1 /* Generate assembler source containing symbol information 2 * 3 * Copyright 2002 by Kai Germaschewski 4 * 5 * This software may be used and distributed according to the terms 6 * of the GNU General Public License, incorporated herein by reference. 7 * 8 * Usage: nm -n vmlinux | scripts/kallsyms [--all-symbols] > symbols.S 9 * 10 * Table compression uses all the unused char codes on the symbols and 11 * maps these to the most used substrings (tokens). For instance, it might 12 * map char code 0xF7 to represent "write_" and then in every symbol where 13 * "write_" appears it can be replaced by 0xF7, saving 5 bytes. 14 * The used codes themselves are also placed in the table so that the 15 * decompresion can work without "special cases". 16 * Applied to kernel symbols, this usually produces a compression ratio 17 * of about 50%. 18 * 19 */ 20 21 #include <stdbool.h> 22 #include <stdio.h> 23 #include <stdlib.h> 24 #include <string.h> 25 #include <ctype.h> 26 #include <limits.h> 27 28 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0])) 29 30 #define _stringify_1(x) #x 31 #define _stringify(x) _stringify_1(x) 32 33 #define KSYM_NAME_LEN 128 34 35 /* 36 * A substantially bigger size than the current maximum. 37 * 38 * It cannot be defined as an expression because it gets stringified 39 * for the fscanf() format string. Therefore, a _Static_assert() is 40 * used instead to maintain the relationship with KSYM_NAME_LEN. 41 */ 42 #define KSYM_NAME_LEN_BUFFER 512 43 _Static_assert( 44 KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4, 45 "Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN" 46 ); 47 48 struct sym_entry { 49 unsigned long long addr; 50 unsigned int len; 51 unsigned int start_pos; 52 unsigned int percpu_absolute; 53 unsigned char sym[]; 54 }; 55 56 struct addr_range { 57 const char *start_sym, *end_sym; 58 unsigned long long start, end; 59 }; 60 61 static unsigned long long _text; 62 static unsigned long long relative_base; 63 static struct addr_range text_ranges[] = { 64 { "_stext", "_etext" }, 65 { "_sinittext", "_einittext" }, 66 }; 67 #define text_range_text (&text_ranges[0]) 68 #define text_range_inittext (&text_ranges[1]) 69 70 static struct addr_range percpu_range = { 71 "__per_cpu_start", "__per_cpu_end", -1ULL, 0 72 }; 73 74 static struct sym_entry **table; 75 static unsigned int table_size, table_cnt; 76 static int all_symbols; 77 static int absolute_percpu; 78 static int base_relative; 79 80 static int token_profit[0x10000]; 81 82 /* the table that holds the result of the compression */ 83 static unsigned char best_table[256][2]; 84 static unsigned char best_table_len[256]; 85 86 87 static void usage(void) 88 { 89 fprintf(stderr, "Usage: kallsyms [--all-symbols] [--absolute-percpu] " 90 "[--base-relative] < in.map > out.S\n"); 91 exit(1); 92 } 93 94 static char *sym_name(const struct sym_entry *s) 95 { 96 return (char *)s->sym + 1; 97 } 98 99 static bool is_ignored_symbol(const char *name, char type) 100 { 101 /* Symbol names that exactly match to the following are ignored.*/ 102 static const char * const ignored_symbols[] = { 103 /* 104 * Symbols which vary between passes. Passes 1 and 2 must have 105 * identical symbol lists. The kallsyms_* symbols below are 106 * only added after pass 1, they would be included in pass 2 107 * when --all-symbols is specified so exclude them to get a 108 * stable symbol list. 109 */ 110 "kallsyms_addresses", 111 "kallsyms_offsets", 112 "kallsyms_relative_base", 113 "kallsyms_num_syms", 114 "kallsyms_names", 115 "kallsyms_markers", 116 "kallsyms_token_table", 117 "kallsyms_token_index", 118 /* Exclude linker generated symbols which vary between passes */ 119 "_SDA_BASE_", /* ppc */ 120 "_SDA2_BASE_", /* ppc */ 121 NULL 122 }; 123 124 /* Symbol names that begin with the following are ignored.