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 #define _GNU_SOURCE
  28
  29 #include <stdio.h>
  30 #include <stdlib.h>
  31 #include <string.h>
  32 #include <ctype.h>
  33
  34 #define KSYM_NAME_LEN           127
  35
  36
  37 struct sym_entry {
  38         unsigned long long addr;
  39         unsigned int len;
  40         unsigned char *sym;
  41 };
  42
  43
  44 static struct sym_entry *table;
  45 static unsigned int table_size, table_cnt;
  46 static unsigned long long _text, _stext, _etext, _sinittext, _einittext, _sextratext, _eextratext;
  47 static int all_symbols = 0;
  48 static char symbol_prefix_char = '\0';
  49
  50 int token_profit[0x10000];
  51
  52 /* the table that holds the result of the compression */
  53 unsigned char best_table[256][2];
  54 unsigned char best_table_len[256];
  55
  56
  57 static void usage(void)
  58 {
  59         fprintf(stderr, "Usage: kallsyms [--all-symbols] [--symbol-prefix=<prefix char>] < in.map > out.S\n");
  60         exit(1);
  61 }
  62
  63 /*
  64  * This ignores the intensely annoying "mapping symbols" found
  65  * in ARM ELF files: $a, $t and $d.
  66  */
  67 static inline int is_arm_mapping_symbol(const char *str)
  68 {
  69         return str[0] == '$' && strchr("atd", str[1])
  70                && (str[2] == '\0' || str[2] == '.');
  71 }
  72
  73 static int read_symbol(FILE *in, struct sym_entry *s)
  74 {
  75         char str[500];
  76         char *sym, stype;
  77         int rc;
  78
  79         rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str);
  80         if (rc != 3) {
  81                 if (rc != EOF) {
  82                         /* skip line */
  83                         fgets(str, 500, in);
  84                 }
  85                 return -1;
  86         }
  87
  88         sym = str;
  89         /* skip prefix char */
  90         if (symbol_prefix_char && str[0] == symbol_prefix_char)
  91                 sym++;
  92
  93         /* Ignore most absolute/undefined (?) symbols. */
  94         if (strcmp(sym, "_text") == 0)
  95                 _text = s->addr;
  96         else if (strcmp(sym, "_stext") == 0)
  97                 _stext = s->addr;
  98         else if (strcmp(sym, "_etext") == 0)
  99                 _etext = s->addr;
 100         else if (strcmp(sym, "_sinittext") == 0)
 101                 _sinittext = s->addr;
 102         else if (strcmp(sym, "_einittext") == 0)
 103                 _einittext = s->addr;
 104         else if (strcmp(sym, "_sextratext") == 0)
 105                 _sextratext = s->addr;
 106         else if (strcmp(sym, "_eextratext") == 0)
 107                 _eextratext = s->addr;
 108         else if (toupper(stype) == 'A')
 109         {
 110                 /* Keep these useful absolute symbols */
 111                 if (strcmp(sym, "__kernel_syscall_via_break") &&
 112                     strcmp(sym, "__kernel_syscall_via_epc") &&
 113                     strcmp(sym, "__kernel_sigtramp") &&
 114                     strcmp(sym, "__gp"))
 115                         return -1;
 116
 117         }
 118         else if (toupper(stype) == 'U' ||
 119                  is_arm_mapping_symbol(sym))
 120                 return -1;
 121         /* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
 122         else if (str[0] == '$')
 123                 return -1;
 124
 125         /* include the type field in the symbol name, so that it gets
 126          * compressed together */
 127         s->len = strlen(str) + 1;
 128         s->sym = malloc(s->len + 1);
 129         if (!s->sym) {
 130                 fprintf(stderr, "kallsyms failure: "
 131                         "unable to allocate required amount of memory\n");
 132                 exit(EXIT_FAILURE);
 133         }
 134         strcpy((char *)s->sym + 1, str);
 135         s->sym[0] = stype;
 136
 137         return 0;
 138 }
 139
 140 static int symbol_valid(struct sym_entry *s)
 141 {
 142         /* Symbols which vary between passes.  Passes 1 and 2 must have
 143          * identical symbol lists.  The kallsyms_* symbols below are only added
 144          * after pass 1, they would be included in pass 2 when --all-symbols is
 145          * specified so exclude them to get a stable symbol list.
