Re: [PATCH] iio: ssp_sensors: avoid uninitialized variable usage

Nathan Chancellor
2019-03-22T15:01:26Z

On Fri, Mar 22, 2019 at 03:09:22PM +0100, Arnd Bergmann wrote:
> clang points out that 'calculated_time' is only sometimes
> initialized here, which leads to incorrect data being
> passed into another function:
>
> drivers/iio/common/ssp_sensors/ssp_iio.c:95:6: error: variable 'calculated_time' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
> if (indio_dev->scan_timestamp) {
> ^~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/iio/common/ssp_sensors/ssp_iio.c:102:9: note: uninitialized use occurs here
> calculated_time);
> ^~~~~~~~~~~~~~~
> drivers/iio/common/ssp_sensors/ssp_iio.c:95:2: note: remove the 'if' if its condition is always true
> if (indio_dev->scan_timestamp) {
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/iio/common/ssp_sensors/ssp_iio.c:84:25: note: initialize the variable 'calculated_time' to silence this warning
> int64_t calculated_time;
> ^
> The data is subsequently ignored by iio_push_to_buffers_with_timestamp(),
> but the warning still feels legitimate and to work around it, we can
> initialize the time in the other case.
>
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=18501
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/iio/common/ssp_sensors/ssp_iio.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/iio/common/ssp_sensors/ssp_iio.c b/drivers/iio/common/ssp_sensors/ssp_iio.c
> index 645f2e3975db..81e8f4844c90 100644
> --- a/drivers/iio/common/ssp_sensors/ssp_iio.c
> +++ b/drivers/iio/common/ssp_sensors/ssp_iio.c
> @@ -96,6 +96,8 @@ int ssp_common_process_data(struct iio_dev *indio_dev, void *buf,
> memcpy(&time, &((char *)buf)[len], SSP_TIME_SIZE);
> calculated_time =
> timestamp + (int64_t)le32_to_cpu(time) * 1000000;
> + } else {
> + calculated_time = 0;
> }
>
> return iio_push_to_buffers_with_timestamp(indio_dev, spd->buffer,
> --
> 2.20.0
>

I sent a similar change, which is sitting in Jonathan's testing branch:

https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/commit/?id=0643039b4fee4aa54a233ead15dc0b2286f059d7

You made a good point previously that initializing the variable at the
beginning of a function may not always be the best choice. I don't have
a personal preference for which patch stays around so:

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>

Just in case.

Nathan