[lkml]   [2019]   [Apr]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 4.4 044/168] 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:
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");
// current AArch32 NEON implementations do not support double-precision
// floating-point even when it is present in VFP.
"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


Suggested-by: Ard Biesheuvel <>
Signed-off-by: Nathan Chancellor <>
Acked-by: Nicolas Pitre <>
Reviewed-by: Nick Desaulniers <>
Reviewed-by: Stefan Agner <>
Signed-off-by: Russell King <>
Signed-off-by: Sasha Levin <>
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
* 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 d8a780799506..06348a3d50c2 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -35,7 +35,7 @@ $(obj)/csumpartialcopy.o: $(obj)/csumpartialcopygeneric.S
$(obj)/csumpartialcopyuser.o: $(obj)/csumpartialcopygeneric.S

- 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
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 @@

#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'

diff --git a/lib/raid6/Makefile b/lib/raid6/Makefile
index 3b10a48fa040..a84efd4aad37 100644
--- a/lib/raid6/Makefile
+++ b/lib/raid6/Makefile
@@ -23,7 +23,7 @@ endif
NEON_FLAGS := -ffreestanding
ifeq ($(ARCH),arm)
-NEON_FLAGS += -mfloat-abi=softfp -mfpu=neon
+NEON_FLAGS += -march=armv7-a -mfloat-abi=softfp -mfpu=neon
ifeq ($(ARCH),arm64)
CFLAGS_REMOVE_neon1.o += -mgeneral-regs-only

 \ /
  Last update: 2019-04-24 20:07    [W:0.643 / U:1.976 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site