How do I pass parameters to a function in Assembly? I did push Last Param, push Second Param, push First Param..
But I cannot access the parameters within Meh Function.. What I'm doing crashes the program..
format PE console ;Format PE OUT GUI 4.0
entry main
include 'macro/import32.inc'
section '.idata' import data readable ;Import Section.
library msvcrt,'msvcrt.dll'
import msvcrt, printf, 'printf',\
exit,'exit', getchar, 'getchar'
section '.data' data readable writeable ;Constants/Static Section.
InitialValue dd 0
section '.code' code readable executable
main:
push 67
push 66
push 65
call MEH
call [getchar]
mov eax, 0
ret 0
MEH:
push ebx
mov ebp, esp
sub esp, 0
mov eax, [ebp + 8] ; Trying to print first parameter..
push eax
call [printf]
add esp, eax
mov esp, ebp
pop ebx
ret
Let's see...
Say your ESP is 0x00180078 on the outset, then after the three pushes you have
00180078: 67
00180074: 66
00180070: 65
then you call MEH, which immediately pushes ebx so now you have the stack as
00180078: 67
00180074: 66
00180070: 65
0018006C: return address
00180068: ebx value
you now load EBP with ESP = 00180068
sub esp,0 does nothing
mov eax, [ebp+8] ~ 00180068 + 8 = 00180070 = 65
so not the first but rather the last argument
call [printf]
Here comes your problem, though:
add esp, eax
What good was this supposed to do? Assuming printf preserves this argument passed in (which it is incidentally not required to do), why would you add the argument to the stack pointer? That is sure to mess up your return. What you want to do is restore esp to the value of ebp and pop back the saved ebx value.