Factor fail_kw_on_dlt() out.

[libpcap] / gencode.c

/*
 * 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.
 */

#include <config.h>

#ifdef _WIN32
  #include <ws2tcpip.h>
#else
  #include <netinet/in.h>
#endif /* _WIN32 */

#include <stdlib.h>
#include <string.h>
#include <memory.h>
#include <setjmp.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdint.h>
#include <stddef.h>

#include "pcap-int.h"

#include "extract.h"

#include "ethertype.h"
#include "llc.h"
#include "gencode.h"
#include "ieee80211.h"
#include "pflog.h"
#include "ppp.h"
#include "pcap/sll.h"
#include "pcap/ipnet.h"
#include "diag-control.h"
#include "pcap-util.h"

#include "scanner.h"

#if defined(__linux__)
#include <linux/types.h>
#include <linux/if_packet.h>
#include <linux/filter.h>
#endif

#ifdef _WIN32
  #ifdef HAVE_NPCAP_BPF_H
    /* Defines BPF extensions for Npcap */
    #include <npcap-bpf.h>
  #endif
  #ifdef INET6
    #if defined(__MINGW32__) && defined(DEFINE_ADDITIONAL_IPV6_STUFF)
/* IPv6 address */
struct in6_addr
  {
    union
      {
        uint8_t         u6_addr8[16];
        uint16_t        u6_addr16[8];
        uint32_t        u6_addr32[4];
      } in6_u;
#define s6_addr                 in6_u.u6_addr8
#define s6_addr16               in6_u.u6_addr16
#define s6_addr32               in6_u.u6_addr32
#define s6_addr64               in6_u.u6_addr64
  };

typedef unsigned short  sa_family_t;

#define __SOCKADDR_COMMON(sa_prefix) \
  sa_family_t sa_prefix##family

/* Ditto, for IPv6.  */
struct sockaddr_in6
  {
    __SOCKADDR_COMMON (sin6_);
    uint16_t sin6_port;         /* Transport layer port # */
    uint32_t sin6_flowinfo;     /* IPv6 flow information */
    struct in6_addr sin6_addr;  /* IPv6 address */
  };

      #ifndef EAI_ADDRFAMILY
struct addrinfo {
        int     ai_flags;       /* AI_PASSIVE, AI_CANONNAME */
        int     ai_family;      /* PF_xxx */
        int     ai_socktype;    /* SOCK_xxx */
        int     ai_protocol;    /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
        size_t  ai_addrlen;     /* length of ai_addr */
        char    *ai_canonname;  /* canonical name for hostname */
        struct sockaddr *ai_addr;       /* binary address */
        struct addrinfo *ai_next;       /* next structure in linked list */
};
      #endif /* EAI_ADDRFAMILY */
    #endif /* defined(__MINGW32__) && defined(DEFINE_ADDITIONAL_IPV6_STUFF) */
  #endif /* INET6 */
#else /* _WIN32 */
  #include <netdb.h>    /* for "struct addrinfo" */
#endif /* _WIN32 */
#include <pcap/namedb.h>

#include "nametoaddr.h"

#define ETHERMTU        1500

#ifndef IPPROTO_HOPOPTS
#define IPPROTO_HOPOPTS 0
#endif
#ifndef IPPROTO_ROUTING
#define IPPROTO_ROUTING 43
#endif
#ifndef IPPROTO_FRAGMENT
#define IPPROTO_FRAGMENT 44
#endif
#ifndef IPPROTO_DSTOPTS
#define IPPROTO_DSTOPTS 60
#endif
#ifndef IPPROTO_SCTP
#define IPPROTO_SCTP 132
#endif

#define GENEVE_PORT 6081
#define VXLAN_PORT  4789


/*
 * from: NetBSD: if_arc.h,v 1.13 1999/11/19 20:41:19 thorpej Exp
 */

/* RFC 1051 */
#define ARCTYPE_IP_OLD          240     /* IP protocol */
#define ARCTYPE_ARP_OLD         241     /* address resolution protocol */

/* RFC 1201 */
#define ARCTYPE_IP              212     /* IP protocol */
#define ARCTYPE_ARP             213     /* address resolution protocol */
#define ARCTYPE_REVARP          214     /* reverse addr resolution protocol */

#define ARCTYPE_ATALK           221     /* Appletalk */
#define ARCTYPE_BANIAN          247     /* Banyan Vines */
#define ARCTYPE_IPX             250     /* Novell IPX */

#define ARCTYPE_INET6           0xc4    /* IPng */
#define ARCTYPE_DIAGNOSE        0x80    /* as per ANSI/ATA 878.1 */


/* Based on UNI3.1 standard by ATM Forum */

/* ATM traffic types based on VPI=0 and (the following VCI */
#define VCI_PPC                 0x05    /* Point-to-point signal msg */
#define VCI_BCC                 0x02    /* Broadcast signal msg */
#define VCI_OAMF4SC             0x03    /* Segment OAM F4 flow cell */
#define VCI_OAMF4EC             0x04    /* End-to-end OAM F4 flow cell */
#define VCI_METAC               0x01    /* Meta signal msg */
#define VCI_ILMIC               0x10    /* ILMI msg */

/* Q.2931 signalling messages */
#define CALL_PROCEED            0x02    /* call proceeding */
#define CONNECT                 0x07    /* connect */
#define CONNECT_ACK             0x0f    /* connect_ack */
#define SETUP                   0x05    /* setup */
#define RELEASE                 0x4d    /* release */
#define RELEASE_DONE            0x5a    /* release_done */
#define RESTART                 0x46    /* restart */
#define RESTART_ACK             0x4e    /* restart ack */
#define STATUS                  0x7d    /* status */
#define STATUS_ENQ              0x75    /* status ack */
#define ADD_PARTY               0x80    /* add party */
#define ADD_PARTY_ACK           0x81    /* add party ack */
#define ADD_PARTY_REJ           0x82    /* add party rej */
#define DROP_PARTY              0x83    /* drop party */
#define DROP_PARTY_ACK          0x84    /* drop party ack */

/* Information Element Parameters in the signalling messages */
#define CAUSE                   0x08    /* cause */
#define ENDPT_REF               0x54    /* endpoint reference */
#define AAL_PARA                0x58    /* ATM adaptation layer parameters */
#define TRAFF_DESCRIP           0x59    /* atm traffic descriptors */
#define CONNECT_ID              0x5a    /* connection identifier */
#define QOS_PARA                0x5c    /* quality of service parameters */
#define B_HIGHER                0x5d    /* broadband higher layer information */
#define B_BEARER                0x5e    /* broadband bearer capability */
#define B_LOWER                 0x5f    /* broadband lower information */
#define CALLING_PARTY           0x6c    /* calling party number */
#define CALLED_PARTY            0x70    /* called party number */

#define Q2931                   0x09

/* Q.2931 signalling general messages format */
#define PROTO_POS       0       /* offset of protocol discriminator */
#define CALL_REF_POS    2       /* offset of call reference value */
#define MSG_TYPE_POS    5       /* offset of message type */
#define MSG_LEN_POS     7       /* offset of message length */
#define IE_BEGIN_POS    9       /* offset of first information element */

/* format of signalling messages */
#define TYPE_POS        0
#define LEN_POS         2
#define FIELD_BEGIN_POS 4


/* SunATM header for ATM packet */
#define SUNATM_DIR_POS          0
#define SUNATM_VPI_POS          1
#define SUNATM_VCI_POS          2
#define SUNATM_PKT_BEGIN_POS    4       /* Start of ATM packet */

/* Protocol type values in the bottom for bits of the byte at SUNATM_DIR_POS. */
#define PT_LANE         0x01    /* LANE */
#define PT_LLC          0x02    /* LLC encapsulation */
#define PT_ILMI         0x05    /* ILMI */
#define PT_QSAAL        0x06    /* Q.SAAL */


/* Types missing from some systems */

/*
 * Network layer protocol identifiers
 */
#ifndef ISO8473_CLNP
#define ISO8473_CLNP            0x81
#endif
#ifndef ISO9542_ESIS
#define ISO9542_ESIS            0x82
#endif
#ifndef ISO9542X25_ESIS
#define ISO9542X25_ESIS         0x8a
#endif
#ifndef ISO10589_ISIS
#define ISO10589_ISIS           0x83
#endif

#define ISIS_L1_LAN_IIH      15
#define ISIS_L2_LAN_IIH      16
#define ISIS_PTP_IIH         17
#define ISIS_L1_LSP          18
#define ISIS_L2_LSP          20
#define ISIS_L1_CSNP         24
#define ISIS_L2_CSNP         25
#define ISIS_L1_PSNP         26
#define ISIS_L2_PSNP         27

#ifndef ISO8878A_CONS
#define ISO8878A_CONS           0x84
#endif
#ifndef ISO10747_IDRP
#define ISO10747_IDRP           0x85
#endif

// Same as in tcpdump/print-sl.c.
#define SLIPDIR_IN 0
#define SLIPDIR_OUT 1

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

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

/*
 * "Push" the current value of the link-layer header type and link-layer
 * header offset onto a "stack", and set a new value.  (It's not a
 * full-blown stack; we keep only the top two items.)
 */
#define PUSH_LINKHDR(cs, new_linktype, new_is_variable, new_constant_part, new_reg) \
{ \
        (cs)->prevlinktype = (cs)->linktype; \
        (cs)->off_prevlinkhdr = (cs)->off_linkhdr; \
        (cs)->linktype = (new_linktype); \
        (cs)->off_linkhdr.is_variable = (new_is_variable); \
        (cs)->off_linkhdr.constant_part = (new_constant_part); \
        (cs)->off_linkhdr.reg = (new_reg); \
        (cs)->is_encap = 0; \
}

/*
 * Offset "not set" value.
 */
#define OFFSET_NOT_SET  0xffffffffU

/*
 * Absolute offsets, which are offsets from the beginning of the raw
 * packet data, are, in the general case, the sum of a variable value
 * and a constant value; the variable value may be absent, in which
 * case the offset is only the constant value, and the constant value
 * may be zero, in which case the offset is only the variable value.
 *
 * bpf_abs_offset is a structure containing all that information:
 *
 *   is_variable is 1 if there's a variable part.
 *
 *   constant_part is the constant part of the value, possibly zero;
 *
 *   if is_variable is 1, reg is the register number for a register
 *   containing the variable value if the register has been assigned,
 *   and -1 otherwise.
 */
typedef struct {
        int     is_variable;
        u_int   constant_part;
        int     reg;
} bpf_abs_offset;

/*
 * Value passed to gen_load_a() to indicate what the offset argument
 * is relative to the beginning of.
 */
enum e_offrel {
        OR_PACKET,              /* full packet data */
        OR_LINKHDR,             /* link-layer header */
        OR_PREVLINKHDR,         /* previous link-layer header */
        OR_LLC,                 /* 802.2 LLC header */
        OR_PREVMPLSHDR,         /* previous MPLS header */
        OR_LINKTYPE,            /* link-layer type */
        OR_LINKPL,              /* link-layer payload */
        OR_LINKPL_NOSNAP,       /* link-layer payload, with no SNAP header at the link layer */
        OR_TRAN_IPV4,           /* transport-layer header, with IPv4 network layer */
        OR_TRAN_IPV6            /* transport-layer header, with IPv6 network layer */
};

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

/*
 * A chunk can store any of:
 *  - a string (guaranteed alignment 1 but present for completeness)
 *  - a block
 *  - an slist
 *  - an arth
 * For this simple allocator every allocated chunk gets rounded up to the
 * alignment needed for any chunk.
 */
struct chunk_align {
        char dummy;
        union {
                char c;
                struct block b;
                struct slist s;
                struct arth a;
        } u;
};
#define CHUNK_ALIGN (offsetof(struct chunk_align, u))

/* Code generator state */

struct _compiler_state {
        jmp_buf top_ctx;
        pcap_t *bpf_pcap;
        int error_set;

        struct icode ic;

        int snaplen;

        int linktype;
        int prevlinktype;
        int outermostlinktype;

        bpf_u_int32 netmask;
        int no_optimize;

        /* Hack for handling VLAN and MPLS stacks. */
        u_int label_stack_depth;
        u_int vlan_stack_depth;

        /* XXX */
        u_int pcap_fddipad;

        /*
         * As errors are handled by a longjmp, anything allocated must
         * be freed in the longjmp handler, so it must be reachable
         * from that handler.
         *
         * One thing that's allocated is the result of pcap_nametoaddrinfo();
         * it must be freed with freeaddrinfo().  This variable points to
         * any addrinfo structure that would need to be freed.
         */
        struct addrinfo *ai;

        /*
         * Another thing that's allocated is the result of pcap_ether_aton();
         * it must be freed with free().  This variable points to any
         * address that would need to be freed.
         */
        u_char *e;

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

        /*
         * Absolute offset of the beginning of the link-layer header.
         */
        bpf_abs_offset off_linkhdr;

        /*
         * If we're checking a link-layer header for a packet encapsulated
         * in another protocol layer, this is the equivalent information
         * for the previous layers' link-layer header from the beginning
         * of the raw packet data.
         */
        bpf_abs_offset off_prevlinkhdr;

        /*
         * This is the equivalent information for the outermost layers'
         * link-layer header.
         */
        bpf_abs_offset off_outermostlinkhdr;

        /*
         * Absolute offset of the beginning of the link-layer payload.
         */
        bpf_abs_offset off_linkpl;

        /*
         * "off_linktype" is the offset to information in the link-layer
         * header giving the packet type. This is an absolute offset
         * from the beginning of the packet.
         *
         * For Ethernet, it's the offset of the Ethernet type field; this
         * means that it must have a value that skips VLAN tags.
         *
         * For link-layer types that always use 802.2 headers, it's the
         * offset of the LLC header; this means that it must have a value
         * that skips VLAN tags.
         *
         * 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.
         *
         * off_linktype.constant_part is set to OFFSET_NOT_SET for no
         * encapsulation, in which case, IP is assumed.
         */
        bpf_abs_offset off_linktype;

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

        /* TRUE if "geneve" or "vxlan" appeared in the filter; it
         * causes us to generate code that checks for a Geneve or
         * VXLAN header respectively and assume that later filters
         * apply to the encapsulated payload.
         */
        int is_encap;

        /*
         * TRUE if we need variable length part of VLAN offset
         */
        int is_vlan_vloffset;

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

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

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

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

        /*
         * These are offsets to the beginning of the network-layer header.
         * They are relative to the beginning of the link-layer payload
         * (i.e., they don't include off_linkhdr.constant_part or
         * off_linkpl.constant_part).
         *
         * 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.
         */
        u_int off_nl;
        u_int off_nl_nosnap;

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

        /*
         * Memory chunks.
         */
        struct chunk chunks[NCHUNKS];
        int cur_chunk;
};

/*
 * For use by routines outside this file.
 */
/* VARARGS */
void
bpf_set_error(compiler_state_t *cstate, const char *fmt, ...)
{
        va_list ap;

        /*
         * If we've already set an error, don't override it.
         * The lexical analyzer reports some errors by setting
         * the error and then returning a LEX_ERROR token, which
         * is not recognized by any grammar rule, and thus forces
         * the parse to stop.  We don't want the error reported
         * by the lexical analyzer to be overwritten by the syntax
         * error.
         */
        if (!cstate->error_set) {
                va_start(ap, fmt);
                (void)vsnprintf(cstate->bpf_pcap->errbuf, PCAP_ERRBUF_SIZE,
                    fmt, ap);
                va_end(ap);
                cstate->error_set = 1;
        }
}

/*
 * For use *ONLY* in routines in this file.
 */
static void PCAP_NORETURN bpf_error(compiler_state_t *, const char *, ...)
    PCAP_PRINTFLIKE(2, 3);

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

        va_start(ap, fmt);
        (void)vsnprintf(cstate->bpf_pcap->errbuf, PCAP_ERRBUF_SIZE,
            fmt, ap);
        va_end(ap);
        longjmp(cstate->top_ctx, 1);
        /*NOTREACHED*/
#ifdef _AIX
        PCAP_UNREACHABLE
#endif /* _AIX */
}

static int init_linktype(compiler_state_t *, pcap_t *);

static void init_regs(compiler_state_t *);
static int alloc_reg(compiler_state_t *);
static void free_reg(compiler_state_t *, int);

static void initchunks(compiler_state_t *cstate);
static void *newchunk_nolongjmp(compiler_state_t *cstate, size_t);
static void *newchunk(compiler_state_t *cstate, size_t);
static void freechunks(compiler_state_t *cstate);
static inline struct block *new_block(compiler_state_t *cstate, int);
static inline struct slist *new_stmt(compiler_state_t *cstate, int);
static struct block *gen_retblk(compiler_state_t *cstate, int);
static inline void syntax(compiler_state_t *cstate);

static void backpatch(struct block *, struct block *);
static void merge(struct block *, struct block *);
static struct block *gen_cmp(compiler_state_t *, enum e_offrel, u_int,
    u_int, bpf_u_int32);
static struct block *gen_cmp_gt(compiler_state_t *, enum e_offrel, u_int,
    u_int, bpf_u_int32);
static struct block *gen_cmp_ge(compiler_state_t *, enum e_offrel, u_int,
    u_int, bpf_u_int32);
static struct block *gen_cmp_lt(compiler_state_t *, enum e_offrel, u_int,
    u_int, bpf_u_int32);
static struct block *gen_cmp_le(compiler_state_t *, enum e_offrel, u_int,
    u_int, bpf_u_int32);
static struct block *gen_mcmp(compiler_state_t *, enum e_offrel, u_int,
    u_int, bpf_u_int32, bpf_u_int32);
static struct block *gen_bcmp(compiler_state_t *, enum e_offrel, u_int,
    u_int, const u_char *);
static struct block *gen_ncmp(compiler_state_t *, enum e_offrel, u_int,
    u_int, bpf_u_int32, int, int, bpf_u_int32);
static struct slist *gen_load_absoffsetrel(compiler_state_t *, bpf_abs_offset *,
    u_int, u_int);
static struct slist *gen_load_a(compiler_state_t *, enum e_offrel, u_int,
    u_int);
static struct slist *gen_loadx_iphdrlen(compiler_state_t *);
static struct block *gen_uncond(compiler_state_t *, int);
static inline struct block *gen_true(compiler_state_t *);
static inline struct block *gen_false(compiler_state_t *);
static struct block *gen_ether_linktype(compiler_state_t *, bpf_u_int32);
static struct block *gen_ipnet_linktype(compiler_state_t *, bpf_u_int32);
static struct block *gen_linux_sll_linktype(compiler_state_t *, bpf_u_int32);
static struct slist *gen_load_pflog_llprefixlen(compiler_state_t *);
static struct slist *gen_load_prism_llprefixlen(compiler_state_t *);
static struct slist *gen_load_avs_llprefixlen(compiler_state_t *);
static struct slist *gen_load_radiotap_llprefixlen(compiler_state_t *);
static struct slist *gen_load_ppi_llprefixlen(compiler_state_t *);
static void insert_compute_vloffsets(compiler_state_t *, struct block *);
static struct slist *gen_abs_offset_varpart(compiler_state_t *,
    bpf_abs_offset *);
static bpf_u_int32 ethertype_to_ppptype(bpf_u_int32);
static struct block *gen_linktype(compiler_state_t *, bpf_u_int32);
static struct block *gen_snap(compiler_state_t *, bpf_u_int32, bpf_u_int32);
static struct block *gen_llc_linktype(compiler_state_t *, bpf_u_int32);
static struct block *gen_hostop(compiler_state_t *, bpf_u_int32, bpf_u_int32,
    int, u_int, u_int);
#ifdef INET6
static struct block *gen_hostop6(compiler_state_t *, struct in6_addr *,
    struct in6_addr *, int, u_int, u_int);
#endif
static struct block *gen_ahostop(compiler_state_t *, const uint8_t, int);
static struct block *gen_ehostop(compiler_state_t *, const u_char *, int);
static struct block *gen_fhostop(compiler_state_t *, const u_char *, int);
static struct block *gen_thostop(compiler_state_t *, const u_char *, int);
static struct block *gen_wlanhostop(compiler_state_t *, const u_char *, int);
static struct block *gen_ipfchostop(compiler_state_t *, const u_char *, int);
static struct block *gen_dnhostop(compiler_state_t *, bpf_u_int32, int);
static struct block *gen_mpls_linktype(compiler_state_t *, bpf_u_int32);
static struct block *gen_host(compiler_state_t *, bpf_u_int32, bpf_u_int32,
    int, int, int);
#ifdef INET6
static struct block *gen_host6(compiler_state_t *, struct in6_addr *,
    struct in6_addr *, int, int, int);
#endif
#ifndef INET6
static struct block *gen_gateway(compiler_state_t *, const u_char *,
    struct addrinfo *, int, int);
#endif
static struct block *gen_ipfrag(compiler_state_t *);
static struct block *gen_portatom(compiler_state_t *, int, bpf_u_int32);
static struct block *gen_portrangeatom(compiler_state_t *, u_int, bpf_u_int32,
    bpf_u_int32);
static struct block *gen_portatom6(compiler_state_t *, int, bpf_u_int32);
static struct block *gen_portrangeatom6(compiler_state_t *, u_int, bpf_u_int32,
    bpf_u_int32);
static struct block *gen_portop(compiler_state_t *, u_int, u_int, int);
static struct block *gen_port(compiler_state_t *, u_int, int, int);
static struct block *gen_portrangeop(compiler_state_t *, u_int, u_int,
    bpf_u_int32, int);
static struct block *gen_portrange(compiler_state_t *, u_int, u_int, int, int);
struct block *gen_portop6(compiler_state_t *, u_int, u_int, int);
static struct block *gen_port6(compiler_state_t *, u_int, int, int);
static struct block *gen_portrangeop6(compiler_state_t *, u_int, u_int,
    bpf_u_int32, int);
static struct block *gen_portrange6(compiler_state_t *, u_int, u_int, int, int);
static int lookup_proto(compiler_state_t *, const char *, int);
#if !defined(NO_PROTOCHAIN)
static struct block *gen_protochain(compiler_state_t *, bpf_u_int32, int);
#endif /* !defined(NO_PROTOCHAIN) */
static struct block *gen_proto(compiler_state_t *, bpf_u_int32, int, int);
static struct slist *xfer_to_x(compiler_state_t *, struct arth *);
static struct slist *xfer_to_a(compiler_state_t *, struct arth *);
static struct block *gen_mac_multicast(compiler_state_t *, int);
static struct block *gen_len(compiler_state_t *, int, int);
static struct block *gen_encap_ll_check(compiler_state_t *cstate);

static struct block *gen_atmfield_code_internal(compiler_state_t *, int,
    bpf_u_int32, int, int);
static struct block *gen_atmtype_llc(compiler_state_t *);
static struct block *gen_msg_abbrev(compiler_state_t *, int type);

static void
initchunks(compiler_state_t *cstate)
{
        int i;

        for (i = 0; i < NCHUNKS; i++) {
                cstate->chunks[i].n_left = 0;
                cstate->chunks[i].m = NULL;
        }
        cstate->cur_chunk = 0;
}

static void *
newchunk_nolongjmp(compiler_state_t *cstate, size_t n)
{
        struct chunk *cp;
        int k;
        size_t size;

        /* Round up to chunk alignment. */
        n = (n + CHUNK_ALIGN - 1) & ~(CHUNK_ALIGN - 1);

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

static void *
newchunk(compiler_state_t *cstate, size_t n)
{
        void *p;

        p = newchunk_nolongjmp(cstate, n);
        if (p == NULL) {
                longjmp(cstate->top_ctx, 1);
                /*NOTREACHED*/
        }
        return (p);
}

static void
freechunks(compiler_state_t *cstate)
{
        int i;

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

/*
 * A strdup whose allocations are freed after code generation is over.
 * This is used by the lexical analyzer, so it can't longjmp; it just
 * returns NULL on an allocation error, and the callers must check
 * for it.
 */
char *
sdup(compiler_state_t *cstate, const char *s)
{
        size_t n = strlen(s) + 1;
        char *cp = newchunk_nolongjmp(cstate, n);

        if (cp == NULL)
                return (NULL);
        pcapint_strlcpy(cp, s, n);
        return (cp);
}

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

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

        return p;
}

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

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

        return p;
}

static struct block *
gen_retblk_internal(compiler_state_t *cstate, int v)
{
        struct block *b = new_block(cstate, BPF_RET|BPF_K);

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

static struct block *
gen_retblk(compiler_state_t *cstate, int v)
{
        if (setjmp(cstate->top_ctx)) {
                /*
                 * gen_retblk() only fails because a memory
                 * allocation failed in newchunk(), meaning
                 * that it can't return a pointer.
                 *
                 * Return NULL.
                 */
                return NULL;
        }
        return gen_retblk_internal(cstate, v);
}

static inline PCAP_NORETURN_DEF void
syntax(compiler_state_t *cstate)
{
        bpf_error(cstate, "syntax error in filter expression");
}

static PCAP_NORETURN_DEF void
fail_kw_on_dlt(compiler_state_t *cstate, const char *keyword)
{
        bpf_error(cstate, "'%s' not supported on %s", keyword,
            pcap_datalink_val_to_description_or_dlt(cstate->linktype));
}

int
pcap_compile(pcap_t *p, struct bpf_program *program,
             const char *buf, int optimize, bpf_u_int32 mask)
{
#ifdef _WIN32
        int err;
        WSADATA wsaData;
#endif
        compiler_state_t cstate;
        yyscan_t scanner = NULL;
        YY_BUFFER_STATE in_buffer = NULL;
        u_int len;
        int rc;

        /*
         * If this pcap_t hasn't been activated, it doesn't have a
         * link-layer type, so we can't use it.
         */
        if (!p->activated) {
                (void)snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
                    "not-yet-activated pcap_t passed to pcap_compile");
                return (PCAP_ERROR);
        }

#ifdef _WIN32
        /*
         * Initialize Winsock, asking for the latest version (2.2),
         * as we may be calling Winsock routines to translate
         * host names to addresses.
         */
        err = WSAStartup(MAKEWORD(2, 2), &wsaData);
        if (err != 0) {
                pcapint_fmt_errmsg_for_win32_err(p->errbuf, PCAP_ERRBUF_SIZE,
                    err, "Error calling WSAStartup()");
                return (PCAP_ERROR);
        }
#endif

#ifdef ENABLE_REMOTE
        /*
         * If the device on which we're capturing need to be notified
         * that a new filter is being compiled, do so.
         *
         * This allows them to save a copy of it, in case, for example,
         * they're implementing a form of remote packet capture, and
         * want the remote machine to filter out the packets in which
         * it's sending the packets it's captured.
         *
         * XXX - the fact that we happen to be compiling a filter
         * doesn't necessarily mean we'll be installing it as the
         * filter for this pcap_t; we might be running it from userland
         * on captured packets to do packet classification.  We really
         * need a better way of handling this, but this is all that
         * the WinPcap remote capture code did.
         */
        if (p->save_current_filter_op != NULL)
                (p->save_current_filter_op)(p, buf);
#endif

        initchunks(&cstate);
        cstate.no_optimize = 0;
#ifdef INET6
        cstate.ai = NULL;
#endif
        cstate.e = NULL;
        cstate.ic.root = NULL;
        cstate.ic.cur_mark = 0;
        cstate.bpf_pcap = p;
        cstate.error_set = 0;
        init_regs(&cstate);

        cstate.netmask = mask;

        cstate.snaplen = pcap_snapshot(p);
        if (cstate.snaplen == 0) {
                (void)snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
                         "snaplen of 0 rejects all packets");
                rc = PCAP_ERROR;
                goto quit;
        }

        if (pcap_lex_init(&scanner) != 0) {
                pcapint_fmt_errmsg_for_errno(p->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "can't initialize scanner");
                rc = PCAP_ERROR;
                goto quit;
        }
        in_buffer = pcap__scan_string(buf ? buf : "", scanner);

        /*
         * Associate the compiler state with the lexical analyzer
         * state.
         */
        pcap_set_extra(&cstate, scanner);

        if (init_linktype(&cstate, p) == -1) {
                rc = PCAP_ERROR;
                goto quit;
        }
        if (pcap_parse(scanner, &cstate) != 0) {
#ifdef INET6
                if (cstate.ai != NULL)
                        freeaddrinfo(cstate.ai);
#endif
                if (cstate.e != NULL)
                        free(cstate.e);
                rc = PCAP_ERROR;
                goto quit;
        }

        if (cstate.ic.root == NULL) {
                cstate.ic.root = gen_retblk(&cstate, cstate.snaplen);

                /*
                 * Catch errors reported by gen_retblk().
                 */
                if (cstate.ic.root== NULL) {
                        rc = PCAP_ERROR;
                        goto quit;
                }
        }

        if (optimize && !cstate.no_optimize) {
                if (bpf_optimize(&cstate.ic, p->errbuf) == -1) {
                        /* Failure */
                        rc = PCAP_ERROR;
                        goto quit;
                }
                if (cstate.ic.root == NULL ||
                    (cstate.ic.root->s.code == (BPF_RET|BPF_K) && cstate.ic.root->s.k == 0)) {
                        (void)snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
                            "expression rejects all packets");
                        rc = PCAP_ERROR;
                        goto quit;
                }
        }
        program->bf_insns = icode_to_fcode(&cstate.ic,
            cstate.ic.root, &len, p->errbuf);
        if (program->bf_insns == NULL) {
                /* Failure */
                rc = PCAP_ERROR;
                goto quit;
        }
        program->bf_len = len;

        rc = 0;  /* We're all okay */

quit:
        /*
         * Clean up everything for the lexical analyzer.
         */
        if (in_buffer != NULL)
                pcap__delete_buffer(in_buffer, scanner);
        if (scanner != NULL)
                pcap_lex_destroy(scanner);

        /*
         * Clean up our own allocated memory.
         */
        freechunks(&cstate);

#ifdef _WIN32
        WSACleanup();
#endif

        return (rc);
}

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

        p = pcap_open_dead(linktype_arg, snaplen_arg);
        if (p == NULL)
                return (PCAP_ERROR);
        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(struct block *list, struct block *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(struct block *b0, struct block *b1)
{
        register struct block **p = &b0;

