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
32namespace gold
33{
34
35class Object;
36class Input_objects;
37class Symbol_table;
38
39class 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  Icf()
68  : id_section_(), section_id_(), kept_section_id_(),
69    fptr_section_id_(),
70    num_tracked_relocs(NULL), icf_ready_(false),
71    reloc_info_list_()
72  { }
73
74  // Returns the kept folded identical section corresponding to
75  // dup_obj and dup_shndx.
76  Section_id
77  get_folded_section(Object* dup_obj, unsigned int dup_shndx);
78
79  // Forms groups of identical sections where the first member
80  // of each group is the kept section during folding.
81  void
82  find_identical_sections(const Input_objects* input_objects,
83                          Symbol_table* symtab);
84
85  // This is set when ICF has been run and the groups of
86  // identical sections have been formed.
87  void
88  icf_ready()
89  { this->icf_ready_ = true; }
90
91  // Returns true if ICF has been run.
92  bool
93  is_icf_ready()
94  { return this->icf_ready_; }
95
96  // Unfolds the section denoted by OBJ and SHNDX if folded.
97  void
98  unfold_section(Object* obj, unsigned int shndx);
99
100  // Returns the kept section corresponding to the
101  // given section.
102  bool
103  is_section_folded(Object* obj, unsigned int shndx);
104
105  // Given an object and a section index, this returns true if the
106  // pointer of the function defined in this section is taken.
107  bool
108  section_has_function_pointers(Object* obj, unsigned int shndx)
109  {
110    return (this->fptr_section_id_.find(Section_id(obj, shndx))
111            != this->fptr_section_id_.end());
112  }
113
114  // Records that a pointer of the function defined in this section
115  // is taken.
116  void
117  set_section_has_function_pointers(Object* obj, unsigned int shndx)
118  {
119    this->fptr_section_id_.insert(Section_id(obj, shndx));
120  }
121
122  // Checks if the section_name should be searched for relocs
123  // corresponding to taken function pointers.  Ignores eh_frame
124  // and vtable sections.
125  inline bool
126  check_section_for_function_pointers(const std::string& section_name,
127                                      Target* target)
128  {
129    return (parameters->options().icf_safe_folding()
130	    && target->can_check_for_function_pointers()
131	    && target->section_may_have_icf_unsafe_pointers(
132	        section_name.c_str()));
133  }
134
135  // Returns a map of a section to info (Reloc_info) about its relocations.
136  Reloc_info_list&
137  reloc_info_list()
138  { return this->reloc_info_list_; }
139
140  // Returns a mapping of each section to a unique integer.
141  Uniq_secn_id_map&
142  section_to_int_map()
143  { return this->section_id_; }
144
145 private:
146
147  // Maps integers to sections.
148  std::vector<Section_id> id_section_;
149  // Does the reverse.
150  Uniq_secn_id_map section_id_;
151  // Given a section id, this maps it to the id of the kept
152  // section.  If the id's are the same then this section is
153  // not folded.
154  std::vector<unsigned int> kept_section_id_;
155  // Given a section id, this says if the pointer to this
156  // function is taken in which case it is dangerous to fold
157  // this function.
158  Secn_fptr_taken_set fptr_section_id_;
159  unsigned int* num_tracked_relocs;
160  // Flag to indicate if ICF has been run.
161  bool icf_ready_;
162  // This list is populated by gc_process_relocs in gc.h.
163  Reloc_info_list reloc_info_list_;
164};
165
166// This function returns true if this section corresponds to a function that
167// should be considered by icf as a possible candidate for folding.  Some
168// earlier gcc versions, like 4.0.3, put constructors and destructors in
169// .gnu.linkonce.t sections and hence should be included too.
170inline bool
171is_section_foldable_candidate(const std::string& section_name)
172{
173  const char* section_name_cstr = section_name.c_str();
174  return (is_prefix_of(".text", section_name_cstr)
175          || is_prefix_of(".gnu.linkonce.t", section_name_cstr));
176}
177
178} // End of namespace gold.
179
180#endif
181