MessageBox and Registers

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RauL

Joined: 17 Feb 2005
Posts: 7

RauL 15 Jul 2007, 07:51

Hello,

I was just trying this out, but got stuck. I'd be glad if someone can help me out.

Consider that I have 19286300h in eax. The MessageBox function needs the address to a memory location from which it can read a null-terminated string. Now I'd like to pass the content of the eax register, as in above (the 4 bytes) as the string. Thus I assume I'd get a 3 letter word shown up (considering the fourth byte to be a null-terminator). But I'm a bit confused on how to do this. Because with whatever I tried, Windows tries to read the memory address located in eax and tries to reference it, which it fails to. I want to treat the value in eax itself as a string.

15 Jul 2007, 07:51

madmatt

Joined: 07 Oct 2003
Posts: 1045
Location: Michigan, USA

madmatt 15 Jul 2007, 08:00

It's not possible to do it the way you want, you'd have to define the data somewhere then reference the data label. Like:

Code:

lstring dd 0x19286300
...
mov     eax, lstring

15 Jul 2007, 08:00

SFeLi

Joined: 03 Nov 2004
Posts: 138

SFeLi 15 Jul 2007, 11:47

Code:

start:  mov     eax,0x00434241
        ;...
        push    eax
        mov     edx,esp
        stdcall [MessageBox],NULL,edx,NULL,MB_ICONINFORMATION
        pop     eax
        retn

15 Jul 2007, 11:47

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