1/* 2 * Copyright (c) 1988, 1989, 1990, 1991, 1993, 1994, 1995, 1996 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that: (1) source code distributions 7 * retain the above copyright notice and this paragraph in its entirety, (2) 8 * distributions including binary code include the above copyright notice and 9 * this paragraph in its entirety in the documentation or other materials 10 * provided with the distribution, and (3) all advertising materials mentioning 11 * features or use of this software display the following acknowledgement: 12 * ``This product includes software developed by the University of California, 13 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of 14 * the University nor the names of its contributors may be used to endorse 15 * or promote products derived from this software without specific prior 16 * written permission. 17 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED 18 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF 19 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. 20 * 21 * Optimization module for tcpdump intermediate representation. 22 */ 23#ifndef lint 24static const char rcsid[] _U_ = 25 "@(#) $Header: /tcpdump/master/libpcap/optimize.c,v 1.85.2.3 2007/09/12 21:29:45 guy Exp $ (LBL)"; 26#endif 27 28#ifdef HAVE_CONFIG_H 29#include "config.h" 30#endif 31 32#include <stdio.h> 33#include <stdlib.h> 34#include <memory.h> 35#include <string.h> 36 37#include <errno.h> 38 39#include "pcap-int.h" 40 41#include "gencode.h" 42 43#ifdef HAVE_OS_PROTO_H 44#include "os-proto.h" 45#endif 46 47#ifdef BDEBUG 48extern int dflag; 49#endif 50 51#if defined(MSDOS) && !defined(__DJGPP__) 52extern int _w32_ffs (int mask); 53#define ffs _w32_ffs 54#endif 55 56/* 57 * Represents a deleted instruction. 58 */ 59#define NOP -1 60 61/* 62 * Register numbers for use-def values. 63 * 0 through BPF_MEMWORDS-1 represent the corresponding scratch memory 64 * location. A_ATOM is the accumulator and X_ATOM is the index 65 * register. 66 */ 67#define A_ATOM BPF_MEMWORDS 68#define X_ATOM (BPF_MEMWORDS+1) 69 70/* 71 * This define is used to represent *both* the accumulator and 72 * x register in use-def computations. 73 * Currently, the use-def code assumes only one definition per instruction. 74 */ 75#define AX_ATOM N_ATOMS 76 77/* 78 * A flag to indicate that further optimization is needed. 79 * Iterative passes are continued until a given pass yields no 80 * branch movement. 81 */ 82static int done; 83 84/* 85 * A block is marked if only if its mark equals the current mark. 86 * Rather than traverse the code array, marking each item, 'cur_mark' is 87 * incremented. This automatically makes each element unmarked. 88 */ 89static int cur_mark; 90#define isMarked(p) ((p)->mark == cur_mark) 91#define unMarkAll() cur_mark += 1 92#define Mark(p) ((p)->mark = cur_mark) 93 94static void opt_init(struct block *); 95static void opt_cleanup(void); 96 97static void make_marks(struct block *); 98static void mark_code(struct block *); 99 100static void intern_blocks(struct block *); 101 102static int eq_slist(struct slist *, struct slist *); 103 104static void find_levels_r(struct block *); 105 106static void find_levels(struct block *); 107static void find_dom(struct block *); 108static void propedom(struct edge *); 109static void find_edom(struct block *); 110static void find_closure(struct block *); 111static int atomuse(struct stmt *); 112static int atomdef(struct stmt *); 113static void compute_local_ud(struct block *); 114static void find_ud(struct block *); 115static void init_val(void); 116static int F(int, int, int); 117static inline void vstore(struct stmt *, int *, int, int); 118static void opt_blk(struct block *, int); 119static int use_conflict(struct block *, struct block *); 120static void opt_j(struct edge *); 121static void or_pullup(struct block *); 122static void and_pullup(struct block *); 123static void opt_blks(struct block *, int); 124static inline void link_inedge(struct edge *, struct block *); 125static void find_inedges(struct block *); 126static void opt_root(struct block **); 127static void opt_loop(struct block *, int); 128static void fold_op(struct stmt *, int, int); 129static inline struct slist *this_op(struct slist *); 130static void opt_not(struct block *); 131static void opt_peep(struct block *); 132static void opt_stmt(struct stmt *, int[], int); 133static void deadstmt(struct stmt *, struct stmt *[]); 134static void opt_deadstores(struct block *); 135static struct block *fold_edge(struct block *, struct edge *); 136static inline int eq_blk(struct block *, struct block *); 137static int slength(struct slist *); 138static int count_blocks(struct block *); 139static void number_blks_r(struct block *); 140static int count_stmts(struct block *); 141static int convert_code_r(struct block *); 142#ifdef BDEBUG 143static void opt_dump(struct block *); 144#endif 145 146static int n_blocks; 147struct block **blocks; 148static int n_edges; 149struct edge **edges; 150 151/* 152 * A bit vector set representation of the dominators. 153 * We round up the set size to the next power of two. 154 */ 155static int nodewords; 156static int edgewords; 157struct block **levels; 158bpf_u_int32 *space; 159#define BITS_PER_WORD (8*sizeof(bpf_u_int32)) 160/* 161 * True if a is in uset {p} 162 */ 163#define SET_MEMBER(p, a) \ 164((p)[(unsigned)(a) / BITS_PER_WORD] & (1 << ((unsigned)(a) % BITS_PER_WORD))) 165 166/* 167 * Add 'a' to uset p. 168 */ 169#define SET_INSERT(p, a) \ 170(p)[(unsigned)(a) / BITS_PER_WORD] |= (1 << ((unsigned)(a) % BITS_PER_WORD)) 171 172/* 173 * Delete 'a' from uset p. 174 */ 175#define SET_DELETE(p, a) \ 176(p)[(unsigned)(a) / BITS_PER_WORD] &= ~(1 << ((unsigned)(a) % BITS_PER_WORD)) 177 178/* 179 * a := a intersect b 180 */ 181#define SET_INTERSECT(a, b, n)\ 182{\ 183 register bpf_u_int32 *_x = a, *_y = b;\ 184 register int _n = n;\ 185 while (--_n >= 0) *_x++ &= *_y++;\ 186} 187 188/* 189 * a := a - b 190 */ 191#define SET_SUBTRACT(a, b, n)\ 192{\ 193 register bpf_u_int32 *_x = a, *_y = b;\ 194 register int _n = n;\ 195 while (--_n >= 0) *_x++ &=~ *_y++;\ 196} 197 198/* 199 * a := a union b 200 */ 201#define SET_UNION(a, b, n)\ 202{\ 203 register bpf_u_int32 *_x = a, *_y = b;\ 204 register int _n = n;\ 205 while (--_n >= 0) *_x++ |= *_y++;\ 206} 207 208static uset all_dom_sets; 209static uset all_closure_sets; 210static uset all_edge_sets; 211 212#ifndef MAX 213#define MAX(a,b) ((a)>(b)?(a):(b)) 214#endif 215 216static void 217find_levels_r(b) 218 struct block *b; 219{ 220 int level; 221 222 if (isMarked(b)) 223 return; 224 225 Mark(b); 226 b->link = 0; 227 228 if (JT(b)) { 229 find_levels_r(JT(b)); 230 find_levels_r(JF(b)); 231 level = MAX(JT(b)->level, JF(b)->level) + 1; 232 } else 233 level = 0; 234 b->level = level; 235 b->link = levels[level]; 236 levels[level] = b; 237} 238 239/* 240 * Level graph. The levels go from 0 at the leaves to 241 * N_LEVELS at the root. The levels[] array points to the 242 * first node of the level list, whose elements are linked 243 * with the 'link' field of the struct block. 