1 // gc.h -- garbage collection of unused sections
3 // Copyright 2009, 2010, 2011, 2012 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.
39 template<int size, bool big_endian>
40 class Sized_relobj_file;
42 template<int sh_type, int size, bool big_endian>
46 class General_options;
49 class Garbage_collection
53 typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
54 typedef std::map<Section_id, Sections_reachable> Section_ref;
55 typedef std::queue<Section_id> Worklist_type;
56 // This maps the name of the section which can be represented as a C
57 // identifier (cident) to the list of sections that have that name.
58 // Different object files can have cident sections with the same name.
59 typedef std::map<std::string, Sections_reachable> Cident_section_map;
62 : is_worklist_ready_(false)
65 // Accessor methods for the private members.
69 { return referenced_list_; }
73 { return this->section_reloc_map_; }
77 { return this->work_list_; }
81 { return this->is_worklist_ready_; }
85 { this->is_worklist_ready_ = true; }
88 do_transitive_closure();
91 is_section_garbage(Object* obj, unsigned int shndx)
92 { return (this->referenced_list().find(Section_id(obj, shndx))
93 == this->referenced_list().end()); }
97 { return &cident_sections_; }
100 add_cident_section(std::string section_name,
102 { this->cident_sections_[section_name].insert(secn); }
104 // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
105 // DST_SHNDX-th section of DST_OBJECT.
107 add_reference(Object* src_object, unsigned int src_shndx,
108 Object* dst_object, unsigned int dst_shndx)
110 Section_id src_id(src_object, src_shndx);
111 Section_id dst_id(dst_object, dst_shndx);
112 Section_ref::iterator p = this->section_reloc_map_.find(src_id);
113 if (p == this->section_reloc_map_.end())
114 this->section_reloc_map_[src_id].insert(dst_id);
116 p->second.insert(dst_id);
121 Worklist_type work_list_;
122 bool is_worklist_ready_;
123 Section_ref section_reloc_map_;
124 Sections_reachable referenced_list_;
125 Cident_section_map cident_sections_;
128 // Data to pass between successive invocations of do_layout
129 // in object.cc while garbage collecting. This data structure
130 // is filled by using the data from Read_symbols_data.
135 unsigned char* section_headers_data;
137 unsigned char* section_names_data;
138 // Size of section name data in bytes.
139 section_size_type section_names_size;
141 unsigned char* symbols_data;
142 // Size of symbol data in bytes.
143 section_size_type symbols_size;
144 // Offset of external symbols within symbol data. This structure
145 // sometimes contains only external symbols, in which case this will
146 // be zero. Sometimes it contains all symbols.
147 section_offset_type external_symbols_offset;
149 unsigned char* symbol_names_data;
150 // Size of symbol name data in bytes.
151 section_size_type symbol_names_size;
154 // Relocations of type SHT_REL store the addend value in their bytes.
155 // This function returns the size of the embedded addend which is
156 // nothing but the size of the relocation.
158 template<typename Classify_reloc>
160 get_embedded_addend_size(int sh_type, int r_type, Relobj* obj)
162 if (sh_type != elfcpp::SHT_REL)
164 Classify_reloc classify_reloc;
165 return classify_reloc.get_size_for_reloc(r_type, obj);
168 // This function implements the generic part of reloc
169 // processing to map a section to all the sections it
170 // references through relocs. It is called only during
171 // garbage collection (--gc-sections) and identical code
174 template<int size, bool big_endian, typename Target_type, int sh_type,
175 typename Scan, typename Classify_reloc>
178 Symbol_table* symtab,
181 Sized_relobj_file<size, big_endian>* src_obj,
182 unsigned int src_indx,
183 const unsigned char* prelocs,
188 const unsigned char* plocal_syms)
192 typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
193 const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
194 const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
196 Icf::Sections_reachable_info* secvec = NULL;
197 Icf::Symbol_info* symvec = NULL;
198 Icf::Addend_info* addendvec = NULL;
199 Icf::Offset_info* offsetvec = NULL;
200 Icf::Reloc_addend_size_info* reloc_addend_size_vec = NULL;
201 bool is_icf_tracked = false;
202 const char* cident_section_name = NULL;
204 std::string src_section_name = (parameters->options().icf_enabled()
205 ? src_obj->section_name(src_indx)
208 bool check_section_for_function_pointers = false;
210 if (parameters->options().icf_enabled()
211 && is_section_foldable_candidate(src_section_name.c_str()))
213 is_icf_tracked = true;
214 Section_id src_id(src_obj, src_indx);
215 Icf::Reloc_info* reloc_info =
216 &symtab->icf()->reloc_info_list()[src_id];
217 secvec = &reloc_info->section_info;
218 symvec = &reloc_info->symbol_info;
219 addendvec = &reloc_info->addend_info;
220 offsetvec = &reloc_info->offset_info;
221 reloc_addend_size_vec = &reloc_info->reloc_addend_size_info;
224 check_section_for_function_pointers =
225 symtab->icf()->check_section_for_function_pointers(src_section_name,
228 for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
230 Reltype reloc(prelocs);
231 typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
232 unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
233 unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
234 typename elfcpp::Elf_types<size>::Elf_Swxword addend =
235 Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);
237 unsigned int dst_indx;
238 typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
241 if (r_sym < local_count)
243 gold_assert(plocal_syms != NULL);
244 typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
246 dst_indx = lsym.get_st_shndx();
248 dst_indx = src_obj->adjust_sym_shndx(r_sym, dst_indx, &is_ordinary);
250 dst_off = lsym.get_st_value() + addend;
254 Address symvalue = dst_off - addend;
258 loc.object = dst_obj;
259 loc.shndx = dst_indx;
260 loc.offset = convert_types<off_t, Address>(dst_off);
261 // Look through function descriptors.