 146          */
 147         static char *special_symbols[] = {
 148                 "kallsyms_addresses",
 149                 "kallsyms_num_syms",
 150                 "kallsyms_names",
 151                 "kallsyms_markers",
 152                 "kallsyms_token_table",
 153                 "kallsyms_token_index",
 154
 155         /* Exclude linker generated symbols which vary between passes */
 156                 "_SDA_BASE_",           /* ppc */
 157                 "_SDA2_BASE_",          /* ppc */
 158                 NULL };
 159         int i;
 160         int offset = 1;
 161
 162         /* skip prefix char */
 163         if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
 164                 offset++;
 165
 166         /* if --all-symbols is not specified, then symbols outside the text
 167          * and inittext sections are discarded */
 168         if (!all_symbols) {
 169                 if ((s->addr < _stext || s->addr > _etext)
 170                     && (s->addr < _sinittext || s->addr > _einittext)
 171                     && (s->addr < _sextratext || s->addr > _eextratext))
 172                         return 0;
 173                 /* Corner case.  Discard any symbols with the same value as
 174                  * _etext _einittext or _eextratext; they can move between pass
 175                  * 1 and 2 when the kallsyms data are added.  If these symbols
 176                  * move then they may get dropped in pass 2, which breaks the
 177                  * kallsyms rules.
 178                  */
 179                 if ((s->addr == _etext && strcmp((char*)s->sym + offset, "_etext")) ||
 180                     (s->addr == _einittext && strcmp((char*)s->sym + offset, "_einittext")) ||
 181                     (s->addr == _eextratext && strcmp((char*)s->sym + offset, "_eextratext")))
 182                         return 0;
 183         }
 184
 185         /* Exclude symbols which vary between passes. */
 186         if (strstr((char *)s->sym + offset, "_compiled."))
 187                 return 0;
 188
 189         for (i = 0; special_symbols[i]; i++)
 190                 if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 )
 191                         return 0;
 192
 193         return 1;
 194 }
 195
 196 static void read_map(FILE *in)
 197 {
 198         while (!feof(in)) {
 199                 if (table_cnt >= table_size) {
 200                         table_size += 10000;
 201                         table = realloc(table, sizeof(*table) * table_size);
 202                         if (!table) {
 203                                 fprintf(stderr, "out of memory\n");
 204                                 exit (1);
 205                         }
 206                 }
 207                 if (read_symbol(in, &table[table_cnt]) == 0)
 208                         table_cnt++;
 209         }
 210 }
 211
 212 static void output_label(char *label)
 213 {
 214         if (symbol_prefix_char)
 215                 printf(".globl %c%s\n", symbol_prefix_char, label);
 216         else
 217                 printf(".globl %s\n", label);
 218         printf("\tALGN\n");
 219         if (symbol_prefix_char)
 220                 printf("%c%s:\n", symbol_prefix_char, label);
 221         else
 222                 printf("%s:\n", label);
 223 }
 224
 225 /* uncompress a compressed symbol. When this function is called, the best table
 226  * might still be compressed itself, so the function needs to be recursive */
 227 static int expand_symbol(unsigned char *data, int len, char *result)
 228 {
 229         int c, rlen, total=0;
 230
 231         while (len) {
 232                 c = *data;
 233                 /* if the table holds a single char that is the same as the one
 234                  * we are looking for, then end the search */
 235                 if (best_table[c][0]==c && best_table_len[c]==1) {
 236                         *result++ = c;
 237                         total++;
 238                 } else {
 239                         /* if not, recurse and expand */
 240                         rlen = expand_symbol(best_table[c], best_table_len[c], result);
 241                         total += rlen;
 242                         result += rlen;
 243                 }
 244                 data++;
 245                 len--;
 246         }
 247         *result=0;
 248
 249         return total;
 250 }
 251
 252 static void write_src(void)
 253 {
 254         unsigned int i, k, off;
 255         unsigned int best_idx[256];
 256         unsigned int *markers;
 257         char buf[KSYM_NAME_LEN+1];
 258
 259         printf("#include <asm/types.h>\n");
 260         printf("#if BITS_PER_LONG == 64\n");
 261         printf("#define PTR .quad\n");
 262         printf("#define ALGN .align 8\n");
 263         printf("#else\n");
 264         printf("#define PTR .long\n");
 265         printf("#define ALGN .align 4\n");
 266         printf("#endif\n");
 267
 268         printf("\t.section .rodata, \"a\"\n");
 269
 270         /* Provide proper symbols relocatability by their '_text'
 271          * relativeness.  The symbol names cannot be used to construct
 272          * normal symbol references as the list of symbols contains
 273          * symbols that are declared static and are private to their
 274          * .o files.  This prevents .tmp_kallsyms.o or any other
 275          * object from referencing them.
