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 KSYM_NAME_LEN 128 31 32 struct sym_entry { 33 unsigned long long addr; 34 unsigned int len; 35 unsigned int start_pos; 36 unsigned int percpu_absolute; 37 unsigned char sym[0]; 38 }; 39 40 struct addr_range { 41 const char *start_sym, *end_sym; 42 unsigned long long start, end; 43 }; 44 45 static unsigned long long _text; 46 static unsigned long long relative_base; 47 static struct addr_range text_ranges[] = { 48 { "_stext", "_etext" }, 49 { "_sinittext", "_einittext" }, 50 }; 51 #define text_range_text (&text_ranges[0]) 52 #define text_range_inittext (&text_ranges[1]) 53 54 static struct addr_range percpu_range = { 55 "__per_cpu_start", "__per_cpu_end", -1ULL, 0 56 }; 57 58 static struct sym_entry **table; 59 static unsigned int table_size, table_cnt; 60 static int all_symbols; 61 static int absolute_percpu; 62 static int base_relative; 63 64 static int token_profit[0x10000]; 65 66 /* the table that holds the result of the compression */ 67 static unsigned char best_table[256][2]; 68 static unsigned char best_table_len[256]; 69 70 71 static void usage(void) 72 { 73 fprintf(stderr, "Usage: kallsyms [--all-symbols] " 74 "[--base-relative] < in.map > out.S\n"); 75 exit(1); 76 } 77 78 static char *sym_name(const struct sym_entry *s) 79 { 80 return (char *)s->sym + 1; 81 } 82 83 static bool is_ignored_symbol(const char *name, char type) 84 { 85 static const char * const ignored_symbols[] = { 86 /* 87 * Symbols which vary between passes. Passes 1 and 2 must have 88 * identical symbol lists. The kallsyms_* symbols below are 89 * only added after pass 1, they would be included in pass 2 90 * when --all-symbols is specified so exclude them to get a 91 * stable symbol list. 92 */ 93 "kallsyms_addresses", 94 "kallsyms_offsets", 95 "kallsyms_relative_base", 96 "kallsyms_num_syms", 97 "kallsyms_names", 98 "kallsyms_markers", 99 "kallsyms_token_table", 100 "kallsyms_token_index", 101 /* Exclude linker generated symbols which vary between passes */ 102 "_SDA_BASE_", /* ppc */ 103 "_SDA2_BASE_", /* ppc */ 104 NULL 105 }; 106 107 static const char * const ignored_prefixes[] = { 108 "$", /* local symbols for ARM, MIPS, etc. */ 109 ".LASANPC", /* s390 kasan local symbols */ 110 "__crc_", /* modversions */ 111 "__efistub_", /* arm64 EFI stub namespace */ 112 NULL 113 }; 114 115 static const char * const ignored_suffixes[] = { 116 "_from_arm", /* arm */ 117 "_from_thumb", /* arm */ 118 "_veneer", /* arm */ 119 NULL 120 }; 121 122 const char * const *p; 123 124 /* Exclude symbols which vary between passes. */ 125 for (p = ignored_symbols; *p; p++) 126 if (!strcmp(name, *p)) 127 return true; 128 129 for (p = ignored_prefixes; *p; p++) 130 if (!strncmp(name, *p, strlen(*p))) 131 return true; 132 133 for (p = ignored_suffixes; *p; p++) { 134 int l = strlen(name) - strlen(*p); 135 136 if (l >= 0 && !strcmp(name + l, *p)) 137 return true; 138 } 139 140 if (type == 'U' || type == 'u') 141 return true; 142 /* exclude debugging symbols */ 143 if (type == 'N' || type == 'n') 144 return true; 145 146 if (toupper(type) == 'A') { 147 /* Keep these useful absolute symbols */ 148 if (strcmp(name, "__kernel_syscall_via_break") && 149 strcmp(name, "__kernel_syscall_via_epc") && 150 strcmp(name, "__kernel_sigtramp") && 151 strcmp(name, "__gp")) 152 return true; 153 } 154 155 return false; 156 } 157 158 static void check_symbol_range(const char *sym, unsigned long long addr, 159 struct addr_range *ranges, int entries) 160 { 161 size_t i; 162 struct addr_range *ar; 163 164 for (i = 0; i < entries; ++i) { 165 ar = &ranges[i]; 166 167 if (strcmp(sym, ar->start_sym) == 0) { 168 ar->start = addr; 169 return; 170 } else if (strcmp(sym, ar->end_sym) == 0) { 171 ar->end = addr; 172 return; 173 } 174 } 175 } 176 177 static struct sym_entry *read_symbol(FILE *in) 178 { 179 char name[500], type; 180 unsigned long long addr; 181 unsigned int len; 182 struct sym_entry *sym; 183 int rc; 184 185 rc = fscanf(in, "%llx %c %499s\n", &addr, &type, name); 186 if (rc != 3) { 187 if (rc != EOF && fgets(name, 500, in) == NULL) 188 fprintf(stderr, "Read error or end of file.