Add support for operations that test 802.11 SA or DA fields, and for

[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[] =
    "@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.176 2002-08-08 08:22:45 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>
#include <sys/time.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>

#include "pcap-int.h"

#include "ethertype.h"
#include "nlpid.h"
#include "llc.h"
#include "gencode.h"
#include "atmuni31.h"
#include "sunatmpos.h"
#include "ppp.h"
#include "sll.h"
#include "arcnet.h"
#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 offsets. */
static u_int    orig_linktype = -1, orig_nl = -1, orig_nl_nosnap = -1;

/* XXX */
#ifdef PCAP_FDDIPAD
int     pcap_fddipad = PCAP_FDDIPAD;
#else
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(int);

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

static struct block *root;

/*
 * 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 it this ever
 * goes into a library that would probably not be a good idea.
 */
#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(u_int, u_int, bpf_int32);
static struct block *gen_cmp_gt(u_int, u_int, bpf_int32);
static struct block *gen_mcmp(u_int, u_int, bpf_int32, bpf_u_int32);
static struct block *gen_bcmp(u_int, u_int, const u_char *);
static struct block *gen_ncmp(bpf_u_int32, bpf_u_int32, bpf_u_int32,
    bpf_u_int32, bpf_u_int32, int);
static struct block *gen_uncond(int);
static inline struct block *gen_true(void);
static inline struct block *gen_false(void);
static struct block *gen_linktype(int);
static struct block *gen_snap(bpf_u_int32, bpf_u_int32, u_int);
static struct block *gen_llc(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_dnhostop(bpf_u_int32, int, u_int);
static struct block *gen_host(bpf_u_int32, bpf_u_int32, int, int);
#ifdef INET6
static struct block *gen_host6(struct in6_addr *, struct in6_addr *, 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);
#ifdef INET6
static struct block *gen_portatom6(int, bpf_int32);
#endif
struct block *gen_portop(int, int, int);
static struct block *gen_port(int, int, int);
#ifdef INET6
struct block *gen_portop6(int, int, int);
static struct block *gen_port6(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_msg_abbrev(int type);

static void *
newchunk(n)
        u_int n;
{
        struct chunk *cp;
        int k, 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);
                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,
             char *buf, int optimize, bpf_u_int32 mask)
{
        extern int n_errors;
        int len;

        no_optimize = 0;
        n_errors = 0;
        root = NULL;
        bpf_pcap = p;
        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(buf ? buf : "");
        init_linktype(pcap_datalink(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,
             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;
{
        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(offset, size, v)
        u_int offset, size;
        bpf_int32 v;
{
        struct slist *s;
        struct block *b;

        s = new_stmt(BPF_LD|BPF_ABS|size);
        s->s.k = offset;

        b = new_block(JMP(BPF_JEQ));
        b->stmts = s;
        b->s.k = v;

        return b;
}

static struct block *
gen_cmp_gt(offset, size, v)
        u_int offset, size;
        bpf_int32 v;
{
        struct slist *s;
        struct block *b;

        s = new_stmt(BPF_LD|BPF_ABS|size);
        s->s.k = offset;

        b = new_block(JMP(BPF_JGT));
        b->stmts = s;
        b->s.k = v;

        return b;
}

static struct block *
gen_mcmp(offset, size, v, mask)
        u_int offset, size;
        bpf_int32 v;
        bpf_u_int32 mask;
{
        struct block *b = gen_cmp(offset, size, v);
        struct slist *s;

        if (mask != 0xffffffff) {
                s = new_stmt(BPF_ALU|BPF_AND|BPF_K);
                s->s.k = mask;
                b->stmts->next = s;
        }
        return b;
}

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

static struct block *
gen_ncmp(datasize, offset, mask, jtype, jvalue, reverse)
        bpf_u_int32 datasize, offset, mask, jtype, jvalue;
        int reverse;
{
        struct slist *s;
        struct block *b;
 
        s = new_stmt(BPF_LD|datasize|BPF_ABS);
        s->s.k = offset;
 
        if (mask != 0xffffffff) {
                s->next = new_stmt(BPF_ALU|BPF_AND|BPF_K);
                s->next->s.k = mask;
        }
 
        b = new_block(JMP(jtype));
        b->stmts = s;
        b->s.k = jvalue;
        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.
 */

/*
 * "off_linktype" is the offset to information in the link-layer header
 * giving the packet type.
 *
 * 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 the link layer includes an ATM pseudo-header.
 */
static int is_atm = 0;

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

/*
 * This is the offset to the message type for Q.2931 messages.
 */
static u_int off_msg_type;

/*
 * These are offsets to the beginning of the network-layer header.
 *
 * 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(type)
        int type;
{
        linktype = type;

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

        orig_linktype = -1;
        orig_nl = -1;
        orig_nl_nosnap = -1;

        switch (type) {

        case DLT_ARCNET:
                off_linktype = 2;
                off_nl = 6;     /* XXX in reality, variable! */
                off_nl_nosnap = 6;      /* no 802.2 LLC */
                return;

        case DLT_EN10MB:
                off_linktype = 12;
                off_nl = 14;            /* Ethernet II */
                off_nl_nosnap = 17;     /* 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_nl = 16;
                off_nl_nosnap = 16;     /* 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_nl = 24;
                off_nl_nosnap = 24;     /* no 802.2 LLC */
                return;

