projects / mirror_ubuntu-hirsute-kernel.git / blame
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| fcf1b6a3 ND |
1 | ============================== |
| 2 | Building Linux with Clang/LLVM | |
| 3 | ============================== | |
| 4 | ||
| 5 | This document covers how to build the Linux kernel with Clang and LLVM | |
| 6 | utilities. | |
| 7 | ||
| 8 | About | |
| 9 | ----- | |
| 10 | ||
| 11 | The Linux kernel has always traditionally been compiled with GNU toolchains | |
| 12 | such as GCC and binutils. Ongoing work has allowed for `Clang | |
| 13 | <https://clang.llvm.org/>`_ and `LLVM <https://llvm.org/>`_ utilities to be | |
| 14 | used as viable substitutes. Distributions such as `Android | |
| 15 | <https://www.android.com/>`_, `ChromeOS | |
| 16 | <https://www.chromium.org/chromium-os>`_, and `OpenMandriva | |
| 17 | <https://www.openmandriva.org/>`_ use Clang built kernels. `LLVM is a | |
| 18 | collection of toolchain components implemented in terms of C++ objects | |
| 19 | <https://www.aosabook.org/en/llvm.html>`_. Clang is a front-end to LLVM that | |
| 20 | supports C and the GNU C extensions required by the kernel, and is pronounced | |
| 21 | "klang," not "see-lang." | |
| 22 | ||
| 23 | Clang | |
| 24 | ----- | |
| 25 | ||
| 26 | The compiler used can be swapped out via `CC=` command line argument to `make`. | |
| 27 | `CC=` should be set when selecting a config and during a build. | |
| 28 | ||
| 29 | make CC=clang defconfig | |
| 30 | ||
| 31 | make CC=clang | |
| 32 | ||
| 33 | Cross Compiling | |
| 34 | --------------- | |
| 35 | ||
| 36 | A single Clang compiler binary will typically contain all supported backends, | |
| 37 | which can help simplify cross compiling. | |
| 38 | ||
| 39 | ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang | |
| 40 | ||
| 41 | `CROSS_COMPILE` is not used to prefix the Clang compiler binary, instead | |
| 42 | `CROSS_COMPILE` is used to set a command line flag: `--target <triple>`. For | |
| 43 | example: | |
| 44 | ||
| 45 | clang --target aarch64-linux-gnu foo.c | |
| 46 | ||
| 47 | LLVM Utilities | |
| 48 | -------------- | |
| 49 | ||
| 50 | LLVM has substitutes for GNU binutils utilities. These can be invoked as | |
| 51 | additional parameters to `make`. | |
| 52 | ||
| 53 | make CC=clang AS=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\ | |
| 54 | OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-objsize \\ | |
| 55 | READELF=llvm-readelf HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar \\ | |
| 56 | HOSTLD=ld.lld | |
| 57 | ||
| 58 | Getting Help | |
| 59 | ------------ | |
| 60 | ||
| 61 | - `Website <https://clangbuiltlinux.github.io/>`_ | |
| 62 | - `Mailing List <https://groups.google.com/forum/#!forum/clang-built-linux>`_: <clang-built-linux@googlegroups.com> | |
| 63 | - `Issue Tracker <https://github.com/ClangBuiltLinux/linux/issues>`_ | |
| 64 | - IRC: #clangbuiltlinux on chat.freenode.net | |
| 65 | - `Telegram <https://t.me/ClangBuiltLinux>`_: @ClangBuiltLinux | |
| 66 | - `Wiki <https://github.com/ClangBuiltLinux/linux/wiki>`_ | |
| 67 | - `Beginner Bugs <https://github.com/ClangBuiltLinux/linux/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22>`_ | |
| 68 | ||
| 69 | Getting LLVM | |
| 70 | ------------- | |
| 71 | ||
| 72 | - http://releases.llvm.org/download.html | |
| 73 | - https://github.com/llvm/llvm-project | |
| 74 | - https://llvm.org/docs/GettingStarted.html | |
| 75 | - https://llvm.org/docs/CMake.html | |
| 76 | - https://apt.llvm.org/ | |
| 77 | - https://www.archlinux.org/packages/extra/x86_64/llvm/ | |
| 78 | - https://github.com/ClangBuiltLinux/tc-build | |
| 79 | - https://github.com/ClangBuiltLinux/linux/wiki/Building-Clang-from-source | |
| 80 | - https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/ |