From fe3f5fc8280c8697ec793b7090ae2845abf570f5 Mon Sep 17 00:00:00 2001 From: Roland Pesch Date: Sat, 30 Mar 1991 02:13:24 +0000 Subject: [PATCH] Restructured manual; introduced introductory sample session. --- gdb/doc/gdb.texinfo | 5935 ++++++++++++++++++++++--------------------- 1 file changed, 3101 insertions(+), 2834 deletions(-) diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo index 88574d4f8e9..49c72215299 100644 --- a/gdb/doc/gdb.texinfo +++ b/gdb/doc/gdb.texinfo @@ -8,17 +8,18 @@ @c _HOST__ architectures (and you can of course get the full source, @c with all configurations, from wherever you got this). _if__(0) +_0__ THIS IS THE FULL SOURCE. The full source needs to be run through m4 before either tex- or info- formatting: for example, - m4 pretex.m4 none.m4 m680x0.m4 as.texinfo >as-680x0.texinfo + m4 pretex.m4 none.m4 m680x0.m4 gdb.texinfo >gdb-680x0.texinfo will produce (assuming your path finds either GNU or SysV m4; Berkeley won't do) a file suitable for formatting. See the text in "pretex.m4" for a fuller explanation (and the macro definitions). - +_1__ _fi__(0) @c -@synindex ky cp +@syncodeindex ky cp @c FOR UPDATES LEADING TO THIS DRAFT, GDB CHANGELOG CONSULTED BETWEEN: @c Tue Feb 26 01:47:07 1991 Cygnus John Gilmore (cygnus at yuba) @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint) @@ -220,14 +221,176 @@ HPPA architecture support. @end itemize -@node Invocation, User Interface, New Features, Top -@chapter Starting _GDBN__ +@node Sample Session,,, +@chapter A Sample _GDB__ Session + +You can use this manual at your leisure to read all about _GDBN__. +However, a handful of commands are enough to get started using the +debugger. This chapter illustrates these commands. + +In this sample session, we emphasize user input like this: @var{input}, +to make it easier to pick out from the surrounding output. + +We'll be using _GDBN__ to inspect GNU @code{m4} (a generic macro +processor). + +_0__@smallexample +$ @var{cd gm4/common} + +$ @var{_GDBP__ m4} +Reading symbol data from m4...done. +@end smallexample + +@noindent +_GDBN__ only reads enough symbol data to know where to find the rest +when needed; as a result, the first prompt comes up very quickly. + +@smallexample +(_GDBP__) @var{break m4_changequote} +Breakpoint 1 at 0x59d4: file builtin.c, line 812. +@end smallexample + +@noindent +We've chosen to see how the @code{m4} builtin @samp{changequote} +works. We know the relevant subroutine is @samp{m4_changequote} (from +inspecting the source), so we set a breakpoint there. + +@smallexample +(_GDBP__) @var{run} +Starting program: /s1/gnu/src/gm4/common/m4 +@var{`usual' quotes } +usual quotes +@end smallexample + +@noindent +Now we've started @code{m4} running under _GDBN__ control; while we don't touch +the @samp{m4_changequote} subroutine, the program runs as usual. + +@smallexample +@var{changequote(<,>)} + +Breakpoint 1, m4_changequote (argc=3, argv=0x2b958) at builtin.c:812 +812 if (bad_argc(TOKEN_DATA_TEXT(argv[0]), argc, 1, 3)) +@end smallexample +@noindent +Once we've encountered the breakpoint, _GDBN__ suspends execution +of our program, displaying information about where it stopped. + +@smallexample +(_GDBP__) @var{s} +bad_argc (name=0xf833cfb4
, argc=3, min=1, max=3) at builtin.c:230 +230 if (min > 0 && argc < min) @{ +@end smallexample +@noindent +We single-stepped with the command @samp{s}; since there was a subroutine +call, we've stopped in the first line of that subroutine, not in the next line +of @code{m4_changequote}. + +The command @samp{next} would have taken us to the next line of the same +subroutine. Now that we've stopped deeper in the stack, we can use the +@samp{backtrace} command (which can also be spelled @samp{bt}) to get +information about where we are. + +@smallexample +(_GDBP__) @var{bt} +#0 bad_argc (name=0xf833cfb4
, argc=3, + min=1, max=3) at builtin.c:230 +#1 0x59ec in m4_changequote (argc=3, argv=0x2b958) at builtin.c:812 +#2 0x6e38 in expand_macro (sym=0x2b060) at macro.c:242 +#3 0x6840 in expand_token (obs=0x0, t=176224, td=0xf7fffb08) at macro.c:71 +#4 0x6794 in expand_input () at macro.c:40 +#5 0x28dc in main (argc=0, argv=0xf7fffbf8) at m4.c:174 +@end smallexample + +@noindent +We'll tell _GDBN__ to finish execution of this subroutine, to get back +to @code{m4_changequote}. + +@smallexample +(_GDBP__) @var{finish} +Run till exit from #0 bad_argc (name=0xf833cfb4
, argc=3, min=1, max=3) at builtin.c:230 +0x59ec in m4_changequote (argc=3, argv=0x2b958) at builtin.c:812 +812 if (bad_argc(TOKEN_DATA_TEXT(argv[0]), argc, 1, 3)) +Value returned is $1 = false +(_GDBP__) @var{s} +815 lquote = (argc >= 2) ? TOKEN_DATA_TEXT(argv[1])[0] : DEF_LQUOTE; +(_GDBP__) @var{whatis lquote} +type = char +(_GDBP__) @var{p lquote} +$2 = 96 '`' +@end smallexample + +@noindent +When we stepped to another line, @code{m4} was about to set a variable +@samp{lquote}; we inspected its type with @samp{whatis} and its value +with @samp{p} (the @samp{print} command). We can see some context by +displaying the surrounding source code, with the @samp{l} (@code{list}) +command. + +@smallexample +(_GDBP__) @var{l} +810 token_data **argv; +811 @{ +812 if (bad_argc(TOKEN_DATA_TEXT(argv[0]), argc, 1, 3)) +813 return; +814 +815 lquote = (argc >= 2) ? TOKEN_DATA_TEXT(argv[1])[0] : DEF_LQUOTE; +816 rquote = (argc >= 3) ? TOKEN_DATA_TEXT(argv[2])[0] : DEF_RQUOTE; +817 @} +818 +819 /* +(_GDBP__) @var{s} +816 rquote = (argc >= 3) ? TOKEN_DATA_TEXT(argv[2])[0] : DEF_RQUOTE; +(_GDBP__) @var{s} +817 @} +(_GDBP__) @var{p lquote} +$3 = 60 '<' +(_GDBP__) @var{p rquote} +$4 = 62 '>' +@end smallexample + +@noindent +We proceeded past another line with @samp{s}, and inspected the new +values of @code{m4}'s internal variables @code{rquote} and +@code{lquote}. + +Since we're done with our inspection of this subroutine, we'll tell +_GDBN__ to allow @code{m4} to continue running, with the @samp{c} +(@code{continue}) command: + +@smallexample +(_GDBP__) @var{c} +Continuing. + +@var{`usual' quotes } +`usual' quotes not these + +Program exited normally. +(_GDBP__) @var{quit} + +$ +_1__@end smallexample + +@noindent +Finally, when we ended the @code{m4} run, _GDBN__ told us +``@code{Program exited normally.}'' We ended our _GDBN__ session with +the _GDBN__ @samp{quit} command. + + +@node Starting and Stopping,,, +@chapter Starting and Stopping + +@node Starting _GDBN__,,, +@section Starting _GDBN__ _GDBN__ is invoked with the shell command @samp{_GDBP__}. Once started, it reads commands from the terminal until you tell it to exit. -The most usual way to start _GDBN__ is with one argument or two, specifying -an executable program as the argument: +You can start by just calling @samp{_GDBP__} with no arguments or +options; but the most usual way to start _GDBN__ is with one argument or +two, specifying an executable program as the argument: @example _GDBP__ program @end example @@ -245,7 +408,7 @@ in sequential order. The order makes a difference when the @samp{-x} option is used. @node File Options, Mode Options, Invocation, Invocation -@section Options and Arguments to Choose Files +@subsection Options and Arguments to Choose Files As shown above, any arguments other than options specify an executable file and core file; that is, the first argument encountered with no @@ -275,8 +438,8 @@ Execute _GDBN__ commands from file @var{file}. @xref{Command Files}. Add @var{directory} to the path to search for source files. @end table -@node Mode Options, Remote i960-Nindy, File Options, Invocation -@section Options to Choose Modes +@node Mode Options, , , +@subsection Options to Choose Modes @table @code @item -nx @@ -323,7 +486,7 @@ _GDBN__ for remote debugging. _if__(_I960__) @node i960-Nindy Remote,,, -@section _GDBN__ with a Remote Intel 960 (Nindy) +@subsection _GDBN__ with a Remote Intel 960 (Nindy) ``Nindy'' is the name of a Rom Monitor program for Intel 960 target systems. When _GDBN__ is configured to control a remote Intel 960 using @@ -341,7 +504,7 @@ By using the @samp{target} command at any point during your _GDBN__ session. @end itemize @node Nindy Startup,,, -@subsection Startup with Nindy +@subsubsection Startup with Nindy The command-line options for Nindy are detailed below. If you simply start @code{_GDBP__} without using options to specify a serial port, you are @@ -355,7 +518,7 @@ responding to the prompt with an empty line. If you do this, and later wish to attach to Nindy, use @samp{target} (@pxref{Target Commands}). @node Nindy Options,,, -@subsection Options for Nindy +@subsubsection Options for Nindy These are the startup options for beginning your _GDBN__ session with a Nindy-960 board attached: @@ -402,7 +565,7 @@ _fi__(_I960__) _if__(_AMD29K__) @node EB29K Remote,,, -@section Starting _GDBN__ with a Remote EB29K +@subsection _GDBN__ with a Remote EB29K @cindex EB29K board @cindex running 29K programs @@ -415,12 +578,12 @@ you've hooked the cable between the PC's @samp{COM1} port and @samp{/dev/ttya} on the Unix system. @node Comms (EB29K),,, -@subsection Communications Setup +@subsubsection Communications Setup The next step is to set up the PC's port, by doing something like the following in DOS on the PC: -@example +_0__@example C:\> MODE com1:9600,n,8,1,none -@end example +_1__@end example @noindent This example---run on an MS DOS 4.0 system---sets the PC port to 9600 bps, no parity, eight data bits, one stop bit, and no ``retry'' action; @@ -431,9 +594,9 @@ end of the connection as well. To give control of the PC to the Unix side of the serial line, type the following at the DOS console: -@example +_0__@example C:\> CTTY com1 -@end example +_1__@end example @noindent (Later, if you wish to return control to the DOS console, you can use the command @samp{CTTY con}---but you must send it over the device that @@ -472,7 +635,7 @@ start the PC program @samp{EBMON} (an EB29K control program supplied with your board by AMD). You should see an initial display from @code{EBMON} similar to the one in our example, ending with the @code{EBMON} prompt @samp{#}--- -@example +_0__@example C:\> g: G:\> CD \usr\joe\work29k @@ -501,7 +664,7 @@ Am29027 Available = No Byte Write Available = Yes # ~. -@end example +_1__@end example Then exit the @code{cu} or @code{tip} program (done in the example by typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} will keep @@ -516,8 +679,8 @@ other way---perhaps floppy-disk transfer---of getting the 29K program from the Unix system to the PC; _GDBN__ will @emph{not} download it over the serial line. -@node _GDBP__-EB29K -@subsection EB29K cross-debugging +@node _GDBP__-EB29K,,, +@subsubsection EB29K cross-debugging Finally, @code{cd} to the directory containing an image of your 29K program on the Unix system, and start _GDBN__---specifying as argument the name of your 29K program: @@ -558,7 +721,7 @@ Type @samp{CTTY con} to return command input to the main DOS console, and type @samp{~.} to leave @code{tip} or @code{cu}. @node Remote Log, , Remote Commands, Remote -@subsection Remote Log +@subsubsection Remote Log @kindex eb.log @cindex log file for EB29K The @samp{target amd-eb} command creates a file @file{eb.log} in the @@ -569,9 +732,54 @@ another window often helps to debug trouble with @code{EBMON}, or unexpected events on the PC side of the connection. _fi__(_AMD29K__) -@node User Interface, Files, Invocation, Top -@chapter _GDBN__ Commands and Displays +@node Stopping _GDBN__,,, +@section Stopping _GDBN__ +@cindex exiting _GDBN__ +@kindex quit +To exit _GDBN__, use the @samp{quit} command (abbreviated @samp{q}), or type +an end-of-file character (usually @kbd{C-d}). + +@cindex interrupt +An interrupt (often @kbd{C-c}) will not exit from _GDBN__, but rather +will terminate the action of any _GDBN__ command that is in progress and +return to _GDBN__ command level. It is safe to type the interrupt +character at any time because _GDBN__ does not allow it to take effect +until a time when it is safe. +If you've been using _GDBN__ to control an attached process or device, +you can release it with the @samp{detach} command; @pxref{Attach}. + +@node Shell Commands,,, +@section Shell Commands +If you just need to execute occasional shell commands during your +debugging session, there's no need to stop or suspend _GDBN__; you can +just use the @samp{shell} command. + +@table @code +@item shell @var{command string} +@kindex shell +@cindex shell escape +Directs _GDBN__ to invoke an inferior shell to execute @var{command string}. +The environment variable @code{SHELL} is used if it exists, otherwise _GDBN__ +uses @samp{/bin/sh}. +@end table + +The utility @samp{make} is often needed in development environments. +You don't have to use the @samp{shell} command for this purpose in _GDBN__: + +@table @code +@item make @dots{} +@kindex make +@cindex calling make +Causes _GDBN__ to execute an inferior @code{make} program with the specified +arguments. This is equivalent to @samp{shell make @dots{}}. +@end table + +@node Commands,,, +@chapter _GDBN__ Commands + +@node Command Syntax,,, +@section Command Syntax A _GDBN__ command is a single line of input. There is no limit on how long it can be. It starts with a command name, which is followed by arguments whose meaning depends on the command name. For example, the command @@ -599,3419 +807,3539 @@ differently when repeated because that is more useful. A line of input starting with @samp{#} is a comment; it does nothing. This is useful mainly in command files (@xref{Command Files}). +@node Help,,, +@section Getting Help @cindex online documentation @kindex help -@table @code -@item help -@itemx help @var{category} -@itemx help @var{command} You can always ask _GDBN__ itself for information on its commands, using the -command @samp{help}. With a command name as argument, it will display a -paragraph on how to use the command. Used with no arguments, -@samp{help} displays a short list of named categories of commands; you -can then use @samp{help @var{category}} to list the individual commands -in a category. - -@kindex info version -@item info version -As _GDBN__ evolves, new commands are introduced, and old ones may wither -away. If multiple versions of _GDBN__ are in use at your site, it may -occasionally be useful to make sure what version of _GDBN__ you're running. -_GDBN__ announces its version whenever it starts up; but you can make it -repeat this information with the @samp{info version} command. -@end table - -@cindex prompt -_GDBN__ indicates its readiness to read a command by printing a string -called the @dfn{prompt}. This string is normally @samp{(_GDBP__)}. You can -change the prompt string with the @samp{set prompt} command. For -instance, when debugging _GDBN__ with _GDBN__, it is useful to change the prompt -in one of the _GDBN__s so that you tell which one you are talking to. - -@table @code -@item set prompt @var{newprompt} -@kindex set prompt -Directs _GDBN__ to use @var{newprompt} as its prompt string henceforth. -@kindex show prompt -@item show prompt -Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}} -@end table - -@cindex exiting _GDBN__ -@kindex quit -To exit _GDBN__, use the @samp{quit} command (abbreviated @samp{q}), or type -an end-of-file character (usually @ctrl{d}). An interrupt (often -@ctrl{c}) will not exit from _GDBN__, but rather will terminate the action -of any _GDBN__ command that is in progress and return to _GDBN__ command level. -It is safe to type the interrupt character at any time because _GDBN__ does -not allow it to take effect until a time when it is safe. - -@cindex readline -@cindex command line editing -@cindex history substitution -_GDBN__ reads its input commands via the @code{readline} interface. This -GNU library provides consistent behavior for programs which provide a -command line interface to the user. Advantages are @samp{emacs}-style -or @samp{vi}-style inline editing of commands, @samp{csh}-like history -substitution, and a storage and recall of command history across -debugging sessions. - -You may control the behavior of command line editing in _GDBN__ with the -command @samp{set}. You may check the status of any of these settings -with the command @samp{show}. +command @samp{help}. @table @code -@kindex set editing -@cindex editing -@item set editing -@itemx set editing on -Enable command line editing (enabled by default). - -@item set editing off -Disable command line editing. +@item help +Used with no arguments, @samp{help} displays a short list of named +categories of commands: +@example +(_GDBP__) help +List of classes of commands: + +running -- Running the program +stack -- Examining the stack +data -- Examining data +breakpoints -- Making program stop at certain points +files -- Specifying and examining files +status -- Status inquiries +support -- Support facilities +user-defined -- User-defined commands +aliases -- Aliases of other commands +obscure -- Obscure features + +Type "help" followed by a class name for a list of commands in that class. +Type "help" followed by command name for full documentation. +Command name abbreviations are allowed if unambiguous. +(_GDBP__) +@end example -@kindex show editing -@item show editing -Show whether command line editing is enabled. +@item help @var{category} +Using one of the general help categories as an argument, you can get a +list of the individual commands in a category. For example, here is the +help display for category @samp{status}: +@example +(_GDBP__) help status +Status inquiries. -@cindex history file -@kindex set history file -@item set history file @var{filename} -Set the name of the _GDBN__ command history file to @samp{filename}. This is -the file from which _GDBN__ will read an initial command history -list or to which it will write this list when it exits. This list is -accessed through history expansion or through the history -command editing characters listed below. This file defaults to the -value of the environmental variable @code{GDBHISTFILE}, or to -@code{./.gdb_history} if this variable is not set. +List of commands: -@cindex history write -@kindex set history write -@item set history write -@itemx set history write on -Make _GDBN__ record command history in a file, whose name may be specified with the -@samp{set history file} command. By default, this option is disabled. +show -- Generic command for showing things set with "set" +info -- Generic command for printing status -@item set history write off -Make _GDBN__ stop recording command history in a file. +Type "help" followed by command name for full documentation. +Command name abbreviations are allowed if unambiguous. +(_GDBP__) +@end example -@cindex history size -@kindex set history size -@item set history size @var{size} -Set the number of commands which _GDBN__ will keep in its history list. -This defaults to the value of the environmental variable -@code{HISTSIZE}, or to 256 if this variable is not set. +@item help @var{command} +With a command name as @samp{help} argument, _GDBN__ will display a +short paragraph on how to use that command. @end table -@cindex history expansion -History expansion assigns special meaning to the character @samp{!} -(@pxref{Event Designators}). Since @samp{!} is also the logical not -operator in C, history expansion is off by default. If you decide to -enable history expansion with the @samp{set history expansion on} -command, you may sometimes need to follow @samp{!} (when it is used as -logical not, in an expression) with a space or a tab to prevent it from -being expanded. The @code{readline} history facilities will not attempt -substitution on the strings @samp{!=} and @samp{!(}, even when history -expansion is enabled. - -The commands to control history expansion are: +In addition to @samp{help}, you can use the _GDBN__ commands @samp{info} +and @samp{show} to inquire about the state of your program, or the state +of _GDBN__ itself. Both commands support many ``sub-commands'', or +topics of inquiry; this manual introduces each of them in the +appropriate context. The listings under ``@code{info}'' and under +``@code{show}'' in the Index point to all the sub-commands +(@pxref{Index}). @table @code - -@kindex set history expansion -@item set history expansion on -@itemx set history expansion -Enable history expansion. History expansion is off by default. - -@item set history expansion off -Disable history expansion. - -The @code{readline} code comes with more complete documentation of -editing and history expansion features. Users unfamiliar with @samp{emacs} -or @samp{vi} may wish to read it. @xref{Command Line Editing}. - -@kindex show history -@item show history -@itemx show history file -@itemx show history write -@itemx show history size -@itemx show history expansion -These commands display the state of the _GDBN__ history parameters. -@samp{show history} by itself displays all four states. +@kindex info +@item info +This command is for describing the state of your program; for example, +it can list the arguments given to your program (@samp{info args}), the +registers currently in use (@samp{info registers}), or the breakpoints +you've set (@samp{info breakpoints}). You can get a complete list of +the @code{info} sub-commands with @samp{help info}. @kindex show -@kindex info set @item show -@itemx info set -This chapter introduces a number of internal _GDBN__ variables that you -can control with the @samp{set} command, and display with the -@samp{show} command. A number of others are introduced throughout the -manual. To display all the settable parameters and their current +In contrast, @samp{show} is for describing the state of _GDBN__ itself. +You can change most of the things you can @code{show}, by using the +related command @samp{set}; for example, you can control what number +system is used for displays with @samp{set radix}, or simply inquire +which possibility is currently in use with @samp{show radix}. + +@kindex info set +To display all the settable parameters and their current values, you can use @samp{show} with no arguments; you may also use @samp{info set}. Both commands produce the same display. +@c FIXME: "info set" violates the rule that "info" is for state of +@c FIXME...program. Ck w/ GNU: "info set" to be called something else, +@c FIXME...or change desc of rule---eg "state of prog and debugging session"? + + +@kindex show version +@item show version +@c FIXME: chgd to "show version" from "info". Verify John doing same to GDBv4. +This @samp{show} subcommand is one of those with no corresponding +@samp{set} subcommand. As _GDBN__ evolves, new commands are introduced, +and old ones may wither away. If multiple versions of _GDBN__ are in +use at your site, it may occasionally be useful to make sure what +version of _GDBN__ you're running. It is also useful to include this +information in _GDBN__ bug-reports. _GDBN__ announces its version +number if you start it with no arguments; but you can make it give this +information on request, with the @samp{show version} command. @end table -@table @code -@kindex info editing -@item info editing -Display the last ten commands in the command history. +@node Running,,, +@chapter Running Programs Under _GDBN__ -@item info editing @var{n} -Print ten commands centered on command number @var{n}. +@node Compilation,,, +@section Compiling for Debugging -@item info editing + -Print ten commands just after the commands last printed. +In order to debug a program effectively, you need to ask for debugging +information when you compile it. This debugging information is stored +in the object file; it describes the data type of each variable or +function and the correspondence between source line numbers and +addresses in the executable code. -@end table +To request debugging information, specify the @samp{-g} option when you run +the compiler. -Occasionally it is useful to execute a shell command from within _GDBN__. -This can be done with the @samp{shell} command. +The Unix C compiler is unable to handle the @samp{-g} and @samp{-O} options +together. This means that you cannot ask for optimization if you ask for +debugger information. -@table @code -@item shell @var{command string} -@kindex shell -@cindex shell escape -Directs _GDBN__ to invoke an inferior shell to execute @var{command string}. -The environment variable @code{SHELL} is used if it exists, otherwise _GDBN__ -uses @samp{/bin/sh}. -@end table +The GNU C compiler supports @samp{-g} with or without @samp{-O}, making it +possible to debug optimized code. We recommend that you @emph{always} use +@samp{-g} whenever you compile a program. You may think the program is +correct, but there's no sense in pushing your luck. -The utility @samp{make} is often needed in development environments. -You don't have to use the @samp{shell} command for this purpose in _GDBN__: +Some things do not work as well with @samp{-g -O} as with just +@samp{-g}, particularly on machines with instruction scheduling. If in +doubt, recompile with @samp{-g} alone, and if this fixes the problem, +please report it as a bug (including a test case---@pxref{_GDBN__ Bugs}). -@table @code -@item make @dots{} -@kindex make -@cindex calling make -Causes _GDBN__ to execute an inferior @code{make} program with the specified -arguments. This is equivalent to @samp{shell make @dots{}}. -@end table +Older versions of the GNU C compiler, _GCC__, permitted a variant option +@samp{-gg} for debugging information. _GDBN__ no longer supports this format; +if your GNU C compiler has this option, do not use it. -@cindex screen size -@cindex pauses in output -Certain commands to _GDBN__ may produce large amounts of information output -to the screen. To help you read all of it, _GDBN__ pauses and asks you for -input at the end of each page of output. Type @key{RET} when you want -to continue the output. Normally _GDBN__ knows the size of the screen from -the termcap data base together with the value of the @code{TERM} -environment variable and the @code{stty rows} and @code{stty cols} -settings. If this is not correct, you can override it with -the @samp{set screen-height} and @samp{set screen-width} commands: - -_GDBN__ also uses the screen width setting to determine when to wrap lines -of output. Depending what is being printed, it tries to break the -line at a readable place, rather than simply letting it overflow onto -the following line. +@ignore +@comment As far as I know, there are no cases in which _GDBN__ will +@comment produce strange output in this case. (but no promises). +If your program includes archives made with the @code{ar} program, and +if the object files used as input to @code{ar} were compiled without the +@samp{-g} option and have names longer than 15 characters, _GDBN__ will get +confused reading the program's symbol table. No error message will be +given, but _GDBN__ may behave strangely. The reason for this problem is a +deficiency in the Unix archive file format, which cannot represent file +names longer than 15 characters. -@table @code -@item set screen-height @var{lpp} -@itemx show screen-height -@itemx set screen-width @var{cpl} -@itemx show screen-width -@kindex set screen-height -@kindex set screen-width -@kindex show screen-width -@kindex show screen-height -These @samp{set} commands specify a screen height of @var{lpp} lines and -a screen width of @var{cpl} characters. The associated @samp{show} -commands display the current settings. +To avoid this problem, compile the archive members with the @samp{-g} +option or use shorter file names. Alternatively, use a version of GNU +@code{ar} dated more recently than August 1989. +@end ignore -If you specify a height of zero lines, _GDBN__ will not pause during output -no matter how long the output is. This is useful if output is to a file -or to an editor buffer. -@end table -@cindex number representation -@cindex entering numbers -You can always enter numbers in octal, decimal, or hexadecimal in _GDBN__ by -the usual conventions: octal numbers begin with @samp{0}, decimal -numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}. -Numbers that begin with none of these are, by default, entered in base -10; likewise, the default display for numbers---when no particular -format is specified---is base 10. You can change the default base for -both input and output with the @samp{set radix} command. +@node Starting,,, +@section Starting your Program +@cindex starting +@cindex running +@kindex run +To start your program under _GDBN__, use the @samp{run} command. Except on +VxWorks, the program must already have been specified using the +@samp{file} or @samp{exec-file} command, or with an argument to _GDBN__ +(@pxref{Files}). -@table @code -@kindex set radix -@item set radix @var{base} -Set the default base for numeric input and display. Supported choices -for @var{base} are decimal 8, 10, 16. @var{base} must itself be -specified either unambiguously or using the current default radix; for -example, any of +On targets that support processes, @samp{run} creates an inferior +process and makes that process run your program. On other targets, +@samp{run} jumps to the location it has recorded for the start of the +program. -@example -set radix 012 -set radix 10. -set radix 0xa -@end example +The execution of a program is affected by certain information it +receives from its superior. _GDBN__ provides ways to specify this +information, which you must do @i{before} starting the program. (You +can change it after starting the program, but such changes do not affect +the program unless you start it over again.) This information may be +divided into three categories: -@noindent -will set the base to decimal. On the other hand, @samp{set radix 10} -will leave the radix unchanged no matter what it was. +@table @asis +@item The @i{arguments.} +You specify the arguments to give the program as the arguments of the +@samp{run} command. If a shell is available on your target, the shell +is used to pass the arguments, so that you may use normal conventions +(for example regular expression expansion or variable substitution) in +describing the arguments. In Unix systems, you can control which shell +is used with the @code{SHELL} environment variable. -@kindex show radix -@item show radix -Display the current default base for numeric input and display. +@item The @i{environment.} +The program normally inherits its environment from _GDBN__, but you can +use the _GDBN__ commands @samp{set environment} and +@samp{unset environment} to change parts of the environment that will +be given to the program.@refill +@item The @i{working directory.