aboutsummaryrefslogtreecommitdiff
path: root/gold/resolve.cc
blob: 980831b7950eee7b479e1be0396eff83a89de5f7 (plain)
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
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
// resolve.cc -- symbol resolution for gold

// Copyright 2006, 2007 Free Software Foundation, Inc.
// Written by Ian Lance Taylor <iant@google.com>.

// This file is part of gold.

// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// (at your option) any later version.

// This program 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 General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
// MA 02110-1301, USA.

#include "gold.h"

#include "elfcpp.h"
#include "target.h"
#include "object.h"
#include "symtab.h"

namespace gold
{

// Symbol methods used in this file.

// Override the fields in Symbol.

template<int size, bool big_endian>
void
Symbol::override_base(const elfcpp::Sym<size, big_endian>& sym,
		      Object* object, const char* version)
{
  gold_assert(this->source_ == FROM_OBJECT);
  this->u_.from_object.object = object;
  if (version != NULL && this->version() != version)
    {
      gold_assert(this->version() == NULL);
      this->version_ = version;
    }
  // FIXME: Handle SHN_XINDEX.
  this->u_.from_object.shndx = sym.get_st_shndx();
  this->type_ = sym.get_st_type();
  this->binding_ = sym.get_st_bind();
  this->visibility_ = sym.get_st_visibility();
  this->nonvis_ = sym.get_st_nonvis();
  if (object->is_dynamic())
    this->in_dyn_ = true;
  else
    this->in_reg_ = true;
}

// Override the fields in Sized_symbol.

template<int size>
template<bool big_endian>
void
Sized_symbol<size>::override(const elfcpp::Sym<size, big_endian>& sym,
			     Object* object, const char* version)
{
  this->override_base(sym, object, version);
  this->value_ = sym.get_st_value();
  this->symsize_ = sym.get_st_size();
}

// Override TOSYM with symbol FROMSYM, defined in OBJECT, with version
// VERSION.  This handles all aliases of TOSYM.

template<int size, bool big_endian>
void
Symbol_table::override(Sized_symbol<size>* tosym,
		       const elfcpp::Sym<size, big_endian>& fromsym,
		       Object* object, const char* version)
{
  tosym->override(fromsym, object, version);
  if (tosym->has_alias())
    {
      Symbol* sym = this->weak_aliases_[tosym];
      gold_assert(sym != NULL);
      Sized_symbol<size>* ssym;
      ssym = this->get_sized_symbol SELECT_SIZE_NAME(size) (sym
							    SELECT_SIZE(size));
      do
	{
	  ssym->override(fromsym, object, version);
	  sym = this->weak_aliases_[ssym];
	  gold_assert(sym != NULL);
	  ssym = this->get_sized_symbol SELECT_SIZE_NAME(size) (
						sym SELECT_SIZE(size));
	}
      while (ssym != tosym);
    }
}

// The resolve functions build a little code for each symbol.
// Bit 0: 0 for global, 1 for weak.
// Bit 1: 0 for regular object, 1 for shared object
// Bits 2-3: 0 for normal, 1 for undefined, 2 for common
// This gives us values from 0 to 11.

static const int global_or_weak_shift = 0;
static const unsigned int global_flag = 0 << global_or_weak_shift;
static const unsigned int weak_flag = 1 << global_or_weak_shift;

static const int regular_or_dynamic_shift = 1;
static const unsigned int regular_flag = 0 << regular_or_dynamic_shift;
static const unsigned int dynamic_flag = 1 << regular_or_dynamic_shift;

static const int def_undef_or_common_shift = 2;
static const unsigned int def_flag = 0 << def_undef_or_common_shift;
static const unsigned int undef_flag = 1 << def_undef_or_common_shift;
static const unsigned int common_flag = 2 << def_undef_or_common_shift;

// This convenience function combines all the flags based on facts
// about the symbol.

