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        if (strlen(str) > KSYM_NAME_LEN) {
 119                fprintf(stderr, "Symbol %s too long for kallsyms (%zu vs %d).\n"
 120                                "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
 121                        str, strlen(str), KSYM_NAME_LEN);
 122                return -1;
 123        }
 124
 125        sym = str;
 126        /* skip prefix char */
 127        if (symbol_prefix_char && str[0] == symbol_prefix_char)
 128                sym++;
 129
 130        /* Ignore most absolute/undefined (?) symbols. */
 131        if (strcmp(sym, "_text") == 0)
 132                _text = s->addr;
 133        else if (read_symbol_tr(sym, s->addr) == 0)
 134                /* nothing to do */;
 135        else if (toupper(stype) == 'A')
 136        {
 137                /* Keep these useful absolute symbols */
 138                if (strcmp(sym, "__kernel_syscall_via_break") &&
 139                    strcmp(sym, "__kernel_syscall_via_epc") &&
 140                    strcmp(sym, "__kernel_sigtramp") &&
 141                    strcmp(sym, "__gp"))
 142                        return -1;
 143
 144        }
 145        else if (toupper(stype) == 'U' ||
 146                 is_arm_mapping_symbol(sym))
 147                return -1;
 148        /* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
 149        else if (str[0] == '$')
 150                return -1;
 151        /* exclude debugging symbols */
 152        else if (stype == 'N')
 153                return -1;
 154
 155        /* include the type field in the symbol name, so that it gets
 156         * compressed together */
 157        s->len = strlen(str) + 1;
 158        s->sym = malloc(s->len + 1);
 159        if (!s->sym) {
 160                fprintf(stderr, "kallsyms failure: "
 161                        "unable to allocate required amount of memory\n");
 162                exit(EXIT_FAILURE);
 163        }
 164        strcpy((char *)s->sym + 1, str);
 165        s->sym[0] = stype;
 166
 167        return 0;
 168}
 169
 170static int symbol_valid_tr(struct sym_entry *s)
 171{
 172        size_t i;
 173        struct text_range *tr;
 174
 175        for (i = 0; i < ARRAY_SIZE(text_ranges); ++i) {
 176                tr = &text_ranges[i];
 177
 178                if (s->addr >= tr->start && s->addr <= tr->end)
 179                        return 1;
 180        }
 181
 182        return 0;
 183}
 184
 185static int symbol_valid(struct sym_entry *s)
 186{
 187        /* Symbols which vary between passes.  Passes 1 and 2 must have
 188         * identical symbol lists.  The kallsyms_* symbols below are only added
 189         * after pass 1, they would be included in pass 2 when --all-symbols is
 190         * specified so exclude them to get a stable symbol list.
 191         */
 192        static char *special_symbols[] = {
 193                "kallsyms_addresses",
 194                "kallsyms_num_syms",
 195                "kallsyms_names",
 196                "kallsyms_markers",
 197                "kallsyms_token_table",
 198                "kallsyms_token_index",
 199
 200        /* Exclude linker generated symbols which vary between passes */
 201                "_SDA_BASE_",           /* ppc */
 202                "_SDA2_BASE_",          /* ppc */
 203                NULL };
 204        int i;
 205        int offset = 1;
 206
 207        if (s->addr < kernel_start_addr)
 208                return 0;
 209
 210        /* skip prefix char */
 211        if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
 212                offset++;
 213
 214        /* if --all-symbols is not specified, then symbols outside the text
 215         * and inittext sections are discarded */
 216        if (!all_symbols) {
 217                if (symbol_valid_tr(s) == 0)
 218                        return 0;
 219                /* Corner case.  Discard any symbols with the same value as
 220                 * _etext _einittext; they can move between pass 1 and 2 when
 221                 * the kallsyms data are added.  If these symbols move then
 222                 * they may get dropped in pass 2, which breaks the kallsyms
 223                 * rules.
 224                 */
 225                if ((s->addr == text_range_text->end &&
 226                                strcmp((char *)s->sym + offset, text_range_text->etext)) ||
 227                    (s->addr == text_range_inittext->end &&
 228                                strcmp((char *)s->sym + offset, text_range_inittext->etext)))
 229                        return 0;
 230        }
 231
 232        /* Exclude symbols which vary between passes. */
 233        if (strstr((char *)s->sym + offset, "_compiled."))
