On Thu, Feb 27, 2020 at 8:23 AM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > 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> > --- Applied to linux-kbuild. Thanks. > Changes V2 -> V3: > * Drop Randy's Suggested-by tag. Sorry Randy, I do appreciate the review > though. > * Add F: line to MAINTAINERS. > > Changes V1 -> V2: > * s/On going/ongoing/ > * add Randy's Suggested-by > * add Nathan and Sedat's Reviewed-by > * Upgrade Kees' Sugguested-by to Reviewed-by > * s/suffix/prefix/ > > Documentation/kbuild/index.rst | 1 + > Documentation/kbuild/llvm.rst | 80 ++++++++++++++++++++++++++++++++++ > MAINTAINERS | 1 + > 3 files changed, 82 insertions(+) > create mode 100644 Documentation/kbuild/llvm.rst > > diff --git a/Documentation/kbuild/index.rst b/Documentation/kbuild/index.rst > index 0f144fad99a6..3882bd5f7728 100644 > --- 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 > > diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst > new file mode 100644 > index 000000000000..d6c79eb4e23e > --- /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/ > diff --git a/MAINTAINERS b/MAINTAINERS > index 8b85f22b9b69..79e1f9bfb2b6 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -4124,6 +4124,7 @@ B: https://github.com/ClangBuiltLinux/linux/issues > 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> > -- > 2.25.0.265.gbab2e86ba0-goog > -- Best Regards Masahiro Yamada