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

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

int
finish_parse(compiler_state_t *cstate, struct block *p)
{
        /*
         * Catch errors reported by us and routines below us, and return -1
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (-1);

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

        /*
         * For DLT_PPI captures, generate a check of the per-packet
         * DLT value to make sure it's DLT_IEEE802_11.
         *
         * XXX - TurboCap cards use DLT_PPI for Ethernet.
         * Can we just define some DLT_ETHERNET_WITH_PHDR pseudo-header
         * with appropriate Ethernet information and use that rather
         * than using something such as DLT_PPI where you don't know
         * the link-layer header type until runtime, which, in the
         * general case, would force us to generate both Ethernet *and*
         * 802.11 code (*and* anything else for which PPI is used)
         * and choose between them early in the BPF program?
         */
        if (cstate->linktype == DLT_PPI) {
                struct block *ppi_dlt_check = gen_cmp(cstate, OR_PACKET,
                        4, BPF_W, SWAPLONG(DLT_IEEE802_11));
                gen_and(ppi_dlt_check, p);
        }

        backpatch(p, gen_retblk_internal(cstate, cstate->snaplen));
        p->sense = !p->sense;
        backpatch(p, gen_retblk_internal(cstate, 0));
        cstate->ic.root = p->head;
        return (0);
}

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

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

static struct block *
gen_cmp(compiler_state_t *cstate, enum e_offrel offrel, u_int offset,
    u_int size, bpf_u_int32 v)
{
        return gen_ncmp(cstate, offrel, offset, size, 0xffffffff, BPF_JEQ, 0, v);
}

static struct block *
gen_cmp_gt(compiler_state_t *cstate, enum e_offrel offrel, u_int offset,
    u_int size, bpf_u_int32 v)
{
        return gen_ncmp(cstate, offrel, offset, size, 0xffffffff, BPF_JGT, 0, v);
}

static struct block *
gen_cmp_ge(compiler_state_t *cstate, enum e_offrel offrel, u_int offset,
    u_int size, bpf_u_int32 v)
{
        return gen_ncmp(cstate, offrel, offset, size, 0xffffffff, BPF_JGE, 0, v);
}

static struct block *
gen_cmp_lt(compiler_state_t *cstate, enum e_offrel offrel, u_int offset,
    u_int size, bpf_u_int32 v)
{
        return gen_ncmp(cstate, offrel, offset, size, 0xffffffff, BPF_JGE, 1, v);
}

static struct block *
gen_cmp_le(compiler_state_t *cstate, enum e_offrel offrel, u_int offset,
    u_int size, bpf_u_int32 v)
{
        return gen_ncmp(cstate, offrel, offset, size, 0xffffffff, BPF_JGT, 1, v);
}

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

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

        b = NULL;
        while (size >= 4) {
                register const u_char *p = &v[size - 4];

                tmp = gen_cmp(cstate, offrel, offset + size - 4, BPF_W,
                    EXTRACT_BE_U_4(p));
                if (b != NULL)
                        gen_and(b, tmp);
                b = tmp;
                size -= 4;
        }
        while (size >= 2) {
                register const u_char *p = &v[size - 2];

                tmp = gen_cmp(cstate, offrel, offset + size - 2, BPF_H,
                    EXTRACT_BE_U_2(p));
                if (b != NULL)
                        gen_and(b, tmp);
                b = tmp;
                size -= 2;
        }
        if (size > 0) {
                tmp = gen_cmp(cstate, offrel, offset, BPF_B, v[0]);
                if (b != NULL)
                        gen_and(b, tmp);
                b = tmp;
        }
        return b;
}

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

        s = gen_load_a(cstate, offrel, offset, size);

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

        b = new_block(cstate, JMP(jtype));
        b->stmts = s;
        b->s.k = v;
        if (reverse)
                gen_not(b);
        return b;
}

static int
init_linktype(compiler_state_t *cstate, pcap_t *p)
{
        cstate->pcap_fddipad = p->fddipad;

        /*
         * We start out with only one link-layer header.
         */
        cstate->outermostlinktype = pcap_datalink(p);
        cstate->off_outermostlinkhdr.constant_part = 0;
        cstate->off_outermostlinkhdr.is_variable = 0;
        cstate->off_outermostlinkhdr.reg = -1;

        cstate->prevlinktype = cstate->outermostlinktype;
        cstate->off_prevlinkhdr.constant_part = 0;
        cstate->off_prevlinkhdr.is_variable = 0;
        cstate->off_prevlinkhdr.reg = -1;

        cstate->linktype = cstate->outermostlinktype;
        cstate->off_linkhdr.constant_part = 0;
        cstate->off_linkhdr.is_variable = 0;
        cstate->off_linkhdr.reg = -1;

        /*
         * XXX
         */
        cstate->off_linkpl.constant_part = 0;
        cstate->off_linkpl.is_variable = 0;
        cstate->off_linkpl.reg = -1;

        cstate->off_linktype.constant_part = 0;
        cstate->off_linktype.is_variable = 0;
        cstate->off_linktype.reg = -1;

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

        /*
         * And not encapsulated with either Geneve or VXLAN.
         */
        cstate->is_encap = 0;

        /*
         * No variable length VLAN offset by default
         */
        cstate->is_vlan_vloffset = 0;

        /*
         * And assume we're not doing SS7.
         */
        cstate->off_li = OFFSET_NOT_SET;
        cstate->off_li_hsl = OFFSET_NOT_SET;
        cstate->off_sio = OFFSET_NOT_SET;
        cstate->off_opc = OFFSET_NOT_SET;
        cstate->off_dpc = OFFSET_NOT_SET;
        cstate->off_sls = OFFSET_NOT_SET;

        cstate->label_stack_depth = 0;
        cstate->vlan_stack_depth = 0;

        switch (cstate->linktype) {

        case DLT_ARCNET:
                cstate->off_linktype.constant_part = 2;
                cstate->off_linkpl.constant_part = 6;
                cstate->off_nl = 0;             /* XXX in reality, variable! */
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_ARCNET_LINUX:
                cstate->off_linktype.constant_part = 4;
                cstate->off_linkpl.constant_part = 8;
                cstate->off_nl = 0;             /* XXX in reality, variable! */
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_EN10MB:
                cstate->off_linktype.constant_part = 12;
                cstate->off_linkpl.constant_part = 14;  /* Ethernet header length */
                cstate->off_nl = 0;             /* Ethernet II */
                cstate->off_nl_nosnap = 3;      /* 802.3+802.2 */
                break;

        case DLT_SLIP:
                /*
                 * SLIP doesn't have a link level type.  The 16 byte
                 * header is hacked into our SLIP driver.
                 */
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                cstate->off_linkpl.constant_part = 16;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_SLIP_BSDOS:
                /* XXX this may be the same as the DLT_PPP_BSDOS case */
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                /* XXX end */
                cstate->off_linkpl.constant_part = 24;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_NULL:
        case DLT_LOOP:
                cstate->off_linktype.constant_part = 0;
                cstate->off_linkpl.constant_part = 4;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_ENC:
                cstate->off_linktype.constant_part = 0;
                cstate->off_linkpl.constant_part = 12;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_PPP:
        case DLT_PPP_PPPD:
        case DLT_C_HDLC:                /* BSD/OS Cisco HDLC */
        case DLT_HDLC:                  /* NetBSD (Cisco) HDLC */
        case DLT_PPP_SERIAL:            /* NetBSD sync/async serial PPP */
                cstate->off_linktype.constant_part = 2; /* skip HDLC-like framing */
                cstate->off_linkpl.constant_part = 4;   /* skip HDLC-like framing and protocol field */
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_PPP_ETHER:
                /*
                 * This does not include the Ethernet header, and
                 * only covers session state.
                 */
                cstate->off_linktype.constant_part = 6;
                cstate->off_linkpl.constant_part = 8;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_PPP_BSDOS:
                cstate->off_linktype.constant_part = 5;
                cstate->off_linkpl.constant_part = 24;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        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?
                 */
                cstate->off_linktype.constant_part = 13;
                cstate->off_linktype.constant_part += cstate->pcap_fddipad;
                cstate->off_linkpl.constant_part = 13;  /* FDDI MAC header length */
                cstate->off_linkpl.constant_part += cstate->pcap_fddipad;
                cstate->off_nl = 8;             /* 802.2+SNAP */
                cstate->off_nl_nosnap = 3;      /* 802.2 */
                break;

        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).
                 */
                cstate->off_linktype.constant_part = 14;
                cstate->off_linkpl.constant_part = 14;  /* Token Ring MAC header length */
                cstate->off_nl = 8;             /* 802.2+SNAP */
                cstate->off_nl_nosnap = 3;      /* 802.2 */
                break;

        case DLT_PRISM_HEADER:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_IEEE802_11_RADIO:
                cstate->off_linkhdr.is_variable = 1;
                /* Fall through, 802.11 doesn't have a variable link
                 * prefix but is otherwise the same. */
                /* FALLTHROUGH */

        case DLT_IEEE802_11:
                /*
                 * 802.11 doesn't really have a link-level type field.
                 * We set "off_linktype.constant_part" to the offset of
                 * the LLC header.
                 *
                 * To check for Ethernet types, we assume that SSAP = SNAP
                 * is being used and pick out the encapsulated Ethernet type.
                 * XXX - should we generate code to check for SNAP?
                 *
                 * We also handle variable-length radio headers here.
                 * The Prism header is in theory variable-length, but in
                 * practice it's always 144 bytes long.  However, some
                 * drivers on Linux use ARPHRD_IEEE80211_PRISM, but
                 * sometimes or always supply an AVS header, so we
                 * have to check whether the radio header is a Prism
                 * header or an AVS header, so, in practice, it's
                 * variable-length.
                 */
                cstate->off_linktype.constant_part = 24;
                cstate->off_linkpl.constant_part = 0;   /* link-layer header is variable-length */
                cstate->off_linkpl.is_variable = 1;
                cstate->off_nl = 8;             /* 802.2+SNAP */
                cstate->off_nl_nosnap = 3;      /* 802.2 */
                break;

        case DLT_PPI:
                /*
                 * At the moment we treat PPI the same way that we treat
                 * normal Radiotap encoded packets. The difference is in
                 * the function that generates the code at the beginning
                 * to compute the header length.  Since this code generator
                 * of PPI supports bare 802.11 encapsulation only (i.e.
                 * the encapsulated DLT should be DLT_IEEE802_11) we
                 * generate code to check for this too.
                 */
                cstate->off_linktype.constant_part = 24;
                cstate->off_linkpl.constant_part = 0;   /* link-layer header is variable-length */
                cstate->off_linkpl.is_variable = 1;
                cstate->off_linkhdr.is_variable = 1;
                cstate->off_nl = 8;             /* 802.2+SNAP */
                cstate->off_nl_nosnap = 3;      /* 802.2 */
                break;

        case DLT_ATM_RFC1483:
        case DLT_ATM_CLIP:      /* Linux ATM defines this */
                /*
                 * assume routed, non-ISO PDUs
                 * (i.e., LLC = 0xAA-AA-03, OUT = 0x00-00-00)
                 *
                 * XXX - what about ISO PDUs, e.g. CLNP, ISIS, ESIS,
                 * or PPP with the PPP NLPID (e.g., PPPoA)?  The
                 * latter would presumably be treated the way PPPoE
                 * should be, so you can do "pppoe and udp port 2049"
                 * or "pppoa and tcp port 80" and have it check for
                 * PPPo{A,E} and a PPP protocol of IP and....
                 */
                cstate->off_linktype.constant_part = 0;
                cstate->off_linkpl.constant_part = 0;   /* packet begins with LLC header */
                cstate->off_nl = 8;             /* 802.2+SNAP */
                cstate->off_nl_nosnap = 3;      /* 802.2 */
                break;

        case DLT_SUNATM:
                /*
                 * Full Frontal ATM; you get AALn PDUs with an ATM
                 * pseudo-header.
                 */
                cstate->is_atm = 1;
                cstate->off_vpi = SUNATM_VPI_POS;
                cstate->off_vci = SUNATM_VCI_POS;
                cstate->off_proto = PROTO_POS;
                cstate->off_payload = SUNATM_PKT_BEGIN_POS;
                cstate->off_linktype.constant_part = cstate->off_payload;
                cstate->off_linkpl.constant_part = cstate->off_payload; /* if LLC-encapsulated */
                cstate->off_nl = 8;             /* 802.2+SNAP */
                cstate->off_nl_nosnap = 3;      /* 802.2 */
                break;

        case DLT_RAW:
        case DLT_IPV4:
        case DLT_IPV6:
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                cstate->off_linkpl.constant_part = 0;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_LINUX_SLL:     /* fake header for Linux cooked socket v1 */
                cstate->off_linktype.constant_part = 14;
                cstate->off_linkpl.constant_part = 16;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_LINUX_SLL2:    /* fake header for Linux cooked socket v2 */
                cstate->off_linktype.constant_part = 0;
                cstate->off_linkpl.constant_part = 20;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        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.
                 */
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                cstate->off_linkpl.constant_part = 0;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_IP_OVER_FC:
                /*
                 * RFC 2625 IP-over-Fibre-Channel doesn't really have a
                 * link-level type field.  We set "off_linktype" to the
                 * offset of the LLC header.
                 *
                 * To check for Ethernet types, we assume that SSAP = SNAP
                 * is being used and pick out the encapsulated Ethernet type.
                 * XXX - should we generate code to check for SNAP? RFC
                 * 2625 says SNAP should be used.
                 */
                cstate->off_linktype.constant_part = 16;
                cstate->off_linkpl.constant_part = 16;
                cstate->off_nl = 8;             /* 802.2+SNAP */
                cstate->off_nl_nosnap = 3;      /* 802.2 */
                break;

        case DLT_FRELAY:
                /*
                 * XXX - we should set this to handle SNAP-encapsulated
                 * frames (NLPID of 0x80).
                 */
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                cstate->off_linkpl.constant_part = 0;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

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

        case DLT_APPLE_IP_OVER_IEEE1394:
                cstate->off_linktype.constant_part = 16;
                cstate->off_linkpl.constant_part = 18;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_SYMANTEC_FIREWALL:
                cstate->off_linktype.constant_part = 6;
                cstate->off_linkpl.constant_part = 44;
                cstate->off_nl = 0;             /* Ethernet II */
                cstate->off_nl_nosnap = 0;      /* XXX - what does it do with 802.3 packets? */
                break;

        case DLT_PFLOG:
                cstate->off_linktype.constant_part = 0;
                cstate->off_linkpl.constant_part = 0;   /* link-layer header is variable-length */
                cstate->off_linkpl.is_variable = 1;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */
                break;

        case DLT_JUNIPER_MFR:
        case DLT_JUNIPER_MLFR:
        case DLT_JUNIPER_MLPPP:
        case DLT_JUNIPER_PPP:
        case DLT_JUNIPER_CHDLC:
        case DLT_JUNIPER_FRELAY:
                cstate->off_linktype.constant_part = 4;
                cstate->off_linkpl.constant_part = 4;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = OFFSET_NOT_SET; /* no 802.2 LLC */
                break;

        case DLT_JUNIPER_ATM1:
                cstate->off_linktype.constant_part = 4;         /* in reality variable between 4-8 */
                cstate->off_linkpl.constant_part = 4;   /* in reality variable between 4-8 */
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 10;
                break;

        case DLT_JUNIPER_ATM2:
                cstate->off_linktype.constant_part = 8;         /* in reality variable between 8-12 */
                cstate->off_linkpl.constant_part = 8;   /* in reality variable between 8-12 */
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 10;
                break;

                /* frames captured on a Juniper PPPoE service PIC
                 * contain raw ethernet frames */
        case DLT_JUNIPER_PPPOE:
        case DLT_JUNIPER_ETHER:
                cstate->off_linkpl.constant_part = 14;
                cstate->off_linktype.constant_part = 16;
                cstate->off_nl = 18;            /* Ethernet II */
                cstate->off_nl_nosnap = 21;     /* 802.3+802.2 */
                break;

        case DLT_JUNIPER_PPPOE_ATM:
                cstate->off_linktype.constant_part = 4;
                cstate->off_linkpl.constant_part = 6;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = OFFSET_NOT_SET; /* no 802.2 LLC */
                break;

        case DLT_JUNIPER_GGSN:
                cstate->off_linktype.constant_part = 6;
                cstate->off_linkpl.constant_part = 12;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = OFFSET_NOT_SET; /* no 802.2 LLC */
                break;

        case DLT_JUNIPER_ES:
                cstate->off_linktype.constant_part = 6;
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;      /* not really a network layer but raw IP addresses */
                cstate->off_nl = OFFSET_NOT_SET;        /* not really a network layer but raw IP addresses */
                cstate->off_nl_nosnap = OFFSET_NOT_SET; /* no 802.2 LLC */
                break;

        case DLT_JUNIPER_MONITOR:
                cstate->off_linktype.constant_part = 12;
                cstate->off_linkpl.constant_part = 12;
                cstate->off_nl = 0;                     /* raw IP/IP6 header */
                cstate->off_nl_nosnap = OFFSET_NOT_SET; /* no 802.2 LLC */
                break;

        case DLT_BACNET_MS_TP:
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;
                cstate->off_nl = OFFSET_NOT_SET;
                cstate->off_nl_nosnap = OFFSET_NOT_SET;
                break;

        case DLT_JUNIPER_SERVICES:
                cstate->off_linktype.constant_part = 12;
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;      /* L3 proto location dep. on cookie type */
                cstate->off_nl = OFFSET_NOT_SET;        /* L3 proto location dep. on cookie type */
                cstate->off_nl_nosnap = OFFSET_NOT_SET; /* no 802.2 LLC */
                break;

        case DLT_JUNIPER_VP:
                cstate->off_linktype.constant_part = 18;
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;
                cstate->off_nl = OFFSET_NOT_SET;
                cstate->off_nl_nosnap = OFFSET_NOT_SET;
                break;

        case DLT_JUNIPER_ST:
                cstate->off_linktype.constant_part = 18;
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;
                cstate->off_nl = OFFSET_NOT_SET;
                cstate->off_nl_nosnap = OFFSET_NOT_SET;
                break;

        case DLT_JUNIPER_ISM:
                cstate->off_linktype.constant_part = 8;
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;
                cstate->off_nl = OFFSET_NOT_SET;
                cstate->off_nl_nosnap = OFFSET_NOT_SET;
                break;

        case DLT_JUNIPER_VS:
        case DLT_JUNIPER_SRX_E2E:
        case DLT_JUNIPER_FIBRECHANNEL:
        case DLT_JUNIPER_ATM_CEMIC:
                cstate->off_linktype.constant_part = 8;
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;
                cstate->off_nl = OFFSET_NOT_SET;
                cstate->off_nl_nosnap = OFFSET_NOT_SET;
                break;

        case DLT_MTP2:
                cstate->off_li = 2;
                cstate->off_li_hsl = 4;
                cstate->off_sio = 3;
                cstate->off_opc = 4;
                cstate->off_dpc = 4;
                cstate->off_sls = 7;
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;
                cstate->off_nl = OFFSET_NOT_SET;
                cstate->off_nl_nosnap = OFFSET_NOT_SET;
                break;

        case DLT_MTP2_WITH_PHDR:
                cstate->off_li = 6;
                cstate->off_li_hsl = 8;
                cstate->off_sio = 7;
                cstate->off_opc = 8;
                cstate->off_dpc = 8;
                cstate->off_sls = 11;
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;
                cstate->off_nl = OFFSET_NOT_SET;
                cstate->off_nl_nosnap = OFFSET_NOT_SET;
                break;

        case DLT_ERF:
                cstate->off_li = 22;
                cstate->off_li_hsl = 24;
                cstate->off_sio = 23;
                cstate->off_opc = 24;
                cstate->off_dpc = 24;
                cstate->off_sls = 27;
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;
                cstate->off_nl = OFFSET_NOT_SET;
                cstate->off_nl_nosnap = OFFSET_NOT_SET;
                break;

        case DLT_PFSYNC:
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                cstate->off_linkpl.constant_part = 4;
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = 0;
                break;

        case DLT_AX25_KISS:
                /*
                 * Currently, only raw "link[N:M]" filtering is supported.
                 */
                cstate->off_linktype.constant_part = OFFSET_NOT_SET;    /* variable, min 15, max 71 steps of 7 */
                cstate->off_linkpl.constant_part = OFFSET_NOT_SET;
                cstate->off_nl = OFFSET_NOT_SET;        /* variable, min 16, max 71 steps of 7 */
                cstate->off_nl_nosnap = OFFSET_NOT_SET; /* no 802.2 LLC */
                break;

        case DLT_IPNET:
                cstate->off_linktype.constant_part = 1;
                cstate->off_linkpl.constant_part = 24;  /* ipnet header length */
                cstate->off_nl = 0;
                cstate->off_nl_nosnap = OFFSET_NOT_SET;
                break;

        case DLT_NETANALYZER:
                cstate->off_linkhdr.constant_part = 4;  /* Ethernet header is past 4-byte pseudo-header */
                cstate->off_linktype.constant_part = cstate->off_linkhdr.constant_part + 12;
                cstate->off_linkpl.constant_part = cstate->off_linkhdr.constant_part + 14;      /* pseudo-header+Ethernet header length */
                cstate->off_nl = 0;             /* Ethernet II */
                cstate->off_nl_nosnap = 3;      /* 802.3+802.2 */
                break;

        case DLT_NETANALYZER_TRANSPARENT:
                cstate->off_linkhdr.constant_part = 12; /* MAC header is past 4-byte pseudo-header, preamble, and SFD */
                cstate->off_linktype.constant_part = cstate->off_linkhdr.constant_part + 12;
                cstate->off_linkpl.constant_part = cstate->off_linkhdr.constant_part + 14;      /* pseudo-header+preamble+SFD+Ethernet header length */
                cstate->off_nl = 0;             /* Ethernet II */
                cstate->off_nl_nosnap = 3;      /* 802.3+802.2 */
                break;

        default:
                /*
                 * For values in the range in which we've assigned new
                 * DLT_ values, only raw "link[N:M]" filtering is supported.
                 */
                if (cstate->linktype >= DLT_HIGH_MATCHING_MIN &&
                    cstate->linktype <= DLT_HIGH_MATCHING_MAX) {
                        cstate->off_linktype.constant_part = OFFSET_NOT_SET;
                        cstate->off_linkpl.constant_part = OFFSET_NOT_SET;
                        cstate->off_nl = OFFSET_NOT_SET;
                        cstate->off_nl_nosnap = OFFSET_NOT_SET;
                } else {
                        bpf_set_error(cstate, "unknown data link type %d (min %d, max %d)",
                            cstate->linktype, DLT_HIGH_MATCHING_MIN, DLT_HIGH_MATCHING_MAX);
                        return (-1);
                }
                break;
        }

        cstate->off_outermostlinkhdr = cstate->off_prevlinkhdr = cstate->off_linkhdr;
        return (0);
}

/*
 * Load a value relative to the specified absolute offset.
 */
static struct slist *
gen_load_absoffsetrel(compiler_state_t *cstate, bpf_abs_offset *abs_offset,
    u_int offset, u_int size)
{
        struct slist *s, *s2;

        s = gen_abs_offset_varpart(cstate, abs_offset);

        /*
         * If "s" is non-null, it has code to arrange that the X register
         * contains the variable part of the absolute offset, so we
         * generate a load relative to that, with an offset of
         * abs_offset->constant_part + offset.
         *
         * Otherwise, we can do an absolute load with an offset of
         * abs_offset->constant_part + offset.
         */
        if (s != NULL) {
                /*
                 * "s" points to a list of statements that puts the
                 * variable part of the absolute offset into the X register.
                 * Do an indirect load, to use the X register as an offset.
                 */
                s2 = new_stmt(cstate, BPF_LD|BPF_IND|size);
                s2->s.k = abs_offset->constant_part + offset;
                sappend(s, s2);
        } else {
                /*
                 * There is no variable part of the absolute offset, so
                 * just do an absolute load.
                 */
                s = new_stmt(cstate, BPF_LD|BPF_ABS|size);
                s->s.k = abs_offset->constant_part + offset;
        }
        return s;
}

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

        /*
         * Squelch warnings from compilers that *don't* assume that
         * offrel always has a valid enum value and therefore don't
         * assume that we'll always go through one of the case arms.
         *
         * If we have a default case, compilers that *do* assume that
         * will then complain about the default case code being
         * unreachable.
         *
         * Damned if you do, damned if you don't.
         */
        s = NULL;

        switch (offrel) {

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

        case OR_LINKHDR:
                s = gen_load_absoffsetrel(cstate, &cstate->off_linkhdr, offset, size);
                break;

        case OR_PREVLINKHDR:
                s = gen_load_absoffsetrel(cstate, &cstate->off_prevlinkhdr, offset, size);
                break;

        case OR_LLC:
                s = gen_load_absoffsetrel(cstate, &cstate->off_linkpl, offset, size);
                break;

        case OR_PREVMPLSHDR:
                s = gen_load_absoffsetrel(cstate, &cstate->off_linkpl, cstate->off_nl - 4 + offset, size);
                break;

        case OR_LINKPL:
                s = gen_load_absoffsetrel(cstate, &cstate->off_linkpl, cstate->off_nl + offset, size);
                break;

        case OR_LINKPL_NOSNAP:
                s = gen_load_absoffsetrel(cstate, &cstate->off_linkpl, cstate->off_nl_nosnap + offset, size);
                break;

        case OR_LINKTYPE:
                s = gen_load_absoffsetrel(cstate, &cstate->off_linktype, offset, size);
                break;

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

                /*
                 * Load the item at {offset of the link-layer payload} +
                 * {offset, relative to the start of the link-layer
                 * payload, of the IPv4 header} + {length of the IPv4 header} +
                 * {specified offset}.
                 *
                 * If the offset of the link-layer payload is variable,
                 * the variable part of that offset is included in the
                 * value in the X register, and we include the constant
                 * part in the offset of the load.
                 */
                s2 = new_stmt(cstate, BPF_LD|BPF_IND|size);
                s2->s.k = cstate->off_linkpl.constant_part + cstate->off_nl + offset;
                sappend(s, s2);
                break;

        case OR_TRAN_IPV6:
                s = gen_load_absoffsetrel(cstate, &cstate->off_linkpl, cstate->off_nl + 40 + offset, size);
                break;
        }
        return s;
}

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

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

                /*
                 * The A register now contains the length of the IP header.
                 * We need to add to it the variable part of the offset of
                 * the link-layer payload, which is still in the X
                 * register, and move the result into the X register.
                 */
                sappend(s, new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_X));
                sappend(s, new_stmt(cstate, BPF_MISC|BPF_TAX));
        } else {
                /*
                 * The offset of the link-layer payload is a constant,
                 * so no code was generated to load the (nonexistent)
                 * variable part of that offset.
                 *
                 * This means we can use the 4*([k]&0xf) addressing
                 * mode.  Load the length of the IPv4 header, which
                 * is at an offset of cstate->off_nl from the beginning of
                 * the link-layer payload, and thus at an offset of
                 * cstate->off_linkpl.constant_part + cstate->off_nl from the beginning
                 * of the raw packet data, using that addressing mode.
                 */
                s = new_stmt(cstate, BPF_LDX|BPF_MSH|BPF_B);
                s->s.k = cstate->off_linkpl.constant_part + cstate->off_nl;
        }
        return s;
}


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

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

        return b;
}

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

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

/*
 * Generate code to match a particular packet type.
 *
 * "proto" is an Ethernet type value, if > ETHERMTU, or an LLC SAP
 * value, if <= ETHERMTU.  We use that to determine whether to
 * match the type/length field or to check the type/length field for
 * a value <= ETHERMTU to see whether it's a type field and then do
 * the appropriate test.
 */
static struct block *
gen_ether_linktype(compiler_state_t *cstate, bpf_u_int32 ll_proto)
{
        struct block *b0, *b1;

        switch (ll_proto) {

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

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

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

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

                /*
                 * Now we generate code to check for 802.3
                 * frames in general.
                 */
                b0 = gen_cmp_le(cstate, OR_LINKTYPE, 0, BPF_H, ETHERMTU);

                /*
                 * 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(cstate, OR_LINKTYPE, 0, BPF_H, 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 or equal than
                 * 1500, which means it's an 802.3 length field.
                 */
                b0 = gen_cmp_le(cstate, OR_LINKTYPE, 0, BPF_H, ETHERMTU);

                /*
                 * 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 (ll_proto == ETHERTYPE_ATALK)
                        b1 = gen_snap(cstate, 0x080007, ETHERTYPE_ATALK);
                else    /* ll_proto == ETHERTYPE_AARP */
                        b1 = gen_snap(cstate, 0x000000, ETHERTYPE_AARP);
                gen_and(b0, b1);

                /*
                 * Check for Ethernet encapsulation (Ethertalk
                 * phase 1?); we just check for the Ethernet
                 * protocol type.
                 */
                b0 = gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H, ll_proto);

                gen_or(b0, b1);
                return b1;

        default:
                if (ll_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_le(cstate, OR_LINKTYPE, 0, BPF_H, ETHERMTU);
                        b1 = gen_cmp(cstate, OR_LINKTYPE, 2, BPF_B, ll_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
                         * "ll_proto" is > ETHERMTU, this test
                         * will fail and the frame won't match,
                         * which is what we want).
                         */
                        return gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H, ll_proto);
                }
        }
}

static struct block *
gen_loopback_linktype(compiler_state_t *cstate, bpf_u_int32 ll_proto)
{
        /*
         * For DLT_NULL, the link-layer header is a 32-bit word
         * containing an AF_ value in *host* byte order, and for
         * DLT_ENC, the link-layer header begins with a 32-bit
         * 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.
         */
        if (cstate->linktype == DLT_NULL || cstate->linktype == DLT_ENC) {
                /*
                 * The AF_ value is in host byte order, but the BPF
                 * interpreter will convert it to network byte order.
                 *
                 * If this is a save file, and it's from a machine
                 * with the opposite byte order to ours, we byte-swap
                 * the AF_ value.
                 *
                 * Then we run it through "htonl()", and generate
                 * code to compare against the result.
                 */
                if (cstate->bpf_pcap->rfile != NULL && cstate->bpf_pcap->swapped)
                        ll_proto = SWAPLONG(ll_proto);
                ll_proto = htonl(ll_proto);
        }
        return (gen_cmp(cstate, OR_LINKHDR, 0, BPF_W, ll_proto));
}

