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

[Ben Dooks]

On 24/06/2026 00:47, 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.

Trying to get rid of the address space warning, which requires the
__force part.

> ; cat >/tmp/a.c <<'EOF'
> #define __iomem __attribute__((noderef, address_space(__iomem)))
>   
> static int f(void __iomem *p)
> {
> 	return (unsigned long)p;
> }
>
> static int g(void __iomem *p)
> {
> 	return (long)p;
> }
> EOF
> ; sparse /tmp/a.c
> /tmp/a.c:10:17: warning: cast removes address space '__iomem' of expression
> ; sparse -Wcast-from-as /tmp/a.c
> /tmp/a.c:5:17: warning: cast removes address space '__iomem' of expression
> /tmp/a.c:10:17: warning: cast removes address space '__iomem' of expression
> ; sparse -Wall /tmp/a.c
> /tmp/a.c:10:17: warning: cast removes address space '__iomem' of expression
> ; sparse -Wsparse-all /tmp/a.c
> /tmp/a.c:5:17: warning: cast removes address space '__iomem' of expression
> /tmp/a.c:10:17: warning: cast removes address space '__iomem' of expression


--
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius

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