Cleaning the stack

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Andy

Joined: 17 Oct 2011
Posts: 43

Andy 18 Oct 2011, 12:49

Hi guys,

First of all I'm new to forum and beginer in assembler. I am using a high level language that support fasm inline. Actually I use fasm to generate some raw machine codes to improve the speed of my programs. I started for test with calling Beep function from kernel32.dll. The prototype is Beep(frequence,duration).

My code looks like that :

Code:

0x
68 E8 03             ;push 1000 - duration
68 E8 03             ;push 1000 - frequence
B8 FF 79 83 7C       ;mov eax, address of Beep function (I get this in high level, it's not 7C8379FF, this is just example)
FF D0                ;call eax
C3                   ;ret

can someone help me to understand how to clean the stack for cdecl call convention?
Thanks in advance!

Last edited by Andy on 03 Nov 2011, 20:32; edited 3 times in total

18 Oct 2011, 12:49

DJ Mauretto

Joined: 14 Mar 2007
Posts: 464
Location: Rome,Italy

DJ Mauretto 18 Oct 2011, 13:18

Hello,
With cdecl calling convention you must clean up the stack in this way :

Code:

push a
push b
call function name
add esp, size*2                       ; size  * number of arguments( if you use 32 bit 4*2)

For stdcall you do not have to clean the stack:

Code:

push a
push b
push c
call function name

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18 Oct 2011, 13:18

sinsi

Joined: 10 Aug 2007
Posts: 778
Location: Adelaide

sinsi 18 Oct 2011, 13:34

Those 66s look a bit strange, that's a size override. Not pushing dwords?

18 Oct 2011, 13:34

Andy

Joined: 17 Oct 2011
Posts: 43

Andy 18 Oct 2011, 13:43

yes, freq and duration are dwords, I used wrong opcodes?

18 Oct 2011, 13:43

DJ Mauretto

Joined: 14 Mar 2007
Posts: 464
Location: Rome,Italy

DJ Mauretto 18 Oct 2011, 13:49

Quote:

yes, freq and duration are dwords, I used wrong opcodes?

Yes

what language are you using?
C language ?
Java ?
Visual Basic ?

Code:

68 00 10                        ; push 1000
68 00 10                        ; push 1000
B8 FF 79 83 7C                   ; mov eax,7c8379ff
FF D8                             ; call eax
C3                               ; ret

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18 Oct 2011, 13:49

Andy

Joined: 17 Oct 2011
Posts: 43

Andy 18 Oct 2011, 14:01

auch, it's my fault, I typed wrong it's 68 in my example. I am using AutoIt. Thanks for your help guys, seems I made many mistakes today, actually my error wasn't in this raw code, but anyway I learn something: to clean up the stack. I have just one more question, where I can find some good beginers FASM tutorials?

18 Oct 2011, 14:01

DJ Mauretto

Joined: 14 Mar 2007
Posts: 464
Location: Rome,Italy

DJ Mauretto 18 Oct 2011, 14:14

Quote:

I am using AutoIt

Quote:

where I can find some good beginers FASM tutorials

http://flatassembler.net/docs.php Wink

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18 Oct 2011, 14:14

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