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 /* exclude debugging symbols */ 112 else if (stype == 'N') 113 return -1; 114 115 /* include the type field in the symbol name, so that it gets 116 * compressed together */ 117 s->len = strlen(str) + 1; 118 s->sym = malloc(s->len + 1); 119 if (!s->sym) { 120 fprintf(stderr, "kallsyms failure: " 121 "unable to allocate required amount of memory\n"); 122 exit(EXIT_FAILURE); 123 } 124 strcpy((char *)s->sym + 1, str); 125 s->sym[0] = stype; 126 127 return 0; 128 } 129 130 static int symbol_valid(struct sym_entry *s) 131 { 132 /* Symbols which vary between passes. Passes 1 and 2 must have 133 * identical symbol lists. The kallsyms_* symbols below are only added 134 * after pass 1, they would be included in pass 2 when --all-symbols is 135 * specified so exclude them to get a stable symbol list. 136 */ 137 static char *special_symbols[] = { 138 "kallsyms_addresses", 139 "kallsyms_num_syms", 140 "kallsyms_names", 141 "kallsyms_markers", 142 "kallsyms_token_table", 143 "kallsyms_token_index", 144 145 /* Exclude linker generated symbols which vary between passes */ 146 "_SDA_BASE_", /* ppc */ 147 "_SDA2_BASE_", /* ppc */ 148 NULL }; 149 int i; 150 int offset = 1; 151 152 /* skip prefix char */ 153 if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char) 154 offset++; 155 156 /* if --all-symbols is not specified, then symbols outside the text 157 * and inittext sections are discarded */ 158 if (!all_symbols) { 159 if ((s->addr < _stext || s->addr > _etext) 160 && (s->addr < _sinittext || s->addr > _einittext)) 161 return 0; 162 /* Corner case. Discard any symbols with the same value as 163 * _etext _einittext; they can move between pass 1 and 2 when 164 * the kallsyms data are added. If these symbols move then 165 * they may get dropped in pass 2, which breaks the kallsyms 166 * rules. 167 */ 168 if ((s->addr == _etext && 169 strcmp((char *)s->sym + offset, "_etext")) || 170 (s->addr == _einittext && 171 strcmp((char *)s->sym + offset, "_einittext"))) 172 return 0; 173 } 174 175 /* Exclude symbols which vary between passes. */ 176 if (strstr((char *)s->sym + offset, "_compiled.")) 177 return 0; 178 179 for (i = 0; special_symbols[i]; i++) 180 if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 ) 181 return 0; 182 183 return 1; 184 } 185 186 static void read_map(FILE *in) 187 { 188 while (!feof(in)) { 189 if (table_cnt >= table_size) { 190 table_size += 10000; 191 table = realloc(table, sizeof(*table) * table_size); 192 if (!table) { 193 fprintf(stderr, "out of memory\n"); 194 exit (1); 195 } 196 } 197 if (read_symbol(in, &table[table_cnt]) == 0) { 198 table[table_cnt].start_pos = table_cnt; 199 table_cnt++; 200 } 201 } 202 } 203 204 static void output_label(char *label) 205 { 206 if (symbol_prefix_char) 207 printf(".globl %c%s\n", symbol_prefix_char, label); 208 else 209 printf(".globl %s\n", label); 210 printf("\tALGN\n"); 211 if (symbol_prefix_char) 212 printf("%c%s:\n", symbol_prefix_char, label); 213 else 214 printf("%s:\n", label); 215 } 216 217 /* uncompress a compressed symbol. When this function is called, the best table 218 * might still be compressed itself, so the function needs to be recursive */ 219 static int expand_symbol(unsigned char *data, int len, char *result) 220 { 221 int c, rlen, total=0; 222 223 while (len) { 224 c = *data; 225 /* if the table holds a single char that is the same as the one 226 * we are looking for, then end the search */ 227 if (best_table[c][0]==c && best_table_len[c]==1) { 228 *result++ = c; 229 total++; 230 } else { 231 /* if not, recurse and expand */ 232 rlen = expand_symbol(best_table[c], best_table_len[c], result); 233 total += rlen; 234 result += rlen; 235 } 236 data++; 237 len--; 238 } 239 *result=0; 240 241 return total; 242 } 243 244 static void write_src(void) 245 { 246 unsigned int i, k, off; 247 unsigned int