instruction as it is being executed, and gdb does not do
that currently. If gdb finds that it is unable to set a
hardware breakpoint with the awatch
or rwatch
command, it
will print a message like this:
Expression cannot be implemented with read/access watchpoint.
Sometimes, gdb cannot set a hardware watchpoint because the data type of the watched expression is wider than what a hardware watchpoint on the target machine can handle. For example, some systems can only watch regions that are up to 4 bytes wide; on such systems you cannot set hardware watchpoints for an expression that yields a double-precision floating-point number (which is typically 8 bytes wide). As a work-around, it might be possible to break the large region into a series of smaller ones and watch them with separate watchpoints.
If you set too many hardware watchpoints, gdb might be unable to insert all of them when you resume the execution of your program. Since the precise number of active watchpoints is unknown until such time as the program is about to be resumed, gdb might not be able to warn you about this when you set the watchpoints, and the warning will be printed only when the program is resumed:
Hardware watchpoint num: Could not insert watchpoint
If this happens, delete or disable some of the watchpoints.
Watching complex expressions that reference many variables can also exhaust the resources available for hardware-assisted watchpoints. That's because gdb needs to watch every variable in the expression with separately allocated resources.
If you call a function interactively using print
or call
,
any watchpoints you have set will be inactive until gdb reaches another
kind of breakpoint or the call completes.
gdb automatically deletes watchpoints that watch local
(automatic) variables, or expressions that involve such variables, when
they go out of scope, that is, when the execution leaves the block in
which these variables were defined. In particular, when the program
being debugged terminates, all local variables go out of scope,
and so only watchpoints that watch global variables remain set. If you
rerun the program, you will need to set all such watchpoints again. One
way of doing that would be to set a code breakpoint at the entry to the
main
function and when it breaks, set all the watchpoints.
In multi-threaded programs, watchpoints will detect changes to the watched expression from every thread.
Warning: In multi-threaded programs, software watchpoints have only limited usefulness. If gdb creates a software watchpoint, it can only watch the value of an expression in a single thread. If you are confident that the expression can only change due to the current thread's activity (and if you are also confident that no other thread can become current), then you can use software watchpoints as usual. However, gdb may not notice when a non-current thread's activity changes the expression. (Hardware watchpoints, in contrast, watch an expression in all threads.)
See set remote hardware-watchpoint-limit.
You can use catchpoints to cause the debugger to stop for certain
kinds of program events, such as C++ exceptions or the loading of a
shared library. Use the catch
command to set a catchpoint.
catch
eventthrow
catch
exception
catch exception Program_Error
),
the debugger will stop only when this specific exception is raised.
Otherwise, the debugger stops execution when any Ada exception is raised.
When inserting an exception catchpoint on a user-defined exception whose
name is identical to one of the exceptions defined by the language, the
fully qualified name must be used as the exception name. Otherwise,
gdb will assume that it should stop on the pre-defined exception
rather than the user-defined one. For instance, assuming an exception
called Constraint_Error
is defined in package Pck
, then
the command to use to catch such exceptions is catch exception
Pck.Constraint_Error.
exception unhandled
assert
exec
exec
. This is currently only available for HP-UX
and gnu/Linux.
syscall
syscall
[name | number] ...
name can be any system call name that is valid for the underlying OS. Just what syscalls are valid depends on the OS. On GNU and Unix systems, you can find the full list of valid syscall names on /usr/include/asm/unistd.h.
Normally, gdb knows in advance which syscalls are valid for each OS, so you can use the gdb command-line completion facilities (see command completion) to list the available choices.
You may also specify the system call numerically. A syscall's number is the value passed to the OS's syscall dispatcher to identify the requested service. When you specify the syscall by its name, gdb uses its database of syscalls to convert the name into the corresponding numeric code, but using the number directly may be useful if gdb's database does not have the complete list of syscalls on your system (e.g., because gdb lags behind the OS upgrades).
The example below illustrates how this command works if you don't provide arguments to it:
(gdb) catch syscall Catchpoint 1 (syscall) (gdb) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'close'), \ 0xffffe424 in __kernel_vsyscall () (gdb) c Continuing. Catchpoint 1 (returned from syscall 'close'), \ 0xffffe424 in __kernel_vsyscall () (gdb)
Here is an example of catching a system call by name:
(gdb) catch syscall chroot Catchpoint 1 (syscall 'chroot' [61]) (gdb) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'chroot'), \ 0xffffe424 in __kernel_vsyscall () (gdb) c Continuing. Catchpoint 1 (returned from syscall 'chroot'), \ 0xffffe424 in __kernel_vsyscall () (gdb)
An example of specifying a system call numerically. In the case below, the syscall number has a corresponding entry in the XML file, so gdb finds its name and prints it:
(gdb) catch syscall 252 Catchpoint 1 (syscall(s) 'exit_group') (gdb) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'exit_group'), \ 0xffffe424 in __kernel_vsyscall () (gdb) c Continuing. Program exited normally. (gdb)
However, there can be situations when there is no corresponding name in XML file for that syscall number. In this case, gdb prints a warning message saying that it was not able to find the syscall name, but the catchpoint will be set anyway. See the example below:
(gdb) catch syscall 764 warning: The number '764' does not represent a known syscall. Catchpoint 2 (syscall 764) (gdb)
If you configure gdb using the ‘--without-expat’ option, it will not be able to display syscall names. Also, if your architecture does not have an XML file describing its system calls, you will not be able to see the syscall names. It is important to notice that these two features are used for accessing the syscall name database. In either case, you will see a warning like this:
(gdb) catch syscall warning: Could not open "syscalls/i386-linux.xml" warning: Could not load the syscall XML file 'syscalls/i386-linux.xml'. GDB will not be able to display syscall names. Catchpoint 1 (syscall) (gdb)
Of course, the file name will change depending on your architecture and system.
Still using the example above, you can also try to catch a syscall by its number. In this case, you would see something like:
(gdb) catch syscall 252 Catchpoint 1 (syscall(s) 252)
Again, in this case gdb would not be able to display syscall's names.
fork
fork
. This is currently only available for HP-UX
and gnu/Linux.
vfork
vfork
. This is currently only available for HP-UX
and gnu/Linux.
tcatch
eventUse the info break
command to list the current catchpoints.
There are currently some limitations to C++ exception handling
(catch throw
and catch catch
) in gdb:
Sometimes catch
is not the best way to debug exception handling:
if you need to know exactly where an exception is raised, it is better to
stop before the exception handler is called, since that way you
can see the stack before any unwinding takes place. If you set a
breakpoint in an exception handler instead, it may not be easy to find
out where the exception was raised.
To stop just before an exception handler is called, you need some
knowledge of the implementation. In the case of gnu C++, exceptions are
raised by calling a library function named __raise_exception
which has the following ANSI C interface:
/* addr is where the exception identifier is stored. id is the exception identifier. */ void __raise_exception (void **addr, void *id);
To make the debugger catch all exceptions before any stack
unwinding takes place, set a breakpoint on __raise_exception
(see Breakpoints; Watchpoints; and Exceptions).
With a conditional breakpoint (see Break Conditions) that depends on the value of id, you can stop your program when a specific exception is raised. You can use multiple conditional breakpoints to stop your program when any of a number of exceptions are raised.
It is often necessary to eliminate a breakpoint, watchpoint, or catchpoint once it has done its job and you no longer want your program to stop there. This is called deleting the breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten.
With the clear
command you can delete breakpoints according to
where they are in your program. With the delete
command you can
delete individual breakpoints, watchpoints, or catchpoints by specifying
their breakpoint numbers.
It is not necessary to delete a breakpoint to proceed past it. gdb automatically ignores breakpoints on the first instruction to be executed when you continue execution without changing the execution address.
clear
clear
locationclear
functionclear
filename:
functionclear
linenumclear
filename:
linenumdelete
[breakpoints
] [range...
]set
confirm off
). You can abbreviate this command as d
.
Rather than deleting a breakpoint, watchpoint, or catchpoint, you might prefer to disable it. This makes the breakpoint inoperative as if it had been deleted, but remembers the information on the breakpoint so that you can enable it again later.
You disable and enable breakpoints, watchpoints, and catchpoints with
the enable
and disable
commands, optionally specifying
one or more breakpoint numbers as arguments. Use info break
to
print a list of all breakpoints, watchpoints, and catchpoints if you
do not know which numbers to use.
Disabling and enabling a breakpoint that has multiple locations affects all of its locations.
A breakpoint, watchpoint, or catchpoint can have any of four different states of enablement:
break
command starts out in this state.
tbreak
command starts out in this state.
You can use the following commands to enable or disable breakpoints, watchpoints, and catchpoints:
disable
[breakpoints
] [range...
]disable
as dis
.
enable
[breakpoints
] [range...
]enable
[breakpoints
] once
range...
enable
[breakpoints
] delete
range...
tbreak
command start out in this state.
Except for a breakpoint set with tbreak
(see Setting Breakpoints), breakpoints that you set are initially enabled;
subsequently, they become disabled or enabled only when you use one of
the commands above. (The command until
can set and delete a
breakpoint of its own, but it does not change the state of your other
breakpoints; see Continuing and Stepping.)
The simplest sort of breakpoint breaks every time your program reaches a specified place. You can also specify a condition for a breakpoint. A condition is just a Boolean expression in your programming language (see Expressions). A breakpoint with a condition evaluates the expression each time your program reaches it, and your program stops only if the condition is true.
This is the converse of using assertions for program validation; in that situation, you want to stop when the assertion is violated—that is, when the condition is false. In C, if you want to test an assertion expressed by the condition assert, you should set the condition ‘! assert’ on the appropriate breakpoint.
Conditions are also accepted for watchpoints; you may not need them, since a watchpoint is inspecting the value of an expression anyhow—but it might be simpler, say, to just set a watchpoint on a variable name, and specify a condition that tests whether the new value is an interesting one.
Break conditions can have side effects, and may even call functions in your program. This can be useful, for example, to activate functions that log program progress, or to use your own print functions to format special data structures. The effects are completely predictable unless there is another enabled breakpoint at the same address. (In that case, gdb might see the other breakpoint first and stop your program without checking the condition of this one.) Note that breakpoint commands are usually more convenient and flexible than break conditions for the purpose of performing side effects when a breakpoint is reached (see Breakpoint Command Lists).
Break conditions can be specified when a breakpoint is set, by using
‘if’ in the arguments to the break
command. See Setting Breakpoints. They can also be changed at any time
with the condition
command.
You can also use the if
keyword with the watch
command.
The catch
command does not recognize the if
keyword;
condition
is the only way to impose a further condition on a
catchpoint.
condition
bnum expressioncondition
, gdb checks expression immediately for
syntactic correctness, and to determine whether symbols in it have
referents in the context of your breakpoint. If expression uses
symbols not referenced in the context of the breakpoint, gdb
prints an error message:
No symbol "foo" in current context.
gdb does
not actually evaluate expression at the time the condition
command (or a command that sets a breakpoint with a condition, like
break if ...
) is given, however. See Expressions.
condition
bnumA special case of a breakpoint condition is to stop only when the breakpoint has been reached a certain number of times. This is so useful that there is a special way to do it, using the ignore count of the breakpoint. Every breakpoint has an ignore count, which is an integer. Most of the time, the ignore count is zero, and therefore has no effect. But if your program reaches a breakpoint whose ignore count is positive, then instead of stopping, it just decrements the ignore count by one and continues. As a result, if the ignore count value is n, the breakpoint does not stop the next n times your program reaches it.
ignore
bnum countTo make the breakpoint stop the next time it is reached, specify a count of zero.
When you use continue
to resume execution of your program from a
breakpoint, you can specify an ignore count directly as an argument to
continue
, rather than using ignore
. See Continuing and Stepping.
If a breakpoint has a positive ignore count and a condition, the condition is not checked. Once the ignore count reaches zero, gdb resumes checking the condition.
You could achieve the effect of the ignore count with a condition such as ‘$foo-- <= 0’ using a debugger convenience variable that is decremented each time. See Convenience Variables.
Ignore counts apply to breakpoints, watchpoints, and catchpoints.
You can give any breakpoint (or watchpoint or catchpoint) a series of commands to execute when your program stops due to that breakpoint. For example, you might want to print the values of certain expressions, or enable other breakpoints.
commands
[range...
]...
command-list ...
end
end
to terminate the commands.
To remove all commands from a breakpoint, type commands
and
follow it immediately with end
; that is, give no commands.
With no argument, commands
refers to the last breakpoint,
watchpoint, or catchpoint set (not to the breakpoint most recently
encountered). If the most recent breakpoints were set with a single
command, then the commands
will apply to all the breakpoints
set by that command. This applies to breakpoints set by
rbreak
, and also applies when a single break
command
creates multiple breakpoints (see Ambiguous Expressions).
Pressing <RET> as a means of repeating the last gdb command is disabled within a command-list.
You can use breakpoint commands to start your program up again. Simply
use the continue
command, or step
, or any other command
that resumes execution.
Any other commands in the command list, after a command that resumes
execution, are ignored. This is because any time you resume execution
(even with a simple next
or step
), you may encounter
another breakpoint—which could have its own command list, leading to
ambiguities about which list to execute.
If the first command you specify in a command list is silent
, the
usual message about stopping at a breakpoint is not printed. This may
be desirable for breakpoints that are to print a specific message and
then continue. If none of the remaining commands print anything, you
see no sign that the breakpoint was reached. silent
is
meaningful only at the beginning of a breakpoint command list.
The commands echo
, output
, and printf
allow you to
print precisely controlled output, and are often useful in silent
breakpoints. See Commands for Controlled Output.
For example, here is how you could use breakpoint commands to print the
value of x
at entry to foo
whenever x
is positive.
break foo if x>0 commands silent printf "x is %d\n",x cont end
One application for breakpoint commands is to compensate for one bug so
you can test for another. Put a breakpoint just after the erroneous line
of code, give it a condition to detect the case in which something
erroneous has been done, and give it commands to assign correct values
to any variables that need them. End with the continue
command
so that your program does not stop, and start with the silent
command so that no output is produced. Here is an example:
break 403 commands silent set x = y + 4 cont end
To save breakpoint definitions to a file use the save breakpoints
command.
save breakpoints [
filename]
source
command (see Command Files). Note that watchpoints
with expressions involving local variables may fail to be recreated
because it may not be possible to access the context where the
watchpoint is valid anymore. Because the saved breakpoint definitions
are simply a sequence of gdb commands that recreate the
breakpoints, you can edit the file in your favorite editing program,
and remove the breakpoint definitions you're not interested in, or
that can no longer be recreated.
The gnu/Linux tool SystemTap
provides a way for
applications to embed static probes, using sys/sdt.h. gdb
can list the available probes, and you can put breakpoints at the
probe points (see Specify Location).
You can examine the available SystemTap
static probes using
info probes
:
info probes [
provider [
name [
objfile]]]
SystemTap
static probes.
If given, provider is a regular expression used to select which providers to list. If omitted, all providers are listed.
If given, name is a regular expression used to select which probes to list. If omitted, all probes are listed.
If given, objfile is a regular expression used to select which object files (executable or shared libraries) to examine. If not given, all object files are considered.
A probe may specify up to ten arguments. These are available at the
point at which the probe is defined—that is, when the current PC is
at the probe's location. The arguments are available using the
convenience variables (see Convenience Vars)
$_probe_arg0
...$_probe_arg9
. Each probe argument is
an integer of the appropriate size; types are not preserved. The
convenience variable $_probe_argc
holds the number of arguments
at the current probe point.
These variables are always available, but attempts to access them at any location other than a probe point will cause gdb to give an error.
If you request too many active hardware-assisted breakpoints and watchpoints, you will see this error message:
Stopped; cannot insert breakpoints. You may have requested too many hardware breakpoints and watchpoints.
This message is printed when you attempt to resume the program, since only then gdb knows exactly how many hardware breakpoints and watchpoints it needs to insert.
When this message is printed, you need to disable or remove some of the hardware-assisted breakpoints and watchpoints, and then continue.
Some processor architectures place constraints on the addresses at which breakpoints may be placed. For architectures thus constrained, gdb will attempt to adjust the breakpoint's address to comply with the constraints dictated by the architecture.
One example of such an architecture is the Fujitsu FR-V. The FR-V is a VLIW architecture in which a number of RISC-like instructions may be bundled together for parallel execution. The FR-V architecture constrains the location of a breakpoint instruction within such a bundle to the instruction with the lowest address. gdb honors this constraint by adjusting a breakpoint's address to the first in the bundle.
It is not uncommon for optimized code to have bundles which contain instructions from different source statements, thus it may happen that a breakpoint's address will be adjusted from one source statement to another. Since this adjustment may significantly alter gdb's breakpoint related behavior from what the user expects, a warning is printed when the breakpoint is first set and also when the breakpoint is hit.
A warning like the one below is printed when setting a breakpoint that's been subject to address adjustment:
warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.
Such warnings are printed both for user settable and gdb's internal breakpoints. If you see one of these warnings, you should verify that a breakpoint set at the adjusted address will have the desired affect. If not, the breakpoint in question may be removed and other breakpoints may be set which will have the desired behavior. E.g., it may be sufficient to place the breakpoint at a later instruction. A conditional breakpoint may also be useful in some cases to prevent the breakpoint from triggering too often.
gdb will also issue a warning when stopping at one of these adjusted breakpoints:
warning: Breakpoint 1 address previously adjusted from 0x00010414 to 0x00010410.
When this warning is encountered, it may be too late to take remedial action except in cases where the breakpoint is hit earlier or more frequently than expected.
Continuing means resuming program execution until your program
completes normally. In contrast, stepping means executing just
one more “step” of your program, where “step” may mean either one
line of source code, or one machine instruction (depending on what
particular command you use). Either when continuing or when stepping,
your program may stop even sooner, due to a breakpoint or a signal. (If
it stops due to a signal, you may want to use handle
, or use
‘signal 0’ to resume execution. See Signals.)
continue
[ignore-count]c
[ignore-count]fg
[ignore-count]ignore
(see Break Conditions).
The argument ignore-count is meaningful only when your program
stopped due to a breakpoint. At other times, the argument to
continue
is ignored.
The synonyms c
and fg
(for foreground, as the
debugged program is deemed to be the foreground program) are provided
purely for convenience, and have exactly the same behavior as
continue
.
To resume execution at a different place, you can use return
(see Returning from a Function) to go back to the
calling function; or jump
(see Continuing at a Different Address) to go to an arbitrary location in your program.
A typical technique for using stepping is to set a breakpoint (see Breakpoints; Watchpoints; and Catchpoints) at the beginning of the function or the section of your program where a problem is believed to lie, run your program until it stops at that breakpoint, and then step through the suspect area, examining the variables that are interesting, until you see the problem happen.
step
s
.
Warning: If you use thestep
command while control is within a function that was compiled without debugging information, execution proceeds until control reaches a function that does have debugging information. Likewise, it will not step into a function which is compiled without debugging information. To step through functions without debugging information, use thestepi
command, described below.
The step
command only stops at the first instruction of a source
line. This prevents the multiple stops that could otherwise occur in
switch
statements, for
loops, etc. step
continues
to stop if a function that has debugging information is called within
the line. In other words, step
steps inside any functions
called within the line.
Also, the step
command only enters a function if there is line
number information for the function. Otherwise it acts like the
next
command. This avoids problems when using cc -gl
on MIPS machines. Previously, step
entered subroutines if there
was any debugging information about the routine.
step
countstep
, but do so count times. If a
breakpoint is reached, or a signal not related to stepping occurs before
count steps, stepping stops right away.
next
[count]step
, but function calls that appear within
the line of code are executed without stopping. Execution stops when
control reaches a different line of code at the original stack level
that was executing when you gave the next
command. This command
is abbreviated n
.
An argument count is a repeat count, as for step
.
The next
command only stops at the first instruction of a
source line. This prevents multiple stops that could otherwise occur in
switch
statements, for
loops, etc.
set step-mode
set step-mode on
set step-mode on
command causes the step
command to
stop at the first instruction of a function which contains no debug line
information rather than stepping over it.
This is useful in cases where you may be interested in inspecting the
machine instructions of a function which has no symbolic info and do not
want gdb to automatically skip over this function.
set step-mode off
step
command to step over any functions which contains no
debug information. This is the default.
show step-mode
finish
fin
.
Contrast this with the return
command (see Returning from a Function).
until
u
next
command, except that when until
encounters a jump, it
automatically continues execution until the program counter is greater
than the address of the jump.
This means that when you reach the end of a loop after single stepping
though it, until
makes your program continue execution until it
exits the loop. In contrast, a next
command at the end of a loop
simply steps back to the beginning of the loop, which forces you to step
through the next iteration.
until
always stops your program if it attempts to exit the current
stack frame.
until
may produce somewhat counterintuitive results if the order
of machine code does not match the order of the source lines. For
example, in the following excerpt from a debugging session, the f
(frame
) command shows that execution is stopped at line
206
; yet when we use until
, we get to line 195
:
(gdb) f #0 main (argc=4, argv=0xf7fffae8) at m4.c:206 206 expand_input(); (gdb) until 195 for ( ; argc > 0; NEXTARG) {
This happened because, for execution efficiency, the compiler had
generated code for the loop closure test at the end, rather than the
start, of the loop—even though the test in a C for
-loop is
written before the body of the loop. The until
command appeared
to step back to the beginning of the loop when it advanced to this
expression; however, it has not really gone to an earlier
statement—not in terms of the actual machine code.
until
with no argument works by means of single
instruction stepping, and hence is slower than until
with an
argument.
until
locationu
locationuntil
without an argument. The specified
location is actually reached only if it is in the current frame. This
implies that until
can be used to skip over recursive function
invocations. For instance in the code below, if the current location is
line 96
, issuing until 99
will execute the program up to
line 99
in the same invocation of factorial, i.e., after the inner
invocations have returned.
94 int factorial (int value) 95 { 96 if (value > 1) { 97 value *= factorial (value - 1); 98 } 99 return (value); 100 }
advance
locationuntil
, but advance
will
not skip over recursive function calls, and the target location doesn't
have to be in the same frame as the current one.
stepi
stepi
argsi
It is often useful to do ‘display/i $pc’ when stepping by machine instructions. This makes gdb automatically display the next instruction to be executed, each time your program stops. See Automatic Display.
An argument is a repeat count, as in step
.
nexti
nexti
argni
An argument is a repeat count, as in next
.
A signal is an asynchronous event that can happen in a program. The
operating system defines the possible kinds of signals, and gives each
kind a name and a number. For example, in Unix SIGINT
is the
signal a program gets when you type an interrupt character (often Ctrl-c);
SIGSEGV
is the signal a program gets from referencing a place in
memory far away from all the areas in use; SIGALRM
occurs when
the alarm clock timer goes off (which happens only if your program has
requested an alarm).
Some signals, including SIGALRM
, are a normal part of the
functioning of your program. Others, such as SIGSEGV
, indicate
errors; these signals are fatal (they kill your program immediately) if the
program has not specified in advance some other way to handle the signal.
SIGINT
does not indicate an error in your program, but it is normally
fatal so it can carry out the purpose of the interrupt: to kill the program.
gdb has the ability to detect any occurrence of a signal in your program. You can tell gdb in advance what to do for each kind of signal.
Normally, gdb is set up to let the non-erroneous signals like
SIGALRM
be silently passed to your program
(so as not to interfere with their role in the program's functioning)
but to stop your program immediately whenever an error signal happens.
You can change these settings with the handle
command.
info signals
info handle
info signals
siginfo handle
is an alias for info signals
.
handle
signal [keywords...
]The keywords allowed by the handle
command can be abbreviated.
Their full names are:
nostop
stop
print
keyword as well.
print
noprint
nostop
keyword as well.
pass
noignore
pass
and noignore
are synonyms.
nopass
ignore
nopass
and ignore
are synonyms.
When a signal stops your program, the signal is not visible to the
program until you
continue. Your program sees the signal then, if pass
is in
effect for the signal in question at that time. In other words,
after gdb reports a signal, you can use the handle
command with pass
or nopass
to control whether your
program sees that signal when you continue.
The default is set to nostop
, noprint
, pass
for
non-erroneous signals such as SIGALRM
, SIGWINCH
and
SIGCHLD
, and to stop
, print
, pass
for the
erroneous signals.
You can also use the signal
command to prevent your program from
seeing a signal, or cause it to see a signal it normally would not see,
or to give it any signal at any time. For example, if your program stopped
due to some sort of memory reference error, you might store correct
values into the erroneous variables and continue, hoping to see more
execution; but your program would probably terminate immediately as
a result of the fatal signal once it saw the signal. To prevent this,
you can continue with ‘signal 0’. See Giving your Program a Signal.
On some targets, gdb can inspect extra signal information
associated with the intercepted signal, before it is actually
delivered to the program being debugged. This information is exported
by the convenience variable $_siginfo
, and consists of data
that is passed by the kernel to the signal handler at the time of the
receipt of a signal. The data type of the information itself is
target dependent. You can see the data type using the ptype
$_siginfo
command. On Unix systems, it typically corresponds to the
standard siginfo_t
type, as defined in the signal.h
system header.
Here's an example, on a gnu/Linux system, printing the stray referenced address that raised a segmentation fault.
(gdb) continue Program received signal SIGSEGV, Segmentation fault. 0x0000000000400766 in main () 69 *(int *)p = 0; (gdb) ptype $_siginfo type = struct { int si_signo; int si_errno; int si_code; union { int _pad[28]; struct {...} _kill; struct {...} _timer; struct {...} _rt; struct {...} _sigchld; struct {...} _sigfault; struct {...} _sigpoll; } _sifields; } (gdb) ptype $_siginfo._sifields._sigfault type = struct { void *si_addr; } (gdb) p $_siginfo._sifields._sigfault.si_addr $1 = (void *) 0x7ffff7ff7000
Depending on target support, $_siginfo
may also be writable.
gdb supports debugging programs with multiple threads (see Debugging Programs with Multiple Threads). There are two modes of controlling execution of your program within the debugger. In the default mode, referred to as all-stop mode, when any thread in your program stops (for example, at a breakpoint or while being stepped), all other threads in the program are also stopped by gdb. On some targets, gdb also supports non-stop mode, in which other threads can continue to run freely while you examine the stopped thread in the debugger.
In all-stop mode, whenever your program stops under gdb for any reason, all threads of execution stop, not just the current thread. This allows you to examine the overall state of the program, including switching between threads, without worrying that things may change underfoot.
Conversely, whenever you restart the program, all threads start
executing. This is true even when single-stepping with commands
like step
or next
.
In particular, gdb cannot single-step all threads in lockstep. Since thread scheduling is up to your debugging target's operating system (not controlled by gdb), other threads may execute more than one statement while the current thread completes a single step. Moreover, in general other threads stop in the middle of a statement, rather than at a clean statement boundary, when the program stops.
You might even find your program stopped in another thread after continuing or even single-stepping. This happens whenever some other thread runs into a breakpoint, a signal, or an exception before the first thread completes whatever you requested.
Whenever gdb stops your program, due to a breakpoint or a signal, it automatically selects the thread where that breakpoint or signal happened. gdb alerts you to the context switch with a message such as ‘[Switching to Thread n]’ to identify the thread.
On some OSes, you can modify gdb's default behavior by locking the OS scheduler to allow only a single thread to run.
set scheduler-locking
modeoff
, then there is no
locking and any thread may run at any time. If on
, then only the
current thread may run when the inferior is resumed. The step
mode optimizes for single-stepping; it prevents other threads
from preempting the current thread while you are stepping, so that
the focus of debugging does not change unexpectedly.
Other threads only rarely (or never) get a chance to run
when you step. They are more likely to run when you ‘next’ over a
function call, and they are completely free to run when you use commands
like ‘continue’, ‘until’, or ‘finish’. However, unless another
thread hits a breakpoint during its timeslice, gdb does not change
the current thread away from the thread that you are debugging.
show scheduler-locking
By default, when you issue one of the execution commands such as
continue
, next
or step
, gdb allows only
threads of the current inferior to run. For example, if gdb
is attached to two inferiors, each with two threads, the
continue
command resumes only the two threads of the current
inferior. This is useful, for example, when you debug a program that
forks and you want to hold the parent stopped (so that, for instance,
it doesn't run to exit), while you debug the child. In other
situations, you may not be interested in inspecting the current state
of any of the processes gdb is attached to, and you may want
to resume them all until some breakpoint is hit. In the latter case,
you can instruct gdb to allow all threads of all the
inferiors to run with the set schedule-multiple
command.
set schedule-multiple
on
, all threads of
all processes are allowed to run. When off
, only the threads
of the current process are resumed. The default is off
. The
scheduler-locking
mode takes precedence when set to on
,
or while you are stepping and set to step
.
show schedule-multiple
For some multi-threaded targets, gdb supports an optional mode of operation in which you can examine stopped program threads in the debugger while other threads continue to execute freely. This minimizes intrusion when debugging live systems, such as programs where some threads have real-time constraints or must continue to respond to external events. This is referred to as non-stop mode.
In non-stop mode, when a thread stops to report a debugging event,
only that thread is stopped; gdb does not stop other
threads as well, in contrast to the all-stop mode behavior. Additionally,
execution commands such as continue
and step
apply by default
only to the current thread in non-stop mode, rather than all threads as
in all-stop mode. This allows you to control threads explicitly in
ways that are not possible in all-stop mode — for example, stepping
one thread while allowing others to run freely, stepping
one thread while holding all others stopped, or stepping several threads
independently and simultaneously.
To enter non-stop mode, use this sequence of commands before you run or attach to your program:
# Enable the async interface. set target-async 1 # If using the CLI, pagination breaks non-stop. set pagination off # Finally, turn it on! set non-stop on
You can use these commands to manipulate the non-stop mode setting:
set non-stop on
set non-stop off
show non-stop
Note these commands only reflect whether non-stop mode is enabled,
not whether the currently-executing program is being run in non-stop mode.
In particular, the set non-stop
preference is only consulted when
gdb starts or connects to the target program, and it is generally
not possible to switch modes once debugging has started. Furthermore,
since not all targets support non-stop mode, even when you have enabled
non-stop mode, gdb may still fall back to all-stop operation by
default.
In non-stop mode, all execution commands apply only to the current thread
by default. That is, continue
only continues one thread.
To continue all threads, issue continue -a
or c -a
.
You can use gdb's background execution commands (see Background Execution) to run some threads in the background while you continue to examine or step others from gdb. The MI execution commands (see GDB/MI Program Execution) are always executed asynchronously in non-stop mode.
Suspending execution is done with the interrupt
command when
running in the background, or Ctrl-c during foreground execution.
In all-stop mode, this stops the whole process;
but in non-stop mode the interrupt applies only to the current thread.
To stop the whole program, use interrupt -a
.
Other execution commands do not currently support the -a
option.
In non-stop mode, when a thread stops, gdb doesn't automatically make that thread current, as it does in all-stop mode. This is because the thread stop notifications are asynchronous with respect to gdb's command interpreter, and it would be confusing if gdb unexpectedly changed to a different thread just as you entered a command to operate on the previously current thread.
gdb's execution commands have two variants: the normal foreground (synchronous) behavior, and a background (asynchronous) behavior. In foreground execution, gdb waits for the program to report that some thread has stopped before prompting for another command. In background execution, gdb immediately gives a command prompt so that you can issue other commands while your program runs.
You need to explicitly enable asynchronous mode before you can use background execution commands. You can use these commands to manipulate the asynchronous mode setting:
set target-async on
set target-async off
show target-async
If the target doesn't support async mode, gdb issues an error message if you attempt to use the background execution commands.
To specify background execution, add a &
to the command. For example,
the background form of the continue
command is continue&
, or
just c&
. The execution commands that accept background execution
are:
run
attach
step
stepi
next
nexti
continue
finish
until
Background execution is especially useful in conjunction with non-stop
mode for debugging programs with multiple threads; see Non-Stop Mode.
However, you can also use these commands in the normal all-stop mode with
the restriction that you cannot issue another execution command until the
previous one finishes. Examples of commands that are valid in all-stop
mode while the program is running include help
and info break
.
You can interrupt your program while it is running in the background by
using the interrupt
command.
interrupt
interrupt -a
interrupt
stops the whole process, but in non-stop mode, it stops
only the current thread. To stop the whole program in non-stop mode,
use interrupt -a
.
When your program has multiple threads (see Debugging Programs with Multiple Threads), you can choose whether to set breakpoints on all threads, or on a particular thread.
break
linespec thread
threadnobreak
linespec thread
threadno if ...
Use the qualifier ‘thread threadno’ with a breakpoint command to specify that you only want gdb to stop the program when a particular thread reaches this breakpoint. threadno is one of the numeric thread identifiers assigned by gdb, shown in the first column of the ‘info threads’ display.
If you do not specify ‘thread threadno’ when you set a breakpoint, the breakpoint applies to all threads of your program.
You can use the thread
qualifier on conditional breakpoints as
well; in this case, place ‘thread threadno’ before or
after the breakpoint condition, like this:
(gdb) break frik.c:13 thread 28 if bartab > lim
There is an unfortunate side effect when using gdb to debug multi-threaded programs. If one thread stops for a breakpoint, or for some other reason, and another thread is blocked in a system call, then the system call may return prematurely. This is a consequence of the interaction between multiple threads and the signals that gdb uses to implement breakpoints and other events that stop execution.
To handle this problem, your program should check the return value of each system call and react appropriately. This is good programming style anyways.
For example, do not write code like this:
sleep (10);
The call to sleep
will return early if a different thread stops
at a breakpoint or for some other reason.
Instead, write this:
int unslept = 10; while (unslept > 0) unslept = sleep (unslept);
A system call is allowed to return early, so the system is still conforming to its specification. But gdb does cause your multi-threaded program to behave differently than it would without gdb.
Also, gdb uses internal breakpoints in the thread library to monitor certain events such as thread creation and thread destruction. When such an event happens, a system call in another thread may return prematurely, even though your program does not appear to stop.
If you want to build on non-stop mode and observe program behavior without any chance of disruption by gdb, you can set variables to disable all of the debugger's attempts to modify state, whether by writing memory, inserting breakpoints, etc. These operate at a low level, intercepting operations from all commands.
When all of these are set to off
, then gdb is said to
be observer mode. As a convenience, the variable
observer
can be set to disable these, plus enable non-stop
mode.
Note that gdb will not prevent you from making nonsensical
combinations of these settings. For instance, if you have enabled
may-insert-breakpoints
but disabled may-write-memory
,
then breakpoints that work by writing trap instructions into the code
stream will still not be able to be placed.
set observer on
set observer off
on
, this disables all the permission variables
below (except for insert-fast-tracepoints
), plus enables
non-stop debugging. Setting this to off
switches back to
normal debugging, though remaining in non-stop mode.
show observer
set may-write-registers on
set may-write-registers off
print
, or the
jump
command. It defaults to on
.
show may-write-registers
set may-write-memory on
set may-write-memory off
print
. It
defaults to on
.
show may-write-memory
set may-insert-breakpoints on
set may-insert-breakpoints off
on
.
show may-insert-breakpoints
set may-insert-tracepoints on
set may-insert-tracepoints off
may-insert-fast-tracepoints
. It defaults to on
.
show may-insert-tracepoints
set may-insert-fast-tracepoints on
set may-insert-fast-tracepoints off
may-insert-tracepoints
. It defaults to on
.
show may-insert-fast-tracepoints
set may-interrupt on
set may-interrupt off
off
, the
interrupt
command will have no effect, nor will
Ctrl-c. It defaults to on
.
show may-interrupt
When you are debugging a program, it is not unusual to realize that you have gone too far, and some event of interest has already happened. If the target environment supports it, gdb can allow you to “rewind” the program by running it backward.
A target environment that supports reverse execution should be able to “undo” the changes in machine state that have taken place as the program was executing normally. Variables, registers etc. should revert to their previous values. Obviously this requires a great deal of sophistication on the part of the target environment; not all target environments can support reverse execution.
When a program is executed in reverse, the instructions that have most recently been executed are “un-executed”, in reverse order. The program counter runs backward, following the previous thread of execution in reverse. As each instruction is “un-executed”, the values of memory and/or registers that were changed by that instruction are reverted to their previous states. After executing a piece of source code in reverse, all side effects of that code should be “undone”, and all variables should be returned to their prior values5.
If you are debugging in a target environment that supports reverse execution, gdb provides the following commands.
reverse-continue
[ignore-count]rc
[ignore-count]reverse-step
[count]Like the step
command, reverse-step
will only stop
at the beginning of a source line. It “un-executes” the previously
executed source line. If the previous source line included calls to
debuggable functions, reverse-step
will step (backward) into
the called function, stopping at the beginning of the last
statement in the called function (typically a return statement).
Also, as with the step
command, if non-debuggable functions are
called, reverse-step
will run thru them backward without stopping.
reverse-stepi
[count]reverse-stepi
will take you
back from the destination of the jump to the jump instruction itself.
reverse-next
[count]reverse-next
will take you back
to the caller of that function, before the function was called,
just as the normal next
command would take you from the last
line of a function back to its return to its caller
6.
reverse-nexti
[count]nexti
, reverse-nexti
executes a single instruction
in reverse, except that called functions are “un-executed” atomically.
That is, if the previously executed instruction was a return from
another function, reverse-nexti
will continue to execute
in reverse until the call to that function (from the current stack
frame) is reached.
reverse-finish
finish
command takes you to the point where the
current function returns, reverse-finish
takes you to the point
where it was called. Instead of ending up at the end of the current
function invocation, you end up at the beginning.
set exec-direction
set exec-direction reverse
step, stepi, next, nexti, continue, and finish
. The return
command cannot be used in reverse mode.
set exec-direction forward
On some platforms, gdb provides a special process record and replay target that can record a log of the process execution, and replay it later with both forward and reverse execution commands.
When this target is in use, if the execution log includes the record for the next instruction, gdb will debug in replay mode. In the replay mode, the inferior does not really execute code instructions. Instead, all the events that normally happen during code execution are taken from the execution log. While code is not really executed in replay mode, the values of registers (including the program counter register) and the memory of the inferior are still changed as they normally would. Their contents are taken from the execution log.
If the record for the next instruction is not in the execution log, gdb will debug in record mode. In this mode, the inferior executes normally, and gdb records the execution log for future replay.
The process record and replay target supports reverse execution (see Reverse Execution), even if the platform on which the inferior runs does not. However, the reverse execution is limited in this case by the range of the instructions recorded in the execution log. In other words, reverse execution on platforms that don't support it directly can only be done in the replay mode.
When debugging in the reverse direction, gdb will work in replay mode as long as the execution log includes the record for the previous instruction; otherwise, it will work in record mode, if the platform supports reverse execution, or stop if not.
For architecture environments that support process record and replay, gdb provides the following commands:
target record
Both record
and rec
are aliases of target record
.
Displaced stepping (see displaced stepping) will be automatically disabled when process record and replay target is started. That's because the process record and replay target doesn't support displaced stepping.
If the inferior is in the non-stop mode (see Non-Stop Mode) or in the asynchronous execution mode (see Background Execution), the process record and replay target cannot be started because it doesn't support these two modes.
record stop
When you stop the process record and replay target in record mode (at the end of the execution log), the inferior will be stopped at the next instruction that would have been recorded. In other words, if you record for a while and then stop recording, the inferior process will be left in the same state as if the recording never happened.
On the other hand, if the process record and replay target is stopped while in replay mode (that is, not at the end of the execution log, but at some earlier point), the inferior process will become “live” at that earlier state, and it will then be possible to continue the usual “live” debugging of the process from that state.
When the inferior process exits, or gdb detaches from it, process record and replay target will automatically stop itself.
record save
filenamerecord restore
filenamerecord save
.
set record insn-number-max
limitIf limit is a positive number, then gdb will start
deleting instructions from the log once the number of the record
instructions becomes greater than limit. For every new recorded
instruction, gdb will delete the earliest recorded
instruction to keep the number of recorded instructions at the limit.
(Since deleting recorded instructions loses information, gdb
lets you control what happens when the limit is reached, by means of
the stop-at-limit
option, described below.)
If limit is zero, gdb will never delete recorded instructions from the execution log. The number of recorded instructions is unlimited in this case.
show record insn-number-max
set record stop-at-limit
If this option is OFF, gdb will automatically delete the oldest record to make room for each new one, without asking.
show record stop-at-limit
stop-at-limit
.
set record memory-query
If this option is OFF (the default), gdb will automatically ignore the effect of such instructions on memory. Later, when gdb replays this execution log, it will mark the log of this instruction as not accessible, and it will not affect the replay results.
show record memory-query
memory-query
.
info record
record delete
When your program has stopped, the first thing you need to know is where it stopped and how it got there.
Each time your program performs a function call, information about the call is generated. That information includes the location of the call in your program, the arguments of the call, and the local variables of the function being called. The information is saved in a block of data called a stack frame. The stack frames are allocated in a region of memory called the call stack.
When your program stops, the gdb commands for examining the stack allow you to see all of this information.
One of the stack frames is selected by gdb and many gdb commands refer implicitly to the selected frame. In particular, whenever you ask gdb for the value of a variable in your program, the value is found in the selected frame. There are special gdb commands to select whichever frame you are interested in. See Selecting a Frame.
When your program stops, gdb automatically selects the
currently executing frame and describes it briefly, similar to the
frame
command (see Information about a Frame).
The call stack is divided up into contiguous pieces called stack frames, or frames for short; each frame is the data associated with one call to one function. The frame contains the arguments given to the function, the function's local variables, and the address at which the function is executing.
When your program is started, the stack has only one frame, that of the
function main
. This is called the initial frame or the
outermost frame. Each time a function is called, a new frame is
made. Each time a function returns, the frame for that function invocation
is eliminated. If a function is recursive, there can be many frames for
the same function. The frame for the function in which execution is
actually occurring is called the innermost frame. This is the most
recently created of all the stack frames that still exist.
Inside your program, stack frames are identified by their addresses. A stack frame consists of many bytes, each of which has its own address; each kind of computer has a convention for choosing one byte whose address serves as the address of the frame. Usually this address is kept in a register called the frame pointer register (see $fp) while execution is going on in that frame.
gdb assigns numbers to all existing stack frames, starting with zero for the innermost frame, one for the frame that called it, and so on upward. These numbers do not really exist in your program; they are assigned by gdb to give you a way of designating stack frames in gdb commands.
Some compilers provide a way to compile functions so that they operate without stack frames. (For example, the gcc option
‘-fomit-frame-pointer’
generates functions without a frame.) This is occasionally done with heavily used library functions to save the frame setup time. gdb has limited facilities for dealing with these function invocations. If the innermost function invocation has no stack frame, gdb nevertheless regards it as though it had a separate frame, which is numbered zero as usual, allowing correct tracing of the function call chain. However, gdb has no provision for frameless functions elsewhere in the stack.
frame
argsframe
command allows you to move from one stack frame to another,
and to print the stack frame you select. args may be either the
address of the frame or the stack frame number. Without an argument,
frame
prints the current stack frame.
select-frame
select-frame
command allows you to move from one stack frame
to another without printing the frame. This is the silent version of
frame
.
A backtrace is a summary of how your program got where it is. It shows one line per frame, for many frames, starting with the currently executing frame (frame zero), followed by its caller (frame one), and on up the stack.
backtrace
bt
You can stop the backtrace at any time by typing the system interrupt
character, normally Ctrl-c.
backtrace
nbt
nbacktrace -
nbt -
nbacktrace full
bt full
bt full
nbt full -
nThe names where
and info stack
(abbreviated info s
)
are additional aliases for backtrace
.
In a multi-threaded program, gdb by default shows the
backtrace only for the current thread. To display the backtrace for
several or all of the threads, use the command thread apply
(see thread apply). For example, if you type thread
apply all backtrace, gdb will display the backtrace for all
the threads; this is handy when you debug a core dump of a
multi-threaded program.
Each line in the backtrace shows the frame number and the function name.
The program counter value is also shown—unless you use set
print address off
. The backtrace also shows the source file name and
line number, as well as the arguments to the function. The program
counter value is omitted if it is at the beginning of the code for that
line number.
Here is an example of a backtrace. It was made with the command ‘bt 3’, so it shows the innermost three frames.
#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) at builtin.c:993 #1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08) at macro.c:71 (More stack frames follow...)
The display for frame zero does not begin with a program counter
value, indicating that your program has stopped at the beginning of the
code for line 993
of builtin.c
.
The value of parameter data
in frame 1 has been replaced by
...
. By default, gdb prints the value of a parameter
only if it is a scalar (integer, pointer, enumeration, etc). See command
set print frame-arguments in Print Settings for more details
on how to configure the way function parameter values are printed.
If your program was compiled with optimizations, some compilers will optimize away arguments passed to functions if those arguments are never used after the call. Such optimizations generate code that passes arguments through registers, but doesn't store those arguments in the stack frame. gdb has no way of displaying such arguments in stack frames other than the innermost one. Here's what such a backtrace might look like:
#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) at builtin.c:993 #1 0x6e38 in expand_macro (sym=<optimized out>) at macro.c:242 #2 0x6840 in expand_token (obs=0x0, t=<optimized out>, td=0xf7fffb08) at macro.c:71 (More stack frames follow...)
The values of arguments that were not saved in their stack frames are shown as ‘<optimized out>’.
If you need to display the values of such optimized-out arguments, either deduce that from other variables whose values depend on the one you are interested in, or recompile without optimizations.
Most programs have a standard user entry point—a place where system
libraries and startup code transition into user code. For C this is
main
7.
When gdb finds the entry function in a backtrace
it will terminate the backtrace, to avoid tracing into highly
system-specific (and generally uninteresting) code.
If you need to examine the startup code, or limit the number of levels in a backtrace, you can change this behavior:
set backtrace past-main
set backtrace past-main on
set backtrace past-main off
show backtrace past-main
set backtrace past-entry
set backtrace past-entry on
main
(or equivalent) is called.
set backtrace past-entry off
show backtrace past-entry
set backtrace limit
nset backtrace limit 0
show backtrace limit
Most commands for examining the stack and other data in your program work on whichever stack frame is selected at the moment. Here are the commands for selecting a stack frame; all of them finish by printing a brief description of the stack frame just selected.
frame
nf
nmain
.
frame
addrf
addrOn the SPARC architecture, frame
needs two addresses to
select an arbitrary frame: a frame pointer and a stack pointer.
On the MIPS and Alpha architecture, it needs two addresses: a stack pointer and a program counter.
On the 29k architecture, it needs three addresses: a register stack pointer, a program counter, and a memory stack pointer.
up
ndown
ndown
as do
.
All of these commands end by printing two lines of output describing the frame. The first line shows the frame number, the function name, the arguments, and the source file and line number of execution in that frame. The second line shows the text of that source line.
For example:
(gdb) up #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc) at env.c:10 10 read_input_file (argv[i]);
After such a printout, the list
command with no arguments
prints ten lines centered on the point of execution in the frame.
You can also edit the program at the point of execution with your favorite
editing program by typing edit
.
See Printing Source Lines,
for details.
up-silently
ndown-silently
nup
and down
,
respectively; they differ in that they do their work silently, without
causing display of the new frame. They are intended primarily for use
in gdb command scripts, where the output might be unnecessary and
distracting.
There are several other commands to print information about the selected stack frame.
frame
f
f
. With an
argument, this command is used to select a stack frame.
See Selecting a Frame.
info frame
info f
The verbose description is useful when
something has gone wrong that has made the stack format fail to fit
the usual conventions.
info frame
addrinfo f
addrframe
command.
See Selecting a Frame.
info args
info locals
info catch
up
,
down
, or frame
commands); then type info catch
.
See Setting Catchpoints.
gdb can print parts of your program's source, since the debugging information recorded in the program tells gdb what source files were used to build it. When your program stops, gdb spontaneously prints the line where it stopped. Likewise, when you select a stack frame (see Selecting a Frame), gdb prints the line where execution in that frame has stopped. You can print other portions of source files by explicit command.
If you use gdb through its gnu Emacs interface, you may prefer to use Emacs facilities to view source; see Using gdb under gnu Emacs.
To print lines from a source file, use the list
command
(abbreviated l
). By default, ten lines are printed.
There are several ways to specify what part of the file you want to
print; see Specify Location, for the full list.
Here are the forms of the list
command most commonly used:
list
linenumlist
functionlist
list
command, this prints lines following the last lines
printed; however, if the last line printed was a solitary line printed
as part of displaying a stack frame (see Examining the Stack), this prints lines centered around that line.
list -
By default, gdb prints ten source lines with any of these forms of
the list
command. You can change this using set listsize
:
set listsize
countlist
command display count source lines (unless
the list
argument explicitly specifies some other number).
show listsize
list
prints.
Repeating a list
command with <RET> discards the argument,
so it is equivalent to typing just list
. This is more useful
than listing the same lines again. An exception is made for an
argument of ‘-’; that argument is preserved in repetition so that
each repetition moves up in the source file.
In general, the list
command expects you to supply zero, one or two
linespecs. Linespecs specify source lines; there are several ways
of writing them (see Specify Location), but the effect is always
to specify some source line.
Here is a complete description of the possible arguments for list
:
list
linespeclist
first,
lastlist
command has two linespecs, and the
source file of the second linespec is omitted, this refers to
the same source file as the first linespec.
list ,
lastlist
first,
list +
list -
list
Several gdb commands accept arguments that specify a location of your program's code. Since gdb is a source-level debugger, a location usually specifies some line in the source code; for that reason, locations are also known as linespecs.
Here are all the different ways of specifying a code location that gdb understands:
-
offset+
offsetlist
command, the current line is the last one
printed; for the breakpoint commands, this is the line at which
execution stopped in the currently selected stack frame
(see Frames, for a description of stack frames.) When
used as the second of the two linespecs in a list
command,
this specifies the line offset lines up or down from the first
linespec.
:
linenum:
label:
function*
addresslist
and edit
, this specifies a source
line that contains address. For break
and other
breakpoint oriented commands, this can be used to set breakpoints in
parts of your program which do not have debugging information or
source files.
Here address may be any expression valid in the current working language (see working language) that specifies a code address. In addition, as a convenience, gdb extends the semantics of expressions used in locations to cover the situations that frequently happen during debugging. Here are the various forms of address:
&
function. In Ada, this is function'Address
(although the Pascal form also works).
This form specifies the address of the function's first instruction,
before the stack frame and arguments have been set up.
'
filename'::
funcaddrprobe:
[objfile:
][provider:
]nameSystemTap
provides a way for
applications to embed static probes. This form of linespec specifies
the location of such a static probe. See
http://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps
for more information on static probes.
If objfile is given, only probes coming from that shared library or executable are considered. If provider is given, then only probes from that provider are considered.
See Static Probe Points, for more information on finding and using static probes.
Some probes have an associated semaphore variable; for instance, this
happens automatically if you defined your probe using a DTrace-style
.d file. If your probe has a semaphore, gdb will
automatically enable it when you specify a breakpoint using the
‘probe:’ notation. But, if you put a breakpoint at a probe's
location by some other method (e.g., break file:line
), then
gdb will not automatically set the semaphore.
To edit the lines in a source file, use the edit
command.
The editing program of your choice
is invoked with the current line set to
the active line in the program.
Alternatively, there are several ways to specify what part of the file you
want to print if you want to see other parts of the program:
edit
locationlocation
. Editing starts at
that location, e.g., at the specified source line of the
specified file. See Specify Location, for all the possible forms
of the location argument; here are the forms of the edit
command most commonly used:
edit
numberedit
functionYou can customize gdb to use any editor you want
8.
By default, it is /bin/ex, but you can change this
by setting the environment variable EDITOR
before using
gdb. For example, to configure gdb to use the
vi
editor, you could use these commands with the sh
shell:
EDITOR=/usr/bin/vi export EDITOR gdb ...
or in the csh
shell,
setenv EDITOR /usr/bin/vi gdb ...
There are two commands for searching through the current source file for a regular expression.
forward-search
regexpsearch
regexpfo
.
reverse-search
regexprev
.
Executable programs sometimes do not record the directories of the source files from which they were compiled, just the names. Even when they do, the directories could be moved between the compilation and your debugging session. gdb has a list of directories to search for source files; this is called the source path. Each time gdb wants a source file, it tries all the directories in the list, in the order they are present in the list, until it finds a file with the desired name.
For example, suppose an executable references the file /usr/src/foo-1.0/lib/foo.c, and our source path is /mnt/cross. The file is first looked up literally; if this fails, /mnt/cross/usr/src/foo-1.0/lib/foo.c is tried; if this fails, /mnt/cross/foo.c is opened; if this fails, an error message is printed. gdb does not look up the parts of the source file name, such as /mnt/cross/src/foo-1.0/lib/foo.c. Likewise, the subdirectories of the source path are not searched: if the source path is /mnt/cross, and the binary refers to foo.c, gdb would not find it under /mnt/cross/usr/src/foo-1.0/lib.
Plain file names, relative file names with leading directories, file names containing dots, etc. are all treated as described above; for instance, if the source path is /mnt/cross, and the source file is recorded as ../lib/foo.c, gdb would first try ../lib/foo.c, then /mnt/cross/../lib/foo.c, and after that—/mnt/cross/foo.c.
Note that the executable search path is not used to locate the source files.
Whenever you reset or rearrange the source path, gdb clears out any information it has cached about where source files are found and where each line is in the file.
When you start gdb, its source path includes only ‘cdir’
and ‘cwd’, in that order.
To add other directories, use the directory
command.
The search path is used to find both program source files and gdb script files (read using the ‘-command’ option and ‘source’ command).
In addition to the source path, gdb provides a set of commands that manage a list of source path substitution rules. A substitution rule specifies how to rewrite source directories stored in the program's debug information in case the sources were moved to a different directory between compilation and debugging. A rule is made of two strings, the first specifying what needs to be rewritten in the path, and the second specifying how it should be rewritten. In set substitute-path, we name these two parts from and to respectively. gdb does a simple string replacement of from with to at the start of the directory part of the source file name, and uses that result instead of the original file name to look up the sources.
Using the previous example, suppose the foo-1.0 tree has been
moved from /usr/src to /mnt/cross, then you can tell
gdb to replace /usr/src in all source path names with
/mnt/cross. The first lookup will then be
/mnt/cross/foo-1.0/lib/foo.c in place of the original location
of /usr/src/foo-1.0/lib/foo.c. To define a source path
substitution rule, use the set substitute-path
command
(see set substitute-path).
To avoid unexpected substitution results, a rule is applied only if the from part of the directory name ends at a directory separator. For instance, a rule substituting /usr/source into /mnt/cross will be applied to /usr/source/foo-1.0 but not to /usr/sourceware/foo-2.0. And because the substitution is applied only at the beginning of the directory name, this rule will not be applied to /root/usr/source/baz.c either.
In many cases, you can achieve the same result using the directory
command. However, set substitute-path
can be more efficient in
the case where the sources are organized in a complex tree with multiple
subdirectories. With the directory
command, you need to add each
subdirectory of your project. If you moved the entire tree while
preserving its internal organization, then set substitute-path
allows you to direct the debugger to all the sources with one single
command.
set substitute-path
is also more than just a shortcut command.
The source path is only used if the file at the original location no
longer exists. On the other hand, set substitute-path
modifies
the debugger behavior to look at the rewritten location instead. So, if
for any reason a source file that is not relevant to your executable is
located at the original location, a substitution rule is the only
method available to point gdb at the new location.
You can configure a default source path substitution rule by configuring gdb with the ‘--with-relocated-sources=dir’ option. The dir should be the name of a directory under gdb's configured prefix (set with ‘--prefix’ or ‘--exec-prefix’), and directory names in debug information under dir will be adjusted automatically if the installed gdb is moved to a new location. This is useful if gdb, libraries or executables with debug information and corresponding source code are being moved together.
directory
dirname ...
dir
dirname ...
You can use the string ‘$cdir’ to refer to the compilation
directory (if one is recorded), and ‘$cwd’ to refer to the current
working directory. ‘$cwd’ is not the same as ‘.’—the former
tracks the current working directory as it changes during your gdb
session, while the latter is immediately expanded to the current
directory at the time you add an entry to the source path.
directory
set directories
path-listshow directories
set substitute-path
from toFor example, if the file /foo/bar/baz.c was moved to /mnt/cross/baz.c, then the command
(gdb) set substitute-path /usr/src /mnt/cross
will tell gdb to replace ‘/usr/src’ with ‘/mnt/cross’, which will allow gdb to find the file baz.c even though it was moved.
In the case when more than one substitution rule have been defined, the rules are evaluated one by one in the order where they have been defined. The first one matching, if any, is selected to perform the substitution.
For instance, if we had entered the following commands:
(gdb) set substitute-path /usr/src/include /mnt/include (gdb) set substitute-path /usr/src /mnt/src
gdb would then rewrite /usr/src/include/defs.h into
/mnt/include/defs.h by using the first rule. However, it would
use the second rule to rewrite /usr/src/lib/foo.c into
/mnt/src/lib/foo.c.
unset substitute-path [path]
If no path is specified, then all substitution rules are deleted.
show substitute-path [path]
If no path is specified, then print all existing source path substitution rules.
If your source path is cluttered with directories that are no longer of interest, gdb may sometimes cause confusion by finding the wrong versions of source. You can correct the situation as follows:
directory
with no argument to reset the source path to its default value.
directory
with suitable arguments to reinstall the
directories you want in the source path. You can add all the
directories in one command.
You can use the command info line
to map source lines to program
addresses (and vice versa), and the command disassemble
to display
a range of addresses as machine instructions. You can use the command
set disassemble-next-line
to set whether to disassemble next
source line when execution stops. When run under gnu Emacs
mode, the info line
command causes the arrow to point to the
line specified. Also, info line
prints addresses in symbolic form as
well as hex.
info line
linespecFor example, we can use info line
to discover the location of
the object code for the first line of function
m4_changequote
:
(gdb) info line m4_changequote Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
We can also inquire (using *
addr as the form for
linespec) what source line covers a particular address:
(gdb) info line *0x63ff Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
After info line
, the default address for the x
command
is changed to the starting address of the line, so that ‘x/i’ is
sufficient to begin examining the machine code (see Examining Memory). Also, this address is saved as the value of the
convenience variable $_
(see Convenience Variables).
disassemble
disassemble /m
disassemble /r
/m
modifier and print the raw instructions in hex as well as
in symbolic form by specifying the /r
.
The default memory range is the function surrounding the
program counter of the selected frame. A single argument to this
command is a program counter value; gdb dumps the function
surrounding this value. When two arguments are given, they should
be separated by a comma, possibly surrounded by whitespace. The
arguments specify a range of addresses to dump, in one of two forms:
,
end,+
length+
length (exclusive).
When 2 arguments are specified, the name of the function is also printed (since there could be several functions in the given range).
The argument(s) can be any expression yielding a numeric value, such as ‘0x32c4’, ‘&main+10’ or ‘$pc - 8’.
If the range of memory being disassembled contains current program counter,
the instruction at that location is shown with a =>
marker.
The following example shows the disassembly of a range of addresses of HP PA-RISC 2.0 code:
(gdb) disas 0x32c4, 0x32e4 Dump of assembler code from 0x32c4 to 0x32e4: 0x32c4 <main+204>: addil 0,dp 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26 0x32cc <main+212>: ldil 0x3000,r31 0x32d0 <main+216>: ble 0x3f8(sr4,r31) 0x32d4 <main+220>: ldo 0(r31),rp 0x32d8 <main+224>: addil -0x800,dp 0x32dc <main+228>: ldo 0x588(r1),r26 0x32e0 <main+232>: ldil 0x3000,r31 End of assembler dump.
Here is an example showing mixed source+assembly for Intel x86, when the program is stopped just after function prologue:
(gdb) disas /m main Dump of assembler code for function main: 5 { 0x08048330 <+0>: push %ebp 0x08048331 <+1>: mov %esp,%ebp 0x08048333 <+3>: sub $0x8,%esp 0x08048336 <+6>: and $0xfffffff0,%esp 0x08048339 <+9>: sub $0x10,%esp 6 printf ("Hello.\n"); => 0x0804833c <+12>: movl $0x8048440,(%esp) 0x08048343 <+19>: call 0x8048284 <puts@plt> 7 return 0; 8 } 0x08048348 <+24>: mov $0x0,%eax 0x0804834d <+29>: leave 0x0804834e <+30>: ret End of assembler dump.
Here is another example showing raw instructions in hex for AMD x86-64,
(gdb) disas /r 0x400281,+10 Dump of assembler code from 0x400281 to 0x40028b: 0x0000000000400281: 38 36 cmp %dh,(%rsi) 0x0000000000400283: 2d 36 34 2e 73 sub $0x732e3436,%eax 0x0000000000400288: 6f outsl %ds:(%rsi),(%dx) 0x0000000000400289: 2e 32 00 xor %cs:(%rax),%al End of assembler dump.
Some architectures have more than one commonly-used set of instruction mnemonics or other syntax.
For programs that were dynamically linked and use shared libraries, instructions that call functions or branch to locations in the shared libraries might show a seemingly bogus location—it's actually a location of the relocation table. On some architectures, gdb might be able to resolve these to actual function names.
set disassembly-flavor
instruction-setdisassemble
or x/i
commands.
Currently this command is only defined for the Intel x86 family. You
can set instruction-set to either intel
or att
.
The default is att
, the AT&T flavor used by default by Unix
assemblers for x86-based targets.
show disassembly-flavor
set disassemble-next-line
show disassemble-next-line
The usual way to examine data in your program is with the print
command (abbreviated p
), or its synonym inspect
. It
evaluates and prints the value of an expression of the language your
program is written in (see Using gdb with Different Languages). It may also print the expression using a
Python-based pretty-printer (see Pretty Printing).
print
exprprint /
f exprprint
print /
fA more low-level way of examining data is with the x
command.
It examines data in memory at a specified address and prints it in a
specified format. See Examining Memory.
If you are interested in information about types, or about how the
fields of a struct or a class are declared, use the ptype
exp
command rather than print
. See Examining the Symbol Table.
print
and many other gdb commands accept an expression and
compute its value. Any kind of constant, variable or operator defined
by the programming language you are using is valid in an expression in
gdb. This includes conditional expressions, function calls,
casts, and string constants. It also includes preprocessor macros, if
you compiled your program to include this information; see
Compilation.
gdb supports array constants in expressions input by
the user. The syntax is {element, element...}. For example,
you can use the command print {1, 2, 3}
to create an array
of three integers. If you pass an array to a function or assign it
to a program variable, gdb copies the array to memory that
is malloc
ed in the target program.
Because C is so widespread, most of the expressions shown in examples in this manual are in C. See Using gdb with Different Languages, for information on how to use expressions in other languages.
In this section, we discuss operators that you can use in gdb expressions regardless of your programming language.
Casts are supported in all languages, not just in C, because it is so useful to cast a number into a pointer in order to examine a structure at that address in memory.
gdb supports these operators, in addition to those common to programming languages:
@
::
{
type}
addrExpressions can sometimes contain some ambiguous elements. For instance, some programming languages (notably Ada, C++ and Objective-C) permit a single function name to be defined several times, for application in different contexts. This is called overloading. Another example involving Ada is generics. A generic package is similar to C++ templates and is typically instantiated several times, resulting in the same function name being defined in different contexts.
In some cases and depending on the language, it is possible to adjust the expression to remove the ambiguity. For instance in C++, you can specify the signature of the function you want to break on, as in break function(types). In Ada, using the fully qualified name of your function often makes the expression unambiguous as well.
When an ambiguity that needs to be resolved is detected, the debugger has the capability to display a menu of numbered choices for each possibility, and then waits for the selection with the prompt ‘>’. The first option is always ‘[0] cancel’, and typing 0 <RET> aborts the current command. If the command in which the expression was used allows more than one choice to be selected, the next option in the menu is ‘[1] all’, and typing 1 <RET> selects all possible choices.
For example, the following session excerpt shows an attempt to set a
breakpoint at the overloaded symbol String::after
.
We choose three particular definitions of that function name:
(gdb) b String::after [0] cancel [1] all [2] file:String.cc; line number:867 [3] file:String.cc; line number:860 [4] file:String.cc; line number:875 [5] file:String.cc; line number:853 [6] file:String.cc; line number:846 [7] file:String.cc; line number:735 > 2 4 6 Breakpoint 1 at 0xb26c: file String.cc, line 867. Breakpoint 2 at 0xb344: file String.cc, line 875. Breakpoint 3 at 0xafcc: file String.cc, line 846. Multiple breakpoints were set. Use the "delete" command to delete unwanted breakpoints. (gdb)
set multiple-symbols
modeBy default, mode is set to all
. If the command with which
the expression is used allows more than one choice, then gdb
automatically selects all possible choices. For instance, inserting
a breakpoint on a function using an ambiguous name results in a breakpoint
inserted on each possible match. However, if a unique choice must be made,
then gdb uses the menu to help you disambiguate the expression.
For instance, printing the address of an overloaded function will result
in the use of the menu.
When mode is set to ask
, the debugger always uses the menu
when an ambiguity is detected.
Finally, when mode is set to cancel
, the debugger reports
an error due to the ambiguity and the command is aborted.
show multiple-symbols
multiple-symbols
setting.
The most common kind of expression to use is the name of a variable in your program.
Variables in expressions are understood in the selected stack frame (see Selecting a Frame); they must be either:
or
This means that in the function
foo (a) int a; { bar (a); { int b = test (); bar (b); } }
you can examine and use the variable a
whenever your program is
executing within the function foo
, but you can only use or
examine the variable b
while your program is executing inside
the block where b
is declared.
There is an exception: you can refer to a variable or function whose
scope is a single source file even if the current execution point is not
in this file. But it is possible to have more than one such variable or
function with the same name (in different source files). If that
happens, referring to that name has unpredictable effects. If you wish,
you can specify a static variable in a particular function or file,
using the colon-colon (::
) notation:
file::variable function::variable
Here file or function is the name of the context for the
static variable. In the case of file names, you can use quotes to
make sure gdb parses the file name as a single word—for example,
to print a global value of x
defined in f2.c:
(gdb) p 'f2.c'::x
This use of ‘::’ is very rarely in conflict with the very similar use of the same notation in C++. gdb also supports use of the C++ scope resolution operator in gdb expressions.
Warning: Occasionally, a local variable may appear to have the wrong value at certain points in a function—just after entry to a new scope, and just before exit.You may see this problem when you are stepping by machine instructions. This is because, on most machines, it takes more than one instruction to set up a stack frame (including local variable definitions); if you are stepping by machine instructions, variables may appear to have the wrong values until the stack frame is completely built. On exit, it usually also takes more than one machine instruction to destroy a stack frame; after you begin stepping through that group of instructions, local variable definitions may be gone.
This may also happen when the compiler does significant optimizations. To be sure of always seeing accurate values, turn off all optimization when compiling.
Another possible effect of compiler optimizations is to optimize unused variables out of existence, or assign variables to registers (as opposed to memory addresses). Depending on the support for such cases offered by the debug info format used by the compiler, gdb might not be able to display values for such local variables. If that happens, gdb will print a message like this:
No symbol "foo" in current context.
To solve such problems, either recompile without optimizations, or use a different debug info format, if the compiler supports several such formats. For example, gcc, the gnu C/C++ compiler, usually supports the -gstabs+ option. -gstabs+ produces debug info in a format that is superior to formats such as COFF. You may be able to use DWARF 2 (-gdwarf-2), which is also an effective form for debug info. See Options for Debugging Your Program or GCC. See C and C++, for more information about debug info formats that are best suited to C++ programs.
If you ask to print an object whose contents are unknown to gdb, e.g., because its data type is not completely specified by the debug information, gdb will say ‘<incomplete type>’. See incomplete type, for more about this.
Strings are identified as arrays of char
values without specified
signedness. Arrays of either signed char
or unsigned char
get
printed as arrays of 1 byte sized integers. -fsigned-char
or
-funsigned-char
gcc options have no effect as gdb
defines literal string type "char"
as char
without a sign.
For program code
char var0[] = "A"; signed char var1[] = "A";
You get during debugging
(gdb) print var0 $1 = "A" (gdb) print var1 $2 = {65 'A', 0 '\0'}
It is often useful to print out several successive objects of the same type in memory; a section of an array, or an array of dynamically determined size for which only a pointer exists in the program.
You can do this by referring to a contiguous span of memory as an artificial array, using the binary operator ‘@’. The left operand of ‘@’ should be the first element of the desired array and be an individual object. The right operand should be the desired length of the array. The result is an array value whose elements are all of the type of the left argument. The first element is actually the left argument; the second element comes from bytes of memory immediately following those that hold the first element, and so on. Here is an example. If a program says
int *array = (int *) malloc (len * sizeof (int));
you can print the contents of array
with
p *array@len
The left operand of ‘@’ must reside in memory. Array values made with ‘@’ in this way behave just like other arrays in terms of subscripting, and are coerced to pointers when used in expressions. Artificial arrays most often appear in expressions via the value history (see Value History), after printing one out.
Another way to create an artificial array is to use a cast. This re-interprets a value as if it were an array. The value need not be in memory:
(gdb) p/x (short[2])0x12345678 $1 = {0x1234, 0x5678}
As a convenience, if you leave the array length out (as in ‘(type[])value’) gdb calculates the size to fill the value (as ‘sizeof(value)/sizeof(type)’:
(gdb) p/x (short[])0x12345678 $2 = {0x1234, 0x5678}
Sometimes the artificial array mechanism is not quite enough; in
moderately complex data structures, the elements of interest may not
actually be adjacent—for example, if you are interested in the values
of pointers in an array. One useful work-around in this situation is
to use a convenience variable (see Convenience Variables) as a counter in an expression that prints the first
interesting value, and then repeat that expression via <RET>. For
instance, suppose you have an array dtab
of pointers to
structures, and you are interested in the values of a field fv
in each structure. Here is an example of what you might type:
set $i = 0 p dtab[$i++]->fv <RET> <RET> ...
By default, gdb prints a value according to its data type. Sometimes this is not what you want. For example, you might want to print a number in hex, or a pointer in decimal. Or you might want to view data in memory at a certain address as a character string or as an instruction. To do these things, specify an output format when you print a value.
The simplest use of output formats is to say how to print a value
already computed. This is done by starting the arguments of the
print
command with a slash and a format letter. The format
letters supported are:
x
d
u
o
t
a
(gdb) p/a 0x54320 $3 = 0x54320 <_initialize_vx+396>
The command info symbol 0x54320
yields similar results.
See info symbol.
c
Without this format, gdb displays char
,
unsigned char
, and signed char
data as character
constants. Single-byte members of vectors are displayed as integer
data.
f
s
Without this format, gdb displays pointers to and arrays of
char
, unsigned char
, and signed char
as
strings. Single-byte members of a vector are displayed as an integer
array.
r
For example, to print the program counter in hex (see Registers), type
p/x $pc
Note that no space is required before the slash; this is because command names in gdb cannot contain a slash.
To reprint the last value in the value history with a different format,
you can use the print
command with just a format and no
expression. For example, ‘p/x’ reprints the last value in hex.
You can use the command x
(for “examine”) to examine memory in
any of several formats, independently of your program's data types.
x/
nfu addrx
addrx
x
command to examine memory.
n, f, and u are all optional parameters that specify how much memory to display and how to format it; addr is an expression giving the address where you want to start displaying memory. If you use defaults for nfu, you need not type the slash ‘/’. Several commands set convenient defaults for addr.
print
(‘x’, ‘d’, ‘u’, ‘o’, ‘t’, ‘a’, ‘c’,
‘f’, ‘s’), and in addition ‘i’ (for machine instructions).
The default is ‘x’ (hexadecimal) initially. The default changes
each time you use either x
or print
.
b
h
w
g
Each time you specify a unit size with x
, that size becomes the
default unit the next time you use x
. For the ‘i’ format,
the unit size is ignored and is normally not written. For the ‘s’ format,
the unit size defaults to ‘b’, unless it is explicitly given.
Use x /hs to display 16-bit char strings and x /ws to display
32-bit strings. The next use of x /s will again display 8-bit strings.
Note that the results depend on the programming language of the
current compilation unit. If the language is C, the ‘s’
modifier will use the UTF-16 encoding while ‘w’ will use
UTF-32. The encoding is set by the programming language and cannot
be altered.
info breakpoints
(to
the address of the last breakpoint listed), info line
(to the
starting address of a line), and print
(if you use it to display
a value from memory).
For example, ‘x/3uh 0x54320’ is a request to display three halfwords
(h
) of memory, formatted as unsigned decimal integers (‘u’),
starting at address 0x54320
. ‘x/4xw $sp’ prints the four
words (‘w’) of memory above the stack pointer (here, ‘$sp’;
see Registers) in hexadecimal (‘x’).
Since the letters indicating unit sizes are all distinct from the letters specifying output formats, you do not have to remember whether unit size or format comes first; either order works. The output specifications ‘4xw’ and ‘4wx’ mean exactly the same thing. (However, the count n must come first; ‘wx4’ does not work.)
Even though the unit size u is ignored for the formats ‘s’
and ‘i’, you might still want to use a count n; for example,
‘3i’ specifies that you want to see three machine instructions,
including any operands. For convenience, especially when used with
the display
command, the ‘i’ format also prints branch delay
slot instructions, if any, beyond the count specified, which immediately
follow the last instruction that is within the count. The command
disassemble
gives an alternative way of inspecting machine
instructions; see Source and Machine Code.
All the defaults for the arguments to x
are designed to make it
easy to continue scanning memory with minimal specifications each time
you use x
. For example, after you have inspected three machine
instructions with ‘x/3i addr’, you can inspect the next seven
with just ‘x/7’. If you use <RET> to repeat the x
command,
the repeat count n is used again; the other arguments default as
for successive uses of x
.
When examining machine instructions, the instruction at current program
counter is shown with a =>
marker. For example:
(gdb) x/5i $pc-6 0x804837f <main+11>: mov %esp,%ebp 0x8048381 <main+13>: push %ecx 0x8048382 <main+14>: sub $0x4,%esp => 0x8048385 <main+17>: movl $0x8048460,(%esp) 0x804838c <main+24>: call 0x80482d4 <puts@plt>
The addresses and contents printed by the x
command are not saved
in the value history because there is often too much of them and they
would get in the way. Instead, gdb makes these values available for
subsequent use in expressions as values of the convenience variables
$_
and $__
. After an x
command, the last address
examined is available for use in expressions in the convenience variable
$_
. The contents of that address, as examined, are available in
the convenience variable $__
.
If the x
command has a repeat count, the address and contents saved
are from the last memory unit printed; this is not the same as the last
address printed if several units were printed on the last line of output.
When you are debugging a program running on a remote target machine
(see Remote Debugging), you may wish to verify the program's image in the
remote machine's memory against the executable file you downloaded to
the target. The compare-sections
command is provided for such
situations.
compare-sections
[section-name]"qCRC"
remote request.
If you find that you want to print the value of an expression frequently (to see how it changes), you might want to add it to the automatic display list so that gdb prints its value each time your program stops. Each expression added to the list is given a number to identify it; to remove an expression from the list, you specify that number. The automatic display looks like this:
2: foo = 38 3: bar[5] = (struct hack *) 0x3804
This display shows item numbers, expressions and their current values. As with
displays you request manually using x
or print
, you can
specify the output format you prefer; in fact, display
decides
whether to use print
or x
depending your format
specification—it uses x
if you specify either the ‘i’
or ‘s’ format, or a unit size; otherwise it uses print
.
display
exprdisplay
does not repeat if you press <RET> again after using it.
display/
fmt exprdisplay/
fmt addrFor example, ‘display/i $pc’ can be helpful, to see the machine instruction about to be executed each time execution stops (‘$pc’ is a common name for the program counter; see Registers).
undisplay
dnums...
delete display
dnums...
2-4
.
undisplay
does not repeat if you press <RET> after using it.
(Otherwise you would just get the error ‘No display number ...’.)
disable display
dnums...
2-4
.
enable display
dnums...
2-4
.
display
info display
If a display expression refers to local variables, then it does not make
sense outside the lexical context for which it was set up. Such an
expression is disabled when execution enters a context where one of its
variables is not defined. For example, if you give the command
display last_char
while inside a function with an argument
last_char
, gdb displays this argument while your program
continues to stop inside that function. When it stops elsewhere—where
there is no variable last_char
—the display is disabled
automatically. The next time your program stops where last_char
is meaningful, you can enable the display expression once again.
gdb provides the following ways to control how arrays, structures, and symbols are printed.
