linux-kernel - Re: [PATCH] riscv: lib: Support csum on GCC <11

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Message-ID: <20240118-museum-ample-11d649f95de8@spud>
Date: Thu, 18 Jan 2024 22:05:44 +0000
From: Conor Dooley <conor@...nel.org>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: lib: Support csum on GCC <11

On Thu, Jan 18, 2024 at 01:53:59PM -0800, Charlie Jenkins wrote:
> The OutputOperands field for asm goto statements is only supported
> starting from GCC 11. Split the asm goto to remove the use of this
> feature.
> 
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> Fixes: a04c192eabfb ("riscv: Add checksum library")
> ---
> The OutputOperands field for asm goto statements is only supported
> starting from GCC 11. Split the asm goto to remove the use of this
> feature.

Maybe this is a super naive question, but is it possible to just not
use the custom csum code for gcc older than 11?

> ---
>  arch/riscv/lib/csum.c | 42 ++++++++++++++++++++++++++++++------------
>  1 file changed, 30 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c
> index 06ce8e7250d9..23be289f52b6 100644
> --- a/arch/riscv/lib/csum.c
> +++ b/arch/riscv/lib/csum.c
> @@ -177,22 +177,35 @@ do_csum_with_alignment(const unsigned char *buff, int len)
>  				  : no_zbb);
>  
>  #ifdef CONFIG_32BIT
> -		asm_volatile_goto(".option push			\n\
> +		/*
> +		 * OutputOperands in asm goto is not supported until GCC 11, so
> +		 * this asm has to be split to be compatible.
> +		 */
> +		asm (".option push				\n\
>  		.option arch,+zbb				\n\
>  			rori	%[fold_temp], %[csum], 16	\n\
>  			andi	%[offset], %[offset], 1		\n\
>  			add	%[csum], %[fold_temp], %[csum]	\n\
> -			beq	%[offset], zero, %l[end]	\n\
> -			rev8	%[csum], %[csum]		\n\
>  		.option pop"
>  			: [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp)
> -			: [offset] "r" (offset)
> -			:
> -			: end);
> +			: [offset] "r" (offset));
> +
> +		if (offset == 0)
> +			goto end;
> +
> +		asm (".option push				\n\
> +		.option arch, +zbb				\n\
> +			rev8	%[csum], %[csum]		\n\
> +		.option pop"
> +			: [csum] "+r" (csum));
>  
>  		return (unsigned short)csum;
>  #else /* !CONFIG_32BIT */
> -		asm_volatile_goto(".option push			\n\
> +		/*
> +		 * OutputOperands in asm goto is not supported until GCC 11, so
> +		 * this asm has to be split to be compatible.
> +		 */
> +		asm (".option push				\n\
>  		.option arch,+zbb				\n\
>  			rori	%[fold_temp], %[csum], 32	\n\
>  			add	%[csum], %[fold_temp], %[csum]	\n\
> @@ -200,13 +213,18 @@ do_csum_with_alignment(const unsigned char *buff, int len)
>  			roriw	%[fold_temp], %[csum], 16	\n\
>  			addw	%[csum], %[fold_temp], %[csum]	\n\
>  			andi	%[offset], %[offset], 1		\n\
> -			beq	%[offset], zero, %l[end]	\n\
> -			rev8	%[csum], %[csum]		\n\
>  		.option pop"
>  			: [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp)
> -			: [offset] "r" (offset)
> -			:
> -			: end);
> +			: [offset] "r" (offset));
> +
> +		if (offset == 0)
> +			goto end;
> +
> +		asm (".option push				\n\
> +		.option arch, +zbb				\n\
> +			rev8	%[csum], %[csum]		\n\
> +		.option pop"
> +			: [csum] "+r" (csum));
>  
>  		return (csum << 16) >> 48;
>  #endif /* !CONFIG_32BIT */
> 
> ---
> base-commit: 080c4324fa5e81ff3780206a138223abfb57a68e
> change-id: 20240118-csum_remove_output_operands_asm_goto-49922c141ce7
> -- 
> - Charlie
> 
> 

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