best_idx[256]; 248 unsigned int *markers; 249 char buf[KSYM_NAME_LEN]; 250 251 printf("#include <asm/types.h>\n"); 252 printf("#if BITS_PER_LONG == 64\n"); 253 printf("#define PTR .quad\n"); 254 printf("#define ALGN .align 8\n"); 255 printf("#else\n"); 256 printf("#define PTR .long\n"); 257 printf("#define ALGN .align 4\n"); 258 printf("#endif\n"); 259 260 printf("\t.section .rodata, \"a\"\n"); 261 262 /* Provide proper symbols relocatability by their '_text' 263 * relativeness. The symbol names cannot be used to construct 264 * normal symbol references as the list of symbols contains 265 * symbols that are declared static and are private to their 266 * .o files. This prevents .tmp_kallsyms.o or any other 267 * object from referencing them. 268 */ 269 output_label("kallsyms_addresses"); 270 for (i = 0; i < table_cnt; i++) { 271 if (toupper(table[i].sym[0]) != 'A') { 272 if (_text <= table[i].addr) 273 printf("\tPTR\t_text + %#llx\n", 274 table[i].addr - _text); 275 else 276 printf("\tPTR\t_text - %#llx\n", 277 _text - table[i].addr); 278 } else { 279 printf("\tPTR\t%#llx\n", table[i].addr); 280 } 281 } 282 printf("\n"); 283 284 output_label("kallsyms_num_syms"); 285 printf("\tPTR\t%d\n", table_cnt); 286 printf("\n"); 287 288 /* table of offset markers, that give the offset in the compressed stream 289 * every 256 symbols */ 290 markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256)); 291 if (!markers) { 292 fprintf(stderr, "kallsyms failure: " 293 "unable to allocate required memory\n"); 294 exit(EXIT_FAILURE); 295 } 296 297 output_label("kallsyms_names"); 298 off = 0; 299 for (i = 0; i < table_cnt; i++) { 300 if ((i & 0xFF) == 0) 301 markers[i >> 8] = off; 302 303 printf("\t.byte 0x%02x", table[i].len); 304 for (k = 0; k < table[i].len; k++) 305 printf(", 0x%02x", table[i].sym[k]); 306 printf("\n"); 307 308 off += table[i].len + 1; 309 } 310 printf("\n"); 311 312 output_label("kallsyms_markers"); 313 for (i = 0; i < ((table_cnt + 255) >> 8); i++) 314 printf("\tPTR\t%d\n", markers[i]); 315 printf("\n"); 316 317 free(markers); 318 319 output_label("kallsyms_token_table"); 320 off = 0; 321 for (i = 0; i < 256; i++) { 322 best_idx[i] = off; 323 expand_symbol(best_table[i], best_table_len[i], buf); 324 printf("\t.asciz\t\"%s\"\n", buf); 325 off += strlen(buf) + 1; 326 } 327 printf("\n"); 328 329 output_label("kallsyms_token_index"); 330 for (i = 0; i < 256; i++) 331 printf("\t.short\t%d\n", best_idx[i]); 332 printf("\n"); 333 } 334 335 336 /* table lookup compression functions */ 337 338 /* count all the possible tokens in a symbol */ 339 static void learn_symbol(unsigned char *symbol, int len) 340 { 341 int i; 342 343 for (i = 0; i < len - 1; i++) 344 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++; 345 } 346 347 /* decrease the count for all the possible tokens in a symbol */ 348 static void forget_symbol(unsigned char *symbol, int len) 349 { 350 int i; 351 352 for (i = 0; i < len - 1; i++) 353 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--; 354 } 355 356 /* remove all the invalid symbols from the table and do the initial token count */ 357 static void build_initial_tok_table(void) 358 { 359 unsigned int i, pos; 360 361 pos = 0; 362 for (i = 0; i < table_cnt; i++) { 363 if ( symbol_valid(&table[i]) ) { 364 if (pos != i) 365 table[pos] = table[i]; 366 learn_symbol(table[pos].sym, table[pos].len); 367 pos++; 368 } 369 } 370 table_cnt = pos; 371 } 372 373 static void *find_token(unsigned char *str, int len, unsigned char *token) 374 { 375 int i; 376 377 for (i = 0; i < len - 1; i++) { 378 if (str[i] == token[0] && str[i+1] == token[1]) 379 return &str[i]; 380 } 381 return NULL; 382 } 383 384 /* replace a given token in all the valid symbols. Use the sampled symbols 385 * to update the counts */ 386 static void compress_symbols(unsigned char *str, int idx) 387 { 388 unsigned int i, len, size; 389 