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[]; 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 /* Symbol names that exactly match to the following are ignored.*/ 86 static const char * const ignored_symbols[] = { 87 /* 88 * Symbols which vary between passes. Passes 1 and 2 must have 89 * identical symbol lists. The kallsyms_* symbols below are 90 * only added after pass 1, they would be included in pass 2 91 * when --all-symbols is specified so exclude them to get a 92 * stable symbol list. 93 */ 94 "kallsyms_addresses", 95 "kallsyms_offsets", 96 "kallsyms_relative_base", 97 "kallsyms_num_syms", 98 "kallsyms_names", 99 "kallsyms_markers", 100 "kallsyms_token_table", 101 "kallsyms_token_index", 102 /* Exclude linker generated symbols which vary between passes */ 103 "_SDA_BASE_", /* ppc */ 104 "_SDA2_BASE_", /* ppc */ 105 NULL 106 }; 107 108 /* Symbol names that begin with the following are ignored.*/ 109 static const char * const ignored_prefixes[] = { 110 "$", /* local symbols for ARM, MIPS, etc. */ 111 ".LASANPC", /* s390 kasan local symbols */ 112 "__crc_", /* modversions */ 113 "__efistub_", /* arm64 EFI stub namespace */ 114 "__kvm_nvhe_", /* arm64 non-VHE KVM namespace */ 115 NULL 116 }; 117 118 /* Symbol names that end with the following are ignored.*/ 119 static const char * const ignored_suffixes[] = { 120 "_from_arm", /* arm */ 121 "_from_thumb", /* arm */ 122 "_veneer", /* arm */ 123 NULL 124 }; 125 126 /* Symbol names that contain the following are ignored.*/ 127 static const char * const ignored_matches[] = { 128 ".long_branch.", /* ppc stub */ 129 ".plt_branch.", /* ppc stub */ 130 NULL 131 }; 132 133 const char * const *p; 134 135 for (p = ignored_symbols; *p; p++) 136 if (!strcmp(name, *p)) 137 return true; 138 139 for (p = ignored_prefixes; *p; p++) 140 if (!strncmp(name, *p, strlen(*p))) 141 return true; 142 143 for (p = ignored_suffixes; *p; p++) { 144 int l = strlen(name) - strlen(*p); 145 146 if (l >= 0 && !strcmp(name + l, *p)) 147 return true; 148 } 149 150 for (p = ignored_matches; *p; p++) { 151 if (strstr(name, *p)) 152 return true; 153 } 154 155 if (type == 'U' || type == 'u') 156 return true; 157 /* exclude debugging symbols */ 158 if (type == 'N' || type == 'n') 159 return true; 160 161 if (toupper(type) == 'A') { 162 /* Keep these useful absolute symbols */ 163 if (strcmp(name, "__kernel_syscall_via_break") && 164 strcmp(name, "__kernel_syscall_via_epc") && 165 strcmp(name, "__kernel_sigtramp") && 166 strcmp(name, "__gp")) 167 return true; 168 } 169 170 return false; 171 } 172 173 static void check_symbol_range(const char *sym, unsigned long long addr, 174 struct addr_range *ranges, int entries) 175 { 176 size_t i; 177 struct addr_range *ar; 178 179 for (i = 0; i < entries; ++i) { 180 ar = &ranges[i]; 181 182 if (strcmp(sym, ar->start_sym) == 0) { 183 ar->start = addr; 184 return; 185 } else if (strcmp(sym, ar->end_sym) == 0) { 186 ar->end = addr; 187 return; 188 } 189 } 190 } 191 192 static struct sym_entry *read_symbol(FILE *in) 193 { 194 char name[500], type; 195 unsigned long long addr; 196 unsigned int len; 197 struct sym_entry *sym; 198 int rc; 199 200 rc = fscanf(in, "%llx %c %499s\n", &addr, &type, name); 201 if (rc != 3) { 202 if (rc != EOF && fgets(name, 500, in) == NULL) 203 fprintf(stderr, "Read error or end of file.