/*
 * "proto" is an Ethernet type value and for IPNET, if it is not IPv4
 * or IPv6 then we have an error.
 */
static struct block *
gen_ipnet_linktype(compiler_state_t *cstate, bpf_u_int32 ll_proto)
{
        switch (ll_proto) {

        case ETHERTYPE_IP:
                return gen_cmp(cstate, OR_LINKTYPE, 0, BPF_B, IPH_AF_INET);
                /*NOTREACHED*/

        case ETHERTYPE_IPV6:
                return gen_cmp(cstate, OR_LINKTYPE, 0, BPF_B, IPH_AF_INET6);
                /*NOTREACHED*/

        default:
                break;
        }

        return gen_false(cstate);
}

/*
 * Generate code to match a particular packet type.
 *
 * "ll_proto" is an Ethernet type value, if > ETHERMTU, or an LLC SAP
 * value, if <= ETHERMTU.  We use that to determine whether to
 * match the type field or to check the type field for the special
 * LINUX_SLL_P_802_2 value and then do the appropriate test.
 */
static struct block *
gen_linux_sll_linktype(compiler_state_t *cstate, bpf_u_int32 ll_proto)
{
        struct block *b0, *b1;

        switch (ll_proto) {

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

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

                /*
                 * Now check for 802.3 frames and OR that with
                 * the previous test.
                 */
                b0 = gen_cmp(cstate, OR_LINKTYPE, 0, 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(cstate, OR_LINKTYPE, 0, BPF_H, 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(cstate, OR_LINKTYPE, 0, 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 (ll_proto == ETHERTYPE_ATALK)
                        b1 = gen_snap(cstate, 0x080007, ETHERTYPE_ATALK);
                else    /* ll_proto == ETHERTYPE_AARP */
                        b1 = gen_snap(cstate, 0x000000, ETHERTYPE_AARP);
                gen_and(b0, b1);

                /*
                 * Check for Ethernet encapsulation (Ethertalk
                 * phase 1?); we just check for the Ethernet
                 * protocol type.
                 */
                b0 = gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H, ll_proto);

                gen_or(b0, b1);
                return b1;

        default:
                if (ll_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(cstate, OR_LINKTYPE, 0, BPF_H, LINUX_SLL_P_802_2);
                        b1 = gen_cmp(cstate, OR_LINKHDR, cstate->off_linkpl.constant_part, BPF_B,
                             ll_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
                         * "ll_proto" is > ETHERMTU, this test
                         * will fail and the frame won't match,
                         * which is what we want).
                         */
                        return gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H, ll_proto);
                }
        }
}

/*
 * Load a value relative to the beginning of the link-layer header after the
 * pflog header.
 */
static struct slist *
gen_load_pflog_llprefixlen(compiler_state_t *cstate)
{
        struct slist *s1, *s2;

        /*
         * Generate code to load the length of the pflog header into
         * the register assigned to hold that length, if one has been
         * assigned.  (If one hasn't been assigned, no code we've
         * generated uses that prefix, so we don't need to generate any
         * code to load it.)
         */
        if (cstate->off_linkpl.reg != -1) {
                /*
                 * The length is in the first byte of the header.
                 */
                s1 = new_stmt(cstate, BPF_LD|BPF_B|BPF_ABS);
                s1->s.k = 0;

                /*
                 * Round it up to a multiple of 4.
                 * Add 3, and clear the lower 2 bits.
                 */
                s2 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
                s2->s.k = 3;
                sappend(s1, s2);
                s2 = new_stmt(cstate, BPF_ALU|BPF_AND|BPF_K);
                s2->s.k = 0xfffffffc;
                sappend(s1, s2);

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

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

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

static struct slist *
gen_load_prism_llprefixlen(compiler_state_t *cstate)
{
        struct slist *s1, *s2;
        struct slist *sjeq_avs_cookie;
        struct slist *sjcommon;

        /*
         * This code is not compatible with the optimizer, as
         * we are generating jmp instructions within a normal
         * slist of instructions
         */
        cstate->no_optimize = 1;

        /*
         * Generate code to load the length of the radio header into
         * the register assigned to hold that length, if one has been
         * assigned.  (If one hasn't been assigned, no code we've
         * generated uses that prefix, so we don't need to generate any
         * code to load it.)
         *
         * Some Linux drivers use ARPHRD_IEEE80211_PRISM but sometimes
         * or always use the AVS header rather than the Prism header.
         * We load a 4-byte big-endian value at the beginning of the
         * raw packet data, and see whether, when masked with 0xFFFFF000,
         * it's equal to 0x80211000.  If so, that indicates that it's
         * an AVS header (the masked-out bits are the version number).
         * Otherwise, it's a Prism header.
         *
         * XXX - the Prism header is also, in theory, variable-length,
         * but no known software generates headers that aren't 144
         * bytes long.
         */
        if (cstate->off_linkhdr.reg != -1) {
                /*
                 * Load the cookie.
                 */
                s1 = new_stmt(cstate, BPF_LD|BPF_W|BPF_ABS);
                s1->s.k = 0;

                /*
                 * AND it with 0xFFFFF000.
                 */
                s2 = new_stmt(cstate, BPF_ALU|BPF_AND|BPF_K);
                s2->s.k = 0xFFFFF000;
                sappend(s1, s2);

                /*
                 * Compare with 0x80211000.
                 */
                sjeq_avs_cookie = new_stmt(cstate, JMP(BPF_JEQ));
                sjeq_avs_cookie->s.k = 0x80211000;
                sappend(s1, sjeq_avs_cookie);

                /*
                 * If it's AVS:
                 *
                 * The 4 bytes at an offset of 4 from the beginning of
                 * the AVS header are the length of the AVS header.
                 * That field is big-endian.
                 */
                s2 = new_stmt(cstate, BPF_LD|BPF_W|BPF_ABS);
                s2->s.k = 4;
                sappend(s1, s2);
                sjeq_avs_cookie->s.jt = s2;

                /*
                 * Now jump to the code to allocate a register
                 * into which to save the header length and
                 * store the length there.  (The "jump always"
                 * instruction needs to have the k field set;
                 * it's added to the PC, so, as we're jumping
                 * over a single instruction, it should be 1.)
                 */
                sjcommon = new_stmt(cstate, JMP(BPF_JA));
                sjcommon->s.k = 1;
                sappend(s1, sjcommon);

                /*
                 * Now for the code that handles the Prism header.
                 * Just load the length of the Prism header (144)
                 * into the A register.  Have the test for an AVS
                 * header branch here if we don't have an AVS header.
                 */
                s2 = new_stmt(cstate, BPF_LD|BPF_W|BPF_IMM);
                s2->s.k = 144;
                sappend(s1, s2);
                sjeq_avs_cookie->s.jf = s2;

                /*
                 * Now allocate a register to hold that value and store
                 * it.  The code for the AVS header will jump here after
                 * loading the length of the AVS header.
                 */
                s2 = new_stmt(cstate, BPF_ST);
                s2->s.k = cstate->off_linkhdr.reg;
                sappend(s1, s2);
                sjcommon->s.jf = s2;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

/*
 * At the moment we treat PPI as normal Radiotap encoded
 * packets. The difference is in the function that generates
 * the code at the beginning to compute the header length.
 * Since this code generator of PPI supports bare 802.11
 * encapsulation only (i.e. the encapsulated DLT should be
 * DLT_IEEE802_11) we generate code to check for this too;
 * that's done in finish_parse().
 */
static struct slist *
gen_load_ppi_llprefixlen(compiler_state_t *cstate)
{
        struct slist *s1, *s2;

        /*
         * Generate code to load the length of the radiotap header
         * into the register assigned to hold that length, if one has
         * been assigned.
         */
        if (cstate->off_linkhdr.reg != -1) {
                /*
                 * The 2 bytes at offsets of 2 and 3 from the beginning
                 * of the radiotap header are the length of the radiotap
                 * header; unfortunately, it's little-endian, so we have
                 * to load it a byte at a time and construct the value.
                 */

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

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

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

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

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

/*
 * Load a value relative to the beginning of the link-layer header after the 802.11
 * header, i.e. LLC_SNAP.
 * The link-layer header doesn't necessarily begin at the beginning
 * of the packet data; there might be a variable-length prefix containing
 * radio information.
 */
static struct slist *
gen_load_802_11_header_len(compiler_state_t *cstate, struct slist *s, struct slist *snext)
{
        struct slist *s2;
        struct slist *sjset_data_frame_1;
        struct slist *sjset_data_frame_2;
        struct slist *sjset_qos;
        struct slist *sjset_radiotap_flags_present;
        struct slist *sjset_radiotap_ext_present;
        struct slist *sjset_radiotap_tsft_present;
        struct slist *sjset_tsft_datapad, *sjset_notsft_datapad;
        struct slist *s_roundup;

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

        /*
         * This code is not compatible with the optimizer, as
         * we are generating jmp instructions within a normal
         * slist of instructions
         */
        cstate->no_optimize = 1;

        /*
         * If "s" is non-null, it has code to arrange that the X register
         * contains the length of the prefix preceding the link-layer
         * header.
         *
         * Otherwise, the length of the prefix preceding the link-layer
         * header is "off_outermostlinkhdr.constant_part".
         */
        if (s == NULL) {
                /*
                 * There is no variable-length header preceding the
                 * link-layer header.
                 *
                 * Load the length of the fixed-length prefix preceding
                 * the link-layer header (if any) into the X register,
                 * and store it in the cstate->off_linkpl.reg register.
                 * That length is off_outermostlinkhdr.constant_part.
                 */
                s = new_stmt(cstate, BPF_LDX|BPF_IMM);
                s->s.k = cstate->off_outermostlinkhdr.constant_part;
        }

        /*
         * The X register contains the offset of the beginning of the
         * link-layer header; add 24, which is the minimum length
         * of the MAC header for a data frame, to that, and store it
         * in cstate->off_linkpl.reg, and then load the Frame Control field,
         * which is at the offset in the X register, with an indexed load.
         */
        s2 = new_stmt(cstate, BPF_MISC|BPF_TXA);
        sappend(s, s2);
        s2 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s2->s.k = 24;
        sappend(s, s2);
        s2 = new_stmt(cstate, BPF_ST);
        s2->s.k = cstate->off_linkpl.reg;
        sappend(s, s2);

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

        /*
         * Check the Frame Control field to see if this is a data frame;
         * a data frame has the 0x08 bit (b3) in that field set and the
         * 0x04 bit (b2) clear.
         */
        sjset_data_frame_1 = new_stmt(cstate, JMP(BPF_JSET));
        sjset_data_frame_1->s.k = 0x08;
        sappend(s, sjset_data_frame_1);

        /*
         * If b3 is set, test b2, otherwise go to the first statement of
         * the rest of the program.
         */
        sjset_data_frame_1->s.jt = sjset_data_frame_2 = new_stmt(cstate, JMP(BPF_JSET));
        sjset_data_frame_2->s.k = 0x04;
        sappend(s, sjset_data_frame_2);
        sjset_data_frame_1->s.jf = snext;

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

        /*
         * If it's set, add 2 to cstate->off_linkpl.reg, to skip the QoS
         * field.
         * Otherwise, go to the first statement of the rest of the
         * program.
         */
        sjset_qos->s.jt = s2 = new_stmt(cstate, BPF_LD|BPF_MEM);
        s2->s.k = cstate->off_linkpl.reg;
        sappend(s, s2);
        s2 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_IMM);
        s2->s.k = 2;
        sappend(s, s2);
        s2 = new_stmt(cstate, BPF_ST);
        s2->s.k = cstate->off_linkpl.reg;
        sappend(s, s2);

        /*
         * If we have a radiotap header, look at it to see whether
         * there's Atheros padding between the MAC-layer header
         * and the payload.
         *
         * Note: all of the fields in the radiotap header are
         * little-endian, so we byte-swap all of the values
         * we test against, as they will be loaded as big-endian
         * values.
         *
         * XXX - in the general case, we would have to scan through
         * *all* the presence bits, if there's more than one word of
         * presence bits.  That would require a loop, meaning that
         * we wouldn't be able to run the filter in the kernel.
         *
         * We assume here that the Atheros adapters that insert the
         * annoying padding don't have multiple antennae and therefore
         * do not generate radiotap headers with multiple presence words.
         */
        if (cstate->linktype == DLT_IEEE802_11_RADIO) {
                /*
                 * Is the IEEE80211_RADIOTAP_FLAGS bit (0x0000002) set
                 * in the first presence flag word?
                 */
                sjset_qos->s.jf = s2 = new_stmt(cstate, BPF_LD|BPF_ABS|BPF_W);
                s2->s.k = 4;
                sappend(s, s2);

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

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

                /*
                 * Otherwise, is the "extension" bit set in that word?
                 */
                sjset_radiotap_ext_present = new_stmt(cstate, JMP(BPF_JSET));
                sjset_radiotap_ext_present->s.k = SWAPLONG(0x80000000);
                sappend(s, sjset_radiotap_ext_present);
                sjset_radiotap_flags_present->s.jt = sjset_radiotap_ext_present;

                /*
                 * If so, skip all of this.
                 */
                sjset_radiotap_ext_present->s.jt = snext;

                /*
                 * Otherwise, is the IEEE80211_RADIOTAP_TSFT bit set?
                 */
                sjset_radiotap_tsft_present = new_stmt(cstate, JMP(BPF_JSET));
                sjset_radiotap_tsft_present->s.k = SWAPLONG(0x00000001);
                sappend(s, sjset_radiotap_tsft_present);
                sjset_radiotap_ext_present->s.jf = sjset_radiotap_tsft_present;

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

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

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

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

                /*
                 * In either case, if IEEE80211_RADIOTAP_F_DATAPAD is
                 * set, round the length of the 802.11 header to
                 * a multiple of 4.  Do that by adding 3 and then
                 * dividing by and multiplying by 4, which we do by
                 * ANDing with ~3.
                 */
                s_roundup = new_stmt(cstate, BPF_LD|BPF_MEM);
                s_roundup->s.k = cstate->off_linkpl.reg;
                sappend(s, s_roundup);
                s2 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_IMM);
                s2->s.k = 3;
                sappend(s, s2);
                s2 = new_stmt(cstate, BPF_ALU|BPF_AND|BPF_IMM);
                s2->s.k = (bpf_u_int32)~3;
                sappend(s, s2);
                s2 = new_stmt(cstate, BPF_ST);
                s2->s.k = cstate->off_linkpl.reg;
                sappend(s, s2);

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

        return s;
}

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

        /* There is an implicit dependency between the link
         * payload and link header since the payload computation
         * includes the variable part of the header. Therefore,
         * if nobody else has allocated a register for the link
         * header and we need it, do it now. */
        if (cstate->off_linkpl.reg != -1 && cstate->off_linkhdr.is_variable &&
            cstate->off_linkhdr.reg == -1)
                cstate->off_linkhdr.reg = alloc_reg(cstate);

        /*
         * For link-layer types that have a variable-length header
         * preceding the link-layer header, generate code to load
         * the offset of the link-layer header into the register
         * assigned to that offset, if any.
         *
         * XXX - this, and the next switch statement, won't handle
         * encapsulation of 802.11 or 802.11+radio information in
         * some other protocol stack.  That's significantly more
         * complicated.
         */
        switch (cstate->outermostlinktype) {

        case DLT_PRISM_HEADER:
                s = gen_load_prism_llprefixlen(cstate);
                break;

        case DLT_IEEE802_11_RADIO_AVS:
                s = gen_load_avs_llprefixlen(cstate);
                break;

        case DLT_IEEE802_11_RADIO:
                s = gen_load_radiotap_llprefixlen(cstate);
                break;

        case DLT_PPI:
                s = gen_load_ppi_llprefixlen(cstate);
                break;

        default:
                s = NULL;
                break;
        }

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

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

        case DLT_PFLOG:
                s = gen_load_pflog_llprefixlen(cstate);
                break;
        }

        /*
         * If there is no initialization yet and we need variable
         * length offsets for VLAN, initialize them to zero
         */
        if (s == NULL && cstate->is_vlan_vloffset) {
                struct slist *s2;

                if (cstate->off_linkpl.reg == -1)
                        cstate->off_linkpl.reg = alloc_reg(cstate);
                if (cstate->off_linktype.reg == -1)
                        cstate->off_linktype.reg = alloc_reg(cstate);

                s = new_stmt(cstate, BPF_LD|BPF_W|BPF_IMM);
                s->s.k = 0;
                s2 = new_stmt(cstate, BPF_ST);
                s2->s.k = cstate->off_linkpl.reg;
                sappend(s, s2);
                s2 = new_stmt(cstate, BPF_ST);
                s2->s.k = cstate->off_linktype.reg;
                sappend(s, s2);
        }

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

/*
 * Take an absolute offset, and:
 *
 *    if it has no variable part, return NULL;
 *
 *    if it has a variable part, generate code to load the register
 *    containing that variable part into the X register, returning
 *    a pointer to that code - if no register for that offset has
 *    been allocated, allocate it first.
 *
 * (The code to set that register will be generated later, but will
 * be placed earlier in the code sequence.)
 */
static struct slist *
gen_abs_offset_varpart(compiler_state_t *cstate, bpf_abs_offset *off)
{
        struct slist *s;

        if (off->is_variable) {
                if (off->reg == -1) {
                        /*
                         * We haven't yet assigned a register for the
                         * variable part of the offset of the link-layer
                         * header; allocate one.
                         */
                        off->reg = alloc_reg(cstate);
                }

                /*
                 * Load the register containing the variable part of the
                 * offset of the link-layer header into the X register.
                 */
                s = new_stmt(cstate, BPF_LDX|BPF_MEM);
                s->s.k = off->reg;
                return s;
        } else {
                /*
                 * That offset isn't variable, there's no variable part,
                 * so we don't need to generate any code.
                 */
                return NULL;
        }
}

/*
 * Map an Ethernet type to the equivalent PPP type.
 */
static bpf_u_int32
ethertype_to_ppptype(bpf_u_int32 ll_proto)
{
        switch (ll_proto) {

        case ETHERTYPE_IP:
                ll_proto = PPP_IP;
                break;

        case ETHERTYPE_IPV6:
                ll_proto = PPP_IPV6;
                break;

        case ETHERTYPE_DN:
                ll_proto = PPP_DECNET;
                break;

        case ETHERTYPE_ATALK:
                ll_proto = PPP_APPLE;
                break;

        case ETHERTYPE_NS:
                ll_proto = PPP_NS;
                break;

        case LLCSAP_ISONS:
                ll_proto = PPP_OSI;
                break;

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

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

/*
 * Generate any tests that, for encapsulation of a link-layer packet
 * inside another protocol stack, need to be done to check for those
 * link-layer packets (and that haven't already been done by a check
 * for that encapsulation).
 */
static struct block *
gen_prevlinkhdr_check(compiler_state_t *cstate)
{
        struct block *b0;

        if (cstate->is_encap)
                return gen_encap_ll_check(cstate);

        switch (cstate->prevlinktype) {

        case DLT_SUNATM:
                /*
                 * This is LANE-encapsulated Ethernet; check that the LANE
                 * packet doesn't begin with an LE Control marker, i.e.
                 * that it's data, not a control message.
                 *
                 * (We've already generated a test for LANE.)
                 */
                b0 = gen_cmp(cstate, OR_PREVLINKHDR, SUNATM_PKT_BEGIN_POS, BPF_H, 0xFF00);
                gen_not(b0);
                return b0;

        default:
                /*
                 * No such tests are necessary.
                 */
                return NULL;
        }
        /*NOTREACHED*/
}

/*
 * The three different values we should check for when checking for an
 * IPv6 packet with DLT_NULL.
 */
#define BSD_AFNUM_INET6_BSD     24      /* NetBSD, OpenBSD, BSD/OS, Npcap */
#define BSD_AFNUM_INET6_FREEBSD 28      /* FreeBSD */
#define BSD_AFNUM_INET6_DARWIN  30      /* macOS, iOS, other Darwin-based OSes */

/*
 * Generate code to match a particular packet type by matching the
 * link-layer type field or fields in the 802.2 LLC header.
 *
 * "proto" is an Ethernet type value, if > ETHERMTU, or an LLC SAP
 * value, if <= ETHERMTU.
 */
static struct block *
gen_linktype(compiler_state_t *cstate, bpf_u_int32 ll_proto)
{
        struct block *b0, *b1, *b2;

        /* are we checking MPLS-encapsulated packets? */
        if (cstate->label_stack_depth > 0)
                return gen_mpls_linktype(cstate, ll_proto);

        switch (cstate->linktype) {

        case DLT_EN10MB:
        case DLT_NETANALYZER:
        case DLT_NETANALYZER_TRANSPARENT:
                /* Geneve has an EtherType regardless of whether there is an
                 * L2 header. VXLAN always has an EtherType. */
                if (!cstate->is_encap)
                        b0 = gen_prevlinkhdr_check(cstate);
                else
                        b0 = NULL;

                b1 = gen_ether_linktype(cstate, ll_proto);
                if (b0 != NULL)
                        gen_and(b0, b1);
                return b1;
                /*NOTREACHED*/

        case DLT_C_HDLC:
        case DLT_HDLC:
                switch (ll_proto) {

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

                default:
                        return gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H, ll_proto);
                        /*NOTREACHED*/
                }

        case DLT_IEEE802_11:
        case DLT_PRISM_HEADER:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_IEEE802_11_RADIO:
        case DLT_PPI:
                /*
                 * Check that we have a data frame.
                 */
                b0 = gen_mcmp(cstate, OR_LINKHDR, 0, BPF_B,
                        IEEE80211_FC0_TYPE_DATA,
                        IEEE80211_FC0_TYPE_MASK);

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

        case DLT_FDDI:
                /*
                 * XXX - check for LLC frames.
                 */
                return gen_llc_linktype(cstate, ll_proto);
                /*NOTREACHED*/

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

        case DLT_ATM_RFC1483:
        case DLT_ATM_CLIP:
        case DLT_IP_OVER_FC:
                return gen_llc_linktype(cstate, ll_proto);
                /*NOTREACHED*/

        case DLT_SUNATM:
                /*
                 * Check for an LLC-encapsulated version of this protocol;
                 * if we were checking for LANE, linktype would no longer
                 * be DLT_SUNATM.
                 *
                 * Check for LLC encapsulation and then check the protocol.
                 */
                b0 = gen_atmfield_code_internal(cstate, A_PROTOTYPE, PT_LLC, BPF_JEQ, 0);
                b1 = gen_llc_linktype(cstate, ll_proto);
                gen_and(b0, b1);
                return b1;
                /*NOTREACHED*/

        case DLT_LINUX_SLL:
                return gen_linux_sll_linktype(cstate, ll_proto);
                /*NOTREACHED*/

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

                case ETHERTYPE_IP:
                        /* Check for a version number of 4. */
                        return gen_mcmp(cstate, OR_LINKHDR, 0, BPF_B, 0x40, 0xF0);

                case ETHERTYPE_IPV6:
                        /* Check for a version number of 6. */
                        return gen_mcmp(cstate, OR_LINKHDR, 0, BPF_B, 0x60, 0xF0);

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

        case DLT_IPV4:
                /*
                 * Raw IPv4, so no type field.
                 */
                if (ll_proto == ETHERTYPE_IP)
                        return gen_true(cstate);        /* always true */

                /* Checking for something other than IPv4; always false */
                return gen_false(cstate);
                /*NOTREACHED*/

        case DLT_IPV6:
                /*
                 * Raw IPv6, so no type field.
                 */
                if (ll_proto == ETHERTYPE_IPV6)
                        return gen_true(cstate);        /* always true */

                /* Checking for something other than IPv6; always false */
                return gen_false(cstate);
                /*NOTREACHED*/

        case DLT_PPP:
        case DLT_PPP_PPPD:
        case DLT_PPP_SERIAL:
        case DLT_PPP_ETHER:
                /*
                 * We use Ethernet protocol types inside libpcap;
                 * map them to the corresponding PPP protocol types.
                 */
                return gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H,
                    ethertype_to_ppptype(ll_proto));
                /*NOTREACHED*/

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

                case ETHERTYPE_IP:
                        /*
                         * Also check for Van Jacobson-compressed IP.
                         * XXX - do this for other forms of PPP?
                         */
                        b0 = gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H, PPP_IP);
                        b1 = gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H, PPP_VJC);
                        gen_or(b0, b1);
                        b0 = gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H, PPP_VJNC);
                        gen_or(b1, b0);
                        return b0;

                default:
                        return gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H,
                            ethertype_to_ppptype(ll_proto));
                }
                /*NOTREACHED*/

        case DLT_NULL:
        case DLT_LOOP:
        case DLT_ENC:
                switch (ll_proto) {

                case ETHERTYPE_IP:
                        return (gen_loopback_linktype(cstate, AF_INET));

                case ETHERTYPE_IPV6:
                        /*
                         * AF_ values may, unfortunately, be platform-
                         * dependent; AF_INET isn't, because everybody
                         * used 4.2BSD's value, but AF_INET6 is, because
                         * 4.2BSD didn't have a value for it (given that
                         * IPv6 didn't exist back in the early 1980's),
                         * and they all picked their own values.
                         *
                         * This means that, if we're reading from a
                         * savefile, we need to check for all the
                         * possible values.
                         *
                         * If we're doing a live capture, we only need
                         * to check for this platform's value; however,
                         * Npcap uses 24, which isn't Windows's AF_INET6
                         * value.  (Given the multiple different values,
                         * programs that read pcap files shouldn't be
                         * checking for their platform's AF_INET6 value
                         * anyway, they should check for all of the
                         * possible values. and they might as well do
                         * that even for live captures.)
                         */
                        if (cstate->bpf_pcap->rfile != NULL) {
                                /*
                                 * Savefile - check for all three
                                 * possible IPv6 values.
                                 */
                                b0 = gen_loopback_linktype(cstate, BSD_AFNUM_INET6_BSD);
                                b1 = gen_loopback_linktype(cstate, BSD_AFNUM_INET6_FREEBSD);
                                gen_or(b0, b1);
                                b0 = gen_loopback_linktype(cstate, BSD_AFNUM_INET6_DARWIN);
                                gen_or(b0, b1);
                                return (b1);
                        } else {
                                /*
                                 * Live capture, so we only need to
                                 * check for the value used on this
                                 * platform.
                                 */
#ifdef _WIN32
                                /*
                                 * Npcap doesn't use Windows's AF_INET6,
                                 * as that collides with AF_IPX on
                                 * some BSDs (both have the value 23).
                                 * Instead, it uses 24.
                                 */
                                return (gen_loopback_linktype(cstate, 24));
#else /* _WIN32 */
#ifdef AF_INET6
                                return (gen_loopback_linktype(cstate, AF_INET6));
#else /* AF_INET6 */
                                /*
                                 * I guess this platform doesn't support
                                 * IPv6, so we just reject all packets.
                                 */
                                return gen_false(cstate);
#endif /* AF_INET6 */
#endif /* _WIN32 */
                        }

                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(cstate);
                }

        case DLT_PFLOG:
                /*
                 * af field is host byte order in contrast to the rest of
                 * the packet.
                 */
                if (ll_proto == ETHERTYPE_IP)
                        return (gen_cmp(cstate, OR_LINKHDR, offsetof(struct pfloghdr, af),
                            BPF_B, AF_INET));
                else if (ll_proto == ETHERTYPE_IPV6)
                        return (gen_cmp(cstate, OR_LINKHDR, offsetof(struct pfloghdr, af),
                            BPF_B, AF_INET6));
                else
                        return gen_false(cstate);
                /*NOTREACHED*/

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

                default:
                        return gen_false(cstate);

                case ETHERTYPE_IPV6:
                        return (gen_cmp(cstate, OR_LINKTYPE, 0, BPF_B,
                                ARCTYPE_INET6));

                case ETHERTYPE_IP:
                        b0 = gen_cmp(cstate, OR_LINKTYPE, 0, BPF_B,
                            ARCTYPE_IP);
                        b1 = gen_cmp(cstate, OR_LINKTYPE, 0, BPF_B,
                            ARCTYPE_IP_OLD);
                        gen_or(b0, b1);
                        return (b1);

                case ETHERTYPE_ARP:
                        b0 = gen_cmp(cstate, OR_LINKTYPE, 0, BPF_B,
                            ARCTYPE_ARP);
                        b1 = gen_cmp(cstate, OR_LINKTYPE, 0, BPF_B,
                            ARCTYPE_ARP_OLD);
                        gen_or(b0, b1);
                        return (b1);

                case ETHERTYPE_REVARP:
                        return (gen_cmp(cstate, OR_LINKTYPE, 0, BPF_B,
                            ARCTYPE_REVARP));

                case ETHERTYPE_ATALK:
                        return (gen_cmp(cstate, OR_LINKTYPE, 0, BPF_B,
                            ARCTYPE_ATALK));
                }
                /*NOTREACHED*/

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

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

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

                case ETHERTYPE_IPV6:
                        /*
                         * Check for the special NLPID for IPv6.
                         */
                        return gen_cmp(cstate, OR_LINKHDR, 2, BPF_H, (0x03<<8) | 0x8e);

                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(cstate, OR_LINKHDR, 2, BPF_H, (0x03<<8) | ISO8473_CLNP);
                        b1 = gen_cmp(cstate, OR_LINKHDR, 2, BPF_H, (0x03<<8) | ISO9542_ESIS);
                        b2 = gen_cmp(cstate, OR_LINKHDR, 2, BPF_H, (0x03<<8) | ISO10589_ISIS);
                        gen_or(b1, b2);
                        gen_or(b0, b2);
                        return b2;