 276          */
 277         output_label("kallsyms_addresses");
 278         for (i = 0; i < table_cnt; i++) {
 279                 if (toupper(table[i].sym[0]) != 'A') {
 280                         if (_text <= table[i].addr)
 281                                 printf("\tPTR\t_text + %#llx\n",
 282                                         table[i].addr - _text);
 283                         else
 284                                 printf("\tPTR\t_text - %#llx\n",
 285                                         _text - table[i].addr);
 286                 } else {
 287                         printf("\tPTR\t%#llx\n", table[i].addr);
 288                 }
 289         }
 290         printf("\n");
 291
 292         output_label("kallsyms_num_syms");
 293         printf("\tPTR\t%d\n", table_cnt);
 294         printf("\n");
 295
 296         /* table of offset markers, that give the offset in the compressed stream
 297          * every 256 symbols */
 298         markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
 299         if (!markers) {
 300                 fprintf(stderr, "kallsyms failure: "
 301                         "unable to allocate required memory\n");
 302                 exit(EXIT_FAILURE);
 303         }
 304
 305         output_label("kallsyms_names");
 306         off = 0;
 307         for (i = 0; i < table_cnt; i++) {
 308                 if ((i & 0xFF) == 0)
 309                         markers[i >> 8] = off;
 310
 311                 printf("\t.byte 0x%02x", table[i].len);
 312                 for (k = 0; k < table[i].len; k++)
 313                         printf(", 0x%02x", table[i].sym[k]);
 314                 printf("\n");
 315
 316                 off += table[i].len + 1;
 317         }
 318         printf("\n");
 319
 320         output_label("kallsyms_markers");
 321         for (i = 0; i < ((table_cnt + 255) >> 8); i++)
 322                 printf("\tPTR\t%d\n", markers[i]);
 323         printf("\n");
 324
 325         free(markers);
 326
 327         output_label("kallsyms_token_table");
 328         off = 0;
 329         for (i = 0; i < 256; i++) {
 330                 best_idx[i] = off;
 331                 expand_symbol(best_table[i], best_table_len[i], buf);
 332                 printf("\t.asciz\t\"%s\"\n", buf);
 333                 off += strlen(buf) + 1;
 334         }
 335         printf("\n");
 336
 337         output_label("kallsyms_token_index");
 338         for (i = 0; i < 256; i++)
 339                 printf("\t.short\t%d\n", best_idx[i]);
 340         printf("\n");
 341 }
 342
 343
 344 /* table lookup compression functions */
 345
 346 /* count all the possible tokens in a symbol */
 347 static void learn_symbol(unsigned char *symbol, int len)
 348 {
 349         int i;
 350
 351         for (i = 0; i < len - 1; i++)
 352                 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
 353 }
 354
 355 /* decrease the count for all the possible tokens in a symbol */
 356 static void forget_symbol(unsigned char *symbol, int len)
 357 {
 358         int i;
 359
 360         for (i = 0; i < len - 1; i++)
 361                 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
 362 }
 363
 364 /* remove all the invalid symbols from the table and do the initial token count */
 365 static void build_initial_tok_table(void)
 366 {
 367         unsigned int i, pos;
 368
 369         pos = 0;
 370         for (i = 0; i < table_cnt; i++) {
 371                 if ( symbol_valid(&table[i]) ) {
 372                         if (pos != i)
 373                                 table[pos] = table[i];
 374                         learn_symbol(table[pos].sym, table[pos].len);
 375                         pos++;
 376                 }
 377         }
 378         table_cnt = pos;
 379 }
 380
 381 /* replace a given token in all the valid symbols. Use the sampled symbols
 382  * to update the counts */
 383 static void compress_symbols(unsigned char *str, int idx)
 384 {
 385         unsigned int i, len, size;
 386         unsigned char *p1, *p2;
 387
 388         for (i = 0; i < table_cnt; i++) {
 389
 390                 len = table[i].len;
 391                 p1 = table[i].sym;
 392
 393                 /* find the token on the symbol */
 394                 p2 = memmem(p1, len, str, 2);
 395                 if (!p2) continue;
 396
 397                 /* decrease the counts for this symbol's tokens */
