http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56028
Pawel Sikora <pluto at agmk dot net> changed:
What |Removed |Added
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CC| |pluto at agmk dot net
--- Comment #7 from Pawel Sikora <pluto at agmk dot net> 2013-01-18 18:23:27
UTC ---
(In reply to comment #6)
> The fact that a data-race-free program cannot observe the non-atomicity of a
> 64-bit store, though true, is beside the point. The plain fact is that
> hardware registers (for which volatile was intended) really do care about the
> size of the store. A pair of 32-bit stores does not necessarily mean the same
> thing to hardware as does a single 64-bit store. Given that C is intended to
> be used for device drivers, volatile stores of reasonably-sized basic types
> must be atomic, and on 64-bit systems, "reasonably-sized" very clearly
> includes
> 64-bit stores.
even 'movq' on x86-64 could be split into 32-bit transfers by mainboard h/w.
devices connected to x86-64 should be aware of this!
btw, iirc the x87-fpu load/store can give you atomic 64-bit transfer.
