Messages in this thread | | | Date | Wed, 12 Jun 2019 10:25:20 +0100 | From | Dave Martin <> | Subject | Re: [PATCH v2] arm64: Don't unconditionally add -Wno-psabi to KBUILD_CFLAGS |
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On Tue, Jun 11, 2019 at 10:19:32AM -0700, Nathan Chancellor wrote: > This is a GCC only option, which warns about ABI changes within GCC, so > unconditionally adding it breaks Clang with tons of: > > warning: unknown warning option '-Wno-psabi' [-Wunknown-warning-option] > > and link time failures: > > ld.lld: error: undefined symbol: __efistub___stack_chk_guard > >>> referenced by arm-stub.c:73 > (/home/nathan/cbl/linux/drivers/firmware/efi/libstub/arm-stub.c:73) > >>> arm-stub.stub.o:(__efistub_install_memreserve_table) > in archive ./drivers/firmware/efi/libstub/lib.a > > These failures come from the lack of -fno-stack-protector, which is > added via cc-option in drivers/firmware/efi/libstub/Makefile. When an > unknown flag is added to KBUILD_CFLAGS, clang will noisily warn that it > is ignoring the option like above, unlike gcc, who will just error. > > $ echo "int main() { return 0; }" > tmp.c > > $ clang -Wno-psabi tmp.c; echo $? > warning: unknown warning option '-Wno-psabi' [-Wunknown-warning-option] > 1 warning generated. > 0 > > $ gcc -Wsometimes-uninitialized tmp.c; echo $? > gcc: error: unrecognized command line option > ‘-Wsometimes-uninitialized’; did you mean ‘-Wmaybe-uninitialized’? > 1 > > For cc-option to work properly with clang and behave like gcc, -Werror > is needed, which was done in commit c3f0d0bc5b01 ("kbuild, LLVMLinux: > Add -Werror to cc-option to support clang"). > > $ clang -Werror -Wno-psabi tmp.c; echo $? > error: unknown warning option '-Wno-psabi' > [-Werror,-Wunknown-warning-option] > 1 > > As a consequence of this, when an unknown flag is unconditionally added > to KBUILD_CFLAGS, it will cause cc-option to always fail and those flags > will never get added: > > $ clang -Werror -Wno-psabi -fno-stack-protector tmp.c; echo $? > error: unknown warning option '-Wno-psabi' > [-Werror,-Wunknown-warning-option] > 1 > > This can be seen when compiling the whole kernel as some warnings that > are normally disabled (see below) show up. The full list of flags > missing from drivers/firmware/efi/libstub are the following (gathered > from diffing .arm64-stub.o.cmd): > > -fno-delete-null-pointer-checks > -Wno-address-of-packed-member > -Wframe-larger-than=2048 > -Wno-unused-const-variable > -fno-strict-overflow > -fno-merge-all-constants > -fno-stack-check > -Werror=date-time > -Werror=incompatible-pointer-types > -ffreestanding > -fno-stack-protector > > Use cc-disable-warning so that it gets disabled for GCC and does nothing > for Clang. > > Fixes: ebcc5928c5d9 ("arm64: Silence gcc warnings about arch ABI drift") > Link: https://github.com/ClangBuiltLinux/linux/issues/511 > Reported-by: Qian Cai <cai@lca.pw> > Acked-by: Dave Martin <Dave.Martin@arm.com> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > --- > > v1 -> v2: > > * Improve commit message explanation, I wasn't entirely happy with the > first one; let me know if there are any issues/questions. > > * Carry forward Dave's ack and Nick's review (let me know if you > disagree with the commit messasge rewording). > > arch/arm64/Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index 8fbd583b18e1..e9d2e578cbe6 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -51,7 +51,7 @@ endif > > KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) $(brokengasinst) > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > -KBUILD_CFLAGS += -Wno-psabi > +KBUILD_CFLAGS += $(call cc-disable-warning, psabi) > KBUILD_AFLAGS += $(lseinstr) $(brokengasinst) > > KBUILD_CFLAGS += $(call cc-option,-mabi=lp64)
Looks OK to me. Thanks for the additional explanation.
Cheers ---Dave
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