static unsigned int
symbol_to_bits(elfcpp::STB binding, bool is_dynamic,
	       unsigned int shndx, elfcpp::STT type)
{
  unsigned int bits;

  switch (binding)
    {
    case elfcpp::STB_GLOBAL:
      bits = global_flag;
      break;

    case elfcpp::STB_WEAK:
      bits = weak_flag;
      break;

    case elfcpp::STB_LOCAL:
      // We should only see externally visible symbols in the symbol
      // table.
      gold_error(_("invalid STB_LOCAL symbol in external symbols"));
      bits = global_flag;

    default:
      // Any target which wants to handle STB_LOOS, etc., needs to
      // define a resolve method.
      gold_error(_("unsupported symbol binding"));
      bits = global_flag;
    }

  if (is_dynamic)
    bits |= dynamic_flag;
  else
    bits |= regular_flag;

  switch (shndx)
    {
    case elfcpp::SHN_UNDEF:
      bits |= undef_flag;
      break;

    case elfcpp::SHN_COMMON:
      bits |= common_flag;
      break;

    default:
      if (type == elfcpp::STT_COMMON)
	bits |= common_flag;
      else
        bits |= def_flag;
      break;
    }

  return bits;
}

// Resolve a symbol.  This is called the second and subsequent times
// we see a symbol.  TO is the pre-existing symbol.  ORIG_SYM is the
// new symbol, seen in OBJECT.  SYM is almost always identical to
// ORIG_SYM, but may be munged (for instance, if we determine the
// symbol is in a to-be-discarded section, we'll set sym's shndx to
// UNDEFINED).  VERSION of the version of SYM.

template<int size, bool big_endian>
void
Symbol_table::resolve(Sized_symbol<size>* to,
		      const elfcpp::Sym<size, big_endian>& sym,
		      const elfcpp::Sym<size, big_endian>& orig_sym,
		      Object* object, const char* version)
{
  if (object->target()->has_resolve())
    {
      Sized_target<size, big_endian>* sized_target;
      sized_target = object->sized_target
                     SELECT_SIZE_ENDIAN_NAME(size, big_endian) (
                         SELECT_SIZE_ENDIAN_ONLY(size, big_endian));
      sized_target->resolve(to, sym, object, version);
      return;
    }

  if (!object->is_dynamic())
    {
      // Record that we've seen this symbol in a regular object.
      to->set_in_reg();
    }
  else
    {
      // Record that we've seen this symbol in a dynamic object.
      to->set_in_dyn();
    }

  unsigned int frombits = symbol_to_bits(sym.get_st_bind(),
                                         object->is_dynamic(),
                                         sym.get_st_shndx(),
                                         sym.get_st_type());

  bool adjust_common_sizes;
  if (Symbol_table::should_override(to, frombits, object,
				    &adjust_common_sizes))
    {
      typename Sized_symbol<size>::Size_type tosize = to->symsize();

      this->override(to, sym, object, version);

      if (adjust_common_sizes && tosize > to->symsize())
        to->set_symsize(tosize);
    }
  else
    {
      if (adjust_common_sizes && sym.get_st_size() > to->symsize())
        to->set_symsize(sym.get_st_size());
    }

  // A new weak undefined reference, merging with an old weak
  // reference, could be a One Definition Rule (ODR) violation --
  // especially if the types or sizes of the references differ.  We'll
  // store such pairs and look them up later to make sure they
  // actually refer to the same lines of code.  (Note: not all ODR
  // violations can be found this way, and not everything this finds
  // is an ODR violation.  But it's helpful to warn about.)
  // We use orig_sym here because we want the symbol exactly as it
  // appears in the object file, not munged via our future processing.
  if (orig_sym.get_st_bind() == elfcpp::STB_WEAK
      && to->binding() == elfcpp::STB_WEAK
      && orig_sym.get_st_shndx() != elfcpp::SHN_UNDEF
      && to->shndx() != elfcpp::SHN_UNDEF
      && orig_sym.get_st_size() != 0    // Ignore weird 0-sized symbols.
      && to->symsize() != 0
      && (orig_sym.get_st_type() != to->type()
          || orig_sym.get_st_size() != to->symsize())
      // C does not have a concept of ODR, so we only need to do this
      // on C++ symbols.  These have (mangled) names starting with _Z.
      && to->name()[0] == '_' && to->name()[1] == 'Z')
    {
      Symbol_location from_location
          = { object, orig_sym.get_st_shndx(), orig_sym.get_st_value() };
      Symbol_location to_location = { to->object(), to->shndx(), to->value() };
      this->candidate_odr_violations_[to->name()].insert(from_location);
      this->candidate_odr_violations_[to->name()].insert(to_location);
    }
}

