Re: [GD-Windows] Re : Strange prolog function issue

[deldav <del...@fr...>]

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=20

Hope that helps.

-----Message d'origine-----
De : gam...@li... =
[mailto:gam...@li...] De la part =
de
Emmanuel Astier
Envoy=E9 : mercredi 26 juillet 2006 01:13
=C0 : Game Development for MS Windows
Objet : [GD-Windows] Re : Strange prolog function issue

Hi,=20
=20
It only happens in release build. And as you said, I suspect a compiler =
bug.
=20
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.
=20
Thanks for your help,
we send a mail to microsoft, we will wait for their anwser...
=20
Emmanuel

Ps : Kent, replying to your mails only replies to you, not to the =
list...=20

----- Message d'origine ----
De : Kent Quirk <ken...@co...> =C0 : Emmanuel Astier =
<e_a...@ya...>; Game Development for MS Windows
<gam...@li...>
Envoy=E9 le : Mardi, 25 Juillet 2006, 6h09mn 40s Objet : Re: =
[GD-Windows] Strange prolog function issue


Emmanuel Astier wrote:
> Hi all,
> =20
> =20
> I have here a very strange issue.
> =20
> We have a function using a local std::string, exceptions, and a =
alloca.
> =20
> 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 ).
> =20
> <snip>
> =20
> I could not reproduce this ebp offset that makes the exception handler =
fail in a small sample.=20
> 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 ?=20
>  =20

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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