gdb - Unix, Linux Command



gdb The GNU Debugger


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]]


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.


-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



To Starting GDB

# gdb `which python` /var/cores/core.python.30520


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/".

warning: JITed object file architecture unknown is not compatible with target architecture i386:x86-64.
Core was generated by `python ./'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f0a37aac40d in doupdate () from /lib/x86_64-linux-gnu/


To Back Trace:

$(gdb) bt


#0  0x00007f0a37aac40d in doupdate () from /lib/x86_64-linux-gnu/
#1  0x00007f0a37aa07e6 in wrefresh () from /lib/x86_64-linux-gnu/
#2  0x00007f0a37a99616 in ?? () from /lib/x86_64-linux-gnu/
#3  0x00007f0a37a9a325 in wgetch () from /lib/x86_64-linux-gnu/
#4  0x00007f0a37cc6ec3 in ?? () from /usr/lib/python2.7/lib-dynload/
#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 ()


To Disassembly:

$ (gdb) disas doupdate


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)


To Check Registers

$(gdb) i r


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


To Memory Mappings

$(gdb) i proc m


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/
  0x7f0a37ab8000     0x7f0a37cb8000   0x200000    0x2d000 /lib/x86_64-linux-gnu/
  0x7f0a37cb8000     0x7f0a37cb9000     0x1000    0x2d000 /lib/x86_64-linux-gnu/
  0x7f0a37cb9000     0x7f0a37cba000     0x1000    0x2e000 /lib/x86_64-linux-gnu/
  0x7f0a37cba000     0x7f0a37ccd000    0x13000        0x0 /usr/lib/python2.7/lib-dynload/
  0x7f0a37ccd000     0x7f0a37ecc000   0x1ff000    0x13000 /usr/lib/python2.7/lib-dynload/
  0x7f0a37ecc000     0x7f0a37ecd000     0x1000    0x12000 /usr/lib/python2.7/lib-dynload/
  0x7f0a37ecd000     0x7f0a37ecf000     0x2000    0x13000 /usr/lib/python2.7/lib-dynload/
  0x7f0a38050000     0x7f0a38066000    0x16000        0x0 /lib/x86_64-linux-gnu/
  0x7f0a38066000     0x7f0a38265000   0x1ff000    0x16000 /lib/x86_64-linux-gnu/
  0x7f0a38265000     0x7f0a38266000     0x1000    0x15000 /lib/x86_64-linux-gnu/
  0x7f0a38266000     0x7f0a3828b000    0x25000        0x0 /lib/x86_64-linux-gnu/
  0x7f0a3828b000     0x7f0a3848a000   0x1ff000    0x25000 /lib/x86_64-linux-gnu/


To apply Breakpoints

$(gdb) b *doupdate + 289

No symbol table is loaded. Use the "file" command.