On Fri, Aug 06, 2021 at 10:27:01AM -0700, Nick Desaulniers wrote: > LLVM_IAS=1 controls enabling clang's integrated assembler via > -integrated-as. This was an explicit opt in until we could enable > assembler support in Clang for more architecures. Now we have support > and CI coverage of LLVM_IAS=1 for all architecures except a few more > bugs affecting s390 and powerpc.
The powerpc and s390 folks have been testing with clang, I think they should have been on CC for this change (done now). > This commit flips the default from opt in via LLVM_IAS=1 to opt out via > LLVM_IAS=0. CI systems or developers that were previously doing builds > with CC=clang or LLVM=1 without explicitly setting LLVM_IAS must now > explicitly opt out via LLVM_IAS=0, otherwise they will be implicitly > opted-in. > > This finally shortens the command line invocation when cross compiling > with LLVM to simply: > > $ make ARCH=arm64 LLVM=1 > > Signed-off-by: Nick Desaulniers <ndesaulni...@google.com> I am still not really sure how I feel about this. I would prefer not to break people's builds but I suppose this is inevitabile eventually. A little support matrix that I drafted up where based on ARCH and clang version for LLVM_IAS=1 support: | 10.x | 11.x | 12.x | 13.x | 14.x | ARCH=arm | NO | NO | NO | YES | YES | ARCH=arm64 | NO | YES | YES | YES | YES | ARCH=i386 | YES | YES | YES | YES | YES | ARCH=mips* | YES | YES | YES | YES | YES | ARCH=powerpc | NO | NO | NO | NO | NO | ARCH=s390 | NO | NO | NO | NO | NO | ARCH=x86_64 | NO | YES | YES | YES | YES | The main issue that I have with this change is that all of these architectures work fine with CC=clang and their build commands that used to work fine will not with this change, as they will have to specify LLVM_IAS=0. I think that making this change for LLVM=1 makes sense but changing the default for just CC=clang feels like a bit much at this point in time. I would love to hear from others on this though, I am not going to object much further than this. Regardless of that concern, this patch does what it says so: Reviewed-by: Nathan Chancellor <nat...@kernel.org> > --- > Changes v1 -> v2: > * Drop "Currently" from Documentation/, as per Matthew. > * Drop Makefile and riscv Makefile, rebase on > https://lore.kernel.org/lkml/20210805150102.131008-1-masahi...@kernel.org/ > as per Masahiro. > * Base is kbuild/for-next, plus > > https://lore.kernel.org/lkml/20210802183910.1802120-1-ndesaulni...@google.com/ > https://lore.kernel.org/lkml/20210805150102.131008-1-masahi...@kernel.org/. > > Documentation/kbuild/llvm.rst | 14 ++++++++------ > scripts/Makefile.clang | 6 +++--- > 2 files changed, 11 insertions(+), 9 deletions(-) > > diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst > index f8a360958f4c..e87ed5479963 100644 > --- a/Documentation/kbuild/llvm.rst > +++ b/Documentation/kbuild/llvm.rst > @@ -60,17 +60,14 @@ They can be enabled individually. The full list of the > parameters: :: > OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf \ > HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar HOSTLD=ld.lld > > -Currently, the integrated assembler is disabled by default. You can pass > -``LLVM_IAS=1`` to enable it. > +The integrated assembler is enabled by default. You can pass ``LLVM_IAS=0`` > to > +disable it. > > Omitting CROSS_COMPILE > ---------------------- > > As explained above, ``CROSS_COMPILE`` is used to set ``--target=<triple>``. > > -Unless ``LLVM_IAS=1`` is specified, ``CROSS_COMPILE`` is also used to derive > -``--prefix=<path>`` to search for the GNU assembler and linker. > - > If ``CROSS_COMPILE`` is not specified, the ``--target=<triple>`` is inferred > from ``ARCH``. > > @@ -78,7 +75,12 @@ That means if you use only LLVM tools, ``CROSS_COMPILE`` > becomes unnecessary. > > For example, to cross-compile the arm64 kernel:: > > - make ARCH=arm64 LLVM=1 LLVM_IAS=1 > + make ARCH=arm64 LLVM=1 > + > +If ``LLVM_IAS=0`` is specified, ``CROSS_COMPILE`` is also used to derive > +``--prefix=<path>`` to search for the GNU assembler and linker. :: > + > + make ARCH=arm64 LLVM=1 LLVM_IAS=0 CROSS_COMPILE=aarch64-linux-gnu- > > Supported Architectures > ----------------------- > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang > index 1f4e3eb70f88..3ae63bd35582 100644 > --- a/scripts/Makefile.clang > +++ b/scripts/Makefile.clang > @@ -22,12 +22,12 @@ else > CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%)) > endif # CROSS_COMPILE > > -ifeq ($(LLVM_IAS),1) > -CLANG_FLAGS += -integrated-as > -else > +ifeq ($(LLVM_IAS),0) > CLANG_FLAGS += -no-integrated-as > GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit)) > CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE)) > +else > +CLANG_FLAGS += -integrated-as > endif > CLANG_FLAGS += -Werror=unknown-warning-option > KBUILD_CFLAGS += $(CLANG_FLAGS) > > base-commit: d7a86429dbc691bf540688fcc8542cc20246a85b > prerequisite-patch-id: 0d3072ecb5fd06ff6fd6ea81fe601f6c54c23910 > prerequisite-patch-id: 2654829756eb8a094a0ffad1679caa75a4d86619 > prerequisite-patch-id: a51e7885ca2376d008bbf146a5589da247806f7b > prerequisite-patch-id: 6a0342755115ec459610657edac1075f069faa3d > -- > 2.32.0.605.g8dce9f2422-goog >