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From: David Sterba <dsterba@suse.cz>
To: Qu Wenruo <wqu@suse.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v2 07/13] btrfs-progs: Fix Wmaybe-uninitialized warning
Date: Wed, 5 Dec 2018 14:40:05 +0100
Message-ID: <20181205134005.GB3905@twin.jikos.cz> (raw)
In-Reply-To: <20181205064018.27755-8-wqu@suse.com>

On Wed, Dec 05, 2018 at 02:40:12PM +0800, Qu Wenruo wrote:
> GCC 8.2.1 will report the following warning with "make W=1":
> 
>   ctree.c: In function 'btrfs_next_sibling_tree_block':
>   ctree.c:2990:21: warning: 'slot' may be used uninitialized in this function [-Wmaybe-uninitialized]
>     path->slots[level] = slot;
>     ~~~~~~~~~~~~~~~~~~~^~~~~~
> 
> The culprit is the following code:
> 
> 	int slot;		<< Not initialized
> 	int level = path->lowest_level + 1;
>  	BUG_ON(path->lowest_level + 1 >= BTRFS_MAX_LEVEL);
>  	while(level < BTRFS_MAX_LEVEL) {
> 		slot = path->slots[level] + 1;
> 		^^^^^^ but we initialize @slot here.
> 		...
> 	}
> 	path->slots[level] = slot;
> 
> It's possible that compiler doesn't get enough hint for BUG_ON() on
> lowest_level + 1 >= BTRFS_MAX_LEVEL case.
> 
> Fix it by using a do {} while() loop other than while() {} loop, to
> ensure we will run the loop for at least once.

I was hoping that we can actually add the hint to BUG_ON so the code
does not continue if the condition is true.

  reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-05  6:40 [PATCH v2 00/13] btrfs-progs: Make W=1 great (no "again") Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 01/13] btrfs-progs: Makefile.extrawarn: Import cc-disable-warning Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 02/13] btrfs-progs: fix gcc8 default build warning caused by '-Wformat-truncation' Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 03/13] btrfs-progs: Makefile.extrawarn: Don't warn on sign compare Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 04/13] btrfs-progs: Fix Wempty-body warning Qu Wenruo
2018-12-13 18:59   ` David Sterba
2018-12-13 23:54     ` Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 05/13] btrfs-progs: Fix Wimplicit-fallthrough warning Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 06/13] btrfs-progs: Fix Wsuggest-attribute=format warning Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 07/13] btrfs-progs: Fix Wmaybe-uninitialized warning Qu Wenruo
2018-12-05 13:40   ` David Sterba [this message]
2018-12-05 14:03     ` Qu Wenruo
2019-01-15 17:42       ` David Sterba
2018-12-05  6:40 ` [PATCH v2 08/13] btrfs-progs: Fix Wtype-limits warning Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 09/13] btrfs-progs: Fix missing-prototypes warning caused by non-static functions Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 10/13] btrfs-progs: Move btrfs_check_nodesize to fsfeatures.c to fix missing-prototypes warning Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 11/13] btrfs-progs: Introduce rescue.h to resolve missing-prototypes for chunk and super rescue Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 12/13] btrfs-progs: Add utils.h include to solve missing-prototypes warning Qu Wenruo
2018-12-05  6:40 ` [PATCH v2 13/13] btrfs-progs: free-space-tree: Remove unsued function Qu Wenruo

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