/external/bsd/libpcap/dist/gencode.c

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/*	$NetBSD: gencode.c,v 1.6 2013/12/31 17:08:23 christos Exp $	*/

/*#define CHASE_CHAIN*/
/*
 * Copyright (c) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that: (1) source code distributions
 * retain the above copyright notice and this paragraph in its entirety, (2)
 * distributions including binary code include the above copyright notice and
 * this paragraph in its entirety in the documentation or other materials
 * provided with the distribution, and (3) all advertising materials mentioning
 * features or use of this software display the following acknowledgement:
 * ``This product includes software developed by the University of California,
 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
 * the University nor the names of its contributors may be used to endorse
 * or promote products derived from this software without specific prior
 * written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */
#ifndef lint
static const char rcsid[] _U_ =
    "@(#) Header: /tcpdump/master/libpcap/gencode.c,v 1.309 2008-12-23 20:13:29 guy Exp  (LBL)";
#endif

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

#ifdef WIN32
#include <pcap-stdinc.h>
#else /* WIN32 */
#if HAVE_INTTYPES_H
#include <inttypes.h>
#elif HAVE_STDINT_H
#include <stdint.h>
#endif
#ifdef HAVE_SYS_BITYPES_H
#include <sys/bitypes.h>
#endif
#include <sys/types.h>
#include <sys/socket.h>
#endif /* WIN32 */

/*
 * XXX - why was this included even on UNIX?
 */
#ifdef __MINGW32__
#include "ip6_misc.h"
#endif

#ifndef WIN32

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

#include <netinet/in.h>
#include <arpa/inet.h>

#endif /* WIN32 */

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

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

#include "pcap-int.h"

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

#define ETHERMTU	1500

#ifndef IPPROTO_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

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

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

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

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

/* XXX */
static int	pcap_fddipad;

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

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

static void init_linktype(pcap_t *);

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

static struct block *root;

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

#ifdef INET6
/*
 * 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.
 */
static struct addrinfo *ai;
#endif

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

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

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

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

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

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

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

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

static void
freechunks()
{
	int i;

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

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

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

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

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

	return p;
}

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

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

	return p;
}

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

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

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

static bpf_u_int32 netmask;
static int snaplen;
int no_optimize;
#ifdef WIN32
static int
pcap_compile_unsafe(pcap_t *p, struct bpf_program *program,
	     const char *buf, int optimize, bpf_u_int32 mask);

int
pcap_compile(pcap_t *p, struct bpf_program *program,
	     const char *buf, int optimize, bpf_u_int32 mask)
{
	int result;

	EnterCriticalSection(&g_PcapCompileCriticalSection);

	result = pcap_compile_unsafe(p, program, buf, optimize, mask);

	LeaveCriticalSection(&g_PcapCompileCriticalSection);
	
	return result;
}

static int
pcap_compile_unsafe(pcap_t *p, struct bpf_program *program,
	     const char *buf, int optimize, bpf_u_int32 mask)
#else /* WIN32 */
int
pcap_compile(pcap_t *p, struct bpf_program *program,
	     const char *buf, int optimize, bpf_u_int32 mask)
#endif /* WIN32 */
{
	extern int n_errors;
	const char * volatile xbuf = buf;
	u_int len;

	/*
	 * 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) {
		snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
		    "not-yet-activated pcap_t passed to pcap_compile");
		return (-1);
	}
	no_optimize = 0;
	n_errors = 0;
	root = NULL;
	bpf_pcap = p;
	init_regs();
	if (setjmp(top_ctx)) {
#ifdef INET6
		if (ai != NULL) {
			freeaddrinfo(ai);
			ai = NULL;
		}
#endif
		lex_cleanup();
		freechunks();
		return (-1);
	}

	netmask = mask;

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

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

	if (n_errors)
		syntax();

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	s = gen_load_a(offrel, offset, size);

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

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

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

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

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

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

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

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

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

/*
 * "off_linktype" is the offset to information in the link-layer header
 * giving the packet type.  This offset is relative to the beginning
 * of the link-layer header (i.e., it doesn't include off_ll).
 *
 * For Ethernet, it's the offset of the Ethernet type field.
 *
 * For link-layer types that always use 802.2 headers, it's the
 * offset of the LLC header.
 *
 * For PPP, it's the offset of the PPP type field.
 *
 * For Cisco HDLC, it's the offset of the CHDLC type field.
 *
 * For BSD loopback, it's the offset of the AF_ value.
 *
 * For Linux cooked sockets, it's the offset of the type field.
 *
 * It's set to -1 for no encapsulation, in which case, IP is assumed.
 */
static u_int off_linktype;

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

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

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

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

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

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

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

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

static int linktype;