// Handle the core of symbol resolution.  This is called with the
// existing symbol, TO, and a bitflag describing the new symbol.  This
// returns true if we should override the existing symbol with the new
// one, and returns false otherwise.  It sets *ADJUST_COMMON_SIZES to
// true if we should set the symbol size to the maximum of the TO and
// FROM sizes.  It handles error conditions.

bool
Symbol_table::should_override(const Symbol* to, unsigned int frombits,
                              Object* object, bool* adjust_common_sizes)
{
  *adjust_common_sizes = false;

  unsigned int tobits = symbol_to_bits(to->binding(),
                                       (to->source() == Symbol::FROM_OBJECT
                                        && to->object()->is_dynamic()),
                                       to->shndx(),
                                       to->type());

  // FIXME: Warn if either but not both of TO and SYM are STT_TLS.

  // We use a giant switch table for symbol resolution.  This code is
  // unwieldy, but: 1) it is efficient; 2) we definitely handle all
  // cases; 3) it is easy to change the handling of a particular case.
  // The alternative would be a series of conditionals, but it is easy
  // to get the ordering wrong.  This could also be done as a table,
  // but that is no easier to understand than this large switch
  // statement.

  // These are the values generated by the bit codes.
  enum
  {
    DEF =              global_flag | regular_flag | def_flag,
    WEAK_DEF =         weak_flag   | regular_flag | def_flag,
    DYN_DEF =          global_flag | dynamic_flag | def_flag,
    DYN_WEAK_DEF =     weak_flag   | dynamic_flag | def_flag,
    UNDEF =            global_flag | regular_flag | undef_flag,
    WEAK_UNDEF =       weak_flag   | regular_flag | undef_flag,
    DYN_UNDEF =        global_flag | dynamic_flag | undef_flag,
    DYN_WEAK_UNDEF =   weak_flag   | dynamic_flag | undef_flag,
    COMMON =           global_flag | regular_flag | common_flag,
    WEAK_COMMON =      weak_flag   | regular_flag | common_flag,
    DYN_COMMON =       global_flag | dynamic_flag | common_flag,
    DYN_WEAK_COMMON =  weak_flag   | dynamic_flag | common_flag
  };

  switch (tobits * 16 + frombits)
    {
    case DEF * 16 + DEF:
      // Two definitions of the same symbol.
      // FIXME: Do a better job of reporting locations.
      gold_error(_("%s: multiple definition of %s"),
		 object != NULL ? object->name().c_str() : _("command line"),
		 to->name());
      gold_error(_("%s: previous definition here"),
		 (to->source() == Symbol::FROM_OBJECT
		  ? to->object()->name().c_str()
		  : _("command line")));
      return false;

    case WEAK_DEF * 16 + DEF:
      // We've seen a weak definition, and now we see a strong
      // definition.  In the original SVR4 linker, this was treated as
      // a multiple definition error.  In the Solaris linker and the
      // GNU linker, a weak definition followed by a regular
      // definition causes the weak definition to be overridden.  We
      // are currently compatible with the GNU linker.  In the future
      // we should add a target specific option to change this.
      // FIXME.
      return true;

    case DYN_DEF * 16 + DEF:
    case DYN_WEAK_DEF * 16 + DEF:
      // We've seen a definition in a dynamic object, and now we see a
      // definition in a regular object.  The definition in the
      // regular object overrides the definition in the dynamic
      // object.
      return true;

    case UNDEF * 16 + DEF:
    case WEAK_UNDEF * 16 + DEF:
    case DYN_UNDEF * 16 + DEF:
    case DYN_WEAK_UNDEF * 16 + DEF:
      // We've seen an undefined reference, and now we see a
      // definition.  We use the definition.
      return true;

