gold/icf.h

   1 // icf.h --  Identical Code Folding
   2
   3 // Copyright (C) 2009-2019 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 std::vector<unsigned int> Reloc_addend_size_info;
  47   typedef Unordered_map<Section_id,
  48                         unsigned int,
  49                         Section_id_hash> Uniq_secn_id_map;
  50   typedef Unordered_set<Section_id, Section_id_hash> Secn_fptr_taken_set;
  51
  52   typedef struct
  53   {
  54     // This stores the section corresponding to the reloc.
  55     Sections_reachable_info section_info;
  56     // This stores the symbol corresponding to the reloc.
  57     Symbol_info symbol_info;
  58     // This stores the symbol value and the addend for a reloc.
  59     Addend_info addend_info;
  60     Offset_info offset_info;
  61     Reloc_addend_size_info reloc_addend_size_info;
  62   } Reloc_info;
  63
  64   typedef Unordered_map<Section_id, Reloc_info,
  65                         Section_id_hash> Reloc_info_list;
  66
  67   // A region of some other section that should be considered part of
  68   // a section for ICF purposes. This is used to avoid folding sections
  69   // that have identical text and relocations but different .eh_frame
  70   // information.
  71   typedef struct
  72   {
  73         Section_id section;
  74         section_offset_type offset;
  75         section_size_type length;
  76   } Extra_identity_info;
  77
  78   typedef std::multimap<Section_id, Extra_identity_info> Extra_identity_list;
  79
  80   Icf()
  81   : id_section_(), section_id_(), kept_section_id_(),
  82     fptr_section_id_(),
  83     icf_ready_(false),
  84     reloc_info_list_()
  85   { }
  86
  87   // Returns the kept folded identical section corresponding to
  88   // dup_obj and dup_shndx.
  89   Section_id
  90   get_folded_section(Relobj* dup_obj, unsigned int dup_shndx);
  91
  92   // Forms groups of identical sections where the first member
  93   // of each group is the kept section during folding.
  94   void
  95   find_identical_sections(const Input_objects* input_objects,
  96                           Symbol_table* symtab);
  97
  98   // This is set when ICF has been run and the groups of
  99   // identical sections have been formed.
 100   void
 101   icf_ready()
 102   { this->icf_ready_ = true; }
 103
 104   // Returns true if ICF has been run.
 105   bool
 106   is_icf_ready()
 107   { return this->icf_ready_; }
 108
 109   // Unfolds the section denoted by OBJ and SHNDX if folded.
 110   void
 111   unfold_section(Relobj* obj, unsigned int shndx);
 112
 113   // Returns the kept section corresponding to the
 114   // given section.
 115   bool
 116   is_section_folded(Relobj* obj, unsigned int shndx);
 117
 118   // Given an object and a section index, this returns true if the
 119   // pointer of the function defined in this section is taken.
 120   bool
 121   section_has_function_pointers(Relobj* obj, unsigned int shndx)
 122   {
 123     return (this->fptr_section_id_.find(Section_id(obj, shndx))
 124             != this->fptr_section_id_.end());
 125   }
 126
 127   // Records that a pointer of the function defined in this section
 128   // is taken.
 129   void
 130   set_section_has_function_pointers(Relobj* obj, unsigned int shndx)
 131   {
 132     this->fptr_section_id_.insert(Section_id(obj, shndx));
 133   }
 134
 135   // Checks if the section_name should be searched for relocs
 136   // corresponding to taken function pointers.  Ignores eh_frame
 137   // and vtable sections.
 138   inline bool
 139   check_section_for_function_pointers(const std::string& section_name,
 140                                       Target* target)
 141   {
 142     return (parameters->options().icf_safe_folding()
 143             && target->can_check_for_function_pointers()
 144             && target->section_may_have_icf_unsafe_pointers(
 145                 section_name.c_str()));
 146   }
 147
 148   // Returns a map of a section to info (Reloc_info) about its relocations.
 149   Reloc_info_list&
 150   reloc_info_list()
 151   { return this->reloc_info_list_; }
 152
 153   // Returns a map from section to region of a different section that should
 154   // be considered part of the key section for ICF purposes.
 155   Extra_identity_list&
 156   extra_identity_list()
 157   { return this->extra_identity_list_; }
 158
 159   // Returns a mapping of each section to a unique integer.
 160   Uniq_secn_id_map&
 161   section_to_int_map()
 162   { return this->section_id_; }
 163
 164  private:
 165
 166   bool
 167   add_ehframe_links(Relobj* object, unsigned int ehframe_shndx,
 168                     Reloc_info& ehframe_relocs);
 169
 170   // Maps integers to sections.
 171   std::vector<Section_id> id_section_;
 172   // Does the reverse.
 173   Uniq_secn_id_map section_id_;
 174   // Given a section id, this maps it to the id of the kept
 175   // section.  If the id's are the same then this section is
 176   // not folded.
 177   std::vector<unsigned int> kept_section_id_;
 178   // Given a section id, this says if the pointer to this
 179   // function is taken in which case it is dangerous to fold
 180   // this function.
 181   Secn_fptr_taken_set fptr_section_id_;
 182   // Flag to indicate if ICF has been run.
 183   bool icf_ready_;
 184   // This list is populated by gc_process_relocs in gc.h.
 185   Reloc_info_list reloc_info_list_;
 186   // Regions of other sections that should be considered part of
 187   // each section for ICF purposes.
 188   Extra_identity_list extra_identity_list_;
 189 };
 190
 191 // This function returns true if this section corresponds to a function that
 192 // should be considered by icf as a possible candidate for folding.  Some
 193 // earlier gcc versions, like 4.0.3, put constructors and destructors in
 194 // .gnu.linkonce.t sections and hence should be included too.
 195 // The mechanism used to safely fold functions referenced by .eh_frame
 196 // requires folding .gcc_except_table sections as well; see "Notes regarding
 197 // C++ exception handling" at the top of icf.cc for an explanation why.
 198 inline bool
 199 is_section_foldable_candidate(const std::string& section_name)
 200 {
 201   const char* section_name_cstr = section_name.c_str();
 202   return (is_prefix_of(".text", section_name_cstr)
 203           || is_prefix_of(".gcc_except_table", section_name_cstr)
 204           || is_prefix_of(".gnu.linkonce.t", section_name_cstr));
 205 }
 206
 207 } // End of namespace gold.
 208
 209 #endif