1 \input texinfo @c -*-texinfo-*-
2 @c Copyright (c) 1988 1989 1990 1991 1992 1993 Free Software Foundation, Inc.
5 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
6 @c of @set vars. However, you can override filename with makeinfo -o.
12 @settitle Debugging with @value{GDBN}
15 @settitle Debugging with @value{GDBN} (@value{TARGET})
17 @setchapternewpage odd
28 @c readline appendices use @vindex
32 @c Determine the edition number in *three* places by hand:
33 @c 1. First ifinfo section 2. title page 3. top node
34 @c To find the locations, search for !!set
36 @c GDB CHANGELOG CONSULTED BETWEEN:
37 @c Fri Oct 11 23:27:06 1991 John Gilmore (gnu at cygnus.com)
38 @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint)
40 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
43 @c This is a dir.info fragment to support semi-automated addition of
44 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
47 * Gdb:: The GNU debugger.
54 This file documents the GNU debugger @value{GDBN}.
56 @c !!set edition, date, version
57 This is Edition 4.09, August 1993,
58 of @cite{Debugging with @value{GDBN}: the GNU Source-Level Debugger}
59 for GDB Version @value{GDBVN}.
61 Copyright (C) 1988, '89, '90, '91, '92, '93 Free Software Foundation, Inc.
63 Permission is granted to make and distribute verbatim copies of
64 this manual provided the copyright notice and this permission notice
65 are preserved on all copies.
68 Permission is granted to process this file through TeX and print the
69 results, provided the printed document carries copying permission
70 notice identical to this one except for the removal of this paragraph
71 (this paragraph not being relevant to the printed manual).
74 Permission is granted to copy and distribute modified versions of this
75 manual under the conditions for verbatim copying, provided also that the
76 entire resulting derived work is distributed under the terms of a
77 permission notice identical to this one.
79 Permission is granted to copy and distribute translations of this manual
80 into another language, under the above conditions for modified versions.
84 @title Debugging with @value{GDBN}
85 @subtitle The GNU Source-Level Debugger
87 @subtitle (@value{TARGET})
90 @c !!set edition, date, version
91 @subtitle Edition 4.09, for @value{GDBN} version @value{GDBVN}
93 @author Richard M. Stallman and Roland H. Pesch
97 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par
98 \hfill {\it Debugging with @value{GDBN}}\par
99 \hfill \TeX{}info \texinfoversion\par
100 \hfill pesch\@cygnus.com\par
104 @vskip 0pt plus 1filll
105 Copyright @copyright{} 1988, '89, '90, '91, '92, '93 Free Software
108 Published by the Free Software Foundation @*
109 675 Massachusetts Avenue, @*
110 Cambridge, MA 02139 USA @*
111 Printed copies are available for $20 each. @*
112 ISBN 1-882114-11-6 @*
114 Permission is granted to make and distribute verbatim copies of
115 this manual provided the copyright notice and this permission notice
116 are preserved on all copies.
118 Permission is granted to copy and distribute modified versions of this
119 manual under the conditions for verbatim copying, provided also that the
120 entire resulting derived work is distributed under the terms of a
121 permission notice identical to this one.
123 Permission is granted to copy and distribute translations of this manual
124 into another language, under the above conditions for modified versions.
130 @top Debugging with @value{GDBN}
132 This file describes @value{GDBN}, the GNU symbolic debugger.
134 @c !!set edition, date, version
135 This is Edition 4.09, April 1993, for GDB Version @value{GDBVN}.
138 * Summary:: Summary of @value{GDBN}
140 * New Features:: New features since GDB version 3.5
143 * Sample Session:: A sample @value{GDBN} session
146 * Invocation:: Getting in and out of @value{GDBN}
147 * Commands:: @value{GDBN} commands
148 * Running:: Running programs under @value{GDBN}
149 * Stopping:: Stopping and continuing
150 * Stack:: Examining the stack
151 * Source:: Examining source files
152 * Data:: Examining data
154 * Languages:: Using @value{GDBN} with different languages
157 * C:: C language support
159 @c remnant makeinfo bug, blank line needed after two end-ifs?
161 * Symbols:: Examining the symbol table
162 * Altering:: Altering execution
163 * GDB Files:: @value{GDBN} files
164 * Targets:: Specifying a debugging target
165 * Controlling GDB:: Controlling @value{GDBN}
166 * Sequences:: Canned sequences of commands
168 * Emacs:: Using @value{GDBN} under GNU Emacs
171 * GDB Bugs:: Reporting bugs in @value{GDBN}
172 * Command Line Editing:: Facilities of the readline library
173 * Using History Interactively::
177 @ifclear PRECONFIGURED
178 * Formatting Documentation:: How to format and print GDB documentation
179 * Installing GDB:: Installing GDB
187 @unnumbered Summary of @value{GDBN}
189 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
190 going on ``inside'' another program while it executes---or what another
191 program was doing at the moment it crashed.
193 @value{GDBN} can do four main kinds of things (plus other things in support of
194 these) to help you catch bugs in the act:
198 Start your program, specifying anything that might affect its behavior.
201 Make your program stop on specified conditions.
204 Examine what has happened, when your program has stopped.
207 Change things in your program, so you can experiment with correcting the
208 effects of one bug and go on to learn about another.
213 You can use @value{GDBN} to debug programs written in C or C++.
216 You can use @value{GDBN} to debug programs written in C, C++, and
221 @value{GDBN} can be used to debug programs written in Fortran, although
222 it does not yet support entering expressions, printing values, etc.
223 using Fortran syntax. It may be necessary to refer to some variables
224 with a trailing underscore.
229 * Free Software:: Freely redistributable software
230 * Contributors:: Contributors to GDB
234 @unnumberedsec Free software
236 @value{GDBN} is @dfn{free software}, protected by the GNU General Public License
237 (GPL). The GPL gives you the freedom to copy or adapt a licensed
238 program---but every person getting a copy also gets with it the
239 freedom to modify that copy (which means that they must get access to
240 the source code), and the freedom to distribute further copies.
241 Typical software companies use copyrights to limit your freedoms; the
242 Free Software Foundation uses the GPL to preserve these freedoms.
244 Fundamentally, the General Public License is a license which says that
245 you have these freedoms and that you cannot take these freedoms away
249 @unnumberedsec Contributors to GDB
251 Richard Stallman was the original author of GDB, and of many other GNU
252 programs. Many others have contributed to its development. This
253 section attempts to credit major contributors. One of the virtues of
254 free software is that everyone is free to contribute to it; with
255 regret, we cannot actually acknowledge everyone here. The file
256 @file{ChangeLog} in the GDB distribution approximates a blow-by-blow
259 Changes much prior to version 2.0 are lost in the mists of time.
262 @emph{Plea:} Additions to this section are particularly welcome. If you
263 or your friends (or enemies, to be evenhanded) have been unfairly
264 omitted from this list, we would like to add your names!
267 So that they may not regard their long labor as thankless, we
268 particularly thank those who shepherded GDB through major releases: Fred
269 Fish (release 4.9), Stu Grossman and John Gilmore (releases 4.8, 4.7,
270 4.6, 4.5, 4.4), John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim
271 Kingdon (releases 3.5, 3.4, 3.3); and Randy Smith (releases 3.2, 3.1,
272 3.0). As major maintainer of GDB for some period, each contributed
273 significantly to the structure, stability, and capabilities of the
276 Richard Stallman, assisted at various times by Peter TerMaat, Chris
277 Hanson, and Richard Mlynarik, handled releases through 2.8.
280 Michael Tiemann is the author of most of the GNU C++ support in GDB,
281 with significant additional contributions from Per Bothner. James
282 Clark wrote the GNU C++ demangler. Early work on C++ was by Peter
283 TerMaat (who also did much general update work leading to release 3.0).
286 GDB 4 uses the BFD subroutine library to examine multiple
287 object-file formats; BFD was a joint project of David V.
288 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
290 David Johnson wrote the original COFF support; Pace Willison did
291 the original support for encapsulated COFF.
293 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
294 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
295 support. Jean-Daniel Fekete contributed Sun 386i support. Chris
296 Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki
297 Hasei contributed Sony/News OS 3 support. David Johnson contributed
298 Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support.
299 Keith Packard contributed NS32K support. Doug Rabson contributed
300 Acorn Risc Machine support. Chris Smith contributed Convex support
301 (and Fortran debugging). Jonathan Stone contributed Pyramid support.
302 Michael Tiemann contributed SPARC support. Tim Tucker contributed
303 support for the Gould NP1 and Gould Powernode. Pace Willison
304 contributed Intel 386 support. Jay Vosburgh contributed Symmetry
307 Rich Schaefer and Peter Schauer helped with support of SunOS shared
310 Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
311 several machine instruction sets.
313 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
314 develop remote debugging. Intel Corporation and Wind River Systems
315 contributed remote debugging modules for their products.
317 Brian Fox is the author of the readline libraries providing
318 command-line editing and command history.
320 Andrew Beers of SUNY Buffalo wrote the language-switching code,
322 the Modula-2 support,
324 and contributed the Languages chapter of this manual.
326 Fred Fish wrote most of the support for Unix System Vr4.
328 He also enhanced the command-completion support to cover C++ overloaded
332 Hitachi America, Ltd. sponsored the support for Hitachi microprocessors.
336 @unnumbered New Features since GDB Version 3.5
340 Using the new command @code{target}, you can select at runtime whether
341 you are debugging local files, local processes, standalone systems over
342 a serial port, realtime systems over a TCP/IP connection, etc. The
343 command @code{load} can download programs into a remote system. Serial
344 stubs are available for Motorola 680x0, Intel 80386, and Sparc remote
345 systems; GDB also supports debugging realtime processes running under
346 VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a
347 debugger stub on the target system. Internally, GDB now uses a function
348 vector to mediate access to different targets; if you need to add your
349 own support for a remote protocol, this makes it much easier.
352 GDB now sports watchpoints as well as breakpoints. You can use a
353 watchpoint to stop execution whenever the value of an expression
354 changes, without having to predict a particular place in your program
355 where this may happen.
358 Commands that issue wide output now insert newlines at places designed
359 to make the output more readable.
361 @item Object Code Formats
362 GDB uses a new library called the Binary File Descriptor (BFD) Library
363 to permit it to switch dynamically, without reconfiguration or
364 recompilation, between different object-file formats. Formats currently
365 supported are COFF, ELF, a.out, Intel 960 b.out, MIPS ECOFF, HPPA SOM
366 (with stabs debugging), and S-records; files may be read as .o files,
367 archive libraries, or core dumps. BFD is available as a subroutine
368 library so that other programs may take advantage of it, and the other
369 GNU binary utilities are being converted to use it.
371 @item Configuration and Ports
372 Compile-time configuration (to select a particular architecture and
373 operating system) is much easier. The script @code{configure} now
374 allows you to configure GDB as either a native debugger or a
375 cross-debugger. @xref{Installing GDB}, for details on how to
379 The user interface to the GDB control variables is simpler,
380 and is consolidated in two commands, @code{set} and @code{show}. Output
381 lines are now broken at readable places, rather than overflowing onto
382 the next line. You can suppress output of machine-level addresses,
383 displaying only source language information.
386 GDB now supports C++ multiple inheritance (if used with a GCC
387 version 2 compiler), and also has limited support for C++ exception
388 handling, with the commands @code{catch} and @code{info catch}: GDB
389 can break when an exception is raised, before the stack is peeled back
390 to the exception handler's context.
394 GDB now has preliminary support for the GNU Modula-2 compiler, currently
395 under development at the State University of New York at Buffalo.
396 Coordinated development of both GDB and the GNU Modula-2 compiler will
397 continue. Other Modula-2 compilers are currently not supported, and
398 attempting to debug programs compiled with them will likely result in an
399 error as the symbol table of the executable is read in.
402 @item Command Rationalization
403 Many GDB commands have been renamed to make them easier to remember
404 and use. In particular, the subcommands of @code{info} and
405 @code{show}/@code{set} are grouped to make the former refer to the state
406 of your program, and the latter refer to the state of GDB itself.
407 @xref{Renamed Commands}, for details on what commands were renamed.
409 @item Shared Libraries
410 GDB 4 can debug programs and core files that use SunOS, SVR4, or IBM RS/6000
414 GDB 4 has a reference card. @xref{Formatting Documentation,,Formatting
415 the Documentation}, for instructions about how to print it.
421 @chapter A Sample @value{GDBN} Session
423 You can use this manual at your leisure to read all about @value{GDBN}.
424 However, a handful of commands are enough to get started using the
425 debugger. This chapter illustrates those commands.
428 In this sample session, we emphasize user input like this: @b{input},
429 to make it easier to pick out from the surrounding output.
432 @c FIXME: this example may not be appropriate for some configs, where
433 @c FIXME...primary interest is in remote use.
435 One of the preliminary versions of GNU @code{m4} (a generic macro
436 processor) exhibits the following bug: sometimes, when we change its
437 quote strings from the default, the commands used to capture one macro
438 definition within another stop working. In the following short @code{m4}
439 session, we define a macro @code{foo} which expands to @code{0000}; we
440 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
441 same thing. However, when we change the open quote string to
442 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
443 procedure fails to define a new synonym @code{baz}:
452 @b{define(bar,defn(`foo'))}
456 @b{changequote(<QUOTE>,<UNQUOTE>)}
458 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
461 m4: End of input: 0: fatal error: EOF in string
465 Let us use @value{GDBN} to try to see what is going on.
468 $ @b{@value{GDBP} m4}
469 @c FIXME: this falsifies the exact text played out, to permit smallbook
470 @c FIXME... format to come out better.
471 GDB is free software and you are welcome to distribute copies
472 of it under certain conditions; type "show copying" to see
474 There is absolutely no warranty for GDB; type "show warranty"
476 GDB @value{GDBVN}, Copyright 1993 Free Software Foundation, Inc...
481 @value{GDBN} reads only enough symbol data to know where to find the rest when
482 needed; as a result, the first prompt comes up very quickly. We now
483 tell @value{GDBN} to use a narrower display width than usual, so that examples
484 will fit in this manual.
487 (@value{GDBP}) @b{set width 70}
491 We need to see how the @code{m4} built-in @code{changequote} works.
492 Having looked at the source, we know the relevant subroutine is
493 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
494 @code{break} command.
497 (@value{GDBP}) @b{break m4_changequote}
498 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
502 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
503 control; as long as control does not reach the @code{m4_changequote}
504 subroutine, the program runs as usual:
507 (@value{GDBP}) @b{run}
508 Starting program: /work/Editorial/gdb/gnu/m4/m4
516 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
517 suspends execution of @code{m4}, displaying information about the
518 context where it stops.
521 @b{changequote(<QUOTE>,<UNQUOTE>)}
523 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
525 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
529 Now we use the command @code{n} (@code{next}) to advance execution to
530 the next line of the current function.
534 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
539 @code{set_quotes} looks like a promising subroutine. We can go into it
540 by using the command @code{s} (@code{step}) instead of @code{next}.
541 @code{step} goes to the next line to be executed in @emph{any}
542 subroutine, so it steps into @code{set_quotes}.
546 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
548 530 if (lquote != def_lquote)
552 The display that shows the subroutine where @code{m4} is now
553 suspended (and its arguments) is called a stack frame display. It
554 shows a summary of the stack. We can use the @code{backtrace}
555 command (which can also be spelled @code{bt}), to see where we are
556 in the stack as a whole: the @code{backtrace} command displays a
557 stack frame for each active subroutine.
560 (@value{GDBP}) @b{bt}
561 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
563 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
565 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
566 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
568 #4 0x79dc in expand_input () at macro.c:40
569 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
573 We will step through a few more lines to see what happens. The first two
574 times, we can use @samp{s}; the next two times we use @code{n} to avoid
575 falling into the @code{xstrdup} subroutine.
579 0x3b5c 532 if (rquote != def_rquote)
581 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
582 def_lquote : xstrdup(lq);
584 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
587 538 len_lquote = strlen(rquote);
591 The last line displayed looks a little odd; we can examine the variables
592 @code{lquote} and @code{rquote} to see if they are in fact the new left
593 and right quotes we specified. We use the command @code{p}
594 (@code{print}) to see their values.
597 (@value{GDBP}) @b{p lquote}
598 $1 = 0x35d40 "<QUOTE>"
599 (@value{GDBP}) @b{p rquote}
600 $2 = 0x35d50 "<UNQUOTE>"
604 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
605 To look at some context, we can display ten lines of source
606 surrounding the current line with the @code{l} (@code{list}) command.
612 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
614 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
617 538 len_lquote = strlen(rquote);
618 539 len_rquote = strlen(lquote);
625 Let us step past the two lines that set @code{len_lquote} and
626 @code{len_rquote}, and then examine the values of those variables.
630 539 len_rquote = strlen(lquote);
633 (@value{GDBP}) @b{p len_lquote}
635 (@value{GDBP}) @b{p len_rquote}
640 That certainly looks wrong, assuming @code{len_lquote} and
641 @code{len_rquote} are meant to be the lengths of @code{lquote} and
642 @code{rquote} respectively. We can set them to better values using
643 the @code{p} command, since it can print the value of
644 any expression---and that expression can include subroutine calls and
648 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
650 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
655 Is that enough to fix the problem of using the new quotes with the
656 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
657 executing with the @code{c} (@code{continue}) command, and then try the
658 example that caused trouble initially:
664 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
671 Success! The new quotes now work just as well as the default ones. The
672 problem seems to have been just the two typos defining the wrong
673 lengths. We allow @code{m4} exit by giving it an EOF as input:
677 Program exited normally.
681 The message @samp{Program exited normally.} is from @value{GDBN}; it
682 indicates @code{m4} has finished executing. We can end our @value{GDBN}
683 session with the @value{GDBN} @code{quit} command.
686 (@value{GDBP}) @b{quit}
691 @chapter Getting In and Out of @value{GDBN}
693 This chapter discusses how to start @value{GDBN}, and how to get out of it.
694 (The essentials: type @samp{@value{GDBP}} to start GDB, and type @kbd{quit}
695 or @kbd{C-d} to exit.)
698 * Invoking GDB:: How to start @value{GDBN}
699 * Quitting GDB:: How to quit @value{GDBN}
700 * Shell Commands:: How to use shell commands inside @value{GDBN}
704 @section Invoking @value{GDBN}
707 For details on starting up @value{GDBP} as a
708 remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi
709 Remote,,@value{GDBN} and Hitachi Microprocessors}.
712 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
713 @value{GDBN} reads commands from the terminal until you tell it to exit.
715 You can also run @code{@value{GDBP}} with a variety of arguments and options,
716 to specify more of your debugging environment at the outset.
719 The command-line options described here are designed
720 to cover a variety of situations; in some environments, some of these
721 options may effectively be unavailable.
724 The most usual way to start @value{GDBN} is with one argument,
725 specifying an executable program:
728 @value{GDBP} @var{program}
733 You can also start with both an executable program and a core file
737 @value{GDBP} @var{program} @var{core}
740 You can, instead, specify a process ID as a second argument, if you want
741 to debug a running process:
744 @value{GDBP} @var{program} 1234
748 would attach @value{GDBN} to process @code{1234} (unless you also have a file
749 named @file{1234}; @value{GDBN} does check for a core file first).
751 Taking advantage of the second command-line argument requires a fairly
752 complete operating system; when you use @value{GDBN} as a remote debugger
753 attached to a bare board, there may not be any notion of ``process'',
754 and there is often no way to get a core dump.
758 You can further control how @value{GDBN} starts up by using command-line
759 options. @value{GDBN} itself can remind you of the options available.
769 to display all available options and briefly describe their use
770 (@samp{@value{GDBP} -h} is a shorter equivalent).
772 All options and command line arguments you give are processed
773 in sequential order. The order makes a difference when the
774 @samp{-x} option is used.
780 * Remote Serial:: @value{GDBN} remote serial protocol
783 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
786 * UDI29K Remote:: @value{GDBN} and the UDI protocol for AMD29K
787 * EB29K Remote:: @value{GDBN} with a remote EB29K
790 * VxWorks Remote:: @value{GDBN} and VxWorks
793 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
796 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
799 * MIPS Remote:: @value{GDBN} and MIPS boards
802 * Simulator:: Simulated CPU target
805 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
807 * File Options:: Choosing files
808 * Mode Options:: Choosing modes
816 @subsection Choosing files
819 When @value{GDBN} starts, it reads any arguments other than options as
820 specifying an executable file and core file (or process ID). This is
821 the same as if the arguments were specified by the @samp{-se} and
822 @samp{-c} options respectively. (@value{GDBN} reads the first argument
823 that does not have an associated option flag as equivalent to the
824 @samp{-se} option followed by that argument; and the second argument
825 that does not have an associated option flag, if any, as equivalent to
826 the @samp{-c} option followed by that argument.)
829 When @value{GDBN} starts, it reads any argument other than options as
830 specifying an executable file. This is the same as if the argument was
831 specified by the @samp{-se} option.
834 Many options have both long and short forms; both are shown in the
835 following list. @value{GDBN} also recognizes the long forms if you truncate
836 them, so long as enough of the option is present to be unambiguous.
837 (If you prefer, you can flag option arguments with @samp{--} rather
838 than @samp{-}, though we illustrate the more usual convention.)
841 @item -symbols @var{file}
843 Read symbol table from file @var{file}.
845 @item -exec @var{file}
847 Use file @var{file} as the executable file to execute when
852 appropriate, and for examining pure data in conjunction with a core
857 Read symbol table from file @var{file} and use it as the executable
861 @item -core @var{file}
863 Use file @var{file} as a core dump to examine.
865 @item -c @var{number}
866 Connect to process ID @var{number}, as with the @code{attach} command
867 (unless there is a file in core-dump format named @var{number}, in which
868 case @samp{-c} specifies that file as a core dump to read).
871 @item -command @var{file}
873 Execute @value{GDBN} commands from file @var{file}. @xref{Command
874 Files,, Command files}.
876 @item -directory @var{directory}
877 @itemx -d @var{directory}
878 Add @var{directory} to the path to search for source files.
883 @emph{Warning: this option depends on operating system facilities that are not
884 supported on all systems.}@*
885 If memory-mapped files are available on your system through the @code{mmap}
886 system call, you can use this option
887 to have @value{GDBN} write the symbols from your
888 program into a reusable file in the current directory. If the program you are debugging is
889 called @file{/tmp/fred}, the mapped symbol file will be @file{./fred.syms}.
890 Future @value{GDBN} debugging sessions will notice the presence of this file,
891 and will quickly map in symbol information from it, rather than reading
892 the symbol table from the executable program.
894 @c FIXME! Really host, not target?
895 The @file{.syms} file is specific to the host machine where @value{GDBN}
896 is run. It holds an exact image of the internal @value{GDBN} symbol
897 table. It cannot be shared across multiple host platforms.
902 Read each symbol file's entire symbol table immediately, rather than
903 the default, which is to read it incrementally as it is needed.
904 This makes startup slower, but makes future operations faster.
908 The @code{-mapped} and @code{-readnow} options are typically combined in
909 order to build a @file{.syms} file that contains complete symbol
910 information. (@xref{Files,,Commands to specify files}, for information
911 on @file{.syms} files.) A simple GDB invocation to do nothing but build
912 a @file{.syms} file for future use is:
915 gdb -batch -nx -mapped -readnow programname
920 @subsection Choosing modes
922 You can run @value{GDBN} in various alternative modes---for example, in
923 batch mode or quiet mode.
928 Do not execute commands from any initialization files (normally called
929 @file{@value{GDBINIT}}). Normally, the commands in these files are
930 executed after all the command options and arguments have been
931 processed. @xref{Command Files,,Command files}.
935 ``Quiet''. Do not print the introductory and copyright messages. These
936 messages are also suppressed in batch mode.
939 Run in batch mode. Exit with status @code{0} after processing all the
940 command files specified with @samp{-x} (and all commands from
941 initialization files, if not inhibited with @samp{-n}). Exit with
942 nonzero status if an error occurs in executing the @value{GDBN} commands
943 in the command files.
945 Batch mode may be useful for running @value{GDBN} as a filter, for example to
946 download and run a program on another computer; in order to make this
947 more useful, the message
950 Program exited normally.
954 (which is ordinarily issued whenever a program running under @value{GDBN} control
955 terminates) is not issued when running in batch mode.
957 @item -cd @var{directory}
958 Run @value{GDBN} using @var{directory} as its working directory,
959 instead of the current directory.
962 @item -context @var{authentication}
963 When the Energize programming system starts up @value{GDBN}, it uses this
964 option to trigger an alternate mode of interaction.
965 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
966 as a client in the Energize environment. Avoid this option when you run
967 @value{GDBN} directly from the command line. See @ref{Energize,,Using
968 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
974 Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
975 to output the full file name and line number in a standard,
976 recognizable fashion each time a stack frame is displayed (which
977 includes each time your program stops). This recognizable format looks
978 like two @samp{\032} characters, followed by the file name, line number
979 and character position separated by colons, and a newline. The
980 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
981 a signal to display the source code for the frame.
986 Set the line speed (baud rate or bits per second) of any serial
987 interface used by @value{GDBN} for remote debugging.
989 @item -tty @var{device}
990 Run using @var{device} for your program's standard input and output.
991 @c FIXME: kingdon thinks there is more to -tty. Investigate.
996 @section Quitting @value{GDBN}
997 @cindex exiting @value{GDBN}
998 @cindex leaving @value{GDBN}
1004 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or type
1005 an end-of-file character (usually @kbd{C-d}).
1009 An interrupt (often @kbd{C-c}) will not exit from @value{GDBN}, but rather
1010 will terminate the action of any @value{GDBN} command that is in progress and
1011 return to @value{GDBN} command level. It is safe to type the interrupt
1012 character at any time because @value{GDBN} does not allow it to take effect
1013 until a time when it is safe.
1016 If you have been using @value{GDBN} to control an attached process or
1017 device, you can release it with the @code{detach} command
1018 (@pxref{Attach, ,Debugging an already-running process}).
1021 @node Shell Commands
1022 @section Shell commands
1024 If you need to execute occasional shell commands during your
1025 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1026 just use the @code{shell} command.
1029 @item shell @var{command string}
1031 @cindex shell escape
1032 Invoke a the standard shell to execute @var{command string}.
1034 If it exists, the environment variable @code{SHELL} determines which
1035 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
1039 The utility @code{make} is often needed in development environments.
1040 You do not have to use the @code{shell} command for this purpose in
1044 @item make @var{make-args}
1046 @cindex calling make
1047 Execute the @code{make} program with the specified
1048 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1052 @chapter @value{GDBN} Commands
1054 You can abbreviate a @value{GDBN} command to the first few letters of the command
1055 name, if that abbreviation is unambiguous; and you can repeat certain
1056 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1057 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1058 show you the alternatives available, if there is more than one possibility).
1061 * Command Syntax:: How to give commands to @value{GDBN}
1062 * Completion:: Command completion
1063 * Help:: How to ask @value{GDBN} for help
1066 @node Command Syntax
1067 @section Command syntax
1069 A @value{GDBN} command is a single line of input. There is no limit on
1070 how long it can be. It starts with a command name, which is followed by
1071 arguments whose meaning depends on the command name. For example, the
1072 command @code{step} accepts an argument which is the number of times to
1073 step, as in @samp{step 5}. You can also use the @code{step} command
1074 with no arguments. Some command names do not allow any arguments.
1076 @cindex abbreviation
1077 @value{GDBN} command names may always be truncated if that abbreviation is
1078 unambiguous. Other possible command abbreviations are listed in the
1079 documentation for individual commands. In some cases, even ambiguous
1080 abbreviations are allowed; for example, @code{s} is specially defined as
1081 equivalent to @code{step} even though there are other commands whose
1082 names start with @code{s}. You can test abbreviations by using them as
1083 arguments to the @code{help} command.
1085 @cindex repeating commands
1087 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1088 repeat the previous command. Certain commands (for example, @code{run})
1089 will not repeat this way; these are commands for which unintentional
1090 repetition might cause trouble and which you are unlikely to want to
1093 The @code{list} and @code{x} commands, when you repeat them with
1094 @key{RET}, construct new arguments rather than repeating
1095 exactly as typed. This permits easy scanning of source or memory.
1097 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1098 output, in a way similar to the common utility @code{more}
1099 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1100 @key{RET} too many in this situation, @value{GDBN} disables command
1101 repetition after any command that generates this sort of display.
1105 Any text from a @kbd{#} to the end of the line is a comment; it does
1106 nothing. This is useful mainly in command files (@pxref{Command
1107 Files,,Command files}).
1110 @section Command completion
1113 @cindex word completion
1114 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1115 only one possibility; it can also show you what the valid possibilities
1116 are for the next word in a command, at any time. This works for @value{GDBN}
1117 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1119 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1120 of a word. If there is only one possibility, @value{GDBN} will fill in the
1121 word, and wait for you to finish the command (or press @key{RET} to
1122 enter it). For example, if you type
1124 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1125 @c complete accuracy in these examples; space introduced for clarity.
1126 @c If texinfo enhancements make it unnecessary, it would be nice to
1127 @c replace " @key" by "@key" in the following...
1129 (@value{GDBP}) info bre @key{TAB}
1133 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1134 the only @code{info} subcommand beginning with @samp{bre}:
1137 (@value{GDBP}) info breakpoints
1141 You can either press @key{RET} at this point, to run the @code{info
1142 breakpoints} command, or backspace and enter something else, if
1143 @samp{breakpoints} does not look like the command you expected. (If you
1144 were sure you wanted @code{info breakpoints} in the first place, you
1145 might as well just type @key{RET} immediately after @samp{info bre},
1146 to exploit command abbreviations rather than command completion).
1148 If there is more than one possibility for the next word when you press
1149 @key{TAB}, @value{GDBN} will sound a bell. You can either supply more
1150 characters and try again, or just press @key{TAB} a second time, and
1151 @value{GDBN} will display all the possible completions for that word. For
1152 example, you might want to set a breakpoint on a subroutine whose name
1153 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1154 just sounds the bell. Typing @key{TAB} again will display all the
1155 function names in your program that begin with those characters, for
1159 (@value{GDBP}) b make_ @key{TAB}
1160 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1161 make_a_section_from_file make_environ
1162 make_abs_section make_function_type
1163 make_blockvector make_pointer_type
1164 make_cleanup make_reference_type
1165 make_command make_symbol_completion_list
1166 (@value{GDBP}) b make_
1170 After displaying the available possibilities, @value{GDBN} copies your
1171 partial input (@samp{b make_} in the example) so you can finish the
1174 If you just want to see the list of alternatives in the first place, you
1175 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1176 means @kbd{@key{META} ?}. You can type this
1178 either by holding down a
1179 key designated as the @key{META} shift on your keyboard (if there is
1180 one) while typing @kbd{?}, or
1182 as @key{ESC} followed by @kbd{?}.
