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 _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, "_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         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                     && (s->addr < _sextratext || s->addr > _eextratext))
 165                         return 0;
 166                 /* Corner case.  Discard any symbols with the same value as
 167                  * _etext _einittext or _eextratext; they can move between pass
 168                  * 1 and 2 when the kallsyms data are added.  If these symbols
 169                  * move then they may get dropped in pass 2, which breaks the
 170                  * kallsyms rules.
 171                  */
 172                 if ((s->addr == _etext && strcmp((char*)s->sym + offset, "_etext")) ||
 173                     (s->addr == _einittext && strcmp((char*)s->sym + offset, "_einittext")) ||
 174                     (s->addr == _eextratext && strcmp((char*)s->sym + offset, "_eextratext")))
 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_cnt++;
 202         }
 203 }
 204
 205 static void output_label(char *label)
 206 {
 207         if (symbol_prefix_char)
 208                 printf(".globl %c%s\n", symbol_prefix_char, label);
 209         else
 210                 printf(".globl %s\n", label);
 211         printf("\tALGN\n");
 212         if (symbol_prefix_char)
 213                 printf("%c%s:\n", symbol_prefix_char, label);
 214         else
 215                 printf("%s:\n", label);
 216 }
 217
 218 /* uncompress a compressed symbol. When this function is called, the best table
 219  * might still be compressed itself, so the function needs to be recursive */
 220 static int expand_symbol(unsigned char *data, int len, char *result)
 221 {
 222         int c, rlen, total=0;
 223
 224         while (len) {
 225                 c = *data;
 226                 /* if the table holds a single char that is the same as the one
 227                  * we are looking for, then end the search */
 228                 if (best_table[c][0]==c && best_table_len[c]==1) {
 229                         *result++ = c;
 230                         total++;
 231                 } else {
 232                         /* if not, recurse and expand */
 233                         rlen = expand_symbol(best_table[c], best_table_len[c], result);
 234                         total += rlen;
 235                         result += rlen;
 236                 }
 237                 data++;
 238                 len--;
 239         }
 240         *result=0;
 241
 242         return total;
 243 }
 244
 245 static void write_src(void)
 246 {
 247         unsigned int i, k, off;
 248         unsigned int best_idx[256];
 249         unsigned int *markers;
 250         char buf[KSYM_NAME_LEN+1];
 251
 252         printf("#include <asm/types.h>\n");
 253         printf("#if BITS_PER_LONG == 64\n");
 254         printf("#define PTR .quad\n");
 255         printf("#define ALGN .align 8\n");
 256         printf("#else\n");
 257         printf("#define PTR .long\n");
 258         printf("#define ALGN .align 4\n");
 259         printf("#endif\n");
 260
 261         printf(".data\n");
 262
 263         output_label("kallsyms_addresses");
 264         for (i = 0; i < table_cnt; i++) {
 265                 printf("\tPTR\t%#llx\n", table[i].addr);
 266         }
 267         printf("\n");
 268
 269         output_label("kallsyms_num_syms");
 270         printf("\tPTR\t%d\n", table_cnt);
 271         printf("\n");
 272
 273         /* table of offset markers, that give the offset in the compressed stream
 274          * every 256 symbols */
 275         markers = (unsigned int *) malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
 276
 277         output_label("kallsyms_names");
 278         off = 0;
 279         for (i = 0; i < table_cnt; i++) {
 280                 if ((i & 0xFF) == 0)
 281                         markers[i >> 8] = off;
 282
 283                 printf("\t.byte 0x%02x", table[i].len);
 284                 for (k = 0; k < table[i].len; k++)
 285                         printf(", 0x%02x", table[i].sym[k]);
 286                 printf("\n");
 287
 288                 off += table[i].len + 1;
 289         }
 290         printf("\n");
 291
 292         output_label("kallsyms_markers");
 293         for (i = 0; i < ((table_cnt + 255) >> 8); i++)
 294                 printf("\tPTR\t%d\n", markers[i]);
 295         printf("\n");
 296
 297         free(markers);
 298
 299         output_label("kallsyms_token_table");
 300         off = 0;
 301         for (i = 0; i < 256; i++) {
 302                 best_idx[i] = off;
 303                 expand_symbol(best_table[i], best_table_len[i], buf);
 304                 printf("\t.asciz\t\"%s\"\n", buf);
 305                 off += strlen(buf) + 1;
 306         }
 307         printf("\n");
 308
 309         output_label("kallsyms_token_index");
 310         for (i = 0; i < 256; i++)
 311                 printf("\t.short\t%d\n", best_idx[i]);
 312         printf("\n");
 313 }
 314
 315
 316 /* table lookup compression functions */
 317
 318 /* count all the possible tokens in a symbol */
 319 static void learn_symbol(unsigned char *symbol, int len)
 320 {
 321         int i;
 322
 323         for (i = 0; i < len - 1; i++)
 324                 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
 325 }
 326
 327 /* decrease the count for all the possible tokens in a symbol */
 328 static void forget_symbol(unsigned char *symbol, int len)
 329 {
 330         int i;
 331
 332         for (i = 0; i < len - 1; i++)
