linux-kernel - Re: [PATCH FOR-NEXT] riscv: Add norvc after .option arch in runtime const

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Message-ID: <f8b56a02-c508-4bc9-a503-48e487ced86e@rivosinc.com>
Date: Tue, 1 Apr 2025 11:27:06 +0200
From: Clément Léger <cleger@...osinc.com>
To: Charlie Jenkins <charlie@...osinc.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alex@...ti.fr>, Klara Modin <klarasmodin@...il.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH FOR-NEXT] riscv: Add norvc after .option arch in runtime
 const



On 31/03/2025 20:45, Charlie Jenkins wrote:
> .option arch clobbers .option norvc. Prevent gas from emitting
> compressed instructions in the runtime const alternative blocks by
> setting .option norvc after .option arch. This issue starts appearing on
> gcc 15, which adds zca to the march.
> 
> Reported by: Klara Modin <klarasmodin@...il.com>
> 
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> Fixes: a44fb5722199 ("riscv: Add runtime constant support")
> Closes: https://lore.kernel.org/all/cc8f3525-20b7-445b-877b-2add28a160a2@gmail.com/
> ---
>  arch/riscv/include/asm/runtime-const.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/runtime-const.h b/arch/riscv/include/asm/runtime-const.h
> index c07d049fdd5d2999c57d8a90e7363829c5462368..451fd76b881152919f22de8f5c56b51171acbf3c 100644
> --- a/arch/riscv/include/asm/runtime-const.h
> +++ b/arch/riscv/include/asm/runtime-const.h
> @@ -56,6 +56,7 @@
>  #define RISCV_RUNTIME_CONST_64_ZBA				\
>  	".option push\n\t"					\
>  	".option arch,+zba\n\t"					\
> +	".option norvc\n\t"					\

Hey Charlie,

Could ".option arch,+zba,-c" be used as well ? That way, c is treated
like any other arch option. Or does norvc has other side effects ?

Thanks,

Clément

>  	"slli	%[__tmp],%[__tmp],32\n\t"			\
>  	"add.uw %[__ret],%[__ret],%[__tmp]\n\t"			\
>  	"nop\n\t"						\
> @@ -65,6 +66,7 @@
>  #define RISCV_RUNTIME_CONST_64_ZBKB				\
>  	".option push\n\t"					\
>  	".option arch,+zbkb\n\t"				\
> +	".option norvc\n\t"					\
>  	"pack	%[__ret],%[__ret],%[__tmp]\n\t"			\
>  	"nop\n\t"						\
>  	"nop\n\t"						\
> 
> ---
> base-commit: b2117b630c48be69d2782ed79fefe35dcd192ce6
> change-id: 20250331-fix_runtime_const_norvc-407af1f24541