kernel/kallsyms.c

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