linux/kernel/kallsyms.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * kallsyms.c: in-kernel printing of symbolic oopses and stack traces.
   4 *
   5 * Rewritten and vastly simplified by Rusty Russell for in-kernel
   6 * module loader:
   7 *   Copyright 2002 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
   8 *
   9 * ChangeLog:
  10 *
  11 * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
  12 *      Changed the compression method from stem compression to "table lookup"
  13 *      compression (see scripts/kallsyms.c for a more complete description)
  14 */
  15#include <linux/kallsyms.h>
  16#include <linux/init.h>
  17#include <linux/seq_file.h>
  18#include <linux/fs.h>
  19#include <linux/kdb.h>
  20#include <linux/err.h>
  21#include <linux/proc_fs.h>
  22#include <linux/sched.h>        /* for cond_resched */
  23#include <linux/ctype.h>
  24#include <linux/slab.h>
  25#include <linux/filter.h>
  26#include <linux/ftrace.h>
  27#include <linux/kprobes.h>
  28#include <linux/compiler.h>
  29
  30/*
  31 * These will be re-linked against their real values
  32 * during the second link stage.
  33 */
  34extern const unsigned long kallsyms_addresses[] __weak;
  35extern const int kallsyms_offsets[] __weak;
  36extern const u8 kallsyms_names[] __weak;
  37
  38/*
  39 * Tell the compiler that the count isn't in the small data section if the arch
  40 * has one (eg: FRV).
  41 */
  42extern const unsigned int kallsyms_num_syms
  43__section(".rodata") __attribute__((weak));
  44
  45extern const unsigned long kallsyms_relative_base
  46__section(".rodata") __attribute__((weak));
  47
  48extern const char kallsyms_token_table[] __weak;
  49extern const u16 kallsyms_token_index[] __weak;
  50
  51extern const unsigned int kallsyms_markers[] __weak;
  52
  53/*
  54 * Expand a compressed symbol data into the resulting uncompressed string,
  55 * if uncompressed string is too long (>= maxlen), it will be truncated,
  56 * given the offset to where the symbol is in the compressed stream.
  57 */
  58static unsigned int kallsyms_expand_symbol(unsigned int off,
  59                                           char *result, size_t maxlen)
  60{
  61        int len, skipped_first = 0;
  62        const char *tptr;
  63        const u8 *data;
  64
  65        /* Get the compressed symbol length from the first symbol byte. */
  66        data = &kallsyms_names[off];
  67        len = *data;
  68        data++;
  69
  70        /*
  71         * Update the offset to return the offset for the next symbol on
  72         * the compressed stream.
  73         */
  74        off += len + 1;
  75
  76        /*
  77         * For every byte on the compressed symbol data, copy the table
  78         * entry for that byte.
  79         */
  80        while (len) {
  81                tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
  82                data++;
  83                len--;
  84
  85                while (*tptr) {
  86                        if (skipped_first) {
  87                                if (maxlen <= 1)
  88                                        goto tail;
  89                                *result = *tptr;
  90                                result++;
  91                                maxlen--;
  92                        } else
  93                                skipped_first = 1;
  94                        tptr++;
  95                }
  96        }
  97
  98tail:
  99        if (maxlen)
 100                *result = '\0';
 101
 102        /* Return to offset to the next symbol. */
 103        return off;
 104}
 105
 106/*
 107 * Get symbol type information. This is encoded as a single char at the
 108 * beginning of the symbol name.
 109 */
 110static char kallsyms_get_symbol_type(unsigned int off)
 111{
 112        /*
 113         * Get just the first code, look it up in the token table,
 114         * and return the first char from this token.
 115         */
 116        return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
 117}
 118
 119
 120/*
 121 * Find the offset on the compressed stream given and index in the
 122 * kallsyms array.
