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. 134 */ 135 static char *special_symbols[] = { 136 /* Exclude linker generated symbols which vary between passes */ 137 "_SDA_BASE_", /* ppc */ 138 "_SDA2_BASE_", /* ppc */ 139 NULL }; 140 int i; 141 int offset = 1; 142 143 /* skip prefix char */ 144 if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char) 145 offset++; 146 147 /* if --all-symbols is not specified, then symbols outside the text 148 * and inittext sections are discarded */ 149 if (!all_symbols) { 150 if ((s->addr < _stext || s->addr > _etext) 151 && (s->addr < _sinittext || s->addr > _einittext)) 152 return 0; 153 /* Corner case. Discard any symbols with the same value as 154 * _etext _einittext; they can move between pass 1 and 2 when 155 * the kallsyms data are added. If these symbols move then 156 * they may get dropped in pass 2, which breaks the kallsyms 157 * rules. 158 */ 159 if ((s->addr == _etext && 160 strcmp((char *)s->sym + offset, "_etext")) || 161 (s->addr == _einittext && 162 strcmp((char *)s->sym + offset, "_einittext"))) 163 return 0; 164 } 165 166 /* Exclude symbols which vary between passes. */ 167 if (strstr((char *)s->sym + offset, "_compiled.") || 168 strncmp((char*)s->sym + offset, "__compound_literal.", 19) == 0 || 169 strncmp((char*)s->sym + offset, "__compound_literal$", 19) == 0) 170 return 0; 171 172 for (i = 0; special_symbols[i]; i++) 173 if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 ) 174 return 0; 175 176 return 1; 177 } 178 179 static void read_map(FILE *in) 180 { 181 while (!feof(in)) { 182 if (table_cnt >= table_size) { 183 table_size += 10000; 184 table = realloc(table, sizeof(*table) * table_size); 185 if (!table) { 186 fprintf(stderr, "out of memory\n"); 187 exit (1); 188 } 189 } 190 if (read_symbol(in, &table[table_cnt]) == 0) { 191 table[table_cnt].start_pos = table_cnt; 192 table_cnt++; 193 } 194 } 195 } 196 197 static void output_label(char *label) 198 { 199 if (symbol_prefix_char) 200 printf(".globl %c%s\n", symbol_prefix_char, label); 201 else 202 printf(".globl %s\n", label); 203 printf("\tALGN\n"); 204 if (symbol_prefix_char) 205 printf("%c%s:\n", symbol_prefix_char, label); 206 else 207 printf("%s:\n", label); 208 } 209 210 /* uncompress a compressed symbol. When this function is called, the best table 211 * might still be compressed itself, so the function needs to be recursive */ 212 static int expand_symbol(unsigned char *data, int len, char *result) 213 { 214 int c, rlen, total=0; 215 216 while (len) { 217 c = *data; 218 /* if the table holds a single char that is the same as the one 219 * we are looking for, then end the search */ 220 if (best_table[c][0]==c && best_table_len[c]==1) { 221 *result++ = c; 222 total++; 223 } else { 224 /* if not, recurse and expand */ 225 rlen = expand_symbol(best_table[c], best_table_len[c], result); 226 total += rlen; 227 result += rlen; 228 } 229 data++; 230 len--; 231 } 232 *result=0; 233 234 return total; 235 } 236 237 static void write_src(void) 238 { 239 unsigned int i, k, off; 240 unsigned int best_idx[256]; 241 unsigned int *markers; 242 char buf[KSYM_NAME_LEN]; 243 244 printf("#include <asm/types.h>\n"); 245 printf("#if BITS_PER_LONG == 64\n"); 246 printf("#define PTR .quad\n"); 247 printf("#define ALGN .align 8\n"); 248 printf("#else\n"); 249 printf("#define PTR .long\n"); 250 printf("#define ALGN .align 4\n"); 251 printf("#endif\n"); 252 253 printf("\t.section .rodata, \"a\"\n"); 254 255 /* Provide proper symbols relocatability by their '_text' 256 * relativeness. The symbol names cannot be used to construct 257 * normal symbol