gold/resolve.cc

   1 // resolve.cc -- symbol resolution for gold
   2
   3 #include "gold.h"
   4
   5 #include "elfcpp.h"
   6 #include "target.h"
   7 #include "object.h"
   8 #include "symtab.h"
   9
  10 namespace gold
  11 {
  12
  13 // Symbol methods used in this file.
  14
  15 // Override the fields in Symbol.
  16
  17 template<int size, bool big_endian>
  18 void
  19 Symbol::override_base(const elfcpp::Sym<size, big_endian>& sym,
  20                       Object* object)
  21 {
  22   gold_assert(this->source_ == FROM_OBJECT);
  23   this->u_.from_object.object = object;
  24   // FIXME: Handle SHN_XINDEX.
  25   this->u_.from_object.shnum = sym.get_st_shndx();
  26   this->type_ = sym.get_st_type();
  27   this->binding_ = sym.get_st_bind();
  28   this->visibility_ = sym.get_st_visibility();
  29   this->nonvis_ = sym.get_st_nonvis();
  30 }
  31
  32 // Override the fields in Sized_symbol.
  33
  34 template<int size>
  35 template<bool big_endian>
  36 void
  37 Sized_symbol<size>::override(const elfcpp::Sym<size, big_endian>& sym,
  38                              Object* object)
  39 {
  40   this->override_base(sym, object);
  41   this->value_ = sym.get_st_value();
  42   this->symsize_ = sym.get_st_size();
  43 }
  44
  45 // Resolve a symbol.  This is called the second and subsequent times
  46 // we see a symbol.  TO is the pre-existing symbol.  SYM is the new
  47 // symbol, seen in OBJECT.
  48
  49 template<int size, bool big_endian>
  50 void
  51 Symbol_table::resolve(Sized_symbol<size>* to,
  52                       const elfcpp::Sym<size, big_endian>& sym,
  53                       Object* object)
  54 {
  55   if (object->target()->has_resolve())
  56     {
  57       Sized_target<size, big_endian>* sized_target;
  58       sized_target = object->sized_target
  59                      SELECT_SIZE_ENDIAN_NAME(size, big_endian) (
  60                          SELECT_SIZE_ENDIAN_ONLY(size, big_endian));
  61       sized_target->resolve(to, sym, object);
  62       return;
  63     }
  64
  65   // Build a little code for each symbol.
  66   // Bit 0: 0 for global, 1 for weak.
  67   // Bit 1: 0 for regular object, 1 for shared object
  68   // Bits 2-3: 0 for normal, 1 for undefined, 2 for common
  69   // This gives us values from 0 to 11:
  70
  71   enum
  72   {
  73     DEF = 0,
  74     WEAK_DEF = 1,
  75     DYN_DEF = 2,
  76     DYN_WEAK_DEF = 3,
  77     UNDEF = 4,
  78     WEAK_UNDEF = 5,
  79     DYN_UNDEF = 6,
  80     DYN_WEAK_UNDEF = 7,
  81     COMMON = 8,
  82     WEAK_COMMON = 9,
  83     DYN_COMMON = 10,
  84     DYN_WEAK_COMMON = 11
  85   };
  86
  87   int tobits;
  88   switch (to->binding())
  89     {
  90     case elfcpp::STB_GLOBAL:
  91       tobits = 0;
  92       break;
  93
  94     case elfcpp::STB_WEAK:
  95       tobits = 1;
  96       break;
  97
  98     case elfcpp::STB_LOCAL:
  99       // We should only see externally visible symbols in the symbol
 100       // table.
 101       gold_unreachable();
 102
 103     default:
 104       // Any target which wants to handle STB_LOOS, etc., needs to
 105       // define a resolve method.
 106       gold_unreachable();
 107     }
 108
 109   if (to->source() == Symbol::FROM_OBJECT
 110       && to->object()->is_dynamic())
 111     tobits |= (1 << 1);
 112
 113   switch (to->shnum())
 114     {
 115     case elfcpp::SHN_UNDEF:
 116       tobits |= (1 << 2);
 117       break;
 118
 119     case elfcpp::SHN_COMMON:
 120       tobits |= (2 << 2);
 121       break;
 122
 123     default:
 124       if (to->type() == elfcpp::STT_COMMON)
 125         tobits |= (2 << 2);
 126       break;
 127     }
 128
 129   int frombits;
 130   switch (sym.get_st_bind())
 131     {
 132     case elfcpp::STB_GLOBAL:
 133       frombits = 0;
 134       break;
 135
 136     case elfcpp::STB_WEAK:
 137       frombits = 1;
 138       break;
 139
 140     case elfcpp::STB_LOCAL:
 141       fprintf(stderr,
 142               _("%s: %s: invalid STB_LOCAL symbol %s in external symbols\n"),
 143               program_name, object->name().c_str(), to->name());
 144       gold_exit(false);
 145
 146     default:
 147       fprintf(stderr,
 148               _("%s: %s: unsupported symbol binding %d for symbol %s\n"),
 149               program_name, object->name().c_str(),
 150               static_cast<int>(sym.get_st_bind()), to->name());
 151       gold_exit(false);
 152     }
 153
 154   if (object->is_dynamic())
 155     {
 156       frombits |= (1 << 1);
 157
 158       // Record that we've seen this symbol in a dynamic object.
