Use common code for handling absolute offsets.

Define a structure that, for absolute offsets, has a Boolean flag
indicating whether the offset has a variable part, the constant part of
the offset, and the register, if any, holding the variable part of the
offset.  Have a routine that either generates code to load the X
register with the variable part of the offset or generates no code, and
use that instead of the existing routines for specific offsets.

Use instances of that structure instead of individual variables.

Add a macro to save the current link-layer header absolute offset and
set it to a new value.

1 files changed, 188 insertions, 260 deletions

diff --git a/gencode.c b/gencode.c
index 1ad664b0..d0059118 100644
--- a/gencode.c
+++ b/gencode.c
@@ -163,6 +163,29 @@ static void free_reg(int);
 static struct block *root;
 
 /*
+ * Absolute offsets, which are offsets from the beginning of the raw
+ * packet data, are, in the general case, the sum of a variable value
+ * and a constant value; the variable value may be absent, in which
+ * case the offset is only the constant value, and the constant value
+ * may be zero, in which case the offset is only the variable value.
+ *
+ * bpf_abs_offset is a structure containing all that information:
+ *
+ *   is_variable is 1 if there's a variable part.
+ *
+ *   constant_part is the constant part of the value, possibly zero;
+ *
+ *   if is_variable is 1, reg is the register number for a register
+ *   containing the variable value if the register has been assigned,
+ *   and -1 otherwise.
+ */
+typedef struct {
+	int	is_variable;
+	u_int	constant_part;
+	int	reg;
+} bpf_abs_offset;
+
+/*
  * Value passed to gen_load_a() to indicate what the offset argument
  * is relative to the beginning of.
  */
@@ -243,9 +266,7 @@ static struct slist *gen_load_avs_llprefixlen(void);
 static struct slist *gen_load_radiotap_llprefixlen(void);
 static struct slist *gen_load_ppi_llprefixlen(void);
 static void insert_compute_vloffsets(struct block *);
-static struct slist *gen_llprefixlen(void);
-static struct slist *gen_prevlinkhdrprefixlen(void);
-static struct slist *gen_off_linkpl(void);
+static struct slist *gen_abs_offset_varpart(bpf_abs_offset *);
 static int ethertype_to_ppptype(int);
 static struct block *gen_linktype(int);
 static struct block *gen_snap(bpf_u_int32, bpf_u_int32);
@@ -776,22 +797,9 @@ gen_ncmp(offrel, offset, size, mask, jtype, reverse, v)
  */
 
 /*
- * The offset of the beginning of the link-layer payload, from the beginning
- * of the raw packet data, is, in the general case, the sum of a variable
- * value and a constant value; the variable value may be absent, in which
- * case the offset is only the constant value, and the constant value may
- * be zero, in which case the offset is only the variable value.
- *
- * off_linkhdr_constant_part is the constant value.
- *
- * reg_off_linkhdr is the register number for a register containing the
- * variable value, and -1 otherwise.
- *
- * off_linkhdr_is_variable is 1 if there's a variable part.
+ * Absolute offset of the beginning of the link-layer header.
  */
-static u_int off_linkhdr_constant_part;
-static int reg_off_linkhdr;
-static int off_linkhdr_is_variable;
+static bpf_abs_offset off_linkhdr;
 
 /*
  * If we're checking a link-layer header for a packet encapsulated in
@@ -799,40 +807,38 @@ static int off_linkhdr_is_variable;
  * previous layers' link-layer header from the beginning of the raw
  * packet data.
  */
-static u_int off_prevlinkhdr_constant_part;
-static int reg_off_prevlinkhdr;
-static int off_prevlinkhdr_is_variable;
+static bpf_abs_offset off_prevlinkhdr;
 
 /*
  * This is the equivalent information for the outermost layers' link-layer
  * header.
  */
-static u_int off_outermostlinkhdr_constant_part;
-static int reg_off_outermostlinkhdr;
-static int off_outermostlinkhdr_is_variable;
+static bpf_abs_offset off_outermostlinkhdr;
 
 /*
- * The offset of the beginning of the link-layer payload, from the beginning
- * of the raw packet data, is, in the general case, the sum of a variable
- * value and a constant value; the variable value may be absent, in which
- * case the offset is only the constant value, and the constant value may
- * be zero, in which case the offset is only the variable value.
- *
- * off_linkpl_constant_part is the constant value.
- *
- * reg_off_linkpl is the register number for a register containing the
- * variable value, and -1 otherwise.
- *
- * off_linkpl_is_variable is 1 if there's a variable part.
+ * "Push" the current value of the link-layer header type and link-layer
+ * header offset onto a "stack", and set a new value.  (It's not a
+ * full-blown stack; we keep only the top two items.)
+ */
+#define PUSH_LINKHDR(new_linktype, new_is_variable, new_constant_part, new_reg) \
+{ \
+	prevlinktype = new_linktype; \
+	off_prevlinkhdr = off_linkhdr; \
+	linktype = new_linktype; \
+	off_linkhdr.is_variable = new_is_variable; \
+	off_linkhdr.constant_part = new_constant_part; \
+	off_linkhdr.reg = new_reg; \
+}
+
+/*
+ * Absolute offset of the beginning of the link-layer payload.
  */
-static u_int off_linkpl_constant_part;
-static int off_linkpl_is_variable;
-static int reg_off_linkpl;
+static bpf_abs_offset off_linkpl;
 
