Re: [PATCH] ptrdiff_t is not uintptr_t, damnit

Al Viro
2007-08-20T00:58:29Z

On Mon, Aug 20, 2007 at 01:29:21AM +0100, Anton Altaparmakov wrote:
> Hi,
>
> On 20 Aug 2007, at 01:19, David Brownell wrote:
> >On Sunday 19 August 2007, Al Viro wrote:
> >>is wrong; for one thing, it's a bad C (it's what uintptr_t is for;
> >>in general
> >>we are not even promised that ptrdiff_t is large enough to hold a
> >>pointer,
> >
> >ISTR we don't *have* a uintptr_t on all architectures, or that would
> >be the appropriate thing to use in these 32/64 bit ABI scenarios.
> >
> >
> >>Use unsigned long or uintptr_t instead.
> >
> >I suspect you mean "unsigned long long"...
>
> No he doesn't. "unsigned long" is guaranteed to be large enough to
> hold a pointer (at least on Linux anyway).
>
> On a 32-bit arch "unsigned long" is 32-bit and pointers are 32-bit.

... while unsigned long long is 64bit, which is definitely not what
one wants. For sparse it's "unsigned long is special".

FWIW, this patch puts it in linux/types.h as unsigned long. Eventually
we might want to switch explicit casts to/from unsigned long in such contexts
to uintptr_t, but for now we can't start complaining about unsigned long -
too many places are using it. I'll see what can be done to get sane
assistance from sparse in that kind of work...