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

Andrew Jones
2024-01-19T09:41:33Z

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@rivosinc.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
>
>
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