| Message ID | 20221228-drop-qunused-arguments-v1-8-658cbc8fc592@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Remove clang's -Qunused-arguments from KBUILD_CPPFLAGS | expand |
On Wed, Jan 4, 2023 at 11:55 AM Nathan Chancellor <nathan@kernel.org> wrote: > > When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it > warns: > > clang-16: error: argument unused during compilation: '-fno-stack-clash-protection' [-Werror,-Wunused-command-line-argument] > > This flag is supported for 64-bit powerpc but not 32-bit, hence the warning. > Just remove the flag from vgettimeofday-32.o's CFLAGS when using clang, as has > been done for other flags previously. > > Signed-off-by: Nathan Chancellor <nathan@kernel.org> Hmm...so this was added by the top level Makefile doing a cc-option test. How did the test pass if this was unsupported? That worries me that perhaps other cc-option tests are passing erroneously for certain ppc -m32/-m64 configs? > --- > Cc: mpe@ellerman.id.au > Cc: npiggin@gmail.com > Cc: christophe.leroy@csgroup.eu > Cc: linuxppc-dev@lists.ozlabs.org > --- > arch/powerpc/kernel/vdso/Makefile | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile > index 769b62832b38..4ee7d36ce752 100644 > --- a/arch/powerpc/kernel/vdso/Makefile > +++ b/arch/powerpc/kernel/vdso/Makefile > @@ -16,6 +16,11 @@ ifneq ($(c-gettimeofday-y),) > CFLAGS_vgettimeofday-32.o += -ffreestanding -fasynchronous-unwind-tables > CFLAGS_REMOVE_vgettimeofday-32.o = $(CC_FLAGS_FTRACE) > CFLAGS_REMOVE_vgettimeofday-32.o += -mcmodel=medium -mabi=elfv1 -mabi=elfv2 -mcall-aixdesc > + # This flag is supported by clang for 64-bit but not 32-bit so it will cause > + # an unused command line flag warning for this file. > + ifdef CONFIG_CC_IS_CLANG > + CFLAGS_REMOVE_vgettimeofday-32.o += -fno-stack-clash-protection > + endif > CFLAGS_vgettimeofday-64.o += -include $(c-gettimeofday-y) > CFLAGS_vgettimeofday-64.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > CFLAGS_vgettimeofday-64.o += $(call cc-option, -fno-stack-protector) > > -- > 2.39.0
On Mon, Jan 09, 2023 at 02:12:55PM -0800, Nick Desaulniers wrote: > On Wed, Jan 4, 2023 at 11:55 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > > When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it > > warns: > > > > clang-16: error: argument unused during compilation: '-fno-stack-clash-protection' [-Werror,-Wunused-command-line-argument] > > > > This flag is supported for 64-bit powerpc but not 32-bit, hence the warning. > > Just remove the flag from vgettimeofday-32.o's CFLAGS when using clang, as has > > been done for other flags previously. > > > > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > > Hmm...so this was added by the top level Makefile doing a cc-option > test. How did the test pass if this was unsupported? That worries me > that perhaps other cc-option tests are passing erroneously for certain > ppc -m32/-m64 configs? Sure, that is a reasonable concern. I should have expanded upon this a little bit more in the commit message. Is this any better? When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it warns: clang-16: error: argument unused during compilation: '-fno-stack-clash-protection' [-Werror,-Wunused-command-line-argument] This warning happens because vgettimeofday-32.c gets its base CFLAGS from the main kernel, which may contain flags that are only supported on a 64-bit target but not a 32-bit one, which is the case here. -fstack-clash-protection and its negation are only suppported by the 64-bit powerpc target but that flag is included in an invocation for a 32-bit powerpc target, so clang points out that while the flag is one that it recognizes, it is not actually used by this compiler job. To eliminate the warning, remove -fno-stack-clash-protection from vgettimeofday-32.c's CFLAGS when using clang, as has been done for other flags previously. Cheers, Nathan > > --- > > Cc: mpe@ellerman.id.au > > Cc: npiggin@gmail.com > > Cc: christophe.leroy@csgroup.eu > > Cc: linuxppc-dev@lists.ozlabs.org > > --- > > arch/powerpc/kernel/vdso/Makefile | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile > > index 769b62832b38..4ee7d36ce752 100644 > > --- a/arch/powerpc/kernel/vdso/Makefile > > +++ b/arch/powerpc/kernel/vdso/Makefile > > @@ -16,6 +16,11 @@ ifneq ($(c-gettimeofday-y),) > > CFLAGS_vgettimeofday-32.o += -ffreestanding -fasynchronous-unwind-tables > > CFLAGS_REMOVE_vgettimeofday-32.o = $(CC_FLAGS_FTRACE) > > CFLAGS_REMOVE_vgettimeofday-32.o += -mcmodel=medium -mabi=elfv1 -mabi=elfv2 -mcall-aixdesc > > + # This flag is supported by clang for 64-bit but not 32-bit so it will cause > > + # an unused command line flag warning for this file. > > + ifdef CONFIG_CC_IS_CLANG > > + CFLAGS_REMOVE_vgettimeofday-32.o += -fno-stack-clash-protection > > + endif > > CFLAGS_vgettimeofday-64.o += -include $(c-gettimeofday-y) > > CFLAGS_vgettimeofday-64.