gold/copy-relocs.cc

   1 // copy-relocs.cc -- handle COPY relocations for gold.
   2
   3 // Copyright 2006, 2007, 2008 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::Copy_reloc_entry methods.
  32
  33 // Emit the reloc if appropriate.
  34
  35 template<int sh_type, int size, bool big_endian>
  36 void
  37 Copy_relocs<sh_type, size, big_endian>::Copy_reloc_entry::emit(
  38     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
  39 {
  40   // If the symbol is no longer defined in a dynamic object, then we
  41   // emitted a COPY relocation, and we do not want to emit this
  42   // dynamic relocation.
  43   if (this->sym_->is_from_dynobj())
  44     reloc_section->add_global(this->sym_, this->reloc_type_,
  45                               this->output_section_, this->relobj_,
  46                               this->shndx_, this->address_,
  47                               this->addend_);
  48 }
  49
  50 // Copy_relocs methods.
  51
  52 // Handle a relocation against a symbol which may force us to generate
  53 // a COPY reloc.
  54
  55 template<int sh_type, int size, bool big_endian>
  56 void
  57 Copy_relocs<sh_type, size, big_endian>::copy_reloc(
  58     Symbol_table* symtab,
  59     Layout* layout,
  60     Sized_symbol<size>* sym,
  61     Sized_relobj<size, big_endian>* object,
  62     unsigned int shndx,
  63     Output_section *output_section,
  64     const Reloc& rel,
  65     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
  66 {
  67   if (this->need_copy_reloc(sym, object, shndx))
  68     this->emit_copy_reloc(symtab, layout, sym, reloc_section);
  69   else
  70     {
  71       // We may not need a COPY relocation.  Save this relocation to
  72       // possibly be emitted later.
  73       this->save(sym, object, shndx, output_section, rel);
  74     }
  75 }
  76
  77 // Return whether we need a COPY reloc for a relocation against SYM.
  78 // The relocation is begin applied to section SHNDX in OBJECT.
  79
  80 template<int sh_type, int size, bool big_endian>
  81 bool
  82 Copy_relocs<sh_type, size, big_endian>::need_copy_reloc(
  83     Sized_symbol<size>* sym,
  84     Sized_relobj<size, big_endian>* object,
  85     unsigned int shndx) const
  86 {
  87   // FIXME: Handle -z nocopyrelocs.
  88
  89   if (sym->symsize() == 0)
  90     return false;
  91
  92   // If this is a readonly section, then we need a COPY reloc.
  93   // Otherwise we can use a dynamic reloc.  Note that calling
  94   // section_flags here can be slow, as the information is not cached;
  95   // fortunately we shouldn't see too many potential COPY relocs.
  96   if ((object->section_flags(shndx) & elfcpp::SHF_WRITE) == 0)
  97     return true;
  98
  99   return false;
 100 }
 101
 102 // Emit a COPY relocation for SYM.
 103
 104 template<int sh_type, int size, bool big_endian>
 105 void
 106 Copy_relocs<sh_type, size, big_endian>::emit_copy_reloc(
 107     Symbol_table* symtab,
 108     Layout* layout,
 109     Sized_symbol<size>* sym,
 110     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
 111 {
 112   typename elfcpp::Elf_types<size>::Elf_WXword symsize = sym->symsize();
 113
 114   // There is no defined way to determine the required alignment of
 115   // the symbol.  We know that the symbol is defined in a dynamic
 116   // object.  We start with the alignment of the section in which it
 117   // is defined; presumably we do not require an alignment larger than
 118   // that.  Then we reduce that alignment if the symbol is not aligned
 119   // within the section.
