Re: [PATCH] i2c: atr: annotate i2c_atr_adap_desc->aliases with __counted_by_ptr

[Luca Ceresoli]

On Tue Apr 28, 2026 at 10:27 PM CEST, Rosen Penev wrote:
> On Tue, Apr 28, 2026 at 2:30 AM Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx> wrote:
>>
>> Hello Thorsten,
>>
>> +Cc Romain, author of the involved code
>> +Cc Rosen, author of a similar patch elsewhere in i2c-atr [0]
>>
>> [0] https://lore.kernel.org/linux-i2c/20260327030310.8502-1-rosenp@xxxxxxxxx/
>>
>> On Mon Apr 27, 2026 at 7:28 PM CEST, Thorsten Blum wrote:
>> > Add the __counted_by_ptr() compiler attribute to ->aliases to improve
>> > bounds checking via CONFIG_UBSAN_BOUNDS and CONFIG_FORTIFY_SOURCE.
>> >
>> > Signed-off-by: Thorsten Blum <thorsten.blum@xxxxxxxxx>
>> > ---
>> >  include/linux/i2c-atr.h | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/include/linux/i2c-atr.h b/include/linux/i2c-atr.h
>> > index 2bb54dc87c8e..b52a7b9ec536 100644
>> > --- a/include/linux/i2c-atr.h
>> > +++ b/include/linux/i2c-atr.h
>> > @@ -71,7 +71,7 @@ struct i2c_atr_adap_desc {
>> >       struct device *parent;
>> >       struct fwnode_handle *bus_handle;
>> >       size_t num_aliases;
>> > -     u16 *aliases;
>> > +     u16 *aliases __counted_by_ptr(num_aliases);
>>
>> I'm not fully proficient about all counted_by things, but the patch looks
>> OK to me, and definitely @num_aliases is the number of items @aliases must
>> have, so:
> I prefer my patch.
>
> __counted_by is supported by more versions of GCC/Clang than __counted_by_ptr.

At a quick grep check, they seem to be different things: __counted_by for
arrays embedded in structs, __counted_by_ptr for pointers in structs for
dynamically allocated arrays. I wish this were documented, though,
especially as their implementation is currently identical. :-/

Based on this, I think both Rosen's and Thorsten's changes are OK, using
different macros for different members.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com