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Message-Id: <20190424170854.213828097@linuxfoundation.org>
Date: Wed, 24 Apr 2019 19:08:40 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Nathan Chancellor <natechancellor@...il.com>,
Nicolas Pitre <nico@...aro.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Stefan Agner <stefan@...er.ch>,
Russell King <rmk+kernel@...linux.org.uk>,
Sasha Levin <sashal@...nel.org>
Subject: [PATCH 3.18 023/104] ARM: 8833/1: Ensure that NEON code always compiles with Clang
[ Upstream commit de9c0d49d85dc563549972edc5589d195cd5e859 ]
While building arm32 allyesconfig, I ran into the following errors:
arch/arm/lib/xor-neon.c:17:2: error: You should compile this file with
'-mfloat-abi=softfp -mfpu=neon'
In file included from lib/raid6/neon1.c:27:
/home/nathan/cbl/prebuilt/lib/clang/8.0.0/include/arm_neon.h:28:2:
error: "NEON support not enabled"
Building V=1 showed NEON_FLAGS getting passed along to Clang but
__ARM_NEON__ was not getting defined. Ultimately, it boils down to Clang
only defining __ARM_NEON__ when targeting armv7, rather than armv6k,
which is the '-march' value for allyesconfig.
>>From lib/Basic/Targets/ARM.cpp in the Clang source:
// This only gets set when Neon instructions are actually available, unlike
// the VFP define, hence the soft float and arch check. This is subtly
// different from gcc, we follow the intent which was that it should be set
// when Neon instructions are actually available.
if ((FPU & NeonFPU) && !SoftFloat && ArchVersion >= 7) {
Builder.defineMacro("__ARM_NEON", "1");
Builder.defineMacro("__ARM_NEON__");
// current AArch32 NEON implementations do not support double-precision
// floating-point even when it is present in VFP.
Builder.defineMacro("__ARM_NEON_FP",
"0x" + Twine::utohexstr(HW_FP & ~HW_FP_DP));
}
Ard Biesheuvel recommended explicitly adding '-march=armv7-a' at the
beginning of the NEON_FLAGS definitions so that __ARM_NEON__ always gets
definined by Clang. This doesn't functionally change anything because
that code will only run where NEON is supported, which is implicitly
armv7.
Link: https://github.com/ClangBuiltLinux/linux/issues/287
Suggested-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
Acked-by: Nicolas Pitre <nico@...aro.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Reviewed-by: Stefan Agner <stefan@...er.ch>
Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
Documentation/arm/kernel_mode_neon.txt | 4 ++--
arch/arm/lib/Makefile | 2 +-
arch/arm/lib/xor-neon.c | 2 +-
lib/raid6/Makefile | 2 +-
4 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/Documentation/arm/kernel_mode_neon.txt b/Documentation/arm/kernel_mode_neon.txt
index 525452726d31..b9e060c5b61e 100644
--- a/Documentation/arm/kernel_mode_neon.txt
+++ b/Documentation/arm/kernel_mode_neon.txt
@@ -6,7 +6,7 @@ TL;DR summary
* Use only NEON instructions, or VFP instructions that don't rely on support
code
* Isolate your NEON code in a separate compilation unit, and compile it with
- '-mfpu=neon -mfloat-abi=softfp'
+ '-march=armv7-a -mfpu=neon -mfloat-abi=softfp'
* Put kernel_neon_begin() and kernel_neon_end() calls around the calls into your
NEON code
* Don't sleep in your NEON code, and be aware that it will be executed with
@@ -87,7 +87,7 @@ instructions appearing in unexpected places if no special care is taken.
Therefore, the recommended and only supported way of using NEON/VFP in the
kernel is by adhering to the following rules:
* isolate the NEON code in a separate compilation unit and compile it with
- '-mfpu=neon -mfloat-abi=softfp';
+ '-march=armv7-a -mfpu=neon -mfloat-abi=softfp';
* issue the calls to kernel_neon_begin(), kernel_neon_end() as well as the calls
into the unit containing the NEON code from a compilation unit which is *not*
built with the GCC flag '-mfpu=neon' set.
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 0573faab96ad..830b2ddcc346 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -46,7 +46,7 @@ $(obj)/csumpartialcopy.o: $(obj)/csumpartialcopygeneric.S
$(obj)/csumpartialcopyuser.o: $(obj)/csumpartialcopygeneric.S
ifeq ($(CONFIG_KERNEL_MODE_NEON),y)
- NEON_FLAGS := -mfloat-abi=softfp -mfpu=neon
+ NEON_FLAGS := -march=armv7-a -mfloat-abi=softfp -mfpu=neon
CFLAGS_xor-neon.o += $(NEON_FLAGS)
obj-$(CONFIG_XOR_BLOCKS) += xor-neon.o
endif
diff --git a/arch/arm/lib/xor-neon.c b/arch/arm/lib/xor-neon.c
index 2c40aeab3eaa..c691b901092f 100644
--- a/arch/arm/lib/xor-neon.c
+++ b/arch/arm/lib/xor-neon.c
@@ -14,7 +14,7 @@
MODULE_LICENSE("GPL");
#ifndef __ARM_NEON__
-#error You should compile this file with '-mfloat-abi=softfp -mfpu=neon'
+#error You should compile this file with '-march=armv7-a -mfloat-abi=softfp -mfpu=neon'
#endif
/*
diff --git a/lib/raid6/Makefile b/lib/raid6/Makefile
index c7dab0645554..1c3330dc5eab 100644
--- a/lib/raid6/Makefile
+++ b/lib/raid6/Makefile
@@ -23,7 +23,7 @@ endif
ifeq ($(CONFIG_KERNEL_MODE_NEON),y)
NEON_FLAGS := -ffreestanding
ifeq ($(ARCH),arm)
-NEON_FLAGS += -mfloat-abi=softfp -mfpu=neon
+NEON_FLAGS += -march=armv7-a -mfloat-abi=softfp -mfpu=neon
endif
ifeq ($(ARCH),arm64)
CFLAGS_REMOVE_neon1.o += -mgeneral-regs-only
--
2.19.1
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