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gdb Command in Linux
NAME
gdb The GNU Debugger
SYNOPSIS
gdb [-help] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps] [-tty=dev] [-s symfile] [-e prog] [-se prog] [-c core] [-x cmds] [-d 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.OPTIONS
| TAG | DESCRIPTION |
|---|---|
| -help -h | List all options, with brief explanations. |
| -symbols=file -s file | Read symbol table from file file. |
| -write | Enable writing into executable and core files.. |
| -exec=file -e file | Use file file as the executable file to execute when appropriate, and for examining pure data in conjunction with a core dump. |
| -se=file | Read symbol table from file file and use it as the executable file. |
| -core=file -c file | Use file file as a core dump to examine. |
| -command=file -x file | Execute GDB commands from file file. |
| -directory=directory -d directory | Add directory to the path to search for source files. |
| -nx -n | Do not execute commands from any '.gdbinit' initialization files. Normally, the commands in these files are executed after all the command options and arguments have been processed. |
| -quiet -q | ''Quiet''. Do not print the introductory and copyright messages. These messages are also suppressed in batch mode. |
| -batch | Run in batch mode. Exit with status 0 after processing all the command files specified with '-x' (and '.gdbinit', if not inhibited). Exit with nonzero status if an error occurs in executing the GDB commands in the command files. |
| -cd=directory | Run GDB using directory as its working directory, instead of the current directory. |
| -fullname -f | 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, |
| -b bps | Set the line speed (baud rate or bits per second) of any serial interface used by GDB for remote debugging. |
| -tty=device | Run using device for your program's standard input and output |
EXAMPLES
Example-1:
To Starting GDB
# gdb `which python` /var/cores/core.python.30520
output:
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 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: . Find the GDB manual and other documentation resources online at: . For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from /usr/bin/python...(no debugging symbols found)...done. warning: core file may not match specified executable file. [New LWP 30520] [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". warning: JITed object file architecture unknown is not compatible with target architecture i386:x86-64. Core was generated by `python ./cachetop.py'. Program terminated with signal SIGSEGV, Segmentation fault. #0 0x00007f0a37aac40d in doupdate () from /lib/x86_64-linux-gnu/libncursesw.so.5
Example-2:
To Back Trace:
$(gdb) bt
output:
#0 0x00007f0a37aac40d in doupdate () from /lib/x86_64-linux-gnu/libncursesw.so.5
#1 0x00007f0a37aa07e6 in wrefresh () from /lib/x86_64-linux-gnu/libncursesw.so.5
#2 0x00007f0a37a99616 in ?? () from /lib/x86_64-linux-gnu/libncursesw.so.5
#3 0x00007f0a37a9a325 in wgetch () from /lib/x86_64-linux-gnu/libncursesw.so.5
#4 0x00007f0a37cc6ec3 in ?? () from /usr/lib/python2.7/lib-dynload/_curses.x86_64-linux-gnu.so
#5 0x00000000004c4d5a in PyEval_EvalFrameEx ()
#6 0x00000000004c2e05 in PyEval_EvalCodeEx ()
#7 0x00000000004def08 in ?? ()
#8 0x00000000004b1153 in PyObject_Call ()
#9 0x00000000004c73ec in PyEval_EvalFrameEx ()
#10 0x00000000004c2e05 in PyEval_EvalCodeEx ()
#11 0x00000000004caf42 in PyEval_EvalFrameEx ()
#12 0x00000000004c2e05 in PyEval_EvalCodeEx ()
#13 0x00000000004c2ba9 in PyEval_EvalCode ()
#14 0x00000000004f20ef in ?? ()
#15 0x00000000004eca72 in PyRun_FileExFlags ()
#16 0x00000000004eb1f1 in PyRun_SimpleFileExFlags ()
#17 0x000000000049e18a in Py_Main ()
#18 0x00007f0a3be10830 in __libc_start_main (main=0x49daf0 , argc=2, argv=0x7ffd33d94838, init=, fini=, rtld_fini=,
stack_end=0x7ffd33d94828) at ../csu/libc-start.c:291
#19 0x000000000049da19 in _start ()
Example-3:
To Disassembly:
$ (gdb) disas doupdate
output:
Dump of assembler code for function doupdate: 0x00007f0a37aac2e0 <+0>: push %r15 0x00007f0a37aac2e2 <+2>: push %r14 0x00007f0a37aac2e4 <+4>: push %r13 0x00007f0a37aac2e6 <+6>: push %r12 0x00007f0a37aac2e8 <+8>: push %rbp 0x00007f0a37aac2e9 <+9>: push %rbx 0x00007f0a37aac2ea <+10>: sub $0xc8,%rsp [...] ---Type to continue, or q to quit--- [...] 0x00007f0a37aac3f7 <+279>: cmpb $0x0,0x21(%rcx) 0x00007f0a37aac3fb <+283>: je 0x7f0a37aacc3b <doupdate+2395> 0x00007f0a37aac401 <+289>: mov 0x20cb68(%rip),%rax # 0x7f0a37cb8f70 0x00007f0a37aac408 <+296>: mov (%rax),%rsi 0x00007f0a37aac40b <+299>: xor %eax,%eax => 0x00007f0a37aac40d <+301>: mov 0x10(%rsi),%rdi 0x00007f0a37aac411 <+305>: cmpb $0x0,0x1c(%rdi) 0x00007f0a37aac415 <+309>: jne 0x7f0a37aac6f7 <doupdate+1047> 0x00007f0a37aac41b <+315>: movswl 0x4(%rcx),%ecx 0x00007f0a37aac41f <+319>: movswl 0x74(%rdx),%edi 0x00007f0a37aac423 <+323>: mov %rax,0x40(%rsp) [...]
