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Fix gcc array subscript above bounds warning

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In a debug build, certain GCC versions flag an array bounds warning in
the below code from dnode_sync.c

    } else {
            int i;
            ASSERT(dn->dn_next_nblkptr[txgoff] < dnp->dn_nblkptr);
            /* the blkptrs we are losing better be unallocated */
            for (i = dn->dn_next_nblkptr[txgoff];
                i < dnp->dn_nblkptr; i++)
                    ASSERT(BP_IS_HOLE(&dnp->dn_blkptr[i]));

This usage is in fact safe, since the ASSERT ensures the index does
not exceed to maximum possible number of block pointers. However gcc
can't determine that the assignment 'i = dn->dn_next_nblkptr[txgoff];'
falls within the array bounds so it issues a warning.  To avoid this,
initialize i to zero to make gcc happy but skip the elements before
dn->dn_next_nblkptr[txgoff] in the loop body.  Since a dnode contains
at most 3 block pointers this overhead should be negligible.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #950
This commit is contained in:
Ned Bass 2012-12-26 14:56:41 -08:00 committed by Brian Behlendorf
parent e44056fcb6
commit 37f000c5aa
1 changed files with 4 additions and 3 deletions
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7
module/zfs/dnode_sync.c
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@ -666,9 +666,10 @@ dnode_sync(dnode_t *dn, dmu_tx_t *tx)
int i;
ASSERT(dn->dn_next_nblkptr[txgoff] < dnp->dn_nblkptr);
/* the blkptrs we are losing better be unallocated */
for (i = dn->dn_next_nblkptr[txgoff];
i < dnp->dn_nblkptr; i++)
ASSERT(BP_IS_HOLE(&dnp->dn_blkptr[i]));
for (i = 0; i < dnp->dn_nblkptr; i++) {
if (i >= dn->dn_next_nblkptr[txgoff])
ASSERT(BP_IS_HOLE(&dnp->dn_blkptr[i]));
}
#endif
}
mutex_enter(&dn->dn_mtx);