scripts/kallsyms.c

   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 /* maximum token length used. It doesn't pay to increase it a lot, because
  33  * very long substrings probably don't repeat themselves too often. */
  34 #define MAX_TOK_SIZE            11
  35 #define KSYM_NAME_LEN           127
  36
  37 /* we use only a subset of the complete symbol table to gather the token count,
  38  * to speed up compression, at the expense of a little compression ratio */
  39 #define WORKING_SET             1024
  40
  41 /* first find the best token only on the list of tokens that would profit more
  42  * than GOOD_BAD_THRESHOLD. Only if this list is empty go to the "bad" list.
  43  * Increasing this value will put less tokens on the "good" list, so the search
  44  * is faster. However, if the good list runs out of tokens, we must painfully
  45  * search the bad list. */
  46 #define GOOD_BAD_THRESHOLD      10
  47
  48 /* token hash parameters */
  49 #define HASH_BITS               18
  50 #define HASH_TABLE_SIZE         (1 << HASH_BITS)
  51 #define HASH_MASK               (HASH_TABLE_SIZE - 1)
  52 #define HASH_BASE_OFFSET        2166136261U
  53 #define HASH_FOLD(a)            ((a)&(HASH_MASK))
  54
  55 /* flags to mark symbols */
  56 #define SYM_FLAG_VALID          1
  57 #define SYM_FLAG_SAMPLED        2
  58
  59 struct sym_entry {
  60         unsigned long long addr;
  61         char type;
  62         unsigned char flags;
  63         unsigned char len;
  64         unsigned char *sym;
  65 };
  66
  67
  68 static struct sym_entry *table;
  69 static int size, cnt;
  70 static unsigned long long _stext, _etext, _sinittext, _einittext;
  71 static int all_symbols = 0;
  72 static char symbol_prefix_char = '\0';
  73
  74 struct token {
  75         unsigned char data[MAX_TOK_SIZE];
  76         unsigned char len;
  77         /* profit: the number of bytes that could be saved by inserting this
  78          * token into the table */
  79         int profit;
  80         struct token *next;     /* next token on the hash list */
  81         struct token *right;    /* next token on the good/bad list */
  82         struct token *left;    /* previous token on the good/bad list */
  83         struct token *smaller; /* token that is less one letter than this one */
  84         };
  85
  86 struct token bad_head, good_head;
  87 struct token *hash_table[HASH_TABLE_SIZE];
  88
  89 /* the table that holds the result of the compression */
  90 unsigned char best_table[256][MAX_TOK_SIZE+1];
  91 unsigned char best_table_len[256];
  92
  93
  94 static void
  95 usage(void)
  96 {
  97         fprintf(stderr, "Usage: kallsyms [--all-symbols] [--symbol-prefix=<prefix char>] < in.map > out.S\n");
  98         exit(1);
  99 }
 100
 101 /*
 102  * This ignores the intensely annoying "mapping symbols" found
 103  * in ARM ELF files: $a, $t and $d.