Example-4:
To Check Registers
$(gdb) i r
output:
rax 0x0 0 rbx 0x1993060 26816608 rcx 0x19902a0 26804896 rdx 0x19ce7d0 27060176 rsi 0x0 0 rdi 0x19ce7d0 27060176 rbp 0x7f0a3848eb10 0x7f0a3848eb10 rsp 0x7ffd33d93c00 0x7ffd33d93c00 r8 0x7f0a37cb93e0 139681862489056 r9 0x0 0 r10 0x8 8 r11 0x202 514 r12 0x0 0 r13 0x0 0 r14 0x7f0a3848eb10 139681870703376 r15 0x19ce7d0 27060176 rip 0x7f0a37aac40d 0x7f0a37aac40d <doupdate+301> eflags 0x10246 [ PF ZF IF RF ] cs 0x33 51 ss 0x2b 43 ds 0x0 0 es 0x0 0 fs 0x0 0 gs 0x0 0
Example-5:
To Memory Mappings
$(gdb) i proc m
output:
Mapped address spaces:
Start Addr End Addr Size Offset objfile
0x400000 0x6e7000 0x2e7000 0x0 /usr/bin/python2.7
0x8e6000 0x8e8000 0x2000 0x2e6000 /usr/bin/python2.7
0x8e8000 0x95f000 0x77000 0x2e8000 /usr/bin/python2.7
0x7f0a37a8b000 0x7f0a37ab8000 0x2d000 0x0 /lib/x86_64-linux-gnu/libncursesw.so.5.9
0x7f0a37ab8000 0x7f0a37cb8000 0x200000 0x2d000 /lib/x86_64-linux-gnu/libncursesw.so.5.9
0x7f0a37cb8000 0x7f0a37cb9000 0x1000 0x2d000 /lib/x86_64-linux-gnu/libncursesw.so.5.9
0x7f0a37cb9000 0x7f0a37cba000 0x1000 0x2e000 /lib/x86_64-linux-gnu/libncursesw.so.5.9
0x7f0a37cba000 0x7f0a37ccd000 0x13000 0x0 /usr/lib/python2.7/lib-dynload/_curses.x86_64-linux-gnu.so
0x7f0a37ccd000 0x7f0a37ecc000 0x1ff000 0x13000 /usr/lib/python2.7/lib-dynload/_curses.x86_64-linux-gnu.so
0x7f0a37ecc000 0x7f0a37ecd000 0x1000 0x12000 /usr/lib/python2.7/lib-dynload/_curses.x86_64-linux-gnu.so
0x7f0a37ecd000 0x7f0a37ecf000 0x2000 0x13000 /usr/lib/python2.7/lib-dynload/_curses.x86_64-linux-gnu.so
0x7f0a38050000 0x7f0a38066000 0x16000 0x0 /lib/x86_64-linux-gnu/libgcc_s.so.1
0x7f0a38066000 0x7f0a38265000 0x1ff000 0x16000 /lib/x86_64-linux-gnu/libgcc_s.so.1
0x7f0a38265000 0x7f0a38266000 0x1000 0x15000 /lib/x86_64-linux-gnu/libgcc_s.so.1
0x7f0a38266000 0x7f0a3828b000 0x25000 0x0 /lib/x86_64-linux-gnu/libtinfo.so.5.9
0x7f0a3828b000 0x7f0a3848a000 0x1ff000 0x25000 /lib/x86_64-linux-gnu/libtinfo.so.5.9
[...]
Example-6:
To apply Breakpoints
$(gdb) b *doupdate + 289
output:
No symbol table is loaded. Use the "file" command.
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