Windows Assembly Doubt - x86

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+4 Q:

Windows Assembly Doubt - x86

Hey guys,

I'm building a Windows Assembly program without any macro. So I downloaded a program that was using macros, and I'm converting this into "pure" assembly code.

However I'm facing one issue here. There's a label @@: that I don't understand, and also a jump jne @F that I didn't get it. What are these 2 symbols?

MyWndProc:

    push ebp
    mov ebp, esp

    cmp DWORD PTR [ebp+12], 2 ;WM_DESTROY=2
    jne @F
      push ecx
      push NULL
      mov dword ptr ecx, 7e42ca5ah ;address of PostQuitMessage
      call ecx
      pop ecx
    @@:

    push DWORD PTR [ebp+20]
    push DWORD PTR [ebp+16]
    push DWORD PTR [ebp+12]
    push DWORD PTR [ebp+8]
    call DefWindowProc
    ;mov dword ptr edx, 7e42c17eh
    ;call edx

    leave
    ret 16

Also for PostQuitMessage API I could hard-code the memory address (on WinXP 32bits SP3 english), but for DefWindowProc it compiles, but it breaks when executing. Does someone know why?

Thanks for support guys.

PS.: I'm using masm32

+3 A:

The @@ is an anonymous local label. You could have many of them in the file The jne @F means jump to the nearest @@ ahead of the current location.

Carl Norum 2010-10-06 18:50:03

Ok thanks. How about the DefWindowProc question? Any ideia?

jyzuz 2010-10-06 18:56:22

Couldn't tell you without more code. Is DefWindowProc another one of your routines?

Carl Norum 2010-10-06 20:06:58

No, `DefWindowProc` it's a Windows API. This routine is responsible to get the windows messages... I've found it address on my machine using arwin tool, but this is the only API that I can't hardcode.. but I don't know why I can't do the same I did with `PostQuitMessage`...

jyzuz 2010-10-06 20:26:13

Then you need to make a global symbol declaration for it, and then use the linker to make sure everything gets matched up. I'm not sure you can depend on it always having the same address. I am not a windows API expert, though.

Carl Norum 2010-10-06 21:02:27

ansaurus

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Windows Assembly Doubt - x86

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