 123 */
 124static unsigned int get_symbol_offset(unsigned long pos)
 125{
 126        const u8 *name;
 127        int i;
 128
 129        /*
 130         * Use the closest marker we have. We have markers every 256 positions,
 131         * so that should be close enough.
 132         */
 133        name = &kallsyms_names[kallsyms_markers[pos >> 8]];
 134
 135        /*
 136         * Sequentially scan all the symbols up to the point we're searching
 137         * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
 138         * so we just need to add the len to the current pointer for every
 139         * symbol we wish to skip.
 140         */
 141        for (i = 0; i < (pos & 0xFF); i++)
 142                name = name + (*name) + 1;
 143
 144        return name - kallsyms_names;
 145}
 146
 147static unsigned long kallsyms_sym_address(int idx)
 148{
 149        if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
 150                return kallsyms_addresses[idx];
 151
 152        /* values are unsigned offsets if --absolute-percpu is not in effect */
 153        if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
 154                return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
 155
 156        /* ...otherwise, positive offsets are absolute values */
 157        if (kallsyms_offsets[idx] >= 0)
 158                return kallsyms_offsets[idx];
 159
 160        /* ...and negative offsets are relative to kallsyms_relative_base - 1 */
 161        return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
 162}
 163
 164/* Lookup the address for this symbol. Returns 0 if not found. */
 165unsigned long kallsyms_lookup_name(const char *name)
 166{
 167        char namebuf[KSYM_NAME_LEN];
 168        unsigned long i;
 169        unsigned int off;
 170
 171        for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 172                off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 173
 174                if (strcmp(namebuf, name) == 0)
 175                        return kallsyms_sym_address(i);
 176        }
 177        return module_kallsyms_lookup_name(name);
 178}
 179
 180int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 181                                      unsigned long),
 182                            void *data)
 183{
 184        char namebuf[KSYM_NAME_LEN];
 185        unsigned long i;
 186        unsigned int off;
 187        int ret;
 188
 189        for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 190                off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 191                ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
 192                if (ret != 0)
 193                        return ret;
 194        }
 195        return module_kallsyms_on_each_symbol(fn, data);
 196}
 197
 198static unsigned long get_symbol_pos(unsigned long addr,
 199                                    unsigned long *symbolsize,
 200                                    unsigned long *offset)
 201{
 202        unsigned long symbol_start = 0, symbol_end = 0;
 203        unsigned long i, low, high, mid;
 204
 205        /* This kernel should never had been booted. */
 206        if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
 207                BUG_ON(!kallsyms_addresses);
 208        else
 209                BUG_ON(!kallsyms_offsets);
 210
 211        /* Do a binary search on the sorted kallsyms_addresses array. */
 212        low = 0;
 213        high = kallsyms_num_syms;
 214
 215        while (high - low > 1) {
 216                mid = low + (high - low) / 2;
 217                if (kallsyms_sym_address(mid) <= addr)
 218                        low = mid;
 219                else
 220                        high = mid;
 221        }
 222
 223        /*
 224         * Search for the first aliased symbol. Aliased
 225         * symbols are symbols with the same address.
 226         */
 227        while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
 228                --low;
 229
 230        symbol_start = kallsyms_sym_address(low);
 231
 232        /* Search for next non-aliased symbol. */
 233        for (i = low + 1; i < kallsyms_num_syms; i++) {
 234                if (kallsyms_sym_address(i) > symbol_start) {
 235                        symbol_end = kallsyms_sym_address(i);
 236                        break;
 237                }
 238        }
 239
 240        /* If we found no next symbol, we use the end of the section. */
 241        if (!symbol_end) {
 242                if (is_kernel_inittext(addr))
 243                        symbol_end = (unsigned long)_einittext;
 244                else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
 245                        symbol_end = (unsigned long)_end;
 246                else
 247                        symbol_end = (unsigned long)_etext;
 248        }
 249
 250        if (symbolsize)
 251                *symbolsize = symbol_end - symbol_start;
 252        if (offset)
 253                *offset = addr - symbol_start;
 254
 255        return low;
 256}
 257
 258/*
 259 * Lookup an address but don't bother to find any names.
