linux-kernel - Re: [PATCH] raid6/ppc: Fix build for clang

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Message-ID: <87y3ad76pg.fsf@concordia.ellerman.id.au>
Date:   Thu, 01 Nov 2018 15:38:35 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Nick Desaulniers <ndesaulniers@...gle.com>, joel@....id.au
Cc:     LKML <linux-kernel@...r.kernel.org>, linuxppc-dev@...ts.ozlabs.org,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>, jji@...ibm.com
Subject: Re: [PATCH] raid6/ppc: Fix build for clang

Nick Desaulniers <ndesaulniers@...gle.com> writes:
> On Tue, Oct 30, 2018 at 8:28 PM Joel Stanley <joel@....id.au> wrote:
>>
>> We cannot build these files with clang as it does not allow altivec
>> instructions in assembly when -msoft-float is passed.
>>
>> Jinsong Ji <jji@...ibm.com> wrote:
>> > We currently disable Altivec/VSX support when enabling soft-float.  So
>> > any usage of vector builtins will break.
>> >
>> > Enable Altivec/VSX with soft-float may need quite some clean up work, so
>> > I guess this is currently a limitation.
>> >
>> > Removing -msoft-float will make it work (and we are lucky that no
>> > floating point instructions will be generated as well).
>>
>> This is a workaround until the issue is resolved in clang.
>>
>> Link: https://bugs.llvm.org/show_bug.cgi?id=31177
>> Link: https://github.com/ClangBuiltLinux/linux/issues/239
>> Signed-off-by: Joel Stanley <joel@....id.au>
>
> Hopefully we can have this fixed up soon.  I'll try to see who works
> on Clang+PPC here and see if they can help move that bug along. Thanks
> for the patch!
>
>> ---
>>  lib/raid6/Makefile | 15 +++++++++++++++
>>  1 file changed, 15 insertions(+)
>>
>> diff --git a/lib/raid6/Makefile b/lib/raid6/Makefile
>> index 2f8b61dfd9b0..3a844e6fd01c 100644
>> --- a/lib/raid6/Makefile
>> +++ b/lib/raid6/Makefile
>> @@ -18,6 +18,21 @@ quiet_cmd_unroll = UNROLL  $@
>>
>>  ifeq ($(CONFIG_ALTIVEC),y)
>>  altivec_flags := -maltivec $(call cc-option,-mabi=altivec)
>> +
>> +ifdef CONFIG_CC_IS_CLANG
>
> Note that the top level makefile detects clang via:
>
> ifeq ($(cc-name),clang)
>
> Does that not work here? I'd prefer to keep compiler detection in
> Makefiles consistent, if it works?

cc-name is being removed in favor of CONFIG_CC_IS_CLANG:

https://lore.kernel.org/lkml/1540905994-6073-1-git-send-email-yamada.masahiro@socionext.com/

cheers