gold/gc.h

   1 // gc.h -- garbage collection of unused sections
   2
   3 // Copyright 2009, 2010 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 #include "icf.h"
  32
  33 namespace gold
  34 {
  35
  36 class Object;
  37
  38 template<int size, bool big_endian>
  39 class Sized_relobj;
  40
  41 template<int sh_type, int size, bool big_endian>
  42 class Reloc_types;
  43
  44 class Output_section;
  45 class General_options;
  46 class Layout;
  47
  48 typedef std::pair<Object *, unsigned int> Section_id;
  49
  50 class Garbage_collection
  51 {
  52   struct Section_id_hash
  53   {
  54     size_t operator()(const Section_id& loc) const
  55     { return reinterpret_cast<uintptr_t>(loc.first) ^ loc.second; }
  56   };
  57
  58  public:
  59
  60   typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
  61   typedef std::map<Section_id, Sections_reachable> Section_ref;
  62   typedef std::queue<Section_id> Worklist_type;
  63   // This maps the name of the section which can be represented as a C
  64   // identifier (cident) to the list of sections that have that name.
  65   // Different object files can have cident sections with the same name.
  66   typedef std::map<std::string, Sections_reachable> Cident_section_map;
  67
  68   Garbage_collection()
  69   : is_worklist_ready_(false)
  70   { }
  71
  72   // Accessor methods for the private members.
  73
  74   Sections_reachable&
  75   referenced_list()
  76   { return referenced_list_; }
  77
  78   Section_ref&
  79   section_reloc_map()
  80   { return this->section_reloc_map_; }
  81
  82   Worklist_type&
  83   worklist()
  84   { return this->work_list_; }
  85
  86   bool
  87   is_worklist_ready()
  88   { return this->is_worklist_ready_; }
  89
  90   void
  91   worklist_ready()
  92   { this->is_worklist_ready_ = true; }
  93
  94   void
  95   do_transitive_closure();
  96
  97   bool
  98   is_section_garbage(Object* obj, unsigned int shndx)
  99   { return (this->referenced_list().find(Section_id(obj, shndx))
 100             == this->referenced_list().end()); }
 101
 102   Cident_section_map*
 103   cident_sections()
 104   { return &cident_sections_; }
 105
 106   void
 107   add_cident_section(std::string section_name,
 108                      Section_id secn)
 109   { this->cident_sections_[section_name].insert(secn); }
 110
 111  private:
 112
 113   Worklist_type work_list_;
 114   bool is_worklist_ready_;
 115   Section_ref section_reloc_map_;
 116   Sections_reachable referenced_list_;
 117   Cident_section_map cident_sections_;
 118 };
 119
 120 // Data to pass between successive invocations of do_layout
 121 // in object.cc while garbage collecting.  This data structure
 122 // is filled by using the data from Read_symbols_data.
 123
 124 struct Symbols_data
 125 {
 126   // Section headers.
 127   unsigned char* section_headers_data;
 128   // Section names.
 129   unsigned char* section_names_data;
 130   // Size of section name data in bytes.
 131   section_size_type section_names_size;
 132   // Symbol data.
 133   unsigned char* symbols_data;
 134   // Size of symbol data in bytes.
 135   section_size_type symbols_size;
 136   // Offset of external symbols within symbol data.  This structure
 137   // sometimes contains only external symbols, in which case this will
 138   // be zero.  Sometimes it contains all symbols.
 139   section_offset_type external_symbols_offset;
 140   // Symbol names.
 141   unsigned char* symbol_names_data;
 142   // Size of symbol name data in bytes.
 143   section_size_type symbol_names_size;
 144 };
 145
 146 // This function implements the generic part of reloc
 147 // processing to map a section to all the sections it
 148 // references through relocs.  It is called only during
 149 // garbage collection (--gc-sections) and identical code
 150 // folding (--icf).
