linux/scripts/kallsyms.c
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   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 *      Table compression uses all the unused char codes on the symbols and
  11 *  maps these to the most used substrings (tokens). For instance, it might
  12 *  map char code 0xF7 to represent "write_" and then in every symbol where
  13 *  "write_" appears it can be replaced by 0xF7, saving 5 bytes.
  14 *      The used codes themselves are also placed in the table so that the
  15 *  decompresion can work without "special cases".
  16 *      Applied to kernel symbols, this usually produces a compression ratio
  17 *  of about 50%.
  18 *
  19 */
  20
  21#include <stdio.h>
  22#include <stdlib.h>
  23#include <string.h>
  24#include <ctype.h>
  25
  26#ifndef ARRAY_SIZE
  27#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
  28#endif
  29
  30#define KSYM_NAME_LEN           128
  31
  32struct sym_entry {
  33        unsigned long long addr;
  34        unsigned int len;
  35        unsigned int start_pos;
  36        unsigned char *sym;
  37};
  38
  39struct text_range {
  40        const char *stext, *etext;
  41        unsigned long long start, end;
  42};
  43
  44static unsigned long long _text;
  45static struct text_range text_ranges[] = {
  46        { "_stext",     "_etext"     },
  47        { "_sinittext", "_einittext" },
  48        { "_stext_l1",  "_etext_l1"  }, /* Blackfin on-chip L1 inst SRAM */
  49        { "_stext_l2",  "_etext_l2"  }, /* Blackfin on-chip L2 SRAM */
  50};
  51#define text_range_text     (&text_ranges[0])
  52#define text_range_inittext (&text_ranges[1])
  53
  54static struct sym_entry *table;
  55static unsigned int table_size, table_cnt;
  56static int all_symbols = 0;
  57static char symbol_prefix_char = '\0';
  58static unsigned long long kernel_start_addr = 0;
  59
  60int token_profit[0x10000];
  61
  62/* the table that holds the result of the compression */
  63unsigned char best_table[256][2];
  64unsigned char best_table_len[256];
  65
  66
  67static void usage(void)
  68{
  69        fprintf(stderr, "Usage: kallsyms [--all-symbols] "
  70                        "[--symbol-prefix=<prefix char>] "
  71                        "[--page-offset=<CONFIG_PAGE_OFFSET>] "
  72                        "< in.map > out.S\n");
  73        exit(1);
  74}
  75
  76/*
  77 * This ignores the intensely annoying "mapping symbols" found
  78 * in ARM ELF files: $a, $t and $d.
  79 */
  80static inline int is_arm_mapping_symbol(const char *str)
  81{
  82        return str[0] == '$' && strchr("atd", str[1])
  83               && (str[2] == '\0' || str[2] == '.');
  84}
  85
  86static int read_symbol_tr(const char *sym, unsigned long long addr)
  87{
  88        size_t i;
  89        struct text_range *tr;
  90
  91        for (i = 0; i < ARRAY_SIZE(text_ranges); ++i) {
  92                tr = &text_ranges[i];
  93
  94                if (strcmp(sym, tr->stext) == 0) {
  95                        tr->start = addr;
  96                        return 0;
  97                } else if (strcmp(sym, tr->etext) == 0) {
  98                        tr->end = addr;
  99                        return 0;
 100                }
 101        }
 102
 103        return 1;
 104}
 105
 106static int read_symbol(FILE *in, struct sym_entry *s)
 107{
 108        char str[500];
 109        char *sym, stype;
 110        int rc;
 111
 112        rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str);
 113        if (rc != 3) {
 114                if (rc != EOF && fgets(str, 500, in) == NULL)
 115                        fprintf(stderr, "Read error or end of file.\n");
 116                return -1;
 117        }
 118
 119        sym = str;
 120        /* skip prefix char */
 121        if (symbol_prefix_char && str[0] == symbol_prefix_char)
 122                sym++;
 123
 124        /* Ignore most absolute/undefined (?) symbols. */
 125        if (strcmp(sym, "_text") == 0)
 126                _text = s->addr;
 127        else if (read_symbol_tr(sym, s->addr) == 0)
