linux-kernel - [PATCH 4.9 179/223] iio: iio-utils: Fix possible incorrect mask calculation

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Message-Id: <20190802092249.313005775@linuxfoundation.org>
Date:   Fri,  2 Aug 2019 11:36:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Bastien Nocera <hadess@...ess.net>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 179/223] iio: iio-utils: Fix possible incorrect mask calculation

[ 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@...il.com> in
iio-sensor-proxy:
https://github.com/hadess/iio-sensor-proxy/commit/9615ceac7c134d838660e209726cd86aa2064fd3

Signed-off-by: Bastien Nocera <hadess@...ess.net>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Signed-off-by: Sasha Levin <sashal@...nel.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 7a6d61c6c012..55272fef3b50 100644
--- a/tools/iio/iio_utils.c
+++ b/tools/iio/iio_utils.c
@@ -159,9 +159,9 @@ 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