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 #define KSYM_NAME_LEN           128
  33
  34 struct sym_entry {
  35         unsigned long long addr;
  36         unsigned int len;
  37         unsigned int start_pos;
  38         unsigned char *sym;
  39 };
  40
  41 static struct sym_entry *table;
  42 static unsigned int table_size, table_cnt;
  43 static unsigned long long _text, _stext, _etext, _sinittext, _einittext;
  44 static int all_symbols = 0;
  45 static char symbol_prefix_char = '\0';
  46
  47 int token_profit[0x10000];
  48
  49 /* the table that holds the result of the compression */
  50 unsigned char best_table[256][2];
  51 unsigned char best_table_len[256];
  52
  53
  54 static void usage(void)
  55 {
  56         fprintf(stderr, "Usage: kallsyms [--all-symbols] [--symbol-prefix=<prefix char>] < in.map > out.S\n");
  57         exit(1);
  58 }
  59
  60 /*
  61  * This ignores the intensely annoying "mapping symbols" found
  62  * in ARM ELF files: $a, $t and $d.
  63  */
  64 static inline int is_arm_mapping_symbol(const char *str)
  65 {
  66         return str[0] == '$' && strchr("atd", str[1])
  67                && (str[2] == '\0' || str[2] == '.');
  68 }
  69
  70 static int read_symbol(FILE *in, struct sym_entry *s)
  71 {
  72         char str[500];
  73         char *sym, stype;
  74         int rc;
  75
  76         rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str);
  77         if (rc != 3) {
  78                 if (rc != EOF) {
  79                         /* skip line */
  80                         fgets(str, 500, in);
  81                 }
  82                 return -1;
  83         }
  84
  85         sym = str;
  86         /* skip prefix char */
  87         if (symbol_prefix_char && str[0] == symbol_prefix_char)
  88                 sym++;
  89
  90         /* Ignore most absolute/undefined (?) symbols. */
  91         if (strcmp(sym, "_text") == 0)
  92                 _text = s->addr;
  93         else if (strcmp(sym, "_stext") == 0)
  94                 _stext = s->addr;
  95         else if (strcmp(sym, "_etext") == 0)
  96                 _etext = s->addr;
  97         else if (strcmp(sym, "_sinittext") == 0)
  98                 _sinittext = s->addr;
  99         else if (strcmp(sym, "_einittext") == 0)
 100                 _einittext = s->addr;
 101         else if (toupper(stype) == 'A')
 102         {
 103                 /* Keep these useful absolute symbols */
 104                 if (strcmp(sym, "__kernel_syscall_via_break") &&
 105                     strcmp(sym, "__kernel_syscall_via_epc") &&
 106                     strcmp(sym, "__kernel_sigtramp") &&
 107                     strcmp(sym, "__gp"))
 108                         return -1;
 109
 110         }
 111         else if (toupper(stype) == 'U' ||
 112                  is_arm_mapping_symbol(sym))
 113                 return -1;
 114         /* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
 115         else if (str[0] == '$')
 116                 return -1;
 117
 118         /* include the type field in the symbol name, so that it gets
 119          * compressed together */
 120         s->len = strlen(str) + 1;
 121         s->sym = malloc(s->len + 1);
 122         if (!s->sym) {
 123                 fprintf(stderr, "kallsyms failure: "
 124                         "unable to allocate required amount of memory\n");
 125                 exit(EXIT_FAILURE);
 126         }
 127         strcpy((char *)s->sym + 1, str);
 128         s->sym[0] = stype;
 129
 130         return 0;
 131 }
 132
 133 static int symbol_valid(struct sym_entry *s)
 134 {
 135         /* Symbols which vary between passes.  Passes 1 and 2 must have
 136          * identical symbol lists.  The kallsyms_* symbols below are only added
 137          * after pass 1, they would be included in pass 2 when --all-symbols is
 138          * specified so exclude them to get a stable symbol list.
