Re: [PATCH v1 0/2] firewire: Simplify storing pointers in device id struct

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Subject: Re: [PATCH v1 0/2] firewire: Simplify storing pointers in device id
 struct
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Hello again,

On Wed, Apr 22, 2026 at 10:30:24AM +0200, Uwe Kleine-K=F6nig (The Capable H=
ub) wrote:
> On Wed, Apr 22, 2026 at 10:19:21AM +0300, Andy Shevchenko wrote:
> > On Tue, Apr 21, 2026 at 04:07:42PM +0200, Uwe Kleine-K=F6nig (The Capab=
le Hub) wrote:
> > > On Tue, Apr 21, 2026 at 09:53:57PM +0900, Takashi Sakamoto wrote:
> > > > On Mon, Apr 20, 2026 at 07:39:32PM +0200, Christian A. Ehrhardt wro=
te:
> > > > > On Mon, Apr 20, 2026 at 06:08:16PM +0900, Takashi Sakamoto wrote:
> >=20
> > ...
> >=20
> > > > Thanks for the references. It looks like there is not much to consi=
der
> > > > outside of mm subsystem. But I have some concerns if supporting
> > > > ARM/RISC-V adoptation of CHERI extension in Linux FireWire subsyste=
m.
> > > >=20
> > > > Any structures in UAPI header of this subsystem are defined with
> > > > an assumption that the size of pointer in the existing System V
> > > > architectures is up to 64 bits at most. We can see many usage of
> > > > '__u64' type member for pointers (e.g. 'rom' in fw_cdev_get_info
> > > > structure). I imagine to need defining specific structures for this=
 kind
> > > > of 'fat' pointer. (The same assumption lays on compat ioctl.)
> > >=20
> > > The Standard C answer to that is: The assumption that you can fit a
> > > pointer in an unsigned long or u64 is not generally justified. This is
> > > "only" given for all current Linux archtectures. And if you want an
> > > integer type to store a pointer, use uintptr_t.
> >=20
> > No, please don't. Linus was clear about this. Use `unsigned long` in th=
at case.
>=20
> On CHERI we have sizeof(unsigned long) =3D 4 and sizeof(void *) =3D 8, so
> what Linus wants doesn't work.

Correction, we have sizeof(unsigned long) =3D 8 and sizeof(void *) =3D 16 or
course.

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