 104  */
 105 static inline int
 106 is_arm_mapping_symbol(const char *str)
 107 {
 108         return str[0] == '$' && strchr("atd", str[1])
 109                && (str[2] == '\0' || str[2] == '.');
 110 }
 111
 112 static int
 113 read_symbol(FILE *in, struct sym_entry *s)
 114 {
 115         char str[500];
 116         char *sym;
 117         int rc;
 118
 119         rc = fscanf(in, "%llx %c %499s\n", &s->addr, &s->type, str);
 120         if (rc != 3) {
 121                 if (rc != EOF) {
 122                         /* skip line */
 123                         fgets(str, 500, in);
 124                 }
 125                 return -1;
 126         }
 127
 128         sym = str;
 129         /* skip prefix char */
 130         if (symbol_prefix_char && str[0] == symbol_prefix_char)
 131                 sym++;
 132
 133         /* Ignore most absolute/undefined (?) symbols. */
 134         if (strcmp(sym, "_stext") == 0)
 135                 _stext = s->addr;
 136         else if (strcmp(sym, "_etext") == 0)
 137                 _etext = s->addr;
 138         else if (strcmp(sym, "_sinittext") == 0)
 139                 _sinittext = s->addr;
 140         else if (strcmp(sym, "_einittext") == 0)
 141                 _einittext = s->addr;
 142         else if (toupper(s->type) == 'A')
 143         {
 144                 /* Keep these useful absolute symbols */
 145                 if (strcmp(sym, "__kernel_syscall_via_break") &&
 146                     strcmp(sym, "__kernel_syscall_via_epc") &&
 147                     strcmp(sym, "__kernel_sigtramp") &&
 148                     strcmp(sym, "__gp"))
 149                         return -1;
 150
 151         }
 152         else if (toupper(s->type) == 'U' ||
 153                  is_arm_mapping_symbol(sym))
 154                 return -1;
 155
 156         /* include the type field in the symbol name, so that it gets
 157          * compressed together */
 158         s->len = strlen(str) + 1;
 159         s->sym = (char *) malloc(s->len + 1);
 160         strcpy(s->sym + 1, str);
 161         s->sym[0] = s->type;
 162
 163         return 0;
 164 }
 165
 166 static int
 167 symbol_valid(struct sym_entry *s)
 168 {
 169         /* Symbols which vary between passes.  Passes 1 and 2 must have
 170          * identical symbol lists.  The kallsyms_* symbols below are only added
 171          * after pass 1, they would be included in pass 2 when --all-symbols is
 172          * specified so exclude them to get a stable symbol list.
 173          */
 174         static char *special_symbols[] = {
 175                 "kallsyms_addresses",
 176                 "kallsyms_num_syms",
 177                 "kallsyms_names",
 178                 "kallsyms_markers",
 179                 "kallsyms_token_table",
 180                 "kallsyms_token_index",
 181
 182         /* Exclude linker generated symbols which vary between passes */
 183                 "_SDA_BASE_",           /* ppc */
 184                 "_SDA2_BASE_",          /* ppc */
 185                 NULL };
 186         int i;
 187         int offset = 1;
 188
 189         /* skip prefix char */
 190         if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
 191                 offset++;
 192
 193         /* if --all-symbols is not specified, then symbols outside the text
 194          * and inittext sections are discarded */
 195         if (!all_symbols) {
 196                 if ((s->addr < _stext || s->addr > _etext)
 197                     && (s->addr < _sinittext || s->addr > _einittext))
 198                         return 0;
 199                 /* Corner case.  Discard any symbols with the same value as
 200                  * _etext or _einittext, they can move between pass 1 and 2
 201                  * when the kallsyms data is added.  If these symbols move then
 202                  * they may get dropped in pass 2, which breaks the kallsyms
 203                  * rules.
 204                  */
 205                 if ((s->addr == _etext && strcmp(s->sym + offset, "_etext")) ||
 206                     (s->addr == _einittext && strcmp(s->sym + offset, "_einittext")))
 207                         return 0;
 208         }
 209
 210         /* Exclude symbols which vary between passes. */
 211         if (strstr(s->sym + offset, "_compiled."))