244 */ 245static void 246find_levels(root) 247 struct block *root; 248{ 249 memset((char *)levels, 0, n_blocks * sizeof(*levels)); 250 unMarkAll(); 251 find_levels_r(root); 252} 253 254/* 255 * Find dominator relationships. 256 * Assumes graph has been leveled. 257 */ 258static void 259find_dom(root) 260 struct block *root; 261{ 262 int i; 263 struct block *b; 264 bpf_u_int32 *x; 265 266 /* 267 * Initialize sets to contain all nodes. 268 */ 269 x = all_dom_sets; 270 i = n_blocks * nodewords; 271 while (--i >= 0) 272 *x++ = ~0; 273 /* Root starts off empty. */ 274 for (i = nodewords; --i >= 0;) 275 root->dom[i] = 0; 276 277 /* root->level is the highest level no found. */ 278 for (i = root->level; i >= 0; --i) { 279 for (b = levels[i]; b; b = b->link) { 280 SET_INSERT(b->dom, b->id); 281 if (JT(b) == 0) 282 continue; 283 SET_INTERSECT(JT(b)->dom, b->dom, nodewords); 284 SET_INTERSECT(JF(b)->dom, b->dom, nodewords); 285 } 286 } 287} 288 289static void 290propedom(ep) 291 struct edge *ep; 292{ 293 SET_INSERT(ep->edom, ep->id); 294 if (ep->succ) { 295 SET_INTERSECT(ep->succ->et.edom, ep->edom, edgewords); 296 SET_INTERSECT(ep->succ->ef.edom, ep->edom, edgewords); 297 } 298} 299 300/* 301 * Compute edge dominators. 302 * Assumes graph has been leveled and predecessors established. 303 */ 304static void 305find_edom(root) 306 struct block *root; 307{ 308 int i; 309 uset x; 310 struct block *b; 311 312 x = all_edge_sets; 313 for (i = n_edges * edgewords; --i >= 0; ) 314 x[i] = ~0; 315 316 /* root->level is the highest level no found. */ 317 memset(root->et.edom, 0, edgewords * sizeof(*(uset)0)); 318 memset(root->ef.edom, 0, edgewords * sizeof(*(uset)0)); 319 for (i = root->level; i >= 0; --i) { 320 for (b = levels[i]; b != 0; b = b->link) { 321 propedom(&b->et); 322 propedom(&b->ef); 323 } 324 } 325} 326 327/* 328 * Find the backwards transitive closure of the flow graph. These sets 329 * are backwards in the sense that we find the set of nodes that reach 330 * a given node, not the set of nodes that can be reached by a node. 331 * 332 * Assumes graph has been leveled. 333 */ 334static void 335find_closure(root) 336 struct block *root; 337{ 338 int i; 339 struct block *b; 340 341 /* 342 * Initialize sets to contain no nodes. 343 */ 344 memset((char *)all_closure_sets, 0, 345 n_blocks * nodewords * sizeof(*all_closure_sets)); 346 347 /* root->level is the highest level no found. */ 348 for (i = root->level; i >= 0; --i) { 349 for (b = levels[i]; b; b = b->link) { 350 SET_INSERT(b->closure, b->id); 351 if (JT(b) == 0) 352 continue; 353 SET_UNION(JT(b)->closure, b->closure, nodewords); 354 SET_UNION(JF(b)->closure, b->closure, nodewords); 355 } 356 } 357} 358 359/* 360 * Return the register number that is used by s. If A and X are both 361 * used, return AX_ATOM. If no register is used, return -1. 362 * 363 * The implementation should probably change to an array access. 364 */ 365static int 366atomuse(s) 367 struct stmt *s; 368{ 369 register int c = s->code; 370 371 if (c == NOP) 372 return -1; 373 374 switch (BPF_CLASS(c)) { 375 376 case BPF_RET: 377 return (BPF_RVAL(c) == BPF_A) ? A_ATOM : 378 (BPF_RVAL(c) == BPF_X) ? X_ATOM : -1; 379 380 case BPF_LD: 381 case BPF_LDX: 382 return (BPF_MODE(c) == BPF_IND) ? X_ATOM : 383 (BPF_MODE(c) == BPF_MEM) ? s->k : -1; 384 385 case BPF_ST: 386 return A_ATOM; 387 388 case BPF_STX: 389 return X_ATOM; 390 391 case BPF_JMP: 392 case BPF_ALU: 393 if (BPF_SRC(c) == BPF_X) 394 return AX_ATOM; 395 return A_ATOM; 396 397 case BPF_MISC: 398 return BPF_MISCOP(c) == BPF_TXA ? X_ATOM : A_ATOM; 399 } 400 abort(); 401 /* NOTREACHED */ 402} 403 404/* 405 * Return the register number that is defined by 's'. We assume that 406 * a single stmt cannot define more than one register. If no register 407 * is defined, return -1. 408 * 409 * The implementation should probably change to an array access. 410 */ 411static int 412atomdef(s) 413 struct stmt *s; 414{ 415 if (s->code == NOP) 416 return -1; 417 418 switch (BPF_CLASS(s->code)) { 419 420 case BPF_LD: 421 case BPF_ALU: 422 return A_ATOM; 423 424 case BPF_LDX: 425 return X_ATOM; 426 427 case BPF_ST: 428 case BPF_STX: 429 return s->k; 430 431 case BPF_MISC: 432 return BPF_MISCOP(s->code) == BPF_TAX ? X_ATOM : A_ATOM; 433 } 434 return -1; 435} 436 437/* 438 * Compute the sets of registers used, defined, and killed by 'b'. 439 * 440 * "Used" means that a statement in 'b' uses the register before any 441 * statement in 'b' defines it, i.e. it uses the value left in 442 * that register by a predecessor block of this block. 443 * "Defined" means that a statement in 'b' defines it. 444 * "Killed" means that a statement in 'b' defines it before any 445 * statement in 'b' uses it, i.e. it kills the value left in that 446 * register by a predecessor block of this block. 447 */ 448static void 449compute_local_ud(b) 450 struct block *b; 451{ 452 struct slist *s; 453 atomset def = 0, use = 0, kill = 0; 454 int atom; 455 456 for (s = b->stmts; s; s = s->next) { 457 if (s->s.code == NOP) 458 continue; 459 atom = atomuse(&s->s); 460 if (atom >= 0) { 461 if (atom == AX_ATOM) { 462 if (!ATOMELEM(def, X_ATOM)) 463 use |= ATOMMASK(X_ATOM); 464 if (!ATOMELEM(def, A_ATOM)) 465 use |= ATOMMASK(A_ATOM); 466 } 467 else if (atom < N_ATOMS) { 468 if (!ATOMELEM(def, atom)) 469 use |= ATOMMASK(atom); 470 } 471 else 472 abort(); 473 } 474 atom = atomdef(&s->s); 475 if (atom >= 0) { 476 if (!ATOMELEM(use, atom)) 477 kill |= ATOMMASK(atom); 478 def |= ATOMMASK(atom); 479 } 480 } 481 if (BPF_CLASS(b->s.code) == BPF_JMP) { 482 /* 483 * XXX - what about RET? 484 */ 485 atom = atomuse(&b->s); 486 if (atom >= 0) { 487 if (atom == AX_ATOM) { 488 if (!ATOMELEM(def, X_ATOM)) 489 use |= ATOMMASK(X_ATOM); 490 if (!ATOMELEM(def, A_ATOM)) 491 use |= ATOMMASK(A_ATOM); 492 } 493 else if (atom < N_ATOMS) { 494 if (!ATOMELEM(def, atom)) 495 use |= ATOMMASK(atom); 496 } 497 else 498 abort(); 499 } 500 } 501 502 b->def = def; 503 b->kill = kill; 504 b->in_use = use; 505} 506 507/* 508 * Assume graph is already leveled. 509 */ 510static void 511find_ud(root) 512 struct block *root; 513{ 514 int i, maxlevel; 515 struct block *p; 516 517 /* 518 * root->level is the highest level no found; 519 * count down from there. 520 */ 521 maxlevel = root->level; 522 for (i = maxlevel; i >= 0; --i) 523 for (p = levels[i]; p; p = p->link) { 524 compute_local_ud(p); 525 p->out_use = 0; 526 } 527 528 for (i = 1; i <= maxlevel; ++i) { 529 for (p = levels[i]; p; p = p->link) { 530 p->out_use |= JT(p)->in_use | JF(p)->in_use; 531 p->in_use |= p->out_use &~ p->kill; 532 } 533 } 534} 535 536/* 537 * These data structures are used in a Cocke and Shwarz style 538 * value numbering scheme. Since the flowgraph is acyclic, 539 * exit values can be propagated from a node's predecessors 540 * provided it is uniquely defined. 