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

        case DLT_PPP:
        case DLT_C_HDLC:                /* BSD/OS Cisco HDLC */
        case DLT_PPP_SERIAL:            /* NetBSD sync/async serial PPP */
                off_linktype = 2;
                off_nl = 4;
                off_nl_nosnap = 4;      /* 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_nl = 8;
                off_nl_nosnap = 8;      /* no 802.2 LLC */
                return;

        case DLT_PPP_BSDOS:
                off_linktype = 5;
                off_nl = 24;
                off_nl_nosnap = 24;     /* 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_nl = 21;            /* FDDI+802.2+SNAP */
                off_nl_nosnap = 16;     /* FDDI+802.2 */
#ifdef PCAP_FDDIPAD
                off_nl += pcap_fddipad;
                off_nl_nosnap += pcap_fddipad;
#endif
                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_nl = 22;            /* Token Ring+802.2+SNAP */
                off_nl_nosnap = 17;     /* Token Ring+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.
                 */
                off_linktype = 24;
                off_nl = 32;            /* 802.11+802.2+SNAP */
                off_nl_nosnap = 27;     /* 802.11+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_linktype = 144+24;
                off_nl = 144+32;        /* Prism+802.11+802.2+SNAP */
                off_nl_nosnap = 144+27; /* Prism+802.11+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)
                 */
                off_linktype = 0;
                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_linktype = SUNATM_PKT_BEGIN_POS;
                off_vpi = SUNATM_VPI_POS;
                off_vci = SUNATM_VCI_POS;
                off_proto = PROTO_POS;
                off_msg_type = SUNATM_PKT_BEGIN_POS+MSG_TYPE_POS;
                off_nl = SUNATM_PKT_BEGIN_POS+8;        /* 802.2+SNAP */
                off_nl_nosnap = SUNATM_PKT_BEGIN_POS+3; /* 802.2 */
                return;

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

        case DLT_FRELAY:
                /*
                 * XXX - we should set this to handle SNAP-encapsulated
                 * frames (NLPID of 0x80).
                 */
                off_linktype = -1;
                off_nl = 0;
                off_nl_nosnap = 0;      /* no 802.2 LLC */
                return;
        }
        bpf_error("unknown data link type %d", linktype);
        /* NOTREACHED */
}

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))

static struct block *
gen_linktype(proto)
        register int proto;
{
        struct block *b0, *b1, *b2;

        switch (linktype) {

        case DLT_EN10MB:
                switch (proto) {

                case LLCSAP_ISONS:
                        /*
                         * OSI protocols always use 802.2 encapsulation.
                         * XXX - should we check both the DSAP and the
                         * SSAP, like this, or should we check just the
                         * DSAP?
                         */
                        b0 = gen_cmp_gt(off_linktype, BPF_H, ETHERMTU);
                        gen_not(b0);
                        b1 = gen_cmp(off_linktype + 2, BPF_H, (bpf_int32)
                                     ((LLCSAP_ISONS << 8) | LLCSAP_ISONS));
                        gen_and(b0, b1);
                        return b1;

                case LLCSAP_NETBEUI:
                        /*
                         * NetBEUI always uses 802.2 encapsulation.
                         * XXX - should we check both the DSAP and the
                         * SSAP, like this, or should we check just the
                         * DSAP?
                         */
                        b0 = gen_cmp_gt(off_linktype, BPF_H, ETHERMTU);
                        gen_not(b0);
                        b1 = gen_cmp(off_linktype + 2, BPF_H, (bpf_int32)
                                     ((LLCSAP_NETBEUI << 8) | LLCSAP_NETBEUI));
                        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(off_linktype + 2, BPF_B,
                            (bpf_int32)LLCSAP_IPX);
                        b1 = gen_cmp(off_linktype + 2, 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, 14);
                        gen_or(b0, b1);

                        /*
                         * Now we generate code to check for 802.3
                         * frames in general.
                         */
                        b0 = gen_cmp_gt(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(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(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, 14);
                        else    /* proto == ETHERTYPE_AARP */
                                b1 = gen_snap(0x000000, ETHERTYPE_AARP, 14);
                        gen_and(b0, b1);

                        /*
                         * Check for Ethernet encapsulation (Ethertalk
                         * phase 1?); we just check for the Ethernet
                         * protocol type.
                         */
                        b0 = gen_cmp(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(off_linktype, BPF_H, ETHERMTU);
                                gen_not(b0);
                                b1 = gen_cmp(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(off_linktype, BPF_H,
                                    (bpf_int32)proto);
                        }
                }
                break;

        case DLT_IEEE802_11:
        case DLT_PRISM_HEADER:
        case DLT_FDDI:
        case DLT_IEEE802:
        case DLT_ATM_RFC1483:
        case DLT_ATM_CLIP:
                return gen_llc(proto);
                break;

        case DLT_SUNATM:
                /*
                 * Check for LLC encapsulation and then check the protocol.
                 * XXX - also check for LANE and then check for an Ethernet
                 * type?
                 */
                b0 = gen_atmfield_code(A_PROTOTYPE, PT_LLC, BPF_JEQ, 0);
                b1 = gen_llc(proto);
                gen_and(b0, b1);
                return b1;