1184 @cindex quotes in commands
1185 @cindex completion of quoted strings
1186 Sometimes the string you need, while logically a ``word'', may contain
1187 parentheses or other characters that @value{GDBN} normally excludes from its
1188 notion of a word. To permit word completion to work in this situation,
1189 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1192 The most likely situation where you might need this is in typing the
1193 name of a C++ function. This is because C++ allows function overloading
1194 (multiple definitions of the same function, distinguished by argument
1195 type). For example, when you want to set a breakpoint you may need to
1196 distinguish whether you mean the version of @code{name} that takes an
1197 @code{int} parameter, @code{name(int)}, or the version that takes a
1198 @code{float} parameter, @code{name(float)}. To use the word-completion
1199 facilities in this situation, type a single quote @code{'} at the
1200 beginning of the function name. This alerts @value{GDBN} that it may need to
1201 consider more information than usual when you press @key{TAB} or
1202 @kbd{M-?} to request word completion:
1205 (@value{GDBP}) b 'bubble( @key{M-?}
1206 bubble(double,double) bubble(int,int)
1207 (@value{GDBP}) b 'bubble(
1210 In some cases, @value{GDBN} can tell that completing a name will require
1211 quotes. When this happens, @value{GDBN} will insert the quote for you (while
1212 completing as much as it can) if you do not type the quote in the first
1216 (@value{GDBP}) b bub @key{TAB}
1217 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1218 (@value{GDBP}) b 'bubble(
1222 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1223 you have not yet started typing the argument list when you ask for
1224 completion on an overloaded symbol.
1229 @section Getting help
1230 @cindex online documentation
1233 You can always ask @value{GDBN} itself for information on its commands, using the
1234 command @code{help}.
1240 You can use @code{help} (abbreviated @code{h}) with no arguments to
1241 display a short list of named classes of commands:
1245 List of classes of commands:
1247 running -- Running the program
1248 stack -- Examining the stack
1249 data -- Examining data
1250 breakpoints -- Making program stop at certain points
1251 files -- Specifying and examining files
1252 status -- Status inquiries
1253 support -- Support facilities
1254 user-defined -- User-defined commands
1255 aliases -- Aliases of other commands
1256 obscure -- Obscure features
1258 Type "help" followed by a class name for a list of
1259 commands in that class.
1260 Type "help" followed by command name for full
1262 Command name abbreviations are allowed if unambiguous.
1266 @item help @var{class}
1267 Using one of the general help classes as an argument, you can get a
1268 list of the individual commands in that class. For example, here is the
1269 help display for the class @code{status}:
1272 (@value{GDBP}) help status
1277 @c Line break in "show" line falsifies real output, but needed
1278 @c to fit in smallbook page size.
1279 show -- Generic command for showing things set
1281 info -- Generic command for printing status
1283 Type "help" followed by command name for full
1285 Command name abbreviations are allowed if unambiguous.
1289 @item help @var{command}
1290 With a command name as @code{help} argument, @value{GDBN} will display a
1291 short paragraph on how to use that command.
1294 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1295 and @code{show} to inquire about the state of your program, or the state
1296 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1297 manual introduces each of them in the appropriate context. The listings
1298 under @code{info} and under @code{show} in the Index point to
1299 all the sub-commands. @xref{Index}.
1306 This command (abbreviated @code{i}) is for describing the state of your
1307 program. For example, you can list the arguments given to your program
1308 with @code{info args}, list the registers currently in use with @code{info
1309 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1310 You can get a complete list of the @code{info} sub-commands with
1311 @w{@code{help info}}.
1315 In contrast, @code{show} is for describing the state of @value{GDBN} itself.
1316 You can change most of the things you can @code{show}, by using the
1317 related command @code{set}; for example, you can control what number
1318 system is used for displays with @code{set radix}, or simply inquire
1319 which is currently in use with @code{show radix}.
1322 To display all the settable parameters and their current
1323 values, you can use @code{show} with no arguments; you may also use
1324 @code{info set}. Both commands produce the same display.
1325 @c FIXME: "info set" violates the rule that "info" is for state of
1326 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1327 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1331 Here are three miscellaneous @code{show} subcommands, all of which are
1332 exceptional in lacking corresponding @code{set} commands:
1335 @kindex show version
1336 @cindex version number
1338 Show what version of @value{GDBN} is running. You should include this
1339 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1340 use at your site, you may occasionally want to determine which version
1341 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1342 and old ones may wither away. The version number is also announced
1343 when you start @value{GDBN}.
1345 @kindex show copying
1347 Display information about permission for copying @value{GDBN}.
1349 @kindex show warranty
1351 Display the GNU ``NO WARRANTY'' statement.
1355 @chapter Running Programs Under @value{GDBN}
1357 When you run a program under @value{GDBN}, you must first generate
1358 debugging information when you compile it.
1360 You may start it with its arguments, if any, in an environment of your
1361 choice. You may redirect your program's input and output, debug an
1362 already running process, or kill a child process.
1366 * Compilation:: Compiling for debugging
1367 * Starting:: Starting your program
1369 * Arguments:: Your program's arguments
1370 * Environment:: Your program's environment
1371 * Working Directory:: Your program's working directory
1372 * Input/Output:: Your program's input and output
1373 * Attach:: Debugging an already-running process
1374 * Kill Process:: Killing the child process
1375 * Process Information:: Additional process information
1380 @section Compiling for debugging
1382 In order to debug a program effectively, you need to generate
1383 debugging information when you compile it. This debugging information
1384 is stored in the object file; it describes the data type of each
1385 variable or function and the correspondence between source line numbers
1386 and addresses in the executable code.
1388 To request debugging information, specify the @samp{-g} option when you run
1391 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1392 options together. Using those compilers, you cannot generate optimized
1393 executables containing debugging information.
1395 @value{NGCC}, the GNU C compiler, supports @samp{-g} with or without
1396 @samp{-O}, making it possible to debug optimized code. We recommend
1397 that you @emph{always} use @samp{-g} whenever you compile a program.
1398 You may think your program is correct, but there is no sense in pushing
1401 @cindex optimized code, debugging
1402 @cindex debugging optimized code
1403 When you debug a program compiled with @samp{-g -O}, remember that the
1404 optimizer is rearranging your code; the debugger will show you what is
1405 really there. Do not be too surprised when the execution path does not
1406 exactly match your source file! An extreme example: if you define a
1407 variable, but never use it, @value{GDBN} will never see that
1408 variable---because the compiler optimizes it out of existence.
1410 Some things do not work as well with @samp{-g -O} as with just
1411 @samp{-g}, particularly on machines with instruction scheduling. If in
1412 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1413 please report it as a bug (including a test case!).
1415 Older versions of the GNU C compiler permitted a variant option
1416 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1417 format; if your GNU C compiler has this option, do not use it.
1421 @section Starting your program
1429 Use the @code{run} command to start your program under @value{GDBN}. You must
1430 first specify the program name
1434 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1435 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1436 command (@pxref{Files, ,Commands to specify files}).
1441 If you are running your program in an execution environment that
1442 supports processes, @code{run} creates an inferior process and makes
1443 that process run your program. (In environments without processes,
1444 @code{run} jumps to the start of your program.)
1446 The execution of a program is affected by certain information it
1447 receives from its superior. @value{GDBN} provides ways to specify this
1448 information, which you must do @emph{before} starting your program. (You
1449 can change it after starting your program, but such changes will only affect
1450 your program the next time you start it.) This information may be
1451 divided into four categories:
1454 @item The @emph{arguments.}
1455 Specify the arguments to give your program as the arguments of the
1456 @code{run} command. If a shell is available on your target, the shell
1457 is used to pass the arguments, so that you may use normal conventions
1458 (such as wildcard expansion or variable substitution) in describing
1459 the arguments. In Unix systems, you can control which shell is used
1460 with the @code{SHELL} environment variable. @xref{Arguments, ,Your
1461 program's arguments}.
1463 @item The @emph{environment.}
1464 Your program normally inherits its environment from @value{GDBN}, but you can
1465 use the @value{GDBN} commands @code{set environment} and @code{unset
1466 environment} to change parts of the environment that will be given to
1467 your program. @xref{Environment, ,Your program's environment}.
1469 @item The @emph{working directory.}
1470 Your program inherits its working directory from @value{GDBN}. You can set
1471 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1472 @xref{Working Directory, ,Your program's working directory}.
1474 @item The @emph{standard input and output.}
1475 Your program normally uses the same device for standard input and
1476 standard output as @value{GDBN} is using. You can redirect input and output
1477 in the @code{run} command line, or you can use the @code{tty} command to
1478 set a different device for your program.
1479 @xref{Input/Output, ,Your program's input and output}.
1482 @emph{Warning:} While input and output redirection work, you cannot use
1483 pipes to pass the output of the program you are debugging to another
1484 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1489 When you issue the @code{run} command, your program begins to execute
1490 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1491 of how to arrange for your program to stop. Once your program has
1492 stopped, you may call functions in your program, using the @code{print}
1493 or @code{call} commands. @xref{Data, ,Examining Data}.
1495 If the modification time of your symbol file has changed since the
1496 last time @value{GDBN} read its symbols, @value{GDBN} will discard its symbol table and
1497 re-read it. When it does this, @value{GDBN} tries to retain your current
1502 @section Your program's arguments
1504 @cindex arguments (to your program)
1505 The arguments to your program can be specified by the arguments of the
1506 @code{run} command. They are passed to a shell, which expands wildcard
1507 characters and performs redirection of I/O, and thence to your program.
1508 Your @code{SHELL} environment variable (if it exists) specifies what
1509 shell @value{GDBN} if you do not define @code{SHELL}, @value{GDBN} uses
1512 @code{run} with no arguments uses the same arguments used by the previous
1513 @code{run}, or those set by the @code{set args} command.
1518 Specify the arguments to be used the next time your program is run. If
1519 @code{set args} has no arguments, @code{run} will execute your program
1520 with no arguments. Once you have run your program with arguments,
1521 using @code{set args} before the next @code{run} is the only way to run
1522 it again without arguments.
1526 Show the arguments to give your program when it is started.
1530 @section Your program's environment
1532 @cindex environment (of your program)
1533 The @dfn{environment} consists of a set of environment variables and
1534 their values. Environment variables conventionally record such things as
1535 your user name, your home directory, your terminal type, and your search
1536 path for programs to run. Usually you set up environment variables with
1537 the shell and they are inherited by all the other programs you run. When
1538 debugging, it can be useful to try running your program with a modified
1539 environment without having to start @value{GDBN} over again.
1542 @item path @var{directory}
1544 Add @var{directory} to the front of the @code{PATH} environment variable
1545 (the search path for executables), for both @value{GDBN} and your program.
1546 You may specify several directory names, separated by @samp{:} or
1547 whitespace. If @var{directory} is already in the path, it is moved to
1548 the front, so it will be searched sooner.
1550 You can use the string @samp{$cwd} to refer to whatever is the current
1551 working directory at the time @value{GDBN} searches the path. If you
1552 use @samp{.} instead, it refers to the directory where you executed the
1553 @code{path} command. @value{GDBN} replaces @samp{.} in the
1554 @var{directory} argument (with the current path) before adding
1555 @var{directory} to the search path.
1556 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1557 @c document that, since repeating it would be a no-op.
1561 Display the list of search paths for executables (the @code{PATH}
1562 environment variable).
1564 @item show environment @r{[}@var{varname}@r{]}
1565 @kindex show environment
1566 Print the value of environment variable @var{varname} to be given to
1567 your program when it starts. If you do not supply @var{varname},
1568 print the names and values of all environment variables to be given to
1569 your program. You can abbreviate @code{environment} as @code{env}.
1571 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1572 @kindex set environment
1573 Set environment variable @var{varname} to @var{value}. The value
1574 changes for your program only, not for @value{GDBN} itself. @var{value} may
1575 be any string; the values of environment variables are just strings, and
1576 any interpretation is supplied by your program itself. The @var{value}
1577 parameter is optional; if it is eliminated, the variable is set to a
1579 @c "any string" here does not include leading, trailing
1580 @c blanks. Gnu asks: does anyone care?
1582 For example, this command:
1589 tells a Unix program, when subsequently run, that its user is named
1590 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1591 are not actually required.)
1593 @item unset environment @var{varname}
1594 @kindex unset environment
1595 Remove variable @var{varname} from the environment to be passed to your
1596 program. This is different from @samp{set env @var{varname} =};
1597 @code{unset environment} removes the variable from the environment,
1598 rather than assigning it an empty value.
1601 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1602 by your @code{SHELL} environment variable if it exists (or
1603 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1604 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1605 @file{.bashrc} for BASH---any variables you set in that file will affect
1606 your program. You may wish to move setting of environment variables to
1607 files that are only run when you sign on, such as @file{.login} or
1610 @node Working Directory
1611 @section Your program's working directory
1613 @cindex working directory (of your program)
1614 Each time you start your program with @code{run}, it inherits its
1615 working directory from the current working directory of @value{GDBN}.
1616 The @value{GDBN} working directory is initially whatever it inherited
1617 from its parent process (typically the shell), but you can specify a new
1618 working directory in @value{GDBN} with the @code{cd} command.
1620 The @value{GDBN} working directory also serves as a default for the commands
1621 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1625 @item cd @var{directory}
1627 Set the @value{GDBN} working directory to @var{directory}.
1631 Print the @value{GDBN} working directory.
1635 @section Your program's input and output
1640 By default, the program you run under @value{GDBN} does input and output to
1641 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal to
1642 its own terminal modes to interact with you, but it records the terminal
1643 modes your program was using and switches back to them when you continue
1644 running your program.
1648 @kindex info terminal
1649 Displays information recorded by @value{GDBN} about the terminal modes your
1653 You can redirect your program's input and/or output using shell
1654 redirection with the @code{run} command. For example,
1661 starts your program, diverting its output to the file @file{outfile}.
1664 @cindex controlling terminal
1665 Another way to specify where your program should do input and output is
1666 with the @code{tty} command. This command accepts a file name as
1667 argument, and causes this file to be the default for future @code{run}
1668 commands. It also resets the controlling terminal for the child
1669 process, for future @code{run} commands. For example,
1676 directs that processes started with subsequent @code{run} commands
1677 default to do input and output on the terminal @file{/dev/ttyb} and have
1678 that as their controlling terminal.
1680 An explicit redirection in @code{run} overrides the @code{tty} command's
1681 effect on the input/output device, but not its effect on the controlling
1684 When you use the @code{tty} command or redirect input in the @code{run}
1685 command, only the input @emph{for your program} is affected. The input
1686 for @value{GDBN} still comes from your terminal.
1689 @section Debugging an already-running process
1694 @item attach @var{process-id}
1695 This command attaches to a running process---one that was started
1696 outside @value{GDBN}. (@code{info files} will show your active
1697 targets.) The command takes as argument a process ID. The usual way to
1698 find out the process-id of a Unix process is with the @code{ps} utility,
1699 or with the @samp{jobs -l} shell command.
1701 @code{attach} will not repeat if you press @key{RET} a second time after
1702 executing the command.
1705 To use @code{attach}, your program must be running in an environment
1706 which supports processes; for example, @code{attach} does not work for
1707 programs on bare-board targets that lack an operating system. You must
1708 also have permission to send the process a signal.
1710 When using @code{attach}, you should first use the @code{file} command
1711 to specify the program running in the process and load its symbol table.
1712 @xref{Files, ,Commands to Specify Files}.
1714 The first thing @value{GDBN} does after arranging to debug the specified
1715 process is to stop it. You can examine and modify an attached process
1716 with all the @value{GDBN} commands that are ordinarily available when you start
1717 processes with @code{run}. You can insert breakpoints; you can step and
1718 continue; you can modify storage. If you would rather the process
1719 continue running, you may use the @code{continue} command after
1720 attaching @value{GDBN} to the process.
1725 When you have finished debugging the attached process, you can use the
1726 @code{detach} command to release it from @value{GDBN} control. Detaching
1727 the process continues its execution. After the @code{detach} command,
1728 that process and @value{GDBN} become completely independent once more, and you
1729 are ready to @code{attach} another process or start one with @code{run}.
1730 @code{detach} will not repeat if you press @key{RET} again after
1731 executing the command.
1734 If you exit @value{GDBN} or use the @code{run} command while you have an attached
1735 process, you kill that process. By default, you will be asked for
1736 confirmation if you try to do either of these things; you can control
1737 whether or not you need to confirm by using the @code{set confirm} command
1738 (@pxref{Messages/Warnings, ,Optional warnings and messages}).
1742 @section Killing the child process
1747 Kill the child process in which your program is running under @value{GDBN}.
1750 This command is useful if you wish to debug a core dump instead of a
1751 running process. @value{GDBN} ignores any core dump file while your program
1755 On some operating systems, a program cannot be executed outside @value{GDBN}
1756 while you have breakpoints set on it inside @value{GDBN}. You can use the
1757 @code{kill} command in this situation to permit running your program
1758 outside the debugger.
1760 The @code{kill} command is also useful if you wish to recompile and
1761 relink your program, since on many systems it is impossible to modify an
1762 executable file while it is running in a process. In this case, when you
1763 next type @code{run}, @value{GDBN} will notice that the file has changed, and
1764 will re-read the symbol table (while trying to preserve your current
1765 breakpoint settings).
1767 @node Process Information
1768 @section Additional process information
1771 @cindex process image
1772 Some operating systems provide a facility called @samp{/proc} that can
1773 be used to examine the image of a running process using file-system
1774 subroutines. If @value{GDBN} is configured for an operating system with this
1775 facility, the command @code{info proc} is available to report on several
1776 kinds of information about the process running your program.
1781 Summarize available information about the process.
1783 @item info proc mappings
1784 @kindex info proc mappings
1785 Report on the address ranges accessible in the program, with information
1786 on whether your program may read, write, or execute each range.
1788 @item info proc times
1789 @kindex info proc times
1790 Starting time, user CPU time, and system CPU time for your program and
1794 @kindex info proc id
1795 Report on the process IDs related to your program: its own process ID,
1796 the ID of its parent, the process group ID, and the session ID.
1798 @item info proc status
1799 @kindex info proc status
1800 General information on the state of the process. If the process is
1801 stopped, this report includes the reason for stopping, and any signal
1805 Show all the above information about the process.
1810 @chapter Stopping and Continuing
1812 The principal purposes of using a debugger are so that you can stop your
1813 program before it terminates; or so that, if your program runs into
1814 trouble, you can investigate and find out why.
1816 Inside @value{GDBN}, your program may stop for any of several reasons, such
1821 a breakpoint, or reaching a new line after a @value{GDBN}
1822 command such as @code{step}. You may then examine and change
1823 variables, set new breakpoints or remove old ones, and then continue
1824 execution. Usually, the messages shown by @value{GDBN} provide ample
1825 explanation of the status of your program---but you can also explicitly
1826 request this information at any time.
1830 @kindex info program
1831 Display information about the status of your program: whether it is
1841 * Breakpoints:: Breakpoints, watchpoints, and exceptions
1844 * Breakpoints:: Breakpoints and watchpoints
1846 @c Remnant makeinfo bug requires blank line after *successful* end-if in menu:
1848 * Continuing and Stepping:: Resuming execution
1854 @c makeinfo node-defaulting requires adjacency of @node and sectioning cmds
1855 @c ...hence distribute @node Breakpoints over two possible @if expansions.
1859 @section Breakpoints, watchpoints, and exceptions
1863 @section Breakpoints and watchpoints
1867 A @dfn{breakpoint} makes your program stop whenever a certain point in
1868 the program is reached. For each breakpoint, you can add various
1869 conditions to control in finer detail whether your program will stop.
1870 You can set breakpoints with the @code{break} command and its variants
1871 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
1872 your program should stop by line number, function name or exact address
1875 In languages with exception handling (such as GNU C++), you can also set
1876 breakpoints where an exception is raised (@pxref{Exception Handling,
1877 ,Breakpoints and exceptions}).
1881 @cindex memory tracing
1882 @cindex breakpoint on memory address
1883 @cindex breakpoint on variable modification
1884 A @dfn{watchpoint} is a special breakpoint that stops your program
1885 when the value of an expression changes. You must use a different
1886 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
1887 watchpoints}), but aside from that, you can manage a watchpoint like
1888 any other breakpoint: you enable, disable, and delete both breakpoints
1889 and watchpoints using the same commands.
1891 You can arrange to have values from your program displayed automatically
1892 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,
1893 ,Automatic display}.
1895 @cindex breakpoint numbers
1896 @cindex numbers for breakpoints
1897 @value{GDBN} assigns a number to each breakpoint or watchpoint when you
1898 create it; these numbers are successive integers starting with one. In
1899 many of the commands for controlling various features of breakpoints you
1900 use the breakpoint number to say which breakpoint you want to change.
1901 Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
1902 no effect on your program until you enable it again.
1905 * Set Breaks:: Setting breakpoints
1906 * Set Watchpoints:: Setting watchpoints
1908 * Exception Handling:: Breakpoints and exceptions
1911 * Delete Breaks:: Deleting breakpoints
1912 * Disabling:: Disabling breakpoints
1913 * Conditions:: Break conditions
1914 * Break Commands:: Breakpoint command lists
1916 * Breakpoint Menus:: Breakpoint menus
1919 * Error in Breakpoints:: ``Cannot insert breakpoints''
1924 @subsection Setting breakpoints
1926 @c FIXME LMB what does GDB do if no code on line of breakpt?
1927 @c consider in particular declaration with/without initialization.
1929 @c FIXME 2 is there stuff on this already? break at fun start, already init?
1934 @cindex latest breakpoint
1935 Breakpoints are set with the @code{break} command (abbreviated
1936 @code{b}). The debugger convenience variable @samp{$bpnum} records the
1937 number of the beakpoint you've set most recently; see @ref{Convenience
1938 Vars,, Convenience variables}, for a discussion of what you can do with
1939 convenience variables.
1941 You have several ways to say where the breakpoint should go.
1944 @item break @var{function}
1945 Set a breakpoint at entry to function @var{function}.
1947 When using source languages that permit overloading of symbols, such as
1948 C++, @var{function} may refer to more than one possible place to break.
1949 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
1952 @item break +@var{offset}
1953 @itemx break -@var{offset}
1954 Set a breakpoint some number of lines forward or back from the position
1955 at which execution stopped in the currently selected frame.
1957 @item break @var{linenum}
1958 Set a breakpoint at line @var{linenum} in the current source file.
1959 That file is the last file whose source text was printed. This
1960 breakpoint will stop your program just before it executes any of the
1963 @item break @var{filename}:@var{linenum}
1964 Set a breakpoint at line @var{linenum} in source file @var{filename}.
1966 @item break @var{filename}:@var{function}
1967 Set a breakpoint at entry to function @var{function} found in file
1968 @var{filename}. Specifying a file name as well as a function name is
1969 superfluous except when multiple files contain similarly named
1972 @item break *@var{address}
1973 Set a breakpoint at address @var{address}. You can use this to set
1974 breakpoints in parts of your program which do not have debugging
1975 information or source files.
1978 When called without any arguments, @code{break} sets a breakpoint at
1979 the next instruction to be executed in the selected stack frame
1980 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
1981 innermost, this will cause your program to stop as soon as control
1982 returns to that frame. This is similar to the effect of a
1983 @code{finish} command in the frame inside the selected frame---except
1984 that @code{finish} does not leave an active breakpoint. If you use
1985 @code{break} without an argument in the innermost frame, @value{GDBN} will stop
1986 the next time it reaches the current location; this may be useful
1989 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
1990 least one instruction has been executed. If it did not do this, you
1991 would be unable to proceed past a breakpoint without first disabling the
1992 breakpoint. This rule applies whether or not the breakpoint already
1993 existed when your program stopped.
1995 @item break @dots{} if @var{cond}
1996 Set a breakpoint with condition @var{cond}; evaluate the expression
1997 @var{cond} each time the breakpoint is reached, and stop only if the
1998 value is nonzero---that is, if @var{cond} evaluates as true.
1999 @samp{@dots{}} stands for one of the possible arguments described
2000 above (or no argument) specifying where to break. @xref{Conditions,
2001 ,Break conditions}, for more information on breakpoint conditions.
2003 @item tbreak @var{args}
2005 Set a breakpoint enabled only for one stop. @var{args} are the
2006 same as for the @code{break} command, and the breakpoint is set in the same
2007 way, but the breakpoint is automatically disabled after the first time your
2008 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2010 @item rbreak @var{regex}
2012 @cindex regular expression
2013 @c FIXME what kind of regexp?
2014 Set breakpoints on all functions matching the regular expression
2015 @var{regex}. This command
2016 sets an unconditional breakpoint on all matches, printing a list of all
2017 breakpoints it set. Once these breakpoints are set, they are treated
2018 just like the breakpoints set with the @code{break} command. They can
2019 be deleted, disabled, made conditional, etc., in the standard ways.
2022 When debugging C++ programs, @code{rbreak} is useful for setting
2023 breakpoints on overloaded functions that are not members of any special
2027 @kindex info breakpoints
2028 @cindex @code{$_} and @code{info breakpoints}
2029 @item info breakpoints @r{[}@var{n}@r{]}
2030 @itemx info break @r{[}@var{n}@r{]}
2031 @itemx info watchpoints @r{[}@var{n}@r{]}
2032 Print a table of all breakpoints and watchpoints set and not
2033 deleted, with the following columns for each breakpoint:
2036 @item Breakpoint Numbers
2038 Breakpoint or watchpoint.
2040 Whether the breakpoint is marked to be disabled or deleted when hit.
2041 @item Enabled or Disabled
2042 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2043 that are not enabled.
2045 Where the breakpoint is in your program, as a memory address
2047 Where the breakpoint is in the source for your program, as a file and
2052 If a breakpoint is conditional, @code{info break} shows the condition on
2053 the line following the affected breakpoint; breakpoint commands, if any,
2054 are listed after that.
2057 @code{info break} with a breakpoint
2058 number @var{n} as argument lists only that breakpoint. The
2059 convenience variable @code{$_} and the default examining-address for
2060 the @code{x} command are set to the address of the last breakpoint
2061 listed (@pxref{Memory, ,Examining memory}).
2064 @value{GDBN} allows you to set any number of breakpoints at the same place in
2065 your program. There is nothing silly or meaningless about this. When
2066 the breakpoints are conditional, this is even useful
2067 (@pxref{Conditions, ,Break conditions}).
2069 @cindex negative breakpoint numbers
2070 @cindex internal @value{GDBN} breakpoints
2071 @value{GDBN} itself sometimes sets breakpoints in your program for special
2072 purposes, such as proper handling of @code{longjmp} (in C programs).
2073 These internal breakpoints are assigned negative numbers, starting with
2074 @code{-1}; @samp{info breakpoints} does not display them.
2076 You can see these breakpoints with the @value{GDBN} maintenance command
2077 @samp{maint info breakpoints}.
2080 @kindex maint info breakpoints
2081 @item maint info breakpoints
2082 Using the same format as @samp{info breakpoints}, display both the
2083 breakpoints you've set explicitly, and those @value{GDBN} is using for
2084 internal purposes. Internal breakpoints are shown with negative
2085 breakpoint numbers. The type column identifies what kind of breakpoint
2090 Normal, explicitly set breakpoint.
2093 Normal, explicitly set watchpoint.
2096 Internal breakpoint, used to handle correctly stepping through
2097 @code{longjmp} calls.
2099 @item longjmp resume
2100 Internal breakpoint at the target of a @code{longjmp}.
2103 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2106 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2112 @node Set Watchpoints
2113 @subsection Setting watchpoints
2114 @cindex setting watchpoints
2116 You can use a watchpoint to stop execution whenever the value of an
2117 expression changes, without having to predict a particular place
2118 where this may happen.
2120 Watchpoints currently execute two orders of magnitude more slowly than
2121 other breakpoints, but this can be well worth it to catch errors where
2122 you have no clue what part of your program is the culprit. Some
2123 processors provide special hardware to support watchpoint evaluation; future
2124 releases of @value{GDBN} will use such hardware if it is available.
2128 @item watch @var{expr}
2129 Set a watchpoint for an expression.
2131 @kindex info watchpoints
2132 @item info watchpoints
2133 This command prints a list of watchpoints and breakpoints; it is the
2134 same as @code{info break}.
2138 @node Exception Handling
2139 @subsection Breakpoints and exceptions
2140 @cindex exception handlers
2142 Some languages, such as GNU C++, implement exception handling. You can
2143 use @value{GDBN} to examine what caused your program to raise an exception,
2144 and to list the exceptions your program is prepared to handle at a
2145 given point in time.
2148 @item catch @var{exceptions}
2150 You can set breakpoints at active exception handlers by using the
2151 @code{catch} command. @var{exceptions} is a list of names of exceptions
2155 You can use @code{info catch} to list active exception handlers.
2156 @xref{Frame Info, ,Information about a frame}.
2158 There are currently some limitations to exception handling in @value{GDBN}.
2159 These will be corrected in a future release.
2163 If you call a function interactively, @value{GDBN} normally returns
2164 control to you when the function has finished executing. If the call
2165 raises an exception, however, the call may bypass the mechanism that
2166 returns control to you and cause your program to simply continue
2167 running until it hits a breakpoint, catches a signal that @value{GDBN} is
2168 listening for, or exits.
2170 You cannot raise an exception interactively.
2172 You cannot interactively install an exception handler.
2175 @cindex raise exceptions
2176 Sometimes @code{catch} is not the best way to debug exception handling:
2177 if you need to know exactly where an exception is raised, it is better to
2178 stop @emph{before} the exception handler is called, since that way you
2179 can see the stack before any unwinding takes place. If you set a
2180 breakpoint in an exception handler instead, it may not be easy to find
2181 out where the exception was raised.
2183 To stop just before an exception handler is called, you need some
2184 knowledge of the implementation. In the case of GNU C++, exceptions are
2185 raised by calling a library function named @code{__raise_exception}
2186 which has the following ANSI C interface:
2189 /* @var{addr} is where the exception identifier is stored.
2190 ID is the exception identifier. */
2191 void __raise_exception (void **@var{addr}, void *@var{id});
2195 To make the debugger catch all exceptions before any stack
2196 unwinding takes place, set a breakpoint on @code{__raise_exception}
2197 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2199 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2200 that depends on the value of @var{id}, you can stop your program when
2201 a specific exception is raised. You can use multiple conditional
2202 breakpoints to stop your program when any of a number of exceptions are
2207 @subsection Deleting breakpoints
2209 @cindex clearing breakpoints, watchpoints
2210 @cindex deleting breakpoints, watchpoints
2211 It is often necessary to eliminate a breakpoint or watchpoint once it
2212 has done its job and you no longer want your program to stop there. This
2213 is called @dfn{deleting} the breakpoint. A breakpoint that has been
2214 deleted no longer exists; it is forgotten.
