[PATCH] xfs: work around bogus gcc warning in xfs_allocbt_init_cursor

[PATCH] xfs: work around bogus gcc warning in xfs_allocbt_init_cursor

[Christoph Hellwig]

GCC 4.6 complains about an array subscript is above array bounds when
using the btree index to index into the agf_levels array.  The only
two indices passed in are 0 and 1, and we have an assert insuring that.

Replace the trick of using the array index directly with using constants
in the already existing branch for assigning the XFS_BTREE_LASTREC_UPDATE
flag.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: xfs/fs/xfs/xfs_alloc_btree.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc_btree.c	2011-06-17 14:16:27.929065669 +0200
+++ xfs/fs/xfs/xfs_alloc_btree.c	2011-06-17 14:17:22.145729599 +0200
@@ -427,13 +427,16 @@ xfs_allocbt_init_cursor(
 
 	cur->bc_tp = tp;
 	cur->bc_mp = mp;
-	cur->bc_nlevels = be32_to_cpu(agf->agf_levels[btnum]);
 	cur->bc_btnum = btnum;
 	cur->bc_blocklog = mp->m_sb.sb_blocklog;
-
 	cur->bc_ops = &xfs_allocbt_ops;
-	if (btnum == XFS_BTNUM_CNT)
+
+	if (btnum == XFS_BTNUM_CNT) {
+		cur->bc_nlevels = be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNT]);
 		cur->bc_flags = XFS_BTREE_LASTREC_UPDATE;
+	} else {
+		cur->bc_nlevels = be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]);
+	}
 
 	cur->bc_private.a.agbp = agbp;
 	cur->bc_private.a.agno = agno;

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Re: [PATCH] xfs: work around bogus gcc warning in xfs_allocbt_init_cursor

[Dave Chinner]

On Fri, Jun 17, 2011 at 09:12:14AM -0400, Christoph Hellwig wrote:
> GCC 4.6 complains about an array subscript is above array bounds when
> using the btree index to index into the agf_levels array.  The only
> two indices passed in are 0 and 1, and we have an assert insuring that.
> 
> Replace the trick of using the array index directly with using constants
> in the already existing branch for assigning the XFS_BTREE_LASTREC_UPDATE
> flag.

Ugh.

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> Index: xfs/fs/xfs/xfs_alloc_btree.c
> ===================================================================
> --- xfs.orig/fs/xfs/xfs_alloc_btree.c	2011-06-17 14:16:27.929065669 +0200
> +++ xfs/fs/xfs/xfs_alloc_btree.c	2011-06-17 14:17:22.145729599 +0200
> @@ -427,13 +427,16 @@ xfs_allocbt_init_cursor(
>  
>  	cur->bc_tp = tp;
>  	cur->bc_mp = mp;
> -	cur->bc_nlevels = be32_to_cpu(agf->agf_levels[btnum]);
>  	cur->bc_btnum = btnum;
>  	cur->bc_blocklog = mp->m_sb.sb_blocklog;
> -
>  	cur->bc_ops = &xfs_allocbt_ops;
> -	if (btnum == XFS_BTNUM_CNT)
> +
> +	if (btnum == XFS_BTNUM_CNT) {
> +		cur->bc_nlevels = be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNT]);
>  		cur->bc_flags = XFS_BTREE_LASTREC_UPDATE;
> +	} else {
> +		cur->bc_nlevels = be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]);
> +	}
>  
>  	cur->bc_private.a.agbp = agbp;
>  	cur->bc_private.a.agno = agno;

Looks fine.

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com

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