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// merge.h -- handle section merging 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_MERGE_H

#define GOLD_MERGE_H

#include <climits>

#include <map>

#include <vector>

#include "stringpool.h"

#include "output.h"

namespace gold

{

class Merge_map;

// For each object with merge sections, we store an Object_merge_map.

// This is used to map locations in input sections to a merged output

// section.  The output section itself is not recorded here--it can be

// found in the output_sections_ field of the Object.

class Object_merge_map

{

 public:

  Object_merge_map()

    : first_shnum_(-1U), first_map_(),

      second_shnum_(-1U), second_map_(),

      section_merge_maps_()

  { }

  ~Object_merge_map();

  // Add a mapping for MERGE_MAP, for the bytes from OFFSET to OFFSET

  // + LENGTH in the input section SHNDX to OUTPUT_OFFSET in the

  // output section.  An OUTPUT_OFFSET of -1 means that the bytes are

  // discarded.  OUTPUT_OFFSET is relative to the start of the merged

  // data in the output section.

  void

  add_mapping(const Merge_map*, unsigned int shndx, section_offset_type offset,

              section_size_type length, section_offset_type output_offset);

  // Get the output offset for an input address.  MERGE_MAP is the map

  // we are looking for, or NULL if we don't care.  The input address

  // is at offset OFFSET in section SHNDX.  This sets *OUTPUT_OFFSET

  // to the offset in the output section; this will be -1 if the bytes

  // are not being copied to the output.  This returns true if the

  // mapping is known, false otherwise.  *OUTPUT_OFFSET is relative to

  // the start of the merged data in the output section.

  bool

  get_output_offset(const Merge_map*, unsigned int shndx,

                    section_offset_type offset,

                    section_offset_type *output_offset);

  // Return whether this is the merge map for section SHNDX.

  bool

  is_merge_section_for(const Merge_map*, unsigned int shndx);

  // Initialize an mapping from input offsets to output addresses for

  // section SHNDX.  STARTING_ADDRESS is the output address of the

  // merged section.

  template<int size>

  void

  initialize_input_to_output_map(

      unsigned int shndx,

      typename elfcpp::Elf_types<size>::Elf_Addr starting_address,

      Unordered_map<section_offset_type,

                    typename elfcpp::Elf_types<size>::Elf_Addr>*);

 private:

  // Map input section offsets to a length and an output section

  // offset.  An output section offset of -1 means that this part of

  // the input section is being discarded.

  struct Input_merge_entry

  {

    // The offset in the input section.

    section_offset_type input_offset;

    // The length.

    section_size_type length;

    // The offset in the output section.

    section_offset_type output_offset;

  };

  // A less-than comparison routine for Input_merge_entry.

  struct Input_merge_compare

  {

    bool

    operator()(const Input_merge_entry& i1, const Input_merge_entry& i2) const

    { return i1.input_offset < i2.input_offset; }

  };

  // A list of entries for a particular input section.

  struct Input_merge_map

  {

    typedef std::vector<Input_merge_entry> Entries;

    // We store these with the Relobj, and we look them up by input

    // section.  It is possible to have two different merge maps

    // associated with a single output section.  For example, this

    // happens routinely with .rodata, when merged string constants

    // and merged fixed size constants are both put into .rodata.  The

    // output offset that we store is not the offset from the start of

    // the output section; it is the offset from the start of the

    // merged data in the output section.  That means that the caller

    // is going to add the offset of the merged data within the output

    // section, which means that the caller needs to know which set of

    // merged data it found the entry in.  So it's not enough to find

    // this data based on the input section and the output section; we

    // also have to find it based on a set of merged data in the

    // output section.  In order to verify that we are looking at the

    // right data, we store a pointer to the Merge_map here, and we

    // pass in a pointer when looking at the data.  If we are asked to

    // look up information for a different Merge_map, we report that

    // we don't have it, rather than trying a lookup and returning an

    // answer which will receive the wrong offset.

    const Merge_map* merge_map;

    // The list of mappings.

    Entries entries;

    // Whether the ENTRIES field is sorted by input_offset.

    bool sorted;

    Input_merge_map()

      : merge_map(NULL), entries(), sorted(true)

    { }

  };

  // Map input section indices to merge maps.

  typedef std::map<unsigned int, Input_merge_map*> Section_merge_maps;

  // Return a pointer to the Input_merge_map to use for the input

  // section SHNDX, or NULL.

  Input_merge_map*

  get_input_merge_map(unsigned int shndx);

  // Get or make the the Input_merge_map to use for the section SHNDX

  // with MERGE_MAP.

