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 * ChangeLog: 11 * 12 * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com> 13 * Changed the compression method from stem compression to "table lookup" 14 * compression 15 * 16 * Table compression uses all the unused char codes on the symbols and 17 * maps these to the most used substrings (tokens). For instance, it might 18 * map char code 0xF7 to represent "write_" and then in every symbol where 19 * "write_" appears it can be replaced by 0xF7, saving 5 bytes. 20 * The used codes themselves are also placed in the table so that the 21 * decompresion can work without "special cases". 22 * Applied to kernel symbols, this usually produces a compression ratio 23 * of about 50%. 24 * 25 */ 26 27 #include <stdio.h> 28 #include <stdlib.h> 29 #include <string.h> 30 #include <ctype.h> 31 32 #define KSYM_NAME_LEN 128 33 34 35 struct sym_entry { 36 unsigned long long addr; 37 unsigned int len; 38 unsigned char *sym; 39 }; 40 41 42 static struct sym_entry *table; 43 static unsigned int table_size, table_cnt; 44 static unsigned long long _text, _stext, _etext, _sinittext, _einittext, _sextratext, _eextratext; 45 static int all_symbols = 0; 46 static char symbol_prefix_char = '\0'; 47 48 int token_profit[0x10000]; 49 50 /* the table that holds the result of the compression */ 51 unsigned char best_table[256][2]; 52 unsigned char best_table_len[256]; 53 54 55 static void usage(void) 56 { 57 fprintf(stderr, "Usage: kallsyms [--all-symbols] [--symbol-prefix=<prefix char>] < in.map > out.S\n"); 58 exit(1); 59 } 60 61 /* 62 * This ignores the intensely annoying "mapping symbols" found 63 * in ARM ELF files: $a, $t and $d. 64 */ 65 static inline int is_arm_mapping_symbol(const char *str) 66 { 67 return str[0] == '$' && strchr("atd", str[1]) 68 && (str[2] == '\0' || str[2] == '.'); 69 } 70 71 static int read_symbol(FILE *in, struct sym_entry *s) 72 { 73 char str[500]; 74 char *sym, stype; 75 int rc; 76 77 rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str); 78 if (rc != 3) { 79 if (rc != EOF) { 80 /* skip line */ 81 fgets(str, 500, in); 82 } 83 return -1; 84 } 85 86 sym = str; 87 /* skip prefix char */ 88 if (symbol_prefix_char && str[0] == symbol_prefix_char) 89 sym++; 90 91 /* Ignore most absolute/undefined (?) symbols. */ 92 if (strcmp(sym, "_text") == 0) 93 _text = s->addr; 94 else if (strcmp(sym, "_stext") == 0) 95 _stext = s->addr; 96 else if (strcmp(sym, "_etext") == 0) 97 _etext = s->addr; 98 else if (strcmp(sym, "_sinittext") == 0) 99 _sinittext = s->addr; 100 else if (strcmp(sym, "_einittext") == 0) 101 _einittext = s->addr; 102 else if (strcmp(sym, "_sextratext") == 0) 103 _sextratext = s->addr; 104 else if (strcmp(sym, "_eextratext") == 0) 105 _eextratext = s->addr; 106 else if (toupper(stype) == 'A') 107 { 108 /* Keep these useful absolute symbols */ 109 if (strcmp(sym, "__kernel_syscall_via_break") && 110 strcmp(sym, "__kernel_syscall_via_epc") && 111 strcmp(sym, "__kernel_sigtramp") && 112 strcmp(sym, "__gp")) 113 return -1; 114 115 } 116 else if (toupper(stype) == 'U' || 117 is_arm_mapping_symbol(sym)) 118 return -1; 119 /* exclude also MIPS ELF local symbols ($L123 instead of .L123) */ 120 else if (str[0] == '$') 121 return -1; 122 123 /* include the type field in the symbol name, so that it gets 124 * compressed together */ 125 s->len = strlen(str) + 1; 126 s->sym = malloc(s->len + 1); 127 if (!s->sym) { 128 fprintf(stderr, "kallsyms failure: " 129 "unable to allocate