NetBSD/usr.sbin/pppd/gencode.c

/*	From NetBSD: gencode.c,v 1.2 1995/03/06 11:38:21 mycroft Exp */

/*
 * Copyright (c) 1990, 1991, 1992, 1993, 1994
 *	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 char rcsid[] =
    "@(#) Header: gencode.c,v 1.55 94/06/20 19:07:53 leres Exp (LBL)";
#endif

#include <stdio.h>
#include <memory.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>

#include <net/ppp_defs.h>
#include <netinet/in.h>

#include "bpf_compile.h"
#include "gencode.h"

#include <setjmp.h>
#ifdef __STDC__
#include <stdarg.h>
#include <stdlib.h>
#else
#include <varargs.h>
#endif

#ifndef __GNUC__
#define inline
#endif

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

static jmp_buf top_ctx;
static char errbuf[PCAP_ERRBUF_SIZE];

/* VARARGS */
volatile void
#ifdef __STDC__
bpf_error(char *fmt, ...)
#else
bpf_error(fmt, va_alist)
	char *fmt;
	va_dcl
#endif
{
	va_list ap;

#ifdef __STDC__
	va_start(ap, fmt);
#else
	va_start(ap);
#endif
	vsprintf(errbuf, fmt, ap);
	va_end(ap);
	longjmp(top_ctx, 1);
	/* NOTREACHED */
}

char *
bpf_geterr()
{
	return errbuf;
}

static void init_linktype();

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

static struct block *root;

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

static struct chunk chunks[NCHUNKS];
static int cur_chunk = -1;

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

static void backpatch(struct block *, struct block *);
static void merge(struct block *, struct block *);
static struct block *gen_cmp(u_int, u_int, long);
static struct block *gen_mcmp(u_int, u_int, long, u_long);
#if 0
static struct block *gen_bcmp(u_int, u_int, u_char *);
#endif
static struct block *gen_uncond(int);
static inline struct block *gen_true(void);
static inline struct block *gen_false(void);
static struct block *gen_linktype(int);
static struct block *gen_hostop(u_long, u_long, int, int, u_int, u_int);
static struct block *gen_host(u_long, u_long, int, int);
static struct block *gen_ipfrag(void);
static struct block *gen_portatom(int, long);
struct block *gen_portop(int, int, int);
static struct block *gen_port(int, int, int);
static int lookup_proto(char *, int);
static struct block *gen_proto(int, int, int);
static u_long net_mask(u_long *);
static u_long net_mask(u_long *);
static struct slist *xfer_to_x(struct arth *);
static struct slist *xfer_to_a(struct arth *);
static struct block *gen_len(int, int);

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

	/* XXX Round up to nearest long. */
	n = (n + sizeof(long) - 1) & ~(sizeof(long) - 1);

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

static void
freechunks()
{
	int i;

	for (i = 0; i < NCHUNKS; ++i)
		if (chunks[i].m)
			free(chunks[i].m);
	cur_chunk = -1;
}

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

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

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

	return p;
}

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

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

	return p;
}

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

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

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

static int snaplen;

int
bpf_compile(program, buf, optimize)
    struct bpf_program *program;
    char *buf;
    int optimize;
{
	extern int n_errors;
	int len;

	if (setjmp(top_ctx))
		return (-1);

	snaplen = PPP_HDRLEN;

	lex_init(buf ? buf : "");
	init_linktype();
	pcap_parse();

	if (n_errors)
		syntax();

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

	if (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;

	freechunks();
	return (0);
}

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

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

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

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

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

void
finish_parse(p)
	struct block *p;
{
	backpatch(p, gen_retblk(snaplen));
	p->sense = !p->sense;
	backpatch(p, gen_retblk(0));
	root = p->head;
}

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

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

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

static struct block *
gen_cmp(offset, size, v)
	unsigned int offset, size;
	long v;
{
	struct slist *s;
	struct block *b;

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

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

	return b;
}

static struct block *
gen_mcmp(offset, size, v, mask)
	unsigned int offset, size;
	long v;
	unsigned long mask;
{
	struct block *b = gen_cmp(offset, size, v);
	struct slist *s;

