Re: [PATCH] iio: inkern: Avoid risky abs() usage in iio_multiply_value()

Andy Shevchenko
2026-03-31T18:37:34Z

On Tue, Mar 31, 2026 at 02:13:29PM +0200, Romain Gantois wrote:
> On Tuesday, 31 March 2026 12:08:26 CEST Andy Shevchenko wrote:
> > On Tue, Mar 31, 2026 at 12:29:22PM +0300, Andy Shevchenko wrote:
> > > On Tue, Mar 31, 2026 at 10:49:59AM +0200, Romain Gantois wrote:

...

> > > > - *result = multiplier * abs(val);
> > > > - *result += div_s64(multiplier * abs(val2), denominator);
> > > > + *result = multiplier * abs((s64)val);
> > > > + *result += div_s64(multiplier * abs((s64)val2), denominator);
> > >
> > > Right, but here we get val and val2 from either static values from the
> > > driver (when it is SCALE channel), or when channel has PROCESSED support.
> > > In the latter one it might theoretically be possible to go till the
> > > INT_MIN, but practically I don't know how, except for the broken driver
> > > code in the first place. With that being said, I think it's better to
> > > validate somewhere the multipliers (when it's SCALE or PROCESSED
> > > channel). I also noted that for the _PROCESSED some drivers keep a
> > > garbage in val2. That probably needs to be addressed as well (exempli
> > > gratia: bmi270_read_raw() does that).
> >
> > Actually the data in the val and val2 should be aligned with the returned
> > type, hence the potential bugs might only come from the untested drivers.
> > Which means that this patch doesn't improve the situation.
>
> I'm a bit confused: when you say "the returned type" what returning function
> are you referring to?

_read_channel(). It returns the type of the value in IIO namespace.

> Also, doesn't the patch still fix the bug for potentially
> untested drivers which use PROCESSED?

No it doesn't. It just makes it different, but not necessary working.