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scripts/Makefile.clang: default to LLVM_IAS=1
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 <[email protected]> Reviewed-by: Nathan Chancellor <[email protected]> Signed-off-by: Masahiro Yamada <[email protected]>
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Documentation/kbuild/llvm.rst

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@@ -60,25 +60,27 @@ They can be enabled individually. The full list of the parameters: ::
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OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf \
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HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar HOSTLD=ld.lld
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Currently, the integrated assembler is disabled by default. You can pass
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``LLVM_IAS=1`` to enable it.
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The integrated assembler is enabled by default. You can pass ``LLVM_IAS=0`` to
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disable it.
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Omitting CROSS_COMPILE
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----------------------
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As explained above, ``CROSS_COMPILE`` is used to set ``--target=<triple>``.
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Unless ``LLVM_IAS=1`` is specified, ``CROSS_COMPILE`` is also used to derive
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``--prefix=<path>`` to search for the GNU assembler and linker.
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If ``CROSS_COMPILE`` is not specified, the ``--target=<triple>`` is inferred
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from ``ARCH``.
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That means if you use only LLVM tools, ``CROSS_COMPILE`` becomes unnecessary.
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For example, to cross-compile the arm64 kernel::
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make ARCH=arm64 LLVM=1 LLVM_IAS=1
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make ARCH=arm64 LLVM=1
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If ``LLVM_IAS=0`` is specified, ``CROSS_COMPILE`` is also used to derive
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``--prefix=<path>`` to search for the GNU assembler and linker. ::
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make ARCH=arm64 LLVM=1 LLVM_IAS=0 CROSS_COMPILE=aarch64-linux-gnu-
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Supported Architectures
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-----------------------

scripts/Makefile.clang

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@@ -22,12 +22,12 @@ else
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CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
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endif # CROSS_COMPILE
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ifeq ($(LLVM_IAS),1)
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CLANG_FLAGS += -integrated-as
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else
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ifeq ($(LLVM_IAS),0)
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CLANG_FLAGS += -no-integrated-as
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GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
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CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
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else
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CLANG_FLAGS += -integrated-as
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endif
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CLANG_FLAGS += -Werror=unknown-warning-option
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KBUILD_CFLAGS += $(CLANG_FLAGS)

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