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	Wed, 24 Jun 2026 00:04:37 +0000
Date: Wed, 24 Jun 2026 01:04:36 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
To: Ben Dooks <ben.dooks@codethink.co.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] lib/iomem_copy: fix __iomem casts
Message-ID: <20260624000436.GH2636677@ZenIV>
References: <20260622124857.379868-1-ben.dooks@codethink.co.uk>
 <20260623234720.GG2636677@ZenIV>
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Sender: Al Viro <viro@ftp.linux.org.uk>

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...