 /*
  * "off_linktype" is the offset to information in the link-layer header
  * giving the packet type.  This offset is relative to the beginning
- * of the link-layer header - i.e., it doesn't include off_linkhdr_constant_part - so
+ * of the link-layer header - i.e., it doesn't include off_linkhdr.constant_part - so
  * loads with an offset that includes "off_linktype" should use
  * OR_LINKHDR.
  *
@@ -890,7 +896,7 @@ static u_int off_payload;
 /*
  * These are offsets to the beginning of the network-layer header.
  * They are relative to the beginning of the link-layer payload (i.e.,
- * they don't include off_linkhdr_constant_part or off_linkpl_constant_part).
+ * they don't include off_linkhdr.constant_part or off_linkpl.constant_part).
  *
  * If the link layer never uses 802.2 LLC:
  *
@@ -928,26 +934,26 @@ init_linktype(p)
 	 * We start out with only one link-layer header.
 	 */
 	outermostlinktype = pcap_datalink(p);
-	off_outermostlinkhdr_constant_part = 0;
-	off_outermostlinkhdr_is_variable = 0;
-	reg_off_outermostlinkhdr = -1;
+	off_outermostlinkhdr.constant_part = 0;
+	off_outermostlinkhdr.is_variable = 0;
+	off_outermostlinkhdr.reg = -1;
 
 	prevlinktype = outermostlinktype;
-	off_prevlinkhdr_constant_part = 0;
-	off_prevlinkhdr_is_variable = 0;
-	reg_off_prevlinkhdr = -1;
+	off_prevlinkhdr.constant_part = 0;
+	off_prevlinkhdr.is_variable = 0;
+	off_prevlinkhdr.reg = -1;
 
 	linktype = outermostlinktype;
-	off_linkhdr_constant_part = 0;
-	off_linkhdr_is_variable = 0;
-	reg_off_linkhdr = -1;
+	off_linkhdr.constant_part = 0;
+	off_linkhdr.is_variable = 0;
+	off_linkhdr.reg = -1;
 
 	/*
 	 * XXX
 	 */
-	off_linkpl_constant_part = 0;
-	off_linkpl_is_variable = 0;
-	reg_off_linkpl = -1;
+	off_linkpl.constant_part = 0;
+	off_linkpl.is_variable = 0;
+	off_linkpl.reg = -1;
 
 	/*
 	 * Assume it's not raw ATM with a pseudo-header, for now.
@@ -975,21 +981,21 @@ init_linktype(p)
 
 	case DLT_ARCNET:
 		off_linktype = 2;
-		off_linkpl_constant_part = 6;
+		off_linkpl.constant_part = 6;
 		off_nl = 0;		/* XXX in reality, variable! */
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
 
 	case DLT_ARCNET_LINUX:
 		off_linktype = 4;
-		off_linkpl_constant_part = 8;
+		off_linkpl.constant_part = 8;
 		off_nl = 0;		/* XXX in reality, variable! */
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
 
 	case DLT_EN10MB:
 		off_linktype = 12;
-		off_linkpl_constant_part = 14;	/* Ethernet header length */
+		off_linkpl.constant_part = 14;	/* Ethernet header length */
 		off_nl = 0;		/* Ethernet II */
 		off_nl_nosnap = 3;	/* 802.3+802.2 */
 		return;
@@ -1000,7 +1006,7 @@ init_linktype(p)
 		 * header is hacked into our SLIP driver.
 		 */
 		off_linktype = -1;
-		off_linkpl_constant_part = 16;
+		off_linkpl.constant_part = 16;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
@@ -1009,7 +1015,7 @@ init_linktype(p)
 		/* XXX this may be the same as the DLT_PPP_BSDOS case */
 		off_linktype = -1;
 		/* XXX end */
-		off_linkpl_constant_part = 24;
+		off_linkpl.constant_part = 24;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
@@ -1017,14 +1023,14 @@ init_linktype(p)
 	case DLT_NULL:
 	case DLT_LOOP:
 		off_linktype = 0;
-		off_linkpl_constant_part = 4;
+		off_linkpl.constant_part = 4;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
 
 	case DLT_ENC:
 		off_linktype = 0;
-		off_linkpl_constant_part = 12;
+		off_linkpl.constant_part = 12;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
@@ -1034,7 +1040,7 @@ init_linktype(p)
 	case DLT_C_HDLC:		/* BSD/OS Cisco HDLC */
 	case DLT_PPP_SERIAL:		/* NetBSD sync/async serial PPP */
 		off_linktype = 2;	/* skip HDLC-like framing */
-		off_linkpl_constant_part = 4;	/* skip HDLC-like framing and protocol field */
+		off_linkpl.constant_part = 4;	/* skip HDLC-like framing and protocol field */
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
@@ -1045,14 +1051,14 @@ init_linktype(p)
 		 * only covers session state.
 		 */
 		off_linktype = 6;
-		off_linkpl_constant_part = 8;
+		off_linkpl.constant_part = 8;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
 
 	case DLT_PPP_BSDOS:
 		off_linktype = 5;
-		off_linkpl_constant_part = 24;
+		off_linkpl.constant_part = 24;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
@@ -1068,8 +1074,8 @@ init_linktype(p)
 		 */
 		off_linktype = 13;
 		off_linktype += pcap_fddipad;
-		off_linkpl_constant_part = 13;	/* FDDI MAC header length */
-		off_linkpl_constant_part += pcap_fddipad;
+		off_linkpl.constant_part = 13;	/* FDDI MAC header length */
+		off_linkpl.constant_part += pcap_fddipad;
 		off_nl = 8;		/* 802.2+SNAP */
 		off_nl_nosnap = 3;	/* 802.2 */
 		return;
@@ -1099,7 +1105,7 @@ init_linktype(p)
 		 * 8 - figure out which byte that is).
 		 */
 		off_linktype = 14;
-		off_linkpl_constant_part = 14;	/* Token Ring MAC header length */
+		off_linkpl.constant_part = 14;	/* Token Ring MAC header length */
 		off_nl = 8;		/* 802.2+SNAP */
 		off_nl_nosnap = 3;	/* 802.2 */
 		return;
@@ -1126,8 +1132,8 @@ init_linktype(p)
 		 * variable-length.
 		 */
 		off_linktype = 24;
-		off_linkpl_constant_part = 0;	/* link-layer header is variable-length */
-		off_linkpl_is_variable = 1;
+		off_linkpl.constant_part = 0;	/* link-layer header is variable-length */
+		off_linkpl.is_variable = 1;
 		off_nl = 8;		/* 802.2+SNAP */
 		off_nl_nosnap = 3;	/* 802.2 */
 		return;
@@ -1143,8 +1149,8 @@ init_linktype(p)
 		 * generate code to check for this too.
 		 */
 		off_linktype = 24;
-		off_linkpl_constant_part = 0;	/* link-layer header is variable-length */
-		off_linkpl_is_variable = 1;
+		off_linkpl.constant_part = 0;	/* link-layer header is variable-length */
+		off_linkpl.is_variable = 1;
 		off_nl = 8;		/* 802.2+SNAP */
 		off_nl_nosnap = 3;	/* 802.2 */
 		return;
@@ -1163,7 +1169,7 @@ init_linktype(p)
 		 * PPPo{A,E} and a PPP protocol of IP and....
 		 */
 		off_linktype = 0;
-		off_linkpl_constant_part = 0;	/* packet begins with LLC header */
+		off_linkpl.constant_part = 0;	/* packet begins with LLC header */
 		off_nl = 8;		/* 802.2+SNAP */
 		off_nl_nosnap = 3;	/* 802.2 */
 		return;
@@ -1179,7 +1185,7 @@ init_linktype(p)
 		off_proto = PROTO_POS;
 		off_payload = SUNATM_PKT_BEGIN_POS;
 		off_linktype = off_payload;
-		off_linkpl_constant_part = off_payload;	/* if LLC-encapsulated */
+		off_linkpl.constant_part = off_payload;	/* if LLC-encapsulated */
 		off_nl = 8;		/* 802.2+SNAP */
 		off_nl_nosnap = 3;	/* 802.2 */
 		return;
@@ -1188,14 +1194,14 @@ init_linktype(p)
 	case DLT_IPV4:
 	case DLT_IPV6:
 		off_linktype = -1;
-		off_linkpl_constant_part = 0;
+		off_linkpl.constant_part = 0;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
 
