linux-kernel - Re: [PATCH v2] riscv: lib: Check if output in asm goto supported

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Date: Fri, 19 Jan 2024 10:41:14 +0100
From: Andrew Jones <ajones@...tanamicro.com>
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 v2] riscv: lib: Check if output in asm goto supported

On Thu, Jan 18, 2024 at 02:36:45PM -0800, Charlie Jenkins wrote:
> The output field of an asm goto statement is not supported by all
> compilers. If it is not supported, fallback to the non-optimized code.
> 
> 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.
> ---
> Changes in v2:
> - Use CC_HAS_ASM_GOTO_TIED_OUTPUT
> - Link to v1: https://lore.kernel.org/r/20240118-csum_remove_output_operands_asm_goto-v1-1-47c672bb9d4b@rivosinc.com
> ---
>  arch/riscv/lib/csum.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c
> index 06ce8e7250d9..af3df5274ccb 100644
> --- a/arch/riscv/lib/csum.c
> +++ b/arch/riscv/lib/csum.c
> @@ -156,6 +156,7 @@ do_csum_with_alignment(const unsigned char *buff, int len)
>  	end = (const unsigned long *)(buff + len);
>  	csum = do_csum_common(ptr, end, data);
>  
> +#ifdef CC_HAS_ASM_GOTO_TIED_OUTPUT

Can't we just add another IS_ENABLED() to the if rather than this #ifdef?

>  	/*
>  	 * Zbb support saves 6 instructions, so not worth checking without
>  	 * alternatives if supported
> @@ -214,6 +215,7 @@ do_csum_with_alignment(const unsigned char *buff, int len)
>  		return csum >> 16;
>  	}
>  no_zbb:
> +#endif /* CC_HAS_ASM_GOTO_TIED_OUTPUT */
>  #ifndef CONFIG_32BIT
>  	csum += ror64(csum, 32);
>  	csum >>= 32;

BTW, I wonder how/if the check for CC_HAS_ASM_GOTO_TIED_OUTPUT in
init/Kconfig is working as expected. I see $CC, as opposed to $(CC),
being used there. I believe $CC is just the expansion of $C with a
'C' appended.

Thanks,
drew

> 
> ---
> base-commit: 080c4324fa5e81ff3780206a138223abfb57a68e
> change-id: 20240118-csum_remove_output_operands_asm_goto-49922c141ce7
> -- 
> - Charlie
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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