unsigned char *p1, *p2; 390 391 for (i = 0; i < table_cnt; i++) { 392 393 len = table[i].len; 394 p1 = table[i].sym; 395 396 /* find the token on the symbol */ 397 p2 = find_token(p1, len, str); 398 if (!p2) continue; 399 400 /* decrease the counts for this symbol's tokens */ 401 forget_symbol(table[i].sym, len); 402 403 size = len; 404 405 do { 406 *p2 = idx; 407 p2++; 408 size -= (p2 - p1); 409 memmove(p2, p2 + 1, size); 410 p1 = p2; 411 len--; 412 413 if (size < 2) break; 414 415 /* find the token on the symbol */ 416 p2 = find_token(p1, size, str); 417 418 } while (p2); 419 420 table[i].len = len; 421 422 /* increase the counts for this symbol's new tokens */ 423 learn_symbol(table[i].sym, len); 424 } 425 } 426 427 /* search the token with the maximum profit */ 428 static int find_best_token(void) 429 { 430 int i, best, bestprofit; 431 432 bestprofit=-10000; 433 best = 0; 434 435 for (i = 0; i < 0x10000; i++) { 436 if (token_profit[i] > bestprofit) { 437 best = i; 438 bestprofit = token_profit[i]; 439 } 440 } 441 return best; 442 } 443 444 /* this is the core of the algorithm: calculate the "best" table */ 445 static void optimize_result(void) 446 { 447 int i, best; 448 449 /* using the '\0' symbol last allows compress_symbols to use standard 450 * fast string functions */ 451 for (i = 255; i >= 0; i--) { 452 453 /* if this table slot is empty (it is not used by an actual 454 * original char code */ 455 if (!best_table_len[i]) { 456 457 /* find the token with the breates profit value */ 458 best = find_best_token(); 459 460 /* place it in the "best" table */ 461 best_table_len[i] = 2; 462 best_table[i][0] = best & 0xFF; 463 best_table[i][1] = (best >> 8) & 0xFF; 464 465 /* replace this token in all the valid symbols */ 466 compress_symbols(best_table[i], i); 467 } 468 } 469 } 470 471 /* start by placing the symbols that are actually used on the table */ 472 static void insert_real_symbols_in_table(void) 473 { 474 unsigned int i, j, c; 475 476 memset(best_table, 0, sizeof(best_table)); 477 memset(best_table_len, 0, sizeof(best_table_len)); 478 479 for (i = 0; i < table_cnt; i++) { 480 for (j = 0; j < table[i].len; j++) { 481 c = table[i].sym[j]; 482 best_table[c][0]=c; 483 best_table_len[c]=1; 484 } 485 } 486 } 487 488 static void optimize_token_table(void) 489 { 490 build_initial_tok_table(); 491 492 insert_real_symbols_in_table(); 493 494 /* When valid symbol is not registered, exit to error */ 495 if (!table_cnt) { 496 fprintf(stderr, "No valid symbol.\n"); 497 exit(1); 498 } 499 500 optimize_result(); 501 } 502 503 static int compare_symbols(const void *a, const void *b) 504 { 505 const struct sym_entry *sa; 506 const struct sym_entry *sb; 507 int wa, wb; 508 509 sa = a; 510 sb = b; 511 512 /* sort by address first */ 513 if (sa->addr > sb->addr) 514 return 1; 515 if (sa->addr < sb->addr) 516 return -1; 517 518 /* sort by "weakness" type */ 519 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W'); 520 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W'); 521 if (wa != wb) 522 return wa - wb; 523 524 /* sort by initial order, so that other symbols are left undisturbed */ 525 return sa->start_pos - sb->start_pos; 526 } 527 528 static void sort_symbols(void) 529 { 530 qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols); 531 } 532 533 int main(int argc, char **argv) 534 { 535 if (argc >= 2) { 536 int i; 537 for (i = 1; i < argc; i++) { 538 if(strcmp(argv[i], "--all-symbols") == 0) 539 all_symbols = 1; 540 else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) { 541 char *p = &argv[i][16]; 542 /* skip quote */ 543 if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\'')) 544 p++; 545 symbol_prefix_char = *p; 546 } else 547 usage(); 548 } 549 } else if (argc != 1) 550 usage(); 551 552 read_map(stdin); 553 sort_symbols(); 554 optimize_token_table(); 555 write_src(); 556 557 return 0; 558 } 559