summary refs log tree commit diff
path: root/elf/dl-lookup.c
blob: b3695aeb99496e8f54713d2c63c3193d141263cc (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
/* Look up a symbol in the loaded objects.
   Copyright (C) 1995-2002, 2003, 2004, 2005 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 Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 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
   Lesser General Public License for more details.

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

#include <alloca.h>
#include <libintl.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 <tls.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.  */
#ifdef SHARED
# define bump_num_relocations() ++GL(dl_num_relocations)
#else
# define bump_num_relocations() ((void) 0)
#endif


/* The actual lookup code.  */
#include "do-lookup.h"


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

  /* Avoid self-references and references to objects which cannot be
     unloaded anyway.  */
  if (undef_map == map)
    return 0;

  /* Make sure nobody can unload the object while we are at it.  */
  __rtld_lock_lock_recursive (GL(dl_load_lock));

  /* Avoid references to objects which cannot be unloaded anyway.  */
  if (map->l_type != lt_loaded
      || (map->l_flags_1 & DF_1_NODELETE) != 0)
    goto out;

  /* If the object with the undefined reference cannot be removed ever
     just make sure the same is true for the object which contains the
     definition.  */
  if (undef_map->l_type != lt_loaded
      || (undef_map->l_flags_1 & DF_1_NODELETE) != 0)
    {
      map->l_flags_1 |= DF_1_NODELETE;
      goto out;
    }

  /* Determine whether UNDEF_MAP already has a reference to MAP.  First
     look in the normal dependencies.  */
  if (undef_map->l_searchlist.r_list != NULL)
    {
      list = undef_map->l_initfini;

      for (i = 0; list[i] != NULL; ++i)
	if (list[i] == map)
	  goto out;
    }

  /* 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)
      goto out;

  /* 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.  */
  runp = GL(dl_ns)[undef_map->l_ns]._ns_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
	 behavior.  */
      if (__builtin_expect (act < undef_map->l_reldepsmax, 1))
	undef_map->l_reldeps[undef_map->l_reldepsact++] = map;

      /* Display information if we are debugging.  */
      if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_FILES, 0))
	_dl_debug_printf ("\
\nfile=%s [%lu];  needed by %s [%lu] (relocation dependency)\n\n",
			  map->l_name[0] ? map->l_name : rtld_progname,
			  map->l_ns,
			  undef_map->l_name[0]
			  ? undef_map->l_name : rtld_progname,
			  undef_map->l_ns);
    }
  else
    /* Whoa, that was bad luck.  We have to search again.  */
    result = -1;

 out:
  /* Release the lock.  */
  __rtld_lock_unlock_recursive (GL(dl_load_lock));

  return result;
}

static void
internal_function
_dl_debug_bindings (const char *undef_name, struct link_map *undef_map,
		    const ElfW(Sym) **ref, struct r_scope_elem *symbol_scope[],
		    struct sym_val *value,
		    const struct r_found_version *version, int type_class,
		    int protected);


/* Search loaded objects' symbol tables for a definition of the symbol
   UNDEF_NAME, perhaps with a requested version for the symbol.  */
lookup_t
internal_function
_dl_lookup_symbol_x (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 type_class, int flags, struct link_map *skip_map)
{
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct r_scope_elem **scope = symbol_scope;

  bump_num_relocations ();

  /* No other flag than DL_LOOKUP_ADD_DEPENDENCY is allowed if we look
     up a versioned symbol.  */
  assert (version == NULL || flags == 0 || flags == DL_LOOKUP_ADD_DEPENDENCY);

  size_t i = 0;
  if (__builtin_expect (skip_map != NULL, 0))
    {
      /* Search the relevant loaded objects for a definition.  */
      while ((*scope)->r_list[i] != skip_map)
	++i;

      assert (i < (*scope)->r_nlist);
    }

  /* Search the relevant loaded objects for a definition.  */
  for (size_t start = i; *scope != NULL; start = 0, ++scope)
    {
      int res = do_lookup_x (undef_name, hash, *ref, &current_value, *scope,
			     start, version, flags, skip_map, type_class);
      if (res > 0)
	break;

      if (__builtin_expect (res, 0) < 0 && skip_map == NULL)
	{
	  /* Oh, oh.  The file named in the relocation entry does not
	     contain the needed symbol.  This code is never reached
	     for unversioned lookups.  */
	  assert (version != NULL);
	  const char *reference_name = undef_map ? undef_map->l_name : NULL;

	  /* XXX We cannot translate the message.  */
	  _dl_signal_cerror (0, (reference_name[0]
				 ? reference_name
				 : (rtld_progname ?: "<main program>")),
			     N_("relocation error"),
			     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)
	  && skip_map == NULL)
	{
	  /* We could find no value for a strong reference.  */
	  const char *reference_name = undef_map ? undef_map->l_name : "";
	  const char *versionstr = version ? ", version " : "";
	  const char *versionname = (version && version->name
				     ? version->name : "");