These settings are useful for debugging programs in any language:
set print address
set print address on
on
. For example, this is what a stack frame display looks like with
set print address on
:
(gdb) f #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>") at input.c:530 530 if (lquote != def_lquote)
set print address off
set print address off
:
(gdb) set print addr off (gdb) f #0 set_quotes (lq="<<", rq=">>") at input.c:530 530 if (lquote != def_lquote)
You can use ‘set print address off’ to eliminate all machine
dependent displays from the gdb interface. For example, with
print address off
, you should get the same text for backtraces on
all machines—whether or not they involve pointer arguments.
show print address
When gdb prints a symbolic address, it normally prints the
closest earlier symbol plus an offset. If that symbol does not uniquely
identify the address (for example, it is a name whose scope is a single
source file), you may need to clarify. One way to do this is with
info line
, for example ‘info line *0x4537’. Alternately,
you can set gdb to print the source file and line number when
it prints a symbolic address:
set print symbol-filename on
set print symbol-filename off
show print symbol-filename
Another situation where it is helpful to show symbol filenames and line numbers is when disassembling code; gdb shows you the line number and source file that corresponds to each instruction.
Also, you may wish to see the symbolic form only if the address being printed is reasonably close to the closest earlier symbol:
set print max-symbolic-offset
max-offsetshow print max-symbolic-offset
If you have a pointer and you are not sure where it points, try
‘set print symbol-filename on’. Then you can determine the name
and source file location of the variable where it points, using
‘p/a pointer’. This interprets the address in symbolic form.
For example, here gdb shows that a variable ptt
points
at another variable t
, defined in hi2.c:
(gdb) set print symbol-filename on (gdb) p/a ptt $4 = 0xe008 <t in hi2.c>
Warning: For pointers that point to a local variable, ‘p/a’
does not show the symbol name and filename of the referent, even with
the appropriate set print
options turned on.
Other settings control how different kinds of objects are printed:
set print array
set print array on
set print array off
show print array
set print array-indexes
set print array-indexes on
set print array-indexes off
show print array-indexes
set print elements
number-of-elementsset print elements
command.
This limit also applies to the display of strings.
When gdb starts, this limit is set to 200.
Setting number-of-elements to zero means that the printing is unlimited.
show print elements
set print frame-arguments
valueall
scalars
...
. This is the default. Here is an example where
only scalar arguments are shown:
#1 0x08048361 in call_me (i=3, s=..., ss=0xbf8d508c, u=..., e=green) at frame-args.c:23
none
...
. In this case, the example above now becomes:
#1 0x08048361 in call_me (i=..., s=..., ss=..., u=..., e=...) at frame-args.c:23
By default, only scalar arguments are printed. This command can be used
to configure the debugger to print the value of all arguments, regardless
of their type. However, it is often advantageous to not print the value
of more complex parameters. For instance, it reduces the amount of
information printed in each frame, making the backtrace more readable.
Also, it improves performance when displaying Ada frames, because
the computation of large arguments can sometimes be CPU-intensive,
especially in large applications. Setting print frame-arguments
to scalars
(the default) or none
avoids this computation,
thus speeding up the display of each Ada frame.
show print frame-arguments
set print repeats
"<repeats
n times>"
, where n is the number of
identical repetitions, instead of displaying the identical elements
themselves. Setting the threshold to zero will cause all elements to
be individually printed. The default threshold is 10.
show print repeats
set print null-stop
show print null-stop
set print pretty on
$1 = { next = 0x0, flags = { sweet = 1, sour = 1 }, meat = 0x54 "Pork" }
set print pretty off
$1 = {next = 0x0, flags = {sweet = 1, sour = 1}, \ meat = 0x54 "Pork"}
This is the default format.
show print pretty
set print sevenbit-strings on
\
nnn. This setting is
best if you are working in English (ascii) and you use the
high-order bit of characters as a marker or “meta” bit.
set print sevenbit-strings off
show print sevenbit-strings
set print union on
set print union off
"{...}"
instead.
show print union
For example, given the declarations
typedef enum {Tree, Bug} Species; typedef enum {Big_tree, Acorn, Seedling} Tree_forms; typedef enum {Caterpillar, Cocoon, Butterfly} Bug_forms; struct thing { Species it; union { Tree_forms tree; Bug_forms bug; } form; }; struct thing foo = {Tree, {Acorn}};
with set print union on
in effect ‘p foo’ would print
$1 = {it = Tree, form = {tree = Acorn, bug = Cocoon}}
and with set print union off
in effect it would print
$1 = {it = Tree, form = {...}}
set print union
affects programs written in C-like languages
and in Pascal.
These settings are of interest when debugging C++ programs:
set print demangle
set print demangle on
show print demangle
set print asm-demangle
set print asm-demangle on
show print asm-demangle
set demangle-style
styleauto
gnu
g++
) encoding algorithm.
This is the default.
hp
aCC
) encoding algorithm.
lucid
lcc
) encoding algorithm.
arm
cfront
-generated executables. gdb would
require further enhancement to permit that.
show demangle-style
set print object
set print object on
set print object off
show print object
set print static-members
set print static-members on
set print static-members off
show print static-members
set print pascal_static-members
set print pascal_static-members on
set print pascal_static-members off
show print pascal_static-members
set print vtbl
set print vtbl on
vtbl
commands do not work on programs compiled with the HP
ANSI C++ compiler (aCC
).)
set print vtbl off
show print vtbl
gdb provides a mechanism to allow pretty-printing of values using Python code. It greatly simplifies the display of complex objects. This mechanism works for both MI and the CLI.
When gdb prints a value, it first sees if there is a pretty-printer registered for the value. If there is then gdb invokes the pretty-printer to print the value. Otherwise the value is printed normally.
Pretty-printers are normally named. This makes them easy to manage. The ‘info pretty-printer’ command will list all the installed pretty-printers with their names. If a pretty-printer can handle multiple data types, then its subprinters are the printers for the individual data types. Each such subprinter has its own name. The format of the name is printer-name;subprinter-name.
Pretty-printers are installed by registering them with gdb. Typically they are automatically loaded and registered when the corresponding debug information is loaded, thus making them available without having to do anything special.
There are three places where a pretty-printer can be registered.
See Selecting Pretty-Printers, for further information on how pretty-printers are selected,
See Writing a Pretty-Printer, for implementing pretty printers for new types.
Here is how a C++ std::string
looks without a pretty-printer:
(gdb) print s $1 = { static npos = 4294967295, _M_dataplus = { <std::allocator<char>> = { <__gnu_cxx::new_allocator<char>> = { <No data fields>}, <No data fields> }, members of std::basic_string<char, std::char_traits<char>, std::allocator<char> >::_Alloc_hider: _M_p = 0x804a014 "abcd" } }
With a pretty-printer for std::string
only the contents are printed:
(gdb) print s $2 = "abcd"
info pretty-printer [
object-regexp [
name-regexp]]
object-regexp is a regular expression matching the objects
whose pretty-printers to list.
Objects can be global
, the program space's file
(see Progspaces In Python),
and the object files within that program space (see Objfiles In Python).
See Selecting Pretty-Printers, for details on how gdb
looks up a printer from these three objects.
name-regexp is a regular expression matching the name of the printers to list.
disable pretty-printer [
object-regexp [
name-regexp]]
enable pretty-printer [
object-regexp [
name-regexp]]
Example:
Suppose we have three pretty-printers installed: one from library1.so
named foo
that prints objects of type foo
, and
another from library2.so named bar
that prints two types of objects,
bar1
and bar2
.
(gdb) info pretty-printer library1.so: foo library2.so: bar bar1 bar2 (gdb) info pretty-printer library2 library2.so: bar bar1 bar2 (gdb) disable pretty-printer library1 1 printer disabled 2 of 3 printers enabled (gdb) info pretty-printer library1.so: foo [disabled] library2.so: bar bar1 bar2 (gdb) disable pretty-printer library2 bar:bar1 1 printer disabled 1 of 3 printers enabled (gdb) info pretty-printer library2 library1.so: foo [disabled] library2.so: bar bar1 [disabled] bar2 (gdb) disable pretty-printer library2 bar 1 printer disabled 0 of 3 printers enabled (gdb) info pretty-printer library2 library1.so: foo [disabled] library2.so: bar [disabled] bar1 [disabled] bar2
Note that for bar
the entire printer can be disabled,
as can each individual subprinter.
Values printed by the print
command are saved in the gdb
value history. This allows you to refer to them in other expressions.
Values are kept until the symbol table is re-read or discarded
(for example with the file
or symbol-file
commands).
When the symbol table changes, the value history is discarded,
since the values may contain pointers back to the types defined in the
symbol table.
The values printed are given history numbers by which you can
refer to them. These are successive integers starting with one.
print
shows you the history number assigned to a value by
printing ‘$num = ’ before the value; here num is the
history number.
To refer to any previous value, use ‘$’ followed by the value's
history number. The way print
labels its output is designed to
remind you of this. Just $
refers to the most recent value in
the history, and $$
refers to the value before that.
$$
n refers to the nth value from the end; $$2
is the value just prior to $$
, $$1
is equivalent to
$$
, and $$0
is equivalent to $
.
For example, suppose you have just printed a pointer to a structure and want to see the contents of the structure. It suffices to type
p *$
If you have a chain of structures where the component next
points
to the next one, you can print the contents of the next one with this:
p *$.next
You can print successive links in the chain by repeating this command—which you can do by just typing <RET>.
Note that the history records values, not expressions. If the value of
x
is 4 and you type these commands:
print x set x=5
then the value recorded in the value history by the print
command
remains 4 even though the value of x
has changed.
show values
show
values
does not change the history.
show values
nshow values +
show values +
produces no display.
Pressing <RET> to repeat show values
n has exactly the
same effect as ‘show values +’.
gdb provides convenience variables that you can use within gdb to hold on to a value and refer to it later. These variables exist entirely within gdb; they are not part of your program, and setting a convenience variable has no direct effect on further execution of your program. That is why you can use them freely.
Convenience variables are prefixed with ‘$’. Any name preceded by ‘$’ can be used for a convenience variable, unless it is one of the predefined machine-specific register names (see Registers). (Value history references, in contrast, are numbers preceded by ‘$’. See Value History.)
You can save a value in a convenience variable with an assignment expression, just as you would set a variable in your program. For example:
set $foo = *object_ptr
would save in $foo
the value contained in the object pointed to by
object_ptr
.
Using a convenience variable for the first time creates it, but its
value is void
until you assign a new value. You can alter the
value with another assignment at any time.
Convenience variables have no fixed types. You can assign a convenience variable any type of value, including structures and arrays, even if that variable already has a value of a different type. The convenience variable, when used as an expression, has the type of its current value.
show convenience
show conv
.
init-if-undefined $
variable =
expressionIf the variable is already defined then the expression is not evaluated so any side-effects do not occur.
One of the ways to use a convenience variable is as a counter to be incremented or a pointer to be advanced. For example, to print a field from successive elements of an array of structures:
set $i = 0 print bar[$i++]->contents
Repeat that command by typing <RET>.
Some convenience variables are created automatically by gdb and given values likely to be useful.
$_
$_
is automatically set by the x
command to
the last address examined (see Examining Memory). Other
commands which provide a default address for x
to examine also
set $_
to that address; these commands include info line
and info breakpoint
. The type of $_
is void *
except when set by the x
command, in which case it is a pointer
to the type of $__
.
$__
$__
is automatically set by the x
command
to the value found in the last address examined. Its type is chosen
to match the format in which the data was printed.
$_exitcode
$_exitcode
is automatically set to the exit code when
the program being debugged terminates.
$_probe_argc
$_probe_arg0...$_probe_arg9
$_sdata
$_sdata
contains extra collected static tracepoint
data. See Tracepoint Action Lists. Note that
$_sdata
could be empty, if not inspecting a trace buffer, or
if extra static tracepoint data has not been collected.
$_siginfo
$_siginfo
contains extra signal information
(see extra signal information). Note that $_siginfo
could be empty, if the application has not yet received any signals.
For example, it will be empty before you execute the run
command.
$_tlb
$_tlb
is automatically set when debugging
applications running on MS-Windows in native mode or connected to
gdbserver that supports the qGetTIBAddr
request.
See General Query Packets.
This variable contains the address of the thread information block.
On HP-UX systems, if you refer to a function or variable name that begins with a dollar sign, gdb searches for a user or system name first, before it searches for a convenience variable.
gdb also supplies some convenience functions. These have a syntax similar to convenience variables. A convenience function can be used in an expression just like an ordinary function; however, a convenience function is implemented internally to gdb.
help function
You can refer to machine register contents, in expressions, as variables
with names starting with ‘$’. The names of registers are different
for each machine; use info registers
to see the names used on
your machine.
info registers
info all-registers
info registers
regname ...
gdb has four “standard” register names that are available (in
expressions) on most machines—whenever they do not conflict with an
architecture's canonical mnemonics for registers. The register names
$pc
and $sp
are used for the program counter register and
the stack pointer. $fp
is used for a register that contains a
pointer to the current stack frame, and $ps
is used for a
register that contains the processor status. For example,
you could print the program counter in hex with
p/x $pc
or print the instruction to be executed next with
x/i $pc
or add four to the stack pointer10 with
set $sp += 4
Whenever possible, these four standard register names are available on
your machine even though the machine has different canonical mnemonics,
so long as there is no conflict. The info registers
command
shows the canonical names. For example, on the SPARC, info
registers
displays the processor status register as $psr
but you
can also refer to it as $ps
; and on x86-based machines $ps
is an alias for the eflags register.
gdb always considers the contents of an ordinary register as an integer when the register is examined in this way. Some machines have special registers which can hold nothing but floating point; these registers are considered to have floating point values. There is no way to refer to the contents of an ordinary register as floating point value (although you can print it as a floating point value with ‘print/f $regname’).
Some registers have distinct “raw” and “virtual” data formats. This
means that the data format in which the register contents are saved by
the operating system is not the same one that your program normally
sees. For example, the registers of the 68881 floating point
coprocessor are always saved in “extended” (raw) format, but all C
programs expect to work with “double” (virtual) format. In such
cases, gdb normally works with the virtual format only (the format
that makes sense for your program), but the info registers
command
prints the data in both formats.
Some machines have special registers whose contents can be interpreted
in several different ways. For example, modern x86-based machines
have SSE and MMX registers that can hold several values packed
together in several different formats. gdb refers to such
registers in struct
notation:
(gdb) print $xmm1 $1 = { v4_float = {0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044}, v2_double = {9.92129282474342e-303, 2.7585945287983262e-313}, v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000", v8_int16 = {0, 0, 14072, 315, 11, 0, 13, 0}, v4_int32 = {0, 20657912, 11, 13}, v2_int64 = {88725056443645952, 55834574859}, uint128 = 0x0000000d0000000b013b36f800000000 }
To set values of such registers, you need to tell gdb which
view of the register you wish to change, as if you were assigning
value to a struct
member:
(gdb) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF
Normally, register values are relative to the selected stack frame (see Selecting a Frame). This means that you get the value that the register would contain if all stack frames farther in were exited and their saved registers restored. In order to see the true contents of hardware registers, you must select the innermost frame (with ‘frame 0’).
However, gdb must deduce where registers are saved, from the machine code generated by your compiler. If some registers are not saved, or if gdb is unable to locate the saved registers, the selected stack frame makes no difference.
Depending on the configuration, gdb may be able to give you more information about the status of the floating point hardware.
info float
Depending on the configuration, gdb may be able to give you more information about the status of the vector unit.
info vector
gdb provides interfaces to useful OS facilities that can help you debug your program.
When gdb runs on a Posix system (such as GNU or Unix
machines), it interfaces with the inferior via the ptrace
system call. The operating system creates a special sata structure,
called struct user
, for this interface. You can use the
command info udot
to display the contents of this data
structure.
info udot
struct user
maintained by the OS
kernel for the program being debugged. gdb displays the
contents of struct user
as a list of hex numbers, similar to
the examine
command.
Some operating systems supply an auxiliary vector to programs at startup. This is akin to the arguments and environment that you specify for a program, but contains a system-dependent variety of binary values that tell system libraries important details about the hardware, operating system, and process. Each value's purpose is identified by an integer tag; the meanings are well-known but system-specific. Depending on the configuration and operating system facilities, gdb may be able to show you this information. For remote targets, this functionality may further depend on the remote stub's support of the ‘qXfer:auxv:read’ packet, see qXfer auxiliary vector read.
info auxv
On some targets, gdb can access operating-system-specific information and display it to user, without interpretation. For remote targets, this functionality depends on the remote stub's support of the ‘qXfer:osdata:read’ packet, see qXfer osdata read.
info os
info os processes
Memory region attributes allow you to describe special handling required by regions of your target's memory. gdb uses attributes to determine whether to allow certain types of memory accesses; whether to use specific width accesses; and whether to cache target memory. By default the description of memory regions is fetched from the target (if the current target supports this), but the user can override the fetched regions.
Defined memory regions can be individually enabled and disabled. When a memory region is disabled, gdb uses the default attributes when accessing memory in that region. Similarly, if no memory regions have been defined, gdb uses the default attributes when accessing all memory.
When a memory region is defined, it is given a number to identify it; to enable, disable, or remove a memory region, you specify that number.
mem
lower upper attributes...
mem auto
delete mem
nums...
disable mem
nums...
enable mem
nums...
info mem
The access mode attributes set whether gdb may make read or write accesses to a memory region.
While these attributes prevent gdb from performing invalid memory accesses, they do nothing to prevent the target system, I/O DMA, etc. from accessing memory.
ro
wo
rw
The access size attribute tells gdb to use specific sized accesses in the memory region. Often memory mapped device registers require specific sized accesses. If no access size attribute is specified, gdb may use accesses of any size.
8
16
32
64
The data cache attributes set whether gdb will cache target memory. While this generally improves performance by reducing debug protocol overhead, it can lead to incorrect results because gdb does not know about volatile variables or memory mapped device registers.
cache
nocache
gdb can be instructed to refuse accesses to memory that is not explicitly described. This can be useful if accessing such regions has undesired effects for a specific target, or to provide better error checking. The following commands control this behaviour.
set mem inaccessible-by-default [on|off]
on
is specified, make gdb treat memory not
explicitly described by the memory ranges as non-existent and refuse accesses
to such memory. The checks are only performed if there's at least one
memory range defined. If off
is specified, make gdb
treat the memory not explicitly described by the memory ranges as RAM.
The default value is on
.
show mem inaccessible-by-default
You can use the commands dump
, append
, and
restore
to copy data between target memory and a file. The
dump
and append
commands write data to a file, and the
restore
command reads data from a file back into the inferior's
memory. Files may be in binary, Motorola S-record, Intel hex, or
Tektronix Hex format; however, gdb can only append to binary
files.
dump
[format] memory
filename start_addr end_addrdump
[format] value
filename exprThe format parameter may be any one of:
binary
ihex
srec
tekhex
gdb uses the same definitions of these formats as the gnu binary utilities, like ‘objdump’ and ‘objcopy’. If format is omitted, gdb dumps the data in raw binary form.
append
[binary
] memory
filename start_addr end_addrappend
[binary
] value
filename exprrestore
filename [binary
] bias start endrestore
command can automatically recognize any known bfd
file format, except for raw binary. To restore a raw binary file you
must specify the optional keyword binary
after the filename.
If bias is non-zero, its value will be added to the addresses contained in the file. Binary files always start at address zero, so they will be restored at address bias. Other bfd files have a built-in location; they will be restored at offset bias from that location.
If start and/or end are non-zero, then only data between file offset start and file offset end will be restored. These offsets are relative to the addresses in the file, before the bias argument is applied.
A core file or core dump is a file that records the memory image of a running process and its process status (register values etc.). Its primary use is post-mortem debugging of a program that crashed while it ran outside a debugger. A program that crashes automatically produces a core file, unless this feature is disabled by the user. See Files, for information on invoking gdb in the post-mortem debugging mode.
Occasionally, you may wish to produce a core file of the program you are debugging in order to preserve a snapshot of its state. gdb has a special command for that.
generate-core-file [
file]
gcore [
file]
Note that this command is implemented only for some systems (as of this writing, gnu/Linux, FreeBSD, Solaris, Unixware, and S390).
If the program you are debugging uses a different character set to represent characters and strings than the one gdb uses itself, gdb can automatically translate between the character sets for you. The character set gdb uses we call the host character set; the one the inferior program uses we call the target character set.
For example, if you are running gdb on a gnu/Linux system, which
uses the ISO Latin 1 character set, but you are using gdb's
remote protocol (see Remote Debugging) to debug a program
running on an IBM mainframe, which uses the ebcdic character set,
then the host character set is Latin-1, and the target character set is
ebcdic. If you give gdb the command set
target-charset EBCDIC-US
, then gdb translates between
ebcdic and Latin 1 as you print character or string values, or use
character and string literals in expressions.
gdb has no way to automatically recognize which character set
the inferior program uses; you must tell it, using the set
target-charset
command, described below.
Here are the commands for controlling gdb's character set support:
set target-charset
charsetset host-charset
charsetBy default, gdb uses a host character set appropriate to the
system it is running on; you can override that default using the
set host-charset
command. On some systems, gdb cannot
automatically determine the appropriate host character set. In this
case, gdb uses ‘UTF-8’.
gdb can only use certain character sets as its host character
set. If you type set host-charset <TAB><TAB>,
gdb will list the host character sets it supports.
set charset
charsetshow charset
show host-charset
show target-charset
set target-wide-charset
charsetwchar_t
type. To
display the list of supported wide character sets, type
set target-wide-charset <TAB><TAB>.
show target-wide-charset
Here is an example of gdb's character set support in action. Assume that the following source code has been placed in the file charset-test.c:
#include <stdio.h> char ascii_hello[] = {72, 101, 108, 108, 111, 44, 32, 119, 111, 114, 108, 100, 33, 10, 0}; char ibm1047_hello[] = {200, 133, 147, 147, 150, 107, 64, 166, 150, 153, 147, 132, 90, 37, 0}; main () { printf ("Hello, world!\n"); }
In this program, ascii_hello
and ibm1047_hello
are arrays
containing the string ‘Hello, world!’ followed by a newline,
encoded in the ascii and ibm1047 character sets.
We compile the program, and invoke the debugger on it:
$ gcc -g charset-test.c -o charset-test $ gdb -nw charset-test GNU gdb 2001-12-19-cvs Copyright 2001 Free Software Foundation, Inc. ... (gdb)
We can use the show charset
command to see what character sets
gdb is currently using to interpret and display characters and
strings:
(gdb) show charset The current host and target character set is `ISO-8859-1'. (gdb)
For the sake of printing this manual, let's use ascii as our initial character set:
(gdb) set charset ASCII (gdb) show charset The current host and target character set is `ASCII'. (gdb)
Let's assume that ascii is indeed the correct character set for our
host system — in other words, let's assume that if gdb prints
characters using the ascii character set, our terminal will display
them properly. Since our current target character set is also
ascii, the contents of ascii_hello
print legibly:
(gdb) print ascii_hello $1 = 0x401698 "Hello, world!\n" (gdb) print ascii_hello[0] $2 = 72 'H' (gdb)
gdb uses the target character set for character and string literals you use in expressions:
(gdb) print '+' $3 = 43 '+' (gdb)
The ascii character set uses the number 43 to encode the ‘+’ character.
gdb relies on the user to tell it which character set the
target program uses. If we print ibm1047_hello
while our target
character set is still ascii, we get jibberish:
(gdb) print ibm1047_hello $4 = 0x4016a8 "\310\205\223\223\226k@\246\226\231\223\204Z%" (gdb) print ibm1047_hello[0] $5 = 200 '\310' (gdb)
If we invoke the set target-charset
followed by <TAB><TAB>,
gdb tells us the character sets it supports:
(gdb) set target-charset ASCII EBCDIC-US IBM1047 ISO-8859-1 (gdb) set target-charset
We can select ibm1047 as our target character set, and examine the
program's strings again. Now the ascii string is wrong, but
gdb translates the contents of ibm1047_hello
from the
target character set, ibm1047, to the host character set,
ascii, and they display correctly:
(gdb) set target-charset IBM1047 (gdb) show charset The current host character set is `ASCII'. The current target character set is `IBM1047'. (gdb) print ascii_hello $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012" (gdb) print ascii_hello[0] $7 = 72 '\110' (gdb) print ibm1047_hello $8 = 0x4016a8 "Hello, world!\n" (gdb) print ibm1047_hello[0] $9 = 200 'H' (gdb)
As above, gdb uses the target character set for character and string literals you use in expressions:
(gdb) print '+' $10 = 78 '+' (gdb)
The ibm1047 character set uses the number 78 to encode the ‘+’ character.
gdb caches data exchanged between the debugger and a remote target (see Remote Debugging). Such caching generally improves performance, because it reduces the overhead of the remote protocol by bundling memory reads and writes into large chunks. Unfortunately, simply caching everything would lead to incorrect results, since gdb does not necessarily know anything about volatile values, memory-mapped I/O addresses, etc. Furthermore, in non-stop mode (see Non-Stop Mode) memory can be changed while a gdb command is executing. Therefore, by default, gdb only caches data known to be on the stack11. Other regions of memory can be explicitly marked as cacheable; see see Memory Region Attributes.
set remotecache on
set remotecache off
show remotecache
set stack-cache on
set stack-cache off
ON
, use
caching. By default, this option is ON
.
show stack-cache
info dcache
[line
]If a line number is specified, the contents of that line will be printed in hex.
Memory can be searched for a particular sequence of bytes with the
find
command.
find
[/
sn] start_addr, +
len,
val1 [,
val2, ...
]find
[/
sn] start_addr,
end_addr,
val1 [,
val2, ...
]s and n are optional parameters. They may be specified in either order, apart or together.
b
h
w
g
All values are interpreted in the current language. This means, for example, that if the current source language is C/C++ then searching for the string “hello” includes the trailing '\0'.
If the value size is not specified, it is taken from the
value's type in the current language.
This is useful when one wants to specify the search
pattern as a mixture of types.
Note that this means, for example, that in the case of C-like languages
a search for an untyped 0x42 will search for ‘(int) 0x42’
which is typically four bytes.
You can use strings as search values. Quote them with double-quotes
("
).
The string value is copied into the search pattern byte by byte,
regardless of the endianness of the target and the size specification.
The address of each match found is printed as well as a count of the number of matches found.
The address of the last value found is stored in convenience variable ‘$_’. A count of the number of matches is stored in ‘$numfound’.
For example, if stopped at the printf
in this function:
void hello () { static char hello[] = "hello-hello"; static struct { char c; short s; int i; } __attribute__ ((packed)) mixed = { 'c', 0x1234, 0x87654321 }; printf ("%s\n", hello); }
you get during debugging:
(gdb) find &hello[0], +sizeof(hello), "hello" 0x804956d <hello.1620+6> 1 pattern found (gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o' 0x8049567 <hello.1620> 0x804956d <hello.1620+6> 2 patterns found (gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l' 0x8049567 <hello.1620> 1 pattern found (gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321 0x8049560 <mixed.1625> 1 pattern found (gdb) print $numfound $1 = 1 (gdb) print $_ $2 = (void *) 0x8049560
Almost all compilers support optimization. With optimization disabled, the compiler generates assembly code that corresponds directly to your source code, in a simplistic way. As the compiler applies more powerful optimizations, the generated assembly code diverges from your original source code. With help from debugging information generated by the compiler, gdb can map from the running program back to constructs from your original source.
gdb is more accurate with optimization disabled. If you can recompile without optimization, it is easier to follow the progress of your program during debugging. But, there are many cases where you may need to debug an optimized version.
When you debug a program compiled with ‘-g -O’, remember that the optimizer has rearranged your code; the debugger shows you what is really there. Do not be too surprised when the execution path does not exactly match your source file! An extreme example: if you define a variable, but never use it, gdb never sees that variable—because the compiler optimizes it out of existence.
Some things do not work as well with ‘-g -O’ as with just ‘-g’, particularly on machines with instruction scheduling. If in doubt, recompile with ‘-g’ alone, and if this fixes the problem, please report it to us as a bug (including a test case!). See Variables, for more information about debugging optimized code.
Inlining is an optimization that inserts a copy of the function
body directly at each call site, instead of jumping to a shared
routine. gdb displays inlined functions just like
non-inlined functions. They appear in backtraces. You can view their
arguments and local variables, step into them with step
, skip
them with next
, and escape from them with finish
.
You can check whether a function was inlined by using the
info frame
command.
For gdb to support inlined functions, the compiler must record information about inlining in the debug information — gcc using the dwarf 2 format does this, and several other compilers do also. gdb only supports inlined functions when using dwarf 2. Versions of gcc before 4.1 do not emit two required attributes (‘DW_AT_call_file’ and ‘DW_AT_call_line’); gdb does not display inlined function calls with earlier versions of gcc. It instead displays the arguments and local variables of inlined functions as local variables in the caller.
The body of an inlined function is directly included at its call site; unlike a non-inlined function, there are no instructions devoted to the call. gdb still pretends that the call site and the start of the inlined function are different instructions. Stepping to the call site shows the call site, and then stepping again shows the first line of the inlined function, even though no additional instructions are executed.
This makes source-level debugging much clearer; you can see both the
context of the call and then the effect of the call. Only stepping by
a single instruction using stepi
or nexti
does not do
this; single instruction steps always show the inlined body.
There are some ways that gdb does not pretend that inlined function calls are the same as normal calls:
finish
command. This is a limitation of compiler-generated
debugging information; after finish
, you can step to the next line
and print a variable where your program stored the return value.
Some languages, such as C and C++, provide a way to define and invoke “preprocessor macros” which expand into strings of tokens. gdb can evaluate expressions containing macro invocations, show the result of macro expansion, and show a macro's definition, including where it was defined.
You may need to compile your program specially to provide gdb with information about preprocessor macros. Most compilers do not include macros in their debugging information, even when you compile with the -g flag. See Compilation.
A program may define a macro at one point, remove that definition later, and then provide a different definition after that. Thus, at different points in the program, a macro may have different definitions, or have no definition at all. If there is a current stack frame, gdb uses the macros in scope at that frame's source code line. Otherwise, gdb uses the macros in scope at the current listing location; see List.
Whenever gdb evaluates an expression, it always expands any macro invocations present in the expression. gdb also provides the following commands for working with macros explicitly.
macro expand
expressionmacro exp
expressionmacro expand-once
expressionmacro exp1
expressioninfo macro
macromacro define
macro replacement-listmacro define
macro(
arglist)
replacement-listA definition introduced by this command is in scope in every
expression evaluated in gdb, until it is removed with the
macro undef
command, described below. The definition overrides
all definitions for macro present in the program being debugged,
as well as any previous user-supplied definition.
macro undef
macromacro
define
command, described above; it cannot remove definitions present
in the program being debugged.
macro list
macro define
command.
Here is a transcript showing the above commands in action. First, we show our source files:
$ cat sample.c #include <stdio.h> #include "sample.h" #define M 42 #define ADD(x) (M + x) main () { #define N 28 printf ("Hello, world!\n"); #undef N printf ("We're so creative.\n"); #define N 1729 printf ("Goodbye, world!\n"); } $ cat sample.h #define Q < $
Now, we compile the program using the gnu C compiler, gcc. We pass the -gdwarf-2 and -g3 flags to ensure the compiler includes information about preprocessor macros in the debugging information.
$ gcc -gdwarf-2 -g3 sample.c -o sample $
Now, we start gdb on our sample program:
$ gdb -nw sample GNU gdb 2002-05-06-cvs Copyright 2002 Free Software Foundation, Inc. GDB is free software, ... (gdb)
We can expand macros and examine their definitions, even when the program is not running. gdb uses the current listing position to decide which macro definitions are in scope:
(gdb) list main 3 4 #define M 42 5 #define ADD(x) (M + x) 6 7 main () 8 { 9 #define N 28 10 printf ("Hello, world!\n"); 11 #undef N 12 printf ("We're so creative.\n"); (gdb) info macro ADD Defined at /home/jimb/gdb/macros/play/sample.c:5 #define ADD(x) (M + x) (gdb) info macro Q Defined at /home/jimb/gdb/macros/play/sample.h:1 included at /home/jimb/gdb/macros/play/sample.c:2 #define Q < (gdb) macro expand ADD(1) expands to: (42 + 1) (gdb) macro expand-once ADD(1) expands to: once (M + 1) (gdb)
In the example above, note that macro expand-once
expands only
the macro invocation explicit in the original text — the invocation of
ADD
— but does not expand the invocation of the macro M
,
which was introduced by ADD
.
Once the program is running, gdb uses the macro definitions in force at the source line of the current stack frame:
(gdb) break main Breakpoint 1 at 0x8048370: file sample.c, line 10. (gdb) run Starting program: /home/jimb/gdb/macros/play/sample Breakpoint 1, main () at sample.c:10 10 printf ("Hello, world!\n"); (gdb)
At line 10, the definition of the macro N
at line 9 is in force:
(gdb) info macro N Defined at /home/jimb/gdb/macros/play/sample.c:9 #define N 28 (gdb) macro expand N Q M expands to: 28 < 42 (gdb) print N Q M $1 = 1 (gdb)
As we step over directives that remove N
's definition, and then
give it a new definition, gdb finds the definition (or lack
thereof) in force at each point:
(gdb) next Hello, world! 12 printf ("We're so creative.\n"); (gdb) info macro N The symbol `N' has no definition as a C/C++ preprocessor macro at /home/jimb/gdb/macros/play/sample.c:12 (gdb) next We're so creative. 14 printf ("Goodbye, world!\n"); (gdb) info macro N Defined at /home/jimb/gdb/macros/play/sample.c:13 #define N 1729 (gdb) macro expand N Q M expands to: 1729 < 42 (gdb) print N Q M $2 = 0 (gdb)
In addition to source files, macros can be defined on the compilation command line using the -Dname=value syntax. For macros defined in such a way, gdb displays the location of their definition as line zero of the source file submitted to the compiler.
(gdb) info macro __STDC__ Defined at /home/jimb/gdb/macros/play/sample.c:0 -D__STDC__=1 (gdb)
In some applications, it is not feasible for the debugger to interrupt the program's execution long enough for the developer to learn anything helpful about its behavior. If the program's correctness depends on its real-time behavior, delays introduced by a debugger might cause the program to change its behavior drastically, or perhaps fail, even when the code itself is correct. It is useful to be able to observe the program's behavior without interrupting it.
Using gdb's trace
and collect
commands, you can
specify locations in the program, called tracepoints, and
arbitrary expressions to evaluate when those tracepoints are reached.
Later, using the tfind
command, you can examine the values
those expressions had when the program hit the tracepoints. The
expressions may also denote objects in memory—structures or arrays,
for example—whose values gdb should record; while visiting
a particular tracepoint, you may inspect those objects as if they were
in memory at that moment. However, because gdb records these
values without interacting with you, it can do so quickly and
unobtrusively, hopefully not disturbing the program's behavior.
The tracepoint facility is currently available only for remote targets. See Targets. In addition, your remote target must know how to collect trace data. This functionality is implemented in the remote stub; however, none of the stubs distributed with gdb support tracepoints as of this writing. The format of the remote packets used to implement tracepoints are described in Tracepoint Packets.
It is also possible to get trace data from a file, in a manner reminiscent
of corefiles; you specify the filename, and use tfind
to search
through the file. See Trace Files, for more details.
This chapter describes the tracepoint commands and features.
Before running such a trace experiment, an arbitrary number of tracepoints can be set. A tracepoint is actually a special type of breakpoint (see Set Breaks), so you can manipulate it using standard breakpoint commands. For instance, as with breakpoints, tracepoint numbers are successive integers starting from one, and many of the commands associated with tracepoints take the tracepoint number as their argument, to identify which tracepoint to work on.
For each tracepoint, you can specify, in advance, some arbitrary set of data that you want the target to collect in the trace buffer when it hits that tracepoint. The collected data can include registers, local variables, or global data. Later, you can use gdb commands to examine the values these data had at the time the tracepoint was hit.
Tracepoints do not support every breakpoint feature. Ignore counts on tracepoints have no effect, and tracepoints cannot run gdb commands when they are hit. Tracepoints may not be thread-specific either.
Some targets may support fast tracepoints, which are inserted in a different way (such as with a jump instead of a trap), that is faster but possibly restricted in where they may be installed.
Regular and fast tracepoints are dynamic tracing facilities, meaning that they can be used to insert tracepoints at (almost) any location in the target. Some targets may also support controlling static tracepoints from gdb. With static tracing, a set of instrumentation points, also known as markers, are embedded in the target program, and can be activated or deactivated by name or address. These are usually placed at locations which facilitate investigating what the target is actually doing. gdb's support for static tracing includes being able to list instrumentation points, and attach them with gdb defined high level tracepoints that expose the whole range of convenience of gdb's tracepoints support. Namely, support for collecting registers values and values of global or local (to the instrumentation point) variables; tracepoint conditions and trace state variables. The act of installing a gdb static tracepoint on an instrumentation point, or marker, is referred to as probing a static tracepoint marker.
gdbserver
supports tracepoints on some target systems.
See Tracepoints support in gdbserver
.
This section describes commands to set tracepoints and associated conditions and actions.
trace
locationtrace
command is very similar to the break
command.
Its argument location can be a source line, a function name, or
an address in the target program. See Specify Location. The
trace
command defines a tracepoint, which is a point in the
target program where the debugger will briefly stop, collect some
data, and then allow the program to continue. Setting a tracepoint or
changing its actions doesn't take effect until the next tstart
command, and once a trace experiment is running, further changes will
not have any effect until the next trace experiment starts.
Here are some examples of using the trace
command:
(gdb) trace foo.c:121 // a source file and line number (gdb) trace +2 // 2 lines forward (gdb) trace my_function // first source line of function (gdb) trace *my_function // EXACT start address of function (gdb) trace *0x2117c4 // an address
You can abbreviate trace
as tr
.
trace
location if
condftrace
location [ if
cond ]
ftrace
command sets a fast tracepoint. For targets that
support them, fast tracepoints will use a more efficient but possibly
less general technique to trigger data collection, such as a jump
instruction instead of a trap, or some sort of hardware support. It
may not be possible to create a fast tracepoint at the desired
location, in which case the command will exit with an explanatory
message.
gdb handles arguments to ftrace
exactly as for
trace
.
strace
location [ if
cond ]
strace
command sets a static tracepoint. For targets that
support it, setting a static tracepoint probes a static
instrumentation point, or marker, found at location. It may not
be possible to set a static tracepoint at the desired location, in
which case the command will exit with an explanatory message.
gdb handles arguments to strace
exactly as for
trace
, with the addition that the user can also specify
-m
marker as location. This probes the marker
identified by the marker string identifier. This identifier
depends on the static tracepoint backend library your program is
using. You can find all the marker identifiers in the ‘ID’ field
of the info static-tracepoint-markers
command output.
See Listing Static Tracepoint Markers. For example, in the following small program using the UST
tracing engine:
main () { trace_mark(ust, bar33, "str %s", "FOOBAZ"); }
the marker id is composed of joining the first two arguments to the
trace_mark
call with a slash, which translates to:
(gdb) info static-tracepoint-markers Cnt Enb ID Address What 1 n ust/bar33 0x0000000000400ddc in main at stexample.c:22 Data: "str %s" [etc...]
so you may probe the marker above with:
(gdb) strace -m ust/bar33
Static tracepoints accept an extra collect action — collect
$_sdata
. This collects arbitrary user data passed in the probe point
call to the tracing library. In the UST example above, you'll see
that the third argument to trace_mark
is a printf-like format
string. The user data is then the result of running that formating
string against the following arguments. Note that info
static-tracepoint-markers
command output lists that format string in
the ‘Data:’ field.
You can inspect this data when analyzing the trace buffer, by printing the $_sdata variable like any other variable available to gdb. See Tracepoint Action Lists.
The convenience variable $tpnum
records the tracepoint number
of the most recently set tracepoint.
delete tracepoint
[num]delete
command can remove tracepoints also.
Examples:
(gdb) delete trace 1 2 3 // remove three tracepoints (gdb) delete trace // remove all tracepoints
You can abbreviate this command as del tr
.
These commands are deprecated; they are equivalent to plain disable
and enable
.
disable tracepoint
[num]enable tracepoint
command.
enable tracepoint
[num]passcount
[n [num]]passcount
command sets the
passcount of the most recently defined tracepoint. If no passcount is
given, the trace experiment will run until stopped explicitly by the
user.
Examples:
(gdb) passcount 5 2 // Stop on the 5th execution of
// tracepoint 2
(gdb) passcount 12 // Stop on the 12th execution of the
// most recently defined tracepoint.
(gdb) trace foo (gdb) pass 3 (gdb) trace bar (gdb) pass 2 (gdb) trace baz (gdb) pass 1 // Stop tracing when foo has been
// executed 3 times OR when bar has
// been executed 2 times
// OR when baz has been executed 1 time.
The simplest sort of tracepoint collects data every time your program reaches a specified place. You can also specify a condition for a tracepoint. A condition is just a Boolean expression in your programming language (see Expressions). A tracepoint with a condition evaluates the expression each time your program reaches it, and data collection happens only if the condition is true.
Tracepoint conditions can be specified when a tracepoint is set, by
using ‘if’ in the arguments to the trace
command.
See Setting Tracepoints. They can
also be set or changed at any time with the condition
command,
just as with breakpoints.
Unlike breakpoint conditions, gdb does not actually evaluate the conditional expression itself. Instead, gdb encodes the expression into an agent expression (see Agent Expressions) suitable for execution on the target, independently of gdb. Global variables become raw memory locations, locals become stack accesses, and so forth.
For instance, suppose you have a function that is usually called frequently, but should not be called after an error has occurred. You could use the following tracepoint command to collect data about calls of that function that happen while the error code is propagating through the program; an unconditional tracepoint could end up collecting thousands of useless trace frames that you would have to search through.
(gdb) trace normal_operation if errcode > 0
A trace state variable is a special type of variable that is
created and managed by target-side code. The syntax is the same as
that for GDB's convenience variables (a string prefixed with “$”),
but they are stored on the target. They must be created explicitly,
using a tvariable
command. They are always 64-bit signed
integers.
Trace state variables are remembered by gdb, and downloaded to the target along with tracepoint information when the trace experiment starts. There are no intrinsic limits on the number of trace state variables, beyond memory limitations of the target.
Although trace state variables are managed by the target, you can use
them in print commands and expressions as if they were convenience
variables; gdb will get the current value from the target
while the trace experiment is running. Trace state variables share
the same namespace as other “$” variables, which means that you
cannot have trace state variables with names like $23
or
$pc
, nor can you have a trace state variable and a convenience
variable with the same name.
tvariable $
name [ =
expression ]
tvariable
command creates a new trace state variable named
$
name, and optionally gives it an initial value of
expression. expression is evaluated when this command is
entered; the result will be converted to an integer if possible,
otherwise gdb will report an error. A subsequent
tvariable
command specifying the same name does not create a
variable, but instead assigns the supplied initial value to the
existing variable of that name, overwriting any previous initial
value. The default initial value is 0.
info tvariables
delete tvariable
[ $
name ...
]actions
[num]actions
without bothering about its number). You specify the
actions themselves on the following lines, one action at a time, and
terminate the actions list with a line containing just end
. So
far, the only defined actions are collect
, teval
, and
while-stepping
.
actions
is actually equivalent to commands
(see Breakpoint Command Lists), except that only the defined
actions are allowed; any other gdb command is rejected.
To remove all actions from a tracepoint, type ‘actions num’ and follow it immediately with ‘end’.
(gdb) collect data // collect some data (gdb) while-stepping 5 // single-step 5 times, collect data (gdb) end // signals the end of actions.
In the following example, the action list begins with collect
commands indicating the things to be collected when the tracepoint is
hit. Then, in order to single-step and collect additional data
following the tracepoint, a while-stepping
command is used,
followed by the list of things to be collected after each step in a
sequence of single steps. The while-stepping
command is
terminated by its own separate end
command. Lastly, the action
list is terminated by an end
command.
(gdb) trace foo (gdb) actions Enter actions for tracepoint 1, one per line: > collect bar,baz > collect $regs > while-stepping 12 > collect $pc, arr[i] > end end
collect
expr1,
expr2, ...
$regs
$args
$locals
$_probe_argc
SystemTap
probe at
which the tracepoint is located.
See Static Probe Points
$_probe_arg
NSystemTap
probe at which the tracepoint is located.
See Static Probe Points
$_sdata
printf
function call. The
tracing library is able to collect user specified data formatted to a
character string using the format provided by the programmer that
instrumented the program. Other backends have similar mechanisms.
Here's an example of a UST marker call:
const char master_name[] = "$your_name"; trace_mark(channel1, marker1, "hello %s", master_name)
In this case, collecting $_sdata
collects the string
‘hello $yourname’. When analyzing the trace buffer, you can
inspect ‘$_sdata’ like any other variable available to
gdb.
You can give several consecutive collect
commands, each one
with a single argument, or one collect
command with several
arguments separated by commas; the effect is the same.
The command info scope
(see info scope) is
particularly useful for figuring out what data to collect.
teval
expr1,
expr2, ...
collect
action were used.
while-stepping
nwhile-stepping
command is followed by the list of what to collect while stepping
(followed by its own end
command):
> while-stepping 12 > collect $regs, myglobal > end >
Note that $pc
is not automatically collected by
while-stepping
; you need to explicitly collect that register if
you need it. You may abbreviate while-stepping
as ws
or
stepping
.
set default-collect
expr1,
expr2, ...
collect
action prepended
to every tracepoint action list. The expressions are parsed
individually for each tracepoint, so for instance a variable named
xyz
may be interpreted as a global for one tracepoint, and a
local for another, as appropriate to the tracepoint's location.
show default-collect
info tracepoints
[num...
]info breakpoints
; in fact, info tracepoints
is the same
command, simply restricting itself to tracepoints.
A tracepoint's listing may include additional information specific to tracing:
passcount
n command
(gdb) info trace Num Type Disp Enb Address What 1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7 while-stepping 20 collect globfoo, $regs end collect globfoo2 end pass count 1200 (gdb)
This command can be abbreviated info tp
.
info static-tracepoint-markers
For each marker, the following columns are printed:
In addition, the following information may be printed for each marker:
(gdb) info static-tracepoint-markers Cnt ID Enb Address What 1 ust/bar2 y 0x0000000000400e1a in main at stexample.c:25 Data: number1 %d number2 %d Probed by static tracepoints: #2 2 ust/bar33 n 0x0000000000400c87 in main at stexample.c:24 Data: str %s (gdb)
tstart
tstop
Note: a trace experiment and data collection may stop automatically if any tracepoint's passcount is reached (see Tracepoint Passcounts), or if the trace buffer becomes full.
tstatus
Here is an example of the commands we described so far:
(gdb) trace gdb_c_test (gdb) actions Enter actions for tracepoint #1, one per line. > collect $regs,$locals,$args > while-stepping 11 > collect $regs > end > end (gdb) tstart [time passes ...] (gdb) tstop
You can choose to continue running the trace experiment even if
gdb disconnects from the target, voluntarily or
involuntarily. For commands such as detach
, the debugger will
ask what you want to do with the trace. But for unexpected
terminations (gdb crash, network outage), it would be
unfortunate to lose hard-won trace data, so the variable
disconnected-tracing
lets you decide whether the trace should
continue running without gdb.
set disconnected-tracing on
set disconnected-tracing off
detach
or
quit
will ask you directly what to do about a running trace no
matter what this variable's setting, so the variable is mainly useful
for handling unexpected situations, such as loss of the network.
show disconnected-tracing
When you reconnect to the target, the trace experiment may or may not still be running; it might have filled the trace buffer in the meantime, or stopped for one of the other reasons. If it is running, it will continue after reconnection.
Upon reconnection, the target will upload information about the tracepoints in effect. gdb will then compare that information to the set of tracepoints currently defined, and attempt to match them up, allowing for the possibility that the numbers may have changed due to creation and deletion in the meantime. If one of the target's tracepoints does not match any in gdb, the debugger will create a new tracepoint, so that you have a number with which to specify that tracepoint. This matching-up process is necessarily heuristic, and it may result in useless tracepoints being created; you may simply delete them if they are of no use.
If your target agent supports a circular trace buffer, then you can run a trace experiment indefinitely without filling the trace buffer; when space runs out, the agent deletes already-collected trace frames, oldest first, until there is enough room to continue collecting. This is especially useful if your tracepoints are being hit too often, and your trace gets terminated prematurely because the buffer is full. To ask for a circular trace buffer, simply set ‘circular-trace-buffer’ to on. You can set this at any time, including during tracing; if the agent can do it, it will change buffer handling on the fly, otherwise it will not take effect until the next run.
set circular-trace-buffer on
set circular-trace-buffer off
show circular-trace-buffer
There are a number of restrictions on the use of tracepoints. As described above, tracepoint data gathering occurs on the target without interaction from gdb. Thus the full capabilities of the debugger are not available during data gathering, and then at data examination time, you will be limited by only having what was collected. The following items describe some common problems, but it is not exhaustive, and you may run into additional difficulties not mentioned here.
$locals
or $args
, during while-stepping
may
behave erratically. The stepping action may enter a new scope (for
instance by stepping into a function), or the location of the variable
may change (for instance it is loaded into a register). The
tracepoint data recorded uses the location information for the
variables that is correct for the tracepoint location. When the
tracepoint is created, it is not possible, in general, to determine
where the steps of a while-stepping
sequence will advance the
program—particularly if a conditional branch is stepped.
*ptr@50
can be used to collect the 50 element array pointed to
by ptr
.
*$esp@300
(adjust to use the name of the actual stack pointer register on your
target architecture, and the amount of stack you wish to capture).
Then the backtrace
command will show a partial backtrace when
using a trace frame. The number of stack frames that can be examined
depends on the sizes of the frames in the collected stack. Note that
if you ask for a block so large that it goes past the bottom of the
stack, the target agent may report an error trying to read from an
invalid address.
$pc
must be the same as the address of
the tracepoint and use that when you are looking at a trace frame
for that tracepoint. However, this cannot work if the tracepoint has
multiple locations (for instance if it was set in a function that was
inlined), or if it has a while-stepping
loop. In those cases
gdb will warn you that it can't infer $pc
, and default
it to zero.
After the tracepoint experiment ends, you use gdb commands
for examining the trace data. The basic idea is that each tracepoint
collects a trace snapshot every time it is hit and another
snapshot every time it single-steps. All these snapshots are
consecutively numbered from zero and go into a buffer, and you can
examine them later. The way you examine them is to focus on a
specific trace snapshot. When the remote stub is focused on a trace
snapshot, it will respond to all gdb requests for memory and
registers by reading from the buffer which belongs to that snapshot,
rather than from real memory or registers of the program being
debugged. This means that all gdb commands
(print
, info registers
, backtrace
, etc.) will
behave as if we were currently debugging the program state as it was
when the tracepoint occurred. Any requests for data that are not in
the buffer will fail.
tfind
nThe basic command for selecting a trace snapshot from the buffer is
tfind
n, which finds trace snapshot number n,
counting from zero. If no argument n is given, the next
snapshot is selected.
Here are the various forms of using the tfind
command.
tfind start
tfind 0
(since 0 is the number of the first snapshot).
tfind none
tfind end
tfind
tfind -
tfind tracepoint
numtfind pc
addrtfind outside
addr1,
addr2tfind range
addr1,
addr2tfind line
[file:
]ntfind line
repeatedly can appear to have the same effect as
stepping from line to line in a live debugging session.
The default arguments for the tfind
commands are specifically
designed to make it easy to scan through the trace buffer. For
instance, tfind
with no argument selects the next trace
snapshot, and tfind -
with no argument selects the previous
trace snapshot. So, by giving one tfind
command, and then
simply hitting <RET> repeatedly you can examine all the trace
snapshots in order. Or, by saying tfind -
and then hitting
<RET> repeatedly you can examine the snapshots in reverse order.
The tfind line
command with no argument selects the snapshot
for the next source line executed. The tfind pc
command with
no argument selects the next snapshot with the same program counter
(PC) as the current frame. The tfind tracepoint
command with
no argument selects the next trace snapshot collected by the same
tracepoint as the current one.
In addition to letting you scan through the trace buffer manually, these commands make it easy to construct gdb scripts that scan through the trace buffer and print out whatever collected data you are interested in. Thus, if we want to examine the PC, FP, and SP registers from each trace frame in the buffer, we can say this:
(gdb) tfind start (gdb) while ($trace_frame != -1) > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \ $trace_frame, $pc, $sp, $fp > tfind > end Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
Or, if we want to examine the variable X
at each source line in
the buffer:
(gdb) tfind start (gdb) while ($trace_frame != -1) > printf "Frame %d, X == %d\n", $trace_frame, X > tfind line > end Frame 0, X = 1 Frame 7, X = 2 Frame 13, X = 255
tdump
This command takes no arguments. It prints all the data collected at the current trace snapshot.
(gdb) trace 444 (gdb) actions Enter actions for tracepoint #2, one per line: > collect $regs, $locals, $args, gdb_long_test > end (gdb) tstart (gdb) tfind line 444 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66) at gdb_test.c:444 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", ) (gdb) tdump Data collected at tracepoint 2, trace frame 1: d0 0xc4aa0085 -995491707 d1 0x18 24 d2 0x80 128 d3 0x33 51 d4 0x71aea3d 119204413 d5 0x22 34 d6 0xe0 224 d7 0x380035 3670069 a0 0x19e24a 1696330 a1 0x3000668 50333288 a2 0x100 256 a3 0x322000 3284992 a4 0x3000698 50333336 a5 0x1ad3cc 1758156 fp 0x30bf3c 0x30bf3c sp 0x30bf34 0x30bf34 ps 0x0 0 pc 0x20b2c8 0x20b2c8 fpcontrol 0x0 0 fpstatus 0x0 0 fpiaddr 0x0 0 p = 0x20e5b4 "gdb-test" p1 = (void *) 0x11 p2 = (void *) 0x22 p3 = (void *) 0x33 p4 = (void *) 0x44 p5 = (void *) 0x55 p6 = (void *) 0x66 gdb_long_test = 17 '\021' (gdb)
tdump
works by scanning the tracepoint's current collection
actions and printing the value of each expression listed. So
tdump
can fail, if after a run, you change the tracepoint's
actions to mention variables that were not collected during the run.
Also, for tracepoints with while-stepping
loops, tdump
uses the collected value of $pc
to distinguish between trace
frames that were collected at the tracepoint hit, and frames that were
collected while stepping. This allows it to correctly choose whether
to display the basic list of collections, or the collections from the
body of the while-stepping loop. However, if $pc
was not collected,
then tdump
will always attempt to dump using the basic collection
list, and may fail if a while-stepping frame does not include all the
same data that is collected at the tracepoint hit.
save tracepoints
filename
This command saves all current tracepoint definitions together with
their actions and passcounts, into a file filename
suitable for use in a later debugging session. To read the saved
tracepoint definitions, use the source
command (see Command Files). The save-tracepoints
command is a deprecated
alias for save tracepoints
(int) $trace_frame
(int) $tracepoint
(int) $trace_line
(char []) $trace_file
(char []) $trace_func
$tracepoint
.
Note: $trace_file
is not suitable for use in printf
,
use output
instead.
Here's a simple example of using these convenience variables for stepping through all the trace snapshots and printing some of their data. Note that these are not the same as trace state variables, which are managed by the target.
(gdb) tfind start (gdb) while $trace_frame != -1 > output $trace_file > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint > tfind > end
In some situations, the target running a trace experiment may no
longer be available; perhaps it crashed, or the hardware was needed
for a different activity. To handle these cases, you can arrange to
dump the trace data into a file, and later use that file as a source
of trace data, via the target tfile
command.
tsave [ -r ]
filename-r
(“remote”) to direct the target to save
the data directly into filename in its own filesystem, which may be
more efficient if the trace buffer is very large. (Note, however, that
target tfile
can only read from files accessible to the host.)
target tfile
filenametstatus
will report
the state of the trace run at the moment the data was saved, as well
as the current trace frame you are examining. filename must be
on a filesystem accessible to the host.
If your program is too large to fit completely in your target system's memory, you can sometimes use overlays to work around this problem. gdb provides some support for debugging programs that use overlays.
Suppose you have a computer whose instruction address space is only 64 kilobytes long, but which has much more memory which can be accessed by other means: special instructions, segment registers, or memory management hardware, for example. Suppose further that you want to adapt a program which is larger than 64 kilobytes to run on this system.
One solution is to identify modules of your program which are relatively independent, and need not call each other directly; call these modules overlays. Separate the overlays from the main program, and place their machine code in the larger memory. Place your main program in instruction memory, but leave at least enough space there to hold the largest overlay as well.
Now, to call a function located in an overlay, you must first copy that overlay's machine code from the large memory into the space set aside for it in the instruction memory, and then jump to its entry point there.
Data Instruction Larger Address Space Address Space Address Space +-----------+ +-----------+ +-----------+ | | | | | | +-----------+ +-----------+ +-----------+<-- overlay 1 | program | | main | .----| overlay 1 | load address | variables | | program | | +-----------+ | and heap | | | | | | +-----------+ | | | +-----------+<-- overlay 2 | | +-----------+ | | | load address +-----------+ | | | .-| overlay 2 | | | | | | | mapped --->+-----------+ | | +-----------+ address | | | | | | | overlay | <-' | | | | area | <---' +-----------+<-- overlay 3 | | <---. | | load address +-----------+ `--| overlay 3 | | | | | +-----------+ | | +-----------+ | | +-----------+ A code overlay
The diagram (see A code overlay) shows a system with separate data and instruction address spaces. To map an overlay, the program copies its code from the larger address space to the instruction address space. Since the overlays shown here all use the same mapped address, only one may be mapped at a time. For a system with a single address space for data and instructions, the diagram would be similar, except that the program variables and heap would share an address space with the main program and the overlay area.
An overlay loaded into instruction memory and ready for use is called a mapped overlay; its mapped address is its address in the instruction memory. An overlay not present (or only partially present) in instruction memory is called unmapped; its load address is its address in the larger memory. The mapped address is also called the virtual memory address, or VMA; the load address is also called the load memory address, or LMA.
Unfortunately, overlays are not a completely transparent way to adapt a program to limited instruction memory. They introduce a new set of global constraints you must keep in mind as you design your program:
The overlay system described above is rather simple, and could be improved in many ways:
To use gdb's overlay support, each overlay in your program must correspond to a separate section of the executable file. The section's virtual memory address and load memory address must be the overlay's mapped and load addresses. Identifying overlays with sections allows gdb to determine the appropriate address of a function or variable, depending on whether the overlay is mapped or not.
gdb's overlay commands all start with the word overlay
;
you can abbreviate this as ov
or ovly
. The commands are:
overlay off
overlay manual
overlay map-overlay
and overlay unmap-overlay
commands described below.
overlay map-overlay
overlayoverlay map
overlayoverlay unmap-overlay
overlayoverlay unmap
overlayoverlay auto
overlay load-target
overlay load
overlay list-overlays
overlay list
Normally, when gdb prints a code address, it includes the name of the function the address falls in:
(gdb) print main $3 = {int ()} 0x11a0 <main>
When overlay debugging is enabled, gdb recognizes code in
unmapped overlays, and prints the names of unmapped functions with
asterisks around them. For example, if foo
is a function in an
unmapped overlay, gdb prints it this way:
(gdb) overlay list No sections are mapped. (gdb) print foo $5 = {int (int)} 0x100000 <*foo*>
When foo
's overlay is mapped, gdb prints the function's
name normally:
(gdb) overlay list Section .ov.foo.text, loaded at 0x100000 - 0x100034, mapped at 0x1016 - 0x104a (gdb) print foo $6 = {int (int)} 0x1016 <foo>
When overlay debugging is enabled, gdb can find the correct
address for functions and variables in an overlay, whether or not the
overlay is mapped. This allows most gdb commands, like
break
and disassemble
, to work normally, even on unmapped
code. However, gdb's breakpoint support has some limitations:
gdb can automatically track which overlays are mapped and which
are not, given some simple co-operation from the overlay manager in the
inferior. If you enable automatic overlay debugging with the
overlay auto
command (see Overlay Commands), gdb
looks in the inferior's memory for certain variables describing the
current state of the overlays.
Here are the variables your overlay manager must define to support gdb's automatic overlay debugging:
_ovly_table
:struct { /* The overlay's mapped address. */ unsigned long vma; /* The size of the overlay, in bytes. */ unsigned long size; /* The overlay's load address. */ unsigned long lma; /* Non-zero if the overlay is currently mapped; zero otherwise. */ unsigned long mapped; }
_novlys
:_ovly_table
.
To decide whether a particular overlay is mapped or not, gdb
looks for an entry in _ovly_table
whose vma
and
lma
members equal the VMA and LMA of the overlay's section in the
executable file. When gdb finds a matching entry, it consults
the entry's mapped
member to determine whether the overlay is
currently mapped.
In addition, your overlay manager may define a function called
_ovly_debug_event
. If this function is defined, gdb
will silently set a breakpoint there. If the overlay manager then
calls this function whenever it has changed the overlay table, this
will enable gdb to accurately keep track of which overlays
are in program memory, and update any breakpoints that may be set
in overlays. This will allow breakpoints to work even if the
overlays are kept in ROM or other non-writable memory while they
are not being executed.
When linking a program which uses overlays, you must place the overlays at their load addresses, while relocating them to run at their mapped addresses. To do this, you must write a linker script (see Overlay Description). Unfortunately, since linker scripts are specific to a particular host system, target architecture, and target memory layout, this manual cannot provide portable sample code demonstrating gdb's overlay support.
However, the gdb source distribution does contain an overlaid program, with linker scripts for a few systems, as part of its test suite. The program consists of the following files from gdb/testsuite/gdb.base:
d10v-elf
and m32r-elf
targets.
You can build the test program using the d10v-elf
GCC
cross-compiler like this:
$ d10v-elf-gcc -g -c overlays.c $ d10v-elf-gcc -g -c ovlymgr.c $ d10v-elf-gcc -g -c foo.c $ d10v-elf-gcc -g -c bar.c $ d10v-elf-gcc -g -c baz.c $ d10v-elf-gcc -g -c grbx.c $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \ baz.o grbx.o -Wl,-Td10v.ld -o overlays
The build process is identical for any other architecture, except that
you must substitute the appropriate compiler and linker script for the
target system for d10v-elf-gcc
and d10v.ld
.
Although programming languages generally have common aspects, they are
rarely expressed in the same manner. For instance, in ANSI C,
dereferencing a pointer p
is accomplished by *p
, but in
Modula-2, it is accomplished by p^
. Values can also be
represented (and displayed) differently. Hex numbers in C appear as
‘0x1ae’, while in Modula-2 they appear as ‘1AEH’.
Language-specific information is built into gdb for some languages, allowing you to express operations like the above in your program's native language, and allowing gdb to output values in a manner consistent with the syntax of your program's native language. The language you use to build expressions is called the working language.
There are two ways to control the working language—either have gdb
set it automatically, or select it manually yourself. You can use the
set language
command for either purpose. On startup, gdb
defaults to setting the language automatically. The working language is
used to determine how expressions you type are interpreted, how values
are printed, etc.
In addition to the working language, every source file that
gdb knows about has its own working language. For some object
file formats, the compiler might indicate which language a particular
source file is in. However, most of the time gdb infers the
language from the name of the file. The language of a source file
controls whether C++ names are demangled—this way backtrace
can
show each frame appropriately for its own language. There is no way to
set the language of a source file from within gdb, but you can
set the language associated with a filename extension. See Displaying the Language.
This is most commonly a problem when you use a program, such
as cfront
or f2c
, that generates C but is written in
another language. In that case, make the
program use #line
directives in its C output; that way
gdb will know the correct language of the source code of the original
program, and will display that source code, not the generated C code.
If a source file name ends in one of the following extensions, then gdb infers that its language is the one indicated.
In addition, you may set the language associated with a filename extension. See Displaying the Language.
If you allow gdb to set the language automatically, expressions are interpreted the same way in your debugging session and your program.
If you wish, you may set the language manually. To do this, issue the
command ‘set language lang’, where lang is the name of
a language, such as
c
or modula-2
.
For a list of the supported languages, type ‘set language’.
Setting the language manually prevents gdb from updating the working language automatically. This can lead to confusion if you try to debug a program when the working language is not the same as the source language, when an expression is acceptable to both languages—but means different things. For instance, if the current source file were written in C, and gdb was parsing Modula-2, a command such as:
print a = b + c
might not have the effect you intended. In C, this means to add
b
and c
and place the result in a
. The result
printed would be the value of a
. In Modula-2, this means to compare
a
to the result of b+c
, yielding a BOOLEAN
value.
To have gdb set the working language automatically, use ‘set language local’ or ‘set language auto’. gdb then infers the working language. That is, when your program stops in a frame (usually by encountering a breakpoint), gdb sets the working language to the language recorded for the function in that frame. If the language for a frame is unknown (that is, if the function or block corresponding to the frame was defined in a source file that does not have a recognized extension), the current working language is not changed, and gdb issues a warning.
This may not seem necessary for most programs, which are written entirely in one source language. However, program modules and libraries written in one source language can be used by a main program written in a different source language. Using ‘set language auto’ in this case frees you from having to set the working language manually.
The following commands help you find out which language is the working language, and also what language source files were written in.
show language
print
to
build and compute expressions that may involve variables in your program.
info frame
info source
In unusual circumstances, you may have source files with extensions not in the standard list. You can then set the extension associated with a language explicitly:
set extension-language
ext languageinfo extensions
Warning: In this release, the gdb commands for type and range checking are included, but they do not yet have any effect. This section documents the intended facilities.
Some languages are designed to guard you against making seemingly common errors through a series of compile- and run-time checks. These include checking the type of arguments to functions and operators, and making sure mathematical overflows are caught at run time. Checks such as these help to ensure a program's correctness once it has been compiled by eliminating type mismatches, and providing active checks for range errors when your program is running.
gdb can check for conditions like the above if you wish.
Although gdb does not check the statements in your program,
it can check expressions entered directly into gdb for
evaluation via the print
command, for example. As with the
working language, gdb can also decide whether or not to check
automatically based on your program's source language.
See Supported Languages, for the default
settings of supported languages.
Some languages, such as Modula-2, are strongly typed, meaning that the arguments to operators and functions have to be of the correct type, otherwise an error occurs. These checks prevent type mismatch errors from ever causing any run-time problems. For example,
1 + 2 ⇒ 3
but
error--> 1 + 2.3
The second example fails because the CARDINAL
1 is not
type-compatible with the REAL
2.3.
For the expressions you use in gdb commands, you can tell the gdb type checker to skip checking; to treat any mismatches as errors and abandon the expression; or to only issue warnings when type mismatches occur, but evaluate the expression anyway. When you choose the last of these, gdb evaluates expressions like the second example above, but also issues a warning.
Even if you turn type checking off, there may be other reasons
related to type that prevent gdb from evaluating an expression.
For instance, gdb does not know how to add an int
and
a struct foo
. These particular type errors have nothing to do
with the language in use, and usually arise from expressions, such as
the one described above, which make little sense to evaluate anyway.
Each language defines to what degree it is strict about type. For instance, both Modula-2 and C require the arguments to arithmetical operators to be numbers. In C, enumerated types and pointers can be represented as numbers, so that they are valid arguments to mathematical operators. See Supported Languages, for further details on specific languages.
gdb provides some additional commands for controlling the type checker:
set check type auto
set check type on
set check type off
set check type warn
show type
In some languages (such as Modula-2), it is an error to exceed the bounds of a type; this is enforced with run-time checks. Such range checking is meant to ensure program correctness by making sure computations do not overflow, or indices on an array element access do not exceed the bounds of the array.
For expressions you use in gdb commands, you can tell gdb to treat range errors in one of three ways: ignore them, always treat them as errors and abandon the expression, or issue warnings but evaluate the expression anyway.
A range error can result from numerical overflow, from exceeding an array index bound, or when you type a constant that is not a member of any type. Some languages, however, do not treat overflows as an error. In many implementations of C, mathematical overflow causes the result to “wrap around” to lower values—for example, if m is the largest integer value, and s is the smallest, then
m + 1 ⇒ s
This, too, is specific to individual languages, and in some cases specific to individual compilers or machines. See Supported Languages, for further details on specific languages.
gdb provides some additional commands for controlling the range checker:
set check range auto
set check range on
set check range off
set check range warn
show range
gdb supports C, C++, D, Objective-C, Fortran, Java, OpenCL C, Pascal,
assembly, Modula-2, and Ada.
Some gdb features may be used in expressions regardless of the
language you use: the gdb @
and ::
operators,
and the ‘{type}addr’ construct (see Expressions) can be used with the constructs of any supported
language.
The following sections detail to what degree each source language is supported by gdb. These sections are not meant to be language tutorials or references, but serve only as a reference guide to what the gdb expression parser accepts, and what input and output formats should look like for different languages. There are many good books written on each of these languages; please look to these for a language reference or tutorial.
Since C and C++ are so closely related, many features of gdb apply to both languages. Whenever this is the case, we discuss those languages together.
The C++ debugging facilities are jointly implemented by the C++
compiler and gdb. Therefore, to debug your C++ code
effectively, you must compile your C++ programs with a supported
C++ compiler, such as gnu g++
, or the HP ANSI C++
compiler (aCC
).
For best results when using gnu C++, use the DWARF 2 debugging
format; if it doesn't work on your system, try the stabs+ debugging
format. You can select those formats explicitly with the g++
command-line options -gdwarf-2 and -gstabs+.
See Options for Debugging Your Program or GCC.
Operators must be defined on values of specific types. For instance,
+
is defined on numbers, but not on structures. Operators are
often defined on groups of types.
For the purposes of C and C++, the following definitions hold:
int
with any of its storage-class
specifiers; char
; enum
; and, for C++, bool
.
float
, double
, and
long double
(if supported by the target platform).
(
type *)
.
The following operators are supported. They are listed here in order of increasing precedence:
,
=
=
op=
b,
and translated to a =
a op b.
op=
and =
have the same precedence.
op is any one of the operators |
, ^
, &
,
<<
, >>
, +
, -
, *
, /
, %
.
?:
?
b :
c can be thought
of as: if a then b else c. a should be of an
integral type.
||
&&
|
^
&
==
, !=
<
, >
, <=
, >=
<<
, >>
@
+
, -
*
, /
, %
++
, --
*
++
.
&
++
.
For debugging C++, gdb implements a use of ‘&’ beyond what is
allowed in the C++ language itself: you can use ‘&(&ref)’
to examine the address
where a C++ reference variable (declared with ‘&ref’) is
stored.
-
++
.
!
++
.
~
++
.
.
, ->
struct
and union
data.
.*
, ->*
[]
[
i]
is defined as
*(
a+
i)
. Same precedence as ->
.
()
->
.
::
struct
, union
,
and class
types.
::
::
,
above.
If an operator is redefined in the user code, gdb usually attempts to invoke the redefined version instead of using the operator's predefined meaning.
gdb allows you to express the constants of C and C++ in the following ways:
long
value.
float
(as opposed to the default double
) type; or with
a letter ‘l’ or ‘L’, which specifies a long double
constant.
'
), or a number—the ordinal value of the corresponding character
(usually its ascii value). Within quotes, the single character may
be represented by a letter or by escape sequences, which are of
the form ‘\nnn’, where nnn is the octal representation
of the character's ordinal value; or of the form ‘\x’, where
‘x’ is a predefined special character—for example,
‘\n’ for newline.
"
). Any valid character constant (as described
above) may appear. Double quotes within the string must be preceded by
a backslash, so for instance ‘"a\"b'c"’ is a string of five
characters.
gdb expression handling can interpret most C++ expressions.
Warning: gdb can only debug C++ code if you use the proper compiler and the proper debug format. Currently, gdb works best when debugging C++ code that is compiled with gcc 2.95.3 or with gcc 3.1 or newer, using the options -gdwarf-2 or -gstabs+. DWARF 2 is preferred over stabs+. Most configurations of gcc emit either DWARF 2 or stabs+ as their default debug format, so you usually don't need to specify a debug format explicitly. Other compilers and/or debug formats are likely to work badly or not at all when using gdb to debug C++ code.
count = aml->GetOriginal(x, y)
this
following the same rules as C++.
It does perform integral conversions and promotions, floating-point promotions, arithmetic conversions, pointer conversions, conversions of class objects to base classes, and standard conversions such as those of functions or arrays to pointers; it requires an exact match on the number of function arguments.
Overload resolution is always performed, unless you have specified
set overload-resolution off
. See gdb Features for C++.
You must specify set overload-resolution off
in order to use an
explicit function signature to call an overloaded function, as in
p 'foo(char,int)'('x', 13)
The gdb command-completion facility can simplify this; see Command Completion.
In the parameter list shown when gdb displays a frame, the values of reference variables are not displayed (unlike other variables); this avoids clutter, since references are often used for large structures. The address of a reference variable is always shown, unless you have specified ‘set print address off’.
::
—your
expressions can use it just as expressions in your program do. Since
one scope may be defined in another, you can use ::
repeatedly if
necessary, for example in an expression like
‘scope1::scope2::name’. gdb also allows
resolving name scope by reference to source files, in both C and C++
debugging (see Program Variables).
In addition, when used with HP's C++ compiler, gdb supports calling virtual functions correctly, printing out virtual bases of objects, calling functions in a base subobject, casting objects, and invoking user-defined operators.
If you allow gdb to set type and range checking automatically, they
both default to off
whenever the working language changes to
C or C++. This happens regardless of whether you or gdb
selects the working language.
If you allow gdb to set the language automatically, it recognizes source files whose names end with .c, .C, or .cc, etc, and when gdb enters code compiled from one of these files, it sets the working language to C or C++. See Having gdb Infer the Source Language, for further details.
By default, when gdb parses C or C++ expressions, type checking is not used. However, if you turn type checking on, gdb considers two variables type equivalent if:
typedef
.
Range checking, if turned on, is done on mathematical operations. Array indices are not checked, since they are often used to index a pointer that is not itself an array.
The set print union
and show print union
commands apply to
the union
type. When set to ‘on’, any union
that is
inside a struct
or class
is also printed. Otherwise, it
appears as ‘{...}’.
The @
operator aids in the debugging of dynamic arrays, formed
with pointers and a memory allocation function. See Expressions.
Some gdb commands are particularly useful with C++, and some are designed specifically for use with C++. Here is a summary:
rbreak
regexcatch throw
catch catch
ptype
typenameset print demangle
show print demangle
set print asm-demangle
show print asm-demangle
set print object
show print object
set print vtbl
show print vtbl
vtbl
commands do not work on programs compiled with the HP
ANSI C++ compiler (aCC
).)
set overload-resolution on
set overload-resolution off
show overload-resolution
(
types)
rather than just symbol. You can
also use the gdb command-line word completion facilities to list the
available choices, or to finish the type list for you.
See Command Completion, for details on how to do this.
gdb can examine, set and perform computations with numbers in
decimal floating point format, which in the C language correspond to the
_Decimal32
, _Decimal64
and _Decimal128
types as
specified by the extension to support decimal floating-point arithmetic.
There are two encodings in use, depending on the architecture: BID (Binary Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for PowerPC. gdb will use the appropriate encoding for the configured target.
Because of a limitation in libdecnumber, the library used by gdb to manipulate decimal floating point numbers, it is not possible to convert (using a cast, for example) integers wider than 32-bit to decimal float.
In addition, in order to imitate gdb's behaviour with binary floating point computations, error checking in decimal float operations ignores underflow, overflow and divide by zero exceptions.
In the PowerPC architecture, gdb provides a set of pseudo-registers
to inspect _Decimal128
values stored in floating point registers.
See PowerPC for more details.
gdb can be used to debug programs written in D and compiled with GDC, LDC or DMD compilers. Currently gdb supports only one D specific feature — dynamic arrays.
This section provides information about some commands and command options that are useful for debugging Objective-C code. See also info classes, and info selectors, for a few more commands specific to Objective-C support.
The following commands have been extended to accept Objective-C method names as line specifications:
clear
break
info line
jump
list
A fully qualified Objective-C method name is specified as
-[Class methodName]
where the minus sign is used to indicate an instance method and a
plus sign (not shown) is used to indicate a class method. The class
name Class and method name methodName are enclosed in
brackets, similar to the way messages are specified in Objective-C
source code. For example, to set a breakpoint at the create
instance method of class Fruit
in the program currently being
debugged, enter:
break -[Fruit create]
To list ten program lines around the initialize
class method,
enter:
list +[NSText initialize]
In the current version of gdb, the plus or minus sign is required. In future versions of gdb, the plus or minus sign will be optional, but you can use it to narrow the search. It is also possible to specify just a method name:
break create
You must specify the complete method name, including any colons. If
your program's source files contain more than one create
method,
you'll be presented with a numbered list of classes that implement that
method. Indicate your choice by number, or type ‘0’ to exit if
none apply.
