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

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Date:   Mon, 5 Nov 2018 13:52:35 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     sedat.dilek@...il.com
Cc:     natechancellor@...il.com, linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] efi/libstub: Disable some warnings for x86{,_64}

On 24 October 2018 at 09:22, Sedat Dilek <sedat.dilek@...il.com> wrote:
> On Tue, Oct 23, 2018 at 7:53 PM Nathan Chancellor
> <natechancellor@...il.com> wrote:
>>
>> 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.
>
> Thanks Nathan.
>
> Reviewed-by: Sedat Dilek <sedat.dilek@...il.com>
> Tested-by: Sedat Dilek <sedat.dilek@...il.com>
> [ Reported-by: Sedat Dilek <sedat.dilek@...il.com> ]
> [ See duplicate "arch/x86/include/asm/processor.h: Warning
> -Waddress-of-packed-member "
> <https://github.com/ClangBuiltLinux/linux/issues/234> ]
>

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