linux-kernel - [PATCH] regmap: maple: work around gcc-14.1 false-positive warning

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Message-Id: <20240719104030.1382465-1-arnd@kernel.org>
Date: Fri, 19 Jul 2024 12:40:24 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Mark Brown <broonie@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Arnd Bergmann <arnd@...db.de>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Richard Fitzgerald <rf@...nsource.cirrus.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Colin Ian King <colin.i.king@...il.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] regmap: maple: work around gcc-14.1 false-positive warning

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

With gcc-14.1, there is a false-postive -Wuninitialized warning in
regcache_maple_drop:

drivers/base/regmap/regcache-maple.c: In function 'regcache_maple_drop':
drivers/base/regmap/regcache-maple.c:113:23: error: 'lower_index' is used uninitialized [-Werror=uninitialized]
  113 |         unsigned long lower_index, lower_last;
      |                       ^~~~~~~~~~~
drivers/base/regmap/regcache-maple.c:113:36: error: 'lower_last' is used uninitialized [-Werror=uninitialized]
  113 |         unsigned long lower_index, lower_last;
      |                                    ^~~~~~~~~~

I've created a reduced test case to see if this needs to be reported
as a gcc, but it appears that the gcc-14.x branch already has a change
that turns this into a more sensible -Wmaybe-uninitialized warning, so
I ended up not reporting it so far.

The reduced test case also produces a warning for gcc-13 and gcc-12
but I don't see that with the version in the kernel.

Link: https://godbolt.org/z/oKbohKqd3
Link: https://lore.kernel.org/all/CAMuHMdWj=FLmkazPbYKPevDrcym2_HDb_U7Mb9YE9ovrP0jJfA@mail.gmail.com/
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
I'm still not convinced that this is the best solution, but I had no
other ideas here.
---
 drivers/base/regmap/regcache-maple.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regcache-maple.c b/drivers/base/regmap/regcache-maple.c
index f0df2da6d522..2dea9d259c49 100644
--- a/drivers/base/regmap/regcache-maple.c
+++ b/drivers/base/regmap/regcache-maple.c
@@ -110,7 +110,8 @@ static int regcache_maple_drop(struct regmap *map, unsigned int min,
 	struct maple_tree *mt = map->cache;
 	MA_STATE(mas, mt, min, max);
 	unsigned long *entry, *lower, *upper;
-	unsigned long lower_index, lower_last;
+	/* initialized to work around false-positive -Wuninitialized warning */
+	unsigned long lower_index = 0, lower_last = 0;
 	unsigned long upper_index, upper_last;
 	int ret = 0;
 
-- 
2.39.2