From: Nick Desaulniers Date: Wed, 26 Feb 2020 23:23:36 +0000 (-0800) Subject: BACKPORT: Documentation/llvm: add documentation on building w/ Clang/LLVM X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=107f393ff0a8c9d7b61ea8a1695bd81ca91d2ffc;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git BACKPORT: 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: Kees Cook Reviewed-by: Kees Cook Reviewed-by: Nathan Chancellor Reviewed-by: Sedat Dilek Signed-off-by: Nick Desaulniers Signed-off-by: Masahiro Yamada (cherry picked from commit fcf1b6a35c16ac500fa908a4022238e5d666eabf) Change-Id: I33bc4a97cf9e9ef923712bb490df0bceac81dade --- diff --git a/Documentation/kbuild/00-INDEX b/Documentation/kbuild/00-INDEX index 8c5e6aa78004..b367200c94b5 100644 --- a/Documentation/kbuild/00-INDEX +++ b/Documentation/kbuild/00-INDEX @@ -1,5 +1,7 @@ 00-INDEX - this file: info on the kernel build process +llvm.txt + - how to compile Linux with llvm headers_install.txt - how to export Linux headers for use by userspace kbuild.txt diff --git a/Documentation/kbuild/llvm.txt b/Documentation/kbuild/llvm.txt new file mode 100644 index 000000000000..0c30444a7368 --- /dev/null +++ b/Documentation/kbuild/llvm.txt @@ -0,0 +1,83 @@ +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=]{.title-ref} command line +argument to [make]{.title-ref}. [CC=]{.title-ref} 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]{.title-ref} is not used to prefix the Clang compiler +binary, instead [CROSS\_COMPILE]{.title-ref} is used to set a command +line flag: [--target ]{.title-ref}. 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]{.title-ref}. + +> 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): + +- [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 +------------ + +- +- +- +- +- +- +- +- +-