gold/resolve.cc

   1 // resolve.cc -- symbol resolution for gold
   2
   3 // Copyright 2006, 2007, 2008 Free Software Foundation, Inc.
   4 // Written by Ian Lance Taylor <iant@google.com>.
   5
   6 // This file is part of gold.
   7
   8 // This program is free software; you can redistribute it and/or modify
   9 // it under the terms of the GNU General Public License as published by
  10 // the Free Software Foundation; either version 3 of the License, or
  11 // (at your option) any later version.
  12
  13 // This program is distributed in the hope that it will be useful,
  14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 // GNU General Public License for more details.
  17
  18 // You should have received a copy of the GNU General Public License
  19 // along with this program; if not, write to the Free Software
  20 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  21 // MA 02110-1301, USA.
  22
  23 #include "gold.h"
  24
  25 #include "elfcpp.h"
  26 #include "target.h"
  27 #include "object.h"
  28 #include "symtab.h"
  29 #include "plugin.h"
  30
  31 namespace gold
  32 {
  33
  34 // Symbol methods used in this file.
  35
  36 // This symbol is being overridden by another symbol whose version is
  37 // VERSION.  Update the VERSION_ field accordingly.
  38
  39 inline void
  40 Symbol::override_version(const char* version)
  41 {
  42   if (version == NULL)
  43     {
  44       // This is the case where this symbol is NAME/VERSION, and the
  45       // version was not marked as hidden.  That makes it the default
  46       // version, so we create NAME/NULL.  Later we see another symbol
  47       // NAME/NULL, and that symbol is overriding this one.  In this
  48       // case, since NAME/VERSION is the default, we make NAME/NULL
  49       // override NAME/VERSION as well.  They are already the same
  50       // Symbol structure.  Setting the VERSION_ field to NULL ensures
  51       // that it will be output with the correct, empty, version.
  52       this->version_ = version;
  53     }
  54   else
  55     {
  56       // This is the case where this symbol is NAME/VERSION_ONE, and
  57       // now we see NAME/VERSION_TWO, and NAME/VERSION_TWO is
  58       // overriding NAME.  If VERSION_ONE and VERSION_TWO are
  59       // different, then this can only happen when VERSION_ONE is NULL
  60       // and VERSION_TWO is not hidden.
  61       gold_assert(this->version_ == version || this->version_ == NULL);
  62       this->version_ = version;
  63     }
  64 }
  65
  66 // Override the fields in Symbol.
  67
  68 template<int size, bool big_endian>
  69 void
  70 Symbol::override_base(const elfcpp::Sym<size, big_endian>& sym,
  71                       unsigned int st_shndx, bool is_ordinary,
  72                       Object* object, const char* version)
  73 {
  74   gold_assert(this->source_ == FROM_OBJECT);
  75   this->u_.from_object.object = object;
  76   this->override_version(version);
  77   this->u_.from_object.shndx = st_shndx;
  78   this->is_ordinary_shndx_ = is_ordinary;
  79   this->type_ = sym.get_st_type();
  80   this->binding_ = sym.get_st_bind();
  81   this->visibility_ = sym.get_st_visibility();
  82   this->nonvis_ = sym.get_st_nonvis();
  83   if (object->is_dynamic())
  84     this->in_dyn_ = true;
  85   else
  86     this->in_reg_ = true;
  87 }
  88
  89 // Override the fields in Sized_symbol.
  90
  91 template<int size>
  92 template<bool big_endian>
  93 void
  94 Sized_symbol<size>::override(const elfcpp::Sym<size, big_endian>& sym,
  95                              unsigned st_shndx, bool is_ordinary,
  96                              Object* object, const char* version)
  97 {
  98   this->override_base(sym, st_shndx, is_ordinary, object, version);
  99   this->value_ = sym.get_st_value();
 100   this->symsize_ = sym.get_st_size();
 101 }
 102
 103 // Override TOSYM with symbol FROMSYM, defined in OBJECT, with version
 104 // VERSION.  This handles all aliases of TOSYM.
 105
 106 template<int size, bool big_endian>
 107 void
 108 Symbol_table::override(Sized_symbol<size>* tosym,
 109                        const elfcpp::Sym<size, big_endian>& fromsym,
 110                        unsigned int st_shndx, bool is_ordinary,
 111                        Object* object, const char* version)
 112 {
 113   tosym->override(fromsym, st_shndx, is_ordinary, object, version);
 114   if (tosym->has_alias())
 115     {
 116       Symbol* sym = this->weak_aliases_[tosym];
 117       gold_assert(sym != NULL);
 118       Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 119       do
 120         {
 121           ssym->override(fromsym, st_shndx, is_ordinary, object, version);
 122           sym = this->weak_aliases_[ssym];
 123           gold_assert(sym != NULL);
 124           ssym = this->get_sized_symbol<size>(sym);
 125         }
 126       while (ssym != tosym);
 127     }
 128 }
 129
 130 // The resolve functions build a little code for each symbol.
