From: Nick Desaulniers ndesaulniers@google.com
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@chromium.org Reviewed-by: Kees Cook keescook@chromium.org Reviewed-by: Nathan Chancellor natechancellor@gmail.com Reviewed-by: Sedat Dilek sedat.dilek@gmail.com Signed-off-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Masahiro Yamada masahiroy@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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@googlegroups.com +- `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@oracle.com