Logo Search packages:      
Sourcecode: nmap version File versions

optimize.c

/*
 * Copyright (c) 1988, 1989, 1990, 1991, 1993, 1994, 1995, 1996
 *    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.
 *
 *  Optimization module for tcpdump intermediate representation.
 */
#ifndef lint
static const char rcsid[] _U_ =
    "@(#) $Header: /CVS/nmap/libpcap-possiblymodified/optimize.c,v 1.4 2004/08/01 05:34:47 fyodor Exp $ (LBL)";
#endif

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

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>

#include <errno.h>

#include "pcap-int.h"

#include "gencode.h"

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

#ifdef BDEBUG
extern int dflag;
#endif

#define A_ATOM BPF_MEMWORDS
#define X_ATOM (BPF_MEMWORDS+1)

#define NOP -1

/*
 * This define is used to represent *both* the accumulator and
 * x register in use-def computations.
 * Currently, the use-def code assumes only one definition per instruction.
 */
#define AX_ATOM N_ATOMS

/*
 * A flag to indicate that further optimization is needed.
 * Iterative passes are continued until a given pass yields no
 * branch movement.
 */
static int done;

/*
 * A block is marked if only if its mark equals the current mark.
 * Rather than traverse the code array, marking each item, 'cur_mark' is
 * incremented.  This automatically makes each element unmarked.
 */
static int cur_mark;
#define isMarked(p) ((p)->mark == cur_mark)
#define unMarkAll() cur_mark += 1
#define Mark(p) ((p)->mark = cur_mark)

static void opt_init(struct block *);
static void opt_cleanup(void);

static void make_marks(struct block *);
static void mark_code(struct block *);

static void intern_blocks(struct block *);

static int eq_slist(struct slist *, struct slist *);

static void find_levels_r(struct block *);

static void find_levels(struct block *);
static void find_dom(struct block *);
static void propedom(struct edge *);
static void find_edom(struct block *);
static void find_closure(struct block *);
static int atomuse(struct stmt *);
static int atomdef(struct stmt *);
static void compute_local_ud(struct block *);
static void find_ud(struct block *);
static void init_val(void);
static int F(int, int, int);
static inline void vstore(struct stmt *, int *, int, int);
static void opt_blk(struct block *, int);
static int use_conflict(struct block *, struct block *);
static void opt_j(struct edge *);
static void or_pullup(struct block *);
static void and_pullup(struct block *);
static void opt_blks(struct block *, int);
static inline void link_inedge(struct edge *, struct block *);
static void find_inedges(struct block *);
static void opt_root(struct block **);
static void opt_loop(struct block *, int);
static void fold_op(struct stmt *, int, int);
static inline struct slist *this_op(struct slist *);
static void opt_not(struct block *);
static void opt_peep(struct block *);
static void opt_stmt(struct stmt *, int[], int);
static void deadstmt(struct stmt *, struct stmt *[]);
static void opt_deadstores(struct block *);
static struct block *fold_edge(struct block *, struct edge *);
static inline int eq_blk(struct block *, struct block *);
static int slength(struct slist *);
static int count_blocks(struct block *);
static void number_blks_r(struct block *);
static int count_stmts(struct block *);
static int convert_code_r(struct block *);
#ifdef BDEBUG
static void opt_dump(struct block *);
#endif

static int n_blocks;
struct block **blocks;
static int n_edges;
struct edge **edges;

/*
 * A bit vector set representation of the dominators.
 * We round up the set size to the next power of two.
 */
static int nodewords;
static int edgewords;
struct block **levels;
bpf_u_int32 *space;
#define BITS_PER_WORD (8*sizeof(bpf_u_int32))
/*
 * True if a is in uset {p}
 */
#define SET_MEMBER(p, a) \
((p)[(unsigned)(a) / BITS_PER_WORD] & (1 << ((unsigned)(a) % BITS_PER_WORD)))

/*
 * Add 'a' to uset p.
 */
#define SET_INSERT(p, a) \
(p)[(unsigned)(a) / BITS_PER_WORD] |= (1 << ((unsigned)(a) % BITS_PER_WORD))

/*
 * Delete 'a' from uset p.
 */
#define SET_DELETE(p, a) \
(p)[(unsigned)(a) / BITS_PER_WORD] &= ~(1 << ((unsigned)(a) % BITS_PER_WORD))

/*
 * a := a intersect b
 */
#define SET_INTERSECT(a, b, n)\
{\
      register bpf_u_int32 *_x = a, *_y = b;\
      register int _n = n;\
      while (--_n >= 0) *_x++ &= *_y++;\
}

/*
 * a := a - b
 */
#define SET_SUBTRACT(a, b, n)\
{\
      register bpf_u_int32 *_x = a, *_y = b;\
      register int _n = n;\
      while (--_n >= 0) *_x++ &=~ *_y++;\
}

/*
 * a := a union b
 */
#define SET_UNION(a, b, n)\
{\
      register bpf_u_int32 *_x = a, *_y = b;\
      register int _n = n;\
      while (--_n >= 0) *_x++ |= *_y++;\
}

static uset all_dom_sets;
static uset all_closure_sets;
static uset all_edge_sets;

#ifndef MAX
#define MAX(a,b) ((a)>(b)?(a):(b))
#endif

static void
find_levels_r(b)
      struct block *b;
{
      int level;

      if (isMarked(b))
            return;

      Mark(b);
      b->link = 0;

      if (JT(b)) {
            find_levels_r(JT(b));
            find_levels_r(JF(b));
            level = MAX(JT(b)->level, JF(b)->level) + 1;
      } else
            level = 0;
      b->level = level;
      b->link = levels[level];
      levels[level] = b;
}

/*
 * Level graph.  The levels go from 0 at the leaves to
 * N_LEVELS at the root.  The levels[] array points to the
 * first node of the level list, whose elements are linked
 * with the 'link' field of the struct block.
 */
static void
find_levels(root)
      struct block *root;
{
      memset((char *)levels, 0, n_blocks * sizeof(*levels));
      unMarkAll();
      find_levels_r(root);
}

/*
 * Find dominator relationships.
 * Assumes graph has been leveled.
 */
static void
find_dom(root)
      struct block *root;
{
      int i;
      struct block *b;
      bpf_u_int32 *x;

      /*
       * Initialize sets to contain all nodes.
       */
      x = all_dom_sets;
      i = n_blocks * nodewords;
      while (--i >= 0)
            *x++ = ~0;
      /* Root starts off empty. */
      for (i = nodewords; --i >= 0;)
            root->dom[i] = 0;

      /* root->level is the highest level no found. */
      for (i = root->level; i >= 0; --i) {
            for (b = levels[i]; b; b = b->link) {
                  SET_INSERT(b->dom, b->id);
                  if (JT(b) == 0)
                        continue;
                  SET_INTERSECT(JT(b)->dom, b->dom, nodewords);
                  SET_INTERSECT(JF(b)->dom, b->dom, nodewords);
            }
      }
}

static void
propedom(ep)
      struct edge *ep;
{
      SET_INSERT(ep->edom, ep->id);
      if (ep->succ) {
            SET_INTERSECT(ep->succ->et.edom, ep->edom, edgewords);
            SET_INTERSECT(ep->succ->ef.edom, ep->edom, edgewords);
      }
}

