about summary refs log tree commit diff
path: root/elf/dl-lookup.c
blob: 9a2a1052f1cb5db13cd1ec4fc61d0a9edd83af9c (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, 1996, 1997, 1998 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 <link.h>
#include <assert.h>
#include <string.h>
#include <unistd.h>

#include "dl-hash.h"
#include <dl-machine.h>

#define VERSTAG(tag)	(DT_NUM + DT_PROCNUM + 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;								      \
  })


/* Inner part of the lookup functions.  We return a value > 0 if we
   found the symbol, the value 0 if nothing is found and < 0 if
   something bad happened.  */
static inline int
do_lookup (const char *undef_name, unsigned long int hash,
	   const ElfW(Sym) *ref, struct sym_val *result,
	   struct link_map *scope, size_t i, const char *reference_name,
	   const struct r_found_version *version, struct link_map *skip,
	   int reloc_type)
{
  struct link_map **list = scope->l_searchlist;
  size_t n = scope->l_nsearchlist;
  struct link_map *map;

  for (; i < n; ++i)
    {
      const ElfW(Sym) *symtab;
      const char *strtab;
      const ElfW(Half) *verstab;
      ElfW(Symndx) symidx;

      map = list[i];

      /* Here come the extra test needed for `_dl_lookup_symbol_skip'.  */
      if (skip != NULL && map == skip)
	continue;

      /* Skip objects that could not be opened, which can occur in trace
	 mode.  */
      if (map->l_opencount == 0)
	continue;

      /* Don't search the executable when resolving a copy reloc.  */
      if (elf_machine_lookup_noexec_p (reloc_type)
	  && map->l_type == lt_executable)
	continue;

      /* Skip objects without symbol tables.  */
      if (map->l_info[DT_SYMTAB] == NULL)
	continue;

      /* Print some debugging info if wanted.  */
      if (_dl_debug_symbols)
	_dl_debug_message (1, "symbol=", undef_name, ";  lookup in file=",
			   map->l_name[0] ? map->l_name : _dl_argv[0],
			   "\n", NULL);

      symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
      strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
      verstab = map->l_versyms;

      /* Search the appropriate hash bucket in this object's symbol table
	 for a definition for the same symbol name.  */
      for (symidx = map->l_buckets[hash % map->l_nbuckets];
	   symidx != STN_UNDEF;
	   symidx = map->l_chain[symidx])
	{
	  const ElfW(Sym) *sym = &symtab[symidx];

	  if (sym->st_value == 0 || /* No value.  */
	      (elf_machine_lookup_noplt_p (reloc_type) /* Reject PLT entry.  */
	       && sym->st_shndx == SHN_UNDEF))
	    continue;

	  if (ELFW(ST_TYPE) (sym->st_info) > STT_FUNC)
	    /* Ignore all but STT_NOTYPE, STT_OBJECT and STT_FUNC entries
	       since these are no code/data definitions.  */
	    continue;

	  if (sym != ref && strcmp (strtab + sym->st_name, undef_name))
	    /* Not the symbol we are looking for.  */
	    continue;

	  if (version == NULL)
	    {
	      /* No specific version is selected.  When the object
		 file also does not define a version we have a match.
		 Otherwise we only accept the default version, i.e.,
		 the version which name is "".  */
	      if (verstab != NULL)
		{
		  ElfW(Half) ndx = verstab[symidx] & 0x7fff;
		  if (ndx > 2) /* map->l_versions[ndx].hash != 0) */
		    continue;
		}
	    }
	  else
	    {
	      if (verstab == NULL)
		{
		  /* We need a versioned system but haven't found any.
		     If this is the object which is referenced in the
		     verneed entry it is a bug in the library since a
		     symbol must not simply disappear.  */
		  if (version->filename != NULL
		      && _dl_name_match_p (version->filename, map))
		    return -2;
		  /* Otherwise we accept the symbol.  */
		}
	      else
		{
		  /* We can match the version information or use the
		     default one if it is not hidden.  */
		  ElfW(Half) ndx = verstab[symidx] & 0x7fff;
		  if ((map->l_versions[ndx].hash != version->hash
		       || strcmp (map->l_versions[ndx].name, version->name))
		      && (version->hidden || map->l_versions[ndx].hash
			  || (verstab[symidx] & 0x8000)))
		    /* It's not the version we want.  */
		    continue;
		}
	    }

	  switch (ELFW(ST_BIND) (sym->st_info))
	    {
	    case STB_GLOBAL:
	      /* Global definition.  Just what we need.  */
	      result->s = sym;
	      result->m = map;
	      return 1;
	    case STB_WEAK:
	      /* Weak definition.  Use this value if we don't find
		 another.  */
	      if (! result->s)
		{
		  result->s = sym;
		  result->m = map;
		}
	      break;
	    default:
	      /* Local symbols are ignored.  */
	      break;
	    }

