Index: uipc_mbuf.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_mbuf.c,v
retrieving revision 1.218
diff -u -p -r1.218 uipc_mbuf.c
--- uipc_mbuf.c	31 Jan 2016 00:18:07 -0000	1.218
+++ uipc_mbuf.c	11 Feb 2016 12:20:07 -0000
@@ -539,6 +539,7 @@ m_copym0(struct mbuf *m0, int off, int l
 	struct mbuf *m, *n, **np;
 	struct mbuf *top;
 	int copyhdr = 0;
+	unsigned long align;
 
 	if (off < 0 || len < 0)
 		panic("m_copym0: off %d, len %d", off, len);
@@ -581,12 +582,24 @@ m_copym0(struct mbuf *m0, int off, int l
 				n->m_len = M_TRAILINGSPACE(n);
 				n->m_len = min(n->m_len, len);
 				n->m_len = min(n->m_len, m->m_len - off);
+
+				/* duplicate the alignment of the payload */
+				align = m->m_data - m->m_ext.ext_buf;
+				align += off;
+				n->m_data += align & ALIGNBYTES;
+
 				memcpy(mtod(n, caddr_t), mtod(m, caddr_t) + off,
 				    n->m_len);
 			}
-		} else
+		} else {
+			/* duplicate data layout */
+			n->m_data += m->m_data -
+			    (m->m_flags & M_PKTHDR ? m->m_pktdat : m->m_dat);
+			n->m_data += off;
+
 			memcpy(mtod(n, caddr_t), mtod(m, caddr_t) + off,
 			    n->m_len);
+		}
 		if (len != M_COPYALL)
 			len -= n->m_len;
 		off += n->m_len;