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// resolve.cc -- symbol resolution for gold

// Copyright 2006, 2007, 2008, 2009, 2010 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"

#include "plugin.h"

namespace gold

{

// Symbol methods used in this file.

// This symbol is being overridden by another symbol whose version is

// VERSION.  Update the VERSION_ field accordingly.

inline void

Symbol::override_version(const char* version)

{

  if (version == NULL)

    {

      // This is the case where this symbol is NAME/VERSION, and the

      // version was not marked as hidden.  That makes it the default

      // version, so we create NAME/NULL.  Later we see another symbol

      // NAME/NULL, and that symbol is overriding this one.  In this

      // case, since NAME/VERSION is the default, we make NAME/NULL

      // override NAME/VERSION as well.  They are already the same

      // Symbol structure.  Setting the VERSION_ field to NULL ensures

      // that it will be output with the correct, empty, version.

      this->version_ = version;

    }

  else

    {

      // This is the case where this symbol is NAME/VERSION_ONE, and

      // now we see NAME/VERSION_TWO, and NAME/VERSION_TWO is

      // overriding NAME.  If VERSION_ONE and VERSION_TWO are

      // different, then this can only happen when VERSION_ONE is NULL

      // and VERSION_TWO is not hidden.

      gold_assert(this->version_ == version || this->version_ == NULL);

      this->version_ = version;

    }

}

// This symbol is being overidden by another symbol whose visibility

// is VISIBILITY.  Updated the VISIBILITY_ field accordingly.

inline void

Symbol::override_visibility(elfcpp::STV visibility)

{

  // The rule for combining visibility is that we always choose the

  // most constrained visibility.  In order of increasing constraint,

  // visibility goes PROTECTED, HIDDEN, INTERNAL.  This is the reverse

  // of the numeric values, so the effect is that we always want the

  // smallest non-zero value.

  if (visibility != elfcpp::STV_DEFAULT)

    {

      if (this->visibility_ == elfcpp::STV_DEFAULT)

        this->visibility_ = visibility;

      else if (this->visibility_ > visibility)

        this->visibility_ = visibility;

    }

}

// Override the fields in Symbol.

template<int size, bool big_endian>

void

Symbol::override_base(const elfcpp::Sym<size, big_endian>& sym,

                      unsigned int st_shndx, bool is_ordinary,

                      Object* object, const char* version)

{

  gold_assert(this->source_ == FROM_OBJECT);

  this->u_.from_object.object = object;

  this->override_version(version);

  this->u_.from_object.shndx = st_shndx;

  this->is_ordinary_shndx_ = is_ordinary;

  this->type_ = sym.get_st_type();

  this->binding_ = sym.get_st_bind();

  this->override_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,

                             unsigned st_shndx, bool is_ordinary,

                             Object* object, const char* version)

{

  this->override_base(sym, st_shndx, is_ordinary, 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,

                       unsigned int st_shndx, bool is_ordinary,

                       Object* object, const char* version)

{

  tosym->override(fromsym, st_shndx, is_ordinary, object, version);

  if (tosym->has_alias())

    {

      Symbol* sym = this->weak_aliases_[tosym];

      gold_assert(sym != NULL);

      Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);

      do

        {

          ssym->override(fromsym, st_shndx, is_ordinary, object, version);

          sym = this->weak_aliases_[ssym];

          gold_assert(sym != NULL);

          ssym = this->get_sized_symbol<size>(sym);

        }

      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, bool is_ordinary, elfcpp::STT type)

{

  unsigned int bits;

  switch (binding)

    {

    case elfcpp::STB_GLOBAL:

    case elfcpp::STB_GNU_UNIQUE:

      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 %d"), static_cast<int>(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:

      if (!is_ordinary)

        bits |= common_flag;

      break;

    default:

      if (type == elfcpp::STT_COMMON)

        bits |= common_flag;

      else if (!is_ordinary && Symbol::is_common_shndx(shndx))

        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.  ST_SHNDX is the

// section index for SYM, possibly adjusted for many sections.

