Re: [RFC][PATCH 05/12] arch: Introduce arch_{,try_}_cmpxchg128{,_local}()

Peter Zijlstra
2023-01-12T10:36:36Z

On Mon, Jan 09, 2023 at 06:50:24PM +0000, Mark Rutland wrote:

> Similarly, I'd suggest:
>
> | #define __CMPXCHG128(name, mb, cl...) \
> | static __always_inline u128 \
> | __lse__cmpxchg128##name(volatile u128 *ptr, u128 old, u128 new) \
> | { \
> | asm volatile( \
> | __LSE_PREAMBLE \
> | " casp" #mb "\t%[old], %H[old], %[new], %H[new], %[v]\n" \
> | : [old] "+&r" (old), \
> | [v] "+Q" (*(u128 *)ptr) \
> | : [new] "r" (new) \
> | : cl); \
> | \
> | return old; \
> | }
> |
> | __CMPXCHG128( , )
> | __CMPXCHG128(_mb, al, "memory")
> |
> | #undef __CMPXCHG128

clang-16 seems to hate on this like:

arch/arm64/include/asm/atomic_lse.h:342:1: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths]
arch/arm64/include/asm/atomic_lse.h:334:17: note: expanded from macro '__CMPXCHG128'
: [old] "+&r" (old), \
^

(much the same for the ll_sc version; if you want the full build thing,
holler and I'll bounce you the robot mail).