 120   gold_assert(sym->is_from_dynobj());
 121   bool is_ordinary;
 122   unsigned int shndx = sym->shndx(&is_ordinary);
 123   gold_assert(is_ordinary);
 124   typename elfcpp::Elf_types<size>::Elf_WXword addralign =
 125     sym->object()->section_addralign(shndx);
 126
 127   typename Sized_symbol<size>::Value_type value = sym->value();
 128   while ((value & (addralign - 1)) != 0)
 129     addralign >>= 1;
 130
 131   if (this->dynbss_ == NULL)
 132     {
 133       this->dynbss_ = new Output_data_space(addralign, "** dynbss");
 134       layout->add_output_section_data(".bss",
 135                                       elfcpp::SHT_NOBITS,
 136                                       elfcpp::SHF_ALLOC | elfcpp::SHF_WRITE,
 137                                       this->dynbss_);
 138     }
 139
 140   Output_data_space* dynbss = this->dynbss_;
 141
 142   if (addralign > dynbss->addralign())
 143     dynbss->set_space_alignment(addralign);
 144
 145   section_size_type dynbss_size =
 146     convert_to_section_size_type(dynbss->current_data_size());
 147   dynbss_size = align_address(dynbss_size, addralign);
 148   section_size_type offset = dynbss_size;
 149   dynbss->set_current_data_size(dynbss_size + symsize);
 150
 151   // Define the symbol as being copied.
 152   symtab->define_with_copy_reloc(sym, dynbss, offset);
 153
 154   // Add the COPY relocation to the dynamic reloc section.
 155   this->add_copy_reloc(sym, offset, reloc_section);
 156 }
 157
 158 // Add a COPY relocation for SYM to RELOC_SECTION.
 159
 160 template<int sh_type, int size, bool big_endian>
 161 void
 162 Copy_relocs<sh_type, size, big_endian>::add_copy_reloc(
 163     Symbol* sym,
 164     section_size_type offset,
 165     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
 166 {
 167   reloc_section->add_global(sym, this->copy_reloc_type_, this->dynbss_,
 168                             offset, 0);
 169 }
 170
 171 // Save a relocation to possibly be emitted later.
 172
 173 template<int sh_type, int size, bool big_endian>
 174 void
 175 Copy_relocs<sh_type, size, big_endian>::save(
 176     Symbol* sym,
 177     Sized_relobj<size, big_endian>* object,
 178     unsigned int shndx,
 179     Output_section* output_section,
 180     const Reloc& rel)
 181 {
 182   unsigned int reloc_type = elfcpp::elf_r_type<size>(rel.get_r_info());
 183   typename elfcpp::Elf_types<size>::Elf_Addr addend =
 184     Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&rel);
 185   this->entries_.push_back(Copy_reloc_entry(sym, reloc_type, object, shndx,
 186                                             output_section, rel.get_r_offset(),
 187                                             addend));
 188 }
 189
 190 // Emit any saved relocs.
 191
 192 template<int sh_type, int size, bool big_endian>
 193 void
 194 Copy_relocs<sh_type, size, big_endian>::emit(
 195     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
 196 {
 197   for (typename Copy_reloc_entries::iterator p = this->entries_.begin();
 198        p != this->entries_.end();
 199        ++p)
 200     p->emit(reloc_section);
 201
 202   // We no longer need the saved information.
 203   this->entries_.clear();
 204 }
 205
 206 // Instantiate the templates we need.
 207
 208 #ifdef HAVE_TARGET_32_LITTLE
 209 template
 210 class Copy_relocs<elfcpp::SHT_REL, 32, false>;
 211
 212 template
 213 class Copy_relocs<elfcpp::SHT_RELA, 32, false>;
 214 #endif
 215
 216 #ifdef HAVE_TARGET_32_BIG
 217 template
 218 class Copy_relocs<elfcpp::SHT_REL, 32, true>;
 219
 220 template
 221 class Copy_relocs<elfcpp::SHT_RELA, 32, true>;
 222 #endif
 223
 224 #ifdef HAVE_TARGET_64_LITTLE
 225 template
 226 class Copy_relocs<elfcpp::SHT_REL, 64, false>;
 227
 228 template
 229 class Copy_relocs<elfcpp::SHT_RELA, 64, false>;
 230 #endif
 231
 232 #ifdef HAVE_TARGET_64_BIG
 233 template
 234 class Copy_relocs<elfcpp::SHT_REL, 64, true>;
 235
 236 template
 237 class Copy_relocs<elfcpp::SHT_RELA, 64, true>;
 238 #endif
 239
 240 } // End namespace gold.