Re: [Qemu-devel] testandset asm fix

[Piotras]

I didn't noticed that the patch was committed.


Piotrek

On Mon, 7 Feb 2005 14:26:36 +0000, Piotras <address@hidden> wrote:
> What about IRQ latency?
> 
> Piotrek
> 
> On Mon, 07 Feb 2005 14:47:29 +0100, Fabrice Bellard <address@hidden> wrote:
> > OK. Anyway, the locking in QEMU is mostly boggus. If SMP is implemented
> > someday with host threads, then it will be the right time to correct it !
> >
> > Fabrice.
> >
> > Paul Brook wrote:
> > > The inline assembly used for the x86/x86-64 host testandset routine is 
> > > bogus.
> > > The operand constraints are wrong (Fails to compile at -O0).
> > > Also the return value is incorrect. It should return 0 if the lock was
> > > successfully acquired.
> > >
> > > Patch below fixes it. The additional sete test is unnecessary, we can 
> > > just use
> > > the comparison/writeback value.
> > >
> > > Paul
> > >
> > > Index: exec-all.h
> > > ===================================================================
> > > RCS file: /cvsroot/qemu/qemu/exec-all.h,v
> > > retrieving revision 1.26
> > > diff -u -p -r1.26 exec-all.h
> > > --- exec-all.h 10 Jan 2005 23:23:48 -0000 1.26
> > > +++ exec-all.h 6 Feb 2005 14:35:43 -0000
> > > @@ -392,28 +392,24 @@ static inline int testandset (int *p)
> > >  #ifdef __i386__
> > >  static inline int testandset (int *p)
> > >  {
> > > -    char ret;
> > > -    long int readval;
> > > -
> > > -    __asm__ __volatile__ ("lock; cmpxchgl %3, %1; sete %0"
> > > -                          : "=q" (ret), "=m" (*p), "=a" (readval)
> > > -                          : "r" (1), "m" (*p), "a" (0)
> > > -                          : "memory");
> > > -    return ret;
> > > +    long int readval = 0;
> > > +
> > > +    __asm__ __volatile__ ("lock; cmpxchgl %2, %0"
> > > +                          : "+m" (*p), "+a" (readval)
> > > +                          : "r" (1));
> > > +    return readval;
> > >  }
> > >  #endif
> > >
> > >  #ifdef __x86_64__
> > >  static inline int testandset (int *p)
> > >  {
> > > -    char ret;
> > > -    int readval;
> > > -
> > > -    __asm__ __volatile__ ("lock; cmpxchgl %3, %1; sete %0"
> > > -                          : "=q" (ret), "=m" (*p), "=a" (readval)
> > > -                          : "r" (1), "m" (*p), "a" (0)
> > > -                          : "memory");
> > > -    return ret;
> > > +    long int readval = 0;
> > > +
> > > +    __asm__ __volatile__ ("lock; cmpxchgl %2, %0"
> > > +                          : "+m" (*p), "+a" (readval)
> > > +                          : "r" (1));
> > > +    return readval;
> > >  }
> > >  #endif
> > >
> > >
> > >
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> > >
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> >
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