2216 With the @code{clear} command you can delete breakpoints according to
2217 where they are in your program. With the @code{delete} command you can
2218 delete individual breakpoints or watchpoints by specifying their
2221 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2222 automatically ignores breakpoints on the first instruction to be executed
2223 when you continue execution without changing the execution address.
2228 Delete any breakpoints at the next instruction to be executed in the
2229 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2230 the innermost frame is selected, this is a good way to delete a
2231 breakpoint where your program just stopped.
2233 @item clear @var{function}
2234 @itemx clear @var{filename}:@var{function}
2235 Delete any breakpoints set at entry to the function @var{function}.
2237 @item clear @var{linenum}
2238 @itemx clear @var{filename}:@var{linenum}
2239 Delete any breakpoints set at or within the code of the specified line.
2241 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2242 @cindex delete breakpoints
2245 Delete the breakpoints or watchpoints of the numbers specified as
2246 arguments. If no argument is specified, delete all breakpoints (@value{GDBN}
2247 asks confirmation, unless you have @code{set confirm off}). You
2248 can abbreviate this command as @code{d}.
2252 @subsection Disabling breakpoints
2254 @cindex disabled breakpoints
2255 @cindex enabled breakpoints
2256 Rather than deleting a breakpoint or watchpoint, you might prefer to
2257 @dfn{disable} it. This makes the breakpoint inoperative as if it had
2258 been deleted, but remembers the information on the breakpoint so that
2259 you can @dfn{enable} it again later.
2261 You disable and enable breakpoints and watchpoints with the
2262 @code{enable} and @code{disable} commands, optionally specifying one or
2263 more breakpoint numbers as arguments. Use @code{info break} or
2264 @code{info watch} to print a list of breakpoints or watchpoints if you
2265 do not know which numbers to use.
2267 A breakpoint or watchpoint can have any of four different states of
2272 Enabled. The breakpoint will stop your program. A breakpoint set
2273 with the @code{break} command starts out in this state.
2275 Disabled. The breakpoint has no effect on your program.
2277 Enabled once. The breakpoint will stop your program, but
2278 when it does so it will become disabled. A breakpoint set
2279 with the @code{tbreak} command starts out in this state.
2281 Enabled for deletion. The breakpoint will stop your program, but
2282 immediately after it does so it will be deleted permanently.
2285 You can use the following commands to enable or disable breakpoints and
2289 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2290 @kindex disable breakpoints
2293 Disable the specified breakpoints---or all breakpoints, if none are
2294 listed. A disabled breakpoint has no effect but is not forgotten. All
2295 options such as ignore-counts, conditions and commands are remembered in
2296 case the breakpoint is enabled again later. You may abbreviate
2297 @code{disable} as @code{dis}.
2299 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2300 @kindex enable breakpoints
2302 Enable the specified breakpoints (or all defined breakpoints). They
2303 become effective once again in stopping your program.
2305 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2306 Enable the specified breakpoints temporarily. Each will be disabled
2307 again the next time it stops your program.
2309 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2310 Enable the specified breakpoints to work once and then die. Each of
2311 the breakpoints will be deleted the next time it stops your program.
2314 Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2315 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2316 subsequently, they become disabled or enabled only when you use one of
2317 the commands above. (The command @code{until} can set and delete a
2318 breakpoint of its own, but it will not change the state of your other
2319 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2323 @subsection Break conditions
2324 @cindex conditional breakpoints
2325 @cindex breakpoint conditions
2327 @c FIXME what is scope of break condition expr? Context where wanted?
2328 @c in particular for a watchpoint?
2329 The simplest sort of breakpoint breaks every time your program reaches a
2330 specified place. You can also specify a @dfn{condition} for a
2331 breakpoint. A condition is just a Boolean expression in your
2332 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2333 a condition evaluates the expression each time your program reaches it,
2334 and your program stops only if the condition is @emph{true}.
2336 This is the converse of using assertions for program validation; in that
2337 situation, you want to stop when the assertion is violated---that is,
2338 when the condition is false. In C, if you want to test an assertion expressed
2339 by the condition @var{assert}, you should set the condition
2340 @samp{! @var{assert}} on the appropriate breakpoint.
2342 Conditions are also accepted for watchpoints; you may not need them,
2343 since a watchpoint is inspecting the value of an expression anyhow---but
2344 it might be simpler, say, to just set a watchpoint on a variable name,
2345 and specify a condition that tests whether the new value is an interesting
2348 Break conditions can have side effects, and may even call functions in
2349 your program. This can be useful, for example, to activate functions
2350 that log program progress, or to use your own print functions to
2351 format special data structures. The effects are completely predictable
2352 unless there is another enabled breakpoint at the same address. (In
2353 that case, @value{GDBN} might see the other breakpoint first and stop your
2354 program without checking the condition of this one.) Note that
2355 breakpoint commands are usually more convenient and flexible for the
2356 purpose of performing side effects when a breakpoint is reached
2357 (@pxref{Break Commands, ,Breakpoint command lists}).
2359 Break conditions can be specified when a breakpoint is set, by using
2360 @samp{if} in the arguments to the @code{break} command. @xref{Set
2361 Breaks, ,Setting breakpoints}. They can also be changed at any time
2362 with the @code{condition} command. The @code{watch} command does not
2363 recognize the @code{if} keyword; @code{condition} is the only way to
2364 impose a further condition on a watchpoint.
2367 @item condition @var{bnum} @var{expression}
2369 Specify @var{expression} as the break condition for breakpoint or
2370 watchpoint number @var{bnum}. From now on, this breakpoint will stop
2371 your program only if the value of @var{expression} is true (nonzero, in
2372 C). When you use @code{condition}, @value{GDBN} checks @var{expression}
2373 immediately for syntactic correctness, and to determine whether symbols
2374 in it have referents in the context of your breakpoint.
2375 @c FIXME so what does GDB do if there is no referent? Moreover, what
2376 @c about watchpoints?
2378 not actually evaluate @var{expression} at the time the @code{condition}
2379 command is given, however. @xref{Expressions, ,Expressions}.
2381 @item condition @var{bnum}
2382 Remove the condition from breakpoint number @var{bnum}. It becomes
2383 an ordinary unconditional breakpoint.
2386 @cindex ignore count (of breakpoint)
2387 A special case of a breakpoint condition is to stop only when the
2388 breakpoint has been reached a certain number of times. This is so
2389 useful that there is a special way to do it, using the @dfn{ignore
2390 count} of the breakpoint. Every breakpoint has an ignore count, which
2391 is an integer. Most of the time, the ignore count is zero, and
2392 therefore has no effect. But if your program reaches a breakpoint whose
2393 ignore count is positive, then instead of stopping, it just decrements
2394 the ignore count by one and continues. As a result, if the ignore count
2395 value is @var{n}, the breakpoint will not stop the next @var{n} times it
2399 @item ignore @var{bnum} @var{count}
2401 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2402 The next @var{count} times the breakpoint is reached, your program's
2403 execution will not stop; other than to decrement the ignore count, @value{GDBN}
2406 To make the breakpoint stop the next time it is reached, specify
2409 When you use @code{continue} to resume execution of your program from a
2410 breakpoint, you can specify an ignore count directly as an argument to
2411 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
2412 Stepping,,Continuing and stepping}.
2414 If a breakpoint has a positive ignore count and a condition, the condition
2415 is not checked. Once the ignore count reaches zero, the condition will
2418 You could achieve the effect of the ignore count with a condition such
2419 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2420 is decremented each time. @xref{Convenience Vars, ,Convenience
2424 @node Break Commands
2425 @subsection Breakpoint command lists
2427 @cindex breakpoint commands
2428 You can give any breakpoint (or watchpoint) a series of commands to
2429 execute when your program stops due to that breakpoint. For example, you
2430 might want to print the values of certain expressions, or enable other
2434 @item commands @r{[}@var{bnum}@r{]}
2435 @itemx @dots{} @var{command-list} @dots{}
2439 Specify a list of commands for breakpoint number @var{bnum}. The commands
2440 themselves appear on the following lines. Type a line containing just
2441 @code{end} to terminate the commands.
2443 To remove all commands from a breakpoint, type @code{commands} and
2444 follow it immediately with @code{end}; that is, give no commands.
2446 With no @var{bnum} argument, @code{commands} refers to the last
2447 breakpoint or watchpoint set (not to the breakpoint most recently
2451 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2452 disabled within a @var{command-list}.
2454 You can use breakpoint commands to start your program up again. Simply
2455 use the @code{continue} command, or @code{step}, or any other command
2456 that resumes execution.
2458 Any other commands in the command list, after a command that resumes
2459 execution, are ignored. This is because any time you resume execution
2460 (even with a simple @code{next} or @code{step}), you may encounter
2461 another breakpoint---which could have its own command list, leading to
2462 ambiguities about which list to execute.
2465 If the first command you specify in a command list is @code{silent}, the
2466 usual message about stopping at a breakpoint is not printed. This may
2467 be desirable for breakpoints that are to print a specific message and
2468 then continue. If none of the remaining commands print anything, you
2469 will see no sign that the breakpoint was reached. @code{silent} is
2470 meaningful only at the beginning of a breakpoint command list.
2472 The commands @code{echo}, @code{output}, and @code{printf} allow you to
2473 print precisely controlled output, and are often useful in silent
2474 breakpoints. @xref{Output, ,Commands for controlled output}.
2476 For example, here is how you could use breakpoint commands to print the
2477 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2483 printf "x is %d\n",x
2488 One application for breakpoint commands is to compensate for one bug so
2489 you can test for another. Put a breakpoint just after the erroneous line
2490 of code, give it a condition to detect the case in which something
2491 erroneous has been done, and give it commands to assign correct values
2492 to any variables that need them. End with the @code{continue} command
2493 so that your program does not stop, and start with the @code{silent}
2494 command so that no output is produced. Here is an example:
2506 @node Breakpoint Menus
2507 @subsection Breakpoint menus
2509 @cindex symbol overloading
2511 Some programming languages (notably C++) permit a single function name
2512 to be defined several times, for application in different contexts.
2513 This is called @dfn{overloading}. When a function name is overloaded,
2514 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
2515 a breakpoint. If you realize this will be a problem, you can use
2516 something like @samp{break @var{function}(@var{types})} to specify which
2517 particular version of the function you want. Otherwise, @value{GDBN} offers
2518 you a menu of numbered choices for different possible breakpoints, and
2519 waits for your selection with the prompt @samp{>}. The first two
2520 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
2521 sets a breakpoint at each definition of @var{function}, and typing
2522 @kbd{0} aborts the @code{break} command without setting any new
2525 For example, the following session excerpt shows an attempt to set a
2526 breakpoint at the overloaded symbol @code{String::after}.
2527 We choose three particular definitions of that function name:
2529 @c FIXME! This is likely to change to show arg type lists, at least
2531 (@value{GDBP}) b String::after
2534 [2] file:String.cc; line number:867
2535 [3] file:String.cc; line number:860
2536 [4] file:String.cc; line number:875
2537 [5] file:String.cc; line number:853
2538 [6] file:String.cc; line number:846
2539 [7] file:String.cc; line number:735
2541 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2542 Breakpoint 2 at 0xb344: file String.cc, line 875.
2543 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2544 Multiple breakpoints were set.
2545 Use the "delete" command to delete unwanted
2552 @node Error in Breakpoints
2553 @subsection ``Cannot insert breakpoints''
2555 @c FIXME: "cannot insert breakpoints" error, v unclear.
2556 @c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91
2557 @c some light may be shed by looking at instances of
2558 @c ONE_PROCESS_WRITETEXT. But error message seems possible otherwise
2559 @c too. pesch, 20sep91
2560 Under some operating systems, breakpoints cannot be used in a program if
2561 any other process is running that program. In this situation,
2562 attempting to run or continue a program with a breakpoint causes @value{GDBN}
2563 to stop the other process.
2565 When this happens, you have three ways to proceed:
2569 Remove or disable the breakpoints, then continue.
2572 Suspend @value{GDBN}, and copy the file containing your program to a new name.
2573 Resume @value{GDBN} and use the @code{exec-file} command to specify that @value{GDBN}
2574 should run your program under that name. Then start your program again.
2576 @c FIXME: RMS commented here "Show example". Maybe when someone
2577 @c explains the first FIXME: in this section...
2580 Relink your program so that the text segment is nonsharable, using the
2581 linker option @samp{-N}. The operating system limitation may not apply
2582 to nonsharable executables.
2586 @node Continuing and Stepping
2587 @section Continuing and stepping
2591 @cindex resuming execution
2592 @dfn{Continuing} means resuming program execution until your program
2593 completes normally. In contrast, @dfn{stepping} means executing just
2594 one more ``step'' of your program, where ``step'' may mean either one
2595 line of source code, or one machine instruction (depending on what
2596 particular command you use). Either when continuing
2597 or when stepping, your program may stop even sooner, due to
2602 a breakpoint or a signal. (If due to a signal, you may want to use
2603 @code{handle}, or use @samp{signal 0} to resume execution.
2604 @xref{Signals, ,Signals}.)
2608 @item continue @r{[}@var{ignore-count}@r{]}
2609 @itemx c @r{[}@var{ignore-count}@r{]}
2610 @itemx fg @r{[}@var{ignore-count}@r{]}
2614 Resume program execution, at the address where your program last stopped;
2615 any breakpoints set at that address are bypassed. The optional argument
2616 @var{ignore-count} allows you to specify a further number of times to
2617 ignore a breakpoint at this location; its effect is like that of
2618 @code{ignore} (@pxref{Conditions, ,Break conditions}).
2620 The argument @var{ignore-count} is meaningful only when your program
2621 stopped due to a breakpoint. At other times, the argument to
2622 @code{continue} is ignored.
2624 The synonyms @code{c} and @code{fg} are provided purely for convenience,
2625 and have exactly the same behavior as @code{continue}.
2628 To resume execution at a different place, you can use @code{return}
2629 (@pxref{Returning, ,Returning from a function}) to go back to the
2630 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
2631 different address}) to go to an arbitrary location in your program.
2633 A typical technique for using stepping is to set a breakpoint
2635 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions})
2638 (@pxref{Breakpoints, ,Breakpoints and watchpoints})
2641 beginning of the function or the section of your program where a
2642 problem is believed to lie, run your program until it stops at that
2643 breakpoint, and then step through the suspect area, examining the
2644 variables that are interesting, until you see the problem happen.
2650 Continue running your program until control reaches a different source
2651 line, then stop it and return control to @value{GDBN}. This command is
2652 abbreviated @code{s}.
2655 @emph{Warning:} If you use the @code{step} command while control is
2656 within a function that was compiled without debugging information,
2657 execution proceeds until control reaches a function that does have
2658 debugging information.
2661 @item step @var{count}
2662 Continue running as in @code{step}, but do so @var{count} times. If a
2663 breakpoint is reached,
2665 or a signal not related to stepping occurs before @var{count} steps,
2667 stepping stops right away.
2669 @item next @r{[}@var{count}@r{]}
2672 Continue to the next source line in the current (innermost) stack frame.
2673 Similar to @code{step}, but any function calls appearing within the line
2674 of code are executed without stopping. Execution stops when control
2675 reaches a different line of code at the stack level which was executing
2676 when the @code{next} command was given. This command is abbreviated
2679 An argument @var{count} is a repeat count, as for @code{step}.
2681 @code{next} within a function that lacks debugging information acts like
2682 @code{step}, but any function calls appearing within the code of the
2683 function are executed without stopping.
2687 Continue running until just after function in the selected stack frame
2688 returns. Print the returned value (if any).
2690 Contrast this with the @code{return} command (@pxref{Returning,
2691 ,Returning from a function}).
2697 Continue running until a source line past the current line, in the
2698 current stack frame, is reached. This command is used to avoid single
2699 stepping through a loop more than once. It is like the @code{next}
2700 command, except that when @code{until} encounters a jump, it
2701 automatically continues execution until the program counter is greater
2702 than the address of the jump.
2704 This means that when you reach the end of a loop after single stepping
2705 though it, @code{until} will cause your program to continue execution
2706 until the loop is exited. In contrast, a @code{next} command at the end
2707 of a loop will simply step back to the beginning of the loop, which
2708 would force you to step through the next iteration.
2710 @code{until} always stops your program if it attempts to exit the current
2713 @code{until} may produce somewhat counterintuitive results if the order
2714 of machine code does not match the order of the source lines. For
2715 example, in the following excerpt from a debugging session, the @code{f}
2716 (@code{frame}) command shows that execution is stopped at line
2717 @code{206}; yet when we use @code{until}, we get to line @code{195}:
2721 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
2723 (@value{GDBP}) until
2724 195 for ( ; argc > 0; NEXTARG) @{
2727 This happened because, for execution efficiency, the compiler had
2728 generated code for the loop closure test at the end, rather than the
2729 start, of the loop---even though the test in a C @code{for}-loop is
2730 written before the body of the loop. The @code{until} command appeared
2731 to step back to the beginning of the loop when it advanced to this
2732 expression; however, it has not really gone to an earlier
2733 statement---not in terms of the actual machine code.
2735 @code{until} with no argument works by means of single
2736 instruction stepping, and hence is slower than @code{until} with an
2739 @item until @var{location}
2740 @itemx u @var{location}
2741 Continue running your program until either the specified location is
2742 reached, or the current stack frame returns. @var{location} is any of
2743 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
2744 ,Setting breakpoints}). This form of the command uses breakpoints,
2745 and hence is quicker than @code{until} without an argument.
2751 Execute one machine instruction, then stop and return to the debugger.
2753 It is often useful to do @samp{display/i $pc} when stepping by machine
2754 instructions. This will cause the next instruction to be executed to
2755 be displayed automatically at each stop. @xref{Auto Display,
2756 ,Automatic display}.
2758 An argument is a repeat count, as in @code{step}.
2765 Execute one machine instruction, but if it is a function call,
2766 proceed until the function returns.
2768 An argument is a repeat count, as in @code{next}.
2776 A signal is an asynchronous event that can happen in a program. The
2777 operating system defines the possible kinds of signals, and gives each
2778 kind a name and a number. For example, in Unix @code{SIGINT} is the
2779 signal a program gets when you type an interrupt (often @kbd{C-c});
2780 @code{SIGSEGV} is the signal a program gets from referencing a place in
2781 memory far away from all the areas in use; @code{SIGALRM} occurs when
2782 the alarm clock timer goes off (which happens only if your program has
2783 requested an alarm).
2785 @cindex fatal signals
2786 Some signals, including @code{SIGALRM}, are a normal part of the
2787 functioning of your program. Others, such as @code{SIGSEGV}, indicate
2788 errors; these signals are @dfn{fatal} (kill your program immediately) if the
2789 program has not specified in advance some other way to handle the signal.
2790 @code{SIGINT} does not indicate an error in your program, but it is normally
2791 fatal so it can carry out the purpose of the interrupt: to kill the program.
2793 @value{GDBN} has the ability to detect any occurrence of a signal in your
2794 program. You can tell @value{GDBN} in advance what to do for each kind of
2797 @cindex handling signals
2798 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
2799 (so as not to interfere with their role in the functioning of your program)
2800 but to stop your program immediately whenever an error signal happens.
2801 You can change these settings with the @code{handle} command.
2805 @kindex info signals
2806 Print a table of all the kinds of signals and how @value{GDBN} has been told to
2807 handle each one. You can use this to see the signal numbers of all
2808 the defined types of signals.
2810 @item handle @var{signal} @var{keywords}@dots{}
2812 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can be the
2813 number of a signal or its name (with or without the @samp{SIG} at the
2814 beginning). The @var{keywords} say what change to make.
2818 The keywords allowed by the @code{handle} command can be abbreviated.
2819 Their full names are:
2823 @value{GDBN} should not stop your program when this signal happens. It may
2824 still print a message telling you that the signal has come in.
2827 @value{GDBN} should stop your program when this signal happens. This implies
2828 the @code{print} keyword as well.
2831 @value{GDBN} should print a message when this signal happens.
2834 @value{GDBN} should not mention the occurrence of the signal at all. This
2835 implies the @code{nostop} keyword as well.
2838 @value{GDBN} should allow your program to see this signal; your program will be
2839 able to handle the signal, or may be terminated if the signal is fatal
2843 @value{GDBN} should not allow your program to see this signal.
2847 When a signal stops your program, the signal is not visible until you
2848 continue. Your program will see the signal then, if @code{pass} is in
2849 effect for the signal in question @emph{at that time}. In other words,
2850 after @value{GDBN} reports a signal, you can use the @code{handle}
2851 command with @code{pass} or @code{nopass} to control whether that
2852 signal will be seen by your program when you later continue it.
2854 You can also use the @code{signal} command to prevent your program from
2855 seeing a signal, or cause it to see a signal it normally would not see,
2856 or to give it any signal at any time. For example, if your program stopped
2857 due to some sort of memory reference error, you might store correct
2858 values into the erroneous variables and continue, hoping to see more
2859 execution; but your program would probably terminate immediately as
2860 a result of the fatal signal once it saw the signal. To prevent this,
2861 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
2866 @chapter Examining the Stack
2868 When your program has stopped, the first thing you need to know is where it
2869 stopped and how it got there.
2872 Each time your program performs a function call, the information about
2873 where in your program the call was made from is saved in a block of data
2874 called a @dfn{stack frame}. The frame also contains the arguments of the
2875 call and the local variables of the function that was called. All the
2876 stack frames are allocated in a region of memory called the @dfn{call
2879 When your program stops, the @value{GDBN} commands for examining the
2880 stack allow you to see all of this information.
2882 @cindex selected frame
2883 One of the stack frames is @dfn{selected} by @value{GDBN} and many
2884 @value{GDBN} commands refer implicitly to the selected frame. In
2885 particular, whenever you ask @value{GDBN} for the value of a variable in
2886 your program, the value is found in the selected frame. There are
2887 special @value{GDBN} commands to select whichever frame you are
2890 When your program stops, @value{GDBN} automatically selects the
2891 currently executing frame and describes it briefly as the @code{frame}
2892 command does (@pxref{Frame Info, ,Information about a frame}).
2895 * Frames:: Stack frames
2896 * Backtrace:: Backtraces
2897 * Selection:: Selecting a frame
2898 * Frame Info:: Information on a frame
2900 * MIPS Stack:: MIPS machines and the function stack
2905 @section Stack frames
2909 The call stack is divided up into contiguous pieces called @dfn{stack
2910 frames}, or @dfn{frames} for short; each frame is the data associated
2911 with one call to one function. The frame contains the arguments given
2912 to the function, the function's local variables, and the address at
2913 which the function is executing.
2915 @cindex initial frame
2916 @cindex outermost frame
2917 @cindex innermost frame
2918 When your program is started, the stack has only one frame, that of the
2919 function @code{main}. This is called the @dfn{initial} frame or the
2920 @dfn{outermost} frame. Each time a function is called, a new frame is
2921 made. Each time a function returns, the frame for that function invocation
2922 is eliminated. If a function is recursive, there can be many frames for
2923 the same function. The frame for the function in which execution is
2924 actually occurring is called the @dfn{innermost} frame. This is the most
2925 recently created of all the stack frames that still exist.
2927 @cindex frame pointer
2928 Inside your program, stack frames are identified by their addresses. A
2929 stack frame consists of many bytes, each of which has its own address; each
2930 kind of computer has a convention for choosing one of those bytes whose
2931 address serves as the address of the frame. Usually this address is kept
2932 in a register called the @dfn{frame pointer register} while execution is
2933 going on in that frame.
2935 @cindex frame number
2936 @value{GDBN} assigns numbers to all existing stack frames, starting with
2937 zero for the innermost frame, one for the frame that called it,
2938 and so on upward. These numbers do not really exist in your program;
2939 they are assigned by @value{GDBN} to give you a way of designating stack
2940 frames in @value{GDBN} commands.
2942 @c below produces an acceptable overful hbox. --mew 13aug1993
2943 @cindex frameless execution
2944 Some compilers provide a way to compile functions so that they operate
2945 without stack frames. (For example, the @code{@value{GCC}} option
2946 @samp{-fomit-frame-pointer} will generate functions without a frame.)
2947 This is occasionally done with heavily used library functions to save
2948 the frame setup time. @value{GDBN} has limited facilities for dealing
2949 with these function invocations. If the innermost function invocation
2950 has no stack frame, @value{GDBN} will nevertheless regard it as though
2951 it had a separate frame, which is numbered zero as usual, allowing
2952 correct tracing of the function call chain. However, @value{GDBN} has
2953 no provision for frameless functions elsewhere in the stack.
2958 A backtrace is a summary of how your program got where it is. It shows one
2959 line per frame, for many frames, starting with the currently executing
2960 frame (frame zero), followed by its caller (frame one), and on up the
2968 Print a backtrace of the entire stack: one line per frame for all
2969 frames in the stack.
2971 You can stop the backtrace at any time by typing the system interrupt
2972 character, normally @kbd{C-c}.
2974 @item backtrace @var{n}
2976 Similar, but print only the innermost @var{n} frames.
2978 @item backtrace -@var{n}
2980 Similar, but print only the outermost @var{n} frames.
2986 The names @code{where} and @code{info stack} (abbreviated @code{info s})
2987 are additional aliases for @code{backtrace}.
2989 Each line in the backtrace shows the frame number and the function name.
2990 The program counter value is also shown---unless you use @code{set
2991 print address off}. The backtrace also shows the source file name and
2992 line number, as well as the arguments to the function. The program
2993 counter value is omitted if it is at the beginning of the code for that
2996 Here is an example of a backtrace. It was made with the command
2997 @samp{bt 3}, so it shows the innermost three frames.
3001 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3003 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3004 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3006 (More stack frames follow...)
3011 The display for frame zero does not begin with a program counter
3012 value, indicating that your program has stopped at the beginning of the
3013 code for line @code{993} of @code{builtin.c}.
3016 @section Selecting a frame
3018 Most commands for examining the stack and other data in your program work on
3019 whichever stack frame is selected at the moment. Here are the commands for
3020 selecting a stack frame; all of them finish by printing a brief description
3021 of the stack frame just selected.
3028 Select frame number @var{n}. Recall that frame zero is the innermost
3029 (currently executing) frame, frame one is the frame that called the
3030 innermost one, and so on. The highest-numbered frame is the one for
3033 @item frame @var{addr}
3035 Select the frame at address @var{addr}. This is useful mainly if the
3036 chaining of stack frames has been damaged by a bug, making it
3037 impossible for @value{GDBN} to assign numbers properly to all frames. In
3038 addition, this can be useful when your program has multiple stacks and
3039 switches between them.
3042 On the SPARC architecture, @code{frame} needs two addresses to
3043 select an arbitrary frame: a frame pointer and a stack pointer.
3044 @c note to future updaters: this is conditioned on a flag
3045 @c FRAME_SPECIFICATION_DYADIC in the tm-*.h files, currently only used
3046 @c by SPARC, hence the specific attribution. Generalize or list all
3047 @c possibilities if more supported machines start doing this.
3052 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3053 advances toward the outermost frame, to higher frame numbers, to frames
3054 that have existed longer. @var{n} defaults to one.
3059 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3060 advances toward the innermost frame, to lower frame numbers, to frames
3061 that were created more recently. @var{n} defaults to one. You may
3062 abbreviate @code{down} as @code{do}.
3065 All of these commands end by printing two lines of output describing the
3066 frame. The first line shows the frame number, the function name, the
3067 arguments, and the source file and line number of execution in that
3068 frame. The second line shows the text of that source line.
3074 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3076 10 read_input_file (argv[i]);
3080 After such a printout, the @code{list} command with no arguments will
3081 print ten lines centered on the point of execution in the frame.
3082 @xref{List, ,Printing source lines}.
3085 @item up-silently @var{n}
3086 @itemx down-silently @var{n}
3087 @kindex down-silently
3089 These two commands are variants of @code{up} and @code{down},
3090 respectively; they differ in that they do their work silently, without
3091 causing display of the new frame. They are intended primarily for use
3092 in @value{GDBN} command scripts, where the output might be unnecessary and
3097 @section Information about a frame
3099 There are several other commands to print information about the selected
3105 When used without any argument, this command does not change which
3106 frame is selected, but prints a brief description of the currently
3107 selected stack frame. It can be abbreviated @code{f}. With an
3108 argument, this command is used to select a stack frame.
3109 @xref{Selection, ,Selecting a frame}.
3115 This command prints a verbose description of the selected stack frame,
3116 including the address of the frame, the addresses of the next frame down
3117 (called by this frame) and the next frame up (caller of this frame), the
3118 language that the source code corresponding to this frame was written in,
3119 the address of the frame's arguments, the program counter saved in it
3120 (the address of execution in the caller frame), and which registers
3121 were saved in the frame. The verbose description is useful when
3122 something has gone wrong that has made the stack format fail to fit
3123 the usual conventions.
3125 @item info frame @var{addr}
3126 @itemx info f @var{addr}
3127 Print a verbose description of the frame at address @var{addr},
3128 without selecting that frame. The selected frame remains unchanged by
3133 Print the arguments of the selected frame, each on a separate line.
3137 Print the local variables of the selected frame, each on a separate
3138 line. These are all variables (declared either static or automatic)
3139 accessible at the point of execution of the selected frame.
3144 @cindex catch exceptions
3145 @cindex exception handlers
3146 Print a list of all the exception handlers that are active in the
3147 current stack frame at the current point of execution. To see other
3148 exception handlers, visit the associated frame (using the @code{up},
3149 @code{down}, or @code{frame} commands); then type @code{info catch}.
3150 @xref{Exception Handling, ,Breakpoints and exceptions}.
3156 @section MIPS machines and the function stack
3158 @cindex stack on MIPS
3160 MIPS based computers use an unusual stack frame, which sometimes
3161 requires @value{GDBN} to search backward in the object code to find the
3162 beginning of a function.
3164 @cindex response time, MIPS debugging
3165 To improve response time (especially for embedded applications, where
3166 @value{GDBN} may be restricted to a slow serial line for this search)
3167 you may want to limit the size of this search, using one of these
3169 @c FIXME! So what happens when GDB does *not* find the beginning of a
3172 @cindex @code{heuristic-fence-post} (MIPS)
3174 @item set heuristic-fence-post @var{limit}
3175 Restrict @var{GDBN} to examining at most @var{limit} bytes in its search
3176 for the beginning of a function. A value of @code{0} (the default)
3177 means there is no limit.
3179 @item show heuristic-fence-post
3180 Display the current limit.
3184 These commands are available @emph{only} when @value{GDBN} is configured
3185 for debugging programs on MIPS processors.
