The AVS radio header is variable-length, and fields were added to it

[libpcap] / gencode.c

/*#define CHASE_CHAIN*/
/*
 * Copyright (c) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that: (1) source code distributions
 * retain the above copyright notice and this paragraph in its entirety, (2)
 * distributions including binary code include the above copyright notice and
 * this paragraph in its entirety in the documentation or other materials
 * provided with the distribution, and (3) all advertising materials mentioning
 * features or use of this software display the following acknowledgement:
 * ``This product includes software developed by the University of California,
 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
 * the University nor the names of its contributors may be used to endorse
 * or promote products derived from this software without specific prior
 * written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */
#ifndef lint
static const char rcsid[] _U_ =
    "@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.304 2007-12-29 02:34:23 guy Exp $ (LBL)";
#endif

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#ifdef WIN32
#include <pcap-stdinc.h>
#else /* WIN32 */
#include <sys/types.h>
#include <sys/socket.h>
#endif /* WIN32 */

/*
 * XXX - why was this included even on UNIX?
 */
#ifdef __MINGW32__
#include "IP6_misc.h"
#endif

#ifndef WIN32

#ifdef __NetBSD__
#include <sys/param.h>
#endif

#include <netinet/in.h>

#endif /* WIN32 */

#include <stdlib.h>
#include <string.h>
#include <memory.h>
#include <setjmp.h>
#include <stdarg.h>

#ifdef MSDOS
#include "pcap-dos.h"
#endif

#include "pcap-int.h"

#include "ethertype.h"
#include "nlpid.h"
#include "llc.h"
#include "gencode.h"
#include "ieee80211.h"
#include "atmuni31.h"
#include "sunatmpos.h"
#include "ppp.h"
#include "pcap/sll.h"
#include "arcnet.h"
#ifdef HAVE_NET_PFVAR_H
#include <sys/socket.h>
#include <net/if.h>
#include <net/pfvar.h>
#include <net/if_pflog.h>
#endif
#ifndef offsetof
#define offsetof(s, e) ((size_t)&((s *)0)->e)
#endif
#ifdef INET6
#ifndef WIN32
#include <netdb.h>      /* for "struct addrinfo" */
#endif /* WIN32 */
#endif /*INET6*/
#include <pcap/namedb.h>

#define ETHERMTU        1500

#ifndef IPPROTO_SCTP
#define IPPROTO_SCTP 132
#endif

#ifdef HAVE_OS_PROTO_H
#include "os-proto.h"
#endif

#define JMP(c) ((c)|BPF_JMP|BPF_K)

/* Locals */
static jmp_buf top_ctx;
static pcap_t *bpf_pcap;

/* Hack for updating VLAN, MPLS, and PPPoE offsets. */
#ifdef WIN32
static u_int    orig_linktype = (u_int)-1, orig_nl = (u_int)-1, label_stack_depth = (u_int)-1;
#else
static u_int    orig_linktype = -1U, orig_nl = -1U, label_stack_depth = -1U;
#endif

/* XXX */
#ifdef PCAP_FDDIPAD
static int      pcap_fddipad;
#endif

/* VARARGS */
void
bpf_error(const char *fmt, ...)
{
        va_list ap;

        va_start(ap, fmt);
        if (bpf_pcap != NULL)
                (void)vsnprintf(pcap_geterr(bpf_pcap), PCAP_ERRBUF_SIZE,
                    fmt, ap);
        va_end(ap);
        longjmp(top_ctx, 1);
        /* NOTREACHED */
}

static void init_linktype(pcap_t *);

static void init_regs(void);
static int alloc_reg(void);
static void free_reg(int);

static struct block *root;

/*
 * Value passed to gen_load_a() to indicate what the offset argument
 * is relative to.
 */
enum e_offrel {
        OR_PACKET,      /* relative to the beginning of the packet */
        OR_LINK,        /* relative to the beginning of the link-layer header */
        OR_MACPL,       /* relative to the end of the MAC-layer header */
        OR_NET,         /* relative to the network-layer header */
        OR_NET_NOSNAP,  /* relative to the network-layer header, with no SNAP header at the link layer */
        OR_TRAN_IPV4,   /* relative to the transport-layer header, with IPv4 network layer */
        OR_TRAN_IPV6    /* relative to the transport-layer header, with IPv6 network layer */
};

/*
 * We divy out chunks of memory rather than call malloc each time so
 * we don't have to worry about leaking memory.  It's probably
 * not a big deal if all this memory was wasted but if this ever
 * goes into a library that would probably not be a good idea.
 *
 * XXX - this *is* in a library....
 */
#define NCHUNKS 16
#define CHUNK0SIZE 1024
struct chunk {
        u_int n_left;
        void *m;
};

static struct chunk chunks[NCHUNKS];
static int cur_chunk;

static void *newchunk(u_int);
static void freechunks(void);
static inline struct block *new_block(int);
static inline struct slist *new_stmt(int);
static struct block *gen_retblk(int);
static inline void syntax(void);

static void backpatch(struct block *, struct block *);
static void merge(struct block *, struct block *);
static struct block *gen_cmp(enum e_offrel, u_int, u_int, bpf_int32);
static struct block *gen_cmp_gt(enum e_offrel, u_int, u_int, bpf_int32);
static struct block *gen_cmp_ge(enum e_offrel, u_int, u_int, bpf_int32);
static struct block *gen_cmp_lt(enum e_offrel, u_int, u_int, bpf_int32);
static struct block *gen_cmp_le(enum e_offrel, u_int, u_int, bpf_int32);
static struct block *gen_mcmp(enum e_offrel, u_int, u_int, bpf_int32,
    bpf_u_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_llrel(u_int, u_int);
static struct slist *gen_load_macplrel(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);
static inline struct block *gen_true(void);
static inline struct block *gen_false(void);
static struct block *gen_ether_linktype(int);
static struct block *gen_linux_sll_linktype(int);
static struct slist *gen_load_radiotap_llprefixlen(void);
static struct slist *gen_load_ppi_llprefixlen(void);
static struct slist *gen_load_avs_llprefixlen(void);
static void insert_compute_vloffsets(struct block *);
static struct slist *gen_llprefixlen(void);
static struct slist *gen_off_macpl(void);
static int ethertype_to_ppptype(int);
static struct block *gen_linktype(int);
static struct block *gen_snap(bpf_u_int32, bpf_u_int32);
static struct block *gen_llc_linktype(int);
static struct block *gen_hostop(bpf_u_int32, bpf_u_int32, int, int, u_int, u_int);
#ifdef INET6
static struct block *gen_hostop6(struct in6_addr *, struct in6_addr *, int, int, u_int, u_int);
#endif
static struct block *gen_ahostop(const u_char *, int);
static struct block *gen_ehostop(const u_char *, int);
static struct block *gen_fhostop(const u_char *, int);
static struct block *gen_thostop(const u_char *, int);
static struct block *gen_wlanhostop(const u_char *, int);
static struct block *gen_ipfchostop(const u_char *, int);
static struct block *gen_dnhostop(bpf_u_int32, int);
static struct block *gen_mpls_linktype(int);
static struct block *gen_host(bpf_u_int32, bpf_u_int32, int, int, int);
#ifdef INET6
static struct block *gen_host6(struct in6_addr *, struct in6_addr *, int, int, int);
#endif
#ifndef INET6
static struct block *gen_gateway(const u_char *, bpf_u_int32 **, int, int);
#endif
static struct block *gen_ipfrag(void);
static struct block *gen_portatom(int, bpf_int32);
static struct block *gen_portrangeatom(int, bpf_int32, bpf_int32);
#ifdef INET6
static struct block *gen_portatom6(int, bpf_int32);
static struct block *gen_portrangeatom6(int, bpf_int32, bpf_int32);
#endif
struct block *gen_portop(int, int, int);
static struct block *gen_port(int, int, int);
struct block *gen_portrangeop(int, int, int, int);
static struct block *gen_portrange(int, int, int, int);
#ifdef INET6
struct block *gen_portop6(int, int, int);
static struct block *gen_port6(int, int, int);
struct block *gen_portrangeop6(int, int, int, int);
static struct block *gen_portrange6(int, int, int, int);
#endif
static int lookup_proto(const char *, int);
static struct block *gen_protochain(int, int, int);
static struct block *gen_proto(int, int, int);
static struct slist *xfer_to_x(struct arth *);
static struct slist *xfer_to_a(struct arth *);
static struct block *gen_mac_multicast(int);
static struct block *gen_len(int, int);
static struct block *gen_check_802_11_data_frame(void);

static struct block *gen_ppi_dlt_check(void);
static struct block *gen_msg_abbrev(int type);

static void *
newchunk(n)
        u_int n;
{
        struct chunk *cp;
        int k;
        size_t size;

#ifndef __NetBSD__
        /* XXX Round up to nearest long. */
        n = (n + sizeof(long) - 1) & ~(sizeof(long) - 1);
#else
        /* XXX Round up to structure boundary. */
        n = ALIGN(n);
#endif

        cp = &chunks[cur_chunk];
        if (n > cp->n_left) {
                ++cp, k = ++cur_chunk;
                if (k >= NCHUNKS)
                        bpf_error("out of memory");
                size = CHUNK0SIZE << k;
                cp->m = (void *)malloc(size);
                if (cp->m == NULL)
                        bpf_error("out of memory");
                memset((char *)cp->m, 0, size);
                cp->n_left = size;
                if (n > size)
                        bpf_error("out of memory");
        }
        cp->n_left -= n;
        return (void *)((char *)cp->m + cp->n_left);
}

static void
freechunks()
{
        int i;

        cur_chunk = 0;
        for (i = 0; i < NCHUNKS; ++i)
                if (chunks[i].m != NULL) {
                        free(chunks[i].m);
                        chunks[i].m = NULL;
                }
}

/*
 * A strdup whose allocations are freed after code generation is over.
 */
char *
sdup(s)
        register const char *s;
{
        int n = strlen(s) + 1;
        char *cp = newchunk(n);

        strlcpy(cp, s, n);
        return (cp);
}

static inline struct block *
new_block(code)
        int code;
{
        struct block *p;

        p = (struct block *)newchunk(sizeof(*p));
        p->s.code = code;
        p->head = p;

        return p;
}

static inline struct slist *
new_stmt(code)
        int code;
{
        struct slist *p;

        p = (struct slist *)newchunk(sizeof(*p));
        p->s.code = code;

        return p;
}

static struct block *
gen_retblk(v)
        int v;
{
        struct block *b = new_block(BPF_RET|BPF_K);

        b->s.k = v;
        return b;
}

static inline void
syntax()
{
        bpf_error("syntax error in filter expression");
}

static bpf_u_int32 netmask;
static int snaplen;
int no_optimize;

int
pcap_compile(pcap_t *p, struct bpf_program *program,
             const char *buf, int optimize, bpf_u_int32 mask)
{
        extern int n_errors;
        const char * volatile xbuf = buf;
        int len;

        no_optimize = 0;
        n_errors = 0;
        root = NULL;
        bpf_pcap = p;
        init_regs();
        if (setjmp(top_ctx)) {
                lex_cleanup();
                freechunks();
                return (-1);
        }

        netmask = mask;

        snaplen = pcap_snapshot(p);
        if (snaplen == 0) {
                snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
                         "snaplen of 0 rejects all packets");
                return -1;
        }

        lex_init(xbuf ? xbuf : "");
        init_linktype(p);
        (void)pcap_parse();

        if (n_errors)
                syntax();

        if (root == NULL)
                root = gen_retblk(snaplen);

        if (optimize && !no_optimize) {
                bpf_optimize(&root);
                if (root == NULL ||
                    (root->s.code == (BPF_RET|BPF_K) && root->s.k == 0))
                        bpf_error("expression rejects all packets");
        }
        program->bf_insns = icode_to_fcode(root, &len);
        program->bf_len = len;

        lex_cleanup();
        freechunks();
        return (0);
}

/*
 * entry point for using the compiler with no pcap open
 * pass in all the stuff that is needed explicitly instead.
 */
int
pcap_compile_nopcap(int snaplen_arg, int linktype_arg,
                    struct bpf_program *program,
             const char *buf, int optimize, bpf_u_int32 mask)
{
        pcap_t *p;
        int ret;

        p = pcap_open_dead(linktype_arg, snaplen_arg);
        if (p == NULL)
                return (-1);
        ret = pcap_compile(p, program, buf, optimize, mask);
        pcap_close(p);
        return (ret);
}

/*
 * Clean up a "struct bpf_program" by freeing all the memory allocated
 * in it.
 */
void
pcap_freecode(struct bpf_program *program)
{
        program->bf_len = 0;
        if (program->bf_insns != NULL) {
                free((char *)program->bf_insns);
                program->bf_insns = NULL;
        }
}

/*
 * Backpatch the blocks in 'list' to 'target'.  The 'sense' field indicates
 * which of the jt and jf fields has been resolved and which is a pointer
 * back to another unresolved block (or nil).  At least one of the fields
 * in each block is already resolved.
 */
static void
backpatch(list, target)
        struct block *list, *target;
{
        struct block *next;

        while (list) {
                if (!list->sense) {
                        next = JT(list);
                        JT(list) = target;
                } else {
                        next = JF(list);
                        JF(list) = target;
                }
                list = next;
        }
}

/*
 * Merge the lists in b0 and b1, using the 'sense' field to indicate
 * which of jt and jf is the link.
 */
static void
merge(b0, b1)
        struct block *b0, *b1;
{
        register struct block **p = &b0;

        /* Find end of list. */
        while (*p)
                p = !((*p)->sense) ? &JT(*p) : &JF(*p);

        /* Concatenate the lists. */
        *p = b1;
}

void
finish_parse(p)
        struct block *p;
{
        struct block *ppi_dlt_check;

        /*
         * Insert before the statements of the first (root) block any
         * statements needed to load the lengths of any variable-length
         * headers into registers.
         *
         * XXX - a fancier strategy would be to insert those before the
         * statements of all blocks that use those lengths and that
         * have no predecessors that use them, so that we only compute
         * the lengths if we need them.  There might be even better
         * approaches than that.
         *
         * However, those strategies would be more complicated, and
         * as we don't generate code to compute a length if the
         * program has no tests that use the length, and as most
         * tests will probably use those lengths, we would just
         * postpone computing the lengths so that it's not done
         * for tests that fail early, and it's not clear that's
         * worth the effort.
         */
        insert_compute_vloffsets(p->head);
        
        /*
         * For DLT_PPI captures, generate a check of the per-packet
         * DLT value to make sure it's DLT_IEEE802_11.
         */
        ppi_dlt_check = gen_ppi_dlt_check();
        if (ppi_dlt_check != NULL)
                gen_and(ppi_dlt_check, p);

        backpatch(p, gen_retblk(snaplen));
        p->sense = !p->sense;
        backpatch(p, gen_retblk(0));
        root = p->head;
}

void
gen_and(b0, b1)
        struct block *b0, *b1;
{
        backpatch(b0, b1->head);
        b0->sense = !b0->sense;
        b1->sense = !b1->sense;
        merge(b1, b0);
        b1->sense = !b1->sense;
        b1->head = b0->head;
}

void
gen_or(b0, b1)
        struct block *b0, *b1;
{
        b0->sense = !b0->sense;
        backpatch(b0, b1->head);
        b0->sense = !b0->sense;
        merge(b1, b0);
        b1->head = b0->head;
}

void
gen_not(b)
        struct block *b;
{
        b->sense = !b->sense;
}

static struct block *
gen_cmp(offrel, offset, size, v)
        enum e_offrel offrel;
        u_int offset, size;
        bpf_int32 v;
{
        return gen_ncmp(offrel, offset, size, 0xffffffff, BPF_JEQ, 0, v);
}

static struct block *
gen_cmp_gt(offrel, offset, size, v)
        enum e_offrel offrel;
        u_int offset, size;
        bpf_int32 v;
{
        return gen_ncmp(offrel, offset, size, 0xffffffff, BPF_JGT, 0, v);
}

static struct block *
gen_cmp_ge(offrel, offset, size, v)
        enum e_offrel offrel;
        u_int offset, size;
        bpf_int32 v;
{
        return gen_ncmp(offrel, offset, size, 0xffffffff, BPF_JGE, 0, v);
}

static struct block *
gen_cmp_lt(offrel, offset, size, v)
        enum e_offrel offrel;
        u_int offset, size;
        bpf_int32 v;
{
        return gen_ncmp(offrel, offset, size, 0xffffffff, BPF_JGE, 1, v);
}

static struct block *
gen_cmp_le(offrel, offset, size, v)
        enum e_offrel offrel;
        u_int offset, size;
        bpf_int32 v;
{
        return gen_ncmp(offrel, offset, size, 0xffffffff, BPF_JGT, 1, v);
}

static struct block *
gen_mcmp(offrel, offset, size, v, mask)
        enum e_offrel offrel;
        u_int offset, size;
        bpf_int32 v;
        bpf_u_int32 mask;
{
        return gen_ncmp(offrel, offset, size, mask, BPF_JEQ, 0, v);
}

static struct block *
gen_bcmp(offrel, offset, size, v)
        enum e_offrel offrel;
        register u_int offset, size;
        register const u_char *v;
{
        register struct block *b, *tmp;

        b = NULL;
        while (size >= 4) {
                register const u_char *p = &v[size - 4];
                bpf_int32 w = ((bpf_int32)p[0] << 24) |
                    ((bpf_int32)p[1] << 16) | ((bpf_int32)p[2] << 8) | p[3];

                tmp = gen_cmp(offrel, offset + size - 4, BPF_W, w);
                if (b != NULL)
                        gen_and(b, tmp);
                b = tmp;
                size -= 4;
        }
        while (size >= 2) {
                register const u_char *p = &v[size - 2];
                bpf_int32 w = ((bpf_int32)p[0] << 8) | p[1];

                tmp = gen_cmp(offrel, offset + size - 2, BPF_H, w);
                if (b != NULL)
                        gen_and(b, tmp);
                b = tmp;
                size -= 2;
        }
        if (size > 0) {
                tmp = gen_cmp(offrel, offset, BPF_B, (bpf_int32)v[0]);
                if (b != NULL)
                        gen_and(b, tmp);
                b = tmp;
        }
        return b;
}

/*
 * AND the field of size "size" at offset "offset" relative to the header
 * specified by "offrel" with "mask", and compare it with the value "v"
 * with the test specified by "jtype"; if "reverse" is true, the test
 * should test the opposite of "jtype".
 */
static struct block *
gen_ncmp(offrel, offset, size, mask, jtype, reverse, v)
        enum e_offrel offrel;
        bpf_int32 v;
        bpf_u_int32 offset, size, mask, jtype;
        int reverse;
{
        struct slist *s, *s2;
        struct block *b;

        s = gen_load_a(offrel, offset, size);

        if (mask != 0xffffffff) {
                s2 = new_stmt(BPF_ALU|BPF_AND|BPF_K);
                s2->s.k = mask;
                sappend(s, s2);
        }

        b = new_block(JMP(jtype));
        b->stmts = s;
        b->s.k = v;
        if (reverse && (jtype == BPF_JGT || jtype == BPF_JGE))
                gen_not(b);
        return b;
}

/*
 * Various code constructs need to know the layout of the data link
 * layer.  These variables give the necessary offsets from the beginning
 * of the packet data.
 */

/*
 * This is the offset of the beginning of the link-layer header from
 * the beginning of the raw packet data.
 *
 * It's usually 0, except for 802.11 with a fixed-length radio header.
 * (For 802.11 with a variable-length radio header, we have to generate
 * code to compute that offset; off_ll is 0 in that case.)
 */
static u_int off_ll;

/*
 * If there's a variable-length header preceding the link-layer header,
 * "reg_off_ll" is the register number for a register containing the
 * length of that header, and therefore the offset of the link-layer
 * header from the beginning of the raw packet data.  Otherwise,
 * "reg_off_ll" is -1.
 */
static int reg_off_ll;

/*
 * This is the offset of the beginning of the MAC-layer header from
 * the beginning of the link-layer header.
 * It's usually 0, except for ATM LANE, where it's the offset, relative
 * to the beginning of the raw packet data, of the Ethernet header.
 */
static u_int off_mac;

/*
 * This is the offset of the beginning of the MAC-layer payload,
 * from the beginning of the raw packet data.
 *
 * I.e., it's the sum of the length of the link-layer header (without,
 * for example, any 802.2 LLC header, so it's the MAC-layer
 * portion of that header), plus any prefix preceding the
 * link-layer header.
 */
static u_int off_macpl;

/*
 * This is 1 if the offset of the beginning of the MAC-layer payload
 * from the beginning of the link-layer header is variable-length.
 */
static int off_macpl_is_variable;

/*
 * If the link layer has variable_length headers, "reg_off_macpl"
 * is the register number for a register containing the length of the
 * link-layer header plus the length of any variable-length header
 * preceding the link-layer header.  Otherwise, "reg_off_macpl"
 * is -1.
 */
static int reg_off_macpl;

/*
 * "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_ll).
 *
 * For Ethernet, it's the offset of the Ethernet type field.
 *
 * For link-layer types that always use 802.2 headers, it's the
 * offset of the LLC header.
 *
 * For PPP, it's the offset of the PPP type field.
 *
 * For Cisco HDLC, it's the offset of the CHDLC type field.
 *
 * For BSD loopback, it's the offset of the AF_ value.
 *
 * 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.
 */
static u_int off_linktype;

/*
 * TRUE if "pppoes" appeared in the filter; it causes link-layer type
 * checks to check the PPP header, assumed to follow a LAN-style link-
 * layer header and a PPPoE session header.
 */
static int is_pppoes = 0;

/*
 * TRUE if the link layer includes an ATM pseudo-header.
 */
static int is_atm = 0;

/*
 * TRUE if "lane" appeared in the filter; it causes us to generate
 * code that assumes LANE rather than LLC-encapsulated traffic in SunATM.
 */
static int is_lane = 0;

/*
 * These are offsets for the ATM pseudo-header.
 */
static u_int off_vpi;
static u_int off_vci;
static u_int off_proto;

/*
 * These are offsets for the MTP2 fields.
 */
static u_int off_li;

/*
 * These are offsets for the MTP3 fields.
 */
static u_int off_sio;
static u_int off_opc;
static u_int off_dpc;
static u_int off_sls;

/*
 * This is the offset of the first byte after the ATM pseudo_header,
 * or -1 if there is no ATM pseudo-header.
 */
static u_int off_payload;

/*
 * These are offsets to the beginning of the network-layer header.
 * They are relative to the beginning of the MAC-layer payload (i.e.,
 * they don't include off_ll or off_macpl).
 *
 * If the link layer never uses 802.2 LLC:
 *
 *      "off_nl" and "off_nl_nosnap" are the same.
 *
 * If the link layer always uses 802.2 LLC:
 *
 *      "off_nl" is the offset if there's a SNAP header following
 *      the 802.2 header;
 *
 *      "off_nl_nosnap" is the offset if there's no SNAP header.
 *
 * If the link layer is Ethernet:
 *
 *      "off_nl" is the offset if the packet is an Ethernet II packet
 *      (we assume no 802.3+802.2+SNAP);
 *
 *      "off_nl_nosnap" is the offset if the packet is an 802.3 packet
 *      with an 802.2 header following it.
 */
static u_int off_nl;
static u_int off_nl_nosnap;

static int linktype;

static void
init_linktype(p)
        pcap_t *p;
{
        linktype = pcap_datalink(p);
#ifdef PCAP_FDDIPAD
        pcap_fddipad = p->fddipad;
#endif

        /*
         * Assume it's not raw ATM with a pseudo-header, for now.
         */
        off_mac = 0;
        is_atm = 0;
        is_lane = 0;
        off_vpi = -1;
        off_vci = -1;
        off_proto = -1;
        off_payload = -1;

        /*
         * And that we're not doing PPPoE.
         */
        is_pppoes = 0;

        /*
         * And assume we're not doing SS7.
         */
        off_li = -1;
        off_sio = -1;
        off_opc = -1;
        off_dpc = -1;
        off_sls = -1;

        /*
         * Also assume it's not 802.11.
         */
        off_ll = 0;
        off_macpl = 0;
        off_macpl_is_variable = 0;

        orig_linktype = -1;
        orig_nl = -1;
        label_stack_depth = 0;

        reg_off_ll = -1;
        reg_off_macpl = -1;

        switch (linktype) {

        case DLT_ARCNET:
                off_linktype = 2;
                off_macpl = 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_macpl = 8;
                off_nl = 0;             /* XXX in reality, variable! */
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        case DLT_EN10MB:
                off_linktype = 12;
                off_macpl = 14;         /* Ethernet header length */
                off_nl = 0;             /* Ethernet II */
                off_nl_nosnap = 3;      /* 802.3+802.2 */
                return;

        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_macpl = 16;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        case DLT_SLIP_BSDOS:
                /* XXX this may be the same as the DLT_PPP_BSDOS case */
                off_linktype = -1;
                /* XXX end */
                off_macpl = 24;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        case DLT_NULL:
        case DLT_LOOP:
                off_linktype = 0;
                off_macpl = 4;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        case DLT_ENC:
                off_linktype = 0;
                off_macpl = 12;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        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;
                off_macpl = 4;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        case DLT_PPP_ETHER:
                /*
                 * This does no include the Ethernet header, and
                 * only covers session state.
                 */
                off_linktype = 6;
                off_macpl = 8;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        case DLT_PPP_BSDOS:
                off_linktype = 5;
                off_macpl = 24;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        case DLT_FDDI:
                /*
                 * FDDI doesn't really have a link-level type field.
                 * We set "off_linktype" 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.
                 * XXX - should we generate code to check for SNAP?
                 */
                off_linktype = 13;
#ifdef PCAP_FDDIPAD
                off_linktype += pcap_fddipad;
#endif
                off_macpl = 13;         /* FDDI MAC header length */
#ifdef PCAP_FDDIPAD
                off_macpl += pcap_fddipad;
#endif
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
                return;

        case DLT_IEEE802:
                /*
                 * Token Ring doesn't really have a link-level type field.
                 * We set "off_linktype" 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.
                 * XXX - should we generate code to check for SNAP?
                 *
                 * XXX - the header is actually variable-length.
                 * Some various Linux patched versions gave 38
                 * as "off_linktype" and 40 as "off_nl"; however,
                 * if a token ring packet has *no* routing
                 * information, i.e. is not source-routed, the correct
                 * values are 20 and 22, as they are in the vanilla code.
                 *
                 * A packet is source-routed iff the uppermost bit
                 * of the first byte of the source address, at an
                 * offset of 8, has the uppermost bit set.  If the
                 * packet is source-routed, the total number of bytes
                 * of routing information is 2 plus bits 0x1F00 of
                 * the 16-bit value at an offset of 14 (shifted right
                 * 8 - figure out which byte that is).
                 */
                off_linktype = 14;
                off_macpl = 14;         /* Token Ring MAC header length */
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
                return;

        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.
                 *
                 * To check for Ethernet types, we assume that SSAP = SNAP
                 * is being used and pick out the encapsulated Ethernet type.
                 * XXX - should we generate code to check for SNAP?
                 *
                 * XXX - the header is actually variable-length.  We
                 * assume a 24-byte link-layer header, as appears in
                 * data frames in networks with no bridges.  If the
                 * fromds and tods 802.11 header bits are both set,
                 * it's actually supposed to be 30 bytes.
                 */
                off_linktype = 24;
                off_macpl = 0;          /* link-layer header is variable-length */
                off_macpl_is_variable = 1;
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
                return;

        case DLT_PRISM_HEADER:
                /*
                 * Same as 802.11, but with an additional header before
                 * the 802.11 header, containing a bunch of additional
                 * information including radio-level information.
                 *
                 * The header is 144 bytes long.
                 *
                 * XXX - same variable-length header problem; at least
                 * the Prism header is fixed-length.
                 */
                off_ll = 144;
                off_linktype = 24;
                off_macpl = 0;          /* link-layer header is variable-length */
                off_macpl_is_variable = 1;
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
                return;

        case DLT_IEEE802_11_RADIO_AVS:
                /*
                 * Same as 802.11, but with an additional header before
                 * the 802.11 header, containing a bunch of additional
                 * information including radio-level information.
                 *
                 * The radiotap header is variable length, and we
                 * generate code to compute its length and store it
                 * in a register.  These offsets are relative to the
                 * beginning of the 802.11 header.
                 *
                 * XXX - in Linux, do any drivers that supply an AVS
                 * header supply a link-layer type other than
                 * ARPHRD_IEEE80211_PRISM?  If so, we should map that
                 * to DLT_IEEE802_11_RADIO_AVS; if not, or if there are
                 * any drivers that supply an AVS header but supply
                 * an ARPHRD value of ARPHRD_IEEE80211_PRISM, we'll
                 * have to check the header in the generated code to
                 * determine whether it's Prism or AVS.
                 */
                off_linktype = 24;
                off_macpl = 0;          /* link-layer header is variable-length */
                off_macpl_is_variable = 1;
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
                return;
                
