linux-kernel - Re: [PATCH 11/19] regmap: avoid undefined return from regmap_read

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Message-ID: <20130126095916.GB23505@n2100.arm.linux.org.uk>
Date:	Sat, 26 Jan 2013 09:59:16 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 11/19] regmap: avoid undefined return from
	regmap_read_debugfs

On Sat, Jan 26, 2013 at 05:49:29PM +0800, Mark Brown wrote:
> Oh, ffs.  This is a false positive from the compiler - there is no case
> where it can actually do this as we will bail out before the walk if the
> list is empty so we'll always take at least one trip through our
> list_for_each_entry() and either return or set ret.  It should be smart
> enough to work out that the list_empty() means list_for_each_entry()
> will iterate over at least one entry or more conservative in what it
> warns about.

Why not code the function in a way that avoids the problem altogether?

	/*
	 * This should never happen; we return above if we fail to
	 * allocate and we should never be in this code if there are
	 * no registers at all.
	 */
-	if (list_empty(&map->debugfs_off_cache)) {
-		WARN_ON(list_empty(&map->debugfs_off_cache));
-		return base;
-	}
+	WARN_ON(list_empty(&map->debugfs_off_cache));
+	ret = base;

	/* Find the relevant block */
	list_for_each_entry(c, &map->debugfs_off_cache, list) {
		if (from >= c->min && from <= c->max) {
			*pos = c->min;
			return c->base_reg;
		}

		*pos = c->min;
		ret = c->base_reg;
	}

	return ret;
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