 128                /* nothing to do */;
 129        else if (toupper(stype) == 'A')
 130        {
 131                /* Keep these useful absolute symbols */
 132                if (strcmp(sym, "__kernel_syscall_via_break") &&
 133                    strcmp(sym, "__kernel_syscall_via_epc") &&
 134                    strcmp(sym, "__kernel_sigtramp") &&
 135                    strcmp(sym, "__gp"))
 136                        return -1;
 137
 138        }
 139        else if (toupper(stype) == 'U' ||
 140                 is_arm_mapping_symbol(sym))
 141                return -1;
 142        /* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
 143        else if (str[0] == '$')
 144                return -1;
 145        /* exclude debugging symbols */
 146        else if (stype == 'N')
 147                return -1;
 148
 149        /* include the type field in the symbol name, so that it gets
 150         * compressed together */
 151        s->len = strlen(str) + 1;
 152        s->sym = malloc(s->len + 1);
 153        if (!s->sym) {
 154                fprintf(stderr, "kallsyms failure: "
 155                        "unable to allocate required amount of memory\n");
 156                exit(EXIT_FAILURE);
 157        }
 158        strcpy((char *)s->sym + 1, str);
 159        s->sym[0] = stype;
 160
 161        return 0;
 162}
 163
 164static int symbol_valid_tr(struct sym_entry *s)
 165{
 166        size_t i;
 167        struct text_range *tr;
 168
 169        for (i = 0; i < ARRAY_SIZE(text_ranges); ++i) {
 170                tr = &text_ranges[i];
 171
 172                if (s->addr >= tr->start && s->addr <= tr->end)
 173                        return 1;
 174        }
 175
 176        return 0;
 177}
 178
 179static int symbol_valid(struct sym_entry *s)
 180{
 181        /* Symbols which vary between passes.  Passes 1 and 2 must have
 182         * identical symbol lists.  The kallsyms_* symbols below are only added
 183         * after pass 1, they would be included in pass 2 when --all-symbols is
 184         * specified so exclude them to get a stable symbol list.
 185         */
 186        static char *special_symbols[] = {
 187                "kallsyms_addresses",
 188                "kallsyms_num_syms",
 189                "kallsyms_names",
 190                "kallsyms_markers",
 191                "kallsyms_token_table",
 192                "kallsyms_token_index",
 193
 194        /* Exclude linker generated symbols which vary between passes */
 195                "_SDA_BASE_",           /* ppc */
 196                "_SDA2_BASE_",          /* ppc */
 197                NULL };
 198        int i;
 199        int offset = 1;
 200
 201        if (s->addr < kernel_start_addr)
 202                return 0;
 203
 204        /* skip prefix char */
 205        if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
 206                offset++;
 207
 208        /* if --all-symbols is not specified, then symbols outside the text
 209         * and inittext sections are discarded */
 210        if (!all_symbols) {
 211                if (symbol_valid_tr(s) == 0)
 212                        return 0;
 213                /* Corner case.  Discard any symbols with the same value as
 214                 * _etext _einittext; they can move between pass 1 and 2 when
 215                 * the kallsyms data are added.  If these symbols move then
 216                 * they may get dropped in pass 2, which breaks the kallsyms
 217                 * rules.
 218                 */
 219                if ((s->addr == text_range_text->end &&
 220                                strcmp((char *)s->sym + offset, text_range_text->etext)) ||
 221                    (s->addr == text_range_inittext->end &&
 222                                strcmp((char *)s->sym + offset, text_range_inittext->etext)))
 223                        return 0;
 224        }
 225
 226        /* Exclude symbols which vary between passes. */
 227        if (strstr((char *)s->sym + offset, "_compiled."))