 260 */
 261int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
 262                                unsigned long *offset)
 263{
 264        char namebuf[KSYM_NAME_LEN];
 265
 266        if (is_ksym_addr(addr)) {
 267                get_symbol_pos(addr, symbolsize, offset);
 268                return 1;
 269        }
 270        return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf) ||
 271               !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
 272}
 273
 274/*
 275 * Lookup an address
 276 * - modname is set to NULL if it's in the kernel.
 277 * - We guarantee that the returned name is valid until we reschedule even if.
 278 *   It resides in a module.
 279 * - We also guarantee that modname will be valid until rescheduled.
 280 */
 281const char *kallsyms_lookup(unsigned long addr,
 282                            unsigned long *symbolsize,
 283                            unsigned long *offset,
 284                            char **modname, char *namebuf)
 285{
 286        const char *ret;
 287
 288        namebuf[KSYM_NAME_LEN - 1] = 0;
 289        namebuf[0] = 0;
 290
 291        if (is_ksym_addr(addr)) {
 292                unsigned long pos;
 293
 294                pos = get_symbol_pos(addr, symbolsize, offset);
 295                /* Grab name */
 296                kallsyms_expand_symbol(get_symbol_offset(pos),
 297                                       namebuf, KSYM_NAME_LEN);
 298                if (modname)
 299                        *modname = NULL;
 300                return namebuf;
 301        }
 302
 303        /* See if it's in a module or a BPF JITed image. */
 304        ret = module_address_lookup(addr, symbolsize, offset,
 305                                    modname, namebuf);
 306        if (!ret)
 307                ret = bpf_address_lookup(addr, symbolsize,
 308                                         offset, modname, namebuf);
 309
 310        if (!ret)
 311                ret = ftrace_mod_address_lookup(addr, symbolsize,
 312                                                offset, modname, namebuf);
 313        return ret;
 314}
 315
 316int lookup_symbol_name(unsigned long addr, char *symname)
 317{
 318        symname[0] = '\0';
 319        symname[KSYM_NAME_LEN - 1] = '\0';
 320
 321        if (is_ksym_addr(addr)) {
 322                unsigned long pos;
 323
 324                pos = get_symbol_pos(addr, NULL, NULL);
 325                /* Grab name */
 326                kallsyms_expand_symbol(get_symbol_offset(pos),
 327                                       symname, KSYM_NAME_LEN);
 328                return 0;
 329        }
 330        /* See if it's in a module. */
 331        return lookup_module_symbol_name(addr, symname);
 332}
 333
 334int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
 335                        unsigned long *offset, char *modname, char *name)
 336{
 337        name[0] = '\0';
 338        name[KSYM_NAME_LEN - 1] = '\0';
 339
 340        if (is_ksym_addr(addr)) {
 341                unsigned long pos;
 342
 343                pos = get_symbol_pos(addr, size, offset);
 344                /* Grab name */
 345                kallsyms_expand_symbol(get_symbol_offset(pos),
 346                                       name, KSYM_NAME_LEN);
 347                modname[0] = '\0';
 348                return 0;
 349        }
 350        /* See if it's in a module. */
 351        return lookup_module_symbol_attrs(addr, size, offset, modname, name);
 352}
 353
 354/* Look up a kernel symbol and return it in a text buffer. */
 355static int __sprint_symbol(char *buffer, unsigned long address,
 356                           int symbol_offset, int add_offset)
 357{
 358        char *modname;
 359        const char *name;
 360        unsigned long offset, size;
 361        int len;
 362
 363        address += symbol_offset;
 364        name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
 365        if (!name)
 366                return sprintf(buffer, "0x%lx", address - symbol_offset);
 367
 368        if (name != buffer)
 369                strcpy(buffer, name);
 370        len = strlen(buffer);
 371        offset -= symbol_offset;
 372
 373        if (add_offset)
 374                len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
 375
 376        if (modname)
 377                len += sprintf(buffer + len, " [%s]", modname);
 378
 379        return len;
 380}
 381
 382/**
 383 * sprint_symbol - Look up a kernel symbol and return it in a text buffer
 384 * @buffer: buffer to be stored
 385 * @address: address to lookup
 386 *
 387 * This function looks up a kernel symbol with @address and stores its name,
 388 * offset, size and module name to @buffer if possible. If no symbol was found,
 389 * just saves its @address as is.
