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    Subject[PATCH -tip v3 06/11] kcsan: Restrict supported compilers
    From
    The first version of Clang that supports -tsan-distinguish-volatile will
    be able to support KCSAN. The first Clang release to do so, will be
    Clang 11. This is due to satisfying all the following requirements:

    1. Never emit calls to __tsan_func_{entry,exit}.

    2. __no_kcsan functions should not call anything, not even
    kcsan_{enable,disable}_current(), when using __{READ,WRITE}_ONCE => Requires
    leaving them plain!

    3. Support atomic_{read,set}*() with KCSAN, which rely on
    arch_atomic_{read,set}*() using __{READ,WRITE}_ONCE() => Because of
    #2, rely on Clang 11's -tsan-distinguish-volatile support. We will
    double-instrument atomic_{read,set}*(), but that's reasonable given
    it's still lower cost than the data_race() variant due to avoiding 2
    extra calls (kcsan_{en,dis}able_current() calls).

    4. __always_inline functions inlined into __no_kcsan functions are never
    instrumented.

    5. __always_inline functions inlined into instrumented functions are
    instrumented.

    6. __no_kcsan_or_inline functions may be inlined into __no_kcsan functions =>
    Implies leaving 'noinline' off of __no_kcsan_or_inline.

    7. Because of #6, __no_kcsan and __no_kcsan_or_inline functions should never be
    spuriously inlined into instrumented functions, causing the accesses of the
    __no_kcsan function to be instrumented.

    Older versions of Clang do not satisfy #3. The latest GCC currently doesn't
    support at least #1, #3, and #7.

    Link: https://lkml.kernel.org/r/CANpmjNMTsY_8241bS7=XAfqvZHFLrVEkv_uM4aDUWE_kh3Rvbw@mail.gmail.com
    Acked-by: Will Deacon <will@kernel.org>
    Signed-off-by: Marco Elver <elver@google.com>
    ---
    lib/Kconfig.kcsan | 9 ++++++++-
    1 file changed, 8 insertions(+), 1 deletion(-)

    diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
    index a7276035ca0d..3f3b5bca7a8f 100644
    --- a/lib/Kconfig.kcsan
    +++ b/lib/Kconfig.kcsan
    @@ -3,6 +3,12 @@
    config HAVE_ARCH_KCSAN
    bool

    +config HAVE_KCSAN_COMPILER
    + def_bool CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-distinguish-volatile=1)
    + help
    + For the list of compilers that support KCSAN, please see
    + <file:Documentation/dev-tools/kcsan.rst>.
    +
    config KCSAN_KCOV_BROKEN
    def_bool KCOV && CC_HAS_SANCOV_TRACE_PC
    depends on CC_IS_CLANG
    @@ -15,7 +21,8 @@ config KCSAN_KCOV_BROKEN

    menuconfig KCSAN
    bool "KCSAN: dynamic data race detector"
    - depends on HAVE_ARCH_KCSAN && DEBUG_KERNEL && !KASAN
    + depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER
    + depends on DEBUG_KERNEL && !KASAN
    depends on !KCSAN_KCOV_BROKEN
    select STACKTRACE
    help
    --
    2.26.2.761.g0e0b3e54be-goog
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