1. 14 Apr, 2020 5 commits
  2. 08 Apr, 2020 1 commit
    • Masahiro Yamada's avatar
      kbuild: support LLVM=1 to switch the default tools to Clang/LLVM · a0d1c951
      Masahiro Yamada authored
      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: default avatarMasahiro Yamada <masahiroy@kernel.org>
      Reviewed-by: default avatarNathan Chancellor <natechancellor@gmail.com>
      Tested-by: Nathan Chancellor <natechancellor@gmail.com> # build
      Tested-by: default avatarNick Desaulniers <ndesaulniers@google.com>
      Reviewed-by: default avatarNick Desaulniers <ndesaulniers@google.com>
      a0d1c951
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