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 #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
  64   Garbage_collection()
  65   : is_worklist_ready_(false)
  66   { }
  67
  68   // Accessor methods for the private members.
  69
  70   Sections_reachable&
  71   referenced_list()
  72   { return referenced_list_; }
  73
  74   Section_ref&
  75   section_reloc_map()
  76   { return this->section_reloc_map_; }
  77
  78   Worklist_type&
  79   worklist()
  80   { return this->work_list_; }
  81
  82   bool
  83   is_worklist_ready()
  84   { return this->is_worklist_ready_; }
  85
  86   void
  87   worklist_ready()
  88   { this->is_worklist_ready_ = true; }
  89
  90   void
  91   do_transitive_closure();
  92
  93   bool
  94   is_section_garbage(Object* obj, unsigned int shndx)
  95   { return (this->referenced_list().find(Section_id(obj, shndx))
  96             == this->referenced_list().end()); }
  97  private:
  98
  99   Worklist_type work_list_;
 100   bool is_worklist_ready_;
 101   Section_ref section_reloc_map_;
 102   Sections_reachable referenced_list_;
 103 };
 104
 105 // Data to pass between successive invocations of do_layout
 106 // in object.cc while garbage collecting.  This data structure
 107 // is filled by using the data from Read_symbols_data.
 108
 109 struct Symbols_data
 110 {
 111   // Section headers.
 112   unsigned char* section_headers_data;
 113   // Section names.
 114   unsigned char* section_names_data;
 115   // Size of section name data in bytes.
 116   section_size_type section_names_size;
 117   // Symbol data.
 118   unsigned char* symbols_data;
 119   // Size of symbol data in bytes.
 120   section_size_type symbols_size;
 121   // Offset of external symbols within symbol data.  This structure
 122   // sometimes contains only external symbols, in which case this will
 123   // be zero.  Sometimes it contains all symbols.
 124   section_offset_type external_symbols_offset;
 125   // Symbol names.
 126   unsigned char* symbol_names_data;
 127   // Size of symbol name data in bytes.
 128   section_size_type symbol_names_size;
 129 };
 130
 131 // This function implements the generic part of reloc
 132 // processing to map a section to all the sections it
 133 // references through relocs.  It is called only during
 134 // garbage collection (--gc-sections) and identical code
 135 // folding (--icf).
 136
 137 template<int size, bool big_endian, typename Target_type, int sh_type,
 138          typename Scan>
 139 inline void
 140 gc_process_relocs(
 141     const General_options& ,
 142     Symbol_table* symtab,
 143     Layout*,
 144     Target_type* ,
 145     Sized_relobj<size, big_endian>* src_obj,
 146     unsigned int src_indx,
 147     const unsigned char* prelocs,
 148     size_t reloc_count,
 149     Output_section*,
 150     bool ,
 151     size_t local_count,
 152     const unsigned char* plocal_syms)
 153 {
 154   Object *dst_obj;
 155   unsigned int dst_indx;
 156
 157   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
 158   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
 159   const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
 160
 161   std::vector<Section_id>* secvec = NULL;
 162   std::vector<Symbol*>* symvec = NULL;
 163   std::vector<std::pair<long long, long long> >* addendvec = NULL;
 164   bool is_icf_tracked = false;
 165
 166   if (parameters->options().icf()
 167       && is_prefix_of(".text.", (src_obj)->section_name(src_indx).c_str()))
 168     {
 169       is_icf_tracked = true;
 170       Section_id src_id(src_obj, src_indx);
 171       secvec = &symtab->icf()->section_reloc_list()[src_id];
 172       symvec = &symtab->icf()->symbol_reloc_list()[src_id];
 173       addendvec = &symtab->icf()->addend_reloc_list()[src_id];
 174     }
 175
 176   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
 177     {
 178       Reltype reloc(prelocs);
 179       typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
 180       unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
 181       typename elfcpp::Elf_types<size>::Elf_Swxword addend =
 182       Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);
 183
 184       if (r_sym < local_count)
 185         {
 186           gold_assert(plocal_syms != NULL);
 187           typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
 188                                                       + r_sym * sym_size);
 189           unsigned int shndx = lsym.get_st_shndx();
 190           bool is_ordinary;
 191           shndx = src_obj->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
 192           if (!is_ordinary)
 193             continue;
 194           dst_obj = src_obj;
 195           dst_indx = shndx;
 196           Section_id dst_id(dst_obj, dst_indx);
 197           if (is_icf_tracked)
 198             {
 199               (*secvec).push_back(dst_id);
 200               (*symvec).push_back(NULL);
 201               long long symvalue = static_cast<long long>(lsym.get_st_value());
 202               (*addendvec).push_back(std::make_pair(symvalue,
 203                                               static_cast<long long>(addend)));
 204             }
 205           if (shndx == src_indx)
 206             continue;
 207         }
 208       else
 209         {
 210           Symbol* gsym = src_obj->global_symbol(r_sym);
 211           gold_assert(gsym != NULL);
 212           if (gsym->is_forwarder())
 213             gsym = symtab->resolve_forwards(gsym);
 214           if (gsym->source() != Symbol::FROM_OBJECT)
 215             continue;
 216           bool is_ordinary;
 217           dst_obj = gsym->object();
 218           dst_indx = gsym->shndx(&is_ordinary);
 219           if (!is_ordinary)
 220             continue;
 221           Section_id dst_id(dst_obj, dst_indx);
 222           if (is_icf_tracked)
 223             {
 224               (*secvec).push_back(dst_id);
 225               (*symvec).push_back(gsym);
 226               Sized_symbol<size>* sized_gsym =
 227                         static_cast<Sized_symbol<size>* >(gsym);
 228               long long symvalue =
 229                         static_cast<long long>(sized_gsym->value());
 230               (*addendvec).push_back(std::make_pair(symvalue,
 231                                         static_cast<long long>(addend)));
 232             }
 233         }
 234       if (parameters->options().gc_sections())
 235         {
 236           Section_id src_id(src_obj, src_indx);
 237           Section_id dst_id(dst_obj, dst_indx);
 238           Garbage_collection::Section_ref::iterator map_it;
 239           map_it = symtab->gc()->section_reloc_map().find(src_id);
 240           if (map_it == symtab->gc()->section_reloc_map().end())
 241             {
 242               symtab->gc()->section_reloc_map()[src_id].insert(dst_id);
 243             }
 244           else
 245             {
 246               Garbage_collection::Sections_reachable& v(map_it->second);
 247               v.insert(dst_id);
 248             }
 249         }
 250     }
 251   return;
 252 }
 253
 254 } // End of namespace gold.
 255
 256 #endif