]> The Tcpdump Group git mirrors - libpcap/blobdiff - gencode.c
Convert off_linktype to use variable offsets.
[libpcap] / gencode.c
index 1ad664b0983553352ce542dddcaf46882a5e3cf0..c5229550243f1ec49a59191c360cb92feb72e282 100644 (file)
--- a/gencode.c
+++ b/gencode.c
@@ -162,21 +162,44 @@ 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.
  */
 enum e_offrel {
-       OR_PACKET,      /* full packet data */
-       OR_LINKHDR,     /* link-layer header */
-       OR_PREVLINKHDR, /* previous link-layer header */
-       OR_LLC,         /* 802.2 LLC header */
-       OR_LINKPL,      /* link-layer payload */
-       OR_MPLSPL,      /* MPLS payload */
-       OR_NET,         /* network-layer header */
-       OR_NET_NOSNAP,  /* network-layer header, with no SNAP header at the link layer */
-       OR_TRAN_IPV4,   /* transport-layer header, with IPv4 network layer */
-       OR_TRAN_IPV6    /* transport-layer header, with IPv6 network layer */
+       OR_PACKET,              /* full packet data */
+       OR_LINKHDR,             /* link-layer header */
+       OR_PREVLINKHDR,         /* previous link-layer header */
+       OR_LLC,                 /* 802.2 LLC header */
+       OR_PREVMPLSHDR,         /* previous MPLS header */
+       OR_LINKTYPE,            /* link-layer type */
+       OR_LINKPL,              /* link-layer payload */
+       OR_LINKPL_NOSNAP,       /* link-layer payload, with no SNAP header at the link layer */
+       OR_TRAN_IPV4,           /* transport-layer header, with IPv4 network layer */
+       OR_TRAN_IPV6            /* transport-layer header, with IPv6 network layer */
 };
 
 #ifdef INET6
@@ -227,9 +250,7 @@ static struct block *gen_mcmp(enum e_offrel, u_int, u_int, bpf_int32,
 static struct block *gen_bcmp(enum e_offrel, u_int, u_int, const u_char *);
 static struct block *gen_ncmp(enum e_offrel, bpf_u_int32, bpf_u_int32,
     bpf_u_int32, bpf_u_int32, int, bpf_int32);
-static struct slist *gen_load_linkhdrrel(u_int, u_int);
-static struct slist *gen_load_prevlinkhdrrel(u_int, u_int);
-static struct slist *gen_load_linkplrel(u_int, u_int);
+static struct slist *gen_load_absoffsetrel(bpf_abs_offset *, u_int, u_int);
 static struct slist *gen_load_a(enum e_offrel, u_int, u_int);
 static struct slist *gen_loadx_iphdrlen(void);
 static struct block *gen_uncond(int);
@@ -243,9 +264,7 @@ 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 +795,9 @@ 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
@@ -799,42 +805,38 @@ 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
- * loads with an offset that includes "off_linktype" should use
- * OR_LINKHDR.
+ * giving the packet type. This is an absolute offset from the beginning
+ * of the packet.
  *
  * For Ethernet, it's the offset of the Ethernet type field; this
  * means that it must have a value that skips VLAN tags.
@@ -851,9 +853,10 @@ static int reg_off_linkpl;
  *
  * For Linux cooked sockets, it's the offset of the type field.
  *
- * It's set to -1 for no encapsulation, in which case, IP is assumed.
+ * off_linktype.constant_part is set to -1 for no encapsulation,
+ * in which case, IP is assumed.
  */
-static u_int off_linktype;
+static bpf_abs_offset off_linktype;
 
 /*
  * TRUE if the link layer includes an ATM pseudo-header.
@@ -890,7 +893,7 @@ 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 +931,30 @@ 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;
+
+       off_linktype.constant_part = 0;
+       off_linktype.is_variable = 0;
+       off_linktype.reg = -1;
 
        /*
         * Assume it's not raw ATM with a pseudo-header, for now.
@@ -974,88 +981,88 @@ init_linktype(p)
        switch (linktype) {
 
        case DLT_ARCNET:
-               off_linktype = 2;
-               off_linkpl_constant_part = 6;
+               off_linktype.constant_part = 2;
+               off_linkpl.constant_part = 6;
                off_nl = 0;             /* XXX in reality, variable! */
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_ARCNET_LINUX:
-               off_linktype = 4;
-               off_linkpl_constant_part = 8;
+               off_linktype.constant_part = 4;
+               off_linkpl.constant_part = 8;
                off_nl = 0;             /* XXX in reality, variable! */
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_EN10MB:
-               off_linktype = 12;
-               off_linkpl_constant_part = 14;  /* Ethernet header length */
+               off_linktype.constant_part = 12;
+               off_linkpl.constant_part = 14;  /* Ethernet header length */
                off_nl = 0;             /* Ethernet II */
                off_nl_nosnap = 3;      /* 802.3+802.2 */
-               return;
+               break;
 
        case DLT_SLIP:
                /*
                 * SLIP doesn't have a link level type.  The 16 byte
                 * header is hacked into our SLIP driver.
                 */
-               off_linktype = -1;
-               off_linkpl_constant_part = 16;
+               off_linktype.constant_part = -1;
+               off_linkpl.constant_part = 16;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_SLIP_BSDOS:
                /* XXX this may be the same as the DLT_PPP_BSDOS case */
-               off_linktype = -1;
+               off_linktype.constant_part = -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;
+               break;
 
        case DLT_NULL:
        case DLT_LOOP:
-               off_linktype = 0;
-               off_linkpl_constant_part = 4;
+               off_linktype.constant_part = 0;
+               off_linkpl.constant_part = 4;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_ENC:
-               off_linktype = 0;
-               off_linkpl_constant_part = 12;
+               off_linktype.constant_part = 0;
+               off_linkpl.constant_part = 12;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_PPP:
        case DLT_PPP_PPPD:
        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_linktype.constant_part = 2; /* skip HDLC-like framing */
+               off_linkpl.constant_part = 4;   /* skip HDLC-like framing and protocol field */
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_PPP_ETHER:
                /*
                 * This does no include the Ethernet header, and
                 * only covers session state.
                 */
-               off_linktype = 6;
-               off_linkpl_constant_part = 8;
+               off_linktype.constant_part = 6;
+               off_linkpl.constant_part = 8;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_PPP_BSDOS:
-               off_linktype = 5;
-               off_linkpl_constant_part = 24;
+               off_linktype.constant_part = 5;
+               off_linkpl.constant_part = 24;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_FDDI:
                /*
@@ -1066,13 +1073,13 @@ init_linktype(p)
                 * is being used and pick out the encapsulated Ethernet type.
                 * XXX - should we generate code to check for SNAP?
                 */
-               off_linktype = 13;
-               off_linktype += pcap_fddipad;
-               off_linkpl_constant_part = 13;  /* FDDI MAC header length */
-               off_linkpl_constant_part += pcap_fddipad;
+               off_linktype.constant_part = 13;
+               off_linktype.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;
+               break;
 
        case DLT_IEEE802:
                /*
@@ -1098,19 +1105,24 @@ init_linktype(p)
                 * the 16-bit value at an offset of 14 (shifted right
                 * 8 - figure out which byte that is).
                 */
-               off_linktype = 14;
-               off_linkpl_constant_part = 14;  /* Token Ring MAC header length */
+               off_linktype.constant_part = 14;
+               off_linkpl.constant_part = 14;  /* Token Ring MAC header length */
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
-               return;
+               break;
 
