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iio: iio-utils: Fix possible incorrect mask calculation

Message ID c4b10f0d0d765c1ae972cdf896ddc490fe898c8a.camel@hadess.net (mailing list archive)
State New, archived
Headers show
Series iio: iio-utils: Fix possible incorrect mask calculation | expand

Commit Message

Bastien Nocera June 24, 2019, 11:34 a.m. UTC 
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
---
 tools/iio/iio_utils.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Jonathan Cameron June 26, 2019, 7:38 p.m. UTC | #1 
On Mon, 24 Jun 2019 13:34:47 +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

Needs a Signed-off-by:

Otherwise good fix!

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)) {
>
diff mbox series

Patch

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)) {