1 \input texinfo @c -*-texinfo-*-
3 @c Free Software Foundation, Inc.
6 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
7 @c of @set vars. However, you can override filename with makeinfo -o.
12 @settitle Debugging with @value{GDBN}
13 @setchapternewpage odd
24 @c readline appendices use @vindex
27 @c !!set GDB manual's edition---not the same as GDB version!
30 @c !!set GDB manual's revision date
31 @set DATE February 1999
33 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
35 @c This is a dir.info fragment to support semi-automated addition of
36 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
37 @dircategory Programming & development tools.
39 * Gdb: (gdb). The @sc{gnu} debugger.
43 This file documents the @sc{gnu} debugger @value{GDBN}.
46 This is the @value{EDITION} Edition, @value{DATE},
47 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
48 for @value{GDBN} Version @value{GDBVN}.
50 Copyright (C) 1988-1999 Free Software Foundation, Inc.
52 Permission is granted to make and distribute verbatim copies of
53 this manual provided the copyright notice and this permission notice
54 are preserved on all copies.
57 Permission is granted to process this file through TeX and print the
58 results, provided the printed document carries copying permission
59 notice identical to this one except for the removal of this paragraph
60 (this paragraph not being relevant to the printed manual).
63 Permission is granted to copy and distribute modified versions of this
64 manual under the conditions for verbatim copying, provided also that the
65 entire resulting derived work is distributed under the terms of a
66 permission notice identical to this one.
68 Permission is granted to copy and distribute translations of this manual
69 into another language, under the above conditions for modified versions.
73 @title Debugging with @value{GDBN}
74 @subtitle The @sc{gnu} Source-Level Debugger
76 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
77 @subtitle @value{DATE}
78 @author Richard M. Stallman and Roland H. Pesch
82 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
83 \hfill {\it Debugging with @value{GDBN}}\par
84 \hfill \TeX{}info \texinfoversion\par
88 @c ISBN seems to be wrong...
90 @vskip 0pt plus 1filll
91 Copyright @copyright{} 1988-1999 Free Software Foundation, Inc.
93 Published by the Free Software Foundation @*
94 59 Temple Place - Suite 330, @*
95 Boston, MA 02111-1307 USA @*
96 Printed copies are available for $20 each. @*
99 Permission is granted to make and distribute verbatim copies of
100 this manual provided the copyright notice and this permission notice
101 are preserved on all copies.
103 Permission is granted to copy and distribute modified versions of this
104 manual under the conditions for verbatim copying, provided also that the
105 entire resulting derived work is distributed under the terms of a
106 permission notice identical to this one.
108 Permission is granted to copy and distribute translations of this manual
109 into another language, under the above conditions for modified versions.
114 @node Top, Summary, (dir), (dir)
116 @top Debugging with @value{GDBN}
118 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
120 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
123 Copyright (C) 1988-1999 Free Software Foundation, Inc.
126 * Summary:: Summary of @value{GDBN}
127 * Sample Session:: A sample @value{GDBN} session
129 * Invocation:: Getting in and out of @value{GDBN}
130 * Commands:: @value{GDBN} commands
131 * Running:: Running programs under @value{GDBN}
132 * Stopping:: Stopping and continuing
133 * Stack:: Examining the stack
134 * Source:: Examining source files
135 * Data:: Examining data
137 * Languages:: Using @value{GDBN} with different languages
139 * Symbols:: Examining the symbol table
140 * Altering:: Altering execution
141 * GDB Files:: @value{GDBN} files
142 * Targets:: Specifying a debugging target
143 * Configurations:: Configuration-specific information
144 * Controlling GDB:: Controlling @value{GDBN}
145 * Sequences:: Canned sequences of commands
146 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
147 * Annotations:: @value{GDBN}'s annotations interface.
149 * GDB Bugs:: Reporting bugs in @value{GDBN}
150 * Formatting Documentation:: How to format and print @value{GDBN} documentation
152 * Command Line Editing:: Command Line Editing
153 * Using History Interactively:: Using History Interactively
154 * Installing GDB:: Installing GDB
158 @node Summary, Sample Session, Top, Top
159 @unnumbered Summary of @value{GDBN}
161 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
162 going on ``inside'' another program while it executes---or what another
163 program was doing at the moment it crashed.
165 @value{GDBN} can do four main kinds of things (plus other things in support of
166 these) to help you catch bugs in the act:
170 Start your program, specifying anything that might affect its behavior.
173 Make your program stop on specified conditions.
176 Examine what has happened, when your program has stopped.
179 Change things in your program, so you can experiment with correcting the
180 effects of one bug and go on to learn about another.
183 You can use @value{GDBN} to debug programs written in C and C++.
184 For more information, see @ref{Support,,Supported languages}.
185 For more information, see @ref{C,,C and C++}.
189 Support for Modula-2 and Chill is partial. For information on Modula-2,
190 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
193 Debugging Pascal programs which use sets, subranges, file variables, or
194 nested functions does not currently work. @value{GDBN} does not support
195 entering expressions, printing values, or similar features using Pascal
199 @value{GDBN} can be used to debug programs written in Fortran, although
200 it may be necessary to refer to some variables with a trailing
204 * Free Software:: Freely redistributable software
205 * Contributors:: Contributors to GDB
208 @node Free Software, Contributors, Summary, Summary
209 @unnumberedsec Free software
211 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
212 General Public License
213 (GPL). The GPL gives you the freedom to copy or adapt a licensed
214 program---but every person getting a copy also gets with it the
215 freedom to modify that copy (which means that they must get access to
216 the source code), and the freedom to distribute further copies.
217 Typical software companies use copyrights to limit your freedoms; the
218 Free Software Foundation uses the GPL to preserve these freedoms.
220 Fundamentally, the General Public License is a license which says that
221 you have these freedoms and that you cannot take these freedoms away
224 @node Contributors, , Free Software, Summary
225 @unnumberedsec Contributors to @value{GDBN}
227 Richard Stallman was the original author of @value{GDBN}, and of many
228 other @sc{gnu} programs. Many others have contributed to its
229 development. This section attempts to credit major contributors. One
230 of the virtues of free software is that everyone is free to contribute
231 to it; with regret, we cannot actually acknowledge everyone here. The
232 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
233 blow-by-blow account.
235 Changes much prior to version 2.0 are lost in the mists of time.
238 @emph{Plea:} Additions to this section are particularly welcome. If you
239 or your friends (or enemies, to be evenhanded) have been unfairly
240 omitted from this list, we would like to add your names!
243 So that they may not regard their many labors as thankless, we
244 particularly thank those who shepherded @value{GDBN} through major
246 Jim Blandy (release 4.18);
247 Jason Molenda (release 4.17);
248 Stan Shebs (release 4.14);
249 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
250 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
251 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
252 Jim Kingdon (releases 3.5, 3.4, and 3.3);
253 and Randy Smith (releases 3.2, 3.1, and 3.0).
255 Richard Stallman, assisted at various times by Peter TerMaat, Chris
256 Hanson, and Richard Mlynarik, handled releases through 2.8.
258 Michael Tiemann is the author of most of the @sc{gnu} C++ support in
259 @value{GDBN}, with significant additional contributions from Per
260 Bothner. James Clark wrote the @sc{gnu} C++ demangler. Early work on
261 C++ was by Peter TerMaat (who also did much general update work leading
264 @value{GDBN} 4 uses the BFD subroutine library to examine multiple
265 object-file formats; BFD was a joint project of David V.
266 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
268 David Johnson wrote the original COFF support; Pace Willison did
269 the original support for encapsulated COFF.
271 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
273 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
274 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
276 Jean-Daniel Fekete contributed Sun 386i support.
277 Chris Hanson improved the HP9000 support.
278 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
279 David Johnson contributed Encore Umax support.
280 Jyrki Kuoppala contributed Altos 3068 support.
281 Jeff Law contributed HP PA and SOM support.
282 Keith Packard contributed NS32K support.
283 Doug Rabson contributed Acorn Risc Machine support.
284 Bob Rusk contributed Harris Nighthawk CX-UX support.
285 Chris Smith contributed Convex support (and Fortran debugging).
286 Jonathan Stone contributed Pyramid support.
287 Michael Tiemann contributed SPARC support.
288 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
289 Pace Willison contributed Intel 386 support.
290 Jay Vosburgh contributed Symmetry support.
292 Andreas Schwab contributed M68K Linux support.
294 Rich Schaefer and Peter Schauer helped with support of SunOS shared
297 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
298 about several machine instruction sets.
300 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
301 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
302 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
303 and RDI targets, respectively.
305 Brian Fox is the author of the readline libraries providing
306 command-line editing and command history.
308 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
309 Modula-2 support, and contributed the Languages chapter of this manual.
311 Fred Fish wrote most of the support for Unix System Vr4.
312 He also enhanced the command-completion support to cover C++ overloaded
315 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
318 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
320 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
322 Toshiba sponsored the support for the TX39 Mips processor.
324 Matsushita sponsored the support for the MN10200 and MN10300 processors.
326 Fujitsu sponsored the support for SPARClite and FR30 processors.
328 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
331 Michael Snyder added support for tracepoints.
333 Stu Grossman wrote gdbserver.
335 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
336 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
338 The following people at the Hewlett-Packard Company contributed
339 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
340 (narrow mode), HP's implementation of kernel threads, HP's aC++
341 compiler, and the terminal user interface: Ben Krepp, Richard Title,
342 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
343 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
344 information in this manual.
346 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
347 development since 1991. Cygnus engineers who have worked on @value{GDBN}
348 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
349 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
350 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
351 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
352 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
353 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
354 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
355 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
356 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
357 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
358 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
359 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
360 Zuhn have made contributions both large and small.
363 @node Sample Session, Invocation, Summary, Top
364 @chapter A Sample @value{GDBN} Session
366 You can use this manual at your leisure to read all about @value{GDBN}.
367 However, a handful of commands are enough to get started using the
368 debugger. This chapter illustrates those commands.
371 In this sample session, we emphasize user input like this: @b{input},
372 to make it easier to pick out from the surrounding output.
375 @c FIXME: this example may not be appropriate for some configs, where
376 @c FIXME...primary interest is in remote use.
378 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
379 processor) exhibits the following bug: sometimes, when we change its
380 quote strings from the default, the commands used to capture one macro
381 definition within another stop working. In the following short @code{m4}
382 session, we define a macro @code{foo} which expands to @code{0000}; we
383 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
384 same thing. However, when we change the open quote string to
385 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
386 procedure fails to define a new synonym @code{baz}:
395 @b{define(bar,defn(`foo'))}
399 @b{changequote(<QUOTE>,<UNQUOTE>)}
401 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
404 m4: End of input: 0: fatal error: EOF in string
408 Let us use @value{GDBN} to try to see what is going on.
411 $ @b{@value{GDBP} m4}
412 @c FIXME: this falsifies the exact text played out, to permit smallbook
413 @c FIXME... format to come out better.
414 @value{GDBN} is free software and you are welcome to distribute copies
415 of it under certain conditions; type "show copying" to see
417 There is absolutely no warranty for @value{GDBN}; type "show warranty"
420 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
425 @value{GDBN} reads only enough symbol data to know where to find the
426 rest when needed; as a result, the first prompt comes up very quickly.
427 We now tell @value{GDBN} to use a narrower display width than usual, so
428 that examples fit in this manual.
431 (@value{GDBP}) @b{set width 70}
435 We need to see how the @code{m4} built-in @code{changequote} works.
436 Having looked at the source, we know the relevant subroutine is
437 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
438 @code{break} command.
441 (@value{GDBP}) @b{break m4_changequote}
442 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
446 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
447 control; as long as control does not reach the @code{m4_changequote}
448 subroutine, the program runs as usual:
451 (@value{GDBP}) @b{run}
452 Starting program: /work/Editorial/gdb/gnu/m4/m4
460 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
461 suspends execution of @code{m4}, displaying information about the
462 context where it stops.
465 @b{changequote(<QUOTE>,<UNQUOTE>)}
467 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
469 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
473 Now we use the command @code{n} (@code{next}) to advance execution to
474 the next line of the current function.
478 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
483 @code{set_quotes} looks like a promising subroutine. We can go into it
484 by using the command @code{s} (@code{step}) instead of @code{next}.
485 @code{step} goes to the next line to be executed in @emph{any}
486 subroutine, so it steps into @code{set_quotes}.
490 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
492 530 if (lquote != def_lquote)
496 The display that shows the subroutine where @code{m4} is now
497 suspended (and its arguments) is called a stack frame display. It
498 shows a summary of the stack. We can use the @code{backtrace}
499 command (which can also be spelled @code{bt}), to see where we are
500 in the stack as a whole: the @code{backtrace} command displays a
501 stack frame for each active subroutine.
504 (@value{GDBP}) @b{bt}
505 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
507 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
509 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
510 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
512 #4 0x79dc in expand_input () at macro.c:40
513 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
517 We step through a few more lines to see what happens. The first two
518 times, we can use @samp{s}; the next two times we use @code{n} to avoid
519 falling into the @code{xstrdup} subroutine.
523 0x3b5c 532 if (rquote != def_rquote)
525 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
526 def_lquote : xstrdup(lq);
528 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
531 538 len_lquote = strlen(rquote);
535 The last line displayed looks a little odd; we can examine the variables
536 @code{lquote} and @code{rquote} to see if they are in fact the new left
537 and right quotes we specified. We use the command @code{p}
538 (@code{print}) to see their values.
541 (@value{GDBP}) @b{p lquote}
542 $1 = 0x35d40 "<QUOTE>"
543 (@value{GDBP}) @b{p rquote}
544 $2 = 0x35d50 "<UNQUOTE>"
548 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
549 To look at some context, we can display ten lines of source
550 surrounding the current line with the @code{l} (@code{list}) command.
556 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
558 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
561 538 len_lquote = strlen(rquote);
562 539 len_rquote = strlen(lquote);
569 Let us step past the two lines that set @code{len_lquote} and
570 @code{len_rquote}, and then examine the values of those variables.
574 539 len_rquote = strlen(lquote);
577 (@value{GDBP}) @b{p len_lquote}
579 (@value{GDBP}) @b{p len_rquote}
584 That certainly looks wrong, assuming @code{len_lquote} and
585 @code{len_rquote} are meant to be the lengths of @code{lquote} and
586 @code{rquote} respectively. We can set them to better values using
587 the @code{p} command, since it can print the value of
588 any expression---and that expression can include subroutine calls and
592 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
594 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
599 Is that enough to fix the problem of using the new quotes with the
600 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
601 executing with the @code{c} (@code{continue}) command, and then try the
602 example that caused trouble initially:
608 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
615 Success! The new quotes now work just as well as the default ones. The
616 problem seems to have been just the two typos defining the wrong
617 lengths. We allow @code{m4} exit by giving it an EOF as input:
621 Program exited normally.
625 The message @samp{Program exited normally.} is from @value{GDBN}; it
626 indicates @code{m4} has finished executing. We can end our @value{GDBN}
627 session with the @value{GDBN} @code{quit} command.
630 (@value{GDBP}) @b{quit}
633 @node Invocation, Commands, Sample Session, Top
634 @chapter Getting In and Out of @value{GDBN}
636 This chapter discusses how to start @value{GDBN}, and how to get out of it.
640 type @samp{@value{GDBP}} to start @value{GDBN}.
642 type @kbd{quit} or @kbd{C-d} to exit.
646 * Invoking GDB:: How to start @value{GDBN}
647 * Quitting GDB:: How to quit @value{GDBN}
648 * Shell Commands:: How to use shell commands inside @value{GDBN}
651 @node Invoking GDB, Quitting GDB, Invocation, Invocation
652 @section Invoking @value{GDBN}
654 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
655 @value{GDBN} reads commands from the terminal until you tell it to exit.
657 You can also run @code{@value{GDBP}} with a variety of arguments and options,
658 to specify more of your debugging environment at the outset.
660 The command-line options described here are designed
661 to cover a variety of situations; in some environments, some of these
662 options may effectively be unavailable.
664 The most usual way to start @value{GDBN} is with one argument,
665 specifying an executable program:
668 @value{GDBP} @var{program}
672 You can also start with both an executable program and a core file
676 @value{GDBP} @var{program} @var{core}
679 You can, instead, specify a process ID as a second argument, if you want
680 to debug a running process:
683 @value{GDBP} @var{program} 1234
687 would attach @value{GDBN} to process @code{1234} (unless you also have a file
688 named @file{1234}; @value{GDBN} does check for a core file first).
690 Taking advantage of the second command-line argument requires a fairly
691 complete operating system; when you use @value{GDBN} as a remote
692 debugger attached to a bare board, there may not be any notion of
693 ``process'', and there is often no way to get a core dump. @value{GDBN}
694 will warn you if it is unable to attach or to read core dumps.
696 You can run @code{@value{GDBP}} without printing the front material, which describes
697 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
704 You can further control how @value{GDBN} starts up by using command-line
705 options. @value{GDBN} itself can remind you of the options available.
715 to display all available options and briefly describe their use
716 (@samp{@value{GDBP} -h} is a shorter equivalent).
718 All options and command line arguments you give are processed
719 in sequential order. The order makes a difference when the
720 @samp{-x} option is used.
724 * File Options:: Choosing files
725 * Mode Options:: Choosing modes
728 @node File Options, Mode Options, Invoking GDB, Invoking GDB
729 @subsection Choosing files
731 When @value{GDBN} starts, it reads any arguments other than options as
732 specifying an executable file and core file (or process ID). This is
733 the same as if the arguments were specified by the @samp{-se} and
734 @samp{-c} options respectively. (@value{GDBN} reads the first argument
735 that does not have an associated option flag as equivalent to the
736 @samp{-se} option followed by that argument; and the second argument
737 that does not have an associated option flag, if any, as equivalent to
738 the @samp{-c} option followed by that argument.)
740 If @value{GDBN} has not been configured to included core file support,
741 such as for most embedded targets, then it will complain about a second
742 argument and ignore it.
744 Many options have both long and short forms; both are shown in the
745 following list. @value{GDBN} also recognizes the long forms if you truncate
746 them, so long as enough of the option is present to be unambiguous.
747 (If you prefer, you can flag option arguments with @samp{--} rather
748 than @samp{-}, though we illustrate the more usual convention.)
750 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
751 @c way, both those who look for -foo and --foo in the index, will find
755 @item -symbols @var{file}
757 @cindex @code{--symbols}
759 Read symbol table from file @var{file}.
761 @item -exec @var{file}
763 @cindex @code{--exec}
765 Use file @var{file} as the executable file to execute when appropriate,
766 and for examining pure data in conjunction with a core dump.
770 Read symbol table from file @var{file} and use it as the executable
773 @item -core @var{file}
775 @cindex @code{--core}
777 Use file @var{file} as a core dump to examine.
779 @item -c @var{number}
780 Connect to process ID @var{number}, as with the @code{attach} command
781 (unless there is a file in core-dump format named @var{number}, in which
782 case @samp{-c} specifies that file as a core dump to read).
784 @item -command @var{file}
786 @cindex @code{--command}
788 Execute @value{GDBN} commands from file @var{file}. @xref{Command
789 Files,, Command files}.
791 @item -directory @var{directory}
792 @itemx -d @var{directory}
793 @cindex @code{--directory}
795 Add @var{directory} to the path to search for source files.
799 @cindex @code{--mapped}
801 @emph{Warning: this option depends on operating system facilities that are not
802 supported on all systems.}@*
803 If memory-mapped files are available on your system through the @code{mmap}
804 system call, you can use this option
805 to have @value{GDBN} write the symbols from your
806 program into a reusable file in the current directory. If the program you are debugging is
807 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
808 Future @value{GDBN} debugging sessions notice the presence of this file,
809 and can quickly map in symbol information from it, rather than reading
810 the symbol table from the executable program.
812 The @file{.syms} file is specific to the host machine where @value{GDBN}
813 is run. It holds an exact image of the internal @value{GDBN} symbol
814 table. It cannot be shared across multiple host platforms.
818 @cindex @code{--readnow}
820 Read each symbol file's entire symbol table immediately, rather than
821 the default, which is to read it incrementally as it is needed.
822 This makes startup slower, but makes future operations faster.
826 You typically combine the @code{-mapped} and @code{-readnow} options in
827 order to build a @file{.syms} file that contains complete symbol
828 information. (@xref{Files,,Commands to specify files}, for information
829 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
830 but build a @file{.syms} file for future use is:
833 gdb -batch -nx -mapped -readnow programname
836 @node Mode Options, , File Options, Invoking GDB
837 @subsection Choosing modes
839 You can run @value{GDBN} in various alternative modes---for example, in
840 batch mode or quiet mode.
847 Do not execute commands found in any initialization files (normally
848 called @file{.gdbinit}, or @file{gdb.ini} on PCs). Normally,
849 @value{GDBN} executes the commands in these files after all the command
850 options and arguments have been processed. @xref{Command Files,,Command
856 @cindex @code{--quiet}
857 @cindex @code{--silent}
859 ``Quiet''. Do not print the introductory and copyright messages. These
860 messages are also suppressed in batch mode.
863 @cindex @code{--batch}
864 Run in batch mode. Exit with status @code{0} after processing all the
865 command files specified with @samp{-x} (and all commands from
866 initialization files, if not inhibited with @samp{-n}). Exit with
867 nonzero status if an error occurs in executing the @value{GDBN} commands
868 in the command files.
870 Batch mode may be useful for running @value{GDBN} as a filter, for
871 example to download and run a program on another computer; in order to
872 make this more useful, the message
875 Program exited normally.
879 (which is ordinarily issued whenever a program running under
880 @value{GDBN} control terminates) is not issued when running in batch
885 @cindex @code{--nowindows}
887 ``No windows''. If @value{GDBN} comes with a graphical user interface
888 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
889 interface. If no GUI is available, this option has no effect.
893 @cindex @code{--windows}
895 If @value{GDBN} includes a GUI, then this option requires it to be
898 @item -cd @var{directory}
900 Run @value{GDBN} using @var{directory} as its working directory,
901 instead of the current directory.
905 @cindex @code{--fullname}
907 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
908 subprocess. It tells @value{GDBN} to output the full file name and line
909 number in a standard, recognizable fashion each time a stack frame is
910 displayed (which includes each time your program stops). This
911 recognizable format looks like two @samp{\032} characters, followed by
912 the file name, line number and character position separated by colons,
913 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
914 @samp{\032} characters as a signal to display the source code for the
918 @cindex @code{--epoch}
919 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
920 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
921 routines so as to allow Epoch to display values of expressions in a
924 @item -annotate @var{level}
925 @cindex @code{--annotate}
926 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
927 effect is identical to using @samp{set annotate @var{level}}
928 (@pxref{Annotations}).
929 Annotation level controls how much information does @value{GDBN} print
930 together with its prompt, values of expressions, source lines, and other
931 types of output. Level 0 is the normal, level 1 is for use when
932 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
933 maximum annotation suitable for programs that control @value{GDBN}.
936 @cindex @code{--async}
937 Use the asynchronous event loop for the command-line interface.
938 @value{GDBN} processes all events, such as user keyboard input, via a
939 special event loop. This allows @value{GDBN} to accept and process user
940 commands in parallel with the debugged process being
941 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
942 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
943 suspended when the debuggee runs.}, so you don't need to wait for
944 control to return to @value{GDBN} before you type the next command.
945 (@emph{Note:} as of version 5.0, the target side of the asynchronous
946 operation is not yet in place, so @samp{-async} does not work fully
948 @c FIXME: when the target side of the event loop is done, the above NOTE
949 @c should be removed.
951 When the standard input is connected to a terminal device, @value{GDBN}
952 uses the asynchronous event loop by default, unless disabled by the
953 @samp{-noasync} option.
956 @cindex @code{--noasync}
957 Disable the asynchronous event loop for the command-line interface.
959 @item -baud @var{bps}
961 @cindex @code{--baud}
963 Set the line speed (baud rate or bits per second) of any serial
964 interface used by @value{GDBN} for remote debugging.
966 @item -tty @var{device}
967 @itemx -t @var{device}
970 Run using @var{device} for your program's standard input and output.
971 @c FIXME: kingdon thinks there is more to -tty. Investigate.
973 @c resolve the situation of these eventually
975 @c @cindex @code{--tui}
976 @c Use a Terminal User Interface. For information, use your Web browser to
977 @c read the file @file{TUI.html}, which is usually installed in the
978 @c directory @code{/opt/langtools/wdb/doc} on HP-UX systems. Do not use
979 @c this option if you run @value{GDBN} from Emacs (see @pxref{Emacs, ,Using
980 @c @value{GDBN} under @sc{gnu} Emacs}).
983 @c @cindex @code{--xdb}
984 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
985 @c For information, see the file @file{xdb_trans.html}, which is usually
986 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
989 @item -interpreter @var{interp}
990 @cindex @code{--interpreter}
991 Use the interpreter @var{interp} for interface with the controlling
992 program or device. This option is meant to be set by programs which
993 communicate with @value{GDBN} using it as a back end. For example,
994 @samp{--interpreter=mi} causes @value{GDBN} to use the @dfn{gdbmi
996 @c FIXME: There should be an @xref here to the GDB/MI docs, but
997 @c gdbmi.texi doesn't have a single node to reference!
1000 @cindex @code{--write}
1001 Open the executable and core files for both reading and writing. This
1002 is equivalent to the @samp{set write on} command inside @value{GDBN}
1006 @cindex @code{--statistics}
1007 This option causes @value{GDBN} to print statistics about time and
1008 memory usage after it completes each command and returns to the prompt.
1011 @cindex @code{--version}
1012 This option causes @value{GDBN} to print its version number and
1013 no-warranty blurb, and exit.
1017 @node Quitting GDB, Shell Commands, Invoking GDB, Invocation
1018 @section Quitting @value{GDBN}
1019 @cindex exiting @value{GDBN}
1020 @cindex leaving @value{GDBN}
1023 @kindex quit @r{[}@var{expression}@r{]}
1025 @item quit @r{[}@var{expression}@r{]}
1027 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1028 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1029 do not supply @var{expression}, @value{GDBN} will terminate normally;
1030 otherwise it will terminate using the result of @var{expression} as the
1035 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1036 terminates the action of any @value{GDBN} command that is in progress and
1037 returns to @value{GDBN} command level. It is safe to type the interrupt
1038 character at any time because @value{GDBN} does not allow it to take effect
1039 until a time when it is safe.
1041 If you have been using @value{GDBN} to control an attached process or
1042 device, you can release it with the @code{detach} command
1043 (@pxref{Attach, ,Debugging an already-running process}).
1045 @node Shell Commands, , Quitting GDB, Invocation
1046 @section Shell commands
1048 If you need to execute occasional shell commands during your
1049 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1050 just use the @code{shell} command.
1054 @cindex shell escape
1055 @item shell @var{command string}
1056 Invoke a standard shell to execute @var{command string}.
1057 If it exists, the environment variable @code{SHELL} determines which
1058 shell to run. Otherwise @value{GDBN} uses the default shell
1059 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1062 The utility @code{make} is often needed in development environments.
1063 You do not have to use the @code{shell} command for this purpose in
1068 @cindex calling make
1069 @item make @var{make-args}
1070 Execute the @code{make} program with the specified
1071 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1074 @node Commands, Running, Invocation, Top
1075 @chapter @value{GDBN} Commands
1077 You can abbreviate a @value{GDBN} command to the first few letters of the command
1078 name, if that abbreviation is unambiguous; and you can repeat certain
1079 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1080 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1081 show you the alternatives available, if there is more than one possibility).
1084 * Command Syntax:: How to give commands to @value{GDBN}
1085 * Completion:: Command completion
1086 * Help:: How to ask @value{GDBN} for help
1089 @node Command Syntax, Completion, Commands, Commands
1090 @section Command syntax
1092 A @value{GDBN} command is a single line of input. There is no limit on
1093 how long it can be. It starts with a command name, which is followed by
1094 arguments whose meaning depends on the command name. For example, the
1095 command @code{step} accepts an argument which is the number of times to
1096 step, as in @samp{step 5}. You can also use the @code{step} command
1097 with no arguments. Some commands do not allow any arguments.
1099 @cindex abbreviation
1100 @value{GDBN} command names may always be truncated if that abbreviation is
1101 unambiguous. Other possible command abbreviations are listed in the
1102 documentation for individual commands. In some cases, even ambiguous
1103 abbreviations are allowed; for example, @code{s} is specially defined as
1104 equivalent to @code{step} even though there are other commands whose
1105 names start with @code{s}. You can test abbreviations by using them as
1106 arguments to the @code{help} command.
1108 @cindex repeating commands
1110 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1111 repeat the previous command. Certain commands (for example, @code{run})
1112 will not repeat this way; these are commands whose unintentional
1113 repetition might cause trouble and which you are unlikely to want to
1116 The @code{list} and @code{x} commands, when you repeat them with
1117 @key{RET}, construct new arguments rather than repeating
1118 exactly as typed. This permits easy scanning of source or memory.
1120 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1121 output, in a way similar to the common utility @code{more}
1122 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1123 @key{RET} too many in this situation, @value{GDBN} disables command
1124 repetition after any command that generates this sort of display.
1128 Any text from a @kbd{#} to the end of the line is a comment; it does
1129 nothing. This is useful mainly in command files (@pxref{Command
1130 Files,,Command files}).
1132 @node Completion, Help, Command Syntax, Commands
1133 @section Command completion
1136 @cindex word completion
1137 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1138 only one possibility; it can also show you what the valid possibilities
1139 are for the next word in a command, at any time. This works for @value{GDBN}
1140 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1142 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1143 of a word. If there is only one possibility, @value{GDBN} fills in the
1144 word, and waits for you to finish the command (or press @key{RET} to
1145 enter it). For example, if you type
1147 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1148 @c complete accuracy in these examples; space introduced for clarity.
1149 @c If texinfo enhancements make it unnecessary, it would be nice to
1150 @c replace " @key" by "@key" in the following...
1152 (@value{GDBP}) info bre @key{TAB}
1156 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1157 the only @code{info} subcommand beginning with @samp{bre}:
1160 (@value{GDBP}) info breakpoints
1164 You can either press @key{RET} at this point, to run the @code{info
1165 breakpoints} command, or backspace and enter something else, if
1166 @samp{breakpoints} does not look like the command you expected. (If you
1167 were sure you wanted @code{info breakpoints} in the first place, you
1168 might as well just type @key{RET} immediately after @samp{info bre},
1169 to exploit command abbreviations rather than command completion).
1171 If there is more than one possibility for the next word when you press
1172 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1173 characters and try again, or just press @key{TAB} a second time;
1174 @value{GDBN} displays all the possible completions for that word. For
1175 example, you might want to set a breakpoint on a subroutine whose name
1176 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1177 just sounds the bell. Typing @key{TAB} again displays all the
1178 function names in your program that begin with those characters, for
1182 (@value{GDBP}) b make_ @key{TAB}
1183 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1184 make_a_section_from_file make_environ
1185 make_abs_section make_function_type
1186 make_blockvector make_pointer_type
1187 make_cleanup make_reference_type
1188 make_command make_symbol_completion_list
1189 (@value{GDBP}) b make_
1193 After displaying the available possibilities, @value{GDBN} copies your
1194 partial input (@samp{b make_} in the example) so you can finish the
1197 If you just want to see the list of alternatives in the first place, you
1198 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1199 means @kbd{@key{META} ?}. You can type this either by holding down a
1200 key designated as the @key{META} shift on your keyboard (if there is
1201 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1203 @cindex quotes in commands
1204 @cindex completion of quoted strings
1205 Sometimes the string you need, while logically a ``word'', may contain
1206 parentheses or other characters that @value{GDBN} normally excludes from
1207 its notion of a word. To permit word completion to work in this
1208 situation, you may enclose words in @code{'} (single quote marks) in
1209 @value{GDBN} commands.
1211 The most likely situation where you might need this is in typing the
1212 name of a C++ function. This is because C++ allows function overloading
1213 (multiple definitions of the same function, distinguished by argument
1214 type). For example, when you want to set a breakpoint you may need to
1215 distinguish whether you mean the version of @code{name} that takes an
1216 @code{int} parameter, @code{name(int)}, or the version that takes a
1217 @code{float} parameter, @code{name(float)}. To use the word-completion
1218 facilities in this situation, type a single quote @code{'} at the
1219 beginning of the function name. This alerts @value{GDBN} that it may need to
1220 consider more information than usual when you press @key{TAB} or
1221 @kbd{M-?} to request word completion:
1224 (@value{GDBP}) b 'bubble( @kbd{M-?}
1225 bubble(double,double) bubble(int,int)
1226 (@value{GDBP}) b 'bubble(
1229 In some cases, @value{GDBN} can tell that completing a name requires using
1230 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1231 completing as much as it can) if you do not type the quote in the first
1235 (@value{GDBP}) b bub @key{TAB}
1236 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1237 (@value{GDBP}) b 'bubble(
1241 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1242 you have not yet started typing the argument list when you ask for
1243 completion on an overloaded symbol.
1245 For more information about overloaded functions, see @ref{C plus plus
1246 expressions, ,C++ expressions}. You can use the command @code{set
1247 overload-resolution off} to disable overload resolution;
1248 see @ref{Debugging C plus plus, ,@value{GDBN} features for C++}.
1251 @node Help, , Completion, Commands
1252 @section Getting help
1253 @cindex online documentation
1256 You can always ask @value{GDBN} itself for information on its commands,
1257 using the command @code{help}.
1263 You can use @code{help} (abbreviated @code{h}) with no arguments to
1264 display a short list of named classes of commands:
1268 List of classes of commands:
1270 aliases -- Aliases of other commands
1271 breakpoints -- Making program stop at certain points
1272 data -- Examining data
1273 files -- Specifying and examining files
1274 internals -- Maintenance commands
1275 obscure -- Obscure features
1276 running -- Running the program
1277 stack -- Examining the stack
1278 status -- Status inquiries
1279 support -- Support facilities
1280 tracepoints -- Tracing of program execution without@*
1281 stopping the program
1282 user-defined -- User-defined commands
1284 Type "help" followed by a class name for a list of
1285 commands in that class.
1286 Type "help" followed by command name for full
1288 Command name abbreviations are allowed if unambiguous.
1291 @c the above line break eliminates huge line overfull...
1293 @item help @var{class}
1294 Using one of the general help classes as an argument, you can get a
1295 list of the individual commands in that class. For example, here is the
1296 help display for the class @code{status}:
1299 (@value{GDBP}) help status
1304 @c Line break in "show" line falsifies real output, but needed
1305 @c to fit in smallbook page size.
1306 info -- Generic command for showing things
1307 about the program being debugged
1308 show -- Generic command for showing things
1311 Type "help" followed by command name for full
1313 Command name abbreviations are allowed if unambiguous.
1317 @item help @var{command}
1318 With a command name as @code{help} argument, @value{GDBN} displays a
1319 short paragraph on how to use that command.
1322 @item apropos @var{args}
1323 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1324 commands, and their documentation, for the regular expression specified in
1325 @var{args}. It prints out all matches found. For example:
1331 @noindent results in:
1335 set symbol-reloading -- Set dynamic symbol table reloading multiple times in one run
1336 show symbol-reloading -- Show dynamic symbol table reloading multiple times in one run
1341 @item complete @var{args}
1342 The @code{complete @var{args}} command lists all the possible completions
1343 for the beginning of a command. Use @var{args} to specify the beginning of the
1344 command you want completed. For example:
1350 @noindent results in:
1361 @noindent This is intended for use by @sc{gnu} Emacs.
1364 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1365 and @code{show} to inquire about the state of your program, or the state
1366 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1367 manual introduces each of them in the appropriate context. The listings
1368 under @code{info} and under @code{show} in the Index point to
1369 all the sub-commands. @xref{Index}.
1376 This command (abbreviated @code{i}) is for describing the state of your
1377 program. For example, you can list the arguments given to your program
1378 with @code{info args}, list the registers currently in use with @code{info
1379 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1380 You can get a complete list of the @code{info} sub-commands with
1381 @w{@code{help info}}.
1385 You can assign the result of an expression to an environment variable with
1386 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1387 @code{set prompt $}.
1391 In contrast to @code{info}, @code{show} is for describing the state of
1392 @value{GDBN} itself.
1393 You can change most of the things you can @code{show}, by using the
1394 related command @code{set}; for example, you can control what number
1395 system is used for displays with @code{set radix}, or simply inquire
1396 which is currently in use with @code{show radix}.
1399 To display all the settable parameters and their current
1400 values, you can use @code{show} with no arguments; you may also use
1401 @code{info set}. Both commands produce the same display.
1402 @c FIXME: "info set" violates the rule that "info" is for state of
1403 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1404 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1408 Here are three miscellaneous @code{show} subcommands, all of which are
1409 exceptional in lacking corresponding @code{set} commands:
1412 @kindex show version
1413 @cindex version number
1415 Show what version of @value{GDBN} is running. You should include this
1416 information in @value{GDBN} bug-reports. If multiple versions of
1417 @value{GDBN} are in use at your site, you may need to determine which
1418 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1419 commands are introduced, and old ones may wither away. Also, many
1420 system vendors ship variant versions of @value{GDBN}, and there are
1421 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1422 The version number is the same as the one announced when you start
1425 @kindex show copying
1427 Display information about permission for copying @value{GDBN}.
1429 @kindex show warranty
1431 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1432 if your version of @value{GDBN} comes with one.
1436 @node Running, Stopping, Commands, Top
1437 @chapter Running Programs Under @value{GDBN}
1439 When you run a program under @value{GDBN}, you must first generate
1440 debugging information when you compile it.
1442 You may start @value{GDBN} with its arguments, if any, in an environment
1443 of your choice. If you are doing native debugging, you may redirect
1444 your program's input and output, debug an already running process, or
1445 kill a child process.
1448 * Compilation:: Compiling for debugging
1449 * Starting:: Starting your program
1450 * Arguments:: Your program's arguments
1451 * Environment:: Your program's environment
1453 * Working Directory:: Your program's working directory
1454 * Input/Output:: Your program's input and output
1455 * Attach:: Debugging an already-running process
1456 * Kill Process:: Killing the child process
1458 * Threads:: Debugging programs with multiple threads
1459 * Processes:: Debugging programs with multiple processes
1462 @node Compilation, Starting, Running, Running
1463 @section Compiling for debugging
1465 In order to debug a program effectively, you need to generate
1466 debugging information when you compile it. This debugging information
1467 is stored in the object file; it describes the data type of each
1468 variable or function and the correspondence between source line numbers
1469 and addresses in the executable code.
1471 To request debugging information, specify the @samp{-g} option when you run
1474 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1475 options together. Using those compilers, you cannot generate optimized
1476 executables containing debugging information.
1478 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1479 without @samp{-O}, making it possible to debug optimized code. We
1480 recommend that you @emph{always} use @samp{-g} whenever you compile a
1481 program. You may think your program is correct, but there is no sense
1482 in pushing your luck.
1484 @cindex optimized code, debugging
1485 @cindex debugging optimized code
1486 When you debug a program compiled with @samp{-g -O}, remember that the
1487 optimizer is rearranging your code; the debugger shows you what is
1488 really there. Do not be too surprised when the execution path does not
1489 exactly match your source file! An extreme example: if you define a
1490 variable, but never use it, @value{GDBN} never sees that
1491 variable---because the compiler optimizes it out of existence.
1493 Some things do not work as well with @samp{-g -O} as with just
1494 @samp{-g}, particularly on machines with instruction scheduling. If in
1495 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1496 please report it to us as a bug (including a test case!).
1498 Older versions of the @sc{gnu} C compiler permitted a variant option
1499 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1500 format; if your @sc{gnu} C compiler has this option, do not use it.
1503 @node Starting, Arguments, Compilation, Running
1504 @section Starting your program
1512 Use the @code{run} command to start your program under @value{GDBN}.
1513 You must first specify the program name (except on VxWorks) with an
1514 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1515 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1516 (@pxref{Files, ,Commands to specify files}).
1520 If you are running your program in an execution environment that
1521 supports processes, @code{run} creates an inferior process and makes
1522 that process run your program. (In environments without processes,
1523 @code{run} jumps to the start of your program.)
1525 The execution of a program is affected by certain information it
1526 receives from its superior. @value{GDBN} provides ways to specify this
1527 information, which you must do @emph{before} starting your program. (You
1528 can change it after starting your program, but such changes only affect
1529 your program the next time you start it.) This information may be
1530 divided into four categories:
1533 @item The @emph{arguments.}
1534 Specify the arguments to give your program as the arguments of the
1535 @code{run} command. If a shell is available on your target, the shell
1536 is used to pass the arguments, so that you may use normal conventions
1537 (such as wildcard expansion or variable substitution) in describing
1539 In Unix systems, you can control which shell is used with the
1540 @code{SHELL} environment variable.
1541 @xref{Arguments, ,Your program's arguments}.
1543 @item The @emph{environment.}
1544 Your program normally inherits its environment from @value{GDBN}, but you can
1545 use the @value{GDBN} commands @code{set environment} and @code{unset
1546 environment} to change parts of the environment that affect
1547 your program. @xref{Environment, ,Your program's environment}.
1549 @item The @emph{working directory.}
1550 Your program inherits its working directory from @value{GDBN}. You can set
1551 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1552 @xref{Working Directory, ,Your program's working directory}.
1554 @item The @emph{standard input and output.}
1555 Your program normally uses the same device for standard input and
1556 standard output as @value{GDBN} is using. You can redirect input and output
1557 in the @code{run} command line, or you can use the @code{tty} command to
1558 set a different device for your program.
1559 @xref{Input/Output, ,Your program's input and output}.
1562 @emph{Warning:} While input and output redirection work, you cannot use
1563 pipes to pass the output of the program you are debugging to another
1564 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1568 When you issue the @code{run} command, your program begins to execute
1569 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1570 of how to arrange for your program to stop. Once your program has
1571 stopped, you may call functions in your program, using the @code{print}
1572 or @code{call} commands. @xref{Data, ,Examining Data}.
1574 If the modification time of your symbol file has changed since the last
1575 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1576 table, and reads it again. When it does this, @value{GDBN} tries to retain
1577 your current breakpoints.
1579 @node Arguments, Environment, Starting, Running
1580 @section Your program's arguments
1582 @cindex arguments (to your program)
1583 The arguments to your program can be specified by the arguments of the
1585 They are passed to a shell, which expands wildcard characters and
1586 performs redirection of I/O, and thence to your program. Your
1587 @code{SHELL} environment variable (if it exists) specifies what shell
1588 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1589 the default shell (@file{/bin/sh} on Unix).
1591 On non-Unix systems, the program is usually invoked directly by
1592 @value{GDBN}, which emulates I/O redirection via the appropriate system
1593 calls, and the wildcard characters are expanded by the startup code of
1594 the program, not by the shell.
1596 @code{run} with no arguments uses the same arguments used by the previous
1597 @code{run}, or those set by the @code{set args} command.
1602 Specify the arguments to be used the next time your program is run. If
1603 @code{set args} has no arguments, @code{run} executes your program
1604 with no arguments. Once you have run your program with arguments,
1605 using @code{set args} before the next @code{run} is the only way to run
1606 it again without arguments.
1610 Show the arguments to give your program when it is started.
1613 @node Environment, Working Directory, Arguments, Running
1614 @section Your program's environment
1616 @cindex environment (of your program)
1617 The @dfn{environment} consists of a set of environment variables and
1618 their values. Environment variables conventionally record such things as
1619 your user name, your home directory, your terminal type, and your search
1620 path for programs to run. Usually you set up environment variables with
1621 the shell and they are inherited by all the other programs you run. When
1622 debugging, it can be useful to try running your program with a modified
1623 environment without having to start @value{GDBN} over again.
1627 @item path @var{directory}
1628 Add @var{directory} to the front of the @code{PATH} environment variable
1629 (the search path for executables), for both @value{GDBN} and your program.
1630 You may specify several directory names, separated by whitespace or by a
1631 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1632 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1633 is moved to the front, so it is searched sooner.
1635 You can use the string @samp{$cwd} to refer to whatever is the current
1636 working directory at the time @value{GDBN} searches the path. If you
1637 use @samp{.} instead, it refers to the directory where you executed the
1638 @code{path} command. @value{GDBN} replaces @samp{.} in the
1639 @var{directory} argument (with the current path) before adding
1640 @var{directory} to the search path.
1641 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1642 @c document that, since repeating it would be a no-op.
1646 Display the list of search paths for executables (the @code{PATH}
1647 environment variable).
1649 @kindex show environment
1650 @item show environment @r{[}@var{varname}@r{]}
1651 Print the value of environment variable @var{varname} to be given to
1652 your program when it starts. If you do not supply @var{varname},
1653 print the names and values of all environment variables to be given to
1654 your program. You can abbreviate @code{environment} as @code{env}.
1656 @kindex set environment
1657 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1658 Set environment variable @var{varname} to @var{value}. The value
1659 changes for your program only, not for @value{GDBN} itself. @var{value} may
1660 be any string; the values of environment variables are just strings, and
1661 any interpretation is supplied by your program itself. The @var{value}
1662 parameter is optional; if it is eliminated, the variable is set to a
1664 @c "any string" here does not include leading, trailing
1665 @c blanks. Gnu asks: does anyone care?
1667 For example, this command:
1674 tells the debugged program, when subsequently run, that its user is named
1675 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1676 are not actually required.)
1678 @kindex unset environment
1679 @item unset environment @var{varname}
1680 Remove variable @var{varname} from the environment to be passed to your
1681 program. This is different from @samp{set env @var{varname} =};
1682 @code{unset environment} removes the variable from the environment,
1683 rather than assigning it an empty value.
1686 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1688 by your @code{SHELL} environment variable if it exists (or
1689 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1690 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1691 @file{.bashrc} for BASH---any variables you set in that file affect
1692 your program. You may wish to move setting of environment variables to
1693 files that are only run when you sign on, such as @file{.login} or
1696 @node Working Directory, Input/Output, Environment, Running
1697 @section Your program's working directory
1699 @cindex working directory (of your program)
1700 Each time you start your program with @code{run}, it inherits its
1701 working directory from the current working directory of @value{GDBN}.
1702 The @value{GDBN} working directory is initially whatever it inherited
1703 from its parent process (typically the shell), but you can specify a new
1704 working directory in @value{GDBN} with the @code{cd} command.
1706 The @value{GDBN} working directory also serves as a default for the commands
1707 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1712 @item cd @var{directory}
1713 Set the @value{GDBN} working directory to @var{directory}.
1717 Print the @value{GDBN} working directory.
1720 @node Input/Output, Attach, Working Directory, Running
1721 @section Your program's input and output
1726 By default, the program you run under @value{GDBN} does input and output to
1727 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1728 to its own terminal modes to interact with you, but it records the terminal
1729 modes your program was using and switches back to them when you continue
1730 running your program.
1733 @kindex info terminal
1735 Displays information recorded by @value{GDBN} about the terminal modes your
1739 You can redirect your program's input and/or output using shell
1740 redirection with the @code{run} command. For example,
1747 starts your program, diverting its output to the file @file{outfile}.
1750 @cindex controlling terminal
1751 Another way to specify where your program should do input and output is
1752 with the @code{tty} command. This command accepts a file name as
1753 argument, and causes this file to be the default for future @code{run}
1754 commands. It also resets the controlling terminal for the child
1755 process, for future @code{run} commands. For example,
1762 directs that processes started with subsequent @code{run} commands
1763 default to do input and output on the terminal @file{/dev/ttyb} and have
1764 that as their controlling terminal.
