GDB: The GNU Project Debugger

Chen Weixiang @ Jul 19, 2016 | TAG: Linux

This article introduces the usage of GDB.

Overview

GDB, the GNU Project debugger, allows 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:

  • Start your program, specifying anything that might affect its behavior.
  • Make your program stop on specified conditions.
  • Examine what has happened, when your program has stopped.
  • Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.

The program being debugged can be written in Ada, C, C++, Objective-C, Pascal and many other languages. Those programs might be executing on the same machine as GDB (native) or on another machine (remote). GDB can run on most popular UNIX and Microsoft Windows variants.

GDB Quick Reference

Refer to GDB_Quick_Reference.

Example

Save the following source code to ~/example/ex-gdb.c:

#include <stdio.h>
#include <stdlib.h>

#define ARRAY_SIZE  16
#define COLUMN_SIZE 5

static int maxSize = ARRAY_SIZE;

int array[ARRAY_SIZE];
int (*pArray)[ARRAY_SIZE];

void setArray(void)
{
    int i;

    for (i = 0; i < maxSize; ++i)
    {
        array[i] = i + 1;
    }
}

void printArray(void)
{
    int i;
    pArray = &array;

    int halfMaxSize = (int)maxSize/2;
    halfMaxSize = (halfMaxSize > COLUMN_SIZE) ? COLUMN_SIZE : halfMaxSize;
    for (i = 0; i < maxSize; ++i)
    {
        if ((i > 0) && (i%halfMaxSize == 0))
        {
            printf("\n");
        }

        printf("%2d\t", (*pArray)[i]);
    }
    printf("\n");
}

int main(int argc, char *argv[])
{
    if (argc == 2)
    {
        maxSize = atoi(argv[1]);
    }

    setArray();
    printArray();

    return 0;
}

Build the source code with the following command:

chenwx@chenwx ~/example $ gcc -g -o ex-gdb ex-gdb.c
chenwx@chenwx ~/example $ ll
-rwxrwxr-x 1 chenwx chenwx 10K Aug 15 08:34 ex-gdb
-rw-rw-r-- 1 chenwx chenwx 513 Aug 14 16:15 ex-gdb.c

Starting and Stoping GDB

Commands Description
gdb start GDB, with no debugging files
gdb program begin debugging program
gdb program core debug coredump core produced by program
quit
EOF (eg C-d)		 exit GDB
INTERRUPT (eg C-c) terminate current command, or send to running process 

chenwx@chenwx ~/example $ gdb
GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.04) 7.11.1
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".

chenwx@chenwx ~/example $ gdb ex-gdb
GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.04) 7.11.1
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ex-gdb...done.

(gdb) q
chenwx@chenwx ~/example $

GDB Help

Commands Description
help list classes of commands
help class one-line descriptions for commands in class
help command describe command 

(gdb) h
List of classes of commands:

aliases -- Aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without stopping the program
user-defined -- User-defined commands

Type "help" followed by a class name for a list of commands in that class.
Type "help all" for the list of all commands.
Type "help" followed by command name for full documentation.
Type "apropos word" to search for commands related to "word".
Command name abbreviations are allowed if unambiguous.

(gdb) h aliases
Aliases of other commands.

List of commands:

ni -- Step one instruction
rc -- Continue program being debugged but run it in reverse
rni -- Step backward one instruction
rsi -- Step backward exactly one instruction
si -- Step one instruction exactly
stepping -- Specify single-stepping behavior at a tracepoint
tp -- Set a tracepoint at specified location
tty -- Set terminal for future runs of program being debugged
where -- Print backtrace of all stack frames
ws -- Specify single-stepping behavior at a tracepoint

Type "help" followed by command name for full documentation.
Type "apropos word" to search for commands related to "word".
Command name abbreviations are allowed if unambiguous.

(gdb) h ni     
Step one instruction, but proceed through subroutine calls.
Usage: nexti [N]
Argument N means step N times (or till program stops for another reason).

