linux-kernel - Re: [PATCH 2/7] riscv: Implement cmpxchg8/16() using Zabha

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Message-ID: <ZlZurXUUUfXHZJaX@andrea>
Date: Wed, 29 May 2024 01:54:21 +0200
From: Andrea Parri <parri.andrea@...il.com>
To: Alexandre Ghiti <alexghiti@...osinc.com>
Cc: Jonathan Corbet <corbet@....net>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>,
	Arnd Bergmann <arnd@...db.de>, Leonardo Bras <leobras@...hat.com>,
	Guo Ren <guoren@...nel.org>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 2/7] riscv: Implement cmpxchg8/16() using Zabha

> +zabha:									\
> +	__asm__ __volatile__ (						\
> +		prepend							\
> +		"	amocas" cas_sfx " %0, %z2, %1\n"		\
> +		append							\
> +		: "+&r" (r), "+A" (*(p))				\
> +		: "rJ" (n)						\
> +		: "memory");						\

Couldn't a platform have Zabha but not have Zacas?  I don't see how this
asm goto could work in such case, what am I missing?

  Andrea