/*
 * Compute edge dominators.
 * Assumes graph has been leveled and predecessors established.
 */
static void
find_edom(root)
      struct block *root;
{
      int i;
      uset x;
      struct block *b;

      x = all_edge_sets;
      for (i = n_edges * edgewords; --i >= 0; )
            x[i] = ~0;

      /* root->level is the highest level no found. */
      memset(root->et.edom, 0, edgewords * sizeof(*(uset)0));
      memset(root->ef.edom, 0, edgewords * sizeof(*(uset)0));
      for (i = root->level; i >= 0; --i) {
            for (b = levels[i]; b != 0; b = b->link) {
                  propedom(&b->et);
                  propedom(&b->ef);
            }
      }
}

/*
 * Find the backwards transitive closure of the flow graph.  These sets
 * are backwards in the sense that we find the set of nodes that reach
 * a given node, not the set of nodes that can be reached by a node.
 *
 * Assumes graph has been leveled.
 */
static void
find_closure(root)
      struct block *root;
{
      int i;
      struct block *b;

      /*
       * Initialize sets to contain no nodes.
       */
      memset((char *)all_closure_sets, 0,
            n_blocks * nodewords * sizeof(*all_closure_sets));

      /* root->level is the highest level no found. */
      for (i = root->level; i >= 0; --i) {
            for (b = levels[i]; b; b = b->link) {
                  SET_INSERT(b->closure, b->id);
                  if (JT(b) == 0)
                        continue;
                  SET_UNION(JT(b)->closure, b->closure, nodewords);
                  SET_UNION(JF(b)->closure, b->closure, nodewords);
            }
      }
}

/*
 * Return the register number that is used by s.  If A and X are both
 * used, return AX_ATOM.  If no register is used, return -1.
 *
 * The implementation should probably change to an array access.
 */
static int
atomuse(s)
      struct stmt *s;
{
      register int c = s->code;

      if (c == NOP)
            return -1;

      switch (BPF_CLASS(c)) {

      case BPF_RET:
            return (BPF_RVAL(c) == BPF_A) ? A_ATOM :
                  (BPF_RVAL(c) == BPF_X) ? X_ATOM : -1;

      case BPF_LD:
      case BPF_LDX:
            return (BPF_MODE(c) == BPF_IND) ? X_ATOM :
                  (BPF_MODE(c) == BPF_MEM) ? s->k : -1;

      case BPF_ST:
            return A_ATOM;

      case BPF_STX:
            return X_ATOM;

      case BPF_JMP:
      case BPF_ALU:
            if (BPF_SRC(c) == BPF_X)
                  return AX_ATOM;
            return A_ATOM;

      case BPF_MISC:
            return BPF_MISCOP(c) == BPF_TXA ? X_ATOM : A_ATOM;
      }
      abort();
      /* NOTREACHED */
}

/*
 * Return the register number that is defined by 's'.  We assume that
 * a single stmt cannot define more than one register.  If no register
 * is defined, return -1.
 *
 * The implementation should probably change to an array access.
 */
static int
atomdef(s)
      struct stmt *s;
{
      if (s->code == NOP)
            return -1;

      switch (BPF_CLASS(s->code)) {

      case BPF_LD:
      case BPF_ALU:
            return A_ATOM;

      case BPF_LDX:
            return X_ATOM;

      case BPF_ST:
      case BPF_STX:
            return s->k;

      case BPF_MISC:
            return BPF_MISCOP(s->code) == BPF_TAX ? X_ATOM : A_ATOM;
      }
      return -1;
}

static void
compute_local_ud(b)
      struct block *b;
{
      struct slist *s;
      atomset def = 0, use = 0, kill = 0;
      int atom;

      for (s = b->stmts; s; s = s->next) {
            if (s->s.code == NOP)
                  continue;
            atom = atomuse(&s->s);
            if (atom >= 0) {
                  if (atom == AX_ATOM) {
                        if (!ATOMELEM(def, X_ATOM))
                              use |= ATOMMASK(X_ATOM);
                        if (!ATOMELEM(def, A_ATOM))
                              use |= ATOMMASK(A_ATOM);
                  }
                  else if (atom < N_ATOMS) {
                        if (!ATOMELEM(def, atom))
                              use |= ATOMMASK(atom);
                  }
                  else
                        abort();
            }
            atom = atomdef(&s->s);
            if (atom >= 0) {
                  if (!ATOMELEM(use, atom))
                        kill |= ATOMMASK(atom);
                  def |= ATOMMASK(atom);
            }
      }
      if (!ATOMELEM(def, A_ATOM) && BPF_CLASS(b->s.code) == BPF_JMP)
            use |= ATOMMASK(A_ATOM);

      b->def = def;
      b->kill = kill;
      b->in_use = use;
}

/*
 * Assume graph is already leveled.
 */
static void
find_ud(root)
      struct block *root;
{
      int i, maxlevel;
      struct block *p;

      /*
       * root->level is the highest level no found;
       * count down from there.
       */
      maxlevel = root->level;
      for (i = maxlevel; i >= 0; --i)
            for (p = levels[i]; p; p = p->link) {
                  compute_local_ud(p);
                  p->out_use = 0;
            }

      for (i = 1; i <= maxlevel; ++i) {
            for (p = levels[i]; p; p = p->link) {
                  p->out_use |= JT(p)->in_use | JF(p)->in_use;
                  p->in_use |= p->out_use &~ p->kill;
            }
      }
}

/*
 * These data structures are used in a Cocke and Shwarz style
 * value numbering scheme.  Since the flowgraph is acyclic,
 * exit values can be propagated from a node's predecessors
 * provided it is uniquely defined.
 */
struct valnode {
      int code;
      int v0, v1;
      int val;
      struct valnode *next;
};

#define MODULUS 213
static struct valnode *hashtbl[MODULUS];
static int curval;
static int maxval;

/* Integer constants mapped with the load immediate opcode. */
#define K(i) F(BPF_LD|BPF_IMM|BPF_W, i, 0L)

struct vmapinfo {
      int is_const;
      bpf_int32 const_val;
};

struct vmapinfo *vmap;
struct valnode *vnode_base;
struct valnode *next_vnode;

static void
init_val()
{
      curval = 0;
      next_vnode = vnode_base;
      memset((char *)vmap, 0, maxval * sizeof(*vmap));
      memset((char *)hashtbl, 0, sizeof hashtbl);
}

