gold/copy-relocs.h

   1 // copy-relocs.h -- handle COPY relocations for gold   -*- C++ -*-
   2
   3 // Copyright (C) 2006-2017 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)