 212                 return 0;
 213
 214         for (i = 0; special_symbols[i]; i++)
 215                 if( strcmp(s->sym + offset, special_symbols[i]) == 0 )
 216                         return 0;
 217
 218         return 1;
 219 }
 220
 221 static void
 222 read_map(FILE *in)
 223 {
 224         while (!feof(in)) {
 225                 if (cnt >= size) {
 226                         size += 10000;
 227                         table = realloc(table, sizeof(*table) * size);
 228                         if (!table) {
 229                                 fprintf(stderr, "out of memory\n");
 230                                 exit (1);
 231                         }
 232                 }
 233                 if (read_symbol(in, &table[cnt]) == 0)
 234                         cnt++;
 235         }
 236 }
 237
 238 static void output_label(char *label)
 239 {
 240         if (symbol_prefix_char)
 241                 printf(".globl %c%s\n", symbol_prefix_char, label);
 242         else
 243                 printf(".globl %s\n", label);
 244         printf("\tALGN\n");
 245         if (symbol_prefix_char)
 246                 printf("%c%s:\n", symbol_prefix_char, label);
 247         else
 248                 printf("%s:\n", label);
 249 }
 250
 251 /* uncompress a compressed symbol. When this function is called, the best table
 252  * might still be compressed itself, so the function needs to be recursive */
 253 static int expand_symbol(unsigned char *data, int len, char *result)
 254 {
 255         int c, rlen, total=0;
 256
 257         while (len) {
 258                 c = *data;
 259                 /* if the table holds a single char that is the same as the one
 260                  * we are looking for, then end the search */
 261                 if (best_table[c][0]==c && best_table_len[c]==1) {
 262                         *result++ = c;
 263                         total++;
 264                 } else {
 265                         /* if not, recurse and expand */
 266                         rlen = expand_symbol(best_table[c], best_table_len[c], result);
 267                         total += rlen;
 268                         result += rlen;
 269                 }
 270                 data++;
 271                 len--;
 272         }
 273         *result=0;
 274
 275         return total;
 276 }
 277
 278 static void
 279 write_src(void)
 280 {
 281         int i, k, off, valid;
 282         unsigned int best_idx[256];
 283         unsigned int *markers;
 284         char buf[KSYM_NAME_LEN+1];
 285
 286         printf("#include <asm/types.h>\n");
 287         printf("#if BITS_PER_LONG == 64\n");
 288         printf("#define PTR .quad\n");
 289         printf("#define ALGN .align 8\n");
 290         printf("#else\n");
 291         printf("#define PTR .long\n");
 292         printf("#define ALGN .align 4\n");
 293         printf("#endif\n");
 294
 295         printf(".data\n");
 296
 297         output_label("kallsyms_addresses");
 298         valid = 0;
 299         for (i = 0; i < cnt; i++) {
 300                 if (table[i].flags & SYM_FLAG_VALID) {
 301                         printf("\tPTR\t%#llx\n", table[i].addr);
 302                         valid++;
 303                 }
 304         }
 305         printf("\n");
 306
 307         output_label("kallsyms_num_syms");
 308         printf("\tPTR\t%d\n", valid);
 309         printf("\n");
 310
 311         /* table of offset markers, that give the offset in the compressed stream
 312          * every 256 symbols */
 313         markers = (unsigned int *) malloc(sizeof(unsigned int)*((valid + 255) / 256));
 314
 315         output_label("kallsyms_names");
 316         valid = 0;
 317         off = 0;
 318         for (i = 0; i < cnt; i++) {
 319
 320                 if (!table[i].flags & SYM_FLAG_VALID)
 321                         continue;
 322
 323                 if ((valid & 0xFF) == 0)
 324                         markers[valid >> 8] = off;
 325
 326                 printf("\t.byte 0x%02x", table[i].len);
 327                 for (k = 0; k < table[i].len; k++)
 328                         printf(", 0x%02x", table[i].sym[k]);
 329                 printf("\n");
 330
 331                 off += table[i].len + 1;
 332                 valid++;
 333         }
 334         printf("\n");
 335
 336         output_label("kallsyms_markers");
 337         for (i = 0; i < ((valid + 255) >> 8); i++)
 338                 printf("\tPTR\t%d\n", markers[i]);
 339         printf("\n");
 340
 341         free(markers);
 342
 343         output_label("kallsyms_token_table");
 344         off = 0;
 345         for (i = 0; i < 256; i++) {
 346                 best_idx[i] = off;