/* Because we really don't have an IR, this stuff is a little messy. */
static int
F(code, v0, v1)
      int code;
      int v0, v1;
{
      u_int hash;
      int val;
      struct valnode *p;

      hash = (u_int)code ^ (v0 << 4) ^ (v1 << 8);
      hash %= MODULUS;

      for (p = hashtbl[hash]; p; p = p->next)
            if (p->code == code && p->v0 == v0 && p->v1 == v1)
                  return p->val;

      val = ++curval;
      if (BPF_MODE(code) == BPF_IMM &&
          (BPF_CLASS(code) == BPF_LD || BPF_CLASS(code) == BPF_LDX)) {
            vmap[val].const_val = v0;
            vmap[val].is_const = 1;
      }
      p = next_vnode++;
      p->val = val;
      p->code = code;
      p->v0 = v0;
      p->v1 = v1;
      p->next = hashtbl[hash];
      hashtbl[hash] = p;

      return val;
}

static inline void
vstore(s, valp, newval, alter)
      struct stmt *s;
      int *valp;
      int newval;
      int alter;
{
      if (alter && *valp == newval)
            s->code = NOP;
      else
            *valp = newval;
}

static void
fold_op(s, v0, v1)
      struct stmt *s;
      int v0, v1;
{
      bpf_int32 a, b;

      a = vmap[v0].const_val;
      b = vmap[v1].const_val;

      switch (BPF_OP(s->code)) {
      case BPF_ADD:
            a += b;
            break;

      case BPF_SUB:
            a -= b;
            break;

      case BPF_MUL:
            a *= b;
            break;

      case BPF_DIV:
            if (b == 0)
                  bpf_error("division by zero");
            a /= b;
            break;

      case BPF_AND:
            a &= b;
            break;

      case BPF_OR:
            a |= b;
            break;

      case BPF_LSH:
            a <<= b;
            break;

      case BPF_RSH:
            a >>= b;
            break;

      case BPF_NEG:
            a = -a;
            break;

      default:
            abort();
      }
      s->k = a;
      s->code = BPF_LD|BPF_IMM;
      done = 0;
}

static inline struct slist *
this_op(s)
      struct slist *s;
{
      while (s != 0 && s->s.code == NOP)
            s = s->next;
      return s;
}

static void
opt_not(b)
      struct block *b;
{
      struct block *tmp = JT(b);

      JT(b) = JF(b);
      JF(b) = tmp;
}

static void
opt_peep(b)
      struct block *b;
{
      struct slist *s;
      struct slist *next, *last;
      int val;

      s = b->stmts;
      if (s == 0)
            return;

      last = s;
      while (1) {
            s = this_op(s);
            if (s == 0)
                  break;
            next = this_op(s->next);
            if (next == 0)
                  break;
            last = next;

            /*
             * st  M[k] -->   st  M[k]
             * ldx M[k]       tax
             */
            if (s->s.code == BPF_ST &&
                next->s.code == (BPF_LDX|BPF_MEM) &&
                s->s.k == next->s.k) {
                  done = 0;
                  next->s.code = BPF_MISC|BPF_TAX;
            }
            /*
             * ld  #k   -->   ldx  #k
             * tax                  txa
             */
            if (s->s.code == (BPF_LD|BPF_IMM) &&
                next->s.code == (BPF_MISC|BPF_TAX)) {
                  s->s.code = BPF_LDX|BPF_IMM;
                  next->s.code = BPF_MISC|BPF_TXA;
                  done = 0;
            }
            /*
             * This is an ugly special case, but it happens
             * when you say tcp[k] or udp[k] where k is a constant.
             */
            if (s->s.code == (BPF_LD|BPF_IMM)) {
                  struct slist *add, *tax, *ild;

                  /*
                   * Check that X isn't used on exit from this
                   * block (which the optimizer might cause).
                   * We know the code generator won't generate
                   * any local dependencies.
                   */
                  if (ATOMELEM(b->out_use, X_ATOM))
                        break;

                  if (next->s.code != (BPF_LDX|BPF_MSH|BPF_B))
                        add = next;
                  else
                        add = this_op(next->next);
                  if (add == 0 || add->s.code != (BPF_ALU|BPF_ADD|BPF_X))
                        break;

                  tax = this_op(add->next);
                  if (tax == 0 || tax->s.code != (BPF_MISC|BPF_TAX))
                        break;

                  ild = this_op(tax->next);
                  if (ild == 0 || BPF_CLASS(ild->s.code) != BPF_LD ||
                      BPF_MODE(ild->s.code) != BPF_IND)
                        break;
                  /*
                   * XXX We need to check that X is not
                   * subsequently used.  We know we can eliminate the
                   * accumulator modifications since it is defined
                   * by the last stmt of this sequence.
                   *
                   * We want to turn this sequence:
                   *
                   * (004) ldi     #0x2         {s}
                   * (005) ldxms   [14]         {next}  -- optional
                   * (006) addx                 {add}
                   * (007) tax                  {tax}
                   * (008) ild     [x+0]        {ild}
                   *
                   * into this sequence:
                   *
                   * (004) nop
                   * (005) ldxms   [14]
                   * (006) nop
                   * (007) nop
                   * (008) ild     [x+2]
                   *
                   */
                  ild->s.k += s->s.k;
                  s->s.code = NOP;
                  add->s.code = NOP;
                  tax->s.code = NOP;
                  done = 0;
            }
            s = next;
      }
      /*
       * If we have a subtract to do a comparison, and the X register
       * is a known constant, we can merge this value into the
       * comparison.
       */
      if (BPF_OP(b->s.code) == BPF_JEQ) {
            if (last->s.code == (BPF_ALU|BPF_SUB|BPF_X) &&
                !ATOMELEM(b->out_use, A_ATOM)) {
                  val = b->val[X_ATOM];
                  if (vmap[val].is_const) {
                        /*
                         * sub x  ->      nop
                         * jeq #y   jeq #(x+y)
                         */
                        b->s.k += vmap[val].const_val;
                        last->s.code = NOP;
                        done = 0;
                  } else if (b->s.k == 0) {
                        /*
                         * sub #x  ->     nop
                         * jeq #0   jeq #x
                         */
                        last->s.code = NOP;
                        b->s.code = BPF_CLASS(b->s.code) |
                              BPF_OP(b->s.code) | BPF_X;
                        done = 0;
                  }
            }
            /*
             * Likewise, a constant subtract can be simplified.
             */
            else if (last->s.code == (BPF_ALU|BPF_SUB|BPF_K) &&
                   !ATOMELEM(b->out_use, A_ATOM)) {

                  last->s.code = NOP;
                  b->s.k += last->s.k;
                  done = 0;
            }
      }
      /*
       * and #k   nop
       * jeq #0  ->     jset #k
       */
      if (last->s.code == (BPF_ALU|BPF_AND|BPF_K) &&
          !ATOMELEM(b->out_use, A_ATOM) && b->s.k == 0) {
            b->s.k = last->s.k;
            b->s.code = BPF_JMP|BPF_K|BPF_JSET;
            last->s.code = NOP;
            done = 0;
            opt_not(b);
      }
      /*
       * jset #0        ->   never
       * jset #ffffffff ->   always
       */
      if (b->s.code == (BPF_JMP|BPF_K|BPF_JSET)) {
            if (b->s.k == 0)
                  JT(b) = JF(b);
            if (b->s.k == 0xffffffff)
                  JF(b) = JT(b);
      }
      /*
       * If the accumulator is a known constant, we can compute the
       * comparison result.
       */
      val = b->val[A_ATOM];
      if (vmap[val].is_const && BPF_SRC(b->s.code) == BPF_K) {
            bpf_int32 v = vmap[val].const_val;
            switch (BPF_OP(b->s.code)) {

            case BPF_JEQ:
                  v = v == b->s.k;
                  break;

            case BPF_JGT:
                  v = (unsigned)v > b->s.k;
                  break;

            case BPF_JGE:
                  v = (unsigned)v >= b->s.k;
                  break;

            case BPF_JSET:
                  v &= b->s.k;
                  break;

            default:
                  abort();
            }
            if (JF(b) != JT(b))
                  done = 0;
            if (v)
                  JF(b) = JT(b);
            else
                  JT(b) = JF(b);
      }
}

