* [PATCH v2] iio: iio-utils: Fix possible incorrect mask calculation
@ 2019-06-27 7:20 Bastien Nocera
2019-06-27 19:38 ` Jonathan Cameron
0 siblings, 1 reply; 2+ messages in thread
From: Bastien Nocera @ 2019-06-27 7:20 UTC (permalink / raw)
To: linux-iio; +Cc: Jonathan Cameron
On some machines, iio-sensor-proxy was returning all 0's for IIO sensor
values. It turns out that the bits_used for this sensor is 32, which makes
the mask calculation:
*mask = (1 << 32) - 1;
If the compiler interprets the 1 literals as 32-bit ints, it generates
undefined behavior depending on compiler version and optimization level.
On my system, it optimizes out the shift, so the mask value becomes
*mask = (1) - 1;
With a mask value of 0, iio-sensor-proxy will always return 0 for every axis.
Avoid incorrect 0 values caused by compiler optimization.
See original fix by Brett Dutro <brett.dutro@gmail.com> in
iio-sensor-proxy:
https://github.com/hadess/iio-sensor-proxy/commit/9615ceac7c134d838660e209726cd86aa2064fd3
Signed-off-by: Bastien Nocera <hadess@hadess.net>
---
tools/iio/iio_utils.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/tools/iio/iio_utils.c b/tools/iio/iio_utils.c
index a22b6e8fad46..7399eb7f1378 100644
--- a/tools/iio/iio_utils.c
+++ b/tools/iio/iio_utils.c
@@ -156,9 +156,9 @@ int iioutils_get_type(unsigned *is_signed, unsigned *bytes, unsigned *bits_used,
*be = (endianchar == 'b');
*bytes = padint / 8;
if (*bits_used == 64)
- *mask = ~0;
+ *mask = ~(0ULL);
else
- *mask = (1ULL << *bits_used) - 1;
+ *mask = (1ULL << *bits_used) - 1ULL;
*is_signed = (signchar == 's');
if (fclose(sysfsfp)) {
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] iio: iio-utils: Fix possible incorrect mask calculation
2019-06-27 7:20 [PATCH v2] iio: iio-utils: Fix possible incorrect mask calculation Bastien Nocera
@ 2019-06-27 19:38 ` Jonathan Cameron
0 siblings, 0 replies; 2+ messages in thread
From: Jonathan Cameron @ 2019-06-27 19:38 UTC (permalink / raw)
To: Bastien Nocera; +Cc: linux-iio
On Thu, 27 Jun 2019 09:20:45 +0200
Bastien Nocera <hadess@hadess.net> wrote:
> On some machines, iio-sensor-proxy was returning all 0's for IIO sensor
> values. It turns out that the bits_used for this sensor is 32, which makes
> the mask calculation:
>
> *mask = (1 << 32) - 1;
>
> If the compiler interprets the 1 literals as 32-bit ints, it generates
> undefined behavior depending on compiler version and optimization level.
> On my system, it optimizes out the shift, so the mask value becomes
>
> *mask = (1) - 1;
>
> With a mask value of 0, iio-sensor-proxy will always return 0 for every axis.
>
> Avoid incorrect 0 values caused by compiler optimization.
>
> See original fix by Brett Dutro <brett.dutro@gmail.com> in
> iio-sensor-proxy:
> https://github.com/hadess/iio-sensor-proxy/commit/9615ceac7c134d838660e209726cd86aa2064fd3
>
> Signed-off-by: Bastien Nocera <hadess@hadess.net>
Applied to the togreg branch of iio.git.
thanks,
Jonathan
> ---
> tools/iio/iio_utils.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/iio/iio_utils.c b/tools/iio/iio_utils.c
> index a22b6e8fad46..7399eb7f1378 100644
> --- a/tools/iio/iio_utils.c
> +++ b/tools/iio/iio_utils.c
> @@ -156,9 +156,9 @@ int iioutils_get_type(unsigned *is_signed, unsigned *bytes, unsigned *bits_used,
> *be = (endianchar == 'b');
> *bytes = padint / 8;
> if (*bits_used == 64)
> - *mask = ~0;
> + *mask = ~(0ULL);
> else
> - *mask = (1ULL << *bits_used) - 1;
> + *mask = (1ULL << *bits_used) - 1ULL;
>
> *is_signed = (signchar == 's');
> if (fclose(sysfsfp)) {
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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