1 // copy-relocs.h -- handle COPY relocations for gold -*- C++ -*-
2
3 // Copyright (C) 2006-2023 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)