EnumWindows with window handles dump gives errors!!!

[xandaz]

    Hey guys.... why does this return error? check it out...

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.data
WindowHandles dd 50000 dup(0) ; huge number to prevent overflow
lpWindowHandles dd offset WindowHandles
.code
....
invoke EnumWindows,addr EnumProc,NULL
....
EnumProc PROC hWnd:DWORD,Arg:DWORD

mov edi,lpWindowHandles
mov eax,hWnd
stosd
cld
invoke GetWindowText,eax,addr WindowName
invoke SendMessage,hListbox,LB_ADDSTRING,NULL,addr WindowName
mov lpWindowHandles,edi
mov eax,TRUE
ret

EnumProc endp


Why is this not working? Someone ?  :lol
Thanks and bye

[Gunner]

What kind of errors?  You are NOT preserving edi!
EnumProc PROC uses edi hWnd:DWORD,Arg:DWORD

[dedndave]

Rob is right
but, i noticed something that was a little odd

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stosd
cld

you shouldn't have to CLD - it should already be cleared
and, if you do have to CLD, you might want to do it before the STOSD  :P

[xandaz]

 yes ded. i kinda made that mistake but only here. But why do i need to preserve edi? when i do the mov edi,lpWindowHandles and lpWindowHandles,edi i don't think there's any danger. is there? let me try that out.

[oex]

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[xandaz]

   its working fine now. thanks

[xandaz]

   works fine with pushes, but, still... why do i need to preserce edi? I load it in the beggining of EnumProc and deload it in the end. What difference does it make to push and pop? Someone pls clarify me. Thanks

[MichaelW]

You need to preserve EDI because EnumProc is a callback. Since Windows is calling it, it needs to follow the register-preservation conventions.

[Gunner]

re read my post above....  you don't need to uses push/pop...  instead put USES EDI after the word proc... easier then using push reg and remembering to pop it before leaving the proc

[xandaz]

    Oh ok. Since windows is calling the callback function and it may be useing edi, you preserve it to prevent errors. Thanks. That was kinda hard to understand. I'm such a dumbo. Thanks guys and byebye. :)

[Gunner]

Well, anytime you use esi, edi ebx in a proc you must save their contents, especially in a callback procedure... it is proper programming etiquette  :bg

open up the help file masm32/help/asmintro.chm and read the section called Register Preservation Convention