// IS_ORDINARY is whether ST_SHNDX is a normal section index rather

// than a special code.  ORIG_ST_SHNDX is the original section index,

// before any munging because of discarded sections, except that all

// non-ordinary section indexes are mapped to SHN_UNDEF.  VERSION is

// 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,

                      unsigned int st_shndx, bool is_ordinary,

                      unsigned int orig_st_shndx,

                      Object* object, const char* version)

{

  if (parameters->target().has_resolve())

    {

      Sized_target<size, big_endian>* sized_target;

      sized_target = parameters->sized_target<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 if (st_shndx == elfcpp::SHN_UNDEF

           && (to->visibility() == elfcpp::STV_HIDDEN

               || to->visibility() == elfcpp::STV_INTERNAL))

    {

      // A dynamic object cannot reference a hidden or internal symbol

      // defined in another object.

      gold_warning(_("%s symbol '%s' in %s is referenced by DSO %s"),

                   (to->visibility() == elfcpp::STV_HIDDEN

                    ? "hidden"

                    : "internal"),

                   to->demangled_name().c_str(),

                   to->object()->name().c_str(),

                   object->name().c_str());

      return;

    }

  else

    {

      // Record that we've seen this symbol in a dynamic object.

      to->set_in_dyn();

    }

  // Record if we've seen this symbol in a real ELF object (i.e., the

  // symbol is referenced from outside the world known to the plugin).

  if (object->pluginobj() == NULL)

    to->set_in_real_elf();

  // If we're processing replacement files, allow new symbols to override

  // the placeholders from the plugin objects.

  if (to->source() == Symbol::FROM_OBJECT)

    {

      Pluginobj* obj = to->object()->pluginobj();

      if (obj != NULL

          && parameters->options().plugins()->in_replacement_phase())

        {

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

          return;

        }

    }

  // 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.  We also check

  // combinations of weak and strong, which might occur if one case is

  // inline and the other is not.  (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.)

  bool to_is_ordinary;

  if (parameters->options().detect_odr_violations()

      && (sym.get_st_bind() == elfcpp::STB_WEAK

          || to->binding() == elfcpp::STB_WEAK)

      && orig_st_shndx != elfcpp::SHN_UNDEF

      && to->shndx(&to_is_ordinary) != elfcpp::SHN_UNDEF

      && to_is_ordinary

      && sym.get_st_size() != 0    // Ignore weird 0-sized symbols.

      && to->symsize() != 0

      && (sym.get_st_type() != to->type()

          || 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 fromloc

          = { object, orig_st_shndx, sym.get_st_value() };

      Symbol_location toloc = { to->object(), to->shndx(&to_is_ordinary),

                                to->value() };

      this->candidate_odr_violations_[to->name()].insert(fromloc);

      this->candidate_odr_violations_[to->name()].insert(toloc);

    }

  unsigned int frombits = symbol_to_bits(sym.get_st_bind(),

                                         object->is_dynamic(),

                                         st_shndx, is_ordinary,

                                         sym.get_st_type());

  bool adjust_common_sizes;

  bool adjust_dyndef;

  typename Sized_symbol<size>::Size_type tosize = to->symsize();

  if (Symbol_table::should_override(to, frombits, OBJECT, object,

                                    &adjust_common_sizes,

                                    &adjust_dyndef))

    {

      elfcpp::STB tobinding = to->binding();

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

      if (adjust_common_sizes && tosize > to->symsize())

        to->set_symsize(tosize);

      if (adjust_dyndef)

        {

          // We are overriding an UNDEF or WEAK UNDEF with a DYN DEF.

          // Remember which kind of UNDEF it was for future reference.

          to->set_undef_binding(tobinding);

        }

    }

  else

    {

      if (adjust_common_sizes && sym.get_st_size() > tosize)

        to->set_symsize(sym.get_st_size());

      if (adjust_dyndef)

        {

          // We are keeping a DYN DEF after seeing an UNDEF or WEAK UNDEF.

