Wednesday, 11 September 2013

GDB Debugger Basic Commands


Very Basic GDB Tutorial, actually these are my handy notes!!!!..

Setting Breakpoint :

break *_start

Execute Next Instruction :

next
step
n
s

Continue Execution :

continue
c


Data :

2 main points we check is 'REGISTERS' and 'MEMORY'


Display Register Values : (Decimal , Binary , Hex )

print /d   --> Decimal
print /t   --> Binary
print /x   --> Hex


O/P :

(gdb) print /d $eax
$17 = 13

(gdb) print /t $eax
$18 = 1101

(gdb) print /x $eax
$19 = 0xd
(gdb)



Display values of specific memory locations :

command : x/nyz    (Examine)

n --> Number of fields to display      ==>
y --> Format for output                ==>  c (character) , d (decimal) , x (Hexadecimal)
z --> Size of field to be displayed    ==>  b (byte)  , h (halfword), w (word 32 Bit)


Below command displays 42 bytes of variable 'output' in character mode ,

(gdb) x/42cb &output
0x80490ac <output>:     84 'T'  104 'h' 101 'e' 32 ' '  112 'p' 114 'r' 111 'o' 99 'c'
0x80490b4 <output+8>:   101 'e' 115 's' 115 's' 111 'o' 114 'r' 32 ' '  86 'V'  101 'e'
0x80490bc <output+16>:  110 'n' 100 'd' 111 'o' 114 'r' 32 ' '  73 'I'  68 'D'  32 ' '
0x80490c4 <output+24>:  105 'i' 115 's' 32 ' '  39 '\'' 120 'x' 120 'x' 120 'x' 120 'x'
0x80490cc <output+32>:  120 'x' 120 'x' 120 'x' 120 'x' 120 'x' 120 'x' 120 'x' 120 'x'
0x80490d4 <output+40>:  39 '\'' 10 '\n'
(gdb)


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