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-rw-r--r--Documentation/kbuild/index.rst1
-rw-r--r--Documentation/kbuild/kconfig-language.rst27
-rw-r--r--Documentation/kbuild/llvm.rst80
3 files changed, 105 insertions, 3 deletions
diff --git a/Documentation/kbuild/index.rst b/Documentation/kbuild/index.rst
index 82daf2efcb73..cee2f99f734b 100644
--- a/Documentation/kbuild/index.rst
+++ b/Documentation/kbuild/index.rst
@@ -20,6 +20,7 @@ Kernel Build System
issues
reproducible-builds
gcc-plugins
+ llvm
.. only:: subproject and html
diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
index d0111dd26410..a1601ec3317b 100644
--- a/Documentation/kbuild/kconfig-language.rst
+++ b/Documentation/kbuild/kconfig-language.rst
@@ -159,11 +159,11 @@ applicable everywhere (see syntax).
Given the following example::
config FOO
- tristate
+ tristate "foo"
imply BAZ
config BAZ
- tristate
+ tristate "baz"
depends on BAR
The following values are possible:
@@ -173,7 +173,10 @@ applicable everywhere (see syntax).
=== === ============= ==============
n y n N/m/y
m y m M/y/n
- y y y Y/n
+ y y y Y/m/n
+ n m n N/m
+ m m m M/n
+ y m n M/n
y n * N
=== === ============= ==============
@@ -181,6 +184,24 @@ applicable everywhere (see syntax).
ability to hook into a secondary subsystem while allowing the user to
configure that subsystem out without also having to unset these drivers.
+ Note: If the combination of FOO=y and BAR=m causes a link error,
+ you can guard the function call with IS_REACHABLE()::
+
+ foo_init()
+ {
+ if (IS_REACHABLE(CONFIG_BAZ))
+ baz_register(&foo);
+ ...
+ }
+
+ Note: If the feature provided by BAZ is highly desirable for FOO,
+ FOO should imply not only BAZ, but also its dependency BAR::
+
+ config FOO
+ tristate "foo"
+ imply BAR
+ imply BAZ
+
- limiting menu display: "visible if" <expr>
This attribute is only applicable to menu blocks, if the condition is
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@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/