This is a note to let you know that I've just added the patch titled Documentation/llvm: add documentation on building w/ Clang/LLVM to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: documentation-llvm-add-documentation-on-building-w-clang-llvm.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Fri 21 Aug 2020 04:30:09 PM CEST From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Date: Wed, 26 Feb 2020 15:23:36 -0800 Subject: Documentation/llvm: add documentation on building w/ Clang/LLVM From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> commit fcf1b6a35c16ac500fa908a4022238e5d666eabf upstream. added to kbuild documentation. Provides more official info on building kernels with Clang and LLVM than our wiki. Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx> Reviewed-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- Documentation/kbuild/index.rst | 1 Documentation/kbuild/llvm.rst | 80 +++++++++++++++++++++++++++++++++++++++++ MAINTAINERS | 1 3 files changed, 82 insertions(+) create mode 100644 Documentation/kbuild/llvm.rst --- a/Documentation/kbuild/index.rst +++ b/Documentation/kbuild/index.rst @@ -19,6 +19,7 @@ Kernel Build System issues reproducible-builds + llvm .. only:: subproject and html --- /dev/null +++ b/Documentation/kbuild/llvm.rst @@ -0,0 +1,80 @@ +============================== +Building Linux with Clang/LLVM +============================== + +This document covers how to build the Linux kernel with Clang and LLVM +utilities. + +About +----- + +The Linux kernel has always traditionally been compiled with GNU toolchains +such as GCC and binutils. Ongoing work has allowed for `Clang +<https://clang.llvm.org/>`_ and `LLVM <https://llvm.org/>`_ utilities to be +used as viable substitutes. Distributions such as `Android +<https://www.android.com/>`_, `ChromeOS +<https://www.chromium.org/chromium-os>`_, and `OpenMandriva +<https://www.openmandriva.org/>`_ use Clang built kernels. `LLVM is a +collection of toolchain components implemented in terms of C++ objects +<https://www.aosabook.org/en/llvm.html>`_. Clang is a front-end to LLVM that +supports C and the GNU C extensions required by the kernel, and is pronounced +"klang," not "see-lang." + +Clang +----- + +The compiler used can be swapped out via `CC=` command line argument to `make`. +`CC=` should be set when selecting a config and during a build. + + make CC=clang defconfig + + make CC=clang + +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 + +`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 +example: + + clang --target aarch64-linux-gnu foo.c + +LLVM Utilities +-------------- + +LLVM has substitutes for GNU binutils utilities. These can be invoked as +additional parameters to `make`. + + make CC=clang AS=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\ + OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-objsize \\ + READELF=llvm-readelf HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar \\ + HOSTLD=ld.lld + +Getting Help +------------ + +- `Website <https://clangbuiltlinux.github.io/>`_ +- `Mailing List <https://groups.google.com/forum/#!forum/clang-built-linux>`_: <clang-built-linux@xxxxxxxxxxxxxxxx> +- `Issue Tracker <https://github.com/ClangBuiltLinux/linux/issues>`_ +- IRC: #clangbuiltlinux on chat.freenode.net +- `Telegram <https://t.me/ClangBuiltLinux>`_: @ClangBuiltLinux +- `Wiki <https://github.com/ClangBuiltLinux/linux/wiki>`_ +- `Beginner Bugs <https://github.com/ClangBuiltLinux/linux/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22>`_ + +Getting LLVM +------------- + +- http://releases.llvm.org/download.html +- https://github.com/llvm/llvm-project +- https://llvm.org/docs/GettingStarted.html +- https://llvm.org/docs/CMake.html +- https://apt.llvm.org/ +- https://www.archlinux.org/packages/extra/x86_64/llvm/ +- https://github.com/ClangBuiltLinux/tc-build +- https://github.com/ClangBuiltLinux/linux/wiki/Building-Clang-from-source +- https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/ --- a/MAINTAINERS +++ b/MAINTAINERS @@ -4028,6 +4028,7 @@ B: https://github.com/ClangBuiltLinux/li C: irc://chat.freenode.net/clangbuiltlinux S: Supported K: \b(?i:clang|llvm)\b +F: Documentation/kbuild/llvm.rst CLEANCACHE API M: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> Patches currently in stable-queue which might be from ndesaulniers@xxxxxxxxxx are queue-5.4/kbuild-support-llvm-1-to-switch-the-default-tools-to-clang-llvm.patch queue-5.4/kbuild-remove-python2-variable.patch queue-5.4/net-wan-wanxl-use-m68kcc-instead-of-m68kas-for-rebuilding-firmware.patch queue-5.4/kbuild-remove-as-variable.patch queue-5.4/net-wan-wanxl-use-allow-to-pass-cross_compile_m68k-for-rebuilding-firmware.patch queue-5.4/kbuild-replace-as-clang-with-llvm_ias-1.patch queue-5.4/documentation-llvm-fix-the-name-of-llvm-size.patch queue-5.4/documentation-llvm-add-documentation-on-building-w-clang-llvm.patch queue-5.4/x86-boot-kbuild-allow-readelf-executable-to-be-specified.patch