As another example, to clear a breakpoint established at the
makeKeyAndOrderFront:
method of the NSWindow
class, enter:
clear -[NSWindow makeKeyAndOrderFront:]
The print command has also been extended to accept methods. For example:
print -[object hash]
will tell gdb to send the hash
message to object
and print the result. Also, an additional command has been added,
print-object
or po
for short, which is meant to print
the description of an object. However, this command may only work
with certain Objective-C libraries that have a particular hook
function, _NSPrintForDebugger
, defined.
This section provides information about gdbs OpenCL C support.
gdb supports the builtin scalar and vector datatypes specified
by OpenCL 1.1. In addition the half- and double-precision floating point
data types of the cl_khr_fp16
and cl_khr_fp64
OpenCL
extensions are also known to gdb.
gdb supports accesses to vector components including the access as lvalue where possible. Since OpenCL C is based on C99 most C expressions supported by gdb can be used as well.
gdb supports the operators specified by OpenCL 1.1 for scalar and vector data types.
gdb can be used to debug programs written in Fortran, but it currently supports only the features of Fortran 77 language.
Some Fortran compilers (gnu Fortran 77 and Fortran 95 compilers among them) append an underscore to the names of variables and functions. When you debug programs compiled by those compilers, you will need to refer to variables and functions with a trailing underscore.
Operators must be defined on values of specific types. For instance,
+
is defined on numbers, but not on characters or other non-
arithmetic types. Operators are often defined on groups of types.
**
:
%
Fortran symbols are usually case-insensitive, so gdb by default uses case-insensitive matches for Fortran symbols. You can change that with the ‘set case-insensitive’ command, see Symbols, for the details.
gdb has some commands to support Fortran-specific features, such as displaying common blocks.
info common
[common-name]COMMON
block whose name is common-name. With no argument, the names of
all COMMON
blocks visible at the current program location are
printed.
Debugging Pascal programs which use sets, subranges, file variables, or nested functions does not currently work. gdb does not support entering expressions, printing values, or similar features using Pascal syntax.
The Pascal-specific command set print pascal_static-members
controls whether static members of Pascal objects are displayed.
See pascal_static-members.
The extensions made to gdb to support Modula-2 only support output from the gnu Modula-2 compiler (which is currently being developed). Other Modula-2 compilers are not currently supported, and attempting to debug executables produced by them is most likely to give an error as gdb reads in the executable's symbol table.
Operators must be defined on values of specific types. For instance,
+
is defined on numbers, but not on structures. Operators are
often defined on groups of types. For the purposes of Modula-2, the
following definitions hold:
INTEGER
, CARDINAL
, and
their subranges.
CHAR
and its subranges.
REAL
.
POINTER TO
type.
SET
and BITSET
types.
BOOLEAN
.
The following operators are supported, and appear in order of increasing precedence:
,
:=
:=
value is
value.
<
, >
<=
, >=
<
.
=
, <>
, #
<
. In gdb scripts, only <>
is
available for inequality, since #
conflicts with the script
comment character.
IN
<
.
OR
AND
, &
@
+
, -
*
/
*
.
DIV
, MOD
*
.
-
INTEGER
and REAL
data.
^
NOT
^
.
.
RECORD
field selector. Defined on RECORD
data. Same
precedence as ^
.
[]
ARRAY
data. Same precedence as ^
.
()
PROCEDURE
objects. Same precedence
as ^
.
::
, .
Warning: Set expressions and their operations are not yet supported, so gdb treats the use of the operatorIN
, or the use of operators+
,-
,*
,/
,=
, ,<>
,#
,<=
, and>=
on sets as an error.
Modula-2 also makes available several built-in procedures and functions. In describing these, the following metavariables are used:
ARRAY
variable.
CHAR
constant or variable.
SET OF
mtype (where mtype is the type of m).
All Modula-2 built-in procedures also return a result, described below.
ABS(
n)
CAP(
c)
CHR(
i)
DEC(
v)
DEC(
v,
i)
EXCL(
m,
s)
FLOAT(
i)
HIGH(
a)
INC(
v)
INC(
v,
i)
INCL(
m,
s)
MAX(
t)
MIN(
t)
ODD(
i)
ORD(
x)
SIZE(
x)
TRUNC(
r)
TSIZE(
x)
VAL(
t,
i)
Warning: Sets and their operations are not yet supported, so gdb treats the use of proceduresINCL
andEXCL
as an error.
gdb allows you to express the constants of Modula-2 in the following ways:
'
) or double ("
). They may
also be expressed by their ordinal value (their ascii value, usually)
followed by a ‘C’.
'
) or double ("
).
Escape sequences in the style of C are also allowed. See C and C++ Constants, for a brief explanation of escape
sequences.
TRUE
and
FALSE
.
Currently gdb can print the following data types in Modula-2 syntax: array types, record types, set types, pointer types, procedure types, enumerated types, subrange types and base types. You can also print the contents of variables declared using these type. This section gives a number of simple source code examples together with sample gdb sessions.
The first example contains the following section of code:
VAR s: SET OF CHAR ; r: [20..40] ;
and you can request gdb to interrogate the type and value of
r
and s
.
(gdb) print s {'A'..'C', 'Z'} (gdb) ptype s SET OF CHAR (gdb) print r 21 (gdb) ptype r [20..40]
Likewise if your source code declares s
as:
VAR s: SET ['A'..'Z'] ;
then you may query the type of s
by:
(gdb) ptype s type = SET ['A'..'Z']
Note that at present you cannot interactively manipulate set expressions using the debugger.
The following example shows how you might declare an array in Modula-2 and how you can interact with gdb to print its type and contents:
VAR s: ARRAY [-10..10] OF CHAR ;
(gdb) ptype s ARRAY [-10..10] OF CHAR
Note that the array handling is not yet complete and although the type
is printed correctly, expression handling still assumes that all
arrays have a lower bound of zero and not -10
as in the example
above.
Here are some more type related Modula-2 examples:
TYPE colour = (blue, red, yellow, green) ; t = [blue..yellow] ; VAR s: t ; BEGIN s := blue ;
The gdb interaction shows how you can query the data type and value of a variable.
(gdb) print s $1 = blue (gdb) ptype t type = [blue..yellow]
In this example a Modula-2 array is declared and its contents
displayed. Observe that the contents are written in the same way as
their C
counterparts.
VAR s: ARRAY [1..5] OF CARDINAL ; BEGIN s[1] := 1 ;
(gdb) print s $1 = {1, 0, 0, 0, 0} (gdb) ptype s type = ARRAY [1..5] OF CARDINAL
The Modula-2 language interface to gdb also understands pointer types as shown in this example:
VAR s: POINTER TO ARRAY [1..5] OF CARDINAL ; BEGIN NEW(s) ; s^[1] := 1 ;
and you can request that gdb describes the type of s
.
(gdb) ptype s type = POINTER TO ARRAY [1..5] OF CARDINAL
gdb handles compound types as we can see in this example. Here we combine array types, record types, pointer types and subrange types:
TYPE foo = RECORD f1: CARDINAL ; f2: CHAR ; f3: myarray ; END ; myarray = ARRAY myrange OF CARDINAL ; myrange = [-2..2] ; VAR s: POINTER TO ARRAY myrange OF foo ;
and you can ask gdb to describe the type of s
as shown
below.
(gdb) ptype s type = POINTER TO ARRAY [-2..2] OF foo = RECORD f1 : CARDINAL; f2 : CHAR; f3 : ARRAY [-2..2] OF CARDINAL; END
If type and range checking are set automatically by gdb, they
both default to on
whenever the working language changes to
Modula-2. This happens regardless of whether you or gdb
selected the working language.
If you allow gdb to set the language automatically, then entering code compiled from a file whose name ends with .mod sets the working language to Modula-2. See Having gdb Infer the Source Language, for further details.
A few changes have been made to make Modula-2 programs easier to debug. This is done primarily via loosening its type strictness:
:=
) returns the value of its right-hand
argument.
Warning: in this release, gdb does not yet perform type or range checking.
gdb considers two Modula-2 variables type equivalent if:
TYPE
t1 =
t2 statement
As long as type checking is enabled, any attempt to combine variables whose types are not equivalent is an error.
Range checking is done on all mathematical operations, assignment, array index bounds, and all built-in functions and procedures.
::
and .
There are a few subtle differences between the Modula-2 scope operator
(.
) and the gdb scope operator (::
). The two have
similar syntax:
module . id scope :: id
where scope is the name of a module or a procedure, module the name of a module, and id is any declared identifier within your program, except another module.
Using the ::
operator makes gdb search the scope
specified by scope for the identifier id. If it is not
found in the specified scope, then gdb searches all scopes
enclosing the one specified by scope.
Using the .
operator makes gdb search the current scope for
the identifier specified by id that was imported from the
definition module specified by module. With this operator, it is
an error if the identifier id was not imported from definition
module module, or if id is not an identifier in
module.
Some gdb commands have little use when debugging Modula-2 programs.
Five subcommands of set print
and show print
apply
specifically to C and C++: ‘vtbl’, ‘demangle’,
‘asm-demangle’, ‘object’, and ‘union’. The first four
apply to C++, and the last to the C union
type, which has no direct
analogue in Modula-2.
The @
operator (see Expressions), while available
with any language, is not useful with Modula-2. Its
intent is to aid the debugging of dynamic arrays, which cannot be
created in Modula-2 as they can in C or C++. However, because an
address can be specified by an integral constant, the construct
‘{type}adrexp’ is still useful.
In gdb scripts, the Modula-2 inequality operator #
is
interpreted as the beginning of a comment. Use <>
instead.
The extensions made to gdb for Ada only support output from the gnu Ada (GNAT) compiler. Other Ada compilers are not currently supported, and attempting to debug executables produced by them is most likely to be difficult.
The Ada mode of gdb supports a fairly large subset of Ada expression syntax, with some extensions. The philosophy behind the design of this subset is
Thus, for brevity, the debugger acts as if all names declared in user-written packages are directly visible, even if they are not visible according to Ada rules, thus making it unnecessary to fully qualify most names with their packages, regardless of context. Where this causes ambiguity, gdb asks the user's intent.
The debugger will start in Ada mode if it detects an Ada main program. As for other languages, it will enter Ada mode when stopped in a program that was translated from an Ada source file.
While in Ada mode, you may use `–' for comments. This is useful mostly for documenting command files. The standard gdb comment (‘#’) still works at the beginning of a line in Ada mode, but not in the middle (to allow based literals).
The debugger supports limited overloading. Given a subprogram call in which
the function symbol has multiple definitions, it will use the number of
actual parameters and some information about their types to attempt to narrow
the set of definitions. It also makes very limited use of context, preferring
procedures to functions in the context of the call
command, and
functions to procedures elsewhere.
Here are the notable omissions from the subset:
in
) operator.
Characters.Latin_1
are not available and
concatenation is not implemented. Thus, escape characters in strings are
not currently available.
and
, or
,
xor
, not
, and relational tests other than equality)
are not implemented.
(gdb) set An_Array := (1, 2, 3, 4, 5, 6) (gdb) set An_Array := (1, others => 0) (gdb) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6) (gdb) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9)) (gdb) set A_Record := (1, "Peter", True); (gdb) set A_Record := (Name => "Peter", Id => 1, Alive => True)
Changing a
discriminant's value by assigning an aggregate has an
undefined effect if that discriminant is used within the record.
However, you can first modify discriminants by directly assigning to
them (which normally would not be allowed in Ada), and then performing an
aggregate assignment. For example, given a variable A_Rec
declared to have a type such as:
type Rec (Len : Small_Integer := 0) is record Id : Integer; Vals : IntArray (1 .. Len); end record;
you can assign a value with a different size of Vals
with two
assignments:
(gdb) set A_Rec.Len := 4 (gdb) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))
As this example also illustrates, gdb is very loose about the usual
rules concerning aggregates. You may leave out some of the
components of an array or record aggregate (such as the Len
component in the assignment to A_Rec
above); they will retain their
original values upon assignment. You may freely use dynamic values as
indices in component associations. You may even use overlapping or
redundant component associations, although which component values are
assigned in such cases is not defined.
new
operator is not implemented.
True
and False
, when not part of a qualified name,
are interpreted as if implicitly prefixed by Standard
, regardless of
context.
Should your program
redefine these names in a package or procedure (at best a dubious practice),
you will have to use fully qualified names to access their new definitions.
As it does for other languages, gdb makes certain generic extensions to Ada (see Expressions):
@
N displays the values of E and the
N-1 adjacent variables following it in memory as an array. In
Ada, this operator is generally not necessary, since its prime use is
in displaying parts of an array, and slicing will usually do this in
Ada. However, there are occasional uses when debugging programs in
which certain debugging information has been optimized away.
::
var means “the variable named var that
appears in function or file B.” When B is a file name,
you must typically surround it in single quotes.
{
type}
addr means “the variable of type
type that appears at address addr.”
In addition, gdb provides a few other shortcuts and outright additions specific to Ada:
(gdb) set x := y + 3 (gdb) print A(tmp := y + 1)
(gdb) break f (gdb) condition 1 (report(i); k += 1; A(k) > 100)
"One line.["0a"]Next line.["0a"]"
contains an ASCII newline character (Ada.Characters.Latin_1.LF
)
after each period.
(gdb) print 'max(x, y)
(3 => 10, 17, 1)
That is, in contrast to valid Ada, only the first component has a =>
clause.
(gdb) print <JMPBUF_SAVE>[0]
It is sometimes necessary to debug the program during elaboration, and
before reaching the main procedure.
As defined in the Ada Reference
Manual, the elaboration code is invoked from a procedure called
adainit
. To run your program up to the beginning of
elaboration, simply use the following two commands:
tbreak adainit
and run
.
Support for Ada tasks is analogous to that for threads (see Threads). gdb provides the following task-related commands:
info tasks
(gdb) info tasks ID TID P-ID Pri State Name 1 8088000 0 15 Child Activation Wait main_task 2 80a4000 1 15 Accept Statement b 3 809a800 1 15 Child Activation Wait a * 4 80ae800 3 15 Runnable c
In this listing, the asterisk before the last task indicates it to be the task currently being inspected.
Unactivated
Runnable
Terminated
Child Activation Wait
Accept Statement
Waiting on entry call
Async Select Wait
Delay Sleep
Child Termination Wait
Wait Child in Term Alt
Accepting RV with
tasknoinfo task
taskno(gdb) info tasks ID TID P-ID Pri State Name 1 8077880 0 15 Child Activation Wait main_task * 2 807c468 1 15 Runnable task_1 (gdb) info task 2 Ada Task: 0x807c468 Name: task_1 Thread: 0x807f378 Parent: 1 (main_task) Base Priority: 15 State: Runnable
task
(gdb) info tasks ID TID P-ID Pri State Name 1 8077870 0 15 Child Activation Wait main_task * 2 807c458 1 15 Runnable t (gdb) task [Current task is 2]
task
tasknothread
threadno
command (see Threads). It switches the context of debugging
from the current task to the given task.
(gdb) info tasks ID TID P-ID Pri State Name 1 8077870 0 15 Child Activation Wait main_task * 2 807c458 1 15 Runnable t (gdb) task 1 [Switching to task 1] #0 0x8067726 in pthread_cond_wait () (gdb) bt #0 0x8067726 in pthread_cond_wait () #1 0x8056714 in system.os_interface.pthread_cond_wait () #2 0x805cb63 in system.task_primitives.operations.sleep () #3 0x806153e in system.tasking.stages.activate_tasks () #4 0x804aacc in un () at un.adb:5
break
linespec task
tasknobreak
linespec task
taskno if ...
break ... thread ...
command (see Thread Stops).
linespec specifies source lines, as described
in Specify Location.
Use the qualifier ‘task taskno’ with a breakpoint command to specify that you only want gdb to stop the program when a particular Ada task reaches this breakpoint. taskno is one of the numeric task identifiers assigned by gdb, shown in the first column of the ‘info tasks’ display.
If you do not specify ‘task taskno’ when you set a breakpoint, the breakpoint applies to all tasks of your program.
You can use the task
qualifier on conditional breakpoints as
well; in this case, place ‘task taskno’ before the
breakpoint condition (before the if
).
For example,
(gdb) info tasks ID TID P-ID Pri State Name 1 140022020 0 15 Child Activation Wait main_task 2 140045060 1 15 Accept/Select Wait t2 3 140044840 1 15 Runnable t1 * 4 140056040 1 15 Runnable t3 (gdb) b 15 task 2 Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15. (gdb) cont Continuing. task # 1 running task # 2 running Breakpoint 5, test_task_debug () at test_task_debug.adb:15 15 flush; (gdb) info tasks ID TID P-ID Pri State Name 1 140022020 0 15 Child Activation Wait main_task * 2 140045060 1 15 Runnable t2 3 140044840 1 15 Runnable t1 4 140056040 1 15 Delay Sleep t3
When inspecting a core file, as opposed to debugging a live program, tasking support may be limited or even unavailable, depending on the platform being used. For instance, on x86-linux, the list of tasks is available, but task switching is not supported. On Tru64, however, task switching will work as usual.
On certain platforms, including Tru64, the debugger needs to perform some memory writes in order to provide Ada tasking support. When inspecting a core file, this means that the core file must be opened with read-write privileges, using the command ‘"set write on"’ (see Patching). Under these circumstances, you should make a backup copy of the core file before inspecting it with gdb.
The Ravenscar Profile is a subset of the Ada tasking features, specifically designed for systems with safety-critical real-time requirements.
set ravenscar task-switching on
set ravenscar task-switching off
show ravenscar task-switching
Besides the omissions listed previously (see Omissions from Ada), we know of several problems with and limitations of Ada mode in gdb, some of which will be fixed with planned future releases of the debugger and the GNU Ada compiler.
Standard
for any of
the standard symbols defined by the Ada language. gdb knows about
this: it will strip the prefix from names when you use it, and will never
look for a name you have so qualified among local symbols, nor match against
symbols in other packages or subprograms. If you have
defined entities anywhere in your program other than parameters and
local variables whose simple names match names in Standard
,
GNAT's lack of qualification here can cause confusion. When this happens,
you can usually resolve the confusion
by qualifying the problematic names with package
Standard
explicitly.
Older versions of the compiler sometimes generate erroneous debugging information, resulting in the debugger incorrectly printing the value of affected entities. In some cases, the debugger is able to work around an issue automatically. In other cases, the debugger is able to work around the issue, but the work-around has to be specifically enabled.
set ada trust-PAD-over-XVS on
PAD
and PAD___XVS
types are involved (see ada/exp_dbug.ads
in the GCC sources for
a complete description of the encoding used by the GNAT compiler).
This is the default.
set ada trust-PAD-over-XVS off
ada
trust-PAD-over-XVS
to off
activates a work-around which may fix
the issue. It is always safe to set ada trust-PAD-over-XVS
to
off
, but this incurs a slight performance penalty, so it is
recommended to leave this setting to on
unless necessary.
In addition to the other fully-supported programming languages,
gdb also provides a pseudo-language, called minimal
.
It does not represent a real programming language, but provides a set
of capabilities close to what the C or assembly languages provide.
This should allow most simple operations to be performed while debugging
an application that uses a language currently not supported by gdb.
If the language is set to auto
, gdb will automatically
select this language if the current frame corresponds to an unsupported
language.
The commands described in this chapter allow you to inquire about the symbols (names of variables, functions and types) defined in your program. This information is inherent in the text of your program and does not change as your program executes. gdb finds it in your program's symbol table, in the file indicated when you started gdb (see Choosing Files), or by one of the file-management commands (see Commands to Specify Files).
Occasionally, you may need to refer to symbols that contain unusual characters, which gdb ordinarily treats as word delimiters. The most frequent case is in referring to static variables in other source files (see Program Variables). File names are recorded in object files as debugging symbols, but gdb would ordinarily parse a typical file name, like foo.c, as the three words ‘foo’ ‘.’ ‘c’. To allow gdb to recognize ‘foo.c’ as a single symbol, enclose it in single quotes; for example,
p 'foo.c'::x
looks up the value of x
in the scope of the file foo.c.
set case-sensitive on
set case-sensitive off
set case-sensitive auto
set
case-sensitive
lets you do that by specifying on
for
case-sensitive matches or off
for case-insensitive ones. If
you specify auto
, case sensitivity is reset to the default
suitable for the source language. The default is case-sensitive
matches for all languages except for Fortran, for which the default is
case-insensitive matches.
show case-sensitive
info address
symbolNote the contrast with ‘print &symbol’, which does not work at all for a register variable, and for a stack local variable prints the exact address of the current instantiation of the variable.
info symbol
addr(gdb) info symbol 0x54320 _initialize_vx + 396 in section .text
This is the opposite of the info address
command. You can use
it to find out the name of a variable or a function given its address.
For dynamically linked executables, the name of executable or shared library containing the symbol is also printed:
(gdb) info symbol 0x400225 _start + 5 in section .text of /tmp/a.out (gdb) info symbol 0x2aaaac2811cf __read_nocancel + 6 in section .text of /usr/lib64/libc.so.6
whatis [
arg]
$
, the
last value in the value history. If arg is an expression, it is
not actually evaluated, and any side-effecting operations (such as
assignments or function calls) inside it do not take place. If
arg is a type name, it may be the name of a type or typedef, or
for C code it may have the form ‘class class-name’,
‘struct struct-tag’, ‘union union-tag’ or
‘enum enum-tag’.
See Expressions.
ptype [
arg]
ptype
accepts the same arguments as whatis
, but prints a
detailed description of the type, instead of just the name of the type.
See Expressions.
For example, for this variable declaration:
struct complex {double real; double imag;} v;
the two commands give this output:
(gdb) whatis v type = struct complex (gdb) ptype v type = struct complex { double real; double imag; }
As with whatis
, using ptype
without an argument refers to
the type of $
, the last value in the value history.
Sometimes, programs use opaque data types or incomplete specifications of complex data structure. If the debug information included in the program does not allow gdb to display a full declaration of the data type, it will say ‘<incomplete type>’. For example, given these declarations:
struct foo; struct foo *fooptr;
but no definition for struct foo
itself, gdb will say:
(gdb) ptype foo $1 = <incomplete type>
“Incomplete type” is C terminology for data types that are not completely specified.
info types
regexpinfo types
value
, but
‘i type ^value$’ gives information only on types whose complete
name is value
.
This command differs from ptype
in two ways: first, like
whatis
, it does not print a detailed description; second, it
lists all source files where a type is defined.
info scope
location(gdb) info scope command_line_handler Scope for command_line_handler: Symbol rl is an argument at stack/frame offset 8, length 4. Symbol linebuffer is in static storage at address 0x150a18, length 4. Symbol linelength is in static storage at address 0x150a1c, length 4. Symbol p is a local variable in register $esi, length 4. Symbol p1 is a local variable in register $ebx, length 4. Symbol nline is a local variable in register $edx, length 4. Symbol repeat is a local variable at frame offset -8, length 4.
This command is especially useful for determining what data to collect during a trace experiment, see collect.
info source
info sources
info functions
info functions
regexpstep
; ‘info fun ^step’ finds those whose names
start with step
. If a function name contains characters
that conflict with the regular expression language (e.g.
‘operator*()’), they may be quoted with a backslash.
info variables
info variables
regexpinfo classes
info classes
regexpinfo selectors
info selectors
regexpSome systems allow individual object files that make up your program to be replaced without stopping and restarting your program. For example, in VxWorks you can simply recompile a defective object file and keep on running. If you are running on one of these systems, you can allow gdb to reload the symbols for automatically relinked modules:
set symbol-reloading on
set symbol-reloading off
symbol-reloading
off, since otherwise gdb
may discard symbols when linking large programs, that may contain
several modules (from different directories or libraries) with the same
name.
show symbol-reloading
on
or off
setting.
set opaque-type-resolution on
struct
, class
, or
union
—for example, struct MyType *
—that is used in one
source file although the full declaration of struct MyType
is in
another source file. The default is on.
A change in the setting of this subcommand will not take effect until
the next time symbols for a file are loaded.
set opaque-type-resolution off
{<no data fields>}
show opaque-type-resolution
maint print symbols
filenamemaint print psymbols
filenamemaint print msymbols
filenameinfo sources
to find out which files these are. If you
use ‘maint print psymbols’ instead, the dump shows information about
symbols that gdb only knows partially—that is, symbols defined in
files that gdb has skimmed, but not yet read completely. Finally,
‘maint print msymbols’ dumps just the minimal symbol information
required for each object file from which gdb has read some symbols.
See Commands to Specify Files, for a discussion of how
gdb reads symbols (in the description of symbol-file
).
maint info symtabs
[ regexp ]maint info psymtabs
[ regexp ]struct symtab
or struct partial_symtab
structures whose names match regexp. If regexp is not
given, list them all. The output includes expressions which you can
copy into a gdb debugging this one to examine a particular
structure in more detail. For example:
(gdb) maint info psymtabs dwarf2read { objfile /home/gnu/build/gdb/gdb ((struct objfile *) 0x82e69d0) { psymtab /home/gnu/src/gdb/dwarf2read.c ((struct partial_symtab *) 0x8474b10) readin no fullname (null) text addresses 0x814d3c8 -- 0x8158074 globals (* (struct partial_symbol **) 0x8507a08 @ 9) statics (* (struct partial_symbol **) 0x40e95b78 @ 2882) dependencies (none) } } (gdb) maint info symtabs (gdb)
We see that there is one partial symbol table whose filename contains the string ‘dwarf2read’, belonging to the ‘gdb’ executable; and we see that gdb has not read in any symtabs yet at all. If we set a breakpoint on a function, that will cause gdb to read the symtab for the compilation unit containing that function:
(gdb) break dwarf2_psymtab_to_symtab Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c, line 1574. (gdb) maint info symtabs { objfile /home/gnu/build/gdb/gdb ((struct objfile *) 0x82e69d0) { symtab /home/gnu/src/gdb/dwarf2read.c ((struct symtab *) 0x86c1f38) dirname (null) fullname (null) blockvector ((struct blockvector *) 0x86c1bd0) (primary) linetable ((struct linetable *) 0x8370fa0) debugformat DWARF 2 } } (gdb)
Once you think you have found an error in your program, you might want to find out for certain whether correcting the apparent error would lead to correct results in the rest of the run. You can find the answer by experiment, using the gdb features for altering execution of the program.
For example, you can store new values into variables or memory locations, give your program a signal, restart it at a different address, or even return prematurely from a function.
To alter the value of a variable, evaluate an assignment expression. See Expressions. For example,
print x=4
stores the value 4 into the variable x
, and then prints the
value of the assignment expression (which is 4).
See Using gdb with Different Languages, for more
information on operators in supported languages.
If you are not interested in seeing the value of the assignment, use the
set
command instead of the print
command. set
is
really the same as print
except that the expression's value is
not printed and is not put in the value history (see Value History). The expression is evaluated only for its effects.
If the beginning of the argument string of the set
command
appears identical to a set
subcommand, use the set
variable
command instead of just set
. This command is identical
to set
except for its lack of subcommands. For example, if your
program has a variable width
, you get an error if you try to set
a new value with just ‘set width=13’, because gdb has the
command set width
:
(gdb) whatis width type = double (gdb) p width $4 = 13 (gdb) set width=47 Invalid syntax in expression.
The invalid expression, of course, is ‘=47’. In
order to actually set the program's variable width
, use
(gdb) set var width=47
Because the set
command has many subcommands that can conflict
with the names of program variables, it is a good idea to use the
set variable
command instead of just set
. For example, if
your program has a variable g
, you run into problems if you try
to set a new value with just ‘set g=4’, because gdb has
the command set gnutarget
, abbreviated set g
:
(gdb) whatis g type = double (gdb) p g $1 = 1 (gdb) set g=4 (gdb) p g $2 = 1 (gdb) r The program being debugged has been started already. Start it from the beginning? (y or n) y Starting program: /home/smith/cc_progs/a.out "/home/smith/cc_progs/a.out": can't open to read symbols: Invalid bfd target. (gdb) show g The current BFD target is "=4".
The program variable g
did not change, and you silently set the
gnutarget
to an invalid value. In order to set the variable
g
, use
(gdb) set var g=4
gdb allows more implicit conversions in assignments than C; you can freely store an integer value into a pointer variable or vice versa, and you can convert any structure to any other structure that is the same length or shorter.
To store values into arbitrary places in memory, use the ‘{...}’
construct to generate a value of specified type at a specified address
(see Expressions). For example, {int}0x83040
refers
to memory location 0x83040
as an integer (which implies a certain size
and representation in memory), and
set {int}0x83040 = 4
stores the value 4 into that memory location.
Ordinarily, when you continue your program, you do so at the place where
it stopped, with the continue
command. You can instead continue at
an address of your own choosing, with the following commands:
jump
linespecjump
locationtbreak
command in conjunction with
jump
. See Setting Breakpoints.
The jump
command does not change the current stack frame, or
the stack pointer, or the contents of any memory location or any
register other than the program counter. If line linespec is in
a different function from the one currently executing, the results may
be bizarre if the two functions expect different patterns of arguments or
of local variables. For this reason, the jump
command requests
confirmation if the specified line is not in the function currently
executing. However, even bizarre results are predictable if you are
well acquainted with the machine-language code of your program.
On many systems, you can get much the same effect as the jump
command by storing a new value into the register $pc
. The
difference is that this does not start your program running; it only
changes the address of where it will run when you continue. For
example,
set $pc = 0x485
makes the next continue
command or stepping command execute at
address 0x485
, rather than at the address where your program stopped.
See Continuing and Stepping.
The most common occasion to use the jump
command is to back
up—perhaps with more breakpoints set—over a portion of a program
that has already executed, in order to examine its execution in more
detail.
signal
signalsignal 2
and signal
SIGINT
are both ways of sending an interrupt signal.
Alternatively, if signal is zero, continue execution without
giving a signal. This is useful when your program stopped on account of
a signal and would ordinary see the signal when resumed with the
continue
command; ‘signal 0’ causes it to resume without a
signal.
signal
does not repeat when you press <RET> a second time
after executing the command.
Invoking the signal
command is not the same as invoking the
kill
utility from the shell. Sending a signal with kill
causes gdb to decide what to do with the signal depending on
the signal handling tables (see Signals). The signal
command
passes the signal directly to your program.
return
return
expressionreturn
command. If you give an
expression argument, its value is used as the function's return
value.
When you use return
, gdb discards the selected stack frame
(and all frames within it). You can think of this as making the
discarded frame return prematurely. If you wish to specify a value to
be returned, give that value as the argument to return
.
This pops the selected stack frame (see Selecting a Frame), and any other frames inside of it, leaving its caller as the innermost remaining frame. That frame becomes selected. The specified value is stored in the registers used for returning values of functions.
The return
command does not resume execution; it leaves the
program stopped in the state that would exist if the function had just
returned. In contrast, the finish
command (see Continuing and Stepping) resumes execution until the
selected stack frame returns naturally.
gdb needs to know how the expression argument should be set for
the inferior. The concrete registers assignment depends on the OS ABI and the
type being returned by the selected stack frame. For example it is common for
OS ABI to return floating point values in FPU registers while integer values in
CPU registers. Still some ABIs return even floating point values in CPU
registers. Larger integer widths (such as long long int
) also have
specific placement rules. gdb already knows the OS ABI from its
current target so it needs to find out also the type being returned to make the
assignment into the right register(s).
Normally, the selected stack frame has debug info. gdb will always
use the debug info instead of the implicit type of expression when the
debug info is available. For example, if you type return -1, and the
function in the current stack frame is declared to return a long long
int
, gdb transparently converts the implicit int
value of -1
into a long long int
:
Breakpoint 1, func () at gdb.base/return-nodebug.c:29 29 return 31; (gdb) return -1 Make func return now? (y or n) y #0 0x004004f6 in main () at gdb.base/return-nodebug.c:43 43 printf ("result=%lld\n", func ()); (gdb)
However, if the selected stack frame does not have a debug info, e.g., if the
function was compiled without debug info, gdb has to find out the type
to return from user. Specifying a different type by mistake may set the value
in different inferior registers than the caller code expects. For example,
typing return -1 with its implicit type int
would set only a part
of a long long int
result for a debug info less function (on 32-bit
architectures). Therefore the user is required to specify the return type by
an appropriate cast explicitly:
Breakpoint 2, 0x0040050b in func () (gdb) return -1 Return value type not available for selected stack frame. Please use an explicit cast of the value to return. (gdb) return (long long int) -1 Make selected stack frame return now? (y or n) y #0 0x00400526 in main () (gdb)
print
exprcall
exprvoid
returned values.
You can use this variant of the print
command if you want to
execute a function from your program that does not return anything
(a.k.a. a void function), but without cluttering the output
with void
returned values that gdb will otherwise
print. If the result is not void, it is printed and saved in the
value history.
It is possible for the function you call via the print
or
call
command to generate a signal (e.g., if there's a bug in
the function, or if you passed it incorrect arguments). What happens
in that case is controlled by the set unwindonsignal
command.
Similarly, with a C++ program it is possible for the function you
call via the print
or call
command to generate an
exception that is not handled due to the constraints of the dummy
frame. In this case, any exception that is raised in the frame, but has
an out-of-frame exception handler will not be found. GDB builds a
dummy-frame for the inferior function call, and the unwinder cannot
seek for exception handlers outside of this dummy-frame. What happens
in that case is controlled by the
set unwind-on-terminating-exception
command.
set unwindonsignal
show unwindonsignal
set unwind-on-terminating-exception
show unwind-on-terminating-exception
Sometimes, a function you wish to call is actually a weak alias for another function. In such case, gdb might not pick up the type information, including the types of the function arguments, which causes gdb to call the inferior function incorrectly. As a result, the called function will function erroneously and may even crash. A solution to that is to use the name of the aliased function instead.
By default, gdb opens the file containing your program's executable code (or the corefile) read-only. This prevents accidental alterations to machine code; but it also prevents you from intentionally patching your program's binary.
If you'd like to be able to patch the binary, you can specify that
explicitly with the set write
command. For example, you might
want to turn on internal debugging flags, or even to make emergency
repairs.
set write on
set write off
If you have already loaded a file, you must load it again (using the
exec-file
or core-file
command) after changing set
write
, for your new setting to take effect.
show write
gdb needs to know the file name of the program to be debugged, both in order to read its symbol table and in order to start your program. To debug a core dump of a previous run, you must also tell gdb the name of the core dump file.
You may want to specify executable and core dump file names. The usual way to do this is at start-up time, using the arguments to gdb's start-up commands (see Getting In and Out of gdb).
Occasionally it is necessary to change to a different file during a
gdb session. Or you may run gdb and forget to
specify a file you want to use. Or you are debugging a remote target
via gdbserver
(see file). In these situations the gdb commands to specify
new files are useful.
file
filenamerun
command. If you do not specify a
directory and the file is not found in the gdb working directory,
gdb uses the environment variable PATH
as a list of
directories to search, just as the shell does when looking for a program
to run. You can change the value of this variable, for both gdb
and your program, using the path
command.
You can load unlinked object .o files into gdb using
the file
command. You will not be able to “run” an object
file, but you can disassemble functions and inspect variables. Also,
if the underlying BFD functionality supports it, you could use
gdb -write to patch object files using this technique. Note
that gdb can neither interpret nor modify relocations in this
case, so branches and some initialized variables will appear to go to
the wrong place. But this feature is still handy from time to time.
file
file
with no argument makes gdb discard any information it
has on both executable file and the symbol table.
exec-file
[ filename ]PATH
if necessary to locate your program. Omitting filename means to
discard information on the executable file.
symbol-file
[ filename ]PATH
is
searched when necessary. Use the file
command to get both symbol
table and program to run from the same file.
symbol-file
with no argument clears out gdb information on your
program's symbol table.
The symbol-file
command causes gdb to forget the contents of
some breakpoints and auto-display expressions. This is because they may
contain pointers to the internal data recording symbols and data types,
which are part of the old symbol table data being discarded inside
gdb.
symbol-file
does not repeat if you press <RET> again after
executing it once.
When gdb is configured for a particular environment, it understands debugging information in whatever format is the standard generated for that environment; you may use either a gnu compiler, or other compilers that adhere to the local conventions. Best results are usually obtained from gnu compilers; for example, using gcc you can generate debugging information for optimized code.
For most kinds of object files, with the exception of old SVR3 systems
using COFF, the symbol-file
command does not normally read the
symbol table in full right away. Instead, it scans the symbol table
quickly to find which source files and which symbols are present. The
details are read later, one source file at a time, as they are needed.
The purpose of this two-stage reading strategy is to make gdb
start up faster. For the most part, it is invisible except for
occasional pauses while the symbol table details for a particular source
file are being read. (The set verbose
command can turn these
pauses into messages if desired. See Optional Warnings and Messages.)
We have not implemented the two-stage strategy for COFF yet. When the
symbol table is stored in COFF format, symbol-file
reads the
symbol table data in full right away. Note that “stabs-in-COFF”
still does the two-stage strategy, since the debug info is actually
in stabs format.
symbol-file
[ -readnow
] filenamefile
[ -readnow
] filenamecore-file
[filename]core
core-file
with no argument specifies that no core file is
to be used.
Note that the core file is ignored when your program is actually running
under gdb. So, if you have been running your program and you
wish to debug a core file instead, you must kill the subprocess in which
the program is running. To do this, use the kill
command
(see Killing the Child Process).
add-symbol-file
filename addressadd-symbol-file
filename address [ -readnow
]add-symbol-file
filename -ssection address ...
add-symbol-file
command reads additional symbol table
information from the file filename. You would use this command
when filename has been dynamically loaded (by some other means)
into the program that is running. address should be the memory
address at which the file has been loaded; gdb cannot figure
this out for itself. You can additionally specify an arbitrary number
of ‘-ssection address’ pairs, to give an explicit
section name and base address for that section. You can specify any
address as an expression.
The symbol table of the file filename is added to the symbol table
originally read with the symbol-file
command. You can use the
add-symbol-file
command any number of times; the new symbol data
thus read keeps adding to the old. To discard all old symbol data
instead, use the symbol-file
command without any arguments.
Although filename is typically a shared library file, an executable file, or some other object file which has been fully relocated for loading into a process, you can also load symbolic information from relocatable .o files, as long as:
add-symbol-file
command.
Some embedded operating systems, like Sun Chorus and VxWorks, can load
relocatable files into an already running program; such systems
typically make the requirements above easy to meet. However, it's
important to recognize that many native systems use complex link
procedures (.linkonce
section factoring and C++ constructor table
assembly, for example) that make the requirements difficult to meet. In
general, one cannot assume that using add-symbol-file
to read a
relocatable object file's symbolic information will have the same effect
as linking the relocatable object file into the program in the normal
way.
add-symbol-file
does not repeat if you press <RET> after using it.
add-symbol-file-from-memory
addresssyscall DSO
into each
process's address space; this DSO provides kernel-specific code for
some system calls. The argument can be any expression whose
evaluation yields the address of the file's shared object file header.
For this command to work, you must have used symbol-file
or
exec-file
commands in advance.
add-shared-symbol-files
library-fileassf
library-fileadd-shared-symbol-files
command can currently be used only
in the Cygwin build of gdb on MS-Windows OS, where it is an
alias for the dll-symbols
command (see Cygwin Native).
gdb automatically looks for shared libraries, however if
gdb does not find yours, you can invoke
add-shared-symbol-files
. It takes one argument: the shared
library's file name. assf
is a shorthand alias for
add-shared-symbol-files
.
section
section addrsection
command changes the base address of the named
section of the exec file to addr. This can be used if the
exec file does not contain section addresses, (such as in the
a.out
format), or when the addresses specified in the file
itself are wrong. Each section must be changed separately. The
info files
command, described below, lists all the sections and
their addresses.
info files
info target
info files
and info target
are synonymous; both print the
current target (see Specifying a Debugging Target),
including the names of the executable and core dump files currently in
use by gdb, and the files from which symbols were loaded. The
command help target
lists all possible targets rather than
current ones.
maint info sections
maint info sections
. In addition to the section information
displayed by info files
, this command displays the flags and file
offset of each section in the executable and core dump files. In addition,
maint info sections
provides the following command options (which
may be arbitrarily combined):
ALLOBJ
ALLOC
LOAD
.bss
sections.
RELOC
READONLY
CODE
DATA
ROM
CONSTRUCTOR
HAS_CONTENTS
NEVER_LOAD
COFF_SHARED_LIBRARY
IS_COMMON
set trust-readonly-sections on
The default is off.
set trust-readonly-sections off
show trust-readonly-sections
All file-specifying commands allow both absolute and relative file names as arguments. gdb always converts the file name to an absolute file name and remembers it that way.
gdb supports gnu/Linux, MS-Windows, HP-UX, SunOS, SVr4, Irix, and IBM RS/6000 AIX shared libraries.
On MS-Windows gdb must be linked with the Expat library to support shared libraries. See Expat.
gdb automatically loads symbol definitions from shared libraries
when you use the run
command, or when you examine a core file.
(Before you issue the run
command, gdb does not understand
references to a function in a shared library, however—unless you are
debugging a core file).
On HP-UX, if the program loads a library explicitly, gdb
automatically loads the symbols at the time of the shl_load
call.
There are times, however, when you may wish to not automatically load symbol definitions from shared libraries, such as when they are particularly large or there are many of them.
To control the automatic loading of shared library symbols, use the commands:
set auto-solib-add
modeon
, symbols from all shared object libraries
will be loaded automatically when the inferior begins execution, you
attach to an independently started inferior, or when the dynamic linker
informs gdb that a new library has been loaded. If mode
is off
, symbols must be loaded manually, using the
sharedlibrary
command. The default value is on
.
If your program uses lots of shared libraries with debug info that takes large amounts of memory, you can decrease the gdb memory footprint by preventing it from automatically loading the symbols from shared libraries. To that end, type set auto-solib-add off before running the inferior, then load each library whose debug symbols you do need with sharedlibrary regexp, where regexp is a regular expression that matches the libraries whose symbols you want to be loaded.
show auto-solib-add
To explicitly load shared library symbols, use the sharedlibrary
command:
info share
regexinfo sharedlibrary
regexsharedlibrary
regexshare
regexrun
. If
regex is omitted all shared libraries required by your program are
loaded.
nosharedlibrary
Sometimes you may wish that gdb stops and gives you control
when any of shared library events happen. Use the set
stop-on-solib-events
command for this:
set stop-on-solib-events
show stop-on-solib-events
Shared libraries are also supported in many cross or remote debugging configurations. gdb needs to have access to the target's libraries; this can be accomplished either by providing copies of the libraries on the host system, or by asking gdb to automatically retrieve the libraries from the target. If copies of the target libraries are provided, they need to be the same as the target libraries, although the copies on the target can be stripped as long as the copies on the host are not.
For remote debugging, you need to tell gdb where the target libraries are, so that it can load the correct copies—otherwise, it may try to load the host's libraries. gdb has two variables to specify the search directories for target libraries.
set sysroot
pathset sysroot
to find shared
libraries, they need to be laid out in the same way that they are on
the target, with e.g. a /lib and /usr/lib hierarchy
under path.
If path starts with the sequence remote:, gdb will
retrieve the target libraries from the remote system. This is only
supported when using a remote target that supports the remote get
command (see Sending files to a remote system).
The part of path following the initial remote:
(if present) is used as system root prefix on the remote file system.
12
For targets with an MS-DOS based filesystem, such as MS-Windows and SymbianOS, gdb tries prefixing a few variants of the target absolute file name with path. But first, on Unix hosts, gdb converts all backslash directory separators into forward slashes, because the backslash is not a directory separator on Unix:
c:\foo\bar.dll ⇒ c:/foo/bar.dll
Then, gdb attempts prefixing the target file name with path, and looks for the resulting file name in the host file system:
c:/foo/bar.dll ⇒ /path/to/sysroot/c:/foo/bar.dll
If that does not find the shared library, gdb tries removing the ‘:’ character from the drive spec, both for convenience, and, for the case of the host file system not supporting file names with colons:
c:/foo/bar.dll ⇒ /path/to/sysroot/c/foo/bar.dll
This makes it possible to have a system root that mirrors a target with more than one drive. E.g., you may want to setup your local copies of the target system shared libraries like so (note ‘c’ vs ‘z’):
/path/to/sysroot/c/sys/bin/foo.dll /path/to/sysroot/c/sys/bin/bar.dll /path/to/sysroot/z/sys/bin/bar.dll
and point the system root at /path/to/sysroot, so that gdb can find the correct copies of both c:\sys\bin\foo.dll, and z:\sys\bin\bar.dll.
If that still does not find the shared library, gdb tries removing the whole drive spec from the target file name:
c:/foo/bar.dll ⇒ /path/to/sysroot/foo/bar.dll
This last lookup makes it possible to not care about the drive name, if you don't want or need to.
The set solib-absolute-prefix
command is an alias for set
sysroot
.
You can set the default system root by using the configure-time ‘--with-sysroot’ option. If the system root is inside gdb's configured binary prefix (set with ‘--prefix’ or ‘--exec-prefix’), then the default system root will be updated automatically if the installed gdb is moved to a new location.
show sysroot
set solib-search-path
pathshow solib-search-path
set target-file-system-kind
kindShared library file names as reported by the target system may not
make sense as is on the system gdb is running on. For
example, when remote debugging a target that has MS-DOS based file
system semantics, from a Unix host, the target may be reporting to
gdb a list of loaded shared libraries with file names such as
c:\Windows\kernel32.dll. On Unix hosts, there's no concept of
drive letters, so the ‘c:\’ prefix is not normally understood as
indicating an absolute file name, and neither is the backslash
normally considered a directory separator character. In that case,
the native file system would interpret this whole absolute file name
as a relative file name with no directory components. This would make
it impossible to point gdb at a copy of the remote target's
shared libraries on the host using set sysroot
, and impractical
with set solib-search-path
. Setting
target-file-system-kind
to dos-based
tells gdb
to interpret such file names similarly to how the target would, and to
map them to file names valid on gdb's native file system
semantics. The value of kind can be "auto"
, in addition
to one of the supported file system kinds. In that case, gdb
tries to determine the appropriate file system variant based on the
current target's operating system (see Configuring the Current ABI). The supported file system settings are:
unix
dos-based
auto
gdb allows you to put a program's debugging information in a file separate from the executable itself, in a way that allows gdb to find and load the debugging information automatically. Since debugging information can be very large—sometimes larger than the executable code itself—some systems distribute debugging information for their executables in separate files, which users can install only when they need to debug a problem.
gdb supports two ways of specifying the separate debug info file:
Depending on the way the debug info file is specified, gdb uses two different methods of looking for the debug file:
So, for example, suppose you ask gdb to debug
/usr/bin/ls, which has a debug link that specifies the
file ls.debug, and a build ID whose value in hex is
abcdef1234
. If the global debug directory is
/usr/lib/debug, then gdb will look for the following
debug information files, in the indicated order:
You can set the global debugging info directory's name, and view the name gdb is currently using.
set debug-file-directory
directoriesshow debug-file-directory
You can also adjust the current verbosity of the build id locating.
set build-id-verbose 0
set build-id-verbose 1
set build-id-verbose 2
show build-id-verbose
A debug link is a special section of the executable file named
.gnu_debuglink
. The section must contain:
Any executable file format can carry a debug link, as long as it can
contain a section named .gnu_debuglink
with the contents
described above.
The build ID is a special section in the executable file (and in other
ELF binary files that gdb may consider). This section is
often named .note.gnu.build-id
, but that name is not mandatory.
It contains unique identification for the built files—the ID remains
the same across multiple builds of the same build tree. The default
algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
content for the build ID string. The same section with an identical
value is present in the original built binary with symbols, in its
stripped variant, and in the separate debugging information file.
The debugging information file itself should be an ordinary
executable, containing a full set of linker symbols, sections, and
debugging information. The sections of the debugging information file
should have the same names, addresses, and sizes as the original file,
but they need not contain any data—much like a .bss
section
in an ordinary executable.
The gnu binary utilities (Binutils) package includes the ‘objcopy’ utility that can produce the separated executable / debugging information file pairs using the following commands:
objcopy --only-keep-debug foo foo.debug strip -g foo
These commands remove the debugging information from the executable file foo and place it in the file foo.debug. You can use the first, second or both methods to link the two files:
objcopy --add-gnu-debuglink=foo.debug foo
Ulrich Drepper's elfutils package, starting with version 0.53, contains
a version of the strip
command such that the command strip foo -f
foo.debug has the same functionality as the two objcopy
commands and
the ln -s
command above, together.
ld --build-id
or
the gcc counterpart gcc -Wl,--build-id
. Build ID support plus
compatibility fixes for debug files separation are present in gnu binary
utilities (Binutils) package since version 2.18.
The CRC used in .gnu_debuglink
is the CRC-32 defined in
IEEE 802.3 using the polynomial:
x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 + x2 + x + 1
The function is computed byte at a time, taking the least
significant bit of each byte first. The initial pattern
0xffffffff
is used, to ensure leading zeros affect the CRC and
the final result is inverted to ensure trailing zeros also affect the
CRC.
Note: This is the same CRC polynomial as used in handling the
Remote Serial Protocol qCRC
packet (see gdb Remote Serial Protocol). However in the
case of the Remote Serial Protocol, the CRC is computed most
significant bit first, and the result is not inverted, so trailing
zeros have no effect on the CRC value.
To complete the description, we show below the code of the function
which produces the CRC used in .gnu_debuglink
. Inverting the
initially supplied crc
argument means that an initial call to
this function passing in zero will start computing the CRC using
0xffffffff
.
unsigned long gnu_debuglink_crc32 (unsigned long crc, unsigned char *buf, size_t len) { static const unsigned long crc32_table[256] = { 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f, 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9, 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d }; unsigned char *end; crc = ~crc & 0xffffffff; for (end = buf + len; buf < end; ++buf) crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8); return ~crc & 0xffffffff; }
This computation does not apply to the “build ID” method.
When gdb finds a symbol file, it scans the symbols in the file in order to construct an internal symbol table. This lets most gdb operations work quickly—at the cost of a delay early on. For large programs, this delay can be quite lengthy, so gdb provides a way to build an index, which speeds up startup.
The index is stored as a section in the symbol file. gdb can write the index to a file, then you can put it into the symbol file using objcopy.
To create an index file, use the save gdb-index
command:
save gdb-index
directoryOnce you have created an index file you can merge it into your symbol file, here named symfile, using objcopy:
$ objcopy --add-section .gdb_index=symfile.gdb-index \ --set-section-flags .gdb_index=readonly symfile symfile
There are currently some limitation on indices. They only work when for DWARF debugging information, not stabs. And, they do not currently work for programs using Ada.
gdb comes with a program, gdb-add-index, which can be used to add the index to a symbol file. It takes the symbol file as its only argument:
$ gdb-add-index symfile
While reading a symbol file, gdb occasionally encounters problems,
such as symbol types it does not recognize, or known bugs in compiler
output. By default, gdb does not notify you of such problems, since
they are relatively common and primarily of interest to people
debugging compilers. If you are interested in seeing information
about ill-constructed symbol tables, you can either ask gdb to print
only one message about each such type of problem, no matter how many
times the problem occurs; or you can ask gdb to print more messages,
to see how many times the problems occur, with the set
complaints
command (see Optional Warnings and Messages).
The messages currently printed, and their meanings, include:
inner block not inside outer block in
symbolgdb circumvents the problem by treating the inner block as if it had
the same scope as the outer block. In the error message, symbol
may be shown as “(don't know)
” if the outer block is not a
function.
block at
address out of order
gdb does not circumvent this problem, and has trouble
locating symbols in the source file whose symbols it is reading. (You
can often determine what source file is affected by specifying
set verbose on
. See Optional Warnings and Messages.)
bad block start address patched
gdb circumvents the problem by treating the symbol scope block as
starting on the previous source line.
bad string table offset in symbol
ngdb circumvents the problem by considering the symbol to have the
name foo
, which may cause other problems if many symbols end up
with this name.
unknown symbol type 0x
nn0x
nn is the symbol type of the
uncomprehended information, in hexadecimal.
gdb circumvents the error by ignoring this symbol information.
This usually allows you to debug your program, though certain symbols
are not accessible. If you encounter such a problem and feel like
debugging it, you can debug gdb
with itself, breakpoint
on complain
, then go up to the function read_dbx_symtab
and examine *bufp
to see the symbol.
stub type has NULL name
const/volatile indicator missing (ok if using g++ v1.x), got...
info mismatch between compiler and debugger
gdb will sometimes read an auxiliary data file. These files are kept in a directory known as the data directory.
You can set the data directory's name, and view the name gdb is currently using.
set data-directory
directoryshow data-directory
You can set the default data directory by using the configure-time ‘--with-gdb-datadir’ option. If the data directory is inside gdb's configured binary prefix (set with ‘--prefix’ or ‘--exec-prefix’), then the default data directory will be updated automatically if the installed gdb is moved to a new location.
The data directory may also be specified with the
--data-directory
command line option.
See Mode Options.
A target is the execution environment occupied by your program.
Often, gdb runs in the same host environment as your program;
in that case, the debugging target is specified as a side effect when
you use the file
or core
commands. When you need more
flexibility—for example, running gdb on a physically separate
host, or controlling a standalone system over a serial port or a
realtime system over a TCP/IP connection—you can use the target
command to specify one of the target types configured for gdb
(see Commands for Managing Targets).
It is possible to build gdb for several different target architectures. When gdb is built like that, you can choose one of the available architectures with the set architecture command.
set architecture
arch"auto"
, in addition to one of the
supported architectures.
show architecture
set processor
processor
set architecture
and show architecture
.
There are multiple classes of targets such as: processes, executable files or
recording sessions. Core files belong to the process class, making core file
and process mutually exclusive. Otherwise, gdb can work concurrently
on multiple active targets, one in each class. This allows you to (for
example) start a process and inspect its activity, while still having access to
the executable file after the process finishes. Or if you start process
recording (see Reverse Execution) and reverse-step
there, you are
presented a virtual layer of the recording target, while the process target
remains stopped at the chronologically last point of the process execution.
Use the core-file
and exec-file
commands to select a new core
file or executable target (see Commands to Specify Files). To
specify as a target a process that is already running, use the attach
command (see Debugging an Already-running Process).
target
type parametersFurther parameters are interpreted by the target protocol, but typically include things like device names or host names to connect with, process numbers, and baud rates.
The target
command does not repeat if you press <RET> again
after executing the command.
help target
info target
or info files
(see Commands to Specify Files).
help target
nameset gnutarget
argsset gnutarget
command. Unlike most target
commands,
with gnutarget
the target
refers to a program, not a machine.
Warning: To specify a file format with set gnutarget
,
you must know the actual BFD name.
show gnutarget
show gnutarget
command to display what file format
gnutarget
is set to read. If you have not set gnutarget
,
gdb will determine the file format for each file automatically,
and show gnutarget
displays ‘The current BDF target is "auto"’.
Here are some common targets (available, or not, depending on the GDB configuration):
target exec
programtarget core
filenametarget remote
mediumFor example, if you have a board connected to /dev/ttya on the machine running gdb, you could say:
target remote /dev/ttya
target remote
supports the load
command. This is only
useful if you have some other way of getting the stub to the target
system, and you can put it somewhere in memory where it won't get
clobbered by the download.
target sim
[simargs] ...
target sim load run
works; however, you cannot assume that a specific memory map, device drivers, or even basic I/O is available, although some simulators do provide these. For info about any processor-specific simulator details, see the appropriate section in Embedded Processors.
Some configurations may include these targets as well:
target nrom
devDifferent targets are available on different configurations of gdb; your configuration may have more or fewer targets.
Many remote targets require you to download the executable's code once you've successfully established a connection. You may wish to control various aspects of this process.
set hash
show hash
set debug monitor
show debug monitor
load
filenameload
command may be available. Where it exists, it
is meant to make filename (an executable) available for debugging
on the remote system—by downloading, or dynamic linking, for example.
load
also records the filename symbol table in gdb, like
the add-symbol-file
command.
If your gdb does not have a load
command, attempting to
execute it gets the error message “You can't do that when your
target is ...
”
The file is loaded at whatever address is specified in the executable. For some object file formats, you can specify the load address when you link the program; for other formats, like a.out, the object file format specifies a fixed address.
Depending on the remote side capabilities, gdb may be able to load programs into flash memory.
load
does not repeat if you press <RET> again after using it.
Some types of processors, such as the MIPS, PowerPC, and Renesas SH, offer the ability to run either big-endian or little-endian byte orders. Usually the executable or symbol will include a bit to designate the endian-ness, and you will not need to worry about which to use. However, you may still find it useful to adjust gdb's idea of processor endian-ness manually.
set endian big
set endian little
set endian auto
show endian
Note that these commands merely adjust interpretation of symbolic data on the host, and that they have absolutely no effect on the target system.
If you are trying to debug a program running on a machine that cannot run gdb in the usual way, it is often useful to use remote debugging. For example, you might use remote debugging on an operating system kernel, or on a small system which does not have a general purpose operating system powerful enough to run a full-featured debugger.
Some configurations of gdb have special serial or TCP/IP interfaces to make this work with particular debugging targets. In addition, gdb comes with a generic serial protocol (specific to gdb, but not specific to any particular target system) which you can use if you write the remote stubs—the code that runs on the remote system to communicate with gdb.
Other remote targets may be available in your
configuration of gdb; use help target
to list them.
On the gdb host machine, you will need an unstripped copy of your program, since gdb needs symbol and debugging information. Start up gdb as usual, using the name of the local copy of your program as the first argument.
gdb can communicate with the target over a serial line, or
over an IP network using TCP or UDP. In
each case, gdb uses the same protocol for debugging your
program; only the medium carrying the debugging packets varies. The
target remote
command establishes a connection to the target.
Its arguments indicate which medium to use:
target remote
serial-devicetarget remote /dev/ttyb
If you're using a serial line, you may want to give gdb the
‘--baud’ option, or use the set remotebaud
command
(see set remotebaud) before the
target
command.
target remote
host:
porttarget remote tcp:
host:
portFor example, to connect to port 2828 on a terminal server named
manyfarms
:
target remote manyfarms:2828
If your remote target is actually running on the same machine as your debugger session (e.g. a simulator for your target running on the same host), you can omit the hostname. For example, to connect to port 1234 on your local machine:
target remote :1234
Note that the colon is still required here.
target remote udp:
host:
portmanyfarms
:
target remote udp:manyfarms:2828
When using a UDP connection for remote debugging, you should
keep in mind that the `U' stands for “Unreliable”. UDP
can silently drop packets on busy or unreliable networks, which will
cause havoc with your debugging session.
target remote |
command/bin/sh
; it should expect remote
protocol packets on its standard input, and send replies on its
standard output. You could use this to run a stand-alone simulator
that speaks the remote debugging protocol, to make net connections
using programs like ssh
, or for other similar tricks.
If command closes its standard output (perhaps by exiting),
gdb will try to send it a SIGTERM
signal. (If the
program has already exited, this will have no effect.)
Once the connection has been established, you can use all the usual commands to examine and change data. The remote program is already running; you can use step and continue, and you do not need to use run.
Whenever gdb is waiting for the remote program, if you type the interrupt character (often Ctrl-c), gdb attempts to stop the program. This may or may not succeed, depending in part on the hardware and the serial drivers the remote system uses. If you type the interrupt character once again, gdb displays this prompt:
Interrupted while waiting for the program. Give up (and stop debugging it)? (y or n)
If you type y, gdb abandons the remote debugging session. (If you decide you want to try again later, you can use ‘target remote’ again to connect once more.) If you type n, gdb goes back to waiting.
detach
detach
command to release it from gdb control.
Detaching from the target normally resumes its execution, but the results
will depend on your particular remote stub. After the detach
command, gdb is free to connect to another target.
disconnect
disconnect
command behaves like detach
, except that
the target is generally not resumed. It will wait for gdb
(this instance or another one) to connect and continue debugging. After
the disconnect
command, gdb is again free to connect to
another target.
monitor
cmd
Some remote targets offer the ability to transfer files over the same
connection used to communicate with gdb. This is convenient
for targets accessible through other means, e.g. gnu/Linux systems
running gdbserver
over a network interface. For other targets,
e.g. embedded devices with only a single serial port, this may be
the only way to upload or download files.
Not all remote targets support these commands.
remote put
hostfile targetfileremote get
targetfile hostfileremote delete
targetfilegdbserver
Programgdbserver
is a control program for Unix-like systems, which
allows you to connect your program with a remote gdb via
target remote
—but without linking in the usual debugging stub.
gdbserver
is not a complete replacement for the debugging stubs,
because it requires essentially the same operating-system facilities
that gdb itself does. In fact, a system that can run
gdbserver
to connect to a remote gdb could also run
gdb locally! gdbserver
is sometimes useful nevertheless,
because it is a much smaller program than gdb itself. It is
also easier to port than all of gdb, so you may be able to get
started more quickly on a new system by using gdbserver
.
Finally, if you develop code for real-time systems, you may find that
the tradeoffs involved in real-time operation make it more convenient to
do as much development work as possible on another system, for example
by cross-compiling. You can use gdbserver
to make a similar
choice for debugging.
gdb and gdbserver
communicate via either a serial line
or a TCP connection, using the standard gdb remote serial
protocol.
Warning:gdbserver
does not have any built-in security. Do not rungdbserver
connected to any public network; a gdb connection togdbserver
provides access to the target system with the same privileges as the user runninggdbserver
.
gdbserver
Run gdbserver
on the target system. You need a copy of the
program you want to debug, including any libraries it requires.
gdbserver
does not need your program's symbol table, so you can
strip the program if necessary to save space. gdb on the host
system does all the symbol handling.
To use the server, you must tell it how to communicate with gdb; the name of your program; and the arguments for your program. The usual syntax is:
target> gdbserver comm program [ args ... ]
comm is either a device name (to use a serial line) or a TCP hostname and portnumber. For example, to debug Emacs with the argument ‘foo.txt’ and communicate with gdb over the serial port /dev/com1:
target> gdbserver /dev/com1 emacs foo.txt
gdbserver
waits passively for the host gdb to communicate
with it.
To use a TCP connection instead of a serial line:
target> gdbserver host:2345 emacs foo.txt
The only difference from the previous example is the first argument,
specifying that you are communicating with the host gdb via
TCP. The ‘host:2345’ argument means that gdbserver
is to
expect a TCP connection from machine ‘host’ to local TCP port 2345.
(Currently, the ‘host’ part is ignored.) You can choose any number
you want for the port number as long as it does not conflict with any
TCP ports already in use on the target system (for example, 23
is
reserved for telnet
).13 You must use the same port number with the host gdb
target remote
command.
On some targets, gdbserver
can also attach to running programs.
This is accomplished via the --attach
argument. The syntax is:
target> gdbserver --attach comm pid
pid is the process ID of a currently running process. It isn't necessary
to point gdbserver
at a binary for the running process.
You can debug processes by name instead of process ID if your target has the
pidof
utility:
target> gdbserver --attach comm `pidof program`
In case more than one copy of program is running, or program
has multiple threads, most versions of pidof
support the
-s
option to only return the first process ID.
gdbserver
When you connect to gdbserver
using target remote
,
gdbserver
debugs the specified program only once. When the
program exits, or you detach from it, gdb closes the connection
and gdbserver
exits.
If you connect using target extended-remote, gdbserver
enters multi-process mode. When the debugged program exits, or you
detach from it, gdb stays connected to gdbserver
even
though no program is running. The run
and attach
commands instruct gdbserver
to run or attach to a new program.
The run
command uses set remote exec-file
(see set remote exec-file) to select the program to run. Command line
arguments are supported, except for wildcard expansion and I/O
redirection (see Arguments).
To start gdbserver
without supplying an initial command to run
or process ID to attach, use the --multi command line option.
Then you can connect using target extended-remote and start
the program you want to debug.
gdbserver
does not automatically exit in multi-process mode.
You can terminate it by using monitor exit
(see Monitor Commands for gdbserver).
gdbserver
The --debug option tells gdbserver
to display extra
status information about the debugging process. The
--remote-debug option tells gdbserver
to display
remote protocol debug output. These options are intended for
gdbserver
development and for bug reports to the developers.
The --wrapper option specifies a wrapper to launch programs for debugging. The option should be followed by the name of the wrapper, then any command-line arguments to pass to the wrapper, then -- indicating the end of the wrapper arguments.
gdbserver
runs the specified wrapper program with a combined
command line including the wrapper arguments, then the name of the
program to debug, then any arguments to the program. The wrapper
runs until it executes your program, and then gdb gains control.
You can use any program that eventually calls execve
with
its arguments as a wrapper. Several standard Unix utilities do
this, e.g. env
and nohup
. Any Unix shell script ending
with exec "$@"
will also work.
For example, you can use env
to pass an environment variable to
the debugged program, without setting the variable in gdbserver
's
environment:
$ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog
gdbserver
Run gdb on the host system.
First make sure you have the necessary symbol files. Load symbols for
your application using the file
command before you connect. Use
set sysroot
to locate target libraries (unless your gdb
was compiled with the correct sysroot using --with-sysroot
).
The symbol file and target libraries must exactly match the executable
and libraries on the target, with one exception: the files on the host
system should not be stripped, even if the files on the target system
are. Mismatched or missing files will lead to confusing results
during debugging. On gnu/Linux targets, mismatched or missing
files may also prevent gdbserver
from debugging multi-threaded
programs.
Connect to your target (see Connecting to a Remote Target).
For TCP connections, you must start up gdbserver
prior to using
the target remote
command. Otherwise you may get an error whose
text depends on the host system, but which usually looks something like
‘Connection refused’. Don't use the load
command in gdb when using gdbserver
, since the program is
already on the target.
gdbserver
During a gdb session using gdbserver
, you can use the
monitor
command to send special requests to gdbserver
.
Here are the available commands.
monitor help
monitor set debug 0
monitor set debug 1
monitor set remote-debug 0
monitor set remote-debug 1
monitor set libthread-db-search-path [PATH]
libthread_db
(see set libthread-db-search-path). If you omit path,
‘libthread-db-search-path’ will be reset to an empty list.
monitor exit
disconnect
to close the debugging session. gdbserver
will
detach from any attached processes and kill any processes it created.
Use monitor exit
to terminate gdbserver
at the end
of a multi-process mode debug session.
gdbserver
On some targets, gdbserver
supports tracepoints, fast
tracepoints and static tracepoints.
For fast or static tracepoints to work, a special library called the
in-process agent (IPA), must be loaded in the inferior process.
This library is built and distributed as an integral part of
gdbserver
. In addition, support for static tracepoints
requires building the in-process agent library with static tracepoints
support. At present, the UST (LTTng Userspace Tracer,
http://lttng.org/ust) tracing engine is supported. This support
is automatically available if UST development headers are found in the
standard include path when gdbserver
is built, or if
gdbserver
was explicitly configured using --with-ust
to point at such headers. You can explicitly disable the support
using --with-ust=no.
There are several ways to load the in-process agent in your program:
Specifying it as dependency at link time
-linproctrace
to the link command.
Using the system's preloading mechanisms
LD_PRELOAD=libinproctrace.so
in the environment. See also the description of gdbserver
's
--wrapper command line option.
Using
gdb to force loading the agent at run time
dlopen
. You'll use the call
command for that. For example:
(gdb) call dlopen ("libinproctrace.so", ...)
Note that on most Unix systems, for the dlopen
function to be
available, the program needs to be linked with -ldl
.
On systems that have a userspace dynamic loader, like most Unix
systems, when you connect to gdbserver
using target
remote
, you'll find that the program is stopped at the dynamic
loader's entry point, and no shared library has been loaded in the
program's address space yet, including the in-process agent. In that
case, before being able to use any of the fast or static tracepoints
features, you need to let the loader run and load the shared
libraries. The simplest way to do that is to run the program to the
main procedure. E.g., if debugging a C or C++ program, start
gdbserver
like so:
$ gdbserver :9999 myprogram
Start GDB and connect to gdbserver
like so, and run to main:
$ gdb myprogram (gdb) target remote myhost:9999 0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2 (gdb) b main (gdb) continue
The in-process tracing agent library should now be loaded into the
process; you can confirm it with the info sharedlibrary
command, which will list libinproctrace.so as loaded in the
process. You are now ready to install fast tracepoints, list static
tracepoint markers, probe static tracepoints markers, and start
tracing.
This section documents the configuration options available when debugging remote programs. For the options related to the File I/O extensions of the remote protocol, see system-call-allowed.
set remoteaddresssize
bitsshow remoteaddresssize
set remotebaud
nshow remotebaud
set remotebreak
BREAK
signal to the remote
when you type Ctrl-c to interrupt the program running
on the remote. If set to off, gdb sends the ‘Ctrl-C’
character instead. The default is off, since most remote systems
expect to see ‘Ctrl-C’ as the interrupt signal.
show remotebreak
BREAK
or ‘Ctrl-C’ to
interrupt the remote program.
set remoteflow on
set remoteflow off
RTS
/CTS
)
on the serial port used to communicate to the remote target.
show remoteflow
set remotelogbase
baseascii
, octal
, and hex
. The default is
ascii
.
show remotelogbase
set remotelogfile
fileshow remotelogfile.
set remotetimeout
numshow remotetimeout
set remote hardware-watchpoint-limit
limitset remote hardware-breakpoint-limit
limitset remote exec-file
filenameshow remote exec-file
run
with target
extended-remote
. This should be set to a filename valid on the
target system. If it is not set, the target will use a default
filename (e.g. the last program run).
set remote interrupt-sequence
BREAK
or
‘BREAK-g’ as the
sequence to the remote target in order to interrupt the execution.
‘Ctrl-C’ is a default. Some system prefers BREAK
which
is high level of serial line for some certain time.
Linux kernel prefers ‘BREAK-g’, a.k.a Magic SysRq g.
It is BREAK
signal followed by character g
.
show interrupt-sequence
BREAK
or BREAK-g
is sent by gdb to interrupt the remote program.
BREAK-g
is BREAK signal followed by g
and
also known as Magic SysRq g.
set remote interrupt-on-connect
BREAK
followed by g
which is known as Magic SysRq g in order to connect gdb.
show interrupt-on-connect
set tcp auto-retry on
set tcp connect-timeout
.
set tcp auto-retry off
show tcp auto-retry
set tcp connect-timeout
secondsset tcp auto-retry on
) and waiting for connections
that are merely slow to complete, and represents an approximate cumulative
value.
show tcp connect-timeout
The gdb remote protocol autodetects the packets supported by your debugging stub. If you need to override the autodetection, you can use these commands to enable or disable individual packets. Each packet can be set to ‘on’ (the remote target supports this packet), ‘off’ (the remote target does not support this packet), or ‘auto’ (detect remote target support for this packet). They all default to ‘auto’. For more information about each packet, see Remote Protocol.
During normal use, you should not have to use any of these commands. If you do, that may be a bug in your remote debugging stub, or a bug in gdb. You may want to report the problem to the gdb developers.
For each packet name, the command to enable or disable the
packet is set remote
name-packet
. The available settings
are:
Command Name | Remote Packet | Related Features
|
fetch-register
| p
| info registers
|
set-register
| P
| set
|
binary-download
| X
| load , set
|
read-aux-vector
| qXfer:auxv:read
| info auxv
|
symbol-lookup
| qSymbol
| Detecting multiple threads
|
attach
| vAttach
| attach
|
verbose-resume
| vCont
| Stepping or resuming multiple threads
|
run
| vRun
| run
|
software-breakpoint
| Z0
| break
|
hardware-breakpoint
| Z1
| hbreak
|
write-watchpoint
| Z2
| watch
|
read-watchpoint
| Z3
| rwatch
|
access-watchpoint
| Z4
| awatch
|
target-features
| qXfer:features:read
| set architecture
|
library-info
| qXfer:libraries:read
| info sharedlibrary
|
memory-map
| qXfer:memory-map:read
| info mem
|
read-sdata-object
| qXfer:sdata:read
| print $_sdata
|
read-spu-object
| qXfer:spu:read
| info spu
|
write-spu-object
| qXfer:spu:write
| info spu
|
read-siginfo-object
| qXfer:siginfo:read
| print $_siginfo
|
write-siginfo-object
| qXfer:siginfo:write
| set $_siginfo
|
threads
| qXfer:threads:read
| info threads
|
get-thread-local-
| qGetTLSAddr
| Displaying __thread variables
|
get-thread-information-block-address
| qGetTIBAddr
| Display MS-Windows Thread Information Block.
|
search-memory
| qSearch:memory
| find
|
supported-packets
| qSupported
| Remote communications parameters
|
pass-signals
| QPassSignals
| handle signal
|
hostio-close-packet
| vFile:close
| remote get , remote put
|
hostio-open-packet
| vFile:open
| remote get , remote put
|
hostio-pread-packet
| vFile:pread
| remote get , remote put
|
hostio-pwrite-packet
| vFile:pwrite
| remote get , remote put
|
hostio-unlink-packet
| vFile:unlink
| remote delete
|
noack-packet
| QStartNoAckMode
| Packet acknowledgment
|
osdata
| qXfer:osdata:read
| info os
|
query-attached
| qAttached
| Querying remote process attach state.
|
traceframe-info
| qXfer:traceframe-info:read
| Traceframe info
|
The stub files provided with gdb implement the target side of the communication protocol, and the gdb side is implemented in the gdb source file remote.c. Normally, you can simply allow these subroutines to communicate, and ignore the details. (If you're implementing your own stub file, you can still ignore the details: start with one of the existing stub files. sparc-stub.c is the best organized, and therefore the easiest to read.)
To debug a program running on another machine (the debugging target machine), you must first arrange for all the usual prerequisites for the program to run by itself. For example, for a C program, you need:
The next step is to arrange for your program to use a serial port to communicate with the machine where gdb is running (the host machine). In general terms, the scheme looks like this:
On certain remote targets, you can use an auxiliary program
gdbserver
instead of linking a stub into your program.
See Using the gdbserver
Program, for details.
The debugging stub is specific to the architecture of the remote machine; for example, use sparc-stub.c to debug programs on sparc boards.
These working remote stubs are distributed with gdb:
i386-stub.c
m68k-stub.c
sh-stub.c
sparc-stub.c
sparcl-stub.c
The README file in the gdb distribution may list other recently added stubs.
The debugging stub for your architecture supplies these three subroutines:
set_debug_traps
handle_exception
to run when your
program stops. You must call this subroutine explicitly near the
beginning of your program.
handle_exception
handle_exception
to
run when a trap is triggered.
handle_exception
takes control when your program stops during
execution (for example, on a breakpoint), and mediates communications
with gdb on the host machine. This is where the communications
protocol is implemented; handle_exception
acts as the gdb
representative on the target machine. It begins by sending summary
information on the state of your program, then continues to execute,
retrieving and transmitting any information gdb needs, until you
execute a gdb command that makes your program resume; at that point,
handle_exception
returns control to your own code on the target
machine.
breakpoint
handle_exception
—in effect, to gdb. On some machines,
simply receiving characters on the serial port may also trigger a trap;
again, in that situation, you don't need to call breakpoint
from
your own program—simply running ‘target remote’ from the host
gdb session gets control.
Call breakpoint
if none of these is true, or if you simply want
to make certain your program stops at a predetermined point for the
start of your debugging session.
The debugging stubs that come with gdb are set up for a particular chip architecture, but they have no information about the rest of your debugging target machine.
First of all you need to tell the stub how to communicate with the serial port.
int getDebugChar()
getchar
for your target system; a
different name is used to allow you to distinguish the two if you wish.
void putDebugChar(int)
putchar
for your target system; a
different name is used to allow you to distinguish the two if you wish.
If you want gdb to be able to stop your program while it is
running, you need to use an interrupt-driven serial driver, and arrange
for it to stop when it receives a ^C
(‘\003’, the control-C
character). That is the character which gdb uses to tell the
remote system to stop.
Getting the debugging target to return the proper status to gdb
probably requires changes to the standard stub; one quick and dirty way
is to just execute a breakpoint instruction (the “dirty” part is that
gdb reports a SIGTRAP
instead of a SIGINT
).
Other routines you need to supply are:
void exceptionHandler (int
exception_number, void *
exception_address)
For the 386, exception_address should be installed as an interrupt
gate so that interrupts are masked while the handler runs. The gate
should be at privilege level 0 (the most privileged level). The
sparc and 68k stubs are able to mask interrupts themselves without
help from exceptionHandler
.
void flush_i_cache()
On target machines that have instruction caches, gdb requires this function to make certain that the state of your program is stable.
You must also make sure this library routine is available:
void *memset(void *, int, int)
memset
that sets an area of
memory to a known value. If you have one of the free versions of
libc.a
, memset
can be found there; otherwise, you must
either obtain it from your hardware manufacturer, or write your own.