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

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

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

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

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

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

	reg_off_ll = -1;
	reg_off_macpl = -1;

	switch (linktype) {

	case DLT_ARCNET:
		off_linktype = 2;
		off_macpl = 6;
		off_nl = 0;		/* XXX in reality, variable! */
		off_nl_nosnap = 0;	/* no 802.2 LLC */
		return;

	case DLT_ARCNET_LINUX:
		off_linktype = 4;
		off_macpl = 8;
		off_nl = 0;		/* XXX in reality, variable! */
		off_nl_nosnap = 0;	/* no 802.2 LLC */
		return;

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

	case DLT_SLIP:
		/*
		 * SLIP doesn't have a link level type.  The 16 byte
		 * header is hacked into our SLIP driver.
		 */
		off_linktype = -1;
		off_macpl = 16;
		off_nl = 0;
		off_nl_nosnap = 0;	/* no 802.2 LLC */
		return;

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

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

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

	case DLT_PPP:
	case DLT_PPP_PPPD:
	case DLT_C_HDLC:		/* BSD/OS Cisco HDLC */
	case DLT_PPP_SERIAL:		/* NetBSD sync/async serial PPP */
		off_linktype = 2;
		off_macpl = 4;
		off_nl = 0;
		off_nl_nosnap = 0;	/* no 802.2 LLC */
		return;

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

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

	case DLT_FDDI:
		/*
		 * FDDI doesn't really have a link-level type field.
		 * We set "off_linktype" to the offset of the LLC header.
		 *
		 * To check for Ethernet types, we assume that SSAP = SNAP
		 * is being used and pick out the encapsulated Ethernet type.
		 * XXX - should we generate code to check for SNAP?
		 */
		off_linktype = 13;
		off_linktype += pcap_fddipad;
		off_macpl = 13;		/* FDDI MAC header length */
		off_macpl += pcap_fddipad;
		off_nl = 8;		/* 802.2+SNAP */
		off_nl_nosnap = 3;	/* 802.2 */
		return;

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

	case DLT_IEEE802_11:
	case DLT_PRISM_HEADER:
	case DLT_IEEE802_11_RADIO_AVS:
	case DLT_IEEE802_11_RADIO:
		/*
		 * 802.11 doesn't really have a link-level type field.
		 * We set "off_linktype" to the offset of the LLC header.
		 *
		 * To check for Ethernet types, we assume that SSAP = SNAP
		 * is being used and pick out the encapsulated Ethernet type.
		 * XXX - should we generate code to check for SNAP?
		 *
		 * 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.
		 */
		off_linktype = 24;
		off_macpl = 0;		/* link-layer header is variable-length */
		off_macpl_is_variable = 1;
		off_nl = 8;		/* 802.2+SNAP */
		off_nl_nosnap = 3;	/* 802.2 */
		return;

	case DLT_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.
		 */
		off_linktype = 24;
		off_macpl = 0;		/* link-layer header is variable-length */
		off_macpl_is_variable = 1;
		off_nl = 8;		/* 802.2+SNAP */
		off_nl_nosnap = 3;	/* 802.2 */
		return;

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

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

	case DLT_RAW:
	case DLT_IPV4:
	case DLT_IPV6:
		off_linktype = -1;
		off_macpl = 0;
		off_nl = 0;
		off_nl_nosnap = 0;	/* no 802.2 LLC */
		return;

	case DLT_LINUX_SLL:	/* fake header for Linux cooked socket */
		off_linktype = 14;
		off_macpl = 16;
		off_nl = 0;
		off_nl_nosnap = 0;	/* no 802.2 LLC */
		return;

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

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

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

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

	case DLT_APPLE_IP_OVER_IEEE1394:
		off_linktype = 16;
		off_macpl = 18;
		off_nl = 0;
		off_nl_nosnap = 0;	/* no 802.2 LLC */
		return;

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

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

        case DLT_JUNIPER_MFR:
        case DLT_JUNIPER_MLFR:
        case DLT_JUNIPER_MLPPP:
        case DLT_JUNIPER_PPP:
        case DLT_JUNIPER_CHDLC:
        case DLT_JUNIPER_FRELAY:
                off_linktype = 4;
		off_macpl = 4;
		off_nl = 0;
		off_nl_nosnap = -1;	/* no 802.2 LLC */
                return;

	case DLT_JUNIPER_ATM1:
		off_linktype = 4;	/* in reality variable between 4-8 */
		off_macpl = 4;	/* in reality variable between 4-8 */
		off_nl = 0;
		off_nl_nosnap = 10;
		return;

	case DLT_JUNIPER_ATM2:
		off_linktype = 8;	/* in reality variable between 8-12 */
		off_macpl = 8;	/* in reality variable between 8-12 */
		off_nl = 0;
		off_nl_nosnap = 10;
		return;

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

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

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

	case DLT_JUNIPER_ES:
		off_linktype = 6;
		off_macpl = -1;		/* not really a network layer but raw IP addresses */
		off_nl = -1;		/* not really a network layer but raw IP addresses */
		off_nl_nosnap = -1;	/* no 802.2 LLC */
		return;