\n"); 204 return NULL; 205 } 206 if (strlen(name) >= KSYM_NAME_LEN) { 207 fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n" 208 "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n", 209 name, strlen(name), KSYM_NAME_LEN); 210 return NULL; 211 } 212 213 if (strcmp(name, "_text") == 0) 214 _text = addr; 215 216 /* Ignore most absolute/undefined (?) symbols. */ 217 if (is_ignored_symbol(name, type)) 218 return NULL; 219 220 check_symbol_range(name, addr, text_ranges, ARRAY_SIZE(text_ranges)); 221 check_symbol_range(name, addr, &percpu_range, 1); 222 223 /* include the type field in the symbol name, so that it gets 224 * compressed together */ 225 226 len = strlen(name) + 1; 227 228 sym = malloc(sizeof(*sym) + len + 1); 229 if (!sym) { 230 fprintf(stderr, "kallsyms failure: " 231 "unable to allocate required amount of memory\n"); 232 exit(EXIT_FAILURE); 233 } 234 sym->addr = addr; 235 sym->len = len; 236 sym->sym[0] = type; 237 strcpy(sym_name(sym), name); 238 sym->percpu_absolute = 0; 239 240 return sym; 241 } 242 243 static int symbol_in_range(const struct sym_entry *s, 244 const struct addr_range *ranges, int entries) 245 { 246 size_t i; 247 const struct addr_range *ar; 248 249 for (i = 0; i < entries; ++i) { 250 ar = &ranges[i]; 251 252 if (s->addr >= ar->start && s->addr <= ar->end) 253 return 1; 254 } 255 256 return 0; 257 } 258 259 static int symbol_valid(const struct sym_entry *s) 260 { 261 const char *name = sym_name(s); 262 263 /* if --all-symbols is not specified, then symbols outside the text 264 * and inittext sections are discarded */ 265 if (!all_symbols) { 266 if (symbol_in_range(s, text_ranges, 267 ARRAY_SIZE(text_ranges)) == 0) 268 return 0; 269 /* Corner case. Discard any symbols with the same value as 270 * _etext _einittext; they can move between pass 1 and 2 when 271 * the kallsyms data are added. If these symbols move then 272 * they may get dropped in pass 2, which breaks the kallsyms 273 * rules. 274 */ 275 if ((s->addr == text_range_text->end && 276 strcmp(name, text_range_text->end_sym)) || 277 (s->addr == text_range_inittext->end && 278 strcmp(name, text_range_inittext->end_sym))) 279 return 0; 280 } 281 282 return 1; 283 } 284 285 /* remove all the invalid symbols from the table */ 286 static void shrink_table(void) 287 { 288 unsigned int i, pos; 289 290 pos = 0; 291 for (i = 0; i < table_cnt; i++) { 292 if (symbol_valid(table[i])) { 293 if (pos != i) 294 table[pos] = table[i]; 295 pos++; 296 } else { 297 free(table[i]); 298 } 299 } 300 table_cnt = pos; 301 302 /* When valid symbol is not registered, exit to error */ 303 if (!table_cnt) { 304 fprintf(stderr, "No valid symbol.\n"); 305 exit(1); 306 } 307 } 308 309 static void read_map(FILE *in) 310 { 311 struct sym_entry *sym; 312 313 while (!feof(in)) { 314 sym = read_symbol(in); 315 if (!sym) 316 continue; 317 318 sym->start_pos = table_cnt; 319 320 if (table_cnt >= table_size) { 321 table_size += 10000; 322 table = realloc(table, sizeof(*table) * table_size); 323 if (!table) { 324 fprintf(stderr, "out of memory\n"); 325 exit (1); 326 } 327 } 328 329 table[table_cnt++] = sym; 330 } 331 } 332 333 static void output_label(const char *label) 334 { 335 printf(".globl %s\n", label); 336 printf("\tALGN\n"); 337 printf("%s:\n", label); 338 } 339 340 /* Provide proper symbols relocatability by their '_text' relativeness. */ 341 static void output_address(unsigned long long addr) 342 { 343 if (_text <= addr) 344 printf("\tPTR\t_text + %#llx\n", addr - _text); 345 else 346 printf("\tPTR\t_text - %#llx\n", _text - addr); 347 } 348 349 /* uncompress a compressed symbol. When this function is called, the best table 350 * might still be compressed itself, so the function needs to be recursive */ 351 static int expand_symbol(const unsigned char *data, int len, char *result) 352 { 353 int c, rlen, total=0; 354 355 while (len) { 356 c = *data; 357 /* if the table holds a single char that is the same as the one 358 * we are looking for, then end the search */ 359 if (best_table[c][0]==c && best_table_len[c]==1) { 360 *result++ = c; 361 total++; 362 } else { 363 /* if not, recurse and expand */ 364 rlen = expand_symbol(best_table[c], best_table_len[c], result); 365 total += rlen; 366 result += rlen; 367 } 368 data++; 369 len--; 370 } 371 *result=0; 372 373 return total; 374 } 375 376 static int symbol_absolute(const struct sym_entry *s) 377 { 378 return s->percpu_absolute; 379 } 380 381 static void write_src(void) 382 { 383 unsigned int i, k, off; 384 unsigned int best_idx[256]; 385 unsigned int *markers; 386 char buf[KSYM_NAME_LEN]; 387 388 printf("#include <asm/bitsperlong.h>\n"); 389 printf("#if BITS_PER_LONG == 64\n"); 390 printf("#define PTR .quad\n"); 391 printf("#define ALGN .balign 8\n"); 392 printf("#else\n"); 393 printf("#define PTR .long\n"); 394 printf("#define ALGN .balign 4\n"); 395 printf("#endif\n"); 396 397 printf("\t.section .rodata, \"a\"\n"); 398 399 if (!base_relative) 400 output_label("kallsyms_addresses"); 401 else 402 output_label("kallsyms_offsets"); 403 404 for (i = 0; i < table_cnt; i++) { 405 if (base_relative) { 406 /* 407 * Use the offset relative to the lowest value 408 * encountered of all relative symbols, and emit 409 * non-relocatable fixed offsets that will be fixed 410 * up at runtime. 411 */ 412 413 long long offset; 414 int overflow; 415 416 if (!absolute_percpu) { 417 offset = table[i]->addr - relative_base; 418 overflow = (offset < 0 || offset > UINT_MAX); 419 } else if (symbol_absolute(table[i])) { 420 offset = table[i]->addr; 421 overflow = (offset < 0 || offset > INT_MAX); 422 } else { 423 offset = relative_base - table[i]->addr - 1; 424 overflow = (offset < INT_MIN || offset >= 0); 425 } 426 if (overflow) { 427 fprintf(stderr, "kallsyms failure: " 428 "%s symbol value %#llx out of range in relative mode\n", 429 symbol_absolute(table[i]) ? "absolute" : "relative", 430 table[i]->addr); 431 exit(EXIT_FAILURE); 432 } 433 printf("\t.long\t%#x\n", (int)offset); 434 } else if (!symbol_absolute(table[i])) { 435 output_address(table[i]->addr); 436 } else { 437 printf("\tPTR\t%#llx\n", table[i]->addr); 438 } 439 } 440 printf("\n"); 441 442 if (base_relative) { 443 output_label("kallsyms_relative_base"); 444 output_address(relative_base); 445 printf("\n"); 446 } 447 448 output_label("kallsyms_num_syms"); 449 printf("\t.long\t%u\n", table_cnt); 450 printf("\n"); 451 452 /* table of offset markers, that give the offset in the compressed stream 453 * every 256 symbols */ 454 markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256)); 455 if (!markers) { 456 fprintf(stderr, "kallsyms failure: " 457 "unable to allocate required memory\n"); 458 exit(EXIT_FAILURE); 459 } 460 461 output_label("kallsyms_names"); 462 off = 0; 463 for (i = 0; i < table_cnt; i++) { 464 if ((i & 0xFF) == 0) 465 markers[i >> 8] = off; 466 467 printf("\t.byte 0x%02x", table[i]->len); 468 for (k = 0; k < table[i]->len; k++) 469 printf(", 0x%02x", table[i]->sym[k]); 470 printf("\n"); 471 472 off += table[i]->len + 1; 473 } 474 printf("\n"); 475 476 output_label("kallsyms_markers"); 477 for (i = 0; i < ((table_cnt + 255) >> 8); i++) 478 printf("\t.long\t%u\n", markers[i]); 479 printf("\n"); 480 481 free(markers); 482 483 output_label("kallsyms_token_table"); 484 off = 0; 485 for (i = 0; i < 256; i++) { 486 best_idx[i] = off; 487 expand_symbol(best_table[i], best_table_len[i], buf); 