1766 An explicit redirection in @code{run} overrides the @code{tty} command's
1767 effect on the input/output device, but not its effect on the controlling
1770 When you use the @code{tty} command or redirect input in the @code{run}
1771 command, only the input @emph{for your program} is affected. The input
1772 for @value{GDBN} still comes from your terminal.
1774 @node Attach, Kill Process, Input/Output, Running
1775 @section Debugging an already-running process
1780 @item attach @var{process-id}
1781 This command attaches to a running process---one that was started
1782 outside @value{GDBN}. (@code{info files} shows your active
1783 targets.) The command takes as argument a process ID. The usual way to
1784 find out the process-id of a Unix process is with the @code{ps} utility,
1785 or with the @samp{jobs -l} shell command.
1787 @code{attach} does not repeat if you press @key{RET} a second time after
1788 executing the command.
1791 To use @code{attach}, your program must be running in an environment
1792 which supports processes; for example, @code{attach} does not work for
1793 programs on bare-board targets that lack an operating system. You must
1794 also have permission to send the process a signal.
1796 When you use @code{attach}, the debugger finds the program running in
1797 the process first by looking in the current working directory, then (if
1798 the program is not found) by using the source file search path
1799 (@pxref{Source Path, ,Specifying source directories}). You can also use
1800 the @code{file} command to load the program. @xref{Files, ,Commands to
1803 The first thing @value{GDBN} does after arranging to debug the specified
1804 process is to stop it. You can examine and modify an attached process
1805 with all the @value{GDBN} commands that are ordinarily available when
1806 you start processes with @code{run}. You can insert breakpoints; you
1807 can step and continue; you can modify storage. If you would rather the
1808 process continue running, you may use the @code{continue} command after
1809 attaching @value{GDBN} to the process.
1814 When you have finished debugging the attached process, you can use the
1815 @code{detach} command to release it from @value{GDBN} control. Detaching
1816 the process continues its execution. After the @code{detach} command,
1817 that process and @value{GDBN} become completely independent once more, and you
1818 are ready to @code{attach} another process or start one with @code{run}.
1819 @code{detach} does not repeat if you press @key{RET} again after
1820 executing the command.
1823 If you exit @value{GDBN} or use the @code{run} command while you have an
1824 attached process, you kill that process. By default, @value{GDBN} asks
1825 for confirmation if you try to do either of these things; you can
1826 control whether or not you need to confirm by using the @code{set
1827 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1830 @node Kill Process, Threads, Attach, Running
1831 @section Killing the child process
1836 Kill the child process in which your program is running under @value{GDBN}.
1839 This command is useful if you wish to debug a core dump instead of a
1840 running process. @value{GDBN} ignores any core dump file while your program
1843 On some operating systems, a program cannot be executed outside @value{GDBN}
1844 while you have breakpoints set on it inside @value{GDBN}. You can use the
1845 @code{kill} command in this situation to permit running your program
1846 outside the debugger.
1848 The @code{kill} command is also useful if you wish to recompile and
1849 relink your program, since on many systems it is impossible to modify an
1850 executable file while it is running in a process. In this case, when you
1851 next type @code{run}, @value{GDBN} notices that the file has changed, and
1852 reads the symbol table again (while trying to preserve your current
1853 breakpoint settings).
1855 @node Threads, Processes, Kill Process, Running
1856 @section Debugging programs with multiple threads
1858 @cindex threads of execution
1859 @cindex multiple threads
1860 @cindex switching threads
1861 In some operating systems, such as HP-UX and Solaris, a single program
1862 may have more than one @dfn{thread} of execution. The precise semantics
1863 of threads differ from one operating system to another, but in general
1864 the threads of a single program are akin to multiple processes---except
1865 that they share one address space (that is, they can all examine and
1866 modify the same variables). On the other hand, each thread has its own
1867 registers and execution stack, and perhaps private memory.
1869 @value{GDBN} provides these facilities for debugging multi-thread
1873 @item automatic notification of new threads
1874 @item @samp{thread @var{threadno}}, a command to switch among threads
1875 @item @samp{info threads}, a command to inquire about existing threads
1876 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1877 a command to apply a command to a list of threads
1878 @item thread-specific breakpoints
1882 @emph{Warning:} These facilities are not yet available on every
1883 @value{GDBN} configuration where the operating system supports threads.
1884 If your @value{GDBN} does not support threads, these commands have no
1885 effect. For example, a system without thread support shows no output
1886 from @samp{info threads}, and always rejects the @code{thread} command,
1890 (@value{GDBP}) info threads
1891 (@value{GDBP}) thread 1
1892 Thread ID 1 not known. Use the "info threads" command to
1893 see the IDs of currently known threads.
1895 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1896 @c doesn't support threads"?
1899 @cindex focus of debugging
1900 @cindex current thread
1901 The @value{GDBN} thread debugging facility allows you to observe all
1902 threads while your program runs---but whenever @value{GDBN} takes
1903 control, one thread in particular is always the focus of debugging.
1904 This thread is called the @dfn{current thread}. Debugging commands show
1905 program information from the perspective of the current thread.
1907 @kindex New @var{systag}
1908 @cindex thread identifier (system)
1909 @c FIXME-implementors!! It would be more helpful if the [New...] message
1910 @c included GDB's numeric thread handle, so you could just go to that
1911 @c thread without first checking `info threads'.
1912 Whenever @value{GDBN} detects a new thread in your program, it displays
1913 the target system's identification for the thread with a message in the
1914 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1915 whose form varies depending on the particular system. For example, on
1916 LynxOS, you might see
1919 [New process 35 thread 27]
1923 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1924 the @var{systag} is simply something like @samp{process 368}, with no
1927 @c FIXME!! (1) Does the [New...] message appear even for the very first
1928 @c thread of a program, or does it only appear for the
1929 @c second---i.e., when it becomes obvious we have a multithread
1931 @c (2) *Is* there necessarily a first thread always? Or do some
1932 @c multithread systems permit starting a program with multiple
1933 @c threads ab initio?
1935 @cindex thread number
1936 @cindex thread identifier (GDB)
1937 For debugging purposes, @value{GDBN} associates its own thread
1938 number---always a single integer---with each thread in your program.
1941 @kindex info threads
1943 Display a summary of all threads currently in your
1944 program. @value{GDBN} displays for each thread (in this order):
1947 @item the thread number assigned by @value{GDBN}
1949 @item the target system's thread identifier (@var{systag})
1951 @item the current stack frame summary for that thread
1955 An asterisk @samp{*} to the left of the @value{GDBN} thread number
1956 indicates the current thread.
1960 @c end table here to get a little more width for example
1963 (@value{GDBP}) info threads
1964 3 process 35 thread 27 0x34e5 in sigpause ()
1965 2 process 35 thread 23 0x34e5 in sigpause ()
1966 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
1972 @cindex thread number
1973 @cindex thread identifier (GDB)
1974 For debugging purposes, @value{GDBN} associates its own thread
1975 number---a small integer assigned in thread-creation order---with each
1976 thread in your program.
1978 @kindex New @var{systag}
1979 @cindex thread identifier (system)
1980 @c FIXME-implementors!! It would be more helpful if the [New...] message
1981 @c included GDB's numeric thread handle, so you could just go to that
1982 @c thread without first checking `info threads'.
1983 Whenever @value{GDBN} detects a new thread in your program, it displays
1984 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
1985 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1986 whose form varies depending on the particular system. For example, on
1990 [New thread 2 (system thread 26594)]
1994 when @value{GDBN} notices a new thread.
1997 @kindex info threads
1999 Display a summary of all threads currently in your
2000 program. @value{GDBN} displays for each thread (in this order):
2003 @item the thread number assigned by @value{GDBN}
2005 @item the target system's thread identifier (@var{systag})
2007 @item the current stack frame summary for that thread
2011 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2012 indicates the current thread.
2016 @c end table here to get a little more width for example
2019 (@value{GDBP}) info threads
2020 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") at quicksort.c:137
2021 2 system thread 26606 0x7b0030d8 in __ksleep () from /usr/lib/libc.2
2022 1 system thread 27905 0x7b003498 in _brk () from /usr/lib/libc.2
2026 @kindex thread @var{threadno}
2027 @item thread @var{threadno}
2028 Make thread number @var{threadno} the current thread. The command
2029 argument @var{threadno} is the internal @value{GDBN} thread number, as
2030 shown in the first field of the @samp{info threads} display.
2031 @value{GDBN} responds by displaying the system identifier of the thread
2032 you selected, and its current stack frame summary:
2035 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2036 (@value{GDBP}) thread 2
2037 [Switching to process 35 thread 23]
2038 0x34e5 in sigpause ()
2042 As with the @samp{[New @dots{}]} message, the form of the text after
2043 @samp{Switching to} depends on your system's conventions for identifying
2046 @kindex thread apply
2047 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2048 The @code{thread apply} command allows you to apply a command to one or
2049 more threads. Specify the numbers of the threads that you want affected
2050 with the command argument @var{threadno}. @var{threadno} is the internal
2051 @value{GDBN} thread number, as shown in the first field of the @samp{info
2052 threads} display. To apply a command to all threads, use
2053 @code{thread apply all} @var{args}.
2056 @cindex automatic thread selection
2057 @cindex switching threads automatically
2058 @cindex threads, automatic switching
2059 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2060 signal, it automatically selects the thread where that breakpoint or
2061 signal happened. @value{GDBN} alerts you to the context switch with a
2062 message of the form @samp{[Switching to @var{systag}]} to identify the
2065 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2066 more information about how @value{GDBN} behaves when you stop and start
2067 programs with multiple threads.
2069 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2070 watchpoints in programs with multiple threads.
2072 @node Processes, , Threads, Running
2073 @section Debugging programs with multiple processes
2075 @cindex fork, debugging programs which call
2076 @cindex multiple processes
2077 @cindex processes, multiple
2078 On most systems, @value{GDBN} has no special support for debugging
2079 programs which create additional processes using the @code{fork}
2080 function. When a program forks, @value{GDBN} will continue to debug the
2081 parent process and the child process will run unimpeded. If you have
2082 set a breakpoint in any code which the child then executes, the child
2083 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2084 will cause it to terminate.
2086 However, if you want to debug the child process there is a workaround
2087 which isn't too painful. Put a call to @code{sleep} in the code which
2088 the child process executes after the fork. It may be useful to sleep
2089 only if a certain environment variable is set, or a certain file exists,
2090 so that the delay need not occur when you don't want to run @value{GDBN}
2091 on the child. While the child is sleeping, use the @code{ps} program to
2092 get its process ID. Then tell @value{GDBN} (a new invocation of
2093 @value{GDBN} if you are also debugging the parent process) to attach to
2094 the child process (@pxref{Attach}). From that point on you can debug
2095 the child process just like any other process which you attached to.
2097 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2098 debugging programs that create additional processes using the
2099 @code{fork} or @code{vfork} function.
2101 By default, when a program forks, @value{GDBN} will continue to debug
2102 the parent process and the child process will run unimpeded.
2104 If you want to follow the child process instead of the parent process,
2105 use the command @w{@code{set follow-fork-mode}}.
2108 @kindex set follow-fork-mode
2109 @item set follow-fork-mode @var{mode}
2110 Set the debugger response to a program call of @code{fork} or
2111 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2112 process. The @var{mode} can be:
2116 The original process is debugged after a fork. The child process runs
2117 unimpeded. This is the default.
2120 The new process is debugged after a fork. The parent process runs
2124 The debugger will ask for one of the above choices.
2127 @item show follow-fork-mode
2128 Display the current debugger response to a @code{fork} or @code{vfork} call.
2131 If you ask to debug a child process and a @code{vfork} is followed by an
2132 @code{exec}, @value{GDBN} executes the new target up to the first
2133 breakpoint in the new target. If you have a breakpoint set on
2134 @code{main} in your original program, the breakpoint will also be set on
2135 the child process's @code{main}.
2137 When a child process is spawned by @code{vfork}, you cannot debug the
2138 child or parent until an @code{exec} call completes.
2140 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2141 call executes, the new target restarts. To restart the parent process,
2142 use the @code{file} command with the parent executable name as its
2145 You can use the @code{catch} command to make @value{GDBN} stop whenever
2146 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2147 Catchpoints, ,Setting catchpoints}.
2149 @node Stopping, Stack, Running, Top
2150 @chapter Stopping and Continuing
2152 The principal purposes of using a debugger are so that you can stop your
2153 program before it terminates; or so that, if your program runs into
2154 trouble, you can investigate and find out why.
2156 Inside @value{GDBN}, your program may stop for any of several reasons,
2157 such as a signal, a breakpoint, or reaching a new line after a
2158 @value{GDBN} command such as @code{step}. You may then examine and
2159 change variables, set new breakpoints or remove old ones, and then
2160 continue execution. Usually, the messages shown by @value{GDBN} provide
2161 ample explanation of the status of your program---but you can also
2162 explicitly request this information at any time.
2165 @kindex info program
2167 Display information about the status of your program: whether it is
2168 running or not, what process it is, and why it stopped.
2172 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2173 * Continuing and Stepping:: Resuming execution
2175 * Thread Stops:: Stopping and starting multi-thread programs
2178 @node Breakpoints, Continuing and Stepping, Stopping, Stopping
2179 @section Breakpoints, watchpoints, and catchpoints
2182 A @dfn{breakpoint} makes your program stop whenever a certain point in
2183 the program is reached. For each breakpoint, you can add conditions to
2184 control in finer detail whether your program stops. You can set
2185 breakpoints with the @code{break} command and its variants (@pxref{Set
2186 Breaks, ,Setting breakpoints}), to specify the place where your program
2187 should stop by line number, function name or exact address in the
2190 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2191 breakpoints in shared libraries before the executable is run. There is
2192 a minor limitation on HP-UX systems: you must wait until the executable
2193 is run in order to set breakpoints in shared library routines that are
2194 not called directly by the program (for example, routines that are
2195 arguments in a @code{pthread_create} call).
2198 @cindex memory tracing
2199 @cindex breakpoint on memory address
2200 @cindex breakpoint on variable modification
2201 A @dfn{watchpoint} is a special breakpoint that stops your program
2202 when the value of an expression changes. You must use a different
2203 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2204 watchpoints}), but aside from that, you can manage a watchpoint like
2205 any other breakpoint: you enable, disable, and delete both breakpoints
2206 and watchpoints using the same commands.
2208 You can arrange to have values from your program displayed automatically
2209 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2213 @cindex breakpoint on events
2214 A @dfn{catchpoint} is another special breakpoint that stops your program
2215 when a certain kind of event occurs, such as the throwing of a C++
2216 exception or the loading of a library. As with watchpoints, you use a
2217 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2218 catchpoints}), but aside from that, you can manage a catchpoint like any
2219 other breakpoint. (To stop when your program receives a signal, use the
2220 @code{handle} command; see @ref{Signals, ,Signals}.)
2222 @cindex breakpoint numbers
2223 @cindex numbers for breakpoints
2224 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2225 catchpoint when you create it; these numbers are successive integers
2226 starting with one. In many of the commands for controlling various
2227 features of breakpoints you use the breakpoint number to say which
2228 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2229 @dfn{disabled}; if disabled, it has no effect on your program until you
2232 @cindex breakpoint ranges
2233 @cindex ranges of breakpoints
2234 Some @value{GDBN} commands accept a range of breakpoints on which to
2235 operate. A breakpoint range is either a single breakpoint number, like
2236 @samp{5}, or two such numbers, in increasing order, separated by a
2237 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2238 all breakpoint in that range are operated on.
2241 * Set Breaks:: Setting breakpoints
2242 * Set Watchpoints:: Setting watchpoints
2243 * Set Catchpoints:: Setting catchpoints
2244 * Delete Breaks:: Deleting breakpoints
2245 * Disabling:: Disabling breakpoints
2246 * Conditions:: Break conditions
2247 * Break Commands:: Breakpoint command lists
2248 * Breakpoint Menus:: Breakpoint menus
2249 * Error in Breakpoints:: ``Cannot insert breakpoints''
2252 @node Set Breaks, Set Watchpoints, Breakpoints, Breakpoints
2253 @subsection Setting breakpoints
2255 @c FIXME LMB what does GDB do if no code on line of breakpt?
2256 @c consider in particular declaration with/without initialization.
2258 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2263 @cindex latest breakpoint
2264 Breakpoints are set with the @code{break} command (abbreviated
2265 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2266 number of the breakpoints you've set most recently; see @ref{Convenience
2267 Vars,, Convenience variables}, for a discussion of what you can do with
2268 convenience variables.
2270 You have several ways to say where the breakpoint should go.
2273 @item break @var{function}
2274 Set a breakpoint at entry to function @var{function}.
2275 When using source languages that permit overloading of symbols, such as
2276 C++, @var{function} may refer to more than one possible place to break.
2277 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2279 @item break +@var{offset}
2280 @itemx break -@var{offset}
2281 Set a breakpoint some number of lines forward or back from the position
2282 at which execution stopped in the currently selected @dfn{stack frame}.
2283 (@xref{Frames, ,Frames}, for a description of stack frames.)
2285 @item break @var{linenum}
2286 Set a breakpoint at line @var{linenum} in the current source file.
2287 The current source file is the last file whose source text was printed.
2288 The breakpoint will stop your program just before it executes any of the
2291 @item break @var{filename}:@var{linenum}
2292 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2294 @item break @var{filename}:@var{function}
2295 Set a breakpoint at entry to function @var{function} found in file
2296 @var{filename}. Specifying a file name as well as a function name is
2297 superfluous except when multiple files contain similarly named
2300 @item break *@var{address}
2301 Set a breakpoint at address @var{address}. You can use this to set
2302 breakpoints in parts of your program which do not have debugging
2303 information or source files.
2306 When called without any arguments, @code{break} sets a breakpoint at
2307 the next instruction to be executed in the selected stack frame
2308 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2309 innermost, this makes your program stop as soon as control
2310 returns to that frame. This is similar to the effect of a
2311 @code{finish} command in the frame inside the selected frame---except
2312 that @code{finish} does not leave an active breakpoint. If you use
2313 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2314 the next time it reaches the current location; this may be useful
2317 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2318 least one instruction has been executed. If it did not do this, you
2319 would be unable to proceed past a breakpoint without first disabling the
2320 breakpoint. This rule applies whether or not the breakpoint already
2321 existed when your program stopped.
2323 @item break @dots{} if @var{cond}
2324 Set a breakpoint with condition @var{cond}; evaluate the expression
2325 @var{cond} each time the breakpoint is reached, and stop only if the
2326 value is nonzero---that is, if @var{cond} evaluates as true.
2327 @samp{@dots{}} stands for one of the possible arguments described
2328 above (or no argument) specifying where to break. @xref{Conditions,
2329 ,Break conditions}, for more information on breakpoint conditions.
2332 @item tbreak @var{args}
2333 Set a breakpoint enabled only for one stop. @var{args} are the
2334 same as for the @code{break} command, and the breakpoint is set in the same
2335 way, but the breakpoint is automatically deleted after the first time your
2336 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2339 @item hbreak @var{args}
2340 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2341 @code{break} command and the breakpoint is set in the same way, but the
2342 breakpoint requires hardware support and some target hardware may not
2343 have this support. The main purpose of this is EPROM/ROM code
2344 debugging, so you can set a breakpoint at an instruction without
2345 changing the instruction. This can be used with the new trap-generation
2346 provided by SPARClite DSU and some x86-based targets. These targets
2347 will generate traps when a program accesses some data or instruction
2348 address that is assigned to the debug registers. However the hardware
2349 breakpoint registers can take a limited number of breakpoints. For
2350 example, on the DSU, only two data breakpoints can be set at a time, and
2351 @value{GDBN} will reject this command if more than two are used. Delete
2352 or disable unused hardware breakpoints before setting new ones
2353 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2356 @item thbreak @var{args}
2357 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2358 are the same as for the @code{hbreak} command and the breakpoint is set in
2359 the same way. However, like the @code{tbreak} command,
2360 the breakpoint is automatically deleted after the
2361 first time your program stops there. Also, like the @code{hbreak}
2362 command, the breakpoint requires hardware support and some target hardware
2363 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2364 See also @ref{Conditions, ,Break conditions}.
2367 @cindex regular expression
2368 @item rbreak @var{regex}
2369 Set breakpoints on all functions matching the regular expression
2370 @var{regex}. This command sets an unconditional breakpoint on all
2371 matches, printing a list of all breakpoints it set. Once these
2372 breakpoints are set, they are treated just like the breakpoints set with
2373 the @code{break} command. You can delete them, disable them, or make
2374 them conditional the same way as any other breakpoint.
2376 The syntax of the regular expression is the standard one used with tools
2377 like @file{grep}. Note that this is different from the syntax used by
2378 shells, so for instance @code{foo*} matches all functions that include
2379 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2380 @code{.*} leading and trailing the regular expression you supply, so to
2381 match only functions that begin with @code{foo}, use @code{^foo}.
2383 When debugging C++ programs, @code{rbreak} is useful for setting
2384 breakpoints on overloaded functions that are not members of any special
2387 @kindex info breakpoints
2388 @cindex @code{$_} and @code{info breakpoints}
2389 @item info breakpoints @r{[}@var{n}@r{]}
2390 @itemx info break @r{[}@var{n}@r{]}
2391 @itemx info watchpoints @r{[}@var{n}@r{]}
2392 Print a table of all breakpoints, watchpoints, and catchpoints set and
2393 not deleted, with the following columns for each breakpoint:
2396 @item Breakpoint Numbers
2398 Breakpoint, watchpoint, or catchpoint.
2400 Whether the breakpoint is marked to be disabled or deleted when hit.
2401 @item Enabled or Disabled
2402 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2403 that are not enabled.
2405 Where the breakpoint is in your program, as a memory address.
2407 Where the breakpoint is in the source for your program, as a file and
2412 If a breakpoint is conditional, @code{info break} shows the condition on
2413 the line following the affected breakpoint; breakpoint commands, if any,
2414 are listed after that.
2417 @code{info break} with a breakpoint
2418 number @var{n} as argument lists only that breakpoint. The
2419 convenience variable @code{$_} and the default examining-address for
2420 the @code{x} command are set to the address of the last breakpoint
2421 listed (@pxref{Memory, ,Examining memory}).
2424 @code{info break} displays a count of the number of times the breakpoint
2425 has been hit. This is especially useful in conjunction with the
2426 @code{ignore} command. You can ignore a large number of breakpoint
2427 hits, look at the breakpoint info to see how many times the breakpoint
2428 was hit, and then run again, ignoring one less than that number. This
2429 will get you quickly to the last hit of that breakpoint.
2432 @value{GDBN} allows you to set any number of breakpoints at the same place in
2433 your program. There is nothing silly or meaningless about this. When
2434 the breakpoints are conditional, this is even useful
2435 (@pxref{Conditions, ,Break conditions}).
2437 @cindex negative breakpoint numbers
2438 @cindex internal @value{GDBN} breakpoints
2439 @value{GDBN} itself sometimes sets breakpoints in your program for special
2440 purposes, such as proper handling of @code{longjmp} (in C programs).
2441 These internal breakpoints are assigned negative numbers, starting with
2442 @code{-1}; @samp{info breakpoints} does not display them.
2444 You can see these breakpoints with the @value{GDBN} maintenance command
2445 @samp{maint info breakpoints}.
2448 @kindex maint info breakpoints
2449 @item maint info breakpoints
2450 Using the same format as @samp{info breakpoints}, display both the
2451 breakpoints you've set explicitly, and those @value{GDBN} is using for
2452 internal purposes. Internal breakpoints are shown with negative
2453 breakpoint numbers. The type column identifies what kind of breakpoint
2458 Normal, explicitly set breakpoint.
2461 Normal, explicitly set watchpoint.
2464 Internal breakpoint, used to handle correctly stepping through
2465 @code{longjmp} calls.
2467 @item longjmp resume
2468 Internal breakpoint at the target of a @code{longjmp}.
2471 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2474 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2477 Shared library events.
2484 @node Set Watchpoints, Set Catchpoints, Set Breaks, Breakpoints
2485 @subsection Setting watchpoints
2487 @cindex setting watchpoints
2488 @cindex software watchpoints
2489 @cindex hardware watchpoints
2490 You can use a watchpoint to stop execution whenever the value of an
2491 expression changes, without having to predict a particular place where
2494 Depending on your system, watchpoints may be implemented in software or
2495 hardware. @value{GDBN} does software watchpointing by single-stepping your
2496 program and testing the variable's value each time, which is hundreds of
2497 times slower than normal execution. (But this may still be worth it, to
2498 catch errors where you have no clue what part of your program is the
2501 On some systems, such as HP-UX, Linux and some other x86-based targets,
2502 @value{GDBN} includes support for
2503 hardware watchpoints, which do not slow down the running of your
2508 @item watch @var{expr}
2509 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2510 is written into by the program and its value changes.
2513 @item rwatch @var{expr}
2514 Set a watchpoint that will break when watch @var{expr} is read by the program.
2517 @item awatch @var{expr}
2518 Set a watchpoint that will break when @var{expr} is either read or written into
2521 @kindex info watchpoints
2522 @item info watchpoints
2523 This command prints a list of watchpoints, breakpoints, and catchpoints;
2524 it is the same as @code{info break}.
2527 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2528 watchpoints execute very quickly, and the debugger reports a change in
2529 value at the exact instruction where the change occurs. If @value{GDBN}
2530 cannot set a hardware watchpoint, it sets a software watchpoint, which
2531 executes more slowly and reports the change in value at the next
2532 statement, not the instruction, after the change occurs.
2534 When you issue the @code{watch} command, @value{GDBN} reports
2537 Hardware watchpoint @var{num}: @var{expr}
2541 if it was able to set a hardware watchpoint.
2543 Currently, the @code{awatch} and @code{rwatch} commands can only set
2544 hardware watchpoints, because accesses to data that don't change the
2545 value of the watched expression cannot be detected without examining
2546 every instruction as it is being executed, and @value{GDBN} does not do
2547 that currently. If @value{GDBN} finds that it is unable to set a
2548 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2549 will print a message like this:
2552 Expression cannot be implemented with read/access watchpoint.
2555 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2556 data type of the watched expression is wider than what a hardware
2557 watchpoint on the target machine can handle. For example, some systems
2558 can only watch regions that are up to 4 bytes wide; on such systems you
2559 cannot set hardware watchpoints for an expression that yields a
2560 double-precision floating-point number (which is typically 8 bytes
2561 wide). As a work-around, it might be possible to break the large region
2562 into a series of smaller ones and watch them with separate watchpoints.
2564 If you set too many hardware watchpoints, @value{GDBN} might be unable
2565 to insert all of them when you resume the execution of your program.
2566 Since the precise number of active watchpoints is unknown until such
2567 time as the program is about to be resumed, @value{GDBN} might not be
2568 able to warn you about this when you set the watchpoints, and the
2569 warning will be printed only when the program is resumed:
2572 Hardware watchpoint @var{num}: Could not insert watchpoint
2576 If this happens, delete or disable some of the watchpoints.
2578 The SPARClite DSU will generate traps when a program accesses some data
2579 or instruction address that is assigned to the debug registers. For the
2580 data addresses, DSU facilitates the @code{watch} command. However the
2581 hardware breakpoint registers can only take two data watchpoints, and
2582 both watchpoints must be the same kind. For example, you can set two
2583 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2584 @strong{or} two with @code{awatch} commands, but you cannot set one
2585 watchpoint with one command and the other with a different command.
2586 @value{GDBN} will reject the command if you try to mix watchpoints.
2587 Delete or disable unused watchpoint commands before setting new ones.
2589 If you call a function interactively using @code{print} or @code{call},
2590 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2591 kind of breakpoint or the call completes.
2593 @value{GDBN} automatically deletes watchpoints that watch local
2594 (automatic) variables, or expressions that involve such variables, when
2595 they go out of scope, that is, when the execution leaves the block in
2596 which these variables were defined. In particular, when the program
2597 being debugged terminates, @emph{all} local variables go out of scope,
2598 and so only watchpoints that watch global variables remain set. If you
2599 rerun the program, you will need to set all such watchpoints again. One
2600 way of doing that would be to set a code breakpoint at the entry to the
2601 @code{main} function and when it breaks, set all the watchpoints.
2604 @cindex watchpoints and threads
2605 @cindex threads and watchpoints
2606 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2607 usefulness. With the current watchpoint implementation, @value{GDBN}
2608 can only watch the value of an expression @emph{in a single thread}. If
2609 you are confident that the expression can only change due to the current
2610 thread's activity (and if you are also confident that no other thread
2611 can become current), then you can use watchpoints as usual. However,
2612 @value{GDBN} may not notice when a non-current thread's activity changes
2615 @c FIXME: this is almost identical to the previous paragraph.
2616 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2617 have only limited usefulness. If @value{GDBN} creates a software
2618 watchpoint, it can only watch the value of an expression @emph{in a
2619 single thread}. If you are confident that the expression can only
2620 change due to the current thread's activity (and if you are also
2621 confident that no other thread can become current), then you can use
2622 software watchpoints as usual. However, @value{GDBN} may not notice
2623 when a non-current thread's activity changes the expression. (Hardware
2624 watchpoints, in contrast, watch an expression in all threads.)
2627 @node Set Catchpoints, Delete Breaks, Set Watchpoints, Breakpoints
2628 @subsection Setting catchpoints
2629 @cindex catchpoints, setting
2630 @cindex exception handlers
2631 @cindex event handling
2633 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2634 kinds of program events, such as C++ exceptions or the loading of a
2635 shared library. Use the @code{catch} command to set a catchpoint.
2639 @item catch @var{event}
2640 Stop when @var{event} occurs. @var{event} can be any of the following:
2644 The throwing of a C++ exception.
2648 The catching of a C++ exception.
2652 A call to @code{exec}. This is currently only available for HP-UX.
2656 A call to @code{fork}. This is currently only available for HP-UX.
2660 A call to @code{vfork}. This is currently only available for HP-UX.
2663 @itemx load @var{libname}
2665 The dynamic loading of any shared library, or the loading of the library
2666 @var{libname}. This is currently only available for HP-UX.
2669 @itemx unload @var{libname}
2670 @kindex catch unload
2671 The unloading of any dynamically loaded shared library, or the unloading
2672 of the library @var{libname}. This is currently only available for HP-UX.
2675 @item tcatch @var{event}
2676 Set a catchpoint that is enabled only for one stop. The catchpoint is
2677 automatically deleted after the first time the event is caught.
2681 Use the @code{info break} command to list the current catchpoints.
2683 There are currently some limitations to C++ exception handling
2684 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2688 If you call a function interactively, @value{GDBN} normally returns
2689 control to you when the function has finished executing. If the call
2690 raises an exception, however, the call may bypass the mechanism that
2691 returns control to you and cause your program either to abort or to
2692 simply continue running until it hits a breakpoint, catches a signal
2693 that @value{GDBN} is listening for, or exits. This is the case even if
2694 you set a catchpoint for the exception; catchpoints on exceptions are
2695 disabled within interactive calls.
2698 You cannot raise an exception interactively.
2701 You cannot install an exception handler interactively.
2704 @cindex raise exceptions
2705 Sometimes @code{catch} is not the best way to debug exception handling:
2706 if you need to know exactly where an exception is raised, it is better to
2707 stop @emph{before} the exception handler is called, since that way you
2708 can see the stack before any unwinding takes place. If you set a
2709 breakpoint in an exception handler instead, it may not be easy to find
2710 out where the exception was raised.
2712 To stop just before an exception handler is called, you need some
2713 knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are
2714 raised by calling a library function named @code{__raise_exception}
2715 which has the following ANSI C interface:
2718 /* @var{addr} is where the exception identifier is stored.
2719 @var{id} is the exception identifier. */
2720 void __raise_exception (void **addr, void *id);
2724 To make the debugger catch all exceptions before any stack
2725 unwinding takes place, set a breakpoint on @code{__raise_exception}
2726 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2728 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2729 that depends on the value of @var{id}, you can stop your program when
2730 a specific exception is raised. You can use multiple conditional
2731 breakpoints to stop your program when any of a number of exceptions are
2735 @node Delete Breaks, Disabling, Set Catchpoints, Breakpoints
2736 @subsection Deleting breakpoints
2738 @cindex clearing breakpoints, watchpoints, catchpoints
2739 @cindex deleting breakpoints, watchpoints, catchpoints
2740 It is often necessary to eliminate a breakpoint, watchpoint, or
2741 catchpoint once it has done its job and you no longer want your program
2742 to stop there. This is called @dfn{deleting} the breakpoint. A
2743 breakpoint that has been deleted no longer exists; it is forgotten.
2745 With the @code{clear} command you can delete breakpoints according to
2746 where they are in your program. With the @code{delete} command you can
2747 delete individual breakpoints, watchpoints, or catchpoints by specifying
2748 their breakpoint numbers.
2750 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2751 automatically ignores breakpoints on the first instruction to be executed
2752 when you continue execution without changing the execution address.
2757 Delete any breakpoints at the next instruction to be executed in the
2758 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2759 the innermost frame is selected, this is a good way to delete a
2760 breakpoint where your program just stopped.
2762 @item clear @var{function}
2763 @itemx clear @var{filename}:@var{function}
2764 Delete any breakpoints set at entry to the function @var{function}.
2766 @item clear @var{linenum}
2767 @itemx clear @var{filename}:@var{linenum}
2768 Delete any breakpoints set at or within the code of the specified line.
2770 @cindex delete breakpoints
2773 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2774 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2775 ranges specified as arguments. If no argument is specified, delete all
2776 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2777 confirm off}). You can abbreviate this command as @code{d}.
2780 @node Disabling, Conditions, Delete Breaks, Breakpoints
2781 @subsection Disabling breakpoints
2783 @kindex disable breakpoints
2784 @kindex enable breakpoints
2785 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2786 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2787 it had been deleted, but remembers the information on the breakpoint so
2788 that you can @dfn{enable} it again later.
2790 You disable and enable breakpoints, watchpoints, and catchpoints with
2791 the @code{enable} and @code{disable} commands, optionally specifying one
2792 or more breakpoint numbers as arguments. Use @code{info break} or
2793 @code{info watch} to print a list of breakpoints, watchpoints, and
2794 catchpoints if you do not know which numbers to use.
2796 A breakpoint, watchpoint, or catchpoint can have any of four different
2797 states of enablement:
2801 Enabled. The breakpoint stops your program. A breakpoint set
2802 with the @code{break} command starts out in this state.
2804 Disabled. The breakpoint has no effect on your program.
2806 Enabled once. The breakpoint stops your program, but then becomes
2809 Enabled for deletion. The breakpoint stops your program, but
2810 immediately after it does so it is deleted permanently. A breakpoint
2811 set with the @code{tbreak} command starts out in this state.
2814 You can use the following commands to enable or disable breakpoints,
2815 watchpoints, and catchpoints:
2818 @kindex disable breakpoints
2821 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2822 Disable the specified breakpoints---or all breakpoints, if none are
2823 listed. A disabled breakpoint has no effect but is not forgotten. All
2824 options such as ignore-counts, conditions and commands are remembered in
2825 case the breakpoint is enabled again later. You may abbreviate
2826 @code{disable} as @code{dis}.
2828 @kindex enable breakpoints
2830 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2831 Enable the specified breakpoints (or all defined breakpoints). They
2832 become effective once again in stopping your program.
2834 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2835 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2836 of these breakpoints immediately after stopping your program.
2838 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2839 Enable the specified breakpoints to work once, then die. @value{GDBN}
2840 deletes any of these breakpoints as soon as your program stops there.
2843 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2844 @c confusing: tbreak is also initially enabled.
2845 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2846 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2847 subsequently, they become disabled or enabled only when you use one of
2848 the commands above. (The command @code{until} can set and delete a
2849 breakpoint of its own, but it does not change the state of your other
2850 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2853 @node Conditions, Break Commands, Disabling, Breakpoints
2854 @subsection Break conditions
2855 @cindex conditional breakpoints
2856 @cindex breakpoint conditions
2858 @c FIXME what is scope of break condition expr? Context where wanted?
2859 @c in particular for a watchpoint?
2860 The simplest sort of breakpoint breaks every time your program reaches a
2861 specified place. You can also specify a @dfn{condition} for a
2862 breakpoint. A condition is just a Boolean expression in your
2863 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2864 a condition evaluates the expression each time your program reaches it,
2865 and your program stops only if the condition is @emph{true}.
2867 This is the converse of using assertions for program validation; in that
2868 situation, you want to stop when the assertion is violated---that is,
2869 when the condition is false. In C, if you want to test an assertion expressed
2870 by the condition @var{assert}, you should set the condition
2871 @samp{! @var{assert}} on the appropriate breakpoint.
2873 Conditions are also accepted for watchpoints; you may not need them,
2874 since a watchpoint is inspecting the value of an expression anyhow---but
2875 it might be simpler, say, to just set a watchpoint on a variable name,
2876 and specify a condition that tests whether the new value is an interesting
2879 Break conditions can have side effects, and may even call functions in
2880 your program. This can be useful, for example, to activate functions
2881 that log program progress, or to use your own print functions to
2882 format special data structures. The effects are completely predictable
2883 unless there is another enabled breakpoint at the same address. (In
2884 that case, @value{GDBN} might see the other breakpoint first and stop your
2885 program without checking the condition of this one.) Note that
2886 breakpoint commands are usually more convenient and flexible than break
2888 purpose of performing side effects when a breakpoint is reached
2889 (@pxref{Break Commands, ,Breakpoint command lists}).
2891 Break conditions can be specified when a breakpoint is set, by using
2892 @samp{if} in the arguments to the @code{break} command. @xref{Set
2893 Breaks, ,Setting breakpoints}. They can also be changed at any time
2894 with the @code{condition} command.
2896 You can also use the @code{if} keyword with the @code{watch} command.
2897 The @code{catch} command does not recognize the @code{if} keyword;
2898 @code{condition} is the only way to impose a further condition on a
2903 @item condition @var{bnum} @var{expression}
2904 Specify @var{expression} as the break condition for breakpoint,
2905 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
2906 breakpoint @var{bnum} stops your program only if the value of
2907 @var{expression} is true (nonzero, in C). When you use
2908 @code{condition}, @value{GDBN} checks @var{expression} immediately for
2909 syntactic correctness, and to determine whether symbols in it have
2910 referents in the context of your breakpoint. If @var{expression} uses
2911 symbols not referenced in the context of the breakpoint, @value{GDBN}
2912 prints an error message:
2915 No symbol "foo" in current context.
2920 not actually evaluate @var{expression} at the time the @code{condition}
2921 command (or a command that sets a breakpoint with a condition, like
2922 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
2924 @item condition @var{bnum}
2925 Remove the condition from breakpoint number @var{bnum}. It becomes
2926 an ordinary unconditional breakpoint.
2929 @cindex ignore count (of breakpoint)
2930 A special case of a breakpoint condition is to stop only when the
2931 breakpoint has been reached a certain number of times. This is so
2932 useful that there is a special way to do it, using the @dfn{ignore
2933 count} of the breakpoint. Every breakpoint has an ignore count, which
2934 is an integer. Most of the time, the ignore count is zero, and
2935 therefore has no effect. But if your program reaches a breakpoint whose
2936 ignore count is positive, then instead of stopping, it just decrements
2937 the ignore count by one and continues. As a result, if the ignore count
2938 value is @var{n}, the breakpoint does not stop the next @var{n} times
2939 your program reaches it.
2943 @item ignore @var{bnum} @var{count}
2944 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2945 The next @var{count} times the breakpoint is reached, your program's
2946 execution does not stop; other than to decrement the ignore count, @value{GDBN}
2949 To make the breakpoint stop the next time it is reached, specify
2952 When you use @code{continue} to resume execution of your program from a
2953 breakpoint, you can specify an ignore count directly as an argument to
2954 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
2955 Stepping,,Continuing and stepping}.
2957 If a breakpoint has a positive ignore count and a condition, the
2958 condition is not checked. Once the ignore count reaches zero,
2959 @value{GDBN} resumes checking the condition.
2961 You could achieve the effect of the ignore count with a condition such
2962 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2963 is decremented each time. @xref{Convenience Vars, ,Convenience
2967 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
2970 @node Break Commands, Breakpoint Menus, Conditions, Breakpoints
2971 @subsection Breakpoint command lists
2973 @cindex breakpoint commands
2974 You can give any breakpoint (or watchpoint or catchpoint) a series of
2975 commands to execute when your program stops due to that breakpoint. For
2976 example, you might want to print the values of certain expressions, or
2977 enable other breakpoints.
2982 @item commands @r{[}@var{bnum}@r{]}
2983 @itemx @dots{} @var{command-list} @dots{}
2985 Specify a list of commands for breakpoint number @var{bnum}. The commands
2986 themselves appear on the following lines. Type a line containing just
2987 @code{end} to terminate the commands.
2989 To remove all commands from a breakpoint, type @code{commands} and
2990 follow it immediately with @code{end}; that is, give no commands.
2992 With no @var{bnum} argument, @code{commands} refers to the last
2993 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
2994 recently encountered).
2997 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2998 disabled within a @var{command-list}.
3000 You can use breakpoint commands to start your program up again. Simply
3001 use the @code{continue} command, or @code{step}, or any other command
3002 that resumes execution.
3004 Any other commands in the command list, after a command that resumes
3005 execution, are ignored. This is because any time you resume execution
3006 (even with a simple @code{next} or @code{step}), you may encounter
3007 another breakpoint---which could have its own command list, leading to
3008 ambiguities about which list to execute.
3011 If the first command you specify in a command list is @code{silent}, the
3012 usual message about stopping at a breakpoint is not printed. This may
3013 be desirable for breakpoints that are to print a specific message and
3014 then continue. If none of the remaining commands print anything, you
3015 see no sign that the breakpoint was reached. @code{silent} is
3016 meaningful only at the beginning of a breakpoint command list.
3018 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3019 print precisely controlled output, and are often useful in silent
3020 breakpoints. @xref{Output, ,Commands for controlled output}.
3022 For example, here is how you could use breakpoint commands to print the
3023 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3029 printf "x is %d\n",x
3034 One application for breakpoint commands is to compensate for one bug so
3035 you can test for another. Put a breakpoint just after the erroneous line
3036 of code, give it a condition to detect the case in which something
3037 erroneous has been done, and give it commands to assign correct values
3038 to any variables that need them. End with the @code{continue} command
3039 so that your program does not stop, and start with the @code{silent}
3040 command so that no output is produced. Here is an example:
3051 @node Breakpoint Menus, Error in Breakpoints, Break Commands, Breakpoints
3052 @subsection Breakpoint menus
3054 @cindex symbol overloading
3056 Some programming languages (notably C++) permit a single function name
3057 to be defined several times, for application in different contexts.
3058 This is called @dfn{overloading}. When a function name is overloaded,
3059 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3060 a breakpoint. If you realize this is a problem, you can use
3061 something like @samp{break @var{function}(@var{types})} to specify which
3062 particular version of the function you want. Otherwise, @value{GDBN} offers
3063 you a menu of numbered choices for different possible breakpoints, and
3064 waits for your selection with the prompt @samp{>}. The first two
3065 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3066 sets a breakpoint at each definition of @var{function}, and typing
3067 @kbd{0} aborts the @code{break} command without setting any new
3070 For example, the following session excerpt shows an attempt to set a
3071 breakpoint at the overloaded symbol @code{String::after}.
3072 We choose three particular definitions of that function name:
3074 @c FIXME! This is likely to change to show arg type lists, at least
3077 (@value{GDBP}) b String::after
3080 [2] file:String.cc; line number:867
3081 [3] file:String.cc; line number:860
3082 [4] file:String.cc; line number:875
3083 [5] file:String.cc; line number:853
3084 [6] file:String.cc; line number:846
3085 [7] file:String.cc; line number:735
3087 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3088 Breakpoint 2 at 0xb344: file String.cc, line 875.
3089 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3090 Multiple breakpoints were set.
3091 Use the "delete" command to delete unwanted
3097 @c @ifclear BARETARGET
3098 @node Error in Breakpoints, , Breakpoint Menus, Breakpoints
3099 @subsection ``Cannot insert breakpoints''
3101 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3103 Under some operating systems, breakpoints cannot be used in a program if
3104 any other process is running that program. In this situation,
3105 attempting to run or continue a program with a breakpoint causes
3106 @value{GDBN} to print an error message:
3109 Cannot insert breakpoints.
3110 The same program may be running in another process.
3113 When this happens, you have three ways to proceed:
3117 Remove or disable the breakpoints, then continue.
3120 Suspend @value{GDBN}, and copy the file containing your program to a new
3121 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3122 that @value{GDBN} should run your program under that name.
3123 Then start your program again.
3126 Relink your program so that the text segment is nonsharable, using the
3127 linker option @samp{-N}. The operating system limitation may not apply
3128 to nonsharable executables.
3132 A similar message can be printed if you request too many active
3133 hardware-assisted breakpoints and watchpoints:
3135 @c FIXME: the precise wording of this message may change; the relevant
3136 @c source change is not committed yet (Sep 3, 1999).
3138 Stopped; cannot insert breakpoints.
3139 You may have requested too many hardware breakpoints and watchpoints.
3143 This message is printed when you attempt to resume the program, since
3144 only then @value{GDBN} knows exactly how many hardware breakpoints and
3145 watchpoints it needs to insert.
3147 When this message is printed, you need to disable or remove some of the
3148 hardware-assisted breakpoints and watchpoints, and then continue.
3151 @node Continuing and Stepping, Signals, Breakpoints, Stopping
3152 @section Continuing and stepping
3156 @cindex resuming execution
3157 @dfn{Continuing} means resuming program execution until your program
3158 completes normally. In contrast, @dfn{stepping} means executing just
3159 one more ``step'' of your program, where ``step'' may mean either one
3160 line of source code, or one machine instruction (depending on what
3161 particular command you use). Either when continuing or when stepping,
3162 your program may stop even sooner, due to a breakpoint or a signal. (If
3163 it stops due to a signal, you may want to use @code{handle}, or use
3164 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3170 @item continue @r{[}@var{ignore-count}@r{]}
3171 @itemx c @r{[}@var{ignore-count}@r{]}
3172 @itemx fg @r{[}@var{ignore-count}@r{]}
3173 Resume program execution, at the address where your program last stopped;
3174 any breakpoints set at that address are bypassed. The optional argument
3175 @var{ignore-count} allows you to specify a further number of times to
3176 ignore a breakpoint at this location; its effect is like that of
3177 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3179 The argument @var{ignore-count} is meaningful only when your program
3180 stopped due to a breakpoint. At other times, the argument to
3181 @code{continue} is ignored.
3183 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3184 debugged program is deemed to be the foreground program) are provided
3185 purely for convenience, and have exactly the same behavior as
3189 To resume execution at a different place, you can use @code{return}
3190 (@pxref{Returning, ,Returning from a function}) to go back to the
3191 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3192 different address}) to go to an arbitrary location in your program.
3194 A typical technique for using stepping is to set a breakpoint
3195 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3196 beginning of the function or the section of your program where a problem
3197 is believed to lie, run your program until it stops at that breakpoint,
3198 and then step through the suspect area, examining the variables that are
3199 interesting, until you see the problem happen.