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

        case DLT_MFR:
                break; // not implemented

        case DLT_JUNIPER_MFR:
        case DLT_JUNIPER_MLFR:
        case DLT_JUNIPER_MLPPP:
        case DLT_JUNIPER_ATM1:
        case DLT_JUNIPER_ATM2:
        case DLT_JUNIPER_PPPOE:
        case DLT_JUNIPER_PPPOE_ATM:
        case DLT_JUNIPER_GGSN:
        case DLT_JUNIPER_ES:
        case DLT_JUNIPER_MONITOR:
        case DLT_JUNIPER_SERVICES:
        case DLT_JUNIPER_ETHER:
        case DLT_JUNIPER_PPP:
        case DLT_JUNIPER_FRELAY:
        case DLT_JUNIPER_CHDLC:
        case DLT_JUNIPER_VP:
        case DLT_JUNIPER_ST:
        case DLT_JUNIPER_ISM:
        case DLT_JUNIPER_VS:
        case DLT_JUNIPER_SRX_E2E:
        case DLT_JUNIPER_FIBRECHANNEL:
        case DLT_JUNIPER_ATM_CEMIC:

                /* just lets verify the magic number for now -
                 * on ATM we may have up to 6 different encapsulations on the wire
                 * and need a lot of heuristics to figure out that the payload
                 * might be;
                 *
                 * FIXME encapsulation specific BPF_ filters
                 */
                return gen_mcmp(cstate, OR_LINKHDR, 0, BPF_W, 0x4d474300, 0xffffff00); /* compare the magic number */

        case DLT_BACNET_MS_TP:
                return gen_mcmp(cstate, OR_LINKHDR, 0, BPF_W, 0x55FF0000, 0xffff0000);

        case DLT_IPNET:
                return gen_ipnet_linktype(cstate, ll_proto);

        case DLT_LINUX_IRDA:
        case DLT_DOCSIS:
        case DLT_MTP2:
        case DLT_MTP2_WITH_PHDR:
        case DLT_ERF:
        case DLT_PFSYNC:
        case DLT_LINUX_LAPD:
        case DLT_USB_FREEBSD:
        case DLT_USB_LINUX:
        case DLT_USB_LINUX_MMAPPED:
        case DLT_USBPCAP:
        case DLT_BLUETOOTH_HCI_H4:
        case DLT_BLUETOOTH_HCI_H4_WITH_PHDR:
        case DLT_CAN20B:
        case DLT_CAN_SOCKETCAN:
        case DLT_IEEE802_15_4:
        case DLT_IEEE802_15_4_LINUX:
        case DLT_IEEE802_15_4_NONASK_PHY:
        case DLT_IEEE802_15_4_NOFCS:
        case DLT_IEEE802_15_4_TAP:
        case DLT_IEEE802_16_MAC_CPS_RADIO:
        case DLT_SITA:
        case DLT_RAIF1:
        case DLT_IPMB_KONTRON:
        case DLT_I2C_LINUX:
        case DLT_AX25_KISS:
        case DLT_NFLOG:
                /* Using the fixed-size NFLOG header it is possible to tell only
                 * the address family of the packet, other meaningful data is
                 * either missing or behind TLVs.
                 */
                break; // not implemented

        default:
                /*
                 * Does this link-layer header type have a field
                 * indicating the type of the next protocol?  If
                 * so, off_linktype.constant_part will be the offset of that
                 * field in the packet; if not, it will be OFFSET_NOT_SET.
                 */
                if (cstate->off_linktype.constant_part != OFFSET_NOT_SET) {
                        /*
                         * Yes; assume it's an Ethernet type.  (If
                         * it's not, it needs to be handled specially
                         * above.)
                         */
                        return gen_cmp(cstate, OR_LINKTYPE, 0, BPF_H, ll_proto);
                        /*NOTREACHED */
                }
        }
        bpf_error(cstate, "link-layer type filtering not implemented for %s",
            pcap_datalink_val_to_description_or_dlt(cstate->linktype));
}

/*
 * 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(compiler_state_t *cstate, bpf_u_int32 orgcode, bpf_u_int32 ptype)
{
        u_char snapblock[8];

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

/*
 * Generate code to match frames with an LLC header.
 */
static struct block *
gen_llc_internal(compiler_state_t *cstate)
{
        struct block *b0, *b1;

        switch (cstate->linktype) {

        case DLT_EN10MB:
                /*
                 * We check for an Ethernet type field less or equal than
                 * 1500, which means it's an 802.3 length field.
                 */
                b0 = gen_cmp_le(cstate, OR_LINKTYPE, 0, BPF_H, ETHERMTU);

                /*
                 * Now check for the purported DSAP and SSAP not being
                 * 0xFF, to rule out NetWare-over-802.3.
                 */
                b1 = gen_cmp(cstate, OR_LLC, 0, BPF_H, 0xFFFF);
                gen_not(b1);
                gen_and(b0, b1);
                return b1;

        case DLT_SUNATM:
                /*
                 * We check for LLC traffic.
                 */
                b0 = gen_atmtype_llc(cstate);
                return b0;

        case DLT_IEEE802:       /* Token Ring */
                /*
                 * XXX - check for LLC frames.
                 */
                return gen_true(cstate);

        case DLT_FDDI:
                /*
                 * XXX - check for LLC frames.
                 */
                return gen_true(cstate);

        case DLT_ATM_RFC1483:
                /*
                 * For LLC encapsulation, these are defined to have an
                 * 802.2 LLC header.
                 *
                 * For VC encapsulation, they don't, but there's no
                 * way to check for that; the protocol used on the VC
                 * is negotiated out of band.
                 */
                return gen_true(cstate);

        case DLT_IEEE802_11:
        case DLT_PRISM_HEADER:
        case DLT_IEEE802_11_RADIO:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_PPI:
                /*
                 * Check that we have a data frame.
                 */
                return gen_mcmp(cstate, OR_LINKHDR, 0, BPF_B,
                        IEEE80211_FC0_TYPE_DATA,
                        IEEE80211_FC0_TYPE_MASK);

        default:
                fail_kw_on_dlt(cstate, "llc");
                /*NOTREACHED*/
        }
}

struct block *
gen_llc(compiler_state_t *cstate)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        return gen_llc_internal(cstate);
}

struct block *
gen_llc_i(compiler_state_t *cstate)
{
        struct block *b0, *b1;
        struct slist *s;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        /*
         * Check whether this is an LLC frame.
         */
        b0 = gen_llc_internal(cstate);

        /*
         * Load the control byte and test the low-order bit; it must
         * be clear for I frames.
         */
        s = gen_load_a(cstate, OR_LLC, 2, BPF_B);
        b1 = new_block(cstate, JMP(BPF_JSET));
        b1->s.k = 0x01;
        b1->stmts = s;
        gen_not(b1);
        gen_and(b0, b1);
        return b1;
}

struct block *
gen_llc_s(compiler_state_t *cstate)
{
        struct block *b0, *b1;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        /*
         * Check whether this is an LLC frame.
         */
        b0 = gen_llc_internal(cstate);

        /*
         * Now compare the low-order 2 bit of the control byte against
         * the appropriate value for S frames.
         */
        b1 = gen_mcmp(cstate, OR_LLC, 2, BPF_B, LLC_S_FMT, 0x03);
        gen_and(b0, b1);
        return b1;
}

struct block *
gen_llc_u(compiler_state_t *cstate)
{
        struct block *b0, *b1;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        /*
         * Check whether this is an LLC frame.
         */
        b0 = gen_llc_internal(cstate);

        /*
         * Now compare the low-order 2 bit of the control byte against
         * the appropriate value for U frames.
         */
        b1 = gen_mcmp(cstate, OR_LLC, 2, BPF_B, LLC_U_FMT, 0x03);
        gen_and(b0, b1);
        return b1;
}

struct block *
gen_llc_s_subtype(compiler_state_t *cstate, bpf_u_int32 subtype)
{
        struct block *b0, *b1;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        /*
         * Check whether this is an LLC frame.
         */
        b0 = gen_llc_internal(cstate);

        /*
         * Now check for an S frame with the appropriate type.
         */
        b1 = gen_mcmp(cstate, OR_LLC, 2, BPF_B, subtype, LLC_S_CMD_MASK);
        gen_and(b0, b1);
        return b1;
}

struct block *
gen_llc_u_subtype(compiler_state_t *cstate, bpf_u_int32 subtype)
{
        struct block *b0, *b1;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        /*
         * Check whether this is an LLC frame.
         */
        b0 = gen_llc_internal(cstate);

        /*
         * Now check for a U frame with the appropriate type.
         */
        b1 = gen_mcmp(cstate, OR_LLC, 2, BPF_B, subtype, LLC_U_CMD_MASK);
        gen_and(b0, b1);
        return b1;
}

/*
 * Generate code to match a particular packet type, for link-layer types
 * using 802.2 LLC headers.
 *
 * This is *NOT* used for Ethernet; "gen_ether_linktype()" is used
 * for that - it handles the D/I/X Ethernet vs. 802.3+802.2 issues.
 *
 * "proto" is an Ethernet type value, if > ETHERMTU, or an LLC SAP
 * value, if <= ETHERMTU.  We use that to determine whether to
 * match the DSAP or both DSAP and LSAP or to check the OUI and
 * protocol ID in a SNAP header.
 */
static struct block *
gen_llc_linktype(compiler_state_t *cstate, bpf_u_int32 ll_proto)
{
        /*
         * XXX - handle token-ring variable-length header.
         */
        switch (ll_proto) {

        case LLCSAP_IP:
        case LLCSAP_ISONS:
        case LLCSAP_NETBEUI:
                /*
                 * XXX - should we check both the DSAP and the
                 * SSAP, like this, or should we check just the
                 * DSAP, as we do for other SAP values?
                 */
                return gen_cmp(cstate, OR_LLC, 0, BPF_H, (bpf_u_int32)
                             ((ll_proto << 8) | ll_proto));

        case LLCSAP_IPX:
                /*
                 * XXX - are there ever SNAP frames for IPX on
                 * non-Ethernet 802.x networks?
                 */
                return gen_cmp(cstate, OR_LLC, 0, BPF_B, 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(cstate, 0x080007, ETHERTYPE_ATALK);

        default:
                /*
                 * XXX - we don't have to check for IPX 802.3
                 * here, but should we check for the IPX Ethertype?
                 */
                if (ll_proto <= ETHERMTU) {
                        /*
                         * This is an LLC SAP value, so check
                         * the DSAP.
                         */
                        return gen_cmp(cstate, OR_LLC, 0, BPF_B, ll_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(cstate, 0x000000, ll_proto);
                         *
                         * here; for now, we don't, as per the above.
                         * I don't know whether it's worth the extra CPU
                         * time to do the right check or not.
                         */
                        return gen_cmp(cstate, OR_LLC, 6, BPF_H, ll_proto);
                }
        }
}

static struct block *
gen_hostop(compiler_state_t *cstate, bpf_u_int32 addr, bpf_u_int32 mask,
    int dir, u_int src_off, u_int 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(cstate, addr, mask, Q_SRC, src_off, dst_off);
                b1 = gen_hostop(cstate, addr, mask, Q_DST, src_off, dst_off);
                gen_and(b0, b1);
                return b1;

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

        case Q_ADDR1:
                bpf_error(cstate, "'addr1' and 'address1' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_ADDR2:
                bpf_error(cstate, "'addr2' and 'address2' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_ADDR3:
                bpf_error(cstate, "'addr3' and 'address3' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_ADDR4:
                bpf_error(cstate, "'addr4' and 'address4' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_RA:
                bpf_error(cstate, "'ra' is not a valid qualifier for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_TA:
                bpf_error(cstate, "'ta' is not a valid qualifier for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        default:
                abort();
                /*NOTREACHED*/
        }
        return gen_mcmp(cstate, OR_LINKPL, offset, BPF_W, addr, mask);
}

#ifdef INET6
static struct block *
gen_hostop6(compiler_state_t *cstate, struct in6_addr *addr,
    struct in6_addr *mask, int dir, u_int src_off, u_int dst_off)
{
        struct block *b0, *b1;
        u_int offset;
        /*
         * Code below needs to access four separate 32-bit parts of the 128-bit
         * IPv6 address and mask.  In some OSes this is as simple as using the
         * s6_addr32 pseudo-member of struct in6_addr, which contains a union of
         * 8-, 16- and 32-bit arrays.  In other OSes this is not the case, as
         * far as libpcap sees it.  Hence copy the data before use to avoid
         * potential unaligned memory access and the associated compiler
         * warnings (whether genuine or not).
         */
        bpf_u_int32 a[4], m[4];

        switch (dir) {

        case Q_SRC:
                offset = src_off;
                break;

        case Q_DST:
                offset = dst_off;
                break;

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

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

        case Q_ADDR1:
                bpf_error(cstate, "'addr1' and 'address1' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_ADDR2:
                bpf_error(cstate, "'addr2' and 'address2' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_ADDR3:
                bpf_error(cstate, "'addr3' and 'address3' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_ADDR4:
                bpf_error(cstate, "'addr4' and 'address4' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_RA:
                bpf_error(cstate, "'ra' is not a valid qualifier for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_TA:
                bpf_error(cstate, "'ta' is not a valid qualifier for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        default:
                abort();
                /*NOTREACHED*/
        }
        /* this order is important */
        memcpy(a, addr, sizeof(a));
        memcpy(m, mask, sizeof(m));
        b1 = gen_mcmp(cstate, OR_LINKPL, offset + 12, BPF_W, ntohl(a[3]), ntohl(m[3]));
        b0 = gen_mcmp(cstate, OR_LINKPL, offset + 8, BPF_W, ntohl(a[2]), ntohl(m[2]));
        gen_and(b0, b1);
        b0 = gen_mcmp(cstate, OR_LINKPL, offset + 4, BPF_W, ntohl(a[1]), ntohl(m[1]));
        gen_and(b0, b1);
        b0 = gen_mcmp(cstate, OR_LINKPL, offset + 0, BPF_W, ntohl(a[0]), ntohl(m[0]));
        gen_and(b0, b1);
        return b1;
}
#endif

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

        switch (dir) {
        case Q_SRC:
                return gen_bcmp(cstate, OR_LINKHDR, 6, 6, eaddr);

        case Q_DST:
                return gen_bcmp(cstate, OR_LINKHDR, 0, 6, eaddr);

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

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_ehostop(cstate, eaddr, Q_SRC);
                b1 = gen_ehostop(cstate, eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;

        case Q_ADDR1:
                bpf_error(cstate, "'addr1' and 'address1' are only supported on 802.11 with 802.11 headers");
                /*NOTREACHED*/

        case Q_ADDR2:
                bpf_error(cstate, "'addr2' and 'address2' are only supported on 802.11 with 802.11 headers");
                /*NOTREACHED*/

        case Q_ADDR3:
                bpf_error(cstate, "'addr3' and 'address3' are only supported on 802.11 with 802.11 headers");
                /*NOTREACHED*/

        case Q_ADDR4:
                bpf_error(cstate, "'addr4' and 'address4' are only supported on 802.11 with 802.11 headers");
                /*NOTREACHED*/

        case Q_RA:
                bpf_error(cstate, "'ra' is only supported on 802.11 with 802.11 headers");
                /*NOTREACHED*/

        case Q_TA:
                bpf_error(cstate, "'ta' is only supported on 802.11 with 802.11 headers");
                /*NOTREACHED*/
        }
        abort();
        /*NOTREACHED*/
}

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

        switch (dir) {
        case Q_SRC:
                return gen_bcmp(cstate, OR_LINKHDR, 6 + 1 + cstate->pcap_fddipad, 6, eaddr);

        case Q_DST:
                return gen_bcmp(cstate, OR_LINKHDR, 0 + 1 + cstate->pcap_fddipad, 6, eaddr);

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

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_fhostop(cstate, eaddr, Q_SRC);
                b1 = gen_fhostop(cstate, eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;

        case Q_ADDR1:
                bpf_error(cstate, "'addr1' and 'address1' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR2:
                bpf_error(cstate, "'addr2' and 'address2' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR3:
                bpf_error(cstate, "'addr3' and 'address3' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR4:
                bpf_error(cstate, "'addr4' and 'address4' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_RA:
                bpf_error(cstate, "'ra' is only supported on 802.11");
                /*NOTREACHED*/

        case Q_TA:
                bpf_error(cstate, "'ta' is only supported on 802.11");
                /*NOTREACHED*/
        }
        abort();
        /*NOTREACHED*/
}

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

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

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

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

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_thostop(cstate, eaddr, Q_SRC);
                b1 = gen_thostop(cstate, eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;

        case Q_ADDR1:
                bpf_error(cstate, "'addr1' and 'address1' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR2:
                bpf_error(cstate, "'addr2' and 'address2' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR3:
                bpf_error(cstate, "'addr3' and 'address3' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR4:
                bpf_error(cstate, "'addr4' and 'address4' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_RA:
                bpf_error(cstate, "'ra' is only supported on 802.11");
                /*NOTREACHED*/

        case Q_TA:
                bpf_error(cstate, "'ta' is only supported on 802.11");
                /*NOTREACHED*/
        }
        abort();
        /*NOTREACHED*/
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_wlanhostop(cstate, eaddr, Q_SRC);
                b1 = gen_wlanhostop(cstate, eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;

        /*
         * XXX - add BSSID keyword?
         */
        case Q_ADDR1:
                return (gen_bcmp(cstate, OR_LINKHDR, 4, 6, eaddr));

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

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

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

        case Q_RA:
                /*
                 * Not present in management frames; addr1 in other
                 * frames.
                 */

                /*
                 * If the high-order bit of the type value is 0, this
                 * is a management frame.
                 * I.e, check "(link[0] & 0x08)".
                 */
                s = gen_load_a(cstate, OR_LINKHDR, 0, BPF_B);
                b1 = new_block(cstate, JMP(BPF_JSET));
                b1->s.k = 0x08;
                b1->stmts = s;

                /*
                 * Check addr1.
                 */
                b0 = gen_bcmp(cstate, OR_LINKHDR, 4, 6, eaddr);

                /*
                 * AND that with the check of addr1.
                 */
                gen_and(b1, b0);
                return (b0);

        case Q_TA:
                /*
                 * Not present in management frames; addr2, if present,
                 * in other frames.
                 */

                /*
                 * Not present in CTS or ACK control frames.
                 */
                b0 = gen_mcmp(cstate, OR_LINKHDR, 0, BPF_B, IEEE80211_FC0_TYPE_CTL,
                        IEEE80211_FC0_TYPE_MASK);
                gen_not(b0);
                b1 = gen_mcmp(cstate, OR_LINKHDR, 0, BPF_B, IEEE80211_FC0_SUBTYPE_CTS,
                        IEEE80211_FC0_SUBTYPE_MASK);
                gen_not(b1);
                b2 = gen_mcmp(cstate, OR_LINKHDR, 0, BPF_B, IEEE80211_FC0_SUBTYPE_ACK,
                        IEEE80211_FC0_SUBTYPE_MASK);
                gen_not(b2);
                gen_and(b1, b2);
                gen_or(b0, b2);

                /*
                 * If the high-order bit of the type value is 0, this
                 * is a management frame.
                 * I.e, check "(link[0] & 0x08)".
                 */
                s = gen_load_a(cstate, OR_LINKHDR, 0, BPF_B);
                b1 = new_block(cstate, JMP(BPF_JSET));
                b1->s.k = 0x08;
                b1->stmts = s;

                /*
                 * AND that with the check for frames other than
                 * CTS and ACK frames.
                 */
                gen_and(b1, b2);

                /*
                 * Check addr2.
                 */
                b1 = gen_bcmp(cstate, OR_LINKHDR, 10, 6, eaddr);
                gen_and(b2, b1);
                return b1;
        }
        abort();
        /*NOTREACHED*/
}

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

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

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

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

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_ipfchostop(cstate, eaddr, Q_SRC);
                b1 = gen_ipfchostop(cstate, eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;

        case Q_ADDR1:
                bpf_error(cstate, "'addr1' and 'address1' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR2:
                bpf_error(cstate, "'addr2' and 'address2' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR3:
                bpf_error(cstate, "'addr3' and 'address3' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR4:
                bpf_error(cstate, "'addr4' and 'address4' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_RA:
                bpf_error(cstate, "'ra' is only supported on 802.11");
                /*NOTREACHED*/

        case Q_TA:
                bpf_error(cstate, "'ta' is only supported on 802.11");
                /*NOTREACHED*/
        }
        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(compiler_state_t *cstate, bpf_u_int32 addr, int dir)
{
        struct block *b0, *b1, *b2, *tmp;
        u_int offset_lh;        /* offset if long header is received */
        u_int offset_sh;        /* offset if short header is received */

        switch (dir) {

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

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

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

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

        case Q_ADDR1:
                bpf_error(cstate, "'addr1' and 'address1' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_ADDR2:
                bpf_error(cstate, "'addr2' and 'address2' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_ADDR3:
                bpf_error(cstate, "'addr3' and 'address3' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_ADDR4:
                bpf_error(cstate, "'addr4' and 'address4' are not valid qualifiers for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_RA:
                bpf_error(cstate, "'ra' is not a valid qualifier for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        case Q_TA:
                bpf_error(cstate, "'ta' is not a valid qualifier for addresses other than 802.11 MAC addresses");
                /*NOTREACHED*/

        default:
                abort();
                /*NOTREACHED*/
        }
        /*
         * In a DECnet message inside an Ethernet frame the first two bytes
         * immediately after EtherType are the [litle-endian] DECnet message
         * length, which is irrelevant in this context.
         *
         * "pad = 1" means the third byte equals 0x81, thus it is the PLENGTH
         * 8-bit bitmap of the optional padding before the packet route header.
         * The bitmap always has bit 7 set to 1 and in this case has bits 0-6
         * (TOTAL-PAD-SEQUENCE-LENGTH) set to integer value 1.  The latter
         * means there aren't any PAD bytes after the bitmap, so the header
         * begins at the fourth byte.  "pad = 0" means bit 7 of the third byte
         * is set to 0, thus the header begins at the third byte.
         *
         * The header can be in several (as mentioned above) formats, all of
         * which begin with the FLAGS 8-bit bitmap, which always has bit 7
         * (PF, "pad field") set to 0 regardless of any padding present before
         * the header.  "Short header" means bits 0-2 of the bitmap encode the
         * integer value 2 (SFDP), and "long header" means value 6 (LFDP).
         *
         * To test PLENGTH and FLAGS, use multiple-byte constants with the
         * values and the masks, this maps to the required single bytes of
         * the message correctly on both big-endian and little-endian hosts.
         * For the DECnet address use SWAPSHORT(), which always swaps bytes,
         * because the wire encoding is little-endian and BPF multiple-byte
         * loads are big-endian.  When the destination address is near enough
         * to PLENGTH and FLAGS, generate one 32-bit comparison instead of two
         * smaller ones.
         */
        /* Check for pad = 1, long header case */
        tmp = gen_mcmp(cstate, OR_LINKPL, 2, BPF_H, 0x8106U, 0xFF07U);
        b1 = gen_cmp(cstate, OR_LINKPL, 2 + 1 + offset_lh,
            BPF_H, SWAPSHORT(addr));
        gen_and(tmp, b1);
        /* Check for pad = 0, long header case */
        tmp = gen_mcmp(cstate, OR_LINKPL, 2, BPF_B, 0x06U, 0x07U);
        b2 = gen_cmp(cstate, OR_LINKPL, 2 + offset_lh, BPF_H,
            SWAPSHORT(addr));
        gen_and(tmp, b2);
        gen_or(b2, b1);
        /* Check for pad = 1, short header case */
        if (dir == Q_DST) {
                b2 = gen_mcmp(cstate, OR_LINKPL, 2, BPF_W,
                    0x81020000U | SWAPSHORT(addr),
                    0xFF07FFFFU);
        } else {
                tmp = gen_mcmp(cstate, OR_LINKPL, 2, BPF_H, 0x8102U, 0xFF07U);
                b2 = gen_cmp(cstate, OR_LINKPL, 2 + 1 + offset_sh, BPF_H,
                    SWAPSHORT(addr));
                gen_and(tmp, b2);
        }
        gen_or(b2, b1);
        /* Check for pad = 0, short header case */
        if (dir == Q_DST) {
                b2 = gen_mcmp(cstate, OR_LINKPL, 2, BPF_W,
                    0x02000000U | SWAPSHORT(addr) << 8,
                    0x07FFFF00U);
        } else {
                tmp = gen_mcmp(cstate, OR_LINKPL, 2, BPF_B, 0x02U, 0x07U);
                b2 = gen_cmp(cstate, OR_LINKPL, 2 + offset_sh, BPF_H,
                    SWAPSHORT(addr));
                gen_and(tmp, b2);
        }
        gen_or(b2, b1);

        return b1;
}

/*
 * Generate a check for IPv4 or IPv6 for MPLS-encapsulated packets;
 * test the bottom-of-stack bit, and then check the version number
 * field in the IP header.
 */
static struct block *
gen_mpls_linktype(compiler_state_t *cstate, bpf_u_int32 ll_proto)
{
        struct block *b0, *b1;

        switch (ll_proto) {

        case ETHERTYPE_IP:
                /* match the bottom-of-stack bit */
                b0 = gen_mcmp(cstate, OR_LINKPL, (u_int)-2, BPF_B, 0x01, 0x01);
                /* match the IPv4 version number */
                b1 = gen_mcmp(cstate, OR_LINKPL, 0, BPF_B, 0x40, 0xf0);
                gen_and(b0, b1);
                return b1;

        case ETHERTYPE_IPV6:
                /* match the bottom-of-stack bit */
                b0 = gen_mcmp(cstate, OR_LINKPL, (u_int)-2, BPF_B, 0x01, 0x01);
                /* match the IPv4 version number */
                b1 = gen_mcmp(cstate, OR_LINKPL, 0, BPF_B, 0x60, 0xf0);
                gen_and(b0, b1);
                return b1;

 default:
         /* FIXME add other L3 proto IDs */
         bpf_error(cstate, "unsupported protocol over mpls");
         /*NOTREACHED*/
 }
}

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

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

        switch (proto) {

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

        case Q_LINK:
                bpf_error(cstate, "link-layer modifier applied to %s", typestr);

        case Q_IP:
                b0 = gen_linktype(cstate, ETHERTYPE_IP);
                b1 = gen_hostop(cstate, addr, mask, dir, 12, 16);
                gen_and(b0, b1);
                return b1;

        case Q_RARP:
                b0 = gen_linktype(cstate, ETHERTYPE_REVARP);
                b1 = gen_hostop(cstate, addr, mask, dir, 14, 24);
                gen_and(b0, b1);
                return b1;

        case Q_ARP:
                b0 = gen_linktype(cstate, ETHERTYPE_ARP);
                b1 = gen_hostop(cstate, addr, mask, dir, 14, 24);
                gen_and(b0, b1);
                return b1;

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

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

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

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

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

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

        case Q_ATALK:
                bpf_error(cstate, "AppleTalk host filtering not implemented");

        case Q_DECNET:
                b0 = gen_linktype(cstate, ETHERTYPE_DN);
                b1 = gen_dnhostop(cstate, addr, dir);
                gen_and(b0, b1);
                return b1;

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

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

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

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

        case Q_IPV6:
                bpf_error(cstate, "'ip6' modifier applied to ip host");

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

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

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

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

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

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

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

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

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

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

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

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

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

        case Q_ISIS_L1:
                bpf_error(cstate, "'l1' modifier applied to %s", typestr);

        case Q_ISIS_L2:
                bpf_error(cstate, "'l2' modifier applied to %s", typestr);

        case Q_ISIS_IIH:
                bpf_error(cstate, "'iih' modifier applied to %s", typestr);

        case Q_ISIS_SNP:
                bpf_error(cstate, "'snp' modifier applied to %s", typestr);

        case Q_ISIS_CSNP:
                bpf_error(cstate, "'csnp' modifier applied to %s", typestr);

        case Q_ISIS_PSNP:
                bpf_error(cstate, "'psnp' modifier applied to %s", typestr);

        case Q_ISIS_LSP:
                bpf_error(cstate, "'lsp' modifier applied to %s", typestr);

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

        case Q_CARP:
                bpf_error(cstate, "'carp' modifier applied to %s", typestr);

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

#ifdef INET6
static struct block *
gen_host6(compiler_state_t *cstate, struct in6_addr *addr,
    struct in6_addr *mask, int proto, int dir, int type)
{
        struct block *b0, *b1;
        const char *typestr;

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

        switch (proto) {

        case Q_DEFAULT:
        case Q_IPV6:
                b0 = gen_linktype(cstate, ETHERTYPE_IPV6);
                b1 = gen_hostop6(cstate, addr, mask, dir, 8, 24);
                gen_and(b0, b1);
                return b1;

        case Q_LINK:
                bpf_error(cstate, "link-layer modifier applied to ip6 %s", typestr);

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

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

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

        case Q_SCTP:
                bpf_error(cstate, "'sctp' modifier applied to ip6 %s", typestr);

        case Q_TCP:
                bpf_error(cstate, "'tcp' modifier applied to ip6 %s", typestr);

        case Q_UDP:
                bpf_error(cstate, "'udp' modifier applied to ip6 %s", typestr);

        case Q_ICMP:
                bpf_error(cstate, "'icmp' modifier applied to ip6 %s", typestr);

        case Q_IGMP:
                bpf_error(cstate, "'igmp' modifier applied to ip6 %s", typestr);

        case Q_IGRP:
                bpf_error(cstate, "'igrp' modifier applied to ip6 %s", typestr);

        case Q_ATALK:
                bpf_error(cstate, "AppleTalk modifier applied to ip6 %s", typestr);

