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Re: [PATCH] 2.6.35.4: Fixed simple warning (array subscript is above arr

To: Poyo VL <poyo_vl@xxxxxxxxx>
Subject: Re: [PATCH] 2.6.35.4: Fixed simple warning (array subscript is above array bounds)
From: Alex Elder <aelder@xxxxxxx>
Date: Thu, 16 Sep 2010 11:42:02 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <388312.90213.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
References: <388312.90213.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Reply-to: aelder@xxxxxxx
On Thu, 2010-09-02 at 02:10 -0700, Poyo VL wrote:
> From: Ionut Gabriel Popescu <poyo_vl@xxxxxxxxx>
> 
> When I tried to compile, I got the following warning:
> fs/xfs/xfs_dir2_block.c: In function ‘xfs_dir2_sf_to_block’:
> fs/xfs/xfs_dir2_block.c:1153:26: warning: array subscript is above array 
> bounds
> The code (fs/xfs/xfs_dir2_block.c line 1153) is:
> dep->name[0] = dep->name[1] = '.';
> dep is a pointer to a xfs_dir2_data_entry_t structure where name is defined 
> as:
> __u8            name[1];    /* name bytes, no null */
> So it is a single element array, name[0] not also name[1] so I got that 
> warning.
> Patching is a simple replacement of 1 with 2.

It looks to me like this will work.  But I would like
a second opinion on that before I commit this change.

An xfs_dir2_data_entry structure is defined the way
it is to be informative; its physical representation
is different when it's actually used.  The name array
is sized based on the actual name length, and the tag
lies somewhere after that--at the very end of the
(dynamically-sized) data entry.

Additionally, the alignment of the overall structure
will be 64 bits because of hte inumber field.  Expanding
the name field by another byte will not change that.

So I think this change is OK.  Can anyone else
back me up?

Reviewed-by: Alex Elder <aelder@xxxxxxx>

> Signed-off-by: Ionut Gabriel Popescu <poyo_vl@xxxxxxxxx>
> ---
> 
> --- a/fs/xfs/xfs_dir2_data.h    2010-09-02 11:13:11.632007536 +0300
> +++ b/fs/xfs/xfs_dir2_data.h    2010-09-02 11:13:28.080006488 +0300
> @@ -87,7 +87,7 @@
>  typedef struct xfs_dir2_data_entry {
>      __be64            inumber;    /* inode number */
>      __u8            namelen;    /* name length */
> -    __u8            name[1];    /* name bytes, no null */
> +    __u8            name[2];    /* name bytes, no null */
>                          /* variable offset */
>      __be16            tag;        /* starting offset of us */
>  } xfs_dir2_data_entry_t;
> 
> 
>       



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