 	case DLT_LINUX_SLL:	/* fake header for Linux cooked socket */
 		off_linktype = 14;
-		off_linkpl_constant_part = 16;
+		off_linkpl.constant_part = 16;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
@@ -1207,7 +1213,7 @@ init_linktype(p)
 		 * "long" DDP packet following.
 		 */
 		off_linktype = -1;
-		off_linkpl_constant_part = 0;
+		off_linkpl.constant_part = 0;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
@@ -1224,7 +1230,7 @@ init_linktype(p)
 		 * 2625 says SNAP should be used.
 		 */
 		off_linktype = 16;
-		off_linkpl_constant_part = 16;
+		off_linkpl.constant_part = 16;
 		off_nl = 8;		/* 802.2+SNAP */
 		off_nl_nosnap = 3;	/* 802.2 */
 		return;
@@ -1235,7 +1241,7 @@ init_linktype(p)
 		 * frames (NLPID of 0x80).
 		 */
 		off_linktype = -1;
-		off_linkpl_constant_part = 0;
+		off_linkpl.constant_part = 0;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
@@ -1247,21 +1253,21 @@ init_linktype(p)
                  */
 	case DLT_MFR:
 		off_linktype = -1;
-		off_linkpl_constant_part = 0;
+		off_linkpl.constant_part = 0;
 		off_nl = 4;
 		off_nl_nosnap = 0;	/* XXX - for now -> no 802.2 LLC */
 		return;
 
 	case DLT_APPLE_IP_OVER_IEEE1394:
 		off_linktype = 16;
-		off_linkpl_constant_part = 18;
+		off_linkpl.constant_part = 18;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
 
 	case DLT_SYMANTEC_FIREWALL:
 		off_linktype = 6;
-		off_linkpl_constant_part = 44;
+		off_linkpl.constant_part = 44;
 		off_nl = 0;		/* Ethernet II */
 		off_nl_nosnap = 0;	/* XXX - what does it do with 802.3 packets? */
 		return;
@@ -1269,7 +1275,7 @@ init_linktype(p)
 #ifdef HAVE_NET_PFVAR_H
 	case DLT_PFLOG:
 		off_linktype = 0;
-		off_linkpl_constant_part = PFLOG_HDRLEN;
+		off_linkpl.constant_part = PFLOG_HDRLEN;
 		off_nl = 0;
 		off_nl_nosnap = 0;	/* no 802.2 LLC */
 		return;
@@ -1282,21 +1288,21 @@ init_linktype(p)
         case DLT_JUNIPER_CHDLC:
         case DLT_JUNIPER_FRELAY:
                 off_linktype = 4;
-		off_linkpl_constant_part = 4;
+		off_linkpl.constant_part = 4;
 		off_nl = 0;
 		off_nl_nosnap = -1;	/* no 802.2 LLC */
                 return;
 
 	case DLT_JUNIPER_ATM1:
 		off_linktype = 4;		/* in reality variable between 4-8 */
-		off_linkpl_constant_part = 4;	/* in reality variable between 4-8 */
+		off_linkpl.constant_part = 4;	/* in reality variable between 4-8 */
 		off_nl = 0;
 		off_nl_nosnap = 10;
 		return;
 
 	case DLT_JUNIPER_ATM2:
 		off_linktype = 8;		/* in reality variable between 8-12 */
-		off_linkpl_constant_part = 8;	/* in reality variable between 8-12 */
+		off_linkpl.constant_part = 8;	/* in reality variable between 8-12 */
 		off_nl = 0;
 		off_nl_nosnap = 10;
 		return;
@@ -1305,7 +1311,7 @@ init_linktype(p)
 		 * contain raw ethernet frames */
 	case DLT_JUNIPER_PPPOE:
         case DLT_JUNIPER_ETHER:
-        	off_linkpl_constant_part = 14;
+        	off_linkpl.constant_part = 14;
 		off_linktype = 16;
 		off_nl = 18;		/* Ethernet II */
 		off_nl_nosnap = 21;	/* 802.3+802.2 */
@@ -1313,63 +1319,63 @@ init_linktype(p)
 
 	case DLT_JUNIPER_PPPOE_ATM:
 		off_linktype = 4;
-		off_linkpl_constant_part = 6;
+		off_linkpl.constant_part = 6;
 		off_nl = 0;
 		off_nl_nosnap = -1;	/* no 802.2 LLC */
 		return;
 
 	case DLT_JUNIPER_GGSN:
 		off_linktype = 6;
-		off_linkpl_constant_part = 12;
+		off_linkpl.constant_part = 12;
 		off_nl = 0;
 		off_nl_nosnap = -1;	/* no 802.2 LLC */
 		return;
 