541 */ 542struct valnode { 543 int code; 544 int v0, v1; 545 int val; 546 struct valnode *next; 547}; 548 549#define MODULUS 213 550static struct valnode *hashtbl[MODULUS]; 551static int curval; 552static int maxval; 553 554/* Integer constants mapped with the load immediate opcode. */ 555#define K(i) F(BPF_LD|BPF_IMM|BPF_W, i, 0L) 556 557struct vmapinfo { 558 int is_const; 559 bpf_int32 const_val; 560}; 561 562struct vmapinfo *vmap; 563struct valnode *vnode_base; 564struct valnode *next_vnode; 565 566static void 567init_val() 568{ 569 curval = 0; 570 next_vnode = vnode_base; 571 memset((char *)vmap, 0, maxval * sizeof(*vmap)); 572 memset((char *)hashtbl, 0, sizeof hashtbl); 573} 574 575/* Because we really don't have an IR, this stuff is a little messy. */ 576static int 577F(code, v0, v1) 578 int code; 579 int v0, v1; 580{ 581 u_int hash; 582 int val; 583 struct valnode *p; 584 585 hash = (u_int)code ^ (v0 << 4) ^ (v1 << 8); 586 hash %= MODULUS; 587 588 for (p = hashtbl[hash]; p; p = p->next) 589 if (p->code == code && p->v0 == v0 && p->v1 == v1) 590 return p->val; 591 592 val = ++curval; 593 if (BPF_MODE(code) == BPF_IMM && 594 (BPF_CLASS(code) == BPF_LD || BPF_CLASS(code) == BPF_LDX)) { 595 vmap[val].const_val = v0; 596 vmap[val].is_const = 1; 597 } 598 p = next_vnode++; 599 p->val = val; 600 p->code = code; 601 p->v0 = v0; 602 p->v1 = v1; 603 p->next = hashtbl[hash]; 604 hashtbl[hash] = p; 605 606 return val; 607} 608 609static inline void 610vstore(s, valp, newval, alter) 611 struct stmt *s; 612 int *valp; 613 int newval; 614 int alter; 615{ 616 if (alter && *valp == newval) 617 s->code = NOP; 618 else 619 *valp = newval; 620} 621 622static void 623fold_op(s, v0, v1) 624 struct stmt *s; 625 int v0, v1; 626{ 627 bpf_u_int32 a, b; 628 629 a = vmap[v0].const_val; 630 b = vmap[v1].const_val; 631 632 switch (BPF_OP(s->code)) { 633 case BPF_ADD: 634 a += b; 635 break; 636 637 case BPF_SUB: 638 a -= b; 639 break; 640 641 case BPF_MUL: 642 a *= b; 643 break; 644 645 case BPF_DIV: 646 if (b == 0) 647 bpf_error("division by zero"); 648 a /= b; 649 break; 650 651 case BPF_AND: 652 a &= b; 653 break; 654 655 case BPF_OR: 656 a |= b; 657 break; 658 659 case BPF_LSH: 660 a <<= b; 661 break; 662 663 case BPF_RSH: 664 a >>= b; 665 break; 666 667 case BPF_NEG: 668 a = -a; 669 break; 670 671 default: 672 abort(); 673 } 674 s->k = a; 675 s->code = BPF_LD|BPF_IMM; 676 done = 0; 677} 678 679static inline struct slist * 680this_op(s) 681 struct slist *s; 682{ 683 while (s != 0 && s->s.code == NOP) 684 s = s->next; 685 return s; 686} 687 688static void 689opt_not(b) 690 struct block *b; 691{ 692 struct block *tmp = JT(b); 693 694 JT(b) = JF(b); 695 JF(b) = tmp; 696} 697 698static void 699opt_peep(b) 700 struct block *b; 701{ 702 struct slist *s; 703 struct slist *next, *last; 704 int val; 705 706 s = b->stmts; 707 if (s == 0) 708 return; 709 710 last = s; 711 for (/*empty*/; /*empty*/; s = next) { 712 /* 713 * Skip over nops. 714 */ 715 s = this_op(s); 716 if (s == 0) 717 break; /* nothing left in the block */ 718 719 /* 720 * Find the next real instruction after that one 721 * (skipping nops). 722 */ 723 next = this_op(s->next); 724 if (next == 0) 725 break; /* no next instruction */ 726 last = next; 727 728 /* 729 * st M[k] --> st M[k] 730 * ldx M[k] tax 731 */ 732 if (s->s.code == BPF_ST && 733 next->s.code == (BPF_LDX|BPF_MEM) && 734 s->s.k == next->s.k) { 735 done = 0; 736 next->s.code = BPF_MISC|BPF_TAX; 737 } 738 /* 739 * ld #k --> ldx #k 740 * tax txa 741 */ 742 if (s->s.code == (BPF_LD|BPF_IMM) && 743 next->s.code == (BPF_MISC|BPF_TAX)) { 744 s->s.code = BPF_LDX|BPF_IMM; 745 next->s.code = BPF_MISC|BPF_TXA; 746 done = 0; 747 } 748 /* 749 * This is an ugly special case, but it happens 750 * when you say tcp[k] or udp[k] where k is a constant. 751 */ 752 if (s->s.code == (BPF_LD|BPF_IMM)) { 753 struct slist *add, *tax, *ild; 754 755 /* 756 * Check that X isn't used on exit from this 757 * block (which the optimizer might cause). 758 * We know the code generator won't generate 759 * any local dependencies. 760 */ 761 if (ATOMELEM(b->out_use, X_ATOM)) 762 continue; 763 764 /* 765 * Check that the instruction following the ldi 766 * is an addx, or it's an ldxms with an addx 767 * following it (with 0 or more nops between the 768 * ldxms and addx). 769 */ 770 if (next->s.code != (BPF_LDX|BPF_MSH|BPF_B)) 771 add = next; 772 else 773 add = this_op(next->next); 774 if (add == 0 || add->s.code != (BPF_ALU|BPF_ADD|BPF_X)) 775 continue; 776 777 /* 778 * Check that a tax follows that (with 0 or more 779 * nops between them). 780 */ 781 tax = this_op(add->next); 782 if (tax == 0 || tax->s.code != (BPF_MISC|BPF_TAX)) 783 continue; 784 785 /* 786 * Check that an ild follows that (with 0 or more 787 * nops between them). 788 */ 789 ild = this_op(tax->next); 790 if (ild == 0 || BPF_CLASS(ild->s.code) != BPF_LD || 791 BPF_MODE(ild->s.code) != BPF_IND) 792 continue; 793 /* 794 * We want to turn this sequence: 795 * 796 * (004) ldi #0x2 {s} 797 * (005) ldxms [14] {next} -- optional 798 * (006) addx {add} 799 * (007) tax {tax} 800 * (008) ild [x+0] {ild} 801 * 802 * into this sequence: 803 * 804 * (004) nop 805 * (005) ldxms [14] 806 * (006) nop 807 * (007) nop 808 * (008) ild [x+2] 809 * 810 * XXX We need to check that X is not 811 * subsequently used, because we want to change 812 * what'll be in it after this sequence. 813 * 814 * We know we can eliminate the accumulator 815 * modifications earlier in the sequence since 816 * it is defined by the last stmt of this sequence 817 * (i.e., the last statement of the sequence loads 818 * a value into the accumulator, so we can eliminate 819 * earlier operations on the accumulator). 820 */ 821 ild->s.k += s->s.k; 822 s->s.code = NOP; 823 add->s.code = NOP; 824 tax->s.code = NOP; 825 done = 0; 826 } 827 } 828 /* 829 * If the comparison at the end of a block is an equality 830 * comparison against a constant, and nobody uses the value 831 * we leave in the A register at the end of a block, and 832 * the operation preceding the comparison is an arithmetic 833 * operation, we can sometime optimize it away. 834 */ 835 if (b->s.code == (BPF_JMP|BPF_JEQ|BPF_K) && 836 !ATOMELEM(b->out_use, A_ATOM)) { 837 /* 838 * We can optimize away certain subtractions of the 839 * X register. 