3205 Continue running your program until control reaches a different source
3206 line, then stop it and return control to @value{GDBN}. This command is
3207 abbreviated @code{s}.
3210 @c "without debugging information" is imprecise; actually "without line
3211 @c numbers in the debugging information". (gcc -g1 has debugging info but
3212 @c not line numbers). But it seems complex to try to make that
3213 @c distinction here.
3214 @emph{Warning:} If you use the @code{step} command while control is
3215 within a function that was compiled without debugging information,
3216 execution proceeds until control reaches a function that does have
3217 debugging information. Likewise, it will not step into a function which
3218 is compiled without debugging information. To step through functions
3219 without debugging information, use the @code{stepi} command, described
3223 The @code{step} command only stops at the first instruction of a
3224 source line. This prevents the multiple stops that could otherwise occur in
3225 switch statements, for loops, etc. @code{step} continues to stop if a
3226 function that has debugging information is called within the line.
3227 In other words, @code{step} @emph{steps inside} any functions called
3230 Also, the @code{step} command only enters a function if there is line
3231 number information for the function. Otherwise it acts like the
3232 @code{next} command. This avoids problems when using @code{cc -gl}
3233 on MIPS machines. Previously, @code{step} entered subroutines if there
3234 was any debugging information about the routine.
3236 @item step @var{count}
3237 Continue running as in @code{step}, but do so @var{count} times. If a
3238 breakpoint is reached, or a signal not related to stepping occurs before
3239 @var{count} steps, stepping stops right away.
3243 @item next @r{[}@var{count}@r{]}
3244 Continue to the next source line in the current (innermost) stack frame.
3245 This is similar to @code{step}, but function calls that appear within
3246 the line of code are executed without stopping. Execution stops when
3247 control reaches a different line of code at the original stack level
3248 that was executing when you gave the @code{next} command. This command
3249 is abbreviated @code{n}.
3251 An argument @var{count} is a repeat count, as for @code{step}.
3254 @c FIX ME!! Do we delete this, or is there a way it fits in with
3255 @c the following paragraph? --- Vctoria
3257 @c @code{next} within a function that lacks debugging information acts like
3258 @c @code{step}, but any function calls appearing within the code of the
3259 @c function are executed without stopping.
3261 The @code{next} command only stops at the first instruction of a
3262 source line. This prevents multiple stops that could otherwise occur in
3263 switch statements, for loops, etc.
3267 Continue running until just after function in the selected stack frame
3268 returns. Print the returned value (if any).
3270 Contrast this with the @code{return} command (@pxref{Returning,
3271 ,Returning from a function}).
3277 Continue running until a source line past the current line, in the
3278 current stack frame, is reached. This command is used to avoid single
3279 stepping through a loop more than once. It is like the @code{next}
3280 command, except that when @code{until} encounters a jump, it
3281 automatically continues execution until the program counter is greater
3282 than the address of the jump.
3284 This means that when you reach the end of a loop after single stepping
3285 though it, @code{until} makes your program continue execution until it
3286 exits the loop. In contrast, a @code{next} command at the end of a loop
3287 simply steps back to the beginning of the loop, which forces you to step
3288 through the next iteration.
3290 @code{until} always stops your program if it attempts to exit the current
3293 @code{until} may produce somewhat counterintuitive results if the order
3294 of machine code does not match the order of the source lines. For
3295 example, in the following excerpt from a debugging session, the @code{f}
3296 (@code{frame}) command shows that execution is stopped at line
3297 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3301 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3303 (@value{GDBP}) until
3304 195 for ( ; argc > 0; NEXTARG) @{
3307 This happened because, for execution efficiency, the compiler had
3308 generated code for the loop closure test at the end, rather than the
3309 start, of the loop---even though the test in a C @code{for}-loop is
3310 written before the body of the loop. The @code{until} command appeared
3311 to step back to the beginning of the loop when it advanced to this
3312 expression; however, it has not really gone to an earlier
3313 statement---not in terms of the actual machine code.
3315 @code{until} with no argument works by means of single
3316 instruction stepping, and hence is slower than @code{until} with an
3319 @item until @var{location}
3320 @itemx u @var{location}
3321 Continue running your program until either the specified location is
3322 reached, or the current stack frame returns. @var{location} is any of
3323 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3324 ,Setting breakpoints}). This form of the command uses breakpoints,
3325 and hence is quicker than @code{until} without an argument.
3330 @itemx stepi @var{arg}
3332 Execute one machine instruction, then stop and return to the debugger.
3334 It is often useful to do @samp{display/i $pc} when stepping by machine
3335 instructions. This makes @value{GDBN} automatically display the next
3336 instruction to be executed, each time your program stops. @xref{Auto
3337 Display,, Automatic display}.
3339 An argument is a repeat count, as in @code{step}.
3345 @itemx nexti @var{arg}
3347 Execute one machine instruction, but if it is a function call,
3348 proceed until the function returns.
3350 An argument is a repeat count, as in @code{next}.
3353 @node Signals, Thread Stops, Continuing and Stepping, Stopping
3357 A signal is an asynchronous event that can happen in a program. The
3358 operating system defines the possible kinds of signals, and gives each
3359 kind a name and a number. For example, in Unix @code{SIGINT} is the
3360 signal a program gets when you type an interrupt character (often @kbd{C-c});
3361 @code{SIGSEGV} is the signal a program gets from referencing a place in
3362 memory far away from all the areas in use; @code{SIGALRM} occurs when
3363 the alarm clock timer goes off (which happens only if your program has
3364 requested an alarm).
3366 @cindex fatal signals
3367 Some signals, including @code{SIGALRM}, are a normal part of the
3368 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3369 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3370 program has not specified in advance some other way to handle the signal.
3371 @code{SIGINT} does not indicate an error in your program, but it is normally
3372 fatal so it can carry out the purpose of the interrupt: to kill the program.
3374 @value{GDBN} has the ability to detect any occurrence of a signal in your
3375 program. You can tell @value{GDBN} in advance what to do for each kind of
3378 @cindex handling signals
3379 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3380 (so as not to interfere with their role in the functioning of your program)
3381 but to stop your program immediately whenever an error signal happens.
3382 You can change these settings with the @code{handle} command.
3385 @kindex info signals
3388 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3389 handle each one. You can use this to see the signal numbers of all
3390 the defined types of signals.
3392 @code{info handle} is an alias for @code{info signals}.
3395 @item handle @var{signal} @var{keywords}@dots{}
3396 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can
3397 be the number of a signal or its name (with or without the @samp{SIG} at the
3398 beginning). The @var{keywords} say what change to make.
3402 The keywords allowed by the @code{handle} command can be abbreviated.
3403 Their full names are:
3407 @value{GDBN} should not stop your program when this signal happens. It may
3408 still print a message telling you that the signal has come in.
3411 @value{GDBN} should stop your program when this signal happens. This implies
3412 the @code{print} keyword as well.
3415 @value{GDBN} should print a message when this signal happens.
3418 @value{GDBN} should not mention the occurrence of the signal at all. This
3419 implies the @code{nostop} keyword as well.
3422 @value{GDBN} should allow your program to see this signal; your program
3423 can handle the signal, or else it may terminate if the signal is fatal
3427 @value{GDBN} should not allow your program to see this signal.
3431 When a signal stops your program, the signal is not visible to the
3433 continue. Your program sees the signal then, if @code{pass} is in
3434 effect for the signal in question @emph{at that time}. In other words,
3435 after @value{GDBN} reports a signal, you can use the @code{handle}
3436 command with @code{pass} or @code{nopass} to control whether your
3437 program sees that signal when you continue.
3439 You can also use the @code{signal} command to prevent your program from
3440 seeing a signal, or cause it to see a signal it normally would not see,
3441 or to give it any signal at any time. For example, if your program stopped
3442 due to some sort of memory reference error, you might store correct
3443 values into the erroneous variables and continue, hoping to see more
3444 execution; but your program would probably terminate immediately as
3445 a result of the fatal signal once it saw the signal. To prevent this,
3446 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3449 @node Thread Stops, , Signals, Stopping
3450 @section Stopping and starting multi-thread programs
3452 When your program has multiple threads (@pxref{Threads,, Debugging
3453 programs with multiple threads}), you can choose whether to set
3454 breakpoints on all threads, or on a particular thread.
3457 @cindex breakpoints and threads
3458 @cindex thread breakpoints
3459 @kindex break @dots{} thread @var{threadno}
3460 @item break @var{linespec} thread @var{threadno}
3461 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3462 @var{linespec} specifies source lines; there are several ways of
3463 writing them, but the effect is always to specify some source line.
3465 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3466 to specify that you only want @value{GDBN} to stop the program when a
3467 particular thread reaches this breakpoint. @var{threadno} is one of the
3468 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3469 column of the @samp{info threads} display.
3471 If you do not specify @samp{thread @var{threadno}} when you set a
3472 breakpoint, the breakpoint applies to @emph{all} threads of your
3475 You can use the @code{thread} qualifier on conditional breakpoints as
3476 well; in this case, place @samp{thread @var{threadno}} before the
3477 breakpoint condition, like this:
3480 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3485 @cindex stopped threads
3486 @cindex threads, stopped
3487 Whenever your program stops under @value{GDBN} for any reason,
3488 @emph{all} threads of execution stop, not just the current thread. This
3489 allows you to examine the overall state of the program, including
3490 switching between threads, without worrying that things may change
3493 @cindex continuing threads
3494 @cindex threads, continuing
3495 Conversely, whenever you restart the program, @emph{all} threads start
3496 executing. @emph{This is true even when single-stepping} with commands
3497 like @code{step} or @code{next}.
3499 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3500 Since thread scheduling is up to your debugging target's operating
3501 system (not controlled by @value{GDBN}), other threads may
3502 execute more than one statement while the current thread completes a
3503 single step. Moreover, in general other threads stop in the middle of a
3504 statement, rather than at a clean statement boundary, when the program
3507 You might even find your program stopped in another thread after
3508 continuing or even single-stepping. This happens whenever some other
3509 thread runs into a breakpoint, a signal, or an exception before the
3510 first thread completes whatever you requested.
3512 On some OSes, you can lock the OS scheduler and thus allow only a single
3516 @item set scheduler-locking @var{mode}
3517 Set the scheduler locking mode. If it is @code{off}, then there is no
3518 locking and any thread may run at any time. If @code{on}, then only the
3519 current thread may run when the inferior is resumed. The @code{step}
3520 mode optimizes for single-stepping. It stops other threads from
3521 ``seizing the prompt'' by preempting the current thread while you are
3522 stepping. Other threads will only rarely (or never) get a chance to run
3523 when you step. They are more likely to run when you @samp{next} over a
3524 function call, and they are completely free to run when you use commands
3525 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3526 thread hits a breakpoint during its timeslice, they will never steal the
3527 @value{GDBN} prompt away from the thread that you are debugging.
3529 @item show scheduler-locking
3530 Display the current scheduler locking mode.
3534 @node Stack, Source, Stopping, Top
3535 @chapter Examining the Stack
3537 When your program has stopped, the first thing you need to know is where it
3538 stopped and how it got there.
3541 Each time your program performs a function call, information about the call
3543 That information includes the location of the call in your program,
3544 the arguments of the call,
3545 and the local variables of the function being called.
3546 The information is saved in a block of data called a @dfn{stack frame}.
3547 The stack frames are allocated in a region of memory called the @dfn{call
3550 When your program stops, the @value{GDBN} commands for examining the
3551 stack allow you to see all of this information.
3553 @cindex selected frame
3554 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3555 @value{GDBN} commands refer implicitly to the selected frame. In
3556 particular, whenever you ask @value{GDBN} for the value of a variable in
3557 your program, the value is found in the selected frame. There are
3558 special @value{GDBN} commands to select whichever frame you are
3559 interested in. @xref{Selection, ,Selecting a frame}.
3561 When your program stops, @value{GDBN} automatically selects the
3562 currently executing frame and describes it briefly, similar to the
3563 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3566 * Frames:: Stack frames
3567 * Backtrace:: Backtraces
3568 * Selection:: Selecting a frame
3569 * Frame Info:: Information on a frame
3573 @node Frames, Backtrace, Stack, Stack
3574 @section Stack frames
3576 @cindex frame, definition
3578 The call stack is divided up into contiguous pieces called @dfn{stack
3579 frames}, or @dfn{frames} for short; each frame is the data associated
3580 with one call to one function. The frame contains the arguments given
3581 to the function, the function's local variables, and the address at
3582 which the function is executing.
3584 @cindex initial frame
3585 @cindex outermost frame
3586 @cindex innermost frame
3587 When your program is started, the stack has only one frame, that of the
3588 function @code{main}. This is called the @dfn{initial} frame or the
3589 @dfn{outermost} frame. Each time a function is called, a new frame is
3590 made. Each time a function returns, the frame for that function invocation
3591 is eliminated. If a function is recursive, there can be many frames for
3592 the same function. The frame for the function in which execution is
3593 actually occurring is called the @dfn{innermost} frame. This is the most
3594 recently created of all the stack frames that still exist.
3596 @cindex frame pointer
3597 Inside your program, stack frames are identified by their addresses. A
3598 stack frame consists of many bytes, each of which has its own address; each
3599 kind of computer has a convention for choosing one byte whose
3600 address serves as the address of the frame. Usually this address is kept
3601 in a register called the @dfn{frame pointer register} while execution is
3602 going on in that frame.
3604 @cindex frame number
3605 @value{GDBN} assigns numbers to all existing stack frames, starting with
3606 zero for the innermost frame, one for the frame that called it,
3607 and so on upward. These numbers do not really exist in your program;
3608 they are assigned by @value{GDBN} to give you a way of designating stack
3609 frames in @value{GDBN} commands.
3611 @c below produces an acceptable overful hbox. --mew 13aug1993
3612 @cindex frameless execution
3613 Some compilers provide a way to compile functions so that they operate
3614 without stack frames. (For example, the @code{@value{GCC}} option
3615 @samp{-fomit-frame-pointer} generates functions without a frame.)
3616 This is occasionally done with heavily used library functions to save
3617 the frame setup time. @value{GDBN} has limited facilities for dealing
3618 with these function invocations. If the innermost function invocation
3619 has no stack frame, @value{GDBN} nevertheless regards it as though
3620 it had a separate frame, which is numbered zero as usual, allowing
3621 correct tracing of the function call chain. However, @value{GDBN} has
3622 no provision for frameless functions elsewhere in the stack.
3625 @kindex frame@r{, command}
3626 @item frame @var{args}
3627 The @code{frame} command allows you to move from one stack frame to another,
3628 and to print the stack frame you select. @var{args} may be either the
3629 address of the frame or the stack frame number. Without an argument,
3630 @code{frame} prints the current stack frame.
3632 @kindex select-frame
3634 The @code{select-frame} command allows you to move from one stack frame
3635 to another without printing the frame. This is the silent version of
3639 @node Backtrace, Selection, Frames, Stack
3644 @cindex stack traces
3645 A backtrace is a summary of how your program got where it is. It shows one
3646 line per frame, for many frames, starting with the currently executing
3647 frame (frame zero), followed by its caller (frame one), and on up the
3655 Print a backtrace of the entire stack: one line per frame for all
3656 frames in the stack.
3658 You can stop the backtrace at any time by typing the system interrupt
3659 character, normally @kbd{C-c}.
3661 @item backtrace @var{n}
3663 Similar, but print only the innermost @var{n} frames.
3665 @item backtrace -@var{n}
3667 Similar, but print only the outermost @var{n} frames.
3673 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3674 are additional aliases for @code{backtrace}.
3676 Each line in the backtrace shows the frame number and the function name.
3677 The program counter value is also shown---unless you use @code{set
3678 print address off}. The backtrace also shows the source file name and
3679 line number, as well as the arguments to the function. The program
3680 counter value is omitted if it is at the beginning of the code for that
3683 Here is an example of a backtrace. It was made with the command
3684 @samp{bt 3}, so it shows the innermost three frames.
3688 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3690 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3691 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3693 (More stack frames follow...)
3698 The display for frame zero does not begin with a program counter
3699 value, indicating that your program has stopped at the beginning of the
3700 code for line @code{993} of @code{builtin.c}.
3702 @node Selection, Frame Info, Backtrace, Stack
3703 @section Selecting a frame
3705 Most commands for examining the stack and other data in your program work on
3706 whichever stack frame is selected at the moment. Here are the commands for
3707 selecting a stack frame; all of them finish by printing a brief description
3708 of the stack frame just selected.
3711 @kindex frame@r{, selecting}
3715 Select frame number @var{n}. Recall that frame zero is the innermost
3716 (currently executing) frame, frame one is the frame that called the
3717 innermost one, and so on. The highest-numbered frame is the one for
3720 @item frame @var{addr}
3722 Select the frame at address @var{addr}. This is useful mainly if the
3723 chaining of stack frames has been damaged by a bug, making it
3724 impossible for @value{GDBN} to assign numbers properly to all frames. In
3725 addition, this can be useful when your program has multiple stacks and
3726 switches between them.
3728 On the SPARC architecture, @code{frame} needs two addresses to
3729 select an arbitrary frame: a frame pointer and a stack pointer.
3731 On the MIPS and Alpha architecture, it needs two addresses: a stack
3732 pointer and a program counter.
3734 On the 29k architecture, it needs three addresses: a register stack
3735 pointer, a program counter, and a memory stack pointer.
3736 @c note to future updaters: this is conditioned on a flag
3737 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3738 @c as of 27 Jan 1994.
3742 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3743 advances toward the outermost frame, to higher frame numbers, to frames
3744 that have existed longer. @var{n} defaults to one.
3749 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3750 advances toward the innermost frame, to lower frame numbers, to frames
3751 that were created more recently. @var{n} defaults to one. You may
3752 abbreviate @code{down} as @code{do}.
3755 All of these commands end by printing two lines of output describing the
3756 frame. The first line shows the frame number, the function name, the
3757 arguments, and the source file and line number of execution in that
3758 frame. The second line shows the text of that source line.
3766 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3768 10 read_input_file (argv[i]);
3772 After such a printout, the @code{list} command with no arguments
3773 prints ten lines centered on the point of execution in the frame.
3774 @xref{List, ,Printing source lines}.
3777 @kindex down-silently
3779 @item up-silently @var{n}
3780 @itemx down-silently @var{n}
3781 These two commands are variants of @code{up} and @code{down},
3782 respectively; they differ in that they do their work silently, without
3783 causing display of the new frame. They are intended primarily for use
3784 in @value{GDBN} command scripts, where the output might be unnecessary and
3788 @node Frame Info, , Selection, Stack
3789 @section Information about a frame
3791 There are several other commands to print information about the selected
3797 When used without any argument, this command does not change which
3798 frame is selected, but prints a brief description of the currently
3799 selected stack frame. It can be abbreviated @code{f}. With an
3800 argument, this command is used to select a stack frame.
3801 @xref{Selection, ,Selecting a frame}.
3807 This command prints a verbose description of the selected stack frame,
3812 the address of the frame
3814 the address of the next frame down (called by this frame)
3816 the address of the next frame up (caller of this frame)
3818 the language in which the source code corresponding to this frame is written
3820 the address of the frame's arguments
3822 the address of the frame's local variables
3824 the program counter saved in it (the address of execution in the caller frame)
3826 which registers were saved in the frame
3829 @noindent The verbose description is useful when
3830 something has gone wrong that has made the stack format fail to fit
3831 the usual conventions.
3833 @item info frame @var{addr}
3834 @itemx info f @var{addr}
3835 Print a verbose description of the frame at address @var{addr}, without
3836 selecting that frame. The selected frame remains unchanged by this
3837 command. This requires the same kind of address (more than one for some
3838 architectures) that you specify in the @code{frame} command.
3839 @xref{Selection, ,Selecting a frame}.
3843 Print the arguments of the selected frame, each on a separate line.
3847 Print the local variables of the selected frame, each on a separate
3848 line. These are all variables (declared either static or automatic)
3849 accessible at the point of execution of the selected frame.
3852 @cindex catch exceptions, list active handlers
3853 @cindex exception handlers, how to list
3855 Print a list of all the exception handlers that are active in the
3856 current stack frame at the current point of execution. To see other
3857 exception handlers, visit the associated frame (using the @code{up},
3858 @code{down}, or @code{frame} commands); then type @code{info catch}.
3859 @xref{Set Catchpoints, , Setting catchpoints}.
3864 @node Source, Data, Stack, Top
3865 @chapter Examining Source Files
3867 @value{GDBN} can print parts of your program's source, since the debugging
3868 information recorded in the program tells @value{GDBN} what source files were
3869 used to build it. When your program stops, @value{GDBN} spontaneously prints
3870 the line where it stopped. Likewise, when you select a stack frame
3871 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3872 execution in that frame has stopped. You can print other portions of
3873 source files by explicit command.
3875 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
3876 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
3877 @value{GDBN} under @sc{gnu} Emacs}.
3880 * List:: Printing source lines
3881 * Search:: Searching source files
3882 * Source Path:: Specifying source directories
3883 * Machine Code:: Source and machine code
3886 @node List, Search, Source, Source
3887 @section Printing source lines
3891 To print lines from a source file, use the @code{list} command
3892 (abbreviated @code{l}). By default, ten lines are printed.
3893 There are several ways to specify what part of the file you want to print.
3895 Here are the forms of the @code{list} command most commonly used:
3898 @item list @var{linenum}
3899 Print lines centered around line number @var{linenum} in the
3900 current source file.
3902 @item list @var{function}
3903 Print lines centered around the beginning of function
3907 Print more lines. If the last lines printed were printed with a
3908 @code{list} command, this prints lines following the last lines
3909 printed; however, if the last line printed was a solitary line printed
3910 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3911 Stack}), this prints lines centered around that line.
3914 Print lines just before the lines last printed.
3917 By default, @value{GDBN} prints ten source lines with any of these forms of
3918 the @code{list} command. You can change this using @code{set listsize}:
3921 @kindex set listsize
3922 @item set listsize @var{count}
3923 Make the @code{list} command display @var{count} source lines (unless
3924 the @code{list} argument explicitly specifies some other number).
3926 @kindex show listsize
3928 Display the number of lines that @code{list} prints.
3931 Repeating a @code{list} command with @key{RET} discards the argument,
3932 so it is equivalent to typing just @code{list}. This is more useful
3933 than listing the same lines again. An exception is made for an
3934 argument of @samp{-}; that argument is preserved in repetition so that
3935 each repetition moves up in the source file.
3938 In general, the @code{list} command expects you to supply zero, one or two
3939 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3940 of writing them, but the effect is always to specify some source line.
3941 Here is a complete description of the possible arguments for @code{list}:
3944 @item list @var{linespec}
3945 Print lines centered around the line specified by @var{linespec}.
3947 @item list @var{first},@var{last}
3948 Print lines from @var{first} to @var{last}. Both arguments are
3951 @item list ,@var{last}
3952 Print lines ending with @var{last}.
3954 @item list @var{first},
3955 Print lines starting with @var{first}.
3958 Print lines just after the lines last printed.
3961 Print lines just before the lines last printed.
3964 As described in the preceding table.
3967 Here are the ways of specifying a single source line---all the
3972 Specifies line @var{number} of the current source file.
3973 When a @code{list} command has two linespecs, this refers to
3974 the same source file as the first linespec.
3977 Specifies the line @var{offset} lines after the last line printed.
3978 When used as the second linespec in a @code{list} command that has
3979 two, this specifies the line @var{offset} lines down from the
3983 Specifies the line @var{offset} lines before the last line printed.
3985 @item @var{filename}:@var{number}
3986 Specifies line @var{number} in the source file @var{filename}.
3988 @item @var{function}
3989 Specifies the line that begins the body of the function @var{function}.
3990 For example: in C, this is the line with the open brace.
3992 @item @var{filename}:@var{function}
3993 Specifies the line of the open-brace that begins the body of the
3994 function @var{function} in the file @var{filename}. You only need the
3995 file name with a function name to avoid ambiguity when there are
3996 identically named functions in different source files.
3998 @item *@var{address}
3999 Specifies the line containing the program address @var{address}.
4000 @var{address} may be any expression.
4003 @node Search, Source Path, List, Source
4004 @section Searching source files
4006 @kindex reverse-search
4008 There are two commands for searching through the current source file for a
4013 @kindex forward-search
4014 @item forward-search @var{regexp}
4015 @itemx search @var{regexp}
4016 The command @samp{forward-search @var{regexp}} checks each line,
4017 starting with the one following the last line listed, for a match for
4018 @var{regexp}. It lists the line that is found. You can use the
4019 synonym @samp{search @var{regexp}} or abbreviate the command name as
4022 @item reverse-search @var{regexp}
4023 The command @samp{reverse-search @var{regexp}} checks each line, starting
4024 with the one before the last line listed and going backward, for a match
4025 for @var{regexp}. It lists the line that is found. You can abbreviate
4026 this command as @code{rev}.
4029 @node Source Path, Machine Code, Search, Source
4030 @section Specifying source directories
4033 @cindex directories for source files
4034 Executable programs sometimes do not record the directories of the source
4035 files from which they were compiled, just the names. Even when they do,
4036 the directories could be moved between the compilation and your debugging
4037 session. @value{GDBN} has a list of directories to search for source files;
4038 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4039 it tries all the directories in the list, in the order they are present
4040 in the list, until it finds a file with the desired name. Note that
4041 the executable search path is @emph{not} used for this purpose. Neither is
4042 the current working directory, unless it happens to be in the source
4045 If @value{GDBN} cannot find a source file in the source path, and the
4046 object program records a directory, @value{GDBN} tries that directory
4047 too. If the source path is empty, and there is no record of the
4048 compilation directory, @value{GDBN} looks in the current directory as a
4051 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4052 any information it has cached about where source files are found and where
4053 each line is in the file.
4057 When you start @value{GDBN}, its source path includes only @samp{cdir}
4058 and @samp{cwd}, in that order.
4059 To add other directories, use the @code{directory} command.
4062 @item directory @var{dirname} @dots{}
4063 @item dir @var{dirname} @dots{}
4064 Add directory @var{dirname} to the front of the source path. Several
4065 directory names may be given to this command, separated by @samp{:}
4066 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4067 part of absolute file names) or
4068 whitespace. You may specify a directory that is already in the source
4069 path; this moves it forward, so @value{GDBN} searches it sooner.
4075 @cindex compilation directory
4076 @cindex current directory
4077 @cindex working directory
4078 @cindex directory, current
4079 @cindex directory, compilation
4080 You can use the string @samp{$cdir} to refer to the compilation
4081 directory (if one is recorded), and @samp{$cwd} to refer to the current
4082 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4083 tracks the current working directory as it changes during your @value{GDBN}
4084 session, while the latter is immediately expanded to the current
4085 directory at the time you add an entry to the source path.
4088 Reset the source path to empty again. This requires confirmation.
4090 @c RET-repeat for @code{directory} is explicitly disabled, but since
4091 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4093 @item show directories
4094 @kindex show directories
4095 Print the source path: show which directories it contains.
4098 If your source path is cluttered with directories that are no longer of
4099 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4100 versions of source. You can correct the situation as follows:
4104 Use @code{directory} with no argument to reset the source path to empty.
4107 Use @code{directory} with suitable arguments to reinstall the
4108 directories you want in the source path. You can add all the
4109 directories in one command.
4112 @node Machine Code, , Source Path, Source
4113 @section Source and machine code
4115 You can use the command @code{info line} to map source lines to program
4116 addresses (and vice versa), and the command @code{disassemble} to display
4117 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4118 mode, the @code{info line} command causes the arrow to point to the
4119 line specified. Also, @code{info line} prints addresses in symbolic form as
4124 @item info line @var{linespec}
4125 Print the starting and ending addresses of the compiled code for
4126 source line @var{linespec}. You can specify source lines in any of
4127 the ways understood by the @code{list} command (@pxref{List, ,Printing
4131 For example, we can use @code{info line} to discover the location of
4132 the object code for the first line of function
4133 @code{m4_changequote}:
4135 @c FIXME: I think this example should also show the addresses in
4136 @c symbolic form, as they usually would be displayed.
4138 (@value{GDBP}) info line m4_changequote
4139 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4143 We can also inquire (using @code{*@var{addr}} as the form for
4144 @var{linespec}) what source line covers a particular address:
4146 (@value{GDBP}) info line *0x63ff
4147 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4150 @cindex @code{$_} and @code{info line}
4151 @kindex x@r{, and }@code{info line}
4152 After @code{info line}, the default address for the @code{x} command
4153 is changed to the starting address of the line, so that @samp{x/i} is
4154 sufficient to begin examining the machine code (@pxref{Memory,
4155 ,Examining memory}). Also, this address is saved as the value of the
4156 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4161 @cindex assembly instructions
4162 @cindex instructions, assembly
4163 @cindex machine instructions
4164 @cindex listing machine instructions
4166 This specialized command dumps a range of memory as machine
4167 instructions. The default memory range is the function surrounding the
4168 program counter of the selected frame. A single argument to this
4169 command is a program counter value; @value{GDBN} dumps the function
4170 surrounding this value. Two arguments specify a range of addresses
4171 (first inclusive, second exclusive) to dump.
4174 The following example shows the disassembly of a range of addresses of
4175 HP PA-RISC 2.0 code:
4178 (@value{GDBP}) disas 0x32c4 0x32e4
4179 Dump of assembler code from 0x32c4 to 0x32e4:
4180 0x32c4 <main+204>: addil 0,dp
4181 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4182 0x32cc <main+212>: ldil 0x3000,r31
4183 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4184 0x32d4 <main+220>: ldo 0(r31),rp
4185 0x32d8 <main+224>: addil -0x800,dp
4186 0x32dc <main+228>: ldo 0x588(r1),r26
4187 0x32e0 <main+232>: ldil 0x3000,r31
4188 End of assembler dump.
4191 Some architectures have more than one commonly-used set of instruction
4192 mnemonics or other syntax.
4195 @kindex set disassembly-flavor
4196 @cindex assembly instructions
4197 @cindex instructions, assembly
4198 @cindex machine instructions
4199 @cindex listing machine instructions
4200 @cindex Intel disassembly flavor
4201 @cindex AT&T disassembly flavor
4202 @item set disassembly-flavor @var{instruction-set}
4203 Select the instruction set to use when disassembling the
4204 program via the @code{disassemble} or @code{x/i} commands.
4206 Currently this command is only defined for the Intel x86 family. You
4207 can set @var{instruction-set} to either @code{intel} or @code{att}.
4208 The default is @code{att}, the AT&T flavor used by default by Unix
4209 assemblers for x86-based targets.
4213 @node Data, Languages, Source, Top
4214 @chapter Examining Data
4216 @cindex printing data
4217 @cindex examining data
4220 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4221 @c document because it is nonstandard... Under Epoch it displays in a
4222 @c different window or something like that.
4223 The usual way to examine data in your program is with the @code{print}
4224 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4225 evaluates and prints the value of an expression of the language your
4226 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4227 Different Languages}).
4230 @item print @var{expr}
4231 @itemx print /@var{f} @var{expr}
4232 @var{expr} is an expression (in the source language). By default the
4233 value of @var{expr} is printed in a format appropriate to its data type;
4234 you can choose a different format by specifying @samp{/@var{f}}, where
4235 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4239 @itemx print /@var{f}
4240 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4241 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4242 conveniently inspect the same value in an alternative format.
4245 A more low-level way of examining data is with the @code{x} command.
4246 It examines data in memory at a specified address and prints it in a
4247 specified format. @xref{Memory, ,Examining memory}.
4249 If you are interested in information about types, or about how the
4250 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4251 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4255 * Expressions:: Expressions
4256 * Variables:: Program variables
4257 * Arrays:: Artificial arrays
4258 * Output Formats:: Output formats
4259 * Memory:: Examining memory
4260 * Auto Display:: Automatic display
4261 * Print Settings:: Print settings
4262 * Value History:: Value history
4263 * Convenience Vars:: Convenience variables
4264 * Registers:: Registers
4265 * Floating Point Hardware:: Floating point hardware
4268 @node Expressions, Variables, Data, Data
4269 @section Expressions
4272 @code{print} and many other @value{GDBN} commands accept an expression and
4273 compute its value. Any kind of constant, variable or operator defined
4274 by the programming language you are using is valid in an expression in
4275 @value{GDBN}. This includes conditional expressions, function calls, casts
4276 and string constants. It unfortunately does not include symbols defined
4277 by preprocessor @code{#define} commands.
4279 @value{GDBN} supports array constants in expressions input by
4280 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4281 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4282 memory that is @code{malloc}ed in the target program.
4284 Because C is so widespread, most of the expressions shown in examples in
4285 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4286 Languages}, for information on how to use expressions in other
4289 In this section, we discuss operators that you can use in @value{GDBN}
4290 expressions regardless of your programming language.
4292 Casts are supported in all languages, not just in C, because it is so
4293 useful to cast a number into a pointer in order to examine a structure
4294 at that address in memory.
4295 @c FIXME: casts supported---Mod2 true?
4297 @value{GDBN} supports these operators, in addition to those common
4298 to programming languages:
4302 @samp{@@} is a binary operator for treating parts of memory as arrays.
4303 @xref{Arrays, ,Artificial arrays}, for more information.
4306 @samp{::} allows you to specify a variable in terms of the file or
4307 function where it is defined. @xref{Variables, ,Program variables}.
4309 @cindex @{@var{type}@}
4310 @cindex type casting memory
4311 @cindex memory, viewing as typed object
4312 @cindex casts, to view memory
4313 @item @{@var{type}@} @var{addr}
4314 Refers to an object of type @var{type} stored at address @var{addr} in
4315 memory. @var{addr} may be any expression whose value is an integer or
4316 pointer (but parentheses are required around binary operators, just as in
4317 a cast). This construct is allowed regardless of what kind of data is
4318 normally supposed to reside at @var{addr}.
4321 @node Variables, Arrays, Expressions, Data
4322 @section Program variables
4324 The most common kind of expression to use is the name of a variable
4327 Variables in expressions are understood in the selected stack frame
4328 (@pxref{Selection, ,Selecting a frame}); they must be either:
4332 global (or file-static)
4339 visible according to the scope rules of the
4340 programming language from the point of execution in that frame
4343 @noindent This means that in the function
4358 you can examine and use the variable @code{a} whenever your program is
4359 executing within the function @code{foo}, but you can only use or
4360 examine the variable @code{b} while your program is executing inside
4361 the block where @code{b} is declared.
4363 @cindex variable name conflict
4364 There is an exception: you can refer to a variable or function whose
4365 scope is a single source file even if the current execution point is not
4366 in this file. But it is possible to have more than one such variable or
4367 function with the same name (in different source files). If that
4368 happens, referring to that name has unpredictable effects. If you wish,
4369 you can specify a static variable in a particular function or file,
4370 using the colon-colon notation:
4372 @cindex colon-colon, context for variables/functions
4374 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4378 @var{file}::@var{variable}
4379 @var{function}::@var{variable}
4383 Here @var{file} or @var{function} is the name of the context for the
4384 static @var{variable}. In the case of file names, you can use quotes to
4385 make sure @value{GDBN} parses the file name as a single word---for example,
4386 to print a global value of @code{x} defined in @file{f2.c}:
4389 (@value{GDBP}) p 'f2.c'::x
4392 @cindex C++ scope resolution
4393 This use of @samp{::} is very rarely in conflict with the very similar
4394 use of the same notation in C++. @value{GDBN} also supports use of the C++
4395 scope resolution operator in @value{GDBN} expressions.
4396 @c FIXME: Um, so what happens in one of those rare cases where it's in
4399 @cindex wrong values
4400 @cindex variable values, wrong
4402 @emph{Warning:} Occasionally, a local variable may appear to have the
4403 wrong value at certain points in a function---just after entry to a new
4404 scope, and just before exit.
4406 You may see this problem when you are stepping by machine instructions.
4407 This is because, on most machines, it takes more than one instruction to
4408 set up a stack frame (including local variable definitions); if you are
4409 stepping by machine instructions, variables may appear to have the wrong
4410 values until the stack frame is completely built. On exit, it usually
4411 also takes more than one machine instruction to destroy a stack frame;
4412 after you begin stepping through that group of instructions, local
4413 variable definitions may be gone.
4415 This may also happen when the compiler does significant optimizations.
4416 To be sure of always seeing accurate values, turn off all optimization
4419 @cindex ``No symbol "foo" in current context''
4420 Another possible effect of compiler optimizations is to optimize
4421 unused variables out of existence, or assign variables to registers (as
4422 opposed to memory addresses). Depending on the support for such cases
4423 offered by the debug info format used by the compiler, @value{GDBN}
4424 might not be able to display values for such local variables. If that
4425 happens, @value{GDBN} will print a message like this:
4428 No symbol "foo" in current context.
4431 To solve such problems, either recompile without optimizations, or use a
4432 different debug info format, if the compiler supports several such
4433 formats. For example, @value{NGCC}, the @sc{gnu} C/C++ compiler usually
4434 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4435 in a format that is superior to formats such as COFF. You may be able
4436 to use DWARF-2 (@samp{-gdwarf-2}), which is also an effective form for
4437 debug info. See @ref{Debugging Options,,Options for Debugging Your
4438 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4442 @node Arrays, Output Formats, Variables, Data
4443 @section Artificial arrays
4445 @cindex artificial array
4447 It is often useful to print out several successive objects of the
4448 same type in memory; a section of an array, or an array of
4449 dynamically determined size for which only a pointer exists in the
4452 You can do this by referring to a contiguous span of memory as an
4453 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4454 operand of @samp{@@} should be the first element of the desired array
4455 and be an individual object. The right operand should be the desired length
4456 of the array. The result is an array value whose elements are all of
4457 the type of the left argument. The first element is actually the left
4458 argument; the second element comes from bytes of memory immediately
4459 following those that hold the first element, and so on. Here is an
4460 example. If a program says
4463 int *array = (int *) malloc (len * sizeof (int));
4467 you can print the contents of @code{array} with
4473 The left operand of @samp{@@} must reside in memory. Array values made
4474 with @samp{@@} in this way behave just like other arrays in terms of
4475 subscripting, and are coerced to pointers when used in expressions.
4476 Artificial arrays most often appear in expressions via the value history
4477 (@pxref{Value History, ,Value history}), after printing one out.
4479 Another way to create an artificial array is to use a cast.
4480 This re-interprets a value as if it were an array.
4481 The value need not be in memory:
4483 (@value{GDBP}) p/x (short[2])0x12345678
4484 $1 = @{0x1234, 0x5678@}
4487 As a convenience, if you leave the array length out (as in
4488 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4489 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4491 (@value{GDBP}) p/x (short[])0x12345678
4492 $2 = @{0x1234, 0x5678@}
4495 Sometimes the artificial array mechanism is not quite enough; in
4496 moderately complex data structures, the elements of interest may not
4497 actually be adjacent---for example, if you are interested in the values
4498 of pointers in an array. One useful work-around in this situation is
4499 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4500 variables}) as a counter in an expression that prints the first
4501 interesting value, and then repeat that expression via @key{RET}. For
4502 instance, suppose you have an array @code{dtab} of pointers to
4503 structures, and you are interested in the values of a field @code{fv}
4504 in each structure. Here is an example of what you might type:
4514 @node Output Formats, Memory, Arrays, Data
4515 @section Output formats
4517 @cindex formatted output
4518 @cindex output formats
4519 By default, @value{GDBN} prints a value according to its data type. Sometimes
4520 this is not what you want. For example, you might want to print a number
4521 in hex, or a pointer in decimal. Or you might want to view data in memory
4522 at a certain address as a character string or as an instruction. To do
4523 these things, specify an @dfn{output format} when you print a value.
4525 The simplest use of output formats is to say how to print a value
4526 already computed. This is done by starting the arguments of the
4527 @code{print} command with a slash and a format letter. The format
4528 letters supported are:
4532 Regard the bits of the value as an integer, and print the integer in
4536 Print as integer in signed decimal.
4539 Print as integer in unsigned decimal.
4542 Print as integer in octal.
4545 Print as integer in binary. The letter @samp{t} stands for ``two''.
4546 @footnote{@samp{b} cannot be used because these format letters are also
4547 used with the @code{x} command, where @samp{b} stands for ``byte'';
4548 see @ref{Memory,,Examining memory}.}
4551 @cindex unknown address, locating
4552 Print as an address, both absolute in hexadecimal and as an offset from
4553 the nearest preceding symbol. You can use this format used to discover
4554 where (in what function) an unknown address is located:
4557 (@value{GDBP}) p/a 0x54320
4558 $3 = 0x54320 <_initialize_vx+396>
4562 Regard as an integer and print it as a character constant.
4565 Regard the bits of the value as a floating point number and print
4566 using typical floating point syntax.
4569 For example, to print the program counter in hex (@pxref{Registers}), type
4576 Note that no space is required before the slash; this is because command
4577 names in @value{GDBN} cannot contain a slash.
4579 To reprint the last value in the value history with a different format,
4580 you can use the @code{print} command with just a format and no
4581 expression. For example, @samp{p/x} reprints the last value in hex.
4583 @node Memory, Auto Display, Output Formats, Data
4584 @section Examining memory
4586 You can use the command @code{x} (for ``examine'') to examine memory in
4587 any of several formats, independently of your program's data types.
4589 @cindex examining memory
4592 @item x/@var{nfu} @var{addr}
4595 Use the @code{x} command to examine memory.
4598 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4599 much memory to display and how to format it; @var{addr} is an
4600 expression giving the address where you want to start displaying memory.
4601 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4602 Several commands set convenient defaults for @var{addr}.
4605 @item @var{n}, the repeat count
4606 The repeat count is a decimal integer; the default is 1. It specifies
4607 how much memory (counting by units @var{u}) to display.
4608 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4611 @item @var{f}, the display format
4612 The display format is one of the formats used by @code{print},
4613 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4614 The default is @samp{x} (hexadecimal) initially.
4615 The default changes each time you use either @code{x} or @code{print}.
4617 @item @var{u}, the unit size
4618 The unit size is any of
4624 Halfwords (two bytes).
4626 Words (four bytes). This is the initial default.
4628 Giant words (eight bytes).
4631 Each time you specify a unit size with @code{x}, that size becomes the
4632 default unit the next time you use @code{x}. (For the @samp{s} and
4633 @samp{i} formats, the unit size is ignored and is normally not written.)
4635 @item @var{addr}, starting display address
4636 @var{addr} is the address where you want @value{GDBN} to begin displaying
4637 memory. The expression need not have a pointer value (though it may);
4638 it is always interpreted as an integer address of a byte of memory.
4639 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4640 @var{addr} is usually just after the last address examined---but several
4641 other commands also set the default address: @code{info breakpoints} (to
4642 the address of the last breakpoint listed), @code{info line} (to the
4643 starting address of a line), and @code{print} (if you use it to display
4644 a value from memory).
4647 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4648 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4649 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4650 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4651 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4653 Since the letters indicating unit sizes are all distinct from the
4654 letters specifying output formats, you do not have to remember whether
4655 unit size or format comes first; either order works. The output
4656 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4657 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4659 Even though the unit size @var{u} is ignored for the formats @samp{s}
4660 and @samp{i}, you might still want to use a count @var{n}; for example,
4661 @samp{3i} specifies that you want to see three machine instructions,
4662 including any operands. The command @code{disassemble} gives an
4663 alternative way of inspecting machine instructions; see @ref{Machine
4664 Code,,Source and machine code}.
4666 All the defaults for the arguments to @code{x} are designed to make it
4667 easy to continue scanning memory with minimal specifications each time
4668 you use @code{x}. For example, after you have inspected three machine
4669 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4670 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4671 the repeat count @var{n} is used again; the other arguments default as
4672 for successive uses of @code{x}.
4674 @cindex @code{$_}, @code{$__}, and value history
4675 The addresses and contents printed by the @code{x} command are not saved
4676 in the value history because there is often too much of them and they
4677 would get in the way. Instead, @value{GDBN} makes these values available for
4678 subsequent use in expressions as values of the convenience variables
4679 @code{$_} and @code{$__}. After an @code{x} command, the last address
4680 examined is available for use in expressions in the convenience variable
4681 @code{$_}. The contents of that address, as examined, are available in
4682 the convenience variable @code{$__}.
4684 If the @code{x} command has a repeat count, the address and contents saved
4685 are from the last memory unit printed; this is not the same as the last
4686 address printed if several units were printed on the last line of output.
4688 @node Auto Display, Print Settings, Memory, Data
4689 @section Automatic display
4690 @cindex automatic display
4691 @cindex display of expressions
4693 If you find that you want to print the value of an expression frequently
4694 (to see how it changes), you might want to add it to the @dfn{automatic
4695 display list} so that @value{GDBN} prints its value each time your program stops.
4696 Each expression added to the list is given a number to identify it;
4697 to remove an expression from the list, you specify that number.
4698 The automatic display looks like this:
4702 3: bar[5] = (struct hack *) 0x3804
4706 This display shows item numbers, expressions and their current values. As with
4707 displays you request manually using @code{x} or @code{print}, you can
4708 specify the output format you prefer; in fact, @code{display} decides
4709 whether to use @code{print} or @code{x} depending on how elaborate your
4710 format specification is---it uses @code{x} if you specify a unit size,
4711 or one of the two formats (@samp{i} and @samp{s}) that are only
4712 supported by @code{x}; otherwise it uses @code{print}.
4716 @item display @var{expr}
4717 Add the expression @var{expr} to the list of expressions to display
4718 each time your program stops. @xref{Expressions, ,Expressions}.
4720 @code{display} does not repeat if you press @key{RET} again after using it.
4722 @item display/@var{fmt} @var{expr}
4723 For @var{fmt} specifying only a display format and not a size or
4724 count, add the expression @var{expr} to the auto-display list but
4725 arrange to display it each time in the specified format @var{fmt}.
4726 @xref{Output Formats,,Output formats}.
4728 @item display/@var{fmt} @var{addr}
4729 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4730 number of units, add the expression @var{addr} as a memory address to
4731 be examined each time your program stops. Examining means in effect
4732 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4735 For example, @samp{display/i $pc} can be helpful, to see the machine
4736 instruction about to be executed each time execution stops (@samp{$pc}
4737 is a common name for the program counter; @pxref{Registers, ,Registers}).
4740 @kindex delete display
4742 @item undisplay @var{dnums}@dots{}
4743 @itemx delete display @var{dnums}@dots{}
4744 Remove item numbers @var{dnums} from the list of expressions to display.
4746 @code{undisplay} does not repeat if you press @key{RET} after using it.
4747 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4749 @kindex disable display
4750 @item disable display @var{dnums}@dots{}
4751 Disable the display of item numbers @var{dnums}. A disabled display
4752 item is not printed automatically, but is not forgotten. It may be
4753 enabled again later.
4755 @kindex enable display
4756 @item enable display @var{dnums}@dots{}
4757 Enable display of item numbers @var{dnums}. It becomes effective once
4758 again in auto display of its expression, until you specify otherwise.
4761 Display the current values of the expressions on the list, just as is
4762 done when your program stops.
4764 @kindex info display
4766 Print the list of expressions previously set up to display
4767 automatically, each one with its item number, but without showing the
4768 values. This includes disabled expressions, which are marked as such.