-       case DLT_IEEE802_11:
        case DLT_PRISM_HEADER:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_IEEE802_11_RADIO:
+               off_linkhdr.is_variable = 1;
+               /* Fall through, 802.11 doesn't have a variable link
+                * prefix but is otherwise the same. */
+
+       case DLT_IEEE802_11:
                /*
                 * 802.11 doesn't really have a link-level type field.
-                * We set "off_linktype" to the offset of the LLC header.
+                * We set "off_linktype.constant_part" to the offset of
+                * the LLC header.
                 *
                 * To check for Ethernet types, we assume that SSAP = SNAP
                 * is being used and pick out the encapsulated Ethernet type.
@@ -1125,12 +1137,12 @@ init_linktype(p)
                 * header or an AVS header, so, in practice, it's
                 * variable-length.
                 */
-               off_linktype = 24;
-               off_linkpl_constant_part = 0;   /* link-layer header is variable-length */
-               off_linkpl_is_variable = 1;
+               off_linktype.constant_part = 24;
+               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;
+               break;
 
        case DLT_PPI:
                /*
@@ -1142,12 +1154,13 @@ init_linktype(p)
                 * the encapsulated DLT should be DLT_IEEE802_11) we
                 * 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_linktype.constant_part = 24;
+               off_linkpl.constant_part = 0;   /* link-layer header is variable-length */
+               off_linkpl.is_variable = 1;
+               off_linkhdr.is_variable = 1;
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
-               return;
+               break;
 
        case DLT_ATM_RFC1483:
        case DLT_ATM_CLIP:      /* Linux ATM defines this */
@@ -1162,11 +1175,11 @@ init_linktype(p)
                 * or "pppoa and tcp port 80" and have it check for
                 * PPPo{A,E} and a PPP protocol of IP and....
                 */
-               off_linktype = 0;
-               off_linkpl_constant_part = 0;   /* packet begins with LLC header */
+               off_linktype.constant_part = 0;
+               off_linkpl.constant_part = 0;   /* packet begins with LLC header */
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
-               return;
+               break;
 
        case DLT_SUNATM:
                /*
@@ -1178,27 +1191,27 @@ init_linktype(p)
                off_vci = SUNATM_VCI_POS;
                off_proto = PROTO_POS;
                off_payload = SUNATM_PKT_BEGIN_POS;
-               off_linktype = off_payload;
-               off_linkpl_constant_part = off_payload; /* if LLC-encapsulated */
+               off_linktype.constant_part = off_payload;
+               off_linkpl.constant_part = off_payload; /* if LLC-encapsulated */
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
-               return;
+               break;
 
        case DLT_RAW:
        case DLT_IPV4:
        case DLT_IPV6:
-               off_linktype = -1;
-               off_linkpl_constant_part = 0;
+               off_linktype.constant_part = -1;
+               off_linkpl.constant_part = 0;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_LINUX_SLL:     /* fake header for Linux cooked socket */
-               off_linktype = 14;
-               off_linkpl_constant_part = 16;
+               off_linktype.constant_part = 14;
+               off_linkpl.constant_part = 16;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_LTALK:
                /*
@@ -1206,11 +1219,11 @@ init_linktype(p)
                 * but really it just indicates whether there is a "short" or
                 * "long" DDP packet following.
                 */
-               off_linktype = -1;
-               off_linkpl_constant_part = 0;
+               off_linktype.constant_part = -1;
+               off_linkpl.constant_part = 0;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_IP_OVER_FC:
                /*
@@ -1223,22 +1236,22 @@ init_linktype(p)
                 * XXX - should we generate code to check for SNAP? RFC
                 * 2625 says SNAP should be used.
                 */
-               off_linktype = 16;
-               off_linkpl_constant_part = 16;
+               off_linktype.constant_part = 16;
+               off_linkpl.constant_part = 16;
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
-               return;
+               break;
 
        case DLT_FRELAY:
                /*
                 * XXX - we should set this to handle SNAP-encapsulated
                 * frames (NLPID of 0x80).
                 */
-               off_linktype = -1;
-               off_linkpl_constant_part = 0;
+               off_linktype.constant_part = -1;
+               off_linkpl.constant_part = 0;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
                 /*
                  * the only BPF-interesting FRF.16 frames are non-control frames;
@@ -1246,33 +1259,33 @@ init_linktype(p)
                  * so lets start with offset 4 for now and increments later on (FIXME);
                  */
        case DLT_MFR:
-               off_linktype = -1;
-               off_linkpl_constant_part = 0;
+               off_linktype.constant_part = -1;
+               off_linkpl.constant_part = 0;
                off_nl = 4;
                off_nl_nosnap = 0;      /* XXX - for now -> no 802.2 LLC */
-               return;
+               break;
 
        case DLT_APPLE_IP_OVER_IEEE1394:
-               off_linktype = 16;
-               off_linkpl_constant_part = 18;
+               off_linktype.constant_part = 16;
+               off_linkpl.constant_part = 18;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_SYMANTEC_FIREWALL:
-               off_linktype = 6;
-               off_linkpl_constant_part = 44;
+               off_linktype.constant_part = 6;
+               off_linkpl.constant_part = 44;
                off_nl = 0;             /* Ethernet II */
                off_nl_nosnap = 0;      /* XXX - what does it do with 802.3 packets? */
-               return;
+               break;
 
 #ifdef HAVE_NET_PFVAR_H
        case DLT_PFLOG:
-               off_linktype = 0;
-               off_linkpl_constant_part = PFLOG_HDRLEN;
+               off_linktype.constant_part = 0;
+               off_linkpl.constant_part = PFLOG_HDRLEN;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
-               return;
+               break;
 #endif
 
         case DLT_JUNIPER_MFR:
@@ -1281,108 +1294,108 @@ init_linktype(p)
         case DLT_JUNIPER_PPP:
         case DLT_JUNIPER_CHDLC:
         case DLT_JUNIPER_FRELAY:
-                off_linktype = 4;
-               off_linkpl_constant_part = 4;
+                off_linktype.constant_part = 4;
+               off_linkpl.constant_part = 4;
                off_nl = 0;
                off_nl_nosnap = -1;     /* no 802.2 LLC */
-                return;
+                break;
 
        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_linktype.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;
+               break;
 
        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_linktype.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;
+               break;
 