\n"); 189 return NULL; 190 } 191 if (strlen(name) >= KSYM_NAME_LEN) { 192 fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n" 193 "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n", 194 name, strlen(name), KSYM_NAME_LEN); 195 return NULL; 196 } 197 198 if (strcmp(name, "_text") == 0) 199 _text = addr; 200 201 /* Ignore most absolute/undefined (?) symbols. */ 202 if (is_ignored_symbol(name, type)) 203 return NULL; 204 205 check_symbol_range(name, addr, text_ranges, ARRAY_SIZE(text_ranges)); 206 check_symbol_range(name, addr, &percpu_range, 1); 207 208 /* include the type field in the symbol name, so that it gets 209 * compressed together */ 210 211 len = strlen(name) + 1; 212 213 sym = malloc(sizeof(*sym) + len + 1); 214 if (!sym) { 215 fprintf(stderr, "kallsyms failure: " 216 "unable to allocate required amount of memory\n"); 217 exit(EXIT_FAILURE); 218 } 219 sym->addr = addr; 220 sym->len = len; 221 sym->sym[0] = type; 222 strcpy(sym_name(sym), name); 223 sym->percpu_absolute = 0; 224 225 return sym; 226 } 227 228 static int symbol_in_range(const struct sym_entry *s, 229 const struct addr_range *ranges, int entries) 230 { 231 size_t i; 232 const struct addr_range *ar; 233 234 for (i = 0; i < entries; ++i) { 235 ar = &ranges[i]; 236 237 if (s->addr >= ar->start && s->addr <= ar->end) 238 return 1; 239 } 240 241 return 0; 242 } 243 244 static int symbol_valid(const struct sym_entry *s) 245 { 246 const char *name = sym_name(s); 247 248 /* if --all-symbols is not specified, then symbols outside the text 249 * and inittext sections are discarded */ 250 if (!all_symbols) { 251 if (symbol_in_range(s, text_ranges, 252 ARRAY_SIZE(text_ranges)) == 0) 253 return 0; 254 /* Corner case. Discard any symbols with the same value as 255 * _etext _einittext; they can move between pass 1 and 2 when 256 * the kallsyms data are added. If these symbols move then 257 * they may get dropped in pass 2, which breaks the kallsyms 258 * rules. 259 */ 260 if ((s->addr == text_range_text->end && 261 strcmp(name, text_range_text->end_sym)) || 262 (s->addr == text_range_inittext->end && 263 strcmp(name, text_range_inittext->end_sym))) 264 return 0; 265 } 266 267 return 1; 268 } 269 270 /* remove all the invalid symbols from the table */ 271 static void shrink_table(void) 272 { 273 unsigned int i, pos; 274 275 pos = 0; 276 for (i = 0; i < table_cnt; i++) { 277 if (symbol_valid(table[i])) { 278 if (pos != i) 279 table[pos] = table[i]; 280 pos++; 281 } else { 282 free(table[i]); 283 } 284 } 285 table_cnt = pos; 286 287 /* When valid symbol is not registered, exit to error */ 288 if (!table_cnt) { 289 fprintf(stderr, "No valid symbol.\n"); 290 exit(1); 291 } 292 } 293 294 static void read_map(FILE *in) 295 { 296 struct sym_entry *sym; 297 298 while (!feof(in)) { 299 sym = read_symbol(in); 300 if (!sym) 301 continue; 302 303 sym->start_pos = table_cnt; 304 305 if (table_cnt >= table_size) { 306 table_size += 10000; 307 table = realloc(table, sizeof(*table) * table_size); 308 if (!table) { 309 fprintf(stderr, "out of memory\n"); 310 exit (1); 311 } 312 } 313 314 table[table_cnt++] = sym; 315 } 316 } 317 318 static void output_label(const char *label) 319 { 320 printf(".globl %s\n", label); 321 printf("\tALGN\n"); 322 printf("%s:\n", label); 323 } 324 325 /* Provide proper symbols