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// gc.h -- garbage collection of unused sections

// Copyright 2009, 2010 Free Software Foundation, Inc.

// Written by Sriraman Tallam <tmsriram@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_GC_H

#define GOLD_GC_H

#include <queue>

#include <vector>

#include "elfcpp.h"

#include "symtab.h"

#include "object.h"

#include "icf.h"

namespace gold

{

class Object;

template<int size, bool big_endian>

class Sized_relobj_file;

template<int sh_type, int size, bool big_endian>

class Reloc_types;

class Output_section;

class General_options;

class Layout;

class Garbage_collection

{

 public:

  typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;

  typedef std::map<Section_id, Sections_reachable> Section_ref;

  typedef std::queue<Section_id> Worklist_type;

  // This maps the name of the section which can be represented as a C

  // identifier (cident) to the list of sections that have that name.

  // Different object files can have cident sections with the same name.

  typedef std::map<std::string, Sections_reachable> Cident_section_map;

  Garbage_collection()

  : is_worklist_ready_(false)

  { }

  // Accessor methods for the private members.

  Sections_reachable&

  referenced_list()

  { return referenced_list_; }

  Section_ref&

  section_reloc_map()

  { return this->section_reloc_map_; }

  Worklist_type&

  worklist()

  { return this->work_list_; }

  bool

  is_worklist_ready()

  { return this->is_worklist_ready_; }

  void

  worklist_ready()

  { this->is_worklist_ready_ = true; }

  void

  do_transitive_closure();

  bool

  is_section_garbage(Object* obj, unsigned int shndx)

  { return (this->referenced_list().find(Section_id(obj, shndx))

            == this->referenced_list().end()); }

  Cident_section_map*

  cident_sections()

  { return &cident_sections_; }

  void

  add_cident_section(std::string section_name,

                     Section_id secn)

  { this->cident_sections_[section_name].insert(secn); }

  // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to

  // DST_SHNDX-th section of DST_OBJECT.

  void

  add_reference(Object* src_object, unsigned int src_shndx,

                Object* dst_object, unsigned int dst_shndx)

  {

    Section_id src_id(src_object, src_shndx);

    Section_id dst_id(dst_object, dst_shndx);

    Section_ref::iterator p = this->section_reloc_map_.find(src_id);

    if (p == this->section_reloc_map_.end())

      this->section_reloc_map_[src_id].insert(dst_id);

    else

      p->second.insert(dst_id);

  }

 private:

  Worklist_type work_list_;

  bool is_worklist_ready_;

  Section_ref section_reloc_map_;

  Sections_reachable referenced_list_;

  Cident_section_map cident_sections_;

};

// Data to pass between successive invocations of do_layout

// in object.cc while garbage collecting.  This data structure

// is filled by using the data from Read_symbols_data.

struct Symbols_data

{

  // Section headers.

  unsigned char* section_headers_data;

  // Section names.

  unsigned char* section_names_data;

  // Size of section name data in bytes.

  section_size_type section_names_size;

  // Symbol data.

  unsigned char* symbols_data;

  // Size of symbol data in bytes.

  section_size_type symbols_size;

  // Offset of external symbols within symbol data.  This structure

  // sometimes contains only external symbols, in which case this will

  // be zero.  Sometimes it contains all symbols.

  section_offset_type external_symbols_offset;

  // Symbol names.

  unsigned char* symbol_names_data;

  // Size of symbol name data in bytes.

  section_size_type symbol_names_size;

};

// Relocations of type SHT_REL store the addend value in their bytes.

// This function returns the size of the embedded addend which is

// nothing but the size of the relocation.

template<typename Classify_reloc>

inline unsigned int

get_embedded_addend_size(int sh_type, int r_type, Relobj* obj)

{

  if (sh_type != elfcpp::SHT_REL)

    return 0;

  Classify_reloc classify_reloc;

  return classify_reloc.get_size_for_reloc(r_type, obj);

}

// This function implements the generic part of reloc

// processing to map a section to all the sections it

// references through relocs.  It is called only during

// garbage collection (--gc-sections) and identical code

// folding (--icf).

template<int size, bool big_endian, typename Target_type, int sh_type,

         typename Scan, typename Classify_reloc>

inline void

gc_process_relocs(

    Symbol_table* symtab,

    Layout*,

    Target_type* target,

    Sized_relobj_file<size, big_endian>* src_obj,

    unsigned int src_indx,

    const unsigned char* prelocs,

    size_t reloc_count,

    Output_section*,

    bool,

    size_t local_count,

    const unsigned char* plocal_syms)

{

  Object* dst_obj;

  unsigned int dst_indx;

  Scan scan;

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

  const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;

  const int sym_size = elfcpp::Elf_sizes<size>::sym_size;

  Icf::Sections_reachable_info* secvec = NULL;

  Icf::Symbol_info* symvec = NULL;

  Icf::Addend_info* addendvec = NULL;

  Icf::Offset_info* offsetvec = NULL;

  Icf::Reloc_addend_size_info* reloc_addend_size_vec = NULL;

  bool is_icf_tracked = false;

  const char* cident_section_name = NULL;

  std::string src_section_name = (parameters->options().icf_enabled()

                                  ? src_obj->section_name(src_indx)

                                  : "");

  bool check_section_for_function_pointers = false;

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

      && is_section_foldable_candidate(src_section_name.c_str()))

    {

      is_icf_tracked = true;

      Section_id src_id(src_obj, src_indx);

