Re: [PATCH v2 2/7] Revert "kbuild: disable clang's default use of -fmerge-all-constants"

[Nathan Chancellor]

On Mon, Aug 31, 2020 at 05:23:21PM -0700, Nick Desaulniers wrote:
> This reverts commit 87e0d4f0f37fb0c8c4aeeac46fff5e957738df79.
> 
> This was fixed in clang-6; the minimum supported version of clang in the
> kernel is clang-10 (10.0.1).
> 
> Link: https://reviews.llvm.org/rL329300.
> Link: https://github.com/ClangBuiltLinux/linux/issues/9
> Suggested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>

> ---
>  Makefile | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 37739ee53f27..144ac6a073ff 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -932,15 +932,6 @@ KBUILD_CFLAGS += $(call cc-disable-warning, maybe-uninitialized)
>  # disable invalid "can't wrap" optimizations for signed / pointers
>  KBUILD_CFLAGS	+= $(call cc-option,-fno-strict-overflow)
>  
> -# clang sets -fmerge-all-constants by default as optimization, but this
> -# is non-conforming behavior for C and in fact breaks the kernel, so we
> -# need to disable it here generally.
> -KBUILD_CFLAGS	+= $(call cc-option,-fno-merge-all-constants)
> -
> -# for gcc -fno-merge-all-constants disables everything, but it is fine
> -# to have actual conforming behavior enabled.
> -KBUILD_CFLAGS	+= $(call cc-option,-fmerge-constants)
> -
>  # Make sure -fstack-check isn't enabled (like gentoo apparently did)
>  KBUILD_CFLAGS  += $(call cc-option,-fno-stack-check,)
>  
> -- 
> 2.28.0.402.g5ffc5be6b7-goog
>