3189 @chapter Examining Source Files
3191 @value{GDBN} can print parts of your program's source, since the debugging
3192 information recorded in the program tells @value{GDBN} what source files were
3193 used to build it. When your program stops, @value{GDBN} spontaneously prints
3194 the line where it stopped. Likewise, when you select a stack frame
3195 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3196 execution in that frame has stopped. You can print other portions of
3197 source files by explicit command.
3200 If you use @value{GDBN} through its GNU Emacs interface, you may prefer to use
3201 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under GNU
3206 * List:: Printing source lines
3208 * Search:: Searching source files
3211 * Source Path:: Specifying source directories
3212 * Machine Code:: Source and machine code
3216 @section Printing source lines
3220 To print lines from a source file, use the @code{list} command
3221 (abbreviated @code{l}). There are several ways to specify what part
3222 of the file you want to print.
3224 Here are the forms of the @code{list} command most commonly used:
3227 @item list @var{linenum}
3228 Print lines centered around line number @var{linenum} in the
3229 current source file.
3231 @item list @var{function}
3232 Print lines centered around the beginning of function
3236 Print more lines. If the last lines printed were printed with a
3237 @code{list} command, this prints lines following the last lines
3238 printed; however, if the last line printed was a solitary line printed
3239 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3240 Stack}), this prints lines centered around that line.
3243 Print lines just before the lines last printed.
3246 By default, @value{GDBN} prints ten source lines with any of these forms of
3247 the @code{list} command. You can change this using @code{set listsize}:
3250 @item set listsize @var{count}
3251 @kindex set listsize
3252 Make the @code{list} command display @var{count} source lines (unless
3253 the @code{list} argument explicitly specifies some other number).
3256 @kindex show listsize
3257 Display the number of lines that @code{list} will currently display by
3261 Repeating a @code{list} command with @key{RET} discards the argument,
3262 so it is equivalent to typing just @code{list}. This is more useful
3263 than listing the same lines again. An exception is made for an
3264 argument of @samp{-}; that argument is preserved in repetition so that
3265 each repetition moves up in the source file.
3268 In general, the @code{list} command expects you to supply zero, one or two
3269 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3270 of writing them but the effect is always to specify some source line.
3271 Here is a complete description of the possible arguments for @code{list}:
3274 @item list @var{linespec}
3275 Print lines centered around the line specified by @var{linespec}.
3277 @item list @var{first},@var{last}
3278 Print lines from @var{first} to @var{last}. Both arguments are
3281 @item list ,@var{last}
3282 Print lines ending with @var{last}.
3284 @item list @var{first},
3285 Print lines starting with @var{first}.
3288 Print lines just after the lines last printed.
3291 Print lines just before the lines last printed.
3294 As described in the preceding table.
3297 Here are the ways of specifying a single source line---all the
3302 Specifies line @var{number} of the current source file.
3303 When a @code{list} command has two linespecs, this refers to
3304 the same source file as the first linespec.
3307 Specifies the line @var{offset} lines after the last line printed.
3308 When used as the second linespec in a @code{list} command that has
3309 two, this specifies the line @var{offset} lines down from the
3313 Specifies the line @var{offset} lines before the last line printed.
3315 @item @var{filename}:@var{number}
3316 Specifies line @var{number} in the source file @var{filename}.
3318 @item @var{function}
3319 @c FIXME: "of the open-brace" is C-centric. When we add other langs...
3320 Specifies the line of the open-brace that begins the body of the
3321 function @var{function}.
3323 @item @var{filename}:@var{function}
3324 Specifies the line of the open-brace that begins the body of the
3325 function @var{function} in the file @var{filename}. You only need the
3326 file name with a function name to avoid ambiguity when there are
3327 identically named functions in different source files.
3329 @item *@var{address}
3330 Specifies the line containing the program address @var{address}.
3331 @var{address} may be any expression.
3336 @section Searching source files
3338 @kindex reverse-search
3340 There are two commands for searching through the current source file for a
3344 @item forward-search @var{regexp}
3345 @itemx search @var{regexp}
3347 @kindex forward-search
3348 The command @samp{forward-search @var{regexp}} checks each line,
3349 starting with the one following the last line listed, for a match for
3350 @var{regexp}. It lists the line that is found. You can use
3351 synonym @samp{search @var{regexp}} or abbreviate the command name as
3354 @item reverse-search @var{regexp}
3355 The command @samp{reverse-search @var{regexp}} checks each line, starting
3356 with the one before the last line listed and going backward, for a match
3357 for @var{regexp}. It lists the line that is found. You can abbreviate
3358 this command as @code{rev}.
3363 @section Specifying source directories
3366 @cindex directories for source files
3367 Executable programs sometimes do not record the directories of the source
3368 files from which they were compiled, just the names. Even when they do,
3369 the directories could be moved between the compilation and your debugging
3370 session. @value{GDBN} has a list of directories to search for source files;
3371 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
3372 it tries all the directories in the list, in the order they are present
3373 in the list, until it finds a file with the desired name. Note that
3374 the executable search path is @emph{not} used for this purpose. Neither is
3375 the current working directory, unless it happens to be in the source
3378 If @value{GDBN} cannot find a source file in the source path, and the object
3379 program records a directory, @value{GDBN} tries that directory too. If the
3380 source path is empty, and there is no record of the compilation
3381 directory, @value{GDBN} will, as a last resort, look in the current
3384 Whenever you reset or rearrange the source path, @value{GDBN} will clear out
3385 any information it has cached about where source files are found, where
3386 each line is in the file, etc.
3389 When you start @value{GDBN}, its source path is empty.
3390 To add other directories, use the @code{directory} command.
3393 @item directory @var{dirname} @dots{}
3394 Add directory @var{dirname} to the front of the source path. Several
3395 directory names may be given to this command, separated by @samp{:} or
3396 whitespace. You may specify a directory that is already in the source
3397 path; this moves it forward, so it will be searched sooner.
3401 @cindex compilation directory
3402 @cindex current directory
3403 @cindex working directory
3404 @cindex directory, current
3405 @cindex directory, compilation
3406 You can use the string @samp{$cdir} to refer to the compilation
3407 directory (if one is recorded), and @samp{$cwd} to refer to the current
3408 working directory. @samp{$cwd} is not the same as @samp{.}---the former
3409 tracks the current working directory as it changes during your @value{GDBN}
3410 session, while the latter is immediately expanded to the current
3411 directory at the time you add an entry to the source path.
3414 Reset the source path to empty again. This requires confirmation.
3416 @c RET-repeat for @code{directory} is explicitly disabled, but since
3417 @c repeating it would be a no-op we do not say that. (thanks to RMS)
3419 @item show directories
3420 @kindex show directories
3421 Print the source path: show which directories it contains.
3424 If your source path is cluttered with directories that are no longer of
3425 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
3426 versions of source. You can correct the situation as follows:
3430 Use @code{directory} with no argument to reset the source path to empty.
3433 Use @code{directory} with suitable arguments to reinstall the
3434 directories you want in the source path. You can add all the
3435 directories in one command.
3439 @section Source and machine code
3441 You can use the command @code{info line} to map source lines to program
3442 addresses (and vice versa), and the command @code{disassemble} to display
3443 a range of addresses as machine instructions.
3446 @item info line @var{linespec}
3448 Print the starting and ending addresses of the compiled code for
3449 source line @var{linespec}. You can specify source lines in any of
3450 the ways understood by the @code{list} command (@pxref{List, ,Printing
3454 For example, we can use @code{info line} to discover the location of
3455 the object code for the first line of function
3456 @code{m4_changequote}:
3459 (@value{GDBP}) info line m4_changecom
3460 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3464 We can also inquire (using @code{*@var{addr}} as the form for
3465 @var{linespec}) what source line covers a particular address:
3467 (@value{GDBP}) info line *0x63ff
3468 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3471 @cindex @code{$_} and @code{info line}
3472 After @code{info line}, the default address for the @code{x} command
3473 is changed to the starting address of the line, so that @samp{x/i} is
3474 sufficient to begin examining the machine code (@pxref{Memory,
3475 ,Examining memory}). Also, this address is saved as the value of the
3476 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
3482 @cindex assembly instructions
3483 @cindex instructions, assembly
3484 @cindex machine instructions
3485 @cindex listing machine instructions
3486 This specialized command dumps a range of memory as machine
3487 instructions. The default memory range is the function surrounding the
3488 program counter of the selected frame. A single argument to this
3489 command is a program counter value; the function surrounding this value
3490 will be dumped. Two arguments specify a range of addresses (first
3491 inclusive, second exclusive) to dump.
3494 @ifclear H8EXCLUSIVE
3495 We can use @code{disassemble} to inspect the object code
3496 range shown in the last @code{info line} example (the example
3497 shows SPARC machine instructions):
3501 (@value{GDBP}) disas 0x63e4 0x6404
3502 Dump of assembler code from 0x63e4 to 0x6404:
3503 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3504 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3505 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3506 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3507 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3508 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3509 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3510 0x6400 <builtin_init+5368>: nop
3511 End of assembler dump.
3516 For example, here is the beginning of the output for the
3517 disassembly of a function @code{fact}:
3521 (@value{GDBP}) disas fact
3522 Dump of assembler code for function fact:
3524 0x802c <fact>: 6d f2 mov.w r2,@@-r7
3525 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
3526 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
3527 0x8032 <fact+6>: 0d 76 mov.w r7,r6
3528 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
3529 0x8038 <fact+12> 19 11 sub.w r1,r1
3537 @chapter Examining Data
3539 @cindex printing data
3540 @cindex examining data
3543 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
3544 @c document because it is nonstandard... Under Epoch it displays in a
3545 @c different window or something like that.
3546 The usual way to examine data in your program is with the @code{print}
3547 command (abbreviated @code{p}), or its synonym @code{inspect}.
3549 It evaluates and prints the value of an expression of the language your
3550 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
3555 @item print @var{exp}
3556 @itemx print /@var{f} @var{exp}
3557 @var{exp} is an expression (in the source language). By default the
3558 value of @var{exp} is printed in a format appropriate to its data type;
3559 you can choose a different format by specifying @samp{/@var{f}}, where
3560 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
3564 @itemx print /@var{f}
3565 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
3566 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
3567 conveniently inspect the same value in an alternative format.
3570 A more low-level way of examining data is with the @code{x} command.
3571 It examines data in memory at a specified address and prints it in a
3572 specified format. @xref{Memory, ,Examining memory}.
3574 If you are interested in information about types, or about how the fields
3579 are declared, use the @code{ptype @var{exp}}
3580 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
3583 * Expressions:: Expressions
3584 * Variables:: Program variables
3585 * Arrays:: Artificial arrays
3586 * Output Formats:: Output formats
3587 * Memory:: Examining memory
3588 * Auto Display:: Automatic display
3589 * Print Settings:: Print settings
3590 * Value History:: Value history
3591 * Convenience Vars:: Convenience variables
3592 * Registers:: Registers
3594 * Floating Point Hardware:: Floating point hardware
3599 @section Expressions
3602 @code{print} and many other @value{GDBN} commands accept an expression and
3603 compute its value. Any kind of constant, variable or operator defined
3604 by the programming language you are using is valid in an expression in
3605 @value{GDBN}. This includes conditional expressions, function calls, casts
3606 and string constants. It unfortunately does not include symbols defined
3607 by preprocessor @code{#define} commands.
3610 Because C is so widespread, most of the expressions shown in examples in
3611 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
3612 Languages}, for information on how to use expressions in other
3615 In this section, we discuss operators that you can use in @value{GDBN}
3616 expressions regardless of your programming language.
3618 Casts are supported in all languages, not just in C, because it is so
3619 useful to cast a number into a pointer so as to examine a structure
3620 at that address in memory.
3621 @c FIXME: casts supported---Mod2 true?
3624 @value{GDBN} supports these operators in addition to those of programming
3629 @samp{@@} is a binary operator for treating parts of memory as arrays.
3630 @xref{Arrays, ,Artificial arrays}, for more information.
3633 @samp{::} allows you to specify a variable in terms of the file or
3634 function where it is defined. @xref{Variables, ,Program variables}.
3636 @item @{@var{type}@} @var{addr}
3637 @cindex @{@var{type}@}
3638 @cindex type casting memory
3639 @cindex memory, viewing as typed object
3640 @cindex casts, to view memory
3641 Refers to an object of type @var{type} stored at address @var{addr} in
3642 memory. @var{addr} may be any expression whose value is an integer or
3643 pointer (but parentheses are required around binary operators, just as in
3644 a cast). This construct is allowed regardless of what kind of data is
3645 normally supposed to reside at @var{addr}.
3649 @section Program variables
3651 The most common kind of expression to use is the name of a variable
3654 Variables in expressions are understood in the selected stack frame
3655 (@pxref{Selection, ,Selecting a frame}); they must either be global
3656 (or static) or be visible according to the scope rules of the
3657 programming language from the point of execution in that frame. This
3658 means that in the function
3673 you can examine and use the variable @code{a} whenever your program is
3674 executing within the function @code{foo}, but you can only use or
3675 examine the variable @code{b} while your program is executing inside
3676 the block where @code{b} is declared.
3678 @cindex variable name conflict
3679 There is an exception: you can refer to a variable or function whose
3680 scope is a single source file even if the current execution point is not
3681 in this file. But it is possible to have more than one such variable or
3682 function with the same name (in different source files). If that
3683 happens, referring to that name has unpredictable effects. If you wish,
3684 you can specify a static variable in a particular function or file,
3685 using the colon-colon notation:
3689 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
3693 @var{file}::@var{variable}
3694 @var{function}::@var{variable}
3698 Here @var{file} or @var{function} is the name of the context for the
3699 static @var{variable}. In the case of file names, you can use quotes to
3700 make sure @value{GDBN} parses the file name as a single word---for example,
3701 to print a global value of @code{x} defined in @file{f2.c}:
3704 (@value{GDBP}) p 'f2.c'::x
3708 @cindex C++ scope resolution
3709 This use of @samp{::} is very rarely in conflict with the very similar
3710 use of the same notation in C++. @value{GDBN} also supports use of the C++
3711 scope resolution operator in @value{GDBN} expressions.
3712 @c FIXME: Um, so what happens in one of those rare cases where it's in
3716 @cindex wrong values
3717 @cindex variable values, wrong
3719 @emph{Warning:} Occasionally, a local variable may appear to have the
3720 wrong value at certain points in a function---just after entry to a new
3721 scope, and just before exit.
3723 You may see this problem when you are stepping by machine instructions.
3724 This is because on most machines, it takes more than one instruction to
3725 set up a stack frame (including local variable definitions); if you are
3726 stepping by machine instructions, variables may appear to have the wrong
3727 values until the stack frame is completely built. On exit, it usually
3728 also takes more than one machine instruction to destroy a stack frame;
3729 after you begin stepping through that group of instructions, local
3730 variable definitions may be gone.
3733 @section Artificial arrays
3735 @cindex artificial array
3737 It is often useful to print out several successive objects of the
3738 same type in memory; a section of an array, or an array of
3739 dynamically determined size for which only a pointer exists in the
3742 You can do this by referring to a contiguous span of memory as an
3743 @dfn{artificial array}, using the binary operator @samp{@@}. The left
3744 operand of @samp{@@} should be the first element of the desired array,
3745 as an individual object. The right operand should be the desired length
3746 of the array. The result is an array value whose elements are all of
3747 the type of the left argument. The first element is actually the left
3748 argument; the second element comes from bytes of memory immediately
3749 following those that hold the first element, and so on. Here is an
3750 example. If a program says
3753 int *array = (int *) malloc (len * sizeof (int));
3757 you can print the contents of @code{array} with
3763 The left operand of @samp{@@} must reside in memory. Array values made
3764 with @samp{@@} in this way behave just like other arrays in terms of
3765 subscripting, and are coerced to pointers when used in expressions.
3766 Artificial arrays most often appear in expressions via the value history
3767 (@pxref{Value History, ,Value history}), after printing one out.
3769 Sometimes the artificial array mechanism is not quite enough; in
3770 moderately complex data structures, the elements of interest may not
3771 actually be adjacent---for example, if you are interested in the values
3772 of pointers in an array. One useful work-around in this situation is
3773 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
3774 variables}) as a counter in an expression that prints the first
3775 interesting value, and then repeat that expression via @key{RET}. For
3776 instance, suppose you have an array @code{dtab} of pointers to
3777 structures, and you are interested in the values of a field @code{fv}
3778 in each structure. Here is an example of what you might type:
3788 @node Output Formats
3789 @section Output formats
3791 @cindex formatted output
3792 @cindex output formats
3793 By default, @value{GDBN} prints a value according to its data type. Sometimes
3794 this is not what you want. For example, you might want to print a number
3795 in hex, or a pointer in decimal. Or you might want to view data in memory
3796 at a certain address as a character string or as an instruction. To do
3797 these things, specify an @dfn{output format} when you print a value.
3799 The simplest use of output formats is to say how to print a value
3800 already computed. This is done by starting the arguments of the
3801 @code{print} command with a slash and a format letter. The format
3802 letters supported are:
3806 Regard the bits of the value as an integer, and print the integer in
3810 Print as integer in signed decimal.
3813 Print as integer in unsigned decimal.
3816 Print as integer in octal.
3819 Print as integer in binary. The letter @samp{t} stands for ``two''.
3820 @footnote{@samp{b} cannot be used because these format letters are also
3821 used with the @code{x} command, where @samp{b} stands for ``byte'';
3822 @pxref{Memory,,Examining memory}.}
3825 Print as an address, both absolute in hex and as an offset from the
3826 nearest preceding symbol. This format can be used to discover where (in
3827 what function) an unknown address is located:
3830 (@value{GDBP}) p/a 0x54320
3831 $3 = 0x54320 <_initialize_vx+396>
3835 Regard as an integer and print it as a character constant.
3838 Regard the bits of the value as a floating point number and print
3839 using typical floating point syntax.
3842 For example, to print the program counter in hex (@pxref{Registers}), type
3849 Note that no space is required before the slash; this is because command
3850 names in @value{GDBN} cannot contain a slash.
3852 To reprint the last value in the value history with a different format,
3853 you can use the @code{print} command with just a format and no
3854 expression. For example, @samp{p/x} reprints the last value in hex.
3857 @section Examining memory
3859 You can use the command @code{x} (for ``examine'') to examine memory in
3860 any of several formats, independently of your program's data types.
3862 @cindex examining memory
3865 @item x/@var{nfu} @var{addr}
3868 Use the @code{x} command to examine memory.
3871 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
3872 much memory to display and how to format it; @var{addr} is an
3873 expression giving the address where you want to start displaying memory.
3874 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
3875 Several commands set convenient defaults for @var{addr}.
3878 @item @var{n}, the repeat count
3879 The repeat count is a decimal integer; the default is 1. It specifies
3880 how much memory (counting by units @var{u}) to display.
3881 @c This really is **decimal**; unaffected by 'set radix' as of GDB
3884 @item @var{f}, the display format
3885 The display format is one of the formats used by @code{print},
3886 or @samp{s} (null-terminated string) or @samp{i} (machine instruction).
3887 The default is @samp{x} (hexadecimal) initially, or the format from the
3888 last time you used either @code{x} or @code{print}.
3890 @item @var{u}, the unit size
3891 The unit size is any of
3897 Halfwords (two bytes).
3899 Words (four bytes). This is the initial default.
3901 Giant words (eight bytes).
3904 Each time you specify a unit size with @code{x}, that size becomes the
3905 default unit the next time you use @code{x}. (For the @samp{s} and
3906 @samp{i} formats, the unit size is ignored and is normally not written.)
3908 @item @var{addr}, starting display address
3909 @var{addr} is the address where you want @value{GDBN} to begin displaying
3910 memory. The expression need not have a pointer value (though it may);
3911 it is always interpreted as an integer address of a byte of memory.
3912 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
3913 @var{addr} is usually just after the last address examined---but several
3914 other commands also set the default address: @code{info breakpoints} (to
3915 the address of the last breakpoint listed), @code{info line} (to the
3916 starting address of a line), and @code{print} (if you use it to display
3917 a value from memory).
3920 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
3921 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
3922 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
3923 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
3924 @pxref{Registers}) in hexadecimal (@samp{x}).
3926 Since the letters indicating unit sizes are all distinct from the
3927 letters specifying output formats, you do not have to remember whether
3928 unit size or format comes first; either order will work. The output
3929 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
3930 (However, the count @var{n} must come first; @samp{wx4} will not work.)
3932 Even though the unit size @var{u} is ignored for the formats @samp{s}
3933 and @samp{i}, you might still want to use a count @var{n}; for example,
3934 @samp{3i} specifies that you want to see three machine instructions,
3935 including any operands. The command @code{disassemble} gives an
3936 alternative way of inspecting machine instructions; @pxref{Machine
3937 Code,,Source and machine code}.
3939 All the defaults for the arguments to @code{x} are designed to make it
3940 easy to continue scanning memory with minimal specifications each time
3941 you use @code{x}. For example, after you have inspected three machine
3942 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
3943 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
3944 the repeat count @var{n} is used again; the other arguments default as
3945 for successive uses of @code{x}.
3947 @cindex @code{$_}, @code{$__}, and value history
3948 The addresses and contents printed by the @code{x} command are not saved
3949 in the value history because there is often too much of them and they
3950 would get in the way. Instead, @value{GDBN} makes these values available for
3951 subsequent use in expressions as values of the convenience variables
3952 @code{$_} and @code{$__}. After an @code{x} command, the last address
3953 examined is available for use in expressions in the convenience variable
3954 @code{$_}. The contents of that address, as examined, are available in
3955 the convenience variable @code{$__}.
3957 If the @code{x} command has a repeat count, the address and contents saved
3958 are from the last memory unit printed; this is not the same as the last
3959 address printed if several units were printed on the last line of output.
3962 @section Automatic display
3963 @cindex automatic display
3964 @cindex display of expressions
3966 If you find that you want to print the value of an expression frequently
3967 (to see how it changes), you might want to add it to the @dfn{automatic
3968 display list} so that @value{GDBN} will print its value each time your program stops.
3969 Each expression added to the list is given a number to identify it;
3970 to remove an expression from the list, you specify that number.
3971 The automatic display looks like this:
3975 3: bar[5] = (struct hack *) 0x3804
3979 This display shows item numbers, expressions and their current values. As with
3980 displays you request manually using @code{x} or @code{print}, you can
3981 specify the output format you prefer; in fact, @code{display} decides
3982 whether to use @code{print} or @code{x} depending on how elaborate your
3983 format specification is---it uses @code{x} if you specify a unit size,
3984 or one of the two formats (@samp{i} and @samp{s}) that are only
3985 supported by @code{x}; otherwise it uses @code{print}.
3988 @item display @var{exp}
3990 Add the expression @var{exp} to the list of expressions to display
3991 each time your program stops. @xref{Expressions, ,Expressions}.
3993 @code{display} will not repeat if you press @key{RET} again after using it.
3995 @item display/@var{fmt} @var{exp}
3996 For @var{fmt} specifying only a display format and not a size or
3997 count, add the expression @var{exp} to the auto-display list but
3998 arrange to display it each time in the specified format @var{fmt}.
3999 @xref{Output Formats,,Output formats}.
4001 @item display/@var{fmt} @var{addr}
4002 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4003 number of units, add the expression @var{addr} as a memory address to
4004 be examined each time your program stops. Examining means in effect
4005 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4008 For example, @samp{display/i $pc} can be helpful, to see the machine
4009 instruction about to be executed each time execution stops (@samp{$pc}
4010 is a common name for the program counter; @pxref{Registers}).
4013 @item undisplay @var{dnums}@dots{}
4014 @itemx delete display @var{dnums}@dots{}
4015 @kindex delete display
4017 Remove item numbers @var{dnums} from the list of expressions to display.
4019 @code{undisplay} will not repeat if you press @key{RET} after using it.
4020 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4022 @item disable display @var{dnums}@dots{}
4023 @kindex disable display
4024 Disable the display of item numbers @var{dnums}. A disabled display
4025 item is not printed automatically, but is not forgotten. It may be
4026 enabled again later.
4028 @item enable display @var{dnums}@dots{}
4029 @kindex enable display
4030 Enable display of item numbers @var{dnums}. It becomes effective once
4031 again in auto display of its expression, until you specify otherwise.
4034 Display the current values of the expressions on the list, just as is
4035 done when your program stops.
4038 @kindex info display
4039 Print the list of expressions previously set up to display
4040 automatically, each one with its item number, but without showing the
4041 values. This includes disabled expressions, which are marked as such.
4042 It also includes expressions which would not be displayed right now
4043 because they refer to automatic variables not currently available.
4046 If a display expression refers to local variables, then it does not make
4047 sense outside the lexical context for which it was set up. Such an
4048 expression is disabled when execution enters a context where one of its
4049 variables is not defined. For example, if you give the command
4050 @code{display last_char} while inside a function with an argument
4051 @code{last_char}, then this argument will be displayed while your program
4052 continues to stop inside that function. When it stops elsewhere---where
4053 there is no variable @code{last_char}---display is disabled. The next time
4054 your program stops where @code{last_char} is meaningful, you can enable the
4055 display expression once again.
4057 @node Print Settings
4058 @section Print settings
4060 @cindex format options
4061 @cindex print settings
4062 @value{GDBN} provides the following ways to control how arrays, structures,
4063 and symbols are printed.
4066 These settings are useful for debugging programs in any language:
4069 @item set print address
4070 @itemx set print address on
4071 @kindex set print address
4072 @value{GDBN} will print memory addresses showing the location of stack
4073 traces, structure values, pointer values, breakpoints, and so forth,
4074 even when it also displays the contents of those addresses. The default
4075 is on. For example, this is what a stack frame display looks like, with
4076 @code{set print address on}:
4081 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4083 530 if (lquote != def_lquote)
4087 @item set print address off
4088 Do not print addresses when displaying their contents. For example,
4089 this is the same stack frame displayed with @code{set print address off}:
4093 (@value{GDBP}) set print addr off
4095 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4096 530 if (lquote != def_lquote)
4100 You can use @samp{set print address off} to eliminate all machine
4101 dependent displays from the @value{GDBN} interface. For example, with
4102 @code{print address off}, you should get the same text for backtraces on
4103 all machines---whether or not they involve pointer arguments.
4105 @item show print address
4106 @kindex show print address
4107 Show whether or not addresses are to be printed.
4110 When @value{GDBN} prints a symbolic address, it normally prints the
4111 closest earlier symbol plus an offset. If that symbol does not uniquely
4112 identify the address (for example, it is a name whose scope is a single
4113 source file), you may need to disambiguate. One way to do this is with
4114 @code{info line}, for example @code{info line *0x4537}. Alternately,
4115 you can set @value{GDBN} to print the source file and line number when
4116 it prints a symbolic address:
4119 @item set print symbol-filename on
4120 @kindex set print symbol-filename
4121 Tell @value{GDBN} to print the source file name and line number of a
4122 symbol in the symbolic form of an address.
4124 @item set print symbol-filename off
4125 Do not print source file name and line number of a symbol. This is the
4128 @item show print symbol-filename
4129 @kindex show print symbol-filename
4130 Show whether or not @value{GDBN} will print the source file name and
4131 line number of a symbol in the symbolic form of an address.
4134 Also, you may wish to see the symbolic form only if the address being
4135 printed is reasonably close to the closest earlier symbol:
4138 @item set print max-symbolic-offset @var{max-offset}
4139 @kindex set print max-symbolic-offset
4140 Tell @value{GDBN} to only display the symbolic form of an address if the
4141 offset between the closest earlier symbol and the address is less than
4142 @var{max-offset}. The default is 0, which means to always print the
4143 symbolic form of an address, if any symbol precedes it.
4145 @item show print max-symbolic-offset
4146 @kindex show print max-symbolic-offset
4147 Ask how large the maximum offset is that @value{GDBN} will print in a
4152 @item set print array
4153 @itemx set print array on
4154 @kindex set print array
4155 @value{GDBN} will pretty-print arrays. This format is more convenient to read,
4156 but uses more space. The default is off.
4158 @item set print array off
4159 Return to compressed format for arrays.
4161 @item show print array
4162 @kindex show print array
4163 Show whether compressed or pretty format is selected for displaying
4166 @item set print elements @var{number-of-elements}
4167 @kindex set print elements
4168 If @value{GDBN} is printing a large array, it will stop printing after it has
4169 printed the number of elements set by the @code{set print elements} command.
4170 This limit also applies to the display of strings.
4171 Setting the number of elements to zero means that the printing is unlimited.
4173 @item show print elements
4174 @kindex show print elements
4175 Display the number of elements of a large array that @value{GDBN} will print
4176 before losing patience.
4178 @item set print pretty on
4179 @kindex set print pretty
4180 Cause @value{GDBN} to print structures in an indented format with one member per
4196 @item set print pretty off
4197 Cause @value{GDBN} to print structures in a compact format, like this:
4201 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4202 meat = 0x54 "Pork"@}
4207 This is the default format.
4209 @item show print pretty
4210 @kindex show print pretty
4211 Show which format @value{GDBN} will use to print structures.
4213 @item set print sevenbit-strings on
4214 @kindex set print sevenbit-strings
4215 Print using only seven-bit characters; if this option is set,
4216 @value{GDBN} will display any eight-bit characters (in strings or character
4217 values) using the notation @code{\}@var{nnn}. For example, @kbd{M-a} is
4218 displayed as @code{\341}.
4220 @item set print sevenbit-strings off
4221 Print using either seven-bit or eight-bit characters, as required. This
4224 @item show print sevenbit-strings
4225 @kindex show print sevenbit-strings
4226 Show whether or not @value{GDBN} will print only seven-bit characters.
4228 @item set print union on
4229 @kindex set print union
4230 Tell @value{GDBN} to print unions which are contained in structures. This is the
4233 @item set print union off
4234 Tell @value{GDBN} not to print unions which are contained in structures.
4236 @item show print union
4237 @kindex show print union
4238 Ask @value{GDBN} whether or not it will print unions which are contained in
4241 For example, given the declarations
4244 typedef enum @{Tree, Bug@} Species;
4245 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
4246 typedef enum @{Caterpillar, Cocoon, Butterfly@}
4257 struct thing foo = @{Tree, @{Acorn@}@};
4261 with @code{set print union on} in effect @samp{p foo} would print
4264 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
4268 and with @code{set print union off} in effect it would print
4271 $1 = @{it = Tree, form = @{...@}@}
4278 These settings are of interest when debugging C++ programs:
4281 @item set print demangle
4282 @itemx set print demangle on
4283 @kindex set print demangle
4284 Print C++ names in their source form rather than in the encoded
4285 (``mangled'') form passed to the assembler and linker for type-safe
4286 linkage. The default is @samp{on}.