	  /* XXX We cannot translate the message.  */
	  _dl_signal_cerror (0, (reference_name[0]
				 ? reference_name
				 : (rtld_progname ?: "<main program>")),
			     N_("symbol lookup error"),
			     make_string (undefined_msg, undef_name,
					  versionstr, versionname));
	}
      *ref = NULL;
      return 0;
    }

  int protected = (*ref
		   && ELFW(ST_VISIBILITY) ((*ref)->st_other) == STV_PROTECTED);
  if (__builtin_expect (protected != 0, 0))
    {
      /* It is very tricky.  We need to figure out what value to
         return for the protected symbol.  */
      if (type_class == ELF_RTYPE_CLASS_PLT)
	{
	  if (current_value.s != NULL && current_value.m != undef_map)
	    {
	      current_value.s = *ref;
	      current_value.m = undef_map;
	    }
	}
      else
	{
	  struct sym_val protected_value = { NULL, NULL };

	  for (scope = symbol_scope; *scope != NULL; i = 0, ++scope)
	    if (do_lookup_x (undef_name, hash, *ref, &protected_value,
			     *scope, i, version, flags, skip_map,
			     ELF_RTYPE_CLASS_PLT) != 0)
	      break;

	  if (protected_value.s != NULL && protected_value.m != undef_map)
	    {
	      current_value.s = *ref;
	      current_value.m = undef_map;
	    }
	}
    }

  /* 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_type == lt_loaded, 0)
      /* Don't do this for explicit lookups as opposed to implicit
	 runtime lookups.  */
      && (flags & DL_LOOKUP_ADD_DEPENDENCY) != 0
      /* 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_x (undef_name, undef_map, ref,
				  symbol_scope, version, type_class,
				  flags, skip_map);

  /* The object is used.  */
  current_value.m->l_used = 1;

  if (__builtin_expect (GLRO(dl_debug_mask)
			& (DL_DEBUG_BINDINGS|DL_DEBUG_PRELINK), 0))
    _dl_debug_bindings (undef_name, undef_map, ref, symbol_scope,
			&current_value, version, type_class, protected);

  *ref = current_value.s;
  return LOOKUP_VALUE (current_value.m);
}


/* 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 *) D_PTR (map, l_info[DT_HASH]);

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


static void
internal_function
_dl_debug_bindings (const char *undef_name, struct link_map *undef_map,
		    const ElfW(Sym) **ref, struct r_scope_elem *symbol_scope[],
		    struct sym_val *value,
		    const struct r_found_version *version, int type_class,
		    int protected)
{
  const char *reference_name = undef_map->l_name;

  if (GLRO(dl_debug_mask) & DL_DEBUG_BINDINGS)
    {
      _dl_debug_printf ("binding file %s [%lu] to %s [%lu]: %s symbol `%s'",
			(reference_name[0]
			 ? reference_name
			 : (rtld_progname ?: "<main program>")),
			undef_map->l_ns,
			value->m->l_name[0] ? value->m->l_name : rtld_progname,
			value->m->l_ns,
			protected ? "protected" : "normal", undef_name);
      if (version)
	_dl_debug_printf_c (" [%s]\n", version->name);
      else
	_dl_debug_printf_c ("\n");
    }
#ifdef SHARED
  if (GLRO(dl_debug_mask) & DL_DEBUG_PRELINK)
    {
      int conflict = 0;
      struct sym_val val = { NULL, NULL };

      if ((GLRO(dl_trace_prelink_map) == NULL
	   || GLRO(dl_trace_prelink_map) == GL(dl_ns)[LM_ID_BASE]._ns_loaded)
	  && undef_map != GL(dl_ns)[LM_ID_BASE]._ns_loaded)
	{
	  const unsigned long int hash = _dl_elf_hash (undef_name);

	  do_lookup_x (undef_name, hash, *ref, &val,
		       undef_map->l_local_scope[0], 0, version, 0, NULL,
		       type_class);

	  if (val.s != value->s || val.m != value->m)
	    conflict = 1;
	}

# ifdef USE_TLS
      if (value->s
	  && (__builtin_expect (ELFW(ST_TYPE) (value->s->st_info)
				== STT_TLS, 0)))
	type_class = 4;
# endif

      if (conflict
	  || GLRO(dl_trace_prelink_map) == undef_map
	  || GLRO(dl_trace_prelink_map) == NULL
	  || type_class == 4)
	{
	  _dl_printf ("%s 0x%0*Zx 0x%0*Zx -> 0x%0*Zx 0x%0*Zx ",
		      conflict ? "conflict" : "lookup",
		      (int) sizeof (ElfW(Addr)) * 2,
		      (size_t) undef_map->l_map_start,
		      (int) sizeof (ElfW(Addr)) * 2,
		      (size_t) (((ElfW(Addr)) *ref) - undef_map->l_map_start),
		      (int) sizeof (ElfW(Addr)) * 2,
		      (size_t) (value->s ? value->m->l_map_start : 0),
		      (int) sizeof (ElfW(Addr)) * 2,
		      (size_t) (value->s ? value->s->st_value : 0));

	  if (conflict)
	    _dl_printf ("x 0x%0*Zx 0x%0*Zx ",
			(int) sizeof (ElfW(Addr)) * 2,
			(size_t) (val.s ? val.m->l_map_start : 0),
			(int) sizeof (ElfW(Addr)) * 2,
			(size_t) (val.s ? val.s->st_value : 0));

	  _dl_printf ("/%x %s\n", type_class, undef_name);
	}
    }
#endif
}