libxfs: Fix attr leaf block definition

struct xfs_attr_leafblock contains 'entries' array which is declared
with size 1 altough it can in fact contain much more entries. Since this
array is followed by further struct members, gcc (at least in version
4.8.3) thinks that the array has the fixed size of 1 element and thus
optimizes away all accesses beyond the end of array resulting in
non-working code. In particular this problem was seen with
xfsprogs-3.1.8.

Signed-off-by: Jan Kara <jack@suse.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/libxfs/xfs_da_format.h b/libxfs/xfs_da_format.h
index 74bcbabfa52329bda4d932daeab73ae624bde7f1..b14bbd6bb05fad090571bcada4e4867e35040b87 100644 (file)
--- a/libxfs/xfs_da_format.h
+++ b/libxfs/xfs_da_format.h
@@ -680,8 +680,15 @@ typedef struct xfs_attr_leaf_name_remote {
 typedef struct xfs_attr_leafblock {
        xfs_attr_leaf_hdr_t     hdr;    /* constant-structure header block */
        xfs_attr_leaf_entry_t   entries[1];     /* sorted on key, not name */
-       xfs_attr_leaf_name_local_t namelist;    /* grows from bottom of buf */
-       xfs_attr_leaf_name_remote_t valuelist;  /* grows from bottom of buf */
+       /*
+        * The rest of the block contains the following structures after the
+        * leaf entries, growing from the bottom up. The variables are never
+        * referenced and definining them can actually make gcc optimize away
+        * accesses to the 'entries' array above index 0 so don't do that.
+        *
+        * xfs_attr_leaf_name_local_t namelist;
+        * xfs_attr_leaf_name_remote_t valuelist;
+        */
 } xfs_attr_leafblock_t;
 
 /*