linux-kernel - Re: [RFC][PATCH 05/12] arch: Introduce arch_{,try_}_cmpxchg128{,

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Message-ID: <Y7/ijxXMGqYCqSRe@hirez.programming.kicks-ass.net>
Date:   Thu, 12 Jan 2023 11:35:59 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     torvalds@...ux-foundation.org, corbet@....net, will@...nel.org,
        boqun.feng@...il.com, catalin.marinas@....com, dennis@...nel.org,
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        agordeev@...ux.ibm.com, borntraeger@...ux.ibm.com,
        svens@...ux.ibm.com, Herbert Xu <herbert@...dor.apana.org.au>,
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        Andrew Morton <akpm@...ux-foundation.org>, vbabka@...e.cz,
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        linux-arch@...r.kernel.org
Subject: Re: [RFC][PATCH 05/12] arch: Introduce
 arch_{,try_}_cmpxchg128{,_local}()

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).