 398                 forget_symbol(table[i].sym, len);
 399
 400                 size = len;
 401
 402                 do {
 403                         *p2 = idx;
 404                         p2++;
 405                         size -= (p2 - p1);
 406                         memmove(p2, p2 + 1, size);
 407                         p1 = p2;
 408                         len--;
 409
 410                         if (size < 2) break;
 411
 412                         /* find the token on the symbol */
 413                         p2 = memmem(p1, size, str, 2);
 414
 415                 } while (p2);
 416
 417                 table[i].len = len;
 418
 419                 /* increase the counts for this symbol's new tokens */
 420                 learn_symbol(table[i].sym, len);
 421         }
 422 }
 423
 424 /* search the token with the maximum profit */
 425 static int find_best_token(void)
 426 {
 427         int i, best, bestprofit;
 428
 429         bestprofit=-10000;
 430         best = 0;
 431
 432         for (i = 0; i < 0x10000; i++) {
 433                 if (token_profit[i] > bestprofit) {
 434                         best = i;
 435                         bestprofit = token_profit[i];
 436                 }
 437         }
 438         return best;
 439 }
 440
 441 /* this is the core of the algorithm: calculate the "best" table */
 442 static void optimize_result(void)
 443 {
 444         int i, best;
 445
 446         /* using the '\0' symbol last allows compress_symbols to use standard
 447          * fast string functions */
 448         for (i = 255; i >= 0; i--) {
 449
 450                 /* if this table slot is empty (it is not used by an actual
 451                  * original char code */
 452                 if (!best_table_len[i]) {
 453
 454                         /* find the token with the breates profit value */
 455                         best = find_best_token();
 456
 457                         /* place it in the "best" table */
 458                         best_table_len[i] = 2;
 459                         best_table[i][0] = best & 0xFF;
 460                         best_table[i][1] = (best >> 8) & 0xFF;
 461
 462                         /* replace this token in all the valid symbols */
 463                         compress_symbols(best_table[i], i);
 464                 }
 465         }
 466 }
 467
 468 /* start by placing the symbols that are actually used on the table */
 469 static void insert_real_symbols_in_table(void)
 470 {
 471         unsigned int i, j, c;
 472
 473         memset(best_table, 0, sizeof(best_table));
 474         memset(best_table_len, 0, sizeof(best_table_len));
 475
 476         for (i = 0; i < table_cnt; i++) {
 477                 for (j = 0; j < table[i].len; j++) {
 478                         c = table[i].sym[j];
 479                         best_table[c][0]=c;
 480                         best_table_len[c]=1;
 481                 }
 482         }
 483 }
 484
 485 static void optimize_token_table(void)
 486 {
 487         build_initial_tok_table();
 488
 489         insert_real_symbols_in_table();
 490
 491         /* When valid symbol is not registered, exit to error */
 492         if (!table_cnt) {
 493                 fprintf(stderr, "No valid symbol.\n");
 494                 exit(1);
 495         }
 496
 497         optimize_result();
 498 }
 499
 500
 501 int main(int argc, char **argv)
 502 {
 503         if (argc >= 2) {
 504                 int i;
 505                 for (i = 1; i < argc; i++) {
 506                         if(strcmp(argv[i], "--all-symbols") == 0)
 507                                 all_symbols = 1;
 508                         else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
 509                                 char *p = &argv[i][16];
 510                                 /* skip quote */
 511                                 if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
 512                                         p++;
 513                                 symbol_prefix_char = *p;
 514                         } else
 515                                 usage();
 516                 }
 517         } else if (argc != 1)
 518                 usage();
 519
 520         read_map(stdin);
 521         optimize_token_table();
 522         write_src();
 523
 524         return 0;
 525 }