/*
 * Compute the symbolic value of expression of 's', and update
 * anything it defines in the value table 'val'.  If 'alter' is true,
 * do various optimizations.  This code would be cleaner if symbolic
 * evaluation and code transformations weren't folded together.
 */
static void
opt_stmt(s, val, alter)
      struct stmt *s;
      int val[];
      int alter;
{
      int op;
      int v;

      switch (s->code) {

      case BPF_LD|BPF_ABS|BPF_W:
      case BPF_LD|BPF_ABS|BPF_H:
      case BPF_LD|BPF_ABS|BPF_B:
            v = F(s->code, s->k, 0L);
            vstore(s, &val[A_ATOM], v, alter);
            break;

      case BPF_LD|BPF_IND|BPF_W:
      case BPF_LD|BPF_IND|BPF_H:
      case BPF_LD|BPF_IND|BPF_B:
            v = val[X_ATOM];
            if (alter && vmap[v].is_const) {
                  s->code = BPF_LD|BPF_ABS|BPF_SIZE(s->code);
                  s->k += vmap[v].const_val;
                  v = F(s->code, s->k, 0L);
                  done = 0;
            }
            else
                  v = F(s->code, s->k, v);
            vstore(s, &val[A_ATOM], v, alter);
            break;

      case BPF_LD|BPF_LEN:
            v = F(s->code, 0L, 0L);
            vstore(s, &val[A_ATOM], v, alter);
            break;

      case BPF_LD|BPF_IMM:
            v = K(s->k);
            vstore(s, &val[A_ATOM], v, alter);
            break;

      case BPF_LDX|BPF_IMM:
            v = K(s->k);
            vstore(s, &val[X_ATOM], v, alter);
            break;

      case BPF_LDX|BPF_MSH|BPF_B:
            v = F(s->code, s->k, 0L);
            vstore(s, &val[X_ATOM], v, alter);
            break;

      case BPF_ALU|BPF_NEG:
            if (alter && vmap[val[A_ATOM]].is_const) {
                  s->code = BPF_LD|BPF_IMM;
                  s->k = -vmap[val[A_ATOM]].const_val;
                  val[A_ATOM] = K(s->k);
            }
            else
                  val[A_ATOM] = F(s->code, val[A_ATOM], 0L);
            break;

      case BPF_ALU|BPF_ADD|BPF_K:
      case BPF_ALU|BPF_SUB|BPF_K:
      case BPF_ALU|BPF_MUL|BPF_K:
      case BPF_ALU|BPF_DIV|BPF_K:
      case BPF_ALU|BPF_AND|BPF_K:
      case BPF_ALU|BPF_OR|BPF_K:
      case BPF_ALU|BPF_LSH|BPF_K:
      case BPF_ALU|BPF_RSH|BPF_K:
            op = BPF_OP(s->code);
            if (alter) {
                  if (s->k == 0) {
                        /* don't optimize away "sub #0"
                         * as it may be needed later to
                         * fixup the generated math code */
                        if (op == BPF_ADD ||
                            op == BPF_LSH || op == BPF_RSH ||
                            op == BPF_OR) {
                              s->code = NOP;
                              break;
                        }
                        if (op == BPF_MUL || op == BPF_AND) {
                              s->code = BPF_LD|BPF_IMM;
                              val[A_ATOM] = K(s->k);
                              break;
                        }
                  }
                  if (vmap[val[A_ATOM]].is_const) {
                        fold_op(s, val[A_ATOM], K(s->k));
                        val[A_ATOM] = K(s->k);
                        break;
                  }
            }
            val[A_ATOM] = F(s->code, val[A_ATOM], K(s->k));
            break;

      case BPF_ALU|BPF_ADD|BPF_X:
      case BPF_ALU|BPF_SUB|BPF_X:
      case BPF_ALU|BPF_MUL|BPF_X:
      case BPF_ALU|BPF_DIV|BPF_X:
      case BPF_ALU|BPF_AND|BPF_X:
      case BPF_ALU|BPF_OR|BPF_X:
      case BPF_ALU|BPF_LSH|BPF_X:
      case BPF_ALU|BPF_RSH|BPF_X:
            op = BPF_OP(s->code);
            if (alter && vmap[val[X_ATOM]].is_const) {
                  if (vmap[val[A_ATOM]].is_const) {
                        fold_op(s, val[A_ATOM], val[X_ATOM]);
                        val[A_ATOM] = K(s->k);
                  }
                  else {
                        s->code = BPF_ALU|BPF_K|op;
                        s->k = vmap[val[X_ATOM]].const_val;
                        done = 0;
                        val[A_ATOM] =
                              F(s->code, val[A_ATOM], K(s->k));
                  }
                  break;
            }
            /*
             * Check if we're doing something to an accumulator
             * that is 0, and simplify.  This may not seem like
             * much of a simplification but it could open up further
             * optimizations.
             * XXX We could also check for mul by 1, etc.
             */
            if (alter && vmap[val[A_ATOM]].is_const
                && vmap[val[A_ATOM]].const_val == 0) {
                  if (op == BPF_ADD || op == BPF_OR) {
                        s->code = BPF_MISC|BPF_TXA;
                        vstore(s, &val[A_ATOM], val[X_ATOM], alter);
                        break;
                  }
                  else if (op == BPF_MUL || op == BPF_DIV ||
                         op == BPF_AND || op == BPF_LSH || op == BPF_RSH) {
                        s->code = BPF_LD|BPF_IMM;
                        s->k = 0;
                        vstore(s, &val[A_ATOM], K(s->k), alter);
                        break;
                  }
                  else if (op == BPF_NEG) {
                        s->code = NOP;
                        break;
                  }
            }
            val[A_ATOM] = F(s->code, val[A_ATOM], val[X_ATOM]);
            break;

      case BPF_MISC|BPF_TXA:
            vstore(s, &val[A_ATOM], val[X_ATOM], alter);
            break;

      case BPF_LD|BPF_MEM:
            v = val[s->k];
            if (alter && vmap[v].is_const) {
                  s->code = BPF_LD|BPF_IMM;
                  s->k = vmap[v].const_val;
                  done = 0;
            }
            vstore(s, &val[A_ATOM], v, alter);
            break;

      case BPF_MISC|BPF_TAX:
            vstore(s, &val[X_ATOM], val[A_ATOM], alter);
            break;

      case BPF_LDX|BPF_MEM:
            v = val[s->k];
            if (alter && vmap[v].is_const) {
                  s->code = BPF_LDX|BPF_IMM;
                  s->k = vmap[v].const_val;
                  done = 0;
            }
            vstore(s, &val[X_ATOM], v, alter);
            break;