                /* 
                 * At the moment we treat PPI as normal Radiotap encoded
                 * packets. The difference is in the function that generates
                 * the code at the beginning to compute the header length.
                 * Since this code generator of PPI supports bare 802.11
                 * encapsulation only (i.e. the encapsulated DLT should be
                 * DLT_IEEE802_11) we generate code to check for this too.
                 */
        case DLT_PPI:
        case DLT_IEEE802_11_RADIO:
                /*
                 * Same as 802.11, but with an additional header before
                 * the 802.11 header, containing a bunch of additional
                 * information including radio-level information.
                 *
                 * The radiotap header is variable length, and we
                 * generate code to compute its length and store it
                 * in a register.  These offsets are relative to the
                 * beginning of the 802.11 header.
                 */
                off_linktype = 24;
                off_macpl = 0;          /* link-layer header is variable-length */
                off_macpl_is_variable = 1;
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
                return;

        case DLT_ATM_RFC1483:
        case DLT_ATM_CLIP:      /* Linux ATM defines this */
                /*
                 * assume routed, non-ISO PDUs
                 * (i.e., LLC = 0xAA-AA-03, OUT = 0x00-00-00)
                 *
                 * XXX - what about ISO PDUs, e.g. CLNP, ISIS, ESIS,
                 * or PPP with the PPP NLPID (e.g., PPPoA)?  The
                 * latter would presumably be treated the way PPPoE
                 * should be, so you can do "pppoe and udp port 2049"
                 * 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_macpl = 0;          /* packet begins with LLC header */
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
                return;

        case DLT_SUNATM:
                /*
                 * Full Frontal ATM; you get AALn PDUs with an ATM
                 * pseudo-header.
                 */
                is_atm = 1;
                off_vpi = SUNATM_VPI_POS;
                off_vci = SUNATM_VCI_POS;
                off_proto = PROTO_POS;
                off_mac = -1;   /* assume LLC-encapsulated, so no MAC-layer header */
                off_payload = SUNATM_PKT_BEGIN_POS;
                off_linktype = off_payload;
                off_macpl = off_payload;        /* if LLC-encapsulated */
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
                return;

        case DLT_RAW:
                off_linktype = -1;
                off_macpl = 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_macpl = 16;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        case DLT_LTALK:
                /*
                 * LocalTalk does have a 1-byte type field in the LLAP header,
                 * but really it just indicates whether there is a "short" or
                 * "long" DDP packet following.
                 */
                off_linktype = -1;
                off_macpl = 0;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        case DLT_IP_OVER_FC:
                /*
                 * RFC 2625 IP-over-Fibre-Channel doesn't really have a
                 * link-level type field.  We set "off_linktype" 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.
                 * XXX - should we generate code to check for SNAP? RFC
                 * 2625 says SNAP should be used.
                 */
                off_linktype = 16;
                off_macpl = 16;
                off_nl = 8;             /* 802.2+SNAP */
                off_nl_nosnap = 3;      /* 802.2 */
                return;

        case DLT_FRELAY:
                /*
                 * XXX - we should set this to handle SNAP-encapsulated
                 * frames (NLPID of 0x80).
                 */
                off_linktype = -1;
                off_macpl = 0;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

                /*
                 * the only BPF-interesting FRF.16 frames are non-control frames;
                 * Frame Relay has a variable length link-layer
                 * so lets start with offset 4 for now and increments later on (FIXME);
                 */
        case DLT_MFR:
                off_linktype = -1;
                off_macpl = 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_macpl = 18;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;

        case DLT_LINUX_IRDA:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_DOCSIS:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_SYMANTEC_FIREWALL:
                off_linktype = 6;
                off_macpl = 44;
                off_nl = 0;             /* Ethernet II */
                off_nl_nosnap = 0;      /* XXX - what does it do with 802.3 packets? */
                return;

#ifdef HAVE_NET_PFVAR_H
        case DLT_PFLOG:
                off_linktype = 0;
                off_macpl = PFLOG_HDRLEN;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;
#endif

        case DLT_JUNIPER_MFR:
        case DLT_JUNIPER_MLFR:
        case DLT_JUNIPER_MLPPP:
        case DLT_JUNIPER_PPP:
        case DLT_JUNIPER_CHDLC:
        case DLT_JUNIPER_FRELAY:
                off_linktype = 4;
                off_macpl = 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_macpl = 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_macpl = 8;  /* in reality variable between 8-12 */
                off_nl = 0;
                off_nl_nosnap = 10;
                return;

                /* frames captured on a Juniper PPPoE service PIC
                 * contain raw ethernet frames */
        case DLT_JUNIPER_PPPOE:
        case DLT_JUNIPER_ETHER:
                off_macpl = 14;
                off_linktype = 16;
                off_nl = 18;            /* Ethernet II */
                off_nl_nosnap = 21;     /* 802.3+802.2 */
                return;

        case DLT_JUNIPER_PPPOE_ATM:
                off_linktype = 4;
                off_macpl = 6;
                off_nl = 0;
                off_nl_nosnap = -1;     /* no 802.2 LLC */
                return;

        case DLT_JUNIPER_GGSN:
                off_linktype = 6;
                off_macpl = 12;
                off_nl = 0;
                off_nl_nosnap = -1;     /* no 802.2 LLC */
                return;

        case DLT_JUNIPER_ES:
                off_linktype = 6;
                off_macpl = -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_macpl = 12;
                off_nl = 0;             /* raw IP/IP6 header */
                off_nl_nosnap = -1;     /* no 802.2 LLC */
                return;

        case DLT_JUNIPER_SERVICES:
                off_linktype = 12;
                off_macpl = -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_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_JUNIPER_ST:
                off_linktype = 18;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_JUNIPER_ISM:
                off_linktype = 8;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_MTP2:
                off_li = 2;
                off_sio = 3;
                off_opc = 4;
                off_dpc = 4;
                off_sls = 7;
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_MTP2_WITH_PHDR:
                off_li = 6;
                off_sio = 7;
                off_opc = 8;
                off_dpc = 8;
                off_sls = 11;
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_ERF:
                off_li = 22;
                off_sio = 23;
                off_opc = 24;
                off_dpc = 24;
                off_sls = 27;
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

#ifdef DLT_PFSYNC
        case DLT_PFSYNC:
                off_linktype = -1;
                off_macpl = 4;
                off_nl = 0;
                off_nl_nosnap = 0;
                return;
#endif

        case DLT_LINUX_LAPD:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_USB:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_BLUETOOTH_HCI_H4:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_USB_LINUX:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_CAN20B:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_IEEE802_15_4_LINUX:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_IEEE802_16_MAC_CPS_RADIO:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_IEEE802_15_4:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_SITA:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_RAIF1:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_IPMB:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        case DLT_BLUETOOTH_HCI_H4_WITH_PHDR:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                off_linktype = -1;
                off_macpl = -1;
                off_nl = -1;
                off_nl_nosnap = -1;
                return;

        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_macpl = -1;
                off_nl = -1;            /* variable, min 16, max 71 steps of 7 */
                off_nl_nosnap = -1;     /* no 802.2 LLC */
                off_mac = 1;            /* step over the kiss length byte */
                return;
        }
        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_llrel(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_ll".
         */
        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 = offset;
                sappend(s, s2);
        } else {
                /*
                 * There is no variable-length header preceding the
                 * link-layer header; add in off_ll, 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 = offset + off_ll;
        }
        return s;
}

/*
 * Load a value relative to the beginning of the MAC-layer payload.
 */
static struct slist *
gen_load_macplrel(offset, size)
        u_int offset, size;
{
        struct slist *s, *s2;

        s = gen_off_macpl();

        /*
         * If s is non-null, the offset of the MAC-layer payload is
         * variable, and s points to a list of instructions that
         * arrange that the X register contains that offset.
         *
         * Otherwise, the offset of the MAC-layer payload is constant,
         * and is in off_macpl.
         */
        if (s != NULL) {
                /*
                 * The offset of the MAC-layer payload is in 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 = offset;
                sappend(s, s2);
        } else {
                /*
                 * The offset of the MAC-layer payload is constant,
                 * and is in off_macpl; load the value at that offset
                 * plus the specified offset.
                 */
                s = new_stmt(BPF_LD|BPF_ABS|size);
                s->s.k = off_macpl + offset;
        }
        return s;
}

/*
 * Load a value relative to the beginning of the specified header.
 */
static struct slist *
gen_load_a(offrel, offset, size)
        enum e_offrel offrel;
        u_int offset, size;
{
        struct slist *s, *s2;

        switch (offrel) {

        case OR_PACKET:
                s = new_stmt(BPF_LD|BPF_ABS|size);
                s->s.k = offset;
                break;

        case OR_LINK:
                s = gen_load_llrel(offset, size);
                break;

        case OR_MACPL:
                s = gen_load_macplrel(offset, size);
                break;

        case OR_NET:
                s = gen_load_macplrel(off_nl + offset, size);
                break;

        case OR_NET_NOSNAP:
                s = gen_load_macplrel(off_nl_nosnap + offset, size);
                break;

        case OR_TRAN_IPV4:
                /*
                 * Load the X register with the length of the IPv4 header
                 * (plus the offset of the link-layer header, if it's
                 * preceded by a variable-length header such as a radio
                 * header), in bytes.
                 */
                s = gen_loadx_iphdrlen();

                /*
                 * Load the item at {offset of the MAC-layer payload} +
                 * {offset, relative to the start of the MAC-layer
                 * paylod, of the IPv4 header} + {length of the IPv4 header} +
                 * {specified offset}.
                 *
                 * (If the offset of the MAC-layer payload is variable,
                 * it's included in the value in the X register, and
                 * off_macpl is 0.)
                 */
                s2 = new_stmt(BPF_LD|BPF_IND|size);
                s2->s.k = off_macpl + off_nl + offset;
                sappend(s, s2);
                break;

        case OR_TRAN_IPV6:
                s = gen_load_macplrel(off_nl + 40 + offset, size);
                break;

        default:
                abort();
                return NULL;
        }
        return s;
}

/*
 * Generate code to load into the X register the sum of the length of
 * the IPv4 header and any variable-length header preceding the link-layer
 * header.
 */
static struct slist *
gen_loadx_iphdrlen()
{
        struct slist *s, *s2;

        s = gen_off_macpl();
        if (s != NULL) {
                /*
                 * There's a variable-length prefix preceding the
                 * link-layer header, or the link-layer header is itself
                 * variable-length.  "s" points to a list of statements
                 * that put the offset of the MAC-layer payload into
                 * the X register.
                 *
                 * The 4*([k]&0xf) addressing mode can't be used, as we
                 * don't have a constant offset, so we have to load the
                 * value in question into the A register and add to it
                 * the value from the X register.
                 */
                s2 = new_stmt(BPF_LD|BPF_IND|BPF_B);
                s2->s.k = off_nl;
                sappend(s, s2);
                s2 = new_stmt(BPF_ALU|BPF_AND|BPF_K);
                s2->s.k = 0xf;
                sappend(s, s2);
                s2 = new_stmt(BPF_ALU|BPF_LSH|BPF_K);
                s2->s.k = 2;
                sappend(s, s2);

                /*
                 * The A register now contains the length of the
                 * IP header.  We need to add to it the offset of
                 * the MAC-layer payload, which is still in the X
                 * register, and move the result into the X register.
                 */
                sappend(s, new_stmt(BPF_ALU|BPF_ADD|BPF_X));
                sappend(s, new_stmt(BPF_MISC|BPF_TAX));
        } else {
                /*
                 * There is no variable-length header preceding the
                 * link-layer header, and the link-layer header is
                 * fixed-length; load the length of the IPv4 header,
                 * which is at an offset of off_nl from the beginning
                 * of the MAC-layer payload, and thus at an offset
                 * of off_mac_pl + off_nl from the beginning of the
                 * raw packet data.
                 */
                s = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
                s->s.k = off_macpl + off_nl;
        }
        return s;
}

static struct block *
gen_uncond(rsense)
        int rsense;
{
        struct block *b;
        struct slist *s;

        s = new_stmt(BPF_LD|BPF_IMM);
        s->s.k = !rsense;
        b = new_block(JMP(BPF_JEQ));
        b->stmts = s;

        return b;
}

static inline struct block *
gen_true()
{
        return gen_uncond(1);
}

static inline struct block *
gen_false()
{
        return gen_uncond(0);
}

/*
 * Byte-swap a 32-bit number.
 * ("htonl()" or "ntohl()" won't work - we want to byte-swap even on
 * big-endian platforms.)
 */
#define SWAPLONG(y) \
((((y)&0xff)<<24) | (((y)&0xff00)<<8) | (((y)&0xff0000)>>8) | (((y)>>24)&0xff))

/*
 * Generate code to match a particular packet type.
 *
 * "proto" is an Ethernet type value, if > ETHERMTU, or an LLC SAP
 * value, if <= ETHERMTU.  We use that to determine whether to
 * match the type/length field or to check the type/length field for
 * a value <= ETHERMTU to see whether it's a type field and then do
 * the appropriate test.
 */
static struct block *
gen_ether_linktype(proto)
        register int proto;
{
        struct block *b0, *b1;

        switch (proto) {

        case LLCSAP_ISONS:
        case LLCSAP_IP:
        case LLCSAP_NETBEUI:
                /*
                 * OSI protocols and NetBEUI always use 802.2 encapsulation,
                 * so we check the DSAP and SSAP.
                 *
                 * LLCSAP_IP checks for IP-over-802.2, rather
                 * than IP-over-Ethernet or IP-over-SNAP.
                 *
                 * XXX - should we check both the DSAP and the
                 * SSAP, like this, or should we check just the
                 * DSAP, as we do for other types <= ETHERMTU
                 * (i.e., other SAP values)?
                 */
                b0 = gen_cmp_gt(OR_LINK, off_linktype, BPF_H, ETHERMTU);
                gen_not(b0);
                b1 = gen_cmp(OR_MACPL, 0, BPF_H, (bpf_int32)
                             ((proto << 8) | proto));
                gen_and(b0, b1);
                return b1;

        case LLCSAP_IPX:
                /*
                 * Check for;
                 *
                 *      Ethernet_II frames, which are Ethernet
                 *      frames with a frame type of ETHERTYPE_IPX;
                 *
                 *      Ethernet_802.3 frames, which are 802.3
                 *      frames (i.e., the type/length field is
                 *      a length field, <= ETHERMTU, rather than
                 *      a type field) with the first two bytes
                 *      after the Ethernet/802.3 header being
                 *      0xFFFF;
                 *
                 *      Ethernet_802.2 frames, which are 802.3
                 *      frames with an 802.2 LLC header and
                 *      with the IPX LSAP as the DSAP in the LLC
                 *      header;
                 *
                 *      Ethernet_SNAP frames, which are 802.3
                 *      frames with an LLC header and a SNAP
                 *      header and with an OUI of 0x000000
                 *      (encapsulated Ethernet) and a protocol
                 *      ID of ETHERTYPE_IPX in the SNAP header.
                 *
                 * XXX - should we generate the same code both
                 * for tests for LLCSAP_IPX and for ETHERTYPE_IPX?
                 */

                /*
                 * This generates code to check both for the
                 * IPX LSAP (Ethernet_802.2) and for Ethernet_802.3.
                 */
                b0 = gen_cmp(OR_MACPL, 0, BPF_B, (bpf_int32)LLCSAP_IPX);
                b1 = gen_cmp(OR_MACPL, 0, BPF_H, (bpf_int32)0xFFFF);
                gen_or(b0, b1);

                /*
                 * Now we add code to check for SNAP frames with
                 * ETHERTYPE_IPX, i.e. Ethernet_SNAP.
                 */
                b0 = gen_snap(0x000000, ETHERTYPE_IPX);
                gen_or(b0, b1);

                /*
                 * Now we generate code to check for 802.3
                 * frames in general.
                 */
                b0 = gen_cmp_gt(OR_LINK, off_linktype, BPF_H, ETHERMTU);
                gen_not(b0);

                /*
                 * Now add the check for 802.3 frames before the
                 * check for Ethernet_802.2 and Ethernet_802.3,
                 * as those checks should only be done on 802.3
                 * frames, not on Ethernet frames.
                 */
                gen_and(b0, b1);

                /*
                 * Now add the check for Ethernet_II frames, and
                 * do that before checking for the other frame
                 * types.
                 */
                b0 = gen_cmp(OR_LINK, off_linktype, BPF_H,
                    (bpf_int32)ETHERTYPE_IPX);
                gen_or(b0, b1);
                return b1;

        case ETHERTYPE_ATALK:
        case ETHERTYPE_AARP:
                /*
                 * EtherTalk (AppleTalk protocols on Ethernet link
                 * layer) may use 802.2 encapsulation.
                 */

                /*
                 * Check for 802.2 encapsulation (EtherTalk phase 2?);
                 * we check for an Ethernet type field less than
                 * 1500, which means it's an 802.3 length field.
                 */
                b0 = gen_cmp_gt(OR_LINK, off_linktype, BPF_H, ETHERMTU);
                gen_not(b0);

                /*
                 * 802.2-encapsulated ETHERTYPE_ATALK packets are
                 * SNAP packets with an organization code of
                 * 0x080007 (Apple, for Appletalk) and a protocol
                 * type of ETHERTYPE_ATALK (Appletalk).
                 *
                 * 802.2-encapsulated ETHERTYPE_AARP packets are
                 * SNAP packets with an organization code of
                 * 0x000000 (encapsulated Ethernet) and a protocol
                 * type of ETHERTYPE_AARP (Appletalk ARP).
                 */
                if (proto == ETHERTYPE_ATALK)
                        b1 = gen_snap(0x080007, ETHERTYPE_ATALK);
                else    /* proto == ETHERTYPE_AARP */
                        b1 = gen_snap(0x000000, ETHERTYPE_AARP);
                gen_and(b0, b1);

                /*
                 * Check for Ethernet encapsulation (Ethertalk
                 * phase 1?); we just check for the Ethernet
                 * protocol type.
                 */
                b0 = gen_cmp(OR_LINK, off_linktype, BPF_H, (bpf_int32)proto);

                gen_or(b0, b1);
                return b1;

        default:
                if (proto <= ETHERMTU) {
                        /*
                         * This is an LLC SAP value, so the frames
                         * that match would be 802.2 frames.
                         * Check that the frame is an 802.2 frame
                         * (i.e., that the length/type field is
                         * a length field, <= ETHERMTU) and
                         * then check the DSAP.
                         */
                        b0 = gen_cmp_gt(OR_LINK, off_linktype, BPF_H, ETHERMTU);
                        gen_not(b0);
                        b1 = gen_cmp(OR_LINK, off_linktype + 2, BPF_B,
                            (bpf_int32)proto);
                        gen_and(b0, b1);
                        return b1;
                } else {
                        /*
                         * This is an Ethernet type, so compare
                         * the length/type field with it (if
                         * the frame is an 802.2 frame, the length
                         * field will be <= ETHERMTU, and, as
                         * "proto" is > ETHERMTU, this test
                         * will fail and the frame won't match,
                         * which is what we want).
                         */
                        return gen_cmp(OR_LINK, off_linktype, BPF_H,
                            (bpf_int32)proto);
                }
        }
}

/*
 * Generate code to match a particular packet type.
 *
 * "proto" is an Ethernet type value, if > ETHERMTU, or an LLC SAP
 * value, if <= ETHERMTU.  We use that to determine whether to
 * match the type field or to check the type field for the special
 * LINUX_SLL_P_802_2 value and then do the appropriate test.
 */
static struct block *
gen_linux_sll_linktype(proto)
        register int proto;
{
        struct block *b0, *b1;

        switch (proto) {

        case LLCSAP_ISONS:
        case LLCSAP_IP:
        case LLCSAP_NETBEUI:
                /*
                 * OSI protocols and NetBEUI always use 802.2 encapsulation,
                 * so we check the DSAP and SSAP.
                 *
                 * LLCSAP_IP checks for IP-over-802.2, rather
                 * than IP-over-Ethernet or IP-over-SNAP.
                 *
                 * XXX - should we check both the DSAP and the
                 * SSAP, like this, or should we check just the
                 * DSAP, as we do for other types <= ETHERMTU
                 * (i.e., other SAP values)?
                 */
                b0 = gen_cmp(OR_LINK, off_linktype, BPF_H, LINUX_SLL_P_802_2);
                b1 = gen_cmp(OR_MACPL, 0, BPF_H, (bpf_int32)
                             ((proto << 8) | proto));
                gen_and(b0, b1);
                return b1;

        case LLCSAP_IPX:
                /*
                 *      Ethernet_II frames, which are Ethernet
                 *      frames with a frame type of ETHERTYPE_IPX;
                 *
                 *      Ethernet_802.3 frames, which have a frame
                 *      type of LINUX_SLL_P_802_3;
                 *
                 *      Ethernet_802.2 frames, which are 802.3
                 *      frames with an 802.2 LLC header (i.e, have
                 *      a frame type of LINUX_SLL_P_802_2) and
                 *      with the IPX LSAP as the DSAP in the LLC
                 *      header;
                 *
                 *      Ethernet_SNAP frames, which are 802.3
                 *      frames with an LLC header and a SNAP
                 *      header and with an OUI of 0x000000
                 *      (encapsulated Ethernet) and a protocol
                 *      ID of ETHERTYPE_IPX in the SNAP header.
                 *
                 * First, do the checks on LINUX_SLL_P_802_2
                 * frames; generate the check for either
                 * Ethernet_802.2 or Ethernet_SNAP frames, and
                 * then put a check for LINUX_SLL_P_802_2 frames
                 * before it.
                 */
                b0 = gen_cmp(OR_MACPL, 0, BPF_B, (bpf_int32)LLCSAP_IPX);
                b1 = gen_snap(0x000000, ETHERTYPE_IPX);
                gen_or(b0, b1);
                b0 = gen_cmp(OR_LINK, off_linktype, 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_LINK, off_linktype, BPF_H, LINUX_SLL_P_802_3);
                gen_or(b0, b1);

                /*
                 * Now add the check for Ethernet_II frames, and
                 * do that before checking for the other frame
                 * types.
                 */
                b0 = gen_cmp(OR_LINK, off_linktype, BPF_H,
                    (bpf_int32)ETHERTYPE_IPX);
                gen_or(b0, b1);
                return b1;

        case ETHERTYPE_ATALK:
        case ETHERTYPE_AARP:
                /*
                 * EtherTalk (AppleTalk protocols on Ethernet link
                 * layer) may use 802.2 encapsulation.
                 */

                /*
                 * Check for 802.2 encapsulation (EtherTalk phase 2?);
                 * we check for the 802.2 protocol type in the
                 * "Ethernet type" field.
                 */
                b0 = gen_cmp(OR_LINK, off_linktype, BPF_H, LINUX_SLL_P_802_2);

                /*
                 * 802.2-encapsulated ETHERTYPE_ATALK packets are
                 * SNAP packets with an organization code of
                 * 0x080007 (Apple, for Appletalk) and a protocol
                 * type of ETHERTYPE_ATALK (Appletalk).
                 *
                 * 802.2-encapsulated ETHERTYPE_AARP packets are
                 * SNAP packets with an organization code of
                 * 0x000000 (encapsulated Ethernet) and a protocol
                 * type of ETHERTYPE_AARP (Appletalk ARP).
                 */
                if (proto == ETHERTYPE_ATALK)
                        b1 = gen_snap(0x080007, ETHERTYPE_ATALK);
                else    /* proto == ETHERTYPE_AARP */
                        b1 = gen_snap(0x000000, ETHERTYPE_AARP);
                gen_and(b0, b1);

                /*
                 * Check for Ethernet encapsulation (Ethertalk
                 * phase 1?); we just check for the Ethernet
                 * protocol type.
                 */
                b0 = gen_cmp(OR_LINK, off_linktype, BPF_H, (bpf_int32)proto);

                gen_or(b0, b1);
                return b1;

        default:
                if (proto <= ETHERMTU) {
                        /*
                         * This is an LLC SAP value, so the frames
                         * that match would be 802.2 frames.
                         * Check for the 802.2 protocol type
                         * in the "Ethernet type" field, and
                         * then check the DSAP.
                         */
                        b0 = gen_cmp(OR_LINK, off_linktype, BPF_H,
                            LINUX_SLL_P_802_2);
                        b1 = gen_cmp(OR_LINK, off_macpl, BPF_B,
                             (bpf_int32)proto);
                        gen_and(b0, b1);
                        return b1;
                } else {
                        /*
                         * This is an Ethernet type, so compare
                         * the length/type field with it (if
                         * the frame is an 802.2 frame, the length
                         * field will be <= ETHERMTU, and, as
                         * "proto" is > ETHERMTU, this test
                         * will fail and the frame won't match,
                         * which is what we want).
                         */
                        return gen_cmp(OR_LINK, off_linktype, BPF_H,
                            (bpf_int32)proto);
                }
        }
}

static struct slist *
gen_load_radiotap_llprefixlen()
{
        struct slist *s1, *s2;

        /*
         * Generate code to load the length of the radiotap header into
         * the register assigned to hold that length, if one has been
         * assigned.  (If one hasn't been assigned, no code we've
         * generated uses that prefix, so we don't need to generate any
         * code to load it.)
         */
        if (reg_off_ll != -1) {
                /*
                 * The 2 bytes at offsets of 2 and 3 from the beginning
                 * of the radiotap header are the length of the radiotap
                 * header; unfortunately, it's little-endian, so we have
                 * to load it a byte at a time and construct the value.
                 */

                /*
                 * Load the high-order byte, at an offset of 3, shift it
                 * left a byte, and put the result in the X register.
                 */
                s1 = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s1->s.k = 3;
                s2 = new_stmt(BPF_ALU|BPF_LSH|BPF_K);
                sappend(s1, s2);
                s2->s.k = 8;
                s2 = new_stmt(BPF_MISC|BPF_TAX);
                sappend(s1, s2);

                /*
                 * Load the next byte, at an offset of 2, and OR the
                 * value from the X register into it.
                 */
                s2 = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                sappend(s1, s2);
                s2->s.k = 2;
                s2 = new_stmt(BPF_ALU|BPF_OR|BPF_X);
                sappend(s1, s2);

                /*
                 * Now allocate a register to hold that value and store
                 * it.
                 */
                s2 = new_stmt(BPF_ST);
                s2->s.k = reg_off_ll;
                sappend(s1, s2);

                /*
                 * Now move it into the X register.
                 */
                s2 = new_stmt(BPF_MISC|BPF_TAX);
                sappend(s1, s2);

                return (s1);
        } else
                return (NULL);
}

/* 
 * At the moment we treat PPI as normal Radiotap encoded
 * packets. The difference is in the function that generates
 * the code at the beginning to compute the header length.
 * Since this code generator of PPI supports bare 802.11
 * encapsulation only (i.e. the encapsulated DLT should be
 * DLT_IEEE802_11) we generate code to check for this too;
 * that's done in finish_parse().
 */
static struct slist *
gen_load_ppi_llprefixlen()
{
        struct slist *s1, *s2;
        
        /*
         * Generate code to load the length of the radiotap header
         * into the register assigned to hold that length, if one has
         * been assigned.
         */
        if (reg_off_ll != -1) {
                /*
                 * The 2 bytes at offsets of 2 and 3 from the beginning
                 * of the radiotap header are the length of the radiotap
                 * header; unfortunately, it's little-endian, so we have
                 * to load it a byte at a time and construct the value.
                 */

                /*
                 * Load the high-order byte, at an offset of 3, shift it
                 * left a byte, and put the result in the X register.
                 */
                s1 = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s1->s.k = 3;
                s2 = new_stmt(BPF_ALU|BPF_LSH|BPF_K);
                sappend(s1, s2);
                s2->s.k = 8;
                s2 = new_stmt(BPF_MISC|BPF_TAX);
                sappend(s1, s2);