                /* frames captured on a Juniper PPPoE service PIC
                 * contain raw ethernet frames */
        case DLT_JUNIPER_PPPOE:
         case DLT_JUNIPER_ETHER:
-               off_linkpl_constant_part = 14;
-               off_linktype = 16;
+               off_linkpl.constant_part = 14;
+               off_linktype.constant_part = 16;
                off_nl = 18;            /* Ethernet II */
                off_nl_nosnap = 21;     /* 802.3+802.2 */
-               return;
+               break;
 
        case DLT_JUNIPER_PPPOE_ATM:
-               off_linktype = 4;
-               off_linkpl_constant_part = 6;
+               off_linktype.constant_part = 4;
+               off_linkpl.constant_part = 6;
                off_nl = 0;
                off_nl_nosnap = -1;     /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_JUNIPER_GGSN:
-               off_linktype = 6;
-               off_linkpl_constant_part = 12;
+               off_linktype.constant_part = 6;
+               off_linkpl.constant_part = 12;
                off_nl = 0;
                off_nl_nosnap = -1;     /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_JUNIPER_ES:
-               off_linktype = 6;
-               off_linkpl_constant_part = -1;  /* not really a network layer but raw IP addresses */
+               off_linktype.constant_part = 6;
+               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;
+               break;
 
        case DLT_JUNIPER_MONITOR:
-               off_linktype = 12;
-               off_linkpl_constant_part = 12;
+               off_linktype.constant_part = 12;
+               off_linkpl.constant_part = 12;
                off_nl = 0;             /* raw IP/IP6 header */
                off_nl_nosnap = -1;     /* no 802.2 LLC */
-               return;
+               break;
 
        case DLT_BACNET_MS_TP:
-               off_linktype = -1;
-               off_linkpl_constant_part = -1;
+               off_linktype.constant_part = -1;
+               off_linkpl.constant_part = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
-               return;
+               break;
 
        case DLT_JUNIPER_SERVICES:
-               off_linktype = 12;
-               off_linkpl_constant_part = -1;  /* L3 proto location dep. on cookie type */
+               off_linktype.constant_part = 12;
+               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;
+               break;
 
        case DLT_JUNIPER_VP:
-               off_linktype = 18;
-               off_linkpl_constant_part = -1;
+               off_linktype.constant_part = 18;
+               off_linkpl.constant_part = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
-               return;
+               break;
 
        case DLT_JUNIPER_ST:
-               off_linktype = 18;
-               off_linkpl_constant_part = -1;
+               off_linktype.constant_part = 18;
+               off_linkpl.constant_part = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
-               return;
+               break;
 
        case DLT_JUNIPER_ISM:
-               off_linktype = 8;
-               off_linkpl_constant_part = -1;
+               off_linktype.constant_part = 8;
+               off_linkpl.constant_part = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
-               return;
+               break;
 
        case DLT_JUNIPER_VS:
        case DLT_JUNIPER_SRX_E2E:
        case DLT_JUNIPER_FIBRECHANNEL:
        case DLT_JUNIPER_ATM_CEMIC:
-               off_linktype = 8;
-               off_linkpl_constant_part = -1;
+               off_linktype.constant_part = 8;
+               off_linkpl.constant_part = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
-               return;
+               break;
 
        case DLT_MTP2:
                off_li = 2;
@@ -1391,11 +1404,11 @@ init_linktype(p)
                off_opc = 4;
                off_dpc = 4;
                off_sls = 7;
-               off_linktype = -1;
-               off_linkpl_constant_part = -1;
+               off_linktype.constant_part = -1;
+               off_linkpl.constant_part = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
-               return;
+               break;
 
        case DLT_MTP2_WITH_PHDR:
                off_li = 6;
@@ -1404,11 +1417,11 @@ init_linktype(p)
                off_opc = 8;
                off_dpc = 8;
                off_sls = 11;
-               off_linktype = -1;
-               off_linkpl_constant_part = -1;
+               off_linktype.constant_part = -1;
+               off_linkpl.constant_part = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
-               return;
+               break;
 
        case DLT_ERF:
                off_li = 22;
@@ -1417,51 +1430,51 @@ init_linktype(p)
                off_opc = 24;
                off_dpc = 24;
                off_sls = 27;
-               off_linktype = -1;
-               off_linkpl_constant_part = -1;
+               off_linktype.constant_part = -1;
+               off_linkpl.constant_part = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
-               return;
+               break;
 
        case DLT_PFSYNC:
-               off_linktype = -1;
-               off_linkpl_constant_part = 4;
+               off_linktype.constant_part = -1;
+               off_linkpl.constant_part = 4;
                off_nl = 0;
                off_nl_nosnap = 0;
-               return;
+               break;
 
        case DLT_AX25_KISS:
                /*
                 * 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_linktype.constant_part = -1;        /* variable, min 15, max 71 steps of 7 */
+               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;
+               break;
 
        case DLT_IPNET:
-               off_linktype = 1;
-               off_linkpl_constant_part = 24;  /* ipnet header length */
+               off_linktype.constant_part = 1;
+               off_linkpl.constant_part = 24;  /* ipnet header length */
                off_nl = 0;
                off_nl_nosnap = -1;
-               return;
+               break;
 
        case DLT_NETANALYZER:
-               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_linkhdr.constant_part = 4;  /* Ethernet header is past 4-byte pseudo-header */
+               off_linktype.constant_part = off_linkhdr.constant_part + 12;
+               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;
+               break;
 
        case DLT_NETANALYZER_TRANSPARENT:
-               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_linkhdr.constant_part = 12; /* MAC header is past 4-byte pseudo-header, preamble, and SFD */
+               off_linktype.constant_part = off_linkhdr.constant_part + 12;
+               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;
+               break;
 
        default:
                /*
@@ -1470,149 +1483,54 @@ init_linktype(p)
                 */
                if (linktype >= DLT_MATCHING_MIN &&
                    linktype <= DLT_MATCHING_MAX) {
-                       off_linktype = -1;
-                       off_linkpl_constant_part = -1;
+                       off_linktype.constant_part = -1;
+                       off_linkpl.constant_part = -1;
                        off_nl = -1;
                        off_nl_nosnap = -1;
-                       return;
+               } else {
+                       bpf_error("unknown data link type %d", linktype);
                }
-
+               break;
        }
-       bpf_error("unknown data link type %d", linktype);
-       /* NOTREACHED */
-}
 
-/*
- * Load a value relative to the beginning of the link-layer header.
- * The link-layer header doesn't necessarily begin at the beginning
- * of the packet data; there might be a variable-length prefix containing
- * radio information.
- */
-static struct slist *
-gen_load_linkhdrrel(offset, size)
-       u_int offset, size;
-{
-       struct slist *s, *s2;
-
-       s = gen_llprefixlen();
-
-       /*
-        * If "s" is non-null, it has code to arrange that the X register
-        * contains the length of the prefix preceding the link-layer
-        * header.
-        *
-        * Otherwise, the length of the prefix preceding the link-layer
-        * header is "off_linkhdr_constant_part".
-        */
-       if (s != NULL) {
-               /*
-                * There's a variable-length prefix preceding the
-                * link-layer header.  "s" points to a list of statements
-                * that put the length of that prefix into the X register.
-                * 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;
-               sappend(s, s2);
-       } else {
-               /*
-                * There is no variable-length header preceding the
-                * 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;
-       }
-       return s;
+       off_outermostlinkhdr = off_prevlinkhdr = off_linkhdr;
 }
 
 /*
- * Load a value relative to the beginning of the previous link-layer header,
- * if we're also looking at an inner link-layer header encapsulated
- * within other protocol layers.
- *
- * The link-layer header doesn't necessarily begin at the beginning
- * of the packet data; there might be a variable-length prefix containing
- * radio information.
+ * Load a value relative to the specified absolute offset.
  */
 static struct slist *
-gen_load_prevlinkhdrrel(offset, size)
-       u_int offset, size;
+gen_load_absoffsetrel(bpf_abs_offset *abs_offset, u_int offset, u_int size)
 {
        struct slist *s, *s2;
 
-       s = gen_prevlinkhdrprefixlen();
+       s = gen_abs_offset_varpart(abs_offset);
 