 	case DLT_JUNIPER_ES:
 		off_linktype = 6;
-		off_linkpl_constant_part = -1;	/* not really a network layer but raw IP addresses */
+		off_linkpl.constant_part = -1;	/* not really a network layer but raw IP addresses */
 		off_nl = -1;		/* not really a network layer but raw IP addresses */
 		off_nl_nosnap = -1;	/* no 802.2 LLC */
 		return;
 
 	case DLT_JUNIPER_MONITOR:
 		off_linktype = 12;
-		off_linkpl_constant_part = 12;
+		off_linkpl.constant_part = 12;
 		off_nl = 0;		/* raw IP/IP6 header */
 		off_nl_nosnap = -1;	/* no 802.2 LLC */
 		return;
 
 	case DLT_BACNET_MS_TP:
 		off_linktype = -1;
-		off_linkpl_constant_part = -1;
+		off_linkpl.constant_part = -1;
 		off_nl = -1;
 		off_nl_nosnap = -1;
 		return;
 
 	case DLT_JUNIPER_SERVICES:
 		off_linktype = 12;
-		off_linkpl_constant_part = -1;	/* L3 proto location dep. on cookie type */
+		off_linkpl.constant_part = -1;	/* L3 proto location dep. on cookie type */
 		off_nl = -1;		/* L3 proto location dep. on cookie type */
 		off_nl_nosnap = -1;	/* no 802.2 LLC */
 		return;
 
 	case DLT_JUNIPER_VP:
 		off_linktype = 18;
-		off_linkpl_constant_part = -1;
+		off_linkpl.constant_part = -1;
 		off_nl = -1;
 		off_nl_nosnap = -1;
 		return;
 
 	case DLT_JUNIPER_ST:
 		off_linktype = 18;
-		off_linkpl_constant_part = -1;
+		off_linkpl.constant_part = -1;
 		off_nl = -1;
 		off_nl_nosnap = -1;
 		return;
 
 	case DLT_JUNIPER_ISM:
 		off_linktype = 8;
-		off_linkpl_constant_part = -1;
+		off_linkpl.constant_part = -1;
 		off_nl = -1;
 		off_nl_nosnap = -1;
 		return;
@@ -1379,7 +1385,7 @@ init_linktype(p)
 	case DLT_JUNIPER_FIBRECHANNEL:
 	case DLT_JUNIPER_ATM_CEMIC:
 		off_linktype = 8;
-		off_linkpl_constant_part = -1;
+		off_linkpl.constant_part = -1;
 		off_nl = -1;
 		off_nl_nosnap = -1;
 		return;
@@ -1392,7 +1398,7 @@ init_linktype(p)
 		off_dpc = 4;
 		off_sls = 7;
 		off_linktype = -1;
-		off_linkpl_constant_part = -1;
+		off_linkpl.constant_part = -1;
 		off_nl = -1;
 		off_nl_nosnap = -1;
 		return;
@@ -1405,7 +1411,7 @@ init_linktype(p)
 		off_dpc = 8;
 		off_sls = 11;
 		off_linktype = -1;
-		off_linkpl_constant_part = -1;
+		off_linkpl.constant_part = -1;
 		off_nl = -1;
 		off_nl_nosnap = -1;
 		return;
@@ -1418,14 +1424,14 @@ init_linktype(p)
 		off_dpc = 24;
 		off_sls = 27;
 		off_linktype = -1;
-		off_linkpl_constant_part = -1;
+		off_linkpl.constant_part = -1;
 		off_nl = -1;
 		off_nl_nosnap = -1;
 		return;
 
 	case DLT_PFSYNC:
 		off_linktype = -1;
-		off_linkpl_constant_part = 4;
+		off_linkpl.constant_part = 4;
 		off_nl = 0;
 		off_nl_nosnap = 0;
 		return;
@@ -1435,30 +1441,30 @@ init_linktype(p)
 		 * Currently, only raw "link[N:M]" filtering is supported.
 		 */
 		off_linktype = -1;	/* variable, min 15, max 71 steps of 7 */
-		off_linkpl_constant_part = -1;
+		off_linkpl.constant_part = -1;
 		off_nl = -1;		/* variable, min 16, max 71 steps of 7 */
 		off_nl_nosnap = -1;	/* no 802.2 LLC */
 		return;
 
 	case DLT_IPNET:
 		off_linktype = 1;
-		off_linkpl_constant_part = 24;	/* ipnet header length */
+		off_linkpl.constant_part = 24;	/* ipnet header length */
 		off_nl = 0;
 		off_nl_nosnap = -1;
 		return;
 
 	case DLT_NETANALYZER:
-		off_linkhdr_constant_part = 4;	/* Ethernet header is past 4-byte pseudo-header */
+		off_linkhdr.constant_part = 4;	/* Ethernet header is past 4-byte pseudo-header */
 		off_linktype = 12;
-		off_linkpl_constant_part = off_linkhdr_constant_part + 14;	/* pseudo-header+Ethernet header length */
+		off_linkpl.constant_part = off_linkhdr.constant_part + 14;	/* pseudo-header+Ethernet header length */
 		off_nl = 0;		/* Ethernet II */
 		off_nl_nosnap = 3;	/* 802.3+802.2 */
 		return;
 
 	case DLT_NETANALYZER_TRANSPARENT:
-		off_linkhdr_constant_part = 12;	/* MAC header is past 4-byte pseudo-header, preamble, and SFD */
+		off_linkhdr.constant_part = 12;	/* MAC header is past 4-byte pseudo-header, preamble, and SFD */
 		off_linktype = 12;
-		off_linkpl_constant_part = off_linkhdr_constant_part + 14;	/* pseudo-header+preamble+SFD+Ethernet header length */
+		off_linkpl.constant_part = off_linkhdr.constant_part + 14;	/* pseudo-header+preamble+SFD+Ethernet header length */
 		off_nl = 0;		/* Ethernet II */
 		off_nl_nosnap = 3;	/* 802.3+802.2 */
 		return;
@@ -1471,7 +1477,7 @@ init_linktype(p)
 		if (linktype >= DLT_MATCHING_MIN &&
 		    linktype <= DLT_MATCHING_MAX) {
 			off_linktype = -1;
-			off_linkpl_constant_part = -1;
+			off_linkpl.constant_part = -1;
 			off_nl = -1;
 			off_nl_nosnap = -1;
 			return;
@@ -1494,7 +1500,7 @@ gen_load_linkhdrrel(offset, size)
 {
 	struct slist *s, *s2;
 