      case BPF_ST:
            vstore(s, &val[s->k], val[A_ATOM], alter);
            break;

      case BPF_STX:
            vstore(s, &val[s->k], val[X_ATOM], alter);
            break;
      }
}

static void
deadstmt(s, last)
      register struct stmt *s;
      register struct stmt *last[];
{
      register int atom;

      atom = atomuse(s);
      if (atom >= 0) {
            if (atom == AX_ATOM) {
                  last[X_ATOM] = 0;
                  last[A_ATOM] = 0;
            }
            else
                  last[atom] = 0;
      }
      atom = atomdef(s);
      if (atom >= 0) {
            if (last[atom]) {
                  done = 0;
                  last[atom]->code = NOP;
            }
            last[atom] = s;
      }
}

static void
opt_deadstores(b)
      register struct block *b;
{
      register struct slist *s;
      register int atom;
      struct stmt *last[N_ATOMS];

      memset((char *)last, 0, sizeof last);

      for (s = b->stmts; s != 0; s = s->next)
            deadstmt(&s->s, last);
      deadstmt(&b->s, last);

      for (atom = 0; atom < N_ATOMS; ++atom)
            if (last[atom] && !ATOMELEM(b->out_use, atom)) {
                  last[atom]->code = NOP;
                  done = 0;
            }
}

static void
opt_blk(b, do_stmts)
      struct block *b;
      int do_stmts;
{
      struct slist *s;
      struct edge *p;
      int i;
      bpf_int32 aval;

#if 0
      for (s = b->stmts; s && s->next; s = s->next)
            if (BPF_CLASS(s->s.code) == BPF_JMP) {
                  do_stmts = 0;
                  break;
            }
#endif

      /*
       * Initialize the atom values.
       * If we have no predecessors, everything is undefined.
       * Otherwise, we inherent our values from our predecessors.
       * If any register has an ambiguous value (i.e. control paths are
       * merging) give it the undefined value of 0.
       */
      p = b->in_edges;
      if (p == 0)
            memset((char *)b->val, 0, sizeof(b->val));
      else {
            memcpy((char *)b->val, (char *)p->pred->val, sizeof(b->val));
            while ((p = p->next) != NULL) {
                  for (i = 0; i < N_ATOMS; ++i)
                        if (b->val[i] != p->pred->val[i])
                              b->val[i] = 0;
            }
      }
      aval = b->val[A_ATOM];
      for (s = b->stmts; s; s = s->next)
            opt_stmt(&s->s, b->val, do_stmts);

      /*
       * This is a special case: if we don't use anything from this
       * block, and we load the accumulator with value that is
       * already there, or if this block is a return,
       * eliminate all the statements.
       */
      if (do_stmts &&
          ((b->out_use == 0 && aval != 0 &&b->val[A_ATOM] == aval) ||
           BPF_CLASS(b->s.code) == BPF_RET)) {
            if (b->stmts != 0) {
                  b->stmts = 0;
                  done = 0;
            }
      } else {
            opt_peep(b);
            opt_deadstores(b);
      }
      /*
       * Set up values for branch optimizer.
       */
      if (BPF_SRC(b->s.code) == BPF_K)
            b->oval = K(b->s.k);
      else
            b->oval = b->val[X_ATOM];
      b->et.code = b->s.code;
      b->ef.code = -b->s.code;
}

/*
 * Return true if any register that is used on exit from 'succ', has
 * an exit value that is different from the corresponding exit value
 * from 'b'.
 */
static int
use_conflict(b, succ)
      struct block *b, *succ;
{
      int atom;
      atomset use = succ->out_use;

      if (use == 0)
            return 0;

      for (atom = 0; atom < N_ATOMS; ++atom)
            if (ATOMELEM(use, atom))
                  if (b->val[atom] != succ->val[atom])
                        return 1;
      return 0;
}

static struct block *
fold_edge(child, ep)
      struct block *child;
      struct edge *ep;
{
      int sense;
      int aval0, aval1, oval0, oval1;
      int code = ep->code;

      if (code < 0) {
            code = -code;
            sense = 0;
      } else
            sense = 1;

      if (child->s.code != code)
            return 0;

      aval0 = child->val[A_ATOM];
      oval0 = child->oval;
      aval1 = ep->pred->val[A_ATOM];
      oval1 = ep->pred->oval;

      if (aval0 != aval1)
            return 0;

      if (oval0 == oval1)
            /*
             * The operands are identical, so the
             * result is true if a true branch was
             * taken to get here, otherwise false.
             */
            return sense ? JT(child) : JF(child);

      if (sense && code == (BPF_JMP|BPF_JEQ|BPF_K))
            /*
             * At this point, we only know the comparison if we
             * came down the true branch, and it was an equality
             * comparison with a constant.  We rely on the fact that
             * distinct constants have distinct value numbers.
             */
            return JF(child);

      return 0;
}

static void
opt_j(ep)
      struct edge *ep;
{
      register int i, k;
      register struct block *target;

      if (JT(ep->succ) == 0)
            return;

      if (JT(ep->succ) == JF(ep->succ)) {
            /*
             * Common branch targets can be eliminated, provided
             * there is no data dependency.
             */
            if (!use_conflict(ep->pred, ep->succ->et.succ)) {
                  done = 0;
                  ep->succ = JT(ep->succ);
            }
      }
      /*
       * For each edge dominator that matches the successor of this
       * edge, promote the edge successor to the its grandchild.
       *
       * XXX We violate the set abstraction here in favor a reasonably
       * efficient loop.
       */
 top:
      for (i = 0; i < edgewords; ++i) {
            register bpf_u_int32 x = ep->edom[i];

            while (x != 0) {
                  k = ffs(x) - 1;
                  x &=~ (1 << k);
                  k += i * BITS_PER_WORD;

                  target = fold_edge(ep->succ, edges[k]);
                  /*
                   * Check that there is no data dependency between
                   * nodes that will be violated if we move the edge.
                   */
                  if (target != 0 && !use_conflict(ep->pred, target)) {
                        done = 0;
                        ep->succ = target;
                        if (JT(target) != 0)
                              /*
                               * Start over unless we hit a leaf.
                               */
                              goto top;
                        return;
                  }
            }
      }
}


static void
or_pullup(b)
      struct block *b;
{
      int val, at_top;
      struct block *pull;
      struct block **diffp, **samep;
      struct edge *ep;

      ep = b->in_edges;
      if (ep == 0)
            return;

      /*
       * Make sure each predecessor loads the same value.
       * XXX why?
       */
      val = ep->pred->val[A_ATOM];
      for (ep = ep->next; ep != 0; ep = ep->next)
            if (val != ep->pred->val[A_ATOM])
                  return;

      if (JT(b->in_edges->pred) == b)
            diffp = &JT(b->in_edges->pred);
      else
            diffp = &JF(b->in_edges->pred);

      at_top = 1;
      while (1) {
            if (*diffp == 0)
                  return;

            if (JT(*diffp) != JT(b))
                  return;

            if (!SET_MEMBER((*diffp)->dom, b->id))
                  return;

            if ((*diffp)->val[A_ATOM] != val)
                  break;

            diffp = &JF(*diffp);
            at_top = 0;
      }
      samep = &JF(*diffp);
      while (1) {
            if (*samep == 0)
                  return;

            if (JT(*samep) != JT(b))
                  return;

            if (!SET_MEMBER((*samep)->dom, b->id))
                  return;

            if ((*samep)->val[A_ATOM] == val)
                  break;

