static analysis bug report in drivers/staging/iio/dac/ad5380.c

static analysis bug report in drivers/staging/iio/dac/ad5380.c

[Colin Ian King]

Hi,

Static analysis with Coverity Scan has detected a potential assignment
bug in ad5380.c:

217        case IIO_CHAN_INFO_CALIBBIAS:
218                ret = regmap_read(st->regmap,
AD5380_REG_OFFSET(chan->address),
219                                        val);
220                if (ret)
221                        return ret;
222                *val >>= chan->scan_type.shift;

CID 43178 (#1 of 1): Unused value (UNUSED_VALUE)assigned_pointer:
Assigning value from val - (1 << chan->scan_type.realbits) / 2 to val
here, but that stored value is not used.

223                val -= (1 << chan->scan_type.realbits) / 2;
224                return IIO_VAL_INT;

val is a pointer and so updating it before a return is probably not the
intention.  I suspect the intention was probably:

		   *val -= (1 << chan->scan_type.realbits) / 2;

However, I'm not confident about this as the following case has:

225        case IIO_CHAN_INFO_SCALE:
226                *val = 2 * st->vref;
227                *val2 = chan->scan_type.realbits;
228                return IIO_VAL_FRACTIONAL_LOG2;

which may imply the update maybe to *val2 instead, e.g.:

		*val2 -= (1 << chan->scan_type.realbits) / 2;

Any ideas?

Colin

Re: static analysis bug report in drivers/staging/iio/dac/ad5380.c

[Lars-Peter Clausen]

On 8/15/19 12:21 PM, Colin Ian King wrote:
> Hi,
> 
> Static analysis with Coverity Scan has detected a potential assignment
> bug in ad5380.c:
> 
> 217        case IIO_CHAN_INFO_CALIBBIAS:
> 218                ret = regmap_read(st->regmap,
> AD5380_REG_OFFSET(chan->address),
> 219                                        val);
> 220                if (ret)
> 221                        return ret;
> 222                *val >>= chan->scan_type.shift;
> 
> CID 43178 (#1 of 1): Unused value (UNUSED_VALUE)assigned_pointer:
> Assigning value from val - (1 << chan->scan_type.realbits) / 2 to val
> here, but that stored value is not used.
> 
> 223                val -= (1 << chan->scan_type.realbits) / 2;
> 224                return IIO_VAL_INT;
> 
> val is a pointer and so updating it before a return is probably not the
> intention.  I suspect the intention was probably:
> 
> 		   *val -= (1 << chan->scan_type.realbits) / 2;
> 
> However, I'm not confident about this as the following case has:
> 
> 225        case IIO_CHAN_INFO_SCALE:
> 226                *val = 2 * st->vref;
> 227                *val2 = chan->scan_type.realbits;
> 228                return IIO_VAL_FRACTIONAL_LOG2;
> 
> which may imply the update maybe to *val2 instead, e.g.:
> 
> 		*val2 -= (1 << chan->scan_type.realbits) / 2;
> 
> Any ideas?

Updating changing val to *val is the right fix in this case.