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@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: clang-built-linux@googlegroups.com

diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
index 77374c1..d7fe840 100644 (file)
--- 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)