Merge branch 'vendor/XZ'
[dragonfly.git] / contrib / binutils-2.24 / gold / gc.h
1 // gc.h -- garbage collection of unused sections
2
3 // Copyright 2009, 2010, 2011, 2012 Free Software Foundation, Inc.
4 // Written by Sriraman Tallam <tmsriram@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_GC_H
24 #define GOLD_GC_H
25
26 #include <queue>
27 #include <vector>
28
29 #include "elfcpp.h"
30 #include "symtab.h"
31 #include "object.h"
32 #include "icf.h"
33
34 namespace gold
35 {
36
37 class Object;
38
39 template<int size, bool big_endian>
40 class Sized_relobj_file;
41
42 template<int sh_type, int size, bool big_endian>
43 struct Reloc_types;
44
45 class Output_section;
46 class General_options;
47 class Layout;
48
49 class Garbage_collection
50 {
51  public:
52
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;
60
61   Garbage_collection()
62   : is_worklist_ready_(false)
63   { }
64
65   // Accessor methods for the private members.
66
67   Sections_reachable&
68   referenced_list()
69   { return referenced_list_; }
70
71   Section_ref&
72   section_reloc_map()
73   { return this->section_reloc_map_; }
74
75   Worklist_type&
76   worklist()
77   { return this->work_list_; }
78
79   bool
80   is_worklist_ready()
81   { return this->is_worklist_ready_; }
82
83   void
84   worklist_ready()
85   { this->is_worklist_ready_ = true; }
86
87   void
88   do_transitive_closure();
89
90   bool
91   is_section_garbage(Object* obj, unsigned int shndx)
92   { return (this->referenced_list().find(Section_id(obj, shndx))
93             == this->referenced_list().end()); }
94
95   Cident_section_map*
96   cident_sections()
97   { return &cident_sections_; }
98
99   void
100   add_cident_section(std::string section_name,
101                      Section_id secn)
102   { this->cident_sections_[section_name].insert(secn); }
103
104   // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
105   // DST_SHNDX-th section of DST_OBJECT.
106   void
107   add_reference(Object* src_object, unsigned int src_shndx,
108                 Object* dst_object, unsigned int dst_shndx)
109   {
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);
115     else
116       p->second.insert(dst_id);
117   }
118
119  private:
120
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_;
126 };
127
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.
131
132 struct Symbols_data
133 {
134   // Section headers.
135   unsigned char* section_headers_data;
136   // Section names.
137   unsigned char* section_names_data;
138   // Size of section name data in bytes.
139   section_size_type section_names_size;
140   // Symbol data.
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;
148   // Symbol names.
149   unsigned char* symbol_names_data;
150   // Size of symbol name data in bytes.
151   section_size_type symbol_names_size;
152 };
153
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.
157
158 template<typename Classify_reloc>
159 inline unsigned int
160 get_embedded_addend_size(int sh_type, int r_type, Relobj* obj)
161 {
162   if (sh_type != elfcpp::SHT_REL)
163     return 0;
164   Classify_reloc classify_reloc;
165   return classify_reloc.get_size_for_reloc(r_type, obj);
166 }
167
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
172 // folding (--icf).
173
174 template<int size, bool big_endian, typename Target_type, int sh_type,
175          typename Scan, typename Classify_reloc>
176 inline void
177 gc_process_relocs(
178     Symbol_table* symtab,
179     Layout*,
180     Target_type* target,
181     Sized_relobj_file<size, big_endian>* src_obj,
182     unsigned int src_indx,
183     const unsigned char* prelocs,
184     size_t reloc_count,
185     Output_section*,
186     bool,
187     size_t local_count,
188     const unsigned char* plocal_syms)
189 {
190   Scan scan;
191
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;
195
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;
203
204   std::string src_section_name = (parameters->options().icf_enabled()
205                                   ? src_obj->section_name(src_indx)
206                                   : "");
207
208   bool check_section_for_function_pointers = false;
209
210   if (parameters->options().icf_enabled()
211       && is_section_foldable_candidate(src_section_name.c_str()))
212     {
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;
222     }
223
224   check_section_for_function_pointers =
225     symtab->icf()->check_section_for_function_pointers(src_section_name,
226                                                        target);
227
228   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
229     {
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);
236       Object* dst_obj;
237       unsigned int dst_indx;
238       typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
239       Address dst_off;
240
241       if (r_sym < local_count)
242         {
243           gold_assert(plocal_syms != NULL);
244           typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
245                                                       + r_sym * sym_size);
246           dst_indx = lsym.get_st_shndx();
247           bool is_ordinary;
248           dst_indx = src_obj->adjust_sym_shndx(r_sym, dst_indx, &is_ordinary);
249           dst_obj = src_obj;
250           dst_off = lsym.get_st_value() + addend;
251
252           if (is_icf_tracked)
253             {
254               Address symvalue = dst_off - addend;
255               if (is_ordinary) 
256                 (*secvec).push_back(Section_id(dst_obj, dst_indx));
257               else
258                 (*secvec).push_back(Section_id(NULL, 0));
259               (*symvec).push_back(NULL);
260               (*addendvec).push_back(std::make_pair(
261                                         static_cast<long long>(symvalue),
262                                         static_cast<long long>(addend)));
263               uint64_t reloc_offset =
264                 convert_to_section_size_type(reloc.get_r_offset());
265               (*offsetvec).push_back(reloc_offset);
266               (*reloc_addend_size_vec).push_back(
267                 get_embedded_addend_size<Classify_reloc>(sh_type, r_type,
268                                                          src_obj));
269             }
270
271           // When doing safe folding, check to see if this relocation is that
272           // of a function pointer being taken.
