about summary refs log tree commit diff
path: root/elf/dl-lookup.c
blob: 2b58ff32aac22d1f6c4a8efae8a5fe16b042f3a9 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
/* Look up a symbol in the loaded objects.
   Copyright (C) 1995,96,97,98,99,2000  Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <alloca.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <ldsodefs.h>
#include "dl-hash.h"
#include <dl-machine.h>
#include <bits/libc-lock.h>

#include <assert.h>

#define VERSTAG(tag)	(DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGIDX (tag))

/* We need this string more than once.  */
static const char undefined_msg[] = "undefined symbol: ";


struct sym_val
  {
    const ElfW(Sym) *s;
    struct link_map *m;
  };


#define make_string(string, rest...) \
  ({									      \
    const char *all[] = { string, ## rest };				      \
    size_t len, cnt;							      \
    char *result, *cp;							      \
									      \
    len = 1;								      \
    for (cnt = 0; cnt < sizeof (all) / sizeof (all[0]); ++cnt)		      \
      len += strlen (all[cnt]);						      \
									      \
    cp = result = alloca (len);						      \
    for (cnt = 0; cnt < sizeof (all) / sizeof (all[0]); ++cnt)		      \
      cp = __stpcpy (cp, all[cnt]);					      \
									      \
    result;								      \
  })

/* Statistics function.  */
unsigned long int _dl_num_relocations;

/* During the program run we must not modify the global data of
   loaded shared object simultanously in two threads.  Therefore we
   protect `_dl_open' and `_dl_close' in dl-close.c.

   This must be a recursive lock since the initializer function of
   the loaded object might as well require a call to this function.
   At this time it is not anymore a problem to modify the tables.  */
__libc_lock_define (extern, _dl_load_lock)


/* We have two different situations when looking up a simple: with or
   without versioning.  gcc is not able to optimize a single function
   definition serving for both purposes so we define two functions.  */
#define VERSIONED	0
#define PROTECTED	0
#include "do-lookup.h"

#define VERSIONED	1
#define PROTECTED	0
#include "do-lookup.h"


/* Add extra dependency on MAP to UNDEF_MAP.  */
static int
add_dependency (struct link_map *undef_map, struct link_map *map)
{
  struct link_map **list;
  unsigned int act;
  unsigned int i;
  int result = 0;

  /* Make sure nobody can unload the object while we are at it.  */
  __libc_lock_lock (_dl_load_lock);

  /* Determine whether UNDEF_MAP already has a reference to MAP.  First
     look in the normal dependencies.  */
  list = undef_map->l_searchlist.r_list;
  act = undef_map->l_searchlist.r_nlist;

  for (i = 0; i < act; ++i)
    if (list[i] == map)
      break;

  if (__builtin_expect (i == act, 1))
    {
      /* No normal dependency.  See whether we already had to add it
	 to the special list of dynamic dependencies.  */
      list = undef_map->l_reldeps;
      act = undef_map->l_reldepsact;

      for (i = 0; i < act; ++i)
	if (list[i] == map)
	  break;

      if (i == act)
	{
	  /* The object is not yet in the dependency list.  Before we add
	     it make sure just one more time the object we are about to
	     reference is still available.  There is a brief period in
	     which the object could have been removed since we found the
	     definition.  */
	  struct link_map *runp = _dl_loaded;

	  while (runp != NULL && runp != map)
	    runp = runp->l_next;

	  if (runp != NULL)
	    {
	      /* The object is still available.  Add the reference now.  */
	      if (__builtin_expect (act >= undef_map->l_reldepsmax, 0))
		{
		  /* Allocate more memory for the dependency list.  Since
		     this can never happen during the startup phase we can
		     use `realloc'.  */
		  void *newp;

		  undef_map->l_reldepsmax += 5;
		  newp = realloc (undef_map->l_reldeps,
				  undef_map->l_reldepsmax
				  * sizeof(struct link_map *));

		  if (__builtin_expect (newp != NULL, 1))
		    undef_map->l_reldeps = (struct link_map **) newp;
		  else
		    /* Correct the addition.  */
		    undef_map->l_reldepsmax -= 5;
		}