      Icf::Reloc_info* reloc_info =

        &symtab->icf()->reloc_info_list()[src_id];

      secvec = &reloc_info->section_info;

      symvec = &reloc_info->symbol_info;

      addendvec = &reloc_info->addend_info;

      offsetvec = &reloc_info->offset_info;

      reloc_addend_size_vec = &reloc_info->reloc_addend_size_info;

    }

  check_section_for_function_pointers =

    symtab->icf()->check_section_for_function_pointers(src_section_name,

                                                       target);

  for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)

    {

      Reltype reloc(prelocs);

      typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();

      unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);

      unsigned int r_type = elfcpp::elf_r_type<size>(r_info);

      typename elfcpp::Elf_types<size>::Elf_Swxword addend =

      Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);

      if (r_sym < local_count)

        {

          gold_assert(plocal_syms != NULL);

          typename elfcpp::Sym<size, big_endian> lsym(plocal_syms

                                                      + r_sym * sym_size);

          unsigned int shndx = lsym.get_st_shndx();

          bool is_ordinary;

          shndx = src_obj->adjust_sym_shndx(r_sym, shndx, &is_ordinary);

          dst_obj = src_obj;

          dst_indx = shndx;

          if (is_icf_tracked)

            {

              if (is_ordinary)

                (*secvec).push_back(Section_id(dst_obj, dst_indx));

              else

                (*secvec).push_back(Section_id(NULL, 0));

              (*symvec).push_back(NULL);

              long long symvalue = static_cast<long long>(lsym.get_st_value());

              (*addendvec).push_back(std::make_pair(symvalue,

                                              static_cast<long long>(addend)));

              uint64_t reloc_offset =

                convert_to_section_size_type(reloc.get_r_offset());

              (*offsetvec).push_back(reloc_offset);

              (*reloc_addend_size_vec).push_back(

                get_embedded_addend_size<Classify_reloc>(sh_type, r_type,

                                                         src_obj));

            }

          // When doing safe folding, check to see if this relocation is that

          // of a function pointer being taken.

          if (is_ordinary

              && check_section_for_function_pointers

              && lsym.get_st_type() != elfcpp::STT_OBJECT

              && scan.local_reloc_may_be_function_pointer(symtab, NULL, NULL,

                                                          src_obj, src_indx,

                                                          NULL, reloc, r_type,

                                                          lsym))

            symtab->icf()->set_section_has_function_pointers(

              src_obj, lsym.get_st_shndx());

          if (!is_ordinary || shndx == src_indx)

            continue;

        }

      else

        {

          Symbol* gsym = src_obj->global_symbol(r_sym);

          gold_assert(gsym != NULL);

          if (gsym->is_forwarder())

            gsym = symtab->resolve_forwards(gsym);

          dst_obj = NULL;

          dst_indx = 0;

          bool is_ordinary = false;

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

            {

              dst_obj = gsym->object();

              dst_indx = gsym->shndx(&is_ordinary);

            }

          // When doing safe folding, check to see if this relocation is that

          // of a function pointer being taken.

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

              && check_section_for_function_pointers

              && gsym->type() != elfcpp::STT_OBJECT

              && (!is_ordinary

                  || scan.global_reloc_may_be_function_pointer(

                       symtab, NULL, NULL, src_obj, src_indx, NULL, reloc,

                       r_type, gsym)))

            symtab->icf()->set_section_has_function_pointers(dst_obj, dst_indx);

          // If the symbol name matches '__start_XXX' then the section with

          // the C identifier like name 'XXX' should not be garbage collected.

          // A similar treatment to symbols with the name '__stop_XXX'.

          if (is_prefix_of(cident_section_start_prefix, gsym->name()))

            {

              cident_section_name = (gsym->name()

                                     + strlen(cident_section_start_prefix));

            }

          else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))

            {

              cident_section_name = (gsym->name()

                                     + strlen(cident_section_stop_prefix));

            }

          if (is_icf_tracked)

            {

              if (is_ordinary && gsym->source() == Symbol::FROM_OBJECT)

                (*secvec).push_back(Section_id(dst_obj, dst_indx));

              else

                (*secvec).push_back(Section_id(NULL, 0));

              (*symvec).push_back(gsym);

              Sized_symbol<size>* sized_gsym =

                        static_cast<Sized_symbol<size>* >(gsym);

              long long symvalue =

                        static_cast<long long>(sized_gsym->value());

              (*addendvec).push_back(std::make_pair(symvalue,

                                        static_cast<long long>(addend)));

              uint64_t reloc_offset =

                convert_to_section_size_type(reloc.get_r_offset());

              (*offsetvec).push_back(reloc_offset);

              (*reloc_addend_size_vec).push_back(

                get_embedded_addend_size<Classify_reloc>(sh_type, r_type,

                                                         src_obj));

            }

          if (gsym->source() != Symbol::FROM_OBJECT)

            continue;

          if (!is_ordinary)

            continue;

        }

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

        {

          symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx);

          if (cident_section_name != NULL)

            {

              Garbage_collection::Cident_section_map::iterator ele =

                symtab->gc()->cident_sections()->find(std::string(cident_section_name));

              if (ele == symtab->gc()->cident_sections()->end())

                continue;

              Section_id src_id(src_obj, src_indx);

              Garbage_collection::Sections_reachable&

                v(symtab->gc()->section_reloc_map()[src_id]);

              Garbage_collection::Sections_reachable& cident_secn(ele->second);

              for (Garbage_collection::Sections_reachable::iterator it_v

                     = cident_secn.begin();

                   it_v != cident_secn.end();

                   ++it_v)

                {

                  v.insert(*it_v);

                }

            }

        }

    }

  return;

}

} // End of namespace gold.

#endif