Messages in this thread | | | From | Segher Boessenkool <> | Subject | Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures | Date | Thu, 16 Aug 2007 22:50:38 +0200 |
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> Note that "volatile" > is a type-qualifier, not a type itself, so a cast of the _object_ > itself > to a qualified-type i.e. (volatile int) would not make the access > itself > volatile-qualified.
There is no such thing as "volatile-qualified access" defined anywhere; there only is the concept of a "volatile-qualified *object*".
> To serve our purposes, it is necessary for us to take the address of > this > (non-volatile) object, cast the resulting _pointer_ to the > corresponding > volatile-qualified pointer-type, and then dereference it. This makes > that > particular _access_ be volatile-qualified, without the object itself > being > such. Also note that the (dereferenced) result is also a valid lvalue > and > hence can be used in "*(volatile int *)&a = b;" kind of construction > (which we use for the atomic_set case).
There is a quite convincing argument that such an access _is_ an access to a volatile object; see GCC PR21568 comment #9. This probably isn't the last word on the matter though...
Segher
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