1 // copy-relocs.cc -- handle COPY relocations for gold.
2 
3 // Copyright (C) 2006-2020 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 methods.
32 
33 // Handle a relocation against a symbol which may force us to generate
34 // a COPY reloc.
35 
36 template<int sh_type, int size, bool big_endian>
37 void
38 Copy_relocs<sh_type, size, big_endian>::copy_reloc(
39     Symbol_table* symtab,
40     Layout* layout,
41     Sized_symbol<size>* sym,
42     Sized_relobj_file<size, big_endian>* object,
43     unsigned int shndx,
44     Output_section* output_section,
45     unsigned int r_type,
46     typename elfcpp::Elf_types<size>::Elf_Addr r_offset,
47     typename elfcpp::Elf_types<size>::Elf_Swxword r_addend,
48     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
49 {
50   if (this->need_copy_reloc(sym, object, shndx))
51     this->make_copy_reloc(symtab, layout, sym, object, reloc_section);
52   else
53     {
54       // We may not need a COPY relocation.  Save this relocation to
55       // possibly be emitted later.
56       this->save(sym, object, shndx, output_section,
57 		 r_type, r_offset, r_addend);
58     }
59 }
60 
61 // Return whether we need a COPY reloc for a relocation against SYM.
62 // The relocation is begin applied to section SHNDX in OBJECT.
63 
64 template<int sh_type, int size, bool big_endian>
65 bool
66 Copy_relocs<sh_type, size, big_endian>::need_copy_reloc(
67     Sized_symbol<size>* sym,
68     Sized_relobj_file<size, big_endian>* object,
69     unsigned int shndx) const
70 {
71   if (!parameters->options().copyreloc())
72     return false;
73 
74   if (sym->symsize() == 0)
75     return false;
76 
77   // If this is a readonly section, then we need a COPY reloc.
78   // Otherwise we can use a dynamic reloc.  Note that calling
79   // section_flags here can be slow, as the information is not cached;
80   // fortunately we shouldn't see too many potential COPY relocs.
81   if ((object->section_flags(shndx) & elfcpp::SHF_WRITE) == 0)
82     return true;
83 
84   return false;
85 }
86 
87 // Emit a COPY relocation for SYM.
88 
89 template<int sh_type, int size, bool big_endian>
90 void
91 Copy_relocs<sh_type, size, big_endian>::emit_copy_reloc(
92     Symbol_table* symtab,
93     Sized_symbol<size>* sym,
94     Output_data* posd,
95     off_t offset,
96     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
97 {
98   // Define the symbol as being copied.
99   symtab->define_with_copy_reloc(sym, posd, offset);
100 
101   // Add the COPY relocation to the dynamic reloc section.
102   reloc_section->add_global_generic(sym, this->copy_reloc_type_, posd,
103 				    offset, 0);
104 }
105 
106 // Make a COPY relocation for SYM and emit it.
107 
108 template<int sh_type, int size, bool big_endian>
109 void
110 Copy_relocs<sh_type, size, big_endian>::make_copy_reloc(
111     Symbol_table* symtab,
112     Layout* layout,
113     Sized_symbol<size>* sym,
114     Sized_relobj_file<size, big_endian>* object,
115     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
116 {
117   // We should not be here if -z nocopyreloc is given.
118   gold_assert(parameters->options().copyreloc());
119 
120   gold_assert(sym->is_from_dynobj());
121 
122   // The symbol must not have protected visibility.
123   if (sym->is_protected())
124     {
125       gold_error(_("%s: cannot make copy relocation for "
126 		   "protected symbol '%s', defined in %s"),
127 		 object->name().c_str(),
128 		 sym->name(),
129 		 sym->object()->name().c_str());
130     }
131 
132   typename elfcpp::Elf_types<size>::Elf_WXword symsize = sym->symsize();
133 
134   // There is no defined way to determine the required alignment of
135   // the symbol.  We know that the symbol is defined in a dynamic
136   // object.  We start with the alignment of the section in which it
137   // is defined; presumably we do not require an alignment larger than
138   // that.  Then we reduce that alignment if the symbol is not aligned
139   // within the section.
140   bool is_ordinary;
141   unsigned int shndx = sym->shndx(&is_ordinary);
142   gold_assert(is_ordinary);
143   typename elfcpp::Elf_types<size>::Elf_WXword addralign;
144   bool is_readonly = false;
145 
146   {
147     // Lock the object so we can read from it.  This is only called
148     // single-threaded from scan_relocs, so it is OK to lock.
149     // Unfortunately we have no way to pass in a Task token.
150     const Task* dummy_task = reinterpret_cast<const Task*>(-1);
151     Object* obj = sym->object();
152     Task_lock_obj<Object> tl(dummy_task, obj);
153     addralign = obj->section_addralign(shndx);
154     if (parameters->options().relro())
155       {
156 	if ((obj->section_flags(shndx) & elfcpp::SHF_WRITE) == 0)
157 	  is_readonly = true;
158 	else
159 	  {
160 	    // Symbols in .data.rel.ro should also be treated as read-only.