If you do not use the GNU C compiler, you may need other standard library subroutines as well; this varies from one stub to another, but in general the stubs are likely to use any of the common library subroutines which gcc generates as inline code.
In summary, when your program is ready to debug, you must follow these steps.
getDebugChar
,putDebugChar
,flush_i_cache
,memset
,exceptionHandler
.
set_debug_traps(); breakpoint();
exceptionHook
. Normally you just use:
void (*exceptionHook)() = 0;
but if before calling set_debug_traps
, you set it to point to a
function in your program, that function is called when
gdb continues after stopping on a trap (for example, bus
error). The function indicated by exceptionHook
is called with
one parameter: an int
which is the exception number.
While nearly all gdb commands are available for all native and cross versions of the debugger, there are some exceptions. This chapter describes things that are only available in certain configurations.
There are three major categories of configurations: native configurations, where the host and target are the same, embedded operating system configurations, which are usually the same for several different processor architectures, and bare embedded processors, which are quite different from each other.
This section describes details specific to particular native configurations.
On HP-UX systems, if you refer to a function or variable name that begins with a dollar sign, gdb searches for a user or system name first, before it searches for a convenience variable.
BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
interface that provides a uniform interface for accessing kernel virtual
memory images, including live systems and crash dumps. gdb
uses this interface to allow you to debug live kernels and kernel crash
dumps on many native BSD configurations. This is implemented as a
special kvm
debugging target. For debugging a live system, load
the currently running kernel into gdb and connect to the
kvm
target:
(gdb) target kvm
For debugging crash dumps, provide the file name of the crash dump as an argument:
(gdb) target kvm /var/crash/bsd.0
Once connected to the kvm
target, the following commands are
available:
kvm pcb
kvm proc
Many versions of SVR4 and compatible systems provide a facility called
‘/proc’ that can be used to examine the image of a running
process using file-system subroutines. If gdb is configured
for an operating system with this facility, the command info
proc
is available to report information about the process running
your program, or about any process running on your system. info
proc
works only on SVR4 systems that include the procfs
code.
This includes, as of this writing, gnu/Linux, OSF/1 (Digital
Unix), Solaris, Irix, and Unixware, but not HP-UX, for example.
info proc
info proc
process-idOn some systems, process-id can be of the form
‘[pid]/tid’ which specifies a certain thread ID
within a process. If the optional pid part is missing, it means
a thread from the process being debugged (the leading ‘/’ still
needs to be present, or else gdb will interpret the number as
a process ID rather than a thread ID).
info proc mappings
info proc stat
info proc status
info proc all
info proc
subcommands.
set procfs-trace
procfs
API calls.
show procfs-trace
procfs
API call tracing.
set procfs-file
fileprocfs
API trace to the named
file. gdb appends the trace info to the previous
contents of the file. The default is to display the trace on the
standard output.
show procfs-file
procfs
API trace is written.
proc-trace-entry
proc-trace-exit
proc-untrace-entry
proc-untrace-exit
syscall
interface.
info pidlist
info meminfo
djgpp is a port of the gnu development tools to MS-DOS and MS-Windows. djgpp programs are 32-bit protected-mode programs that use the DPMI (DOS Protected-Mode Interface) API to run on top of real-mode DOS systems and their emulations.
gdb supports native debugging of djgpp programs, and defines a few commands specific to the djgpp port. This subsection describes those commands.
info dos
info dos sysinfo
info dos gdt
info dos ldt
info dos idt
A typical djgpp program uses 3 segments: a code segment, a data segment (used for both data and the stack), and a DOS segment (which allows access to DOS/BIOS data structures and absolute addresses in conventional memory). However, the DPMI host will usually define additional segments in order to support the DPMI environment.
These commands allow to display entries from the descriptor tables. Without an argument, all entries from the specified table are displayed. An argument, which should be an integer expression, means display a single entry whose index is given by the argument. For example, here's a convenient way to display information about the debugged program's data segment:
(gdb) info dos ldt $ds
0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)
This comes in handy when you want to see whether a pointer is outside the data segment's limit (i.e. garbled).
info dos pde
info dos pte
Without an argument, info dos pde displays the entire Page Directory, and info dos pte displays all the entries in all of the Page Tables. An argument, an integer expression, given to the info dos pde command means display only that entry from the Page Directory table. An argument given to the info dos pte command means display entries from a single Page Table, the one pointed to by the specified entry in the Page Directory.
These commands are useful when your program uses DMA (Direct Memory Access), which needs physical addresses to program the DMA controller.
These commands are supported only with some DPMI servers.
info dos address-pte
addri
is stored:
(gdb) info dos address-pte __djgpp_base_address + (char *)&i
Page Table entry for address 0x11a00d30:
Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30
This says that i
is stored at offset 0xd30
from the page
whose physical base address is 0x02698000
, and shows all the
attributes of that page.
Note that you must cast the addresses of variables to a char *
,
since otherwise the value of __djgpp_base_address
, the base
address of all variables and functions in a djgpp program, will
be added using the rules of C pointer arithmetics: if i
is
declared an int
, gdb will add 4 times the value of
__djgpp_base_address
to the address of i
.
Here's another example, it displays the Page Table entry for the transfer buffer:
(gdb) info dos address-pte *((unsigned *)&_go32_info_block + 3)
Page Table entry for address 0x29110:
Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110
(The + 3
offset is because the transfer buffer's address is the
3rd member of the _go32_info_block
structure.) The output
clearly shows that this DPMI server maps the addresses in conventional
memory 1:1, i.e. the physical (0x00029000
+ 0x110
) and
linear (0x29110
) addresses are identical.
This command is supported only with some DPMI servers.
In addition to native debugging, the DJGPP port supports remote debugging via a serial data link. The following commands are specific to remote serial debugging in the DJGPP port of gdb.
set com1base
addrset com1irq
irqIRQ
) line to use
for the COM1 serial port.
There are similar commands ‘set com2base’, ‘set com3irq’,
etc. for setting the port address and the IRQ
lines for the
other 3 COM ports.
The related commands ‘show com1base’, ‘show com1irq’ etc.
display the current settings of the base address and the IRQ
lines used by the COM ports.
info serial
gdb supports native debugging of MS Windows programs, including DLLs with and without symbolic debugging information.
MS-Windows programs that call SetConsoleMode
to switch off the
special meaning of the ‘Ctrl-C’ keystroke cannot be interrupted
by typing C-c. For this reason, gdb on MS-Windows
supports C-<BREAK> as an alternative interrupt key
sequence, which can be used to interrupt the debuggee even if it
ignores C-c.
There are various additional Cygwin-specific commands, described in this section. Working with DLLs that have no debugging symbols is described in Non-debug DLL Symbols.
info w32
info w32 selector
GetThreadSelectorEntry
function.
It takes an optional argument that is evaluated to
a long value to give the information about this given selector.
Without argument, this command displays information
about the six segment registers.
info w32 thread-information-block
$fs
selector for 32-bit programs and $gs
for 64-bit programs).
info dll
info shared
.
dll-symbols
set cygwin-exceptions
modeon
, gdb will break on exceptions that
happen inside the Cygwin DLL. If mode is off
,
gdb will delay recognition of exceptions, and may ignore some
exceptions which seem to be caused by internal Cygwin DLL
“bookkeeping”. This option is meant primarily for debugging the
Cygwin DLL itself; the default value is off
to avoid annoying
gdb users with false SIGSEGV
signals.
show cygwin-exceptions
set new-console
modeon
the debuggee will
be started in a new console on next start.
If mode is off
, the debuggee will
be started in the same console as the debugger.
show new-console
set new-group
modeshow new-group
set debugevents
OutputDebugString
API call.
set debugexec
set debugexceptions
set debugmemory
set shell
show shell
Very often on windows, some of the DLLs that your program relies on do not include symbolic debugging information (for example, kernel32.dll). When gdb doesn't recognize any debugging symbols in a DLL, it relies on the minimal amount of symbolic information contained in the DLL's export table. This section describes working with such symbols, known internally to gdb as “minimal symbols”.
Note that before the debugged program has started execution, no DLLs
will have been loaded. The easiest way around this problem is simply to
start the program — either by setting a breakpoint or letting the
program run once to completion. It is also possible to force
gdb to load a particular DLL before starting the executable —
see the shared library information in Files, or the
dll-symbols
command in Cygwin Native. Currently,
explicitly loading symbols from a DLL with no debugging information will
cause the symbol names to be duplicated in gdb's lookup table,
which may adversely affect symbol lookup performance.
In keeping with the naming conventions used by the Microsoft debugging
tools, DLL export symbols are made available with a prefix based on the
DLL name, for instance KERNEL32!CreateFileA
. The plain name is
also entered into the symbol table, so CreateFileA
is often
sufficient. In some cases there will be name clashes within a program
(particularly if the executable itself includes full debugging symbols)
necessitating the use of the fully qualified name when referring to the
contents of the DLL. Use single-quotes around the name to avoid the
exclamation mark (“!”) being interpreted as a language operator.
Note that the internal name of the DLL may be all upper-case, even
though the file name of the DLL is lower-case, or vice-versa. Since
symbols within gdb are case-sensitive this may cause
some confusion. If in doubt, try the info functions
and
info variables
commands or even maint print msymbols
(see Symbols). Here's an example:
(gdb) info function CreateFileA All functions matching regular expression "CreateFileA": Non-debugging symbols: 0x77e885f4 CreateFileA 0x77e885f4 KERNEL32!CreateFileA
(gdb) info function ! All functions matching regular expression "!": Non-debugging symbols: 0x6100114c cygwin1!__assert 0x61004034 cygwin1!_dll_crt0@0 0x61004240 cygwin1!dll_crt0(per_process *) [etc...]
Symbols extracted from a DLL's export table do not contain very much type information. All that gdb can do is guess whether a symbol refers to a function or variable depending on the linker section that contains the symbol. Also note that the actual contents of the memory contained in a DLL are not available unless the program is running. This means that you cannot examine the contents of a variable or disassemble a function within a DLL without a running program.
Variables are generally treated as pointers and dereferenced automatically. For this reason, it is often necessary to prefix a variable name with the address-of operator (“&”) and provide explicit type information in the command. Here's an example of the type of problem:
(gdb) print 'cygwin1!__argv' $1 = 268572168
(gdb) x 'cygwin1!__argv' 0x10021610: "\230y\""
And two possible solutions:
(gdb) print ((char **)'cygwin1!__argv')[0] $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
(gdb) x/2x &'cygwin1!__argv' 0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000 (gdb) x/x 0x10021608 0x10021608: 0x0022fd98 (gdb) x/s 0x0022fd98 0x22fd98: "/cygdrive/c/mydirectory/myprogram"
Setting a break point within a DLL is possible even before the program starts execution. However, under these circumstances, gdb can't examine the initial instructions of the function in order to skip the function's frame set-up code. You can work around this by using “*&” to set the breakpoint at a raw memory address:
(gdb) break *&'python22!PyOS_Readline' Breakpoint 1 at 0x1e04eff0
The author of these extensions is not entirely convinced that setting a break point within a shared DLL like kernel32.dll is completely safe.
This subsection describes gdb commands specific to the gnu Hurd native debugging.
set signals
set sigs
sigs
is a shorthand alias for
signals
.
show signals
show sigs
set signal-thread
set sigthread
libc
signal
thread. That thread is run when a signal is delivered to a running
process. set sigthread
is the shorthand alias of set
signal-thread
.
show signal-thread
show sigthread
set stopped
SIGSTOP
signal. The stopped process can be
continued by delivering a signal to it.
show stopped
set exceptions
show exceptions
set task pause
set thread default pause on
or set
thread pause on
(see below) to pause individual threads.
show task pause
set task detach-suspend-count
show task detach-suspend-count
set task exception-port
set task excp
set task excp
is a shorthand alias.
set noninvasive
set task pause
, set exceptions
, and
set signals
to values opposite to the defaults.
info send-rights
info receive-rights
info port-rights
info port-sets
info dead-names
info ports
info psets
info ports
for info
port-rights
and info psets
for info port-sets
.
set thread pause
set
task pause off
(see above), this command comes in handy to suspend
only the current thread.
show thread pause
set thread run
show thread run
set thread detach-suspend-count
set thread
takeover-suspend-count
to force it to an absolute value.
show thread detach-suspend-count
set thread exception-port
set thread excp
set task exception-port
(see above).
set thread excp
is the shorthand alias.
set thread takeover-suspend-count
set thread default
show thread default
set thread
commands has a set thread
default
counterpart (e.g., set thread default pause
, set
thread default exception-port
, etc.). The thread default
variety of commands sets the default thread properties for all
threads; you can then change the properties of individual threads with
the non-default commands.
gdb provides the following commands specific to the QNX Neutrino target:
set debug nto-debug
show debug nto-debug
gdb provides the following commands specific to the Darwin target:
set debug darwin
numshow debug darwin
set debug mach-o
numshow debug mach-o
set mach-exceptions on
set mach-exceptions off
show mach-exceptions
This section describes configurations involving the debugging of embedded operating systems that are available for several different architectures.
gdb includes the ability to debug programs running on various real-time operating systems.
target vxworks
machinenameOn VxWorks, load
links filename dynamically on the
current target system as well as adding its symbols in gdb.
gdb enables developers to spawn and debug tasks running on networked
VxWorks targets from a Unix host. Already-running tasks spawned from
the VxWorks shell can also be debugged. gdb uses code that runs on
both the Unix host and on the VxWorks target. The program
gdb
is installed and executed on the Unix host. (It may be
installed with the name vxgdb
, to distinguish it from a
gdb for debugging programs on the host itself.)
VxWorks-timeout
argsvxworks-timeout
.
This option is set by the user, and args represents the number of
seconds gdb waits for responses to rpc's. You might use this if
your VxWorks target is a slow software simulator or is on the far side
of a thin network line.
The following information on connecting to VxWorks was current when this manual was produced; newer releases of VxWorks may use revised procedures.
To use gdb with VxWorks, you must rebuild your VxWorks kernel
to include the remote debugging interface routines in the VxWorks
library rdb.a. To do this, define INCLUDE_RDB
in the
VxWorks configuration file configAll.h and rebuild your VxWorks
kernel. The resulting kernel contains rdb.a, and spawns the
source debugging task tRdbTask
when VxWorks is booted. For more
information on configuring and remaking VxWorks, see the manufacturer's
manual.
Once you have included rdb.a in your VxWorks system image and set
your Unix execution search path to find gdb, you are ready to
run gdb. From your Unix host, run gdb
(or
vxgdb
, depending on your installation).
gdb comes up showing the prompt:
(vxgdb)
The gdb command target
lets you connect to a VxWorks target on the
network. To connect to a target whose host name is “tt
”, type:
(vxgdb) target vxworks tt
gdb displays messages like these:
Attaching remote machine across net... Connected to tt.
gdb then attempts to read the symbol tables of any object modules loaded into the VxWorks target since it was last booted. gdb locates these files by searching the directories listed in the command search path (see Your Program's Environment); if it fails to find an object file, it displays a message such as:
prog.o: No such file or directory.
When this happens, add the appropriate directory to the search path with
the gdb command path
, and execute the target
command again.
If you have connected to the VxWorks target and you want to debug an
object that has not yet been loaded, you can use the gdb
load
command to download a file from Unix to VxWorks
incrementally. The object file given as an argument to the load
command is actually opened twice: first by the VxWorks target in order
to download the code, then by gdb in order to read the symbol
table. This can lead to problems if the current working directories on
the two systems differ. If both systems have NFS mounted the same
filesystems, you can avoid these problems by using absolute paths.
Otherwise, it is simplest to set the working directory on both systems
to the directory in which the object file resides, and then to reference
the file by its name, without any path. For instance, a program
prog.o may reside in vxpath/vw/demo/rdb in VxWorks
and in hostpath/vw/demo/rdb on the host. To load this
program, type this on VxWorks:
-> cd "vxpath/vw/demo/rdb"
Then, in gdb, type:
(vxgdb) cd hostpath/vw/demo/rdb (vxgdb) load prog.o
gdb displays a response similar to this:
Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
You can also use the load
command to reload an object module
after editing and recompiling the corresponding source file. Note that
this makes gdb delete all currently-defined breakpoints,
auto-displays, and convenience variables, and to clear the value
history. (This is necessary in order to preserve the integrity of
debugger's data structures that reference the target system's symbol
table.)
You can also attach to an existing task using the attach
command as
follows:
(vxgdb) attach task
where task is the VxWorks hexadecimal task ID. The task can be running or suspended when you attach to it. Running tasks are suspended at the time of attachment.
This section goes into details specific to particular embedded configurations.
Whenever a specific embedded processor has a simulator, gdb allows to send an arbitrary command to the simulator.
sim
commandtarget rdi
devtarget rdp
devgdb provides the following ARM-specific commands:
set arm disassembler
"std"
style is the standard style.
show arm disassembler
set arm apcs32
show arm apcs32
set arm fpu
fputypeauto
softfpa
fpa
softvfp
vfp
show arm fpu
set arm abi
show arm abi
set arm fallback-mode (arm|thumb|auto)
T
bit in the CPSR
register).
show arm fallback-mode
set arm force-mode (arm|thumb|auto)
show arm force-mode
set debug arm
show debug arm
The following commands are available when an ARM target is debugged using the RDI interface:
rdilogfile
[file]rdilogenable
[arg]"yes"
enables logging, with an argument 0 or "no"
disables it. With
no arguments displays the current setting. When logging is enabled,
ADP packets exchanged between gdb and the RDI target device
are logged to a file.
set rdiromatzero
target rdi
command.
show rdiromatzero
set rdiheartbeat
show rdiheartbeat
target sim
[simargs] ...
--swi-support=
typeall
.
none
demon
angel
redboot
all
target m32r
devtarget m32rsdi
devThe following gdb commands are specific to the M32R monitor:
set download-path
pathshow download-path
set board-address
addrshow board-address
set server-address
addrshow server-address
upload
[file]tload
[file]upload
command.
The following commands are available for M32R/SDI:
sdireset
sdistatus
debug_chaos
use_debug_dma
use_mon_code
use_ib_break
use_dbt_break
The Motorola m68k configuration includes ColdFire support, and a target command for the following ROM monitor.
target dbug
dev
The MicroBlaze is a soft-core processor supported on various Xilinx
FPGAs, such as Spartan or Virtex series. Boards with these processors
usually have JTAG ports which connect to a host system running the Xilinx
Embedded Development Kit (EDK) or Software Development Kit (SDK).
This host system is used to download the configuration bitstream to
the target FPGA. The Xilinx Microprocessor Debugger (XMD) program
communicates with the target board using the JTAG interface and
presents a gdbserver
interface to the board. By default
xmd
uses port 1234
. (While it is possible to change
this default port, it requires the use of undocumented xmd
commands. Contact Xilinx support if you need to do this.)
Use these GDB commands to connect to the MicroBlaze target processor.
target remote :1234
xmd
.
target remote
xmd-host:1234
xmd
running on a different system named xmd-host.
load
set debug microblaze
nshow debug microblaze
ngdb can use the MIPS remote debugging protocol to talk to a MIPS board attached to a serial line. This is available when you configure gdb with ‘--target=mips-idt-ecoff’.
Use these gdb commands to specify the connection to your target board:
target mips
portgdb
with the
name of your program as the argument. To connect to the board, use the
command ‘target mips port’, where port is the name of
the serial port connected to the board. If the program has not already
been downloaded to the board, you may use the load
command to
download it. You can then use all the usual gdb commands.
For example, this sequence connects to the target board through a serial port, and loads and runs a program called prog through the debugger:
host$ gdb prog
gdb is free software and ...
(gdb) target mips /dev/ttyb
(gdb) load prog
(gdb) run
target mips
hostname:
portnumbertarget pmon
porttarget ddb
porttarget lsi
porttarget r3900
devtarget array
devgdb also supports these special commands for MIPS targets:
set mipsfpu double
set mipsfpu single
set mipsfpu none
set mipsfpu auto
show mipsfpu
In previous versions the only choices were double precision or no floating point, so ‘set mipsfpu on’ will select double precision and ‘set mipsfpu off’ will select no floating point.
As usual, you can inquire about the mipsfpu
variable with
‘show mipsfpu’.
set timeout
secondsset retransmit-timeout
secondsshow timeout
show retransmit-timeout
set timeout
seconds command. The
default is 5 seconds. Similarly, you can control the timeout used while
waiting for an acknowledgment of a packet with the set
retransmit-timeout
seconds command. The default is 3 seconds.
You can inspect both values with show timeout
and show
retransmit-timeout
. (These commands are only available when
gdb is configured for ‘--target=mips-idt-ecoff’.)
The timeout set by set timeout
does not apply when gdb
is waiting for your program to stop. In that case, gdb waits
forever because it has no way of knowing how long the program is going
to run before stopping.
set syn-garbage-limit
numshow syn-garbage-limit
set monitor-prompt
promptshow monitor-prompt
set monitor-warnings
lsi
target. When on, gdb will
display warning messages whose codes are returned by the lsi
PMON monitor for breakpoint commands.
show monitor-warnings
pmon
commandSee OR1k Architecture document (www.opencores.org) for more information about platform and commands.
target jtag jtag://
host:
portExample: target jtag jtag://localhost:9999
or1ksim
commandor1ksim
OpenRISC 1000 Architectural
Simulator, proprietary commands can be executed.
info or1k spr
info or1k spr
groupinfo or1k spr
groupnoinfo or1k spr
group registerinfo or1k spr
registerinfo or1k spr
groupno registernoinfo or1k spr
registernospr
group register valuespr
register valuespr
groupno registerno valuespr
registerno valueSome implementations of OpenRISC 1000 Architecture also have hardware trace. It is very similar to gdb trace, except it does not interfere with normal program execution and is thus much faster. Hardware breakpoints/watchpoint triggers can be set using:
$LEA/$LDATA
$SEA/$SDATA
$AEA/$ADATA
$FETCH
When triggered, it can capture low level data, like: PC
, LSEA
,
LDATA
, SDATA
, READSPR
, WRITESPR
, INSTR
.
hwatch
conditionalhwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)
hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)
htrace info
htrace trigger
conditionalhtrace qualifier
conditionalhtrace stop
conditionalhtrace record [
data]*
htrace enable
htrace disable
htrace rewind [
filename]
If filename is specified, new trace file is made and any newly collected data
will be written there.
htrace print [
start [
len]]
htrace mode continuous
htrace mode suspend
gdb supports using the DVC (Data Value Compare) register to implement in hardware simple hardware watchpoint conditions of the form:
(gdb) watch ADDRESS|VARIABLE \ if ADDRESS|VARIABLE == CONSTANT EXPRESSION
The DVC register will be automatically used when gdb detects
such pattern in a condition expression, and the created watchpoint uses one
debug register (either the exact-watchpoints
option is on and the
variable is scalar, or the variable has a length of one byte). This feature
is available in native gdb running on a Linux kernel version 2.6.34
or newer.
When running on PowerPC embedded processors, gdb automatically uses
ranged hardware watchpoints, unless the exact-watchpoints
option is on,
in which case watchpoints using only one debug register are created when
watching variables of scalar types.
You can create an artificial array to watch an arbitrary memory region using one of the following commands (see Expressions):
(gdb) watch *((char *) address)@length (gdb) watch {char[length]} address
PowerPC embedded processors support hardware accelerated
ranged breakpoints. A ranged breakpoint stops execution of
the inferior whenever it executes an instruction at any address within
the range it specifies. To set a ranged breakpoint in gdb,
use the break-range
command.
gdb provides the following PowerPC-specific commands:
break-range
start-location,
end-locationset powerpc soft-float
show powerpc soft-float
set powerpc vector-abi
show powerpc vector-abi
set powerpc exact-watchpoints
show powerpc exact-watchpoints
target dink32
devtarget ppcbug
devtarget ppcbug1
devtarget sds
devThe following commands specific to the SDS protocol are supported by gdb:
set sdstimeout
nsecshow sdstimeout
sds
commandtarget op50n
devtarget w89k
dev
gdb enables developers to debug tasks running on
Sparclet targets from a Unix host.
gdb uses code that runs on
both the Unix host and on the Sparclet target. The program
gdb
is installed and executed on the Unix host.
remotetimeout
argsremotetimeout
.
This option is set by the user, and args represents the number of
seconds gdb waits for responses.
When compiling for debugging, include the options ‘-g’ to get debug information and ‘-Ttext’ to relocate the program to where you wish to load it on the target. You may also want to add the options ‘-n’ or ‘-N’ in order to reduce the size of the sections. Example:
sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
You can use objdump
to verify that the addresses are what you intended:
sparclet-aout-objdump --headers --syms prog
Once you have set
your Unix execution search path to find gdb, you are ready to
run gdb. From your Unix host, run gdb
(or sparclet-aout-gdb
, depending on your installation).
gdb comes up showing the prompt:
(gdbslet)
The gdb command file
lets you choose with program to debug.
(gdbslet) file prog
gdb then attempts to read the symbol table of prog. gdb locates the file by searching the directories listed in the command search path. If the file was compiled with debug information (option ‘-g’), source files will be searched as well. gdb locates the source files by searching the directories listed in the directory search path (see Your Program's Environment). If it fails to find a file, it displays a message such as:
prog: No such file or directory.
When this happens, add the appropriate directories to the search paths with
the gdb commands path
and dir
, and execute the
target
command again.
The gdb command target
lets you connect to a Sparclet target.
To connect to a target on serial port “ttya
”, type:
(gdbslet) target sparclet /dev/ttya Remote target sparclet connected to /dev/ttya main () at ../prog.c:3
gdb displays messages like these:
Connected to ttya.
Once connected to the Sparclet target,
you can use the gdb
load
command to download the file from the host to the target.
The file name and load offset should be given as arguments to the load
command.
Since the file format is aout, the program must be loaded to the starting
address. You can use objdump
to find out what this value is. The load
offset is an offset which is added to the VMA (virtual memory address)
of each of the file's sections.
For instance, if the program
prog was linked to text address 0x1201000, with data at 0x12010160
and bss at 0x12010170, in gdb, type:
(gdbslet) load prog 0x12010000 Loading section .text, size 0xdb0 vma 0x12010000
If the code is loaded at a different address then what the program was linked
to, you may need to use the section
and add-symbol-file
commands
to tell gdb where to map the symbol table.
You can now begin debugging the task using gdb's execution control
commands, b
, step
, run
, etc. See the gdb
manual for the list of commands.
(gdbslet) b main Breakpoint 1 at 0x12010000: file prog.c, line 3. (gdbslet) run Starting program: prog Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3 3 char *symarg = 0; (gdbslet) step 4 char *execarg = "hello!"; (gdbslet)
target sparclite
devWhen configured for debugging Zilog Z8000 targets, gdb includes a Z8000 simulator.
For the Z8000 family, ‘target sim’ simulates either the Z8002 (the unsegmented variant of the Z8000 architecture) or the Z8001 (the segmented variant). The simulator recognizes which architecture is appropriate by inspecting the object code.
target sim
argsAfter specifying this target, you can debug programs for the simulated
CPU in the same style as programs for your host computer; use the
file
command to load a new program image, the run
command
to run your program, and so on.
As well as making available all the usual machine registers (see Registers), the Z8000 simulator provides three additional items of information as specially named registers:
cycles
insts
time
You can refer to these values in gdb expressions with the usual conventions; for example, ‘b fputc if $cycles>5000’ sets a conditional breakpoint that suspends only after at least 5000 simulated clock ticks.
When configured for debugging the Atmel AVR, gdb supports the following AVR-specific commands:
info io_registers
When configured for debugging CRIS, gdb provides the following CRIS-specific commands:
set cris-version
vershow cris-version
set cris-dwarf2-cfi
gcc-cris
whose version is below
R59
.
show cris-dwarf2-cfi
set cris-mode
modeshow cris-mode
For the Renesas Super-H processor, gdb provides these commands:
regs
set sh calling-convention
conventionshow sh calling-convention
This section describes characteristics of architectures that affect all uses of gdb with the architecture, both native and cross.
set struct-convention
modestruct
s and
union
s from functions to mode. Possible values of
mode are "pcc"
, "reg"
, and "default"
(the
default). "default"
or "pcc"
means that struct
s
are returned on the stack, while "reg"
means that a
struct
or a union
whose size is 1, 2, 4, or 8 bytes will
be returned in a register.
show struct-convention
struct
s
from functions.
set rstack_high_address
addressset rstack_high_address
command. The argument should be an
address, which you probably want to precede with ‘0x’ to specify in
hexadecimal.
show rstack_high_address
See the following section.
Alpha- and MIPS-based computers use an unusual stack frame, which sometimes requires gdb to search backward in the object code to find the beginning of a function.
To improve response time (especially for embedded applications, where gdb may be restricted to a slow serial line for this search) you may want to limit the size of this search, using one of these commands:
set heuristic-fence-post
limitheuristic-fence-post
must search
and therefore the longer it takes to run. You should only need to use
this command when debugging a stripped executable.
show heuristic-fence-post
These commands are available only when gdb is configured for debugging programs on Alpha or MIPS processors.
Several MIPS-specific commands are available when debugging MIPS programs:
set mips abi
argshow mips abi
set mipsfpu
show mipsfpu
set mips mask-address
argshow mips mask-address
set remote-mips64-transfers-32bit-regs
show remote-mips64-transfers-32bit-regs
set debug mips
show debug mips
When gdb is debugging the HP PA architecture, it provides the following special commands:
set debug hppa
show debug hppa
maint print unwind
addressWhen gdb is debugging the Cell Broadband Engine SPU architecture, it provides the following special commands:
info spu event
info spu signal
info spu mailbox
info spu dma
info spu proxydma
When gdb is debugging a combined PowerPC/SPU application on the Cell Broadband Engine, it provides in addition the following special commands:
set spu stop-on-load
argon
, gdb
will give control to the user when a new SPE thread enters its main
function. The default is off
.
show spu stop-on-load
set spu auto-flush-cache
argon
, gdb will automatically cause the SPE software-managed
cache to be flushed whenever SPE execution stops. This provides a consistent
view of PowerPC memory that is accessed via the cache. If an application
does not use the software-managed cache, this option has no effect.
show spu auto-flush-cache
When gdb is debugging the PowerPC architecture, it provides a set of
pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point
numbers stored in the floating point registers. These values must be stored
in two consecutive registers, always starting at an even register like
f0
or f2
.
The pseudo-registers go from $dl0
through $dl15
, and are formed
by joining the even/odd register pairs f0
and f1
for $dl0
,
f2
and f3
for $dl1
and so on.
For POWER7 processors, gdb provides a set of pseudo-registers, the 64-bit wide Extended Floating Point Registers (‘f32’ through ‘f63’).
You can alter the way gdb interacts with you by using the
set
command. For commands controlling how gdb displays
data, see Print Settings. Other settings are
described here.
gdb indicates its readiness to read a command by printing a string
called the prompt. This string is normally ‘(gdb)’. You
can change the prompt string with the set prompt
command. For
instance, when debugging gdb with gdb, it is useful to change
the prompt in one of the gdb sessions so that you can always tell
which one you are talking to.
Note: set prompt
does not add a space for you after the
prompt you set. This allows you to set a prompt which ends in a space
or a prompt that does not.
set prompt
newpromptshow prompt
gdb reads its input commands via the Readline interface. This
gnu library provides consistent behavior for programs which provide a
command line interface to the user. Advantages are gnu Emacs-style
or vi-style inline editing of commands, csh
-like history
substitution, and a storage and recall of command history across
debugging sessions.
You may control the behavior of command line editing in gdb with the
command set
.
set editing
set editing on
set editing off
show editing
See Command Line Editing,
for more details about the Readline
interface. Users unfamiliar with gnu Emacs or vi
are
encouraged to read that chapter.
gdb can keep track of the commands you type during your debugging sessions, so that you can be certain of precisely what happened. Use these commands to manage the gdb command history facility.
gdb uses the gnu History library, a part of the Readline package, to provide the history facility. See Using History Interactively, for the detailed description of the History library.
To issue a command to gdb without affecting certain aspects of the state which is seen by users, prefix it with ‘server ’ (see Server Prefix). This means that this command will not affect the command history, nor will it affect gdb's notion of which command to repeat if <RET> is pressed on a line by itself.
The server prefix does not affect the recording of values into the value
history; to print a value without recording it into the value history,
use the output
command instead of the print
command.
Here is the description of gdb commands related to command history.
set history filename
fnameGDBHISTFILE
, or to
./.gdb_history (./_gdb_history on MS-DOS) if this variable
is not set.
set history save
set history save on
set history filename
command. By default, this option is disabled.
set history save off
set history size
sizeHISTSIZE
, or to 256 if this variable is not set.
History expansion assigns special meaning to the character !. See Event Designators, for more details.
Since ! is also the logical not operator in C, history expansion
is off by default. If you decide to enable history expansion with the
set history expansion on
command, you may sometimes need to
follow ! (when it is used as logical not, in an expression) with
a space or a tab to prevent it from being expanded. The readline
history facilities do not attempt substitution on the strings
!= and !(, even when history expansion is enabled.
The commands to control history expansion are:
set history expansion on
set history expansion
set history expansion off
show history
show history filename
show history save
show history size
show history expansion
show history
by itself displays all four states.
show commands
show commands
nshow commands +
Certain commands to gdb may produce large amounts of information output to the screen. To help you read all of it, gdb pauses and asks you for input at the end of each page of output. Type <RET> when you want to continue the output, or q to discard the remaining output. Also, the screen width setting determines when to wrap lines of output. Depending on what is being printed, gdb tries to break the line at a readable place, rather than simply letting it overflow onto the following line.
Normally gdb knows the size of the screen from the terminal
driver software. For example, on Unix gdb uses the termcap data base
together with the value of the TERM
environment variable and the
stty rows
and stty cols
settings. If this is not correct,
you can override it with the set height
and set
width
commands:
set height
lppshow height
set width
cplshow width
set
commands specify a screen height of lpp lines and
a screen width of cpl characters. The associated show
commands display the current settings.
If you specify a height of zero lines, gdb does not pause during output no matter how long the output is. This is useful if output is to a file or to an editor buffer.
Likewise, you can specify ‘set width 0’ to prevent gdb
from wrapping its output.
set pagination on
set pagination off
set height 0
. Note that
running gdb with the --batch option (see -batch) also automatically disables pagination.
show pagination
You can always enter numbers in octal, decimal, or hexadecimal in gdb by the usual conventions: octal numbers begin with ‘0’, decimal numbers end with ‘.’, and hexadecimal numbers begin with ‘0x’. Numbers that neither begin with ‘0’ or ‘0x’, nor end with a ‘.’ are, by default, entered in base 10; likewise, the default display for numbers—when no particular format is specified—is base 10. You can change the default base for both input and output with the commands described below.
set input-radix
baseset input-radix 012 set input-radix 10. set input-radix 0xa
sets the input base to decimal. On the other hand, ‘set input-radix 10’ leaves the input radix unchanged, no matter what it was, since ‘10’, being without any leading or trailing signs of its base, is interpreted in the current radix. Thus, if the current radix is 16, ‘10’ is interpreted in hex, i.e. as 16 decimal, which doesn't change the radix.
set output-radix
baseshow input-radix
show output-radix
set radix
[base]show radix
set radix
sets the radix of input and output to
the same base; without an argument, it resets the radix back to its
default value of 10.
gdb can determine the ABI (Application Binary Interface) of your application automatically. However, sometimes you need to override its conclusions. Use these commands to manage gdb's view of the current ABI.
One gdb configuration can debug binaries for multiple operating
system targets, either via remote debugging or native emulation.
gdb will autodetect the OS ABI (Operating System ABI) in use,
but you can override its conclusion using the set osabi
command.
One example where this is useful is in debugging of binaries which use
an alternate C library (e.g. uClibc for gnu/Linux) which does
not have the same identifying marks that the standard C library for your
platform provides.
show osabi
set osabi
set osabi
abi
Generally, the way that an argument of type float
is passed to a
function depends on whether the function is prototyped. For a prototyped
(i.e. ANSI/ISO style) function, float
arguments are passed unchanged,
according to the architecture's convention for float
. For unprototyped
(i.e. K&R style) functions, float
arguments are first promoted to type
double
and then passed.
Unfortunately, some forms of debug information do not reliably indicate whether a function is prototyped. If gdb calls a function that is not marked as prototyped, it consults set coerce-float-to-double.
set coerce-float-to-double
set coerce-float-to-double on
float
will be promoted to double
when passed
to an unprototyped function. This is the default setting.
set coerce-float-to-double off
float
will be passed directly to unprototyped
functions.
show coerce-float-to-double
float
to double
.
gdb needs to know the ABI used for your program's C++
objects. The correct C++ ABI depends on which C++ compiler was
used to build your application. gdb only fully supports
programs with a single C++ ABI; if your program contains code using
multiple C++ ABI's or if gdb can not identify your
program's ABI correctly, you can tell gdb which ABI to use.
Currently supported ABI's include “gnu-v2”, for g++
versions
before 3.0, “gnu-v3”, for g++
versions 3.0 and later, and
“hpaCC” for the HP ANSI C++ compiler. Other C++ compilers may
use the “gnu-v2” or “gnu-v3” ABI's as well. The default setting is
“auto”.
show cp-abi
set cp-abi
set cp-abi
abiset cp-abi auto
By default, gdb is silent about its inner workings. If you are
running on a slow machine, you may want to use the set verbose
command. This makes gdb tell you when it does a lengthy
internal operation, so you will not think it has crashed.
Currently, the messages controlled by set verbose
are those
which announce that the symbol table for a source file is being read;
see symbol-file
in Commands to Specify Files.
set verbose on
set verbose off
show verbose
set verbose
is on or off.
By default, if gdb encounters bugs in the symbol table of an object file, it is silent; but if you are debugging a compiler, you may find this information useful (see Errors Reading Symbol Files).
set complaints
limitshow complaints
By default, gdb is cautious, and asks what sometimes seems to be a lot of stupid questions to confirm certain commands. For example, if you try to run a program which is already running:
(gdb) run The program being debugged has been started already. Start it from the beginning? (y or n)
If you are willing to unflinchingly face the consequences of your own commands, you can disable this “feature”:
set confirm off
set confirm on
show confirm
If you need to debug user-defined commands or sourced files you may find it useful to enable command tracing. In this mode each command will be printed as it is executed, prefixed with one or more ‘+’ symbols, the quantity denoting the call depth of each command.
set trace-commands on
set trace-commands off
show trace-commands
gdb has commands that enable optional debugging messages from various gdb subsystems; normally these commands are of interest to gdb maintainers, or when reporting a bug. This section documents those commands.
set exec-done-display
show exec-done-display
set debug arch
show debug arch
set debug aix-thread
show debug aix-thread
set debug check-physname
show debug check-physname
set debug dwarf2-die
show debug dwarf2-die
set debug displaced
show debug displaced
set debug event
show debug event
set debug expression
show debug expression
set debug frame
show debug frame
set debug gnu-nat
show debug gnu-nat
set debug infrun
show debug infrun
set debug jit
show debug jit
set debug lin-lwp
show debug lin-lwp
set debug lin-lwp-async
show debug lin-lwp-async
set debug observer
show debug observer
set debug overload
show debug overload
set debug parser
yydebug
variable in the expression
parser. See Tracing Your Parser, for
details. The default is off.
show debug parser
set debug remote
show debug remote
set debug serial
show debug serial
set debug solib-frv
show debug solib-frv
set debug target
run
command.
show debug target
set debug timestamp
show debug timestamp
set debugvarobj
show debugvarobj
set debug xml
show debug xml
set interactive-mode
on
, forces gdb to assume that GDB was started
in a terminal. In practice, this means that gdb should wait
for the user to answer queries generated by commands entered at
the command prompt. If off
, forces gdb to operate
in the opposite mode, and it uses the default answers to all queries.
If auto
(the default), gdb tries to determine whether
its standard input is a terminal, and works in interactive-mode if it
is, non-interactively otherwise.
In the vast majority of cases, the debugger should be able to guess correctly which mode should be used. But this setting can be useful in certain specific cases, such as running a MinGW gdb inside a cygwin window.
show interactive-mode
gdb provides two mechanisms for extension. The first is based on composition of gdb commands, and the second is based on the Python scripting language.
To facilitate the use of these extensions, gdb is capable of evaluating the contents of a file. When doing so, gdb can recognize which scripting language is being used by looking at the filename extension. Files with an unrecognized filename extension are always treated as a gdb Command Files. See Command files.
You can control how gdb evaluates these files with the following setting:
set script-extension off
set script-extension soft
set script-extension strict
show script-extension
script-extension
option.
Aside from breakpoint commands (see Breakpoint Command Lists), gdb provides two ways to store sequences of commands for execution as a unit: user-defined commands and command files.
A user-defined command is a sequence of gdb commands to
which you assign a new name as a command. This is done with the
define
command. User commands may accept up to 10 arguments
separated by whitespace. Arguments are accessed within the user command
via $arg0...$arg9
. A trivial example:
define adder print $arg0 + $arg1 + $arg2 end
To execute the command use:
adder 1 2 3
This defines the command adder
, which prints the sum of
its three arguments. Note the arguments are text substitutions, so they may
reference variables, use complex expressions, or even perform inferior
functions calls.
In addition, $argc
may be used to find out how many arguments have
been passed. This expands to a number in the range 0...10.
define adder if $argc == 2 print $arg0 + $arg1 end if $argc == 3 print $arg0 + $arg1 + $arg2 end end
define
commandnameThe definition of the command is made up of other gdb command lines,
which are given following the define
command. The end of these
commands is marked by a line containing end
.
document
commandnamehelp
. The command commandname must already be
defined. This command reads lines of documentation just as define
reads the lines of the command definition, ending with end
.
After the document
command is finished, help
on command
commandname displays the documentation you have written.
You may use the document
command again to change the
documentation of a command. Redefining the command with define
does not change the documentation.
dont-repeat
help user-defined
show user
show user
commandnameshow max-user-call-depth
set max-user-call-depth
max-user-call-depth
controls how many recursion
levels are allowed in user-defined commands before gdb suspects an
infinite recursion and aborts the command.
In addition to the above commands, user-defined commands frequently use control flow commands, described in Command Files.
When user-defined commands are executed, the commands of the definition are not printed. An error in any command stops execution of the user-defined command.
If used interactively, commands that would ask for confirmation proceed without asking when used inside a user-defined command. Many gdb commands that normally print messages to say what they are doing omit the messages when used in a user-defined command.
You may define hooks, which are a special kind of user-defined command. Whenever you run the command ‘foo’, if the user-defined command ‘hook-foo’ exists, it is executed (with no arguments) before that command.
A hook may also be defined which is run after the command you executed. Whenever you run the command ‘foo’, if the user-defined command ‘hookpost-foo’ exists, it is executed (with no arguments) after that command. Post-execution hooks may exist simultaneously with pre-execution hooks, for the same command.
It is valid for a hook to call the command which it hooks. If this occurs, the hook is not re-executed, thereby avoiding infinite recursion.
In addition, a pseudo-command, ‘stop’ exists. Defining (‘hook-stop’) makes the associated commands execute every time execution stops in your program: before breakpoint commands are run, displays are printed, or the stack frame is printed.
For example, to ignore SIGALRM
signals while
single-stepping, but treat them normally during normal execution,
you could define:
define hook-stop handle SIGALRM nopass end define hook-run handle SIGALRM pass end define hook-continue handle SIGALRM pass end
As a further example, to hook at the beginning and end of the echo
command, and to add extra text to the beginning and end of the message,
you could define:
define hook-echo echo <<<--- end define hookpost-echo echo --->>>\n end (gdb) echo Hello World <<<---Hello World--->>> (gdb)
You can define a hook for any single-word command in gdb, but
not for command aliases; you should define a hook for the basic command
name, e.g. backtrace
rather than bt
.
You can hook a multi-word command by adding hook-
or
hookpost-
to the last word of the command, e.g.
‘define target hook-remote’ to add a hook to ‘target remote’.
If an error occurs during the execution of your hook, execution of gdb commands stops and gdb issues a prompt (before the command that you actually typed had a chance to run).
If you try to define a hook which does not match any known command, you
get a warning from the define
command.
A command file for gdb is a text file made of lines that are gdb commands. Comments (lines starting with #) may also be included. An empty line in a command file does nothing; it does not mean to repeat the last command, as it would from the terminal.
You can request the execution of a command file with the source
command. Note that the source
command is also used to evaluate
scripts that are not Command Files. The exact behavior can be configured
using the script-extension
setting.
See Extending GDB.
source [-s] [-v]
filenameThe lines in a command file are generally executed sequentially, unless the order of execution is changed by one of the flow-control commands described below. The commands are not printed as they are executed. An error in any command terminates execution of the command file and control is returned to the console.
gdb first searches for filename in the current directory. If the file is not found there, and filename does not specify a directory, then gdb also looks for the file on the source search path (specified with the ‘directory’ command); except that $cdir is not searched because the compilation directory is not relevant to scripts.
If -s
is specified, then gdb searches for filename
on the search path even if filename specifies a directory.
The search is done by appending filename to each element of the
search path. So, for example, if filename is mylib/myscript
and the search path contains /home/user then gdb will
look for the script /home/user/mylib/myscript.
The search is also done if filename is an absolute path.
For example, if filename is /tmp/myscript and
the search path contains /home/user then gdb will
look for the script /home/user/tmp/myscript.
For DOS-like systems, if filename contains a drive specification,
it is stripped before concatenation. For example, if filename is
d:myscript and the search path contains c:/tmp then gdb
will look for the script c:/tmp/myscript.
If -v
, for verbose mode, is given then gdb displays
each command as it is executed. The option must be given before
filename, and is interpreted as part of the filename anywhere else.
Commands that would ask for confirmation if used interactively proceed without asking when used in a command file. Many gdb commands that normally print messages to say what they are doing omit the messages when called from command files.
gdb also accepts command input from standard input. In this mode, normal output goes to standard output and error output goes to standard error. Errors in a command file supplied on standard input do not terminate execution of the command file—execution continues with the next command.
gdb < cmds > log 2>&1
(The syntax above will vary depending on the shell used.) This example will execute commands from the file cmds. All output and errors would be directed to log.
Since commands stored on command files tend to be more general than commands typed interactively, they frequently need to deal with complicated situations, such as different or unexpected values of variables and symbols, changes in how the program being debugged is built, etc. gdb provides a set of flow-control commands to deal with these complexities. Using these commands, you can write complex scripts that loop over data structures, execute commands conditionally, etc.
if
else
if
command takes a single argument, which is an
expression to evaluate. It is followed by a series of commands that
are executed only if the expression is true (its value is nonzero).
There can then optionally be an else
line, followed by a series
of commands that are only executed if the expression was false. The
end of the list is marked by a line containing end
.
while
if
: the command takes a single argument, which is an expression
to evaluate, and must be followed by the commands to execute, one per
line, terminated by an end
. These commands are called the
body of the loop. The commands in the body of while
are
executed repeatedly as long as the expression evaluates to true.
loop_break
while
loop in whose body it is included.
Execution of the script continues after that while
s end
line.
loop_continue
while
loop in whose body it is included. Execution
branches to the beginning of the while
loop, where it evaluates
the controlling expression.
end
if
,
else
, or while
flow-control commands.
During the execution of a command file or a user-defined command, normal gdb output is suppressed; the only output that appears is what is explicitly printed by the commands in the definition. This section describes three commands useful for generating exactly the output you want.
echo
textA backslash at the end of text can be used, as in C, to continue the command onto subsequent lines. For example,
echo This is some text\n\ which is continued\n\ onto several lines.\n
produces the same output as
echo This is some text\n echo which is continued\n echo onto several lines.\n
output
expressionoutput/
fmt expressionprint
. See Output Formats, for more information.
printf
template,
expressions...
printf (template, expressions...);
As in C
printf
, ordinary characters in template
are printed verbatim, while conversion specification introduced
by the ‘%’ character cause subsequent expressions to be
evaluated, their values converted and formatted according to type and
style information encoded in the conversion specifications, and then
printed.
For example, you can print two values in hex like this:
printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
printf
supports all the standard C
conversion
specifications, including the flags and modifiers between the ‘%’
character and the conversion letter, with the following exceptions:
LC_NUMERIC'
) is not supported.
Note that the ‘ll’ type modifier is supported only if the
underlying C
implementation used to build gdb supports
the long long int
type, and the ‘L’ type modifier is
supported only if long double
type is available.
As in C
, printf
supports simple backslash-escape
sequences, such as \n
, ‘\t’, ‘\\’, ‘\"’,
‘\a’, and ‘\f’, that consist of backslash followed by a
single character. Octal and hexadecimal escape sequences are not
supported.
Additionally, printf
supports conversion specifications for DFP
(Decimal Floating Point) types using the following length modifiers
together with a floating point specifier.
letters:
Decimal32
types.
Decimal64
types.
Decimal128
types.
If the underlying C
implementation used to build gdb has
support for the three length modifiers for DFP types, other modifiers
such as width and precision will also be available for gdb to use.
In case there is no such C
support, no additional modifiers will be
available and the value will be printed in the standard way.
Here's an example of printing DFP types using the above conversion letters:
printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
eval
template,
expressions...
You can script gdb using the Python programming language. This feature is available only if gdb was configured using --with-python.
Python scripts used by gdb should be installed in data-directory/python, where data-directory is the data directory as determined at gdb startup (see Data Files). This directory, known as the python directory, is automatically added to the Python Search Path in order to allow the Python interpreter to locate all scripts installed at this location.
gdb provides one command for accessing the Python interpreter, and one related setting:
python
[code]python
command can be used to evaluate Python code.
If given an argument, the python
command will evaluate the
argument as a Python command. For example:
(gdb) python print 23 23
If you do not provide an argument to python
, it will act as a
multi-line command, like define
. In this case, the Python
script is made up of subsequent command lines, given after the
python
command. This command list is terminated using a line
containing end
. For example:
(gdb) python >print 23 >end 23
maint set python print-stack
maint set
python print-stack
: if on
, the default, then Python stack
printing is enabled; if off
, then Python stack printing is
disabled.
maint set python auto-load
maint set python auto-load
: if on
, the default, then
Python auto-loading is enabled; if off
, then Python
auto-loading is disabled.
It is also possible to execute a Python script from the gdb interpreter:
source
script-namescript-extension
setting. See Extending GDB.
python execfile ("script-name")
execfile
Python built-in function,
and thus is always available.
You can get quick online help for gdb's Python API by issuing the command python help (gdb).
Functions and methods which have two or more optional arguments allow
them to be specified using keyword syntax. This allows passing some
optional arguments while skipping others. Example:
gdb.some_function ('foo', bar = 1, baz = 2)
.
At startup, gdb overrides Python's sys.stdout
and
sys.stderr
to print using gdb's output-paging streams.
A Python program which outputs to one of these streams may have its
output interrupted by the user (see Screen Size). In this
situation, a Python KeyboardInterrupt
exception is thrown.
gdb introduces a new Python module, named gdb
. All
methods and classes added by gdb are placed in this module.
gdb automatically import
s the gdb
module for
use in all scripts evaluated by the python
command.
Evaluate command, a string, as a gdb CLI command. If a GDB exception happens while command runs, it is translated as described in Exception Handling.
from_tty specifies whether gdb ought to consider this command as having originated from the user invoking it interactively. It must be a boolean value. If omitted, it defaults to
False
.By default, any output produced by command is sent to gdb's standard output. If the to_string parameter is
True
, then output will be collected bygdb.execute
and returned as a string. The default isFalse
, in which case the return value isNone
. If to_string isTrue
, the gdb virtual terminal will be temporarily set to unlimited width and height, and its pagination will be disabled; see Screen Size.
Return a sequence holding all of gdb's breakpoints. See Breakpoints In Python, for more information.
Return the value of a gdb parameter. parameter is a string naming the parameter to look up; parameter may contain spaces if the parameter has a multi-part name. For example, ‘print object’ is a valid parameter name.
If the named parameter does not exist, this function throws a
gdb.error
(see Exception Handling). Otherwise, the parameter's value is converted to a Python value of the appropriate type, and returned.
Return a value from gdb's value history (see Value History). number indicates which history element to return. If number is negative, then gdb will take its absolute value and count backward from the last element (i.e., the most recent element) to find the value to return. If number is zero, then gdb will return the most recent element. If the element specified by number doesn't exist in the value history, a
gdb.error
exception will be raised.If no exception is raised, the return value is always an instance of
gdb.Value
(see Values From Inferior).
Parse expression as an expression in the current language, evaluate it, and return the result as a
gdb.Value
. expression must be a string.This function can be useful when implementing a new command (see Commands In Python), as it provides a way to parse the command's argument as an expression. It is also useful simply to compute values, for example, it is the only way to get the value of a convenience variable (see Convenience Vars) as a
gdb.Value
.
Put event, a callable object taking no arguments, into gdb's internal event queue. This callable will be invoked at some later point, during gdb's event processing. Events posted using
post_event
will be run in the order in which they were posted; however, there is no way to know when they will be processed relative to other events inside gdb.gdb is not thread-safe. If your Python program uses multiple threads, you must be careful to only call gdb-specific functions in the main gdb thread.
post_event
ensures this. For example:(gdb) python >import threading > >class Writer(): > def __init__(self, message): > self.message = message; > def __call__(self): > gdb.write(self.message) > >class MyThread1 (threading.Thread): > def run (self): > gdb.post_event(Writer("Hello ")) > >class MyThread2 (threading.Thread): > def run (self): > gdb.post_event(Writer("World\n")) > >MyThread1().start() >MyThread2().start() >end (gdb) Hello World
Print a string to gdb's paginated output stream. The optional stream determines the stream to print to. The default stream is gdb's standard output stream. Possible stream values are:
STDOUT
- gdb's standard output stream.
STDERR
- gdb's standard error stream.
STDLOG
- gdb's log stream (see Logging Output).
Writing to
sys.stdout
orsys.stderr
will automatically call this function and will automatically direct the output to the relevant stream.
Flush the buffer of a gdb paginated stream so that the contents are displayed immediately. gdb will flush the contents of a stream automatically when it encounters a newline in the buffer. The optional stream determines the stream to flush. The default stream is gdb's standard output stream. Possible stream values are:
STDOUT
- gdb's standard output stream.
STDERR
- gdb's standard error stream.
STDLOG
- gdb's log stream (see Logging Output).
Flushing
sys.stdout
orsys.stderr
will automatically call this function for the relevant stream.
Return the name of the current target character set (see Character Sets). This differs from
gdb.parameter('target-charset')
in that ‘auto’ is never returned.
Return the name of the current target wide character set (see Character Sets). This differs from
gdb.parameter('target-wide-charset')
in that ‘auto’ is never returned.
Return the name of the shared library holding the given address as a string, or
None
.
Return locations of the line specified by expression, or of the current line if no argument was given. This function returns a Python tuple containing two elements. The first element contains a string holding any unparsed section of expression (or
None
if the expression has been fully parsed). The second element contains eitherNone
or another tuple that contains all the locations that match the expression represented asgdb.Symtab_and_line
objects (see Symbol Tables In Python). If expression is provided, it is decoded the way that gdb's inbuiltbreak
oredit
commands do (see Specify Location).
When executing the python
command, Python exceptions
uncaught within the Python code are translated to calls to
gdb error-reporting mechanism. If the command that called
python
does not handle the error, gdb will
terminate it and print an error message containing the Python
exception name, the associated value, and the Python call stack
backtrace at the point where the exception was raised. Example:
(gdb) python print foo Traceback (most recent call last): File "<string>", line 1, in <module> NameError: name 'foo' is not defined
gdb errors that happen in gdb commands invoked by Python code are converted to Python exceptions. The type of the Python exception depends on the error.
gdb.error
RuntimeError
, for compatibility with earlier
versions of gdb.
If an error occurring in gdb does not fit into some more
specific category, then the generated exception will have this type.
gdb.MemoryError
gdb.error
which is thrown when an
operation tried to access invalid memory in the inferior.
KeyboardInterrupt
KeyboardInterrupt
exception.
In all cases, your exception handler will see the gdb error message as its value and the Python call stack backtrace at the Python statement closest to where the gdb error occured as the traceback.
When implementing gdb commands in Python via gdb.Command
,
it is useful to be able to throw an exception that doesn't cause a
traceback to be printed. For example, the user may have invoked the
command incorrectly. Use the gdb.GdbError
exception
to handle this case. Example:
(gdb) python >class HelloWorld (gdb.Command): > """Greet the whole world.""" > def __init__ (self): > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_OBSCURE) > def invoke (self, args, from_tty): > argv = gdb.string_to_argv (args) > if len (argv) != 0: > raise gdb.GdbError ("hello-world takes no arguments") > print "Hello, World!" >HelloWorld () >end (gdb) hello-world 42 hello-world takes no arguments
gdb provides values it obtains from the inferior program in
an object of type gdb.Value
. gdb uses this object
for its internal bookkeeping of the inferior's values, and for
fetching values when necessary.
Inferior values that are simple scalars can be used directly in
Python expressions that are valid for the value's data type. Here's
an example for an integer or floating-point value some_val
:
bar = some_val + 2
As result of this, bar
will also be a gdb.Value
object
whose values are of the same type as those of some_val
.
Inferior values that are structures or instances of some class can
be accessed using the Python dictionary syntax. For example, if
some_val
is a gdb.Value
instance holding a structure, you
can access its foo
element with:
bar = some_val['foo']
Again, bar
will also be a gdb.Value
object.
A gdb.Value
that represents a function can be executed via
inferior function call. Any arguments provided to the call must match
the function's prototype, and must be provided in the order specified
by that prototype.
For example, some_val
is a gdb.Value
instance
representing a function that takes two integers as arguments. To
execute this function, call it like so:
result = some_val (10,20)
Any values returned from a function call will be stored as a
gdb.Value
.
The following attributes are provided:
If this object is addressable, this read-only attribute holds a
gdb.Value
object representing the address. Otherwise, this attribute holdsNone
.
This read-only boolean attribute is true if the compiler optimized out this value, thus it is not available for fetching from the inferior.
The type of this
gdb.Value
. The value of this attribute is agdb.Type
object (see Types In Python).
The dynamic type of this
gdb.Value
. This uses C++ run-time type information (RTTI) to determine the dynamic type of the value. If this value is of class type, it will return the class in which the value is embedded, if any. If this value is of pointer or reference to a class type, it will compute the dynamic type of the referenced object, and return a pointer or reference to that type, respectively. In all other cases, it will return the value's static type.Note that this feature will only work when debugging a C++ program that includes RTTI for the object in question. Otherwise, it will just return the static type of the value as in ptype foo (see ptype).
The following methods are provided:
Many Python values can be converted directly to a
gdb.Value
via this object initializer. Specifically:
- Python boolean
- A Python boolean is converted to the boolean type from the current language.
- Python integer
- A Python integer is converted to the C
long
type for the current architecture.- Python long
- A Python long is converted to the C
long long
type for the current architecture.- Python float
- A Python float is converted to the C
double
type for the current architecture.- Python string
- A Python string is converted to a target string, using the current target encoding.
gdb.Value
- If
val
is agdb.Value
, then a copy of the value is made.gdb.LazyString
- If
val
is agdb.LazyString
(see Lazy Strings In Python), then the lazy string'svalue
method is called, and its result is used.
Return a new instance of
gdb.Value
that is the result of casting this instance to the type described by type, which must be agdb.Type
object. If the cast cannot be performed for some reason, this method throws an exception.
For pointer data types, this method returns a new
gdb.Value
object whose contents is the object pointed to by the pointer. For example, iffoo
is a C pointer to anint
, declared in your C program asint *foo;then you can use the corresponding
gdb.Value
to access whatfoo
points to like this:bar = foo.dereference ()The result
bar
will be agdb.Value
object holding the value pointed to byfoo
.
Like
Value.cast
, but works as if the C++dynamic_cast
operator were used. Consult a C++ reference for details.
Like
Value.cast
, but works as if the C++reinterpret_cast
operator were used. Consult a C++ reference for details.
If this
gdb.Value
represents a string, then this method converts the contents to a Python string. Otherwise, this method will throw an exception.Strings are recognized in a language-specific way; whether a given
gdb.Value
represents a string is determined by the current language.For C-like languages, a value is a string if it is a pointer to or an array of characters or ints. The string is assumed to be terminated by a zero of the appropriate width. However if the optional length argument is given, the string will be converted to that given length, ignoring any embedded zeros that the string may contain.
If the optional encoding argument is given, it must be a string naming the encoding of the string in the
gdb.Value
, such as"ascii"
,"iso-8859-6"
or"utf-8"
. It accepts the same encodings as the corresponding argument to Python'sstring.decode
method, and the Python codec machinery will be used to convert the string. If encoding is not given, or if encoding is the empty string, then either thetarget-charset
(see Character Sets) will be used, or a language-specific encoding will be used, if the current language is able to supply one.The optional errors argument is the same as the corresponding argument to Python's
string.decode
method.If the optional length argument is given, the string will be fetched and converted to the given length.
If this
gdb.Value
represents a string, then this method converts the contents to agdb.LazyString
(see Lazy Strings In Python). Otherwise, this method will throw an exception.If the optional encoding argument is given, it must be a string naming the encoding of the
gdb.LazyString
. Some examples are: ‘ascii’, ‘iso-8859-6’ or ‘utf-8’. If the encoding argument is an encoding that gdb does recognize, gdb will raise an error.When a lazy string is printed, the gdb encoding machinery is used to convert the string during printing. If the optional encoding argument is not provided, or is an empty string, gdb will automatically select the encoding most suitable for the string type. For further information on encoding in gdb please see Character Sets.
If the optional length argument is given, the string will be fetched and encoded to the length of characters specified. If the length argument is not provided, the string will be fetched and encoded until a null of appropriate width is found.
gdb represents types from the inferior using the class
gdb.Type
.
The following type-related functions are available in the gdb
module:
This function looks up a type by name. name is the name of the type to look up. It must be a string.
If block is given, then name is looked up in that scope. Otherwise, it is searched for globally.
Ordinarily, this function will return an instance of
gdb.Type
. If the named type cannot be found, it will throw an exception.
An instance of Type
has the following attributes:
The type code for this type. The type code will be one of the
TYPE_CODE_
constants defined below.
The following methods are provided:
For structure and union types, this method returns the fields. Range types have two fields, the minimum and maximum values. Enum types have one field per enum constant. Function and method types have one field per parameter. The base types of C++ classes are also represented as fields. If the type has no fields, or does not fit into one of these categories, an empty sequence will be returned.
Each field is an object, with some pre-defined attributes:
bitpos
- This attribute is not available for
static
fields (as in C++ or Java). For non-static
fields, the value is the bit position of the field.name
- The name of the field, or
None
for anonymous fields.artificial
- This is
True
if the field is artificial, usually meaning that it was provided by the compiler and not the user. This attribute is always provided, and isFalse
if the field is not artificial.is_base_class
- This is
True
if the field represents a base class of a C++ structure. This attribute is always provided, and isFalse
if the field is not a base class of the type that is the argument offields
, or if that type was not a C++ class.bitsize
- If the field is packed, or is a bitfield, then this will have a non-zero value, which is the size of the field in bits. Otherwise, this will be zero; in this case the field's size is given by its type.
type
- The type of the field. This is usually an instance of
Type
, but it can beNone
in some situations.
Return a new
gdb.Type
object which represents an array of this type. If one argument is given, it is the inclusive upper bound of the array; in this case the lower bound is zero. If two arguments are given, the first argument is the lower bound of the array, and the second argument is the upper bound of the array. An array's length must not be negative, but the bounds can be.
Return a new
gdb.Type
object which represents aconst
-qualified variant of this type.
Return a new
gdb.Type
object which represents avolatile
-qualified variant of this type.
Return a new
gdb.Type
object which represents an unqualified variant of this type. That is, the result is neitherconst
norvolatile
.
Return a Python
Tuple
object that contains two elements: the low bound of the argument type and the high bound of that type. If the type does not have a range, gdb will raise agdb.error
exception (see Exception Handling).
Return a new
gdb.Type
that represents the real type, after removing all layers of typedefs.
Return a new
gdb.Type
object which represents the target type of this type.For a pointer type, the target type is the type of the pointed-to object. For an array type (meaning C-like arrays), the target type is the type of the elements of the array. For a function or method type, the target type is the type of the return value. For a complex type, the target type is the type of the elements. For a typedef, the target type is the aliased type.
If the type does not have a target, this method will throw an exception.
If this
gdb.Type
is an instantiation of a template, this will return a newgdb.Type
which represents the type of the nth template argument.If this
gdb.Type
is not a template type, this will throw an exception. Ordinarily, only C++ code will have template types.If block is given, then name is looked up in that scope. Otherwise, it is searched for globally.
Each type has a code, which indicates what category this type falls
into. The available type categories are represented by constants
defined in the gdb
module:
TYPE_CODE_PTR
TYPE_CODE_ARRAY
TYPE_CODE_STRUCT
TYPE_CODE_UNION
TYPE_CODE_ENUM
TYPE_CODE_FLAGS
TYPE_CODE_FUNC
TYPE_CODE_INT
TYPE_CODE_FLT
TYPE_CODE_VOID
void
.
TYPE_CODE_SET
TYPE_CODE_RANGE
TYPE_CODE_STRING
TYPE_CODE_BITSTRING
TYPE_CODE_ERROR
TYPE_CODE_METHOD
TYPE_CODE_METHODPTR
TYPE_CODE_MEMBERPTR
TYPE_CODE_REF
TYPE_CODE_CHAR
TYPE_CODE_BOOL
TYPE_CODE_COMPLEX
TYPE_CODE_TYPEDEF
TYPE_CODE_NAMESPACE
TYPE_CODE_DECFLOAT
TYPE_CODE_INTERNAL_FUNCTION
Further support for types is provided in the gdb.types
Python module (see gdb.types).
An example output is provided (see Pretty Printing).
A pretty-printer is just an object that holds a value and implements a specific interface, defined here.
gdb will call this method on a pretty-printer to compute the children of the pretty-printer's value.
This method must return an object conforming to the Python iterator protocol. Each item returned by the iterator must be a tuple holding two elements. The first element is the “name” of the child; the second element is the child's value. The value can be any Python object which is convertible to a gdb value.
This method is optional. If it does not exist, gdb will act as though the value has no children.
The CLI may call this method and use its result to change the formatting of a value. The result will also be supplied to an MI consumer as a ‘displayhint’ attribute of the variable being printed.
This method is optional. If it does exist, this method must return a string.
Some display hints are predefined by gdb:
- ‘array’
- Indicate that the object being printed is “array-like”. The CLI uses this to respect parameters such as
set print elements
andset print array
.- ‘map’
- Indicate that the object being printed is “map-like”, and that the children of this value can be assumed to alternate between keys and values.
- ‘string’
- Indicate that the object being printed is “string-like”. If the printer's
to_string
method returns a Python string of some kind, then gdb will call its internal language-specific string-printing function to format the string. For the CLI this means adding quotation marks, possibly escaping some characters, respectingset print elements
, and the like.
gdb will call this method to display the string representation of the value passed to the object's constructor.
When printing from the CLI, if the
to_string
method exists, then gdb will prepend its result to the values returned bychildren
. Exactly how this formatting is done is dependent on the display hint, and may change as more hints are added. Also, depending on the print settings (see Print Settings), the CLI may print just the result ofto_string
in a stack trace, omitting the result ofchildren
.If this method returns a string, it is printed verbatim.
Otherwise, if this method returns an instance of
gdb.Value
, then gdb prints this value. This may result in a call to another pretty-printer.If instead the method returns a Python value which is convertible to a
gdb.Value
, then gdb performs the conversion and prints the resulting value. Again, this may result in a call to another pretty-printer. Python scalars (integers, floats, and booleans) and strings are convertible togdb.Value
; other types are not.Finally, if this method returns
None
then no further operations are peformed in this method and nothing is printed.If the result is not one of these types, an exception is raised.
gdb provides a function which can be used to look up the
default pretty-printer for a gdb.Value
:
This function takes a
gdb.Value
object as an argument. If a pretty-printer for this value exists, then it is returned. If no such printer exists, then this returnsNone
.
The Python list gdb.pretty_printers
contains an array of
functions or callable objects that have been registered via addition
as a pretty-printer. Printers in this list are called global
printers, they're available when debugging all inferiors.
Each gdb.Progspace
contains a pretty_printers
attribute.
Each gdb.Objfile
also contains a pretty_printers
attribute.
Each function on these lists is passed a single gdb.Value
argument and should return a pretty-printer object conforming to the
interface definition above (see Pretty Printing API). If a function
cannot create a pretty-printer for the value, it should return
None
.
gdb first checks the pretty_printers
attribute of each
gdb.Objfile
in the current program space and iteratively calls
each enabled lookup routine in the list for that gdb.Objfile
until it receives a pretty-printer object.
If no pretty-printer is found in the objfile lists, gdb then
searches the pretty-printer list of the current program space,
calling each enabled function until an object is returned.
After these lists have been exhausted, it tries the global
gdb.pretty_printers
list, again calling each enabled function until an
object is returned.
The order in which the objfiles are searched is not specified. For a given list, functions are always invoked from the head of the list, and iterated over sequentially until the end of the list, or a printer object is returned.
For various reasons a pretty-printer may not work. For example, the underlying data structure may have changed and the pretty-printer is out of date.
The consequences of a broken pretty-printer are severe enough that
gdb provides support for enabling and disabling individual
printers. For example, if print frame-arguments
is on,
a backtrace can become highly illegible if any argument is printed
with a broken printer.
Pretty-printers are enabled and disabled by attaching an enabled
attribute to the registered function or callable object. If this attribute
is present and its value is False
, the printer is disabled, otherwise
the printer is enabled.
A pretty-printer consists of two parts: a lookup function to detect if the type is supported, and the printer itself.
Here is an example showing how a std::string
printer might be
written. See Pretty Printing API, for details on the API this class
must provide.
class StdStringPrinter(object): "Print a std::string" def __init__(self, val): self.val = val def to_string(self): return self.val['_M_dataplus']['_M_p'] def display_hint(self): return 'string'
And here is an example showing how a lookup function for the printer example above might be written.
def str_lookup_function(val): lookup_tag = val.type.tag if lookup_tag == None: return None regex = re.compile("^std::basic_string<char,.*>$") if regex.match(lookup_tag): return StdStringPrinter(val) return None
The example lookup function extracts the value's type, and attempts to
match it to a type that it can pretty-print. If it is a type the
printer can pretty-print, it will return a printer object. If not, it
returns None
.
We recommend that you put your core pretty-printers into a Python package. If your pretty-printers are for use with a library, we further recommend embedding a version number into the package name. This practice will enable gdb to load multiple versions of your pretty-printers at the same time, because they will have different names.
You should write auto-loaded code (see Auto-loading) such that it
can be evaluated multiple times without changing its meaning. An
ideal auto-load file will consist solely of import
s of your
printer modules, followed by a call to a register pretty-printers with
the current objfile.
Taken as a whole, this approach will scale nicely to multiple inferiors, each potentially using a different library version. Embedding a version number in the Python package name will ensure that gdb is able to load both sets of printers simultaneously. Then, because the search for pretty-printers is done by objfile, and because your auto-loaded code took care to register your library's printers with a specific objfile, gdb will find the correct printers for the specific version of the library used by each inferior.
To continue the std::string
example (see Pretty Printing API),
this code might appear in gdb.libstdcxx.v6
:
def register_printers(objfile): objfile.pretty_printers.add(str_lookup_function)
And then the corresponding contents of the auto-load file would be:
import gdb.libstdcxx.v6 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
The previous example illustrates a basic pretty-printer. There are a few things that can be improved on. The printer doesn't have a name, making it hard to identify in a list of installed printers. The lookup function has a name, but lookup functions can have arbitrary, even identical, names.
Second, the printer only handles one type, whereas a library typically has several types. One could install a lookup function for each desired type in the library, but one could also have a single lookup function recognize several types. The latter is the conventional way this is handled. If a pretty-printer can handle multiple data types, then its subprinters are the printers for the individual data types.
The gdb.printing
module provides a formal way of solving these
problems (see gdb.printing).
Here is another example that handles multiple types.
These are the types we are going to pretty-print:
struct foo { int a, b; }; struct bar { struct foo x, y; };
Here are the printers:
class fooPrinter: """Print a foo object.""" def __init__(self, val): self.val = val def to_string(self): return ("a=<" + str(self.val["a"]) + "> b=<" + str(self.val["b"]) + ">") class barPrinter: """Print a bar object.""" def __init__(self, val): self.val = val def to_string(self): return ("x=<" + str(self.val["x"]) + "> y=<" + str(self.val["y"]) + ">")
This example doesn't need a lookup function, that is handled by the
gdb.printing
module. Instead a function is provided to build up
the object that handles the lookup.
import gdb.printing def build_pretty_printer(): pp = gdb.printing.RegexpCollectionPrettyPrinter( "my_library") pp.add_printer('foo', '^foo$', fooPrinter) pp.add_printer('bar', '^bar$', barPrinter) return pp
And here is the autoload support:
import gdb.printing import my_library gdb.printing.register_pretty_printer( gdb.current_objfile(), my_library.build_pretty_printer())
Finally, when this printer is loaded into gdb, here is the corresponding output of ‘info pretty-printer’:
(gdb) info pretty-printer my_library.so: my_library foo bar
Programs which are being run under gdb are called inferiors
(see Inferiors and Programs). Python scripts can access
information about and manipulate inferiors controlled by gdb
via objects of the gdb.Inferior
class.
The following inferior-related functions are available in the gdb
module:
A gdb.Inferior
object has the following attributes:
A gdb.Inferior
object has the following methods:
Returns
True
if thegdb.Inferior
object is valid,False
if not. Agdb.Inferior
object will become invalid if the inferior no longer exists within gdb. All othergdb.Inferior
methods will throw an exception if it is invalid at the time the method is called.
This method returns a tuple holding all the threads which are valid when it is called. If there are no valid threads, the method will return an empty tuple.
Read length bytes of memory from the inferior, starting at address. Returns a buffer object, which behaves much like an array or a string. It can be modified and given to the
gdb.write_memory
function.
Write the contents of buffer to the inferior, starting at address. The buffer parameter must be a Python object which supports the buffer protocol, i.e., a string, an array or the object returned from
gdb.read_memory
. If given, length determines the number of bytes from buffer to be written.
Search a region of the inferior memory starting at address with the given length using the search pattern supplied in pattern. The pattern parameter must be a Python object which supports the buffer protocol, i.e., a string, an array or the object returned from
gdb.read_memory
. Returns a PythonLong
containing the address where the pattern was found, orNone
if the pattern could not be found.
gdb provides a general event facility so that Python code can be notified of various state changes, particularly changes that occur in the inferior.
An event is just an object that describes some state change. The type of the object and its attributes will vary depending on the details of the change. All the existing events are described below.
In order to be notified of an event, you must register an event handler
with an event registry. An event registry is an object in the
gdb.events
module which dispatches particular events. A registry
provides methods to register and unregister event handlers:
Here is an example:
def exit_handler (event): print "event type: exit" print "exit code: %d" % (event.exit_code) gdb.events.exited.connect (exit_handler)
In the above example we connect our handler exit_handler
to the
registry events.exited
. Once connected, exit_handler
gets
called when the inferior exits. The argument event in this example is
of type gdb.ExitedEvent
. As you can see in the example the
ExitedEvent
object has an attribute which indicates the exit code of
the inferior.
The following is a listing of the event registries that are available and details of the events they emit:
events.cont
gdb.ThreadEvent
.
Some events can be thread specific when gdb is running in non-stop
mode. When represented in Python, these events all extend
gdb.ThreadEvent
. Note, this event is not emitted directly; instead,
events which are emitted by this or other modules might extend this event.
Examples of these events are gdb.BreakpointEvent
and
gdb.ContinueEvent
.
Emits gdb.ContinueEvent
which extends gdb.ThreadEvent
.
This event indicates that the inferior has been continued after a stop. For
inherited attribute refer to gdb.ThreadEvent
above.
events.exited
events.ExitedEvent
which indicates that the inferior has exited.
events.ExitedEvent
has one optional attribute. This attribute
will exist only in the case that the inferior exited with some
status.
events.stop
gdb.StopEvent
which extends gdb.ThreadEvent
.
Indicates that the inferior has stopped. All events emitted by this registry
extend StopEvent. As a child of gdb.ThreadEvent
, gdb.StopEvent
will indicate the stopped thread when gdb is running in non-stop
mode. Refer to gdb.ThreadEvent
above for more details.
Emits gdb.SignalEvent
which extends gdb.StopEvent
.
