root/kernel/kallsyms.c

DEFINITIONS

1. kallsyms_expand_symbol
2. kallsyms_get_symbol_type
3. get_symbol_offset
4. kallsyms_sym_address
5. kallsyms_lookup_name
6. kallsyms_on_each_symbol
7. get_symbol_pos
8. kallsyms_lookup_size_offset
9. kallsyms_lookup
10. lookup_symbol_name
11. lookup_symbol_attrs
12. __sprint_symbol
13. sprint_symbol
14. sprint_symbol_no_offset
15. sprint_backtrace
16. arch_get_kallsym
17. get_ksymbol_arch
18. get_ksymbol_mod
19. get_ksymbol_ftrace_mod
20. get_ksymbol_bpf
21. get_ksymbol_core
22. reset_iter
23. update_iter_mod
24. update_iter
25. s_next
26. s_start
27. s_stop
28. s_show
29. kallsyms_for_perf
30. kallsyms_show_value
31. kallsyms_open
32. kdb_walk_kallsyms
33. kallsyms_init

   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/compiler.h>
  28 
  29 /*
  30  * These will be re-linked against their real values
  31  * during the second link stage.
  32  */
  33 extern const unsigned long kallsyms_addresses[] __weak;
  34 extern const int kallsyms_offsets[] __weak;
  35 extern const u8 kallsyms_names[] __weak;
  36 
  37 /*
  38  * Tell the compiler that the count isn't in the small data section if the arch
  39  * has one (eg: FRV).
  40  */
  41 extern const unsigned int kallsyms_num_syms
  42 __attribute__((weak, section(".rodata")));
  43 
  44 extern const unsigned long kallsyms_relative_base
  45 __attribute__((weak, section(".rodata")));
  46 
  47 extern const u8 kallsyms_token_table[] __weak;
  48 extern const u16 kallsyms_token_index[] __weak;
  49 
  50 extern const unsigned int kallsyms_markers[] __weak;
  51 
  52 /*
  53  * Expand a compressed symbol data into the resulting uncompressed string,
  54  * if uncompressed string is too long (>= maxlen), it will be truncated,
  55  * given the offset to where the symbol is in the compressed stream.
  56  */
  57 static unsigned int kallsyms_expand_symbol(unsigned int off,
  58                                            char *result, size_t maxlen)
  59 {
  60         int len, skipped_first = 0;
  61         const u8 *tptr, *data;
  62 
  63         /* Get the compressed symbol length from the first symbol byte. */
  64         data = &kallsyms_names[off];
  65         len = *data;
  66         data++;
  67 
  68         /*
  69          * Update the offset to return the offset for the next symbol on
  70          * the compressed stream.
  71          */
  72         off += len + 1;
  73 
  74         /*
  75          * For every byte on the compressed symbol data, copy the table
  76          * entry for that byte.
  77          */
  78         while (len) {
  79                 tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
  80                 data++;
  81                 len--;
  82 
  83                 while (*tptr) {
  84                         if (skipped_first) {
  85                                 if (maxlen <= 1)
  86                                         goto tail;
  87                                 *result = *tptr;
  88                                 result++;
  89                                 maxlen--;
  90                         } else
  91                                 skipped_first = 1;
  92                         tptr++;
  93                 }
  94         }
  95 
  96 tail:
  97         if (maxlen)
  98                 *result = '\0';
  99 
 100         /* Return to offset to the next symbol. */
 101         return off;
 102 }
 103 
 104 /*
 105  * Get symbol type information. This is encoded as a single char at the
 106  * beginning of the symbol name.
 107  */
 108 static char kallsyms_get_symbol_type(unsigned int off)
 109 {
 110         /*
 111          * Get just the first code, look it up in the token table,
 112          * and return the first char from this token.
 113          */
 114         return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
 115 }
 116 
 117 
 118 /*
 119  * Find the offset on the compressed stream given and index in the
 120  * kallsyms array.
 121  */
 122 static unsigned int get_symbol_offset(unsigned long pos)
 123 {
 124         const u8 *name;
 125         int i;
 126 
 127         /*
 128          * Use the closest marker we have. We have markers every 256 positions,
 129          * so that should be close enough.
 130          */
 131         name = &kallsyms_names[kallsyms_markers[pos >> 8]];
 132 
 133         /*
 134          * Sequentially scan all the symbols up to the point we're searching
 135          * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
 136          * so we just need to add the len to the current pointer for every
 137          * symbol we wish to skip.