 228                return 0;
 229
 230        for (i = 0; special_symbols[i]; i++)
 231                if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 )
 232                        return 0;
 233
 234        return 1;
 235}
 236
 237static void read_map(FILE *in)
 238{
 239        while (!feof(in)) {
 240                if (table_cnt >= table_size) {
 241                        table_size += 10000;
 242                        table = realloc(table, sizeof(*table) * table_size);
 243                        if (!table) {
 244                                fprintf(stderr, "out of memory\n");
 245                                exit (1);
 246                        }
 247                }
 248                if (read_symbol(in, &table[table_cnt]) == 0) {
 249                        table[table_cnt].start_pos = table_cnt;
 250                        table_cnt++;
 251                }
 252        }
 253}
 254
 255static void output_label(char *label)
 256{
 257        if (symbol_prefix_char)
 258                printf(".globl %c%s\n", symbol_prefix_char, label);
 259        else
 260                printf(".globl %s\n", label);
 261        printf("\tALGN\n");
 262        if (symbol_prefix_char)
 263                printf("%c%s:\n", symbol_prefix_char, label);
 264        else
 265                printf("%s:\n", label);
 266}
 267
 268/* uncompress a compressed symbol. When this function is called, the best table
 269 * might still be compressed itself, so the function needs to be recursive */
 270static int expand_symbol(unsigned char *data, int len, char *result)
 271{
 272        int c, rlen, total=0;
 273
 274        while (len) {
 275                c = *data;
 276                /* if the table holds a single char that is the same as the one
 277                 * we are looking for, then end the search */
 278                if (best_table[c][0]==c && best_table_len[c]==1) {
 279                        *result++ = c;
 280                        total++;
 281                } else {
 282                        /* if not, recurse and expand */
 283                        rlen = expand_symbol(best_table[c], best_table_len[c], result);
 284                        total += rlen;
 285                        result += rlen;
 286                }
 287                data++;
 288                len--;
 289        }
 290        *result=0;
 291
 292        return total;
 293}
 294
 295static void write_src(void)
 296{
 297        unsigned int i, k, off;
 298        unsigned int best_idx[256];
 299        unsigned int *markers;
 300        char buf[KSYM_NAME_LEN];
 301
 302        printf("#include <asm/types.h>\n");
 303        printf("#if BITS_PER_LONG == 64\n");
 304        printf("#define PTR .quad\n");
 305        printf("#define ALGN .align 8\n");
 306        printf("#else\n");
 307        printf("#define PTR .long\n");
 308        printf("#define ALGN .align 4\n");
 309        printf("#endif\n");
 310
 311        printf("\t.section .rodata, \"a\"\n");
 312
 313        /* Provide proper symbols relocatability by their '_text'
 314         * relativeness.  The symbol names cannot be used to construct
 315         * normal symbol references as the list of symbols contains
 316         * symbols that are declared static and are private to their
 317         * .o files.  This prevents .tmp_kallsyms.o or any other
 318         * object from referencing them.
 319         */
 320        output_label("kallsyms_addresses");
 321        for (i = 0; i < table_cnt; i++) {
 322                if (toupper(table[i].sym[0]) != 'A') {
 323                        if (_text <= table[i].addr)
 324                                printf("\tPTR\t_text + %#llx\n",
 325                                        table[i].addr - _text);
 326                        else
 327                                printf("\tPTR\t_text - %#llx\n",
 328                                        _text - table[i].addr);
 329                } else {
 330                        printf("\tPTR\t%#llx\n", table[i].addr);
 331                }
 332        }
 333        printf("\n");
 334
 335        output_label("kallsyms_num_syms");
 336        printf("\tPTR\t%d\n", table_cnt);
 337        printf("\n");
 338
 339        /* table of offset markers, that give the offset in the compressed stream
 340         * every 256 symbols */
 341        markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
 342        if (!markers) {
 343                fprintf(stderr, "kallsyms failure: "
 344                        "unable to allocate required memory\n");
 345                exit(EXIT_FAILURE);
 346        }
 347
 348        output_label("kallsyms_names");
 349        off = 0;
 350        for (i = 0; i < table_cnt; i++) {
 351                if ((i & 0xFF) == 0)
 352                        markers[i >> 8] = off;
 353
 354                printf("\t.byte 0x%02x", table[i].len);
 355                for (k = 0; k < table[i].len; k++)
 356                        printf(", 0x%02x", table[i].sym[k]);
 357                printf("\n");
 358
 359                off += table[i].len + 1;
