From e08831baa032e62786d88b68e26c54389e2486b6 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Mon, 2 Aug 2021 11:39:10 -0700 Subject: 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 Reviewed-by: Fangrui Song Signed-off-by: Nick Desaulniers Reviewed-by: Nathan Chancellor Signed-off-by: Masahiro Yamada --- Documentation/kbuild/llvm.rst | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) (limited to 'Documentation/kbuild') 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=``. 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=``. + +Unless ``LLVM_IAS=1`` is specified, ``CROSS_COMPILE`` is also used to derive +``--prefix=`` to search for the GNU assembler and linker. + +If ``CROSS_COMPILE`` is not specified, the ``--target=`` 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 ----------------------- -- cgit v1.2.3-59-g8ed1b