4769 It also includes expressions which would not be displayed right now
4770 because they refer to automatic variables not currently available.
4773 If a display expression refers to local variables, then it does not make
4774 sense outside the lexical context for which it was set up. Such an
4775 expression is disabled when execution enters a context where one of its
4776 variables is not defined. For example, if you give the command
4777 @code{display last_char} while inside a function with an argument
4778 @code{last_char}, @value{GDBN} displays this argument while your program
4779 continues to stop inside that function. When it stops elsewhere---where
4780 there is no variable @code{last_char}---the display is disabled
4781 automatically. The next time your program stops where @code{last_char}
4782 is meaningful, you can enable the display expression once again.
4784 @node Print Settings, Value History, Auto Display, Data
4785 @section Print settings
4787 @cindex format options
4788 @cindex print settings
4789 @value{GDBN} provides the following ways to control how arrays, structures,
4790 and symbols are printed.
4793 These settings are useful for debugging programs in any language:
4796 @kindex set print address
4797 @item set print address
4798 @itemx set print address on
4799 @value{GDBN} prints memory addresses showing the location of stack
4800 traces, structure values, pointer values, breakpoints, and so forth,
4801 even when it also displays the contents of those addresses. The default
4802 is @code{on}. For example, this is what a stack frame display looks like with
4803 @code{set print address on}:
4808 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4810 530 if (lquote != def_lquote)
4814 @item set print address off
4815 Do not print addresses when displaying their contents. For example,
4816 this is the same stack frame displayed with @code{set print address off}:
4820 (@value{GDBP}) set print addr off
4822 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4823 530 if (lquote != def_lquote)
4827 You can use @samp{set print address off} to eliminate all machine
4828 dependent displays from the @value{GDBN} interface. For example, with
4829 @code{print address off}, you should get the same text for backtraces on
4830 all machines---whether or not they involve pointer arguments.
4832 @kindex show print address
4833 @item show print address
4834 Show whether or not addresses are to be printed.
4837 When @value{GDBN} prints a symbolic address, it normally prints the
4838 closest earlier symbol plus an offset. If that symbol does not uniquely
4839 identify the address (for example, it is a name whose scope is a single
4840 source file), you may need to clarify. One way to do this is with
4841 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4842 you can set @value{GDBN} to print the source file and line number when
4843 it prints a symbolic address:
4846 @kindex set print symbol-filename
4847 @item set print symbol-filename on
4848 Tell @value{GDBN} to print the source file name and line number of a
4849 symbol in the symbolic form of an address.
4851 @item set print symbol-filename off
4852 Do not print source file name and line number of a symbol. This is the
4855 @kindex show print symbol-filename
4856 @item show print symbol-filename
4857 Show whether or not @value{GDBN} will print the source file name and
4858 line number of a symbol in the symbolic form of an address.
4861 Another situation where it is helpful to show symbol filenames and line
4862 numbers is when disassembling code; @value{GDBN} shows you the line
4863 number and source file that corresponds to each instruction.
4865 Also, you may wish to see the symbolic form only if the address being
4866 printed is reasonably close to the closest earlier symbol:
4869 @kindex set print max-symbolic-offset
4870 @item set print max-symbolic-offset @var{max-offset}
4871 Tell @value{GDBN} to only display the symbolic form of an address if the
4872 offset between the closest earlier symbol and the address is less than
4873 @var{max-offset}. The default is 0, which tells @value{GDBN}
4874 to always print the symbolic form of an address if any symbol precedes it.
4876 @kindex show print max-symbolic-offset
4877 @item show print max-symbolic-offset
4878 Ask how large the maximum offset is that @value{GDBN} prints in a
4882 @cindex wild pointer, interpreting
4883 @cindex pointer, finding referent
4884 If you have a pointer and you are not sure where it points, try
4885 @samp{set print symbol-filename on}. Then you can determine the name
4886 and source file location of the variable where it points, using
4887 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4888 For example, here @value{GDBN} shows that a variable @code{ptt} points
4889 at another variable @code{t}, defined in @file{hi2.c}:
4892 (@value{GDBP}) set print symbol-filename on
4893 (@value{GDBP}) p/a ptt
4894 $4 = 0xe008 <t in hi2.c>
4898 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
4899 does not show the symbol name and filename of the referent, even with
4900 the appropriate @code{set print} options turned on.
4903 Other settings control how different kinds of objects are printed:
4906 @kindex set print array
4907 @item set print array
4908 @itemx set print array on
4909 Pretty print arrays. This format is more convenient to read,
4910 but uses more space. The default is off.
4912 @item set print array off
4913 Return to compressed format for arrays.
4915 @kindex show print array
4916 @item show print array
4917 Show whether compressed or pretty format is selected for displaying
4920 @kindex set print elements
4921 @item set print elements @var{number-of-elements}
4922 Set a limit on how many elements of an array @value{GDBN} will print.
4923 If @value{GDBN} is printing a large array, it stops printing after it has
4924 printed the number of elements set by the @code{set print elements} command.
4925 This limit also applies to the display of strings.
4926 When @value{GDBN} starts, this limit is set to 200.
4927 Setting @var{number-of-elements} to zero means that the printing is unlimited.
4929 @kindex show print elements
4930 @item show print elements
4931 Display the number of elements of a large array that @value{GDBN} will print.
4932 If the number is 0, then the printing is unlimited.
4934 @kindex set print null-stop
4935 @item set print null-stop
4936 Cause @value{GDBN} to stop printing the characters of an array when the first
4937 @sc{null} is encountered. This is useful when large arrays actually
4938 contain only short strings.
4941 @kindex set print pretty
4942 @item set print pretty on
4943 Cause @value{GDBN} to print structures in an indented format with one member
4944 per line, like this:
4959 @item set print pretty off
4960 Cause @value{GDBN} to print structures in a compact format, like this:
4964 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4965 meat = 0x54 "Pork"@}
4970 This is the default format.
4972 @kindex show print pretty
4973 @item show print pretty
4974 Show which format @value{GDBN} is using to print structures.
4976 @kindex set print sevenbit-strings
4977 @item set print sevenbit-strings on
4978 Print using only seven-bit characters; if this option is set,
4979 @value{GDBN} displays any eight-bit characters (in strings or
4980 character values) using the notation @code{\}@var{nnn}. This setting is
4981 best if you are working in English (@sc{ascii}) and you use the
4982 high-order bit of characters as a marker or ``meta'' bit.
4984 @item set print sevenbit-strings off
4985 Print full eight-bit characters. This allows the use of more
4986 international character sets, and is the default.
4988 @kindex show print sevenbit-strings
4989 @item show print sevenbit-strings
4990 Show whether or not @value{GDBN} is printing only seven-bit characters.
4992 @kindex set print union
4993 @item set print union on
4994 Tell @value{GDBN} to print unions which are contained in structures. This
4995 is the default setting.
4997 @item set print union off
4998 Tell @value{GDBN} not to print unions which are contained in structures.
5000 @kindex show print union
5001 @item show print union
5002 Ask @value{GDBN} whether or not it will print unions which are contained in
5005 For example, given the declarations
5008 typedef enum @{Tree, Bug@} Species;
5009 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5010 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5021 struct thing foo = @{Tree, @{Acorn@}@};
5025 with @code{set print union on} in effect @samp{p foo} would print
5028 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5032 and with @code{set print union off} in effect it would print
5035 $1 = @{it = Tree, form = @{...@}@}
5041 These settings are of interest when debugging C++ programs:
5045 @kindex set print demangle
5046 @item set print demangle
5047 @itemx set print demangle on
5048 Print C++ names in their source form rather than in the encoded
5049 (``mangled'') form passed to the assembler and linker for type-safe
5050 linkage. The default is on.
5052 @kindex show print demangle
5053 @item show print demangle
5054 Show whether C++ names are printed in mangled or demangled form.
5056 @kindex set print asm-demangle
5057 @item set print asm-demangle
5058 @itemx set print asm-demangle on
5059 Print C++ names in their source form rather than their mangled form, even
5060 in assembler code printouts such as instruction disassemblies.
5063 @kindex show print asm-demangle
5064 @item show print asm-demangle
5065 Show whether C++ names in assembly listings are printed in mangled
5068 @kindex set demangle-style
5069 @cindex C++ symbol decoding style
5070 @cindex symbol decoding style, C++
5071 @item set demangle-style @var{style}
5072 Choose among several encoding schemes used by different compilers to
5073 represent C++ names. The choices for @var{style} are currently:
5077 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5080 Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm.
5081 This is the default.
5084 Decode based on the HP ANSI C++ (@code{aCC}) encoding algorithm.
5087 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
5090 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
5091 @strong{Warning:} this setting alone is not sufficient to allow
5092 debugging @code{cfront}-generated executables. @value{GDBN} would
5093 require further enhancement to permit that.
5096 If you omit @var{style}, you will see a list of possible formats.
5098 @kindex show demangle-style
5099 @item show demangle-style
5100 Display the encoding style currently in use for decoding C++ symbols.
5102 @kindex set print object
5103 @item set print object
5104 @itemx set print object on
5105 When displaying a pointer to an object, identify the @emph{actual}
5106 (derived) type of the object rather than the @emph{declared} type, using
5107 the virtual function table.
5109 @item set print object off
5110 Display only the declared type of objects, without reference to the
5111 virtual function table. This is the default setting.
5113 @kindex show print object
5114 @item show print object
5115 Show whether actual, or declared, object types are displayed.
5117 @kindex set print static-members
5118 @item set print static-members
5119 @itemx set print static-members on
5120 Print static members when displaying a C++ object. The default is on.
5122 @item set print static-members off
5123 Do not print static members when displaying a C++ object.
5125 @kindex show print static-members
5126 @item show print static-members
5127 Show whether C++ static members are printed, or not.
5129 @c These don't work with HP ANSI C++ yet.
5130 @kindex set print vtbl
5131 @item set print vtbl
5132 @itemx set print vtbl on
5133 Pretty print C++ virtual function tables. The default is off.
5134 (The @code{vtbl} commands do not work on programs compiled with the HP
5135 ANSI C++ compiler (@code{aCC}).)
5137 @item set print vtbl off
5138 Do not pretty print C++ virtual function tables.
5140 @kindex show print vtbl
5141 @item show print vtbl
5142 Show whether C++ virtual function tables are pretty printed, or not.
5145 @node Value History, Convenience Vars, Print Settings, Data
5146 @section Value history
5148 @cindex value history
5149 Values printed by the @code{print} command are saved in the @value{GDBN}
5150 @dfn{value history}. This allows you to refer to them in other expressions.
5151 Values are kept until the symbol table is re-read or discarded
5152 (for example with the @code{file} or @code{symbol-file} commands).
5153 When the symbol table changes, the value history is discarded,
5154 since the values may contain pointers back to the types defined in the
5159 @cindex history number
5160 The values printed are given @dfn{history numbers} by which you can
5161 refer to them. These are successive integers starting with one.
5162 @code{print} shows you the history number assigned to a value by
5163 printing @samp{$@var{num} = } before the value; here @var{num} is the
5166 To refer to any previous value, use @samp{$} followed by the value's
5167 history number. The way @code{print} labels its output is designed to
5168 remind you of this. Just @code{$} refers to the most recent value in
5169 the history, and @code{$$} refers to the value before that.
5170 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5171 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5172 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5174 For example, suppose you have just printed a pointer to a structure and
5175 want to see the contents of the structure. It suffices to type
5181 If you have a chain of structures where the component @code{next} points
5182 to the next one, you can print the contents of the next one with this:
5189 You can print successive links in the chain by repeating this
5190 command---which you can do by just typing @key{RET}.
5192 Note that the history records values, not expressions. If the value of
5193 @code{x} is 4 and you type these commands:
5201 then the value recorded in the value history by the @code{print} command
5202 remains 4 even though the value of @code{x} has changed.
5207 Print the last ten values in the value history, with their item numbers.
5208 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5209 values} does not change the history.
5211 @item show values @var{n}
5212 Print ten history values centered on history item number @var{n}.
5215 Print ten history values just after the values last printed. If no more
5216 values are available, @code{show values +} produces no display.
5219 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5220 same effect as @samp{show values +}.
5222 @node Convenience Vars, Registers, Value History, Data
5223 @section Convenience variables
5225 @cindex convenience variables
5226 @value{GDBN} provides @dfn{convenience variables} that you can use within
5227 @value{GDBN} to hold on to a value and refer to it later. These variables
5228 exist entirely within @value{GDBN}; they are not part of your program, and
5229 setting a convenience variable has no direct effect on further execution
5230 of your program. That is why you can use them freely.
5232 Convenience variables are prefixed with @samp{$}. Any name preceded by
5233 @samp{$} can be used for a convenience variable, unless it is one of
5234 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5235 (Value history references, in contrast, are @emph{numbers} preceded
5236 by @samp{$}. @xref{Value History, ,Value history}.)
5238 You can save a value in a convenience variable with an assignment
5239 expression, just as you would set a variable in your program.
5243 set $foo = *object_ptr
5247 would save in @code{$foo} the value contained in the object pointed to by
5250 Using a convenience variable for the first time creates it, but its
5251 value is @code{void} until you assign a new value. You can alter the
5252 value with another assignment at any time.
5254 Convenience variables have no fixed types. You can assign a convenience
5255 variable any type of value, including structures and arrays, even if
5256 that variable already has a value of a different type. The convenience
5257 variable, when used as an expression, has the type of its current value.
5260 @kindex show convenience
5261 @item show convenience
5262 Print a list of convenience variables used so far, and their values.
5263 Abbreviated @code{show conv}.
5266 One of the ways to use a convenience variable is as a counter to be
5267 incremented or a pointer to be advanced. For example, to print
5268 a field from successive elements of an array of structures:
5272 print bar[$i++]->contents
5276 Repeat that command by typing @key{RET}.
5278 Some convenience variables are created automatically by @value{GDBN} and given
5279 values likely to be useful.
5284 The variable @code{$_} is automatically set by the @code{x} command to
5285 the last address examined (@pxref{Memory, ,Examining memory}). Other
5286 commands which provide a default address for @code{x} to examine also
5287 set @code{$_} to that address; these commands include @code{info line}
5288 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5289 except when set by the @code{x} command, in which case it is a pointer
5290 to the type of @code{$__}.
5294 The variable @code{$__} is automatically set by the @code{x} command
5295 to the value found in the last address examined. Its type is chosen
5296 to match the format in which the data was printed.
5300 The variable @code{$_exitcode} is automatically set to the exit code when
5301 the program being debugged terminates.
5304 On HP-UX systems, if you refer to a function or variable name that
5305 begins with a dollar sign, @value{GDBN} searches for a user or system
5306 name first, before it searches for a convenience variable.
5308 @node Registers, Floating Point Hardware, Convenience Vars, Data
5312 You can refer to machine register contents, in expressions, as variables
5313 with names starting with @samp{$}. The names of registers are different
5314 for each machine; use @code{info registers} to see the names used on
5318 @kindex info registers
5319 @item info registers
5320 Print the names and values of all registers except floating-point
5321 registers (in the selected stack frame).
5323 @kindex info all-registers
5324 @cindex floating point registers
5325 @item info all-registers
5326 Print the names and values of all registers, including floating-point
5329 @item info registers @var{regname} @dots{}
5330 Print the @dfn{relativized} value of each specified register @var{regname}.
5331 As discussed in detail below, register values are normally relative to
5332 the selected stack frame. @var{regname} may be any register name valid on
5333 the machine you are using, with or without the initial @samp{$}.
5336 @value{GDBN} has four ``standard'' register names that are available (in
5337 expressions) on most machines---whenever they do not conflict with an
5338 architecture's canonical mnemonics for registers. The register names
5339 @code{$pc} and @code{$sp} are used for the program counter register and
5340 the stack pointer. @code{$fp} is used for a register that contains a
5341 pointer to the current stack frame, and @code{$ps} is used for a
5342 register that contains the processor status. For example,
5343 you could print the program counter in hex with
5350 or print the instruction to be executed next with
5357 or add four to the stack pointer@footnote{This is a way of removing
5358 one word from the stack, on machines where stacks grow downward in
5359 memory (most machines, nowadays). This assumes that the innermost
5360 stack frame is selected; setting @code{$sp} is not allowed when other
5361 stack frames are selected. To pop entire frames off the stack,
5362 regardless of machine architecture, use @code{return};
5363 see @ref{Returning, ,Returning from a function}.} with
5369 Whenever possible, these four standard register names are available on
5370 your machine even though the machine has different canonical mnemonics,
5371 so long as there is no conflict. The @code{info registers} command
5372 shows the canonical names. For example, on the SPARC, @code{info
5373 registers} displays the processor status register as @code{$psr} but you
5374 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5375 is an alias for the @sc{eflags} register.
5377 @value{GDBN} always considers the contents of an ordinary register as an
5378 integer when the register is examined in this way. Some machines have
5379 special registers which can hold nothing but floating point; these
5380 registers are considered to have floating point values. There is no way
5381 to refer to the contents of an ordinary register as floating point value
5382 (although you can @emph{print} it as a floating point value with
5383 @samp{print/f $@var{regname}}).
5385 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5386 means that the data format in which the register contents are saved by
5387 the operating system is not the same one that your program normally
5388 sees. For example, the registers of the 68881 floating point
5389 coprocessor are always saved in ``extended'' (raw) format, but all C
5390 programs expect to work with ``double'' (virtual) format. In such
5391 cases, @value{GDBN} normally works with the virtual format only (the format
5392 that makes sense for your program), but the @code{info registers} command
5393 prints the data in both formats.
5395 Normally, register values are relative to the selected stack frame
5396 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5397 value that the register would contain if all stack frames farther in
5398 were exited and their saved registers restored. In order to see the
5399 true contents of hardware registers, you must select the innermost
5400 frame (with @samp{frame 0}).
5402 However, @value{GDBN} must deduce where registers are saved, from the machine
5403 code generated by your compiler. If some registers are not saved, or if
5404 @value{GDBN} is unable to locate the saved registers, the selected stack
5405 frame makes no difference.
5407 @node Floating Point Hardware, , Registers, Data
5408 @section Floating point hardware
5409 @cindex floating point
5411 Depending on the configuration, @value{GDBN} may be able to give
5412 you more information about the status of the floating point hardware.
5417 Display hardware-dependent information about the floating
5418 point unit. The exact contents and layout vary depending on the
5419 floating point chip. Currently, @samp{info float} is supported on
5420 the ARM and x86 machines.
5423 @node Languages, Symbols, Data, Top
5424 @chapter Using @value{GDBN} with Different Languages
5427 Although programming languages generally have common aspects, they are
5428 rarely expressed in the same manner. For instance, in ANSI C,
5429 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
5430 Modula-2, it is accomplished by @code{p^}. Values can also be
5431 represented (and displayed) differently. Hex numbers in C appear as
5432 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
5434 @cindex working language
5435 Language-specific information is built into @value{GDBN} for some languages,
5436 allowing you to express operations like the above in your program's
5437 native language, and allowing @value{GDBN} to output values in a manner
5438 consistent with the syntax of your program's native language. The
5439 language you use to build expressions is called the @dfn{working
5443 * Setting:: Switching between source languages
5444 * Show:: Displaying the language
5445 * Checks:: Type and range checks
5446 * Support:: Supported languages
5449 @node Setting, Show, Languages, Languages
5450 @section Switching between source languages
5452 There are two ways to control the working language---either have @value{GDBN}
5453 set it automatically, or select it manually yourself. You can use the
5454 @code{set language} command for either purpose. On startup, @value{GDBN}
5455 defaults to setting the language automatically. The working language is
5456 used to determine how expressions you type are interpreted, how values
5459 In addition to the working language, every source file that
5460 @value{GDBN} knows about has its own working language. For some object
5461 file formats, the compiler might indicate which language a particular
5462 source file is in. However, most of the time @value{GDBN} infers the
5463 language from the name of the file. The language of a source file
5464 controls whether C++ names are demangled---this way @code{backtrace} can
5465 show each frame appropriately for its own language. There is no way to
5466 set the language of a source file from within @value{GDBN}, but you can
5467 set the language associated with a filename extension. @xref{Show, ,
5468 Displaying the language}.
5470 This is most commonly a problem when you use a program, such
5471 as @code{cfront} or @code{f2c}, that generates C but is written in
5472 another language. In that case, make the
5473 program use @code{#line} directives in its C output; that way
5474 @value{GDBN} will know the correct language of the source code of the original
5475 program, and will display that source code, not the generated C code.
5478 * Filenames:: Filename extensions and languages.
5479 * Manually:: Setting the working language manually
5480 * Automatically:: Having @value{GDBN} infer the source language
5483 @node Filenames, Manually, Setting, Setting
5484 @subsection List of filename extensions and languages
5486 If a source file name ends in one of the following extensions, then
5487 @value{GDBN} infers that its language is the one indicated.
5512 Modula-2 source file
5516 Assembler source file. This actually behaves almost like C, but
5517 @value{GDBN} does not skip over function prologues when stepping.
5520 In addition, you may set the language associated with a filename
5521 extension. @xref{Show, , Displaying the language}.
5523 @node Manually, Automatically, Filenames, Setting
5524 @subsection Setting the working language
5526 If you allow @value{GDBN} to set the language automatically,
5527 expressions are interpreted the same way in your debugging session and
5530 @kindex set language
5531 If you wish, you may set the language manually. To do this, issue the
5532 command @samp{set language @var{lang}}, where @var{lang} is the name of
5534 @code{c} or @code{modula-2}.
5535 For a list of the supported languages, type @samp{set language}.
5537 Setting the language manually prevents @value{GDBN} from updating the working
5538 language automatically. This can lead to confusion if you try
5539 to debug a program when the working language is not the same as the
5540 source language, when an expression is acceptable to both
5541 languages---but means different things. For instance, if the current
5542 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5550 might not have the effect you intended. In C, this means to add
5551 @code{b} and @code{c} and place the result in @code{a}. The result
5552 printed would be the value of @code{a}. In Modula-2, this means to compare
5553 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5555 @node Automatically, , Manually, Setting
5556 @subsection Having @value{GDBN} infer the source language
5558 To have @value{GDBN} set the working language automatically, use
5559 @samp{set language local} or @samp{set language auto}. @value{GDBN}
5560 then infers the working language. That is, when your program stops in a
5561 frame (usually by encountering a breakpoint), @value{GDBN} sets the
5562 working language to the language recorded for the function in that
5563 frame. If the language for a frame is unknown (that is, if the function
5564 or block corresponding to the frame was defined in a source file that
5565 does not have a recognized extension), the current working language is
5566 not changed, and @value{GDBN} issues a warning.
5568 This may not seem necessary for most programs, which are written
5569 entirely in one source language. However, program modules and libraries
5570 written in one source language can be used by a main program written in
5571 a different source language. Using @samp{set language auto} in this
5572 case frees you from having to set the working language manually.
5574 @node Show, Checks, Setting, Languages
5575 @section Displaying the language
5577 The following commands help you find out which language is the
5578 working language, and also what language source files were written in.
5580 @kindex show language
5581 @kindex info frame@r{, show the source language}
5582 @kindex info source@r{, show the source language}
5585 Display the current working language. This is the
5586 language you can use with commands such as @code{print} to
5587 build and compute expressions that may involve variables in your program.
5590 Display the source language for this frame. This language becomes the
5591 working language if you use an identifier from this frame.
5592 @xref{Frame Info, ,Information about a frame}, to identify the other
5593 information listed here.
5596 Display the source language of this source file.
5597 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
5598 information listed here.
5601 In unusual circumstances, you may have source files with extensions
5602 not in the standard list. You can then set the extension associated
5603 with a language explicitly:
5605 @kindex set extension-language
5606 @kindex info extensions
5608 @item set extension-language @var{.ext} @var{language}
5609 Set source files with extension @var{.ext} to be assumed to be in
5610 the source language @var{language}.
5612 @item info extensions
5613 List all the filename extensions and the associated languages.
5616 @node Checks, Support, Show, Languages
5617 @section Type and range checking
5620 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5621 checking are included, but they do not yet have any effect. This
5622 section documents the intended facilities.
5624 @c FIXME remove warning when type/range code added
5626 Some languages are designed to guard you against making seemingly common
5627 errors through a series of compile- and run-time checks. These include
5628 checking the type of arguments to functions and operators, and making
5629 sure mathematical overflows are caught at run time. Checks such as
5630 these help to ensure a program's correctness once it has been compiled
5631 by eliminating type mismatches, and providing active checks for range
5632 errors when your program is running.
5634 @value{GDBN} can check for conditions like the above if you wish.
5635 Although @value{GDBN} does not check the statements in your program, it
5636 can check expressions entered directly into @value{GDBN} for evaluation via
5637 the @code{print} command, for example. As with the working language,
5638 @value{GDBN} can also decide whether or not to check automatically based on
5639 your program's source language. @xref{Support, ,Supported languages},
5640 for the default settings of supported languages.
5643 * Type Checking:: An overview of type checking
5644 * Range Checking:: An overview of range checking
5647 @cindex type checking
5648 @cindex checks, type
5649 @node Type Checking, Range Checking, Checks, Checks
5650 @subsection An overview of type checking
5652 Some languages, such as Modula-2, are strongly typed, meaning that the
5653 arguments to operators and functions have to be of the correct type,
5654 otherwise an error occurs. These checks prevent type mismatch
5655 errors from ever causing any run-time problems. For example,
5663 The second example fails because the @code{CARDINAL} 1 is not
5664 type-compatible with the @code{REAL} 2.3.
5666 For the expressions you use in @value{GDBN} commands, you can tell the
5667 @value{GDBN} type checker to skip checking;
5668 to treat any mismatches as errors and abandon the expression;
5669 or to only issue warnings when type mismatches occur,
5670 but evaluate the expression anyway. When you choose the last of
5671 these, @value{GDBN} evaluates expressions like the second example above, but
5672 also issues a warning.
5674 Even if you turn type checking off, there may be other reasons
5675 related to type that prevent @value{GDBN} from evaluating an expression.
5676 For instance, @value{GDBN} does not know how to add an @code{int} and
5677 a @code{struct foo}. These particular type errors have nothing to do
5678 with the language in use, and usually arise from expressions, such as
5679 the one described above, which make little sense to evaluate anyway.
5681 Each language defines to what degree it is strict about type. For
5682 instance, both Modula-2 and C require the arguments to arithmetical
5683 operators to be numbers. In C, enumerated types and pointers can be
5684 represented as numbers, so that they are valid arguments to mathematical
5685 operators. @xref{Support, ,Supported languages}, for further
5686 details on specific languages.
5688 @value{GDBN} provides some additional commands for controlling the type checker:
5690 @kindex set check@r{, type}
5691 @kindex set check type
5692 @kindex show check type
5694 @item set check type auto
5695 Set type checking on or off based on the current working language.
5696 @xref{Support, ,Supported languages}, for the default settings for
5699 @item set check type on
5700 @itemx set check type off
5701 Set type checking on or off, overriding the default setting for the
5702 current working language. Issue a warning if the setting does not
5703 match the language default. If any type mismatches occur in
5704 evaluating an expression while type checking is on, @value{GDBN} prints a
5705 message and aborts evaluation of the expression.
5707 @item set check type warn
5708 Cause the type checker to issue warnings, but to always attempt to
5709 evaluate the expression. Evaluating the expression may still
5710 be impossible for other reasons. For example, @value{GDBN} cannot add
5711 numbers and structures.
5714 Show the current setting of the type checker, and whether or not @value{GDBN}
5715 is setting it automatically.
5718 @cindex range checking
5719 @cindex checks, range
5720 @node Range Checking, , Type Checking, Checks
5721 @subsection An overview of range checking
5723 In some languages (such as Modula-2), it is an error to exceed the
5724 bounds of a type; this is enforced with run-time checks. Such range
5725 checking is meant to ensure program correctness by making sure
5726 computations do not overflow, or indices on an array element access do
5727 not exceed the bounds of the array.
5729 For expressions you use in @value{GDBN} commands, you can tell
5730 @value{GDBN} to treat range errors in one of three ways: ignore them,
5731 always treat them as errors and abandon the expression, or issue
5732 warnings but evaluate the expression anyway.
5734 A range error can result from numerical overflow, from exceeding an
5735 array index bound, or when you type a constant that is not a member
5736 of any type. Some languages, however, do not treat overflows as an
5737 error. In many implementations of C, mathematical overflow causes the
5738 result to ``wrap around'' to lower values---for example, if @var{m} is
5739 the largest integer value, and @var{s} is the smallest, then
5742 @var{m} + 1 @result{} @var{s}
5745 This, too, is specific to individual languages, and in some cases
5746 specific to individual compilers or machines. @xref{Support, ,
5747 Supported languages}, for further details on specific languages.
5749 @value{GDBN} provides some additional commands for controlling the range checker:
5751 @kindex set check@r{, range}
5752 @kindex set check range
5753 @kindex show check range
5755 @item set check range auto
5756 Set range checking on or off based on the current working language.
5757 @xref{Support, ,Supported languages}, for the default settings for
5760 @item set check range on
5761 @itemx set check range off
5762 Set range checking on or off, overriding the default setting for the
5763 current working language. A warning is issued if the setting does not
5764 match the language default. If a range error occurs and range checking is on,
5765 then a message is printed and evaluation of the expression is aborted.
5767 @item set check range warn
5768 Output messages when the @value{GDBN} range checker detects a range error,
5769 but attempt to evaluate the expression anyway. Evaluating the
5770 expression may still be impossible for other reasons, such as accessing
5771 memory that the process does not own (a typical example from many Unix
5775 Show the current setting of the range checker, and whether or not it is
5776 being set automatically by @value{GDBN}.
5779 @node Support, , Checks, Languages
5780 @section Supported languages
5782 @value{GDBN} supports C, C++, Fortran, Java, Chill, assembly, and Modula-2.
5783 @c This is false ...
5784 Some @value{GDBN} features may be used in expressions regardless of the
5785 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
5786 and the @samp{@{type@}addr} construct (@pxref{Expressions,
5787 ,Expressions}) can be used with the constructs of any supported
5790 The following sections detail to what degree each source language is
5791 supported by @value{GDBN}. These sections are not meant to be language
5792 tutorials or references, but serve only as a reference guide to what the
5793 @value{GDBN} expression parser accepts, and what input and output
5794 formats should look like for different languages. There are many good
5795 books written on each of these languages; please look to these for a
5796 language reference or tutorial.
5800 * Modula-2:: Modula-2
5804 @node C, Modula-2, Support, Support
5805 @subsection C and C++
5808 @cindex expressions in C or C++
5810 Since C and C++ are so closely related, many features of @value{GDBN} apply
5811 to both languages. Whenever this is the case, we discuss those languages
5816 @cindex @sc{gnu} C++
5817 The C++ debugging facilities are jointly implemented by the C++
5818 compiler and @value{GDBN}. Therefore, to debug your C++ code
5819 effectively, you must compile your C++ programs with a supported
5820 C++ compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C++
5821 compiler (@code{aCC}).
5823 For best results when using @sc{gnu} C++, use the stabs debugging
5824 format. You can select that format explicitly with the @code{g++}
5825 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
5826 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
5827 CC, gcc.info, Using @sc{gnu} CC}, for more information.
5830 * C Operators:: C and C++ operators
5831 * C Constants:: C and C++ constants
5832 * C plus plus expressions:: C++ expressions
5833 * C Defaults:: Default settings for C and C++
5834 * C Checks:: C and C++ type and range checks
5835 * Debugging C:: @value{GDBN} and C
5836 * Debugging C plus plus:: @value{GDBN} features for C++
5839 @node C Operators, C Constants, C, C
5840 @subsubsection C and C++ operators
5842 @cindex C and C++ operators
5844 Operators must be defined on values of specific types. For instance,
5845 @code{+} is defined on numbers, but not on structures. Operators are
5846 often defined on groups of types.
5848 For the purposes of C and C++, the following definitions hold:
5853 @emph{Integral types} include @code{int} with any of its storage-class
5854 specifiers; @code{char}; @code{enum}; and, for C++, @code{bool}.
5857 @emph{Floating-point types} include @code{float}, @code{double}, and
5858 @code{long double} (if supported by the target platform).
5861 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
5864 @emph{Scalar types} include all of the above.
5869 The following operators are supported. They are listed here
5870 in order of increasing precedence:
5874 The comma or sequencing operator. Expressions in a comma-separated list
5875 are evaluated from left to right, with the result of the entire
5876 expression being the last expression evaluated.
5879 Assignment. The value of an assignment expression is the value
5880 assigned. Defined on scalar types.
5883 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5884 and translated to @w{@code{@var{a} = @var{a op b}}}.
5885 @w{@code{@var{op}=}} and @code{=} have the same precedence.
5886 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5887 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5890 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5891 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5895 Logical @sc{or}. Defined on integral types.
5898 Logical @sc{and}. Defined on integral types.
5901 Bitwise @sc{or}. Defined on integral types.
5904 Bitwise exclusive-@sc{or}. Defined on integral types.
5907 Bitwise @sc{and}. Defined on integral types.
5910 Equality and inequality. Defined on scalar types. The value of these
5911 expressions is 0 for false and non-zero for true.
5913 @item <@r{, }>@r{, }<=@r{, }>=
5914 Less than, greater than, less than or equal, greater than or equal.
5915 Defined on scalar types. The value of these expressions is 0 for false
5916 and non-zero for true.
5919 left shift, and right shift. Defined on integral types.
5922 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5925 Addition and subtraction. Defined on integral types, floating-point types and
5928 @item *@r{, }/@r{, }%
5929 Multiplication, division, and modulus. Multiplication and division are
5930 defined on integral and floating-point types. Modulus is defined on
5934 Increment and decrement. When appearing before a variable, the
5935 operation is performed before the variable is used in an expression;
5936 when appearing after it, the variable's value is used before the
5937 operation takes place.
5940 Pointer dereferencing. Defined on pointer types. Same precedence as
5944 Address operator. Defined on variables. Same precedence as @code{++}.
5946 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5947 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5948 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
5949 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5953 Negative. Defined on integral and floating-point types. Same
5954 precedence as @code{++}.
5957 Logical negation. Defined on integral types. Same precedence as
5961 Bitwise complement operator. Defined on integral types. Same precedence as
5966 Structure member, and pointer-to-structure member. For convenience,
5967 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5968 pointer based on the stored type information.
5969 Defined on @code{struct} and @code{union} data.
5972 Dereferences of pointers to members.
5975 Array indexing. @code{@var{a}[@var{i}]} is defined as
5976 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5979 Function parameter list. Same precedence as @code{->}.
5982 C++ scope resolution operator. Defined on @code{struct}, @code{union},
5983 and @code{class} types.
5986 Doubled colons also represent the @value{GDBN} scope operator
5987 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
5991 If an operator is redefined in the user code, @value{GDBN} usually
5992 attempts to invoke the redefined version instead of using the operator's
5999 @node C Constants, C plus plus expressions, C Operators, C
6000 @subsubsection C and C++ constants
6002 @cindex C and C++ constants
6004 @value{GDBN} allows you to express the constants of C and C++ in the
6009 Integer constants are a sequence of digits. Octal constants are
6010 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6011 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6012 @samp{l}, specifying that the constant should be treated as a
6016 Floating point constants are a sequence of digits, followed by a decimal
6017 point, followed by a sequence of digits, and optionally followed by an
6018 exponent. An exponent is of the form:
6019 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6020 sequence of digits. The @samp{+} is optional for positive exponents.
6021 A floating-point constant may also end with a letter @samp{f} or
6022 @samp{F}, specifying that the constant should be treated as being of
6023 the @code{float} (as opposed to the default @code{double}) type; or with
6024 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
6028 Enumerated constants consist of enumerated identifiers, or their
6029 integral equivalents.
6032 Character constants are a single character surrounded by single quotes
6033 (@code{'}), or a number---the ordinal value of the corresponding character
6034 (usually its @sc{ascii} value). Within quotes, the single character may
6035 be represented by a letter or by @dfn{escape sequences}, which are of
6036 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6037 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6038 @samp{@var{x}} is a predefined special character---for example,
6039 @samp{\n} for newline.
6042 String constants are a sequence of character constants surrounded by
6043 double quotes (@code{"}). Any valid character constant (as described
6044 above) may appear. Double quotes within the string must be preceded by
6045 a backslash, so for instance @samp{"a\"b'c"} is a string of five
6049 Pointer constants are an integral value. You can also write pointers
6050 to constants using the C operator @samp{&}.
6053 Array constants are comma-separated lists surrounded by braces @samp{@{}
6054 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6055 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6056 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6060 * C plus plus expressions::
6067 @node C plus plus expressions, C Defaults, C Constants, C
6068 @subsubsection C++ expressions
6070 @cindex expressions in C++
6071 @value{GDBN} expression handling can interpret most C++ expressions.
6073 @cindex C++ support, not in @sc{coff}
6074 @cindex @sc{coff} versus C++
6075 @cindex C++ and object formats
6076 @cindex object formats and C++
6077 @cindex a.out and C++
6078 @cindex @sc{ecoff} and C++
6079 @cindex @sc{xcoff} and C++
6080 @cindex @sc{elf}/stabs and C++
6081 @cindex @sc{elf}/@sc{dwarf} and C++
6082 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6083 @c periodically whether this has happened...
6085 @emph{Warning:} @value{GDBN} can only debug C++ code if you use the
6086 proper compiler. Typically, C++ debugging depends on the use of
6087 additional debugging information in the symbol table, and thus requires
6088 special support. In particular, if your compiler generates a.out, MIPS
6089 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
6090 symbol table, these facilities are all available. (With @sc{gnu} CC,
6091 you can use the @samp{-gstabs} option to request stabs debugging
6092 extensions explicitly.) Where the object code format is standard
6093 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
6094 support in @value{GDBN} does @emph{not} work.
6099 @cindex member functions
6101 Member function calls are allowed; you can use expressions like
6104 count = aml->GetOriginal(x, y)
6108 @cindex namespace in C++
6110 While a member function is active (in the selected stack frame), your
6111 expressions have the same namespace available as the member function;
6112 that is, @value{GDBN} allows implicit references to the class instance
6113 pointer @code{this} following the same rules as C++.
6115 @cindex call overloaded functions
6116 @cindex overloaded functions, calling
6117 @cindex type conversions in C++
6119 You can call overloaded functions; @value{GDBN} resolves the function
6120 call to the right definition, with some restrictions. @value{GDBN} does not
6121 perform overload resolution involving user-defined type conversions,
6122 calls to constructors, or instantiations of templates that do not exist
6123 in the program. It also cannot handle ellipsis argument lists or
6126 It does perform integral conversions and promotions, floating-point
6127 promotions, arithmetic conversions, pointer conversions, conversions of
6128 class objects to base classes, and standard conversions such as those of
6129 functions or arrays to pointers; it requires an exact match on the
6130 number of function arguments.
6132 Overload resolution is always performed, unless you have specified
6133 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6134 ,@value{GDBN} features for C++}.
6136 You must specify @code{set overload-resolution off} in order to use an
6137 explicit function signature to call an overloaded function, as in
6139 p 'foo(char,int)'('x', 13)
6142 The @value{GDBN} command-completion facility can simplify this;
6143 see @ref{Completion, ,Command completion}.
6145 @cindex reference declarations
6147 @value{GDBN} understands variables declared as C++ references; you can use
6148 them in expressions just as you do in C++ source---they are automatically
6151 In the parameter list shown when @value{GDBN} displays a frame, the values of
6152 reference variables are not displayed (unlike other variables); this
6153 avoids clutter, since references are often used for large structures.
6154 The @emph{address} of a reference variable is always shown, unless
6155 you have specified @samp{set print address off}.
6158 @value{GDBN} supports the C++ name resolution operator @code{::}---your
6159 expressions can use it just as expressions in your program do. Since
6160 one scope may be defined in another, you can use @code{::} repeatedly if
6161 necessary, for example in an expression like
6162 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
6163 resolving name scope by reference to source files, in both C and C++
6164 debugging (@pxref{Variables, ,Program variables}).
6167 In addition, when used with HP's C++ compiler, @value{GDBN} supports
6168 calling virtual functions correctly, printing out virtual bases of
6169 objects, calling functions in a base subobject, casting objects, and
6170 invoking user-defined operators.
6172 @node C Defaults, C Checks, C plus plus expressions, C
6173 @subsubsection C and C++ defaults
6175 @cindex C and C++ defaults
6177 If you allow @value{GDBN} to set type and range checking automatically, they
6178 both default to @code{off} whenever the working language changes to
6179 C or C++. This happens regardless of whether you or @value{GDBN}
6180 selects the working language.
6182 If you allow @value{GDBN} to set the language automatically, it
6183 recognizes source files whose names end with @file{.c}, @file{.C}, or
6184 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
6185 these files, it sets the working language to C or C++.
6186 @xref{Automatically, ,Having @value{GDBN} infer the source language},
6187 for further details.
6189 @c Type checking is (a) primarily motivated by Modula-2, and (b)
6190 @c unimplemented. If (b) changes, it might make sense to let this node
6191 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
6193 @node C Checks, Debugging C, C Defaults, C
6194 @subsubsection C and C++ type and range checks
6196 @cindex C and C++ checks
6198 By default, when @value{GDBN} parses C or C++ expressions, type checking
6199 is not used. However, if you turn type checking on, @value{GDBN}
6200 considers two variables type equivalent if:
6204 The two variables are structured and have the same structure, union, or
6208 The two variables have the same type name, or types that have been
6209 declared equivalent through @code{typedef}.
6212 @c leaving this out because neither J Gilmore nor R Pesch understand it.
6215 The two @code{struct}, @code{union}, or @code{enum} variables are
6216 declared in the same declaration. (Note: this may not be true for all C
6221 Range checking, if turned on, is done on mathematical operations. Array
6222 indices are not checked, since they are often used to index a pointer
6223 that is not itself an array.
6225 @node Debugging C, Debugging C plus plus, C Checks, C
6226 @subsubsection @value{GDBN} and C
6228 The @code{set print union} and @code{show print union} commands apply to
6229 the @code{union} type. When set to @samp{on}, any @code{union} that is
6230 inside a @code{struct} or @code{class} is also printed. Otherwise, it
6231 appears as @samp{@{...@}}.
6233 The @code{@@} operator aids in the debugging of dynamic arrays, formed
6234 with pointers and a memory allocation function. @xref{Expressions,
6238 * Debugging C plus plus::
6241 @node Debugging C plus plus, , Debugging C, C
6242 @subsubsection @value{GDBN} features for C++
6244 @cindex commands for C++
6246 Some @value{GDBN} commands are particularly useful with C++, and some are
6247 designed specifically for use with C++. Here is a summary:
6250 @cindex break in overloaded functions
6251 @item @r{breakpoint menus}
6252 When you want a breakpoint in a function whose name is overloaded,
6253 @value{GDBN} breakpoint menus help you specify which function definition
6254 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
6256 @cindex overloading in C++
6257 @item rbreak @var{regex}
6258 Setting breakpoints using regular expressions is helpful for setting
6259 breakpoints on overloaded functions that are not members of any special
6261 @xref{Set Breaks, ,Setting breakpoints}.
6263 @cindex C++ exception handling
6266 Debug C++ exception handling using these commands. @xref{Set
6267 Catchpoints, , Setting catchpoints}.
6270 @item ptype @var{typename}
6271 Print inheritance relationships as well as other information for type
6273 @xref{Symbols, ,Examining the Symbol Table}.
6275 @cindex C++ symbol display
6276 @item set print demangle
6277 @itemx show print demangle
6278 @itemx set print asm-demangle
6279 @itemx show print asm-demangle
6280 Control whether C++ symbols display in their source form, both when
6281 displaying code as C++ source and when displaying disassemblies.
6282 @xref{Print Settings, ,Print settings}.
6284 @item set print object
6285 @itemx show print object
6286 Choose whether to print derived (actual) or declared types of objects.
6287 @xref{Print Settings, ,Print settings}.
6289 @item set print vtbl
6290 @itemx show print vtbl
6291 Control the format for printing virtual function tables.
6292 @xref{Print Settings, ,Print settings}.
6293 (The @code{vtbl} commands do not work on programs compiled with the HP
6294 ANSI C++ compiler (@code{aCC}).)
6296 @kindex set overload-resolution
6297 @cindex overloaded functions, overload resolution
6298 @item set overload-resolution on
6299 Enable overload resolution for C++ expression evaluation. The default
6300 is on. For overloaded functions, @value{GDBN} evaluates the arguments
6301 and searches for a function whose signature matches the argument types,
6302 using the standard C++ conversion rules (see @ref{C plus plus expressions, ,C++
6303 expressions}, for details). If it cannot find a match, it emits a
6306 @item set overload-resolution off
6307 Disable overload resolution for C++ expression evaluation. For
6308 overloaded functions that are not class member functions, @value{GDBN}
6309 chooses the first function of the specified name that it finds in the
6310 symbol table, whether or not its arguments are of the correct type. For
6311 overloaded functions that are class member functions, @value{GDBN}
6312 searches for a function whose signature @emph{exactly} matches the
6315 @item @r{Overloaded symbol names}
6316 You can specify a particular definition of an overloaded symbol, using
6317 the same notation that is used to declare such symbols in C++: type
6318 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
6319 also use the @value{GDBN} command-line word completion facilities to list the
6320 available choices, or to finish the type list for you.
6321 @xref{Completion,, Command completion}, for details on how to do this.
6324 @node Modula-2, Chill, C, Support
6325 @subsection Modula-2
6327 @cindex Modula-2, @value{GDBN} support
6329 The extensions made to @value{GDBN} to support Modula-2 only support
6330 output from the @sc{gnu} Modula-2 compiler (which is currently being
6331 developed). Other Modula-2 compilers are not currently supported, and
6332 attempting to debug executables produced by them is most likely
6333 to give an error as @value{GDBN} reads in the executable's symbol
6336 @cindex expressions in Modula-2
6338 * M2 Operators:: Built-in operators
6339 * Built-In Func/Proc:: Built-in functions and procedures
6340 * M2 Constants:: Modula-2 constants
6341 * M2 Defaults:: Default settings for Modula-2
6342 * Deviations:: Deviations from standard Modula-2
6343 * M2 Checks:: Modula-2 type and range checks
6344 * M2 Scope:: The scope operators @code{::} and @code{.}
6345 * GDB/M2:: @value{GDBN} and Modula-2
6348 @node M2 Operators, Built-In Func/Proc, Modula-2, Modula-2
6349 @subsubsection Operators
6350 @cindex Modula-2 operators
6352 Operators must be defined on values of specific types. For instance,
6353 @code{+} is defined on numbers, but not on structures. Operators are
6354 often defined on groups of types. For the purposes of Modula-2, the
6355 following definitions hold:
6360 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
6364 @emph{Character types} consist of @code{CHAR} and its subranges.
6367 @emph{Floating-point types} consist of @code{REAL}.
6370 @emph{Pointer types} consist of anything declared as @code{POINTER TO
6374 @emph{Scalar types} consist of all of the above.
6377 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
6380 @emph{Boolean types} consist of @code{BOOLEAN}.
6384 The following operators are supported, and appear in order of
6385 increasing precedence:
6389 Function argument or array index separator.
6392 Assignment. The value of @var{var} @code{:=} @var{value} is
6396 Less than, greater than on integral, floating-point, or enumerated
6400 Less than or equal to, greater than or equal to
6401 on integral, floating-point and enumerated types, or set inclusion on
6402 set types. Same precedence as @code{<}.