4288 @item show print demangle
4289 @kindex show print demangle
4290 Show whether C++ names will be printed in mangled or demangled form.
4292 @item set print asm-demangle
4293 @itemx set print asm-demangle on
4294 @kindex set print asm-demangle
4295 Print C++ names in their source form rather than their mangled form, even
4296 in assembler code printouts such as instruction disassemblies.
4299 @item show print asm-demangle
4300 @kindex show print asm-demangle
4301 Show whether C++ names in assembly listings will be printed in mangled
4304 @item set demangle-style @var{style}
4305 @kindex set demangle-style
4306 @cindex C++ symbol decoding style
4307 @cindex symbol decoding style, C++
4308 Choose among several encoding schemes used by different compilers to
4309 represent C++ names. The choices for @var{style} are currently:
4313 Allow @value{GDBN} to choose a decoding style by inspecting your program.
4316 Decode based on the GNU C++ compiler (@code{g++}) encoding algorithm.
4319 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
4322 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
4323 @strong{Warning:} this setting alone is not sufficient to allow
4324 debugging @code{cfront}-generated executables. @value{GDBN} would
4325 require further enhancement to permit that.
4328 @item show demangle-style
4329 @kindex show demangle-style
4330 Display the encoding style currently in use for decoding C++ symbols.
4332 @item set print object
4333 @itemx set print object on
4334 @kindex set print object
4335 When displaying a pointer to an object, identify the @emph{actual}
4336 (derived) type of the object rather than the @emph{declared} type, using
4337 the virtual function table.
4339 @item set print object off
4340 Display only the declared type of objects, without reference to the
4341 virtual function table. This is the default setting.
4343 @item show print object
4344 @kindex show print object
4345 Show whether actual, or declared, object types will be displayed.
4347 @item set print vtbl
4348 @itemx set print vtbl on
4349 @kindex set print vtbl
4350 Pretty print C++ virtual function tables. The default is off.
4352 @item set print vtbl off
4353 Do not pretty print C++ virtual function tables.
4355 @item show print vtbl
4356 @kindex show print vtbl
4357 Show whether C++ virtual function tables are pretty printed, or not.
4362 @section Value history
4364 @cindex value history
4365 Values printed by the @code{print} command are saved in the @value{GDBN} @dfn{value
4366 history} so that you can refer to them in other expressions. Values are
4367 kept until the symbol table is re-read or discarded (for example with
4368 the @code{file} or @code{symbol-file} commands). When the symbol table
4369 changes, the value history is discarded, since the values may contain
4370 pointers back to the types defined in the symbol table.
4374 @cindex history number
4375 The values printed are given @dfn{history numbers} by which you can
4376 refer to them. These are successive integers starting with one.
4377 @code{print} shows you the history number assigned to a value by
4378 printing @samp{$@var{num} = } before the value; here @var{num} is the
4381 To refer to any previous value, use @samp{$} followed by the value's
4382 history number. The way @code{print} labels its output is designed to
4383 remind you of this. Just @code{$} refers to the most recent value in
4384 the history, and @code{$$} refers to the value before that.
4385 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
4386 is the value just prior to @code{$$}, @code{$$1} is equivalent to
4387 @code{$$}, and @code{$$0} is equivalent to @code{$}.
4389 For example, suppose you have just printed a pointer to a structure and
4390 want to see the contents of the structure. It suffices to type
4396 If you have a chain of structures where the component @code{next} points
4397 to the next one, you can print the contents of the next one with this:
4404 You can print successive links in the chain by repeating this
4405 command---which you can do by just typing @key{RET}.
4407 Note that the history records values, not expressions. If the value of
4408 @code{x} is 4 and you type these commands:
4416 then the value recorded in the value history by the @code{print} command
4417 remains 4 even though the value of @code{x} has changed.
4422 Print the last ten values in the value history, with their item numbers.
4423 This is like @samp{p@ $$9} repeated ten times, except that @code{show
4424 values} does not change the history.
4426 @item show values @var{n}
4427 Print ten history values centered on history item number @var{n}.
4430 Print ten history values just after the values last printed. If no more
4431 values are available, produces no display.
4434 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
4435 same effect as @samp{show values +}.
4437 @node Convenience Vars
4438 @section Convenience variables
4440 @cindex convenience variables
4441 @value{GDBN} provides @dfn{convenience variables} that you can use within
4442 @value{GDBN} to hold on to a value and refer to it later. These variables
4443 exist entirely within @value{GDBN}; they are not part of your program, and
4444 setting a convenience variable has no direct effect on further execution
4445 of your program. That is why you can use them freely.
4447 Convenience variables are prefixed with @samp{$}. Any name preceded by
4448 @samp{$} can be used for a convenience variable, unless it is one of
4449 the predefined machine-specific register names (@pxref{Registers}).
4450 (Value history references, in contrast, are @emph{numbers} preceded
4451 by @samp{$}. @xref{Value History, ,Value history}.)
4453 You can save a value in a convenience variable with an assignment
4454 expression, just as you would set a variable in your program.
4458 set $foo = *object_ptr
4462 would save in @code{$foo} the value contained in the object pointed to by
4465 Using a convenience variable for the first time creates it, but its
4466 value is @code{void} until you assign a new value. You can alter the
4467 value with another assignment at any time.
4469 Convenience variables have no fixed types. You can assign a convenience
4470 variable any type of value, including structures and arrays, even if
4471 that variable already has a value of a different type. The convenience
4472 variable, when used as an expression, has the type of its current value.
4475 @item show convenience
4476 @kindex show convenience
4477 Print a list of convenience variables used so far, and their values.
4478 Abbreviated @code{show con}.
4481 One of the ways to use a convenience variable is as a counter to be
4482 incremented or a pointer to be advanced. For example, to print
4483 a field from successive elements of an array of structures:
4487 print bar[$i++]->contents
4488 @i{@dots{} repeat that command by typing @key{RET}.}
4491 Some convenience variables are created automatically by @value{GDBN} and given
4492 values likely to be useful.
4497 The variable @code{$_} is automatically set by the @code{x} command to
4498 the last address examined (@pxref{Memory, ,Examining memory}). Other
4499 commands which provide a default address for @code{x} to examine also
4500 set @code{$_} to that address; these commands include @code{info line}
4501 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
4502 except when set by the @code{x} command, in which case it is a pointer
4503 to the type of @code{$__}.
4507 The variable @code{$__} is automatically set by the @code{x} command
4508 to the value found in the last address examined. Its type is chosen
4509 to match the format in which the data was printed.
4516 You can refer to machine register contents, in expressions, as variables
4517 with names starting with @samp{$}. The names of registers are different
4518 for each machine; use @code{info registers} to see the names used on
4522 @item info registers
4523 @kindex info registers
4524 Print the names and values of all registers except floating-point
4525 registers (in the selected stack frame).
4527 @item info all-registers
4528 @kindex info all-registers
4529 @cindex floating point registers
4530 Print the names and values of all registers, including floating-point
4533 @item info registers @var{regname} @dots{}
4534 Print the relativized value of each specified register @var{regname}.
4535 @var{regname} may be any register name valid on the machine you are using, with
4536 or without the initial @samp{$}.
4539 @value{GDBN} has four ``standard'' register names that are available (in
4540 expressions) on most machines---whenever they do not conflict with an
4541 architecture's canonical mnemonics for registers. The register names
4542 @code{$pc} and @code{$sp} are used for the program counter register and
4543 the stack pointer. @code{$fp} is used for a register that contains a
4544 pointer to the current stack frame, and @code{$ps} is used for a
4545 register that contains the processor status. For example,
4546 you could print the program counter in hex with
4553 or print the instruction to be executed next with
4560 or add four to the stack pointer@footnote{This is a way of removing
4561 one word from the stack, on machines where stacks grow downward in
4562 memory (most machines, nowadays). This assumes that the innermost
4563 stack frame is selected; setting @code{$sp} is not allowed when other
4564 stack frames are selected. To pop entire frames off the stack,
4565 regardless of machine architecture, use @code{return};
4566 @pxref{Returning, ,Returning from a function}.} with
4572 Whenever possible, these four standard register names are available on
4573 your machine even though the machine has different canonical mnemonics,
4574 so long as there is no conflict. The @code{info registers} command
4575 shows the canonical names. For example, on the SPARC, @code{info
4576 registers} displays the processor status register as @code{$psr} but you
4577 can also refer to it as @code{$ps}.
4579 @value{GDBN} always considers the contents of an ordinary register as an
4580 integer when the register is examined in this way. Some machines have
4581 special registers which can hold nothing but floating point; these
4582 registers are considered to have floating point values. There is no way
4583 to refer to the contents of an ordinary register as floating point value
4584 (although you can @emph{print} it as a floating point value with
4585 @samp{print/f $@var{regname}}).
4587 Some registers have distinct ``raw'' and ``virtual'' data formats. This
4588 means that the data format in which the register contents are saved by
4589 the operating system is not the same one that your program normally
4590 sees. For example, the registers of the 68881 floating point
4591 coprocessor are always saved in ``extended'' (raw) format, but all C
4592 programs expect to work with ``double'' (virtual) format. In such
4593 cases, @value{GDBN} normally works with the virtual format only (the format that
4594 makes sense for your program), but the @code{info registers} command
4595 prints the data in both formats.
4597 Normally, register values are relative to the selected stack frame
4598 (@pxref{Selection, ,Selecting a frame}). This means that you get the
4599 value that the register would contain if all stack frames farther in
4600 were exited and their saved registers restored. In order to see the
4601 true contents of hardware registers, you must select the innermost
4602 frame (with @samp{frame 0}).
4604 However, @value{GDBN} must deduce where registers are saved, from the machine
4605 code generated by your compiler. If some registers are not saved, or if
4606 @value{GDBN} is unable to locate the saved registers, the selected stack
4607 frame will make no difference.
4611 @item set rstack_high_address @var{address}
4612 @kindex set rstack_high_address
4613 @cindex AMD 29K register stack
4614 @cindex register stack, AMD29K
4615 On AMD 29000 family processors, registers are saved in a separate
4616 ``register stack''. There is no way for @value{GDBN} to determine the extent
4617 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
4618 enough''. This may result in @value{GDBN} referencing memory locations that
4619 do not exist. If necessary, you can get around this problem by
4620 specifying the ending address of the register stack with the @code{set
4621 rstack_high_address} command. The argument should be an address, which
4622 you will probably want to precede with @samp{0x} to specify in
4625 @item show rstack_high_address
4626 @kindex show rstack_high_address
4627 Display the current limit of the register stack, on AMD 29000 family
4633 @node Floating Point Hardware
4634 @section Floating point hardware
4635 @cindex floating point
4637 @c FIXME! Really host, not target?
4638 Depending on the host machine architecture, @value{GDBN} may be able to give
4639 you more information about the status of the floating point hardware.
4644 Display hardware-dependent information about the floating
4645 point unit. The exact contents and layout vary depending on the
4646 floating point chip; on some platforms, @samp{info float} is not
4649 @c FIXME: this is a cop-out. Try to get examples, explanations. Only
4650 @c FIXME...supported currently on arm's and 386's. Mark properly with
4651 @c FIXME... m4 macros to isolate general statements from hardware-dep,
4652 @c FIXME... at that point.
4657 @chapter Using @value{GDBN} with Different Languages
4661 Although programming languages generally have common aspects, they are
4662 rarely expressed in the same manner. For instance, in ANSI C,
4663 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
4664 Modula-2, it is accomplished by @code{p^}. Values can also be
4665 represented (and displayed) differently. Hex numbers in C are written
4666 like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
4669 @cindex working language
4670 Language-specific information is built into @value{GDBN} for some languages,
4671 allowing you to express operations like the above in your program's
4672 native language, and allowing @value{GDBN} to output values in a manner
4673 consistent with the syntax of your program's native language. The
4674 language you use to build expressions, called the @dfn{working
4675 language}, can be selected manually, or @value{GDBN} can set it
4679 * Setting:: Switching between source languages
4680 * Show:: Displaying the language
4682 * Checks:: Type and range checks
4685 * Support:: Supported languages
4689 @section Switching between source languages
4691 There are two ways to control the working language---either have @value{GDBN}
4692 set it automatically, or select it manually yourself. You can use the
4693 @code{set language} command for either purpose. On startup, @value{GDBN}
4694 defaults to setting the language automatically.
4697 * Manually:: Setting the working language manually
4698 * Automatically:: Having @value{GDBN} infer the source language
4702 @subsection Setting the working language
4704 If you allow @value{GDBN} to set the language automatically,
4705 expressions are interpreted the same way in your debugging session and
4708 @kindex set language
4709 If you wish, you may set the language manually. To do this, issue the
4710 command @samp{set language @var{lang}}, where @var{lang} is the name of
4716 @code{c} or @code{modula-2}.
4718 For a list of the supported languages, type @samp{set language}.
4719 @c FIXME: rms: eventually this command should be "help set language".
4722 Setting the language manually prevents @value{GDBN} from updating the working
4723 language automatically. This can lead to confusion if you try
4724 to debug a program when the working language is not the same as the
4725 source language, when an expression is acceptable to both
4726 languages---but means different things. For instance, if the current
4727 source file were written in C, and @value{GDBN} was parsing Modula-2, a
4735 might not have the effect you intended. In C, this means to add
4736 @code{b} and @code{c} and place the result in @code{a}. The result
4737 printed would be the value of @code{a}. In Modula-2, this means to compare
4738 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
4742 @subsection Having @value{GDBN} infer the source language
4744 To have @value{GDBN} set the working language automatically, use @samp{set
4745 language local} or @samp{set language auto}. @value{GDBN} then infers the
4746 language that a program was written in by looking at the name of its
4747 source files, and examining their extensions:
4752 Modula-2 source file
4763 This information is recorded for each function or procedure in a source
4764 file. When your program stops in a frame (usually by encountering a
4765 breakpoint), @value{GDBN} sets the working language to the language recorded
4766 for the function in that frame. If the language for a frame is unknown
4767 (that is, if the function or block corresponding to the frame was
4768 defined in a source file that does not have a recognized extension), the
4769 current working language is not changed, and @value{GDBN} issues a warning.
4771 This may not seem necessary for most programs, which are written
4772 entirely in one source language. However, program modules and libraries
4773 written in one source language can be used by a main program written in
4774 a different source language. Using @samp{set language auto} in this
4775 case frees you from having to set the working language manually.
4778 @section Displaying the language
4780 The following commands will help you find out which language is the
4781 working language, and also what language source files were written in.
4783 @kindex show language
4788 Display the current working language. This is the
4789 language you can use with commands such as @code{print} to
4790 build and compute expressions that may involve variables in your program.
4793 Among the other information listed here (@pxref{Frame Info, ,Information
4794 about a frame}) is the source language for this frame. This is the
4795 language that will become the working language if you ever use an
4796 identifier that is in this frame.
4799 Among the other information listed here (@pxref{Symbols, ,Examining the
4800 Symbol Table}) is the source language of this source file.
4805 @section Type and range checking
4808 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
4809 checking are included, but they do not yet have any effect. This
4810 section documents the intended facilities.
4812 @c FIXME remove warning when type/range code added
4814 Some languages are designed to guard you against making seemingly common
4815 errors through a series of compile- and run-time checks. These include
4816 checking the type of arguments to functions and operators, and making
4817 sure mathematical overflows are caught at run time. Checks such as
4818 these help to ensure a program's correctness once it has been compiled
4819 by eliminating type mismatches, and providing active checks for range
4820 errors when your program is running.
4822 @value{GDBN} can check for conditions like the above if you wish.
4823 Although @value{GDBN} will not check the statements in your program, it
4824 can check expressions entered directly into @value{GDBN} for evaluation via
4825 the @code{print} command, for example. As with the working language,
4826 @value{GDBN} can also decide whether or not to check automatically based on
4827 your program's source language. @xref{Support, ,Supported languages},
4828 for the default settings of supported languages.
4831 * Type Checking:: An overview of type checking
4832 * Range Checking:: An overview of range checking
4835 @cindex type checking
4836 @cindex checks, type
4838 @subsection An overview of type checking
4840 Some languages, such as Modula-2, are strongly typed, meaning that the
4841 arguments to operators and functions have to be of the correct type,
4842 otherwise an error occurs. These checks prevent type mismatch
4843 errors from ever causing any run-time problems. For example,
4851 The second example fails because the @code{CARDINAL} 1 is not
4852 type-compatible with the @code{REAL} 2.3.
4854 For expressions you use in @value{GDBN} commands, you can tell the @value{GDBN}
4855 type checker to skip checking; to treat any mismatches as errors and
4856 abandon the expression; or only issue warnings when type mismatches
4857 occur, but evaluate the expression anyway. When you choose the last of
4858 these, @value{GDBN} evaluates expressions like the second example above, but
4859 also issues a warning.
4861 Even though you may turn type checking off, other type-based reasons may
4862 prevent @value{GDBN} from evaluating an expression. For instance, @value{GDBN} does not
4863 know how to add an @code{int} and a @code{struct foo}. These particular
4864 type errors have nothing to do with the language in use, and usually
4865 arise from expressions, such as the one described above, which make
4866 little sense to evaluate anyway.
4868 Each language defines to what degree it is strict about type. For
4869 instance, both Modula-2 and C require the arguments to arithmetical
4870 operators to be numbers. In C, enumerated types and pointers can be
4871 represented as numbers, so that they are valid arguments to mathematical
4872 operators. @xref{Support, ,Supported languages}, for further
4873 details on specific languages.
4875 @value{GDBN} provides some additional commands for controlling the type checker:
4878 @kindex set check type
4879 @kindex show check type
4881 @item set check type auto
4882 Set type checking on or off based on the current working language.
4883 @xref{Support, ,Supported languages}, for the default settings for
4886 @item set check type on
4887 @itemx set check type off
4888 Set type checking on or off, overriding the default setting for the
4889 current working language. Issue a warning if the setting does not
4890 match the language default. If any type mismatches occur in
4891 evaluating an expression while typechecking is on, @value{GDBN} prints a
4892 message and aborts evaluation of the expression.
4894 @item set check type warn
4895 Cause the type checker to issue warnings, but to always attempt to
4896 evaluate the expression. Evaluating the expression may still
4897 be impossible for other reasons. For example, @value{GDBN} cannot add
4898 numbers and structures.
4901 Show the current setting of the type checker, and whether or not @value{GDBN} is
4902 setting it automatically.
4905 @cindex range checking
4906 @cindex checks, range
4907 @node Range Checking
4908 @subsection An overview of range checking
4910 In some languages (such as Modula-2), it is an error to exceed the
4911 bounds of a type; this is enforced with run-time checks. Such range
4912 checking is meant to ensure program correctness by making sure
4913 computations do not overflow, or indices on an array element access do
4914 not exceed the bounds of the array.
4916 For expressions you use in @value{GDBN} commands, you can tell
4917 @value{GDBN} to treat range errors in one of three ways: ignore them,
4918 always treat them as errors and abandon the expression, or issue
4919 warnings but evaluate the expression anyway.
4921 A range error can result from numerical overflow, from exceeding an
4922 array index bound, or when you type a constant that is not a member
4923 of any type. Some languages, however, do not treat overflows as an
4924 error. In many implementations of C, mathematical overflow causes the
4925 result to ``wrap around'' to lower values---for example, if @var{m} is
4926 the largest integer value, and @var{s} is the smallest, then
4929 @var{m} + 1 @result{} @var{s}
4932 This, too, is specific to individual languages, and in some cases
4933 specific to individual compilers or machines. @xref{Support, ,
4934 Supported languages}, for further details on specific languages.
4936 @value{GDBN} provides some additional commands for controlling the range checker:
4939 @kindex set check range
4940 @kindex show check range
4942 @item set check range auto
4943 Set range checking on or off based on the current working language.
4944 @xref{Support, ,Supported languages}, for the default settings for
4947 @item set check range on
4948 @itemx set check range off
4949 Set range checking on or off, overriding the default setting for the
4950 current working language. A warning is issued if the setting does not
4951 match the language default. If a range error occurs, then a message
4952 is printed and evaluation of the expression is aborted.
4954 @item set check range warn
4955 Output messages when the @value{GDBN} range checker detects a range error,
4956 but attempt to evaluate the expression anyway. Evaluating the
4957 expression may still be impossible for other reasons, such as accessing
4958 memory that the process does not own (a typical example from many Unix
4962 Show the current setting of the range checker, and whether or not it is
4963 being set automatically by @value{GDBN}.
4968 @section Supported languages
4971 @value{GDBN} 4 supports C, C++, and Modula-2.
4974 @value{GDBN} 4 supports C, and C++.
4976 Some @value{GDBN} features may be used in expressions regardless of the
4977 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
4978 and the @samp{@{type@}addr} construct (@pxref{Expressions,
4979 ,Expressions}) can be used with the constructs of any supported
4982 The following sections detail to what degree each source language is
4983 supported by @value{GDBN}. These sections are not meant to be language
4984 tutorials or references, but serve only as a reference guide to what the
4985 @value{GDBN} expression parser will accept, and what input and output
4986 formats should look like for different languages. There are many good
4987 books written on each of these languages; please look to these for a
4988 language reference or tutorial.
4993 * Modula-2:: Modula-2
4997 @subsection C and C++
4999 @cindex expressions in C or C++
5001 Since C and C++ are so closely related, many features of @value{GDBN} apply
5002 to both languages. Whenever this is the case, we discuss both languages
5006 @c Cancel this below, under same condition, at end of this chapter!
5013 The C++ debugging facilities are jointly implemented by the GNU C++
5014 compiler and @value{GDBN}. Therefore, to debug your C++ code effectively,
5015 you must compile your C++ programs with the GNU C++ compiler,
5020 @chapter C Language Support
5022 @cindex expressions in C
5024 Information specific to the C language is built into @value{GDBN} so that you
5025 can use C expressions while degugging. This also permits @value{GDBN} to
5026 output values in a manner consistent with C conventions.
5029 * C Operators:: C operators
5030 * C Constants:: C constants
5031 * Debugging C:: @value{GDBN} and C
5036 * C Operators:: C and C++ operators
5037 * C Constants:: C and C++ constants
5038 * Cplus expressions:: C++ expressions
5039 * C Defaults:: Default settings for C and C++
5041 * C Checks:: C and C++ type and range checks
5044 * Debugging C:: @value{GDBN} and C
5045 * Debugging C plus plus:: Special features for C++
5050 @cindex C and C++ operators
5052 @subsubsection C and C++ operators
5057 @section C operators
5060 Operators must be defined on values of specific types. For instance,
5061 @code{+} is defined on numbers, but not on structures. Operators are
5062 often defined on groups of types.
5065 For the purposes of C and C++, the following definitions hold:
5070 @emph{Integral types} include @code{int} with any of its storage-class
5071 specifiers; @code{char}; and @code{enum}.
5074 @emph{Floating-point types} include @code{float} and @code{double}.
5077 @emph{Pointer types} include all types defined as @code{(@var{type}
5081 @emph{Scalar types} include all of the above.
5085 The following operators are supported. They are listed here
5086 in order of increasing precedence:
5090 The comma or sequencing operator. Expressions in a comma-separated list
5091 are evaluated from left to right, with the result of the entire
5092 expression being the last expression evaluated.
5095 Assignment. The value of an assignment expression is the value
5096 assigned. Defined on scalar types.
5099 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5100 and translated to @w{@code{@var{a} = @var{a op b}}}.
5101 @w{@code{@var{op}=}} and @code{=} have the same precendence.
5102 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5103 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5106 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5107 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5111 Logical @sc{or}. Defined on integral types.
5114 Logical @sc{and}. Defined on integral types.
5117 Bitwise @sc{or}. Defined on integral types.
5120 Bitwise exclusive-@sc{or}. Defined on integral types.
5123 Bitwise @sc{and}. Defined on integral types.
5126 Equality and inequality. Defined on scalar types. The value of these
5127 expressions is 0 for false and non-zero for true.
5129 @item <@r{, }>@r{, }<=@r{, }>=
5130 Less than, greater than, less than or equal, greater than or equal.
5131 Defined on scalar types. The value of these expressions is 0 for false
5132 and non-zero for true.
5135 left shift, and right shift. Defined on integral types.
5138 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5141 Addition and subtraction. Defined on integral types, floating-point types and
5144 @item *@r{, }/@r{, }%
5145 Multiplication, division, and modulus. Multiplication and division are
5146 defined on integral and floating-point types. Modulus is defined on
5150 Increment and decrement. When appearing before a variable, the
5151 operation is performed before the variable is used in an expression;
5152 when appearing after it, the variable's value is used before the
5153 operation takes place.
5156 Pointer dereferencing. Defined on pointer types. Same precedence as
5160 Address operator. Defined on variables. Same precedence as @code{++}.
5163 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5164 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5165 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
5166 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5171 Negative. Defined on integral and floating-point types. Same
5172 precedence as @code{++}.
5175 Logical negation. Defined on integral types. Same precedence as
5179 Bitwise complement operator. Defined on integral types. Same precedence as
5184 Structure member, and pointer-to-structure member. For convenience,
5185 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5186 pointer based on the stored type information.
5187 Defined on @code{struct} and @code{union} data.
5190 Array indexing. @code{@var{a}[@var{i}]} is defined as
5191 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5194 Function parameter list. Same precedence as @code{->}.
5198 C++ scope resolution operator. Defined on
5199 @code{struct}, @code{union}, and @code{class} types.
5207 represent the @value{GDBN} scope operator (@pxref{Expressions,
5210 Same precedence as @code{::}, above.
5215 @cindex C and C++ constants
5217 @subsubsection C and C++ constants
5219 @value{GDBN} allows you to express the constants of C and C++ in the
5225 @section C constants
5227 @value{GDBN} allows you to express the constants of C in the
5233 Integer constants are a sequence of digits. Octal constants are
5234 specified by a leading @samp{0} (ie. zero), and hexadecimal constants by
5235 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
5236 @samp{l}, specifying that the constant should be treated as a
5240 Floating point constants are a sequence of digits, followed by a decimal
5241 point, followed by a sequence of digits, and optionally followed by an
5242 exponent. An exponent is of the form:
5243 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
5244 sequence of digits. The @samp{+} is optional for positive exponents.
5247 Enumerated constants consist of enumerated identifiers, or their
5248 integral equivalents.
5251 Character constants are a single character surrounded by single quotes
5252 (@code{'}), or a number---the ordinal value of the corresponding character
5253 (usually its @sc{ASCII} value). Within quotes, the single character may
5254 be represented by a letter or by @dfn{escape sequences}, which are of
5255 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
5256 of the character's ordinal value; or of the form @samp{\@var{x}}, where
5257 @samp{@var{x}} is a predefined special character---for example,
5258 @samp{\n} for newline.
5261 String constants are a sequence of character constants surrounded
5262 by double quotes (@code{"}).
5265 Pointer constants are an integral value. You can also write pointers
5266 to constants using the C operator @samp{&}.
5269 Array constants are comma-separated lists surrounded by braces @samp{@{}
5270 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
5271 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
5272 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
5276 @node Cplus expressions
5277 @subsubsection C++ expressions
5279 @cindex expressions in C++
5280 @value{GDBN} expression handling has a number of extensions to
5281 interpret a significant subset of C++ expressions.
5283 @cindex C++ support, not in @sc{coff}
5284 @cindex @sc{coff} versus C++
5285 @cindex C++ and object formats
5286 @cindex object formats and C++
5287 @cindex a.out and C++
5288 @cindex @sc{ecoff} and C++
5289 @cindex @sc{xcoff} and C++
5290 @cindex @sc{elf}/stabs and C++
5291 @cindex @sc{elf}/@sc{dwarf} and C++
5293 @emph{Warning:} Most of these extensions depend on the use of additional
5294 debugging information in the symbol table, and thus require a rich,
5295 extendable object code format. In particular, if your system uses
5296 a.out, MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or Sun @sc{elf} with stabs
5297 extensions to the symbol table, these facilities are all available.
5298 Where the object code format is standard @sc{coff}, on the other hand,
5299 most of the C++ support in @value{GDBN} will @emph{not} work, nor can it.
5300 For the standard SVr4 debugging format, @sc{dwarf} in @sc{elf}, the
5301 standard is still evolving, so the C++ support in @value{GDBN} is still
5302 fragile; when this debugging format stabilizes, however, C++ support
5303 will also be available on systems that use it.
5308 @cindex member functions
5310 Member function calls are allowed; you can use expressions like
5313 count = aml->GetOriginal(x, y)
5317 @cindex namespace in C++
5319 While a member function is active (in the selected stack frame), your
5320 expressions have the same namespace available as the member function;
5321 that is, @value{GDBN} allows implicit references to the class instance
5322 pointer @code{this} following the same rules as C++.
5324 @cindex call overloaded functions
5325 @cindex type conversions in C++
5327 You can call overloaded functions; @value{GDBN} will resolve the function
5328 call to the right definition, with one restriction---you must use
5329 arguments of the type required by the function that you want to call.
5330 @value{GDBN} will not perform conversions requiring constructors or
5331 user-defined type operators.
5333 @cindex reference declarations
5335 @value{GDBN} understands variables declared as C++ references; you can use them in
5336 expressions just as you do in C++ source---they are automatically
5339 In the parameter list shown when @value{GDBN} displays a frame, the values of
5340 reference variables are not displayed (unlike other variables); this
5341 avoids clutter, since references are often used for large structures.
5342 The @emph{address} of a reference variable is always shown, unless
5343 you have specified @samp{set print address off}.
5346 @value{GDBN} supports the C++ name resolution operator @code{::}---your
5347 expressions can use it just as expressions in your program do. Since
5348 one scope may be defined in another, you can use @code{::} repeatedly if
5349 necessary, for example in an expression like
5350 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
5351 resolving name scope by reference to source files, in both C and C++
5352 debugging (@pxref{Variables, ,Program variables}).
5356 @subsubsection C and C++ defaults
5357 @cindex C and C++ defaults
5359 If you allow @value{GDBN} to set type and range checking automatically, they
5360 both default to @code{off} whenever the working language changes to
5361 C or C++. This happens regardless of whether you, or @value{GDBN},
5362 selected the working language.
5364 If you allow @value{GDBN} to set the language automatically, it sets the
5365 working language to C or C++ on entering code compiled from a source file
5366 whose name ends with @file{.c}, @file{.C}, or @file{.cc}.
5367 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
5371 @c Type checking is (a) primarily motivated by Modula-2, and (b)
5372 @c unimplemented. If (b) changes, it might make sense to let this node
5373 @c appear even if Mod-2 does not, but meanwhile ignore it. pesch 16jul93.
