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SubjectRe: [PATCH 2/2] MIPS: Loongson64: Wrap -mno-branch-likely with cc-option
On Mon, Jan 24, 2022 at 12:40:58PM -0800, Nick Desaulniers wrote:
> On Thu, Jan 20, 2022 at 1:40 PM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > This flag is not supported by clang, which results in a warning:
> >
> > clang-14: warning: argument unused during compilation: '-mno-branch-likely' [-Wunused-command-line-argument]
> >
> > This breaks cc-option, which adds -Werror to make this warning fatal and
> > catch flags that are not supported. Wrap the flag in cc-option so that
> > it does not cause cc-option to fail, which can cause randconfigs to be
> > really noisy.
> >
> > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>
> We should convert more of these tests to Kconfig checks that run once
> per configuration, rather than multiple times for a build. IIRC Linus
> mentioned this somewhere...yeah, the -Wimplicit-fallthrough patches.
> See
> dee2b702bcf06 ("kconfig: Add support for -Wimplicit-fallthrough")
>
> I wonder if we can check ARCH or SUBARCH in Kconfig to limit invoking
> the tool under test for certain arch specific command line flags?
>
> I'll take this patch over such a larger change, but I think towards
> the goal of speeding up already configured builds, we eventually want
> to be migrating cc-option and ld-option checks to Kconfig.
>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

Something like this appears to work, if that is more preferrable?

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 058446f01487..a27a3ade810e 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -3232,3 +3232,9 @@ endmenu
source "arch/mips/kvm/Kconfig"

source "arch/mips/vdso/Kconfig"
+
+config CC_MNO_BRANCH_LIKELY
+ string
+ default "-mno-branch-likely"
+ depends on MACH_LOONGSON64 || MACH_LOONGSON2EF
+ depends on $(cc-option,-mno-branch-likely)
diff --git a/arch/mips/loongson2ef/Platform b/arch/mips/loongson2ef/Platform
index 50e659aca543..66ed09581417 100644
--- a/arch/mips/loongson2ef/Platform
+++ b/arch/mips/loongson2ef/Platform
@@ -41,6 +41,6 @@ cflags-y += $(call cc-option,-mno-loongson-mmi)
# Loongson Machines' Support
#

-cflags-$(CONFIG_MACH_LOONGSON2EF) += -I$(srctree)/arch/mips/include/asm/mach-loongson2ef -mno-branch-likely
+cflags-$(CONFIG_MACH_LOONGSON2EF) += -I$(srctree)/arch/mips/include/asm/mach-loongson2ef $(CONFIG_CC_MNO_BRANCH_LIKELY)
load-$(CONFIG_LEMOTE_FULOONG2E) += 0xffffffff80100000
load-$(CONFIG_LEMOTE_MACH2F) += 0xffffffff80200000
diff --git a/arch/mips/loongson64/Platform b/arch/mips/loongson64/Platform
index 3e660d6d3c2b..88fbdfe9ffcc 100644
--- a/arch/mips/loongson64/Platform
+++ b/arch/mips/loongson64/Platform
@@ -33,5 +33,5 @@ cflags-y += $(call cc-option,-mno-loongson-mmi)
# Loongson Machines' Support
#

-cflags-$(CONFIG_MACH_LOONGSON64) += -I$(srctree)/arch/mips/include/asm/mach-loongson64 -mno-branch-likely
+cflags-$(CONFIG_MACH_LOONGSON64) += -I$(srctree)/arch/mips/include/asm/mach-loongson64 $(CONFIG_CC_MNO_BRANCH_LIKELY)
load-$(CONFIG_CPU_LOONGSON64) += 0xffffffff80200000
> > ---
> > arch/mips/loongson64/Platform | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/mips/loongson64/Platform b/arch/mips/loongson64/Platform
> > index 981d3abc150e..acf9edc9b15d 100644
> > --- a/arch/mips/loongson64/Platform
> > +++ b/arch/mips/loongson64/Platform
> > @@ -26,5 +26,6 @@ cflags-y += $(call cc-option,-mno-loongson-mmi)
> > # Loongson Machines' Support
> > #
> >
> > -cflags-$(CONFIG_MACH_LOONGSON64) += -I$(srctree)/arch/mips/include/asm/mach-loongson64 -mno-branch-likely
> > +cflags-$(CONFIG_MACH_LOONGSON64) += -I$(srctree)/arch/mips/include/asm/mach-loongson64
> > +cflags-$(CONFIG_MACH_LOONGSON64) += $(call cc-option,-mno-branch-likely)
> > load-$(CONFIG_CPU_LOONGSON64) += 0xffffffff80200000
> > --
> > 2.34.1
> >
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers

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