 390 *
 391 * This function returns the number of bytes stored in @buffer.
 392 */
 393int sprint_symbol(char *buffer, unsigned long address)
 394{
 395        return __sprint_symbol(buffer, address, 0, 1);
 396}
 397EXPORT_SYMBOL_GPL(sprint_symbol);
 398
 399/**
 400 * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
 401 * @buffer: buffer to be stored
 402 * @address: address to lookup
 403 *
 404 * This function looks up a kernel symbol with @address and stores its name
 405 * and module name to @buffer if possible. If no symbol was found, just saves
 406 * its @address as is.
 407 *
 408 * This function returns the number of bytes stored in @buffer.
 409 */
 410int sprint_symbol_no_offset(char *buffer, unsigned long address)
 411{
 412        return __sprint_symbol(buffer, address, 0, 0);
 413}
 414EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
 415
 416/**
 417 * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
 418 * @buffer: buffer to be stored
 419 * @address: address to lookup
 420 *
 421 * This function is for stack backtrace and does the same thing as
 422 * sprint_symbol() but with modified/decreased @address. If there is a
 423 * tail-call to the function marked "noreturn", gcc optimized out code after
 424 * the call so that the stack-saved return address could point outside of the
 425 * caller. This function ensures that kallsyms will find the original caller
 426 * by decreasing @address.
 427 *
 428 * This function returns the number of bytes stored in @buffer.
 429 */
 430int sprint_backtrace(char *buffer, unsigned long address)
 431{
 432        return __sprint_symbol(buffer, address, -1, 1);
 433}
 434
 435/* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
 436struct kallsym_iter {
 437        loff_t pos;
 438        loff_t pos_arch_end;
 439        loff_t pos_mod_end;
 440        loff_t pos_ftrace_mod_end;
 441        loff_t pos_bpf_end;
 442        unsigned long value;
 443        unsigned int nameoff; /* If iterating in core kernel symbols. */
 444        char type;
 445        char name[KSYM_NAME_LEN];
 446        char module_name[MODULE_NAME_LEN];
 447        int exported;
 448        int show_value;
 449};
 450
 451int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
 452                            char *type, char *name)
 453{
 454        return -EINVAL;
 455}
 456
 457static int get_ksymbol_arch(struct kallsym_iter *iter)
 458{
 459        int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
 460                                   &iter->value, &iter->type,
 461                                   iter->name);
 462
 463        if (ret < 0) {
 464                iter->pos_arch_end = iter->pos;
 465                return 0;
 466        }
 467
 468        return 1;
 469}
 470
 471static int get_ksymbol_mod(struct kallsym_iter *iter)
 472{
 473        int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
 474                                     &iter->value, &iter->type,
 475                                     iter->name, iter->module_name,
 476                                     &iter->exported);
 477        if (ret < 0) {
 478                iter->pos_mod_end = iter->pos;
 479                return 0;
 480        }
 481
 482        return 1;
 483}
 484
 485/*
 486 * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
 487 * purposes. In that case "__builtin__ftrace" is used as a module name, even
 488 * though "__builtin__ftrace" is not a module.
