2020-10-05 15:07:54

by Anand Ashok Dumbre

Subject: [LINUX PATCH v3] iio: core: Fix IIO_VAL_FRACTIONAL calculation for negative values

Fixes IIO_VAL_FRACTIONAL for case when the result is negative and
exponent is 0.

example: if the result is -0.75, tmp0 will be 0 and tmp1 = 75
This causes the output to lose sign because of %d in snprintf
which works for tmp0 <= -1.

Signed-off-by: Anand Ashok Dumbre <[email protected]>
Reported-by: kernel test robot <[email protected]> #error: uninitialized symbol tmp
Reported-by: Dan Carpenter <[email protected]>
---

Changes in v3:
Fixed a bug caught by kernel test robot and used correct variable

---
drivers/iio/industrialio-core.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index cdcd16f1..ffd5176 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -592,6 +592,7 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
{
unsigned long long tmp;
int tmp0, tmp1;
+ s64 tmp2;
bool scale_db = false;

switch (type) {
@@ -614,10 +615,13 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
else
return scnprintf(buf, len, "%d.%09u", vals[0], vals[1]);
case IIO_VAL_FRACTIONAL:
- tmp = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
+ tmp2 = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
tmp1 = vals[1];
- tmp0 = (int)div_s64_rem(tmp, 1000000000, &tmp1);
- return scnprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
+ tmp0 = (int)div_s64_rem(tmp2, 1000000000, &tmp1);
+ if ((tmp2 < 0) && (tmp0 == 0))
+ return snprintf(buf, len, "-0.%09u", abs(tmp1));
+ else
+ return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
case IIO_VAL_FRACTIONAL_LOG2:
tmp = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
tmp0 = (int)div_s64_rem(tmp, 1000000000LL, &tmp1);
--
2.7.4

2020-10-10 23:16:37

by Jonathan Cameron

Subject: Re: [LINUX PATCH v3] iio: core: Fix IIO_VAL_FRACTIONAL calculation for negative values

On Mon, 5 Oct 2020 08:05:16 -0700
Anand Ashok Dumbre <[email protected]> wrote:

> Fixes IIO_VAL_FRACTIONAL for case when the result is negative and
> exponent is 0.
>
> example: if the result is -0.75, tmp0 will be 0 and tmp1 = 75
> This causes the output to lose sign because of %d in snprintf
> which works for tmp0 <= -1.
>
> Signed-off-by: Anand Ashok Dumbre <[email protected]>
> Reported-by: kernel test robot <[email protected]> #error: uninitialized symbol tmp
> Reported-by: Dan Carpenter <[email protected]>
As this doesn't have a fixes tag etc and from v2 discussion was only hit
with a new driver, I'm not currently taking this a a fix.
If people want me to rush it in / backport to stable then let me know

Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to poke at it.

Thanks,

Jonathan

> ---
>
> Changes in v3:
> Fixed a bug caught by kernel test robot and used correct variable
>
> ---
> drivers/iio/industrialio-core.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index cdcd16f1..ffd5176 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -592,6 +592,7 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
> {
> unsigned long long tmp;
> int tmp0, tmp1;
> + s64 tmp2;
> bool scale_db = false;
>
> switch (type) {
> @@ -614,10 +615,13 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
> else
> return scnprintf(buf, len, "%d.%09u", vals[0], vals[1]);
> case IIO_VAL_FRACTIONAL:
> - tmp = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
> + tmp2 = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
> tmp1 = vals[1];
> - tmp0 = (int)div_s64_rem(tmp, 1000000000, &tmp1);
> - return scnprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
> + tmp0 = (int)div_s64_rem(tmp2, 1000000000, &tmp1);
> + if ((tmp2 < 0) && (tmp0 == 0))
> + return snprintf(buf, len, "-0.%09u", abs(tmp1));
> + else
> + return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
> case IIO_VAL_FRACTIONAL_LOG2:
> tmp = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
> tmp0 = (int)div_s64_rem(tmp, 1000000000LL, &tmp1);