840 */ 841 if (last->s.code == (BPF_ALU|BPF_SUB|BPF_X)) { 842 val = b->val[X_ATOM]; 843 if (vmap[val].is_const) { 844 /* 845 * If we have a subtract to do a comparison, 846 * and the X register is a known constant, 847 * we can merge this value into the 848 * comparison: 849 * 850 * sub x -> nop 851 * jeq #y jeq #(x+y) 852 */ 853 b->s.k += vmap[val].const_val; 854 last->s.code = NOP; 855 done = 0; 856 } else if (b->s.k == 0) { 857 /* 858 * If the X register isn't a constant, 859 * and the comparison in the test is 860 * against 0, we can compare with the 861 * X register, instead: 862 * 863 * sub x -> nop 864 * jeq #0 jeq x 865 */ 866 last->s.code = NOP; 867 b->s.code = BPF_JMP|BPF_JEQ|BPF_X; 868 done = 0; 869 } 870 } 871 /* 872 * Likewise, a constant subtract can be simplified: 873 * 874 * sub #x -> nop 875 * jeq #y -> jeq #(x+y) 876 */ 877 else if (last->s.code == (BPF_ALU|BPF_SUB|BPF_K)) { 878 last->s.code = NOP; 879 b->s.k += last->s.k; 880 done = 0; 881 } 882 /* 883 * And, similarly, a constant AND can be simplified 884 * if we're testing against 0, i.e.: 885 * 886 * and #k nop 887 * jeq #0 -> jset #k 888 */ 889 else if (last->s.code == (BPF_ALU|BPF_AND|BPF_K) && 890 b->s.k == 0) { 891 b->s.k = last->s.k; 892 b->s.code = BPF_JMP|BPF_K|BPF_JSET; 893 last->s.code = NOP; 894 done = 0; 895 opt_not(b); 896 } 897 } 898 /* 899 * jset #0 -> never 900 * jset #ffffffff -> always 901 */ 902 if (b->s.code == (BPF_JMP|BPF_K|BPF_JSET)) { 903 if (b->s.k == 0) 904 JT(b) = JF(b); 905 if (b->s.k == 0xffffffff) 906 JF(b) = JT(b); 907 } 908 /* 909 * If the accumulator is a known constant, we can compute the 910 * comparison result. 911 */ 912 val = b->val[A_ATOM]; 913 if (vmap[val].is_const && BPF_SRC(b->s.code) == BPF_K) { 914 bpf_int32 v = vmap[val].const_val; 915 switch (BPF_OP(b->s.code)) { 916 917 case BPF_JEQ: 918 v = v == b->s.k; 919 break; 920 921 case BPF_JGT: 922 v = (unsigned)v > b->s.k; 923 break; 924 925 case BPF_JGE: 926 v = (unsigned)v >= b->s.k; 927 break; 928 929 case BPF_JSET: 930 v &= b->s.k; 931 break; 932 933 default: 934 abort(); 935 } 936 if (JF(b) != JT(b)) 937 done = 0; 938 if (v) 939 JF(b) = JT(b); 940 else 941 JT(b) = JF(b); 942 } 943} 944 945/* 946 * Compute the symbolic value of expression of 's', and update 947 * anything it defines in the value table 'val'. If 'alter' is true, 948 * do various optimizations. This code would be cleaner if symbolic 949 * evaluation and code transformations weren't folded together. 950 */ 951static void 952opt_stmt(s, val, alter) 953 struct stmt *s; 954 int val[]; 955 int alter; 956{ 957 int op; 958 int v; 959 960 switch (s->code) { 961 962 case BPF_LD|BPF_ABS|BPF_W: 963 case BPF_LD|BPF_ABS|BPF_H: 964 case BPF_LD|BPF_ABS|BPF_B: 965 v = F(s->code, s->k, 0L); 966 vstore(s, &val[A_ATOM], v, alter); 967 break; 968 969 case BPF_LD|BPF_IND|BPF_W: 970 case BPF_LD|BPF_IND|BPF_H: 971 case BPF_LD|BPF_IND|BPF_B: 972 v = val[X_ATOM]; 973 if (alter && vmap[v].is_const) { 974 s->code = BPF_LD|BPF_ABS|BPF_SIZE(s->code); 975 s->k += vmap[v].const_val; 976 v = F(s->code, s->k, 0L); 977 done = 0; 978 } 979 else 980 v = F(s->code, s->k, v); 981 vstore(s, &val[A_ATOM], v, alter); 982 break; 983 984 case BPF_LD|BPF_LEN: 985 v = F(s->code, 0L, 0L); 986 vstore(s, &val[A_ATOM], v, alter); 987 break; 988 989 case BPF_LD|BPF_IMM: 990 v = K(s->k); 991 vstore(s, &val[A_ATOM], v, alter); 992 break; 993 994 case BPF_LDX|BPF_IMM: 995 v = K(s->k); 996 vstore(s, &val[X_ATOM], v, alter); 997 break; 998 999 case BPF_LDX|BPF_MSH|BPF_B: 1000 v = F(s->code, s->k, 0L); 1001 vstore(s, &val[X_ATOM], v, alter); 1002 break; 1003 1004 case BPF_ALU|BPF_NEG: 1005 if (alter && vmap[val[A_ATOM]].is_const) { 1006 s->code = BPF_LD|BPF_IMM; 1007 s->k = -vmap[val[A_ATOM]].const_val; 1008 val[A_ATOM] = K(s->k); 1009 } 1010 else 1011 val[A_ATOM] = F(s->code, val[A_ATOM], 0L); 1012 break; 1013 1014 case BPF_ALU|BPF_ADD|BPF_K: 1015 case BPF_ALU|BPF_SUB|BPF_K: 1016 case BPF_ALU|BPF_MUL|BPF_K: 1017 case BPF_ALU|BPF_DIV|BPF_K: 1018 case BPF_ALU|BPF_AND|BPF_K: 1019 case BPF_ALU|BPF_OR|BPF_K: 1020 case BPF_ALU|BPF_LSH|BPF_K: 1021 case BPF_ALU|BPF_RSH|BPF_K: 1022 op = BPF_OP(s->code); 1023 if (alter) { 1024 if (s->k == 0) { 1025 /* don't optimize away "sub #0" 1026 * as it may be needed later to 1027 * fixup the generated math code */ 1028 if (op == BPF_ADD || 1029 op == BPF_LSH || op == BPF_RSH || 1030 op == BPF_OR) { 1031 s->code = NOP; 1032 break; 1033 } 1034 if (op == BPF_MUL || op == BPF_AND) { 1035 s->code = BPF_LD|BPF_IMM; 1036 val[A_ATOM] = K(s->k); 1037 break; 1038 } 1039 } 1040 if (vmap[val[A_ATOM]].is_const) { 1041 fold_op(s, val[A_ATOM], K(s->k)); 1042 val[A_ATOM] = K(s->k); 1043 break; 1044 } 1045 } 1046 val[A_ATOM] = F(s->code, val[A_ATOM], K(s->k)); 1047 break; 1048 1049 case BPF_ALU|BPF_ADD|BPF_X: 1050 case BPF_ALU|BPF_SUB|BPF_X: 1051 case BPF_ALU|BPF_MUL|BPF_X: 1052 case BPF_ALU|BPF_DIV|BPF_X: 1053 case BPF_ALU|BPF_AND|BPF_X: 1054 case BPF_ALU|BPF_OR|BPF_X: 1055 case BPF_ALU|BPF_LSH|BPF_X: 1056 case BPF_ALU|BPF_RSH|BPF_X: 1057 op = BPF_OP(s->code); 1058 if (alter && vmap[val[X_ATOM]].is_const) { 1059 if (vmap[val[A_ATOM]].is_const) { 1060 fold_op(s, val[A_ATOM], val[X_ATOM]); 1061 val[A_ATOM] = K(s->k); 1062 } 1063 else { 1064 s->code = BPF_ALU|BPF_K|op; 1065 s->k = vmap[val[X_ATOM]].const_val; 1066 done = 0; 1067 val[A_ATOM] = 1068 F(s->code, val[A_ATOM], K(s->k)); 1069 } 1070 break; 1071 } 1072 /* 1073 * Check if we're doing something to an accumulator 1074 * that is 0, and simplify. This may not seem like 1075 * much of a simplification but it could open up further 1076 * optimizations. 1077 * XXX We could also check for mul by 1, etc. 1078 */ 1079 if (alter && vmap[val[A_ATOM]].is_const 1080 && vmap[val[A_ATOM]].const_val == 0) { 1081 if (op == BPF_ADD || op == BPF_OR) { 1082 s->code = BPF_MISC|BPF_TXA; 1083 vstore(s, &val[A_ATOM], val[X_ATOM], alter); 1084 break; 1085 } 1086 else if (op == BPF_MUL || op == BPF_DIV || 1087 op == BPF_AND || op == BPF_LSH || op == BPF_RSH) { 1088 s->code = BPF_LD|BPF_IMM; 1089 s->k = 0; 1090 vstore(s, &val[A_ATOM], K(s->k), alter); 1091 break; 1092 } 1093 else if (op == BPF_NEG) { 1094 s->code = NOP; 1095 break; 1096 } 1097 } 1098 val[A_ATOM] = F(s->code, val[A_ATOM], val[X_ATOM]); 1099 break; 1100 1101 case BPF_MISC|BPF_TXA: 1102 vstore(s, &val[A_ATOM], val[X_ATOM], alter); 1103 break; 1104 1105 case BPF_LD|BPF_MEM: 1106 v = val[s->k]; 1107 if (alter && vmap[v].is_const) { 1108 s->code = BPF_LD|BPF_IMM; 1109 s->k = vmap[v].const_val; 1110 done = 0; 1111 } 1112 vstore(s, &val[A_ATOM], v, alter); 1113 break; 1114 1115 case BPF_MISC|BPF_TAX: 1116 vstore(s, &val[X_ATOM], val[A_ATOM], alter); 1117 break; 1118 1119 case BPF_LDX|BPF_MEM: 1120 v = val[s->k]; 1121 if (alter && vmap[v].is_const) { 1122 s->code = BPF_LDX|BPF_IMM; 1123 s->k = vmap[v].const_val; 1124 done = 0; 1125 } 1126 vstore(s, &val[X_ATOM], v, alter); 1127 break; 1128 1129 case BPF_ST: 1130 vstore(s, &val[s->k], val[A_ATOM], alter); 1131 break; 1132 1133 case BPF_STX: 1134 vstore(s, &val[s->k], val[X_ATOM], alter); 1135 break; 1136 } 1137} 1138 1139static void 1140deadstmt(s, last) 1141 register struct stmt *s; 1142 register struct stmt *last[]; 1143{ 1144 register int atom; 1145 1146 atom = atomuse(s); 1147 if (atom >= 0) { 1148 if (atom == AX_ATOM) { 1149 last[X_ATOM] = 0; 1150 last[A_ATOM] = 0; 1151 } 1152 else 1153 last[atom] = 0; 1154 } 1155 atom = atomdef(s); 1156 if (atom >= 0) { 1157 if (last[atom]) { 1158 done = 0; 1159 last[atom]->code = NOP; 1160 } 1161 last[atom] = s; 1162 } 1163} 1164 1165static void 1166opt_deadstores(b) 1167 register struct block *b; 1168{ 1169 register struct slist *s; 1170 register int atom; 1171 struct stmt *last[N_ATOMS]; 1172 1173 memset((char *)last, 0, sizeof last); 1174 1175 for (s = b->stmts; s != 0; s = s->next) 1176 deadstmt(&s->s, last); 1177 deadstmt(&b->s, last); 1178 1179 for (atom = 0; atom < N_ATOMS; ++atom) 1180 if (last[atom] && !ATOMELEM(b->out_use, atom)) { 1181 last[atom]->code = NOP; 1182 done = 0; 1183 } 1184} 1185 1186static void 1187opt_blk(b, do_stmts) 1188 struct block *b; 1189 int do_stmts; 1190{ 1191 struct slist *s; 1192 struct edge *p; 1193 int i; 1194 bpf_int32 aval, xval; 1195 1196#if 0 1197 for (s = b->stmts; s && s->next; s = s->next) 1198 if (BPF_CLASS(s->s.code) == BPF_JMP) { 1199 do_stmts = 0; 1200 break; 1201 } 1202#endif 1203 1204 /* 1205 * Initialize the atom values. 