262 parameters->target().function_location(&loc);
263 if (loc.shndx != dst_indx)
265 // Modify symvalue/addend to the code entry.
266 symvalue = loc.offset;
269 (*secvec).push_back(Section_id(loc.object, loc.shndx));
272 (*secvec).push_back(Section_id(NULL, 0));
273 (*symvec).push_back(NULL);
274 (*addendvec).push_back(std::make_pair(
275 static_cast<long long>(symvalue),
276 static_cast<long long>(addend)));
277 uint64_t reloc_offset =
278 convert_to_section_size_type(reloc.get_r_offset());
279 (*offsetvec).push_back(reloc_offset);
280 (*reloc_addend_size_vec).push_back(
281 get_embedded_addend_size<Classify_reloc>(sh_type, r_type,
285 // When doing safe folding, check to see if this relocation is that
286 // of a function pointer being taken.
288 && check_section_for_function_pointers
289 && lsym.get_st_type() != elfcpp::STT_OBJECT
290 && scan.local_reloc_may_be_function_pointer(symtab, NULL, NULL,
294 symtab->icf()->set_section_has_function_pointers(
295 src_obj, lsym.get_st_shndx());
297 if (!is_ordinary || dst_indx == src_indx)
302 Symbol* gsym = src_obj->global_symbol(r_sym);
303 gold_assert(gsym != NULL);
304 if (gsym->is_forwarder())
305 gsym = symtab->resolve_forwards(gsym);
309 bool is_ordinary = false;
310 if (gsym->source() == Symbol::FROM_OBJECT)
312 dst_obj = gsym->object();
313 dst_indx = gsym->shndx(&is_ordinary);
315 dst_off = static_cast<const Sized_symbol<size>*>(gsym)->value();
318 // When doing safe folding, check to see if this relocation is that
319 // of a function pointer being taken.
320 if (gsym->source() == Symbol::FROM_OBJECT
321 && check_section_for_function_pointers
322 && gsym->type() != elfcpp::STT_OBJECT
324 || scan.global_reloc_may_be_function_pointer(
325 symtab, NULL, NULL, src_obj, src_indx, NULL, reloc,
327 symtab->icf()->set_section_has_function_pointers(dst_obj, dst_indx);
329 // If the symbol name matches '__start_XXX' then the section with
330 // the C identifier like name 'XXX' should not be garbage collected.
331 // A similar treatment to symbols with the name '__stop_XXX'.
332 if (is_prefix_of(cident_section_start_prefix, gsym->name()))
334 cident_section_name = (gsym->name()
335 + strlen(cident_section_start_prefix));
337 else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))
339 cident_section_name = (gsym->name()
340 + strlen(cident_section_stop_prefix));
344 Address symvalue = dst_off - addend;
345 if (is_ordinary && gsym->source() == Symbol::FROM_OBJECT)
348 loc.object = dst_obj;
349 loc.shndx = dst_indx;
350 loc.offset = convert_types<off_t, Address>(dst_off);
351 // Look through function descriptors.
352 parameters->target().function_location(&loc);
353 if (loc.shndx != dst_indx)
355 // Modify symvalue/addend to the code entry.
356 symvalue = loc.offset;
359 (*secvec).push_back(Section_id(loc.object, loc.shndx));
362 (*secvec).push_back(Section_id(NULL, 0));
363 (*symvec).push_back(gsym);
364 (*addendvec).push_back(std::make_pair(
365 static_cast<long long>(symvalue),
366 static_cast<long long>(addend)));
367 uint64_t reloc_offset =
368 convert_to_section_size_type(reloc.get_r_offset());
369 (*offsetvec).push_back(reloc_offset);
370 (*reloc_addend_size_vec).push_back(
371 get_embedded_addend_size<Classify_reloc>(sh_type, r_type,
375 if (gsym->source() != Symbol::FROM_OBJECT)
380 if (parameters->options().gc_sections())
382 symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx);
383 parameters->sized_target<size, big_endian>()
384 ->gc_add_reference(symtab, src_obj, src_indx,
385 dst_obj, dst_indx, dst_off);
386 if (cident_section_name != NULL)
388 Garbage_collection::Cident_section_map::iterator ele =
389 symtab->gc()->cident_sections()->find(std::string(cident_section_name));
390 if (ele == symtab->gc()->cident_sections()->end())
392 Section_id src_id(src_obj, src_indx);
393 Garbage_collection::Sections_reachable&
394 v(symtab->gc()->section_reloc_map()[src_id]);
395 Garbage_collection::Sections_reachable& cident_secn(ele->second);
396 for (Garbage_collection::Sections_reachable::iterator it_v
397 = cident_secn.begin();
398 it_v != cident_secn.end();
409 } // End of namespace gold.