Re: [Qemu-devel] testandset asm fix

[Piotras <piotras@gmail.com>]

What about IRQ latency?


Piotrek

On Mon, 07 Feb 2005 14:47:29 +0100, Fabrice Bellard <fabrice@bellard.org> 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
> >
> >
> >
> > _______________________________________________
> > Qemu-devel mailing list
> > Qemu-devel@nongnu.org
> > http://lists.nongnu.org/mailman/listinfo/qemu-devel
> >
> >
> 
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