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    SubjectRe: [RFC][PATCH 05/12] arch: Introduce arch_{,try_}_cmpxchg128{,_local}()
    On Wed, Dec 21, 2022 at 05:25:20PM -0800, Boqun Feng wrote:

    > > +#define __CMPXCHG128(name, mb, cl...) \
    > > +static __always_inline u128 \
    > > +__lse__cmpxchg128##name(volatile u128 *ptr, u128 old, u128 new) \
    > > +{ \
    > > + union __u128_halves r, o = { .full = (old) }, \
    > > + n = { .full = (new) }; \
    > > + register unsigned long x0 asm ("x0") = o.low; \
    > > + register unsigned long x1 asm ("x1") = o.high; \
    > > + register unsigned long x2 asm ("x2") = n.low; \
    > > + register unsigned long x3 asm ("x3") = n.high; \
    > > + register unsigned long x4 asm ("x4") = (unsigned long)ptr; \
    > > + \
    > > + asm volatile( \
    > > + __LSE_PREAMBLE \
    > > + " casp" #mb "\t%[old1], %[old2], %[new1], %[new2], %[v]\n"\
    > > + : [old1] "+&r" (x0), [old2] "+&r" (x1), \
    > > + [v] "+Q" (*(unsigned long *)ptr) \
    > > + : [new1] "r" (x2), [new2] "r" (x3), [ptr] "r" (x4), \
    >
    > Issue #1: the line below can be removed, otherwise..
    >
    > > + [oldval1] "r" (r.low), [oldval2] "r" (r.high) \
    >
    > warning:
    >
    > ./arch/arm64/include/asm/atomic_lse.h: In function '__lse__cmpxchg128_mb':
    > ./arch/arm64/include/asm/atomic_lse.h:309:27: warning: 'r.<U97b8>.low' is used uninitialized [-Wuninitialized]
    > 309 | [oldval1] "r" (r.low), [oldval2] "r" (r.high)
    >
    >
    > > + : cl); \
    > > + \
    > > + r.low = x0; r.high = x1; \
    > > + \
    > > + return r.full; \
    > > +}
    > > +
    > > +__CMPXCHG128( , )
    > > +__CMPXCHG128(_mb, al, "memory")
    > > +
    > > +#undef __CMPXCHG128
    > > +
    > > #endif /* __ASM_ATOMIC_LSE_H */
    > > --- a/arch/arm64/include/asm/cmpxchg.h
    > > +++ b/arch/arm64/include/asm/cmpxchg.h
    > > @@ -147,6 +147,19 @@ __CMPXCHG_DBL(_mb)
    > >
    > > #undef __CMPXCHG_DBL
    > >
    > > +#define __CMPXCHG128(name) \
    > > +static inline long __cmpxchg128##name(volatile u128 *ptr, \
    >
    > Issue #2: this should be
    >
    > static inline u128 __cmpxchg128##name(..)
    >
    > because cmpxchg* needs to return the old value.

    Duh.. fixed both. Pushed out to queue/core/wip-u128. I'll probably
    continue all this in two weeks (yay xmas break!).

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