    case COMMON * 16 + DEF:
    case WEAK_COMMON * 16 + DEF:
    case DYN_COMMON * 16 + DEF:
    case DYN_WEAK_COMMON * 16 + DEF:
      // We've seen a common symbol and now we see a definition.  The
      // definition overrides.  FIXME: We should optionally issue, version a
      // warning.
      return true;

    case DEF * 16 + WEAK_DEF:
    case WEAK_DEF * 16 + WEAK_DEF:
      // We've seen a definition and now we see a weak definition.  We
      // ignore the new weak definition.
      return false;

    case DYN_DEF * 16 + WEAK_DEF:
    case DYN_WEAK_DEF * 16 + WEAK_DEF:
      // We've seen a dynamic definition and now we see a regular weak
      // definition.  The regular weak definition overrides.
      return true;

    case UNDEF * 16 + WEAK_DEF:
    case WEAK_UNDEF * 16 + WEAK_DEF:
    case DYN_UNDEF * 16 + WEAK_DEF:
    case DYN_WEAK_UNDEF * 16 + WEAK_DEF:
      // A weak definition of a currently undefined symbol.
      return true;

    case COMMON * 16 + WEAK_DEF:
    case WEAK_COMMON * 16 + WEAK_DEF:
      // A weak definition does not override a common definition.
      return false;

    case DYN_COMMON * 16 + WEAK_DEF:
    case DYN_WEAK_COMMON * 16 + WEAK_DEF:
      // A weak definition does override a definition in a dynamic
      // object.  FIXME: We should optionally issue a warning.
      return true;

    case DEF * 16 + DYN_DEF:
    case WEAK_DEF * 16 + DYN_DEF:
    case DYN_DEF * 16 + DYN_DEF:
    case DYN_WEAK_DEF * 16 + DYN_DEF:
      // Ignore a dynamic definition if we already have a definition.
      return false;

    case UNDEF * 16 + DYN_DEF:
    case WEAK_UNDEF * 16 + DYN_DEF:
    case DYN_UNDEF * 16 + DYN_DEF:
    case DYN_WEAK_UNDEF * 16 + DYN_DEF:
      // Use a dynamic definition if we have a reference.
      return true;

    case COMMON * 16 + DYN_DEF:
    case WEAK_COMMON * 16 + DYN_DEF:
    case DYN_COMMON * 16 + DYN_DEF:
    case DYN_WEAK_COMMON * 16 + DYN_DEF:
      // Ignore a dynamic definition if we already have a common
      // definition.
      return false;

    case DEF * 16 + DYN_WEAK_DEF:
    case WEAK_DEF * 16 + DYN_WEAK_DEF:
    case DYN_DEF * 16 + DYN_WEAK_DEF:
    case DYN_WEAK_DEF * 16 + DYN_WEAK_DEF:
      // Ignore a weak dynamic definition if we already have a
      // definition.
      return false;

    case UNDEF * 16 + DYN_WEAK_DEF:
    case WEAK_UNDEF * 16 + DYN_WEAK_DEF:
    case DYN_UNDEF * 16 + DYN_WEAK_DEF:
    case DYN_WEAK_UNDEF * 16 + DYN_WEAK_DEF:
      // Use a weak dynamic definition if we have a reference.
      return true;

    case COMMON * 16 + DYN_WEAK_DEF:
    case WEAK_COMMON * 16 + DYN_WEAK_DEF:
    case DYN_COMMON * 16 + DYN_WEAK_DEF:
    case DYN_WEAK_COMMON * 16 + DYN_WEAK_DEF:
      // Ignore a weak dynamic definition if we already have a common
      // definition.
      return false;

    case DEF * 16 + UNDEF:
    case WEAK_DEF * 16 + UNDEF:
    case DYN_DEF * 16 + UNDEF:
    case DYN_WEAK_DEF * 16 + UNDEF:
    case UNDEF * 16 + UNDEF:
      // A new undefined reference tells us nothing.
      return false;

    case WEAK_UNDEF * 16 + UNDEF:
    case DYN_UNDEF * 16 + UNDEF:
    case DYN_WEAK_UNDEF * 16 + UNDEF:
      // A strong undef overrides a dynamic or weak undef.
      return true;