} +The program inherits its working directory from _GDBN__. You can set _GDBN__'s +working directory with the @samp{cd} command in _GDBN__. @end table -By default, _GDBN__ is silent about its inner workings. If you are running -on a slow machine, you may want to use the @samp{set verbose} command. -It will make _GDBN__ tell you when it does a lengthy internal operation, so -you won't think it has crashed. +When you issue the @samp{run} command, your program begins to execute +immediately. @xref{Stopping}, for discussion of how to arrange for your +program to stop. -Currently, the messages controlled by @samp{set verbose} are those which -announce that the symbol table for a source file is being read -(@pxref{Files}, in the description of the command -@samp{symbol-file}). -@c The following is the right way to do it, but emacs 18.55 doesn't support -@c @ref, and neither the emacs lisp manual version of texinfmt or makeinfo -@c is released. -@ignore -see @samp{symbol-file} in @ref{Files}). -@end ignore +Note that once your program has been started by the @samp{run} command, +you may evaluate expressions that involve calls to functions in the +inferior, using the @samp{print} or @samp{call} commands. @xref{Data}. -@table @code -@kindex set verbose -@item set verbose on -Enables _GDBN__'s output of certain informational messages. +If the modification time of your symbol file has changed since the last +time _GDBN__ read its symbols, _GDBN__ will discard its symbol table and re-read +it. In this process, it tries to retain your current breakpoints. -@item set verbose off -Disables _GDBN__'s output of certain informational messages. +@menu +* Arguments:: Specifying the arguments for your program. +* Environment:: Specifying the environment for your program. +* Working Directory:: Specifying the working directory for giving + to your program when it is run. +* Input/Output:: Specifying the program's standard input and output. +* Attach:: Debugging a process started outside _GDBN__. +* Kill Process:: Getting rid of the child process running your program. +@end menu -@kindex show verbose -@item show verbose -Displays whether @samp{set verbose} is on or off. -@end table +@node Arguments, Environment, Running, Running +@section Your Program's Arguments -By default, if _GDBN__ encounters bugs in the symbol table of an object file, -it prints a single message about each type of problem it finds, then -shuts up. You can suppress these messages, or allow more than one such -message to be printed if you want to see how frequent the problems are. -@xref{Files}. +@cindex arguments (to your program) +The arguments to your program are specified by the arguments of the +@samp{run} command. They are passed to a shell, which expands wildcard +characters and performs redirection of I/O, and thence to the program. +@samp{run} with no arguments uses the same arguments used by the previous +@samp{run}. + +@kindex set args @table @code -@kindex set complaints -@item set complaints @var{limit} -Permits _GDBN__ to output @var{limit} complaints about each type of unusual -symbols before becoming silent about the problem. Set @var{limit} to -zero to suppress all complaints; set it to a large number to prevent -complaints from being suppressed. +@item set args +The command @samp{set args} can be used to specify the arguments to be used +the next time the program is run. If @samp{set args} has no arguments, it +means to use no arguments the next time the program is run. If you have +run your program with arguments and want to run it again with no arguments, +this is the only way to do so. -@kindex show complaints -@item show complaints -Displays how many symbol complaints _GDBN__ is permitted to produce. +@item show args +@kindex show args +Show the arguments to give your program when it is started. @end table -By default, _GDBN__ is cautious, and asks what sometimes seem to be a lot of -stupid questions. For example, if you try to run a program which is -already running: -@example - -(_GDBP__) run -The program being debugged has been started already. -Start it from the beginning? (y or n) -@end example +@node Environment, Working Directory, Arguments, Running +@section Your Program's Environment -If you're willing to unflinchingly face the consequences of your own -commands, you can disable this ``feature'': +@cindex environment (of your program) +The @dfn{environment} consists of a set of @dfn{environment variables} and +their values. Environment variables conventionally record such things as +your user name, your home directory, your terminal type, and your search +path for programs to run. Usually you set up environment variables with +the shell and they are inherited by all the other programs you run. When +debugging, it can be useful to try running the program with different +environments without having to start the debugger over again. @table @code -@kindex set caution -@cindex flinching -@cindex stupid questions -@item set caution off -Disables cautious questions. +@item show environment @var{varname} +@kindex show environment +Print the value of environment variable @var{varname} to be given to +your program when it is started. -@item set caution on -Enables cautious questions (the default). +@item show environment +Print the names and values of all environment variables to be given to +your program when it is started. -@item show caution -@kindex show caution -Displays state of cautious questions. -@end table +@item set environment @var{varname} @var{value} +@itemx set environment @var{varname} = @var{value} +@kindex set environment +Sets environment variable @var{varname} to @var{value}, for your program +only, not for _GDBN__ itself. @var{value} may be any string; the values of +environment variables are just strings, and any interpretation is +supplied by your program itself. The @var{value} parameter is optional; +if it is eliminated, the variable is set to a null value. -@node Files, Compilation, User Interface, Top -@chapter Specifying _GDBN__'s Files +For example, this command: -@cindex core dump file -@cindex executable file -@cindex symbol table -_GDBN__ needs to know the file name of the program to be debugged, both in -order to read its symbol table and in order to start the program. To -debug a core dump of a previous run, _GDBN__ must be told the file name of -the core dump. +@example +set env USER = foo +@end example -The usual way to specify the executable and core dump file names is with -the command arguments given when you start _GDBN__, as discussed in -@pxref{Invocation}. +@noindent +tells the program, when subsequently run, to assume it is being run +on behalf of the user named @samp{foo}. -But occasionally it is necessary to change to a different file during a -_GDBN__ session. Or you may run _GDBN__ and forget to specify the files you -want to use. In these situations the _GDBN__ commands to specify new files -are useful. +@item delete environment @var{varname} +@itemx unset environment @var{varname} +@kindex delete environment +@kindex unset environment +Remove variable @var{varname} from the environment to be passed to your +program. This is different from @samp{set env @var{varname}@ =}; +@samp{delete environment} removes the variable from the environment, +rather than assigning it an empty value. This command can be +abbreviated @samp{d e}. +@end table -@table @code -@item file @var{filename} -@kindex file -Use @var{filename} as the program to be debugged. It is read for its -symbols, for getting the contents of pure memory, and it is the program -executed when you use the @samp{run} command. If you do not specify a -directory and the file is not found in _GDBN__'s working directory, _GDBN__ will -use the environment variable @code{PATH} as a list of directories to -search, just as the shell does when looking for a program to run. +@node Working Directory, Input/Output, Environment, Running +@section Your Program's Working Directory -@samp{file} with no argument makes both executable file and symbol -table become unspecified. +@cindex working directory (of your program) +Each time you start your program with @samp{run}, it inherits its +working directory from the current working directory of _GDBN__. _GDBN__'s +working directory is initially whatever it inherited from its parent +process (typically the shell), but you can specify a new working +directory in _GDBN__ with the @samp{cd} command. -@item exec-file @var{filename} -@kindex exec-file -Specify that the program to be run (but not the symbol table) is found -in @var{filename}. _GDBN__ will search the environment variable @code{PATH} -if necessary to locate the program. +The _GDBN__ working directory also serves as a default for the commands +that specify files for _GDBN__ to operate on. @xref{Files}. -@item symbol-file @var{filename} -@kindex symbol-file -Read symbol table information from file @var{filename}. @code{PATH} is -searched when necessary. Use the @samp{file} command to get both symbol -table and program to run from the same file. +@table @code +@item cd @var{directory} +@kindex cd +Set _GDBN__'s working directory to @var{directory}. -@samp{symbol-file} with no argument clears out _GDBN__'s information on your -program's symbol table. +@item pwd +@kindex pwd +Print _GDBN__'s working directory. +@end table -The @samp{symbol-file} command causes _GDBN__ to forget the contents of its -convenience variables, the value history, and all breakpoints and -auto-display expressions. This is because they may contain pointers to -the internal data recording symbols and data types, which are part of -the old symbol table data being discarded inside _GDBN__. +@node Input/Output, Attach, Working Directory, Running +@section Your Program's Input and Output -On some kinds of object files, the @samp{symbol-file} command does not -actually read the symbol table in full right away. Instead, it scans -the symbol table quickly to find which source files and which symbols -are present. The details are read later, one source file at a time, -when they are needed. +@cindex redirection +@cindex i/o +@cindex terminal +@cindex controlling terminal +By default, the program you run under _GDBN__ does input and output to the same +terminal that _GDBN__ uses. -The purpose of this two-stage reading strategy is to make _GDBN__ start up -faster. For the most part, it is invisible except for occasional pauses -while the symbol table details for a particular source file are being -read. (The @samp{set verbose} command can turn these pauses into -messages if desired. @xref{User Interface}). +You can redirect the program's input and/or output using @samp{sh}-style +redirection commands in the @samp{run} command. For example, -When the symbol table is stored in COFF format, @samp{symbol-file} does -read the symbol table data in full right away. We haven't implemented -the two-stage strategy for COFF yet. +_0__@example +run > outfile +_1__@end example -When _GDBN__ is configured for a particular environment, it will understand -debugging information in whatever format is the standard generated for -that environment; you may use either the GNU compiler _GCC__, or other -compilers that adhere to the local conventions. Best results are -usually obtained from _GCC__; for example, using _GCC__ you can generate -debugging information for optimized code. +@noindent +starts the program, diverting its output to the file @file{outfile}. -While the symbol file is being read, _GDBN__ will occasionally encounter -problems, such as symbol types it does not recognize, or known bugs in -compiler output. By default, it prints one message about each such -type of problem, no matter how many times the problem occurs. You can -ask it to print more messages, to see how many times the problems occur, -or can shut the messages off entirely, with the @samp{set -complaints} command (@xref{User Interface}). +@kindex tty +Another way to specify where the program should do input and output is +with the @samp{tty} command. This command accepts a file name as +argument, and causes this file to be the default for future @samp{run} +commands. It also resets the controlling terminal for the child +process, for future @samp{run} commands. For example, -The messages currently printed, and their meanings, are: +@example +tty /dev/ttyb +@end example -@table @code -@item inner block not inside outer block in @var{symbol} +@noindent +directs that processes started with subsequent @samp{run} commands +default to do input and output on the terminal @file{/dev/ttyb} and have +that as their controlling terminal. -The symbol information shows where symbol scopes begin and end -(such as at the start of a function or a block of statements). This -error indicates that an inner scope block is not fully contained -in its outer scope blocks. _GDBN__ circumvents the problem by treating -the inner block as if it had the same scope as the outer block. -@var{symbol} may be ``(don't know)'' if the outer block is not -a function. +An explicit redirection in @samp{run} overrides the @samp{tty} command's +effect on input/output redirection, but not its effect on the +controlling terminal. -@item block at @var{address} out of order +When you use the @samp{tty} command or redirect input in the @samp{run} +command, only the @emph{input for your program} is affected. The input +for _GDBN__ still comes from your terminal. -The symbol information for symbol scope blocks should occur in -order of increasing addresses. This error indicates that it does not -do so. _GDBN__ does not circumvent this problem, and will have trouble -locating symbols in the source file whose symbols being read. (You -can often determine what source file is affected by turning on -@samp{info verbose}. @xref{User Interface}.) +@node Attach, Kill Process, Input/Output, Running +@section Debugging an Already-Running Process +@kindex attach +@cindex attach -@item bad block start address patched +@table @code +@item attach @var{process--id} +This command attaches to a running process, if your currently selected +target supports processes. (@samp{info files} will show your active +targets). The command takes as argument a process ID. -The symbol information for a symbol scope block has a start address -smaller than the address of the preceding source line. This is known -to occur in the SunOS 4.1.1 (and earlier) C compiler. _GDBN__ circumvents -the problem by treating the symbol scope block as starting on the -previous source line. +You specify a process ID to debug an already-running process that was +started outside of _GDBN__. (The usual way to find out the process-id of +a Unix process is with the @code{ps} utility, or with the @code{jobs -l} +shell command.) In this case, you must have permission to send the +process a signal, and it must have the same effective user ID as the +debugger. +@end table -@comment @item{encountered DBX-style class variable debugging information. -@comment You seem to have compiled your program with "g++ -g0" instead of "g++ -g". -@comment Therefore _GDBN__ will not know about your class variables} -@comment -@comment This error indicates that the symbol information produced for a C++ -@comment program includes zero-size fields, which indicated static fields in -@comment a previous release of the G++ compiler. This message is probably -@comment obsolete. -@comment -@item bad string table offset in symbol @var{n} +When using @samp{attach}, you should first use the @samp{file} command +to specify the program running in the process and load its symbol table. -Symbol number @var{n} contains a pointer into the string table which is -larger than the size of the string table. _GDBN__ circumvents the problem -by considering the symbol to have the name @code{foo}, which may cause -other problems if many symbols end up with this name. @cindex{foo} +The first thing _GDBN__ does after arranging to debug the process is to stop +it. You can examine and modify an attached process with all the _GDBN__ +commands that ordinarily available when you start processes with +@samp{run}. You can insert breakpoints; you can step and continue; you +can modify storage. If you would rather the process continue running, +you may use the @samp{continue} command after attaching _GDBN__ to the +process. -@item unknown symbol type @code{0xNN} +@kindex detach +When you have finished debugging the attached process, you can use the +@samp{detach} command to release it from _GDBN__'s control. Detaching +the process continues its execution. After the @samp{detach} command, +that process and _GDBN__ become completely independent once more, and you +are ready to @samp{attach} another process or start one with @samp{run}. -The symbol information contains new data types that _GDBN__ does not yet -know how to read. @code{0xNN} is the symbol type of the misunderstood -information, in hexadecimal. _GDBN__ circumvents the error by ignoring -this symbol information. This will usually allow the program to be -debugged, though certain symbols will not be accessible. If you -encounter such a problem and feel like debugging it, you can debug _GDBP__ -with itself, breakpoint on "complain", then go "up" to -read_dbx_symtab() and examine *bufp to see the symbol. +If you exit _GDBN__ or use the @samp{run} command while you have an attached +process, you kill that process. By default, you will be asked for +confirmation if you try to do either of these things; you can control +whether or not this happens by using the @samp{set caution} command +(@pxref{User Interface}). -@c @item stub type has NULL name -@c -@c FIXME, Mike Tiemann needs to write about what this means. +@node Kill Process, , Attach, Running +@section Killing the Child Process -@item const/volatile indicator missing, got 'X' +@table @code +@item kill +@kindex kill +Kill the child process in which your program is running under _GDBN__. +@end table -The symbol information for a C++ type is missing some information that -the compiler should have output for it. +This command is useful if you wish to debug a core dump instead. _GDBN__ +ignores any core dump file if it is actually running the program. -@item C++ type mismatch between compiler and debugger +On some operating systems, you can't execute your program in another +process while breakpoints are active inside _GDBN__. The @samp{kill} +command is also useful in this situation, if you wish to run the program +outside the debugger. -The debugger could not parse a type specification output by the compiler -for some C++ object. +The @samp{kill} command is also useful if you wish to recompile and +relink the program, since on many systems it is impossible to modify an +executable file which is running in a process. In this case, when you +next type @samp{run}, _GDBN__ will notice that the file has changed, and +will re-read the symbol table (while trying to preserve your current +breakpoint settings). -@end table +@node Stopping, Stack, Running, Top +@chapter Stopping and Continuing -@item core-file @var{filename} -@itemx core @var{filename} -@kindex core -@kindex core-file -Specify the whereabouts of a core dump file to be used as the ``contents -of memory''. Traditionally, core files contain only some parts of the -address space of the process that generated them; _GDBN__ can access the -executable file itself for other parts. +When you run a program normally, it runs until it terminates. The +principal purpose of using a debugger is so that you can stop it before +that point; or so that if the program runs into trouble you can +investigate and find out why. -@samp{core-file} with no argument specifies that no core file is -to be used. +@menu +* Signals:: Fatal signals in your program just stop it; + then you can use _GDBN__ to see what is going on. +* Breakpoints:: Breakpoints let you stop your program when it + reaches a specified point in the code. + an expression changes. +* Continuing:: Resuming execution until the next signal or breakpoint. +* Stepping:: Stepping runs the program a short distance and + then stops it wherever it has come to. +@end menu -Note that the core file is ignored when your program is actually running -under _GDBN__. So, if you have been running the program and you wish to -debug a core file instead, you must kill the subprocess in which the -program is running. To do this, use the @samp{kill} command -(@pxref{Kill Process}). +@node Signals, Breakpoints, Stopping, Stopping +@section Signals +@cindex signals -@item load @var{filename} -@kindex load -This command will dynamically link @var{filename} on the current target, -performing any necessary downloads, then add @var{filename}'s symbol -table in the same way as the @samp{add-syms} command. +A signal is an asynchronous event that can happen in a program. The +operating system defines the possible kinds of signals, and gives each kind +a name and a number. For example, @code{SIGINT} is the signal a program +gets when you type @kbd{Ctrl-c}; @code{SIGSEGV} is the signal a program +gets from referencing a place in memory far away from all the areas in use; +@code{SIGALRM} occurs when the alarm clock timer goes off (which happens +only if the program has requested an alarm). -@item add-syms @var{filename} @var{address} -@kindex add-syms -@cindex dynamic linking -The @samp{add-syms} command reads additional symbol table information -from the file @var{filename}. You would use this command when that file -has been dynamically loaded (by some other means) into the program that -is running. @var{address} should be the memory address at which the -file has been loaded; _GDBN__ cannot figure this out for itself. +@cindex fatal signals +Some signals, including @code{SIGALRM}, are a normal part of the +functioning of the program. Others, such as @code{SIGSEGV}, indicate +errors; these signals are @dfn{fatal} (kill the program immediately) if the +program has not specified in advance some other way to handle the signal. +@code{SIGINT} does not indicate an error in the program, but it is normally +fatal so it can carry out the purpose of @kbd{Ctrl-c}: to kill the program. -The symbol table of the file @var{filename} is added to the symbol table -originally read with the @samp{symbol-file} command. You can use the -@samp{add-syms} command any number of times; the new symbol data thus -read keeps adding to the old. The @samp{symbol-file} command forgets -all the symbol data _GDBN__ has read. +_GDBN__ has the ability to detect any occurrence of a signal in the program +running under _GDBN__'s control. You can tell _GDBN__ in advance what to do for +each kind of signal. -@item info files -@itemx info target -@kindex info files -@kindex info target -@samp{info files} and @samp{info target} are synonymous; both print the -current targets (@pxref{Targets}), including the names of the -executable and core dump files currently in use by _GDBN__, and the files -from which symbols were loaded. +@cindex handling signals +Normally, _GDBN__ is set up to ignore non-erroneous signals like @code{SIGALRM} +(so as not to interfere with their role in the functioning of the program) +but to stop the program immediately whenever an error signal happens. +You can change these settings with the @samp{handle} command. -Beware: the similar command @samp{info targets} lists all possible -targets rather than current ones. +@table @code +@item info signal +@kindex info signal +Print a table of all the kinds of signals and how _GDBN__ has been told to +handle each one. You can use this to see the signal numbers of all +the defined types of signals. +@item handle @var{signal} @var{keywords}@dots{} +@kindex handle +Change the way _GDBN__ handles signal @var{signal}. @var{signal} can be the +number of a signal or its name (with or without the @samp{SIG} at the +beginning). The @var{keywords} say what change to make. @end table -While all three file-specifying commands allow both absolute and relative -file names as arguments, _GDBN__ always converts the file name to an absolute -one and remembers it that way. - -@kindex sharedlibrary -@kindex share -@cindex shared libraries - -_GDBN__ supports the SunOS shared library format. Symbols from a shared -library cannot be referenced before the shared library has been linked -with the program. (That is to say, after one types @samp{run} and -the function @code{main()} has been entered; or when examining core -files.) Once the shared library has been linked in, you can use the -following commands: +The keywords allowed by the @samp{handle} command can be abbreviated. +Their full names are @table @code -@item sharedlibrary @var{regex} -@itemx share @var{regex} -Load shared object library symbols for files matching a UNIX regular -expression. +@item nostop +_GDBN__ should not stop the program when this signal happens. It may +still print a message telling you that the signal has come in. -@item share -@itemx sharedlibrary -Load symbols for all shared libraries. +@item stop +_GDBN__ should stop the program when this signal happens. This implies +the @samp{print} keyword as well. -@item info share -@itemx info sharedlibrary -@kindex info sharedlibrary -@kindex info share -Print the names of the shared libraries which are currently loaded. -@end table +@item print +_GDBN__ should print a message when this signal happens. +@item noprint +_GDBN__ should not mention the occurrence of the signal at all. This +implies the @samp{nostop} keyword as well. -@node Compilation, Targets, Files, Top -@chapter Compiling for Debugging +@item pass +_GDBN__ should allow the program to see this signal; the program will be +able to handle the signal, or may be terminated if the signal is fatal +and not handled. -In order to debug a program effectively, you need to ask for debugging -information when you compile it. This debugging information is stored -in the object file; it describes the data type of each variable or -function and the correspondence between source line numbers and -addresses in the executable code. +@item nopass +_GDBN__ should not allow the program to see this signal. +@end table -To request debugging information, specify the @samp{-g} option when you run -the compiler. +When a signal has been set to stop the program, the program cannot see the +signal until you continue. It will see the signal then, if @samp{pass} is +in effect for the signal in question @i{at that time}. In other words, +after _GDBN__ reports a signal, you can use the @samp{handle} command with +@samp{pass} or @samp{nopass} to control whether that signal will be seen by +the program when you later continue it. -The Unix C compiler is unable to handle the @samp{-g} and @samp{-O} options -together. This means that you cannot ask for optimization if you ask for -debugger information. +You can also use the @samp{signal} command to prevent the program from +seeing a signal, or cause it to see a signal it normally would not see, +or to give it any signal at any time. @xref{Signaling}. -The GNU C compiler supports @samp{-g} with or without @samp{-O}, making it -possible to debug optimized code. We recommend that you @emph{always} use -@samp{-g} whenever you compile a program. You may think the program is -correct, but there's no sense in pushing your luck. +@node Breakpoints, Continuing, Signals, Stopping +@section Breakpoints -Some things do not work as well with @samp{-g -O} as with just -@samp{-g}, particularly on machines with instruction scheduling. If in -doubt, recompile with @samp{-g} alone, and if this fixes the problem, -please report it as a bug (including a test case---@pxref{_GDBN__ Bugs}). +@cindex breakpoints +A @dfn{breakpoint} makes your program stop whenever a certain point in the +program is reached. You set breakpoints explicitly with _GDBN__ commands, +specifying the place where the program should stop by line number, function +name or exact address in the program. You can add various other conditions +to control whether the program will stop. -Older versions of the GNU C compiler, _GCC__, permitted a variant option -@samp{-gg} for debugging information. _GDBN__ no longer supports this format; -if your GNU C compiler has this option, do not use it. +Each breakpoint is assigned a number when it is created; these numbers are +successive integers starting with 1. In many of the commands for controlling +various features of breakpoints you use the breakpoint number to say which +breakpoint you want to change. Each breakpoint may be @dfn{enabled} or +@dfn{disabled}; if disabled, it has no effect on the program until you +enable it again. -@ignore -@comment As far as I know, there are no cases in which _GDBN__ will -@comment produce strange output in this case. (but no promises). -If your program includes archives made with the @code{ar} program, and -if the object files used as input to @code{ar} were compiled without the -@samp{-g} option and have names longer than 15 characters, _GDBN__ will get -confused reading the program's symbol table. No error message will be -given, but _GDBN__ may behave strangely. The reason for this problem is a -deficiency in the Unix archive file format, which cannot represent file -names longer than 15 characters. +@table @code +@kindex info break +@kindex $_ +@item info break +The command @samp{info break} prints a list of all breakpoints set and not +deleted, showing their numbers, where in the program they are, and any +special features in use for them. Disabled breakpoints are included in the +list, but marked as disabled. @samp{info break} with a breakpoint number +as argument lists only that breakpoint. The convenience variable @code{$_} +and the default examining-address for the @samp{x} command are set to the +address of the last breakpoint listed (@pxref{Memory}). -To avoid this problem, compile the archive members with the @samp{-g} -option or use shorter file names. Alternatively, use a version of GNU -@code{ar} dated more recently than August 1989. -@end ignore +@kindex info watch +@item info watch +This command prints a list of watchpoints. -@node Targets, Running, Compilation, Top -@chapter Specifying a Debugging Target -@cindex debugging target -@kindex target -A @dfn{target} is an interface between the debugger and a particular -kind of file or process. +@cindex watchpoints +A @dfn{watchpoint} is a special breakpoint that stops your program when +the value of an expression changes. You can use a watchpoint to stop +execution whenever the value of an expression changes, without having to +predict a particular place in the inferior process where this may +happen. Aside from the different syntax in setting a watchpoint, it is +managed exactly like any other breakpoint and is enabled, disabled, and +deleted using exactly the same commands. -Often, you will be able to run _GDBN__ in the same host environment as the -program you are debugging; in that case, the debugging target can just be -specified as a side effect of the @samp{file} or @samp{core} commands. -When you need more flexibility---for example, running _GDBN__ on a -physically separate host, controlling standalone systems over a -serial port, or realtime systems over a TCP/IP connection---you can use -the @samp{target} command. +Watchpoints currently execute two orders of magnitude more slowly than +other breakpoints, but this can well be worth it to catch errors where +you have no clue what part of your program is the culprit. Some +processors provide special hardware to implement this feature; future +releases of _GDBN__ will use such hardware if it is available. + +@end table @menu -* Active Targets:: Active Targets -* Target Commands:: Commands for Managing Targets +* Set Breaks:: How to establish breakpoints. +* Exception Handling:: How _GDBN__ supports exception handling for C++. +* Delete Breaks:: How to remove breakpoints no longer needed. +* Disabling:: How to disable breakpoints (turn them off temporarily). +* Conditions:: Making extra conditions on whether to stop. +* Break Commands:: Commands to be executed at a breakpoint. +* Error in Breakpoints:: @end menu -@node Active Targets, Target Commands, Targets, Targets -@section Active Targets -@cindex stacking targets -@cindex active targets -@cindex multiple targets +@node Set Breaks, Exception Handling, Breakpoints, Breakpoints +@subsection Setting Breakpoints -Targets are managed in three @dfn{strata} that correspond to different -classes of target: processes, core files, and executable files. This -allows you to (for example) start a process and inspect its activity -without abandoning your work on a core file. +@kindex break +@kindex watch +Breakpoints are set with the @samp{break} command (abbreviated @samp{b}). +Watchpoints are set with the @samp{watch} command. -More than one target can potentially respond to a request. In -particular, when you access memory _GDBN__ will walk down the three strata of -targets until it finds a target that can handle that particular address. +You have several ways to say where the breakpoint should go. -Strata are always examined in a fixed order: first a process if there is -one, then a core file if there is one, and finally an executable file if -there is one of those. +@table @code +@item break @var{function} +Set a breakpoint at entry to function @var{function}. -When you specify a new target in a given stratum, it replaces any target -previously in that stratum. +@item break @var{+offset} +@itemx break @var{-offset} +Set a breakpoint some number of lines forward or back from the position +at which execution stopped in the currently selected frame. -To get rid of a target without replacing it, use the @samp{detach} -command. The related command @samp{attach} provides you with a way of -choosing a particular running process as a new target. @xref{Attach}. +@item break @var{linenum} +Set a breakpoint at line @var{linenum} in the current source file. +That file is the last file whose source text was printed. This +breakpoint will stop the program just before it executes any of the +code on that line. -@node Target Commands, , Active Targets, Targets -@section Commands for Managing Targets +@item break @var{filename}:@var{linenum} +Set a breakpoint at line @var{linenum} in source file @var{filename}. -@table @code -@item target @var{type} @var{parameters} -Connects the _GDBN__ host environment to a target machine or process. A -target is typically a protocol for talking to debugging facilities. You -use the argument @var{type} to specify the type or protocol of the -target machine; for example, @samp{target vxworks} for a TCP/IP link to -a VxWorks system. +@item break @var{filename}:@var{function} +Set a breakpoint at entry to function @var{function} found in file +@var{filename}. Specifying a file name as well as a function name is +superfluous except when multiple files contain similarly named +functions. + +@item break *@var{address} +Set a breakpoint at address @var{address}. You can use this to set +breakpoints in parts of the program which do not have debugging +information or source files. + +@item break +Set a breakpoint at the next instruction to be executed in the selected +stack frame (@pxref{Stack}). In any selected frame but the innermost, +this will cause the program to stop as soon as control returns to that +frame. This is equivalent to a @samp{finish} command in the frame +inside the selected frame. If this is done in the innermost frame, _GDBN__ +will stop the next time it reaches the current location; this may be +useful inside of loops. + +_GDBN__ normally ignores breakpoints when it resumes execution, until at +least one instruction has been executed. If it did not do this, you +would be unable to proceed past a breakpoint without first disabling the +breakpoint. This rule applies whether or not the breakpoint already +existed when the program stopped. + +@item break @dots{} if @var{cond} +Set a breakpoint with condition @var{cond}; evaluate the expression +@var{cond} each time the breakpoint is reached, and stop only if the +value is nonzero. @samp{@dots{}} stands for one of the possible +arguments described above (or no argument) specifying where to break. +@xref{Conditions}, for more information on breakpoint conditions. + +@item tbreak @var{args} +@kindex tbreak +Set a breakpoint enabled only for one stop. @var{args} are the +same as in the @samp{break} command, and the breakpoint is set in the same +way, but the breakpoint is automatically disabled the first time it +is hit. @xref{Disabling}. + +@item rbreak @var{regex} +@kindex rbreak +Set a breakpoint on all functions matching @var{regex}. This is +useful for setting breakpoints on overloaded functions that are not +members of any special classes. This command sets an unconditional +breakpoint on all matches, printing a list of all breakpoints it set. +Once these breakpoints are set, they are treated just like the +breakpoints set with the @samp{break} command. They can be deleted, +disabled, made conditional, etc., in the standard ways. + +@kindex watch +@item watch @var{expr} +Set a watchpoint for an expression. +@end table + +_GDBN__ allows you to set any number of breakpoints at the same place in the +program. There is nothing silly or meaningless about this. When the +breakpoints are conditional, this is even useful (@pxref{Conditions}). + +@node Exception Handling, Delete Breaks, Set Breaks, Breakpoints +@subsection Breakpoints and Exceptions +@cindex exception handlers + +Some languages, such as GNU C++, implement exception handling. _GDBN__ +can be used to examine what caused the program to raise an exception +and to list the exceptions the program is prepared to handle at a +given point in time. + +@cindex raise exceptions +GNU C++ raises an exception by calling a library function named +@code{__raise_exception} which has the following ANSI C interface: -Further @var{parameters} are interpreted by the target protocol, but -typically include things like device names or host names to connect -with, process numbers, and baud rates. Executing @example - target @var{type} + /* ADDR is where the exception identifier is stored. + ID is the exception identifier. */ + void __raise_exception (void **addr, void *id); @end example @noindent -(without any parameters) will issue a message about what -parameters are required for that target type. +You can make the debugger catch all exceptions @emph{before} any stack +unwinding takes place: set a breakpoint on @code{__raise_exception} +(@pxref{Breakpoints}). If you set a breakpoint in an exception handler +instead, it may not be easy to find out where the exception was raised. -@item info targets -@kindex info targets -Displays the names of all targets available. Beware: the similar -command @samp{info target} displays targets currently in use rather than -all available ones. @samp{info files} gives the same information as -@samp{info target} (@pxref{Files}). +By using a conditional breakpoint (@xref{Conditions}), you can cause +the debugger to stop only when a specific exception is raised. +Multiple conditional breakpoints can be used to stop the program when +any of a number of exceptions are raised. + +@table @code +@item catch @var{exceptions} +@kindex catch + +Breakpoints can be set at active exception handlers by using the +@samp{catch} command. @var{exceptions} is a list of names of exceptions +to catch. @end table -Here are some common targets (available, or not, depending on _GDBN__ -configuration): +You can use @samp{info catch} to list active exception handlers; +@pxref{Frame Info}. -@table @code -@item target exec @var{prog} -@kindex target exec -An executable file. @samp{target exec @var{prog}} is the same as -@samp{exec-file @var{prog}}. +There are currently some limitations to exception handling in _GDBN__. +These will be corrected in a future release. -@item target core @var{filename} -@kindex target core -A core dump file. @samp{target core @var{filename}} is the same as -@samp{core-file @var{filename}}. +@itemize @bullet +@item +If you call a function interactively, _GDBN__ will normally return +control to you when the function has finished executing. If the call +raises an exception, however, the call may bypass the mechanism that +returns control to the user and cause the program to simply continue +running until it hits a breakpoint, catches a signal that _GDBN__ is +listening for, or exits. +@item +You cannot raise an exception interactively. +@item +You cannot interactively install an exception handler. +@end itemize -@item target remote @var{dev} -@kindex target remote -Remote serial target in _GDBP__-specific protocol. The argument @var{dev} -specifies what serial device to use for the connection (e.g. -@code{/dev/ttya}). +@node Delete Breaks, Disabling, Exception Handling, Breakpoints +@subsection Deleting Breakpoints -_if__(_AMD29K__) -@item target amd-eb @var{dev} @var{speed} @var{PROG} -@kindex target amd-eb -@cindex AMD EB29K -Remote PC-resident AMD EB29K board, attached over serial lines. -@var{dev} is the serial device, as for @samp{target remote}; -@samp{speed} allows you to specify the linespeed; and @var{PROG} is the -name of the program to be debugged, as it appears to DOS on the PC. -@xref{AMD29K Remote}. +@cindex clearing breakpoints, watchpoints +@cindex deleting breakpoints, watchpoints +It is often necessary to eliminate a breakpoint once it has done its job +and you no longer want the program to stop there. This is called +@dfn{deleting} the breakpoint. A breakpoint that has been deleted no +longer exists in any sense; it is forgotten. -_fi__(_AMD29K__) -_if__(_I960__) -@item target nindy @var{devicename} -@kindex target nindy -An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is -the name of the serial device to use for the connection, e.g. -@samp{/dev/ttya}. +With the @samp{clear} command you can delete breakpoints according to where +they are in the program. With the @samp{delete} command you can delete +individual breakpoints by specifying their breakpoint numbers. -_fi__(_I960__) -_if__(_VXWORKS__) -@item target vxworks @var{machinename} -@kindex target vxworks -A VxWorks system, attached via TCP/IP. The argument @var{machinename} -is the target system's machine name or IP address. +It is not necessary to delete a breakpoint to proceed past it. _GDBN__ +automatically ignores breakpoints on the first instruction to be executed +when you continue execution without changing the execution address. -_fi__(_VXWORKS__) +@table @code +@item clear +@kindex clear +Delete any breakpoints at the next instruction to be executed in the +selected stack frame (@pxref{Selection}). When the innermost frame +is selected, this is a good way to delete a breakpoint that the program +just stopped at. + +@item clear @var{function} +@itemx clear @var{filename}:@var{function} +Delete any breakpoints set at entry to the function @var{function}. + +@item clear @var{linenum} +@itemx clear @var{filename}:@var{linenum} +Delete any breakpoints set at or within the code of the specified line. + +@item delete breakpoints @var{bnums}@dots{} +@itemx delete @var{bnums}@dots{} +@itemx delete +@kindex delete breakpoints +@kindex delete +Delete the breakpoints of the numbers specified as arguments. If no +argument is specified, delete all breakpoints. @end table -_if__(_GENERIC__) -Different targets are available on different configurations of _GDBN__; your -configuration may have more or fewer targets. -_fi__(_GENERIC__) +@node Disabling, Conditions, Delete Breaks, Breakpoints +@subsection Disabling Breakpoints -@node Running, Stopping, Targets, Top -@chapter Running Programs Under _GDBN__ +@cindex disabled breakpoints +@cindex enabled breakpoints +Rather than deleting a breakpoint, you might prefer to @dfn{disable} it. +This makes the breakpoint inoperative as if it had been deleted, but +remembers the information on the breakpoint so that you can @dfn{enable} +it again later. -@cindex running -@kindex run -To start your program under _GDBN__, use the @samp{run} command. Except on -VxWorks, the program must already have been specified using the -@samp{file} or @samp{exec-file} command, or with an argument to _GDBN__ -(@pxref{Files}). +You disable and enable breakpoints with the @samp{enable} and +@samp{disable} commands, optionally specifying one or more breakpoint +numbers as arguments. Use @samp{info break} to print a list of +breakpoints if you don't know which breakpoint numbers to use. -On targets that support processes, @samp{run} creates an inferior -process and makes that process run your program. On other targets, -@samp{run} jumps to the location it has recorded for the start of the -program. +A breakpoint can have any of four different states of enablement: -The execution of a program is affected by certain information it -receives from its superior. _GDBN__ provides ways to specify this -information, which you must do @i{before} starting the program. (You -can change it after starting the program, but such changes do not affect -the program unless you start it over again.) This information may be -divided into three categories: +@itemize @bullet +@item +Enabled. The breakpoint will stop the program. A breakpoint made +with the @samp{break} command starts out in this state. +@item +Disabled. The breakpoint has no effect on the program. +@item +Enabled once. The breakpoint will stop the program, but +when it does so it will become disabled. A breakpoint made +with the @samp{tbreak} command starts out in this state. +@item +Enabled for deletion. The breakpoint will stop the program, but +immediately after it does so it will be deleted permanently. +@end itemize -@table @asis -@item The @i{arguments.