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 <stdio.h> 22 #include <stdlib.h> 23 #include <string.h> 24 #include <ctype.h> 25 26 #define KSYM_NAME_LEN 128 27 28 struct sym_entry { 29 unsigned long long addr; 30 unsigned int len; 31 unsigned int start_pos; 32 unsigned char *sym; 33 }; 34 35 static struct sym_entry *table; 36 static unsigned int table_size, table_cnt; 37 static unsigned long long _text, _stext, _etext, _sinittext, _einittext; 38 static int all_symbols = 0; 39 static char symbol_prefix_char = '\0'; 40 41 int token_profit[0x10000]; 42 43 /* the table that holds the result of the compression */ 44 unsigned char best_table[256][2]; 45 unsigned char best_table_len[256]; 46 47 48 static void usage(void) 49 { 50 fprintf(stderr, "Usage: kallsyms [--all-symbols] [--symbol-prefix=<prefix char>] < in.map > out.S\n"); 51 exit(1); 52 } 53 54 /* 55 * This ignores the intensely annoying "mapping symbols" found 56 * in ARM ELF files: $a, $t and $d. 57 */ 58 static inline int is_arm_mapping_symbol(const char *str) 59 { 60 return str[0] == '$' && strchr("atd", str[1]) 61 && (str[2] == '\0' || str[2] == '.'); 62 } 63 64 static int read_symbol(FILE *in, struct sym_entry *s) 65 { 66 char str[500]; 67 char *sym, stype; 68 int rc; 69 70 rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str); 71 if (rc != 3) { 72 if (rc != EOF) { 73 /* skip line */ 74 fgets(str, 500, in); 75 } 76 return -1; 77 } 78 79 sym = str; 80 /* skip prefix char */ 81 if (symbol_prefix_char && str[0] == symbol_prefix_char) 82 sym++; 83 84 /* Ignore most absolute/undefined (?) symbols. */ 85 if (strcmp(sym, "_text") == 0) 86 _text = s->addr; 87 else if (strcmp(sym, "_stext") == 0) 88 _stext = s->addr; 89 else if (strcmp(sym, "_etext") == 0) 90 _etext = s->addr; 91 else if (strcmp(sym, "_sinittext") == 0) 92 _sinittext = s->addr; 93 else if (strcmp(sym, "_einittext") == 0) 94 _einittext = s->addr; 95 else if (toupper(stype) == 'A') 96 { 97 /* Keep these useful absolute symbols */ 98 if (strcmp(sym, "__kernel_syscall_via_break") && 99 strcmp(sym, "__kernel_syscall_via_epc") && 100 strcmp(sym, "__kernel_sigtramp") && 101 strcmp(sym, "__gp")) 102 return -1; 103 104 } 105 else if (toupper(stype) == 'U' || 106 is_arm_mapping_symbol(sym)) 107 return -1; 108 /* exclude also MIPS ELF local symbols ($L123 instead of .L123) */ 109 else if (str[0] == '$') 110 return -1; 111 112 /* include the type field in the symbol name, so that it gets 113 * compressed together */ 114 s->len = strlen(str) + 1; 115 s->sym = malloc(s->len + 1); 116 if (!s->sym) { 117 fprintf(stderr, "kallsyms failure: " 118 "unable to allocate required amount of memory\n"); 119 exit(EXIT_FAILURE); 120 } 121 strcpy((char *)s->sym + 1, str); 122 s->sym[0] = stype; 123 124 return 0; 125 } 126 127 static int symbol_valid(struct sym_entry *s) 128 { 129 /* Symbols which vary between passes. Passes 1 and 2 must have 130 * identical symbol lists. The kallsyms_* symbols below are only added 131 * after pass 1, they would be included in pass 2 when --all-symbols is 132 * specified so exclude them to get a stable symbol list. 133 */ 134 static char *special_symbols[] = { 135 "kallsyms_addresses", 136 "kallsyms_num_syms", 137 "kallsyms_names", 138 "kallsyms_markers", 139 "kallsyms_token_table", 140 "kallsyms_token_index", 141 142 /* Exclude linker generated symbols which vary between passes */ 143 "_SDA_BASE_", /* ppc */ 144 "_SDA2_BASE_", /* ppc */ 145 NULL }; 146 int i; 147 int offset = 1; 