        case DLT_LINUX_SLL:
                switch (proto) {

                case LLCSAP_ISONS:
                        /*
                         * OSI protocols always use 802.2 encapsulation.
                         * XXX - should we check both the DSAP and the
                         * LSAP, like this, or should we check just the
                         * DSAP?
                         */
                        b0 = gen_cmp(off_linktype, BPF_H, LINUX_SLL_P_802_2);
                        b1 = gen_cmp(off_linktype + 2, BPF_H, (bpf_int32)
                                     ((LLCSAP_ISONS << 8) | LLCSAP_ISONS));
                        gen_and(b0, b1);
                        return b1;

                case LLCSAP_NETBEUI:
                        /*
                         * NetBEUI always uses 802.2 encapsulation.
                         * XXX - should we check both the DSAP and the
                         * LSAP, like this, or should we check just the
                         * DSAP?
                         */
                        b0 = gen_cmp(off_linktype, BPF_H, LINUX_SLL_P_802_2);
                        b1 = gen_cmp(off_linktype + 2, BPF_H, (bpf_int32)
                                     ((LLCSAP_NETBEUI << 8) | LLCSAP_NETBEUI));
                        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(off_linktype + 2, BPF_B,
                            (bpf_int32)LLCSAP_IPX);
                        b1 = gen_snap(0x000000, ETHERTYPE_IPX,
                            off_linktype + 2);
                        gen_or(b0, b1);
                        b0 = gen_cmp(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(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(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(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,
                                    off_linktype + 2);
                        else    /* proto == ETHERTYPE_AARP */
                                b1 = gen_snap(0x000000, ETHERTYPE_AARP,
                                    off_linktype + 2);
                        gen_and(b0, b1);

                        /*
                         * Check for Ethernet encapsulation (Ethertalk
                         * phase 1?); we just check for the Ethernet
                         * protocol type.
                         */
                        b0 = gen_cmp(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(off_linktype, BPF_H,
                                    LINUX_SLL_P_802_2);
                                b1 = gen_cmp(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(off_linktype, BPF_H,
                                    (bpf_int32)proto);
                        }
                }
                break;

        case DLT_SLIP:
        case DLT_SLIP_BSDOS:
        case DLT_RAW:
                /*
                 * These types don't provide any type field; packets
                 * are always IP.
                 *
                 * 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:
#ifdef INET6
                case ETHERTYPE_IPV6:
#endif
                        return gen_true();              /* always true */

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

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

                case ETHERTYPE_IP:
                        proto = PPP_IP;                 /* XXX was 0x21 */
                        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;
                }
                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:
                        b0 = gen_cmp(off_linktype, BPF_H, PPP_IP);
                        b1 = gen_cmp(off_linktype, BPF_H, PPP_VJC);
                        gen_or(b0, b1);
                        b0 = gen_cmp(off_linktype, BPF_H, PPP_VJNC);
                        gen_or(b1, b0);
                        return b0;

#ifdef INET6
                case ETHERTYPE_IPV6:
                        proto = PPP_IPV6;
                        /* more to go? */
                        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;
                }
                break;

        case DLT_NULL:
        case DLT_LOOP:
                /*
                 * For DLT_NULL, the link-layer header is a 32-bit
                 * word 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) {
                        /*
                         * 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(0, BPF_W, (bpf_int32)proto));

        case DLT_ARCNET:
                /*
                 * 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(2, BPF_B,
                                        (bpf_int32)htonl(ARCTYPE_INET6)));
#endif /* INET6 */
                case ETHERTYPE_IP:
                        b0 = gen_cmp(2, BPF_B, (bpf_int32)htonl(ARCTYPE_IP));
                        b1 = gen_cmp(2, BPF_B,
                                        (bpf_int32)htonl(ARCTYPE_IP_OLD));
                        gen_or(b0, b1);
                        return(b1);
                case ETHERTYPE_ARP:
                        b0 = gen_cmp(2, BPF_B, (bpf_int32)htonl(ARCTYPE_ARP));
                        b1 = gen_cmp(2, BPF_B,
                                        (bpf_int32)htonl(ARCTYPE_ARP_OLD));
                        gen_or(b0, b1);
                        return(b1);
                case ETHERTYPE_REVARP:
                        return(gen_cmp(2, BPF_B,
                                        (bpf_int32)htonl(ARCTYPE_REVARP)));
                case ETHERTYPE_ATALK:
                        return(gen_cmp(2, BPF_B,
                                        (bpf_int32)htonl(ARCTYPE_ATALK)));
                }
                break;

        case DLT_LTALK:
                switch (proto) {
                case ETHERTYPE_ATALK:
                        return gen_true();
                default:
                        return gen_false();
                }
                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(2, BPF_H, (0x03<<8) | 0xcc);

#ifdef INET6
                case ETHERTYPE_IPV6:
                        /*
                         * Check for the special NLPID for IPv6.
                         */
                        return gen_cmp(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(2, BPF_H, (0x03<<8) | ISO8473_CLNP);
                        b1 = gen_cmp(2, BPF_H, (0x03<<8) | ISO9542_ESIS);
                        b2 = gen_cmp(2, BPF_H, (0x03<<8) | ISO10589_ISIS);
                        gen_or(b1, b2);
                        gen_or(b0, b2);
                        return b2;

                default:
                        return gen_false();
                }
                break;
        }

        /*
         * 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 == -1)
                abort();

