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scripts/Makefile.clang: default to LLVM_IAS=1

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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.

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 <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Nick Desaulniers 2021-08-06 10:27:01 -07:00 committed by Masahiro Yamada
parent 52cc02b910
commit f12b034afe
2 changed files with 11 additions and 9 deletions
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14
Documentation/kbuild/llvm.rst
View File

@ -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
-----------------------

6
scripts/Makefile.clang
View File

@ -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)