148 149 /* skip prefix char */ 150 if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char) 151 offset++; 152 153 /* if --all-symbols is not specified, then symbols outside the text 154 * and inittext sections are discarded */ 155 if (!all_symbols) { 156 if ((s->addr < _stext || s->addr > _etext) 157 && (s->addr < _sinittext || s->addr > _einittext)) 158 return 0; 159 /* Corner case. Discard any symbols with the same value as 160 * _etext _einittext; they can move between pass 1 and 2 when 161 * the kallsyms data are added. If these symbols move then 162 * they may get dropped in pass 2, which breaks the kallsyms 163 * rules. 164 */ 165 if ((s->addr == _etext && 166 strcmp((char *)s->sym + offset, "_etext")) || 167 (s->addr == _einittext && 168 strcmp((char *)s->sym + offset, "_einittext"))) 169 return 0; 170 } 171 172 /* Exclude symbols which vary between passes. */ 173 if (strstr((char *)s->sym + offset, "_compiled.")) 174 return 0; 175 176 for (i = 0; special_symbols[i]; i++) 177 if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 ) 178 return 0; 179 180 return 1; 181 } 182 183 static void read_map(FILE *in) 184 { 185 while (!feof(in)) { 186 if (table_cnt >= table_size) { 187 table_size += 10000; 188 table = realloc(table, sizeof(*table) * table_size); 189 if (!table) { 190 fprintf(stderr, "out of memory\n"); 191 exit (1); 192 } 193 } 194 if (read_symbol(in, &table[table_cnt]) == 0) { 195 table[table_cnt].start_pos = table_cnt; 196 table_cnt++; 197 } 198 } 199 } 200 201 static void output_label(char *label) 202 { 203 if (symbol_prefix_char) 204 printf(".globl %c%s\n", symbol_prefix_char, label); 205 else 206 printf(".globl %s\n", label); 207 printf("\tALGN\n"); 208 if (symbol_prefix_char) 209 printf("%c%s:\n", symbol_prefix_char, label); 210 else 211 printf("%s:\n", label); 212 } 213 214 /* uncompress a compressed symbol. When this function is called, the best table 215 * might still be compressed itself, so the function needs to be recursive */ 216 static int expand_symbol(unsigned char *data, int len, char *result) 217 { 218 int c, rlen, total=0; 219 220 while (len) { 221 c = *data; 222 /* if the table holds a single char that is the same as the one 223 * we are looking for, then end the search */ 224 if (best_table[c][0]==c && best_table_len[c]==1) { 225 *result++ = c; 226 total++; 227 } else { 228 /* if not, recurse and expand */ 229 rlen = expand_symbol(best_table[c], best_table_len[c], result); 230 total += rlen; 231 result += rlen; 232 } 233 data++; 234 len--; 235 } 236 *result=0; 237 238 return total; 239 } 240 241 static void write_src(void) 242 { 243 unsigned int i, k, off; 244 unsigned int best_idx[256]; 245 unsigned int *markers; 246 char buf[KSYM_NAME_LEN]; 247 248 printf("#include <asm/types.h>\n"); 249 printf("#if BITS_PER_LONG == 64\n"); 250 printf("#define PTR .quad\n"); 251 printf("#define ALGN .align 8\n"); 252 printf("#else\n"); 253 printf("#define PTR .long\n"); 254 printf("#define ALGN .align 4\n"); 255 printf("#endif\n"); 256 257 printf("\t.section .rodata, \"a\"\n"); 258 259 /* Provide proper symbols relocatability by their '_text' 260 * relativeness. The symbol names cannot be used to construct 261 * normal symbol references as the list of symbols contains 262 * symbols that are declared static and are private to their 263 * .o files. This prevents .tmp_kallsyms.o or any other 264 * object from referencing them. 265 */ 266 output_label("kallsyms_addresses"); 267 for (i = 0; i < table_cnt; i++) { 268 if (toupper(table[i].sym[0]) != 'A') { 269 if (_text <= table[i].addr) 270 printf("\tPTR\t_text + %#llx\n", 271 table[i].addr - _text); 272 else 273 printf("\tPTR\t_text - %#llx\n", 274 _text - table[i].addr); 275 } else { 276 printf("\tPTR\t%#llx\n", table[i].addr); 277 } 278 } 279 printf("\n"); 280 281 output_label("kallsyms_num_syms"); 282 printf("\tPTR\t%d\n", table_cnt); 283 printf("\n"); 284 285 /* table of offset markers, that give the offset in the compressed stream 286 * every 256 symbols */ 287 markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256)); 288 if (!markers) { 289 fprintf(stderr, "kallsyms failure: " 290 "unable to allocate required memory\n"); 291 exit(EXIT_FAILURE); 292 } 293 294 output_label("kallsyms_names"); 295 off = 0; 296 for (i = 0; i < table_cnt; i++) { 297 if ((i & 0xFF) == 0) 298 markers[i >> 8] = off; 299 300 printf("\t.byte 0x%02x", table[i].len); 301 for (k = 0; k < table[i].len; k++) 302 printf(", 0x%02x", table[i].sym[k]); 303 printf("\n"); 304 305 off += table[i].len + 1; 306 } 307 printf("\n"); 308 309 output_label("kallsyms_markers"); 310 for (i = 0; i < ((table_cnt + 255) >> 8); i++) 311 printf("\tPTR\t%d\n", markers[i]); 312 printf("\n"); 313 314 free(markers); 315 316 output_label("kallsyms_token_table"); 317 off = 0; 318 for (i = 0; i < 256; i++) { 319 best_idx[i] = off; 320 expand_symbol(best_table[i], best_table_len[i], buf); 321 printf("\t.asciz\t\"%s\"\n", buf); 322 off += strlen(buf) + 1; 323 } 324 printf("\n"); 325 326 output_label("kallsyms_token_index"); 327 for (i = 0; i < 256; i++) 328 printf("\t.short\t%d\n", best_idx[i]); 329 printf("\n"); 330 } 331 332 333 /* table lookup compression functions */ 334 335 /* count all the possible tokens in a symbol */ 336 static void learn_symbol(unsigned char *symbol, int len) 337 { 338 int i; 339 340 for (i = 0; i < len - 1; i++) 341 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++; 342 } 343 344 /* decrease the count for all the possible tokens in a symbol */ 345 static void forget_symbol(unsigned char *symbol, int len) 346 { 347 int i; 348 349 for (i = 0; i < len - 1; i++) 350 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--; 351 } 352 353 /* remove all the invalid symbols from the table and do the initial token count */ 354 static void build_initial_tok_table(void) 355 { 356 unsigned int i, pos; 357 358 pos = 0; 359 for (i = 0; i < table_cnt; i++) { 360 if ( symbol_valid(&table[i]) ) { 361 if (pos != i) 362 table[pos] = table[i]; 363 learn_symbol(table[pos].sym, table[pos].len); 364 pos++; 365 } 366 } 367 table_cnt = pos; 368 } 369 370 static void *find_token(unsigned char *str, int len, unsigned char *token) 371 { 372 int i; 373 374 for (i = 0; i < len - 1; i++) { 375 if (str[i] == token[0] && str[i+1] == token[1]) 376 return &str[i]; 377 } 378 return NULL; 379 } 380 381 /* replace a given token in all the valid symbols. Use the sampled symbols 382 * to update the counts */ 383 static void compress_symbols(unsigned char *str, int idx) 384 { 385 unsigned int i, len, size; 386 unsigned char *p1, *p2; 387 388 for (i = 0; i < table_cnt; i++) { 389 390 len = table[i].len; 391 p1 = table[i].sym; 392 393 /* find the token on the symbol */ 394 p2 = find_token(p1, len, str); 395 if (!p2) continue; 396 397 /* decrease the counts for this symbol's tokens */ 398 forget_symbol(table[i].sym, len); 399 400 size = len; 401 402 do { 403 *p2 = idx; 404 p2++; 405 size -= (p2 - p1); 406 memmove(p2, p2 + 1, size); 407 p1 = p2; 408 len--; 409 410 if (size < 2) break; 411 412 /* find the token on the symbol */ 413 p2 = find_token(p1, size, str); 414 415 } while (p2); 416 417 table[i].len = len; 418 419 /* increase the counts for this symbol's new tokens */ 420 learn_symbol(table[i].sym, len); 421 } 422 } 423 424 /* search the token with the maximum profit */ 425 static int find_best_token(void) 426 { 427 int i, best, bestprofit; 428 429 bestprofit=-10000; 430 best = 0; 431 432 for (i = 0; i < 0x10000; i++) { 433 if (token_profit[i] > bestprofit) { 434 best = i; 435 bestprofit = token_profit[i]; 436 } 437 } 438 return best; 439 } 440 441 /* this is the core of the algorithm: calculate the "best" table */ 442 static void optimize_result(void) 443 { 444 int i, best; 445 446 /* using the '\0' symbol last allows compress_symbols to use standard 447 * fast string functions */ 448 for (i = 255; i >= 0; i--) { 449 450 /* if this table slot is empty (it is not used by an actual 451 * original char code */ 452 if (!best_table_len[i]) { 453 454 /* find the token with the breates profit value */ 455 best = find_best_token(); 456 457 /* place it in the "best" table */ 458 best_table_len[i] = 2; 459 best_table[i][0] = best & 0xFF; 460 best_table[i][1] = (best >> 8) & 0xFF; 461 462 /* replace this token in all the valid symbols */ 463 compress_symbols(best_table[i], i); 464 } 465 } 466 } 467 468 /* start by placing the symbols that are actually used on the table */ 469 static void insert_real_symbols_in_table(void) 470 { 471 unsigned int i, j, c; 472 473 memset(best_table, 0, sizeof(best_table)); 474 memset(best_table_len, 0, sizeof(best_table_len)); 475 476 for (i = 0; i < table_cnt; i++) { 477 for (j = 0; j < table[i].len; j++) { 478 c = table[i].sym[j]; 479 best_table[c][0]=c; 480 best_table_len[c]=1; 481 } 482 } 483 } 484 485 static void optimize_token_table(void) 486 { 487 build_initial_tok_table(); 488 489 insert_real_symbols_in_table(); 490 491 /* When valid symbol is not registered, exit to error */ 492 if (!table_cnt) { 493 fprintf(stderr, "No valid symbol.\n"); 494 exit(1); 495 } 496 497 optimize_result(); 498 } 499 500 static int compare_symbols(const void *a, const void *b) 501 { 502 const struct sym_entry *sa; 503 const struct sym_entry *sb; 504 int wa, wb; 505 506 sa = a; 507 sb = b; 508 509 /* sort by address first */ 510 if (sa->addr > sb->addr) 511 return 1; 512 if (sa->addr < sb->addr) 513 return -1; 514 515 /* sort by "weakness" type */ 516 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W'); 517 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W'); 518 if (wa != wb) 519 return wa - wb; 520 521 /* sort by initial order, so that other symbols are left undisturbed */ 522 return sa->start_pos - sb->start_pos; 523 } 524 525 static void sort_symbols(void) 526 { 527 qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols); 528 } 529 530 int main(int argc, char **argv) 531 { 532 if (argc >= 2) { 533 int i; 534 for (i = 1; i < argc; i++) { 535 if(strcmp(argv[i], "--all-symbols") == 0) 536 all_symbols = 1; 537 else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) { 538 char *p = &argv[i][16]; 539 /* skip quote */ 540 if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\'')) 541 p++; 542 symbol_prefix_char = *p; 543 } else 544 usage(); 545 } 546 } else if (argc != 1) 547 usage(); 548 549 read_map(stdin); 550 sort_symbols(); 551 optimize_token_table(); 552 write_src(); 553 554 return 0; 555 } 556