linux-kernel - Re: [PATCH v2 3/3] ARM: spinlock: use unified assembler language syntax

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Message-ID: <nycvar.YSQ.7.76.1901051112560.1783@knanqh.ubzr>
Date:   Sat, 5 Jan 2019 11:13:30 -0500 (EST)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Stefan Agner <stefan@...er.ch>
cc:     linux@...linux.org.uk, ndesaulniers@...gle.com,
        natechancellor@...il.com, arnd@...db.de, ard.biesheuvel@...aro.org,
        peterz@...radead.org, mingo@...hat.com, will.deacon@....com,
        julien.thierry@....com, mark.rutland@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 3/3] ARM: spinlock: use unified assembler language
 syntax

On Thu, 3 Jan 2019, Stefan Agner wrote:

> Convert the conditional infix to a postfix to make sure this inline
> assembly is unified syntax. Since gcc assumes non-unified syntax
> when emitting ARM instructions, make sure to define the syntax as
> unified.
> 
> This allows to use LLVM's integrated assembler.

Same comment as for patch 2/3.


> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> ---
> Changes since v1:
> - Explicitly use unified syntax for inline assembly
> 
> 
>  arch/arm/include/asm/spinlock.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h
> index 099c78fcf62d..8f009e788ad4 100644
> --- a/arch/arm/include/asm/spinlock.h
> +++ b/arch/arm/include/asm/spinlock.h
> @@ -210,11 +210,12 @@ static inline void arch_read_lock(arch_rwlock_t *rw)
>  
>  	prefetchw(&rw->lock);
>  	__asm__ __volatile__(
> +"	.syntax unified\n"
>  "1:	ldrex	%0, [%2]\n"
>  "	adds	%0, %0, #1\n"
>  "	strexpl	%1, %0, [%2]\n"
>  	WFE("mi")
> -"	rsbpls	%0, %1, #0\n"
> +"	rsbspl	%0, %1, #0\n"
>  "	bmi	1b"
>  	: "=&r" (tmp), "=&r" (tmp2)
>  	: "r" (&rw->lock)
> -- 
> 2.20.1
> 
>