} -You specify the arguments to give the program as the arguments of the -@samp{run} command. If a shell is available on your target, the shell -is used to pass the arguments, so that you may use normal conventions -(for example regular expression expansion or variable substitution) in -describing the arguments. In Unix systems, you can control which shell -is used with the @code{SHELL} environment variable. +You can use the following commands to enable or disable a breakpoint: -@item The @i{environment.} -The program normally inherits its environment from _GDBN__, but you can -use the _GDBN__ commands @samp{set environment} and -@samp{unset environment} to change parts of the environment that will -be given to the program.@refill +@table @code +@item disable breakpoints @var{bnums}@dots{} +@itemx disable @var{bnums}@dots{} +@itemx disable +@kindex disable breakpoints +@kindex disable +Disable the specified breakpoints---or all breakpoints, if none are +listed. A disabled breakpoint has no effect but is not forgotten. All +options such as ignore-counts, conditions and commands are remembered in +case the breakpoint is enabled again later. -@item The @i{working directory.} -The program inherits its working directory from _GDBN__. You can set _GDBN__'s -working directory with the @samp{cd} command in _GDBN__. +@item enable breakpoints @var{bnums}@dots{} +@itemx enable @var{bnums}@dots{} +@itemx enable +@kindex enable breakpoints +@kindex enable +Enable the specified breakpoints (or all defined breakpoints). They +become effective once again in stopping the program, until you specify +otherwise. + +@item enable breakpoints once @var{bnums}@dots{} +@itemx enable once @var{bnums}@dots{} +Enable the specified breakpoints temporarily. Each will be disabled +again the next time it stops the program (unless you have used one of +these commands to specify a different state before that time comes). + +@item enable breakpoints delete @var{bnums}@dots{} +@itemx enable delete @var{bnums}@dots{} +Enable the specified breakpoints to work once and then die. Each of +the breakpoints will be deleted the next time it stops the program +(unless you have used one of these commands to specify a different +state before that time comes). @end table -When you issue the @samp{run} command, your program begins to execute -immediately. @xref{Stopping}, for discussion of how to arrange for your -program to stop. +Save for a breakpoint set with @samp{tbreak} (@pxref{Set Breaks}), +breakpoints that you set are enabled or disabled only when you use one +of the commands above. (The command @samp{until} can set and delete a +breakpoint on its own, but it will not change the state of your +breakpoints). -Note that once your program has been started by the @samp{run} command, -you may evaluate expressions that involve calls to functions in the -inferior, using the @samp{print} or @samp{call} commands. @xref{Data}. +@node Conditions, Break Commands, Disabling, Breakpoints +@subsection Break Conditions +@cindex conditional breakpoints +@cindex breakpoint conditions -If the modification time of your symbol file has changed since the last -time _GDBN__ read its symbols, _GDBN__ will discard its symbol table and re-read -it. In this process, it tries to retain your current breakpoints. +The simplest sort of breakpoint breaks every time the program reaches a +specified place. You can also specify a @dfn{condition} for a +breakpoint. A condition is just a boolean expression in your +programming language. (@xref{Expressions}). A breakpoint with a +condition evaluates the expression each time the program reaches it, and +the program stops only if the condition is true. -@menu -* Arguments:: Specifying the arguments for your program. -* Environment:: Specifying the environment for your program. -* Working Directory:: Specifying the working directory for giving - to your program when it is run. -* Input/Output:: Specifying the program's standard input and output. -* Attach:: Debugging a process started outside _GDBN__. -* Kill Process:: Getting rid of the child process running your program. -@end menu +Break conditions may have side effects, and may even call functions in your +program. These may sound like strange things to do, but their effects are +completely predictable unless there is another enabled breakpoint at the +same address. (In that case, _GDBN__ might see the other breakpoint first and +stop the program without checking the condition of this one.) Note that +breakpoint commands are usually more convenient and flexible for the +purpose of performing side effects when a breakpoint is reached +(@pxref{Break Commands}). -@node Arguments, Environment, Running, Running -@section Your Program's Arguments +Break conditions can be specified when a breakpoint is set, by using +@samp{if} in the arguments to the @samp{break} command. @xref{Set Breaks}. +They can also be changed at any time with the @samp{condition} command: -@cindex arguments (to your program) -The arguments to your program are specified by the arguments of the -@samp{run} command. They are passed to a shell, which expands wildcard -characters and performs redirection of I/O, and thence to the program. +@table @code +@item condition @var{bnum} @var{expression} +@kindex condition +Specify @var{expression} as the break condition for breakpoint number +@var{bnum}. From now on, this breakpoint will stop the program only if +the value of @var{expression} is true (nonzero, in C). @var{expression} +is not evaluated at the time the @samp{condition} command is given. +When you call @samp{condition}, the expression you specify is checked +immediately for syntactic correctness, and to determine whether symbols +in it have referents in the context of your breakpoint. +@xref{Expressions}. -@samp{run} with no arguments uses the same arguments used by the previous -@samp{run}. +@item condition @var{bnum} +Remove the condition from breakpoint number @var{bnum}. It becomes +an ordinary unconditional breakpoint. +@end table + +@cindex ignore count (of breakpoint) +A special case of a breakpoint condition is to stop only when the +breakpoint has been reached a certain number of times. This is so +useful that there is a special way to do it, using the @dfn{ignore +count} of the breakpoint. Every breakpoint has an ignore count, which +is an integer. Most of the time, the ignore count is zero, and +therefore has no effect. But if the program reaches a breakpoint whose +ignore count is positive, then instead of stopping, it just decrements +the ignore count by one and continues. As a result, if the ignore count +value is @var{n}, the breakpoint will not stop the next @var{n} times it +is reached. -@kindex set args @table @code -@item set args -The command @samp{set args} can be used to specify the arguments to be used -the next time the program is run. If @samp{set args} has no arguments, it -means to use no arguments the next time the program is run. If you have -run your program with arguments and want to run it again with no arguments, -this is the only way to do so. +@item ignore @var{bnum} @var{count} +@kindex ignore +Set the ignore count of breakpoint number @var{bnum} to @var{count}. +The next @var{count} times the breakpoint is reached, your program's +execution will not stop; other than to decrement the ignore count, _GDBN__ +takes no action. -@item show args -@kindex show args -Show the arguments to give your program when it is started. +To make the breakpoint stop the next time it is reached, specify +a count of zero. + +@item continue @var{count} +@itemx cont @var{count} +@itemx c @var{count} +@itemx fg @var{count} +@kindex cont @var{count} +@kindex continue @var{count} +Continue execution of the program, setting the ignore count of the +breakpoint that the program stopped at to @var{count} minus one. +Thus, the program will not stop at this breakpoint until the +@var{count}'th time it is reached. + +This command is allowed only when the program stopped due to a +breakpoint. At other times, the argument to @samp{cont} is ignored. + +The synonym @samp{fg} is provided purely for convenience, and has +exactly the same behavior as other forms of the command. @end table -@node Environment, Working Directory, Arguments, Running -@section Your Program's Environment +If a breakpoint has a positive ignore count and a condition, the condition +is not checked. Once the ignore count reaches zero, the condition will +be checked. -@cindex environment (of your program) -The @dfn{environment} consists of a set of @dfn{environment variables} and -their values. Environment variables conventionally record such things as -your user name, your home directory, your terminal type, and your search -path for programs to run. Usually you set up environment variables with -the shell and they are inherited by all the other programs you run. When -debugging, it can be useful to try running the program with different -environments without having to start the debugger over again. +Note that you could achieve the effect of the ignore count with a +condition such as _0__@w{@samp{$foo-- <= 0}}_1__ using a debugger convenience +variable that is decremented each time. @xref{Convenience Vars}. + +@node Break Commands, Error in Breakpoints, Conditions, Breakpoints +@subsection Commands Executed on Breaking + +@cindex breakpoint commands +You can give any breakpoint a series of commands to execute when the +program stops due to that breakpoint. For example, you might want to +print the values of certain expressions, or enable other breakpoints. + +@table @code +@item commands @var{bnum} +@kindex commands +Specify a list of commands for breakpoint number @var{bnum}. The commands +themselves appear on the following lines. Type a line containing just +@samp{end} to terminate the commands. + +To remove all commands from a breakpoint, use the command +@samp{commands} and follow it immediately by @samp{end}; that is, give +no commands. + +With no arguments, @samp{commands} refers to the last breakpoint set +(not to the breakpoint most recently encountered). +@end table + +You can use breakpoint commands to start the program up again. Simply +use the @samp{cont} command, or @samp{step}, or any other command to +resume execution. However, if you do this, any further commands in the +same breakpoint's command list are ignored. When the program stops +again, _GDBN__ will act according to the cause of that stop. + +@kindex silent +If the first command specified is @samp{silent}, the usual message about +stopping at a breakpoint is not printed. This may be desirable for +breakpoints that are to print a specific message and then continue. +If the remaining commands too print nothing, you will see no sign that +the breakpoint was reached at all. @samp{silent} is not really a command; +it is meaningful only at the beginning of the commands for a breakpoint. -@table @code -@item show environment @var{varname} -@kindex show environment -Print the value of environment variable @var{varname} to be given to -your program when it is started. +The commands @samp{echo} and @samp{output} that allow you to print precisely +controlled output are often useful in silent breakpoints. @xref{Output}. -@item show environment -Print the names and values of all environment variables to be given to -your program when it is started. +For example, here is how you could use breakpoint commands to print the +value of @code{x} at entry to @code{foo} whenever it is positive. -@item set environment @var{varname} @var{value} -@itemx set environment @var{varname} = @var{value} -@kindex set environment -Sets environment variable @var{varname} to @var{value}, for your program -only, not for _GDBN__ itself. @var{value} may be any string; the values of -environment variables are just strings, and any interpretation is -supplied by your program itself. The @var{value} parameter is optional; -if it is eliminated, the variable is set to a null value. +_0__@example +break foo if x>0 +commands +silent +echo x is\040 +output x +echo \n +cont +end +_1__@end example -For example, this command: +One application for breakpoint commands is to correct one bug so you can +test another. Put a breakpoint just after the erroneous line of code, give +it a condition to detect the case in which something erroneous has been +done, and give it commands to assign correct values to any variables that +need them. End with the @samp{cont} command so that the program does not +stop, and start with the @samp{silent} command so that no output is +produced. Here is an example: @example -set env USER = foo +break 403 +commands +silent +set x = y + 4 +cont +end @end example -@noindent -tells the program, when subsequently run, to assume it is being run -on behalf of the user named @samp{foo}. +One deficiency in the operation of automatically continuing breakpoints +under Unix appears when your program uses raw mode for the terminal. +_GDBN__ switches back to its own terminal modes (not raw) before executing +commands, and then must switch back to raw mode when your program is +continued. This causes any pending terminal input to be lost. +In the GNU system, this will be fixed by changing the behavior of +terminal modes. -@item delete environment @var{varname} -@itemx unset environment @var{varname} -@kindex delete environment -@kindex unset environment -Remove variable @var{varname} from the environment to be passed to your -program. This is different from @samp{set env @var{varname}@ =}; -@samp{delete environment} removes the variable from the environment, -rather than assigning it an empty value. This command can be -abbreviated @samp{d e}. -@end table +Under Unix, when you have this problem, you might be able to get around +it by putting your actions into the breakpoint condition instead of +commands. For example -@node Working Directory, Input/Output, Environment, Running -@section Your Program's Working Directory +@example +condition 5 (x = y + 4), 0 +@end example -@cindex working directory (of your program) -Each time you start your program with @samp{run}, it inherits its -working directory from the current working directory of _GDBN__. _GDBN__'s -working directory is initially whatever it inherited from its parent -process (typically the shell), but you can specify a new working -directory in _GDBN__ with the @samp{cd} command. +@noindent +specifies a condition expression (@xref{Expressions}) that will change +@code{x} as needed, then always have the value 0 so the program will not +stop. Loss of input is avoided here because break conditions are +evaluated without changing the terminal modes. When you want to have +nontrivial conditions for performing the side effects, the operators +@samp{&&}, @samp{||} and @samp{?@dots{}:} may be useful. -The _GDBN__ working directory also serves as a default for the commands -that specify files for _GDBN__ to operate on. @xref{Files}. +@node Error in Breakpoints, , Break Commands, Breakpoints +@subsection ``Cannot Insert Breakpoints'' -@table @code -@item cd @var{directory} -@kindex cd -Set _GDBN__'s working directory to @var{directory}. +@c FIXME: "cannot insert breakpoints" error, v unclear. +@c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91 +Under some operating systems, breakpoints cannot be used in a program if +any other process is running that program. In this situation, +attempting to run or continue a program with a breakpoint will cause _GDBN__ +to stop the other process. -@item pwd -@kindex pwd -Print _GDBN__'s working directory. -@end table +When this happens, you have three ways to proceed: -@node Input/Output, Attach, Working Directory, Running -@section Your Program's Input and Output +@enumerate +@item +Remove or disable the breakpoints, then continue. -@cindex redirection -@cindex i/o -@cindex terminal -@cindex controlling terminal -By default, the program you run under _GDBN__ does input and output to the same -terminal that _GDBN__ uses. +@item +Suspend _GDBN__, and copy the file containing the program to a new name. +Resume _GDBN__ and use the @samp{exec-file} command to specify that _GDBN__ +should run the program under that name. Then start the program again. -You can redirect the program's input and/or output using @samp{sh}-style -redirection commands in the @samp{run} command. For example, +@item +Relink the program so that the text segment is nonsharable, using the +linker option @samp{-N}. The operating system limitation may not apply +to nonsharable executables. +@end enumerate -@example -run > outfile -@end example +@node Continuing, Stepping, Breakpoints, Stopping +@section Continuing -@noindent -starts the program, diverting its output to the file @file{outfile}. +After your program stops, most likely you will want it to run some more if +the bug you are looking for has not happened yet. -@kindex tty -Another way to specify where the program should do input and output is -with the @samp{tty} command. This command accepts a file name as -argument, and causes this file to be the default for future @samp{run} -commands. It also resets the controlling terminal for the child -process, for future @samp{run} commands. For example, +@table @code +@item continue +@item cont +@kindex cont +@kindex continue +Continue running the program at the place where it stopped. +@end table -@example -tty /dev/ttyb -@end example +If the program stopped at a breakpoint, the place to continue running +is the address of the breakpoint. You might expect that continuing would +just stop at the same breakpoint immediately. In fact, @samp{cont} +takes special care to prevent that from happening. You do not need +to delete the breakpoint to proceed through it after stopping at it. -@noindent -directs that processes started with subsequent @samp{run} commands -default to do input and output on the terminal @file{/dev/ttyb} and have -that as their controlling terminal. +You can, however, specify an ignore-count for the breakpoint that the +program stopped at, by means of an argument to the @samp{cont} command. +@xref{Conditions}. -An explicit redirection in @samp{run} overrides the @samp{tty} command's -effect on input/output redirection, but not its effect on the -controlling terminal. +If the program stopped because of a signal other than @code{SIGINT} or +@code{SIGTRAP}, continuing will cause the program to see that signal. +You may not want this to happen. For example, if the program stopped +due to some sort of memory reference error, you might store correct +values into the erroneous variables and continue, hoping to see more +execution; but the program would probably terminate immediately as +a result of the fatal signal once it sees the signal. To prevent this, +you can continue with @samp{signal 0}. @xref{Signaling}. You can +also act in advance to control what signals your program will see, using +the @samp{handle} command (@pxref{Signals}). -When you use the @samp{tty} command or redirect input in the @samp{run} -command, only the @emph{input for your program} is affected. The input -for _GDBN__ still comes from your terminal. +@node Stepping, , Continuing, Stopping +@section Stepping -@node Attach, Kill Process, Input/Output, Running -@section Debugging an Already-Running Process -@kindex attach -@cindex attach +@cindex stepping +@dfn{Stepping} means setting your program in motion for a limited time, so +that control will return automatically to the debugger after one line of +code or one machine instruction. Breakpoints are active during stepping +and the program will stop for them even if it has not gone as far as the +stepping command specifies. @table @code -@item attach @var{process--id} -This command attaches to a running process, if your currently selected -target supports processes. (@samp{info files} will show your active -targets). The command takes as argument a process ID. +@item step +@kindex step +Continue running the program until control reaches a different line, +then stop it and return control to the debugger. This command is +abbreviated @samp{s}. -You specify a process ID to debug an already-running process that was -started outside of _GDBN__. (The usual way to find out the process-id of -a Unix process is with the @code{ps} utility, or with the @code{jobs -l} -shell command.) In this case, you must have permission to send the -process a signal, and it must have the same effective user ID as the -debugger. -@end table +This command may be given when control is within a function for which +there is no debugging information. In that case, execution will proceed +until control reaches a different function, or is about to return from +this function. An argument repeats this action. -When using @samp{attach}, you should first use the @samp{file} command -to specify the program running in the process and load its symbol table. +@item step @var{count} +Continue running as in @samp{step}, but do so @var{count} times. If a +breakpoint is reached or a signal not related to stepping occurs before +@var{count} steps, stepping stops right away. -The first thing _GDBN__ does after arranging to debug the process is to stop -it. You can examine and modify an attached process with all the _GDBN__ -commands that ordinarily available when you start processes with -@samp{run}. You can insert breakpoints; you can step and continue; you -can modify storage. If you would rather the process continue running, -you may use the @samp{continue} command after attaching _GDBN__ to the -process. +@item next +@kindex next +Similar to @samp{step}, but any function calls appearing within the line of +code are executed without stopping. Execution stops when control reaches a +different line of code at the stack level which was executing when the +@samp{next} command was given. This command is abbreviated @samp{n}. -@kindex detach -When you have finished debugging the attached process, you can use the -@samp{detach} command to release it from _GDBN__'s control. Detaching -the process continues its execution. After the @samp{detach} command, -that process and _GDBN__ become completely independent once more, and you -are ready to @samp{attach} another process or start one with @samp{run}. +An argument is a repeat count, as in @samp{step}. -If you exit _GDBN__ or use the @samp{run} command while you have an attached -process, you kill that process. By default, you will be asked for -confirmation if you try to do either of these things; you can control -whether or not this happens by using the @samp{set caution} command -(@pxref{User Interface}). +@samp{next} within a function without debugging information acts as does +@samp{step}, but any function calls appearing within the code of the +function are executed without stopping. + +@item finish +@kindex finish +Continue running until just after the selected stack frame returns (or +until there is some other reason to stop, such as a fatal signal or a +breakpoint). Print value returned by the selected stack frame (if any). + +Contrast this with the @samp{return} command (@pxref{Returning}). -@node Kill Process, , Attach, Running -@section Killing the Child Process +@item until +@kindex until +This command is used to avoid single stepping through a loop more than +once. It is like the @samp{next} command, except that when @samp{until} +encounters a jump, it automatically continues execution until the +program counter is greater than the address of the jump. -@table @code -@item kill -@kindex kill -Kill the child process in which your program is running under _GDBN__. -@end table +This means that when you reach the end of a loop after single stepping +though it, @samp{until} will cause the program to continue execution +until the loop is exited. In contrast, a @samp{next} command at the end +of a loop will simply step back to the beginning of the loop, which +would force you to step through the next iteration. -This command is useful if you wish to debug a core dump instead. _GDBN__ -ignores any core dump file if it is actually running the program. +@samp{until} always stops the program if it attempts to exit the current +stack frame. -On some operating systems, you can't execute your program in another -process while breakpoints are active inside _GDBN__. The @samp{kill} -command is also useful in this situation, if you wish to run the program -outside the debugger. +@samp{until} may produce somewhat counterintuitive results if the order +of the source lines does not match the actual order of execution. For +example, in a typical C @code{for}-loop, the third expression in the +@code{for}-statement (the loop-step expression) is executed after the +statements in the body of the loop, but is written before them. +Therefore, the @samp{until} command would appear to step back to the +beginning of the loop when it advances to this expression. However, it +has not really done so, not in terms of the actual machine code. -The @samp{kill} command is also useful if you wish to recompile and -relink the program, since on many systems it is impossible to modify an -executable file which is running in a process. In this case, when you -next type @samp{run}, _GDBN__ will notice that the file has changed, and -will re-read the symbol table (while trying to preserve your current -breakpoint settings). +Note that @samp{until} with no argument works by means of single +instruction stepping, and hence is slower than @samp{until} with an +argument. -@node Stopping, Stack, Running, Top -@chapter Stopping and Continuing +@item until @var{location} +Continue running the program until either the specified location is +reached, or the current (innermost) stack frame returns. @var{location} +is any of the forms of argument acceptable to @samp{break} (@pxref{Set +Breaks}). This form of the command uses breakpoints, and hence is +quicker than @samp{until} without an argument. -When you run a program normally, it runs until it terminates. The -principal purpose of using a debugger is so that you can stop it before -that point; or so that if the program runs into trouble you can -investigate and find out why. +@item stepi +@itemx si +@kindex stepi +@kindex si +Execute one machine instruction, then stop and return to the debugger. -@menu -* Signals:: Fatal signals in your program just stop it; - then you can use _GDBN__ to see what is going on. -* Breakpoints:: Breakpoints let you stop your program when it - reaches a specified point in the code. - an expression changes. -* Continuing:: Resuming execution until the next signal or breakpoint. -* Stepping:: Stepping runs the program a short distance and - then stops it wherever it has come to. -@end menu +It is often useful to do @samp{display/i $pc} when stepping by machine +instructions. This will cause the next instruction to be executed to +be displayed automatically at each stop. @xref{Auto Display}. -@node Signals, Breakpoints, Stopping, Stopping -@section Signals -@cindex signals +An argument is a repeat count, as in @samp{step}. -A signal is an asynchronous event that can happen in a program. The -operating system defines the possible kinds of signals, and gives each kind -a name and a number. For example, @code{SIGINT} is the signal a program -gets when you type @kbd{Ctrl-c}; @code{SIGSEGV} is the signal a program -gets from referencing a place in memory far away from all the areas in use; -@code{SIGALRM} occurs when the alarm clock timer goes off (which happens -only if the program has requested an alarm). +@item nexti +@itemx ni +@kindex nexti +@kindex ni +Execute one machine instruction, but if it is a subroutine call, +proceed until the subroutine returns. -@cindex fatal signals -Some signals, including @code{SIGALRM}, are a normal part of the -functioning of the program. Others, such as @code{SIGSEGV}, indicate -errors; these signals are @dfn{fatal} (kill the program immediately) if the -program has not specified in advance some other way to handle the signal. -@code{SIGINT} does not indicate an error in the program, but it is normally -fatal so it can carry out the purpose of @kbd{Ctrl-c}: to kill the program. +An argument is a repeat count, as in @samp{next}. +@end table -_GDBN__ has the ability to detect any occurrence of a signal in the program -running under _GDBN__'s control. You can tell _GDBN__ in advance what to do for -each kind of signal. +A typical technique for using stepping is to put a breakpoint +(@pxref{Breakpoints}) at the beginning of the function or the section of +the program in which a problem is believed to lie, and then step through +the suspect area, examining the variables that are interesting, until the +problem happens. -@cindex handling signals -Normally, _GDBN__ is set up to ignore non-erroneous signals like @code{SIGALRM} -(so as not to interfere with their role in the functioning of the program) -but to stop the program immediately whenever an error signal happens. -You can change these settings with the @samp{handle} command. +The @samp{cont} command can be used after stepping to resume execution +until the next breakpoint or signal. -@table @code -@item info signal -@kindex info signal -Print a table of all the kinds of signals and how _GDBN__ has been told to -handle each one. You can use this to see the signal numbers of all -the defined types of signals. +@node Stack, Source, Stopping, Top +@chapter Examining the Stack -@item handle @var{signal} @var{keywords}@dots{} -@kindex handle -Change the way _GDBN__ handles signal @var{signal}. @var{signal} can be the -number of a signal or its name (with or without the @samp{SIG} at the -beginning). The @var{keywords} say what change to make. -@end table +When your program has stopped, the first thing you need to know is where it +stopped and how it got there. -The keywords allowed by the @samp{handle} command can be abbreviated. -Their full names are +@cindex call stack +Each time your program performs a function call, the information about +where in the program the call was made from is saved in a block of data +called a @dfn{stack frame}. The frame also contains the arguments of the +call and the local variables of the function that was called. All the +stack frames are allocated in a region of memory called the @dfn{call +stack}. -@table @code -@item nostop -_GDBN__ should not stop the program when this signal happens. It