1*4882a593Smuzhiyun.. _kbuild_llvm: 2*4882a593Smuzhiyun 3*4882a593Smuzhiyun============================== 4*4882a593SmuzhiyunBuilding Linux with Clang/LLVM 5*4882a593Smuzhiyun============================== 6*4882a593Smuzhiyun 7*4882a593SmuzhiyunThis document covers how to build the Linux kernel with Clang and LLVM 8*4882a593Smuzhiyunutilities. 9*4882a593Smuzhiyun 10*4882a593SmuzhiyunAbout 11*4882a593Smuzhiyun----- 12*4882a593Smuzhiyun 13*4882a593SmuzhiyunThe Linux kernel has always traditionally been compiled with GNU toolchains 14*4882a593Smuzhiyunsuch as GCC and binutils. Ongoing work has allowed for `Clang 15*4882a593Smuzhiyun<https://clang.llvm.org/>`_ and `LLVM <https://llvm.org/>`_ utilities to be 16*4882a593Smuzhiyunused as viable substitutes. Distributions such as `Android 17*4882a593Smuzhiyun<https://www.android.com/>`_, `ChromeOS 18*4882a593Smuzhiyun<https://www.chromium.org/chromium-os>`_, and `OpenMandriva 19*4882a593Smuzhiyun<https://www.openmandriva.org/>`_ use Clang built kernels. `LLVM is a 20*4882a593Smuzhiyuncollection of toolchain components implemented in terms of C++ objects 21*4882a593Smuzhiyun<https://www.aosabook.org/en/llvm.html>`_. Clang is a front-end to LLVM that 22*4882a593Smuzhiyunsupports C and the GNU C extensions required by the kernel, and is pronounced 23*4882a593Smuzhiyun"klang," not "see-lang." 24*4882a593Smuzhiyun 25*4882a593SmuzhiyunClang 26*4882a593Smuzhiyun----- 27*4882a593Smuzhiyun 28*4882a593SmuzhiyunThe compiler used can be swapped out via ``CC=`` command line argument to ``make``. 29*4882a593Smuzhiyun``CC=`` should be set when selecting a config and during a build. :: 30*4882a593Smuzhiyun 31*4882a593Smuzhiyun make CC=clang defconfig 32*4882a593Smuzhiyun 33*4882a593Smuzhiyun make CC=clang 34*4882a593Smuzhiyun 35*4882a593SmuzhiyunCross Compiling 36*4882a593Smuzhiyun--------------- 37*4882a593Smuzhiyun 38*4882a593SmuzhiyunA single Clang compiler binary will typically contain all supported backends, 39*4882a593Smuzhiyunwhich can help simplify cross compiling. :: 40*4882a593Smuzhiyun 41*4882a593Smuzhiyun ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang 42*4882a593Smuzhiyun 43*4882a593Smuzhiyun``CROSS_COMPILE`` is not used to prefix the Clang compiler binary, instead 44*4882a593Smuzhiyun``CROSS_COMPILE`` is used to set a command line flag: ``--target=<triple>``. For 45*4882a593Smuzhiyunexample: :: 46*4882a593Smuzhiyun 47*4882a593Smuzhiyun clang --target=aarch64-linux-gnu foo.c 48*4882a593Smuzhiyun 49*4882a593SmuzhiyunLLVM Utilities 50*4882a593Smuzhiyun-------------- 51*4882a593Smuzhiyun 52*4882a593SmuzhiyunLLVM has substitutes for GNU binutils utilities. Kbuild supports ``LLVM=1`` 53*4882a593Smuzhiyunto enable them. :: 54*4882a593Smuzhiyun 55*4882a593Smuzhiyun make LLVM=1 56*4882a593Smuzhiyun 57*4882a593SmuzhiyunThey can be enabled individually. The full list of the parameters: :: 58*4882a593Smuzhiyun 59*4882a593Smuzhiyun make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \ 60*4882a593Smuzhiyun OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf \ 61*4882a593Smuzhiyun HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar HOSTLD=ld.lld 62*4882a593Smuzhiyun 63*4882a593SmuzhiyunCurrently, the integrated assembler is disabled by default. You can pass 64*4882a593Smuzhiyun``LLVM_IAS=1`` to enable it. 65*4882a593Smuzhiyun 66*4882a593SmuzhiyunGetting Help 67*4882a593Smuzhiyun------------ 68*4882a593Smuzhiyun 69*4882a593Smuzhiyun- `Website <https://clangbuiltlinux.github.io/>`_ 70*4882a593Smuzhiyun- `Mailing List <https://groups.google.com/forum/#!forum/clang-built-linux>`_: <clang-built-linux@googlegroups.com> 71*4882a593Smuzhiyun- `Issue Tracker <https://github.com/ClangBuiltLinux/linux/issues>`_ 72*4882a593Smuzhiyun- IRC: #clangbuiltlinux on chat.freenode.net 73*4882a593Smuzhiyun- `Telegram <https://t.me/ClangBuiltLinux>`_: @ClangBuiltLinux 74*4882a593Smuzhiyun- `Wiki <https://github.com/ClangBuiltLinux/linux/wiki>`_ 75*4882a593Smuzhiyun- `Beginner Bugs <https://github.com/ClangBuiltLinux/linux/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22>`_ 76*4882a593Smuzhiyun 77*4882a593Smuzhiyun.. _getting_llvm: 78*4882a593Smuzhiyun 79*4882a593SmuzhiyunGetting LLVM 80*4882a593Smuzhiyun------------- 81*4882a593Smuzhiyun 82*4882a593Smuzhiyun- https://releases.llvm.org/download.html 83*4882a593Smuzhiyun- https://github.com/llvm/llvm-project 84*4882a593Smuzhiyun- https://llvm.org/docs/GettingStarted.html 85*4882a593Smuzhiyun- https://llvm.org/docs/CMake.html 86*4882a593Smuzhiyun- https://apt.llvm.org/ 87*4882a593Smuzhiyun- https://www.archlinux.org/packages/extra/x86_64/llvm/ 88*4882a593Smuzhiyun- https://github.com/ClangBuiltLinux/tc-build 89*4882a593Smuzhiyun- https://github.com/ClangBuiltLinux/linux/wiki/Building-Clang-from-source 90*4882a593Smuzhiyun- https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/ 91