 159       to->set_in_dyn();
 160     }
 161
 162   switch (sym.get_st_shndx())
 163     {
 164     case elfcpp::SHN_UNDEF:
 165       frombits |= (1 << 2);
 166       break;
 167
 168     case elfcpp::SHN_COMMON:
 169       frombits |= (2 << 2);
 170       break;
 171
 172     default:
 173       if (sym.get_st_type() == elfcpp::STT_COMMON)
 174         frombits |= (2 << 2);
 175       break;
 176     }
 177
 178   if ((tobits & (1 << 1)) != (frombits & (1 << 1)))
 179     {
 180       // This symbol is seen in both a dynamic object and a regular
 181       // object.  That means that we need the symbol to go into the
 182       // dynamic symbol table, so that the dynamic linker can use the
 183       // regular symbol to override or define the dynamic symbol.
 184       to->set_needs_dynsym_entry();
 185     }
 186
 187   // FIXME: Warn if either but not both of TO and SYM are STT_TLS.
 188
 189   // We use a giant switch table for symbol resolution.  This code is
 190   // unwieldy, but: 1) it is efficient; 2) we definitely handle all
 191   // cases; 3) it is easy to change the handling of a particular case.
 192   // The alternative would be a series of conditionals, but it is easy
 193   // to get the ordering wrong.  This could also be done as a table,
 194   // but that is no easier to understand than this large switch
 195   // statement.
 196
 197   switch (tobits * 16 + frombits)
 198     {
 199     case DEF * 16 + DEF:
 200       // Two definitions of the same symbol.
 201       fprintf(stderr, "%s: %s: multiple definition of %s\n",
 202               program_name, object->name().c_str(), to->name());
 203       // FIXME: Report locations.  Record that we have seen an error.
 204       return;
 205
 206     case WEAK_DEF * 16 + DEF:
 207       // We've seen a weak definition, and now we see a strong
 208       // definition.  In the original SVR4 linker, this was treated as
 209       // a multiple definition error.  In the Solaris linker and the
 210       // GNU linker, a weak definition followed by a regular
 211       // definition causes the weak definition to be overridden.  We
 212       // are currently compatible with the GNU linker.  In the future
 213       // we should add a target specific option to change this.
 214       // FIXME.
 215       to->override(sym, object);
 216       return;
 217
 218     case DYN_DEF * 16 + DEF:
 219     case DYN_WEAK_DEF * 16 + DEF:
 220       // We've seen a definition in a dynamic object, and now we see a
 221       // definition in a regular object.  The definition in the
 222       // regular object overrides the definition in the dynamic
 223       // object.
 224       to->override(sym, object);
 225       return;
 226
 227     case UNDEF * 16 + DEF:
 228     case WEAK_UNDEF * 16 + DEF:
 229     case DYN_UNDEF * 16 + DEF:
 230     case DYN_WEAK_UNDEF * 16 + DEF:
 231       // We've seen an undefined reference, and now we see a
 232       // definition.  We use the definition.
 233       to->override(sym, object);
 234       return;
 235
 236     case COMMON * 16 + DEF:
 237     case WEAK_COMMON * 16 + DEF:
 238     case DYN_COMMON * 16 + DEF:
 239     case DYN_WEAK_COMMON * 16 + DEF:
 240       // We've seen a common symbol and now we see a definition.  The
 241       // definition overrides.  FIXME: We should optionally issue a
 242       // warning.
 243       to->override(sym, object);
 244       return;
 245
 246     case DEF * 16 + WEAK_DEF:
 247     case WEAK_DEF * 16 + WEAK_DEF:
 248       // We've seen a definition and now we see a weak definition.  We
 249       // ignore the new weak definition.
 250       return;
 251
 252     case DYN_DEF * 16 + WEAK_DEF:
 253     case DYN_WEAK_DEF * 16 + WEAK_DEF:
 254       // We've seen a dynamic definition and now we see a regular weak
 255       // definition.  The regular weak definition overrides.