may -still print a message telling you that the signal has come in. +When your program stops, the _GDBN__ commands for examining the stack allow you +to see all of this information. -@item stop -_GDBN__ should stop the program when this signal happens. This implies -the @samp{print} keyword as well. +One of the stack frames is @dfn{selected} by _GDBN__ and many _GDBN__ commands +refer implicitly to the selected frame. In particular, whenever you ask +_GDBN__ for the value of a variable in the program, the value is found in the +selected frame. There are special _GDBN__ commands to select whichever frame +you are interested in. -@item print -_GDBN__ should print a message when this signal happens. +When the program stops, _GDBN__ automatically selects the currently executing +frame and describes it briefly as the @samp{frame} command does +(@pxref{Frame Info, Info}). -@item noprint -_GDBN__ should not mention the occurrence of the signal at all. This -implies the @samp{nostop} keyword as well. +@menu +* Frames:: Explanation of stack frames and terminology. +* Backtrace:: Summarizing many frames at once. +* Selection:: How to select a stack frame. +* Frame Info:: Information on a Frame +@end menu -@item pass -_GDBN__ should allow the program to see this signal; the program will be -able to handle the signal, or may be terminated if the signal is fatal -and not handled. +@node Frames, Backtrace, Stack, Stack +@section Stack Frames -@item nopass -_GDBN__ should not allow the program to see this signal. -@end table +@cindex frame +@cindex stack frame +The call stack is divided up into contiguous pieces called @dfn{stack +frames}, or @dfn{frames} for short; each frame is the data associated +with one call to one function. The frame contains the arguments given +to the function, the function's local variables, and the address at +which the function is executing. -When a signal has been set to stop the program, the program cannot see the -signal until you continue. It will see the signal then, if @samp{pass} is -in effect for the signal in question @i{at that time}. In other words, -after _GDBN__ reports a signal, you can use the @samp{handle} command with -@samp{pass} or @samp{nopass} to control whether that signal will be seen by -the program when you later continue it. +@cindex initial frame +@cindex outermost frame +@cindex innermost frame +When your program is started, the stack has only one frame, that of the +function @code{main}. This is called the @dfn{initial} frame or the +@dfn{outermost} frame. Each time a function is called, a new frame is +made. Each time a function returns, the frame for that function invocation +is eliminated. If a function is recursive, there can be many frames for +the same function. The frame for the function in which execution is +actually occurring is called the @dfn{innermost} frame. This is the most +recently created of all the stack frames that still exist. -You can also use the @samp{signal} command to prevent the program from -seeing a signal, or cause it to see a signal it normally would not see, -or to give it any signal at any time. @xref{Signaling}. +@cindex frame pointer +Inside your program, stack frames are identified by their addresses. A +stack frame consists of many bytes, each of which has its own address; each +kind of computer has a convention for choosing one of those bytes whose +address serves as the address of the frame. Usually this address is kept +in a register called the @dfn{frame pointer register} while execution is +going on in that frame. -@node Breakpoints, Continuing, Signals, Stopping -@section Breakpoints +@cindex frame number +_GDBN__ assigns numbers to all existing stack frames, starting with zero for +the innermost frame, one for the frame that called it, and so on upward. +These numbers do not really exist in your program; they are to give you a +way of talking about stack frames in _GDBN__ commands. -@cindex breakpoints -A @dfn{breakpoint} makes your program stop whenever a certain point in the -program is reached. You set breakpoints explicitly with _GDBN__ commands, -specifying the place where the program should stop by line number, function -name or exact address in the program. You can add various other conditions -to control whether the program will stop. +@cindex selected frame +Many _GDBN__ commands refer implicitly to one stack frame, called the +@dfn{selected} stack frame. You can select any frame using one set of +_GDBN__ commands, and then other commands will operate on that frame. When +your program stops, _GDBN__ automatically selects the innermost frame. -Each breakpoint is assigned a number when it is created; these numbers are -successive integers starting with 1. In many of the commands for controlling -various features of breakpoints you use the breakpoint number to say which -breakpoint you want to change. Each breakpoint may be @dfn{enabled} or -@dfn{disabled}; if disabled, it has no effect on the program until you -enable it again. +@cindex frameless execution +Some compilers allow functions to be compiled to run without a frame +reserved for them on the stack. (For example, the _GCC__ option +@samp{-fomit-frame-pointer} will generate functions without a frame.) +This is occasionally done with heavily used library functions to save +the frame setup time. _GDBN__ has limited facilities for dealing with these +function invocations; if the innermost function invocation has no stack +frame, _GDBN__ will give it a virtual stack frame of 0 and correctly allow +tracing of the function call chain. Results are undefined if a function +invocation besides the innermost one is frameless. -@table @code -@kindex info break -@kindex $_ -@item info break -The command @samp{info break} prints a list of all breakpoints set and not -deleted, showing their numbers, where in the program they are, and any -special features in use for them. Disabled breakpoints are included in the -list, but marked as disabled. @samp{info break} with a breakpoint number -as argument lists only that breakpoint. The convenience variable @code{$_} -and the default examining-address for the @samp{x} command are set to the -address of the last breakpoint listed (@pxref{Memory}). +@node Backtrace, Selection, Frames, Stack +@section Backtraces -@kindex info watch -@item info watch -This command prints a list of watchpoints. +A backtrace is a summary of how the program got where it is. It shows one +line per frame, for many frames, starting with the currently executing +frame (frame zero), followed by its caller (frame one), and on up the +stack. -@cindex watchpoints -A @dfn{watchpoint} is a special breakpoint that stops your program when -the value of an expression changes. You can use a watchpoint to stop -execution whenever the value of an expression changes, without having to -predict a particular place in the inferior process where this may -happen. Aside from the different syntax in setting a watchpoint, it is -managed exactly like any other breakpoint and is enabled, disabled, and -deleted using exactly the same commands. +@table @code +@item backtrace +@itemx bt +@kindex backtrace +@kindex bt +Print a backtrace of the entire stack: one line per frame for all +frames in the stack. -Watchpoints currently execute two orders of magnitude more slowly than -other breakpoints, but this can well be worth it to catch errors where -you have no clue what part of your program is the culprit. Some -processors provide special hardware to implement this feature; future -releases of _GDBN__ will use such hardware if it is available. +You can stop the backtrace at any time by typing the system interrupt +character, normally @kbd{Control-C}. + +@item backtrace @var{n} +@itemx bt @var{n} +Similar, but print only the innermost @var{n} frames. +@item backtrace @var{-n} +@itemx bt @var{-n} +Similar, but print only the outermost @var{n} frames. @end table -@menu -* Set Breaks:: How to establish breakpoints. -* Exception Handling:: How _GDBN__ supports exception handling for C++. -* Delete Breaks:: How to remove breakpoints no longer needed. -* Disabling:: How to disable breakpoints (turn them off temporarily). -* Conditions:: Making extra conditions on whether to stop. -* Break Commands:: Commands to be executed at a breakpoint. -* Error in Breakpoints:: -@end menu +@kindex where +@kindex info stack +The names @samp{where} and @samp{info stack} are additional aliases +for @samp{backtrace}. -@node Set Breaks, Exception Handling, Breakpoints, Breakpoints -@subsection Setting Breakpoints +Every line in the backtrace shows the frame number and the function +name. The program counter value is also shown---unless you use +@samp{set addressprint off}. -@kindex break -@kindex watch -Breakpoints are set with the @samp{break} command (abbreviated @samp{b}). -Watchpoints are set with the @samp{watch} command. +If the function is in a source file whose symbol table data has been +fully read, the backtrace shows the source file name and line number, as +well as the arguments to the function. When the line number is shown, +the program counter value is omitted if it is at the beginning of the +code for that line number. -You have several ways to say where the breakpoint should go. +Here is an example of a backtrace. It was made with the command +@samp{bt 3}, so it shows the innermost three frames. -@table @code -@item break @var{function} -Set a breakpoint at entry to function @var{function}. +@example +#0 rtx_equal_p (x=(rtx) 0x8e58c, y=(rtx) 0x1086c4) \ +(/gp/rms/cc/rtlanal.c line 337) +#1 0x246b0 in expand_call (...) (...) +#2 0x21cfc in expand_expr (...) (...) +(More stack frames follow...) +@end example -@item break @var{+offset} -@itemx break @var{-offset} -Set a breakpoint some number of lines forward or back from the position -at which execution stopped in the currently selected frame. +@noindent +The functions @code{expand_call} and @code{expand_expr} are in a file +whose symbol details have not been fully read. Full detail is available +for the function @code{rtx_equal_p}, which is in the file +@file{rtlanal.c}. Its arguments, named @code{x} and @code{y}, are shown +with their typed values. -@item break @var{linenum} -Set a breakpoint at line @var{linenum} in the current source file. -That file is the last file whose source text was printed. This -breakpoint will stop the program just before it executes any of the -code on that line. +@node Selection, Frame Info, Backtrace, Stack +@section Selecting a Frame -@item break @var{filename}:@var{linenum} -Set a breakpoint at line @var{linenum} in source file @var{filename}. +Most commands for examining the stack and other data in the program work on +whichever stack frame is selected at the moment. Here are the commands for +selecting a stack frame; all of them finish by printing a brief description +of the stack frame just selected. -@item break @var{filename}:@var{function} -Set a breakpoint at entry to function @var{function} found in file -@var{filename}. Specifying a file name as well as a function name is -superfluous except when multiple files contain similarly named -functions. +@table @code +@item frame @var{n} +@kindex frame +Select frame number @var{n}. Recall that frame zero is the innermost +(currently executing) frame, frame one is the frame that called the +innermost one, and so on. The highest-numbered frame is @code{main}'s +frame. -@item break *@var{address} -Set a breakpoint at address @var{address}. You can use this to set -breakpoints in parts of the program which do not have debugging -information or source files. +@item frame @var{addr} +Select the frame at address @var{addr}. This is useful mainly if the +chaining of stack frames has been damaged by a bug, making it +impossible for _GDBN__ to assign numbers properly to all frames. In +addition, this can be useful when the program has multiple stacks and +switches between them. -@item break -Set a breakpoint at the next instruction to be executed in the selected -stack frame (@pxref{Stack}). In any selected frame but the innermost, -this will cause the program to stop as soon as control returns to that -frame. This is equivalent to a @samp{finish} command in the frame -inside the selected frame. If this is done in the innermost frame, _GDBN__ -will stop the next time it reaches the current location; this may be -useful inside of loops. +@item up @var{n} +@kindex up +Select the frame @var{n} frames up from the frame previously selected. +For positive numbers @var{n}, this advances toward the outermost +frame, to higher frame numbers, to frames that have existed longer. +@var{n} defaults to one. -_GDBN__ normally ignores breakpoints when it resumes execution, until at -least one instruction has been executed. If it did not do this, you -would be unable to proceed past a breakpoint without first disabling the -breakpoint. This rule applies whether or not the breakpoint already -existed when the program stopped. +@item down @var{n} +@kindex down +Select the frame @var{n} frames down from the frame previously +selected. For positive numbers @var{n}, this advances toward the +innermost frame, to lower frame numbers, to frames that were created +more recently. @var{n} defaults to one. +@end table -@item break @dots{} if @var{cond} -Set a breakpoint with condition @var{cond}; evaluate the expression -@var{cond} each time the breakpoint is reached, and stop only if the -value is nonzero. @samp{@dots{}} stands for one of the possible -arguments described above (or no argument) specifying where to break. -@xref{Conditions}, for more information on breakpoint conditions. +All of these commands end by printing some information on the frame that +has been selected: the frame number, the function name, the arguments, the +source file and line number of execution in that frame, and the text of +that source line. For example: -@item tbreak @var{args} -@kindex tbreak -Set a breakpoint enabled only for one stop. @var{args} are the -same as in the @samp{break} command, and the breakpoint is set in the same -way, but the breakpoint is automatically disabled the first time it -is hit. @xref{Disabling}. +@example +#3 main (argc=3, argv=??, env=??) at main.c:67 +67 read_input_file (argv[i]); +@end example -@item rbreak @var{regex} -@kindex rbreak -Set a breakpoint on all functions matching @var{regex}. This is -useful for setting breakpoints on overloaded functions that are not -members of any special classes. This command sets an unconditional -breakpoint on all matches, printing a list of all breakpoints it set. -Once these breakpoints are set, they are treated just like the -breakpoints set with the @samp{break} command. They can be deleted, -disabled, made conditional, etc., in the standard ways. +After such a printout, the @samp{list} command with no arguments will print +ten lines centered on the point of execution in the frame. @xref{List}. -@kindex watch -@item watch @var{expr} -Set a watchpoint for an expression. -@end table +@table @code +@item up-silently @var{n} +@itemx down-silently @var{n} +@kindex down-silently +@kindex up-silently +These two commands are variants of @samp{up} and @samp{down}, +respectively; they differ in that they do their work silently, without +causing display of the new frame. They are intended primarily for use +in _GDBN__ command scripts, where the output might be unnecessary and +distracting. -_GDBN__ allows you to set any number of breakpoints at the same place in the -program. There is nothing silly or meaningless about this. When the -breakpoints are conditional, this is even useful (@pxref{Conditions}). +@end table -@node Exception Handling, Delete Breaks, Set Breaks, Breakpoints -@subsection Breakpoints and Exceptions -@cindex exception handlers +@node Frame Info, , Selection, Stack +@section Information on a Frame -Some languages, such as GNU C++, implement exception handling. _GDBN__ -can be used to examine what caused the program to raise an exception -and to list the exceptions the program is prepared to handle at a -given point in time. +There are several other commands to print information about the selected +stack frame. -@cindex raise exceptions -GNU C++ raises an exception by calling a library function named -@code{__raise_exception} which has the following ANSI C interface: +@table @code +@item frame +When used without any argument, this command does not change which frame +is selected, but still prints a brief description of the currently +selected stack frame. It can be abbreviated @samp{f}. With an +argument, this command is used to select a stack frame; with no +argument, it does not change which frame is selected, but still prints +the same kind of information. -@example - /* ADDR is where the exception identifier is stored. - ID is the exception identifier. */ - void __raise_exception (void **addr, void *id); -@end example +@item info frame +@kindex info frame +This command prints a verbose description of the selected stack frame, +including the address of the frame, the addresses of the next frame in +(called by this frame) and the next frame out (caller of this frame), +the address of the frame's arguments, the program counter saved in it +(the address of execution in the caller frame), and which registers +were saved in the frame. The verbose description is useful when +something has gone wrong that has made the stack format fail to fit +the usual conventions. -@noindent -You can make the debugger catch all exceptions @emph{before} any stack -unwinding takes place: set a breakpoint on @code{__raise_exception} -(@pxref{Breakpoints}). If you set a breakpoint in an exception handler -instead, it may not be easy to find out where the exception was raised. +@item info frame @var{addr} +Print a verbose description of the frame at address @var{addr}, +without selecting that frame. The selected frame remains unchanged by +this command. -By using a conditional breakpoint (@xref{Conditions}), you can cause -the debugger to stop only when a specific exception is raised. -Multiple conditional breakpoints can be used to stop the program when -any of a number of exceptions are raised. +@item info args +@kindex info args +Print the arguments of the selected frame, each on a separate line. -@table @code -@item catch @var{exceptions} -@kindex catch +@item info locals +@kindex info locals +Print the local variables of the selected frame, each on a separate +line. These are all variables declared static or automatic within all +program blocks that execution in this frame is currently inside of. -Breakpoints can be set at active exception handlers by using the -@samp{catch} command. @var{exceptions} is a list of names of exceptions -to catch. +@item info catch +@kindex info catch +@cindex catch exceptions +@cindex exception handlers +Print a list of all the exception handlers that are active in the +current stack frame given the current value of @code{pc}. To see other +exception handlers, visit the associated frame (using the @samp{up}, +@samp{down}, or @samp{frame} commands); then type @samp{info catch}. +@xref{Exception Handling}. @end table -You can use @samp{info catch} to list active exception handlers; -@pxref{Frame Info}. - -There are currently some limitations to exception handling in _GDBN__. -These will be corrected in a future release. +@node Source, Data, Stack, Top +@chapter Examining Source Files -@itemize @bullet -@item -If you call a function interactively, _GDBN__ will normally return -control to you when the function has finished executing. If the call -raises an exception, however, the call may bypass the mechanism that -returns control to the user and cause the program to simply continue -running until it hits a breakpoint, catches a signal that _GDBN__ is -listening for, or exits. -@item -You cannot raise an exception interactively. -@item -You cannot interactively install an exception handler. -@end itemize +_GDBN__ knows which source files your program was compiled from, and +can print parts of their text. When your program stops, _GDBN__ +spontaneously prints the line it stopped in. Likewise, when you +select a stack frame (@pxref{Selection}), _GDBN__ prints the line +which execution in that frame has stopped in. You can also +print parts of source files by explicit command. -@node Delete Breaks, Disabling, Exception Handling, Breakpoints -@subsection Deleting Breakpoints +@menu +* List:: Using the @samp{list} command to print source files. +* Search:: Commands for searching source files. +* Source Path:: Specifying the directories to search for source files. +@end menu -@cindex clearing breakpoints, watchpoints -@cindex deleting breakpoints, watchpoints -It is often necessary to eliminate a breakpoint once it has done its job -and you no longer want the program to stop there. This is called -@dfn{deleting} the breakpoint. A breakpoint that has been deleted no -longer exists in any sense; it is forgotten. +@node List, Search, Source, Source +@section Printing Source Lines -With the @samp{clear} command you can delete breakpoints according to where -they are in the program. With the @samp{delete} command you can delete -individual breakpoints by specifying their breakpoint numbers. +@kindex list +@kindex l +To print lines from a source file, use the @samp{list} command +(abbreviated @samp{l}). There are several ways to specify what part +of the file you want to print. -It is not necessary to delete a breakpoint to proceed past it. _GDBN__ -automatically ignores breakpoints on the first instruction to be executed -when you continue execution without changing the execution address. +Here are the forms of the @samp{list} command most commonly used: @table @code -@item clear -@kindex clear -Delete any breakpoints at the next instruction to be executed in the -selected stack frame (@pxref{Selection}). When the innermost frame -is selected, this is a good way to delete a breakpoint that the program -just stopped at. +@item list @var{linenum} +Print ten lines centered around line number @var{linenum} in the +current source file. -@item clear @var{function} -@itemx clear @var{filename}:@var{function} -Delete any breakpoints set at entry to the function @var{function}. +@item list @var{function} +Print ten lines centered around the beginning of function +@var{function}. -@item clear @var{linenum} -@itemx clear @var{filename}:@var{linenum} -Delete any breakpoints set at or within the code of the specified line. +@item list +Print ten more lines. If the last lines printed were printed with a +@samp{list} command, this prints ten lines following the last lines +printed; however, if the last line printed was a solitary line printed +as part of displaying a stack frame (@pxref{Stack}), this prints ten +lines centered around that line. -@item delete breakpoints @var{bnums}@dots{} -@itemx delete @var{bnums}@dots{} -@itemx delete -@kindex delete breakpoints -@kindex delete -Delete the breakpoints of the numbers specified as arguments. If no -argument is specified, delete all breakpoints. +@item list - +Print ten lines just before the lines last printed. @end table -@node Disabling, Conditions, Delete Breaks, Breakpoints -@subsection Disabling Breakpoints - -@cindex disabled breakpoints -@cindex enabled breakpoints -Rather than deleting a breakpoint, you might prefer to @dfn{disable} it. -This makes the breakpoint inoperative as if it had been deleted, but -remembers the information on the breakpoint so that you can @dfn{enable} -it again later. +Repeating a @samp{list} command with @key{RET} discards the argument, +so it is equivalent to typing just @samp{list}. This is more useful +than listing the same lines again. An exception is made for an +argument of @samp{-}; that argument is preserved in repetition so that +each repetition moves up in the file. -You disable and enable breakpoints with the @samp{enable} and -@samp{disable} commands, optionally specifying one or more breakpoint -numbers as arguments. Use @samp{info break} to print a list of -breakpoints if you don't know which breakpoint numbers to use. +@cindex linespec +In general, the @samp{list} command expects you to supply zero, one or two +@dfn{linespecs}. Linespecs specify source lines; there are several ways +of writing them but the effect is always to specify some source line. +Here is a complete description of the possible arguments for @samp{list}: -A breakpoint can have any of four different states of enablement: +@table @code +@item list @var{linespec} +Print ten lines centered around the line specified by @var{linespec}. -@itemize @bullet -@item -Enabled. The breakpoint will stop the program. A breakpoint made -with the @samp{break} command starts out in this state. -@item -Disabled. The breakpoint has no effect on the program. -@item -Enabled once. The breakpoint will stop the program, but -when it does so it will become disabled. A breakpoint made -with the @samp{tbreak} command starts out in this state. -@item -Enabled for deletion. The breakpoint will stop the program, but -immediately after it does so it will be deleted permanently. -@end itemize +@item list @var{first},@var{last} +Print lines from @var{first} to @var{last}. Both arguments are +linespecs. -You can use the following commands to enable or disable a breakpoint: +@item list ,@var{last} +Print ten lines ending with @var{last}. -@table @code -@item disable breakpoints @var{bnums}@dots{} -@itemx disable @var{bnums}@dots{} -@itemx disable -@kindex disable breakpoints -@kindex disable -Disable the specified breakpoints---or all breakpoints, if none are -listed. A disabled breakpoint has no effect but is not forgotten. All -options such as ignore-counts, conditions and commands are remembered in -case the breakpoint is enabled again later. +@item list @var{first}, +Print ten lines starting with @var{first}. -@item enable breakpoints @var{bnums}@dots{} -@itemx enable @var{bnums}@dots{} -@itemx enable -@kindex enable breakpoints -@kindex enable -Enable the specified breakpoints (or all defined breakpoints). They -become effective once again in stopping the program, until you specify -otherwise. +@item list + +Print ten lines just after the lines last printed. -@item enable breakpoints once @var{bnums}@dots{} -@itemx enable once @var{bnums}@dots{} -Enable the specified breakpoints temporarily. Each will be disabled -again the next time it stops the program (unless you have used one of -these commands to specify a different state before that time comes). +@item list - +Print ten lines just before the lines last printed. -@item enable breakpoints delete @var{bnums}@dots{} -@itemx enable delete @var{bnums}@dots{} -Enable the specified breakpoints to work once and then die. Each of -the breakpoints will be deleted the next time it stops the program -(unless you have used one of these commands to specify a different -state before that time comes). +@item list +As described in the preceding table. @end table -Save for a breakpoint set with @samp{tbreak} (@pxref{Set Breaks}), -breakpoints that you set are enabled or disabled only when you use one -of the commands above. (The command @samp{until} can set and delete a -breakpoint on its own, but it will not change the state of your -breakpoints). - -@node Conditions, Break Commands, Disabling, Breakpoints -@subsection Break Conditions -@cindex conditional breakpoints -@cindex breakpoint conditions - -The simplest sort of breakpoint breaks every time the program reaches a -specified place. You can also specify a @dfn{condition} for a -breakpoint. A condition is just a boolean expression in your -programming language. (@xref{Expressions}). A breakpoint with a -condition evaluates the expression each time the program reaches it, and -the program stops only if the condition is true. +Here are the ways of specifying a single source line---all the +kinds of linespec. -Break conditions may have side effects, and may even call functions in your -program. These may sound like strange things to do, but their effects are -completely predictable unless there is another enabled breakpoint at the -same address. (In that case, _GDBN__ might see the other breakpoint first and -stop the program without checking the condition of this one.) Note that -breakpoint commands are usually more convenient and flexible for the -purpose of performing side effects when a breakpoint is reached -(@pxref{Break Commands}). +@table @code +@item @var{linenum} +Specifies line @var{linenum} of the current source file. +When a @samp{list} command has two linespecs, this refers to +the same source file as the first linespec. -Break conditions can be specified when a breakpoint is set, by using -@samp{if} in the arguments to the @samp{break} command. @xref{Set Breaks}. -They can also be changed at any time with the @samp{condition} command: +@item +@var{offset} +Specifies the line @var{offset} lines after the last line printed. +When used as the second linespec in a @samp{list} command that has +two, this specifies the line @var{offset} lines down from the +first linespec. -@table @code -@item condition @var{bnum} @var{expression} -@kindex condition -Specify @var{expression} as the break condition for breakpoint number -@var{bnum}. From now on, this breakpoint will stop the program only if -the value of @var{expression} is true (nonzero, in C). @var{expression} -is not evaluated at the time the @samp{condition} command is given. -When you call @samp{condition}, the expression you specify is checked -immediately for syntactic correctness, and to determine whether symbols -in it have referents in the context of your breakpoint. -@xref{Expressions}. +@item -@var{offset} +Specifies the line @var{offset} lines before the last line printed. -@item condition @var{bnum} -Remove the condition from breakpoint number @var{bnum}. It becomes -an ordinary unconditional breakpoint. -@end table +@item @var{filename}:@var{linenum} +Specifies line @var{linenum} in the source file @var{filename}. -@cindex ignore count (of breakpoint) -A special case of a breakpoint condition is to stop only when the -breakpoint has been reached a certain number of times. This is so -useful that there is a special way to do it, using the @dfn{ignore -count} of the breakpoint. Every breakpoint has an ignore count, which -is an integer. Most of the time, the ignore count is zero, and -therefore has no effect. But if the program reaches a breakpoint whose -ignore count is positive, then instead of stopping, it just decrements -the ignore count by one and continues. As a result, if the ignore count -value is @var{n}, the breakpoint will not stop the next @var{n} times it -is reached. +@item @var{function} +Specifies the line of the open-brace that begins the body of the +function @var{function}. -@table @code -@item ignore @var{bnum} @var{count} -@kindex ignore -Set the ignore count of breakpoint number @var{bnum} to @var{count}. -The next @var{count} times the breakpoint is reached, your program's -execution will not stop; other than to decrement the ignore count, _GDBN__ -takes no action. +@item @var{filename}:@var{function} +Specifies the line of the open-brace that begins the body of the +function @var{function} in the file @var{filename}. The file name is +needed with a function name only for disambiguation of identically +named functions in different source files. -To make the breakpoint stop the next time it is reached, specify -a count of zero. +@item *@var{address} +Specifies the line containing the program address @var{address}. +@var{address} may be any expression. +@end table -@item continue @var{count} -@itemx cont @var{count} -@itemx c @var{count} -@itemx fg @var{count} -@kindex cont @var{count} -@kindex continue @var{count} -Continue execution of the program, setting the ignore count of the -breakpoint that the program stopped at to @var{count} minus one. -Thus, the program will not stop at this breakpoint until the -@var{count}'th time it is reached. +One other command is used to map source lines to program addresses. -This command is allowed only when the program stopped due to a -breakpoint. At other times, the argument to @samp{cont} is ignored. +@table @code +@item info line @var{linenum} +@kindex info line +Print the starting and ending addresses of the compiled code for +source line @var{linenum}. -The synonym @samp{fg} is provided purely for convenience, and has -exactly the same behavior as other forms of the command. +@kindex $_ +The default examine address for the @samp{x} command is changed to the +starting address of the line, so that @samp{x/i} is sufficient to +begin examining the machine code (@pxref{Memory}). Also, this address +is saved as the value of the convenience variable @code{$_} +(@pxref{Convenience Vars}). @end table -If a breakpoint has a positive ignore count and a condition, the condition -is not checked. Once the ignore count reaches zero, the condition will -be checked. +@node Search, Source Path, List, Source +@section Searching Source Files +@cindex searching +@kindex search +@kindex forward-search +@kindex reverse-search -Note that you could achieve the effect of the ignore count with a -condition such as @w{@samp{$foo-- <= 0}} using a debugger convenience -variable that is decremented each time. @xref{Convenience Vars}. +There are two commands for searching through the current source file for a +regular expression. -@node Break Commands, Error in Breakpoints, Conditions, Breakpoints -@subsection Commands Executed on Breaking +The command @samp{forward-search @var{regexp}} checks each line, starting +with the one following the last line listed, for a match for @var{regexp}. +It lists the line that is found. You can abbreviate the command name +as @samp{fo}. The synonym @samp{search @var{regexp}} is also supported. -@cindex breakpoint commands -You can give any breakpoint a series of commands to execute when the -program stops due to that breakpoint. For example, you might want to -print the values of certain expressions, or enable other breakpoints. +The command @samp{reverse-search @var{regexp}} checks each line, starting +with the one before the last line listed and going backward, for a match +for @var{regexp}. It lists the line that is found. You can abbreviate +this command with as little as @samp{rev}. -@table @code -@item commands @var{bnum} -@kindex commands -Specify a list of commands for breakpoint number @var{bnum}. The commands -themselves appear on the following lines. Type a line containing just -@samp{end} to terminate the commands. +@node Source Path, , Search, Source +@section Specifying Source Directories -To remove all commands from a breakpoint, use the command -@samp{commands} and follow it immediately by @samp{end}; that is, give -no commands. +@cindex source path +@cindex directories for source files +Executable programs sometimes do not record the directories of the source +files from which they were compiled, just the names. Even when they do, +the directories could be moved between the compilation and your debugging +session. _GDBN__ remembers a list of directories to search for source files; +this is called the @dfn{source path}. Each time _GDBN__ wants a source file, +it tries all the directories in the list, in the order they are present +in the list, until it finds a file with the desired name. Note that +the executable search path is @emph{not} used for this purpose. Neither is +the current working directory, unless it happens to be in the source +path. -With no arguments, @samp{commands} refers to the last breakpoint set -(not to the breakpoint most recently encountered). -@end table +If it can't find a source file in the source path, and the object program +records what directory it was compiled in, _GDBN__ tries that directory too. +If the source path is empty, and there is no record of the compilation +directory, _GDBN__ will, as a last resort, look in the current directory. -You can use breakpoint commands to start the program up again. Simply -use the @samp{cont} command, or @samp{step}, or any other command to -resume execution. However, if you do this, any further commands in the -same breakpoint's command list are ignored. When the program stops -again, _GDBN__ will act according to the cause of that stop. +Whenever you reset or rearrange the source path, _GDBN__ will clear out +any information it has cached about where source files are found, where +each line is in the file, etc. -@kindex silent -If the first command specified is @samp{silent}, the usual message about -stopping at a breakpoint is not printed. This may be desirable for -breakpoints that are to print a specific message and then continue. -If the remaining commands too print nothing, you will see no sign that -the breakpoint was reached at all. @samp{silent} is not really a command; -it is meaningful only at the beginning of the commands for a breakpoint. +@kindex directory +When you start _GDBN__, its source path is empty. +To add other directories, use the @samp{directory} command. -The commands @samp{echo} and @samp{output} that allow you to print precisely -controlled output are often useful in silent breakpoints. @xref{Output}. +@table @code +@item directory @var{dirnames...