Re: [PATCH] lib/iomem_copy: fix __iomem casts

[Al Viro]

On Wed, Jun 24, 2026 at 12:47:20AM +0100, Al Viro wrote:
> On Mon, Jun 22, 2026 at 01:48:57PM +0100, Ben Dooks wrote:
> > The iomem_copy.c code discards __iomem address space when using
> > the IS_ALIGNED() macro. It would make more sense to fix this in
> > one place by aing a PTR_ALIGNED_LONG() macro and then doing the
> > necessary casts there before invoking IS_ALIGNED().
> > 
> > As part of this, also force the pointer to an unsigned long as
> > pointers are generally not signed, although there is no warning
> > as yet on treating pointers as signed.
> 
> > +#define PTR_ALIGNED_LONG(__ptr) IS_ALIGNED((__force unsigned long)__ptr, sizeof(long))
> 
> Casting to unsigned long is fine (indeed, casting a pointer to long had
> been very odd in the first place), but... why __force?  Casts to unsigned long
> (de facto uintptr_t) do *not* require __force - they are explicitly allowed,
> unless you pass -Wcast-from-as in sparse arguments.  -Wall does not turn
> those on; -Wsparse-all would, but kbuild doesn't pass that.

FWIW, we have 170+ places where IS_ALIGNED((unsigned long)pointer, _)
or IS_ALIGNED((uintptr_t)pointer, _) is used in the tree...