 256       to->override(sym, object);
 257       return;
 258
 259     case UNDEF * 16 + WEAK_DEF:
 260     case WEAK_UNDEF * 16 + WEAK_DEF:
 261     case DYN_UNDEF * 16 + WEAK_DEF:
 262     case DYN_WEAK_UNDEF * 16 + WEAK_DEF:
 263       // A weak definition of a currently undefined symbol.
 264       to->override(sym, object);
 265       return;
 266
 267     case COMMON * 16 + WEAK_DEF:
 268     case WEAK_COMMON * 16 + WEAK_DEF:
 269       // A weak definition does not override a common definition.
 270       return;
 271
 272     case DYN_COMMON * 16 + WEAK_DEF:
 273     case DYN_WEAK_COMMON * 16 + WEAK_DEF:
 274       // A weak definition does override a definition in a dynamic
 275       // object.  FIXME: We should optionally issue a warning.
 276       to->override(sym, object);
 277       return;
 278
 279     case DEF * 16 + DYN_DEF:
 280     case WEAK_DEF * 16 + DYN_DEF:
 281     case DYN_DEF * 16 + DYN_DEF:
 282     case DYN_WEAK_DEF * 16 + DYN_DEF:
 283       // Ignore a dynamic definition if we already have a definition.
 284       return;
 285
 286     case UNDEF * 16 + DYN_DEF:
 287     case WEAK_UNDEF * 16 + DYN_DEF:
 288     case DYN_UNDEF * 16 + DYN_DEF:
 289     case DYN_WEAK_UNDEF * 16 + DYN_DEF:
 290       // Use a dynamic definition if we have a reference.
 291       to->override(sym, object);
 292       return;
 293
 294     case COMMON * 16 + DYN_DEF:
 295     case WEAK_COMMON * 16 + DYN_DEF:
 296     case DYN_COMMON * 16 + DYN_DEF:
 297     case DYN_WEAK_COMMON * 16 + DYN_DEF:
 298       // Ignore a dynamic definition if we already have a common
 299       // definition.
 300       return;
 301
 302     case DEF * 16 + DYN_WEAK_DEF:
 303     case WEAK_DEF * 16 + DYN_WEAK_DEF:
 304     case DYN_DEF * 16 + DYN_WEAK_DEF:
 305     case DYN_WEAK_DEF * 16 + DYN_WEAK_DEF:
 306       // Ignore a weak dynamic definition if we already have a
 307       // definition.
 308       return;
 309
 310     case UNDEF * 16 + DYN_WEAK_DEF:
 311     case WEAK_UNDEF * 16 + DYN_WEAK_DEF:
 312     case DYN_UNDEF * 16 + DYN_WEAK_DEF:
 313     case DYN_WEAK_UNDEF * 16 + DYN_WEAK_DEF:
 314       // Use a weak dynamic definition if we have a reference.
 315       to->override(sym, object);
 316       return;
 317
 318     case COMMON * 16 + DYN_WEAK_DEF:
 319     case WEAK_COMMON * 16 + DYN_WEAK_DEF:
 320     case DYN_COMMON * 16 + DYN_WEAK_DEF:
 321     case DYN_WEAK_COMMON * 16 + DYN_WEAK_DEF:
 322       // Ignore a weak dynamic definition if we already have a common
 323       // definition.
 324       return;
 325
 326     case DEF * 16 + UNDEF:
 327     case WEAK_DEF * 16 + UNDEF:
 328     case DYN_DEF * 16 + UNDEF:
 329     case DYN_WEAK_DEF * 16 + UNDEF:
 330     case UNDEF * 16 + UNDEF:
 331       // A new undefined reference tells us nothing.
 332       return;
 333
 334     case WEAK_UNDEF * 16 + UNDEF:
 335     case DYN_UNDEF * 16 + UNDEF:
 336     case DYN_WEAK_UNDEF * 16 + UNDEF:
 337       // A strong undef overrides a dynamic or weak undef.
 338       to->override(sym, object);
 339       return;
 340
 341     case COMMON * 16 + UNDEF:
 342     case WEAK_COMMON * 16 + UNDEF:
 343     case DYN_COMMON * 16 + UNDEF:
 344     case DYN_WEAK_COMMON * 16 + UNDEF:
 345       // A new undefined reference tells us nothing.
