On Tue, 3 Mar 2020 at 17:11, Chris Hall <gcc@xxxxxxx> wrote: > > > Another <stdatomic.h> issue ? > > ----- > > In Section 7.17.7.5 "The atomic_fetch and modify generic functions", the > C11/C18 Standards say: > > 1 The following operations perform arithmetic and bitwise > computations. All of these operations are applicable to an > object of any atomic integer type. ... > > 5 NOTE The operation of the atomic_fetch and modify generic functions > are nearly equivalent to the operation of the corresponding > op= compound assignment operators. The only differences are > that the compound assignment operators are not guaranteed to > operate atomically, and the value yielded by a compound > assignment operator is the updated value of the object, > whereas the value returned by the atomic_fetch and modify > generic functions is the previous value of the atomic object. > > So given: > > _Atomic(uint64_t*) foo ; > uint64_t* bar ; > > bar = atomic_fetch_add(&foo, 1) ; > > why do gcc 9.2/glibc 2.30 add 1 and not 8 to the address ? That's https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64843
