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| author | Nick Desaulniers <ndesaulniers@google.com> | 2021-08-02 11:39:10 -0700 |
|---|---|---|
| committer | Masahiro Yamada <masahiroy@kernel.org> | 2021-08-10 09:13:25 +0900 |
| commit | e08831baa032e62786d88b68e26c54389e2486b6 (patch) | |
| tree | f88f9ff4f57a9086c087a04c69d4507b9159716e /Documentation/kbuild | |
| parent | 231ad7f409f16b9f9505f69e058dff488a7e6bde (diff) | |
| download | lwn-e08831baa032e62786d88b68e26c54389e2486b6.tar.gz lwn-e08831baa032e62786d88b68e26c54389e2486b6.zip | |
Documentation/llvm: update CROSS_COMPILE inferencing
As noted by Masahiro, document how we can generally infer CROSS_COMPILE
(and the more specific details about --target and --prefix) based on
ARCH.
Change use of env vars to command line parameters.
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Fangrui Song <maskray@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Diffstat (limited to 'Documentation/kbuild')
| -rw-r--r-- | Documentation/kbuild/llvm.rst | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst index b18401d2ba82..f8a360958f4c 100644 --- a/Documentation/kbuild/llvm.rst +++ b/Documentation/kbuild/llvm.rst @@ -38,7 +38,7 @@ Cross Compiling A single Clang compiler binary will typically contain all supported backends, which can help simplify cross compiling. :: - ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang + make ARCH=arm64 CC=clang CROSS_COMPILE=aarch64-linux-gnu- ``CROSS_COMPILE`` is not used to prefix the Clang compiler binary, instead ``CROSS_COMPILE`` is used to set a command line flag: ``--target=<triple>``. For @@ -63,6 +63,23 @@ They can be enabled individually. The full list of the parameters: :: Currently, the integrated assembler is disabled by default. You can pass ``LLVM_IAS=1`` to enable 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``. + +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 + Supported Architectures ----------------------- |