 346       return;
 347
 348     case DEF * 16 + WEAK_UNDEF:
 349     case WEAK_DEF * 16 + WEAK_UNDEF:
 350     case DYN_DEF * 16 + WEAK_UNDEF:
 351     case DYN_WEAK_DEF * 16 + WEAK_UNDEF:
 352     case UNDEF * 16 + WEAK_UNDEF:
 353     case WEAK_UNDEF * 16 + WEAK_UNDEF:
 354     case DYN_UNDEF * 16 + WEAK_UNDEF:
 355     case DYN_WEAK_UNDEF * 16 + WEAK_UNDEF:
 356     case COMMON * 16 + WEAK_UNDEF:
 357     case WEAK_COMMON * 16 + WEAK_UNDEF:
 358     case DYN_COMMON * 16 + WEAK_UNDEF:
 359     case DYN_WEAK_COMMON * 16 + WEAK_UNDEF:
 360       // A new weak undefined reference tells us nothing.
 361       return;
 362
 363     case DEF * 16 + DYN_UNDEF:
 364     case WEAK_DEF * 16 + DYN_UNDEF:
 365     case DYN_DEF * 16 + DYN_UNDEF:
 366     case DYN_WEAK_DEF * 16 + DYN_UNDEF:
 367     case UNDEF * 16 + DYN_UNDEF:
 368     case WEAK_UNDEF * 16 + DYN_UNDEF:
 369     case DYN_UNDEF * 16 + DYN_UNDEF:
 370     case DYN_WEAK_UNDEF * 16 + DYN_UNDEF:
 371     case COMMON * 16 + DYN_UNDEF:
 372     case WEAK_COMMON * 16 + DYN_UNDEF:
 373     case DYN_COMMON * 16 + DYN_UNDEF:
 374     case DYN_WEAK_COMMON * 16 + DYN_UNDEF:
 375       // A new dynamic undefined reference tells us nothing.
 376       return;
 377
 378     case DEF * 16 + DYN_WEAK_UNDEF:
 379     case WEAK_DEF * 16 + DYN_WEAK_UNDEF:
 380     case DYN_DEF * 16 + DYN_WEAK_UNDEF:
 381     case DYN_WEAK_DEF * 16 + DYN_WEAK_UNDEF:
 382     case UNDEF * 16 + DYN_WEAK_UNDEF:
 383     case WEAK_UNDEF * 16 + DYN_WEAK_UNDEF:
 384     case DYN_UNDEF * 16 + DYN_WEAK_UNDEF:
 385     case DYN_WEAK_UNDEF * 16 + DYN_WEAK_UNDEF:
 386     case COMMON * 16 + DYN_WEAK_UNDEF:
 387     case WEAK_COMMON * 16 + DYN_WEAK_UNDEF:
 388     case DYN_COMMON * 16 + DYN_WEAK_UNDEF:
 389     case DYN_WEAK_COMMON * 16 + DYN_WEAK_UNDEF:
 390       // A new weak dynamic undefined reference tells us nothing.
 391       return;
 392
 393     case DEF * 16 + COMMON:
 394       // A common symbol does not override a definition.
 395       return;
 396
 397     case WEAK_DEF * 16 + COMMON:
 398     case DYN_DEF * 16 + COMMON:
 399     case DYN_WEAK_DEF * 16 + COMMON:
 400       // A common symbol does override a weak definition or a dynamic
 401       // definition.
 402       to->override(sym, object);
 403       return;
 404
 405     case UNDEF * 16 + COMMON:
 406     case WEAK_UNDEF * 16 + COMMON:
 407     case DYN_UNDEF * 16 + COMMON:
 408     case DYN_WEAK_UNDEF * 16 + COMMON:
 409       // A common symbol is a definition for a reference.
 410       to->override(sym, object);
 411       return;
 412
 413     case COMMON * 16 + COMMON:
 414       // Set the size to the maximum.
 415       if (sym.get_st_size() > to->symsize())
 416         to->set_symsize(sym.get_st_size());
 417       return;
 418
 419     case WEAK_COMMON * 16 + COMMON:
 420       // I'm not sure just what a weak common symbol means, but
 421       // presumably it can be overridden by a regular common symbol.
 422       to->override(sym, object);
 423       return;
 424
 425     case DYN_COMMON * 16 + COMMON:
 426     case DYN_WEAK_COMMON * 16 + COMMON:
 427       {
 428         // Use the real common symbol, but adjust the size if necessary.
 429         typename Sized_symbol<size>::Size_type symsize = to->symsize();
 430         to->override(sym, object);
 431         if (to->symsize() < symsize)
 432           to->set_symsize(symsize);
 433       }
 434       return;
 435
 436     case DEF * 16 + WEAK_COMMON:
 437     case WEAK_DEF * 16 + WEAK_COMMON:
 438     case DYN_DEF * 16 + WEAK_COMMON:
 439     case DYN_WEAK_DEF * 16 + WEAK_COMMON:
 440       // Whatever a weak common symbol is, it won't override a
 441       // definition.
