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