	  /* There cannot be another entry for this symbol so stop here.  */
	  break;
	}

      /* If this current map is the one mentioned in the verneed entry
	 and we have not found a weak entry, it is a bug.  */
      if (symidx == STN_UNDEF && version != NULL && version->filename != NULL
	  && _dl_name_match_p (version->filename, map))
	return -1;
    }

  /* We have not found anything until now.  */
  return 0;
}

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

ElfW(Addr)
_dl_lookup_symbol (const char *undef_name, const ElfW(Sym) **ref,
		   struct link_map *symbol_scope[],
		   const char *reference_name,
		   int reloc_type)
{
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct link_map **scope;

  /* 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, reference_name, NULL, NULL, reloc_type))
      break;

  if (current_value.s == NULL)
    {
      if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
	/* We could find no value for a strong reference.  */
	_dl_signal_error (0, (reference_name  && reference_name[0]
			      ? reference_name
			      : (_dl_argv[0] ?: "<main program>")),
			  make_string (undefined_msg, undef_name));
      *ref = NULL;
      return 0;
    }

  if (_dl_debug_bindings)
    _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],
		       ": symbol `", undef_name, "'\n", NULL);

  *ref = current_value.s;
  return current_value.m->l_addr;
}


/* 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.  */
ElfW(Addr)
_dl_lookup_symbol_skip (const char *undef_name, const ElfW(Sym) **ref,
			struct link_map *symbol_scope[],
			const char *reference_name,
			struct link_map *skip_map)
{
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct link_map **scope;
  size_t i;

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

  if (! do_lookup (undef_name, hash, *ref, &current_value,
		   *scope, i, reference_name, NULL, skip_map, 0))
    while (*++scope)
      if (do_lookup (undef_name, hash, *ref, &current_value,
		     *scope, 0, reference_name, NULL, skip_map, 0))
	break;

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

  if (_dl_debug_bindings)
    _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],
		       ": symbol `", undef_name, "' (skip)\n", NULL);

  *ref = current_value.s;
  return current_value.m->l_addr;
}


/* 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.  */
ElfW(Addr)
_dl_lookup_versioned_symbol (const char *undef_name, const ElfW(Sym) **ref,
			     struct link_map *symbol_scope[],
			     const char *reference_name,
			     const struct r_found_version *version,
			     int reloc_type)
{
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct link_map **scope;

  /* Search the relevant loaded objects for a definition.  */
  for (scope = symbol_scope; *scope; ++scope)
    {
      int res = do_lookup (undef_name, hash, *ref, &current_value,
			   *scope, 0, reference_name, version, NULL, reloc_type);
      if (res > 0)
	break;

      if (res < 0)
	/* Oh, oh.  The file named in the relocation entry does not
	   contain the needed symbol.  */
	_dl_signal_error (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)" : ""));
    }

  if (current_value.s == NULL)
    {
      if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
	/* We could find no value for a strong reference.  */
	_dl_signal_error (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;
    }

  if (_dl_debug_bindings)
    _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],
		       ": symbol `", undef_name, "' [", version->name,
		       "]\n", NULL);

  *ref = current_value.s;
  return current_value.m->l_addr;
}


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

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

  if (! do_lookup (undef_name, hash, *ref, &current_value,
		   *scope, i, reference_name, version, skip_map, 0))
    while (*++scope)
      if (do_lookup (undef_name, hash, *ref, &current_value,
		     *scope, 0, reference_name, version, skip_map, 0))
	break;

  if (current_value.s == NULL)
    {
      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);
	  _dl_signal_error (0, (reference_name && reference_name[0]
				? reference_name
				: (_dl_argv[0] ?: "<main program>")), buf);
	}
      *ref = NULL;
      return 0;
    }

  if (_dl_debug_bindings)
    _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],
		       ": symbol `", undef_name, "' [", version->name,
		       "] (skip)\n", NULL);

  *ref = current_value.s;
  return current_value.m->l_addr;
}


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

void
_dl_setup_hash (struct link_map *map)
{
  ElfW(Symndx) *hash;
  ElfW(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;
}