Re: [PATCH] efi/libstub: Disable some warnings for x86{,_64}

From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	linux-efi@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] efi/libstub: Disable some warnings for x86{,_64}
Date: Mon, 15 Oct 2018 13:16:00 -0700	[thread overview]
Message-ID: <CAKwvOdn-mZ8-w9+rFJ0tiYPdgbdQ_1DeO8w1MzHABtJ5ianBhQ@mail.gmail.com> (raw)
In-Reply-To: <20181015194650.GA11458@flashbox>

On Mon, Oct 15, 2018 at 12:46 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> On Mon, Oct 15, 2018 at 12:40:36PM -0700, Nick Desaulniers wrote:
> > On Fri, Oct 12, 2018 at 6:06 PM Nathan Chancellor
> > <natechancellor@gmail.com> 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@gmail.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 \
> >
> > Hi Nathan, thanks for this patch.
> >
> > Should this be:
> > $(call cc-disable-warning, pointer-sign)
> > as well?
> >
>
> According to commit 1d6bf3a9a546 ("kbuild: add -Wno-pointer-sign flag
> unconditionally") in -next, all supported compilers recognize the flag
> so I don't think it's necessary.

No problem.
Tested-by: Nick Desaulniers <ndesaulniers@google.com>

>
> > > +                                  $(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
> > >
> >
> >
> > --
> > Thanks,
> > ~Nick Desaulniers
>
> Thanks for the review!
> Nathan

-- 
Thanks,
~Nick Desaulniers