    case COMMON * 16 + UNDEF:
    case WEAK_COMMON * 16 + UNDEF:
    case DYN_COMMON * 16 + UNDEF:
    case DYN_WEAK_COMMON * 16 + UNDEF:
      // A new undefined reference tells us nothing.
      return false;

    case DEF * 16 + WEAK_UNDEF:
    case WEAK_DEF * 16 + WEAK_UNDEF:
    case DYN_DEF * 16 + WEAK_UNDEF:
    case DYN_WEAK_DEF * 16 + WEAK_UNDEF:
    case UNDEF * 16 + WEAK_UNDEF:
    case WEAK_UNDEF * 16 + WEAK_UNDEF:
    case DYN_UNDEF * 16 + WEAK_UNDEF:
    case DYN_WEAK_UNDEF * 16 + WEAK_UNDEF:
    case COMMON * 16 + WEAK_UNDEF:
    case WEAK_COMMON * 16 + WEAK_UNDEF:
    case DYN_COMMON * 16 + WEAK_UNDEF:
    case DYN_WEAK_COMMON * 16 + WEAK_UNDEF:
      // A new weak undefined reference tells us nothing.
      return false;

    case DEF * 16 + DYN_UNDEF:
    case WEAK_DEF * 16 + DYN_UNDEF:
    case DYN_DEF * 16 + DYN_UNDEF:
    case DYN_WEAK_DEF * 16 + DYN_UNDEF:
    case UNDEF * 16 + DYN_UNDEF:
    case WEAK_UNDEF * 16 + DYN_UNDEF:
    case DYN_UNDEF * 16 + DYN_UNDEF:
    case DYN_WEAK_UNDEF * 16 + DYN_UNDEF:
    case COMMON * 16 + DYN_UNDEF:
    case WEAK_COMMON * 16 + DYN_UNDEF:
    case DYN_COMMON * 16 + DYN_UNDEF:
    case DYN_WEAK_COMMON * 16 + DYN_UNDEF:
      // A new dynamic undefined reference tells us nothing.
      return false;

    case DEF * 16 + DYN_WEAK_UNDEF:
    case WEAK_DEF * 16 + DYN_WEAK_UNDEF:
    case DYN_DEF * 16 + DYN_WEAK_UNDEF:
    case DYN_WEAK_DEF * 16 + DYN_WEAK_UNDEF:
    case UNDEF * 16 + DYN_WEAK_UNDEF:
    case WEAK_UNDEF * 16 + DYN_WEAK_UNDEF:
    case DYN_UNDEF * 16 + DYN_WEAK_UNDEF:
    case DYN_WEAK_UNDEF * 16 + DYN_WEAK_UNDEF:
    case COMMON * 16 + DYN_WEAK_UNDEF:
    case WEAK_COMMON * 16 + DYN_WEAK_UNDEF:
    case DYN_COMMON * 16 + DYN_WEAK_UNDEF:
    case DYN_WEAK_COMMON * 16 + DYN_WEAK_UNDEF:
      // A new weak dynamic undefined reference tells us nothing.
      return false;

    case DEF * 16 + COMMON:
      // A common symbol does not override a definition.
      return false;

    case WEAK_DEF * 16 + COMMON:
    case DYN_DEF * 16 + COMMON:
    case DYN_WEAK_DEF * 16 + COMMON:
      // A common symbol does override a weak definition or a dynamic
      // definition.
      return true;

    case UNDEF * 16 + COMMON:
    case WEAK_UNDEF * 16 + COMMON:
    case DYN_UNDEF * 16 + COMMON:
    case DYN_WEAK_UNDEF * 16 + COMMON:
      // A common symbol is a definition for a reference.
      return true;

    case COMMON * 16 + COMMON:
      // Set the size to the maximum.
      *adjust_common_sizes = true;
      return false;

    case WEAK_COMMON * 16 + COMMON:
      // I'm not sure just what a weak common symbol means, but
      // presumably it can be overridden by a regular common symbol.
      return true;

    case DYN_COMMON * 16 + COMMON:
    case DYN_WEAK_COMMON * 16 + COMMON:
      // Use the real common symbol, but adjust the size if necessary.
      *adjust_common_sizes = true;
      return true;

