Commit d31d4d6b authored by Marco Elver's avatar Marco Elver Committed by Thomas Gleixner

kcsan: Pass option tsan-instrument-read-before-write to Clang

Clang (unlike GCC) removes reads before writes with matching addresses
in the same basic block. This is an optimization for TSAN, since writes
will always cause conflict if the preceding read would have.

However, for KCSAN we cannot rely on this option, because we apply
several special rules to writes, in particular when the
KCSAN_ASSUME_PLAIN_WRITES_ATOMIC option is selected. To avoid missing
potential data races, pass the -tsan-instrument-read-before-write option
to Clang if it is available [1].

[1] https://github.com/llvm/llvm-project/commit/151ed6aa38a3ec6c01973b35f684586b6e1c0f7eSigned-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarWill Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20200521142047.169334-5-elver@google.com

parent 75d75b7a
...@@ -13,6 +13,7 @@ endif ...@@ -13,6 +13,7 @@ endif
# of some options does not break KCSAN nor causes false positive reports. # of some options does not break KCSAN nor causes false positive reports.
CFLAGS_KCSAN := -fsanitize=thread \ CFLAGS_KCSAN := -fsanitize=thread \
$(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) \ $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) \
$(call cc-option,$(call cc-param,tsan-instrument-read-before-write=1)) \
$(call cc-param,tsan-distinguish-volatile=1) $(call cc-param,tsan-distinguish-volatile=1)
endif # CONFIG_KCSAN endif # CONFIG_KCSAN
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