gold/copy-relocs.cc

   1 // copy-relocs.cc -- handle COPY relocations for gold.
   2
   3 // Copyright (C) 2006-2016 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 #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     unsigned int r_type,
  46     typename elfcpp::Elf_types<size>::Elf_Addr r_offset,
  47     typename elfcpp::Elf_types<size>::Elf_Swxword r_addend,
  48     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
  49 {
  50   if (this->need_copy_reloc(sym, object, shndx))
  51     this->make_copy_reloc(symtab, layout, sym, reloc_section);
  52   else
  53     {
  54       // We may not need a COPY relocation.  Save this relocation to
  55       // possibly be emitted later.
  56       this->save(sym, object, shndx, output_section,
  57                  r_type, r_offset, r_addend);
  58     }
  59 }
  60
  61 // Return whether we need a COPY reloc for a relocation against SYM.
  62 // The relocation is begin applied to section SHNDX in OBJECT.
  63
  64 template<int sh_type, int size, bool big_endian>
  65 bool
  66 Copy_relocs<sh_type, size, big_endian>::need_copy_reloc(
  67     Sized_symbol<size>* sym,
  68     Sized_relobj_file<size, big_endian>* object,
  69     unsigned int shndx) const
  70 {
  71   if (!parameters->options().copyreloc())
  72     return false;
  73
  74   if (sym->symsize() == 0)
  75     return false;
  76
  77   // If this is a readonly section, then we need a COPY reloc.
  78   // Otherwise we can use a dynamic reloc.  Note that calling
  79   // section_flags here can be slow, as the information is not cached;
  80   // fortunately we shouldn't see too many potential COPY relocs.
  81   if ((object->section_flags(shndx) & elfcpp::SHF_WRITE) == 0)
  82     return true;
  83
  84   return false;
  85 }
  86
  87 // Emit a COPY relocation for SYM.
  88
  89 template<int sh_type, int size, bool big_endian>
  90 void
  91 Copy_relocs<sh_type, size, big_endian>::emit_copy_reloc(
  92     Symbol_table* symtab,
  93     Sized_symbol<size>* sym,
  94     Output_data* posd,
  95     off_t offset,
  96     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
  97 {
  98   // Define the symbol as being copied.
  99   symtab->define_with_copy_reloc(sym, posd, offset);
 100
 101   // Add the COPY relocation to the dynamic reloc section.
 102   reloc_section->add_global_generic(sym, this->copy_reloc_type_, posd,
 103                                     offset, 0);
 104 }
 105
 106 // Make a COPY relocation for SYM and emit it.
 107
 108 template<int sh_type, int size, bool big_endian>
 109 void
 110 Copy_relocs<sh_type, size, big_endian>::make_copy_reloc(
 111     Symbol_table* symtab,
 112     Layout* layout,
 113     Sized_symbol<size>* sym,
 114     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
 115 {
 116   // We should not be here if -z nocopyreloc is given.
 117   gold_assert(parameters->options().copyreloc());
 118
 119   typename elfcpp::Elf_types<size>::Elf_WXword symsize = sym->symsize();
 120
 121   // There is no defined way to determine the required alignment of
 122   // the symbol.  We know that the symbol is defined in a dynamic
 123   // object.  We start with the alignment of the section in which it
 124   // is defined; presumably we do not require an alignment larger than
 125   // that.  Then we reduce that alignment if the symbol is not aligned
 126   // within the section.
 127   gold_assert(sym->is_from_dynobj());
 128   bool is_ordinary;
 129   unsigned int shndx = sym->shndx(&is_ordinary);
 130   gold_assert(is_ordinary);
 131   typename elfcpp::Elf_types<size>::Elf_WXword addralign;
 132
 133   {
 134     // Lock the object so we can read from it.  This is only called
 135     // single-threaded from scan_relocs, so it is OK to lock.
 136     // Unfortunately we have no way to pass in a Task token.
 137     const Task* dummy_task = reinterpret_cast<const Task*>(-1);
 138     Object* obj = sym->object();
 139     Task_lock_obj<Object> tl(dummy_task, obj);
 140     addralign = obj->section_addralign(shndx);
 141   }
 142
 143   typename Sized_symbol<size>::Value_type value = sym->value();
 144   while ((value & (addralign - 1)) != 0)
 145     addralign >>= 1;
 146
 147   // Mark the dynamic object as needed for the --as-needed option.