    case DEF * 16 + WEAK_COMMON:
    case WEAK_DEF * 16 + WEAK_COMMON:
    case DYN_DEF * 16 + WEAK_COMMON:
    case DYN_WEAK_DEF * 16 + WEAK_COMMON:
      // Whatever a weak common symbol is, it won't override a
      // definition.
      return false;

    case UNDEF * 16 + WEAK_COMMON:
    case WEAK_UNDEF * 16 + WEAK_COMMON:
    case DYN_UNDEF * 16 + WEAK_COMMON:
    case DYN_WEAK_UNDEF * 16 + WEAK_COMMON:
      // A weak common symbol is better than an undefined symbol.
      return true;

    case COMMON * 16 + WEAK_COMMON:
    case WEAK_COMMON * 16 + WEAK_COMMON:
    case DYN_COMMON * 16 + WEAK_COMMON:
    case DYN_WEAK_COMMON * 16 + WEAK_COMMON:
      // Ignore a weak common symbol in the presence of a real common
      // symbol.
      return false;

    case DEF * 16 + DYN_COMMON:
    case WEAK_DEF * 16 + DYN_COMMON:
    case DYN_DEF * 16 + DYN_COMMON:
    case DYN_WEAK_DEF * 16 + DYN_COMMON:
      // Ignore a dynamic common symbol in the presence of a
      // definition.
      return false;

    case UNDEF * 16 + DYN_COMMON:
    case WEAK_UNDEF * 16 + DYN_COMMON:
    case DYN_UNDEF * 16 + DYN_COMMON:
    case DYN_WEAK_UNDEF * 16 + DYN_COMMON:
      // A dynamic common symbol is a definition of sorts.
      return true;

    case COMMON * 16 + DYN_COMMON:
    case WEAK_COMMON * 16 + DYN_COMMON:
    case DYN_COMMON * 16 + DYN_COMMON:
    case DYN_WEAK_COMMON * 16 + DYN_COMMON:
      // Set the size to the maximum.
      *adjust_common_sizes = true;
      return false;

    case DEF * 16 + DYN_WEAK_COMMON:
    case WEAK_DEF * 16 + DYN_WEAK_COMMON:
    case DYN_DEF * 16 + DYN_WEAK_COMMON:
    case DYN_WEAK_DEF * 16 + DYN_WEAK_COMMON:
      // A common symbol is ignored in the face of a definition.
      return false;

    case UNDEF * 16 + DYN_WEAK_COMMON:
    case WEAK_UNDEF * 16 + DYN_WEAK_COMMON:
    case DYN_UNDEF * 16 + DYN_WEAK_COMMON:
    case DYN_WEAK_UNDEF * 16 + DYN_WEAK_COMMON:
      // I guess a weak common symbol is better than a definition.
      return true;

    case COMMON * 16 + DYN_WEAK_COMMON:
    case WEAK_COMMON * 16 + DYN_WEAK_COMMON:
    case DYN_COMMON * 16 + DYN_WEAK_COMMON:
    case DYN_WEAK_COMMON * 16 + DYN_WEAK_COMMON:
      // Set the size to the maximum.
      *adjust_common_sizes = true;
      return false;

    default:
      gold_unreachable();
    }
}

// A special case of should_override which is only called for a strong
// defined symbol from a regular object file.  This is used when
// defining special symbols.

bool
Symbol_table::should_override_with_special(const Symbol* to)
{
  bool adjust_common_sizes;
  unsigned int frombits = global_flag | regular_flag | def_flag;
  bool ret = Symbol_table::should_override(to, frombits, NULL,
					   &adjust_common_sizes);
  gold_assert(!adjust_common_sizes);
  return ret;
}

// Override symbol base with a special symbol.

