linux-kernel - Re: [PATCH] efi/libstub: Disable some warnings for x86{,

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Date:   Tue, 23 Oct 2018 10:53:09 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>
Subject: Re: [PATCH] efi/libstub: Disable some warnings for x86{,_64}

On Fri, Oct 12, 2018 at 06:03:49PM -0700, Nathan Chancellor wrote:
> When building the kernel with Clang, some disabled warnings appear
> because this Makefile overrides KBUILD_CFLAGS for x86{,_64}. Add them to
> this list so that the build is clean again.
> 
> -Wpointer-sign was disabled for the whole kernel before the beginning
> of git history.
> 
> -Waddress-of-packed-member was disabled for the whole kernel in
> commit bfb38988c51e ("kbuild: clang: Disable 'address-of-packed-member'
> warning") and for x86/boot/compressed in commit 20c6c1890455 ("x86/boot:
> Disable the address-of-packed-member compiler warning").
> 
> -Wgnu was disabled for the whole kernel in commit 61163efae020 ("kbuild:
> LLVMLinux: Add Kbuild support for building kernel with Clang") and for
> x86/boot/compressed in commit 6c3b56b19730 ("x86/boot: Disable Clang
> warnings about GNU extensions").
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/112
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
> 
> Nick expressed concern that this Makefile is overwriting KBUILD_CFLAGS
> and suggested potentially rewriting the x86 portion of this Makefile to
> behave like the arm/arm64 one where problematic flags are filtered out.
> While that comes to fruition, it would be nice for this folder to behave
> like the rest of the kernel when it comes to this warnings so that the
> build is cleaner, thus this patch.
> 
>  drivers/firmware/efi/libstub/Makefile | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index c51627660dbb..d9845099635e 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -9,7 +9,10 @@ cflags-$(CONFIG_X86_32)		:= -march=i386
>  cflags-$(CONFIG_X86_64)		:= -mcmodel=small
>  cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ -O2 \
>  				   -fPIC -fno-strict-aliasing -mno-red-zone \
> -				   -mno-mmx -mno-sse -fshort-wchar
> +				   -mno-mmx -mno-sse -fshort-wchar \
> +				   -Wno-pointer-sign \
> +				   $(call cc-disable-warning, address-of-packed-member) \
> +				   $(call cc-disable-warning, gnu)
>  
>  # arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
>  # disable the stackleak plugin
> -- 
> 2.19.1
> 

+ Sedat for review/testing.