 347                 expand_symbol(best_table[i],best_table_len[i],buf);
 348                 printf("\t.asciz\t\"%s\"\n", buf);
 349                 off += strlen(buf) + 1;
 350         }
 351         printf("\n");
 352
 353         output_label("kallsyms_token_index");
 354         for (i = 0; i < 256; i++)
 355                 printf("\t.short\t%d\n", best_idx[i]);
 356         printf("\n");
 357 }
 358
 359
 360 /* table lookup compression functions */
 361
 362 static inline unsigned int rehash_token(unsigned int hash, unsigned char data)
 363 {
 364         return ((hash * 16777619) ^ data);
 365 }
 366
 367 static unsigned int hash_token(unsigned char *data, int len)
 368 {
 369         unsigned int hash=HASH_BASE_OFFSET;
 370         int i;
 371
 372         for (i = 0; i < len; i++)
 373                 hash = rehash_token(hash, data[i]);
 374
 375         return HASH_FOLD(hash);
 376 }
 377
 378 /* find a token given its data and hash value */
 379 static struct token *find_token_hash(unsigned char *data, int len, unsigned int hash)
 380 {
 381         struct token *ptr;
 382
 383         ptr = hash_table[hash];
 384
 385         while (ptr) {
 386                 if ((ptr->len == len) && (memcmp(ptr->data, data, len) == 0))
 387                         return ptr;
 388                 ptr=ptr->next;
 389         }
 390
 391         return NULL;
 392 }
 393
 394 static inline void insert_token_in_group(struct token *head, struct token *ptr)
 395 {
 396         ptr->right = head->right;
 397         ptr->right->left = ptr;
 398         head->right = ptr;
 399         ptr->left = head;
 400 }
 401
 402 static inline void remove_token_from_group(struct token *ptr)
 403 {
 404         ptr->left->right = ptr->right;
 405         ptr->right->left = ptr->left;
 406 }
 407
 408
 409 /* build the counts for all the tokens that start with "data", and have lenghts
 410  * from 2 to "len" */
 411 static void learn_token(unsigned char *data, int len)
 412 {
 413         struct token *ptr,*last_ptr;
 414         int i, newprofit;
 415         unsigned int hash = HASH_BASE_OFFSET;
 416         unsigned int hashes[MAX_TOK_SIZE + 1];
 417
 418         if (len > MAX_TOK_SIZE)
 419                 len = MAX_TOK_SIZE;
 420
 421         /* calculate and store the hash values for all the sub-tokens */
 422         hash = rehash_token(hash, data[0]);
 423         for (i = 2; i <= len; i++) {
 424                 hash = rehash_token(hash, data[i-1]);
 425                 hashes[i] = HASH_FOLD(hash);
 426         }
 427
 428         last_ptr = NULL;
 429         ptr = NULL;
 430
 431         for (i = len; i >= 2; i--) {
 432                 hash = hashes[i];
 433
 434                 if (!ptr) ptr = find_token_hash(data, i, hash);
 435
 436                 if (!ptr) {
 437                         /* create a new token entry */
 438                         ptr = (struct token *) malloc(sizeof(*ptr));
 439
 440                         memcpy(ptr->data, data, i);
 441                         ptr->len = i;
 442
 443                         /* when we create an entry, it's profit is 0 because
 444                          * we also take into account the size of the token on
 445                          * the compressed table. We then subtract GOOD_BAD_THRESHOLD
 446                          * so that the test to see if this token belongs to
 447                          * the good or bad list, is a comparison to zero */
 448                         ptr->profit = -GOOD_BAD_THRESHOLD;
 449
 450                         ptr->next = hash_table[hash];
 451                         hash_table[hash] = ptr;
 452
 453                         insert_token_in_group(&bad_head, ptr);
 454
 455                         ptr->smaller = NULL;
 456                 } else {
 457                         newprofit = ptr->profit + (ptr->len - 1);
 458                         /* check to see if this token needs to be moved to a
 459                          * different list */
 460                         if((ptr->profit < 0) && (newprofit >= 0)) {
 461                                 remove_token_from_group(ptr);
 462                                 insert_token_in_group(&good_head,ptr);
 463                         }
 464                         ptr->profit = newprofit;
 465                 }
 466
 467                 if (last_ptr) last_ptr->smaller = ptr;
 468                 last_ptr = ptr;
 469
 470                 ptr = ptr->smaller;
 471         }
 472 }
 473
 474 /* decrease the counts for all the tokens that start with "data", and have lenghts
 475  * from 2 to "len". This function is much simpler than learn_token because we have
 476  * more guarantees (tho tokens exist, the ->smaller pointer is set, etc.)