 131 // Bit 0: 0 for global, 1 for weak.
 132 // Bit 1: 0 for regular object, 1 for shared object
 133 // Bits 2-3: 0 for normal, 1 for undefined, 2 for common
 134 // This gives us values from 0 to 11.
 135
 136 static const int global_or_weak_shift = 0;
 137 static const unsigned int global_flag = 0 << global_or_weak_shift;
 138 static const unsigned int weak_flag = 1 << global_or_weak_shift;
 139
 140 static const int regular_or_dynamic_shift = 1;
 141 static const unsigned int regular_flag = 0 << regular_or_dynamic_shift;
 142 static const unsigned int dynamic_flag = 1 << regular_or_dynamic_shift;
 143
 144 static const int def_undef_or_common_shift = 2;
 145 static const unsigned int def_flag = 0 << def_undef_or_common_shift;
 146 static const unsigned int undef_flag = 1 << def_undef_or_common_shift;
 147 static const unsigned int common_flag = 2 << def_undef_or_common_shift;
 148
 149 // This convenience function combines all the flags based on facts
 150 // about the symbol.
 151
 152 static unsigned int
 153 symbol_to_bits(elfcpp::STB binding, bool is_dynamic,
 154                unsigned int shndx, bool is_ordinary, elfcpp::STT type)
 155 {
 156   unsigned int bits;
 157
 158   switch (binding)
 159     {
 160     case elfcpp::STB_GLOBAL:
 161       bits = global_flag;
 162       break;
 163
 164     case elfcpp::STB_WEAK:
 165       bits = weak_flag;
 166       break;
 167
 168     case elfcpp::STB_LOCAL:
 169       // We should only see externally visible symbols in the symbol
 170       // table.
 171       gold_error(_("invalid STB_LOCAL symbol in external symbols"));
 172       bits = global_flag;
 173
 174     default:
 175       // Any target which wants to handle STB_LOOS, etc., needs to
 176       // define a resolve method.
 177       gold_error(_("unsupported symbol binding"));
 178       bits = global_flag;
 179     }
 180
 181   if (is_dynamic)
 182     bits |= dynamic_flag;
 183   else
 184     bits |= regular_flag;
 185
 186   switch (shndx)
 187     {
 188     case elfcpp::SHN_UNDEF:
 189       bits |= undef_flag;
 190       break;
 191
 192     case elfcpp::SHN_COMMON:
 193       if (!is_ordinary)
 194         bits |= common_flag;
 195       break;
 196
 197     default:
 198       if (type == elfcpp::STT_COMMON)
 199         bits |= common_flag;
 200       else
 201         bits |= def_flag;
 202       break;
 203     }
 204
 205   return bits;
 206 }
 207
 208 // Resolve a symbol.  This is called the second and subsequent times
 209 // we see a symbol.  TO is the pre-existing symbol.  ST_SHNDX is the
 210 // section index for SYM, possibly adjusted for many sections.
 211 // IS_ORDINARY is whether ST_SHNDX is a normal section index rather
 212 // than a special code.  ORIG_ST_SHNDX is the original section index,
 213 // before any munging because of discarded sections, except that all
 214 // non-ordinary section indexes are mapped to SHN_UNDEF.  VERSION is
 215 // the version of SYM.
 216
 217 template<int size, bool big_endian>
 218 void
 219 Symbol_table::resolve(Sized_symbol<size>* to,
 220                       const elfcpp::Sym<size, big_endian>& sym,
 221                       unsigned int st_shndx, bool is_ordinary,
 222                       unsigned int orig_st_shndx,
 223                       Object* object, const char* version)
 224 {
 225   if (object->target()->has_resolve())
 226     {
 227       Sized_target<size, big_endian>* sized_target;
 228       sized_target = object->sized_target<size, big_endian>();
 229       sized_target->resolve(to, sym, object, version);
 230       return;
 231     }
 232
 233   if (!object->is_dynamic())
 234     {
 235       // Record that we've seen this symbol in a regular object.
 236       to->set_in_reg();
 237     }
 238   else
 239     {
 240       // Record that we've seen this symbol in a dynamic object.
