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Marco Elver authored
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. Signed-off-by:
Marco Elver <elver@google.com> Signed-off-by:
Borislav Petkov <bp@suse.de> Signed-off-by:
Thomas Gleixner <tglx@linutronix.de> Acked-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by:
Will Deacon <will@kernel.org> Link: https://lkml.kernel.org/r/CANpmjNMTsY_8241bS7=XAfqvZHFLrVEkv_uM4aDUWE_kh3Rvbw@mail.gmail.com Link: https://lkml.kernel.org/r/20200521142047.169334-7-elver@google.com
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