This event indicates that the inferior or one of its threads has received as
signal. gdb.SignalEvent
has the following attributes:
Also emits gdb.BreakpointEvent
which extends gdb.StopEvent
.
gdb.BreakpointEvent
event indicates that a breakpoint has been hit, and
has the following attributes:
A reference to the breakpoint that was hit of type
gdb.Breakpoint
. See Breakpoints In Python, for details of thegdb.Breakpoint
object.
Python scripts can access information about, and manipulate inferior threads
controlled by gdb, via objects of the gdb.InferiorThread
class.
The following thread-related functions are available in the gdb
module:
This function returns the thread object for the selected thread. If there is no selected thread, this will return
None
.
A gdb.InferiorThread
object has the following attributes:
The name of the thread. If the user specified a name using
thread name
, then this returns that name. Otherwise, if an OS-supplied name is available, then it is returned. Otherwise, this returnsNone
.This attribute can be assigned to. The new value must be a string object, which sets the new name, or
None
, which removes any user-specified thread name.
ID of the thread, as assigned by the operating system. This attribute is a tuple containing three integers. The first is the Process ID (PID); the second is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID). Either the LWPID or TID may be 0, which indicates that the operating system does not use that identifier.
A gdb.InferiorThread
object has the following methods:
Returns
True
if thegdb.InferiorThread
object is valid,False
if not. Agdb.InferiorThread
object will become invalid if the thread exits, or the inferior that the thread belongs is deleted. All othergdb.InferiorThread
methods will throw an exception if it is invalid at the time the method is called.
You can implement new gdb CLI commands in Python. A CLI
command is implemented using an instance of the gdb.Command
class, most commonly using a subclass.
The object initializer for
Command
registers the new command with gdb. This initializer is normally invoked from the subclass' own__init__
method.name is the name of the command. If name consists of multiple words, then the initial words are looked for as prefix commands. In this case, if one of the prefix commands does not exist, an exception is raised.
There is no support for multi-line commands.
command_class should be one of the ‘COMMAND_’ constants defined below. This argument tells gdb how to categorize the new command in the help system.
completer_class is an optional argument. If given, it should be one of the ‘COMPLETE_’ constants defined below. This argument tells gdb how to perform completion for this command. If not given, gdb will attempt to complete using the object's
complete
method (see below); if no such method is found, an error will occur when completion is attempted.prefix is an optional argument. If
True
, then the new command is a prefix command; sub-commands of this command may be registered.The help text for the new command is taken from the Python documentation string for the command's class, if there is one. If no documentation string is provided, the default value “This command is not documented.” is used.
By default, a gdb command is repeated when the user enters a blank line at the command prompt. A command can suppress this behavior by invoking the
dont_repeat
method. This is similar to the user commanddont-repeat
, see dont-repeat.
This method is called by gdb when this command is invoked.
argument is a string. It is the argument to the command, after leading and trailing whitespace has been stripped.
from_tty is a boolean argument. When true, this means that the command was entered by the user at the terminal; when false it means that the command came from elsewhere.
If this method throws an exception, it is turned into a gdb
error
call. Otherwise, the return value is ignored.To break argument up into an argv-like string use
gdb.string_to_argv
. This function behaves identically to gdb's internal argument lexerbuildargv
. It is recommended to use this for consistency. Arguments are separated by spaces and may be quoted. Example:print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"") ['1', '2 "3', '4 "5', "6 '7"]
This method is called by gdb when the user attempts completion on this command. All forms of completion are handled by this method, that is, the <TAB> and <M-?> key bindings (see Completion), and the
complete
command (see complete).The arguments text and word are both strings. text holds the complete command line up to the cursor's location. word holds the last word of the command line; this is computed using a word-breaking heuristic.
The
complete
method can return several values:
- If the return value is a sequence, the contents of the sequence are used as the completions. It is up to
complete
to ensure that the contents actually do complete the word. A zero-length sequence is allowed, it means that there were no completions available. Only string elements of the sequence are used; other elements in the sequence are ignored.- If the return value is one of the ‘COMPLETE_’ constants defined below, then the corresponding gdb-internal completion function is invoked, and its result is used.
- All other results are treated as though there were no available completions.
When a new command is registered, it must be declared as a member of
some general class of commands. This is used to classify top-level
commands in the on-line help system; note that prefix commands are not
listed under their own category but rather that of their top-level
command. The available classifications are represented by constants
defined in the gdb
module:
COMMAND_NONE
COMMAND_RUNNING
start
, step
, and continue
are in this category.
Type help running at the gdb prompt to see a list of
commands in this category.
COMMAND_DATA
call
, find
, and print
are in this category. Type
help data at the gdb prompt to see a list of commands
in this category.
COMMAND_STACK
backtrace
, frame
, and return
are in this
category. Type help stack at the gdb prompt to see a
list of commands in this category.
COMMAND_FILES
file
, list
and section
are in this category.
Type help files at the gdb prompt to see a list of
commands in this category.
COMMAND_SUPPORT
help
, make
, and shell
are in this category. Type
help support at the gdb prompt to see a list of
commands in this category.
COMMAND_STATUS
info
, macro
,
and show
are in this category. Type help status at the
gdb prompt to see a list of commands in this category.
COMMAND_BREAKPOINTS
break
,
clear
, and delete
are in this category. Type help
breakpoints at the gdb prompt to see a list of commands in
this category.
COMMAND_TRACEPOINTS
trace
,
actions
, and tfind
are in this category. Type
help tracepoints at the gdb prompt to see a list of
commands in this category.
COMMAND_OBSCURE
checkpoint
,
fork
, and stop
are in this category. Type help
obscure at the gdb prompt to see a list of commands in this
category.
COMMAND_MAINTENANCE
maintenance
and flushregs
commands are in this category.
Type help internals at the gdb prompt to see a list of
commands in this category.
A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it
from the complete
method. These predefined completion
constants are all defined in the gdb
module:
COMPLETE_NONE
COMPLETE_FILENAME
COMPLETE_LOCATION
COMPLETE_COMMAND
COMPLETE_SYMBOL
The following code snippet shows how a trivial CLI command can be implemented in Python:
class HelloWorld (gdb.Command): """Greet the whole world.""" def __init__ (self): super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_OBSCURE) def invoke (self, arg, from_tty): print "Hello, World!" HelloWorld ()
The last line instantiates the class, and is necessary to trigger the
registration of the command with gdb. Depending on how the
Python code is read into gdb, you may need to import the
gdb
module explicitly.
You can implement new gdb parameters using Python. A new
parameter is implemented as an instance of the gdb.Parameter
class.
Parameters are exposed to the user via the set
and
show
commands. See Help.
There are many parameters that already exist and can be set in
gdb. Two examples are: set follow fork
and
set charset
. Setting these parameters influences certain
behavior in gdb. Similarly, you can define parameters that
can be used to influence behavior in custom Python scripts and commands.
The object initializer for
Parameter
registers the new parameter with gdb. This initializer is normally invoked from the subclass' own__init__
method.name is the name of the new parameter. If name consists of multiple words, then the initial words are looked for as prefix parameters. An example of this can be illustrated with the
set print
set of parameters. If name isprint foo
, thenset print foo
.If name consists of multiple words, and no prefix parameter group can be found, an exception is raised.
command-class should be one of the ‘COMMAND_’ constants (see Commands In Python). This argument tells gdb how to categorize the new parameter in the help system.
parameter-class should be one of the ‘PARAM_’ constants defined below. This argument tells gdb the type of the new parameter; this information is used for input validation and completion.
If parameter-class is
PARAM_ENUM
, then enum-sequence must be a sequence of strings. These strings represent the possible values for the parameter.If parameter-class is not
PARAM_ENUM
, then the presence of a fourth argument will cause an exception to be thrown.The help text for the new parameter is taken from the Python documentation string for the parameter's class, if there is one. If there is no documentation string, a default value is used.
If this attribute exists, and is a string, then its value is used as the help text for this parameter's
set
command. The value is examined whenParameter.__init__
is invoked; subsequent changes have no effect.
If this attribute exists, and is a string, then its value is used as the help text for this parameter's
show
command. The value is examined whenParameter.__init__
is invoked; subsequent changes have no effect.
The
value
attribute holds the underlying value of the parameter. It can be read and assigned to just as any other attribute. gdb does validation when assignments are made.
There are two methods that should be implemented in any
Parameter
class. These are:
gdb will call this method when a parameter's value has been changed via the
set
API (for example, set foo off). Thevalue
attribute has already been populated with the new value and may be used in output. This method must return a string.
gdb will call this method when a parameter's
show
API has been invoked (for example, show foo). The argumentsvalue
receives the string representation of the current value. This method must return a string.
When a new parameter is defined, its type must be specified. The
available types are represented by constants defined in the gdb
module:
PARAM_BOOLEAN
True
and False
are the only valid values.
PARAM_AUTO_BOOLEAN
None
.
PARAM_UINTEGER
PARAM_INTEGER
PARAM_STRING
PARAM_STRING_NOESCAPE
PARAM_OPTIONAL_FILENAME
None
.
PARAM_FILENAME
PARAM_STRING_NOESCAPE
, but uses file names for completion.
PARAM_ZINTEGER
PARAM_INTEGER
, except 0
is interpreted as itself.
PARAM_ENUM
You can implement new convenience functions (see Convenience Vars)
in Python. A convenience function is an instance of a subclass of the
class gdb.Function
.
The initializer for
Function
registers the new function with gdb. The argument name is the name of the function, a string. The function will be visible to the user as a convenience variable of typeinternal function
, whose name is the same as the given name.The documentation for the new function is taken from the documentation string for the new class.
When a convenience function is evaluated, its arguments are converted to instances of
gdb.Value
, and then the function'sinvoke
method is called. Note that gdb does not predetermine the arity of convenience functions. Instead, all available arguments are passed toinvoke
, following the standard Python calling convention. In particular, a convenience function can have default values for parameters without ill effect.The return value of this method is used as its value in the enclosing expression. If an ordinary Python value is returned, it is converted to a
gdb.Value
following the usual rules.
The following code snippet shows how a trivial convenience function can be implemented in Python:
class Greet (gdb.Function): """Return string to greet someone. Takes a name as argument.""" def __init__ (self): super (Greet, self).__init__ ("greet") def invoke (self, name): return "Hello, %s!" % name.string () Greet ()
The last line instantiates the class, and is necessary to trigger the
registration of the function with gdb. Depending on how the
Python code is read into gdb, you may need to import the
gdb
module explicitly.
A program space, or progspace, represents a symbolic view of an address space. It consists of all of the objfiles of the program. See Objfiles In Python. See program spaces, for more details about program spaces.
The following progspace-related functions are available in the
gdb
module:
This function returns the program space of the currently selected inferior. See Inferiors and Programs.
Each progspace is represented by an instance of the gdb.Progspace
class.
The
pretty_printers
attribute is a list of functions. It is used to look up pretty-printers. AValue
is passed to each function in order; if the function returnsNone
, then the search continues. Otherwise, the return value should be an object which is used to format the value. See Pretty Printing API, for more information.
gdb loads symbols for an inferior from various symbol-containing files (see Files). These include the primary executable file, any shared libraries used by the inferior, and any separate debug info files (see Separate Debug Files). gdb calls these symbol-containing files objfiles.
The following objfile-related functions are available in the
gdb
module:
When auto-loading a Python script (see Auto-loading), gdb sets the “current objfile” to the corresponding objfile. This function returns the current objfile. If there is no current objfile, this function returns
None
.
Return a sequence of all the objfiles current known to gdb. See Objfiles In Python.
Each objfile is represented by an instance of the gdb.Objfile
class.
The
pretty_printers
attribute is a list of functions. It is used to look up pretty-printers. AValue
is passed to each function in order; if the function returnsNone
, then the search continues. Otherwise, the return value should be an object which is used to format the value. See Pretty Printing API, for more information.
A gdb.Objfile
object has the following methods:
Returns
True
if thegdb.Objfile
object is valid,False
if not. Agdb.Objfile
object can become invalid if the object file it refers to is not loaded in gdb any longer. All othergdb.Objfile
methods will throw an exception if it is invalid at the time the method is called.
When the debugged program stops, gdb is able to analyze its call
stack (see Stack frames). The gdb.Frame
class
represents a frame in the stack. A gdb.Frame
object is only valid
while its corresponding frame exists in the inferior's stack. If you try
to use an invalid frame object, gdb will throw a gdb.error
exception (see Exception Handling).
Two gdb.Frame
objects can be compared for equality with the ==
operator, like:
(gdb) python print gdb.newest_frame() == gdb.selected_frame () True
The following frame-related functions are available in the gdb
module:
Return a string explaining the reason why gdb stopped unwinding frames, as expressed by the given reason code (an integer, see the
unwind_stop_reason
method further down in this section).
A gdb.Frame
object has the following methods:
Returns true if the
gdb.Frame
object is valid, false if not. A frame object can become invalid if the frame it refers to doesn't exist anymore in the inferior. Allgdb.Frame
methods will throw an exception if it is invalid at the time the method is called.
Returns the type of the frame. The value can be one of:
gdb.NORMAL_FRAME
- An ordinary stack frame.
gdb.DUMMY_FRAME
- A fake stack frame that was created by gdb when performing an inferior function call.
gdb.INLINE_FRAME
- A frame representing an inlined function. The function was inlined into a
gdb.NORMAL_FRAME
that is older than this one.gdb.SIGTRAMP_FRAME
- A signal trampoline frame. This is the frame created by the OS when it calls into a signal handler.
gdb.ARCH_FRAME
- A fake stack frame representing a cross-architecture call.
gdb.SENTINEL_FRAME
- This is like
gdb.NORMAL_FRAME
, but it is only used for the newest frame.
Return an integer representing the reason why it's not possible to find more frames toward the outermost frame. Use
gdb.frame_stop_reason_string
to convert the value returned by this function to a string.
Return the symbol for the function corresponding to this frame. See Symbols In Python.
Return the value of variable in this frame. If the optional argument block is provided, search for the variable from that block; otherwise start at the frame's current block (which is determined by the frame's current program counter). variable must be a string or a
gdb.Symbol
object. block must be agdb.Block
object.
Within each frame, gdb maintains information on each block
stored in that frame. These blocks are organized hierarchically, and
are represented individually in Python as a gdb.Block
.
Please see Frames In Python, for a more in-depth discussion on
frames. Furthermore, see Examining the Stack, for more
detailed technical information on gdb's book-keeping of the
stack.
The following block-related functions are available in the gdb
module:
Return the
gdb.Block
containing the given pc value. If the block cannot be found for the pc value specified, the function will returnNone
.
A gdb.Block
object has the following methods:
Returns
True
if thegdb.Block
object is valid,False
if not. A block object can become invalid if the block it refers to doesn't exist anymore in the inferior. All othergdb.Block
methods will throw an exception if it is invalid at the time the method is called. This method is also made available to the Python iterator object thatgdb.Block
provides in an iteration context and via the Pythoniter
built-in function.
A gdb.Block
object has the following attributes:
gdb represents every variable, function and type as an
entry in a symbol table. See Examining the Symbol Table.
Similarly, Python represents these symbols in gdb with the
gdb.Symbol
object.
The following symbol-related functions are available in the gdb
module:
This function searches for a symbol by name. The search scope can be restricted to the parameters defined in the optional domain and block arguments.
name is the name of the symbol. It must be a string. The optional block argument restricts the search to symbols visible in that block. The block argument must be a
gdb.Block
object. If omitted, the block for the current frame is used. The optional domain argument restricts the search to the domain type. The domain argument must be a domain constant defined in thegdb
module and described later in this chapter.The result is a tuple of two elements. The first element is a
gdb.Symbol
object orNone
if the symbol is not found. If the symbol is found, the second element isTrue
if the symbol is a field of a method's object (e.g.,this
in C++), otherwise it isFalse
. If the symbol is not found, the second element isFalse
.
This function searches for a global symbol by name. The search scope can be restricted to by the domain argument.
name is the name of the symbol. It must be a string. The optional domain argument restricts the search to the domain type. The domain argument must be a domain constant defined in the
gdb
module and described later in this chapter.The result is a
gdb.Symbol
object orNone
if the symbol is not found.
A gdb.Symbol
object has the following attributes:
The symbol table in which the symbol appears. This attribute is represented as a
gdb.Symtab
object. See Symbol Tables In Python. This attribute is not writable.
The name of the symbol as a string. This attribute is not writable.
The name of the symbol, as used by the linker (i.e., may be mangled). This attribute is not writable.
The name of the symbol in a form suitable for output. This is either
name
orlinkage_name
, depending on whether the user asked gdb to display demangled or mangled names.
A gdb.Symbol
object has the following methods:
The available domain categories in gdb.Symbol
are represented
as constants in the gdb
module:
SYMBOL_UNDEF_DOMAIN
SYMBOL_VAR_DOMAIN
SYMBOL_STRUCT_DOMAIN
SYMBOL_LABEL_DOMAIN
SYMBOL_VARIABLES_DOMAIN
SYMBOLS_VAR_DOMAIN
; it
contains everything minus functions and types.
SYMBOL_FUNCTION_DOMAIN
SYMBOL_TYPES_DOMAIN
The available address class categories in gdb.Symbol
are represented
as constants in the gdb
module:
SYMBOL_LOC_UNDEF
SYMBOL_LOC_CONST
SYMBOL_LOC_STATIC
SYMBOL_LOC_REGISTER
SYMBOL_LOC_ARG
SYMBOL_LOC_REF_ARG
LOC_ARG
except that the value's address is stored at the
offset, not the value itself.
SYMBOL_LOC_REGPARM_ADDR
LOC_REGISTER
except
the register holds the address of the argument instead of the argument
itself.
SYMBOL_LOC_LOCAL
SYMBOL_LOC_TYPEDEF
SYMBOL_STRUCT_DOMAIN
all
have this class.
SYMBOL_LOC_BLOCK
SYMBOL_LOC_CONST_BYTES
SYMBOL_LOC_UNRESOLVED
SYMBOL_LOC_OPTIMIZED_OUT
SYMBOL_LOC_COMPUTED
Access to symbol table data maintained by gdb on the inferior
is exposed to Python via two objects: gdb.Symtab_and_line
and
gdb.Symtab
. Symbol table and line data for a frame is returned
from the find_sal
method in gdb.Frame
object.
See Frames In Python.
For more information on gdb's symbol table management, see Examining the Symbol Table, for more information.
A gdb.Symtab_and_line
object has the following attributes:
The symbol table object (
gdb.Symtab
) for this frame. This attribute is not writable.
A gdb.Symtab_and_line
object has the following methods:
Returns
True
if thegdb.Symtab_and_line
object is valid,False
if not. Agdb.Symtab_and_line
object can become invalid if the Symbol table and line object it refers to does not exist in gdb any longer. All othergdb.Symtab_and_line
methods will throw an exception if it is invalid at the time the method is called.
A gdb.Symtab
object has the following attributes:
The symbol table's source filename. This attribute is not writable.
The symbol table's backing object file. See Objfiles In Python. This attribute is not writable.
A gdb.Symtab
object has the following methods:
Returns
True
if thegdb.Symtab
object is valid,False
if not. Agdb.Symtab
object can become invalid if the symbol table it refers to does not exist in gdb any longer. All othergdb.Symtab
methods will throw an exception if it is invalid at the time the method is called.
Python code can manipulate breakpoints via the gdb.Breakpoint
class.
Create a new breakpoint. spec is a string naming the location of the breakpoint, or an expression that defines a watchpoint. The contents can be any location recognized by the
break
command, or in the case of a watchpoint, by thewatch
command. The optional type denotes the breakpoint to create from the types defined later in this chapter. This argument can be either:BP_BREAKPOINT
orBP_WATCHPOINT
. type defaults toBP_BREAKPOINT
. The optional internal argument allows the breakpoint to become invisible to the user. The breakpoint will neither be reported when created, nor will it be listed in the output frominfo breakpoints
(but will be listed with themaint info breakpoints
command). The optional wp_class argument defines the class of watchpoint to create, if type isBP_WATCHPOINT
. If a watchpoint class is not provided, it is assumed to be a WP_WRITE class.
The
gdb.Breakpoint
class can be sub-classed and, in particular, you may choose to implement thestop
method. If this method is defined as a sub-class ofgdb.Breakpoint
, it will be called when the inferior reaches any location of a breakpoint which instantiates that sub-class. If the method returnsTrue
, the inferior will be stopped at the location of the breakpoint, otherwise the inferior will continue.If there are multiple breakpoints at the same location with a
stop
method, each one will be called regardless of the return status of the previous. This ensures that allstop
methods have a chance to execute at that location. In this scenario if one of the methods returnsTrue
but the others returnFalse
, the inferior will still be stopped.Example
stop
implementation:class MyBreakpoint (gdb.Breakpoint): def stop (self): inf_val = gdb.parse_and_eval("foo") if inf_val == 3: return True return False
The available watchpoint types represented by constants are defined in the
gdb
module:
Return
True
if thisBreakpoint
object is valid,False
otherwise. ABreakpoint
object can become invalid if the user deletes the breakpoint. In this case, the object still exists, but the underlying breakpoint does not. In the cases of watchpoint scope, the watchpoint remains valid even if execution of the inferior leaves the scope of that watchpoint.
Permanently deletes the gdb breakpoint. This also invalidates the Python
Breakpoint
object. Any further access to this object's attributes or methods will raise an error.
This attribute is
True
if the breakpoint is enabled, andFalse
otherwise. This attribute is writable.
This attribute is
True
if the breakpoint is silent, andFalse
otherwise. This attribute is writable.Note that a breakpoint can also be silent if it has commands and the first command is
silent
. This is not reported by thesilent
attribute.
If the breakpoint is thread-specific, this attribute holds the thread id. If the breakpoint is not thread-specific, this attribute is
None
. This attribute is writable.
If the breakpoint is Ada task-specific, this attribute holds the Ada task id. If the breakpoint is not task-specific (or the underlying language is not Ada), this attribute is
None
. This attribute is writable.
This attribute holds the ignore count for the breakpoint, an integer. This attribute is writable.
This attribute holds the breakpoint's number — the identifier used by the user to manipulate the breakpoint. This attribute is not writable.
This attribute holds the breakpoint's type — the identifier used to determine the actual breakpoint type or use-case. This attribute is not writable.
This attribute tells whether the breakpoint is visible to the user when set, or when the ‘info breakpoints’ command is run. This attribute is not writable.
The available types are represented by constants defined in the gdb
module:
BP_BREAKPOINT
BP_WATCHPOINT
BP_HARDWARE_WATCHPOINT
BP_READ_WATCHPOINT
BP_ACCESS_WATCHPOINT
This attribute holds the hit count for the breakpoint, an integer. This attribute is writable, but currently it can only be set to zero.
This attribute holds the location of the breakpoint, as specified by the user. It is a string. If the breakpoint does not have a location (that is, it is a watchpoint) the attribute's value is
None
. This attribute is not writable.
This attribute holds a breakpoint expression, as specified by the user. It is a string. If the breakpoint does not have an expression (the breakpoint is not a watchpoint) the attribute's value is
None
. This attribute is not writable.
This attribute holds the condition of the breakpoint, as specified by the user. It is a string. If there is no condition, this attribute's value is
None
. This attribute is writable.
This attribute holds the commands attached to the breakpoint. If there are commands, this attribute's value is a string holding all the commands, separated by newlines. If there are no commands, this attribute is
None
. This attribute is not writable.
A lazy string is a string whose contents is not retrieved or encoded until it is needed.
A gdb.LazyString
is represented in gdb as an
address
that points to a region of memory, an encoding
that will be used to encode that region of memory, and a length
to delimit the region of memory that represents the string. The
difference between a gdb.LazyString
and a string wrapped within
a gdb.Value
is that a gdb.LazyString
will be treated
differently by gdb when printing. A gdb.LazyString
is
retrieved and encoded during printing, while a gdb.Value
wrapping a string is immediately retrieved and encoded on creation.
A gdb.LazyString
object has the following functions:
Convert the
gdb.LazyString
to agdb.Value
. This value will point to the string in memory, but will lose all the delayed retrieval, encoding and handling that gdb applies to agdb.LazyString
.
This attribute holds the address of the string. This attribute is not writable.
This attribute holds the length of the string in characters. If the length is -1, then the string will be fetched and encoded up to the first null of appropriate width. This attribute is not writable.
This attribute holds the encoding that will be applied to the string when the string is printed by gdb. If the encoding is not set, or contains an empty string, then gdb will select the most appropriate encoding when the string is printed. This attribute is not writable.
This attribute holds the type that is represented by the lazy string's type. For a lazy string this will always be a pointer type. To resolve this to the lazy string's character type, use the type's
target
method. See Types In Python. This attribute is not writable.
When a new object file is read (for example, due to the file
command, or because the inferior has loaded a shared library),
gdb will look for Python support scripts in several ways:
objfile-gdb.py and .debug_gdb_scripts
section.
The auto-loading feature is useful for supplying application-specific debugging commands and scripts.
Auto-loading can be enabled or disabled.
set auto-load-scripts [yes|no]
show auto-load-scripts
When reading an auto-loaded file, gdb sets the
current objfile. This is available via the gdb.current_objfile
function (see Objfiles In Python). This can be useful for
registering objfile-specific pretty-printers.
When a new object file is read, gdb looks for
a file named objfile-gdb.py,
where objfile is the object file's real name, formed by ensuring
that the file name is absolute, following all symlinks, and resolving
.
and ..
components. If this file exists and is
readable, gdb will evaluate it as a Python script.
If this file does not exist, and if the parameter
debug-file-directory
is set (see Separate Debug Files),
then gdb will look for real-name in all of the
directories mentioned in the value of debug-file-directory
.
Finally, if this file does not exist, then gdb will look for
a file named data-directory/python/auto-load/real-name, where
data-directory is gdb's data directory (available via
show data-directory
, see Data Files), and real-name
is the object file's real name, as described above.
gdb does not track which files it has already auto-loaded this way. gdb will load the associated script every time the corresponding objfile is opened. So your -gdb.py file should be careful to avoid errors if it is evaluated more than once.
.debug_gdb_scripts
sectionFor systems using file formats like ELF and COFF, when gdb loads a new object file it will look for a special section named ‘.debug_gdb_scripts’. If this section exists, its contents is a list of names of scripts to load.
gdb will look for each specified script file first in the current directory and then along the source search path (see Specifying Source Directories), except that $cdir is not searched, since the compilation directory is not relevant to scripts.
Entries can be placed in section .debug_gdb_scripts
with,
for example, this GCC macro:
/* Note: The "MS" section flags are to remove duplicates. */ #define DEFINE_GDB_SCRIPT(script_name) \ asm("\ .pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n\ .byte 1\n\ .asciz \"" script_name "\"\n\ .popsection \n\ ");
Then one can reference the macro in a header or source file like this:
DEFINE_GDB_SCRIPT ("my-app-scripts.py")
The script name may include directories if desired.
If the macro is put in a header, any application or library using this header will get a reference to the specified script.
Given the multiple ways of auto-loading Python scripts, it might not always be clear which one to choose. This section provides some guidance.
Benefits of the -gdb.py way:
Scripts specified in the .debug_gdb_scripts
section are searched for
in the source search path.
For publicly installed libraries, e.g., libstdc++, there typically
isn't a source directory in which to find the script.
Benefits of the .debug_gdb_scripts
way:
Scripts for libraries done the -gdb.py way require an objfile to trigger their loading. When an application is statically linked the only objfile available is the executable, and it is cumbersome to attach all the scripts from all the input libraries to the executable's -gdb.py script.
Some classes can be entirely inlined, and thus there may not be an associated shared library to attach a -gdb.py script to.
In some circumstances, apps can be built out of large collections of internal
libraries, and the build infrastructure necessary to install the
-gdb.py scripts in a place where gdb can find them is
cumbersome. It may be easier to specify the scripts in the
.debug_gdb_scripts
section as relative paths, and add a path to the
top of the source tree to the source search path.
gdb comes with a module to assist writing Python code.
This module provides a collection of utilities for working with pretty-printers.
PrettyPrinter (
name,
subprinters=None)
SubPrettyPrinter (
name)
RegexpCollectionPrettyPrinter (
name)
register_pretty_printer (
obj,
printer)
This module provides a collection of utilities for working with
gdb.Types
objects.
get_basic_type (
type)
C++ example:
typedef const int const_int; const_int foo (3); const_int& foo_ref (foo); int main () { return 0; }
Then in gdb:
(gdb) start (gdb) python import gdb.types (gdb) python foo_ref = gdb.parse_and_eval("foo_ref") (gdb) python print gdb.types.get_basic_type(foo_ref.type) int
has_field (
type,
field)
True
if type, assumed to be a type with fields
(e.g., a structure or union), has field field.
make_enum_dict (
enum_type)
dictionary
type produced from enum_type.
gdb supports multiple command interpreters, and some command infrastructure to allow users or user interface writers to switch between interpreters or run commands in other interpreters.
gdb currently supports two command interpreters, the console interpreter (sometimes called the command-line interpreter or cli) and the machine interface interpreter (or gdb/mi). This manual describes both of these interfaces in great detail.
By default, gdb will start with the console interpreter. However, the user may choose to start gdb with another interpreter by specifying the -i or --interpreter startup options. Defined interpreters include:
console
mi
mi2
). Used primarily
by programs wishing to use gdb as a backend for a debugger GUI
or an IDE. For more information, see The gdb/mi Interface.
mi2
mi1
The interpreter being used by gdb may not be dynamically switched at runtime. Although possible, this could lead to a very precarious situation. Consider an IDE using gdb/mi. If a user enters the command "interpreter-set console" in a console view, gdb would switch to using the console interpreter, rendering the IDE inoperable!
Although you may only choose a single interpreter at startup, you may execute
commands in any interpreter from the current interpreter using the appropriate
command. If you are running the console interpreter, simply use the
interpreter-exec
command:
interpreter-exec mi "-data-list-register-names"
gdb/mi has a similar command, although it is only available in versions of gdb which support gdb/mi version 2 (or greater).
The gdb Text User Interface (TUI) is a terminal
interface which uses the curses
library to show the source
file, the assembly output, the program registers and gdb
commands in separate text windows. The TUI mode is supported only
on platforms where a suitable version of the curses
library
is available.
The TUI mode is enabled by default when you invoke gdb as either ‘gdbtui’ or ‘gdb -tui’. You can also switch in and out of TUI mode while gdb runs by using various TUI commands and key bindings, such as C-x C-a. See TUI Key Bindings.
In TUI mode, gdb can display several text windows:
The source and assembly windows show the current program position by highlighting the current line and marking it with a ‘>’ marker. Breakpoints are indicated with two markers. The first marker indicates the breakpoint type:
B
b
H
h
The second marker indicates whether the breakpoint is enabled or not:
+
-
The source, assembly and register windows are updated when the current thread changes, when the frame changes, or when the program counter changes.
These windows are not all visible at the same time. The command window is always visible. The others can be arranged in several layouts:
A status line above the command window shows the following information:
No process
.
??
is displayed.
??
is displayed.
The TUI installs several key bindings in the readline keymaps (see Command Line Editing). The following key bindings are installed for both TUI mode and the gdb standard mode.
Think of this key binding as the Emacs C-x 1 binding.
Think of it as the Emacs C-x 2 binding.
Think of it as the Emacs C-x o binding.
The following key bindings only work in the TUI mode:
Because the arrow keys scroll the active window in the TUI mode, they are not available for their normal use by readline unless the command window has the focus. When another window is active, you must use other readline key bindings such as C-p, C-n, C-b and C-f to control the command window.
The TUI also provides a SingleKey mode, which binds several frequently used gdb commands to single keys. Type C-x s to switch into this mode, where the following key bindings are used:
Other keys temporarily switch to the gdb command prompt. The key that was pressed is inserted in the editing buffer so that it is possible to type most gdb commands without interaction with the TUI SingleKey mode. Once the command is entered the TUI SingleKey mode is restored. The only way to permanently leave this mode is by typing q or C-x s.
The TUI has specific commands to control the text windows. These commands are always available, even when gdb is not in the TUI mode. When gdb is in the standard mode, most of these commands will automatically switch to the TUI mode.
Note that if gdb's stdout
is not connected to a
terminal, or gdb has been started with the machine interface
interpreter (see The gdb/mi Interface), most of
these commands will fail with an error, because it would not be
possible or desirable to enable curses window management.
info win
layout next
layout prev
layout src
layout asm
layout split
layout regs
focus next
focus prev
focus src
focus asm
focus regs
focus cmd
refresh
tui reg float
tui reg general
tui reg next
general
, float
, system
, vector
,
all
, save
, restore
.
tui reg system
update
winheight
name +
countwinheight
name -
counttabset
ncharsSeveral configuration variables control the appearance of TUI windows.
set tui border-kind
kindspace
ascii
acs
set tui border-mode
modeset tui active-border-mode
modenormal
standout
reverse
half
half-standout
bold
bold-standout
A special interface allows you to use gnu Emacs to view (and edit) the source files for the program you are debugging with gdb.
To use this interface, use the command M-x gdb in Emacs. Give the executable file you want to debug as an argument. This command starts gdb as a subprocess of Emacs, with input and output through a newly created Emacs buffer.
Running gdb under Emacs can be just like running gdb normally except for two things:
This applies both to gdb commands and their output, and to the input and output done by the program you are debugging.
This is useful because it means that you can copy the text of previous commands and input them again; you can even use parts of the output in this way.
All the facilities of Emacs' Shell mode are available for interacting with your program. In particular, you can send signals the usual way—for example, C-c C-c for an interrupt, C-c C-z for a stop.
Each time gdb displays a stack frame, Emacs automatically finds the source file for that frame and puts an arrow (‘=>’) at the left margin of the current line. Emacs uses a separate buffer for source display, and splits the screen to show both your gdb session and the source.
Explicit gdb list
or search commands still produce output as
usual, but you probably have no reason to use them from Emacs.
We call this text command mode. Emacs 22.1, and later, also uses a graphical mode, enabled by default, which provides further buffers that can control the execution and describe the state of your program. See GDB Graphical Interface.
If you specify an absolute file name when prompted for the M-x
gdb argument, then Emacs sets your current working directory to where
your program resides. If you only specify the file name, then Emacs
sets your current working directory to to the directory associated
with the previous buffer. In this case, gdb may find your
program by searching your environment's PATH
variable, but on
some operating systems it might not find the source. So, although the
gdb input and output session proceeds normally, the auxiliary
buffer does not display the current source and line of execution.
The initial working directory of gdb is printed on the top line of the GUD buffer and this serves as a default for the commands that specify files for gdb to operate on. See Commands to Specify Files.
By default, M-x gdb calls the program called gdb. If you
need to call gdb by a different name (for example, if you
keep several configurations around, with different names) you can
customize the Emacs variable gud-gdb-command-name
to run the
one you want.
In the GUD buffer, you can use these special Emacs commands in addition to the standard Shell mode commands:
step
command; also
update the display window to show the current file and location.
next
command. Then update the display window
to show the current file and location.
stepi
command; update
display window accordingly.
finish
command.
continue
command.
up
command.
down
command.
In any source file, the Emacs command C-x <SPC> (gud-break
)
tells gdb to set a breakpoint on the source line point is on.
In text command mode, if you type M-x speedbar, Emacs displays a separate frame which shows a backtrace when the GUD buffer is current. Move point to any frame in the stack and type <RET> to make it become the current frame and display the associated source in the source buffer. Alternatively, click Mouse-2 to make the selected frame become the current one. In graphical mode, the speedbar displays watch expressions.
If you accidentally delete the source-display buffer, an easy way to get
it back is to type the command f
in the gdb buffer, to
request a frame display; when you run under Emacs, this recreates
the source buffer if necessary to show you the context of the current
frame.
The source files displayed in Emacs are in ordinary Emacs buffers which are visiting the source files in the usual way. You can edit the files with these buffers if you wish; but keep in mind that gdb communicates with Emacs in terms of line numbers. If you add or delete lines from the text, the line numbers that gdb knows cease to correspond properly with the code.
A more detailed description of Emacs' interaction with gdb is given in the Emacs manual (see Debuggers).
gdb/mi is a line based machine oriented text interface to gdb and is activated by specifying using the --interpreter command line option (see Mode Options). It is specifically intended to support the development of systems which use the debugger as just one small component of a larger system.
This chapter is a specification of the gdb/mi interface. It is written in the form of a reference manual.
Note that gdb/mi is still under construction, so some of the features described below are incomplete and subject to change (see gdb/mi Development and Front Ends).
This chapter uses the following notation:
|
separates two alternatives.
[
something ]
indicates that something is optional:
it may or may not be given.
(
group )*
means that group inside the parentheses
may repeat zero or more times.
(
group )+
means that group inside the parentheses
may repeat one or more times.
"
string"
means a literal string.
Interaction of a GDB/MI frontend with gdb involves three parts—commands sent to gdb, responses to those commands and notifications. Each command results in exactly one response, indicating either successful completion of the command, or an error. For the commands that do not resume the target, the response contains the requested information. For the commands that resume the target, the response only indicates whether the target was successfully resumed. Notifications is the mechanism for reporting changes in the state of the target, or in gdb state, that cannot conveniently be associated with a command and reported as part of that command response.
The important examples of notifications are:
There's no guarantee that whenever an MI command reports an error, gdb or the target are in any specific state, and especially, the state is not reverted to the state before the MI command was processed. Therefore, whenever an MI command results in an error, we recommend that the frontend refreshes all the information shown in the user interface.
In most cases when gdb accesses the target, this access is done in context of a specific thread and frame (see Frames). Often, even when accessing global data, the target requires that a thread be specified. The CLI interface maintains the selected thread and frame, and supplies them to target on each command. This is convenient, because a command line user would not want to specify that information explicitly on each command, and because user interacts with gdb via a single terminal, so no confusion is possible as to what thread and frame are the current ones.
In the case of MI, the concept of selected thread and frame is less useful. First, a frontend can easily remember this information itself. Second, a graphical frontend can have more than one window, each one used for debugging a different thread, and the frontend might want to access additional threads for internal purposes. This increases the risk that by relying on implicitly selected thread, the frontend may be operating on a wrong one. Therefore, each MI command should explicitly specify which thread and frame to operate on. To make it possible, each MI command accepts the ‘--thread’ and ‘--frame’ options, the value to each is gdb identifier for thread and frame to operate on.
Usually, each top-level window in a frontend allows the user to select a thread and a frame, and remembers the user selection for further operations. However, in some cases gdb may suggest that the current thread be changed. For example, when stopping on a breakpoint it is reasonable to switch to the thread where breakpoint is hit. For another example, if the user issues the CLI ‘thread’ command via the frontend, it is desirable to change the frontend's selected thread to the one specified by user. gdb communicates the suggestion to change current thread using the ‘=thread-selected’ notification. No such notification is available for the selected frame at the moment.
Note that historically, MI shares the selected thread with CLI, so
frontends used the -thread-select
to execute commands in the
right context. However, getting this to work right is cumbersome. The
simplest way is for frontend to emit -thread-select
command
before every command. This doubles the number of commands that need
to be sent. The alternative approach is to suppress -thread-select
if the selected thread in gdb is supposed to be identical to the
thread the frontend wants to operate on. However, getting this
optimization right can be tricky. In particular, if the frontend
sends several commands to gdb, and one of the commands changes the
selected thread, then the behaviour of subsequent commands will
change. So, a frontend should either wait for response from such
problematic commands, or explicitly add -thread-select
for
all subsequent commands. No frontend is known to do this exactly
right, so it is suggested to just always pass the ‘--thread’ and
‘--frame’ options.
On some targets, gdb is capable of processing MI commands
even while the target is running. This is called asynchronous
command execution (see Background Execution). The frontend may
specify a preferrence for asynchronous execution using the
-gdb-set target-async 1
command, which should be emitted before
either running the executable or attaching to the target. After the
frontend has started the executable or attached to the target, it can
find if asynchronous execution is enabled using the
-list-target-features
command.
Even if gdb can accept a command while target is running, many commands that access the target do not work when the target is running. Therefore, asynchronous command execution is most useful when combined with non-stop mode (see Non-Stop Mode). Then, it is possible to examine the state of one thread, while other threads are running.
When a given thread is running, MI commands that try to access the
target in the context of that thread may not work, or may work only on
some targets. In particular, commands that try to operate on thread's
stack will not work, on any target. Commands that read memory, or
modify breakpoints, may work or not work, depending on the target. Note
that even commands that operate on global state, such as print
,
set
, and breakpoint commands, still access the target in the
context of a specific thread, so frontend should try to find a
stopped thread and perform the operation on that thread (using the
‘--thread’ option).
Which commands will work in the context of a running thread is
highly target dependent. However, the two commands
-exec-interrupt
, to stop a thread, and -thread-info
,
to find the state of a thread, will always work.
gdb may be used to debug several processes at the same time. On some platfroms, gdb may support debugging of several hardware systems, each one having several cores with several different processes running on each core. This section describes the MI mechanism to support such debugging scenarios.
The key observation is that regardless of the structure of the target, MI can have a global list of threads, because most commands that accept the ‘--thread’ option do not need to know what process that thread belongs to. Therefore, it is not necessary to introduce neither additional ‘--process’ option, nor an notion of the current process in the MI interface. The only strictly new feature that is required is the ability to find how the threads are grouped into processes.
To allow the user to discover such grouping, and to support arbitrary
hierarchy of machines/cores/processes, MI introduces the concept of a
thread group. Thread group is a collection of threads and other
thread groups. A thread group always has a string identifier, a type,
and may have additional attributes specific to the type. A new
command, -list-thread-groups
, returns the list of top-level
thread groups, which correspond to processes that gdb is
debugging at the moment. By passing an identifier of a thread group
to the -list-thread-groups
command, it is possible to obtain
the members of specific thread group.
To allow the user to easily discover processes, and other objects, he
wishes to debug, a concept of available thread group is
introduced. Available thread group is an thread group that
gdb is not debugging, but that can be attached to, using the
-target-attach
command. The list of available top-level thread
groups can be obtained using ‘-list-thread-groups --available’.
In general, the content of a thread group may be only retrieved only
after attaching to that thread group.
Thread groups are related to inferiors (see Inferiors and Programs). Each inferior corresponds to a thread group of a special type ‘process’, and some additional operations are permitted on such thread groups.
==>
|
mi-command
==>
[
token ]
cli-command nl, where
cli-command is any existing gdb CLI command.
==>
[
token ] "-"
operation ( " "
option )*
[ " --" ] ( " "
parameter )*
nl
==>
==>
"-"
parameter [ " "
parameter ]
==>
|
c-string
==>
==>
==>
"""
seven-bit-iso-c-string-content """
==>
CR | CR-LF
Notes:
Pragmatics:
The output from gdb/mi consists of zero or more out-of-band records followed, optionally, by a single result record. This result record is for the most recent command. The sequence of output records is terminated by ‘(gdb)’.
If an input command was prefixed with a token then the corresponding output for that command will also be prefixed by that same token.
==>
(
out-of-band-record )* [
result-record ] "(gdb)"
nl
==>
[
token ] "^"
result-class ( ","
result )*
nl
==>
|
stream-record
==>
|
status-async-output |
notify-async-output
==>
[
token ] "*"
async-output
==>
[
token ] "+"
async-output
==>
[
token ] "="
async-output
==>
( ","
result )*
nl
==>
"done" | "running" | "connected" | "error" | "exit"
==>
"stopped" |
others (where others will be added
depending on the needs—this is still in development).
==>
"="
value
==>
==>
|
tuple |
list
==>
==>
"{}" | "{"
result ( ","
result )* "}"
==>
"[]" | "["
value ( ","
value )* "]" | "["
result ( ","
result )* "]"
==>
|
target-stream-output |
log-stream-output
==>
"~"
c-string
==>
"@"
c-string
==>
"&"
c-string
==>
CR | CR-LF
==>
Notes:
See gdb/mi Stream Records, for more details about the various output records.
For the developers convenience CLI commands can be entered directly,
but there may be some unexpected behaviour. For example, commands
that query the user will behave as if the user replied yes, breakpoint
command lists are not executed and some CLI commands, such as
if
, when
and define
, prompt for further input with
‘>’, which is not valid MI output.
This feature may be removed at some stage in the future and it is
recommended that front ends use the -interpreter-exec
command
(see -interpreter-exec).
The application which takes the MI output and presents the state of the program being debugged to the user is called a front end.
Although gdb/mi is still incomplete, it is currently being used by a variety of front ends to gdb. This makes it difficult to introduce new functionality without breaking existing usage. This section tries to minimize the problems by describing how the protocol might change.
Some changes in MI need not break a carefully designed front end, and for these the MI version will remain unchanged. The following is a list of changes that may occur within one level, so front ends should parse MI output in a way that can handle them:
in_scope
(see -var-update) may be extended.
If the changes are likely to break front ends, the MI version level will be increased by one. This will allow the front end to parse the output according to the MI version. Apart from mi0, new versions of gdb will not support old versions of MI and it will be the responsibility of the front end to work with the new one.
The best way to avoid unexpected changes in MI that might break your front end is to make your project known to gdb developers and follow development on gdb@sourceware.org and gdb-patches@sourceware.org.
In addition to a number of out-of-band notifications, the response to a gdb/mi command includes one of the following result indications:
"^done" [ ","
results ]
"^running"
"^connected"
"^error" ","
c-string"^exit"
gdb internally maintains a number of output streams: the console, the target, and the log. The output intended for each of these streams is funneled through the gdb/mi interface using stream records.
Each stream record begins with a unique prefix character which identifies its stream (see gdb/mi Output Syntax). In addition to the prefix, each stream record contains a string-output. This is either raw text (with an implicit new line) or a quoted C string (which does not contain an implicit newline).
"~"
string-output"@"
string-output"&"
string-outputAsync records are used to notify the gdb/mi client of additional changes that have occurred. Those changes can either be a consequence of gdb/mi commands (e.g., a breakpoint modified) or a result of target activity (e.g., target stopped).
The following is the list of possible async records:
*running,thread-id="
thread"
*stopped,reason="
reason",thread-id="
id",stopped-threads="
stopped",core="
core"
breakpoint-hit
watchpoint-trigger
read-watchpoint-trigger
access-watchpoint-trigger
function-finished
location-reached
watchpoint-scope
end-stepping-range
exited-signalled
exited
exited-normally
signal-received
The id field identifies the thread that directly caused the stop
– for example by hitting a breakpoint. Depending on whether all-stop
mode is in effect (see All-Stop Mode), gdb may either
stop all threads, or only the thread that directly triggered the stop.
If all threads are stopped, the stopped field will have the
value of "all"
. Otherwise, the value of the stopped
field will be a list of thread identifiers. Presently, this list will
always include a single thread, but frontend should be prepared to see
several threads in the list. The core field reports the
processor core on which the stop event has happened. This field may be absent
if such information is not available.
=thread-group-added,id="
id"
=thread-group-removed,id="
id"
=thread-group-started,id="
id",pid="
pid"
=thread-group-exited,id="
id"[,exit-code="
code"]
=thread-created,id="
id",group-id="
gid"
=thread-exited,id="
id",group-id="
gid"
=thread-selected,id="
id"
-thread-select
command but is emitted whenever an MI command that is not documented
to change the selected thread actually changes it. In particular,
invoking, directly or indirectly (via user-defined command), the CLI
thread
command, will generate this notification.
We suggest that in response to this notification, front ends
highlight the selected thread and cause subsequent commands to apply to
that thread.
=library-loaded,...
=library-unloaded,...
=library-loaded
notification.
The thread-group field, if present, specifies the id of the
thread group in whose context the library was unloaded. If the field is
absent, it means the library was unloaded in the context of all present
thread groups.
Response from many MI commands includes an information about stack frame. This information is a tuple that may have the following fields:
level
func
addr
file
line
from
Whenever gdb has to report an information about a thread, it uses a tuple with the following fields:
id
target-id
details
state
core
Whenever a *stopped
record is emitted because the program
stopped after hitting an exception catchpoint (see Set Catchpoints),
gdb provides the name of the exception that was raised via
the exception-name
field.
This subsection presents several simple examples of interaction using the gdb/mi interface. In these examples, ‘->’ means that the following line is passed to gdb/mi as input, while ‘<-’ means the output received from gdb/mi.
Note the line breaks shown in the examples are here only for readability, they don't appear in the real output.
Setting a breakpoint generates synchronous output which contains detailed information of the breakpoint.
-> -break-insert main <- ^done,bkpt={number="1",type="breakpoint",disp="keep", enabled="y",addr="0x08048564",func="main",file="myprog.c", fullname="/home/nickrob/myprog.c",line="68",times="0"} <- (gdb)
Program execution generates asynchronous records and MI gives the reason that execution stopped.
-> -exec-run <- ^running <- (gdb) <- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0", frame={addr="0x08048564",func="main", args=[{name="argc",value="1"},{name="argv",value="0xbfc4d4d4"}], file="myprog.c",fullname="/home/nickrob/myprog.c",line="68"} <- (gdb) -> -exec-continue <- ^running <- (gdb) <- *stopped,reason="exited-normally" <- (gdb)
Quitting gdb just prints the result class ‘^exit’.
-> (gdb) <- -gdb-exit <- ^exit
Please note that ‘^exit’ is printed immediately, but it might take some time for gdb to actually exit. During that time, gdb performs necessary cleanups, including killing programs being debugged or disconnecting from debug hardware, so the frontend should wait till gdb exits and should only forcibly kill gdb if it fails to exit in reasonable time.
Here's what happens if you pass a non-existent command:
-> -rubbish <- ^error,msg="Undefined MI command: rubbish" <- (gdb)
The remaining sections describe blocks of commands. Each block of commands is laid out in a fashion similar to this section.
The motivation for this collection of commands.
A brief introduction to this collection of commands as a whole.
For each command in the block, the following is described:
-command args...
The corresponding gdb CLI command(s), if any.
Example(s) formatted for readability. Some of the described commands have not been implemented yet and these are labeled N.A. (not available).
This section documents gdb/mi commands for manipulating breakpoints.
-break-after
Command-break-after number count
The breakpoint number number is not in effect until it has been hit count times. To see how this is reflected in the output of the ‘-break-list’ command, see the description of the ‘-break-list’ command below.
The corresponding gdb command is ‘ignore’.
(gdb) -break-insert main ^done,bkpt={number="1",type="breakpoint",disp="keep", enabled="y",addr="0x000100d0",func="main",file="hello.c", fullname="/home/foo/hello.c",line="5",times="0"} (gdb) -break-after 1 3 ~ ^done (gdb) -break-list ^done,BreakpointTable={nr_rows="1",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",times="0",ignore="3"}]} (gdb)
-break-commands
Command-break-commands number [ command1 ... commandN ]
Specifies the CLI commands that should be executed when breakpoint number is hit. The parameters command1 to commandN are the commands. If no command is specified, any previously-set commands are cleared. See Break Commands. Typical use of this functionality is tracing a program, that is, printing of values of some variables whenever breakpoint is hit and then continuing.
The corresponding gdb command is ‘commands’.
(gdb) -break-insert main ^done,bkpt={number="1",type="breakpoint",disp="keep", enabled="y",addr="0x000100d0",func="main",file="hello.c", fullname="/home/foo/hello.c",line="5",times="0"} (gdb) -break-commands 1 "print v" "continue" ^done (gdb)
-break-condition
Command-break-condition number expr
Breakpoint number will stop the program only if the condition in expr is true. The condition becomes part of the ‘-break-list’ output (see the description of the ‘-break-list’ command below).
The corresponding gdb command is ‘condition’.
(gdb) -break-condition 1 1 ^done (gdb) -break-list ^done,BreakpointTable={nr_rows="1",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",cond="1",times="0",ignore="3"}]} (gdb)
-break-delete
Command-break-delete ( breakpoint )+
Delete the breakpoint(s) whose number(s) are specified in the argument list. This is obviously reflected in the breakpoint list.
The corresponding gdb command is ‘delete’.
(gdb) -break-delete 1 ^done (gdb) -break-list ^done,BreakpointTable={nr_rows="0",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[]} (gdb)
-break-disable
Command-break-disable ( breakpoint )+
Disable the named breakpoint(s). The field ‘enabled’ in the break list is now set to ‘n’ for the named breakpoint(s).
The corresponding gdb command is ‘disable’.
(gdb) -break-disable 2 ^done (gdb) -break-list ^done,BreakpointTable={nr_rows="1",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="n", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",times="0"}]} (gdb)
-break-enable
Command-break-enable ( breakpoint )+
Enable (previously disabled) breakpoint(s).
The corresponding gdb command is ‘enable’.
(gdb) -break-enable 2 ^done (gdb) -break-list ^done,BreakpointTable={nr_rows="1",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",times="0"}]} (gdb)
-break-info
Command-break-info breakpoint
Get information about a single breakpoint.
The corresponding gdb command is ‘info break breakpoint’.
N.A.
-break-insert
Command-break-insert [ -t ] [ -h ] [ -f ] [ -d ] [ -a ] [ -c condition ] [ -i ignore-count ] [ -p thread ] [ location ]
If specified, location, can be one of:
The possible optional parameters of this command are:
The result is in the form:
^done,bkpt={number="number",type="type",disp="del"|"keep", enabled="y"|"n",addr="hex",func="funcname",file="filename", fullname="full_filename",line="lineno",[thread="threadno,] times="times"}
where number is the gdb number for this breakpoint, funcname is the name of the function where the breakpoint was inserted, filename is the name of the source file which contains this function, lineno is the source line number within that file and times the number of times that the breakpoint has been hit (always 0 for -break-insert but may be greater for -break-info or -break-list which use the same output).
Note: this format is open to change.
The corresponding gdb commands are ‘break’, ‘tbreak’, ‘hbreak’, ‘thbreak’, and ‘rbreak’.
(gdb) -break-insert main ^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c", fullname="/home/foo/recursive2.c,line="4",times="0"} (gdb) -break-insert -t foo ^done,bkpt={number="2",addr="0x00010774",file="recursive2.c", fullname="/home/foo/recursive2.c,line="11",times="0"} (gdb) -break-list ^done,BreakpointTable={nr_rows="2",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x0001072c", func="main",file="recursive2.c", fullname="/home/foo/recursive2.c,"line="4",times="0"}, bkpt={number="2",type="breakpoint",disp="del",enabled="y", addr="0x00010774",func="foo",file="recursive2.c", fullname="/home/foo/recursive2.c",line="11",times="0"}]} (gdb) -break-insert -r foo.* ~int foo(int, int); ^done,bkpt={number="3",addr="0x00010774",file="recursive2.c, "fullname="/home/foo/recursive2.c",line="11",times="0"} (gdb)
-break-list
Command-break-list
Displays the list of inserted breakpoints, showing the following fields:
If there are no breakpoints or watchpoints, the BreakpointTable
body
field is an empty list.
The corresponding gdb command is ‘info break’.
(gdb) -break-list ^done,BreakpointTable={nr_rows="2",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",line="5",times="0"}, bkpt={number="2",type="breakpoint",disp="keep",enabled="y", addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c", line="13",times="0"}]} (gdb)
Here's an example of the result when there are no breakpoints:
(gdb) -break-list ^done,BreakpointTable={nr_rows="0",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[]} (gdb)
-break-passcount
Command-break-passcount tracepoint-number passcount
Set the passcount for tracepoint tracepoint-number to passcount. If the breakpoint referred to by tracepoint-number is not a tracepoint, error is emitted. This corresponds to CLI command ‘passcount’.
-break-watch
Command-break-watch [ -a | -r ]
Create a watchpoint. With the ‘-a’ option it will create an access watchpoint, i.e., a watchpoint that triggers either on a read from or on a write to the memory location. With the ‘-r’ option, the watchpoint created is a read watchpoint, i.e., it will trigger only when the memory location is accessed for reading. Without either of the options, the watchpoint created is a regular watchpoint, i.e., it will trigger when the memory location is accessed for writing. See Setting Watchpoints.
Note that ‘-break-list’ will report a single list of watchpoints and breakpoints inserted.
The corresponding gdb commands are ‘watch’, ‘awatch’, and ‘rwatch’.
Setting a watchpoint on a variable in the main
function:
(gdb) -break-watch x ^done,wpt={number="2",exp="x"} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-trigger",wpt={number="2",exp="x"}, value={old="-268439212",new="55"}, frame={func="main",args=[],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="5"} (gdb)
Setting a watchpoint on a variable local to a function. gdb will stop the program execution twice: first for the variable changing value, then for the watchpoint going out of scope.
(gdb) -break-watch C ^done,wpt={number="5",exp="C"} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-trigger", wpt={number="5",exp="C"},value={old="-276895068",new="3"}, frame={func="callee4",args=[], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-scope",wpnum="5", frame={func="callee3",args=[{name="strarg", value="0x11940 \"A string argument.\""}], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"} (gdb)
Listing breakpoints and watchpoints, at different points in the program execution. Note that once the watchpoint goes out of scope, it is deleted.
(gdb) -break-watch C ^done,wpt={number="2",exp="C"} (gdb) -break-list ^done,BreakpointTable={nr_rows="2",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",times="1"}, bkpt={number="2",type="watchpoint",disp="keep", enabled="y",addr="",what="C",times="0"}]} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-trigger",wpt={number="2",exp="C"}, value={old="-276895068",new="3"}, frame={func="callee4",args=[], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"} (gdb) -break-list ^done,BreakpointTable={nr_rows="2",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"}, bkpt={number="2",type="watchpoint",disp="keep", enabled="y",addr="",what="C",times="-5"}]} (gdb) -exec-continue ^running ^done,reason="watchpoint-scope",wpnum="2", frame={func="callee3",args=[{name="strarg", value="0x11940 \"A string argument.\""}], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"} (gdb) -break-list ^done,BreakpointTable={nr_rows="1",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8", times="1"}]} (gdb)
-exec-arguments
Command-exec-arguments args
Set the inferior program arguments, to be used in the next ‘-exec-run’.
The corresponding gdb command is ‘set args’.
(gdb) -exec-arguments -v word ^done (gdb)
-environment-cd
Command-environment-cd pathdir
Set gdb's working directory.
The corresponding gdb command is ‘cd’.
(gdb) -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb ^done (gdb)
-environment-directory
Command-environment-directory [ -r ] [ pathdir ]+
Add directories pathdir to beginning of search path for source files. If the ‘-r’ option is used, the search path is reset to the default search path. If directories pathdir are supplied in addition to the ‘-r’ option, the search path is first reset and then addition occurs as normal. Multiple directories may be specified, separated by blanks. Specifying multiple directories in a single command results in the directories added to the beginning of the search path in the same order they were presented in the command. If blanks are needed as part of a directory name, double-quotes should be used around the name. In the command output, the path will show up separated by the system directory-separator character. The directory-separator character must not be used in any directory name. If no directories are specified, the current search path is displayed.
The corresponding gdb command is ‘dir’.
(gdb) -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd" (gdb) -environment-directory "" ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd" (gdb) -environment-directory -r /home/jjohnstn/src/gdb /usr/src ^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd" (gdb) -environment-directory -r ^done,source-path="$cdir:$cwd" (gdb)
-environment-path
Command-environment-path [ -r ] [ pathdir ]+
Add directories pathdir to beginning of search path for object files. If the ‘-r’ option is used, the search path is reset to the original search path that existed at gdb start-up. If directories pathdir are supplied in addition to the ‘-r’ option, the search path is first reset and then addition occurs as normal. Multiple directories may be specified, separated by blanks. Specifying multiple directories in a single command results in the directories added to the beginning of the search path in the same order they were presented in the command. If blanks are needed as part of a directory name, double-quotes should be used around the name. In the command output, the path will show up separated by the system directory-separator character. The directory-separator character must not be used in any directory name. If no directories are specified, the current path is displayed.
The corresponding gdb command is ‘path’.
(gdb) -environment-path ^done,path="/usr/bin" (gdb) -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin ^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin" (gdb) -environment-path -r /usr/local/bin ^done,path="/usr/local/bin:/usr/bin" (gdb)
-environment-pwd
Command-environment-pwd
Show the current working directory.
The corresponding gdb command is ‘pwd’.
(gdb) -environment-pwd ^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb" (gdb)
-thread-info
Command-thread-info [ thread-id ]
Reports information about either a specific thread, if the thread-id parameter is present, or about all threads. When printing information about all threads, also reports the current thread.
The ‘info thread’ command prints the same information about all threads.
The result is a list of threads. The following attributes are defined for a given thread:
thread name
command, then this name is given. Otherwise, if
gdb can extract the thread name from the target, then that
name is given. If gdb cannot find the thread name, then this
field is omitted.
stopped
running
-thread-info ^done,threads=[ {id="2",target-id="Thread 0xb7e14b90 (LWP 21257)", frame={level="0",addr="0xffffe410",func="__kernel_vsyscall", args=[]},state="running"}, {id="1",target-id="Thread 0xb7e156b0 (LWP 21254)", frame={level="0",addr="0x0804891f",func="foo", args=[{name="i",value="10"}], file="/tmp/a.c",fullname="/tmp/a.c",line="158"}, state="running"}], current-thread-id="1" (gdb)
-thread-list-ids
Command-thread-list-ids
Produces a list of the currently known gdb thread ids. At the end of the list it also prints the total number of such threads.
This command is retained for historical reasons, the
-thread-info
command should be used instead.
Part of ‘info threads’ supplies the same information.
(gdb) -thread-list-ids ^done,thread-ids={thread-id="3",thread-id="2",thread-id="1"}, current-thread-id="1",number-of-threads="3" (gdb)
-thread-select
Command-thread-select threadnum
Make threadnum the current thread. It prints the number of the new current thread, and the topmost frame for that thread.
This command is deprecated in favor of explicitly using the ‘--thread’ option to each command.
The corresponding gdb command is ‘thread’.
(gdb) -exec-next ^running (gdb) *stopped,reason="end-stepping-range",thread-id="2",line="187", file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c" (gdb) -thread-list-ids ^done, thread-ids={thread-id="3",thread-id="2",thread-id="1"}, number-of-threads="3" (gdb) -thread-select 3 ^done,new-thread-id="3", frame={level="0",func="vprintf", args=[{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""}, {name="arg",value="0x2"}],file="vprintf.c",line="31"} (gdb)
These are the asynchronous commands which generate the out-of-band record ‘*stopped’. Currently gdb only really executes asynchronously with remote targets and this interaction is mimicked in other cases.
-exec-continue
Command-exec-continue [--reverse] [--all|--thread-group N]
Resumes the execution of the inferior program, which will continue to execute until it reaches a debugger stop event. If the ‘--reverse’ option is specified, execution resumes in reverse until it reaches a stop event. Stop events may include
The corresponding gdb corresponding is ‘continue’.
-exec-continue ^running (gdb) @Hello world *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame={ func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c", line="13"} (gdb)
-exec-finish
Command-exec-finish [--reverse]
Resumes the execution of the inferior program until the current function is exited. Displays the results returned by the function. If the ‘--reverse’ option is specified, resumes the reverse execution of the inferior program until the point where current function was called.
The corresponding gdb command is ‘finish’.
Function returning void
.
-exec-finish ^running (gdb) @hello from foo *stopped,reason="function-finished",frame={func="main",args=[], file="hello.c",fullname="/home/foo/bar/hello.c",line="7"} (gdb)
Function returning other than void
. The name of the internal
gdb variable storing the result is printed, together with the
value itself.
-exec-finish ^running (gdb) *stopped,reason="function-finished",frame={addr="0x000107b0",func="foo", args=[{name="a",value="1"],{name="b",value="9"}}, file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, gdb-result-var="$1",return-value="0" (gdb)
-exec-interrupt
Command-exec-interrupt [--all|--thread-group N]
Interrupts the background execution of the target. Note how the token associated with the stop message is the one for the execution command that has been interrupted. The token for the interrupt itself only appears in the ‘^done’ output. If the user is trying to interrupt a non-running program, an error message will be printed.
Note that when asynchronous execution is enabled, this command is asynchronous just like other execution commands. That is, first the ‘^done’ response will be printed, and the target stop will be reported after that using the ‘*stopped’ notification.
In non-stop mode, only the context thread is interrupted by default. All threads (in all inferiors) will be interrupted if the ‘--all’ option is specified. If the ‘--thread-group’ option is specified, all threads in that group will be interrupted.
The corresponding gdb command is ‘interrupt’.
(gdb) 111-exec-continue 111^running (gdb) 222-exec-interrupt 222^done (gdb) 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt", frame={addr="0x00010140",func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="13"} (gdb) (gdb) -exec-interrupt ^error,msg="mi_cmd_exec_interrupt: Inferior not executing." (gdb)
-exec-jump
Command-exec-jump location
Resumes execution of the inferior program at the location specified by parameter. See Specify Location, for a description of the different forms of location.
The corresponding gdb command is ‘jump’.
-exec-jump foo.c:10 *running,thread-id="all" ^running
-exec-next
Command-exec-next [--reverse]
Resumes execution of the inferior program, stopping when the beginning of the next source line is reached.
If the ‘--reverse’ option is specified, resumes reverse execution of the inferior program, stopping at the beginning of the previous source line. If you issue this command on the first line of a function, it will take you back to the caller of that function, to the source line where the function was called.
The corresponding gdb command is ‘next’.
-exec-next ^running (gdb) *stopped,reason="end-stepping-range",line="8",file="hello.c" (gdb)
-exec-next-instruction
Command-exec-next-instruction [--reverse]
Executes one machine instruction. If the instruction is a function call, continues until the function returns. If the program stops at an instruction in the middle of a source line, the address will be printed as well.
If the ‘--reverse’ option is specified, resumes reverse execution of the inferior program, stopping at the previous instruction. If the previously executed instruction was a return from another function, it will continue to execute in reverse until the call to that function (from the current stack frame) is reached.
The corresponding gdb command is ‘nexti’.
(gdb) -exec-next-instruction ^running (gdb) *stopped,reason="end-stepping-range", addr="0x000100d4",line="5",file="hello.c" (gdb)
-exec-return
Command-exec-return
Makes current function return immediately. Doesn't execute the inferior. Displays the new current frame.
The corresponding gdb command is ‘return’.
(gdb) 200-break-insert callee4 200^done,bkpt={number="1",addr="0x00010734", file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"} (gdb) 000-exec-run 000^running (gdb) 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1", frame={func="callee4",args=[], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"} (gdb) 205-break-delete 205^done (gdb) 111-exec-return 111^done,frame={level="0",func="callee3", args=[{name="strarg", value="0x11940 \"A string argument.\""}], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"} (gdb)
-exec-run
Command-exec-run [--all | --thread-group N]
Starts execution of the inferior from the beginning. The inferior executes until either a breakpoint is encountered or the program exits. In the latter case the output will include an exit code, if the program has exited exceptionally.
When no option is specified, the current inferior is started. If the ‘--thread-group’ option is specified, it should refer to a thread group of type ‘process’, and that thread group will be started. If the ‘--all’ option is specified, then all inferiors will be started.
The corresponding gdb command is ‘run’.
(gdb) -break-insert main ^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c",line="4"} (gdb) -exec-run ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1", frame={func="main",args=[],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="4"} (gdb)
Program exited normally:
(gdb) -exec-run ^running (gdb) x = 55 *stopped,reason="exited-normally" (gdb)
Program exited exceptionally:
(gdb) -exec-run ^running (gdb) x = 55 *stopped,reason="exited",exit-code="01" (gdb)
Another way the program can terminate is if it receives a signal such as
SIGINT
. In this case, gdb/mi displays this:
(gdb) *stopped,reason="exited-signalled",signal-name="SIGINT", signal-meaning="Interrupt"
-exec-step
Command-exec-step [--reverse]
Resumes execution of the inferior program, stopping when the beginning of the next source line is reached, if the next source line is not a function call. If it is, stop at the first instruction of the called function. If the ‘--reverse’ option is specified, resumes reverse execution of the inferior program, stopping at the beginning of the previously executed source line.
The corresponding gdb command is ‘step’.
Stepping into a function:
-exec-step ^running (gdb) *stopped,reason="end-stepping-range", frame={func="foo",args=[{name="a",value="10"}, {name="b",value="0"}],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="11"} (gdb)
Regular stepping:
-exec-step ^running (gdb) *stopped,reason="end-stepping-range",line="14",file="recursive2.c" (gdb)
-exec-step-instruction
Command-exec-step-instruction [--reverse]
Resumes the inferior which executes one machine instruction. If the ‘--reverse’ option is specified, resumes reverse execution of the inferior program, stopping at the previously executed instruction. The output, once gdb has stopped, will vary depending on whether we have stopped in the middle of a source line or not. In the former case, the address at which the program stopped will be printed as well.
The corresponding gdb command is ‘stepi’.
(gdb) -exec-step-instruction ^running (gdb) *stopped,reason="end-stepping-range", frame={func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="10"} (gdb) -exec-step-instruction ^running (gdb) *stopped,reason="end-stepping-range", frame={addr="0x000100f4",func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="10"} (gdb)
-exec-until
Command-exec-until [ location ]
Executes the inferior until the location specified in the argument is reached. If there is no argument, the inferior executes until a source line greater than the current one is reached. The reason for stopping in this case will be ‘location-reached’.
The corresponding gdb command is ‘until’.
(gdb) -exec-until recursive2.c:6 ^running (gdb) x = 55 *stopped,reason="location-reached",frame={func="main",args=[], file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6"} (gdb)
-stack-info-frame
Command-stack-info-frame
Get info on the selected frame.
The corresponding gdb command is ‘info frame’ or ‘frame’ (without arguments).
(gdb) -stack-info-frame ^done,frame={level="1",addr="0x0001076c",func="callee3", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"} (gdb)
-stack-info-depth
Command-stack-info-depth [ max-depth ]
Return the depth of the stack. If the integer argument max-depth is specified, do not count beyond max-depth frames.
There's no equivalent gdb command.
For a stack with frame levels 0 through 11:
(gdb) -stack-info-depth ^done,depth="12" (gdb) -stack-info-depth 4 ^done,depth="4" (gdb) -stack-info-depth 12 ^done,depth="12" (gdb) -stack-info-depth 11 ^done,depth="11" (gdb) -stack-info-depth 13 ^done,depth="12" (gdb)
-stack-list-arguments
Command-stack-list-arguments print-values [ low-frame high-frame ]
Display a list of the arguments for the frames between low-frame and high-frame (inclusive). If low-frame and high-frame are not provided, list the arguments for the whole call stack. If the two arguments are equal, show the single frame at the corresponding level. It is an error if low-frame is larger than the actual number of frames. On the other hand, high-frame may be larger than the actual number of frames, in which case only existing frames will be returned.
If print-values is 0 or --no-values
, print only the names of
the variables; if it is 1 or --all-values
, print also their
values; and if it is 2 or --simple-values
, print the name,
type and value for simple data types, and the name and type for arrays,
structures and unions.
Use of this command to obtain arguments in a single frame is deprecated in favor of the ‘-stack-list-variables’ command.
gdb does not have an equivalent command. gdbtk
has a
‘gdb_get_args’ command which partially overlaps with the
functionality of ‘-stack-list-arguments’.
(gdb) -stack-list-frames ^done, stack=[ frame={level="0",addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"}, frame={level="1",addr="0x0001076c",func="callee3", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"}, frame={level="2",addr="0x0001078c",func="callee2", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22"}, frame={level="3",addr="0x000107b4",func="callee1", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27"}, frame={level="4",addr="0x000107e0",func="main", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32"}] (gdb) -stack-list-arguments 0 ^done, stack-args=[ frame={level="0",args=[]}, frame={level="1",args=[name="strarg"]}, frame={level="2",args=[name="intarg",name="strarg"]}, frame={level="3",args=[name="intarg",name="strarg",name="fltarg"]}, frame={level="4",args=[]}] (gdb) -stack-list-arguments 1 ^done, stack-args=[ frame={level="0",args=[]}, frame={level="1", args=[{name="strarg",value="0x11940 \"A string argument.\""}]}, frame={level="2",args=[ {name="intarg",value="2"}, {name="strarg",value="0x11940 \"A string argument.\""}]}, {frame={level="3",args=[ {name="intarg",value="2"}, {name="strarg",value="0x11940 \"A string argument.\""}, {name="fltarg",value="3.5"}]}, frame={level="4",args=[]}] (gdb) -stack-list-arguments 0 2 2 ^done,stack-args=[frame={level="2",args=[name="intarg",name="strarg"]}] (gdb) -stack-list-arguments 1 2 2 ^done,stack-args=[frame={level="2", args=[{name="intarg",value="2"}, {name="strarg",value="0x11940 \"A string argument.\""}]}] (gdb)
-stack-list-frames
Command-stack-list-frames [ low-frame high-frame ]
List the frames currently on the stack. For each frame it displays the following info:
$pc
value for that frame.
$pc
.
If invoked without arguments, this command prints a backtrace for the whole stack. If given two integer arguments, it shows the frames whose levels are between the two arguments (inclusive). If the two arguments are equal, it shows the single frame at the corresponding level. It is an error if low-frame is larger than the actual number of frames. On the other hand, high-frame may be larger than the actual number of frames, in which case only existing frames will be returned.
The corresponding gdb commands are ‘backtrace’ and ‘where’.
Full stack backtrace:
(gdb) -stack-list-frames ^done,stack= [frame={level="0",addr="0x0001076c",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11"}, frame={level="1",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="2",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="4",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="5",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="6",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="7",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="8",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="9",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="10",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="11",addr="0x00010738",func="main", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4"}] (gdb)
Show frames between low_frame and high_frame:
(gdb) -stack-list-frames 3 5 ^done,stack= [frame={level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="4",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="5",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}] (gdb)
Show a single frame:
(gdb) -stack-list-frames 3 3 ^done,stack= [frame={level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}] (gdb)
-stack-list-locals
Command-stack-list-locals print-values
Display the local variable names for the selected frame. If
print-values is 0 or --no-values
, print only the names of
the variables; if it is 1 or --all-values
, print also their
values; and if it is 2 or --simple-values
, print the name,
type and value for simple data types, and the name and type for arrays,
structures and unions. In this last case, a frontend can immediately
display the value of simple data types and create variable objects for
other data types when the user wishes to explore their values in
more detail.
This command is deprecated in favor of the ‘-stack-list-variables’ command.
‘info locals’ in gdb, ‘gdb_get_locals’ in gdbtk
.
(gdb) -stack-list-locals 0 ^done,locals=[name="A",name="B",name="C"] (gdb) -stack-list-locals --all-values ^done,locals=[{name="A",value="1"},{name="B",value="2"}, {name="C",value="{1, 2, 3}"}] -stack-list-locals --simple-values ^done,locals=[{name="A",type="int",value="1"}, {name="B",type="int",value="2"},{name="C",type="int [3]"}] (gdb)
-stack-list-variables
Command-stack-list-variables print-values
Display the names of local variables and function arguments for the selected frame. If
print-values is 0 or --no-values
, print only the names of
the variables; if it is 1 or --all-values
, print also their
values; and if it is 2 or --simple-values
, print the name,
type and value for simple data types, and the name and type for arrays,
structures and unions.
(gdb) -stack-list-variables --thread 1 --frame 0 --all-values ^done,variables=[{name="x",value="11"},{name="s",value="{a = 1, b = 2}"}] (gdb)
-stack-select-frame
Command-stack-select-frame framenum
Change the selected frame. Select a different frame framenum on the stack.
This command in deprecated in favor of passing the ‘--frame’ option to every command.
The corresponding gdb commands are ‘frame’, ‘up’, ‘down’, ‘select-frame’, ‘up-silent’, and ‘down-silent’.
(gdb) -stack-select-frame 2 ^done (gdb)
Variable objects are "object-oriented" MI interface for examining and changing values of expressions. Unlike some other MI interfaces that work with expressions, variable objects are specifically designed for simple and efficient presentation in the frontend. A variable object is identified by string name. When a variable object is created, the frontend specifies the expression for that variable object. The expression can be a simple variable, or it can be an arbitrary complex expression, and can even involve CPU registers. After creating a variable object, the frontend can invoke other variable object operations—for example to obtain or change the value of a variable object, or to change display format.
Variable objects have hierarchical tree structure. Any variable object that corresponds to a composite type, such as structure in C, has a number of child variable objects, for example corresponding to each element of a structure. A child variable object can itself have children, recursively. Recursion ends when we reach leaf variable objects, which always have built-in types. Child variable objects are created only by explicit request, so if a frontend is not interested in the children of a particular variable object, no child will be created.
For a leaf variable object it is possible to obtain its value as a string, or set the value from a string. String value can be also obtained for a non-leaf variable object, but it's generally a string that only indicates the type of the object, and does not list its contents. Assignment to a non-leaf variable object is not allowed.