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

        case Q_LAT:
                bpf_error(cstate, "'lat' modifier applied to ip6 %s", typestr);

        case Q_SCA:
                bpf_error(cstate, "'sca' modifier applied to ip6 %s", typestr);

        case Q_MOPRC:
                bpf_error(cstate, "'moprc' modifier applied to ip6 %s", typestr);

        case Q_MOPDL:
                bpf_error(cstate, "'mopdl' modifier applied to ip6 %s", typestr);

        case Q_ICMPV6:
                bpf_error(cstate, "'icmp6' modifier applied to ip6 %s", typestr);

        case Q_AH:
                bpf_error(cstate, "'ah' modifier applied to ip6 %s", typestr);

        case Q_ESP:
                bpf_error(cstate, "'esp' modifier applied to ip6 %s", typestr);

        case Q_PIM:
                bpf_error(cstate, "'pim' modifier applied to ip6 %s", typestr);

        case Q_VRRP:
                bpf_error(cstate, "'vrrp' modifier applied to ip6 %s", typestr);

        case Q_AARP:
                bpf_error(cstate, "'aarp' modifier applied to ip6 %s", typestr);

        case Q_ISO:
                bpf_error(cstate, "'iso' modifier applied to ip6 %s", typestr);

        case Q_ESIS:
                bpf_error(cstate, "'esis' modifier applied to ip6 %s", typestr);

        case Q_ISIS:
                bpf_error(cstate, "'isis' modifier applied to ip6 %s", typestr);

        case Q_CLNP:
                bpf_error(cstate, "'clnp' modifier applied to ip6 %s", typestr);

        case Q_STP:
                bpf_error(cstate, "'stp' modifier applied to ip6 %s", typestr);

        case Q_IPX:
                bpf_error(cstate, "'ipx' modifier applied to ip6 %s", typestr);

        case Q_NETBEUI:
                bpf_error(cstate, "'netbeui' modifier applied to ip6 %s", typestr);

        case Q_ISIS_L1:
                bpf_error(cstate, "'l1' modifier applied to ip6 %s", typestr);

        case Q_ISIS_L2:
                bpf_error(cstate, "'l2' modifier applied to ip6 %s", typestr);

        case Q_ISIS_IIH:
                bpf_error(cstate, "'iih' modifier applied to ip6 %s", typestr);

        case Q_ISIS_SNP:
                bpf_error(cstate, "'snp' modifier applied to ip6 %s", typestr);

        case Q_ISIS_CSNP:
                bpf_error(cstate, "'csnp' modifier applied to ip6 %s", typestr);

        case Q_ISIS_PSNP:
                bpf_error(cstate, "'psnp' modifier applied to ip6 %s", typestr);

        case Q_ISIS_LSP:
                bpf_error(cstate, "'lsp' modifier applied to ip6 %s", typestr);

        case Q_RADIO:
                bpf_error(cstate, "'radio' modifier applied to ip6 %s", typestr);

        case Q_CARP:
                bpf_error(cstate, "'carp' modifier applied to ip6 %s", typestr);

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

#ifndef INET6
static struct block *
gen_gateway(compiler_state_t *cstate, const u_char *eaddr,
    struct addrinfo *alist, int proto, int dir)
{
        struct block *b0, *b1, *tmp;
        struct addrinfo *ai;
        struct sockaddr_in *sin;

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

        switch (proto) {
        case Q_DEFAULT:
        case Q_IP:
        case Q_ARP:
        case Q_RARP:
                switch (cstate->linktype) {
                case DLT_EN10MB:
                case DLT_NETANALYZER:
                case DLT_NETANALYZER_TRANSPARENT:
                        b1 = gen_prevlinkhdr_check(cstate);
                        b0 = gen_ehostop(cstate, eaddr, Q_OR);
                        if (b1 != NULL)
                                gen_and(b1, b0);
                        break;
                case DLT_FDDI:
                        b0 = gen_fhostop(cstate, eaddr, Q_OR);
                        break;
                case DLT_IEEE802:
                        b0 = gen_thostop(cstate, eaddr, Q_OR);
                        break;
                case DLT_IEEE802_11:
                case DLT_PRISM_HEADER:
                case DLT_IEEE802_11_RADIO_AVS:
                case DLT_IEEE802_11_RADIO:
                case DLT_PPI:
                        b0 = gen_wlanhostop(cstate, eaddr, Q_OR);
                        break;
                case DLT_IP_OVER_FC:
                        b0 = gen_ipfchostop(cstate, eaddr, Q_OR);
                        break;
                case DLT_SUNATM:
                        /*
                         * This is LLC-multiplexed traffic; if it were
                         * LANE, cstate->linktype would have been set to
                         * DLT_EN10MB.
                         */
                         /* FALLTHROUGH */
                default:
                        bpf_error(cstate,
                            "'gateway' supported only on ethernet/FDDI/token ring/802.11/ATM LANE/Fibre Channel");
                }
                b1 = NULL;
                for (ai = alist; ai != NULL; ai = ai->ai_next) {
                        /*
                         * Does it have an address?
                         */
                        if (ai->ai_addr != NULL) {
                                /*
                                 * Yes.  Is it an IPv4 address?
                                 */
                                if (ai->ai_addr->sa_family == AF_INET) {
                                        /*
                                         * Generate an entry for it.
                                         */
                                        sin = (struct sockaddr_in *)ai->ai_addr;
                                        tmp = gen_host(cstate,
                                            ntohl(sin->sin_addr.s_addr),
                                            0xffffffff, proto, Q_OR, Q_HOST);
                                        /*
                                         * Is it the *first* IPv4 address?
                                         */
                                        if (b1 == NULL) {
                                                /*
                                                 * Yes, so start with it.
                                                 */
                                                b1 = tmp;
                                        } else {
                                                /*
                                                 * No, so OR it into the
                                                 * existing set of
                                                 * addresses.
                                                 */
                                                gen_or(b1, tmp);
                                                b1 = tmp;
                                        }
                                }
                        }
                }
                if (b1 == NULL) {
                        /*
                         * No IPv4 addresses found.
                         */
                        return (NULL);
                }
                gen_not(b1);
                gen_and(b0, b1);
                return b1;
        }
        bpf_error(cstate, "illegal modifier of 'gateway'");
        /*NOTREACHED*/
}
#endif

static struct block *
gen_proto_abbrev_internal(compiler_state_t *cstate, int proto)
{
        struct block *b0;
        struct block *b1 = NULL;

        switch (proto) {

        case Q_SCTP:
                b1 = gen_proto(cstate, IPPROTO_SCTP, Q_DEFAULT, Q_DEFAULT);
                break;

        case Q_TCP:
                b1 = gen_proto(cstate, IPPROTO_TCP, Q_DEFAULT, Q_DEFAULT);
                break;

        case Q_UDP:
                b1 = gen_proto(cstate, IPPROTO_UDP, Q_DEFAULT, Q_DEFAULT);
                break;

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

#ifndef IPPROTO_IGMP
#define IPPROTO_IGMP    2
#endif

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

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

#ifndef IPPROTO_PIM
#define IPPROTO_PIM     103
#endif

        case Q_PIM:
                b1 = gen_proto(cstate, IPPROTO_PIM, Q_DEFAULT, Q_DEFAULT);
                break;

#ifndef IPPROTO_VRRP
#define IPPROTO_VRRP    112
#endif

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

#ifndef IPPROTO_CARP
#define IPPROTO_CARP    112
#endif

        case Q_CARP:
                b1 = gen_proto(cstate, IPPROTO_CARP, Q_IP, Q_DEFAULT);
                break;

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

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

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

        case Q_LINK:
                break; // invalid syntax

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

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

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

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

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

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

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

        case Q_IPV6:
                b1 = gen_linktype(cstate, ETHERTYPE_IPV6);
                break;

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

#ifndef IPPROTO_AH
#define IPPROTO_AH      51
#endif
        case Q_AH:
                b1 = gen_proto(cstate, IPPROTO_AH, Q_DEFAULT, Q_DEFAULT);
                break;

#ifndef IPPROTO_ESP
#define IPPROTO_ESP     50
#endif
        case Q_ESP:
                b1 = gen_proto(cstate, IPPROTO_ESP, Q_DEFAULT, Q_DEFAULT);
                break;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        case Q_RADIO:
                break; // invalid syntax

        default:
                abort();
        }
        if (b1)
                return b1;
        bpf_error(cstate, "'%s' cannot be used as an abbreviation", pqkw(proto));
}

struct block *
gen_proto_abbrev(compiler_state_t *cstate, int proto)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        return gen_proto_abbrev_internal(cstate, proto);
}

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

        /* not IPv4 frag other than the first frag */
        s = gen_load_a(cstate, OR_LINKPL, 6, BPF_H);
        b = new_block(cstate, JMP(BPF_JSET));
        b->s.k = 0x1fff;
        b->stmts = s;
        gen_not(b);

        return b;
}

/*
 * Generate a comparison to a port value in the transport-layer header
 * at the specified offset from the beginning of that header.
 *
 * XXX - this handles a variable-length prefix preceding the link-layer
 * header, such as the radiotap or AVS radio prefix, but doesn't handle
 * variable-length link-layer headers (such as Token Ring or 802.11
 * headers).
 */
static struct block *
gen_portatom(compiler_state_t *cstate, int off, bpf_u_int32 v)
{
        return gen_cmp(cstate, OR_TRAN_IPV4, off, BPF_H, v);
}

static struct block *
gen_portatom6(compiler_state_t *cstate, int off, bpf_u_int32 v)
{
        return gen_cmp(cstate, OR_TRAN_IPV6, off, BPF_H, v);
}

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

        /* ip proto 'proto' and not a fragment other than the first fragment */
        tmp = gen_cmp(cstate, OR_LINKPL, 9, BPF_B, proto);
        b0 = gen_ipfrag(cstate);
        gen_and(tmp, b0);

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

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

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

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

        case Q_ADDR1:
                bpf_error(cstate, "'addr1' and 'address1' are not valid qualifiers for ports");
                /*NOTREACHED*/

        case Q_ADDR2:
                bpf_error(cstate, "'addr2' and 'address2' are not valid qualifiers for ports");
                /*NOTREACHED*/

        case Q_ADDR3:
                bpf_error(cstate, "'addr3' and 'address3' are not valid qualifiers for ports");
                /*NOTREACHED*/

        case Q_ADDR4:
                bpf_error(cstate, "'addr4' and 'address4' are not valid qualifiers for ports");
                /*NOTREACHED*/

        case Q_RA:
                bpf_error(cstate, "'ra' is not a valid qualifier for ports");
                /*NOTREACHED*/

        case Q_TA:
                bpf_error(cstate, "'ta' is not a valid qualifier for ports");
                /*NOTREACHED*/

        default:
                abort();
                /*NOTREACHED*/
        }
        gen_and(b0, b1);

        return b1;
}

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

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

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

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

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

struct block *
gen_portop6(compiler_state_t *cstate, u_int port, u_int proto, int dir)
{
        struct block *b0, *b1, *tmp;

        /* ip6 proto 'proto' */
        /* XXX - catch the first fragment of a fragmented packet? */
        b0 = gen_cmp(cstate, OR_LINKPL, 6, BPF_B, proto);

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

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

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

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

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

        return b1;
}

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

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

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

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

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

/* gen_portrange code */
static struct block *
gen_portrangeatom(compiler_state_t *cstate, u_int off, bpf_u_int32 v1,
    bpf_u_int32 v2)
{
        struct block *b1, *b2;

        if (v1 > v2) {
                /*
                 * Reverse the order of the ports, so v1 is the lower one.
                 */
                bpf_u_int32 vtemp;

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

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

        gen_and(b1, b2);

        return b2;
}

static struct block *
gen_portrangeop(compiler_state_t *cstate, u_int port1, u_int port2,
    bpf_u_int32 proto, int dir)
{
        struct block *b0, *b1, *tmp;

        /* ip proto 'proto' and not a fragment other than the first fragment */
        tmp = gen_cmp(cstate, OR_LINKPL, 9, BPF_B, proto);
        b0 = gen_ipfrag(cstate);
        gen_and(tmp, b0);

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

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

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

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

        case Q_ADDR1:
                bpf_error(cstate, "'addr1' and 'address1' are not valid qualifiers for port ranges");
                /*NOTREACHED*/

        case Q_ADDR2:
                bpf_error(cstate, "'addr2' and 'address2' are not valid qualifiers for port ranges");
                /*NOTREACHED*/

        case Q_ADDR3:
                bpf_error(cstate, "'addr3' and 'address3' are not valid qualifiers for port ranges");
                /*NOTREACHED*/

        case Q_ADDR4:
                bpf_error(cstate, "'addr4' and 'address4' are not valid qualifiers for port ranges");
                /*NOTREACHED*/

        case Q_RA:
                bpf_error(cstate, "'ra' is not a valid qualifier for port ranges");
                /*NOTREACHED*/

        case Q_TA:
                bpf_error(cstate, "'ta' is not a valid qualifier for port ranges");
                /*NOTREACHED*/

        default:
                abort();
                /*NOTREACHED*/
        }
        gen_and(b0, b1);

        return b1;
}

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

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

        switch (ip_proto) {
        case IPPROTO_UDP:
        case IPPROTO_TCP:
        case IPPROTO_SCTP:
                b1 = gen_portrangeop(cstate, port1, port2, (bpf_u_int32)ip_proto,
                    dir);
                break;

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

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

static struct block *
gen_portrangeatom6(compiler_state_t *cstate, u_int off, bpf_u_int32 v1,
    bpf_u_int32 v2)
{
        struct block *b1, *b2;

        if (v1 > v2) {
                /*
                 * Reverse the order of the ports, so v1 is the lower one.
                 */
                bpf_u_int32 vtemp;

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

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

        gen_and(b1, b2);

        return b2;
}

static struct block *
gen_portrangeop6(compiler_state_t *cstate, u_int port1, u_int port2,
    bpf_u_int32 proto, int dir)
{
        struct block *b0, *b1, *tmp;

        /* ip6 proto 'proto' */
        /* XXX - catch the first fragment of a fragmented packet? */
        b0 = gen_cmp(cstate, OR_LINKPL, 6, BPF_B, proto);

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

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

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

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

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

        return b1;
}

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

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

        switch (ip_proto) {
        case IPPROTO_UDP:
        case IPPROTO_TCP:
        case IPPROTO_SCTP:
                b1 = gen_portrangeop6(cstate, port1, port2, (bpf_u_int32)ip_proto,
                    dir);
                break;

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

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

static int
lookup_proto(compiler_state_t *cstate, const char *name, 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(cstate, "unknown ip proto '%s'", name);
                break;

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

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

#if !defined(NO_PROTOCHAIN)
static struct block *
gen_protochain(compiler_state_t *cstate, bpf_u_int32 v, int proto)
{
        struct block *b0, *b;
        struct slist *s[100];
        int fix2, fix3, fix4, fix5;
        int ahcheck, again, end;
        int i, max;
        int reg2 = alloc_reg(cstate);

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

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

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

        /*
         * To quote a comment in optimize.c:
         *
         * "These data structures are used in a Cocke and Schwartz style
         * value numbering scheme.  Since the flowgraph is acyclic,
         * exit values can be propagated from a node's predecessors
         * provided it is uniquely defined."
         *
         * "Acyclic" means "no backward branches", which means "no
         * loops", so we have to turn the optimizer off.
         */
        cstate->no_optimize = 1;

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

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

                /* A = ip->ip_p */
                s[i] = new_stmt(cstate, BPF_LD|BPF_ABS|BPF_B);
                s[i]->s.k = cstate->off_linkpl.constant_part + cstate->off_nl + 9;
                i++;
                /* X = ip->ip_hl << 2 */
                s[i] = new_stmt(cstate, BPF_LDX|BPF_MSH|BPF_B);
                s[i]->s.k = cstate->off_linkpl.constant_part + cstate->off_nl;
                i++;
                break;

        case Q_IPV6:
                b0 = gen_linktype(cstate, ETHERTYPE_IPV6);

                /* A = ip6->ip_nxt */
                s[i] = new_stmt(cstate, BPF_LD|BPF_ABS|BPF_B);
                s[i]->s.k = cstate->off_linkpl.constant_part + cstate->off_nl + 6;
                i++;
                /* X = sizeof(struct ip6_hdr) */
                s[i] = new_stmt(cstate, BPF_LDX|BPF_IMM);
                s[i]->s.k = 40;
                i++;
                break;

        default:
                bpf_error(cstate, "unsupported proto to gen_protochain");
                /*NOTREACHED*/
        }

        /* again: if (A == v) goto end; else fall through; */
        again = i;
        s[i] = new_stmt(cstate, 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(cstate, 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++;

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

                v6start = i;
                /* if (A == IPPROTO_HOPOPTS) goto v6advance */
                s[i] = new_stmt(cstate, 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(cstate, 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(cstate, 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(cstate, 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 + packet head];
                 * X = X + (P[X + packet head + 1] + 1) * 8;
                 */
                /* A = P[X + packet head] */
                s[i] = new_stmt(cstate, BPF_LD|BPF_IND|BPF_B);
                s[i]->s.k = cstate->off_linkpl.constant_part + cstate->off_nl;
                i++;
                /* MEM[reg2] = A */
                s[i] = new_stmt(cstate, BPF_ST);
                s[i]->s.k = reg2;
                i++;
                /* A = P[X + packet head + 1]; */
                s[i] = new_stmt(cstate, BPF_LD|BPF_IND|BPF_B);
                s[i]->s.k = cstate->off_linkpl.constant_part + cstate->off_nl + 1;
                i++;
                /* A += 1 */
                s[i] = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
                s[i]->s.k = 1;
                i++;
                /* A *= 8 */
                s[i] = new_stmt(cstate, BPF_ALU|BPF_MUL|BPF_K);
                s[i]->s.k = 8;
                i++;
                /* A += X */
                s[i] = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_X);
                s[i]->s.k = 0;
                i++;
                /* X = A; */
                s[i] = new_stmt(cstate, BPF_MISC|BPF_TAX);
                i++;
                /* A = MEM[reg2] */
                s[i] = new_stmt(cstate, BPF_LD|BPF_MEM);
                s[i]->s.k = reg2;
                i++;

                /* goto again; (must use BPF_JA for backward jump) */
                s[i] = new_stmt(cstate, 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 {
                /* nop */
                s[i] = new_stmt(cstate, 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(cstate, 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(cstate, BPF_MISC|BPF_TXA);
        i++;
        /* A = P[X + packet head]; */
        s[i] = new_stmt(cstate, BPF_LD|BPF_IND|BPF_B);
        s[i]->s.k = cstate->off_linkpl.constant_part + cstate->off_nl;
        i++;
        /* MEM[reg2] = A */
        s[i] = new_stmt(cstate, BPF_ST);
        s[i]->s.k = reg2;
        i++;
        /* A = X */
        s[i - 1]->s.jt = s[i] = new_stmt(cstate, BPF_MISC|BPF_TXA);
        i++;
        /* A += 1 */
        s[i] = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s[i]->s.k = 1;
        i++;
        /* X = A */
        s[i] = new_stmt(cstate, BPF_MISC|BPF_TAX);
        i++;
        /* A = P[X + packet head] */
        s[i] = new_stmt(cstate, BPF_LD|BPF_IND|BPF_B);
        s[i]->s.k = cstate->off_linkpl.constant_part + cstate->off_nl;
        i++;
        /* A += 2 */
        s[i] = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s[i]->s.k = 2;
        i++;
        /* A *= 4 */
        s[i] = new_stmt(cstate, BPF_ALU|BPF_MUL|BPF_K);
        s[i]->s.k = 4;
        i++;
        /* X = A; */
        s[i] = new_stmt(cstate, BPF_MISC|BPF_TAX);
        i++;
        /* A = MEM[reg2] */
        s[i] = new_stmt(cstate, BPF_LD|BPF_MEM);
        s[i]->s.k = reg2;
        i++;

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

        /* end: nop */
        end = i;
        s[i] = new_stmt(cstate, 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(cstate, JMP(BPF_JEQ));
        b->stmts = s[1];        /*remember, s[0] is dummy*/
        b->s.k = v;

        free_reg(cstate, reg2);

        gen_and(b0, b);
        return b;
}
#endif /* !defined(NO_PROTOCHAIN) */

/*
 * Generate code that checks whether the packet is a packet for protocol
 * <proto> and whether the type field in that protocol's header has
 * the value <v>, e.g. if <proto> is Q_IP, it checks whether it's an
 * IP packet and checks the protocol number in the IP header against <v>.
 *
 * If <proto> is Q_DEFAULT, i.e. just "proto" was specified, it checks
 * against Q_IP and Q_IPV6.
 */
static struct block *
gen_proto(compiler_state_t *cstate, bpf_u_int32 v, int proto, int dir)
{
        struct block *b0, *b1;
        struct block *b2;

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

        switch (proto) {
        case Q_DEFAULT:
                b0 = gen_proto(cstate, v, Q_IP, dir);
                b1 = gen_proto(cstate, v, Q_IPV6, dir);
                gen_or(b0, b1);
                return b1;

        case Q_LINK:
                return gen_linktype(cstate, v);

        case Q_IP:
                /*
                 * For FDDI, RFC 1188 says that SNAP encapsulation is used,
                 * not LLC encapsulation with LLCSAP_IP.
                 *
                 * For IEEE 802 networks - which includes 802.5 token ring
                 * (which is what DLT_IEEE802 means) and 802.11 - RFC 1042
                 * says that SNAP encapsulation is used, not LLC encapsulation
                 * with LLCSAP_IP.
                 *
                 * For LLC-encapsulated ATM/"Classical IP", RFC 1483 and
                 * RFC 2225 say that SNAP encapsulation is used, not LLC
                 * encapsulation with LLCSAP_IP.
                 *
                 * So we always check for ETHERTYPE_IP.
                 */
                b0 = gen_linktype(cstate, ETHERTYPE_IP);
                b1 = gen_cmp(cstate, OR_LINKPL, 9, BPF_B, v);
                gen_and(b0, b1);
                return b1;

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

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

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

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

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

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

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

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

        case Q_ATALK:
                bpf_error(cstate, "AppleTalk encapsulation is not specifiable");
                /*NOTREACHED*/

        case Q_DECNET:
                bpf_error(cstate, "DECNET encapsulation is not specifiable");
                /*NOTREACHED*/

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

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

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

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

        case Q_IPV6:
                b0 = gen_linktype(cstate, ETHERTYPE_IPV6);
                /*
                 * Also check for a fragment header before the final
                 * header.
                 */
                b2 = gen_cmp(cstate, OR_LINKPL, 6, BPF_B, IPPROTO_FRAGMENT);
                b1 = gen_cmp(cstate, OR_LINKPL, 40, BPF_B, v);
                gen_and(b2, b1);
                b2 = gen_cmp(cstate, OR_LINKPL, 6, BPF_B, v);
                gen_or(b2, b1);
                gen_and(b0, b1);
                return b1;

        case Q_ICMPV6:
                bpf_error(cstate, "'icmp6 proto' is bogus");
                /*NOTREACHED*/

        case Q_AH:
                bpf_error(cstate, "'ah proto' is bogus");
                /*NOTREACHED*/

        case Q_ESP:
                bpf_error(cstate, "'esp proto' is bogus");
                /*NOTREACHED*/

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

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

        case Q_AARP:
                bpf_error(cstate, "'aarp proto' is bogus");
                /*NOTREACHED*/

        case Q_ISO:
                switch (cstate->linktype) {

                case DLT_FRELAY:
                        /*
                         * Frame Relay packets typically have an OSI
                         * NLPID at the beginning; "gen_linktype(cstate, 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(cstate, OR_LINKHDR, 2, BPF_H, (0x03<<8) | v);
                        /*NOTREACHED*/

                case DLT_C_HDLC:
                case DLT_HDLC:
                        /*
                         * Cisco uses an Ethertype lookalike - for OSI,
                         * it's 0xfefe.
                         */
                        b0 = gen_linktype(cstate, LLCSAP_ISONS<<8 | LLCSAP_ISONS);
                        /* OSI in C-HDLC is stuffed with a fudge byte */
                        b1 = gen_cmp(cstate, OR_LINKPL_NOSNAP, 1, BPF_B, v);
                        gen_and(b0, b1);
                        return b1;

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

        case Q_ESIS:
                bpf_error(cstate, "'esis proto' is bogus");
                /*NOTREACHED*/

        case Q_ISIS:
                b0 = gen_proto(cstate, ISO10589_ISIS, Q_ISO, Q_DEFAULT);
                /*
                 * 4 is the offset of the PDU type relative to the IS-IS
                 * header.
                 */
                b1 = gen_cmp(cstate, OR_LINKPL_NOSNAP, 4, BPF_B, v);
                gen_and(b0, b1);
                return b1;

        case Q_CLNP:
                bpf_error(cstate, "'clnp proto' is not supported");
                /*NOTREACHED*/

        case Q_STP:
                bpf_error(cstate, "'stp proto' is bogus");
                /*NOTREACHED*/

        case Q_IPX:
                bpf_error(cstate, "'ipx proto' is bogus");
                /*NOTREACHED*/

        case Q_NETBEUI:
                bpf_error(cstate, "'netbeui proto' is bogus");
                /*NOTREACHED*/

        case Q_ISIS_L1:
                bpf_error(cstate, "'l1 proto' is bogus");
                /*NOTREACHED*/

        case Q_ISIS_L2:
                bpf_error(cstate, "'l2 proto' is bogus");
                /*NOTREACHED*/

        case Q_ISIS_IIH:
                bpf_error(cstate, "'iih proto' is bogus");
                /*NOTREACHED*/

        case Q_ISIS_SNP:
                bpf_error(cstate, "'snp proto' is bogus");
                /*NOTREACHED*/

        case Q_ISIS_CSNP:
                bpf_error(cstate, "'csnp proto' is bogus");
                /*NOTREACHED*/

        case Q_ISIS_PSNP:
                bpf_error(cstate, "'psnp proto' is bogus");
                /*NOTREACHED*/

        case Q_ISIS_LSP:
                bpf_error(cstate, "'lsp proto' is bogus");
                /*NOTREACHED*/

        case Q_RADIO:
                bpf_error(cstate, "'radio proto' is bogus");
                /*NOTREACHED*/

        case Q_CARP:
                bpf_error(cstate, "'carp proto' is bogus");
                /*NOTREACHED*/

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

/*
 * Convert a non-numeric name to a port number.
 */
static int
nametoport(compiler_state_t *cstate, const char *name, int ipproto)
{
        struct addrinfo hints, *res, *ai;
        int error;
        struct sockaddr_in *in4;
#ifdef INET6
        struct sockaddr_in6 *in6;
#endif
        int port = -1;

        /*
         * We check for both TCP and UDP in case there are
         * ambiguous entries.
         */
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = PF_UNSPEC;
        hints.ai_socktype = (ipproto == IPPROTO_TCP) ? SOCK_STREAM : SOCK_DGRAM;
        hints.ai_protocol = ipproto;
        error = getaddrinfo(NULL, name, &hints, &res);
        if (error != 0) {
                switch (error) {

                case EAI_NONAME:
                case EAI_SERVICE:
                        /*
                         * No such port.  Just return -1.
                         */
                        break;

#ifdef EAI_SYSTEM
                case EAI_SYSTEM:
                        /*
                         * We don't use strerror() because it's not
                         * guaranteed to be thread-safe on all platforms
                         * (probably because it might use a non-thread-local
                         * buffer into which to format an error message
                         * if the error code isn't one for which it has
                         * a canned string; three cheers for C string
                         * handling).
                         */
                        bpf_set_error(cstate, "getaddrinfo(\"%s\" fails with system error: %d",
                            name, errno);
                        port = -2;      /* a real error */
                        break;
#endif

                default:
                        /*
                         * This is a real error, not just "there's
                         * no such service name".
                         *
                         * We don't use gai_strerror() because it's not
                         * guaranteed to be thread-safe on all platforms
                         * (probably because it might use a non-thread-local
                         * buffer into which to format an error message
                         * if the error code isn't one for which it has
                         * a canned string; three cheers for C string
                         * handling).
                         */
                        bpf_set_error(cstate, "getaddrinfo(\"%s\") fails with error: %d",
                            name, error);
                        port = -2;      /* a real error */
                        break;
                }
        } else {
                /*
                 * OK, we found it.  Did it find anything?
                 */
                for (ai = res; ai != NULL; ai = ai->ai_next) {
                        /*
                         * Does it have an address?
                         */
                        if (ai->ai_addr != NULL) {
                                /*
                                 * Yes.  Get a port number; we're done.
                                 */
                                if (ai->ai_addr->sa_family == AF_INET) {
                                        in4 = (struct sockaddr_in *)ai->ai_addr;
                                        port = ntohs(in4->sin_port);
                                        break;
                                }
#ifdef INET6
                                if (ai->ai_addr->sa_family == AF_INET6) {
                                        in6 = (struct sockaddr_in6 *)ai->ai_addr;
                                        port = ntohs(in6->sin6_port);
                                        break;
                                }
#endif
                        }
                }
                freeaddrinfo(res);
        }
        return port;
}

/*
 * Convert a string to a port number.
 */
static bpf_u_int32
stringtoport(compiler_state_t *cstate, const char *string, size_t string_size,
    int *proto)
{
        stoulen_ret ret;
        char *cpy;
        bpf_u_int32 val;
        int tcp_port = -1;
        int udp_port = -1;

        /*
         * See if it's a number.
         */
        ret = stoulen(string, string_size, &val, cstate);
        switch (ret) {

        case STOULEN_OK:
                /* Unknown port type - it's just a number. */
                *proto = PROTO_UNDEF;
                break;

        case STOULEN_NOT_OCTAL_NUMBER:
        case STOULEN_NOT_HEX_NUMBER:
        case STOULEN_NOT_DECIMAL_NUMBER:
                /*
                 * Not a valid number; try looking it up as a port.
                 */
                cpy = malloc(string_size + 1);  /* +1 for terminating '\0' */
                memcpy(cpy, string, string_size);
                cpy[string_size] = '\0';
                tcp_port = nametoport(cstate, cpy, IPPROTO_TCP);
                if (tcp_port == -2) {
                        /*
                         * We got a hard error; the error string has
                         * already been set.
                         */
                        free(cpy);
                        longjmp(cstate->top_ctx, 1);
                        /*NOTREACHED*/
                }
                udp_port = nametoport(cstate, cpy, IPPROTO_UDP);
                if (udp_port == -2) {
                        /*
                         * We got a hard error; the error string has
                         * already been set.
                         */
                        free(cpy);
                        longjmp(cstate->top_ctx, 1);
                        /*NOTREACHED*/
                }