Executing Program

Commands Description
show args display argument list
set args arglist specify arglist for next run
set args specify empty argument list
show environment show all environment variables
show env var show value of environment variable var
set environment varname string set environment variable var
unset env var remove var from environment
run arglist start your program with arglist
run start your program with current argument list
run … < inf > outf start your program with input, output redirected
kill kill running program
tty dev use dev as stdin and stdout for next run 

chenwx@chenwx ~/example $ gdb ex-gdb
GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.04) 7.11.1
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ex-gdb...done.

(gdb) set args 10
(gdb) show args
Argument list to give program being debugged when it is started is "10".

(gdb) r
Starting program: /home/chenwx/example/ex-gdb 10
 1	 2	 3	 4	 5
 6	 7	 8	 9	10
[Inferior 1 (process 9323) exited normally]

(gdb) set args
(gdb) show args
Argument list to give program being debugged when it is started is "".

(gdb) r
Starting program: /home/chenwx/example/ex-gdb
 1	 2	 3	 4	 5
 6	 7	 8	 9	10
11	12	13	14	15
16
[Inferior 1 (process 9324) exited normally]

(gdb) r 13
Starting program: /home/chenwx/example/ex-gdb 13
 1	 2	 3	 4	 5
 6	 7	 8	 9	10
11	12	13
[Inferior 1 (process 9373) exited normally]
(gdb) show args
Argument list to give program being debugged when it is started is "13".

(gdb) k
The program is not being run.

(gdb) show env HOME
HOME = /home/chenwx

Breakpoints and Watchpoints

Commands Description
info break show defined breakpoints
info watch show defined watchpoints
break [file:]line set breakpoint at line number [in file], eg: break main.c:37
break [file:]fun set breakpoint at fun() [in file]
break +offset
break -offset		 set break at offset lines from current stop
break *addr set breakpoint at address addr
break set breakpoint at next instruction
break … if expr break conditionally on nonzero expr
cond n [expr] new conditional expression on breakpoint n; make unconditional if no expr
tbreak … temporary break; disable when reached
rbreak regex break on all functions matching regex
watch expr set a watchpoint for expression expr
catch event break at event, which may be catch, throw, exec, fork, vfork, load, or unload.
clear delete breakpoints at next instruction
clear [file:]fun delete breakpoints at entry to fun()
clear [file:]line delete breakpoints on source line
delete [n] delete breakpoints [ or breakpoint n ]
disable [n] disable breakpoints [ or breakpoint n ]
enable [n] enable breakpoints [ or breakpoint n ]
enable once [n] enable breakpoints [ or breakpoint n ]; disable again when reached
enable del [n] enable breakpoints [ or breakpoint n ]; delete when reached
ignore n count ignore breakpoint n, count times
commands n
[silent]
command-list
end		 execute GDB command-list every time breakpoint n is reached. [ silent ] suppresses default display ]. end of command-list 

(gdb) b 18 if i==5
Breakpoint 1 at 0x4005c3: file ex-gdb.c, line 18.

(gdb) b printArray
Breakpoint 2 at 0x4005ef: file ex-gdb.c, line 25.

(gdb) b ex-gdb.c:45
Breakpoint 3 at 0x400694: file ex-gdb.c, line 45.

(gdb) info b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00000000004005c3 in setArray at ex-gdb.c:18
	stop only if i==5
2       breakpoint     keep y   0x00000000004005ef in printArray at ex-gdb.c:25
3       breakpoint     keep y   0x0000000000400694 in main at ex-gdb.c:45

(gdb) dis 3
(gdb) info b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00000000004005c3 in setArray at ex-gdb.c:18
	stop only if i==5
2       breakpoint     keep y   0x00000000004005ef in printArray at ex-gdb.c:25
3       breakpoint     keep n   0x0000000000400694 in main at ex-gdb.c:45

(gdb) en 3
(gdb) info b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00000000004005c3 in setArray at ex-gdb.c:18
	stop only if i==5
2       breakpoint     keep y   0x00000000004005ef in printArray at ex-gdb.c:25
3       breakpoint     keep y   0x0000000000400694 in main at ex-gdb.c:45

(gdb) del 3
(gdb) info b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00000000004005c3 in setArray at ex-gdb.c:18
	stop only if i==5
2       breakpoint     keep y   0x00000000004005ef in printArray at ex-gdb.c:25

(gdb) r
Starting program: /home/chenwx/example/ex-gdb

Breakpoint 1, setArray () at ex-gdb.c:18
18	        array[i] = i + 1;

(gdb) p i
$1 = 5

(gdb) cond 1 i==10

(gdb) info b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00000000004005c3 in setArray at ex-gdb.c:18
	stop only if i==10
	breakpoint already hit 1 time
2       breakpoint     keep y   0x00000000004005ef in printArray at ex-gdb.c:25

(gdb) c
Continuing.

