Addition Parameter x64

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yq8

Joined: 08 May 2015
Posts: 15

yq8 03 Dec 2015, 17:07

Hi,

Can someone help me to convert this asm snippet from 32 format to 64 bit format:

Code:

mov eax, dword[esp+0x4]
mov ecx, 0xd
add eax, ecx
ret

my idea wold be this :

Code:

mov rax, qword[rsp+0x8]
mov rcx, 0xd
add rax, rcx
ret

but thats wrong >.<
The x64 calling conventiosna re different.
params are passed in registers, and I dunno how to do that.
Can someone help me to adjust my snippet?

03 Dec 2015, 17:07

tthsqe

Joined: 20 May 2009
Posts: 767

tthsqe 03 Dec 2015, 18:20

Hello yq8. It depends if you want the linux or MS versions.
https://en.wikipedia.org/wiki/X86_calling_conventions
For MS, the first four int args are passed in rcx, rdx, r8, r9 and the return is rax

Code:

mov rax, rcx
add rax, 0x0d
ret

or

lea rax, [rcx+0x0d]
ret

03 Dec 2015, 18:20

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