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

#if 0
static struct block *
gen_bcmp(offset, size, v)
	unsigned int offset, size;
	unsigned char *v;
{
	struct block *b, *tmp;

	b = NULL;
	while (size >= 4) {
		unsigned char *p = &v[size - 4];
		long w = (p[0] << 24) | (p[1] << 16) | (p[2] << 8) | p[3];
		tmp = gen_cmp(offset + size - 4, BPF_W, w);
		if (b != NULL)
			gen_and(b, tmp);
		b = tmp;
		size -= 4;
	}
	while (size >= 2) {
		unsigned char *p = &v[size - 2];
		long w = (p[0] << 8) | p[1];
		tmp = gen_cmp(offset + size - 2, BPF_H, w);
		if (b != NULL)
			gen_and(b, tmp);
		b = tmp;
		size -= 2;
	}
	if (size > 0) {
		tmp = gen_cmp(offset, BPF_B, (long)v[0]);
		if (b != NULL)
			gen_and(b, tmp);
		b = tmp;
	}
	return b;
}
#endif

/*
 * Various code constructs need to know the layout of the data link
 * layer.  These variables give the necessary offsets.  off_linktype
 * is set to -1 for no encapsulation, in which case, IP is assumed.
 */
static unsigned int off_linktype;
static unsigned int off_nl;

static void
init_linktype()
{
	off_linktype = 2;
	off_nl = 4;
}

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);
}

static struct block *
gen_linktype(proto)
	int proto;
{
	return gen_cmp(off_linktype, BPF_H, (long)proto);
}

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

	switch (dir) {

	case Q_SRC:
		offset = src_off;
		break;

	case Q_DST:
		offset = dst_off;
		break;

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

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

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

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

	switch (proto) {

	case Q_DEFAULT:
		b0 = gen_host(addr, mask, Q_IP, dir);
		return b0;

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

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

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

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

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

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

	switch (proto) {

	case Q_TCP:
		b0 = gen_linktype(PPP_IP);
		b1 = gen_cmp(off_nl + 9, BPF_B, (long)IPPROTO_TCP);
		gen_and(b0, b1);
		break;

	case Q_UDP:
		b0 =  gen_linktype(PPP_IP);
		b1 = gen_cmp(off_nl + 9, BPF_B, (long)IPPROTO_UDP);
		gen_and(b0, b1);
		break;

	case Q_ICMP:
		b0 =  gen_linktype(PPP_IP);
		b1 = gen_cmp(off_nl + 9, BPF_B, (long)IPPROTO_ICMP);
		gen_and(b0, b1);
		break;

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

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

	default:
		abort();
	}
	return b1;
}

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

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

	return b;
}

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

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

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

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

	return b;
}

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

	/* ip proto 'proto' */
	tmp = gen_cmp(off_nl + 9, BPF_B, (long)proto);
	b0 = gen_ipfrag();
	gen_and(tmp, b0);

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

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

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

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

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

	return b1;
}

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

	/* PPP proto ip */
	b0 =  gen_linktype(PPP_IP);

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

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

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

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

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

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

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

static struct block *
gen_proto(v, proto, dir)
	int v;
	int proto;
	int dir;
{
	struct block *b0, *b1;

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

	switch (proto) {
	case Q_DEFAULT:
	case Q_IP:
		b0 = gen_linktype(PPP_IP);
		b1 = gen_cmp(off_nl + 9, BPF_B, (long)v);
		gen_and(b0, b1);
		return b1;

	case Q_LINK:
		return gen_linktype(v);

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

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

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

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

/*
 * Left justify 'addr' and return its resulting network mask.
 */
static unsigned long
net_mask(addr)
	unsigned long *addr;
{
	register unsigned long m = 0xffffffff;

	if (*addr)
		while ((*addr & 0xff000000) == 0)
			*addr <<= 8, m <<= 8;

	return m;
}

struct block *
gen_scode(name, q)
	char *name;
	struct qual q;
{
	int proto = q.proto;
	int dir = q.dir;
	unsigned long mask, addr, **alist;
	struct block *b, *tmp;
	int port, real_proto;

	switch (q.addr) {

	case Q_NET:
		addr = pcap_nametonetaddr(name);
		if (addr == 0)
			bpf_error("unknown network '%s'", name);
		mask = net_mask(&addr);
		return gen_host(addr, mask, proto, dir);

	case Q_DEFAULT:
	case Q_HOST:
		if (proto == Q_LINK) {
			bpf_error("link-level host name not supported");
			break;
		} else {
			alist = pcap_nametoaddr(name);
			if (alist == NULL || *alist == NULL)
				bpf_error("unknown host '%s'", name);
			b = gen_host(**alist++, 0xffffffffL, proto, dir);
			while (*alist) {
				tmp = gen_host(**alist++, 0xffffffffL,
					       proto, dir);
				gen_or(b, tmp);
				b = tmp;
			}
			return b;
		}

