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   // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
 112   // DST_SHNDX-th section of DST_OBJECT.
 113   void
 114   add_reference(Object* src_object, unsigned int src_shndx,
 115                 Object* dst_object, unsigned int dst_shndx)
 116   {
 117     Section_id src_id(src_object, src_shndx);
 118     Section_id dst_id(dst_object, dst_shndx);
 119     Section_ref::iterator p = this->section_reloc_map_.find(src_id);
 120     if (p == this->section_reloc_map_.end())
 121       this->section_reloc_map_[src_id].insert(dst_id);
 122     else
 123       p->second.insert(dst_id);
 124   }
 125
 126  private:
 127
 128   Worklist_type work_list_;
 129   bool is_worklist_ready_;
 130   Section_ref section_reloc_map_;
 131   Sections_reachable referenced_list_;
 132   Cident_section_map cident_sections_;
 133 };
 134
 135 // Data to pass between successive invocations of do_layout
 136 // in object.cc while garbage collecting.  This data structure
 137 // is filled by using the data from Read_symbols_data.
 138
 139 struct Symbols_data
 140 {
 141   // Section headers.
 142   unsigned char* section_headers_data;
 143   // Section names.
 144   unsigned char* section_names_data;
 145   // Size of section name data in bytes.
 146   section_size_type section_names_size;
 147   // Symbol data.
 148   unsigned char* symbols_data;
 149   // Size of symbol data in bytes.
 150   section_size_type symbols_size;
 151   // Offset of external symbols within symbol data.  This structure
 152   // sometimes contains only external symbols, in which case this will
 153   // be zero.  Sometimes it contains all symbols.
 154   section_offset_type external_symbols_offset;
 155   // Symbol names.
 156   unsigned char* symbol_names_data;
 157   // Size of symbol name data in bytes.
 158   section_size_type symbol_names_size;
 159 };
 160
 161 // This function implements the generic part of reloc
 162 // processing to map a section to all the sections it
 163 // references through relocs.  It is called only during
 164 // garbage collection (--gc-sections) and identical code
 165 // folding (--icf).
 166
 167 template<int size, bool big_endian, typename Target_type, int sh_type,
 168          typename Scan>
 169 inline void
 170 gc_process_relocs(
 171     Symbol_table* symtab,
 172     Layout*,
 173     Target_type* ,
 174     Sized_relobj<size, big_endian>* src_obj,
 175     unsigned int src_indx,
 176     const unsigned char* prelocs,
 177     size_t reloc_count,
 178     Output_section*,
 179     bool ,
 180     size_t local_count,
 181     const unsigned char* plocal_syms)
 182 {
 183   Object *dst_obj;
 184   unsigned int dst_indx;
 185
 186   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
 187   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
 188   const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
 189
 190   std::vector<Section_id>* secvec = NULL;
 191   std::vector<Symbol*>* symvec = NULL;
 192   std::vector<std::pair<long long, long long> >* addendvec = NULL;
 193   bool is_icf_tracked = false;
 194   const char* cident_section_name = NULL;
 195
 196   if (parameters->options().icf_enabled()
 197       && is_section_foldable_candidate(src_obj->section_name(src_indx).c_str()))
 198     {
 199       is_icf_tracked = true;
 200       Section_id src_id(src_obj, src_indx);
 201       secvec = &symtab->icf()->section_reloc_list()[src_id];
 202       symvec = &symtab->icf()->symbol_reloc_list()[src_id];
 203       addendvec = &symtab->icf()->addend_reloc_list()[src_id];
 204     }
 205
 206   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
 207     {
 208       Reltype reloc(prelocs);
 209       typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
 210       unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
 211       typename elfcpp::Elf_types<size>::Elf_Swxword addend =
 212       Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);
 213
 214       if (r_sym < local_count)
 215         {
 216           gold_assert(plocal_syms != NULL);
 217           typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
 218                                                       + r_sym * sym_size);
 219           unsigned int shndx = lsym.get_st_shndx();
 220           bool is_ordinary;
 221           shndx = src_obj->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
 222           if (!is_ordinary)
 223             continue;
 224           dst_obj = src_obj;
 225           dst_indx = shndx;
 226           Section_id dst_id(dst_obj, dst_indx);
 227           if (is_icf_tracked)
 228             {
 229               (*secvec).push_back(dst_id);
 230               (*symvec).push_back(NULL);
 231               long long symvalue = static_cast<long long>(lsym.get_st_value());
 232               (*addendvec).push_back(std::make_pair(symvalue,
 233                                               static_cast<long long>(addend)));
 234             }
 235           if (shndx == src_indx)
 236             continue;
 237         }
 238       else
 239         {
 240           Symbol* gsym = src_obj->global_symbol(r_sym);
 241           gold_assert(gsym != NULL);
 242           if (gsym->is_forwarder())
 243             gsym = symtab->resolve_forwards(gsym);
 244           if (gsym->source() != Symbol::FROM_OBJECT)
 245             continue;
 246           bool is_ordinary;
 247           dst_obj = gsym->object();
 248           dst_indx = gsym->shndx(&is_ordinary);
 249           if (!is_ordinary)
 250             continue;
 251           Section_id dst_id(dst_obj, dst_indx);
 252           // If the symbol name matches '__start_XXX' then the section with
 253           // the C identifier like name 'XXX' should not be garbage collected.
 254           // A similar treatment to symbols with the name '__stop_XXX'.
 255           if (is_prefix_of(cident_section_start_prefix, gsym->name()))
 256             {
 257               cident_section_name = (gsym->name()
 258                                      + strlen(cident_section_start_prefix));
 259             }
 260           else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))
 261             {
 262               cident_section_name = (gsym->name()
 263                                      + strlen(cident_section_stop_prefix));
 264             }
 265           if (is_icf_tracked)
 266             {
 267               (*secvec).push_back(dst_id);
 268               (*symvec).push_back(gsym);
 269               Sized_symbol<size>* sized_gsym =
 270                         static_cast<Sized_symbol<size>* >(gsym);
 271               long long symvalue =
 272                         static_cast<long long>(sized_gsym->value());
 273               (*addendvec).push_back(std::make_pair(symvalue,
 274                                         static_cast<long long>(addend)));
 275             }
 276         }
 277       if (parameters->options().gc_sections())
 278         {
 279           symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx);
 280           if (cident_section_name != NULL)
 281             {
 282               Garbage_collection::Cident_section_map::iterator ele =
 283                 symtab->gc()->cident_sections()->find(std::string(cident_section_name));
 284               if (ele == symtab->gc()->cident_sections()->end())
 285                 continue;
 286               Section_id src_id(src_obj, src_indx);
 287               Garbage_collection::Sections_reachable&
 288                 v(symtab->gc()->section_reloc_map()[src_id]);
 289               Garbage_collection::Sections_reachable& cident_secn(ele->second);
 290               for (Garbage_collection::Sections_reachable::iterator it_v
 291                      = cident_secn.begin();
 292                    it_v != cident_secn.end();
 293                    ++it_v)
 294                 {
 295                   v.insert(*it_v);
 296                 }
 297             }
 298         }
 299     }
 300   return;
 301 }
 302
 303 } // End of namespace gold.
 304
 305 #endif