 241       to->set_in_dyn();
 242     }
 243
 244   // Record if we've seen this symbol in a real ELF object (i.e., the
 245   // symbol is referenced from outside the world known to the plugin).
 246   if (object->pluginobj() == NULL)
 247     to->set_in_real_elf();
 248
 249   // If we're processing replacement files, allow new symbols to override
 250   // the placeholders from the plugin objects.
 251   if (to->source() == Symbol::FROM_OBJECT)
 252     {
 253       Pluginobj* obj = to->object()->pluginobj();
 254       if (obj != NULL
 255           && parameters->options().plugins()->in_replacement_phase())
 256         {
 257           this->override(to, sym, st_shndx, is_ordinary, object, version);
 258           return;
 259         }
 260     }
 261
 262   unsigned int frombits = symbol_to_bits(sym.get_st_bind(),
 263                                          object->is_dynamic(),
 264                                          st_shndx, is_ordinary,
 265                                          sym.get_st_type());
 266
 267   bool adjust_common_sizes;
 268   if (Symbol_table::should_override(to, frombits, object,
 269                                     &adjust_common_sizes))
 270     {
 271       typename Sized_symbol<size>::Size_type tosize = to->symsize();
 272
 273       this->override(to, sym, st_shndx, is_ordinary, object, version);
 274
 275       if (adjust_common_sizes && tosize > to->symsize())
 276         to->set_symsize(tosize);
 277     }
 278   else
 279     {
 280       if (adjust_common_sizes && sym.get_st_size() > to->symsize())
 281         to->set_symsize(sym.get_st_size());
 282     }
 283
 284   // A new weak undefined reference, merging with an old weak
 285   // reference, could be a One Definition Rule (ODR) violation --
 286   // especially if the types or sizes of the references differ.  We'll
 287   // store such pairs and look them up later to make sure they
 288   // actually refer to the same lines of code.  (Note: not all ODR
 289   // violations can be found this way, and not everything this finds
 290   // is an ODR violation.  But it's helpful to warn about.)
 291   bool to_is_ordinary;
 292   if (parameters->options().detect_odr_violations()
 293       && sym.get_st_bind() == elfcpp::STB_WEAK
 294       && to->binding() == elfcpp::STB_WEAK
 295       && orig_st_shndx != elfcpp::SHN_UNDEF
 296       && to->shndx(&to_is_ordinary) != elfcpp::SHN_UNDEF
 297       && to_is_ordinary
 298       && sym.get_st_size() != 0    // Ignore weird 0-sized symbols.
 299       && to->symsize() != 0
 300       && (sym.get_st_type() != to->type()
 301           || sym.get_st_size() != to->symsize())
 302       // C does not have a concept of ODR, so we only need to do this
 303       // on C++ symbols.  These have (mangled) names starting with _Z.
 304       && to->name()[0] == '_' && to->name()[1] == 'Z')
 305     {
 306       Symbol_location fromloc
 307           = { object, orig_st_shndx, sym.get_st_value() };
 308       Symbol_location toloc = { to->object(), to->shndx(&to_is_ordinary),
 309                                 to->value() };
 310       this->candidate_odr_violations_[to->name()].insert(fromloc);
 311       this->candidate_odr_violations_[to->name()].insert(toloc);
 312     }
 313 }
 314
 315 // Handle the core of symbol resolution.  This is called with the
 316 // existing symbol, TO, and a bitflag describing the new symbol.  This
 317 // returns true if we should override the existing symbol with the new
 318 // one, and returns false otherwise.  It sets *ADJUST_COMMON_SIZES to
 319 // true if we should set the symbol size to the maximum of the TO and
 320 // FROM sizes.  It handles error conditions.
 321
 322 bool
 323 Symbol_table::should_override(const Symbol* to, unsigned int frombits,
 324                               Object* object, bool* adjust_common_sizes)
 325 {
 326   *adjust_common_sizes = false;
 327
 328   unsigned int tobits;
 329   if (to->source() == Symbol::IS_UNDEFINED)
 330     tobits = symbol_to_bits(to->binding(), false, elfcpp::SHN_UNDEF, true,
 331                             to->type());
 332   else if (to->source() != Symbol::FROM_OBJECT)
 333     tobits = symbol_to_bits(to->binding(), false, elfcpp::SHN_ABS, false,
 334                             to->type());
 335   else
 336     {
 337       bool is_ordinary;
 338       unsigned int shndx = to->shndx(&is_ordinary);
 339       tobits = symbol_to_bits(to->binding(),
 340                               to->object()->is_dynamic(),
 341                               shndx,
 342                               is_ordinary,
 343                               to->type());
 344     }
 345
 346   // FIXME: Warn if either but not both of TO and SYM are STT_TLS.
