1 // copy-relocs.h -- handle COPY relocations for gold   -*- C++ -*-
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 #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:
Copy_relocs(unsigned int copy_reloc_type)56   Copy_relocs(unsigned int copy_reloc_type)
57     : entries_(), copy_reloc_type_(copy_reloc_type), dynbss_(NULL)
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*,
69 	     Layout*,
70 	     Sized_symbol<size>* sym,
71              Sized_relobj_file<size, big_endian>* object,
72 	     unsigned int shndx,
73 	     Output_section* output_section,
74 	     unsigned int r_type,
75 	     typename elfcpp::Elf_types<size>::Elf_Addr r_offset,
76 	     typename elfcpp::Elf_types<size>::Elf_Swxword r_addend,
77 	     Output_data_reloc<sh_type, true, size, big_endian>*);
78 
79   // Return whether there are any saved relocations.
80   bool
any_saved_relocs()81   any_saved_relocs() const
82   { return !this->entries_.empty(); }
83 
84   // Emit any saved relocations which turn out to be needed.  This is
85   // called after all the relocs have been scanned.
86   void
87   emit(Output_data_reloc<sh_type, true, size, big_endian>*);
88 
89   // Emit a COPY reloc.
90   void
91   emit_copy_reloc(Symbol_table*, Sized_symbol<size>*,
92 		  Output_data*, off_t,
93 		  Output_data_reloc<sh_type, true, size, big_endian>*);
94 
95  protected:
96   typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
97   typedef typename elfcpp::Elf_types<size>::Elf_Addr Addend;
98 
99   // This POD class holds the relocations we are saving.  We will emit
100   // these relocations if it turns out that the symbol does not
101   // require a COPY relocation.
102   struct Copy_reloc_entry
103   {
Copy_reloc_entryCopy_reloc_entry104     Copy_reloc_entry(Symbol* sym, unsigned int reloc_type,
105 		     Sized_relobj_file<size, big_endian>* relobj,
106                      unsigned int shndx,
107 		     Output_section* output_section,
108 		     Address address, Addend addend)
109       : sym_(sym), reloc_type_(reloc_type), relobj_(relobj),
110 	shndx_(shndx), output_section_(output_section),
111 	address_(address), addend_(addend)
112     { }
113 
114     Symbol* sym_;
115     unsigned int reloc_type_;
116     Sized_relobj_file<size, big_endian>* relobj_;
117     unsigned int shndx_;
118     Output_section* output_section_;
119     Address address_;
120     Addend addend_;
121   };
122 
123   // Make a new COPY reloc and emit it.
124   void
125   make_copy_reloc(Symbol_table*, Layout*, Sized_symbol<size>*,
126 		  Sized_relobj_file<size, big_endian>* object,
127 		  Output_data_reloc<sh_type, true, size, big_endian>*);
128 
129   // A list of relocs to be saved.
130   typedef std::vector<Copy_reloc_entry> Copy_reloc_entries;
131 
132   // The list of relocs we are saving.
133   Copy_reloc_entries entries_;
134 
135  private:
136   // Return whether we need a COPY reloc.
137   bool
138   need_copy_reloc(Sized_symbol<size>* gsym,
139                   Sized_relobj_file<size, big_endian>* object,
140 		  unsigned int shndx) const;
141 
142   // Save a reloc against SYM for possible emission later.
143   void
144   save(Symbol*,
145        Sized_relobj_file<size, big_endian>*,
146        unsigned int shndx,
147        Output_section*,
148        unsigned int r_type,
149        typename elfcpp::Elf_types<size>::Elf_Addr r_offset,
150        typename elfcpp::Elf_types<size>::Elf_Swxword r_addend);
151 
152   // The target specific relocation type of the COPY relocation.
153   const unsigned int copy_reloc_type_;
154   // The dynamic BSS data which goes into the .bss section.  This is
155   // where variables which require COPY relocations are placed.
156   Output_data_space* dynbss_;
157 };
158 
159 } // End namespace gold.
160 
161 #endif // !defined(GOLD_COPY_RELOCS_H)
162