relocatability by their '_text' relativeness. */ 326 static void output_address(unsigned long long addr) 327 { 328 if (_text <= addr) 329 printf("\tPTR\t_text + %#llx\n", addr - _text); 330 else 331 printf("\tPTR\t_text - %#llx\n", _text - addr); 332 } 333 334 /* uncompress a compressed symbol. When this function is called, the best table 335 * might still be compressed itself, so the function needs to be recursive */ 336 static int expand_symbol(const unsigned char *data, int len, char *result) 337 { 338 int c, rlen, total=0; 339 340 while (len) { 341 c = *data; 342 /* if the table holds a single char that is the same as the one 343 * we are looking for, then end the search */ 344 if (best_table[c][0]==c && best_table_len[c]==1) { 345 *result++ = c; 346 total++; 347 } else { 348 /* if not, recurse and expand */ 349 rlen = expand_symbol(best_table[c], best_table_len[c], result); 350 total += rlen; 351 result += rlen; 352 } 353 data++; 354 len--; 355 } 356 *result=0; 357 358 return total; 359 } 360 361 static int symbol_absolute(const struct sym_entry *s) 362 { 363 return s->percpu_absolute; 364 } 365 366 static void write_src(void) 367 { 368 unsigned int i, k, off; 369 unsigned int best_idx[256]; 370 unsigned int *markers; 371 char buf[KSYM_NAME_LEN]; 372 373 printf("#include <asm/bitsperlong.h>\n"); 374 printf("#if BITS_PER_LONG == 64\n"); 375 printf("#define PTR .quad\n"); 376 printf("#define ALGN .balign 8\n"); 377 printf("#else\n"); 378 printf("#define PTR .long\n"); 379 printf("#define ALGN .balign 4\n"); 380 printf("#endif\n"); 381 382 printf("\t.section .rodata, \"a\"\n"); 383 384 if (!base_relative) 385 output_label("kallsyms_addresses"); 386 else 387 output_label("kallsyms_offsets"); 388 389 for (i = 0; i < table_cnt; i++) { 390 if (base_relative) { 391 /* 392 * Use the offset relative to the lowest value 393 * encountered of all relative symbols, and emit 394 * non-relocatable fixed offsets that will be fixed 395 * up at runtime. 396 */ 397 398 long long offset; 399 int overflow; 400 401 if (!absolute_percpu) { 402 offset = table[i]->addr - relative_base; 403 overflow = (offset < 0 || offset > UINT_MAX); 404 } else if (symbol_absolute(table[i])) { 405 offset = table[i]->addr; 406 overflow = (offset < 0 || offset > INT_MAX); 407 } else { 408 offset = relative_base - table[i]->addr - 1; 409 overflow = (offset < INT_MIN || offset >= 0); 410 } 411 if (overflow) { 412 fprintf(stderr, "kallsyms failure: " 413 "%s symbol value %#llx out of range in relative mode\n", 414 symbol_absolute(table[i]) ? "absolute" : "relative", 415 table[i]->addr); 416 exit(EXIT_FAILURE); 417 } 418 printf("\t.long\t%#x\n", (int)offset); 419 } else if (!symbol_absolute(table[i])) { 420 output_address(table[i]->addr); 421 } else { 422 printf("\tPTR\t%#llx\n", table[i]->addr); 423 } 424 } 425 printf("\n"); 426 427 if (base_relative) { 428 output_label("kallsyms_relative_base"); 429 output_address(relative_base); 430 printf("\n"); 431 } 432 433 output_label("kallsyms_num_syms"); 434 printf("\t.long\t%u\n", table_cnt); 435 printf("\n"); 436 437 /* table of offset markers, that give the offset in the compressed stream 438 * every 256 symbols */ 439 markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256)); 440 if (!markers) { 441 fprintf(stderr, "kallsyms failure: " 442 "unable to allocate required memory\n"); 443 exit(EXIT_FAILURE); 444 } 445 446 output_label("kallsyms_names"); 447 off = 0; 448 for (i = 0; i < table_cnt; i++) { 449 if ((i & 0xFF) == 0) 450 markers[i >> 8] = off; 451 452 printf("\t.byte 0x%02x", table[i]->len); 453 for (k = 0; k < table[i]->len; k++) 454 printf(", 0x%02x", table[i]->sym[k]); 455 printf("\n"); 456 457 off += table[i]->len + 1; 458 } 459 printf("\n"); 460 461 