On Tue, Aug 3, 2021 at 3:39 AM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > We get constant feedback that the command line invocation of make is too > long when compiling with LLVM. CROSS_COMPILE is helpful when a toolchain > has a prefix of the target triple, or is an absolute path outside of > $PATH. > > Since a Clang binary is generally multi-targeted, we can infer a given > target from SRCARCH/ARCH. If CROSS_COMPILE is not set, simply set > --target= for CLANG_FLAGS, KBUILD_CFLAGS, and KBUILD_AFLAGS based on > $SRCARCH. > > Previously, we'd cross compile via: > $ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make LLVM=1 LLVM_IAS=1 > Now: > $ ARCH=arm64 make LLVM=1 LLVM_IAS=1 > > For native builds (not involving cross compilation) we now explicitly > specify a target triple rather than rely on the implicit host triple. > > Link: https://github.com/ClangBuiltLinux/linux/issues/1399 > Suggested-by: Arnd Bergmann <arnd@xxxxxxxxxx> > Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Suggested-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> > Suggested-by: Nathan Chancellor <nathan@xxxxxxxxxx> > Acked-by: Arnd Bergmann <arnd@xxxxxxxxxx> > Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx> > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > --- > Changes v5 -> v6: > * Use indirection as per Linus. We now have CLANG_TARGET_FLAGS and a > few variables suffixed with $SRCARCH. > * Add Linus' SB tag. > * Change hexagon target triple from -gnu to -musl. > > Changes v3 -> v4: > * Reword commit message and oneline, as per Nathan. > * Drop documentation change (it's the next patch, could be squashed in, > I guess). > * Drop LLVM_IAS=1 requirement, as per Masahiro. > * Carry Arnd's and Nathan's AB/RB/TB tags, confirmed OK on IRC+Discord. > > Changes v2 -> v3: > * Drop check/requirement for LLVM=1, as per Masahiro. > * Change oneliner from LLVM=1 LLVM_IAS=1 to CC=clang LLVM_IAS=1. > * Don't carry forward Nathan's RB/TB tags. :( Sorry Nathan, but thank > you for testing+reviewing v2. > * Update wording of docs slightly. > > Changes v1 -> v2: > * Fix typos in commit message as per Geert and Masahiro. > * Use SRCARCH instead of ARCH, simplifying x86 handling, as per > Masahiro. Add his sugguested by tag. > * change commit oneline from 'drop' to 'infer.' > * Add detail about explicit host --target and relationship of ARCH to > SRCARCH, as per Masahiro. > > Changes RFC -> v1: > * Rebase onto linux-kbuild/for-next > * Keep full target triples since missing the gnueabi suffix messes up > 32b ARM. Drop Fangrui's sugguested by tag. Update commit message to > drop references to arm64. > * Flush out TODOS. > * Add note about -EL/-EB, -m32/-m64. > * Add note to Documentation/. > > scripts/Makefile.clang | 25 +++++++++++++++++++++++-- > 1 file changed, 23 insertions(+), 2 deletions(-) > > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang > index 297932e973d4..1f4e3eb70f88 100644 > --- a/scripts/Makefile.clang > +++ b/scripts/Makefile.clang > @@ -1,6 +1,27 @@ > -ifneq ($(CROSS_COMPILE),) > +# Individual arch/{arch}/Makefiles should use -EL/-EB to set intended > +# endianness and -m32/-m64 to set word size based on Kconfigs instead of > +# relying on the target triple. > +CLANG_TARGET_FLAGS_arm := arm-linux-gnueabi > +CLANG_TARGET_FLAGS_arm64 := aarch64-linux-gnu > +CLANG_TARGET_FLAGS_hexagon := hexagon-linux-musl > +CLANG_TARGET_FLAGS_m68k := m68k-linux-gnu > +CLANG_TARGET_FLAGS_mips := mipsel-linux-gnu > +CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu > +CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu > +CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu > +CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu > +CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH)) > + > +ifeq ($(CROSS_COMPILE),) > +ifeq ($(CLANG_TARGET_FLAGS),) > +$(error Specify CROSS_COMPILE or add '--target=' option to scripts/Makefile.clang) When I was browsing the code, I noticed a nit. I believe non-build targets such as 'make help', 'make clean' etc. should succeed without any correct CROSS_COMPILE set since they do not use the compiler at all. The remaining architectures may fail to clean. $ export LLVM=1 $ make ARCH=csky clean scripts/Makefile.clang:17: *** Specify CROSS_COMPILE or add '--target=' option to scripts/Makefile.clang. Stop. I decided to not be worried about it because it is fixable later. I will pick it up unless a significant issue is found. > +else > +CLANG_FLAGS += --target=$(CLANG_TARGET_FLAGS) > +endif # CLANG_TARGET_FLAGS > +else > CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%)) > -endif > +endif # CROSS_COMPILE > + > ifeq ($(LLVM_IAS),1) > CLANG_FLAGS += -integrated-as > else > -- > 2.32.0.554.ge1b32706d8-goog > -- Best Regards Masahiro Yamada
