On Wed, Jan 24, 2007 at 08:08:12PM +1100, Paul Mackerras wrote: > Mathieu Desnoyers writes: > > > +static __inline__ int local_dec_if_positive(local_t *l) > > +{ > > + int t; > > + > > + __asm__ __volatile__( > > +"1: lwarx %0,0,%1 # local_dec_if_positive\n\ > > + addic. %0,%0,-1\n\ > > + blt- 2f\n" > > + PPC405_ERR77(0,%1) > > +" stwcx. %0,0,%1\n\ > > + bne- 1b" > > This has the same bugs that we fixed recently in atomic_dec_if_positive; > first, on 64-bit machines, the lwarx will zero-extend the word loaded > from memory, and so the result of the addic will be negative only if > the word was originally 0. Secondly, even on 32-bit machines, > 0x80000000 will be considered positive since decrementing it gives > 0x7fffffff, which is positive. > > > +/* Use these for per-cpu local_t variables: on some archs they are > > + * much more efficient than these naive implementations. Note they take > > + * a variable, not an address. > > + * > > + * This could be done better if we moved the per cpu data directly > > + * after GS. > > + */ > > What's "GS"? Does this comment really apply on powerpc? >
1) It's an (application visible) i386/x86_64 segment register used to make memory addressing more confusing. 2) Because of 1), obviously not ;-) Gabriel - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/