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    Subject[PATCH v2] kcov: add __no_sanitize_coverage to fix noinstr for all architectures
    From
    Until now no compiler supported an attribute to disable coverage
    instrumentation as used by KCOV.

    To work around this limitation on x86, noinstr functions have their
    coverage instrumentation turned into nops by objtool. However, this
    solution doesn't scale automatically to other architectures, such as
    arm64, which are migrating to use the generic entry code.

    Clang [1] and GCC [2] have added support for the attribute recently.
    [1] https://github.com/llvm/llvm-project/commit/280333021e9550d80f5c1152a34e33e81df1e178
    [2] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=cec4d4a6782c9bd8d071839c50a239c49caca689
    The changes will appear in Clang 13 and GCC 12.

    Add __no_sanitize_coverage for both compilers, and add it to noinstr.

    Note: In the Clang case, __has_feature(coverage_sanitizer) is only true
    if the feature is enabled, and therefore we do not require an additional
    defined(CONFIG_KCOV) (like in the GCC case where __has_attribute(..) is
    always true) to avoid adding redundant attributes to functions if KCOV
    is off. That being said, compilers that support the attribute will not
    generate errors/warnings if the attribute is redundantly used; however,
    where possible let's avoid it as it reduces preprocessed code size and
    associated compile-time overheads.

    Signed-off-by: Marco Elver <elver@google.com>
    Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    ---
    v2:
    * Implement __has_feature(coverage_sanitizer) in Clang
    (https://reviews.llvm.org/D103159) and use instead of version check.
    * Add Peter's Ack.
    ---
    include/linux/compiler-clang.h | 11 +++++++++++
    include/linux/compiler-gcc.h | 6 ++++++
    include/linux/compiler_types.h | 2 +-
    3 files changed, 18 insertions(+), 1 deletion(-)

    diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
    index adbe76b203e2..e15eebfa8e5d 100644
    --- a/include/linux/compiler-clang.h
    +++ b/include/linux/compiler-clang.h
    @@ -45,6 +45,17 @@
    #define __no_sanitize_undefined
    #endif

    +/*
    + * Support for __has_feature(coverage_sanitizer) was added in Clang 13 together
    + * with no_sanitize("coverage"). Prior versions of Clang support coverage
    + * instrumentation, but cannot be queried for support by the preprocessor.
    + */
    +#if __has_feature(coverage_sanitizer)
    +#define __no_sanitize_coverage __attribute__((no_sanitize("coverage")))
    +#else
    +#define __no_sanitize_coverage
    +#endif
    +
    /*
    * Not all versions of clang implement the type-generic versions
    * of the builtin overflow checkers. Fortunately, clang implements
    diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
    index 5d97ef738a57..cb9217fc60af 100644
    --- a/include/linux/compiler-gcc.h
    +++ b/include/linux/compiler-gcc.h
    @@ -122,6 +122,12 @@
    #define __no_sanitize_undefined
    #endif

    +#if defined(CONFIG_KCOV) && __has_attribute(__no_sanitize_coverage__)
    +#define __no_sanitize_coverage __attribute__((no_sanitize_coverage))
    +#else
    +#define __no_sanitize_coverage
    +#endif
    +
    #if GCC_VERSION >= 50100
    #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
    #endif
    diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
    index d29bda7f6ebd..cc2bee7f0977 100644
    --- a/include/linux/compiler_types.h
    +++ b/include/linux/compiler_types.h
    @@ -210,7 +210,7 @@ struct ftrace_likely_data {
    /* Section for code which can't be instrumented at all */
    #define noinstr \
    noinline notrace __attribute((__section__(".noinstr.text"))) \
    - __no_kcsan __no_sanitize_address
    + __no_kcsan __no_sanitize_address __no_sanitize_coverage

    #endif /* __KERNEL__ */

    --
    2.31.1.818.g46aad6cb9e-goog
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