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    SubjectRe: [PATCH 7/10] local_t : powerpc
    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
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