        /*
         * If "s" is non-null, it has code to arrange that the X register
-        * contains the length of the prefix preceding the link-layer
-        * header.
-        *
-        * Otherwise, the length of the prefix preceding the link-layer
-        * header is "off_prevlinkhdr_constant_part".
-        */
-       if (s != NULL) {
-               /*
-                * There's a variable-length prefix preceding the
-                * link-layer header.  "s" points to a list of statements
-                * that put the length of that prefix into the X register.
-                * 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;
-               sappend(s, s2);
-       } else {
-               /*
-                * There is no variable-length header preceding the
-                * 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;
-       }
-       return s;
-}
-
-/*
- * Load a value relative to the beginning of the link-layer payload.
- */
-static struct slist *
-gen_load_linkplrel(offset, size)
-       u_int offset, size;
-{
-       struct slist *s, *s2;
-
-       s = gen_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.
+        * contains the variable part of the absolute offset, so we
+        * generate a load relative to that, with an offset of
+        * abs_offset->constant_part + offset.
         *
-        * Otherwise, the offset of the link-layer payload is constant,
-        * and is in off_linkpl_constant_part.
+        * Otherwise, we can do an absolute load with an offset of
+        * abs_offset->constant_part + offset.
         */
        if (s != NULL) {
                /*
-                * The variable part of the offset of the link-layer payload
-                * is in the X register.  Do an indirect load, to use the X
-                * register as part of the offset of the load.
+                * "s" points to a list of statements that puts the
+                * variable part of the absolute offset into the X register.
+                * Do an indirect load, to use the X register as an offset.
                 */
                s2 = new_stmt(BPF_LD|BPF_IND|size);
-               s2->s.k = off_linkpl_constant_part + offset;
+               s2->s.k = abs_offset->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
-                * at that offset plus the specified offset.
+                * There is no variable part of the absolute offset, so
+                * just do an absolute load.
                 */
                s = new_stmt(BPF_LD|BPF_ABS|size);
-               s->s.k = off_linkpl_constant_part + offset;
+               s->s.k = abs_offset->constant_part + offset;
        }
        return s;
 }
@@ -1635,25 +1553,31 @@ gen_load_a(offrel, offset, size)
                break;
 
        case OR_LINKHDR:
-               s = gen_load_linkhdrrel(offset, size);
+               s = gen_load_absoffsetrel(&off_linkhdr, offset, size);
                break;
 
        case OR_PREVLINKHDR:
-               s = gen_load_prevlinkhdrrel(offset, size);
+               s = gen_load_absoffsetrel(&off_prevlinkhdr, offset, size);
                break;
 
        case OR_LLC:
+               s = gen_load_absoffsetrel(&off_linkpl, offset, size);
+               break;
+
+       case OR_PREVMPLSHDR:
+               s = gen_load_absoffsetrel(&off_linkpl, off_nl - 4 + offset, size);
+               break;
+
        case OR_LINKPL:
-       case OR_MPLSPL:
-               s = gen_load_linkplrel(offset, size);
+               s = gen_load_absoffsetrel(&off_linkpl, off_nl + offset, size);
                break;
 
-       case OR_NET:
-               s = gen_load_linkplrel(off_nl + offset, size);
+       case OR_LINKPL_NOSNAP:
+               s = gen_load_absoffsetrel(&off_linkpl, off_nl_nosnap + offset, size);
                break;
 
-       case OR_NET_NOSNAP:
-               s = gen_load_linkplrel(off_nl_nosnap + offset, size);
+       case OR_LINKTYPE:
+               s = gen_load_absoffsetrel(&off_linktype, offset, size);
                break;
 
        case OR_TRAN_IPV4:
@@ -1677,12 +1601,12 @@ 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;
 
        case OR_TRAN_IPV6:
-               s = gen_load_linkplrel(off_nl + 40 + offset, size);
+               s = gen_load_absoffsetrel(&off_linkpl, off_nl + 40 + offset, size);
                break;
 
        default:
@@ -1702,7 +1626,7 @@ 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
@@ -1715,7 +1639,7 @@ gen_loadx_iphdrlen()
                 * the value from the X register.
                 */
                s2 = new_stmt(BPF_LD|BPF_IND|BPF_B);
-               s2->s.k = off_nl;
+               s2->s.k = off_linkpl.constant_part + off_nl;
                sappend(s, s2);
                s2 = new_stmt(BPF_ALU|BPF_AND|BPF_K);
                s2->s.k = 0xf;
@@ -1742,11 +1666,11 @@ 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;
 }
@@ -1818,7 +1742,7 @@ gen_ether_linktype(proto)
                 * DSAP, as we do for other types <= ETHERMTU
                 * (i.e., other SAP values)?
                 */
-               b0 = gen_cmp_gt(OR_LINKHDR, off_linktype, BPF_H, ETHERMTU);
+               b0 = gen_cmp_gt(OR_LINKTYPE, 0, BPF_H, ETHERMTU);
                gen_not(b0);
                b1 = gen_cmp(OR_LLC, 0, BPF_H, (bpf_int32)
                             ((proto << 8) | proto));
@@ -1873,7 +1797,7 @@ gen_ether_linktype(proto)
                 * Now we generate code to check for 802.3
                 * frames in general.
                 */
-               b0 = gen_cmp_gt(OR_LINKHDR, off_linktype, BPF_H, ETHERMTU);
+               b0 = gen_cmp_gt(OR_LINKTYPE, 0, BPF_H, ETHERMTU);
                gen_not(b0);
 
                /*
@@ -1889,8 +1813,7 @@ gen_ether_linktype(proto)
                 * do that before checking for the other frame
                 * types.
                 */
-               b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H,
-                   (bpf_int32)ETHERTYPE_IPX);
+               b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, (bpf_int32)ETHERTYPE_IPX);
                gen_or(b0, b1);
                return b1;
 
@@ -1906,7 +1829,7 @@ gen_ether_linktype(proto)
                 * we check for an Ethernet type field less than
                 * 1500, which means it's an 802.3 length field.
                 */
-               b0 = gen_cmp_gt(OR_LINKHDR, off_linktype, BPF_H, ETHERMTU);
+               b0 = gen_cmp_gt(OR_LINKTYPE, 0, BPF_H, ETHERMTU);
                gen_not(b0);
 
                /*
@@ -1931,7 +1854,7 @@ gen_ether_linktype(proto)
                 * phase 1?); we just check for the Ethernet
                 * protocol type.
                 */
-               b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H, (bpf_int32)proto);
+               b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, (bpf_int32)proto);
 
                gen_or(b0, b1);
                return b1;
@@ -1946,10 +1869,9 @@ gen_ether_linktype(proto)
                         * a length field, <= ETHERMTU) and
                         * then check the DSAP.
                         */
-                       b0 = gen_cmp_gt(OR_LINKHDR, off_linktype, BPF_H, ETHERMTU);
+                       b0 = gen_cmp_gt(OR_LINKTYPE, 0, BPF_H, ETHERMTU);
                        gen_not(b0);
-                       b1 = gen_cmp(OR_LINKHDR, off_linktype + 2, BPF_B,
-                           (bpf_int32)proto);
+                       b1 = gen_cmp(OR_LINKTYPE, 2, BPF_B, (bpf_int32)proto);
                        gen_and(b0, b1);
                        return b1;
                } else {
@@ -1962,7 +1884,7 @@ gen_ether_linktype(proto)
                         * will fail and the frame won't match,
                         * which is what we want).
                         */
-                       return gen_cmp(OR_LINKHDR, off_linktype, BPF_H,
+                       return gen_cmp(OR_LINKTYPE, 0, BPF_H,
                            (bpf_int32)proto);
                }
        }
@@ -1979,12 +1901,11 @@ gen_ipnet_linktype(proto)
        switch (proto) {
 
        case ETHERTYPE_IP:
-               return gen_cmp(OR_LINKHDR, off_linktype, BPF_B,
-                   (bpf_int32)IPH_AF_INET);
+               return gen_cmp(OR_LINKTYPE, 0, BPF_B, (bpf_int32)IPH_AF_INET);
                /* NOTREACHED */
 
        case ETHERTYPE_IPV6:
-               return gen_cmp(OR_LINKHDR, off_linktype, BPF_B,
+               return gen_cmp(OR_LINKTYPE, 0, BPF_B,
                    (bpf_int32)IPH_AF_INET6);
                /* NOTREACHED */
 