                /*
                 * Load the next byte, at an offset of 2, and OR the
                 * value from the X register into it.
                 */
                s2 = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                sappend(s1, s2);
                s2->s.k = 2;
                s2 = new_stmt(BPF_ALU|BPF_OR|BPF_X);
                sappend(s1, s2);

                /*
                 * Now allocate a register to hold that value and store
                 * it.
                 */
                s2 = new_stmt(BPF_ST);
                s2->s.k = reg_off_ll;
                sappend(s1, s2);

                /*
                 * Now move it into the X register.
                 */
                s2 = new_stmt(BPF_MISC|BPF_TAX);
                sappend(s1, s2);

                return (s1);
        } else
                return (NULL);
}

static struct slist *
gen_load_avs_llprefixlen()
{
        struct slist *s1, *s2;

        /*
         * Generate code to load the length of the AVS header into
         * the register assigned to hold that length, if one has been
         * assigned.  (If one hasn't been assigned, no code we've
         * generated uses that prefix, so we don't need to generate any
         * code to load it.)
         */
        if (reg_off_ll != -1) {
                /*
                 * The 4 bytes at an offset of 4 from the beginning of
                 * the AVS header are the length of the AVS header.
                 * That field is big-endian.
                 */
                s1 = new_stmt(BPF_LD|BPF_W|BPF_ABS);
                s1->s.k = 4;

                /*
                 * Now allocate a register to hold that value and store
                 * it.
                 */
                s2 = new_stmt(BPF_ST);
                s2->s.k = reg_off_ll;
                sappend(s1, s2);

                /*
                 * Now move it into the X register.
                 */
                s2 = new_stmt(BPF_MISC|BPF_TAX);
                sappend(s1, s2);

                return (s1);
        } else
                return (NULL);
}

/*
 * Load a value relative to the beginning of the link-layer header after the 802.11
 * header, i.e. LLC_SNAP.
 * 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_802_11_header_len(struct slist *s, struct slist *snext)
{
        struct slist *s2;
        struct slist *sjset_data_frame_1;
        struct slist *sjset_data_frame_2;
        struct slist *sjset_qos;
        struct slist *sjset_radiotap_flags;
        struct slist *sjset_radiotap_tsft;
        struct slist *sjset_tsft_datapad, *sjset_notsft_datapad;
        struct slist *s_roundup;

        if (reg_off_macpl == -1) {
                /*
                 * No register has been assigned to the offset of
                 * the MAC-layer payload, which means nobody needs
                 * it; don't bother computing it - just return
                 * what we already have.
                 */
                return (s);
        }

        /*
         * This code is not compatible with the optimizer, as
         * we are generating jmp instructions within a normal
         * slist of instructions
         */
        no_optimize = 1;
        
        /*
         * 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_ll".
         */
        if (s == NULL) {
                /*
                 * There is no variable-length header preceding the
                 * link-layer header.
                 *
                 * 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_macpl register.
                 * That length is off_ll.
                 */
                s = new_stmt(BPF_LDX|BPF_IMM);
                s->s.k = off_ll;
        }

        /*
         * 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_macpl, 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);
        sappend(s, s2);
        s2 = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
        s2->s.k = 24;
        sappend(s, s2);
        s2 = new_stmt(BPF_ST);
        s2->s.k = reg_off_macpl;
        sappend(s, s2);

        s2 = new_stmt(BPF_LD|BPF_IND|BPF_B);
        s2->s.k = 0;
        sappend(s, s2);

        /*
         * Check the Frame Control field to see if this is a data frame;
         * a data frame has the 0x08 bit (b3) in that field set and the
         * 0x04 bit (b2) clear.
         */
        sjset_data_frame_1 = new_stmt(JMP(BPF_JSET));
        sjset_data_frame_1->s.k = 0x08;
        sappend(s, sjset_data_frame_1);
                
        /*
         * If b3 is set, test b2, otherwise go to the first statement of
         * the rest of the program.
         */
        sjset_data_frame_1->s.jt = sjset_data_frame_2 = new_stmt(JMP(BPF_JSET));
        sjset_data_frame_2->s.k = 0x04;
        sappend(s, sjset_data_frame_2);
        sjset_data_frame_1->s.jf = snext;

        /*
         * If b2 is not set, this is a data frame; test the QoS bit.
         * Otherwise, go to the first statement of the rest of the
         * program.
         */
        sjset_data_frame_2->s.jt = snext;
        sjset_data_frame_2->s.jf = sjset_qos = new_stmt(JMP(BPF_JSET));
        sjset_qos->s.k = 0x80;  /* QoS bit */
        sappend(s, sjset_qos);
                
        /*
         * If it's set, add 2 to reg_off_macpl, 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_macpl;
        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_macpl;
        sappend(s, s2);

        /*
         * If we have a radiotap header, look at it to see whether
         * there's Atheros padding between the MAC-layer header
         * and the payload.
         *
         * Note: all of the fields in the radiotap header are
         * little-endian, so we byte-swap all of the values
         * we test against, as they will be loaded as big-endian
         * values.
         */
        if (linktype == DLT_IEEE802_11_RADIO) {
                /*
                 * Is the IEEE80211_RADIOTAP_FLAGS bit (0x0000002) set
                 * in the presence flag?
                 */
                sjset_qos->s.jf = s2 = new_stmt(BPF_LD|BPF_ABS|BPF_W);
                s2->s.k = 4;
                sappend(s, s2);

                sjset_radiotap_flags = new_stmt(JMP(BPF_JSET));
                sjset_radiotap_flags->s.k = SWAPLONG(0x00000002);
                sappend(s, sjset_radiotap_flags);

                /*
                 * If not, skip all of this.
                 */
                sjset_radiotap_flags->s.jf = snext;

                /*
                 * Otherwise, is the IEEE80211_RADIOTAP_TSFT bit set?
                 */
                sjset_radiotap_tsft = sjset_radiotap_flags->s.jt =
                    new_stmt(JMP(BPF_JSET));
                sjset_radiotap_tsft->s.k = SWAPLONG(0x00000001);
                sappend(s, sjset_radiotap_tsft);

                /*
                 * If IEEE80211_RADIOTAP_TSFT is set, the flags field is
                 * at an offset of 16 from the beginning of the raw packet
                 * data (8 bytes for the radiotap header and 8 bytes for
                 * the TSFT field).
                 *
                 * Test whether the IEEE80211_RADIOTAP_F_DATAPAD bit (0x20)
                 * is set.
                 */
                sjset_radiotap_tsft->s.jt = s2 = new_stmt(BPF_LD|BPF_ABS|BPF_B);
                s2->s.k = 16;
                sappend(s, s2);

                sjset_tsft_datapad = new_stmt(JMP(BPF_JSET));
                sjset_tsft_datapad->s.k = 0x20;
                sappend(s, sjset_tsft_datapad);

                /*
                 * If IEEE80211_RADIOTAP_TSFT is not set, the flags field is
                 * at an offset of 8 from the beginning of the raw packet
                 * data (8 bytes for the radiotap header).
                 *
                 * Test whether the IEEE80211_RADIOTAP_F_DATAPAD bit (0x20)
                 * is set.
                 */
                sjset_radiotap_tsft->s.jf = s2 = new_stmt(BPF_LD|BPF_ABS|BPF_B);
                s2->s.k = 8;
                sappend(s, s2);

                sjset_notsft_datapad = new_stmt(JMP(BPF_JSET));
                sjset_notsft_datapad->s.k = 0x20;
                sappend(s, sjset_notsft_datapad);

                /*
                 * In either case, if IEEE80211_RADIOTAP_F_DATAPAD is
                 * set, round the length of the 802.11 header to
                 * a multiple of 4.  Do that by adding 3 and then
                 * dividing by and multiplying by 4, which we do by
                 * ANDing with ~3.
                 */
                s_roundup = new_stmt(BPF_LD|BPF_MEM);
                s_roundup->s.k = reg_off_macpl;
                sappend(s, s_roundup);
                s2 = new_stmt(BPF_ALU|BPF_ADD|BPF_IMM);
                s2->s.k = 3;
                sappend(s, s2);
                s2 = new_stmt(BPF_ALU|BPF_AND|BPF_IMM);
                s2->s.k = ~3;
                sappend(s, s2);
                s2 = new_stmt(BPF_ST);
                s2->s.k = reg_off_macpl;
                sappend(s, s2);

                sjset_tsft_datapad->s.jt = s_roundup;
                sjset_tsft_datapad->s.jf = snext;
                sjset_notsft_datapad->s.jt = s_roundup;
                sjset_notsft_datapad->s.jf = snext;
        } else
                sjset_qos->s.jf = snext;

        return s;
}

static void
insert_compute_vloffsets(b)
        struct block *b;
{
        struct slist *s;

        /*
         * For link-layer types that have a variable-length header
         * preceding the link-layer header, generate code to load
         * the offset of the link-layer header into the register
         * assigned to that offset, if any.
         */
        switch (linktype) {

        case DLT_IEEE802_11_RADIO:
                s = gen_load_radiotap_llprefixlen();
                break;

        case DLT_PPI:
                s = gen_load_ppi_llprefixlen();
                break;

        case DLT_IEEE802_11_RADIO_AVS:
                s = gen_load_avs_llprefixlen();
                break;

        default:
                s = NULL;
                break;
        }

        /*
         * For link-layer types that have a variable-length link-layer
         * header, generate code to load the offset of the MAC-layer
         * payload into the register assigned to that offset, if any.
         */
        switch (linktype) {

        case DLT_IEEE802_11:
        case DLT_IEEE802_11_RADIO:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_PRISM_HEADER:
        case DLT_PPI:
                s = gen_load_802_11_header_len(s, b->stmts);
                break;
        }

        /*
         * If we have any offset-loading code, append all the
         * existing statements in the block to those statements,
         * and make the resulting list the list of statements
         * for the block.
         */
        if (s != NULL) {
                sappend(s, b->stmts);
                b->stmts = s;
        }
}

static struct block *
gen_ppi_dlt_check(void)
{
        struct slist *s_load_dlt;
        struct block *b;

        if (linktype == DLT_PPI)
        {
                /* Create the statements that check for the DLT
                 */
                s_load_dlt = new_stmt(BPF_LD|BPF_W|BPF_ABS);
                s_load_dlt->s.k = 4;

                b = new_block(JMP(BPF_JEQ));

                b->stmts = s_load_dlt;
                b->s.k = SWAPLONG(DLT_IEEE802_11);
        }
        else
        {
                b = NULL;
        }

        return b;
}

static struct slist *
gen_radiotap_llprefixlen(void)
{
        struct slist *s;

        if (reg_off_ll == -1) {
                /*
                 * We haven't yet assigned a register for the length
                 * of the radiotap header; allocate one.
                 */
                reg_off_ll = alloc_reg();
        }

        /*
         * Load the register containing the radiotap length
         * into the X register.
         */
        s = new_stmt(BPF_LDX|BPF_MEM);
        s->s.k = reg_off_ll;
        return s;
}

/* 
 * At the moment we treat PPI as normal Radiotap encoded
 * packets. The difference is in the function that generates
 * the code at the beginning to compute the header length.
 * Since this code generator of PPI supports bare 802.11
 * encapsulation only (i.e. the encapsulated DLT should be
 * DLT_IEEE802_11) we generate code to check for this too.
 */
static struct slist *
gen_ppi_llprefixlen(void)
{
        struct slist *s;

        if (reg_off_ll == -1) {
                /*
                 * We haven't yet assigned a register for the length
                 * of the radiotap header; allocate one.
                 */
                reg_off_ll = alloc_reg();
        }

        /*
         * Load the register containing the PPI length
         * into the X register.
         */
        s = new_stmt(BPF_LDX|BPF_MEM);
        s->s.k = reg_off_ll;
        return s;
}

static struct slist *
gen_avs_llprefixlen(void)
{
        struct slist *s;

        if (reg_off_ll == -1) {
                /*
                 * We haven't yet assigned a register for the length
                 * of the radiotap header; allocate one.
                 */
                reg_off_ll = alloc_reg();
        }

        /*
         * Load the register containing the AVS length
         * into the X register.
         */
        s = new_stmt(BPF_LDX|BPF_MEM);
        s->s.k = reg_off_ll;
        return s;
}

/*
 * Generate code to compute the 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_llprefixlen(void)
{
        switch (linktype) {

        case DLT_PPI:
                return gen_ppi_llprefixlen();

        case DLT_IEEE802_11_RADIO:
                return gen_radiotap_llprefixlen();

        case DLT_IEEE802_11_RADIO_AVS:
                return gen_avs_llprefixlen();

        default:
                return NULL;
        }
}

/*
 * Generate code to load the register containing the offset of the
 * MAC-layer payload into the X register; if no register for that offset
 * has been allocated, allocate it first.
 */
static struct slist *
gen_off_macpl(void)
{
        struct slist *s;

        if (off_macpl_is_variable) {
                if (reg_off_macpl == -1) {
                        /*
                         * We haven't yet assigned a register for the offset
                         * of the MAC-layer payload; allocate one.
                         */
                        reg_off_macpl = alloc_reg();
                }

                /*
                 * Load the register containing the offset of the MAC-layer
                 * payload into the X register.
                 */
                s = new_stmt(BPF_LDX|BPF_MEM);
                s->s.k = reg_off_macpl;
                return s;
        } else {
                /*
                 * That offset isn't variable, so we don't need to
                 * generate any code.
                 */
                return NULL;
        }
}

/*
 * Map an Ethernet type to the equivalent PPP type.
 */
static int
ethertype_to_ppptype(proto)
        int proto;
{
        switch (proto) {

        case ETHERTYPE_IP:
                proto = PPP_IP;
                break;

#ifdef INET6
        case ETHERTYPE_IPV6:
                proto = PPP_IPV6;
                break;
#endif

        case ETHERTYPE_DN:
                proto = PPP_DECNET;
                break;

        case ETHERTYPE_ATALK:
                proto = PPP_APPLE;
                break;

        case ETHERTYPE_NS:
                proto = PPP_NS;
                break;

        case LLCSAP_ISONS:
                proto = PPP_OSI;
                break;

        case LLCSAP_8021D:
                /*
                 * I'm assuming the "Bridging PDU"s that go
                 * over PPP are Spanning Tree Protocol
                 * Bridging PDUs.
                 */
                proto = PPP_BRPDU;
                break;

        case LLCSAP_IPX:
                proto = PPP_IPX;
                break;
        }
        return (proto);
}

/*
 * Generate code to match a particular packet type by matching the
 * link-layer type field or fields in the 802.2 LLC header.
 *
 * "proto" is an Ethernet type value, if > ETHERMTU, or an LLC SAP
 * value, if <= ETHERMTU.
 */
static struct block *
gen_linktype(proto)
        register int proto;
{
        struct block *b0, *b1, *b2;

        /* are we checking MPLS-encapsulated packets? */
        if (label_stack_depth > 0) {
                switch (proto) {
                case ETHERTYPE_IP:
                case PPP_IP:
                        /* FIXME add other L3 proto IDs */
                        return gen_mpls_linktype(Q_IP); 

                case ETHERTYPE_IPV6:
                case PPP_IPV6:
                        /* FIXME add other L3 proto IDs */
                        return gen_mpls_linktype(Q_IPV6); 

                default:
                        bpf_error("unsupported protocol over mpls");
                        /* NOTREACHED */
                }
        }

        /*
         * Are we testing PPPoE packets?
         */
        if (is_pppoes) {
                /*
                 * The PPPoE session header is part of the
                 * MAC-layer payload, so all references
                 * should be relative to the beginning of
                 * that payload.
                 */

                /*
                 * We use Ethernet protocol types inside libpcap;
                 * map them to the corresponding PPP protocol types.
                 */
                proto = ethertype_to_ppptype(proto);
                return gen_cmp(OR_MACPL, off_linktype, BPF_H, (bpf_int32)proto);
        }

        switch (linktype) {

        case DLT_EN10MB:
                return gen_ether_linktype(proto);
                /*NOTREACHED*/
                break;

        case DLT_C_HDLC:
                switch (proto) {

                case LLCSAP_ISONS:
                        proto = (proto << 8 | LLCSAP_ISONS);
                        /* fall through */

                default:
                        return gen_cmp(OR_LINK, off_linktype, BPF_H,
                            (bpf_int32)proto);
                        /*NOTREACHED*/
                        break;
                }
                break;

        case DLT_PPI:
        case DLT_IEEE802_11:
        case DLT_IEEE802_11_RADIO:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_PRISM_HEADER:
                /*
                 * Check that we have a data frame.
                 */
                b0 = gen_check_802_11_data_frame();

                /*
                 * Now check for the specified link-layer type.
                 */
                b1 = gen_llc_linktype(proto);
                gen_and(b0, b1);
                return b1;
                /*NOTREACHED*/
                break;

        case DLT_FDDI:
                /*
                 * XXX - check for asynchronous frames, as per RFC 1103.
                 */
                return gen_llc_linktype(proto);
                /*NOTREACHED*/
                break;

        case DLT_IEEE802:
                /*
                 * XXX - check for LLC PDUs, as per IEEE 802.5.
                 */
                return gen_llc_linktype(proto);
                /*NOTREACHED*/
                break;

        case DLT_ATM_RFC1483:
        case DLT_ATM_CLIP:
        case DLT_IP_OVER_FC:
                return gen_llc_linktype(proto);
                /*NOTREACHED*/
                break;

        case DLT_SUNATM:
                /*
                 * If "is_lane" is set, check for a LANE-encapsulated
                 * version of this protocol, otherwise check for an
                 * LLC-encapsulated version of this protocol.
                 *
                 * We assume LANE means Ethernet, not Token Ring.
                 */
                if (is_lane) {
                        /*
                         * Check that the packet doesn't begin with an
                         * LE Control marker.  (We've already generated
                         * a test for LANE.)
                         */
                        b0 = gen_cmp(OR_LINK, SUNATM_PKT_BEGIN_POS, BPF_H,
                            0xFF00);
                        gen_not(b0);

                        /*
                         * Now generate an Ethernet test.
                         */
                        b1 = gen_ether_linktype(proto);
                        gen_and(b0, b1);
                        return b1;
                } else {
                        /*
                         * Check for LLC encapsulation and then check the
                         * protocol.
                         */
                        b0 = gen_atmfield_code(A_PROTOTYPE, PT_LLC, BPF_JEQ, 0);
                        b1 = gen_llc_linktype(proto);
                        gen_and(b0, b1);
                        return b1;
                }
                /*NOTREACHED*/
                break;

        case DLT_LINUX_SLL:
                return gen_linux_sll_linktype(proto);
                /*NOTREACHED*/
                break;

        case DLT_SLIP:
        case DLT_SLIP_BSDOS:
        case DLT_RAW:
                /*
                 * These types don't provide any type field; packets
                 * are always IPv4 or IPv6.
                 *
                 * XXX - for IPv4, check for a version number of 4, and,
                 * for IPv6, check for a version number of 6?
                 */
                switch (proto) {

                case ETHERTYPE_IP:
                        /* Check for a version number of 4. */
                        return gen_mcmp(OR_LINK, 0, BPF_B, 0x40, 0xF0);
#ifdef INET6
                case ETHERTYPE_IPV6:
                        /* Check for a version number of 6. */
                        return gen_mcmp(OR_LINK, 0, BPF_B, 0x60, 0xF0);
#endif

                default:
                        return gen_false();             /* always false */
                }
                /*NOTREACHED*/
                break;

        case DLT_PPP:
        case DLT_PPP_PPPD:
        case DLT_PPP_SERIAL:
        case DLT_PPP_ETHER:
                /*
                 * We use Ethernet protocol types inside libpcap;
                 * map them to the corresponding PPP protocol types.
                 */
                proto = ethertype_to_ppptype(proto);
                return gen_cmp(OR_LINK, off_linktype, BPF_H, (bpf_int32)proto);
                /*NOTREACHED*/
                break;

        case DLT_PPP_BSDOS:
                /*
                 * We use Ethernet protocol types inside libpcap;
                 * map them to the corresponding PPP protocol types.
                 */
                switch (proto) {

                case ETHERTYPE_IP:
                        /*
                         * Also check for Van Jacobson-compressed IP.
                         * XXX - do this for other forms of PPP?
                         */
                        b0 = gen_cmp(OR_LINK, off_linktype, BPF_H, PPP_IP);
                        b1 = gen_cmp(OR_LINK, off_linktype, BPF_H, PPP_VJC);
                        gen_or(b0, b1);
                        b0 = gen_cmp(OR_LINK, off_linktype, BPF_H, PPP_VJNC);
                        gen_or(b1, b0);
                        return b0;

                default:
                        proto = ethertype_to_ppptype(proto);
                        return gen_cmp(OR_LINK, off_linktype, BPF_H,
                                (bpf_int32)proto);
                }
                /*NOTREACHED*/
                break;

        case DLT_NULL:
        case DLT_LOOP:
        case DLT_ENC:
                /*
                 * For DLT_NULL, the link-layer header is a 32-bit
                 * word containing an AF_ value in *host* byte order,
                 * and for DLT_ENC, the link-layer header begins
                 * with a 32-bit work containing an AF_ value in
                 * host byte order.
                 *
                 * In addition, if we're reading a saved capture file,
                 * the host byte order in the capture may not be the
                 * same as the host byte order on this machine.
                 *
                 * For DLT_LOOP, the link-layer header is a 32-bit
                 * word containing an AF_ value in *network* byte order.
                 *
                 * XXX - AF_ values may, unfortunately, be platform-
                 * dependent; for example, FreeBSD's AF_INET6 is 24
                 * whilst NetBSD's and OpenBSD's is 26.
                 *
                 * This means that, when reading a capture file, just
                 * checking for our AF_INET6 value won't work if the
                 * capture file came from another OS.
                 */
                switch (proto) {

                case ETHERTYPE_IP:
                        proto = AF_INET;
                        break;

#ifdef INET6
                case ETHERTYPE_IPV6:
                        proto = AF_INET6;
                        break;
#endif

                default:
                        /*
                         * Not a type on which we support filtering.
                         * XXX - support those that have AF_ values
                         * #defined on this platform, at least?
                         */
                        return gen_false();
                }

                if (linktype == DLT_NULL || linktype == DLT_ENC) {
                        /*
                         * The AF_ value is in host byte order, but
                         * the BPF interpreter will convert it to
                         * network byte order.
                         *
                         * If this is a save file, and it's from a
                         * machine with the opposite byte order to
                         * ours, we byte-swap the AF_ value.
                         *
                         * Then we run it through "htonl()", and
                         * generate code to compare against the result.
                         */
                        if (bpf_pcap->sf.rfile != NULL &&
                            bpf_pcap->sf.swapped)
                                proto = SWAPLONG(proto);
                        proto = htonl(proto);
                }
                return (gen_cmp(OR_LINK, 0, BPF_W, (bpf_int32)proto));

#ifdef HAVE_NET_PFVAR_H
        case DLT_PFLOG:
                /*
                 * af field is host byte order in contrast to the rest of
                 * the packet.
                 */
                if (proto == ETHERTYPE_IP)
                        return (gen_cmp(OR_LINK, offsetof(struct pfloghdr, af),
                            BPF_B, (bpf_int32)AF_INET));
#ifdef INET6
                else if (proto == ETHERTYPE_IPV6)
                        return (gen_cmp(OR_LINK, offsetof(struct pfloghdr, af),
                            BPF_B, (bpf_int32)AF_INET6));
#endif /* INET6 */
                else
                        return gen_false();
                /*NOTREACHED*/
                break;
#endif /* HAVE_NET_PFVAR_H */

        case DLT_ARCNET:
        case DLT_ARCNET_LINUX:
                /*
                 * XXX should we check for first fragment if the protocol
                 * uses PHDS?
                 */
                switch (proto) {

                default:
                        return gen_false();

#ifdef INET6
                case ETHERTYPE_IPV6:
                        return (gen_cmp(OR_LINK, off_linktype, BPF_B,
                                (bpf_int32)ARCTYPE_INET6));
#endif /* INET6 */

                case ETHERTYPE_IP:
                        b0 = gen_cmp(OR_LINK, off_linktype, BPF_B,
                                     (bpf_int32)ARCTYPE_IP);
                        b1 = gen_cmp(OR_LINK, off_linktype, BPF_B,
                                     (bpf_int32)ARCTYPE_IP_OLD);
                        gen_or(b0, b1);
                        return (b1);

                case ETHERTYPE_ARP:
                        b0 = gen_cmp(OR_LINK, off_linktype, BPF_B,
                                     (bpf_int32)ARCTYPE_ARP);
                        b1 = gen_cmp(OR_LINK, off_linktype, BPF_B,
                                     (bpf_int32)ARCTYPE_ARP_OLD);
                        gen_or(b0, b1);
                        return (b1);

                case ETHERTYPE_REVARP:
                        return (gen_cmp(OR_LINK, off_linktype, BPF_B,
                                        (bpf_int32)ARCTYPE_REVARP));

                case ETHERTYPE_ATALK:
                        return (gen_cmp(OR_LINK, off_linktype, BPF_B,
                                        (bpf_int32)ARCTYPE_ATALK));
                }
                /*NOTREACHED*/
                break;

        case DLT_LTALK:
                switch (proto) {
                case ETHERTYPE_ATALK:
                        return gen_true();
                default:
                        return gen_false();
                }
                /*NOTREACHED*/
                break;

        case DLT_FRELAY:
                /*
                 * XXX - assumes a 2-byte Frame Relay header with
                 * DLCI and flags.  What if the address is longer?
                 */
                switch (proto) {

                case ETHERTYPE_IP:
                        /*
                         * Check for the special NLPID for IP.
                         */
                        return gen_cmp(OR_LINK, 2, BPF_H, (0x03<<8) | 0xcc);

#ifdef INET6
                case ETHERTYPE_IPV6:
                        /*
                         * Check for the special NLPID for IPv6.
                         */
                        return gen_cmp(OR_LINK, 2, BPF_H, (0x03<<8) | 0x8e);
#endif

                case LLCSAP_ISONS:
                        /*
                         * Check for several OSI protocols.
                         *
                         * Frame Relay packets typically have an OSI
                         * NLPID at the beginning; we check for each
                         * of them.
                         *
                         * What we check for is the NLPID and a frame
                         * control field of UI, i.e. 0x03 followed
                         * by the NLPID.
                         */
                        b0 = gen_cmp(OR_LINK, 2, BPF_H, (0x03<<8) | ISO8473_CLNP);
                        b1 = gen_cmp(OR_LINK, 2, BPF_H, (0x03<<8) | ISO9542_ESIS);
                        b2 = gen_cmp(OR_LINK, 2, BPF_H, (0x03<<8) | ISO10589_ISIS);
                        gen_or(b1, b2);
                        gen_or(b0, b2);
                        return b2;

                default:
                        return gen_false();
                }
                /*NOTREACHED*/
                break;

        case DLT_MFR:
                bpf_error("Multi-link Frame Relay link-layer type filtering not implemented");

        case DLT_JUNIPER_MFR:
        case DLT_JUNIPER_MLFR:
        case DLT_JUNIPER_MLPPP:
        case DLT_JUNIPER_ATM1:
        case DLT_JUNIPER_ATM2:
        case DLT_JUNIPER_PPPOE:
        case DLT_JUNIPER_PPPOE_ATM:
        case DLT_JUNIPER_GGSN:
        case DLT_JUNIPER_ES:
        case DLT_JUNIPER_MONITOR:
        case DLT_JUNIPER_SERVICES:
        case DLT_JUNIPER_ETHER:
        case DLT_JUNIPER_PPP:
        case DLT_JUNIPER_FRELAY:
        case DLT_JUNIPER_CHDLC:
        case DLT_JUNIPER_VP:
        case DLT_JUNIPER_ST:
        case DLT_JUNIPER_ISM:
                /* just lets verify the magic number for now -
                 * on ATM we may have up to 6 different encapsulations on the wire
                 * and need a lot of heuristics to figure out that the payload
                 * might be;
                 *
                 * FIXME encapsulation specific BPF_ filters
                 */
                return gen_mcmp(OR_LINK, 0, BPF_W, 0x4d474300, 0xffffff00); /* compare the magic number */

        case DLT_LINUX_IRDA:
                bpf_error("IrDA link-layer type filtering not implemented");

        case DLT_DOCSIS:
                bpf_error("DOCSIS link-layer type filtering not implemented");

        case DLT_MTP2:
        case DLT_MTP2_WITH_PHDR:
                bpf_error("MTP2 link-layer type filtering not implemented");

        case DLT_ERF:
                bpf_error("ERF link-layer type filtering not implemented");

