| Message ID | 8b5ad111c555eb548c4f3da6d55e426a15ebf59b.camel@hadess.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] iio: iio-utils: Fix possible incorrect mask calculation | expand |
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)) { >
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)) {
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(-)