        /*
         * Any type not handled above should always have an Ethernet
         * type at an offset of "off_linktype".  (PPP is partially
         * handled above - the protocol type is mapped from the
         * Ethernet and LLC types we use internally to the corresponding
         * PPP type - but the PPP type is always specified by a value
         * at "off_linktype", so we don't have to do the code generation
         * above.)
         */
        return gen_cmp(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, offset)
        bpf_u_int32 orgcode;
        bpf_u_int32 ptype;
        u_int offset;
{
        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(offset, 8, snapblock);
}

/*
 * Check for a given protocol value assuming an 802.2 LLC header.
 */
static struct block *
gen_llc(proto)
        int proto;
{
        /*
         * XXX - handle token-ring variable-length header.
         */
        switch (proto) {

        case LLCSAP_ISONS:
                return gen_cmp(off_linktype, BPF_H, (long)
                             ((LLCSAP_ISONS << 8) | LLCSAP_ISONS));

        case LLCSAP_NETBEUI:
                return gen_cmp(off_linktype, BPF_H, (long)
                             ((LLCSAP_NETBEUI << 8) | LLCSAP_NETBEUI));

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

        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(off_linktype, 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,
                         *          off_linktype);
                         *
                         * 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(off_linktype+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(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(offset + 12, BPF_W, ntohl(a[3]), ntohl(m[3]));
        b0 = gen_mcmp(offset + 8, BPF_W, ntohl(a[2]), ntohl(m[2]));
        gen_and(b0, b1);
        b0 = gen_mcmp(offset + 4, BPF_W, ntohl(a[1]), ntohl(m[1]));
        gen_and(b0, b1);
        b0 = gen_mcmp(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(6, 6, eaddr);

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

        case Q_DST:
#ifdef PCAP_FDDIPAD
                return gen_bcmp(0 + 1 + pcap_fddipad, 6, eaddr);
#else
                return gen_bcmp(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(8, 6, eaddr);

        case Q_DST:
                return gen_bcmp(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)
 */
static struct block *
gen_wlanhostop(eaddr, dir)
        register const u_char *eaddr;
        register int dir;
{
        register struct block *b0, *b1, *b2, *b3;
        register struct slist *s;

        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.
                 */

                /*
                 * 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., first check "!(link[0] & 0x04)".
                 */
                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 0;
                b0 = new_block(JMP(BPF_JSET));
                b0->s.k = 0x04;
                b0->stmts = s;
                gen_not(b0);

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

                /*
                 * For management frames, test the SA at 10.
                 */
                b1 = gen_bcmp(10, 6, eaddr);
                gen_and(b2, b1);
                b3 = b1;

                /*
                 * If the high-order bit of the type value is 0, this
                 * is a data frame; check From DS.
                 *
                 * I.e., check "(link[0] & 0x08) && !(link[1] & 0x02)".
                 */
                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 0;
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x08;
                b1->stmts = s;

                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 1;
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x02; /* From DS */
                b2->stmts = s;
                gen_not(b2);
                gen_and(b1, b2);

                /*
                 * For data frames with From DS not set, test the SA at 10;
                 * then combine that test with the management frame test.
                 */
                b1 = gen_bcmp(10, 6, eaddr);
                gen_and(b2, b1);
                gen_or(b3, b1);
                b3 = b1;

                /*
                 * Now, check for a data frame with From DS set and
                 * To DS not set.
                 *
                 * I.e., check "(link[0] & 0x08) && (link[1] & 0x02)
                 * && !(link[1] & 0x01)".
                 */
                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 0;
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x08;
                b1->stmts = s;

                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 1;
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x02; /* From DS */
                b2->stmts = s;
                gen_and(b1, b2);
                b1 = b2;

                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 1;
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x01; /* To DS */
                b2->stmts = s;
                gen_not(b2);
                gen_and(b1, b2);        /* Data && From DS and not To DS */

                /*
                 * Test the SA at 16, and OR the previous SA tests
                 * with it.
                 */
                b1 = gen_bcmp(16, 6, eaddr);
                gen_and(b2, b1);
                gen_or(b3, b1);
                b3 = b1;

                /*
                 * And now for a data frame with From DS set and To DS set.
                 */
                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 0;
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x08;
                b1->stmts = s;

                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 1;
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x02; /* From DS */
                b2->stmts = s;
                gen_and(b1, b2);
                b1 = b2;

                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 1;
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x01; /* To DS */
                b2->stmts = s;
                gen_and(b1, b2);        /* Data && From DS and To DS */

                /*
                 * Test the SA at 24, and OR the previous SA tests
                 * with it.
                 */
                b1 = gen_bcmp(24, 6, eaddr);
                gen_and(b2, b1);
                gen_or(b3, b1);

                gen_and(b0, b1);
                return b1;

        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.
                 */

                /*
                 * 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 a DA.
                 *
                 * I.e., first check "!(link[0] & 0x04)".
                 */
                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 0;
                b0 = new_block(JMP(BPF_JSET));
                b0->s.k = 0x04;
                b0->stmts = s;
                gen_not(b0);

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

                /*
                 * For management frames, test the DA at 4.
                 */
                b1 = gen_bcmp(4, 6, eaddr);
                gen_and(b2, b1);
                b3 = b1;

                /*
                 * If the high-order bit of the type value is 0, this
                 * is a data frame; check To DS.
                 *
                 * I.e., check "(link[0] & 0x08) && !(link[1] & 0x01)".
                 */
                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 0;
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x08;
                b1->stmts = s;