6404 @item =@r{, }<>@r{, }#
6405 Equality and two ways of expressing inequality, valid on scalar types.
6406 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
6407 available for inequality, since @code{#} conflicts with the script
6411 Set membership. Defined on set types and the types of their members.
6412 Same precedence as @code{<}.
6415 Boolean disjunction. Defined on boolean types.
6418 Boolean conjunction. Defined on boolean types.
6421 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6424 Addition and subtraction on integral and floating-point types, or union
6425 and difference on set types.
6428 Multiplication on integral and floating-point types, or set intersection
6432 Division on floating-point types, or symmetric set difference on set
6433 types. Same precedence as @code{*}.
6436 Integer division and remainder. Defined on integral types. Same
6437 precedence as @code{*}.
6440 Negative. Defined on @code{INTEGER} and @code{REAL} data.
6443 Pointer dereferencing. Defined on pointer types.
6446 Boolean negation. Defined on boolean types. Same precedence as
6450 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
6451 precedence as @code{^}.
6454 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
6457 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
6461 @value{GDBN} and Modula-2 scope operators.
6465 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
6466 treats the use of the operator @code{IN}, or the use of operators
6467 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
6468 @code{<=}, and @code{>=} on sets as an error.
6471 @cindex Modula-2 built-ins
6472 @node Built-In Func/Proc, M2 Constants, M2 Operators, Modula-2
6473 @subsubsection Built-in functions and procedures
6475 Modula-2 also makes available several built-in procedures and functions.
6476 In describing these, the following metavariables are used:
6481 represents an @code{ARRAY} variable.
6484 represents a @code{CHAR} constant or variable.
6487 represents a variable or constant of integral type.
6490 represents an identifier that belongs to a set. Generally used in the
6491 same function with the metavariable @var{s}. The type of @var{s} should
6492 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
6495 represents a variable or constant of integral or floating-point type.
6498 represents a variable or constant of floating-point type.
6504 represents a variable.
6507 represents a variable or constant of one of many types. See the
6508 explanation of the function for details.
6511 All Modula-2 built-in procedures also return a result, described below.
6515 Returns the absolute value of @var{n}.
6518 If @var{c} is a lower case letter, it returns its upper case
6519 equivalent, otherwise it returns its argument.
6522 Returns the character whose ordinal value is @var{i}.
6525 Decrements the value in the variable @var{v} by one. Returns the new value.
6527 @item DEC(@var{v},@var{i})
6528 Decrements the value in the variable @var{v} by @var{i}. Returns the
6531 @item EXCL(@var{m},@var{s})
6532 Removes the element @var{m} from the set @var{s}. Returns the new
6535 @item FLOAT(@var{i})
6536 Returns the floating point equivalent of the integer @var{i}.
6539 Returns the index of the last member of @var{a}.
6542 Increments the value in the variable @var{v} by one. Returns the new value.
6544 @item INC(@var{v},@var{i})
6545 Increments the value in the variable @var{v} by @var{i}. Returns the
6548 @item INCL(@var{m},@var{s})
6549 Adds the element @var{m} to the set @var{s} if it is not already
6550 there. Returns the new set.
6553 Returns the maximum value of the type @var{t}.
6556 Returns the minimum value of the type @var{t}.
6559 Returns boolean TRUE if @var{i} is an odd number.
6562 Returns the ordinal value of its argument. For example, the ordinal
6563 value of a character is its @sc{ascii} value (on machines supporting the
6564 @sc{ascii} character set). @var{x} must be of an ordered type, which include
6565 integral, character and enumerated types.
6568 Returns the size of its argument. @var{x} can be a variable or a type.
6570 @item TRUNC(@var{r})
6571 Returns the integral part of @var{r}.
6573 @item VAL(@var{t},@var{i})
6574 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6578 @emph{Warning:} Sets and their operations are not yet supported, so
6579 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
6583 @cindex Modula-2 constants
6584 @node M2 Constants, M2 Defaults, Built-In Func/Proc, Modula-2
6585 @subsubsection Constants
6587 @value{GDBN} allows you to express the constants of Modula-2 in the following
6593 Integer constants are simply a sequence of digits. When used in an
6594 expression, a constant is interpreted to be type-compatible with the
6595 rest of the expression. Hexadecimal integers are specified by a
6596 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6599 Floating point constants appear as a sequence of digits, followed by a
6600 decimal point and another sequence of digits. An optional exponent can
6601 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6602 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6603 digits of the floating point constant must be valid decimal (base 10)
6607 Character constants consist of a single character enclosed by a pair of
6608 like quotes, either single (@code{'}) or double (@code{"}). They may
6609 also be expressed by their ordinal value (their @sc{ascii} value, usually)
6610 followed by a @samp{C}.
6613 String constants consist of a sequence of characters enclosed by a
6614 pair of like quotes, either single (@code{'}) or double (@code{"}).
6615 Escape sequences in the style of C are also allowed. @xref{C
6616 Constants, ,C and C++ constants}, for a brief explanation of escape
6620 Enumerated constants consist of an enumerated identifier.
6623 Boolean constants consist of the identifiers @code{TRUE} and
6627 Pointer constants consist of integral values only.
6630 Set constants are not yet supported.
6633 @node M2 Defaults, Deviations, M2 Constants, Modula-2
6634 @subsubsection Modula-2 defaults
6635 @cindex Modula-2 defaults
6637 If type and range checking are set automatically by @value{GDBN}, they
6638 both default to @code{on} whenever the working language changes to
6639 Modula-2. This happens regardless of whether you or @value{GDBN}
6640 selected the working language.
6642 If you allow @value{GDBN} to set the language automatically, then entering
6643 code compiled from a file whose name ends with @file{.mod} sets the
6644 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6645 the language automatically}, for further details.
6647 @node Deviations, M2 Checks, M2 Defaults, Modula-2
6648 @subsubsection Deviations from standard Modula-2
6649 @cindex Modula-2, deviations from
6651 A few changes have been made to make Modula-2 programs easier to debug.
6652 This is done primarily via loosening its type strictness:
6656 Unlike in standard Modula-2, pointer constants can be formed by
6657 integers. This allows you to modify pointer variables during
6658 debugging. (In standard Modula-2, the actual address contained in a
6659 pointer variable is hidden from you; it can only be modified
6660 through direct assignment to another pointer variable or expression that
6661 returned a pointer.)
6664 C escape sequences can be used in strings and characters to represent
6665 non-printable characters. @value{GDBN} prints out strings with these
6666 escape sequences embedded. Single non-printable characters are
6667 printed using the @samp{CHR(@var{nnn})} format.
6670 The assignment operator (@code{:=}) returns the value of its right-hand
6674 All built-in procedures both modify @emph{and} return their argument.
6677 @node M2 Checks, M2 Scope, Deviations, Modula-2
6678 @subsubsection Modula-2 type and range checks
6679 @cindex Modula-2 checks
6682 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6685 @c FIXME remove warning when type/range checks added
6687 @value{GDBN} considers two Modula-2 variables type equivalent if:
6691 They are of types that have been declared equivalent via a @code{TYPE
6692 @var{t1} = @var{t2}} statement
6695 They have been declared on the same line. (Note: This is true of the
6696 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
6699 As long as type checking is enabled, any attempt to combine variables
6700 whose types are not equivalent is an error.
6702 Range checking is done on all mathematical operations, assignment, array
6703 index bounds, and all built-in functions and procedures.
6705 @node M2 Scope, GDB/M2, M2 Checks, Modula-2
6706 @subsubsection The scope operators @code{::} and @code{.}
6709 @cindex colon, doubled as scope operator
6711 @kindex colon-colon@r{, in Modula-2}
6712 @c Info cannot handle :: but TeX can.
6718 There are a few subtle differences between the Modula-2 scope operator
6719 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6724 @var{module} . @var{id}
6725 @var{scope} :: @var{id}
6729 where @var{scope} is the name of a module or a procedure,
6730 @var{module} the name of a module, and @var{id} is any declared
6731 identifier within your program, except another module.
6733 Using the @code{::} operator makes @value{GDBN} search the scope
6734 specified by @var{scope} for the identifier @var{id}. If it is not
6735 found in the specified scope, then @value{GDBN} searches all scopes
6736 enclosing the one specified by @var{scope}.
6738 Using the @code{.} operator makes @value{GDBN} search the current scope for
6739 the identifier specified by @var{id} that was imported from the
6740 definition module specified by @var{module}. With this operator, it is
6741 an error if the identifier @var{id} was not imported from definition
6742 module @var{module}, or if @var{id} is not an identifier in
6745 @node GDB/M2, , M2 Scope, Modula-2
6746 @subsubsection @value{GDBN} and Modula-2
6748 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6749 Five subcommands of @code{set print} and @code{show print} apply
6750 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6751 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6752 apply to C++, and the last to the C @code{union} type, which has no direct
6753 analogue in Modula-2.
6755 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6756 with any language, is not useful with Modula-2. Its
6757 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6758 created in Modula-2 as they can in C or C++. However, because an
6759 address can be specified by an integral constant, the construct
6760 @samp{@{@var{type}@}@var{adrexp}} is still useful.
6762 @cindex @code{#} in Modula-2
6763 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6764 interpreted as the beginning of a comment. Use @code{<>} instead.
6766 @node Chill, , Modula-2, Support
6769 The extensions made to @value{GDBN} to support Chill only support output
6770 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
6771 supported, and attempting to debug executables produced by them is most
6772 likely to give an error as @value{GDBN} reads in the executable's symbol
6775 @c This used to say "... following Chill related topics ...", but since
6776 @c menus are not shown in the printed manual, it would look awkward.
6777 This section covers the Chill related topics and the features
6778 of @value{GDBN} which support these topics.
6781 * How modes are displayed:: How modes are displayed
6782 * Locations:: Locations and their accesses
6783 * Values and their Operations:: Values and their Operations
6784 * Chill type and range checks::
6788 @node How modes are displayed, Locations, Chill, Chill
6789 @subsubsection How modes are displayed
6791 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
6792 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
6793 slightly from the standard specification of the Chill language. The
6796 @c FIXME: this @table's contents effectively disable @code by using @r
6797 @c on every @item. So why does it need @code?
6799 @item @r{@emph{Discrete modes:}}
6802 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
6805 @emph{Boolean Mode} which is predefined by @code{BOOL},
6807 @emph{Character Mode} which is predefined by @code{CHAR},
6809 @emph{Set Mode} which is displayed by the keyword @code{SET}.
6811 (@value{GDBP}) ptype x
6812 type = SET (karli = 10, susi = 20, fritzi = 100)
6814 If the type is an unnumbered set the set element values are omitted.
6816 @emph{Range Mode} which is displayed by @code{type = <basemode>
6817 (<lower bound> : <upper bound>)}, where @code{<lower bound>, <upper
6818 bound>} can be of any discrete literal expression (e.g. set element
6822 @item @r{@emph{Powerset Mode:}}
6823 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
6824 the member mode of the powerset. The member mode can be any discrete mode.
6826 (@value{GDBP}) ptype x
6827 type = POWERSET SET (egon, hugo, otto)
6830 @item @r{@emph{Reference Modes:}}
6833 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
6834 followed by the mode name to which the reference is bound.
6836 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
6839 @item @r{@emph{Procedure mode}}
6840 The procedure mode is displayed by @code{type = PROC(<parameter list>)
6841 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
6842 list>} is a list of the parameter modes. @code{<return mode>} indicates
6843 the mode of the result of the procedure if any. The exceptionlist lists
6844 all possible exceptions which can be raised by the procedure.
6847 @item @r{@emph{Instance mode}}
6848 The instance mode is represented by a structure, which has a static
6849 type, and is therefore not really of interest.
6852 @item @r{@emph{Synchronization Modes:}}
6855 @emph{Event Mode} which is displayed by @code{EVENT (<event length>)},
6856 where @code{(<event length>)} is optional.
6858 @emph{Buffer Mode} which is displayed by @code{BUFFER (<buffer length>)
6859 <buffer element mode>}, where @code{(<buffer length>)} is optional.
6862 @item @r{@emph{Timing Modes:}}
6865 @emph{Duration Mode} which is predefined by @code{DURATION}
6867 @emph{Absolute Time Mode} which is predefined by @code{TIME}
6870 @item @r{@emph{Real Modes:}}
6871 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
6873 @item @r{@emph{String Modes:}}
6876 @emph{Character String Mode} which is displayed by @code{CHARS(<string
6877 length>)}, followed by the keyword @code{VARYING} if the String Mode is
6880 @emph{Bit String Mode} which is displayed by @code{BOOLS(<string
6884 @item @r{@emph{Array Mode:}}
6885 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
6886 followed by the element mode (which may in turn be an array mode).
6888 (@value{GDBP}) ptype x
6891 SET (karli = 10, susi = 20, fritzi = 100)
6894 @item @r{@emph{Structure Mode}}
6895 The Structure mode is displayed by the keyword @code{STRUCT(<field
6896 list>)}. The @code{<field list>} consists of names and modes of fields
6897 of the structure. Variant structures have the keyword @code{CASE <field>
6898 OF <variant fields> ESAC} in their field list. Since the current version
6899 of the GNU Chill compiler doesn't implement tag processing (no runtime
6900 checks of variant fields, and therefore no debugging info), the output
6901 always displays all variant fields.
6903 (@value{GDBP}) ptype str
6917 @node Locations, Values and their Operations, How modes are displayed, Chill
6918 @subsubsection Locations and their accesses
6920 A location in Chill is an object which can contain values.
6922 A value of a location is generally accessed by the (declared) name of
6923 the location. The output conforms to the specification of values in
6924 Chill programs. How values are specified
6925 is the topic of the next section, @ref{Values and their Operations}.
6927 The pseudo-location @code{RESULT} (or @code{result}) can be used to
6928 display or change the result of a currently-active procedure:
6935 This does the same as the Chill action @code{RESULT EXPR} (which
6936 is not available in @value{GDBN}).
6938 Values of reference mode locations are printed by @code{PTR(<hex
6939 value>)} in case of a free reference mode, and by @code{(REF <reference
6940 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
6941 represents the address where the reference points to. To access the
6942 value of the location referenced by the pointer, use the dereference
6945 Values of procedure mode locations are displayed by @code{@{ PROC
6946 (<argument modes> ) <return mode> @} <address> <name of procedure
6947 location>}. @code{<argument modes>} is a list of modes according to the
6948 parameter specification of the procedure and @code{<address>} shows the
6949 address of the entry point.
6952 Locations of instance modes are displayed just like a structure with two
6953 fields specifying the @emph{process type} and the @emph{copy number} of
6954 the investigated instance location@footnote{This comes from the current
6955 implementation of instances. They are implemented as a structure (no
6956 na). The output should be something like @code{[<name of the process>;
6957 <instance number>]}.}. The field names are @code{__proc_type} and
6960 Locations of synchronization modes are displayed like a structure with
6961 the field name @code{__event_data} in case of a event mode location, and
6962 like a structure with the field @code{__buffer_data} in case of a buffer
6963 mode location (refer to previous paragraph).
6965 Structure Mode locations are printed by @code{[.<field name>: <value>,
6966 ...]}. The @code{<field name>} corresponds to the structure mode
6967 definition and the layout of @code{<value>} varies depending of the mode
6968 of the field. If the investigated structure mode location is of variant
6969 structure mode, the variant parts of the structure are enclosed in curled
6970 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
6971 on the same memory location and represent the current values of the
6972 memory location in their specific modes. Since no tag processing is done
6973 all variants are displayed. A variant field is printed by
6974 @code{(<variant name>) = .<field name>: <value>}. (who implements the
6977 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
6978 [.cs: []], (susi) = [.ds: susi]}]
6982 Substructures of string mode-, array mode- or structure mode-values
6983 (e.g. array slices, fields of structure locations) are accessed using
6984 certain operations which are described in the next section, @ref{Values
6985 and their Operations}.
6987 A location value may be interpreted as having a different mode using the
6988 location conversion. This mode conversion is written as @code{<mode
6989 name>(<location>)}. The user has to consider that the sizes of the modes
6990 have to be equal otherwise an error occurs. Furthermore, no range
6991 checking of the location against the destination mode is performed, and
6992 therefore the result can be quite confusing.
6995 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
6998 @node Values and their Operations, Chill type and range checks, Locations, Chill
6999 @subsubsection Values and their Operations
7001 Values are used to alter locations, to investigate complex structures in
7002 more detail or to filter relevant information out of a large amount of
7003 data. There are several (mode dependent) operations defined which enable
7004 such investigations. These operations are not only applicable to
7005 constant values but also to locations, which can become quite useful
7006 when debugging complex structures. During parsing the command line
7007 (e.g. evaluating an expression) @value{GDBN} treats location names as
7008 the values behind these locations.
7010 This section describes how values have to be specified and which
7011 operations are legal to be used with such values.
7014 @item Literal Values
7015 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
7016 For detailed specification refer to the @sc{gnu} Chill implementation Manual
7018 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
7019 @c be converted to a @ref.
7024 @emph{Integer Literals} are specified in the same manner as in Chill
7025 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
7027 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
7029 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
7032 @emph{Set Literals} are defined by a name which was specified in a set
7033 mode. The value delivered by a Set Literal is the set value. This is
7034 comparable to an enumeration in C/C++ language.
7036 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
7037 emptiness literal delivers either the empty reference value, the empty
7038 procedure value or the empty instance value.
7041 @emph{Character String Literals} are defined by a sequence of characters
7042 enclosed in single- or double quotes. If a single- or double quote has
7043 to be part of the string literal it has to be stuffed (specified twice).
7045 @emph{Bitstring Literals} are specified in the same manner as in Chill
7046 programs (refer z200/88 chpt 5.2.4.8).
7048 @emph{Floating point literals} are specified in the same manner as in
7049 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
7054 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
7055 name>} can be omitted if the mode of the tuple is unambiguous. This
7056 unambiguity is derived from the context of a evaluated expression.
7057 @code{<tuple>} can be one of the following:
7060 @item @emph{Powerset Tuple}
7061 @item @emph{Array Tuple}
7062 @item @emph{Structure Tuple}
7063 Powerset tuples, array tuples and structure tuples are specified in the
7064 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
7067 @item String Element Value
7068 A string element value is specified by @code{<string value>(<index>)},
7069 where @code{<index>} is a integer expression. It delivers a character
7070 value which is equivalent to the character indexed by @code{<index>} in
7073 @item String Slice Value
7074 A string slice value is specified by @code{<string value>(<slice
7075 spec>)}, where @code{<slice spec>} can be either a range of integer
7076 expressions or specified by @code{<start expr> up <size>}.
7077 @code{<size>} denotes the number of elements which the slice contains.
7078 The delivered value is a string value, which is part of the specified
7081 @item Array Element Values
7082 An array element value is specified by @code{<array value>(<expr>)} and
7083 delivers a array element value of the mode of the specified array.
7085 @item Array Slice Values
7086 An array slice is specified by @code{<array value>(<slice spec>)}, where
7087 @code{<slice spec>} can be either a range specified by expressions or by
7088 @code{<start expr> up <size>}. @code{<size>} denotes the number of
7089 arrayelements the slice contains. The delivered value is an array value
7090 which is part of the specified array.
7092 @item Structure Field Values
7093 A structure field value is derived by @code{<structure value>.<field
7094 name>}, where @code{<field name>} indicates the name of a field specified
7095 in the mode definition of the structure. The mode of the delivered value
7096 corresponds to this mode definition in the structure definition.
7098 @item Procedure Call Value
7099 The procedure call value is derived from the return value of the
7100 procedure@footnote{If a procedure call is used for instance in an
7101 expression, then this procedure is called with all its side
7102 effects. This can lead to confusing results if used carelessly.}.
7104 Values of duration mode locations are represented by @code{ULONG} literals.
7106 Values of time mode locations are represented by @code{TIME(<secs>:<nsecs>)}.
7109 This is not implemented yet:
7110 @item Built-in Value
7112 The following built in functions are provided:
7124 @item @code{UPPER()}
7125 @item @code{LOWER()}
7126 @item @code{LENGTH()}
7130 @item @code{ARCSIN()}
7131 @item @code{ARCCOS()}
7132 @item @code{ARCTAN()}
7139 For a detailed description refer to the GNU Chill implementation manual
7143 @item Zero-adic Operator Value
7144 The zero-adic operator value is derived from the instance value for the
7145 current active process.
7147 @item Expression Values
7148 The value delivered by an expression is the result of the evaluation of
7149 the specified expression. If there are error conditions (mode
7150 incompatibility, etc.) the evaluation of expressions is aborted with a
7151 corresponding error message. Expressions may be parenthesised which
7152 causes the evaluation of this expression before any other expression
7153 which uses the result of the parenthesised expression. The following
7154 operators are supported by @value{GDBN}:
7157 @item @code{OR, ORIF, XOR}
7158 @itemx @code{AND, ANDIF}
7160 Logical operators defined over operands of boolean mode.
7163 Equality and inequality operators defined over all modes.
7167 Relational operators defined over predefined modes.
7170 @itemx @code{*, /, MOD, REM}
7171 Arithmetic operators defined over predefined modes.
7174 Change sign operator.
7177 String concatenation operator.
7180 String repetition operator.
7183 Referenced location operator which can be used either to take the
7184 address of a location (@code{->loc}), or to dereference a reference
7185 location (@code{loc->}).
7187 @item @code{OR, XOR}
7190 Powerset and bitstring operators.
7194 Powerset inclusion operators.
7197 Membership operator.
7201 @node Chill type and range checks, Chill defaults, Values and their Operations, Chill
7202 @subsubsection Chill type and range checks
7204 @value{GDBN} considers two Chill variables mode equivalent if the sizes
7205 of the two modes are equal. This rule applies recursively to more
7206 complex datatypes which means that complex modes are treated
7207 equivalent if all element modes (which also can be complex modes like
7208 structures, arrays, etc.) have the same size.
7210 Range checking is done on all mathematical operations, assignment, array
7211 index bounds and all built in procedures.
7213 Strong type checks are forced using the @value{GDBN} command @code{set
7214 check strong}. This enforces strong type and range checks on all
7215 operations where Chill constructs are used (expressions, built in
7216 functions, etc.) in respect to the semantics as defined in the z.200
7217 language specification.
7219 All checks can be disabled by the @value{GDBN} command @code{set check
7223 @c Deviations from the Chill Standard Z200/88
7224 see last paragraph ?
7227 @node Chill defaults, , Chill type and range checks, Chill
7228 @subsubsection Chill defaults
7230 If type and range checking are set automatically by @value{GDBN}, they
7231 both default to @code{on} whenever the working language changes to
7232 Chill. This happens regardless of whether you or @value{GDBN}
7233 selected the working language.
7235 If you allow @value{GDBN} to set the language automatically, then entering
7236 code compiled from a file whose name ends with @file{.ch} sets the
7237 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
7238 the language automatically}, for further details.
7240 @node Symbols, Altering, Languages, Top
7241 @chapter Examining the Symbol Table
7243 The commands described in this chapter allow you to inquire about the
7244 symbols (names of variables, functions and types) defined in your
7245 program. This information is inherent in the text of your program and
7246 does not change as your program executes. @value{GDBN} finds it in your
7247 program's symbol table, in the file indicated when you started @value{GDBN}
7248 (@pxref{File Options, ,Choosing files}), or by one of the
7249 file-management commands (@pxref{Files, ,Commands to specify files}).
7251 @cindex symbol names
7252 @cindex names of symbols
7253 @cindex quoting names
7254 Occasionally, you may need to refer to symbols that contain unusual
7255 characters, which @value{GDBN} ordinarily treats as word delimiters. The
7256 most frequent case is in referring to static variables in other
7257 source files (@pxref{Variables,,Program variables}). File names
7258 are recorded in object files as debugging symbols, but @value{GDBN} would
7259 ordinarily parse a typical file name, like @file{foo.c}, as the three words
7260 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
7261 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
7268 looks up the value of @code{x} in the scope of the file @file{foo.c}.
7271 @kindex info address
7272 @item info address @var{symbol}
7273 Describe where the data for @var{symbol} is stored. For a register
7274 variable, this says which register it is kept in. For a non-register
7275 local variable, this prints the stack-frame offset at which the variable
7278 Note the contrast with @samp{print &@var{symbol}}, which does not work
7279 at all for a register variable, and for a stack local variable prints
7280 the exact address of the current instantiation of the variable.
7283 @item whatis @var{expr}
7284 Print the data type of expression @var{expr}. @var{expr} is not
7285 actually evaluated, and any side-effecting operations (such as
7286 assignments or function calls) inside it do not take place.
7287 @xref{Expressions, ,Expressions}.
7290 Print the data type of @code{$}, the last value in the value history.
7293 @item ptype @var{typename}
7294 Print a description of data type @var{typename}. @var{typename} may be
7295 the name of a type, or for C code it may have the form @samp{class
7296 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
7297 @var{union-tag}} or @samp{enum @var{enum-tag}}.
7299 @item ptype @var{expr}
7301 Print a description of the type of expression @var{expr}. @code{ptype}
7302 differs from @code{whatis} by printing a detailed description, instead
7303 of just the name of the type.
7305 For example, for this variable declaration:
7308 struct complex @{double real; double imag;@} v;
7312 the two commands give this output:
7316 (@value{GDBP}) whatis v
7317 type = struct complex
7318 (@value{GDBP}) ptype v
7319 type = struct complex @{
7327 As with @code{whatis}, using @code{ptype} without an argument refers to
7328 the type of @code{$}, the last value in the value history.
7331 @item info types @var{regexp}
7333 Print a brief description of all types whose names match @var{regexp}
7334 (or all types in your program, if you supply no argument). Each
7335 complete typename is matched as though it were a complete line; thus,
7336 @samp{i type value} gives information on all types in your program whose
7337 names include the string @code{value}, but @samp{i type ^value$} gives
7338 information only on types whose complete name is @code{value}.
7340 This command differs from @code{ptype} in two ways: first, like
7341 @code{whatis}, it does not print a detailed description; second, it
7342 lists all source files where a type is defined.
7346 Show the name of the current source file---that is, the source file for
7347 the function containing the current point of execution---and the language
7350 @kindex info sources
7352 Print the names of all source files in your program for which there is
7353 debugging information, organized into two lists: files whose symbols
7354 have already been read, and files whose symbols will be read when needed.
7356 @kindex info functions
7357 @item info functions
7358 Print the names and data types of all defined functions.
7360 @item info functions @var{regexp}
7361 Print the names and data types of all defined functions
7362 whose names contain a match for regular expression @var{regexp}.
7363 Thus, @samp{info fun step} finds all functions whose names
7364 include @code{step}; @samp{info fun ^step} finds those whose names
7365 start with @code{step}.
7367 @kindex info variables
7368 @item info variables
7369 Print the names and data types of all variables that are declared
7370 outside of functions (i.e., excluding local variables).
7372 @item info variables @var{regexp}
7373 Print the names and data types of all variables (except for local
7374 variables) whose names contain a match for regular expression
7378 This was never implemented.
7379 @kindex info methods
7381 @itemx info methods @var{regexp}
7382 The @code{info methods} command permits the user to examine all defined
7383 methods within C++ program, or (with the @var{regexp} argument) a
7384 specific set of methods found in the various C++ classes. Many
7385 C++ classes provide a large number of methods. Thus, the output
7386 from the @code{ptype} command can be overwhelming and hard to use. The
7387 @code{info-methods} command filters the methods, printing only those
7388 which match the regular-expression @var{regexp}.
7391 @cindex reloading symbols
7392 Some systems allow individual object files that make up your program to
7393 be replaced without stopping and restarting your program. For example,
7394 in VxWorks you can simply recompile a defective object file and keep on
7395 running. If you are running on one of these systems, you can allow
7396 @value{GDBN} to reload the symbols for automatically relinked modules:
7399 @kindex set symbol-reloading
7400 @item set symbol-reloading on
7401 Replace symbol definitions for the corresponding source file when an
7402 object file with a particular name is seen again.
7404 @item set symbol-reloading off
7405 Do not replace symbol definitions when re-encountering object files of
7406 the same name. This is the default state; if you are not running on a
7407 system that permits automatically relinking modules, you should leave
7408 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7409 when linking large programs, that may contain several modules (from
7410 different directories or libraries) with the same name.
7412 @kindex show symbol-reloading
7413 @item show symbol-reloading
7414 Show the current @code{on} or @code{off} setting.
7417 @kindex set opaque-type-resolution
7418 @item set opaque-type-resolution on
7419 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
7420 declared as a pointer to a @code{struct}, @code{class}, or
7421 @code{union}---for example, @code{struct MyType *}---that is used in one
7422 source file although the full declaration of @code{struct MyType} is in
7423 another source file. The default is on.
7425 A change in the setting of this subcommand will not take effect until
7426 the next time symbols for a file are loaded.
7428 @item set opaque-type-resolution off
7429 Tell @value{GDBN} not to resolve opaque types. In this case, the type
7430 is printed as follows:
7432 @{<no data fields>@}
7435 @kindex show opaque-type-resolution
7436 @item show opaque-type-resolution
7437 Show whether opaque types are resolved or not.
7439 @kindex maint print symbols
7441 @kindex maint print psymbols
7442 @cindex partial symbol dump
7443 @item maint print symbols @var{filename}
7444 @itemx maint print psymbols @var{filename}
7445 @itemx maint print msymbols @var{filename}
7446 Write a dump of debugging symbol data into the file @var{filename}.
7447 These commands are used to debug the @value{GDBN} symbol-reading code. Only
7448 symbols with debugging data are included. If you use @samp{maint print
7449 symbols}, @value{GDBN} includes all the symbols for which it has already
7450 collected full details: that is, @var{filename} reflects symbols for
7451 only those files whose symbols @value{GDBN} has read. You can use the
7452 command @code{info sources} to find out which files these are. If you
7453 use @samp{maint print psymbols} instead, the dump shows information about
7454 symbols that @value{GDBN} only knows partially---that is, symbols defined in
7455 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
7456 @samp{maint print msymbols} dumps just the minimal symbol information
7457 required for each object file from which @value{GDBN} has read some symbols.
7458 @xref{Files, ,Commands to specify files}, for a discussion of how
7459 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
7462 @node Altering, GDB Files, Symbols, Top
7463 @chapter Altering Execution
7465 Once you think you have found an error in your program, you might want to
7466 find out for certain whether correcting the apparent error would lead to
7467 correct results in the rest of the run. You can find the answer by
7468 experiment, using the @value{GDBN} features for altering execution of the
7471 For example, you can store new values into variables or memory
7472 locations, give your program a signal, restart it at a different
7473 address, or even return prematurely from a function.
7476 * Assignment:: Assignment to variables
7477 * Jumping:: Continuing at a different address
7478 * Signaling:: Giving your program a signal
7479 * Returning:: Returning from a function
7480 * Calling:: Calling your program's functions
7481 * Patching:: Patching your program
7484 @node Assignment, Jumping, Altering, Altering
7485 @section Assignment to variables
7488 @cindex setting variables
7489 To alter the value of a variable, evaluate an assignment expression.
7490 @xref{Expressions, ,Expressions}. For example,
7497 stores the value 4 into the variable @code{x}, and then prints the
7498 value of the assignment expression (which is 4).
7499 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
7500 information on operators in supported languages.
7502 @kindex set variable
7503 @cindex variables, setting
7504 If you are not interested in seeing the value of the assignment, use the
7505 @code{set} command instead of the @code{print} command. @code{set} is
7506 really the same as @code{print} except that the expression's value is
7507 not printed and is not put in the value history (@pxref{Value History,
7508 ,Value history}). The expression is evaluated only for its effects.
7510 If the beginning of the argument string of the @code{set} command
7511 appears identical to a @code{set} subcommand, use the @code{set
7512 variable} command instead of just @code{set}. This command is identical
7513 to @code{set} except for its lack of subcommands. For example, if your
7514 program has a variable @code{width}, you get an error if you try to set
7515 a new value with just @samp{set width=13}, because @value{GDBN} has the
7516 command @code{set width}:
7519 (@value{GDBP}) whatis width
7521 (@value{GDBP}) p width
7523 (@value{GDBP}) set width=47
7524 Invalid syntax in expression.
7528 The invalid expression, of course, is @samp{=47}. In
7529 order to actually set the program's variable @code{width}, use
7532 (@value{GDBP}) set var width=47
7535 Because the @code{set} command has many subcommands that can conflict
7536 with the names of program variables, it is a good idea to use the
7537 @code{set variable} command instead of just @code{set}. For example, if
7538 your program has a variable @code{g}, you run into problems if you try
7539 to set a new value with just @samp{set g=4}, because @value{GDBN} has
7540 the command @code{set gnutarget}, abbreviated @code{set g}:
7544 (@value{GDBP}) whatis g
7548 (@value{GDBP}) set g=4
7552 The program being debugged has been started already.
7553 Start it from the beginning? (y or n) y
7554 Starting program: /home/smith/cc_progs/a.out
7555 "/home/smith/cc_progs/a.out": can't open to read symbols: Invalid bfd target.
7556 (@value{GDBP}) show g
7557 The current BFD target is "=4".
7562 The program variable @code{g} did not change, and you silently set the
7563 @code{gnutarget} to an invalid value. In order to set the variable
7567 (@value{GDBP}) set var g=4
7570 @value{GDBN} allows more implicit conversions in assignments than C; you can
7571 freely store an integer value into a pointer variable or vice versa,
7572 and you can convert any structure to any other structure that is the
7573 same length or shorter.
7574 @comment FIXME: how do structs align/pad in these conversions?
7575 @comment /doc@cygnus.com 18dec1990
7577 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
7578 construct to generate a value of specified type at a specified address
7579 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
7580 to memory location @code{0x83040} as an integer (which implies a certain size
7581 and representation in memory), and
7584 set @{int@}0x83040 = 4
7588 stores the value 4 into that memory location.
7590 @node Jumping, Signaling, Assignment, Altering
7591 @section Continuing at a different address
7593 Ordinarily, when you continue your program, you do so at the place where
7594 it stopped, with the @code{continue} command. You can instead continue at
7595 an address of your own choosing, with the following commands:
7599 @item jump @var{linespec}
7600 Resume execution at line @var{linespec}. Execution stops again
7601 immediately if there is a breakpoint there. @xref{List, ,Printing
7602 source lines}, for a description of the different forms of
7603 @var{linespec}. It is common practice to use the @code{tbreak} command
7604 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
7607 The @code{jump} command does not change the current stack frame, or
7608 the stack pointer, or the contents of any memory location or any
7609 register other than the program counter. If line @var{linespec} is in
7610 a different function from the one currently executing, the results may
7611 be bizarre if the two functions expect different patterns of arguments or
7612 of local variables. For this reason, the @code{jump} command requests
7613 confirmation if the specified line is not in the function currently
7614 executing. However, even bizarre results are predictable if you are
7615 well acquainted with the machine-language code of your program.
7617 @item jump *@var{address}
7618 Resume execution at the instruction at address @var{address}.
7621 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
7622 On many systems, you can get much the same effect as the @code{jump}
7623 command by storing a new value into the register @code{$pc}. The
7624 difference is that this does not start your program running; it only
7625 changes the address of where it @emph{will} run when you continue. For
7633 makes the next @code{continue} command or stepping command execute at
7634 address @code{0x485}, rather than at the address where your program stopped.
7635 @xref{Continuing and Stepping, ,Continuing and stepping}.
7637 The most common occasion to use the @code{jump} command is to back
7638 up---perhaps with more breakpoints set---over a portion of a program
7639 that has already executed, in order to examine its execution in more
7643 @node Signaling, Returning, Jumping, Altering
7644 @section Giving your program a signal
7648 @item signal @var{signal}
7649 Resume execution where your program stopped, but immediately give it the
7650 signal @var{signal}. @var{signal} can be the name or the number of a
7651 signal. For example, on many systems @code{signal 2} and @code{signal
7652 SIGINT} are both ways of sending an interrupt signal.
7654 Alternatively, if @var{signal} is zero, continue execution without
7655 giving a signal. This is useful when your program stopped on account of
7656 a signal and would ordinary see the signal when resumed with the
7657 @code{continue} command; @samp{signal 0} causes it to resume without a
7660 @code{signal} does not repeat when you press @key{RET} a second time
7661 after executing the command.
7665 Invoking the @code{signal} command is not the same as invoking the
7666 @code{kill} utility from the shell. Sending a signal with @code{kill}
7667 causes @value{GDBN} to decide what to do with the signal depending on
7668 the signal handling tables (@pxref{Signals}). The @code{signal} command
7669 passes the signal directly to your program.
7672 @node Returning, Calling, Signaling, Altering
7673 @section Returning from a function
7676 @cindex returning from a function
7679 @itemx return @var{expression}
7680 You can cancel execution of a function call with the @code{return}
7681 command. If you give an
7682 @var{expression} argument, its value is used as the function's return
7686 When you use @code{return}, @value{GDBN} discards the selected stack frame
7687 (and all frames within it). You can think of this as making the
7688 discarded frame return prematurely. If you wish to specify a value to
7689 be returned, give that value as the argument to @code{return}.
7691 This pops the selected stack frame (@pxref{Selection, ,Selecting a
7692 frame}), and any other frames inside of it, leaving its caller as the
7693 innermost remaining frame. That frame becomes selected. The
7694 specified value is stored in the registers used for returning values
7697 The @code{return} command does not resume execution; it leaves the
7698 program stopped in the state that would exist if the function had just
7699 returned. In contrast, the @code{finish} command (@pxref{Continuing
7700 and Stepping, ,Continuing and stepping}) resumes execution until the
7701 selected stack frame returns naturally.
7703 @node Calling, Patching, Returning, Altering
7704 @section Calling program functions
7706 @cindex calling functions
7709 @item call @var{expr}
7710 Evaluate the expression @var{expr} without displaying @code{void}
7714 You can use this variant of the @code{print} command if you want to
7715 execute a function from your program, but without cluttering the output
7716 with @code{void} returned values. If the result is not void, it
7717 is printed and saved in the value history.
7719 For the A29K, a user-controlled variable @code{call_scratch_address},
7720 specifies the location of a scratch area to be used when @value{GDBN}
7721 calls a function in the target. This is necessary because the usual
7722 method of putting the scratch area on the stack does not work in systems
7723 that have separate instruction and data spaces.
7725 @node Patching, , Calling, Altering
7726 @section Patching programs
7728 @cindex patching binaries
7729 @cindex writing into executables
7730 @cindex writing into corefiles
7732 By default, @value{GDBN} opens the file containing your program's
7733 executable code (or the corefile) read-only. This prevents accidental
7734 alterations to machine code; but it also prevents you from intentionally
7735 patching your program's binary.
7737 If you'd like to be able to patch the binary, you can specify that
7738 explicitly with the @code{set write} command. For example, you might
7739 want to turn on internal debugging flags, or even to make emergency
7745 @itemx set write off
7746 If you specify @samp{set write on}, @value{GDBN} opens executable and
7747 core files for both reading and writing; if you specify @samp{set write
7748 off} (the default), @value{GDBN} opens them read-only.
7750 If you have already loaded a file, you must load it again (using the
7751 @code{exec-file} or @code{core-file} command) after changing @code{set
7752 write}, for your new setting to take effect.
7756 Display whether executable files and core files are opened for writing
7760 @node GDB Files, Targets, Altering, Top
7761 @chapter @value{GDBN} Files
7763 @value{GDBN} needs to know the file name of the program to be debugged,
7764 both in order to read its symbol table and in order to start your
7765 program. To debug a core dump of a previous run, you must also tell
7766 @value{GDBN} the name of the core dump file.
7769 * Files:: Commands to specify files
7770 * Symbol Errors:: Errors reading symbol files
7773 @node Files, Symbol Errors, GDB Files, GDB Files
7774 @section Commands to specify files
7776 @cindex symbol table
7777 @cindex core dump file
7779 You may want to specify executable and core dump file names. The usual
7780 way to do this is at start-up time, using the arguments to
7781 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
7782 Out of @value{GDBN}}).
7784 Occasionally it is necessary to change to a different file during a
7785 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
7786 a file you want to use. In these situations the @value{GDBN} commands
7787 to specify new files are useful.
7790 @cindex executable file
7792 @item file @var{filename}
7793 Use @var{filename} as the program to be debugged. It is read for its
7794 symbols and for the contents of pure memory. It is also the program
7795 executed when you use the @code{run} command. If you do not specify a
7796 directory and the file is not found in the @value{GDBN} working directory,
7797 @value{GDBN} uses the environment variable @code{PATH} as a list of
7798 directories to search, just as the shell does when looking for a program
7799 to run. You can change the value of this variable, for both @value{GDBN}
7800 and your program, using the @code{path} command.
7802 On systems with memory-mapped files, an auxiliary file
7803 @file{@var{filename}.syms} may hold symbol table information for
7804 @var{filename}. If so, @value{GDBN} maps in the symbol table from
7805 @file{@var{filename}.syms}, starting up more quickly. See the
7806 descriptions of the file options @samp{-mapped} and @samp{-readnow}
7807 (available on the command line, and with the commands @code{file},
7808 @code{symbol-file}, or @code{add-symbol-file}, described below),
7809 for more information.
7812 @code{file} with no argument makes @value{GDBN} discard any information it
7813 has on both executable file and the symbol table.
7816 @item exec-file @r{[} @var{filename} @r{]}
7817 Specify that the program to be run (but not the symbol table) is found
7818 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
7819 if necessary to locate your program. Omitting @var{filename} means to
7820 discard information on the executable file.
7823 @item symbol-file @r{[} @var{filename} @r{]}
7824 Read symbol table information from file @var{filename}. @code{PATH} is
7825 searched when necessary. Use the @code{file} command to get both symbol
7826 table and program to run from the same file.
7828 @code{symbol-file} with no argument clears out @value{GDBN} information on your
7829 program's symbol table.
7831 The @code{symbol-file} command causes @value{GDBN} to forget the contents
7832 of its convenience variables, the value history, and all breakpoints and
7833 auto-display expressions. This is because they may contain pointers to
7834 the internal data recording symbols and data types, which are part of
7835 the old symbol table data being discarded inside @value{GDBN}.
7837 @code{symbol-file} does not repeat if you press @key{RET} again after
7840 When @value{GDBN} is configured for a particular environment, it
7841 understands debugging information in whatever format is the standard
7842 generated for that environment; you may use either a @sc{gnu} compiler, or
7843 other compilers that adhere to the local conventions.
7844 Best results are usually obtained from @sc{gnu} compilers; for example,
7845 using @code{@value{GCC}} you can generate debugging information for
7848 For most kinds of object files, with the exception of old SVR3 systems
7849 using COFF, the @code{symbol-file} command does not normally read the
7850 symbol table in full right away. Instead, it scans the symbol table
7851 quickly to find which source files and which symbols are present. The
7852 details are read later, one source file at a time, as they are needed.
7854 The purpose of this two-stage reading strategy is to make @value{GDBN}
7855 start up faster. For the most part, it is invisible except for
7856 occasional pauses while the symbol table details for a particular source
7857 file are being read. (The @code{set verbose} command can turn these
7858 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
7859 warnings and messages}.)
7861 We have not implemented the two-stage strategy for COFF yet. When the
7862 symbol table is stored in COFF format, @code{symbol-file} reads the
7863 symbol table data in full right away. Note that ``stabs-in-COFF''
7864 still does the two-stage strategy, since the debug info is actually
7868 @cindex reading symbols immediately
7869 @cindex symbols, reading immediately
7871 @cindex memory-mapped symbol file
7872 @cindex saving symbol table
7873 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7874 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7875 You can override the @value{GDBN} two-stage strategy for reading symbol
7876 tables by using the @samp{-readnow} option with any of the commands that
7877 load symbol table information, if you want to be sure @value{GDBN} has the
7878 entire symbol table available.
7880 If memory-mapped files are available on your system through the
7881 @code{mmap} system call, you can use another option, @samp{-mapped}, to
7882 cause @value{GDBN} to write the symbols for your program into a reusable
7883 file. Future @value{GDBN} debugging sessions map in symbol information
7884 from this auxiliary symbol file (if the program has not changed), rather
7885 than spending time reading the symbol table from the executable
7886 program. Using the @samp{-mapped} option has the same effect as
7887 starting @value{GDBN} with the @samp{-mapped} command-line option.
7889 You can use both options together, to make sure the auxiliary symbol
7890 file has all the symbol information for your program.
7892 The auxiliary symbol file for a program called @var{myprog} is called
7893 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
7894 than the corresponding executable), @value{GDBN} always attempts to use
7895 it when you debug @var{myprog}; no special options or commands are
7898 The @file{.syms} file is specific to the host machine where you run
7899 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
7900 symbol table. It cannot be shared across multiple host platforms.
7902 @c FIXME: for now no mention of directories, since this seems to be in
7903 @c flux. 13mar1992 status is that in theory GDB would look either in
7904 @c current dir or in same dir as myprog; but issues like competing
7905 @c GDB's, or clutter in system dirs, mean that in practice right now
7906 @c only current dir is used. FFish says maybe a special GDB hierarchy
7907 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
7912 @item core-file @r{[} @var{filename} @r{]}
7913 Specify the whereabouts of a core dump file to be used as the ``contents
7914 of memory''. Traditionally, core files contain only some parts of the
7915 address space of the process that generated them; @value{GDBN} can access the
7916 executable file itself for other parts.
7918 @code{core-file} with no argument specifies that no core file is
7921 Note that the core file is ignored when your program is actually running
7922 under @value{GDBN}. So, if you have been running your program and you
7923 wish to debug a core file instead, you must kill the subprocess in which
7924 the program is running. To do this, use the @code{kill} command
7925 (@pxref{Kill Process, ,Killing the child process}).
7927 @kindex add-symbol-file
7928 @cindex dynamic linking
7929 @item add-symbol-file @var{filename} @var{address}
7930 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7931 @itemx add-symbol-file @var{filename} @var{address} @var{data_address} @var{bss_address}
7932 @itemx add-symbol-file @var{filename} @r{-T}@var{section} @var{address}
7933 The @code{add-symbol-file} command reads additional symbol table
7934 information from the file @var{filename}. You would use this command
7935 when @var{filename} has been dynamically loaded (by some other means)
7936 into the program that is running. @var{address} should be the memory
7937 address at which the file has been loaded; @value{GDBN} cannot figure
7938 this out for itself. You can specify up to three addresses, in which
7939 case they are taken to be the addresses of the text, data, and bss
7940 segments respectively. For complicated cases, you can specify an
7941 arbitrary number of @samp{@r{-T}@var{section} @var{address}} pairs, to
7942 give an explicit section name and base address for that section. You
7943 can specify any @var{address} as an expression.
7945 The symbol table of the file @var{filename} is added to the symbol table
7946 originally read with the @code{symbol-file} command. You can use the
7947 @code{add-symbol-file} command any number of times; the new symbol data
7948 thus read keeps adding to the old. To discard all old symbol data
7949 instead, use the @code{symbol-file} command without any arguments.
7951 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
7953 You can use the @samp{-mapped} and @samp{-readnow} options just as with
7954 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
7955 table information for @var{filename}.
