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

[Ben Dooks <ben.dooks@codethink.co.uk>]

On 24/06/2026 17:25, Al Viro wrote:
> On Wed, Jun 24, 2026 at 11:17:17AM +0100, Ben Dooks wrote:
>> 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.
> 
> It does not require __force - not with the type we are casting to being
> unsigned long.  As the examples you've quoted demonstrate.  See
> evaluate_cast() in sparse evaluate.c:
>          if ((ttype == &ulong_ctype || ttype == uintptr_ctype) && !Wcast_from_as)
> 		tas = &bad_address_space;
> with
>          if (!tas && valid_as(sas))
> 		warning(expr->pos, "cast removes address space '%s' of expression", show_as(sas));
> several lines below.
> 
> And yes, it is deliberate.

Ah we should also have checked for intptr or long type there,
the original code had long which causes sparse to complain here.


-- 
Ben Dooks				http://www.codethink.co.uk/
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