	      /* If we didn't manage to allocate memory for the list this
		 is no fatal mistake.  We simply increment the use counter
		 of the referenced object and don't record the dependencies.
		 This means this increment can never be reverted and the
		 object will never be unloaded.  This is semantically the
		 correct behaviour.  */
	      if (__builtin_expect (act < undef_map->l_reldepsmax, 1))
		undef_map->l_reldeps[undef_map->l_reldepsact++] = map;

	      /* And increment the counter in the referenced object.  */
	      ++map->l_opencount;

	      /* Display information if we are debugging.  */
	      if (__builtin_expect (_dl_debug_files, 0))
		_dl_debug_message (1, "\nfile=",
				   map->l_name[0] ? map->l_name : _dl_argv[0],
				   ";  needed by ",
				   undef_map->l_name[0]
				   ? undef_map->l_name : _dl_argv[0],
				   " (relocation dependency)\n\n", NULL);
	    }
	  else
	    /* Whoa, that was bad luck.  We have to search again.  */
	    result = -1;
	}
    }

  /* Release the lock.  */
  __libc_lock_unlock (_dl_load_lock);

  return result;
}


/* Search loaded objects' symbol tables for a definition of the symbol
   UNDEF_NAME.  */

lookup_t
internal_function
_dl_lookup_symbol (const char *undef_name, struct link_map *undef_map,
		   const ElfW(Sym) **ref, struct r_scope_elem *symbol_scope[],
		   int reloc_type, int explicit)
{
  const char *reference_name = undef_map ? undef_map->l_name : NULL;
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct r_scope_elem **scope;
  int protected;
  int noexec = elf_machine_lookup_noexec_p (reloc_type);
  int noplt = elf_machine_lookup_noplt_p (reloc_type);

  ++_dl_num_relocations;

  /* Search the relevant loaded objects for a definition.  */
  for (scope = symbol_scope; *scope; ++scope)
    if (do_lookup (undef_name, hash, *ref, &current_value, *scope, 0, NULL,
		   noexec, noplt))
      {
	/* We have to check whether this would bind UNDEF_MAP to an object
	   in the global scope which was dynamically loaded.  In this case
	   we have to prevent the latter from being unloaded unless the
	   UNDEF_MAP object is also unloaded.  */
	if (__builtin_expect (current_value.m->l_global, 0)
	    && (__builtin_expect (current_value.m->l_type, lt_library)
		== lt_loaded)
	    && undef_map != current_value.m
	    /* Don't do this for explicit lookups as opposed to implicit
	       runtime lookups.  */
	    && __builtin_expect (! explicit, 1)
	    /* Add UNDEF_MAP to the dependencies.  */
	    && add_dependency (undef_map, current_value.m) < 0)
	  /* Something went wrong.  Perhaps the object we tried to reference
	     was just removed.  Try finding another definition.  */
	  return _dl_lookup_symbol (undef_name, undef_map, ref, symbol_scope,
				    reloc_type, 0);

	break;
      }

  if (__builtin_expect (current_value.s == NULL, 0))
    {
      if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
	/* We could find no value for a strong reference.  */
	/* XXX We cannot translate the messages.  */
	_dl_signal_cerror (0, (reference_name && reference_name[0]
			       ? reference_name
			       : (_dl_argv[0] ?: "<main program>")),
			   make_string (undefined_msg, undef_name));
      *ref = NULL;
      return 0;
    }

  protected = *ref && ELFW(ST_VISIBILITY) ((*ref)->st_other) == STV_PROTECTED;

  if (__builtin_expect (_dl_debug_bindings, 0))
    _dl_debug_message (1, "binding file ",
		       (reference_name && reference_name[0]
			? reference_name
			: (_dl_argv[0] ?: "<main program>")),
		       " to ", current_value.m->l_name[0]
		       ? current_value.m->l_name : _dl_argv[0],
		       ": ", protected ? "protected" : "normal",
		       " symbol `", undef_name, "'\n", NULL);

