linux-kernel - [PATCH v2] raid6/ppc: Fix build for clang

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Message-Id: <20181102004455.10157-1-joel@jms.id.au>
Date:   Fri,  2 Nov 2018 11:14:55 +1030
From:   Joel Stanley <joel@....id.au>
To:     Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jinsong Ji <jji@...ibm.com>
Subject: [PATCH v2] raid6/ppc: Fix build for clang

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>
---
v2: fix typo in comment, thanks Jinsong

 lib/raid6/Makefile | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/lib/raid6/Makefile b/lib/raid6/Makefile
index 2f8b61dfd9b0..7ed43eaa02ef 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
+# clang ppc port does not yet support -maltivec when -msoft-float is
+# enabled. A future release of clang will resolve this
+# https://bugs.llvm.org/show_bug.cgi?id=31177
+CFLAGS_REMOVE_altivec1.o  += -msoft-float
+CFLAGS_REMOVE_altivec2.o  += -msoft-float
+CFLAGS_REMOVE_altivec4.o  += -msoft-float
+CFLAGS_REMOVE_altivec8.o  += -msoft-float
+CFLAGS_REMOVE_altivec8.o  += -msoft-float
+CFLAGS_REMOVE_vpermxor1.o += -msoft-float
+CFLAGS_REMOVE_vpermxor2.o += -msoft-float
+CFLAGS_REMOVE_vpermxor4.o += -msoft-float
+CFLAGS_REMOVE_vpermxor8.o += -msoft-float
+endif
 endif
 
 # The GCC option -ffreestanding is required in order to compile code containing
-- 
2.19.1