* [PATCH v2 0/2] Harden clang against unknown flag options
@ 2021-09-16 18:40 Nathan Chancellor
2021-09-16 18:40 ` [PATCH v2 1/2] x86/build: Do not add -falign flags unconditionally for clang Nathan Chancellor
2021-09-16 18:40 ` [PATCH v2 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS Nathan Chancellor
0 siblings, 2 replies; 5+ messages in thread
From: Nathan Chancellor @ 2021-09-16 18:40 UTC (permalink / raw)
To: Masahiro Yamada
Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86,
H. Peter Anvin, Nick Desaulniers, linux-kernel, linux-kbuild,
llvm, Nathan Chancellor
Hi all,
This series cleans up an issue that was noticed by the kernel test robot
where flags that clang does not implement support for are
unconditionally added to the command line, which causes all subsequent
calls to cc-{disable-warning,option} to fail, meaning developers are
flooded with unnecessary and pointless warnings.
The first patch handles the problematic flags with cc-option for clang
and the second patch ensures we catch new additions of unknown flags so
that they can be handled properly.
I intend for this to be merged via the kbuild tree but it can go via
-tip if there is any objection to that.
Cheers,
Nathan
v1 -> v2: https://lore.kernel.org/r/20210824022640.2170859-1-nathan@kernel.org/
* Patch 1: Change prefix to "x86/build" (Borislav).
* Patch 1: Add link to v1 thread for more context (Borislav).
* Patch 1: Add Borislav's ack.
* Patch 2: Expand comment in source to make it clear that clang only
warns on certain unimplemented optimization flags.
* Series: Add Nick's review.
Nathan Chancellor (2):
x86/build: Do not add -falign flags unconditionally for clang
kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS
arch/x86/Makefile_32.cpu | 12 +++++++++---
scripts/Makefile.clang | 5 +++++
2 files changed, 14 insertions(+), 3 deletions(-)
base-commit: a9086b878b7fd65894eb8cb1fa395dd469970566
--
2.33.0
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH v2 1/2] x86/build: Do not add -falign flags unconditionally for clang 2021-09-16 18:40 [PATCH v2 0/2] Harden clang against unknown flag options Nathan Chancellor @ 2021-09-16 18:40 ` Nathan Chancellor 2021-09-19 2:01 ` Masahiro Yamada 2021-09-16 18:40 ` [PATCH v2 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS Nathan Chancellor 1 sibling, 1 reply; 5+ messages in thread From: Nathan Chancellor @ 2021-09-16 18:40 UTC (permalink / raw) To: Masahiro Yamada Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86, H. Peter Anvin, Nick Desaulniers, linux-kernel, linux-kbuild, llvm, Nathan Chancellor, kernel test robot, Borislav Petkov clang does not support -falign-jumps and only recently gained support for -falign-loops. When one of the configuration options that adds these flags is enabled, clang warns and all cc-{disable-warning,option} that follow fail because -Werror gets added to test for the presence of this warning: clang-14: warning: optimization flag '-falign-jumps=0' is not supported [-Wignored-optimization-argument] To resolve this, add a couple of cc-option calls when building with clang; gcc has supported these options since 3.2 so there is no point in testing for their support. -falign-functions was implemented in clang-7, -falign-loops was implemented in clang-14, and -falign-jumps has not been implemented yet. Link: https://lore.kernel.org/r/YSQE2f5teuvKLkON@Ryzen-9-3900X.localdomain/ Link: https://lore.kernel.org/r/20210824022640.2170859-2-nathan@kernel.org/ Reported-by: kernel test robot <lkp@intel.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Acked-by: Borislav Petkov <bp@suse.de> Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- arch/x86/Makefile_32.cpu | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/arch/x86/Makefile_32.cpu b/arch/x86/Makefile_32.cpu index e7355f8b51c2..94834c4b5e5e 100644 --- a/arch/x86/Makefile_32.cpu +++ b/arch/x86/Makefile_32.cpu @@ -4,6 +4,12 @@ tune = $(call cc-option,-mtune=$(1),$(2)) +ifdef CONFIG_CC_IS_CLANG +align := -falign-functions=0 $(call cc-option,-falign-jumps=0) $(call cc-option,-falign-loops=0) +else +align := -falign-functions=0 -falign-jumps=0 -falign-loops=0 +endif + cflags-$(CONFIG_M486SX) += -march=i486 cflags-$(CONFIG_M486) += -march=i486 cflags-$(CONFIG_M586) += -march=i586 @@ -19,11 +25,11 @@ cflags-$(CONFIG_MK6) += -march=k6 # They make zero difference whatsosever to performance at this time. cflags-$(CONFIG_MK7) += -march=athlon cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8,-march=athlon) -cflags-$(CONFIG_MCRUSOE) += -march=i686 -falign-functions=0 -falign-jumps=0 -falign-loops=0 -cflags-$(CONFIG_MEFFICEON) += -march=i686 $(call tune,pentium3) -falign-functions=0 -falign-jumps=0 -falign-loops=0 +cflags-$(CONFIG_MCRUSOE) += -march=i686 $(align) +cflags-$(CONFIG_MEFFICEON) += -march=i686 $(call tune,pentium3) $(align) cflags-$(CONFIG_MWINCHIPC6) += $(call cc-option,-march=winchip-c6,-march=i586) cflags-$(CONFIG_MWINCHIP3D) += $(call cc-option,-march=winchip2,-march=i586) -cflags-$(CONFIG_MCYRIXIII) += $(call cc-option,-march=c3,-march=i486) -falign-functions=0 -falign-jumps=0 -falign-loops=0 +cflags-$(CONFIG_MCYRIXIII) += $(call cc-option,-march=c3,-march=i486) $(align) cflags-$(CONFIG_MVIAC3_2) += $(call cc-option,-march=c3-2,-march=i686) cflags-$(CONFIG_MVIAC7) += -march=i686 cflags-$(CONFIG_MCORE2) += -march=i686 $(call tune,core2) base-commit: a9086b878b7fd65894eb8cb1fa395dd469970566 -- 2.33.0 ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2 1/2] x86/build: Do not add -falign flags unconditionally for clang 2021-09-16 18:40 ` [PATCH v2 1/2] x86/build: Do not add -falign flags unconditionally for clang Nathan Chancellor @ 2021-09-19 2:01 ` Masahiro Yamada 0 siblings, 0 replies; 5+ messages in thread From: Masahiro Yamada @ 2021-09-19 2:01 UTC (permalink / raw) To: Nathan Chancellor Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, X86 ML, H. Peter Anvin, Nick Desaulniers, Linux Kernel Mailing List, Linux Kbuild mailing list, llvm, kernel test robot, Borislav Petkov On Fri, Sep 17, 2021 at 3:42 AM Nathan Chancellor <nathan@kernel.org> wrote: > > clang does not support -falign-jumps and only recently gained support > for -falign-loops. When one of the configuration options that adds these > flags is enabled, clang warns and all cc-{disable-warning,option} that > follow fail because -Werror gets added to test for the presence of this > warning: > > clang-14: warning: optimization flag '-falign-jumps=0' is not supported > [-Wignored-optimization-argument] > > To resolve this, add a couple of cc-option calls when building with > clang; gcc has supported these options since 3.2 so there is no point in > testing for their support. -falign-functions was implemented in clang-7, > -falign-loops was implemented in clang-14, and -falign-jumps has not > been implemented yet. > > Link: https://lore.kernel.org/r/YSQE2f5teuvKLkON@Ryzen-9-3900X.localdomain/ > Link: https://lore.kernel.org/r/20210824022640.2170859-2-nathan@kernel.org/ > Reported-by: kernel test robot <lkp@intel.com> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > Acked-by: Borislav Petkov <bp@suse.de> > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > --- > arch/x86/Makefile_32.cpu | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/Makefile_32.cpu b/arch/x86/Makefile_32.cpu > index e7355f8b51c2..94834c4b5e5e 100644 > --- a/arch/x86/Makefile_32.cpu > +++ b/arch/x86/Makefile_32.cpu > @@ -4,6 +4,12 @@ > > tune = $(call cc-option,-mtune=$(1),$(2)) > > +ifdef CONFIG_CC_IS_CLANG > +align := -falign-functions=0 $(call cc-option,-falign-jumps=0) $(call cc-option,-falign-loops=0) > +else > +align := -falign-functions=0 -falign-jumps=0 -falign-loops=0 > +endif > + > cflags-$(CONFIG_M486SX) += -march=i486 > cflags-$(CONFIG_M486) += -march=i486 > cflags-$(CONFIG_M586) += -march=i586 > @@ -19,11 +25,11 @@ cflags-$(CONFIG_MK6) += -march=k6 > # They make zero difference whatsosever to performance at this time. > cflags-$(CONFIG_MK7) += -march=athlon > cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8,-march=athlon) > -cflags-$(CONFIG_MCRUSOE) += -march=i686 -falign-functions=0 -falign-jumps=0 -falign-loops=0 > -cflags-$(CONFIG_MEFFICEON) += -march=i686 $(call tune,pentium3) -falign-functions=0 -falign-jumps=0 -falign-loops=0 > +cflags-$(CONFIG_MCRUSOE) += -march=i686 $(align) > +cflags-$(CONFIG_MEFFICEON) += -march=i686 $(call tune,pentium3) $(align) > cflags-$(CONFIG_MWINCHIPC6) += $(call cc-option,-march=winchip-c6,-march=i586) > cflags-$(CONFIG_MWINCHIP3D) += $(call cc-option,-march=winchip2,-march=i586) > -cflags-$(CONFIG_MCYRIXIII) += $(call cc-option,-march=c3,-march=i486) -falign-functions=0 -falign-jumps=0 -falign-loops=0 > +cflags-$(CONFIG_MCYRIXIII) += $(call cc-option,-march=c3,-march=i486) $(align) > cflags-$(CONFIG_MVIAC3_2) += $(call cc-option,-march=c3-2,-march=i686) > cflags-$(CONFIG_MVIAC7) += -march=i686 > cflags-$(CONFIG_MCORE2) += -march=i686 $(call tune,core2) > > base-commit: a9086b878b7fd65894eb8cb1fa395dd469970566 > -- > 2.33.0 > Applied to linux-kbuild. Thanks. -- Best Regards Masahiro Yamada ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v2 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS 2021-09-16 18:40 [PATCH v2 0/2] Harden clang against unknown flag options Nathan Chancellor 2021-09-16 18:40 ` [PATCH v2 1/2] x86/build: Do not add -falign flags unconditionally for clang Nathan Chancellor @ 2021-09-16 18:40 ` Nathan Chancellor 2021-09-19 2:01 ` Masahiro Yamada 1 sibling, 1 reply; 5+ messages in thread From: Nathan Chancellor @ 2021-09-16 18:40 UTC (permalink / raw) To: Masahiro Yamada Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86, H. Peter Anvin, Nick Desaulniers, linux-kernel, linux-kbuild, llvm, Nathan Chancellor Similar to commit 589834b3a009 ("kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS"). Clang ignores certain GCC flags that it has not implemented, only emitting a warning: $ echo | clang -fsyntax-only -falign-jumps -x c - clang-14: warning: optimization flag '-falign-jumps' is not supported [-Wignored-optimization-argument] When one of these flags gets added to KBUILD_CFLAGS unconditionally, all subsequent cc-{disable-warning,option} calls fail because -Werror was added to these invocations to turn the above warning and the equivalent -W flag warning into errors. To catch the presence of these flags earlier, turn -Wignored-optimization-argument into an error so that the flags can either be implemented or ignored via cc-option and there are no more weird errors. Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- scripts/Makefile.clang | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang index 4cce8fd0779c..51fc23e2e9e5 100644 --- a/scripts/Makefile.clang +++ b/scripts/Makefile.clang @@ -29,7 +29,12 @@ CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE)) else CLANG_FLAGS += -fintegrated-as endif +# By default, clang only warns when it encounters an unknown warning flag or +# certain optimization flags it knows it has not implemented. +# Make it behave more like gcc by erroring when these flags are encountered +# so they can be implemented or wrapped in cc-option. CLANG_FLAGS += -Werror=unknown-warning-option +CLANG_FLAGS += -Werror=ignored-optimization-argument KBUILD_CFLAGS += $(CLANG_FLAGS) KBUILD_AFLAGS += $(CLANG_FLAGS) export CLANG_FLAGS -- 2.33.0 ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS 2021-09-16 18:40 ` [PATCH v2 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS Nathan Chancellor @ 2021-09-19 2:01 ` Masahiro Yamada 0 siblings, 0 replies; 5+ messages in thread From: Masahiro Yamada @ 2021-09-19 2:01 UTC (permalink / raw) To: Nathan Chancellor Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, X86 ML, H. Peter Anvin, Nick Desaulniers, Linux Kernel Mailing List, Linux Kbuild mailing list, llvm On Fri, Sep 17, 2021 at 3:42 AM Nathan Chancellor <nathan@kernel.org> wrote: > > Similar to commit 589834b3a009 ("kbuild: Add > -Werror=unknown-warning-option to CLANG_FLAGS"). > > Clang ignores certain GCC flags that it has not implemented, only > emitting a warning: > > $ echo | clang -fsyntax-only -falign-jumps -x c - > clang-14: warning: optimization flag '-falign-jumps' is not supported > [-Wignored-optimization-argument] > > When one of these flags gets added to KBUILD_CFLAGS unconditionally, all > subsequent cc-{disable-warning,option} calls fail because -Werror was > added to these invocations to turn the above warning and the equivalent > -W flag warning into errors. > > To catch the presence of these flags earlier, turn > -Wignored-optimization-argument into an error so that the flags can > either be implemented or ignored via cc-option and there are no more > weird errors. > > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > --- Applied to linux-kbuild. Thanks. > scripts/Makefile.clang | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang > index 4cce8fd0779c..51fc23e2e9e5 100644 > --- a/scripts/Makefile.clang > +++ b/scripts/Makefile.clang > @@ -29,7 +29,12 @@ CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE)) > else > CLANG_FLAGS += -fintegrated-as > endif > +# By default, clang only warns when it encounters an unknown warning flag or > +# certain optimization flags it knows it has not implemented. > +# Make it behave more like gcc by erroring when these flags are encountered > +# so they can be implemented or wrapped in cc-option. > CLANG_FLAGS += -Werror=unknown-warning-option > +CLANG_FLAGS += -Werror=ignored-optimization-argument > KBUILD_CFLAGS += $(CLANG_FLAGS) > KBUILD_AFLAGS += $(CLANG_FLAGS) > export CLANG_FLAGS > -- > 2.33.0 > -- Best Regards Masahiro Yamada ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-09-19 2:03 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-09-16 18:40 [PATCH v2 0/2] Harden clang against unknown flag options Nathan Chancellor 2021-09-16 18:40 ` [PATCH v2 1/2] x86/build: Do not add -falign flags unconditionally for clang Nathan Chancellor 2021-09-19 2:01 ` Masahiro Yamada 2021-09-16 18:40 ` [PATCH v2 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS Nathan Chancellor 2021-09-19 2:01 ` Masahiro Yamada
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