| Message ID | 20200217211149.44132-1-natechancellor@gmail.com (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | 72cf3b3df423c1bbd8fa1056fed009d3a260f8a9 |
| Delegated to: | Paul Burton |
| Headers | show |
| Series | MIPS: vdso: Wrap -mexplicit-relocs in cc-option | expand |
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) > --
On Tue, Feb 18, 2020 at 10:28:15AM -0800, Nick Desaulniers wrote: > 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> Thank you for double checking and the review! Cheers, Nathan
Hello, Nathan Chancellor 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. Applied to mips-fixes. > commit 72cf3b3df423 > https://git.kernel.org/mips/c/72cf3b3df423 > > 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> Thanks, Paul [ This message was auto-generated; if you believe anything is incorrect then please email paulburton@kernel.org to report it. ]
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)
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> --- arch/mips/vdso/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)