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| author | Alex Bennée | 2016-09-30 23:30:53 +0200 |
|---|---|---|
| committer | Paolo Bonzini | 2016-10-04 10:00:25 +0200 |
| commit | e653bc6b0ff645c25b8a2eb607c18a5c98b59db6 (patch) | |
| tree | 2a558ef7e18bf2a423d2a52ebc7bfb9135e95f01 /include | |
| parent | atomic.h: fix __SANITIZE_THREAD__ build (diff) | |
| download | qemu-e653bc6b0ff645c25b8a2eb607c18a5c98b59db6.tar.gz qemu-e653bc6b0ff645c25b8a2eb607c18a5c98b59db6.tar.xz qemu-e653bc6b0ff645c25b8a2eb607c18a5c98b59db6.zip | |
atomic.h: comment on use of atomic_read/set
Add some notes on the use of the relaxed atomic access helpers and their
importance for defined behaviour in C11's multi-threaded memory model.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20160930213106.20186-3-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'include')
| -rw-r--r-- | include/qemu/atomic.h | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h index c493f89059..c4f6950fcb 100644 --- a/include/qemu/atomic.h +++ b/include/qemu/atomic.h @@ -92,6 +92,12 @@ /* Weak atomic operations prevent the compiler moving other * loads/stores past the atomic operation load/store. However there is * no explicit memory barrier for the processor. + * + * The C11 memory model says that variables that are accessed from + * different threads should at least be done with __ATOMIC_RELAXED + * primitives or the result is undefined. Generally this has little to + * no effect on the generated code but not using the atomic primitives + * will get flagged by sanitizers as a violation. */ #define atomic_read(ptr) \ ({ \ |