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flat assembler > Macroinstructions > invoke bug?

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madmatt



Joined: 07 Oct 2003
Posts: 1046
Location: Michigan, USA
My program kept crashing and noticed something that didn't look right.

Code:
       ;the orginal invoke command
        invoke  CnvtSItoA64, debugtxt, 0, edx+8*4

        00402163 ff7220           push    dword ptr edx+0x20
        00402166 6a00             push    0x0 ;<---- Shouldn't this be a DWORD size?
        00402168 6828104000       push    0x401028
        0040216d ff1551324000     call    dword ptr Winprint+0x3251 00403251    
Post 22 Aug 2005, 21:25
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decard



Joined: 11 Sep 2003
Posts: 1095
Location: Poland
Nothing is wrong with that, opcode 0x6a is "push byte constant" opcode, but it actually pushes a dword (substracts 4 from esp).
Hey, if it was a bug then almost no win32 app would work:
Code:
invoke MessageBox, 0, text, title, 0
    

Wink
Post 22 Aug 2005, 21:38
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madmatt



Joined: 07 Oct 2003
Posts: 1046
Location: Michigan, USA
Hmmm, didn't know that Surprised. Thanks for clearing that up Smile . Looked from the disassembly that something was wrong. Oh well, back to programming, false alarm Smile
Post 22 Aug 2005, 22:17
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Reverend



Joined: 24 Aug 2004
Posts: 408
Location: Poland
Push opcode always moves dword value on the stack. It's just a feature in x86 that when the value is between -128 and 127 it is stored as a byte. You can always manually do like this: 'db 68h, 00h, 00h, 00h, 00h'
Post 22 Aug 2005, 22:22
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