 234                return 0;
 235
 236        for (i = 0; special_symbols[i]; i++)
 237                if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 )
 238                        return 0;
 239
 240        return 1;
 241}
 242
 243static void read_map(FILE *in)
 244{
 245        while (!feof(in)) {
 246                if (table_cnt >= table_size) {
 247                        table_size += 10000;
 248                        table = realloc(table, sizeof(*table) * table_size);
 249                        if (!table) {
 250                                fprintf(stderr, "out of memory\n");
 251                                exit (1);
 252                        }
 253                }
 254                if (read_symbol(in, &table[table_cnt]) == 0) {
 255                        table[table_cnt].start_pos = table_cnt;
 256                        table_cnt++;
 257                }
 258        }
 259}
 260
 261static void output_label(char *label)
 262{
 263        if (symbol_prefix_char)
 264                printf(".globl %c%s\n", symbol_prefix_char, label);
 265        else
 266                printf(".globl %s\n", label);
 267        printf("\tALGN\n");
 268        if (symbol_prefix_char)
 269                printf("%c%s:\n", symbol_prefix_char, label);
 270        else
 271                printf("%s:\n", label);
 272}
 273
 274/* uncompress a compressed symbol. When this function is called, the best table
 275 * might still be compressed itself, so the function needs to be recursive */
 276static int expand_symbol(unsigned char *data, int len, char *result)
 277{
 278        int c, rlen, total=0;
 279
 280        while (len) {
 281                c = *data;
 282                /* if the table holds a single char that is the same as the one
 283                 * we are looking for, then end the search */
 284                if (best_table[c][0]==c && best_table_len[c]==1) {
 285                        *result++ = c;
 286                        total++;
 287                } else {
 288                        /* if not, recurse and expand */
 289                        rlen = expand_symbol(best_table[c], best_table_len[c], result);
 290                        total += rlen;
 291                        result += rlen;
 292                }
 293                data++;
 294                len--;
 295        }
 296        *result=0;
 297
 298        return total;
 299}
 300
 301static void write_src(void)
 302{
 303        unsigned int i, k, off;
 304        unsigned int best_idx[256];
 305        unsigned int *markers;
 306        char buf[KSYM_NAME_LEN];
 307
 308        printf("#include <asm/types.h>\n");
 309        printf("#if BITS_PER_LONG == 64\n");
 310        printf("#define PTR .quad\n");
 311        printf("#define ALGN .align 8\n");
 312        printf("#else\n");
 313        printf("#define PTR .long\n");
 314        printf("#define ALGN .align 4\n");
 315        printf("#endif\n");
 316
 317        printf("\t.section .rodata, \"a\"\n");
 318
 319        /* Provide proper symbols relocatability by their '_text'
 320         * relativeness.  The symbol names cannot be used to construct
 321         * normal symbol references as the list of symbols contains
 322         * symbols that are declared static and are private to their
 323         * .o files.  This prevents .tmp_kallsyms.o or any other
 324         * object from referencing them.
 325         */
 326        output_label("kallsyms_addresses");
 327        for (i = 0; i < table_cnt; i++) {
 328                if (toupper(table[i].sym[0]) != 'A') {
 329                        if (_text <= table[i].addr)
 330                                printf("\tPTR\t_text + %#llx\n",
 331                                        table[i].addr - _text);
 332                        else
 333                                printf("\tPTR\t_text - %#llx\n",
 334                                        _text - table[i].addr);
 335                } else {
 336                        printf("\tPTR\t%#llx\n", table[i].addr);
 337                }
 338        }
 339        printf("\n");
 340
 341        output_label("kallsyms_num_syms");
 342        printf("\tPTR\t%d\n", table_cnt);
 343        printf("\n");
 344
 345        /* table of offset markers, that give the offset in the compressed stream
 346         * every 256 symbols */
 347        markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
 348        if (!markers) {
 349                fprintf(stderr, "kallsyms failure: "
 350                        "unable to allocate required memory\n");
 351                exit(EXIT_FAILURE);
 352        }
 353
 354        output_label("kallsyms_names");
 355        off = 0;
 356        for (i = 0; i < table_cnt; i++) {
 357                if ((i & 0xFF) == 0)
 358                        markers[i >> 8] = off;
 359
 360                printf("\t.byte 0x%02x", table[i].len);
 361                for (k = 0; k < table[i].len; k++)
 362                        printf(", 0x%02x", table[i].sym[k]);
 363                printf("\n");
 364
 365                off += table[i].len + 1;