#ifdef DLT_PFSYNC
        case DLT_PFSYNC:
                bpf_error("PFSYNC link-layer type filtering not implemented");
#endif

        case DLT_LINUX_LAPD:
                bpf_error("LAPD link-layer type filtering not implemented");

        case DLT_USB:
        case DLT_USB_LINUX:
                bpf_error("USB link-layer type filtering not implemented");

        case DLT_BLUETOOTH_HCI_H4:
        case DLT_BLUETOOTH_HCI_H4_WITH_PHDR:
                bpf_error("Bluetooth link-layer type filtering not implemented");

        case DLT_CAN20B:
                bpf_error("CAN20B link-layer type filtering not implemented");

        case DLT_IEEE802_15_4:
        case DLT_IEEE802_15_4_LINUX:
                bpf_error("IEEE 802.15.4 link-layer type filtering not implemented");

        case DLT_IEEE802_16_MAC_CPS_RADIO:
                bpf_error("IEEE 802.16 link-layer type filtering not implemented");

        case DLT_SITA:
                bpf_error("SITA link-layer type filtering not implemented");

        case DLT_RAIF1:
                bpf_error("RAIF1 link-layer type filtering not implemented");

        case DLT_IPMB:
                bpf_error("IPMB link-layer type filtering not implemented");

        case DLT_AX25_KISS:
                bpf_error("AX.25 link-layer type filtering not implemented");
        }

        /*
         * All the types that have no encapsulation should either be
         * handled as DLT_SLIP, DLT_SLIP_BSDOS, and DLT_RAW are, if
         * all packets are IP packets, or should be handled in some
         * special case, if none of them are (if some are and some
         * aren't, the lack of encapsulation is a problem, as we'd
         * have to find some other way of determining the packet type).
         *
         * Therefore, if "off_linktype" is -1, there's an error.
         */
        if (off_linktype == (u_int)-1)
                abort();

        /*
         * Any type not handled above should always have an Ethernet
         * type at an offset of "off_linktype".
         */
        return gen_cmp(OR_LINK, off_linktype, BPF_H, (bpf_int32)proto);
}

/*
 * Check for an LLC SNAP packet with a given organization code and
 * protocol type; we check the entire contents of the 802.2 LLC and
 * snap headers, checking for DSAP and SSAP of SNAP and a control
 * field of 0x03 in the LLC header, and for the specified organization
 * code and protocol type in the SNAP header.
 */
static struct block *
gen_snap(orgcode, ptype)
        bpf_u_int32 orgcode;
        bpf_u_int32 ptype;
{
        u_char snapblock[8];

        snapblock[0] = LLCSAP_SNAP;     /* DSAP = SNAP */
        snapblock[1] = LLCSAP_SNAP;     /* SSAP = SNAP */
        snapblock[2] = 0x03;            /* control = UI */
        snapblock[3] = (orgcode >> 16); /* upper 8 bits of organization code */
        snapblock[4] = (orgcode >> 8);  /* middle 8 bits of organization code */
        snapblock[5] = (orgcode >> 0);  /* lower 8 bits of organization code */
        snapblock[6] = (ptype >> 8);    /* upper 8 bits of protocol type */
        snapblock[7] = (ptype >> 0);    /* lower 8 bits of protocol type */
        return gen_bcmp(OR_MACPL, 0, 8, snapblock);
}

/*
 * Generate code to match a particular packet type, for link-layer types
 * using 802.2 LLC headers.
 *
 * This is *NOT* used for Ethernet; "gen_ether_linktype()" is used
 * for that - it handles the D/I/X Ethernet vs. 802.3+802.2 issues.
 *
 * "proto" is an Ethernet type value, if > ETHERMTU, or an LLC SAP
 * value, if <= ETHERMTU.  We use that to determine whether to
 * match the DSAP or both DSAP and LSAP or to check the OUI and
 * protocol ID in a SNAP header.
 */
static struct block *
gen_llc_linktype(proto)
        int proto;
{
        /*
         * XXX - handle token-ring variable-length header.
         */
        switch (proto) {

        case LLCSAP_IP:
        case LLCSAP_ISONS:
        case LLCSAP_NETBEUI:
                /*
                 * XXX - should we check both the DSAP and the
                 * SSAP, like this, or should we check just the
                 * DSAP, as we do for other types <= ETHERMTU
                 * (i.e., other SAP values)?
                 */
                return gen_cmp(OR_MACPL, 0, BPF_H, (bpf_u_int32)
                             ((proto << 8) | proto));

        case LLCSAP_IPX:
                /*
                 * XXX - are there ever SNAP frames for IPX on
                 * non-Ethernet 802.x networks?
                 */
                return gen_cmp(OR_MACPL, 0, BPF_B,
                    (bpf_int32)LLCSAP_IPX);

        case ETHERTYPE_ATALK:
                /*
                 * 802.2-encapsulated ETHERTYPE_ATALK packets are
                 * SNAP packets with an organization code of
                 * 0x080007 (Apple, for Appletalk) and a protocol
                 * type of ETHERTYPE_ATALK (Appletalk).
                 *
                 * XXX - check for an organization code of
                 * encapsulated Ethernet as well?
                 */
                return gen_snap(0x080007, ETHERTYPE_ATALK);

        default:
                /*
                 * XXX - we don't have to check for IPX 802.3
                 * here, but should we check for the IPX Ethertype?
                 */
                if (proto <= ETHERMTU) {
                        /*
                         * This is an LLC SAP value, so check
                         * the DSAP.
                         */
                        return gen_cmp(OR_MACPL, 0, BPF_B, (bpf_int32)proto);
                } else {
                        /*
                         * This is an Ethernet type; we assume that it's
                         * unlikely that it'll appear in the right place
                         * at random, and therefore check only the
                         * location that would hold the Ethernet type
                         * in a SNAP frame with an organization code of
                         * 0x000000 (encapsulated Ethernet).
                         *
                         * XXX - if we were to check for the SNAP DSAP and
                         * LSAP, as per XXX, and were also to check for an
                         * organization code of 0x000000 (encapsulated
                         * Ethernet), we'd do
                         *
                         *      return gen_snap(0x000000, proto);
                         *
                         * here; for now, we don't, as per the above.
                         * I don't know whether it's worth the extra CPU
                         * time to do the right check or not.
                         */
                        return gen_cmp(OR_MACPL, 6, BPF_H, (bpf_int32)proto);
                }
        }
}

static struct block *
gen_hostop(addr, mask, dir, proto, src_off, dst_off)
        bpf_u_int32 addr;
        bpf_u_int32 mask;
        int dir, proto;
        u_int src_off, dst_off;
{
        struct block *b0, *b1;
        u_int offset;

        switch (dir) {

        case Q_SRC:
                offset = src_off;
                break;

        case Q_DST:
                offset = dst_off;
                break;

        case Q_AND:
                b0 = gen_hostop(addr, mask, Q_SRC, proto, src_off, dst_off);
                b1 = gen_hostop(addr, mask, Q_DST, proto, src_off, dst_off);
                gen_and(b0, b1);
                return b1;

        case Q_OR:
        case Q_DEFAULT:
                b0 = gen_hostop(addr, mask, Q_SRC, proto, src_off, dst_off);
                b1 = gen_hostop(addr, mask, Q_DST, proto, src_off, dst_off);
                gen_or(b0, b1);
                return b1;

        default:
                abort();
        }
        b0 = gen_linktype(proto);
        b1 = gen_mcmp(OR_NET, offset, BPF_W, (bpf_int32)addr, mask);
        gen_and(b0, b1);
        return b1;
}

#ifdef INET6
static struct block *
gen_hostop6(addr, mask, dir, proto, src_off, dst_off)
        struct in6_addr *addr;
        struct in6_addr *mask;
        int dir, proto;
        u_int src_off, dst_off;
{
        struct block *b0, *b1;
        u_int offset;
        u_int32_t *a, *m;

        switch (dir) {

        case Q_SRC:
                offset = src_off;
                break;

        case Q_DST:
                offset = dst_off;
                break;

        case Q_AND:
                b0 = gen_hostop6(addr, mask, Q_SRC, proto, src_off, dst_off);
                b1 = gen_hostop6(addr, mask, Q_DST, proto, src_off, dst_off);
                gen_and(b0, b1);
                return b1;

        case Q_OR:
        case Q_DEFAULT:
                b0 = gen_hostop6(addr, mask, Q_SRC, proto, src_off, dst_off);
                b1 = gen_hostop6(addr, mask, Q_DST, proto, src_off, dst_off);
                gen_or(b0, b1);
                return b1;

        default:
                abort();
        }
        /* 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]));
        gen_and(b0, b1);
        b0 = gen_mcmp(OR_NET, 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]));
        gen_and(b0, b1);
        b0 = gen_linktype(proto);
        gen_and(b0, b1);
        return b1;
}
#endif /*INET6*/

static struct block *
gen_ehostop(eaddr, dir)
        register const u_char *eaddr;
        register int dir;
{
        register struct block *b0, *b1;

        switch (dir) {
        case Q_SRC:
                return gen_bcmp(OR_LINK, off_mac + 6, 6, eaddr);

        case Q_DST:
                return gen_bcmp(OR_LINK, off_mac + 0, 6, eaddr);

        case Q_AND:
                b0 = gen_ehostop(eaddr, Q_SRC);
                b1 = gen_ehostop(eaddr, Q_DST);
                gen_and(b0, b1);
                return b1;

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_ehostop(eaddr, Q_SRC);
                b1 = gen_ehostop(eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;
        }
        abort();
        /* NOTREACHED */
}

/*
 * Like gen_ehostop, but for DLT_FDDI
 */
static struct block *
gen_fhostop(eaddr, dir)
        register const u_char *eaddr;
        register int dir;
{
        struct block *b0, *b1;

        switch (dir) {
        case Q_SRC:
#ifdef PCAP_FDDIPAD
                return gen_bcmp(OR_LINK, 6 + 1 + pcap_fddipad, 6, eaddr);
#else
                return gen_bcmp(OR_LINK, 6 + 1, 6, eaddr);
#endif

        case Q_DST:
#ifdef PCAP_FDDIPAD
                return gen_bcmp(OR_LINK, 0 + 1 + pcap_fddipad, 6, eaddr);
#else
                return gen_bcmp(OR_LINK, 0 + 1, 6, eaddr);
#endif

        case Q_AND:
                b0 = gen_fhostop(eaddr, Q_SRC);
                b1 = gen_fhostop(eaddr, Q_DST);
                gen_and(b0, b1);
                return b1;

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_fhostop(eaddr, Q_SRC);
                b1 = gen_fhostop(eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;
        }
        abort();
        /* NOTREACHED */
}

/*
 * Like gen_ehostop, but for DLT_IEEE802 (Token Ring)
 */
static struct block *
gen_thostop(eaddr, dir)
        register const u_char *eaddr;
        register int dir;
{
        register struct block *b0, *b1;

        switch (dir) {
        case Q_SRC:
                return gen_bcmp(OR_LINK, 8, 6, eaddr);

        case Q_DST:
                return gen_bcmp(OR_LINK, 2, 6, eaddr);

        case Q_AND:
                b0 = gen_thostop(eaddr, Q_SRC);
                b1 = gen_thostop(eaddr, Q_DST);
                gen_and(b0, b1);
                return b1;

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_thostop(eaddr, Q_SRC);
                b1 = gen_thostop(eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;
        }
        abort();
        /* NOTREACHED */
}

/*
 * Like gen_ehostop, but for DLT_IEEE802_11 (802.11 wireless LAN) and
 * various 802.11 + radio headers.
 */
static struct block *
gen_wlanhostop(eaddr, dir)
        register const u_char *eaddr;
        register int dir;
{
        register struct block *b0, *b1, *b2;
        register struct slist *s;

#ifdef ENABLE_WLAN_FILTERING_PATCH
        /*
         * TODO GV 20070613
         * We need to disable the optimizer because the optimizer is buggy
         * and wipes out some LD instructions generated by the below
         * code to validate the Frame Control bits
         */
        no_optimize = 1;
#endif /* ENABLE_WLAN_FILTERING_PATCH */

        switch (dir) {
        case Q_SRC:
                /*
                 * Oh, yuk.
                 *
                 *      For control frames, there is no SA.
                 *
                 *      For management frames, SA is at an
                 *      offset of 10 from the beginning of
                 *      the packet.
                 *
                 *      For data frames, SA is at an offset
                 *      of 10 from the beginning of the packet
                 *      if From DS is clear, at an offset of
                 *      16 from the beginning of the packet
                 *      if From DS is set and To DS is clear,
                 *      and an offset of 24 from the beginning
                 *      of the packet if From DS is set and To DS
                 *      is set.
                 */

                /*
                 * Generate the tests to be done for data frames
                 * with From DS set.
                 *
                 * First, check for To DS set, i.e. check "link[1] & 0x01".
                 */
                s = gen_load_a(OR_LINK, 1, BPF_B);
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x01; /* To DS */
                b1->stmts = s;

                /*
                 * If To DS is set, the SA is at 24.
                 */
                b0 = gen_bcmp(OR_LINK, 24, 6, eaddr);
                gen_and(b1, b0);

                /*
                 * Now, check for To DS not set, i.e. check
                 * "!(link[1] & 0x01)".
                 */
                s = gen_load_a(OR_LINK, 1, BPF_B);
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x01; /* To DS */
                b2->stmts = s;
                gen_not(b2);

                /*
                 * If To DS is not set, the SA is at 16.
                 */
                b1 = gen_bcmp(OR_LINK, 16, 6, eaddr);
                gen_and(b2, b1);

                /*
                 * Now OR together the last two checks.  That gives
                 * the complete set of checks for data frames with
                 * From DS set.
                 */
                gen_or(b1, b0);

                /*
                 * Now check for From DS being set, and AND that with
                 * the ORed-together checks.
                 */
                s = gen_load_a(OR_LINK, 1, BPF_B);
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x02; /* From DS */
                b1->stmts = s;
                gen_and(b1, b0);

                /*
                 * Now check for data frames with From DS not set.
                 */
                s = gen_load_a(OR_LINK, 1, BPF_B);
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x02; /* From DS */
                b2->stmts = s;
                gen_not(b2);

                /*
                 * If From DS isn't set, the SA is at 10.
                 */
                b1 = gen_bcmp(OR_LINK, 10, 6, eaddr);
                gen_and(b2, b1);

                /*
                 * Now OR together the checks for data frames with
                 * From DS not set and for data frames with From DS
                 * set; that gives the checks done for data frames.
                 */
                gen_or(b1, b0);

                /*
                 * Now check for a data frame.
                 * I.e, check "link[0] & 0x08".
                 */
                s = gen_load_a(OR_LINK, 0, BPF_B);
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x08;
                b1->stmts = s;

                /*
                 * AND that with the checks done for data frames.
                 */
                gen_and(b1, b0);

                /*
                 * If the high-order bit of the type value is 0, this
                 * is a management frame.
                 * I.e, check "!(link[0] & 0x08)".
                 */
                s = gen_load_a(OR_LINK, 0, BPF_B);
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x08;
                b2->stmts = s;
                gen_not(b2);

                /*
                 * For management frames, the SA is at 10.
                 */
                b1 = gen_bcmp(OR_LINK, 10, 6, eaddr);
                gen_and(b2, b1);

                /*
                 * OR that with the checks done for data frames.
                 * That gives the checks done for management and
                 * data frames.
                 */
                gen_or(b1, b0);

                /*
                 * If the low-order bit of the type value is 1,
                 * this is either a control frame or a frame
                 * with a reserved type, and thus not a
                 * frame with an SA.
                 *
                 * I.e., check "!(link[0] & 0x04)".
                 */
                s = gen_load_a(OR_LINK, 0, BPF_B);
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x04;
                b1->stmts = s;
                gen_not(b1);

                /*
                 * AND that with the checks for data and management
                 * frames.
                 */
                gen_and(b1, b0);
                return b0;

        case Q_DST:
                /*
                 * Oh, yuk.
                 *
                 *      For control frames, there is no DA.
                 *
                 *      For management frames, DA is at an
                 *      offset of 4 from the beginning of
                 *      the packet.
                 *
                 *      For data frames, DA is at an offset
                 *      of 4 from the beginning of the packet
                 *      if To DS is clear and at an offset of
                 *      16 from the beginning of the packet
                 *      if To DS is set.
                 */

                /*
                 * Generate the tests to be done for data frames.
                 *
                 * First, check for To DS set, i.e. "link[1] & 0x01".
                 */
                s = gen_load_a(OR_LINK, 1, BPF_B);
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x01; /* To DS */
                b1->stmts = s;

                /*
                 * If To DS is set, the DA is at 16.
                 */
                b0 = gen_bcmp(OR_LINK, 16, 6, eaddr);
                gen_and(b1, b0);

                /*
                 * Now, check for To DS not set, i.e. check
                 * "!(link[1] & 0x01)".
                 */
                s = gen_load_a(OR_LINK, 1, BPF_B);
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x01; /* To DS */
                b2->stmts = s;
                gen_not(b2);

                /*
                 * If To DS is not set, the DA is at 4.
                 */
                b1 = gen_bcmp(OR_LINK, 4, 6, eaddr);
                gen_and(b2, b1);

                /*
                 * Now OR together the last two checks.  That gives
                 * the complete set of checks for data frames.
                 */
                gen_or(b1, b0);

                /*
                 * Now check for a data frame.
                 * I.e, check "link[0] & 0x08".
                 */
                s = gen_load_a(OR_LINK, 0, BPF_B);
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x08;
                b1->stmts = s;

                /*
                 * AND that with the checks done for data frames.
                 */
                gen_and(b1, b0);

                /*
                 * If the high-order bit of the type value is 0, this
                 * is a management frame.
                 * I.e, check "!(link[0] & 0x08)".
                 */
                s = gen_load_a(OR_LINK, 0, BPF_B);
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x08;
                b2->stmts = s;
                gen_not(b2);

                /*
                 * For management frames, the DA is at 4.
                 */
                b1 = gen_bcmp(OR_LINK, 4, 6, eaddr);
                gen_and(b2, b1);

                /*
                 * OR that with the checks done for data frames.
                 * That gives the checks done for management and
                 * data frames.
                 */
                gen_or(b1, b0);

                /*
                 * If the low-order bit of the type value is 1,
                 * this is either a control frame or a frame
                 * with a reserved type, and thus not a
                 * frame with an SA.
                 *
                 * I.e., check "!(link[0] & 0x04)".
                 */
                s = gen_load_a(OR_LINK, 0, BPF_B);
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x04;
                b1->stmts = s;
                gen_not(b1);

                /*
                 * AND that with the checks for data and management
                 * frames.
                 */
                gen_and(b1, b0);
                return b0;

        /*
         * XXX - add RA, TA, and BSSID keywords?
         */
        case Q_ADDR1:
                return (gen_bcmp(OR_LINK, 4, 6, eaddr));

        case Q_ADDR2:
                /*
                 * Not present in CTS or ACK control frames.
                 */
                b0 = gen_mcmp(OR_LINK, 0, BPF_B, IEEE80211_FC0_TYPE_CTL,
                        IEEE80211_FC0_TYPE_MASK);
                gen_not(b0);
                b1 = gen_mcmp(OR_LINK, 0, BPF_B, IEEE80211_FC0_SUBTYPE_CTS,
                        IEEE80211_FC0_SUBTYPE_MASK);
                gen_not(b1);
                b2 = gen_mcmp(OR_LINK, 0, BPF_B, IEEE80211_FC0_SUBTYPE_ACK,
                        IEEE80211_FC0_SUBTYPE_MASK);
                gen_not(b2);
                gen_and(b1, b2);
                gen_or(b0, b2);
                b1 = gen_bcmp(OR_LINK, 10, 6, eaddr);
                gen_and(b2, b1);
                return b1;

        case Q_ADDR3:
                /*
                 * Not present in control frames.
                 */
                b0 = gen_mcmp(OR_LINK, 0, BPF_B, IEEE80211_FC0_TYPE_CTL,
                        IEEE80211_FC0_TYPE_MASK);
                gen_not(b0);
                b1 = gen_bcmp(OR_LINK, 16, 6, eaddr);
                gen_and(b0, b1);
                return b1;

        case Q_ADDR4:
                /*
                 * Present only if the direction mask has both "From DS"
                 * and "To DS" set.  Neither control frames nor management
                 * frames should have both of those set, so we don't
                 * check the frame type.
                 */
                b0 = gen_mcmp(OR_LINK, 1, BPF_B,
                        IEEE80211_FC1_DIR_DSTODS, IEEE80211_FC1_DIR_MASK);
                b1 = gen_bcmp(OR_LINK, 24, 6, eaddr);
                gen_and(b0, b1);
                return b1;

        case Q_AND:
                b0 = gen_wlanhostop(eaddr, Q_SRC);
                b1 = gen_wlanhostop(eaddr, Q_DST);
                gen_and(b0, b1);
                return b1;

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_wlanhostop(eaddr, Q_SRC);
                b1 = gen_wlanhostop(eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;
        }
        abort();
        /* NOTREACHED */
}

/*
 * Like gen_ehostop, but for RFC 2625 IP-over-Fibre-Channel.
 * (We assume that the addresses are IEEE 48-bit MAC addresses,
 * as the RFC states.)
 */
static struct block *
gen_ipfchostop(eaddr, dir)
        register const u_char *eaddr;
        register int dir;
{
        register struct block *b0, *b1;

        switch (dir) {
        case Q_SRC:
                return gen_bcmp(OR_LINK, 10, 6, eaddr);

        case Q_DST:
                return gen_bcmp(OR_LINK, 2, 6, eaddr);

        case Q_AND:
                b0 = gen_ipfchostop(eaddr, Q_SRC);
                b1 = gen_ipfchostop(eaddr, Q_DST);
                gen_and(b0, b1);
                return b1;

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_ipfchostop(eaddr, Q_SRC);
                b1 = gen_ipfchostop(eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;
        }
        abort();
        /* NOTREACHED */
}

/*
 * This is quite tricky because there may be pad bytes in front of the
 * DECNET header, and then there are two possible data packet formats that
 * carry both src and dst addresses, plus 5 packet types in a format that
 * carries only the src node, plus 2 types that use a different format and
 * also carry just the src node.
 *
 * Yuck.
 *
 * Instead of doing those all right, we just look for data packets with
 * 0 or 1 bytes of padding.  If you want to look at other packets, that
 * will require a lot more hacking.
 *
 * To add support for filtering on DECNET "areas" (network numbers)
 * one would want to add a "mask" argument to this routine.  That would
 * make the filter even more inefficient, although one could be clever
 * and not generate masking instructions if the mask is 0xFFFF.
 */
static struct block *
gen_dnhostop(addr, dir)
        bpf_u_int32 addr;
        int dir;
{
        struct block *b0, *b1, *b2, *tmp;
        u_int offset_lh;        /* offset if long header is received */
        u_int offset_sh;        /* offset if short header is received */

        switch (dir) {

        case Q_DST:
                offset_sh = 1;  /* follows flags */
                offset_lh = 7;  /* flgs,darea,dsubarea,HIORD */
                break;

        case Q_SRC:
                offset_sh = 3;  /* follows flags, dstnode */
                offset_lh = 15; /* flgs,darea,dsubarea,did,sarea,ssub,HIORD */
                break;

        case Q_AND:
                /* Inefficient because we do our Calvinball dance twice */
                b0 = gen_dnhostop(addr, Q_SRC);
                b1 = gen_dnhostop(addr, Q_DST);
                gen_and(b0, b1);
                return b1;

        case Q_OR:
        case Q_DEFAULT:
                /* Inefficient because we do our Calvinball dance twice */
                b0 = gen_dnhostop(addr, Q_SRC);
                b1 = gen_dnhostop(addr, Q_DST);
                gen_or(b0, b1);
                return b1;

        case Q_ISO:
                bpf_error("ISO host filtering not implemented");

        default:
                abort();
        }
        b0 = gen_linktype(ETHERTYPE_DN);
        /* Check for pad = 1, long header case */
        tmp = gen_mcmp(OR_NET, 2, BPF_H,
            (bpf_int32)ntohs(0x0681), (bpf_int32)ntohs(0x07FF));
        b1 = gen_cmp(OR_NET, 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));
        gen_and(tmp, b2);
        gen_or(b2, b1);
        /* Check for pad = 1, short header case */
        tmp = gen_mcmp(OR_NET, 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));
        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));
        gen_and(tmp, b2);
        gen_or(b2, b1);

        /* Combine with test for linktype */
        gen_and(b0, b1);
        return b1;
}

/*
 * Generate a check for IPv4 or IPv6 for MPLS-encapsulated packets;
 * test the bottom-of-stack bit, and then check the version number
 * field in the IP header.
 */
static struct block *
gen_mpls_linktype(proto)
        int proto;
{
        struct block *b0, *b1;

        switch (proto) {

        case Q_IP:
                /* match the bottom-of-stack bit */
                b0 = gen_mcmp(OR_NET, -2, BPF_B, 0x01, 0x01);
                /* match the IPv4 version number */
                b1 = gen_mcmp(OR_NET, 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);
                /* match the IPv4 version number */
                b1 = gen_mcmp(OR_NET, 0, BPF_B, 0x60, 0xf0);
                gen_and(b0, b1);
                return b1;
 
       default:
                abort();
        }
}

static struct block *
gen_host(addr, mask, proto, dir, type)
        bpf_u_int32 addr;
        bpf_u_int32 mask;
        int proto;
        int dir;
        int type;
{
        struct block *b0, *b1;
        const char *typestr;

        if (type == Q_NET)
                typestr = "net";
        else
                typestr = "host";

        switch (proto) {

        case Q_DEFAULT:
                b0 = gen_host(addr, mask, Q_IP, dir, type);
                /*
                 * Only check for non-IPv4 addresses if we're not
                 * checking MPLS-encapsulated packets.
                 */
                if (label_stack_depth == 0) {
                        b1 = gen_host(addr, mask, Q_ARP, dir, type);
                        gen_or(b0, b1);
                        b0 = gen_host(addr, mask, Q_RARP, dir, type);
                        gen_or(b1, b0);
                }
                return b0;

        case Q_IP:
                return gen_hostop(addr, mask, dir, ETHERTYPE_IP, 12, 16);

        case Q_RARP:
                return gen_hostop(addr, mask, dir, ETHERTYPE_REVARP, 14, 24);

        case Q_ARP:
                return gen_hostop(addr, mask, dir, ETHERTYPE_ARP, 14, 24);

        case Q_TCP:
                bpf_error("'tcp' modifier applied to %s", typestr);

        case Q_SCTP:
                bpf_error("'sctp' modifier applied to %s", typestr);

        case Q_UDP:
                bpf_error("'udp' modifier applied to %s", typestr);

        case Q_ICMP:
                bpf_error("'icmp' modifier applied to %s", typestr);

        case Q_IGMP:
                bpf_error("'igmp' modifier applied to %s", typestr);

        case Q_IGRP:
                bpf_error("'igrp' modifier applied to %s", typestr);

        case Q_PIM:
                bpf_error("'pim' modifier applied to %s", typestr);

        case Q_VRRP:
                bpf_error("'vrrp' modifier applied to %s", typestr);

        case Q_ATALK:
                bpf_error("ATALK host filtering not implemented");

        case Q_AARP:
                bpf_error("AARP host filtering not implemented");

        case Q_DECNET:
                return gen_dnhostop(addr, dir);

        case Q_SCA:
                bpf_error("SCA host filtering not implemented");

        case Q_LAT:
                bpf_error("LAT host filtering not implemented");

        case Q_MOPDL:
                bpf_error("MOPDL host filtering not implemented");

        case Q_MOPRC:
                bpf_error("MOPRC host filtering not implemented");