 148   sym->object()->set_is_needed();
 149
 150   if (this->dynbss_ == NULL)
 151     {
 152       this->dynbss_ = new Output_data_space(addralign, "** dynbss");
 153       layout->add_output_section_data(".bss",
 154                                       elfcpp::SHT_NOBITS,
 155                                       elfcpp::SHF_ALLOC | elfcpp::SHF_WRITE,
 156                                       this->dynbss_, ORDER_BSS, false);
 157     }
 158
 159   Output_data_space* dynbss = this->dynbss_;
 160
 161   if (addralign > dynbss->addralign())
 162     dynbss->set_space_alignment(addralign);
 163
 164   section_size_type dynbss_size =
 165     convert_to_section_size_type(dynbss->current_data_size());
 166   dynbss_size = align_address(dynbss_size, addralign);
 167   section_size_type offset = dynbss_size;
 168   dynbss->set_current_data_size(dynbss_size + symsize);
 169
 170   this->emit_copy_reloc(symtab, sym, dynbss, offset, reloc_section);
 171 }
 172
 173 // Save a relocation to possibly be emitted later.
 174
 175 template<int sh_type, int size, bool big_endian>
 176 void
 177 Copy_relocs<sh_type, size, big_endian>::save(
 178     Symbol* sym,
 179     Sized_relobj_file<size, big_endian>* object,
 180     unsigned int shndx,
 181     Output_section* output_section,
 182     unsigned int r_type,
 183     typename elfcpp::Elf_types<size>::Elf_Addr r_offset,
 184     typename elfcpp::Elf_types<size>::Elf_Swxword r_addend)
 185 {
 186   this->entries_.push_back(Copy_reloc_entry(sym, r_type, object, shndx,
 187                                             output_section, r_offset,
 188                                             r_addend));
 189 }
 190
 191 // Emit any saved relocs.
 192
 193 template<int sh_type, int size, bool big_endian>
 194 void
 195 Copy_relocs<sh_type, size, big_endian>::emit(
 196     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
 197 {
 198   for (typename Copy_reloc_entries::iterator p = this->entries_.begin();
 199        p != this->entries_.end();
 200        ++p)
 201     {
 202       Copy_reloc_entry& entry = *p;
 203
 204       // If the symbol is no longer defined in a dynamic object, then we
 205       // emitted a COPY relocation, and we do not want to emit this
 206       // dynamic relocation.
 207       if (entry.sym_->is_from_dynobj())
 208         reloc_section->add_global_generic(entry.sym_, entry.reloc_type_,
 209                                           entry.output_section_, entry.relobj_,
 210                                           entry.shndx_, entry.address_,
 211                                           entry.addend_);
 212     }
 213
 214   // We no longer need the saved information.
 215   this->entries_.clear();
 216 }
 217
 218 // Instantiate the templates we need.
 219
 220 #ifdef HAVE_TARGET_32_LITTLE
 221 template
 222 class Copy_relocs<elfcpp::SHT_REL, 32, false>;
 223
 224 template
 225 class Copy_relocs<elfcpp::SHT_RELA, 32, false>;
 226 #endif
 227
 228 #ifdef HAVE_TARGET_32_BIG
 229 template
 230 class Copy_relocs<elfcpp::SHT_REL, 32, true>;
 231
 232 template
 233 class Copy_relocs<elfcpp::SHT_RELA, 32, true>;
 234 #endif
 235
 236 #ifdef HAVE_TARGET_64_LITTLE
 237 template
 238 class Copy_relocs<elfcpp::SHT_REL, 64, false>;
 239
 240 template
 241 class Copy_relocs<elfcpp::SHT_RELA, 64, false>;
 242 #endif
 243
 244 #ifdef HAVE_TARGET_64_BIG
 245 template
 246 class Copy_relocs<elfcpp::SHT_REL, 64, true>;
 247
 248 template
 249 class Copy_relocs<elfcpp::SHT_RELA, 64, true>;
 250 #endif
 251
 252 } // End namespace gold.