| Message ID | 20190126040111.9013-1-natechancellor@gmail.com (mailing list archive) |
|---|---|
| State | Mainlined, archived |
| Commit | de9c0d49d85dc563549972edc5589d195cd5e859 |
| Headers | show |
| Series | [RESEND] ARM: Ensure that NEON code always compiles with Clang | expand |
On 26.01.2019 05:01, Nathan Chancellor wrote: > 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> > --- > > Resending with Nicolas's ack and Nick's review, to give others a chance > to pitch in with review/testing before submitting it to the patch > system (specifically Stefan, sorry I should have included you in the > previous posting). No worries. Looks good to me. Reviewed-by: Stefan Agner <stefan@agner.ch> -- Stefan > > With this patch and: > * A tip of tree LLVM build (I used apt.llvm.org) > * Clang GCOV support: > https://lore.kernel.org/lkml/20190122233749.42220-1-trong@android.com/ > * Two minor hacks for unrelated issues that are still being worked through: > * > https://raw.githubusercontent.com/nathanchance/patches/c313b2fa0efb/linux/build-hax/0003-DO-NOT-UPSTREAM-ARM-Don-t-select-HAVE_FUNCTION_TRACE.patch > (see https://github.com/ClangBuiltLinux/linux/issues/35) > * > https://gist.githubusercontent.com/nathanchance/b2f5a4015abade1a41e78d5fc3235c5b/raw/744321882ab05511331f26896bad7c9f0056a6a5/gistfile1.txt > (see https://github.com/ClangBuiltLinux/linux/issues/325) > > I can build and link a little endian allyesconfig ARM kernel. This > patch alone works with GCC 8.2.0 and binutils 2.31.1. > > 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 ad25fd1872c7..0bff0176db2c 100644 > --- a/arch/arm/lib/Makefile > +++ b/arch/arm/lib/Makefile > @@ -39,7 +39,7 @@ $(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 4e90d443d1b0..e723eacf7868 100644 > --- a/lib/raid6/Makefile > +++ b/lib/raid6/Makefile > @@ -39,7 +39,7 @@ 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 > CFLAGS_recov_neon_inner.o += $(NEON_FLAGS) > ifeq ($(ARCH),arm64)
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 ad25fd1872c7..0bff0176db2c 100644 --- a/arch/arm/lib/Makefile +++ b/arch/arm/lib/Makefile @@ -39,7 +39,7 @@ $(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 4e90d443d1b0..e723eacf7868 100644 --- a/lib/raid6/Makefile +++ b/lib/raid6/Makefile @@ -39,7 +39,7 @@ 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 CFLAGS_recov_neon_inner.o += $(NEON_FLAGS) ifeq ($(ARCH),arm64)