  Input_merge_map*

  get_or_make_input_merge_map(const Merge_map* merge_map, unsigned int shndx);

  // Any given object file will normally only have a couple of input

  // sections with mergeable contents.  So we keep the first two input

  // section numbers inline, and push any further ones into a map.  A

  // value of -1U in first_shnum_ or second_shnum_ means that we don't

  // have a corresponding entry.

  unsigned int first_shnum_;

  Input_merge_map first_map_;

  unsigned int second_shnum_;

  Input_merge_map second_map_;

  Section_merge_maps section_merge_maps_;

};

// This class manages mappings from input sections to offsets in an

// output section.  This is used where input sections are merged.  The

// actual data is stored in fields in Object.

class Merge_map

{

 public:

  Merge_map()

  { }

  // Add a mapping for the bytes from OFFSET to OFFSET + LENGTH in the

  // input section SHNDX in object OBJECT to OUTPUT_OFFSET in the

  // output section.  An OUTPUT_OFFSET of -1 means that the bytes are

  // discarded.  OUTPUT_OFFSET is not the offset from the start of the

  // output section, it is the offset from the start of the merged

  // data within the output section.

  void

  add_mapping(Relobj* object, unsigned int shndx,

              section_offset_type offset, section_size_type length,

              section_offset_type output_offset);

  // Return the output offset for an input address.  The input address

  // is at offset OFFSET in section SHNDX in OBJECT.  This sets

  // *OUTPUT_OFFSET to the offset in the output section; this will be

  // -1 if the bytes are not being copied to the output.  This returns

  // true if the mapping is known, false otherwise.  This returns the

  // value stored by add_mapping, namely the offset from the start of

  // the merged data within the output section.

  bool

  get_output_offset(const Relobj* object, unsigned int shndx,

                    section_offset_type offset,

                    section_offset_type *output_offset) const;

  // Return whether this is the merge mapping for section SHNDX in

  // OBJECT.  This should return true when get_output_offset would

  // return true for some input offset.

  bool

  is_merge_section_for(const Relobj* object, unsigned int shndx) const;

};

// A general class for SHF_MERGE data, to hold functions shared by

// fixed-size constant data and string data.

class Output_merge_base : public Output_section_data

{

 public:

  Output_merge_base(uint64_t entsize, uint64_t addralign)

    : Output_section_data(addralign), merge_map_(), entsize_(entsize)

  { }

  // Return the entry size.

  uint64_t

  entsize() const

  { return this->entsize_; }

  // Whether this is a merge string section.  This is only true of

  // Output_merge_string.

  bool

  is_string()

  { return this->do_is_string(); }

 protected:

  // Return the output offset for an input offset.

  bool

  do_output_offset(const Relobj* object, unsigned int shndx,

                   section_offset_type offset,

                   section_offset_type* poutput) const;

  // Return whether this is the merge section for an input section.

  bool

  do_is_merge_section_for(const Relobj*, unsigned int shndx) const;

  // Add a mapping from an OFFSET in input section SHNDX in object

  // OBJECT to an OUTPUT_OFFSET in the output section.  OUTPUT_OFFSET

  // is the offset from the start of the merged data in the output

  // section.

  void

  add_mapping(Relobj* object, unsigned int shndx, section_offset_type offset,

              section_size_type length, section_offset_type output_offset)

  {

    this->merge_map_.add_mapping(object, shndx, offset, length, output_offset);

  }

  // This may be overriden by the child class.

  virtual bool

  do_is_string()

  { return false; }

 private:

  // A mapping from input object/section/offset to offset in output

  // section.

  Merge_map merge_map_;

  // The entry size.  For fixed-size constants, this is the size of

  // the constants.  For strings, this is the size of a character.

  uint64_t entsize_;

};

// Handle SHF_MERGE sections with fixed-size constant data.

class Output_merge_data : public Output_merge_base

{

 public:

  Output_merge_data(uint64_t entsize, uint64_t addralign)

    : Output_merge_base(entsize, addralign), p_(NULL), len_(0), alc_(0),

      input_count_(0),

      hashtable_(128, Merge_data_hash(this), Merge_data_eq(this))

  { }

 protected:

  // Add an input section.

  bool

  do_add_input_section(Relobj* object, unsigned int shndx);

  // Set the final data size.

  void

  set_final_data_size();

  // Write the data to the file.

  void

  do_write(Output_file*);

  // Write the data to a buffer.

  void

  do_write_to_buffer(unsigned char*);

  // Write to a map file.

  void

  do_print_to_mapfile(Mapfile* mapfile) const

  { mapfile->print_output_data(this, _("** merge constants")); }

  // Print merge stats to stderr.

  void

  do_print_merge_stats(const char* section_name);

 private:

  // We build a hash table of the fixed-size constants.  Each constant

  // is stored as a pointer into the section data we are accumulating.

