From: Alex Bennée Date: Fri, 30 Sep 2016 21:30:53 +0000 (+0100) Subject: atomic.h: comment on use of atomic_read/set X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=e653bc6b0ff645c25b8a2eb607c18a5c98b59db6;p=qemu.git 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 Message-Id: <20160930213106.20186-3-alex.bennee@linaro.org> Signed-off-by: Paolo Bonzini --- 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) \ ({ \