Breakpoint 1, setArray () at ex-gdb.c:18
18	        array[i] = i + 1;

(gdb) p i
$2 = 10

(gdb) tb 28
Temporary breakpoint 4 at 0x40060c: file ex-gdb.c, line 28.

(gdb) info b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00000000004005c3 in setArray at ex-gdb.c:18
	stop only if i==10
	breakpoint already hit 2 times
2       breakpoint     keep y   0x00000000004005ef in printArray at ex-gdb.c:25
	breakpoint already hit 1 time
4       breakpoint     del  y   0x000000000040060c in printArray at ex-gdb.c:28

(gdb) c
Continuing.

Temporary breakpoint 4, printArray () at ex-gdb.c:28
28	    halfMaxSize = (halfMaxSize > COLUMN_SIZE) ? COLUMN_SIZE : halfMaxSize;

(gdb) info b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00000000004005c3 in setArray at ex-gdb.c:18
	stop only if i==10
	breakpoint already hit 2 times
2       breakpoint     keep y   0x00000000004005ef in printArray at ex-gdb.c:25
	breakpoint already hit 1 time

Program Stack

Commands Description
backtrace [n]
bt [n]		 print trace of all frames in stack; or of n frames — innermost if n > 0, outermost if n < 0
frame [n] select frame number n or frame at address n; if no n, display current frame
up n select frame n frames up
down n select frame n frames down
info frame [addr] describe selected frame, or frame at addr
info args arguments of selected frame
info locals local variables of selected frame
info reg [rn] …
info all-reg [rn]		 register values [ for regs rn ] in selected frame; all-reg includes floating point 

(gdb) bt
#0  printArray () at ex-gdb.c:28
#1  0x00000000004006b7 in main (argc=1, argv=0x7fffffffe1c8) at ex-gdb.c:49

(gdb) frame
#0  printArray () at ex-gdb.c:28
28	    halfMaxSize = (halfMaxSize > COLUMN_SIZE) ? COLUMN_SIZE : halfMaxSize;

(gdb) info frame
Stack level 0, frame at 0x7fffffffe0d0:
 rip = 0x40060c in printArray (ex-gdb.c:28); saved rip = 0x4006b7
 called by frame at 0x7fffffffe0f0
 source language c.
 Arglist at 0x7fffffffe0c0, args:
 Locals at 0x7fffffffe0c0, Previous frame's sp is 0x7fffffffe0d0
 Saved registers:
  rbp at 0x7fffffffe0c0, rip at 0x7fffffffe0c8

(gdb) info args
No arguments.

(gdb) info locals
i = 0
halfMaxSize = 8

(gdb) info reg
rax            0x8	8
rbx            0x0	0
rcx            0x0	0
rdx            0x0	0
rsi            0x7fffffffe1c8	140737488347592
rdi            0x1	1
rbp            0x7fffffffe0c0	0x7fffffffe0c0
rsp            0x7fffffffe0b0	0x7fffffffe0b0
r8             0x400730	4196144
r9             0x7ffff7de78e0	140737351940320
r10            0x846	2118
r11            0x7ffff7a2e740	140737348036416
r12            0x4004c0	4195520
r13            0x7fffffffe1c0	140737488347584
r14            0x0	0
r15            0x0	0
rip            0x40060c	0x40060c <printArray+37>
eflags         0x202	[ IF ]
cs             0x33	51
ss             0x2b	43
ds             0x0	0
es             0x0	0
fs             0x0	0
gs             0x0	0