 347
 348   // We use a giant switch table for symbol resolution.  This code is
 349   // unwieldy, but: 1) it is efficient; 2) we definitely handle all
 350   // cases; 3) it is easy to change the handling of a particular case.
 351   // The alternative would be a series of conditionals, but it is easy
 352   // to get the ordering wrong.  This could also be done as a table,
 353   // but that is no easier to understand than this large switch
 354   // statement.
 355
 356   // These are the values generated by the bit codes.
 357   enum
 358   {
 359     DEF =              global_flag | regular_flag | def_flag,
 360     WEAK_DEF =         weak_flag   | regular_flag | def_flag,
 361     DYN_DEF =          global_flag | dynamic_flag | def_flag,
 362     DYN_WEAK_DEF =     weak_flag   | dynamic_flag | def_flag,
 363     UNDEF =            global_flag | regular_flag | undef_flag,
 364     WEAK_UNDEF =       weak_flag   | regular_flag | undef_flag,
 365     DYN_UNDEF =        global_flag | dynamic_flag | undef_flag,
 366     DYN_WEAK_UNDEF =   weak_flag   | dynamic_flag | undef_flag,
 367     COMMON =           global_flag | regular_flag | common_flag,
 368     WEAK_COMMON =      weak_flag   | regular_flag | common_flag,
 369     DYN_COMMON =       global_flag | dynamic_flag | common_flag,
 370     DYN_WEAK_COMMON =  weak_flag   | dynamic_flag | common_flag
 371   };
 372
 373   switch (tobits * 16 + frombits)
 374     {
 375     case DEF * 16 + DEF:
 376       // Two definitions of the same symbol.
 377
 378       // If either symbol is defined by an object included using
 379       // --just-symbols, then don't warn.  This is for compatibility
 380       // with the GNU linker.  FIXME: This is a hack.
 381       if ((to->source() == Symbol::FROM_OBJECT && to->object()->just_symbols())
 382           || object->just_symbols())
 383         return false;
 384
 385       // FIXME: Do a better job of reporting locations.
 386       gold_error(_("%s: multiple definition of %s"),
 387                  object != NULL ? object->name().c_str() : _("command line"),
 388                  to->demangled_name().c_str());
 389       gold_error(_("%s: previous definition here"),
 390                  (to->source() == Symbol::FROM_OBJECT
 391                   ? to->object()->name().c_str()
 392                   : _("command line")));
 393       return false;
 394
 395     case WEAK_DEF * 16 + DEF:
 396       // We've seen a weak definition, and now we see a strong
 397       // definition.  In the original SVR4 linker, this was treated as
 398       // a multiple definition error.  In the Solaris linker and the
 399       // GNU linker, a weak definition followed by a regular
 400       // definition causes the weak definition to be overridden.  We
 401       // are currently compatible with the GNU linker.  In the future
 402       // we should add a target specific option to change this.
 403       // FIXME.
 404       return true;
 405
 406     case DYN_DEF * 16 + DEF:
 407     case DYN_WEAK_DEF * 16 + DEF:
 408       // We've seen a definition in a dynamic object, and now we see a
 409       // definition in a regular object.  The definition in the
 410       // regular object overrides the definition in the dynamic
 411       // object.
 412       return true;
 413
 414     case UNDEF * 16 + DEF:
 415     case WEAK_UNDEF * 16 + DEF:
 416     case DYN_UNDEF * 16 + DEF:
 417     case DYN_WEAK_UNDEF * 16 + DEF:
 418       // We've seen an undefined reference, and now we see a
 419       // definition.  We use the definition.
 420       return true;
 421
 422     case COMMON * 16 + DEF:
 423     case WEAK_COMMON * 16 + DEF:
 424     case DYN_COMMON * 16 + DEF:
 425     case DYN_WEAK_COMMON * 16 + DEF:
 426       // We've seen a common symbol and now we see a definition.  The
 427       // definition overrides.  FIXME: We should optionally issue, version a
 428       // warning.
 429       return true;
 430
 431     case DEF * 16 + WEAK_DEF:
 432     case WEAK_DEF * 16 + WEAK_DEF:
 433       // We've seen a definition and now we see a weak definition.  We
 434       // ignore the new weak definition.
 435       return false;
 436
 437     case DYN_DEF * 16 + WEAK_DEF:
 438     case DYN_WEAK_DEF * 16 + WEAK_DEF:
 439       // We've seen a dynamic definition and now we see a regular weak
 440       // definition.  The regular weak definition overrides.
