linux-kernel - [PATCH] mfd: arizona: fix undefined behavior

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Message-Id: <20190322143345.1208144-1-arnd@arndb.de>
Date:   Fri, 22 Mar 2019 15:33:37 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Sapthagiri Baratam <sapthagiri.baratam@...rus.com>,
        Colin Ian King <colin.king@...onical.com>,
        patches@...nsource.cirrus.com, linux-kernel@...r.kernel.org
Subject: [PATCH] mfd: arizona: fix undefined behavior

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>
---
 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 27b61639cdc7..0ca0fc9a67fd 100644
--- a/drivers/mfd/arizona-core.c
+++ b/drivers/mfd/arizona-core.c
@@ -996,7 +996,7 @@ 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);
-- 
2.20.0