Re: [ros-svn] [arty] 14588: Commit for blight: fix stack alignment.

[Hartmut Birr]

Hi,

why do you change this file? Alloca.c isn't used and should be removed.
If we have an alloca function somewhere in our source, it must be
completely written in assembler because the stack layout and the using
of ebp depends on the compilers optimisation.

- Hartmut

[e-mail] wrote:
> Commit for blight: fix stack alignment.
>
> Updated files:
> trunk/reactos/lib/crtdll/stdlib/alloca.c
>
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[art yerkes]

On Mon, 11 Apr 2005 19:32:08 +0200
Hartmut Birr [e-mail] wrote:
> Hi,
>
> why do you change this file? Alloca.c isn't used and should be removed.
> If we have an alloca function somewhere in our source, it must be
> completely written in assembler because the stack layout and the using
> of ebp depends on the compilers optimisation.

Sorry, blight asked me to commit it.
-- 
Here's a simple experiment. Stand on a train track between two locomotives
which are pushing on you with equal force in opposite directions. You will
exhibit no net motion. None the less, you may soon begin to notice that
something important is happening.
-- Robert Stirniman

[Mark Junker]

Hartmut Birr schrieb:
> why do you change this file? Alloca.c isn't used and should be removed.
> If we have an alloca function somewhere in our source, it must be
> completely written in assembler because the stack layout and the using
> of ebp depends on the compilers optimisation.

I agree with you. This function should really be completely written in 
assembler - optimizing builds will probably create a buggy function when 
stack frames are omitted (for example). Anyway, there should be an i386 
sub-folder where this implementation should be moved to.

Regards,
Mark

[James Tabor]

Hartmut Birr wrote:
> Hi,
>
> why do you change this file? Alloca.c isn't used and should be removed.
> If we have an alloca function somewhere in our source, it must be
> completely written in assembler because the stack layout and the using
> of ebp depends on the compilers optimisation.
> Hartmut
>
> [e-mail] wrote:
> > Commit for blight: fix stack alignment.
> >
> > Updated files:
> > trunk/reactos/lib/crtdll/stdlib/alloca.c

Rewrite it! Make lib/crtdll/stdlib/i386/alloca.s and powerpc/alloca.s.
James

[Hartmut Birr]

James Tabor wrote:
> Hartmut Birr wrote:
> > Hi,  
> > why do you change this file? Alloca.c isn't used and should be removed.
> > If we have an alloca function somewhere in our source, it must be
> > completely written in assembler because the stack layout and the using
> > of ebp depends on the compilers optimisation.
> > Hartmut
> >
> > [e-mail] wrote:
> > > Commit for blight: fix stack alignment.
> > >
> > > Updated files:
> > > trunk/reactos/lib/crtdll/stdlib/alloca.c
>
> Rewrite it! Make lib/crtdll/stdlib/i386/alloca.s and powerpc/alloca.s.
> James

Hi,

I think it isn't possible to write the alloca function outside from
compiler. The compiler may use esp instead of ebp to access local
variables. In this case it isn't possible to manipulate esp. I remember
same old problems from hal:

pushf 
cli
 ...
 popf

This sequence has crashed reactos on optimized builds, because there
was accessed a local variable inside pushf/popf by using esp+offset.

- Hartmut