Re: [PATCH 3/3] Kbuild: use -std=gnu11 for KBUILD_USERCFLAGS

[Nathan Chancellor <nathan@kernel.org>]

On Tue, Mar 01, 2022 at 03:52:33PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> As we change the C language standard for the kernel from gnu89 to
> gnu11, it makes sense to also update the version for user space
> compilation.
> 
> Some users have older native compilers than what they use for
> kernel builds, so I considered using gnu99 as the default version
> for wider compatibility with gcc-4.6 and earlier.
> 
> However, testing with older compilers showed that we already require
> HOSTCC version 5.1 as well because a lot of host tools include
> linux/compiler.h that uses __has_attribute():
> 
>   CC      tools/objtool/exec-cmd.o
> In file included from tools/include/linux/compiler_types.h:36:0,
>                  from tools/include/linux/compiler.h:5,
>                  from exec-cmd.c:2:
> tools/include/linux/compiler-gcc.h:19:5: error: "__has_attribute" is not defined [-Werror=undef]

For what it's worth, I think this is a bug:

https://lore.kernel.org/r/c1b1a299-c60d-28a4-07ab-1ecd211d6da9@i-love.sakura.ne.jp/
https://lore.kernel.org/r/20220102120201.594408-1-xu.xin16@zte.com.cn/

I never got clear feedback on resolving it from the first thread and
nobody bothered to pick up the second patch.

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Nobody has yelled that loud though, so this is probably fine.

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
>  Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index 37ef6a555dcd..7c9be7f1ccd4 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -432,7 +432,7 @@ HOSTCXX	= g++
>  endif
>  
>  export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \
> -			    -O2 -fomit-frame-pointer -std=gnu89 \
> +			    -O2 -fomit-frame-pointer -std=gnu11 \
>  			    -Wdeclaration-after-statement
>  export KBUILD_USERLDFLAGS :=
>  
> -- 
> 2.29.2
> 
>