Messages in this thread | | | From | Nick Desaulniers <> | Date | Tue, 1 Jun 2021 10:42:41 -0700 | Subject | Re: [PATCH v2] kcov: add __no_sanitize_coverage to fix noinstr for all architectures |
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On Thu, May 27, 2021 at 9:27 AM Marco Elver <elver@google.com> wrote: > > 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.
I'm not against a version check for supporting older releases (in addition to the cleaner feature check, since the feature check was non-existent); we can clean it up someday when clang-13 is the minimally supported version. Would having an additional version check help support existing/older releases here?
> + */ > +#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 >
-- Thanks, ~Nick Desaulniers
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