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > > CFLAGS_vgettimeofday-64.o += $(call cc-option, -fno-stack-protector) > > > > -- > > 2.39.0 > > > > -- > Thanks, > ~Nick Desaulniers
On Mon, Jan 9, 2023 at 2:38 PM Nathan Chancellor <nathan@kernel.org> wrote: > > On Mon, Jan 09, 2023 at 02:12:55PM -0800, Nick Desaulniers wrote: > > On Wed, Jan 4, 2023 at 11:55 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > > > > When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it > > > warns: > > > > > > clang-16: error: argument unused during compilation: '-fno-stack-clash-protection' [-Werror,-Wunused-command-line-argument] > > > > > > This flag is supported for 64-bit powerpc but not 32-bit, hence the warning. > > > Just remove the flag from vgettimeofday-32.o's CFLAGS when using clang, as has > > > been done for other flags previously. > > > > > > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > > > > Hmm...so this was added by the top level Makefile doing a cc-option > > test. How did the test pass if this was unsupported? That worries me > > that perhaps other cc-option tests are passing erroneously for certain > > ppc -m32/-m64 configs? > > Sure, that is a reasonable concern. I should have expanded upon this a > little bit more in the commit message. Is this any better? > > When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it > warns: > > clang-16: error: argument unused during compilation: '-fno-stack-clash-protection' [-Werror,-Wunused-command-line-argument] > > This warning happens because vgettimeofday-32.c gets its base CFLAGS > from the main kernel, which may contain flags that are only supported > on a 64-bit target but not a 32-bit one, which is the case here. > -fstack-clash-protection and its negation are only suppported by the > 64-bit powerpc target but that flag is included in an invocation for a > 32-bit powerpc target, so clang points out that while the flag is one > that it recognizes, it is not actually used by this compiler job. > > To eliminate the warning, remove -fno-stack-clash-protection from > vgettimeofday-32.c's CFLAGS when using clang, as has been done for > other flags previously. Ah, ok that makes more sense. Sorry for my confusion, but if you wouldn't mind adding the additional info in v3 it might help others (or just me!) You may add my RB to such a v3 w/ updated commit message.
diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile index 769b62832b38..4ee7d36ce752 100644 --- a/arch/powerpc/kernel/vdso/Makefile +++ b/arch/powerpc/kernel/vdso/Makefile @@ -16,6 +16,11 @@ ifneq ($(c-gettimeofday-y),) CFLAGS_vgettimeofday-32.o += -ffreestanding -fasynchronous-unwind-tables CFLAGS_REMOVE_vgettimeofday-32.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_vgettimeofday-32.o += -mcmodel=medium -mabi=elfv1 -mabi=elfv2 -mcall-aixdesc + # This flag is supported by clang for 64-bit but not 32-bit so it will cause + # an unused command line flag warning for this file. + ifdef CONFIG_CC_IS_CLANG + CFLAGS_REMOVE_vgettimeofday-32.o += -fno-stack-clash-protection + endif CFLAGS_vgettimeofday-64.o += -include $(c-gettimeofday-y) CFLAGS_vgettimeofday-64.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) CFLAGS_vgettimeofday-64.o += $(call cc-option, -fno-stack-protector)
When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it warns: clang-16: error: argument unused during compilation: '-fno-stack-clash-protection' [-Werror,-Wunused-command-line-argument] This flag is supported for 64-bit powerpc but not 32-bit, hence the warning. Just remove the flag from vgettimeofday-32.o's CFLAGS when using clang, as has been done for other flags previously. Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- Cc: mpe@ellerman.id.au Cc: npiggin@gmail.com Cc: christophe.leroy@csgroup.eu Cc: linuxppc-dev@lists.ozlabs.org --- arch/powerpc/kernel/vdso/Makefile | 5 +++++ 1 file changed, 5 insertions(+)