gold/icf.h

   1 // icf.h --  Identical Code Folding
   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_ICF_H
  24 #define GOLD_ICF_H
  25
  26 #include <vector>
  27
  28 #include "elfcpp.h"
  29 #include "symtab.h"
  30 #include "object.h"
  31
  32 namespace gold
  33 {
  34
  35 class Object;
  36 class Input_objects;
  37 class Symbol_table;
  38
  39 class Icf
  40 {
  41  public:
  42   typedef std::vector<Section_id> Sections_reachable_list;
  43   typedef std::vector<Symbol*> Symbol_info;
  44   typedef std::vector<std::pair<long long, long long> > Addend_info;
  45   typedef Unordered_map<Section_id,
  46                         Sections_reachable_list,
  47                         Section_id_hash> Section_list;
  48   typedef Unordered_map<Section_id, Symbol_info, Section_id_hash> Symbol_list;
  49   typedef Unordered_map<Section_id, Addend_info, Section_id_hash> Addend_list;
  50   typedef Unordered_map<Section_id,
  51                         unsigned int,
  52                         Section_id_hash> Uniq_secn_id_map;
  53   typedef Unordered_set<Section_id, Section_id_hash> Secn_fptr_taken_set;
  54
  55   Icf()
  56   : id_section_(), section_id_(), kept_section_id_(),
  57     fptr_section_id_(),
  58     num_tracked_relocs(NULL), icf_ready_(false),
  59     section_reloc_list_(), symbol_reloc_list_(),
  60     addend_reloc_list_()
  61   { }
  62
  63   // Returns the kept folded identical section corresponding to
  64   // dup_obj and dup_shndx.
  65   Section_id
  66   get_folded_section(Object* dup_obj, unsigned int dup_shndx);
  67
  68   // Forms groups of identical sections where the first member
  69   // of each group is the kept section during folding.
  70   void
  71   find_identical_sections(const Input_objects* input_objects,
  72                           Symbol_table* symtab);
  73
  74   // This is set when ICF has been run and the groups of
  75   // identical sections have been formed.
  76   void
  77   icf_ready()
  78   { this->icf_ready_ = true; }
  79
  80   // Returns true if ICF has been run.
  81   bool
  82   is_icf_ready()
  83   { return this->icf_ready_; }
  84
  85   // Unfolds the section denoted by OBJ and SHNDX if folded.
  86   void
  87   unfold_section(Object* obj, unsigned int shndx);
  88
  89   // Returns the kept section corresponding to the
  90   // given section.
  91   bool
  92   is_section_folded(Object* obj, unsigned int shndx);
  93
  94   // Given an object and a section index, this returns true if the
  95   // pointer of the function defined in this section is taken.
  96   bool
  97   section_has_function_pointers(Object *obj, unsigned int shndx)
  98   {
  99     return (this->fptr_section_id_.find(Section_id(obj, shndx))
 100             != this->fptr_section_id_.end());
 101   }
 102
 103   // Records that a pointer of the function defined in this section
 104   // is taken.
 105   void
 106   set_section_has_function_pointers(Object *obj, unsigned int shndx)
 107   {
 108     this->fptr_section_id_.insert(Section_id(obj, shndx));
 109   }
 110
 111   // Checks if the section_name should be searched for relocs
 112   // corresponding to taken function pointers.  Ignores eh_frame
 113   // and vtable sections.
 114   inline bool
 115   check_section_for_function_pointers(std::string section_name,
 116                                       Target* target)
 117   {
 118     return (parameters->options().icf_safe_folding()
 119             && target->can_check_for_function_pointers()
 120             && !is_prefix_of(".rodata._ZTV", section_name.c_str())
 121             && !is_prefix_of(".eh_frame", section_name.c_str()));
 122   }
 123
 124   // Returns a map of a section to a list of all sections referenced
 125   // by its relocations.
 126   Section_list&
 127   section_reloc_list()
 128   { return this->section_reloc_list_; }
 129
 130   // Returns a map of  a section to a list of all symbols referenced
 131   // by its relocations.
 132   Symbol_list&
 133   symbol_reloc_list()
 134   { return this->symbol_reloc_list_; }
 135
 136   // Returns a maps of a section to a list of symbol values and addends
 137   // of its relocations.
 138   Addend_list&
 139   addend_reloc_list()
 140   { return this->addend_reloc_list_; }
 141
 142   // Returns a mapping of each section to a unique integer.
 143   Uniq_secn_id_map&
 144   section_to_int_map()
 145   { return this->section_id_; }
 146
 147  private:
 148
 149   // Maps integers to sections.
 150   std::vector<Section_id> id_section_;
 151   // Does the reverse.
 152   Uniq_secn_id_map section_id_;
 153   // Given a section id, this maps it to the id of the kept
 154   // section.  If the id's are the same then this section is
 155   // not folded.
 156   std::vector<unsigned int> kept_section_id_;
 157   // Given a section id, this says if the pointer to this
 158   // function is taken in which case it is dangerous to fold
 159   // this function.
 160   Secn_fptr_taken_set fptr_section_id_;
 161   unsigned int* num_tracked_relocs;
 162   // Flag to indicate if ICF has been run.
 163   bool icf_ready_;
 164
 165   // These lists are populated by gc_process_relocs in gc.h.
 166   Section_list section_reloc_list_;
 167   Symbol_list symbol_reloc_list_;
 168   Addend_list addend_reloc_list_;
 169 };
 170
 171 // This function returns true if this section corresponds to a function that
 172 // should be considered by icf as a possible candidate for folding.  Some
 173 // earlier gcc versions, like 4.0.3, put constructors and destructors in
 174 // .gnu.linkonce.t sections and hence should be included too.
 175 inline bool
 176 is_section_foldable_candidate(const char* section_name)
 177 {
 178   return (is_prefix_of(".text", section_name)
 179           || is_prefix_of(".gnu.linkonce.t", section_name));
 180 }
 181
 182 } // End of namespace gold.
 183
 184 #endif