required amount of memory\n"); 130 exit(EXIT_FAILURE); 131 } 132 strcpy((char *)s->sym + 1, str); 133 s->sym[0] = stype; 134 135 return 0; 136 } 137 138 static int symbol_valid(struct sym_entry *s) 139 { 140 /* Symbols which vary between passes. Passes 1 and 2 must have 141 * identical symbol lists. The kallsyms_* symbols below are only added 142 * after pass 1, they would be included in pass 2 when --all-symbols is 143 * specified so exclude them to get a stable symbol list. 144 */ 145 static char *special_symbols[] = { 146 "kallsyms_addresses", 147 "kallsyms_num_syms", 148 "kallsyms_names", 149 "kallsyms_markers", 150 "kallsyms_token_table", 151 "kallsyms_token_index", 152 153 /* Exclude linker generated symbols which vary between passes */ 154 "_SDA_BASE_", /* ppc */ 155 "_SDA2_BASE_", /* ppc */ 156 NULL }; 157 int i; 158 int offset = 1; 159 160 /* skip prefix char */ 161 if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char) 162 offset++; 163 164 /* if --all-symbols is not specified, then symbols outside the text 165 * and inittext sections are discarded */ 166 if (!all_symbols) { 167 if ((s->addr < _stext || s->addr > _etext) 168 && (s->addr < _sinittext || s->addr > _einittext) 169 && (s->addr < _sextratext || s->addr > _eextratext)) 170 return 0; 171 /* Corner case. Discard any symbols with the same value as 172 * _etext _einittext or _eextratext; they can move between pass 173 * 1 and 2 when the kallsyms data are added. If these symbols 174 * move then they may get dropped in pass 2, which breaks the 175 * kallsyms rules. 176 */ 177 if ((s->addr == _etext && strcmp((char*)s->sym + offset, "_etext")) || 178 (s->addr == _einittext && strcmp((char*)s->sym + offset, "_einittext")) || 179 (s->addr == _eextratext && strcmp((char*)s->sym + offset, "_eextratext"))) 180 return 0; 181 } 182 183 /* Exclude symbols which vary between passes. */ 184 if (strstr((char *)s->sym + offset, "_compiled.")) 185 return 0; 186 187 for (i = 0; special_symbols[i]; i++) 188 if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 ) 189 return 0; 190 191 return 1; 192 } 193 194 static void read_map(FILE *in) 195 { 196 while (!feof(in)) { 197 if (table_cnt >= table_size) { 198 table_size += 10000; 199 table = realloc(table, sizeof(*table) * table_size); 200 if (!table) { 201 fprintf(stderr, "out of memory\n"); 202 exit (1); 203 } 204 } 205 if (read_symbol(in, &table[table_cnt]) == 0) 206 table_cnt++; 207 } 208 } 209 210 static void output_label(char *label) 211 { 212 if (symbol_prefix_char) 213 printf(".globl %c%s\n", symbol_prefix_char, label); 214 else 215 printf(".globl %s\n", label); 216 printf("\tALGN\n"); 217 if (symbol_prefix_char) 218 printf("%c%s:\n", symbol_prefix_char, label); 219 else 220 printf("%s:\n", label); 221 } 222 223 /* uncompress a compressed symbol. When this function is called, the best table 224 * might still be compressed itself, so the function needs to be recursive */ 225 static int expand_symbol(unsigned char *data, int len, char *result) 226 { 227 int c, rlen, total=0; 228 229 while (len) { 230 c = *data; 231 /* if the table holds a single char that is the same as the one 232 * we are looking for, then end the search */ 233 if (best_table[c][0]==c && best_table_len[c]==1) { 234 *result++ = c; 235 total++; 236 } else { 237 /* if not, recurse and expand */ 238 rlen = expand_symbol(best_table[c], best_table_len[c], result); 239 total += rlen; 240 result += rlen; 241 } 242 data++; 243 len--; 244 } 245 *result=0; 246 247 return