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