references as the list of symbols contains 258 * symbols that are declared static and are private to their 259 * .o files. This prevents .tmp_kallsyms.o or any other 260 * object from referencing them. 261 */ 262 output_label("kallsyms_addresses"); 263 for (i = 0; i < table_cnt; i++) { 264 if (toupper(table[i].sym[0]) != 'A') { 265 if (_text <= table[i].addr) 266 printf("\tPTR\t_text + %#llx\n", 267 table[i].addr - _text); 268 else 269 printf("\tPTR\t_text - %#llx\n", 270 _text - table[i].addr); 271 } else { 272 printf("\tPTR\t%#llx\n", table[i].addr); 273 } 274 } 275 printf("\n"); 276 277 output_label("kallsyms_num_syms"); 278 printf("\tPTR\t%d\n", table_cnt); 279 printf("\n"); 280 281 /* table of offset markers, that give the offset in the compressed stream 282 * every 256 symbols */ 283 markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256)); 284 if (!markers) { 285 fprintf(stderr, "kallsyms failure: " 286 "unable to allocate required memory\n"); 287 exit(EXIT_FAILURE); 288 } 289 290 output_label("kallsyms_names"); 291 off = 0; 292 for (i = 0; i < table_cnt; i++) { 293 if ((i & 0xFF) == 0) 294 markers[i >> 8] = off; 295 296 printf("\t.byte 0x%02x", table[i].len); 297 for (k = 0; k < table[i].len; k++) 298 printf(", 0x%02x", table[i].sym[k]); 299 printf("\n"); 300 301 off += table[i].len + 1; 302 } 303 printf("\n"); 304 305 output_label("kallsyms_markers"); 306 for (i = 0; i < ((table_cnt + 255) >> 8); i++) 307 printf("\tPTR\t%d\n", markers[i]); 308 printf("\n"); 309 310 free(markers); 311 312 output_label("kallsyms_token_table"); 313 off = 0; 314 for (i = 0; i < 256; i++) { 315 best_idx[i] = off; 316 expand_symbol(best_table[i], best_table_len[i], buf); 317 printf("\t.asciz\t\"%s\"\n", buf); 318 off += strlen(buf) + 1; 319 } 320 printf("\n"); 321 322 output_label("kallsyms_token_index"); 323 for (i = 0; i < 256; i++) 324 printf("\t.short\t%d\n", best_idx[i]); 325 printf("\n"); 326 } 327 328 329 /* table lookup compression functions */ 330 331 /* count all the possible tokens in a symbol */ 332 static void learn_symbol(unsigned char *symbol, int len) 333 { 334 int i; 335 336 for (i = 0; i < len - 1; i++) 337 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++; 338 } 339 340 /* decrease the count for all the possible tokens in a symbol */ 341 static void forget_symbol(unsigned char *symbol, int len) 342 { 343 int i; 344 345 for (i = 0; i < len - 1; i++) 346 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--; 347 } 348 349 /* remove all the invalid symbols from the table and do the initial token count */ 350 static void build_initial_tok_table(void) 351 { 352 unsigned int i, pos; 353 354 pos = 0; 355 for (i = 0; i < table_cnt; i++) { 356 if ( symbol_valid(&table[i]) ) { 357 if (pos != i) 358 table[pos] = table[i]; 359 learn_symbol(table[pos].sym, table[pos].len); 360 pos++; 361 } 362 } 363 table_cnt = pos; 364 } 365 366 static void *find_token(unsigned char *str, int len, unsigned char *token) 367 { 368 int i; 369 370 for (i = 0; i < len - 1; i++) { 371 if (str[i] == token[0] && str[i+1] == token[1]) 372 return &str[i]; 373 } 374 return NULL; 375 } 376 377 /* replace a given token in all the valid symbols. Use the sampled symbols 378 * to update the counts */ 379 static void compress_symbols(unsigned char *str, int idx) 380 { 381 unsigned int i, len, size; 382 unsigned char *p1, *p2; 383 384 for (i = 0; i < table_cnt; i++) { 385 386 len = table[i].len; 387 p1 = table[i].sym; 388 389 /* find the token on the symbol */ 390 p2 = find_token(p1, len, str); 391 if (!p2) continue; 392 393 /* decrease the counts for this symbol's tokens */ 394 