                /*
                 * We need to check /etc/services for ambiguous entries.
                 * If we find an ambiguous entry, and it has the
                 * same port number, change the proto to PROTO_UNDEF
                 * so both TCP and UDP will be checked.
                 */
                if (tcp_port >= 0) {
                        val = (bpf_u_int32)tcp_port;
                        *proto = IPPROTO_TCP;
                        if (udp_port >= 0) {
                                if (udp_port == tcp_port)
                                        *proto = PROTO_UNDEF;
#ifdef notdef
                                else
                                        /* Can't handle ambiguous names that refer
                                           to different port numbers. */
                                        warning("ambiguous port %s in /etc/services",
                                                cpy);
#endif
                        }
                        free(cpy);
                        break;
                }
                if (udp_port >= 0) {
                        val = (bpf_u_int32)udp_port;
                        *proto = IPPROTO_UDP;
                        free(cpy);
                        break;
                }
                bpf_set_error(cstate, "'%s' is not a valid port", cpy);
                free(cpy);
                longjmp(cstate->top_ctx, 1);
                /*NOTREACHED*/
#ifdef _AIX
                PCAP_UNREACHABLE
#endif /* _AIX */

        case STOULEN_ERROR:
                /* Error already set. */
                longjmp(cstate->top_ctx, 1);
                /*NOTREACHED*/
#ifdef _AIX
                PCAP_UNREACHABLE
#endif /* _AIX */

        default:
                /* Should not happen */
                bpf_set_error(cstate, "stoulen returned %d - this should not happen", ret);
                longjmp(cstate->top_ctx, 1);
                /*NOTREACHED*/
        }
        return (val);
}

/*
 * Convert a string in the form PPP-PPP, which correspond to ports, to
 * a starting and ending port in a port range.
 */
static void
stringtoportrange(compiler_state_t *cstate, const char *string,
    bpf_u_int32 *port1, bpf_u_int32 *port2, int *proto)
{
        char *hyphen_off;
        const char *first, *second;
        size_t first_size, second_size;
        int save_proto;

        if ((hyphen_off = strchr(string, '-')) == NULL)
                bpf_error(cstate, "port range '%s' contains no hyphen", string);

        /*
         * Make sure there are no other hyphens.
         *
         * XXX - we support named ports, but there are some port names
         * in /etc/services that include hyphens, so this would rule
         * that out.
         */
        if (strchr(hyphen_off + 1, '-') != NULL)
                bpf_error(cstate, "port range '%s' contains more than one hyphen",
                    string);

        /*
         * Get the length of the first port.
         */
        first = string;
        first_size = hyphen_off - string;
        if (first_size == 0) {
                /* Range of "-port", which we don't support. */
                bpf_error(cstate, "port range '%s' has no starting port", string);
        }

        /*
         * Try to convert it to a port.
         */
        *port1 = stringtoport(cstate, first, first_size, proto);
        save_proto = *proto;

        /*
         * Get the length of the second port.
         */
        second = hyphen_off + 1;
        second_size = strlen(second);
        if (second_size == 0) {
                /* Range of "port-", which we don't support. */
                bpf_error(cstate, "port range '%s' has no ending port", string);
        }

        /*
         * Try to convert it to a port.
         */
        *port2 = stringtoport(cstate, second, second_size, proto);
        if (*proto != save_proto)
                *proto = PROTO_UNDEF;
}

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        switch (q.addr) {

        case Q_NET:
                addr = pcap_nametonetaddr(name);
                if (addr == 0)
                        bpf_error(cstate, "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(cstate, addr, mask, proto, dir, q.addr);

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

                        case DLT_EN10MB:
                        case DLT_NETANALYZER:
                        case DLT_NETANALYZER_TRANSPARENT:
                                eaddr = pcap_ether_hostton(name);
                                if (eaddr == NULL)
                                        bpf_error(cstate,
                                            "unknown ether host '%s'", name);
                                tmp = gen_prevlinkhdr_check(cstate);
                                b = gen_ehostop(cstate, eaddr, dir);
                                if (tmp != NULL)
                                        gen_and(tmp, b);
                                free(eaddr);
                                return b;

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

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

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

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

                        bpf_error(cstate, "only ethernet/FDDI/token ring/802.11/ATM LANE/Fibre Channel supports link-level host name");
                } else if (proto == Q_DECNET) {
                        /*
                         * A long time ago on Ultrix libpcap supported
                         * translation of DECnet host names into DECnet
                         * addresses, but this feature is history now.
                         */
                        bpf_error(cstate, "invalid DECnet address '%s'", name);
                } else {
#ifdef INET6
                        memset(&mask128, 0xff, sizeof(mask128));
#endif
                        res0 = res = pcap_nametoaddrinfo(name);
                        if (res == NULL)
                                bpf_error(cstate, "unknown host '%s'", name);
                        cstate->ai = res;
                        b = tmp = NULL;
                        tproto = proto;
#ifdef INET6
                        tproto6 = proto;
#endif
                        if (cstate->off_linktype.constant_part == OFFSET_NOT_SET &&
                            tproto == Q_DEFAULT) {
                                tproto = Q_IP;
#ifdef INET6
                                tproto6 = Q_IPV6;
#endif
                        }
                        for (res = res0; res; res = res->ai_next) {
                                switch (res->ai_family) {
                                case AF_INET:
#ifdef INET6
                                        if (tproto == Q_IPV6)
                                                continue;
#endif

                                        sin4 = (struct sockaddr_in *)
                                                res->ai_addr;
                                        tmp = gen_host(cstate, ntohl(sin4->sin_addr.s_addr),
                                                0xffffffff, tproto, dir, q.addr);
                                        break;
#ifdef INET6
                                case AF_INET6:
                                        if (tproto6 == Q_IP)
                                                continue;

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

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

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

                        else if (real_proto == IPPROTO_TCP)
                                bpf_error(cstate, "port '%s' is tcp", name);
                        else
                                /* override PROTO_UNDEF */
                                real_proto = IPPROTO_SCTP;
                }
                if (port < 0)
                        bpf_error(cstate, "illegal port number %d < 0", port);
                if (port > 65535)
                        bpf_error(cstate, "illegal port number %d > 65535", port);
                b = gen_port(cstate, port, real_proto, dir);
                gen_or(gen_port6(cstate, port, real_proto, dir), b);
                return b;

        case Q_PORTRANGE:
                if (proto != Q_DEFAULT &&
                    proto != Q_UDP && proto != Q_TCP && proto != Q_SCTP)
                        bpf_error(cstate, "illegal qualifier of 'portrange'");
                stringtoportrange(cstate, name, &port1, &port2, &real_proto);
                if (proto == Q_UDP) {
                        if (real_proto == IPPROTO_TCP)
                                bpf_error(cstate, "port in range '%s' is tcp", name);
                        else if (real_proto == IPPROTO_SCTP)
                                bpf_error(cstate, "port in range '%s' is sctp", name);
                        else
                                /* override PROTO_UNDEF */
                                real_proto = IPPROTO_UDP;
                }
                if (proto == Q_TCP) {
                        if (real_proto == IPPROTO_UDP)
                                bpf_error(cstate, "port in range '%s' is udp", name);
                        else if (real_proto == IPPROTO_SCTP)
                                bpf_error(cstate, "port in range '%s' is sctp", name);
                        else
                                /* override PROTO_UNDEF */
                                real_proto = IPPROTO_TCP;
                }
                if (proto == Q_SCTP) {
                        if (real_proto == IPPROTO_UDP)
                                bpf_error(cstate, "port in range '%s' is udp", name);
                        else if (real_proto == IPPROTO_TCP)
                                bpf_error(cstate, "port in range '%s' is tcp", name);
                        else
                                /* override PROTO_UNDEF */
                                real_proto = IPPROTO_SCTP;
                }
                if (port1 > 65535)
                        bpf_error(cstate, "illegal port number %d > 65535", port1);
                if (port2 > 65535)
                        bpf_error(cstate, "illegal port number %d > 65535", port2);

                b = gen_portrange(cstate, port1, port2, real_proto, dir);
                gen_or(gen_portrange6(cstate, port1, port2, real_proto, dir), b);
                return b;

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

                res = pcap_nametoaddrinfo(name);
                cstate->ai = res;
                if (res == NULL)
                        bpf_error(cstate, "unknown host '%s'", name);
                b = gen_gateway(cstate, eaddr, res, proto, dir);
                cstate->ai = NULL;
                freeaddrinfo(res);
                free(eaddr);
                if (b == NULL)
                        bpf_error(cstate, "unknown host '%s'", name);
                return b;
#else
                bpf_error(cstate, "'gateway' not supported in this configuration");
#endif /*INET6*/

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

#if !defined(NO_PROTOCHAIN)
        case Q_PROTOCHAIN:
                real_proto = lookup_proto(cstate, name, proto);
                if (real_proto >= 0)
                        return gen_protochain(cstate, real_proto, proto);
                else
                        bpf_error(cstate, "unknown protocol: %s", name);
#endif /* !defined(NO_PROTOCHAIN) */

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

struct block *
gen_mcode(compiler_state_t *cstate, const char *s1, const char *s2,
    bpf_u_int32 masklen, struct qual q)
{
        register int nlen, mlen;
        bpf_u_int32 n, m;
        uint64_t m64;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        nlen = pcapint_atoin(s1, &n);
        if (nlen < 0)
                bpf_error(cstate, "invalid IPv4 address '%s'", s1);
        /* Promote short ipaddr */
        n <<= 32 - nlen;

        if (s2 != NULL) {
                mlen = pcapint_atoin(s2, &m);
                if (mlen < 0)
                        bpf_error(cstate, "invalid IPv4 address '%s'", s2);
                /* Promote short ipaddr */
                m <<= 32 - mlen;
                if ((n & ~m) != 0)
                        bpf_error(cstate, "non-network bits set in \"%s mask %s\"",
                            s1, s2);
        } else {
                /* Convert mask len to mask */
                if (masklen > 32)
                        bpf_error(cstate, "mask length must be <= 32");
                m64 = UINT64_C(0xffffffff) << (32 - masklen);
                m = (bpf_u_int32)m64;
                if ((n & ~m) != 0)
                        bpf_error(cstate, "non-network bits set in \"%s/%d\"",
                            s1, masklen);
        }

        switch (q.addr) {

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

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

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        proto = q.proto;
        dir = q.dir;
        if (s == NULL) {
                /*
                 * v contains a 32-bit unsigned parsed from a string of the
                 * form {N}, which could be decimal, hexadecimal or octal.
                 * Although it would be possible to use the value as a raw
                 * 16-bit DECnet address when the value fits into 16 bits, this
                 * would be a questionable feature: DECnet address wire
                 * encoding is little-endian, so this would not work as
                 * intuitively as the same works for [big-endian] IPv4
                 * addresses (0x01020304 means 1.2.3.4).
                 */
                if (proto == Q_DECNET)
                        bpf_error(cstate, "invalid DECnet address '%u'", v);
                vlen = 32;
        } else if (proto == Q_DECNET) {
                /*
                 * s points to a string of the form {N}.{N}, {N}.{N}.{N} or
                 * {N}.{N}.{N}.{N}, of which only the first potentially stands
                 * for a valid DECnet address.
                 */
                vlen = pcapint_atodn(s, &v);
                if (vlen == 0)
                        bpf_error(cstate, "invalid DECnet address '%s'", s);
        } else {
                /*
                 * s points to a string of the form {N}.{N}, {N}.{N}.{N} or
                 * {N}.{N}.{N}.{N}, all of which potentially stand for a valid
                 * IPv4 address.
                 */
                vlen = pcapint_atoin(s, &v);
                if (vlen < 0)
                        bpf_error(cstate, "invalid IPv4 address '%s'", s);
        }

        switch (q.addr) {

        case Q_DEFAULT:
        case Q_HOST:
        case Q_NET:
                if (proto == Q_DECNET)
                        return gen_host(cstate, v, 0, proto, dir, q.addr);
                else if (proto == Q_LINK) {
                        bpf_error(cstate, "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(cstate, v, mask, proto, dir, q.addr);
                }

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

                if (v > 65535)
                        bpf_error(cstate, "illegal port number %u > 65535", v);

            {
                struct block *b;
                b = gen_port(cstate, v, proto, dir);
                gen_or(gen_port6(cstate, v, proto, dir), b);
                return b;
            }

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

                if (v > 65535)
                        bpf_error(cstate, "illegal port number %u > 65535", v);

            {
                struct block *b;
                b = gen_portrange(cstate, v, v, proto, dir);
                gen_or(gen_portrange6(cstate, v, v, proto, dir), b);
                return b;
            }

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

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

#if !defined(NO_PROTOCHAIN)
        case Q_PROTOCHAIN:
                return gen_protochain(cstate, v, proto);
#endif

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

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

#ifdef INET6
struct block *
gen_mcode6(compiler_state_t *cstate, const char *s, bpf_u_int32 masklen,
    struct qual q)
{
        struct addrinfo *res;
        struct in6_addr *addr;
        struct in6_addr mask;
        struct block *b;
        bpf_u_int32 a[4], m[4]; /* Same as in gen_hostop6(). */

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

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

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

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

        switch (q.addr) {

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

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

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

struct block *
gen_ecode(compiler_state_t *cstate, const char *s, struct qual q)
{
        struct block *b, *tmp;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        if ((q.addr == Q_HOST || q.addr == Q_DEFAULT) && q.proto == Q_LINK) {
                cstate->e = pcap_ether_aton(s);
                if (cstate->e == NULL)
                        bpf_error(cstate, "malloc");
                switch (cstate->linktype) {
                case DLT_EN10MB:
                case DLT_NETANALYZER:
                case DLT_NETANALYZER_TRANSPARENT:
                        tmp = gen_prevlinkhdr_check(cstate);
                        b = gen_ehostop(cstate, cstate->e, (int)q.dir);
                        if (tmp != NULL)
                                gen_and(tmp, b);
                        break;
                case DLT_FDDI:
                        b = gen_fhostop(cstate, cstate->e, (int)q.dir);
                        break;
                case DLT_IEEE802:
                        b = gen_thostop(cstate, cstate->e, (int)q.dir);
                        break;
                case DLT_IEEE802_11:
                case DLT_PRISM_HEADER:
                case DLT_IEEE802_11_RADIO_AVS:
                case DLT_IEEE802_11_RADIO:
                case DLT_PPI:
                        b = gen_wlanhostop(cstate, cstate->e, (int)q.dir);
                        break;
                case DLT_IP_OVER_FC:
                        b = gen_ipfchostop(cstate, cstate->e, (int)q.dir);
                        break;
                default:
                        free(cstate->e);
                        cstate->e = NULL;
                        bpf_error(cstate, "ethernet addresses supported only on ethernet/FDDI/token ring/802.11/ATM LANE/Fibre Channel");
                        /*NOTREACHED*/
                }
                free(cstate->e);
                cstate->e = NULL;
                return (b);
        }
        bpf_error(cstate, "ethernet address used in non-ether expression");
        /*NOTREACHED*/
}

void
sappend(struct slist *s0, struct slist *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(compiler_state_t *cstate, struct arth *a)
{
        struct slist *s;

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

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

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

/*
 * Modify "index" to use the value stored into its register as an
 * offset relative to the beginning of the header for the protocol
 * "proto", and allocate a register and put an item "size" bytes long
 * (1, 2, or 4) at that offset into that register, making it the register
 * for "index".
 */
static struct arth *
gen_load_internal(compiler_state_t *cstate, int proto, struct arth *inst,
    bpf_u_int32 size)
{
        int size_code;
        struct slist *s, *tmp;
        struct block *b;
        int regno = alloc_reg(cstate);

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

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

        case 1:
                size_code = BPF_B;
                break;

        case 2:
                size_code = BPF_H;
                break;

        case 4:
                size_code = BPF_W;
                break;
        }
        switch (proto) {
        default:
                bpf_error(cstate, "'%s' does not support the index operation", pqkw(proto));

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

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

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

        case Q_LINK:
                /*
                 * The offset is relative to the beginning of
                 * the link-layer header.
                 *
                 * XXX - what about ATM LANE?  Should the index be
                 * relative to the beginning of the AAL5 frame, so
                 * that 0 refers to the beginning of the LE Control
                 * field, or relative to the beginning of the LAN
                 * frame, so that 0 refers, for Ethernet LANE, to
                 * the beginning of the destination address?
                 */
                s = gen_abs_offset_varpart(cstate, &cstate->off_linkhdr);

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

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

        case Q_IP:
        case Q_ARP:
        case Q_RARP:
        case Q_ATALK:
        case Q_DECNET:
        case Q_SCA:
        case Q_LAT:
        case Q_MOPRC:
        case Q_MOPDL:
        case Q_IPV6:
                /*
                 * The offset is relative to the beginning of
                 * the network-layer header.
                 * XXX - are there any cases where we want
                 * cstate->off_nl_nosnap?
                 */
                s = gen_abs_offset_varpart(cstate, &cstate->off_linkpl);

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

                /*
                 * Load the item at the sum of the offset we've put in the
                 * X register, the offset of the start of the network
                 * layer header from the beginning of the link-layer
                 * payload, and the constant part of the offset of the
                 * start of the link-layer payload.
                 */
                tmp = new_stmt(cstate, BPF_LD|BPF_IND|size_code);
                tmp->s.k = cstate->off_linkpl.constant_part + cstate->off_nl;
                sappend(s, tmp);
                sappend(inst->s, s);

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

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

                /*
                 * The X register now contains the sum of the variable
                 * part of the offset of the link-layer payload and the
                 * length of the network-layer header.
                 *
                 * Load into the A register the offset relative to
                 * the beginning of the transport layer header,
                 * add the X register to that, move that to the
                 * X register, and load with an offset from the
                 * X register equal to the sum of the constant part of
                 * the offset of the link-layer payload and the offset,
                 * relative to the beginning of the link-layer payload,
                 * of the network-layer header.
                 */
                sappend(s, xfer_to_a(cstate, inst));
                sappend(s, new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_X));
                sappend(s, new_stmt(cstate, BPF_MISC|BPF_TAX));
                sappend(s, tmp = new_stmt(cstate, BPF_LD|BPF_IND|size_code));
                tmp->s.k = cstate->off_linkpl.constant_part + cstate->off_nl;
                sappend(inst->s, s);

                /*
                 * Do the computation only if the packet contains
                 * the protocol in question - which is true only
                 * if this is an IP datagram and is the first or
                 * only fragment of that datagram.
                 */
                gen_and(gen_proto_abbrev_internal(cstate, proto), b = gen_ipfrag(cstate));
                if (inst->b)
                        gen_and(inst->b, b);
                gen_and(gen_proto_abbrev_internal(cstate, Q_IP), b);
                inst->b = b;
                break;
        case Q_ICMPV6:
                /*
                 * Do the computation only if the packet contains
                 * the protocol in question.
                 */
                b = gen_proto_abbrev_internal(cstate, Q_IPV6);
                if (inst->b)
                        gen_and(inst->b, b);
                inst->b = b;

                /*
                 * Check if we have an icmp6 next header
                 */
                b = gen_cmp(cstate, OR_LINKPL, 6, BPF_B, 58);
                if (inst->b)
                        gen_and(inst->b, b);
                inst->b = b;

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

                /*
                 * Load the item at the sum of the offset we've put in the
                 * X register, the offset of the start of the network
                 * layer header from the beginning of the link-layer
                 * payload, and the constant part of the offset of the
                 * start of the link-layer payload.
                 */
                tmp = new_stmt(cstate, BPF_LD|BPF_IND|size_code);
                tmp->s.k = cstate->off_linkpl.constant_part + cstate->off_nl + 40;

                sappend(s, tmp);
                sappend(inst->s, s);

                break;
        }
        inst->regno = regno;
        s = new_stmt(cstate, BPF_ST);
        s->s.k = regno;
        sappend(inst->s, s);

        return inst;
}

struct arth *
gen_load(compiler_state_t *cstate, int proto, struct arth *inst,
    bpf_u_int32 size)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        return gen_load_internal(cstate, proto, inst, size);
}

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

        s0 = xfer_to_x(cstate, a1);
        s1 = xfer_to_a(cstate, a0);
        if (code == BPF_JEQ) {
                s2 = new_stmt(cstate, BPF_ALU|BPF_SUB|BPF_X);
                b = new_block(cstate, JMP(code));
                sappend(s1, s2);
        }
        else
                b = new_block(cstate, 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(cstate, a0->regno);
        free_reg(cstate, 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 block *
gen_relation(compiler_state_t *cstate, int code, struct arth *a0,
    struct arth *a1, int reversed)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        return gen_relation_internal(cstate, code, a0, a1, reversed);
}

struct arth *
gen_loadlen(compiler_state_t *cstate)
{
        int regno;
        struct arth *a;
        struct slist *s;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        regno = alloc_reg(cstate);
        a = (struct arth *)newchunk(cstate, sizeof(*a));
        s = new_stmt(cstate, BPF_LD|BPF_LEN);
        s->next = new_stmt(cstate, BPF_ST);
        s->next->s.k = regno;
        a->s = s;
        a->regno = regno;

        return a;
}

static struct arth *
gen_loadi_internal(compiler_state_t *cstate, bpf_u_int32 val)
{
        struct arth *a;
        struct slist *s;
        int reg;

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

        reg = alloc_reg(cstate);

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

        return a;
}

struct arth *
gen_loadi(compiler_state_t *cstate, bpf_u_int32 val)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        return gen_loadi_internal(cstate, val);
}

/*
 * The a_arg dance is to avoid annoying whining by compilers that
 * a might be clobbered by longjmp - yeah, it might, but *WHO CARES*?
 * It's not *used* after setjmp returns.
 */
struct arth *
gen_neg(compiler_state_t *cstate, struct arth *a_arg)
{
        struct arth *a = a_arg;
        struct slist *s;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

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

        return a;
}

/*
 * The a0_arg dance is to avoid annoying whining by compilers that
 * a0 might be clobbered by longjmp - yeah, it might, but *WHO CARES*?
 * It's not *used* after setjmp returns.
 */
struct arth *
gen_arth(compiler_state_t *cstate, int code, struct arth *a0_arg,
    struct arth *a1)
{
        struct arth *a0 = a0_arg;
        struct slist *s0, *s1, *s2;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        /*
         * Disallow division by, or modulus by, zero; we do this here
         * so that it gets done even if the optimizer is disabled.
         *
         * Also disallow shifts by a value greater than 31; we do this
         * here, for the same reason.
         */
        if (code == BPF_DIV) {
                if (a1->s->s.code == (BPF_LD|BPF_IMM) && a1->s->s.k == 0)
                        bpf_error(cstate, "division by zero");
        } else if (code == BPF_MOD) {
                if (a1->s->s.code == (BPF_LD|BPF_IMM) && a1->s->s.k == 0)
                        bpf_error(cstate, "modulus by zero");
        } else if (code == BPF_LSH || code == BPF_RSH) {
                if (a1->s->s.code == (BPF_LD|BPF_IMM) && a1->s->s.k > 31)
                        bpf_error(cstate, "shift by more than 31 bits");
        }
        s0 = xfer_to_x(cstate, a1);
        s1 = xfer_to_a(cstate, a0);
        s2 = new_stmt(cstate, BPF_ALU|BPF_X|code);

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

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

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

        return a0;
}

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

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

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

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

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

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

        return b;
}

struct block *
gen_greater(compiler_state_t *cstate, int n)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        return gen_len(cstate, BPF_JGE, n);
}

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

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

        return b;
}

/*
 * This is for "byte {idx} {op} {val}"; "idx" is treated as relative to
 * the beginning of the link-layer header.
 * XXX - that means you can't test values in the radiotap header, but
 * as that header is difficult if not impossible to parse generally
 * without a loop, that might not be a severe problem.  A new keyword
 * "radio" could be added for that, although what you'd really want
 * would be a way of testing particular radio header values, which
 * would generate code appropriate to the radio header in question.
 */
struct block *
gen_byteop(compiler_state_t *cstate, int op, int idx, bpf_u_int32 val)
{
        struct block *b;
        struct slist *s;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        switch (op) {
        default:
                abort();

        case '=':
                return gen_cmp(cstate, OR_LINKHDR, (u_int)idx, BPF_B, val);

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

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

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

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

        return b;
}

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        switch (proto) {

        case Q_DEFAULT:
        case Q_LINK:
                switch (cstate->linktype) {
                case DLT_ARCNET:
                case DLT_ARCNET_LINUX:
                        // ARCnet broadcast is [8-bit] destination address 0.
                        return gen_ahostop(cstate, 0, Q_DST);
                case DLT_EN10MB:
                case DLT_NETANALYZER:
                case DLT_NETANALYZER_TRANSPARENT:
                        b1 = gen_prevlinkhdr_check(cstate);
                        b0 = gen_ehostop(cstate, ebroadcast, Q_DST);
                        if (b1 != NULL)
                                gen_and(b1, b0);
                        return b0;
                case DLT_FDDI:
                        return gen_fhostop(cstate, ebroadcast, Q_DST);
                case DLT_IEEE802:
                        return gen_thostop(cstate, ebroadcast, Q_DST);
                case DLT_IEEE802_11:
                case DLT_PRISM_HEADER:
                case DLT_IEEE802_11_RADIO_AVS:
                case DLT_IEEE802_11_RADIO:
                case DLT_PPI:
                        return gen_wlanhostop(cstate, ebroadcast, Q_DST);
                case DLT_IP_OVER_FC:
                        return gen_ipfchostop(cstate, ebroadcast, Q_DST);
                }
                fail_kw_on_dlt(cstate, "broadcast");
                /*NOTREACHED*/

        case Q_IP:
                /*
                 * We treat a netmask of PCAP_NETMASK_UNKNOWN (0xffffffff)
                 * as an indication that we don't know the netmask, and fail
                 * in that case.
                 */
                if (cstate->netmask == PCAP_NETMASK_UNKNOWN)
                        bpf_error(cstate, "netmask not known, so 'ip broadcast' not supported");
                b0 = gen_linktype(cstate, ETHERTYPE_IP);
                hostmask = ~cstate->netmask;
                b1 = gen_mcmp(cstate, OR_LINKPL, 16, BPF_W, 0, hostmask);
                b2 = gen_mcmp(cstate, OR_LINKPL, 16, BPF_W, hostmask, hostmask);
                gen_or(b1, b2);
                gen_and(b0, b2);
                return b2;
        }
        bpf_error(cstate, "only link-layer/IP broadcast filters supported");
        /*NOTREACHED*/
}

/*
 * 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(compiler_state_t *cstate, int offset)
{
        register struct block *b0;
        register struct slist *s;

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

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        switch (proto) {

        case Q_DEFAULT:
        case Q_LINK:
                switch (cstate->linktype) {
                case DLT_ARCNET:
                case DLT_ARCNET_LINUX:
                        // ARCnet multicast is the same as broadcast.
                        return gen_ahostop(cstate, 0, Q_DST);
                case DLT_EN10MB:
                case DLT_NETANALYZER:
                case DLT_NETANALYZER_TRANSPARENT:
                        b1 = gen_prevlinkhdr_check(cstate);
                        /* ether[0] & 1 != 0 */
                        b0 = gen_mac_multicast(cstate, 0);
                        if (b1 != NULL)
                                gen_and(b1, b0);
                        return b0;
                case DLT_FDDI:
                        /*
                         * XXX TEST THIS: MIGHT NOT PORT PROPERLY XXX
                         *
                         * XXX - was that referring to bit-order issues?
                         */
                        /* fddi[1] & 1 != 0 */
                        return gen_mac_multicast(cstate, 1);
                case DLT_IEEE802:
                        /* tr[2] & 1 != 0 */
                        return gen_mac_multicast(cstate, 2);
                case DLT_IEEE802_11:
                case DLT_PRISM_HEADER:
                case DLT_IEEE802_11_RADIO_AVS:
                case DLT_IEEE802_11_RADIO:
                case DLT_PPI:
                        /*
                         * Oh, yuk.
                         *
                         *      For control frames, there is no DA.
                         *
                         *      For management frames, DA is at an
                         *      offset of 4 from the beginning of
                         *      the packet.
                         *
                         *      For data frames, DA is at an offset
                         *      of 4 from the beginning of the packet
                         *      if To DS is clear and at an offset of
                         *      16 from the beginning of the packet
                         *      if To DS is set.
                         */

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

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

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

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

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

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

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

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

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

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

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

                        /*
                         * AND that with the checks for data and management
                         * frames.
                         */
                        gen_and(b1, b0);
                        return b0;
                case DLT_IP_OVER_FC:
                        b0 = gen_mac_multicast(cstate, 2);
                        return b0;
                default:
                        break;
                }
                fail_kw_on_dlt(cstate, "multicast");
                /*NOTREACHED*/

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

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

#ifdef __linux__
/*
 * This is Linux; we require PF_PACKET support.  If this is a *live* capture,
 * we can look at special meta-data in the filter expression; otherwise we
 * can't because it is either a savefile (rfile != NULL) or a pcap_t created
 * using pcap_open_dead() (rfile == NULL).  Thus check for a flag that
 * pcap_activate() conditionally sets.
 */
static void
require_basic_bpf_extensions(compiler_state_t *cstate, const char *keyword)
{
        if (cstate->bpf_pcap->bpf_codegen_flags & BPF_SPECIAL_BASIC_HANDLING)
                return;
        bpf_error(cstate, "%s not supported on %s (not a live capture)",
            keyword,
            pcap_datalink_val_to_description_or_dlt(cstate->linktype));
}
#endif // __linux__

struct block *
gen_ifindex(compiler_state_t *cstate, int ifindex)
{
        register struct block *b0;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        /*
         * Only some data link types support ifindex qualifiers.
         */
        switch (cstate->linktype) {
        case DLT_LINUX_SLL2:
                /* match packets on this interface */
                b0 = gen_cmp(cstate, OR_LINKHDR, 4, BPF_W, ifindex);
                break;
        default:
#if defined(__linux__)
                require_basic_bpf_extensions(cstate, "ifindex");
                /* match ifindex */
                b0 = gen_cmp(cstate, OR_LINKHDR, SKF_AD_OFF + SKF_AD_IFINDEX, BPF_W,
                             ifindex);
#else /* defined(__linux__) */
                fail_kw_on_dlt(cstate, "ifindex");
                /*NOTREACHED*/
#endif /* defined(__linux__) */
        }
        return (b0);
}