 441       return true;
 442
 443     case UNDEF * 16 + WEAK_DEF:
 444     case WEAK_UNDEF * 16 + WEAK_DEF:
 445     case DYN_UNDEF * 16 + WEAK_DEF:
 446     case DYN_WEAK_UNDEF * 16 + WEAK_DEF:
 447       // A weak definition of a currently undefined symbol.
 448       return true;
 449
 450     case COMMON * 16 + WEAK_DEF:
 451     case WEAK_COMMON * 16 + WEAK_DEF:
 452       // A weak definition does not override a common definition.
 453       return false;
 454
 455     case DYN_COMMON * 16 + WEAK_DEF:
 456     case DYN_WEAK_COMMON * 16 + WEAK_DEF:
 457       // A weak definition does override a definition in a dynamic
 458       // object.  FIXME: We should optionally issue a warning.
 459       return true;
 460
 461     case DEF * 16 + DYN_DEF:
 462     case WEAK_DEF * 16 + DYN_DEF:
 463     case DYN_DEF * 16 + DYN_DEF:
 464     case DYN_WEAK_DEF * 16 + DYN_DEF:
 465       // Ignore a dynamic definition if we already have a definition.
 466       return false;
 467
 468     case UNDEF * 16 + DYN_DEF:
 469     case WEAK_UNDEF * 16 + DYN_DEF:
 470     case DYN_UNDEF * 16 + DYN_DEF:
 471     case DYN_WEAK_UNDEF * 16 + DYN_DEF:
 472       // Use a dynamic definition if we have a reference.
 473       return true;
 474
 475     case COMMON * 16 + DYN_DEF:
 476     case WEAK_COMMON * 16 + DYN_DEF:
 477     case DYN_COMMON * 16 + DYN_DEF:
 478     case DYN_WEAK_COMMON * 16 + DYN_DEF:
 479       // Ignore a dynamic definition if we already have a common
 480       // definition.
 481       return false;
 482
 483     case DEF * 16 + DYN_WEAK_DEF:
 484     case WEAK_DEF * 16 + DYN_WEAK_DEF:
 485     case DYN_DEF * 16 + DYN_WEAK_DEF:
 486     case DYN_WEAK_DEF * 16 + DYN_WEAK_DEF:
 487       // Ignore a weak dynamic definition if we already have a
 488       // definition.
 489       return false;
 490
 491     case UNDEF * 16 + DYN_WEAK_DEF:
 492     case WEAK_UNDEF * 16 + DYN_WEAK_DEF:
 493     case DYN_UNDEF * 16 + DYN_WEAK_DEF:
 494     case DYN_WEAK_UNDEF * 16 + DYN_WEAK_DEF:
 495       // Use a weak dynamic definition if we have a reference.
 496       return true;
 497
 498     case COMMON * 16 + DYN_WEAK_DEF:
 499     case WEAK_COMMON * 16 + DYN_WEAK_DEF:
 500     case DYN_COMMON * 16 + DYN_WEAK_DEF:
 501     case DYN_WEAK_COMMON * 16 + DYN_WEAK_DEF:
 502       // Ignore a weak dynamic definition if we already have a common
 503       // definition.
 504       return false;
 505
 506     case DEF * 16 + UNDEF:
 507     case WEAK_DEF * 16 + UNDEF:
 508     case DYN_DEF * 16 + UNDEF:
 509     case DYN_WEAK_DEF * 16 + UNDEF:
 510     case UNDEF * 16 + UNDEF:
 511       // A new undefined reference tells us nothing.
 512       return false;
 513
 514     case WEAK_UNDEF * 16 + UNDEF:
 515     case DYN_UNDEF * 16 + UNDEF:
 516     case DYN_WEAK_UNDEF * 16 + UNDEF:
 517       // A strong undef overrides a dynamic or weak undef.
 518       return true;
 519
 520     case COMMON * 16 + UNDEF:
 521     case WEAK_COMMON * 16 + UNDEF:
 522     case DYN_COMMON * 16 + UNDEF:
 523     case DYN_WEAK_COMMON * 16 + UNDEF:
 524       // A new undefined reference tells us nothing.