7957 @kindex add-shared-symbol-file
7958 @item add-shared-symbol-file
7959 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
7960 operating system for the Motorola 88k. @value{GDBN} automatically looks for
7961 shared libraries, however if @value{GDBN} does not find yours, you can run
7962 @code{add-shared-symbol-file}. It takes no arguments.
7966 The @code{section} command changes the base address of section SECTION of
7967 the exec file to ADDR. This can be used if the exec file does not contain
7968 section addresses, (such as in the a.out format), or when the addresses
7969 specified in the file itself are wrong. Each section must be changed
7970 separately. The @code{info files} command, described below, lists all
7971 the sections and their addresses.
7977 @code{info files} and @code{info target} are synonymous; both print the
7978 current target (@pxref{Targets, ,Specifying a Debugging Target}),
7979 including the names of the executable and core dump files currently in
7980 use by @value{GDBN}, and the files from which symbols were loaded. The
7981 command @code{help target} lists all possible targets rather than
7986 All file-specifying commands allow both absolute and relative file names
7987 as arguments. @value{GDBN} always converts the file name to an absolute file
7988 name and remembers it that way.
7990 @cindex shared libraries
7991 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
7994 @value{GDBN} automatically loads symbol definitions from shared libraries
7995 when you use the @code{run} command, or when you examine a core file.
7996 (Before you issue the @code{run} command, @value{GDBN} does not understand
7997 references to a function in a shared library, however---unless you are
7998 debugging a core file).
8000 On HP-UX, if the program loads a library explicitly, @value{GDBN}
8001 automatically loads the symbols at the time of the @code{shl_load} call.
8003 @c FIXME: some @value{GDBN} release may permit some refs to undef
8004 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8005 @c FIXME...lib; check this from time to time when updating manual
8008 @kindex info sharedlibrary
8011 @itemx info sharedlibrary
8012 Print the names of the shared libraries which are currently loaded.
8014 @kindex sharedlibrary
8016 @item sharedlibrary @var{regex}
8017 @itemx share @var{regex}
8018 Load shared object library symbols for files matching a
8019 Unix regular expression.
8020 As with files loaded automatically, it only loads shared libraries
8021 required by your program for a core file or after typing @code{run}. If
8022 @var{regex} is omitted all shared libraries required by your program are
8026 On HP-UX systems, @value{GDBN} detects the loading of a shared library
8027 and automatically reads in symbols from the newly loaded library, up to
8028 a threshold that is initially set but that you can modify if you wish.
8030 Beyond that threshold, symbols from shared libraries must be explicitly
8031 loaded. To load these symbols, use the command @code{sharedlibrary
8032 @var{filename}}. The base address of the shared library is determined
8033 automatically by @value{GDBN} and need not be specified.
8035 To display or set the threshold, use the commands:
8038 @kindex set auto-solib-add
8039 @item set auto-solib-add @var{threshold}
8040 Set the autoloading size threshold, in megabytes. If @var{threshold} is
8041 nonzero, symbols from all shared object libraries will be loaded
8042 automatically when the inferior begins execution or when the dynamic
8043 linker informs @value{GDBN} that a new library has been loaded, until
8044 the symbol table of the program and libraries exceeds this threshold.
8045 Otherwise, symbols must be loaded manually, using the
8046 @code{sharedlibrary} command. The default threshold is 100 megabytes.
8048 @kindex show auto-solib-add
8049 @item show auto-solib-add
8050 Display the current autoloading size threshold, in megabytes.
8053 @node Symbol Errors, , Files, GDB Files
8054 @section Errors reading symbol files
8056 While reading a symbol file, @value{GDBN} occasionally encounters problems,
8057 such as symbol types it does not recognize, or known bugs in compiler
8058 output. By default, @value{GDBN} does not notify you of such problems, since
8059 they are relatively common and primarily of interest to people
8060 debugging compilers. If you are interested in seeing information
8061 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
8062 only one message about each such type of problem, no matter how many
8063 times the problem occurs; or you can ask @value{GDBN} to print more messages,
8064 to see how many times the problems occur, with the @code{set
8065 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
8068 The messages currently printed, and their meanings, include:
8071 @item inner block not inside outer block in @var{symbol}
8073 The symbol information shows where symbol scopes begin and end
8074 (such as at the start of a function or a block of statements). This
8075 error indicates that an inner scope block is not fully contained
8076 in its outer scope blocks.
8078 @value{GDBN} circumvents the problem by treating the inner block as if it had
8079 the same scope as the outer block. In the error message, @var{symbol}
8080 may be shown as ``@code{(don't know)}'' if the outer block is not a
8083 @item block at @var{address} out of order
8085 The symbol information for symbol scope blocks should occur in
8086 order of increasing addresses. This error indicates that it does not
8089 @value{GDBN} does not circumvent this problem, and has trouble
8090 locating symbols in the source file whose symbols it is reading. (You
8091 can often determine what source file is affected by specifying
8092 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
8095 @item bad block start address patched
8097 The symbol information for a symbol scope block has a start address
8098 smaller than the address of the preceding source line. This is known
8099 to occur in the SunOS 4.1.1 (and earlier) C compiler.
8101 @value{GDBN} circumvents the problem by treating the symbol scope block as
8102 starting on the previous source line.
8104 @item bad string table offset in symbol @var{n}
8107 Symbol number @var{n} contains a pointer into the string table which is
8108 larger than the size of the string table.
8110 @value{GDBN} circumvents the problem by considering the symbol to have the
8111 name @code{foo}, which may cause other problems if many symbols end up
8114 @item unknown symbol type @code{0x@var{nn}}
8116 The symbol information contains new data types that @value{GDBN} does
8117 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
8118 uncomprehended information, in hexadecimal.
8120 @value{GDBN} circumvents the error by ignoring this symbol information.
8121 This usually allows you to debug your program, though certain symbols
8122 are not accessible. If you encounter such a problem and feel like
8123 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
8124 on @code{complain}, then go up to the function @code{read_dbx_symtab}
8125 and examine @code{*bufp} to see the symbol.
8127 @item stub type has NULL name
8129 @value{GDBN} could not find the full definition for a struct or class.
8131 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
8132 The symbol information for a C++ member function is missing some
8133 information that recent versions of the compiler should have output for
8136 @item info mismatch between compiler and debugger
8138 @value{GDBN} could not parse a type specification output by the compiler.
8142 @node Targets, Configurations, GDB Files, Top
8143 @chapter Specifying a Debugging Target
8145 @cindex debugging target
8148 A @dfn{target} is the execution environment occupied by your program.
8150 Often, @value{GDBN} runs in the same host environment as your program;
8151 in that case, the debugging target is specified as a side effect when
8152 you use the @code{file} or @code{core} commands. When you need more
8153 flexibility---for example, running @value{GDBN} on a physically separate
8154 host, or controlling a standalone system over a serial port or a
8155 realtime system over a TCP/IP connection---you can use the @code{target}
8156 command to specify one of the target types configured for @value{GDBN}
8157 (@pxref{Target Commands, ,Commands for managing targets}).
8160 * Active Targets:: Active targets
8161 * Target Commands:: Commands for managing targets
8162 * Byte Order:: Choosing target byte order
8163 * Remote:: Remote debugging
8164 * KOD:: Kernel Object Display
8168 @node Active Targets, Target Commands, Targets, Targets
8169 @section Active targets
8171 @cindex stacking targets
8172 @cindex active targets
8173 @cindex multiple targets
8175 There are three classes of targets: processes, core files, and
8176 executable files. @value{GDBN} can work concurrently on up to three
8177 active targets, one in each class. This allows you to (for example)
8178 start a process and inspect its activity without abandoning your work on
8181 For example, if you execute @samp{gdb a.out}, then the executable file
8182 @code{a.out} is the only active target. If you designate a core file as
8183 well---presumably from a prior run that crashed and coredumped---then
8184 @value{GDBN} has two active targets and uses them in tandem, looking
8185 first in the corefile target, then in the executable file, to satisfy
8186 requests for memory addresses. (Typically, these two classes of target
8187 are complementary, since core files contain only a program's
8188 read-write memory---variables and so on---plus machine status, while
8189 executable files contain only the program text and initialized data.)
8191 When you type @code{run}, your executable file becomes an active process
8192 target as well. When a process target is active, all @value{GDBN}
8193 commands requesting memory addresses refer to that target; addresses in
8194 an active core file or executable file target are obscured while the
8195 process target is active.
8197 Use the @code{core-file} and @code{exec-file} commands to select a new
8198 core file or executable target (@pxref{Files, ,Commands to specify
8199 files}). To specify as a target a process that is already running, use
8200 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
8203 @node Target Commands, Byte Order, Active Targets, Targets
8204 @section Commands for managing targets
8207 @item target @var{type} @var{parameters}
8208 Connects the @value{GDBN} host environment to a target machine or
8209 process. A target is typically a protocol for talking to debugging
8210 facilities. You use the argument @var{type} to specify the type or
8211 protocol of the target machine.
8213 Further @var{parameters} are interpreted by the target protocol, but
8214 typically include things like device names or host names to connect
8215 with, process numbers, and baud rates.
8217 The @code{target} command does not repeat if you press @key{RET} again
8218 after executing the command.
8222 Displays the names of all targets available. To display targets
8223 currently selected, use either @code{info target} or @code{info files}
8224 (@pxref{Files, ,Commands to specify files}).
8226 @item help target @var{name}
8227 Describe a particular target, including any parameters necessary to
8230 @kindex set gnutarget
8231 @item set gnutarget @var{args}
8232 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
8233 knows whether it is reading an @dfn{executable},
8234 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
8235 with the @code{set gnutarget} command. Unlike most @code{target} commands,
8236 with @code{gnutarget} the @code{target} refers to a program, not a machine.
8239 @emph{Warning:} To specify a file format with @code{set gnutarget},
8240 you must know the actual BFD name.
8244 @xref{Files, , Commands to specify files}.
8246 @kindex show gnutarget
8247 @item show gnutarget
8248 Use the @code{show gnutarget} command to display what file format
8249 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
8250 @value{GDBN} will determine the file format for each file automatically,
8251 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
8254 Here are some common targets (available, or not, depending on the GDB
8259 @item target exec @var{program}
8260 An executable file. @samp{target exec @var{program}} is the same as
8261 @samp{exec-file @var{program}}.
8264 @item target core @var{filename}
8265 A core dump file. @samp{target core @var{filename}} is the same as
8266 @samp{core-file @var{filename}}.
8268 @kindex target remote
8269 @item target remote @var{dev}
8270 Remote serial target in GDB-specific protocol. The argument @var{dev}
8271 specifies what serial device to use for the connection (e.g.
8272 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
8273 supports the @code{load} command. This is only useful if you have
8274 some other way of getting the stub to the target system, and you can put
8275 it somewhere in memory where it won't get clobbered by the download.
8279 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
8287 works; however, you cannot assume that a specific memory map, device
8288 drivers, or even basic I/O is available, although some simulators do
8289 provide these. For info about any processor-specific simulator details,
8290 see the appropriate section in @ref{Embedded Processors, ,Embedded
8295 Some configurations may include these targets as well:
8300 @item target nrom @var{dev}
8301 NetROM ROM emulator. This target only supports downloading.
8305 Different targets are available on different configurations of @value{GDBN};
8306 your configuration may have more or fewer targets.
8308 Many remote targets require you to download the executable's code
8309 once you've successfully established a connection.
8313 @kindex load @var{filename}
8314 @item load @var{filename}
8315 Depending on what remote debugging facilities are configured into
8316 @value{GDBN}, the @code{load} command may be available. Where it exists, it
8317 is meant to make @var{filename} (an executable) available for debugging
8318 on the remote system---by downloading, or dynamic linking, for example.
8319 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
8320 the @code{add-symbol-file} command.
8322 If your @value{GDBN} does not have a @code{load} command, attempting to
8323 execute it gets the error message ``@code{You can't do that when your
8324 target is @dots{}}''
8326 The file is loaded at whatever address is specified in the executable.
8327 For some object file formats, you can specify the load address when you
8328 link the program; for other formats, like a.out, the object file format
8329 specifies a fixed address.
8330 @c FIXME! This would be a good place for an xref to the GNU linker doc.
8332 @code{load} does not repeat if you press @key{RET} again after using it.
8335 @node Byte Order, Remote, Target Commands, Targets
8336 @section Choosing target byte order
8338 @cindex choosing target byte order
8339 @cindex target byte order
8340 @kindex set endian big
8341 @kindex set endian little
8342 @kindex set endian auto
8345 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
8346 offer the ability to run either big-endian or little-endian byte
8347 orders. Usually the executable or symbol will include a bit to
8348 designate the endian-ness, and you will not need to worry about
8349 which to use. However, you may still find it useful to adjust
8350 @value{GDBN}'s idea of processor endian-ness manually.
8353 @kindex set endian big
8354 @item set endian big
8355 Instruct @value{GDBN} to assume the target is big-endian.
8357 @kindex set endian little
8358 @item set endian little
8359 Instruct @value{GDBN} to assume the target is little-endian.
8361 @kindex set endian auto
8362 @item set endian auto
8363 Instruct @value{GDBN} to use the byte order associated with the
8367 Display @value{GDBN}'s current idea of the target byte order.
8371 Note that these commands merely adjust interpretation of symbolic
8372 data on the host, and that they have absolutely no effect on the
8375 @node Remote, KOD, Byte Order, Targets
8376 @section Remote debugging
8377 @cindex remote debugging
8379 If you are trying to debug a program running on a machine that cannot run
8380 @value{GDBN} in the usual way, it is often useful to use remote debugging.
8381 For example, you might use remote debugging on an operating system kernel,
8382 or on a small system which does not have a general purpose operating system
8383 powerful enough to run a full-featured debugger.
8385 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
8386 to make this work with particular debugging targets. In addition,
8387 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
8388 but not specific to any particular target system) which you can use if you
8389 write the remote stubs---the code that runs on the remote system to
8390 communicate with @value{GDBN}.
8392 Other remote targets may be available in your
8393 configuration of @value{GDBN}; use @code{help target} to list them.
8396 * Remote Serial:: @value{GDBN} remote serial protocol
8399 @node Remote Serial, , Remote, Remote
8400 @subsection The @value{GDBN} remote serial protocol
8402 @cindex remote serial debugging, overview
8403 To debug a program running on another machine (the debugging
8404 @dfn{target} machine), you must first arrange for all the usual
8405 prerequisites for the program to run by itself. For example, for a C
8410 A startup routine to set up the C runtime environment; these usually
8411 have a name like @file{crt0}. The startup routine may be supplied by
8412 your hardware supplier, or you may have to write your own.
8415 A C subroutine library to support your program's
8416 subroutine calls, notably managing input and output.
8419 A way of getting your program to the other machine---for example, a
8420 download program. These are often supplied by the hardware
8421 manufacturer, but you may have to write your own from hardware
8425 The next step is to arrange for your program to use a serial port to
8426 communicate with the machine where @value{GDBN} is running (the @dfn{host}
8427 machine). In general terms, the scheme looks like this:
8431 @value{GDBN} already understands how to use this protocol; when everything
8432 else is set up, you can simply use the @samp{target remote} command
8433 (@pxref{Targets,,Specifying a Debugging Target}).
8435 @item On the target,
8436 you must link with your program a few special-purpose subroutines that
8437 implement the @value{GDBN} remote serial protocol. The file containing these
8438 subroutines is called a @dfn{debugging stub}.
8440 On certain remote targets, you can use an auxiliary program
8441 @code{gdbserver} instead of linking a stub into your program.
8442 @xref{Server,,Using the @code{gdbserver} program}, for details.
8445 The debugging stub is specific to the architecture of the remote
8446 machine; for example, use @file{sparc-stub.c} to debug programs on
8449 @cindex remote serial stub list
8450 These working remote stubs are distributed with @value{GDBN}:
8458 For Intel 386 and compatible architectures.
8462 @cindex Motorola 680x0
8464 For Motorola 680x0 architectures.
8470 For Hitachi SH architectures.
8473 @kindex sparc-stub.c
8475 For @sc{sparc} architectures.
8478 @kindex sparcl-stub.c
8481 For Fujitsu @sc{sparclite} architectures.
8485 The @file{README} file in the @value{GDBN} distribution may list other
8486 recently added stubs.
8489 * Stub Contents:: What the stub can do for you
8490 * Bootstrapping:: What you must do for the stub
8491 * Debug Session:: Putting it all together
8492 * Protocol:: Definition of the communication protocol
8493 * Server:: Using the `gdbserver' program
8494 * NetWare:: Using the `gdbserve.nlm' program
8497 @node Stub Contents, Bootstrapping, Remote Serial, Remote Serial
8498 @subsubsection What the stub can do for you
8500 @cindex remote serial stub
8501 The debugging stub for your architecture supplies these three
8505 @item set_debug_traps
8506 @kindex set_debug_traps
8507 @cindex remote serial stub, initialization
8508 This routine arranges for @code{handle_exception} to run when your
8509 program stops. You must call this subroutine explicitly near the
8510 beginning of your program.
8512 @item handle_exception
8513 @kindex handle_exception
8514 @cindex remote serial stub, main routine
8515 This is the central workhorse, but your program never calls it
8516 explicitly---the setup code arranges for @code{handle_exception} to
8517 run when a trap is triggered.
8519 @code{handle_exception} takes control when your program stops during
8520 execution (for example, on a breakpoint), and mediates communications
8521 with @value{GDBN} on the host machine. This is where the communications
8522 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
8523 representative on the target machine. It begins by sending summary
8524 information on the state of your program, then continues to execute,
8525 retrieving and transmitting any information @value{GDBN} needs, until you
8526 execute a @value{GDBN} command that makes your program resume; at that point,
8527 @code{handle_exception} returns control to your own code on the target
8531 @cindex @code{breakpoint} subroutine, remote
8532 Use this auxiliary subroutine to make your program contain a
8533 breakpoint. Depending on the particular situation, this may be the only
8534 way for @value{GDBN} to get control. For instance, if your target
8535 machine has some sort of interrupt button, you won't need to call this;
8536 pressing the interrupt button transfers control to
8537 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
8538 simply receiving characters on the serial port may also trigger a trap;
8539 again, in that situation, you don't need to call @code{breakpoint} from
8540 your own program---simply running @samp{target remote} from the host
8541 @value{GDBN} session gets control.
8543 Call @code{breakpoint} if none of these is true, or if you simply want
8544 to make certain your program stops at a predetermined point for the
8545 start of your debugging session.
8548 @node Bootstrapping, Debug Session, Stub Contents, Remote Serial
8549 @subsubsection What you must do for the stub
8551 @cindex remote stub, support routines
8552 The debugging stubs that come with @value{GDBN} are set up for a particular
8553 chip architecture, but they have no information about the rest of your
8554 debugging target machine.
8556 First of all you need to tell the stub how to communicate with the
8560 @item int getDebugChar()
8561 @kindex getDebugChar
8562 Write this subroutine to read a single character from the serial port.
8563 It may be identical to @code{getchar} for your target system; a
8564 different name is used to allow you to distinguish the two if you wish.
8566 @item void putDebugChar(int)
8567 @kindex putDebugChar
8568 Write this subroutine to write a single character to the serial port.
8569 It may be identical to @code{putchar} for your target system; a
8570 different name is used to allow you to distinguish the two if you wish.
8573 @cindex control C, and remote debugging
8574 @cindex interrupting remote targets
8575 If you want @value{GDBN} to be able to stop your program while it is
8576 running, you need to use an interrupt-driven serial driver, and arrange
8577 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
8578 character). That is the character which @value{GDBN} uses to tell the
8579 remote system to stop.
8581 Getting the debugging target to return the proper status to @value{GDBN}
8582 probably requires changes to the standard stub; one quick and dirty way
8583 is to just execute a breakpoint instruction (the ``dirty'' part is that
8584 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
8586 Other routines you need to supply are:
8589 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
8590 @kindex exceptionHandler
8591 Write this function to install @var{exception_address} in the exception
8592 handling tables. You need to do this because the stub does not have any
8593 way of knowing what the exception handling tables on your target system
8594 are like (for example, the processor's table might be in @sc{rom},
8595 containing entries which point to a table in @sc{ram}).
8596 @var{exception_number} is the exception number which should be changed;
8597 its meaning is architecture-dependent (for example, different numbers
8598 might represent divide by zero, misaligned access, etc). When this
8599 exception occurs, control should be transferred directly to
8600 @var{exception_address}, and the processor state (stack, registers,
8601 and so on) should be just as it is when a processor exception occurs. So if
8602 you want to use a jump instruction to reach @var{exception_address}, it
8603 should be a simple jump, not a jump to subroutine.
8605 For the 386, @var{exception_address} should be installed as an interrupt
8606 gate so that interrupts are masked while the handler runs. The gate
8607 should be at privilege level 0 (the most privileged level). The
8608 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
8609 help from @code{exceptionHandler}.
8611 @item void flush_i_cache()
8612 @kindex flush_i_cache
8613 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
8614 instruction cache, if any, on your target machine. If there is no
8615 instruction cache, this subroutine may be a no-op.
8617 On target machines that have instruction caches, @value{GDBN} requires this
8618 function to make certain that the state of your program is stable.
8622 You must also make sure this library routine is available:
8625 @item void *memset(void *, int, int)
8627 This is the standard library function @code{memset} that sets an area of
8628 memory to a known value. If you have one of the free versions of
8629 @code{libc.a}, @code{memset} can be found there; otherwise, you must
8630 either obtain it from your hardware manufacturer, or write your own.
8633 If you do not use the GNU C compiler, you may need other standard
8634 library subroutines as well; this varies from one stub to another,
8635 but in general the stubs are likely to use any of the common library
8636 subroutines which @code{@value{GCC}} generates as inline code.
8639 @node Debug Session, Protocol, Bootstrapping, Remote Serial
8640 @subsubsection Putting it all together
8642 @cindex remote serial debugging summary
8643 In summary, when your program is ready to debug, you must follow these
8648 Make sure you have the supporting low-level routines
8649 (@pxref{Bootstrapping,,What you must do for the stub}):
8651 @code{getDebugChar}, @code{putDebugChar},
8652 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
8656 Insert these lines near the top of your program:
8664 For the 680x0 stub only, you need to provide a variable called
8665 @code{exceptionHook}. Normally you just use:
8668 void (*exceptionHook)() = 0;
8672 but if before calling @code{set_debug_traps}, you set it to point to a
8673 function in your program; that function is called when
8674 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
8675 error). The function indicated by @code{exceptionHook} is called with
8676 one parameter: an @code{int} which is the exception number.
8679 Compile and link together: your program, the @value{GDBN} debugging stub for
8680 your target architecture, and the supporting subroutines.
8683 Make sure you have a serial connection between your target machine and
8684 the @value{GDBN} host, and identify the serial port on the host.
8687 @c The "remote" target now provides a `load' command, so we should
8688 @c document that. FIXME.
8689 Download your program to your target machine (or get it there by
8690 whatever means the manufacturer provides), and start it.
8693 To start remote debugging, run @value{GDBN} on the host machine, and specify
8694 as an executable file the program that is running in the remote machine.
8695 This tells @value{GDBN} how to find your program's symbols and the contents
8699 @cindex serial line, @code{target remote}
8700 Establish communication using the @code{target remote} command.
8701 Its argument specifies how to communicate with the target
8702 machine---either via a devicename attached to a direct serial line, or a
8703 TCP port (usually to a terminal server which in turn has a serial line
8704 to the target). For example, to use a serial line connected to the
8705 device named @file{/dev/ttyb}:
8708 target remote /dev/ttyb
8711 @cindex TCP port, @code{target remote}
8712 To use a TCP connection, use an argument of the form
8713 @code{@var{host}:port}. For example, to connect to port 2828 on a
8714 terminal server named @code{manyfarms}:
8717 target remote manyfarms:2828
8721 Now you can use all the usual commands to examine and change data and to
8722 step and continue the remote program.
8724 To resume the remote program and stop debugging it, use the @code{detach}
8727 @cindex interrupting remote programs
8728 @cindex remote programs, interrupting
8729 Whenever @value{GDBN} is waiting for the remote program, if you type the
8730 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
8731 program. This may or may not succeed, depending in part on the hardware
8732 and the serial drivers the remote system uses. If you type the
8733 interrupt character once again, @value{GDBN} displays this prompt:
8736 Interrupted while waiting for the program.
8737 Give up (and stop debugging it)? (y or n)
8740 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
8741 (If you decide you want to try again later, you can use @samp{target
8742 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
8743 goes back to waiting.
8745 @node Protocol, Server, Debug Session, Remote Serial
8746 @subsubsection Communication protocol
8748 @cindex debugging stub, example
8749 @cindex remote stub, example
8750 @cindex stub example, remote debugging
8751 The stub files provided with @value{GDBN} implement the target side of the
8752 communication protocol, and the @value{GDBN} side is implemented in the
8753 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
8754 these subroutines to communicate, and ignore the details. (If you're
8755 implementing your own stub file, you can still ignore the details: start
8756 with one of the existing stub files. @file{sparc-stub.c} is the best
8757 organized, and therefore the easiest to read.)
8759 However, there may be occasions when you need to know something about
8760 the protocol---for example, if there is only one serial port to your
8761 target machine, you might want your program to do something special if
8762 it recognizes a packet meant for @value{GDBN}.
8764 In the examples below, @samp{<-} and @samp{->} are used to indicate
8765 transmitted and received data respectfully.
8767 @cindex protocol, @value{GDBN} remote serial
8768 @cindex serial protocol, @value{GDBN} remote
8769 @cindex remote serial protocol
8770 All @value{GDBN} commands and responses (other than acknowledgments)
8771 are sent as a @var{packet}. A @var{packet} is introduced with the
8772 character @samp{$}, this is followed by an optional two-digit
8773 @var{sequence-id} and the character @samp{:}, the actual
8774 @var{packet-data}, and the terminating character @samp{#} followed by a
8775 two-digit @var{checksum}:
8778 @code{$}@var{packet-data}@code{#}@var{checksum}
8781 or, with the optional @var{sequence-id}:
8783 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
8786 @cindex checksum, for @value{GDBN} remote
8788 The two-digit @var{checksum} is computed as the modulo 256 sum of all
8789 characters between the leading @samp{$} and the trailing @samp{#} (that
8790 consisting of both the optional @var{sequence-id}@code{:} and the actual
8791 @var{packet-data}) (an eight bit unsigned checksum).
8793 @cindex sequence-id, for @value{GDBN} remote
8795 The two-digit @var{sequence-id}, when present, is returned with the
8796 acknowledgment. Beyond that its meaning is poorly defined.
8797 @value{GDBN} is not known to output @var{sequence-id}s.
8799 When either the host or the target machine receives a packet, the first
8800 response expected is an acknowledgment: either @samp{+} (to indicate
8801 the package was received correctly) or @samp{-} (to request
8805 <- @code{$}@var{packet-data}@code{#}@var{checksum}
8809 If the received packet included a @var{sequence-id} than that is
8810 appended to a positive acknowledgment:
8813 <- @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
8814 -> @code{+}@var{sequence-id}
8817 The host (@value{GDBN}) sends @var{command}s, and the target (the
8818 debugging stub incorporated in your program) sends a @var{response}. In
8819 the case of step and continue @var{command}s, the response is only sent
8820 when the operation has completed (the target has again stopped).
8822 @var{packet-data} consists of a sequence of characters with the
8823 exception of @samp{#} and @samp{$} (see @samp{X} packet for an
8824 exception). @samp{:} can not appear as the third character in a packet.
8825 Fields within the packet should be separated using @samp{,} and @samp{;}
8826 (unfortunately some packets chose to use @samp{:}). Except where
8827 otherwise noted all numbers are represented in HEX with leading zeros
8830 Response @var{data} can be run-length encoded to save space. A @samp{*}
8831 means that the next character is an @sc{ascii} encoding giving a repeat count
8832 which stands for that many repetitions of the character preceding the
8833 @samp{*}. The encoding is @code{n+29}, yielding a printable character
8834 where @code{n >=3} (which is where rle starts to win). The printable
8835 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
8836 value greater than 126 should not be used.
8838 Some remote systems have used a different run-length encoding mechanism
8839 loosely refered to as the cisco encoding. Following the @samp{*}
8840 character are two hex digits that indicate the size of the packet.
8847 means the same as "0000".
8849 The error response, returned for some packets includes a two character
8850 error number. That number is not well defined.
8852 For any @var{command} not supported by the stub, an empty response
8853 (@samp{$#00}) should be returned. That way it is possible to extend the
8854 protocol. A newer @value{GDBN} can tell if a packet is supported based
8857 Below is a complete list of all currently defined @var{command}s and
8858 their corresponding response @var{data}:
8860 @multitable @columnfractions .30 .30 .40
8865 @item extended ops @emph{(optional)}
8868 Use the extended remote protocol. Sticky---only needs to be set once.
8869 The extended remote protocol support the @samp{R} packet.
8873 Stubs that support the extended remote protocol return @samp{} which,
8874 unfortunately, is identical to the response returned by stubs that do not
8875 support protocol extensions.
8880 Indicate the reason the target halted. The reply is the same as for step
8889 @tab Reserved for future use
8891 @item set program arguments @strong{(reserved)} @emph{(optional)}
8892 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
8894 Initialized @samp{argv[]} array passed into program. @var{arglen}
8895 specifies the number of bytes in the hex encoded byte stream @var{arg}.
8896 See @file{gdbserver} for more details.
8898 @tab reply @code{OK}
8900 @tab reply @code{E}@var{NN}
8902 @item set baud @strong{(deprecated)}
8903 @tab @code{b}@var{baud}
8905 Change the serial line speed to @var{baud}. JTC: @emph{When does the
8906 transport layer state change? When it's received, or after the ACK is
8907 transmitted. In either case, there are problems if the command or the
8908 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
8909 to add something like this, and get it working for the first time, they
8910 ought to modify ser-unix.c to send some kind of out-of-band message to a
8911 specially-setup stub and have the switch happen "in between" packets, so
8912 that from remote protocol's point of view, nothing actually
8915 @item set breakpoint @strong{(deprecated)}
8916 @tab @code{B}@var{addr},@var{mode}
8918 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
8919 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
8923 @tab @code{c}@var{addr}
8925 @var{addr} is address to resume. If @var{addr} is omitted, resume at
8931 @item continue with signal @emph{(optional)}
8932 @tab @code{C}@var{sig}@code{;}@var{addr}
8934 Continue with signal @var{sig} (hex signal number). If
8935 @code{;}@var{addr} is omitted, resume at same address.
8940 @item toggle debug @emph{(deprecated)}
8945 @item detach @emph{(optional)}
8948 Detach @value{GDBN} from the remote system. Sent to the remote target before
8949 @value{GDBN} disconnects.
8951 @tab reply @emph{no response}
8953 @value{GDBN} does not check for any response after sending this packet
8957 @tab Reserved for future use
8961 @tab Reserved for future use
8965 @tab Reserved for future use
8969 @tab Reserved for future use
8971 @item read registers
8973 @tab Read general registers.
8975 @tab reply @var{XX...}
8977 Each byte of register data is described by two hex digits. The bytes
8978 with the register are transmitted in target byte order. The size of
8979 each register and their position within the @samp{g} @var{packet} are
8980 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
8981 @var{REGISTER_NAME} macros. The specification of several standard
8982 @code{g} packets is specified below.
8984 @tab @code{E}@var{NN}
8988 @tab @code{G}@var{XX...}
8990 See @samp{g} for a description of the @var{XX...} data.
8992 @tab reply @code{OK}
8995 @tab reply @code{E}@var{NN}
9000 @tab Reserved for future use
9002 @item set thread @emph{(optional)}
9003 @tab @code{H}@var{c}@var{t...}
9005 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
9006 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
9007 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
9008 thread used in other operations. If zero, pick a thread, any thread.
9010 @tab reply @code{OK}
9013 @tab reply @code{E}@var{NN}
9017 @c 'H': How restrictive (or permissive) is the thread model. If a
9018 @c thread is selected and stopped, are other threads allowed
9019 @c to continue to execute? As I mentioned above, I think the
9020 @c semantics of each command when a thread is selected must be
9021 @c described. For example:
9023 @c 'g': If the stub supports threads and a specific thread is
9024 @c selected, returns the register block from that thread;
9025 @c otherwise returns current registers.
9027 @c 'G' If the stub supports threads and a specific thread is
9028 @c selected, sets the registers of the register block of
9029 @c that thread; otherwise sets current registers.
9031 @item cycle step @strong{(draft)} @emph{(optional)}
9032 @tab @code{i}@var{addr}@code{,}@var{nnn}
9034 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
9035 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
9036 step starting at that address.
9038 @item signal then cycle step @strong{(reserved)} @emph{(optional)}
9041 See @samp{i} and @samp{S} for likely syntax and semantics.
9045 @tab Reserved for future use
9049 @tab Reserved for future use
9051 @item kill request @emph{(optional)}
9054 FIXME: @emph{There is no description of how operate when a specific
9055 thread context has been selected (ie. does 'k' kill only that thread?)}.
9059 @tab Reserved for future use
9063 @tab Reserved for future use
9066 @tab @code{m}@var{addr}@code{,}@var{length}
9068 Read @var{length} bytes of memory starting at address @var{addr}.
9069 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
9070 using word alligned accesses. FIXME: @emph{A word aligned memory
9071 transfer mechanism is needed.}
9073 @tab reply @var{XX...}
9075 @var{XX...} is mem contents. Can be fewer bytes than requested if able
9076 to read only part of the data. Neither @value{GDBN} nor the stub assume that
9077 sized memory transfers are assumed using word alligned accesses. FIXME:
9078 @emph{A word aligned memory transfer mechanism is needed.}
9080 @tab reply @code{E}@var{NN}
9081 @tab @var{NN} is errno
9084 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
9086 Write @var{length} bytes of memory starting at address @var{addr}.
9087 @var{XX...} is the data.
9089 @tab reply @code{OK}
9092 @tab reply @code{E}@var{NN}
9094 for an error (this includes the case where only part of the data was
9099 @tab Reserved for future use
9103 @tab Reserved for future use
9107 @tab Reserved for future use
9111 @tab Reserved for future use
9113 @item read reg @strong{(reserved)}
9114 @tab @code{p}@var{n...}
9118 @tab return @var{r....}
9119 @tab The hex encoded value of the register in target byte order.
9121 @item write reg @emph{(optional)}
9122 @tab @code{P}@var{n...}@code{=}@var{r...}
9124 Write register @var{n...} with value @var{r...}, which contains two hex
9125 digits for each byte in the register (target byte order).
9127 @tab reply @code{OK}
9130 @tab reply @code{E}@var{NN}
9133 @item general query @emph{(optional)}
9134 @tab @code{q}@var{query}
9136 Request info about @var{query}. In general @value{GDBN} @var{query}'s
9137 have a leading upper case letter. Custom vendor queries should use a
9138 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
9139 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
9140 must ensure that they match the full @var{query} name.
9142 @tab reply @code{XX...}
9143 @tab Hex encoded data from query. The reply can not be empty.
9145 @tab reply @code{E}@var{NN}
9149 @tab Indicating an unrecognized @var{query}.
9151 @item general set @emph{(optional)}
9152 @tab @code{Q}@var{var}@code{=}@var{val}
9154 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
9157 @item reset @emph{(deprecated)}
9160 Reset the entire system.
9162 @item remote restart @emph{(optional)}
9163 @tab @code{R}@var{XX}
9165 Restart the remote server. @var{XX} while needed has no clear
9166 definition. FIXME: @emph{An example interaction explaining how this
9167 packet is used in extended-remote mode is needed}.
9169 @item step @emph{(optional)}
9170 @tab @code{s}@var{addr}
9172 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9178 @item step with signal @emph{(optional)}
9179 @tab @code{S}@var{sig}@code{;}@var{addr}
9181 Like @samp{C} but step not continue.
9186 @item search @emph{(optional)}
9187 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
9189 Search backwards starting at address @var{addr} for a match with pattern
9190 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
9191 bytes. @var{addr} must be at least 3 digits.
9193 @item thread alive @emph{(optional)}
9194 @tab @code{T}@var{XX}
9195 @tab Find out if the thread XX is alive.
9197 @tab reply @code{OK}
9198 @tab thread is still alive
9200 @tab reply @code{E}@var{NN}
9205 @tab Reserved for future use
9209 @tab Reserved for future use
9213 @tab Reserved for future use
9217 @tab Reserved for future use
9221 @tab Reserved for future use
9225 @tab Reserved for future use
9229 @tab Reserved for future use
9231 @item write mem (binary) @emph{(optional)}
9232 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
9234 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
9235 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
9236 escaped using @code{0x7d}.
9238 @tab reply @code{OK}
9241 @tab reply @code{E}@var{NN}
9246 @tab Reserved for future use
9250 @tab Reserved for future use
9252 @item remove break or watchpoint @strong{(draft)} @emph{(optional)}
9253 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
9257 @item insert break or watchpoint @strong{(draft)} @emph{(optional)}
9258 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
9260 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
9261 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
9262 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
9263 bytes. For a software breakpoint, @var{length} specifies the size of
9264 the instruction to be patched. For hardware breakpoints and watchpoints
9265 @var{length} specifies the memory region to be monitored. To avoid
9266 potential problems with duplicate packets, the operations should be
9267 implemented in an ident-potentent way.
9269 @tab reply @code{E}@var{NN}
9272 @tab reply @code{OK}
9276 @tab If not supported.
9280 @tab Reserved for future use
9284 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
9285 receive any of the below as a reply. In the case of the @samp{C},
9286 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
9287 when the target halts. In the below the exact meaning of @samp{signal
9288 number} is poorly defined. In general one of the UNIX signal numbering
9289 conventions is used.
9291 @multitable @columnfractions .4 .6
9293 @item @code{S}@var{AA}
9294 @tab @var{AA} is the signal number
9296 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
9298 @var{AA} = two hex digit signal number; @var{n...} = register number
9299 (hex), @var{r...} = target byte ordered register contents, size defined
9300 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
9301 thread process ID, this is a hex integer; @var{n...} = other string not
9302 starting with valid hex digit. @value{GDBN} should ignore this
9303 @var{n...}, @var{r...} pair and go on to the next. This way we can
9304 extend the protocol.
9306 @item @code{W}@var{AA}
9308 The process exited, and @var{AA} is the exit status. This is only
9309 applicable for certains sorts of targets.
9311 @item @code{X}@var{AA}
9313 The process terminated with signal @var{AA}.
9315 @item @code{N}@var{AA}@code{;}@var{tttttttt}@code{;}@var{dddddddd}@code{;}@var{bbbbbbbb} @strong{(obsolete)}
9317 @var{AA} = signal number; @var{tttttttt} = address of symbol "_start";
9318 @var{dddddddd} = base of data section; @var{bbbbbbbb} = base of bss
9319 section. @emph{Note: only used by Cisco Systems targets. The difference
9320 between this reply and the "qOffsets" query is that the 'N' packet may
9321 arrive spontaneously whereas the 'qOffsets' is a query initiated by the
9324 @item @code{O}@var{XX...}
9326 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
9327 while the program is running and the debugger should continue to wait
9332 The following set and query packets have already been defined.
9334 @multitable @columnfractions .2 .2 .6
9336 @item current thread
9337 @tab @code{q}@code{C}
9338 @tab Return the current thread id.
9340 @tab reply @code{QC}@var{pid}
9342 Where @var{pid} is a HEX encoded 16 bit process id.
9345 @tab Any other reply implies the old pid.
9347 @item all thread ids
9348 @tab @code{q}@code{fThreadInfo}
9350 @tab @code{q}@code{sThreadInfo}
9352 Obtain a list of active thread ids from the target (OS). Since there
9353 may be too many active threads to fit into one reply packet, this query
9354 works iteratively: it may require more than one query/reply sequence to
9355 obtain the entire list of threads. The first query of the sequence will
9356 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
9357 sequence will be the @code{qs}@code{ThreadInfo} query.
9360 @tab NOTE: replaces the @code{qL} query (see below).
9362 @tab reply @code{m}@var{<id>}
9363 @tab A single thread id
9365 @tab reply @code{m}@var{<id>,}@var{<id>...}
9366 @tab a comma-separated list of thread ids
9369 @tab (lower case 'el') denotes end of list.
9373 In response to each query, the target will reply with a list of one
9374 or more thread ids, in big-endian hex, separated by commas. GDB will
9375 respond to each reply with a request for more thread ids (using the
9376 @code{qs} form of the query), until the target responds with @code{l}
9377 (lower-case el, for @code{'last'}).
9379 @item extra thread info
9380 @tab @code{qfThreadExtraInfo,}@var{<id>}
9385 Where @var{<id>} is a thread-id in big-endian hex.
9386 Obtain a printable string description of a thread's attributes from
9387 the target OS. This string may contain anything that the target OS
9388 thinks is interesting for @value{GDBN} to tell the user about the thread.
9389 The string is displayed in @value{GDBN}'s @samp{info threads} display.
9390 Some examples of possible thread extra info strings are "Runnable", or
9393 @tab reply @var{XX...}
9395 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
9396 printable string containing the extra information about the thread's
9399 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
9400 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
9405 Obtain thread information from RTOS. Where: @var{startflag} (one hex
9406 digit) is one to indicate the first query and zero to indicate a
9407 subsequent query; @var{threadcount} (two hex digits) is the maximum
9408 number of threads the response packet can contain; and @var{nextthread}
9409 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
9410 returned in the response as @var{argthread}.
9413 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
9416 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
9421 Where: @var{count} (two hex digits) is the number of threads being
9422 returned; @var{done} (one hex digit) is zero to indicate more threads
9423 and one indicates no further threads; @var{argthreadid} (eight hex
9424 digits) is @var{nextthread} from the request packet; @var{thread...} is
9425 a sequence of thread IDs from the target. @var{threadid} (eight hex
9426 digits). See @code{remote.c:parse_threadlist_response()}.
9428 @item compute CRC of memory block
9429 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
9432 @tab reply @code{E}@var{NN}
9433 @tab An error (such as memory fault)
9435 @tab reply @code{C}@var{CRC32}
9436 @tab A 32 bit cyclic redundancy check of the specified memory region.
9438 @item query sect offs
9439 @tab @code{q}@code{Offsets}
9441 Get section offsets that the target used when re-locating the downloaded
9442 image. @emph{Note: while a @code{Bss} offset is included in the
9443 response, @value{GDBN} ignores this and instead applies the @code{Data}
9444 offset to the @code{Bss} section.}
9446 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
9448 @item thread info request
9449 @tab @code{q}@code{P}@var{mode}@var{threadid}
9451 Returns information on @var{threadid}. Where: @var{mode} is a hex
9452 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
9456 See @code{remote.c:remote_unpack_thread_info_response()}.
9458 @item remote command
9459 @tab @code{q}@code{Rcmd,}@var{COMMAND}
9461 @var{COMMAND} (hex encoded) is passed to the local interpreter for
9462 execution. Invalid commands should be reported using the output string.
9463 Before the final result packet, the target may also respond with a
9464 number of intermediate @code{O}@var{OUTPUT} console output
9465 packets. @emph{Implementors should note that providing access to a
9466 stubs's interpreter may have security implications}.
9468 @tab reply @code{OK}
9470 A command response with no output.
9472 @tab reply @var{OUTPUT}
9474 A command response with the hex encoded output string @var{OUTPUT}.
9476 @tab reply @code{E}@var{NN}
9478 Indicate a badly formed request.
9483 When @samp{q}@samp{Rcmd} is not recognized.
9487 The following @samp{g}/@samp{G} packets have previously been defined.
9488 In the below, some thirty-two bit registers are transferred as sixty-four
9489 bits. Those registers should be zero/sign extended (which?) to fill the
9490 space allocated. Register bytes are transfered in target byte order.
9491 The two nibbles within a register byte are transfered most-significant -
9494 @multitable @columnfractions .5 .5
9498 All registers are transfered as thirty-two bit quantities in the order:
9499 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
9500 registers; fsr; fir; fp.
9504 All registers are transfered as sixty-four bit quantities (including
9505 thirty-two bit registers such as @code{sr}). The ordering is the same
9510 Example sequence of a target being re-started. Notice how the restart
9511 does not get any direct output:
9516 @emph{target restarts}
9519 -> @code{T001:1234123412341234}
9523 Example sequence of a target being stepped by a single instruction:
9531 -> @code{T001:1234123412341234}
9539 @node Server, NetWare, Protocol, Remote Serial
9540 @subsubsection Using the @code{gdbserver} program
9543 @cindex remote connection without stubs
9544 @code{gdbserver} is a control program for Unix-like systems, which
9545 allows you to connect your program with a remote @value{GDBN} via
9546 @code{target remote}---but without linking in the usual debugging stub.
9548 @code{gdbserver} is not a complete replacement for the debugging stubs,
9549 because it requires essentially the same operating-system facilities
9550 that @value{GDBN} itself does. In fact, a system that can run
9551 @code{gdbserver} to connect to a remote @value{GDBN} could also run
9552 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
9553 because it is a much smaller program than @value{GDBN} itself. It is
9554 also easier to port than all of @value{GDBN}, so you may be able to get
9555 started more quickly on a new system by using @code{gdbserver}.
9556 Finally, if you develop code for real-time systems, you may find that
9557 the tradeoffs involved in real-time operation make it more convenient to
9558 do as much development work as possible on another system, for example
9559 by cross-compiling. You can use @code{gdbserver} to make a similar
9560 choice for debugging.
9562 @value{GDBN} and @code{gdbserver} communicate via either a serial line
9563 or a TCP connection, using the standard @value{GDBN} remote serial
9567 @item On the target machine,
9568 you need to have a copy of the program you want to debug.
9569 @code{gdbserver} does not need your program's symbol table, so you can
9570 strip the program if necessary to save space. @value{GDBN} on the host
9571 system does all the symbol handling.
9573 To use the server, you must tell it how to communicate with @value{GDBN};
9574 the name of your program; and the arguments for your program. The
9578 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
9581 @var{comm} is either a device name (to use a serial line) or a TCP
9582 hostname and portnumber. For example, to debug Emacs with the argument
9583 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
9587 target> gdbserver /dev/com1 emacs foo.txt
9590 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
9593 To use a TCP connection instead of a serial line:
9596 target> gdbserver host:2345 emacs foo.txt
9599 The only difference from the previous example is the first argument,
9600 specifying that you are communicating with the host @value{GDBN} via
9601 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
9602 expect a TCP connection from machine @samp{host} to local TCP port 2345.
9603 (Currently, the @samp{host} part is ignored.) You can choose any number
9604 you want for the port number as long as it does not conflict with any
9605 TCP ports already in use on the target system (for example, @code{23} is
9606 reserved for @code{telnet}).@footnote{If you choose a port number that
9607 conflicts with another service, @code{gdbserver} prints an error message
9608 and exits.} You must use the same port number with the host @value{GDBN}
9609 @code{target remote} command.
9611 @item On the @value{GDBN} host machine,
9612 you need an unstripped copy of your program, since @value{GDBN} needs
9613 symbols and debugging information. Start up @value{GDBN} as usual,
9614 using the name of the local copy of your program as the first argument.
