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    SubjectRe: [PATCH] compiler-clang: add build check for clang 10.0.1
    On Wed, Aug 26, 2020 at 01:14:19PM -0700, Nick Desaulniers wrote:
    > During Plumbers 2020, we voted to just support the latest release of
    > Clang for now. Add a compile time check for this.
    >
    > Older clang's may work, but we will likely drop workarounds for older
    > versions.

    I think this part of the commit message is a little wishy-washy. If we
    are breaking the build for clang < 10.0.1, we are not saying "may work",
    we are saying "won't work". Because of this, we should take the
    opportunity to clean up behind us and revert/remove parts of:

    87e0d4f0f37f ("kbuild: disable clang's default use of -fmerge-all-constants")
    b0fe66cf0950 ("ARM: 8905/1: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer")
    b9249cba25a5 ("arm64: bti: Require clang >= 10.0.1 for in-kernel BTI support")
    3acf4be23528 ("arm64: vdso: Fix compilation with clang older than 8")

    This could be a series or a part of this commit, I do not have a
    strong preference. If we are not going to clean up behind us, this
    should be a warning and not an error.

    > Link: https://github.com/ClangBuiltLinux/linux/issues/9
    > Link: https://github.com/ClangBuiltLinux/linux/issues/941
    > Suggested-by: Sedat Dilek <sedat.dilek@gmail.com>
    > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

    Otherwise, I agree with Kees's comments. With them addressed, feel free
    to add:

    Acked-by: Nathan Chancellor <natechancellor@gmail.com>

    > ---
    > include/linux/compiler-clang.h | 8 ++++++++
    > 1 file changed, 8 insertions(+)
    >
    > diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
    > index cee0c728d39a..7338d3ffd240 100644
    > --- a/include/linux/compiler-clang.h
    > +++ b/include/linux/compiler-clang.h
    > @@ -3,6 +3,14 @@
    > #error "Please don't include <linux/compiler-clang.h> directly, include <linux/compiler.h> instead."
    > #endif
    >
    > +#define CLANG_VERSION (__clang_major__ * 10000 \
    > + + __clang_minor__ * 100 \
    > + + __clang_patchlevel__)
    > +
    > +#if CLANG_VERSION < 100001
    > +# error Sorry, your compiler is too old - please upgrade it.
    > +#endif
    > +
    > /* Compiler specific definitions for Clang compiler */
    >
    > /* same as gcc, this was present in clang-2.6 so we can assume it works
    > --
    > 2.28.0.297.g1956fa8f8d-goog
    >

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