@@ -2026,7 +1947,7 @@ gen_linux_sll_linktype(proto)
                 * DSAP, as we do for other types <= ETHERMTU
                 * (i.e., other SAP values)?
                 */
-               b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H, LINUX_SLL_P_802_2);
+               b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, LINUX_SLL_P_802_2);
                b1 = gen_cmp(OR_LLC, 0, BPF_H, (bpf_int32)
                             ((proto << 8) | proto));
                gen_and(b0, b1);
@@ -2061,14 +1982,14 @@ gen_linux_sll_linktype(proto)
                b0 = gen_cmp(OR_LLC, 0, BPF_B, (bpf_int32)LLCSAP_IPX);
                b1 = gen_snap(0x000000, ETHERTYPE_IPX);
                gen_or(b0, b1);
-               b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H, LINUX_SLL_P_802_2);
+               b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, LINUX_SLL_P_802_2);
                gen_and(b0, b1);
 
                /*
                 * Now check for 802.3 frames and OR that with
                 * the previous test.
                 */
-               b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H, LINUX_SLL_P_802_3);
+               b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, LINUX_SLL_P_802_3);
                gen_or(b0, b1);
 
                /*
@@ -2076,8 +1997,7 @@ gen_linux_sll_linktype(proto)
                 * do that before checking for the other frame
                 * types.
                 */
-               b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H,
-                   (bpf_int32)ETHERTYPE_IPX);
+               b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, (bpf_int32)ETHERTYPE_IPX);
                gen_or(b0, b1);
                return b1;
 
@@ -2093,7 +2013,7 @@ gen_linux_sll_linktype(proto)
                 * we check for the 802.2 protocol type in the
                 * "Ethernet type" field.
                 */
-               b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H, LINUX_SLL_P_802_2);
+               b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, LINUX_SLL_P_802_2);
 
                /*
                 * 802.2-encapsulated ETHERTYPE_ATALK packets are
@@ -2117,7 +2037,7 @@ gen_linux_sll_linktype(proto)
                 * phase 1?); we just check for the Ethernet
                 * protocol type.
                 */
-               b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H, (bpf_int32)proto);
+               b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, (bpf_int32)proto);
 
                gen_or(b0, b1);
                return b1;
@@ -2131,9 +2051,8 @@ gen_linux_sll_linktype(proto)
                         * in the "Ethernet type" field, and
                         * then check the DSAP.
                         */
-                       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,
+                       b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, LINUX_SLL_P_802_2);
+                       b1 = gen_cmp(OR_LINKHDR, off_linkpl.constant_part, BPF_B,
                             (bpf_int32)proto);
                        gen_and(b0, b1);
                        return b1;
@@ -2147,8 +2066,7 @@ gen_linux_sll_linktype(proto)
                         * will fail and the frame won't match,
                         * which is what we want).
                         */
-                       return gen_cmp(OR_LINKHDR, off_linktype, BPF_H,
-                           (bpf_int32)proto);
+                       return gen_cmp(OR_LINKTYPE, 0, BPF_H, (bpf_int32)proto);
                }
        }
 }
@@ -2186,7 +2104,7 @@ 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 +2166,7 @@ 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 +2193,7 @@ 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 +2207,7 @@ 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 +2233,7 @@ 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 +2268,7 @@ 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 +2301,7 @@ 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 +2336,7 @@ 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 +2369,7 @@ 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 +2392,7 @@ 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 +2401,18 @@ 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 +2421,7 @@ 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 +2457,19 @@ 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 +2549,7 @@ 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 +2558,7 @@ 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;
@@ -2659,6 +2577,15 @@ insert_compute_vloffsets(b)
 {
        struct slist *s;
 
+       /* There is an implicit dependency between the link
+        * payload and link header since the payload computation
+        * includes the variable part of the header. Therefore,
+        * if nobody else has allocated a register for the link
+        * header and we need it, do it now. */
+       if (off_linkpl.reg != -1 && off_linkhdr.is_variable &&
+           off_linkhdr.reg == -1)
+               off_linkhdr.reg = alloc_reg();
+
        /*
         * For link-layer types that have a variable-length header
         * preceding the link-layer header, generate code to load
@@ -2748,62 +2675,31 @@ 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)
-{
-       struct slist *s;
-
-       if (off_linkhdr_is_variable) {
-               if (reg_off_linkhdr == -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();
-               }
-
-               /*
-                * 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_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)
+gen_abs_offset_varpart(bpf_abs_offset *off)
 {
        struct slist *s;
 
-       if (off_prevlinkhdr_is_variable) {
-               if (reg_off_prevlinkhdr == -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_prevlinkhdr = alloc_reg();
+                       off->reg = alloc_reg();
                }
 
                /*
@@ -2811,45 +2707,7 @@ gen_prevlinkhdrprefixlen(void)
                 * 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 {
                /*
@@ -2997,8 +2855,7 @@ gen_linktype(proto)
                        /* fall through */
 
                default:
-                       return gen_cmp(OR_LINKHDR, off_linktype, BPF_H,
-                           (bpf_int32)proto);
+                       return gen_cmp(OR_LINKTYPE, 0, BPF_H, (bpf_int32)proto);
                        /*NOTREACHED*/
                        break;
                }
@@ -3125,7 +2982,7 @@ gen_linktype(proto)
                 * map them to the corresponding PPP protocol types.
                 */
                proto = ethertype_to_ppptype(proto);
-               return gen_cmp(OR_LINKHDR, off_linktype, BPF_H, (bpf_int32)proto);
+               return gen_cmp(OR_LINKTYPE, 0, BPF_H, (bpf_int32)proto);
                /*NOTREACHED*/
                break;
 
