1 // icf.h -- Identical Code Folding 2 3 // Copyright (C) 2009-2020 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 210