1 // copy-relocs.cc -- handle COPY relocations for gold. 2 3 // Copyright (C) 2006-2014 Free Software Foundation, Inc. 4 // Written by Ian Lance Taylor <iant (at) 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 #include "gold.h" 24 25 #include "symtab.h" 26 #include "copy-relocs.h" 27 28 namespace gold 29 { 30 31 // Copy_relocs methods. 32 33 // Handle a relocation against a symbol which may force us to generate 34 // a COPY reloc. 35 36 template<int sh_type, int size, bool big_endian> 37 void 38 Copy_relocs<sh_type, size, big_endian>::copy_reloc( 39 Symbol_table* symtab, 40 Layout* layout, 41 Sized_symbol<size>* sym, 42 Sized_relobj_file<size, big_endian>* object, 43 unsigned int shndx, 44 Output_section* output_section, 45 const Reloc& rel, 46 Output_data_reloc<sh_type, true, size, big_endian>* reloc_section) 47 { 48 if (this->need_copy_reloc(sym, object, shndx)) 49 this->make_copy_reloc(symtab, layout, sym, reloc_section); 50 else 51 { 52 // We may not need a COPY relocation. Save this relocation to 53 // possibly be emitted later. 54 this->save(sym, object, shndx, output_section, rel); 55 } 56 } 57 58 // Return whether we need a COPY reloc for a relocation against SYM. 59 // The relocation is begin applied to section SHNDX in OBJECT. 60 61 template<int sh_type, int size, bool big_endian> 62 bool 63 Copy_relocs<sh_type, size, big_endian>::need_copy_reloc( 64 Sized_symbol<size>* sym, 65 Sized_relobj_file<size, big_endian>* object, 66 unsigned int shndx) const 67 { 68 if (!parameters->options().copyreloc()) 69 return false; 70 71 if (sym->symsize() == 0) 72 return false; 73 74 // If this is a readonly section, then we need a COPY reloc. 75 // Otherwise we can use a dynamic reloc. Note that calling 76 // section_flags here can be slow, as the information is not cached; 77 // fortunately we shouldn't see too many potential COPY relocs. 78 if ((object->section_flags(shndx) & elfcpp::SHF_WRITE) == 0) 79 return true; 80 81 return false; 82 } 83 84 // Emit a COPY relocation for SYM. 85 86 template<int sh_type, int size, bool big_endian> 87 void 88 Copy_relocs<sh_type, size, big_endian>::emit_copy_reloc( 89 Symbol_table* symtab, 90 Sized_symbol<size>* sym, 91 Output_data* posd, 92 off_t offset, 93 Output_data_reloc<sh_type, true, size, big_endian>* reloc_section) 94 { 95 // Define the symbol as being copied. 96 symtab->define_with_copy_reloc(sym, posd, offset); 97 98 // Add the COPY relocation to the dynamic reloc section. 99 reloc_section->add_global_generic(sym, this->copy_reloc_type_, posd, 100 offset, 0); 101 } 102 103 // Make a COPY relocation for SYM and emit it. 104 105 template<int sh_type, int size, bool big_endian> 106 void 107 Copy_relocs<sh_type, size, big_endian>::make_copy_reloc( 108 Symbol_table* symtab, 109 Layout* layout, 110 Sized_symbol<size>* sym, 111 Output_data_reloc<sh_type, true, size, big_endian>* reloc_section) 112 { 113 // We should not be here if -z nocopyreloc is given. 114 gold_assert(parameters->options().copyreloc()); 115 116 typename elfcpp::Elf_types<size>::Elf_WXword symsize = sym->symsize(); 117 118 // There is no defined way to determine the required alignment of 119 // the symbol. We know that the symbol is defined in a dynamic 120 // object. We start with the alignment of the section in which it 121 // is defined; presumably we do not require an alignment larger than 122 // that. Then we reduce that alignment if the symbol is not aligned 123 // within the section. 124 gold_assert(sym->is_from_dynobj()); 125 bool is_ordinary; 126 unsigned int shndx = sym->shndx(&is_ordinary); 127 gold_assert(is_ordinary); 128 typename elfcpp::Elf_types<size>::Elf_WXword addralign; 129 130 { 131 // Lock the object so we can read from it. This is only called 132 // single-threaded from scan_relocs, so it is OK to lock. 133 // Unfortunately we have no way to pass in a Task token. 