Re: [PATCH 1/1] btrfs-progs: fix compiler warning

From: Christian Hesse <mail@eworm.de>
To: David Sterba <dsterba@suse.cz>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 1/1] btrfs-progs: fix compiler warning
Date: Tue, 3 Jun 2014 20:04:11 +0200	[thread overview]
Message-ID: <20140603200411.6202ee70@leda.localdomain> (raw)
In-Reply-To: <20140603165225.GR22324@twin.jikos.cz>

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David Sterba <dsterba@suse.cz> on Tue, 2014/06/03 18:52:
> On Tue, Jun 03, 2014 at 01:29:19PM +0200, Christian Hesse wrote:
> > gcc 4.9.0 gives a warning: array subscript is above array bounds
> > 
> > Checking for "greater or equal" instead of just "equal" fixes this.
> 
> That fixes the warning, but I don't see the code path that leads to
>  level >= BTRFS_MAX_LEVEL
> 
> On the first pass, when level = 1 and the first while() reaches at most
> BTRFS_MAX_LEVEL, the equality test is enough. So it has to go through
> the second while() where level is decremented and in the range
> [1..BTRFS_MAX_LEVEL-1] before 'goto again' jumps to the first while
> again.

I suppose gcc does not know how much level can be increased within
function next_leaf(). level > BTRFS_MAX_LEVEL is never met at runtime, but
this way gcc knows that level can never be bigger than BTRFS_MAX_LEVEL.

Any better way to fix this?
-- 
Schoene Gruesse
Chris
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