On Mon, Nov 24, 2014 at 11:14:42AM -0800, Linus Torvalds wrote:
> On Mon, Nov 24, 2014 at 11:07 AM, Christian Borntraeger
> <borntraeger@xxxxxxxxxx> wrote:
> >
> > Looks really nice, but does not work with ACCESS_ONCE is on the left-hand side:
>
> Oh, I forgot about that. And that was indeed why I had done that whole
> helper macro originally, with ACCESS_ONCE() itself just being the
> dereference of the pointer.
OK, how about the following?
It complains if the variable is too large, for example, long long on
32-bit systems or large structures. It is OK loading from and storing
to small structures as well, which I am having a hard time thinking of
as a disadvantage.
Thanx, Paul
------------------------------------------------------------------------
#define get_scalar_volatile_pointer(x) ({ \
volatile typeof(x) *__vp = &(x); \
BUILD_BUG_ON(sizeof(*__vp) != sizeof(char) && \
sizeof(*__vp) != sizeof(short) && \
sizeof(*__vp) != sizeof(int) && \
sizeof(*__vp) != sizeof(long)); \
__vp; })
#define ACCESS_ONCE(x) (*get_scalar_volatile_pointer(x))
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