Re: Re : Strange prolog function issue

alloca allocates its memory from the stack and that space is automatically freed when the function returns.
That's why the compiler mess with esp and ebp ... 590h should be the size of your alloca (perhaps rounded to keep stack alignement)

Beware (from msdn):
	In Windows XP, if _alloca is called inside a try/catch block, you must call _resetstkoflw in the catch block 

Hope that helps.

-----Message d'origine-----
De : [email protected] [mailto:[email protected]] De la part de
Emmanuel Astier
Envoyé : mercredi 26 juillet 2006 01:13
À : Game Development for MS Windows
Objet : [GD-Windows] Re : Strange prolog function issue

Hi, 
 
It only happens in release build. And as you said, I suspect a compiler bug.
 
Actually, I don't understand when the compiler decide to switch to a different prolog for the function, where ebp doesn't have the
same meaning.
It is all fine as the function code knows the different ebp meaning, and has no trouble accessing local vars, but the exception
handler seems not to be aware of the change in the ebp meaning.
 
Thanks for your help,
we send a mail to microsoft, we will wait for their anwser...
 
Emmanuel

Ps : Kent, replying to your mails only replies to you, not to the list... 

----- Message d'origine ----
De : Kent Quirk <[email protected]> À : Emmanuel Astier <[email protected]>; Game Development for MS Windows
<[email protected]>
Envoyé le : Mardi, 25 Juillet 2006, 6h09mn 40s Objet : Re: [GD-Windows] Strange prolog function issue


Emmanuel Astier wrote:
> Hi all,
>  
>  
> I have here a very strange issue.
>  
> We have a function using a local std::string, exceptions, and a alloca.
>  
> When the exception is thrown, the unwind mecanism tries to delete the std::string, but it deletes it at a wrong address( there is
a 0x590 offset ).
>  
> <snip>
>  
> I could not reproduce this ebp offset that makes the exception handler fail in a small sample. 
> So do you know in which case the compiler does not put esp in ebp, but put an offset in it ?
> And do you know how to fix it ( other than what we're doing : stopping using alloca with exceptions ), if it is a kind a known
issue ? 
>   

Does the bug occur in both debug and release builds? Have you tried setting the optimization manually for that file?  In any large
project, I usually find a couple of files that drive some form of compiler bug under full optimization, and I have to manually turn
down the optimization on that particular file or do some sort of special (heavily
commented!) adaptation, such as moving a function's location in the source file, or in the header file. You might also try playing
with a couple of exception-related compiler switches. Compilers are complicated beasts, and any project of a significant size is
likely to drive a bug or two.

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