 477  * The two separate functions exist only because of compression performance */
 478 static void forget_token(unsigned char *data, int len)
 479 {
 480         struct token *ptr;
 481         int i, newprofit;
 482         unsigned int hash=0;
 483
 484         if (len > MAX_TOK_SIZE) len = MAX_TOK_SIZE;
 485
 486         hash = hash_token(data, len);
 487         ptr = find_token_hash(data, len, hash);
 488
 489         for (i = len; i >= 2; i--) {
 490
 491                 newprofit = ptr->profit - (ptr->len - 1);
 492                 if ((ptr->profit >= 0) && (newprofit < 0)) {
 493                         remove_token_from_group(ptr);
 494                         insert_token_in_group(&bad_head, ptr);
 495                 }
 496                 ptr->profit=newprofit;
 497
 498                 ptr=ptr->smaller;
 499         }
 500 }
 501
 502 /* count all the possible tokens in a symbol */
 503 static void learn_symbol(unsigned char *symbol, int len)
 504 {
 505         int i;
 506
 507         for (i = 0; i < len - 1; i++)
 508                 learn_token(symbol + i, len - i);
 509 }
 510
 511 /* decrease the count for all the possible tokens in a symbol */
 512 static void forget_symbol(unsigned char *symbol, int len)
 513 {
 514         int i;
 515
 516         for (i = 0; i < len - 1; i++)
 517                 forget_token(symbol + i, len - i);
 518 }
 519
 520 /* set all the symbol flags and do the initial token count */
 521 static void build_initial_tok_table(void)
 522 {
 523         int i, use_it, valid;
 524
 525         valid = 0;
 526         for (i = 0; i < cnt; i++) {
 527                 table[i].flags = 0;
 528                 if ( symbol_valid(&table[i]) ) {
 529                         table[i].flags |= SYM_FLAG_VALID;
 530                         valid++;
 531                 }
 532         }
 533
 534         use_it = 0;
 535         for (i = 0; i < cnt; i++) {
 536
 537                 /* subsample the available symbols. This method is almost like
 538                  * a Bresenham's algorithm to get uniformly distributed samples
 539                  * across the symbol table */
 540                 if (table[i].flags & SYM_FLAG_VALID) {
 541
 542                         use_it += WORKING_SET;
 543
 544                         if (use_it >= valid) {
 545                                 table[i].flags |= SYM_FLAG_SAMPLED;
 546                                 use_it -= valid;
 547                         }
 548                 }
 549                 if (table[i].flags & SYM_FLAG_SAMPLED)
 550                         learn_symbol(table[i].sym, table[i].len);
 551         }
 552 }
 553
 554 /* replace a given token in all the valid symbols. Use the sampled symbols
 555  * to update the counts */
 556 static void compress_symbols(unsigned char *str, int tlen, int idx)
 557 {
 558         int i, len, learn, size;
 559         unsigned char *p;
 560
 561         for (i = 0; i < cnt; i++) {
 562
 563                 if (!(table[i].flags & SYM_FLAG_VALID)) continue;
 564
 565                 len = table[i].len;
 566                 learn = 0;
 567                 p = table[i].sym;
 568
 569                 do {
 570                         /* find the token on the symbol */
 571                         p = (unsigned char *) strstr((char *) p, (char *) str);
 572                         if (!p) break;
 573
 574                         if (!learn) {
 575                                 /* if this symbol was used to count, decrease it */
 576                                 if (table[i].flags & SYM_FLAG_SAMPLED)
 577                                         forget_symbol(table[i].sym, len);
 578                                 learn = 1;
 579                         }
 580
 581                         *p = idx;
 582                         size = (len - (p - table[i].sym)) - tlen + 1;
 583                         memmove(p + 1, p + tlen, size);
 584                         p++;
 585                         len -= tlen - 1;
 586
 587                 } while (size >= tlen);
 588
 589                 if(learn) {
 590                         table[i].len = len;
 591                         /* if this symbol was used to count, learn it again */
 592                         if(table[i].flags & SYM_FLAG_SAMPLED)
 593                                 learn_symbol(table[i].sym, len);
 594                 }
 595         }
 596 }
 597
 598 /* search the token with the maximum profit */