 525       return false;
 526
 527     case DEF * 16 + WEAK_UNDEF:
 528     case WEAK_DEF * 16 + WEAK_UNDEF:
 529     case DYN_DEF * 16 + WEAK_UNDEF:
 530     case DYN_WEAK_DEF * 16 + WEAK_UNDEF:
 531     case UNDEF * 16 + WEAK_UNDEF:
 532     case WEAK_UNDEF * 16 + WEAK_UNDEF:
 533     case DYN_UNDEF * 16 + WEAK_UNDEF:
 534     case DYN_WEAK_UNDEF * 16 + WEAK_UNDEF:
 535     case COMMON * 16 + WEAK_UNDEF:
 536     case WEAK_COMMON * 16 + WEAK_UNDEF:
 537     case DYN_COMMON * 16 + WEAK_UNDEF:
 538     case DYN_WEAK_COMMON * 16 + WEAK_UNDEF:
 539       // A new weak undefined reference tells us nothing.
 540       return false;
 541
 542     case DEF * 16 + DYN_UNDEF:
 543     case WEAK_DEF * 16 + DYN_UNDEF:
 544     case DYN_DEF * 16 + DYN_UNDEF:
 545     case DYN_WEAK_DEF * 16 + DYN_UNDEF:
 546     case UNDEF * 16 + DYN_UNDEF:
 547     case WEAK_UNDEF * 16 + DYN_UNDEF:
 548     case DYN_UNDEF * 16 + DYN_UNDEF:
 549     case DYN_WEAK_UNDEF * 16 + DYN_UNDEF:
 550     case COMMON * 16 + DYN_UNDEF:
 551     case WEAK_COMMON * 16 + DYN_UNDEF:
 552     case DYN_COMMON * 16 + DYN_UNDEF:
 553     case DYN_WEAK_COMMON * 16 + DYN_UNDEF:
 554       // A new dynamic undefined reference tells us nothing.
 555       return false;
 556
 557     case DEF * 16 + DYN_WEAK_UNDEF:
 558     case WEAK_DEF * 16 + DYN_WEAK_UNDEF:
 559     case DYN_DEF * 16 + DYN_WEAK_UNDEF:
 560     case DYN_WEAK_DEF * 16 + DYN_WEAK_UNDEF:
 561     case UNDEF * 16 + DYN_WEAK_UNDEF:
 562     case WEAK_UNDEF * 16 + DYN_WEAK_UNDEF:
 563     case DYN_UNDEF * 16 + DYN_WEAK_UNDEF:
 564     case DYN_WEAK_UNDEF * 16 + DYN_WEAK_UNDEF:
 565     case COMMON * 16 + DYN_WEAK_UNDEF:
 566     case WEAK_COMMON * 16 + DYN_WEAK_UNDEF:
 567     case DYN_COMMON * 16 + DYN_WEAK_UNDEF:
 568     case DYN_WEAK_COMMON * 16 + DYN_WEAK_UNDEF:
 569       // A new weak dynamic undefined reference tells us nothing.
 570       return false;
 571
 572     case DEF * 16 + COMMON:
 573       // A common symbol does not override a definition.
 574       return false;
 575
 576     case WEAK_DEF * 16 + COMMON:
 577     case DYN_DEF * 16 + COMMON:
 578     case DYN_WEAK_DEF * 16 + COMMON:
 579       // A common symbol does override a weak definition or a dynamic
 580       // definition.
 581       return true;
 582
 583     case UNDEF * 16 + COMMON:
 584     case WEAK_UNDEF * 16 + COMMON:
 585     case DYN_UNDEF * 16 + COMMON:
 586     case DYN_WEAK_UNDEF * 16 + COMMON:
 587       // A common symbol is a definition for a reference.
 588       return true;
 589
 590     case COMMON * 16 + COMMON:
 591       // Set the size to the maximum.
 592       *adjust_common_sizes = true;
 593       return false;
 594
 595     case WEAK_COMMON * 16 + COMMON:
 596       // I'm not sure just what a weak common symbol means, but
 597       // presumably it can be overridden by a regular common symbol.
 598       return true;
 599
 600     case DYN_COMMON * 16 + COMMON:
 601     case DYN_WEAK_COMMON * 16 + COMMON:
 602       // Use the real common symbol, but adjust the size if necessary.
 603       *adjust_common_sizes = true;
 604       return true;
 605
 606     case DEF * 16 + WEAK_COMMON:
 607     case WEAK_DEF * 16 + WEAK_COMMON:
 608     case DYN_DEF * 16 + WEAK_COMMON:
 609     case DYN_WEAK_DEF * 16 + WEAK_COMMON:
 610       // Whatever a weak common symbol is, it won't override a
 611       // definition.