A frontend does not need to read the values of all variable objects each time the program stops. Instead, MI provides an update command that lists all variable objects whose values has changed since the last update operation. This considerably reduces the amount of data that must be transferred to the frontend. As noted above, children variable objects are created on demand, and only leaf variable objects have a real value. As result, gdb will read target memory only for leaf variables that frontend has created.
The automatic update is not always desirable. For example, a frontend might want to keep a value of some expression for future reference, and never update it. For another example, fetching memory is relatively slow for embedded targets, so a frontend might want to disable automatic update for the variables that are either not visible on the screen, or “closed”. This is possible using so called “frozen variable objects”. Such variable objects are never implicitly updated.
Variable objects can be either fixed or floating. For the fixed variable object, the expression is parsed when the variable object is created, including associating identifiers to specific variables. The meaning of expression never changes. For a floating variable object the values of variables whose names appear in the expressions are re-evaluated every time in the context of the current frame. Consider this example:
void do_work(...) { struct work_state state; if (...) do_work(...); }
If a fixed variable object for the state
variable is created in
this function, and we enter the recursive call, the the variable
object will report the value of state
in the top-level
do_work
invocation. On the other hand, a floating variable
object will report the value of state
in the current frame.
If an expression specified when creating a fixed variable object refers to a local variable, the variable object becomes bound to the thread and frame in which the variable object is created. When such variable object is updated, gdb makes sure that the thread/frame combination the variable object is bound to still exists, and re-evaluates the variable object in context of that thread/frame.
The following is the complete set of gdb/mi operations defined to access this functionality:
Operation | Description
|
-enable-pretty-printing
| enable Python-based pretty-printing
|
-var-create
| create a variable object
|
-var-delete
| delete the variable object and/or its children
|
-var-set-format
| set the display format of this variable
|
-var-show-format
| show the display format of this variable
|
-var-info-num-children
| tells how many children this object has
|
-var-list-children
| return a list of the object's children
|
-var-info-type
| show the type of this variable object
|
-var-info-expression
| print parent-relative expression that this variable object represents
|
-var-info-path-expression
| print full expression that this variable object represents
|
-var-show-attributes
| is this variable editable? does it exist here?
|
-var-evaluate-expression
| get the value of this variable
|
-var-assign
| set the value of this variable
|
-var-update
| update the variable and its children
|
-var-set-frozen
| set frozeness attribute
|
-var-set-update-range
| set range of children to display on update
|
In the next subsection we describe each operation in detail and suggest how it can be used.
-enable-pretty-printing
Command-enable-pretty-printing
gdb allows Python-based visualizers to affect the output of the MI variable object commands. However, because there was no way to implement this in a fully backward-compatible way, a front end must request that this functionality be enabled.
Once enabled, this feature cannot be disabled.
Note that if Python support has not been compiled into gdb, this command will still succeed (and do nothing).
This feature is currently (as of gdb 7.0) experimental, and may work differently in future versions of gdb.
-var-create
Command-var-create {name | "-"} {frame-addr | "*" | "@"} expression
This operation creates a variable object, which allows the monitoring of a variable, the result of an expression, a memory cell or a CPU register.
The name parameter is the string by which the object can be referenced. It must be unique. If ‘-’ is specified, the varobj system will generate a string “varNNNNNN” automatically. It will be unique provided that one does not specify name of that format. The command fails if a duplicate name is found.
The frame under which the expression should be evaluated can be specified by frame-addr. A ‘*’ indicates that the current frame should be used. A ‘@’ indicates that a floating variable object must be created.
expression is any expression valid on the current language set (must not begin with a ‘*’), or one of the following:
A varobj's contents may be provided by a Python-based pretty-printer. In this
case the varobj is known as a dynamic varobj. Dynamic varobjs
have slightly different semantics in some cases. If the
-enable-pretty-printing
command is not sent, then gdb
will never create a dynamic varobj. This ensures backward
compatibility for existing clients.
This operation returns attributes of the newly-created varobj. These are:
struct
), or for a dynamic varobj, this value
will not be interesting.
display_hint
method. See Pretty Printing API.
Typical output will look like this:
name="name",numchild="N",type="type",thread-id="M", has_more="has_more"
-var-delete
Command-var-delete [ -c ] name
Deletes a previously created variable object and all of its children. With the ‘-c’ option, just deletes the children.
Returns an error if the object name is not found.
-var-set-format
Command-var-set-format name format-spec
Sets the output format for the value of the object name to be format-spec.
The syntax for the format-spec is as follows:
format-spec ==> {binary | decimal | hexadecimal | octal | natural}
The natural format is the default format choosen automatically
based on the variable type (like decimal for an int
, hex
for pointers, etc.).
For a variable with children, the format is set only on the variable itself, and the children are not affected.
-var-show-format
Command-var-show-format name
Returns the format used to display the value of the object name.
format ==> format-spec
-var-info-num-children
Command-var-info-num-children name
Returns the number of children of a variable object name:
numchild=n
Note that this number is not completely reliable for a dynamic varobj. It will return the current number of children, but more children may be available.
-var-list-children
Command-var-list-children [print-values] name [from to]
Return a list of the children of the specified variable object and
create variable objects for them, if they do not already exist. With
a single argument or if print-values has a value of 0 or
--no-values
, print only the names of the variables; if
print-values is 1 or --all-values
, also print their
values; and if it is 2 or --simple-values
print the name and
value for simple data types and just the name for arrays, structures
and unions.
from and to, if specified, indicate the range of children to report. If from or to is less than zero, the range is reset and all children will be reported. Otherwise, children starting at from (zero-based) and up to and excluding to will be reported.
If a child range is requested, it will only affect the current call to
-var-list-children
, but not future calls to -var-update
.
For this, you must instead use -var-set-update-range
. The
intent of this approach is to enable a front end to implement any
update approach it likes; for example, scrolling a view may cause the
front end to request more children with -var-list-children
, and
then the front end could call -var-set-update-range
with a
different range to ensure that future updates are restricted to just
the visible items.
For each child the following results are returned:
For a dynamic varobj, this value cannot be used to form an expression. There is no way to do this at all with a dynamic varobj.
For C/C++ structures there are several pseudo children returned to designate access qualifiers. For these pseudo children exp is ‘public’, ‘private’, or ‘protected’. In this case the type and value are not present.
A dynamic varobj will not report the access qualifying
pseudo-children, regardless of the language. This information is not
available at all with a dynamic varobj.
The result may have its own attributes:
display_hint
method. See Pretty Printing API.
(gdb) -var-list-children n ^done,numchild=n,children=[child={name=name,exp=exp, numchild=n,type=type},(repeats N times)] (gdb) -var-list-children --all-values n ^done,numchild=n,children=[child={name=name,exp=exp, numchild=n,value=value,type=type},(repeats N times)]
-var-info-type
Command-var-info-type name
Returns the type of the specified variable name. The type is returned as a string in the same format as it is output by the gdb CLI:
type=typename
-var-info-expression
Command-var-info-expression name
Returns a string that is suitable for presenting this variable object in user interface. The string is generally not valid expression in the current language, and cannot be evaluated.
For example, if a
is an array, and variable object
A
was created for a
, then we'll get this output:
(gdb) -var-info-expression A.1 ^done,lang="C",exp="1"
Here, the values of lang
can be {"C" | "C++" | "Java"}
.
Note that the output of the -var-list-children
command also
includes those expressions, so the -var-info-expression
command
is of limited use.
-var-info-path-expression
Command-var-info-path-expression name
Returns an expression that can be evaluated in the current
context and will yield the same value that a variable object has.
Compare this with the -var-info-expression
command, which
result can be used only for UI presentation. Typical use of
the -var-info-path-expression
command is creating a
watchpoint from a variable object.
This command is currently not valid for children of a dynamic varobj, and will give an error when invoked on one.
For example, suppose C
is a C++ class, derived from class
Base
, and that the Base
class has a member called
m_size
. Assume a variable c
is has the type of
C
and a variable object C
was created for variable
c
. Then, we'll get this output:
(gdb) -var-info-path-expression C.Base.public.m_size ^done,path_expr=((Base)c).m_size)
-var-show-attributes
Command-var-show-attributes name
List attributes of the specified variable object name:
status=attr [ ( ,attr )* ]
where attr is { { editable | noneditable } | TBD }
.
-var-evaluate-expression
Command-var-evaluate-expression [-f format-spec] name
Evaluates the expression that is represented by the specified variable
object and returns its value as a string. The format of the string
can be specified with the ‘-f’ option. The possible values of
this option are the same as for -var-set-format
(see -var-set-format). If the ‘-f’ option is not specified,
the current display format will be used. The current display format
can be changed using the -var-set-format
command.
value=value
Note that one must invoke -var-list-children
for a variable
before the value of a child variable can be evaluated.
-var-assign
Command-var-assign name expression
Assigns the value of expression to the variable object specified
by name. The object must be ‘editable’. If the variable's
value is altered by the assign, the variable will show up in any
subsequent -var-update
list.
(gdb) -var-assign var1 3 ^done,value="3" (gdb) -var-update * ^done,changelist=[{name="var1",in_scope="true",type_changed="false"}] (gdb)
-var-update
Command-var-update [print-values] {name | "*"}
Reevaluate the expressions corresponding to the variable object
name and all its direct and indirect children, and return the
list of variable objects whose values have changed; name must
be a root variable object. Here, “changed” means that the result of
-var-evaluate-expression
before and after the
-var-update
is different. If ‘*’ is used as the variable
object names, all existing variable objects are updated, except
for frozen ones (see -var-set-frozen). The option
print-values determines whether both names and values, or just
names are printed. The possible values of this option are the same
as for -var-list-children
(see -var-list-children). It is
recommended to use the ‘--all-values’ option, to reduce the
number of MI commands needed on each program stop.
With the ‘*’ parameter, if a variable object is bound to a currently running thread, it will not be updated, without any diagnostic.
If -var-set-update-range
was previously used on a varobj, then
only the selected range of children will be reported.
-var-update
reports all the changed varobjs in a tuple named
‘changelist’.
Each item in the change list is itself a tuple holding:
"true"
"false"
"invalid"
file
command. The front end should normally choose to delete these variable
objects.
In the future new values may be added to this list so the front should
be prepared for this possibility. See GDB/MI Development and Front Ends.
The ‘numchild’ field in other varobj responses is generally not valid for a dynamic varobj – it will show the number of children that gdb knows about, but because dynamic varobjs lazily instantiate their children, this will not reflect the number of children which may be available.
The ‘new_num_children’ attribute only reports changes to the
number of children known by gdb. This is the only way to
detect whether an update has removed children (which necessarily can
only happen at the end of the update range).
-var-set-update-range
), then they will
be listed in this attribute.
(gdb) -var-assign var1 3 ^done,value="3" (gdb) -var-update --all-values var1 ^done,changelist=[{name="var1",value="3",in_scope="true", type_changed="false"}] (gdb)
-var-set-frozen
Command-var-set-frozen name flag
Set the frozenness flag on the variable object name. The
flag parameter should be either ‘1’ to make the variable
frozen or ‘0’ to make it unfrozen. If a variable object is
frozen, then neither itself, nor any of its children, are
implicitly updated by -var-update
of
a parent variable or by -var-update *
. Only
-var-update
of the variable itself will update its value and
values of its children. After a variable object is unfrozen, it is
implicitly updated by all subsequent -var-update
operations.
Unfreezing a variable does not update it, only subsequent
-var-update
does.
(gdb) -var-set-frozen V 1 ^done (gdb)
-var-set-update-range
command-var-set-update-range name from to
Set the range of children to be returned by future invocations of
-var-update
.
from and to indicate the range of children to report. If from or to is less than zero, the range is reset and all children will be reported. Otherwise, children starting at from (zero-based) and up to and excluding to will be reported.
(gdb) -var-set-update-range V 1 2 ^done
-var-set-visualizer
command-var-set-visualizer name visualizer
Set a visualizer for the variable object name.
visualizer is the visualizer to use. The special value ‘None’ means to disable any visualizer in use.
If not ‘None’, visualizer must be a Python expression. This expression must evaluate to a callable object which accepts a single argument. gdb will call this object with the value of the varobj name as an argument (this is done so that the same Python pretty-printing code can be used for both the CLI and MI). When called, this object must return an object which conforms to the pretty-printing interface (see Pretty Printing API).
The pre-defined function gdb.default_visualizer
may be used to
select a visualizer by following the built-in process
(see Selecting Pretty-Printers). This is done automatically when
a varobj is created, and so ordinarily is not needed.
This feature is only available if Python support is enabled. The MI
command -list-features
(see GDB/MI Miscellaneous Commands)
can be used to check this.
Resetting the visualizer:
(gdb) -var-set-visualizer V None ^done
Reselecting the default (type-based) visualizer:
(gdb) -var-set-visualizer V gdb.default_visualizer ^done
Suppose SomeClass
is a visualizer class. A lambda expression
can be used to instantiate this class for a varobj:
(gdb) -var-set-visualizer V "lambda val: SomeClass()" ^done
This section describes the gdb/mi commands that manipulate data: examine memory and registers, evaluate expressions, etc.
-data-disassemble
Command-data-disassemble [ -s start-addr -e end-addr ] | [ -f filename -l linenum [ -n lines ] ] -- mode
Where:
$pc
)
The output for each instruction is composed of four fields:
Note that whatever included in the instruction field, is not manipulated directly by gdb/mi, i.e., it is not possible to adjust its format.
There's no direct mapping from this command to the CLI.
Disassemble from the current value of $pc
to $pc + 20
:
(gdb) -data-disassemble -s $pc -e "$pc + 20" -- 0 ^done, asm_insns=[ {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}, {address="0x000107c8",func-name="main",offset="12", inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"}, {address="0x000107cc",func-name="main",offset="16", inst="sethi %hi(0x11800), %o2"}, {address="0x000107d0",func-name="main",offset="20", inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"}] (gdb)
Disassemble the whole main
function. Line 32 is part of
main
.
-data-disassemble -f basics.c -l 32 -- 0 ^done,asm_insns=[ {address="0x000107bc",func-name="main",offset="0", inst="save %sp, -112, %sp"}, {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}, [...] {address="0x0001081c",func-name="main",offset="96",inst="ret "}, {address="0x00010820",func-name="main",offset="100",inst="restore "}] (gdb)
Disassemble 3 instructions from the start of main
:
(gdb) -data-disassemble -f basics.c -l 32 -n 3 -- 0 ^done,asm_insns=[ {address="0x000107bc",func-name="main",offset="0", inst="save %sp, -112, %sp"}, {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}] (gdb)
Disassemble 3 instructions from the start of main
in mixed mode:
(gdb) -data-disassemble -f basics.c -l 32 -n 3 -- 1 ^done,asm_insns=[ src_and_asm_line={line="31", file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \ testsuite/gdb.mi/basics.c",line_asm_insn=[ {address="0x000107bc",func-name="main",offset="0", inst="save %sp, -112, %sp"}]}, src_and_asm_line={line="32", file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \ testsuite/gdb.mi/basics.c",line_asm_insn=[ {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}]}] (gdb)
-data-evaluate-expression
Command-data-evaluate-expression expr
Evaluate expr as an expression. The expression could contain an inferior function call. The function call will execute synchronously. If the expression contains spaces, it must be enclosed in double quotes.
The corresponding gdb commands are ‘print’, ‘output’, and
‘call’. In gdbtk
only, there's a corresponding
‘gdb_eval’ command.
In the following example, the numbers that precede the commands are the tokens described in gdb/mi Command Syntax. Notice how gdb/mi returns the same tokens in its output.
211-data-evaluate-expression A 211^done,value="1" (gdb) 311-data-evaluate-expression &A 311^done,value="0xefffeb7c" (gdb) 411-data-evaluate-expression A+3 411^done,value="4" (gdb) 511-data-evaluate-expression "A + 3" 511^done,value="4" (gdb)
-data-list-changed-registers
Command-data-list-changed-registers
Display a list of the registers that have changed.
gdb doesn't have a direct analog for this command; gdbtk
has the corresponding command ‘gdb_changed_register_list’.
On a PPC MBX board:
(gdb) -exec-continue ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame={ func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c", line="5"} (gdb) -data-list-changed-registers ^done,changed-registers=["0","1","2","4","5","6","7","8","9", "10","11","13","14","15","16","17","18","19","20","21","22","23", "24","25","26","27","28","30","31","64","65","66","67","69"] (gdb)
-data-list-register-names
Command-data-list-register-names [ ( regno )+ ]
Show a list of register names for the current target. If no arguments are given, it shows a list of the names of all the registers. If integer numbers are given as arguments, it will print a list of the names of the registers corresponding to the arguments. To ensure consistency between a register name and its number, the output list may include empty register names.
gdb does not have a command which corresponds to
‘-data-list-register-names’. In gdbtk
there is a
corresponding command ‘gdb_regnames’.
For the PPC MBX board:
(gdb) -data-list-register-names ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7", "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18", "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29", "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9", "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20", "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31", "", "pc","ps","cr","lr","ctr","xer"] (gdb) -data-list-register-names 1 2 3 ^done,register-names=["r1","r2","r3"] (gdb)
-data-list-register-values
Command-data-list-register-values fmt [ ( regno )*]
Display the registers' contents. fmt is the format according to which the registers' contents are to be returned, followed by an optional list of numbers specifying the registers to display. A missing list of numbers indicates that the contents of all the registers must be returned.
Allowed formats for fmt are:
x
o
t
d
r
N
The corresponding gdb commands are ‘info reg’, ‘info
all-reg’, and (in gdbtk
) ‘gdb_fetch_registers’.
For a PPC MBX board (note: line breaks are for readability only, they don't appear in the actual output):
(gdb) -data-list-register-values r 64 65 ^done,register-values=[{number="64",value="0xfe00a300"}, {number="65",value="0x00029002"}] (gdb) -data-list-register-values x ^done,register-values=[{number="0",value="0xfe0043c8"}, {number="1",value="0x3fff88"},{number="2",value="0xfffffffe"}, {number="3",value="0x0"},{number="4",value="0xa"}, {number="5",value="0x3fff68"},{number="6",value="0x3fff58"}, {number="7",value="0xfe011e98"},{number="8",value="0x2"}, {number="9",value="0xfa202820"},{number="10",value="0xfa202808"}, {number="11",value="0x1"},{number="12",value="0x0"}, {number="13",value="0x4544"},{number="14",value="0xffdfffff"}, {number="15",value="0xffffffff"},{number="16",value="0xfffffeff"}, {number="17",value="0xefffffed"},{number="18",value="0xfffffffe"}, {number="19",value="0xffffffff"},{number="20",value="0xffffffff"}, {number="21",value="0xffffffff"},{number="22",value="0xfffffff7"}, {number="23",value="0xffffffff"},{number="24",value="0xffffffff"}, {number="25",value="0xffffffff"},{number="26",value="0xfffffffb"}, {number="27",value="0xffffffff"},{number="28",value="0xf7bfffff"}, {number="29",value="0x0"},{number="30",value="0xfe010000"}, {number="31",value="0x0"},{number="32",value="0x0"}, {number="33",value="0x0"},{number="34",value="0x0"}, {number="35",value="0x0"},{number="36",value="0x0"}, {number="37",value="0x0"},{number="38",value="0x0"}, {number="39",value="0x0"},{number="40",value="0x0"}, {number="41",value="0x0"},{number="42",value="0x0"}, {number="43",value="0x0"},{number="44",value="0x0"}, {number="45",value="0x0"},{number="46",value="0x0"}, {number="47",value="0x0"},{number="48",value="0x0"}, {number="49",value="0x0"},{number="50",value="0x0"}, {number="51",value="0x0"},{number="52",value="0x0"}, {number="53",value="0x0"},{number="54",value="0x0"}, {number="55",value="0x0"},{number="56",value="0x0"}, {number="57",value="0x0"},{number="58",value="0x0"}, {number="59",value="0x0"},{number="60",value="0x0"}, {number="61",value="0x0"},{number="62",value="0x0"}, {number="63",value="0x0"},{number="64",value="0xfe00a300"}, {number="65",value="0x29002"},{number="66",value="0x202f04b5"}, {number="67",value="0xfe0043b0"},{number="68",value="0xfe00b3e4"}, {number="69",value="0x20002b03"}] (gdb)
-data-read-memory
Command
This command is deprecated, use -data-read-memory-bytes
instead.
-data-read-memory [ -o byte-offset ] address word-format word-size nr-rows nr-cols [ aschar ]
where:
print
command (see Output Formats).
This command displays memory contents as a table of nr-rows by
nr-cols words, each word being word-size bytes. In total,
nr-rows *
nr-cols *
word-size bytes are read
(returned as ‘total-bytes’). Should less than the requested number
of bytes be returned by the target, the missing words are identified
using ‘N/A’. The number of bytes read from the target is returned
in ‘nr-bytes’ and the starting address used to read memory in
‘addr’.
The address of the next/previous row or page is available in ‘next-row’ and ‘prev-row’, ‘next-page’ and ‘prev-page’.
The corresponding gdb command is ‘x’. gdbtk
has
‘gdb_get_mem’ memory read command.
Read six bytes of memory starting at bytes+6
but then offset by
-6
bytes. Format as three rows of two columns. One byte per
word. Display each word in hex.
(gdb) 9-data-read-memory -o -6 -- bytes+6 x 1 3 2 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6", next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396", prev-page="0x0000138a",memory=[ {addr="0x00001390",data=["0x00","0x01"]}, {addr="0x00001392",data=["0x02","0x03"]}, {addr="0x00001394",data=["0x04","0x05"]}] (gdb)
Read two bytes of memory starting at address shorts + 64
and
display as a single word formatted in decimal.
(gdb) 5-data-read-memory shorts+64 d 2 1 1 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2", next-row="0x00001512",prev-row="0x0000150e", next-page="0x00001512",prev-page="0x0000150e",memory=[ {addr="0x00001510",data=["128"]}] (gdb)
Read thirty two bytes of memory starting at bytes+16
and format
as eight rows of four columns. Include a string encoding with ‘x’
used as the non-printable character.
(gdb) 4-data-read-memory bytes+16 x 1 8 4 x 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32", next-row="0x000013c0",prev-row="0x0000139c", next-page="0x000013c0",prev-page="0x00001380",memory=[ {addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"}, {addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"}, {addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"}, {addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"}, {addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"}, {addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"}, {addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"}, {addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"}] (gdb)
-data-read-memory-bytes
Command-data-read-memory-bytes [ -o byte-offset ] address count
where:
This command attempts to read all accessible memory regions in the specified range. First, all regions marked as unreadable in the memory map (if one is defined) will be skipped. See Memory Region Attributes. Second, gdb will attempt to read the remaining regions. For each one, if reading full region results in an errors, gdb will try to read a subset of the region.
In general, every single byte in the region may be readable or not, and the only way to read every readable byte is to try a read at every address, which is not practical. Therefore, gdb will attempt to read all accessible bytes at either beginning or the end of the region, using a binary division scheme. This heuristic works well for reading accross a memory map boundary. Note that if a region has a readable range that is neither at the beginning or the end, gdb will not read it.
The result record (see GDB/MI Result Records) that is output of the command includes a field named ‘memory’ whose content is a list of tuples. Each tuple represent a successfully read memory block and has the following fields:
begin
end
offset
-data-read-memory-bytes
.
contents
The corresponding gdb command is ‘x’.
(gdb) -data-read-memory-bytes &a 10 ^done,memory=[{begin="0xbffff154",offset="0x00000000", end="0xbffff15e", contents="01000000020000000300"}] (gdb)
-data-write-memory-bytes
Command-data-write-memory-bytes address contents
where:
There's no corresponding gdb command.
(gdb) -data-write-memory-bytes &a "aabbccdd" ^done (gdb)
The commands defined in this section implement MI support for tracepoints. For detailed introduction, see Tracepoints.
-trace-find
Command-trace-find mode [parameters...]
Find a trace frame using criteria defined by mode and parameters. The following table lists permissible modes and their parameters. For details of operation, see tfind.
If ‘none’ was passed as mode, the response does not have fields. Otherwise, the response may have the following fields:
The corresponding gdb command is ‘tfind’.
-trace-define-variable name [ value ]
Create trace variable name if it does not exist. If value is specified, sets the initial value of the specified trace variable to that value. Note that the name should start with the ‘$’ character.
The corresponding gdb command is ‘tvariable’.
-trace-list-variables
Return a table of all defined trace variables. Each element of the table has the following fields:
The corresponding gdb command is ‘tvariables’.
(gdb) -trace-list-variables ^done,trace-variables={nr_rows="1",nr_cols="3", hdr=[{width="15",alignment="-1",col_name="name",colhdr="Name"}, {width="11",alignment="-1",col_name="initial",colhdr="Initial"}, {width="11",alignment="-1",col_name="current",colhdr="Current"}], body=[variable={name="$trace_timestamp",initial="0"} variable={name="$foo",initial="10",current="15"}]} (gdb)
-trace-save [-r ] filename
Saves the collected trace data to filename. Without the ‘-r’ option, the data is downloaded from the target and saved in a local file. With the ‘-r’ option the target is asked to perform the save.
The corresponding gdb command is ‘tsave’.
-trace-start
Starts a tracing experiments. The result of this command does not have any fields.
The corresponding gdb command is ‘tstart’.
-trace-status
Obtains the status of a tracing experiment. The result may include the following fields:
-trace-stop
command. The value of ‘overflow’ means
the tracing buffer is full. The value of ‘disconnection’ means
tracing was automatically stopped when gdb has disconnected.
The value of ‘passcount’ means tracing was stopped when a
tracepoint was passed a maximal number of times for that tracepoint.
This field is present if ‘supported’ field is not ‘0’.
1
means that the
trace buffer is circular and old trace frames will be discarded if
necessary to make room, 0
means that the trace buffer is linear
and may fill up.
1
means that
tracing will continue after gdb disconnects, 0
means
that the trace run will stop.
The corresponding gdb command is ‘tstatus’.
-trace-stop
Stops a tracing experiment. The result of this command has the same
fields as -trace-status
, except that the ‘supported’ and
‘running’ fields are not output.
The corresponding gdb command is ‘tstop’.
-symbol-list-lines
Command-symbol-list-lines filename
Print the list of lines that contain code and their associated program addresses for the given source filename. The entries are sorted in ascending PC order.
There is no corresponding gdb command.
(gdb) -symbol-list-lines basics.c ^done,lines=[{pc="0x08048554",line="7"},{pc="0x0804855a",line="8"}] (gdb)
This section describes the GDB/MI commands to specify executable file names and to read in and obtain symbol table information.
-file-exec-and-symbols
Command-file-exec-and-symbols file
Specify the executable file to be debugged. This file is the one from which the symbol table is also read. If no file is specified, the command clears the executable and symbol information. If breakpoints are set when using this command with no arguments, gdb will produce error messages. Otherwise, no output is produced, except a completion notification.
The corresponding gdb command is ‘file’.
(gdb) -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb)
-file-exec-file
Command-file-exec-file file
Specify the executable file to be debugged. Unlike ‘-file-exec-and-symbols’, the symbol table is not read from this file. If used without argument, gdb clears the information about the executable file. No output is produced, except a completion notification.
The corresponding gdb command is ‘exec-file’.
(gdb) -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb)
-file-list-exec-source-file
Command-file-list-exec-source-file
List the line number, the current source file, and the absolute path to the current source file for the current executable. The macro information field has a value of ‘1’ or ‘0’ depending on whether or not the file includes preprocessor macro information.
The gdb equivalent is ‘info source’
(gdb) 123-file-list-exec-source-file 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1" (gdb)
-file-list-exec-source-files
Command-file-list-exec-source-files
List the source files for the current executable.
It will always output the filename, but only when gdb can find the absolute file name of a source file, will it output the fullname.
The gdb equivalent is ‘info sources’.
gdbtk
has an analogous command ‘gdb_listfiles’.
(gdb) -file-list-exec-source-files ^done,files=[ {file=foo.c,fullname=/home/foo.c}, {file=/home/bar.c,fullname=/home/bar.c}, {file=gdb_could_not_find_fullpath.c}] (gdb)
-file-symbol-file
Command-file-symbol-file file
Read symbol table info from the specified file argument. When used without arguments, clears gdb's symbol table info. No output is produced, except for a completion notification.
The corresponding gdb command is ‘symbol-file’.
(gdb) -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb)
-target-attach
Command-target-attach pid | gid | file
Attach to a process pid or a file file outside of gdb, or a thread group gid. If attaching to a thread group, the id previously returned by ‘-list-thread-groups --available’ must be used.
The corresponding gdb command is ‘attach’.
(gdb) -target-attach 34 =thread-created,id="1" *stopped,thread-id="1",frame={addr="0xb7f7e410",func="bar",args=[]} ^done (gdb)
-target-detach
Command-target-detach [ pid | gid ]
Detach from the remote target which normally resumes its execution. If either pid or gid is specified, detaches from either the specified process, or specified thread group. There's no output.
The corresponding gdb command is ‘detach’.
(gdb) -target-detach ^done (gdb)
-target-disconnect
Command-target-disconnect
Disconnect from the remote target. There's no output and the target is generally not resumed.
The corresponding gdb command is ‘disconnect’.
(gdb) -target-disconnect ^done (gdb)
-target-download
Command-target-download
Loads the executable onto the remote target. It prints out an update message every half second, which includes the fields:
Each message is sent as status record (see gdb/mi Output Syntax).
In addition, it prints the name and size of the sections, as they are downloaded. These messages include the following fields:
At the end, a summary is printed.
The corresponding gdb command is ‘load’.
Note: each status message appears on a single line. Here the messages have been broken down so that they can fit onto a page.
(gdb) -target-download +download,{section=".text",section-size="6668",total-size="9880"} +download,{section=".text",section-sent="512",section-size="6668", total-sent="512",total-size="9880"} +download,{section=".text",section-sent="1024",section-size="6668", total-sent="1024",total-size="9880"} +download,{section=".text",section-sent="1536",section-size="6668", total-sent="1536",total-size="9880"} +download,{section=".text",section-sent="2048",section-size="6668", total-sent="2048",total-size="9880"} +download,{section=".text",section-sent="2560",section-size="6668", total-sent="2560",total-size="9880"} +download,{section=".text",section-sent="3072",section-size="6668", total-sent="3072",total-size="9880"} +download,{section=".text",section-sent="3584",section-size="6668", total-sent="3584",total-size="9880"} +download,{section=".text",section-sent="4096",section-size="6668", total-sent="4096",total-size="9880"} +download,{section=".text",section-sent="4608",section-size="6668", total-sent="4608",total-size="9880"} +download,{section=".text",section-sent="5120",section-size="6668", total-sent="5120",total-size="9880"} +download,{section=".text",section-sent="5632",section-size="6668", total-sent="5632",total-size="9880"} +download,{section=".text",section-sent="6144",section-size="6668", total-sent="6144",total-size="9880"} +download,{section=".text",section-sent="6656",section-size="6668", total-sent="6656",total-size="9880"} +download,{section=".init",section-size="28",total-size="9880"} +download,{section=".fini",section-size="28",total-size="9880"} +download,{section=".data",section-size="3156",total-size="9880"} +download,{section=".data",section-sent="512",section-size="3156", total-sent="7236",total-size="9880"} +download,{section=".data",section-sent="1024",section-size="3156", total-sent="7748",total-size="9880"} +download,{section=".data",section-sent="1536",section-size="3156", total-sent="8260",total-size="9880"} +download,{section=".data",section-sent="2048",section-size="3156", total-sent="8772",total-size="9880"} +download,{section=".data",section-sent="2560",section-size="3156", total-sent="9284",total-size="9880"} +download,{section=".data",section-sent="3072",section-size="3156", total-sent="9796",total-size="9880"} ^done,address="0x10004",load-size="9880",transfer-rate="6586", write-rate="429" (gdb)
No equivalent.
N.A.
-target-select
Command-target-select type parameters ...
Connect gdb to the remote target. This command takes two args:
The output is a connection notification, followed by the address at which the target program is, in the following form:
^connected,addr="address",func="function name", args=[arg list]
The corresponding gdb command is ‘target’.
(gdb) -target-select remote /dev/ttya ^connected,addr="0xfe00a300",func="??",args=[] (gdb)
-target-file-put
Command-target-file-put hostfile targetfile
Copy file hostfile from the host system (the machine running gdb) to targetfile on the target system.
The corresponding gdb command is ‘remote put’.
(gdb) -target-file-put localfile remotefile ^done (gdb)
-target-file-get
Command-target-file-get targetfile hostfile
Copy file targetfile from the target system to hostfile on the host system.
The corresponding gdb command is ‘remote get’.
(gdb) -target-file-get remotefile localfile ^done (gdb)
-target-file-delete
Command-target-file-delete targetfile
Delete targetfile from the target system.
The corresponding gdb command is ‘remote delete’.
(gdb) -target-file-delete remotefile ^done (gdb)
-gdb-exit
Command-gdb-exit
Exit gdb immediately.
Approximately corresponds to ‘quit’.
(gdb) -gdb-exit ^exit
-gdb-set
Command-gdb-set
Set an internal gdb variable.
The corresponding gdb command is ‘set’.
(gdb) -gdb-set $foo=3 ^done (gdb)
-gdb-show
Command-gdb-show
Show the current value of a gdb variable.
The corresponding gdb command is ‘show’.
(gdb) -gdb-show annotate ^done,value="0" (gdb)
-gdb-version
Command-gdb-version
Show version information for gdb. Used mostly in testing.
The gdb equivalent is ‘show version’. gdb by default shows this information when you start an interactive session.
(gdb) -gdb-version ~GNU gdb 5.2.1 ~Copyright 2000 Free Software Foundation, Inc. ~GDB is free software, covered by the GNU General Public License, and ~you are welcome to change it and/or distribute copies of it under ~ certain conditions. ~Type "show copying" to see the conditions. ~There is absolutely no warranty for GDB. Type "show warranty" for ~ details. ~This GDB was configured as "--host=sparc-sun-solaris2.5.1 --target=ppc-eabi". ^done (gdb)
-list-features
CommandReturns a list of particular features of the MI protocol that this version of gdb implements. A feature can be a command, or a new field in an output of some command, or even an important bugfix. While a frontend can sometimes detect presence of a feature at runtime, it is easier to perform detection at debugger startup.
The command returns a list of strings, with each string naming an available feature. Each returned string is just a name, it does not have any internal structure. The list of possible feature names is given below.
Example output:
(gdb) -list-features ^done,result=["feature1","feature2"]
The current list of features is:
-var-set-frozen
command, as well
as possible presense of the frozen
field in the output
of -varobj-create
.
-break-insert
command.
-var-list-children
-thread-info
command.
-data-read-memory-bytes
and the
-data-write-memory-bytes
commands.
-list-target-features
Command
Returns a list of particular features that are supported by the
target. Those features affect the permitted MI commands, but
unlike the features reported by the -list-features
command, the
features depend on which target GDB is using at the moment. Whenever
a target can change, due to commands such as -target-select
,
-target-attach
or -exec-run
, the list of target features
may change, and the frontend should obtain it again.
Example output:
(gdb) -list-features ^done,result=["async"]
The current list of features is:
-list-thread-groups
Command-list-thread-groups [ --available ] [ --recurse 1 ] [ group ... ]
Lists thread groups (see Thread groups). When a single thread group is passed as the argument, lists the children of that group. When several thread group are passed, lists information about those thread groups. Without any parameters, lists information about all top-level thread groups.
Normally, thread groups that are being debugged are reported. With the ‘--available’ option, gdb reports thread groups available on the target.
The output of this command may have either a ‘threads’ result or a ‘groups’ result. The ‘thread’ result has a list of tuples as value, with each tuple describing a thread (see GDB/MI Thread Information). The ‘groups’ result has a list of tuples as value, each tuple describing a thread group. If top-level groups are requested (that is, no parameter is passed), or when several groups are passed, the output always has a ‘groups’ result. The format of the ‘group’ result is described below.
To reduce the number of roundtrips it's possible to list thread groups together with their children, by passing the ‘--recurse’ option and the recursion depth. Presently, only recursion depth of 1 is permitted. If this option is present, then every reported thread group will also include its children, either as ‘group’ or ‘threads’ field.
In general, any combination of option and parameters is permitted, with the following caveats:
The ‘groups’ result is a list of tuples, where each tuple may have the following fields:
id
type
pid
num_children
threads
cores
executable
gdb -list-thread-groups ^done,groups=[{id="17",type="process",pid="yyy",num_children="2"}] -list-thread-groups 17 ^done,threads=[{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)", frame={level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]},state="running"}, {id="1",target-id="Thread 0xb7e156b0 (LWP 21254)", frame={level="0",addr="0x0804891f",func="foo",args=[{name="i",value="10"}], file="/tmp/a.c",fullname="/tmp/a.c",line="158"},state="running"}]] -list-thread-groups --available ^done,groups=[{id="17",type="process",pid="yyy",num_children="2",cores=[1,2]}] -list-thread-groups --available --recurse 1 ^done,groups=[{id="17", types="process",pid="yyy",num_children="2",cores=[1,2], threads=[{id="1",target-id="Thread 0xb7e14b90",cores=[1]}, {id="2",target-id="Thread 0xb7e14b90",cores=[2]}]},..] -list-thread-groups --available --recurse 1 17 18 ^done,groups=[{id="17", types="process",pid="yyy",num_children="2",cores=[1,2], threads=[{id="1",target-id="Thread 0xb7e14b90",cores=[1]}, {id="2",target-id="Thread 0xb7e14b90",cores=[2]}]},...]
-add-inferior
Command-add-inferior
Creates a new inferior (see Inferiors and Programs). The created inferior is not associated with any executable. Such association may be established with the ‘-file-exec-and-symbols’ command (see GDB/MI File Commands). The command response has a single field, ‘thread-group’, whose value is the identifier of the thread group corresponding to the new inferior.
gdb -add-inferior ^done,thread-group="i3"
-interpreter-exec
Command-interpreter-exec interpreter command
Execute the specified command in the given interpreter.
The corresponding gdb command is ‘interpreter-exec’.
(gdb) -interpreter-exec console "break main" &"During symbol reading, couldn't parse type; debugger out of date?.\n" &"During symbol reading, bad structure-type format.\n" ~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n" ^done (gdb)
-inferior-tty-set
Command-inferior-tty-set /dev/pts/1
Set terminal for future runs of the program being debugged.
The corresponding gdb command is ‘set inferior-tty’ /dev/pts/1.
(gdb) -inferior-tty-set /dev/pts/1 ^done (gdb)
-inferior-tty-show
Command-inferior-tty-show
Show terminal for future runs of program being debugged.
The corresponding gdb command is ‘show inferior-tty’.
(gdb) -inferior-tty-set /dev/pts/1 ^done (gdb) -inferior-tty-show ^done,inferior_tty_terminal="/dev/pts/1" (gdb)
-enable-timings
Command-enable-timings [yes | no]
Toggle the printing of the wallclock, user and system times for an MI command as a field in its output. This command is to help frontend developers optimize the performance of their code. No argument is equivalent to ‘yes’.
No equivalent.
(gdb) -enable-timings ^done (gdb) -break-insert main ^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x080484ed",func="main",file="myprog.c", fullname="/home/nickrob/myprog.c",line="73",times="0"}, time={wallclock="0.05185",user="0.00800",system="0.00000"} (gdb) -enable-timings no ^done (gdb) -exec-run ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0", frame={addr="0x080484ed",func="main",args=[{name="argc",value="1"}, {name="argv",value="0xbfb60364"}],file="myprog.c", fullname="/home/nickrob/myprog.c",line="73"} (gdb)
This chapter describes annotations in gdb. Annotations were designed to interface gdb to graphical user interfaces or other similar programs which want to interact with gdb at a relatively high level.
The annotation mechanism has largely been superseded by gdb/mi (see GDB/MI).
Annotations start with a newline character, two ‘control-z’ characters, and the name of the annotation. If there is no additional information associated with this annotation, the name of the annotation is followed immediately by a newline. If there is additional information, the name of the annotation is followed by a space, the additional information, and a newline. The additional information cannot contain newline characters.
Any output not beginning with a newline and two ‘control-z’ characters denotes literal output from gdb. Currently there is no need for gdb to output a newline followed by two ‘control-z’ characters, but if there was such a need, the annotations could be extended with an ‘escape’ annotation which means those three characters as output.
The annotation level, which is specified using the --annotate command line option (see Mode Options), controls how much information gdb prints together with its prompt, values of expressions, source lines, and other types of output. Level 0 is for no annotations, level 1 is for use when gdb is run as a subprocess of gnu Emacs, level 3 is the maximum annotation suitable for programs that control gdb, and level 2 annotations have been made obsolete (see Limitations of the Annotation Interface).
set annotate
levelset annotate
sets the level of
annotations to the specified level.
show annotate
This chapter describes level 3 annotations.
A simple example of starting up gdb with annotations is:
$ gdb --annotate=3 GNU gdb 6.0 Copyright 2003 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-pc-linux-gnu" ^Z^Zpre-prompt (gdb) ^Z^Zprompt quit ^Z^Zpost-prompt $
Here ‘quit’ is input to gdb; the rest is output from gdb. The three lines beginning ‘^Z^Z’ (where ‘^Z’ denotes a ‘control-z’ character) are annotations; the rest is output from gdb.
If you prefix a command with ‘server ’ then it will not affect the command history, nor will it affect gdb's notion of which command to repeat if <RET> is pressed on a line by itself. This means that commands can be run behind a user's back by a front-end in a transparent manner.
The server
prefix does not affect the recording of values into
the value history; to print a value without recording it into the
value history, use the output
command instead of the
print
command.
Using this prefix also disables confirmation requests (see confirmation requests).
When gdb prompts for input, it annotates this fact so it is possible to know when to send output, when the output from a given command is over, etc.
Different kinds of input each have a different input type. Each
input type has three annotations: a pre-
annotation, which
denotes the beginning of any prompt which is being output, a plain
annotation, which denotes the end of the prompt, and then a post-
annotation which denotes the end of any echo which may (or may not) be
associated with the input. For example, the prompt
input type
features the following annotations:
^Z^Zpre-prompt ^Z^Zprompt ^Z^Zpost-prompt
prompt
commands
commands
command. The annotations are repeated for each command which is input.
overload-choice
query
prompt-for-continue
set height 0
to disable
prompting. This is because the counting of lines is buggy in the
presence of annotations.
^Z^Zquit
This annotation occurs right before gdb responds to an interrupt.
^Z^Zerror
This annotation occurs right before gdb responds to an error.
Quit and error annotations indicate that any annotations which gdb was
in the middle of may end abruptly. For example, if a
value-history-begin
annotation is followed by a error
, one
cannot expect to receive the matching value-history-end
. One
cannot expect not to receive it either, however; an error annotation
does not necessarily mean that gdb is immediately returning all the way
to the top level.
A quit or error annotation may be preceded by
^Z^Zerror-begin
Any output between that and the quit or error annotation is the error message.
Warning messages are not yet annotated.
The following annotations say that certain pieces of state may have changed.
^Z^Zframes-invalid
backtrace
command) may
have changed.
^Z^Zbreakpoints-invalid
When the program starts executing due to a gdb command such as
step
or continue
,
^Z^Zstarting
is output. When the program stops,
^Z^Zstopped
is output. Before the stopped
annotation, a variety of
annotations describe how the program stopped.
^Z^Zexited
exit-status^Z^Zsignalled
^Z^Zsignalled
, the
annotation continues:
intro-text ^Z^Zsignal-name name ^Z^Zsignal-name-end middle-text ^Z^Zsignal-string string ^Z^Zsignal-string-end end-text
where name is the name of the signal, such as SIGILL
or
SIGSEGV
, and string is the explanation of the signal, such
as Illegal Instruction
or Segmentation fault
.
intro-text, middle-text, and end-text are for the
user's benefit and have no particular format.
^Z^Zsignal
signalled
, but gdb is
just saying that the program received the signal, not that it was
terminated with it.
^Z^Zbreakpoint
number^Z^Zwatchpoint
numberThe following annotation is used instead of displaying source code:
^Z^Zsource filename:line:character:middle:addr
where filename is an absolute file name indicating which source file, line is the line number within that file (where 1 is the first line in the file), character is the character position within the file (where 0 is the first character in the file) (for most debug formats this will necessarily point to the beginning of a line), middle is ‘middle’ if addr is in the middle of the line, or ‘beg’ if addr is at the beginning of the line, and addr is the address in the target program associated with the source which is being displayed. addr is in the form ‘0x’ followed by one or more lowercase hex digits (note that this does not depend on the language).
This chapter documents gdb's just-in-time (JIT) compilation interface. A JIT compiler is a program or library that generates native executable code at runtime and executes it, usually in order to achieve good performance while maintaining platform independence.
Programs that use JIT compilation are normally difficult to debug because portions of their code are generated at runtime, instead of being loaded from object files, which is where gdb normally finds the program's symbols and debug information. In order to debug programs that use JIT compilation, gdb has an interface that allows the program to register in-memory symbol files with gdb at runtime.
If you are using gdb to debug a program that uses this interface, then it should work transparently so long as you have not stripped the binary. If you are developing a JIT compiler, then the interface is documented in the rest of this chapter. At this time, the only known client of this interface is the LLVM JIT.
Broadly speaking, the JIT interface mirrors the dynamic loader interface. The JIT compiler communicates with gdb by writing data into a global variable and calling a fuction at a well-known symbol. When gdb attaches, it reads a linked list of symbol files from the global variable to find existing code, and puts a breakpoint in the function so that it can find out about additional code.
These are the relevant struct declarations that a C program should include to implement the interface:
typedef enum { JIT_NOACTION = 0, JIT_REGISTER_FN, JIT_UNREGISTER_FN } jit_actions_t; struct jit_code_entry { struct jit_code_entry *next_entry; struct jit_code_entry *prev_entry; const char *symfile_addr; uint64_t symfile_size; }; struct jit_descriptor { uint32_t version; /* This type should be jit_actions_t, but we use uint32_t to be explicit about the bitwidth. */ uint32_t action_flag; struct jit_code_entry *relevant_entry; struct jit_code_entry *first_entry; }; /* GDB puts a breakpoint in this function. */ void __attribute__((noinline)) __jit_debug_register_code() { }; /* Make sure to specify the version statically, because the debugger may check the version before we can set it. */ struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };
If the JIT is multi-threaded, then it is important that the JIT synchronize any modifications to this global data properly, which can easily be done by putting a global mutex around modifications to these structures.
To register code with gdb, the JIT should follow this protocol:
action_flag
to JIT_REGISTER
and call
__jit_debug_register_code
.
When gdb is attached and the breakpoint fires, gdb uses the
relevant_entry
pointer so it doesn't have to walk the list looking for
new code. However, the linked list must still be maintained in order to allow
gdb to attach to a running process and still find the symbol files.
If code is freed, then the JIT should use the following protocol:
relevant_entry
field of the descriptor at the code entry.
action_flag
to JIT_UNREGISTER
and call
__jit_debug_register_code
.
If the JIT frees or recompiles code without unregistering it, then gdb and the JIT will leak the memory used for the associated symbol files.
Your bug reports play an essential role in making gdb reliable.
Reporting a bug may help you by bringing a solution to your problem, or it may not. But in any case the principal function of a bug report is to help the entire community by making the next version of gdb work better. Bug reports are your contribution to the maintenance of gdb.
In order for a bug report to serve its purpose, you must include the information that enables us to fix the bug.
If you are not sure whether you have found a bug, here are some guidelines:
A number of companies and individuals offer support for gnu products. If you obtained gdb from a support organization, we recommend you contact that organization first.
You can find contact information for many support companies and individuals in the file etc/SERVICE in the gnu Emacs distribution.
In any event, we also recommend that you submit bug reports for gdb. The preferred method is to submit them directly using gdb's Bugs web page. Alternatively, the e-mail gateway can be used.
Do not send bug reports to ‘info-gdb’, or to ‘help-gdb’, or to any newsgroups. Most users of gdb do not want to receive bug reports. Those that do have arranged to receive ‘bug-gdb’.
The mailing list ‘bug-gdb’ has a newsgroup ‘gnu.gdb.bug’ which serves as a repeater. The mailing list and the newsgroup carry exactly the same messages. Often people think of posting bug reports to the newsgroup instead of mailing them. This appears to work, but it has one problem which can be crucial: a newsgroup posting often lacks a mail path back to the sender. Thus, if we need to ask for more information, we may be unable to reach you. For this reason, it is better to send bug reports to the mailing list.
The fundamental principle of reporting bugs usefully is this: report all the facts. If you are not sure whether to state a fact or leave it out, state it!
Often people omit facts because they think they know what causes the problem and assume that some details do not matter. Thus, you might assume that the name of the variable you use in an example does not matter. Well, probably it does not, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the debugger into doing the right thing despite the bug. Play it safe and give a specific, complete example. That is the easiest thing for you to do, and the most helpful.
Keep in mind that the purpose of a bug report is to enable us to fix the bug. It may be that the bug has been reported previously, but neither you nor we can know that unless your bug report is complete and self-contained.
Sometimes people give a few sketchy facts and ask, “Does this ring a bell?” Those bug reports are useless, and we urge everyone to refuse to respond to them except to chide the sender to report bugs properly.
To enable us to fix the bug, you should include all these things:
show
version
.
Without this, we will not know whether there is any point in looking for the bug in the current version of gdb.
If we were to try to guess the arguments, we would probably guess wrong and then we might not encounter the bug.
Of course, if the bug is that gdb gets a fatal signal, then we will certainly notice it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong. You might as well not give us a chance to make a mistake.
Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of gdb is out of synch, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and ours would not. If you told us to expect a crash, then when ours fails to crash, we would know that the bug was not happening for us. If you had not told us to expect a crash, then we would not be able to draw any conclusion from our observations.
To collect all this information, you can use a session recording program such as script, which is available on many Unix systems. Just run your gdb session inside script and then include the typescript file with your bug report.
Another way to record a gdb session is to run gdb inside Emacs and then save the entire buffer to a file.
The line numbers in our development sources will not match those in your sources. Your line numbers would convey no useful information to us.
Here are some things that are not necessary:
Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it.
This is often time consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. We recommend that you save your time for something else.
Of course, if you can find a simpler example to report instead of the original one, that is a convenience for us. Errors in the output will be easier to spot, running under the debugger will take less time, and so on.
However, simplification is not vital; if you do not want to do this, report the bug anyway and send us the entire test case you used.
A patch for the bug does help us if it is a good one. But do not omit the necessary information, such as the test case, on the assumption that a patch is all we need. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all.
Sometimes with a program as complicated as gdb it is very hard to construct an example that will make the program follow a certain path through the code. If you do not send us the example, we will not be able to construct one, so we will not be able to verify that the bug is fixed.
And if we cannot understand what bug you are trying to fix, or why your patch should be an improvement, we will not install it. A test case will help us to understand.
Such guesses are usually wrong. Even we cannot guess right about such things without first using the debugger to find the facts.
This chapter describes the basic features of the gnu command line editing interface.
The following paragraphs describe the notation used to represent keystrokes.
The text C-k is read as `Control-K' and describes the character produced when the <k> key is pressed while the Control key is depressed.
The text M-k is read as `Meta-K' and describes the character produced when the Meta key (if you have one) is depressed, and the <k> key is pressed. The Meta key is labeled <ALT> on many keyboards. On keyboards with two keys labeled <ALT> (usually to either side of the space bar), the <ALT> on the left side is generally set to work as a Meta key. The <ALT> key on the right may also be configured to work as a Meta key or may be configured as some other modifier, such as a Compose key for typing accented characters.
If you do not have a Meta or <ALT> key, or another key working as a Meta key, the identical keystroke can be generated by typing <ESC> first, and then typing <k>. Either process is known as metafying the <k> key.
The text M-C-k is read as `Meta-Control-k' and describes the character produced by metafying C-k.
In addition, several keys have their own names. Specifically, <DEL>, <ESC>, <LFD>, <SPC>, <RET>, and <TAB> all stand for themselves when seen in this text, or in an init file (see Readline Init File). If your keyboard lacks a <LFD> key, typing <C-j> will produce the desired character. The <RET> key may be labeled <Return> or <Enter> on some keyboards.
Often during an interactive session you type in a long line of text, only to notice that the first word on the line is misspelled. The Readline library gives you a set of commands for manipulating the text as you type it in, allowing you to just fix your typo, and not forcing you to retype the majority of the line. Using these editing commands, you move the cursor to the place that needs correction, and delete or insert the text of the corrections. Then, when you are satisfied with the line, you simply press <RET>. You do not have to be at the end of the line to press <RET>; the entire line is accepted regardless of the location of the cursor within the line.
In order to enter characters into the line, simply type them. The typed character appears where the cursor was, and then the cursor moves one space to the right. If you mistype a character, you can use your erase character to back up and delete the mistyped character.
Sometimes you may mistype a character, and not notice the error until you have typed several other characters. In that case, you can type C-b to move the cursor to the left, and then correct your mistake. Afterwards, you can move the cursor to the right with C-f.
When you add text in the middle of a line, you will notice that characters to the right of the cursor are `pushed over' to make room for the text that you have inserted. Likewise, when you delete text behind the cursor, characters to the right of the cursor are `pulled back' to fill in the blank space created by the removal of the text. A list of the bare essentials for editing the text of an input line follows.
(Depending on your configuration, the <Backspace> key be set to delete the character to the left of the cursor and the <DEL> key set to delete the character underneath the cursor, like C-d, rather than the character to the left of the cursor.)
The above table describes the most basic keystrokes that you need in order to do editing of the input line. For your convenience, many other commands have been added in addition to C-b, C-f, C-d, and <DEL>. Here are some commands for moving more rapidly about the line.
Notice how C-f moves forward a character, while M-f moves forward a word. It is a loose convention that control keystrokes operate on characters while meta keystrokes operate on words.
Killing text means to delete the text from the line, but to save it away for later use, usually by yanking (re-inserting) it back into the line. (`Cut' and `paste' are more recent jargon for `kill' and `yank'.)
If the description for a command says that it `kills' text, then you can be sure that you can get the text back in a different (or the same) place later.
When you use a kill command, the text is saved in a kill-ring. Any number of consecutive kills save all of the killed text together, so that when you yank it back, you get it all. The kill ring is not line specific; the text that you killed on a previously typed line is available to be yanked back later, when you are typing another line. Here is the list of commands for killing text.
Here is how to yank the text back into the line. Yanking means to copy the most-recently-killed text from the kill buffer.
You can pass numeric arguments to Readline commands. Sometimes the argument acts as a repeat count, other times it is the sign of the argument that is significant. If you pass a negative argument to a command which normally acts in a forward direction, that command will act in a backward direction. For example, to kill text back to the start of the line, you might type ‘M-- C-k’.
The general way to pass numeric arguments to a command is to type meta digits before the command. If the first `digit' typed is a minus sign (‘-’), then the sign of the argument will be negative. Once you have typed one meta digit to get the argument started, you can type the remainder of the digits, and then the command. For example, to give the C-d command an argument of 10, you could type ‘M-1 0 C-d’, which will delete the next ten characters on the input line.
Readline provides commands for searching through the command history for lines containing a specified string. There are two search modes: incremental and non-incremental.
Incremental searches begin before the user has finished typing the
search string.
As each character of the search string is typed, Readline displays
the next entry from the history matching the string typed so far.
An incremental search requires only as many characters as needed to
find the desired history entry.
To search backward in the history for a particular string, type
C-r. Typing C-s searches forward through the history.
The characters present in the value of the isearch-terminators
variable
are used to terminate an incremental search.
If that variable has not been assigned a value, the <ESC> and
C-J characters will terminate an incremental search.
C-g will abort an incremental search and restore the original line.
When the search is terminated, the history entry containing the
search string becomes the current line.
To find other matching entries in the history list, type C-r or C-s as appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a Readline command will terminate the search and execute that command. For instance, a <RET> will terminate the search and accept the line, thereby executing the command from the history list. A movement command will terminate the search, make the last line found the current line, and begin editing.
Readline remembers the last incremental search string. If two C-rs are typed without any intervening characters defining a new search string, any remembered search string is used.
Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the contents of the current line.
Although the Readline library comes with a set of Emacs-like keybindings installed by default, it is possible to use a different set of keybindings. Any user can customize programs that use Readline by putting commands in an inputrc file, conventionally in his home directory. The name of this file is taken from the value of the environment variable INPUTRC. If that variable is unset, the default is ~/.inputrc. If that file does not exist or cannot be read, the ultimate default is /etc/inputrc.
When a program which uses the Readline library starts up, the init file is read, and the key bindings are set.
In addition, the C-x C-r
command re-reads this init file, thus
incorporating any changes that you might have made to it.
There are only a few basic constructs allowed in the Readline init file. Blank lines are ignored. Lines beginning with a ‘#’ are comments. Lines beginning with a ‘$’ indicate conditional constructs (see Conditional Init Constructs). Other lines denote variable settings and key bindings.
set
command within the init file.
The syntax is simple:
set variable value
Here, for example, is how to
change from the default Emacs-like key binding to use
vi
line editing commands:
set editing-mode vi
Variable names and values, where appropriate, are recognized without regard to case. Unrecognized variable names are ignored.
Boolean variables (those that can be set to on or off) are set to on if the value is null or empty, on (case-insensitive), or 1. Any other value results in the variable being set to off.
A great deal of run-time behavior is changeable with the following variables.
bell-style
bind-tty-special-chars
comment-begin
insert-comment
command is executed. The default value
is "#"
.
completion-display-width
completion-ignore-case
completion-map-case
completion-prefix-display-length
completion-query-items
100
.
convert-meta
disable-completion
self-insert
. The default is ‘off’.
editing-mode
editing-mode
variable controls which default set of
key bindings is used. By default, Readline starts up in Emacs editing
mode, where the keystrokes are most similar to Emacs. This variable can be
set to either ‘emacs’ or ‘vi’.
echo-control-characters
enable-keypad
enable-meta-key
expand-tilde
history-preserve-point
previous-history
or next-history
. The default is ‘off’.
history-size
horizontal-scroll-mode
input-meta
meta-flag
is a
synonym for this variable.
isearch-terminators
keymap
keymap
names are
emacs
,
emacs-standard
,
emacs-meta
,
emacs-ctlx
,
vi
,
vi-move
,
vi-command
, and
vi-insert
.
vi
is equivalent to vi-command
; emacs
is
equivalent to emacs-standard
. The default value is emacs
.
The value of the editing-mode
variable also affects the
default keymap.
mark-directories
mark-modified-lines
mark-symlinked-directories
mark-directories
).
The default is ‘off’.
match-hidden-files
menu-complete-display-prefix
output-meta
page-completions
more
-like pager
to display a screenful of possible completions at a time.
This variable is ‘on’ by default.
print-completions-horizontally
revert-all-at-newline
accept-line
is executed. By default,
history lines may be modified and retain individual undo lists across
calls to readline
. The default is ‘off’.
show-all-if-ambiguous
show-all-if-unmodified
skip-completed-text
visible-stats
Once you know the name of the command, simply place on a line in the init file the name of the key you wish to bind the command to, a colon, and then the name of the command. There can be no space between the key name and the colon – that will be interpreted as part of the key name. The name of the key can be expressed in different ways, depending on what you find most comfortable.
In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro).
Control-u: universal-argument Meta-Rubout: backward-kill-word Control-o: "> output"
In the above example, C-u is bound to the function
universal-argument
,
M-DEL is bound to the function backward-kill-word
, and
C-o is bound to run the macro
expressed on the right hand side (that is, to insert the text
‘> output’ into the line).
A number of symbolic character names are recognized while
processing this key binding syntax:
DEL,
ESC,
ESCAPE,
LFD,
NEWLINE,
RET,
RETURN,
RUBOUT,
SPACE,
SPC,
and
TAB.
"\C-u": universal-argument "\C-x\C-r": re-read-init-file "\e[11~": "Function Key 1"
In the above example, C-u is again bound to the function
universal-argument
(just as it was in the first example),
‘C-x C-r’ is bound to the function re-read-init-file
,
and ‘<ESC> <[> <1> <1> <~>’ is bound to insert
the text ‘Function Key 1’.
The following gnu Emacs style escape sequences are available when specifying key sequences:
In addition to the gnu Emacs style escape sequences, a second set of backslash escapes is available:
\a
\b
\d
\f
\n
\r
\t
\v
\
nnn\x
HHWhen entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed to be a function name. In the macro body, the backslash escapes described above are expanded. Backslash will quote any other character in the macro text, including ‘"’ and ‘'’. For example, the following binding will make ‘C-x \’ insert a single ‘\’ into the line:
"\C-x\\": "\\"
Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key bindings and variable settings to be performed as the result of tests. There are four parser directives used.
$if
$if
construct allows bindings to be made based on the
editing mode, the terminal being used, or the application using
Readline. The text of the test extends to the end of the line;
no characters are required to isolate it.
mode
mode=
form of the $if
directive is used to test
whether Readline is in emacs
or vi
mode.
This may be used in conjunction
with the ‘set keymap’ command, for instance, to set bindings in
the emacs-standard
and emacs-ctlx
keymaps only if
Readline is starting out in emacs
mode.
term
term=
form may be used to include terminal-specific
key bindings, perhaps to bind the key sequences output by the
terminal's function keys. The word on the right side of the
‘=’ is tested against both the full name of the terminal and
the portion of the terminal name before the first ‘-’. This
allows sun
to match both sun
and sun-cmd
,
for instance.
application
$if Bash # Quote the current or previous word "\C-xq": "\eb\"\ef\"" $endif
$endif
$if
command.
$else
$if
directive are executed if
the test fails.
$include
$include /etc/inputrc
Here is an example of an inputrc file. This illustrates key binding, variable assignment, and conditional syntax.
# This file controls the behaviour of line input editing for # programs that use the GNU Readline library. Existing # programs include FTP, Bash, and GDB. # # You can re-read the inputrc file with C-x C-r. # Lines beginning with '#' are comments. # # First, include any systemwide bindings and variable # assignments from /etc/Inputrc $include /etc/Inputrc # # Set various bindings for emacs mode. set editing-mode emacs $if mode=emacs Meta-Control-h: backward-kill-word Text after the function name is ignored # # Arrow keys in keypad mode # #"\M-OD": backward-char #"\M-OC": forward-char #"\M-OA": previous-history #"\M-OB": next-history # # Arrow keys in ANSI mode # "\M-[D": backward-char "\M-[C": forward-char "\M-[A": previous-history "\M-[B": next-history # # Arrow keys in 8 bit keypad mode # #"\M-\C-OD": backward-char #"\M-\C-OC": forward-char #"\M-\C-OA": previous-history #"\M-\C-OB": next-history # # Arrow keys in 8 bit ANSI mode # #"\M-\C-[D": backward-char #"\M-\C-[C": forward-char #"\M-\C-[A": previous-history #"\M-\C-[B": next-history C-q: quoted-insert $endif # An old-style binding. This happens to be the default. TAB: complete # Macros that are convenient for shell interaction $if Bash # edit the path "\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f" # prepare to type a quoted word -- # insert open and close double quotes # and move to just after the open quote "\C-x\"": "\"\"\C-b" # insert a backslash (testing backslash escapes # in sequences and macros) "\C-x\\": "\\" # Quote the current or previous word "\C-xq": "\eb\"\ef\"" # Add a binding to refresh the line, which is unbound "\C-xr": redraw-current-line # Edit variable on current line. "\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y=" $endif # use a visible bell if one is available set bell-style visible # don't strip characters to 7 bits when reading set input-meta on # allow iso-latin1 characters to be inserted rather # than converted to prefix-meta sequences set convert-meta off # display characters with the eighth bit set directly # rather than as meta-prefixed characters set output-meta on # if there are more than 150 possible completions for # a word, ask the user if he wants to see all of them set completion-query-items 150 # For FTP $if Ftp "\C-xg": "get \M-?" "\C-xt": "put \M-?" "\M-.": yank-last-arg $endif
This section describes Readline commands that may be bound to key sequences. Command names without an accompanying key sequence are unbound by default.
In the following descriptions, point refers to the current cursor
position, and mark refers to a cursor position saved by the
set-mark
command.
The text between the point and mark is referred to as the region.
beginning-of-line (C-a)
end-of-line (C-e)
forward-char (C-f)
backward-char (C-b)
forward-word (M-f)
backward-word (M-b)
clear-screen (C-l)
redraw-current-line ()
accept-line (Newline or Return)
add_history()
.
If this line is a modified history line, the history line is restored
to its original state.
previous-history (C-p)
next-history (C-n)
beginning-of-history (M-<)
end-of-history (M->)
reverse-search-history (C-r)
forward-search-history (C-s)
non-incremental-reverse-search-history (M-p)
non-incremental-forward-search-history (M-n)
history-search-forward ()
history-search-backward ()
yank-nth-arg (M-C-y)
yank-last-arg (M-. or M-_)
yank-nth-arg
.
Successive calls to yank-last-arg
move back through the history
list, inserting the last word (or the word specified by the argument to
the first call) of each line in turn.
Any numeric argument supplied to these successive calls determines
the direction to move through the history. A negative argument switches
the direction through the history (back or forward).
The history expansion facilities are used to extract the last argument,
as if the ‘!$’ history expansion had been specified.
delete-char (C-d)
delete-char
, then
return eof.
backward-delete-char (Rubout)
forward-backward-delete-char ()
quoted-insert (C-q or C-v)
tab-insert (M-<TAB>)
self-insert (a, b, A, 1, !, ...)
transpose-chars (C-t)
transpose-words (M-t)
upcase-word (M-u)
downcase-word (M-l)
capitalize-word (M-c)
overwrite-mode ()
emacs
mode; vi
mode does overwrite differently.
Each call to readline()
starts in insert mode.
In overwrite mode, characters bound to self-insert
replace
the text at point rather than pushing the text to the right.
Characters bound to backward-delete-char
replace the character
before point with a space.
By default, this command is unbound.
kill-line (C-k)
backward-kill-line (C-x Rubout)
unix-line-discard (C-u)
kill-whole-line ()
kill-word (M-d)
forward-word
.
backward-kill-word (M-<DEL>)
backward-word
.
unix-word-rubout (C-w)
unix-filename-rubout ()
delete-horizontal-space ()
kill-region ()
copy-region-as-kill ()
copy-backward-word ()
backward-word
.
By default, this command is unbound.
copy-forward-word ()
forward-word
.
By default, this command is unbound.
yank (C-y)
yank-pop (M-y)
yank
or yank-pop
.
digit-argument (
M-0,
M-1, ...
M--)
universal-argument ()
universal-argument
again ends the numeric argument, but is otherwise ignored.
As a special case, if this command is immediately followed by a
character that is neither a digit or minus sign, the argument count
for the next command is multiplied by four.
The argument count is initially one, so executing this function the
first time makes the argument count four, a second time makes the
argument count sixteen, and so on.
By default, this is not bound to a key.
complete (<TAB>)
possible-completions (M-?)
completion-display-width
, the value of
the environment variable COLUMNS, or the screen width, in that order.
insert-completions (M-*)
possible-completions
.
menu-complete ()
complete
, but replaces the word to be completed
with a single match from the list of possible completions.
Repeated execution of menu-complete
steps through the list
of possible completions, inserting each match in turn.
At the end of the list of completions, the bell is rung
(subject to the setting of bell-style
)
and the original text is restored.
An argument of n moves n positions forward in the list
of matches; a negative argument may be used to move backward
through the list.
This command is intended to be bound to <TAB>, but is unbound
by default.
menu-complete-backward ()
menu-complete
, but moves backward through the list
of possible completions, as if menu-complete
had been given a
negative argument.
delete-char-or-list ()
delete-char
).
If at the end of the line, behaves identically to
possible-completions
.
This command is unbound by default.
start-kbd-macro (C-x ()
end-kbd-macro (C-x ))
call-last-kbd-macro (C-x e)
re-read-init-file (C-x C-r)
abort (C-g)
bell-style
).
do-uppercase-version (M-a, M-b, M-
x, ...)
prefix-meta (<ESC>)
undo (C-_ or C-x C-u)
revert-line (M-r)
undo
command enough times to get back to the beginning.
tilde-expand (M-~)
set-mark (C-@)
exchange-point-and-mark (C-x C-x)
character-search (C-])
character-search-backward (M-C-])
skip-csi-sequence ()
insert-comment (M-#)
comment-begin
variable is inserted at the beginning of the current line.
If a numeric argument is supplied, this command acts as a toggle: if
the characters at the beginning of the line do not match the value
of comment-begin
, the value is inserted, otherwise
the characters in comment-begin
are deleted from the beginning of
the line.
In either case, the line is accepted as if a newline had been typed.
dump-functions ()
dump-variables ()
dump-macros ()
emacs-editing-mode (C-e)
vi
command mode, this causes a switch to emacs
editing mode.
vi-editing-mode (M-C-j)
emacs
editing mode, this causes a switch to vi
editing mode.
While the Readline library does not have a full set of vi
editing functions, it does contain enough to allow simple editing
of the line. The Readline vi
mode behaves as specified in
the posix standard.
In order to switch interactively between emacs
and vi
editing modes, use the command M-C-j (bound to emacs-editing-mode
when in vi
mode and to vi-editing-mode in emacs
mode).
The Readline default is emacs
mode.
When you enter a line in vi
mode, you are already placed in
`insertion' mode, as if you had typed an ‘i’. Pressing <ESC>
switches you into `command' mode, where you can edit the text of the
line with the standard vi
movement keys, move to previous
history lines with ‘k’ and subsequent lines with ‘j’, and
so forth.
This chapter describes how to use the gnu History Library interactively, from a user's standpoint. It should be considered a user's guide. For information on using the gnu History Library in your own programs, see Programming with GNU History.
The History library provides a history expansion feature that is similar
to the history expansion provided by csh
. This section
describes the syntax used to manipulate the history information.
History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the current input line, or fix errors in previous commands quickly.
History expansion takes place in two parts. The first is to determine which line from the history list should be used during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is called the event, and the portions of that line that are acted upon are called words. Various modifiers are available to manipulate the selected words. The line is broken into words in the same fashion that Bash does, so that several words surrounded by quotes are considered one word. History expansions are introduced by the appearance of the history expansion character, which is ‘!’ by default.
An event designator is a reference to a command line entry in the history list. Unless the reference is absolute, events are relative to the current position in the history list.
!
!
n!-
n!!
!
string!?
string[?]
^
string1^
string2^
!!:s/
string1/
string2/
.
!#
Word designators are used to select desired words from the event. A ‘:’ separates the event specification from the word designator. It may be omitted if the word designator begins with a ‘^’, ‘$’, ‘*’, ‘-’, or ‘%’. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.
For example,
!!
!!:$
!$
.
!fi:2
fi
.
Here are the word designators:
0 (zero)
0
th word. For many applications, this is the command word.
^
$
%
-
y*
0
th. This is a synonym for ‘1-$’.
It is not an error to use ‘*’ if there is just one word in the event;
the empty string is returned in that case.
*
-
If a word designator is supplied without an event specification, the previous command is used as the event.
After the optional word designator, you can add a sequence of one or more of the following modifiers, each preceded by a ‘:’.
h
t
r
e
p
s/
old/
new/
&
g
a
gs/
old/
new/
,
or with ‘&’.
G
The GDB project mourns the loss of the following long-time contributors:
Fred Fish
Michael Snyder
Beyond their technical contributions to the project, they were also enjoyable members of the Free Software Community. We will miss them.
The gdb 4 release includes an already-formatted reference card, ready for printing with PostScript or Ghostscript, in the gdb subdirectory of the main source directory14. If you can use PostScript or Ghostscript with your printer, you can print the reference card immediately with refcard.ps.
The release also includes the source for the reference card. You can format it, using TeX, by typing:
make refcard.dvi
The gdb reference card is designed to print in landscape mode on US “letter” size paper; that is, on a sheet 11 inches wide by 8.5 inches high. You will need to specify this form of printing as an option to your dvi output program.
All the documentation for gdb comes as part of the machine-readable
distribution. The documentation is written in Texinfo format, which is
a documentation system that uses a single source file to produce both
on-line information and a printed manual. You can use one of the Info
formatting commands to create the on-line version of the documentation
and TeX (or texi2roff
) to typeset the printed version.
gdb includes an already formatted copy of the on-line Info
version of this manual in the gdb subdirectory. The main Info
file is gdb-Momonga (7.3.1-1m.mo8)/gdb/gdb.info, and it refers to
subordinate files matching ‘gdb.info*’ in the same directory. If
necessary, you can print out these files, or read them with any editor;
but they are easier to read using the info
subsystem in gnu
Emacs or the standalone info
program, available as part of the
gnu Texinfo distribution.
If you want to format these Info files yourself, you need one of the
Info formatting programs, such as texinfo-format-buffer
or
makeinfo
.
If you have makeinfo
installed, and are in the top level
gdb source directory (gdb-Momonga (7.3.1-1m.mo8), in the case of
version Momonga (7.3.1-1m.mo8)), you can make the Info file by typing:
cd gdb make gdb.info
If you want to typeset and print copies of this manual, you need TeX, a program to print its dvi output files, and texinfo.tex, the Texinfo definitions file.
TeX is a typesetting program; it does not print files directly, but produces output files called dvi files. To print a typeset document, you need a program to print dvi files. If your system has TeX installed, chances are it has such a program. The precise command to use depends on your system; lpr -d is common; another (for PostScript devices) is dvips. The dvi print command may require a file name without any extension or a ‘.dvi’ extension.
TeX also requires a macro definitions file called texinfo.tex. This file tells TeX how to typeset a document written in Texinfo format. On its own, TeX cannot either read or typeset a Texinfo file. texinfo.tex is distributed with GDB and is located in the gdb-version-number/texinfo directory.
If you have TeX and a dvi printer program installed, you can typeset and print this manual. First switch to the gdb subdirectory of the main source directory (for example, to gdb-Momonga (7.3.1-1m.mo8)/gdb) and type:
make gdb.dvi
Then give gdb.dvi to your dvi printing program.
Building gdb requires various tools and packages to be available. Other packages will be used only if they are found.
Expat is used for:
The ‘zlib’ library is likely included with your operating system
distribution; if it is not, you can get the latest version from
http://zlib.net.
iconv
implementation. If you are
on a GNU system, then this is provided by the GNU C Library. Some
other systems also provide a working iconv
.
On systems with iconv
, you can install GNU Libiconv. If you
have previously installed Libiconv, you can use the
--with-libiconv-prefix option to configure.
gdb's top-level configure and Makefile will
arrange to build Libiconv if a directory named libiconv appears
in the top-most source directory. If Libiconv is built this way, and
if the operating system does not provide a suitable iconv
implementation, then the just-built library will automatically be used
by gdb. One easy way to set this up is to download GNU
Libiconv, unpack it, and then rename the directory holding the
Libiconv source code to ‘libiconv’.
gdb comes with a configure script that automates the process
of preparing gdb for installation; you can then use make
to
build the gdb
program.
The gdb distribution includes all the source code you need for gdb in a single directory, whose name is usually composed by appending the version number to ‘gdb’.
For example, the gdb version Momonga (7.3.1-1m.mo8) distribution is in the gdb-Momonga (7.3.1-1m.mo8) directory. That directory contains:
gdb-Momonga (7.3.1-1m.mo8)/configure
(and supporting files)gdb-Momonga (7.3.1-1m.mo8)/gdb
gdb-Momonga (7.3.1-1m.mo8)/bfd
gdb-Momonga (7.3.1-1m.mo8)/include
gdb-Momonga (7.3.1-1m.mo8)/libiberty
gdb-Momonga (7.3.1-1m.mo8)/opcodes
gdb-Momonga (7.3.1-1m.mo8)/readline
gdb-Momonga (7.3.1-1m.mo8)/glob
gdb-Momonga (7.3.1-1m.mo8)/mmalloc
The simplest way to configure and build gdb is to run configure from the gdb-version-number source directory, which in this example is the gdb-Momonga (7.3.1-1m.mo8) directory.
First switch to the gdb-version-number source directory if you are not already in it; then run configure. Pass the identifier for the platform on which gdb will run as an argument.
For example:
cd gdb-Momonga (7.3.1-1m.mo8) ./configure host make
where host is an identifier such as ‘sun4’ or ‘decstation’, that identifies the platform where gdb will run. (You can often leave off host; configure tries to guess the correct value by examining your system.)
Running ‘configure host’ and then running make
builds the
bfd, readline, mmalloc, and libiberty
libraries, then gdb
itself. The configured source files, and the
binaries, are left in the corresponding source directories.
configure is a Bourne-shell (/bin/sh
) script; if your
system does not recognize this automatically when you run a different
shell, you may need to run sh
on it explicitly:
sh configure host
If you run configure from a directory that contains source directories for multiple libraries or programs, such as the gdb-Momonga (7.3.1-1m.mo8) source directory for version Momonga (7.3.1-1m.mo8), configure creates configuration files for every directory level underneath (unless you tell it not to, with the ‘--norecursion’ option).
