[ 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@linaro.org Signed-off-by: Nathan Chancellor natechancellor@gmail.com Acked-by: Nicolas Pitre nico@linaro.org Reviewed-by: Nick Desaulniers ndesaulniers@google.com Reviewed-by: Stefan Agner stefan@agner.ch Signed-off-by: Russell King rmk+kernel@armlinux.org.uk Signed-off-by: Sasha Levin sashal@kernel.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 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: $(obj)/csumpartialcopygeneric.S
ifeq ($(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 3b10a48fa040..a84efd4aad37 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