 366        }
 367        printf("\n");
 368
 369        output_label("kallsyms_markers");
 370        for (i = 0; i < ((table_cnt + 255) >> 8); i++)
 371                printf("\tPTR\t%d\n", markers[i]);
 372        printf("\n");
 373
 374        free(markers);
 375
 376        output_label("kallsyms_token_table");
 377        off = 0;
 378        for (i = 0; i < 256; i++) {
 379                best_idx[i] = off;
 380                expand_symbol(best_table[i], best_table_len[i], buf);
 381                printf("\t.asciz\t\"%s\"\n", buf);
 382                off += strlen(buf) + 1;
 383        }
 384        printf("\n");
 385
 386        output_label("kallsyms_token_index");
 387        for (i = 0; i < 256; i++)
 388                printf("\t.short\t%d\n", best_idx[i]);
 389        printf("\n");
 390}
 391
 392
 393/* table lookup compression functions */
 394
 395/* count all the possible tokens in a symbol */
 396static void learn_symbol(unsigned char *symbol, int len)
 397{
 398        int i;
 399
 400        for (i = 0; i < len - 1; i++)
 401                token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
 402}
 403
 404/* decrease the count for all the possible tokens in a symbol */
 405static void forget_symbol(unsigned char *symbol, int len)
 406{
 407        int i;
 408
 409        for (i = 0; i < len - 1; i++)
 410                token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
 411}
 412
 413/* remove all the invalid symbols from the table and do the initial token count */
 414static void build_initial_tok_table(void)
 415{
 416        unsigned int i, pos;
 417
 418        pos = 0;
 419        for (i = 0; i < table_cnt; i++) {
 420                if ( symbol_valid(&table[i]) ) {
 421                        if (pos != i)
 422                                table[pos] = table[i];
 423                        learn_symbol(table[pos].sym, table[pos].len);
 424                        pos++;
 425                }
 426        }
 427        table_cnt = pos;
 428}
 429
 430static void *find_token(unsigned char *str, int len, unsigned char *token)
 431{
 432        int i;
 433
 434        for (i = 0; i < len - 1; i++) {
 435                if (str[i] == token[0] && str[i+1] == token[1])
 436                        return &str[i];
 437        }
 438        return NULL;
 439}
 440
 441/* replace a given token in all the valid symbols. Use the sampled symbols
 442 * to update the counts */
 443static void compress_symbols(unsigned char *str, int idx)
 444{
 445        unsigned int i, len, size;
 446        unsigned char *p1, *p2;
 447
 448        for (i = 0; i < table_cnt; i++) {
 449
 450                len = table[i].len;
 451                p1 = table[i].sym;
 452
 453                /* find the token on the symbol */
 454                p2 = find_token(p1, len, str);
 455                if (!p2) continue;
 456
 457                /* decrease the counts for this symbol's tokens */
 458                forget_symbol(table[i].sym, len);
 459
 460                size = len;
 461
 462                do {
 463                        *p2 = idx;
 464                        p2++;
 465                        size -= (p2 - p1);
 466                        memmove(p2, p2 + 1, size);
 467                        p1 = p2;
 468                        len--;
 469
 470                        if (size < 2) break;
 471
 472                        /* find the token on the symbol */
 473                        p2 = find_token(p1, size, str);
 474
 475                } while (p2);
 476
 477                table[i].len = len;
 478
 479                /* increase the counts for this symbol's new tokens */
 480                learn_symbol(table[i].sym, len);
 481        }
 482}
 483
 484/* search the token with the maximum profit */
 485static int find_best_token(void)
 486{
 487        int i, best, bestprofit;
 488
 489        bestprofit=-10000;
 490        best = 0;
 491
 492        for (i = 0; i < 0x10000; i++) {
 493                if (token_profit[i] > bestprofit) {
 494                        best = i;
 495                        bestprofit = token_profit[i];
 496                }
 497        }
 498        return best;
 499}
 500
 501/* this is the core of the algorithm: calculate the "best" table */
 502static void optimize_result(void)
 503{
 504        int i, best;
 505
 506        /* using the '\0' symbol last allows compress_symbols to use standard
 507         * fast string functions */
 508        for (i = 255; i >= 0; i--) {
 509
 510                /* if this table slot is empty (it is not used by an actual
 511                 * original char code */
 512                if (!best_table_len[i]) {
 513
 514                        /* find the token with the breates profit value */
 515                        best = find_best_token();
 516                        if (token_profit[best] == 0)
 517                                break;
 518
 519                        /* place it in the "best" table */
 520                        best_table_len[i] = 2;
 521                        best_table[i][0] = best & 0xFF;