            /* XXX Need to check that there are no data dependencies
               between dp0 and dp1.  Currently, the code generator
               will not produce such dependencies. */
            samep = &JF(*samep);
      }
#ifdef notdef
      /* XXX This doesn't cover everything. */
      for (i = 0; i < N_ATOMS; ++i)
            if ((*samep)->val[i] != pred->val[i])
                  return;
#endif
      /* Pull up the node. */
      pull = *samep;
      *samep = JF(pull);
      JF(pull) = *diffp;

      /*
       * At the top of the chain, each predecessor needs to point at the
       * pulled up node.  Inside the chain, there is only one predecessor
       * to worry about.
       */
      if (at_top) {
            for (ep = b->in_edges; ep != 0; ep = ep->next) {
                  if (JT(ep->pred) == b)
                        JT(ep->pred) = pull;
                  else
                        JF(ep->pred) = pull;
            }
      }
      else
            *diffp = pull;

      done = 0;
}

static void
and_pullup(b)
      struct block *b;
{
      int val, at_top;
      struct block *pull;
      struct block **diffp, **samep;
      struct edge *ep;

      ep = b->in_edges;
      if (ep == 0)
            return;

      /*
       * Make sure each predecessor loads the same value.
       */
      val = ep->pred->val[A_ATOM];
      for (ep = ep->next; ep != 0; ep = ep->next)
            if (val != ep->pred->val[A_ATOM])
                  return;

      if (JT(b->in_edges->pred) == b)
            diffp = &JT(b->in_edges->pred);
      else
            diffp = &JF(b->in_edges->pred);

      at_top = 1;
      while (1) {
            if (*diffp == 0)
                  return;

            if (JF(*diffp) != JF(b))
                  return;

            if (!SET_MEMBER((*diffp)->dom, b->id))
                  return;

            if ((*diffp)->val[A_ATOM] != val)
                  break;

            diffp = &JT(*diffp);
            at_top = 0;
      }
      samep = &JT(*diffp);
      while (1) {
            if (*samep == 0)
                  return;

            if (JF(*samep) != JF(b))
                  return;

            if (!SET_MEMBER((*samep)->dom, b->id))
                  return;

            if ((*samep)->val[A_ATOM] == val)
                  break;

            /* XXX Need to check that there are no data dependencies
               between diffp and samep.  Currently, the code generator
               will not produce such dependencies. */
            samep = &JT(*samep);
      }
#ifdef notdef
      /* XXX This doesn't cover everything. */
      for (i = 0; i < N_ATOMS; ++i)
            if ((*samep)->val[i] != pred->val[i])
                  return;
#endif
      /* Pull up the node. */
      pull = *samep;
      *samep = JT(pull);
      JT(pull) = *diffp;

      /*
       * At the top of the chain, each predecessor needs to point at the
       * pulled up node.  Inside the chain, there is only one predecessor
       * to worry about.
       */
      if (at_top) {
            for (ep = b->in_edges; ep != 0; ep = ep->next) {
                  if (JT(ep->pred) == b)
                        JT(ep->pred) = pull;
                  else
                        JF(ep->pred) = pull;
            }
      }
      else
            *diffp = pull;

      done = 0;
}

static void
opt_blks(root, do_stmts)
      struct block *root;
      int do_stmts;
{
      int i, maxlevel;
      struct block *p;

      init_val();
      maxlevel = root->level;

      find_inedges(root);
      for (i = maxlevel; i >= 0; --i)
            for (p = levels[i]; p; p = p->link)
                  opt_blk(p, do_stmts);

      if (do_stmts)
            /*
             * No point trying to move branches; it can't possibly
             * make a difference at this point.
             */
            return;

      for (i = 1; i <= maxlevel; ++i) {
            for (p = levels[i]; p; p = p->link) {
                  opt_j(&p->et);
                  opt_j(&p->ef);
            }
      }

      find_inedges(root);
      for (i = 1; i <= maxlevel; ++i) {
            for (p = levels[i]; p; p = p->link) {
                  or_pullup(p);
                  and_pullup(p);
            }
      }
}

static inline void
link_inedge(parent, child)
      struct edge *parent;
      struct block *child;
{
      parent->next = child->in_edges;
      child->in_edges = parent;
}

static void
find_inedges(root)
      struct block *root;
{
      int i;
      struct block *b;

      for (i = 0; i < n_blocks; ++i)
            blocks[i]->in_edges = 0;

      /*
       * Traverse the graph, adding each edge to the predecessor
       * list of its successors.  Skip the leaves (i.e. level 0).
       */
      for (i = root->level; i > 0; --i) {
            for (b = levels[i]; b != 0; b = b->link) {
                  link_inedge(&b->et, JT(b));
                  link_inedge(&b->ef, JF(b));
            }
      }
}

static void
opt_root(b)
      struct block **b;
{
      struct slist *tmp, *s;

      s = (*b)->stmts;
      (*b)->stmts = 0;
      while (BPF_CLASS((*b)->s.code) == BPF_JMP && JT(*b) == JF(*b))
            *b = JT(*b);

      tmp = (*b)->stmts;
      if (tmp != 0)
            sappend(s, tmp);
      (*b)->stmts = s;

      /*
       * If the root node is a return, then there is no
       * point executing any statements (since the bpf machine
       * has no side effects).
       */
      if (BPF_CLASS((*b)->s.code) == BPF_RET)
            (*b)->stmts = 0;
}

static void
opt_loop(root, do_stmts)
      struct block *root;
      int do_stmts;
{

#ifdef BDEBUG
      if (dflag > 1) {
            printf("opt_loop(root, %d) begin\n", do_stmts);
            opt_dump(root);
      }
#endif
      do {
            done = 1;
            find_levels(root);
            find_dom(root);
            find_closure(root);
            find_ud(root);
            find_edom(root);
            opt_blks(root, do_stmts);
#ifdef BDEBUG
            if (dflag > 1) {
                  printf("opt_loop(root, %d) bottom, done=%d\n", do_stmts, done);
                  opt_dump(root);
            }
#endif
      } while (!done);
}

/*
 * Optimize the filter code in its dag representation.
 */
void
bpf_optimize(rootp)
      struct block **rootp;
{
      struct block *root;

      root = *rootp;

      opt_init(root);
      opt_loop(root, 0);
      opt_loop(root, 1);
      intern_blocks(root);
#ifdef BDEBUG
      if (dflag > 1) {
            printf("after intern_blocks()\n");
            opt_dump(root);
      }
#endif
      opt_root(rootp);
#ifdef BDEBUG
      if (dflag > 1) {
            printf("after opt_root()\n");
            opt_dump(root);
      }
#endif
      opt_cleanup();
}

static void
make_marks(p)
      struct block *p;
{
      if (!isMarked(p)) {
            Mark(p);
            if (BPF_CLASS(p->s.code) != BPF_RET) {
                  make_marks(JT(p));
                  make_marks(JF(p));
            }
      }
}

