[PATCH 4.4 121/158] iio: iio-utils: Fix possible incorrect mask calculation

Greg Kroah-Hartman
2019-08-02T09:34:46Z

[ Upstream commit 208a68c8393d6041a90862992222f3d7943d44d6 ]

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>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 5eb6793f3972..2d0dcd6fc64c 100644
--- a/tools/iio/iio_utils.c
+++ b/tools/iio/iio_utils.c
@@ -163,9 +163,9 @@ 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)) {
--
2.20.1