linux/Documentation/kbuild
Masahiro Yamada a0d1c951ef kbuild: support LLVM=1 to switch the default tools to Clang/LLVM
As Documentation/kbuild/llvm.rst implies, building the kernel with a
full set of LLVM tools gets very verbose and unwieldy.

Provide a single switch LLVM=1 to use Clang and LLVM tools instead
of GCC and Binutils. You can pass it from the command line or as an
environment variable.

Please note LLVM=1 does not turn on the integrated assembler. You need
to pass LLVM_IAS=1 to use it. When the upstream kernel is ready for the
integrated assembler, I think we can make it default.

We discussed what we need, and we agreed to go with a simple boolean
flag that switches both target and host tools:

  https://lkml.org/lkml/2020/3/28/494
  https://lkml.org/lkml/2020/4/3/43

Some items discussed, but not adopted:

- LLVM_DIR

  When multiple versions of LLVM are installed, I just thought supporting
  LLVM_DIR=/path/to/my/llvm/bin/ might be useful.

  CC      = $(LLVM_DIR)clang
  LD      = $(LLVM_DIR)ld.lld
    ...

  However, we can handle this by modifying PATH. So, we decided to not do
  this.

- LLVM_SUFFIX

  Some distributions (e.g. Debian) package specific versions of LLVM with
  naming conventions that use the version as a suffix.

  CC      = clang$(LLVM_SUFFIX)
  LD      = ld.lld(LLVM_SUFFIX)
    ...

  will allow a user to pass LLVM_SUFFIX=-11 to use clang-11 etc.,
  but the suffixed versions in /usr/bin/ are symlinks to binaries in
  /usr/lib/llvm-#/bin/, so this can also be handled by PATH.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com> # build
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
2020-04-09 03:18:21 +09:00
..
gcc-plugins.rst docs: move gcc-plugins to the kbuild manual 2020-03-10 11:20:46 -06:00
headers_install.rst Kbuild updates for v5.3 2019-07-12 16:03:16 -07:00
index.rst Kbuild updates for v5.7 2020-03-31 16:03:39 -07:00
issues.rst docs: kbuild: fix build with pdf and fix some minor issues 2019-07-15 11:03:04 -03:00
kbuild.rst kbuild: support LLVM=1 to switch the default tools to Clang/LLVM 2020-04-09 03:18:21 +09:00
kconfig-language.rst kconfig: make 'imply' obey the direct dependency 2020-03-13 10:05:34 +09:00
kconfig-macro-language.rst kbuild: doc: fix references to other documents 2020-03-13 10:02:27 +09:00
Kconfig.recursion-issue-01 kbuild: document recursive dependency limitation / resolution 2015-10-08 15:36:16 +02:00
Kconfig.recursion-issue-02 kbuild: document recursive dependency limitation / resolution 2015-10-08 15:36:16 +02:00
kconfig.rst kbuild: create modules.builtin without Makefile.modbuiltin or tristate.conf 2020-01-07 02:18:39 +09:00
Kconfig.select-break kbuild: document recursive dependency limitation / resolution 2015-10-08 15:36:16 +02:00
llvm.rst kbuild: support LLVM=1 to switch the default tools to Clang/LLVM 2020-04-09 03:18:21 +09:00
makefiles.rst kbuild: doc: fix references to other documents 2020-03-13 10:02:27 +09:00
modules.rst modpost: move the namespace field in Module.symvers last 2020-03-17 08:59:03 +09:00
reproducible-builds.rst kheaders: make headers archive reproducible 2019-10-05 15:29:49 +09:00