output_label("kallsyms_markers"); 462 for (i = 0; i < ((table_cnt + 255) >> 8); i++) 463 printf("\t.long\t%u\n", markers[i]); 464 printf("\n"); 465 466 free(markers); 467 468 output_label("kallsyms_token_table"); 469 off = 0; 470 for (i = 0; i < 256; i++) { 471 best_idx[i] = off; 472 expand_symbol(best_table[i], best_table_len[i], buf); 473 printf("\t.asciz\t\"%s\"\n", buf); 474 off += strlen(buf) + 1; 475 } 476 printf("\n"); 477 478 output_label("kallsyms_token_index"); 479 for (i = 0; i < 256; i++) 480 printf("\t.short\t%d\n", best_idx[i]); 481 printf("\n"); 482 } 483 484 485 /* table lookup compression functions */ 486 487 /* count all the possible tokens in a symbol */ 488 static void learn_symbol(const unsigned char *symbol, int len) 489 { 490 int i; 491 492 for (i = 0; i < len - 1; i++) 493 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++; 494 } 495 496 /* decrease the count for all the possible tokens in a symbol */ 497 static void forget_symbol(const unsigned char *symbol, int len) 498 { 499 int i; 500 501 for (i = 0; i < len - 1; i++) 502 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--; 503 } 504 505 /* do the initial token count */ 506 static void build_initial_tok_table(void) 507 { 508 unsigned int i; 509 510 for (i = 0; i < table_cnt; i++) 511 learn_symbol(table[i]->sym, table[i]->len); 512 } 513 514 static unsigned char *find_token(unsigned char *str, int len, 515 const unsigned char *token) 516 { 517 int i; 518 519 for (i = 0; i < len - 1; i++) { 520 if (str[i] == token[0] && str[i+1] == token[1]) 521 return &str[i]; 522 } 523 return NULL; 524 } 525 526 /* replace a given token in all the valid symbols. Use the sampled symbols 527 * to update the counts */ 528 static void compress_symbols(const unsigned char *str, int idx) 529 { 530 unsigned int i, len, size; 531 unsigned char *p1, *p2; 532 533 for (i = 0; i < table_cnt; i++) { 534 535 len = table[i]->len; 536 p1 = table[i]->sym; 537 538 /* find the token on the symbol */ 539 p2 = find_token(p1, len, str); 540 if (!p2) continue; 541 542 /* decrease the counts for this symbol's tokens */ 543 forget_symbol(table[i]->sym, len); 544 545 size = len; 546 547 do { 548 *p2 = idx; 549 p2++; 550 size -= (p2 - p1); 551 memmove(p2, p2 + 1, size); 552 p1 = p2; 553 len--; 554 555 if (size < 2) break; 556 557 /* find the token on the symbol */ 558 p2 = find_token(p1, size, str); 559 560 } while (p2); 561 562 table[i]->len = len; 563 564 /* increase the counts for this symbol's new tokens */ 565 learn_symbol(table[i]->sym, len); 566 } 567 } 568 569 /* search the token with the maximum profit */ 570 static int find_best_token(void) 571 { 572 int i, best, bestprofit; 573 574 bestprofit=-10000; 575 best = 0; 576 577 for (i = 0; i < 0x10000; i++) { 578 if (token_profit[i] > bestprofit) { 579 best = i; 580 bestprofit = token_profit[i]; 581 } 582 } 583 return best; 584 } 585 586 /* this is the core of the algorithm: calculate the "best" table */ 587 static void optimize_result(void) 588 { 589 int i, best; 590 591 /* using the '\0' symbol last allows compress_symbols to use standard 592 * fast string functions */ 593 for (i = 255; i >= 0; i--) { 594 595 /* if this table slot is empty (it is not used by an actual 596 * original char code */ 597 if (!best_table_len[i]) { 598 599 /* find the token with the best profit value */ 600 best = find_best_token(); 601 if (token_profit[best] == 0) 602 break; 603 604 /* place it in the "best" table */ 605 best_table_len[i] = 2; 606 best_table[i][0] = best & 0xFF; 607 best_table[i][1] = (best >> 8) & 0xFF; 608 609 /* replace this token in all the valid symbols */ 610 compress_symbols(best_table[i], i); 611 } 612 } 613 } 614 615 /* start by placing the symbols that are