          // Remember which kind of UNDEF it was.

          to->set_undef_binding(sym.get_st_bind());

        }

      // The ELF ABI says that even for a reference to a symbol we

      // merge the visibility.

      to->override_visibility(sym.get_st_visibility());

    }

  if (adjust_common_sizes && parameters->options().warn_common())

    {

      if (tosize > sym.get_st_size())

        Symbol_table::report_resolve_problem(false,

                                             _("common of '%s' overriding "

                                               "smaller common"),

                                             to, OBJECT, object);

      else if (tosize < sym.get_st_size())

        Symbol_table::report_resolve_problem(false,

                                             _("common of '%s' overidden by "

                                               "larger common"),

                                             to, OBJECT, object);

      else

        Symbol_table::report_resolve_problem(false,

                                             _("multiple common of '%s'"),

                                             to, OBJECT, object);

    }

}

// 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,

                              Defined defined, Object* object,

                              bool* adjust_common_sizes,

                              bool* adjust_dyndef)

{

  *adjust_common_sizes = false;

  *adjust_dyndef = false;

  unsigned int tobits;

  if (to->source() == Symbol::IS_UNDEFINED)

    tobits = symbol_to_bits(to->binding(), false, elfcpp::SHN_UNDEF, true,

                            to->type());

  else if (to->source() != Symbol::FROM_OBJECT)

    tobits = symbol_to_bits(to->binding(), false, elfcpp::SHN_ABS, false,

                            to->type());

  else

    {

      bool is_ordinary;

      unsigned int shndx = to->shndx(&is_ordinary);

      tobits = symbol_to_bits(to->binding(),

                              to->object()->is_dynamic(),

                              shndx,

                              is_ordinary,

                              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.

      // If either symbol is defined by an object included using

      // --just-symbols, then don't warn.  This is for compatibility

      // with the GNU linker.  FIXME: This is a hack.

      if ((to->source() == Symbol::FROM_OBJECT && to->object()->just_symbols())

          || (object != NULL && object->just_symbols()))

        return false;

      if (!parameters->options().muldefs())

        Symbol_table::report_resolve_problem(true,

                                             _("multiple definition of '%s'"),

                                             to, defined, object);

      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.

      if (parameters->options().warn_common())

        Symbol_table::report_resolve_problem(false,

                                             _("definition of '%s' overriding "

                                               "common"),

                                             to, defined, object);

      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.

      if (parameters->options().warn_common())

        Symbol_table::report_resolve_problem(false,

                                             _("definition of '%s' overriding "

                                               "dynamic common definition"),

                                             to, defined, object);

      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 DYN_UNDEF * 16 + DYN_DEF:

    case DYN_WEAK_UNDEF * 16 + DYN_DEF:

      // Use a dynamic definition if we have a reference.

      return true;

    case WEAK_UNDEF * 16 + DYN_DEF:

      // When overriding a weak undef by a dynamic definition,

      // we need to remember that the original undef was weak.

      *adjust_dyndef = true;

      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:

      // When overriding an undef by a dynamic weak definition,

      // we need to remember that the original undef was not weak.

      *adjust_dyndef = true;

      return true;

    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 WEAK_UNDEF * 16 + DYN_WEAK_DEF:

      // When overriding a weak undef by a dynamic definition,

      // we need to remember that the original undef was weak.

      *adjust_dyndef = true;

      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 UNDEF * 16 + UNDEF:

      // A new undefined reference tells us nothing.

      return false;

    case DYN_DEF * 16 + UNDEF:

    case DYN_WEAK_DEF * 16 + UNDEF:

      // For a dynamic def, we need to remember which kind of undef we see.

      *adjust_dyndef = true;

      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 UNDEF * 16 + WEAK_UNDEF:

    case WEAK_UNDEF * 16 + WEAK_UNDEF:

    case DYN_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 unless the

      // exisiting symbol is a dynamic weak reference.

      return false;

    case DYN_WEAK_UNDEF * 16 + WEAK_UNDEF:

      // A new weak reference overrides an existing dynamic weak reference.

      // This is necessary because a dynamic weak reference remembers

      // the old binding, which may not be weak.  If we keeps the existing

      // dynamic weak reference, the weakness may be dropped in the output.

      return true;

    case DYN_DEF * 16 + WEAK_UNDEF:

    case DYN_WEAK_DEF * 16 + WEAK_UNDEF:

      // For a dynamic def, we need to remember which kind of undef we see.

      *adjust_dyndef = true;

      return false;

    case DEF * 16 + DYN_UNDEF:

    case WEAK_DEF * 16 + DYN_UNDEF:

    case DYN_DEF * 16 + DYN_UNDEF: