gold/copy-relocs.h

   1 // copy-relocs.h -- handle COPY relocations for gold   -*- C++ -*-
   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 #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     : copy_reloc_type_(copy_reloc_type), dynbss_(NULL), entries_()
  58   { }
  59
  60   // This is called while scanning relocs if we see a relocation
  61   // against a symbol which may force us to generate a COPY reloc.
  62   // SYM is the symbol.  OBJECT is the object whose relocs we are
  63   // scanning.  The relocation is being applied to section SHNDX in
  64   // OBJECT.  OUTPUT_SECTION is the output section where section SHNDX
  65   // will wind up.  REL is the reloc itself.  The Output_data_reloc
  66   // section is where the dynamic relocs are put.
  67   void
  68   copy_reloc(Symbol_table*, Layout*, Sized_symbol<size>* sym,
  69              Sized_relobj<size, big_endian>* object,
  70              unsigned int shndx, Output_section* output_section,
  71              const Reloc& rel,
  72              Output_data_reloc<sh_type, true, size, big_endian>*);
  73
  74   // Return whether there are any saved relocations.
  75   bool
  76   any_saved_relocs() const
  77   { return !this->entries_.empty(); }
  78
  79   // Emit any saved relocations which turn out to be needed.  This is
  80   // called after all the relocs have been scanned.
  81   void
  82   emit(Output_data_reloc<sh_type, true, size, big_endian>*);
  83
  84  private:
  85   typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
  86   typedef typename elfcpp::Elf_types<size>::Elf_Addr Addend;
  87
  88   // This POD class holds the relocations we are saving.  We will emit
  89   // these relocations if it turns out that the symbol does not
  90   // require a COPY relocation.
  91   class Copy_reloc_entry
  92   {
  93    public:
  94     Copy_reloc_entry(Symbol* sym, unsigned int reloc_type,
  95                      Sized_relobj<size, big_endian>* relobj,
  96                      unsigned int shndx,
  97                      Output_section* output_section,
  98                      Address address, Addend addend)
  99       : sym_(sym), reloc_type_(reloc_type), relobj_(relobj),
 100         shndx_(shndx), output_section_(output_section),
 101         address_(address), addend_(addend)
 102     { }
 103
 104     // Emit this reloc if appropriate.  This is called after we have
 105     // scanned all the relocations, so we know whether we emitted a
 106     // COPY relocation for SYM_.
 107     void
 108     emit(Output_data_reloc<sh_type, true, size, big_endian>*);
 109
 110    private:
 111     Symbol* sym_;
 112     unsigned int reloc_type_;
 113     Sized_relobj<size, big_endian>* relobj_;
 114     unsigned int shndx_;
 115     Output_section* output_section_;
 116     Address address_;
 117     Addend addend_;
 118   };
 119
 120   // A list of relocs to be saved.
 121   typedef std::vector<Copy_reloc_entry> Copy_reloc_entries;
 122
 123   // Return whether we need a COPY reloc.
 124   bool
 125   need_copy_reloc(Sized_symbol<size>* gsym,
 126                   Sized_relobj<size, big_endian>* object,
 127                   unsigned int shndx) const;
 128
 129   // Emit a COPY reloc.
 130   void
 131   emit_copy_reloc(Symbol_table*, Layout*, Sized_symbol<size>*,
 132                   Output_data_reloc<sh_type, true, size, big_endian>*);
 133
 134   // Add a COPY reloc to the dynamic reloc section.
 135   void
 136   add_copy_reloc(Symbol*, section_size_type,
 137                  Output_data_reloc<sh_type, true, size, big_endian>*);
 138
 139   // Save a reloc against SYM for possible emission later.
 140   void
 141   save(Symbol*, Sized_relobj<size, big_endian>*, unsigned int shndx,
 142        Output_section*, const Reloc& rel);
 143
 144   // The target specific relocation type of the COPY relocation.
 145   const unsigned int copy_reloc_type_;
 146   // The dynamic BSS data which goes into the .bss section.  This is
 147   // where variables which require COPY relocations are placed.
 148   Output_data_space* dynbss_;
 149   // The list of relocs we are saving.
 150   Copy_reloc_entries entries_;
 151 };
 152
 153 } // End namespace gold.
 154
 155 #endif // !defined(GOLD_COPY_RELOCS_H)