Execution Control

Commands Description
continue [count] continue running; if count specified this breakpoint next count times
step [count] execute until another line reached; repeat count times if specified
stepi [count]
si [count]		 step by machine instructions rather than source lines
next [count] execute next line, including any function calls
nexti [count]
ni [count]		 next machine instruction rather than source line
until [location] run until next instruction (or location)
finish run until selected stack frame returns
return [expr] pop selected stack frame without executing [ setting return value ]
signal num resume execution with signal s (none if 0)
jump line
jump *address		 resume execution at specified line number or address
set var=expr evaluate expr without displaying it; use for altering program variables

Display

Commands Description
print [/f] [expr] show value of expr [ or last value $ ] according to format f in the following table
call [/f] expr like print but does not display void

The format f of print and call commands:

  • x - hexadecimal
  • d - signed decimal
  • u - unsigned decimal
  • o - octal
  • t - binary
  • a - address, absolute and relative
  • c - character
  • f - floating point

For instances:

  • 以十六进制输出

    p /x expr

  • 以有符号十进制输出

    p /d expr

  • 以无符号十进制输出

    p /u expr

  • 以八进制输出

    p /o expr

  • 以二进制输出

    p /t expr

  • 以地址格式输出

    p /a expr

  • 以单字符输出

    p /c expr

  • 以浮点数输出

    p /f expr

  • 打印局部变量i所占空间的大小

    p /x sizeof(i)

(gdb) p i
$3 = 0

(gdb) p maxSize
$4 = 16
Commands Description
x [/Nuf] expr examine memory at address expr; optional format spec follows slash, see the following tables

The N is the count of how many units to display. The u is the following format:

  • b - individual bytes
  • h - halfwords (two bytes)
  • w - words (four bytes)
  • g - giant words (eight bytes)

The f is printing format. Any print format, or the following options:

  • s - null-terminated string
  • i - machine instructions

For instances:

  • 以十六进制输出

    x /x expr
    x /8bx expr
    x /8hx expr
    x /8wx expr
    x /8gx expr

  • 以有符号十进制输出

    x /d expr
    x /8bd expr
    x /8hd expr
    x /8wd expr
    x /8gd expr

  • 以无符号十进制输出

    x /u expr
    x /8bu expr
    x /8hu expr
    x /8wu expr
    x /8gu expr

  • 以八进制输出

    x /o expr
    x /8bo expr
    x /8ho expr
    x /8wo expr
    x /8go expr

  • 以二进制输出

    x /t expr
    x /8bt expr
    x /8ht expr
    x /8wt expr
    x /8gt expr

  • 以地址格式输出

    x /a expr
    x /8ba expr
    x /8ha expr
    x /8wa expr
    x /8ga expr

  • 以单字符输出

    x /c expr
    x /8bc expr
    x /8hc expr
    x /8wc expr
    x /8gc expr

  • 以浮点数输出

    x /f expr
    x /8bf expr
    x /8hf expr
    x /8wf expr
    x /8gf expr

  • 以字符串输出

    x /s expr
    x /8bs expr
    x /8hs expr
    x /8ws expr
    x /8gs expr

  • 反汇编

    x /i expr
    x /8bi expr
    x /8hi expr
    x /8wi expr
    x /8gi expr

    通常，使用 x /10i $ip-20 来查看当前的汇编($ip是指令寄存器).

(gdb) x /16d pArray
0x601080 <array>:	1	2	3	4
0x601090 <array+16>:	5	6	7	8
0x6010a0 <array+32>:	9	10	11	12
0x6010b0 <array+48>:	13	14	15	16

(gdb) x /16x pArray
0x601080 <array>:	0x00000001	0x00000002	0x00000003	0x00000004
0x601090 <array+16>:	0x00000005	0x00000006	0x00000007	0x00000008
0x6010a0 <array+32>:	0x00000009	0x0000000a	0x0000000b	0x0000000c
0x6010b0 <array+48>:	0x0000000d	0x0000000e	0x0000000f	0x00000010
Commands Description
disassem [addr] display memory as machine instructions

Automatic Display

Commands Description
info display numbered list of display expressions
display [/f] expr show value of expr each time program stops [ according to format f ]
display display all enabled expressions on list
undisplay n remove number(s) n from list of automatically displayed expressions
disable disp n disable display for expression(s) number n
enable disp n enable display for expression(s) number n 

(gdb) b 18
Breakpoint 1 at 0x4005c3: file ex-gdb.c, line 18.

