Re: [PATCH] x86/raid6: correctly check for assembler capabilities

NeilBrown
2015-02-03T20:50:50Z

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On Tue, 03 Feb 2015 21:31:30 +0100 Paul Bolle <pebolle@tiscali.nl> wrote:

> On Fri, 2015-01-23 at 08:29 +0000, Jan Beulich wrote:
> > Just like for AVX2 (which simply needs an #if -> #ifdef conversion),
> > SSSE3 assembler support should be checked for before using it.
> >
> > Signed-off-by: Jan Beulich <jbeulich@suse.com>
> > Cc: Jim Kukunas <james.t.kukunas@linux.intel.com>
> > Cc: Neil Brown <neilb@suse.de>
>
> This patch became commit be46ac86a81b ("x86/raid6: correctly check for
> assembler capabilities") in today's linux-next (ie, next-20150203). I
> noticed because a script I use to check linux-next spotted a potential
> problem with it.
>
> > ---
> > arch/x86/Makefile | 1 +
> > lib/raid6/algos.c | 2 +-
> > lib/raid6/recov_avx2.c | 2 +-
> > lib/raid6/recov_ssse3.c | 6 ++++++
> > 4 files changed, 9 insertions(+), 2 deletions(-)
> >
> > --- 3.19-rc5/arch/x86/Makefile
> > +++ 3.19-rc5-raid6-SSSE3/arch/x86/Makefile
> > @@ -148,6 +148,7 @@ cfi-sections := $(call as-instr,.cfi_sec
> >
> > # does binutils support specific instructions?
> > asinstr := $(call as-instr,fxsaveq (%rax),-DCONFIG_AS_FXSAVEQ=1)
> > +asinstr += $(call as-instr,pshufb %xmm0$(comma)%xmm0,-DCONFIG_AS_SSSE3=1)
>
> This Makefile defines a preprocessor macro with a CONFIG_ prefix. Almost
> all macros with that prefix are defined through the kconfig system. A
> handful, like CONFIG_AS_SSSE3 and a few other macros defined in this
> Makefile, are not. Apparently this is a pet peeve I share with few
> people, but would any other prefix than CONFIG_ work for you too?

Actually the prefix of this macro is "CONFIG_AS_", not "CONFIG_" :-)
CONFIG_AS_ is reserved for assembly magic, and is never used by the the
kconfig system.

(Well..... I might have made bits of that up, but "git grep 'config AS_'"
doesn't find anything).

NeilBrown

>
> > asinstr += $(call as-instr,crc32l %eax$(comma)%eax,-DCONFIG_AS_CRC32=1)
> > avx_instr := $(call as-instr,vxorps %ymm0$(comma)%ymm1$(comma)%ymm2,-DCONFIG_AS_AVX=1)
> > avx2_instr :=$(call as-instr,vpbroadcastb %xmm0$(comma)%ymm1,-DCONFIG_AS_AVX2=1)
>
>
> Paul Bolle

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