134 const Task* dummy_task = reinterpret_cast<const Task*>(-1); 135 Object* obj = sym->object(); 136 Task_lock_obj<Object> tl(dummy_task, obj); 137 addralign = obj->section_addralign(shndx); 138 } 139 140 typename Sized_symbol<size>::Value_type value = sym->value(); 141 while ((value & (addralign - 1)) != 0) 142 addralign >>= 1; 143 144 // Mark the dynamic object as needed for the --as-needed option. 145 sym->object()->set_is_needed(); 146 147 if (this->dynbss_ == NULL) 148 { 149 this->dynbss_ = new Output_data_space(addralign, "** dynbss"); 150 layout->add_output_section_data(".bss", 151 elfcpp::SHT_NOBITS, 152 elfcpp::SHF_ALLOC | elfcpp::SHF_WRITE, 153 this->dynbss_, ORDER_BSS, false); 154 } 155 156 Output_data_space* dynbss = this->dynbss_; 157 158 if (addralign > dynbss->addralign()) 159 dynbss->set_space_alignment(addralign); 160 161 section_size_type dynbss_size = 162 convert_to_section_size_type(dynbss->current_data_size()); 163 dynbss_size = align_address(dynbss_size, addralign); 164 section_size_type offset = dynbss_size; 165 dynbss->set_current_data_size(dynbss_size + symsize); 166 167 this->emit_copy_reloc(symtab, sym, dynbss, offset, reloc_section); 168 } 169 170 // Save a relocation to possibly be emitted later. 171 172 template<int sh_type, int size, bool big_endian> 173 void 174 Copy_relocs<sh_type, size, big_endian>::save( 175 Symbol* sym, 176 Sized_relobj_file<size, big_endian>* object, 177 unsigned int shndx, 178 Output_section* output_section, 179 const Reloc& rel) 180 { 181 unsigned int reloc_type = elfcpp::elf_r_type<size>(rel.get_r_info()); 182 typename elfcpp::Elf_types<size>::Elf_Addr addend = 183 Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&rel); 184 this->entries_.push_back(Copy_reloc_entry(sym, reloc_type, object, shndx, 185 output_section, rel.get_r_offset(), 186 addend)); 187 } 188 189 // Emit any saved relocs. 190 191 template<int sh_type, int size, bool big_endian> 192 void 193 Copy_relocs<sh_type, size, big_endian>::emit( 194 Output_data_reloc<sh_type, true, size, big_endian>* reloc_section) 195 { 196 for (typename Copy_reloc_entries::iterator p = this->entries_.begin(); 197 p != this->entries_.end(); 198 ++p) 199 { 200 Copy_reloc_entry& entry = *p; 201 202 // If the symbol is no longer defined in a dynamic object, then we 203 // emitted a COPY relocation, and we do not want to emit this 204 // dynamic relocation. 205 if (entry.sym_->is_from_dynobj()) 206 reloc_section->add_global_generic(entry.sym_, entry.reloc_type_, 207 entry.output_section_, entry.relobj_, 208 entry.shndx_, entry.address_, 209 entry.addend_); 210 } 211 212 // We no longer need the saved information. 213 this->entries_.clear(); 214 } 215 216 // Instantiate the templates we need. 217 218 #ifdef HAVE_TARGET_32_LITTLE 219 template 220 class Copy_relocs<elfcpp::SHT_REL, 32, false>; 221 222 template 223 class Copy_relocs<elfcpp::SHT_RELA, 32, false>; 224 #endif 225 226 #ifdef HAVE_TARGET_32_BIG 227 template 228 class Copy_relocs<elfcpp::SHT_REL, 32, true>; 229 230 template 231 class Copy_relocs<elfcpp::SHT_RELA, 32, true>; 232 #endif 233 234 #ifdef HAVE_TARGET_64_LITTLE 235 template 236 class Copy_relocs<elfcpp::SHT_REL, 64, false>; 237 238 template 239 class Copy_relocs<elfcpp::SHT_RELA, 64, false>; 240 #endif 241 242 #ifdef HAVE_TARGET_64_BIG 243 template 244 class Copy_relocs<elfcpp::SHT_REL, 64, true>; 245 246 template 247 class Copy_relocs<elfcpp::SHT_RELA, 64, true>; 248 #endif 249 250 } // End namespace gold. 251