                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 1;
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x01; /* To DS */
                b2->stmts = s;
                gen_not(b2);
                gen_and(b1, b2);

                /*
                 * For data frames with To DS not set, test the DA at 4;
                 * then combine that test with the management frame test.
                 */
                b1 = gen_bcmp(4, 6, eaddr);
                gen_and(b2, b1);
                gen_or(b3, b1);
                b3 = b1;

                /*
                 * Now, check for a data frame with To DS set.
                 *
                 * I.e., check "(link[0] & 0x08) && (link[1] & 0x01)".
                 */
                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 0;
                b1 = new_block(JMP(BPF_JSET));
                b1->s.k = 0x08;
                b1->stmts = s;

                s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                s->s.k = 1;
                b2 = new_block(JMP(BPF_JSET));
                b2->s.k = 0x01; /* To DS */
                b2->stmts = s;
                gen_and(b1, b2);

                /*
                 * Test the DA at 16, and OR the previous DA tests
                 * with it.
                 */
                b1 = gen_bcmp(16, 6, eaddr);
                gen_and(b2, b1);
                gen_or(b3, b1);

                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 */
}

/*
 * 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, base_off)
        bpf_u_int32 addr;
        int dir;
        u_int base_off;
{
        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, base_off);
                b1 = gen_dnhostop(addr, Q_DST, base_off);
                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, base_off);
                b1 = gen_dnhostop(addr, Q_DST, base_off);
                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(base_off + 2, BPF_H,
            (bpf_int32)ntohs(0x0681), (bpf_int32)ntohs(0x07FF));
        b1 = gen_cmp(base_off + 2 + 1 + offset_lh,
            BPF_H, (bpf_int32)ntohs(addr));
        gen_and(tmp, b1);
        /* Check for pad = 0, long header case */
        tmp = gen_mcmp(base_off + 2, BPF_B, (bpf_int32)0x06, (bpf_int32)0x7);
        b2 = gen_cmp(base_off + 2 + offset_lh, BPF_H, (bpf_int32)ntohs(addr));
        gen_and(tmp, b2);
        gen_or(b2, b1);
        /* Check for pad = 1, short header case */
        tmp = gen_mcmp(base_off + 2, BPF_H,
            (bpf_int32)ntohs(0x0281), (bpf_int32)ntohs(0x07FF));
        b2 = gen_cmp(base_off + 2 + 1 + offset_sh,
            BPF_H, (bpf_int32)ntohs(addr));
        gen_and(tmp, b2);
        gen_or(b2, b1);
        /* Check for pad = 0, short header case */
        tmp = gen_mcmp(base_off + 2, BPF_B, (bpf_int32)0x02, (bpf_int32)0x7);
        b2 = gen_cmp(base_off + 2 + offset_sh, BPF_H, (bpf_int32)ntohs(addr));
        gen_and(tmp, b2);
        gen_or(b2, b1);

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

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

        switch (proto) {

        case Q_DEFAULT:
                b0 = gen_host(addr, mask, Q_IP, dir);
                if (off_linktype != -1) {
                    b1 = gen_host(addr, mask, Q_ARP, dir);
                    gen_or(b0, b1);
                    b0 = gen_host(addr, mask, Q_RARP, dir);
                    gen_or(b1, b0);
                }
                return b0;

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

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

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

        case Q_TCP:
                bpf_error("'tcp' modifier applied to host");

        case Q_SCTP:
                bpf_error("'sctp' modifier applied to host");

        case Q_UDP:
                bpf_error("'udp' modifier applied to host");

        case Q_ICMP:
                bpf_error("'icmp' modifier applied to host");

        case Q_IGMP:
                bpf_error("'igmp' modifier applied to host");

        case Q_IGRP:
                bpf_error("'igrp' modifier applied to host");

        case Q_PIM:
                bpf_error("'pim' modifier applied to host");

        case Q_VRRP:
                bpf_error("'vrrp' modifier applied to host");

        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, off_nl);

        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 host");
#endif /* INET6 */

        case Q_AH:
                bpf_error("'ah' modifier applied to host");

        case Q_ESP:
                bpf_error("'esp' modifier applied to host");

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

        case Q_ESIS:
                bpf_error("'esis' modifier applied to host");

        case Q_ISIS:
                bpf_error("'isis' modifier applied to host");

        case Q_CLNP:
                bpf_error("'clnp' modifier applied to host");

        case Q_STP:
                bpf_error("'stp' modifier applied to host");

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

        case Q_NETBEUI:
                bpf_error("'netbeui' modifier applied to host");

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

#ifdef INET6
static struct block *
gen_host6(addr, mask, proto, dir)
        struct in6_addr *addr;
        struct in6_addr *mask;
        int proto;
        int dir;
{
        switch (proto) {

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

        case Q_IP:
                bpf_error("'ip' modifier applied to ip6 host");

        case Q_RARP:
                bpf_error("'rarp' modifier applied to ip6 host");

        case Q_ARP:
                bpf_error("'arp' modifier applied to ip6 host");

        case Q_SCTP:
                bpf_error("'sctp' modifier applied to host");

        case Q_TCP:
                bpf_error("'tcp' modifier applied to host");

        case Q_UDP:
                bpf_error("'udp' modifier applied to host");

        case Q_ICMP:
                bpf_error("'icmp' modifier applied to host");

        case Q_IGMP:
                bpf_error("'igmp' modifier applied to host");

        case Q_IGRP:
                bpf_error("'igrp' modifier applied to host");

        case Q_PIM:
                bpf_error("'pim' modifier applied to host");

        case Q_VRRP:
                bpf_error("'vrrp' modifier applied to host");

