Re: [Qemu-devel] [RFC/experimental patch] qemu (x86_64 on x86_64 -no-kqemu) compiles with gcc4 and works

[Anthony Liguori]

Axel Zeuner wrote:
> Hi Anthony,
>
> On Thursday 29 March 2007 04:07, you wrote:
>   
> > Axel Zeuner wrote:
> >     
> > > Hi Anthony,
> > >
> > > On Monday 26 March 2007 01:44, you wrote:
> > >       
> > > > Axel Zeuner wrote:
> > > >         
> > > > > On Saturday 24 March 2007 21:15, Anthony Liguori wrote:
> > > > >           
> > > > > > The tricky thing I still can't figure out is how to get ASM_SOFTMMU
> > > > > > working.  The problem is GLUE(st, SUFFIX) function.  First GCC cannot
> > > > > > deal with the register pressure.  The problem I can't seem to fix
> > > > > > though is that GCC sticks %1 in %esi because we're only using an "r"
> > > > > > constraint, not a "q" constraint.  This results in the generation of
> > > > > > %sib which is an invalid register.  However, refactoring the code to
> > > > > > not require a "q" constraint doesn't seem to help either.
> > > > > >             
> > > > > Hi Anthony,
> > > > > could you please try the attached patch for softmmu_header.h? Allows
> > > > > compiling with gcc4 and ASM_SOFTMMU.
> > > > >           
> > > > That did the trick.  Could you explain what your changes did?
> > > >         
> > > QEMU/i386 has only 3 three available registers if TARGET_I386 is selected
> > > because ebx,ebp,esi,edi are used by the environment and T0, T1, T3( AKA
> > > A0). This makes inline assembly really ugly. The called external C
> > > functions in ASM_SOFTMMU are REGPARM(1,2), i.e. require their first
> > > arguments in eax, edx.
> > >       
> > Based on some feedback from Paul Brook, I wrote another patch that just
> > disables the use of register variables for GCC4.  I think this is a
> > considerably less hackish way to go about this.
> >
> > The generated code won't be as nice of course but at least it works.
> > The patch applies against your cvtasm patches.
> >     
> Looks good to me, sorry I had no time yet to test your patch. Did you check 
> the performance impact of your changes? 
> Perhaps it is possible to use register variables in dependence of the register 
> count of the host processor.
>   

Yes, I need to update the patch to include a && defined(__i386__) and 
also to add the proper guards to the other architectures.

Regards,

Anthony Liguori

> Kind Regards
> Axel
>
>