Commit e08831ba authored by Nick Desaulniers's avatar Nick Desaulniers Committed by Masahiro Yamada
Browse files

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: default avatarMasahiro Yamada <masahiroy@kernel.org>
Reviewed-by: default avatarFangrui Song <maskray@google.com>
Signed-off-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Reviewed-by: default avatarNathan Chancellor <nathan@kernel.org>
Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
parent 231ad7f4

Documentation/kbuild/llvm.rst

+18 −1
Original line number Diff line number Diff line
@@ -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

-----------------------