 360        }
 361        printf("\n");
 362
 363        output_label("kallsyms_markers");
 364        for (i = 0; i < ((table_cnt + 255) >> 8); i++)
 365                printf("\tPTR\t%d\n", markers[i]);
 366        printf("\n");
 367
 368        free(markers);
 369
 370        output_label("kallsyms_token_table");
 371        off = 0;
 372        for (i = 0; i < 256; i++) {
 373                best_idx[i] = off;
 374                expand_symbol(best_table[i], best_table_len[i], buf);
 375                printf("\t.asciz\t\"%s\"\n", buf);
 376                off += strlen(buf) + 1;
 377        }
 378        printf("\n");
 379
 380        output_label("kallsyms_token_index");
 381        for (i = 0; i < 256; i++)
 382                printf("\t.short\t%d\n", best_idx[i]);
 383        printf("\n");
 384}
 385
 386
 387/* table lookup compression functions */
 388
 389/* count all the possible tokens in a symbol */
 390static void learn_symbol(unsigned char *symbol, int len)
 391{
 392        int i;
 393
 394        for (i = 0; i < len - 1; i++)
 395                token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
 396}
 397
 398/* decrease the count for all the possible tokens in a symbol */
 399static void forget_symbol(unsigned char *symbol, int len)
 400{
 401        int i;
 402
 403        for (i = 0; i < len - 1; i++)
 404                token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
 405}
 406
 407/* remove all the invalid symbols from the table and do the initial token count */
 408static void build_initial_tok_table(void)
 409{
 410        unsigned int i, pos;
 411
 412        pos = 0;
 413        for (i = 0; i < table_cnt; i++) {
 414                if ( symbol_valid(&table[i]) ) {
 415                        if (pos != i)
 416                                table[pos] = table[i];
 417                        learn_symbol(table[pos].sym, table[pos].len);
 418                        pos++;
 419                }
 420        }
 421        table_cnt = pos;
 422}
 423
 424static void *find_token(unsigned char *str, int len, unsigned char *token)
 425{
 426        int i;
 427
 428        for (i = 0; i < len - 1; i++) {
 429                if (str[i] == token[0] && str[i+1] == token[1])
 430                        return &str[i];
 431        }
 432        return NULL;
 433}
 434
 435/* replace a given token in all the valid symbols. Use the sampled symbols
 436 * to update the counts */
 437static void compress_symbols(unsigned char *str, int idx)
 438{
 439        unsigned int i, len, size;
 440        unsigned char *p1, *p2;
 441
 442        for (i = 0; i < table_cnt; i++) {
 443
 444                len = table[i].len;
 445                p1 = table[i].sym;
 446
 447                /* find the token on the symbol */
 448                p2 = find_token(p1, len, str);
 449                if (!p2) continue;
 450
 451                /* decrease the counts for this symbol's tokens */
 452                forget_symbol(table[i].sym, len);
 453
 454                size = len;
 455
 456                do {
 457                        *p2 = idx;
 458                        p2++;
 459                        size -= (p2 - p1);
 460                        memmove(p2, p2 + 1, size);
 461                        p1 = p2;
 462                        len--;
 463
 464                        if (size < 2) break;
 465
 466                        /* find the token on the symbol */
 467                        p2 = find_token(p1, size, str);
 468
 469                } while (p2);
 470
 471                table[i].len = len;
 472
 473                /* increase the counts for this symbol's new tokens */
 474                learn_symbol(table[i].sym, len);
 475        }
 476}
 477
 478/* search the token with the maximum profit */
 479static int find_best_token(void)
 480{
 481        int i, best, bestprofit;
 482
 483        bestprofit=-10000;
 484        best = 0;
 485
 486        for (i = 0; i < 0x10000; i++) {
 487                if (token_profit[i] > bestprofit) {
 488                        best = i;
 489                        bestprofit = token_profit[i];
 490                }
 491        }
 492        return best;
 493}
 494
 495/* this is the core of the algorithm: calculate the "best" table */
 496static void optimize_result(void)
 497{
 498        int i, best;
 499
 500        /* using the '\0' symbol last allows compress_symbols to use standard
 501         * fast string functions */
 502        for (i = 255; i >= 0; i--) {
 503
 504                /* if this table slot is empty (it is not used by an actual
 505                 * original char code */
 506                if (!best_table_len[i]) {
 507
 508                        /* find the token with the breates profit value */
 509                        best = find_best_token();
 510                        if (token_profit[best] == 0)
 511                                break;
 512
 513                        /* place it in the "best" table */
 514                        best_table_len[i] = 2;
 515                        best_table[i][0] = best & 0xFF;