1206 */ 1207 p = b->in_edges; 1208 if (p == 0) { 1209 /* 1210 * We have no predecessors, so everything is undefined 1211 * upon entry to this block. 1212 */ 1213 memset((char *)b->val, 0, sizeof(b->val)); 1214 } else { 1215 /* 1216 * Inherit values from our predecessors. 1217 * 1218 * First, get the values from the predecessor along the 1219 * first edge leading to this node. 1220 */ 1221 memcpy((char *)b->val, (char *)p->pred->val, sizeof(b->val)); 1222 /* 1223 * Now look at all the other nodes leading to this node. 1224 * If, for the predecessor along that edge, a register 1225 * has a different value from the one we have (i.e., 1226 * control paths are merging, and the merging paths 1227 * assign different values to that register), give the 1228 * register the undefined value of 0. 1229 */ 1230 while ((p = p->next) != NULL) { 1231 for (i = 0; i < N_ATOMS; ++i) 1232 if (b->val[i] != p->pred->val[i]) 1233 b->val[i] = 0; 1234 } 1235 } 1236 aval = b->val[A_ATOM]; 1237 xval = b->val[X_ATOM]; 1238 for (s = b->stmts; s; s = s->next) 1239 opt_stmt(&s->s, b->val, do_stmts); 1240 1241 /* 1242 * This is a special case: if we don't use anything from this 1243 * block, and we load the accumulator or index register with a 1244 * value that is already there, or if this block is a return, 1245 * eliminate all the statements. 1246 * 1247 * XXX - what if it does a store? 1248 * 1249 * XXX - why does it matter whether we use anything from this 1250 * block? If the accumulator or index register doesn't change 1251 * its value, isn't that OK even if we use that value? 1252 * 1253 * XXX - if we load the accumulator with a different value, 1254 * and the block ends with a conditional branch, we obviously 1255 * can't eliminate it, as the branch depends on that value. 1256 * For the index register, the conditional branch only depends 1257 * on the index register value if the test is against the index 1258 * register value rather than a constant; if nothing uses the 1259 * value we put into the index register, and we're not testing 1260 * against the index register's value, and there aren't any 1261 * other problems that would keep us from eliminating this 1262 * block, can we eliminate it? 1263 */ 1264 if (do_stmts && 1265 ((b->out_use == 0 && aval != 0 && b->val[A_ATOM] == aval && 1266 xval != 0 && b->val[X_ATOM] == xval) || 1267 BPF_CLASS(b->s.code) == BPF_RET)) { 1268 if (b->stmts != 0) { 1269 b->stmts = 0; 1270 done = 0; 1271 } 1272 } else { 1273 opt_peep(b); 1274 opt_deadstores(b); 1275 } 1276 /* 1277 * Set up values for branch optimizer. 1278 */ 1279 if (BPF_SRC(b->s.code) == BPF_K) 1280 b->oval = K(b->s.k); 1281 else 1282 b->oval = b->val[X_ATOM]; 1283 b->et.code = b->s.code; 1284 b->ef.code = -b->s.code; 1285} 1286 1287/* 1288 * Return true if any register that is used on exit from 'succ', has 1289 * an exit value that is different from the corresponding exit value 1290 * from 'b'. 1291 */ 1292static int 1293use_conflict(b, succ) 1294 struct block *b, *succ; 1295{ 1296 int atom; 1297 atomset use = succ->out_use; 1298 1299 if (use == 0) 1300 return 0; 1301 1302 for (atom = 0; atom < N_ATOMS; ++atom) 1303 if (ATOMELEM(use, atom)) 1304 if (b->val[atom] != succ->val[atom]) 1305 return 1; 1306 return 0; 1307} 1308 1309static struct block * 1310fold_edge(child, ep) 1311 struct block *child; 1312 struct edge *ep; 1313{ 1314 int sense; 1315 int aval0, aval1, oval0, oval1; 1316 int code = ep->code; 1317 1318 if (code < 0) { 1319 code = -code; 1320 sense = 0; 1321 } else 1322 sense = 1; 1323 1324 if (child->s.code != code) 1325 return 0; 1326 1327 aval0 = child->val[A_ATOM]; 1328 oval0 = child->oval; 1329 aval1 = ep->pred->val[A_ATOM]; 1330 oval1 = ep->pred->oval; 1331 1332 if (aval0 != aval1) 1333 return 0; 1334 1335 if (oval0 == oval1) 1336 /* 1337 * The operands of the branch instructions are 1338 * identical, so the result is true if a true 1339 * branch was taken to get here, otherwise false. 1340 */ 1341 return sense ? JT(child) : JF(child); 1342 1343 if (sense && code == (BPF_JMP|BPF_JEQ|BPF_K)) 1344 /* 1345 * At this point, we only know the comparison if we 1346 * came down the true branch, and it was an equality 1347 * comparison with a constant. 1348 * 1349 * I.e., if we came down the true branch, and the branch 1350 * was an equality comparison with a constant, we know the 1351 * accumulator contains that constant. If we came down 1352 * the false branch, or the comparison wasn't with a 1353 * constant, we don't know what was in the accumulator. 1354 * 1355 * We rely on the fact that distinct constants have distinct 1356 * value numbers. 1357 */ 1358 return JF(child); 1359 1360 return 0; 1361} 1362 1363#include "ffs.h" 1364static void 1365opt_j(ep) 1366 struct edge *ep; 1367{ 1368 register int i, k; 1369 register struct block *target; 1370 1371 if (JT(ep->succ) == 0) 1372 return; 1373 1374 if (JT(ep->succ) == JF(ep->succ)) { 1375 /* 1376 * Common branch targets can be eliminated, provided 1377 * there is no data dependency. 1378 */ 1379 if (!use_conflict(ep->pred, ep->succ->et.succ)) { 1380 done = 0; 1381 ep->succ = JT(ep->succ); 1382 } 1383 } 1384 /* 1385 * For each edge dominator that matches the successor of this 1386 * edge, promote the edge successor to the its grandchild. 1387 * 1388 * XXX We violate the set abstraction here in favor a reasonably 1389 * efficient loop. 1390 */ 1391 top: 1392 for (i = 0; i < edgewords; ++i) { 1393 register bpf_u_int32 x = ep->edom[i]; 1394 1395 while (x != 0) { 1396 k = ffs(x) - 1; 1397 x &=~ (1 << k); 1398 k += i * BITS_PER_WORD; 1399 1400 target = fold_edge(ep->succ, edges[k]); 1401 /* 1402 * Check that there is no data dependency between 1403 * nodes that will be violated if we move the edge. 1404 */ 1405 if (target != 0 && !use_conflict(ep->pred, target)) { 1406 done = 0; 1407 ep->succ = target; 1408 if (JT(target) != 0) 1409 /* 1410 * Start over unless we hit a leaf. 1411 */ 1412 goto top; 1413 return; 1414 } 1415 } 1416 } 1417} 1418 1419 1420static void 1421or_pullup(b) 1422 struct block *b; 1423{ 1424 int val, at_top; 1425 struct block *pull; 1426 struct block **diffp, **samep; 1427 struct edge *ep; 1428 1429 ep = b->in_edges; 1430 if (ep == 0) 1431 return; 1432 1433 /* 1434 * Make sure each predecessor loads the same value. 