  // A key in the hash table.  This is an offset in the section

  // contents we are building.

  typedef section_offset_type Merge_data_key;

  // Compute the hash code.  To do this we need a pointer back to the

  // object holding the data.

  class Merge_data_hash

  {

   public:

    Merge_data_hash(const Output_merge_data* pomd)

      : pomd_(pomd)

    { }

    size_t

    operator()(Merge_data_key) const;

   private:

    const Output_merge_data* pomd_;

  };

  friend class Merge_data_hash;

  // Compare two entries in the hash table for equality.  To do this

  // we need a pointer back to the object holding the data.  Note that

  // we now have a pointer to the object stored in two places in the

  // hash table.  Fixing this would require specializing the hash

  // table, which would be hard to do portably.

  class Merge_data_eq

  {

   public:

    Merge_data_eq(const Output_merge_data* pomd)

      : pomd_(pomd)

    { }

    bool

    operator()(Merge_data_key k1, Merge_data_key k2) const;

   private:

    const Output_merge_data* pomd_;

  };

  friend class Merge_data_eq;

  // The type of the hash table.

  typedef Unordered_set<Merge_data_key, Merge_data_hash, Merge_data_eq>

    Merge_data_hashtable;

  // Given a hash table key, which is just an offset into the section

  // data, return a pointer to the corresponding constant.

  const unsigned char*

  constant(Merge_data_key k) const

  {

    gold_assert(k >= 0 && k < static_cast<section_offset_type>(this->len_));

    return this->p_ + k;

  }

  // Add a constant to the output.

  void

  add_constant(const unsigned char*);

  // The accumulated data.

  unsigned char* p_;

  // The length of the accumulated data.

  section_size_type len_;

  // The size of the allocated buffer.

  section_size_type alc_;

  // The number of entries seen in input files.

  size_t input_count_;

  // The hash table.

  Merge_data_hashtable hashtable_;

};

// Handle SHF_MERGE sections with string data.  This is a template

// based on the type of the characters in the string.

template<typename Char_type>

class Output_merge_string : public Output_merge_base

{

 public:

  Output_merge_string(uint64_t addralign)

    : Output_merge_base(sizeof(Char_type), addralign), stringpool_(),

      merged_strings_(), input_count_(0)

  {

    gold_assert(addralign <= sizeof(Char_type));

    this->stringpool_.set_no_zero_null();

  }

 protected:

  // Add an input section.

  bool

  do_add_input_section(Relobj* object, unsigned int shndx);

  // Do all the final processing after the input sections are read in.

  // Returns the final data size.

  section_size_type

  finalize_merged_data();

  // Set the final data size.

  void

  set_final_data_size();

  // Write the data to the file.

  void

  do_write(Output_file*);

  // Write the data to a buffer.

  void

  do_write_to_buffer(unsigned char*);

  // Write to a map file.

  void

  do_print_to_mapfile(Mapfile* mapfile) const

  { mapfile->print_output_data(this, _("** merge strings")); }

  // Print merge stats to stderr.

  void

  do_print_merge_stats(const char* section_name);

  // Writes the stringpool to a buffer.

  void

  stringpool_to_buffer(unsigned char* buffer, section_size_type buffer_size)

  { this->stringpool_.write_to_buffer(buffer, buffer_size); }

  // Clears all the data in the stringpool, to save on memory.

  void

  clear_stringpool()

  { this->stringpool_.clear(); }

  // Whether this is a merge string section.

  virtual bool

  do_is_string()

  { return true; }

 private:

  // The name of the string type, for stats.

  const char*

  string_name();

  // As we see input sections, we build a mapping from object, section

  // index and offset to strings.

  struct Merged_string

  {

    // The input object where the string was found.

    Relobj* object;

    // The input section in the input object.

    unsigned int shndx;

    // The offset in the input section.

    section_offset_type offset;

    // The string itself, a pointer into a Stringpool.

    const Char_type* string;

    // The length of the string in bytes, including the null terminator.

    size_t length;

    // The key in the Stringpool.

    Stringpool::Key stringpool_key;

    Merged_string(Relobj *objecta, unsigned int shndxa,

                  section_offset_type offseta, const Char_type* stringa,

                  size_t lengtha, Stringpool::Key stringpool_keya)

      : object(objecta), shndx(shndxa), offset(offseta), string(stringa),

        length(lengtha), stringpool_key(stringpool_keya)

    { }

  };

  typedef std::vector<Merged_string> Merged_strings;

  // As we see the strings, we add them to a Stringpool.

  Stringpool_template<Char_type> stringpool_;

  // Map from a location in an input object to an entry in the

  // Stringpool.

  Merged_strings merged_strings_;

  // The number of entries seen in input files.

  size_t input_count_;

};

} // End namespace gold.

#endif // !defined(GOLD_MERGE_H)