 138          */
 139         for (i = 0; i < (pos & 0xFF); i++)
 140                 name = name + (*name) + 1;
 141 
 142         return name - kallsyms_names;
 143 }
 144 
 145 static unsigned long kallsyms_sym_address(int idx)
 146 {
 147         if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
 148                 return kallsyms_addresses[idx];
 149 
 150         /* values are unsigned offsets if --absolute-percpu is not in effect */
 151         if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
 152                 return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
 153 
 154         /* ...otherwise, positive offsets are absolute values */
 155         if (kallsyms_offsets[idx] >= 0)
 156                 return kallsyms_offsets[idx];
 157 
 158         /* ...and negative offsets are relative to kallsyms_relative_base - 1 */
 159         return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
 160 }
 161 
 162 /* Lookup the address for this symbol. Returns 0 if not found. */
 163 unsigned long kallsyms_lookup_name(const char *name)
 164 {
 165         char namebuf[KSYM_NAME_LEN];
 166         unsigned long i;
 167         unsigned int off;
 168 
 169         for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 170                 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 171 
 172                 if (strcmp(namebuf, name) == 0)
 173                         return kallsyms_sym_address(i);
 174         }
 175         return module_kallsyms_lookup_name(name);
 176 }
 177 EXPORT_SYMBOL_GPL(kallsyms_lookup_name);
 178 
 179 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 180                                       unsigned long),
 181                             void *data)
 182 {
 183         char namebuf[KSYM_NAME_LEN];
 184         unsigned long i;
 185         unsigned int off;
 186         int ret;
 187 
 188         for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 189                 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 190                 ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
 191                 if (ret != 0)
 192                         return ret;
 193         }
 194         return module_kallsyms_on_each_symbol(fn, data);
 195 }
 196 EXPORT_SYMBOL_GPL(kallsyms_on_each_symbol);
 197 
 198 static 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  */
 261 int 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  */
 281 const 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 
 316 int 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 
 334 int 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. */
 355 static 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  */
 393 int sprint_symbol(char *buffer, unsigned long address)
 394 {
 395         return __sprint_symbol(buffer, address, 0, 1);
 396 }
 397 EXPORT_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  */
 410 int sprint_symbol_no_offset(char *buffer, unsigned long address)
 411 {
 412         return __sprint_symbol(buffer, address, 0, 0);
 413 }
 414 EXPORT_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  */
 430 int 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. */
 436 struct 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         unsigned long value;
 442         unsigned int nameoff; /* If iterating in core kernel symbols. */
 443         char type;
 444         char name[KSYM_NAME_LEN];
 445         char module_name[MODULE_NAME_LEN];
 446         int exported;
 447         int show_value;
 448 };
 449 
 450 int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
 451                             char *type, char *name)
 452 {
 453         return -EINVAL;
 454 }
 455 
 456 static int get_ksymbol_arch(struct kallsym_iter *iter)
 457 {
 458         int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
 459                                    &iter->value, &iter->type,
 460                                    iter->name);
 461 
 462         if (ret < 0) {
 463                 iter->pos_arch_end = iter->pos;
 464                 return 0;
 465         }
 466 
 467         return 1;
 468 }
 469 
 470 static int get_ksymbol_mod(struct kallsym_iter *iter)
 471 {
 472         int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
 473                                      &iter->value, &iter->type,
 474                                      iter->name, iter->module_name,
 475                                      &iter->exported);
 476         if (ret < 0) {
 477                 iter->pos_mod_end = iter->pos;
 478                 return 0;
 479         }
 480 
 481         return 1;
 482 }
 483 
 484 static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
 485 {
 486         int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
 487                                          &iter->value, &iter->type,
 488                                          iter->name, iter->module_name,
 489                                          &iter->exported);
 490         if (ret < 0) {
 491                 iter->pos_ftrace_mod_end = iter->pos;
 492                 return 0;
 493         }
 494 
 495         return 1;
 496 }
 497 
 498 static int get_ksymbol_bpf(struct kallsym_iter *iter)
 499 {
 500         strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
 501         iter->exported = 0;
 502         return bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
 503                                &iter->value, &iter->type,
 504                                iter->name) < 0 ? 0 : 1;
 505 }
 506 
 507 /* Returns space to next name. */
 508 static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
 509 {
 510         unsigned off = iter->nameoff;
 511 
 512         iter->module_name[0] = '\0';
 513         iter->value = kallsyms_sym_address(iter->pos);
 514 
 515         iter->type = kallsyms_get_symbol_type(off);
 516 
 517         off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
 518 
 519         return off - iter->nameoff;
 520 }
 521 
 522 static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
 523 {
 524         iter->name[0] = '\0';
 525         iter->nameoff = get_symbol_offset(new_pos);
 526         iter->pos = new_pos;
 527         if (new_pos == 0) {
 528                 iter->pos_arch_end = 0;
 529                 iter->pos_mod_end = 0;
 530                 iter->pos_ftrace_mod_end = 0;
 531         }
 532 }
 533 
 534 /*
 535  * The end position (last + 1) of each additional kallsyms section is recorded
 536  * in iter->pos_..._end as each section is added, and so can be used to
 537  * determine which get_ksymbol_...() function to call next.