-	s = gen_llprefixlen();
+	s = gen_abs_offset_varpart(&off_linkhdr);
 
 	/*
 	 * If "s" is non-null, it has code to arrange that the X register
@@ -1502,7 +1508,7 @@ gen_load_linkhdrrel(offset, size)
 	 * header.
 	 *
 	 * Otherwise, the length of the prefix preceding the link-layer
-	 * header is "off_linkhdr_constant_part".
+	 * header is "off_linkhdr.constant_part".
 	 */
 	if (s != NULL) {
 		/*
@@ -1512,17 +1518,17 @@ gen_load_linkhdrrel(offset, size)
 		 * do an indirect load, to use the X register as an offset.
 		 */
 		s2 = new_stmt(BPF_LD|BPF_IND|size);
-		s2->s.k = off_linkhdr_constant_part + offset;
+		s2->s.k = off_linkhdr.constant_part + offset;
 		sappend(s, s2);
 	} else {
 		/*
 		 * There is no variable-length header preceding the
-		 * link-layer header; add in off_linkhdr_constant_part, which, if
+		 * link-layer header; add in off_linkhdr.constant_part, which, if
 		 * there's a fixed-length header preceding the
 		 * link-layer header, is the length of that header.
 		 */
 		s = new_stmt(BPF_LD|BPF_ABS|size);
-		s->s.k = off_linkhdr_constant_part + offset;
+		s->s.k = off_linkhdr.constant_part + offset;
 	}
 	return s;
 }
@@ -1542,7 +1548,7 @@ gen_load_prevlinkhdrrel(offset, size)
 {
 	struct slist *s, *s2;
 
-	s = gen_prevlinkhdrprefixlen();
+	s = gen_abs_offset_varpart(&off_prevlinkhdr);
 
 	/*
 	 * If "s" is non-null, it has code to arrange that the X register
@@ -1550,7 +1556,7 @@ gen_load_prevlinkhdrrel(offset, size)
 	 * header.
 	 *
 	 * Otherwise, the length of the prefix preceding the link-layer
-	 * header is "off_prevlinkhdr_constant_part".
+	 * header is "off_prevlinkhdr.constant_part".
 	 */
 	if (s != NULL) {
 		/*
@@ -1560,17 +1566,17 @@ gen_load_prevlinkhdrrel(offset, size)
 		 * do an indirect load, to use the X register as an offset.
 		 */
 		s2 = new_stmt(BPF_LD|BPF_IND|size);
-		s2->s.k = off_prevlinkhdr_constant_part + offset;
+		s2->s.k = off_prevlinkhdr.constant_part + offset;
 		sappend(s, s2);
 	} else {
 		/*
 		 * There is no variable-length header preceding the
-		 * link-layer header; add in off_prevlinkhdr_constant_part, which,
+		 * link-layer header; add in off_prevlinkhdr.constant_part, which,
 		 * if there's a fixed-length header preceding the
 		 * link-layer header, is the length of that header.
 		 */
 		s = new_stmt(BPF_LD|BPF_ABS|size);
-		s->s.k = off_prevlinkhdr_constant_part + offset;
+		s->s.k = off_prevlinkhdr.constant_part + offset;
 	}
 	return s;
 }
@@ -1584,17 +1590,17 @@ gen_load_linkplrel(offset, size)
 {
 	struct slist *s, *s2;
 
-	s = gen_off_linkpl();
+	s = gen_abs_offset_varpart(&off_linkpl);
 
 	/*
 	 * If s is non-null, the offset of the link-layer payload is
 	 * variable, and s points to a list of instructions that
 	 * arrange that the X register contains the variable part
 	 * of that offset.  The sum of that variable part and
-	 * off_linkpl_constant_part is the offset.
+	 * off_linkpl.constant_part is the offset.
 	 *
 	 * Otherwise, the offset of the link-layer payload is constant,
-	 * and is in off_linkpl_constant_part.
+	 * and is in off_linkpl.constant_part.
 	 */
 	if (s != NULL) {
 		/*
@@ -1603,16 +1609,16 @@ gen_load_linkplrel(offset, size)
 		 * register as part of the offset of the load.
 		 */
 		s2 = new_stmt(BPF_LD|BPF_IND|size);
-		s2->s.k = off_linkpl_constant_part + offset;
+		s2->s.k = off_linkpl.constant_part + offset;
 		sappend(s, s2);
 	} else {
 		/*
 		 * The offset of the link-layer payload is constant,
-		 * and is in off_linkpl_constant_part; load the value
+		 * and is in off_linkpl.constant_part; load the value
 		 * at that offset plus the specified offset.
 		 */
 		s = new_stmt(BPF_LD|BPF_ABS|size);
-		s->s.k = off_linkpl_constant_part + offset;
+		s->s.k = off_linkpl.constant_part + offset;
 	}
 	return s;
 }
@@ -1677,7 +1683,7 @@ gen_load_a(offrel, offset, size)
 		 * part in the offset of the load.
 		 */
 		s2 = new_stmt(BPF_LD|BPF_IND|size);
-		s2->s.k = off_linkpl_constant_part + off_nl + offset;
+		s2->s.k = off_linkpl.constant_part + off_nl + offset;
 		sappend(s, s2);
 		break;
 
@@ -1702,7 +1708,7 @@ gen_loadx_iphdrlen()
 {
 	struct slist *s, *s2;
 
