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// copy-relocs.h -- handle COPY relocations for gold   -*- C++ -*-

// Copyright 2006, 2007, 2008 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.

#ifndef GOLD_COPY_RELOCS_H

#define GOLD_COPY_RELOCS_H

#include "elfcpp.h"

#include "reloc-types.h"

#include "output.h"

namespace gold

{

// This class is used to manage COPY relocations.  We try to avoid

// them when possible.  A COPY relocation may be required when an

// executable refers to a variable defined in a shared library.  COPY

// relocations are problematic because they tie the executable to the

// exact size of the variable in the shared library.  We can avoid

// them if all the references to the variable are in a writeable

// section.  In that case we can simply use dynamic relocations.

// However, when scanning relocs, we don't know when we see the

// relocation whether we will be forced to use a COPY relocation or

// not.  So we have to save the relocation during the reloc scanning,

// and then emit it as a dynamic relocation if necessary.  This class

// implements that.  It is used by the target specific code.

// The template parameter SH_TYPE is the type of the reloc section to

// be used for COPY relocs: elfcpp::SHT_REL or elfcpp::SHT_RELA.

template<int sh_type, int size, bool big_endian>

class Copy_relocs

{

 private:

  typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reloc;

 public:

  Copy_relocs(unsigned int copy_reloc_type)

    : copy_reloc_type_(copy_reloc_type), dynbss_(NULL), entries_()

  { }

  // This is called while scanning relocs if we see a relocation

  // against a symbol which may force us to generate a COPY reloc.

  // SYM is the symbol.  OBJECT is the object whose relocs we are

  // scanning.  The relocation is being applied to section SHNDX in

  // OBJECT.  OUTPUT_SECTION is the output section where section SHNDX

  // will wind up.  REL is the reloc itself.  The Output_data_reloc

  // section is where the dynamic relocs are put.

  void

  copy_reloc(Symbol_table*, Layout*, Sized_symbol<size>* sym,

             Sized_relobj_file<size, big_endian>* object,

             unsigned int shndx, Output_section* output_section,

             const Reloc& rel,

             Output_data_reloc<sh_type, true, size, big_endian>*);

  // Return whether there are any saved relocations.

  bool

  any_saved_relocs() const

  { return !this->entries_.empty(); }

  // Emit any saved relocations which turn out to be needed.  This is

  // called after all the relocs have been scanned.

  void

  emit(Output_data_reloc<sh_type, true, size, big_endian>*);

  // Emit a COPY reloc.

  void

  emit_copy_reloc(Symbol_table*, Sized_symbol<size>*,

                  Output_data*, off_t,

                  Output_data_reloc<sh_type, true, size, big_endian>*);

 private:

  typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;

  typedef typename elfcpp::Elf_types<size>::Elf_Addr Addend;

  // This POD class holds the relocations we are saving.  We will emit

  // these relocations if it turns out that the symbol does not

  // require a COPY relocation.

  class Copy_reloc_entry

  {

   public:

    Copy_reloc_entry(Symbol* sym, unsigned int reloc_type,

                     Sized_relobj_file<size, big_endian>* relobj,

                     unsigned int shndx,

                     Output_section* output_section,

                     Address address, Addend addend)

      : sym_(sym), reloc_type_(reloc_type), relobj_(relobj),

        shndx_(shndx), output_section_(output_section),

        address_(address), addend_(addend)

    { }

    // Emit this reloc if appropriate.  This is called after we have

    // scanned all the relocations, so we know whether we emitted a

    // COPY relocation for SYM_.

    void

    emit(Output_data_reloc<sh_type, true, size, big_endian>*);

   private:

    Symbol* sym_;

    unsigned int reloc_type_;

    Sized_relobj_file<size, big_endian>* relobj_;

    unsigned int shndx_;

    Output_section* output_section_;

    Address address_;

    Addend addend_;

  };

  // A list of relocs to be saved.

  typedef std::vector<Copy_reloc_entry> Copy_reloc_entries;

  // Return whether we need a COPY reloc.

  bool

  need_copy_reloc(Sized_symbol<size>* gsym,

                  Sized_relobj_file<size, big_endian>* object,

                  unsigned int shndx) const;

  // Make a new COPY reloc and emit it.

  void

  make_copy_reloc(Symbol_table*, Layout*, Sized_symbol<size>*,

                  Output_data_reloc<sh_type, true, size, big_endian>*);

  // Save a reloc against SYM for possible emission later.

  void

  save(Symbol*, Sized_relobj_file<size, big_endian>*, unsigned int shndx,

       Output_section*, const Reloc& rel);

  // The target specific relocation type of the COPY relocation.

  const unsigned int copy_reloc_type_;

  // The dynamic BSS data which goes into the .bss section.  This is

  // where variables which require COPY relocations are placed.

  Output_data_space* dynbss_;

  // The list of relocs we are saving.

  Copy_reloc_entries entries_;

};

} // End namespace gold.

#endif // !defined(GOLD_COPY_RELOCS_H)