1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988 1989 1990 1991 1992 1993 1994 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
31 @c !!set GDB manual's edition---not the same as GDB version!
34 @c !!set GDB manual's revision date
35 @set DATE January 1994
37 @c GDB CHANGELOG CONSULTED BETWEEN:
38 @c Fri Oct 11 23:27:06 1991 John Gilmore (gnu at cygnus.com)
39 @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint)
41 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
44 @c This is a dir.info fragment to support semi-automated addition of
45 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
48 * Gdb:: The GNU debugger.
55 This file documents the GNU debugger @value{GDBN}.
58 This is Edition @value{EDITION}, @value{DATE},
59 of @cite{Debugging with @value{GDBN}: the GNU Source-Level Debugger}
60 for GDB Version @value{GDBVN}.
62 Copyright (C) 1988, '89, '90, '91, '92, '93 Free Software Foundation, Inc.
64 Permission is granted to make and distribute verbatim copies of
65 this manual provided the copyright notice and this permission notice
66 are preserved on all copies.
69 Permission is granted to process this file through TeX and print the
70 results, provided the printed document carries copying permission
71 notice identical to this one except for the removal of this paragraph
72 (this paragraph not being relevant to the printed manual).
75 Permission is granted to copy and distribute modified versions of this
76 manual under the conditions for verbatim copying, provided also that the
77 entire resulting derived work is distributed under the terms of a
78 permission notice identical to this one.
80 Permission is granted to copy and distribute translations of this manual
81 into another language, under the above conditions for modified versions.
85 @title Debugging with @value{GDBN}
86 @subtitle The GNU Source-Level Debugger
88 @subtitle (@value{TARGET})
91 @subtitle Edition @value{EDITION}, for @value{GDBN} version @value{GDBVN}
92 @subtitle @value{DATE}
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 This is Edition @value{EDITION}, @value{DATE}, for GDB Version @value{GDBVN}.
137 * Summary:: Summary of @value{GDBN}
139 * New Features:: New features since GDB version 3.5
142 * Sample Session:: A sample @value{GDBN} session
145 * Invocation:: Getting in and out of @value{GDBN}
146 * Commands:: @value{GDBN} commands
147 * Running:: Running programs under @value{GDBN}
148 * Stopping:: Stopping and continuing
149 * Stack:: Examining the stack
150 * Source:: Examining source files
151 * Data:: Examining data
153 * Languages:: Using @value{GDBN} with different languages
156 * C:: C language support
158 @c remnant makeinfo bug, blank line needed after two end-ifs?
160 * Symbols:: Examining the symbol table
161 * Altering:: Altering execution
162 * GDB Files:: @value{GDBN} files
163 * Targets:: Specifying a debugging target
164 * Controlling GDB:: Controlling @value{GDBN}
165 * Sequences:: Canned sequences of commands
167 * Emacs:: Using @value{GDBN} under GNU Emacs
170 * GDB Bugs:: Reporting bugs in @value{GDBN}
171 * Command Line Editing:: Facilities of the readline library
172 * Using History Interactively::
176 @ifclear PRECONFIGURED
177 * Formatting Documentation:: How to format and print GDB documentation
178 * Installing GDB:: Installing GDB
186 @unnumbered Summary of @value{GDBN}
188 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
189 going on ``inside'' another program while it executes---or what another
190 program was doing at the moment it crashed.
192 @value{GDBN} can do four main kinds of things (plus other things in support of
193 these) to help you catch bugs in the act:
197 Start your program, specifying anything that might affect its behavior.
200 Make your program stop on specified conditions.
203 Examine what has happened, when your program has stopped.
206 Change things in your program, so you can experiment with correcting the
207 effects of one bug and go on to learn about another.
211 You can use @value{GDBN} to debug programs written in C or C++.
212 @c "MOD2" used as a "miscellaneous languages" flag here.
213 @c This is acceptable while there is no real doc for Chill and Pascal.
215 For more information, see @ref{Support,,Supported languages}.
218 For more information, see @ref{C,,C and C++}.
220 Support for Modula-2 and Chill is partial. For information on Modula-2,
221 see @ref{Modula-2,,Modula-2}. There is no further documentation on Chill yet.
223 Debugging Pascal programs which use sets, subranges, file variables, or nested
224 functions does not currently work. @value{GDBN} does not support
225 entering expressions, printing values, or similar features using Pascal syntax.
229 @value{GDBN} can be used to debug programs written in Fortran, although
230 it does not yet support entering expressions, printing values, or
231 similar features using Fortran syntax. It may be necessary to refer to
232 some variables with a trailing underscore.
237 * Free Software:: Freely redistributable software
238 * Contributors:: Contributors to GDB
242 @unnumberedsec Free software
244 @value{GDBN} is @dfn{free software}, protected by the GNU General Public License
245 (GPL). The GPL gives you the freedom to copy or adapt a licensed
246 program---but every person getting a copy also gets with it the
247 freedom to modify that copy (which means that they must get access to
248 the source code), and the freedom to distribute further copies.
249 Typical software companies use copyrights to limit your freedoms; the
250 Free Software Foundation uses the GPL to preserve these freedoms.
252 Fundamentally, the General Public License is a license which says that
253 you have these freedoms and that you cannot take these freedoms away
257 @unnumberedsec Contributors to GDB
259 Richard Stallman was the original author of GDB, and of many other GNU
260 programs. Many others have contributed to its development. This
261 section attempts to credit major contributors. One of the virtues of
262 free software is that everyone is free to contribute to it; with
263 regret, we cannot actually acknowledge everyone here. The file
264 @file{ChangeLog} in the GDB distribution approximates a blow-by-blow
267 Changes much prior to version 2.0 are lost in the mists of time.
270 @emph{Plea:} Additions to this section are particularly welcome. If you
271 or your friends (or enemies, to be evenhanded) have been unfairly
272 omitted from this list, we would like to add your names!
275 So that they may not regard their long labor as thankless, we
276 particularly thank those who shepherded GDB through major releases: Fred
277 Fish (releases 4.12, 4.11, 4.10, 4.9), Stu Grossman and John Gilmore (releases
278 4.8, 4.7, 4.6, 4.5, 4.4), John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and
279 3.9); Jim Kingdon (releases 3.5, 3.4, 3.3); and Randy Smith (releases
280 3.2, 3.1, 3.0). As major maintainer of GDB for some period, each
281 contributed significantly to the structure, stability, and capabilities
282 of the entire debugger.
284 Richard Stallman, assisted at various times by Peter TerMaat, Chris
285 Hanson, and Richard Mlynarik, handled releases through 2.8.
288 Michael Tiemann is the author of most of the GNU C++ support in GDB,
289 with significant additional contributions from Per Bothner. James
290 Clark wrote the GNU C++ demangler. Early work on C++ was by Peter
291 TerMaat (who also did much general update work leading to release 3.0).
294 GDB 4 uses the BFD subroutine library to examine multiple
295 object-file formats; BFD was a joint project of David V.
296 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
298 David Johnson wrote the original COFF support; Pace Willison did
299 the original support for encapsulated COFF.
301 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
302 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
303 support. Jean-Daniel Fekete contributed Sun 386i support. Chris
304 Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki
305 Hasei contributed Sony/News OS 3 support. David Johnson contributed
306 Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support.
307 Keith Packard contributed NS32K support. Doug Rabson contributed
308 Acorn Risc Machine support. Chris Smith contributed Convex support
309 (and Fortran debugging). Jonathan Stone contributed Pyramid support.
310 Michael Tiemann contributed SPARC support. Tim Tucker contributed
311 support for the Gould NP1 and Gould Powernode. Pace Willison
312 contributed Intel 386 support. Jay Vosburgh contributed Symmetry
315 Rich Schaefer and Peter Schauer helped with support of SunOS shared
318 Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
319 several machine instruction sets.
321 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
322 develop remote debugging. Intel Corporation and Wind River Systems
323 contributed remote debugging modules for their products.
325 Brian Fox is the author of the readline libraries providing
326 command-line editing and command history.
328 Andrew Beers of SUNY Buffalo wrote the language-switching code,
330 the Modula-2 support,
332 and contributed the Languages chapter of this manual.
334 Fred Fish wrote most of the support for Unix System Vr4.
336 He also enhanced the command-completion support to cover C++ overloaded
340 Hitachi America, Ltd. sponsored the support for Hitachi microprocessors.
344 @unnumbered New Features since GDB Version 3.5
348 Using the new command @code{target}, you can select at runtime whether
349 you are debugging local files, local processes, standalone systems over
350 a serial port, or realtime systems over a TCP/IP connection. The
351 command @code{load} can download programs into a remote system. Serial
352 stubs are available for Motorola 680x0, Intel 80386, and Sparc remote
353 systems; GDB also supports debugging realtime processes running under
354 VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a
355 debugger stub on the target system. Internally, GDB now uses a function
356 vector to mediate access to different targets; if you need to add your
357 own support for a remote protocol, this makes it much easier.
360 GDB now sports watchpoints as well as breakpoints. You can use a
361 watchpoint to stop execution whenever the value of an expression
362 changes, without having to predict a particular place in your program
363 where this may happen.
366 Commands that issue wide output now insert newlines at places designed
367 to make the output more readable.
369 @item Object Code Formats
370 GDB uses a new library called the Binary File Descriptor (BFD) Library
371 to permit it to switch dynamically, without reconfiguration or
372 recompilation, between different object-file formats. Formats currently
373 supported are COFF, ELF, a.out, Intel 960 b.out, MIPS ECOFF, HPPA SOM
374 (with stabs debugging), and S-records; files may be read as .o files,
375 archive libraries, or core dumps. BFD is available as a subroutine
376 library so that other programs may take advantage of it, and the other
377 GNU binary utilities are being converted to use it.
379 @item Configuration and Ports
380 Compile-time configuration (to select a particular architecture and
381 operating system) is much easier. The script @code{configure} now
382 allows you to configure GDB as either a native debugger or a
383 cross-debugger. @xref{Installing GDB}, for details on how to
387 The user interface to the GDB control variables is simpler,
388 and is consolidated in two commands, @code{set} and @code{show}. Output
389 lines are now broken at readable places, rather than overflowing onto
390 the next line. You can suppress output of machine-level addresses,
391 displaying only source language information.
394 GDB now supports C++ multiple inheritance (if used with a GCC
395 version 2 compiler), and also has limited support for C++ exception
396 handling, with the commands @code{catch} and @code{info catch}: GDB
397 can break when an exception is raised, before the stack is peeled back
398 to the exception handler's context.
402 GDB now has preliminary support for the GNU Modula-2 compiler, currently
403 under development at the State University of New York at Buffalo.
404 Coordinated development of both GDB and the GNU Modula-2 compiler will
405 continue. Other Modula-2 compilers are currently not supported, and
406 attempting to debug programs compiled with them will likely result in an
407 error as the symbol table of the executable is read in.
410 @item Command Rationalization
411 Many GDB commands have been renamed to make them easier to remember
412 and use. In particular, the subcommands of @code{info} and
413 @code{show}/@code{set} are grouped to make the former refer to the state
414 of your program, and the latter refer to the state of GDB itself.
415 @xref{Renamed Commands}, for details on what commands were renamed.
417 @item Shared Libraries
418 GDB 4 can debug programs and core files that use SunOS, SVR4, or IBM RS/6000
422 On some systems, GDB 4 has facilities to debug multi-thread programs.
425 GDB 4 has a reference card. @xref{Formatting Documentation,,Formatting
426 the Documentation}, for instructions about how to print it.
432 @chapter A Sample @value{GDBN} Session
434 You can use this manual at your leisure to read all about @value{GDBN}.
435 However, a handful of commands are enough to get started using the
436 debugger. This chapter illustrates those commands.
439 In this sample session, we emphasize user input like this: @b{input},
440 to make it easier to pick out from the surrounding output.
443 @c FIXME: this example may not be appropriate for some configs, where
444 @c FIXME...primary interest is in remote use.
446 One of the preliminary versions of GNU @code{m4} (a generic macro
447 processor) exhibits the following bug: sometimes, when we change its
448 quote strings from the default, the commands used to capture one macro
449 definition within another stop working. In the following short @code{m4}
450 session, we define a macro @code{foo} which expands to @code{0000}; we
451 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
452 same thing. However, when we change the open quote string to
453 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
454 procedure fails to define a new synonym @code{baz}:
463 @b{define(bar,defn(`foo'))}
467 @b{changequote(<QUOTE>,<UNQUOTE>)}
469 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
472 m4: End of input: 0: fatal error: EOF in string
476 Let us use @value{GDBN} to try to see what is going on.
479 $ @b{@value{GDBP} m4}
480 @c FIXME: this falsifies the exact text played out, to permit smallbook
481 @c FIXME... format to come out better.
482 GDB is free software and you are welcome to distribute copies
483 of it under certain conditions; type "show copying" to see
485 There is absolutely no warranty for GDB; type "show warranty"
487 GDB @value{GDBVN}, Copyright 1993 Free Software Foundation, Inc...
492 @value{GDBN} reads only enough symbol data to know where to find the
493 rest when needed; as a result, the first prompt comes up very quickly.
494 We now tell @value{GDBN} to use a narrower display width than usual, so
495 that examples fit in this manual.
498 (@value{GDBP}) @b{set width 70}
502 We need to see how the @code{m4} built-in @code{changequote} works.
503 Having looked at the source, we know the relevant subroutine is
504 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
505 @code{break} command.
508 (@value{GDBP}) @b{break m4_changequote}
509 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
513 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
514 control; as long as control does not reach the @code{m4_changequote}
515 subroutine, the program runs as usual:
518 (@value{GDBP}) @b{run}
519 Starting program: /work/Editorial/gdb/gnu/m4/m4
527 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
528 suspends execution of @code{m4}, displaying information about the
529 context where it stops.
532 @b{changequote(<QUOTE>,<UNQUOTE>)}
534 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
536 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
540 Now we use the command @code{n} (@code{next}) to advance execution to
541 the next line of the current function.
545 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
550 @code{set_quotes} looks like a promising subroutine. We can go into it
551 by using the command @code{s} (@code{step}) instead of @code{next}.
552 @code{step} goes to the next line to be executed in @emph{any}
553 subroutine, so it steps into @code{set_quotes}.
557 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
559 530 if (lquote != def_lquote)
563 The display that shows the subroutine where @code{m4} is now
564 suspended (and its arguments) is called a stack frame display. It
565 shows a summary of the stack. We can use the @code{backtrace}
566 command (which can also be spelled @code{bt}), to see where we are
567 in the stack as a whole: the @code{backtrace} command displays a
568 stack frame for each active subroutine.
571 (@value{GDBP}) @b{bt}
572 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
574 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
576 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
577 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
579 #4 0x79dc in expand_input () at macro.c:40
580 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
584 We step through a few more lines to see what happens. The first two
585 times, we can use @samp{s}; the next two times we use @code{n} to avoid
586 falling into the @code{xstrdup} subroutine.
590 0x3b5c 532 if (rquote != def_rquote)
592 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
593 def_lquote : xstrdup(lq);
595 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
598 538 len_lquote = strlen(rquote);
602 The last line displayed looks a little odd; we can examine the variables
603 @code{lquote} and @code{rquote} to see if they are in fact the new left
604 and right quotes we specified. We use the command @code{p}
605 (@code{print}) to see their values.
608 (@value{GDBP}) @b{p lquote}
609 $1 = 0x35d40 "<QUOTE>"
610 (@value{GDBP}) @b{p rquote}
611 $2 = 0x35d50 "<UNQUOTE>"
615 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
616 To look at some context, we can display ten lines of source
617 surrounding the current line with the @code{l} (@code{list}) command.
623 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
625 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
628 538 len_lquote = strlen(rquote);
629 539 len_rquote = strlen(lquote);
636 Let us step past the two lines that set @code{len_lquote} and
637 @code{len_rquote}, and then examine the values of those variables.
641 539 len_rquote = strlen(lquote);
644 (@value{GDBP}) @b{p len_lquote}
646 (@value{GDBP}) @b{p len_rquote}
651 That certainly looks wrong, assuming @code{len_lquote} and
652 @code{len_rquote} are meant to be the lengths of @code{lquote} and
653 @code{rquote} respectively. We can set them to better values using
654 the @code{p} command, since it can print the value of
655 any expression---and that expression can include subroutine calls and
659 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
661 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
666 Is that enough to fix the problem of using the new quotes with the
667 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
668 executing with the @code{c} (@code{continue}) command, and then try the
669 example that caused trouble initially:
675 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
682 Success! The new quotes now work just as well as the default ones. The
683 problem seems to have been just the two typos defining the wrong
684 lengths. We allow @code{m4} exit by giving it an EOF as input:
688 Program exited normally.
692 The message @samp{Program exited normally.} is from @value{GDBN}; it
693 indicates @code{m4} has finished executing. We can end our @value{GDBN}
694 session with the @value{GDBN} @code{quit} command.
697 (@value{GDBP}) @b{quit}
702 @chapter Getting In and Out of @value{GDBN}
704 This chapter discusses how to start @value{GDBN}, and how to get out of it.
705 (The essentials: type @samp{@value{GDBP}} to start GDB, and type @kbd{quit}
706 or @kbd{C-d} to exit.)
709 * Invoking GDB:: How to start @value{GDBN}
710 * Quitting GDB:: How to quit @value{GDBN}
711 * Shell Commands:: How to use shell commands inside @value{GDBN}
715 @section Invoking @value{GDBN}
718 For details on starting up @value{GDBP} as a
719 remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi
720 Remote,,@value{GDBN} and Hitachi Microprocessors}.
723 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
724 @value{GDBN} reads commands from the terminal until you tell it to exit.
726 You can also run @code{@value{GDBP}} with a variety of arguments and options,
727 to specify more of your debugging environment at the outset.
730 The command-line options described here are designed
731 to cover a variety of situations; in some environments, some of these
732 options may effectively be unavailable.
735 The most usual way to start @value{GDBN} is with one argument,
736 specifying an executable program:
739 @value{GDBP} @var{program}
744 You can also start with both an executable program and a core file
748 @value{GDBP} @var{program} @var{core}
751 You can, instead, specify a process ID as a second argument, if you want
752 to debug a running process:
755 @value{GDBP} @var{program} 1234
759 would attach @value{GDBN} to process @code{1234} (unless you also have a file
760 named @file{1234}; @value{GDBN} does check for a core file first).
762 Taking advantage of the second command-line argument requires a fairly
763 complete operating system; when you use @value{GDBN} as a remote debugger
764 attached to a bare board, there may not be any notion of ``process'',
765 and there is often no way to get a core dump.
769 You can further control how @value{GDBN} starts up by using command-line
770 options. @value{GDBN} itself can remind you of the options available.
780 to display all available options and briefly describe their use
781 (@samp{@value{GDBP} -h} is a shorter equivalent).
783 All options and command line arguments you give are processed
784 in sequential order. The order makes a difference when the
785 @samp{-x} option is used.
791 * Remote Serial:: @value{GDBN} remote serial protocol
794 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
797 * UDI29K Remote:: The UDI protocol for AMD29K
798 * EB29K Remote:: The EBMON protocol for AMD29K
801 * VxWorks Remote:: @value{GDBN} and VxWorks
804 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
807 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
810 * MIPS Remote:: @value{GDBN} and MIPS boards
813 * Simulator:: Simulated CPU target
816 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
818 * File Options:: Choosing files
819 * Mode Options:: Choosing modes
827 @subsection Choosing files
830 When @value{GDBN} starts, it reads any arguments other than options as
831 specifying an executable file and core file (or process ID). This is
832 the same as if the arguments were specified by the @samp{-se} and
833 @samp{-c} options respectively. (@value{GDBN} reads the first argument
834 that does not have an associated option flag as equivalent to the
835 @samp{-se} option followed by that argument; and the second argument
836 that does not have an associated option flag, if any, as equivalent to
837 the @samp{-c} option followed by that argument.)
840 When @value{GDBN} starts, it reads any argument other than options as
841 specifying an executable file. This is the same as if the argument was
842 specified by the @samp{-se} option.
845 Many options have both long and short forms; both are shown in the
846 following list. @value{GDBN} also recognizes the long forms if you truncate
847 them, so long as enough of the option is present to be unambiguous.
848 (If you prefer, you can flag option arguments with @samp{--} rather
849 than @samp{-}, though we illustrate the more usual convention.)
852 @item -symbols @var{file}
854 Read symbol table from file @var{file}.
856 @item -exec @var{file}
858 Use file @var{file} as the executable file to execute when
863 appropriate, and for examining pure data in conjunction with a core
868 Read symbol table from file @var{file} and use it as the executable
872 @item -core @var{file}
874 Use file @var{file} as a core dump to examine.
876 @item -c @var{number}
877 Connect to process ID @var{number}, as with the @code{attach} command
878 (unless there is a file in core-dump format named @var{number}, in which
879 case @samp{-c} specifies that file as a core dump to read).
882 @item -command @var{file}
884 Execute @value{GDBN} commands from file @var{file}. @xref{Command
885 Files,, Command files}.
887 @item -directory @var{directory}
888 @itemx -d @var{directory}
889 Add @var{directory} to the path to search for source files.
894 @emph{Warning: this option depends on operating system facilities that are not
895 supported on all systems.}@*
896 If memory-mapped files are available on your system through the @code{mmap}
897 system call, you can use this option
898 to have @value{GDBN} write the symbols from your
899 program into a reusable file in the current directory. If the program you are debugging is
900 called @file{/tmp/fred}, the mapped symbol file is @file{./fred.syms}.
901 Future @value{GDBN} debugging sessions notice the presence of this file,
902 and can quickly map in symbol information from it, rather than reading
903 the symbol table from the executable program.
905 @c FIXME! Really host, not target?
906 The @file{.syms} file is specific to the host machine where @value{GDBN}
907 is run. It holds an exact image of the internal @value{GDBN} symbol
908 table. It cannot be shared across multiple host platforms.
913 Read each symbol file's entire symbol table immediately, rather than
914 the default, which is to read it incrementally as it is needed.
915 This makes startup slower, but makes future operations faster.
919 The @code{-mapped} and @code{-readnow} options are typically combined in
920 order to build a @file{.syms} file that contains complete symbol
921 information. (@xref{Files,,Commands to specify files}, for information
922 on @file{.syms} files.) A simple GDB invocation to do nothing but build
923 a @file{.syms} file for future use is:
926 gdb -batch -nx -mapped -readnow programname
931 @subsection Choosing modes
933 You can run @value{GDBN} in various alternative modes---for example, in
934 batch mode or quiet mode.
939 Do not execute commands from any initialization files (normally called
940 @file{@value{GDBINIT}}). Normally, the commands in these files are
941 executed after all the command options and arguments have been
942 processed. @xref{Command Files,,Command files}.
946 ``Quiet''. Do not print the introductory and copyright messages. These
947 messages are also suppressed in batch mode.
950 Run in batch mode. Exit with status @code{0} after processing all the
951 command files specified with @samp{-x} (and all commands from
952 initialization files, if not inhibited with @samp{-n}). Exit with
953 nonzero status if an error occurs in executing the @value{GDBN} commands
954 in the command files.
956 Batch mode may be useful for running @value{GDBN} as a filter, for example to
957 download and run a program on another computer; in order to make this
958 more useful, the message
961 Program exited normally.
965 (which is ordinarily issued whenever a program running under @value{GDBN} control
966 terminates) is not issued when running in batch mode.
968 @item -cd @var{directory}
969 Run @value{GDBN} using @var{directory} as its working directory,
970 instead of the current directory.
973 @item -context @var{authentication}
974 When the Energize programming system starts up @value{GDBN}, it uses this
975 option to trigger an alternate mode of interaction.
976 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
977 as a client in the Energize environment. Avoid this option when you run
978 @value{GDBN} directly from the command line. See @ref{Energize,,Using
979 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
985 Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
986 to output the full file name and line number in a standard,
987 recognizable fashion each time a stack frame is displayed (which
988 includes each time your program stops). This recognizable format looks
989 like two @samp{\032} characters, followed by the file name, line number
990 and character position separated by colons, and a newline. The
991 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
992 a signal to display the source code for the frame.
997 Set the line speed (baud rate or bits per second) of any serial
998 interface used by @value{GDBN} for remote debugging.
1000 @item -tty @var{device}
1001 Run using @var{device} for your program's standard input and output.
1002 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1007 @section Quitting @value{GDBN}
1008 @cindex exiting @value{GDBN}
1009 @cindex leaving @value{GDBN}
1015 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or type
1016 an end-of-file character (usually @kbd{C-d}).
1020 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1021 terminates the action of any @value{GDBN} command that is in progress and
1022 returns to @value{GDBN} command level. It is safe to type the interrupt
1023 character at any time because @value{GDBN} does not allow it to take effect
1024 until a time when it is safe.
1027 If you have been using @value{GDBN} to control an attached process or
1028 device, you can release it with the @code{detach} command
1029 (@pxref{Attach, ,Debugging an already-running process}).
1032 @node Shell Commands
1033 @section Shell commands
1035 If you need to execute occasional shell commands during your
1036 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1037 just use the @code{shell} command.
1040 @item shell @var{command string}
1042 @cindex shell escape
1043 Invoke a the standard shell to execute @var{command string}.
1045 If it exists, the environment variable @code{SHELL} determines which
1046 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
1050 The utility @code{make} is often needed in development environments.
1051 You do not have to use the @code{shell} command for this purpose in
1055 @item make @var{make-args}
1057 @cindex calling make
1058 Execute the @code{make} program with the specified
1059 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1063 @chapter @value{GDBN} Commands
1065 You can abbreviate a @value{GDBN} command to the first few letters of the command
1066 name, if that abbreviation is unambiguous; and you can repeat certain
1067 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1068 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1069 show you the alternatives available, if there is more than one possibility).
1072 * Command Syntax:: How to give commands to @value{GDBN}
1073 * Completion:: Command completion
1074 * Help:: How to ask @value{GDBN} for help
1077 @node Command Syntax
1078 @section Command syntax
1080 A @value{GDBN} command is a single line of input. There is no limit on
1081 how long it can be. It starts with a command name, which is followed by
1082 arguments whose meaning depends on the command name. For example, the
1083 command @code{step} accepts an argument which is the number of times to
1084 step, as in @samp{step 5}. You can also use the @code{step} command
1085 with no arguments. Some command names do not allow any arguments.
1087 @cindex abbreviation
1088 @value{GDBN} command names may always be truncated if that abbreviation is
1089 unambiguous. Other possible command abbreviations are listed in the
1090 documentation for individual commands. In some cases, even ambiguous
1091 abbreviations are allowed; for example, @code{s} is specially defined as
1092 equivalent to @code{step} even though there are other commands whose
1093 names start with @code{s}. You can test abbreviations by using them as
1094 arguments to the @code{help} command.
1096 @cindex repeating commands
1098 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1099 repeat the previous command. Certain commands (for example, @code{run})
1100 will not repeat this way; these are commands whose unintentional
1101 repetition might cause trouble and which you are unlikely to want to
1104 The @code{list} and @code{x} commands, when you repeat them with
1105 @key{RET}, construct new arguments rather than repeating
1106 exactly as typed. This permits easy scanning of source or memory.
1108 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1109 output, in a way similar to the common utility @code{more}
1110 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1111 @key{RET} too many in this situation, @value{GDBN} disables command
1112 repetition after any command that generates this sort of display.
1116 Any text from a @kbd{#} to the end of the line is a comment; it does
1117 nothing. This is useful mainly in command files (@pxref{Command
1118 Files,,Command files}).
1121 @section Command completion
1124 @cindex word completion
1125 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1126 only one possibility; it can also show you what the valid possibilities
1127 are for the next word in a command, at any time. This works for @value{GDBN}
1128 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1130 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1131 of a word. If there is only one possibility, @value{GDBN} fills in the
1132 word, and waits for you to finish the command (or press @key{RET} to
1133 enter it). For example, if you type
1135 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1136 @c complete accuracy in these examples; space introduced for clarity.
1137 @c If texinfo enhancements make it unnecessary, it would be nice to
1138 @c replace " @key" by "@key" in the following...
1140 (@value{GDBP}) info bre @key{TAB}
1144 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1145 the only @code{info} subcommand beginning with @samp{bre}:
1148 (@value{GDBP}) info breakpoints
1152 You can either press @key{RET} at this point, to run the @code{info
1153 breakpoints} command, or backspace and enter something else, if
1154 @samp{breakpoints} does not look like the command you expected. (If you
1155 were sure you wanted @code{info breakpoints} in the first place, you
1156 might as well just type @key{RET} immediately after @samp{info bre},
1157 to exploit command abbreviations rather than command completion).
1159 If there is more than one possibility for the next word when you press
1160 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1161 characters and try again, or just press @key{TAB} a second time;
1162 @value{GDBN} displays all the possible completions for that word. For
1163 example, you might want to set a breakpoint on a subroutine whose name
1164 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1165 just sounds the bell. Typing @key{TAB} again displays all the
1166 function names in your program that begin with those characters, for
1170 (@value{GDBP}) b make_ @key{TAB}
1171 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1172 make_a_section_from_file make_environ
1173 make_abs_section make_function_type
1174 make_blockvector make_pointer_type
1175 make_cleanup make_reference_type
1176 make_command make_symbol_completion_list
1177 (@value{GDBP}) b make_
1181 After displaying the available possibilities, @value{GDBN} copies your
1182 partial input (@samp{b make_} in the example) so you can finish the
1185 If you just want to see the list of alternatives in the first place, you
1186 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1187 means @kbd{@key{META} ?}. You can type this
1189 either by holding down a
1190 key designated as the @key{META} shift on your keyboard (if there is
1191 one) while typing @kbd{?}, or
1193 as @key{ESC} followed by @kbd{?}.
1195 @cindex quotes in commands
1196 @cindex completion of quoted strings
1197 Sometimes the string you need, while logically a ``word'', may contain
1198 parentheses or other characters that @value{GDBN} normally excludes from its
1199 notion of a word. To permit word completion to work in this situation,
1200 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1203 The most likely situation where you might need this is in typing the
1204 name of a C++ function. This is because C++ allows function overloading
1205 (multiple definitions of the same function, distinguished by argument
1206 type). For example, when you want to set a breakpoint you may need to
1207 distinguish whether you mean the version of @code{name} that takes an
1208 @code{int} parameter, @code{name(int)}, or the version that takes a
1209 @code{float} parameter, @code{name(float)}. To use the word-completion
1210 facilities in this situation, type a single quote @code{'} at the
1211 beginning of the function name. This alerts @value{GDBN} that it may need to
1212 consider more information than usual when you press @key{TAB} or
1213 @kbd{M-?} to request word completion:
1216 (@value{GDBP}) b 'bubble( @key{M-?}
1217 bubble(double,double) bubble(int,int)
1218 (@value{GDBP}) b 'bubble(
1221 In some cases, @value{GDBN} can tell that completing a name requires using
1222 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1223 completing as much as it can) if you do not type the quote in the first
1227 (@value{GDBP}) b bub @key{TAB}
1228 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1229 (@value{GDBP}) b 'bubble(
1233 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1234 you have not yet started typing the argument list when you ask for
1235 completion on an overloaded symbol.
1240 @section Getting help
1241 @cindex online documentation
1244 You can always ask @value{GDBN} itself for information on its commands, using the
1245 command @code{help}.
1251 You can use @code{help} (abbreviated @code{h}) with no arguments to
1252 display a short list of named classes of commands:
1256 List of classes of commands:
1258 running -- Running the program
1259 stack -- Examining the stack
1260 data -- Examining data
1261 breakpoints -- Making program stop at certain points
1262 files -- Specifying and examining files
1263 status -- Status inquiries
1264 support -- Support facilities
1265 user-defined -- User-defined commands
1266 aliases -- Aliases of other commands
1267 obscure -- Obscure features
1269 Type "help" followed by a class name for a list of
1270 commands in that class.
1271 Type "help" followed by command name for full
1273 Command name abbreviations are allowed if unambiguous.
1277 @item help @var{class}
1278 Using one of the general help classes as an argument, you can get a
1279 list of the individual commands in that class. For example, here is the
1280 help display for the class @code{status}:
1283 (@value{GDBP}) help status
1288 @c Line break in "show" line falsifies real output, but needed
1289 @c to fit in smallbook page size.
1290 show -- Generic command for showing things set
1292 info -- Generic command for printing status
1294 Type "help" followed by command name for full
1296 Command name abbreviations are allowed if unambiguous.
1300 @item help @var{command}
1301 With a command name as @code{help} argument, @value{GDBN} displays a
1302 short paragraph on how to use that command.
1305 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1306 and @code{show} to inquire about the state of your program, or the state
1307 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1308 manual introduces each of them in the appropriate context. The listings
1309 under @code{info} and under @code{show} in the Index point to
1310 all the sub-commands. @xref{Index}.
1317 This command (abbreviated @code{i}) is for describing the state of your
1318 program. For example, you can list the arguments given to your program
1319 with @code{info args}, list the registers currently in use with @code{info
1320 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1321 You can get a complete list of the @code{info} sub-commands with
1322 @w{@code{help info}}.
1326 In contrast, @code{show} is for describing the state of @value{GDBN} itself.
1327 You can change most of the things you can @code{show}, by using the
1328 related command @code{set}; for example, you can control what number
1329 system is used for displays with @code{set radix}, or simply inquire
1330 which is currently in use with @code{show radix}.
1333 To display all the settable parameters and their current
1334 values, you can use @code{show} with no arguments; you may also use
1335 @code{info set}. Both commands produce the same display.
1336 @c FIXME: "info set" violates the rule that "info" is for state of
1337 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1338 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1342 Here are three miscellaneous @code{show} subcommands, all of which are
1343 exceptional in lacking corresponding @code{set} commands:
1346 @kindex show version
1347 @cindex version number
1349 Show what version of @value{GDBN} is running. You should include this
1350 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1351 use at your site, you may occasionally want to determine which version
1352 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1353 and old ones may wither away. The version number is also announced
1354 when you start @value{GDBN}.
1356 @kindex show copying
1358 Display information about permission for copying @value{GDBN}.
1360 @kindex show warranty
1362 Display the GNU ``NO WARRANTY'' statement.
1366 @chapter Running Programs Under @value{GDBN}
1368 When you run a program under @value{GDBN}, you must first generate
1369 debugging information when you compile it.
1371 You may start it with its arguments, if any, in an environment of your
1372 choice. You may redirect your program's input and output, debug an
1373 already running process, or kill a child process.
1377 * Compilation:: Compiling for debugging
1378 * Starting:: Starting your program
1380 * Arguments:: Your program's arguments
1381 * Environment:: Your program's environment
1382 * Working Directory:: Your program's working directory
1383 * Input/Output:: Your program's input and output
1384 * Attach:: Debugging an already-running process
1385 * Kill Process:: Killing the child process
1386 * Process Information:: Additional process information
1387 * Threads:: Debugging programs with multiple threads
1392 @section Compiling for debugging
1394 In order to debug a program effectively, you need to generate
1395 debugging information when you compile it. This debugging information
1396 is stored in the object file; it describes the data type of each
1397 variable or function and the correspondence between source line numbers
1398 and addresses in the executable code.
1400 To request debugging information, specify the @samp{-g} option when you run
1403 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1404 options together. Using those compilers, you cannot generate optimized
1405 executables containing debugging information.
1407 @value{NGCC}, the GNU C compiler, supports @samp{-g} with or without
1408 @samp{-O}, making it possible to debug optimized code. We recommend
1409 that you @emph{always} use @samp{-g} whenever you compile a program.
1410 You may think your program is correct, but there is no sense in pushing
1413 @cindex optimized code, debugging
1414 @cindex debugging optimized code
1415 When you debug a program compiled with @samp{-g -O}, remember that the
1416 optimizer is rearranging your code; the debugger shows you what is
1417 really there. Do not be too surprised when the execution path does not
1418 exactly match your source file! An extreme example: if you define a
1419 variable, but never use it, @value{GDBN} never sees that
1420 variable---because the compiler optimizes it out of existence.
1422 Some things do not work as well with @samp{-g -O} as with just
1423 @samp{-g}, particularly on machines with instruction scheduling. If in
1424 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1425 please report it as a bug (including a test case!).
1427 Older versions of the GNU C compiler permitted a variant option
1428 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1429 format; if your GNU C compiler has this option, do not use it.
1433 @section Starting your program
1441 Use the @code{run} command to start your program under @value{GDBN}. You must
1442 first specify the program name
1446 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1447 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1448 command (@pxref{Files, ,Commands to specify files}).
1453 If you are running your program in an execution environment that
1454 supports processes, @code{run} creates an inferior process and makes
1455 that process run your program. (In environments without processes,
1456 @code{run} jumps to the start of your program.)
1458 The execution of a program is affected by certain information it
1459 receives from its superior. @value{GDBN} provides ways to specify this
1460 information, which you must do @emph{before} starting your program. (You
1461 can change it after starting your program, but such changes only affect
1462 your program the next time you start it.) This information may be
1463 divided into four categories:
1466 @item The @emph{arguments.}
1467 Specify the arguments to give your program as the arguments of the
1468 @code{run} command. If a shell is available on your target, the shell
1469 is used to pass the arguments, so that you may use normal conventions
1470 (such as wildcard expansion or variable substitution) in describing
1471 the arguments. In Unix systems, you can control which shell is used
1472 with the @code{SHELL} environment variable. @xref{Arguments, ,Your
1473 program's arguments}.
1475 @item The @emph{environment.}
1476 Your program normally inherits its environment from @value{GDBN}, but you can
1477 use the @value{GDBN} commands @code{set environment} and @code{unset
1478 environment} to change parts of the environment that affect
1479 your program. @xref{Environment, ,Your program's environment}.
1481 @item The @emph{working directory.}
1482 Your program inherits its working directory from @value{GDBN}. You can set
1483 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1484 @xref{Working Directory, ,Your program's working directory}.
1486 @item The @emph{standard input and output.}
1487 Your program normally uses the same device for standard input and
1488 standard output as @value{GDBN} is using. You can redirect input and output
1489 in the @code{run} command line, or you can use the @code{tty} command to
1490 set a different device for your program.
1491 @xref{Input/Output, ,Your program's input and output}.
1494 @emph{Warning:} While input and output redirection work, you cannot use
1495 pipes to pass the output of the program you are debugging to another
1496 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1501 When you issue the @code{run} command, your program begins to execute
1502 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1503 of how to arrange for your program to stop. Once your program has
1504 stopped, you may call functions in your program, using the @code{print}
1505 or @code{call} commands. @xref{Data, ,Examining Data}.
1507 If the modification time of your symbol file has changed since the last
1508 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1509 table, and reads it again. When it does this, @value{GDBN} tries to retain
1510 your current breakpoints.
1514 @section Your program's arguments
1516 @cindex arguments (to your program)
1517 The arguments to your program can be specified by the arguments of the
1518 @code{run} command. They are passed to a shell, which expands wildcard
1519 characters and performs redirection of I/O, and thence to your program.
1520 Your @code{SHELL} environment variable (if it exists) specifies what
1521 shell @value{GDBN} if you do not define @code{SHELL}, @value{GDBN} uses
1524 @code{run} with no arguments uses the same arguments used by the previous
1525 @code{run}, or those set by the @code{set args} command.
1530 Specify the arguments to be used the next time your program is run. If
1531 @code{set args} has no arguments, @code{run} executes your program
1532 with no arguments. Once you have run your program with arguments,
1533 using @code{set args} before the next @code{run} is the only way to run
1534 it again without arguments.
1538 Show the arguments to give your program when it is started.
1542 @section Your program's environment
1544 @cindex environment (of your program)
1545 The @dfn{environment} consists of a set of environment variables and
1546 their values. Environment variables conventionally record such things as
1547 your user name, your home directory, your terminal type, and your search
1548 path for programs to run. Usually you set up environment variables with
1549 the shell and they are inherited by all the other programs you run. When
1550 debugging, it can be useful to try running your program with a modified
1551 environment without having to start @value{GDBN} over again.
1554 @item path @var{directory}
1556 Add @var{directory} to the front of the @code{PATH} environment variable
1557 (the search path for executables), for both @value{GDBN} and your program.
1558 You may specify several directory names, separated by @samp{:} or
1559 whitespace. If @var{directory} is already in the path, it is moved to
1560 the front, so it is searched sooner.
1562 You can use the string @samp{$cwd} to refer to whatever is the current
1563 working directory at the time @value{GDBN} searches the path. If you
1564 use @samp{.} instead, it refers to the directory where you executed the
1565 @code{path} command. @value{GDBN} replaces @samp{.} in the
1566 @var{directory} argument (with the current path) before adding
1567 @var{directory} to the search path.
1568 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1569 @c document that, since repeating it would be a no-op.
1573 Display the list of search paths for executables (the @code{PATH}
1574 environment variable).
1576 @item show environment @r{[}@var{varname}@r{]}
1577 @kindex show environment
1578 Print the value of environment variable @var{varname} to be given to
1579 your program when it starts. If you do not supply @var{varname},
1580 print the names and values of all environment variables to be given to
1581 your program. You can abbreviate @code{environment} as @code{env}.
1583 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1584 @kindex set environment
1585 Set environment variable @var{varname} to @var{value}. The value
1586 changes for your program only, not for @value{GDBN} itself. @var{value} may
1587 be any string; the values of environment variables are just strings, and
1588 any interpretation is supplied by your program itself. The @var{value}
1589 parameter is optional; if it is eliminated, the variable is set to a
1591 @c "any string" here does not include leading, trailing
1592 @c blanks. Gnu asks: does anyone care?
1594 For example, this command:
1601 tells a Unix program, when subsequently run, that its user is named
1602 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1603 are not actually required.)
1605 @item unset environment @var{varname}
1606 @kindex unset environment
1607 Remove variable @var{varname} from the environment to be passed to your
1608 program. This is different from @samp{set env @var{varname} =};
1609 @code{unset environment} removes the variable from the environment,
1610 rather than assigning it an empty value.
1613 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1614 by your @code{SHELL} environment variable if it exists (or
1615 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1616 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1617 @file{.bashrc} for BASH---any variables you set in that file affect
1618 your program. You may wish to move setting of environment variables to
1619 files that are only run when you sign on, such as @file{.login} or
1622 @node Working Directory
1623 @section Your program's working directory
1625 @cindex working directory (of your program)
1626 Each time you start your program with @code{run}, it inherits its
1627 working directory from the current working directory of @value{GDBN}.
1628 The @value{GDBN} working directory is initially whatever it inherited
1629 from its parent process (typically the shell), but you can specify a new
1630 working directory in @value{GDBN} with the @code{cd} command.
1632 The @value{GDBN} working directory also serves as a default for the commands
1633 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1637 @item cd @var{directory}
1639 Set the @value{GDBN} working directory to @var{directory}.
1643 Print the @value{GDBN} working directory.
1647 @section Your program's input and output
1652 By default, the program you run under @value{GDBN} does input and output to
1653 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal to
1654 its own terminal modes to interact with you, but it records the terminal
1655 modes your program was using and switches back to them when you continue
1656 running your program.
1660 @kindex info terminal
1661 Displays information recorded by @value{GDBN} about the terminal modes your
1665 You can redirect your program's input and/or output using shell
1666 redirection with the @code{run} command. For example,
1673 starts your program, diverting its output to the file @file{outfile}.
1676 @cindex controlling terminal
1677 Another way to specify where your program should do input and output is
1678 with the @code{tty} command. This command accepts a file name as
1679 argument, and causes this file to be the default for future @code{run}
1680 commands. It also resets the controlling terminal for the child
1681 process, for future @code{run} commands. For example,
1688 directs that processes started with subsequent @code{run} commands
1689 default to do input and output on the terminal @file{/dev/ttyb} and have
1690 that as their controlling terminal.
1692 An explicit redirection in @code{run} overrides the @code{tty} command's
1693 effect on the input/output device, but not its effect on the controlling
1696 When you use the @code{tty} command or redirect input in the @code{run}
1697 command, only the input @emph{for your program} is affected. The input
1698 for @value{GDBN} still comes from your terminal.
1701 @section Debugging an already-running process
1706 @item attach @var{process-id}
1707 This command attaches to a running process---one that was started
1708 outside @value{GDBN}. (@code{info files} shows your active
1709 targets.) The command takes as argument a process ID. The usual way to
1710 find out the process-id of a Unix process is with the @code{ps} utility,
1711 or with the @samp{jobs -l} shell command.
1713 @code{attach} does not repeat if you press @key{RET} a second time after
1714 executing the command.
1717 To use @code{attach}, your program must be running in an environment
1718 which supports processes; for example, @code{attach} does not work for
1719 programs on bare-board targets that lack an operating system. You must
1720 also have permission to send the process a signal.
1722 When using @code{attach}, you should first use the @code{file} command
1723 to specify the program running in the process and load its symbol table.
1724 @xref{Files, ,Commands to Specify Files}.
1726 The first thing @value{GDBN} does after arranging to debug the specified
1727 process is to stop it. You can examine and modify an attached process
1728 with all the @value{GDBN} commands that are ordinarily available when you start
1729 processes with @code{run}. You can insert breakpoints; you can step and
1730 continue; you can modify storage. If you would rather the process
1731 continue running, you may use the @code{continue} command after
1732 attaching @value{GDBN} to the process.
1737 When you have finished debugging the attached process, you can use the
1738 @code{detach} command to release it from @value{GDBN} control. Detaching
1739 the process continues its execution. After the @code{detach} command,
1740 that process and @value{GDBN} become completely independent once more, and you
1741 are ready to @code{attach} another process or start one with @code{run}.
1742 @code{detach} does not repeat if you press @key{RET} again after
1743 executing the command.
1746 If you exit @value{GDBN} or use the @code{run} command while you have an
1747 attached process, you kill that process. By default, @value{GDBN} asks
1748 for confirmation if you try to do either of these things; you can
1749 control whether or not you need to confirm by using the @code{set
1750 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1755 @section Killing the child process
1760 Kill the child process in which your program is running under @value{GDBN}.
1763 This command is useful if you wish to debug a core dump instead of a
1764 running process. @value{GDBN} ignores any core dump file while your program
1768 On some operating systems, a program cannot be executed outside @value{GDBN}
1769 while you have breakpoints set on it inside @value{GDBN}. You can use the
1770 @code{kill} command in this situation to permit running your program
1771 outside the debugger.
1773 The @code{kill} command is also useful if you wish to recompile and
1774 relink your program, since on many systems it is impossible to modify an
1775 executable file while it is running in a process. In this case, when you
1776 next type @code{run}, @value{GDBN} notices that the file has changed, and
1777 reads the symbol table again (while trying to preserve your current
1778 breakpoint settings).
1780 @node Process Information
1781 @section Additional process information
1784 @cindex process image
1785 Some operating systems provide a facility called @samp{/proc} that can
1786 be used to examine the image of a running process using file-system
1787 subroutines. If @value{GDBN} is configured for an operating system with this
1788 facility, the command @code{info proc} is available to report on several
1789 kinds of information about the process running your program.
1794 Summarize available information about the process.
1796 @item info proc mappings
1797 @kindex info proc mappings
1798 Report on the address ranges accessible in the program, with information
1799 on whether your program may read, write, or execute each range.
1801 @item info proc times
1802 @kindex info proc times
1803 Starting time, user CPU time, and system CPU time for your program and
1807 @kindex info proc id
1808 Report on the process IDs related to your program: its own process ID,
1809 the ID of its parent, the process group ID, and the session ID.
1811 @item info proc status
1812 @kindex info proc status
1813 General information on the state of the process. If the process is
1814 stopped, this report includes the reason for stopping, and any signal
1818 Show all the above information about the process.
1822 @section Debugging programs with multiple threads
1824 @cindex threads of execution
1825 @cindex multiple threads
1826 @cindex switching threads
1827 In some operating systems, a single program may have more than one
1828 @dfn{thread} of execution. The precise semantics of threads differ from
1829 one operating system to another, but in general the threads of a single
1830 program are akin to multiple processes---except that they share one
1831 address space (that is, they can all examine and modify the same
1832 variables). On the other hand, each thread has its own registers and
1833 execution stack, and perhaps private memory.
1835 @value{GDBN} provides these facilities for debugging multi-thread
1839 @item automatic notification of new threads
1840 @item @samp{thread @var{threadno}}, a command to switch among threads
1841 @item @samp{info threads}, a command to inquire about existing threads
1842 @item thread-specific breakpoints
1846 @emph{Warning:} These facilities are not yet available on every
1847 @value{GDBN} configuration where the operating system supports threads.
1848 If your @value{GDBN} does not support threads, these commands have no
1849 effect. For example, a system without thread support shows no output
1850 from @samp{info threads}, and always rejects the @code{thread} command,
1854 (@value{GDBP}) info threads
1855 (@value{GDBP}) thread 1
1856 Thread ID 1 not known. Use the "info threads" command to
1857 see the IDs of currently known threads.
1859 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1860 @c doesn't support threads"?
1863 @cindex focus of debugging
1864 @cindex current thread
1865 The @value{GDBN} thread debugging facility allows you to observe all
1866 threads while your program runs---but whenever @value{GDBN} takes
1867 control, one thread in particular is always the focus of debugging.
1868 This thread is called the @dfn{current thread}. Debugging commands show
1869 program information from the perspective of the current thread.
1871 @kindex New @var{systag}
1872 @cindex thread identifier (system)
1873 @c FIXME-implementors!! It would be more helpful if the [New...] message
1874 @c included GDB's numeric thread handle, so you could just go to that
1875 @c thread without first checking `info threads'.
1876 Whenever @value{GDBN} detects a new thread in your program, it displays
1877 the target system's identification for the thread with a message in the
1878 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1879 whose form varies depending on the particular system. For example, on
1880 LynxOS, you might see
1883 [New process 35 thread 27]
1887 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1888 the @var{systag} is simply something like @samp{process 368}, with no
1891 @c FIXME!! (1) Does the [New...] message appear even for the very first
1892 @c thread of a program, or does it only appear for the
1893 @c second---i.e., when it becomes obvious we have a multithread
1895 @c (2) *Is* there necessarily a first thread always? Or do some
1896 @c multithread systems permit starting a program with multiple
1897 @c threads ab initio?
1899 @cindex thread number
1900 @cindex thread identifier (GDB)
1901 For debugging purposes, @value{GDBN} associates its own thread
1902 number---always a single integer---with each thread in your program.
1906 @kindex info threads
1907 Display a summary of all threads currently in your
1908 program. @value{GDBN} displays for each thread (in this order):
1911 @item the thread number assigned by @value{GDBN}
1913 @item the target system's thread identifier (@var{systag})
1915 @item the current stack frame summary for that thread
1919 An asterisk @samp{*} to the left of the @value{GDBN} thread number
1920 indicates the current thread.
1924 @c end table here to get a little more width for example
1927 (@value{GDBP}) info threads
1928 3 process 35 thread 27 0x34e5 in sigpause ()
1929 2 process 35 thread 23 0x34e5 in sigpause ()
1930 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
1935 @item thread @var{threadno}
1936 @kindex thread @var{threadno}
1937 Make thread number @var{threadno} the current thread. The command
1938 argument @var{threadno} is the internal @value{GDBN} thread number, as
1939 shown in the first field of the @samp{info threads} display.
1940 @value{GDBN} responds by displaying the system identifier of the thread
1941 you selected, and its current stack frame summary:
1944 @c FIXME!! This example made up; find a GDB w/threads and get real one
1945 (@value{GDBP}) thread 2
1946 [Switching to process 35 thread 23]
1947 0x34e5 in sigpause ()
1951 As with the @samp{[New @dots{}]} message, the form of the text after
1952 @samp{Switching to} depends on your system's conventions for identifying
1956 @cindex automatic thread selection
1957 @cindex switching threads automatically
1958 @cindex threads, automatic switching
1959 Whenever @value{GDBN} stops your program, due to a breakpoint or a
1960 signal, it automatically selects the thread where that breakpoint or
1961 signal happened. @value{GDBN} alerts you to the context switch with a
1962 message of the form @samp{[Switching to @var{systag}]} to identify the
1965 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
1966 more information about how @value{GDBN} behaves when you stop and start
1967 programs with multiple threads.
1969 @xref{Set Watchpoints,,Setting watchpoints}, for information about
1970 watchpoints in programs with multiple threads.
1974 @chapter Stopping and Continuing
1976 The principal purposes of using a debugger are so that you can stop your
1977 program before it terminates; or so that, if your program runs into
1978 trouble, you can investigate and find out why.
1980 Inside @value{GDBN}, your program may stop for any of several reasons, such
1985 a breakpoint, or reaching a new line after a @value{GDBN}
1986 command such as @code{step}. You may then examine and change
1987 variables, set new breakpoints or remove old ones, and then continue
1988 execution. Usually, the messages shown by @value{GDBN} provide ample
1989 explanation of the status of your program---but you can also explicitly
1990 request this information at any time.
1994 @kindex info program
1995 Display information about the status of your program: whether it is
2005 * Breakpoints:: Breakpoints, watchpoints, and exceptions
2008 * Breakpoints:: Breakpoints and watchpoints
2010 @c Remnant makeinfo bug requires blank line after *successful* end-if in menu:
2012 * Continuing and Stepping:: Resuming execution
2017 * Thread Stops:: Stopping and starting multi-thread programs
2021 @c makeinfo node-defaulting requires adjacency of @node and sectioning cmds
2022 @c ...hence distribute @node Breakpoints over two possible @if expansions.
2026 @section Breakpoints, watchpoints, and exceptions
2030 @section Breakpoints and watchpoints
2034 A @dfn{breakpoint} makes your program stop whenever a certain point in
2035 the program is reached. For each breakpoint, you can add
2036 conditions to control in finer detail whether your program stops.
2037 You can set breakpoints with the @code{break} command and its variants
2038 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
2039 your program should stop by line number, function name or exact address
2042 In languages with exception handling (such as GNU C++), you can also set
2043 breakpoints where an exception is raised (@pxref{Exception Handling,,
2044 Breakpoints and exceptions}).
2048 @cindex memory tracing
2049 @cindex breakpoint on memory address
2050 @cindex breakpoint on variable modification
2051 A @dfn{watchpoint} is a special breakpoint that stops your program
2052 when the value of an expression changes. You must use a different
2053 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2054 watchpoints}), but aside from that, you can manage a watchpoint like
2055 any other breakpoint: you enable, disable, and delete both breakpoints
2056 and watchpoints using the same commands.
2058 You can arrange to have values from your program displayed automatically
2059 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2062 @cindex breakpoint numbers
2063 @cindex numbers for breakpoints
2064 @value{GDBN} assigns a number to each breakpoint or watchpoint when you
2065 create it; these numbers are successive integers starting with one. In
2066 many of the commands for controlling various features of breakpoints you
2067 use the breakpoint number to say which breakpoint you want to change.
2068 Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
2069 no effect on your program until you enable it again.
2072 * Set Breaks:: Setting breakpoints
2073 * Set Watchpoints:: Setting watchpoints
2075 * Exception Handling:: Breakpoints and exceptions
2078 * Delete Breaks:: Deleting breakpoints
2079 * Disabling:: Disabling breakpoints
2080 * Conditions:: Break conditions
2081 * Break Commands:: Breakpoint command lists
2083 * Breakpoint Menus:: Breakpoint menus
2086 * Error in Breakpoints:: ``Cannot insert breakpoints''
2091 @subsection Setting breakpoints
2093 @c FIXME LMB what does GDB do if no code on line of breakpt?
2094 @c consider in particular declaration with/without initialization.
2096 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2101 @cindex latest breakpoint
2102 Breakpoints are set with the @code{break} command (abbreviated
2103 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2104 number of the beakpoint you've set most recently; see @ref{Convenience
2105 Vars,, Convenience variables}, for a discussion of what you can do with
2106 convenience variables.
2108 You have several ways to say where the breakpoint should go.
2111 @item break @var{function}
2112 Set a breakpoint at entry to function @var{function}.
2114 When using source languages that permit overloading of symbols, such as
2115 C++, @var{function} may refer to more than one possible place to break.
2116 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2119 @item break +@var{offset}
2120 @itemx break -@var{offset}
2121 Set a breakpoint some number of lines forward or back from the position
2122 at which execution stopped in the currently selected frame.
2124 @item break @var{linenum}
2125 Set a breakpoint at line @var{linenum} in the current source file.
2126 That file is the last file whose source text was printed. This
2127 breakpoint stops your program just before it executes any of the
2130 @item break @var{filename}:@var{linenum}
2131 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2133 @item break @var{filename}:@var{function}
2134 Set a breakpoint at entry to function @var{function} found in file
2135 @var{filename}. Specifying a file name as well as a function name is
2136 superfluous except when multiple files contain similarly named
2139 @item break *@var{address}
2140 Set a breakpoint at address @var{address}. You can use this to set
2141 breakpoints in parts of your program which do not have debugging
2142 information or source files.
2145 When called without any arguments, @code{break} sets a breakpoint at
2146 the next instruction to be executed in the selected stack frame
2147 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2148 innermost, this makes your program stop as soon as control
2149 returns to that frame. This is similar to the effect of a
2150 @code{finish} command in the frame inside the selected frame---except
2151 that @code{finish} does not leave an active breakpoint. If you use
2152 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2153 the next time it reaches the current location; this may be useful
2156 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2157 least one instruction has been executed. If it did not do this, you
2158 would be unable to proceed past a breakpoint without first disabling the
2159 breakpoint. This rule applies whether or not the breakpoint already
2160 existed when your program stopped.
2162 @item break @dots{} if @var{cond}
2163 Set a breakpoint with condition @var{cond}; evaluate the expression
2164 @var{cond} each time the breakpoint is reached, and stop only if the
2165 value is nonzero---that is, if @var{cond} evaluates as true.
2166 @samp{@dots{}} stands for one of the possible arguments described
2167 above (or no argument) specifying where to break. @xref{Conditions,
2168 ,Break conditions}, for more information on breakpoint conditions.
2170 @item tbreak @var{args}
2172 Set a breakpoint enabled only for one stop. @var{args} are the
2173 same as for the @code{break} command, and the breakpoint is set in the same
2174 way, but the breakpoint is automatically disabled after the first time your
2175 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2177 @item rbreak @var{regex}
2179 @cindex regular expression
2180 @c FIXME what kind of regexp?
2181 Set breakpoints on all functions matching the regular expression
2182 @var{regex}. This command
2183 sets an unconditional breakpoint on all matches, printing a list of all
2184 breakpoints it set. Once these breakpoints are set, they are treated
2185 just like the breakpoints set with the @code{break} command. You can
2186 delete them, disable them, or make them conditional the same way as any
2190 When debugging C++ programs, @code{rbreak} is useful for setting
2191 breakpoints on overloaded functions that are not members of any special
2195 @kindex info breakpoints
2196 @cindex @code{$_} and @code{info breakpoints}
2197 @item info breakpoints @r{[}@var{n}@r{]}
2198 @itemx info break @r{[}@var{n}@r{]}
2199 @itemx info watchpoints @r{[}@var{n}@r{]}
2200 Print a table of all breakpoints and watchpoints set and not
2201 deleted, with the following columns for each breakpoint:
2204 @item Breakpoint Numbers
2206 Breakpoint or watchpoint.
2208 Whether the breakpoint is marked to be disabled or deleted when hit.
2209 @item Enabled or Disabled
2210 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2211 that are not enabled.
2213 Where the breakpoint is in your program, as a memory address
2215 Where the breakpoint is in the source for your program, as a file and
2220 If a breakpoint is conditional, @code{info break} shows the condition on
2221 the line following the affected breakpoint; breakpoint commands, if any,
2222 are listed after that.
2225 @code{info break} with a breakpoint
2226 number @var{n} as argument lists only that breakpoint. The
2227 convenience variable @code{$_} and the default examining-address for
2228 the @code{x} command are set to the address of the last breakpoint
2229 listed (@pxref{Memory, ,Examining memory}).
2232 @value{GDBN} allows you to set any number of breakpoints at the same place in
2233 your program. There is nothing silly or meaningless about this. When
2234 the breakpoints are conditional, this is even useful
2235 (@pxref{Conditions, ,Break conditions}).
2237 @cindex negative breakpoint numbers
2238 @cindex internal @value{GDBN} breakpoints
2239 @value{GDBN} itself sometimes sets breakpoints in your program for special
2240 purposes, such as proper handling of @code{longjmp} (in C programs).
2241 These internal breakpoints are assigned negative numbers, starting with
2242 @code{-1}; @samp{info breakpoints} does not display them.
2244 You can see these breakpoints with the @value{GDBN} maintenance command
2245 @samp{maint info breakpoints}.
2248 @kindex maint info breakpoints
2249 @item maint info breakpoints
2250 Using the same format as @samp{info breakpoints}, display both the
2251 breakpoints you've set explicitly, and those @value{GDBN} is using for
2252 internal purposes. Internal breakpoints are shown with negative
2253 breakpoint numbers. The type column identifies what kind of breakpoint
2258 Normal, explicitly set breakpoint.
2261 Normal, explicitly set watchpoint.
2264 Internal breakpoint, used to handle correctly stepping through
2265 @code{longjmp} calls.
2267 @item longjmp resume
2268 Internal breakpoint at the target of a @code{longjmp}.
2271 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2274 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2280 @node Set Watchpoints
2281 @subsection Setting watchpoints
2282 @cindex setting watchpoints
2284 You can use a watchpoint to stop execution whenever the value of an
2285 expression changes, without having to predict a particular place
2286 where this may happen.
2288 Watchpoints currently execute two orders of magnitude more slowly than
2289 other breakpoints, but this can be well worth it to catch errors where
2290 you have no clue what part of your program is the culprit.
2293 @c this "future releases" promise has been in too long, is getting
2294 @c embarrassing. But...
2295 @c FIXME: in future updates, check whether hardware watchpoints in on any
2296 @c platforms yet. As of 26jan94, they're very close on HPPA running
2297 @c Berkeley and on Irix 4.
2298 Some processors provide special hardware to support watchpoint
2299 evaluation; future releases of @value{GDBN} will use such hardware if it
2305 @item watch @var{expr}
2306 Set a watchpoint for an expression.
2308 @kindex info watchpoints
2309 @item info watchpoints
2310 This command prints a list of watchpoints and breakpoints; it is the
2311 same as @code{info break}.
2316 @cindex watchpoints and threads
2317 @cindex threads and watchpoints
2318 @emph{Warning:} in multi-thread programs, watchpoints have only limited
2319 usefulness. With the current watchpoint implementation, @value{GDBN}
2320 can only watch the value of an expression @emph{in a single thread}. If
2321 you are confident that the expression can only change due to the current
2322 thread's activity (and if you are also confident that no other thread
2323 can become current), then you can use watchpoints as usual. However,
2324 @value{GDBN} may not notice when a non-current thread's activity changes
2330 @node Exception Handling
2331 @subsection Breakpoints and exceptions
2332 @cindex exception handlers
2334 Some languages, such as GNU C++, implement exception handling. You can
2335 use @value{GDBN} to examine what caused your program to raise an exception,
2336 and to list the exceptions your program is prepared to handle at a
2337 given point in time.
2340 @item catch @var{exceptions}
2342 You can set breakpoints at active exception handlers by using the
2343 @code{catch} command. @var{exceptions} is a list of names of exceptions
2347 You can use @code{info catch} to list active exception handlers.
2348 @xref{Frame Info, ,Information about a frame}.
2350 There are currently some limitations to exception handling in @value{GDBN}:
2354 If you call a function interactively, @value{GDBN} normally returns
2355 control to you when the function has finished executing. If the call
2356 raises an exception, however, the call may bypass the mechanism that
2357 returns control to you and cause your program to simply continue
2358 running until it hits a breakpoint, catches a signal that @value{GDBN} is
2359 listening for, or exits.
2362 You cannot raise an exception interactively.
2365 You cannot install an exception handler interactively.
2368 @cindex raise exceptions
2369 Sometimes @code{catch} is not the best way to debug exception handling:
2370 if you need to know exactly where an exception is raised, it is better to
2371 stop @emph{before} the exception handler is called, since that way you
2372 can see the stack before any unwinding takes place. If you set a
2373 breakpoint in an exception handler instead, it may not be easy to find
2374 out where the exception was raised.
2376 To stop just before an exception handler is called, you need some
2377 knowledge of the implementation. In the case of GNU C++, exceptions are
2378 raised by calling a library function named @code{__raise_exception}
2379 which has the following ANSI C interface:
2382 /* @var{addr} is where the exception identifier is stored.
2383 ID is the exception identifier. */
2384 void __raise_exception (void **@var{addr}, void *@var{id});
2388 To make the debugger catch all exceptions before any stack
2389 unwinding takes place, set a breakpoint on @code{__raise_exception}
2390 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2392 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2393 that depends on the value of @var{id}, you can stop your program when
2394 a specific exception is raised. You can use multiple conditional
2395 breakpoints to stop your program when any of a number of exceptions are
2400 @subsection Deleting breakpoints
2402 @cindex clearing breakpoints, watchpoints
2403 @cindex deleting breakpoints, watchpoints
2404 It is often necessary to eliminate a breakpoint or watchpoint once it
2405 has done its job and you no longer want your program to stop there. This
2406 is called @dfn{deleting} the breakpoint. A breakpoint that has been
2407 deleted no longer exists; it is forgotten.
2409 With the @code{clear} command you can delete breakpoints according to
2410 where they are in your program. With the @code{delete} command you can
2411 delete individual breakpoints or watchpoints by specifying their
2414 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2415 automatically ignores breakpoints on the first instruction to be executed
2416 when you continue execution without changing the execution address.
2421 Delete any breakpoints at the next instruction to be executed in the
2422 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2423 the innermost frame is selected, this is a good way to delete a
2424 breakpoint where your program just stopped.
2426 @item clear @var{function}
2427 @itemx clear @var{filename}:@var{function}
2428 Delete any breakpoints set at entry to the function @var{function}.
2430 @item clear @var{linenum}
2431 @itemx clear @var{filename}:@var{linenum}
2432 Delete any breakpoints set at or within the code of the specified line.
2434 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2435 @cindex delete breakpoints
2438 Delete the breakpoints or watchpoints of the numbers specified as
2439 arguments. If no argument is specified, delete all breakpoints (@value{GDBN}
2440 asks confirmation, unless you have @code{set confirm off}). You
2441 can abbreviate this command as @code{d}.
2445 @subsection Disabling breakpoints
2447 @cindex disabled breakpoints
2448 @cindex enabled breakpoints
2449 Rather than deleting a breakpoint or watchpoint, you might prefer to
2450 @dfn{disable} it. This makes the breakpoint inoperative as if it had
2451 been deleted, but remembers the information on the breakpoint so that
2452 you can @dfn{enable} it again later.
2454 You disable and enable breakpoints and watchpoints with the
2455 @code{enable} and @code{disable} commands, optionally specifying one or
2456 more breakpoint numbers as arguments. Use @code{info break} or
2457 @code{info watch} to print a list of breakpoints or watchpoints if you
2458 do not know which numbers to use.
2460 A breakpoint or watchpoint can have any of four different states of
2465 Enabled. The breakpoint stops your program. A breakpoint set
2466 with the @code{break} command starts out in this state.
2468 Disabled. The breakpoint has no effect on your program.
2470 Enabled once. The breakpoint stops your program, but then becomes
2471 disabled. A breakpoint set with the @code{tbreak} command starts out in
2474 Enabled for deletion. The breakpoint stops your program, but
2475 immediately after it does so it is deleted permanently.
2478 You can use the following commands to enable or disable breakpoints and
2482 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2483 @kindex disable breakpoints
2486 Disable the specified breakpoints---or all breakpoints, if none are
2487 listed. A disabled breakpoint has no effect but is not forgotten. All
2488 options such as ignore-counts, conditions and commands are remembered in
2489 case the breakpoint is enabled again later. You may abbreviate
2490 @code{disable} as @code{dis}.
2492 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2493 @kindex enable breakpoints
2495 Enable the specified breakpoints (or all defined breakpoints). They
2496 become effective once again in stopping your program.
2498 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2499 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2500 of these breakpoints immediately after stopping your program.
2502 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2503 Enable the specified breakpoints to work once, then die. @value{GDBN}
2504 deletes any of these breakpoints as soon as your program stops there.
2507 Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2508 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2509 subsequently, they become disabled or enabled only when you use one of
2510 the commands above. (The command @code{until} can set and delete a
2511 breakpoint of its own, but it does not change the state of your other
2512 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2516 @subsection Break conditions
2517 @cindex conditional breakpoints
2518 @cindex breakpoint conditions
2520 @c FIXME what is scope of break condition expr? Context where wanted?
2521 @c in particular for a watchpoint?
2522 The simplest sort of breakpoint breaks every time your program reaches a
2523 specified place. You can also specify a @dfn{condition} for a
2524 breakpoint. A condition is just a Boolean expression in your
2525 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2526 a condition evaluates the expression each time your program reaches it,
2527 and your program stops only if the condition is @emph{true}.
2529 This is the converse of using assertions for program validation; in that
2530 situation, you want to stop when the assertion is violated---that is,
2531 when the condition is false. In C, if you want to test an assertion expressed
2532 by the condition @var{assert}, you should set the condition
2533 @samp{! @var{assert}} on the appropriate breakpoint.
2535 Conditions are also accepted for watchpoints; you may not need them,
2536 since a watchpoint is inspecting the value of an expression anyhow---but
2537 it might be simpler, say, to just set a watchpoint on a variable name,
2538 and specify a condition that tests whether the new value is an interesting
2541 Break conditions can have side effects, and may even call functions in
2542 your program. This can be useful, for example, to activate functions
2543 that log program progress, or to use your own print functions to
2544 format special data structures. The effects are completely predictable
2545 unless there is another enabled breakpoint at the same address. (In
2546 that case, @value{GDBN} might see the other breakpoint first and stop your
2547 program without checking the condition of this one.) Note that
2548 breakpoint commands are usually more convenient and flexible for the
2549 purpose of performing side effects when a breakpoint is reached
2550 (@pxref{Break Commands, ,Breakpoint command lists}).
2552 Break conditions can be specified when a breakpoint is set, by using
2553 @samp{if} in the arguments to the @code{break} command. @xref{Set
2554 Breaks, ,Setting breakpoints}. They can also be changed at any time
2555 with the @code{condition} command. The @code{watch} command does not
2556 recognize the @code{if} keyword; @code{condition} is the only way to
2557 impose a further condition on a watchpoint.
2560 @item condition @var{bnum} @var{expression}
2562 Specify @var{expression} as the break condition for breakpoint or
2563 watchpoint number @var{bnum}. After you set a condition, breakpoint
2564 @var{bnum} stops your program only if the value of @var{expression} is
2565 true (nonzero, in C). When you use @code{condition}, @value{GDBN}
2566 checks @var{expression} immediately for syntactic correctness, and to
2567 determine whether symbols in it have referents in the context of your
2569 @c FIXME so what does GDB do if there is no referent? Moreover, what
2570 @c about watchpoints?
2572 not actually evaluate @var{expression} at the time the @code{condition}
2573 command is given, however. @xref{Expressions, ,Expressions}.
2575 @item condition @var{bnum}
2576 Remove the condition from breakpoint number @var{bnum}. It becomes
2577 an ordinary unconditional breakpoint.
2580 @cindex ignore count (of breakpoint)
2581 A special case of a breakpoint condition is to stop only when the
2582 breakpoint has been reached a certain number of times. This is so
2583 useful that there is a special way to do it, using the @dfn{ignore
2584 count} of the breakpoint. Every breakpoint has an ignore count, which
2585 is an integer. Most of the time, the ignore count is zero, and
2586 therefore has no effect. But if your program reaches a breakpoint whose
2587 ignore count is positive, then instead of stopping, it just decrements
2588 the ignore count by one and continues. As a result, if the ignore count
2589 value is @var{n}, the breakpoint does not stop the next @var{n} times
2590 your program reaches it.
2593 @item ignore @var{bnum} @var{count}
2595 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2596 The next @var{count} times the breakpoint is reached, your program's
2597 execution does not stop; other than to decrement the ignore count, @value{GDBN}
2600 To make the breakpoint stop the next time it is reached, specify
2603 When you use @code{continue} to resume execution of your program from a
2604 breakpoint, you can specify an ignore count directly as an argument to
2605 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
2606 Stepping,,Continuing and stepping}.
2608 If a breakpoint has a positive ignore count and a condition, the
2609 condition is not checked. Once the ignore count reaches zero,
2610 @value{GDBN} resumes checking the condition.
2612 You could achieve the effect of the ignore count with a condition such
2613 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2614 is decremented each time. @xref{Convenience Vars, ,Convenience
2618 @node Break Commands
2619 @subsection Breakpoint command lists
2621 @cindex breakpoint commands
2622 You can give any breakpoint (or watchpoint) a series of commands to
2623 execute when your program stops due to that breakpoint. For example, you
2624 might want to print the values of certain expressions, or enable other
2628 @item commands @r{[}@var{bnum}@r{]}
2629 @itemx @dots{} @var{command-list} @dots{}
2633 Specify a list of commands for breakpoint number @var{bnum}. The commands
2634 themselves appear on the following lines. Type a line containing just
2635 @code{end} to terminate the commands.
2637 To remove all commands from a breakpoint, type @code{commands} and
2638 follow it immediately with @code{end}; that is, give no commands.
2640 With no @var{bnum} argument, @code{commands} refers to the last
2641 breakpoint or watchpoint set (not to the breakpoint most recently
2645 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2646 disabled within a @var{command-list}.
2648 You can use breakpoint commands to start your program up again. Simply
2649 use the @code{continue} command, or @code{step}, or any other command
2650 that resumes execution.
2652 Any other commands in the command list, after a command that resumes
2653 execution, are ignored. This is because any time you resume execution
2654 (even with a simple @code{next} or @code{step}), you may encounter
2655 another breakpoint---which could have its own command list, leading to
2656 ambiguities about which list to execute.
2659 If the first command you specify in a command list is @code{silent}, the
2660 usual message about stopping at a breakpoint is not printed. This may
2661 be desirable for breakpoints that are to print a specific message and
2662 then continue. If none of the remaining commands print anything, you
2663 see no sign that the breakpoint was reached. @code{silent} is
2664 meaningful only at the beginning of a breakpoint command list.
2666 The commands @code{echo}, @code{output}, and @code{printf} allow you to
2667 print precisely controlled output, and are often useful in silent
2668 breakpoints. @xref{Output, ,Commands for controlled output}.
2670 For example, here is how you could use breakpoint commands to print the
2671 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2677 printf "x is %d\n",x
2682 One application for breakpoint commands is to compensate for one bug so
2683 you can test for another. Put a breakpoint just after the erroneous line
2684 of code, give it a condition to detect the case in which something
2685 erroneous has been done, and give it commands to assign correct values
2686 to any variables that need them. End with the @code{continue} command
2687 so that your program does not stop, and start with the @code{silent}
2688 command so that no output is produced. Here is an example:
2700 @node Breakpoint Menus
2701 @subsection Breakpoint menus
2703 @cindex symbol overloading
2705 Some programming languages (notably C++) permit a single function name
2706 to be defined several times, for application in different contexts.
2707 This is called @dfn{overloading}. When a function name is overloaded,
2708 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
2709 a breakpoint. If you realize this is a problem, you can use
2710 something like @samp{break @var{function}(@var{types})} to specify which
2711 particular version of the function you want. Otherwise, @value{GDBN} offers
2712 you a menu of numbered choices for different possible breakpoints, and
2713 waits for your selection with the prompt @samp{>}. The first two
2714 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
2715 sets a breakpoint at each definition of @var{function}, and typing
2716 @kbd{0} aborts the @code{break} command without setting any new
2719 For example, the following session excerpt shows an attempt to set a
2720 breakpoint at the overloaded symbol @code{String::after}.
2721 We choose three particular definitions of that function name:
2723 @c FIXME! This is likely to change to show arg type lists, at least
2725 (@value{GDBP}) b String::after
2728 [2] file:String.cc; line number:867
2729 [3] file:String.cc; line number:860
2730 [4] file:String.cc; line number:875
2731 [5] file:String.cc; line number:853
2732 [6] file:String.cc; line number:846
2733 [7] file:String.cc; line number:735
2735 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2736 Breakpoint 2 at 0xb344: file String.cc, line 875.
2737 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2738 Multiple breakpoints were set.
2739 Use the "delete" command to delete unwanted
2746 @node Error in Breakpoints
2747 @subsection ``Cannot insert breakpoints''
2749 @c FIXME: "cannot insert breakpoints" error, v unclear.
2750 @c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91
2751 @c some light may be shed by looking at instances of
2752 @c ONE_PROCESS_WRITETEXT. But error message seems possible otherwise
2753 @c too. pesch, 20sep91
2754 Under some operating systems, breakpoints cannot be used in a program if
2755 any other process is running that program. In this situation,
2756 attempting to run or continue a program with a breakpoint causes @value{GDBN}
2757 to stop the other process.
2759 When this happens, you have three ways to proceed:
2763 Remove or disable the breakpoints, then continue.
2766 Suspend @value{GDBN}, and copy the file containing your program to a new name.
2767 Resume @value{GDBN} and use the @code{exec-file} command to specify that @value{GDBN}
2768 should run your program under that name. Then start your program again.
2770 @c FIXME: RMS commented here "Show example". Maybe when someone
2771 @c explains the first FIXME: in this section...
2774 Relink your program so that the text segment is nonsharable, using the
2775 linker option @samp{-N}. The operating system limitation may not apply
2776 to nonsharable executables.
2780 @node Continuing and Stepping
2781 @section Continuing and stepping
2785 @cindex resuming execution
2786 @dfn{Continuing} means resuming program execution until your program
2787 completes normally. In contrast, @dfn{stepping} means executing just
2788 one more ``step'' of your program, where ``step'' may mean either one
2789 line of source code, or one machine instruction (depending on what
2790 particular command you use). Either when continuing
2791 or when stepping, your program may stop even sooner, due to
2796 a breakpoint or a signal. (If due to a signal, you may want to use
2797 @code{handle}, or use @samp{signal 0} to resume execution.
2798 @xref{Signals, ,Signals}.)
2802 @item continue @r{[}@var{ignore-count}@r{]}
2803 @itemx c @r{[}@var{ignore-count}@r{]}
2804 @itemx fg @r{[}@var{ignore-count}@r{]}
2808 Resume program execution, at the address where your program last stopped;
2809 any breakpoints set at that address are bypassed. The optional argument
2810 @var{ignore-count} allows you to specify a further number of times to
2811 ignore a breakpoint at this location; its effect is like that of
2812 @code{ignore} (@pxref{Conditions, ,Break conditions}).
2814 The argument @var{ignore-count} is meaningful only when your program
2815 stopped due to a breakpoint. At other times, the argument to
2816 @code{continue} is ignored.
2818 The synonyms @code{c} and @code{fg} are provided purely for convenience,
2819 and have exactly the same behavior as @code{continue}.
2822 To resume execution at a different place, you can use @code{return}
2823 (@pxref{Returning, ,Returning from a function}) to go back to the
2824 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
2825 different address}) to go to an arbitrary location in your program.
2827 A typical technique for using stepping is to set a breakpoint
2829 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions})
2832 (@pxref{Breakpoints, ,Breakpoints and watchpoints})
2835 beginning of the function or the section of your program where a
2836 problem is believed to lie, run your program until it stops at that
2837 breakpoint, and then step through the suspect area, examining the
2838 variables that are interesting, until you see the problem happen.
2844 Continue running your program until control reaches a different source
2845 line, then stop it and return control to @value{GDBN}. This command is
2846 abbreviated @code{s}.
2849 @emph{Warning:} If you use the @code{step} command while control is
2850 within a function that was compiled without debugging information,
2851 execution proceeds until control reaches a function that does have
2852 debugging information.
2855 @item step @var{count}
2856 Continue running as in @code{step}, but do so @var{count} times. If a
2857 breakpoint is reached,
2859 or a signal not related to stepping occurs before @var{count} steps,
2861 stepping stops right away.
2863 @item next @r{[}@var{count}@r{]}
2866 Continue to the next source line in the current (innermost) stack frame.
2867 Similar to @code{step}, but any function calls appearing within the line
2868 of code are executed without stopping. Execution stops when control
2869 reaches a different line of code at the stack level which was executing
2870 when the @code{next} command was given. This command is abbreviated
2873 An argument @var{count} is a repeat count, as for @code{step}.
2875 @code{next} within a function that lacks debugging information acts like
2876 @code{step}, but any function calls appearing within the code of the
2877 function are executed without stopping.
2881 Continue running until just after function in the selected stack frame
2882 returns. Print the returned value (if any).
2884 Contrast this with the @code{return} command (@pxref{Returning,
2885 ,Returning from a function}).
2891 Continue running until a source line past the current line, in the
2892 current stack frame, is reached. This command is used to avoid single
2893 stepping through a loop more than once. It is like the @code{next}
2894 command, except that when @code{until} encounters a jump, it
2895 automatically continues execution until the program counter is greater
2896 than the address of the jump.
2898 This means that when you reach the end of a loop after single stepping
2899 though it, @code{until} makes your program continue execution until it
2900 exits the loop. In contrast, a @code{next} command at the end of a loop
2901 simply steps back to the beginning of the loop, which forces you to step
2902 through the next iteration.
2904 @code{until} always stops your program if it attempts to exit the current
2907 @code{until} may produce somewhat counterintuitive results if the order
2908 of machine code does not match the order of the source lines. For
2909 example, in the following excerpt from a debugging session, the @code{f}
2910 (@code{frame}) command shows that execution is stopped at line
2911 @code{206}; yet when we use @code{until}, we get to line @code{195}:
2915 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
2917 (@value{GDBP}) until
2918 195 for ( ; argc > 0; NEXTARG) @{
2921 This happened because, for execution efficiency, the compiler had
2922 generated code for the loop closure test at the end, rather than the
2923 start, of the loop---even though the test in a C @code{for}-loop is
2924 written before the body of the loop. The @code{until} command appeared
2925 to step back to the beginning of the loop when it advanced to this
2926 expression; however, it has not really gone to an earlier
2927 statement---not in terms of the actual machine code.
2929 @code{until} with no argument works by means of single
2930 instruction stepping, and hence is slower than @code{until} with an
2933 @item until @var{location}
2934 @itemx u @var{location}
2935 Continue running your program until either the specified location is
2936 reached, or the current stack frame returns. @var{location} is any of
2937 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
2938 ,Setting breakpoints}). This form of the command uses breakpoints,
2939 and hence is quicker than @code{until} without an argument.
2945 Execute one machine instruction, then stop and return to the debugger.
2947 It is often useful to do @samp{display/i $pc} when stepping by machine
2948 instructions. This makes @value{GDBN} automatically display the next
2949 instruction to be executed, each time your program stops. @xref{Auto
2950 Display,, Automatic display}.
2952 An argument is a repeat count, as in @code{step}.
2959 Execute one machine instruction, but if it is a function call,
2960 proceed until the function returns.
2962 An argument is a repeat count, as in @code{next}.
2970 A signal is an asynchronous event that can happen in a program. The
2971 operating system defines the possible kinds of signals, and gives each
2972 kind a name and a number. For example, in Unix @code{SIGINT} is the
2973 signal a program gets when you type an interrupt (often @kbd{C-c});
2974 @code{SIGSEGV} is the signal a program gets from referencing a place in
2975 memory far away from all the areas in use; @code{SIGALRM} occurs when
2976 the alarm clock timer goes off (which happens only if your program has
2977 requested an alarm).
2979 @cindex fatal signals
2980 Some signals, including @code{SIGALRM}, are a normal part of the
2981 functioning of your program. Others, such as @code{SIGSEGV}, indicate
2982 errors; these signals are @dfn{fatal} (kill your program immediately) if the
2983 program has not specified in advance some other way to handle the signal.
2984 @code{SIGINT} does not indicate an error in your program, but it is normally
2985 fatal so it can carry out the purpose of the interrupt: to kill the program.
2987 @value{GDBN} has the ability to detect any occurrence of a signal in your
2988 program. You can tell @value{GDBN} in advance what to do for each kind of
2991 @cindex handling signals
2992 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
2993 (so as not to interfere with their role in the functioning of your program)
2994 but to stop your program immediately whenever an error signal happens.
2995 You can change these settings with the @code{handle} command.
2999 @kindex info signals
3000 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3001 handle each one. You can use this to see the signal numbers of all
3002 the defined types of signals.
3004 @item handle @var{signal} @var{keywords}@dots{}
3006 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can be the
3007 number of a signal or its name (with or without the @samp{SIG} at the
3008 beginning). The @var{keywords} say what change to make.
3012 The keywords allowed by the @code{handle} command can be abbreviated.
3013 Their full names are:
3017 @value{GDBN} should not stop your program when this signal happens. It may
3018 still print a message telling you that the signal has come in.
3021 @value{GDBN} should stop your program when this signal happens. This implies
3022 the @code{print} keyword as well.
3025 @value{GDBN} should print a message when this signal happens.
3028 @value{GDBN} should not mention the occurrence of the signal at all. This
3029 implies the @code{nostop} keyword as well.
3032 @value{GDBN} should allow your program to see this signal; your program
3033 can handle the signal, or else it may terminate if the signal is fatal
3037 @value{GDBN} should not allow your program to see this signal.
3041 When a signal stops your program, the signal is not visible until you
3042 continue. Your program sees the signal then, if @code{pass} is in
3043 effect for the signal in question @emph{at that time}. In other words,
3044 after @value{GDBN} reports a signal, you can use the @code{handle}
3045 command with @code{pass} or @code{nopass} to control whether your
3046 program sees that signal when you continue.
3048 You can also use the @code{signal} command to prevent your program from
3049 seeing a signal, or cause it to see a signal it normally would not see,
3050 or to give it any signal at any time. For example, if your program stopped
3051 due to some sort of memory reference error, you might store correct
3052 values into the erroneous variables and continue, hoping to see more
3053 execution; but your program would probably terminate immediately as
3054 a result of the fatal signal once it saw the signal. To prevent this,
3055 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3061 @section Stopping and starting multi-thread programs
3063 When your program has multiple threads (@pxref{Threads,, Debugging
3064 programs with multiple threads}), you can choose whether to set
3065 breakpoints on all threads, or on a particular thread.
3068 @cindex breakpoints and threads
3069 @cindex thread breakpoints
3070 @kindex break @dots{} thread @var{threadno}
3071 @item break @var{linespec} thread @var{threadno}
3072 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3073 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3074 to specify that you only want @value{GDBN} to stop the program when a
3075 particular thread reaches this breakpoint. @var{threadno} is one of the
3076 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3077 column of the @samp{info threads} display.
3079 If you do not specify @samp{thread @var{threadno}} when you set a
3080 breakpoint, the breakpoint applies to @emph{all} threads of your
3083 You can use the @code{thread} qualifier on conditional breakpoints as
3084 well; in this case, place @samp{thread @var{threadno}} before the
3085 breakpoint condition, like this:
3088 (gdb) break frik.c:13 thread 28 if bartab > lim
3092 @cindex stopped threads
3093 @cindex threads, stopped
3094 Whenever your program stops under @value{GDBN} for any reason,
3095 @emph{all} threads of execution stop, not just the current thread. This
3096 allows you to examine the overall state of the program, including
3097 switching between threads, without worrying that things may change
3100 @cindex continuing threads
3101 @cindex threads, continuing
3102 Conversely, whenever you restart the program, @emph{all} threads start
3103 executing. @emph{This is true even when single-stepping} with commands
3104 like @code{step} or @code{next}.
3106 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3107 Since thread scheduling is up to your debugging target's operating
3108 system (not controlled by @value{GDBN}), other threads may
3109 execute more than one statement while the current thread completes a
3110 single step. Moreover, in general other threads stop in the middle of a
3111 statement, rather than at a clean statement boundary, when the program
3114 You might even find your program stopped in another thread after
3115 continuing or even single-stepping. This happens whenever some other
3116 thread runs into a breakpoint, a signal, or an exception before the
3117 first thread completes whatever you requested.
3121 @chapter Examining the Stack
3123 When your program has stopped, the first thing you need to know is where it
3124 stopped and how it got there.
3127 Each time your program performs a function call, the information about
3128 where in your program the call was made from is saved in a block of data
3129 called a @dfn{stack frame}. The frame also contains the arguments of the
3130 call and the local variables of the function that was called. All the
3131 stack frames are allocated in a region of memory called the @dfn{call
3134 When your program stops, the @value{GDBN} commands for examining the
3135 stack allow you to see all of this information.
3137 @cindex selected frame
3138 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3139 @value{GDBN} commands refer implicitly to the selected frame. In
3140 particular, whenever you ask @value{GDBN} for the value of a variable in
3141 your program, the value is found in the selected frame. There are
3142 special @value{GDBN} commands to select whichever frame you are
3145 When your program stops, @value{GDBN} automatically selects the
3146 currently executing frame and describes it briefly as the @code{frame}
3147 command does (@pxref{Frame Info, ,Information about a frame}).
3150 * Frames:: Stack frames
3151 * Backtrace:: Backtraces
3152 * Selection:: Selecting a frame
3153 * Frame Info:: Information on a frame
3155 * MIPS Stack:: MIPS machines and the function stack
3160 @section Stack frames
3164 The call stack is divided up into contiguous pieces called @dfn{stack
3165 frames}, or @dfn{frames} for short; each frame is the data associated
3166 with one call to one function. The frame contains the arguments given
3167 to the function, the function's local variables, and the address at
3168 which the function is executing.
3170 @cindex initial frame
3171 @cindex outermost frame
3172 @cindex innermost frame
3173 When your program is started, the stack has only one frame, that of the
3174 function @code{main}. This is called the @dfn{initial} frame or the
3175 @dfn{outermost} frame. Each time a function is called, a new frame is
3176 made. Each time a function returns, the frame for that function invocation
3177 is eliminated. If a function is recursive, there can be many frames for
3178 the same function. The frame for the function in which execution is
3179 actually occurring is called the @dfn{innermost} frame. This is the most
3180 recently created of all the stack frames that still exist.
3182 @cindex frame pointer
3183 Inside your program, stack frames are identified by their addresses. A
3184 stack frame consists of many bytes, each of which has its own address; each
3185 kind of computer has a convention for choosing one of those bytes whose
3186 address serves as the address of the frame. Usually this address is kept
3187 in a register called the @dfn{frame pointer register} while execution is
3188 going on in that frame.
3190 @cindex frame number
3191 @value{GDBN} assigns numbers to all existing stack frames, starting with
3192 zero for the innermost frame, one for the frame that called it,
3193 and so on upward. These numbers do not really exist in your program;
3194 they are assigned by @value{GDBN} to give you a way of designating stack
3195 frames in @value{GDBN} commands.
3197 @c below produces an acceptable overful hbox. --mew 13aug1993
3198 @cindex frameless execution
3199 Some compilers provide a way to compile functions so that they operate
3200 without stack frames. (For example, the @code{@value{GCC}} option
3201 @samp{-fomit-frame-pointer} generates functions without a frame.)
3202 This is occasionally done with heavily used library functions to save
3203 the frame setup time. @value{GDBN} has limited facilities for dealing
3204 with these function invocations. If the innermost function invocation
3205 has no stack frame, @value{GDBN} nevertheless regards it as though
3206 it had a separate frame, which is numbered zero as usual, allowing
3207 correct tracing of the function call chain. However, @value{GDBN} has
3208 no provision for frameless functions elsewhere in the stack.
3213 A backtrace is a summary of how your program got where it is. It shows one
3214 line per frame, for many frames, starting with the currently executing
3215 frame (frame zero), followed by its caller (frame one), and on up the
3223 Print a backtrace of the entire stack: one line per frame for all
3224 frames in the stack.
3226 You can stop the backtrace at any time by typing the system interrupt
3227 character, normally @kbd{C-c}.
3229 @item backtrace @var{n}
3231 Similar, but print only the innermost @var{n} frames.
3233 @item backtrace -@var{n}
3235 Similar, but print only the outermost @var{n} frames.
3241 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3242 are additional aliases for @code{backtrace}.
3244 Each line in the backtrace shows the frame number and the function name.
3245 The program counter value is also shown---unless you use @code{set
3246 print address off}. The backtrace also shows the source file name and
3247 line number, as well as the arguments to the function. The program
3248 counter value is omitted if it is at the beginning of the code for that
3251 Here is an example of a backtrace. It was made with the command
3252 @samp{bt 3}, so it shows the innermost three frames.
3256 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3258 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3259 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3261 (More stack frames follow...)
3266 The display for frame zero does not begin with a program counter
3267 value, indicating that your program has stopped at the beginning of the
3268 code for line @code{993} of @code{builtin.c}.
3271 @section Selecting a frame
3273 Most commands for examining the stack and other data in your program work on
3274 whichever stack frame is selected at the moment. Here are the commands for
3275 selecting a stack frame; all of them finish by printing a brief description
3276 of the stack frame just selected.
3283 Select frame number @var{n}. Recall that frame zero is the innermost
3284 (currently executing) frame, frame one is the frame that called the
3285 innermost one, and so on. The highest-numbered frame is the one for
3288 @item frame @var{addr}
3290 Select the frame at address @var{addr}. This is useful mainly if the
3291 chaining of stack frames has been damaged by a bug, making it
3292 impossible for @value{GDBN} to assign numbers properly to all frames. In
3293 addition, this can be useful when your program has multiple stacks and
3294 switches between them.
3296 @ifclear H8EXCLUSIVE
3297 On the SPARC architecture, @code{frame} needs two addresses to
3298 select an arbitrary frame: a frame pointer and a stack pointer.
3300 On the MIPS and Alpha architecture, it needs two addresses: a stack
3301 pointer and a program counter.
3303 On the 29k architecture, it needs three addresses: a register stack
3304 pointer, a program counter, and a memory stack pointer.
3305 @c note to future updaters: this is conditioned on a flag
3306 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3307 @c as of 27 Jan 1994.
3312 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3313 advances toward the outermost frame, to higher frame numbers, to frames
3314 that have existed longer. @var{n} defaults to one.
3319 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3320 advances toward the innermost frame, to lower frame numbers, to frames
3321 that were created more recently. @var{n} defaults to one. You may
3322 abbreviate @code{down} as @code{do}.
3325 All of these commands end by printing two lines of output describing the
3326 frame. The first line shows the frame number, the function name, the
3327 arguments, and the source file and line number of execution in that
3328 frame. The second line shows the text of that source line.
3336 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3338 10 read_input_file (argv[i]);
3342 After such a printout, the @code{list} command with no arguments
3343 prints ten lines centered on the point of execution in the frame.
3344 @xref{List, ,Printing source lines}.
3347 @item up-silently @var{n}
3348 @itemx down-silently @var{n}
3349 @kindex down-silently
3351 These two commands are variants of @code{up} and @code{down},
3352 respectively; they differ in that they do their work silently, without
3353 causing display of the new frame. They are intended primarily for use
3354 in @value{GDBN} command scripts, where the output might be unnecessary and
3359 @section Information about a frame
3361 There are several other commands to print information about the selected
3367 When used without any argument, this command does not change which
3368 frame is selected, but prints a brief description of the currently
3369 selected stack frame. It can be abbreviated @code{f}. With an
3370 argument, this command is used to select a stack frame.
3371 @xref{Selection, ,Selecting a frame}.
3377 This command prints a verbose description of the selected stack frame,
3378 including the address of the frame, the addresses of the next frame down
3379 (called by this frame) and the next frame up (caller of this frame), the
3380 language that the source code corresponding to this frame was written in,
3381 the address of the frame's arguments, the program counter saved in it
3382 (the address of execution in the caller frame), and which registers
3383 were saved in the frame. The verbose description is useful when
3384 something has gone wrong that has made the stack format fail to fit
3385 the usual conventions.
3387 @item info frame @var{addr}
3388 @itemx info f @var{addr}
3389 Print a verbose description of the frame at address @var{addr}, without
3390 selecting that frame. The selected frame remains unchanged by this
3391 command. This requires the same kind of address (more than one for some
3392 architectures) that you specify in the @code{frame} command.
3393 @xref{Selection, ,Selecting a frame}.
3397 Print the arguments of the selected frame, each on a separate line.
3401 Print the local variables of the selected frame, each on a separate
3402 line. These are all variables (declared either static or automatic)
3403 accessible at the point of execution of the selected frame.
3408 @cindex catch exceptions
3409 @cindex exception handlers
3410 Print a list of all the exception handlers that are active in the
3411 current stack frame at the current point of execution. To see other
3412 exception handlers, visit the associated frame (using the @code{up},
3413 @code{down}, or @code{frame} commands); then type @code{info catch}.
3414 @xref{Exception Handling, ,Breakpoints and exceptions}.
3420 @section MIPS machines and the function stack
3422 @cindex stack on MIPS
3424 MIPS based computers use an unusual stack frame, which sometimes
3425 requires @value{GDBN} to search backward in the object code to find the
3426 beginning of a function.
3428 @cindex response time, MIPS debugging
3429 To improve response time (especially for embedded applications, where
3430 @value{GDBN} may be restricted to a slow serial line for this search)
3431 you may want to limit the size of this search, using one of these
3433 @c FIXME! So what happens when GDB does *not* find the beginning of a
3436 @cindex @code{heuristic-fence-post} (MIPS)
3438 @item set heuristic-fence-post @var{limit}
3439 Restrict @value{GDBN} to examining at most @var{limit} bytes in its search
3440 for the beginning of a function. A value of @code{0} (the default)
3441 means there is no limit.
3443 @item show heuristic-fence-post
3444 Display the current limit.
3448 These commands are available @emph{only} when @value{GDBN} is configured
3449 for debugging programs on MIPS processors.
3453 @chapter Examining Source Files
3455 @value{GDBN} can print parts of your program's source, since the debugging
3456 information recorded in the program tells @value{GDBN} what source files were
3457 used to build it. When your program stops, @value{GDBN} spontaneously prints
3458 the line where it stopped. Likewise, when you select a stack frame
3459 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3460 execution in that frame has stopped. You can print other portions of
3461 source files by explicit command.
3464 If you use @value{GDBN} through its GNU Emacs interface, you may prefer to use
3465 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under GNU
3470 * List:: Printing source lines
3472 * Search:: Searching source files
3475 * Source Path:: Specifying source directories
3476 * Machine Code:: Source and machine code
3480 @section Printing source lines
3484 To print lines from a source file, use the @code{list} command
3485 (abbreviated @code{l}). There are several ways to specify what part
3486 of the file you want to print.
3488 Here are the forms of the @code{list} command most commonly used:
3491 @item list @var{linenum}
3492 Print lines centered around line number @var{linenum} in the
3493 current source file.
3495 @item list @var{function}
3496 Print lines centered around the beginning of function
3500 Print more lines. If the last lines printed were printed with a
3501 @code{list} command, this prints lines following the last lines
3502 printed; however, if the last line printed was a solitary line printed
3503 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3504 Stack}), this prints lines centered around that line.
3507 Print lines just before the lines last printed.
3510 By default, @value{GDBN} prints ten source lines with any of these forms of
3511 the @code{list} command. You can change this using @code{set listsize}:
3514 @item set listsize @var{count}
3515 @kindex set listsize
3516 Make the @code{list} command display @var{count} source lines (unless
3517 the @code{list} argument explicitly specifies some other number).
3520 @kindex show listsize
3521 Display the number of lines that @code{list} prints.
3524 Repeating a @code{list} command with @key{RET} discards the argument,
3525 so it is equivalent to typing just @code{list}. This is more useful
3526 than listing the same lines again. An exception is made for an
3527 argument of @samp{-}; that argument is preserved in repetition so that
3528 each repetition moves up in the source file.
3531 In general, the @code{list} command expects you to supply zero, one or two
3532 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3533 of writing them but the effect is always to specify some source line.
3534 Here is a complete description of the possible arguments for @code{list}:
3537 @item list @var{linespec}
3538 Print lines centered around the line specified by @var{linespec}.
3540 @item list @var{first},@var{last}
3541 Print lines from @var{first} to @var{last}. Both arguments are
3544 @item list ,@var{last}
3545 Print lines ending with @var{last}.
3547 @item list @var{first},
3548 Print lines starting with @var{first}.
3551 Print lines just after the lines last printed.
3554 Print lines just before the lines last printed.
3557 As described in the preceding table.
3560 Here are the ways of specifying a single source line---all the
3565 Specifies line @var{number} of the current source file.
3566 When a @code{list} command has two linespecs, this refers to
3567 the same source file as the first linespec.
3570 Specifies the line @var{offset} lines after the last line printed.
3571 When used as the second linespec in a @code{list} command that has
3572 two, this specifies the line @var{offset} lines down from the
3576 Specifies the line @var{offset} lines before the last line printed.
3578 @item @var{filename}:@var{number}
3579 Specifies line @var{number} in the source file @var{filename}.
3581 @item @var{function}
3582 @c FIXME: "of the open-brace" is C-centric. When we add other langs...
3583 Specifies the line of the open-brace that begins the body of the
3584 function @var{function}.
3586 @item @var{filename}:@var{function}
3587 Specifies the line of the open-brace that begins the body of the
3588 function @var{function} in the file @var{filename}. You only need the
3589 file name with a function name to avoid ambiguity when there are
3590 identically named functions in different source files.
3592 @item *@var{address}
3593 Specifies the line containing the program address @var{address}.
3594 @var{address} may be any expression.
3599 @section Searching source files
3601 @kindex reverse-search
3603 There are two commands for searching through the current source file for a
3607 @item forward-search @var{regexp}
3608 @itemx search @var{regexp}
3610 @kindex forward-search
3611 The command @samp{forward-search @var{regexp}} checks each line,
3612 starting with the one following the last line listed, for a match for
3613 @var{regexp}. It lists the line that is found. You can use
3614 synonym @samp{search @var{regexp}} or abbreviate the command name as
3617 @item reverse-search @var{regexp}
3618 The command @samp{reverse-search @var{regexp}} checks each line, starting
3619 with the one before the last line listed and going backward, for a match
3620 for @var{regexp}. It lists the line that is found. You can abbreviate
3621 this command as @code{rev}.
3626 @section Specifying source directories
3629 @cindex directories for source files
3630 Executable programs sometimes do not record the directories of the source
3631 files from which they were compiled, just the names. Even when they do,
3632 the directories could be moved between the compilation and your debugging
3633 session. @value{GDBN} has a list of directories to search for source files;
3634 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
3635 it tries all the directories in the list, in the order they are present
3636 in the list, until it finds a file with the desired name. Note that
3637 the executable search path is @emph{not} used for this purpose. Neither is
3638 the current working directory, unless it happens to be in the source
3641 If @value{GDBN} cannot find a source file in the source path, and the
3642 object program records a directory, @value{GDBN} tries that directory
3643 too. If the source path is empty, and there is no record of the
3644 compilation directory, @value{GDBN} looks in the current directory as a
3647 Whenever you reset or rearrange the source path, @value{GDBN} clears out
3648 any information it has cached about where source files are found and where
3649 each line is in the file.
3652 When you start @value{GDBN}, its source path is empty.
3653 To add other directories, use the @code{directory} command.
3656 @item directory @var{dirname} @dots{}
3657 Add directory @var{dirname} to the front of the source path. Several
3658 directory names may be given to this command, separated by @samp{:} or
3659 whitespace. You may specify a directory that is already in the source
3660 path; this moves it forward, so @value{GDBN} searches it sooner.
3666 @cindex compilation directory
3667 @cindex current directory
3668 @cindex working directory
3669 @cindex directory, current
3670 @cindex directory, compilation
3671 You can use the string @samp{$cdir} to refer to the compilation
3672 directory (if one is recorded), and @samp{$cwd} to refer to the current
3673 working directory. @samp{$cwd} is not the same as @samp{.}---the former
3674 tracks the current working directory as it changes during your @value{GDBN}
3675 session, while the latter is immediately expanded to the current
3676 directory at the time you add an entry to the source path.
3679 Reset the source path to empty again. This requires confirmation.
3681 @c RET-repeat for @code{directory} is explicitly disabled, but since
3682 @c repeating it would be a no-op we do not say that. (thanks to RMS)
3684 @item show directories
3685 @kindex show directories
3686 Print the source path: show which directories it contains.
3689 If your source path is cluttered with directories that are no longer of
3690 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
3691 versions of source. You can correct the situation as follows:
3695 Use @code{directory} with no argument to reset the source path to empty.
3698 Use @code{directory} with suitable arguments to reinstall the
3699 directories you want in the source path. You can add all the
3700 directories in one command.
3704 @section Source and machine code
3706 You can use the command @code{info line} to map source lines to program
3707 addresses (and vice versa), and the command @code{disassemble} to display
3708 a range of addresses as machine instructions.
3711 @item info line @var{linespec}
3713 Print the starting and ending addresses of the compiled code for
3714 source line @var{linespec}. You can specify source lines in any of
3715 the ways understood by the @code{list} command (@pxref{List, ,Printing
3719 For example, we can use @code{info line} to discover the location of
3720 the object code for the first line of function
3721 @code{m4_changequote}:
3724 (@value{GDBP}) info line m4_changecom
3725 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3729 We can also inquire (using @code{*@var{addr}} as the form for
3730 @var{linespec}) what source line covers a particular address:
3732 (@value{GDBP}) info line *0x63ff
3733 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3736 @cindex @code{$_} and @code{info line}
3737 After @code{info line}, the default address for the @code{x} command
3738 is changed to the starting address of the line, so that @samp{x/i} is
3739 sufficient to begin examining the machine code (@pxref{Memory,
3740 ,Examining memory}). Also, this address is saved as the value of the
3741 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
3747 @cindex assembly instructions
3748 @cindex instructions, assembly
3749 @cindex machine instructions
3750 @cindex listing machine instructions
3751 This specialized command dumps a range of memory as machine
3752 instructions. The default memory range is the function surrounding the
3753 program counter of the selected frame. A single argument to this
3754 command is a program counter value; @value{GDBN} dumps the function
3755 surrounding this value. Two arguments specify a range of addresses
3756 (first inclusive, second exclusive) to dump.
3759 @ifclear H8EXCLUSIVE
3760 We can use @code{disassemble} to inspect the object code
3761 range shown in the last @code{info line} example (the example
3762 shows SPARC machine instructions):
3766 (@value{GDBP}) disas 0x63e4 0x6404
3767 Dump of assembler code from 0x63e4 to 0x6404:
3768 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3769 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3770 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3771 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3772 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3773 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3774 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3775 0x6400 <builtin_init+5368>: nop
3776 End of assembler dump.
3781 For example, here is the beginning of the output for the
3782 disassembly of a function @code{fact}:
3786 (@value{GDBP}) disas fact
3787 Dump of assembler code for function fact:
3789 0x802c <fact>: 6d f2 mov.w r2,@@-r7
3790 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
3791 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
3792 0x8032 <fact+6>: 0d 76 mov.w r7,r6
3793 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
3794 0x8038 <fact+12> 19 11 sub.w r1,r1
3802 @chapter Examining Data
3804 @cindex printing data
3805 @cindex examining data
3808 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
3809 @c document because it is nonstandard... Under Epoch it displays in a
3810 @c different window or something like that.
3811 The usual way to examine data in your program is with the @code{print}
3812 command (abbreviated @code{p}), or its synonym @code{inspect}.
3814 It evaluates and prints the value of an expression of the language your
3815 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
3820 @item print @var{exp}
3821 @itemx print /@var{f} @var{exp}
3822 @var{exp} is an expression (in the source language). By default the
3823 value of @var{exp} is printed in a format appropriate to its data type;
3824 you can choose a different format by specifying @samp{/@var{f}}, where
3825 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
3829 @itemx print /@var{f}
3830 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
3831 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
3832 conveniently inspect the same value in an alternative format.
3835 A more low-level way of examining data is with the @code{x} command.
3836 It examines data in memory at a specified address and prints it in a
3837 specified format. @xref{Memory, ,Examining memory}.
3839 If you are interested in information about types, or about how the fields
3844 are declared, use the @code{ptype @var{exp}}
3845 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
3848 * Expressions:: Expressions
3849 * Variables:: Program variables
3850 * Arrays:: Artificial arrays
3851 * Output Formats:: Output formats
3852 * Memory:: Examining memory
3853 * Auto Display:: Automatic display
3854 * Print Settings:: Print settings
3855 * Value History:: Value history
3856 * Convenience Vars:: Convenience variables
3857 * Registers:: Registers
3859 * Floating Point Hardware:: Floating point hardware
3864 @section Expressions
3867 @code{print} and many other @value{GDBN} commands accept an expression and
3868 compute its value. Any kind of constant, variable or operator defined
3869 by the programming language you are using is valid in an expression in
3870 @value{GDBN}. This includes conditional expressions, function calls, casts
3871 and string constants. It unfortunately does not include symbols defined
3872 by preprocessor @code{#define} commands.
3875 Because C is so widespread, most of the expressions shown in examples in
3876 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
3877 Languages}, for information on how to use expressions in other
3880 In this section, we discuss operators that you can use in @value{GDBN}
3881 expressions regardless of your programming language.
3883 Casts are supported in all languages, not just in C, because it is so
3884 useful to cast a number into a pointer so as to examine a structure
3885 at that address in memory.
3886 @c FIXME: casts supported---Mod2 true?
3889 @value{GDBN} supports these operators in addition to those of programming
3894 @samp{@@} is a binary operator for treating parts of memory as arrays.
3895 @xref{Arrays, ,Artificial arrays}, for more information.
3898 @samp{::} allows you to specify a variable in terms of the file or
3899 function where it is defined. @xref{Variables, ,Program variables}.
3901 @item @{@var{type}@} @var{addr}
3902 @cindex @{@var{type}@}
3903 @cindex type casting memory
3904 @cindex memory, viewing as typed object
3905 @cindex casts, to view memory
3906 Refers to an object of type @var{type} stored at address @var{addr} in
3907 memory. @var{addr} may be any expression whose value is an integer or
3908 pointer (but parentheses are required around binary operators, just as in
3909 a cast). This construct is allowed regardless of what kind of data is
3910 normally supposed to reside at @var{addr}.
3914 @section Program variables
3916 The most common kind of expression to use is the name of a variable
3919 Variables in expressions are understood in the selected stack frame
3920 (@pxref{Selection, ,Selecting a frame}); they must either be global
3921 (or static) or be visible according to the scope rules of the
3922 programming language from the point of execution in that frame. This
3923 means that in the function
3938 you can examine and use the variable @code{a} whenever your program is
3939 executing within the function @code{foo}, but you can only use or
3940 examine the variable @code{b} while your program is executing inside
3941 the block where @code{b} is declared.
3943 @cindex variable name conflict
3944 There is an exception: you can refer to a variable or function whose
3945 scope is a single source file even if the current execution point is not
3946 in this file. But it is possible to have more than one such variable or
3947 function with the same name (in different source files). If that
3948 happens, referring to that name has unpredictable effects. If you wish,
3949 you can specify a static variable in a particular function or file,
3950 using the colon-colon notation:
3954 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
3958 @var{file}::@var{variable}
3959 @var{function}::@var{variable}
3963 Here @var{file} or @var{function} is the name of the context for the
3964 static @var{variable}. In the case of file names, you can use quotes to
3965 make sure @value{GDBN} parses the file name as a single word---for example,
3966 to print a global value of @code{x} defined in @file{f2.c}:
3969 (@value{GDBP}) p 'f2.c'::x
3973 @cindex C++ scope resolution
3974 This use of @samp{::} is very rarely in conflict with the very similar
3975 use of the same notation in C++. @value{GDBN} also supports use of the C++
3976 scope resolution operator in @value{GDBN} expressions.
3977 @c FIXME: Um, so what happens in one of those rare cases where it's in
3981 @cindex wrong values
3982 @cindex variable values, wrong
3984 @emph{Warning:} Occasionally, a local variable may appear to have the
3985 wrong value at certain points in a function---just after entry to a new
3986 scope, and just before exit.
3988 You may see this problem when you are stepping by machine instructions.
3989 This is because on most machines, it takes more than one instruction to
3990 set up a stack frame (including local variable definitions); if you are
3991 stepping by machine instructions, variables may appear to have the wrong
3992 values until the stack frame is completely built. On exit, it usually
3993 also takes more than one machine instruction to destroy a stack frame;
3994 after you begin stepping through that group of instructions, local
3995 variable definitions may be gone.
3998 @section Artificial arrays
4000 @cindex artificial array
4002 It is often useful to print out several successive objects of the
4003 same type in memory; a section of an array, or an array of
4004 dynamically determined size for which only a pointer exists in the
4007 You can do this by referring to a contiguous span of memory as an
4008 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4009 operand of @samp{@@} should be the first element of the desired array,
4010 as an individual object. The right operand should be the desired length
4011 of the array. The result is an array value whose elements are all of
4012 the type of the left argument. The first element is actually the left
4013 argument; the second element comes from bytes of memory immediately
4014 following those that hold the first element, and so on. Here is an
4015 example. If a program says
4018 int *array = (int *) malloc (len * sizeof (int));
4022 you can print the contents of @code{array} with
4028 The left operand of @samp{@@} must reside in memory. Array values made
4029 with @samp{@@} in this way behave just like other arrays in terms of
4030 subscripting, and are coerced to pointers when used in expressions.
4031 Artificial arrays most often appear in expressions via the value history
4032 (@pxref{Value History, ,Value history}), after printing one out.
4034 Sometimes the artificial array mechanism is not quite enough; in
4035 moderately complex data structures, the elements of interest may not
4036 actually be adjacent---for example, if you are interested in the values
4037 of pointers in an array. One useful work-around in this situation is
4038 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4039 variables}) as a counter in an expression that prints the first
4040 interesting value, and then repeat that expression via @key{RET}. For
4041 instance, suppose you have an array @code{dtab} of pointers to
4042 structures, and you are interested in the values of a field @code{fv}
4043 in each structure. Here is an example of what you might type:
4053 @node Output Formats
4054 @section Output formats
4056 @cindex formatted output
4057 @cindex output formats
4058 By default, @value{GDBN} prints a value according to its data type. Sometimes
4059 this is not what you want. For example, you might want to print a number
4060 in hex, or a pointer in decimal. Or you might want to view data in memory
4061 at a certain address as a character string or as an instruction. To do
4062 these things, specify an @dfn{output format} when you print a value.
4064 The simplest use of output formats is to say how to print a value
4065 already computed. This is done by starting the arguments of the
4066 @code{print} command with a slash and a format letter. The format
4067 letters supported are:
4071 Regard the bits of the value as an integer, and print the integer in
4075 Print as integer in signed decimal.
4078 Print as integer in unsigned decimal.
4081 Print as integer in octal.
4084 Print as integer in binary. The letter @samp{t} stands for ``two''.
4085 @footnote{@samp{b} cannot be used because these format letters are also
4086 used with the @code{x} command, where @samp{b} stands for ``byte'';
4087 @pxref{Memory,,Examining memory}.}
4090 @cindex unknown address, locating
4091 Print as an address, both absolute in hexadecimal and as an offset from
4092 the nearest preceding symbol. You can use this format used to discover
4093 where (in what function) an unknown address is located:
4096 (@value{GDBP}) p/a 0x54320
4097 $3 = 0x54320 <_initialize_vx+396>
4101 Regard as an integer and print it as a character constant.
4104 Regard the bits of the value as a floating point number and print
4105 using typical floating point syntax.
4108 For example, to print the program counter in hex (@pxref{Registers}), type
4115 Note that no space is required before the slash; this is because command
4116 names in @value{GDBN} cannot contain a slash.
4118 To reprint the last value in the value history with a different format,
4119 you can use the @code{print} command with just a format and no
4120 expression. For example, @samp{p/x} reprints the last value in hex.
4123 @section Examining memory
4125 You can use the command @code{x} (for ``examine'') to examine memory in
4126 any of several formats, independently of your program's data types.
4128 @cindex examining memory
4131 @item x/@var{nfu} @var{addr}
4134 Use the @code{x} command to examine memory.
4137 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4138 much memory to display and how to format it; @var{addr} is an
4139 expression giving the address where you want to start displaying memory.
4140 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4141 Several commands set convenient defaults for @var{addr}.
4144 @item @var{n}, the repeat count
4145 The repeat count is a decimal integer; the default is 1. It specifies
4146 how much memory (counting by units @var{u}) to display.
4147 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4150 @item @var{f}, the display format
4151 The display format is one of the formats used by @code{print},
4152 or @samp{s} (null-terminated string) or @samp{i} (machine instruction).
4153 The default is @samp{x} (hexadecimal) initially, or the format from the
4154 last time you used either @code{x} or @code{print}.
4156 @item @var{u}, the unit size
4157 The unit size is any of
4163 Halfwords (two bytes).
4165 Words (four bytes). This is the initial default.
4167 Giant words (eight bytes).
4170 Each time you specify a unit size with @code{x}, that size becomes the
4171 default unit the next time you use @code{x}. (For the @samp{s} and
4172 @samp{i} formats, the unit size is ignored and is normally not written.)
4174 @item @var{addr}, starting display address
4175 @var{addr} is the address where you want @value{GDBN} to begin displaying
4176 memory. The expression need not have a pointer value (though it may);
4177 it is always interpreted as an integer address of a byte of memory.
4178 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4179 @var{addr} is usually just after the last address examined---but several
4180 other commands also set the default address: @code{info breakpoints} (to
4181 the address of the last breakpoint listed), @code{info line} (to the
4182 starting address of a line), and @code{print} (if you use it to display
4183 a value from memory).
4186 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4187 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4188 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4189 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4190 @pxref{Registers}) in hexadecimal (@samp{x}).
4192 Since the letters indicating unit sizes are all distinct from the
4193 letters specifying output formats, you do not have to remember whether
4194 unit size or format comes first; either order works. The output
4195 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4196 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4198 Even though the unit size @var{u} is ignored for the formats @samp{s}
4199 and @samp{i}, you might still want to use a count @var{n}; for example,
4200 @samp{3i} specifies that you want to see three machine instructions,
4201 including any operands. The command @code{disassemble} gives an
4202 alternative way of inspecting machine instructions; @pxref{Machine
4203 Code,,Source and machine code}.
4205 All the defaults for the arguments to @code{x} are designed to make it
4206 easy to continue scanning memory with minimal specifications each time
4207 you use @code{x}. For example, after you have inspected three machine
4208 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4209 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4210 the repeat count @var{n} is used again; the other arguments default as
4211 for successive uses of @code{x}.
4213 @cindex @code{$_}, @code{$__}, and value history
4214 The addresses and contents printed by the @code{x} command are not saved
4215 in the value history because there is often too much of them and they
4216 would get in the way. Instead, @value{GDBN} makes these values available for
4217 subsequent use in expressions as values of the convenience variables
4218 @code{$_} and @code{$__}. After an @code{x} command, the last address
4219 examined is available for use in expressions in the convenience variable
4220 @code{$_}. The contents of that address, as examined, are available in
4221 the convenience variable @code{$__}.
4223 If the @code{x} command has a repeat count, the address and contents saved
4224 are from the last memory unit printed; this is not the same as the last
4225 address printed if several units were printed on the last line of output.
4228 @section Automatic display
4229 @cindex automatic display
4230 @cindex display of expressions
4232 If you find that you want to print the value of an expression frequently
4233 (to see how it changes), you might want to add it to the @dfn{automatic
4234 display list} so that @value{GDBN} prints its value each time your program stops.
4235 Each expression added to the list is given a number to identify it;
4236 to remove an expression from the list, you specify that number.
4237 The automatic display looks like this:
4241 3: bar[5] = (struct hack *) 0x3804
4245 This display shows item numbers, expressions and their current values. As with
4246 displays you request manually using @code{x} or @code{print}, you can
4247 specify the output format you prefer; in fact, @code{display} decides
4248 whether to use @code{print} or @code{x} depending on how elaborate your
4249 format specification is---it uses @code{x} if you specify a unit size,
4250 or one of the two formats (@samp{i} and @samp{s}) that are only
4251 supported by @code{x}; otherwise it uses @code{print}.
4254 @item display @var{exp}
4256 Add the expression @var{exp} to the list of expressions to display
4257 each time your program stops. @xref{Expressions, ,Expressions}.
4259 @code{display} does not repeat if you press @key{RET} again after using it.
4261 @item display/@var{fmt} @var{exp}
4262 For @var{fmt} specifying only a display format and not a size or
4263 count, add the expression @var{exp} to the auto-display list but
4264 arrange to display it each time in the specified format @var{fmt}.
4265 @xref{Output Formats,,Output formats}.
4267 @item display/@var{fmt} @var{addr}
4268 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4269 number of units, add the expression @var{addr} as a memory address to
4270 be examined each time your program stops. Examining means in effect
4271 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4274 For example, @samp{display/i $pc} can be helpful, to see the machine
4275 instruction about to be executed each time execution stops (@samp{$pc}
4276 is a common name for the program counter; @pxref{Registers}).
4279 @item undisplay @var{dnums}@dots{}
4280 @itemx delete display @var{dnums}@dots{}
4281 @kindex delete display
4283 Remove item numbers @var{dnums} from the list of expressions to display.
4285 @code{undisplay} does not repeat if you press @key{RET} after using it.
4286 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4288 @item disable display @var{dnums}@dots{}
4289 @kindex disable display
4290 Disable the display of item numbers @var{dnums}. A disabled display
4291 item is not printed automatically, but is not forgotten. It may be
4292 enabled again later.
4294 @item enable display @var{dnums}@dots{}
4295 @kindex enable display
4296 Enable display of item numbers @var{dnums}. It becomes effective once
4297 again in auto display of its expression, until you specify otherwise.
4300 Display the current values of the expressions on the list, just as is
4301 done when your program stops.
4304 @kindex info display
4305 Print the list of expressions previously set up to display
4306 automatically, each one with its item number, but without showing the
4307 values. This includes disabled expressions, which are marked as such.
4308 It also includes expressions which would not be displayed right now
4309 because they refer to automatic variables not currently available.
4312 If a display expression refers to local variables, then it does not make
4313 sense outside the lexical context for which it was set up. Such an
4314 expression is disabled when execution enters a context where one of its
4315 variables is not defined. For example, if you give the command
4316 @code{display last_char} while inside a function with an argument
4317 @code{last_char}, @value{GDBN} displays this argument while your program
4318 continues to stop inside that function. When it stops elsewhere---where
4319 there is no variable @code{last_char}---the display is disabled
4320 automatically. The next time your program stops where @code{last_char}
4321 is meaningful, you can enable the display expression once again.
4323 @node Print Settings
4324 @section Print settings
4326 @cindex format options
4327 @cindex print settings
4328 @value{GDBN} provides the following ways to control how arrays, structures,
4329 and symbols are printed.
4332 These settings are useful for debugging programs in any language:
4335 @item set print address
4336 @itemx set print address on
4337 @kindex set print address
4338 @value{GDBN} prints memory addresses showing the location of stack
4339 traces, structure values, pointer values, breakpoints, and so forth,
4340 even when it also displays the contents of those addresses. The default
4341 is @code{on}. For example, this is what a stack frame display looks like, with
4342 @code{set print address on}:
4347 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4349 530 if (lquote != def_lquote)
4353 @item set print address off
4354 Do not print addresses when displaying their contents. For example,
4355 this is the same stack frame displayed with @code{set print address off}:
4359 (@value{GDBP}) set print addr off
4361 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4362 530 if (lquote != def_lquote)
4366 You can use @samp{set print address off} to eliminate all machine
4367 dependent displays from the @value{GDBN} interface. For example, with
4368 @code{print address off}, you should get the same text for backtraces on
4369 all machines---whether or not they involve pointer arguments.
4371 @item show print address
4372 @kindex show print address
4373 Show whether or not addresses are to be printed.
4376 When @value{GDBN} prints a symbolic address, it normally prints the
4377 closest earlier symbol plus an offset. If that symbol does not uniquely
4378 identify the address (for example, it is a name whose scope is a single
4379 source file), you may need to disambiguate. One way to do this is with
4380 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4381 you can set @value{GDBN} to print the source file and line number when
4382 it prints a symbolic address:
4385 @item set print symbol-filename on
4386 @kindex set print symbol-filename
4387 Tell @value{GDBN} to print the source file name and line number of a
4388 symbol in the symbolic form of an address.
4390 @item set print symbol-filename off
4391 Do not print source file name and line number of a symbol. This is the
4394 @item show print symbol-filename
4395 @kindex show print symbol-filename
4396 Show whether or not @value{GDBN} will print the source file name and
4397 line number of a symbol in the symbolic form of an address.
4400 Another situation where it is helpful to show symbol filenames and line
4401 numbers is when disassembling code; @value{GDBN} shows you the line
4402 number and source file that corresponds to each instruction.
4404 Also, you may wish to see the symbolic form only if the address being
4405 printed is reasonably close to the closest earlier symbol:
4408 @item set print max-symbolic-offset @var{max-offset}
4409 @kindex set print max-symbolic-offset
4410 Tell @value{GDBN} to only display the symbolic form of an address if the
4411 offset between the closest earlier symbol and the address is less than
4412 @var{max-offset}. The default is 0, which means to always print the
4413 symbolic form of an address, if any symbol precedes it.
4415 @item show print max-symbolic-offset
4416 @kindex show print max-symbolic-offset
4417 Ask how large the maximum offset is that @value{GDBN} prints in a
4421 Sometimes @value{GDBN} can tell you more about an address if it does an
4422 extensive search of its symbol information. The default is to provide
4423 a quick symbolic display that is usually correct, but which may not give
4424 the most useful answer when working in some object file formats. If
4425 you are not getting the information you need, try:
4428 @item set print fast-symbolic-addr off
4429 @kindex set print fast-symbolic-addr
4430 Search all symbol information when displaying an address symbolically.
4431 This setting may display more information about static variables, for
4432 example, but also takes longer.
4434 @item set print fast-symbolic-addr
4435 @item set print fast-symbolic-addr on
4436 Search only the ``minimal symbol information'' when displaying symbolic
4437 information about an address. This is the default.
4439 @item show print fast-symbolic-addr
4440 @kindex show print fast-symbolic-addr
4441 Ask whether @value{GDBN} is using a fast or slow method of printing
4445 @cindex wild pointer, interpreting
4446 @cindex pointer, finding referent
4447 If you have a pointer and you are not sure where it points, try
4448 @samp{set print symbol-filename on} and @samp{set print
4449 fast-symbolic-addr off}. Then you can determine the name and source
4450 file location of the variable where it points, using @samp{p/a
4451 @var{pointer}}. This interprets the address in symbolic form. For
4452 example, here @value{GDBN} shows that a variable @code{ptt} points at
4453 another variable @code{t}, defined in @file{hi2.c}:
4456 (@value{GDBP}) set print fast-symbolic-addr off
4457 (@value{GDBP}) set print symbol-filename on
4458 (@value{GDBP}) p/a ptt
4459 $4 = 0xe008 <t in hi2.c>
4463 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
4464 does not show the symbol name and filename of the referent, even with
4465 the appropriate @code{set print} options turned on.
4468 Other settings control how different kinds of objects are printed:
4471 @item set print array
4472 @itemx set print array on
4473 @kindex set print array
4474 Pretty-print arrays. This format is more convenient to read,
4475 but uses more space. The default is off.
4477 @item set print array off
4478 Return to compressed format for arrays.
4480 @item show print array
4481 @kindex show print array
4482 Show whether compressed or pretty format is selected for displaying
4485 @item set print elements @var{number-of-elements}
4486 @kindex set print elements
4487 If @value{GDBN} is printing a large array, it stops printing after it has
4488 printed the number of elements set by the @code{set print elements} command.
4489 This limit also applies to the display of strings.
4490 Setting the number of elements to zero means that the printing is unlimited.
4492 @item show print elements
4493 @kindex show print elements
4494 Display the number of elements of a large array that @value{GDBN} prints
4495 before losing patience.
4497 @item set print pretty on
4498 @kindex set print pretty
4499 Cause @value{GDBN} to print structures in an indented format with one member per
4515 @item set print pretty off
4516 Cause @value{GDBN} to print structures in a compact format, like this:
4520 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4521 meat = 0x54 "Pork"@}
4526 This is the default format.
4528 @item show print pretty
4529 @kindex show print pretty
4530 Show which format @value{GDBN} is using to print structures.
4532 @item set print sevenbit-strings on
4533 @kindex set print sevenbit-strings
4534 Print using only seven-bit characters; if this option is set,
4535 @value{GDBN} displays any eight-bit characters (in strings or
4536 character values) using the notation @code{\}@var{nnn}. This setting is
4537 best if you are working in English (@sc{ascii}) and you use the
4538 high-order bit of characters as a marker or ``meta'' bit.
4540 @item set print sevenbit-strings off
4541 Print full eight-bit characters. This allows the use of more
4542 international character sets, and is the default.
4544 @item show print sevenbit-strings
4545 @kindex show print sevenbit-strings
4546 Show whether or not @value{GDBN} is printing only seven-bit characters.
4548 @item set print union on
4549 @kindex set print union
4550 Tell @value{GDBN} to print unions which are contained in structures. This is the
4553 @item set print union off
4554 Tell @value{GDBN} not to print unions which are contained in structures.
4556 @item show print union
4557 @kindex show print union
4558 Ask @value{GDBN} whether or not it will print unions which are contained in
4561 For example, given the declarations
4564 typedef enum @{Tree, Bug@} Species;
4565 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
4566 typedef enum @{Caterpillar, Cocoon, Butterfly@}
4577 struct thing foo = @{Tree, @{Acorn@}@};
4581 with @code{set print union on} in effect @samp{p foo} would print
4584 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
4588 and with @code{set print union off} in effect it would print
4591 $1 = @{it = Tree, form = @{...@}@}
4598 These settings are of interest when debugging C++ programs:
4601 @item set print demangle
4602 @itemx set print demangle on
4603 @kindex set print demangle
4604 Print C++ names in their source form rather than in the encoded
4605 (``mangled'') form passed to the assembler and linker for type-safe
4606 linkage. The default is @samp{on}.
4608 @item show print demangle
4609 @kindex show print demangle
4610 Show whether C++ names are printed in mangled or demangled form.
4612 @item set print asm-demangle
4613 @itemx set print asm-demangle on
4614 @kindex set print asm-demangle
4615 Print C++ names in their source form rather than their mangled form, even
4616 in assembler code printouts such as instruction disassemblies.
4619 @item show print asm-demangle
4620 @kindex show print asm-demangle
4621 Show whether C++ names in assembly listings are printed in mangled
4624 @item set demangle-style @var{style}
4625 @kindex set demangle-style
4626 @cindex C++ symbol decoding style
4627 @cindex symbol decoding style, C++
4628 Choose among several encoding schemes used by different compilers to
4629 represent C++ names. The choices for @var{style} are currently:
4633 Allow @value{GDBN} to choose a decoding style by inspecting your program.
4636 Decode based on the GNU C++ compiler (@code{g++}) encoding algorithm.
4639 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
4642 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
4643 @strong{Warning:} this setting alone is not sufficient to allow
4644 debugging @code{cfront}-generated executables. @value{GDBN} would
4645 require further enhancement to permit that.
4648 @item show demangle-style
4649 @kindex show demangle-style
4650 Display the encoding style currently in use for decoding C++ symbols.
4652 @item set print object
4653 @itemx set print object on
4654 @kindex set print object
4655 When displaying a pointer to an object, identify the @emph{actual}
4656 (derived) type of the object rather than the @emph{declared} type, using
4657 the virtual function table.
4659 @item set print object off
4660 Display only the declared type of objects, without reference to the
4661 virtual function table. This is the default setting.
4663 @item show print object
4664 @kindex show print object
4665 Show whether actual, or declared, object types are displayed.
4667 @item set print vtbl
4668 @itemx set print vtbl on
4669 @kindex set print vtbl
4670 Pretty print C++ virtual function tables. The default is off.
4672 @item set print vtbl off
4673 Do not pretty print C++ virtual function tables.
4675 @item show print vtbl
4676 @kindex show print vtbl
4677 Show whether C++ virtual function tables are pretty printed, or not.
4682 @section Value history
4684 @cindex value history
4685 Values printed by the @code{print} command are saved in the @value{GDBN} @dfn{value
4686 history} so that you can refer to them in other expressions. Values are
4687 kept until the symbol table is re-read or discarded (for example with
4688 the @code{file} or @code{symbol-file} commands). When the symbol table
4689 changes, the value history is discarded, since the values may contain
4690 pointers back to the types defined in the symbol table.
4694 @cindex history number
4695 The values printed are given @dfn{history numbers} by which you can
4696 refer to them. These are successive integers starting with one.
4697 @code{print} shows you the history number assigned to a value by
4698 printing @samp{$@var{num} = } before the value; here @var{num} is the
4701 To refer to any previous value, use @samp{$} followed by the value's
4702 history number. The way @code{print} labels its output is designed to
4703 remind you of this. Just @code{$} refers to the most recent value in
4704 the history, and @code{$$} refers to the value before that.
4705 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
4706 is the value just prior to @code{$$}, @code{$$1} is equivalent to
4707 @code{$$}, and @code{$$0} is equivalent to @code{$}.
4709 For example, suppose you have just printed a pointer to a structure and
4710 want to see the contents of the structure. It suffices to type
4716 If you have a chain of structures where the component @code{next} points
4717 to the next one, you can print the contents of the next one with this:
4724 You can print successive links in the chain by repeating this
4725 command---which you can do by just typing @key{RET}.
4727 Note that the history records values, not expressions. If the value of
4728 @code{x} is 4 and you type these commands:
4736 then the value recorded in the value history by the @code{print} command
4737 remains 4 even though the value of @code{x} has changed.
4742 Print the last ten values in the value history, with their item numbers.
4743 This is like @samp{p@ $$9} repeated ten times, except that @code{show
4744 values} does not change the history.
4746 @item show values @var{n}
4747 Print ten history values centered on history item number @var{n}.
4750 Print ten history values just after the values last printed. If no more
4751 values are available, produces no display.
4754 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
4755 same effect as @samp{show values +}.
4757 @node Convenience Vars
4758 @section Convenience variables
4760 @cindex convenience variables
4761 @value{GDBN} provides @dfn{convenience variables} that you can use within
4762 @value{GDBN} to hold on to a value and refer to it later. These variables
4763 exist entirely within @value{GDBN}; they are not part of your program, and
4764 setting a convenience variable has no direct effect on further execution
4765 of your program. That is why you can use them freely.
4767 Convenience variables are prefixed with @samp{$}. Any name preceded by
4768 @samp{$} can be used for a convenience variable, unless it is one of
4769 the predefined machine-specific register names (@pxref{Registers}).
4770 (Value history references, in contrast, are @emph{numbers} preceded
4771 by @samp{$}. @xref{Value History, ,Value history}.)
4773 You can save a value in a convenience variable with an assignment
4774 expression, just as you would set a variable in your program.
4778 set $foo = *object_ptr
4782 would save in @code{$foo} the value contained in the object pointed to by
4785 Using a convenience variable for the first time creates it, but its
4786 value is @code{void} until you assign a new value. You can alter the
4787 value with another assignment at any time.
4789 Convenience variables have no fixed types. You can assign a convenience
4790 variable any type of value, including structures and arrays, even if
4791 that variable already has a value of a different type. The convenience
4792 variable, when used as an expression, has the type of its current value.
4795 @item show convenience
4796 @kindex show convenience
4797 Print a list of convenience variables used so far, and their values.
4798 Abbreviated @code{show con}.
4801 One of the ways to use a convenience variable is as a counter to be
4802 incremented or a pointer to be advanced. For example, to print
4803 a field from successive elements of an array of structures:
4807 print bar[$i++]->contents
4808 @i{@dots{} repeat that command by typing @key{RET}.}
4811 Some convenience variables are created automatically by @value{GDBN} and given
4812 values likely to be useful.
4817 The variable @code{$_} is automatically set by the @code{x} command to
4818 the last address examined (@pxref{Memory, ,Examining memory}). Other
4819 commands which provide a default address for @code{x} to examine also
4820 set @code{$_} to that address; these commands include @code{info line}
4821 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
4822 except when set by the @code{x} command, in which case it is a pointer
4823 to the type of @code{$__}.
4827 The variable @code{$__} is automatically set by the @code{x} command
4828 to the value found in the last address examined. Its type is chosen
4829 to match the format in which the data was printed.
4836 You can refer to machine register contents, in expressions, as variables
4837 with names starting with @samp{$}. The names of registers are different
4838 for each machine; use @code{info registers} to see the names used on
4842 @item info registers
4843 @kindex info registers
4844 Print the names and values of all registers except floating-point
4845 registers (in the selected stack frame).
4847 @item info all-registers
4848 @kindex info all-registers
4849 @cindex floating point registers
4850 Print the names and values of all registers, including floating-point
4853 @item info registers @var{regname} @dots{}
4854 Print the relativized value of each specified register @var{regname}.
4855 @var{regname} may be any register name valid on the machine you are using, with
4856 or without the initial @samp{$}.
4859 @value{GDBN} has four ``standard'' register names that are available (in
4860 expressions) on most machines---whenever they do not conflict with an
4861 architecture's canonical mnemonics for registers. The register names
4862 @code{$pc} and @code{$sp} are used for the program counter register and
4863 the stack pointer. @code{$fp} is used for a register that contains a
4864 pointer to the current stack frame, and @code{$ps} is used for a
4865 register that contains the processor status. For example,
4866 you could print the program counter in hex with
4873 or print the instruction to be executed next with
4880 or add four to the stack pointer@footnote{This is a way of removing
4881 one word from the stack, on machines where stacks grow downward in
4882 memory (most machines, nowadays). This assumes that the innermost
4883 stack frame is selected; setting @code{$sp} is not allowed when other
4884 stack frames are selected. To pop entire frames off the stack,
4885 regardless of machine architecture, use @code{return};
4886 @pxref{Returning, ,Returning from a function}.} with
4892 Whenever possible, these four standard register names are available on
4893 your machine even though the machine has different canonical mnemonics,
4894 so long as there is no conflict. The @code{info registers} command
4895 shows the canonical names. For example, on the SPARC, @code{info
4896 registers} displays the processor status register as @code{$psr} but you
4897 can also refer to it as @code{$ps}.
4899 @value{GDBN} always considers the contents of an ordinary register as an
4900 integer when the register is examined in this way. Some machines have
4901 special registers which can hold nothing but floating point; these
4902 registers are considered to have floating point values. There is no way
4903 to refer to the contents of an ordinary register as floating point value
4904 (although you can @emph{print} it as a floating point value with
4905 @samp{print/f $@var{regname}}).
4907 Some registers have distinct ``raw'' and ``virtual'' data formats. This
4908 means that the data format in which the register contents are saved by
4909 the operating system is not the same one that your program normally
4910 sees. For example, the registers of the 68881 floating point
4911 coprocessor are always saved in ``extended'' (raw) format, but all C
4912 programs expect to work with ``double'' (virtual) format. In such
4913 cases, @value{GDBN} normally works with the virtual format only (the format that
4914 makes sense for your program), but the @code{info registers} command
4915 prints the data in both formats.
4917 Normally, register values are relative to the selected stack frame
4918 (@pxref{Selection, ,Selecting a frame}). This means that you get the
4919 value that the register would contain if all stack frames farther in
4920 were exited and their saved registers restored. In order to see the
4921 true contents of hardware registers, you must select the innermost
4922 frame (with @samp{frame 0}).
4924 However, @value{GDBN} must deduce where registers are saved, from the machine
4925 code generated by your compiler. If some registers are not saved, or if
4926 @value{GDBN} is unable to locate the saved registers, the selected stack
4927 frame makes no difference.
4931 @item set rstack_high_address @var{address}
4932 @kindex set rstack_high_address
4933 @cindex AMD 29K register stack
4934 @cindex register stack, AMD29K
4935 On AMD 29000 family processors, registers are saved in a separate
4936 ``register stack''. There is no way for @value{GDBN} to determine the extent
4937 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
4938 enough''. This may result in @value{GDBN} referencing memory locations that
4939 do not exist. If necessary, you can get around this problem by
4940 specifying the ending address of the register stack with the @code{set
4941 rstack_high_address} command. The argument should be an address, which
4942 you probably want to precede with @samp{0x} to specify in
4945 @item show rstack_high_address
4946 @kindex show rstack_high_address
4947 Display the current limit of the register stack, on AMD 29000 family
4953 @node Floating Point Hardware
4954 @section Floating point hardware
4955 @cindex floating point
4957 @c FIXME! Really host, not target?
4958 Depending on the host machine architecture, @value{GDBN} may be able to give
4959 you more information about the status of the floating point hardware.
4964 Display hardware-dependent information about the floating
4965 point unit. The exact contents and layout vary depending on the
4966 floating point chip; on some platforms, @samp{info float} is not
4969 @c FIXME: this is a cop-out. Try to get examples, explanations. Only
4970 @c FIXME...supported currently on arm's and 386's. Mark properly with
4971 @c FIXME... m4 macros to isolate general statements from hardware-dep,
4972 @c FIXME... at that point.
4977 @chapter Using @value{GDBN} with Different Languages
4981 Although programming languages generally have common aspects, they are
4982 rarely expressed in the same manner. For instance, in ANSI C,
4983 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
4984 Modula-2, it is accomplished by @code{p^}. Values can also be
4985 represented (and displayed) differently. Hex numbers in C are written
4986 like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
4989 @cindex working language
4990 Language-specific information is built into @value{GDBN} for some languages,
4991 allowing you to express operations like the above in your program's
4992 native language, and allowing @value{GDBN} to output values in a manner
4993 consistent with the syntax of your program's native language. The
4994 language you use to build expressions, called the @dfn{working
4995 language}, can be selected manually, or @value{GDBN} can set it
4999 * Setting:: Switching between source languages
5000 * Show:: Displaying the language
5002 * Checks:: Type and range checks
5005 * Support:: Supported languages
5009 @section Switching between source languages
5011 There are two ways to control the working language---either have @value{GDBN}
5012 set it automatically, or select it manually yourself. You can use the
5013 @code{set language} command for either purpose. On startup, @value{GDBN}
5014 defaults to setting the language automatically.
5017 * Manually:: Setting the working language manually
5018 * Automatically:: Having @value{GDBN} infer the source language
5022 @subsection Setting the working language
5024 If you allow @value{GDBN} to set the language automatically,
5025 expressions are interpreted the same way in your debugging session and
5028 @kindex set language
5029 If you wish, you may set the language manually. To do this, issue the
5030 command @samp{set language @var{lang}}, where @var{lang} is the name of
5036 @code{c} or @code{modula-2}.
5038 For a list of the supported languages, type @samp{set language}.
5039 @c FIXME: rms: eventually this command should be "help set language".
5042 Setting the language manually prevents @value{GDBN} from updating the working
5043 language automatically. This can lead to confusion if you try
5044 to debug a program when the working language is not the same as the
5045 source language, when an expression is acceptable to both
5046 languages---but means different things. For instance, if the current
5047 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5055 might not have the effect you intended. In C, this means to add
5056 @code{b} and @code{c} and place the result in @code{a}. The result
5057 printed would be the value of @code{a}. In Modula-2, this means to compare
5058 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5062 @subsection Having @value{GDBN} infer the source language
5064 To have @value{GDBN} set the working language automatically, use @samp{set
5065 language local} or @samp{set language auto}. @value{GDBN} then infers the
5066 language that a program was written in by looking at the name of its
5067 source files, and examining their extensions:
5072 Modula-2 source file
5083 This information is recorded for each function or procedure in a source
5084 file. When your program stops in a frame (usually by encountering a
5085 breakpoint), @value{GDBN} sets the working language to the language recorded
5086 for the function in that frame. If the language for a frame is unknown
5087 (that is, if the function or block corresponding to the frame was
5088 defined in a source file that does not have a recognized extension), the
5089 current working language is not changed, and @value{GDBN} issues a warning.
5091 This may not seem necessary for most programs, which are written
5092 entirely in one source language. However, program modules and libraries
5093 written in one source language can be used by a main program written in
5094 a different source language. Using @samp{set language auto} in this
5095 case frees you from having to set the working language manually.
5098 @section Displaying the language
5100 The following commands help you find out which language is the
5101 working language, and also what language source files were written in.
5103 @kindex show language
5108 Display the current working language. This is the
5109 language you can use with commands such as @code{print} to
5110 build and compute expressions that may involve variables in your program.
5113 Among the other information listed here (@pxref{Frame Info, ,Information
5114 about a frame}) is the source language for this frame. This
5115 language becomes the working language if you use an
5116 identifier from this frame.
5119 Among the other information listed here (@pxref{Symbols, ,Examining the
5120 Symbol Table}) is the source language of this source file.
5125 @section Type and range checking
5128 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5129 checking are included, but they do not yet have any effect. This
5130 section documents the intended facilities.
5132 @c FIXME remove warning when type/range code added
5134 Some languages are designed to guard you against making seemingly common
5135 errors through a series of compile- and run-time checks. These include
5136 checking the type of arguments to functions and operators, and making
5137 sure mathematical overflows are caught at run time. Checks such as
5138 these help to ensure a program's correctness once it has been compiled
5139 by eliminating type mismatches, and providing active checks for range
5140 errors when your program is running.
5142 @value{GDBN} can check for conditions like the above if you wish.
5143 Although @value{GDBN} does not check the statements in your program, it
5144 can check expressions entered directly into @value{GDBN} for evaluation via
5145 the @code{print} command, for example. As with the working language,
5146 @value{GDBN} can also decide whether or not to check automatically based on
5147 your program's source language. @xref{Support, ,Supported languages},
5148 for the default settings of supported languages.
5151 * Type Checking:: An overview of type checking
5152 * Range Checking:: An overview of range checking
5155 @cindex type checking
5156 @cindex checks, type
5158 @subsection An overview of type checking
5160 Some languages, such as Modula-2, are strongly typed, meaning that the
5161 arguments to operators and functions have to be of the correct type,
5162 otherwise an error occurs. These checks prevent type mismatch
5163 errors from ever causing any run-time problems. For example,
5171 The second example fails because the @code{CARDINAL} 1 is not
5172 type-compatible with the @code{REAL} 2.3.
5174 For expressions you use in @value{GDBN} commands, you can tell the @value{GDBN}
5175 type checker to skip checking; to treat any mismatches as errors and
5176 abandon the expression; or only issue warnings when type mismatches
5177 occur, but evaluate the expression anyway. When you choose the last of
5178 these, @value{GDBN} evaluates expressions like the second example above, but
5179 also issues a warning.
5181 Even though you may turn type checking off, other type-based reasons may
5182 prevent @value{GDBN} from evaluating an expression. For instance, @value{GDBN} does not
5183 know how to add an @code{int} and a @code{struct foo}. These particular
5184 type errors have nothing to do with the language in use, and usually
5185 arise from expressions, such as the one described above, which make
5186 little sense to evaluate anyway.
5188 Each language defines to what degree it is strict about type. For
5189 instance, both Modula-2 and C require the arguments to arithmetical
5190 operators to be numbers. In C, enumerated types and pointers can be
5191 represented as numbers, so that they are valid arguments to mathematical
5192 operators. @xref{Support, ,Supported languages}, for further
5193 details on specific languages.
5195 @value{GDBN} provides some additional commands for controlling the type checker:
5198 @kindex set check type
5199 @kindex show check type
5201 @item set check type auto
5202 Set type checking on or off based on the current working language.
5203 @xref{Support, ,Supported languages}, for the default settings for
5206 @item set check type on
5207 @itemx set check type off
5208 Set type checking on or off, overriding the default setting for the
5209 current working language. Issue a warning if the setting does not
5210 match the language default. If any type mismatches occur in
5211 evaluating an expression while typechecking is on, @value{GDBN} prints a
5212 message and aborts evaluation of the expression.
5214 @item set check type warn
5215 Cause the type checker to issue warnings, but to always attempt to
5216 evaluate the expression. Evaluating the expression may still
5217 be impossible for other reasons. For example, @value{GDBN} cannot add
5218 numbers and structures.
5221 Show the current setting of the type checker, and whether or not @value{GDBN} is
5222 setting it automatically.
5225 @cindex range checking
5226 @cindex checks, range
5227 @node Range Checking
5228 @subsection An overview of range checking
5230 In some languages (such as Modula-2), it is an error to exceed the
5231 bounds of a type; this is enforced with run-time checks. Such range
5232 checking is meant to ensure program correctness by making sure
5233 computations do not overflow, or indices on an array element access do
5234 not exceed the bounds of the array.
5236 For expressions you use in @value{GDBN} commands, you can tell
5237 @value{GDBN} to treat range errors in one of three ways: ignore them,
5238 always treat them as errors and abandon the expression, or issue
5239 warnings but evaluate the expression anyway.
5241 A range error can result from numerical overflow, from exceeding an
5242 array index bound, or when you type a constant that is not a member
5243 of any type. Some languages, however, do not treat overflows as an
5244 error. In many implementations of C, mathematical overflow causes the
5245 result to ``wrap around'' to lower values---for example, if @var{m} is
5246 the largest integer value, and @var{s} is the smallest, then
5249 @var{m} + 1 @result{} @var{s}
5252 This, too, is specific to individual languages, and in some cases
5253 specific to individual compilers or machines. @xref{Support, ,
5254 Supported languages}, for further details on specific languages.
5256 @value{GDBN} provides some additional commands for controlling the range checker:
5259 @kindex set check range
5260 @kindex show check range
5262 @item set check range auto
5263 Set range checking on or off based on the current working language.
5264 @xref{Support, ,Supported languages}, for the default settings for
5267 @item set check range on
5268 @itemx set check range off
5269 Set range checking on or off, overriding the default setting for the
5270 current working language. A warning is issued if the setting does not
5271 match the language default. If a range error occurs, then a message
5272 is printed and evaluation of the expression is aborted.
5274 @item set check range warn
5275 Output messages when the @value{GDBN} range checker detects a range error,
5276 but attempt to evaluate the expression anyway. Evaluating the
5277 expression may still be impossible for other reasons, such as accessing
5278 memory that the process does not own (a typical example from many Unix
5282 Show the current setting of the range checker, and whether or not it is
5283 being set automatically by @value{GDBN}.
5288 @section Supported languages
5291 @value{GDBN} 4 supports C, C++, and Modula-2.
5294 @value{GDBN} 4 supports C, and C++.
5296 Some @value{GDBN} features may be used in expressions regardless of the
5297 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
5298 and the @samp{@{type@}addr} construct (@pxref{Expressions,
5299 ,Expressions}) can be used with the constructs of any supported
5302 The following sections detail to what degree each source language is
5303 supported by @value{GDBN}. These sections are not meant to be language
5304 tutorials or references, but serve only as a reference guide to what the
5305 @value{GDBN} expression parser accepts, and what input and output
5306 formats should look like for different languages. There are many good
5307 books written on each of these languages; please look to these for a
5308 language reference or tutorial.
5313 * Modula-2:: Modula-2
5317 @subsection C and C++
5319 @cindex expressions in C or C++
5321 Since C and C++ are so closely related, many features of @value{GDBN} apply
5322 to both languages. Whenever this is the case, we discuss both languages
5326 @c Cancel this below, under same condition, at end of this chapter!
5333 The C++ debugging facilities are jointly implemented by the GNU C++
5334 compiler and @value{GDBN}. Therefore, to debug your C++ code
5335 effectively, you must compile your C++ programs with the GNU C++
5336 compiler, @code{g++}.
5338 For best results when debugging C++ programs, use the stabs debugging
5339 format. You can select that format explicitly with the @code{g++}
5340 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
5341 @ref{Debugging Options,,Options for Debugging Your Program or GNU CC,
5342 gcc.info, Using GNU CC}, for more information.
5346 @chapter C Language Support
5348 @cindex expressions in C
5350 Information specific to the C language is built into @value{GDBN} so that you
5351 can use C expressions while degugging. This also permits @value{GDBN} to
5352 output values in a manner consistent with C conventions.
5355 * C Operators:: C operators
5356 * C Constants:: C constants
5357 * Debugging C:: @value{GDBN} and C
5362 * C Operators:: C and C++ operators
5363 * C Constants:: C and C++ constants
5364 * Cplus expressions:: C++ expressions
5365 * C Defaults:: Default settings for C and C++
5367 * C Checks:: C and C++ type and range checks
5370 * Debugging C:: @value{GDBN} and C
5371 * Debugging C plus plus:: Special features for C++
5376 @cindex C and C++ operators
5378 @subsubsection C and C++ operators
5383 @section C operators
5386 Operators must be defined on values of specific types. For instance,
5387 @code{+} is defined on numbers, but not on structures. Operators are
5388 often defined on groups of types.
5391 For the purposes of C and C++, the following definitions hold:
5396 @emph{Integral types} include @code{int} with any of its storage-class
5397 specifiers; @code{char}; and @code{enum}.
5400 @emph{Floating-point types} include @code{float} and @code{double}.
5403 @emph{Pointer types} include all types defined as @code{(@var{type}
5407 @emph{Scalar types} include all of the above.
5411 The following operators are supported. They are listed here
5412 in order of increasing precedence:
5416 The comma or sequencing operator. Expressions in a comma-separated list
5417 are evaluated from left to right, with the result of the entire
5418 expression being the last expression evaluated.
5421 Assignment. The value of an assignment expression is the value
5422 assigned. Defined on scalar types.
5425 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5426 and translated to @w{@code{@var{a} = @var{a op b}}}.
5427 @w{@code{@var{op}=}} and @code{=} have the same precendence.
5428 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5429 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5432 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5433 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5437 Logical @sc{or}. Defined on integral types.
5440 Logical @sc{and}. Defined on integral types.
5443 Bitwise @sc{or}. Defined on integral types.
5446 Bitwise exclusive-@sc{or}. Defined on integral types.
5449 Bitwise @sc{and}. Defined on integral types.
5452 Equality and inequality. Defined on scalar types. The value of these
5453 expressions is 0 for false and non-zero for true.
5455 @item <@r{, }>@r{, }<=@r{, }>=
5456 Less than, greater than, less than or equal, greater than or equal.
5457 Defined on scalar types. The value of these expressions is 0 for false
5458 and non-zero for true.
5461 left shift, and right shift. Defined on integral types.
5464 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5467 Addition and subtraction. Defined on integral types, floating-point types and
5470 @item *@r{, }/@r{, }%
5471 Multiplication, division, and modulus. Multiplication and division are
5472 defined on integral and floating-point types. Modulus is defined on
5476 Increment and decrement. When appearing before a variable, the
5477 operation is performed before the variable is used in an expression;
5478 when appearing after it, the variable's value is used before the
5479 operation takes place.
5482 Pointer dereferencing. Defined on pointer types. Same precedence as
5486 Address operator. Defined on variables. Same precedence as @code{++}.
5489 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5490 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5491 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
5492 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5497 Negative. Defined on integral and floating-point types. Same
5498 precedence as @code{++}.
5501 Logical negation. Defined on integral types. Same precedence as
5505 Bitwise complement operator. Defined on integral types. Same precedence as
5510 Structure member, and pointer-to-structure member. For convenience,
5511 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5512 pointer based on the stored type information.
5513 Defined on @code{struct} and @code{union} data.
5516 Array indexing. @code{@var{a}[@var{i}]} is defined as
5517 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5520 Function parameter list. Same precedence as @code{->}.
5524 C++ scope resolution operator. Defined on
5525 @code{struct}, @code{union}, and @code{class} types.
5533 represent the @value{GDBN} scope operator (@pxref{Expressions,
5536 Same precedence as @code{::}, above.
5541 @cindex C and C++ constants
5543 @subsubsection C and C++ constants
5545 @value{GDBN} allows you to express the constants of C and C++ in the
5551 @section C constants
5553 @value{GDBN} allows you to express the constants of C in the
5559 Integer constants are a sequence of digits. Octal constants are
5560 specified by a leading @samp{0} (ie. zero), and hexadecimal constants by
5561 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
5562 @samp{l}, specifying that the constant should be treated as a
5566 Floating point constants are a sequence of digits, followed by a decimal
5567 point, followed by a sequence of digits, and optionally followed by an
5568 exponent. An exponent is of the form:
5569 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
5570 sequence of digits. The @samp{+} is optional for positive exponents.
5573 Enumerated constants consist of enumerated identifiers, or their
5574 integral equivalents.
5577 Character constants are a single character surrounded by single quotes
5578 (@code{'}), or a number---the ordinal value of the corresponding character
5579 (usually its @sc{ASCII} value). Within quotes, the single character may
5580 be represented by a letter or by @dfn{escape sequences}, which are of
5581 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
5582 of the character's ordinal value; or of the form @samp{\@var{x}}, where
5583 @samp{@var{x}} is a predefined special character---for example,
5584 @samp{\n} for newline.
5587 String constants are a sequence of character constants surrounded
5588 by double quotes (@code{"}).
5591 Pointer constants are an integral value. You can also write pointers
5592 to constants using the C operator @samp{&}.
5595 Array constants are comma-separated lists surrounded by braces @samp{@{}
5596 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
5597 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
5598 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
5602 @node Cplus expressions
5603 @subsubsection C++ expressions
5605 @cindex expressions in C++
5606 @value{GDBN} expression handling has a number of extensions to
5607 interpret a significant subset of C++ expressions.
5609 @cindex C++ support, not in @sc{coff}
5610 @cindex @sc{coff} versus C++
5611 @cindex C++ and object formats
5612 @cindex object formats and C++
5613 @cindex a.out and C++
5614 @cindex @sc{ecoff} and C++
5615 @cindex @sc{xcoff} and C++
5616 @cindex @sc{elf}/stabs and C++
5617 @cindex @sc{elf}/@sc{dwarf} and C++
5618 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
5619 @c periodically whether this has happened...
5621 @emph{Warning:} @value{GDBN} can only debug C++ code if you compile with
5622 the GNU C++ compiler. Moreover, C++ debugging depends on the use of
5623 additional debugging information in the symbol table, and thus requires
5624 special support. @value{GDBN} has this support @emph{only} with the
5625 stabs debug format. In particular, if your compiler generates a.out,
5626 MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions
5627 to the symbol table, these facilities are all available. (With GNU CC,
5628 you can use the @samp{-gstabs} option to request stabs debugging
5629 extensions explicitly.) Where the object code format is standard
5630 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
5631 support in @value{GDBN} does @emph{not} work.
5636 @cindex member functions
5638 Member function calls are allowed; you can use expressions like
5641 count = aml->GetOriginal(x, y)
5645 @cindex namespace in C++
5647 While a member function is active (in the selected stack frame), your
5648 expressions have the same namespace available as the member function;
5649 that is, @value{GDBN} allows implicit references to the class instance
5650 pointer @code{this} following the same rules as C++.
5652 @cindex call overloaded functions
5653 @cindex type conversions in C++
5655 You can call overloaded functions; @value{GDBN} resolves the function
5656 call to the right definition, with one restriction---you must use
5657 arguments of the type required by the function that you want to call.
5658 @value{GDBN} does not perform conversions requiring constructors or
5659 user-defined type operators.
5661 @cindex reference declarations
5663 @value{GDBN} understands variables declared as C++ references; you can use them in
5664 expressions just as you do in C++ source---they are automatically
5667 In the parameter list shown when @value{GDBN} displays a frame, the values of
5668 reference variables are not displayed (unlike other variables); this
5669 avoids clutter, since references are often used for large structures.
5670 The @emph{address} of a reference variable is always shown, unless
5671 you have specified @samp{set print address off}.
5674 @value{GDBN} supports the C++ name resolution operator @code{::}---your
5675 expressions can use it just as expressions in your program do. Since
5676 one scope may be defined in another, you can use @code{::} repeatedly if
5677 necessary, for example in an expression like
5678 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
5679 resolving name scope by reference to source files, in both C and C++
5680 debugging (@pxref{Variables, ,Program variables}).
5684 @subsubsection C and C++ defaults
5685 @cindex C and C++ defaults
5687 If you allow @value{GDBN} to set type and range checking automatically, they
5688 both default to @code{off} whenever the working language changes to
5689 C or C++. This happens regardless of whether you, or @value{GDBN},
5690 selected the working language.
5692 If you allow @value{GDBN} to set the language automatically, it sets the
5693 working language to C or C++ on entering code compiled from a source file
5694 whose name ends with @file{.c}, @file{.C}, or @file{.cc}.
5695 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
5699 @c Type checking is (a) primarily motivated by Modula-2, and (b)
5700 @c unimplemented. If (b) changes, it might make sense to let this node
5701 @c appear even if Mod-2 does not, but meanwhile ignore it. pesch 16jul93.
5703 @subsubsection C and C++ type and range checks
5704 @cindex C and C++ checks
5706 By default, when @value{GDBN} parses C or C++ expressions, type checking
5707 is not used. However, if you turn type checking on, @value{GDBN}
5708 considers two variables type equivalent if:
5712 The two variables are structured and have the same structure, union, or
5716 Two two variables have the same type name, or types that have been
5717 declared equivalent through @code{typedef}.
5720 @c leaving this out because neither J Gilmore nor R Pesch understand it.
5723 The two @code{struct}, @code{union}, or @code{enum} variables are
5724 declared in the same declaration. (Note: this may not be true for all C
5729 Range checking, if turned on, is done on mathematical operations. Array
5730 indices are not checked, since they are often used to index a pointer
5731 that is not itself an array.
5737 @subsubsection @value{GDBN} and C
5741 @section @value{GDBN} and C
5744 The @code{set print union} and @code{show print union} commands apply to
5745 the @code{union} type. When set to @samp{on}, any @code{union} that is
5746 inside a @code{struct}
5751 Otherwise, it appears as @samp{@{...@}}.
5753 The @code{@@} operator aids in the debugging of dynamic arrays, formed
5754 with pointers and a memory allocation function. @xref{Expressions,
5758 @node Debugging C plus plus
5759 @subsubsection @value{GDBN} features for C++
5761 @cindex commands for C++
5762 Some @value{GDBN} commands are particularly useful with C++, and some are
5763 designed specifically for use with C++. Here is a summary:
5766 @cindex break in overloaded functions
5767 @item @r{breakpoint menus}
5768 When you want a breakpoint in a function whose name is overloaded,
5769 @value{GDBN} breakpoint menus help you specify which function definition
5770 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
5772 @cindex overloading in C++
5773 @item rbreak @var{regex}
5774 Setting breakpoints using regular expressions is helpful for setting
5775 breakpoints on overloaded functions that are not members of any special
5777 @xref{Set Breaks, ,Setting breakpoints}.
5779 @cindex C++ exception handling
5780 @item catch @var{exceptions}
5782 Debug C++ exception handling using these commands. @xref{Exception
5783 Handling, ,Breakpoints and exceptions}.
5786 @item ptype @var{typename}
5787 Print inheritance relationships as well as other information for type
5789 @xref{Symbols, ,Examining the Symbol Table}.
5791 @cindex C++ symbol display
5792 @item set print demangle
5793 @itemx show print demangle
5794 @itemx set print asm-demangle
5795 @itemx show print asm-demangle
5796 Control whether C++ symbols display in their source form, both when
5797 displaying code as C++ source and when displaying disassemblies.
5798 @xref{Print Settings, ,Print settings}.
5800 @item set print object
5801 @itemx show print object
5802 Choose whether to print derived (actual) or declared types of objects.
5803 @xref{Print Settings, ,Print settings}.
5805 @item set print vtbl
5806 @itemx show print vtbl
5807 Control the format for printing virtual function tables.
5808 @xref{Print Settings, ,Print settings}.
5810 @item @r{Overloaded symbol names}
5811 You can specify a particular definition of an overloaded symbol, using
5812 the same notation that is used to declare such symbols in C++: type
5813 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
5814 also use the @value{GDBN} command-line word completion facilities to list the
5815 available choices, or to finish the type list for you.
5816 @xref{Completion,, Command completion}, for details on how to do this.
5819 @c cancels "raisesections" under same conditions near bgn of chapter
5825 @subsection Modula-2
5828 The extensions made to @value{GDBN} to support Modula-2 only support
5829 output from the GNU Modula-2 compiler (which is currently being
5830 developed). Other Modula-2 compilers are not currently supported, and
5831 attempting to debug executables produced by them is most likely
5832 to give an error as @value{GDBN} reads in the executable's symbol
5835 @cindex expressions in Modula-2
5837 * M2 Operators:: Built-in operators
5838 * Built-In Func/Proc:: Built-in functions and procedures
5839 * M2 Constants:: Modula-2 constants
5840 * M2 Defaults:: Default settings for Modula-2
5841 * Deviations:: Deviations from standard Modula-2
5842 * M2 Checks:: Modula-2 type and range checks
5843 * M2 Scope:: The scope operators @code{::} and @code{.}
5844 * GDB/M2:: @value{GDBN} and Modula-2
5848 @subsubsection Operators
5849 @cindex Modula-2 operators
5851 Operators must be defined on values of specific types. For instance,
5852 @code{+} is defined on numbers, but not on structures. Operators are
5853 often defined on groups of types. For the purposes of Modula-2, the
5854 following definitions hold:
5859 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
5863 @emph{Character types} consist of @code{CHAR} and its subranges.
5866 @emph{Floating-point types} consist of @code{REAL}.
5869 @emph{Pointer types} consist of anything declared as @code{POINTER TO
5873 @emph{Scalar types} consist of all of the above.
5876 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
5879 @emph{Boolean types} consist of @code{BOOLEAN}.
5883 The following operators are supported, and appear in order of
5884 increasing precedence:
5888 Function argument or array index separator.
5891 Assignment. The value of @var{var} @code{:=} @var{value} is
5895 Less than, greater than on integral, floating-point, or enumerated
5899 Less than, greater than, less than or equal to, greater than or equal to
5900 on integral, floating-point and enumerated types, or set inclusion on
5901 set types. Same precedence as @code{<}.
5903 @item =@r{, }<>@r{, }#
5904 Equality and two ways of expressing inequality, valid on scalar types.
5905 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
5906 available for inequality, since @code{#} conflicts with the script
5910 Set membership. Defined on set types and the types of their members.
5911 Same precedence as @code{<}.
5914 Boolean disjunction. Defined on boolean types.
5917 Boolean conjuction. Defined on boolean types.
5920 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5923 Addition and subtraction on integral and floating-point types, or union
5924 and difference on set types.
5927 Multiplication on integral and floating-point types, or set intersection
5931 Division on floating-point types, or symmetric set difference on set
5932 types. Same precedence as @code{*}.
5935 Integer division and remainder. Defined on integral types. Same
5936 precedence as @code{*}.
5939 Negative. Defined on @code{INTEGER} and @code{REAL} data.
5942 Pointer dereferencing. Defined on pointer types.
5945 Boolean negation. Defined on boolean types. Same precedence as
5949 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
5950 precedence as @code{^}.
5953 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
5956 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
5960 @value{GDBN} and Modula-2 scope operators.
5964 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
5965 treats the use of the operator @code{IN}, or the use of operators
5966 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
5967 @code{<=}, and @code{>=} on sets as an error.
5970 @cindex Modula-2 built-ins
5971 @node Built-In Func/Proc
5972 @subsubsection Built-in functions and procedures
5974 Modula-2 also makes available several built-in procedures and functions.
5975 In describing these, the following metavariables are used:
5980 represents an @code{ARRAY} variable.
5983 represents a @code{CHAR} constant or variable.
5986 represents a variable or constant of integral type.
5989 represents an identifier that belongs to a set. Generally used in the
5990 same function with the metavariable @var{s}. The type of @var{s} should
5991 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
5994 represents a variable or constant of integral or floating-point type.
5997 represents a variable or constant of floating-point type.
6003 represents a variable.
6006 represents a variable or constant of one of many types. See the
6007 explanation of the function for details.
6010 All Modula-2 built-in procedures also return a result, described below.
6014 Returns the absolute value of @var{n}.
6017 If @var{c} is a lower case letter, it returns its upper case
6018 equivalent, otherwise it returns its argument
6021 Returns the character whose ordinal value is @var{i}.
6024 Decrements the value in the variable @var{v}. Returns the new value.
6026 @item DEC(@var{v},@var{i})
6027 Decrements the value in the variable @var{v} by @var{i}. Returns the
6030 @item EXCL(@var{m},@var{s})
6031 Removes the element @var{m} from the set @var{s}. Returns the new
6034 @item FLOAT(@var{i})
6035 Returns the floating point equivalent of the integer @var{i}.
6038 Returns the index of the last member of @var{a}.
6041 Increments the value in the variable @var{v}. Returns the new value.
6043 @item INC(@var{v},@var{i})
6044 Increments the value in the variable @var{v} by @var{i}. Returns the
6047 @item INCL(@var{m},@var{s})
6048 Adds the element @var{m} to the set @var{s} if it is not already
6049 there. Returns the new set.
6052 Returns the maximum value of the type @var{t}.
6055 Returns the minimum value of the type @var{t}.
6058 Returns boolean TRUE if @var{i} is an odd number.
6061 Returns the ordinal value of its argument. For example, the ordinal
6062 value of a character is its ASCII value (on machines supporting the
6063 ASCII character set). @var{x} must be of an ordered type, which include
6064 integral, character and enumerated types.
6067 Returns the size of its argument. @var{x} can be a variable or a type.
6069 @item TRUNC(@var{r})
6070 Returns the integral part of @var{r}.
6072 @item VAL(@var{t},@var{i})
6073 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6077 @emph{Warning:} Sets and their operations are not yet supported, so
6078 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
6082 @cindex Modula-2 constants
6084 @subsubsection Constants
6086 @value{GDBN} allows you to express the constants of Modula-2 in the following
6092 Integer constants are simply a sequence of digits. When used in an
6093 expression, a constant is interpreted to be type-compatible with the
6094 rest of the expression. Hexadecimal integers are specified by a
6095 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6098 Floating point constants appear as a sequence of digits, followed by a
6099 decimal point and another sequence of digits. An optional exponent can
6100 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6101 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6102 digits of the floating point constant must be valid decimal (base 10)
6106 Character constants consist of a single character enclosed by a pair of
6107 like quotes, either single (@code{'}) or double (@code{"}). They may
6108 also be expressed by their ordinal value (their ASCII value, usually)
6109 followed by a @samp{C}.
6112 String constants consist of a sequence of characters enclosed by a
6113 pair of like quotes, either single (@code{'}) or double (@code{"}).
6114 Escape sequences in the style of C are also allowed. @xref{C
6115 Constants, ,C and C++ constants}, for a brief explanation of escape
6119 Enumerated constants consist of an enumerated identifier.
6122 Boolean constants consist of the identifiers @code{TRUE} and
6126 Pointer constants consist of integral values only.
6129 Set constants are not yet supported.
6133 @subsubsection Modula-2 defaults
6134 @cindex Modula-2 defaults
6136 If type and range checking are set automatically by @value{GDBN}, they
6137 both default to @code{on} whenever the working language changes to
6138 Modula-2. This happens regardless of whether you, or @value{GDBN},
6139 selected the working language.
6141 If you allow @value{GDBN} to set the language automatically, then entering
6142 code compiled from a file whose name ends with @file{.mod} sets the
6143 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6144 the language automatically}, for further details.
6147 @subsubsection Deviations from standard Modula-2
6148 @cindex Modula-2, deviations from
6150 A few changes have been made to make Modula-2 programs easier to debug.
6151 This is done primarily via loosening its type strictness:
6155 Unlike in standard Modula-2, pointer constants can be formed by
6156 integers. This allows you to modify pointer variables during
6157 debugging. (In standard Modula-2, the actual address contained in a
6158 pointer variable is hidden from you; it can only be modified
6159 through direct assignment to another pointer variable or expression that
6160 returned a pointer.)
6163 C escape sequences can be used in strings and characters to represent
6164 non-printable characters. @value{GDBN} prints out strings with these
6165 escape sequences embedded. Single non-printable characters are
6166 printed using the @samp{CHR(@var{nnn})} format.
6169 The assignment operator (@code{:=}) returns the value of its right-hand
6173 All built-in procedures both modify @emph{and} return their argument.
6177 @subsubsection Modula-2 type and range checks
6178 @cindex Modula-2 checks
6181 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6184 @c FIXME remove warning when type/range checks added
6186 @value{GDBN} considers two Modula-2 variables type equivalent if:
6190 They are of types that have been declared equivalent via a @code{TYPE
6191 @var{t1} = @var{t2}} statement
6194 They have been declared on the same line. (Note: This is true of the
6195 GNU Modula-2 compiler, but it may not be true of other compilers.)
6198 As long as type checking is enabled, any attempt to combine variables
6199 whose types are not equivalent is an error.
6201 Range checking is done on all mathematical operations, assignment, array
6202 index bounds, and all built-in functions and procedures.
6205 @subsubsection The scope operators @code{::} and @code{.}
6208 @cindex colon, doubled as scope operator
6211 @c Info cannot handle :: but TeX can.
6217 There are a few subtle differences between the Modula-2 scope operator
6218 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6223 @var{module} . @var{id}
6224 @var{scope} :: @var{id}
6228 where @var{scope} is the name of a module or a procedure,
6229 @var{module} the name of a module, and @var{id} is any declared
6230 identifier within your program, except another module.
6232 Using the @code{::} operator makes @value{GDBN} search the scope
6233 specified by @var{scope} for the identifier @var{id}. If it is not
6234 found in the specified scope, then @value{GDBN} searches all scopes
6235 enclosing the one specified by @var{scope}.
6237 Using the @code{.} operator makes @value{GDBN} search the current scope for
6238 the identifier specified by @var{id} that was imported from the
6239 definition module specified by @var{module}. With this operator, it is
6240 an error if the identifier @var{id} was not imported from definition
6241 module @var{module}, or if @var{id} is not an identifier in
6245 @subsubsection @value{GDBN} and Modula-2
6247 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6248 Five subcommands of @code{set print} and @code{show print} apply
6249 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6250 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6251 apply to C++, and the last to the C @code{union} type, which has no direct
6252 analogue in Modula-2.
6254 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6255 while using any language, is not useful with Modula-2. Its
6256 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6257 created in Modula-2 as they can in C or C++. However, because an
6258 address can be specified by an integral constant, the construct
6259 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
6261 @cindex @code{#} in Modula-2
6262 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6263 interpreted as the beginning of a comment. Use @code{<>} instead.
6269 @chapter Examining the Symbol Table
6271 The commands described in this section allow you to inquire about the
6272 symbols (names of variables, functions and types) defined in your
6273 program. This information is inherent in the text of your program and
6274 does not change as your program executes. @value{GDBN} finds it in your
6275 program's symbol table, in the file indicated when you started @value{GDBN}
6276 (@pxref{File Options, ,Choosing files}), or by one of the
6277 file-management commands (@pxref{Files, ,Commands to specify files}).
6279 @c FIXME! This might be intentionally specific to C and C++; if so, move
6280 @c to someplace in C section of lang chapter.
6281 @cindex symbol names
6282 @cindex names of symbols
6283 @cindex quoting names
6284 Occasionally, you may need to refer to symbols that contain unusual
6285 characters, which @value{GDBN} ordinarily treats as word delimiters. The
6286 most frequent case is in referring to static variables in other
6287 source files (@pxref{Variables,,Program variables}). File names
6288 are recorded in object files as debugging symbols, but @value{GDBN} would
6289 ordinarily parse a typical file name, like @file{foo.c}, as the three words
6290 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
6291 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
6298 looks up the value of @code{x} in the scope of the file @file{foo.c}.
6301 @item info address @var{symbol}
6302 @kindex info address
6303 Describe where the data for @var{symbol} is stored. For a register
6304 variable, this says which register it is kept in. For a non-register
6305 local variable, this prints the stack-frame offset at which the variable
6308 Note the contrast with @samp{print &@var{symbol}}, which does not work
6309 at all for a register variable, and for a stack local variable prints
6310 the exact address of the current instantiation of the variable.
6312 @item whatis @var{exp}
6314 Print the data type of expression @var{exp}. @var{exp} is not
6315 actually evaluated, and any side-effecting operations (such as
6316 assignments or function calls) inside it do not take place.
6317 @xref{Expressions, ,Expressions}.
6320 Print the data type of @code{$}, the last value in the value history.
6322 @item ptype @var{typename}
6324 Print a description of data type @var{typename}. @var{typename} may be
6325 the name of a type, or for C code it may have the form
6327 @samp{class @var{class-name}},
6329 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
6330 @samp{enum @var{enum-tag}}.
6332 @item ptype @var{exp}
6334 Print a description of the type of expression @var{exp}. @code{ptype}
6335 differs from @code{whatis} by printing a detailed description, instead
6336 of just the name of the type.
6338 For example, for this variable declaration:
6341 struct complex @{double real; double imag;@} v;
6345 the two commands give this output:
6349 (@value{GDBP}) whatis v
6350 type = struct complex
6351 (@value{GDBP}) ptype v
6352 type = struct complex @{
6360 As with @code{whatis}, using @code{ptype} without an argument refers to
6361 the type of @code{$}, the last value in the value history.
6363 @item info types @var{regexp}
6366 Print a brief description of all types whose name matches @var{regexp}
6367 (or all types in your program, if you supply no argument). Each
6368 complete typename is matched as though it were a complete line; thus,
6369 @samp{i type value} gives information on all types in your program whose
6370 name includes the string @code{value}, but @samp{i type ^value$} gives
6371 information only on types whose complete name is @code{value}.
6373 This command differs from @code{ptype} in two ways: first, like
6374 @code{whatis}, it does not print a detailed description; second, it
6375 lists all source files where a type is defined.
6379 Show the name of the current source file---that is, the source file for
6380 the function containing the current point of execution---and the language
6384 @kindex info sources
6385 Print the names of all source files in your program for which there is
6386 debugging information, organized into two lists: files whose symbols
6387 have already been read, and files whose symbols will be read when needed.
6389 @item info functions
6390 @kindex info functions
6391 Print the names and data types of all defined functions.
6393 @item info functions @var{regexp}
6394 Print the names and data types of all defined functions
6395 whose names contain a match for regular expression @var{regexp}.
6396 Thus, @samp{info fun step} finds all functions whose names
6397 include @code{step}; @samp{info fun ^step} finds those whose names
6398 start with @code{step}.
6400 @item info variables
6401 @kindex info variables
6402 Print the names and data types of all variables that are declared
6403 outside of functions (i.e., excluding local variables).
6405 @item info variables @var{regexp}
6406 Print the names and data types of all variables (except for local
6407 variables) whose names contain a match for regular expression
6411 This was never implemented.
6413 @itemx info methods @var{regexp}
6414 @kindex info methods
6415 The @code{info methods} command permits the user to examine all defined
6416 methods within C++ program, or (with the @var{regexp} argument) a
6417 specific set of methods found in the various C++ classes. Many
6418 C++ classes provide a large number of methods. Thus, the output
6419 from the @code{ptype} command can be overwhelming and hard to use. The
6420 @code{info-methods} command filters the methods, printing only those
6421 which match the regular-expression @var{regexp}.
6424 @item maint print symbols @var{filename}
6425 @itemx maint print psymbols @var{filename}
6426 @itemx maint print msymbols @var{filename}
6427 @kindex maint print symbols
6429 @kindex maint print psymbols
6430 @cindex partial symbol dump
6431 Write a dump of debugging symbol data into the file @var{filename}.
6432 These commands are used to debug the @value{GDBN} symbol-reading code. Only
6433 symbols with debugging data are included. If you use @samp{maint print
6434 symbols}, @value{GDBN} includes all the symbols for which it has already
6435 collected full details: that is, @var{filename} reflects symbols for
6436 only those files whose symbols @value{GDBN} has read. You can use the
6437 command @code{info sources} to find out which files these are. If you
6438 use @samp{maint print psymbols} instead, the dump shows information about
6439 symbols that @value{GDBN} only knows partially---that is, symbols defined in
6440 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
6441 @samp{maint print msymbols} dumps just the minimal symbol information
6442 required for each object file from which @value{GDBN} has read some symbols.
6443 @xref{Files, ,Commands to specify files}, for a discussion of how
6444 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
6448 @chapter Altering Execution
6450 Once you think you have found an error in your program, you might want to
6451 find out for certain whether correcting the apparent error would lead to
6452 correct results in the rest of the run. You can find the answer by
6453 experiment, using the @value{GDBN} features for altering execution of the
6456 For example, you can store new values into variables or memory
6459 give your program a signal, restart it
6462 restart your program
6464 at a different address, or even return prematurely from a function to
6468 * Assignment:: Assignment to variables
6469 * Jumping:: Continuing at a different address
6471 * Signaling:: Giving your program a signal
6474 * Returning:: Returning from a function
6475 * Calling:: Calling your program's functions
6476 * Patching:: Patching your program
6480 @section Assignment to variables
6483 @cindex setting variables
6484 To alter the value of a variable, evaluate an assignment expression.
6485 @xref{Expressions, ,Expressions}. For example,
6492 stores the value 4 into the variable @code{x}, and then prints the
6493 value of the assignment expression (which is 4).
6495 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
6496 information on operators in supported languages.
6499 @kindex set variable
6500 @cindex variables, setting
6501 If you are not interested in seeing the value of the assignment, use the
6502 @code{set} command instead of the @code{print} command. @code{set} is
6503 really the same as @code{print} except that the expression's value is
6504 not printed and is not put in the value history (@pxref{Value History,
6505 ,Value history}). The expression is evaluated only for its effects.
6507 If the beginning of the argument string of the @code{set} command
6508 appears identical to a @code{set} subcommand, use the @code{set
6509 variable} command instead of just @code{set}. This command is identical
6510 to @code{set} except for its lack of subcommands. For example, if
6511 your program has a variable @code{width}, you get
6512 an error if you try to set a new value with just @samp{set width=13},
6513 because @value{GDBN} has the command @code{set width}:
6516 (@value{GDBP}) whatis width
6518 (@value{GDBP}) p width
6520 (@value{GDBP}) set width=47
6521 Invalid syntax in expression.
6525 The invalid expression, of course, is @samp{=47}. In
6526 order to actually set the program's variable @code{width}, use
6529 (@value{GDBP}) set var width=47
6532 @value{GDBN} allows more implicit conversions in assignments than C; you can
6533 freely store an integer value into a pointer variable or vice versa,
6534 and you can convert any structure to any other structure that is the
6535 same length or shorter.
6536 @comment FIXME: how do structs align/pad in these conversions?
6537 @comment /pesch@cygnus.com 18dec1990
6539 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
6540 construct to generate a value of specified type at a specified address
6541 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
6542 to memory location @code{0x83040} as an integer (which implies a certain size
6543 and representation in memory), and
6546 set @{int@}0x83040 = 4
6550 stores the value 4 into that memory location.
6553 @section Continuing at a different address
6555 Ordinarily, when you continue your program, you do so at the place where
6556 it stopped, with the @code{continue} command. You can instead continue at
6557 an address of your own choosing, with the following commands:
6560 @item jump @var{linespec}
6562 Resume execution at line @var{linespec}. Execution stops again
6563 immediately if there is a breakpoint there. @xref{List, ,Printing
6564 source lines}, for a description of the different forms of
6567 The @code{jump} command does not change the current stack frame, or
6568 the stack pointer, or the contents of any memory location or any
6569 register other than the program counter. If line @var{linespec} is in
6570 a different function from the one currently executing, the results may
6571 be bizarre if the two functions expect different patterns of arguments or
6572 of local variables. For this reason, the @code{jump} command requests
6573 confirmation if the specified line is not in the function currently
6574 executing. However, even bizarre results are predictable if you are
6575 well acquainted with the machine-language code of your program.
6577 @item jump *@var{address}
6578 Resume execution at the instruction at address @var{address}.
6581 You can get much the same effect as the @code{jump} command by storing a
6582 new value into the register @code{$pc}. The difference is that this
6583 does not start your program running; it only changes the address where it
6584 @emph{will} run when you continue. For example,
6591 makes the next @code{continue} command or stepping command execute at
6592 address @code{0x485}, rather than at the address where your program stopped.
6593 @xref{Continuing and Stepping, ,Continuing and stepping}.
6595 The most common occasion to use the @code{jump} command is to back up,
6596 perhaps with more breakpoints set, over a portion of a program that has
6597 already executed, in order to examine its execution in more detail.
6602 @section Giving your program a signal
6605 @item signal @var{signal}
6607 Resume execution where your program stopped, but immediately give it the
6608 signal @var{signal}. @var{signal} can be the name or the number of a
6609 signal. For example, on many systems @code{signal 2} and @code{signal
6610 SIGINT} are both ways of sending an interrupt signal.
6612 Alternatively, if @var{signal} is zero, continue execution without
6613 giving a signal. This is useful when your program stopped on account of
6614 a signal and would ordinary see the signal when resumed with the
6615 @code{continue} command; @samp{signal 0} causes it to resume without a
6618 @code{signal} does not repeat when you press @key{RET} a second time
6619 after executing the command.
6623 Invoking the @code{signal} command is not the same as invoking the
6624 @code{kill} utility from the shell. Sending a signal with @code{kill}
6625 causes @value{GDBN} to decide what to do with the signal depending on
6626 the signal handling tables (@pxref{Signals}). The @code{signal} command
6627 passes the signal directly to your program.
6632 @section Returning from a function
6636 @itemx return @var{expression}
6637 @cindex returning from a function
6639 You can cancel execution of a function call with the @code{return}
6640 command. If you give an
6641 @var{expression} argument, its value is used as the function's return
6645 When you use @code{return}, @value{GDBN} discards the selected stack frame
6646 (and all frames within it). You can think of this as making the
6647 discarded frame return prematurely. If you wish to specify a value to
6648 be returned, give that value as the argument to @code{return}.
6650 This pops the selected stack frame (@pxref{Selection, ,Selecting a
6651 frame}), and any other frames inside of it, leaving its caller as the
6652 innermost remaining frame. That frame becomes selected. The
6653 specified value is stored in the registers used for returning values
6656 The @code{return} command does not resume execution; it leaves the
6657 program stopped in the state that would exist if the function had just
6658 returned. In contrast, the @code{finish} command (@pxref{Continuing
6659 and Stepping, ,Continuing and stepping}) resumes execution until the
6660 selected stack frame returns naturally.
6663 @section Calling program functions
6665 @cindex calling functions
6668 @item call @var{expr}
6669 Evaluate the expression @var{expr} without displaying @code{void}
6673 You can use this variant of the @code{print} command if you want to
6674 execute a function from your program, but without cluttering the output
6675 with @code{void} returned values. The result is printed and saved in
6676 the value history, if it is not void.
6679 @section Patching programs
6680 @cindex patching binaries
6681 @cindex writing into executables
6683 @cindex writing into corefiles
6686 By default, @value{GDBN} opens the file containing your program's executable
6691 read-only. This prevents accidental alterations
6692 to machine code; but it also prevents you from intentionally patching
6693 your program's binary.
6695 If you'd like to be able to patch the binary, you can specify that
6696 explicitly with the @code{set write} command. For example, you might
6697 want to turn on internal debugging flags, or even to make emergency
6702 @itemx set write off
6704 If you specify @samp{set write on}, @value{GDBN} opens executable
6708 files for both reading and writing; if you specify @samp{set write
6709 off} (the default), @value{GDBN} opens them read-only.
6711 If you have already loaded a file, you must load it again (using the
6716 command) after changing @code{set write}, for your new setting to take
6721 Display whether executable files
6725 are opened for writing as well as reading.
6729 @chapter @value{GDBN} Files
6731 @value{GDBN} needs to know the file name of the program to be debugged, both in
6732 order to read its symbol table and in order to start your program.
6734 To debug a core dump of a previous run, you must also tell @value{GDBN}
6735 the name of the core dump file.
6739 * Files:: Commands to specify files
6740 * Symbol Errors:: Errors reading symbol files
6744 @section Commands to specify files
6745 @cindex symbol table
6748 @cindex core dump file
6749 The usual way to specify executable and core dump file names is with
6750 the command arguments given when you start @value{GDBN} (@pxref{Invocation,
6751 ,Getting In and Out of @value{GDBN}}.
6754 The usual way to specify an executable file name is with
6755 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
6756 ,Getting In and Out of @value{GDBN}}.
6759 Occasionally it is necessary to change to a different file during a
6760 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
6761 a file you want to use. In these situations the @value{GDBN} commands
6762 to specify new files are useful.
6765 @item file @var{filename}
6766 @cindex executable file
6768 Use @var{filename} as the program to be debugged. It is read for its
6769 symbols and for the contents of pure memory. It is also the program
6770 executed when you use the @code{run} command. If you do not specify a
6771 directory and the file is not found in the @value{GDBN} working directory, @value{GDBN}
6772 uses the environment variable @code{PATH} as a list of directories to
6773 search, just as the shell does when looking for a program to run. You
6774 can change the value of this variable, for both @value{GDBN} and your program,
6775 using the @code{path} command.
6777 On systems with memory-mapped files, an auxiliary file
6778 @file{@var{filename}.syms} may hold symbol table information for
6779 @var{filename}. If so, @value{GDBN} maps in the symbol table from
6780 @file{@var{filename}.syms}, starting up more quickly. See the
6781 descriptions of the options @samp{-mapped} and @samp{-readnow}
6782 (available on the command line, and with the commands @code{file},
6783 @code{symbol-file}, or @code{add-symbol-file}), for more information.
6786 @code{file} with no argument makes @value{GDBN} discard any information it
6787 has on both executable file and the symbol table.
6789 @item exec-file @r{[} @var{filename} @r{]}
6791 Specify that the program to be run (but not the symbol table) is found
6792 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
6793 if necessary to locate your program. Omitting @var{filename} means to
6794 discard information on the executable file.
6796 @item symbol-file @r{[} @var{filename} @r{]}
6798 Read symbol table information from file @var{filename}. @code{PATH} is
6799 searched when necessary. Use the @code{file} command to get both symbol
6800 table and program to run from the same file.
6802 @code{symbol-file} with no argument clears out @value{GDBN} information on your
6803 program's symbol table.
6805 The @code{symbol-file} command causes @value{GDBN} to forget the contents of its
6806 convenience variables, the value history, and all breakpoints and
6807 auto-display expressions. This is because they may contain pointers to
6808 the internal data recording symbols and data types, which are part of
6809 the old symbol table data being discarded inside @value{GDBN}.
6811 @code{symbol-file} does not repeat if you press @key{RET} again after
6814 When @value{GDBN} is configured for a particular environment, it
6815 understands debugging information in whatever format is the standard
6816 generated for that environment; you may use either a GNU compiler, or
6817 other compilers that adhere to the local conventions. Best results are
6818 usually obtained from GNU compilers; for example, using @code{@value{GCC}}
6819 you can generate debugging information for optimized code.
6821 On some kinds of object files, the @code{symbol-file} command does not
6822 normally read the symbol table in full right away. Instead, it scans
6823 the symbol table quickly to find which source files and which symbols
6824 are present. The details are read later, one source file at a time,
6827 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
6828 faster. For the most part, it is invisible except for occasional
6829 pauses while the symbol table details for a particular source file are
6830 being read. (The @code{set verbose} command can turn these pauses
6831 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
6834 We have not implemented the two-stage strategy for COFF yet. When the
6835 symbol table is stored in COFF format, @code{symbol-file} reads the
6836 symbol table data in full right away.
6838 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6839 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6841 @cindex reading symbols immediately
6842 @cindex symbols, reading immediately
6844 @cindex memory-mapped symbol file
6845 @cindex saving symbol table
6846 You can override the @value{GDBN} two-stage strategy for reading symbol
6847 tables by using the @samp{-readnow} option with any of the commands that
6848 load symbol table information, if you want to be sure @value{GDBN} has the
6849 entire symbol table available.
6852 If memory-mapped files are available on your system through the
6853 @code{mmap} system call, you can use another option, @samp{-mapped}, to
6854 cause @value{GDBN} to write the symbols for your program into a reusable
6855 file. Future @value{GDBN} debugging sessions map in symbol information
6856 from this auxiliary symbol file (if the program has not changed), rather
6857 than spending time reading the symbol table from the executable
6858 program. Using the @samp{-mapped} option has the same effect as
6859 starting @value{GDBN} with the @samp{-mapped} command-line option.
6861 You can use both options together, to make sure the auxiliary symbol
6862 file has all the symbol information for your program.
6864 The auxiliary symbol file for a program called @var{myprog} is called
6865 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
6866 than the corresponding executable), @value{GDBN} always attempts to use
6867 it when you debug @var{myprog}; no special options or commands are
6870 The @file{.syms} file is specific to the host machine where you run
6871 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
6872 symbol table. It cannot be shared across multiple host platforms.
6874 @c FIXME: for now no mention of directories, since this seems to be in
6875 @c flux. 13mar1992 status is that in theory GDB would look either in
6876 @c current dir or in same dir as myprog; but issues like competing
6877 @c GDB's, or clutter in system dirs, mean that in practice right now
6878 @c only current dir is used. FFish says maybe a special GDB hierarchy
6879 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
6882 @item core-file @r{[} @var{filename} @r{]}
6885 Specify the whereabouts of a core dump file to be used as the ``contents
6886 of memory''. Traditionally, core files contain only some parts of the
6887 address space of the process that generated them; @value{GDBN} can access the
6888 executable file itself for other parts.
6890 @code{core-file} with no argument specifies that no core file is
6893 Note that the core file is ignored when your program is actually running
6894 under @value{GDBN}. So, if you have been running your program and you wish to
6895 debug a core file instead, you must kill the subprocess in which the
6896 program is running. To do this, use the @code{kill} command
6897 (@pxref{Kill Process, ,Killing the child process}).
6900 @item load @var{filename}
6903 Depending on what remote debugging facilities are configured into
6904 @value{GDBN}, the @code{load} command may be available. Where it exists, it
6905 is meant to make @var{filename} (an executable) available for debugging
6906 on the remote system---by downloading, or dynamic linking, for example.
6907 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
6908 the @code{add-symbol-file} command.
6910 If your @value{GDBN} does not have a @code{load} command, attempting to
6911 execute it gets the error message ``@code{You can't do that when your
6912 target is @dots{}}''
6915 The file is loaded at whatever address is specified in the executable.
6916 For some object file formats, you can specify the load address when you
6917 link the program; for other formats, like a.out, the object file format
6918 specifies a fixed address.
6919 @c FIXME! This would be a good place for an xref to the GNU linker doc.
6922 On VxWorks, @code{load} links @var{filename} dynamically on the
6923 current target system as well as adding its symbols in @value{GDBN}.
6927 @cindex download to Nindy-960
6928 With the Nindy interface to an Intel 960 board, @code{load}
6929 downloads @var{filename} to the 960 as well as adding its symbols in
6934 @cindex download to H8/300 or H8/500
6935 @cindex H8/300 or H8/500 download
6936 @cindex download to Hitachi SH
6937 @cindex Hitachi SH download
6938 When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board
6939 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
6940 the @code{load} command downloads your program to the Hitachi board and also
6941 opens it as the current executable target for @value{GDBN} on your host
6942 (like the @code{file} command).
6945 @code{load} does not repeat if you press @key{RET} again after using it.
6948 @item add-symbol-file @var{filename} @var{address}
6949 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6950 @kindex add-symbol-file
6951 @cindex dynamic linking
6952 The @code{add-symbol-file} command reads additional symbol table information
6953 from the file @var{filename}. You would use this command when @var{filename}
6954 has been dynamically loaded (by some other means) into the program that
6955 is running. @var{address} should be the memory address at which the
6956 file has been loaded; @value{GDBN} cannot figure this out for itself.
6957 You can specify @var{address} as an expression.
6959 The symbol table of the file @var{filename} is added to the symbol table
6960 originally read with the @code{symbol-file} command. You can use the
6961 @code{add-symbol-file} command any number of times; the new symbol data thus
6962 read keeps adding to the old. To discard all old symbol data instead,
6963 use the @code{symbol-file} command.
6965 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
6967 You can use the @samp{-mapped} and @samp{-readnow} options just as with
6968 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
6969 table information for @var{filename}.
6976 @code{info files} and @code{info target} are synonymous; both print
6977 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
6980 names of the executable and core dump files
6983 name of the executable file
6985 currently in use by @value{GDBN}, and the files from which symbols were
6986 loaded. The command @code{help targets} lists all possible targets
6987 rather than current ones.
6990 All file-specifying commands allow both absolute and relative file names
6991 as arguments. @value{GDBN} always converts the file name to an absolute path
6992 name and remembers it that way.
6995 @cindex shared libraries
6996 @value{GDBN} supports SunOS, SVr4, Irix 5, and IBM RS/6000 shared libraries.
6997 @value{GDBN} automatically loads symbol definitions from shared libraries
6998 when you use the @code{run} command, or when you examine a core file.
6999 (Before you issue the @code{run} command, @value{GDBN} does not understand
7000 references to a function in a shared library, however---unless you are
7001 debugging a core file).
7002 @c FIXME: some @value{GDBN} release may permit some refs to undef
7003 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
7004 @c FIXME...lib; check this from time to time when updating manual
7008 @itemx info sharedlibrary
7009 @kindex info sharedlibrary
7011 Print the names of the shared libraries which are currently loaded.
7013 @item sharedlibrary @var{regex}
7014 @itemx share @var{regex}
7015 @kindex sharedlibrary
7017 This is an obsolescent command; you can use it to explicitly load shared
7018 object library symbols for files matching a Unix regular expression, but
7019 as with files loaded automatically, it only loads shared libraries
7020 required by your program for a core file or after typing @code{run}. If
7021 @var{regex} is omitted all shared libraries required by your program are
7027 @section Errors reading symbol files
7029 While reading a symbol file, @value{GDBN} occasionally encounters problems,
7030 such as symbol types it does not recognize, or known bugs in compiler
7031 output. By default, @value{GDBN} does not notify you of such problems, since
7032 they are relatively common and primarily of interest to people
7033 debugging compilers. If you are interested in seeing information
7034 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
7035 only one message about each such type of problem, no matter how many
7036 times the problem occurs; or you can ask @value{GDBN} to print more messages,
7037 to see how many times the problems occur, with the @code{set
7038 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
7041 The messages currently printed, and their meanings, include:
7044 @item inner block not inside outer block in @var{symbol}
7046 The symbol information shows where symbol scopes begin and end
7047 (such as at the start of a function or a block of statements). This
7048 error indicates that an inner scope block is not fully contained
7049 in its outer scope blocks.
7051 @value{GDBN} circumvents the problem by treating the inner block as if it had
7052 the same scope as the outer block. In the error message, @var{symbol}
7053 may be shown as ``@code{(don't know)}'' if the outer block is not a
7056 @item block at @var{address} out of order
7058 The symbol information for symbol scope blocks should occur in
7059 order of increasing addresses. This error indicates that it does not
7062 @value{GDBN} does not circumvent this problem, and has trouble
7063 locating symbols in the source file whose symbols it is reading. (You
7064 can often determine what source file is affected by specifying
7065 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
7068 @item bad block start address patched
7070 The symbol information for a symbol scope block has a start address
7071 smaller than the address of the preceding source line. This is known
7072 to occur in the SunOS 4.1.1 (and earlier) C compiler.
7074 @value{GDBN} circumvents the problem by treating the symbol scope block as
7075 starting on the previous source line.
7077 @item bad string table offset in symbol @var{n}
7080 Symbol number @var{n} contains a pointer into the string table which is
7081 larger than the size of the string table.
7083 @value{GDBN} circumvents the problem by considering the symbol to have the
7084 name @code{foo}, which may cause other problems if many symbols end up
7087 @item unknown symbol type @code{0x@var{nn}}
7089 The symbol information contains new data types that @value{GDBN} does not yet
7090 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
7091 information, in hexadecimal.
7093 @value{GDBN} circumvents the error by ignoring this symbol information. This
7094 usually allows you to debug your program, though certain symbols
7095 are not accessible. If you encounter such a problem and feel like
7096 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
7097 @code{complain}, then go up to the function @code{read_dbx_symtab} and
7098 examine @code{*bufp} to see the symbol.
7100 @item stub type has NULL name
7101 @value{GDBN} could not find the full definition for
7110 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
7112 The symbol information for a C++ member function is missing some
7113 information that recent versions of the compiler should have output
7117 @item info mismatch between compiler and debugger
7119 @value{GDBN} could not parse a type specification output by the compiler.
7123 @chapter Specifying a Debugging Target
7124 @cindex debugging target
7127 A @dfn{target} is the execution environment occupied by your program.
7129 Often, @value{GDBN} runs in the same host environment as your program; in
7130 that case, the debugging target is specified as a side effect when you
7131 use the @code{file} or @code{core} commands. When you need more
7132 flexibility---for example, running @value{GDBN} on a physically separate
7133 host, or controlling a standalone system over a serial port or a
7134 realtime system over a TCP/IP connection---you
7139 can use the @code{target} command to specify one of the target types
7140 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
7144 * Active Targets:: Active targets
7145 * Target Commands:: Commands for managing targets
7146 * Remote:: Remote debugging
7149 @node Active Targets
7150 @section Active targets
7151 @cindex stacking targets
7152 @cindex active targets
7153 @cindex multiple targets
7156 There are three classes of targets: processes, core files, and
7157 executable files. @value{GDBN} can work concurrently on up to three active
7158 targets, one in each class. This allows you to (for example) start a
7159 process and inspect its activity without abandoning your work on a core
7162 For example, if you execute @samp{gdb a.out}, then the executable file
7163 @code{a.out} is the only active target. If you designate a core file as
7164 well---presumably from a prior run that crashed and coredumped---then
7165 @value{GDBN} has two active targets and uses them in tandem, looking
7166 first in the corefile target, then in the executable file, to satisfy
7167 requests for memory addresses. (Typically, these two classes of target
7168 are complementary, since core files contain only a program's
7169 read-write memory---variables and so on---plus machine status, while
7170 executable files contain only the program text and initialized data.)
7173 When you type @code{run}, your executable file becomes an active process
7174 target as well. When a process target is active, all @value{GDBN} commands
7175 requesting memory addresses refer to that target; addresses in an
7179 executable file target are obscured while the process
7183 Use the @code{exec-file} command to select a
7184 new executable target (@pxref{Files, ,Commands to specify
7188 Use the @code{core-file} and @code{exec-file} commands to select a
7189 new core file or executable target (@pxref{Files, ,Commands to specify
7190 files}). To specify as a target a process that is already running, use
7191 the @code{attach} command (@pxref{Attach, ,Debugging an
7192 already-running process}).
7195 @node Target Commands
7196 @section Commands for managing targets
7199 @item target @var{type} @var{parameters}
7200 Connects the @value{GDBN} host environment to a target
7205 machine or process. A target is typically a protocol for talking to
7206 debugging facilities. You use the argument @var{type} to specify the
7207 type or protocol of the target machine.
7209 Further @var{parameters} are interpreted by the target protocol, but
7210 typically include things like device names or host names to connect
7211 with, process numbers, and baud rates.
7214 The @code{target} command does not repeat if you press @key{RET} again
7215 after executing the command.
7219 Displays the names of all targets available. To display targets
7220 currently selected, use either @code{info target} or @code{info files}
7221 (@pxref{Files, ,Commands to specify files}).
7223 @item help target @var{name}
7224 Describe a particular target, including any parameters necessary to
7228 Here are some common targets (available, or not, depending on the GDB
7232 @item target exec @var{program}
7234 An executable file. @samp{target exec @var{program}} is the same as
7235 @samp{exec-file @var{program}}.
7238 @item target core @var{filename}
7240 A core dump file. @samp{target core @var{filename}} is the same as
7241 @samp{core-file @var{filename}}.
7245 @item target remote @var{dev}
7246 @kindex target remote
7247 Remote serial target in GDB-specific protocol. The argument @var{dev}
7248 specifies what serial device to use for the connection (e.g.
7249 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}.
7255 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
7259 @item target udi @var{keyword}
7261 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
7262 argument specifies which 29K board or simulator to use. @xref{UDI29K
7263 Remote,,The UDI protocol for AMD29K}.
7265 @item target amd-eb @var{dev} @var{speed} @var{PROG}
7266 @kindex target amd-eb
7268 Remote PC-resident AMD EB29K board, attached over serial lines.
7269 @var{dev} is the serial device, as for @code{target remote};
7270 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
7271 name of the program to be debugged, as it appears to DOS on the PC.
7272 @xref{EB29K Remote, ,The EBMON protocol for AMD29K}.
7278 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
7279 @ifclear H8EXCLUSIVE
7280 @c Unix only, not currently of interest for H8-only manual
7281 Use special commands @code{device} and @code{speed} to control the serial
7282 line and the communications speed used.
7284 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
7288 @item target nindy @var{devicename}
7289 @kindex target nindy
7290 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
7291 the name of the serial device to use for the connection, e.g.
7292 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
7296 @item target st2000 @var{dev} @var{speed}
7297 @kindex target st2000
7298 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
7299 is the name of the device attached to the ST2000 serial line;
7300 @var{speed} is the communication line speed. The arguments are not used
7301 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
7302 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
7306 @item target vxworks @var{machinename}
7307 @kindex target vxworks
7308 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
7309 is the target system's machine name or IP address.
7310 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
7315 Different targets are available on different configurations of @value{GDBN}; your
7316 configuration may have more or fewer targets.
7320 @section Remote debugging
7321 @cindex remote debugging
7323 If you are trying to debug a program running on a machine that cannot run
7324 GDB in the usual way, it is often useful to use remote debugging. For
7325 example, you might use remote debugging on an operating system kernel, or on
7326 a small system which does not have a general purpose operating system
7327 powerful enough to run a full-featured debugger.
7329 Some configurations of GDB have special serial or TCP/IP interfaces
7330 to make this work with particular debugging targets. In addition,
7331 GDB comes with a generic serial protocol (specific to GDB, but
7332 not specific to any particular target system) which you can use if you
7333 write the remote stubs---the code that runs on the remote system to
7334 communicate with GDB.
7336 Other remote targets may be available in your
7337 configuration of GDB; use @code{help targets} to list them.
7340 @c Text on starting up GDB in various specific cases; it goes up front
7341 @c in manuals configured for any of those particular situations, here
7345 * Remote Serial:: @value{GDBN} remote serial protocol
7348 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
7351 * UDI29K Remote:: The UDI protocol for AMD29K
7352 * EB29K Remote:: The EBMON protocol for AMD29K
7355 * VxWorks Remote:: @value{GDBN} and VxWorks
7358 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
7361 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
7364 * MIPS Remote:: @value{GDBN} and MIPS boards
7367 * Simulator:: Simulated CPU target
7371 @include remote.texi
7374 @node Controlling GDB
7375 @chapter Controlling @value{GDBN}
7377 You can alter the way @value{GDBN} interacts with you by using
7378 the @code{set} command. For commands controlling how @value{GDBN} displays
7379 data, @pxref{Print Settings, ,Print settings}; other settings are described here.
7383 * Editing:: Command editing
7384 * History:: Command history
7385 * Screen Size:: Screen size
7387 * Messages/Warnings:: Optional warnings and messages
7394 @value{GDBN} indicates its readiness to read a command by printing a string
7395 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
7396 can change the prompt string with the @code{set prompt} command. For
7397 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
7398 the prompt in one of the @value{GDBN} sessions so that you can always tell which
7399 one you are talking to.
7402 @item set prompt @var{newprompt}
7404 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
7407 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
7411 @section Command editing
7413 @cindex command line editing
7415 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
7416 GNU library provides consistent behavior for programs which provide a
7417 command line interface to the user. Advantages are @code{emacs}-style
7418 or @code{vi}-style inline editing of commands, @code{csh}-like history
7419 substitution, and a storage and recall of command history across
7422 You may control the behavior of command line editing in @value{GDBN} with the
7429 @itemx set editing on
7430 Enable command line editing (enabled by default).
7432 @item set editing off
7433 Disable command line editing.
7435 @kindex show editing
7437 Show whether command line editing is enabled.
7441 @section Command history
7443 @value{GDBN} can keep track of the commands you type during your
7444 debugging sessions, so that you can be certain of precisely what
7445 happened. Use these commands to manage the @value{GDBN} command
7449 @cindex history substitution
7450 @cindex history file
7451 @kindex set history filename
7453 @item set history filename @var{fname}
7454 Set the name of the @value{GDBN} command history file to @var{fname}.
7455 This is the file where @value{GDBN} reads an initial command history
7456 list, and where it writes the command history from this session when it
7457 exits. You can access this list through history expansion or through
7458 the history command editing characters listed below. This file defaults
7459 to the value of the environment variable @code{GDBHISTFILE}, or to
7460 @file{./.gdb_history} if this variable is not set.
7462 @cindex history save
7463 @kindex set history save
7464 @item set history save
7465 @itemx set history save on
7466 Record command history in a file, whose name may be specified with the
7467 @code{set history filename} command. By default, this option is disabled.
7469 @item set history save off
7470 Stop recording command history in a file.
7472 @cindex history size
7473 @kindex set history size
7474 @item set history size @var{size}
7475 Set the number of commands which @value{GDBN} keeps in its history list.
7476 This defaults to the value of the environment variable
7477 @code{HISTSIZE}, or to 256 if this variable is not set.
7480 @cindex history expansion
7481 History expansion assigns special meaning to the character @kbd{!}.
7482 @ifset have-readline-appendices
7483 @xref{Event Designators}.
7486 Since @kbd{!} is also the logical not operator in C, history expansion
7487 is off by default. If you decide to enable history expansion with the
7488 @code{set history expansion on} command, you may sometimes need to
7489 follow @kbd{!} (when it is used as logical not, in an expression) with
7490 a space or a tab to prevent it from being expanded. The readline
7491 history facilities do not attempt substitution on the strings
7492 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
7494 The commands to control history expansion are:
7498 @kindex set history expansion
7499 @item set history expansion on
7500 @itemx set history expansion
7501 Enable history expansion. History expansion is off by default.
7503 @item set history expansion off
7504 Disable history expansion.
7506 The readline code comes with more complete documentation of
7507 editing and history expansion features. Users unfamiliar with @code{emacs}
7508 or @code{vi} may wish to read it.
7509 @ifset have-readline-appendices
7510 @xref{Command Line Editing}.
7514 @kindex show history
7516 @itemx show history filename
7517 @itemx show history save
7518 @itemx show history size
7519 @itemx show history expansion
7520 These commands display the state of the @value{GDBN} history parameters.
7521 @code{show history} by itself displays all four states.
7526 @kindex show commands
7528 Display the last ten commands in the command history.
7530 @item show commands @var{n}
7531 Print ten commands centered on command number @var{n}.
7533 @item show commands +
7534 Print ten commands just after the commands last printed.
7538 @section Screen size
7539 @cindex size of screen
7540 @cindex pauses in output
7542 Certain commands to @value{GDBN} may produce large amounts of
7543 information output to the screen. To help you read all of it,
7544 @value{GDBN} pauses and asks you for input at the end of each page of
7545 output. Type @key{RET} when you want to continue the output, or @kbd{q}
7546 to discard the remaining output. Also, the screen width setting
7547 determines when to wrap lines of output. Depending on what is being
7548 printed, @value{GDBN} tries to break the line at a readable place,
7549 rather than simply letting it overflow onto the following line.
7551 Normally @value{GDBN} knows the size of the screen from the termcap data base
7552 together with the value of the @code{TERM} environment variable and the
7553 @code{stty rows} and @code{stty cols} settings. If this is not correct,
7554 you can override it with the @code{set height} and @code{set
7558 @item set height @var{lpp}
7560 @itemx set width @var{cpl}
7566 These @code{set} commands specify a screen height of @var{lpp} lines and
7567 a screen width of @var{cpl} characters. The associated @code{show}
7568 commands display the current settings.
7570 If you specify a height of zero lines, @value{GDBN} does not pause during output
7571 no matter how long the output is. This is useful if output is to a file
7572 or to an editor buffer.
7574 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
7575 from wrapping its output.
7580 @cindex number representation
7581 @cindex entering numbers
7583 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
7584 the usual conventions: octal numbers begin with @samp{0}, decimal
7585 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
7586 Numbers that begin with none of these are, by default, entered in base
7587 10; likewise, the default display for numbers---when no particular
7588 format is specified---is base 10. You can change the default base for
7589 both input and output with the @code{set radix} command.
7593 @item set radix @var{base}
7594 Set the default base for numeric input and display. Supported choices
7595 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
7596 specified either unambiguously or using the current default radix; for
7606 sets the base to decimal. On the other hand, @samp{set radix 10}
7607 leaves the radix unchanged no matter what it was.
7611 Display the current default base for numeric input and display.
7614 @node Messages/Warnings
7615 @section Optional warnings and messages
7617 By default, @value{GDBN} is silent about its inner workings. If you are running
7618 on a slow machine, you may want to use the @code{set verbose} command.
7619 It makes @value{GDBN} tell you when it does a lengthy internal operation, so
7620 you will not think it has crashed.
7622 Currently, the messages controlled by @code{set verbose} are those
7623 which announce that the symbol table for a source file is being read;
7624 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
7628 @item set verbose on
7629 Enables @value{GDBN} output of certain informational messages.
7631 @item set verbose off
7632 Disables @value{GDBN} output of certain informational messages.
7634 @kindex show verbose
7636 Displays whether @code{set verbose} is on or off.
7639 By default, if @value{GDBN} encounters bugs in the symbol table of an object
7640 file, it is silent; but if you are debugging a compiler, you may find
7641 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
7644 @kindex set complaints
7645 @item set complaints @var{limit}
7646 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
7647 symbols before becoming silent about the problem. Set @var{limit} to
7648 zero to suppress all complaints; set it to a large number to prevent
7649 complaints from being suppressed.
7651 @kindex show complaints
7652 @item show complaints
7653 Displays how many symbol complaints @value{GDBN} is permitted to produce.
7656 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
7657 lot of stupid questions to confirm certain commands. For example, if
7658 you try to run a program which is already running:
7662 The program being debugged has been started already.
7663 Start it from the beginning? (y or n)
7666 If you are willing to unflinchingly face the consequences of your own
7667 commands, you can disable this ``feature'':
7672 @cindex confirmation
7673 @cindex stupid questions
7674 @item set confirm off
7675 Disables confirmation requests.
7677 @item set confirm on
7678 Enables confirmation requests (the default).
7681 @kindex show confirm
7682 Displays state of confirmation requests.
7685 @c FIXME this does not really belong here. But where *does* it belong?
7686 @cindex reloading symbols
7687 Some systems allow individual object files that make up your program to
7688 be replaced without stopping and restarting your program.
7690 For example, in VxWorks you can simply recompile a defective object file
7691 and keep on running.
7693 If you are running on one of these systems, you can allow @value{GDBN} to
7694 reload the symbols for automatically relinked modules:
7697 @kindex set symbol-reloading
7698 @item set symbol-reloading on
7699 Replace symbol definitions for the corresponding source file when an
7700 object file with a particular name is seen again.
7702 @item set symbol-reloading off
7703 Do not replace symbol definitions when re-encountering object files of
7704 the same name. This is the default state; if you are not running on a
7705 system that permits automatically relinking modules, you should leave
7706 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7707 when linking large programs, that may contain several modules (from
7708 different directories or libraries) with the same name.
7710 @item show symbol-reloading
7711 Show the current @code{on} or @code{off} setting.
7715 @chapter Canned Sequences of Commands
7717 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
7718 command lists}), @value{GDBN} provides two ways to store sequences of commands
7719 for execution as a unit: user-defined commands and command files.
7722 * Define:: User-defined commands
7723 * Hooks:: User-defined command hooks
7724 * Command Files:: Command files
7725 * Output:: Commands for controlled output
7729 @section User-defined commands
7731 @cindex user-defined command
7732 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which you
7733 assign a new name as a command. This is done with the @code{define}
7737 @item define @var{commandname}
7739 Define a command named @var{commandname}. If there is already a command
7740 by that name, you are asked to confirm that you want to redefine it.
7742 The definition of the command is made up of other @value{GDBN} command lines,
7743 which are given following the @code{define} command. The end of these
7744 commands is marked by a line containing @code{end}.
7746 @item document @var{commandname}
7748 Give documentation to the user-defined command @var{commandname}. The
7749 command @var{commandname} must already be defined. This command reads
7750 lines of documentation just as @code{define} reads the lines of the
7751 command definition, ending with @code{end}. After the @code{document}
7752 command is finished, @code{help} on command @var{commandname} displays
7753 the documentation you have specified.
7755 You may use the @code{document} command again to change the
7756 documentation of a command. Redefining the command with @code{define}
7757 does not change the documentation.
7759 @item help user-defined
7760 @kindex help user-defined
7761 List all user-defined commands, with the first line of the documentation
7765 @itemx show user @var{commandname}
7767 Display the @value{GDBN} commands used to define @var{commandname} (but not its
7768 documentation). If no @var{commandname} is given, display the
7769 definitions for all user-defined commands.
7772 User-defined commands do not take arguments. When they are executed, the
7773 commands of the definition are not printed. An error in any command
7774 stops execution of the user-defined command.
7776 Commands that would ask for confirmation if used interactively proceed
7777 without asking when used inside a user-defined command. Many @value{GDBN} commands
7778 that normally print messages to say what they are doing omit the messages
7779 when used in a user-defined command.
7782 @section User-defined command hooks
7783 @cindex command files
7785 You may define @emph{hooks}, which are a special kind of user-defined
7786 command. Whenever you run the command @samp{foo}, if the user-defined
7787 command @samp{hook-foo} exists, it is executed (with no arguments)
7788 before that command.
7790 In addition, a pseudo-command, @samp{stop} exists. Defining
7791 (@samp{hook-stop}) makes the associated commands execute every time
7792 execution stops in your program: before breakpoint commands are run,
7793 displays are printed, or the stack frame is printed.
7796 For example, to ignore @code{SIGALRM} signals while
7797 single-stepping, but treat them normally during normal execution,
7802 handle SIGALRM nopass
7809 define hook-continue
7815 You can define a hook for any single-word command in @value{GDBN}, but
7816 not for command aliases; you should define a hook for the basic command
7817 name, e.g. @code{backtrace} rather than @code{bt}.
7818 @c FIXME! So how does Joe User discover whether a command is an alias
7820 If an error occurs during the execution of your hook, execution of
7821 @value{GDBN} commands stops and @value{GDBN} issues a prompt
7822 (before the command that you actually typed had a chance to run).
7824 If you try to define a hook which does not match any known command, you
7825 get a warning from the @code{define} command.
7828 @section Command files
7830 @cindex command files
7831 A command file for @value{GDBN} is a file of lines that are @value{GDBN} commands. Comments
7832 (lines starting with @kbd{#}) may also be included. An empty line in a
7833 command file does nothing; it does not mean to repeat the last command, as
7834 it would from the terminal.
7837 @cindex @file{@value{GDBINIT}}
7838 When you start @value{GDBN}, it automatically executes commands from its
7839 @dfn{init files}. These are files named @file{@value{GDBINIT}}.
7840 @value{GDBN} reads the init file (if any) in your home directory, then
7841 processes command line options and operands, and then reads the init
7842 file (if any) in the current working directory. This is so the init
7843 file in your home directory can set options (such as @code{set
7844 complaints}) which affect the processing of the command line options and
7845 operands. The init files are not executed if you use the @samp{-nx}
7846 option; @pxref{Mode Options, ,Choosing modes}.
7849 @cindex init file name
7850 On some configurations of @value{GDBN}, the init file is known by a
7851 different name (these are typically environments where a specialized
7852 form of GDB may need to coexist with other forms, hence a different name
7853 for the specialized version's init file). These are the environments
7854 with special init file names:
7859 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
7861 @kindex .os68gdbinit
7863 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
7867 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
7871 You can also request the execution of a command file with the
7872 @code{source} command:
7875 @item source @var{filename}
7877 Execute the command file @var{filename}.
7880 The lines in a command file are executed sequentially. They are not
7881 printed as they are executed. An error in any command terminates execution
7882 of the command file.
7884 Commands that would ask for confirmation if used interactively proceed
7885 without asking when used in a command file. Many @value{GDBN} commands that
7886 normally print messages to say what they are doing omit the messages
7887 when called from command files.
7890 @section Commands for controlled output
7892 During the execution of a command file or a user-defined command, normal
7893 @value{GDBN} output is suppressed; the only output that appears is what is
7894 explicitly printed by the commands in the definition. This section
7895 describes three commands useful for generating exactly the output you
7899 @item echo @var{text}
7901 @c I do not consider backslash-space a standard C escape sequence
7902 @c because it is not in ANSI.
7903 Print @var{text}. Nonprinting characters can be included in
7904 @var{text} using C escape sequences, such as @samp{\n} to print a
7905 newline. @strong{No newline is printed unless you specify one.}
7906 In addition to the standard C escape sequences, a backslash followed
7907 by a space stands for a space. This is useful for displaying a
7908 string with spaces at the beginning or the end, since leading and
7909 trailing spaces are otherwise trimmed from all arguments.
