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gdb(1) GNU Tools gdb(1)

NAME

gdb - The GNU Debugger

SYNOPSIS

ggddbb [-hheellpp] [-nnxx] [-qq] [-bbaattcchh] [-ccdd==dir] [-ff] [-bb bps] [-ttttyy==dev]

[-ss symfile] [-ee prog] [-ssee prog] [-cc core] [-xx cmds] [-dd dir]

[prog[core|procID]]

DESCRIPTION

The purpose of a debugger such as GDB is to allow you to see what is

going on ``inside'' another program while it executes-or what another

program was doing at the moment it crashed. GDB can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act: +o Start your program, specifying anything that might affect its behavior. +o Make your program stop on specified conditions. +o Examine what has happened, when your program has stopped.

+o Change things in your program, so you can experiment with cor-

recting the effects of one bug and go on to learn about another.

You can use GDB to debug programs written in C, C++, and Modula-2.

Fortran support will be added when a GNU Fortran compiler is ready.

GDB is invoked with the shell command ggddbb. Once started, it reads com-

mands from the terminal until you tell it to exit with the GDB command qquuiitt. You can get online help from ggddbb itself by using the command hheellpp. You can run ggddbb with no arguments or options; but the most usual way to start GDB is with one argument or two, specifying an executable program as the argument:

gdb program

You can also start with both an executable program and a core file specified:

gdb program core

You can, instead, specify a process ID as a second argument, if you want to debug a running process:

gdb program 1234

would attach GDB to process 11223344 (unless you also have a file named `11223344'; GDB does check for a core file first). Here are some of the most frequently needed GDB commands: bbrreeaakk [file::]function Set a breakpoint at function (in file). rruunn [arglist] Start your program (with arglist, if specified). bbtt Backtrace: display the program stack. pprriinntt expr Display the value of an expression.

cc Continue running your program (after stopping, e.g. at a break-

point).

nneexxtt Execute next program line (after stopping); step over any func-

tion calls in the line. eeddiitt [file::]function look at the program line where it is presently stopped. lliisstt [file::]function type the text of the program in the vicinity of where it is presently stopped.

sstteepp Execute next program line (after stopping); step into any func-

tion calls in the line. hheellpp [name] Show information about GDB command name, or general information about using GDB. qquuiitt Exit from GDB.

For full details on GDB, see Using GDB: A Guide to the GNU Source-Level

Debugger, by Richard M. Stallman and Roland H. Pesch. The same text is available online as the ggddbb entry in the iinnffoo program. OOPPTTIIOONNSS Any arguments other than options specify an executable file and core file (or process ID); that is, the first argument encountered with no

associated option flag is equivalent to a `-ssee' option, and the second,

if any, is equivalent to a `-cc' option if it's the name of a file.

Many options have both long and short forms; both are shown here. The long forms are also recognized if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can

flag option arguments with `++' rather than `-', though we illustrate

the more usual convention.) All the options and command line arguments you give are processed in

sequential order. The order makes a difference when the `-xx' option is

used.

-hheellpp

-hh List all options, with brief explanations.

-ssyymmbboollss==file

-ss file

Read symbol table from file file.

-wwrriittee Enable writing into executable and core files.

-eexxeecc==file

-ee file

Use file file as the executable file to execute when appropri-

ate, and for examining pure data in conjunction with a core dump.

-ssee==file

Read symbol table from file file and use it as the executable file.

-ccoorree==file

-cc file

Use file file as a core dump to examine.

-ccoommmmaanndd==file

-xx file

Execute GDB commands from file file.

-ddiirreeccttoorryy==directory

-dd directory

Add directory to the path to search for source files.

-nnxx

-nn Do not execute commands from any `..ggddbbiinniitt' initialization

files. Normally, the commands in these files are executed after all the command options and arguments have been processed.

-qquuiieett

-qq ``Quiet''. Do not print the introductory and copyright mes-

sages. These messages are also suppressed in batch mode.

-bbaattcchh Run in batch mode. Exit with status 00 after processing all the

command files specified with `-xx' (and `..ggddbbiinniitt', if not inhib-

ited). Exit with nonzero status if an error occurs in executing the GDB commands in the command files.

Batch mode may be useful for running GDB as a filter, for exam-

ple to download and run a program on another computer; in order to make this more useful, the message Program exited normally. (which is ordinarily issued whenever a program running under GDB control terminates) is not issued when running in batch mode.

-ccdd==directory

Run GDB using directory as its working directory, instead of the current directory.

-ffuullllnnaammee

-ff Emacs sets this option when it runs GDB as a subprocess. It

tells GDB to output the full file name and line number in a

standard, recognizable fashion each time a stack frame is dis-

played (which includes each time the program stops). This rec-

ognizable format looks like two ` 3322' characters, followed by the file name, line number and character position separated by

colons, and a newline. The Emacs-to-GDB interface program uses

the two ` 3322' characters as a signal to display the source code for the frame.

-bb bps Set the line speed (baud rate or bits per second) of any serial

interface used by GDB for remote debugging.

-ttttyy==device

Run using device for your program's standard input and output.