(gdb) b printArray
Breakpoint 2 at 0x4005ef: file ex-gdb.c, line 25.

(gdb) b ex-gdb.c:45
Breakpoint 3 at 0x400694: file ex-gdb.c, line 45.

(gdb) info b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00000000004005c3 in setArray at ex-gdb.c:18
2       breakpoint     keep y   0x00000000004005ef in printArray at ex-gdb.c:25
3       breakpoint     keep y   0x0000000000400694 in main at ex-gdb.c:45

(gdb) disp maxSize
1: maxSize = 16

(gdb) disp i
No symbol "i" in current context.

(gdb) info disp
Auto-display expressions now in effect:
Num Enb Expression
1:   y  maxSize

(gdb) r
Starting program: /home/chenwx/example/ex-gdb

Breakpoint 1, setArray () at ex-gdb.c:18
18	        array[i] = i + 1;
1: maxSize = 16

(gdb) c
Continuing.

Breakpoint 1, setArray () at ex-gdb.c:18
18	        array[i] = i + 1;
1: maxSize = 16

(gdb) c
Continuing.

Breakpoint 1, setArray () at ex-gdb.c:18
18	        array[i] = i + 1;
1: maxSize = 16

Symbol Table

Commands Description
info address s show where symbol s is stored
info func [regex] show names, types of defined functions (all, or matching regex)
info var [regex] show names, types of global variables (all, or matching regex)
whatis [expr]
ptype [expr]		 show data type of expr [ or $ ] without evaluating; ptype gives more detail
ptype type describe type, struct, union, or enum 

(gdb) info addr pArray
Symbol "pArray" is static storage at address 0x6010a0.

(gdb) info addr array
Symbol "array" is static storage at address 0x601060.

(gdb) info func setArray
All functions matching regular expression "setArray":

File b.c:
void setArray(void);

(gdb) whatis setArray
type = void (void)

(gdb) whatis printArray
type = void (void)

(gdb) whatis array
type = int [16]

(gdb) whatis pArray    
type = int (*)[16]

Expressions

Commands Description
expr an expression in C, C++, or Modula-2 (including function calls), or:
addr@len an array of len elements beginning at addr
file::nm a variable or function nm defined in file
{type}addr read memory at addr as specified type
$ most recent displayed value
$n nth displayed value
$$ displayed value previous to $
$$n nth displayed value back from $
$_ last address examined with x
$__ value at address $
$var convenience variable; assign any value
show values [n] show last 10 values [ or surrounding $n ]
show conv display all convenience variables

Signals

Commands Description
info signals show table of signals, GDB action for each
handle signal act specify GDB actions for signal

act for handle signal act:

  • print - announce signal
  • noprint - be silent for signal
  • stop - halt execution on signal
  • nostop - do not halt execution
  • pass - allow your program to handle signal
  • nopass - do not allow your program to see signal
(gdb) handle SIG35 noprint nostop
Signal        Stop	Print	Pass to program	Description
SIG35         No	No	Yes		Real-time event 35

(gdb) info sig
Signal        Stop	Print	Pass to program	Description

SIGHUP        Yes	Yes	Yes		Hangup
SIGINT        Yes	Yes	No		Interrupt
SIGQUIT       Yes	Yes	Yes		Quit
SIGILL        Yes	Yes	Yes		Illegal instruction
SIGTRAP       Yes	Yes	No		Trace/breakpoint trap
...

Working Files

Commands Description
info files display working files and targets in use
file [file] use file for both symbols and executable; with no arg, discard both
core [file] read file as coredump; or discard
exec [file] use file as executable only; or discard
symbol [file] use symbol table from file; or discard
load file dynamically link file and add its symbols
add-sym file addr read additional symbols from file, dynamically loaded at addr
path dirs add dirs to front of path searched for executable and symbol files
show path display executable and symbol file path
info share list names of shared libraries currently loaded 

(gdb) info files
Symbols from "/home/chenwx/example/ex-gdb".
Native process:
	Using the running image of child process 13342.
	While running this, GDB does not access memory from...
Local exec file:
	`/home/chenwx/example/ex-gdb', file type elf64-x86-64.
	Entry point: 0x4004c0
	0x0000000000400238 - 0x0000000000400254 is .interp
	0x0000000000400254 - 0x0000000000400274 is .note.ABI-tag
	0x0000000000400274 - 0x0000000000400298 is .note.gnu.build-id
	0x0000000000400298 - 0x00000000004002b4 is .gnu.hash
    ...