/*
 * Filter on inbound (outbound == 0) or outbound (outbound == 1) traffic.
 * Outbound traffic is sent by this machine, while inbound traffic is
 * sent by a remote machine (and may include packets destined for a
 * unicast or multicast link-layer address we are not subscribing to).
 * These are the same definitions implemented by pcap_setdirection().
 * Capturing only unicast traffic destined for this host is probably
 * better accomplished using a higher-layer filter.
 */
struct block *
gen_inbound_outbound(compiler_state_t *cstate, const int outbound)
{
        register struct block *b0;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        /*
         * Only some data link types support inbound/outbound qualifiers.
         */
        switch (cstate->linktype) {
        case DLT_SLIP:
                b0 = gen_cmp(cstate, OR_LINKHDR, 0, BPF_B,
                          outbound ? SLIPDIR_OUT : SLIPDIR_IN);
                break;

        case DLT_IPNET:
                b0 = gen_cmp(cstate, OR_LINKHDR, 2, BPF_H,
                    outbound ? IPNET_OUTBOUND : IPNET_INBOUND);
                break;

        case DLT_LINUX_SLL:
                /* match outgoing packets */
                b0 = gen_cmp(cstate, OR_LINKHDR, 0, BPF_H, LINUX_SLL_OUTGOING);
                if (! outbound) {
                        /* to filter on inbound traffic, invert the match */
                        gen_not(b0);
                }
                break;

        case DLT_LINUX_SLL2:
                /* match outgoing packets */
                b0 = gen_cmp(cstate, OR_LINKHDR, 10, BPF_B, LINUX_SLL_OUTGOING);
                if (! outbound) {
                        /* to filter on inbound traffic, invert the match */
                        gen_not(b0);
                }
                break;

        case DLT_PFLOG:
                b0 = gen_cmp(cstate, OR_LINKHDR, offsetof(struct pfloghdr, dir), BPF_B,
                    outbound ? PF_OUT : PF_IN);
                break;

        case DLT_PPP_PPPD:
                b0 = gen_cmp(cstate, OR_LINKHDR, 0, BPF_B, outbound ? PPP_PPPD_OUT : PPP_PPPD_IN);
                break;

        case DLT_JUNIPER_MFR:
        case DLT_JUNIPER_MLFR:
        case DLT_JUNIPER_MLPPP:
        case DLT_JUNIPER_ATM1:
        case DLT_JUNIPER_ATM2:
        case DLT_JUNIPER_PPPOE:
        case DLT_JUNIPER_PPPOE_ATM:
        case DLT_JUNIPER_GGSN:
        case DLT_JUNIPER_ES:
        case DLT_JUNIPER_MONITOR:
        case DLT_JUNIPER_SERVICES:
        case DLT_JUNIPER_ETHER:
        case DLT_JUNIPER_PPP:
        case DLT_JUNIPER_FRELAY:
        case DLT_JUNIPER_CHDLC:
        case DLT_JUNIPER_VP:
        case DLT_JUNIPER_ST:
        case DLT_JUNIPER_ISM:
        case DLT_JUNIPER_VS:
        case DLT_JUNIPER_SRX_E2E:
        case DLT_JUNIPER_FIBRECHANNEL:
        case DLT_JUNIPER_ATM_CEMIC:
                /* juniper flags (including direction) are stored
                 * the byte after the 3-byte magic number */
                b0 = gen_mcmp(cstate, OR_LINKHDR, 3, BPF_B, outbound ? 0 : 1, 0x01);
                break;

        default:
                /*
                 * If we have packet meta-data indicating a direction,
                 * and that metadata can be checked by BPF code, check
                 * it.  Otherwise, give up, as this link-layer type has
                 * nothing in the packet data.
                 *
                 * Currently, the only platform where a BPF filter can
                 * check that metadata is Linux with the in-kernel
                 * BPF interpreter.  If other packet capture mechanisms
                 * and BPF filters also supported this, it would be
                 * nice.  It would be even better if they made that
                 * metadata available so that we could provide it
                 * with newer capture APIs, allowing it to be saved
                 * in pcapng files.
                 */
#if defined(__linux__)
                require_basic_bpf_extensions(cstate, outbound ? "outbound" : "inbound");
                /* match outgoing packets */
                b0 = gen_cmp(cstate, OR_LINKHDR, SKF_AD_OFF + SKF_AD_PKTTYPE, BPF_H,
                             PACKET_OUTGOING);
                if (! outbound) {
                        /* to filter on inbound traffic, invert the match */
                        gen_not(b0);
                }
#else /* defined(__linux__) */
                fail_kw_on_dlt(cstate, outbound ? "outbound" : "inbound");
                /*NOTREACHED*/
#endif /* defined(__linux__) */
        }
        return (b0);
}

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

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

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

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

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

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

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

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

        b0 = gen_cmp(cstate, OR_LINKHDR, offsetof(struct pfloghdr, rulenr), BPF_W,
                 (bpf_u_int32)rnr);
        return (b0);
}

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

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

        b0 = gen_cmp(cstate, OR_LINKHDR, offsetof(struct pfloghdr, subrulenr), BPF_W,
            (bpf_u_int32)srnr);
        return (b0);
}

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

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

        b0 = gen_cmp(cstate, OR_LINKHDR, offsetof(struct pfloghdr, reason), BPF_B,
            (bpf_u_int32)reason);
        return (b0);
}

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

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

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

        b0 = gen_cmp(cstate, OR_LINKHDR, offsetof(struct pfloghdr, action), BPF_B,
            (bpf_u_int32)action);
        return (b0);
}

/* IEEE 802.11 wireless header */
struct block *
gen_p80211_type(compiler_state_t *cstate, bpf_u_int32 type, bpf_u_int32 mask)
{
        struct block *b0;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        switch (cstate->linktype) {

        case DLT_IEEE802_11:
        case DLT_PRISM_HEADER:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_IEEE802_11_RADIO:
        case DLT_PPI:
                b0 = gen_mcmp(cstate, OR_LINKHDR, 0, BPF_B, type, mask);
                break;

        default:
                fail_kw_on_dlt(cstate, "type/subtype");
                /*NOTREACHED*/
        }

        return (b0);
}

struct block *
gen_p80211_fcdir(compiler_state_t *cstate, bpf_u_int32 fcdir)
{
        struct block *b0;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        switch (cstate->linktype) {

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

        default:
                fail_kw_on_dlt(cstate, "dir");
                /*NOTREACHED*/
        }

        b0 = gen_mcmp(cstate, OR_LINKHDR, 1, BPF_B, fcdir,
            IEEE80211_FC1_DIR_MASK);

        return (b0);
}

// Process an ARCnet host address string.
struct block *
gen_acode(compiler_state_t *cstate, const char *s, struct qual q)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        switch (cstate->linktype) {

        case DLT_ARCNET:
        case DLT_ARCNET_LINUX:
                if ((q.addr == Q_HOST || q.addr == Q_DEFAULT) &&
                    q.proto == Q_LINK) {
                        uint8_t addr;
                        /*
                         * The lexer currently defines the address format in a
                         * way that makes this error condition never true.
                         * Let's check it anyway in case this part of the lexer
                         * changes in future.
                         */
                        if (! pcapint_atoan(s, &addr))
                            bpf_error(cstate, "invalid ARCnet address '%s'", s);
                        return gen_ahostop(cstate, addr, (int)q.dir);
                } else
                        bpf_error(cstate, "ARCnet address used in non-arc expression");
                /*NOTREACHED*/

        default:
                bpf_error(cstate, "aid supported only on ARCnet");
                /*NOTREACHED*/
        }
}

// Compare an ARCnet host address with the given value.
static struct block *
gen_ahostop(compiler_state_t *cstate, const uint8_t eaddr, int dir)
{
        register struct block *b0, *b1;

        switch (dir) {
        /*
         * ARCnet is different from Ethernet: the source address comes before
         * the destination address, each is one byte long.  This holds for all
         * three "buffer formats" in RFC 1201 Section 2.1, see also page 4-10
         * in the 1983 edition of the "ARCNET Designer's Handbook" published
         * by Datapoint (document number 61610-01).
         */
        case Q_SRC:
                return gen_cmp(cstate, OR_LINKHDR, 0, BPF_B, eaddr);

        case Q_DST:
                return gen_cmp(cstate, OR_LINKHDR, 1, BPF_B, eaddr);

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

        case Q_DEFAULT:
        case Q_OR:
                b0 = gen_ahostop(cstate, eaddr, Q_SRC);
                b1 = gen_ahostop(cstate, eaddr, Q_DST);
                gen_or(b0, b1);
                return b1;

        case Q_ADDR1:
                bpf_error(cstate, "'addr1' and 'address1' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR2:
                bpf_error(cstate, "'addr2' and 'address2' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR3:
                bpf_error(cstate, "'addr3' and 'address3' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_ADDR4:
                bpf_error(cstate, "'addr4' and 'address4' are only supported on 802.11");
                /*NOTREACHED*/

        case Q_RA:
                bpf_error(cstate, "'ra' is only supported on 802.11");
                /*NOTREACHED*/

        case Q_TA:
                bpf_error(cstate, "'ta' is only supported on 802.11");
                /*NOTREACHED*/
        }
        abort();
        /*NOTREACHED*/
}

static struct block *
gen_vlan_tpid_test(compiler_state_t *cstate)
{
        struct block *b0, *b1;

        /* check for VLAN, including 802.1ad and QinQ */
        b0 = gen_linktype(cstate, ETHERTYPE_8021Q);
        b1 = gen_linktype(cstate, ETHERTYPE_8021AD);
        gen_or(b0,b1);
        b0 = b1;
        b1 = gen_linktype(cstate, ETHERTYPE_8021QINQ);
        gen_or(b0,b1);

        return b1;
}

static struct block *
gen_vlan_vid_test(compiler_state_t *cstate, bpf_u_int32 vlan_num)
{
        if (vlan_num > 0x0fff) {
                bpf_error(cstate, "VLAN tag %u greater than maximum %u",
                    vlan_num, 0x0fff);
        }
        return gen_mcmp(cstate, OR_LINKPL, 0, BPF_H, vlan_num, 0x0fff);
}

static struct block *
gen_vlan_no_bpf_extensions(compiler_state_t *cstate, bpf_u_int32 vlan_num,
    int has_vlan_tag)
{
        struct block *b0, *b1;

        b0 = gen_vlan_tpid_test(cstate);

        if (has_vlan_tag) {
                b1 = gen_vlan_vid_test(cstate, vlan_num);
                gen_and(b0, b1);
                b0 = b1;
        }

        /*
         * Both payload and link header type follow the VLAN tags so that
         * both need to be updated.
         */
        cstate->off_linkpl.constant_part += 4;
        cstate->off_linktype.constant_part += 4;

        return b0;
}

#if defined(SKF_AD_VLAN_TAG_PRESENT)
/* add v to variable part of off */
static void
gen_vlan_vloffset_add(compiler_state_t *cstate, bpf_abs_offset *off,
    bpf_u_int32 v, struct slist *s)
{
        struct slist *s2;

        if (!off->is_variable)
                off->is_variable = 1;
        if (off->reg == -1)
                off->reg = alloc_reg(cstate);

        s2 = new_stmt(cstate, BPF_LD|BPF_MEM);
        s2->s.k = off->reg;
        sappend(s, s2);
        s2 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_IMM);
        s2->s.k = v;
        sappend(s, s2);
        s2 = new_stmt(cstate, BPF_ST);
        s2->s.k = off->reg;
        sappend(s, s2);
}

/*
 * patch block b_tpid (VLAN TPID test) to update variable parts of link payload
 * and link type offsets first
 */
static void
gen_vlan_patch_tpid_test(compiler_state_t *cstate, struct block *b_tpid)
{
        struct slist s;

        /* offset determined at run time, shift variable part */
        s.next = NULL;
        cstate->is_vlan_vloffset = 1;
        gen_vlan_vloffset_add(cstate, &cstate->off_linkpl, 4, &s);
        gen_vlan_vloffset_add(cstate, &cstate->off_linktype, 4, &s);

        /* we get a pointer to a chain of or-ed blocks, patch first of them */
        sappend(s.next, b_tpid->head->stmts);
        b_tpid->head->stmts = s.next;
}

/*
 * patch block b_vid (VLAN id test) to load VID value either from packet
 * metadata (using BPF extensions) if SKF_AD_VLAN_TAG_PRESENT is true
 */
static void
gen_vlan_patch_vid_test(compiler_state_t *cstate, struct block *b_vid)
{
        struct slist *s, *s2, *sjeq;
        unsigned cnt;

        s = new_stmt(cstate, BPF_LD|BPF_B|BPF_ABS);
        s->s.k = (bpf_u_int32)(SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT);

        /* true -> next instructions, false -> beginning of b_vid */
        sjeq = new_stmt(cstate, JMP(BPF_JEQ));
        sjeq->s.k = 1;
        sjeq->s.jf = b_vid->stmts;
        sappend(s, sjeq);

        s2 = new_stmt(cstate, BPF_LD|BPF_H|BPF_ABS);
        s2->s.k = (bpf_u_int32)(SKF_AD_OFF + SKF_AD_VLAN_TAG);
        sappend(s, s2);
        sjeq->s.jt = s2;

        /* Jump to the test in b_vid. We need to jump one instruction before
         * the end of the b_vid block so that we only skip loading the TCI
         * from packet data and not the 'and' instruction extracting VID.
         */
        cnt = 0;
        for (s2 = b_vid->stmts; s2; s2 = s2->next)
                cnt++;
        s2 = new_stmt(cstate, JMP(BPF_JA));
        s2->s.k = cnt - 1;
        sappend(s, s2);

        /* insert our statements at the beginning of b_vid */
        sappend(s, b_vid->stmts);
        b_vid->stmts = s;
}

/*
 * Generate check for "vlan" or "vlan <id>" on systems with support for BPF
 * extensions.  Even if kernel supports VLAN BPF extensions, (outermost) VLAN
 * tag can be either in metadata or in packet data; therefore if the
 * SKF_AD_VLAN_TAG_PRESENT test is negative, we need to check link
 * header for VLAN tag. As the decision is done at run time, we need
 * update variable part of the offsets
 */
static struct block *
gen_vlan_bpf_extensions(compiler_state_t *cstate, bpf_u_int32 vlan_num,
    int has_vlan_tag)
{
        struct block *b0, *b_tpid, *b_vid = NULL;
        struct slist *s;

        /* generate new filter code based on extracting packet
         * metadata */
        s = new_stmt(cstate, BPF_LD|BPF_B|BPF_ABS);
        s->s.k = (bpf_u_int32)(SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT);

        b0 = new_block(cstate, JMP(BPF_JEQ));
        b0->stmts = s;
        b0->s.k = 1;

        /*
         * This is tricky. We need to insert the statements updating variable
         * parts of offsets before the traditional TPID and VID tests so
         * that they are called whenever SKF_AD_VLAN_TAG_PRESENT fails but
         * we do not want this update to affect those checks. That's why we
         * generate both test blocks first and insert the statements updating
         * variable parts of both offsets after that. This wouldn't work if
         * there already were variable length link header when entering this
         * function but gen_vlan_bpf_extensions() isn't called in that case.
         */
        b_tpid = gen_vlan_tpid_test(cstate);
        if (has_vlan_tag)
                b_vid = gen_vlan_vid_test(cstate, vlan_num);

        gen_vlan_patch_tpid_test(cstate, b_tpid);
        gen_or(b0, b_tpid);
        b0 = b_tpid;

        if (has_vlan_tag) {
                gen_vlan_patch_vid_test(cstate, b_vid);
                gen_and(b0, b_vid);
                b0 = b_vid;
        }

        return b0;
}
#endif

/*
 * support IEEE 802.1Q VLAN trunk over ethernet
 */
struct block *
gen_vlan(compiler_state_t *cstate, bpf_u_int32 vlan_num, int has_vlan_tag)
{
        struct  block   *b0;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

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

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

        case DLT_EN10MB:
                /*
                 * Newer version of the Linux kernel pass around
                 * packets in which the VLAN tag has been removed
                 * from the packet data and put into metadata.
                 *
                 * This requires special treatment.
                 */
#if defined(SKF_AD_VLAN_TAG_PRESENT)
                /* Verify that this is the outer part of the packet and
                 * not encapsulated somehow. */
                if (cstate->vlan_stack_depth == 0 && !cstate->off_linkhdr.is_variable &&
                    cstate->off_linkhdr.constant_part ==
                    cstate->off_outermostlinkhdr.constant_part) {
                        /*
                         * Do we need special VLAN handling?
                         */
                        if (cstate->bpf_pcap->bpf_codegen_flags & BPF_SPECIAL_VLAN_HANDLING)
                                b0 = gen_vlan_bpf_extensions(cstate, vlan_num,
                                    has_vlan_tag);
                        else
                                b0 = gen_vlan_no_bpf_extensions(cstate,
                                    vlan_num, has_vlan_tag);
                } else
#endif
                        b0 = gen_vlan_no_bpf_extensions(cstate, vlan_num,
                            has_vlan_tag);
                break;

        case DLT_NETANALYZER:
        case DLT_NETANALYZER_TRANSPARENT:
        case DLT_IEEE802_11:
        case DLT_PRISM_HEADER:
        case DLT_IEEE802_11_RADIO_AVS:
        case DLT_IEEE802_11_RADIO:
                /*
                 * These are either Ethernet packets with an additional
                 * metadata header (the NetAnalyzer types), or 802.11
                 * packets, possibly with an additional metadata header.
                 *
                 * For the first of those, the VLAN tag is in the normal
                 * place, so the special-case handling above isn't
                 * necessary.
                 *
                 * For the second of those, we don't do the special-case
                 * handling for now.
                 */
                b0 = gen_vlan_no_bpf_extensions(cstate, vlan_num, has_vlan_tag);
                break;

        default:
                bpf_error(cstate, "no VLAN support for %s",
                      pcap_datalink_val_to_description_or_dlt(cstate->linktype));
                /*NOTREACHED*/
        }

        cstate->vlan_stack_depth++;

        return (b0);
}

/*
 * support for MPLS
 *
 * The label_num_arg dance is to avoid annoying whining by compilers that
 * label_num might be clobbered by longjmp - yeah, it might, but *WHO CARES*?
 * It's not *used* after setjmp returns.
 */
static struct block *
gen_mpls_internal(compiler_state_t *cstate, bpf_u_int32 label_num,
    int has_label_num)
{
        struct  block   *b0, *b1;

        if (cstate->label_stack_depth > 0) {
                /* just match the bottom-of-stack bit clear */
                b0 = gen_mcmp(cstate, OR_PREVMPLSHDR, 2, BPF_B, 0, 0x01);
        } else {
                /*
                 * We're not in an MPLS stack yet, so check the link-layer
                 * type against MPLS.
                 */
                switch (cstate->linktype) {

                case DLT_C_HDLC: /* fall through */
                case DLT_HDLC:
                case DLT_EN10MB:
                case DLT_NETANALYZER:
                case DLT_NETANALYZER_TRANSPARENT:
                        b0 = gen_linktype(cstate, ETHERTYPE_MPLS);
                        break;

                case DLT_PPP:
                        b0 = gen_linktype(cstate, PPP_MPLS_UCAST);
                        break;

                        /* FIXME add other DLT_s ...
                         * for Frame-Relay/and ATM this may get messy due to SNAP headers
                         * leave it for now */

                default:
                        bpf_error(cstate, "no MPLS support for %s",
                            pcap_datalink_val_to_description_or_dlt(cstate->linktype));
                        /*NOTREACHED*/
                }
        }

        /* If a specific MPLS label is requested, check it */
        if (has_label_num) {
                if (label_num > 0xFFFFF) {
                        bpf_error(cstate, "MPLS label %u greater than maximum %u",
                            label_num, 0xFFFFF);
                }
                label_num = label_num << 12; /* label is shifted 12 bits on the wire */
                b1 = gen_mcmp(cstate, OR_LINKPL, 0, BPF_W, label_num,
                    0xfffff000); /* only compare the first 20 bits */
                gen_and(b0, b1);
                b0 = b1;
        }

        /*
         * Change the offsets to point to the type and data fields within
         * the MPLS packet.  Just increment the offsets, so that we
         * can support a hierarchy, e.g. "mpls 100000 && mpls 1024" to
         * capture packets with an outer label of 100000 and an inner
         * label of 1024.
         *
         * Increment the MPLS stack depth as well; this indicates that
         * we're checking MPLS-encapsulated headers, to make sure higher
         * level code generators don't try to match against IP-related
         * protocols such as Q_ARP, Q_RARP etc.
         *
         * XXX - this is a bit of a kludge.  See comments in gen_vlan().
         */
        cstate->off_nl_nosnap += 4;
        cstate->off_nl += 4;
        cstate->label_stack_depth++;
        return (b0);
}

struct block *
gen_mpls(compiler_state_t *cstate, bpf_u_int32 label_num, int has_label_num)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        return gen_mpls_internal(cstate, label_num, has_label_num);
}

/*
 * Support PPPOE discovery and session.
 */
struct block *
gen_pppoed(compiler_state_t *cstate)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        /* check for PPPoE discovery */
        return gen_linktype(cstate, ETHERTYPE_PPPOED);
}

/*
 * RFC 2516 Section 4:
 *
 * The Ethernet payload for PPPoE is as follows:
 *
 *                      1                   2                   3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |  VER  | TYPE  |      CODE     |          SESSION_ID           |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |            LENGTH             |           payload             ~
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 */
struct block *
gen_pppoes(compiler_state_t *cstate, bpf_u_int32 sess_num, int has_sess_num)
{
        struct block *b0, *b1;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        /*
         * Test against the PPPoE session link-layer type.
         */
        b0 = gen_linktype(cstate, ETHERTYPE_PPPOES);

        /* If a specific session is requested, check PPPoE session id */
        if (has_sess_num) {
                if (sess_num > UINT16_MAX) {
                        bpf_error(cstate, "PPPoE session number %u greater than maximum %u",
                            sess_num, UINT16_MAX);
                }
                b1 = gen_cmp(cstate, OR_LINKPL, 2, BPF_H, sess_num);
                gen_and(b0, b1);
                b0 = b1;
        }

        /*
         * Change the offsets to point to the type and data fields within
         * the PPP packet, and note that this is PPPoE rather than
         * raw PPP.
         *
         * XXX - this is a bit of a kludge.  See the comments in
         * gen_vlan().
         *
         * The "network-layer" protocol is PPPoE, which has a 6-byte
         * PPPoE header, followed by a PPP packet.
         *
         * There is no HDLC encapsulation for the PPP packet (it's
         * encapsulated in PPPoES instead), so the link-layer type
         * starts at the first byte of the PPP packet.  For PPPoE,
         * that offset is relative to the beginning of the total
         * link-layer payload, including any 802.2 LLC header, so
         * it's 6 bytes past cstate->off_nl.
         */
        PUSH_LINKHDR(cstate, DLT_PPP, cstate->off_linkpl.is_variable,
            cstate->off_linkpl.constant_part + cstate->off_nl + 6, /* 6 bytes past the PPPoE header */
            cstate->off_linkpl.reg);

        cstate->off_linktype = cstate->off_linkhdr;
        cstate->off_linkpl.constant_part = cstate->off_linkhdr.constant_part + 2;

        cstate->off_nl = 0;
        cstate->off_nl_nosnap = 0;      /* no 802.2 LLC */

        return b0;
}

/* Check that this is Geneve and the VNI is correct if
 * specified. Parameterized to handle both IPv4 and IPv6. */
static struct block *
gen_geneve_check(compiler_state_t *cstate,
    struct block *(*gen_portfn)(compiler_state_t *, u_int, int, int),
    enum e_offrel offrel, bpf_u_int32 vni, int has_vni)
{
        struct block *b0, *b1;

        b0 = gen_portfn(cstate, GENEVE_PORT, IPPROTO_UDP, Q_DST);

        /* Check that we are operating on version 0. Otherwise, we
         * can't decode the rest of the fields. The version is 2 bits
         * in the first byte of the Geneve header. */
        b1 = gen_mcmp(cstate, offrel, 8, BPF_B, 0, 0xc0);
        gen_and(b0, b1);
        b0 = b1;

        if (has_vni) {
                if (vni > 0xffffff) {
                        bpf_error(cstate, "Geneve VNI %u greater than maximum %u",
                            vni, 0xffffff);
                }
                vni <<= 8; /* VNI is in the upper 3 bytes */
                b1 = gen_mcmp(cstate, offrel, 12, BPF_W, vni, 0xffffff00);
                gen_and(b0, b1);
                b0 = b1;
        }

        return b0;
}

/* The IPv4 and IPv6 Geneve checks need to do two things:
 * - Verify that this actually is Geneve with the right VNI.
 * - Place the IP header length (plus variable link prefix if
 *   needed) into register A to be used later to compute
 *   the inner packet offsets. */
static struct block *
gen_geneve4(compiler_state_t *cstate, bpf_u_int32 vni, int has_vni)
{
        struct block *b0, *b1;
        struct slist *s, *s1;

        b0 = gen_geneve_check(cstate, gen_port, OR_TRAN_IPV4, vni, has_vni);

        /* Load the IP header length into A. */
        s = gen_loadx_iphdrlen(cstate);

        s1 = new_stmt(cstate, BPF_MISC|BPF_TXA);
        sappend(s, s1);

        /* Forcibly append these statements to the true condition
         * of the protocol check by creating a new block that is
         * always true and ANDing them. */
        b1 = new_block(cstate, BPF_JMP|BPF_JEQ|BPF_X);
        b1->stmts = s;
        b1->s.k = 0;

        gen_and(b0, b1);

        return b1;
}

static struct block *
gen_geneve6(compiler_state_t *cstate, bpf_u_int32 vni, int has_vni)
{
        struct block *b0, *b1;
        struct slist *s, *s1;

        b0 = gen_geneve_check(cstate, gen_port6, OR_TRAN_IPV6, vni, has_vni);

        /* Load the IP header length. We need to account for a
         * variable length link prefix if there is one. */
        s = gen_abs_offset_varpart(cstate, &cstate->off_linkpl);
        if (s) {
                s1 = new_stmt(cstate, BPF_LD|BPF_IMM);
                s1->s.k = 40;
                sappend(s, s1);

                s1 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_X);
                s1->s.k = 0;
                sappend(s, s1);
        } else {
                s = new_stmt(cstate, BPF_LD|BPF_IMM);
                s->s.k = 40;
        }

        /* Forcibly append these statements to the true condition
         * of the protocol check by creating a new block that is
         * always true and ANDing them. */
        s1 = new_stmt(cstate, BPF_MISC|BPF_TAX);
        sappend(s, s1);

        b1 = new_block(cstate, BPF_JMP|BPF_JEQ|BPF_X);
        b1->stmts = s;
        b1->s.k = 0;

        gen_and(b0, b1);

        return b1;
}

/* We need to store three values based on the Geneve header::
 * - The offset of the linktype.
 * - The offset of the end of the Geneve header.
 * - The offset of the end of the encapsulated MAC header. */
static struct slist *
gen_geneve_offsets(compiler_state_t *cstate)
{
        struct slist *s, *s1, *s_proto;

        /* First we need to calculate the offset of the Geneve header
         * itself. This is composed of the IP header previously calculated
         * (include any variable link prefix) and stored in A plus the
         * fixed sized headers (fixed link prefix, MAC length, and UDP
         * header). */
        s = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s->s.k = cstate->off_linkpl.constant_part + cstate->off_nl + 8;

        /* Stash this in X since we'll need it later. */
        s1 = new_stmt(cstate, BPF_MISC|BPF_TAX);
        sappend(s, s1);

        /* The EtherType in Geneve is 2 bytes in. Calculate this and
         * store it. */
        s1 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s1->s.k = 2;
        sappend(s, s1);

        cstate->off_linktype.reg = alloc_reg(cstate);
        cstate->off_linktype.is_variable = 1;
        cstate->off_linktype.constant_part = 0;

        s1 = new_stmt(cstate, BPF_ST);
        s1->s.k = cstate->off_linktype.reg;
        sappend(s, s1);

        /* Load the Geneve option length and mask and shift to get the
         * number of bytes. It is stored in the first byte of the Geneve
         * header. */
        s1 = new_stmt(cstate, BPF_LD|BPF_IND|BPF_B);
        s1->s.k = 0;
        sappend(s, s1);

        s1 = new_stmt(cstate, BPF_ALU|BPF_AND|BPF_K);
        s1->s.k = 0x3f;
        sappend(s, s1);

        s1 = new_stmt(cstate, BPF_ALU|BPF_MUL|BPF_K);
        s1->s.k = 4;
        sappend(s, s1);

        /* Add in the rest of the Geneve base header. */
        s1 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s1->s.k = 8;
        sappend(s, s1);

        /* Add the Geneve header length to its offset and store. */
        s1 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_X);
        s1->s.k = 0;
        sappend(s, s1);

