savanovich/.gdbinit

## .gdbinit
define pyp
set \$\_unused\_void = PyObject\_Print($arg0, stderr, 1)
printf "\n"
end

## gdb_cheatsheet.rst

      
    Raw
  

              gdb_cheatsheet.rst
            
          
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2


GDB

Controlling Execution

run

set args test1 test2

show args


next

step

finish - takes you out of the function call, if you are already inside one

return - returns to the caller of the current frame in the stack. This means that you can return from a function without actually completing the function code execution.

continue


quit

kill - stops debugging but does not quit the debugger
Break Points

break function_name

break file.c:n

info break

disa/enable *m* - disable/enable break

del *m*


!!!!! condition bp_number [expression]

condition 2 p1 !=p2

condition 2 - deletes condition


!!!!! watch expression - The debugger stops the program when the value of expression changes.

!!!!! rwatch expression - The debugger stops the program whenever the program reads the value of any object involved in the evaluation of expression.

!!!!! awatch expression - The debugger stops the program whenever the program reads or modifies the value of any object involved in the evaluation of expression.


info locals - print all local variables


list n - lists lines in the source code file

list n, m


print expr

p 2*circularArea($2) - $i - refer to previous output

!!! p main::radius - access variable in other stack frame

ptype var - prints structure or union

display expr - (disp)

undisplay

info display

enable/disable display

show path

pwd
Modifying Variables

print var1

set var1=22

print var1


show environment - displays environment variables

set/unset env
Stack

frame - shows the current frame of execution for the program

info frame

info locals

info reg

info all-reg - including math registers

backtrace

up - takes you one level up in the stack

down
Files and Shared Libraries

info files

info share
Macroses

Compile with options gcc -gdwarf-4 -g3 sample.c -o sample
info macro ADD

macro expand ADD(x)
TUI

TUI-Keys


C-x C-a - enter or leave the TUI mode

C-x 2 - change layout (1 or 2 windows)

C-x o - change active window

C-x s - switch TUI SingleKey mode

C-L - refresh


info win (i win) - current window info

focus winname - (fs) - set focus to "SRC", "CMD", "ASM", or "REG" or by position "next" or "prev"

layout type - set layout "src", "asm", "split", or "reg"

tui reg type - set the register window layout "general", "float", "system", or "next"

winheight val - (wh) - set the window height (either an absolute value, or a relative value prefaced with "+" or "-")


C-p - previous command in history

C-n - next command in history

C-f - move cursor forward

C-b - move cursor backward

M-f - move cursor forward word

M-b - move cursor backward word

C-a - move to the start of the line

C-e - move to the end of the line

C-d - delete the character underneath the cursor

C-_ or C-x C-u - undo the last editing command

C-l - clear the screen

C-k - kill to the end of the line

M-d - kill to the end of the current word

M-<DEL> - kill from the cursor the start of the current word

C-w - kill from the cursor to the previous whitespace

C-y - yank the most recently killed text back

M-y - rotate the kill-ring, and yank the new top. You can only do this if the prior command is C-y or M-y
Disassembly

set disassembly-flavor flavor - set the look-and-feel of the disassembly. On Intel machines, valid flavors are intel and att

set disassemble-next-line on
ASM


gdb
(gdb) break label+offset (gdb) break_start (gdb) break *_start+1


gdb
(gdb) x/d 0x100001018 0x100001018 <natural_generator.b>: -1 (gdb) x/d &b 0x100001018 <natural_generator.b>: -1

Stack


gdb
(gdb) x/20x $rsp-20 0x7fffffffe800: 0x00000000 0x00000000 0x00000000 0x00000000 0x7fffffffe810: 0x00000000 0x00000000 0x00000000 0x00000000 0x7fffffffe820: 0x439d1463 0x00000000 0x00000000 0x00000000 0x7fffffffe830: 0x004000c2 0x00000000 0x0000000a 0x00000000 0x7fffffffe840: 0x00000001 0x00000000 0xffffeb0f 0x00007fff

Machine instructions


gdb
(gdb) x/10i $rip => 0x40011f <area+27>: pop %rbp 0x400120 <area+28>: retq 0x400121: jg 0x400123 0x400123: add %al,(%rcx)

Data

Output formats:

d - decimal
x - hexadecimal
t - binary. The letter `t' stands for "two"
u - unsigned
o - octal
f - floating point
i - instruction
c - character
s - string
a - address. You can use this format used to discover where (in what function) an unknown address is located:


gdb
(gdb) p/a 0x54320 $1 = 0x54320 <_initialize_vx+396> (gdb) p/a &h $2 = 0x7ffff7dd7820 <h>
# same as (gdb) info symbol 0x54320 (gdb) info symbol &h h in section .bss of /lib/x86_64-linux-gnu/libc.so.6
(gdb) p (int)$rax $3 = -1

Memmory

Examining Memory:

b - byte
h - halfword (2 bytes)
w - word (4 bytes)
g - giant (8 bytes)
l for a 32-bit long word value
w for a 16-bit word value
b for an 8-bit byte value


gdb
x/nfu addr


n, the repeat count
f, the display format is one of the formats used by print (‘x’, ‘d’, ‘u’, ‘o’, ‘t’, ‘a’, ‘c’, ‘f’, ‘s’), and in addition ‘i’ (for machine instructions). The default is ‘x’ (hexadecimal) initially. The default changes each time you use either x or print.
u, the unit size


gdb
(gdb) x/42cb &output 0x80490ac <output>:84 ‘T’ 104 ‘h’ 101 ‘e’ 32 ‘ ‘ 112 ‘p’ 114 ‘r’ 111 ‘o’99 ‘c’

Misc

Tricks

info locals - print all local variables


p *data@10 - print array


n

<enter> - repeat last command


call PyObject_Print(0x7ffff7f64ea0, stderr, 1)


info threads

thread 2
Run program reverse


gdb
(gdb) target record-full (gdb) next (gdb) reverse-next

https://sourceware.org/gdb/current/onlinedocs/gdb/Reverse-Execution.html
http://stackoverflow.com/questions/1206872/go-to-previous-line-in-gdb
GDB command options

-cd Specify the working directory

-d Specify a directory to search for source files

-nx Do not execute commands from .gdbinit file
Install from source

./configure --with-python --prefix=/home/user/opt/gdb
make
make install
Links

8 gdb tricks you should know
	define pyp
	set \$\_unused\_void = PyObject\_Print($arg0, stderr, 1)
	printf "\n"
	end