@@ -3141,16 +2998,16 @@ gen_linktype(proto)
                         * Also check for Van Jacobson-compressed IP.
                         * XXX - do this for other forms of PPP?
                         */
-                       b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H, PPP_IP);
-                       b1 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H, PPP_VJC);
+                       b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, PPP_IP);
+                       b1 = gen_cmp(OR_LINKTYPE, 0, BPF_H, PPP_VJC);
                        gen_or(b0, b1);
-                       b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_H, PPP_VJNC);
+                       b0 = gen_cmp(OR_LINKTYPE, 0, BPF_H, PPP_VJNC);
                        gen_or(b1, b0);
                        return b0;
 
                default:
                        proto = ethertype_to_ppptype(proto);
-                       return gen_cmp(OR_LINKHDR, off_linktype, BPF_H,
+                       return gen_cmp(OR_LINKTYPE, 0, BPF_H,
                                (bpf_int32)proto);
                }
                /*NOTREACHED*/
@@ -3251,31 +3108,31 @@ gen_linktype(proto)
                        return gen_false();
 
                case ETHERTYPE_IPV6:
-                       return (gen_cmp(OR_LINKHDR, off_linktype, BPF_B,
+                       return (gen_cmp(OR_LINKTYPE, 0, BPF_B,
                                (bpf_int32)ARCTYPE_INET6));
 
                case ETHERTYPE_IP:
-                       b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_B,
+                       b0 = gen_cmp(OR_LINKTYPE, 0, BPF_B,
                                     (bpf_int32)ARCTYPE_IP);
-                       b1 = gen_cmp(OR_LINKHDR, off_linktype, BPF_B,
+                       b1 = gen_cmp(OR_LINKTYPE, 0, BPF_B,
                                     (bpf_int32)ARCTYPE_IP_OLD);
                        gen_or(b0, b1);
                        return (b1);
 
                case ETHERTYPE_ARP:
-                       b0 = gen_cmp(OR_LINKHDR, off_linktype, BPF_B,
+                       b0 = gen_cmp(OR_LINKTYPE, 0, BPF_B,
                                     (bpf_int32)ARCTYPE_ARP);
-                       b1 = gen_cmp(OR_LINKHDR, off_linktype, BPF_B,
+                       b1 = gen_cmp(OR_LINKTYPE, 0, BPF_B,
                                     (bpf_int32)ARCTYPE_ARP_OLD);
                        gen_or(b0, b1);
                        return (b1);
 
                case ETHERTYPE_REVARP:
-                       return (gen_cmp(OR_LINKHDR, off_linktype, BPF_B,
+                       return (gen_cmp(OR_LINKTYPE, 0, BPF_B,
                                        (bpf_int32)ARCTYPE_REVARP));
 
                case ETHERTYPE_ATALK:
-                       return (gen_cmp(OR_LINKHDR, off_linktype, BPF_B,
+                       return (gen_cmp(OR_LINKTYPE, 0, BPF_B,
                                        (bpf_int32)ARCTYPE_ATALK));
                }
                /*NOTREACHED*/
@@ -3440,16 +3297,16 @@ gen_linktype(proto)
                /*
                 * Does this link-layer header type have a field
                 * indicating the type of the next protocol?  If
-                * so, off_linktype will be the offset of that
+                * so, off_linktype.constant_part will be the offset of that
                 * field in the packet; if not, it will be -1.
                 */
-               if (off_linktype != (u_int)-1) {
+               if (off_linktype.constant_part != (u_int)-1) {
                        /*
                         * Yes; assume it's an Ethernet type.  (If
                         * it's not, it needs to be handled specially
                         * above.)
                         */
-                       return gen_cmp(OR_LINKHDR, off_linktype, BPF_H, (bpf_int32)proto);
+                       return gen_cmp(OR_LINKTYPE, 0, BPF_H, (bpf_int32)proto);
                } else {
                        /*
                         * No; report an error.
@@ -3507,7 +3364,7 @@ gen_llc(void)
                 * We check for an Ethernet type field less than
                 * 1500, which means it's an 802.3 length field.
                 */
-               b0 = gen_cmp_gt(OR_LINKHDR, off_linktype, BPF_H, ETHERMTU);
+               b0 = gen_cmp_gt(OR_LINKTYPE, 0, BPF_H, ETHERMTU);
                gen_not(b0);
 
                /*
@@ -3789,7 +3646,7 @@ gen_hostop(addr, mask, dir, proto, src_off, dst_off)
                abort();
        }
        b0 = gen_linktype(proto);
-       b1 = gen_mcmp(OR_NET, offset, BPF_W, (bpf_int32)addr, mask);
+       b1 = gen_mcmp(OR_LINKPL, offset, BPF_W, (bpf_int32)addr, mask);
        gen_and(b0, b1);
        return b1;
 }
@@ -3835,12 +3692,12 @@ gen_hostop6(addr, mask, dir, proto, src_off, dst_off)
        /* this order is important */
        a = (u_int32_t *)addr;
        m = (u_int32_t *)mask;
-       b1 = gen_mcmp(OR_NET, offset + 12, BPF_W, ntohl(a[3]), ntohl(m[3]));
-       b0 = gen_mcmp(OR_NET, offset + 8, BPF_W, ntohl(a[2]), ntohl(m[2]));
+       b1 = gen_mcmp(OR_LINKPL, offset + 12, BPF_W, ntohl(a[3]), ntohl(m[3]));
+       b0 = gen_mcmp(OR_LINKPL, offset + 8, BPF_W, ntohl(a[2]), ntohl(m[2]));
        gen_and(b0, b1);
-       b0 = gen_mcmp(OR_NET, offset + 4, BPF_W, ntohl(a[1]), ntohl(m[1]));
+       b0 = gen_mcmp(OR_LINKPL, offset + 4, BPF_W, ntohl(a[1]), ntohl(m[1]));
        gen_and(b0, b1);
-       b0 = gen_mcmp(OR_NET, offset + 0, BPF_W, ntohl(a[0]), ntohl(m[0]));
+       b0 = gen_mcmp(OR_LINKPL, offset + 0, BPF_W, ntohl(a[0]), ntohl(m[0]));
        gen_and(b0, b1);
        b0 = gen_linktype(proto);
        gen_and(b0, b1);
@@ -4566,25 +4423,25 @@ gen_dnhostop(addr, dir)
        }
        b0 = gen_linktype(ETHERTYPE_DN);
        /* Check for pad = 1, long header case */
-       tmp = gen_mcmp(OR_NET, 2, BPF_H,
+       tmp = gen_mcmp(OR_LINKPL, 2, BPF_H,
            (bpf_int32)ntohs(0x0681), (bpf_int32)ntohs(0x07FF));
-       b1 = gen_cmp(OR_NET, 2 + 1 + offset_lh,
+       b1 = gen_cmp(OR_LINKPL, 2 + 1 + offset_lh,
            BPF_H, (bpf_int32)ntohs((u_short)addr));
        gen_and(tmp, b1);
        /* Check for pad = 0, long header case */
-       tmp = gen_mcmp(OR_NET, 2, BPF_B, (bpf_int32)0x06, (bpf_int32)0x7);
-       b2 = gen_cmp(OR_NET, 2 + offset_lh, BPF_H, (bpf_int32)ntohs((u_short)addr));
+       tmp = gen_mcmp(OR_LINKPL, 2, BPF_B, (bpf_int32)0x06, (bpf_int32)0x7);
+       b2 = gen_cmp(OR_LINKPL, 2 + offset_lh, BPF_H, (bpf_int32)ntohs((u_short)addr));
        gen_and(tmp, b2);
        gen_or(b2, b1);
        /* Check for pad = 1, short header case */
-       tmp = gen_mcmp(OR_NET, 2, BPF_H,
+       tmp = gen_mcmp(OR_LINKPL, 2, BPF_H,
            (bpf_int32)ntohs(0x0281), (bpf_int32)ntohs(0x07FF));
-       b2 = gen_cmp(OR_NET, 2 + 1 + offset_sh, BPF_H, (bpf_int32)ntohs((u_short)addr));
+       b2 = gen_cmp(OR_LINKPL, 2 + 1 + offset_sh, BPF_H, (bpf_int32)ntohs((u_short)addr));
        gen_and(tmp, b2);
        gen_or(b2, b1);
        /* Check for pad = 0, short header case */
-       tmp = gen_mcmp(OR_NET, 2, BPF_B, (bpf_int32)0x02, (bpf_int32)0x7);
-       b2 = gen_cmp(OR_NET, 2 + offset_sh, BPF_H, (bpf_int32)ntohs((u_short)addr));
+       tmp = gen_mcmp(OR_LINKPL, 2, BPF_B, (bpf_int32)0x02, (bpf_int32)0x7);
+       b2 = gen_cmp(OR_LINKPL, 2 + offset_sh, BPF_H, (bpf_int32)ntohs((u_short)addr));
        gen_and(tmp, b2);
        gen_or(b2, b1);
 