 612       return false;
 613
 614     case UNDEF * 16 + WEAK_COMMON:
 615     case WEAK_UNDEF * 16 + WEAK_COMMON:
 616     case DYN_UNDEF * 16 + WEAK_COMMON:
 617     case DYN_WEAK_UNDEF * 16 + WEAK_COMMON:
 618       // A weak common symbol is better than an undefined symbol.
 619       return true;
 620
 621     case COMMON * 16 + WEAK_COMMON:
 622     case WEAK_COMMON * 16 + WEAK_COMMON:
 623     case DYN_COMMON * 16 + WEAK_COMMON:
 624     case DYN_WEAK_COMMON * 16 + WEAK_COMMON:
 625       // Ignore a weak common symbol in the presence of a real common
 626       // symbol.
 627       return false;
 628
 629     case DEF * 16 + DYN_COMMON:
 630     case WEAK_DEF * 16 + DYN_COMMON:
 631     case DYN_DEF * 16 + DYN_COMMON:
 632     case DYN_WEAK_DEF * 16 + DYN_COMMON:
 633       // Ignore a dynamic common symbol in the presence of a
 634       // definition.
 635       return false;
 636
 637     case UNDEF * 16 + DYN_COMMON:
 638     case WEAK_UNDEF * 16 + DYN_COMMON:
 639     case DYN_UNDEF * 16 + DYN_COMMON:
 640     case DYN_WEAK_UNDEF * 16 + DYN_COMMON:
 641       // A dynamic common symbol is a definition of sorts.
 642       return true;
 643
 644     case COMMON * 16 + DYN_COMMON:
 645     case WEAK_COMMON * 16 + DYN_COMMON:
 646     case DYN_COMMON * 16 + DYN_COMMON:
 647     case DYN_WEAK_COMMON * 16 + DYN_COMMON:
 648       // Set the size to the maximum.
 649       *adjust_common_sizes = true;
 650       return false;
 651
 652     case DEF * 16 + DYN_WEAK_COMMON:
 653     case WEAK_DEF * 16 + DYN_WEAK_COMMON:
 654     case DYN_DEF * 16 + DYN_WEAK_COMMON:
 655     case DYN_WEAK_DEF * 16 + DYN_WEAK_COMMON:
 656       // A common symbol is ignored in the face of a definition.
 657       return false;
 658
 659     case UNDEF * 16 + DYN_WEAK_COMMON:
 660     case WEAK_UNDEF * 16 + DYN_WEAK_COMMON:
 661     case DYN_UNDEF * 16 + DYN_WEAK_COMMON:
 662     case DYN_WEAK_UNDEF * 16 + DYN_WEAK_COMMON:
 663       // I guess a weak common symbol is better than a definition.
 664       return true;
 665
 666     case COMMON * 16 + DYN_WEAK_COMMON:
 667     case WEAK_COMMON * 16 + DYN_WEAK_COMMON:
 668     case DYN_COMMON * 16 + DYN_WEAK_COMMON:
 669     case DYN_WEAK_COMMON * 16 + DYN_WEAK_COMMON:
 670       // Set the size to the maximum.
 671       *adjust_common_sizes = true;
 672       return false;
 673
 674     default:
 675       gold_unreachable();
 676     }
 677 }
 678
 679 // A special case of should_override which is only called for a strong
 680 // defined symbol from a regular object file.  This is used when
 681 // defining special symbols.
 682
 683 bool
 684 Symbol_table::should_override_with_special(const Symbol* to)
 685 {
 686   bool adjust_common_sizes;
 687   unsigned int frombits = global_flag | regular_flag | def_flag;
 688   bool ret = Symbol_table::should_override(to, frombits, NULL,
 689                                            &adjust_common_sizes);
 690   gold_assert(!adjust_common_sizes);
 691   return ret;
 692 }
 693
 694 // Override symbol base with a special symbol.
 695
 696 void
 697 Symbol::override_base_with_special(const Symbol* from)
 698 {
 699   gold_assert(this->name_ == from->name_ || this->has_alias());
 700
 701   this->source_ = from->source_;
 702   switch (from->source_)
 703     {
 704     case FROM_OBJECT:
 705       this->u_.from_object = from->u_.from_object;
 706       break;
 707     case IN_OUTPUT_DATA:
 708       this->u_.in_output_data = from->u_.in_output_data;
 709       break;
 710     case IN_OUTPUT_SEGMENT:
 711       this->u_.in_output_segment = from->u_.in_output_segment;
 712       break;
 713     case IS_CONSTANT:
 714     case IS_UNDEFINED:
 715       break;
 716     default:
 717       gold_unreachable();
 718       break;
 719     }
 720
 721   this->override_version(from->version_);
 722   this->type_ = from->type_;
 723   this->binding_ = from->binding_;
 724   this->visibility_ = from->visibility_;
 725   this->nonvis_ = from->nonvis_;
 726
 727   // Special symbols are always considered to be regular symbols.