 489 */
 490static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
 491{
 492        int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
 493                                         &iter->value, &iter->type,
 494                                         iter->name, iter->module_name,
 495                                         &iter->exported);
 496        if (ret < 0) {
 497                iter->pos_ftrace_mod_end = iter->pos;
 498                return 0;
 499        }
 500
 501        return 1;
 502}
 503
 504static int get_ksymbol_bpf(struct kallsym_iter *iter)
 505{
 506        int ret;
 507
 508        strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
 509        iter->exported = 0;
 510        ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
 511                              &iter->value, &iter->type,
 512                              iter->name);
 513        if (ret < 0) {
 514                iter->pos_bpf_end = iter->pos;
 515                return 0;
 516        }
 517
 518        return 1;
 519}
 520
 521/*
 522 * This uses "__builtin__kprobes" as a module name for symbols for pages
 523 * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
 524 * module.
 525 */
 526static int get_ksymbol_kprobe(struct kallsym_iter *iter)
 527{
 528        strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
 529        iter->exported = 0;
 530        return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
 531                                  &iter->value, &iter->type,
 532                                  iter->name) < 0 ? 0 : 1;
 533}
 534
 535/* Returns space to next name. */
 536static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
 537{
 538        unsigned off = iter->nameoff;
 539
 540        iter->module_name[0] = '\0';
 541        iter->value = kallsyms_sym_address(iter->pos);
 542
 543        iter->type = kallsyms_get_symbol_type(off);
 544
 545        off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
 546
 547        return off - iter->nameoff;
 548}
 549
 550static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
 551{
 552        iter->name[0] = '\0';
 553        iter->nameoff = get_symbol_offset(new_pos);
 554        iter->pos = new_pos;
 555        if (new_pos == 0) {
 556                iter->pos_arch_end = 0;
 557                iter->pos_mod_end = 0;
 558                iter->pos_ftrace_mod_end = 0;
 559                iter->pos_bpf_end = 0;
 560        }
 561}
 562
 563/*
 564 * The end position (last + 1) of each additional kallsyms section is recorded
 565 * in iter->pos_..._end as each section is added, and so can be used to
 566 * determine which get_ksymbol_...() function to call next.
 567 */
 568static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
 569{
 570        iter->pos = pos;
 571
 572        if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
 573            get_ksymbol_arch(iter))
 574                return 1;
 575
 576        if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
 577            get_ksymbol_mod(iter))
 578                return 1;
 579
 580        if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
 581            get_ksymbol_ftrace_mod(iter))
 582                return 1;
 583
 584        if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
 585            get_ksymbol_bpf(iter))
 586                return 1;
 587
 588        return get_ksymbol_kprobe(iter);
 589}
 590
 591/* Returns false if pos at or past end of file. */
 592static int update_iter(struct kallsym_iter *iter, loff_t pos)
 593{
 594        /* Module symbols can be accessed randomly. */
 595        if (pos >= kallsyms_num_syms)
 596                return update_iter_mod(iter, pos);
 597
 598        /* If we're not on the desired position, reset to new position. */
 599        if (pos != iter->pos)
 600                reset_iter(iter, pos);
 601
 602        iter->nameoff += get_ksymbol_core(iter);
 603        iter->pos++;
 604
 605        return 1;
 606}
 607
 608static void *s_next(struct seq_file *m, void *p, loff_t *pos)
 609{
 610        (*pos)++;
 611
 612        if (!update_iter(m->private, *pos))
 613                return NULL;
 614        return p;
 615}
 616
 617static void *s_start(struct seq_file *m, loff_t *pos)
 618{
 619        if (!update_iter(m->private, *pos))
 620                return NULL;
 621        return m->private;
 622}
 623
 624static void s_stop(struct seq_file *m, void *p)
 625{
 626}
 627
 628static int s_show(struct seq_file *m, void *p)
 629{
 630        void *value;
 631        struct kallsym_iter *iter = m->private;
 632
 633        /* Some debugging symbols have no name.  Ignore them. */
 634        if (!iter->name[0])
 635                return 0;
 636
 637        value = iter->show_value ? (void *)iter->value : NULL;
 638
 639        if (iter->module_name[0]) {
 640                char type;
 641
 642                /*
 643                 * Label it "global" if it is exported,
 644                 * "local" if not exported.