@@ -4608,17 +4465,17 @@ gen_mpls_linktype(proto)
 
         case Q_IP:
                 /* match the bottom-of-stack bit */
-                b0 = gen_mcmp(OR_NET, -2, BPF_B, 0x01, 0x01);
+                b0 = gen_mcmp(OR_LINKPL, -2, BPF_B, 0x01, 0x01);
                 /* match the IPv4 version number */
-                b1 = gen_mcmp(OR_NET, 0, BPF_B, 0x40, 0xf0);
+                b1 = gen_mcmp(OR_LINKPL, 0, BPF_B, 0x40, 0xf0);
                 gen_and(b0, b1);
                 return b1;
 
        case Q_IPV6:
                 /* match the bottom-of-stack bit */
-                b0 = gen_mcmp(OR_NET, -2, BPF_B, 0x01, 0x01);
+                b0 = gen_mcmp(OR_LINKPL, -2, BPF_B, 0x01, 0x01);
                 /* match the IPv4 version number */
-                b1 = gen_mcmp(OR_NET, 0, BPF_B, 0x60, 0xf0);
+                b1 = gen_mcmp(OR_LINKPL, 0, BPF_B, 0x60, 0xf0);
                 gen_and(b0, b1);
                 return b1;
 
@@ -5202,7 +5059,7 @@ gen_ipfrag()
        struct block *b;
 
        /* not IPv4 frag other than the first frag */
-       s = gen_load_a(OR_NET, 6, BPF_H);
+       s = gen_load_a(OR_LINKPL, 6, BPF_H);
        b = new_block(JMP(BPF_JSET));
        b->s.k = 0x1fff;
        b->stmts = s;
@@ -5243,7 +5100,7 @@ gen_portop(port, proto, dir)
        struct block *b0, *b1, *tmp;
 
        /* ip proto 'proto' and not a fragment other than the first fragment */
-       tmp = gen_cmp(OR_NET, 9, BPF_B, (bpf_int32)proto);
+       tmp = gen_cmp(OR_LINKPL, 9, BPF_B, (bpf_int32)proto);
        b0 = gen_ipfrag();
        gen_and(tmp, b0);
 
@@ -5334,7 +5191,7 @@ gen_portop6(port, proto, dir)
 
        /* ip6 proto 'proto' */
        /* XXX - catch the first fragment of a fragmented packet? */
-       b0 = gen_cmp(OR_NET, 6, BPF_B, (bpf_int32)proto);
+       b0 = gen_cmp(OR_LINKPL, 6, BPF_B, (bpf_int32)proto);
 
        switch (dir) {
        case Q_SRC:
@@ -5435,7 +5292,7 @@ gen_portrangeop(port1, port2, proto, dir)
        struct block *b0, *b1, *tmp;
 
        /* ip proto 'proto' and not a fragment other than the first fragment */
-       tmp = gen_cmp(OR_NET, 9, BPF_B, (bpf_int32)proto);
+       tmp = gen_cmp(OR_LINKPL, 9, BPF_B, (bpf_int32)proto);
        b0 = gen_ipfrag();
        gen_and(tmp, b0);
 
@@ -5538,7 +5395,7 @@ gen_portrangeop6(port1, port2, proto, dir)
 
        /* ip6 proto 'proto' */
        /* XXX - catch the first fragment of a fragmented packet? */
-       b0 = gen_cmp(OR_NET, 6, BPF_B, (bpf_int32)proto);
+       b0 = gen_cmp(OR_LINKPL, 6, BPF_B, (bpf_int32)proto);
 
        switch (dir) {
        case Q_SRC:
@@ -5702,15 +5559,8 @@ gen_protochain(v, proto, dir)
         * branches, and backward branch support is unlikely to appear
         * in kernel BPF engines.)
         */
-       switch (linktype) {
-
-       case DLT_IEEE802_11:
-       case DLT_PRISM_HEADER:
-       case DLT_IEEE802_11_RADIO_AVS:
-       case DLT_IEEE802_11_RADIO:
-       case DLT_PPI:
-               bpf_error("'protochain' not supported with 802.11");
-       }
+       if (off_linkpl.is_variable)
+               bpf_error("'protochain' not supported with variable length headers");
 
        no_optimize = 1; /*this code is not compatible with optimzer yet */
 
@@ -5729,11 +5579,11 @@ 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 +5592,7 @@ 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 +5668,7 @@ 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 +5676,7 @@ 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 +5737,7 @@ 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 +5755,7 @@ 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);
@@ -6033,7 +5883,7 @@ gen_proto(v, proto, dir)
                 */
                b0 = gen_linktype(ETHERTYPE_IP);
 #ifndef CHASE_CHAIN
-               b1 = gen_cmp(OR_NET, 9, BPF_B, (bpf_int32)v);
+               b1 = gen_cmp(OR_LINKPL, 9, BPF_B, (bpf_int32)v);
 #else
                b1 = gen_protochain(v, Q_IP);
 #endif
@@ -6073,13 +5923,13 @@ gen_proto(v, proto, dir)
                         */
                        b0 = gen_linktype(LLCSAP_ISONS<<8 | LLCSAP_ISONS);
                        /* OSI in C-HDLC is stuffed with a fudge byte */
-                       b1 = gen_cmp(OR_NET_NOSNAP, 1, BPF_B, (long)v);
+                       b1 = gen_cmp(OR_LINKPL_NOSNAP, 1, BPF_B, (long)v);
                        gen_and(b0, b1);
                        return b1;
 
                default:
                        b0 = gen_linktype(LLCSAP_ISONS);
-                       b1 = gen_cmp(OR_NET_NOSNAP, 0, BPF_B, (long)v);
+                       b1 = gen_cmp(OR_LINKPL_NOSNAP, 0, BPF_B, (long)v);
                        gen_and(b0, b1);
                        return b1;
                }
@@ -6090,7 +5940,7 @@ gen_proto(v, proto, dir)
                 * 4 is the offset of the PDU type relative to the IS-IS
                 * header.
                 */
-               b1 = gen_cmp(OR_NET_NOSNAP, 4, BPF_B, (long)v);
+               b1 = gen_cmp(OR_LINKPL_NOSNAP, 4, BPF_B, (long)v);
                gen_and(b0, b1);
                return b1;
 