#ifdef INET6
        case Q_IPV6:
                bpf_error("'ip6' modifier applied to ip host");

        case Q_ICMPV6:
                bpf_error("'icmp6' modifier applied to %s", typestr);
#endif /* INET6 */

        case Q_AH:
                bpf_error("'ah' modifier applied to %s", typestr);

        case Q_ESP:
                bpf_error("'esp' modifier applied to %s", typestr);

        case Q_ISO:
                bpf_error("ISO host filtering not implemented");

        case Q_ESIS:
                bpf_error("'esis' modifier applied to %s", typestr);

        case Q_ISIS:
                bpf_error("'isis' modifier applied to %s", typestr);

        case Q_CLNP:
                bpf_error("'clnp' modifier applied to %s", typestr);

        case Q_STP:
                bpf_error("'stp' modifier applied to %s", typestr);

        case Q_IPX:
                bpf_error("IPX host filtering not implemented");

        case Q_NETBEUI:
                bpf_error("'netbeui' modifier applied to %s", typestr);

        case Q_RADIO:
                bpf_error("'radio' modifier applied to %s", typestr);

        default:
                abort();
        }
        /* NOTREACHED */
}

#ifdef INET6
static struct block *
gen_host6(addr, mask, proto, dir, type)
        struct in6_addr *addr;
        struct in6_addr *mask;
        int proto;
        int dir;
        int type;
{
        const char *typestr;

        if (type == Q_NET)
                typestr = "net";
        else
                typestr = "host";

        switch (proto) {

        case Q_DEFAULT:
                return gen_host6(addr, mask, Q_IPV6, dir, type);

        case Q_IP:
                bpf_error("'ip' modifier applied to ip6 %s", typestr);

        case Q_RARP:
                bpf_error("'rarp' modifier applied to ip6 %s", typestr);

        case Q_ARP:
                bpf_error("'arp' modifier applied to ip6 %s", typestr);

        case Q_SCTP:
                bpf_error("'sctp' modifier applied to %s", typestr);

        case Q_TCP:
                bpf_error("'tcp' modifier applied to %s", typestr);

        case Q_UDP:
                bpf_error("'udp' modifier applied to %s", typestr);

        case Q_ICMP:
                bpf_error("'icmp' modifier applied to %s", typestr);

        case Q_IGMP:
                bpf_error("'igmp' modifier applied to %s", typestr);

        case Q_IGRP:
                bpf_error("'igrp' modifier applied to %s", typestr);

        case Q_PIM:
                bpf_error("'pim' modifier applied to %s", typestr);

        case Q_VRRP:
                bpf_error("'vrrp' modifier applied to %s", typestr);

        case Q_ATALK:
                bpf_error("ATALK host filtering not implemented");

        case Q_AARP:
                bpf_error("AARP host filtering not implemented");

        case Q_DECNET:
                bpf_error("'decnet' modifier applied to ip6 %s", typestr);

        case Q_SCA:
                bpf_error("SCA host filtering not implemented");

        case Q_LAT:
                bpf_error("LAT host filtering not implemented");

        case Q_MOPDL:
                bpf_error("MOPDL host filtering not implemented");

        case Q_MOPRC:
                bpf_error("MOPRC host filtering not implemented");

        case Q_IPV6:
                return gen_hostop6(addr, mask, dir, ETHERTYPE_IPV6, 8, 24);

        case Q_ICMPV6:
                bpf_error("'icmp6' modifier applied to %s", typestr);

        case Q_AH:
                bpf_error("'ah' modifier applied to %s", typestr);

        case Q_ESP:
                bpf_error("'esp' modifier applied to %s", typestr);

        case Q_ISO:
                bpf_error("ISO host filtering not implemented");

        case Q_ESIS:
                bpf_error("'esis' modifier applied to %s", typestr);

        case Q_ISIS:
                bpf_error("'isis' modifier applied to %s", typestr);

        case Q_CLNP:
                bpf_error("'clnp' modifier applied to %s", typestr);

        case Q_STP:
                bpf_error("'stp' modifier applied to %s", typestr);

        case Q_IPX:
                bpf_error("IPX host filtering not implemented");

        case Q_NETBEUI:
                bpf_error("'netbeui' modifier applied to %s", typestr);

        case Q_RADIO:
                bpf_error("'radio' modifier applied to %s", typestr);

        default:
                abort();
        }
        /* NOTREACHED */
}
#endif /*INET6*/

#ifndef INET6
static struct block *
gen_gateway(eaddr, alist, proto, dir)
        const u_char *eaddr;
        bpf_u_int32 **alist;
        int proto;
        int dir;
{
        struct block *b0, *b1, *tmp;

        if (dir != 0)
                bpf_error("direction applied to 'gateway'");

        switch (proto) {
        case Q_DEFAULT:
        case Q_IP:
        case Q_ARP:
        case Q_RARP:
                switch (linktype) {
                case DLT_EN10MB:
                        b0 = gen_ehostop(eaddr, Q_OR);
                        break;
                case DLT_FDDI:
                        b0 = gen_fhostop(eaddr, Q_OR);
                        break;
                case DLT_IEEE802:
                        b0 = gen_thostop(eaddr, Q_OR);
                        break;
                case DLT_IEEE802_11:
                case DLT_IEEE802_11_RADIO_AVS:
                case DLT_PPI:
                case DLT_IEEE802_11_RADIO:
                case DLT_PRISM_HEADER:
                        b0 = gen_wlanhostop(eaddr, Q_OR);
                        break;
                case DLT_SUNATM:
                        if (is_lane) {
                                /*
                                 * Check that the packet doesn't begin with an
                                 * LE Control marker.  (We've already generated
                                 * a test for LANE.)
                                 */
                                b1 = gen_cmp(OR_LINK, SUNATM_PKT_BEGIN_POS,
                                    BPF_H, 0xFF00);
                                gen_not(b1);

                                /*
                                 * Now check the MAC address.
                                 */
                                b0 = gen_ehostop(eaddr, Q_OR);
                                gen_and(b1, b0);
                        }
                        break;
                case DLT_IP_OVER_FC:
                        b0 = gen_ipfchostop(eaddr, Q_OR);
                        break;
                default:
                        bpf_error(
                            "'gateway' supported only on ethernet/FDDI/token ring/802.11/Fibre Channel");
                }
                b1 = gen_host(**alist++, 0xffffffff, proto, Q_OR, Q_HOST);
                while (*alist) {
                        tmp = gen_host(**alist++, 0xffffffff, proto, Q_OR,
                            Q_HOST);
                        gen_or(b1, tmp);
                        b1 = tmp;
                }
                gen_not(b1);
                gen_and(b0, b1);
                return b1;
        }
        bpf_error("illegal modifier of 'gateway'");
        /* NOTREACHED */
}
#endif

struct block *
gen_proto_abbrev(proto)
        int proto;
{
        struct block *b0;
        struct block *b1;

        switch (proto) {

        case Q_SCTP:
                b1 = gen_proto(IPPROTO_SCTP, Q_IP, Q_DEFAULT);
#ifdef INET6
                b0 = gen_proto(IPPROTO_SCTP, Q_IPV6, Q_DEFAULT);
                gen_or(b0, b1);
#endif
                break;

        case Q_TCP:
                b1 = gen_proto(IPPROTO_TCP, Q_IP, Q_DEFAULT);
#ifdef INET6
                b0 = gen_proto(IPPROTO_TCP, Q_IPV6, Q_DEFAULT);
                gen_or(b0, b1);
#endif
                break;

        case Q_UDP:
                b1 = gen_proto(IPPROTO_UDP, Q_IP, Q_DEFAULT);
#ifdef INET6
                b0 = gen_proto(IPPROTO_UDP, Q_IPV6, Q_DEFAULT);
                gen_or(b0, b1);
#endif
                break;

        case Q_ICMP:
                b1 = gen_proto(IPPROTO_ICMP, Q_IP, Q_DEFAULT);
                break;

#ifndef IPPROTO_IGMP
#define IPPROTO_IGMP    2
#endif

        case Q_IGMP:
                b1 = gen_proto(IPPROTO_IGMP, Q_IP, Q_DEFAULT);
                break;

#ifndef IPPROTO_IGRP
#define IPPROTO_IGRP    9
#endif
        case Q_IGRP:
                b1 = gen_proto(IPPROTO_IGRP, Q_IP, Q_DEFAULT);
                break;

#ifndef IPPROTO_PIM
#define IPPROTO_PIM     103
#endif

        case Q_PIM:
                b1 = gen_proto(IPPROTO_PIM, Q_IP, Q_DEFAULT);
#ifdef INET6
                b0 = gen_proto(IPPROTO_PIM, Q_IPV6, Q_DEFAULT);
                gen_or(b0, b1);
#endif
                break;

#ifndef IPPROTO_VRRP
#define IPPROTO_VRRP    112
#endif

        case Q_VRRP:
                b1 = gen_proto(IPPROTO_VRRP, Q_IP, Q_DEFAULT);
                break;

        case Q_IP:
                b1 =  gen_linktype(ETHERTYPE_IP);
                break;

        case Q_ARP:
                b1 =  gen_linktype(ETHERTYPE_ARP);
                break;

        case Q_RARP:
                b1 =  gen_linktype(ETHERTYPE_REVARP);
                break;

        case Q_LINK:
                bpf_error("link layer applied in wrong context");

        case Q_ATALK:
                b1 =  gen_linktype(ETHERTYPE_ATALK);
                break;

        case Q_AARP:
                b1 =  gen_linktype(ETHERTYPE_AARP);
                break;

        case Q_DECNET:
                b1 =  gen_linktype(ETHERTYPE_DN);
                break;

        case Q_SCA:
                b1 =  gen_linktype(ETHERTYPE_SCA);
                break;

        case Q_LAT:
                b1 =  gen_linktype(ETHERTYPE_LAT);
                break;

        case Q_MOPDL:
                b1 =  gen_linktype(ETHERTYPE_MOPDL);
                break;

        case Q_MOPRC:
                b1 =  gen_linktype(ETHERTYPE_MOPRC);
                break;

#ifdef INET6
        case Q_IPV6:
                b1 = gen_linktype(ETHERTYPE_IPV6);
                break;

#ifndef IPPROTO_ICMPV6
#define IPPROTO_ICMPV6  58
#endif
        case Q_ICMPV6:
                b1 = gen_proto(IPPROTO_ICMPV6, Q_IPV6, Q_DEFAULT);
                break;
#endif /* INET6 */

#ifndef IPPROTO_AH
#define IPPROTO_AH      51
#endif
        case Q_AH:
                b1 = gen_proto(IPPROTO_AH, Q_IP, Q_DEFAULT);
#ifdef INET6
                b0 = gen_proto(IPPROTO_AH, Q_IPV6, Q_DEFAULT);
                gen_or(b0, b1);
#endif
                break;

#ifndef IPPROTO_ESP
#define IPPROTO_ESP     50
#endif
        case Q_ESP:
                b1 = gen_proto(IPPROTO_ESP, Q_IP, Q_DEFAULT);
#ifdef INET6
                b0 = gen_proto(IPPROTO_ESP, Q_IPV6, Q_DEFAULT);
                gen_or(b0, b1);
#endif
                break;

        case Q_ISO:
                b1 = gen_linktype(LLCSAP_ISONS);
                break;

        case Q_ESIS:
                b1 = gen_proto(ISO9542_ESIS, Q_ISO, Q_DEFAULT);
                break;

        case Q_ISIS:
                b1 = gen_proto(ISO10589_ISIS, Q_ISO, Q_DEFAULT);
                break;

        case Q_ISIS_L1: /* all IS-IS Level1 PDU-Types */
                b0 = gen_proto(ISIS_L1_LAN_IIH, Q_ISIS, Q_DEFAULT);
                b1 = gen_proto(ISIS_PTP_IIH, Q_ISIS, Q_DEFAULT); /* FIXME extract the circuit-type bits */
                gen_or(b0, b1);
                b0 = gen_proto(ISIS_L1_LSP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                b0 = gen_proto(ISIS_L1_CSNP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                b0 = gen_proto(ISIS_L1_PSNP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                break;

        case Q_ISIS_L2: /* all IS-IS Level2 PDU-Types */
                b0 = gen_proto(ISIS_L2_LAN_IIH, Q_ISIS, Q_DEFAULT);
                b1 = gen_proto(ISIS_PTP_IIH, Q_ISIS, Q_DEFAULT); /* FIXME extract the circuit-type bits */
                gen_or(b0, b1);
                b0 = gen_proto(ISIS_L2_LSP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                b0 = gen_proto(ISIS_L2_CSNP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                b0 = gen_proto(ISIS_L2_PSNP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                break;

        case Q_ISIS_IIH: /* all IS-IS Hello PDU-Types */
                b0 = gen_proto(ISIS_L1_LAN_IIH, Q_ISIS, Q_DEFAULT);
                b1 = gen_proto(ISIS_L2_LAN_IIH, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                b0 = gen_proto(ISIS_PTP_IIH, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                break;

        case Q_ISIS_LSP:
                b0 = gen_proto(ISIS_L1_LSP, Q_ISIS, Q_DEFAULT);
                b1 = gen_proto(ISIS_L2_LSP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                break;

        case Q_ISIS_SNP:
                b0 = gen_proto(ISIS_L1_CSNP, Q_ISIS, Q_DEFAULT);
                b1 = gen_proto(ISIS_L2_CSNP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                b0 = gen_proto(ISIS_L1_PSNP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                b0 = gen_proto(ISIS_L2_PSNP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                break;

        case Q_ISIS_CSNP:
                b0 = gen_proto(ISIS_L1_CSNP, Q_ISIS, Q_DEFAULT);
                b1 = gen_proto(ISIS_L2_CSNP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                break;

        case Q_ISIS_PSNP:
                b0 = gen_proto(ISIS_L1_PSNP, Q_ISIS, Q_DEFAULT);
                b1 = gen_proto(ISIS_L2_PSNP, Q_ISIS, Q_DEFAULT);
                gen_or(b0, b1);
                break;

        case Q_CLNP:
                b1 = gen_proto(ISO8473_CLNP, Q_ISO, Q_DEFAULT);
                break;

        case Q_STP:
                b1 = gen_linktype(LLCSAP_8021D);
                break;

        case Q_IPX:
                b1 = gen_linktype(LLCSAP_IPX);
                break;

        case Q_NETBEUI:
                b1 = gen_linktype(LLCSAP_NETBEUI);
                break;

        case Q_RADIO:
                bpf_error("'radio' is not a valid protocol type");

        default:
                abort();
        }
        return b1;
}

static struct block *
gen_ipfrag()
{
        struct slist *s;
        struct block *b;

        /* not ip frag */
        s = gen_load_a(OR_NET, 6, BPF_H);
        b = new_block(JMP(BPF_JSET));
        b->s.k = 0x1fff;
        b->stmts = s;
        gen_not(b);

        return b;
}

/*
 * Generate a comparison to a port value in the transport-layer header
 * at the specified offset from the beginning of that header.
 *
 * XXX - this handles a variable-length prefix preceding the link-layer
 * header, such as the radiotap or AVS radio prefix, but doesn't handle
 * variable-length link-layer headers (such as Token Ring or 802.11
 * headers).
 */
static struct block *
gen_portatom(off, v)
        int off;
        bpf_int32 v;
{
        return gen_cmp(OR_TRAN_IPV4, off, BPF_H, v);
}

#ifdef INET6
static struct block *
gen_portatom6(off, v)
        int off;
        bpf_int32 v;
{
        return gen_cmp(OR_TRAN_IPV6, off, BPF_H, v);
}
#endif/*INET6*/

struct block *
gen_portop(port, proto, dir)
        int port, proto, dir;
{
        struct block *b0, *b1, *tmp;

        /* ip proto 'proto' */
        tmp = gen_cmp(OR_NET, 9, BPF_B, (bpf_int32)proto);
        b0 = gen_ipfrag();
        gen_and(tmp, b0);

        switch (dir) {
        case Q_SRC:
                b1 = gen_portatom(0, (bpf_int32)port);
                break;

        case Q_DST:
                b1 = gen_portatom(2, (bpf_int32)port);
                break;

        case Q_OR:
        case Q_DEFAULT:
                tmp = gen_portatom(0, (bpf_int32)port);
                b1 = gen_portatom(2, (bpf_int32)port);
                gen_or(tmp, b1);
                break;

        case Q_AND:
                tmp = gen_portatom(0, (bpf_int32)port);
                b1 = gen_portatom(2, (bpf_int32)port);
                gen_and(tmp, b1);
                break;

        default:
                abort();
        }
        gen_and(b0, b1);

        return b1;
}

static struct block *
gen_port(port, ip_proto, dir)
        int port;
        int ip_proto;
        int dir;
{
        struct block *b0, *b1, *tmp;

        /*
         * ether proto ip
         *
         * For FDDI, RFC 1188 says that SNAP encapsulation is used,
         * not LLC encapsulation with LLCSAP_IP.
         *
         * For IEEE 802 networks - which includes 802.5 token ring
         * (which is what DLT_IEEE802 means) and 802.11 - RFC 1042
         * says that SNAP encapsulation is used, not LLC encapsulation
         * with LLCSAP_IP.
         *
         * For LLC-encapsulated ATM/"Classical IP", RFC 1483 and
         * RFC 2225 say that SNAP encapsulation is used, not LLC
         * encapsulation with LLCSAP_IP.
         *
         * So we always check for ETHERTYPE_IP.
         */
        b0 =  gen_linktype(ETHERTYPE_IP);

        switch (ip_proto) {
        case IPPROTO_UDP:
        case IPPROTO_TCP:
        case IPPROTO_SCTP:
                b1 = gen_portop(port, ip_proto, dir);
                break;

        case PROTO_UNDEF:
                tmp = gen_portop(port, IPPROTO_TCP, dir);
                b1 = gen_portop(port, IPPROTO_UDP, dir);
                gen_or(tmp, b1);
                tmp = gen_portop(port, IPPROTO_SCTP, dir);
                gen_or(tmp, b1);
                break;

        default:
                abort();
        }
        gen_and(b0, b1);
        return b1;
}

#ifdef INET6
struct block *
gen_portop6(port, proto, dir)
        int port, proto, dir;
{
        struct block *b0, *b1, *tmp;

        /* ip6 proto 'proto' */
        b0 = gen_cmp(OR_NET, 6, BPF_B, (bpf_int32)proto);

        switch (dir) {
        case Q_SRC:
                b1 = gen_portatom6(0, (bpf_int32)port);
                break;

        case Q_DST:
                b1 = gen_portatom6(2, (bpf_int32)port);
                break;

        case Q_OR:
        case Q_DEFAULT:
                tmp = gen_portatom6(0, (bpf_int32)port);
                b1 = gen_portatom6(2, (bpf_int32)port);
                gen_or(tmp, b1);
                break;

        case Q_AND:
                tmp = gen_portatom6(0, (bpf_int32)port);
                b1 = gen_portatom6(2, (bpf_int32)port);
                gen_and(tmp, b1);
                break;

        default:
                abort();
        }
        gen_and(b0, b1);

        return b1;
}

static struct block *
gen_port6(port, ip_proto, dir)
        int port;
        int ip_proto;
        int dir;
{
        struct block *b0, *b1, *tmp;

        /* link proto ip6 */
        b0 =  gen_linktype(ETHERTYPE_IPV6);

        switch (ip_proto) {
        case IPPROTO_UDP:
        case IPPROTO_TCP:
        case IPPROTO_SCTP:
                b1 = gen_portop6(port, ip_proto, dir);
                break;

        case PROTO_UNDEF:
                tmp = gen_portop6(port, IPPROTO_TCP, dir);
                b1 = gen_portop6(port, IPPROTO_UDP, dir);
                gen_or(tmp, b1);
                tmp = gen_portop6(port, IPPROTO_SCTP, dir);
                gen_or(tmp, b1);
                break;

        default:
                abort();
        }
        gen_and(b0, b1);
        return b1;
}
#endif /* INET6 */

/* gen_portrange code */
static struct block *
gen_portrangeatom(off, v1, v2)
        int off;
        bpf_int32 v1, v2;
{
        struct block *b1, *b2;

        if (v1 > v2) {
                /*
                 * Reverse the order of the ports, so v1 is the lower one.
                 */
                bpf_int32 vtemp;

                vtemp = v1;
                v1 = v2;
                v2 = vtemp;
        }

        b1 = gen_cmp_ge(OR_TRAN_IPV4, off, BPF_H, v1);
        b2 = gen_cmp_le(OR_TRAN_IPV4, off, BPF_H, v2);

        gen_and(b1, b2); 

        return b2;
}

struct block *
gen_portrangeop(port1, port2, proto, dir)
        int port1, port2;
        int proto;
        int dir;
{
        struct block *b0, *b1, *tmp;

        /* ip proto 'proto' */
        tmp = gen_cmp(OR_NET, 9, BPF_B, (bpf_int32)proto);
        b0 = gen_ipfrag();
        gen_and(tmp, b0);

        switch (dir) {
        case Q_SRC:
                b1 = gen_portrangeatom(0, (bpf_int32)port1, (bpf_int32)port2);
                break;

        case Q_DST:
                b1 = gen_portrangeatom(2, (bpf_int32)port1, (bpf_int32)port2);
                break;

        case Q_OR:
        case Q_DEFAULT:
                tmp = gen_portrangeatom(0, (bpf_int32)port1, (bpf_int32)port2);
                b1 = gen_portrangeatom(2, (bpf_int32)port1, (bpf_int32)port2);
                gen_or(tmp, b1);
                break;

        case Q_AND:
                tmp = gen_portrangeatom(0, (bpf_int32)port1, (bpf_int32)port2);
                b1 = gen_portrangeatom(2, (bpf_int32)port1, (bpf_int32)port2);
                gen_and(tmp, b1);
                break;

        default:
                abort();
        }
        gen_and(b0, b1);

        return b1;
}

static struct block *
gen_portrange(port1, port2, ip_proto, dir)
        int port1, port2;
        int ip_proto;
        int dir;
{
        struct block *b0, *b1, *tmp;

        /* link proto ip */
        b0 =  gen_linktype(ETHERTYPE_IP);

        switch (ip_proto) {
        case IPPROTO_UDP:
        case IPPROTO_TCP:
        case IPPROTO_SCTP:
                b1 = gen_portrangeop(port1, port2, ip_proto, dir);
                break;

        case PROTO_UNDEF:
                tmp = gen_portrangeop(port1, port2, IPPROTO_TCP, dir);
                b1 = gen_portrangeop(port1, port2, IPPROTO_UDP, dir);
                gen_or(tmp, b1);
                tmp = gen_portrangeop(port1, port2, IPPROTO_SCTP, dir);
                gen_or(tmp, b1);
                break;

        default:
                abort();
        }
        gen_and(b0, b1);
        return b1;
}

#ifdef INET6
static struct block *
gen_portrangeatom6(off, v1, v2)
        int off;
        bpf_int32 v1, v2;
{
        struct block *b1, *b2;

        if (v1 > v2) {
                /*
                 * Reverse the order of the ports, so v1 is the lower one.
                 */
                bpf_int32 vtemp;

                vtemp = v1;
                v1 = v2;
                v2 = vtemp;
        }

        b1 = gen_cmp_ge(OR_TRAN_IPV6, off, BPF_H, v1);
        b2 = gen_cmp_le(OR_TRAN_IPV6, off, BPF_H, v2);

        gen_and(b1, b2); 

        return b2;
}

struct block *
gen_portrangeop6(port1, port2, proto, dir)
        int port1, port2;
        int proto;
        int dir;
{
        struct block *b0, *b1, *tmp;

        /* ip6 proto 'proto' */
        b0 = gen_cmp(OR_NET, 6, BPF_B, (bpf_int32)proto);

        switch (dir) {
        case Q_SRC:
                b1 = gen_portrangeatom6(0, (bpf_int32)port1, (bpf_int32)port2);
                break;

        case Q_DST:
                b1 = gen_portrangeatom6(2, (bpf_int32)port1, (bpf_int32)port2);
                break;

        case Q_OR:
        case Q_DEFAULT:
                tmp = gen_portrangeatom6(0, (bpf_int32)port1, (bpf_int32)port2);
                b1 = gen_portrangeatom6(2, (bpf_int32)port1, (bpf_int32)port2);
                gen_or(tmp, b1);
                break;

        case Q_AND:
                tmp = gen_portrangeatom6(0, (bpf_int32)port1, (bpf_int32)port2);
                b1 = gen_portrangeatom6(2, (bpf_int32)port1, (bpf_int32)port2);
                gen_and(tmp, b1);
                break;

        default:
                abort();
        }
        gen_and(b0, b1);

        return b1;
}

static struct block *
gen_portrange6(port1, port2, ip_proto, dir)
        int port1, port2;
        int ip_proto;
        int dir;
{
        struct block *b0, *b1, *tmp;

        /* link proto ip6 */
        b0 =  gen_linktype(ETHERTYPE_IPV6);

        switch (ip_proto) {
        case IPPROTO_UDP:
        case IPPROTO_TCP:
        case IPPROTO_SCTP:
                b1 = gen_portrangeop6(port1, port2, ip_proto, dir);
                break;

        case PROTO_UNDEF:
                tmp = gen_portrangeop6(port1, port2, IPPROTO_TCP, dir);
                b1 = gen_portrangeop6(port1, port2, IPPROTO_UDP, dir);
                gen_or(tmp, b1);
                tmp = gen_portrangeop6(port1, port2, IPPROTO_SCTP, dir);
                gen_or(tmp, b1);
                break;

        default:
                abort();
        }
        gen_and(b0, b1);
        return b1;
}
#endif /* INET6 */

static int
lookup_proto(name, proto)
        register const char *name;
        register int proto;
{
        register int v;

        switch (proto) {

        case Q_DEFAULT:
        case Q_IP:
        case Q_IPV6:
                v = pcap_nametoproto(name);
                if (v == PROTO_UNDEF)
                        bpf_error("unknown ip proto '%s'", name);
                break;

        case Q_LINK:
                /* XXX should look up h/w protocol type based on linktype */
                v = pcap_nametoeproto(name);
                if (v == PROTO_UNDEF) {
                        v = pcap_nametollc(name);
                        if (v == PROTO_UNDEF)
                                bpf_error("unknown ether proto '%s'", name);
                }
                break;

        case Q_ISO:
                if (strcmp(name, "esis") == 0)
                        v = ISO9542_ESIS;
                else if (strcmp(name, "isis") == 0)
                        v = ISO10589_ISIS;
                else if (strcmp(name, "clnp") == 0)
                        v = ISO8473_CLNP;
                else
                        bpf_error("unknown osi proto '%s'", name);
                break;

        default:
                v = PROTO_UNDEF;
                break;
        }
        return v;
}

#if 0
struct stmt *
gen_joinsp(s, n)
        struct stmt **s;
        int n;
{
        return NULL;
}
#endif

static struct block *
gen_protochain(v, proto, dir)
        int v;
        int proto;
        int dir;
{
#ifdef NO_PROTOCHAIN
        return gen_proto(v, proto, dir);
#else
        struct block *b0, *b;
        struct slist *s[100];
        int fix2, fix3, fix4, fix5;
        int ahcheck, again, end;
        int i, max;
        int reg2 = alloc_reg();

        memset(s, 0, sizeof(s));
        fix2 = fix3 = fix4 = fix5 = 0;

        switch (proto) {
        case Q_IP:
        case Q_IPV6:
                break;
        case Q_DEFAULT:
                b0 = gen_protochain(v, Q_IP, dir);
                b = gen_protochain(v, Q_IPV6, dir);
                gen_or(b0, b);
                return b;
        default:
                bpf_error("bad protocol applied for 'protochain'");
                /*NOTREACHED*/
        }

        /*
         * We don't handle variable-length prefixes before the link-layer
         * header, or variable-length link-layer headers, here yet.
         * We might want to add BPF instructions to do the protochain
         * work, to simplify that and, on platforms that have a BPF
         * interpreter with the new instructions, let the filtering
         * be done in the kernel.  (We already require a modified BPF
         * engine to do the protochain stuff, to support backward
         * branches, and backward branch support is unlikely to appear
         * in kernel BPF engines.)
         */
        switch (linktype) {

        case DLT_IEEE802_11:
        case DLT_IEEE802_11_RADIO:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_PRISM_HEADER:
        case DLT_PPI:
                bpf_error("'protochain' not supported with 802.11");
        }

        no_optimize = 1; /*this code is not compatible with optimzer yet */

        /*
         * s[0] is a dummy entry to protect other BPF insn from damage
         * by s[fix] = foo with uninitialized variable "fix".  It is somewhat
         * hard to find interdependency made by jump table fixup.
         */
        i = 0;
        s[i] = new_stmt(0);     /*dummy*/
        i++;

        switch (proto) {
        case Q_IP:
                b0 = gen_linktype(ETHERTYPE_IP);