-	s = gen_off_linkpl();
+	s = gen_abs_offset_varpart(&off_linkpl);
 	if (s != NULL) {
 		/*
 		 * The offset of the link-layer payload has a variable
@@ -1742,11 +1748,11 @@ gen_loadx_iphdrlen()
 		 * mode.  Load the length of the IPv4 header, which
 		 * is at an offset of off_nl from the beginning of
 		 * the link-layer payload, and thus at an offset of
-		 * off_linkpl_constant_part + off_nl from the beginning
+		 * off_linkpl.constant_part + off_nl from the beginning
 		 * of the raw packet data, using that addressing mode.
 		 */
 		s = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
-		s->s.k = off_linkpl_constant_part + off_nl;
+		s->s.k = off_linkpl.constant_part + off_nl;
 	}
 	return s;
 }
@@ -2133,7 +2139,7 @@ gen_linux_sll_linktype(proto)
 			 */
 			b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H,
 			    LINUX_SLL_P_802_2);
-			b1 = gen_cmp(OR_LINKHDR, off_linkpl_constant_part, BPF_B,
+			b1 = gen_cmp(OR_LINKHDR, off_linkpl.constant_part, BPF_B,
 			     (bpf_int32)proto);
 			gen_and(b0, b1);
 			return b1;
@@ -2186,7 +2192,7 @@ gen_load_prism_llprefixlen()
 	 * but no known software generates headers that aren't 144
 	 * bytes long.
 	 */
-	if (reg_off_linkhdr != -1) {
+	if (off_linkhdr.reg != -1) {
 		/*
 		 * Load the cookie.
 		 */
@@ -2248,7 +2254,7 @@ gen_load_prism_llprefixlen()
 		 * loading the length of the AVS header.
 		 */
 		s2 = new_stmt(BPF_ST);
-		s2->s.k = reg_off_linkhdr;
+		s2->s.k = off_linkhdr.reg;
 		sappend(s1, s2);
 		sjcommon->s.jf = s2;
 
@@ -2275,7 +2281,7 @@ gen_load_avs_llprefixlen()
 	 * generated uses that prefix, so we don't need to generate any
 	 * code to load it.)
 	 */
-	if (reg_off_linkhdr != -1) {
+	if (off_linkhdr.reg != -1) {
 		/*
 		 * The 4 bytes at an offset of 4 from the beginning of
 		 * the AVS header are the length of the AVS header.
@@ -2289,7 +2295,7 @@ gen_load_avs_llprefixlen()
 		 * it.
 		 */
 		s2 = new_stmt(BPF_ST);
-		s2->s.k = reg_off_linkhdr;
+		s2->s.k = off_linkhdr.reg;
 		sappend(s1, s2);
 
 		/*
@@ -2315,7 +2321,7 @@ gen_load_radiotap_llprefixlen()
 	 * generated uses that prefix, so we don't need to generate any
 	 * code to load it.)
 	 */
-	if (reg_off_linkhdr != -1) {
+	if (off_linkhdr.reg != -1) {
 		/*
 		 * The 2 bytes at offsets of 2 and 3 from the beginning
 		 * of the radiotap header are the length of the radiotap
@@ -2350,7 +2356,7 @@ gen_load_radiotap_llprefixlen()
 		 * it.
 		 */
 		s2 = new_stmt(BPF_ST);
-		s2->s.k = reg_off_linkhdr;
+		s2->s.k = off_linkhdr.reg;
 		sappend(s1, s2);
 
 		/*
@@ -2383,7 +2389,7 @@ gen_load_ppi_llprefixlen()
 	 * into the register assigned to hold that length, if one has
 	 * been assigned.
 	 */
-	if (reg_off_linkhdr != -1) {
+	if (off_linkhdr.reg != -1) {
 		/*
 		 * The 2 bytes at offsets of 2 and 3 from the beginning
 		 * of the radiotap header are the length of the radiotap
@@ -2418,7 +2424,7 @@ gen_load_ppi_llprefixlen()
 		 * it.
 		 */
 		s2 = new_stmt(BPF_ST);
-		s2->s.k = reg_off_linkhdr;
+		s2->s.k = off_linkhdr.reg;
 		sappend(s1, s2);
 
 		/*
@@ -2451,7 +2457,7 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
 	struct slist *sjset_tsft_datapad, *sjset_notsft_datapad;
 	struct slist *s_roundup;
 
-	if (reg_off_linkpl == -1) {
+	if (off_linkpl.reg == -1) {
 		/*
 		 * No register has been assigned to the offset of
 		 * the link-layer payload, which means nobody needs
@@ -2474,7 +2480,7 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
 	 * header.
 	 *
 	 * Otherwise, the length of the prefix preceding the link-layer
-	 * header is "off_outermostlinkhdr_constant_part".
+	 * header is "off_outermostlinkhdr.constant_part".
 	 */
 	if (s == NULL) {
 		/*
@@ -2483,18 +2489,18 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
 		 *
 		 * Load the length of the fixed-length prefix preceding
 		 * the link-layer header (if any) into the X register,
-		 * and store it in the reg_off_linkpl register.
-		 * That length is off_outermostlinkhdr_constant_part.
+		 * and store it in the off_linkpl.reg register.
+		 * That length is off_outermostlinkhdr.constant_part.
 		 */
 		s = new_stmt(BPF_LDX|BPF_IMM);
-		s->s.k = off_outermostlinkhdr_constant_part;
+		s->s.k = off_outermostlinkhdr.constant_part;
 	}
 
 	/*
 	 * The X register contains the offset of the beginning of the
 	 * link-layer header; add 24, which is the minimum length
 	 * of the MAC header for a data frame, to that, and store it
-	 * in reg_off_linkpl, and then load the Frame Control field,
+	 * in off_linkpl.reg, and then load the Frame Control field,
 	 * which is at the offset in the X register, with an indexed load.
 	 */
 	s2 = new_stmt(BPF_MISC|BPF_TXA);
@@ -2503,7 +2509,7 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
 	s2->s.k = 24;
 	sappend(s, s2);
 	s2 = new_stmt(BPF_ST);
-	s2->s.k = reg_off_linkpl;
+	s2->s.k = off_linkpl.reg;
 	sappend(s, s2);
 
 	s2 = new_stmt(BPF_LD|BPF_IND|BPF_B);
@@ -2539,19 +2545,19 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
 	sappend(s, sjset_qos);
 
 	/*
-	 * If it's set, add 2 to reg_off_linkpl, to skip the QoS
+	 * If it's set, add 2 to off_linkpl.reg, to skip the QoS
 	 * field.
 	 * Otherwise, go to the first statement of the rest of the
 	 * program.
 	 */
 	sjset_qos->s.jt = s2 = new_stmt(BPF_LD|BPF_MEM);
-	s2->s.k = reg_off_linkpl;
+	s2->s.k = off_linkpl.reg;
 	sappend(s, s2);
 	s2 = new_stmt(BPF_ALU|BPF_ADD|BPF_IMM);
 	s2->s.k = 2;
 	sappend(s, s2);
 	s2 = new_stmt(BPF_ST);
-	s2->s.k = reg_off_linkpl;
+	s2->s.k = off_linkpl.reg;
 	sappend(s, s2);
 