        /* Set the encapsulated type as Ethernet. Even though we may
         * not actually have Ethernet inside there are two reasons this
         * is useful:
         * - The linktype field is always in EtherType format regardless
         *   of whether it is in Geneve or an inner Ethernet frame.
         * - The only link layer that we have specific support for is
         *   Ethernet. We will confirm that the packet actually is
         *   Ethernet at runtime before executing these checks. */
        PUSH_LINKHDR(cstate, DLT_EN10MB, 1, 0, alloc_reg(cstate));

        s1 = new_stmt(cstate, BPF_ST);
        s1->s.k = cstate->off_linkhdr.reg;
        sappend(s, s1);

        /* Calculate whether we have an Ethernet header or just raw IP/
         * MPLS/etc. If we have Ethernet, advance the end of the MAC offset
         * and linktype by 14 bytes so that the network header can be found
         * seamlessly. Otherwise, keep what we've calculated already. */

        /* We have a bare jmp so we can't use the optimizer. */
        cstate->no_optimize = 1;

        /* Load the EtherType in the Geneve header, 2 bytes in. */
        s1 = new_stmt(cstate, BPF_LD|BPF_IND|BPF_H);
        s1->s.k = 2;
        sappend(s, s1);

        /* Load X with the end of the Geneve header. */
        s1 = new_stmt(cstate, BPF_LDX|BPF_MEM);
        s1->s.k = cstate->off_linkhdr.reg;
        sappend(s, s1);

        /* Check if the EtherType is Transparent Ethernet Bridging. At the
         * end of this check, we should have the total length in X. In
         * the non-Ethernet case, it's already there. */
        s_proto = new_stmt(cstate, JMP(BPF_JEQ));
        s_proto->s.k = ETHERTYPE_TEB;
        sappend(s, s_proto);

        s1 = new_stmt(cstate, BPF_MISC|BPF_TXA);
        sappend(s, s1);
        s_proto->s.jt = s1;

        /* Since this is Ethernet, use the EtherType of the payload
         * directly as the linktype. Overwrite what we already have. */
        s1 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s1->s.k = 12;
        sappend(s, s1);

        s1 = new_stmt(cstate, BPF_ST);
        s1->s.k = cstate->off_linktype.reg;
        sappend(s, s1);

        /* Advance two bytes further to get the end of the Ethernet
         * header. */
        s1 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s1->s.k = 2;
        sappend(s, s1);

        /* Move the result to X. */
        s1 = new_stmt(cstate, BPF_MISC|BPF_TAX);
        sappend(s, s1);

        /* Store the final result of our linkpl calculation. */
        cstate->off_linkpl.reg = alloc_reg(cstate);
        cstate->off_linkpl.is_variable = 1;
        cstate->off_linkpl.constant_part = 0;

        s1 = new_stmt(cstate, BPF_STX);
        s1->s.k = cstate->off_linkpl.reg;
        sappend(s, s1);
        s_proto->s.jf = s1;

        cstate->off_nl = 0;

        return s;
}

/* Check to see if this is a Geneve packet. */
struct block *
gen_geneve(compiler_state_t *cstate, bpf_u_int32 vni, int has_vni)
{
        struct block *b0, *b1;
        struct slist *s;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        b0 = gen_geneve4(cstate, vni, has_vni);
        b1 = gen_geneve6(cstate, vni, has_vni);

        gen_or(b0, b1);
        b0 = b1;

        /* Later filters should act on the payload of the Geneve frame,
         * update all of the header pointers. Attach this code so that
         * it gets executed in the event that the Geneve filter matches. */
        s = gen_geneve_offsets(cstate);

        b1 = gen_true(cstate);
        sappend(s, b1->stmts);
        b1->stmts = s;

        gen_and(b0, b1);

        cstate->is_encap = 1;

        return b1;
}

/* Check that this is VXLAN and the VNI is correct if
 * specified. Parameterized to handle both IPv4 and IPv6. */
static struct block *
gen_vxlan_check(compiler_state_t *cstate,
    struct block *(*gen_portfn)(compiler_state_t *, u_int, int, int),
    enum e_offrel offrel, bpf_u_int32 vni, int has_vni)
{
        struct block *b0, *b1;

        b0 = gen_portfn(cstate, VXLAN_PORT, IPPROTO_UDP, Q_DST);

        /* Check that the VXLAN header has the flag bits set
         * correctly. */
        b1 = gen_cmp(cstate, offrel, 8, BPF_B, 0x08);
        gen_and(b0, b1);
        b0 = b1;

        if (has_vni) {
                if (vni > 0xffffff) {
                        bpf_error(cstate, "VXLAN VNI %u greater than maximum %u",
                            vni, 0xffffff);
                }
                vni <<= 8; /* VNI is in the upper 3 bytes */
                b1 = gen_mcmp(cstate, offrel, 12, BPF_W, vni, 0xffffff00);
                gen_and(b0, b1);
                b0 = b1;
        }

        return b0;
}

/* The IPv4 and IPv6 VXLAN checks need to do two things:
 * - Verify that this actually is VXLAN with the right VNI.
 * - Place the IP header length (plus variable link prefix if
 *   needed) into register A to be used later to compute
 *   the inner packet offsets. */
static struct block *
gen_vxlan4(compiler_state_t *cstate, bpf_u_int32 vni, int has_vni)
{
        struct block *b0, *b1;
        struct slist *s, *s1;

        b0 = gen_vxlan_check(cstate, gen_port, OR_TRAN_IPV4, vni, has_vni);

        /* Load the IP header length into A. */
        s = gen_loadx_iphdrlen(cstate);

        s1 = new_stmt(cstate, BPF_MISC|BPF_TXA);
        sappend(s, s1);

        /* Forcibly append these statements to the true condition
         * of the protocol check by creating a new block that is
         * always true and ANDing them. */
        b1 = new_block(cstate, BPF_JMP|BPF_JEQ|BPF_X);
        b1->stmts = s;
        b1->s.k = 0;

        gen_and(b0, b1);

        return b1;
}

static struct block *
gen_vxlan6(compiler_state_t *cstate, bpf_u_int32 vni, int has_vni)
{
        struct block *b0, *b1;
        struct slist *s, *s1;

        b0 = gen_vxlan_check(cstate, gen_port6, OR_TRAN_IPV6, vni, has_vni);

        /* Load the IP header length. We need to account for a
         * variable length link prefix if there is one. */
        s = gen_abs_offset_varpart(cstate, &cstate->off_linkpl);
        if (s) {
                s1 = new_stmt(cstate, BPF_LD|BPF_IMM);
                s1->s.k = 40;
                sappend(s, s1);

                s1 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_X);
                s1->s.k = 0;
                sappend(s, s1);
        } else {
                s = new_stmt(cstate, BPF_LD|BPF_IMM);
                s->s.k = 40;
        }

        /* Forcibly append these statements to the true condition
         * of the protocol check by creating a new block that is
         * always true and ANDing them. */
        s1 = new_stmt(cstate, BPF_MISC|BPF_TAX);
        sappend(s, s1);

        b1 = new_block(cstate, BPF_JMP|BPF_JEQ|BPF_X);
        b1->stmts = s;
        b1->s.k = 0;

        gen_and(b0, b1);

        return b1;
}

/* We need to store three values based on the VXLAN header:
 * - The offset of the linktype.
 * - The offset of the end of the VXLAN header.
 * - The offset of the end of the encapsulated MAC header. */
static struct slist *
gen_vxlan_offsets(compiler_state_t *cstate)
{
        struct slist *s, *s1;

        /* Calculate the offset of the VXLAN header itself. This
         * includes the IP header computed previously (including any
         * variable link prefix) and stored in A plus the fixed size
         * headers (fixed link prefix, MAC length, UDP header). */
        s = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s->s.k = cstate->off_linkpl.constant_part + cstate->off_nl + 8;

        /* Add the VXLAN header length to its offset and store */
        s1 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s1->s.k = 8;
        sappend(s, s1);

        /* Push the link header. VXLAN packets always contain Ethernet
         * frames. */
        PUSH_LINKHDR(cstate, DLT_EN10MB, 1, 0, alloc_reg(cstate));

        s1 = new_stmt(cstate, BPF_ST);
        s1->s.k = cstate->off_linkhdr.reg;
        sappend(s, s1);

        /* As the payload is an Ethernet packet, we can use the
         * EtherType of the payload directly as the linktype. */
        s1 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s1->s.k = 12;
        sappend(s, s1);

        cstate->off_linktype.reg = alloc_reg(cstate);
        cstate->off_linktype.is_variable = 1;
        cstate->off_linktype.constant_part = 0;

        s1 = new_stmt(cstate, BPF_ST);
        s1->s.k = cstate->off_linktype.reg;
        sappend(s, s1);

        /* Two bytes further is the end of the Ethernet header and the
         * start of the payload. */
        s1 = new_stmt(cstate, BPF_ALU|BPF_ADD|BPF_K);
        s1->s.k = 2;
        sappend(s, s1);

        /* Move the result to X. */
        s1 = new_stmt(cstate, BPF_MISC|BPF_TAX);
        sappend(s, s1);

        /* Store the final result of our linkpl calculation. */
        cstate->off_linkpl.reg = alloc_reg(cstate);
        cstate->off_linkpl.is_variable = 1;
        cstate->off_linkpl.constant_part = 0;

        s1 = new_stmt(cstate, BPF_STX);
        s1->s.k = cstate->off_linkpl.reg;
        sappend(s, s1);

        cstate->off_nl = 0;

        return s;
}

/* Check to see if this is a VXLAN packet. */
struct block *
gen_vxlan(compiler_state_t *cstate, bpf_u_int32 vni, int has_vni)
{
        struct block *b0, *b1;
        struct slist *s;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        b0 = gen_vxlan4(cstate, vni, has_vni);
        b1 = gen_vxlan6(cstate, vni, has_vni);

        gen_or(b0, b1);
        b0 = b1;

        /* Later filters should act on the payload of the VXLAN frame,
         * update all of the header pointers. Attach this code so that
         * it gets executed in the event that the VXLAN filter matches. */
        s = gen_vxlan_offsets(cstate);

        b1 = gen_true(cstate);
        sappend(s, b1->stmts);
        b1->stmts = s;

        gen_and(b0, b1);

        cstate->is_encap = 1;

        return b1;
}

/* Check that the encapsulated frame has a link layer header
 * for Ethernet filters. */
static struct block *
gen_encap_ll_check(compiler_state_t *cstate)
{
        struct block *b0;
        struct slist *s, *s1;

        /* The easiest way to see if there is a link layer present
         * is to check if the link layer header and payload are not
         * the same. */

        /* Geneve always generates pure variable offsets so we can
         * compare only the registers. */
        s = new_stmt(cstate, BPF_LD|BPF_MEM);
        s->s.k = cstate->off_linkhdr.reg;

        s1 = new_stmt(cstate, BPF_LDX|BPF_MEM);
        s1->s.k = cstate->off_linkpl.reg;
        sappend(s, s1);

        b0 = new_block(cstate, BPF_JMP|BPF_JEQ|BPF_X);
        b0->stmts = s;
        b0->s.k = 0;
        gen_not(b0);

        return b0;
}

static struct block *
gen_atmfield_code_internal(compiler_state_t *cstate, int atmfield,
    bpf_u_int32 jvalue, int jtype, int reverse)
{
        struct block *b0;

        switch (atmfield) {

        case A_VPI:
                if (!cstate->is_atm)
                        bpf_error(cstate, "'vpi' supported only on raw ATM");
                if (cstate->off_vpi == OFFSET_NOT_SET)
                        abort();
                if (jvalue > UINT8_MAX)
                        bpf_error(cstate, "VPI value %u > %u", jvalue, UINT8_MAX);
                b0 = gen_ncmp(cstate, OR_LINKHDR, cstate->off_vpi, BPF_B,
                    0xffffffffU, jtype, reverse, jvalue);
                break;

        case A_VCI:
                if (!cstate->is_atm)
                        bpf_error(cstate, "'vci' supported only on raw ATM");
                if (cstate->off_vci == OFFSET_NOT_SET)
                        abort();
                if (jvalue > UINT16_MAX)
                        bpf_error(cstate, "VCI value %u > %u", jvalue, UINT16_MAX);
                b0 = gen_ncmp(cstate, OR_LINKHDR, cstate->off_vci, BPF_H,
                    0xffffffffU, jtype, reverse, jvalue);
                break;

        case A_PROTOTYPE:
                if (cstate->off_proto == OFFSET_NOT_SET)
                        abort();        /* XXX - this isn't on FreeBSD */
                b0 = gen_ncmp(cstate, OR_LINKHDR, cstate->off_proto, BPF_B,
                    0x0fU, jtype, reverse, jvalue);
                break;

        case A_MSGTYPE:
                if (cstate->off_payload == OFFSET_NOT_SET)
                        abort();
                b0 = gen_ncmp(cstate, OR_LINKHDR, cstate->off_payload + MSG_TYPE_POS, BPF_B,
                    0xffffffffU, jtype, reverse, jvalue);
                break;

        default:
                abort();
        }
        return b0;
}

static struct block *
gen_atmtype_metac(compiler_state_t *cstate)
{
        struct block *b0, *b1;

        b0 = gen_atmfield_code_internal(cstate, A_VPI, 0, BPF_JEQ, 0);
        b1 = gen_atmfield_code_internal(cstate, A_VCI, 1, BPF_JEQ, 0);
        gen_and(b0, b1);
        return b1;
}

static struct block *
gen_atmtype_sc(compiler_state_t *cstate)
{
        struct block *b0, *b1;

        b0 = gen_atmfield_code_internal(cstate, A_VPI, 0, BPF_JEQ, 0);
        b1 = gen_atmfield_code_internal(cstate, A_VCI, 5, BPF_JEQ, 0);
        gen_and(b0, b1);
        return b1;
}

static struct block *
gen_atmtype_llc(compiler_state_t *cstate)
{
        struct block *b0;

        b0 = gen_atmfield_code_internal(cstate, A_PROTOTYPE, PT_LLC, BPF_JEQ, 0);
        cstate->linktype = cstate->prevlinktype;
        return b0;
}

struct block *
gen_atmfield_code(compiler_state_t *cstate, int atmfield,
    bpf_u_int32 jvalue, int jtype, int reverse)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        return gen_atmfield_code_internal(cstate, atmfield, jvalue, jtype,
            reverse);
}

struct block *
gen_atmtype_abbrev(compiler_state_t *cstate, int type)
{
        struct block *b0, *b1;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        switch (type) {

        case A_METAC:
                /* Get all packets in Meta signalling Circuit */
                if (!cstate->is_atm)
                        bpf_error(cstate, "'metac' supported only on raw ATM");
                b1 = gen_atmtype_metac(cstate);
                break;

        case A_BCC:
                /* Get all packets in Broadcast Circuit*/
                if (!cstate->is_atm)
                        bpf_error(cstate, "'bcc' supported only on raw ATM");
                b0 = gen_atmfield_code_internal(cstate, A_VPI, 0, BPF_JEQ, 0);
                b1 = gen_atmfield_code_internal(cstate, A_VCI, 2, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_OAMF4SC:
                /* Get all cells in Segment OAM F4 circuit*/
                if (!cstate->is_atm)
                        bpf_error(cstate, "'oam4sc' supported only on raw ATM");
                b0 = gen_atmfield_code_internal(cstate, A_VPI, 0, BPF_JEQ, 0);
                b1 = gen_atmfield_code_internal(cstate, 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 (!cstate->is_atm)
                        bpf_error(cstate, "'oam4ec' supported only on raw ATM");
                b0 = gen_atmfield_code_internal(cstate, A_VPI, 0, BPF_JEQ, 0);
                b1 = gen_atmfield_code_internal(cstate, A_VCI, 4, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_SC:
                /*  Get all packets in connection Signalling Circuit */
                if (!cstate->is_atm)
                        bpf_error(cstate, "'sc' supported only on raw ATM");
                b1 = gen_atmtype_sc(cstate);
                break;

        case A_ILMIC:
                /* Get all packets in ILMI Circuit */
                if (!cstate->is_atm)
                        bpf_error(cstate, "'ilmic' supported only on raw ATM");
                b0 = gen_atmfield_code_internal(cstate, A_VPI, 0, BPF_JEQ, 0);
                b1 = gen_atmfield_code_internal(cstate, A_VCI, 16, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_LANE:
                /* Get all LANE packets */
                if (!cstate->is_atm)
                        bpf_error(cstate, "'lane' supported only on raw ATM");
                b1 = gen_atmfield_code_internal(cstate, A_PROTOTYPE, PT_LANE, BPF_JEQ, 0);

                /*
                 * Arrange that all subsequent tests assume LANE
                 * rather than LLC-encapsulated packets, and set
                 * the offsets appropriately for LANE-encapsulated
                 * Ethernet.
                 *
                 * We assume LANE means Ethernet, not Token Ring.
                 */
                PUSH_LINKHDR(cstate, DLT_EN10MB, 0,
                    cstate->off_payload + 2,    /* Ethernet header */
                    -1);
                cstate->off_linktype.constant_part = cstate->off_linkhdr.constant_part + 12;
                cstate->off_linkpl.constant_part = cstate->off_linkhdr.constant_part + 14;      /* Ethernet */
                cstate->off_nl = 0;                     /* Ethernet II */
                cstate->off_nl_nosnap = 3;              /* 802.3+802.2 */
                break;

        default:
                abort();
        }
        return b1;
}

/*
 * Filtering for MTP2 messages based on li value
 * FISU, length is null
 * LSSU, length is 1 or 2
 * MSU, length is 3 or more
 * For MTP2_HSL, sequences are on 2 bytes, and length on 9 bits
 */
struct block *
gen_mtp2type_abbrev(compiler_state_t *cstate, int type)
{
        struct block *b0, *b1;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        switch (type) {

        case M_FISU:
                if ( (cstate->linktype != DLT_MTP2) &&
                     (cstate->linktype != DLT_ERF) &&
                     (cstate->linktype != DLT_MTP2_WITH_PHDR) )
                        bpf_error(cstate, "'fisu' supported only on MTP2");
                /* gen_ncmp(cstate, offrel, offset, size, mask, jtype, reverse, value) */
                b0 = gen_ncmp(cstate, OR_PACKET, cstate->off_li, BPF_B,
                    0x3fU, BPF_JEQ, 0, 0U);
                break;

        case M_LSSU:
                if ( (cstate->linktype != DLT_MTP2) &&
                     (cstate->linktype != DLT_ERF) &&
                     (cstate->linktype != DLT_MTP2_WITH_PHDR) )
                        bpf_error(cstate, "'lssu' supported only on MTP2");
                b0 = gen_ncmp(cstate, OR_PACKET, cstate->off_li, BPF_B,
                    0x3fU, BPF_JGT, 1, 2U);
                b1 = gen_ncmp(cstate, OR_PACKET, cstate->off_li, BPF_B,
                    0x3fU, BPF_JGT, 0, 0U);
                gen_and(b1, b0);
                break;

        case M_MSU:
                if ( (cstate->linktype != DLT_MTP2) &&
                     (cstate->linktype != DLT_ERF) &&
                     (cstate->linktype != DLT_MTP2_WITH_PHDR) )
                        bpf_error(cstate, "'msu' supported only on MTP2");
                b0 = gen_ncmp(cstate, OR_PACKET, cstate->off_li, BPF_B,
                    0x3fU, BPF_JGT, 0, 2U);
                break;

        case MH_FISU:
                if ( (cstate->linktype != DLT_MTP2) &&
                     (cstate->linktype != DLT_ERF) &&
                     (cstate->linktype != DLT_MTP2_WITH_PHDR) )
                        bpf_error(cstate, "'hfisu' supported only on MTP2_HSL");
                /* gen_ncmp(cstate, offrel, offset, size, mask, jtype, reverse, value) */
                b0 = gen_ncmp(cstate, OR_PACKET, cstate->off_li_hsl, BPF_H,
                    0xff80U, BPF_JEQ, 0, 0U);
                break;

        case MH_LSSU:
                if ( (cstate->linktype != DLT_MTP2) &&
                     (cstate->linktype != DLT_ERF) &&
                     (cstate->linktype != DLT_MTP2_WITH_PHDR) )
                        bpf_error(cstate, "'hlssu' supported only on MTP2_HSL");
                b0 = gen_ncmp(cstate, OR_PACKET, cstate->off_li_hsl, BPF_H,
                    0xff80U, BPF_JGT, 1, 0x0100U);
                b1 = gen_ncmp(cstate, OR_PACKET, cstate->off_li_hsl, BPF_H,
                    0xff80U, BPF_JGT, 0, 0U);
                gen_and(b1, b0);
                break;

        case MH_MSU:
                if ( (cstate->linktype != DLT_MTP2) &&
                     (cstate->linktype != DLT_ERF) &&
                     (cstate->linktype != DLT_MTP2_WITH_PHDR) )
                        bpf_error(cstate, "'hmsu' supported only on MTP2_HSL");
                b0 = gen_ncmp(cstate, OR_PACKET, cstate->off_li_hsl, BPF_H,
                    0xff80U, BPF_JGT, 0, 0x0100U);
                break;

        default:
                abort();
        }
        return b0;
}

/*
 * These maximum valid values are all-ones, so they double as the bitmasks
 * before any bitwise shifting.
 */
#define MTP2_SIO_MAXVAL UINT8_MAX
#define MTP3_PC_MAXVAL 0x3fffU
#define MTP3_SLS_MAXVAL 0xfU

static struct block *
gen_mtp3field_code_internal(compiler_state_t *cstate, int mtp3field,
    bpf_u_int32 jvalue, int jtype, int reverse)
{
        struct block *b0;
        u_int newoff_sio;
        u_int newoff_opc;
        u_int newoff_dpc;
        u_int newoff_sls;

        newoff_sio = cstate->off_sio;
        newoff_opc = cstate->off_opc;
        newoff_dpc = cstate->off_dpc;
        newoff_sls = cstate->off_sls;
        switch (mtp3field) {

        /*
         * See UTU-T Rec. Q.703, Section 2.2, Figure 3/Q.703.
         *
         * SIO is the simplest field: the size is one byte and the offset is a
         * multiple of bytes, so the only detail to get right is the value of
         * the [right-to-left] field offset.
         */
        case MH_SIO:
                newoff_sio += 3; /* offset for MTP2_HSL */
                /* FALLTHROUGH */

        case M_SIO:
                if (cstate->off_sio == OFFSET_NOT_SET)
                        bpf_error(cstate, "'sio' supported only on SS7");
                if(jvalue > MTP2_SIO_MAXVAL)
                        bpf_error(cstate, "sio value %u too big; max value = %u",
                            jvalue, MTP2_SIO_MAXVAL);
                // Here the bitmask means "do not apply a bitmask".
                b0 = gen_ncmp(cstate, OR_PACKET, newoff_sio, BPF_B, UINT32_MAX,
                    jtype, reverse, jvalue);
                break;

        /*
         * See UTU-T Rec. Q.704, Section 2.2, Figure 3/Q.704.
         *
         * SLS, OPC and DPC are more complicated: none of these is sized in a
         * multiple of 8 bits, MTP3 encoding is little-endian and MTP packet
         * diagrams are meant to be read right-to-left.  This means in the
         * diagrams within individual fields and concatenations thereof
         * bitwise shifts and masks can be noted in the common left-to-right
         * manner until each final value is ready to be byte-swapped and
         * handed to gen_ncmp().  See also gen_dnhostop(), which solves a
         * similar problem in a similar way.
         *
         * Offsets of fields within the packet header always have the
         * right-to-left meaning.  Note that in DLT_MTP2 and possibly other
         * DLTs the offset does not include the F (Flag) field at the
         * beginning of each message.
         *
         * For example, if the 8-bit SIO field has a 3 byte [RTL] offset, the
         * 32-bit standard routing header has a 4 byte [RTL] offset and could
         * be tested entirely using a single BPF_W comparison.  In this case
         * the 14-bit DPC field [LTR] bitmask would be 0x3FFF, the 14-bit OPC
         * field [LTR] bitmask would be (0x3FFF << 14) and the 4-bit SLS field
         * [LTR] bitmask would be (0xF << 28), all of which conveniently
         * correlates with the [RTL] packet diagram until the byte-swapping is
         * done before use.
         *
         * The code below uses this approach for OPC, which spans 3 bytes.
         * DPC and SLS use shorter loads, SLS also uses a different offset.
         */
        case MH_OPC:
                newoff_opc += 3;

                /* FALLTHROUGH */
        case M_OPC:
                if (cstate->off_opc == OFFSET_NOT_SET)
                        bpf_error(cstate, "'opc' supported only on SS7");
                if (jvalue > MTP3_PC_MAXVAL)
                        bpf_error(cstate, "opc value %u too big; max value = %u",
                            jvalue, MTP3_PC_MAXVAL);
                b0 = gen_ncmp(cstate, OR_PACKET, newoff_opc, BPF_W,
                    SWAPLONG(MTP3_PC_MAXVAL << 14), jtype, reverse,
                    SWAPLONG(jvalue << 14));
                break;

        case MH_DPC:
                newoff_dpc += 3;
                /* FALLTHROUGH */

        case M_DPC:
                if (cstate->off_dpc == OFFSET_NOT_SET)
                        bpf_error(cstate, "'dpc' supported only on SS7");
                if (jvalue > MTP3_PC_MAXVAL)
                        bpf_error(cstate, "dpc value %u too big; max value = %u",
                            jvalue, MTP3_PC_MAXVAL);
                b0 = gen_ncmp(cstate, OR_PACKET, newoff_dpc, BPF_H,
                    SWAPSHORT(MTP3_PC_MAXVAL), jtype, reverse,
                    SWAPSHORT(jvalue));
                break;

        case MH_SLS:
                newoff_sls += 3;
                /* FALLTHROUGH */

        case M_SLS:
                if (cstate->off_sls == OFFSET_NOT_SET)
                        bpf_error(cstate, "'sls' supported only on SS7");
                if (jvalue > MTP3_SLS_MAXVAL)
                         bpf_error(cstate, "sls value %u too big; max value = %u",
                             jvalue, MTP3_SLS_MAXVAL);
                b0 = gen_ncmp(cstate, OR_PACKET, newoff_sls, BPF_B,
                    MTP3_SLS_MAXVAL << 4, jtype, reverse,
                    jvalue << 4);
                break;

        default:
                abort();
        }
        return b0;
}

struct block *
gen_mtp3field_code(compiler_state_t *cstate, int mtp3field,
    bpf_u_int32 jvalue, int jtype, int reverse)
{
        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        return gen_mtp3field_code_internal(cstate, mtp3field, jvalue, jtype,
            reverse);
}

static struct block *
gen_msg_abbrev(compiler_state_t *cstate, 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_internal(cstate, A_MSGTYPE, SETUP, BPF_JEQ, 0);
                break;

        case A_CALLPROCEED:
                b1 = gen_atmfield_code_internal(cstate, A_MSGTYPE, CALL_PROCEED, BPF_JEQ, 0);
                break;

        case A_CONNECT:
                b1 = gen_atmfield_code_internal(cstate, A_MSGTYPE, CONNECT, BPF_JEQ, 0);
                break;

        case A_CONNECTACK:
                b1 = gen_atmfield_code_internal(cstate, A_MSGTYPE, CONNECT_ACK, BPF_JEQ, 0);
                break;

        case A_RELEASE:
                b1 = gen_atmfield_code_internal(cstate, A_MSGTYPE, RELEASE, BPF_JEQ, 0);
                break;

        case A_RELEASE_DONE:
                b1 = gen_atmfield_code_internal(cstate, A_MSGTYPE, RELEASE_DONE, BPF_JEQ, 0);
                break;

        default:
                abort();
        }
        return b1;
}

struct block *
gen_atmmulti_abbrev(compiler_state_t *cstate, int type)
{
        struct block *b0, *b1;

        /*
         * Catch errors reported by us and routines below us, and return NULL
         * on an error.
         */
        if (setjmp(cstate->top_ctx))
                return (NULL);

        switch (type) {

        case A_OAM:
                if (!cstate->is_atm)
                        bpf_error(cstate, "'oam' supported only on raw ATM");
                /* OAM F4 type */
                b0 = gen_atmfield_code_internal(cstate, A_VCI, 3, BPF_JEQ, 0);
                b1 = gen_atmfield_code_internal(cstate, A_VCI, 4, BPF_JEQ, 0);
                gen_or(b0, b1);
                b0 = gen_atmfield_code_internal(cstate, A_VPI, 0, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_OAMF4:
                if (!cstate->is_atm)
                        bpf_error(cstate, "'oamf4' supported only on raw ATM");
                /* OAM F4 type */
                b0 = gen_atmfield_code_internal(cstate, A_VCI, 3, BPF_JEQ, 0);
                b1 = gen_atmfield_code_internal(cstate, A_VCI, 4, BPF_JEQ, 0);
                gen_or(b0, b1);
                b0 = gen_atmfield_code_internal(cstate, A_VPI, 0, BPF_JEQ, 0);
                gen_and(b0, b1);
                break;

        case A_CONNECTMSG:
                /*
                 * Get Q.2931 signalling messages for switched
                 * virtual connection
                 */
                if (!cstate->is_atm)
                        bpf_error(cstate, "'connectmsg' supported only on raw ATM");
                b0 = gen_msg_abbrev(cstate, A_SETUP);
                b1 = gen_msg_abbrev(cstate, A_CALLPROCEED);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(cstate, A_CONNECT);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(cstate, A_CONNECTACK);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(cstate, A_RELEASE);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(cstate, A_RELEASE_DONE);
                gen_or(b0, b1);
                b0 = gen_atmtype_sc(cstate);
                gen_and(b0, b1);
                break;

        case A_METACONNECT:
                if (!cstate->is_atm)
                        bpf_error(cstate, "'metaconnect' supported only on raw ATM");
                b0 = gen_msg_abbrev(cstate, A_SETUP);
                b1 = gen_msg_abbrev(cstate, A_CALLPROCEED);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(cstate, A_CONNECT);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(cstate, A_RELEASE);
                gen_or(b0, b1);
                b0 = gen_msg_abbrev(cstate, A_RELEASE_DONE);
                gen_or(b0, b1);
                b0 = gen_atmtype_metac(cstate);
                gen_and(b0, b1);
                break;

        default:
                abort();
        }
        return b1;
}