hash: document jhash boundary behavior

Due to the uint32_t accesses in the hash computation, keys that aren't
aligned to a uint32_t boundary or multiples of uint32_t in length, may
see accesses beyond the end of the key.  This may cross a page boundary.

Signed-off-by: Chas Williams <chas3@att.com>
Acked-by: Luca Boccassi <bluca@debian.org>
Acked-by: John McNamara <john.mcnamara@intel.com>

diff --git a/lib/librte_hash/rte_jhash.h b/lib/librte_hash/rte_jhash.h
index 207478c..3eca138 100644 (file)
--- a/lib/librte_hash/rte_jhash.h
+++ b/lib/librte_hash/rte_jhash.h
@@ -290,7 +290,10 @@ rte_jhash_32b_2hashes(const uint32_t *k, uint32_t length, uint32_t *pc, uint32_t
 /**
  * The most generic version, hashes an arbitrary sequence
  * of bytes.  No alignment or length assumptions are made about
- * the input key.
+ * the input key.  For keys not aligned to four byte boundaries
+ * or a multiple of four bytes in length, the memory region
+ * just after may be read (but not used in the computation).
+ * This may cross a page boundary.
  *
  * @param key
  *   Key to calculate hash of.