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    SubjectRe: [PATCH v2 1/2] x86/build: Do not add -falign flags unconditionally for clang
    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

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