Index: sys/kern/uipc_mbuf2.c
===================================================================
RCS file: /cvsroot/src/sys/kern/uipc_mbuf2.c,v
retrieving revision 1.30
diff -p -u -r1.30 uipc_mbuf2.c
--- sys/kern/uipc_mbuf2.c	8 Oct 2013 19:59:49 -0000	1.30
+++ sys/kern/uipc_mbuf2.c	3 Feb 2016 23:47:49 -0000
@@ -179,6 +179,15 @@ m_pulldown(struct mbuf *m, int off, int 
 	}
 	if ((off == 0 || offp) && M_LEADINGSPACE(n->m_next) >= hlen &&
 	    !sharedcluster && n->m_next->m_len >= tlen) {
+		KASSERTMSG(((((uintptr_t)n->m_next->m_data & 3) == 0) ||
+			(((uintptr_t)m->m_data & 3) != 0) ||
+			((off & 3) != 0)),
+		    "misaligned mbuf next: next->m_data=%p, off=%d, len=%d",
+		    n->m_next->m_data, off, len);
+		KASSERTMSG(((hlen & 3) == 0 ||
+			((uintptr_t)n->m_next->m_data & 3) != 0),
+		    "misaligning mbuf: m_len=%d, off=%d, len=%d, hlen=%d",
+		    n->m_len, off, len, hlen);
 		n->m_next->m_data -= hlen;
 		n->m_next->m_len += hlen;
 		memcpy(mtod(n->m_next, void *), mtod(n, char *) + off, hlen);