void
Symbol::override_base_with_special(const Symbol* from)
{
  gold_assert(this->name_ == from->name_ || this->has_alias());

  this->source_ = from->source_;
  switch (from->source_)
    {
    case FROM_OBJECT:
      this->u_.from_object = from->u_.from_object;
      break;
    case IN_OUTPUT_DATA:
      this->u_.in_output_data = from->u_.in_output_data;
      break;
    case IN_OUTPUT_SEGMENT:
      this->u_.in_output_segment = from->u_.in_output_segment;
      break;
    case CONSTANT:
      break;
    default:
      gold_unreachable();
      break;
    }

  if (from->version_ != NULL && this->version_ != from->version_)
    {
      gold_assert(this->version_ == NULL);
      this->version_ = from->version_;
    }

  this->type_ = from->type_;
  this->binding_ = from->binding_;
  this->visibility_ = from->visibility_;
  this->nonvis_ = from->nonvis_;

  // Special symbols are always considered to be regular symbols.
  this->in_reg_ = true;

  if (from->needs_dynsym_entry_)
    this->needs_dynsym_entry_ = true;
  if (from->needs_dynsym_value_)
    this->needs_dynsym_value_ = true;

  // We shouldn't see these flags.  If we do, we need to handle them
  // somehow.
  gold_assert(!from->is_target_special_ || this->is_target_special_);
  gold_assert(!from->is_forwarder_);
  gold_assert(!from->has_got_offset_);
  gold_assert(!from->has_plt_offset_);
  gold_assert(!from->has_warning_);
  gold_assert(!from->is_copied_from_dynobj_);
}

// Override a symbol with a special symbol.

template<int size>
void
Sized_symbol<size>::override_with_special(const Sized_symbol<size>* from)
{
  this->override_base_with_special(from);
  this->value_ = from->value_;
  this->symsize_ = from->symsize_;
}

// Override TOSYM with the special symbol FROMSYM.  This handles all
// aliases of TOSYM.

template<int size>
void
Symbol_table::override_with_special(Sized_symbol<size>* tosym,
				    const Sized_symbol<size>* fromsym)
{
  tosym->override_with_special(fromsym);
  if (tosym->has_alias())
    {
      Symbol* sym = this->weak_aliases_[tosym];
      gold_assert(sym != NULL);
      Sized_symbol<size>* ssym;
      ssym = this->get_sized_symbol SELECT_SIZE_NAME(size) (sym
							    SELECT_SIZE(size));
      do
	{
	  ssym->override_with_special(fromsym);
	  sym = this->weak_aliases_[ssym];
	  gold_assert(sym != NULL);
	  ssym = this->get_sized_symbol SELECT_SIZE_NAME(size) (
						sym SELECT_SIZE(size));
	}
      while (ssym != tosym);
    }
}

// Instantiate the templates we need.  We could use the configure
// script to restrict this to only the ones needed for implemented
// targets.

#ifdef HAVE_TARGET_32_LITTLE
template
void
Symbol_table::resolve<32, false>(
    Sized_symbol<32>* to,
    const elfcpp::Sym<32, false>& sym,
    const elfcpp::Sym<32, false>& orig_sym,
    Object* object,
    const char* version);
#endif

#ifdef HAVE_TARGET_32_BIG
template
void
Symbol_table::resolve<32, true>(
    Sized_symbol<32>* to,
    const elfcpp::Sym<32, true>& sym,
    const elfcpp::Sym<32, true>& orig_sym,
    Object* object,
    const char* version);
#endif

#ifdef HAVE_TARGET_64_LITTLE
template
void
Symbol_table::resolve<64, false>(
    Sized_symbol<64>* to,
    const elfcpp::Sym<64, false>& sym,
    const elfcpp::Sym<64, false>& orig_sym,
    Object* object,
    const char* version);
#endif

#ifdef HAVE_TARGET_64_BIG
template
void
Symbol_table::resolve<64, true>(
    Sized_symbol<64>* to,
    const elfcpp::Sym<64, true>& sym,
    const elfcpp::Sym<64, true>& orig_sym,
    Object* object,
    const char* version);
#endif

#if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
template
void
Symbol_table::override_with_special<32>(Sized_symbol<32>*,
					const Sized_symbol<32>*);
#endif

#if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
template
void
Symbol_table::override_with_special<64>(Sized_symbol<64>*,
					const Sized_symbol<64>*);
#endif

} // End namespace gold.