488 printf("\t.asciz\t\"%s\"\n", buf); 489 off += strlen(buf) + 1; 490 } 491 printf("\n"); 492 493 output_label("kallsyms_token_index"); 494 for (i = 0; i < 256; i++) 495 printf("\t.short\t%d\n", best_idx[i]); 496 printf("\n"); 497 } 498 499 500 /* table lookup compression functions */ 501 502 /* count all the possible tokens in a symbol */ 503 static void learn_symbol(const unsigned char *symbol, int len) 504 { 505 int i; 506 507 for (i = 0; i < len - 1; i++) 508 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++; 509 } 510 511 /* decrease the count for all the possible tokens in a symbol */ 512 static void forget_symbol(const unsigned char *symbol, int len) 513 { 514 int i; 515 516 for (i = 0; i < len - 1; i++) 517 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--; 518 } 519 520 /* do the initial token count */ 521 static void build_initial_tok_table(void) 522 { 523 unsigned int i; 524 525 for (i = 0; i < table_cnt; i++) 526 learn_symbol(table[i]->sym, table[i]->len); 527 } 528 529 static unsigned char *find_token(unsigned char *str, int len, 530 const unsigned char *token) 531 { 532 int i; 533 534 for (i = 0; i < len - 1; i++) { 535 if (str[i] == token[0] && str[i+1] == token[1]) 536 return &str[i]; 537 } 538 return NULL; 539 } 540 541 /* replace a given token in all the valid symbols. Use the sampled symbols 542 * to update the counts */ 543 static void compress_symbols(const unsigned char *str, int idx) 544 { 545 unsigned int i, len, size; 546 unsigned char *p1, *p2; 547 548 for (i = 0; i < table_cnt; i++) { 549 550 len = table[i]->len; 551 p1 = table[i]->sym; 552 553 /* find the token on the symbol */ 554 p2 = find_token(p1, len, str); 555 if (!p2) continue; 556 557 /* decrease the counts for this symbol's tokens */ 558 forget_symbol(table[i]->sym, len); 559 560 size = len; 561 562 do { 563 *p2 = idx; 564 p2++; 565 size -= (p2 - p1); 566 memmove(p2, p2 + 1, size); 567 p1 = p2; 568 len--; 569 570 if (size < 2) break; 571 572 /* find the token on the symbol */ 573 p2 = find_token(p1, size, str); 574 575 } while (p2); 576 577 table[i]->len = len; 578 579 /* increase the counts for this symbol's new tokens */ 580 learn_symbol(table[i]->sym, len); 581 } 582 } 583 584 /* search the token with the maximum profit */ 585 static int find_best_token(void) 586 { 587 int i, best, bestprofit; 588 589 bestprofit=-10000; 590 best = 0; 591 592 for (i = 0; i < 0x10000; i++) { 593 if (token_profit[i] > bestprofit) { 594 best = i; 595 bestprofit = token_profit[i]; 596 } 597 } 598 return best; 599 } 600 601 /* this is the core of the algorithm: calculate the "best" table */ 602 static void optimize_result(void) 603 { 604 int i, best; 605 606 /* using the '\0' symbol last allows compress_symbols to use standard 607 * fast string functions */ 608 for (i = 255; i >= 0; i--) { 609 610 /* if this table slot is empty (it is not used by an actual 611 * original char code */ 612 if (!best_table_len[i]) { 613 614 /* find the token with the best profit value */ 615 best = find_best_token(); 616 if (token_profit[best] == 0) 617 break; 618 619 /* place it in the "best" table */ 620 best_table_len[i] = 2; 621 best_table[i][0] = best & 0xFF; 622 best_table[i][1] = (best >> 8) & 0xFF; 623 624 /* replace this token in all the valid symbols */ 625 compress_symbols(best_table[i], i); 626 } 627 } 628 } 629 630 /* start by placing the symbols that are actually used on the table */ 631 static void insert_real_symbols_in_table(void) 632 { 633 unsigned int i, j, c; 634 635 for (i = 0; i < table_cnt; i++) { 636 for (j = 0; j < table[i]->len; j++) { 637 c = table[i]->sym[j]; 638 best_table[c][0]=c; 639 best_table_len[c]=1; 640 } 641 } 642 } 643 644 static void optimize_token_table(void) 645 { 646 build_initial_tok_table(); 647 648 insert_real_symbols_in_table(); 649 650 optimize_result(); 651 } 652 653 /* guess for "linker script provide" symbol */ 654 static int may_be_linker_script_provide_symbol(const struct sym_entry *se) 655 { 656 const char *symbol = sym_name(se); 657 int len = se->len - 1; 658 659 if (len < 8) 660 return 0; 661 662 if (symbol[0] != '_' || symbol[1] != '_') 663 return 0; 664 665 /* __start_XXXXX */ 666 if (!memcmp(symbol + 2, "start_", 6)) 667 return 1; 668 669 /* __stop_XXXXX */ 670 if (!memcmp(symbol + 2, "stop_", 5)) 671 return 1; 672 673 /* __end_XXXXX */ 674 if (!memcmp(symbol + 2, "end_", 4)) 675 return 1; 676 677 /* __XXXXX_start */ 678 if (!memcmp(symbol + len - 6, "_start", 6)) 679 return 1; 680 681 /* __XXXXX_end */ 682 if (!memcmp(symbol + len - 4, "_end", 4)) 683 return 1; 684 685 return 0; 686 } 687 688 static int compare_symbols(const void *a, const void *b) 689 { 690 const struct sym_entry *sa = *(const struct sym_entry **)a; 691 const struct sym_entry *sb = *(const struct sym_entry **)b; 692 int wa, wb; 693 694 /* sort by address first */ 695 if (sa->addr > sb->addr) 696 return 1; 697 if (sa->addr < sb->addr) 698 return -1; 699 700 /* sort by "weakness" type */ 701 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W'); 702 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W'); 703 if (wa != wb) 704 return wa - wb; 705 706 /* sort by "linker script provide" type */ 707 wa = may_be_linker_script_provide_symbol(sa); 708 wb = may_be_linker_script_provide_symbol(sb); 709 if (wa != wb) 710 return wa - wb; 711 712 /* sort by the number of prefix underscores */ 713 wa = strspn(sym_name(sa), "_"); 714 wb = strspn(sym_name(sb), "_"); 715 if (wa != wb) 716 return wa - wb; 717 718 /* sort by initial order, so that other symbols are left undisturbed */ 719 return sa->start_pos - sb->start_pos; 720 } 721 722 static void sort_symbols(void) 723 { 724 qsort(table, table_cnt, sizeof(table[0]), compare_symbols); 725 } 726 727 static void make_percpus_absolute(void) 728 { 729 unsigned int i; 730 731 for (i = 0; i < table_cnt; i++) 732 if (symbol_in_range(table[i], &percpu_range, 1)) { 733 /* 734 * Keep the 'A' override for percpu symbols to 735 * ensure consistent behavior compared to older 736 * versions of this tool. 737 */ 738 table[i]->sym[0] = 'A'; 739 table[i]->percpu_absolute = 1; 740 } 741 } 742 743 /* find the minimum non-absolute symbol address */ 744 static void record_relative_base(void) 745 { 746 unsigned int i; 747 748 for (i = 0; i < table_cnt; i++) 749 if (!symbol_absolute(table[i])) { 750 /* 751 * The table is sorted by address. 752 * Take the first non-absolute symbol value. 753 */ 754 relative_base = table[i]->addr; 755 return; 756 } 757 } 758 759 int main(int argc, char **argv) 760 { 761 if (argc >= 2) { 762 int i; 763 for (i = 1; i < argc; i++) { 764 if(strcmp(argv[i], "--all-symbols") == 0) 765 all_symbols = 1; 766 else if (strcmp(argv[i], "--absolute-percpu") == 0) 767 absolute_percpu = 1; 768 else if (strcmp(argv[i], "--base-relative") == 0) 769 base_relative = 1; 770 else 771 usage(); 772 } 773 } else if (argc != 1) 774 usage(); 775 776 read_map(stdin); 777 shrink_table(); 778 if (absolute_percpu) 779 make_percpus_absolute(); 780 sort_symbols(); 781 if (base_relative) 782 record_relative_base(); 783 optimize_token_table(); 784 write_src(); 785 786 return 0; 787 } 788