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MessageBeep Issue.

 
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Freiza
Grandmaster Cheater
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Joined: 28 Jun 2010
Posts: 662
PostPosted: Thu Mar 08, 2012 4:22 am    Post subject: MessageBeep Issue. Reply with quote
Code:
mov eax,[Emperor.exe+F12B1C]
push 0xffffffff   
call MessageBeep
cmp dword ptr [ecx+04],0000001c
jne here
mov dword ptr [ecx+08],0
here:
mov eax,[ecx+08]
ret
nop


Using MessageBeep function causes to crash the game. Am I using it in incorrect fashion?
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Dark Byte
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Location: The netherlands
PostPosted: Thu Mar 08, 2012 5:35 am    Post subject: Reply with quote
The call to MessageBeep changes registers (like eax) . Save the registers before the call and restore afterwards
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Freiza
Grandmaster Cheater
Reputation: 22

Joined: 28 Jun 2010
Posts: 662
PostPosted: Thu Mar 08, 2012 5:48 am    Post subject: Reply with quote
There is no need of saving eax in my case here. As you can see eax is modified by some pointers. But Registers? Does other register is also changed by MessageBeep ?
Could it be because of the flags?
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Dark Byte
Site Admin
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Joined: 09 May 2003
Posts: 25953
Location: The netherlands
PostPosted: Thu Mar 08, 2012 6:10 am    Post subject: Reply with quote
http://en.wikipedia.org/wiki/X86_calling_convention#stdcall
ECX and EDX might also get changed

Personally I prefer using pushad / popad to save and restore all registers so I don't have to worry about the specific ones (and speed can be neglected)
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