@@ -6172,10 +6022,10 @@ gen_proto(v, proto, dir)
                 * Also check for a fragment header before the final
                 * header.
                 */
-               b2 = gen_cmp(OR_NET, 6, BPF_B, IPPROTO_FRAGMENT);
-               b1 = gen_cmp(OR_NET, 40, BPF_B, (bpf_int32)v);
+               b2 = gen_cmp(OR_LINKPL, 6, BPF_B, IPPROTO_FRAGMENT);
+               b1 = gen_cmp(OR_LINKPL, 40, BPF_B, (bpf_int32)v);
                gen_and(b2, b1);
-               b2 = gen_cmp(OR_NET, 6, BPF_B, (bpf_int32)v);
+               b2 = gen_cmp(OR_LINKPL, 6, BPF_B, (bpf_int32)v);
                gen_or(b2, b1);
 #else
                b1 = gen_protochain(v, Q_IPV6);
@@ -6322,7 +6172,8 @@ gen_scode(name, q)
                        if (alist == NULL || *alist == NULL)
                                bpf_error("unknown host '%s'", name);
                        tproto = proto;
-                       if (off_linktype == (u_int)-1 && tproto == Q_DEFAULT)
+                       if (off_linktype.constant_part == (u_int)-1 &&
+                           tproto == Q_DEFAULT)
                                tproto = Q_IP;
                        b = gen_host(**alist++, 0xffffffff, tproto, dir, q.addr);
                        while (*alist) {
@@ -6340,7 +6191,8 @@ gen_scode(name, q)
                        ai = res;
                        b = tmp = NULL;
                        tproto = tproto6 = proto;
-                       if (off_linktype == -1 && tproto == Q_DEFAULT) {
+                       if (off_linktype.constant_part == -1 &&
+                           tproto == Q_DEFAULT) {
                                tproto = Q_IP;
                                tproto6 = Q_IPV6;
                        }
@@ -6880,7 +6732,7 @@ 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 +6758,7 @@ 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 +6779,7 @@ 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 +6805,7 @@ 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 +6862,7 @@ 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);
 
                /*
@@ -7352,8 +7204,8 @@ gen_broadcast(proto)
                        bpf_error("netmask not known, so 'ip broadcast' not supported");
                b0 = gen_linktype(ETHERTYPE_IP);
                hostmask = ~netmask;
-               b1 = gen_mcmp(OR_NET, 16, BPF_W, (bpf_int32)0, hostmask);
-               b2 = gen_mcmp(OR_NET, 16, BPF_W,
+               b1 = gen_mcmp(OR_LINKPL, 16, BPF_W, (bpf_int32)0, hostmask);
+               b2 = gen_mcmp(OR_LINKPL, 16, BPF_W,
                              (bpf_int32)(~0 & hostmask), hostmask);
                gen_or(b1, b2);
                gen_and(b0, b2);
@@ -7547,13 +7399,13 @@ gen_multicast(proto)
 
        case Q_IP:
                b0 = gen_linktype(ETHERTYPE_IP);
-               b1 = gen_cmp_ge(OR_NET, 16, BPF_B, (bpf_int32)224);
+               b1 = gen_cmp_ge(OR_LINKPL, 16, BPF_B, (bpf_int32)224);
                gen_and(b0, b1);
                return b1;
 
        case Q_IPV6:
                b0 = gen_linktype(ETHERTYPE_IPV6);
-               b1 = gen_cmp(OR_NET, 24, BPF_B, (bpf_int32)255);
+               b1 = gen_cmp(OR_LINKPL, 24, BPF_B, (bpf_int32)255);
                gen_and(b0, b1);
                return b1;
        }
@@ -8039,13 +7891,13 @@ 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
         * skip past this VLAN tag.
         */
-        off_linktype += 4;
+        off_linktype.constant_part += 4;
 
         return b0;
 }
@@ -8100,7 +7952,11 @@ gen_vlan(vlan_num)
        case DLT_NETANALYZER:
        case DLT_NETANALYZER_TRANSPARENT:
 #if defined(SKF_AD_VLAN_TAG) && defined(SKF_AD_VLAN_TAG_PRESENT)
-               if (vlan_stack_depth == 0) {
+               /* Verify that this is the outer part of the packet and
+                * not encapsulated somehow. */
+               if (vlan_stack_depth == 0 && !off_linkhdr.is_variable &&
+                   off_linkhdr.constant_part ==
+                   off_outermostlinkhdr.constant_part) {
                        /*
                         * Do we need special VLAN handling?
                         */
@@ -8112,6 +7968,14 @@ gen_vlan(vlan_num)
 #endif
                        b0 = gen_vlan_no_bpf_extensions(vlan_num);
                 break;
+
+       case DLT_IEEE802_11:
+       case DLT_PRISM_HEADER:
+       case DLT_IEEE802_11_RADIO_AVS:
+       case DLT_IEEE802_11_RADIO:
+               b0 = gen_vlan_no_bpf_extensions(vlan_num);
+               break;
+
        default:
                bpf_error("no VLAN support for data link type %d",
                      linktype);
@@ -8134,7 +7998,7 @@ gen_mpls(label_num)
 
         if (label_stack_depth > 0) {
             /* just match the bottom-of-stack bit clear */
-            b0 = gen_mcmp(OR_MPLSPL, off_nl-2, BPF_B, 0, 0x01);
+            b0 = gen_mcmp(OR_PREVMPLSHDR, 2, BPF_B, 0, 0x01);
         } else {
             /*
              * We're not in an MPLS stack yet, so check the link-layer
@@ -8169,7 +8033,7 @@ gen_mpls(label_num)
        /* If a specific MPLS label is requested, check it */
        if (label_num >= 0) {
                label_num = label_num << 12; /* label is shifted 12 bits on the wire */
-               b1 = gen_mcmp(OR_MPLSPL, off_nl, BPF_W, (bpf_int32)label_num,
+               b1 = gen_mcmp(OR_LINKPL, 0, BPF_W, (bpf_int32)label_num,
                    0xfffff000); /* only compare the first 20 bits */
                gen_and(b0, b1);
                b0 = b1;
@@ -8218,7 +8082,7 @@ gen_pppoes(sess_num)
 
        /* If a specific session is requested, check PPPoE session id */
        if (sess_num >= 0) {
-               b1 = gen_mcmp(OR_LINKPL, off_nl, BPF_W,
+               b1 = gen_mcmp(OR_LINKPL, 0, BPF_W,
                    (bpf_int32)sess_num, 0x0000ffff);
                gen_and(b0, b1);
                b0 = b1;
@@ -8263,18 +8127,12 @@ 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_linktype = off_linkhdr;
+       off_linkpl.constant_part = off_linkhdr.constant_part + 2;
 
        off_nl = 0;
        off_nl_nosnap = 0;      /* no 802.2 LLC */
@@ -8416,14 +8274,11 @@ 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 */
-               off_linktype = 12;
-               off_linkpl_constant_part = off_linkhdr_constant_part + 14;      /* Ethernet */
+               PUSH_LINKHDR(DLT_EN10MB, 0,
+                   off_payload + 2,    /* Ethernet header */
+                   -1);
+               off_linktype.constant_part = off_linkhdr.constant_part + 12;
+               off_linkpl.constant_part = off_linkhdr.constant_part + 14;      /* Ethernet */
                off_nl = 0;                     /* Ethernet II */
                off_nl_nosnap = 3;              /* 802.3+802.2 */
                break;