 139          */
 140         static char *special_symbols[] = {
 141                 "kallsyms_addresses",
 142                 "kallsyms_num_syms",
 143                 "kallsyms_names",
 144                 "kallsyms_markers",
 145                 "kallsyms_token_table",
 146                 "kallsyms_token_index",
 147
 148         /* Exclude linker generated symbols which vary between passes */
 149                 "_SDA_BASE_",           /* ppc */
 150                 "_SDA2_BASE_",          /* ppc */
 151                 NULL };
 152         int i;
 153         int offset = 1;
 154
 155         /* skip prefix char */
 156         if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
 157                 offset++;
 158
 159         /* if --all-symbols is not specified, then symbols outside the text
 160          * and inittext sections are discarded */
 161         if (!all_symbols) {
 162                 if ((s->addr < _stext || s->addr > _etext)
 163                     && (s->addr < _sinittext || s->addr > _einittext))
 164                         return 0;
 165                 /* Corner case.  Discard any symbols with the same value as
 166                  * _etext _einittext; they can move between pass 1 and 2 when
 167                  * the kallsyms data are added.  If these symbols move then
 168                  * they may get dropped in pass 2, which breaks the kallsyms
 169                  * rules.
 170                  */
 171                 if ((s->addr == _etext &&
 172                                 strcmp((char *)s->sym + offset, "_etext")) ||
 173                     (s->addr == _einittext &&
 174                                 strcmp((char *)s->sym + offset, "_einittext")))
 175                         return 0;
 176         }
 177
 178         /* Exclude symbols which vary between passes. */
 179         if (strstr((char *)s->sym + offset, "_compiled."))
 180                 return 0;
 181
 182         for (i = 0; special_symbols[i]; i++)
 183                 if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 )
 184                         return 0;
 185
 186         return 1;
 187 }
 188
 189 static void read_map(FILE *in)
 190 {
 191         while (!feof(in)) {
 192                 if (table_cnt >= table_size) {
 193                         table_size += 10000;
 194                         table = realloc(table, sizeof(*table) * table_size);
 195                         if (!table) {
 196                                 fprintf(stderr, "out of memory\n");
 197                                 exit (1);
 198                         }
 199                 }
 200                 if (read_symbol(in, &table[table_cnt]) == 0) {
 201                         table[table_cnt].start_pos = table_cnt;
 202                         table_cnt++;
 203                 }
 204         }
 205 }
 206
 207 static void output_label(char *label)
 208 {
 209         if (symbol_prefix_char)
 210                 printf(".globl %c%s\n", symbol_prefix_char, label);
 211         else
 212                 printf(".globl %s\n", label);
 213         printf("\tALGN\n");
 214         if (symbol_prefix_char)
 215                 printf("%c%s:\n", symbol_prefix_char, label);
 216         else
 217                 printf("%s:\n", label);
 218 }
 219
 220 /* uncompress a compressed symbol. When this function is called, the best table
 221  * might still be compressed itself, so the function needs to be recursive */
 222 static int expand_symbol(unsigned char *data, int len, char *result)
 223 {
 224         int c, rlen, total=0;
 225
 226         while (len) {
 227                 c = *data;
 228                 /* if the table holds a single char that is the same as the one
 229                  * we are looking for, then end the search */
 230                 if (best_table[c][0]==c && best_table_len[c]==1) {
 231                         *result++ = c;
 232                         total++;
 233                 } else {
 234                         /* if not, recurse and expand */
 235                         rlen = expand_symbol(best_table[c], best_table_len[c], result);
 236                         total += rlen;
 237                         result += rlen;
 238                 }
 239                 data++;
 240                 len--;
 241         }
 242         *result=0;
 243
 244         return total;
 245 }
 246
 247 static void write_src(void)
 248 {
 249         unsigned int i, k, off;
 250         unsigned int best_idx[256];
 251         unsigned int *markers;
 252         char buf[KSYM_NAME_LEN];
 253
 254         printf("#include <asm/types.h>\n");
 255         printf("#if BITS_PER_LONG == 64\n");
 256         printf("#define PTR .quad\n");
 257         printf("#define ALGN .align 8\n");
 258         printf("#else\n");
 259         printf("#define PTR .long\n");
 260         printf("#define ALGN .align 4\n");
 261         printf("#endif\n");
 262
 263         printf("\t.section .rodata, \"a\"\n");
 264
 265         /* Provide proper symbols relocatability by their '_text'
 266          * relativeness.  The symbol names cannot be used to construct
 267          * normal symbol references as the list of symbols contains
 268          * symbols that are declared static and are private to their
 269          * .o files.  This prevents .tmp_kallsyms.o or any other
 270          * object from referencing them.