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

	case DLT_BACNET_MS_TP:
		off_linktype = -1;
		off_macpl = -1;
		off_nl = -1;
		off_nl_nosnap = -1;
		return;

	case DLT_JUNIPER_SERVICES:
		off_linktype = 12;
		off_macpl = -1;		/* L3 proto location dep. on cookie type */
		off_nl = -1;		/* L3 proto location dep. on cookie type */
		off_nl_nosnap = -1;	/* no 802.2 LLC */
		return;

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

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

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

	case DLT_JUNIPER_VS:
	case DLT_JUNIPER_SRX_E2E:
	case DLT_JUNIPER_FIBRECHANNEL:
	case DLT_JUNIPER_ATM_CEMIC:
		off_linktype = 8;
		off_macpl = -1;
		off_nl = -1;
		off_nl_nosnap = -1;
		return;

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

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

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

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

	case DLT_AX25_KISS:
		/*
		 * Currently, only raw "link[N:M]" filtering is supported.
		 */
		off_linktype = -1;	/* variable, min 15, max 71 steps of 7 */
		off_macpl = -1;
		off_nl = -1;		/* variable, min 16, max 71 steps of 7 */
		off_nl_nosnap = -1;	/* no 802.2 LLC */
		off_mac = 1;		/* step over the kiss length byte */
		return;

	case DLT_IPNET:
		off_linktype = 1;
		off_macpl = 24;		/* ipnet header length */
		off_nl = 0;
		off_nl_nosnap = -1;
		return;

	case DLT_NETANALYZER:
		off_mac = 4;		/* MAC header is past 4-byte pseudo-header */
		off_linktype = 16;	/* includes 4-byte pseudo-header */
		off_macpl = 18;		/* pseudo-header+Ethernet header length */
		off_nl = 0;		/* Ethernet II */
		off_nl_nosnap = 3;	/* 802.3+802.2 */
		return;

	case DLT_NETANALYZER_TRANSPARENT:
		off_mac = 12;		/* MAC header is past 4-byte pseudo-header, preamble, and SFD */
		off_linktype = 24;	/* includes 4-byte pseudo-header+preamble+SFD */
		off_macpl = 26;		/* pseudo-header+preamble+SFD+Ethernet header length */
		off_nl = 0;		/* Ethernet II */
		off_nl_nosnap = 3;	/* 802.3+802.2 */
		return;

	default:
		/*
		 * For values in the range in which we've assigned new
		 * DLT_ values, only raw "link[N:M]" filtering is supported.
		 */
		if (linktype >= DLT_MATCHING_MIN &&
		    linktype <= DLT_MATCHING_MAX) {
			off_linktype = -1;
			off_macpl = -1;
			off_nl = -1;
			off_nl_nosnap = -1;
			return;
		}

	}
	bpf_error("unknown data link type %d", linktype);
	/* NOTREACHED */
}

/*
 * Load a value relative to the beginning of the link-layer header.
 * The link-layer header doesn't necessarily begin at the beginning
 * of the packet data; there might be a variable-length prefix containing
 * radio information.
 */
static struct slist *
gen_load_llrel(offset, size)
	u_int offset, size;
{
	struct slist *s, *s2;

	s = gen_llprefixlen();

	/*
	 * If "s" is non-null, it has code to arrange that the X register
	 * contains the length of the prefix preceding the link-layer
	 * header.
	 *
	 * Otherwise, the length of the prefix preceding the link-layer
	 * header is "off_ll".
	 */
	if (s != NULL) {
		/*
		 * There's a variable-length prefix preceding the
		 * link-layer header.  "s" points to a list of statements
		 * that put the length of that prefix into the X register.
		 * do an indirect load, to use the X register as an offset.
		 */
		s2 = new_stmt(BPF_LD|BPF_IND|size);
		s2->s.k = offset;
		sappend(s, s2);
	} else {
		/*
		 * There is no variable-length header preceding the
		 * link-layer header; add in off_ll, which, if there's
		 * a fixed-length header preceding the link-layer header,
		 * is the length of that header.
		 */
		s = new_stmt(BPF_LD|BPF_ABS|size);
		s->s.k = offset + off_ll;
	}
	return s;
}

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

	s = gen_off_macpl();

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

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

	switch (offrel) {

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	return b;
}

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

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

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

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

	switch (proto) {

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

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

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

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

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

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

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

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

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

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

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

		gen_or(b0, b1);
		return b1;

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

/*
 * "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(proto)
	register int proto;
{
	switch (proto) {

	case ETHERTYPE_IP:
		return gen_cmp(OR_LINK, off_linktype, BPF_B,
		    (bpf_int32)IPH_AF_INET);
		/* NOTREACHED */

	case ETHERTYPE_IPV6:
		return gen_cmp(OR_LINK, off_linktype, BPF_B,
		    (bpf_int32)IPH_AF_INET6);
		/* NOTREACHED */

	default:
		break;
	}

	return gen_false();
}

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

	switch (proto) {

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

	case LLCSAP_IPX:
		/*
		 *…