Rather than checking for hlen causing misalignment, we should do the

m_adj() and then check the resulting mbuf for misalignment, copying
backwards to align the mbuf if required.

This fixes a longstanding problem where an mbuf which would have been
properly aligned after an m_adj() was being misaligned and causing an
unaligned access trap in ip_input().  This bug only triggered when booting
diskless.

Reviewed by:	dfr

sys/net/if_loop.c

@@ -242,17 +242,19 @@ if_simloop(ifp, m, af, hlen)
 
 	/* Strip away media header */
 	if (hlen > 0) {
+		m_adj(m, hlen);
 #ifdef __alpha__
 		/* The alpha doesn't like unaligned data.
 		 * We move data down in the first mbuf */
-		if (hlen & 3) {
-			bcopy(m->m_data + hlen, m->m_data, m->m_len - hlen);
-			m->m_len -= hlen;
-			if (m->m_flags & M_PKTHDR)
-				m->m_pkthdr.len -= hlen;
-		} else
+		if (mtod(m, vm_offset_t) & 3) {
+			KASSERT(hlen >= 3, "if_simloop: hlen too small");
+			bcopy(m->m_data, 
+			    (char *)(mtod(m, vm_offset_t) 
+				- (mtod(m, vm_offset_t) & 3)),
+			    m->m_len);
+			mtod(m,vm_offset_t) -= (mtod(m, vm_offset_t) & 3);
+		}
 #endif
-		m_adj(m, hlen);
 	}
 
 	/* Deliver to upper layer protocol */