*/ 125 static const char * const ignored_prefixes[] = { 126 "$", /* local symbols for ARM, MIPS, etc. */ 127 ".L", /* local labels, .LBB,.Ltmpxxx,.L__unnamed_xx,.LASANPC, etc. */ 128 "__crc_", /* modversions */ 129 "__efistub_", /* arm64 EFI stub namespace */ 130 "__kvm_nvhe_$", /* arm64 local symbols in non-VHE KVM namespace */ 131 "__kvm_nvhe_.L", /* arm64 local symbols in non-VHE KVM namespace */ 132 "__AArch64ADRPThunk_", /* arm64 lld */ 133 "__ARMV5PILongThunk_", /* arm lld */ 134 "__ARMV7PILongThunk_", 135 "__ThumbV7PILongThunk_", 136 "__LA25Thunk_", /* mips lld */ 137 "__microLA25Thunk_", 138 NULL 139 }; 140 141 /* Symbol names that end with the following are ignored.*/ 142 static const char * const ignored_suffixes[] = { 143 "_from_arm", /* arm */ 144 "_from_thumb", /* arm */ 145 "_veneer", /* arm */ 146 NULL 147 }; 148 149 /* Symbol names that contain the following are ignored.*/ 150 static const char * const ignored_matches[] = { 151 ".long_branch.", /* ppc stub */ 152 ".plt_branch.", /* ppc stub */ 153 NULL 154 }; 155 156 const char * const *p; 157 158 for (p = ignored_symbols; *p; p++) 159 if (!strcmp(name, *p)) 160 return true; 161 162 for (p = ignored_prefixes; *p; p++) 163 if (!strncmp(name, *p, strlen(*p))) 164 return true; 165 166 for (p = ignored_suffixes; *p; p++) { 167 int l = strlen(name) - strlen(*p); 168 169 if (l >= 0 && !strcmp(name + l, *p)) 170 return true; 171 } 172 173 for (p = ignored_matches; *p; p++) { 174 if (strstr(name, *p)) 175 return true; 176 } 177 178 if (type == 'U' || type == 'u') 179 return true; 180 /* exclude debugging symbols */ 181 if (type == 'N' || type == 'n') 182 return true; 183 184 if (toupper(type) == 'A') { 185 /* Keep these useful absolute symbols */ 186 if (strcmp(name, "__kernel_syscall_via_break") && 187 strcmp(name, "__kernel_syscall_via_epc") && 188 strcmp(name, "__kernel_sigtramp") && 189 strcmp(name, "__gp")) 190 return true; 191 } 192 193 return false; 194 } 195 196 static void check_symbol_range(const char *sym, unsigned long long addr, 197 struct addr_range *ranges, int entries) 198 { 199 size_t i; 200 struct addr_range *ar; 201 202 for (i = 0; i < entries; ++i) { 203 ar = &ranges[i]; 204 205 if (strcmp(sym, ar->start_sym) == 0) { 206 ar->start = addr; 207 return; 208 } else if (strcmp(sym, ar->end_sym) == 0) { 209 ar->end = addr; 210 return; 211 } 212 } 213 } 214 215 static struct sym_entry *read_symbol(FILE *in) 216 { 217 char name[KSYM_NAME_LEN_BUFFER+1], type; 218 unsigned long long addr; 219 unsigned int len; 220 struct sym_entry *sym; 221 int rc; 222 223 rc = fscanf(in, "%llx %c %" _stringify(KSYM_NAME_LEN_BUFFER) "s\n", &addr, &type, name); 224 if (rc != 3) { 225 if (rc != EOF && fgets(name, ARRAY_SIZE(name), in) == NULL) 226 fprintf(stderr, "Read error or end of file.