        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 host");

        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,
                                  off_nl + 8, off_nl + 24);

        case Q_ICMPV6:
                bpf_error("'icmp6' modifier applied to host");

        case Q_AH:
                bpf_error("'ah' modifier applied to host");

        case Q_ESP:
                bpf_error("'esp' modifier applied to host");

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

        case Q_ESIS:
                bpf_error("'esis' modifier applied to host");

        case Q_ISIS:
                bpf_error("'isis' modifier applied to host");

        case Q_CLNP:
                bpf_error("'clnp' modifier applied to host");

        case Q_STP:
                bpf_error("'stp' modifier applied to host");

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

        case Q_NETBEUI:
                bpf_error("'netbeui' modifier applied to host");

        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:
                if (linktype == DLT_EN10MB)
                        b0 = gen_ehostop(eaddr, Q_OR);
                else if (linktype == DLT_FDDI)
                        b0 = gen_fhostop(eaddr, Q_OR);
                else if (linktype == DLT_IEEE802)
                        b0 = gen_thostop(eaddr, Q_OR);
                else if (linktype == DLT_IEEE802_11)
                        b0 = gen_wlanhostop(eaddr, Q_OR);
                else
                        bpf_error(
                            "'gateway' supported only on ethernet/FDDI/token ring/802.11");

                b1 = gen_host(**alist++, 0xffffffff, proto, Q_OR);
                while (*alist) {
                        tmp = gen_host(**alist++, 0xffffffff, proto, Q_OR);
                        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;
{
#ifdef INET6
        struct block *b0;
#endif
        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_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;

        default:
                abort();
        }
        return b1;
}

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

        /* not ip frag */
        s = new_stmt(BPF_LD|BPF_H|BPF_ABS);
        s->s.k = off_nl + 6;
        b = new_block(JMP(BPF_JSET));
        b->s.k = 0x1fff;
        b->stmts = s;
        gen_not(b);

        return b;
}

static struct block *
gen_portatom(off, v)
        int off;
        bpf_int32 v;
{
        struct slist *s;
        struct block *b;

        s = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
        s->s.k = off_nl;

        s->next = new_stmt(BPF_LD|BPF_IND|BPF_H);
        s->next->s.k = off_nl + off;

        b = new_block(JMP(BPF_JEQ));
        b->stmts = s;
        b->s.k = v;

        return b;
}

#ifdef INET6
static struct block *
gen_portatom6(off, v)
        int off;
        bpf_int32 v;
{
        return gen_cmp(off_nl + 40 + 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(off_nl + 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 */
        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;

        /* ip proto 'proto' */
        b0 = gen_cmp(off_nl + 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;

        /* ether proto ip */
        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 */

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)
                        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*/
        }

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

        /*
         * s[0] is a dummy entry to protect other BPF insn from damaged
         * 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_nl + 9;
                i++;
                /* X = ip->ip_hl << 2 */
                s[i] = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
                s[i]->s.k = 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_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_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_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_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_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_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:
                b0 = gen_linktype(ETHERTYPE_IP);
#ifndef CHASE_CHAIN
                b1 = gen_cmp(off_nl + 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(2, BPF_H, (0x03<<8) | v);
                        break;

                default:
                        b0 = gen_linktype(LLCSAP_ISONS);
                        b1 = gen_cmp(off_nl_nosnap, 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(off_nl + 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");

        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 *sin;
        struct sockaddr_in6 *sin6;
        struct addrinfo *res, *res0;
        struct in6_addr mask128;
#endif /*INET6*/
        struct block *b, *tmp;
        int port, real_proto;

        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);

        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:
                                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;

                        default:
                                bpf_error(
                        "only ethernet/FDDI/token ring/802.11 supports link-level host name");
                                break;
                        }
                } 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));
                } else {
#ifndef INET6
                        alist = pcap_nametoaddr(name);
                        if (alist == NULL || *alist == NULL)
                                bpf_error("unknown host '%s'", name);
                        tproto = proto;
                        if (off_linktype == -1 && tproto == Q_DEFAULT)
                                tproto = Q_IP;
                        b = gen_host(**alist++, 0xffffffff, tproto, dir);
                        while (*alist) {
                                tmp = gen_host(**alist++, 0xffffffff,
                                               tproto, dir);
                                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;

                                        sin = (struct sockaddr_in *)
                                                res->ai_addr;
                                        tmp = gen_host(ntohl(sin->sin_addr.s_addr),
                                                0xffffffff, tproto, dir);
                                        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);
                                        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
            {
                struct block *b;
                b = gen_port(port, real_proto, dir);
                gen_or(gen_port6(port, 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");
                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);

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

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);
                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);
                }

        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_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);
                freeaddrinfo(res);
                return b;