You should run the configure script from the top directory in the source tree, the gdb-version-number directory. If you run configure from one of the subdirectories, you will configure only that subdirectory. That is usually not what you want. In particular, if you run the first configure from the gdb subdirectory of the gdb-version-number directory, you will omit the configuration of bfd, readline, and other sibling directories of the gdb subdirectory. This leads to build errors about missing include files such as bfd/bfd.h.
You can install gdb
anywhere; it has no hardwired paths.
However, you should make sure that the shell on your path (named by
the ‘SHELL’ environment variable) is publicly readable. Remember
that gdb uses the shell to start your program—some systems refuse to
let gdb debug child processes whose programs are not readable.
If you want to run gdb versions for several host or target machines,
you need a different gdb
compiled for each combination of
host and target. configure is designed to make this easy by
allowing you to generate each configuration in a separate subdirectory,
rather than in the source directory. If your make
program
handles the ‘VPATH’ feature (gnu make
does), running
make
in each of these directories builds the gdb
program specified there.
To build gdb
in a separate directory, run configure
with the ‘--srcdir’ option to specify where to find the source.
(You also need to specify a path to find configure
itself from your working directory. If the path to configure
would be the same as the argument to ‘--srcdir’, you can leave out
the ‘--srcdir’ option; it is assumed.)
For example, with version Momonga (7.3.1-1m.mo8), you can build gdb in a separate directory for a Sun 4 like this:
cd gdb-Momonga (7.3.1-1m.mo8) mkdir ../gdb-sun4 cd ../gdb-sun4 ../gdb-Momonga (7.3.1-1m.mo8)/configure sun4 make
When configure builds a configuration using a remote source directory, it creates a tree for the binaries with the same structure (and using the same names) as the tree under the source directory. In the example, you'd find the Sun 4 library libiberty.a in the directory gdb-sun4/libiberty, and gdb itself in gdb-sun4/gdb.
Make sure that your path to the configure script has just one instance of gdb in it. If your path to configure looks like ../gdb-Momonga (7.3.1-1m.mo8)/gdb/configure, you are configuring only one subdirectory of gdb, not the whole package. This leads to build errors about missing include files such as bfd/bfd.h.
One popular reason to build several gdb configurations in separate directories is to configure gdb for cross-compiling (where gdb runs on one machine—the host—while debugging programs that run on another machine—the target). You specify a cross-debugging target by giving the ‘--target=target’ option to configure.
When you run make
to build a program or library, you must run
it in a configured directory—whatever directory you were in when you
called configure (or one of its subdirectories).
The Makefile
that configure generates in each source
directory also runs recursively. If you type make
in a source
directory such as gdb-Momonga (7.3.1-1m.mo8) (or in a separate configured
directory configured with ‘--srcdir=dirname/gdb-Momonga (7.3.1-1m.mo8)’), you
will build all the required libraries, and then build GDB.
When you have multiple hosts or targets configured in separate
directories, you can run make
on them in parallel (for example,
if they are NFS-mounted on each of the hosts); they will not interfere
with each other.
The specifications used for hosts and targets in the configure script are based on a three-part naming scheme, but some short predefined aliases are also supported. The full naming scheme encodes three pieces of information in the following pattern:
architecture-vendor-os
For example, you can use the alias sun4
as a host argument,
or as the value for target in a --target=
target
option. The equivalent full name is ‘sparc-sun-sunos4’.
The configure script accompanying gdb does not provide
any query facility to list all supported host and target names or
aliases. configure calls the Bourne shell script
config.sub
to map abbreviations to full names; you can read the
script, if you wish, or you can use it to test your guesses on
abbreviations—for example:
% sh config.sub i386-linux i386-pc-linux-gnu % sh config.sub alpha-linux alpha-unknown-linux-gnu % sh config.sub hp9k700 hppa1.1-hp-hpux % sh config.sub sun4 sparc-sun-sunos4.1.1 % sh config.sub sun3 m68k-sun-sunos4.1.1 % sh config.sub i986v Invalid configuration `i986v': machine `i986v' not recognized
config.sub
is also distributed in the gdb source
directory (gdb-Momonga (7.3.1-1m.mo8), for version Momonga (7.3.1-1m.mo8)).
Here is a summary of the configure options and arguments that are most often useful for building gdb. configure also has several other options not listed here. see What Configure Does, for a full explanation of configure.
configure [--help] [--prefix=dir] [--exec-prefix=dir] [--srcdir=dirname] [--norecursion] [--rm] [--target=target] host
You may introduce options with a single ‘-’ rather than ‘--’ if you prefer; but you may abbreviate option names if you use ‘--’.
--help
--prefix=
dir--exec-prefix=
dir--srcdir=
dirnamemake
, or another
make
that implements the VPATH
feature.--norecursion
--target=
targetThere is no convenient way to generate a list of all available targets.
...
There is no convenient way to generate a list of all available hosts.
There are many other options available as well, but they are generally needed for special purposes only.
gdb can be configured to have a system-wide init file; this file will be read and executed at startup (see What gdb does during startup).
Here is the corresponding configure option:
--with-system-gdbinit=
fileIf gdb has been configured with the option --prefix=$prefix, it may be subject to relocation. Two possible cases:
In addition to commands intended for gdb users, gdb includes a number of commands intended for gdb developers, that are not documented elsewhere in this manual. These commands are provided here for reference. (For commands that turn on debugging messages, see Debugging Output.)
maint agent
expressionmaint agent-eval
expressiongloba +
globb
will include bytecodes to record four bytes of memory at each
of the addresses of globa
and globb
, while discarding
the result of the addition, while an evaluation expression will do the
addition and return the sum.
maint info breakpoints
breakpoint
watchpoint
longjmp
longjmp
calls.
longjmp resume
longjmp
.
until
until
command.
finish
finish
command.
shlib events
set displaced-stepping
show displaced-stepping
set displaced-stepping on
set displaced-stepping off
set displaced-stepping auto
maint check-symtabs
maint cplus first_component
namemaint cplus namespace
maint demangle
namemaint deprecate
command [replacement]maint undeprecate
commandmaint dump-me
SIGQUIT
signal.
maint internal-error
[message-text]maint internal-warning
[message-text]internal_error
or internal_warning
and hence behave as though an internal error
or internal warning has been detected. In addition to reporting the
internal problem, these functions give the user the opportunity to
either quit gdb or create a core file of the current
gdb session.
These commands take an optional parameter message-text that is used as the text of the error or warning message.
Here's an example of using internal-error
:
(gdb) maint internal-error testing, 1, 2 .../maint.c:121: internal-error: testing, 1, 2 A problem internal to GDB has been detected. Further debugging may prove unreliable. Quit this debugging session? (y or n) n Create a core file? (y or n) n (gdb)
maint set internal-error
action [ask|yes|no]
maint show internal-error
actionmaint set internal-warning
action [ask|yes|no]
maint show internal-warning
actionmaint packet
textmaint print architecture
[file]maint print c-tdesc
maint print dummy-frames
(gdb) b add ... (gdb) print add(2,3) Breakpoint 2, add (a=2, b=3) at ... 58 return (a + b); The program being debugged stopped while in a function called from GDB. ... (gdb) maint print dummy-frames 0x1a57c80: pc=0x01014068 fp=0x0200bddc sp=0x0200bdd6 top=0x0200bdd4 id={stack=0x200bddc,code=0x101405c} call_lo=0x01014000 call_hi=0x01014001 (gdb)
Takes an optional file parameter.
maint print registers
[file]maint print raw-registers
[file]maint print cooked-registers
[file]maint print register-groups
[file]The command maint print raw-registers
includes the contents of
the raw register cache; the command maint print cooked-registers
includes the (cooked) value of all registers, including registers which
aren't available on the target nor visible to user; and the
command maint print register-groups
includes the groups that each
register is a member of. See Registers.
These commands take an optional parameter, a file name to which to write the information.
maint print reggroups
[file]The register groups info looks like this:
(gdb) maint print reggroups Group Type general user float user all user vector user system user save internal restore internal
flushregs
maint print objfiles
maint print section-scripts [
regexp]
.debug_gdb_section
section.
If regexp is specified, only print scripts loaded by object files
matching regexp.
For each script, this command prints its name as specified in the objfile,
and the full path if known.
See .debug_gdb_scripts section.
maint print statistics
maint print target-stack
This command prints a short description of each layer that was pushed on the target stack, starting from the top layer down to the bottom one.
maint print type
exprmaint set dwarf2 always-disassemble
maint show dwarf2 always-disassemble
info address
when using DWARF debugging
information.
The default is off
, which means that gdb should try to
describe a variable's location in an easily readable format. When
on
, gdb will instead display the DWARF location
expression in an assembly-like format. Note that some locations are
too complex for gdb to describe simply; in this case you will
always see the disassembly form.
Here is an example of the resulting disassembly:
(gdb) info addr argc Symbol "argc" is a complex DWARF expression: 1: DW_OP_fbreg 0
For more information on these expressions, see the DWARF standard.
maint set dwarf2 max-cache-age
maint show dwarf2 max-cache-age
In object files with inter-compilation-unit references, such as those produced by the GCC option ‘-feliminate-dwarf2-dups’, the DWARF 2 reader needs to frequently refer to previously read compilation units. This setting controls how long a compilation unit will remain in the cache if it is not referenced. A higher limit means that cached compilation units will be stored in memory longer, and more total memory will be used. Setting it to zero disables caching, which will slow down gdb startup, but reduce memory consumption.
maint set profile
maint show profile
Profiling will be disabled until you use the ‘maint set profile’ command to enable it. When you enable profiling, the system will begin collecting timing and execution count data; when you disable profiling or exit gdb, the results will be written to a log file. Remember that if you use profiling, gdb will overwrite the profiling log file (often called gmon.out). If you have a record of important profiling data in a gmon.out file, be sure to move it to a safe location.
Configuring with ‘--enable-profiling’ arranges for gdb to be compiled with the ‘-pg’ compiler option.
maint set show-debug-regs
maint show show-debug-regs
ON
to enable, OFF
to disable. If
enabled, the debug registers values are shown when gdb inserts or
removes a hardware breakpoint or watchpoint, and when the inferior
triggers a hardware-assisted breakpoint or watchpoint.
maint set show-all-tib
maint show show-all-tib
maint space
maint time
maint translate-address
[section] addrinfo address
command (see Symbols), except that this
command also allows to find symbols in other sections.
If section was not specified, the section in which the symbol was found is also printed. For dynamically linked executables, the name of executable or shared library containing the symbol is printed as well.
The following command is useful for non-interactive invocations of gdb, such as in the test suite.
set watchdog
nsecshow watchdog
There may be occasions when you need to know something about the protocol—for example, if there is only one serial port to your target machine, you might want your program to do something special if it recognizes a packet meant for gdb.
In the examples below, ‘->’ and ‘<-’ are used to indicate transmitted and received data, respectively.
All gdb commands and responses (other than acknowledgments and notifications, see Notification Packets) are sent as a packet. A packet is introduced with the character ‘$’, the actual packet-data, and the terminating character ‘#’ followed by a two-digit checksum:
$
packet-data#
checksum
The two-digit checksum is computed as the modulo 256 sum of all characters between the leading ‘$’ and the trailing ‘#’ (an eight bit unsigned checksum).
Implementors should note that prior to gdb 5.0 the protocol specification also included an optional two-digit sequence-id:
$
sequence-id:
packet-data#
checksum
That sequence-id was appended to the acknowledgment. gdb has never output sequence-ids. Stubs that handle packets added since gdb 5.0 must not accept sequence-id.
When either the host or the target machine receives a packet, the first response expected is an acknowledgment: either ‘+’ (to indicate the package was received correctly) or ‘-’ (to request retransmission):
->$
packet-data#
checksum <-+
The ‘+’/‘-’ acknowledgments can be disabled once a connection is established. See Packet Acknowledgment, for details.
The host (gdb) sends commands, and the target (the debugging stub incorporated in your program) sends a response. In the case of step and continue commands, the response is only sent when the operation has completed, and the target has again stopped all threads in all attached processes. This is the default all-stop mode behavior, but the remote protocol also supports gdb's non-stop execution mode; see Remote Non-Stop, for details.
packet-data consists of a sequence of characters with the exception of ‘#’ and ‘$’ (see ‘X’ packet for additional exceptions).
Fields within the packet should be separated using ‘,’ ‘;’ or ‘:’. Except where otherwise noted all numbers are represented in hex with leading zeros suppressed.
Implementors should note that prior to gdb 5.0, the character ‘:’ could not appear as the third character in a packet (as it would potentially conflict with the sequence-id).
Binary data in most packets is encoded either as two hexadecimal digits per byte of binary data. This allowed the traditional remote protocol to work over connections which were only seven-bit clean. Some packets designed more recently assume an eight-bit clean connection, and use a more efficient encoding to send and receive binary data.
The binary data representation uses 7d
(ascii ‘}’)
as an escape character. Any escaped byte is transmitted as the escape
character followed by the original character XORed with 0x20
.
For example, the byte 0x7d
would be transmitted as the two
bytes 0x7d 0x5d
. The bytes 0x23
(ascii ‘#’),
0x24
(ascii ‘$’), and 0x7d
(ascii
‘}’) must always be escaped. Responses sent by the stub
must also escape 0x2a
(ascii ‘*’), so that it
is not interpreted as the start of a run-length encoded sequence
(described next).
Response data can be run-length encoded to save space.
Run-length encoding replaces runs of identical characters with one
instance of the repeated character, followed by a ‘*’ and a
repeat count. The repeat count is itself sent encoded, to avoid
binary characters in data: a value of n is sent as
n+29
. For a repeat count greater or equal to 3, this
produces a printable ascii character, e.g. a space (ascii
code 32) for a repeat count of 3. (This is because run-length
encoding starts to win for counts 3 or more.) Thus, for example,
‘0* ’ is a run-length encoding of “0000”: the space character
after ‘*’ means repeat the leading 0
32 - 29 = 3
more times.
The printable characters ‘#’ and ‘$’ or with a numeric value greater than 126 must not be used. Runs of six repeats (‘#’) or seven repeats (‘$’) can be expanded using a repeat count of only five (‘"’). For example, ‘00000000’ can be encoded as ‘0*"00’.
The error response returned for some packets includes a two character error number. That number is not well defined.
For any command not supported by the stub, an empty response (‘$#00’) should be returned. That way it is possible to extend the protocol. A newer gdb can tell if a packet is supported based on that response.
A stub is required to support the ‘g’, ‘G’, ‘m’, ‘M’, ‘c’, and ‘s’ commands. All other commands are optional.
The following table provides a complete list of all currently defined commands and their corresponding response data. See File-I/O Remote Protocol Extension, for details about the File I/O extension of the remote protocol.
Each packet's description has a template showing the packet's overall syntax, followed by an explanation of the packet's meaning. We include spaces in some of the templates for clarity; these are not part of the packet's syntax. No gdb packet uses spaces to separate its components. For example, a template like ‘foo bar baz’ describes a packet beginning with the three ASCII bytes ‘foo’, followed by a bar, followed directly by a baz. gdb does not transmit a space character between the ‘foo’ and the bar, or between the bar and the baz.
Several packets and replies include a thread-id field to identify a thread. Normally these are positive numbers with a target-specific interpretation, formatted as big-endian hex strings. A thread-id can also be a literal ‘-1’ to indicate all threads, or ‘0’ to pick any thread.
In addition, the remote protocol supports a multiprocess feature in which the thread-id syntax is extended to optionally include both process and thread ID fields, as ‘ppid.tid’. The pid (process) and tid (thread) components each have the format described above: a positive number with target-specific interpretation formatted as a big-endian hex string, literal ‘-1’ to indicate all processes or threads (respectively), or ‘0’ to indicate an arbitrary process or thread. Specifying just a process, as ‘ppid’, is equivalent to ‘ppid.-1’. It is an error to specify all processes but a specific thread, such as ‘p-1.tid’. Note that the ‘p’ prefix is not used for those packets and replies explicitly documented to include a process ID, rather than a thread-id.
The multiprocess thread-id syntax extensions are only used if both gdb and the stub report support for the ‘multiprocess’ feature using ‘qSupported’. See multiprocess extensions, for more information.
Note that all packet forms beginning with an upper- or lower-case letter, other than those described here, are reserved for future use.
Here are the packet descriptions.
Reply:
Reply:
See Stop Reply Packets, for the reply specifications.
argv[]
array passed into program. arglen
specifies the number of bytes in the hex encoded byte stream
arg. See gdbserver
for more details.
Reply:
JTC: When does the transport layer state change? When it's received, or after the ACK is transmitted. In either case, there are problems if the command or the acknowledgment packet is dropped.
Stan: If people really wanted to add something like this, and get
it working for the first time, they ought to modify ser-unix.c to send
some kind of out-of-band message to a specially-setup stub and have the
switch happen "in between" packets, so that from remote protocol's point
of view, nothing actually happened.
Don't use this packet. Use the ‘Z’ and ‘z’ packets instead (see insert breakpoint or watchpoint packet).
Reply: See Stop Reply Packets, for the reply specifications.
Reply:
See Stop Reply Packets, for the reply specifications.
Reply:
See Stop Reply Packets, for the reply specifications.
Reply:
See Stop Reply Packets, for the reply specifications.
Don't use this packet; instead, define a general set packet
(see General Query Packets).
detach
command.
The second form, including a process ID, is used when multiprocess protocol extensions are enabled (see multiprocess extensions), to detach only a specific process. The pid is specified as a big-endian hex string.
Reply:
Reply:
DEPRECATED_REGISTER_RAW_SIZE
and gdbarch_register_name
. The
specification of several standard ‘g’ packets is specified below.
When reading registers from a trace frame (see Using the Collected Data), the stub may also return a string of literal ‘x’'s in place of the register data digits, to indicate that the corresponding register has not been collected, thus its value is unavailable. For example, for an architecture with 4 registers of 4 bytes each, the following reply indicates to gdb that registers 0 and 2 have not been collected, while registers 1 and 3 have been collected, and both have zero value:
->g
<-xxxxxxxx00000000xxxxxxxx00000000
Reply:
Reply:
FIXME: There is no description of how to operate when a specific
thread context has been selected (i.e. does 'k' kill only that
thread?).
The stub need not use any particular size or alignment when gathering data from memory for the response; even if addr is word-aligned and length is a multiple of the word size, the stub is free to use byte accesses, or not. For this reason, this packet may not be suitable for accessing memory-mapped I/O devices. Reply:
Reply:
Reply:
Reply:
Don't use this packet; use the ‘R’ packet instead.
The ‘R’ packet has no reply.
Reply:
See Stop Reply Packets, for the reply specifications.
Reply:
See Stop Reply Packets, for the reply specifications.
Reply:
This packet is only available in extended mode (see extended mode).
Reply:
Currently supported actions are:
The optional argument addr normally associated with the ‘c’, ‘C’, ‘s’, and ‘S’ packets is not supported in ‘vCont’.
The ‘t’ action is only relevant in non-stop mode (see Remote Non-Stop) and may be ignored by the stub otherwise. A stop reply should be generated for any affected thread not already stopped. When a thread is stopped by means of a ‘t’ action, the corresponding stop reply should indicate that the thread has stopped with signal ‘0’, regardless of whether the target uses some other signal as an implementation detail.
Reply:
See Stop Reply Packets, for the reply specifications.
Reply:
The stub must support ‘vCont’ if it reports support for multiprocess extensions (see multiprocess extensions). Note that in this case ‘vCont’ actions can be specified to apply to all threads in a process by using the ‘ppid.-1’ form of the thread-id.
Reply:
Reply:
Reply:
This packet is only available in extended mode (see extended mode).
Reply:
Reply:
Reply:
Each breakpoint and watchpoint packet type is documented separately.
Implementation notes: A remote target shall return an empty string
for an unrecognized breakpoint or watchpoint packet type. A
remote target shall support either both or neither of a given
‘Ztype...’ and ‘ztype...’ packet pair. To
avoid potential problems with duplicate packets, the operations should
be implemented in an idempotent way.
A memory breakpoint is implemented by replacing the instruction at addr with a software breakpoint or trap instruction. The kind is target-specific and typically indicates the size of the breakpoint in bytes that should be inserted. E.g., the arm and mips can insert either a 2 or 4 byte breakpoint. Some architectures have additional meanings for kind; see Architecture-Specific Protocol Details.
Implementation note: It is possible for a target to copy or move code that contains memory breakpoints (e.g., when implementing overlays). The behavior of this packet, in the presence of such a target, is not defined.
Reply:
A hardware breakpoint is implemented using a mechanism that is not dependant on being able to modify the target's memory. kind has the same meaning as in ‘Z0’ packets.
Implementation note: A hardware breakpoint is not affected by code movement.
Reply:
Reply:
Reply:
Reply:
The ‘C’, ‘c’, ‘S’, ‘s’, ‘vCont’, ‘vAttach’, ‘vRun’, ‘vStopped’, and ‘?’ packets can receive any of the below as a reply. Except for ‘?’ and ‘vStopped’, that reply is only returned when the target halts. In the below the exact meaning of signal number is defined by the header include/gdb/signals.h in the gdb source code.
As in the description of request packets, we include spaces in the reply templates for clarity; these are not part of the reply packet's syntax. No gdb stop reply packet uses spaces to separate its components.
The currently defined stop reasons are:
The second form of the response, including the process ID of the exited
process, can be used only when gdb has reported support for
multiprocess protocol extensions; see multiprocess extensions.
The pid is formatted as a big-endian hex string.
The second form of the response, including the process ID of the
terminated process, can be used only when gdb has reported
support for multiprocess protocol extensions; see multiprocess extensions. The pid is formatted as a big-endian hex string.
‘parameter...’ is a list of parameters as defined for this very system call.
The target replies with this packet when it expects gdb to call a host system call on behalf of the target. gdb replies with an appropriate ‘F’ packet and keeps up waiting for the next reply packet from the target. The latest ‘C’, ‘c’, ‘S’ or ‘s’ action is expected to be continued. See File-I/O Remote Protocol Extension, for more details.
Packets starting with ‘q’ are general query packets; packets starting with ‘Q’ are general set packets. General query and set packets are a semi-unified form for retrieving and sending information to and from the stub.
The initial letter of a query or set packet is followed by a name indicating what sort of thing the packet applies to. For example, gdb may use a ‘qSymbol’ packet to exchange symbol definitions with the stub. These packet names follow some conventions:
The name of a query or set packet should be separated from any parameters by a ‘:’; the parameters themselves should be separated by ‘,’ or ‘;’. Stubs must be careful to match the full packet name, and check for a separator or the end of the packet, in case two packet names share a common prefix. New packets should not begin with ‘qC’, ‘qP’, or ‘qL’15.
Like the descriptions of the other packets, each description here has a template showing the packet's overall syntax, followed by an explanation of the packet's meaning. We include spaces in some of the templates for clarity; these are not part of the packet's syntax. No gdb packet uses spaces to separate its components.
Here are the currently defined query and set packets:
Reply:
0xffffffff
is used to ensure leading zeros affect the CRC.
Note: This is the same CRC used in validating separate debug files (see Debugging Information in Separate Files). However the algorithm is slightly different. When validating separate debug files, the CRC is computed taking the least significant bit of each byte first, and the final result is inverted to detect trailing zeros.
Reply:
NOTE: This packet replaces the ‘qL’ query (see below).
Reply:
In response to each query, the target will reply with a list of one or
more thread IDs, separated by commas.
gdb will respond to each reply with a request for more thread
ids (using the ‘qs’ form of the query), until the target responds
with ‘l’ (lower-case ell, for last).
Refer to thread-id syntax, for the format of the thread-id
fields.
thread-id is the thread ID associated with the thread for which to fetch the TLS address. See thread-id syntax.
offset is the (big endian, hex encoded) offset associated with the thread local variable. (This offset is obtained from the debug information associated with the variable.)
lm is the (big endian, hex encoded) OS/ABI-specific encoding of the the load module associated with the thread local storage. For example, a gnu/Linux system will pass the link map address of the shared object associated with the thread local storage under consideration. Other operating environments may choose to represent the load module differently, so the precise meaning of this parameter will vary.
Reply:
thread-id is the thread ID associated with the thread.
Reply:
Don't use this packet; use the ‘qfThreadInfo’ query instead (see above).
Reply:
remote.c:parse_threadlist_response()
.
Reply:
Text
section by xxx from its original address.
Relocate the Data
section by yyy from its original address.
If the object file format provides segment information (e.g. elf
‘PT_LOAD’ program headers), gdb will relocate entire
segments by the supplied offsets.
Note: while a Bss
offset may be included in the response,
gdb ignores this and instead applies the Data
offset
to the Bss
section.
Don't use this packet; use the ‘qThreadExtraInfo’ query instead (see below).
Reply: see remote.c:remote_unpack_thread_info_response()
.
Reply:
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
Use of this packet is controlled by the set non-stop
command;
see Non-Stop Mode.
Reply:
Use of this packet is controlled by the set remote pass-signals
command (see set remote pass-signals).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
Reply:
(Note that the qRcmd
packet's name is separated from the
command by a ‘,’, not a ‘:’, contrary to the naming
conventions above. Please don't use this packet as a model for new
packets.)
Reply:
Reply:
Reply:
The allowed forms for each feature (either a gdbfeature in the ‘qSupported’ packet, or a stubfeature in the response) are:
Whenever the stub receives a ‘qSupported’ request, the supplied set of gdb features should override any previous request. This allows gdb to put the stub in a known state, even if the stub had previously been communicating with a different version of gdb.
The following values of gdbfeature (for the packet sent by gdb) are defined:
Stubs should ignore any unknown values for gdbfeature. Any gdb which sends a ‘qSupported’ packet supports receiving packets of unlimited length (earlier versions of gdb may reject overly long responses). Additional values for gdbfeature may be defined in the future to let the stub take advantage of new features in gdb, e.g. incompatible improvements in the remote protocol—the ‘multiprocess’ feature is an example of such a feature. The stub's reply should be independent of the gdbfeature entries sent by gdb; first gdb describes all the features it supports, and then the stub replies with all the features it supports.
Similarly, gdb will silently ignore unrecognized stub feature responses, as long as each response uses one of the standard forms.
Some features are flags. A stub which supports a flag feature should respond with a ‘+’ form response. Other features require values, and the stub should respond with an ‘=’ form response.
Each feature has a default value, which gdb will use if ‘qSupported’ is not available or if the feature is not mentioned in the ‘qSupported’ response. The default values are fixed; a stub is free to omit any feature responses that match the defaults.
Not all features can be probed, but for those which can, the probing mechanism is useful: in some cases, a stub's internal architecture may not allow the protocol layer to know some information about the underlying target in advance. This is especially common in stubs which may be configured for multiple targets.
These are the currently defined stub features and their properties:
Feature Name | Value Required | Default | Probe Allowed
|
‘PacketSize’ | Yes | ‘-’ | No
|
‘qXfer:auxv:read’ | No | ‘-’ | Yes
|
‘qXfer:features:read’ | No | ‘-’ | Yes
|
‘qXfer:libraries:read’ | No | ‘-’ | Yes
|
‘qXfer:memory-map:read’ | No | ‘-’ | Yes
|
‘qXfer:sdata:read’ | No | ‘-’ | Yes
|
‘qXfer:spu:read’ | No | ‘-’ | Yes
|
‘qXfer:spu:write’ | No | ‘-’ | Yes
|
‘qXfer:siginfo:read’ | No | ‘-’ | Yes
|
‘qXfer:siginfo:write’ | No | ‘-’ | Yes
|
‘qXfer:threads:read’ | No | ‘-’ | Yes
|
‘qXfer:traceframe-info:read’ | No | ‘-’ | Yes
|
‘QNonStop’ | No | ‘-’ | Yes
|
‘QPassSignals’ | No | ‘-’ | Yes
|
‘QStartNoAckMode’ | No | ‘-’ | Yes
|
‘multiprocess’ | No | ‘-’ | No
|
‘ConditionalTracepoints’ | No | ‘-’ | No
|
‘ReverseContinue’ | No | ‘-’ | No
|
‘ReverseStep’ | No | ‘-’ | No
|
‘TracepointSource’ | No | ‘-’ | No
|
‘QAllow’ | No | ‘-’ | No
|
These are the currently defined stub features, in more detail:
Reply:
sym_name (hex encoded) is the name of a symbol whose value the target has previously requested.
sym_value (hex) is the value for symbol sym_name. If gdb cannot supply a value for sym_name, then this field will be empty.
Reply:
info threads
display. Some
examples of possible thread extra info strings are ‘Runnable’, or
‘Blocked on Mutex’.
Reply:
(Note that the qThreadExtraInfo
packet's name is separated from
the command by a ‘,’, not a ‘:’, contrary to the naming
conventions above. Please don't use this packet as a model for new
packets.)
Here are the specific requests of this form defined so far. All ‘qXfer:object:read:...’ requests use the same reply formats, listed below.
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
Targets which maintain a list of libraries in the program's memory do not need to implement this packet; it is designed for platforms where the operating system manages the list of loaded libraries.
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response
(see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response
(see qSupported).
spufs
file on the target system. The
annex specifies which file to read; it must be of the form
id/name, where id specifies an SPU context ID
in the target process, and name identifes the spufs
file
in that context to be accessed.
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response
(see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
Reply:
errno
value.
Here are the specific requests of this form defined so far. All ‘qXfer:object:write:...’ requests use the same reply formats, listed below.
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response
(see qSupported).
spufs
file on the target system. The
annex specifies which file to write; it must be of the form
id/name, where id specifies an SPU context ID
in the target process, and name identifes the spufs
file
in that context to be accessed.
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported).
Reply:
errno
value.
This query is used, for example, to know whether the remote process
should be detached or killed when a gdb session is ended with
the quit
command.
Reply:
This section describes how the remote protocol is applied to specific target architectures. Also see Standard Target Features, for details of XML target descriptions for each architecture.
These breakpoint kinds are defined for the ‘Z0’ and ‘Z1’ packets.
The following g
/G
packets have previously been defined.
In the below, some thirty-two bit registers are transferred as
sixty-four bits. Those registers should be zero/sign extended (which?)
to fill the space allocated. Register bytes are transferred in target
byte order. The two nibbles within a register byte are transferred
most-significant - least-significant.
sr
). The ordering is the same
as MIPS32
.
Here we describe the packets gdb uses to implement tracepoints (see Tracepoints).
Replies:
In the series of action packets for a given tracepoint, at most one can have an ‘S’ before its first action. If such a packet is sent, it and the following packets define “while-stepping” actions. Any prior packets define ordinary actions — that is, those taken when the tracepoint is first hit. If no action packet has an ‘S’, then all the packets in the series specify ordinary tracepoint actions.
The ‘action...’ portion of the packet is a series of actions, concatenated without separators. Each action has one of the following forms:
Any number of actions may be packed together in a single ‘QTDP’ packet, as long as the packet does not exceed the maximum packet length (400 bytes, for many stubs). There may be only one ‘R’ action per tracepoint, and it must precede any ‘M’ or ‘X’ actions. Any registers referred to by ‘M’ and ‘X’ actions must be collected by a preceding ‘R’ action. (The “while-stepping” actions are treated as if they were attached to a separate tracepoint, as far as these restrictions are concerned.)
Replies:
start is the offset of the bytes within the overall source string, while slen is the total length of the source string. This is intended for handling source strings that are longer than will fit in a single packet.
The available string types are ‘at’ for the location, ‘cond’ for the conditional, and ‘cmd’ for an action command. gdb sends a separate packet for each command in the action list, in the same order in which the commands are stored in the list.
The target does not need to do anything with source strings except report them back as part of the replies to the ‘qTfP’/‘qTsP’ query packets.
Although this packet is optional, and gdb will only send it
if the target replies with ‘TracepointSource’ See General Query Packets, it makes both disconnected tracing and trace files
much easier to use. Otherwise the user must be careful that the
tracepoints in effect while looking at trace frames are identical to
the ones in effect during the trace run; even a small discrepancy
could cause ‘tdump’ not to work, or a particular trace frame not
be found.
A successful reply from the stub indicates that the stub has found the requested frame. The response is a series of parts, concatenated without separators, describing the frame we selected. Each part has one of the following forms:
gdb uses this to mark read-only regions of memory, like those
containing program code. Since these areas never change, they should
still have the same contents they did when the tracepoint was hit, so
there's no reason for the stub to refuse to provide their contents.
The reply has the form:
1
if the trace is presently
running, or 0
if not. It is followed by semicolon-separated
optional fields that an agent may use to report additional status.
If the trace is not running, the agent may report any of several explanations as one of the optional fields:
Additional optional fields supply statistical and other information. Although not required, they are extremely useful for users monitoring the progress of a trace run. If a trace has stopped, and these numbers are reported, they must reflect the state of the just-stopped trace.
1
means that the
trace buffer is circular and old trace frames will be discarded if
necessary to make room, 0
means that the trace buffer is linear
and may fill up.
1
means that
tracing will continue after gdb disconnects, 0
means
that the trace run will stop.
Replies:
qTfP
to get the first piece
of data, and multiple qTsP
to get additional pieces. Replies
to these packets generally take the form of the QTDP
packets
that define tracepoints. (FIXME add detailed syntax)
qTfV
to get the first vari of data,
and multiple qTsV
to get additional variables. Replies to
these packets follow the syntax of the QTDV
packets that define
trace state variables.
qTfSTM
to get the
first piece of data, and multiple qTsSTM
to get additional
pieces. Replies to these packets take the following form:
Reply:
address is encoded in hex. id and extra are strings encoded in hex.
In response to each query, the target will reply with a list of one or
more markers, separated by commas. gdb will respond to each
reply with a request for more markers (using the ‘qs’ form of the
query), until the target responds with ‘l’ (lower-case ell, for
last).
qTsSTM
packets that list static
tracepoint markers.
l
indicates that no bytes are
available.
When installing fast tracepoints in memory, the target may need to relocate the instruction currently at the tracepoint address to a different address in memory. For most instructions, a simple copy is enough, but, for example, call instructions that implicitly push the return address on the stack, and relative branches or other PC-relative instructions require offset adjustment, so that the effect of executing the instruction at a different address is the same as if it had executed in the original location.
In response to several of the tracepoint packets, the target may also respond with a number of intermediate ‘qRelocInsn’ request packets before the final result packet, to have gdb handle this relocation operation. If a packet supports this mechanism, its documentation will explicitly say so. See for example the above descriptions for the ‘QTStart’ and ‘QTDP’ packets. The format of the request is:
Replies:
The Host I/O packets allow gdb to perform I/O operations on the far side of a remote link. For example, Host I/O is used to upload and download files to a remote target with its own filesystem. Host I/O uses the same constant values and data structure layout as the target-initiated File-I/O protocol. However, the Host I/O packets are structured differently. The target-initiated protocol relies on target memory to store parameters and buffers. Host I/O requests are initiated by gdb, and the target's memory is not involved. See File-I/O Remote Protocol Extension, for more details on the target-initiated protocol.
The Host I/O request packets all encode a single operation along with its arguments. They have this format:
The valid responses to Host I/O packets are:
These are the supported Host I/O operations:
The data read should be returned as a binary attachment on success.
If zero bytes were read, the response should include an empty binary
attachment (i.e. a trailing semicolon). The return value is the
number of target bytes read; the binary attachment may be longer if
some characters were escaped.
write
system calls, there is no
separate count argument; the length of data in the
packet is used. ‘vFile:write’ returns the number of bytes written,
which may be shorter than the length of data, or -1 if an
error occurred.
When a program on the remote target is running, gdb may
attempt to interrupt it by sending a ‘Ctrl-C’, BREAK
or
a BREAK
followed by g
,
control of which is specified via gdb's ‘interrupt-sequence’.
The precise meaning of BREAK
is defined by the transport
mechanism and may, in fact, be undefined. gdb does not
currently define a BREAK
mechanism for any of the network
interfaces except for TCP, in which case gdb sends the
telnet
BREAK sequence.
‘Ctrl-C’, on the other hand, is defined and implemented for all
transport mechanisms. It is represented by sending the single byte
0x03
without any of the usual packet overhead described in
the Overview section (see Overview). When a 0x03
byte is
transmitted as part of a packet, it is considered to be packet data
and does not represent an interrupt. E.g., an ‘X’ packet
(see X packet), used for binary downloads, may include an unescaped
0x03
as part of its packet.
BREAK
followed by g
is also known as Magic SysRq g.
When Linux kernel receives this sequence from serial port,
it stops execution and connects to gdb.
Stubs are not required to recognize these interrupt mechanisms and the precise meaning associated with receipt of the interrupt is implementation defined. If the target supports debugging of multiple threads and/or processes, it should attempt to interrupt all currently-executing threads and processes. If the stub is successful at interrupting the running program, it should send one of the stop reply packets (see Stop Reply Packets) to gdb as a result of successfully stopping the program in all-stop mode, and a stop reply for each stopped thread in non-stop mode. Interrupts received while the program is stopped are discarded.
The gdb remote serial protocol includes notifications, packets that require no acknowledgment. Both the GDB and the stub may send notifications (although the only notifications defined at present are sent by the stub). Notifications carry information without incurring the round-trip latency of an acknowledgment, and so are useful for low-impact communications where occasional packet loss is not a problem.
A notification packet has the form ‘% data # checksum’, where data is the content of the notification, and checksum is a checksum of data, computed and formatted as for ordinary gdb packets. A notification's data never contains ‘$’, ‘%’ or ‘#’ characters. Upon receiving a notification, the recipient sends no ‘+’ or ‘-’ to acknowledge the notification's receipt or to report its corruption.
Every notification's data begins with a name, which contains no colon characters, followed by a colon character.
Recipients should silently ignore corrupted notifications and notifications they do not understand. Recipients should restart timeout periods on receipt of a well-formed notification, whether or not they understand it.
Senders should only send the notifications described here when this protocol description specifies that they are permitted. In the future, we may extend the protocol to permit existing notifications in new contexts; this rule helps older senders avoid confusing newer recipients.
(Older versions of gdb ignore bytes received until they see the ‘$’ byte that begins an ordinary packet, so new stubs may transmit notifications without fear of confusing older clients. There are no notifications defined for gdb to send at the moment, but we assume that most older stubs would ignore them, as well.)
The following notification packets from the stub to gdb are defined:
gdb's remote protocol supports non-stop debugging of multi-threaded programs, as described in Non-Stop Mode. If the stub supports non-stop mode, it should report that to gdb by including ‘QNonStop+’ in its ‘qSupported’ response (see qSupported).
gdb typically sends a ‘QNonStop’ packet only when establishing a new connection with the stub. Entering non-stop mode does not alter the state of any currently-running threads, but targets must stop all threads in any already-attached processes when entering all-stop mode. gdb uses the ‘?’ packet as necessary to probe the target state after a mode change.
In non-stop mode, when an attached process encounters an event that would otherwise be reported with a stop reply, it uses the asynchronous notification mechanism (see Notification Packets) to inform gdb. In contrast to all-stop mode, where all threads in all processes are stopped when a stop reply is sent, in non-stop mode only the thread reporting the stop event is stopped. That is, when reporting a ‘S’ or ‘T’ response to indicate completion of a step operation, hitting a breakpoint, or a fault, only the affected thread is stopped; any other still-running threads continue to run. When reporting a ‘W’ or ‘X’ response, all running threads belonging to other attached processes continue to run.
Only one stop reply notification at a time may be pending; if additional stop events occur before gdb has acknowledged the previous notification, they must be queued by the stub for later synchronous transmission in response to ‘vStopped’ packets from gdb. Because the notification mechanism is unreliable, the stub is permitted to resend a stop reply notification if it believes gdb may not have received it. gdb ignores additional stop reply notifications received before it has finished processing a previous notification and the stub has completed sending any queued stop events.
Otherwise, gdb must be prepared to receive a stop reply notification at any time. Specifically, they may appear when gdb is not otherwise reading input from the stub, or when gdb is expecting to read a normal synchronous response or a ‘+’/‘-’ acknowledgment to a packet it has sent. Notification packets are distinct from any other communication from the stub so there is no ambiguity.
After receiving a stop reply notification, gdb shall acknowledge it by sending a ‘vStopped’ packet (see vStopped packet) as a regular, synchronous request to the stub. Such acknowledgment is not required to happen immediately, as gdb is permitted to send other, unrelated packets to the stub first, which the stub should process normally.
Upon receiving a ‘vStopped’ packet, if the stub has other queued stop events to report to gdb, it shall respond by sending a normal stop reply response. gdb shall then send another ‘vStopped’ packet to solicit further responses; again, it is permitted to send other, unrelated packets as well which the stub should process normally.
If the stub receives a ‘vStopped’ packet and there are no additional stop events to report, the stub shall return an ‘OK’ response. At this point, if further stop events occur, the stub shall send a new stop reply notification, gdb shall accept the notification, and the process shall be repeated.
In non-stop mode, the target shall respond to the ‘?’ packet as follows. First, any incomplete stop reply notification/‘vStopped’ sequence in progress is abandoned. The target must begin a new sequence reporting stop events for all stopped threads, whether or not it has previously reported those events to gdb. The first stop reply is sent as a synchronous reply to the ‘?’ packet, and subsequent stop replies are sent as responses to ‘vStopped’ packets using the mechanism described above. The target must not send asynchronous stop reply notifications until the sequence is complete. If all threads are running when the target receives the ‘?’ packet, or if the target is not attached to any process, it shall respond ‘OK’.
By default, when either the host or the target machine receives a packet, the first response expected is an acknowledgment: either ‘+’ (to indicate the package was received correctly) or ‘-’ (to request retransmission). This mechanism allows the gdb remote protocol to operate over unreliable transport mechanisms, such as a serial line.
In cases where the transport mechanism is itself reliable (such as a pipe or TCP connection), the ‘+’/‘-’ acknowledgments are redundant. It may be desirable to disable them in that case to reduce communication overhead, or for other reasons. This can be accomplished by means of the ‘QStartNoAckMode’ packet; see QStartNoAckMode.
When in no-acknowledgment mode, neither the stub nor gdb shall send or expect ‘+’/‘-’ protocol acknowledgments. The packet and response format still includes the normal checksum, as described in Overview, but the checksum may be ignored by the receiver.
If the stub supports ‘QStartNoAckMode’ and prefers to operate in
no-acknowledgment mode, it should report that to gdb
by including ‘QStartNoAckMode+’ in its response to ‘qSupported’;
see qSupported.
If gdb also supports ‘QStartNoAckMode’ and it has not been
disabled via the set remote noack-packet off
command
(see Remote Configuration),
gdb may then send a ‘QStartNoAckMode’ packet to the stub.
Only then may the stub actually turn off packet acknowledgments.
gdb sends a final ‘+’ acknowledgment of the stub's ‘OK’
response, which can be safely ignored by the stub.
Note that set remote noack-packet
command only affects negotiation
between gdb and the stub when subsequent connections are made;
it does not affect the protocol acknowledgment state for any current
connection.
Since ‘+’/‘-’ acknowledgments are enabled by default when a
new connection is established,
there is also no protocol request to re-enable the acknowledgments
for the current connection, once disabled.
Example sequence of a target being re-started. Notice how the restart does not get any direct output:
->R00
<-+
target restarts ->?
<-+
<-T001:1234123412341234
->+
Example sequence of a target being stepped by a single instruction:
->G1445...
<-+
->s
<-+
time passes <-T001:1234123412341234
->+
->g
<-+
<-1455...
->+
The File I/O remote protocol extension (short: File-I/O) allows the target to use the host's file system and console I/O to perform various system calls. System calls on the target system are translated into a remote protocol packet to the host system, which then performs the needed actions and returns a response packet to the target system. This simulates file system operations even on targets that lack file systems.
The protocol is defined to be independent of both the host and target systems. It uses its own internal representation of datatypes and values. Both gdb and the target's gdb stub are responsible for translating the system-dependent value representations into the internal protocol representations when data is transmitted.
The communication is synchronous. A system call is possible only when gdb is waiting for a response from the ‘C’, ‘c’, ‘S’ or ‘s’ packets. While gdb handles the request for a system call, the target is stopped to allow deterministic access to the target's memory. Therefore File-I/O is not interruptible by target signals. On the other hand, it is possible to interrupt File-I/O by a user interrupt (‘Ctrl-C’) within gdb.
The target's request to perform a host system call does not finish the latest ‘C’, ‘c’, ‘S’ or ‘s’ action. That means, after finishing the system call, the target returns to continuing the previous activity (continue, step). No additional continue or step request from gdb is required.
(gdb) continue <- target requests 'system call X' target is stopped, gdb executes system call -> gdb returns result ... target continues, gdb returns to wait for the target <- target hits breakpoint and sends a Txx packet
The protocol only supports I/O on the console and to regular files on the host file system. Character or block special devices, pipes, named pipes, sockets or any other communication method on the host system are not supported by this protocol.
File I/O is not supported in non-stop mode.
The File-I/O protocol uses the F
packet as the request as well
as reply packet. Since a File-I/O system call can only occur when
gdb is waiting for a response from the continuing or stepping target,
the File-I/O request is a reply that gdb has to expect as a result
of a previous ‘C’, ‘c’, ‘S’ or ‘s’ packet.
This F
packet contains all information needed to allow gdb
to call the appropriate host system call:
At this point, gdb has to perform the following actions.
m
packet request. This additional communication has to be
expected by the target implementation and is handled as any other m
packet.
M
or X
packet. This packet has to be expected
by the target implementation and is handled as any other M
or X
packet.
Eventually gdb replies with another F
packet which contains all
necessary information for the target to continue. This at least contains
errno
, if has been changed by the system call.
After having done the needed type and value coercion, the target continues the latest continue or step action.
F
Request Packet
The F
request packet has the following format:
parameter... are the parameters to the system call. Parameters are hexadecimal integer values, either the actual values in case of scalar datatypes, pointers to target buffer space in case of compound datatypes and unspecified memory areas, or pointer/length pairs in case of string parameters. These are appended to the call-id as a comma-delimited list. All values are transmitted in ASCII string representation, pointer/length pairs separated by a slash.
F
Reply Packet
The F
reply packet has the following format:
errno is the errno
set by the call, in protocol-specific
representation.
This parameter can be omitted if the call was successful.
Ctrl-C flag is only sent if the user requested a break. In this case, errno must be sent as well, even if the call was successful. The Ctrl-C flag itself consists of the character ‘C’:
F0,0,C
or, if the call was interrupted before the host call has been performed:
F-1,4,C
assuming 4 is the protocol-specific representation of EINTR
.
If the ‘Ctrl-C’ flag is set in the gdb
reply packet (see The F Reply Packet),
the target should behave as if it had
gotten a break message. The meaning for the target is “system call
interrupted by SIGINT
”. Consequentially, the target should actually stop
(as with a break message) and return to gdb with a T02
packet.
It's important for the target to know in which state the system call was interrupted. There are two possible cases:
These two states can be distinguished by the target by the value of the
returned errno
. If it's the protocol representation of EINTR
, the system
call hasn't been performed. This is equivalent to the EINTR
handling
on POSIX systems. In any other case, the target may presume that the
system call has been finished — successfully or not — and should behave
as if the break message arrived right after the system call.
gdb must behave reliably. If the system call has not been called
yet, gdb may send the F
reply immediately, setting EINTR
as
errno
in the packet. If the system call on the host has been finished
before the user requests a break, the full action must be finished by
gdb. This requires sending M
or X
packets as necessary.
The F
packet may only be sent when either nothing has happened
or the full action has been completed.
By default and if not explicitly closed by the target system, the file
descriptors 0, 1 and 2 are connected to the gdb console. Output
on the gdb console is handled as any other file output operation
(write(1, ...)
or write(2, ...)
). Console input is handled
by gdb so that after the target read request from file descriptor
0 all following typing is buffered until either one of the following
conditions is met:
read
system call is treated as finished.
If the user has typed more characters than fit in the buffer given to
the read
call, the trailing characters are buffered in gdb until
either another read(0, ...)
is requested by the target, or debugging
is stopped at the user's request.
int open(const char *pathname, int flags); int open(const char *pathname, int flags, mode_t mode);
flags is the bitwise OR
of the following values:
O_CREAT
O_EXCL
O_CREAT
, if the file already exists it is
an error and open() fails.
O_TRUNC
O_RDWR
or O_WRONLY
is given) it will be
truncated to zero length.
O_APPEND
O_RDONLY
O_WRONLY
O_RDWR
Other bits are silently ignored.
mode is the bitwise OR
of the following values:
S_IRUSR
S_IWUSR
S_IRGRP
S_IWGRP
S_IROTH
S_IWOTH
Other bits are silently ignored.
open
returns the new file descriptor or -1 if an error
occurred.
EEXIST
O_CREAT
and O_EXCL
were used.
EISDIR
EACCES
ENAMETOOLONG
ENOENT
ENODEV
EROFS
EFAULT
ENOSPC
EMFILE
ENFILE
EINTR
int close(int fd);
close
returns zero on success, or -1 if an error occurred.
EBADF
EINTR
int read(int fd, void *buf, unsigned int count);
EBADF
EFAULT
EINTR
int write(int fd, const void *buf, unsigned int count);
EBADF
EFAULT
EFBIG
ENOSPC
EINTR
long lseek (int fd, long offset, int flag);
flag is one of:
SEEK_SET
SEEK_CUR
SEEK_END
EBADF
ESPIPE
EINVAL
EINTR
int rename(const char *oldpath, const char *newpath);
EISDIR
EEXIST
EBUSY
EINVAL
ENOTDIR
EFAULT
EACCES
ENAMETOOLONG
ENOENT
EROFS
ENOSPC
EINTR
int unlink(const char *pathname);
EACCES
EPERM
EBUSY
EFAULT
ENAMETOOLONG
ENOENT
ENOTDIR
EROFS
EINTR
int stat(const char *pathname, struct stat *buf); int fstat(int fd, struct stat *buf);
EBADF
ENOENT
ENOTDIR
EFAULT
EACCES
ENAMETOOLONG
EINTR
int gettimeofday(struct timeval *tv, void *tz);
EINVAL
EFAULT
int isatty(int fd);
EINTR
Note that the isatty
call is treated as a special case: it returns
1 to the target if the file descriptor is attached
to the gdb console, 0 otherwise. Implementing through system calls
would require implementing ioctl
and would be more complex than
needed.
int system(const char *command);
system
return value by calling WEXITSTATUS(retval)
. In case
/bin/sh could not be executed, 127 is returned.
EINTR
gdb takes over the full task of calling the necessary host calls
to perform the system
call. The return value of system
on
the host is simplified before it's returned
to the target. Any termination signal information from the child process
is discarded, and the return value consists
entirely of the exit status of the called command.
Due to security concerns, the system
call is by default refused
by gdb. The user has to allow this call explicitly with the
set remote system-call-allowed 1
command.
set remote system-call-allowed
system
calls in the File I/O
protocol for the remote target. The default is zero (disabled).
show remote system-call-allowed
system
calls are allowed in the File I/O
protocol.
The integral datatypes used in the system calls are int
,
unsigned int
, long
, unsigned long
,
mode_t
, and time_t
.
int
, unsigned int
, mode_t
and time_t
are
implemented as 32 bit values in this protocol.
long
and unsigned long
are implemented as 64 bit types.
See Limits, for corresponding MIN and MAX values (similar to those in limits.h) to allow range checking on host and target.
time_t
datatypes are defined as seconds since the Epoch.
All integral datatypes transferred as part of a memory read or write of a
structured datatype e.g. a struct stat
have to be given in big endian
byte order.
Pointers to target data are transmitted as they are. An exception is made for pointers to buffers for which the length isn't transmitted as part of the function call, namely strings. Strings are transmitted as a pointer/length pair, both as hex values, e.g.
1aaf/12
which is a pointer to data of length 18 bytes at position 0x1aaf.
The length is defined as the full string length in bytes, including
the trailing null byte. For example, the string "hello world"
at address 0x123456 is transmitted as
123456/d
Structured data which is transferred using a memory read or write (for
example, a struct stat
) is expected to be in a protocol-specific format
with all scalar multibyte datatypes being big endian. Translation to
this representation needs to be done both by the target before the F
packet is sent, and by gdb before
it transfers memory to the target. Transferred pointers to structured
data should point to the already-coerced data at any time.
The buffer of type struct stat
used by the target and gdb
is defined as follows:
struct stat { unsigned int st_dev; /* device */ unsigned int st_ino; /* inode */ mode_t st_mode; /* protection */ unsigned int st_nlink; /* number of hard links */ unsigned int st_uid; /* user ID of owner */ unsigned int st_gid; /* group ID of owner */ unsigned int st_rdev; /* device type (if inode device) */ unsigned long st_size; /* total size, in bytes */ unsigned long st_blksize; /* blocksize for filesystem I/O */ unsigned long st_blocks; /* number of blocks allocated */ time_t st_atime; /* time of last access */ time_t st_mtime; /* time of last modification */ time_t st_ctime; /* time of last change */ };
The integral datatypes conform to the definitions given in the appropriate section (see Integral Datatypes, for details) so this structure is of size 64 bytes.
The values of several fields have a restricted meaning and/or range of values.
st_dev
st_ino
st_mode
st_uid
st_gid
st_rdev
st_atime
st_mtime
st_ctime
The target gets a struct stat
of the above representation and is
responsible for coercing it to the target representation before
continuing.
Note that due to size differences between the host, target, and protocol
representations of struct stat
members, these members could eventually
get truncated on the target.
The buffer of type struct timeval
used by the File-I/O protocol
is defined as follows:
struct timeval { time_t tv_sec; /* second */ long tv_usec; /* microsecond */ };
The integral datatypes conform to the definitions given in the appropriate section (see Integral Datatypes, for details) so this structure is of size 8 bytes.
The following values are used for the constants inside of the protocol. gdb and target are responsible for translating these values before and after the call as needed.
All values are given in hexadecimal representation.
O_RDONLY 0x0 O_WRONLY 0x1 O_RDWR 0x2 O_APPEND 0x8 O_CREAT 0x200 O_TRUNC 0x400 O_EXCL 0x800
All values are given in octal representation.
S_IFREG 0100000 S_IFDIR 040000 S_IRUSR 0400 S_IWUSR 0200 S_IXUSR 0100 S_IRGRP 040 S_IWGRP 020 S_IXGRP 010 S_IROTH 04 S_IWOTH 02 S_IXOTH 01
All values are given in decimal representation.
EPERM 1 ENOENT 2 EINTR 4 EBADF 9 EACCES 13 EFAULT 14 EBUSY 16 EEXIST 17 ENODEV 19 ENOTDIR 20 EISDIR 21 EINVAL 22 ENFILE 23 EMFILE 24 EFBIG 27 ENOSPC 28 ESPIPE 29 EROFS 30 ENAMETOOLONG 91 EUNKNOWN 9999
EUNKNOWN
is used as a fallback error value if a host system returns
any error value not in the list of supported error numbers.
SEEK_SET 0 SEEK_CUR 1 SEEK_END 2
All values are given in decimal representation.
INT_MIN -2147483648 INT_MAX 2147483647 UINT_MAX 4294967295 LONG_MIN -9223372036854775808 LONG_MAX 9223372036854775807 ULONG_MAX 18446744073709551615
Example sequence of a write call, file descriptor 3, buffer is at target address 0x1234, 6 bytes should be written:
<-Fwrite,3,1234,6
request memory read from target ->m1234,6
<- XXXXXX return "6 bytes written" ->F6
Example sequence of a read call, file descriptor 3, buffer is at target address 0x1234, 6 bytes should be read:
<-Fread,3,1234,6
request memory write to target ->X1234,6:XXXXXX
return "6 bytes read" ->F6
Example sequence of a read call, call fails on the host due to invalid
file descriptor (EBADF
):
<-Fread,3,1234,6
->F-1,9
Example sequence of a read call, user presses Ctrl-c before syscall on host is called:
<-Fread,3,1234,6
->F-1,4,C
<-T02
Example sequence of a read call, user presses Ctrl-c after syscall on host is called:
<-Fread,3,1234,6
->X1234,6:XXXXXX
<-T02
On some platforms, a dynamic loader (e.g. ld.so) runs in the same process as your application to manage libraries. In this case, gdb can use the loader's symbol table and normal memory operations to maintain a list of shared libraries. On other platforms, the operating system manages loaded libraries. gdb can not retrieve the list of currently loaded libraries through memory operations, so it uses the ‘qXfer:libraries:read’ packet (see qXfer library list read) instead. The remote stub queries the target's operating system and reports which libraries are loaded.
The ‘qXfer:libraries:read’ packet returns an XML document which lists loaded libraries and their offsets. Each library has an associated name and one or more segment or section base addresses, which report where the library was loaded in memory.
For the common case of libraries that are fully linked binaries, the library should have a list of segments. If the target supports dynamic linking of a relocatable object file, its library XML element should instead include a list of allocated sections. The segment or section bases are start addresses, not relocation offsets; they do not depend on the library's link-time base addresses.
gdb must be linked with the Expat library to support XML library lists. See Expat.
A simple memory map, with one loaded library relocated by a single offset, looks like this:
<library-list> <library name="/lib/libc.so.6"> <segment address="0x10000000"/> </library> </library-list>
Another simple memory map, with one loaded library with three allocated sections (.text, .data, .bss), looks like this:
<library-list> <library name="sharedlib.o"> <section address="0x10000000"/> <section address="0x20000000"/> <section address="0x30000000"/> </library> </library-list>
The format of a library list is described by this DTD:
<!-- library-list: Root element with versioning --> <!ELEMENT library-list (library)*> <!ATTLIST library-list version CDATA #FIXED "1.0"> <!ELEMENT library (segment*, section*)> <!ATTLIST library name CDATA #REQUIRED> <!ELEMENT segment EMPTY> <!ATTLIST segment address CDATA #REQUIRED> <!ELEMENT section EMPTY> <!ATTLIST section address CDATA #REQUIRED>
In addition, segments and section descriptors cannot be mixed within a single library element, and you must supply at least one segment or section for each library.
To be able to write into flash memory, gdb needs to obtain a memory map from the target. This section describes the format of the memory map.
The memory map is obtained using the ‘qXfer:memory-map:read’ (see qXfer memory map read) packet and is an XML document that lists memory regions.
gdb must be linked with the Expat library to support XML memory maps. See Expat.
The top-level structure of the document is shown below:
<?xml version="1.0"?> <!DOCTYPE memory-map PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN" "http://sourceware.org/gdb/gdb-memory-map.dtd"> <memory-map> region... </memory-map>
Each region can be either:
<memory type="ram" start="addr" length="length"/>
<memory type="rom" start="addr" length="length"/>
<memory type="flash" start="addr" length="length"> <property name="blocksize">blocksize</property> </memory>
Regions must not overlap. gdb assumes that areas of memory not covered by the memory map are RAM, and uses the ordinary ‘M’ and ‘X’ packets to write to addresses in such ranges.
The formal DTD for memory map format is given below:
<!-- ................................................... --> <!-- Memory Map XML DTD ................................ --> <!-- File: memory-map.dtd .............................. --> <!-- .................................... .............. --> <!-- memory-map.dtd --> <!-- memory-map: Root element with versioning --> <!ELEMENT memory-map (memory | property)> <!ATTLIST memory-map version CDATA #FIXED "1.0.0"> <!ELEMENT memory (property)> <!-- memory: Specifies a memory region, and its type, or device. --> <!ATTLIST memory type CDATA #REQUIRED start CDATA #REQUIRED length CDATA #REQUIRED device CDATA #IMPLIED> <!-- property: Generic attribute tag --> <!ELEMENT property (#PCDATA | property)*> <!ATTLIST property name CDATA #REQUIRED>
To efficiently update the list of threads and their attributes, gdb issues the ‘qXfer:threads:read’ packet (see qXfer threads read) and obtains the XML document with the following structure:
<?xml version="1.0"?> <threads> <thread id="id" core="0"> ... description ... </thread> </threads>
Each ‘thread’ element must have the ‘id’ attribute that identifies the thread (see thread-id syntax). The ‘core’ attribute, if present, specifies which processor core the thread was last executing on. The content of the of ‘thread’ element is interpreted as human-readable auxilliary information.
To be able to know which objects in the inferior can be examined when inspecting a tracepoint hit, gdb needs to obtain the list of memory ranges, registers and trace state variables that have been collected in a traceframe.
This list is obtained using the ‘qXfer:traceframe-info:read’ (see qXfer traceframe info read) packet and is an XML document.
gdb must be linked with the Expat library to support XML traceframe info discovery. See Expat.
The top-level structure of the document is shown below:
<?xml version="1.0"?> <!DOCTYPE traceframe-info PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN" "http://sourceware.org/gdb/gdb-traceframe-info.dtd"> <traceframe-info> block... </traceframe-info>
Each traceframe block can be either:
<memory start="addr" length="length"/>
The formal DTD for the traceframe info format is given below:
<!ELEMENT traceframe-info (memory)* > <!ATTLIST traceframe-info version CDATA #FIXED "1.0"> <!ELEMENT memory EMPTY> <!ATTLIST memory start CDATA #REQUIRED length CDATA #REQUIRED>
In some applications, it is not feasible for the debugger to interrupt the program's execution long enough for the developer to learn anything helpful about its behavior. If the program's correctness depends on its real-time behavior, delays introduced by a debugger might cause the program to fail, even when the code itself is correct. It is useful to be able to observe the program's behavior without interrupting it.
Using GDB's trace
and collect
commands, the user can
specify locations in the program, and arbitrary expressions to evaluate
when those locations are reached. Later, using the tfind
command, she can examine the values those expressions had when the
program hit the trace points. The expressions may also denote objects
in memory — structures or arrays, for example — whose values GDB
should record; while visiting a particular tracepoint, the user may
inspect those objects as if they were in memory at that moment.
However, because GDB records these values without interacting with the
user, it can do so quickly and unobtrusively, hopefully not disturbing
the program's behavior.
When GDB is debugging a remote target, the GDB agent code running on the target computes the values of the expressions itself. To avoid having a full symbolic expression evaluator on the agent, GDB translates expressions in the source language into a simpler bytecode language, and then sends the bytecode to the agent; the agent then executes the bytecode, and records the values for GDB to retrieve later.
The bytecode language is simple; there are forty-odd opcodes, the bulk of which are the usual vocabulary of C operands (addition, subtraction, shifts, and so on) and various sizes of literals and memory reference operations. The bytecode interpreter operates strictly on machine-level values — various sizes of integers and floating point numbers — and requires no information about types or symbols; thus, the interpreter's internal data structures are simple, and each bytecode requires only a few native machine instructions to implement it. The interpreter is small, and strict limits on the memory and time required to evaluate an expression are easy to determine, making it suitable for use by the debugging agent in real-time applications.
The agent represents bytecode expressions as an array of bytes. Each
instruction is one byte long (thus the term bytecode). Some
instructions are followed by operand bytes; for example, the goto
instruction is followed by a destination for the jump.
The bytecode interpreter is a stack-based machine; most instructions pop their operands off the stack, perform some operation, and push the result back on the stack for the next instruction to consume. Each element of the stack may contain either a integer or a floating point value; these values are as many bits wide as the largest integer that can be directly manipulated in the source language. Stack elements carry no record of their type; bytecode could push a value as an integer, then pop it as a floating point value. However, GDB will not generate code which does this. In C, one might define the type of a stack element as follows:
union agent_val { LONGEST l; DOUBLEST d; };
where LONGEST
and DOUBLEST
are typedef
names for
the largest integer and floating point types on the machine.
By the time the bytecode interpreter reaches the end of the expression,
the value of the expression should be the only value left on the stack.
For tracing applications, trace
bytecodes in the expression will
have recorded the necessary data, and the value on the stack may be
discarded. For other applications, like conditional breakpoints, the
value may be useful.
Separate from the stack, the interpreter has two registers:
pc
start
goto
and if_goto
instructions.
There are no instructions to perform side effects on the running program, or call the program's functions; we assume that these expressions are only used for unobtrusive debugging, not for patching the running code.
Most bytecode instructions do not distinguish between the various sizes of values, and operate on full-width values; the upper bits of the values are simply ignored, since they do not usually make a difference to the value computed. The exceptions to this rule are:
ref
n)ext
instruction
exists for this purpose.
ext
n)If the interpreter is unable to evaluate an expression completely for some reason (a memory location is inaccessible, or a divisor is zero, for example), we say that interpretation “terminates with an error”. This means that the problem is reported back to the interpreter's caller in some helpful way. In general, code using agent expressions should assume that they may attempt to divide by zero, fetch arbitrary memory locations, and misbehave in other ways.
Even complicated C expressions compile to a few bytecode instructions;
for example, the expression x + y * z
would typically produce
code like the following, assuming that x
and y
live in
registers, and z
is a global variable holding a 32-bit
int
:
reg 1 reg 2 const32 address of z ref32 ext 32 mul add end
In detail, these mean:
reg 1
x
) onto the
stack.
reg 2
y
).
const32
address of zz
onto the stack.
ref32
z
with z
's value.
ext 32
z
is a signed integer.
mul
y * z
.
add
x + y * z
.
end
Each bytecode description has the following form:
add
(0x02): a b ⇒ a+bIn this example, add
is the name of the bytecode, and
(0x02)
is the one-byte value used to encode the bytecode, in
hexadecimal. The phrase “a b ⇒ a+b” shows
the stack before and after the bytecode executes. Beforehand, the stack
must contain at least two values, a and b; since the top of
the stack is to the right, b is on the top of the stack, and
a is underneath it. After execution, the bytecode will have
popped a and b from the stack, and replaced them with a
single value, a+b. There may be other values on the stack below
those shown, but the bytecode affects only those shown.
Here is another example:
const8
(0x22) n: ⇒ nIn this example, the bytecode const8
takes an operand n
directly from the bytecode stream; the operand follows the const8
bytecode itself. We write any such operands immediately after the name
of the bytecode, before the colon, and describe the exact encoding of
the operand in the bytecode stream in the body of the bytecode
description.
For the const8
bytecode, there are no stack items given before
the ⇒; this simply means that the bytecode consumes no values
from the stack. If a bytecode consumes no values, or produces no
values, the list on either side of the ⇒ may be empty.
If a value is written as a, b, or n, then the bytecode treats it as an integer. If a value is written is addr, then the bytecode treats it as an address.
We do not fully describe the floating point operations here; although this design can be extended in a clean way to handle floating point values, they are not of immediate interest to the customer, so we avoid describing them, to save time.
float
(0x01): ⇒add
(0x02): a b ⇒ a+bsub
(0x03): a b ⇒ a-bmul
(0x04): a b ⇒ a*bdiv_signed
(0x05): a b ⇒ a/bdiv_unsigned
(0x06): a b ⇒ a/brem_signed
(0x07): a b ⇒ a modulo brem_unsigned
(0x08): a b ⇒ a modulo blsh
(0x09): a b ⇒ a<<brsh_signed
(0x0a): a b ⇒ (signed)
a>>brsh_unsigned
(0x0b): a b ⇒ a>>blog_not
(0x0e): a ⇒ !abit_and
(0x0f): a b ⇒ a&band
.
bit_or
(0x10): a b ⇒ a|bor
.
bit_xor
(0x11): a b ⇒ a^bor
.
bit_not
(0x12): a ⇒ ~aequal
(0x13): a b ⇒ a=bless_signed
(0x14): a b ⇒ a<bless_unsigned
(0x15): a b ⇒ a<bext
(0x16) n: a ⇒ a, sign-extended from n bitsThe number of source bits to preserve, n, is encoded as a single
byte unsigned integer following the ext
bytecode.
zero_ext
(0x2a) n: a ⇒ a, zero-extended from n bitsThe number of source bits to preserve, n, is encoded as a single
byte unsigned integer following the zero_ext
bytecode.
ref8
(0x17): addr ⇒ aref16
(0x18): addr ⇒ aref32
(0x19): addr ⇒ aref64
(0x1a): addr ⇒ aref
n, fetch an n-bit value from addr, using the
natural target endianness. Push the fetched value as an unsigned
integer.
Note that addr may not be aligned in any particular way; the
ref
n bytecodes should operate correctly for any address.
If attempting to access memory at addr would cause a processor
exception of some sort, terminate with an error.
ref_float
(0x1b): addr ⇒ dref_double
(0x1c): addr ⇒ dref_long_double
(0x1d): addr ⇒ dl_to_d
(0x1e): a ⇒ dd_to_l
(0x1f): d ⇒ adup
(0x28): a => a aswap
(0x2b): a b => b apop
(0x29): a =>pick
(0x32) n: a ... b => a ... b adup
; if n is one, it copies
the item under the top item, etc. If n exceeds the number of
items on the stack, terminate with an error.
rot
(0x33): a b c => c b aif_goto
(0x20) offset: a ⇒pc
register to start
+ offset.
Thus, an offset of zero denotes the beginning of the expression.
The offset is stored as a sixteen-bit unsigned value, stored
immediately following the if_goto
bytecode. It is always stored
most significant byte first, regardless of the target's normal
endianness. The offset is not guaranteed to fall at any particular
alignment within the bytecode stream; thus, on machines where fetching a
16-bit on an unaligned address raises an exception, you should fetch the
offset one byte at a time.
goto
(0x21) offset: ⇒pc
register to start
+ offset.
The offset is stored in the same way as for the if_goto
bytecode.
const8
(0x22) n: ⇒ nconst16
(0x23) n: ⇒ nconst32
(0x24) n: ⇒ nconst64
(0x25) n: ⇒ next
bytecode.
The constant n is stored in the appropriate number of bytes
following the const
b bytecode. The constant n is
always stored most significant byte first, regardless of the target's
normal endianness. The constant is not guaranteed to fall at any
particular alignment within the bytecode stream; thus, on machines where
fetching a 16-bit on an unaligned address raises an exception, you
should fetch n one byte at a time.
reg
(0x26) n: ⇒ aThe register number n is encoded as a 16-bit unsigned integer
immediately following the reg
bytecode. It is always stored most
significant byte first, regardless of the target's normal endianness.
The register number is not guaranteed to fall at any particular
alignment within the bytecode stream; thus, on machines where fetching a
16-bit on an unaligned address raises an exception, you should fetch the
register number one byte at a time.
getv
(0x2c) n: ⇒ vThe variable number n is encoded as a 16-bit unsigned integer
immediately following the getv
bytecode. It is always stored most
significant byte first, regardless of the target's normal endianness.
The variable number is not guaranteed to fall at any particular
alignment within the bytecode stream; thus, on machines where fetching a
16-bit on an unaligned address raises an exception, you should fetch the
register number one byte at a time.
setv
(0x2d) n: ⇒ vgetv
.
trace
(0x0c): addr size ⇒trace_quick
(0x0d) size: addr ⇒ addrtrace
opcode.
This bytecode is equivalent to the sequence dup const8
size
trace
, but we provide it anyway to save space in bytecode strings.
trace16
(0x30) size: addr ⇒ addrtrace_quick16
, for consistency.
tracev
(0x2e) n: ⇒ agetv
.
end
(0x27): ⇒Agent expressions can be used in several different ways by gdb, and the debugger can generate different bytecode sequences as appropriate.
One possibility is to do expression evaluation on the target rather than the host, such as for the conditional of a conditional tracepoint. In such a case, gdb compiles the source expression into a bytecode sequence that simply gets values from registers or memory, does arithmetic, and returns a result.
Another way to use agent expressions is for tracepoint data
collection. gdb generates a different bytecode sequence for
collection; in addition to bytecodes that do the calculation,
gdb adds trace
bytecodes to save the pieces of
memory that were used.
Some targets don't support floating-point, and some would rather not
have to deal with long long
operations. Also, different targets
will have different stack sizes, and different bytecode buffer lengths.
Thus, GDB needs a way to ask the target about itself. We haven't worked out the details yet, but in general, GDB should be able to send the target a packet asking it to describe itself. The reply should be a packet whose length is explicit, so we can add new information to the packet in future revisions of the agent, without confusing old versions of GDB, and it should contain a version number. It should contain at least the following information:
long long
is supported
Some of the design decisions apparent above are arguable.
First, note that you don't need different bytecodes for different operand sizes. You can generate code without knowing how big the stack elements actually are on the target. If the target only supports 32-bit ints, and you don't send any 64-bit bytecodes, everything just works. The observation here is that the MIPS and the Alpha have only fixed-size registers, and you can still get C's semantics even though most instructions only operate on full-sized words. You just need to make sure everything is properly sign-extended at the right times. So there is no need for 32- and 64-bit variants of the bytecodes. Just implement everything using the largest size you support.
GDB should certainly check to see what sizes the target supports, so the
user can get an error earlier, rather than later. But this information
is not necessary for correctness.
>
or <=
operators?less_
opcodes with log_not
, and swap the order
of the operands, yielding all four asymmetrical comparison operators.
For example, (x <= y)
is ! (x > y)
, which is ! (y <
x)
.
log_not
?ext
?zero_ext
?log_not
is equivalent to const8 0 equal
; it's used in half
the relational operators.
ext
n is equivalent to const8
s-n lsh const8
s-n rsh_signed
, where s is the size of the stack elements;
it follows ref
m and reg bytecodes when the value
should be signed. See the next bulleted item.
zero_ext
n is equivalent to const
m mask
log_and
; it's used whenever we push the value of a register, because we
can't assume the upper bits of the register aren't garbage.
ref
operators?ref
operators, and we
need the ext
bytecode anyway for accessing bitfields.
ref
operators?ref
operators again, and
const32
address ref32
is only one byte longer.
ref
n operators have to support unaligned fetches?In particular, structure bitfields may be several bytes long, but follow no alignment rules; members of packed structures are not necessarily aligned either.
In general, there are many cases where unaligned references occur in
correct C code, either at the programmer's explicit request, or at the
compiler's discretion. Thus, it is simpler to make the GDB agent
bytecodes work correctly in all circumstances than to make GDB guess in
each case whether the compiler did the usual thing.
goto
ops PC-relative?goto
ops?Suppose we have multiple branch ops with different offset sizes. As I generate code left-to-right, all my jumps are forward jumps (there are no loops in expressions), so I never know the target when I emit the jump opcode. Thus, I have to either always assume the largest offset size, or do jump relaxation on the code after I generate it, which seems like a big waste of time.
I can imagine a reasonable expression being longer than 256 bytes. I can't imagine one being longer than 64k. Thus, we need 16-bit offsets. This kind of reasoning is so bogus, but relaxation is pathetic.
The other approach would be to generate code right-to-left. Then I'd
always know my offset size. That might be fun.
reg
bytecode take a 16-bit register number?trace
and trace_quick
?x->y->z
, the agent must record the values of x
and
x->y
as well as the value of x->y->z
.
trace
bytecodes make the interpreter less general?trace
bytecodes, they don't get in
its way.
trace_quick
consume its arguments the way everything else does?trace_quick
is a kludge to save space; it
only exists so we needn't write dup const8
SIZE trace
before every memory reference. Therefore, it's okay for it not to
consume its arguments; it's meant for a specific context in which we
know exactly what it should do with the stack. If we're going to have a
kludge, it should be an effective kludge.
trace16
exist?dup const16
size trace
in those cases.
Whatever we decide to do with trace16
, we should at least leave
opcode 0x30 reserved, to remain compatible with the customer who added
it.
Warning: target descriptions are still under active development, and the contents and format may change between gdb releases. The format is expected to stabilize in the future.
One of the challenges of using gdb to debug embedded systems is that there are so many minor variants of each processor architecture in use. It is common practice for vendors to start with a standard processor core — ARM, PowerPC, or MIPS, for example — and then make changes to adapt it to a particular market niche. Some architectures have hundreds of variants, available from dozens of vendors. This leads to a number of problems:
To address these problems, the gdb remote protocol allows a target system to not only identify itself to gdb, but to actually describe its own features. This lets gdb support processor variants it has never seen before — to the extent that the descriptions are accurate, and that gdb understands them.
gdb must be linked with the Expat library to support XML target descriptions. See Expat.
Target descriptions can be read from the target automatically, or specified by the user manually. The default behavior is to read the description from the target. gdb retrieves it via the remote protocol using ‘qXfer’ requests (see qXfer). The annex in the ‘qXfer’ packet will be ‘target.xml’. The contents of the ‘target.xml’ annex are an XML document, of the form described in Target Description Format.
