1 // copy-relocs.h -- handle COPY relocations for gold -*- C++ -*- 2 3 // Copyright (C) 2006-2020 Free Software Foundation, Inc. 4 // Written by Ian Lance Taylor <iant@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_COPY_RELOCS_H 24 #define GOLD_COPY_RELOCS_H 25 26 #include "elfcpp.h" 27 #include "reloc-types.h" 28 #include "output.h" 29 30 namespace gold 31 { 32 33 // This class is used to manage COPY relocations. We try to avoid 34 // them when possible. A COPY relocation may be required when an 35 // executable refers to a variable defined in a shared library. COPY 36 // relocations are problematic because they tie the executable to the 37 // exact size of the variable in the shared library. We can avoid 38 // them if all the references to the variable are in a writeable 39 // section. In that case we can simply use dynamic relocations. 40 // However, when scanning relocs, we don't know when we see the 41 // relocation whether we will be forced to use a COPY relocation or 42 // not. So we have to save the relocation during the reloc scanning, 43 // and then emit it as a dynamic relocation if necessary. This class 44 // implements that. It is used by the target specific code. 45 46 // The template parameter SH_TYPE is the type of the reloc section to 47 // be used for COPY relocs: elfcpp::SHT_REL or elfcpp::SHT_RELA. 48 49 template<int sh_type, int size, bool big_endian> 50 class Copy_relocs 51 { 52 private: 53 typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reloc; 54 55 public: 56 Copy_relocs(unsigned int copy_reloc_type) 57 : entries_(), copy_reloc_type_(copy_reloc_type), dynbss_(NULL), 58 dynrelro_(NULL) 59 { } 60 61 // This is called while scanning relocs if we see a relocation 62 // against a symbol which may force us to generate a COPY reloc. 63 // SYM is the symbol. OBJECT is the object whose relocs we are 64 // scanning. The relocation is being applied to section SHNDX in 65 // OBJECT. OUTPUT_SECTION is the output section where section SHNDX 66 // will wind up. REL is the reloc itself. The Output_data_reloc 67 // section is where the dynamic relocs are put. 68 void 69 copy_reloc(Symbol_table*, 70 Layout*, 71 Sized_symbol<size>* sym, 72 Sized_relobj_file<size, big_endian>* object, 73 unsigned int shndx, 74 Output_section* output_section, 75 unsigned int r_type, 76 typename elfcpp::Elf_types<size>::Elf_Addr r_offset, 77 typename elfcpp::Elf_types<size>::Elf_Swxword r_addend, 78 Output_data_reloc<sh_type, true, size, big_endian>*); 79 80 // Return whether there are any saved relocations. 81 bool 82 any_saved_relocs() const 83 { return !this->entries_.empty(); } 84 85 // Emit any saved relocations which turn out to be needed. This is 86 // called after all the relocs have been scanned. 87 void 88 emit(Output_data_reloc<sh_type, true, size, big_endian>*); 89 90 // Emit a COPY reloc. 91 void 92 emit_copy_reloc(Symbol_table*, Sized_symbol<size>*, 93 Output_data*, off_t, 94 Output_data_reloc<sh_type, true, size, big_endian>*); 95 96 protected: 97 typedef typename elfcpp::Elf_types<size>::Elf_Addr Address; 98 typedef typename elfcpp::Elf_types<size>::Elf_Addr Addend; 99 100 // This POD class holds the relocations we are saving. We will emit 101 // these relocations if it turns out that the symbol does not 102 // require a COPY relocation. 103 struct Copy_reloc_entry 104 { 105 Copy_reloc_entry(Symbol* sym, unsigned int reloc_type, 106 Sized_relobj_file<size, big_endian>* relobj, 107 unsigned int shndx, 108 Output_section* output_section, 109 Address address, Addend addend) 110 : sym_(sym), reloc_type_(reloc_type), relobj_(relobj), 111 shndx_(shndx), output_section_(output_section), 112 address_(address), addend_(addend) 113 { } 114 115 Symbol* sym_; 116 unsigned int reloc_type_; 117 Sized_relobj_file<size, big_endian>* relobj_; 118 unsigned int shndx_; 119 Output_section* output_section_; 120 Address address_; 121 Addend addend_; 122 }; 123 124 // Make a new COPY reloc and emit it. 125 void 126 make_copy_reloc(Symbol_table*, Layout*, Sized_symbol<size>*, 127 Sized_relobj_file<size, big_endian>* object, 128 Output_data_reloc<sh_type, true, size, big_endian>*); 129 130 // A list of relocs to be saved. 131 typedef std::vector<Copy_reloc_entry> Copy_reloc_entries; 132 133 // The list of relocs we are saving. 134 Copy_reloc_entries entries_; 135 136 private: 137 // Return whether we need a COPY reloc. 138 bool 139 need_copy_reloc(Sized_symbol<size>* gsym, 140 Sized_relobj_file<size, big_endian>* object, 141 unsigned int shndx) const; 142 143 // Save a reloc against SYM for possible emission later. 144 void 145 save(Symbol*, 146 Sized_relobj_file<size, big_endian>*, 147 unsigned int shndx, 148 Output_section*, 149 unsigned int r_type, 150 typename elfcpp::Elf_types<size>::Elf_Addr r_offset, 151 typename elfcpp::Elf_types<size>::Elf_Swxword r_addend); 152 153 // The target specific relocation type of the COPY relocation. 154 const unsigned int copy_reloc_type_; 155 // The dynamic BSS data which goes into the .bss section. This is 156 // where writable variables which require COPY relocations are placed. 157 Output_data_space* dynbss_; 158 // The dynamic read-only data, which goes into the .data.rel.ro section. 159 // This is where read-only variables which require COPY relocations are 160 // placed. 161 Output_data_space* dynrelro_; 162 }; 163 164 } // End namespace gold. 165 166 #endif // !defined(GOLD_COPY_RELOCS_H) 167