linux-kernel - Re: [PATCH linux-next] tools: compiler-gcc.h::Keep compatible with non-clang compilers.

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Message-ID: <Yc81vBwPo/aHMfXB@archlinux-ax161>
Date:   Fri, 31 Dec 2021 09:54:20 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     cgel.zte@...il.com
Cc:     ndesaulniers@...gle.com, keescook@...omium.org,
        wang.yong12@....com.cn, xu.xin16@....com.cn,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH linux-next] tools: compiler-gcc.h::Keep compatible with
 non-clang compilers.

On Fri, Dec 31, 2021 at 10:08:33AM +0000, cgel.zte@...il.com wrote:
> From: xu xin <xu.xin16@....com.cn>
> 
> When HOSTC = gcc (GCC) 4.8.5, there is an error occurring as follows:
> error: Undefined __has_attribute.
> 
> This problem is introduced by commit d0ee23f9d78be ("tools:
> compiler-gcc.h: Guard error attribute use with __has_attribute").

Yes, sorry for breaking this. It has been discussed here with some ideas
for a resolution but I never got any feedback so I never carried it
through, thank you for picking it up.

https://lore.kernel.org/r/c1b1a299-c60d-28a4-07ab-1ecd211d6da9@i-love.sakura.ne.jp/

This patch should probably be sent straight to Linus next time it is
sent, as he directly applied both my commit and the one that it was
fixing. Nick and I do not pick up patches currently although Kees might
be willing to take this one.

> To solve it, this patch is given to keep the comatibility.

                                               ^ compatibility

Might be worth adding "with older GCC versions" at the end of that
sentence.

> Reported-by: Zeal Robot <zealci@....com.cn>
> Co-developed-by: wangyong <wang.yong12@....com.cn>
> Signed-off-by: xu xin <xu.xin16@....com.cn>
> ---
>  tools/include/linux/compiler-gcc.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/tools/include/linux/compiler-gcc.h b/tools/include/linux/compiler-gcc.h
> index 8816f06fc6c7..7da593d3cb91 100644
> --- a/tools/include/linux/compiler-gcc.h
> +++ b/tools/include/linux/compiler-gcc.h
> @@ -16,6 +16,11 @@
>  # define __fallthrough __attribute__ ((fallthrough))
>  #endif
>  
> +
> +#ifndef __has_attribute
> +# define __has_attribute(x) 0  /* Compatibility with non-clang compilers. */

This comment is not really accurate; it implies that clang is the only
one that defines __has_attribute() but GCC 5.x or newer supports
__has_attribute().  A more accurate comment might be:

/* Compatibility with GCC < 5.x */

> +#endif
> +
>  #if __has_attribute(__error__)
>  # define __compiletime_error(message) __attribute__((error(message)))
>  #endif
> -- 
> 2.25.1
>