5375 @subsubsection C and C++ type and range checks
5376 @cindex C and C++ checks
5378 By default, when @value{GDBN} parses C or C++ expressions, type checking
5379 is not used. However, if you turn type checking on, @value{GDBN} will
5380 consider two variables type equivalent if:
5384 The two variables are structured and have the same structure, union, or
5388 Two two variables have the same type name, or types that have been
5389 declared equivalent through @code{typedef}.
5392 @c leaving this out because neither J Gilmore nor R Pesch understand it.
5395 The two @code{struct}, @code{union}, or @code{enum} variables are
5396 declared in the same declaration. (Note: this may not be true for all C
5401 Range checking, if turned on, is done on mathematical operations. Array
5402 indices are not checked, since they are often used to index a pointer
5403 that is not itself an array.
5409 @subsubsection @value{GDBN} and C
5413 @section @value{GDBN} and C
5416 The @code{set print union} and @code{show print union} commands apply to
5417 the @code{union} type. When set to @samp{on}, any @code{union} that is
5418 inside a @code{struct}
5422 will also be printed.
5423 Otherwise, it will appear as @samp{@{...@}}.
5425 The @code{@@} operator aids in the debugging of dynamic arrays, formed
5426 with pointers and a memory allocation function. @xref{Expressions,
5430 @node Debugging C plus plus
5431 @subsubsection @value{GDBN} features for C++
5433 @cindex commands for C++
5434 Some @value{GDBN} commands are particularly useful with C++, and some are
5435 designed specifically for use with C++. Here is a summary:
5438 @cindex break in overloaded functions
5439 @item @r{breakpoint menus}
5440 When you want a breakpoint in a function whose name is overloaded,
5441 @value{GDBN} breakpoint menus help you specify which function definition
5442 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
5444 @cindex overloading in C++
5445 @item rbreak @var{regex}
5446 Setting breakpoints using regular expressions is helpful for setting
5447 breakpoints on overloaded functions that are not members of any special
5449 @xref{Set Breaks, ,Setting breakpoints}.
5451 @cindex C++ exception handling
5452 @item catch @var{exceptions}
5454 Debug C++ exception handling using these commands. @xref{Exception
5455 Handling, ,Breakpoints and exceptions}.
5458 @item ptype @var{typename}
5459 Print inheritance relationships as well as other information for type
5461 @xref{Symbols, ,Examining the Symbol Table}.
5463 @cindex C++ symbol display
5464 @item set print demangle
5465 @itemx show print demangle
5466 @itemx set print asm-demangle
5467 @itemx show print asm-demangle
5468 Control whether C++ symbols display in their source form, both when
5469 displaying code as C++ source and when displaying disassemblies.
5470 @xref{Print Settings, ,Print settings}.
5472 @item set print object
5473 @itemx show print object
5474 Choose whether to print derived (actual) or declared types of objects.
5475 @xref{Print Settings, ,Print settings}.
5477 @item set print vtbl
5478 @itemx show print vtbl
5479 Control the format for printing virtual function tables.
5480 @xref{Print Settings, ,Print settings}.
5482 @item @r{Overloaded symbol names}
5483 You can specify a particular definition of an overloaded symbol, using
5484 the same notation that is used to declare such symbols in C++: type
5485 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
5486 also use the @value{GDBN} command-line word completion facilities to list the
5487 available choices, or to finish the type list for you.
5488 @xref{Completion,, Command completion}, for details on how to do this.
5491 @c cancels "raisesections" under same conditions near bgn of chapter
5497 @subsection Modula-2
5500 The extensions made to @value{GDBN} to support Modula-2 only support
5501 output from the GNU Modula-2 compiler (which is currently being
5502 developed). Other Modula-2 compilers are not currently supported, and
5503 attempting to debug executables produced by them will most likely
5504 result in an error as @value{GDBN} reads in the executable's symbol
5507 @cindex expressions in Modula-2
5509 * M2 Operators:: Built-in operators
5510 * Built-In Func/Proc:: Built-in functions and procedures
5511 * M2 Constants:: Modula-2 constants
5512 * M2 Defaults:: Default settings for Modula-2
5513 * Deviations:: Deviations from standard Modula-2
5514 * M2 Checks:: Modula-2 type and range checks
5515 * M2 Scope:: The scope operators @code{::} and @code{.}
5516 * GDB/M2:: @value{GDBN} and Modula-2
5520 @subsubsection Operators
5521 @cindex Modula-2 operators
5523 Operators must be defined on values of specific types. For instance,
5524 @code{+} is defined on numbers, but not on structures. Operators are
5525 often defined on groups of types. For the purposes of Modula-2, the
5526 following definitions hold:
5531 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
5535 @emph{Character types} consist of @code{CHAR} and its subranges.
5538 @emph{Floating-point types} consist of @code{REAL}.
5541 @emph{Pointer types} consist of anything declared as @code{POINTER TO
5545 @emph{Scalar types} consist of all of the above.
5548 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
5551 @emph{Boolean types} consist of @code{BOOLEAN}.
5555 The following operators are supported, and appear in order of
5556 increasing precedence:
5560 Function argument or array index separator.
5563 Assignment. The value of @var{var} @code{:=} @var{value} is
5567 Less than, greater than on integral, floating-point, or enumerated
5571 Less than, greater than, less than or equal to, greater than or equal to
5572 on integral, floating-point and enumerated types, or set inclusion on
5573 set types. Same precedence as @code{<}.
5575 @item =@r{, }<>@r{, }#
5576 Equality and two ways of expressing inequality, valid on scalar types.
5577 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
5578 available for inequality, since @code{#} conflicts with the script
5582 Set membership. Defined on set types and the types of their members.
5583 Same precedence as @code{<}.
5586 Boolean disjunction. Defined on boolean types.
5589 Boolean conjuction. Defined on boolean types.
5592 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5595 Addition and subtraction on integral and floating-point types, or union
5596 and difference on set types.
5599 Multiplication on integral and floating-point types, or set intersection
5603 Division on floating-point types, or symmetric set difference on set
5604 types. Same precedence as @code{*}.
5607 Integer division and remainder. Defined on integral types. Same
5608 precedence as @code{*}.
5611 Negative. Defined on @code{INTEGER} and @code{REAL} data.
5614 Pointer dereferencing. Defined on pointer types.
5617 Boolean negation. Defined on boolean types. Same precedence as
5621 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
5622 precedence as @code{^}.
5625 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
5628 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
5632 @value{GDBN} and Modula-2 scope operators.
5636 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
5637 will treat the use of the operator @code{IN}, or the use of operators
5638 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
5639 @code{<=}, and @code{>=} on sets as an error.
5642 @cindex Modula-2 built-ins
5643 @node Built-In Func/Proc
5644 @subsubsection Built-in functions and procedures
5646 Modula-2 also makes available several built-in procedures and functions.
5647 In describing these, the following metavariables are used:
5652 represents an @code{ARRAY} variable.
5655 represents a @code{CHAR} constant or variable.
5658 represents a variable or constant of integral type.
5661 represents an identifier that belongs to a set. Generally used in the
5662 same function with the metavariable @var{s}. The type of @var{s} should
5663 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
5666 represents a variable or constant of integral or floating-point type.
5669 represents a variable or constant of floating-point type.
5675 represents a variable.
5678 represents a variable or constant of one of many types. See the
5679 explanation of the function for details.
5682 All Modula-2 built-in procedures also return a result, described below.
5686 Returns the absolute value of @var{n}.
5689 If @var{c} is a lower case letter, it returns its upper case
5690 equivalent, otherwise it returns its argument
5693 Returns the character whose ordinal value is @var{i}.
5696 Decrements the value in the variable @var{v}. Returns the new value.
5698 @item DEC(@var{v},@var{i})
5699 Decrements the value in the variable @var{v} by @var{i}. Returns the
5702 @item EXCL(@var{m},@var{s})
5703 Removes the element @var{m} from the set @var{s}. Returns the new
5706 @item FLOAT(@var{i})
5707 Returns the floating point equivalent of the integer @var{i}.
5710 Returns the index of the last member of @var{a}.
5713 Increments the value in the variable @var{v}. Returns the new value.
5715 @item INC(@var{v},@var{i})
5716 Increments the value in the variable @var{v} by @var{i}. Returns the
5719 @item INCL(@var{m},@var{s})
5720 Adds the element @var{m} to the set @var{s} if it is not already
5721 there. Returns the new set.
5724 Returns the maximum value of the type @var{t}.
5727 Returns the minimum value of the type @var{t}.
5730 Returns boolean TRUE if @var{i} is an odd number.
5733 Returns the ordinal value of its argument. For example, the ordinal
5734 value of a character is its ASCII value (on machines supporting the
5735 ASCII character set). @var{x} must be of an ordered type, which include
5736 integral, character and enumerated types.
5739 Returns the size of its argument. @var{x} can be a variable or a type.
5741 @item TRUNC(@var{r})
5742 Returns the integral part of @var{r}.
5744 @item VAL(@var{t},@var{i})
5745 Returns the member of the type @var{t} whose ordinal value is @var{i}.
5749 @emph{Warning:} Sets and their operations are not yet supported, so
5750 @value{GDBN} will treat the use of procedures @code{INCL} and @code{EXCL} as
5754 @cindex Modula-2 constants
5756 @subsubsection Constants
5758 @value{GDBN} allows you to express the constants of Modula-2 in the following
5764 Integer constants are simply a sequence of digits. When used in an
5765 expression, a constant is interpreted to be type-compatible with the
5766 rest of the expression. Hexadecimal integers are specified by a
5767 trailing @samp{H}, and octal integers by a trailing @samp{B}.
5770 Floating point constants appear as a sequence of digits, followed by a
5771 decimal point and another sequence of digits. An optional exponent can
5772 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
5773 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
5774 digits of the floating point constant must be valid decimal (base 10)
5778 Character constants consist of a single character enclosed by a pair of
5779 like quotes, either single (@code{'}) or double (@code{"}). They may
5780 also be expressed by their ordinal value (their ASCII value, usually)
5781 followed by a @samp{C}.
5784 String constants consist of a sequence of characters enclosed by a
5785 pair of like quotes, either single (@code{'}) or double (@code{"}).
5786 Escape sequences in the style of C are also allowed. @xref{C
5787 Constants, ,C and C++ constants}, for a brief explanation of escape
5791 Enumerated constants consist of an enumerated identifier.
5794 Boolean constants consist of the identifiers @code{TRUE} and
5798 Pointer constants consist of integral values only.
5801 Set constants are not yet supported.
5805 @subsubsection Modula-2 defaults
5806 @cindex Modula-2 defaults
5808 If type and range checking are set automatically by @value{GDBN}, they
5809 both default to @code{on} whenever the working language changes to
5810 Modula-2. This happens regardless of whether you, or @value{GDBN},
5811 selected the working language.
5813 If you allow @value{GDBN} to set the language automatically, then entering
5814 code compiled from a file whose name ends with @file{.mod} will set the
5815 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
5816 the language automatically}, for further details.
5819 @subsubsection Deviations from standard Modula-2
5820 @cindex Modula-2, deviations from
5822 A few changes have been made to make Modula-2 programs easier to debug.
5823 This is done primarily via loosening its type strictness:
5827 Unlike in standard Modula-2, pointer constants can be formed by
5828 integers. This allows you to modify pointer variables during
5829 debugging. (In standard Modula-2, the actual address contained in a
5830 pointer variable is hidden from you; it can only be modified
5831 through direct assignment to another pointer variable or expression that
5832 returned a pointer.)
5835 C escape sequences can be used in strings and characters to represent
5836 non-printable characters. @value{GDBN} will print out strings with these
5837 escape sequences embedded. Single non-printable characters are
5838 printed using the @samp{CHR(@var{nnn})} format.
5841 The assignment operator (@code{:=}) returns the value of its right-hand
5845 All built-in procedures both modify @emph{and} return their argument.
5849 @subsubsection Modula-2 type and range checks
5850 @cindex Modula-2 checks
5853 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
5856 @c FIXME remove warning when type/range checks added
5858 @value{GDBN} considers two Modula-2 variables type equivalent if:
5862 They are of types that have been declared equivalent via a @code{TYPE
5863 @var{t1} = @var{t2}} statement
5866 They have been declared on the same line. (Note: This is true of the
5867 GNU Modula-2 compiler, but it may not be true of other compilers.)
5870 As long as type checking is enabled, any attempt to combine variables
5871 whose types are not equivalent is an error.
5873 Range checking is done on all mathematical operations, assignment, array
5874 index bounds, and all built-in functions and procedures.
5877 @subsubsection The scope operators @code{::} and @code{.}
5880 @cindex colon, doubled as scope operator
5883 @c Info cannot handle :: but TeX can.
5889 There are a few subtle differences between the Modula-2 scope operator
5890 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
5895 @var{module} . @var{id}
5896 @var{scope} :: @var{id}
5900 where @var{scope} is the name of a module or a procedure,
5901 @var{module} the name of a module, and @var{id} is any declared
5902 identifier within your program, except another module.
5904 Using the @code{::} operator makes @value{GDBN} search the scope
5905 specified by @var{scope} for the identifier @var{id}. If it is not
5906 found in the specified scope, then @value{GDBN} will search all scopes
5907 enclosing the one specified by @var{scope}.
5909 Using the @code{.} operator makes @value{GDBN} search the current scope for
5910 the identifier specified by @var{id} that was imported from the
5911 definition module specified by @var{module}. With this operator, it is
5912 an error if the identifier @var{id} was not imported from definition
5913 module @var{module}, or if @var{id} is not an identifier in
5917 @subsubsection @value{GDBN} and Modula-2
5919 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
5920 Five subcommands of @code{set print} and @code{show print} apply
5921 specifically to C and C++: @samp{vtbl}, @samp{demangle},
5922 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
5923 apply to C++, and the last to the C @code{union} type, which has no direct
5924 analogue in Modula-2.
5926 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
5927 while using any language, is not useful with Modula-2. Its
5928 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
5929 created in Modula-2 as they can in C or C++. However, because an
5930 address can be specified by an integral constant, the construct
5931 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
5933 @cindex @code{#} in Modula-2
5934 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
5935 interpreted as the beginning of a comment. Use @code{<>} instead.
5941 @chapter Examining the Symbol Table
5943 The commands described in this section allow you to inquire about the
5944 symbols (names of variables, functions and types) defined in your
5945 program. This information is inherent in the text of your program and
5946 does not change as your program executes. @value{GDBN} finds it in your
5947 program's symbol table, in the file indicated when you started @value{GDBN}
5948 (@pxref{File Options, ,Choosing files}), or by one of the
5949 file-management commands (@pxref{Files, ,Commands to specify files}).
5951 @c FIXME! This might be intentionally specific to C and C++; if so, move
5952 @c to someplace in C section of lang chapter.
5953 @cindex symbol names
5954 @cindex names of symbols
5955 @cindex quoting names
5956 Occasionally, you may need to refer to symbols that contain unusual
5957 characters, which @value{GDBN} ordinarily treats as word delimiters. The
5958 most frequent case is in referring to static variables in other
5959 source files (@pxref{Variables,,Program variables}). File names
5960 are recorded in object files as debugging symbols, but @value{GDBN} would
5961 ordinarily parse a typical file name, like @file{foo.c}, as the three words
5962 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
5963 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
5970 looks up the value of @code{x} in the scope of the file @file{foo.c}.
5973 @item info address @var{symbol}
5974 @kindex info address
5975 Describe where the data for @var{symbol} is stored. For a register
5976 variable, this says which register it is kept in. For a non-register
5977 local variable, this prints the stack-frame offset at which the variable
5980 Note the contrast with @samp{print &@var{symbol}}, which does not work
5981 at all for a register variable, and for a stack local variable prints
5982 the exact address of the current instantiation of the variable.
5984 @item whatis @var{exp}
5986 Print the data type of expression @var{exp}. @var{exp} is not
5987 actually evaluated, and any side-effecting operations (such as
5988 assignments or function calls) inside it do not take place.
5989 @xref{Expressions, ,Expressions}.
5992 Print the data type of @code{$}, the last value in the value history.
5994 @item ptype @var{typename}
5996 Print a description of data type @var{typename}. @var{typename} may be
5997 the name of a type, or for C code it may have the form
5999 @samp{class @var{class-name}},
6001 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
6002 @samp{enum @var{enum-tag}}.
6004 @item ptype @var{exp}
6006 Print a description of the type of expression @var{exp}. @code{ptype}
6007 differs from @code{whatis} by printing a detailed description, instead
6008 of just the name of the type.
6010 For example, for this variable declaration:
6013 struct complex @{double real; double imag;@} v;
6017 the two commands give this output:
6021 (@value{GDBP}) whatis v
6022 type = struct complex
6023 (@value{GDBP}) ptype v
6024 type = struct complex @{
6032 As with @code{whatis}, using @code{ptype} without an argument refers to
6033 the type of @code{$}, the last value in the value history.
6035 @item info types @var{regexp}
6038 Print a brief description of all types whose name matches @var{regexp}
6039 (or all types in your program, if you supply no argument). Each
6040 complete typename is matched as though it were a complete line; thus,
6041 @samp{i type value} gives information on all types in your program whose
6042 name includes the string @code{value}, but @samp{i type ^value$} gives
6043 information only on types whose complete name is @code{value}.
6045 This command differs from @code{ptype} in two ways: first, like
6046 @code{whatis}, it does not print a detailed description; second, it
6047 lists all source files where a type is defined.
6051 Show the name of the current source file---that is, the source file for
6052 the function containing the current point of execution---and the language
6056 @kindex info sources
6057 Print the names of all source files in your program for which there is
6058 debugging information, organized into two lists: files whose symbols
6059 have already been read, and files whose symbols will be read when needed.
6061 @item info functions
6062 @kindex info functions
6063 Print the names and data types of all defined functions.
6065 @item info functions @var{regexp}
6066 Print the names and data types of all defined functions
6067 whose names contain a match for regular expression @var{regexp}.
6068 Thus, @samp{info fun step} finds all functions whose names
6069 include @code{step}; @samp{info fun ^step} finds those whose names
6070 start with @code{step}.
6072 @item info variables
6073 @kindex info variables
6074 Print the names and data types of all variables that are declared
6075 outside of functions (i.e., excluding local variables).
6077 @item info variables @var{regexp}
6078 Print the names and data types of all variables (except for local
6079 variables) whose names contain a match for regular expression
6083 This was never implemented.
6085 @itemx info methods @var{regexp}
6086 @kindex info methods
6087 The @code{info methods} command permits the user to examine all defined
6088 methods within C++ program, or (with the @var{regexp} argument) a
6089 specific set of methods found in the various C++ classes. Many
6090 C++ classes provide a large number of methods. Thus, the output
6091 from the @code{ptype} command can be overwhelming and hard to use. The
6092 @code{info-methods} command filters the methods, printing only those
6093 which match the regular-expression @var{regexp}.
6096 @item maint print symbols @var{filename}
6097 @itemx maint print psymbols @var{filename}
6098 @itemx maint print msymbols @var{filename}
6099 @kindex maint print symbols
6101 @kindex maint print psymbols
6102 @cindex partial symbol dump
6103 Write a dump of debugging symbol data into the file @var{filename}.
6104 These commands are used to debug the @value{GDBN} symbol-reading code. Only
6105 symbols with debugging data are included. If you use @samp{maint print
6106 symbols}, @value{GDBN} includes all the symbols for which it has already
6107 collected full details: that is, @var{filename} reflects symbols for
6108 only those files whose symbols @value{GDBN} has read. You can use the
6109 command @code{info sources} to find out which files these are. If you
6110 use @samp{maint print psymbols} instead, the dump shows information about
6111 symbols that @value{GDBN} only knows partially---that is, symbols defined in
6112 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
6113 @samp{maint print msymbols} dumps just the minimal symbol information
6114 required for each object file from which @value{GDBN} has read some symbols.
6115 @xref{Files, ,Commands to specify files}, for a discussion of how
6116 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
6120 @chapter Altering Execution
6122 Once you think you have found an error in your program, you might want to
6123 find out for certain whether correcting the apparent error would lead to
6124 correct results in the rest of the run. You can find the answer by
6125 experiment, using the @value{GDBN} features for altering execution of the
6128 For example, you can store new values into variables or memory
6131 give your program a signal, restart it
6134 restart your program
6136 at a different address, or even return prematurely from a function to
6140 * Assignment:: Assignment to variables
6141 * Jumping:: Continuing at a different address
6143 * Signaling:: Giving your program a signal
6146 * Returning:: Returning from a function
6147 * Calling:: Calling your program's functions
6148 * Patching:: Patching your program
6152 @section Assignment to variables
6155 @cindex setting variables
6156 To alter the value of a variable, evaluate an assignment expression.
6157 @xref{Expressions, ,Expressions}. For example,
6164 stores the value 4 into the variable @code{x}, and then prints the
6165 value of the assignment expression (which is 4).
6167 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
6168 information on operators in supported languages.
6171 @kindex set variable
6172 @cindex variables, setting
6173 If you are not interested in seeing the value of the assignment, use the
6174 @code{set} command instead of the @code{print} command. @code{set} is
6175 really the same as @code{print} except that the expression's value is
6176 not printed and is not put in the value history (@pxref{Value History,
6177 ,Value history}). The expression is evaluated only for its effects.
6179 If the beginning of the argument string of the @code{set} command
6180 appears identical to a @code{set} subcommand, use the @code{set
6181 variable} command instead of just @code{set}. This command is identical
6182 to @code{set} except for its lack of subcommands. For example, if
6183 your program has a variable @code{width}, you get
6184 an error if you try to set a new value with just @samp{set width=13},
6185 because @value{GDBN} has the command @code{set width}:
6188 (@value{GDBP}) whatis width
6190 (@value{GDBP}) p width
6192 (@value{GDBP}) set width=47
6193 Invalid syntax in expression.
6197 The invalid expression, of course, is @samp{=47}. In
6198 order to actually set the program's variable @code{width}, use
6201 (@value{GDBP}) set var width=47
6204 @value{GDBN} allows more implicit conversions in assignments than C; you can
6205 freely store an integer value into a pointer variable or vice versa,
6206 and you can convert any structure to any other structure that is the
6207 same length or shorter.
6208 @comment FIXME: how do structs align/pad in these conversions?
6209 @comment /pesch@cygnus.com 18dec1990
6211 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
6212 construct to generate a value of specified type at a specified address
6213 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
6214 to memory location @code{0x83040} as an integer (which implies a certain size
6215 and representation in memory), and
6218 set @{int@}0x83040 = 4
6222 stores the value 4 into that memory location.
6225 @section Continuing at a different address
6227 Ordinarily, when you continue your program, you do so at the place where
6228 it stopped, with the @code{continue} command. You can instead continue at
6229 an address of your own choosing, with the following commands:
6232 @item jump @var{linespec}
6234 Resume execution at line @var{linespec}. Execution will stop
6235 immediately if there is a breakpoint there. @xref{List, ,Printing
6236 source lines}, for a description of the different forms of
6239 The @code{jump} command does not change the current stack frame, or
6240 the stack pointer, or the contents of any memory location or any
6241 register other than the program counter. If line @var{linespec} is in
6242 a different function from the one currently executing, the results may
6243 be bizarre if the two functions expect different patterns of arguments or
6244 of local variables. For this reason, the @code{jump} command requests
6245 confirmation if the specified line is not in the function currently
6246 executing. However, even bizarre results are predictable if you are
6247 well acquainted with the machine-language code of your program.
6249 @item jump *@var{address}
6250 Resume execution at the instruction at address @var{address}.
6253 You can get much the same effect as the @code{jump} command by storing a
6254 new value into the register @code{$pc}. The difference is that this
6255 does not start your program running; it only changes the address where it
6256 @emph{will} run when it is continued. For example,
6263 causes the next @code{continue} command or stepping command to execute at
6264 address @code{0x485}, rather than at the address where your program stopped.
6265 @xref{Continuing and Stepping, ,Continuing and stepping}.
6267 The most common occasion to use the @code{jump} command is to back up,
6268 perhaps with more breakpoints set, over a portion of a program that has
6269 already executed, in order to examine its execution in more detail.
6274 @section Giving your program a signal
6277 @item signal @var{signal}
6279 Resume execution where your program stopped, but immediately give it the
6280 signal @var{signal}. @var{signal} can be the name or the number of a
6281 signal. For example, on many systems @code{signal 2} and @code{signal
6282 SIGINT} are both ways of sending an interrupt signal.
6284 Alternatively, if @var{signal} is zero, continue execution without
6285 giving a signal. This is useful when your program stopped on account of
6286 a signal and would ordinary see the signal when resumed with the
6287 @code{continue} command; @samp{signal 0} causes it to resume without a
6290 @code{signal} does not repeat when you press @key{RET} a second time
6291 after executing the command.
6295 Invoking the @code{signal} command is not the same as invoking the
6296 @code{kill} utility from the shell. Sending a signal with @code{kill}
6297 causes @value{GDBN} to decide what to do with the signal depending on
6298 the signal handling tables (@pxref{Signals}). The @code{signal} command
6299 passes the signal directly to your program.
6304 @section Returning from a function
6308 @itemx return @var{expression}
6309 @cindex returning from a function
6311 You can cancel execution of a function call with the @code{return}
6312 command. If you give an
6313 @var{expression} argument, its value is used as the function's return
6317 When you use @code{return}, @value{GDBN} discards the selected stack frame
6318 (and all frames within it). You can think of this as making the
6319 discarded frame return prematurely. If you wish to specify a value to
6320 be returned, give that value as the argument to @code{return}.
6322 This pops the selected stack frame (@pxref{Selection, ,Selecting a
6323 frame}), and any other frames inside of it, leaving its caller as the
6324 innermost remaining frame. That frame becomes selected. The
6325 specified value is stored in the registers used for returning values
6328 The @code{return} command does not resume execution; it leaves the
6329 program stopped in the state that would exist if the function had just
6330 returned. In contrast, the @code{finish} command (@pxref{Continuing
6331 and Stepping, ,Continuing and stepping}) resumes execution until the
6332 selected stack frame returns naturally.
6335 @section Calling program functions
6337 @cindex calling functions
6340 @item call @var{expr}
6341 Evaluate the expression @var{expr} without displaying @code{void}
6345 You can use this variant of the @code{print} command if you want to
6346 execute a function from your program, but without cluttering the output
6347 with @code{void} returned values. The result is printed and saved in
6348 the value history, if it is not void.
6351 @section Patching programs
6352 @cindex patching binaries
6353 @cindex writing into executables
6355 @cindex writing into corefiles
6358 By default, @value{GDBN} opens the file containing your program's executable
6363 read-only. This prevents accidental alterations
6364 to machine code; but it also prevents you from intentionally patching
6365 your program's binary.
6367 If you'd like to be able to patch the binary, you can specify that
6368 explicitly with the @code{set write} command. For example, you might
6369 want to turn on internal debugging flags, or even to make emergency
6374 @itemx set write off
6376 If you specify @samp{set write on}, @value{GDBN} will open executable
6380 files for both reading and writing; if you specify @samp{set write
6381 off} (the default), @value{GDBN} will open them read-only.
6383 If you have already loaded a file, you must load it again (using the
6388 command) after changing @code{set write}, for your new setting to take
6393 Display whether executable files
6397 will be opened for writing as well as reading.
6401 @chapter @value{GDBN} Files
6403 @value{GDBN} needs to know the file name of the program to be debugged, both in
6404 order to read its symbol table and in order to start your program.
6406 To debug a core dump of a previous run, you must also tell @value{GDBN}
6407 the name of the core dump file.
6411 * Files:: Commands to specify files
6412 * Symbol Errors:: Errors reading symbol files
6416 @section Commands to specify files
6417 @cindex symbol table
6420 @cindex core dump file
6421 The usual way to specify executable and core dump file names is with
6422 the command arguments given when you start @value{GDBN} (@pxref{Invocation,
6423 ,Getting In and Out of @value{GDBN}}.
6426 The usual way to specify an executable file name is with
6427 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
6428 ,Getting In and Out of @value{GDBN}}.
6431 Occasionally it is necessary to change to a different file during a
6432 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
6433 a file you want to use. In these situations the @value{GDBN} commands
6434 to specify new files are useful.
6437 @item file @var{filename}
6438 @cindex executable file
6440 Use @var{filename} as the program to be debugged. It is read for its
6441 symbols and for the contents of pure memory. It is also the program
6442 executed when you use the @code{run} command. If you do not specify a
6443 directory and the file is not found in the @value{GDBN} working directory, @value{GDBN}
6444 uses the environment variable @code{PATH} as a list of directories to
6445 search, just as the shell does when looking for a program to run. You
6446 can change the value of this variable, for both @value{GDBN} and your program,
6447 using the @code{path} command.
6449 On systems with memory-mapped files, an auxiliary symbol table file
6450 @file{@var{filename}.syms} may be available for @var{filename}. If it
6451 is, @value{GDBN} will map in the symbol table from
6452 @file{@var{filename}.syms}, starting up more quickly. See the
6453 descriptions of the options @samp{-mapped} and @samp{-readnow} (available
6454 on the command line, and with the commands @code{file}, @code{symbol-file},
6455 or @code{add-symbol-file}), for more information.
6458 @code{file} with no argument makes @value{GDBN} discard any information it
6459 has on both executable file and the symbol table.
6461 @item exec-file @r{[} @var{filename} @r{]}
6463 Specify that the program to be run (but not the symbol table) is found
6464 in @var{filename}. @value{GDBN} will search the environment variable @code{PATH}
6465 if necessary to locate your program. Omitting @var{filename} means to
6466 discard information on the executable file.
6468 @item symbol-file @r{[} @var{filename} @r{]}
6470 Read symbol table information from file @var{filename}. @code{PATH} is
6471 searched when necessary. Use the @code{file} command to get both symbol
6472 table and program to run from the same file.
6474 @code{symbol-file} with no argument clears out @value{GDBN} information on your
6475 program's symbol table.
6477 The @code{symbol-file} command causes @value{GDBN} to forget the contents of its
6478 convenience variables, the value history, and all breakpoints and
6479 auto-display expressions. This is because they may contain pointers to
6480 the internal data recording symbols and data types, which are part of
6481 the old symbol table data being discarded inside @value{GDBN}.
6483 @code{symbol-file} will not repeat if you press @key{RET} again after
6486 When @value{GDBN} is configured for a particular environment, it will
6487 understand debugging information in whatever format is the standard
6488 generated for that environment; you may use either a GNU compiler, or
6489 other compilers that adhere to the local conventions. Best results are
6490 usually obtained from GNU compilers; for example, using @code{@value{GCC}}
6491 you can generate debugging information for optimized code.