                /* A = ip->ip_p */
                s[i] = new_stmt(BPF_LD|BPF_ABS|BPF_B);
                s[i]->s.k = off_macpl + off_nl + 9;
                i++;
                /* X = ip->ip_hl << 2 */
                s[i] = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
                s[i]->s.k = off_macpl + off_nl;
                i++;
                break;
#ifdef INET6
        case Q_IPV6:
                b0 = gen_linktype(ETHERTYPE_IPV6);

                /* A = ip6->ip_nxt */
                s[i] = new_stmt(BPF_LD|BPF_ABS|BPF_B);
                s[i]->s.k = off_macpl + off_nl + 6;
                i++;
                /* X = sizeof(struct ip6_hdr) */
                s[i] = new_stmt(BPF_LDX|BPF_IMM);
                s[i]->s.k = 40;
                i++;
                break;
#endif
        default:
                bpf_error("unsupported proto to gen_protochain");
                /*NOTREACHED*/
        }

        /* again: if (A == v) goto end; else fall through; */
        again = i;
        s[i] = new_stmt(BPF_JMP|BPF_JEQ|BPF_K);
        s[i]->s.k = v;
        s[i]->s.jt = NULL;              /*later*/
        s[i]->s.jf = NULL;              /*update in next stmt*/
        fix5 = i;
        i++;

#ifndef IPPROTO_NONE
#define IPPROTO_NONE    59
#endif
        /* if (A == IPPROTO_NONE) goto end */
        s[i] = new_stmt(BPF_JMP|BPF_JEQ|BPF_K);
        s[i]->s.jt = NULL;      /*later*/
        s[i]->s.jf = NULL;      /*update in next stmt*/
        s[i]->s.k = IPPROTO_NONE;
        s[fix5]->s.jf = s[i];
        fix2 = i;
        i++;

#ifdef INET6
        if (proto == Q_IPV6) {
                int v6start, v6end, v6advance, j;

                v6start = i;
                /* if (A == IPPROTO_HOPOPTS) goto v6advance */
                s[i] = new_stmt(BPF_JMP|BPF_JEQ|BPF_K);
                s[i]->s.jt = NULL;      /*later*/
                s[i]->s.jf = NULL;      /*update in next stmt*/
                s[i]->s.k = IPPROTO_HOPOPTS;
                s[fix2]->s.jf = s[i];
                i++;
                /* if (A == IPPROTO_DSTOPTS) goto v6advance */
                s[i - 1]->s.jf = s[i] = new_stmt(BPF_JMP|BPF_JEQ|BPF_K);
                s[i]->s.jt = NULL;      /*later*/
                s[i]->s.jf = NULL;      /*update in next stmt*/
                s[i]->s.k = IPPROTO_DSTOPTS;
                i++;
                /* if (A == IPPROTO_ROUTING) goto v6advance */
                s[i - 1]->s.jf = s[i] = new_stmt(BPF_JMP|BPF_JEQ|BPF_K);
                s[i]->s.jt = NULL;      /*later*/
                s[i]->s.jf = NULL;      /*update in next stmt*/
                s[i]->s.k = IPPROTO_ROUTING;
                i++;
                /* if (A == IPPROTO_FRAGMENT) goto v6advance; else goto ahcheck; */
                s[i - 1]->s.jf = s[i] = new_stmt(BPF_JMP|BPF_JEQ|BPF_K);
                s[i]->s.jt = NULL;      /*later*/
                s[i]->s.jf = NULL;      /*later*/
                s[i]->s.k = IPPROTO_FRAGMENT;
                fix3 = i;
                v6end = i;
                i++;

                /* v6advance: */
                v6advance = i;

                /*
                 * in short,
                 * A = P[X];
                 * X = X + (P[X + 1] + 1) * 8;
                 */
                /* A = X */
                s[i] = new_stmt(BPF_MISC|BPF_TXA);
                i++;
                /* A = P[X + packet head] */
                s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
                s[i]->s.k = off_macpl + off_nl;
                i++;
                /* MEM[reg2] = A */
                s[i] = new_stmt(BPF_ST);
                s[i]->s.k = reg2;
                i++;
                /* A = X */
                s[i] = new_stmt(BPF_MISC|BPF_TXA);
                i++;
                /* A += 1 */
                s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
                s[i]->s.k = 1;
                i++;
                /* X = A */
                s[i] = new_stmt(BPF_MISC|BPF_TAX);
                i++;
                /* A = P[X + packet head]; */
                s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
                s[i]->s.k = off_macpl + off_nl;
                i++;
                /* A += 1 */
                s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
                s[i]->s.k = 1;
                i++;
                /* A *= 8 */
                s[i] = new_stmt(BPF_ALU|BPF_MUL|BPF_K);
                s[i]->s.k = 8;
                i++;
                /* X = A; */
                s[i] = new_stmt(BPF_MISC|BPF_TAX);
                i++;
                /* A = MEM[reg2] */
                s[i] = new_stmt(BPF_LD|BPF_MEM);
                s[i]->s.k = reg2;
                i++;

                /* goto again; (must use BPF_JA for backward jump) */
                s[i] = new_stmt(BPF_JMP|BPF_JA);
                s[i]->s.k = again - i - 1;
                s[i - 1]->s.jf = s[i];
                i++;

                /* fixup */
                for (j = v6start; j <= v6end; j++)
                        s[j]->s.jt = s[v6advance];
        } else
#endif
        {
                /* nop */
                s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
                s[i]->s.k = 0;
                s[fix2]->s.jf = s[i];
                i++;
        }

        /* ahcheck: */
        ahcheck = i;
        /* if (A == IPPROTO_AH) then fall through; else goto end; */
        s[i] = new_stmt(BPF_JMP|BPF_JEQ|BPF_K);
        s[i]->s.jt = NULL;      /*later*/
        s[i]->s.jf = NULL;      /*later*/
        s[i]->s.k = IPPROTO_AH;
        if (fix3)
                s[fix3]->s.jf = s[ahcheck];
        fix4 = i;
        i++;

        /*
         * in short,
         * A = P[X];
         * X = X + (P[X + 1] + 2) * 4;
         */
        /* A = X */
        s[i - 1]->s.jt = s[i] = new_stmt(BPF_MISC|BPF_TXA);
        i++;
        /* A = P[X + packet head]; */
        s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
        s[i]->s.k = off_macpl + off_nl;
        i++;
        /* MEM[reg2] = A */
        s[i] = new_stmt(BPF_ST);
        s[i]->s.k = reg2;
        i++;
        /* A = X */
        s[i - 1]->s.jt = s[i] = new_stmt(BPF_MISC|BPF_TXA);
        i++;
        /* A += 1 */
        s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
        s[i]->s.k = 1;
        i++;
        /* X = A */
        s[i] = new_stmt(BPF_MISC|BPF_TAX);
        i++;
        /* A = P[X + packet head] */
        s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
        s[i]->s.k = off_macpl + off_nl;
        i++;
        /* A += 2 */
        s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
        s[i]->s.k = 2;
        i++;
        /* A *= 4 */
        s[i] = new_stmt(BPF_ALU|BPF_MUL|BPF_K);
        s[i]->s.k = 4;
        i++;
        /* X = A; */
        s[i] = new_stmt(BPF_MISC|BPF_TAX);
        i++;
        /* A = MEM[reg2] */
        s[i] = new_stmt(BPF_LD|BPF_MEM);
        s[i]->s.k = reg2;
        i++;

        /* goto again; (must use BPF_JA for backward jump) */
        s[i] = new_stmt(BPF_JMP|BPF_JA);
        s[i]->s.k = again - i - 1;
        i++;

        /* end: nop */
        end = i;
        s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
        s[i]->s.k = 0;
        s[fix2]->s.jt = s[end];
        s[fix4]->s.jf = s[end];
        s[fix5]->s.jt = s[end];
        i++;

        /*
         * make slist chain
         */
        max = i;
        for (i = 0; i < max - 1; i++)
                s[i]->next = s[i + 1];
        s[max - 1]->next = NULL;

        /*
         * emit final check
         */
        b = new_block(JMP(BPF_JEQ));
        b->stmts = s[1];        /*remember, s[0] is dummy*/
        b->s.k = v;

        free_reg(reg2);

        gen_and(b0, b);
        return b;
#endif
}

static struct block *
gen_check_802_11_data_frame()
{
        struct slist *s;
        struct block *b0, *b1;

        /*
         * A data frame has the 0x08 bit (b3) in the frame control field set
         * and the 0x04 bit (b2) clear.
         */
        s = gen_load_a(OR_LINK, 0, BPF_B);
        b0 = new_block(JMP(BPF_JSET));
        b0->s.k = 0x08;
        b0->stmts = s;
        
        s = gen_load_a(OR_LINK, 0, BPF_B);
        b1 = new_block(JMP(BPF_JSET));
        b1->s.k = 0x04;
        b1->stmts = s;
        gen_not(b1);

        gen_and(b1, b0);

        return b0;
}

/*
 * Generate code that checks whether the packet is a packet for protocol
 * <proto> and whether the type field in that protocol's header has
 * the value <v>, e.g. if <proto> is Q_IP, it checks whether it's an
 * IP packet and checks the protocol number in the IP header against <v>.
 *
 * If <proto> is Q_DEFAULT, i.e. just "proto" was specified, it checks
 * against Q_IP and Q_IPV6.
 */
static struct block *
gen_proto(v, proto, dir)
        int v;
        int proto;
        int dir;
{
        struct block *b0, *b1;

        if (dir != Q_DEFAULT)
                bpf_error("direction applied to 'proto'");

        switch (proto) {
        case Q_DEFAULT:
#ifdef INET6
                b0 = gen_proto(v, Q_IP, dir);
                b1 = gen_proto(v, Q_IPV6, dir);
                gen_or(b0, b1);
                return b1;
#else
                /*FALLTHROUGH*/
#endif
        case Q_IP:
                /*
                 * For FDDI, RFC 1188 says that SNAP encapsulation is used,
                 * not LLC encapsulation with LLCSAP_IP.
                 *
                 * For IEEE 802 networks - which includes 802.5 token ring
                 * (which is what DLT_IEEE802 means) and 802.11 - RFC 1042
                 * says that SNAP encapsulation is used, not LLC encapsulation
                 * with LLCSAP_IP.
                 *
                 * For LLC-encapsulated ATM/"Classical IP", RFC 1483 and
                 * RFC 2225 say that SNAP encapsulation is used, not LLC
                 * encapsulation with LLCSAP_IP.
                 *
                 * So we always check for ETHERTYPE_IP.
                 */
                b0 = gen_linktype(ETHERTYPE_IP);
#ifndef CHASE_CHAIN
                b1 = gen_cmp(OR_NET, 9, BPF_B, (bpf_int32)v);
#else
                b1 = gen_protochain(v, Q_IP);
#endif
                gen_and(b0, b1);
                return b1;

        case Q_ISO:
                switch (linktype) {

                case DLT_FRELAY:
                        /*
                         * Frame Relay packets typically have an OSI
                         * NLPID at the beginning; "gen_linktype(LLCSAP_ISONS)"
                         * generates code to check for all the OSI
                         * NLPIDs, so calling it and then adding a check
                         * for the particular NLPID for which we're
                         * looking is bogus, as we can just check for
                         * the NLPID.
                         *
                         * What we check for is the NLPID and a frame
                         * control field value of UI, i.e. 0x03 followed
                         * by the NLPID.
                         *
                         * XXX - assumes a 2-byte Frame Relay header with
                         * DLCI and flags.  What if the address is longer?
                         *
                         * XXX - what about SNAP-encapsulated frames?
                         */
                        return gen_cmp(OR_LINK, 2, BPF_H, (0x03<<8) | v);
                        /*NOTREACHED*/
                        break;

                case DLT_C_HDLC:
                        /*
                         * Cisco uses an Ethertype lookalike - for OSI,
                         * it's 0xfefe.
                         */
                        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);
                        gen_and(b0, b1);
                        return b1;

                default:
                        b0 = gen_linktype(LLCSAP_ISONS);
                        b1 = gen_cmp(OR_NET_NOSNAP, 0, BPF_B, (long)v);
                        gen_and(b0, b1);
                        return b1;
                }

        case Q_ISIS:
                b0 = gen_proto(ISO10589_ISIS, Q_ISO, Q_DEFAULT);
                /*
                 * 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);
                gen_and(b0, b1);
                return b1;

        case Q_ARP:
                bpf_error("arp does not encapsulate another protocol");
                /* NOTREACHED */

        case Q_RARP:
                bpf_error("rarp does not encapsulate another protocol");
                /* NOTREACHED */

        case Q_ATALK:
                bpf_error("atalk encapsulation is not specifiable");
                /* NOTREACHED */

        case Q_DECNET:
                bpf_error("decnet encapsulation is not specifiable");
                /* NOTREACHED */

        case Q_SCA:
                bpf_error("sca does not encapsulate another protocol");
                /* NOTREACHED */

        case Q_LAT:
                bpf_error("lat does not encapsulate another protocol");
                /* NOTREACHED */

        case Q_MOPRC:
                bpf_error("moprc does not encapsulate another protocol");
                /* NOTREACHED */

        case Q_MOPDL:
                bpf_error("mopdl does not encapsulate another protocol");
                /* NOTREACHED */

        case Q_LINK:
                return gen_linktype(v);

        case Q_UDP:
                bpf_error("'udp proto' is bogus");
                /* NOTREACHED */

        case Q_TCP:
                bpf_error("'tcp proto' is bogus");
                /* NOTREACHED */

        case Q_SCTP:
                bpf_error("'sctp proto' is bogus");
                /* NOTREACHED */

        case Q_ICMP:
                bpf_error("'icmp proto' is bogus");
                /* NOTREACHED */

        case Q_IGMP:
                bpf_error("'igmp proto' is bogus");
                /* NOTREACHED */

        case Q_IGRP:
                bpf_error("'igrp proto' is bogus");
                /* NOTREACHED */

        case Q_PIM:
                bpf_error("'pim proto' is bogus");
                /* NOTREACHED */

        case Q_VRRP:
                bpf_error("'vrrp proto' is bogus");
                /* NOTREACHED */

#ifdef INET6
        case Q_IPV6:
                b0 = gen_linktype(ETHERTYPE_IPV6);
#ifndef CHASE_CHAIN
                b1 = gen_cmp(OR_NET, 6, BPF_B, (bpf_int32)v);
#else
                b1 = gen_protochain(v, Q_IPV6);
#endif
                gen_and(b0, b1);
                return b1;

        case Q_ICMPV6:
                bpf_error("'icmp6 proto' is bogus");
#endif /* INET6 */

        case Q_AH:
                bpf_error("'ah proto' is bogus");

        case Q_ESP:
                bpf_error("'ah proto' is bogus");

        case Q_STP:
                bpf_error("'stp proto' is bogus");

        case Q_IPX:
                bpf_error("'ipx proto' is bogus");

        case Q_NETBEUI:
                bpf_error("'netbeui proto' is bogus");

        case Q_RADIO:
                bpf_error("'radio proto' is bogus");

        default:
                abort();
                /* NOTREACHED */
        }
        /* NOTREACHED */
}

struct block *
gen_scode(name, q)
        register const char *name;
        struct qual q;
{
        int proto = q.proto;
        int dir = q.dir;
        int tproto;
        u_char *eaddr;
        bpf_u_int32 mask, addr;
#ifndef INET6
        bpf_u_int32 **alist;
#else
        int tproto6;
        struct sockaddr_in *sin4;
        struct sockaddr_in6 *sin6;
        struct addrinfo *res, *res0;
        struct in6_addr mask128;
#endif /*INET6*/
        struct block *b, *tmp;
        int port, real_proto;
        int port1, port2;

        switch (q.addr) {

        case Q_NET:
                addr = pcap_nametonetaddr(name);
                if (addr == 0)
                        bpf_error("unknown network '%s'", name);
                /* Left justify network addr and calculate its network mask */
                mask = 0xffffffff;
                while (addr && (addr & 0xff000000) == 0) {
                        addr <<= 8;
                        mask <<= 8;
                }
                return gen_host(addr, mask, proto, dir, q.addr);

        case Q_DEFAULT:
        case Q_HOST:
                if (proto == Q_LINK) {
                        switch (linktype) {

                        case DLT_EN10MB:
                                eaddr = pcap_ether_hostton(name);
                                if (eaddr == NULL)
                                        bpf_error(
                                            "unknown ether host '%s'", name);
                                b = gen_ehostop(eaddr, dir);
                                free(eaddr);
                                return b;

                        case DLT_FDDI:
                                eaddr = pcap_ether_hostton(name);
                                if (eaddr == NULL)
                                        bpf_error(
                                            "unknown FDDI host '%s'", name);
                                b = gen_fhostop(eaddr, dir);
                                free(eaddr);
                                return b;

                        case DLT_IEEE802:
                                eaddr = pcap_ether_hostton(name);
                                if (eaddr == NULL)
                                        bpf_error(
                                            "unknown token ring host '%s'", name);
                                b = gen_thostop(eaddr, dir);
                                free(eaddr);
                                return b;

                        case DLT_IEEE802_11:
                        case DLT_IEEE802_11_RADIO_AVS:
                        case DLT_IEEE802_11_RADIO:
                        case DLT_PRISM_HEADER:
                        case DLT_PPI:
                                eaddr = pcap_ether_hostton(name);
                                if (eaddr == NULL)
                                        bpf_error(
                                            "unknown 802.11 host '%s'", name);
                                b = gen_wlanhostop(eaddr, dir);
                                free(eaddr);
                                return b;

                        case DLT_IP_OVER_FC:
                                eaddr = pcap_ether_hostton(name);
                                if (eaddr == NULL)
                                        bpf_error(
                                            "unknown Fibre Channel host '%s'", name);
                                b = gen_ipfchostop(eaddr, dir);
                                free(eaddr);
                                return b;

                        case DLT_SUNATM:
                                if (!is_lane)
                                        break;

                                /*
                                 * Check that the packet doesn't begin
                                 * with an LE Control marker.  (We've
                                 * already generated a test for LANE.)
                                 */
                                tmp = gen_cmp(OR_LINK, SUNATM_PKT_BEGIN_POS,
                                    BPF_H, 0xFF00);
                                gen_not(tmp);

                                eaddr = pcap_ether_hostton(name);
                                if (eaddr == NULL)
                                        bpf_error(
                                            "unknown ether host '%s'", name);
                                b = gen_ehostop(eaddr, dir);
                                gen_and(tmp, b);
                                free(eaddr);
                                return b;
                        }

                        bpf_error("only ethernet/FDDI/token ring/802.11/ATM LANE/Fibre Channel supports link-level host name");
                } else if (proto == Q_DECNET) {
                        unsigned short dn_addr = __pcap_nametodnaddr(name);
                        /*
                         * I don't think DECNET hosts can be multihomed, so
                         * there is no need to build up a list of addresses
                         */
                        return (gen_host(dn_addr, 0, proto, dir, q.addr));
                } else {
#ifndef INET6
                        alist = pcap_nametoaddr(name);
                        if (alist == NULL || *alist == NULL)
                                bpf_error("unknown host '%s'", name);
                        tproto = proto;
                        if (off_linktype == (u_int)-1 && tproto == Q_DEFAULT)
                                tproto = Q_IP;
                        b = gen_host(**alist++, 0xffffffff, tproto, dir, q.addr);
                        while (*alist) {
                                tmp = gen_host(**alist++, 0xffffffff,
                                               tproto, dir, q.addr);
                                gen_or(b, tmp);
                                b = tmp;
                        }
                        return b;
#else
                        memset(&mask128, 0xff, sizeof(mask128));
                        res0 = res = pcap_nametoaddrinfo(name);
                        if (res == NULL)
                                bpf_error("unknown host '%s'", name);
                        b = tmp = NULL;
                        tproto = tproto6 = proto;
                        if (off_linktype == -1 && tproto == Q_DEFAULT) {
                                tproto = Q_IP;
                                tproto6 = Q_IPV6;
                        }
                        for (res = res0; res; res = res->ai_next) {
                                switch (res->ai_family) {
                                case AF_INET:
                                        if (tproto == Q_IPV6)
                                                continue;

                                        sin4 = (struct sockaddr_in *)
                                                res->ai_addr;
                                        tmp = gen_host(ntohl(sin4->sin_addr.s_addr),
                                                0xffffffff, tproto, dir, q.addr);
                                        break;
                                case AF_INET6:
                                        if (tproto6 == Q_IP)
                                                continue;

                                        sin6 = (struct sockaddr_in6 *)
                                                res->ai_addr;
                                        tmp = gen_host6(&sin6->sin6_addr,
                                                &mask128, tproto6, dir, q.addr);
                                        break;
                                default:
                                        continue;
                                }
                                if (b)
                                        gen_or(b, tmp);
                                b = tmp;
                        }
                        freeaddrinfo(res0);
                        if (b == NULL) {
                                bpf_error("unknown host '%s'%s", name,
                                    (proto == Q_DEFAULT)
                                        ? ""
                                        : " for specified address family");
                        }
                        return b;
#endif /*INET6*/
                }

        case Q_PORT:
                if (proto != Q_DEFAULT &&
                    proto != Q_UDP && proto != Q_TCP && proto != Q_SCTP)
                        bpf_error("illegal qualifier of 'port'");
                if (pcap_nametoport(name, &port, &real_proto) == 0)
                        bpf_error("unknown port '%s'", name);
                if (proto == Q_UDP) {
                        if (real_proto == IPPROTO_TCP)
                                bpf_error("port '%s' is tcp", name);
                        else if (real_proto == IPPROTO_SCTP)
                                bpf_error("port '%s' is sctp", name);
                        else
                                /* override PROTO_UNDEF */
                                real_proto = IPPROTO_UDP;
                }
                if (proto == Q_TCP) {
                        if (real_proto == IPPROTO_UDP)
                                bpf_error("port '%s' is udp", name);

                        else if (real_proto == IPPROTO_SCTP)
                                bpf_error("port '%s' is sctp", name);
                        else
                                /* override PROTO_UNDEF */
                                real_proto = IPPROTO_TCP;
                }
                if (proto == Q_SCTP) {
                        if (real_proto == IPPROTO_UDP)
                                bpf_error("port '%s' is udp", name);

                        else if (real_proto == IPPROTO_TCP)
                                bpf_error("port '%s' is tcp", name);
                        else
                                /* override PROTO_UNDEF */
                                real_proto = IPPROTO_SCTP;
                }
#ifndef INET6
                return gen_port(port, real_proto, dir);
#else
                b = gen_port(port, real_proto, dir);
                gen_or(gen_port6(port, real_proto, dir), b);
                return b;
#endif /* INET6 */

        case Q_PORTRANGE:
                if (proto != Q_DEFAULT &&
                    proto != Q_UDP && proto != Q_TCP && proto != Q_SCTP)
                        bpf_error("illegal qualifier of 'portrange'");
                if (pcap_nametoportrange(name, &port1, &port2, &real_proto) == 0) 
                        bpf_error("unknown port in range '%s'", name);
                if (proto == Q_UDP) {
                        if (real_proto == IPPROTO_TCP)
                                bpf_error("port in range '%s' is tcp", name);
                        else if (real_proto == IPPROTO_SCTP)
                                bpf_error("port in range '%s' is sctp", name);
                        else
                                /* override PROTO_UNDEF */
                                real_proto = IPPROTO_UDP;
                }
                if (proto == Q_TCP) {
                        if (real_proto == IPPROTO_UDP)
                                bpf_error("port in range '%s' is udp", name);
                        else if (real_proto == IPPROTO_SCTP)
                                bpf_error("port in range '%s' is sctp", name);
                        else
                                /* override PROTO_UNDEF */
                                real_proto = IPPROTO_TCP;
                }
                if (proto == Q_SCTP) {
                        if (real_proto == IPPROTO_UDP)
                                bpf_error("port in range '%s' is udp", name);
                        else if (real_proto == IPPROTO_TCP)
                                bpf_error("port in range '%s' is tcp", name);
                        else
                                /* override PROTO_UNDEF */
                                real_proto = IPPROTO_SCTP;      
                }
#ifndef INET6
                return gen_portrange(port1, port2, real_proto, dir);
#else
                b = gen_portrange(port1, port2, real_proto, dir);
                gen_or(gen_portrange6(port1, port2, real_proto, dir), b);
                return b;
#endif /* INET6 */

        case Q_GATEWAY:
#ifndef INET6
                eaddr = pcap_ether_hostton(name);
                if (eaddr == NULL)
                        bpf_error("unknown ether host: %s", name);

                alist = pcap_nametoaddr(name);
                if (alist == NULL || *alist == NULL)
                        bpf_error("unknown host '%s'", name);
                b = gen_gateway(eaddr, alist, proto, dir);
                free(eaddr);
                return b;
#else
                bpf_error("'gateway' not supported in this configuration");
#endif /*INET6*/

        case Q_PROTO:
                real_proto = lookup_proto(name, proto);
                if (real_proto >= 0)
                        return gen_proto(real_proto, proto, dir);
                else
                        bpf_error("unknown protocol: %s", name);

        case Q_PROTOCHAIN:
                real_proto = lookup_proto(name, proto);
                if (real_proto >= 0)
                        return gen_protochain(real_proto, proto, dir);
                else
                        bpf_error("unknown protocol: %s", name);

        case Q_UNDEF:
                syntax();
                /* NOTREACHED */
        }
        abort();
        /* NOTREACHED */
}

struct block *
gen_mcode(s1, s2, masklen, q)
        register const char *s1, *s2;
        register int masklen;
        struct qual q;
{
        register int nlen, mlen;
        bpf_u_int32 n, m;

        nlen = __pcap_atoin(s1, &n);
        /* Promote short ipaddr */
        n <<= 32 - nlen;

        if (s2 != NULL) {
                mlen = __pcap_atoin(s2, &m);
                /* Promote short ipaddr */
                m <<= 32 - mlen;
                if ((n & ~m) != 0)
                        bpf_error("non-network bits set in \"%s mask %s\"",
                            s1, s2);
        } else {
                /* Convert mask len to mask */
                if (masklen > 32)
                        bpf_error("mask length must be <= 32");
                if (masklen == 0) {
                        /*
                         * X << 32 is not guaranteed by C to be 0; it's
                         * undefined.
                         */
                        m = 0;
                } else
                        m = 0xffffffff << (32 - masklen);
                if ((n & ~m) != 0)
                        bpf_error("non-network bits set in \"%s/%d\"",
                            s1, masklen);
        }

        switch (q.addr) {

        case Q_NET:
                return gen_host(n, m, q.proto, q.dir, q.addr);

        default:
                bpf_error("Mask syntax for networks only");
                /* NOTREACHED */
        }
        /* NOTREACHED */
        return NULL;
}

struct block *
gen_ncode(s, v, q)
        register const char *s;
        bpf_u_int32 v;
        struct qual q;
{
        bpf_u_int32 mask;
        int proto = q.proto;
        int dir = q.dir;
        register int vlen;

        if (s == NULL)
                vlen = 32;
        else if (q.proto == Q_DECNET)
                vlen = __pcap_atodn(s, &v);
        else
                vlen = __pcap_atoin(s, &v);

        switch (q.addr) {

        case Q_DEFAULT:
        case Q_HOST:
        case Q_NET:
                if (proto == Q_DECNET)
                        return gen_host(v, 0, proto, dir, q.addr);
                else if (proto == Q_LINK) {
                        bpf_error("illegal link layer address");
                } else {
                        mask = 0xffffffff;
                        if (s == NULL && q.addr == Q_NET) {
                                /* Promote short net number */
                                while (v && (v & 0xff000000) == 0) {
                                        v <<= 8;
                                        mask <<= 8;
                                }
                        } else {
                                /* Promote short ipaddr */
                                v <<= 32 - vlen;
                                mask <<= 32 - vlen;
                        }
                        return gen_host(v, mask, proto, dir, q.addr);
                }

        case Q_PORT:
                if (proto == Q_UDP)
                        proto = IPPROTO_UDP;
                else if (proto == Q_TCP)
                        proto = IPPROTO_TCP;
                else if (proto == Q_SCTP)
                        proto = IPPROTO_SCTP;
                else if (proto == Q_DEFAULT)
                        proto = PROTO_UNDEF;
                else
                        bpf_error("illegal qualifier of 'port'");

