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3 KiB
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88 lines
3 KiB
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==============================
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Building Linux with Clang/LLVM
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==============================
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This document covers how to build the Linux kernel with Clang and LLVM
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utilities.
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About
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-----
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The Linux kernel has always traditionally been compiled with GNU toolchains
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such as GCC and binutils. Ongoing work has allowed for `Clang
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<https://clang.llvm.org/>`_ and `LLVM <https://llvm.org/>`_ utilities to be
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used as viable substitutes. Distributions such as `Android
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<https://www.android.com/>`_, `ChromeOS
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<https://www.chromium.org/chromium-os>`_, and `OpenMandriva
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<https://www.openmandriva.org/>`_ use Clang built kernels. `LLVM is a
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collection of toolchain components implemented in terms of C++ objects
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<https://www.aosabook.org/en/llvm.html>`_. Clang is a front-end to LLVM that
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supports C and the GNU C extensions required by the kernel, and is pronounced
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"klang," not "see-lang."
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Clang
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-----
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The compiler used can be swapped out via `CC=` command line argument to `make`.
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`CC=` should be set when selecting a config and during a build.
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make CC=clang defconfig
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make CC=clang
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Cross Compiling
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---------------
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A single Clang compiler binary will typically contain all supported backends,
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which can help simplify cross compiling.
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ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang
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`CROSS_COMPILE` is not used to prefix the Clang compiler binary, instead
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`CROSS_COMPILE` is used to set a command line flag: `--target <triple>`. For
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example:
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clang --target aarch64-linux-gnu foo.c
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LLVM Utilities
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--------------
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LLVM has substitutes for GNU binutils utilities. Kbuild supports `LLVM=1`
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to enable them.
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make LLVM=1
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They can be enabled individually. The full list of the parameters:
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make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
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OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-size \\
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READELF=llvm-readelf HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar \\
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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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Getting Help
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------------
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- `Website <https://clangbuiltlinux.github.io/>`_
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- `Mailing List <https://groups.google.com/forum/#!forum/clang-built-linux>`_: <clang-built-linux@googlegroups.com>
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- `Issue Tracker <https://github.com/ClangBuiltLinux/linux/issues>`_
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- IRC: #clangbuiltlinux on chat.freenode.net
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- `Telegram <https://t.me/ClangBuiltLinux>`_: @ClangBuiltLinux
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- `Wiki <https://github.com/ClangBuiltLinux/linux/wiki>`_
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- `Beginner Bugs <https://github.com/ClangBuiltLinux/linux/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22>`_
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Getting LLVM
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-------------
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- http://releases.llvm.org/download.html
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- https://github.com/llvm/llvm-project
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- https://llvm.org/docs/GettingStarted.html
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- https://llvm.org/docs/CMake.html
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- https://apt.llvm.org/
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- https://www.archlinux.org/packages/extra/x86_64/llvm/
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- https://github.com/ClangBuiltLinux/tc-build
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- https://github.com/ClangBuiltLinux/linux/wiki/Building-Clang-from-source
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- https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/
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