total; 248 } 249 250 static void write_src(void) 251 { 252 unsigned int i, k, off; 253 unsigned int best_idx[256]; 254 unsigned int *markers; 255 char buf[KSYM_NAME_LEN]; 256 257 printf("#include <asm/types.h>\n"); 258 printf("#if BITS_PER_LONG == 64\n"); 259 printf("#define PTR .quad\n"); 260 printf("#define ALGN .align 8\n"); 261 printf("#else\n"); 262 printf("#define PTR .long\n"); 263 printf("#define ALGN .align 4\n"); 264 printf("#endif\n"); 265 266 printf("\t.section .rodata, \"a\"\n"); 267 268 /* Provide proper symbols relocatability by their '_text' 269 * relativeness. The symbol names cannot be used to construct 270 * normal symbol references as the list of symbols contains 271 * symbols that are declared static and are private to their 272 * .o files. This prevents .tmp_kallsyms.o or any other 273 * object from referencing them. 274 */ 275 output_label("kallsyms_addresses"); 276 for (i = 0; i < table_cnt; i++) { 277 if (toupper(table[i].sym[0]) != 'A') { 278 if (_text <= table[i].addr) 279 printf("\tPTR\t_text + %#llx\n", 280 table[i].addr - _text); 281 else 282 printf("\tPTR\t_text - %#llx\n", 283 _text - table[i].addr); 284 } else { 285 printf("\tPTR\t%#llx\n", table[i].addr); 286 } 287 } 288 printf("\n"); 289 290 output_label("kallsyms_num_syms"); 291 printf("\tPTR\t%d\n", table_cnt); 292 printf("\n"); 293 294 /* table of offset markers, that give the offset in the compressed stream 295 * every 256 symbols */ 296 markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256)); 297 if (!markers) { 298 fprintf(stderr, "kallsyms failure: " 299 "unable to allocate required memory\n"); 300 exit(EXIT_FAILURE); 301 } 302 303 output_label("kallsyms_names"); 304 off = 0; 305 for (i = 0; i < table_cnt; i++) { 306 if ((i & 0xFF) == 0) 307 markers[i >> 8] = off; 308 309 printf("\t.byte 0x%02x", table[i].len); 310 for (k = 0; k < table[i].len; k++) 311 printf(", 0x%02x", table[i].sym[k]); 312 printf("\n"); 313 314 off += table[i].len + 1; 315 } 316 printf("\n"); 317 318 output_label("kallsyms_markers"); 319 for (i = 0; i < ((table_cnt + 255) >> 8); i++) 320 printf("\tPTR\t%d\n", markers[i]); 321 printf("\n"); 322 323 free(markers); 324 325 output_label("kallsyms_token_table"); 326 off = 0; 327 for (i = 0; i < 256; i++) { 328 best_idx[i] = off; 329 expand_symbol(best_table[i], best_table_len[i], buf); 330 printf("\t.asciz\t\"%s\"\n", buf); 331 off += strlen(buf) + 1; 332 } 333 printf("\n"); 334 335 output_label("kallsyms_token_index"); 336 for (i = 0; i < 256; i++) 337 printf("\t.short\t%d\n", best_idx[i]); 338 printf("\n"); 339 } 340 341 342 /* table lookup compression functions */ 343 344 /* count all the possible tokens in a symbol */ 345 static void learn_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 /* decrease the count for all the possible tokens in a symbol */ 354 static void forget_symbol(unsigned char *symbol, int len) 355 { 356 int i; 357 358 for (i = 0; i < len - 1; i++) 359 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--; 360 } 361 362 /* remove all the invalid symbols from the table and do the initial token count */ 363 static void build_initial_tok_table(void) 364 { 365 unsigned int i, pos; 366 367 pos = 0; 368 for (i = 0; i < table_cnt; i++) { 369 if ( symbol_valid(&table[i]) ) { 370 if (pos != i) 371 table[pos] = table[i]; 372 learn_symbol(table[pos].sym, table[pos].len); 373 pos++; 374 } 375 } 376 table_cnt = pos; 377 } 378 379 static void *find_token(unsigned char *str, int len, unsigned char *token) 