\n"); 227 return NULL; 228 } 229 if (strlen(name) >= KSYM_NAME_LEN) { 230 fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n" 231 "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n", 232 name, strlen(name), KSYM_NAME_LEN); 233 return NULL; 234 } 235 236 if (strcmp(name, "_text") == 0) 237 _text = addr; 238 239 /* Ignore most absolute/undefined (?) symbols. */ 240 if (is_ignored_symbol(name, type)) 241 return NULL; 242 243 check_symbol_range(name, addr, text_ranges, ARRAY_SIZE(text_ranges)); 244 check_symbol_range(name, addr, &percpu_range, 1); 245 246 /* include the type field in the symbol name, so that it gets 247 * compressed together */ 248 249 len = strlen(name) + 1; 250 251 sym = malloc(sizeof(*sym) + len + 1); 252 if (!sym) { 253 fprintf(stderr, "kallsyms failure: " 254 "unable to allocate required amount of memory\n"); 255 exit(EXIT_FAILURE); 256 } 257 sym->addr = addr; 258 sym->len = len; 259 sym->sym[0] = type; 260 strcpy(sym_name(sym), name); 261 sym->percpu_absolute = 0; 262 263 return sym; 264 } 265 266 static int symbol_in_range(const struct sym_entry *s, 267 const struct addr_range *ranges, int entries) 268 { 269 size_t i; 270 const struct addr_range *ar; 271 272 for (i = 0; i < entries; ++i) { 273 ar = &ranges[i]; 274 275 if (s->addr >= ar->start && s->addr <= ar->end) 276 return 1; 277 } 278 279 return 0; 280 } 281 282 static int symbol_valid(const struct sym_entry *s) 283 { 284 const char *name = sym_name(s); 285 286 /* if --all-symbols is not specified, then symbols outside the text 287 * and inittext sections are discarded */ 288 if (!all_symbols) { 289 if (symbol_in_range(s, text_ranges, 290 ARRAY_SIZE(text_ranges)) == 0) 291 return 0; 292 /* Corner case. Discard any symbols with the same value as 293 * _etext _einittext; they can move between pass 1 and 2 when 294 * the kallsyms data are added. If these symbols move then 295 * they may get dropped in pass 2, which breaks the kallsyms 296 * rules. 297 */ 298 if ((s->addr == text_range_text->end && 299 strcmp(name, text_range_text->end_sym)) || 300 (s->addr == text_range_inittext->end && 301 strcmp(name, text_range_inittext->end_sym))) 302 return 0; 303 } 304 305 return 1; 306 } 307 308 /* remove all the invalid symbols from the table */ 309 static void shrink_table(void) 310 { 311 unsigned int i, pos; 312 313 pos = 0; 314 for (i = 0; i < table_cnt; i++) { 315 if (symbol_valid(table[i])) { 316 if (pos != i) 317 table[pos] = table[i]; 318 pos++; 319 } else { 320 free(table[i]); 321 } 322 } 323 table_cnt = pos; 324 325 /* When valid symbol is not registered, exit to error */ 326 if (!table_cnt) { 327 fprintf(stderr, "No valid symbol.\n"); 328 exit(1); 329 } 330 } 331 332 static void read_map(FILE *in) 333 { 334 struct sym_entry *sym; 335 336 while (!feof(in)) { 337 sym = read_symbol(in); 338 if (!sym) 339 continue; 340 341 sym->start_pos = table_cnt; 342 343 if (table_cnt >= table_size) { 344 table_size += 10000; 345 table = realloc(table, sizeof(*table) * table_size); 346 if (!table) { 347 fprintf(stderr, "out of memory\n"); 348 exit (1); 349 } 350 } 351 352 table[table_cnt++] = sym; 353 } 354 } 355 356 static void output_label(const char *label) 357 { 358 printf(".globl %s\n", label); 359 printf("\tALGN\n"); 360 printf("%s:\n", label); 361 } 362 363 /* Provide proper symbols relocatability by their '_text' relativeness. */ 364 static void output_address(unsigned long long addr) 365 { 366 if (_text <= addr) 367 printf("\tPTR\t_text + %#llx\n", addr - _text); 368 else 369 printf("\tPTR\t_text - %#llx\n", _text - addr); 370 } 371 372 /* uncompress a compressed symbol. When this function is called, the best table 373 * might still be compressed itself, so the function needs to be recursive */ 374 static int expand_symbol(const unsigned char *data, int len, char *result) 375 { 376 int c, rlen, total=0; 377 378 while (len) { 379 c = *data; 380 /* if the table holds a single char that is the same as the