ESP substraction and Windows Dialogs

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Uwar

Joined: 09 Oct 2009
Posts: 11

Uwar 09 Oct 2009, 12:31

Why following codes works vary?
IncorrectWindowBorder:

Code:

 start:
    push  ebp
    mov   ebp, esp
    sub   esp, 0x0A

    push  dword 0x00000000
    push  sz_caption
    push  sz_msg
    push  dword 0x00000000
    call  [user32.MessageBoxA]
    
    push  0x00000000 ; return winmain result
    call  [kernel32.ExitProcess]

CorrectWindowBorder

Code:

 start:
    push  ebp
    mov   ebp, esp
    ;sub   esp, 0x0A why esp substraction (for local vars) changes msgBox?

    push  dword 0x00000000
    push  sz_caption
    push  sz_msg
    push  dword 0x00000000
    call  [user32.MessageBoxA]
    
    push  0x00000000 ; return winmain result
    call  [kernel32.ExitProcess]

09 Oct 2009, 12:31

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20761
Location: In your JS exploiting you and your system

revolution 09 Oct 2009, 12:45

You should always subtract a value that is a multiple of 4. The stack needs to be kept dword aligned.

09 Oct 2009, 12:45

Uwar

Joined: 09 Oct 2009
Posts: 11

Uwar 09 Oct 2009, 12:52

Thanks a lot I thought that must be aligned to the word.

09 Oct 2009, 12:52

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