Re: [MinGW-dvlpr] Re: _alloca/_chkstk??

[Danny S. <dan...@cl...>]

----- Original Message -----
From: "Ranjit Mathew"


> >> Is there a particular reason to remove it
> >> though, apart from when statically linking
> >> GCC-compiled objects with MSVC programs
> >> or vice versa?
> >
> > Yes, it plays up with optimisation using
> > -funit-at-a-time in CVS gcc,
>
> More specifically, -funit-at-a-time (which is
> now enabled by -O2) changes the calling
> conventions of local functions (functions that
> are defined, accessible and used within a single
> compilation unit) to use as many (max. three?)
> registers for passing parameters as possible.
>
> MinGW/Cygwin's current implementation of
> __chkstk/_alloca clobbers EAX, resulting in
> a parameter to local functions getting
> converted to garbage.
>
> This specifically causes a crash in
> the GCJ parser on MinGW.
>
> So either __chkstk/_alloca has to be done
> away with or modified to not clobber EAX (and
> use something else to get the stack size value).
>

BTW, this is not a new bug it has been around since 2.95 days.  Here is
a testcase
that shows the behaviour:

http://www.cygwin.com/ml/cygwin/2002-06/msg00122.html

If change regparm(3) to fastcall,  the above testcase succeeds.  Hmm,
maybe that's why MS designed fastcall to use ECX, not EAX as the first
allocated register.

Danny


> Otherwise, 3.4 will be grief incarnate for
> MinGW/Cygwin.
>
> Ranjit.
>
> --
> Ranjit Mathew          Email: rmathew AT hotmail DOT com
>
> Bangalore, INDIA.      Web: http://ranjitmathew.tripod.com/
>
>
>
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