 	/*
@@ -2631,7 +2637,7 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
 		 * ANDing with ~3.
 		 */
 		s_roundup = new_stmt(BPF_LD|BPF_MEM);
-		s_roundup->s.k = reg_off_linkpl;
+		s_roundup->s.k = off_linkpl.reg;
 		sappend(s, s_roundup);
 		s2 = new_stmt(BPF_ALU|BPF_ADD|BPF_IMM);
 		s2->s.k = 3;
@@ -2640,7 +2646,7 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
 		s2->s.k = ~3;
 		sappend(s, s2);
 		s2 = new_stmt(BPF_ST);
-		s2->s.k = reg_off_linkpl;
+		s2->s.k = off_linkpl.reg;
 		sappend(s, s2);
 
 		sjset_tsft_datapad->s.jt = s_roundup;
@@ -2748,25 +2754,31 @@ gen_ppi_dlt_check(void)
 }
 
 /*
- * Generate code to load the register containing the variable part of
- * the offset of the link-layer header into the X register; if no
- * register for that offset has been allocated, allocate it first.
+ * Take an absolute offset, and:
+ *
+ *    if it has no variable part, return NULL;
+ *
+ *    if it has a variable part, generate code to load the register
+ *    containing that variable part into the X register, returning
+ *    a pointer to that code - if no register for that offset has
+ *    been allocated, allocate it first.
+ *
  * (The code to set that register will be generated later, but will
  * be placed earlier in the code sequence.)
  */
 static struct slist *
-gen_llprefixlen(void)
+gen_abs_offset_varpart(bpf_abs_offset *off)
 {
 	struct slist *s;
 
-	if (off_linkhdr_is_variable) {
-		if (reg_off_linkhdr == -1) {
+	if (off->is_variable) {
+		if (off->reg == -1) {
 			/*
 			 * We haven't yet assigned a register for the
 			 * variable part of the offset of the link-layer
 			 * header; allocate one.
 			 */
-			reg_off_linkhdr = alloc_reg();
+			off->reg = alloc_reg();
 		}
 
 		/*
@@ -2774,82 +2786,7 @@ gen_llprefixlen(void)
 		 * offset of the link-layer header into the X register.
 		 */
 		s = new_stmt(BPF_LDX|BPF_MEM);
-		s->s.k = reg_off_linkhdr;
-		return s;
-	} else {
-		/*
-		 * That offset isn't variable, there's no variable part,
-		 * so we don't need to generate any code.
-		 */
-		return NULL;
-	}
-}
-
-/*
- * Generate code to compute the previous link-layer header length, if necessary,
- * putting it into the X register, and to return either a pointer to a
- * "struct slist" for the list of statements in that code, or NULL if
- * no code is necessary.
- */
-static struct slist *
-gen_prevlinkhdrprefixlen(void)
-{
-	struct slist *s;
-
-	if (off_prevlinkhdr_is_variable) {
-		if (reg_off_prevlinkhdr == -1) {
-			/*
-			 * We haven't yet assigned a register for the
-			 * variable part of the offset of the link-layer
-			 * header; allocate one.
-			 */
-			reg_off_prevlinkhdr = alloc_reg();
-		}
-
-		/*
-		 * Load the register containing the variable part of the
-		 * offset of the link-layer header into the X register.
-		 */
-		s = new_stmt(BPF_LDX|BPF_MEM);
-		s->s.k = reg_off_prevlinkhdr;
-		return s;
-	} else {
-		/*
-		 * That offset isn't variable, there's no variable part,
-		 * so we don't need to generate any code.
-		 */
-		return NULL;
-	}
-}
-
-/*
- * Generate code to load the register containing the variable part of
- * the offset of the link-layer payload into the X register; if no
- * register for that offset has been allocated, allocate it first.
- * (The code to set that register will be generated later, but will
- * be placed earlier in the code sequence.)
- */
-static struct slist *
-gen_off_linkpl(void)
-{
-	struct slist *s;
-
-	if (off_linkpl_is_variable) {
-		if (reg_off_linkpl == -1) {
-			/*
-			 * We haven't yet assigned a register for the
-			 * variable part of the offset of the link-layer
-			 * payload; allocate one.
-			 */
-			reg_off_linkpl = alloc_reg();
-		}
-
-		/*
-		 * Load the register containing the variable part of the
-		 * offset of the link-layer payload into the X register.
-		 */
-		s = new_stmt(BPF_LDX|BPF_MEM);
-		s->s.k = reg_off_linkpl;
+		s->s.k = off->reg;
 		return s;
 	} else {
 		/*
@@ -5729,11 +5666,11 @@ gen_protochain(v, proto, dir)
 
 		/* A = ip->ip_p */
 		s[i] = new_stmt(BPF_LD|BPF_ABS|BPF_B);
-		s[i]->s.k = off_linkpl_constant_part + off_nl + 9;
+		s[i]->s.k = off_linkpl.constant_part + off_nl + 9;
 		i++;
 		/* X = ip->ip_hl << 2 */
 		s[i] = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
-		s[i]->s.k = off_linkpl_constant_part + off_nl;
+		s[i]->s.k = off_linkpl.constant_part + off_nl;
 		i++;
 		break;
 
@@ -5742,7 +5679,7 @@ gen_protochain(v, proto, dir)
 