 516                        best_table[i][1] = (best >> 8) & 0xFF;
 517
 518                        /* replace this token in all the valid symbols */
 519                        compress_symbols(best_table[i], i);
 520                }
 521        }
 522}
 523
 524/* start by placing the symbols that are actually used on the table */
 525static void insert_real_symbols_in_table(void)
 526{
 527        unsigned int i, j, c;
 528
 529        memset(best_table, 0, sizeof(best_table));
 530        memset(best_table_len, 0, sizeof(best_table_len));
 531
 532        for (i = 0; i < table_cnt; i++) {
 533                for (j = 0; j < table[i].len; j++) {
 534                        c = table[i].sym[j];
 535                        best_table[c][0]=c;
 536                        best_table_len[c]=1;
 537                }
 538        }
 539}
 540
 541static void optimize_token_table(void)
 542{
 543        build_initial_tok_table();
 544
 545        insert_real_symbols_in_table();
 546
 547        /* When valid symbol is not registered, exit to error */
 548        if (!table_cnt) {
 549                fprintf(stderr, "No valid symbol.\n");
 550                exit(1);
 551        }
 552
 553        optimize_result();
 554}
 555
 556/* guess for "linker script provide" symbol */
 557static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
 558{
 559        const char *symbol = (char *)se->sym + 1;
 560        int len = se->len - 1;
 561
 562        if (len < 8)
 563                return 0;
 564
 565        if (symbol[0] != '_' || symbol[1] != '_')
 566                return 0;
 567
 568        /* __start_XXXXX */
 569        if (!memcmp(symbol + 2, "start_", 6))
 570                return 1;
 571
 572        /* __stop_XXXXX */
 573        if (!memcmp(symbol + 2, "stop_", 5))
 574                return 1;
 575
 576        /* __end_XXXXX */
 577        if (!memcmp(symbol + 2, "end_", 4))
 578                return 1;
 579
 580        /* __XXXXX_start */
 581        if (!memcmp(symbol + len - 6, "_start", 6))
 582                return 1;
 583
 584        /* __XXXXX_end */
 585        if (!memcmp(symbol + len - 4, "_end", 4))
 586                return 1;
 587
 588        return 0;
 589}
 590
 591static int prefix_underscores_count(const char *str)
 592{
 593        const char *tail = str;
 594
 595        while (*tail == '_')
 596                tail++;
 597
 598        return tail - str;
 599}
 600
 601static int compare_symbols(const void *a, const void *b)
 602{
 603        const struct sym_entry *sa;
 604        const struct sym_entry *sb;
 605        int wa, wb;
 606
 607        sa = a;
 608        sb = b;
 609
 610        /* sort by address first */
 611        if (sa->addr > sb->addr)
 612                return 1;
 613        if (sa->addr < sb->addr)
 614                return -1;
 615
 616        /* sort by "weakness" type */
 617        wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
 618        wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
 619        if (wa != wb)
 620                return wa - wb;
 621
 622        /* sort by "linker script provide" type */
 623        wa = may_be_linker_script_provide_symbol(sa);
 624        wb = may_be_linker_script_provide_symbol(sb);
 625        if (wa != wb)
 626                return wa - wb;
 627
 628        /* sort by the number of prefix underscores */
 629        wa = prefix_underscores_count((const char *)sa->sym + 1);
 630        wb = prefix_underscores_count((const char *)sb->sym + 1);
 631        if (wa != wb)
 632                return wa - wb;
 633
 634        /* sort by initial order, so that other symbols are left undisturbed */
 635        return sa->start_pos - sb->start_pos;
 636}
 637
 638static void sort_symbols(void)
 639{
 640        qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
 641}
 642
 643int main(int argc, char **argv)
 644{
 645        if (argc >= 2) {
 646                int i;
 647                for (i = 1; i < argc; i++) {
 648                        if(strcmp(argv[i], "--all-symbols") == 0)
 649                                all_symbols = 1;
 650                        else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
 651                                char *p = &argv[i][16];
 652                                /* skip quote */
 653                                if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
 654                                        p++;
 655                                symbol_prefix_char = *p;
 656                        } else if (strncmp(argv[i], "--page-offset=", 14) == 0) {
 657                                const char *p = &argv[i][14];
 658                                kernel_start_addr = strtoull(p, NULL, 16);
 659                        } else
 660                                usage();
 661                }
 662        } else if (argc != 1)
 663                usage();
 664
 665        read_map(stdin);
 666        sort_symbols();
 667        optimize_token_table();
 668        write_src();
 669
 670        return 0;
 671}
 672
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