/*
 * Mark code array such that isMarked(i) is true
 * only for nodes that are alive.
 */
static void
mark_code(p)
      struct block *p;
{
      cur_mark += 1;
      make_marks(p);
}

/*
 * True iff the two stmt lists load the same value from the packet into
 * the accumulator.
 */
static int
eq_slist(x, y)
      struct slist *x, *y;
{
      while (1) {
            while (x && x->s.code == NOP)
                  x = x->next;
            while (y && y->s.code == NOP)
                  y = y->next;
            if (x == 0)
                  return y == 0;
            if (y == 0)
                  return x == 0;
            if (x->s.code != y->s.code || x->s.k != y->s.k)
                  return 0;
            x = x->next;
            y = y->next;
      }
}

static inline int
eq_blk(b0, b1)
      struct block *b0, *b1;
{
      if (b0->s.code == b1->s.code &&
          b0->s.k == b1->s.k &&
          b0->et.succ == b1->et.succ &&
          b0->ef.succ == b1->ef.succ)
            return eq_slist(b0->stmts, b1->stmts);
      return 0;
}

static void
intern_blocks(root)
      struct block *root;
{
      struct block *p;
      int i, j;
      int done;
 top:
      done = 1;
      for (i = 0; i < n_blocks; ++i)
            blocks[i]->link = 0;

      mark_code(root);

      for (i = n_blocks - 1; --i >= 0; ) {
            if (!isMarked(blocks[i]))
                  continue;
            for (j = i + 1; j < n_blocks; ++j) {
                  if (!isMarked(blocks[j]))
                        continue;
                  if (eq_blk(blocks[i], blocks[j])) {
                        blocks[i]->link = blocks[j]->link ?
                              blocks[j]->link : blocks[j];
                        break;
                  }
            }
      }
      for (i = 0; i < n_blocks; ++i) {
            p = blocks[i];
            if (JT(p) == 0)
                  continue;
            if (JT(p)->link) {
                  done = 0;
                  JT(p) = JT(p)->link;
            }
            if (JF(p)->link) {
                  done = 0;
                  JF(p) = JF(p)->link;
            }
      }
      if (!done)
            goto top;
}

static void
opt_cleanup()
{
      free((void *)vnode_base);
      free((void *)vmap);
      free((void *)edges);
      free((void *)space);
      free((void *)levels);
      free((void *)blocks);
}

/*
 * Return the number of stmts in 's'.
 */
static int
slength(s)
      struct slist *s;
{
      int n = 0;

      for (; s; s = s->next)
            if (s->s.code != NOP)
                  ++n;
      return n;
}

/*
 * Return the number of nodes reachable by 'p'.
 * All nodes should be initially unmarked.
 */
static int
count_blocks(p)
      struct block *p;
{
      if (p == 0 || isMarked(p))
            return 0;
      Mark(p);
      return count_blocks(JT(p)) + count_blocks(JF(p)) + 1;
}

/*
 * Do a depth first search on the flow graph, numbering the
 * the basic blocks, and entering them into the 'blocks' array.`
 */
static void
number_blks_r(p)
      struct block *p;
{
      int n;

      if (p == 0 || isMarked(p))
            return;

      Mark(p);
      n = n_blocks++;
      p->id = n;
      blocks[n] = p;

      number_blks_r(JT(p));
      number_blks_r(JF(p));
}

/*
 * Return the number of stmts in the flowgraph reachable by 'p'.
 * The nodes should be unmarked before calling.
 *
 * Note that "stmts" means "instructions", and that this includes
 *
 *    side-effect statements in 'p' (slength(p->stmts));
 *
 *    statements in the true branch from 'p' (count_stmts(JT(p)));
 *
 *    statements in the false branch from 'p' (count_stmts(JF(p)));
 *
 *    the conditional jump itself (1);
 *
 *    an extra long jump if the true branch requires it (p->longjt);
 *
 *    an extra long jump if the false branch requires it (p->longjf).
 */
static int
count_stmts(p)
      struct block *p;
{
      int n;

      if (p == 0 || isMarked(p))
            return 0;
      Mark(p);
      n = count_stmts(JT(p)) + count_stmts(JF(p));
      return slength(p->stmts) + n + 1 + p->longjt + p->longjf;
}

/*
 * Allocate memory.  All allocation is done before optimization
 * is begun.  A linear bound on the size of all data structures is computed
 * from the total number of blocks and/or statements.
 */
static void
opt_init(root)
      struct block *root;
{
      bpf_u_int32 *p;
      int i, n, max_stmts;

      /*
       * First, count the blocks, so we can malloc an array to map
       * block number to block.  Then, put the blocks into the array.
       */
      unMarkAll();
      n = count_blocks(root);
      blocks = (struct block **)malloc(n * sizeof(*blocks));
      if (blocks == NULL)
            bpf_error("malloc");
      unMarkAll();
      n_blocks = 0;
      number_blks_r(root);

      n_edges = 2 * n_blocks;
      edges = (struct edge **)malloc(n_edges * sizeof(*edges));
      if (edges == NULL)
            bpf_error("malloc");

      /*
       * The number of levels is bounded by the number of nodes.
       */
      levels = (struct block **)malloc(n_blocks * sizeof(*levels));
      if (levels == NULL)
            bpf_error("malloc");

      edgewords = n_edges / (8 * sizeof(bpf_u_int32)) + 1;
      nodewords = n_blocks / (8 * sizeof(bpf_u_int32)) + 1;

      /* XXX */
      space = (bpf_u_int32 *)malloc(2 * n_blocks * nodewords * sizeof(*space)
                         + n_edges * edgewords * sizeof(*space));
      if (space == NULL)
            bpf_error("malloc");
      p = space;
      all_dom_sets = p;
      for (i = 0; i < n; ++i) {
            blocks[i]->dom = p;
            p += nodewords;
      }
      all_closure_sets = p;
      for (i = 0; i < n; ++i) {
            blocks[i]->closure = p;
            p += nodewords;
      }
      all_edge_sets = p;
      for (i = 0; i < n; ++i) {
            register struct block *b = blocks[i];

            b->et.edom = p;
            p += edgewords;
            b->ef.edom = p;
            p += edgewords;
            b->et.id = i;
            edges[i] = &b->et;
            b->ef.id = n_blocks + i;
            edges[n_blocks + i] = &b->ef;
            b->et.pred = b;
            b->ef.pred = b;
      }
      max_stmts = 0;
      for (i = 0; i < n; ++i)
            max_stmts += slength(blocks[i]->stmts) + 1;
      /*
       * We allocate at most 3 value numbers per statement,
       * so this is an upper bound on the number of valnodes
       * we'll need.
       */
      maxval = 3 * max_stmts;
      vmap = (struct vmapinfo *)malloc(maxval * sizeof(*vmap));
      vnode_base = (struct valnode *)malloc(maxval * sizeof(*vnode_base));
      if (vmap == NULL || vnode_base == NULL)
            bpf_error("malloc");
}