380 { 381 int i; 382 383 for (i = 0; i < len - 1; i++) { 384 if (str[i] == token[0] && str[i+1] == token[1]) 385 return &str[i]; 386 } 387 return NULL; 388 } 389 390 /* replace a given token in all the valid symbols. Use the sampled symbols 391 * to update the counts */ 392 static void compress_symbols(unsigned char *str, int idx) 393 { 394 unsigned int i, len, size; 395 unsigned char *p1, *p2; 396 397 for (i = 0; i < table_cnt; i++) { 398 399 len = table[i].len; 400 p1 = table[i].sym; 401 402 /* find the token on the symbol */ 403 p2 = find_token(p1, len, str); 404 if (!p2) continue; 405 406 /* decrease the counts for this symbol's tokens */ 407 forget_symbol(table[i].sym, len); 408 409 size = len; 410 411 do { 412 *p2 = idx; 413 p2++; 414 size -= (p2 - p1); 415 memmove(p2, p2 + 1, size); 416 p1 = p2; 417 len--; 418 419 if (size < 2) break; 420 421 /* find the token on the symbol */ 422 p2 = find_token(p1, size, str); 423 424 } while (p2); 425 426 table[i].len = len; 427 428 /* increase the counts for this symbol's new tokens */ 429 learn_symbol(table[i].sym, len); 430 } 431 } 432 433 /* search the token with the maximum profit */ 434 static int find_best_token(void) 435 { 436 int i, best, bestprofit; 437 438 bestprofit=-10000; 439 best = 0; 440 441 for (i = 0; i < 0x10000; i++) { 442 if (token_profit[i] > bestprofit) { 443 best = i; 444 bestprofit = token_profit[i]; 445 } 446 } 447 return best; 448 } 449 450 /* this is the core of the algorithm: calculate the "best" table */ 451 static void optimize_result(void) 452 { 453 int i, best; 454 455 /* using the '\0' symbol last allows compress_symbols to use standard 456 * fast string functions */ 457 for (i = 255; i >= 0; i--) { 458 459 /* if this table slot is empty (it is not used by an actual 460 * original char code */ 461 if (!best_table_len[i]) { 462 463 /* find the token with the breates profit value */ 464 best = find_best_token(); 465 466 /* place it in the "best" table */ 467 best_table_len[i] = 2; 468 best_table[i][0] = best & 0xFF; 469 best_table[i][1] = (best >> 8) & 0xFF; 470 471 /* replace this token in all the valid symbols */ 472 compress_symbols(best_table[i], i); 473 } 474 } 475 } 476 477 /* start by placing the symbols that are actually used on the table */ 478 static void insert_real_symbols_in_table(void) 479 { 480 unsigned int i, j, c; 481 482 memset(best_table, 0, sizeof(best_table)); 483 memset(best_table_len, 0, sizeof(best_table_len)); 484 485 for (i = 0; i < table_cnt; i++) { 486 for (j = 0; j < table[i].len; j++) { 487 c = table[i].sym[j]; 488 best_table[c][0]=c; 489 best_table_len[c]=1; 490 } 491 } 492 } 493 494 static void optimize_token_table(void) 495 { 496 build_initial_tok_table(); 497 498 insert_real_symbols_in_table(); 499 500 /* When valid symbol is not registered, exit to error */ 501 if (!table_cnt) { 502 fprintf(stderr, "No valid symbol.\n"); 503 exit(1); 504 } 505 506 optimize_result(); 507 } 508 509 510 int main(int argc, char **argv) 511 { 512 if (argc >= 2) { 513 int i; 514 for (i = 1; i < argc; i++) { 515 if(strcmp(argv[i], "--all-symbols") == 0) 516 all_symbols = 1; 517 else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) { 518 char *p = &argv[i][16]; 519 /* skip quote */ 520 if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\'')) 521 p++; 522 symbol_prefix_char = *p; 523 } else 524 usage(); 525 } 526 } else if (argc != 1) 527 usage(); 528 529 read_map(stdin); 530 optimize_token_table(); 531 write_src(); 532 533 return 0; 534 } 535