  if (__builtin_expect (protected == 0, 1))
    {
      *ref = current_value.s;
      return LOOKUP_VALUE (current_value.m);
    }
  else
    {
      /* It is very tricky. We need to figure out what value to
         return for the protected symbol */
      struct sym_val protected_value = { NULL, NULL };

      for (scope = symbol_scope; *scope; ++scope)
	if (do_lookup (undef_name, hash, *ref, &protected_value, *scope, 0,
		       NULL, 0, 1))
	  break;

      if (protected_value.s == NULL || protected_value.m == undef_map)
	{
	  *ref = current_value.s;
	  return LOOKUP_VALUE (current_value.m);
	}

      return LOOKUP_VALUE (undef_map);
    }
}


/* This function is nearly the same as `_dl_lookup_symbol' but it
   skips in the first list all objects until SKIP_MAP is found.  I.e.,
   it only considers objects which were loaded after the described
   object.  If there are more search lists the object described by
   SKIP_MAP is only skipped.  */
lookup_t
internal_function
_dl_lookup_symbol_skip (const char *undef_name,
			struct link_map *undef_map, const ElfW(Sym) **ref,
			struct r_scope_elem *symbol_scope[],
			struct link_map *skip_map)
{
  const char *reference_name = undef_map ? undef_map->l_name : NULL;
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct r_scope_elem **scope;
  size_t i;
  int protected;

  ++_dl_num_relocations;

  /* Search the relevant loaded objects for a definition.  */
  scope = symbol_scope;
  for (i = 0; (*scope)->r_duplist[i] != skip_map; ++i)
    assert (i < (*scope)->r_nduplist);

  while (i >= (*scope)->r_nlist
	 || ! do_lookup (undef_name, hash, *ref, &current_value, *scope, i,
			 skip_map, 0, 0))
    while (*++scope)
      if (do_lookup (undef_name, hash, *ref, &current_value, *scope, 0,
		     skip_map, 0, 0))
	break;

  if (__builtin_expect (current_value.s == NULL, 0))
    {
      *ref = NULL;
      return 0;
    }

  protected = *ref && ELFW(ST_VISIBILITY) ((*ref)->st_other) == STV_PROTECTED;

  if (__builtin_expect (_dl_debug_bindings, 0))
    _dl_debug_message (1, "binding file ",
		       (reference_name && reference_name[0]
			? reference_name
			: (_dl_argv[0] ?: "<main program>")),
		       " to ", current_value.m->l_name[0]
		       ? current_value.m->l_name : _dl_argv[0],
		       ": ", protected ? "protected" : "normal",
		       " symbol `", undef_name, "'\n", NULL);

  if (__builtin_expect (protected == 0, 1))
    {
      *ref = current_value.s;
      return LOOKUP_VALUE (current_value.m);
    }
  else
    {
      /* It is very tricky.  We need to figure out what value to
         return for the protected symbol.  */
      struct sym_val protected_value = { NULL, NULL };

      if (i >= (*scope)->r_nlist
	  || !do_lookup (undef_name, hash, *ref, &protected_value, *scope, i,
			 skip_map, 0, 1))
	while (*++scope)
	  if (do_lookup (undef_name, hash, *ref, &protected_value, *scope, 0,
			 skip_map, 0, 1))
	    break;

      if (protected_value.s == NULL || protected_value.m == undef_map)
	{
	  *ref = current_value.s;
	  return LOOKUP_VALUE (current_value.m);
	}

      return LOOKUP_VALUE (undef_map);
    }
}


/* This function works like _dl_lookup_symbol but it takes an
   additional arguement with the version number of the requested
   symbol.