forget_symbol(table[i].sym, len); 395 396 size = len; 397 398 do { 399 *p2 = idx; 400 p2++; 401 size -= (p2 - p1); 402 memmove(p2, p2 + 1, size); 403 p1 = p2; 404 len--; 405 406 if (size < 2) break; 407 408 /* find the token on the symbol */ 409 p2 = find_token(p1, size, str); 410 411 } while (p2); 412 413 table[i].len = len; 414 415 /* increase the counts for this symbol's new tokens */ 416 learn_symbol(table[i].sym, len); 417 } 418 } 419 420 /* search the token with the maximum profit */ 421 static int find_best_token(void) 422 { 423 int i, best, bestprofit; 424 425 bestprofit=-10000; 426 best = 0; 427 428 for (i = 0; i < 0x10000; i++) { 429 if (token_profit[i] > bestprofit) { 430 best = i; 431 bestprofit = token_profit[i]; 432 } 433 } 434 return best; 435 } 436 437 /* this is the core of the algorithm: calculate the "best" table */ 438 static void optimize_result(void) 439 { 440 int i, best; 441 442 /* using the '\0' symbol last allows compress_symbols to use standard 443 * fast string functions */ 444 for (i = 255; i >= 0; i--) { 445 446 /* if this table slot is empty (it is not used by an actual 447 * original char code */ 448 if (!best_table_len[i]) { 449 450 /* find the token with the breates profit value */ 451 best = find_best_token(); 452 453 /* place it in the "best" table */ 454 best_table_len[i] = 2; 455 best_table[i][0] = best & 0xFF; 456 best_table[i][1] = (best >> 8) & 0xFF; 457 458 /* replace this token in all the valid symbols */ 459 compress_symbols(best_table[i], i); 460 } 461 } 462 } 463 464 /* start by placing the symbols that are actually used on the table */ 465 static void insert_real_symbols_in_table(void) 466 { 467 unsigned int i, j, c; 468 469 memset(best_table, 0, sizeof(best_table)); 470 memset(best_table_len, 0, sizeof(best_table_len)); 471 472 for (i = 0; i < table_cnt; i++) { 473 for (j = 0; j < table[i].len; j++) { 474 c = table[i].sym[j]; 475 best_table[c][0]=c; 476 best_table_len[c]=1; 477 } 478 } 479 } 480 481 static void optimize_token_table(void) 482 { 483 build_initial_tok_table(); 484 485 insert_real_symbols_in_table(); 486 487 /* When valid symbol is not registered, exit to error */ 488 if (!table_cnt) { 489 fprintf(stderr, "No valid symbol.\n"); 490 exit(1); 491 } 492 493 optimize_result(); 494 } 495 496 static int compare_symbols(const void *a, const void *b) 497 { 498 const struct sym_entry *sa; 499 const struct sym_entry *sb; 500 int wa, wb; 501 502 sa = a; 503 sb = b; 504 505 /* sort by address first */ 506 if (sa->addr > sb->addr) 507 return 1; 508 if (sa->addr < sb->addr) 509 return -1; 510 511 /* sort by "weakness" type */ 512 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W'); 513 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W'); 514 if (wa != wb) 515 return wa - wb; 516 517 /* sort by initial order, so that other symbols are left undisturbed */ 518 return sa->start_pos - sb->start_pos; 519 } 520 521 static void sort_symbols(void) 522 { 523 qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols); 524 } 525 526 int main(int argc, char **argv) 527 { 528 if (argc >= 2) { 529 int i; 530 for (i = 1; i < argc; i++) { 531 if(strcmp(argv[i], "--all-symbols") == 0) 532 all_symbols = 1; 533 else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) { 534 char *p = &argv[i][16]; 535 /* skip quote */ 536 if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\'')) 537 p++; 538 symbol_prefix_char = *p; 539 } else 540 usage(); 541 } 542 } else if (argc != 1) 543 usage(); 544 545 read_map(stdin); 546 if (table_cnt) { 547 sort_symbols(); 548 optimize_token_table(); 549 } 550 write_src(); 551 552 return 0; 553 } 554