gold/gc.h

   1 // gc.h -- garbage collection of unused sections
   2
   3 // Copyright 2009 Free Software Foundation, Inc.
   4 // Written by Sriraman Tallam <tmsriram@google.com>.
   5
   6 // This file is part of gold.
   7
   8 // This program is free software; you can redistribute it and/or modify
   9 // it under the terms of the GNU General Public License as published by
  10 // the Free Software Foundation; either version 3 of the License, or
  11 // (at your option) any later version.
  12
  13 // This program is distributed in the hope that it will be useful,
  14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 // GNU General Public License for more details.
  17
  18 // You should have received a copy of the GNU General Public License
  19 // along with this program; if not, write to the Free Software
  20 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  21 // MA 02110-1301, USA.
  22
  23 #ifndef GOLD_GC_H
  24 #define GOLD_GC_H
  25
  26 #include <queue>
  27 #include <vector>
  28
  29 #include "elfcpp.h"
  30 #include "symtab.h"
  31
  32 namespace gold
  33 {
  34
  35 class Object;
  36
  37 template<int size, bool big_endian>
  38 class Sized_relobj;
  39
  40 template<int sh_type, int size, bool big_endian>
  41 class Reloc_types;
  42
  43 class Output_section;
  44 class General_options;
  45 class Layout;
  46
  47 typedef std::pair<Object *, unsigned int> Section_id;
  48
  49 class Garbage_collection
  50 {
  51   struct Section_id_hash
  52   {
  53     size_t operator()(const Section_id& loc) const
  54     { return reinterpret_cast<uintptr_t>(loc.first) ^ loc.second; }
  55   };
  56
  57  public:
  58
  59   typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
  60   typedef std::map<Section_id, Sections_reachable> Section_ref;
  61   typedef std::queue<Section_id> Worklist_type;
  62
  63   Garbage_collection()
  64   : is_worklist_ready_(false)
  65   { }
  66
  67   // Accessor methods for the private members.
  68
  69   Sections_reachable&
  70   referenced_list()
  71   { return referenced_list_; }
  72
  73   Section_ref&
  74   section_reloc_map()
  75   { return this->section_reloc_map_; }
  76
  77   Worklist_type&
  78   worklist()
  79   { return this->work_list_; }
  80
  81   bool
  82   is_worklist_ready()
  83   { return this->is_worklist_ready_; }
  84
  85   void
  86   worklist_ready()
  87   { this->is_worklist_ready_ = true; }
  88
  89   void
  90   do_transitive_closure();
  91
  92   bool
  93   is_section_garbage(Object* obj, unsigned int shndx)
  94   { return (this->referenced_list().find(Section_id(obj, shndx))
  95             == this->referenced_list().end()); }
  96  private:
  97
  98   Worklist_type work_list_;
  99   bool is_worklist_ready_;
 100   Section_ref section_reloc_map_;
 101   Sections_reachable referenced_list_;
 102 };
 103
 104 // Data to pass between successive invocations of do_layout
 105 // in object.cc while garbage collecting.  This data structure
 106 // is filled by using the data from Read_symbols_data.
 107
 108 struct Symbols_data
 109 {
 110   // Section headers.
 111   unsigned char* section_headers_data;
 112   // Section names.
 113   unsigned char* section_names_data;
 114   // Size of section name data in bytes.
 115   section_size_type section_names_size;
 116   // Symbol data.
 117   unsigned char* symbols_data;
 118   // Size of symbol data in bytes.
 119   section_size_type symbols_size;
 120   // Offset of external symbols within symbol data.  This structure
 121   // sometimes contains only external symbols, in which case this will
 122   // be zero.  Sometimes it contains all symbols.
 123   section_offset_type external_symbols_offset;
 124   // Symbol names.
 125   unsigned char* symbol_names_data;
 126   // Size of symbol name data in bytes.
 127   section_size_type symbol_names_size;
 128 };
 129
 130 // This function implements the generic part of reloc
 131 // processing to map a section to all the sections it
 132 // references through relocs.  It is called only during
 133 // garbage collection (--gc-sections) and identical code
 134 // folding (--icf).
