ASM Community

Hi there

first off , i just registered and want to say hello to everybody.
But right on to my problem !
I am fairly new to win32 assembly and i have now made an attempt to implement masta's tutorial about patching
(can be found at http://win32assembly.online.fr/w32_01.txt).
I have altered some stuff and basicly it does the job. But what bothers me is a messed up MessageBox , and i just don't know why it won't work
Link to a picture : http://img156.imageshack.us/img156/2967/msgboxyw9.jpg

If it doesn't jump to the success message (if sequence is not found) which is messed up, i get another MsgBox without caption or text - so my other MsgBox doesn't work either. However, the "welcome" message is as it should be

my source :

.386
.model flat, stdcall
option casemap : none

include \masm32\include\windows.inc
include \masm32\include\user32.inc
include \masm32\include\kernel32.inc

includelib \masm32\lib\user32.lib
includelib \masm32\lib\kernel32.lib

inv equ invoke
.data
;----------------------------------
datei db "hallowelt.exe" ,0
ersetze db "Test"
ersetzemit db "XXXX"
len equ $-ersetzemit
fHandle DWORD 0
fSize DWORD 0
ofstruct OFSTRUCT <>
fpoffset dd ?
memptr dd ?
bread dd ?
bwritten dd ?
;----------------------------------
tintro db "Press OK to patch" ,0
cintro db "Patcher 0.1", 0
cnix db "Nichts gefunden" ,0
cerror db "Error" ,0
terfolg db "Patch done",0
cerfolg db "Erfolg" ,0
;----------------------------------

.code
start :
    inv MessageBox , NULL, addr tintro, addr cintro, MB_OK
    inv OpenFile , addr datei , addr ofstruct, OF_READWRITE
    mov fHandle, eax
    inv GetFileSize , fHandle, NULL
    mov fSize, eax
    inv GlobalAlloc , NULL, fSize
    mov memptr, eax
    inv ReadFile , fHandle, addr memptr, fSize, addr bread, NULL
    mov edi, offset memptr
    mov ecx, fSize
    mov esi, offset ersetze
    mov al, byte ptr 
  loop_:
    repnz scasb
    cmp ecx, 0
    je nichts_gefunden_
    push ecx
    push edi
    push esi
    dec edi
    mov ecx, len
    repz cmpsb
    cmp ecx, 0
    je patch_
    pop esi
    pop edi
    pop ecx
    jmp loop_
  patch_:
    pop esi
    pop edi
    pop ecx
    dec edi
    inc ecx
    mov eax, fSize
    sub eax, ecx
    mov fpoffset, eax
    inv SetFilePointer , fHandle, fpoffset, NULL, FILE_BEGIN
    inv WriteFile , fHandle, addr ersetzemit, len, addr bwritten, NULL
    jmp erfolg_
  nichts_gefunden_:
    inv MessageBox , NULL, addr cnix, addr cerror, MB_OK
    jmp ende_
  erfolg_:
    inv MessageBox , NULL, addr terfolg, addr cerfolg, MB_OK
    jmp ende_
  ende_:
    inv GlobalFree , memptr
    inv CloseHandle , fHandle
    inv ExitProcess , NULL
end start      

would be nice if you could point me to a solution
thank you very much !

f0dder edit: added code tags.

Hi,
thank you for your effort  8) .
I have tried the same now, and modified my source so it would read/write a TXT file and built it again. Now the messageboxes are just fine ... so it means I am doing something wrong when accessing the executable file ?
(hallowelt.exe is just a generic "hello world" program I used as target).
What am I doing wrong ?

thx !

Thank you for your reply, I found my mistake !
I didn't read carefully that GlobalAlloc already returns a pointer to a memory region.
(However, theres another error in my code right below the line you pointed out :
It then must be
mov edi, memptr)
As far as patching exe's is concerned, I just thought it was a nice tutorial and its a bit more entertaining than modifying a simple text file ;)
But I now have read the Community rules and I will comply.