actually used on the table */ 616 static void insert_real_symbols_in_table(void) 617 { 618 unsigned int i, j, c; 619 620 for (i = 0; i < table_cnt; i++) { 621 for (j = 0; j < table[i]->len; j++) { 622 c = table[i]->sym[j]; 623 best_table[c][0]=c; 624 best_table_len[c]=1; 625 } 626 } 627 } 628 629 static void optimize_token_table(void) 630 { 631 build_initial_tok_table(); 632 633 insert_real_symbols_in_table(); 634 635 optimize_result(); 636 } 637 638 /* guess for "linker script provide" symbol */ 639 static int may_be_linker_script_provide_symbol(const struct sym_entry *se) 640 { 641 const char *symbol = sym_name(se); 642 int len = se->len - 1; 643 644 if (len < 8) 645 return 0; 646 647 if (symbol[0] != '_' || symbol[1] != '_') 648 return 0; 649 650 /* __start_XXXXX */ 651 if (!memcmp(symbol + 2, "start_", 6)) 652 return 1; 653 654 /* __stop_XXXXX */ 655 if (!memcmp(symbol + 2, "stop_", 5)) 656 return 1; 657 658 /* __end_XXXXX */ 659 if (!memcmp(symbol + 2, "end_", 4)) 660 return 1; 661 662 /* __XXXXX_start */ 663 if (!memcmp(symbol + len - 6, "_start", 6)) 664 return 1; 665 666 /* __XXXXX_end */ 667 if (!memcmp(symbol + len - 4, "_end", 4)) 668 return 1; 669 670 return 0; 671 } 672 673 static int compare_symbols(const void *a, const void *b) 674 { 675 const struct sym_entry *sa = *(const struct sym_entry **)a; 676 const struct sym_entry *sb = *(const struct sym_entry **)b; 677 int wa, wb; 678 679 /* sort by address first */ 680 if (sa->addr > sb->addr) 681 return 1; 682 if (sa->addr < sb->addr) 683 return -1; 684 685 /* sort by "weakness" type */ 686 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W'); 687 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W'); 688 if (wa != wb) 689 return wa - wb; 690 691 /* sort by "linker script provide" type */ 692 wa = may_be_linker_script_provide_symbol(sa); 693 wb = may_be_linker_script_provide_symbol(sb); 694 if (wa != wb) 695 return wa - wb; 696 697 /* sort by the number of prefix underscores */ 698 wa = strspn(sym_name(sa), "_"); 699 wb = strspn(sym_name(sb), "_"); 700 if (wa != wb) 701 return wa - wb; 702 703 /* sort by initial order, so that other symbols are left undisturbed */ 704 return sa->start_pos - sb->start_pos; 705 } 706 707 static void sort_symbols(void) 708 { 709 qsort(table, table_cnt, sizeof(table[0]), compare_symbols); 710 } 711 712 static void make_percpus_absolute(void) 713 { 714 unsigned int i; 715 716 for (i = 0; i < table_cnt; i++) 717 if (symbol_in_range(table[i], &percpu_range, 1)) { 718 /* 719 * Keep the 'A' override for percpu symbols to 720 * ensure consistent behavior compared to older 721 * versions of this tool. 722 */ 723 table[i]->sym[0] = 'A'; 724 table[i]->percpu_absolute = 1; 725 } 726 } 727 728 /* find the minimum non-absolute symbol address */ 729 static void record_relative_base(void) 730 { 731 unsigned int i; 732 733 for (i = 0; i < table_cnt; i++) 734 if (!symbol_absolute(table[i])) { 735 /* 736 * The table is sorted by address. 737 * Take the first non-absolute symbol value. 738 */ 739 relative_base = table[i]->addr; 740 return; 741 } 742 } 743 744 int main(int argc, char **argv) 745 { 746 if (argc >= 2) { 747 int i; 748 for (i = 1; i < argc; i++) { 749 if(strcmp(argv[i], "--all-symbols") == 0) 750 all_symbols = 1; 751 else if (strcmp(argv[i], "--absolute-percpu") == 0) 752 absolute_percpu = 1; 753 else if (strcmp(argv[i], "--base-relative") == 0) 754 base_relative = 1; 755 else 756 usage(); 757 } 758 } else if (argc != 1) 759 usage(); 760 761 read_map(stdin); 762 shrink_table(); 763 if (absolute_percpu) 764 make_percpus_absolute(); 765 sort_symbols(); 766 if (base_relative) 767 record_relative_base(); 768 optimize_token_table(); 769 write_src(); 770 771 return 0; 772 } 773