1435 * XXX why? 1436 */ 1437 val = ep->pred->val[A_ATOM]; 1438 for (ep = ep->next; ep != 0; ep = ep->next) 1439 if (val != ep->pred->val[A_ATOM]) 1440 return; 1441 1442 if (JT(b->in_edges->pred) == b) 1443 diffp = &JT(b->in_edges->pred); 1444 else 1445 diffp = &JF(b->in_edges->pred); 1446 1447 at_top = 1; 1448 while (1) { 1449 if (*diffp == 0) 1450 return; 1451 1452 if (JT(*diffp) != JT(b)) 1453 return; 1454 1455 if (!SET_MEMBER((*diffp)->dom, b->id)) 1456 return; 1457 1458 if ((*diffp)->val[A_ATOM] != val) 1459 break; 1460 1461 diffp = &JF(*diffp); 1462 at_top = 0; 1463 } 1464 samep = &JF(*diffp); 1465 while (1) { 1466 if (*samep == 0) 1467 return; 1468 1469 if (JT(*samep) != JT(b)) 1470 return; 1471 1472 if (!SET_MEMBER((*samep)->dom, b->id)) 1473 return; 1474 1475 if ((*samep)->val[A_ATOM] == val) 1476 break; 1477 1478 /* XXX Need to check that there are no data dependencies 1479 between dp0 and dp1. Currently, the code generator 1480 will not produce such dependencies. */ 1481 samep = &JF(*samep); 1482 } 1483#ifdef notdef 1484 /* XXX This doesn't cover everything. */ 1485 for (i = 0; i < N_ATOMS; ++i) 1486 if ((*samep)->val[i] != pred->val[i]) 1487 return; 1488#endif 1489 /* Pull up the node. */ 1490 pull = *samep; 1491 *samep = JF(pull); 1492 JF(pull) = *diffp; 1493 1494 /* 1495 * At the top of the chain, each predecessor needs to point at the 1496 * pulled up node. Inside the chain, there is only one predecessor 1497 * to worry about. 1498 */ 1499 if (at_top) { 1500 for (ep = b->in_edges; ep != 0; ep = ep->next) { 1501 if (JT(ep->pred) == b) 1502 JT(ep->pred) = pull; 1503 else 1504 JF(ep->pred) = pull; 1505 } 1506 } 1507 else 1508 *diffp = pull; 1509 1510 done = 0; 1511} 1512 1513static void 1514and_pullup(b) 1515 struct block *b; 1516{ 1517 int val, at_top; 1518 struct block *pull; 1519 struct block **diffp, **samep; 1520 struct edge *ep; 1521 1522 ep = b->in_edges; 1523 if (ep == 0) 1524 return; 1525 1526 /* 1527 * Make sure each predecessor loads the same value. 1528 */ 1529 val = ep->pred->val[A_ATOM]; 1530 for (ep = ep->next; ep != 0; ep = ep->next) 1531 if (val != ep->pred->val[A_ATOM]) 1532 return; 1533 1534 if (JT(b->in_edges->pred) == b) 1535 diffp = &JT(b->in_edges->pred); 1536 else 1537 diffp = &JF(b->in_edges->pred); 1538 1539 at_top = 1; 1540 while (1) { 1541 if (*diffp == 0) 1542 return; 1543 1544 if (JF(*diffp) != JF(b)) 1545 return; 1546 1547 if (!SET_MEMBER((*diffp)->dom, b->id)) 1548 return; 1549 1550 if ((*diffp)->val[A_ATOM] != val) 1551 break; 1552 1553 diffp = &JT(*diffp); 1554 at_top = 0; 1555 } 1556 samep = &JT(*diffp); 1557 while (1) { 1558 if (*samep == 0) 1559 return; 1560 1561 if (JF(*samep) != JF(b)) 1562 return; 1563 1564 if (!SET_MEMBER((*samep)->dom, b->id)) 1565 return; 1566 1567 if ((*samep)->val[A_ATOM] == val) 1568 break; 1569 1570 /* XXX Need to check that there are no data dependencies 1571 between diffp and samep. Currently, the code generator 1572 will not produce such dependencies. */ 1573 samep = &JT(*samep); 1574 } 1575#ifdef notdef 1576 /* XXX This doesn't cover everything. */ 1577 for (i = 0; i < N_ATOMS; ++i) 1578 if ((*samep)->val[i] != pred->val[i]) 1579 return; 1580#endif 1581 /* Pull up the node. */ 1582 pull = *samep; 1583 *samep = JT(pull); 1584 JT(pull) = *diffp; 1585 1586 /* 1587 * At the top of the chain, each predecessor needs to point at the 1588 * pulled up node. Inside the chain, there is only one predecessor 1589 * to worry about. 1590 */ 1591 if (at_top) { 1592 for (ep = b->in_edges; ep != 0; ep = ep->next) { 1593 if (JT(ep->pred) == b) 1594 JT(ep->pred) = pull; 1595 else 1596 JF(ep->pred) = pull; 1597 } 1598 } 1599 else 1600 *diffp = pull; 1601 1602 done = 0; 1603} 1604 1605static void 1606opt_blks(root, do_stmts) 1607 struct block *root; 1608 int do_stmts; 1609{ 1610 int i, maxlevel; 1611 struct block *p; 1612 1613 init_val(); 1614 maxlevel = root->level; 1615 1616 find_inedges(root); 1617 for (i = maxlevel; i >= 0; --i) 1618 for (p = levels[i]; p; p = p->link) 1619 opt_blk(p, do_stmts); 1620 1621 if (do_stmts) 1622 /* 1623 * No point trying to move branches; it can't possibly 1624 * make a difference at this point. 1625 */ 1626 return; 1627 1628 for (i = 1; i <= maxlevel; ++i) { 1629 for (p = levels[i]; p; p = p->link) { 1630 opt_j(&p->et); 1631 opt_j(&p->ef); 1632 } 1633 } 1634 1635 find_inedges(root); 1636 for (i = 1; i <= maxlevel; ++i) { 1637 for (p = levels[i]; p; p = p->link) { 1638 or_pullup(p); 1639 and_pullup(p); 1640 } 1641 } 1642} 1643 1644static inline void 1645link_inedge(parent, child) 1646 struct edge *parent; 1647 struct block *child; 1648{ 1649 parent->next = child->in_edges; 1650 child->in_edges = parent; 1651} 1652 1653static void 1654find_inedges(root) 1655 struct block *root; 1656{ 1657 int i; 1658 struct block *b; 1659 1660 for (i = 0; i < n_blocks; ++i) 1661 blocks[i]->in_edges = 0; 1662 1663 /* 1664 * Traverse the graph, adding each edge to the predecessor 1665 * list of its successors. Skip the leaves (i.e. level 0). 1666 */ 1667 for (i = root->level; i > 0; --i) { 1668 for (b = levels[i]; b != 0; b = b->link) { 1669 link_inedge(&b->et, JT(b)); 1670 link_inedge(&b->ef, JF(b)); 1671 } 1672 } 1673} 1674 1675static void 1676opt_root(b) 1677 struct block **b; 1678{ 1679 struct slist *tmp, *s; 1680 1681 s = (*b)->stmts; 1682 (*b)->stmts = 0; 1683 while (BPF_CLASS((*b)->s.code) == BPF_JMP && JT(*b) == JF(*b)) 1684 *b = JT(*b); 1685 1686 tmp = (*b)->stmts; 1687 if (tmp != 0) 1688 sappend(s, tmp); 1689 (*b)->stmts = s; 1690 1691 /* 1692 * If the root node is a return, then there is no 1693 * point executing any statements (since the bpf machine 1694 * has no side effects). 1695 */ 1696 if (BPF_CLASS((*b)->s.code) == BPF_RET) 1697 (*b)->stmts = 0; 1698} 1699 1700static void 1701opt_loop(root, do_stmts) 1702 struct block *root; 1703 int do_stmts; 1704{ 1705 1706#ifdef BDEBUG 1707 if (dflag > 1) { 1708 printf("opt_loop(root, %d) begin\n", do_stmts); 1709 opt_dump(root); 1710 } 1711#endif 1712 do { 1713 done = 1; 1714 find_levels(root); 1715 find_dom(root); 1716 find_closure(root); 1717 find_ud(root); 1718 find_edom(root); 1719 opt_blks(root, do_stmts); 1720#ifdef BDEBUG 1721 if (dflag > 1) { 1722 printf("opt_loop(root, %d) bottom, done=%d\n", do_stmts, done); 1723 opt_dump(root); 1724 } 1725#endif 1726 } while (!done); 1727} 1728 1729/* 1730 * Optimize the filter code in its dag representation. 