/*
 * Some pointers used to convert the basic block form of the code,
 * into the array form that BPF requires.  'fstart' will point to
 * the malloc'd array while 'ftail' is used during the recursive traversal.
 */
static struct bpf_insn *fstart;
static struct bpf_insn *ftail;

#ifdef BDEBUG
int bids[1000];
#endif

/*
 * Returns true if successful.  Returns false if a branch has
 * an offset that is too large.  If so, we have marked that
 * branch so that on a subsequent iteration, it will be treated
 * properly.
 */
static int
convert_code_r(p)
      struct block *p;
{
      struct bpf_insn *dst;
      struct slist *src;
      int slen;
      u_int off;
      int extrajmps;          /* number of extra jumps inserted */
      struct slist **offset = NULL;

      if (p == 0 || isMarked(p))
            return (1);
      Mark(p);

      if (convert_code_r(JF(p)) == 0)
            return (0);
      if (convert_code_r(JT(p)) == 0)
            return (0);

      slen = slength(p->stmts);
      dst = ftail -= (slen + 1 + p->longjt + p->longjf);
            /* inflate length by any extra jumps */

      p->offset = dst - fstart;

      /* generate offset[] for convenience  */
      if (slen) {
            offset = (struct slist **)calloc(slen, sizeof(struct slist *));
            if (!offset) {
                  bpf_error("not enough core");
                  /*NOTREACHED*/
            }
      }
      src = p->stmts;
      for (off = 0; off < slen && src; off++) {
#if 0
            printf("off=%d src=%x\n", off, src);
#endif
            offset[off] = src;
            src = src->next;
      }

      off = 0;
      for (src = p->stmts; src; src = src->next) {
            if (src->s.code == NOP)
                  continue;
            dst->code = (u_short)src->s.code;
            dst->k = src->s.k;

            /* fill block-local relative jump */
            if (BPF_CLASS(src->s.code) != BPF_JMP || src->s.code == (BPF_JMP|BPF_JA)) {
#if 0
                  if (src->s.jt || src->s.jf) {
                        bpf_error("illegal jmp destination");
                        /*NOTREACHED*/
                  }
#endif
                  goto filled;
            }
            if (off == slen - 2)    /*???*/
                  goto filled;

          {
            int i;
            int jt, jf;
            char *ljerr = "%s for block-local relative jump: off=%d";

#if 0
            printf("code=%x off=%d %x %x\n", src->s.code,
                  off, src->s.jt, src->s.jf);
#endif

            if (!src->s.jt || !src->s.jf) {
                  bpf_error(ljerr, "no jmp destination", off);
                  /*NOTREACHED*/
            }

            jt = jf = 0;
            for (i = 0; i < slen; i++) {
                  if (offset[i] == src->s.jt) {
                        if (jt) {
                              bpf_error(ljerr, "multiple matches", off);
                              /*NOTREACHED*/
                        }

                        dst->jt = i - off - 1;
                        jt++;
                  }
                  if (offset[i] == src->s.jf) {
                        if (jf) {
                              bpf_error(ljerr, "multiple matches", off);
                              /*NOTREACHED*/
                        }
                        dst->jf = i - off - 1;
                        jf++;
                  }
            }
            if (!jt || !jf) {
                  bpf_error(ljerr, "no destination found", off);
                  /*NOTREACHED*/
            }
          }
filled:
            ++dst;
            ++off;
      }
      if (offset)
            free(offset);

#ifdef BDEBUG
      bids[dst - fstart] = p->id + 1;
#endif
      dst->code = (u_short)p->s.code;
      dst->k = p->s.k;
      if (JT(p)) {
            extrajmps = 0;
            off = JT(p)->offset - (p->offset + slen) - 1;
            if (off >= 256) {
                /* offset too large for branch, must add a jump */
                if (p->longjt == 0) {
                  /* mark this instruction and retry */
                  p->longjt++;
                  return(0);
                }
                /* branch if T to following jump */
                dst->jt = extrajmps;
                extrajmps++;
                dst[extrajmps].code = BPF_JMP|BPF_JA;
                dst[extrajmps].k = off - extrajmps;
            }
            else
                dst->jt = off;
            off = JF(p)->offset - (p->offset + slen) - 1;
            if (off >= 256) {
                /* offset too large for branch, must add a jump */
                if (p->longjf == 0) {
                  /* mark this instruction and retry */
                  p->longjf++;
                  return(0);
                }
                /* branch if F to following jump */
                /* if two jumps are inserted, F goes to second one */
                dst->jf = extrajmps;
                extrajmps++;
                dst[extrajmps].code = BPF_JMP|BPF_JA;
                dst[extrajmps].k = off - extrajmps;
            }
            else
                dst->jf = off;
      }
      return (1);
}


/*
 * Convert flowgraph intermediate representation to the
 * BPF array representation.  Set *lenp to the number of instructions.
 */
struct bpf_insn *
icode_to_fcode(root, lenp)
      struct block *root;
      int *lenp;
{
      int n;
      struct bpf_insn *fp;

      /*
       * Loop doing convert_code_r() until no branches remain
       * with too-large offsets.
       */
      while (1) {
          unMarkAll();
          n = *lenp = count_stmts(root);

          fp = (struct bpf_insn *)malloc(sizeof(*fp) * n);
          if (fp == NULL)
                bpf_error("malloc");
          memset((char *)fp, 0, sizeof(*fp) * n);
          fstart = fp;
          ftail = fp + n;

          unMarkAll();
          if (convert_code_r(root))
            break;
          free(fp);
      }

      return fp;
}

/*
 * Make a copy of a BPF program and put it in the "fcode" member of
 * a "pcap_t".
 *
 * If we fail to allocate memory for the copy, fill in the "errbuf"
 * member of the "pcap_t" with an error message, and return -1;
 * otherwise, return 0.
 */
int
install_bpf_program(pcap_t *p, struct bpf_program *fp)
{
      size_t prog_size;

      /*
       * Free up any already installed program.
       */
      pcap_freecode(&p->fcode);

      prog_size = sizeof(*fp->bf_insns) * fp->bf_len;
      p->fcode.bf_len = fp->bf_len;
      p->fcode.bf_insns = (struct bpf_insn *)malloc(prog_size);
      if (p->fcode.bf_insns == NULL) {
            snprintf(p->errbuf, sizeof(p->errbuf),
                   "malloc: %s", pcap_strerror(errno));
            return (-1);
      }
      memcpy(p->fcode.bf_insns, fp->bf_insns, prog_size);
      return (0);
}

#ifdef BDEBUG
static void
opt_dump(root)
      struct block *root;
{
      struct bpf_program f;

      memset(bids, 0, sizeof bids);
      f.bf_insns = icode_to_fcode(root, &f.bf_len);
      bpf_dump(&f, 1);
      putchar('\n');
      free((char *)f.bf_insns);
}
#endif

Generated by  Doxygen 1.6.0   Back to index