 271          */
 272         output_label("kallsyms_addresses");
 273         for (i = 0; i < table_cnt; i++) {
 274                 if (toupper(table[i].sym[0]) != 'A') {
 275                         if (_text <= table[i].addr)
 276                                 printf("\tPTR\t_text + %#llx\n",
 277                                         table[i].addr - _text);
 278                         else
 279                                 printf("\tPTR\t_text - %#llx\n",
 280                                         _text - table[i].addr);
 281                 } else {
 282                         printf("\tPTR\t%#llx\n", table[i].addr);
 283                 }
 284         }
 285         printf("\n");
 286
 287         output_label("kallsyms_num_syms");
 288         printf("\tPTR\t%d\n", table_cnt);
 289         printf("\n");
 290
 291         /* table of offset markers, that give the offset in the compressed stream
 292          * every 256 symbols */
 293         markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
 294         if (!markers) {
 295                 fprintf(stderr, "kallsyms failure: "
 296                         "unable to allocate required memory\n");
 297                 exit(EXIT_FAILURE);
 298         }
 299
 300         output_label("kallsyms_names");
 301         off = 0;
 302         for (i = 0; i < table_cnt; i++) {
 303                 if ((i & 0xFF) == 0)
 304                         markers[i >> 8] = off;
 305
 306                 printf("\t.byte 0x%02x", table[i].len);
 307                 for (k = 0; k < table[i].len; k++)
 308                         printf(", 0x%02x", table[i].sym[k]);
 309                 printf("\n");
 310
 311                 off += table[i].len + 1;
 312         }
 313         printf("\n");
 314
 315         output_label("kallsyms_markers");
 316         for (i = 0; i < ((table_cnt + 255) >> 8); i++)
 317                 printf("\tPTR\t%d\n", markers[i]);
 318         printf("\n");
 319
 320         free(markers);
 321
 322         output_label("kallsyms_token_table");
 323         off = 0;
 324         for (i = 0; i < 256; i++) {
 325                 best_idx[i] = off;
 326                 expand_symbol(best_table[i], best_table_len[i], buf);
 327                 printf("\t.asciz\t\"%s\"\n", buf);
 328                 off += strlen(buf) + 1;
 329         }
 330         printf("\n");
 331
 332         output_label("kallsyms_token_index");
 333         for (i = 0; i < 256; i++)
 334                 printf("\t.short\t%d\n", best_idx[i]);
 335         printf("\n");
 336 }
 337
 338
 339 /* table lookup compression functions */
 340
 341 /* count all the possible tokens in a symbol */
 342 static void learn_symbol(unsigned char *symbol, int len)
 343 {
 344         int i;
 345
 346         for (i = 0; i < len - 1; i++)
 347                 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
 348 }
 349
 350 /* decrease the count for all the possible tokens in a symbol */
 351 static void forget_symbol(unsigned char *symbol, int len)
 352 {
 353         int i;
 354
 355         for (i = 0; i < len - 1; i++)
 356                 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
 357 }
 358
 359 /* remove all the invalid symbols from the table and do the initial token count */
 360 static void build_initial_tok_table(void)
 361 {
 362         unsigned int i, pos;
 363
 364         pos = 0;
 365         for (i = 0; i < table_cnt; i++) {
 366                 if ( symbol_valid(&table[i]) ) {
 367                         if (pos != i)
 368                                 table[pos] = table[i];
 369                         learn_symbol(table[pos].sym, table[pos].len);
 370                         pos++;
 371                 }
 372         }
 373         table_cnt = pos;
 374 }
 375
 376 static void *find_token(unsigned char *str, int len, unsigned char *token)
 377 {
 378         int i;
 379
 380         for (i = 0; i < len - 1; i++) {
 381                 if (str[i] == token[0] && str[i+1] == token[1])
 382                         return &str[i];
 383         }
 384         return NULL;
 385 }
 386
 387 /* replace a given token in all the valid symbols. Use the sampled symbols
 388  * to update the counts */
 389 static void compress_symbols(unsigned char *str, int idx)
 390 {
 391         unsigned int i, len, size;
 392         unsigned char *p1, *p2;
 393
 394         for (i = 0; i < table_cnt; i++) {
 395
 396                 len = table[i].len;
 397                 p1 = table[i].sym;
 398
 399                 /* find the token on the symbol */
 400                 p2 = find_token(p1, len, str);
 401                 if (!p2) continue;
 402
 403                 /* decrease the counts for this symbol's tokens */
 404                 forget_symbol(table[i].sym, len);
 405
 406                 size = len;
 407
 408                 do {
 409                         *p2 = idx;
 410                         p2++;
 411                         size -= (p2 - p1);
 412                         memmove(p2, p2 + 1, size);