 		/* A = ip6->ip_nxt */
 		s[i] = new_stmt(BPF_LD|BPF_ABS|BPF_B);
-		s[i]->s.k = off_linkpl_constant_part + off_nl + 6;
+		s[i]->s.k = off_linkpl.constant_part + off_nl + 6;
 		i++;
 		/* X = sizeof(struct ip6_hdr) */
 		s[i] = new_stmt(BPF_LDX|BPF_IMM);
@@ -5818,7 +5755,7 @@ gen_protochain(v, proto, dir)
 		 */
 		/* A = P[X + packet head] */
 		s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
-		s[i]->s.k = off_linkpl_constant_part + off_nl;
+		s[i]->s.k = off_linkpl.constant_part + off_nl;
 		i++;
 		/* MEM[reg2] = A */
 		s[i] = new_stmt(BPF_ST);
@@ -5826,7 +5763,7 @@ gen_protochain(v, proto, dir)
 		i++;
 		/* A = P[X + packet head + 1]; */
 		s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
-		s[i]->s.k = off_linkpl_constant_part + off_nl + 1;
+		s[i]->s.k = off_linkpl.constant_part + off_nl + 1;
 		i++;
 		/* A += 1 */
 		s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
@@ -5887,7 +5824,7 @@ gen_protochain(v, proto, dir)
 	i++;
 	/* A = P[X + packet head]; */
 	s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
-	s[i]->s.k = off_linkpl_constant_part + off_nl;
+	s[i]->s.k = off_linkpl.constant_part + off_nl;
 	i++;
 	/* MEM[reg2] = A */
 	s[i] = new_stmt(BPF_ST);
@@ -5905,7 +5842,7 @@ gen_protochain(v, proto, dir)
 	i++;
 	/* A = P[X + packet head] */
 	s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
-	s[i]->s.k = off_linkpl_constant_part + off_nl;
+	s[i]->s.k = off_linkpl.constant_part + off_nl;
 	i++;
 	/* A += 2 */
 	s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
@@ -6880,7 +6817,7 @@ gen_load(proto, inst, size)
 		 * frame, so that 0 refers, for Ethernet LANE, to
 		 * the beginning of the destination address?
 		 */
-		s = gen_llprefixlen();
+		s = gen_abs_offset_varpart(&off_linkhdr);
 
 		/*
 		 * If "s" is non-null, it has code to arrange that the
@@ -6906,7 +6843,7 @@ gen_load(proto, inst, size)
 		 * into the X register and then added to the index).
 		 */
 		tmp = new_stmt(BPF_LD|BPF_IND|size);
-		tmp->s.k = off_linkhdr_constant_part;
+		tmp->s.k = off_linkhdr.constant_part;
 		sappend(s, tmp);
 		sappend(inst->s, s);
 		break;
@@ -6927,7 +6864,7 @@ gen_load(proto, inst, size)
 		 * XXX - are there any cases where we want
 		 * off_nl_nosnap?
 		 */
-		s = gen_off_linkpl();
+		s = gen_abs_offset_varpart(&off_linkpl);
 
 		/*
 		 * If "s" is non-null, it has code to arrange that the
@@ -6953,7 +6890,7 @@ gen_load(proto, inst, size)
 		 * start of the link-layer payload.
 		 */
 		tmp = new_stmt(BPF_LD|BPF_IND|size);
-		tmp->s.k = off_linkpl_constant_part + off_nl;
+		tmp->s.k = off_linkpl.constant_part + off_nl;
 		sappend(s, tmp);
 		sappend(inst->s, s);
 
@@ -7010,7 +6947,7 @@ gen_load(proto, inst, size)
 		sappend(s, new_stmt(BPF_ALU|BPF_ADD|BPF_X));
 		sappend(s, new_stmt(BPF_MISC|BPF_TAX));
 		sappend(s, tmp = new_stmt(BPF_LD|BPF_IND|size));
-		tmp->s.k = off_linkpl_constant_part + off_nl;
+		tmp->s.k = off_linkpl.constant_part + off_nl;
 		sappend(inst->s, s);
 
 		/*
@@ -8039,7 +7976,7 @@ gen_vlan_no_bpf_extensions(int vlan_num)
 	 * The payload follows the full header, including the
 	 * VLAN tags, so skip past this VLAN tag.
 	 */
-        off_linkpl_constant_part += 4;
+        off_linkpl.constant_part += 4;
 
 	/*
 	 * The link-layer type information follows the VLAN tags, so
@@ -8263,18 +8200,12 @@ gen_pppoes(sess_num)
 	 * link-layer payload, including any 802.2 LLC header, so
 	 * it's 6 bytes past off_nl.
 	 */
-	prevlinktype = linktype;
-	off_prevlinkhdr_constant_part = off_linkhdr_constant_part;
-	off_prevlinkhdr_is_variable = off_linkhdr_is_variable;
-	reg_off_prevlinkhdr = reg_off_linkhdr;
-
-	linktype = DLT_PPP;
-	off_linkhdr_constant_part = off_linkpl_constant_part + off_nl + 6;	/* 6 bytes past the PPPoE header */
-	reg_off_linkhdr = reg_off_linkpl;
-	off_linkhdr_is_variable = off_linkpl_is_variable;
+	PUSH_LINKHDR(DLT_PPP, off_linkpl.is_variable,
+	    off_linkpl.constant_part + off_nl + 6, /* 6 bytes past the PPPoE header */
+	    off_linkpl.reg);
 
 	off_linktype = 0;
-	off_linkpl_constant_part = off_linkhdr_constant_part + 2;
+	off_linkpl.constant_part = off_linkhdr.constant_part + 2;
 
 	off_nl = 0;
 	off_nl_nosnap = 0;	/* no 802.2 LLC */
@@ -8416,14 +8347,11 @@ gen_atmtype_abbrev(type)
 		 *
 		 * We assume LANE means Ethernet, not Token Ring.
 		 */
-		prevlinktype = linktype;
-		off_prevlinkhdr_constant_part = off_linkhdr_constant_part;
-		off_prevlinkhdr_is_variable = off_linkhdr_is_variable;
-		reg_off_prevlinkhdr = reg_off_linkhdr;
-		linktype = DLT_EN10MB;
-		off_linkhdr_constant_part = off_payload + 2;	/* Ethernet header */
+		PUSH_LINKHDR(DLT_EN10MB, 0,
+		    off_payload + 2,	/* Ethernet header */
+		    -1);
 		off_linktype = 12;
-		off_linkpl_constant_part = off_linkhdr_constant_part + 14;	/* Ethernet */
+		off_linkpl.constant_part = off_linkhdr.constant_part + 14;	/* Ethernet */
 		off_nl = 0;			/* Ethernet II */
 		off_nl_nosnap = 3;		/* 802.3+802.2 */
 		break;