On Fri, Jan 19, 2018 at 4:55 AM, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> So really we should be casting 'b' and 'a' to uintptr_t to be fully
> compliant with the spec.
That's an unnecessary technicality.
Any compiler that doesn't get pointer inequality testing right is not
worth even worrying about. We wouldn't want to use such a compiler,
because it's intentionally generating garbage just to f*ck with us.
Why would you go along with that?
So the only real issue is that pointer subtraction case.
I actually asked (long long ago) for an optinal compiler warning for
"pointer subtraction with non-power-of-2 sizes". Not because of it
being undefined, but simply because it's expensive. The
divide->multiply thing doesn't always work, and a real divide is
really quite expensive on many architectures.
We *should* be careful about it. I guess sparse could be made to warn,
but I'm afraid that we have so many of these things that a warning
isn't reasonable.
And most of the time, a pointer difference really is inside the same
array. The operation doesn't tend to make sense otherwise.
Linus
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