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

struct block *
gen_ecode(eaddr, q)
        register const u_char *eaddr;
        struct qual q;
{
        if ((q.addr == Q_HOST || q.addr == Q_DEFAULT) && q.proto == Q_LINK) {
                if (linktype == DLT_EN10MB)
                        return gen_ehostop(eaddr, (int)q.dir);
                if (linktype == DLT_FDDI)
                        return gen_fhostop(eaddr, (int)q.dir);
                if (linktype == DLT_IEEE802)
                        return gen_thostop(eaddr, (int)q.dir);
                if (linktype == DLT_IEEE802_11)
                        return gen_wlanhostop(eaddr, (int)q.dir);
                bpf_error("ethernet addresses supported only on ethernet/FDDI/token ring/802.11");
        }
        bpf_error("ethernet address used in non-ether expression");
        /* NOTREACHED */
}

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;
}

struct arth *
gen_load(proto, index, size)
        int proto;
        struct arth *index;
        int size;
{
        struct slist *s, *tmp;
        struct block *b;
        int regno = alloc_reg();

        free_reg(index->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_LINK:
                s = xfer_to_x(index);
                tmp = new_stmt(BPF_LD|BPF_IND|size);
                sappend(s, tmp);
                sappend(index->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
                /* XXX Note that we assume a fixed link header here. */
                s = xfer_to_x(index);
                tmp = new_stmt(BPF_LD|BPF_IND|size);
                tmp->s.k = off_nl;
                sappend(s, tmp);
                sappend(index->s, s);

                b = gen_proto_abbrev(proto);
                if (index->b)
                        gen_and(index->b, b);
                index->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:
                s = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
                s->s.k = off_nl;
                sappend(s, xfer_to_a(index));
                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_nl;
                sappend(index->s, s);

                gen_and(gen_proto_abbrev(proto), b = gen_ipfrag());
                if (index->b)
                        gen_and(index->b, b);
#ifdef INET6
                gen_and(gen_proto_abbrev(Q_IP), b);
#endif
                index->b = b;
                break;
#ifdef INET6
        case Q_ICMPV6:
                bpf_error("IPv6 upper-layer protocol is not supported by proto[x]");
                /*NOTREACHED*/
#endif
        }
        index->regno = regno;
        s = new_stmt(BPF_ST);
        s->s.k = regno;
        sappend(index->s, s);

        return index;
}

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;

/*
 * 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 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;
}

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((u_int)idx, BPF_B, (bpf_int32)val);

        case '<':
                b = gen_cmp((u_int)idx, BPF_B, (bpf_int32)val);
                b->s.code = JMP(BPF_JGE);
                gen_not(b);
                return b;

        case '>':
                b = gen_cmp((u_int)idx, BPF_B, (bpf_int32)val);
                b->s.code = JMP(BPF_JGT);
                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:
                if (linktype == DLT_ARCNET)
                        return gen_ahostop(abroadcast, Q_DST);
                if (linktype == DLT_EN10MB)
                        return gen_ehostop(ebroadcast, Q_DST);
                if (linktype == DLT_FDDI)
                        return gen_fhostop(ebroadcast, Q_DST);
                if (linktype == DLT_IEEE802)
                        return gen_thostop(ebroadcast, Q_DST);
                if (linktype == DLT_IEEE802_11)
                        return gen_wlanhostop(ebroadcast, Q_DST);
                bpf_error("not a broadcast link");
                break;

        case Q_IP:
                b0 = gen_linktype(ETHERTYPE_IP);
                hostmask = ~netmask;
                b1 = gen_mcmp(off_nl + 16, BPF_W, (bpf_int32)0, hostmask);
                b2 = gen_mcmp(off_nl + 16, BPF_W,
                              (bpf_int32)(~0 & hostmask), hostmask);
                gen_or(b1, b2);
                gen_and(b0, b2);
                return b2;
        }
        bpf_error("only ether/ip broadcast filters supported");
}

/*
 * 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 = new_stmt(BPF_LD|BPF_B|BPF_ABS);
        s->s.k = offset;
        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, *b3;
        register struct slist *s;

        switch (proto) {

        case Q_DEFAULT:
        case Q_LINK:
                if (linktype == DLT_ARCNET)
                        /* all ARCnet multicasts use the same address */
                        return gen_ahostop(abroadcast, Q_DST);

                if (linktype == DLT_EN10MB) {
                        /* ether[0] & 1 != 0 */
                        return gen_mac_multicast(0);
                }

                if (linktype == DLT_FDDI) {
                        /* XXX TEST THIS: MIGHT NOT PORT PROPERLY XXX */
                        /* fddi[1] & 1 != 0 */
                        return gen_mac_multicast(1);
                }

                /* TODO - check how token ring handles multicast */
                /* if (linktype == DLT_IEEE802) ... */

                if (linktype == DLT_IEEE802_11) {
                        /*
                         * 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.
                         */

                        /*
                         * 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 a DA.
                         *
                         * I.e., first check "!(link[0] & 0x04)".
                         */
                        s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                        s->s.k = 0;
                        b0 = new_block(JMP(BPF_JSET));
                        b0->s.k = 0x04;
                        b0->stmts = s;
                        gen_not(b0);

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

                        /*
                         * For management frames, test the DA at 4.
                         */
                        b1 = gen_mac_multicast(4);
                        gen_and(b2, b1);
                        b3 = b1;

                        /*
                         * If the high-order bit of the type value is 0,
                         * this is a data frame; check To DS.
                         *
                         * I.e., check "(link[0] & 0x08) && !(link[1] & 0x01)".
                         */
                        s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                        s->s.k = 0;
                        b1 = new_block(JMP(BPF_JSET));
                        b1->s.k = 0x08;
                        b1->stmts = s;