 522                        best_table[i][1] = (best >> 8) & 0xFF;
 523
 524                        /* replace this token in all the valid symbols */
 525                        compress_symbols(best_table[i], i);
 526                }
 527        }
 528}
 529
 530/* start by placing the symbols that are actually used on the table */
 531static void insert_real_symbols_in_table(void)
 532{
 533        unsigned int i, j, c;
 534
 535        memset(best_table, 0, sizeof(best_table));
 536        memset(best_table_len, 0, sizeof(best_table_len));
 537
 538        for (i = 0; i < table_cnt; i++) {
 539                for (j = 0; j < table[i].len; j++) {
 540                        c = table[i].sym[j];
 541                        best_table[c][0]=c;
 542                        best_table_len[c]=1;
 543                }
 544        }
 545}
 546
 547static void optimize_token_table(void)
 548{
 549        build_initial_tok_table();
 550
 551        insert_real_symbols_in_table();
 552
 553        /* When valid symbol is not registered, exit to error */
 554        if (!table_cnt) {
 555                fprintf(stderr, "No valid symbol.\n");
 556                exit(1);
 557        }
 558
 559        optimize_result();
 560}
 561
 562/* guess for "linker script provide" symbol */
 563static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
 564{
 565        const char *symbol = (char *)se->sym + 1;
 566        int len = se->len - 1;
 567
 568        if (len < 8)
 569                return 0;
 570
 571        if (symbol[0] != '_' || symbol[1] != '_')
 572                return 0;
 573
 574        /* __start_XXXXX */
 575        if (!memcmp(symbol + 2, "start_", 6))
 576                return 1;
 577
 578        /* __stop_XXXXX */
 579        if (!memcmp(symbol + 2, "stop_", 5))
 580                return 1;
 581
 582        /* __end_XXXXX */
 583        if (!memcmp(symbol + 2, "end_", 4))
 584                return 1;
 585
 586        /* __XXXXX_start */
 587        if (!memcmp(symbol + len - 6, "_start", 6))
 588                return 1;
 589
 590        /* __XXXXX_end */
 591        if (!memcmp(symbol + len - 4, "_end", 4))
 592                return 1;
 593
 594        return 0;
 595}
 596
 597static int prefix_underscores_count(const char *str)
 598{
 599        const char *tail = str;
 600
 601        while (*tail == '_')
 602                tail++;
 603
 604        return tail - str;
 605}
 606
 607static int compare_symbols(const void *a, const void *b)
 608{
 609        const struct sym_entry *sa;
 610        const struct sym_entry *sb;
 611        int wa, wb;
 612
 613        sa = a;
 614        sb = b;
 615
 616        /* sort by address first */
 617        if (sa->addr > sb->addr)
 618                return 1;
 619        if (sa->addr < sb->addr)
 620                return -1;
 621
 622        /* sort by "weakness" type */
 623        wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
 624        wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
 625        if (wa != wb)
 626                return wa - wb;
 627
 628        /* sort by "linker script provide" type */
 629        wa = may_be_linker_script_provide_symbol(sa);
 630        wb = may_be_linker_script_provide_symbol(sb);
 631        if (wa != wb)
 632                return wa - wb;
 633
 634        /* sort by the number of prefix underscores */
 635        wa = prefix_underscores_count((const char *)sa->sym + 1);
 636        wb = prefix_underscores_count((const char *)sb->sym + 1);
 637        if (wa != wb)
 638                return wa - wb;
 639
 640        /* sort by initial order, so that other symbols are left undisturbed */
 641        return sa->start_pos - sb->start_pos;
 642}
 643
 644static void sort_symbols(void)
 645{
 646        qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
 647}
 648
 649int main(int argc, char **argv)
 650{
 651        if (argc >= 2) {
 652                int i;
 653                for (i = 1; i < argc; i++) {
 654                        if(strcmp(argv[i], "--all-symbols") == 0)
 655                                all_symbols = 1;
 656                        else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
 657                                char *p = &argv[i][16];
 658                                /* skip quote */
 659                                if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
 660                                        p++;
 661                                symbol_prefix_char = *p;
 662                        } else if (strncmp(argv[i], "--page-offset=", 14) == 0) {
 663                                const char *p = &argv[i][14];
 664                                kernel_start_addr = strtoull(p, NULL, 16);
 665                        } else
 666                                usage();
 667                }
 668        } else if (argc != 1)
 669                usage();
 670
 671        read_map(stdin);
 672        sort_symbols();
 673        optimize_token_table();
 674        write_src();
 675
 676        return 0;
 677}
 678
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