one 381 * we are looking for, then end the search */ 382 if (best_table[c][0]==c && best_table_len[c]==1) { 383 *result++ = c; 384 total++; 385 } else { 386 /* if not, recurse and expand */ 387 rlen = expand_symbol(best_table[c], best_table_len[c], result); 388 total += rlen; 389 result += rlen; 390 } 391 data++; 392 len--; 393 } 394 *result=0; 395 396 return total; 397 } 398 399 static int symbol_absolute(const struct sym_entry *s) 400 { 401 return s->percpu_absolute; 402 } 403 404 static void write_src(void) 405 { 406 unsigned int i, k, off; 407 unsigned int best_idx[256]; 408 unsigned int *markers; 409 char buf[KSYM_NAME_LEN]; 410 411 printf("#include <asm/bitsperlong.h>\n"); 412 printf("#if BITS_PER_LONG == 64\n"); 413 printf("#define PTR .quad\n"); 414 printf("#define ALGN .balign 8\n"); 415 printf("#else\n"); 416 printf("#define PTR .long\n"); 417 printf("#define ALGN .balign 4\n"); 418 printf("#endif\n"); 419 420 printf("\t.section .rodata, \"a\"\n"); 421 422 if (!base_relative) 423 output_label("kallsyms_addresses"); 424 else 425 output_label("kallsyms_offsets"); 426 427 for (i = 0; i < table_cnt; i++) { 428 if (base_relative) { 429 /* 430 * Use the offset relative to the lowest value 431 * encountered of all relative symbols, and emit 432 * non-relocatable fixed offsets that will be fixed 433 * up at runtime. 434 */ 435 436 long long offset; 437 int overflow; 438 439 if (!absolute_percpu) { 440 offset = table[i]->addr - relative_base; 441 overflow = (offset < 0 || offset > UINT_MAX); 442 } else if (symbol_absolute(table[i])) { 443 offset = table[i]->addr; 444 overflow = (offset < 0 || offset > INT_MAX); 445 } else { 446 offset = relative_base - table[i]->addr - 1; 447 overflow = (offset < INT_MIN || offset >= 0); 448 } 449 if (overflow) { 450 fprintf(stderr, "kallsyms failure: " 451 "%s symbol value %#llx out of range in relative mode\n", 452 symbol_absolute(table[i]) ? "absolute" : "relative", 453 table[i]->addr); 454 exit(EXIT_FAILURE); 455 } 456 printf("\t.long\t%#x\n", (int)offset); 457 } else if (!symbol_absolute(table[i])) { 458 output_address(table[i]->addr); 459 } else { 460 printf("\tPTR\t%#llx\n", table[i]->addr); 461 } 462 } 463 printf("\n"); 464 465 if (base_relative) { 466 output_label("kallsyms_relative_base"); 467 output_address(relative_base); 468 printf("\n"); 469 } 470 471 output_label("kallsyms_num_syms"); 472 printf("\t.long\t%u\n", table_cnt); 473 printf("\n"); 474 475 /* table of offset markers, that give the offset in the compressed stream 476 * every 256 symbols */ 477 markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256)); 478 if (!markers) { 479 fprintf(stderr, "kallsyms failure: " 480 "unable to allocate required memory\n"); 481 exit(EXIT_FAILURE); 482 } 483 484 output_label("kallsyms_names"); 485 off = 0; 486 for (i = 0; i < table_cnt; i++) { 487 if ((i & 0xFF) == 0) 488 markers[i >> 8] = off; 489 490 printf("\t.byte 0x%02x", table[i]->len); 491 for (k = 0; k < table[i]->len; k++) 492 printf(", 0x%02x", table[i]->sym[k]); 493 printf("\n"); 494 495 off += table[i]->len + 1; 496 } 497 printf("\n"); 498 499 output_label("kallsyms_markers"); 500 for (i = 0; i < ((table_cnt + 255) >> 8); i++) 501 printf("\t.long\t%u\n", markers[i]); 502 printf("\n"); 503 504 free(markers); 505 506 output_label("kallsyms_token_table"); 507 off = 0; 508 for (i = 0; i < 256; i++) { 509 best_idx[i] = off; 510 expand_symbol(best_table[i], best_table_len[i], buf); 511 printf("\t.asciz\t\"%s\"\n", buf); 512 off += strlen(buf) + 1; 513 } 514 