1731 */ 1732void 1733bpf_optimize(rootp) 1734 struct block **rootp; 1735{ 1736 struct block *root; 1737 1738 root = *rootp; 1739 1740 opt_init(root); 1741 opt_loop(root, 0); 1742 opt_loop(root, 1); 1743 intern_blocks(root); 1744#ifdef BDEBUG 1745 if (dflag > 1) { 1746 printf("after intern_blocks()\n"); 1747 opt_dump(root); 1748 } 1749#endif 1750 opt_root(rootp); 1751#ifdef BDEBUG 1752 if (dflag > 1) { 1753 printf("after opt_root()\n"); 1754 opt_dump(root); 1755 } 1756#endif 1757 opt_cleanup(); 1758} 1759 1760static void 1761make_marks(p) 1762 struct block *p; 1763{ 1764 if (!isMarked(p)) { 1765 Mark(p); 1766 if (BPF_CLASS(p->s.code) != BPF_RET) { 1767 make_marks(JT(p)); 1768 make_marks(JF(p)); 1769 } 1770 } 1771} 1772 1773/* 1774 * Mark code array such that isMarked(i) is true 1775 * only for nodes that are alive. 1776 */ 1777static void 1778mark_code(p) 1779 struct block *p; 1780{ 1781 cur_mark += 1; 1782 make_marks(p); 1783} 1784 1785/* 1786 * True iff the two stmt lists load the same value from the packet into 1787 * the accumulator. 1788 */ 1789static int 1790eq_slist(x, y) 1791 struct slist *x, *y; 1792{ 1793 while (1) { 1794 while (x && x->s.code == NOP) 1795 x = x->next; 1796 while (y && y->s.code == NOP) 1797 y = y->next; 1798 if (x == 0) 1799 return y == 0; 1800 if (y == 0) 1801 return x == 0; 1802 if (x->s.code != y->s.code || x->s.k != y->s.k) 1803 return 0; 1804 x = x->next; 1805 y = y->next; 1806 } 1807} 1808 1809static inline int 1810eq_blk(b0, b1) 1811 struct block *b0, *b1; 1812{ 1813 if (b0->s.code == b1->s.code && 1814 b0->s.k == b1->s.k && 1815 b0->et.succ == b1->et.succ && 1816 b0->ef.succ == b1->ef.succ) 1817 return eq_slist(b0->stmts, b1->stmts); 1818 return 0; 1819} 1820 1821static void 1822intern_blocks(root) 1823 struct block *root; 1824{ 1825 struct block *p; 1826 int i, j; 1827 int done1; /* don't shadow global */ 1828 top: 1829 done1 = 1; 1830 for (i = 0; i < n_blocks; ++i) 1831 blocks[i]->link = 0; 1832 1833 mark_code(root); 1834 1835 for (i = n_blocks - 1; --i >= 0; ) { 1836 if (!isMarked(blocks[i])) 1837 continue; 1838 for (j = i + 1; j < n_blocks; ++j) { 1839 if (!isMarked(blocks[j])) 1840 continue; 1841 if (eq_blk(blocks[i], blocks[j])) { 1842 blocks[i]->link = blocks[j]->link ? 1843 blocks[j]->link : blocks[j]; 1844 break; 1845 } 1846 } 1847 } 1848 for (i = 0; i < n_blocks; ++i) { 1849 p = blocks[i]; 1850 if (JT(p) == 0) 1851 continue; 1852 if (JT(p)->link) { 1853 done1 = 0; 1854 JT(p) = JT(p)->link; 1855 } 1856 if (JF(p)->link) { 1857 done1 = 0; 1858 JF(p) = JF(p)->link; 1859 } 1860 } 1861 if (!done1) 1862 goto top; 1863} 1864 1865static void 1866opt_cleanup() 1867{ 1868 free((void *)vnode_base); 1869 free((void *)vmap); 1870 free((void *)edges); 1871 free((void *)space); 1872 free((void *)levels); 1873 free((void *)blocks); 1874} 1875 1876/* 1877 * Return the number of stmts in 's'. 1878 */ 1879static int 1880slength(s) 1881 struct slist *s; 1882{ 1883 int n = 0; 1884 1885 for (; s; s = s->next) 1886 if (s->s.code != NOP) 1887 ++n; 1888 return n; 1889} 1890 1891/* 1892 * Return the number of nodes reachable by 'p'. 1893 * All nodes should be initially unmarked. 1894 */ 1895static int 1896count_blocks(p) 1897 struct block *p; 1898{ 1899 if (p == 0 || isMarked(p)) 1900 return 0; 1901 Mark(p); 1902 return count_blocks(JT(p)) + count_blocks(JF(p)) + 1; 1903} 1904 1905/* 1906 * Do a depth first search on the flow graph, numbering the 1907 * the basic blocks, and entering them into the 'blocks' array.` 1908 */ 1909static void 1910number_blks_r(p) 1911 struct block *p; 1912{ 1913 int n; 1914 1915 if (p == 0 || isMarked(p)) 1916 return; 1917 1918 Mark(p); 1919 n = n_blocks++; 1920 p->id = n; 1921 blocks[n] = p; 1922 1923 number_blks_r(JT(p)); 1924 number_blks_r(JF(p)); 1925} 1926 1927/* 1928 * Return the number of stmts in the flowgraph reachable by 'p'. 1929 * The nodes should be unmarked before calling. 1930 * 1931 * Note that "stmts" means "instructions", and that this includes 1932 * 1933 * side-effect statements in 'p' (slength(p->stmts)); 1934 * 1935 * statements in the true branch from 'p' (count_stmts(JT(p))); 1936 * 1937 * statements in the false branch from 'p' (count_stmts(JF(p))); 1938 * 1939 * the conditional jump itself (1); 1940 * 1941 * an extra long jump if the true branch requires it (p->longjt); 1942 * 1943 * an extra long jump if the false branch requires it (p->longjf). 1944 */ 1945static int 1946count_stmts(p) 1947 struct block *p; 1948{ 1949 int n; 1950 1951 if (p == 0 || isMarked(p)) 1952 return 0; 1953 Mark(p); 1954 n = count_stmts(JT(p)) + count_stmts(JF(p)); 1955 return slength(p->stmts) + n + 1 + p->longjt + p->longjf; 1956} 1957 1958/* 1959 * Allocate memory. All allocation is done before optimization 1960 * is begun. A linear bound on the size of all data structures is computed 1961 * from the total number of blocks and/or statements. 1962 */ 1963static void 1964opt_init(root) 1965 struct block *root; 1966{ 1967 bpf_u_int32 *p; 1968 int i, n, max_stmts; 1969 1970 /* 1971 * First, count the blocks, so we can malloc an array to map 1972 * block number to block. Then, put the blocks into the array. 1973 */ 1974 unMarkAll(); 1975 n = count_blocks(root); 1976 blocks = (struct block **)calloc(n, sizeof(*blocks)); 1977 if (blocks == NULL) 1978 bpf_error("malloc"); 1979 unMarkAll(); 1980 n_blocks = 0; 1981 number_blks_r(root); 1982 1983 n_edges = 2 * n_blocks; 1984 edges = (struct edge **)calloc(n_edges, sizeof(*edges)); 1985 if (edges == NULL) 1986 bpf_error("malloc"); 1987 1988 /* 1989 * The number of levels is bounded by the number of nodes. 1990 */ 1991 levels = (struct block **)calloc(n_blocks, sizeof(*levels)); 1992 if (levels == NULL) 1993 bpf_error("malloc"); 1994 1995 edgewords = n_edges / (8 * sizeof(bpf_u_int32)) + 1; 1996 nodewords = n_blocks / (8 * sizeof(bpf_u_int32)) + 1; 1997 1998 /* XXX */ 1999 space = (bpf_u_int32 *)malloc(2 * n_blocks * nodewords * sizeof(*space) 2000 + n_edges * edgewords * sizeof(*space)); 2001 if (space == NULL) 2002 bpf_error("malloc"); 2003 p = space; 2004 all_dom_sets = p; 2005 for (i = 0; i < n; ++i) { 2006 blocks[i]->dom = p; 2007 p += nodewords; 2008 } 2009 all_closure_sets = p; 2010 for (i = 0; i < n; ++i) { 2011 blocks[i]->closure = p; 2012 p += nodewords; 2013 } 2014 all_edge_sets = p; 2015 for (i = 0; i < n; ++i) { 2016 register struct block *b = blocks[i]; 2017 2018 b->et.edom = p; 2019 p += edgewords; 2020 b->ef.edom = p; 2021 p += edgewords; 2022 b->et.id = i; 2023 edges[i] = &b->et; 2024 b->ef.id = n_blocks + i; 2025 edges[n_blocks + i] = &b->ef; 2026 b->et.pred = b; 2027 b->ef.pred = b; 2028 } 2029 max_stmts = 0; 2030 for (i = 0; i < n; ++i) 2031 max_stmts += slength(blocks[i]->stmts) + 1; 2032 /* 2033 * We allocate at most 3 value numbers per statement, 2034 * so this is an upper bound on the number of valnodes 2035 * we'll need. 2036 */ 2037 maxval = 3 * max_stmts; 2038 vmap = (struct vmapinfo *)calloc(maxval, sizeof(*vmap)); 2039 vnode_base = (struct valnode *)calloc(maxval, sizeof(*vnode_base)); 2040 if (vmap == NULL || vnode_base == NULL) 2041 bpf_error("malloc"); 2042} 2043 2044/* 2045 * Some pointers used to convert the basic block form of the code, 2046 * into the array form that BPF requires. 