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_info;
  43   typedef std::vector<Symbol*> Symbol_info;
  44   typedef std::vector<std::pair<long long, long long> > Addend_info;
  45   typedef std::vector<uint64_t> Offset_info;
  46   typedef Unordered_map<Section_id,
  47                         unsigned int,
  48                         Section_id_hash> Uniq_secn_id_map;
  49   typedef Unordered_set<Section_id, Section_id_hash> Secn_fptr_taken_set;
  50
  51   typedef struct
  52   {
  53     // This stores the section corresponding to the reloc.
  54     Sections_reachable_info section_info;
  55     // This stores the symbol corresponding to the reloc.
  56     Symbol_info symbol_info;
  57     // This stores the symbol value and the addend for a reloc.
  58     Addend_info addend_info;
  59     Offset_info offset_info;
  60   } Reloc_info;
  61
  62   typedef Unordered_map<Section_id, Reloc_info,
  63                         Section_id_hash> Reloc_info_list;
  64
  65   Icf()
  66   : id_section_(), section_id_(), kept_section_id_(),
  67     fptr_section_id_(),
  68     num_tracked_relocs(NULL), icf_ready_(false),
  69     reloc_info_list_()
  70   { }
  71
  72   // Returns the kept folded identical section corresponding to
  73   // dup_obj and dup_shndx.
  74   Section_id
  75   get_folded_section(Object* dup_obj, unsigned int dup_shndx);
  76
  77   // Forms groups of identical sections where the first member
  78   // of each group is the kept section during folding.
  79   void
  80   find_identical_sections(const Input_objects* input_objects,
  81                           Symbol_table* symtab);
  82
  83   // This is set when ICF has been run and the groups of
  84   // identical sections have been formed.
  85   void
  86   icf_ready()
  87   { this->icf_ready_ = true; }
  88
  89   // Returns true if ICF has been run.
  90   bool
  91   is_icf_ready()
  92   { return this->icf_ready_; }
  93
  94   // Unfolds the section denoted by OBJ and SHNDX if folded.
  95   void
  96   unfold_section(Object* obj, unsigned int shndx);
  97
  98   // Returns the kept section corresponding to the
  99   // given section.
 100   bool
 101   is_section_folded(Object* obj, unsigned int shndx);
 102
 103   // Given an object and a section index, this returns true if the
 104   // pointer of the function defined in this section is taken.
 105   bool
 106   section_has_function_pointers(Object *obj, unsigned int shndx)
 107   {
 108     return (this->fptr_section_id_.find(Section_id(obj, shndx))
 109             != this->fptr_section_id_.end());
 110   }
 111
 112   // Records that a pointer of the function defined in this section
 113   // is taken.
 114   void
 115   set_section_has_function_pointers(Object *obj, unsigned int shndx)
 116   {
 117     this->fptr_section_id_.insert(Section_id(obj, shndx));
 118   }
 119
 120   // Checks if the section_name should be searched for relocs
 121   // corresponding to taken function pointers.  Ignores eh_frame
 122   // and vtable sections.
 123   inline bool
 124   check_section_for_function_pointers(std::string section_name,
 125                                       Target* target)
 126   {
 127     return (parameters->options().icf_safe_folding()
 128             && target->can_check_for_function_pointers()
 129             && !is_prefix_of(".rodata._ZTV", section_name.c_str())
 130             && !is_prefix_of(".data.rel.ro._ZTV", section_name.c_str())
 131             && !is_prefix_of(".eh_frame", section_name.c_str()));
 132   }
 133
 134   // Returns a map of a section to info (Reloc_info) about its relocations.
 135   Reloc_info_list&
 136   reloc_info_list()
 137   { return this->reloc_info_list_; }
 138
 139   // Returns a mapping of each section to a unique integer.
 140   Uniq_secn_id_map&
 141   section_to_int_map()
 142   { return this->section_id_; }
 143
 144  private:
 145
 146   // Maps integers to sections.
 147   std::vector<Section_id> id_section_;
 148   // Does the reverse.
 149   Uniq_secn_id_map section_id_;
 150   // Given a section id, this maps it to the id of the kept
 151   // section.  If the id's are the same then this section is
 152   // not folded.
 153   std::vector<unsigned int> kept_section_id_;
 154   // Given a section id, this says if the pointer to this
 155   // function is taken in which case it is dangerous to fold
 156   // this function.
 157   Secn_fptr_taken_set fptr_section_id_;
 158   unsigned int* num_tracked_relocs;
 159   // Flag to indicate if ICF has been run.
 160   bool icf_ready_;
 161   // This list is populated by gc_process_relocs in gc.h.
 162   Reloc_info_list reloc_info_list_;
 163 };
 164
 165 // This function returns true if this section corresponds to a function that
 166 // should be considered by icf as a possible candidate for folding.  Some
 167 // earlier gcc versions, like 4.0.3, put constructors and destructors in
 168 // .gnu.linkonce.t sections and hence should be included too.
 169 inline bool
 170 is_section_foldable_candidate(const char* section_name)
 171 {
 172   return (is_prefix_of(".text", section_name)
 173           || is_prefix_of(".gnu.linkonce.t", section_name));
 174 }
 175
 176 } // End of namespace gold.
 177
 178 #endif