6493 On some kinds of object files, the @code{symbol-file} command does not
6494 normally read the symbol table in full right away. Instead, it scans
6495 the symbol table quickly to find which source files and which symbols
6496 are present. The details are read later, one source file at a time,
6499 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
6500 faster. For the most part, it is invisible except for occasional
6501 pauses while the symbol table details for a particular source file are
6502 being read. (The @code{set verbose} command can turn these pauses
6503 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
6506 We have not implemented the two-stage strategy for COFF yet. When the
6507 symbol table is stored in COFF format, @code{symbol-file} reads the
6508 symbol table data in full right away.
6510 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6511 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6513 @cindex reading symbols immediately
6514 @cindex symbols, reading immediately
6516 @cindex memory-mapped symbol file
6517 @cindex saving symbol table
6518 You can override the @value{GDBN} two-stage strategy for reading symbol
6519 tables by using the @samp{-readnow} option with any of the commands that
6520 load symbol table information, if you want to be sure @value{GDBN} has the
6521 entire symbol table available.
6524 If memory-mapped files are available on your system through the
6525 @code{mmap} system call, you can use another option, @samp{-mapped}, to
6526 cause @value{GDBN} to write the symbols for your program into a reusable
6527 file. Future @value{GDBN} debugging sessions will map in symbol information
6528 from this auxiliary symbol file (if the program has not changed), rather
6529 than spending time reading the symbol table from the executable
6530 program. Using the @samp{-mapped} option has the same effect as
6531 starting @value{GDBN} with the @samp{-mapped} command-line option.
6533 You can use both options together, to make sure the auxiliary symbol
6534 file has all the symbol information for your program.
6536 The auxiliary symbol file for a program called @var{myprog} is called
6537 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
6538 than the corresponding executable), @value{GDBN} will always attempt to use
6539 it when you debug @var{myprog}; no special options or commands are
6542 The @file{.syms} file is specific to the host machine where you run
6543 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
6544 symbol table. It cannot be shared across multiple host platforms.
6546 @c FIXME: for now no mention of directories, since this seems to be in
6547 @c flux. 13mar1992 status is that in theory GDB would look either in
6548 @c current dir or in same dir as myprog; but issues like competing
6549 @c GDB's, or clutter in system dirs, mean that in practice right now
6550 @c only current dir is used. FFish says maybe a special GDB hierarchy
6551 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
6554 @item core-file @r{[} @var{filename} @r{]}
6557 Specify the whereabouts of a core dump file to be used as the ``contents
6558 of memory''. Traditionally, core files contain only some parts of the
6559 address space of the process that generated them; @value{GDBN} can access the
6560 executable file itself for other parts.
6562 @code{core-file} with no argument specifies that no core file is
6565 Note that the core file is ignored when your program is actually running
6566 under @value{GDBN}. So, if you have been running your program and you wish to
6567 debug a core file instead, you must kill the subprocess in which the
6568 program is running. To do this, use the @code{kill} command
6569 (@pxref{Kill Process, ,Killing the child process}).
6572 @item load @var{filename}
6575 Depending on what remote debugging facilities are configured into
6576 @value{GDBN}, the @code{load} command may be available. Where it exists, it
6577 is meant to make @var{filename} (an executable) available for debugging
6578 on the remote system---by downloading, or dynamic linking, for example.
6579 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
6580 the @code{add-symbol-file} command.
6582 If your @value{GDBN} does not have a @code{load} command, attempting to
6583 execute it gets the error message ``@code{You can't do that when your
6584 target is @dots{}}''
6587 The file is loaded at whatever address is specified in the executable.
6588 For some object file formats, like a.out, the object file format fixes
6589 the address and so it won't necessarily match the address you gave to
6593 On VxWorks, @code{load} will dynamically link @var{filename} on the
6594 current target system as well as adding its symbols in @value{GDBN}.
6598 @cindex download to Nindy-960
6599 With the Nindy interface to an Intel 960 board, @code{load} will
6600 download @var{filename} to the 960 as well as adding its symbols in
6605 @cindex download to H8/300 or H8/500
6606 @cindex H8/300 or H8/500 download
6607 @cindex download to Hitachi SH
6608 @cindex Hitachi SH download
6609 When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board
6610 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
6611 the @code{load} command downloads your program to the Hitachi board and also
6612 opens it as the current executable target for @value{GDBN} on your host
6613 (like the @code{file} command).
6616 @code{load} will not repeat if you press @key{RET} again after using it.
6619 @item add-symbol-file @var{filename} @var{address}
6620 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6621 @kindex add-symbol-file
6622 @cindex dynamic linking
6623 The @code{add-symbol-file} command reads additional symbol table information
6624 from the file @var{filename}. You would use this command when @var{filename}
6625 has been dynamically loaded (by some other means) into the program that
6626 is running. @var{address} should be the memory address at which the
6627 file has been loaded; @value{GDBN} cannot figure this out for itself.
6628 You can specify @var{address} as an expression.
6630 The symbol table of the file @var{filename} is added to the symbol table
6631 originally read with the @code{symbol-file} command. You can use the
6632 @code{add-symbol-file} command any number of times; the new symbol data thus
6633 read keeps adding to the old. To discard all old symbol data instead,
6634 use the @code{symbol-file} command.
6636 @code{add-symbol-file} will not repeat if you press @key{RET} after using it.
6638 You can use the @samp{-mapped} and @samp{-readnow} options just as with
6639 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
6640 table information for @var{filename}.
6647 @code{info files} and @code{info target} are synonymous; both print
6648 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
6651 names of the executable and core dump files
6654 name of the executable file
6656 currently in use by @value{GDBN}, and the files from which symbols were
6657 loaded. The command @code{help targets} lists all possible targets
6658 rather than current ones.
6661 All file-specifying commands allow both absolute and relative file names
6662 as arguments. @value{GDBN} always converts the file name to an absolute path
6663 name and remembers it that way.
6666 @cindex shared libraries
6667 @value{GDBN} supports SunOS, SVR4, and IBM RS/6000 shared libraries.
6668 @value{GDBN} automatically loads symbol definitions from shared libraries
6669 when you use the @code{run} command, or when you examine a core file.
6670 (Before you issue the @code{run} command, @value{GDBN} will not understand
6671 references to a function in a shared library, however---unless you are
6672 debugging a core file).
6673 @c FIXME: next @value{GDBN} release should permit some refs to undef
6674 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared lib
6678 @itemx info sharedlibrary
6679 @kindex info sharedlibrary
6681 Print the names of the shared libraries which are currently loaded.
6683 @item sharedlibrary @var{regex}
6684 @itemx share @var{regex}
6685 @kindex sharedlibrary
6687 This is an obsolescent command; you can use it to explicitly load shared
6688 object library symbols for files matching a Unix regular expression, but
6689 as with files loaded automatically, it will only load shared libraries
6690 required by your program for a core file or after typing @code{run}. If
6691 @var{regex} is omitted all shared libraries required by your program are
6697 @section Errors reading symbol files
6699 While reading a symbol file, @value{GDBN} will occasionally encounter problems,
6700 such as symbol types it does not recognize, or known bugs in compiler
6701 output. By default, @value{GDBN} does not notify you of such problems, since
6702 they are relatively common and primarily of interest to people
6703 debugging compilers. If you are interested in seeing information
6704 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
6705 only one message about each such type of problem, no matter how many
6706 times the problem occurs; or you can ask @value{GDBN} to print more messages,
6707 to see how many times the problems occur, with the @code{set
6708 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
6711 The messages currently printed, and their meanings, include:
6714 @item inner block not inside outer block in @var{symbol}
6716 The symbol information shows where symbol scopes begin and end
6717 (such as at the start of a function or a block of statements). This
6718 error indicates that an inner scope block is not fully contained
6719 in its outer scope blocks.
6721 @value{GDBN} circumvents the problem by treating the inner block as if it had
6722 the same scope as the outer block. In the error message, @var{symbol}
6723 may be shown as ``@code{(don't know)}'' if the outer block is not a
6726 @item block at @var{address} out of order
6728 The symbol information for symbol scope blocks should occur in
6729 order of increasing addresses. This error indicates that it does not
6732 @value{GDBN} does not circumvent this problem, and will have trouble
6733 locating symbols in the source file whose symbols it is reading. (You
6734 can often determine what source file is affected by specifying
6735 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
6738 @item bad block start address patched
6740 The symbol information for a symbol scope block has a start address
6741 smaller than the address of the preceding source line. This is known
6742 to occur in the SunOS 4.1.1 (and earlier) C compiler.
6744 @value{GDBN} circumvents the problem by treating the symbol scope block as
6745 starting on the previous source line.
6747 @item bad string table offset in symbol @var{n}
6750 Symbol number @var{n} contains a pointer into the string table which is
6751 larger than the size of the string table.
6753 @value{GDBN} circumvents the problem by considering the symbol to have the
6754 name @code{foo}, which may cause other problems if many symbols end up
6757 @item unknown symbol type @code{0x@var{nn}}
6759 The symbol information contains new data types that @value{GDBN} does not yet
6760 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
6761 information, in hexadecimal.
6763 @value{GDBN} circumvents the error by ignoring this symbol information. This
6764 will usually allow your program to be debugged, though certain symbols
6765 will not be accessible. If you encounter such a problem and feel like
6766 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
6767 @code{complain}, then go up to the function @code{read_dbx_symtab} and
6768 examine @code{*bufp} to see the symbol.
6770 @item stub type has NULL name
6771 @value{GDBN} could not find the full definition for
6780 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
6782 The symbol information for a C++ member function is missing some
6783 information that recent versions of the compiler should have output
6787 @item info mismatch between compiler and debugger
6789 @value{GDBN} could not parse a type specification output by the compiler.
6793 @chapter Specifying a Debugging Target
6794 @cindex debugging target
6797 A @dfn{target} is the execution environment occupied by your program.
6799 Often, @value{GDBN} runs in the same host environment as your program; in
6800 that case, the debugging target is specified as a side effect when you
6801 use the @code{file} or @code{core} commands. When you need more
6802 flexibility---for example, running @value{GDBN} on a physically separate
6803 host, or controlling a standalone system over a serial port or a
6804 realtime system over a TCP/IP connection---you
6809 can use the @code{target} command to specify one of the target types
6810 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
6814 * Active Targets:: Active targets
6815 * Target Commands:: Commands for managing targets
6816 * Remote:: Remote debugging
6819 @node Active Targets
6820 @section Active targets
6821 @cindex stacking targets
6822 @cindex active targets
6823 @cindex multiple targets
6826 There are three classes of targets: processes, core files, and
6827 executable files. @value{GDBN} can work concurrently on up to three active
6828 targets, one in each class. This allows you to (for example) start a
6829 process and inspect its activity without abandoning your work on a core
6832 For example, if you execute @samp{gdb a.out}, then the executable file
6833 @code{a.out} is the only active target. If you designate a core file as
6834 well---presumably from a prior run that crashed and coredumped---then
6835 @value{GDBN} has two active targets and will use them in tandem, looking
6836 first in the corefile target, then in the executable file, to satisfy
6837 requests for memory addresses. (Typically, these two classes of target
6838 are complementary, since core files contain only a program's
6839 read-write memory---variables and so on---plus machine status, while
6840 executable files contain only the program text and initialized data.)
6843 When you type @code{run}, your executable file becomes an active process
6844 target as well. When a process target is active, all @value{GDBN} commands
6845 requesting memory addresses refer to that target; addresses in an
6849 executable file target are obscured while the process
6853 Use the @code{exec-file} command to select a
6854 new executable target (@pxref{Files, ,Commands to specify
6858 Use the @code{core-file} and @code{exec-file} commands to select a
6859 new core file or executable target (@pxref{Files, ,Commands to specify
6860 files}). To specify as a target a process that is already running, use
6861 the @code{attach} command (@pxref{Attach, ,Debugging an
6862 already-running process}).
6865 @node Target Commands
6866 @section Commands for managing targets
6869 @item target @var{type} @var{parameters}
6870 Connects the @value{GDBN} host environment to a target
6875 machine or process. A target is typically a protocol for talking to
6876 debugging facilities. You use the argument @var{type} to specify the
6877 type or protocol of the target machine.
6879 Further @var{parameters} are interpreted by the target protocol, but
6880 typically include things like device names or host names to connect
6881 with, process numbers, and baud rates.
6884 The @code{target} command will not repeat if you press @key{RET} again
6885 after executing the command.
6889 Displays the names of all targets available. To display targets
6890 currently selected, use either @code{info target} or @code{info files}
6891 (@pxref{Files, ,Commands to specify files}).
6893 @item help target @var{name}
6894 Describe a particular target, including any parameters necessary to
6898 Here are some common targets (available, or not, depending on the GDB
6902 @item target exec @var{program}
6904 An executable file. @samp{target exec @var{program}} is the same as
6905 @samp{exec-file @var{program}}.
6908 @item target core @var{filename}
6910 A core dump file. @samp{target core @var{filename}} is the same as
6911 @samp{core-file @var{filename}}.
6915 @item target remote @var{dev}
6916 @kindex target remote
6917 Remote serial target in GDB-specific protocol. The argument @var{dev}
6918 specifies what serial device to use for the connection (e.g.
6919 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}.
6925 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
6929 @item target udi @var{keyword}
6931 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
6932 argument specifies which 29K board or simulator to use. @xref{UDI29K
6933 Remote,,@value{GDBN} and the UDI protocol for AMD29K}.
6935 @item target amd-eb @var{dev} @var{speed} @var{PROG}
6936 @kindex target amd-eb
6938 Remote PC-resident AMD EB29K board, attached over serial lines.
6939 @var{dev} is the serial device, as for @code{target remote};
6940 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
6941 name of the program to be debugged, as it appears to DOS on the PC.
6942 @xref{EB29K Remote, ,@value{GDBN} with a remote EB29K}.
6948 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
6949 @ifclear H8EXCLUSIVE
6950 @c Unix only, not currently of interest for H8-only manual
6951 Use special commands @code{device} and @code{speed} to control the serial
6952 line and the communications speed used.
6954 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
6958 @item target nindy @var{devicename}
6959 @kindex target nindy
6960 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
6961 the name of the serial device to use for the connection, e.g.
6962 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
6966 @item target st2000 @var{dev} @var{speed}
6967 @kindex target st2000
6968 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
6969 is the name of the device attached to the ST2000 serial line;
6970 @var{speed} is the communication line speed. The arguments are not used
6971 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
6972 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
6976 @item target vxworks @var{machinename}
6977 @kindex target vxworks
6978 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
6979 is the target system's machine name or IP address.
6980 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
6985 Different targets are available on different configurations of @value{GDBN}; your
6986 configuration may have more or fewer targets.
6990 @section Remote debugging
6991 @cindex remote debugging
6993 If you are trying to debug a program running on a machine that cannot run
6994 GDB in the usual way, it is often useful to use remote debugging. For
6995 example, you might use remote debugging on an operating system kernel, or on
6996 a small system which does not have a general purpose operating system
6997 powerful enough to run a full-featured debugger.
6999 Some configurations of GDB have special serial or TCP/IP interfaces
7000 to make this work with particular debugging targets. In addition,
7001 GDB comes with a generic serial protocol (specific to GDB, but
7002 not specific to any particular target system) which you can use if you
7003 write the remote stubs---the code that will run on the remote system to
7004 communicate with GDB.
7006 Other remote targets may be available in your
7007 configuration of GDB; use @code{help targets} to list them.
7010 @c Text on starting up GDB in various specific cases; it goes up front
7011 @c in manuals configured for any of those particular situations, here
7015 * Remote Serial:: @value{GDBN} remote serial protocol
7018 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
7021 * UDI29K Remote:: @value{GDBN} and the UDI protocol for AMD29K
7022 * EB29K Remote:: @value{GDBN} with a remote EB29K
7025 * VxWorks Remote:: @value{GDBN} and VxWorks
7028 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
7031 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
7034 * MIPS Remote:: @value{GDBN} and MIPS boards
7037 * Simulator:: Simulated CPU target
7041 @include remote.texi
7044 @node Controlling GDB
7045 @chapter Controlling @value{GDBN}
7047 You can alter the way @value{GDBN} interacts with you by using
7048 the @code{set} command. For commands controlling how @value{GDBN} displays
7049 data, @pxref{Print Settings, ,Print settings}; other settings are described here.
7053 * Editing:: Command editing
7054 * History:: Command history
7055 * Screen Size:: Screen size
7057 * Messages/Warnings:: Optional warnings and messages
7064 @value{GDBN} indicates its readiness to read a command by printing a string
7065 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
7066 can change the prompt string with the @code{set prompt} command. For
7067 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
7068 the prompt in one of the @value{GDBN} sessions so that you can always tell which
7069 one you are talking to.
7072 @item set prompt @var{newprompt}
7074 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
7077 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
7081 @section Command editing
7083 @cindex command line editing
7085 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
7086 GNU library provides consistent behavior for programs which provide a
7087 command line interface to the user. Advantages are @code{emacs}-style
7088 or @code{vi}-style inline editing of commands, @code{csh}-like history
7089 substitution, and a storage and recall of command history across
7092 You may control the behavior of command line editing in @value{GDBN} with the
7099 @itemx set editing on
7100 Enable command line editing (enabled by default).
7102 @item set editing off
7103 Disable command line editing.
7105 @kindex show editing
7107 Show whether command line editing is enabled.
7111 @section Command history
7113 @value{GDBN} can keep track of the commands you type during your
7114 debugging sessions, so that you can be certain of precisely what
7115 happened. Use these commands to manage the @value{GDBN} command
7119 @cindex history substitution
7120 @cindex history file
7121 @kindex set history filename
7122 @item set history filename @var{fname}
7123 Set the name of the @value{GDBN} command history file to @var{fname}. This is
7124 the file from which @value{GDBN} will read an initial command history
7125 list or to which it will write this list when it exits. This list is
7126 accessed through history expansion or through the history
7127 command editing characters listed below. This file defaults to the
7128 value of the environment variable @code{GDBHISTFILE}, or to
7129 @file{./.gdb_history} if this variable is not set.
7131 @cindex history save
7132 @kindex set history save
7133 @item set history save
7134 @itemx set history save on
7135 Record command history in a file, whose name may be specified with the
7136 @code{set history filename} command. By default, this option is disabled.
7138 @item set history save off
7139 Stop recording command history in a file.
7141 @cindex history size
7142 @kindex set history size
7143 @item set history size @var{size}
7144 Set the number of commands which @value{GDBN} will keep in its history list.
7145 This defaults to the value of the environment variable
7146 @code{HISTSIZE}, or to 256 if this variable is not set.
7149 @cindex history expansion
7150 History expansion assigns special meaning to the character @kbd{!}.
7151 @ifset have-readline-appendices
7152 @xref{Event Designators}.
7155 Since @kbd{!} is also the logical not operator in C, history expansion
7156 is off by default. If you decide to enable history expansion with the
7157 @code{set history expansion on} command, you may sometimes need to
7158 follow @kbd{!} (when it is used as logical not, in an expression) with
7159 a space or a tab to prevent it from being expanded. The readline
7160 history facilities will not attempt substitution on the strings
7161 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
7163 The commands to control history expansion are:
7167 @kindex set history expansion
7168 @item set history expansion on
7169 @itemx set history expansion
7170 Enable history expansion. History expansion is off by default.
7172 @item set history expansion off
7173 Disable history expansion.
7175 The readline code comes with more complete documentation of
7176 editing and history expansion features. Users unfamiliar with @code{emacs}
7177 or @code{vi} may wish to read it.
7178 @ifset have-readline-appendices
7179 @xref{Command Line Editing}.
7183 @kindex show history
7185 @itemx show history filename
7186 @itemx show history save
7187 @itemx show history size
7188 @itemx show history expansion
7189 These commands display the state of the @value{GDBN} history parameters.
7190 @code{show history} by itself displays all four states.
7195 @kindex show commands
7197 Display the last ten commands in the command history.
7199 @item show commands @var{n}
7200 Print ten commands centered on command number @var{n}.
7202 @item show commands +
7203 Print ten commands just after the commands last printed.
7207 @section Screen size
7208 @cindex size of screen
7209 @cindex pauses in output
7211 Certain commands to @value{GDBN} may produce large amounts of
7212 information output to the screen. To help you read all of it,
7213 @value{GDBN} pauses and asks you for input at the end of each page of
7214 output. Type @key{RET} when you want to continue the output, or @kbd{q}
7215 to discard the remaining output. Also, the screen width setting
7216 determines when to wrap lines of output. Depending on what is being
7217 printed, @value{GDBN} tries to break the line at a readable place,
7218 rather than simply letting it overflow onto the following line.
7220 Normally @value{GDBN} knows the size of the screen from the termcap data base
7221 together with the value of the @code{TERM} environment variable and the
7222 @code{stty rows} and @code{stty cols} settings. If this is not correct,
7223 you can override it with the @code{set height} and @code{set
7227 @item set height @var{lpp}
7229 @itemx set width @var{cpl}
7235 These @code{set} commands specify a screen height of @var{lpp} lines and
7236 a screen width of @var{cpl} characters. The associated @code{show}
7237 commands display the current settings.
7239 If you specify a height of zero lines, @value{GDBN} will not pause during output
7240 no matter how long the output is. This is useful if output is to a file
7241 or to an editor buffer.
7243 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
7244 from wrapping its output.
7249 @cindex number representation
7250 @cindex entering numbers
7252 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
7253 the usual conventions: octal numbers begin with @samp{0}, decimal
7254 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
7255 Numbers that begin with none of these are, by default, entered in base
7256 10; likewise, the default display for numbers---when no particular
7257 format is specified---is base 10. You can change the default base for
7258 both input and output with the @code{set radix} command.
7262 @item set radix @var{base}
7263 Set the default base for numeric input and display. Supported choices
7264 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
7265 specified either unambiguously or using the current default radix; for
7275 will set the base to decimal. On the other hand, @samp{set radix 10}
7276 will leave the radix unchanged no matter what it was.
7280 Display the current default base for numeric input and display.
7283 @node Messages/Warnings
7284 @section Optional warnings and messages
7286 By default, @value{GDBN} is silent about its inner workings. If you are running
7287 on a slow machine, you may want to use the @code{set verbose} command.
7288 It will make @value{GDBN} tell you when it does a lengthy internal operation, so
7289 you will not think it has crashed.
7291 Currently, the messages controlled by @code{set verbose} are those
7292 which announce that the symbol table for a source file is being read;
7293 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
7297 @item set verbose on
7298 Enables @value{GDBN} output of certain informational messages.
7300 @item set verbose off
7301 Disables @value{GDBN} output of certain informational messages.
7303 @kindex show verbose
7305 Displays whether @code{set verbose} is on or off.
7308 By default, if @value{GDBN} encounters bugs in the symbol table of an object
7309 file, it is silent; but if you are debugging a compiler, you may find
7310 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
7313 @kindex set complaints
7314 @item set complaints @var{limit}
7315 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
7316 symbols before becoming silent about the problem. Set @var{limit} to
7317 zero to suppress all complaints; set it to a large number to prevent
7318 complaints from being suppressed.
7320 @kindex show complaints
7321 @item show complaints
7322 Displays how many symbol complaints @value{GDBN} is permitted to produce.
7325 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
7326 lot of stupid questions to confirm certain commands. For example, if
7327 you try to run a program which is already running:
7331 The program being debugged has been started already.
7332 Start it from the beginning? (y or n)
7335 If you are willing to unflinchingly face the consequences of your own
7336 commands, you can disable this ``feature'':
7341 @cindex confirmation
7342 @cindex stupid questions
7343 @item set confirm off
7344 Disables confirmation requests.
7346 @item set confirm on
7347 Enables confirmation requests (the default).
7350 @kindex show confirm
7351 Displays state of confirmation requests.
7354 @c FIXME this does not really belong here. But where *does* it belong?
7355 @cindex reloading symbols
7356 Some systems allow individual object files that make up your program to
7357 be replaced without stopping and restarting your program.
7359 For example, in VxWorks you can simply recompile a defective object file
7360 and keep on running.
7362 If you are running on one of these systems, you can allow @value{GDBN} to
7363 reload the symbols for automatically relinked modules:
7366 @kindex set symbol-reloading
7367 @item set symbol-reloading on
7368 Replace symbol definitions for the corresponding source file when an
7369 object file with a particular name is seen again.
7371 @item set symbol-reloading off
7372 Do not replace symbol definitions when re-encountering object files of
7373 the same name. This is the default state; if you are not running on a
7374 system that permits automatically relinking modules, you should leave
7375 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7376 when linking large programs, that may contain several modules (from
7377 different directories or libraries) with the same name.
7379 @item show symbol-reloading
7380 Show the current @code{on} or @code{off} setting.
7384 @chapter Canned Sequences of Commands
7386 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
7387 command lists}), @value{GDBN} provides two ways to store sequences of commands
7388 for execution as a unit: user-defined commands and command files.
7391 * Define:: User-defined commands
7392 * Hooks:: User-defined command hooks
7393 * Command Files:: Command files
7394 * Output:: Commands for controlled output
7398 @section User-defined commands
7400 @cindex user-defined command
7401 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which you
7402 assign a new name as a command. This is done with the @code{define}
7406 @item define @var{commandname}
7408 Define a command named @var{commandname}. If there is already a command
7409 by that name, you are asked to confirm that you want to redefine it.
7411 The definition of the command is made up of other @value{GDBN} command lines,
7412 which are given following the @code{define} command. The end of these
7413 commands is marked by a line containing @code{end}.
7415 @item document @var{commandname}
7417 Give documentation to the user-defined command @var{commandname}. The
7418 command @var{commandname} must already be defined. This command reads
7419 lines of documentation just as @code{define} reads the lines of the
7420 command definition, ending with @code{end}. After the @code{document}
7421 command is finished, @code{help} on command @var{commandname} will print
7422 the documentation you have specified.
7424 You may use the @code{document} command again to change the
7425 documentation of a command. Redefining the command with @code{define}
7426 does not change the documentation.
7428 @item help user-defined
7429 @kindex help user-defined
7430 List all user-defined commands, with the first line of the documentation
7434 @itemx show user @var{commandname}
7436 Display the @value{GDBN} commands used to define @var{commandname} (but not its
7437 documentation). If no @var{commandname} is given, display the
7438 definitions for all user-defined commands.
7441 User-defined commands do not take arguments. When they are executed, the
7442 commands of the definition are not printed. An error in any command
7443 stops execution of the user-defined command.
7445 Commands that would ask for confirmation if used interactively proceed
7446 without asking when used inside a user-defined command. Many @value{GDBN} commands
7447 that normally print messages to say what they are doing omit the messages
7448 when used in a user-defined command.
7451 @section User-defined command hooks
7452 @cindex command files
7454 You may define @emph{hooks}, which are a special kind of user-defined
7455 command. Whenever you run the command @samp{foo}, if the user-defined
7456 command @samp{hook-foo} exists, it is executed (with no arguments)
7457 before that command.
7459 In addition, a pseudo-command, @samp{stop} exists. Defining
7460 (@samp{hook-stop}) makes the associated commands execute every time
7461 execution stops in your program: before breakpoint commands are run,
7462 displays are printed, or the stack frame is printed.
7465 For example, to ignore @code{SIGALRM} signals while
7466 single-stepping, but treat them normally during normal execution,
7471 handle SIGALRM nopass
7478 define hook-continue
7484 You can define a hook for any single-word command in @value{GDBN}, but
7485 not for command aliases; you should define a hook for the basic command
7486 name, e.g. @code{backtrace} rather than @code{bt}.
7487 @c FIXME! So how does Joe User discover whether a command is an alias
7489 If an error occurs during the execution of your hook, execution of
7490 @value{GDBN} commands stops and @value{GDBN} issues a prompt
7491 (before the command that you actually typed had a chance to run).
7493 If you try to define a hook which does not match any known command, you
7494 will get a warning from the @code{define} command.
7497 @section Command files
7499 @cindex command files
7500 A command file for @value{GDBN} is a file of lines that are @value{GDBN} commands. Comments
7501 (lines starting with @kbd{#}) may also be included. An empty line in a
7502 command file does nothing; it does not mean to repeat the last command, as
7503 it would from the terminal.
7506 @cindex @file{@value{GDBINIT}}
7507 When you start @value{GDBN}, it automatically executes commands from its
7508 @dfn{init files}. These are files named @file{@value{GDBINIT}}. @value{GDBN} reads
7509 the init file (if any) in your home directory and then the init file
7510 (if any) in the current working directory. (The init files are not
7511 executed if you use the @samp{-nx} option; @pxref{Mode Options,
7515 @cindex init file name
7516 On some configurations of @value{GDBN}, the init file is known by a
7517 different name (these are typically environments where a specialized
7518 form of GDB may need to coexist with other forms, hence a different name
7519 for the specialized version's init file). These are the environments
7520 with special init file names:
7525 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
7527 @kindex .os68gdbinit
7529 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
7533 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
7537 You can also request the execution of a command file with the
7538 @code{source} command:
7541 @item source @var{filename}
7543 Execute the command file @var{filename}.
7546 The lines in a command file are executed sequentially. They are not
7547 printed as they are executed. An error in any command terminates execution
7548 of the command file.
7550 Commands that would ask for confirmation if used interactively proceed
7551 without asking when used in a command file. Many @value{GDBN} commands that
7552 normally print messages to say what they are doing omit the messages
7553 when called from command files.
7556 @section Commands for controlled output
7558 During the execution of a command file or a user-defined command, normal
7559 @value{GDBN} output is suppressed; the only output that appears is what is
7560 explicitly printed by the commands in the definition. This section
7561 describes three commands useful for generating exactly the output you
7565 @item echo @var{text}
7567 @c I do not consider backslash-space a standard C escape sequence
7568 @c because it is not in ANSI.
7569 Print @var{text}. Nonprinting characters can be included in
7570 @var{text} using C escape sequences, such as @samp{\n} to print a
7571 newline. @strong{No newline will be printed unless you specify one.}
7572 In addition to the standard C escape sequences, a backslash followed
7573 by a space stands for a space. This is useful for displaying a
7574 string with spaces at the beginning or the end, since leading and
7575 trailing spaces are otherwise trimmed from all arguments.
7576 To print @samp{@w{ }and foo =@w{ }}, use the command
7577 @samp{echo \@w{ }and foo = \@w{ }}.
7579 A backslash at the end of @var{text} can be used, as in C, to continue
7580 the command onto subsequent lines. For example,
7583 echo This is some text\n\
7584 which is continued\n\
7585 onto several lines.\n
7588 produces the same output as
7591 echo This is some text\n
7592 echo which is continued\n
7593 echo onto several lines.\n
7596 @item output @var{expression}
7598 Print the value of @var{expression} and nothing but that value: no
7599 newlines, no @samp{$@var{nn} = }. The value is not entered in the
7600 value history either. @xref{Expressions, ,Expressions}, for more information on
7603 @item output/@var{fmt} @var{expression}
7604 Print the value of @var{expression} in format @var{fmt}. You can use
7605 the same formats as for @code{print}. @xref{Output Formats,,Output
7606 formats}, for more information.