 413                         p1 = p2;
 414                         len--;
 415
 416                         if (size < 2) break;
 417
 418                         /* find the token on the symbol */
 419                         p2 = find_token(p1, size, str);
 420
 421                 } while (p2);
 422
 423                 table[i].len = len;
 424
 425                 /* increase the counts for this symbol's new tokens */
 426                 learn_symbol(table[i].sym, len);
 427         }
 428 }
 429
 430 /* search the token with the maximum profit */
 431 static int find_best_token(void)
 432 {
 433         int i, best, bestprofit;
 434
 435         bestprofit=-10000;
 436         best = 0;
 437
 438         for (i = 0; i < 0x10000; i++) {
 439                 if (token_profit[i] > bestprofit) {
 440                         best = i;
 441                         bestprofit = token_profit[i];
 442                 }
 443         }
 444         return best;
 445 }
 446
 447 /* this is the core of the algorithm: calculate the "best" table */
 448 static void optimize_result(void)
 449 {
 450         int i, best;
 451
 452         /* using the '\0' symbol last allows compress_symbols to use standard
 453          * fast string functions */
 454         for (i = 255; i >= 0; i--) {
 455
 456                 /* if this table slot is empty (it is not used by an actual
 457                  * original char code */
 458                 if (!best_table_len[i]) {
 459
 460                         /* find the token with the breates profit value */
 461                         best = find_best_token();
 462
 463                         /* place it in the "best" table */
 464                         best_table_len[i] = 2;
 465                         best_table[i][0] = best & 0xFF;
 466                         best_table[i][1] = (best >> 8) & 0xFF;
 467
 468                         /* replace this token in all the valid symbols */
 469                         compress_symbols(best_table[i], i);
 470                 }
 471         }
 472 }
 473
 474 /* start by placing the symbols that are actually used on the table */
 475 static void insert_real_symbols_in_table(void)
 476 {
 477         unsigned int i, j, c;
 478
 479         memset(best_table, 0, sizeof(best_table));
 480         memset(best_table_len, 0, sizeof(best_table_len));
 481
 482         for (i = 0; i < table_cnt; i++) {
 483                 for (j = 0; j < table[i].len; j++) {
 484                         c = table[i].sym[j];
 485                         best_table[c][0]=c;
 486                         best_table_len[c]=1;
 487                 }
 488         }
 489 }
 490
 491 static void optimize_token_table(void)
 492 {
 493         build_initial_tok_table();
 494
 495         insert_real_symbols_in_table();
 496
 497         /* When valid symbol is not registered, exit to error */
 498         if (!table_cnt) {
 499                 fprintf(stderr, "No valid symbol.\n");
 500                 exit(1);
 501         }
 502
 503         optimize_result();
 504 }
 505
 506 static int compare_symbols(const void *a, const void *b)
 507 {
 508         const struct sym_entry *sa;
 509         const struct sym_entry *sb;
 510         int wa, wb;
 511
 512         sa = a;
 513         sb = b;
 514
 515         /* sort by address first */
 516         if (sa->addr > sb->addr)
 517                 return 1;
 518         if (sa->addr < sb->addr)
 519                 return -1;
 520
 521         /* sort by "weakness" type */
 522         wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
 523         wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
 524         if (wa != wb)
 525                 return wa - wb;
 526
 527         /* sort by initial order, so that other symbols are left undisturbed */
 528         return sa->start_pos - sb->start_pos;
 529 }
 530
 531 static void sort_symbols(void)
 532 {
 533         qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
 534 }
 535
 536 int main(int argc, char **argv)
 537 {
 538         if (argc >= 2) {
 539                 int i;
 540                 for (i = 1; i < argc; i++) {
 541                         if(strcmp(argv[i], "--all-symbols") == 0)
 542                                 all_symbols = 1;
 543                         else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
 544                                 char *p = &argv[i][16];
 545                                 /* skip quote */
 546                                 if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
 547                                         p++;
 548                                 symbol_prefix_char = *p;
 549                         } else
 550                                 usage();
 551                 }
 552         } else if (argc != 1)
 553                 usage();
 554
 555         read_map(stdin);
 556         sort_symbols();
 557         optimize_token_table();
 558         write_src();
 559
 560         return 0;
 561 }