 333                 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
 334 }
 335
 336 /* remove all the invalid symbols from the table and do the initial token count */
 337 static void build_initial_tok_table(void)
 338 {
 339         unsigned int i, pos;
 340
 341         pos = 0;
 342         for (i = 0; i < table_cnt; i++) {
 343                 if ( symbol_valid(&table[i]) ) {
 344                         if (pos != i)
 345                                 table[pos] = table[i];
 346                         learn_symbol(table[pos].sym, table[pos].len);
 347                         pos++;
 348                 }
 349         }
 350         table_cnt = pos;
 351 }
 352
 353 /* replace a given token in all the valid symbols. Use the sampled symbols
 354  * to update the counts */
 355 static void compress_symbols(unsigned char *str, int idx)
 356 {
 357         unsigned int i, len, size;
 358         unsigned char *p1, *p2;
 359
 360         for (i = 0; i < table_cnt; i++) {
 361
 362                 len = table[i].len;
 363                 p1 = table[i].sym;
 364
 365                 /* find the token on the symbol */
 366                 p2 = memmem(p1, len, str, 2);
 367                 if (!p2) continue;
 368
 369                 /* decrease the counts for this symbol's tokens */
 370                 forget_symbol(table[i].sym, len);
 371
 372                 size = len;
 373
 374                 do {
 375                         *p2 = idx;
 376                         p2++;
 377                         size -= (p2 - p1);
 378                         memmove(p2, p2 + 1, size);
 379                         p1 = p2;
 380                         len--;
 381
 382                         if (size < 2) break;
 383
 384                         /* find the token on the symbol */
 385                         p2 = memmem(p1, size, str, 2);
 386
 387                 } while (p2);
 388
 389                 table[i].len = len;
 390
 391                 /* increase the counts for this symbol's new tokens */
 392                 learn_symbol(table[i].sym, len);
 393         }
 394 }
 395
 396 /* search the token with the maximum profit */
 397 static int find_best_token(void)
 398 {
 399         int i, best, bestprofit;
 400
 401         bestprofit=-10000;
 402         best = 0;
 403
 404         for (i = 0; i < 0x10000; i++) {
 405                 if (token_profit[i] > bestprofit) {
 406                         best = i;
 407                         bestprofit = token_profit[i];
 408                 }
 409         }
 410         return best;
 411 }
 412
 413 /* this is the core of the algorithm: calculate the "best" table */
 414 static void optimize_result(void)
 415 {
 416         int i, best;
 417
 418         /* using the '\0' symbol last allows compress_symbols to use standard
 419          * fast string functions */
 420         for (i = 255; i >= 0; i--) {
 421
 422                 /* if this table slot is empty (it is not used by an actual
 423                  * original char code */
 424                 if (!best_table_len[i]) {
 425
 426                         /* find the token with the breates profit value */
 427                         best = find_best_token();
 428
 429                         /* place it in the "best" table */
 430                         best_table_len[i] = 2;
 431                         best_table[i][0] = best & 0xFF;
 432                         best_table[i][1] = (best >> 8) & 0xFF;
 433
 434                         /* replace this token in all the valid symbols */
 435                         compress_symbols(best_table[i], i);
 436                 }
 437         }
 438 }
 439
 440 /* start by placing the symbols that are actually used on the table */
 441 static void insert_real_symbols_in_table(void)
 442 {
 443         unsigned int i, j, c;
 444
 445         memset(best_table, 0, sizeof(best_table));
 446         memset(best_table_len, 0, sizeof(best_table_len));
 447
 448         for (i = 0; i < table_cnt; i++) {
 449                 for (j = 0; j < table[i].len; j++) {
 450                         c = table[i].sym[j];
 451                         best_table[c][0]=c;
 452                         best_table_len[c]=1;
 453                 }
 454         }
 455 }
 456
 457 static void optimize_token_table(void)
 458 {
 459         build_initial_tok_table();
 460
 461         insert_real_symbols_in_table();
 462
 463         /* When valid symbol is not registered, exit to error */
 464         if (!table_cnt) {
 465                 fprintf(stderr, "No valid symbol.\n");
 466                 exit(1);
 467         }
 468
 469         optimize_result();
 470 }
 471
 472
 473 int main(int argc, char **argv)
 474 {
 475         if (argc >= 2) {
 476                 int i;
 477                 for (i = 1; i < argc; i++) {
 478                         if(strcmp(argv[i], "--all-symbols") == 0)
 479                                 all_symbols = 1;
 480                         else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
 481                                 char *p = &argv[i][16];
 482                                 /* skip quote */
 483                                 if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
 484                                         p++;
 485                                 symbol_prefix_char = *p;
 486                         } else
 487                                 usage();
 488                 }
 489         } else if (argc != 1)
 490                 usage();
 491
 492         read_map(stdin);
 493         optimize_token_table();
 494         write_src();
 495
 496         return 0;
 497 }