 135
 136 template<int size, bool big_endian, typename Target_type, int sh_type,
 137          typename Scan>
 138 inline void
 139 gc_process_relocs(
 140     const General_options& ,
 141     Symbol_table* symtab,
 142     Layout*,
 143     Target_type* ,
 144     Sized_relobj<size, big_endian>* src_obj,
 145     unsigned int src_indx,
 146     const unsigned char* prelocs,
 147     size_t reloc_count,
 148     Output_section*,
 149     bool ,
 150     size_t local_count,
 151     const unsigned char* plocal_syms)
 152 {
 153   Object *dst_obj;
 154   unsigned int dst_indx;
 155
 156   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
 157   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
 158   const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
 159
 160   std::vector<Section_id>* secvec = NULL;
 161   std::vector<Symbol*>* symvec = NULL;
 162   std::vector<std::pair<long long, long long> >* addendvec = NULL;
 163   bool is_icf_tracked = false;
 164
 165   if (parameters->options().icf()
 166       && is_prefix_of(".text.", (src_obj)->section_name(src_indx).c_str()))
 167     {
 168       is_icf_tracked = true;
 169       Section_id src_id(src_obj, src_indx);
 170       secvec = &symtab->icf()->section_reloc_list()[src_id];
 171       symvec = &symtab->icf()->symbol_reloc_list()[src_id];
 172       addendvec = &symtab->icf()->addend_reloc_list()[src_id];
 173     }
 174
 175   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
 176     {
 177       Reltype reloc(prelocs);
 178       typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
 179       unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
 180       typename elfcpp::Elf_types<size>::Elf_Swxword addend =
 181       Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);
 182
 183       if (r_sym < local_count)
 184         {
 185           gold_assert(plocal_syms != NULL);
 186           typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
 187                                                       + r_sym * sym_size);
 188           unsigned int shndx = lsym.get_st_shndx();
 189           bool is_ordinary;
 190           shndx = src_obj->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
 191           if (!is_ordinary)
 192             continue;
 193           dst_obj = src_obj;
 194           dst_indx = shndx;
 195           Section_id dst_id(dst_obj, dst_indx);
 196           if (is_icf_tracked)
 197             {
 198               (*secvec).push_back(dst_id);
 199               (*symvec).push_back(NULL);
 200               long long symvalue = static_cast<long long>(lsym.get_st_value());
 201               (*addendvec).push_back(std::make_pair(symvalue,
 202                                               static_cast<long long>(addend)));
 203             }
 204           if (shndx == src_indx)
 205             continue;
 206         }
 207       else
 208         {
 209           Symbol* gsym = src_obj->global_symbol(r_sym);
 210           gold_assert(gsym != NULL);
 211           if (gsym->is_forwarder())
 212             gsym = symtab->resolve_forwards(gsym);
 213           if (gsym->source() != Symbol::FROM_OBJECT)
 214             continue;
 215           bool is_ordinary;
 216           dst_obj = gsym->object();
 217           dst_indx = gsym->shndx(&is_ordinary);
 218           if (!is_ordinary)
 219             continue;
 220           Section_id dst_id(dst_obj, dst_indx);
 221           if (is_icf_tracked)
 222             {
 223               (*secvec).push_back(dst_id);
 224               (*symvec).push_back(gsym);
 225               Sized_symbol<size>* sized_gsym =
 226                         static_cast<Sized_symbol<size>* >(gsym);
 227               long long symvalue =
 228                         static_cast<long long>(sized_gsym->value());
 229               (*addendvec).push_back(std::make_pair(symvalue,
 230                                         static_cast<long long>(addend)));
 231             }
 232         }
 233       if (parameters->options().gc_sections())
 234         {
 235           Section_id src_id(src_obj, src_indx);
 236           Section_id dst_id(dst_obj, dst_indx);
 237           Garbage_collection::Section_ref::iterator map_it;
 238           map_it = symtab->gc()->section_reloc_map().find(src_id);
 239           if (map_it == symtab->gc()->section_reloc_map().end())
 240             {
 241               symtab->gc()->section_reloc_map()[src_id].insert(dst_id);
 242             }
 243           else
 244             {
 245               Garbage_collection::Sections_reachable& v(map_it->second);
 246               v.insert(dst_id);
 247             }
 248         }
 249     }
 250   return;
 251 }
 252
 253 } // End of namespace gold.
 254
 255 #endif