'fstart' will point to 2047 * the malloc'd array while 'ftail' is used during the recursive traversal. 2048 */ 2049static struct bpf_insn *fstart; 2050static struct bpf_insn *ftail; 2051 2052#ifdef BDEBUG 2053int bids[1000]; 2054#endif 2055 2056/* 2057 * Returns true if successful. Returns false if a branch has 2058 * an offset that is too large. If so, we have marked that 2059 * branch so that on a subsequent iteration, it will be treated 2060 * properly. 2061 */ 2062static int 2063convert_code_r(p) 2064 struct block *p; 2065{ 2066 struct bpf_insn *dst; 2067 struct slist *src; 2068 int slen; 2069 u_int off; 2070 int extrajmps; /* number of extra jumps inserted */ 2071 struct slist **offset = NULL; 2072 2073 if (p == 0 || isMarked(p)) 2074 return (1); 2075 Mark(p); 2076 2077 if (convert_code_r(JF(p)) == 0) 2078 return (0); 2079 if (convert_code_r(JT(p)) == 0) 2080 return (0); 2081 2082 slen = slength(p->stmts); 2083 dst = ftail -= (slen + 1 + p->longjt + p->longjf); 2084 /* inflate length by any extra jumps */ 2085 2086 p->offset = dst - fstart; 2087 2088 /* generate offset[] for convenience */ 2089 if (slen) { 2090 offset = (struct slist **)calloc(slen, sizeof(struct slist *)); 2091 if (!offset) { 2092 bpf_error("not enough core"); 2093 /*NOTREACHED*/ 2094 } 2095 } 2096 src = p->stmts; 2097 for (off = 0; off < slen && src; off++) { 2098#if 0 2099 printf("off=%d src=%x\n", off, src); 2100#endif 2101 offset[off] = src; 2102 src = src->next; 2103 } 2104 2105 off = 0; 2106 for (src = p->stmts; src; src = src->next) { 2107 if (src->s.code == NOP) 2108 continue; 2109 dst->code = (u_short)src->s.code; 2110 dst->k = src->s.k; 2111 2112 /* fill block-local relative jump */ 2113 if (BPF_CLASS(src->s.code) != BPF_JMP || src->s.code == (BPF_JMP|BPF_JA)) { 2114#if 0 2115 if (src->s.jt || src->s.jf) { 2116 bpf_error("illegal jmp destination"); 2117 /*NOTREACHED*/ 2118 } 2119#endif 2120 goto filled; 2121 } 2122 if (off == slen - 2) /*???*/ 2123 goto filled; 2124 2125 { 2126 int i; 2127 int jt, jf; 2128 const char *ljerr = "%s for block-local relative jump: off=%d"; 2129 2130#if 0 2131 printf("code=%x off=%d %x %x\n", src->s.code, 2132 off, src->s.jt, src->s.jf); 2133#endif 2134 2135 if (!src->s.jt || !src->s.jf) { 2136 bpf_error(ljerr, "no jmp destination", off); 2137 /*NOTREACHED*/ 2138 } 2139 2140 jt = jf = 0; 2141 for (i = 0; i < slen; i++) { 2142 if (offset[i] == src->s.jt) { 2143 if (jt) { 2144 bpf_error(ljerr, "multiple matches", off); 2145 /*NOTREACHED*/ 2146 } 2147 2148 dst->jt = i - off - 1; 2149 jt++; 2150 } 2151 if (offset[i] == src->s.jf) { 2152 if (jf) { 2153 bpf_error(ljerr, "multiple matches", off); 2154 /*NOTREACHED*/ 2155 } 2156 dst->jf = i - off - 1; 2157 jf++; 2158 } 2159 } 2160 if (!jt || !jf) { 2161 bpf_error(ljerr, "no destination found", off); 2162 /*NOTREACHED*/ 2163 } 2164 } 2165filled: 2166 ++dst; 2167 ++off; 2168 } 2169 if (offset) 2170 free(offset); 2171 2172#ifdef BDEBUG 2173 bids[dst - fstart] = p->id + 1; 2174#endif 2175 dst->code = (u_short)p->s.code; 2176 dst->k = p->s.k; 2177 if (JT(p)) { 2178 extrajmps = 0; 2179 off = JT(p)->offset - (p->offset + slen) - 1; 2180 if (off >= 256) { 2181 /* offset too large for branch, must add a jump */ 2182 if (p->longjt == 0) { 2183 /* mark this instruction and retry */ 2184 p->longjt++; 2185 return(0); 2186 } 2187 /* branch if T to following jump */ 2188 dst->jt = extrajmps; 2189 extrajmps++; 2190 dst[extrajmps].code = BPF_JMP|BPF_JA; 2191 dst[extrajmps].k = off - extrajmps; 2192 } 2193 else 2194 dst->jt = off; 2195 off = JF(p)->offset - (p->offset + slen) - 1; 2196 if (off >= 256) { 2197 /* offset too large for branch, must add a jump */ 2198 if (p->longjf == 0) { 2199 /* mark this instruction and retry */ 2200 p->longjf++; 2201 return(0); 2202 } 2203 /* branch if F to following jump */ 2204 /* if two jumps are inserted, F goes to second one */ 2205 dst->jf = extrajmps; 2206 extrajmps++; 2207 dst[extrajmps].code = BPF_JMP|BPF_JA; 2208 dst[extrajmps].k = off - extrajmps; 2209 } 2210 else 2211 dst->jf = off; 2212 } 2213 return (1); 2214} 2215 2216 2217/* 2218 * Convert flowgraph intermediate representation to the 2219 * BPF array representation. Set *lenp to the number of instructions. 2220 * 2221 * This routine does *NOT* leak the memory pointed to by fp. It *must 2222 * not* do free(fp) before returning fp; doing so would make no sense, 2223 * as the BPF array pointed to by the return value of icode_to_fcode() 2224 * must be valid - it's being returned for use in a bpf_program structure. 2225 * 2226 * If it appears that icode_to_fcode() is leaking, the problem is that 2227 * the program using pcap_compile() is failing to free the memory in 2228 * the BPF program when it's done - the leak is in the program, not in 2229 * the routine that happens to be allocating the memory. (By analogy, if 2230 * a program calls fopen() without ever calling fclose() on the FILE *, 2231 * it will leak the FILE structure; the leak is not in fopen(), it's in 2232 * the program.) Change the program to use pcap_freecode() when it's 2233 * done with the filter program. See the pcap man page. 2234 */ 2235struct bpf_insn * 2236icode_to_fcode(root, lenp) 2237 struct block *root; 2238 int *lenp; 2239{ 2240 int n; 2241 struct bpf_insn *fp; 2242 2243 /* 2244 * Loop doing convert_code_r() until no branches remain 2245 * with too-large offsets. 2246 */ 2247 while (1) { 2248 unMarkAll(); 2249 n = *lenp = count_stmts(root); 2250 2251 fp = (struct bpf_insn *)malloc(sizeof(*fp) * n); 2252 if (fp == NULL) 2253 bpf_error("malloc"); 2254 memset((char *)fp, 0, sizeof(*fp) * n); 2255 fstart = fp; 2256 ftail = fp + n; 2257 2258 unMarkAll(); 2259 if (convert_code_r(root)) 2260 break; 2261 free(fp); 2262 } 2263 2264 return fp; 2265} 2266 2267/* 2268 * Make a copy of a BPF program and put it in the "fcode" member of 2269 * a "pcap_t". 2270 * 2271 * If we fail to allocate memory for the copy, fill in the "errbuf" 2272 * member of the "pcap_t" with an error message, and return -1; 2273 * otherwise, return 0. 2274 */ 2275int 2276install_bpf_program(pcap_t *p, struct bpf_program *fp) 2277{ 2278 size_t prog_size; 2279 2280 /* 2281 * Free up any already installed program. 2282 */ 2283 pcap_freecode(&p->fcode); 2284 2285 prog_size = sizeof(*fp->bf_insns) * fp->bf_len; 2286 p->fcode.bf_len = fp->bf_len; 2287 p->fcode.bf_insns = (struct bpf_insn *)malloc(prog_size); 2288 if (p->fcode.bf_insns == NULL) { 2289 snprintf(p->errbuf, sizeof(p->errbuf), 2290 "malloc: %s", pcap_strerror(errno)); 2291 return (-1); 2292 } 2293 memcpy(p->fcode.bf_insns, fp->bf_insns, prog_size); 2294 return (0); 2295} 2296 2297#ifdef BDEBUG 2298static void 2299opt_dump(root) 2300 struct block *root; 2301{ 2302 struct bpf_program f; 2303 2304 memset(bids, 0, sizeof bids); 2305 f.bf_insns = icode_to_fcode(root, &f.bf_len); 2306 bpf_dump(&f, 1); 2307 putchar('\n'); 2308 free((char *)f.bf_insns); 2309} 2310#endif 2311