(gdb) show path
Executable and object file path: /home/chenwx/.rvm/gems/ruby-2.2.3/bin:/home/chenwx/.rvm/gems/ruby-2.2.3@global/bin:/home/chenwx/.rvm/rubies/ruby-2.2.3/bin:/home/chenwx/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/home/chenwx/.rvm/bin:/home/chenwx/.rvm/bin

(gdb) info share
From                To                  Syms Read   Shared Object Library
0x00007ffff7dd7ac0  0x00007ffff7df5640  Yes (*)     /lib64/ld-linux-x86-64.so.2
0x00007ffff7a2d8b0  0x00007ffff7b80334  Yes (*)     /lib/x86_64-linux-gnu/libc.so.6
(*): Shared library is missing debugging information.

Source Files

Commands Description
show dir show current source path
dir names add directory names to front of source path
dir clear source path
info source show name of current source file
info sources list all source files in use
list show next ten lines of source
list - show previous ten lines
list lines [file:]num display source surrounding lines, specified as line number num [ in named file ]
list lines [file:]function display source surrounding lines, specified as beginning of function [ in named file ]
list lines +off display source surrounding lines, specified as off lines after last printed
list lines -off display source surrounding lines, specified as off lines previous to last printed
list lines *address display source surrounding lines, specified as line containing address
list f,l from line f to line l
info line num show starting, ending addresses of compiled code for source line num
forw regex search following source lines for regex
rev regex search preceding source lines for regex 

(gdb) show dir
Source directories searched: $cdir:$cwd

(gdb) info source
Current source file is ex-gdb.c
Compilation directory is /home/chenwx/example
Located in /home/chenwx/example/ex-gdb.c
Contains 52 lines.
Source language is c.
Producer is GNU C11 5.4.0 20160609 -mtune=generic -march=x86-64 -g -fstack-protector-strong.
Compiled with DWARF 2 debugging format.
Does not include preprocessor macro info.

(gdb) list
23	{
24	    int i;
25	    pArray = &array;
26
27	    int halfMaxSize = (int)maxSize/2;
28	    halfMaxSize = (halfMaxSize > COLUMN_SIZE) ? COLUMN_SIZE : halfMaxSize;
29	    for (i = 0; i < maxSize; ++i)
30	    {
31	        if ((i > 0) && (i%halfMaxSize == 0))
32	        {

(gdb) list 30,35
30	    {
31	        if ((i > 0) && (i%halfMaxSize == 0))
32	        {
33	            printf("\n");
34	        }
35

(gdb) info line 31
Line 31 of "ex-gdb.c" starts at address 0x400625 <printArray+62> and ends at 0x400638 <printArray+81>.

Shell Commands

Commands Description
cd dir change working directory to dir
pwd print working directory
make … call make
shell cmd execute arbitrary shell command string 

(gdb) pwd
Working directory /home/chenwx/example.

(gdb) shell rm ex-gdb
(gdb) shell ls -l
total 4
-rw-rw-r-- 1 chenwx chenwx 513 Aug 14 16:15 ex-gdb.c

(gdb) shell gcc -g -o ex-gdb ex-gdb.c
(gdb) shell ls -l
total 16
-rwxrwxr-x 1 chenwx chenwx 10176 Aug 15 08:38 ex-gdb
-rw-rw-r-- 1 chenwx chenwx   513 Aug 14 16:15 ex-gdb.c

GDB Scripts

source script

read, execute GDB commands from file script

define cmd command-list end

create new GDB command cmd; execute script defined by command-list.

document cmd help-text end

create online documentation for new GDB command cmd.

Repository

  • Read-only git

You can check out a copy of the git repository directly using the command:

git clone git://sourceware.org/git/binutils-gdb.git

or, refe to gitweb interface of GDB.

References