 151
 152 template<int size, bool big_endian, typename Target_type, int sh_type,
 153          typename Scan>
 154 inline void
 155 gc_process_relocs(
 156     Symbol_table* symtab,
 157     Layout*,
 158     Target_type* ,
 159     Sized_relobj<size, big_endian>* src_obj,
 160     unsigned int src_indx,
 161     const unsigned char* prelocs,
 162     size_t reloc_count,
 163     Output_section*,
 164     bool ,
 165     size_t local_count,
 166     const unsigned char* plocal_syms)
 167 {
 168   Object *dst_obj;
 169   unsigned int dst_indx;
 170
 171   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
 172   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
 173   const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
 174
 175   std::vector<Section_id>* secvec = NULL;
 176   std::vector<Symbol*>* symvec = NULL;
 177   std::vector<std::pair<long long, long long> >* addendvec = NULL;
 178   bool is_icf_tracked = false;
 179   const char* cident_section_name = NULL;
 180
 181   if (parameters->options().icf_enabled()
 182       && is_section_foldable_candidate(src_obj->section_name(src_indx).c_str()))
 183     {
 184       is_icf_tracked = true;
 185       Section_id src_id(src_obj, src_indx);
 186       secvec = &symtab->icf()->section_reloc_list()[src_id];
 187       symvec = &symtab->icf()->symbol_reloc_list()[src_id];
 188       addendvec = &symtab->icf()->addend_reloc_list()[src_id];
 189     }
 190
 191   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
 192     {
 193       Reltype reloc(prelocs);
 194       typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
 195       unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
 196       typename elfcpp::Elf_types<size>::Elf_Swxword addend =
 197       Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);
 198
 199       if (r_sym < local_count)
 200         {
 201           gold_assert(plocal_syms != NULL);
 202           typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
 203                                                       + r_sym * sym_size);
 204           unsigned int shndx = lsym.get_st_shndx();
 205           bool is_ordinary;
 206           shndx = src_obj->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
 207           if (!is_ordinary)
 208             continue;
 209           dst_obj = src_obj;
 210           dst_indx = shndx;
 211           Section_id dst_id(dst_obj, dst_indx);
 212           if (is_icf_tracked)
 213             {
 214               (*secvec).push_back(dst_id);
 215               (*symvec).push_back(NULL);
 216               long long symvalue = static_cast<long long>(lsym.get_st_value());
 217               (*addendvec).push_back(std::make_pair(symvalue,
 218                                               static_cast<long long>(addend)));
 219             }
 220           if (shndx == src_indx)
 221             continue;
 222         }
 223       else
 224         {
 225           Symbol* gsym = src_obj->global_symbol(r_sym);
 226           gold_assert(gsym != NULL);
 227           if (gsym->is_forwarder())
 228             gsym = symtab->resolve_forwards(gsym);
 229           if (gsym->source() != Symbol::FROM_OBJECT)
 230             continue;
 231           bool is_ordinary;
 232           dst_obj = gsym->object();
 233           dst_indx = gsym->shndx(&is_ordinary);
 234           if (!is_ordinary)
 235             continue;
 236           Section_id dst_id(dst_obj, dst_indx);
 237           // If the symbol name matches '__start_XXX' then the section with
 238           // the C identifier like name 'XXX' should not be garbage collected.
 239           // A similar treatment to symbols with the name '__stop_XXX'.
 240           if (is_prefix_of(cident_section_start_prefix, gsym->name()))
 241             {
 242               cident_section_name = (gsym->name()
 243                                      + strlen(cident_section_start_prefix));
 244             }
 245           else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))
 246             {
 247               cident_section_name = (gsym->name()
 248                                      + strlen(cident_section_stop_prefix));
 249             }
 250           if (is_icf_tracked)
 251             {
 252               (*secvec).push_back(dst_id);
 253               (*symvec).push_back(gsym);
 254               Sized_symbol<size>* sized_gsym =
 255                         static_cast<Sized_symbol<size>* >(gsym);
 256               long long symvalue =
 257                         static_cast<long long>(sized_gsym->value());
 258               (*addendvec).push_back(std::make_pair(symvalue,
 259                                         static_cast<long long>(addend)));
 260             }
 261         }
 262       if (parameters->options().gc_sections())
 263         {
 264           Section_id src_id(src_obj, src_indx);
 265           Section_id dst_id(dst_obj, dst_indx);
 266           Garbage_collection::Section_ref::iterator map_it;
 267           map_it = symtab->gc()->section_reloc_map().find(src_id);
 268           if (map_it == symtab->gc()->section_reloc_map().end())
 269             {
 270               symtab->gc()->section_reloc_map()[src_id].insert(dst_id);
 271             }
 272           else
 273             {
 274               Garbage_collection::Sections_reachable& v(map_it->second);
 275               v.insert(dst_id);
 276             }
 277           if (cident_section_name != NULL)
 278             {
 279               Garbage_collection::Cident_section_map::iterator ele =
 280                 symtab->gc()->cident_sections()->find(std::string(cident_section_name));
 281               if (ele == symtab->gc()->cident_sections()->end())
 282                 continue;
 283               Garbage_collection::Sections_reachable&
 284                 v(symtab->gc()->section_reloc_map()[src_id]);
 285               Garbage_collection::Sections_reachable& cident_secn(ele->second);
 286               for (Garbage_collection::Sections_reachable::iterator it_v
 287                      = cident_secn.begin();
 288                    it_v != cident_secn.end();
 289                    ++it_v)
 290                 {
 291                   v.insert(*it_v);
 292                 }
 293             }
 294         }
 295     }
 296   return;
 297 }
 298
 299 } // End of namespace gold.
 300
 301 #endif