} +Add directory @var{dirname} to the front of the source path. Several +directory names may be given to this command, separated by whitespace or +@samp{:}. If a name is already in the source path, it is moved to the +front of the path, so it will be searched sooner. -For example, here is how you could use breakpoint commands to print the -value of @code{x} at entry to @code{foo} whenever it is positive. +@item directory +Reset the source path to empty again. This requires confirmation. -@example -break foo if x>0 -commands -silent -echo x is\040 -output x -echo \n -cont -end -@end example +@item info directories +@kindex info directories +Print the source path: show which directories it contains. +@end table -One application for breakpoint commands is to correct one bug so you can -test another. Put a breakpoint just after the erroneous line of code, give -it a condition to detect the case in which something erroneous has been -done, and give it commands to assign correct values to any variables that -need them. End with the @samp{cont} command so that the program does not -stop, and start with the @samp{silent} command so that no output is -produced. Here is an example: +Because the @samp{directory} command, when used with arguments, adds to +the front of the source path, it can affect files that _GDBN__ has already +found. If the source path contains directories that you do not want, +and these directories contain misleading files with names matching your +source files, the way to correct the situation is as follows: -@example -break 403 -commands -silent -set x = y + 4 -cont -end -@end example +@enumerate +@item +Use @samp{directory} with no argument to reset the source path to empty. -One deficiency in the operation of automatically continuing breakpoints -under Unix appears when your program uses raw mode for the terminal. -_GDBN__ switches back to its own terminal modes (not raw) before executing -commands, and then must switch back to raw mode when your program is -continued. This causes any pending terminal input to be lost. -In the GNU system, this will be fixed by changing the behavior of -terminal modes. +@item +Use @samp{directory} with suitable arguments to add any other +directories you want in the source path. You can add all the directories +in one command. +@end enumerate -Under Unix, when you have this problem, you might be able to get around -it by putting your actions into the breakpoint condition instead of -commands. For example +@node Data, Symbols, Source, Top +@chapter Examining Data + +@cindex printing data +@cindex examining data +@kindex print +@kindex inspect +The usual way to examine data in your program is with the @samp{print} +command (abbreviated @samp{p}), or its synonym @samp{inspect}. It +evaluates and prints the value of any valid expression of the language +the program is written in (for now, C or C++). You type @example -condition 5 (x = y + 4), 0 +print @var{exp} @end example @noindent -specifies a condition expression (@xref{Expressions}) that will change -@code{x} as needed, then always have the value 0 so the program will not -stop. Loss of input is avoided here because break conditions are -evaluated without changing the terminal modes. When you want to have -nontrivial conditions for performing the side effects, the operators -@samp{&&}, @samp{||} and @samp{?@dots{}:} may be useful. - -@node Error in Breakpoints, , Break Commands, Breakpoints -@subsection ``Cannot Insert Breakpoints'' - -@c FIXME: "cannot insert breakpoints" error, v unclear. -@c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91 -Under some operating systems, breakpoints cannot be used in a program if -any other process is running that program. In this situation, -attempting to run or continue a program with a breakpoint will cause _GDBN__ -to stop the other process. +where @var{exp} is any valid expression (in the source language), and +the value of @var{exp} is printed in a format appropriate to its data +type. -When this happens, you have three ways to proceed: +A more low-level way of examining data is with the @samp{x} command. +It examines data in memory at a specified address and prints it in a +specified format. -@enumerate -@item -Remove or disable the breakpoints, then continue. +@menu +* Expressions:: Expressions that can be computed and printed. +* Variables:: Using your program's variables in expressions. +* Arrays:: Examining part of memory as an array. +* Format options:: Controlling how structures and arrays are printed. +* Output formats:: Specifying formats for printing values. +* Auto Display:: Printing certain expressions whenever program stops. +* Value History:: Referring to values previously printed. +* Convenience Vars:: Giving names to values for future reference. +* Registers:: Referring to and storing in machine registers. +@end menu -@item -Suspend _GDBN__, and copy the file containing the program to a new name. -Resume _GDBN__ and use the @samp{exec-file} command to specify that _GDBN__ -should run the program under that name. Then start the program again. +@node Expressions, Variables, Data, Data +@section Expressions -@item -Relink the program so that the text segment is nonsharable, using the -linker option @samp{-N}. The operating system limitation may not apply -to nonsharable executables. -@end enumerate +@cindex expressions +Many different _GDBN__ commands accept an expression and compute its value. +Any kind of constant, variable or operator defined by the programming +language you are using is legal in an expression in _GDBN__. This includes +conditional expressions, function calls, casts and string constants. It +unfortunately does not include symbols defined by preprocessor +@code{#define} commands, or C++ expressions involving @samp{::}, the +name resolution operator. -@node Continuing, Stepping, Breakpoints, Stopping -@section Continuing +Casts are supported in all languages, not just in C, because it is so +useful to cast a number into a pointer so as to examine a structure +at that address in memory. -After your program stops, most likely you will want it to run some more if -the bug you are looking for has not happened yet. +_GDBN__ supports three kinds of operator in addition to those of programming +languages: @table @code -@item continue -@item cont -@kindex cont -@kindex continue -Continue running the program at the place where it stopped. -@end table +@item @@ +@samp{@@} is a binary operator for treating parts of memory as arrays. +@xref{Arrays}, for more information. -If the program stopped at a breakpoint, the place to continue running -is the address of the breakpoint. You might expect that continuing would -just stop at the same breakpoint immediately. In fact, @samp{cont} -takes special care to prevent that from happening. You do not need -to delete the breakpoint to proceed through it after stopping at it. +@item :: +@samp{::} allows you to specify a variable in terms of the file or +function it is defined in. @xref{Variables}. -You can, however, specify an ignore-count for the breakpoint that the -program stopped at, by means of an argument to the @samp{cont} command. -@xref{Conditions}. +@item @{@var{type}@} @var{addr} +Refers to an object of type @var{type} stored at address @var{addr} in +memory. @var{addr} may be any expression whose value is an integer or +pointer (but parentheses are required around nonunary operators, just as in +a cast). This construct is allowed regardless of what kind of data is +officially supposed to reside at @var{addr}.@refill +@end table -If the program stopped because of a signal other than @code{SIGINT} or -@code{SIGTRAP}, continuing will cause the program to see that signal. -You may not want this to happen. For example, if the program stopped -due to some sort of memory reference error, you might store correct -values into the erroneous variables and continue, hoping to see more -execution; but the program would probably terminate immediately as -a result of the fatal signal once it sees the signal. To prevent this, -you can continue with @samp{signal 0}. @xref{Signaling}. You can -also act in advance to control what signals your program will see, using -the @samp{handle} command (@pxref{Signals}). +@node Variables, Arrays, Expressions, Data +@section Program Variables -@node Stepping, , Continuing, Stopping -@section Stepping +The most common kind of expression to use is the name of a variable +in your program. -@cindex stepping -@dfn{Stepping} means setting your program in motion for a limited time, so -that control will return automatically to the debugger after one line of -code or one machine instruction. Breakpoints are active during stepping -and the program will stop for them even if it has not gone as far as the -stepping command specifies. +Variables in expressions are understood in the selected stack frame +(@pxref{Selection}); they must either be global (or static) or be visible +according to the scope rules of the programming language from the point of +execution in that frame. This means that in the function -@table @code -@item step -@kindex step -Continue running the program until control reaches a different line, -then stop it and return control to the debugger. This command is -abbreviated @samp{s}. +@example +foo (a) + int a; +@{ + bar (a); + @{ + int b = test (); + bar (b); + @} +@} +@end example -This command may be given when control is within a function for which -there is no debugging information. In that case, execution will proceed -until control reaches a different function, or is about to return from -this function. An argument repeats this action. +@noindent +the variable @code{a} is usable whenever the program is executing +within the function @code{foo}, but the variable @code{b} is visible +only while the program is executing inside the block in which @code{b} +is declared. -@item step @var{count} -Continue running as in @samp{step}, but do so @var{count} times. If a -breakpoint is reached or a signal not related to stepping occurs before -@var{count} steps, stepping stops right away. +As a special exception, you can refer to a variable or function whose +scope is a single source file even if the current execution point is not +in this file. But it is possible to have more than one such variable +or function with the same name (if they are in different source files). +In such a case, it is not defined which one you will get. If you wish, +you can specify any one of them using the colon-colon construct: -@item next -@kindex next -Similar to @samp{step}, but any function calls appearing within the line of -code are executed without stopping. Execution stops when control reaches a -different line of code at the stack level which was executing when the -@samp{next} command was given. This command is abbreviated @samp{n}. +@cindex colon-colon +@cindex scope +@kindex :: +@example +@var{block}::@var{variable} +@end example -An argument is a repeat count, as in @samp{step}. +@noindent +Here @var{block} is the name of the source file whose variable you want. -@samp{next} within a function without debugging information acts as does -@samp{step}, but any function calls appearing within the code of the -function are executed without stopping. +@cindex name resolution (C++) +Unfortunately, this use of @samp{::} conflicts with the very similar use +of the same notation in C++; accordingly, _GDBN__ does not support use of +the C++ name resolution operator in _GDBN__ expressions. -@item finish -@kindex finish -Continue running until just after the selected stack frame returns (or -until there is some other reason to stop, such as a fatal signal or a -breakpoint). Print value returned by the selected stack frame (if any). +@node Arrays, Format options, Variables, Data +@section Artificial Arrays -Contrast this with the @samp{return} command (@pxref{Returning}). +@cindex artificial array +@kindex @@ +It is often useful to print out several successive objects of the +same type in memory; a section of an array, or an array of +dynamically determined size for which only a pointer exists in the +program. -@item until -@kindex until -This command is used to avoid single stepping through a loop more than -once. It is like the @samp{next} command, except that when @samp{until} -encounters a jump, it automatically continues execution until the -program counter is greater than the address of the jump. +This can be done by constructing an @dfn{artificial array} with the +binary operator @samp{@@}. The left operand of @samp{@@} should be +the first element of the desired array, as an individual object. +The right operand should be the length of the array. The result is +an array value whose elements are all of the type of the left argument. +The first element is actually the left argument; the second element +comes from bytes of memory immediately following those that hold the +first element, and so on. Here is an example. If a program says -This means that when you reach the end of a loop after single stepping -though it, @samp{until} will cause the program to continue execution -until the loop is exited. In contrast, a @samp{next} command at the end -of a loop will simply step back to the beginning of the loop, which -would force you to step through the next iteration. +@example +int *array = (int *) malloc (len * sizeof (int)); +@end example -@samp{until} always stops the program if it attempts to exit the current -stack frame. +@noindent +you can print the contents of @code{array} with -@samp{until} may produce somewhat counterintuitive results if the order -of the source lines does not match the actual order of execution. For -example, in a typical C @code{for}-loop, the third expression in the -@code{for}-statement (the loop-step expression) is executed after the -statements in the body of the loop, but is written before them. -Therefore, the @samp{until} command would appear to step back to the -beginning of the loop when it advances to this expression. However, it -has not really done so, not in terms of the actual machine code. +@example +p *array@@len +@end example -Note that @samp{until} with no argument works by means of single -instruction stepping, and hence is slower than @samp{until} with an -argument. +The left operand of @samp{@@} must reside in memory. Array values made +with @samp{@@} in this way behave just like other arrays in terms of +subscripting, and are coerced to pointers when used in expressions. +(It would probably appear in an expression via the value history, +after you had printed it out.) -@item until @var{location} -Continue running the program until either the specified location is -reached, or the current (innermost) stack frame returns. @var{location} -is any of the forms of argument acceptable to @samp{break} (@pxref{Set -Breaks}). This form of the command uses breakpoints, and hence is -quicker than @samp{until} without an argument. +@node Format options, Output formats, Arrays, Data +@section Format options -@item stepi -@itemx si -@kindex stepi -@kindex si -Execute one machine instruction, then stop and return to the debugger. +@cindex format options +_GDBN__ provides a few ways to control how arrays, structures, and symbols are +printed. -It is often useful to do @samp{display/i $pc} when stepping by machine -instructions. This will cause the next instruction to be executed to -be displayed automatically at each stop. @xref{Auto Display}. +@table @code +@item set array-max @var{number-of-elements} +@kindex set array-max +If _GDBN__ is printing a large array, it will stop printing after it has +printed the number of elements set by the @samp{set array-max} command. +This limit also applies to the display of strings. -An argument is a repeat count, as in @samp{step}. +@item show array-max +@kindex show array-max +Display the number of elements of a large array that _GDBN__ will print +before losing patience. -@item nexti -@itemx ni -@kindex nexti -@kindex ni -Execute one machine instruction, but if it is a subroutine call, -proceed until the subroutine returns. +@item set arrayprint +@itemx set arrayprint on +@kindex set arrayprint +_GDBN__ will pretty print arrays. This format is more convenient to read, +but uses more space. The default is off. -An argument is a repeat count, as in @samp{next}. -@end table +@item set arrayprint off. +Return to compressed format for arrays. -A typical technique for using stepping is to put a breakpoint -(@pxref{Breakpoints}) at the beginning of the function or the section of -the program in which a problem is believed to lie, and then step through -the suspect area, examining the variables that are interesting, until the -problem happens. +@item show arrayprint +@kindex show arrayprint +Show whether compressed or pretty format is selected for displaying +arrays. -The @samp{cont} command can be used after stepping to resume execution -until the next breakpoint or signal. +@item set demangle +@itemx set demangle on +@kindex set demangle +Print C++ names in their source form rather than in the mangled form +in which they are passed to the assembler and linker for type-safe linkage. +The default is on. -@node Stack, Source, Stopping, Top -@chapter Examining the Stack +@item show demangle +@kindex show demangle +Show whether C++ names will be printed in mangled or demangled form. -When your program has stopped, the first thing you need to know is where it -stopped and how it got there. +@item set asm-demangle +@itemx set asm-demangle on +@kindex set asm-demangle +Print C++ names in their source form rather than their mangled form, even +in assembler code printouts such as instruction disassemblies. +The default is off. + +@item show asm-demangle +@kindex show asm-demangle +Show whether C++ names in assembly listings will be printed in mangled +or demangled form. -@cindex call stack -Each time your program performs a function call, the information about -where in the program the call was made from is saved in a block of data -called a @dfn{stack frame}. The frame also contains the arguments of the -call and the local variables of the function that was called. All the -stack frames are allocated in a region of memory called the @dfn{call -stack}. +@item set vtblprint +@itemx set vtblprint on +@kindex set vtblprint +Pretty print C++ virtual function tables. The default is off. -When your program stops, the _GDBN__ commands for examining the stack allow you -to see all of this information. +@item set vtblprint off +Do not pretty print C++ virtual function tables. -One of the stack frames is @dfn{selected} by _GDBN__ and many _GDBN__ commands -refer implicitly to the selected frame. In particular, whenever you ask -_GDBN__ for the value of a variable in the program, the value is found in the -selected frame. There are special _GDBN__ commands to select whichever frame -you are interested in. +@item show vtblprint +@kindex show vtblprint +Show whether C++ virtual function tables are pretty printed, or not. -When the program stops, _GDBN__ automatically selects the currently executing -frame and describes it briefly as the @samp{frame} command does -(@pxref{Frame Info, Info}). +@item set addressprint +@item set addressprint on +@kindex set addressprint +_GDBN__ will print memory addresses in stack traces, structure values, pointer +values, breakpoints, etc. The default is on. -@menu -* Frames:: Explanation of stack frames and terminology. -* Backtrace:: Summarizing many frames at once. -* Selection:: How to select a stack frame. -* Frame Info:: Information on a Frame -@end menu +@item set addressprint off +Do not print addresses. -@node Frames, Backtrace, Stack, Stack -@section Stack Frames +@item show addressprint +@kindex show addressprint +Show whether or not addresses are to be printed. -@cindex frame -@cindex stack frame -The call stack is divided up into contiguous pieces called @dfn{stack -frames}, or @dfn{frames} for short; each frame is the data associated -with one call to one function. The frame contains the arguments given -to the function, the function's local variables, and the address at -which the function is executing. +@item set prettyprint on +@kindex set prettyprint +Cause _GDBN__ to print structures in an indented format with one member per +line, like this: -@cindex initial frame -@cindex outermost frame -@cindex innermost frame -When your program is started, the stack has only one frame, that of the -function @code{main}. This is called the @dfn{initial} frame or the -@dfn{outermost} frame. Each time a function is called, a new frame is -made. Each time a function returns, the frame for that function invocation -is eliminated. If a function is recursive, there can be many frames for -the same function. The frame for the function in which execution is -actually occurring is called the @dfn{innermost} frame. This is the most -recently created of all the stack frames that still exist. +@example +$1 = @{ + next = 0x0, + flags = @{ + sweet = 1, + sour = 1 + @}, + meat = 0x54 "Pork" +@} +@end example -@cindex frame pointer -Inside your program, stack frames are identified by their addresses. A -stack frame consists of many bytes, each of which has its own address; each -kind of computer has a convention for choosing one of those bytes whose -address serves as the address of the frame. Usually this address is kept -in a register called the @dfn{frame pointer register} while execution is -going on in that frame. +@item set prettyprint off +Cause _GDBN__ to print structures in a compact format, like this: -@cindex frame number -_GDBN__ assigns numbers to all existing stack frames, starting with zero for -the innermost frame, one for the frame that called it, and so on upward. -These numbers do not really exist in your program; they are to give you a -way of talking about stack frames in _GDBN__ commands. +@smallexample +$1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, meat \ += 0x54 "Pork"@} +@end smallexample -@cindex selected frame -Many _GDBN__ commands refer implicitly to one stack frame, called the -@dfn{selected} stack frame. You can select any frame using one set of -_GDBN__ commands, and then other commands will operate on that frame. When -your program stops, _GDBN__ automatically selects the innermost frame. +@noindent +This is the default format. -@cindex frameless execution -Some compilers allow functions to be compiled to run without a frame -reserved for them on the stack. (For example, the _GCC__ option -@samp{-fomit-frame-pointer} will generate functions without a frame.) -This is occasionally done with heavily used library functions to save -the frame setup time. _GDBN__ has limited facilities for dealing with these -function invocations; if the innermost function invocation has no stack -frame, _GDBN__ will give it a virtual stack frame of 0 and correctly allow -tracing of the function call chain. Results are undefined if a function -invocation besides the innermost one is frameless. +@item show prettyprint +@kindex show prettyprint +Show which format _GDBN__ will use to print structures. -@node Backtrace, Selection, Frames, Stack -@section Backtraces +@item set unionprint on +@kindex set unionprint +Tell _GDBN__ to print unions which are contained in structures. This is the +default setting. -A backtrace is a summary of how the program got where it is. It shows one -line per frame, for many frames, starting with the currently executing -frame (frame zero), followed by its caller (frame one), and on up the -stack. +@item set unionprint off +Tell _GDBN__ not to print unions which are contained in structures. -@table @code -@item backtrace -@itemx bt -@kindex backtrace -@kindex bt -Print a backtrace of the entire stack: one line per frame for all -frames in the stack. +@item show unionprint +@kindex show unionprint +Ask _GDBN__ whether or not it will print unions which are contained in +structures. -You can stop the backtrace at any time by typing the system interrupt -character, normally @kbd{Control-C}. +For example, given the declarations -@item backtrace @var{n} -@itemx bt @var{n} -Similar, but print only the innermost @var{n} frames. +@smallexample +typedef enum @{Tree, Bug@} Species; +typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms; +typedef enum @{Caterpillar, Cocoon, Butterfly@} Bug_forms; -@item backtrace @var{-n} -@itemx bt @var{-n} -Similar, but print only the outermost @var{n} frames. -@end table +struct thing @{ + Species it; + union @{ + Tree_forms tree; + Bug_forms bug; + @} form; +@}; -@kindex where -@kindex info stack -The names @samp{where} and @samp{info stack} are additional aliases -for @samp{backtrace}. +struct thing foo = @{Tree, @{Acorn@}@}; +@end smallexample -Every line in the backtrace shows the frame number and the function -name. The program counter value is also shown---unless you use -@samp{set addressprint off}. +@noindent +with @samp{set unionprint on} in effect @samp{p foo} would print -If the function is in a source file whose symbol table data has been -fully read, the backtrace shows the source file name and line number, as -well as the arguments to the function. When the line number is shown, -the program counter value is omitted if it is at the beginning of the -code for that line number. +@smallexample +$1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@} +@end smallexample -Here is an example of a backtrace. It was made with the command -@samp{bt 3}, so it shows the innermost three frames. +@noindent +and with @samp{set unionprint off} in effect it would print @example -#0 rtx_equal_p (x=(rtx) 0x8e58c, y=(rtx) 0x1086c4) \ -(/gp/rms/cc/rtlanal.c line 337) -#1 0x246b0 in expand_call (...) (...) -#2 0x21cfc in expand_expr (...) (...) -(More stack frames follow...) +$1 = @{it = Tree, form = @{...@}@} @end example +@end table -@noindent -The functions @code{expand_call} and @code{expand_expr} are in a file -whose symbol details have not been fully read. Full detail is available -for the function @code{rtx_equal_p}, which is in the file -@file{rtlanal.c}. Its arguments, named @code{x} and @code{y}, are shown -with their typed values. - -@node Selection, Frame Info, Backtrace, Stack -@section Selecting a Frame +@node Output formats, Auto Display, Format options, Data +@section Output formats -Most commands for examining the stack and other data in the program work on -whichever stack frame is selected at the moment. Here are the commands for -selecting a stack frame; all of them finish by printing a brief description -of the stack frame just selected. +@cindex formatted output +@cindex output formats +_GDBN__ normally prints all values according to their data types. Sometimes +this is not what you want. For example, you might want to print a number +in hex, or a pointer in decimal. Or you might want to view data in memory +at a certain address as a character string or an instruction. These things +can be done with @dfn{output formats}. -@table @code -@item frame @var{n} -@kindex frame -Select frame number @var{n}. Recall that frame zero is the innermost -(currently executing) frame, frame one is the frame that called the -innermost one, and so on. The highest-numbered frame is @code{main}'s -frame. +The simplest use of output formats is to say how to print a value +already computed. This is done by starting the arguments of the +@samp{print} command with a slash and a format letter. The format +letters supported are: -@item frame @var{addr} -Select the frame at address @var{addr}. This is useful mainly if the -chaining of stack frames has been damaged by a bug, making it -impossible for _GDBN__ to assign numbers properly to all frames. In -addition, this can be useful when the program has multiple stacks and -switches between them. +@table @samp +@item x +Regard the bits of the value as an integer, and print the integer in +hexadecimal. -@item up @var{n} -@kindex up -Select the frame @var{n} frames up from the frame previously selected. -For positive numbers @var{n}, this advances toward the outermost -frame, to higher frame numbers, to frames that have existed longer. -@var{n} defaults to one. +@item d +Print as integer in signed decimal. -@item down @var{n} -@kindex down -Select the frame @var{n} frames down from the frame previously -selected. For positive numbers @var{n}, this advances toward the -innermost frame, to lower frame numbers, to frames that were created -more recently. @var{n} defaults to one. -@end table +@item u +Print as integer in unsigned decimal. -All of these commands end by printing some information on the frame that -has been selected: the frame number, the function name, the arguments, the -source file and line number of execution in that frame, and the text of -that source line. For example: +@item o +Print as integer in octal. +@item a +Print as an address, both absolute in hex and as an offset from the +nearest preceding symbol. This format can be used to discover where (in +what function) an unknown address is located: @example -#3 main (argc=3, argv=??, env=??) at main.c:67 -67 read_input_file (argv[i]); +(_GDBP__) p/a 0x54320 +_0__$3 = 0x54320 <_initialize_vx+396>_1__ @end example -After such a printout, the @samp{list} command with no arguments will print -ten lines centered on the point of execution in the frame. @xref{List}. -@table @code -@item up-silently @var{n} -@itemx down-silently @var{n} -@kindex down-silently -@kindex up-silently -These two commands are variants of @samp{up} and @samp{down}, -respectively; they differ in that they do their work silently, without -causing display of the new frame. They are intended primarily for use -in _GDBN__ command scripts, where the output might be unnecessary and -distracting. +@item c +Regard as an integer and print it as a character constant. +@item f +Regard the bits of the value as a floating point number and print +using typical floating point syntax. @end table -@node Frame Info, , Selection, Stack -@section Information on a Frame +For example, to print the program counter in hex (@pxref{Registers}), type -There are several other commands to print information about the selected -stack frame. +@example +p/x $pc +@end example -@table @code -@item frame -When used without any argument, this command does not change which frame -is selected, but still prints a brief description of the currently -selected stack frame. It can be abbreviated @samp{f}. With an -argument, this command is used to select a stack frame; with no -argument, it does not change which frame is selected, but still prints -the same kind of information. +@noindent +Note that no space is required before the slash; this is because command +names in _GDBN__ cannot contain a slash. -@item info frame -@kindex info frame -This command prints a verbose description of the selected stack frame, -including the address of the frame, the addresses of the next frame in -(called by this frame) and the next frame out (caller of this frame), -the address of the frame's arguments, the program counter saved in it -(the address of execution in the caller frame), and which registers -were saved in the frame. The verbose description is useful when -something has gone wrong that has made the stack format fail to fit -the usual conventions. +To reprint the last value in the value history with a different format, +you can use the @samp{print} command with just a format and no +expression. For example, @samp{p/x} reprints the last value in hex. -@item info frame @var{addr} -Print a verbose description of the frame at address @var{addr}, -without selecting that frame. The selected frame remains unchanged by -this command. +@menu +* Memory:: Examining Memory +@end menu -@item info args -@kindex info args -Print the arguments of the selected frame, each on a separate line. +@node Memory, , Output formats, Output formats +@subsection Examining Memory -@item info locals -@kindex info locals -Print the local variables of the selected frame, each on a separate -line. These are all variables declared static or automatic within all -program blocks that execution in this frame is currently inside of. +@cindex examining memory +@table @code +@kindex disassemble +@item disassemble +This specialized command is provided to dump a range of memory as +machine instructions. The default memory range is the function +surrounding the program counter of the selected frame. A single +argument to this command is a program counter value; the function +surrounding this value will be dumped. Two arguments (separated by one +or more spaces) specify a range of addresses (first inclusive, second +exclusive) to be dumped. -@item info catch -@kindex info catch -@cindex catch exceptions -@cindex exception handlers -Print a list of all the exception handlers that are active in the -current stack frame given the current value of @code{pc}. To see other -exception handlers, visit the associated frame (using the @samp{up}, -@samp{down}, or @samp{frame} commands); then type @samp{info catch}. -@xref{Exception Handling}. +@kindex x +@item x +The command @samp{x} (for `examine') can be used to examine memory +without reference to the program's data types. The format in which you +wish to examine memory is instead explicitly specified. The allowable +formats are a superset of the formats described in the previous section. @end table -@node Source, Data, Stack, Top -@chapter Examining Source Files - -_GDBN__ knows which source files your program was compiled from, and -can print parts of their text. When your program stops, _GDBN__ -spontaneously prints the line it stopped in. Likewise, when you -select a stack frame (@pxref{Selection}), _GDBN__ prints the line -which execution in that frame has stopped in. You can also -print parts of source files by explicit command. - -@menu -* List:: Using the @samp{list} command to print source files. -* Search:: Commands for searching source files. -* Source Path:: Specifying the directories to search for source files. -@end menu +@samp{x} is followed by a slash and an output format specification, +followed by an expression for an address. The expression need not have +a pointer value (though it may); it is used as an integer, as the +address of a byte of memory. @xref{Expressions} for more information on +expressions. For example, @samp{x/4xw $sp} prints the four words of +memory above the stack pointer in hexadecimal. -@node List, Search, Source, Source -@section Printing Source Lines +The output format in this case specifies both how big a unit of memory +to examine and how to print the contents of that unit. It is done +with one or two of the following letters: -@kindex list -@kindex l -To print lines from a source file, use the @samp{list} command -(abbreviated @samp{l}). There are several ways to specify what part -of the file you want to print. +These letters specify just the size of unit to examine: -Here are the forms of the @samp{list} command most commonly used: +@table @samp +@item b +Examine individual bytes. -@table @code -@item list @var{linenum} -Print ten lines centered around line number @var{linenum} in the -current source file. +@item h +Examine halfwords (two bytes each). -@item list @var{function} -Print ten lines centered around the beginning of function -@var{function}. +@item w +Examine words (four bytes each). -@item list -Print ten more lines. If the last lines printed were printed with a -@samp{list} command, this prints ten lines following the last lines -printed; however, if the last line printed was a solitary line printed -as part of displaying a stack frame (@pxref{Stack}), this prints ten -lines centered around that line. +@cindex word +Many assemblers and cpu designers still use `word' for a 16-bit quantity, +as a holdover from specific predecessor machines of the 1970's that really +did use two-byte words. But more generally the term `word' has always +referred to the size of quantity that a machine normally operates on and +stores in its registers. This is 32 bits for all the machines that _GDBN__ +runs on. -@item list - -Print ten lines just before the lines last printed. +@item g +Examine giant words (8 bytes). @end table -Repeating a @samp{list} command with @key{RET} discards the argument, -so it is equivalent to typing just @samp{list}. This is more useful -than listing the same lines again. An exception is made for an -argument of @samp{-}; that argument is preserved in repetition so that -each repetition moves up in the file. +These letters specify just the way to print the contents: -@cindex linespec -In general, the @samp{list} command expects you to supply zero, one or two -@dfn{linespecs}. Linespecs specify source lines; there are several ways -of writing them but the effect is always to specify some source line. -Here is a complete description of the possible arguments for @samp{list}: +@table @samp +@item x +Print as integers in unsigned hexadecimal. -@table @code -@item list @var{linespec} -Print ten lines centered around the line specified by @var{linespec}. +@item d +Print as integers in signed decimal. -@item list @var{first},@var{last} -Print lines from @var{first} to @var{last}. Both arguments are -linespecs. +@item u +Print as integers in unsigned decimal. -@item list ,@var{last} -Print ten lines ending with @var{last}. +@item o +Print as integers in unsigned octal. -@item list @var{first}, -Print ten lines starting with @var{first}. +@item a +Print as an address, both absolute in hex and then relative +to a symbol defined as an address below it. -@item list + -Print ten lines just after the lines last printed. +@item c +Print as character constants. -@item list - -Print ten lines just before the lines last printed. +@item f +Print as floating point. This works only with sizes @samp{w} and +@samp{g}. -@item list -As described in the preceding table. -@end table +@item s +Print a null-terminated string of characters. The specified unit size +is ignored; instead, the unit is however many bytes it takes to reach +a null character (including the null character). -Here are the ways of specifying a single source line---all the -kinds of linespec. +@item i +Print a machine instruction in assembler syntax (or nearly). The +specified unit size is ignored; the number of bytes in an instruction +varies depending on the type of machine, the opcode and the addressing +modes used. The command @samp{disassemble} gives an alternative way of +inspecting machine instructions. +@end table -@table @code -@item @var{linenum} -Specifies line @var{linenum} of the current source file. -When a @samp{list} command has two linespecs, this refers to -the same source file as the first linespec. +If either the manner of printing or the size of unit fails to be specified, +the default is to use the same one that was used last. If you don't want +to use any letters after the slash, you can omit the slash as well. -@item +@var{offset} -Specifies the line @var{offset} lines after the last line printed. -When used as the second linespec in a @samp{list} command that has -two, this specifies the line @var{offset} lines down from the -first linespec. +You can also omit the address to examine. Then the address used is just +after the last unit examined. This is why string and instruction +formats actually compute a unit-size based on the data: so that the next +string or instruction examined will start in the right place. -@item -@var{offset} -Specifies the line @var{offset} lines before the last line printed. +When the @samp{print} command shows a value that resides in memory, +@samp{print} also sets the default address for the @samp{x} command. +@samp{info line} also sets the default for @samp{x}, to the address of +the start of the machine code for the specified line and @samp{info +breakpoints} sets it to the address of the last breakpoint listed. -@item @var{filename}:@var{linenum} -Specifies line @var{linenum} in the source file @var{filename}. +When you use @key{RET} to repeat an @samp{x} command, the address +specified previously (if any) is ignored, so that the repeated command +examines the successive locations in memory rather than the same ones. -@item @var{function} -Specifies the line of the open-brace that begins the body of the -function @var{function}. +You can examine several consecutive units of memory with one command by +writing a repeat-count after the slash (before the format letters, if any). +The repeat count must be a decimal integer. It has the same effect as +repeating the @samp{x} command that many times except that the output may +be more compact with several units per line. For example, -@item @var{filename}:@var{function} -Specifies the line of the open-brace that begins the body of the -function @var{function} in the file @var{filename}. The file name is -needed with a function name only for disambiguation of identically -named functions in different source files. +@example +x/10i $pc +@end example -@item *@var{address} -Specifies the line containing the program address @var{address}. -@var{address} may be any expression. -@end table +@noindent +prints ten instructions starting with the one to be executed next in the +selected frame. After doing this, you could print another seven following +instructions with -One other command is used to map source lines to program addresses. +@example +x/7 +@end example -@table @code -@item info line @var{linenum} -@kindex info line -Print the starting and ending addresses of the compiled code for -source line @var{linenum}. +@noindent +in which the format and address are allowed to default. @kindex $_ -The default examine address for the @samp{x} command is changed to the -starting address of the line, so that @samp{x/i} is sufficient to -begin examining the machine code (@pxref{Memory}). Also, this address -is saved as the value of the convenience variable @code{$_} -(@pxref{Convenience Vars}). -@end table +@kindex $__ +The addresses and contents printed by the @samp{x} command are not put in +the value history because there is often too much of them and they would +get in the way. Instead, _GDBN__ makes these values available for subsequent +use in expressions as values of the convenience variables @code{$_} and +@code{$__}. -@node Search, Source Path, List, Source -@section Searching Source Files -@cindex searching -@kindex search -@kindex forward-search -@kindex reverse-search +After an @samp{x} command, the last address examined is available for use +in expressions in the convenience variable @code{$_}. The contents of that +address, as examined, are available in the convenience variable @code{$__}. -There are two commands for searching through the current source file for a -regular expression. +If the @samp{x} command has a repeat count, the address and contents saved +are from the last memory unit printed; this is not the same as the last +address printed if several units were printed on the last line of output. -The command @samp{forward-search @var{regexp}} checks each line, starting -with the one following the last line listed, for a match for @var{regexp}. -It lists the line that is found. You can abbreviate the command name -as @samp{fo}. The synonym @samp{search @var{regexp}} is also supported. +@node Auto Display, Value History, Output formats, Data +@section Automatic Display +@cindex automatic display +@cindex display of expressions -The command @samp{reverse-search @var{regexp}} checks each line, starting -with the one before the last line listed and going backward, for a match -for @var{regexp}. It lists the line that is found. You can abbreviate -this command with as little as @samp{rev}. +If you find that you want to print the value of an expression frequently +(to see how it changes), you might want to add it to the @dfn{automatic +display list} so that _GDBN__ will print its value each time the program stops. +Each expression added to the list is given a number to identify it; +to remove an expression from the list, you specify that number. +The automatic display looks like this: -@node Source Path, , Search, Source -@section Specifying Source Directories +@example +2: foo = 38 +3: bar[5] = (struct hack *) 0x3804 +@end example -@cindex source path -@cindex directories for source files -Executable programs sometimes do not record the directories of the source -files from which they were compiled, just the names. Even when they do, -the directories could be moved between the compilation and your debugging -session. _GDBN__ remembers a list of directories to search for source files; -this is called the @dfn{source path}. Each time _GDBN__ wants a source file, -it tries all the directories in the list, in the order they are present -in the list, until it finds a file with the desired name. Note that -the executable search path is @emph{not} used for this purpose. Neither is -the current working directory, unless it happens to be in the source -path. +@noindent +showing item numbers, expressions and their current values. -If it can't find a source file in the source path, and the object program -records what directory it was compiled in, _GDBN__ tries that directory too. -If the source path is empty, and there is no record of the compilation -directory, _GDBN__ will, as a last resort, look in the current directory. +If the expression refers to local variables, then it does not make sense +outside the lexical context for which it was set up. Such an expression +is disabled when execution enters a context where one of its variables +is not defined. For example, if you give the command +@samp{display name} while inside a function with an argument +@code{name}, then this argument will be displayed while the program +continues to stop inside that function. When it stops elsewhere---where +there is no variable @samp{name}---display is disabled. The next time +your program stops where @samp{name} is meaningful, you can enable the +display expression once again. -Whenever you reset or rearrange the source path, _GDBN__ will clear out -any information it has cached about where source files are found, where -each line is in the file, etc. +@table @code +@item display @var{exp} +@kindex display +Add the expression @var{exp} to the list of expressions to display +each time the program stops. @xref{Expressions}. -@kindex directory -When you start _GDBN__, its source path is empty. -To add other directories, use the @samp{directory} command. +@item display/@var{fmt} @var{exp} +For @var{fmt} specifying only a display format and not a size or +count, add the expression @var{exp} to the auto-display list but +arranges to display it each time in the specified format @var{fmt}. -@table @code -@item directory @var{dirnames...} -Add directory @var{dirname} to the front of the source path. Several -directory names may be given to this command, separated by whitespace or -@samp{:}. If a name is already in the source path, it is moved to the -front of the path, so it will be searched sooner. +@item display/@var{fmt} @var{addr} +For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a +number of units, add the expression @var{addr} as a memory address to +be examined each time the program stops. Examining means in effect +doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory}. -@item directory -Reset the source path to empty again. This requires confirmation. +@item undisplay @var{dnums}@dots{} +@itemx delete display @var{dnums}@dots{} +@kindex delete display +@kindex undisplay +Remove item numbers @var{dnums} from the list of expressions to display. -@item info directories -@kindex info directories -Print the source path: show which directories it contains. +@item disable display @var{dnums}@dots{} +@kindex disable display +Disable the display of item numbers @var{dnums}. A disabled display +item is not printed automatically, but is not forgotten. It may be +enabled again later. + +@item enable display @var{dnums}@dots{} +@kindex enable display +Enable display of item numbers @var{dnums}. It becomes effective once +again in auto display of its expression, until you specify otherwise. + +@item display +Display the current values of the expressions on the list, just as is +done when the program stops. + +@item info display +@kindex info display +Print the list of expressions previously set up to display +automatically, each one with its item number, but without showing the +values. This includes disabled expressions, which are marked as such. +It also includes expressions which would not be displayed right now +because they refer to automatic variables not currently available. @end table -Because the @samp{directory} command, when used with arguments, adds to -the front of the source path, it can affect files that _GDBN__ has already -found. If the source path contains directories that you do not want, -and these directories contain misleading files with names matching your -source files, the way to correct the situation is as follows: +@node Value History, Convenience Vars, Auto Display, Data +@section Value History -@enumerate -@item -Use @samp{directory} with no argument to reset the source path to empty. +@cindex value history +Values printed by the @samp{print} command are saved in _GDBN__'s @dfn{value +history} so that you can refer to them in other expressions. Values are +kept until the symbol table is re-read or discarded (for example with +the @samp{file} or @samp{symbol-file} commands). When the symbol table +changes, the value history is discarded, since the values may contain +pointers back to the types defined in the symbol table. -@item -Use @samp{directory} with suitable arguments to add any other -directories you want in the source path. You can add all the directories -in one command. -@end enumerate +@cindex @code{$} +@cindex @code{$$} +@cindex history number +The values printed are given @dfn{history numbers} for you to refer to them +by. These are successive integers starting with 1. @samp{print} shows you +the history number assigned to a value by printing @samp{$@var{num} = } +before the value; here @var{num} is the history number. -@node Data, Symbols, Source, Top -@chapter Examining Data +To refer to any previous value, use @samp{$} followed by the value's +history number. The output printed by @samp{print} is designed to +remind you of this. Just @code{$} refers to the most recent value in +the history, and @code{$$} refers to the value before that. +@code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2} +is the value just prior to @code{$$}, @code{$$1} is equivalent to +@code{$$}, and @code{$$0} is equivalent to @code{$}. -@cindex printing data -@cindex examining data -@kindex print -@kindex inspect -The usual way to examine data in your program is with the @samp{print} -command (abbreviated @samp{p}), or its synonym @samp{inspect}. It -evaluates and prints the value of any valid expression of the language -the program is written in (for now, C or C++). You type +For example, suppose you have just printed a pointer to a structure and +want to see the contents of the structure. It suffices to type @example -print @var{exp} +p *$ @end example -@noindent -where @var{exp} is any valid expression (in the source language), and -the value of @var{exp} is printed in a format appropriate to its data -type. - -A more low-level way of examining data is with the @samp{x} command. -It examines data in memory at a specified address and prints it in a -specified format. +If you have a chain of structures where the component @samp{next} points +to the next one, you can print the contents of the next one with this: -@menu -* Expressions:: Expressions that can be computed and printed. -* Variables:: Using your program's variables in expressions. -* Arrays:: Examining part of memory as an array. -* Format options:: Controlling how structures and arrays are printed. -* Output formats:: Specifying formats for printing values. -* Auto Display:: Printing certain expressions whenever program stops. -* Value History:: Referring to values previously printed. -* Convenience Vars:: Giving names to values for future reference. -* Registers:: Referring to and storing in machine registers. -@end menu +@example +p *$.next +@end example -@node Expressions, Variables, Data, Data -@section Expressions +@noindent +It might be useful to repeat this command many times by typing @key{RET}. -@cindex expressions -Many different _GDBN__ commands accept an expression and compute its value. -Any kind of constant, variable or operator defined by the programming -language you are using is legal in an expression in _GDBN__. This includes -conditional expressions, function calls, casts and string constants. It -unfortunately does not include symbols defined by preprocessor -@code{#define} commands, or C++ expressions involving @samp{::}, the -name resolution operator. +Note that the history records values, not expressions. If the value of +@code{x} is 4 and you type this command: -Casts are supported in all languages, not just in C, because it is so -useful to cast a number into a pointer so as to examine a structure -at that address in memory. +@example +print x +set x=5 +@end example -_GDBN__ supports three kinds of operator in addition to those of programming -languages: +@noindent +then the value recorded in the value history by the @samp{print} command +remains 4 even though the value of @code{x} has changed. @table @code -@item @@ -@samp{@@} is a binary operator for treating parts of memory as arrays. -@xref{Arrays}, for more information. +@kindex info values +@item info values +@itemx info history +@kindex info history +These two commands are synonymous. Either form will print the last ten +values in the value history, with their item numbers. This is like +@samp{p@ $$9} repeated ten times, except that @samp{info values} does +not change the history. -@item :: -@samp{::} allows you to specify a variable in terms of the file or -function it is defined in. @xref{Variables}. +@item info values @var{n} +Print ten history values centered on history item number @var{n}. -@item @{@var{type}@} @var{addr} -Refers to an object of type @var{type} stored at address @var{addr} in -memory. @var{addr} may be any expression whose value is an integer or -pointer (but parentheses are required around nonunary operators, just as in -a cast). This construct is allowed regardless of what kind of data is -officially supposed to reside at @var{addr}.@refill +@item info values + +Print ten history values just after the values last printed. @end table -@node Variables, Arrays, Expressions, Data -@section Program Variables +@node Convenience Vars, Registers, Value History, Data +@section Convenience Variables -The most common kind of expression to use is the name of a variable -in your program. +@cindex convenience variables +_GDBN__ provides @dfn{convenience variables} that you can use within _GDBN__ to +hold on to a value and refer to it later. These variables exist entirely +within _GDBN__; they are not part of your program, and setting a convenience +variable has no effect on further execution of your program. That's why +you can use them freely. -Variables in expressions are understood in the selected stack frame -(@pxref{Selection}); they must either be global (or static) or be visible -according to the scope rules of the programming language from the point of -execution in that frame. This means that in the function +Convenience variables have names starting with @samp{$}. Any name starting +with @samp{$} can be used for a convenience variable, unless it is one of +the predefined set of register names (@pxref{Registers}). + +You can save a value in a convenience variable with an assignment +expression, just as you would set a variable in your program. Example: @example -foo (a) - int a; -@{ - bar (a); - @{ - int b = test (); - bar (b); - @} -@} +set $foo = *object_ptr @end example @noindent -the variable @code{a} is usable whenever the program is executing -within the function @code{foo}, but the variable @code{b} is visible -only while the program is executing inside the block in which @code{b} -is declared. +would save in @code{$foo} the value contained in the object pointed to by +@code{object_ptr}. -As a special exception, you can refer to a variable or function whose -scope is a single source file even if the current execution point is not -in this file. But it is possible to have more than one such variable -or function with the same name (if they are in different source files). -In such a case, it is not defined which one you will get. If you wish, -you can specify any one of them using the colon-colon construct: +Using a convenience variable for the first time creates it; but its value +is @code{void} until you assign a new value. You can alter the value with +another assignment at any time. -@cindex colon-colon -@cindex scope -@kindex :: -@example -@var{block}::@var{variable} -@end example +Convenience variables have no fixed types. You can assign a convenience +variable any type of value, including structures and arrays, even if +that variable already has a value of a different type. The convenience +variable as an expression has whatever type its current value has. -@noindent -Here @var{block} is the name of the source file whose variable you want. +@table @code +@item info convenience +@kindex info convenience +Print a list of convenience variables used so far, and their values. +Abbreviated @samp{i con}. +@end table -@cindex name resolution (C++) -Unfortunately, this use of @samp{::} conflicts with the very similar use -of the same notation in C++; accordingly, _GDBN__ does not support use of -the C++ name resolution operator in _GDBN__ expressions. +One of the ways to use a convenience variable is as a counter to be +incremented or a pointer to be advanced. For example: -@node Arrays, Format options, Variables, Data -@section Artificial Arrays +_0__@example +set $i = 0 +print bar[$i++]->contents +@i{@dots{}repeat that command by typing @key{RET}.} +_1__@end example -@cindex artificial array -@kindex @@ -It is often useful to print out several successive objects of the -same type in memory; a section of an array, or an array of -dynamically determined size for which only a pointer exists in the -program. +Some convenience variables are created automatically by _GDBN__ and given +values likely to be useful. -This can be done by constructing an @dfn{artificial array} with the -binary operator @samp{@@}. The left operand of @samp{@@} should be -the first element of the desired array, as an individual object. -The right operand should be the length of the array. The result is -an array value whose elements are all of the type of the left argument. -The first element is actually the left argument; the second element -comes from bytes of memory immediately following those that hold the -first element, and so on. Here is an example. If a program says +@table @code +@item $_ +The variable @code{$_} is automatically set by the @samp{x} command to +the last address examined (@pxref{Memory}). Other commands which +provide a default address for @samp{x} to examine also set @code{$_} +to that address; these commands include @samp{info line} and @samp{info +breakpoint}. -@example -int *array = (int *) malloc (len * sizeof (int)); -@end example +@item $__ +The variable @code{$__} is automatically set by the @samp{x} command +to the value found in the last address examined. +@end table -@noindent -you can print the contents of @code{array} with +@node Registers, , Convenience Vars, Data +@section Registers -@example -p *array@@len -@end example +@cindex registers +Machine register contents can be referred to in expressions as variables +with names starting with @samp{$}. The names of registers are different +for each machine; use @samp{info registers} to see the names used on your +machine. The names @code{$pc} and @code{$sp} are used on most machines for +the program counter register and the stack pointer. Often @code{$fp} is +used for a register that contains a pointer to the current stack frame, +and @code{$ps} is used for a register that contains the processor +status. These standard register names may be available on your machine +even though the @code{info registers} command displays them with a +different name. For example, on the SPARC, @code{info registers} +displays the processor status register as @code{$psr} but you can also +refer to it as @code{$ps}. -The left operand of @samp{@@} must reside in memory. Array values made -with @samp{@@} in this way behave just like other arrays in terms of -subscripting, and are coerced to pointers when used in expressions. -(It would probably appear in an expression via the value history, -after you had printed it out.) +_GDBN__ always considers the contents of an ordinary register as an integer +when the register is examined in this way. Some machines have special +registers which can hold nothing but floating point; these registers are +considered floating point. There is no way to refer to the contents of an +ordinary register as floating point value (although you can @emph{print} +it as a floating point value with @samp{print/f $@var{regname}}). -@node Format options, Output formats, Arrays, Data -@section Format options +Some registers have distinct ``raw'' and ``virtual'' data formats. This +means that the data format in which the register contents are saved by +the operating system is not the same one that your program normally +sees. For example, the registers of the 68881 floating point +coprocessor are always saved in ``extended'' (raw) format, but all C +programs expect to work with ``double'' (virtual) format. In such +cases, _GDBN__ normally works with the virtual format only (the format that +makes sense for your program), but the @samp{info registers} command +prints the data in both formats. -@cindex format options -_GDBN__ provides a few ways to control how arrays, structures, and symbols are -printed. +Register values are relative to the selected stack frame +(@pxref{Selection}). This means that you get the value that the register +would contain if all stack frames farther in were exited and their saved +registers restored. In order to see the real contents of all registers, +you must select the innermost frame (with @samp{frame 0}). + +Some registers are never saved (typically those numbered zero or one) +because they are used for returning function values. In some operating +systems (those using the ``caller saves'' convention), there are other +registers intended for free alteration by a called routine. For these +registers, relativization makes no difference. @table @code -@item set array-max @var{number-of-elements} -@kindex set array-max -If _GDBN__ is printing a large array, it will stop printing after it has -printed the number of elements set by the @samp{set array-max} command. -This limit also applies to the display of strings. +@item info registers +@kindex info registers +Print the names and relativized values of all registers. -@item show array-max -@kindex show array-max -Display the number of elements of a large array that _GDBN__ will print -before losing patience. +@item info registers @var{regname} +Print the relativized value of register @var{regname}. @var{regname} +may be any register name valid on the machine you are using, with +or without the initial @samp{$}. +@end table -@item set arrayprint -@itemx set arrayprint on -@kindex set arrayprint -_GDBN__ will pretty print arrays. This format is more convenient to read, -but uses more space. The default is off. +@subsection Examples -@item set arrayprint off. -Return to compressed format for arrays. +You could print the program counter in hex with -@item show arrayprint -@kindex show arrayprint -Show whether compressed or pretty format is selected for displaying -arrays. +@example +p/x $pc +@end example -@item set demangle -@itemx set demangle on -@kindex set demangle -Print C++ names in their source form rather than in the mangled form -in which they are passed to the assembler and linker for type-safe linkage. -The default is on. +@noindent +or print the instruction to be executed next with -@item show demangle -@kindex show demangle -Show whether C++ names will be printed in mangled or demangled form. +@example +x/i $pc +@end example -@item set asm-demangle -@itemx set asm-demangle on -@kindex set asm-demangle -Print C++ names in their source form rather than their mangled form, even -in assembler code printouts such as instruction disassemblies. -The default is off. +@noindent +or add four to the stack pointer with -@item show asm-demangle -@kindex show asm-demangle -Show whether C++ names in assembly listings will be printed in mangled -or demangled form. +@example +set $sp += 4 +@end example + +@noindent +The last is a way of removing one word from the stack, on machines where +stacks grow downward in memory (most machines, nowadays). This assumes +that the innermost stack frame is selected. Setting @code{$sp} is +not allowed when other stack frames are selected. (To pop entire frames +off the stack, regardless of machine architecture, use @samp{return}; +@pxref{Returning}.) -@item set vtblprint -@itemx set vtblprint on -@kindex set vtblprint -Pretty print C++ virtual function tables. The default is off. +@node Symbols, Altering, Data, Top +@chapter Examining the Symbol Table -@item set vtblprint off -Do not pretty print C++ virtual function tables. +The commands described in this section allow you to inquire about the +symbols (names of variables, functions and types) defined in your +program. This information is found by _GDBN__ in the symbol table loaded by +the @samp{symbol-file} command; it is inherent in the text of your +program and does not change as the program executes. -@item show vtblprint -@kindex show vtblprint -Show whether C++ virtual function tables are pretty printed, or not. +@table @code +@item info address @var{symbol} +@kindex info address +Describe where the data for @var{symbol} is stored. For a register +variable, this says which register it is kept in. For a non-register +local variable, this prints the stack-frame offset at which the variable +is always stored. -@item set addressprint -@item set addressprint on -@kindex set addressprint -_GDBN__ will print memory addresses in stack traces, structure values, pointer -values, breakpoints, etc. The default is on. +Note the contrast with @samp{print &@var{symbol}}, which does not work +at all for a register variables, and for a stack local variable prints +the exact address of the current instantiation of the variable. -@item set addressprint off -Do not print addresses. +@item whatis @var{exp} +@kindex whatis +Print the data type of expression @var{exp}. @var{exp} is not +actually evaluated, and any side-effecting operations (such as +assignments or function calls) inside it do not take place. +@xref{Expressions}. -@item show addressprint -@kindex show addressprint -Show whether or not addresses are to be printed. +@item whatis +Print the data type of @code{$}, the last value in the value history. -@item set prettyprint on -@kindex set prettyprint -Cause _GDBN__ to print structures in an indented format with one member per -line, like this: +@item ptype @var{typename} +@kindex ptype +Print a description of data type @var{typename}. @var{typename} may be +the name of a type, or for C code it may have the form +@samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or +@samp{enum @var{enum-tag}}.@refill -@example -$1 = @{ - next = 0x0, - flags = @{ - sweet = 1, - sour = 1 - @}, - meat = 0x54 "Pork" -@} -@end example +@item ptype @var{exp} +Print a description of the type of expression @var{exp}. This is like +@samp{whatis} except it prints a detailed description, instead of just +the name of the type. For example, if the type of a variable is +@samp{struct complex @{double real; double imag;@}}, @samp{whatis} will +print @samp{struct complex} and @samp{ptype} will print @samp{struct +complex @{double real; double imag;@}} -@item set prettyprint off -Cause _GDBN__ to print structures in a compact format, like this: +@item info sources +@kindex info sources +Print the names of all source files in the program for which there +is debugging information. -@smallexample -$1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, meat \ -= 0x54 "Pork"@} -@end smallexample +@item info functions +@kindex info functions +Print the names and data types of all defined functions. -@noindent -This is the default format. +@item info functions @var{regexp} +Print the names and data types of all defined functions +whose names contain a match for regular expression @var{regexp}. +Thus, @samp{info fun step} finds all functions whose names +include @samp{step}; @samp{info fun ^step} finds those whose names +start with @samp{step}. -@item show prettyprint -@kindex show prettyprint -Show which format _GDBN__ will use to print structures. +@item info variables +@kindex info variables +Print the names and data types of all variables that are declared +outside of functions (i.e., except for local variables). -@item set unionprint on -@kindex set unionprint -Tell _GDBN__ to print unions which are contained in structures. This is the -default setting. +@item info variables @var{regexp} +Print the names and data types of all variables (except for local +variables) whose names contain a match for regular expression +@var{regexp}. -@item set unionprint off -Tell _GDBN__ not to print unions which are contained in structures. -@item show unionprint -@kindex show unionprint -Ask _GDBN__ whether or not it will print unions which are contained in -structures. +@ignore +This was never implemented. +@item info methods +@itemx info methods @var{regexp} +@kindex info methods +The @samp{info-methods} command permits the user to examine all defined +methods within C++ program, or (with the @var{regexp} argument) a +specific set of methods found in the various C++ classes. Many +C++ classes provide a large number of methods. Thus, the output +from the @samp{ptype} command can be overwhelming and hard to use. The +@samp{info-methods} command filters the methods, printing only those +which match the regular-expression @var{regexp}. +@end ignore -For example, given the declarations +@item printsyms @var{filename} +@kindex printsyms +Write a complete dump of the debugger's symbol data into the +file @var{filename}. +@end table -@smallexample -typedef enum @{Tree, Bug@} Species; -typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms; -typedef enum @{Caterpillar, Cocoon, Butterfly@} Bug_forms; +@node Altering, Sequences, Symbols, Top +@chapter Altering Execution -struct thing @{ - Species it; - union @{ - Tree_forms tree; - Bug_forms bug; - @} form; -@}; +Once you think you have found an error in the program, you might want to +find out for certain whether correcting the apparent error would lead to +correct results in the rest of the run. You can find the answer by +experiment, using the _GDBN__ features for altering execution of the +program. -struct thing foo = @{Tree, @{Acorn@}@}; -@end smallexample +For example, you can store new values into variables or memory +locations, give the program a signal, restart it at a different address, +or even return prematurely from a function to its caller. -@noindent -with @samp{set unionprint on} in effect @samp{p foo} would print +@menu +* Assignment:: Altering variable values or memory contents. +* Jumping:: Altering control flow. +* Signaling:: Making signals happen in the program. +* Returning:: Making a function return prematurely. +* Calling:: Calling functions from your program +@end menu -@smallexample -$1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@} -@end smallexample +@node Assignment, Jumping, Altering, Altering +@section Assignment to Variables -@noindent -and with @samp{set unionprint off} in effect it would print +@cindex assignment +@cindex setting variables +To alter the value of a variable, evaluate an assignment expression. +@xref{Expressions}. For example, @example -$1 = @{it = Tree, form = @{...@}@} +print x=4 @end example -@end table - -@node Output formats, Auto Display, Format options, Data -@section Output formats -@cindex formatted output -@cindex output formats -_GDBN__ normally prints all values according to their data types. Sometimes -this is not what you want. For example, you might want to print a number -in hex, or a pointer in decimal. Or you might want to view data in memory -at a certain address as a character string or an instruction. These things -can be done with @dfn{output formats}. +@noindent +would store the value 4 into the variable @code{x}, and then print +the value of the assignment expression (which is 4). -The simplest use of output formats is to say how to print a value -already computed. This is done by starting the arguments of the -@samp{print} command with a slash and a format letter. The format -letters supported are: +All the assignment operators of C are supported, including the +increment operators @samp{++} and @samp{--}, and combining +assignments such as @samp{+=} and _0__@samp{<<=}_1__. -@table @samp -@item x -Regard the bits of the value as an integer, and print the integer in -hexadecimal. +@kindex set +@kindex set variable +@cindex variables, setting +If you are not interested in seeing the value of the assignment, use the +@samp{set} command instead of the @samp{print} command. @samp{set} is +really the same as @samp{print} except that the expression's value is not +printed and is not put in the value history (@pxref{Value History}). The +expression is evaluated only for side effects. -@item d -Print as integer in signed decimal. +Note that if the beginning of the argument string of the @samp{set} command +appears identical to a @samp{set} subcommand, it may be necessary to use +the @samp{set variable} command. This command is identical to @samp{set} +except for its lack of subcommands. -@item u -Print as integer in unsigned decimal. +_GDBN__ allows more implicit conversions in assignments than C does; you can +freely store an integer value into a pointer variable or vice versa, and +any structure can be converted to any other structure that is the same +length or shorter. +@comment FIXME: how do structs align/pad in these conversions? +@comment /pesch@cygnus.com 18dec1990 -@item o -Print as integer in octal. +To store values into arbitrary places in memory, use the @samp{@{@dots{}@}} +construct to generate a value of specified type at a specified address +(@pxref{Expressions}). For example, @code{@{int@}0x83040} would refer +to memory location 0x83040 as an integer (which implies a certain size +and representation in memory), and -@item a -Print as an address, both absolute in hex and as an offset from the -nearest preceding symbol. This format can be used to discover where (in -what function) an unknown address is located: @example -(_GDBP__) p/a 0x54320 -$3 = 0x54320 <_initialize_vx+396> +set @{int@}0x83040 = 4 @end example +would store the value 4 into that memory location. + +@node Jumping, Signaling, Assignment, Altering +@section Continuing at a Different Address + +Ordinarily, when you continue the program, you do so at the place where +it stopped, with the @samp{cont} command. You can instead continue at +an address of your own choosing, with the following commands: + +@table @code +@item jump @var{linenum} +@kindex jump +Resume execution at line number @var{linenum}. Execution may stop +immediately if there is a breakpoint there. -@item c -Regard as an integer and print it as a character constant. +The @samp{jump} command does not change the current stack frame, or +the stack pointer, or the contents of any memory location or any +register other than the program counter. If line @var{linenum} is in +a different function from the one currently executing, the results may +be bizarre if the two functions expect different patterns of arguments or +of local variables. For this reason, the @samp{jump} command requests +confirmation if the specified line is not in the function currently +executing. However, even bizarre results are predictable based on +careful study of the machine-language code of the program. -@item f -Regard the bits of the value as a floating point number and print -using typical floating point syntax. +@item jump *@var{address} +Resume execution at the instruction at address @var{address}. @end table -For example, to print the program counter in hex (@pxref{Registers}), type +You can get much the same effect as the @code{jump} command by storing a +new value into the register @code{$pc}. The difference is that this +does not start the program running; it only changes the address where it +@emph{will} run when it is continued. For example, @example -p/x $pc +set $pc = 0x485 @end example @noindent -Note that no space is required before the slash; this is because command -names in _GDBN__ cannot contain a slash. - -To reprint the last value in the value history with a different format, -you can use the @samp{print} command with just a format and no -expression. For example, @samp{p/x} reprints the last value in hex. +causes the next @samp{cont} command or stepping command to execute at +address 0x485, rather than at the address where the program stopped. +@xref{Stepping}. -@menu -* Memory:: Examining Memory -@end menu +The most common occasion to use the @samp{jump} command is to back up, +perhaps with more breakpoints set, over a portion of a program that has +already executed. -@node Memory, , Output formats, Output formats -@subsection Examining Memory +@node Signaling, Returning, Jumping, Altering +@section Giving the Program a Signal -@cindex examining memory @table @code -@kindex disassemble -@item disassemble -This specialized command is provided to dump a range of memory as -machine instructions. The default memory range is the function -surrounding the program counter of the selected frame. A single -argument to this command is a program counter value; the function -surrounding this value will be dumped. Two arguments (separated by one -or more spaces) specify a range of addresses (first inclusive, second -exclusive) to be dumped. +@item signal @var{signalnum} +@kindex signal +Resume execution where the program stopped, but give it immediately the +signal number @var{signalnum}. -@kindex x -@item x -The command @samp{x} (for `examine') can be used to examine memory -without reference to the program's data types. The format in which you -wish to examine memory is instead explicitly specified. The allowable -formats are a superset of the formats described in the previous section. +Alternatively, if @var{signalnum} is zero, continue execution without +giving a signal. This is useful when the program stopped on account of +a signal and would ordinary see the signal when resumed with the +@samp{cont} command; @samp{signal 0} causes it to resume without a +signal. @end table -@samp{x} is followed by a slash and an output format specification, -followed by an expression for an address. The expression need not have -a pointer value (though it may); it is used as an integer, as the -address of a byte of memory. @xref{Expressions} for more information on -expressions. For example, @samp{x/4xw $sp} prints the four words of -memory above the stack pointer in hexadecimal. +@node Returning, Calling, Signaling, Altering +@section Returning from a Function -The output format in this case specifies both how big a unit of memory -to examine and how to print the contents of that unit. It is done -with one or two of the following letters: +@table @code +@item return +@cindex returning from a function +@kindex return +You can cancel execution of a function call with the @samp{return} +command. +@end table -These letters specify just the size of unit to examine: +This command has the effect of discarding the selected stack +frame (and all frames within it), so that control moves to the caller of +that function. You can think of this as making the discarded frame +return prematurely. -@table @samp -@item b -Examine individual bytes. +First select the stack frame that you wish to return from +(@pxref{Selection}). Then type the @samp{return} command. If you wish +to specify the value to be returned, give that as an argument. -@item h -Examine halfwords (two bytes each). +This pops the selected stack frame (and any other frames inside of it), +leaving its caller as the innermost remaining frame. That frame becomes +selected. The specified value is stored in the registers used for +returning values of functions. -@item w -Examine words (four bytes each). +The @samp{return} command does not resume execution; it leaves the +program stopped in the state that would exist if the function had just +returned. Contrast this with the @samp{finish} command +(@pxref{Stepping}), which resumes execution until the selected stack +frame returns @emph{naturally}. -@cindex word -Many assemblers and cpu designers still use `word' for a 16-bit quantity, -as a holdover from specific predecessor machines of the 1970's that really -did use two-byte words. But more generally the term `word' has always -referred to the size of quantity that a machine normally operates on and -stores in its registers. This is 32 bits for all the machines that _GDBN__ -runs on. +@node Calling, , Returning, Altering +@comment node-name, next, previous, up +@section Calling your Program's Functions -@item g -Examine giant words (8 bytes). +@cindex calling functions +@kindex call +@table @code +@item call @var{expr} +Evaluate the expression @var{expr} without displaying @code{void} +returned values. @end table -These letters specify just the way to print the contents: - -@table @samp -@item x -Print as integers in unsigned hexadecimal. - -@item d -Print as integers in signed decimal. +You can use this variant of the @samp{print} command if you want to +execute some piece of your program, but without cluttering the output +with @code{void} returned values. The result is printed and saved in +the value history, if it is not void. -@item u -Print as integers in unsigned decimal. +@node Files,,, +@chapter _GDBN__'s Files -@item o -Print as integers in unsigned octal. +@section Commands to Specify Files +@cindex core dump file +@cindex symbol table +_GDBN__ needs to know the file name of the program to be debugged, both in +order to read its symbol table and in order to start the program. To +debug a core dump of a previous run, _GDBN__ must be told the file name of +the core dump. -@item a -Print as an address, both absolute in hex and then relative -to a symbol defined as an address below it. +The usual way to specify the executable and core dump file names is with +the command arguments given when you start _GDBN__, as discussed in +@pxref{Invocation}. -@item c -Print as character constants. +But occasionally it is necessary to change to a different file during a +_GDBN__ session. Or you may run _GDBN__ and forget to specify the files you +want to use. In these situations the _GDBN__ commands to specify new files +are useful. -@item f -Print as floating point. This works only with sizes @samp{w} and -@samp{g}. +@table @code +@item file @var{filename} +@cindex executable file +@kindex file +Use @var{filename} as the program to be debugged. It is read for its +symbols, for getting the contents of pure memory, and it is the program +executed when you use the @samp{run} command. If you do not specify a +directory and the file is not found in _GDBN__'s working directory, +_GDBN__ will use the environment variable @code{PATH} as a list of +directories to search, just as the shell does when looking for a program +to run. -@item s -Print a null-terminated string of characters. The specified unit size -is ignored; instead, the unit is however many bytes it takes to reach -a null character (including the null character). +@samp{file} with no argument makes both executable file and symbol +table become unspecified. -@item i -Print a machine instruction in assembler syntax (or nearly). The -specified unit size is ignored; the number of bytes in an instruction -varies depending on the type of machine, the opcode and the addressing -modes used. The command @samp{disassemble} gives an alternative way of -inspecting machine instructions. -@end table +@item exec-file @var{filename} +@kindex exec-file +Specify that the program to be run (but not the symbol table) is found +in @var{filename}. _GDBN__ will search the environment variable @code{PATH} +if necessary to locate the program. -If either the manner of printing or the size of unit fails to be specified, -the default is to use the same one that was used last. If you don't want -to use any letters after the slash, you can omit the slash as well. +@item symbol-file @var{filename} +@kindex symbol-file +Read symbol table information from file @var{filename}. @code{PATH} is +searched when necessary. Use the @samp{file} command to get both symbol +table and program to run from the same file. -You can also omit the address to examine. Then the address used is just -after the last unit examined. This is why string and instruction -formats actually compute a unit-size based on the data: so that the next -string or instruction examined will start in the right place. +@samp{symbol-file} with no argument clears out _GDBN__'s information on your +program's symbol table. -When the @samp{print} command shows a value that resides in memory, -@samp{print} also sets the default address for the @samp{x} command. -@samp{info line} also sets the default for @samp{x}, to the address of -the start of the machine code for the specified line and @samp{info -breakpoints} sets it to the address of the last breakpoint listed. +The @samp{symbol-file} command causes _GDBN__ to forget the contents of its +convenience variables, the value history, and all breakpoints and +auto-display expressions. This is because they may contain pointers to +the internal data recording symbols and data types, which are part of +the old symbol table data being discarded inside _GDBN__. -When you use @key{RET} to repeat an @samp{x} command, the address -specified previously (if any) is ignored, so that the repeated command -examines the successive locations in memory rather than the same ones. +On some kinds of object files, the @samp{symbol-file} command does not +actually read the symbol table in full right away. Instead, it scans +the symbol table quickly to find which source files and which symbols +are present. The details are read later, one source file at a time, +when they are needed. -You can examine several consecutive units of memory with one command by -writing a repeat-count after the slash (before the format letters, if any). -The repeat count must be a decimal integer. It has the same effect as -repeating the @samp{x} command that many times except that the output may -be more compact with several units per line. For example, +The purpose of this two-stage reading strategy is to make _GDBN__ start up +faster. For the most part, it is invisible except for occasional pauses +while the symbol table details for a particular source file are being +read. (The @samp{set verbose} command can turn these pauses into +messages if desired. @xref{User Interface}). -@example -x/10i $pc -@end example +When the symbol table is stored in COFF format, @samp{symbol-file} does +read the symbol table data in full right away. We haven't implemented +the two-stage strategy for COFF yet. -@noindent -prints ten instructions starting with the one to be executed next in the -selected frame. After doing this, you could print another seven following -instructions with +When _GDBN__ is configured for a particular environment, it will understand +debugging information in whatever format is the standard generated for +that environment; you may use either the GNU compiler _GCC__, or other +compilers that adhere to the local conventions. Best results are +usually obtained from _GCC__; for example, using _GCC__ you can generate +debugging information for optimized code. -@example -x/7 -@end example +@item core-file @var{filename} +@itemx core @var{filename} +@kindex core +@kindex core-file +Specify the whereabouts of a core dump file to be used as the ``contents +of memory''. Traditionally, core files contain only some parts of the +address space of the process that generated them; _GDBN__ can access the +executable file itself for other parts. -@noindent -in which the format and address are allowed to default. +@samp{core-file} with no argument specifies that no core file is +to be used. -@kindex $_ -@kindex $__ -The addresses and contents printed by the @samp{x} command are not put in -the value history because there is often too much of them and they would -get in the way. Instead, _GDBN__ makes these values available for subsequent -use in expressions as values of the convenience variables @code{$_} and -@code{$__}. +Note that the core file is ignored when your program is actually running +under _GDBN__. So, if you have been running the program and you wish to +debug a core file instead, you must kill the subprocess in which the +program is running. To do this, use the @samp{kill} command +(@pxref{Kill Process}). -After an @samp{x} command, the last address examined is available for use -in expressions in the convenience variable @code{$_}. The contents of that -address, as examined, are available in the convenience variable @code{$__}. +@item load @var{filename} +@kindex load +This command will dynamically link @var{filename} on the current target, +performing any necessary downloads, then add @var{filename}'s symbol +table in the same way as the @samp{add-syms} command. -If the @samp{x} command has a repeat count, the address and contents saved -are from the last memory unit printed; this is not the same as the last -address printed if several units were printed on the last line of output. +@item add-syms @var{filename} @var{address} +@kindex add-syms +@cindex dynamic linking +The @samp{add-syms} command reads additional symbol table information +from the file @var{filename}. You would use this command when that file +has been dynamically loaded (by some other means) into the program that +is running. @var{address} should be the memory address at which the +file has been loaded; _GDBN__ cannot figure this out for itself. -@node Auto Display, Value History, Output formats, Data -@section Automatic Display -@cindex automatic display -@cindex display of expressions +The symbol table of the file @var{filename} is added to the symbol table +originally read with the @samp{symbol-file} command. You can use the +@samp{add-syms} command any number of times; the new symbol data thus +read keeps adding to the old. The @samp{symbol-file} command forgets +all the symbol data _GDBN__ has read. -If you find that you want to print the value of an expression frequently -(to see how it changes), you might want to add it to the @dfn{automatic -display list} so that _GDBN__ will print its value each time the program stops. -Each expression added to the list is given a number to identify it; -to remove an expression from the list, you specify that number. -The automatic display looks like this: +@item info files +@itemx info target +@kindex info files +@kindex info target +@samp{info files} and @samp{info target} are synonymous; both print the +current targets (@pxref{Targets}), including the names of the +executable and core dump files currently in use by _GDBN__, and the files +from which symbols were loaded. -@example -2: foo = 38 -3: bar[5] = (struct hack *) 0x3804 -@end example +Beware: the similar command @samp{info targets} lists all possible +targets rather than current ones. -@noindent -showing item numbers, expressions and their current values. +@end table -If the expression refers to local variables, then it does not make sense -outside the lexical context for which it was set up. Such an expression -is disabled when execution enters a context where one of its variables -is not defined. For example, if you give the command -@samp{display name} while inside a function with an argument -@code{name}, then this argument will be displayed while the program -continues to stop inside that function. When it stops elsewhere---where -there is no variable @samp{name}---display is disabled. The next time -your program stops where @samp{name} is meaningful, you can enable the -display expression once again. +While all three file-specifying commands allow both absolute and relative +file names as arguments, _GDBN__ always converts the file name to an absolute +one and remembers it that way. -@table @code -@item display @var{exp} -@kindex display -Add the expression @var{exp} to the list of expressions to display -each time the program stops. @xref{Expressions}. +@kindex sharedlibrary +@kindex share +@cindex shared libraries -@item display/@var{fmt} @var{exp} -For @var{fmt} specifying only a display format and not a size or -count, add the expression @var{exp} to the auto-display list but -arranges to display it each time in the specified format @var{fmt}. +_GDBN__ supports the SunOS shared library format. Symbols from a shared +library cannot be referenced before the shared library has been linked +with the program. (That is to say, after one types @samp{run} and +the function @code{main()} has been entered; or when examining core +files.) Once the shared library has been linked in, you can use the +following commands: -@item display/@var{fmt} @var{addr} -For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a -number of units, add the expression @var{addr} as a memory address to -be examined each time the program stops. Examining means in effect -doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory}. +@table @code +@item sharedlibrary @var{regex} +@itemx share @var{regex} +Load shared object library symbols for files matching a UNIX regular +expression. -@item undisplay @var{dnums}@dots{} -@itemx delete display @var{dnums}@dots{} -@kindex delete display -@kindex undisplay -Remove item numbers @var{dnums} from the list of expressions to display. +@item share +@itemx sharedlibrary +Load symbols for all shared libraries. -@item disable display @var{dnums}@dots{} -@kindex disable display -Disable the display of item numbers @var{dnums}. A disabled display -item is not printed automatically, but is not forgotten. It may be -enabled again later. +@item info share +@itemx info sharedlibrary +@kindex info sharedlibrary +@kindex info share +Print the names of the shared libraries which are currently loaded. +@end table -@item enable display @var{dnums}@dots{} -@kindex enable display -Enable display of item numbers @var{dnums}. It becomes effective once -again in auto display of its expression, until you specify otherwise. +@section Errors Reading Symbols +While a symbol file is being read, _GDBN__ will occasionally encounter +problems, such as symbol types it does not recognize, or known bugs in +compiler output. By default, it prints one message about each such +type of problem, no matter how many times the problem occurs. You can +ask it to print more messages, to see how many times the problems occur, +or can shut the messages off entirely, with the @samp{set +complaints} command (@xref{User Interface}). -@item display -Display the current values of the expressions on the list, just as is -done when the program stops. +The messages currently printed, and their meanings, are: -@item info display -@kindex info display -Print the list of expressions previously set up to display -automatically, each one with its item number, but without showing the -values. This includes disabled expressions, which are marked as such. -It also includes expressions which would not be displayed right now -because they refer to automatic variables not currently available. -@end table +@table @code +@item inner block not inside outer block in @var{symbol} -@node Value History, Convenience Vars, Auto Display, Data -@section Value History +The symbol information shows where symbol scopes begin and end +(such as at the start of a function or a block of statements). This +error indicates that an inner scope block is not fully contained +in its outer scope blocks. _GDBN__ circumvents the problem by treating +the inner block as if it had the same scope as the outer block. +@var{symbol} may be ``(don't know)'' if the outer block is not +a function. -@cindex value history -Values printed by the @samp{print} command are saved in _GDBN__'s @dfn{value -history} so that you can refer to them in other expressions. Values are -kept until the symbol table is re-read or discarded (for example with -the @samp{file} or @samp{symbol-file} commands). When the symbol table -changes, the value history is discarded, since the values may contain -pointers back to the types defined in the symbol table. +@item block at @var{address} out of order -@cindex @code{$} -@cindex @code{$$} -@cindex history number -The values printed are given @dfn{history numbers} for you to refer to them -by. These are successive integers starting with 1. @samp{print} shows you -the history number assigned to a value by printing @samp{$@var{num} = } -before the value; here @var{num} is the history number. +The symbol information for symbol scope blocks should occur in +order of increasing addresses. This error indicates that it does not +do so. _GDBN__ does not circumvent this problem, and will have trouble +locating symbols in the source file whose symbols being read. (You +can often determine what source file is affected by turning on +@samp{info verbose}. @xref{User Interface}.) -To refer to any previous value, use @samp{$} followed by the value's -history number. The output printed by @samp{print} is designed to -remind you of this. Just @code{$} refers to the most recent value in -the history, and @code{$$} refers to the value before that. -@code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2} -is the value just prior to @code{$$}, @code{$$1} is equivalent to -@code{$$}, and @code{$$0} is equivalent to @code{$}. +@item bad block start address patched -For example, suppose you have just printed a pointer to a structure and -want to see the contents of the structure. It suffices to type +The symbol information for a symbol scope block has a start address +smaller than the address of the preceding source line. This is known +to occur in the SunOS 4.1.1 (and earlier) C compiler. _GDBN__ circumvents +the problem by treating the symbol scope block as starting on the +previous source line. -@example -p *$ -@end example +@comment @item{encountered DBX-style class variable debugging information. +@comment You seem to have compiled your program with "g++ -g0" instead of "g++ -g". +@comment Therefore _GDBN__ will not know about your class variables} +@comment +@comment This error indicates that the symbol information produced for a C++ +@comment program includes zero-size fields, which indicated static fields in +@comment a previous release of the G++ compiler. This message is probably +@comment obsolete. +@comment +@item bad string table offset in symbol @var{n} -If you have a chain of structures where the component @samp{next} points -to the next one, you can print the contents of the next one with this: +Symbol number @var{n} contains a pointer into the string table which is +larger than the size of the string table. _GDBN__ circumvents the problem +by considering the symbol to have the name @code{foo}, which may cause +other problems if many symbols end up with this name. @cindex{foo} -@example -p *$.next -@end example +@item unknown symbol type @code{0xNN} -@noindent -It might be useful to repeat this command many times by typing @key{RET}. +The symbol information contains new data types that _GDBN__ does not yet +know how to read. @code{0xNN} is the symbol type of the misunderstood +information, in hexadecimal. _GDBN__ circumvents the error by ignoring +this symbol information. This will usually allow the program to be +debugged, though certain symbols will not be accessible. If you +encounter such a problem and feel like debugging it, you can debug _GDBP__ +with itself, breakpoint on "complain", then go "up" to +read_dbx_symtab() and examine *bufp to see the symbol. -Note that the history records values, not expressions. If the value of -@code{x} is 4 and you type this command: +@c @item stub type has NULL name +@c +@c FIXME, Mike Tiemann needs to write about what this means. -@example -print x -set x=5 -@end example +@item const/volatile indicator missing, got 'X' -@noindent -then the value recorded in the value history by the @samp{print} command -remains 4 even though the value of @code{x} has changed. +The symbol information for a C++ type is missing some information that +the compiler should have output for it. -@table @code -@kindex info values -@item info values -@itemx info history -@kindex info history -These two commands are synonymous. Either form will print the last ten -values in the value history, with their item numbers. This is like -@samp{p@ $$9} repeated ten times, except that @samp{info values} does -not change the history. +@item C++ type mismatch between compiler and debugger -@item info values @var{n} -Print ten history values centered on history item number @var{n}. +The debugger could not parse a type specification output by the compiler +for some C++ object. -@item info values + -Print ten history values just after the values last printed. @end table -@node Convenience Vars, Registers, Value History, Data -@section Convenience Variables +@node Targets, Running, Compilation, Top +@chapter Specifying a Debugging Target +@cindex debugging target +@kindex target +A @dfn{target} is an interface between the debugger and a particular +kind of file or process. -@cindex convenience variables -_GDBN__ provides @dfn{convenience variables} that you can use within _GDBN__ to -hold on to a value and refer to it later. These variables exist entirely -within _GDBN__; they are not part of your program, and setting a convenience -variable has no effect on further execution of your program. That's why -you can use them freely. +Often, you will be able to run _GDBN__ in the same host environment as the +program you are debugging; in that case, the debugging target can just be +specified as a side effect of the @samp{file} or @samp{core} commands. +When you need more flexibility---for example, running _GDBN__ on a +physically separate host, controlling standalone systems over a +serial port, or realtime systems over a TCP/IP connection---you can use +the @samp{target} command. -Convenience variables have names starting with @samp{$}. Any name starting -with @samp{$} can be used for a convenience variable, unless it is one of -the predefined set of register names (@pxref{Registers}). +@menu +* Active Targets:: Active Targets +* Target Commands:: Commands for Managing Targets +@end menu -You can save a value in a convenience variable with an assignment -expression, just as you would set a variable in your program. Example: +@node Active Targets, Target Commands, Targets, Targets +@section Active Targets +@cindex stacking targets +@cindex active targets +@cindex multiple targets -@example -set $foo = *object_ptr -@end example +Targets are managed in three @dfn{strata} that correspond to different +classes of target: processes, core files, and executable files. This +allows you to (for example) start a process and inspect its activity +without abandoning your work on a core file. -@noindent -would save in @code{$foo} the value contained in the object pointed to by -@code{object_ptr}. +More than one target can potentially respond to a request. In +particular, when you access memory _GDBN__ will walk down the three strata of +targets until it finds a target that can handle that particular address. -Using a convenience variable for the first time creates it; but its value -is @code{void} until you assign a new value. You can alter the value with -another assignment at any time. +Strata are always examined in a fixed order: first a process if there is +one, then a core file if there is one, and finally an executable file if +there is one of those. -Convenience variables have no fixed types. You can assign a convenience -variable any type of value, including structures and arrays, even if -that variable already has a value of a different type. The convenience -variable as an expression has whatever type its current value has. +When you specify a new target in a given stratum, it replaces any target +previously in that stratum. -@table @code -@item info convenience -@kindex info convenience -Print a list of convenience variables used so far, and their values. -Abbreviated @samp{i con}. -@end table +To get rid of a target without replacing it, use the @samp{detach} +command. The related command @samp{attach} provides you with a way of +choosing a particular running process as a new target. @xref{Attach}. -One of the ways to use a convenience variable is as a counter to be -incremented or a pointer to be advanced. For example: +@node Target Commands, , Active Targets, Targets +@section Commands for Managing Targets +@table @code +@item target @var{type} @var{parameters} +Connects the _GDBN__ host environment to a target machine or process. A +target is typically a protocol for talking to debugging facilities. You +use the argument @var{type} to specify the type or protocol of the +target machine; for example, @samp{target vxworks} for a TCP/IP link to +a VxWorks system. + +Further @var{parameters} are interpreted by the target protocol, but +typically include things like device names or host names to connect +with, process numbers, and baud rates. Executing @example -set $i = 0 -print bar[$i++]->contents -@i{@dots{}repeat that command by typing @key{RET}.} + target @var{type} @end example -Some convenience variables are created automatically by _GDBN__ and given -values likely to be useful. - -@table @code -@item $_ -The variable @code{$_} is automatically set by the @samp{x} command to -the last address examined (@pxref{Memory}). Other commands which -provide a default address for @samp{x} to examine also set @code{$_} -to that address; these commands include @samp{info line} and @samp{info -breakpoint}. +@noindent +(without any parameters) will issue a message about what +parameters are required for that target type. -@item $__ -The variable @code{$__} is automatically set by the @samp{x} command -to the value found in the last address examined. +@item info targets +@kindex info targets +Displays the names of all targets available. Beware: the similar +command @samp{info target} displays targets currently in use rather than +all available ones. @samp{info files} gives the same information as +@samp{info target} (@pxref{Files}). @end table -@node Registers, , Convenience Vars, Data -@section Registers +Here are some common targets (available, or not, depending on _GDBN__ +configuration): -@cindex registers -Machine register contents can be referred to in expressions as variables -with names starting with @samp{$}. The names of registers are different -for each machine; use @samp{info registers} to see the names used on your -machine. The names @code{$pc} and @code{$sp} are used on most machines for -the program counter register and the stack pointer. Often @code{$fp} is -used for a register that contains a pointer to the current stack frame, -and @code{$ps} is used for a register that contains the processor -status. These standard register names may be available on your machine -even though the @code{info registers} command displays them with a -different name. For example, on the SPARC, @code{info registers} -displays the processor status register as @code{$psr} but you can also -refer to it as @code{$ps}. +@table @code +@item target exec @var{prog} +@kindex target exec +An executable file. @samp{target exec @var{prog}} is the same as +@samp{exec-file @var{prog}}. -_GDBN__ always considers the contents of an ordinary register as an integer -when the register is examined in this way. Some machines have special -registers which can hold nothing but floating point; these registers are -considered floating point. There is no way to refer to the contents of an -ordinary register as floating point value (although you can @emph{print} -it as a floating point value with @samp{print/f $@var{regname}}). +@item target core @var{filename} +@kindex target core +A core dump file. @samp{target core @var{filename}} is the same as +@samp{core-file @var{filename}}. -Some registers have distinct ``raw'' and ``virtual'' data formats. This -means that the data format in which the register contents are saved by -the operating system is not the same one that your program normally -sees. For example, the registers of the 68881 floating point -coprocessor are always saved in ``extended'' (raw) format, but all C -programs expect to work with ``double'' (virtual) format. In such -cases, _GDBN__ normally works with the virtual format only (the format that -makes sense for your program), but the @samp{info registers} command -prints the data in both formats. +@item target remote @var{dev} +@kindex target remote +Remote serial target in _GDBP__-specific protocol. The argument @var{dev} +specifies what serial device to use for the connection (e.g. +@code{/dev/ttya}). -Register values are relative to the selected stack frame -(@pxref{Selection}). This means that you get the value that the register -would contain if all stack frames farther in were exited and their saved -registers restored. In order to see the real contents of all registers, -you must select the innermost frame (with @samp{frame 0}). +_if__(_AMD29K__) +@item target amd-eb @var{dev} @var{speed} @var{PROG} +@kindex target amd-eb +@cindex AMD EB29K +Remote PC-resident AMD EB29K board, attached over serial lines. +@var{dev} is the serial device, as for @samp{target remote}; +@samp{speed} allows you to specify the linespeed; and @var{PROG} is the +name of the program to be debugged, as it appears to DOS on the PC. +@xref{EB29K Remote}. -Some registers are never saved (typically those numbered zero or one) -because they are used for returning function values. In some operating -systems (those using the ``caller saves'' convention), there are other -registers intended for free alteration by a called routine. For these -registers, relativization makes no difference. +_fi__(_AMD29K__) +_if__(_I960__) +@item target nindy @var{devicename} +@kindex target nindy +An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is +the name of the serial device to use for the connection, e.g. +@samp{/dev/ttya}. -@table @code -@item info registers -@kindex info registers -Print the names and relativized values of all registers. +_fi__(_I960__) +_if__(_VXWORKS__) +@item target vxworks @var{machinename} +@kindex target vxworks +A VxWorks system, attached via TCP/IP. The argument @var{machinename} +is the target system's machine name or IP address. -@item info registers @var{regname} -Print the relativized value of register @var{regname}. @var{regname} -may be any register name valid on the machine you are using, with -or without the initial @samp{$}. +_fi__(_VXWORKS__) @end table -@subsection Examples - -You could print the program counter in hex with +_if__(_GENERIC__) +Different targets are available on different configurations of _GDBN__; your +configuration may have more or fewer targets. +_fi__(_GENERIC__) -@example -p/x $pc -@end example +@node Remote,,, +@section Remote Debugging +@cindex remote debugging -@noindent -or print the instruction to be executed next with +If you are trying to debug a program running on a machine that can't run +_GDBN__ in the usual way, it is often useful to use remote debugging. For +example, you might be debugging an operating system kernel, or debugging +a small system which does not have a general purpose operating system +powerful enough to run a full-featured debugger. Currently _GDBN__ supports +remote debugging over a serial connection, and (using Sun RPC) over a +TCP/IP connection. -@example -x/i $pc -@end example +The program to be debugged on the remote machine needs to contain a +debugging device driver which talks to _GDBN__ over the serial line. The +same version of _GDBN__ that is used ordinarily can be used for this. +Several sample remote debugging drivers are distributed with _GDBN__; see +the @file{README} file in the _GDBN__ distribution for more information. -@noindent -or add four to the stack pointer with +@menu +* Remote Commands:: Commands used to start and finish remote debugging. +@end menu -@example -set $sp += 4 -@end example +For details of the communication protocol, see the comments in the _GDBN__ +source file @file{remote.c}. -@noindent -The last is a way of removing one word from the stack, on machines where -stacks grow downward in memory (most machines, nowadays). This assumes -that the innermost stack frame is selected. Setting @code{$sp} is -not allowed when other stack frames are selected. (To pop entire frames -off the stack, regardless of machine architecture, use @samp{return}; -@pxref{Returning}.) +@node Remote Commands, , Remote, Remote +@subsection Commands for Remote Debugging -@node Symbols, Altering, Data, Top -@chapter Examining the Symbol Table +To start remote debugging, first run _GDBN__ and specify as an executable file +the program that is running in the remote machine. This tells _GDBN__ how +to find the program's symbols and the contents of its pure text. Then +establish communication using the @samp{target remote} command with a device +name as an argument. For example: -The commands described in this section allow you to inquire about the -symbols (names of variables, functions and types) defined in your -program. This information is found by _GDBN__ in the symbol table loaded by -the @samp{symbol-file} command; it is inherent in the text of your -program and does not change as the program executes. +@example +target remote /dev/ttyb +@end example -@table @code -@item info address @var{symbol} -@kindex info address -Describe where the data for @var{symbol} is stored. For a register -variable, this says which register it is kept in. For a non-register -local variable, this prints the stack-frame offset at which the variable -is always stored. +@noindent +if the serial line is connected to the device named @file{/dev/ttyb}. This +will stop the remote machine if it is not already stopped. -Note the contrast with @samp{print &@var{symbol}}, which does not work -at all for a register variables, and for a stack local variable prints -the exact address of the current instantiation of the variable. +Now you can use all the usual commands to examine and change data and to +step and continue the remote program. -@item whatis @var{exp} -@kindex whatis -Print the data type of expression @var{exp}. @var{exp} is not -actually evaluated, and any side-effecting operations (such as -assignments or function calls) inside it do not take place. -@xref{Expressions}. +To resume the remote program and stop debugging it, use the @samp{detach} +command. -@item whatis -Print the data type of @code{$}, the last value in the value history. +Other remote targets be available in your +configuration of _GDBN__; use @samp{info targets} to list them. -@item ptype @var{typename} -@kindex ptype -Print a description of data type @var{typename}. @var{typename} may be -the name of a type, or for C code it may have the form -@samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or -@samp{enum @var{enum-tag}}.@refill +@table @code +@item reset +@kindex reset +For a target attached through a serial line, this command sends a +``break'' to the remote target system; this is only useful if the target +has been equipped with a circuit to perform a hard reset (or some other +interesting action) when a break is detected. +@end table -@item ptype @var{exp} -Print a description of the type of expression @var{exp}. This is like -@samp{whatis} except it prints a detailed description, instead of just -the name of the type. For example, if the type of a variable is -@samp{struct complex @{double real; double imag;@}}, @samp{whatis} will -print @samp{struct complex} and @samp{ptype} will print @samp{struct -complex @{double real; double imag;@}} +@node Controlling _GDBN__,,, +@chapter Controlling _GDBN__ -@item info sources -@kindex info sources -Print the names of all source files in the program for which there -is debugging information. +You can alter many aspects of _GDBN__'s interaction with you by using +the @samp{set} command. -@item info functions -@kindex info functions -Print the names and data types of all defined functions. +@node Prompt,,, +@section Prompt +@cindex prompt +_GDBN__ indicates its readiness to read a command by printing a string +called the @dfn{prompt}. This string is normally @samp{(_GDBP__)}. You can +change the prompt string with the @samp{set prompt} command. For +instance, when debugging _GDBN__ with _GDBN__, it is useful to change the prompt +in one of the _GDBN__s so that you tell which one you are talking to. -@item info functions @var{regexp} -Print the names and data types of all defined functions -whose names contain a match for regular expression @var{regexp}. -Thus, @samp{info fun step} finds all functions whose names -include @samp{step}; @samp{info fun ^step} finds those whose names -start with @samp{step}. +@table @code +@item set prompt @var{newprompt} +@kindex set prompt +Directs _GDBN__ to use @var{newprompt} as its prompt string henceforth. +@kindex show prompt +@item show prompt +Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}} +@end table -@item info variables -@kindex info variables -Print the names and data types of all variables that are declared -outside of functions (i.e., except for local variables). +@node Editing/History,,, +@section Command Editing and History +@cindex readline +@cindex command line editing +@cindex history substitution +_GDBN__ reads its input commands via the @code{readline} interface. This +GNU library provides consistent behavior for programs which provide a +command line interface to the user. Advantages are @samp{emacs}-style +or @samp{vi}-style inline editing of commands, @samp{csh}-like history +substitution, and a storage and recall of command history across +debugging sessions. -@item info variables @var{regexp} -Print the names and data types of all variables (except for local -variables) whose names contain a match for regular expression -@var{regexp}. +You may control the behavior of command line editing in _GDBN__ with the +command @samp{set}. You may check the status of any of these settings +with the command @samp{show}. +@table @code +@kindex set editing +@cindex editing +@item set editing +@itemx set editing on +Enable command line editing (enabled by default). -@ignore -This was never implemented. -@item info methods -@itemx info methods @var{regexp} -@kindex info methods -The @samp{info-methods} command permits the user to examine all defined -methods within C++ program, or (with the @var{regexp} argument) a -specific set of methods found in the various C++ classes. Many -C++ classes provide a large number of methods. Thus, the output -from the @samp{ptype} command can be overwhelming and hard to use. The -@samp{info-methods} command filters the methods, printing only those -which match the regular-expression @var{regexp}. -@end ignore +@item set editing off +Disable command line editing. -@item printsyms @var{filename} -@kindex printsyms -Write a complete dump of the debugger's symbol data into the -file @var{filename}. -@end table +@kindex show editing +@item show editing +Show whether command line editing is enabled. -@node Altering, Sequences, Symbols, Top -@chapter Altering Execution +@cindex history file +@kindex set history file +@item set history file @var{filename} +Set the name of the _GDBN__ command history file to @samp{filename}. This is +the file from which _GDBN__ will read an initial command history +list or to which it will write this list when it exits. This list is +accessed through history expansion or through the history +command editing characters listed below. This file defaults to the +value of the environmental variable @code{GDBHISTFILE}, or to +@code{./.gdb_history} if this variable is not set. -Once you think you have found an error in the program, you might want to -find out for certain whether correcting the apparent error would lead to -correct results in the rest of the run. You can find the answer by -experiment, using the _GDBN__ features for altering execution of the -program. +@cindex history write +@kindex set history write +@item set history write +@itemx set history write on +Make _GDBN__ record command history in a file, whose name may be specified with the +@samp{set history file} command. By default, this option is disabled. -For example, you can store new values into variables or memory -locations, give the program a signal, restart it at a different address, -or even return prematurely from a function to its caller. +@item set history write off +Make _GDBN__ stop recording command history in a file. -@menu -* Assignment:: Altering variable values or memory contents. -* Jumping:: Altering control flow. -* Signaling:: Making signals happen in the program. -* Returning:: Making a function return prematurely. -* Calling:: Calling functions from your program -@end menu +@cindex history size +@kindex set history size +@item set history size @var{size} +Set the number of commands which _GDBN__ will keep in its history list. +This defaults to the value of the environmental variable +@code{HISTSIZE}, or to 256 if this variable is not set. +@end table -@node Assignment, Jumping, Altering, Altering -@section Assignment to Variables +@cindex history expansion +History expansion assigns special meaning to the character @samp{!} +(@pxref{Event Designators}). Since @samp{!} is also the logical not +operator in C, history expansion is off by default. If you decide to +enable history expansion with the @samp{set history expansion on} +command, you may sometimes need to follow @samp{!} (when it is used as +logical not, in an expression) with a space or a tab to prevent it from +being expanded. The @code{readline} history facilities will not attempt +substitution on the strings @samp{!=} and @samp{!(}, even when history +expansion is enabled. -@cindex assignment -@cindex setting variables -To alter the value of a variable, evaluate an assignment expression. -@xref{Expressions}. For example, +The commands to control history expansion are: -@example -print x=4 -@end example +@table @code -@noindent -would store the value 4 into the variable @code{x}, and then print -the value of the assignment expression (which is 4). +@kindex set history expansion +@item set history expansion on +@itemx set history expansion +Enable history expansion. History expansion is off by default. -All the assignment operators of C are supported, including the -increment operators @samp{++} and @samp{--}, and combining -assignments such as @samp{+=} and @samp{<<=}. +@item set history expansion off +Disable history expansion. -@kindex set -@kindex set variable -@cindex variables, setting -If you are not interested in seeing the value of the assignment, use the -@samp{set} command instead of the @samp{print} command. @samp{set} is -really the same as @samp{print} except that the expression's value is not -printed and is not put in the value history (@pxref{Value History}). The -expression is evaluated only for side effects. +The @code{readline} code comes with more complete documentation of +editing and history expansion features. Users unfamiliar with @samp{emacs} +or @samp{vi} may wish to read it. @xref{Command Line Editing}. -Note that if the beginning of the argument string of the @samp{set} command -appears identical to a @samp{set} subcommand, it may be necessary to use -the @samp{set variable} command. This command is identical to @samp{set} -except for its lack of subcommands. +@kindex show history +@item show history +@itemx show history file +@itemx show history write +@itemx show history size +@itemx show history expansion +These commands display the state of the _GDBN__ history parameters. +@samp{show history} by itself displays all four states. -_GDBN__ allows more implicit conversions in assignments than C does; you can -freely store an integer value into a pointer variable or vice versa, and -any structure can be converted to any other structure that is the same -length or shorter. -@comment FIXME: how do structs align/pad in these conversions? -@comment /pesch@cygnus.com 18dec1990 +@end table -To store values into arbitrary places in memory, use the @samp{@{@dots{}@}} -construct to generate a value of specified type at a specified address -(@pxref{Expressions}). For example, @code{@{int@}0x83040} would refer -to memory location 0x83040 as an integer (which implies a certain size -and representation in memory), and +@table @code +@kindex info editing +@item info editing +Display the last ten commands in the command history. -@example -set @{int@}0x83040 = 4 -@end example +@item info editing @var{n} +Print ten commands centered on command number @var{n}. -would store the value 4 into that memory location. +@item info editing + +Print ten commands just after the commands last printed. -@node Jumping, Signaling, Assignment, Altering -@section Continuing at a Different Address +@end table -Ordinarily, when you continue the program, you do so at the place where -it stopped, with the @samp{cont} command. You can instead continue at -an address of your own choosing, with the following commands: +@node Screen Size,,, +@section Screen Size +@cindex size of screen +@cindex pauses in output +Certain commands to _GDBN__ may produce large amounts of information output +to the screen. To help you read all of it, _GDBN__ pauses and asks you for +input at the end of each page of output. Type @key{RET} when you want +to continue the output. Normally _GDBN__ knows the size of the screen from +the termcap data base together with the value of the @code{TERM} +environment variable and the @code{stty rows} and @code{stty cols} +settings. If this is not correct, you can override it with +the @samp{set screen-height} and @samp{set screen-width} commands: -@table @code -@item jump @var{linenum} -@kindex jump -Resume execution at line number @var{linenum}. Execution may stop -immediately if there is a breakpoint there. +_GDBN__ also uses the screen width setting to determine when to wrap lines +of output. Depending what is being printed, it tries to break the +line at a readable place, rather than simply letting it overflow onto +the following line. -The @samp{jump} command does not change the current stack frame, or -the stack pointer, or the contents of any memory location or any -register other than the program counter. If line @var{linenum} is in -a different function from the one currently executing, the results may -be bizarre if the two functions expect different patterns of arguments or -of local variables. For this reason, the @samp{jump} command requests -confirmation if the specified line is not in the function currently -executing. However, even bizarre results are predictable based on -careful study of the machine-language code of the program. +@table @code +@item set screen-height @var{lpp} +@itemx show screen-height +@itemx set screen-width @var{cpl} +@itemx show screen-width +@kindex set screen-height +@kindex set screen-width +@kindex show screen-width +@kindex show screen-height +These @samp{set} commands specify a screen height of @var{lpp} lines and +a screen width of @var{cpl} characters. The associated @samp{show} +commands display the current settings. -@item jump *@var{address} -Resume execution at the instruction at address @var{address}. +If you specify a height of zero lines, _GDBN__ will not pause during output +no matter how long the output is. This is useful if output is to a file +or to an editor buffer. @end table -You can get much the same effect as the @code{jump} command by storing a -new value into the register @code{$pc}. The difference is that this -does not start the program running; it only changes the address where it -@emph{will} run when it is continued. For example, +@node Numbers,,, +@section Numbers +@cindex number representation +@cindex entering numbers +You can always enter numbers in octal, decimal, or hexadecimal in _GDBN__ by +the usual conventions: octal numbers begin with @samp{0}, decimal +numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}. +Numbers that begin with none of these are, by default, entered in base +10; likewise, the default display for numbers---when no particular +format is specified---is base 10. You can change the default base for +both input and output with the @samp{set radix} command. + +@table @code +@kindex set radix +@item set radix @var{base} +Set the default base for numeric input and display. Supported choices +for @var{base} are decimal 8, 10, 16. @var{base} must itself be +specified either unambiguously or using the current default radix; for +example, any of @example -set $pc = 0x485 +set radix 012 +set radix 10. +set radix 0xa @end example @noindent -causes the next @samp{cont} command or stepping command to execute at -address 0x485, rather than at the address where the program stopped. -@xref{Stepping}. +will set the base to decimal. On the other hand, @samp{set radix 10} +will leave the radix unchanged no matter what it was. -The most common occasion to use the @samp{jump} command is to back up, -perhaps with more breakpoints set, over a portion of a program that has -already executed. +@kindex show radix +@item show radix +Display the current default base for numeric input and display. -@node Signaling, Returning, Jumping, Altering -@section Giving the Program a Signal +@end table + +@node Messages/Warnings,,, +@section Optional Warnings and Messages +By default, _GDBN__ is silent about its inner workings. If you are running +on a slow machine, you may want to use the @samp{set verbose} command. +It will make _GDBN__ tell you when it does a lengthy internal operation, so +you won't think it has crashed. + +Currently, the messages controlled by @samp{set verbose} are those which +announce that the symbol table for a source file is being read +(@pxref{Files}, in the description of the command +@samp{symbol-file}). +@c The following is the right way to do it, but emacs 18.55 doesn't support +@c @ref, and neither the emacs lisp manual version of texinfmt or makeinfo +@c is released. +@ignore +see @samp{symbol-file} in @ref{Files}). +@end ignore @table @code -@item signal @var{signalnum} -@kindex signal -Resume execution where the program stopped, but give it immediately the -signal number @var{signalnum}. +@kindex set verbose +@item set verbose on +Enables _GDBN__'s output of certain informational messages. -Alternatively, if @var{signalnum} is zero, continue execution without -giving a signal. This is useful when the program stopped on account of -a signal and would ordinary see the signal when resumed with the -@samp{cont} command; @samp{signal 0} causes it to resume without a -signal. +@item set verbose off +Disables _GDBN__'s output of certain informational messages. + +@kindex show verbose +@item show verbose +Displays whether @samp{set verbose} is on or off. @end table -@node Returning, Calling, Signaling, Altering -@section Returning from a Function +By default, if _GDBN__ encounters bugs in the symbol table of an object file, +it prints a single message about each type of problem it finds, then +shuts up. You can suppress these messages, or allow more than one such +message to be printed if you want to see how frequent the problems are. +@xref{Files}. @table @code -@item return -@cindex returning from a function -@kindex return -You can cancel execution of a function call with the @samp{return} -command. +@kindex set complaints +@item set complaints @var{limit} +Permits _GDBN__ to output @var{limit} complaints about each type of unusual +symbols before becoming silent about the problem. Set @var{limit} to +zero to suppress all complaints; set it to a large number to prevent +complaints from being suppressed. + +@kindex show complaints +@item show complaints +Displays how many symbol complaints _GDBN__ is permitted to produce. @end table -This command has the effect of discarding the selected stack -frame (and all frames within it), so that control moves to the caller of -that function. You can think of this as making the discarded frame -return prematurely. +By default, _GDBN__ is cautious, and asks what sometimes seem to be a lot of +stupid questions. For example, if you try to run a program which is +already running: +@example -First select the stack frame that you wish to return from -(@pxref{Selection}). Then type the @samp{return} command. If you wish -to specify the value to be returned, give that as an argument. +(_GDBP__) run +The program being debugged has been started already. +Start it from the beginning? (y or n) +@end example -This pops the selected stack frame (and any other frames inside of it), -leaving its caller as the innermost remaining frame. That frame becomes -selected. The specified value is stored in the registers used for -returning values of functions. +If you're willing to unflinchingly face the consequences of your own +commands, you can disable this ``feature'': -The @samp{return} command does not resume execution; it leaves the -program stopped in the state that would exist if the function had just -returned. Contrast this with the @samp{finish} command -(@pxref{Stepping}), which resumes execution until the selected stack -frame returns @emph{naturally}. +@table @code +@kindex set caution +@cindex flinching +@cindex stupid questions +@item set caution off +Disables cautious questions. -@node Calling, , Returning, Altering -@comment node-name, next, previous, up -@section Calling your Program's Functions +@item set caution on +Enables cautious questions (the default). -@cindex calling functions -@kindex call -@table @code -@item call @var{expr} -Evaluate the expression @var{expr} without displaying @code{void} -returned values. +@item show caution +@kindex show caution +Displays state of cautious questions. @end table -You can use this variant of the @samp{print} command if you want to -execute some piece of your program, but without cluttering the output -with @code{void} returned values. The result is printed and saved in -the value history, if it is not void. - @node Sequences, Emacs, Altering, Top @chapter Canned Sequences of Commands @@ -4205,7 +4533,7 @@ All the facilities of Emacs' Shell mode are available for this purpose. @item _GDBN__ displays source code through Emacs. Each time _GDBN__ displays a stack frame, Emacs automatically finds the source file for that frame -and puts an arrow (@samp{=>}) at the left margin of the current line. +and puts an arrow (_0__@samp{=>}_1__) at the left margin of the current line. Emacs uses a separate buffer for source display, and splits the window to show both your _GDBN__ session and the source. @@ -4330,66 +4658,6 @@ environment. Users of this environment can use a new command, each value is printed in its own window. @end ignore -@node Remote, _GDBN__ Bugs, Emacs, Top -@chapter Remote Debugging -@cindex remote debugging - -If you are trying to debug a program running on a machine that can't run -_GDBN__ in the usual way, it is often useful to use remote debugging. For -example, you might be debugging an operating system kernel, or debugging -a small system which does not have a general purpose operating system -powerful enough to run a full-featured debugger. Currently _GDBN__ supports -remote debugging over a serial connection, and (using Sun RPC) over a -TCP/IP connection. - -The program to be debugged on the remote machine needs to contain a -debugging device driver which talks to _GDBN__ over the serial line. The -same version of _GDBN__ that is used ordinarily can be used for this. -Several sample remote debugging drivers are distributed with _GDBN__; see -the @file{README} file in the _GDBN__ distribution for more information. - -@menu -* Remote Commands:: Commands used to start and finish remote debugging. -@end menu - -For details of the communication protocol, see the comments in the _GDBN__ -source file @file{remote.c}. - -@node Remote Commands, , Remote, Remote -@section Commands for Remote Debugging - -To start remote debugging, first run _GDBN__ and specify as an executable file -the program that is running in the remote machine. This tells _GDBN__ how -to find the program's symbols and the contents of its pure text. Then -establish communication using the @samp{target remote} command with a device -name as an argument. For example: - -@example -target remote /dev/ttyb -@end example - -@noindent -if the serial line is connected to the device named @file{/dev/ttyb}. This -will stop the remote machine if it is not already stopped. - -Now you can use all the usual commands to examine and change data and to -step and continue the remote program. - -To resume the remote program and stop debugging it, use the @samp{detach} -command. - -Other remote targets be available in your -configuration of _GDBN__; use @samp{info targets} to list them. - -@table @code -@item reset -@kindex reset -For a target attached through a serial line, this command sends a -``break'' to the remote target system; this is only useful if the target -has been equipped with a circuit to perform a hard reset (or some other -interesting action) when a break is detected. -@end table - @node _GDBN__ Bugs, Installing _GDBN__, Remote, Top @comment node-name, next, previous, up @chapter Reporting Bugs in _GDBN__ @@ -4445,23 +4713,12 @@ for improvement of _GDBN__ are welcome in any case. @cindex Bug Reports @cindex Compiler Bugs, Reporting -@comment The following is meant to be neutral and helpful, not just a plug for -@comment Cygnus; feedback on the issue (to "pesch@cygnus.com" or -@comment "info@cygnus.com"---the latter will reach all of Cygnus) -@comment is welcome. A number of companies and individuals offer support for GNU products. If you obtained _GDBN__ from a support organization, we recommend you contact that organization first. -Among these organizations are Cygnus Support (Palo Alto CA, USA); C2V -(Paris, France); Dynamix Corporation (King of Prussia PA, USA); The Nice -Computer Company (Perth, Australia); Optimal Solutions (Seattle WA, -USA); and The Pharos Group (Las Cruces NM, USA). - -Full contact information is in the file @samp{etc/SERVICE} in the GNU -Emacs distribution. Numerous individual consultants are also listed -there. -@comment END NEUTRAL+HELPFUL section +Contact information for many support companies and individuals is +available in the file @samp{etc/SERVICE} in the GNU Emacs distribution. In any event, we also recommend that you send bug reports for _GDBN__ to one of these addresses: @@ -4520,8 +4777,8 @@ To enable us to fix the bug, you should include all these things: @itemize @bullet @item -The version of _GDBN__. _GDBN__ announces it on startup; you can also print it -at any time using @samp{info version}. +The version of _GDBN__. _GDBN__ announces it if you start with no +arguments; you can also print it at any time using @samp{show version}. Without this, we won't know whether there is any point in looking for the bug in the current version of _GDBN__. @@ -4972,15 +5229,25 @@ Ty Coon, President of Vice That's all there is to it! -@node Commands, Concepts, License, Top -@unnumbered Command Index - -@printindex ky - -@node Concepts, , Commands, Top +@node Index,,, @unnumbered Index @printindex cp +@tex +% I think something like @colophon should be in texinfo. In the +% meantime: +\long\def\colophon{\hbox to0pt{}\vfill +\centerline{The body of this manual is set in} +\centerline{\fontname\tenrm,} +\centerline{with headings in {\bf\fontname\tenbf}} +\centerline{and examples in {\tt\fontname\tentt}.} +\centerline{{\it\fontname\tenit\/} and} +\centerline{{\sl\fontname\tensl\/}} +\centerline{are used for emphasis.}\vfill} +\page\colophon +% Blame: pesch@cygnus.com, 28mar91. +@end tex + @contents @bye -- 2.30.2