Messages in this thread Patch in this message | | | From | Nick Desaulniers <> | Date | Tue, 18 Feb 2020 10:28:15 -0800 | Subject | Re: [PATCH] MIPS: vdso: Wrap -mexplicit-relocs in cc-option |
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On Mon, Feb 17, 2020 at 1:11 PM Nathan Chancellor <natechancellor@gmail.com> wrote: > > 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>
Thanks for the patch, and detailed context. Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
With this patch applied: $ make ARCH=mips CC=clang CROSS_COMPILE=mipsel-linux-gnu- malta_defconfig arch/mips/vdso/ $ lvm-objdump --disassemble arch/mips/vdso/vdso.so.dbg.raw | egrep -h "jarl.*t9" $ llvm-objdump --disassemble arch/mips/vdso/vdso.so.dbg.raw | grep jarl So jarl instructions aren't emitted.
Tested-by: Nick Desaulniers <ndesaulniers@google.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) > --
-- Thanks, ~Nick Desaulniers
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