   XXX We'll see whether we need this separate function.  */
lookup_t
internal_function
_dl_lookup_versioned_symbol (const char *undef_name,
			     struct link_map *undef_map, const ElfW(Sym) **ref,
			     struct r_scope_elem *symbol_scope[],
			     const struct r_found_version *version,
			     int reloc_type, int explicit)
{
  const char *reference_name = undef_map ? undef_map->l_name : NULL;
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct r_scope_elem **scope;
  int protected;
  int noexec = elf_machine_lookup_noexec_p (reloc_type);
  int noplt = elf_machine_lookup_noplt_p (reloc_type);

  ++_dl_num_relocations;

  /* Search the relevant loaded objects for a definition.  */
  for (scope = symbol_scope; *scope; ++scope)
    {
      int res = do_lookup_versioned (undef_name, hash, *ref, &current_value,
				     *scope, 0, version, NULL, noexec, noplt);
      if (res > 0)
	{
	  /* We have to check whether this would bind UNDEF_MAP to an object
	     in the global scope which was dynamically loaded.  In this case
	     we have to prevent the latter from being unloaded unless the
	     UNDEF_MAP object is also unloaded.  */
	  if (__builtin_expect (current_value.m->l_global, 0)
	      && (__builtin_expect (current_value.m->l_type, lt_library)
		  == lt_loaded)
	      && undef_map != current_value.m
	      /* Don't do this for explicit lookups as opposed to implicit
		 runtime lookups.  */
	      && __builtin_expect (! explicit, 1)
	      /* Add UNDEF_MAP to the dependencies.  */
	      && add_dependency (undef_map, current_value.m) < 0)
	    /* Something went wrong.  Perhaps the object we tried to reference
	       was just removed.  Try finding another definition.  */
	    return _dl_lookup_versioned_symbol (undef_name, undef_map, ref,
						symbol_scope, version,
						reloc_type, 0);

	  break;
	}

      if (__builtin_expect (res, 0) < 0)
	{
	  /* Oh, oh.  The file named in the relocation entry does not
	     contain the needed symbol.  */
	  /* XXX We cannot translate the message.  */
	  _dl_signal_cerror (0, (reference_name && reference_name[0]
				 ? reference_name
				 : (_dl_argv[0] ?: "<main program>")),
			     make_string ("symbol ", undef_name, ", version ",
					  version->name,
					  " not defined in file ",
					  version->filename,
					  " with link time reference",
					  res == -2
					  ? " (no version symbols)" : ""));
	  *ref = NULL;
	  return 0;
	}
    }

  if (__builtin_expect (current_value.s == NULL, 0))
    {
      if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
	/* We could find no value for a strong reference.  */
	/* XXX We cannot translate the message.  */
	_dl_signal_cerror (0, (reference_name && reference_name[0]
			       ? reference_name
			       : (_dl_argv[0] ?: "<main program>")),
			   make_string (undefined_msg, undef_name,
					", version ", version->name ?: NULL));
      *ref = NULL;
      return 0;
    }

  protected = *ref && ELFW(ST_VISIBILITY) ((*ref)->st_other) == STV_PROTECTED;

  if (__builtin_expect (_dl_debug_bindings, 0))
    _dl_debug_message (1, "binding file ",
		       (reference_name && reference_name[0]
			? reference_name
			: (_dl_argv[0] ?: "<main program>")),
		       " to ", current_value.m->l_name[0]
		       ? current_value.m->l_name : _dl_argv[0],
		       ": ", protected ? "protected" : "normal",
		       " symbol `", undef_name, "' [", version->name,
		       "]\n", NULL);

  if (__builtin_expect (protected == 0, 1))
    {
      *ref = current_value.s;
      return LOOKUP_VALUE (current_value.m);
    }
  else
    {
      /* It is very tricky. We need to figure out what value to
         return for the protected symbol */
      struct sym_val protected_value = { NULL, NULL };

      for (scope = symbol_scope; *scope; ++scope)
	if (do_lookup_versioned (undef_name, hash, *ref, &protected_value,
				 *scope, 0, version, NULL, 0, 1))
	  break;