printf("\n"); 515 516 output_label("kallsyms_token_index"); 517 for (i = 0; i < 256; i++) 518 printf("\t.short\t%d\n", best_idx[i]); 519 printf("\n"); 520 } 521 522 523 /* table lookup compression functions */ 524 525 /* count all the possible tokens in a symbol */ 526 static void learn_symbol(const unsigned char *symbol, int len) 527 { 528 int i; 529 530 for (i = 0; i < len - 1; i++) 531 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++; 532 } 533 534 /* decrease the count for all the possible tokens in a symbol */ 535 static void forget_symbol(const unsigned char *symbol, int len) 536 { 537 int i; 538 539 for (i = 0; i < len - 1; i++) 540 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--; 541 } 542 543 /* do the initial token count */ 544 static void build_initial_tok_table(void) 545 { 546 unsigned int i; 547 548 for (i = 0; i < table_cnt; i++) 549 learn_symbol(table[i]->sym, table[i]->len); 550 } 551 552 static unsigned char *find_token(unsigned char *str, int len, 553 const unsigned char *token) 554 { 555 int i; 556 557 for (i = 0; i < len - 1; i++) { 558 if (str[i] == token[0] && str[i+1] == token[1]) 559 return &str[i]; 560 } 561 return NULL; 562 } 563 564 /* replace a given token in all the valid symbols. Use the sampled symbols 565 * to update the counts */ 566 static void compress_symbols(const unsigned char *str, int idx) 567 { 568 unsigned int i, len, size; 569 unsigned char *p1, *p2; 570 571 for (i = 0; i < table_cnt; i++) { 572 573 len = table[i]->len; 574 p1 = table[i]->sym; 575 576 /* find the token on the symbol */ 577 p2 = find_token(p1, len, str); 578 if (!p2) continue; 579 580 /* decrease the counts for this symbol's tokens */ 581 forget_symbol(table[i]->sym, len); 582 583 size = len; 584 585 do { 586 *p2 = idx; 587 p2++; 588 size -= (p2 - p1); 589 memmove(p2, p2 + 1, size); 590 p1 = p2; 591 len--; 592 593 if (size < 2) break; 594 595 /* find the token on the symbol */ 596 p2 = find_token(p1, size, str); 597 598 } while (p2); 599 600 table[i]->len = len; 601 602 /* increase the counts for this symbol's new tokens */ 603 learn_symbol(table[i]->sym, len); 604 } 605 } 606 607 /* search the token with the maximum profit */ 608 static int find_best_token(void) 609 { 610 int i, best, bestprofit; 611 612 bestprofit=-10000; 613 best = 0; 614 615 for (i = 0; i < 0x10000; i++) { 616 if (token_profit[i] > bestprofit) { 617 best = i; 618 bestprofit = token_profit[i]; 619 } 620 } 621 return best; 622 } 623 624 /* this is the core of the algorithm: calculate the "best" table */ 625 static void optimize_result(void) 626 { 627 int i, best; 628 629 /* using the '\0' symbol last allows compress_symbols to use standard 630 * fast string functions */ 631 for (i = 255; i >= 0; i--) { 632 633 /* if this table slot is empty (it is not used by an actual 634 * original char code */ 635 if (!best_table_len[i]) { 636 637 /* find the token with the best profit value */ 638 best = find_best_token(); 639 if (token_profit[best] == 0) 640 break; 641 642 /* place it in the "best" table */ 643 best_table_len[i] = 2; 644 best_table[i][0] = best & 0xFF; 645 best_table[i][1] = (best >> 8) & 0xFF; 646 647 /* replace this token in all the valid symbols */ 648 compress_symbols(best_table[i], i); 649 } 650 } 651 } 652 653 /* start by placing the symbols that are actually used on the table */ 654 static void insert_real_symbols_in_table(void) 655 { 656 unsigned int i, j, c; 657 658 for (i = 0; i < table_cnt; i++) { 659 for (j = 0; j < table[i]->len; j++) { 660 c = table[i]->sym[j]; 661 best_table[c][0]=c; 662 best_table_len[c]=1; 663 } 664 } 665 } 666 667 static void optimize_token_table(void) 668 { 669 build_initial_tok_table(); 670 671 insert_real_symbols_in_table(); 672 673 optimize_result(); 674 } 675 676 /* guess for "linker script provide" symbol */ 677 static int may_be_linker_script_provide_symbol(const struct sym_entry *se) 678 { 679 const char *symbol = sym_name(se); 680 int len = se->len - 1; 681 682 if (len < 8) 683 return 0; 684 685 if (symbol[0] != '_' || symbol[1] != '_') 686 return 0; 687 688 /* __start_XXXXX */ 689 if (!memcmp(symbol + 2, "start_", 6)) 690 return 1; 691 692 /* __stop_XXXXX */ 693 if (!memcmp(symbol + 2, "stop_", 5)) 694 return 1; 695 696 /* __end_XXXXX */ 697 if (!memcmp(symbol + 2, "end_", 4)) 698 return 1; 699 700 /* __XXXXX_start */ 701 if (!memcmp(symbol + len - 6, "_start", 6)) 702 return 1; 703 704 /* __XXXXX_end */ 705 if (!memcmp(symbol + len - 4, "_end", 4)) 706 return 1; 707 708 return 0; 709 } 710 711 static int compare_symbols(const void *a, const void *b) 712 { 713 const struct sym_entry *sa = *(const struct sym_entry **)a; 714 const struct sym_entry *sb = *(const struct sym_entry **)b; 715 int wa, wb; 716 717 /* sort by address first */ 718 if (sa->addr > sb->addr) 719 return 1; 720 if (sa->addr < sb->addr) 721 return -1; 722 723 /* sort by "weakness" type */ 724 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W'); 725 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W'); 726 if (wa != wb) 727 return wa - wb; 728 729 /* sort by "linker script provide" type */ 730 wa = may_be_linker_script_provide_symbol(sa); 731 wb = may_be_linker_script_provide_symbol(sb); 732 if (wa != wb) 733 return wa - wb; 734 735 /* sort by the number of prefix underscores */ 736 wa = strspn(sym_name(sa), "_"); 737 wb = strspn(sym_name(sb), "_"); 738 if (wa != wb) 739 return wa - wb; 740 741 /* sort by initial order, so that other symbols are left undisturbed */ 742 return sa->start_pos - sb->start_pos; 743 } 744 745 static void sort_symbols(void) 746 { 747 qsort(table, table_cnt, sizeof(table[0]), compare_symbols); 748 } 749 750 static void make_percpus_absolute(void) 751 { 752 unsigned int i; 753 754 for (i = 0; i < table_cnt; i++) 755 if (symbol_in_range(table[i], &percpu_range, 1)) { 756 /* 757 * Keep the 'A' override for percpu symbols to 758 * ensure consistent behavior compared to older 759 * versions of this tool. 760 */ 761 table[i]->sym[0] = 'A'; 762 table[i]->percpu_absolute = 1; 763 } 764 } 765 766 /* find the minimum non-absolute symbol address */ 767 static void record_relative_base(void) 768 { 769 unsigned int i; 770 771 for (i = 0; i < table_cnt; i++) 772 if (!symbol_absolute(table[i])) { 773 /* 774 * The table is sorted by address. 775 * Take the first non-absolute symbol value. 776 */ 777 relative_base = table[i]->addr; 778 return; 779 } 780 } 781 782 int main(int argc, char **argv) 783 { 784 if (argc >= 2) { 785 int i; 786 for (i = 1; i < argc; i++) { 787 if(strcmp(argv[i], "--all-symbols") == 0) 788 all_symbols = 1; 789 else if (strcmp(argv[i], "--absolute-percpu") == 0) 790 absolute_percpu = 1; 791 else if (strcmp(argv[i], "--base-relative") == 0) 792 base_relative = 1; 793 else 794 usage(); 795 } 796 } else if (argc != 1) 797 usage(); 798 799 read_map(stdin); 800 shrink_table(); 801 if (absolute_percpu) 802 make_percpus_absolute(); 803 sort_symbols(); 804 if (base_relative) 805 record_relative_base(); 806 optimize_token_table(); 807 write_src(); 808 809 return 0; 810 } 811