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

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

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

struct block *
gen_ncode(v, q)
	unsigned long v;
	struct qual q;
{
	unsigned long mask;
	int proto = q.proto;
	int dir = q.dir;

	switch (q.addr) {

	case Q_DEFAULT:
	case Q_HOST:
	case Q_NET:
		if (proto == Q_LINK) {
			bpf_error("illegal link layer address");
		} else {
			mask = net_mask(&v);
			return gen_host(v, mask, proto, dir);
		}

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

		return gen_port((int)v, proto, dir);

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

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

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

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

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

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

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

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

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

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

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

	case 1:
		size = BPF_B;
		break;

	case 2:
		size = BPF_H;
		break;

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

	case Q_LINK:
		s = xfer_to_x(index);
		tmp = new_stmt(BPF_LD|BPF_IND|size);
		sappend(s, tmp);
		sappend(index->s, s);
		break;

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

		b = gen_proto_abbrev(proto);
		if (index->b)
			gen_and(index->b, b);
		index->b = b;
		break;

	case Q_TCP:
	case Q_UDP:
	case Q_ICMP:
		s = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
		s->s.k = off_nl;
		sappend(s, xfer_to_a(index));
		sappend(s, new_stmt(BPF_ALU|BPF_ADD|BPF_X));
		sappend(s, new_stmt(BPF_MISC|BPF_TAX));
		sappend(s, tmp = new_stmt(BPF_LD|BPF_IND|size));
		tmp->s.k = off_nl;
		sappend(index->s, s);

		gen_and(gen_proto_abbrev(proto), b = gen_ipfrag());
		if (index->b)
			gen_and(index->b, b);
		index->b = b;
		break;
	}
	index->regno = regno;
	s = new_stmt(BPF_ST);
	s->s.k = regno;
	sappend(index->s, s);

	return index;
}

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

	s0 = xfer_to_x(a1);
	s1 = xfer_to_a(a0);
	s2 = new_stmt(BPF_ALU|BPF_SUB|BPF_X);
	b = new_block(JMP(code));
	if (reversed)
		gen_not(b);

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

	b->stmts = a0->s;

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

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

	if (tmp)
		gen_and(tmp, b);

	return b;
}

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

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

	return a;
}

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

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

	reg = alloc_reg();

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

	return a;
}

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

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

	return a;
}

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

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

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

	free_reg(a1->regno);

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

	return a0;
}

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

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

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

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

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

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

	return b;
}

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

struct block *
gen_less(n)
	int n;
{
	struct block *b;

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

	return b;
}

struct block *
gen_byteop(op, idx, val)
	int op, idx, val;
{
	struct block *b;
	struct slist *s;

	switch (op) {
	default:
		abort();

	case '=':
		return gen_cmp((unsigned int)idx, BPF_B, (long)val);

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

	case '>':
		b = gen_cmp((unsigned int)idx, BPF_B, (long)val);
		b->s.code = JMP(BPF_JGT);
		return b;

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

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

	return b;
}

struct block *
gen_broadcast(proto)
	int proto;
{
	bpf_error("broadcast not supported");
}

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

	switch (proto) {
	case Q_DEFAULT:
	case Q_IP:
		b0 = gen_linktype(PPP_IP);
		b1 = gen_cmp(off_nl + 16, BPF_B, (long)224);
		b1->s.code = JMP(BPF_JGE);
		gen_and(b0, b1);
		return b1;
	}
	bpf_error("only IP multicast filters supported");
}

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

	b0 = gen_relation(BPF_JEQ,
			  gen_load(Q_LINK, gen_loadi(0), 1),
			  gen_loadi(0),
			  dir);
	return (b0);
}