 728   this->in_reg_ = true;
 729
 730   if (from->needs_dynsym_entry_)
 731     this->needs_dynsym_entry_ = true;
 732   if (from->needs_dynsym_value_)
 733     this->needs_dynsym_value_ = true;
 734
 735   // We shouldn't see these flags.  If we do, we need to handle them
 736   // somehow.
 737   gold_assert(!from->is_target_special_ || this->is_target_special_);
 738   gold_assert(!from->is_forwarder_);
 739   gold_assert(!from->has_plt_offset_);
 740   gold_assert(!from->has_warning_);
 741   gold_assert(!from->is_copied_from_dynobj_);
 742   gold_assert(!from->is_forced_local_);
 743 }
 744
 745 // Override a symbol with a special symbol.
 746
 747 template<int size>
 748 void
 749 Sized_symbol<size>::override_with_special(const Sized_symbol<size>* from)
 750 {
 751   this->override_base_with_special(from);
 752   this->value_ = from->value_;
 753   this->symsize_ = from->symsize_;
 754 }
 755
 756 // Override TOSYM with the special symbol FROMSYM.  This handles all
 757 // aliases of TOSYM.
 758
 759 template<int size>
 760 void
 761 Symbol_table::override_with_special(Sized_symbol<size>* tosym,
 762                                     const Sized_symbol<size>* fromsym)
 763 {
 764   tosym->override_with_special(fromsym);
 765   if (tosym->has_alias())
 766     {
 767       Symbol* sym = this->weak_aliases_[tosym];
 768       gold_assert(sym != NULL);
 769       Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 770       do
 771         {
 772           ssym->override_with_special(fromsym);
 773           sym = this->weak_aliases_[ssym];
 774           gold_assert(sym != NULL);
 775           ssym = this->get_sized_symbol<size>(sym);
 776         }
 777       while (ssym != tosym);
 778     }
 779   if (tosym->binding() == elfcpp::STB_LOCAL)
 780     this->force_local(tosym);
 781 }
 782
 783 // Instantiate the templates we need.  We could use the configure
 784 // script to restrict this to only the ones needed for implemented
 785 // targets.
 786
 787 #ifdef HAVE_TARGET_32_LITTLE
 788 template
 789 void
 790 Symbol_table::resolve<32, false>(
 791     Sized_symbol<32>* to,
 792     const elfcpp::Sym<32, false>& sym,
 793     unsigned int st_shndx,
 794     bool is_ordinary,
 795     unsigned int orig_st_shndx,
 796     Object* object,
 797     const char* version);
 798 #endif
 799
 800 #ifdef HAVE_TARGET_32_BIG
 801 template
 802 void
 803 Symbol_table::resolve<32, true>(
 804     Sized_symbol<32>* to,
 805     const elfcpp::Sym<32, true>& sym,
 806     unsigned int st_shndx,
 807     bool is_ordinary,
 808     unsigned int orig_st_shndx,
 809     Object* object,
 810     const char* version);
 811 #endif
 812
 813 #ifdef HAVE_TARGET_64_LITTLE
 814 template
 815 void
 816 Symbol_table::resolve<64, false>(
 817     Sized_symbol<64>* to,
 818     const elfcpp::Sym<64, false>& sym,
 819     unsigned int st_shndx,
 820     bool is_ordinary,
 821     unsigned int orig_st_shndx,
 822     Object* object,
 823     const char* version);
 824 #endif
 825
 826 #ifdef HAVE_TARGET_64_BIG
 827 template
 828 void
 829 Symbol_table::resolve<64, true>(
 830     Sized_symbol<64>* to,
 831     const elfcpp::Sym<64, true>& sym,
 832     unsigned int st_shndx,
 833     bool is_ordinary,
 834     unsigned int orig_st_shndx,
 835     Object* object,
 836     const char* version);
 837 #endif
 838
 839 #if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
 840 template
 841 void
 842 Symbol_table::override_with_special<32>(Sized_symbol<32>*,
 843                                         const Sized_symbol<32>*);
 844 #endif
 845
 846 #if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
 847 template
 848 void
 849 Symbol_table::override_with_special<64>(Sized_symbol<64>*,
 850                                         const Sized_symbol<64>*);
 851 #endif
 852
 853 } // End namespace gold.