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snifit



Joined: 10 Dec 2004
Posts: 12
Location: Sweden
snifit
I'm trying to do my own proc that has one parameter with the size of a byte.
Depending on the value of that byte the procedure makes different things.

Code:
proc theproc,byteparam
  ; do something
  return
endp    


I can't use the invoke macro since that would use 'call [theproc]' which wouldn't work so i tried to push the parameter myself and then call the proc:

Code:
push onebyte
call theproc    


This does not work either because (my guess) the proc macro doesn't know that it should pop a byte for the "byteparam" parameter.

So I'm wondering if there is some way to do this when using the proc macro?
If not, how should I do?

Code:
  push $
  jmp myownproc
  ; ...

myownproc:
  ; Do something
  pop eax
  ; Add something to eax so I jump to the correct place after the push
  jmp eax    
Post 19 Jan 2005, 12:57
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IronFelix



Joined: 09 Dec 2004
Posts: 141
Location: Russia, Murmansk region
IronFelix
Snifit, let me tell what i know about it. It is not a good idea to put 1 byte to stack because it becomes unaligned.
About your words "This does not work either because (my guess) the proc macro doesn't know that it should pop a byte...". Proc macro doesn't do any pop. You can try this:

myownproc:

byteparam equ ebp+8

push ebp
mov ebp,esp

mov al,[byteparam] ; read passed parameter
; ...
mov esp,ebp
pop ebp
retn 1

When you can call it in this way:

xor eax,eax
or al,[byteparam]
stdcall myownproc,eax

Stdcall is invoke analog, but it make 'call myownproc'.

Regards.
Post 19 Jan 2005, 13:50
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IronFelix



Joined: 09 Dec 2004
Posts: 141
Location: Russia, Murmansk region
IronFelix
Sorry, small mistake: i used 'retn 1' to return from function and had to pass only one byte ('push byte byteparam' instead of using eax)! For my stdcall example at the end of the function must be 'retn 4'.

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Post 19 Jan 2005, 14:12
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JohnFound



Joined: 16 Jun 2003
Posts: 3500
Location: Bulgaria
JohnFound
AFAIK, you never can push one byte using the instruction "push". You can push word or dword only. The only way to push only one byte is to store it in the stack with "mov" instruction and to decrement esp by 1.
Post 19 Jan 2005, 14:15
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snifit



Joined: 10 Dec 2004
Posts: 12
Location: Sweden
snifit
Big thanks guys!
I didn't realize it was such a problem with a single byte at the stack, and if I knew I'd used word or dword instead Smile
Anyways, I fixed it by using a dword value instead and by using the stdcall macro.

Thanks again.
Post 19 Jan 2005, 14:37
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