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

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Date:   Fri, 12 Oct 2018 18:03:49 -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>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] efi/libstub: Disable some warnings for x86{,_64}

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