9615 (You may also need the @w{@samp{--baud}} option if the serial line is
9616 running at anything other than 9600@dmn{bps}.) After that, use @code{target
9617 remote} to establish communications with @code{gdbserver}. Its argument
9618 is either a device name (usually a serial device, like
9619 @file{/dev/ttyb}), or a TCP port descriptor in the form
9620 @code{@var{host}:@var{PORT}}. For example:
9623 (@value{GDBP}) target remote /dev/ttyb
9627 communicates with the server via serial line @file{/dev/ttyb}, and
9630 (@value{GDBP}) target remote the-target:2345
9634 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
9635 For TCP connections, you must start up @code{gdbserver} prior to using
9636 the @code{target remote} command. Otherwise you may get an error whose
9637 text depends on the host system, but which usually looks something like
9638 @samp{Connection refused}.
9641 @node NetWare, , Server, Remote Serial
9642 @subsubsection Using the @code{gdbserve.nlm} program
9644 @kindex gdbserve.nlm
9645 @code{gdbserve.nlm} is a control program for NetWare systems, which
9646 allows you to connect your program with a remote @value{GDBN} via
9647 @code{target remote}.
9649 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
9650 using the standard @value{GDBN} remote serial protocol.
9653 @item On the target machine,
9654 you need to have a copy of the program you want to debug.
9655 @code{gdbserve.nlm} does not need your program's symbol table, so you
9656 can strip the program if necessary to save space. @value{GDBN} on the
9657 host system does all the symbol handling.
9659 To use the server, you must tell it how to communicate with
9660 @value{GDBN}; the name of your program; and the arguments for your
9661 program. The syntax is:
9664 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
9665 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
9668 @var{board} and @var{port} specify the serial line; @var{baud} specifies
9669 the baud rate used by the connection. @var{port} and @var{node} default
9670 to 0, @var{baud} defaults to 9600@dmn{bps}.
9672 For example, to debug Emacs with the argument @samp{foo.txt}and
9673 communicate with @value{GDBN} over serial port number 2 or board 1
9674 using a 19200@dmn{bps} connection:
9677 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
9680 @item On the @value{GDBN} host machine,
9681 you need an unstripped copy of your program, since @value{GDBN} needs
9682 symbols and debugging information. Start up @value{GDBN} as usual,
9683 using the name of the local copy of your program as the first argument.
9684 (You may also need the @w{@samp{--baud}} option if the serial line is
9685 running at anything other than 9600@dmn{bps}. After that, use @code{target
9686 remote} to establish communications with @code{gdbserve.nlm}. Its
9687 argument is a device name (usually a serial device, like
9688 @file{/dev/ttyb}). For example:
9691 (@value{GDBP}) target remote /dev/ttyb
9695 communications with the server via serial line @file{/dev/ttyb}.
9698 @node KOD, , Remote, Targets
9699 @section Kernel Object Display
9701 @cindex kernel object display
9702 @cindex kernel object
9705 Some targets support kernel object display. Using this facility,
9706 @value{GDBN} communicates specially with the underlying operating system
9707 and can display information about operating system-level objects such as
9708 mutexes and other synchronization objects. Exactly which objects can be
9709 displayed is determined on a per-OS basis.
9711 Use the @code{set os} command to set the operating system. This tells
9712 @value{GDBN} which kernel object display module to initialize:
9715 (@value{GDBP}) set os cisco
9718 If @code{set os} succeeds, @value{GDBN} will display some information
9719 about the operating system, and will create a new @code{info} command
9720 which can be used to query the target. The @code{info} command is named
9721 after the operating system:
9724 (@value{GDBP}) info cisco
9725 List of Cisco Kernel Objects
9727 any Any and all objects
9730 Further subcommands can be used to query about particular objects known
9733 There is currently no way to determine whether a given operating system
9734 is supported other than to try it.
9737 @node Configurations, Controlling GDB, Targets, Top
9738 @chapter Configuration-Specific Information
9740 While nearly all @value{GDBN} commands are available for all native and
9741 cross versions of the debugger, there are some exceptions. This chapter
9742 describes things that are only available in certain configurations.
9744 There are three major categories of configurations: native
9745 configurations, where the host and target are the same, embedded
9746 operating system configurations, which are usually the same for several
9747 different processor architectures, and bare embedded processors, which
9748 are quite different from each other.
9753 * Embedded Processors::
9757 @node Native, Embedded OS, Configurations, Configurations
9760 This section describes details specific to particular native
9765 * SVR4 Process Information:: SVR4 process information
9768 @node HP-UX, SVR4 Process Information, Native, Native
9771 On HP-UX systems, if you refer to a function or variable name that
9772 begins with a dollar sign, @value{GDBN} searches for a user or system
9773 name first, before it searches for a convenience variable.
9775 @node SVR4 Process Information, , HP-UX, Native
9776 @subsection SVR4 process information
9779 @cindex process image
9781 Many versions of SVR4 provide a facility called @samp{/proc} that can be
9782 used to examine the image of a running process using file-system
9783 subroutines. If @value{GDBN} is configured for an operating system with
9784 this facility, the command @code{info proc} is available to report on
9785 several kinds of information about the process running your program.
9786 @code{info proc} works only on SVR4 systems that include the
9787 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
9788 and Unixware, but not HP-UX or Linux, for example.
9793 Summarize available information about the process.
9795 @kindex info proc mappings
9796 @item info proc mappings
9797 Report on the address ranges accessible in the program, with information
9798 on whether your program may read, write, or execute each range.
9800 @kindex info proc times
9801 @item info proc times
9802 Starting time, user CPU time, and system CPU time for your program and
9805 @kindex info proc id
9807 Report on the process IDs related to your program: its own process ID,
9808 the ID of its parent, the process group ID, and the session ID.
9810 @kindex info proc status
9811 @item info proc status
9812 General information on the state of the process. If the process is
9813 stopped, this report includes the reason for stopping, and any signal
9817 Show all the above information about the process.
9820 @node Embedded OS, Embedded Processors, Native, Configurations
9821 @section Embedded Operating Systems
9823 This section describes configurations involving the debugging of
9824 embedded operating systems that are available for several different
9828 * VxWorks:: Using @value{GDBN} with VxWorks
9831 @value{GDBN} includes the ability to debug programs running on
9832 various real-time operating systems.
9834 @node VxWorks, , Embedded OS, Embedded OS
9835 @subsection Using @value{GDBN} with VxWorks
9841 @kindex target vxworks
9842 @item target vxworks @var{machinename}
9843 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
9844 is the target system's machine name or IP address.
9848 On VxWorks, @code{load} links @var{filename} dynamically on the
9849 current target system as well as adding its symbols in @value{GDBN}.
9851 @value{GDBN} enables developers to spawn and debug tasks running on networked
9852 VxWorks targets from a Unix host. Already-running tasks spawned from
9853 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
9854 both the Unix host and on the VxWorks target. The program
9855 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
9856 installed with the name @code{vxgdb}, to distinguish it from a
9857 @value{GDBN} for debugging programs on the host itself.)
9860 @item VxWorks-timeout @var{args}
9861 @kindex vxworks-timeout
9862 All VxWorks-based targets now support the option @code{vxworks-timeout}.
9863 This option is set by the user, and @var{args} represents the number of
9864 seconds @value{GDBN} waits for responses to rpc's. You might use this if
9865 your VxWorks target is a slow software simulator or is on the far side
9866 of a thin network line.
9869 The following information on connecting to VxWorks was current when
9870 this manual was produced; newer releases of VxWorks may use revised
9874 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
9875 to include the remote debugging interface routines in the VxWorks
9876 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
9877 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
9878 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
9879 source debugging task @code{tRdbTask} when VxWorks is booted. For more
9880 information on configuring and remaking VxWorks, see the manufacturer's
9882 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
9884 Once you have included @file{rdb.a} in your VxWorks system image and set
9885 your Unix execution search path to find @value{GDBN}, you are ready to
9886 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
9887 @code{vxgdb}, depending on your installation).
9889 @value{GDBN} comes up showing the prompt:
9896 * VxWorks Connection:: Connecting to VxWorks
9897 * VxWorks Download:: VxWorks download
9898 * VxWorks Attach:: Running tasks
9901 @node VxWorks Connection, VxWorks Download, VxWorks, VxWorks
9902 @subsubsection Connecting to VxWorks
9904 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
9905 network. To connect to a target whose host name is ``@code{tt}'', type:
9908 (vxgdb) target vxworks tt
9912 @value{GDBN} displays messages like these:
9915 Attaching remote machine across net...
9920 @value{GDBN} then attempts to read the symbol tables of any object modules
9921 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
9922 these files by searching the directories listed in the command search
9923 path (@pxref{Environment, ,Your program's environment}); if it fails
9924 to find an object file, it displays a message such as:
9927 prog.o: No such file or directory.
9930 When this happens, add the appropriate directory to the search path with
9931 the @value{GDBN} command @code{path}, and execute the @code{target}
9934 @node VxWorks Download, VxWorks Attach, VxWorks Connection, VxWorks
9935 @subsubsection VxWorks download
9937 @cindex download to VxWorks
9938 If you have connected to the VxWorks target and you want to debug an
9939 object that has not yet been loaded, you can use the @value{GDBN}
9940 @code{load} command to download a file from Unix to VxWorks
9941 incrementally. The object file given as an argument to the @code{load}
9942 command is actually opened twice: first by the VxWorks target in order
9943 to download the code, then by @value{GDBN} in order to read the symbol
9944 table. This can lead to problems if the current working directories on
9945 the two systems differ. If both systems have NFS mounted the same
9946 filesystems, you can avoid these problems by using absolute paths.
9947 Otherwise, it is simplest to set the working directory on both systems
9948 to the directory in which the object file resides, and then to reference
9949 the file by its name, without any path. For instance, a program
9950 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
9951 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
9952 program, type this on VxWorks:
9955 -> cd "@var{vxpath}/vw/demo/rdb"
9959 Then, in @value{GDBN}, type:
9962 (vxgdb) cd @var{hostpath}/vw/demo/rdb
9966 @value{GDBN} displays a response similar to this:
9969 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
9972 You can also use the @code{load} command to reload an object module
9973 after editing and recompiling the corresponding source file. Note that
9974 this makes @value{GDBN} delete all currently-defined breakpoints,
9975 auto-displays, and convenience variables, and to clear the value
9976 history. (This is necessary in order to preserve the integrity of
9977 debugger's data structures that reference the target system's symbol
9980 @node VxWorks Attach, , VxWorks Download, VxWorks
9981 @subsubsection Running tasks
9983 @cindex running VxWorks tasks
9984 You can also attach to an existing task using the @code{attach} command as
9988 (vxgdb) attach @var{task}
9992 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
9993 or suspended when you attach to it. Running tasks are suspended at
9994 the time of attachment.
9996 @node Embedded Processors, Architectures, Embedded OS, Configurations
9997 @section Embedded Processors
9999 This section goes into details specific to particular embedded
10003 * A29K Embedded:: AMD A29K Embedded
10005 * H8/300:: Hitachi H8/300
10006 * H8/500:: Hitachi H8/500
10007 * i960:: Intel i960
10008 * M32R/D:: Mitsubishi M32R/D
10009 * M68K:: Motorola M68K
10010 * M88K:: Motorola M88K
10011 * MIPS Embedded:: MIPS Embedded
10012 * PA:: HP PA Embedded
10015 * Sparclet:: Tsqware Sparclet
10016 * Sparclite:: Fujitsu Sparclite
10017 * ST2000:: Tandem ST2000
10018 * Z8000:: Zilog Z8000
10021 @node A29K Embedded, ARM, Embedded Processors, Embedded Processors
10022 @subsection AMD A29K Embedded
10027 * Comms (EB29K):: Communications setup
10028 * gdb-EB29K:: EB29K cross-debugging
10029 * Remote Log:: Remote log
10034 @kindex target adapt
10035 @item target adapt @var{dev}
10036 Adapt monitor for A29K.
10038 @kindex target amd-eb
10039 @item target amd-eb @var{dev} @var{speed} @var{PROG}
10041 Remote PC-resident AMD EB29K board, attached over serial lines.
10042 @var{dev} is the serial device, as for @code{target remote};
10043 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
10044 name of the program to be debugged, as it appears to DOS on the PC.
10045 @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
10049 @node A29K UDI, A29K EB29K, A29K Embedded, A29K Embedded
10050 @subsubsection A29K UDI
10053 @cindex AMD29K via UDI
10055 @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
10056 protocol for debugging the a29k processor family. To use this
10057 configuration with AMD targets running the MiniMON monitor, you need the
10058 program @code{MONTIP}, available from AMD at no charge. You can also
10059 use @value{GDBN} with the UDI-conformant a29k simulator program
10060 @code{ISSTIP}, also available from AMD.
10063 @item target udi @var{keyword}
10065 Select the UDI interface to a remote a29k board or simulator, where
10066 @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
10067 This file contains keyword entries which specify parameters used to
10068 connect to a29k targets. If the @file{udi_soc} file is not in your
10069 working directory, you must set the environment variable @samp{UDICONF}
10073 @node A29K EB29K, Comms (EB29K), A29K UDI, A29K Embedded
10074 @subsubsection EBMON protocol for AMD29K
10076 @cindex EB29K board
10077 @cindex running 29K programs
10079 AMD distributes a 29K development board meant to fit in a PC, together
10080 with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
10081 term, this development system is called the ``EB29K''. To use
10082 @value{GDBN} from a Unix system to run programs on the EB29K board, you
10083 must first connect a serial cable between the PC (which hosts the EB29K
10084 board) and a serial port on the Unix system. In the following, we
10085 assume you've hooked the cable between the PC's @file{COM1} port and
10086 @file{/dev/ttya} on the Unix system.
10088 @node Comms (EB29K), gdb-EB29K, A29K EB29K, A29K Embedded
10089 @subsubsection Communications setup
10091 The next step is to set up the PC's port, by doing something like this
10095 C:\> MODE com1:9600,n,8,1,none
10099 This example---run on an MS DOS 4.0 system---sets the PC port to 9600
10100 bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
10101 you must match the communications parameters when establishing the Unix
10102 end of the connection as well.
10103 @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
10104 @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
10106 @c It's optional, but it's unwise to omit it: who knows what is the
10107 @c default value set when the DOS machines boots? "No retry" means that
10108 @c the DOS serial device driver won't retry the operation if it fails;
10109 @c I understand that this is needed because the GDB serial protocol
10110 @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
10112 To give control of the PC to the Unix side of the serial line, type
10113 the following at the DOS console:
10120 (Later, if you wish to return control to the DOS console, you can use
10121 the command @code{CTTY con}---but you must send it over the device that
10122 had control, in our example over the @file{COM1} serial line.)
10124 From the Unix host, use a communications program such as @code{tip} or
10125 @code{cu} to communicate with the PC; for example,
10128 cu -s 9600 -l /dev/ttya
10132 The @code{cu} options shown specify, respectively, the linespeed and the
10133 serial port to use. If you use @code{tip} instead, your command line
10134 may look something like the following:
10137 tip -9600 /dev/ttya
10141 Your system may require a different name where we show
10142 @file{/dev/ttya} as the argument to @code{tip}. The communications
10143 parameters, including which port to use, are associated with the
10144 @code{tip} argument in the ``remote'' descriptions file---normally the
10145 system table @file{/etc/remote}.
10146 @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
10147 @c the DOS side's comms setup? cu can support -o (odd
10148 @c parity), -e (even parity)---apparently no settings for no parity or
10149 @c for character size. Taken from stty maybe...? John points out tip
10150 @c can set these as internal variables, eg ~s parity=none; man stty
10151 @c suggests that it *might* work to stty these options with stdin or
10152 @c stdout redirected... ---doc@cygnus.com, 25feb91
10154 @c There's nothing to be done for the "none" part of the DOS MODE
10155 @c command. The rest of the parameters should be matched by the
10156 @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
10159 Using the @code{tip} or @code{cu} connection, change the DOS working
10160 directory to the directory containing a copy of your 29K program, then
10161 start the PC program @code{EBMON} (an EB29K control program supplied
10162 with your board by AMD). You should see an initial display from
10163 @code{EBMON} similar to the one that follows, ending with the
10164 @code{EBMON} prompt @samp{#}---
10169 G:\> CD \usr\joe\work29k
10171 G:\USR\JOE\WORK29K> EBMON
10172 Am29000 PC Coprocessor Board Monitor, version 3.0-18
10173 Copyright 1990 Advanced Micro Devices, Inc.
10174 Written by Gibbons and Associates, Inc.
10176 Enter '?' or 'H' for help
10178 PC Coprocessor Type = EB29K
10180 Memory Base = 0xd0000
10182 Data Memory Size = 2048KB
10183 Available I-RAM Range = 0x8000 to 0x1fffff
10184 Available D-RAM Range = 0x80002000 to 0x801fffff
10187 Register Stack Size = 0x800
10188 Memory Stack Size = 0x1800
10191 Am29027 Available = No
10192 Byte Write Available = Yes
10197 Then exit the @code{cu} or @code{tip} program (done in the example by
10198 typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
10199 running, ready for @value{GDBN} to take over.
10201 For this example, we've assumed what is probably the most convenient
10202 way to make sure the same 29K program is on both the PC and the Unix
10203 system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
10204 PC as a file system on the Unix host. If you do not have PC/NFS or
10205 something similar connecting the two systems, you must arrange some
10206 other way---perhaps floppy-disk transfer---of getting the 29K program
10207 from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
10210 @node gdb-EB29K, Remote Log, Comms (EB29K), A29K Embedded
10211 @subsubsection EB29K cross-debugging
10213 Finally, @code{cd} to the directory containing an image of your 29K
10214 program on the Unix system, and start @value{GDBN}---specifying as argument the
10215 name of your 29K program:
10218 cd /usr/joe/work29k
10223 Now you can use the @code{target} command:
10226 target amd-eb /dev/ttya 9600 MYFOO
10227 @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
10228 @c emphasize that this is the name as seen by DOS (since I think DOS is
10229 @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
10233 In this example, we've assumed your program is in a file called
10234 @file{myfoo}. Note that the filename given as the last argument to
10235 @code{target amd-eb} should be the name of the program as it appears to DOS.
10236 In our example this is simply @code{MYFOO}, but in general it can include
10237 a DOS path, and depending on your transfer mechanism may not resemble
10238 the name on the Unix side.
10240 At this point, you can set any breakpoints you wish; when you are ready
10241 to see your program run on the 29K board, use the @value{GDBN} command
10244 To stop debugging the remote program, use the @value{GDBN} @code{detach}
10247 To return control of the PC to its console, use @code{tip} or @code{cu}
10248 once again, after your @value{GDBN} session has concluded, to attach to
10249 @code{EBMON}. You can then type the command @code{q} to shut down
10250 @code{EBMON}, returning control to the DOS command-line interpreter.
10251 Type @kbd{CTTY con} to return command input to the main DOS console,
10252 and type @kbd{~.} to leave @code{tip} or @code{cu}.
10254 @node Remote Log, , gdb-EB29K, A29K Embedded
10255 @subsubsection Remote log
10257 @cindex log file for EB29K
10259 The @code{target amd-eb} command creates a file @file{eb.log} in the
10260 current working directory, to help debug problems with the connection.
10261 @file{eb.log} records all the output from @code{EBMON}, including echoes
10262 of the commands sent to it. Running @samp{tail -f} on this file in
10263 another window often helps to understand trouble with @code{EBMON}, or
10264 unexpected events on the PC side of the connection.
10266 @node ARM, H8/300, A29K Embedded, Embedded Processors
10272 @item target rdi @var{dev}
10273 ARM Angel monitor, via RDI library interface to ADP protocol. You may
10274 use this target to communicate with both boards running the Angel
10275 monitor, or with the EmbeddedICE JTAG debug device.
10278 @item target rdp @var{dev}
10283 @node H8/300, H8/500, ARM, Embedded Processors
10284 @subsection Hitachi H8/300
10288 @kindex target hms@r{, with H8/300}
10289 @item target hms @var{dev}
10290 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
10291 Use special commands @code{device} and @code{speed} to control the serial
10292 line and the communications speed used.
10294 @kindex target e7000@r{, with H8/300}
10295 @item target e7000 @var{dev}
10296 E7000 emulator for Hitachi H8 and SH.
10298 @kindex target sh3@r{, with H8/300}
10299 @kindex target sh3e@r{, with H8/300}
10300 @item target sh3 @var{dev}
10301 @itemx target sh3e @var{dev}
10302 Hitachi SH-3 and SH-3E target systems.
10306 @cindex download to H8/300 or H8/500
10307 @cindex H8/300 or H8/500 download
10308 @cindex download to Hitachi SH
10309 @cindex Hitachi SH download
10310 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
10311 board, the @code{load} command downloads your program to the Hitachi
10312 board and also opens it as the current executable target for
10313 @value{GDBN} on your host (like the @code{file} command).
10315 @value{GDBN} needs to know these things to talk to your
10316 Hitachi SH, H8/300, or H8/500:
10320 that you want to use @samp{target hms}, the remote debugging interface
10321 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
10322 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
10323 the default when @value{GDBN} is configured specifically for the Hitachi SH,
10324 H8/300, or H8/500.)
10327 what serial device connects your host to your Hitachi board (the first
10328 serial device available on your host is the default).
10331 what speed to use over the serial device.
10335 * Hitachi Boards:: Connecting to Hitachi boards.
10336 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
10337 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
10340 @node Hitachi Boards, Hitachi ICE, H8/300, H8/300
10341 @subsubsection Connecting to Hitachi boards
10343 @c only for Unix hosts
10345 @cindex serial device, Hitachi micros
10346 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
10347 need to explicitly set the serial device. The default @var{port} is the
10348 first available port on your host. This is only necessary on Unix
10349 hosts, where it is typically something like @file{/dev/ttya}.
10352 @cindex serial line speed, Hitachi micros
10353 @code{@value{GDBN}} has another special command to set the communications
10354 speed: @samp{speed @var{bps}}. This command also is only used from Unix
10355 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
10356 the DOS @code{mode} command (for instance,
10357 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
10359 The @samp{device} and @samp{speed} commands are available only when you
10360 use a Unix host to debug your Hitachi microprocessor programs. If you
10362 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
10363 called @code{asynctsr} to communicate with the development board
10364 through a PC serial port. You must also use the DOS @code{mode} command
10365 to set up the serial port on the DOS side.
10367 The following sample session illustrates the steps needed to start a
10368 program under @value{GDBN} control on an H8/300. The example uses a
10369 sample H8/300 program called @file{t.x}. The procedure is the same for
10370 the Hitachi SH and the H8/500.
10372 First hook up your development board. In this example, we use a
10373 board attached to serial port @code{COM2}; if you use a different serial
10374 port, substitute its name in the argument of the @code{mode} command.
10375 When you call @code{asynctsr}, the auxiliary comms program used by the
10376 debugger, you give it just the numeric part of the serial port's name;
10377 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
10381 C:\H8300\TEST> asynctsr 2
10382 C:\H8300\TEST> mode com2:9600,n,8,1,p
10384 Resident portion of MODE loaded
10386 COM2: 9600, n, 8, 1, p
10391 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
10392 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
10393 disable it, or even boot without it, to use @code{asynctsr} to control
10394 your development board.
10397 @kindex target hms@r{, and serial protocol}
10398 Now that serial communications are set up, and the development board is
10399 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
10400 the name of your program as the argument. @code{@value{GDBN}} prompts
10401 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
10402 commands to begin your debugging session: @samp{target hms} to specify
10403 cross-debugging to the Hitachi board, and the @code{load} command to
10404 download your program to the board. @code{load} displays the names of
10405 the program's sections, and a @samp{*} for each 2K of data downloaded.
10406 (If you want to refresh @value{GDBN} data on symbols or on the
10407 executable file without downloading, use the @value{GDBN} commands
10408 @code{file} or @code{symbol-file}. These commands, and @code{load}
10409 itself, are described in @ref{Files,,Commands to specify files}.)
10412 (eg-C:\H8300\TEST) @value{GDBP} t.x
10413 @value{GDBN} is free software and you are welcome to distribute copies
10414 of it under certain conditions; type "show copying" to see
10416 There is absolutely no warranty for @value{GDBN}; type "show warranty"
10418 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
10419 (@value{GDBP}) target hms
10420 Connected to remote H8/300 HMS system.
10421 (@value{GDBP}) load t.x
10422 .text : 0x8000 .. 0xabde ***********
10423 .data : 0xabde .. 0xad30 *
10424 .stack : 0xf000 .. 0xf014 *
10427 At this point, you're ready to run or debug your program. From here on,
10428 you can use all the usual @value{GDBN} commands. The @code{break} command
10429 sets breakpoints; the @code{run} command starts your program;
10430 @code{print} or @code{x} display data; the @code{continue} command
10431 resumes execution after stopping at a breakpoint. You can use the
10432 @code{help} command at any time to find out more about @value{GDBN} commands.
10434 Remember, however, that @emph{operating system} facilities aren't
10435 available on your development board; for example, if your program hangs,
10436 you can't send an interrupt---but you can press the @sc{reset} switch!
10438 Use the @sc{reset} button on the development board
10441 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
10442 no way to pass an interrupt signal to the development board); and
10445 to return to the @value{GDBN} command prompt after your program finishes
10446 normally. The communications protocol provides no other way for @value{GDBN}
10447 to detect program completion.
10450 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
10451 development board as a ``normal exit'' of your program.
10453 @node Hitachi ICE, Hitachi Special, Hitachi Boards, H8/300
10454 @subsubsection Using the E7000 in-circuit emulator
10456 @kindex target e7000@r{, with Hitachi ICE}
10457 You can use the E7000 in-circuit emulator to develop code for either the
10458 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
10459 e7000} command to connect @value{GDBN} to your E7000:
10462 @item target e7000 @var{port} @var{speed}
10463 Use this form if your E7000 is connected to a serial port. The
10464 @var{port} argument identifies what serial port to use (for example,
10465 @samp{com2}). The third argument is the line speed in bits per second
10466 (for example, @samp{9600}).
10468 @item target e7000 @var{hostname}
10469 If your E7000 is installed as a host on a TCP/IP network, you can just
10470 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
10473 @node Hitachi Special, , Hitachi ICE, H8/300
10474 @subsubsection Special @value{GDBN} commands for Hitachi micros
10476 Some @value{GDBN} commands are available only for the H8/300:
10480 @kindex set machine
10481 @kindex show machine
10482 @item set machine h8300
10483 @itemx set machine h8300h
10484 Condition @value{GDBN} for one of the two variants of the H8/300
10485 architecture with @samp{set machine}. You can use @samp{show machine}
10486 to check which variant is currently in effect.
10490 @node H8/500, i960, H8/300, Embedded Processors
10495 @kindex set memory @var{mod}
10496 @cindex memory models, H8/500
10497 @item set memory @var{mod}
10499 Specify which H8/500 memory model (@var{mod}) you are using with
10500 @samp{set memory}; check which memory model is in effect with @samp{show
10501 memory}. The accepted values for @var{mod} are @code{small},
10502 @code{big}, @code{medium}, and @code{compact}.
10506 @node i960, M32R/D, H8/500, Embedded Processors
10507 @subsection Intel i960
10511 @kindex target mon960
10512 @item target mon960 @var{dev}
10513 MON960 monitor for Intel i960.
10515 @item target nindy @var{devicename}
10516 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
10517 the name of the serial device to use for the connection, e.g.
10524 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
10525 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
10526 tell @value{GDBN} how to connect to the 960 in several ways:
10530 Through command line options specifying serial port, version of the
10531 Nindy protocol, and communications speed;
10534 By responding to a prompt on startup;
10537 By using the @code{target} command at any point during your @value{GDBN}
10538 session. @xref{Target Commands, ,Commands for managing targets}.
10540 @kindex target nindy
10541 @item target nindy @var{devicename}
10542 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
10543 the name of the serial device to use for the connection, e.g.
10548 @cindex download to Nindy-960
10549 With the Nindy interface to an Intel 960 board, @code{load}
10550 downloads @var{filename} to the 960 as well as adding its symbols in
10554 * Nindy Startup:: Startup with Nindy
10555 * Nindy Options:: Options for Nindy
10556 * Nindy Reset:: Nindy reset command
10559 @node Nindy Startup, Nindy Options, i960, i960
10560 @subsubsection Startup with Nindy
10562 If you simply start @code{@value{GDBP}} without using any command-line
10563 options, you are prompted for what serial port to use, @emph{before} you
10564 reach the ordinary @value{GDBN} prompt:
10567 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
10571 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
10572 identifies the serial port you want to use. You can, if you choose,
10573 simply start up with no Nindy connection by responding to the prompt
10574 with an empty line. If you do this and later wish to attach to Nindy,
10575 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
10577 @node Nindy Options, Nindy Reset, Nindy Startup, i960
10578 @subsubsection Options for Nindy
10580 These are the startup options for beginning your @value{GDBN} session with a
10581 Nindy-960 board attached:
10584 @item -r @var{port}
10585 Specify the serial port name of a serial interface to be used to connect
10586 to the target system. This option is only available when @value{GDBN} is
10587 configured for the Intel 960 target architecture. You may specify
10588 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
10589 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
10590 suffix for a specific @code{tty} (e.g. @samp{-r a}).
10593 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
10594 the ``old'' Nindy monitor protocol to connect to the target system.
10595 This option is only available when @value{GDBN} is configured for the Intel 960
10596 target architecture.
10599 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
10600 connect to a target system that expects the newer protocol, the connection
10601 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
10602 attempts to reconnect at several different line speeds. You can abort
10603 this process with an interrupt.
10607 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
10608 system, in an attempt to reset it, before connecting to a Nindy target.
10611 @emph{Warning:} Many target systems do not have the hardware that this
10612 requires; it only works with a few boards.
10616 The standard @samp{-b} option controls the line speed used on the serial
10620 @node Nindy Reset, , Nindy Options, i960
10621 @subsubsection Nindy reset command
10626 For a Nindy target, this command sends a ``break'' to the remote target
10627 system; this is only useful if the target has been equipped with a
10628 circuit to perform a hard reset (or some other interesting action) when
10629 a break is detected.
10633 @node M32R/D, M68K, i960, Embedded Processors
10634 @subsection Mitsubishi M32R/D
10638 @kindex target m32r
10639 @item target m32r @var{dev}
10640 Mitsubishi M32R/D ROM monitor.
10644 @node M68K, M88K, M32R/D, Embedded Processors
10647 The Motorola m68k configuration includes ColdFire support, and
10648 target command for the following ROM monitors.
10652 @kindex target abug
10653 @item target abug @var{dev}
10654 ABug ROM monitor for M68K.
10656 @kindex target cpu32bug
10657 @item target cpu32bug @var{dev}
10658 CPU32BUG monitor, running on a CPU32 (M68K) board.
10660 @kindex target dbug
10661 @item target dbug @var{dev}
10662 dBUG ROM monitor for Motorola ColdFire.
10665 @item target est @var{dev}
10666 EST-300 ICE monitor, running on a CPU32 (M68K) board.
10668 @kindex target rom68k
10669 @item target rom68k @var{dev}
10670 ROM 68K monitor, running on an M68K IDP board.
10674 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
10675 instead have only a single special target command:
10679 @kindex target es1800
10680 @item target es1800 @var{dev}
10681 ES-1800 emulator for M68K.
10689 @kindex target rombug
10690 @item target rombug @var{dev}
10691 ROMBUG ROM monitor for OS/9000.
10695 @node M88K, MIPS Embedded, M68K, Embedded Processors
10701 @item target bug @var{dev}
10702 BUG monitor, running on a MVME187 (m88k) board.
10706 @node MIPS Embedded, PowerPC, M88K, Embedded Processors
10707 @subsection MIPS Embedded
10709 @cindex MIPS boards
10710 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
10711 MIPS board attached to a serial line. This is available when
10712 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
10715 Use these @value{GDBN} commands to specify the connection to your target board:
10718 @item target mips @var{port}
10719 @kindex target mips @var{port}
10720 To run a program on the board, start up @code{@value{GDBP}} with the
10721 name of your program as the argument. To connect to the board, use the
10722 command @samp{target mips @var{port}}, where @var{port} is the name of
10723 the serial port connected to the board. If the program has not already
10724 been downloaded to the board, you may use the @code{load} command to
10725 download it. You can then use all the usual @value{GDBN} commands.
10727 For example, this sequence connects to the target board through a serial
10728 port, and loads and runs a program called @var{prog} through the
10732 host$ @value{GDBP} @var{prog}
10733 @value{GDBN} is free software and @dots{}
10734 (@value{GDBP}) target mips /dev/ttyb
10735 (@value{GDBP}) load @var{prog}
10739 @item target mips @var{hostname}:@var{portnumber}
10740 On some @value{GDBN} host configurations, you can specify a TCP
10741 connection (for instance, to a serial line managed by a terminal
10742 concentrator) instead of a serial port, using the syntax
10743 @samp{@var{hostname}:@var{portnumber}}.
10745 @item target pmon @var{port}
10746 @kindex target pmon @var{port}
10749 @item target ddb @var{port}
10750 @kindex target ddb @var{port}
10751 NEC's DDB variant of PMON for Vr4300.
10753 @item target lsi @var{port}
10754 @kindex target lsi @var{port}
10755 LSI variant of PMON.
10757 @kindex target r3900
10758 @item target r3900 @var{dev}
10759 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
10761 @kindex target array
10762 @item target array @var{dev}
10763 Array Tech LSI33K RAID controller board.
10769 @value{GDBN} also supports these special commands for MIPS targets:
10772 @item set processor @var{args}
10773 @itemx show processor
10774 @kindex set processor @var{args}
10775 @kindex show processor
10776 Use the @code{set processor} command to set the type of MIPS
10777 processor when you want to access processor-type-specific registers.
10778 For example, @code{set processor @var{r3041}} tells @value{GDBN}
10779 to use the CPO registers appropriate for the 3041 chip.
10780 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
10781 is using. Use the @code{info reg} command to see what registers
10782 @value{GDBN} is using.
10784 @item set mipsfpu double
10785 @itemx set mipsfpu single
10786 @itemx set mipsfpu none
10787 @itemx show mipsfpu
10788 @kindex set mipsfpu
10789 @kindex show mipsfpu
10790 @cindex MIPS remote floating point
10791 @cindex floating point, MIPS remote
10792 If your target board does not support the MIPS floating point
10793 coprocessor, you should use the command @samp{set mipsfpu none} (if you
10794 need this, you may wish to put the command in your @value{GDBN} init
10795 file). This tells @value{GDBN} how to find the return value of
10796 functions which return floating point values. It also allows
10797 @value{GDBN} to avoid saving the floating point registers when calling
10798 functions on the board. If you are using a floating point coprocessor
10799 with only single precision floating point support, as on the @sc{r4650}
10800 processor, use the command @samp{set mipsfpu single}. The default
10801 double precision floating point coprocessor may be selected using
10802 @samp{set mipsfpu double}.
10804 In previous versions the only choices were double precision or no
10805 floating point, so @samp{set mipsfpu on} will select double precision
10806 and @samp{set mipsfpu off} will select no floating point.
10808 As usual, you can inquire about the @code{mipsfpu} variable with
10809 @samp{show mipsfpu}.
10811 @item set remotedebug @var{n}
10812 @itemx show remotedebug
10813 @kindex set remotedebug@r{, MIPS protocol}
10814 @kindex show remotedebug@r{, MIPS protocol}
10815 @cindex @code{remotedebug}, MIPS protocol
10816 @cindex MIPS @code{remotedebug} protocol
10817 @c FIXME! For this to be useful, you must know something about the MIPS
10818 @c FIXME...protocol. Where is it described?
10819 You can see some debugging information about communications with the board
10820 by setting the @code{remotedebug} variable. If you set it to @code{1} using
10821 @samp{set remotedebug 1}, every packet is displayed. If you set it
10822 to @code{2}, every character is displayed. You can check the current value
10823 at any time with the command @samp{show remotedebug}.
10825 @item set timeout @var{seconds}
10826 @itemx set retransmit-timeout @var{seconds}
10827 @itemx show timeout
10828 @itemx show retransmit-timeout
10829 @cindex @code{timeout}, MIPS protocol
10830 @cindex @code{retransmit-timeout}, MIPS protocol
10831 @kindex set timeout
10832 @kindex show timeout
10833 @kindex set retransmit-timeout
10834 @kindex show retransmit-timeout
10835 You can control the timeout used while waiting for a packet, in the MIPS
10836 remote protocol, with the @code{set timeout @var{seconds}} command. The
10837 default is 5 seconds. Similarly, you can control the timeout used while
10838 waiting for an acknowledgement of a packet with the @code{set
10839 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
10840 You can inspect both values with @code{show timeout} and @code{show
10841 retransmit-timeout}. (These commands are @emph{only} available when
10842 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
10844 The timeout set by @code{set timeout} does not apply when @value{GDBN}
10845 is waiting for your program to stop. In that case, @value{GDBN} waits
10846 forever because it has no way of knowing how long the program is going
10847 to run before stopping.
10850 @node PowerPC, PA, MIPS Embedded, Embedded Processors
10851 @subsection PowerPC
10855 @kindex target dink32
10856 @item target dink32 @var{dev}
10857 DINK32 ROM monitor.
10859 @kindex target ppcbug
10860 @item target ppcbug @var{dev}
10861 @kindex target ppcbug1
10862 @item target ppcbug1 @var{dev}
10863 PPCBUG ROM monitor for PowerPC.
10866 @item target sds @var{dev}
10867 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
10871 @node PA, SH, PowerPC, Embedded Processors
10872 @subsection HP PA Embedded
10876 @kindex target op50n
10877 @item target op50n @var{dev}
10878 OP50N monitor, running on an OKI HPPA board.
10880 @kindex target w89k
10881 @item target w89k @var{dev}
10882 W89K monitor, running on a Winbond HPPA board.
10886 @node SH, Sparclet, PA, Embedded Processors
10887 @subsection Hitachi SH
10891 @kindex target hms@r{, with Hitachi SH}
10892 @item target hms @var{dev}
10893 A Hitachi SH board attached via serial line to your host. Use special
10894 commands @code{device} and @code{speed} to control the serial line and
10895 the communications speed used.
10897 @kindex target e7000@r{, with Hitachi SH}
10898 @item target e7000 @var{dev}
10899 E7000 emulator for Hitachi SH.
10901 @kindex target sh3@r{, with SH}
10902 @kindex target sh3e@r{, with SH}
10903 @item target sh3 @var{dev}
10904 @item target sh3e @var{dev}
10905 Hitachi SH-3 and SH-3E target systems.
10909 @node Sparclet, Sparclite, SH, Embedded Processors
10910 @subsection Tsqware Sparclet
10914 @value{GDBN} enables developers to debug tasks running on
10915 Sparclet targets from a Unix host.
10916 @value{GDBN} uses code that runs on
10917 both the Unix host and on the Sparclet target. The program
10918 @code{@value{GDBP}} is installed and executed on the Unix host.
10921 @item timeout @var{args}
10922 @kindex remotetimeout
10923 @value{GDBN} supports the option @code{remotetimeout}.
10924 This option is set by the user, and @var{args} represents the number of
10925 seconds @value{GDBN} waits for responses.
10929 When compiling for debugging, include the options @samp{-g} to get debug
10930 information and @samp{-Ttext} to relocate the program to where you wish to
10931 load it on the target. You may also want to add the options @samp{-n} or
10932 @samp{-N} in order to reduce the size of the sections. Example:
10935 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
10938 You can use @code{objdump} to verify that the addresses are what you intended:
10941 sparclet-aout-objdump --headers --syms prog
10946 your Unix execution search path to find @value{GDBN}, you are ready to
10947 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
10948 (or @code{sparclet-aout-gdb}, depending on your installation).
10950 @value{GDBN} comes up showing the prompt:
10957 * Sparclet File:: Setting the file to debug
10958 * Sparclet Connection:: Connecting to Sparclet
10959 * Sparclet Download:: Sparclet download
10960 * Sparclet Execution:: Running and debugging
10963 @node Sparclet File, Sparclet Connection, Sparclet, Sparclet
10964 @subsubsection Setting file to debug
10966 The @value{GDBN} command @code{file} lets you choose with program to debug.
10969 (gdbslet) file prog
10973 @value{GDBN} then attempts to read the symbol table of @file{prog}.
10974 @value{GDBN} locates
10975 the file by searching the directories listed in the command search
10977 If the file was compiled with debug information (option "-g"), source
10978 files will be searched as well.
10979 @value{GDBN} locates
10980 the source files by searching the directories listed in the directory search
10981 path (@pxref{Environment, ,Your program's environment}).
10983 to find a file, it displays a message such as:
10986 prog: No such file or directory.
10989 When this happens, add the appropriate directories to the search paths with
10990 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
10991 @code{target} command again.
10993 @node Sparclet Connection, Sparclet Download, Sparclet File, Sparclet
10994 @subsubsection Connecting to Sparclet
10996 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
10997 To connect to a target on serial port ``@code{ttya}'', type:
11000 (gdbslet) target sparclet /dev/ttya
11001 Remote target sparclet connected to /dev/ttya
11002 main () at ../prog.c:3
11006 @value{GDBN} displays messages like these:
11012 @node Sparclet Download, Sparclet Execution, Sparclet Connection, Sparclet
11013 @subsubsection Sparclet download
11015 @cindex download to Sparclet
11016 Once connected to the Sparclet target,
11017 you can use the @value{GDBN}
11018 @code{load} command to download the file from the host to the target.
11019 The file name and load offset should be given as arguments to the @code{load}
11021 Since the file format is aout, the program must be loaded to the starting
11022 address. You can use @code{objdump} to find out what this value is. The load
11023 offset is an offset which is added to the VMA (virtual memory address)
11024 of each of the file's sections.
11025 For instance, if the program
11026 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
11027 and bss at 0x12010170, in @value{GDBN}, type:
11030 (gdbslet) load prog 0x12010000
11031 Loading section .text, size 0xdb0 vma 0x12010000
11034 If the code is loaded at a different address then what the program was linked
11035 to, you may need to use the @code{section} and @code{add-symbol-file} commands
11036 to tell @value{GDBN} where to map the symbol table.
11038 @node Sparclet Execution, , Sparclet Download, Sparclet
11039 @subsubsection Running and debugging
11041 @cindex running and debugging Sparclet programs
11042 You can now begin debugging the task using @value{GDBN}'s execution control
11043 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
11044 manual for the list of commands.
11048 Breakpoint 1 at 0x12010000: file prog.c, line 3.
11050 Starting program: prog
11051 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
11052 3 char *symarg = 0;
11054 4 char *execarg = "hello!";
11058 @node Sparclite, ST2000, Sparclet, Embedded Processors
11059 @subsection Fujitsu Sparclite
11063 @kindex target sparclite
11064 @item target sparclite @var{dev}
11065 Fujitsu sparclite boards, used only for the purpose of loading.
11066 You must use an additional command to debug the program.
11067 For example: target remote @var{dev} using @value{GDBN} standard
11072 @node ST2000, Z8000, Sparclite, Embedded Processors
11073 @subsection Tandem ST2000
11075 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
11078 To connect your ST2000 to the host system, see the manufacturer's
11079 manual. Once the ST2000 is physically attached, you can run:
11082 target st2000 @var{dev} @var{speed}
11086 to establish it as your debugging environment. @var{dev} is normally
11087 the name of a serial device, such as @file{/dev/ttya}, connected to the
11088 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
11089 connection (for example, to a serial line attached via a terminal
11090 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
11092 The @code{load} and @code{attach} commands are @emph{not} defined for
11093 this target; you must load your program into the ST2000 as you normally
11094 would for standalone operation. @value{GDBN} reads debugging information
11095 (such as symbols) from a separate, debugging version of the program
11096 available on your host computer.
11097 @c FIXME!! This is terribly vague; what little content is here is
11098 @c basically hearsay.
11100 @cindex ST2000 auxiliary commands
11101 These auxiliary @value{GDBN} commands are available to help you with the ST2000
11105 @item st2000 @var{command}
11106 @kindex st2000 @var{cmd}
11107 @cindex STDBUG commands (ST2000)
11108 @cindex commands to STDBUG (ST2000)
11109 Send a @var{command} to the STDBUG monitor. See the manufacturer's
11110 manual for available commands.
11113 @cindex connect (to STDBUG)
11114 Connect the controlling terminal to the STDBUG command monitor. When
11115 you are done interacting with STDBUG, typing either of two character
11116 sequences gets you back to the @value{GDBN} command prompt:
11117 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
11118 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
11121 @node Z8000, , ST2000, Embedded Processors
11122 @subsection Zilog Z8000
11125 @cindex simulator, Z8000
11126 @cindex Zilog Z8000 simulator
11128 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
11131 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
11132 unsegmented variant of the Z8000 architecture) or the Z8001 (the
11133 segmented variant). The simulator recognizes which architecture is
11134 appropriate by inspecting the object code.
11137 @item target sim @var{args}
11139 @kindex target sim@r{, with Z8000}
11140 Debug programs on a simulated CPU. If the simulator supports setup
11141 options, specify them via @var{args}.
11145 After specifying this target, you can debug programs for the simulated
11146 CPU in the same style as programs for your host computer; use the
11147 @code{file} command to load a new program image, the @code{run} command
11148 to run your program, and so on.
11150 As well as making available all the usual machine registers
11151 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
11152 additional items of information as specially named registers:
11157 Counts clock-ticks in the simulator.
11160 Counts instructions run in the simulator.
11163 Execution time in 60ths of a second.
11167 You can refer to these values in @value{GDBN} expressions with the usual
11168 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
11169 conditional breakpoint that suspends only after at least 5000
11170 simulated clock ticks.
11172 @node Architectures, , Embedded Processors, Configurations
11173 @section Architectures
11175 This section describes characteristics of architectures that affect
11176 all uses of @value{GDBN} with the architecture, both native and cross.
11184 @node A29K, Alpha, Architectures, Architectures
11189 @kindex set rstack_high_address
11190 @cindex AMD 29K register stack
11191 @cindex register stack, AMD29K
11192 @item set rstack_high_address @var{address}
11193 On AMD 29000 family processors, registers are saved in a separate
11194 @dfn{register stack}. There is no way for @value{GDBN} to determine the
11195 extent of this stack. Normally, @value{GDBN} just assumes that the
11196 stack is ``large enough''. This may result in @value{GDBN} referencing
11197 memory locations that do not exist. If necessary, you can get around
11198 this problem by specifying the ending address of the register stack with
11199 the @code{set rstack_high_address} command. The argument should be an
11200 address, which you probably want to precede with @samp{0x} to specify in
11203 @kindex show rstack_high_address
11204 @item show rstack_high_address
11205 Display the current limit of the register stack, on AMD 29000 family
11210 @node Alpha, MIPS, A29K, Architectures
11213 See the following section.
11215 @node MIPS, , Alpha, Architectures
11218 @cindex stack on Alpha
11219 @cindex stack on MIPS
11220 @cindex Alpha stack
11222 Alpha- and MIPS-based computers use an unusual stack frame, which
11223 sometimes requires @value{GDBN} to search backward in the object code to
11224 find the beginning of a function.
11226 @cindex response time, MIPS debugging
11227 To improve response time (especially for embedded applications, where
11228 @value{GDBN} may be restricted to a slow serial line for this search)
11229 you may want to limit the size of this search, using one of these
11233 @cindex @code{heuristic-fence-post} (Alpha,MIPS)
11234 @item set heuristic-fence-post @var{limit}
11235 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
11236 search for the beginning of a function. A value of @var{0} (the
11237 default) means there is no limit. However, except for @var{0}, the
11238 larger the limit the more bytes @code{heuristic-fence-post} must search
11239 and therefore the longer it takes to run.