#ifndef INET6
                return gen_port((int)v, proto, dir);
#else
            {
                struct block *b;
                b = gen_port((int)v, proto, dir);
                gen_or(gen_port6((int)v, proto, dir), b);
                return b;
            }
#endif /* INET6 */

        case Q_PORTRANGE:
                if (proto == Q_UDP)
                        proto = IPPROTO_UDP;
                else if (proto == Q_TCP)
                        proto = IPPROTO_TCP;
                else if (proto == Q_SCTP)
                        proto = IPPROTO_SCTP;
                else if (proto == Q_DEFAULT)
                        proto = PROTO_UNDEF;
                else
                        bpf_error("illegal qualifier of 'portrange'");

#ifndef INET6
                return gen_portrange((int)v, (int)v, proto, dir);
#else
            {
                struct block *b;
                b = gen_portrange((int)v, (int)v, proto, dir);
                gen_or(gen_portrange6((int)v, (int)v, proto, dir), b);
                return b;
            }
#endif /* INET6 */

        case Q_GATEWAY:
                bpf_error("'gateway' requires a name");
                /* NOTREACHED */

        case Q_PROTO:
                return gen_proto((int)v, proto, dir);

        case Q_PROTOCHAIN:
                return gen_protochain((int)v, proto, dir);

        case Q_UNDEF:
                syntax();
                /* NOTREACHED */

        default:
                abort();
                /* NOTREACHED */
        }
        /* NOTREACHED */
}

#ifdef INET6
struct block *
gen_mcode6(s1, s2, masklen, q)
        register const char *s1, *s2;
        register int masklen;
        struct qual q;
{
        struct addrinfo *res;
        struct in6_addr *addr;
        struct in6_addr mask;
        struct block *b;
        u_int32_t *a, *m;

        if (s2)
                bpf_error("no mask %s supported", s2);

        res = pcap_nametoaddrinfo(s1);
        if (!res)
                bpf_error("invalid ip6 address %s", s1);
        if (res->ai_next)
                bpf_error("%s resolved to multiple address", s1);
        addr = &((struct sockaddr_in6 *)res->ai_addr)->sin6_addr;

        if (sizeof(mask) * 8 < masklen)
                bpf_error("mask length must be <= %u", (unsigned int)(sizeof(mask) * 8));
        memset(&mask, 0, sizeof(mask));
        memset(&mask, 0xff, masklen / 8);
        if (masklen % 8) {
                mask.s6_addr[masklen / 8] =
                        (0xff << (8 - masklen % 8)) & 0xff;
        }

        a = (u_int32_t *)addr;
        m = (u_int32_t *)&mask;
        if ((a[0] & ~m[0]) || (a[1] & ~m[1])
         || (a[2] & ~m[2]) || (a[3] & ~m[3])) {
                bpf_error("non-network bits set in \"%s/%d\"", s1, masklen);
        }

        switch (q.addr) {

        case Q_DEFAULT:
        case Q_HOST:
                if (masklen != 128)
                        bpf_error("Mask syntax for networks only");
                /* FALLTHROUGH */

        case Q_NET:
                b = gen_host6(addr, &mask, q.proto, q.dir, q.addr);
                freeaddrinfo(res);
                return b;

        default:
                bpf_error("invalid qualifier against IPv6 address");
                /* NOTREACHED */
        }
        return NULL;
}
#endif /*INET6*/

struct block *
gen_ecode(eaddr, q)
        register const u_char *eaddr;
        struct qual q;
{
        struct block *b, *tmp;

        if ((q.addr == Q_HOST || q.addr == Q_DEFAULT) && q.proto == Q_LINK) {
                switch (linktype) {
                case DLT_EN10MB:
                        return gen_ehostop(eaddr, (int)q.dir);
                case DLT_FDDI:
                        return gen_fhostop(eaddr, (int)q.dir);
                case DLT_IEEE802:
                        return gen_thostop(eaddr, (int)q.dir);
                case DLT_IEEE802_11:
                case DLT_IEEE802_11_RADIO_AVS:
                case DLT_IEEE802_11_RADIO:
                case DLT_PRISM_HEADER:
                case DLT_PPI:
                        return gen_wlanhostop(eaddr, (int)q.dir);
                case DLT_SUNATM:
                        if (is_lane) {
                                /*
                                 * Check that the packet doesn't begin with an
                                 * LE Control marker.  (We've already generated
                                 * a test for LANE.)
                                 */
                                tmp = gen_cmp(OR_LINK, SUNATM_PKT_BEGIN_POS, BPF_H,
                                        0xFF00);
                                gen_not(tmp);

                                /*
                                 * Now check the MAC address.
                                 */
                                b = gen_ehostop(eaddr, (int)q.dir);
                                gen_and(tmp, b);
                                return b;
                        }
                        break;
                case DLT_IP_OVER_FC:
                        return gen_ipfchostop(eaddr, (int)q.dir);
                default:
                        bpf_error("ethernet addresses supported only on ethernet/FDDI/token ring/802.11/ATM LANE/Fibre Channel");
                        break;
                }
        }
        bpf_error("ethernet address used in non-ether expression");
        /* NOTREACHED */
        return NULL;
}

void
sappend(s0, s1)
        struct slist *s0, *s1;
{
        /*
         * This is definitely not the best way to do this, but the
         * lists will rarely get long.
         */
        while (s0->next)
                s0 = s0->next;
        s0->next = s1;
}

static struct slist *
xfer_to_x(a)
        struct arth *a;
{
        struct slist *s;

        s = new_stmt(BPF_LDX|BPF_MEM);
        s->s.k = a->regno;
        return s;
}

static struct slist *
xfer_to_a(a)
        struct arth *a;
{
        struct slist *s;

        s = new_stmt(BPF_LD|BPF_MEM);
        s->s.k = a->regno;
        return s;
}

/*
 * Modify "index" to use the value stored into its register as an
 * offset relative to the beginning of the header for the protocol
 * "proto", and allocate a register and put an item "size" bytes long
 * (1, 2, or 4) at that offset into that register, making it the register
 * for "index".
 */
struct arth *
gen_load(proto, inst, size)
        int proto;
        struct arth *inst;
        int size;
{
        struct slist *s, *tmp;
        struct block *b;
        int regno = alloc_reg();

        free_reg(inst->regno);
        switch (size) {

        default:
                bpf_error("data size must be 1, 2, or 4");

        case 1:
                size = BPF_B;
                break;

        case 2:
                size = BPF_H;
                break;

        case 4:
                size = BPF_W;
                break;
        }
        switch (proto) {
        default:
                bpf_error("unsupported index operation");

        case Q_RADIO:
                /*
                 * The offset is relative to the beginning of the packet
                 * data, if we have a radio header.  (If we don't, this
                 * is an error.)
                 */
                if (linktype != DLT_IEEE802_11_RADIO_AVS &&
                    linktype != DLT_IEEE802_11_RADIO &&
                    linktype != DLT_PRISM_HEADER)
                        bpf_error("radio information not present in capture");

                /*
                 * Load into the X register the offset computed into the
                 * register specifed by "index".
                 */
                s = xfer_to_x(inst);

                /*
                 * Load the item at that offset.
                 */
                tmp = new_stmt(BPF_LD|BPF_IND|size);
                sappend(s, tmp);
                sappend(inst->s, s);
                break;

        case Q_LINK:
                /*
                 * The offset is relative to the beginning of
                 * the link-layer header.
                 *
                 * XXX - what about ATM LANE?  Should the index be
                 * relative to the beginning of the AAL5 frame, so
                 * that 0 refers to the beginning of the LE Control
                 * field, or relative to the beginning of the LAN
                 * frame, so that 0 refers, for Ethernet LANE, to
                 * the beginning of the destination address?
                 */
                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.  Add to it the offset computed
                 * into the register specified by "index", and move that
                 * into the X register.  Otherwise, just load into the X
                 * register the offset computed into the register specifed
                 * by "index".
                 */
                if (s != NULL) {
                        sappend(s, xfer_to_a(inst));
                        sappend(s, new_stmt(BPF_ALU|BPF_ADD|BPF_X));
                        sappend(s, new_stmt(BPF_MISC|BPF_TAX));
                } else
                        s = xfer_to_x(inst);

                /*
                 * Load the item at the sum of the offset we've put in the
                 * X register and the offset of the start of the link
                 * layer header (which is 0 if the radio header is
                 * variable-length; that header length is what we put
                 * into the X register and then added to the index).
                 */
                tmp = new_stmt(BPF_LD|BPF_IND|size);
                tmp->s.k = off_ll;
                sappend(s, tmp);
                sappend(inst->s, s);
                break;

        case Q_IP:
        case Q_ARP:
        case Q_RARP:
        case Q_ATALK:
        case Q_DECNET:
        case Q_SCA:
        case Q_LAT:
        case Q_MOPRC:
        case Q_MOPDL:
#ifdef INET6
        case Q_IPV6:
#endif
                /*
                 * The offset is relative to the beginning of
                 * the network-layer header.
                 * XXX - are there any cases where we want
                 * off_nl_nosnap?
                 */
                s = gen_off_macpl();

                /*
                 * If "s" is non-null, it has code to arrange that the
                 * X register contains the offset of the MAC-layer
                 * payload.  Add to it the offset computed into the
                 * register specified by "index", and move that into
                 * the X register.  Otherwise, just load into the X
                 * register the offset computed into the register specifed
                 * by "index".
                 */
                if (s != NULL) {
                        sappend(s, xfer_to_a(inst));
                        sappend(s, new_stmt(BPF_ALU|BPF_ADD|BPF_X));
                        sappend(s, new_stmt(BPF_MISC|BPF_TAX));
                } else
                        s = xfer_to_x(inst);

                /*
                 * Load the item at the sum of the offset we've put in the
                 * X register, the offset of the start of the network
                 * layer header from the beginning of the MAC-layer
                 * payload, and the purported offset of the start of the
                 * MAC-layer payload (which might be 0 if there's a
                 * variable-length prefix before the link-layer header
                 * or the link-layer header itself is variable-length;
                 * the variable-length offset of the start of the
                 * MAC-layer payload is what we put into the X register
                 * and then added to the index).
                 */
                tmp = new_stmt(BPF_LD|BPF_IND|size);
                tmp->s.k = off_macpl + off_nl;
                sappend(s, tmp);
                sappend(inst->s, s);

                /*
                 * Do the computation only if the packet contains
                 * the protocol in question.
                 */
                b = gen_proto_abbrev(proto);
                if (inst->b)
                        gen_and(inst->b, b);
                inst->b = b;
                break;

        case Q_SCTP:
        case Q_TCP:
        case Q_UDP:
        case Q_ICMP:
        case Q_IGMP:
        case Q_IGRP:
        case Q_PIM:
        case Q_VRRP:
                /*
                 * The offset is relative to the beginning of
                 * the transport-layer header.
                 *
                 * Load the X register with the length of the IPv4 header
                 * (plus the offset of the link-layer header, if it's
                 * a variable-length header), in bytes.
                 *
                 * XXX - are there any cases where we want
                 * off_nl_nosnap?
                 * XXX - we should, if we're built with
                 * IPv6 support, generate code to load either
                 * IPv4, IPv6, or both, as appropriate.
                 */
                s = gen_loadx_iphdrlen();

                /*
                 * The X register now contains the sum of the length
                 * of any variable-length header preceding the link-layer
                 * header, any variable-length link-layer header, and the
                 * length of the network-layer header.
                 *
                 * Load into the A register the offset relative to
                 * the beginning of the transport layer header,
                 * add the X register to that, move that to the
                 * X register, and load with an offset from the
                 * X register equal to the offset of the network
                 * layer header relative to the beginning of
                 * the MAC-layer payload plus the fixed-length
                 * portion of the offset of the MAC-layer payload
                 * from the beginning of the raw packet data.
                 */
                sappend(s, xfer_to_a(inst));
                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_macpl + off_nl;
                sappend(inst->s, s);

                /*
                 * Do the computation only if the packet contains
                 * the protocol in question - which is true only
                 * if this is an IP datagram and is the first or
                 * only fragment of that datagram.
                 */
                gen_and(gen_proto_abbrev(proto), b = gen_ipfrag());
                if (inst->b)
                        gen_and(inst->b, b);
#ifdef INET6
                gen_and(gen_proto_abbrev(Q_IP), b);
#endif
                inst->b = b;
                break;
#ifdef INET6
        case Q_ICMPV6:
                bpf_error("IPv6 upper-layer protocol is not supported by proto[x]");
                /*NOTREACHED*/
#endif
        }
        inst->regno = regno;
        s = new_stmt(BPF_ST);
        s->s.k = regno;
        sappend(inst->s, s);

        return inst;
}

struct block *
gen_relation(code, a0, a1, reversed)
        int code;
        struct arth *a0, *a1;
        int reversed;
{
        struct slist *s0, *s1, *s2;
        struct block *b, *tmp;

        s0 = xfer_to_x(a1);
        s1 = xfer_to_a(a0);
        if (code == BPF_JEQ) {
                s2 = new_stmt(BPF_ALU|BPF_SUB|BPF_X);
                b = new_block(JMP(code));
                sappend(s1, s2);
        }
        else
                b = new_block(BPF_JMP|code|BPF_X);
        if (reversed)
                gen_not(b);

        sappend(s0, s1);
        sappend(a1->s, s0);
        sappend(a0->s, a1->s);

        b->stmts = a0->s;

        free_reg(a0->regno);
        free_reg(a1->regno);

        /* 'and' together protocol checks */
        if (a0->b) {
                if (a1->b) {
                        gen_and(a0->b, tmp = a1->b);
                }
                else
                        tmp = a0->b;
        } else
                tmp = a1->b;

        if (tmp)
                gen_and(tmp, b);

        return b;
}

struct arth *
gen_loadlen()
{
        int regno = alloc_reg();
        struct arth *a = (struct arth *)newchunk(sizeof(*a));
        struct slist *s;

        s = new_stmt(BPF_LD|BPF_LEN);
        s->next = new_stmt(BPF_ST);
        s->next->s.k = regno;
        a->s = s;
        a->regno = regno;

        return a;
}

struct arth *
gen_loadi(val)
        int val;
{
        struct arth *a;
        struct slist *s;
        int reg;

        a = (struct arth *)newchunk(sizeof(*a));

        reg = alloc_reg();

        s = new_stmt(BPF_LD|BPF_IMM);
        s->s.k = val;
        s->next = new_stmt(BPF_ST);
        s->next->s.k = reg;
        a->s = s;
        a->regno = reg;

        return a;
}

struct arth *
gen_neg(a)
        struct arth *a;
{
        struct slist *s;

        s = xfer_to_a(a);
        sappend(a->s, s);
        s = new_stmt(BPF_ALU|BPF_NEG);
        s->s.k = 0;
        sappend(a->s, s);
        s = new_stmt(BPF_ST);
        s->s.k = a->regno;
        sappend(a->s, s);

        return a;
}

struct arth *
gen_arth(code, a0, a1)
        int code;
        struct arth *a0, *a1;
{
        struct slist *s0, *s1, *s2;

        s0 = xfer_to_x(a1);
        s1 = xfer_to_a(a0);
        s2 = new_stmt(BPF_ALU|BPF_X|code);

        sappend(s1, s2);
        sappend(s0, s1);
        sappend(a1->s, s0);
        sappend(a0->s, a1->s);

        free_reg(a0->regno);
        free_reg(a1->regno);

        s0 = new_stmt(BPF_ST);
        a0->regno = s0->s.k = alloc_reg();
        sappend(a0->s, s0);

        return a0;
}

/*
 * Here we handle simple allocation of the scratch registers.
 * If too many registers are alloc'd, the allocator punts.
 */
static int regused[BPF_MEMWORDS];
static int curreg;

/*
 * Initialize the table of used registers and the current register.
 */
static void
init_regs()
{
        curreg = 0;
        memset(regused, 0, sizeof regused);
}

/*
 * Return the next free register.
 */
static int
alloc_reg()
{
        int n = BPF_MEMWORDS;

        while (--n >= 0) {
                if (regused[curreg])
                        curreg = (curreg + 1) % BPF_MEMWORDS;
                else {
                        regused[curreg] = 1;
                        return curreg;
                }
        }
        bpf_error("too many registers needed to evaluate expression");
        /* NOTREACHED */
        return 0;
}

/*
 * Return a register to the table so it can
 * be used later.
 */
static void
free_reg(n)
        int n;
{
        regused[n] = 0;
}

static struct block *
gen_len(jmp, n)
        int jmp, n;
{
        struct slist *s;
        struct block *b;

        s = new_stmt(BPF_LD|BPF_LEN);
        b = new_block(JMP(jmp));
        b->stmts = s;
        b->s.k = n;

        return b;
}

struct block *
gen_greater(n)
        int n;
{
        return gen_len(BPF_JGE, n);
}

/*
 * Actually, this is less than or equal.
 */
struct block *
gen_less(n)
        int n;
{
        struct block *b;

        b = gen_len(BPF_JGT, n);
        gen_not(b);

        return b;
}

/*
 * This is for "byte {idx} {op} {val}"; "idx" is treated as relative to
 * the beginning of the link-layer header.
 * XXX - that means you can't test values in the radiotap header, but
 * as that header is difficult if not impossible to parse generally
 * without a loop, that might not be a severe problem.  A new keyword
 * "radio" could be added for that, although what you'd really want
 * would be a way of testing particular radio header values, which
 * would generate code appropriate to the radio header in question.
 */
struct block *
gen_byteop(op, idx, val)
        int op, idx, val;
{
        struct block *b;
        struct slist *s;

        switch (op) {
        default:
                abort();

        case '=':
                return gen_cmp(OR_LINK, (u_int)idx, BPF_B, (bpf_int32)val);

        case '<':
                b = gen_cmp_lt(OR_LINK, (u_int)idx, BPF_B, (bpf_int32)val);
                return b;

        case '>':
                b = gen_cmp_gt(OR_LINK, (u_int)idx, BPF_B, (bpf_int32)val);
                return b;

        case '|':
                s = new_stmt(BPF_ALU|BPF_OR|BPF_K);
                break;

        case '&':
                s = new_stmt(BPF_ALU|BPF_AND|BPF_K);
                break;
        }
        s->s.k = val;
        b = new_block(JMP(BPF_JEQ));
        b->stmts = s;
        gen_not(b);

        return b;
}

static u_char abroadcast[] = { 0x0 };

struct block *
gen_broadcast(proto)
        int proto;
{
        bpf_u_int32 hostmask;
        struct block *b0, *b1, *b2;
        static u_char ebroadcast[] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };

        switch (proto) {

        case Q_DEFAULT:
        case Q_LINK:
                switch (linktype) {
                case DLT_ARCNET:
                case DLT_ARCNET_LINUX:
                        return gen_ahostop(abroadcast, Q_DST);
                case DLT_EN10MB:
                        return gen_ehostop(ebroadcast, Q_DST);
                case DLT_FDDI:
                        return gen_fhostop(ebroadcast, Q_DST);
                case DLT_IEEE802:
                        return gen_thostop(ebroadcast, Q_DST);
                case DLT_IEEE802_11:
                case DLT_IEEE802_11_RADIO_AVS:
                case DLT_IEEE802_11_RADIO:
                case DLT_PPI:
                case DLT_PRISM_HEADER:
                        return gen_wlanhostop(ebroadcast, Q_DST);
                case DLT_IP_OVER_FC:
                        return gen_ipfchostop(ebroadcast, Q_DST);
                case DLT_SUNATM:
                        if (is_lane) {
                                /*
                                 * Check that the packet doesn't begin with an
                                 * LE Control marker.  (We've already generated
                                 * a test for LANE.)
                                 */
                                b1 = gen_cmp(OR_LINK, SUNATM_PKT_BEGIN_POS,
                                    BPF_H, 0xFF00);
                                gen_not(b1);

                                /*
                                 * Now check the MAC address.
                                 */
                                b0 = gen_ehostop(ebroadcast, Q_DST);
                                gen_and(b1, b0);
                                return b0;
                        }
                        break;
                default:
                        bpf_error("not a broadcast link");
                }
                break;

        case Q_IP:
                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,
                              (bpf_int32)(~0 & hostmask), hostmask);
                gen_or(b1, b2);
                gen_and(b0, b2);
                return b2;
        }
        bpf_error("only link-layer/IP broadcast filters supported");
        /* NOTREACHED */
        return NULL;
}

/*
 * Generate code to test the low-order bit of a MAC address (that's
 * the bottom bit of the *first* byte).
 */
static struct block *
gen_mac_multicast(offset)
        int offset;
{
        register struct block *b0;
        register struct slist *s;

        /* link[offset] & 1 != 0 */
        s = gen_load_a(OR_LINK, offset, BPF_B);
        b0 = new_block(JMP(BPF_JSET));
        b0->s.k = 1;
        b0->stmts = s;
        return b0;
}

struct block *
gen_multicast(proto)
        int proto;
{
        register struct block *b0, *b1, *b2;
        register struct slist *s;

        switch (proto) {

        case Q_DEFAULT:
        case Q_LINK:
                switch (linktype) {
                case DLT_ARCNET:
                case DLT_ARCNET_LINUX:
                        /* all ARCnet multicasts use the same address */
                        return gen_ahostop(abroadcast, Q_DST);
                case DLT_EN10MB:
                        /* ether[0] & 1 != 0 */
                        return gen_mac_multicast(0);
                case DLT_FDDI:
                        /*
                         * XXX TEST THIS: MIGHT NOT PORT PROPERLY XXX
                         *
                         * XXX - was that referring to bit-order issues?
                         */
                        /* fddi[1] & 1 != 0 */
                        return gen_mac_multicast(1);
                case DLT_IEEE802:
                        /* tr[2] & 1 != 0 */
                        return gen_mac_multicast(2);
                case DLT_IEEE802_11:
                case DLT_IEEE802_11_RADIO_AVS:
                case DLT_PPI:
                case DLT_IEEE802_11_RADIO:
                case DLT_PRISM_HEADER:
                        /*
                         * Oh, yuk.
                         *
                         *      For control frames, there is no DA.
                         *
                         *      For management frames, DA is at an
                         *      offset of 4 from the beginning of
                         *      the packet.
                         *
                         *      For data frames, DA is at an offset
                         *      of 4 from the beginning of the packet
                         *      if To DS is clear and at an offset of
                         *      16 from the beginning of the packet
                         *      if To DS is set.
                         */

                        /*
                         * Generate the tests to be done for data frames.
                         *
                         * First, check for To DS set, i.e. "link[1] & 0x01".
                         */
                        s = gen_load_a(OR_LINK, 1, BPF_B);
                        b1 = new_block(JMP(BPF_JSET));
                        b1->s.k = 0x01; /* To DS */
                        b1->stmts = s;

                        /*
                         * If To DS is set, the DA is at 16.
                         */
                        b0 = gen_mac_multicast(16);
                        gen_and(b1, b0);

                        /*
                         * Now, check for To DS not set, i.e. check
                         * "!(link[1] & 0x01)".
                         */
                        s = gen_load_a(OR_LINK, 1, BPF_B);
                        b2 = new_block(JMP(BPF_JSET));
                        b2->s.k = 0x01; /* To DS */
                        b2->stmts = s;
                        gen_not(b2);

                        /*
                         * If To DS is not set, the DA is at 4.
                         */
                        b1 = gen_mac_multicast(4);
                        gen_and(b2, b1);

                        /*
                         * Now OR together the last two checks.  That gives
                         * the complete set of checks for data frames.
                         */
                        gen_or(b1, b0);

                        /*
                         * Now check for a data frame.
                         * I.e, check "link[0] & 0x08".
                         */
                        s = gen_load_a(OR_LINK, 0, BPF_B);
                        b1 = new_block(JMP(BPF_JSET));
                        b1->s.k = 0x08;
                        b1->stmts = s;

                        /*
                         * AND that with the checks done for data frames.
                         */
                        gen_and(b1, b0);

                        /*
                         * If the high-order bit of the type value is 0, this
                         * is a management frame.
                         * I.e, check "!(link[0] & 0x08)".
                         */
                        s = gen_load_a(OR_LINK, 0, BPF_B);
                        b2 = new_block(JMP(BPF_JSET));
                        b2->s.k = 0x08;
                        b2->stmts = s;
                        gen_not(b2);

                        /*
                         * For management frames, the DA is at 4.
                         */
                        b1 = gen_mac_multicast(4);
                        gen_and(b2, b1);

                        /*
                         * OR that with the checks done for data frames.
                         * That gives the checks done for management and
                         * data frames.
                         */
                        gen_or(b1, b0);

                        /*
                         * If the low-order bit of the type value is 1,
                         * this is either a control frame or a frame
                         * with a reserved type, and thus not a
                         * frame with an SA.
                         *
                         * I.e., check "!(link[0] & 0x04)".
                         */
                        s = gen_load_a(OR_LINK, 0, BPF_B);
                        b1 = new_block(JMP(BPF_JSET));
                        b1->s.k = 0x04;
                        b1->stmts = s;
                        gen_not(b1);

                        /*
                         * AND that with the checks for data and management
                         * frames.
                         */
                        gen_and(b1, b0);
                        return b0;
                case DLT_IP_OVER_FC:
                        b0 = gen_mac_multicast(2);
                        return b0;
                case DLT_SUNATM:
                        if (is_lane) {
                                /*
                                 * Check that the packet doesn't begin with an
                                 * LE Control marker.  (We've already generated
                                 * a test for LANE.)
                                 */
                                b1 = gen_cmp(OR_LINK, SUNATM_PKT_BEGIN_POS,
                                    BPF_H, 0xFF00);
                                gen_not(b1);

                                /* ether[off_mac] & 1 != 0 */
                                b0 = gen_mac_multicast(off_mac);
                                gen_and(b1, b0);
                                return b0;
                        }
                        break;
                default:
                        break;
                }
                /* Link not known to support multicasts */
                break;

        case Q_IP:
                b0 = gen_linktype(ETHERTYPE_IP);
                b1 = gen_cmp_ge(OR_NET, 16, BPF_B, (bpf_int32)224);
                gen_and(b0, b1);
                return b1;

#ifdef INET6
        case Q_IPV6:
                b0 = gen_linktype(ETHERTYPE_IPV6);
                b1 = gen_cmp(OR_NET, 24, BPF_B, (bpf_int32)255);
                gen_and(b0, b1);
                return b1;
#endif /* INET6 */
        }
        bpf_error("link-layer multicast filters supported only on ethernet/FDDI/token ring/ARCNET/802.11/ATM LANE/Fibre Channel");
        /* NOTREACHED */
        return NULL;
}

/*
 * generate command for inbound/outbound.  It's here so we can
 * make it link-type specific.  'dir' = 0 implies "inbound",
 * = 1 implies "outbound".
 */
struct block *
gen_inbound(dir)
        int dir;
{
        register struct block *b0;

        /*
         * Only some data link types support inbound/outbound qualifiers.
         */
        switch (linktype) {
        case DLT_SLIP:
                b0 = gen_relation(BPF_JEQ,
                          gen_load(Q_LINK, gen_loadi(0), 1),
                          gen_loadi(0),
                          dir);
                break;

        case DLT_LINUX_SLL:
                if (dir) {
                        /*
                         * Match packets sent by this machine.
                         */
                        b0 = gen_cmp(OR_LINK, 0, BPF_H, LINUX_SLL_OUTGOING);
                } else {
                        /*
                         * Match packets sent to this machine.
                         * (No broadcast or multicast packets, or
                         * packets sent to some other machine and
                         * received promiscuously.)
                         *
                         * XXX - packets sent to other machines probably
                         * shouldn't be matched, but what about broadcast
                         * or multicast packets we received?
                         */
                        b0 = gen_cmp(OR_LINK, 0, BPF_H, LINUX_SLL_HOST);
                }
                break;