      if (protected_value.s == NULL || protected_value.m == undef_map)
	{
	  *ref = current_value.s;
	  return LOOKUP_VALUE (current_value.m);
	}

      return LOOKUP_VALUE (undef_map);
    }
}


/* Similar to _dl_lookup_symbol_skip but takes an additional argument
   with the version we are looking for.  */
lookup_t
internal_function
_dl_lookup_versioned_symbol_skip (const char *undef_name,
				  struct link_map *undef_map,
				  const ElfW(Sym) **ref,
				  struct r_scope_elem *symbol_scope[],
				  const struct r_found_version *version,
				  struct link_map *skip_map)
{
  const char *reference_name = undef_map ? undef_map->l_name : NULL;
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct r_scope_elem **scope;
  size_t i;
  int protected;

  ++_dl_num_relocations;

  /* Search the relevant loaded objects for a definition.  */
  scope = symbol_scope;
  for (i = 0; (*scope)->r_duplist[i] != skip_map; ++i)
    assert (i < (*scope)->r_nduplist);

  if (i >= (*scope)->r_nlist
      || ! do_lookup_versioned (undef_name, hash, *ref, &current_value,
				*scope, i, version, skip_map, 0, 0))
    while (*++scope)
      if (do_lookup_versioned (undef_name, hash, *ref, &current_value, *scope,
			       0, version, skip_map, 0, 0))
	break;

  if (__builtin_expect (current_value.s == NULL, 0))
    {
      if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
	{
	  /* We could find no value for a strong reference.  */
	  const size_t len = strlen (undef_name);
	  char buf[sizeof undefined_msg + len];
	  __mempcpy (__mempcpy (buf, undefined_msg, sizeof undefined_msg - 1),
		     undef_name, len + 1);
	  /* XXX We cannot translate the messages.  */
	  _dl_signal_cerror (0, (reference_name && reference_name[0]
				 ? reference_name
				 : (_dl_argv[0] ?: "<main program>")), buf);
	}
      *ref = NULL;
      return 0;
    }

  protected = *ref && ELFW(ST_VISIBILITY) ((*ref)->st_other) == STV_PROTECTED;

  if (__builtin_expect (_dl_debug_bindings, 0))
    _dl_debug_message (1, "binding file ",
		       (reference_name && reference_name[0]
			? reference_name
			: (_dl_argv[0] ?: "<main program>")),
		       " to ", current_value.m->l_name[0]
		       ? current_value.m->l_name : _dl_argv[0],
		       ": ", protected ? "protected" : "normal",
		       " symbol `", undef_name, "' [", version->name,
		       "]\n", NULL);

  if (__builtin_expect (protected == 0, 1))
    {
      *ref = current_value.s;
      return LOOKUP_VALUE (current_value.m);
    }
  else
    {
      /* It is very tricky. We need to figure out what value to
         return for the protected symbol */
      struct sym_val protected_value = { NULL, NULL };

      if (i >= (*scope)->r_nlist
	  || !do_lookup_versioned (undef_name, hash, *ref, &protected_value,
				   *scope, i, version, skip_map, 0, 1))
	while (*++scope)
	  if (do_lookup_versioned (undef_name, hash, *ref, &protected_value,
				   *scope, 0, version, skip_map, 0, 1))
	    break;

      if (protected_value.s == NULL || protected_value.m == undef_map)
	{
	  *ref = current_value.s;
	  return LOOKUP_VALUE (current_value.m);
	}

      return LOOKUP_VALUE (undef_map);
    }
}


/* Cache the location of MAP's hash table.  */

void
internal_function
_dl_setup_hash (struct link_map *map)
{
  Elf_Symndx *hash;
  Elf_Symndx nchain;

  if (!map->l_info[DT_HASH])
    return;
  hash = (void *)(map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr);

  map->l_nbuckets = *hash++;
  nchain = *hash++;
  map->l_buckets = hash;
  hash += map->l_nbuckets;
  map->l_chain = hash;
}