7910 To print @samp{@w{ }and foo =@w{ }}, use the command
7911 @samp{echo \@w{ }and foo = \@w{ }}.
7913 A backslash at the end of @var{text} can be used, as in C, to continue
7914 the command onto subsequent lines. For example,
7917 echo This is some text\n\
7918 which is continued\n\
7919 onto several lines.\n
7922 produces the same output as
7925 echo This is some text\n
7926 echo which is continued\n
7927 echo onto several lines.\n
7930 @item output @var{expression}
7932 Print the value of @var{expression} and nothing but that value: no
7933 newlines, no @samp{$@var{nn} = }. The value is not entered in the
7934 value history either. @xref{Expressions, ,Expressions}, for more information on
7937 @item output/@var{fmt} @var{expression}
7938 Print the value of @var{expression} in format @var{fmt}. You can use
7939 the same formats as for @code{print}. @xref{Output Formats,,Output
7940 formats}, for more information.
7942 @item printf @var{string}, @var{expressions}@dots{}
7944 Print the values of the @var{expressions} under the control of
7945 @var{string}. The @var{expressions} are separated by commas and may be
7946 either numbers or pointers. Their values are printed as specified by
7947 @var{string}, exactly as if your program were to execute the C
7951 printf (@var{string}, @var{expressions}@dots{});
7954 For example, you can print two values in hex like this:
7957 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
7960 The only backslash-escape sequences that you can use in the format
7961 string are the simple ones that consist of backslash followed by a
7967 @chapter Using @value{GDBN} under GNU Emacs
7970 A special interface allows you to use GNU Emacs to view (and
7971 edit) the source files for the program you are debugging with
7974 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
7975 executable file you want to debug as an argument. This command starts
7976 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
7977 created Emacs buffer.
7979 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
7984 All ``terminal'' input and output goes through the Emacs buffer.
7987 This applies both to @value{GDBN} commands and their output, and to the input
7988 and output done by the program you are debugging.
7990 This is useful because it means that you can copy the text of previous
7991 commands and input them again; you can even use parts of the output
7994 All the facilities of Emacs' Shell mode are available for interacting
7995 with your program. In particular, you can send signals the usual
7996 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
8001 @value{GDBN} displays source code through Emacs.
8004 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
8005 source file for that frame and puts an arrow (@samp{=>}) at the
8006 left margin of the current line. Emacs uses a separate buffer for
8007 source display, and splits the screen to show both your @value{GDBN} session
8010 Explicit @value{GDBN} @code{list} or search commands still produce output as
8011 usual, but you probably have no reason to use them from Emacs.
8014 @emph{Warning:} If the directory where your program resides is not your
8015 current directory, it can be easy to confuse Emacs about the location of
8016 the source files, in which case the auxiliary display buffer does not
8017 appear to show your source. @value{GDBN} can find programs by searching your
8018 environment's @code{PATH} variable, so the @value{GDBN} input and output
8019 session proceeds normally; but Emacs does not get enough information
8020 back from @value{GDBN} to locate the source files in this situation. To
8021 avoid this problem, either start @value{GDBN} mode from the directory where
8022 your program resides, or specify a full path name when prompted for the
8023 @kbd{M-x gdb} argument.
8025 A similar confusion can result if you use the @value{GDBN} @code{file} command to
8026 switch to debugging a program in some other location, from an existing
8027 @value{GDBN} buffer in Emacs.
8030 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
8031 you need to call @value{GDBN} by a different name (for example, if you keep
8032 several configurations around, with different names) you can set the
8033 Emacs variable @code{gdb-command-name}; for example,
8036 (setq gdb-command-name "mygdb")
8040 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
8041 in your @file{.emacs} file) makes Emacs call the program named
8042 ``@code{mygdb}'' instead.
8044 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
8045 addition to the standard Shell mode commands:
8049 Describe the features of Emacs' @value{GDBN} Mode.
8052 Execute to another source line, like the @value{GDBN} @code{step} command; also
8053 update the display window to show the current file and location.
8056 Execute to next source line in this function, skipping all function
8057 calls, like the @value{GDBN} @code{next} command. Then update the display window
8058 to show the current file and location.
8061 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
8062 display window accordingly.
8065 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
8066 display window accordingly.
8069 Execute until exit from the selected stack frame, like the @value{GDBN}
8070 @code{finish} command.
8073 Continue execution of your program, like the @value{GDBN} @code{continue}
8076 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
8079 Go up the number of frames indicated by the numeric argument
8080 (@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}),
8081 like the @value{GDBN} @code{up} command.
8083 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
8086 Go down the number of frames indicated by the numeric argument, like the
8087 @value{GDBN} @code{down} command.
8089 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
8092 Read the number where the cursor is positioned, and insert it at the end
8093 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
8094 around an address that was displayed earlier, type @kbd{disassemble};
8095 then move the cursor to the address display, and pick up the
8096 argument for @code{disassemble} by typing @kbd{C-x &}.
8098 You can customize this further by defining elements of the list
8099 @code{gdb-print-command}; once it is defined, you can format or
8100 otherwise process numbers picked up by @kbd{C-x &} before they are
8101 inserted. A numeric argument to @kbd{C-x &} indicates that you
8102 wish special formatting, and also acts as an index to pick an element of the
8103 list. If the list element is a string, the number to be inserted is
8104 formatted using the Emacs function @code{format}; otherwise the number
8105 is passed as an argument to the corresponding list element.
8108 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
8109 tells @value{GDBN} to set a breakpoint on the source line point is on.
8111 If you accidentally delete the source-display buffer, an easy way to get
8112 it back is to type the command @code{f} in the @value{GDBN} buffer, to
8113 request a frame display; when you run under Emacs, this recreates
8114 the source buffer if necessary to show you the context of the current
8117 The source files displayed in Emacs are in ordinary Emacs buffers
8118 which are visiting the source files in the usual way. You can edit
8119 the files with these buffers if you wish; but keep in mind that @value{GDBN}
8120 communicates with Emacs in terms of line numbers. If you add or
8121 delete lines from the text, the line numbers that @value{GDBN} knows cease
8122 to correspond properly with the code.
8124 @c The following dropped because Epoch is nonstandard. Reactivate
8125 @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990
8127 @kindex emacs epoch environment
8131 Version 18 of Emacs has a built-in window system called the @code{epoch}
8132 environment. Users of this environment can use a new command,
8133 @code{inspect} which performs identically to @code{print} except that
8134 each value is printed in its own window.
8140 @chapter Using @value{GDBN} with Energize
8143 The Energize Programming System is an integrated development environment
8144 that includes a point-and-click interface to many programming tools.
8145 When you use @value{GDBN} in this environment, you can use the standard
8146 Energize graphical interface to drive @value{GDBN}; you can also, if you
8147 choose, type @value{GDBN} commands as usual in a debugging window. Even if
8148 you use the graphical interface, the debugging window (which uses Emacs,
8149 and resembles the standard Emacs interface to @value{GDBN}) displays the
8150 equivalent commands, so that the history of your debugging session is
8153 When Energize starts up a @value{GDBN} session, it uses one of the
8154 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
8155 is the name of the communications protocol used by the Energize system).
8156 This option makes @value{GDBN} run as one of the tools in the Energize Tool
8157 Set: it sends all output to the Energize kernel, and accept input from
8160 See the user manual for the Energize Programming System for
8161 information on how to use the Energize graphical interface and the other
8162 development tools that Energize integrates with @value{GDBN}.
8167 @chapter Reporting Bugs in @value{GDBN}
8168 @cindex bugs in @value{GDBN}
8169 @cindex reporting bugs in @value{GDBN}
8171 Your bug reports play an essential role in making @value{GDBN} reliable.
8173 Reporting a bug may help you by bringing a solution to your problem, or it
8174 may not. But in any case the principal function of a bug report is to help
8175 the entire community by making the next version of @value{GDBN} work better. Bug
8176 reports are your contribution to the maintenance of @value{GDBN}.
8178 In order for a bug report to serve its purpose, you must include the
8179 information that enables us to fix the bug.
8182 * Bug Criteria:: Have you found a bug?
8183 * Bug Reporting:: How to report bugs
8187 @section Have you found a bug?
8188 @cindex bug criteria
8190 If you are not sure whether you have found a bug, here are some guidelines:
8194 @cindex fatal signal
8195 @cindex debugger crash
8196 @cindex crash of debugger
8197 If the debugger gets a fatal signal, for any input whatever, that is a
8198 @value{GDBN} bug. Reliable debuggers never crash.
8201 @cindex error on valid input
8202 If @value{GDBN} produces an error message for valid input, that is a bug.
8205 @cindex invalid input
8206 If @value{GDBN} does not produce an error message for invalid input,
8207 that is a bug. However, you should note that your idea of
8208 ``invalid input'' might be our idea of ``an extension'' or ``support
8209 for traditional practice''.
8212 If you are an experienced user of debugging tools, your suggestions
8213 for improvement of @value{GDBN} are welcome in any case.
8217 @section How to report bugs
8219 @cindex @value{GDBN} bugs, reporting
8221 A number of companies and individuals offer support for GNU products.
8222 If you obtained @value{GDBN} from a support organization, we recommend you
8223 contact that organization first.
8225 You can find contact information for many support companies and
8226 individuals in the file @file{etc/SERVICE} in the GNU Emacs
8229 In any event, we also recommend that you send bug reports for @value{GDBN} to one
8233 bug-gdb@@prep.ai.mit.edu
8234 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
8237 @strong{Do not send bug reports to @samp{info-gdb}, or to
8238 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
8239 receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}.
8241 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
8242 serves as a repeater. The mailing list and the newsgroup carry exactly
8243 the same messages. Often people think of posting bug reports to the
8244 newsgroup instead of mailing them. This appears to work, but it has one
8245 problem which can be crucial: a newsgroup posting often lacks a mail
8246 path back to the sender. Thus, if we need to ask for more information,
8247 we may be unable to reach you. For this reason, it is better to send
8248 bug reports to the mailing list.
8250 As a last resort, send bug reports on paper to:
8254 Free Software Foundation
8259 The fundamental principle of reporting bugs usefully is this:
8260 @strong{report all the facts}. If you are not sure whether to state a
8261 fact or leave it out, state it!
8263 Often people omit facts because they think they know what causes the
8264 problem and assume that some details do not matter. Thus, you might
8265 assume that the name of the variable you use in an example does not matter.
8266 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
8267 stray memory reference which happens to fetch from the location where that
8268 name is stored in memory; perhaps, if the name were different, the contents
8269 of that location would fool the debugger into doing the right thing despite
8270 the bug. Play it safe and give a specific, complete example. That is the
8271 easiest thing for you to do, and the most helpful.
8273 Keep in mind that the purpose of a bug report is to enable us to fix
8274 the bug if it is new to us. It is not as important as what happens if
8275 the bug is already known. Therefore, always write your bug reports on
8276 the assumption that the bug has not been reported previously.
8278 Sometimes people give a few sketchy facts and ask, ``Does this ring a
8279 bell?'' Those bug reports are useless, and we urge everyone to
8280 @emph{refuse to respond to them} except to chide the sender to report
8283 To enable us to fix the bug, you should include all these things:
8287 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
8288 arguments; you can also print it at any time using @code{show version}.
8290 Without this, we will not know whether there is any point in looking for
8291 the bug in the current version of @value{GDBN}.
8294 The type of machine you are using, and the operating system name and
8298 What compiler (and its version) was used to compile @value{GDBN}---e.g.
8299 ``@value{GCC}--2.0''.
8302 What compiler (and its version) was used to compile the program you
8303 are debugging---e.g. ``@value{GCC}--2.0''.
8306 The command arguments you gave the compiler to compile your example and
8307 observe the bug. For example, did you use @samp{-O}? To guarantee
8308 you will not omit something important, list them all. A copy of the
8309 Makefile (or the output from make) is sufficient.
8311 If we were to try to guess the arguments, we would probably guess wrong
8312 and then we might not encounter the bug.
8315 A complete input script, and all necessary source files, that will
8319 A description of what behavior you observe that you believe is
8320 incorrect. For example, ``It gets a fatal signal.''
8322 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
8323 certainly notice it. But if the bug is incorrect output, we might not
8324 notice unless it is glaringly wrong. We are human, after all. You
8325 might as well not give us a chance to make a mistake.
8327 Even if the problem you experience is a fatal signal, you should still
8328 say so explicitly. Suppose something strange is going on, such as,
8329 your copy of @value{GDBN} is out of synch, or you have encountered a
8330 bug in the C library on your system. (This has happened!) Your copy
8331 might crash and ours would not. If you told us to expect a crash,
8332 then when ours fails to crash, we would know that the bug was not
8333 happening for us. If you had not told us to expect a crash, then we
8334 would not be able to draw any conclusion from our observations.
8337 If you wish to suggest changes to the @value{GDBN} source, send us context
8338 diffs. If you even discuss something in the @value{GDBN} source, refer to
8339 it by context, not by line number.
8341 The line numbers in our development sources will not match those in your
8342 sources. Your line numbers would convey no useful information to us.
8345 Here are some things that are not necessary:
8349 A description of the envelope of the bug.
8351 Often people who encounter a bug spend a lot of time investigating
8352 which changes to the input file will make the bug go away and which
8353 changes will not affect it.
8355 This is often time consuming and not very useful, because the way we
8356 will find the bug is by running a single example under the debugger
8357 with breakpoints, not by pure deduction from a series of examples.
8358 We recommend that you save your time for something else.
8360 Of course, if you can find a simpler example to report @emph{instead}
8361 of the original one, that is a convenience for us. Errors in the
8362 output will be easier to spot, running under the debugger will take
8363 less time, and so on.
8365 However, simplification is not vital; if you do not want to do this,
8366 report the bug anyway and send us the entire test case you used.
8369 A patch for the bug.
8371 A patch for the bug does help us if it is a good one. But do not omit
8372 the necessary information, such as the test case, on the assumption that
8373 a patch is all we need. We might see problems with your patch and decide
8374 to fix the problem another way, or we might not understand it at all.
8376 Sometimes with a program as complicated as @value{GDBN} it is very hard to
8377 construct an example that will make the program follow a certain path
8378 through the code. If you do not send us the example, we will not be able
8379 to construct one, so we will not be able to verify that the bug is fixed.
8381 And if we cannot understand what bug you are trying to fix, or why your
8382 patch should be an improvement, we will not install it. A test case will
8383 help us to understand.
8386 A guess about what the bug is or what it depends on.
8388 Such guesses are usually wrong. Even we cannot guess right about such
8389 things without first using the debugger to find the facts.
8392 @c The readline documentation is distributed with the readline code
8393 @c and consists of the two following files:
8396 @c Use -I with makeinfo to point to the appropriate directory,
8397 @c environment var TEXINPUTS with TeX.
8398 @include rluser.texinfo
8399 @include inc-hist.texi
8402 @node Renamed Commands
8403 @appendix Renamed Commands
8405 The following commands were renamed in GDB 4, in order to make the
8406 command set as a whole more consistent and easier to use and remember:
8409 @kindex delete environment
8410 @kindex info copying
8411 @kindex info convenience
8412 @kindex info directories
8413 @kindex info editing
8414 @kindex info history
8415 @kindex info targets
8417 @kindex info version
8418 @kindex info warranty
8419 @kindex set addressprint
8420 @kindex set arrayprint
8421 @kindex set prettyprint
8422 @kindex set screen-height
8423 @kindex set screen-width
8424 @kindex set unionprint
8425 @kindex set vtblprint
8426 @kindex set demangle
8427 @kindex set asm-demangle
8428 @kindex set sevenbit-strings
8429 @kindex set array-max
8431 @kindex set history write
8432 @kindex show addressprint
8433 @kindex show arrayprint
8434 @kindex show prettyprint
8435 @kindex show screen-height
8436 @kindex show screen-width
8437 @kindex show unionprint
8438 @kindex show vtblprint
8439 @kindex show demangle
8440 @kindex show asm-demangle
8441 @kindex show sevenbit-strings
8442 @kindex show array-max
8443 @kindex show caution
8444 @kindex show history write
8449 @c END TEXI2ROFF-KILL
8451 OLD COMMAND NEW COMMAND
8453 --------------- -------------------------------
8454 @c END TEXI2ROFF-KILL
8455 add-syms add-symbol-file
8456 delete environment unset environment
8457 info convenience show convenience
8458 info copying show copying
8459 info directories show directories
8460 info editing show commands
8461 info history show values
8462 info targets help target
8463 info values show values
8464 info version show version
8465 info warranty show warranty
8466 set/show addressprint set/show print address
8467 set/show array-max set/show print elements
8468 set/show arrayprint set/show print array
8469 set/show asm-demangle set/show print asm-demangle
8470 set/show caution set/show confirm
8471 set/show demangle set/show print demangle
8472 set/show history write set/show history save
8473 set/show prettyprint set/show print pretty
8474 set/show screen-height set/show height
8475 set/show screen-width set/show width
8476 set/show sevenbit-strings set/show print sevenbit-strings
8477 set/show unionprint set/show print union
8478 set/show vtblprint set/show print vtbl
8480 unset [No longer an alias for delete]
8486 \vskip \parskip\vskip \baselineskip
8487 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
8488 {\bf Old Command} &&{\bf New Command}\cr
8489 add-syms &&add-symbol-file\cr
8490 delete environment &&unset environment\cr
8491 info convenience &&show convenience\cr
8492 info copying &&show copying\cr
8493 info directories &&show directories \cr
8494 info editing &&show commands\cr
8495 info history &&show values\cr
8496 info targets &&help target\cr
8497 info values &&show values\cr
8498 info version &&show version\cr
8499 info warranty &&show warranty\cr
8500 set{\rm / }show addressprint &&set{\rm / }show print address\cr
8501 set{\rm / }show array-max &&set{\rm / }show print elements\cr
8502 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
8503 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
8504 set{\rm / }show caution &&set{\rm / }show confirm\cr
8505 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
8506 set{\rm / }show history write &&set{\rm / }show history save\cr
8507 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
8508 set{\rm / }show screen-height &&set{\rm / }show height\cr
8509 set{\rm / }show screen-width &&set{\rm / }show width\cr
8510 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
8511 set{\rm / }show unionprint &&set{\rm / }show print union\cr
8512 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
8514 unset &&\rm(No longer an alias for delete)\cr
8517 @c END TEXI2ROFF-KILL
8520 @ifclear PRECONFIGURED
8521 @node Formatting Documentation
8522 @appendix Formatting Documentation
8524 @cindex GDB reference card
8525 @cindex reference card
8526 The GDB 4 release includes an already-formatted reference card, ready
8527 for printing with PostScript or GhostScript, in the @file{gdb}
8528 subdirectory of the main source directory@footnote{In
8529 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
8530 release.}. If you can use PostScript or GhostScript with your printer,
8531 you can print the reference card immediately with @file{refcard.ps}.
8533 The release also includes the source for the reference card. You
8534 can format it, using @TeX{}, by typing:
8540 The GDB reference card is designed to print in landscape mode on US
8541 ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches
8542 high. You will need to specify this form of printing as an option to
8543 your @sc{dvi} output program.
8545 @cindex documentation
8547 All the documentation for GDB comes as part of the machine-readable
8548 distribution. The documentation is written in Texinfo format, which is
8549 a documentation system that uses a single source file to produce both
8550 on-line information and a printed manual. You can use one of the Info
8551 formatting commands to create the on-line version of the documentation
8552 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
8554 GDB includes an already formatted copy of the on-line Info version of
8555 this manual in the @file{gdb} subdirectory. The main Info file is
8556 @file{gdb-@var{version-number}/gdb/gdb.info}, and it refers to
8557 subordinate files matching @samp{gdb.info*} in the same directory. If
8558 necessary, you can print out these files, or read them with any editor;
8559 but they are easier to read using the @code{info} subsystem in GNU Emacs
8560 or the standalone @code{info} program, available as part of the GNU
8561 Texinfo distribution.
8563 If you want to format these Info files yourself, you need one of the
8564 Info formatting programs, such as @code{texinfo-format-buffer} or
8567 If you have @code{makeinfo} installed, and are in the top level GDB
8568 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
8569 make the Info file by typing:
8576 If you want to typeset and print copies of this manual, you need @TeX{},
8577 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
8578 Texinfo definitions file.
8580 @TeX{} is a typesetting program; it does not print files directly, but
8581 produces output files called @sc{dvi} files. To print a typeset
8582 document, you need a program to print @sc{dvi} files. If your system
8583 has @TeX{} installed, chances are it has such a program. The precise
8584 command to use depends on your system; @kbd{lpr -d} is common; another
8585 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
8586 require a file name without any extension or a @samp{.dvi} extension.
8588 @TeX{} also requires a macro definitions file called
8589 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
8590 written in Texinfo format. On its own, @TeX{} cannot read, much less
8591 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
8592 and is located in the @file{gdb-@var{version-number}/texinfo}
8595 If you have @TeX{} and a @sc{dvi} printer program installed, you can
8596 typeset and print this manual. First switch to the the @file{gdb}
8597 subdirectory of the main source directory (for example, to
8598 @file{gdb-@value{GDBVN}/gdb}) and then type:
8604 @node Installing GDB
8605 @appendix Installing GDB
8606 @cindex configuring GDB
8607 @cindex installation
8609 GDB comes with a @code{configure} script that automates the process
8610 of preparing GDB for installation; you can then use @code{make} to
8611 build the @code{gdb} program.
8613 @c irrelevant in info file; it's as current as the code it lives with.
8614 @footnote{If you have a more recent version of GDB than @value{GDBVN},
8615 look at the @file{README} file in the sources; we may have improved the
8616 installation procedures since publishing this manual.}
8619 The GDB distribution includes all the source code you need for GDB in
8620 a single directory, whose name is usually composed by appending the
8621 version number to @samp{gdb}.
8623 For example, the GDB version @value{GDBVN} distribution is in the
8624 @file{gdb-@value{GDBVN}} directory. That directory contains:
8627 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
8628 script for configuring GDB and all its supporting libraries.
8630 @item gdb-@value{GDBVN}/gdb
8631 the source specific to GDB itself
8633 @item gdb-@value{GDBVN}/bfd
8634 source for the Binary File Descriptor library
8636 @item gdb-@value{GDBVN}/include
8639 @item gdb-@value{GDBVN}/libiberty
8640 source for the @samp{-liberty} free software library
8642 @item gdb-@value{GDBVN}/opcodes
8643 source for the library of opcode tables and disassemblers
8645 @item gdb-@value{GDBVN}/readline
8646 source for the GNU command-line interface
8648 @item gdb-@value{GDBVN}/glob
8649 source for the GNU filename pattern-matching subroutine
8651 @item gdb-@value{GDBVN}/mmalloc
8652 source for the GNU memory-mapped malloc package
8655 The simplest way to configure and build GDB is to run @code{configure}
8656 from the @file{gdb-@var{version-number}} source directory, which in
8657 this example is the @file{gdb-@value{GDBVN}} directory.
8659 First switch to the @file{gdb-@var{version-number}} source directory
8660 if you are not already in it; then run @code{configure}. Pass the
8661 identifier for the platform on which GDB will run as an
8667 cd gdb-@value{GDBVN}
8668 ./configure @var{host}
8673 where @var{host} is an identifier such as @samp{sun4} or
8674 @samp{decstation}, that identifies the platform where GDB will run.
8675 (You can often leave off @var{host}; @code{configure} tries to guess the
8676 correct value by examining your system.)
8678 Running @samp{configure @var{host}} and then running @code{make} builds the
8679 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
8680 libraries, then @code{gdb} itself. The configured source files, and the
8681 binaries, are left in the corresponding source directories.
8683 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
8684 system does not recognize this automatically when you run a different
8685 shell, you may need to run @code{sh} on it explicitly:
8688 sh configure @var{host}
8691 If you run @code{configure} from a directory that contains source
8692 directories for multiple libraries or programs, such as the
8693 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
8694 creates configuration files for every directory level underneath (unless
8695 you tell it not to, with the @samp{--norecursion} option).
8697 You can run the @code{configure} script from any of the
8698 subordinate directories in the GDB distribution if you only want to
8699 configure that subdirectory, but be sure to specify a path to it.
8701 For example, with version @value{GDBVN}, type the following to configure only
8702 the @code{bfd} subdirectory:
8706 cd gdb-@value{GDBVN}/bfd
8707 ../configure @var{host}
8711 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
8712 However, you should make sure that the shell on your path (named by
8713 the @samp{SHELL} environment variable) is publicly readable. Remember
8714 that GDB uses the shell to start your program---some systems refuse to
8715 let GDB debug child processes whose programs are not readable.
8718 * Separate Objdir:: Compiling GDB in another directory
8719 * Config Names:: Specifying names for hosts and targets
8720 * configure Options:: Summary of options for configure
8723 @node Separate Objdir
8724 @section Compiling GDB in another directory
8726 If you want to run GDB versions for several host or target machines,
8727 you need a different @code{gdb} compiled for each combination of
8728 host and target. @code{configure} is designed to make this easy by
8729 allowing you to generate each configuration in a separate subdirectory,
8730 rather than in the source directory. If your @code{make} program
8731 handles the @samp{VPATH} feature (GNU @code{make} does), running
8732 @code{make} in each of these directories builds the @code{gdb}
8733 program specified there.
8735 To build @code{gdb} in a separate directory, run @code{configure}
8736 with the @samp{--srcdir} option to specify where to find the source.
8737 (You also need to specify a path to find @code{configure}
8738 itself from your working directory. If the path to @code{configure}
8739 would be the same as the argument to @samp{--srcdir}, you can leave out
8740 the @samp{--srcdir} option; it is assumed.)
8742 For example, with version @value{GDBVN}, you can build GDB in a separate
8743 directory for a Sun 4 like this:
8747 cd gdb-@value{GDBVN}
8750 ../gdb-@value{GDBVN}/configure sun4
8755 When @code{configure} builds a configuration using a remote source
8756 directory, it creates a tree for the binaries with the same structure
8757 (and using the same names) as the tree under the source directory. In
8758 the example, you'd find the Sun 4 library @file{libiberty.a} in the
8759 directory @file{gdb-sun4/libiberty}, and GDB itself in
8760 @file{gdb-sun4/gdb}.
8762 One popular reason to build several GDB configurations in separate
8763 directories is to configure GDB for cross-compiling (where GDB
8764 runs on one machine---the host---while debugging programs that run on
8765 another machine---the target). You specify a cross-debugging target by
8766 giving the @samp{--target=@var{target}} option to @code{configure}.
8768 When you run @code{make} to build a program or library, you must run
8769 it in a configured directory---whatever directory you were in when you
8770 called @code{configure} (or one of its subdirectories).
8772 The @code{Makefile} that @code{configure} generates in each source
8773 directory also runs recursively. If you type @code{make} in a source
8774 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
8775 directory configured with @samp{--srcdir=@var{path}/gdb-@value{GDBVN}}), you
8776 will build all the required libraries, and then build GDB.
8778 When you have multiple hosts or targets configured in separate
8779 directories, you can run @code{make} on them in parallel (for example,
8780 if they are NFS-mounted on each of the hosts); they will not interfere
8784 @section Specifying names for hosts and targets
8786 The specifications used for hosts and targets in the @code{configure}
8787 script are based on a three-part naming scheme, but some short predefined
8788 aliases are also supported. The full naming scheme encodes three pieces
8789 of information in the following pattern:
8792 @var{architecture}-@var{vendor}-@var{os}
8795 For example, you can use the alias @code{sun4} as a @var{host} argument,
8796 or as the value for @var{target} in a @code{--target=@var{target}}
8797 option. The equivalent full name is @samp{sparc-sun-sunos4}.
8799 The @code{configure} script accompanying GDB does not provide
8800 any query facility to list all supported host and target names or
8801 aliases. @code{configure} calls the Bourne shell script
8802 @code{config.sub} to map abbreviations to full names; you can read the
8803 script, if you wish, or you can use it to test your guesses on
8804 abbreviations---for example:
8807 % sh config.sub sun4
8808 sparc-sun-sunos4.1.1
8809 % sh config.sub sun3
8811 % sh config.sub decstation
8813 % sh config.sub hp300bsd
8815 % sh config.sub i386v
8817 % sh config.sub i786v
8818 Invalid configuration `i786v': machine `i786v' not recognized
8822 @code{config.sub} is also distributed in the GDB source
8823 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
8825 @node configure Options
8826 @section @code{configure} options
8828 Here is a summary of the @code{configure} options and arguments that
8829 are most often useful for building @value{GDBN}. @code{configure} also has
8830 several other options not listed here. @inforef{What Configure
8831 Does,,configure.info}, for a full explanation of @code{configure}.
8832 @c FIXME: Would this be more, or less, useful as an xref (ref to printed
8833 @c manual in the printed manual, ref to info file only from the info file)?
8836 configure @r{[}--help@r{]}
8837 @r{[}--prefix=@var{dir}@r{]}
8838 @r{[}--srcdir=@var{path}@r{]}
8839 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
8840 @r{[}--target=@var{target}@r{]} @var{host}
8844 You may introduce options with a single @samp{-} rather than
8845 @samp{--} if you prefer; but you may abbreviate option names if you use
8850 Display a quick summary of how to invoke @code{configure}.
8852 @item -prefix=@var{dir}
8853 Configure the source to install programs and files under directory
8856 @c avoid splitting the warning from the explanation:
8858 @item --srcdir=@var{path}
8859 @strong{Warning: using this option requires GNU @code{make}, or another
8860 @code{make} that implements the @code{VPATH} feature.}@*
8861 Use this option to make configurations in directories separate from the
8862 GDB source directories. Among other things, you can use this to
8863 build (or maintain) several configurations simultaneously, in separate
8864 directories. @code{configure} writes configuration specific files in
8865 the current directory, but arranges for them to use the source in the
8866 directory @var{path}. @code{configure} creates directories under
8867 the working directory in parallel to the source directories below
8871 Configure only the directory level where @code{configure} is executed; do not
8872 propagate configuration to subdirectories.
8875 @emph{Remove} files otherwise built during configuration.
8877 @c This does not work (yet if ever). FIXME.
8878 @c @item --parse=@var{lang} @dots{}
8879 @c Configure the GDB expression parser to parse the listed languages.
8880 @c @samp{all} configures GDB for all supported languages. To get a
8881 @c list of all supported languages, omit the argument. Without this
8882 @c option, GDB is configured to parse all supported languages.
8884 @item --target=@var{target}
8885 Configure GDB for cross-debugging programs running on the specified
8886 @var{target}. Without this option, GDB is configured to debug
8887 programs that run on the same machine (@var{host}) as GDB itself.
8889 There is no convenient way to generate a list of all available targets.
8891 @item @var{host} @dots{}
8892 Configure GDB to run on the specified @var{host}.
8894 There is no convenient way to generate a list of all available hosts.
8898 @code{configure} accepts other options, for compatibility with
8899 configuring other GNU tools recursively; but these are the only
8900 options that affect GDB or its supporting libraries.
8909 % I think something like @colophon should be in texinfo. In the
8911 \long\def\colophon{\hbox to0pt{}\vfill
8912 \centerline{The body of this manual is set in}
8913 \centerline{\fontname\tenrm,}
8914 \centerline{with headings in {\bf\fontname\tenbf}}
8915 \centerline{and examples in {\tt\fontname\tentt}.}
8916 \centerline{{\it\fontname\tenit\/},}
8917 \centerline{{\bf\fontname\tenbf}, and}
8918 \centerline{{\sl\fontname\tensl\/}}
8919 \centerline{are used for emphasis.}\vfill}
8921 % Blame: pesch@cygnus.com, 1991.