Alternatively, you can specify a file to read for the target description. If a file is set, the target will not be queried. The commands to specify a file are:
set tdesc filename
pathunset tdesc filename
show tdesc filename
A target description annex is an XML document which complies with the Document Type Definition provided in the gdb sources in gdb/features/gdb-target.dtd. This means you can use generally available tools like xmllint to check that your feature descriptions are well-formed and valid. However, to help people unfamiliar with XML write descriptions for their targets, we also describe the grammar here.
Target descriptions can identify the architecture of the remote target and (for some architectures) provide information about custom register sets. They can also identify the OS ABI of the remote target. gdb can use this information to autoconfigure for your target, or to warn you if you connect to an unsupported target.
Here is a simple target description:
<target version="1.0"> <architecture>i386:x86-64</architecture> </target>
This minimal description only says that the target uses the x86-64 architecture.
A target description has the following overall form, with [ ] marking optional elements and ... marking repeatable elements. The elements are explained further below.
<?xml version="1.0"?> <!DOCTYPE target SYSTEM "gdb-target.dtd"> <target version="1.0"> [architecture] [osabi] [compatible] [feature...] </target>
The description is generally insensitive to whitespace and line breaks, under the usual common-sense rules. The XML version declaration and document type declaration can generally be omitted (gdb does not require them), but specifying them may be useful for XML validation tools. The ‘version’ attribute for ‘<target>’ may also be omitted, but we recommend including it; if future versions of gdb use an incompatible revision of gdb-target.dtd, they will detect and report the version mismatch.
It can sometimes be valuable to split a target description up into several different annexes, either for organizational purposes, or to share files between different possible target descriptions. You can divide a description into multiple files by replacing any element of the target description with an inclusion directive of the form:
<xi:include href="document"/>
When gdb encounters an element of this form, it will retrieve the named XML document, and replace the inclusion directive with the contents of that document. If the current description was read using ‘qXfer’, then so will be the included document; document will be interpreted as the name of an annex. If the current description was read from a file, gdb will look for document as a file in the same directory where it found the original description.
An ‘<architecture>’ element has this form:
<architecture>arch</architecture>
arch is one of the architectures from the set accepted by
set architecture
(see Specifying a Debugging Target).
This optional field was introduced in gdb version 7.0. Previous versions of gdb ignore it.
An ‘<osabi>’ element has this form:
<osabi>abi-name</osabi>
abi-name is an OS ABI name from the same selection accepted by
set osabi
(see Configuring the Current ABI).
This optional field was introduced in gdb version 7.0. Previous versions of gdb ignore it.
A ‘<compatible>’ element has this form:
<compatible>arch</compatible>
arch is one of the architectures from the set accepted by
set architecture
(see Specifying a Debugging Target).
A ‘<compatible>’ element is used to specify that the target
is able to run binaries in some other than the main target architecture
given by the ‘<architecture>’ element. For example, on the
Cell Broadband Engine, the main architecture is powerpc:common
or powerpc:common64
, but the system is able to run binaries
in the spu
architecture as well. The way to describe this
capability with ‘<compatible>’ is as follows:
<architecture>powerpc:common</architecture> <compatible>spu</compatible>
Each ‘<feature>’ describes some logical portion of the target system. Features are currently used to describe available CPU registers and the types of their contents. A ‘<feature>’ element has this form:
<feature name="name"> [type...] reg... </feature>
Each feature's name should be unique within the description. The name of a feature does not matter unless gdb has some special knowledge of the contents of that feature; if it does, the feature should have its standard name. See Standard Target Features.
Any register's value is a collection of bits which gdb must interpret. The default interpretation is a two's complement integer, but other types can be requested by name in the register description. Some predefined types are provided by gdb (see Predefined Target Types), and the description can define additional composite types.
Each type element must have an ‘id’ attribute, which gives a unique (within the containing ‘<feature>’) name to the type. Types must be defined before they are used.
Some targets offer vector registers, which can be treated as arrays of scalar elements. These types are written as ‘<vector>’ elements, specifying the array element type, type, and the number of elements, count:
<vector id="id" type="type" count="count"/>
If a register's value is usefully viewed in multiple ways, define it with a union type containing the useful representations. The ‘<union>’ element contains one or more ‘<field>’ elements, each of which has a name and a type:
<union id="id"> <field name="name" type="type"/> ... </union>
If a register's value is composed from several separate values, define it with a structure type. There are two forms of the ‘<struct>’ element; a ‘<struct>’ element must either contain only bitfields or contain no bitfields. If the structure contains only bitfields, its total size in bytes must be specified, each bitfield must have an explicit start and end, and bitfields are automatically assigned an integer type. The field's start should be less than or equal to its end, and zero represents the least significant bit.
<struct id="id" size="size"> <field name="name" start="start" end="end"/> ... </struct>
If the structure contains no bitfields, then each field has an explicit type, and no implicit padding is added.
<struct id="id"> <field name="name" type="type"/> ... </struct>
If a register's value is a series of single-bit flags, define it with a flags type. The ‘<flags>’ element has an explicit size and contains one or more ‘<field>’ elements. Each field has a name, a start, and an end. Only single-bit flags are supported.
<flags id="id" size="size"> <field name="name" start="start" end="end"/> ... </flags>
Each register is represented as an element with this form:
<reg name="name" bitsize="size" [regnum="num"] [save-restore="save-restore"] [type="type"] [group="group"]/>
The components are as follows:
p
and P
packets, and registers appear in the g
and G
packets
in order of increasing register number.
yes
or no
. The default is
yes
, which is appropriate for most registers except for
some system control registers; this is not related to the target's
ABI.
int
and float
. int
is an integer type of the correct size
for bitsize, and float
is a floating point type (in the
architecture's normal floating point format) of the correct size for
bitsize. The default is int
.
general
, float
, or vector
. If no
group is specified, gdb will not display the register
in info registers
.
Type definitions in the self-description can build up composite types from basic building blocks, but can not define fundamental types. Instead, standard identifiers are provided by gdb for the fundamental types. The currently supported types are:
int8
int16
int32
int64
int128
uint8
uint16
uint32
uint64
uint128
code_ptr
data_ptr
ieee_single
ieee_double
arm_fpa_ext
i387_ext
i386_eflags
i386_mxcsr
A target description must contain either no registers or all the target's registers. If the description contains no registers, then gdb will assume a default register layout, selected based on the architecture. If the description contains any registers, the default layout will not be used; the standard registers must be described in the target description, in such a way that gdb can recognize them.
This is accomplished by giving specific names to feature elements which contain standard registers. gdb will look for features with those names and verify that they contain the expected registers; if any known feature is missing required registers, or if any required feature is missing, gdb will reject the target description. You can add additional registers to any of the standard features — gdb will display them just as if they were added to an unrecognized feature.
This section lists the known features and their expected contents. Sample XML documents for these features are included in the gdb source tree, in the directory gdb/features.
Names recognized by gdb should include the name of the company or organization which selected the name, and the overall architecture to which the feature applies; so e.g. the feature containing ARM core registers is named ‘org.gnu.gdb.arm.core’.
The names of registers are not case sensitive for the purpose of recognizing standard features, but gdb will only display registers using the capitalization used in the description.
The ‘org.gnu.gdb.arm.core’ feature is required for non-M-profile ARM targets. It should contain registers ‘r0’ through ‘r13’, ‘sp’, ‘lr’, ‘pc’, and ‘cpsr’.
For M-profile targets (e.g. Cortex-M3), the ‘org.gnu.gdb.arm.core’ feature is replaced by ‘org.gnu.gdb.arm.m-profile’. It should contain registers ‘r0’ through ‘r13’, ‘sp’, ‘lr’, ‘pc’, and ‘xpsr’.
The ‘org.gnu.gdb.arm.fpa’ feature is optional. If present, it should contain registers ‘f0’ through ‘f7’ and ‘fps’.
The ‘org.gnu.gdb.xscale.iwmmxt’ feature is optional. If present, it should contain at least registers ‘wR0’ through ‘wR15’ and ‘wCGR0’ through ‘wCGR3’. The ‘wCID’, ‘wCon’, ‘wCSSF’, and ‘wCASF’ registers are optional.
The ‘org.gnu.gdb.arm.vfp’ feature is optional. If present, it should contain at least registers ‘d0’ through ‘d15’. If they are present, ‘d16’ through ‘d31’ should also be included. gdb will synthesize the single-precision registers from halves of the double-precision registers.
The ‘org.gnu.gdb.arm.neon’ feature is optional. It does not need to contain registers; it instructs gdb to display the VFP double-precision registers as vectors and to synthesize the quad-precision registers from pairs of double-precision registers. If this feature is present, ‘org.gnu.gdb.arm.vfp’ must also be present and include 32 double-precision registers.
The ‘org.gnu.gdb.i386.core’ feature is required for i386/amd64 targets. It should describe the following registers:
The register sets may be different, depending on the target.
The ‘org.gnu.gdb.i386.sse’ feature is optional. It should describe registers:
The ‘org.gnu.gdb.i386.avx’ feature is optional and requires the ‘org.gnu.gdb.i386.sse’ feature. It should describe the upper 128 bits of ymm registers:
The ‘org.gnu.gdb.i386.linux’ feature is optional. It should describe a single register, ‘orig_eax’.
The ‘org.gnu.gdb.mips.cpu’ feature is required for MIPS targets. It should contain registers ‘r0’ through ‘r31’, ‘lo’, ‘hi’, and ‘pc’. They may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.mips.cp0’ feature is also required. It should contain at least the ‘status’, ‘badvaddr’, and ‘cause’ registers. They may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.mips.fpu’ feature is currently required, though it may be optional in a future version of gdb. It should contain registers ‘f0’ through ‘f31’, ‘fcsr’, and ‘fir’. They may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.mips.linux’ feature is optional. It should contain a single register, ‘restart’, which is used by the Linux kernel to control restartable syscalls.
‘
org.gnu.gdb.m68k.core’
‘
org.gnu.gdb.coldfire.core’
‘
org.gnu.gdb.fido.core’
‘
org.gnu.gdb.coldfire.fp’
The ‘org.gnu.gdb.power.core’ feature is required for PowerPC targets. It should contain registers ‘r0’ through ‘r31’, ‘pc’, ‘msr’, ‘cr’, ‘lr’, ‘ctr’, and ‘xer’. They may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.power.fpu’ feature is optional. It should contain registers ‘f0’ through ‘f31’ and ‘fpscr’.
The ‘org.gnu.gdb.power.altivec’ feature is optional. It should contain registers ‘vr0’ through ‘vr31’, ‘vscr’, and ‘vrsave’.
The ‘org.gnu.gdb.power.vsx’ feature is optional. It should contain registers ‘vs0h’ through ‘vs31h’. gdb will combine these registers with the floating point registers (‘f0’ through ‘f31’) and the altivec registers (‘vr0’ through ‘vr31’) to present the 128-bit wide registers ‘vs0’ through ‘vs63’, the set of vector registers for POWER7.
The ‘org.gnu.gdb.power.spe’ feature is optional. It should contain registers ‘ev0h’ through ‘ev31h’, ‘acc’, and ‘spefscr’. SPE targets should provide 32-bit registers in ‘org.gnu.gdb.power.core’ and provide the upper halves in ‘ev0h’ through ‘ev31h’. gdb will combine these to present registers ‘ev0’ through ‘ev31’ to the user.
Users of gdb often wish to obtain information about the state of the operating system running on the target—for example the list of processes, or the list of open files. This section describes the mechanism that makes it possible. This mechanism is similar to the target features mechanism (see Target Descriptions), but focuses on a different aspect of target.
Operating system information is retrived from the target via the remote protocol, using ‘qXfer’ requests (see qXfer osdata read). The object name in the request should be ‘osdata’, and the annex identifies the data to be fetched.
When requesting the process list, the annex field in the ‘qXfer’ request should be ‘processes’. The returned data is an XML document. The formal syntax of this document is defined in gdb/features/osdata.dtd.
An example document is:
<?xml version="1.0"?> <!DOCTYPE target SYSTEM "osdata.dtd"> <osdata type="processes"> <item> <column name="pid">1</column> <column name="user">root</column> <column name="command">/sbin/init</column> <column name="cores">1,2,3</column> </item> </osdata>
Each item should include a column whose name is ‘pid’. The value of that column should identify the process on the target. The ‘user’ and ‘command’ columns are optional, and will be displayed by gdb. The ‘cores’ column, if present, should contain a comma-separated list of cores that this process is running on. Target may provide additional columns, which gdb currently ignores.
The trace file comes in three parts: a header, a textual description section, and a trace frame section with binary data.
The header has the form \x7fTRACE0\n
. The first byte is
0x7f
so as to indicate that the file contains binary data,
while the 0
is a version number that may have different values
in the future.
The description section consists of multiple lines of ascii text
separated by newline characters (0xa
). The lines may include a
variety of optional descriptive or context-setting information, such
as tracepoint definitions or register set size. gdb will
ignore any line that it does not recognize. An empty line marks the end
of this section.
The trace frame section consists of a number of consecutive frames. Each frame begins with a two-byte tracepoint number, followed by a four-byte size giving the amount of data in the frame. The data in the frame consists of a number of blocks, each introduced by a character indicating its type (at least register, memory, and trace state variable). The data in this section is raw binary, not a hexadecimal or other encoding; its endianness matches the target's endianness.
R
bytesg
packet in the remote protocol. Note that these are the
actual bytes, in target order and gdb register order, not a
hexadecimal encoding.
M
address length bytes...
V
number valueFuture enhancements of the trace file format may include additional types of blocks.
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#
(a comment): Command Syntax#
in Modula-2: GDB/M2$
: Value History$$
: Value History$_
and info breakpoints
: Set Breaks$_
and info line
: Machine Code$_
, $__
, and value history: Memory$_
, convenience variable: Convenience Vars$__
, convenience variable: Convenience Vars$_exitcode
, convenience variable: Convenience Vars$_probe_arg
, convenience variable: Static Probe Points$_sdata
, collect: Tracepoint Actions$_sdata
, inspect, convenience variable: Convenience Vars$_siginfo
, convenience variable: Convenience Vars$_thread
, convenience variable: Threads$_tlb
, convenience variable: Convenience Vars$bpnum
, convenience variable: Set Breaks$cdir
, convenience variable: Source Path$cwd
, convenience variable: Source Path$tpnum
: Create and Delete Tracepoints$trace_file
: Tracepoint Variables$trace_frame
: Tracepoint Variables$trace_func
: Tracepoint Variables$trace_line
: Tracepoint Variables$tracepoint
: Tracepoint Variables--annotate
: Mode Options--args
: Mode Options--batch
: Mode Options--batch-silent
: Mode Options--baud
: Mode Options--cd
: Mode Options--command
: File Options--core
: File Options--data-directory
: Mode Options--directory
: File Options--epoch
: Mode Options--eval-command
: File Options--exec
: File Options--fullname
: Mode Options--interpreter
: Mode Options--nowindows
: Mode Options--nx
: Mode Options--pid
: File Options--python
: Mode Options--quiet
: Mode Options--readnever
: File Options--readnow
: File Options--return-child-result
: Mode Options--se
: File Options--silent
: Mode Options--statistics
: Mode Options--symbols
: File Options--tty
: Mode Options--tui
: Mode Options--version
: Mode Options--windows
: Mode Options--write
: Mode Options-add-inferior
: GDB/MI Miscellaneous Commands-b
: Mode Options-break-after
: GDB/MI Breakpoint Commands-break-commands
: GDB/MI Breakpoint Commands-break-condition
: GDB/MI Breakpoint Commands-break-delete
: GDB/MI Breakpoint Commands-break-disable
: GDB/MI Breakpoint Commands-break-enable
: GDB/MI Breakpoint Commands-break-info
: GDB/MI Breakpoint Commands-break-insert
: GDB/MI Breakpoint Commands-break-list
: GDB/MI Breakpoint Commands-break-passcount
: GDB/MI Breakpoint Commands-break-watch
: GDB/MI Breakpoint Commands-c
: File Options-d
: File Options-data-disassemble
: GDB/MI Data Manipulation-data-evaluate-expression
: GDB/MI Data Manipulation-data-list-changed-registers
: GDB/MI Data Manipulation-data-list-register-names
: GDB/MI Data Manipulation-data-list-register-values
: GDB/MI Data Manipulation-data-read-memory
: GDB/MI Data Manipulation-data-read-memory-bytes
: GDB/MI Data Manipulation-data-write-memory-bytes
: GDB/MI Data Manipulation-e
: File Options-enable-pretty-printing
: GDB/MI Variable Objects-enable-timings
: GDB/MI Miscellaneous Commands-environment-cd
: GDB/MI Program Context-environment-directory
: GDB/MI Program Context-environment-path
: GDB/MI Program Context-environment-pwd
: GDB/MI Program Context-ex
: File Options-exec-arguments
: GDB/MI Program Context-exec-continue
: GDB/MI Program Execution-exec-finish
: GDB/MI Program Execution-exec-interrupt
: GDB/MI Program Execution-exec-jump
: GDB/MI Program Execution-exec-next
: GDB/MI Program Execution-exec-next-instruction
: GDB/MI Program Execution-exec-return
: GDB/MI Program Execution-exec-run
: GDB/MI Program Execution-exec-step
: GDB/MI Program Execution-exec-step-instruction
: GDB/MI Program Execution-exec-until
: GDB/MI Program Execution-f
: Mode Options-file-exec-and-symbols
: GDB/MI File Commands-file-exec-file
: GDB/MI File Commands-file-list-exec-source-file
: GDB/MI File Commands-file-list-exec-source-files
: GDB/MI File Commands-file-symbol-file
: GDB/MI File Commands-gdb-exit
: GDB/MI Miscellaneous Commands-gdb-set
: GDB/MI Miscellaneous Commands-gdb-show
: GDB/MI Miscellaneous Commands-gdb-version
: GDB/MI Miscellaneous Commands-inferior-tty-set
: GDB/MI Miscellaneous Commands-inferior-tty-show
: GDB/MI Miscellaneous Commands-interpreter-exec
: GDB/MI Miscellaneous Commands-l
: Mode Options-list-features
: GDB/MI Miscellaneous Commands-list-target-features
: GDB/MI Miscellaneous Commands-list-thread-groups
: GDB/MI Miscellaneous Commands-n
: Mode Options-nw
: Mode Options-P
: Mode Options-p
: File Options-q
: Mode Options-r
: File Options-s
: File Options-stack-info-depth
: GDB/MI Stack Manipulation-stack-info-frame
: GDB/MI Stack Manipulation-stack-list-arguments
: GDB/MI Stack Manipulation-stack-list-frames
: GDB/MI Stack Manipulation-stack-list-locals
: GDB/MI Stack Manipulation-stack-list-variables
: GDB/MI Stack Manipulation-stack-select-frame
: GDB/MI Stack Manipulation-symbol-list-lines
: GDB/MI Symbol Query-t
: Mode Options-target-attach
: GDB/MI Target Manipulation-target-detach
: GDB/MI Target Manipulation-target-disconnect
: GDB/MI Target Manipulation-target-download
: GDB/MI Target Manipulation-target-file-delete
: GDB/MI File Transfer Commands-target-file-get
: GDB/MI File Transfer Commands-target-file-put
: GDB/MI File Transfer Commands-target-select
: GDB/MI Target Manipulation-thread-info
: GDB/MI Thread Commands-thread-list-ids
: GDB/MI Thread Commands-thread-select
: GDB/MI Thread Commands-trace-define-variable
: GDB/MI Tracepoint Commands-trace-find
: GDB/MI Tracepoint Commands-trace-list-variables
: GDB/MI Tracepoint Commands-trace-save
: GDB/MI Tracepoint Commands-trace-start
: GDB/MI Tracepoint Commands-trace-status
: GDB/MI Tracepoint Commands-trace-stop
: GDB/MI Tracepoint Commands-var-assign
: GDB/MI Variable Objects-var-create
: GDB/MI Variable Objects-var-delete
: GDB/MI Variable Objects-var-evaluate-expression
: GDB/MI Variable Objects-var-info-expression
: GDB/MI Variable Objects-var-info-num-children
: GDB/MI Variable Objects-var-info-path-expression
: GDB/MI Variable Objects-var-info-type
: GDB/MI Variable Objects-var-list-children
: GDB/MI Variable Objects-var-set-format
: GDB/MI Variable Objects-var-set-frozen
: GDB/MI Variable Objects-var-set-update-range
: GDB/MI Variable Objects-var-set-visualizer
: GDB/MI Variable Objects-var-show-attributes
: GDB/MI Variable Objects-var-show-format
: GDB/MI Variable Objects-var-update
: GDB/MI Variable Objects-w
: Mode Options-x
: File Options.
, Modula-2 scope operator: M2 Scope.debug_gdb_scripts
section: .debug_gdb_scripts section.gnu_debuglink
sections: Separate Debug Files.note.gnu.build-id
sections: Separate Debug Files::
, context for variables/functions: Variables::
, in Modula-2: M2 Scope<compatible>
: Target Description Format<osabi>
: Target Description Format@
, referencing memory as an array: Arrays^connected
: GDB/MI Result Records^done
: GDB/MI Result Records^error
: GDB/MI Result Records^exit
: GDB/MI Result Records^running
: GDB/MI Result Records__init__ on Breakpoint
: Breakpoints In Python__init__ on Command
: Commands In Python__init__ on Function
: Functions In Python__init__ on Parameter
: Parameters In Python__init__ on Value
: Values From Inferior_NSPrintForDebugger
, and printing Objective-C objects: The Print Command with Objective-Cabort (C-g)
: Miscellaneous Commandsaccept-line (Newline or Return)
: Commands For Historyactions
: Tracepoint Actionsadd-inferior
: Inferiors and Programsadd-shared-symbol-files
: Filesadd-symbol-file
: Filesadd-symbol-file-from-memory
: Filesaddr_class
: Symbols In Pythonaddress
: Lazy Strings In Pythonaddress
: Values From Inferioradvance
location: Continuing and Steppingappend
: Dump/Restore Filesapropos
: Helpgdbserver
: Serverarray on Type
: Types In Pythonassf
: Filesattach
: Attachattach&
: Background Executionawatch
: Set Watchpointsb
(break
): Set Breaksbacktrace
: Backtracemain
function: Backtracebackward-char (C-b)
: Commands For Movingbackward-delete-char (Rubout)
: Commands For Textbackward-kill-line (C-x Rubout)
: Commands For Killingbackward-kill-word (M-<DEL>)
: Commands For Killingbackward-word (M-b)
: Commands For Movingbeginning-of-history (M-<)
: Commands For Historybeginning-of-line (C-a)
: Commands For Movingbell-style
: Readline Init File Syntaxbind-tty-special-chars
: Readline Init File Syntaxblock on Frame
: Frames In Pythonblock_for_pc
: Blocks In PythonBP_ACCESS_WATCHPOINT
: Breakpoints In PythonBP_BREAKPOINT
: Breakpoints In PythonBP_HARDWARE_WATCHPOINT
: Breakpoints In PythonBP_READ_WATCHPOINT
: Breakpoints In PythonBP_WATCHPOINT
: Breakpoints In Pythonbreak
: Set Breaksbreak ... task
taskno (Ada): Ada Tasksbreak ... thread
threadno: Thread-Specific Breakpointsbreak
, and Objective-C: Method Names in Commandsbreak-range
: PowerPC Embeddedbreakpoint
: Events In Pythonbreakpoint annotation
: Annotations for Runningbreakpoint
subroutine, remote: Stub Contentsbreakpoints
: Basic Pythonbreakpoints-invalid annotation
: Invalidationbt
(backtrace
): Backtracec
(continue
): Continuing and Steppingc
(SingleKey TUI key): TUI Single Key ModeC-L
: TUI KeysC-x 1
: TUI KeysC-x 2
: TUI KeysC-x A
: TUI KeysC-x a
: TUI KeysC-x C-a
: TUI KeysC-x o
: TUI KeysC-x s
: TUI Keyscall
: Callingcall-last-kbd-macro (C-x e)
: Keyboard Macroscapitalize-word (M-c)
: Commands For Textcast on Value
: Values From Inferiorcatch
: Set Catchpointscd
: Working Directorycdir
: Source Pathcharacter-search (C-])
: Miscellaneous Commandscharacter-search-backward (M-C-])
: Miscellaneous Commandschildren on pretty printer
: Pretty Printing APIclear
: Delete Breaksclear
, and Objective-C: Method Names in Commandsclear-screen (C-l)
: Commands For Movingclone-inferior
: Inferiors and Programscode
: Types In Pythoncollect
(tracepoints): Tracepoint ActionsCOMMAND_BREAKPOINTS
: Commands In PythonCOMMAND_DATA
: Commands In PythonCOMMAND_FILES
: Commands In PythonCOMMAND_MAINTENANCE
: Commands In PythonCOMMAND_NONE
: Commands In PythonCOMMAND_OBSCURE
: Commands In PythonCOMMAND_RUNNING
: Commands In PythonCOMMAND_STACK
: Commands In PythonCOMMAND_STATUS
: Commands In PythonCOMMAND_SUPPORT
: Commands In PythonCOMMAND_TRACEPOINTS
: Commands In Pythoncommands
: Breakpoints In Pythoncommands
: Break Commandscommands annotation
: Promptingcomment-begin
: Readline Init File SyntaxCOMMON
blocks, Fortran: Special Fortran Commandscompare-sections
: Memorycomplete
: Helpcomplete (<TAB>)
: Commands For Completioncomplete on Command
: Commands In PythonCOMPLETE_COMMAND
: Commands In PythonCOMPLETE_FILENAME
: Commands In PythonCOMPLETE_LOCATION
: Commands In PythonCOMPLETE_NONE
: Commands In PythonCOMPLETE_SYMBOL
: Commands In Pythoncompletion-display-width
: Readline Init File Syntaxcompletion-ignore-case
: Readline Init File Syntaxcompletion-map-case
: Readline Init File Syntaxcompletion-prefix-display-length
: Readline Init File Syntaxcompletion-query-items
: Readline Init File Syntaxcondition
: Breakpoints In Pythoncondition
: Conditionsconnect on EventRegistry
: Events In Pythonconst on Type
: Types In Pythoncontinue
: Continuing and Steppingcontinue&
: Background Executionconvert-meta
: Readline Init File Syntaxcopy-backward-word ()
: Commands For Killingcopy-forward-word ()
: Commands For Killingcopy-region-as-kill ()
: Commands For Killingcore-file
: FilesCtrl-o
(operate-and-get-next): Command Syntaxcurrent_objfile
: Objfiles In Pythoncurrent_progspace
: Progspaces In Pythoncwd
: Source Pathd
(delete
): Delete Breaksd
(SingleKey TUI key): TUI Single Key Modedebug_chaos
: M32R/Dlibthread_db
: Threadsdecode_line
: Basic Pythondefault_visualizer
: Pretty Printing APIdefine
: Definedelete
: Delete Breaksdelete checkpoint
checkpoint-id: Checkpoint/Restartdelete display
: Auto Displaydelete mem
: Memory Region Attributesdelete on Breakpoint
: Breakpoints In Pythondelete tracepoint
: Create and Delete Tracepointsdelete tvariable
: Trace State Variablesdelete-char (C-d)
: Commands For Textdelete-char-or-list ()
: Commands For Completiondelete-horizontal-space ()
: Commands For Killingdereference on Value
: Values From Inferiordetach
: Attachdetach (remote)
: Connectingdetach inferiors
infno...
: Inferiors and Programsdigit-argument (
M-0,
M-1, ...
M--)
: Numeric Argumentsdir
: Source Pathdirectory
: Source Pathdis
(disable
): Disablingdisable
: Disablingdisable display
: Auto Displaydisable mem
: Memory Region Attributesdisable pretty-printer
: Pretty-Printer Commandsdisable tracepoint
: Enable and Disable Tracepointsdisable-completion
: Readline Init File Syntaxdisassemble
: Machine Codedisconnect
: Connectingdisconnect on EventRegistry
: Events In Pythondisplay
: Auto Displaydisplay_hint on pretty printer
: Pretty Printing APIdll-symbols
: Cygwin Nativedo
(down
): Selectiondo-uppercase-version (M-a, M-b, M-
x, ...)
: Miscellaneous Commandsdocument
: Definedont-repeat
: Definedont_repeat on Command
: Commands In PythonDown
: TUI Keysdown
: Selectiondown-silently
: Selectiondowncase-word (M-l)
: Commands For Textdump
: Dump/Restore Filesdump-functions ()
: Miscellaneous Commandsdump-macros ()
: Miscellaneous Commandsdump-variables ()
: Miscellaneous Commandsdynamic_cast on Value
: Values From Inferiordynamic_type
: Values From Inferiore
(edit
): Editecho
: Outputedit
: Editediting-mode
: Readline Init File Syntaxelse
: Command Filesenable
: Disablingenable display
: Auto Displayenable mem
: Memory Region Attributesenable pretty-printer
: Pretty-Printer Commandsenable tracepoint
: Enable and Disable Tracepointsenable-keypad
: Readline Init File Syntaxenabled
: Breakpoints In Pythonencoding
: Lazy Strings In Pythonend
: Blocks In Pythonend
(breakpoint commands): Break Commandsend
(if/else/while commands): Command Filesend
(user-defined commands): Defineend-kbd-macro (C-x ))
: Keyboard Macrosend-of-history (M->)
: Commands For Historyend-of-line (C-e)
: Commands For Movingerror annotation
: Errorserror-begin annotation
: Errorseval
: OutputexceptionHandler
: Bootstrappingexchange-point-and-mark (C-x C-x)
: Miscellaneous Commandsexec-file
: Filesexecute
: Basic Pythonexit_code
: Events In Pythonexited annotation
: Annotations for Runningexpand-tilde
: Readline Init File Syntaxexpression
: Breakpoints In Pythonf
(frame
): Selectionf
(SingleKey TUI key): TUI Single Key ModeF
reply packet: The F Reply PacketF
request packet: The F Request Packetfg
(resume foreground execution): Continuing and Steppingfields on Type
: Types In Pythonfile
: Filesfilename
: Symbol Tables In Pythonfilename
: Objfiles In Pythonfilename
: Progspaces In Pythonfin
(finish
): Continuing and Steppingfind
: Searching Memoryfind_sal on Frame
: Frames In Pythonfinish
: Continuing and Steppingfinish&
: Background Executionflush
: Basic Pythonflush_i_cache
: Bootstrappingflushregs
: Maintenance Commandsfocus
: TUI Commandsforward-backward-delete-char ()
: Commands For Textforward-char (C-f)
: Commands For Movingforward-search
: Searchforward-search-history (C-s)
: Commands For Historyforward-word (M-f)
: Commands For Movingframe
, command: Framesframe
, selecting: Selectionframe_stop_reason_string
: Frames In Pythonframes-invalid annotation
: Invalidationftrace
: Create and Delete Tracepointsfullname on Symtab
: Symbol Tables In Pythonfunction
: Blocks In PythonFunction
: Functions In Pythonfunction on Frame
: Frames In Pythong++
, gnu C++ compiler: Cgcore
: Core File Generationgdb.Block
: Blocks In Pythongdb.block_for_pc
: Blocks In Pythongdb.BP_ACCESS_WATCHPOINT
: Breakpoints In Pythongdb.BP_BREAKPOINT
: Breakpoints In Pythongdb.BP_HARDWARE_WATCHPOINT
: Breakpoints In Pythongdb.BP_READ_WATCHPOINT
: Breakpoints In Pythongdb.BP_WATCHPOINT
: Breakpoints In Pythongdb.Breakpoint
: Breakpoints In Pythongdb.breakpoints
: Basic Pythongdb.COMMAND_BREAKPOINTS
: Commands In Pythongdb.COMMAND_DATA
: Commands In Pythongdb.COMMAND_FILES
: Commands In Pythongdb.COMMAND_MAINTENANCE
: Commands In Pythongdb.COMMAND_NONE
: Commands In Pythongdb.COMMAND_OBSCURE
: Commands In Pythongdb.COMMAND_RUNNING
: Commands In Pythongdb.COMMAND_STACK
: Commands In Pythongdb.COMMAND_STATUS
: Commands In Pythongdb.COMMAND_SUPPORT
: Commands In Pythongdb.COMMAND_TRACEPOINTS
: Commands In Pythongdb.COMPLETE_COMMAND
: Commands In Pythongdb.COMPLETE_FILENAME
: Commands In Pythongdb.COMPLETE_LOCATION
: Commands In Pythongdb.COMPLETE_NONE
: Commands In Pythongdb.COMPLETE_SYMBOL
: Commands In Pythongdb.current_objfile
: Objfiles In Pythongdb.current_progspace
: Progspaces In Pythongdb.decode_line
: Basic Pythongdb.default_visualizer
: Pretty Printing APIgdb.error
: Exception Handlinggdb.execute
: Basic Pythongdb.flush
: Basic Pythongdb.Function
: Functions In Pythongdb.GdbError
: Exception Handlinggdb.history
: Basic Pythongdb.Inferior
: Inferiors In Pythongdb.InferiorThread
: Threads In Pythongdb.LazyString
: Lazy Strings In Pythongdb.lookup_global_symbol
: Symbols In Pythongdb.lookup_symbol
: Symbols In Pythongdb.lookup_type
: Types In Pythongdb.MemoryError
: Exception Handlinggdb.newest_frame
: Frames In Pythongdb.Objfile
: Objfiles In Pythongdb.objfiles
: Objfiles In Pythongdb.PARAM_AUTO_BOOLEAN
: Parameters In Pythongdb.PARAM_BOOLEAN
: Parameters In Pythongdb.PARAM_ENUM
: Parameters In Pythongdb.PARAM_FILENAME
: Parameters In Pythongdb.PARAM_INTEGER
: Parameters In Pythongdb.PARAM_OPTIONAL_FILENAME
: Parameters In Pythongdb.PARAM_STRING
: Parameters In Pythongdb.PARAM_STRING_NOESCAPE
: Parameters In Pythongdb.PARAM_UINTEGER
: Parameters In Pythongdb.PARAM_ZINTEGER
: Parameters In Pythongdb.Parameter
: Parameters In Pythongdb.parameter
: Basic Pythongdb.parse_and_eval
: Basic Pythongdb.post_event
: Basic Pythongdb.Progspace
: Progspaces In Pythongdb.progspaces
: Progspaces In Pythongdb.PYTHONDIR
: Basic Pythongdb.read_memory
: Inferiors In Pythongdb.search_memory
: Inferiors In Pythongdb.selected_frame
: Frames In Pythongdb.selected_thread
: Threads In Pythongdb.solib_name
: Basic Pythongdb.STDERR
: Basic Pythongdb.STDLOG
: Basic Pythongdb.STDOUT
: Basic Pythongdb.string_to_argv
: Commands In Pythongdb.Symbol
: Symbols In Pythongdb.SYMBOL_FUNCTIONS_DOMAIN
: Symbols In Pythongdb.SYMBOL_LABEL_DOMAIN
: Symbols In Pythongdb.SYMBOL_LOC_ARG
: Symbols In Pythongdb.SYMBOL_LOC_BLOCK
: Symbols In Pythongdb.SYMBOL_LOC_COMPUTED
: Symbols In Pythongdb.SYMBOL_LOC_CONST
: Symbols In Pythongdb.SYMBOL_LOC_CONST_BYTES
: Symbols In Pythongdb.SYMBOL_LOC_LOCAL
: Symbols In Pythongdb.SYMBOL_LOC_OPTIMIZED_OUT
: Symbols In Pythongdb.SYMBOL_LOC_REF_ARG
: Symbols In Pythongdb.SYMBOL_LOC_REGISTER
: Symbols In Pythongdb.SYMBOL_LOC_REGPARM_ADDR
: Symbols In Pythongdb.SYMBOL_LOC_STATIC
: Symbols In Pythongdb.SYMBOL_LOC_TYPEDEF
: Symbols In Pythongdb.SYMBOL_LOC_UNDEF
: Symbols In Pythongdb.SYMBOL_LOC_UNRESOLVED
: Symbols In Pythongdb.SYMBOL_STRUCT_DOMAIN
: Symbols In Pythongdb.SYMBOL_TYPES_DOMAIN
: Symbols In Pythongdb.SYMBOL_UNDEF_DOMAIN
: Symbols In Pythongdb.SYMBOL_VAR_DOMAIN
: Symbols In Pythongdb.SYMBOL_VARIABLES_DOMAIN
: Symbols In Pythongdb.Symtab
: Symbol Tables In Pythongdb.Symtab_and_line
: Symbol Tables In Pythongdb.target_charset
: Basic Pythongdb.target_wide_charset
: Basic Pythongdb.Type
: Types In Pythongdb.TYPE_CODE_ARRAY
: Types In Pythongdb.TYPE_CODE_BITSTRING
: Types In Pythongdb.TYPE_CODE_BOOL
: Types In Pythongdb.TYPE_CODE_CHAR
: Types In Pythongdb.TYPE_CODE_COMPLEX
: Types In Pythongdb.TYPE_CODE_DECFLOAT
: Types In Pythongdb.TYPE_CODE_ENUM
: Types In Pythongdb.TYPE_CODE_ERROR
: Types In Pythongdb.TYPE_CODE_FLAGS
: Types In Pythongdb.TYPE_CODE_FLT
: Types In Pythongdb.TYPE_CODE_FUNC
: Types In Pythongdb.TYPE_CODE_INT
: Types In Pythongdb.TYPE_CODE_INTERNAL_FUNCTION
: Types In Pythongdb.TYPE_CODE_MEMBERPTR
: Types In Pythongdb.TYPE_CODE_METHOD
: Types In Pythongdb.TYPE_CODE_METHODPTR
: Types In Pythongdb.TYPE_CODE_NAMESPACE
: Types In Pythongdb.TYPE_CODE_PTR
: Types In Pythongdb.TYPE_CODE_RANGE
: Types In Pythongdb.TYPE_CODE_REF
: Types In Pythongdb.TYPE_CODE_SET
: Types In Pythongdb.TYPE_CODE_STRING
: Types In Pythongdb.TYPE_CODE_STRUCT
: Types In Pythongdb.TYPE_CODE_TYPEDEF
: Types In Pythongdb.TYPE_CODE_UNION
: Types In Pythongdb.TYPE_CODE_VOID
: Types In Pythongdb.Value
: Values From Inferiorgdb.WP_ACCESS
: Breakpoints In Pythongdb.WP_READ
: Breakpoints In Pythongdb.WP_WRITE
: Breakpoints In Pythongdb.write
: Basic Pythongdb.write_memory
: Inferiors In Pythongdbserver
: Serverlibthread_db
: Servergenerate-core-file
: Core File Generationget_set_string on parameter
: Parameters In Pythonget_show_string on parameter
: Parameters In PythongetDebugChar
: Bootstrappinggnu_debuglink_crc32
: Separate Debug Filesh
(help
): Helphandle
: Signalshandle_exception
: Stub Contentshbreak
: Set Breakshelp
: Helphelp function
: Convenience Varshelp target
: Target Commandshelp user-defined
: Defineheuristic-fence-post
(Alpha, MIPS): MIPShistory
: Basic Pythonhistory-preserve-point
: Readline Init File Syntaxhistory-search-backward ()
: Commands For Historyhistory-search-forward ()
: Commands For Historyhistory-size
: Readline Init File Syntaxhit_count
: Breakpoints In Pythonhook
: Hookshookpost
: Hookshorizontal-scroll-mode
: Readline Init File Syntaxhtrace
: OpenRISC 1000hwatch
: OpenRISC 1000i
(info
): Helpif
: Command Filesignore
: Conditionsignore_count
: Breakpoints In PythonINCLUDE_RDB
: VxWorksinferior
infno: Inferiors and Programsinferior_thread
: Events In Pythoninferiors
: Inferiors In Pythoninfo
: Helpinfo address
: Symbolsinfo all-registers
: Registersinfo args
: Frame Infoinfo auxv
: OS Informationinfo breakpoints
: Set Breaksinfo catch
: Frame Infoinfo checkpoints
: Checkpoint/Restartinfo classes
: Symbolsinfo common
: Special Fortran Commandsinfo copying
: Helpinfo dcache
: Caching Remote Datainfo display
: Auto Displayinfo dll
: Cygwin Nativeinfo dos
: DJGPP Nativeinfo extensions
: Showinfo f
(info frame
): Frame Infoinfo files
: Filesinfo float
: Floating Point Hardwareinfo frame
: Frame Infoinfo frame
, show the source language: Showinfo functions
: Symbolsinfo handle
: Signalsinfo inferiors
: Inferiors and Programsinfo io_registers
, AVR: AVRinfo line
: Machine Codeinfo line
, and Objective-C: Method Names in Commandsinfo locals
: Frame Infoinfo macro
: Macrosinfo mem
: Memory Region Attributesinfo meminfo
: SVR4 Process Informationinfo or1k spr
: OpenRISC 1000info os
: OS Informationinfo os processes
: OS Informationinfo pidlist
: SVR4 Process Informationinfo pretty-printer
: Pretty-Printer Commandsinfo probes
: Static Probe Pointsinfo proc
: SVR4 Process Informationinfo program
: Stoppinginfo record
: Process Record and Replayinfo registers
: Registersinfo scope
: Symbolsinfo selectors
: Symbolsinfo serial
: DJGPP Nativeinfo set
: Helpinfo share
: Filesinfo sharedlibrary
: Filesinfo signals
: Signalsinfo source
: Symbolsinfo source
, show the source language: Showinfo sources
: Symbolsinfo spu
: SPUinfo stack
: Backtraceinfo static-tracepoint-markers
: Listing Static Tracepoint Markersinfo symbol
: Symbolsinfo target
: Filesinfo task
taskno: Ada Tasksinfo tasks
: Ada Tasksinfo terminal
: Input/Outputinfo threads
: Threadsinfo tp
[n...
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[n...
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: Trace State Variablesinfo types
: Symbolsinfo udot
: OS Informationinfo variables
: Symbolsinfo vector
: Vector Unitinfo w32
: Cygwin Nativeinfo warranty
: Helpinfo watchpoints
[n...
]: Set Watchpointsinfo win
: TUI Commandsinit-if-undefined
: Convenience Varsinput-meta
: Readline Init File Syntaxinsert-comment (M-#)
: Miscellaneous Commandsinsert-completions (M-*)
: Commands For Completioninspect
: Datainterpreter-exec
: Interpretersinterrupt
: Background Executioninvoke on Command
: Commands In Pythoninvoke on Function
: Functions In Pythonis_argument
: Symbols In Pythonis_constant
: Symbols In Pythonis_exited on InferiorThread
: Threads In Pythonis_function
: Symbols In Pythonis_optimized_out
: Values From Inferioris_running on InferiorThread
: Threads In Pythonis_stopped on InferiorThread
: Threads In Pythonis_valid on Block
: Blocks In Pythonis_valid on Breakpoint
: Breakpoints In Pythonis_valid on Frame
: Frames In Pythonis_valid on Inferior
: Inferiors In Pythonis_valid on InferiorThread
: Threads In Pythonis_valid on Objfile
: Objfiles In Pythonis_valid on Symbol
: Symbols In Pythonis_valid on Symtab
: Symbol Tables In Pythonis_valid on Symtab_and_line
: Symbol Tables In Pythonis_variable
: Symbols In Pythonisearch-terminators
: Readline Init File Syntaxjump
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, and Objective-C: Method Names in CommandsKeyboardInterrupt
: Exception Handlingkeymap
: Readline Init File Syntaxkill
: Kill Processkill inferiors
infno...
: Inferiors and Programskill-line (C-k)
: Commands For Killingkill-region ()
: Commands For Killingkill-whole-line ()
: Commands For Killingkill-word (M-d)
: Commands For Killingkvm
: BSD libkvm Interfacel
(list
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: TUI Commandslazy_string on Value
: Values From InferiorLeft
: TUI Keyslength
: Lazy Strings In Pythonline
: Symbol Tables In Pythonlinkage_name
: Symbols In Pythonlist
: Listlist
, and Objective-C: Method Names in Commandslist
, how many lines to display: Listload
filename: Target Commandslocation
: Breakpoints In Pythonlookup_global_symbol
: Symbols In Pythonlookup_symbol
: Symbols In Pythonlookup_type
: Types In Pythonloop_break
: Command Filesloop_continue
: Command Filesmacro define
: Macrosmacro exp1
: Macrosmacro expand
: Macrosmacro list
: Macrosmacro undef
: Macrosmaint agent
: Maintenance Commandsmaint agent-eval
: Maintenance Commandsmaint check-symtabs
: Maintenance Commandsmaint cplus first_component
: Maintenance Commandsmaint cplus namespace
: Maintenance Commandsmaint demangle
: Maintenance Commandsmaint deprecate
: Maintenance Commandsmaint dump-me
: Maintenance Commandsmaint info breakpoints
: Maintenance Commandsmaint info program-spaces
: Inferiors and Programsmaint info psymtabs
: Symbolsmaint info sections
: Filesmaint info sol-threads
: Threadsmaint info symtabs
: Symbolsmaint internal-error
: Maintenance Commandsmaint internal-warning
: Maintenance Commandsmaint packet
: Maintenance Commandsmaint print architecture
: Maintenance Commandsmaint print c-tdesc
: Maintenance Commandsmaint print cooked-registers
: Maintenance Commandsmaint print dummy-frames
: Maintenance Commandsmaint print objfiles
: Maintenance Commandsmaint print psymbols
: Symbolsmaint print raw-registers
: Maintenance Commandsmaint print reggroups
: Maintenance Commandsmaint print register-groups
: Maintenance Commandsmaint print registers
: Maintenance Commandsmaint print section-scripts
: Maintenance Commandsmaint print statistics
: Maintenance Commandsmaint print symbols
: Symbolsmaint print target-stack
: Maintenance Commandsmaint print type
: Maintenance Commandsmaint print unwind
, HPPA: HPPAmaint set dwarf2 always-disassemble
: Maintenance Commandsmaint set dwarf2 max-cache-age
: Maintenance Commandsmaint set internal-error
: Maintenance Commandsmaint set internal-warning
: Maintenance Commandsmaint set profile
: Maintenance Commandsmaint set python auto-load
: Python Commandsmaint set python print-stack
: Python Commandsmaint set show-all-tib
: Maintenance Commandsmaint set show-debug-regs
: Maintenance Commandsmaint show dwarf2 always-disassemble
: Maintenance Commandsmaint show dwarf2 max-cache-age
: Maintenance Commandsmaint show internal-error
: Maintenance Commandsmaint show internal-warning
: Maintenance Commandsmaint show profile
: Maintenance Commandsmaint show show-all-tib
: Maintenance Commandsmaint show show-debug-regs
: Maintenance Commandsmaint space
: Maintenance Commandsmaint time
: Maintenance Commandsmaint translate-address
: Maintenance Commandsmaint undeprecate
: Maintenance Commandsmake
: Shell Commandsmark-modified-lines
: Readline Init File Syntaxmark-symlinked-directories
: Readline Init File Syntaxmatch-hidden-files
: Readline Init File Syntaxmay-insert-breakpoints
: Observer Modemay-insert-fast-tracepoints
: Observer Modemay-insert-tracepoints
: Observer Modemay-interrupt
: Observer Modemay-write-memory
: Observer Modemay-write-registers
: Observer Modemem
: Memory Region Attributesmemset
: Bootstrappingmenu-complete ()
: Commands For Completionmenu-complete-backward ()
: Commands For Completionmenu-complete-display-prefix
: Readline Init File Syntaxmeta-flag
: Readline Init File Syntaxmonitor
: Connectinggdbserver
: Servern
(next
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(SingleKey TUI key): TUI Single Key Modename
: Symbols In Pythonname
: Threads In Pythonname on Frame
: Frames In PythonNew
systag message: Threadsnewer on Frame
: Frames In Pythonnewest_frame
: Frames In Pythonnext
: Continuing and Steppingnext&
: Background Executionnext-history (C-n)
: Commands For Historynexti
: Continuing and Steppingnexti&
: Background Executionni
(nexti
): Continuing and Steppingnon-incremental-forward-search-history (M-n)
: Commands For Historynon-incremental-reverse-search-history (M-p)
: Commands For Historybreakpoint always-inserted
: Set Breaksnosharedlibrary
: Filesnum
: Threads In Pythonnum
: Inferiors In Pythonnumber
: Breakpoints In Pythonobjfile
: Symbol Tables In PythonObjfile
: Objfiles In Pythonobjfiles
: Objfiles In Pythonobserver
: Observer Modeolder on Frame
: Frames In Pythonor1ksim
: OpenRISC 1000output
: Outputoutput-meta
: Readline Init File Syntaxoverlay
: Overlay Commandsoverload-choice annotation
: Promptingoverwrite-mode ()
: Commands For Textpage-completions
: Readline Init File SyntaxPARAM_AUTO_BOOLEAN
: Parameters In PythonPARAM_BOOLEAN
: Parameters In PythonPARAM_ENUM
: Parameters In PythonPARAM_FILENAME
: Parameters In PythonPARAM_INTEGER
: Parameters In PythonPARAM_OPTIONAL_FILENAME
: Parameters In PythonPARAM_STRING
: Parameters In PythonPARAM_STRING_NOESCAPE
: Parameters In PythonPARAM_UINTEGER
: Parameters In PythonPARAM_ZINTEGER
: Parameters In PythonParameter
: Parameters In Pythonparameter
: Basic Pythonparse_and_eval
: Basic Pythonpasscount
: Tracepoint Passcountspath
: Environmentpc
: Symbol Tables In Pythonpc on Frame
: Frames In PythonPgDn
: TUI KeysPgUp
: TUI Keyspid
: Inferiors In Pythontarget remote
to: Connectingpmon
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(print-object
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: Types In Pythonpossible-completions (M-?)
: Commands For Completionpost-commands annotation
: Promptingpost-overload-choice annotation
: Promptingpost-prompt annotation
: Promptingpost-prompt-for-continue annotation
: Promptingpost-query annotation
: Promptingpost_event
: Basic Pythonpre-commands annotation
: Promptingpre-overload-choice annotation
: Promptingpre-prompt annotation
: Promptingpre-prompt-for-continue annotation
: Promptingpre-query annotation
: Promptingprefix-meta (<ESC>)
: Miscellaneous Commandspretty_printers
: Objfiles In Pythonpretty_printers
: Progspaces In Pythonprevious-history (C-p)
: Commands For Historyprint
: Dataprint-object
: The Print Command with Objective-Cprint_name
: Symbols In Pythonprintf
: Outputproc-trace-entry
: SVR4 Process Informationproc-trace-exit
: SVR4 Process Informationproc-untrace-entry
: SVR4 Process Informationproc-untrace-exit
: SVR4 Process Informationprocfs
API calls: SVR4 Process InformationProgspace
: Progspaces In Pythonprogspaces
: Progspaces In Pythonprompt annotation
: Promptingprompt-for-continue annotation
: Promptingptid
: Threads In Pythonptrace
system call: OS Informationptype
: SymbolsputDebugChar
: Bootstrappingpwd
: Working Directorypython
: Python CommandsPYTHONDIR
: Basic Pythonq
(quit
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(SingleKey TUI key): TUI Single Key Modequery annotation
: Promptingquit
[expression]: Quitting GDBquit annotation
: Errorsquoted-insert (C-q or C-v)
: Commands For Textr
(run
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(SingleKey TUI key): TUI Single Key Moderange on Type
: Types In Pythonrbreak
: Set Breaksrc
(reverse-continue
): Reverse Executionrdilogenable
: ARMrdilogfile
: ARMre-read-init-file (C-x C-r)
: Miscellaneous Commandsread_memory on Inferior
: Inferiors In Pythonread_var on Frame
: Frames In Pythonreadnow
: Filesrec
: Process Record and Replayrec del
: Process Record and Replayrec s
: Process Record and Replayrecord
: Process Record and Replayrecord delete
: Process Record and Replayrecord restore
: Process Record and Replayrecord save
: Process Record and Replayrecord stop
: Process Record and Replayredraw-current-line ()
: Commands For Movingreference on Type
: Types In Pythonrefresh
: TUI Commandsregs
, Super-H: Super-Hreinterpret_cast on Value
: Values From Inferiorremote delete
: File Transferremote get
: File Transferremote put
: File Transferremotetimeout
: Sparcletremove-inferiors
: Inferiors and Programsrestart
checkpoint-id: Checkpoint/Restartrestore
: Dump/Restore FilesRET
(repeat last command): Command Syntaxretransmit-timeout
, MIPS protocol: MIPS Embeddedreturn
: Returningreverse-continue
: Reverse Executionreverse-finish
: Reverse Executionreverse-next
: Reverse Executionreverse-nexti
: Reverse Executionreverse-search
: Searchreverse-search-history (C-r)
: Commands For Historyreverse-step
: Reverse Executionreverse-stepi
: Reverse Executionrevert-all-at-newline
: Readline Init File Syntaxrevert-line (M-r)
: Miscellaneous CommandsRight
: TUI Keysrn
(reverse-next
): Reverse Executionrni
(reverse-nexti
): Reverse Executionrs
(step
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(reverse-stepi
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: Startingrun&
: Background Executionrwatch
: Set Watchpointss
(SingleKey TUI key): TUI Single Key Modes
(step
): Continuing and Steppingsave breakpoints
: Save Breakpointssave gdb-index
: Index Filessave tracepoints
: save tracepointssave-tracepoints
: save tracepointssdireset
: M32R/Dsdistatus
: M32R/Dsds
, a command: PowerPC Embeddedsearch
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: Inferiors In Pythonsection
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: Frames In Pythonselect-frame
: Framesselected_frame
: Frames In Pythonselected_thread
: Threads In Pythonself-insert (a, b, A, 1, !, ...)
: Commands For Texttarget remote
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, command prefix: Command Historyset
: Helpset ada trust-PAD-over-XVS
: Ada Glitchesset annotate
: Annotations Overviewset architecture
: Targetsset args
: Argumentsset arm
: ARMset auto-load-scripts
: Auto-loadingset auto-solib-add
: Filesset backtrace
: Backtraceset board-address
: M32R/Dset breakpoint always-inserted
: Set Breaksset breakpoint auto-hw
: Set Breaksset breakpoint pending
: Set Breaksset build-id-verbose
: Separate Debug Filesset can-use-hw-watchpoints
: Set Watchpointsset case-sensitive
: Symbolsset charset
: Character Setsset check range
: Range Checkingset check type
: Type Checkingset circular-trace-buffer
: Starting and Stopping Trace Experimentsset coerce-float-to-double
: ABIset com1base
: DJGPP Nativeset com1irq
: DJGPP Nativeset com2base
: DJGPP Nativeset com2irq
: DJGPP Nativeset com3base
: DJGPP Nativeset com3irq
: DJGPP Nativeset com4base
: DJGPP Nativeset com4irq
: DJGPP Nativeset complaints
: Messages/Warningsset confirm
: Messages/Warningsset cp-abi
: ABIset cygwin-exceptions
: Cygwin Nativeset data-directory
: Data Filesset debug
: Debugging Outputset debug darwin
: Darwinset debug hppa
: HPPAset debug libthread-db
: Threadsset debug mach-o
: Darwinset debug mips
: MIPSset debug monitor
: Target Commandsset debug nto-debug
: Neutrinoset debug-file-directory
: Separate Debug Filesset debugevents
: Cygwin Nativeset debugexceptions
: Cygwin Nativeset debugexec
: Cygwin Nativeset debugmemory
: Cygwin Nativeset default-collect
: Tracepoint Actionsset demangle-style
: Print Settingsset detach-on-fork
: Forksset directories
: Source Pathset disable-randomization
: Startingset disassemble-next-line
: Machine Codeset disassembly-flavor
: Machine Codeset disconnected-tracing
: Starting and Stopping Trace Experimentsset displaced-stepping
: Maintenance Commandsset download-path
: M32R/Dset editing
: Editingset endian
: Byte Orderset environment
: Environmentset exceptions
, Hurd command: Hurd Nativeset exec-direction
: Reverse Executionset exec-done-display
: Debugging Outputset exec-wrapper
: Startingset extension-language
: Showset follow-exec-mode
: Forksset follow-fork-mode
: Forksset gnutarget
: Target Commandsset hash
, for remote monitors: Target Commandsset height
: Screen Sizeset history expansion
: Command Historyset history filename
: Command Historyset history save
: Command Historyset history size
: Command Historyset host-charset
: Character Setsset inferior-tty
: Input/Outputset input-radix
: Numbersset interactive-mode
: Other Misc Settingsset language
: Manuallyset libthread-db-search-path
: Threadsset listsize
: Listset logging
: Logging Outputset mach-exceptions
: Darwinset max-user-call-depth
: Defineset mem inaccessible-by-default
: Memory Region Attributesset mips abi
: MIPSset mips mask-address
: MIPSset mipsfpu
: MIPS Embeddedset monitor-prompt
, MIPS remote: MIPS Embeddedset monitor-warnings
, MIPS remote: MIPS Embeddedset multiple-symbols
: Ambiguous Expressionsset new-console
: Cygwin Nativeset new-group
: Cygwin Nativeset non-stop
: Non-Stop Modeset opaque-type-resolution
: Symbolsset osabi
: ABIset output-radix
: Numbersset overload-resolution
: Debugging C Plus Plusset pagination
: Screen Sizeset powerpc
: PowerPC Embeddedset print
: Print Settingsset print frame-arguments
: Print Settingsset print inferior-events
: Inferiors and Programsset print thread-events
: Threadsset processor
: Targetsset procfs-file
: SVR4 Process Informationset procfs-trace
: SVR4 Process Informationset prompt
: Promptset radix
: Numbersset ravenscar task-switching off
: Ravenscar Profileset ravenscar task-switching on
: Ravenscar Profileset rdiheartbeat
: ARMset rdiromatzero
: ARMset record insn-number-max
: Process Record and Replayset record memory-query
: Process Record and Replayset record stop-at-limit
: Process Record and Replayset remote
: Remote Configurationset remote system-call-allowed
: systemset remote-mips64-transfers-32bit-regs
: MIPSset remotecache
: Caching Remote Dataset remoteflow
: Remote Configurationset retransmit-timeout
: MIPS Embeddedset rstack_high_address
: A29Kset schedule-multiple
: All-Stop Modeset script-extension
: Extending GDBset sdstimeout
: PowerPC Embeddedset server-address
: M32R/Dset sh calling-convention
: Super-Hset shell
: Cygwin Nativeset signal-thread
: Hurd Nativeset signals
, Hurd command: Hurd Nativeset sigs
, Hurd command: Hurd Nativeset sigthread
: Hurd Nativeset solib-absolute-prefix
: Filesset solib-search-path
: Filesset spu
: SPUset stack-cache
: Caching Remote Dataset step-mode
: Continuing and Steppingset stop-on-solib-events
: Filesset stopped
, Hurd command: Hurd Nativeset struct-convention
: i386set substitute-path
: Source Pathset symbol-reloading
: Symbolsset syn-garbage-limit
, MIPS remote: MIPS Embeddedset sysroot
: Filesset target-async
: Background Executionset target-charset
: Character Setsset target-file-system-kind (unix|dos-based|auto)
: Filesset target-wide-charset
: Character Setsset task
, Hurd commands: Hurd Nativeset tcp
: Remote Configurationset thread
, Hurd command: Hurd Nativeset timeout
: MIPS Embeddedset trace-commands
: Messages/Warningsset trust-readonly-sections
: Filesset tui active-border-mode
: TUI Configurationset tui border-kind
: TUI Configurationset tui border-mode
: TUI Configurationset unwind-on-terminating-exception
: Callingset unwindonsignal
: Callingset variable
: Assignmentset verbose
: Messages/Warningsset watchdog
: Maintenance Commandsset width
: Screen Sizeset write
: Patchingset-mark (C-@)
: Miscellaneous Commandsset_debug_traps
: Stub Contentsset_doc
: Parameters In Pythonshare
: Filessharedlibrary
: Filesshell
: Shell Commandsshow
: Helpshow ada trust-PAD-over-XVS
: Ada Glitchesshow annotate
: Annotations Overviewshow architecture
: Targetsshow args
: Argumentsshow arm
: ARMshow auto-load-scripts
: Auto-loadingshow auto-solib-add
: Filesshow backtrace
: Backtraceshow board-address
: M32R/Dshow breakpoint always-inserted
: Set Breaksshow breakpoint auto-hw
: Set Breaksshow breakpoint pending
: Set Breaksshow build-id-verbose
: Separate Debug Filesshow can-use-hw-watchpoints
: Set Watchpointsshow case-sensitive
: Symbolsshow charset
: Character Setsshow check range
: Range Checkingshow check type
: Type Checkingshow circular-trace-buffer
: Starting and Stopping Trace Experimentsshow coerce-float-to-double
: ABIshow com1base
: DJGPP Nativeshow com1irq
: DJGPP Nativeshow com2base
: DJGPP Nativeshow com2irq
: DJGPP Nativeshow com3base
: DJGPP Nativeshow com3irq
: DJGPP Nativeshow com4base
: DJGPP Nativeshow com4irq
: DJGPP Nativeshow commands
: Command Historyshow complaints
: Messages/Warningsshow confirm
: Messages/Warningsshow convenience
: Convenience Varsshow copying
: Helpshow cp-abi
: ABIshow cygwin-exceptions
: Cygwin Nativeshow data-directory
: Data Filesshow debug
: Debugging Outputshow debug darwin
: Darwinshow debug libthread-db
: Threadsshow debug mach-o
: Darwinshow debug mips
: MIPSshow debug monitor
: Target Commandsshow debug nto-debug
: Neutrinoshow debug-file-directory
: Separate Debug Filesshow default-collect
: Tracepoint Actionsshow detach-on-fork
: Forksshow directories
: Source Pathshow disassemble-next-line
: Machine Codeshow disassembly-flavor
: Machine Codeshow disconnected-tracing
: Starting and Stopping Trace Experimentsshow displaced-stepping
: Maintenance Commandsshow download-path
: M32R/Dshow editing
: Editingshow environment
: Environmentshow exceptions
, Hurd command: Hurd Nativeshow exec-done-display
: Debugging Outputshow follow-fork-mode
: Forksshow gnutarget
: Target Commandsshow hash
, for remote monitors: Target Commandsshow height
: Screen Sizeshow history
: Command Historyshow host-charset
: Character Setsshow inferior-tty
: Input/Outputshow input-radix
: Numbersshow interactive-mode
: Other Misc Settingsshow language
: Showshow libthread-db-search-path
: Threadsshow listsize
: Listshow logging
: Logging Outputshow mach-exceptions
: Darwinshow max-user-call-depth
: Defineshow mem inaccessible-by-default
: Memory Region Attributesshow mips abi
: MIPSshow mips mask-address
: MIPSshow mipsfpu
: MIPS Embeddedshow monitor-prompt
, MIPS remote: MIPS Embeddedshow monitor-warnings
, MIPS remote: MIPS Embeddedshow multiple-symbols
: Ambiguous Expressionsshow new-console
: Cygwin Nativeshow new-group
: Cygwin Nativeshow non-stop
: Non-Stop Modeshow opaque-type-resolution
: Symbolsshow osabi
: ABIshow output-radix
: Numbersshow overload-resolution
: Debugging C Plus Plusshow pagination
: Screen Sizeshow paths
: Environmentshow print
: Print Settingsshow print inferior-events
: Inferiors and Programsshow print thread-events
: Threadsshow processor
: Targetsshow procfs-file
: SVR4 Process Informationshow procfs-trace
: SVR4 Process Informationshow prompt
: Promptshow radix
: Numbersshow ravenscar task-switching
: Ravenscar Profileshow rdiheartbeat
: ARMshow rdiromatzero
: ARMshow record insn-number-max
: Process Record and Replayshow record memory-query
: Process Record and Replayshow record stop-at-limit
: Process Record and Replayshow remote
: Remote Configurationshow remote system-call-allowed
: systemshow remote-mips64-transfers-32bit-regs
: MIPSshow remotecache
: Caching Remote Datashow remoteflow
: Remote Configurationshow retransmit-timeout
: MIPS Embeddedshow rstack_high_address
: A29Kshow script-extension
: Extending GDBshow sdstimeout
: PowerPC Embeddedshow server-address
: M32R/Dshow sh calling-convention
: Super-Hshow shell
: Cygwin Nativeshow signal-thread
: Hurd Nativeshow signals
, Hurd command: Hurd Nativeshow sigs
, Hurd command: Hurd Nativeshow sigthread
: Hurd Nativeshow solib-search-path
: Filesshow spu
: SPUshow stack-cache
: Caching Remote Datashow stop-on-solib-events
: Filesshow stopped
, Hurd command: Hurd Nativeshow struct-convention
: i386show substitute-path
: Source Pathshow symbol-reloading
: Symbolsshow syn-garbage-limit
, MIPS remote: MIPS Embeddedshow sysroot
: Filesshow target-async
: Background Executionshow target-charset
: Character Setsshow target-file-system-kind
: Filesshow target-wide-charset
: Character Setsshow task
, Hurd commands: Hurd Nativeshow tcp
: Remote Configurationshow thread
, Hurd command: Hurd Nativeshow timeout
: MIPS Embeddedshow unwind-on-terminating-exception
: Callingshow unwindonsignal
: Callingshow user
: Defineshow values
: Value Historyshow verbose
: Messages/Warningsshow version
: Helpshow warranty
: Helpshow width
: Screen Sizeshow write
: Patchingshow-all-if-ambiguous
: Readline Init File Syntaxshow-all-if-unmodified
: Readline Init File Syntaxshow_doc
: Parameters In Pythonsi
(stepi
): Continuing and Steppingsignal
: Signalingsignal annotation
: Annotations for Runningsignal-name annotation
: Annotations for Runningsignal-name-end annotation
: Annotations for Runningsignal-string annotation
: Annotations for Runningsignal-string-end annotation
: Annotations for Runningsignalled annotation
: Annotations for RunningSIGQUIT
signal, dump core of gdb: Maintenance Commandssilent
: Breakpoints In Pythonsilent
: Break Commandssim
: Z8000sim
, a command: Embedded Processorssizeof
: Types In Pythonskip-completed-text
: Readline Init File Syntaxskip-csi-sequence ()
: Miscellaneous Commandssolib_name
: Basic Pythonsource
: Command Filessource annotation
: Source Annotationsspr
: OpenRISC 1000start
: Blocks In Pythonstart
: Startingstart-kbd-macro (C-x ()
: Keyboard Macrosstarting annotation
: Annotations for RunningSTDERR
: Basic PythonSTDLOG
: Basic PythonSTDOUT
: Basic Pythonstep
: Continuing and Steppingstep&
: Background Executionstepi
: Continuing and Steppingstepi&
: Background Executionstop on gdb.Breakpoint
: Breakpoints In Pythonstop
, a pseudo-command: Hooksstop_signal
: Events In Pythonstopping annotation
: Annotations for Runningstrace
: Create and Delete Tracepointsstring on Value
: Values From Inferiorstrip_typedefs on Type
: Types In Pythonstruct user
contents: OS Informationsuperblock
: Blocks In Pythonswitch on InferiorThread
: Threads In Pythonsymbol-file
: FilesSYMBOL_FUNCTIONS_DOMAIN
: Symbols In PythonSYMBOL_LABEL_DOMAIN
: Symbols In PythonSYMBOL_LOC_ARG
: Symbols In PythonSYMBOL_LOC_BLOCK
: Symbols In PythonSYMBOL_LOC_COMPUTED
: Symbols In PythonSYMBOL_LOC_CONST
: Symbols In PythonSYMBOL_LOC_CONST_BYTES
: Symbols In PythonSYMBOL_LOC_LOCAL
: Symbols In PythonSYMBOL_LOC_OPTIMIZED_OUT
: Symbols In PythonSYMBOL_LOC_REF_ARG
: Symbols In PythonSYMBOL_LOC_REGISTER
: Symbols In PythonSYMBOL_LOC_REGPARM_ADDR
: Symbols In PythonSYMBOL_LOC_STATIC
: Symbols In PythonSYMBOL_LOC_TYPEDEF
: Symbols In PythonSYMBOL_LOC_UNDEF
: Symbols In PythonSYMBOL_LOC_UNRESOLVED
: Symbols In PythonSYMBOL_STRUCT_DOMAIN
: Symbols In PythonSYMBOL_TYPES_DOMAIN
: Symbols In PythonSYMBOL_UNDEF_DOMAIN
: Symbols In PythonSYMBOL_VAR_DOMAIN
: Symbols In PythonSYMBOL_VARIABLES_DOMAIN
: Symbols In Pythonsymtab
: Symbol Tables In Pythonsymtab
: Symbols In Pythonsyscall DSO
: Filessysinfo
: DJGPP Nativetabset
: TUI Commandstag
: Types In Pythontarget
: Target Commandstarget array
: MIPS Embeddedtarget dbug
: M68Ktarget ddb
port: MIPS Embeddedtarget dink32
: PowerPC Embeddedtarget jtag
: OpenRISC 1000target lsi
port: MIPS Embeddedtarget m32r
: M32R/Dtarget m32rsdi
: M32R/Dtarget mips
port: MIPS Embeddedtarget on Type
: Types In Pythontarget op50n
: PAtarget pmon
port: MIPS Embeddedtarget ppcbug
: PowerPC Embeddedtarget ppcbug1
: PowerPC Embeddedtarget r3900
: MIPS Embeddedtarget rdi
: ARMtarget rdp
: ARMtarget record
: Process Record and Replaytarget remote
: Connectingtarget sds
: PowerPC Embeddedtarget sim
, with Z8000: Z8000target sparclite
: Sparclitetarget tfile
: Trace Filestarget vxworks
: VxWorkstarget w89k
: PAtarget_charset
: Basic Pythontarget_wide_charset
: Basic Pythontask
: Breakpoints In Pythontask
(Ada): Ada Taskstbreak
: Set Breakstarget remote
: Connectingtdump
: tdumptemplate_argument on Type
: Types In Pythonteval
(tracepoints): Tracepoint Actionstfile
: Trace Filestfind
: tfindthbreak
: Set Breaksthis
, inside C++ member functions: C Plus Plus Expressionsthread
: Breakpoints In Pythonthread apply
: Threadsthread find
: Threadsthread name
: Threadsthread
threadno: Threadsthreads on Inferior
: Inferiors In Pythontimeout
, MIPS protocol: MIPS Embeddedtload
, M32R: M32R/Dto_string on pretty printer
: Pretty Printing APItrace
: Create and Delete Tracepointsgdbserver
: Servertranspose-chars (C-t)
: Commands For Texttranspose-words (M-t)
: Commands For Texttsave
: Trace Fileststart
: Starting and Stopping Trace Experimentststatus
: Starting and Stopping Trace Experimentststop
: Starting and Stopping Trace Experimentstty
: Input/Outputtui reg
: TUI Commandstvariable
: Trace State Variablestype
: Lazy Strings In Pythontype
: Breakpoints In Pythontype
: Values From Inferiortype on Frame
: Frames In PythonTYPE_CODE_ARRAY
: Types In PythonTYPE_CODE_BITSTRING
: Types In PythonTYPE_CODE_BOOL
: Types In PythonTYPE_CODE_CHAR
: Types In PythonTYPE_CODE_COMPLEX
: Types In PythonTYPE_CODE_DECFLOAT
: Types In PythonTYPE_CODE_ENUM
: Types In PythonTYPE_CODE_ERROR
: Types In PythonTYPE_CODE_FLAGS
: Types In PythonTYPE_CODE_FLT
: Types In PythonTYPE_CODE_FUNC
: Types In PythonTYPE_CODE_INT
: Types In PythonTYPE_CODE_INTERNAL_FUNCTION
: Types In PythonTYPE_CODE_MEMBERPTR
: Types In PythonTYPE_CODE_METHOD
: Types In PythonTYPE_CODE_METHODPTR
: Types In PythonTYPE_CODE_NAMESPACE
: Types In PythonTYPE_CODE_PTR
: Types In PythonTYPE_CODE_RANGE
: Types In PythonTYPE_CODE_REF
: Types In PythonTYPE_CODE_SET
: Types In PythonTYPE_CODE_STRING
: Types In PythonTYPE_CODE_STRUCT
: Types In PythonTYPE_CODE_TYPEDEF
: Types In PythonTYPE_CODE_UNION
: Types In PythonTYPE_CODE_VOID
: Types In Pythonu
(SingleKey TUI key): TUI Single Key Modeu
(until
): Continuing and Steppingtarget remote
: Connectingundisplay
: Auto Displayundo (C-_ or C-x C-u)
: Miscellaneous Commandsuniversal-argument ()
: Numeric Argumentsunix-filename-rubout ()
: Commands For Killingunix-line-discard (C-u)
: Commands For Killingunix-word-rubout (C-w)
: Commands For Killingunqualified on Type
: Types In Pythonunset environment
: Environmentunset substitute-path
: Source Pathuntil
: Continuing and Steppinguntil&
: Background Executionunwind_stop_reason on Frame
: Frames In PythonUp
: TUI Keysup
: Selectionup-silently
: Selectionupcase-word (M-u)
: Commands For Textupdate
: TUI Commandsupload
, M32R: M32R/Duse_dbt_break
: M32R/Duse_debug_dma
: M32R/Duse_ib_break
: M32R/Duse_mon_code
: M32R/Dv
(SingleKey TUI key): TUI Single Key Modevalue
: Parameters In Pythonvalue on LazyString
: Lazy Strings In Pythonvisible
: Breakpoints In Pythonvisible-stats
: Readline Init File Syntaxvolatile on Type
: Types In Pythonvxworks-timeout
: VxWorksw
(SingleKey TUI key): TUI Single Key Modewas_attached
: Inferiors In Pythonwatch
: Set Watchpointswatchpoint annotation
: Annotations for Runningwhatis
: Symbolswhere
: Backtracewhile
: Command Fileswhile-stepping
(tracepoints): Tracepoint Actionswinheight
: TUI CommandsWP_ACCESS
: Breakpoints In PythonWP_READ
: Breakpoints In PythonWP_WRITE
: Breakpoints In Pythonwrite
: Basic Pythonwrite_memory on Inferior
: Inferiors In Pythonx
(examine memory): Memoryx
command, default address: Machine Codex
(examine), and info line
: Machine Codeyank (C-y)
: Commands For Killingyank-last-arg (M-. or M-_)
: Commands For Historyyank-nth-arg (M-C-y)
: Commands For Historyyank-pop (M-y)
: Commands For Killing[1] On
DOS/Windows systems, the home directory is the one pointed to by the
HOME
environment variable.
[2] The completer can be confused by certain kinds of invalid expressions. Also, it only examines the static type of the expression, not the dynamic type.
[3] Currently, only gnu/Linux.
[4] As of this writing, multiple-location breakpoints work only if there's line number information for all the locations. This means that they will generally not work in system libraries, unless you have debug info with line numbers for them.
[5] Note that some side effects are easier to undo than others. For instance, memory and registers are relatively easy, but device I/O is hard. Some targets may be able undo things like device I/O, and some may not.
The contract between gdb and the reverse executing target requires only that the target do something reasonable when gdb tells it to execute backwards, and then report the results back to gdb. Whatever the target reports back to gdb, gdb will report back to the user. gdb assumes that the memory and registers that the target reports are in a consistant state, but gdb accepts whatever it is given.
[6] Unless the code is too heavily optimized.
[7]
Note that embedded programs (the so-called “free-standing”
environment) are not required to have a main
function as the
entry point. They could even have multiple entry points.
[8]
The only restriction is that your editor (say ex
), recognizes the
following command-line syntax:
ex +number file
The optional numeric value +number specifies the number of the line in the file where to start editing.
[9] ‘b’ cannot be used because these format letters are also
used with the x
command, where ‘b’ stands for “byte”;
see Examining Memory.
[10] This is a way of removing
one word from the stack, on machines where stacks grow downward in
memory (most machines, nowadays). This assumes that the innermost
stack frame is selected; setting $sp
is not allowed when other
stack frames are selected. To pop entire frames off the stack,
regardless of machine architecture, use return
;
see Returning from a Function.
[11] In non-stop mode, it is moderately rare for a running thread to modify the stack of a stopped thread in a way that would interfere with a backtrace, and caching of stack reads provides a significant speed up of remote backtraces.
[12] If you want to specify a local system root using a directory that happens to be named remote:, you need to use some equivalent variant of the name like ./remote:.
[13] If you choose a port number that
conflicts with another service, gdbserver
prints an error message
and exits.
[14] In gdb-Momonga (7.3.1-1m.mo8)/gdb/refcard.ps of the version Momonga (7.3.1-1m.mo8) release.
[15] The ‘qP’ and ‘qL’ packets predate these conventions, and have arguments without any terminator for the packet name; we suspect they are in widespread use in places that are difficult to upgrade. The ‘qC’ packet has no arguments, but some existing stubs (e.g. RedBoot) are known to not check for the end of the packet.