invoke bug?

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madmatt

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

madmatt 22 Aug 2005, 21:25

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)]

22 Aug 2005, 21:25

decard

Joined: 11 Sep 2003
Posts: 1092
Location: Poland

decard 22 Aug 2005, 21:38

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

22 Aug 2005, 21:38

madmatt

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

madmatt 22 Aug 2005, 22:17

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

22 Aug 2005, 22:17

Reverend

Joined: 24 Aug 2004
Posts: 408
Location: Poland

Reverend 22 Aug 2005, 22:22

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'

22 Aug 2005, 22:22

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