Commit fcf1b6a3 authored by Nick Desaulniers's avatar Nick Desaulniers Committed by Masahiro Yamada

Documentation/llvm: add documentation on building w/ Clang/LLVM

Added to kbuild documentation. Provides more official info on building
kernels with Clang and LLVM than our wiki.
Suggested-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarNathan Chancellor <natechancellor@gmail.com>
Reviewed-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
parent a1af8d71
...@@ -19,6 +19,7 @@ Kernel Build System ...@@ -19,6 +19,7 @@ Kernel Build System
issues issues
reproducible-builds reproducible-builds
llvm
.. only:: subproject and html .. only:: subproject and html
......
==============================
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/
...@@ -4119,6 +4119,7 @@ B: https://github.com/ClangBuiltLinux/linux/issues ...@@ -4119,6 +4119,7 @@ B: https://github.com/ClangBuiltLinux/linux/issues
C: irc://chat.freenode.net/clangbuiltlinux C: irc://chat.freenode.net/clangbuiltlinux
S: Supported S: Supported
K: \b(?i:clang|llvm)\b K: \b(?i:clang|llvm)\b
F: Documentation/kbuild/llvm.rst
CLEANCACHE API CLEANCACHE API
M: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> M: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
......
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