 645                 */
 646                type = iter->exported ? toupper(iter->type) :
 647                                        tolower(iter->type);
 648                seq_printf(m, "%px %c %s\t[%s]\n", value,
 649                           type, iter->name, iter->module_name);
 650        } else
 651                seq_printf(m, "%px %c %s\n", value,
 652                           iter->type, iter->name);
 653        return 0;
 654}
 655
 656static const struct seq_operations kallsyms_op = {
 657        .start = s_start,
 658        .next = s_next,
 659        .stop = s_stop,
 660        .show = s_show
 661};
 662
 663static inline int kallsyms_for_perf(void)
 664{
 665#ifdef CONFIG_PERF_EVENTS
 666        extern int sysctl_perf_event_paranoid;
 667        if (sysctl_perf_event_paranoid <= 1)
 668                return 1;
 669#endif
 670        return 0;
 671}
 672
 673/*
 674 * We show kallsyms information even to normal users if we've enabled
 675 * kernel profiling and are explicitly not paranoid (so kptr_restrict
 676 * is clear, and sysctl_perf_event_paranoid isn't set).
 677 *
 678 * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
 679 * block even that).
 680 */
 681bool kallsyms_show_value(const struct cred *cred)
 682{
 683        switch (kptr_restrict) {
 684        case 0:
 685                if (kallsyms_for_perf())
 686                        return true;
 687                fallthrough;
 688        case 1:
 689                if (security_capable(cred, &init_user_ns, CAP_SYSLOG,
 690                                     CAP_OPT_NOAUDIT) == 0)
 691                        return true;
 692                fallthrough;
 693        default:
 694                return false;
 695        }
 696}
 697
 698static int kallsyms_open(struct inode *inode, struct file *file)
 699{
 700        /*
 701         * We keep iterator in m->private, since normal case is to
 702         * s_start from where we left off, so we avoid doing
 703         * using get_symbol_offset for every symbol.
 704         */
 705        struct kallsym_iter *iter;
 706        iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
 707        if (!iter)
 708                return -ENOMEM;
 709        reset_iter(iter, 0);
 710
 711        /*
 712         * Instead of checking this on every s_show() call, cache
 713         * the result here at open time.
 714         */
 715        iter->show_value = kallsyms_show_value(file->f_cred);
 716        return 0;
 717}
 718
 719#ifdef  CONFIG_KGDB_KDB
 720const char *kdb_walk_kallsyms(loff_t *pos)
 721{
 722        static struct kallsym_iter kdb_walk_kallsyms_iter;
 723        if (*pos == 0) {
 724                memset(&kdb_walk_kallsyms_iter, 0,
 725                       sizeof(kdb_walk_kallsyms_iter));
 726                reset_iter(&kdb_walk_kallsyms_iter, 0);
 727        }
 728        while (1) {
 729                if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
 730                        return NULL;
 731                ++*pos;
 732                /* Some debugging symbols have no name.  Ignore them. */
 733                if (kdb_walk_kallsyms_iter.name[0])
 734                        return kdb_walk_kallsyms_iter.name;
 735        }
 736}
 737#endif  /* CONFIG_KGDB_KDB */
 738
 739static const struct proc_ops kallsyms_proc_ops = {
 740        .proc_open      = kallsyms_open,
 741        .proc_read      = seq_read,
 742        .proc_lseek     = seq_lseek,
 743        .proc_release   = seq_release_private,
 744};
 745
 746static int __init kallsyms_init(void)
 747{
 748        proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
 749        return 0;
 750}
 751device_initcall(kallsyms_init);
 752