161 	    if (obj->section_name(shndx) == ".data.rel.ro")
162 	      is_readonly = true;
163 	  }
164       }
165   }
166 
167   typename Sized_symbol<size>::Value_type value = sym->value();
168   while ((value & (addralign - 1)) != 0)
169     addralign >>= 1;
170 
171   // Mark the dynamic object as needed for the --as-needed option.
172   sym->object()->set_is_needed();
173 
174   Output_data_space* dynbss;
175 
176   if (is_readonly)
177     {
178       if (this->dynrelro_ == NULL)
179 	{
180 	  this->dynrelro_ = new Output_data_space(addralign, "** dynrelro");
181 	  layout->add_output_section_data(".data.rel.ro",
182 					  elfcpp::SHT_PROGBITS,
183 					  elfcpp::SHF_ALLOC | elfcpp::SHF_WRITE,
184 					  this->dynrelro_, ORDER_RELRO, false);
185 	}
186       dynbss = this->dynrelro_;
187     }
188   else
189     {
190       if (this->dynbss_ == NULL)
191 	{
192 	  this->dynbss_ = new Output_data_space(addralign, "** dynbss");
193 	  layout->add_output_section_data(".bss",
194 					  elfcpp::SHT_NOBITS,
195 					  elfcpp::SHF_ALLOC | elfcpp::SHF_WRITE,
196 					  this->dynbss_, ORDER_BSS, false);
197 	}
198       dynbss = this->dynbss_;
199     }
200 
201   if (addralign > dynbss->addralign())
202     dynbss->set_space_alignment(addralign);
203 
204   section_size_type dynbss_size =
205     convert_to_section_size_type(dynbss->current_data_size());
206   dynbss_size = align_address(dynbss_size, addralign);
207   section_size_type offset = dynbss_size;
208   dynbss->set_current_data_size(dynbss_size + symsize);
209 
210   this->emit_copy_reloc(symtab, sym, dynbss, offset, reloc_section);
211 }
212 
213 // Save a relocation to possibly be emitted later.
214 
215 template<int sh_type, int size, bool big_endian>
216 void
217 Copy_relocs<sh_type, size, big_endian>::save(
218     Symbol* sym,
219     Sized_relobj_file<size, big_endian>* object,
220     unsigned int shndx,
221     Output_section* output_section,
222     unsigned int r_type,
223     typename elfcpp::Elf_types<size>::Elf_Addr r_offset,
224     typename elfcpp::Elf_types<size>::Elf_Swxword r_addend)
225 {
226   this->entries_.push_back(Copy_reloc_entry(sym, r_type, object, shndx,
227 					    output_section, r_offset,
228 					    r_addend));
229 }
230 
231 // Emit any saved relocs.
232 
233 template<int sh_type, int size, bool big_endian>
234 void
235 Copy_relocs<sh_type, size, big_endian>::emit(
236     Output_data_reloc<sh_type, true, size, big_endian>* reloc_section)
237 {
238   for (typename Copy_reloc_entries::iterator p = this->entries_.begin();
239        p != this->entries_.end();
240        ++p)
241     {
242       Copy_reloc_entry& entry = *p;
243 
244       // If the symbol is no longer defined in a dynamic object, then we
245       // emitted a COPY relocation, and we do not want to emit this
246       // dynamic relocation.
247       if (entry.sym_->is_from_dynobj())
248         reloc_section->add_global_generic(entry.sym_, entry.reloc_type_,
249                                           entry.output_section_, entry.relobj_,
250                                           entry.shndx_, entry.address_,
251                                           entry.addend_);
252     }
253 
254   // We no longer need the saved information.
255   this->entries_.clear();
256 }
257 
258 // Instantiate the templates we need.
259 
260 #ifdef HAVE_TARGET_32_LITTLE
261 template
262 class Copy_relocs<elfcpp::SHT_REL, 32, false>;
263 
264 template
265 class Copy_relocs<elfcpp::SHT_RELA, 32, false>;
266 #endif
267 
268 #ifdef HAVE_TARGET_32_BIG
269 template
270 class Copy_relocs<elfcpp::SHT_REL, 32, true>;
271 
272 template
273 class Copy_relocs<elfcpp::SHT_RELA, 32, true>;
274 #endif
275 
276 #ifdef HAVE_TARGET_64_LITTLE
277 template
278 class Copy_relocs<elfcpp::SHT_REL, 64, false>;
279 
280 template
281 class Copy_relocs<elfcpp::SHT_RELA, 64, false>;
282 #endif
283 
284 #ifdef HAVE_TARGET_64_BIG
285 template
286 class Copy_relocs<elfcpp::SHT_REL, 64, true>;
287 
288 template
289 class Copy_relocs<elfcpp::SHT_RELA, 64, true>;
290 #endif
291 
292 } // End namespace gold.
293