 442       return;
 443
 444     case UNDEF * 16 + WEAK_COMMON:
 445     case WEAK_UNDEF * 16 + WEAK_COMMON:
 446     case DYN_UNDEF * 16 + WEAK_COMMON:
 447     case DYN_WEAK_UNDEF * 16 + WEAK_COMMON:
 448       // A weak common symbol is better than an undefined symbol.
 449       to->override(sym, object);
 450       return;
 451
 452     case COMMON * 16 + WEAK_COMMON:
 453     case WEAK_COMMON * 16 + WEAK_COMMON:
 454     case DYN_COMMON * 16 + WEAK_COMMON:
 455     case DYN_WEAK_COMMON * 16 + WEAK_COMMON:
 456       // Ignore a weak common symbol in the presence of a real common
 457       // symbol.
 458       return;
 459
 460     case DEF * 16 + DYN_COMMON:
 461     case WEAK_DEF * 16 + DYN_COMMON:
 462     case DYN_DEF * 16 + DYN_COMMON:
 463     case DYN_WEAK_DEF * 16 + DYN_COMMON:
 464       // Ignore a dynamic common symbol in the presence of a
 465       // definition.
 466       return;
 467
 468     case UNDEF * 16 + DYN_COMMON:
 469     case WEAK_UNDEF * 16 + DYN_COMMON:
 470     case DYN_UNDEF * 16 + DYN_COMMON:
 471     case DYN_WEAK_UNDEF * 16 + DYN_COMMON:
 472       // A dynamic common symbol is a definition of sorts.
 473       to->override(sym, object);
 474       return;
 475
 476     case COMMON * 16 + DYN_COMMON:
 477     case WEAK_COMMON * 16 + DYN_COMMON:
 478     case DYN_COMMON * 16 + DYN_COMMON:
 479     case DYN_WEAK_COMMON * 16 + DYN_COMMON:
 480       // Set the size to the maximum.
 481       if (sym.get_st_size() > to->symsize())
 482         to->set_symsize(sym.get_st_size());
 483       return;
 484
 485     case DEF * 16 + DYN_WEAK_COMMON:
 486     case WEAK_DEF * 16 + DYN_WEAK_COMMON:
 487     case DYN_DEF * 16 + DYN_WEAK_COMMON:
 488     case DYN_WEAK_DEF * 16 + DYN_WEAK_COMMON:
 489       // A common symbol is ignored in the face of a definition.
 490       return;
 491
 492     case UNDEF * 16 + DYN_WEAK_COMMON:
 493     case WEAK_UNDEF * 16 + DYN_WEAK_COMMON:
 494     case DYN_UNDEF * 16 + DYN_WEAK_COMMON:
 495     case DYN_WEAK_UNDEF * 16 + DYN_WEAK_COMMON:
 496       // I guess a weak common symbol is better than a definition.
 497       to->override(sym, object);
 498       return;
 499
 500     case COMMON * 16 + DYN_WEAK_COMMON:
 501     case WEAK_COMMON * 16 + DYN_WEAK_COMMON:
 502     case DYN_COMMON * 16 + DYN_WEAK_COMMON:
 503     case DYN_WEAK_COMMON * 16 + DYN_WEAK_COMMON:
 504       // Set the size to the maximum.
 505       if (sym.get_st_size() > to->symsize())
 506         to->set_symsize(sym.get_st_size());
 507       return;
 508
 509     default:
 510       gold_unreachable();
 511     }
 512 }
 513
 514 // Instantiate the templates we need.  We could use the configure
 515 // script to restrict this to only the ones needed for implemented
 516 // targets.
 517
 518 template
 519 void
 520 Symbol_table::resolve<32, true>(
 521     Sized_symbol<32>* to,
 522     const elfcpp::Sym<32, true>& sym,
 523     Object* object);
 524
 525 template
 526 void
 527 Symbol_table::resolve<32, false>(
 528     Sized_symbol<32>* to,
 529     const elfcpp::Sym<32, false>& sym,
 530     Object* object);
 531
 532 template
 533 void
 534 Symbol_table::resolve<64, true>(
 535     Sized_symbol<64>* to,
 536     const elfcpp::Sym<64, true>& sym,
 537     Object* object);
 538
 539 template
 540 void
 541 Symbol_table::resolve<64, false>(
 542     Sized_symbol<64>* to,
 543     const elfcpp::Sym<64, false>& sym,
 544     Object* object);
 545
 546 } // End namespace gold.