                        s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                        s->s.k = 1;
                        b2 = new_block(JMP(BPF_JSET));
                        b2->s.k = 0x01; /* To DS */
                        b2->stmts = s;
                        gen_not(b2);
                        gen_and(b1, b2);

                        /*
                         * For data frames with To DS not set, test the DA
                         * at 4; then combine that test with the management
                         * frame test.
                         */
                        b1 = gen_mac_multicast(4);
                        gen_and(b2, b1);
                        gen_or(b3, b1);
                        b3 = b1;

                        /*
                         * Now, check for a data frame with To DS set.
                         *
                         * I.e., check "(link[0] & 0x08) && (link[1] & 0x01)".
                         */
                        s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                        s->s.k = 0;
                        b1 = new_block(JMP(BPF_JSET));
                        b1->s.k = 0x08;
                        b1->stmts = s;

                        s = new_stmt(BPF_LD|BPF_B|BPF_ABS);
                        s->s.k = 1;
                        b2 = new_block(JMP(BPF_JSET));
                        b2->s.k = 0x01; /* To DS */
                        b2->stmts = s;
                        gen_and(b1, b2);

                        /*
                         * Test the DA at 16, and OR the previous DA tests
                         * with it.
                         */
                        b1 = gen_mac_multicast(16);
                        gen_and(b2, b1);
                        gen_or(b3, b1);

                        gen_and(b0, b1);
                        return b1;
                }

                /* Link not known to support multicasts */
                break;

        case Q_IP:
                b0 = gen_linktype(ETHERTYPE_IP);
                b1 = gen_cmp(off_nl + 16, BPF_B, (bpf_int32)224);
                b1->s.code = JMP(BPF_JGE);
                gen_and(b0, b1);
                return b1;

#ifdef INET6
        case Q_IPV6:
                b0 = gen_linktype(ETHERTYPE_IPV6);
                b1 = gen_cmp(off_nl + 24, BPF_B, (bpf_int32)255);
                gen_and(b0, b1);
                return b1;
#endif /* INET6 */
        }
        bpf_error("only IP multicast filters supported on ethernet/FDDI");
}

/*
 * 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:
        case DLT_PPP:
                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(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(0, BPF_H, LINUX_SLL_HOST);
                }
                break;

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

struct block *
gen_acode(eaddr, q)
        register const u_char *eaddr;
        struct qual q;
{
        if ((q.addr == Q_HOST || q.addr == Q_DEFAULT) && q.proto == Q_LINK) {
                if (linktype == DLT_ARCNET)
                        return gen_ahostop(eaddr, (int)q.dir);
        }
        bpf_error("ARCnet address used in non-arc expression");
        /* NOTREACHED */
}

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(0, 1, eaddr);

        case Q_DST:
                return gen_bcmp(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;

        /*
         * Change the offsets to point to the type and data fields within
         * the VLAN packet.  This is somewhat of a kludge.
         */
        if (orig_nl == (u_int)-1) {
                orig_linktype = off_linktype;   /* save original values */
                orig_nl = off_nl;
                orig_nl_nosnap = off_nl_nosnap;

                switch (linktype) {

                case DLT_EN10MB:
                        off_linktype = 16;
                        off_nl_nosnap = 18;
                        off_nl = 18;
                        break;

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

        /* check for VLAN */
        b0 = gen_cmp(orig_linktype, BPF_H, (bpf_int32)ETHERTYPE_8021Q);

        /* If a specific VLAN is requested, check VLAN id */
        if (vlan_num >= 0) {
                struct block *b1;

                b1 = gen_cmp(orig_nl, BPF_H, (bpf_int32)vlan_num);
                gen_and(b0, b1);
                b0 = b1;
        }

        return (b0);
}

struct block *
gen_atmfield_code(atmfield, jvalue, jtype, reverse)
        int atmfield;
        bpf_u_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 == -1)
                        abort();
                b0 = gen_ncmp(BPF_B, off_vpi, 0xffffffff, (u_int)jtype,
                    (u_int)jvalue, reverse);
                break;

        case A_VCI:
                if (!is_atm)
                        bpf_error("'vci' supported only on raw ATM");
                if (off_vci == -1)
                        abort();
                b0 = gen_ncmp(BPF_H, off_vci, 0xffffffff, (u_int)jtype,
                    (u_int)jvalue, reverse);
                break;

        case A_PROTOTYPE:
                if (off_proto == -1)
                        abort();        /* XXX - this isn't on FreeBSD */
                b0 = gen_ncmp(BPF_B, off_proto, 0x0f, (u_int)jtype,
                    (u_int)jvalue, reverse);
                break;

        case A_MSGTYPE:
                if (off_msg_type == -1)
                        abort();
                b0 = gen_ncmp(BPF_B, off_msg_type, 0xffffffff,
                    (u_int)jtype, (u_int)jvalue, reverse);
                break;

        case A_CALLREFTYPE:
                if (!is_atm)
                        bpf_error("'callref' supported only on raw ATM");
                if (off_proto == -1)
                        abort();
                b0 = gen_ncmp(BPF_B, off_proto, 0xffffffff, (u_int)jtype,
                    (u_int)jvalue, reverse);
                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);
                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);
                break;

        default:
                abort();
        }
        return b1;
}


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;
}