linux-kernel - [PATCH AUTOSEL 5.2 100/171] mfd: arizona: Fix undefined behavior

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Message-Id: <20190719035643.14300-100-sashal@kernel.org>
Date:   Thu, 18 Jul 2019 23:55:31 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Lee Jones <lee.jones@...aro.org>,
        Sasha Levin <sashal@...nel.org>, patches@...nsource.cirrus.com,
        clang-built-linux@...glegroups.com
Subject: [PATCH AUTOSEL 5.2 100/171] mfd: arizona: Fix undefined behavior

From: Arnd Bergmann <arnd@...db.de>

[ Upstream commit 5da6cbcd2f395981aa9bfc571ace99f1c786c985 ]

When the driver is used with a subdevice that is disabled in the
kernel configuration, clang gets a little confused about the
control flow and fails to notice that n_subdevs is only
uninitialized when subdevs is NULL, and we check for that,
leading to a false-positive warning:

drivers/mfd/arizona-core.c:1423:19: error: variable 'n_subdevs' is uninitialized when used here
      [-Werror,-Wuninitialized]
                              subdevs, n_subdevs, NULL, 0, NULL);
                                       ^~~~~~~~~
drivers/mfd/arizona-core.c:999:15: note: initialize the variable 'n_subdevs' to silence this warning
        int n_subdevs, ret, i;
                     ^
                      = 0

Ideally, we would rearrange the code to avoid all those early
initializations and have an explicit exit in each disabled case,
but it's much easier to chicken out and add one more initialization
here to shut up the warning.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Charles Keepax <ckeepax@...nsource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@...aro.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/mfd/arizona-core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mfd/arizona-core.c b/drivers/mfd/arizona-core.c
index 2bdc7b02157a..4a31907a4525 100644
--- a/drivers/mfd/arizona-core.c
+++ b/drivers/mfd/arizona-core.c
@@ -993,7 +993,7 @@ int arizona_dev_init(struct arizona *arizona)
 	unsigned int reg, val;
 	int (*apply_patch)(struct arizona *) = NULL;
 	const struct mfd_cell *subdevs = NULL;
-	int n_subdevs, ret, i;
+	int n_subdevs = 0, ret, i;
 
 	dev_set_drvdata(arizona->dev, arizona);
 	mutex_init(&arizona->clk_lock);
-- 
2.20.1