 599 static struct token *find_best_token(void)
 600 {
 601         struct token *ptr,*best,*head;
 602         int bestprofit;
 603
 604         bestprofit=-10000;
 605
 606         /* failsafe: if the "good" list is empty search from the "bad" list */
 607         if(good_head.right == &good_head) head = &bad_head;
 608         else head = &good_head;
 609
 610         ptr = head->right;
 611         best = NULL;
 612         while (ptr != head) {
 613                 if (ptr->profit > bestprofit) {
 614                         bestprofit = ptr->profit;
 615                         best = ptr;
 616                 }
 617                 ptr = ptr->right;
 618         }
 619
 620         return best;
 621 }
 622
 623 /* this is the core of the algorithm: calculate the "best" table */
 624 static void optimize_result(void)
 625 {
 626         struct token *best;
 627         int i;
 628
 629         /* using the '\0' symbol last allows compress_symbols to use standard
 630          * fast string functions */
 631         for (i = 255; i >= 0; i--) {
 632
 633                 /* if this table slot is empty (it is not used by an actual
 634                  * original char code */
 635                 if (!best_table_len[i]) {
 636
 637                         /* find the token with the breates profit value */
 638                         best = find_best_token();
 639
 640                         /* place it in the "best" table */
 641                         best_table_len[i] = best->len;
 642                         memcpy(best_table[i], best->data, best_table_len[i]);
 643                         /* zero terminate the token so that we can use strstr
 644                            in compress_symbols */
 645                         best_table[i][best_table_len[i]]='\0';
 646
 647                         /* replace this token in all the valid symbols */
 648                         compress_symbols(best_table[i], best_table_len[i], i);
 649                 }
 650         }
 651 }
 652
 653 /* start by placing the symbols that are actually used on the table */
 654 static void insert_real_symbols_in_table(void)
 655 {
 656         int i, j, c;
 657
 658         memset(best_table, 0, sizeof(best_table));
 659         memset(best_table_len, 0, sizeof(best_table_len));
 660
 661         for (i = 0; i < cnt; i++) {
 662                 if (table[i].flags & SYM_FLAG_VALID) {
 663                         for (j = 0; j < table[i].len; j++) {
 664                                 c = table[i].sym[j];
 665                                 best_table[c][0]=c;
 666                                 best_table_len[c]=1;
 667                         }
 668                 }
 669         }
 670 }
 671
 672 static void optimize_token_table(void)
 673 {
 674         memset(hash_table, 0, sizeof(hash_table));
 675
 676         good_head.left = &good_head;
 677         good_head.right = &good_head;
 678
 679         bad_head.left = &bad_head;
 680         bad_head.right = &bad_head;
 681
 682         build_initial_tok_table();
 683
 684         insert_real_symbols_in_table();
 685
 686         /* When valid symbol is not registered, exit to error */
 687         if (good_head.left == good_head.right &&
 688             bad_head.left == bad_head.right) {
 689                 fprintf(stderr, "No valid symbol.\n");
 690                 exit(1);
 691         }
 692
 693         optimize_result();
 694 }
 695
 696
 697 int
 698 main(int argc, char **argv)
 699 {
 700         if (argc >= 2) {
 701                 int i;
 702                 for (i = 1; i < argc; i++) {
 703                         if(strcmp(argv[i], "--all-symbols") == 0)
 704                                 all_symbols = 1;
 705                         else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
 706                                 char *p = &argv[i][16];
 707                                 /* skip quote */
 708                                 if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
 709                                         p++;
 710                                 symbol_prefix_char = *p;
 711                         } else
 712                                 usage();
 713                 }
 714         } else if (argc != 1)
 715                 usage();
 716
 717         read_map(stdin);
 718         optimize_token_table();
 719         write_src();
 720
 721         return 0;
 722 }