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

[Al Viro]

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.

; 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