kernel/kallsyms.c

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