7608 @item printf @var{string}, @var{expressions}@dots{}
7610 Print the values of the @var{expressions} under the control of
7611 @var{string}. The @var{expressions} are separated by commas and may be
7612 either numbers or pointers. Their values are printed as specified by
7613 @var{string}, exactly as if your program were to execute the C
7617 printf (@var{string}, @var{expressions}@dots{});
7620 For example, you can print two values in hex like this:
7623 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
7626 The only backslash-escape sequences that you can use in the format
7627 string are the simple ones that consist of backslash followed by a
7633 @chapter Using @value{GDBN} under GNU Emacs
7636 A special interface allows you to use GNU Emacs to view (and
7637 edit) the source files for the program you are debugging with
7640 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
7641 executable file you want to debug as an argument. This command starts
7642 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
7643 created Emacs buffer.
7645 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
7650 All ``terminal'' input and output goes through the Emacs buffer.
7653 This applies both to @value{GDBN} commands and their output, and to the input
7654 and output done by the program you are debugging.
7656 This is useful because it means that you can copy the text of previous
7657 commands and input them again; you can even use parts of the output
7660 All the facilities of Emacs' Shell mode are available for interacting
7661 with your program. In particular, you can send signals the usual
7662 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
7667 @value{GDBN} displays source code through Emacs.
7670 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
7671 source file for that frame and puts an arrow (@samp{=>}) at the
7672 left margin of the current line. Emacs uses a separate buffer for
7673 source display, and splits the screen to show both your @value{GDBN} session
7676 Explicit @value{GDBN} @code{list} or search commands still produce output as
7677 usual, but you probably will have no reason to use them.
7680 @emph{Warning:} If the directory where your program resides is not your
7681 current directory, it can be easy to confuse Emacs about the location of
7682 the source files, in which case the auxiliary display buffer will not
7683 appear to show your source. @value{GDBN} can find programs by searching your
7684 environment's @code{PATH} variable, so the @value{GDBN} input and output
7685 session will proceed normally; but Emacs does not get enough information
7686 back from @value{GDBN} to locate the source files in this situation. To
7687 avoid this problem, either start @value{GDBN} mode from the directory where
7688 your program resides, or specify a full path name when prompted for the
7689 @kbd{M-x gdb} argument.
7691 A similar confusion can result if you use the @value{GDBN} @code{file} command to
7692 switch to debugging a program in some other location, from an existing
7693 @value{GDBN} buffer in Emacs.
7696 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
7697 you need to call @value{GDBN} by a different name (for example, if you keep
7698 several configurations around, with different names) you can set the
7699 Emacs variable @code{gdb-command-name}; for example,
7702 (setq gdb-command-name "mygdb")
7706 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
7707 in your @file{.emacs} file) will make Emacs call the program named
7708 ``@code{mygdb}'' instead.
7710 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
7711 addition to the standard Shell mode commands:
7715 Describe the features of Emacs' @value{GDBN} Mode.
7718 Execute to another source line, like the @value{GDBN} @code{step} command; also
7719 update the display window to show the current file and location.
7722 Execute to next source line in this function, skipping all function
7723 calls, like the @value{GDBN} @code{next} command. Then update the display window
7724 to show the current file and location.
7727 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
7728 display window accordingly.
7731 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
7732 display window accordingly.
7735 Execute until exit from the selected stack frame, like the @value{GDBN}
7736 @code{finish} command.
7739 Continue execution of your program, like the @value{GDBN} @code{continue}
7742 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
7745 Go up the number of frames indicated by the numeric argument
7746 (@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}),
7747 like the @value{GDBN} @code{up} command.
7749 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
7752 Go down the number of frames indicated by the numeric argument, like the
7753 @value{GDBN} @code{down} command.
7755 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
7758 Read the number where the cursor is positioned, and insert it at the end
7759 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
7760 around an address that was displayed earlier, type @kbd{disassemble};
7761 then move the cursor to the address display, and pick up the
7762 argument for @code{disassemble} by typing @kbd{C-x &}.
7764 You can customize this further by defining elements of the list
7765 @code{gdb-print-command}; once it is defined, you can format or
7766 otherwise process numbers picked up by @kbd{C-x &} before they are
7767 inserted. A numeric argument to @kbd{C-x &} will both indicate that you
7768 wish special formatting, and act as an index to pick an element of the
7769 list. If the list element is a string, the number to be inserted is
7770 formatted using the Emacs function @code{format}; otherwise the number
7771 is passed as an argument to the corresponding list element.
7774 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
7775 tells @value{GDBN} to set a breakpoint on the source line point is on.
7777 If you accidentally delete the source-display buffer, an easy way to get
7778 it back is to type the command @code{f} in the @value{GDBN} buffer, to
7779 request a frame display; when you run under Emacs, this will recreate
7780 the source buffer if necessary to show you the context of the current
7783 The source files displayed in Emacs are in ordinary Emacs buffers
7784 which are visiting the source files in the usual way. You can edit
7785 the files with these buffers if you wish; but keep in mind that @value{GDBN}
7786 communicates with Emacs in terms of line numbers. If you add or
7787 delete lines from the text, the line numbers that @value{GDBN} knows will cease
7788 to correspond properly with the code.
7790 @c The following dropped because Epoch is nonstandard. Reactivate
7791 @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990
7793 @kindex emacs epoch environment
7797 Version 18 of Emacs has a built-in window system called the @code{epoch}
7798 environment. Users of this environment can use a new command,
7799 @code{inspect} which performs identically to @code{print} except that
7800 each value is printed in its own window.
7806 @chapter Using @value{GDBN} with Energize
7809 The Energize Programming System is an integrated development environment
7810 that includes a point-and-click interface to many programming tools.
7811 When you use @value{GDBN} in this environment, you can use the standard
7812 Energize graphical interface to drive @value{GDBN}; you can also, if you
7813 choose, type @value{GDBN} commands as usual in a debugging window. Even if
7814 you use the graphical interface, the debugging window (which uses Emacs,
7815 and resembles the standard Emacs interface to @value{GDBN}) displays the
7816 equivalent commands, so that the history of your debugging session is
7819 When Energize starts up a @value{GDBN} session, it uses one of the
7820 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
7821 is the name of the communications protocol used by the Energize system).
7822 This option makes @value{GDBN} run as one of the tools in the Energize Tool
7823 Set: it sends all output to the Energize kernel, and accept input from
7826 See the user manual for the Energize Programming System for
7827 information on how to use the Energize graphical interface and the other
7828 development tools that Energize integrates with @value{GDBN}.
7833 @chapter Reporting Bugs in @value{GDBN}
7834 @cindex bugs in @value{GDBN}
7835 @cindex reporting bugs in @value{GDBN}
7837 Your bug reports play an essential role in making @value{GDBN} reliable.
7839 Reporting a bug may help you by bringing a solution to your problem, or it
7840 may not. But in any case the principal function of a bug report is to help
7841 the entire community by making the next version of @value{GDBN} work better. Bug
7842 reports are your contribution to the maintenance of @value{GDBN}.
7844 In order for a bug report to serve its purpose, you must include the
7845 information that enables us to fix the bug.
7848 * Bug Criteria:: Have you found a bug?
7849 * Bug Reporting:: How to report bugs
7853 @section Have you found a bug?
7854 @cindex bug criteria
7856 If you are not sure whether you have found a bug, here are some guidelines:
7860 @cindex fatal signal
7861 @cindex debugger crash
7862 @cindex crash of debugger
7863 If the debugger gets a fatal signal, for any input whatever, that is a
7864 @value{GDBN} bug. Reliable debuggers never crash.
7867 @cindex error on valid input
7868 If @value{GDBN} produces an error message for valid input, that is a bug.
7871 @cindex invalid input
7872 If @value{GDBN} does not produce an error message for invalid input,
7873 that is a bug. However, you should note that your idea of
7874 ``invalid input'' might be our idea of ``an extension'' or ``support
7875 for traditional practice''.
7878 If you are an experienced user of debugging tools, your suggestions
7879 for improvement of @value{GDBN} are welcome in any case.
7883 @section How to report bugs
7885 @cindex @value{GDBN} bugs, reporting
7887 A number of companies and individuals offer support for GNU products.
7888 If you obtained @value{GDBN} from a support organization, we recommend you
7889 contact that organization first.
7891 You can find contact information for many support companies and
7892 individuals in the file @file{etc/SERVICE} in the GNU Emacs
7895 In any event, we also recommend that you send bug reports for @value{GDBN} to one
7899 bug-gdb@@prep.ai.mit.edu
7900 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
7903 @strong{Do not send bug reports to @samp{info-gdb}, or to
7904 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
7905 receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}.
7907 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
7908 serves as a repeater. The mailing list and the newsgroup carry exactly
7909 the same messages. Often people think of posting bug reports to the
7910 newsgroup instead of mailing them. This appears to work, but it has one
7911 problem which can be crucial: a newsgroup posting often lacks a mail
7912 path back to the sender. Thus, if we need to ask for more information,
7913 we may be unable to reach you. For this reason, it is better to send
7914 bug reports to the mailing list.
7916 As a last resort, send bug reports on paper to:
7920 Free Software Foundation
7925 The fundamental principle of reporting bugs usefully is this:
7926 @strong{report all the facts}. If you are not sure whether to state a
7927 fact or leave it out, state it!
7929 Often people omit facts because they think they know what causes the
7930 problem and assume that some details do not matter. Thus, you might
7931 assume that the name of the variable you use in an example does not matter.
7932 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
7933 stray memory reference which happens to fetch from the location where that
7934 name is stored in memory; perhaps, if the name were different, the contents
7935 of that location would fool the debugger into doing the right thing despite
7936 the bug. Play it safe and give a specific, complete example. That is the
7937 easiest thing for you to do, and the most helpful.
7939 Keep in mind that the purpose of a bug report is to enable us to fix
7940 the bug if it is new to us. It is not as important as what happens if
7941 the bug is already known. Therefore, always write your bug reports on
7942 the assumption that the bug has not been reported previously.
7944 Sometimes people give a few sketchy facts and ask, ``Does this ring a
7945 bell?'' Those bug reports are useless, and we urge everyone to
7946 @emph{refuse to respond to them} except to chide the sender to report
7949 To enable us to fix the bug, you should include all these things:
7953 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
7954 arguments; you can also print it at any time using @code{show version}.
7956 Without this, we will not know whether there is any point in looking for
7957 the bug in the current version of @value{GDBN}.
7960 The type of machine you are using, and the operating system name and
7964 What compiler (and its version) was used to compile @value{GDBN}---e.g.
7965 ``@value{GCC}--2.0''.
7968 What compiler (and its version) was used to compile the program you
7969 are debugging---e.g. ``@value{GCC}--2.0''.
7972 The command arguments you gave the compiler to compile your example and
7973 observe the bug. For example, did you use @samp{-O}? To guarantee
7974 you will not omit something important, list them all. A copy of the
7975 Makefile (or the output from make) is sufficient.
7977 If we were to try to guess the arguments, we would probably guess wrong
7978 and then we might not encounter the bug.
7981 A complete input script, and all necessary source files, that will
7985 A description of what behavior you observe that you believe is
7986 incorrect. For example, ``It gets a fatal signal.''
7988 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
7989 certainly notice it. But if the bug is incorrect output, we might not
7990 notice unless it is glaringly wrong. We are human, after all. You
7991 might as well not give us a chance to make a mistake.
7993 Even if the problem you experience is a fatal signal, you should still
7994 say so explicitly. Suppose something strange is going on, such as,
7995 your copy of @value{GDBN} is out of synch, or you have encountered a
7996 bug in the C library on your system. (This has happened!) Your copy
7997 might crash and ours would not. If you told us to expect a crash,
7998 then when ours fails to crash, we would know that the bug was not
7999 happening for us. If you had not told us to expect a crash, then we
8000 would not be able to draw any conclusion from our observations.
8003 If you wish to suggest changes to the @value{GDBN} source, send us context
8004 diffs. If you even discuss something in the @value{GDBN} source, refer to
8005 it by context, not by line number.
8007 The line numbers in our development sources will not match those in your
8008 sources. Your line numbers would convey no useful information to us.
8011 Here are some things that are not necessary:
8015 A description of the envelope of the bug.
8017 Often people who encounter a bug spend a lot of time investigating
8018 which changes to the input file will make the bug go away and which
8019 changes will not affect it.
8021 This is often time consuming and not very useful, because the way we
8022 will find the bug is by running a single example under the debugger
8023 with breakpoints, not by pure deduction from a series of examples.
8024 We recommend that you save your time for something else.
8026 Of course, if you can find a simpler example to report @emph{instead}
8027 of the original one, that is a convenience for us. Errors in the
8028 output will be easier to spot, running under the debugger will take
8031 However, simplification is not vital; if you do not want to do this,
8032 report the bug anyway and send us the entire test case you used.
8035 A patch for the bug.
8037 A patch for the bug does help us if it is a good one. But do not omit
8038 the necessary information, such as the test case, on the assumption that
8039 a patch is all we need. We might see problems with your patch and decide
8040 to fix the problem another way, or we might not understand it at all.
8042 Sometimes with a program as complicated as @value{GDBN} it is very hard to
8043 construct an example that will make the program follow a certain path
8044 through the code. If you do not send us the example, we will not be able
8045 to construct one, so we will not be able to verify that the bug is fixed.
8047 And if we cannot understand what bug you are trying to fix, or why your
8048 patch should be an improvement, we will not install it. A test case will
8049 help us to understand.
8052 A guess about what the bug is or what it depends on.
8054 Such guesses are usually wrong. Even we cannot guess right about such
8055 things without first using the debugger to find the facts.
8058 @c The readline documentation is distributed with the readline code
8059 @c and consists of the two following files:
8062 @c Use -I with makeinfo to point to the appropriate directory,
8063 @c environment var TEXINPUTS with TeX.
8064 @include rluser.texinfo
8065 @include inc-hist.texi
8068 @node Renamed Commands
8069 @appendix Renamed Commands
8071 The following commands were renamed in GDB 4, in order to make the
8072 command set as a whole more consistent and easier to use and remember:
8075 @kindex delete environment
8076 @kindex info copying
8077 @kindex info convenience
8078 @kindex info directories
8079 @kindex info editing
8080 @kindex info history
8081 @kindex info targets
8083 @kindex info version
8084 @kindex info warranty
8085 @kindex set addressprint
8086 @kindex set arrayprint
8087 @kindex set prettyprint
8088 @kindex set screen-height
8089 @kindex set screen-width
8090 @kindex set unionprint
8091 @kindex set vtblprint
8092 @kindex set demangle
8093 @kindex set asm-demangle
8094 @kindex set sevenbit-strings
8095 @kindex set array-max
8097 @kindex set history write
8098 @kindex show addressprint
8099 @kindex show arrayprint
8100 @kindex show prettyprint
8101 @kindex show screen-height
8102 @kindex show screen-width
8103 @kindex show unionprint
8104 @kindex show vtblprint
8105 @kindex show demangle
8106 @kindex show asm-demangle
8107 @kindex show sevenbit-strings
8108 @kindex show array-max
8109 @kindex show caution
8110 @kindex show history write
8115 @c END TEXI2ROFF-KILL
8117 OLD COMMAND NEW COMMAND
8119 --------------- -------------------------------
8120 @c END TEXI2ROFF-KILL
8121 add-syms add-symbol-file
8122 delete environment unset environment
8123 info convenience show convenience
8124 info copying show copying
8125 info directories show directories
8126 info editing show commands
8127 info history show values
8128 info targets help target
8129 info values show values
8130 info version show version
8131 info warranty show warranty
8132 set/show addressprint set/show print address
8133 set/show array-max set/show print elements
8134 set/show arrayprint set/show print array
8135 set/show asm-demangle set/show print asm-demangle
8136 set/show caution set/show confirm
8137 set/show demangle set/show print demangle
8138 set/show history write set/show history save
8139 set/show prettyprint set/show print pretty
8140 set/show screen-height set/show height
8141 set/show screen-width set/show width
8142 set/show sevenbit-strings set/show print sevenbit-strings
8143 set/show unionprint set/show print union
8144 set/show vtblprint set/show print vtbl
8146 unset [No longer an alias for delete]
8152 \vskip \parskip\vskip \baselineskip
8153 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
8154 {\bf Old Command} &&{\bf New Command}\cr
8155 add-syms &&add-symbol-file\cr
8156 delete environment &&unset environment\cr
8157 info convenience &&show convenience\cr
8158 info copying &&show copying\cr
8159 info directories &&show directories \cr
8160 info editing &&show commands\cr
8161 info history &&show values\cr
8162 info targets &&help target\cr
8163 info values &&show values\cr
8164 info version &&show version\cr
8165 info warranty &&show warranty\cr
8166 set{\rm / }show addressprint &&set{\rm / }show print address\cr
8167 set{\rm / }show array-max &&set{\rm / }show print elements\cr
8168 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
8169 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
8170 set{\rm / }show caution &&set{\rm / }show confirm\cr
8171 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
8172 set{\rm / }show history write &&set{\rm / }show history save\cr
8173 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
8174 set{\rm / }show screen-height &&set{\rm / }show height\cr
8175 set{\rm / }show screen-width &&set{\rm / }show width\cr
8176 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
8177 set{\rm / }show unionprint &&set{\rm / }show print union\cr
8178 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
8180 unset &&\rm(No longer an alias for delete)\cr
8183 @c END TEXI2ROFF-KILL
8186 @ifclear PRECONFIGURED
8187 @node Formatting Documentation
8188 @appendix Formatting Documentation
8190 @cindex GDB reference card
8191 @cindex reference card
8192 The GDB 4 release includes an already-formatted reference card, ready
8193 for printing with PostScript or GhostScript, in the @file{gdb}
8194 subdirectory of the main source directory@footnote{In
8195 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
8196 release.}. If you can use PostScript or GhostScript with your printer,
8197 you can print the reference card immediately with @file{refcard.ps}.
8199 The release also includes the source for the reference card. You
8200 can format it, using @TeX{}, by typing:
8206 The GDB reference card is designed to print in landscape mode on US
8207 ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches
8208 high. You will need to specify this form of printing as an option to
8209 your @sc{dvi} output program.
8211 @cindex documentation
8213 All the documentation for GDB comes as part of the machine-readable
8214 distribution. The documentation is written in Texinfo format, which is
8215 a documentation system that uses a single source file to produce both
8216 on-line information and a printed manual. You can use one of the Info
8217 formatting commands to create the on-line version of the documentation
8218 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
8220 GDB includes an already formatted copy of the on-line Info version of
8221 this manual in the @file{gdb} subdirectory. The main Info file is
8222 @file{gdb-@var{version-number}/gdb/gdb.info}, and it refers to
8223 subordinate files matching @samp{gdb.info*} in the same directory. If
8224 necessary, you can print out these files, or read them with any editor;
8225 but they are easier to read using the @code{info} subsystem in GNU Emacs
8226 or the standalone @code{info} program, available as part of the GNU
8227 Texinfo distribution.
8229 If you want to format these Info files yourself, you need one of the
8230 Info formatting programs, such as @code{texinfo-format-buffer} or
8233 If you have @code{makeinfo} installed, and are in the top level GDB
8234 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
8235 make the Info file by typing:
8242 If you want to typeset and print copies of this manual, you need @TeX{},
8243 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
8244 Texinfo definitions file.
8246 @TeX{} is a typesetting program; it does not print files directly, but
8247 produces output files called @sc{dvi} files. To print a typeset
8248 document, you need a program to print @sc{dvi} files. If your system
8249 has @TeX{} installed, chances are it has such a program. The precise
8250 command to use depends on your system; @kbd{lpr -d} is common; another
8251 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
8252 require a file name without any extension or a @samp{.dvi} extension.
8254 @TeX{} also requires a macro definitions file called
8255 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
8256 written in Texinfo format. On its own, @TeX{} cannot read, much less
8257 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
8258 and is located in the @file{gdb-@var{version-number}/texinfo}
8261 If you have @TeX{} and a @sc{dvi} printer program installed, you can
8262 typeset and print this manual. First switch to the the @file{gdb}
8263 subdirectory of the main source directory (for example, to
8264 @file{gdb-@value{GDBVN}/gdb}) and then type:
8270 @node Installing GDB
8271 @appendix Installing GDB
8272 @cindex configuring GDB
8273 @cindex installation
8275 GDB comes with a @code{configure} script that automates the process
8276 of preparing GDB for installation; you can then use @code{make} to
8277 build the @code{gdb} program.
8279 @c irrelevant in info file; it's as current as the code it lives with.
8280 @footnote{If you have a more recent version of GDB than @value{GDBVN},
8281 look at the @file{README} file in the sources; we may have improved the
8282 installation procedures since publishing this manual.}
8285 The GDB distribution includes all the source code you need for GDB in
8286 a single directory, whose name is usually composed by appending the
8287 version number to @samp{gdb}.
8289 For example, the GDB version @value{GDBVN} distribution is in the
8290 @file{gdb-@value{GDBVN}} directory. That directory contains:
8293 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
8294 script for configuring GDB and all its supporting libraries.
8296 @item gdb-@value{GDBVN}/gdb
8297 the source specific to GDB itself
8299 @item gdb-@value{GDBVN}/bfd
8300 source for the Binary File Descriptor library
8302 @item gdb-@value{GDBVN}/include
8305 @item gdb-@value{GDBVN}/libiberty
8306 source for the @samp{-liberty} free software library
8308 @item gdb-@value{GDBVN}/opcodes
8309 source for the library of opcode tables and disassemblers
8311 @item gdb-@value{GDBVN}/readline
8312 source for the GNU command-line interface
8314 @item gdb-@value{GDBVN}/glob
8315 source for the GNU filename pattern-matching subroutine
8317 @item gdb-@value{GDBVN}/mmalloc
8318 source for the GNU memory-mapped malloc package
8321 The simplest way to configure and build GDB is to run @code{configure}
8322 from the @file{gdb-@var{version-number}} source directory, which in
8323 this example is the @file{gdb-@value{GDBVN}} directory.
8325 First switch to the @file{gdb-@var{version-number}} source directory
8326 if you are not already in it; then run @code{configure}. Pass the
8327 identifier for the platform on which GDB will run as an
8333 cd gdb-@value{GDBVN}
8334 ./configure @var{host}
8339 where @var{host} is an identifier such as @samp{sun4} or
8340 @samp{decstation}, that identifies the platform where GDB will run.
8341 (You can often leave off @var{host}; @code{configure} tries to guess the
8342 correct value by examining your system.)
8344 Running @samp{configure @var{host}} and then running @code{make} builds the
8345 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
8346 libraries, then @code{gdb} itself. The configured source files, and the
8347 binaries, are left in the corresponding source directories.
8349 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
8350 system does not recognize this automatically when you run a different
8351 shell, you may need to run @code{sh} on it explicitly:
8354 sh configure @var{host}
8357 If you run @code{configure} from a directory that contains source
8358 directories for multiple libraries or programs, such as the
8359 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
8360 creates configuration files for every directory level underneath (unless
8361 you tell it not to, with the @samp{--norecursion} option).
8363 You can run the @code{configure} script from any of the
8364 subordinate directories in the GDB distribution if you only want to
8365 configure that subdirectory, but be sure to specify a path to it.
8367 For example, with version @value{GDBVN}, type the following to configure only
8368 the @code{bfd} subdirectory:
8372 cd gdb-@value{GDBVN}/bfd
8373 ../configure @var{host}
8377 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
8378 However, you should make sure that the shell on your path (named by
8379 the @samp{SHELL} environment variable) is publicly readable. Remember
8380 that GDB uses the shell to start your program---some systems refuse to
8381 let GDB debug child processes whose programs are not readable.
8384 * Separate Objdir:: Compiling GDB in another directory
8385 * Config Names:: Specifying names for hosts and targets
8386 * configure Options:: Summary of options for configure
8389 @node Separate Objdir
8390 @section Compiling GDB in another directory
8392 If you want to run GDB versions for several host or target machines,
8393 you need a different @code{gdb} compiled for each combination of
8394 host and target. @code{configure} is designed to make this easy by
8395 allowing you to generate each configuration in a separate subdirectory,
8396 rather than in the source directory. If your @code{make} program
8397 handles the @samp{VPATH} feature (GNU @code{make} does), running
8398 @code{make} in each of these directories builds the @code{gdb}
8399 program specified there.
8401 To build @code{gdb} in a separate directory, run @code{configure}
8402 with the @samp{--srcdir} option to specify where to find the source.
8403 (You also need to specify a path to find @code{configure}
8404 itself from your working directory. If the path to @code{configure}
8405 would be the same as the argument to @samp{--srcdir}, you can leave out
8406 the @samp{--srcdir} option; it will be assumed.)
8408 For example, with version @value{GDBVN}, you can build GDB in a separate
8409 directory for a Sun 4 like this:
8413 cd gdb-@value{GDBVN}
8416 ../gdb-@value{GDBVN}/configure sun4
8421 When @code{configure} builds a configuration using a remote source
8422 directory, it creates a tree for the binaries with the same structure
8423 (and using the same names) as the tree under the source directory. In
8424 the example, you'd find the Sun 4 library @file{libiberty.a} in the
8425 directory @file{gdb-sun4/libiberty}, and GDB itself in
8426 @file{gdb-sun4/gdb}.
8428 One popular reason to build several GDB configurations in separate
8429 directories is to configure GDB for cross-compiling (where GDB
8430 runs on one machine---the host---while debugging programs that run on
8431 another machine---the target). You specify a cross-debugging target by
8432 giving the @samp{--target=@var{target}} option to @code{configure}.
8434 When you run @code{make} to build a program or library, you must run
8435 it in a configured directory---whatever directory you were in when you
8436 called @code{configure} (or one of its subdirectories).
8438 The @code{Makefile} that @code{configure} generates in each source
8439 directory also runs recursively. If you type @code{make} in a source
8440 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
8441 directory configured with @samp{--srcdir=@var{path}/gdb-@value{GDBVN}}), you
8442 will build all the required libraries, and then build GDB.
8444 When you have multiple hosts or targets configured in separate
8445 directories, you can run @code{make} on them in parallel (for example,
8446 if they are NFS-mounted on each of the hosts); they will not interfere
8450 @section Specifying names for hosts and targets
8452 The specifications used for hosts and targets in the @code{configure}
8453 script are based on a three-part naming scheme, but some short predefined
8454 aliases are also supported. The full naming scheme encodes three pieces
8455 of information in the following pattern:
8458 @var{architecture}-@var{vendor}-@var{os}
8461 For example, you can use the alias @code{sun4} as a @var{host} argument,
8462 or as the value for @var{target} in a @code{--target=@var{target}}
8463 option. The equivalent full name is @samp{sparc-sun-sunos4}.
8465 The @code{configure} script accompanying GDB does not provide
8466 any query facility to list all supported host and target names or
8467 aliases. @code{configure} calls the Bourne shell script
8468 @code{config.sub} to map abbreviations to full names; you can read the
8469 script, if you wish, or you can use it to test your guesses on
8470 abbreviations---for example:
8473 % sh config.sub sun4
8474 sparc-sun-sunos4.1.1
8475 % sh config.sub sun3
8477 % sh config.sub decstation
8479 % sh config.sub hp300bsd
8481 % sh config.sub i386v
8483 % sh config.sub i786v
8484 Invalid configuration `i786v': machine `i786v' not recognized
8488 @code{config.sub} is also distributed in the GDB source
8489 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
8491 @node configure Options
8492 @section @code{configure} options
8494 Here is a summary of the @code{configure} options and arguments that
8495 are most often useful for building @value{GDBN}. @code{configure} also has
8496 several other options not listed here. @inforef{What Configure
8497 Does,,configure.info}, for a full explanation of @code{configure}.
8498 @c FIXME: Would this be more, or less, useful as an xref (ref to printed
8499 @c manual in the printed manual, ref to info file only from the info file)?
8502 configure @r{[}--help@r{]}
8503 @r{[}--prefix=@var{dir}@r{]}
8504 @r{[}--srcdir=@var{path}@r{]}
8505 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
8506 @r{[}--target=@var{target}@r{]} @var{host}
8510 You may introduce options with a single @samp{-} rather than
8511 @samp{--} if you prefer; but you may abbreviate option names if you use
8516 Display a quick summary of how to invoke @code{configure}.
8518 @item -prefix=@var{dir}
8519 Configure the source to install programs and files under directory
8522 @item --srcdir=@var{path}
8523 @strong{Warning: using this option requires GNU @code{make}, or another
8524 @code{make} that implements the @code{VPATH} feature.}@*
8525 Use this option to make configurations in directories separate from the
8526 GDB source directories. Among other things, you can use this to
8527 build (or maintain) several configurations simultaneously, in separate
8528 directories. @code{configure} writes configuration specific files in
8529 the current directory, but arranges for them to use the source in the
8530 directory @var{path}. @code{configure} will create directories under
8531 the working directory in parallel to the source directories below
8535 Configure only the directory level where @code{configure} is executed; do not
8536 propagate configuration to subdirectories.
8539 @emph{Remove} files otherwise built during configuration.
8541 @c This does not work (yet if ever). FIXME.
8542 @c @item --parse=@var{lang} @dots{}
8543 @c Configure the GDB expression parser to parse the listed languages.
8544 @c @samp{all} configures GDB for all supported languages. To get a
8545 @c list of all supported languages, omit the argument. Without this
8546 @c option, GDB is configured to parse all supported languages.
8548 @item --target=@var{target}
8549 Configure GDB for cross-debugging programs running on the specified
8550 @var{target}. Without this option, GDB is configured to debug
8551 programs that run on the same machine (@var{host}) as GDB itself.
8553 There is no convenient way to generate a list of all available targets.
8555 @item @var{host} @dots{}
8556 Configure GDB to run on the specified @var{host}.
8558 There is no convenient way to generate a list of all available hosts.
8562 @code{configure} accepts other options, for compatibility with
8563 configuring other GNU tools recursively; but these are the only
8564 options that affect GDB or its supporting libraries.
8573 % I think something like @colophon should be in texinfo. In the
8575 \long\def\colophon{\hbox to0pt{}\vfill
8576 \centerline{The body of this manual is set in}
8577 \centerline{\fontname\tenrm,}
8578 \centerline{with headings in {\bf\fontname\tenbf}}
8579 \centerline{and examples in {\tt\fontname\tentt}.}
8580 \centerline{{\it\fontname\tenit\/},}
8581 \centerline{{\bf\fontname\tenbf}, and}
8582 \centerline{{\sl\fontname\tensl\/}}
8583 \centerline{are used for emphasis.}\vfill}
8585 % Blame: pesch@cygnus.com, 1991.