linux-kernel - [PATCH] MIPS: vdso: Wrap -mexplicit-relocs in cc-option

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Date:   Mon, 17 Feb 2020 14:11:49 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Ralf Baechle <ralf@...ux-mips.org>
Cc:     Paul Burton <paulburton@...nel.org>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] MIPS: vdso: Wrap -mexplicit-relocs in cc-option

Clang does not support this option and errors out:

clang-11: error: unknown argument: '-mexplicit-relocs'

Clang does not appear to need this flag like GCC does because the jalr
check that was added in commit 976c23af3ee5 ("mips: vdso: add build
time check that no 'jalr t9' calls left") passes just fine with

$ make ARCH=mips CC=clang CROSS_COMPILE=mipsel-linux-gnu- malta_defconfig arch/mips/vdso/

even before commit d3f703c4359f ("mips: vdso: fix 'jalr t9' crash in
vdso code").

-mrelax-pic-calls has been supported since clang 9, which is the
earliest version that could build a working MIPS kernel, and it is the
default for clang so just leave it be.

Fixes: d3f703c4359f ("mips: vdso: fix 'jalr t9' crash in vdso code")
Link: https://github.com/ClangBuiltLinux/linux/issues/890
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---
 arch/mips/vdso/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
index 77374c1f0c77..d7fe8408603e 100644
--- a/arch/mips/vdso/Makefile
+++ b/arch/mips/vdso/Makefile
@@ -33,7 +33,7 @@ endif
 cflags-vdso := $(ccflags-vdso) \
 	$(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \
 	-O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
-	-mrelax-pic-calls -mexplicit-relocs \
+	-mrelax-pic-calls $(call cc-option, -mexplicit-relocs) \
 	-fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
 	$(call cc-option, -fno-asynchronous-unwind-tables) \
 	$(call cc-option, -fno-stack-protector)
-- 
2.25.1