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/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  */
  34 extern const unsigned long kallsyms_addresses[] __weak;
  35 extern const int kallsyms_offsets[] __weak;
  36 extern 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  */
  42 extern const unsigned int kallsyms_num_syms
  43 __section(".rodata") __attribute__((weak));
  44
  45 extern const unsigned long kallsyms_relative_base
  46 __section(".rodata") __attribute__((weak));
  47
  48 extern const char kallsyms_token_table[] __weak;
  49 extern const u16 kallsyms_token_index[] __weak;
  50
  51 extern 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  */
  58 static 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
  98 tail:
  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  */
 110 static 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  */
 124 static 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
 147 static 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. */
 165 unsigned 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
 180 int 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
 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         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
 451 int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
 452                             char *type, char *name)
 453 {
 454         return -EINVAL;
 455 }
 456
 457 static 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
 471 static 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  */
 490 static 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
 504 static 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  */
 526 static 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. */
 536 static 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
 550 static 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  */
 568 static 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. */
 592 static 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
 608 static 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
 617 static 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
 624 static void s_stop(struct seq_file *m, void *p)
 625 {
 626 }
 627
 628 static 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
 656 static const struct seq_operations kallsyms_op = {
 657         .start = s_start,
 658         .next = s_next,
 659         .stop = s_stop,
 660         .show = s_show
 661 };
 662
 663 static 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  */
 681 bool 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
 698 static 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
 720 const 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
 739 static 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
 746 static int __init kallsyms_init(void)
 747 {
 748         proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
 749         return 0;
 750 }
 751 device_initcall(kallsyms_init);