CODEWITHSUNDEEP
assemblysystem-callsshellcode
Mohammad Reza Ramezani
Mohammad Reza Ramezani

Reputation: 772

shellcode - simplifed code does not work

I dont know why but when I use the hex of below code as shell code it works:

Section .text
global _start
_start:
mov ebx,0
mov eax,1
int 0x80

but when I use the hex of the below code instead, it does not work and segmentation fault occurres:

Section .text
global _start
_start:
xor ebx,ebx
mov al,1
int 0x80

I know that is because of using 'al'. I don`t know why does using of 'eax' works correctly but using 'al' get error?

Thanks a lot.

Ya Ali.

Upvotes: 0

Views: 87

Answers (1)

Alexander Zhak
Alexander Zhak

Reputation: 9272

Because int 0x80 expects 32-bit param. When you pass low 8 bits only (AL), high parts of eax may contain anything (undefined value), so instead of passing 1 you end up passing 0x??????01

Upvotes: 1

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