#ifdef HAVE_NET_PFVAR_H
        case DLT_PFLOG:
                b0 = gen_cmp(OR_LINK, offsetof(struct pfloghdr, dir), BPF_B,
                    (bpf_int32)((dir == 0) ? PF_IN : PF_OUT));
                break;
#endif

        case DLT_PPP_PPPD:
                if (dir) {
                        /* match outgoing packets */
                        b0 = gen_cmp(OR_LINK, 0, BPF_B, PPP_PPPD_OUT);
                } else {
                        /* match incoming packets */
                        b0 = gen_cmp(OR_LINK, 0, BPF_B, PPP_PPPD_IN);
                }
                break;

        case DLT_JUNIPER_MFR:
        case DLT_JUNIPER_MLFR:
        case DLT_JUNIPER_MLPPP:
        case DLT_JUNIPER_ATM1:
        case DLT_JUNIPER_ATM2:
        case DLT_JUNIPER_PPPOE:
        case DLT_JUNIPER_PPPOE_ATM:
        case DLT_JUNIPER_GGSN:
        case DLT_JUNIPER_ES:
        case DLT_JUNIPER_MONITOR:
        case DLT_JUNIPER_SERVICES:
        case DLT_JUNIPER_ETHER:
        case DLT_JUNIPER_PPP:
        case DLT_JUNIPER_FRELAY:
        case DLT_JUNIPER_CHDLC:
        case DLT_JUNIPER_VP:
        case DLT_JUNIPER_ST:
        case DLT_JUNIPER_ISM:
                /* juniper flags (including direction) are stored
                 * the byte after the 3-byte magic number */
                if (dir) {
                        /* match outgoing packets */
                        b0 = gen_mcmp(OR_LINK, 3, BPF_B, 0, 0x01);
                } else {
                        /* match incoming packets */
                        b0 = gen_mcmp(OR_LINK, 3, BPF_B, 1, 0x01);
                }
                break;

        default:
                bpf_error("inbound/outbound not supported on linktype %d",
                    linktype);
                b0 = NULL;
                /* NOTREACHED */
        }
        return (b0);
}

#ifdef HAVE_NET_PFVAR_H
/* PF firewall log matched interface */
struct block *
gen_pf_ifname(const char *ifname)
{
        struct block *b0;
        u_int len, off;

        if (linktype != DLT_PFLOG) {
                bpf_error("ifname supported only on PF linktype");
                /* NOTREACHED */
        }
        len = sizeof(((struct pfloghdr *)0)->ifname);
        off = offsetof(struct pfloghdr, ifname);
        if (strlen(ifname) >= len) {
                bpf_error("ifname interface names can only be %d characters",
                    len-1);
                /* NOTREACHED */
        }
        b0 = gen_bcmp(OR_LINK, off, strlen(ifname), (const u_char *)ifname);
        return (b0);
}

/* PF firewall log ruleset name */
struct block *
gen_pf_ruleset(char *ruleset)
{
        struct block *b0;

        if (linktype != DLT_PFLOG) {
                bpf_error("ruleset supported only on PF linktype");
                /* NOTREACHED */
        }

        if (strlen(ruleset) >= sizeof(((struct pfloghdr *)0)->ruleset)) {
                bpf_error("ruleset names can only be %ld characters",
                    (long)(sizeof(((struct pfloghdr *)0)->ruleset) - 1));
                /* NOTREACHED */
        }

        b0 = gen_bcmp(OR_LINK, offsetof(struct pfloghdr, ruleset),
            strlen(ruleset), (const u_char *)ruleset);
        return (b0);
}

/* PF firewall log rule number */
struct block *
gen_pf_rnr(int rnr)
{
        struct block *b0;

        if (linktype != DLT_PFLOG) {
                bpf_error("rnr supported only on PF linktype");
                /* NOTREACHED */
        }

        b0 = gen_cmp(OR_LINK, offsetof(struct pfloghdr, rulenr), BPF_W,
                 (bpf_int32)rnr);
        return (b0);
}

/* PF firewall log sub-rule number */
struct block *
gen_pf_srnr(int srnr)
{
        struct block *b0;

        if (linktype != DLT_PFLOG) {
                bpf_error("srnr supported only on PF linktype");
                /* NOTREACHED */
        }

        b0 = gen_cmp(OR_LINK, offsetof(struct pfloghdr, subrulenr), BPF_W,
            (bpf_int32)srnr);
        return (b0);
}

/* PF firewall log reason code */
struct block *
gen_pf_reason(int reason)
{
        struct block *b0;

        if (linktype != DLT_PFLOG) {
                bpf_error("reason supported only on PF linktype");
                /* NOTREACHED */
        }

        b0 = gen_cmp(OR_LINK, offsetof(struct pfloghdr, reason), BPF_B,
            (bpf_int32)reason);
        return (b0);
}

/* PF firewall log action */
struct block *
gen_pf_action(int action)
{
        struct block *b0;

        if (linktype != DLT_PFLOG) {
                bpf_error("action supported only on PF linktype");
                /* NOTREACHED */
        }

        b0 = gen_cmp(OR_LINK, offsetof(struct pfloghdr, action), BPF_B,
            (bpf_int32)action);
        return (b0);
}
#else /* !HAVE_NET_PFVAR_H */
struct block *
gen_pf_ifname(const char *ifname)
{
        bpf_error("libpcap was compiled without pf support");
        /* NOTREACHED */
        return (NULL);
}

struct block *
gen_pf_ruleset(char *ruleset)
{
        bpf_error("libpcap was compiled on a machine without pf support");
        /* NOTREACHED */
        return (NULL);
}

struct block *
gen_pf_rnr(int rnr)
{
        bpf_error("libpcap was compiled on a machine without pf support");
        /* NOTREACHED */
        return (NULL);
}

struct block *
gen_pf_srnr(int srnr)
{
        bpf_error("libpcap was compiled on a machine without pf support");
        /* NOTREACHED */
        return (NULL);
}

struct block *
gen_pf_reason(int reason)
{
        bpf_error("libpcap was compiled on a machine without pf support");
        /* NOTREACHED */
        return (NULL);
}

struct block *
gen_pf_action(int action)
{
        bpf_error("libpcap was compiled on a machine without pf support");
        /* NOTREACHED */
        return (NULL);
}
#endif /* HAVE_NET_PFVAR_H */

/* IEEE 802.11 wireless header */
struct block *
gen_p80211_type(int type, int mask)
{
        struct block *b0;

        switch (linktype) {

        case DLT_IEEE802_11:
        case DLT_PRISM_HEADER:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_IEEE802_11_RADIO:
                b0 = gen_mcmp(OR_LINK, 0, BPF_B, (bpf_int32)type,
                    (bpf_int32)mask);
                break;

        default:
                bpf_error("802.11 link-layer types supported only on 802.11");
                /* NOTREACHED */
        }

        return (b0);
}

struct block *
gen_p80211_fcdir(int fcdir)
{
        struct block *b0;

        switch (linktype) {

        case DLT_IEEE802_11:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_IEEE802_11_RADIO:
        case DLT_PRISM_HEADER:
                break;

        default:
                bpf_error("frame direction supported only with 802.11 headers");
                /* NOTREACHED */
        }

        b0 = gen_mcmp(OR_LINK, 1, BPF_B, (bpf_int32)fcdir,
                (bpf_u_int32)IEEE80211_FC1_DIR_MASK);

        return (b0);
}

struct block *
gen_acode(eaddr, q)
        register const u_char *eaddr;
        struct qual q;
{
        switch (linktype) {

        case DLT_ARCNET:
        case DLT_ARCNET_LINUX:
                if ((q.addr == Q_HOST || q.addr == Q_DEFAULT) &&
                    q.proto == Q_LINK)
                        return (gen_ahostop(eaddr, (int)q.dir));
                else {
                        bpf_error("ARCnet address used in non-arc expression");
                        /* NOTREACHED */
                }
                break;

        default:
                bpf_error("aid supported only on ARCnet");
                /* NOTREACHED */
        }
        bpf_error("ARCnet address used in non-arc expression");
        /* NOTREACHED */
        return NULL;
}

static struct block *
gen_ahostop(eaddr, dir)
        register const u_char *eaddr;
        register int dir;
{
        register struct block *b0, *b1;

        switch (dir) {
        /* src comes first, different from Ethernet */
        case Q_SRC:
                return gen_bcmp(OR_LINK, 0, 1, eaddr);

        case Q_DST:
                return gen_bcmp(OR_LINK, 1, 1, eaddr);

        case Q_AND:
                b0 = gen_ahostop(eaddr, Q_SRC);
                b1 = gen_ahostop(eaddr, Q_DST);
                gen_and(b0, b1);
                return b1;

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_ahostop(eaddr, Q_SRC);
                b1 = gen_ahostop(eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;
        }
        abort();
        /* NOTREACHED */
}

/*
 * support IEEE 802.1Q VLAN trunk over ethernet
 */
struct block *
gen_vlan(vlan_num)
        int vlan_num;
{
        struct  block   *b0, *b1;

        /* can't check for VLAN-encapsulated packets inside MPLS */
        if (label_stack_depth > 0)
                bpf_error("no VLAN match after MPLS");

        /*
         * Check for a VLAN packet, and then change the offsets to point
         * to the type and data fields within the VLAN packet.  Just
         * increment the offsets, so that we can support a hierarchy, e.g.
         * "vlan 300 && vlan 200" to capture VLAN 200 encapsulated within
         * VLAN 100.
         *
         * XXX - this is a bit of a kludge.  If we were to split the
         * compiler into a parser that parses an expression and
         * generates an expression tree, and a code generator that
         * takes an expression tree (which could come from our
         * parser or from some other parser) and generates BPF code,
         * we could perhaps make the offsets parameters of routines
         * and, in the handler for an "AND" node, pass to subnodes
         * other than the VLAN node the adjusted offsets.
         *
         * This would mean that "vlan" would, instead of changing the
         * behavior of *all* tests after it, change only the behavior
         * of tests ANDed with it.  That would change the documented
         * semantics of "vlan", which might break some expressions.
         * However, it would mean that "(vlan and ip) or ip" would check
         * both for VLAN-encapsulated IP and IP-over-Ethernet, rather than
         * checking only for VLAN-encapsulated IP, so that could still
         * be considered worth doing; it wouldn't break expressions
         * that are of the form "vlan and ..." or "vlan N and ...",
         * which I suspect are the most common expressions involving
         * "vlan".  "vlan or ..." doesn't necessarily do what the user
         * would really want, now, as all the "or ..." tests would
         * be done assuming a VLAN, even though the "or" could be viewed
         * as meaning "or, if this isn't a VLAN packet...".
         */
        orig_nl = off_nl;

        switch (linktype) {

        case DLT_EN10MB:
                /* check for VLAN */
                b0 = gen_cmp(OR_LINK, off_linktype, BPF_H,
                    (bpf_int32)ETHERTYPE_8021Q);

                /* If a specific VLAN is requested, check VLAN id */
                if (vlan_num >= 0) {
                        b1 = gen_mcmp(OR_MACPL, 0, BPF_H,
                            (bpf_int32)vlan_num, 0x0fff);
                        gen_and(b0, b1);
                        b0 = b1;
                }

                off_macpl += 4;
                off_linktype += 4;
#if 0
                off_nl_nosnap += 4;
                off_nl += 4;
#endif
                break;

        default:
                bpf_error("no VLAN support for data link type %d",
                      linktype);
                /*NOTREACHED*/
        }

        return (b0);
}

/*
 * support for MPLS
 */
struct block *
gen_mpls(label_num)
        int label_num;
{
        struct  block   *b0,*b1;

        /*
         * Change the offsets to point to the type and data fields within
         * the MPLS packet.  Just increment the offsets, so that we
         * can support a hierarchy, e.g. "mpls 100000 && mpls 1024" to
         * capture packets with an outer label of 100000 and an inner
         * label of 1024.
         *
         * XXX - this is a bit of a kludge.  See comments in gen_vlan().
         */
        orig_nl = off_nl;

        if (label_stack_depth > 0) {
            /* just match the bottom-of-stack bit clear */
            b0 = gen_mcmp(OR_MACPL, orig_nl-2, BPF_B, 0, 0x01);
        } else {
            /*
             * Indicate that we're checking MPLS-encapsulated headers,
             * to make sure higher level code generators don't try to
             * match against IP-related protocols such as Q_ARP, Q_RARP
             * etc.
             */
            switch (linktype) {
                
            case DLT_C_HDLC: /* fall through */
            case DLT_EN10MB:
                    b0 = gen_linktype(ETHERTYPE_MPLS);
                    break;
                
            case DLT_PPP:
                    b0 = gen_linktype(PPP_MPLS_UCAST);
                    break;
                
                    /* FIXME add other DLT_s ...
                     * for Frame-Relay/and ATM this may get messy due to SNAP headers
                     * leave it for now */
                
            default:
                    bpf_error("no MPLS support for data link type %d",
                          linktype);
                    b0 = NULL;
                    /*NOTREACHED*/
                    break;
            }
        }

        /* 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_MACPL, orig_nl, BPF_W, (bpf_int32)label_num,
                    0xfffff000); /* only compare the first 20 bits */
                gen_and(b0, b1);
                b0 = b1;
        }

        off_nl_nosnap += 4;
        off_nl += 4;
        label_stack_depth++;
        return (b0);
}

/*
 * Support PPPOE discovery and session.
 */
struct block *
gen_pppoed()
{
        /* check for PPPoE discovery */
        return gen_linktype((bpf_int32)ETHERTYPE_PPPOED);
}

struct block *
gen_pppoes()
{
        struct block *b0;

        /*
         * Test against the PPPoE session link-layer type.
         */
        b0 = gen_linktype((bpf_int32)ETHERTYPE_PPPOES);

        /*
         * Change the offsets to point to the type and data fields within
         * the PPP packet, and note that this is PPPoE rather than
         * raw PPP.
         *
         * XXX - this is a bit of a kludge.  If we were to split the
         * compiler into a parser that parses an expression and
         * generates an expression tree, and a code generator that
         * takes an expression tree (which could come from our
         * parser or from some other parser) and generates BPF code,
         * we could perhaps make the offsets parameters of routines
         * and, in the handler for an "AND" node, pass to subnodes
         * other than the PPPoE node the adjusted offsets.
         *
         * This would mean that "pppoes" would, instead of changing the
         * behavior of *all* tests after it, change only the behavior
         * of tests ANDed with it.  That would change the documented
         * semantics of "pppoes", which might break some expressions.
         * However, it would mean that "(pppoes and ip) or ip" would check
         * both for VLAN-encapsulated IP and IP-over-Ethernet, rather than
         * checking only for VLAN-encapsulated IP, so that could still
         * be considered worth doing; it wouldn't break expressions
         * that are of the form "pppoes and ..." which I suspect are the
         * most common expressions involving "pppoes".  "pppoes or ..."
         * doesn't necessarily do what the user would really want, now,
         * as all the "or ..." tests would be done assuming PPPoE, even
         * though the "or" could be viewed as meaning "or, if this isn't
         * a PPPoE packet...".
         */
        orig_linktype = off_linktype;   /* save original values */
        orig_nl = off_nl;
        is_pppoes = 1;

        /*
         * The "network-layer" protocol is PPPoE, which has a 6-byte
         * PPPoE header, followed by a PPP packet.
         *
         * There is no HDLC encapsulation for the PPP packet (it's
         * encapsulated in PPPoES instead), so the link-layer type
         * starts at the first byte of the PPP packet.  For PPPoE,
         * that offset is relative to the beginning of the total
         * link-layer payload, including any 802.2 LLC header, so
         * it's 6 bytes past off_nl.
         */
        off_linktype = off_nl + 6;

        /*
         * The network-layer offsets are relative to the beginning
         * of the MAC-layer payload; that's past the 6-byte
         * PPPoE header and the 2-byte PPP header.
         */
        off_nl = 6+2;
        off_nl_nosnap = 6+2;

        return b0;
}

struct block *
gen_atmfield_code(atmfield, jvalue, jtype, reverse)
        int atmfield;
        bpf_int32 jvalue;
        bpf_u_int32 jtype;
        int reverse;
{
        struct block *b0;

        switch (atmfield) {

        case A_VPI:
                if (!is_atm)
                        bpf_error("'vpi' supported only on raw ATM");
                if (off_vpi == (u_int)-1)
                        abort();
                b0 = gen_ncmp(OR_LINK, off_vpi, BPF_B, 0xffffffff, jtype,
                    reverse, jvalue);
                break;

        case A_VCI:
                if (!is_atm)
                        bpf_error("'vci' supported only on raw ATM");
                if (off_vci == (u_int)-1)
                        abort();
                b0 = gen_ncmp(OR_LINK, off_vci, BPF_H, 0xffffffff, jtype,
                    reverse, jvalue);
                break;

        case A_PROTOTYPE:
                if (off_proto == (u_int)-1)
                        abort();        /* XXX - this isn't on FreeBSD */
                b0 = gen_ncmp(OR_LINK, off_proto, BPF_B, 0x0f, jtype,
                    reverse, jvalue);
                break;

        case A_MSGTYPE:
                if (off_payload == (u_int)-1)
                        abort();
                b0 = gen_ncmp(OR_LINK, off_payload + MSG_TYPE_POS, BPF_B,
                    0xffffffff, jtype, reverse, jvalue);
                break;

        case A_CALLREFTYPE:
                if (!is_atm)
                        bpf_error("'callref' supported only on raw ATM");
                if (off_proto == (u_int)-1)
                        abort();
                b0 = gen_ncmp(OR_LINK, off_proto, BPF_B, 0xffffffff,
                    jtype, reverse, jvalue);
                break;

        default:
                abort();
        }
        return b0;
}

struct block *
gen_atmtype_abbrev(type)
        int type;
{
        struct block *b0, *b1;

        switch (type) {

        case A_METAC:
                /* Get all packets in Meta signalling Circuit */
                if (!is_atm)
                        bpf_error("'metac' supported only on raw ATM");
                b0 = gen_atmfield_code(A_VPI, 0, BPF_JEQ, 0);
                b1 = gen_atmfield_code(A_VCI, 1, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_BCC:
                /* Get all packets in Broadcast Circuit*/
                if (!is_atm)
                        bpf_error("'bcc' supported only on raw ATM");
                b0 = gen_atmfield_code(A_VPI, 0, BPF_JEQ, 0);
                b1 = gen_atmfield_code(A_VCI, 2, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_OAMF4SC:
                /* Get all cells in Segment OAM F4 circuit*/
                if (!is_atm)
                        bpf_error("'oam4sc' supported only on raw ATM");
                b0 = gen_atmfield_code(A_VPI, 0, BPF_JEQ, 0);
                b1 = gen_atmfield_code(A_VCI, 3, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_OAMF4EC:
                /* Get all cells in End-to-End OAM F4 Circuit*/
                if (!is_atm)
                        bpf_error("'oam4ec' supported only on raw ATM");
                b0 = gen_atmfield_code(A_VPI, 0, BPF_JEQ, 0);
                b1 = gen_atmfield_code(A_VCI, 4, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_SC:
                /*  Get all packets in connection Signalling Circuit */
                if (!is_atm)
                        bpf_error("'sc' supported only on raw ATM");
                b0 = gen_atmfield_code(A_VPI, 0, BPF_JEQ, 0);
                b1 = gen_atmfield_code(A_VCI, 5, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_ILMIC:
                /* Get all packets in ILMI Circuit */
                if (!is_atm)
                        bpf_error("'ilmic' supported only on raw ATM");
                b0 = gen_atmfield_code(A_VPI, 0, BPF_JEQ, 0);
                b1 = gen_atmfield_code(A_VCI, 16, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_LANE:
                /* Get all LANE packets */
                if (!is_atm)
                        bpf_error("'lane' supported only on raw ATM");
                b1 = gen_atmfield_code(A_PROTOTYPE, PT_LANE, BPF_JEQ, 0);

                /*
                 * Arrange that all subsequent tests assume LANE
                 * rather than LLC-encapsulated packets, and set
                 * the offsets appropriately for LANE-encapsulated
                 * Ethernet.
                 *
                 * "off_mac" is the offset of the Ethernet header,
                 * which is 2 bytes past the ATM pseudo-header
                 * (skipping the pseudo-header and 2-byte LE Client
                 * field).  The other offsets are Ethernet offsets
                 * relative to "off_mac".
                 */
                is_lane = 1;
                off_mac = off_payload + 2;      /* MAC header */
                off_linktype = off_mac + 12;
                off_macpl = off_mac + 14;       /* Ethernet */
                off_nl = 0;                     /* Ethernet II */
                off_nl_nosnap = 3;              /* 802.3+802.2 */
                break;

        case A_LLC:
                /* Get all LLC-encapsulated packets */
                if (!is_atm)
                        bpf_error("'llc' supported only on raw ATM");
                b1 = gen_atmfield_code(A_PROTOTYPE, PT_LLC, BPF_JEQ, 0);
                is_lane = 0;
                break;

        default:
                abort();
        }
        return b1;
}

/* 
 * Filtering for MTP2 messages based on li value
 * FISU, length is null
 * LSSU, length is 1 or 2
 * MSU, length is 3 or more
 */
struct block *
gen_mtp2type_abbrev(type)
        int type;
{
        struct block *b0, *b1;

        switch (type) {

        case M_FISU:
                if ( (linktype != DLT_MTP2) &&
                     (linktype != DLT_ERF) &&
                     (linktype != DLT_MTP2_WITH_PHDR) )
                        bpf_error("'fisu' supported only on MTP2");
                /* gen_ncmp(offrel, offset, size, mask, jtype, reverse, value) */
                b0 = gen_ncmp(OR_PACKET, off_li, BPF_B, 0x3f, BPF_JEQ, 0, 0);
                break;

        case M_LSSU:
                if ( (linktype != DLT_MTP2) &&
                     (linktype != DLT_ERF) &&
                     (linktype != DLT_MTP2_WITH_PHDR) )
                        bpf_error("'lssu' supported only on MTP2");
                b0 = gen_ncmp(OR_PACKET, off_li, BPF_B, 0x3f, BPF_JGT, 1, 2);
                b1 = gen_ncmp(OR_PACKET, off_li, BPF_B, 0x3f, BPF_JGT, 0, 0);
                gen_and(b1, b0);
                break;

        case M_MSU:
                if ( (linktype != DLT_MTP2) &&
                     (linktype != DLT_ERF) &&
                     (linktype != DLT_MTP2_WITH_PHDR) )
                        bpf_error("'msu' supported only on MTP2");
                b0 = gen_ncmp(OR_PACKET, off_li, BPF_B, 0x3f, BPF_JGT, 0, 2);
                break;

        default:
                abort();
        }
        return b0;
}

struct block *
gen_mtp3field_code(mtp3field, jvalue, jtype, reverse)
        int mtp3field;
        bpf_u_int32 jvalue;
        bpf_u_int32 jtype;
        int reverse;
{
        struct block *b0;
        bpf_u_int32 val1 , val2 , val3;

        switch (mtp3field) {

        case M_SIO:
                if (off_sio == (u_int)-1)
                        bpf_error("'sio' supported only on SS7");
                /* sio coded on 1 byte so max value 255 */
                if(jvalue > 255)
                        bpf_error("sio value %u too big; max value = 255",
                            jvalue);
                b0 = gen_ncmp(OR_PACKET, off_sio, BPF_B, 0xffffffff,
                    (u_int)jtype, reverse, (u_int)jvalue);
                break;

        case M_OPC:
                if (off_opc == (u_int)-1)
                        bpf_error("'opc' supported only on SS7");
                /* opc coded on 14 bits so max value 16383 */
                if (jvalue > 16383)
                        bpf_error("opc value %u too big; max value = 16383",
                            jvalue);
                /* the following instructions are made to convert jvalue
                 * to the form used to write opc in an ss7 message*/
                val1 = jvalue & 0x00003c00;
                val1 = val1 >>10;
                val2 = jvalue & 0x000003fc;
                val2 = val2 <<6;
                val3 = jvalue & 0x00000003;
                val3 = val3 <<22;
                jvalue = val1 + val2 + val3;
                b0 = gen_ncmp(OR_PACKET, off_opc, BPF_W, 0x00c0ff0f,
                    (u_int)jtype, reverse, (u_int)jvalue);
                break;

        case M_DPC:
                if (off_dpc == (u_int)-1)
                        bpf_error("'dpc' supported only on SS7");
                /* dpc coded on 14 bits so max value 16383 */
                if (jvalue > 16383)
                        bpf_error("dpc value %u too big; max value = 16383",
                            jvalue);
                /* the following instructions are made to convert jvalue
                 * to the forme used to write dpc in an ss7 message*/
                val1 = jvalue & 0x000000ff;
                val1 = val1 << 24;
                val2 = jvalue & 0x00003f00;
                val2 = val2 << 8;
                jvalue = val1 + val2;
                b0 = gen_ncmp(OR_PACKET, off_dpc, BPF_W, 0xff3f0000,
                    (u_int)jtype, reverse, (u_int)jvalue);
                break;

        case M_SLS:
                if (off_sls == (u_int)-1)
                        bpf_error("'sls' supported only on SS7");
                /* sls coded on 4 bits so max value 15 */
                if (jvalue > 15)
                         bpf_error("sls value %u too big; max value = 15",
                             jvalue);
                /* the following instruction is made to convert jvalue
                 * to the forme used to write sls in an ss7 message*/
                jvalue = jvalue << 4;
                b0 = gen_ncmp(OR_PACKET, off_sls, BPF_B, 0xf0,
                    (u_int)jtype,reverse, (u_int)jvalue);
                break;

        default:
                abort();
        }
        return b0;
}

static struct block *
gen_msg_abbrev(type)
        int type;
{
        struct block *b1;

        /*
         * Q.2931 signalling protocol messages for handling virtual circuits
         * establishment and teardown
         */
        switch (type) {

        case A_SETUP:
                b1 = gen_atmfield_code(A_MSGTYPE, SETUP, BPF_JEQ, 0);
                break;

        case A_CALLPROCEED:
                b1 = gen_atmfield_code(A_MSGTYPE, CALL_PROCEED, BPF_JEQ, 0);
                break;

        case A_CONNECT:
                b1 = gen_atmfield_code(A_MSGTYPE, CONNECT, BPF_JEQ, 0);
                break;

        case A_CONNECTACK:
                b1 = gen_atmfield_code(A_MSGTYPE, CONNECT_ACK, BPF_JEQ, 0);
                break;

        case A_RELEASE:
                b1 = gen_atmfield_code(A_MSGTYPE, RELEASE, BPF_JEQ, 0);
                break;

        case A_RELEASE_DONE:
                b1 = gen_atmfield_code(A_MSGTYPE, RELEASE_DONE, BPF_JEQ, 0);
                break;

        default:
                abort();
        }
        return b1;
}

struct block *
gen_atmmulti_abbrev(type)
        int type;
{
        struct block *b0, *b1;

        switch (type) {

        case A_OAM:
                if (!is_atm)
                        bpf_error("'oam' supported only on raw ATM");
                b1 = gen_atmmulti_abbrev(A_OAMF4);
                break;

        case A_OAMF4:
                if (!is_atm)
                        bpf_error("'oamf4' supported only on raw ATM");
                /* OAM F4 type */
                b0 = gen_atmfield_code(A_VCI, 3, BPF_JEQ, 0);
                b1 = gen_atmfield_code(A_VCI, 4, BPF_JEQ, 0);
                gen_or(b0, b1);
                b0 = gen_atmfield_code(A_VPI, 0, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_CONNECTMSG:
                /*
                 * Get Q.2931 signalling messages for switched
                 * virtual connection
                 */
                if (!is_atm)
                        bpf_error("'connectmsg' supported only on raw ATM");
                b0 = gen_msg_abbrev(A_SETUP);
                b1 = gen_msg_abbrev(A_CALLPROCEED);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(A_CONNECT);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(A_CONNECTACK);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(A_RELEASE);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(A_RELEASE_DONE);
                gen_or(b0, b1);
                b0 = gen_atmtype_abbrev(A_SC);
                gen_and(b0, b1);
                break;

        case A_METACONNECT:
                if (!is_atm)
                        bpf_error("'metaconnect' supported only on raw ATM");
                b0 = gen_msg_abbrev(A_SETUP);
                b1 = gen_msg_abbrev(A_CALLPROCEED);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(A_CONNECT);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(A_RELEASE);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(A_RELEASE_DONE);
                gen_or(b0, b1);
                b0 = gen_atmtype_abbrev(A_METAC);
                gen_and(b0, b1);
                break;

        default:
                abort();
        }
        return b1;
}