 538  */
 539 static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
 540 {
 541         iter->pos = pos;
 542 
 543         if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
 544             get_ksymbol_arch(iter))
 545                 return 1;
 546 
 547         if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
 548             get_ksymbol_mod(iter))
 549                 return 1;
 550 
 551         if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
 552             get_ksymbol_ftrace_mod(iter))
 553                 return 1;
 554 
 555         return get_ksymbol_bpf(iter);
 556 }
 557 
 558 /* Returns false if pos at or past end of file. */
 559 static int update_iter(struct kallsym_iter *iter, loff_t pos)
 560 {
 561         /* Module symbols can be accessed randomly. */
 562         if (pos >= kallsyms_num_syms)
 563                 return update_iter_mod(iter, pos);
 564 
 565         /* If we're not on the desired position, reset to new position. */
 566         if (pos != iter->pos)
 567                 reset_iter(iter, pos);
 568 
 569         iter->nameoff += get_ksymbol_core(iter);
 570         iter->pos++;
 571 
 572         return 1;
 573 }
 574 
 575 static void *s_next(struct seq_file *m, void *p, loff_t *pos)
 576 {
 577         (*pos)++;
 578 
 579         if (!update_iter(m->private, *pos))
 580                 return NULL;
 581         return p;
 582 }
 583 
 584 static void *s_start(struct seq_file *m, loff_t *pos)
 585 {
 586         if (!update_iter(m->private, *pos))
 587                 return NULL;
 588         return m->private;
 589 }
 590 
 591 static void s_stop(struct seq_file *m, void *p)
 592 {
 593 }
 594 
 595 static int s_show(struct seq_file *m, void *p)
 596 {
 597         void *value;
 598         struct kallsym_iter *iter = m->private;
 599 
 600         /* Some debugging symbols have no name.  Ignore them. */
 601         if (!iter->name[0])
 602                 return 0;
 603 
 604         value = iter->show_value ? (void *)iter->value : NULL;
 605 
 606         if (iter->module_name[0]) {
 607                 char type;
 608 
 609                 /*
 610                  * Label it "global" if it is exported,
 611                  * "local" if not exported.
 612                  */
 613                 type = iter->exported ? toupper(iter->type) :
 614                                         tolower(iter->type);
 615                 seq_printf(m, "%px %c %s\t[%s]\n", value,
 616                            type, iter->name, iter->module_name);
 617         } else
 618                 seq_printf(m, "%px %c %s\n", value,
 619                            iter->type, iter->name);
 620         return 0;
 621 }
 622 
 623 static const struct seq_operations kallsyms_op = {
 624         .start = s_start,
 625         .next = s_next,
 626         .stop = s_stop,
 627         .show = s_show
 628 };
 629 
 630 static inline int kallsyms_for_perf(void)
 631 {
 632 #ifdef CONFIG_PERF_EVENTS
 633         extern int sysctl_perf_event_paranoid;
 634         if (sysctl_perf_event_paranoid <= 1)
 635                 return 1;
 636 #endif
 637         return 0;
 638 }
 639 
 640 /*
 641  * We show kallsyms information even to normal users if we've enabled
 642  * kernel profiling and are explicitly not paranoid (so kptr_restrict
 643  * is clear, and sysctl_perf_event_paranoid isn't set).
 644  *
 645  * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
 646  * block even that).
 647  */
 648 int kallsyms_show_value(void)
 649 {
 650         switch (kptr_restrict) {
 651         case 0:
 652                 if (kallsyms_for_perf())
 653                         return 1;
 654         /* fallthrough */
 655         case 1:
 656                 if (has_capability_noaudit(current, CAP_SYSLOG))
 657                         return 1;
 658         /* fallthrough */
 659         default:
 660                 return 0;
 661         }
 662 }
 663 
 664 static int kallsyms_open(struct inode *inode, struct file *file)
 665 {
 666         /*
 667          * We keep iterator in m->private, since normal case is to
 668          * s_start from where we left off, so we avoid doing
 669          * using get_symbol_offset for every symbol.
 670          */
 671         struct kallsym_iter *iter;
 672         iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
 673         if (!iter)
 674                 return -ENOMEM;
 675         reset_iter(iter, 0);
 676 
 677         iter->show_value = kallsyms_show_value();
 678         return 0;
 679 }
 680 
 681 #ifdef  CONFIG_KGDB_KDB
 682 const char *kdb_walk_kallsyms(loff_t *pos)
 683 {
 684         static struct kallsym_iter kdb_walk_kallsyms_iter;
 685         if (*pos == 0) {
 686                 memset(&kdb_walk_kallsyms_iter, 0,
 687                        sizeof(kdb_walk_kallsyms_iter));
 688                 reset_iter(&kdb_walk_kallsyms_iter, 0);
 689         }
 690         while (1) {
 691                 if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
 692                         return NULL;
 693                 ++*pos;
 694                 /* Some debugging symbols have no name.  Ignore them. */
 695                 if (kdb_walk_kallsyms_iter.name[0])
 696                         return kdb_walk_kallsyms_iter.name;
 697         }
 698 }
 699 #endif  /* CONFIG_KGDB_KDB */
 700 
 701 static const struct file_operations kallsyms_operations = {
 702         .open = kallsyms_open,
 703         .read = seq_read,
 704         .llseek = seq_lseek,
 705         .release = seq_release_private,
 706 };
 707 
 708 static int __init kallsyms_init(void)
 709 {
 710         proc_create("kallsyms", 0444, NULL, &kallsyms_operations);
 711         return 0;
 712 }
 713 device_initcall(kallsyms_init);