11241 @item show heuristic-fence-post
11242 Display the current limit.
11246 These commands are available @emph{only} when @value{GDBN} is configured
11247 for debugging programs on Alpha or MIPS processors.
11250 @node Controlling GDB, Sequences, Configurations, Top
11251 @chapter Controlling @value{GDBN}
11253 You can alter the way @value{GDBN} interacts with you by using the
11254 @code{set} command. For commands controlling how @value{GDBN} displays
11255 data, see @ref{Print Settings, ,Print settings}. Other settings are
11260 * Editing:: Command editing
11261 * History:: Command history
11262 * Screen Size:: Screen size
11263 * Numbers:: Numbers
11264 * Messages/Warnings:: Optional warnings and messages
11265 * Debugging Output:: Optional messages about internal happenings
11268 @node Prompt, Editing, Controlling GDB, Controlling GDB
11273 @value{GDBN} indicates its readiness to read a command by printing a string
11274 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
11275 can change the prompt string with the @code{set prompt} command. For
11276 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
11277 the prompt in one of the @value{GDBN} sessions so that you can always tell
11278 which one you are talking to.
11280 @emph{Note:} @code{set prompt} does not add a space for you after the
11281 prompt you set. This allows you to set a prompt which ends in a space
11282 or a prompt that does not.
11286 @item set prompt @var{newprompt}
11287 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
11289 @kindex show prompt
11291 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
11294 @node Editing, History, Prompt, Controlling GDB
11295 @section Command editing
11297 @cindex command line editing
11299 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
11300 @sc{gnu} library provides consistent behavior for programs which provide a
11301 command line interface to the user. Advantages are @sc{gnu} Emacs-style
11302 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
11303 substitution, and a storage and recall of command history across
11304 debugging sessions.
11306 You may control the behavior of command line editing in @value{GDBN} with the
11307 command @code{set}.
11310 @kindex set editing
11313 @itemx set editing on
11314 Enable command line editing (enabled by default).
11316 @item set editing off
11317 Disable command line editing.
11319 @kindex show editing
11321 Show whether command line editing is enabled.
11324 @node History, Screen Size, Editing, Controlling GDB
11325 @section Command history
11327 @value{GDBN} can keep track of the commands you type during your
11328 debugging sessions, so that you can be certain of precisely what
11329 happened. Use these commands to manage the @value{GDBN} command
11333 @cindex history substitution
11334 @cindex history file
11335 @kindex set history filename
11336 @kindex GDBHISTFILE
11337 @item set history filename @var{fname}
11338 Set the name of the @value{GDBN} command history file to @var{fname}.
11339 This is the file where @value{GDBN} reads an initial command history
11340 list, and where it writes the command history from this session when it
11341 exits. You can access this list through history expansion or through
11342 the history command editing characters listed below. This file defaults
11343 to the value of the environment variable @code{GDBHISTFILE}, or to
11344 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
11347 @cindex history save
11348 @kindex set history save
11349 @item set history save
11350 @itemx set history save on
11351 Record command history in a file, whose name may be specified with the
11352 @code{set history filename} command. By default, this option is disabled.
11354 @item set history save off
11355 Stop recording command history in a file.
11357 @cindex history size
11358 @kindex set history size
11359 @item set history size @var{size}
11360 Set the number of commands which @value{GDBN} keeps in its history list.
11361 This defaults to the value of the environment variable
11362 @code{HISTSIZE}, or to 256 if this variable is not set.
11365 @cindex history expansion
11366 History expansion assigns special meaning to the character @kbd{!}.
11367 @ifset have-readline-appendices
11368 @xref{Event Designators}.
11371 Since @kbd{!} is also the logical not operator in C, history expansion
11372 is off by default. If you decide to enable history expansion with the
11373 @code{set history expansion on} command, you may sometimes need to
11374 follow @kbd{!} (when it is used as logical not, in an expression) with
11375 a space or a tab to prevent it from being expanded. The readline
11376 history facilities do not attempt substitution on the strings
11377 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
11379 The commands to control history expansion are:
11382 @kindex set history expansion
11383 @item set history expansion on
11384 @itemx set history expansion
11385 Enable history expansion. History expansion is off by default.
11387 @item set history expansion off
11388 Disable history expansion.
11390 The readline code comes with more complete documentation of
11391 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
11392 or @code{vi} may wish to read it.
11393 @ifset have-readline-appendices
11394 @xref{Command Line Editing}.
11398 @kindex show history
11400 @itemx show history filename
11401 @itemx show history save
11402 @itemx show history size
11403 @itemx show history expansion
11404 These commands display the state of the @value{GDBN} history parameters.
11405 @code{show history} by itself displays all four states.
11410 @kindex show commands
11411 @item show commands
11412 Display the last ten commands in the command history.
11414 @item show commands @var{n}
11415 Print ten commands centered on command number @var{n}.
11417 @item show commands +
11418 Print ten commands just after the commands last printed.
11421 @node Screen Size, Numbers, History, Controlling GDB
11422 @section Screen size
11423 @cindex size of screen
11424 @cindex pauses in output
11426 Certain commands to @value{GDBN} may produce large amounts of
11427 information output to the screen. To help you read all of it,
11428 @value{GDBN} pauses and asks you for input at the end of each page of
11429 output. Type @key{RET} when you want to continue the output, or @kbd{q}
11430 to discard the remaining output. Also, the screen width setting
11431 determines when to wrap lines of output. Depending on what is being
11432 printed, @value{GDBN} tries to break the line at a readable place,
11433 rather than simply letting it overflow onto the following line.
11435 Normally @value{GDBN} knows the size of the screen from the terminal
11436 driver software. For example, on Unix @value{GDBN} uses the termcap data base
11437 together with the value of the @code{TERM} environment variable and the
11438 @code{stty rows} and @code{stty cols} settings. If this is not correct,
11439 you can override it with the @code{set height} and @code{set
11446 @kindex show height
11447 @item set height @var{lpp}
11449 @itemx set width @var{cpl}
11451 These @code{set} commands specify a screen height of @var{lpp} lines and
11452 a screen width of @var{cpl} characters. The associated @code{show}
11453 commands display the current settings.
11455 If you specify a height of zero lines, @value{GDBN} does not pause during
11456 output no matter how long the output is. This is useful if output is to a
11457 file or to an editor buffer.
11459 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
11460 from wrapping its output.
11463 @node Numbers, Messages/Warnings, Screen Size, Controlling GDB
11465 @cindex number representation
11466 @cindex entering numbers
11468 You can always enter numbers in octal, decimal, or hexadecimal in
11469 @value{GDBN} by the usual conventions: octal numbers begin with
11470 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
11471 begin with @samp{0x}. Numbers that begin with none of these are, by
11472 default, entered in base 10; likewise, the default display for
11473 numbers---when no particular format is specified---is base 10. You can
11474 change the default base for both input and output with the @code{set
11478 @kindex set input-radix
11479 @item set input-radix @var{base}
11480 Set the default base for numeric input. Supported choices
11481 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
11482 specified either unambiguously or using the current default radix; for
11492 sets the base to decimal. On the other hand, @samp{set radix 10}
11493 leaves the radix unchanged no matter what it was.
11495 @kindex set output-radix
11496 @item set output-radix @var{base}
11497 Set the default base for numeric display. Supported choices
11498 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
11499 specified either unambiguously or using the current default radix.
11501 @kindex show input-radix
11502 @item show input-radix
11503 Display the current default base for numeric input.
11505 @kindex show output-radix
11506 @item show output-radix
11507 Display the current default base for numeric display.
11510 @node Messages/Warnings, Debugging Output , Numbers, Controlling GDB
11511 @section Optional warnings and messages
11513 By default, @value{GDBN} is silent about its inner workings. If you are
11514 running on a slow machine, you may want to use the @code{set verbose}
11515 command. This makes @value{GDBN} tell you when it does a lengthy
11516 internal operation, so you will not think it has crashed.
11518 Currently, the messages controlled by @code{set verbose} are those
11519 which announce that the symbol table for a source file is being read;
11520 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
11523 @kindex set verbose
11524 @item set verbose on
11525 Enables @value{GDBN} output of certain informational messages.
11527 @item set verbose off
11528 Disables @value{GDBN} output of certain informational messages.
11530 @kindex show verbose
11532 Displays whether @code{set verbose} is on or off.
11535 By default, if @value{GDBN} encounters bugs in the symbol table of an
11536 object file, it is silent; but if you are debugging a compiler, you may
11537 find this information useful (@pxref{Symbol Errors, ,Errors reading
11542 @kindex set complaints
11543 @item set complaints @var{limit}
11544 Permits @value{GDBN} to output @var{limit} complaints about each type of
11545 unusual symbols before becoming silent about the problem. Set
11546 @var{limit} to zero to suppress all complaints; set it to a large number
11547 to prevent complaints from being suppressed.
11549 @kindex show complaints
11550 @item show complaints
11551 Displays how many symbol complaints @value{GDBN} is permitted to produce.
11555 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
11556 lot of stupid questions to confirm certain commands. For example, if
11557 you try to run a program which is already running:
11561 The program being debugged has been started already.
11562 Start it from the beginning? (y or n)
11565 If you are willing to unflinchingly face the consequences of your own
11566 commands, you can disable this ``feature'':
11570 @kindex set confirm
11572 @cindex confirmation
11573 @cindex stupid questions
11574 @item set confirm off
11575 Disables confirmation requests.
11577 @item set confirm on
11578 Enables confirmation requests (the default).
11580 @kindex show confirm
11582 Displays state of confirmation requests.
11586 @node Debugging Output, ,Messages/Warnings, Controlling GDB
11587 @section Optional messages about internal happenings
11589 @kindex set debug arch
11590 @item set debug arch
11591 Turns on or off display of gdbarch debugging info. The default is off
11592 @kindex show debug arch
11593 @item show debug arch
11594 Displays the current state of displaying gdbarch debugging info.
11595 @kindex set debug event
11596 @item set debug event
11597 Turns on or off display of @value{GDBN} event debugging info. The
11599 @kindex show debug event
11600 @item show debug event
11601 Displays the current state of displaying @value{GDBN} event debugging
11603 @kindex set debug expression
11604 @item set debug expression
11605 Turns on or off display of @value{GDBN} expression debugging info. The
11607 @kindex show debug expression
11608 @item show debug expression
11609 Displays the current state of displaying @value{GDBN} expression
11611 @kindex set debug overload
11612 @item set debug overload
11613 Turns on or off display of @value{GDBN} C++ overload debugging
11614 info. This includes info such as ranking of functions, etc. The default
11616 @kindex show debug overload
11617 @item show debug overload
11618 Displays the current state of displaying @value{GDBN} C++ overload
11620 @kindex set debug remote
11621 @cindex packets, reporting on stdout
11622 @cindex serial connections, debugging
11623 @item set debug remote
11624 Turns on or off display of reports on all packets sent back and forth across
11625 the serial line to the remote machine. The info is printed on the
11626 @value{GDBN} standard output stream. The default is off.
11627 @kindex show debug remote
11628 @item show debug remote
11629 Displays the state of display of remote packets.
11630 @kindex set debug serial
11631 @item set debug serial
11632 Turns on or off display of @value{GDBN} serial debugging info. The
11634 @kindex show debug serial
11635 @item show debug serial
11636 Displays the current state of displaying @value{GDBN} serial debugging
11638 @kindex set debug target
11639 @item set debug target
11640 Turns on or off display of @value{GDBN} target debugging info. This info
11641 includes what is going on at the target level of GDB, as it happens. The
11643 @kindex show debug target
11644 @item show debug target
11645 Displays the current state of displaying @value{GDBN} target debugging
11647 @kindex set debug varobj
11648 @item set debug varobj
11649 Turns on or off display of @value{GDBN} variable object debugging
11650 info. The default is off.
11651 @kindex show debug varobj
11652 @item show debug varobj
11653 Displays the current state of displaying @value{GDBN} variable object
11657 @node Sequences, Emacs, Controlling GDB, Top
11658 @chapter Canned Sequences of Commands
11660 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
11661 command lists}), @value{GDBN} provides two ways to store sequences of
11662 commands for execution as a unit: user-defined commands and command
11666 * Define:: User-defined commands
11667 * Hooks:: User-defined command hooks
11668 * Command Files:: Command files
11669 * Output:: Commands for controlled output
11672 @node Define, Hooks, Sequences, Sequences
11673 @section User-defined commands
11675 @cindex user-defined command
11676 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
11677 which you assign a new name as a command. This is done with the
11678 @code{define} command. User commands may accept up to 10 arguments
11679 separated by whitespace. Arguments are accessed within the user command
11680 via @var{$arg0@dots{}$arg9}. A trivial example:
11684 print $arg0 + $arg1 + $arg2
11688 To execute the command use:
11695 This defines the command @code{adder}, which prints the sum of
11696 its three arguments. Note the arguments are text substitutions, so they may
11697 reference variables, use complex expressions, or even perform inferior
11703 @item define @var{commandname}
11704 Define a command named @var{commandname}. If there is already a command
11705 by that name, you are asked to confirm that you want to redefine it.
11707 The definition of the command is made up of other @value{GDBN} command lines,
11708 which are given following the @code{define} command. The end of these
11709 commands is marked by a line containing @code{end}.
11714 Takes a single argument, which is an expression to evaluate.
11715 It is followed by a series of commands that are executed
11716 only if the expression is true (nonzero).
11717 There can then optionally be a line @code{else}, followed
11718 by a series of commands that are only executed if the expression
11719 was false. The end of the list is marked by a line containing @code{end}.
11723 The syntax is similar to @code{if}: the command takes a single argument,
11724 which is an expression to evaluate, and must be followed by the commands to
11725 execute, one per line, terminated by an @code{end}.
11726 The commands are executed repeatedly as long as the expression
11730 @item document @var{commandname}
11731 Document the user-defined command @var{commandname}, so that it can be
11732 accessed by @code{help}. The command @var{commandname} must already be
11733 defined. This command reads lines of documentation just as @code{define}
11734 reads the lines of the command definition, ending with @code{end}.
11735 After the @code{document} command is finished, @code{help} on command
11736 @var{commandname} displays the documentation you have written.
11738 You may use the @code{document} command again to change the
11739 documentation of a command. Redefining the command with @code{define}
11740 does not change the documentation.
11742 @kindex help user-defined
11743 @item help user-defined
11744 List all user-defined commands, with the first line of the documentation
11749 @itemx show user @var{commandname}
11750 Display the @value{GDBN} commands used to define @var{commandname} (but
11751 not its documentation). If no @var{commandname} is given, display the
11752 definitions for all user-defined commands.
11756 When user-defined commands are executed, the
11757 commands of the definition are not printed. An error in any command
11758 stops execution of the user-defined command.
11760 If used interactively, commands that would ask for confirmation proceed
11761 without asking when used inside a user-defined command. Many @value{GDBN}
11762 commands that normally print messages to say what they are doing omit the
11763 messages when used in a user-defined command.
11765 @node Hooks, Command Files, Define, Sequences
11766 @section User-defined command hooks
11767 @cindex command hooks
11768 @cindex hooks, for commands
11770 You may define @emph{hooks}, which are a special kind of user-defined
11771 command. Whenever you run the command @samp{foo}, if the user-defined
11772 command @samp{hook-foo} exists, it is executed (with no arguments)
11773 before that command.
11775 @kindex stop@r{, a pseudo-command}
11776 In addition, a pseudo-command, @samp{stop} exists. Defining
11777 (@samp{hook-stop}) makes the associated commands execute every time
11778 execution stops in your program: before breakpoint commands are run,
11779 displays are printed, or the stack frame is printed.
11781 For example, to ignore @code{SIGALRM} signals while
11782 single-stepping, but treat them normally during normal execution,
11787 handle SIGALRM nopass
11791 handle SIGALRM pass
11794 define hook-continue
11795 handle SIGLARM pass
11799 You can define a hook for any single-word command in @value{GDBN}, but
11800 not for command aliases; you should define a hook for the basic command
11801 name, e.g. @code{backtrace} rather than @code{bt}.
11802 @c FIXME! So how does Joe User discover whether a command is an alias
11804 If an error occurs during the execution of your hook, execution of
11805 @value{GDBN} commands stops and @value{GDBN} issues a prompt
11806 (before the command that you actually typed had a chance to run).
11808 If you try to define a hook which does not match any known command, you
11809 get a warning from the @code{define} command.
11811 @node Command Files, Output, Hooks, Sequences
11812 @section Command files
11814 @cindex command files
11815 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
11816 commands. Comments (lines starting with @kbd{#}) may also be included.
11817 An empty line in a command file does nothing; it does not mean to repeat
11818 the last command, as it would from the terminal.
11821 @cindex @file{.gdbinit}
11822 @cindex @file{gdb.ini}
11823 When you start @value{GDBN}, it automatically executes commands from its
11824 @dfn{init files}. These are files named @file{.gdbinit} on Unix, or
11825 @file{gdb.ini} on DOS/Windows. @value{GDBN} reads the init file (if
11826 any) in your home directory@footnote{On DOS/Windows systems, the home
11827 directory is the one pointed to by the @code{HOME} environment
11828 variable.}, then processes command line options and operands, and then
11829 reads the init file (if any) in the current working directory. This is
11830 so the init file in your home directory can set options (such as
11831 @code{set complaints}) which affect the processing of the command line
11832 options and operands. The init files are not executed if you use the
11833 @samp{-nx} option; @pxref{Mode Options, ,Choosing modes}.
11835 @cindex init file name
11836 On some configurations of @value{GDBN}, the init file is known by a
11837 different name (these are typically environments where a specialized
11838 form of @value{GDBN} may need to coexist with other forms, hence a
11839 different name for the specialized version's init file). These are the
11840 environments with special init file names:
11845 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
11847 @kindex .os68gdbinit
11849 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
11853 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
11856 You can also request the execution of a command file with the
11857 @code{source} command:
11861 @item source @var{filename}
11862 Execute the command file @var{filename}.
11865 The lines in a command file are executed sequentially. They are not
11866 printed as they are executed. An error in any command terminates execution
11867 of the command file.
11869 Commands that would ask for confirmation if used interactively proceed
11870 without asking when used in a command file. Many @value{GDBN} commands that
11871 normally print messages to say what they are doing omit the messages
11872 when called from command files.
11874 @node Output, , Command Files, Sequences
11875 @section Commands for controlled output
11877 During the execution of a command file or a user-defined command, normal
11878 @value{GDBN} output is suppressed; the only output that appears is what is
11879 explicitly printed by the commands in the definition. This section
11880 describes three commands useful for generating exactly the output you
11885 @item echo @var{text}
11886 @c I do not consider backslash-space a standard C escape sequence
11887 @c because it is not in ANSI.
11888 Print @var{text}. Nonprinting characters can be included in
11889 @var{text} using C escape sequences, such as @samp{\n} to print a
11890 newline. @strong{No newline is printed unless you specify one.}
11891 In addition to the standard C escape sequences, a backslash followed
11892 by a space stands for a space. This is useful for displaying a
11893 string with spaces at the beginning or the end, since leading and
11894 trailing spaces are otherwise trimmed from all arguments.
11895 To print @samp{@w{ }and foo =@w{ }}, use the command
11896 @samp{echo \@w{ }and foo = \@w{ }}.
11898 A backslash at the end of @var{text} can be used, as in C, to continue
11899 the command onto subsequent lines. For example,
11902 echo This is some text\n\
11903 which is continued\n\
11904 onto several lines.\n
11907 produces the same output as
11910 echo This is some text\n
11911 echo which is continued\n
11912 echo onto several lines.\n
11916 @item output @var{expression}
11917 Print the value of @var{expression} and nothing but that value: no
11918 newlines, no @samp{$@var{nn} = }. The value is not entered in the
11919 value history either. @xref{Expressions, ,Expressions}, for more information
11922 @item output/@var{fmt} @var{expression}
11923 Print the value of @var{expression} in format @var{fmt}. You can use
11924 the same formats as for @code{print}. @xref{Output Formats,,Output
11925 formats}, for more information.
11928 @item printf @var{string}, @var{expressions}@dots{}
11929 Print the values of the @var{expressions} under the control of
11930 @var{string}. The @var{expressions} are separated by commas and may be
11931 either numbers or pointers. Their values are printed as specified by
11932 @var{string}, exactly as if your program were to execute the C
11934 @c FIXME: the above implies that at least all ANSI C formats are
11935 @c supported, but it isn't true: %E and %G don't work (or so it seems).
11936 @c Either this is a bug, or the manual should document what formats are
11940 printf (@var{string}, @var{expressions}@dots{});
11943 For example, you can print two values in hex like this:
11946 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
11949 The only backslash-escape sequences that you can use in the format
11950 string are the simple ones that consist of backslash followed by a
11954 @node Emacs, Annotations, Sequences, Top
11955 @chapter Using @value{GDBN} under @sc{gnu} Emacs
11958 @cindex @sc{gnu} Emacs
11959 A special interface allows you to use @sc{gnu} Emacs to view (and
11960 edit) the source files for the program you are debugging with
11963 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
11964 executable file you want to debug as an argument. This command starts
11965 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
11966 created Emacs buffer.
11967 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
11969 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
11974 All ``terminal'' input and output goes through the Emacs buffer.
11977 This applies both to @value{GDBN} commands and their output, and to the input
11978 and output done by the program you are debugging.
11980 This is useful because it means that you can copy the text of previous
11981 commands and input them again; you can even use parts of the output
11984 All the facilities of Emacs' Shell mode are available for interacting
11985 with your program. In particular, you can send signals the usual
11986 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
11991 @value{GDBN} displays source code through Emacs.
11994 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
11995 source file for that frame and puts an arrow (@samp{=>}) at the
11996 left margin of the current line. Emacs uses a separate buffer for
11997 source display, and splits the screen to show both your @value{GDBN} session
12000 Explicit @value{GDBN} @code{list} or search commands still produce output as
12001 usual, but you probably have no reason to use them from Emacs.
12004 @emph{Warning:} If the directory where your program resides is not your
12005 current directory, it can be easy to confuse Emacs about the location of
12006 the source files, in which case the auxiliary display buffer does not
12007 appear to show your source. @value{GDBN} can find programs by searching your
12008 environment's @code{PATH} variable, so the @value{GDBN} input and output
12009 session proceeds normally; but Emacs does not get enough information
12010 back from @value{GDBN} to locate the source files in this situation. To
12011 avoid this problem, either start @value{GDBN} mode from the directory where
12012 your program resides, or specify an absolute file name when prompted for the
12013 @kbd{M-x gdb} argument.
12015 A similar confusion can result if you use the @value{GDBN} @code{file} command to
12016 switch to debugging a program in some other location, from an existing
12017 @value{GDBN} buffer in Emacs.
12020 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
12021 you need to call @value{GDBN} by a different name (for example, if you keep
12022 several configurations around, with different names) you can set the
12023 Emacs variable @code{gdb-command-name}; for example,
12026 (setq gdb-command-name "mygdb")
12030 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
12031 in your @file{.emacs} file) makes Emacs call the program named
12032 ``@code{mygdb}'' instead.
12034 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
12035 addition to the standard Shell mode commands:
12039 Describe the features of Emacs' @value{GDBN} Mode.
12042 Execute to another source line, like the @value{GDBN} @code{step} command; also
12043 update the display window to show the current file and location.
12046 Execute to next source line in this function, skipping all function
12047 calls, like the @value{GDBN} @code{next} command. Then update the display window
12048 to show the current file and location.
12051 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
12052 display window accordingly.
12054 @item M-x gdb-nexti
12055 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
12056 display window accordingly.
12059 Execute until exit from the selected stack frame, like the @value{GDBN}
12060 @code{finish} command.
12063 Continue execution of your program, like the @value{GDBN} @code{continue}
12066 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
12069 Go up the number of frames indicated by the numeric argument
12070 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
12071 like the @value{GDBN} @code{up} command.
12073 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
12076 Go down the number of frames indicated by the numeric argument, like the
12077 @value{GDBN} @code{down} command.
12079 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
12082 Read the number where the cursor is positioned, and insert it at the end
12083 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
12084 around an address that was displayed earlier, type @kbd{disassemble};
12085 then move the cursor to the address display, and pick up the
12086 argument for @code{disassemble} by typing @kbd{C-x &}.
12088 You can customize this further by defining elements of the list
12089 @code{gdb-print-command}; once it is defined, you can format or
12090 otherwise process numbers picked up by @kbd{C-x &} before they are
12091 inserted. A numeric argument to @kbd{C-x &} indicates that you
12092 wish special formatting, and also acts as an index to pick an element of the
12093 list. If the list element is a string, the number to be inserted is
12094 formatted using the Emacs function @code{format}; otherwise the number
12095 is passed as an argument to the corresponding list element.
12098 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
12099 tells @value{GDBN} to set a breakpoint on the source line point is on.
12101 If you accidentally delete the source-display buffer, an easy way to get
12102 it back is to type the command @code{f} in the @value{GDBN} buffer, to
12103 request a frame display; when you run under Emacs, this recreates
12104 the source buffer if necessary to show you the context of the current
12107 The source files displayed in Emacs are in ordinary Emacs buffers
12108 which are visiting the source files in the usual way. You can edit
12109 the files with these buffers if you wish; but keep in mind that @value{GDBN}
12110 communicates with Emacs in terms of line numbers. If you add or
12111 delete lines from the text, the line numbers that @value{GDBN} knows cease
12112 to correspond properly with the code.
12114 @c The following dropped because Epoch is nonstandard. Reactivate
12115 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
12117 @kindex Emacs Epoch environment
12121 Version 18 of @sc{gnu} Emacs has a built-in window system
12122 called the @code{epoch}
12123 environment. Users of this environment can use a new command,
12124 @code{inspect} which performs identically to @code{print} except that
12125 each value is printed in its own window.
12128 @node Annotations, GDB Bugs, Emacs, Top
12129 @chapter @value{GDBN} Annotations
12130 @include annotate.texi
12132 @node GDB Bugs, Command Line Editing, Annotations, Top
12133 @chapter Reporting Bugs in @value{GDBN}
12134 @cindex bugs in @value{GDBN}
12135 @cindex reporting bugs in @value{GDBN}
12137 Your bug reports play an essential role in making @value{GDBN} reliable.
12139 Reporting a bug may help you by bringing a solution to your problem, or it
12140 may not. But in any case the principal function of a bug report is to help
12141 the entire community by making the next version of @value{GDBN} work better. Bug
12142 reports are your contribution to the maintenance of @value{GDBN}.
12144 In order for a bug report to serve its purpose, you must include the
12145 information that enables us to fix the bug.
12148 * Bug Criteria:: Have you found a bug?
12149 * Bug Reporting:: How to report bugs
12152 @node Bug Criteria, Bug Reporting, GDB Bugs, GDB Bugs
12153 @section Have you found a bug?
12154 @cindex bug criteria
12156 If you are not sure whether you have found a bug, here are some guidelines:
12159 @cindex fatal signal
12160 @cindex debugger crash
12161 @cindex crash of debugger
12163 If the debugger gets a fatal signal, for any input whatever, that is a
12164 @value{GDBN} bug. Reliable debuggers never crash.
12166 @cindex error on valid input
12168 If @value{GDBN} produces an error message for valid input, that is a
12169 bug. (Note that if you're cross debugging, the problem may also be
12170 somewhere in the connection to the target.)
12172 @cindex invalid input
12174 If @value{GDBN} does not produce an error message for invalid input,
12175 that is a bug. However, you should note that your idea of
12176 ``invalid input'' might be our idea of ``an extension'' or ``support
12177 for traditional practice''.
12180 If you are an experienced user of debugging tools, your suggestions
12181 for improvement of @value{GDBN} are welcome in any case.
12184 @node Bug Reporting, , Bug Criteria, GDB Bugs
12185 @section How to report bugs
12186 @cindex bug reports
12187 @cindex @value{GDBN} bugs, reporting
12189 A number of companies and individuals offer support for @sc{gnu} products.
12190 If you obtained @value{GDBN} from a support organization, we recommend you
12191 contact that organization first.
12193 You can find contact information for many support companies and
12194 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
12196 @c should add a web page ref...
12198 In any event, we also recommend that you send bug reports for
12199 @value{GDBN} to this addresses:
12205 @strong{Do not send bug reports to @samp{info-gdb}, or to
12206 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
12207 not want to receive bug reports. Those that do have arranged to receive
12210 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
12211 serves as a repeater. The mailing list and the newsgroup carry exactly
12212 the same messages. Often people think of posting bug reports to the
12213 newsgroup instead of mailing them. This appears to work, but it has one
12214 problem which can be crucial: a newsgroup posting often lacks a mail
12215 path back to the sender. Thus, if we need to ask for more information,
12216 we may be unable to reach you. For this reason, it is better to send
12217 bug reports to the mailing list.
12219 As a last resort, send bug reports on paper to:
12222 @sc{gnu} Debugger Bugs
12223 Free Software Foundation Inc.
12224 59 Temple Place - Suite 330
12225 Boston, MA 02111-1307
12229 The fundamental principle of reporting bugs usefully is this:
12230 @strong{report all the facts}. If you are not sure whether to state a
12231 fact or leave it out, state it!
12233 Often people omit facts because they think they know what causes the
12234 problem and assume that some details do not matter. Thus, you might
12235 assume that the name of the variable you use in an example does not matter.
12236 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
12237 stray memory reference which happens to fetch from the location where that
12238 name is stored in memory; perhaps, if the name were different, the contents
12239 of that location would fool the debugger into doing the right thing despite
12240 the bug. Play it safe and give a specific, complete example. That is the
12241 easiest thing for you to do, and the most helpful.
12243 Keep in mind that the purpose of a bug report is to enable us to fix the
12244 bug. It may be that the bug has been reported previously, but neither
12245 you nor we can know that unless your bug report is complete and
12248 Sometimes people give a few sketchy facts and ask, ``Does this ring a
12249 bell?'' Those bug reports are useless, and we urge everyone to
12250 @emph{refuse to respond to them} except to chide the sender to report
12253 To enable us to fix the bug, you should include all these things:
12257 The version of @value{GDBN}. @value{GDBN} announces it if you start
12258 with no arguments; you can also print it at any time using @code{show
12261 Without this, we will not know whether there is any point in looking for
12262 the bug in the current version of @value{GDBN}.
12265 The type of machine you are using, and the operating system name and
12269 What compiler (and its version) was used to compile @value{GDBN}---e.g.
12270 ``@value{GCC}--2.8.1''.
12273 What compiler (and its version) was used to compile the program you are
12274 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
12275 C Compiler''. For GCC, you can say @code{gcc --version} to get this
12276 information; for other compilers, see the documentation for those
12280 The command arguments you gave the compiler to compile your example and
12281 observe the bug. For example, did you use @samp{-O}? To guarantee
12282 you will not omit something important, list them all. A copy of the
12283 Makefile (or the output from make) is sufficient.
12285 If we were to try to guess the arguments, we would probably guess wrong
12286 and then we might not encounter the bug.
12289 A complete input script, and all necessary source files, that will
12293 A description of what behavior you observe that you believe is
12294 incorrect. For example, ``It gets a fatal signal.''
12296 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
12297 will certainly notice it. But if the bug is incorrect output, we might
12298 not notice unless it is glaringly wrong. You might as well not give us
12299 a chance to make a mistake.
12301 Even if the problem you experience is a fatal signal, you should still
12302 say so explicitly. Suppose something strange is going on, such as, your
12303 copy of @value{GDBN} is out of synch, or you have encountered a bug in
12304 the C library on your system. (This has happened!) Your copy might
12305 crash and ours would not. If you told us to expect a crash, then when
12306 ours fails to crash, we would know that the bug was not happening for
12307 us. If you had not told us to expect a crash, then we would not be able
12308 to draw any conclusion from our observations.
12311 If you wish to suggest changes to the @value{GDBN} source, send us context
12312 diffs. If you even discuss something in the @value{GDBN} source, refer to
12313 it by context, not by line number.
12315 The line numbers in our development sources will not match those in your
12316 sources. Your line numbers would convey no useful information to us.
12320 Here are some things that are not necessary:
12324 A description of the envelope of the bug.
12326 Often people who encounter a bug spend a lot of time investigating
12327 which changes to the input file will make the bug go away and which
12328 changes will not affect it.
12330 This is often time consuming and not very useful, because the way we
12331 will find the bug is by running a single example under the debugger
12332 with breakpoints, not by pure deduction from a series of examples.
12333 We recommend that you save your time for something else.
12335 Of course, if you can find a simpler example to report @emph{instead}
12336 of the original one, that is a convenience for us. Errors in the
12337 output will be easier to spot, running under the debugger will take
12338 less time, and so on.
12340 However, simplification is not vital; if you do not want to do this,
12341 report the bug anyway and send us the entire test case you used.
12344 A patch for the bug.
12346 A patch for the bug does help us if it is a good one. But do not omit
12347 the necessary information, such as the test case, on the assumption that
12348 a patch is all we need. We might see problems with your patch and decide
12349 to fix the problem another way, or we might not understand it at all.
12351 Sometimes with a program as complicated as @value{GDBN} it is very hard to
12352 construct an example that will make the program follow a certain path
12353 through the code. If you do not send us the example, we will not be able
12354 to construct one, so we will not be able to verify that the bug is fixed.
12356 And if we cannot understand what bug you are trying to fix, or why your
12357 patch should be an improvement, we will not install it. A test case will
12358 help us to understand.
12361 A guess about what the bug is or what it depends on.
12363 Such guesses are usually wrong. Even we cannot guess right about such
12364 things without first using the debugger to find the facts.
12367 @c The readline documentation is distributed with the readline code
12368 @c and consists of the two following files:
12370 @c inc-hist.texinfo
12371 @c Use -I with makeinfo to point to the appropriate directory,
12372 @c environment var TEXINPUTS with TeX.
12374 @node Command Line Editing, Using History Interactively, GDB Bugs, Top
12375 @chapter Command Line Editing
12376 @include rluser.texinfo
12379 @node Using History Interactively, Formatting Documentation, Command Line Editing, Top
12380 @chapter Using History Interactively
12381 @include inc-hist.texinfo
12384 @node Formatting Documentation, Installing GDB, Using History Interactively, Top
12385 @appendix Formatting Documentation
12387 @cindex @value{GDBN} reference card
12388 @cindex reference card
12389 The @value{GDBN} 4 release includes an already-formatted reference card, ready
12390 for printing with PostScript or Ghostscript, in the @file{gdb}
12391 subdirectory of the main source directory@footnote{In
12392 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
12393 release.}. If you can use PostScript or Ghostscript with your printer,
12394 you can print the reference card immediately with @file{refcard.ps}.
12396 The release also includes the source for the reference card. You
12397 can format it, using @TeX{}, by typing:
12403 The @value{GDBN} reference card is designed to print in @dfn{landscape}
12404 mode on US ``letter'' size paper;
12405 that is, on a sheet 11 inches wide by 8.5 inches
12406 high. You will need to specify this form of printing as an option to
12407 your @sc{dvi} output program.
12409 @cindex documentation
12411 All the documentation for @value{GDBN} comes as part of the machine-readable
12412 distribution. The documentation is written in Texinfo format, which is
12413 a documentation system that uses a single source file to produce both
12414 on-line information and a printed manual. You can use one of the Info
12415 formatting commands to create the on-line version of the documentation
12416 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
12418 @value{GDBN} includes an already formatted copy of the on-line Info
12419 version of this manual in the @file{gdb} subdirectory. The main Info
12420 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
12421 subordinate files matching @samp{gdb.info*} in the same directory. If
12422 necessary, you can print out these files, or read them with any editor;
12423 but they are easier to read using the @code{info} subsystem in @sc{gnu}
12424 Emacs or the standalone @code{info} program, available as part of the
12425 @sc{gnu} Texinfo distribution.
12427 If you want to format these Info files yourself, you need one of the
12428 Info formatting programs, such as @code{texinfo-format-buffer} or
12431 If you have @code{makeinfo} installed, and are in the top level
12432 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
12433 version @value{GDBVN}), you can make the Info file by typing:
12440 If you want to typeset and print copies of this manual, you need @TeX{},
12441 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
12442 Texinfo definitions file.
12444 @TeX{} is a typesetting program; it does not print files directly, but
12445 produces output files called @sc{dvi} files. To print a typeset
12446 document, you need a program to print @sc{dvi} files. If your system
12447 has @TeX{} installed, chances are it has such a program. The precise
12448 command to use depends on your system; @kbd{lpr -d} is common; another
12449 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
12450 require a file name without any extension or a @samp{.dvi} extension.
12452 @TeX{} also requires a macro definitions file called
12453 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
12454 written in Texinfo format. On its own, @TeX{} cannot either read or
12455 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
12456 and is located in the @file{gdb-@var{version-number}/texinfo}
12459 If you have @TeX{} and a @sc{dvi} printer program installed, you can
12460 typeset and print this manual. First switch to the the @file{gdb}
12461 subdirectory of the main source directory (for example, to
12462 @file{gdb-@value{GDBVN}/gdb}) and type:
12468 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
12470 @node Installing GDB, Index, Formatting Documentation, Top
12471 @appendix Installing @value{GDBN}
12472 @cindex configuring @value{GDBN}
12473 @cindex installation
12475 @value{GDBN} comes with a @code{configure} script that automates the process
12476 of preparing @value{GDBN} for installation; you can then use @code{make} to
12477 build the @code{gdb} program.
12479 @c irrelevant in info file; it's as current as the code it lives with.
12480 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
12481 look at the @file{README} file in the sources; we may have improved the
12482 installation procedures since publishing this manual.}
12485 The @value{GDBN} distribution includes all the source code you need for
12486 @value{GDBN} in a single directory, whose name is usually composed by
12487 appending the version number to @samp{gdb}.
12489 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
12490 @file{gdb-@value{GDBVN}} directory. That directory contains:
12493 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
12494 script for configuring @value{GDBN} and all its supporting libraries
12496 @item gdb-@value{GDBVN}/gdb
12497 the source specific to @value{GDBN} itself
12499 @item gdb-@value{GDBVN}/bfd
12500 source for the Binary File Descriptor library
12502 @item gdb-@value{GDBVN}/include
12503 @sc{gnu} include files
12505 @item gdb-@value{GDBVN}/libiberty
12506 source for the @samp{-liberty} free software library
12508 @item gdb-@value{GDBVN}/opcodes
12509 source for the library of opcode tables and disassemblers
12511 @item gdb-@value{GDBVN}/readline
12512 source for the @sc{gnu} command-line interface
12514 @item gdb-@value{GDBVN}/glob
12515 source for the @sc{gnu} filename pattern-matching subroutine
12517 @item gdb-@value{GDBVN}/mmalloc
12518 source for the @sc{gnu} memory-mapped malloc package
12521 The simplest way to configure and build @value{GDBN} is to run @code{configure}
12522 from the @file{gdb-@var{version-number}} source directory, which in
12523 this example is the @file{gdb-@value{GDBVN}} directory.
12525 First switch to the @file{gdb-@var{version-number}} source directory
12526 if you are not already in it; then run @code{configure}. Pass the
12527 identifier for the platform on which @value{GDBN} will run as an
12533 cd gdb-@value{GDBVN}
12534 ./configure @var{host}
12539 where @var{host} is an identifier such as @samp{sun4} or
12540 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
12541 (You can often leave off @var{host}; @code{configure} tries to guess the
12542 correct value by examining your system.)
12544 Running @samp{configure @var{host}} and then running @code{make} builds the
12545 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
12546 libraries, then @code{gdb} itself. The configured source files, and the
12547 binaries, are left in the corresponding source directories.
12550 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
12551 system does not recognize this automatically when you run a different
12552 shell, you may need to run @code{sh} on it explicitly:
12555 sh configure @var{host}
12558 If you run @code{configure} from a directory that contains source
12559 directories for multiple libraries or programs, such as the
12560 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
12561 creates configuration files for every directory level underneath (unless
12562 you tell it not to, with the @samp{--norecursion} option).
12564 You can run the @code{configure} script from any of the
12565 subordinate directories in the @value{GDBN} distribution if you only want to
12566 configure that subdirectory, but be sure to specify a path to it.
12568 For example, with version @value{GDBVN}, type the following to configure only
12569 the @code{bfd} subdirectory:
12573 cd gdb-@value{GDBVN}/bfd
12574 ../configure @var{host}
12578 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
12579 However, you should make sure that the shell on your path (named by
12580 the @samp{SHELL} environment variable) is publicly readable. Remember
12581 that @value{GDBN} uses the shell to start your program---some systems refuse to
12582 let @value{GDBN} debug child processes whose programs are not readable.
12585 * Separate Objdir:: Compiling @value{GDBN} in another directory
12586 * Config Names:: Specifying names for hosts and targets
12587 * Configure Options:: Summary of options for configure
12590 @node Separate Objdir, Config Names, Installing GDB, Installing GDB
12591 @section Compiling @value{GDBN} in another directory
12593 If you want to run @value{GDBN} versions for several host or target machines,
12594 you need a different @code{gdb} compiled for each combination of
12595 host and target. @code{configure} is designed to make this easy by
12596 allowing you to generate each configuration in a separate subdirectory,
12597 rather than in the source directory. If your @code{make} program
12598 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
12599 @code{make} in each of these directories builds the @code{gdb}
12600 program specified there.
12602 To build @code{gdb} in a separate directory, run @code{configure}
12603 with the @samp{--srcdir} option to specify where to find the source.
12604 (You also need to specify a path to find @code{configure}
12605 itself from your working directory. If the path to @code{configure}
12606 would be the same as the argument to @samp{--srcdir}, you can leave out
12607 the @samp{--srcdir} option; it is assumed.)
12609 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
12610 separate directory for a Sun 4 like this:
12614 cd gdb-@value{GDBVN}
12617 ../gdb-@value{GDBVN}/configure sun4
12622 When @code{configure} builds a configuration using a remote source
12623 directory, it creates a tree for the binaries with the same structure
12624 (and using the same names) as the tree under the source directory. In
12625 the example, you'd find the Sun 4 library @file{libiberty.a} in the
12626 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
12627 @file{gdb-sun4/gdb}.
12629 One popular reason to build several @value{GDBN} configurations in separate
12630 directories is to configure @value{GDBN} for cross-compiling (where
12631 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
12632 programs that run on another machine---the @dfn{target}).
12633 You specify a cross-debugging target by
12634 giving the @samp{--target=@var{target}} option to @code{configure}.
12636 When you run @code{make} to build a program or library, you must run
12637 it in a configured directory---whatever directory you were in when you
12638 called @code{configure} (or one of its subdirectories).
12640 The @code{Makefile} that @code{configure} generates in each source
12641 directory also runs recursively. If you type @code{make} in a source
12642 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
12643 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
12644 will build all the required libraries, and then build GDB.
12646 When you have multiple hosts or targets configured in separate
12647 directories, you can run @code{make} on them in parallel (for example,
12648 if they are NFS-mounted on each of the hosts); they will not interfere
12651 @node Config Names, Configure Options, Separate Objdir, Installing GDB
12652 @section Specifying names for hosts and targets
12654 The specifications used for hosts and targets in the @code{configure}
12655 script are based on a three-part naming scheme, but some short predefined
12656 aliases are also supported. The full naming scheme encodes three pieces
12657 of information in the following pattern:
12660 @var{architecture}-@var{vendor}-@var{os}
12663 For example, you can use the alias @code{sun4} as a @var{host} argument,
12664 or as the value for @var{target} in a @code{--target=@var{target}}
12665 option. The equivalent full name is @samp{sparc-sun-sunos4}.
12667 The @code{configure} script accompanying @value{GDBN} does not provide
12668 any query facility to list all supported host and target names or
12669 aliases. @code{configure} calls the Bourne shell script
12670 @code{config.sub} to map abbreviations to full names; you can read the
12671 script, if you wish, or you can use it to test your guesses on
12672 abbreviations---for example:
12675 % sh config.sub i386-linux
12677 % sh config.sub alpha-linux
12678 alpha-unknown-linux-gnu
12679 % sh config.sub hp9k700
12681 % sh config.sub sun4
12682 sparc-sun-sunos4.1.1
12683 % sh config.sub sun3
12684 m68k-sun-sunos4.1.1
12685 % sh config.sub i986v
12686 Invalid configuration `i986v': machine `i986v' not recognized
12690 @code{config.sub} is also distributed in the @value{GDBN} source
12691 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
12693 @node Configure Options, , Config Names, Installing GDB
12694 @section @code{configure} options
12696 Here is a summary of the @code{configure} options and arguments that
12697 are most often useful for building @value{GDBN}. @code{configure} also has
12698 several other options not listed here. @inforef{What Configure
12699 Does,,configure.info}, for a full explanation of @code{configure}.
12702 configure @r{[}--help@r{]}
12703 @r{[}--prefix=@var{dir}@r{]}
12704 @r{[}--exec-prefix=@var{dir}@r{]}
12705 @r{[}--srcdir=@var{dirname}@r{]}
12706 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
12707 @r{[}--target=@var{target}@r{]}
12712 You may introduce options with a single @samp{-} rather than
12713 @samp{--} if you prefer; but you may abbreviate option names if you use
12718 Display a quick summary of how to invoke @code{configure}.
12720 @item --prefix=@var{dir}
12721 Configure the source to install programs and files under directory
12724 @item --exec-prefix=@var{dir}
12725 Configure the source to install programs under directory
12728 @c avoid splitting the warning from the explanation:
12730 @item --srcdir=@var{dirname}
12731 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
12732 @code{make} that implements the @code{VPATH} feature.}@*
12733 Use this option to make configurations in directories separate from the
12734 @value{GDBN} source directories. Among other things, you can use this to
12735 build (or maintain) several configurations simultaneously, in separate
12736 directories. @code{configure} writes configuration specific files in
12737 the current directory, but arranges for them to use the source in the
12738 directory @var{dirname}. @code{configure} creates directories under
12739 the working directory in parallel to the source directories below
12742 @item --norecursion
12743 Configure only the directory level where @code{configure} is executed; do not
12744 propagate configuration to subdirectories.
12746 @item --target=@var{target}
12747 Configure @value{GDBN} for cross-debugging programs running on the specified
12748 @var{target}. Without this option, @value{GDBN} is configured to debug
12749 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
12751 There is no convenient way to generate a list of all available targets.
12753 @item @var{host} @dots{}
12754 Configure @value{GDBN} to run on the specified @var{host}.
12756 There is no convenient way to generate a list of all available hosts.
12759 There are many other options available as well, but they are generally
12760 needed for special purposes only.
12762 @node Index, , Installing GDB, Top
12768 % I think something like @colophon should be in texinfo. In the
12770 \long\def\colophon{\hbox to0pt{}\vfill
12771 \centerline{The body of this manual is set in}
12772 \centerline{\fontname\tenrm,}
12773 \centerline{with headings in {\bf\fontname\tenbf}}
12774 \centerline{and examples in {\tt\fontname\tentt}.}
12775 \centerline{{\it\fontname\tenit\/},}
12776 \centerline{{\bf\fontname\tenbf}, and}
12777 \centerline{{\sl\fontname\tensl\/}}
12778 \centerline{are used for emphasis.}\vfill}
12780 % Blame: doc@cygnus.com, 1991.