1 // gc.h -- garbage collection of unused sections
3 // Copyright 2009, 2010 Free Software Foundation, Inc.
4 // Written by Sriraman Tallam <tmsriram@google.com>.
6 // This file is part of gold.
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.
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.
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.
38 template<int size, bool big_endian>
41 template<int sh_type, int size, bool big_endian>
45 class General_options;
48 typedef std::pair<Object *, unsigned int> Section_id;
50 class Garbage_collection
52 struct Section_id_hash
54 size_t operator()(const Section_id& loc) const
55 { return reinterpret_cast<uintptr_t>(loc.first) ^ loc.second; }
60 typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
61 typedef std::map<Section_id, Sections_reachable> Section_ref;
62 typedef std::queue<Section_id> Worklist_type;
63 // This maps the name of the section which can be represented as a C
64 // identifier (cident) to the list of sections that have that name.
65 // Different object files can have cident sections with the same name.
66 typedef std::map<std::string, Sections_reachable> Cident_section_map;
69 : is_worklist_ready_(false)
72 // Accessor methods for the private members.
76 { return referenced_list_; }
80 { return this->section_reloc_map_; }
84 { return this->work_list_; }
88 { return this->is_worklist_ready_; }
92 { this->is_worklist_ready_ = true; }
95 do_transitive_closure();
98 is_section_garbage(Object* obj, unsigned int shndx)
99 { return (this->referenced_list().find(Section_id(obj, shndx))
100 == this->referenced_list().end()); }
104 { return &cident_sections_; }
107 add_cident_section(std::string section_name,
109 { this->cident_sections_[section_name].insert(secn); }
111 // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
112 // DST_SHNDX-th section of DST_OBJECT.
114 add_reference(Object* src_object, unsigned int src_shndx,
115 Object* dst_object, unsigned int dst_shndx)
117 Section_id src_id(src_object, src_shndx);
118 Section_id dst_id(dst_object, dst_shndx);
119 Section_ref::iterator p = this->section_reloc_map_.find(src_id);
120 if (p == this->section_reloc_map_.end())
121 this->section_reloc_map_[src_id].insert(dst_id);
123 p->second.insert(dst_id);
128 Worklist_type work_list_;
129 bool is_worklist_ready_;
130 Section_ref section_reloc_map_;
131 Sections_reachable referenced_list_;
132 Cident_section_map cident_sections_;
135 // Data to pass between successive invocations of do_layout
136 // in object.cc while garbage collecting. This data structure
137 // is filled by using the data from Read_symbols_data.
142 unsigned char* section_headers_data;
144 unsigned char* section_names_data;
145 // Size of section name data in bytes.
146 section_size_type section_names_size;
148 unsigned char* symbols_data;
149 // Size of symbol data in bytes.
150 section_size_type symbols_size;
151 // Offset of external symbols within symbol data. This structure
152 // sometimes contains only external symbols, in which case this will
153 // be zero. Sometimes it contains all symbols.
154 section_offset_type external_symbols_offset;
156 unsigned char* symbol_names_data;
157 // Size of symbol name data in bytes.
158 section_size_type symbol_names_size;
161 // This function implements the generic part of reloc
162 // processing to map a section to all the sections it
163 // references through relocs. It is called only during
164 // garbage collection (--gc-sections) and identical code
167 template<int size, bool big_endian, typename Target_type, int sh_type,
171 Symbol_table* symtab,
174 Sized_relobj<size, big_endian>* src_obj,
175 unsigned int src_indx,
176 const unsigned char* prelocs,
181 const unsigned char* plocal_syms)
184 unsigned int dst_indx;
186 typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
187 const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
188 const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
190 std::vector<Section_id>* secvec = NULL;
191 std::vector<Symbol*>* symvec = NULL;
192 std::vector<std::pair<long long, long long> >* addendvec = NULL;
193 bool is_icf_tracked = false;
194 const char* cident_section_name = NULL;
196 if (parameters->options().icf_enabled()
197 && is_section_foldable_candidate(src_obj->section_name(src_indx).c_str()))
199 is_icf_tracked = true;
200 Section_id src_id(src_obj, src_indx);
201 secvec = &symtab->icf()->section_reloc_list()[src_id];
202 symvec = &symtab->icf()->symbol_reloc_list()[src_id];
203 addendvec = &symtab->icf()->addend_reloc_list()[src_id];
206 for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
208 Reltype reloc(prelocs);
209 typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
210 unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
211 typename elfcpp::Elf_types<size>::Elf_Swxword addend =
212 Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);
214 if (r_sym < local_count)
216 gold_assert(plocal_syms != NULL);
217 typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
219 unsigned int shndx = lsym.get_st_shndx();
221 shndx = src_obj->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
226 Section_id dst_id(dst_obj, dst_indx);
229 (*secvec).push_back(dst_id);
230 (*symvec).push_back(NULL);
231 long long symvalue = static_cast<long long>(lsym.get_st_value());
232 (*addendvec).push_back(std::make_pair(symvalue,
233 static_cast<long long>(addend)));
235 if (shndx == src_indx)
240 Symbol* gsym = src_obj->global_symbol(r_sym);
241 gold_assert(gsym != NULL);
242 if (gsym->is_forwarder())
243 gsym = symtab->resolve_forwards(gsym);
244 if (gsym->source() != Symbol::FROM_OBJECT)
247 dst_obj = gsym->object();
248 dst_indx = gsym->shndx(&is_ordinary);
251 Section_id dst_id(dst_obj, dst_indx);
252 // If the symbol name matches '__start_XXX' then the section with
253 // the C identifier like name 'XXX' should not be garbage collected.
254 // A similar treatment to symbols with the name '__stop_XXX'.
255 if (is_prefix_of(cident_section_start_prefix, gsym->name()))
257 cident_section_name = (gsym->name()
258 + strlen(cident_section_start_prefix));
260 else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))
262 cident_section_name = (gsym->name()
263 + strlen(cident_section_stop_prefix));
267 (*secvec).push_back(dst_id);
268 (*symvec).push_back(gsym);
269 Sized_symbol<size>* sized_gsym =
270 static_cast<Sized_symbol<size>* >(gsym);
272 static_cast<long long>(sized_gsym->value());
273 (*addendvec).push_back(std::make_pair(symvalue,
274 static_cast<long long>(addend)));
277 if (parameters->options().gc_sections())
279 symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx);
280 if (cident_section_name != NULL)
282 Garbage_collection::Cident_section_map::iterator ele =
283 symtab->gc()->cident_sections()->find(std::string(cident_section_name));
284 if (ele == symtab->gc()->cident_sections()->end())
286 Section_id src_id(src_obj, src_indx);
287 Garbage_collection::Sections_reachable&
288 v(symtab->gc()->section_reloc_map()[src_id]);
289 Garbage_collection::Sections_reachable& cident_secn(ele->second);
290 for (Garbage_collection::Sections_reachable::iterator it_v
291 = cident_secn.begin();
292 it_v != cident_secn.end();
303 } // End of namespace gold.