273           if (is_ordinary
274               && check_section_for_function_pointers
275               && lsym.get_st_type() != elfcpp::STT_OBJECT
276               && scan.local_reloc_may_be_function_pointer(symtab, NULL, NULL,
277                                                           src_obj, src_indx,
278                                                           NULL, reloc, r_type,
279                                                           lsym))
280             symtab->icf()->set_section_has_function_pointers(
281               src_obj, lsym.get_st_shndx());
282
283           if (!is_ordinary || dst_indx == src_indx)
284             continue;
285         }
286       else
287         {
288           Symbol* gsym = src_obj->global_symbol(r_sym);
289           gold_assert(gsym != NULL);
290           if (gsym->is_forwarder())
291             gsym = symtab->resolve_forwards(gsym);
292
293           dst_obj = NULL;
294           dst_indx = 0;
295           bool is_ordinary = false;
296           if (gsym->source() == Symbol::FROM_OBJECT)
297             {
298               dst_obj = gsym->object();
299               dst_indx = gsym->shndx(&is_ordinary);
300             }
301           dst_off = static_cast<const Sized_symbol<size>*>(gsym)->value();
302           dst_off += addend;
303
304           // When doing safe folding, check to see if this relocation is that
305           // of a function pointer being taken.
306           if (gsym->source() == Symbol::FROM_OBJECT
307               && check_section_for_function_pointers
308               && gsym->type() != elfcpp::STT_OBJECT
309               && (!is_ordinary
310                   || scan.global_reloc_may_be_function_pointer(
311                        symtab, NULL, NULL, src_obj, src_indx, NULL, reloc,
312                        r_type, gsym)))
313             symtab->icf()->set_section_has_function_pointers(dst_obj, dst_indx);
314
315           // If the symbol name matches '__start_XXX' then the section with
316           // the C identifier like name 'XXX' should not be garbage collected.
317           // A similar treatment to symbols with the name '__stop_XXX'.
318           if (is_prefix_of(cident_section_start_prefix, gsym->name()))
319             {
320               cident_section_name = (gsym->name() 
321                                      + strlen(cident_section_start_prefix));
322             }
323           else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))
324             {
325               cident_section_name = (gsym->name() 
326                                      + strlen(cident_section_stop_prefix));
327             }
328           if (is_icf_tracked)
329             {
330               Address symvalue = dst_off - addend;
331               if (is_ordinary && gsym->source() == Symbol::FROM_OBJECT)
332                 (*secvec).push_back(Section_id(dst_obj, dst_indx));
333               else
334                 (*secvec).push_back(Section_id(NULL, 0));
335               (*symvec).push_back(gsym);
336               (*addendvec).push_back(std::make_pair(
337                                         static_cast<long long>(symvalue),
338                                         static_cast<long long>(addend)));
339               uint64_t reloc_offset =
340                 convert_to_section_size_type(reloc.get_r_offset());
341               (*offsetvec).push_back(reloc_offset);
342               (*reloc_addend_size_vec).push_back(
343                 get_embedded_addend_size<Classify_reloc>(sh_type, r_type,
344                                                          src_obj));
345             }
346
347           if (gsym->source() != Symbol::FROM_OBJECT)
348             continue;
349           if (!is_ordinary)
350             continue;
351         }
352       if (parameters->options().gc_sections())
353         {
354           symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx);
355           parameters->sized_target<size, big_endian>()
356             ->gc_add_reference(symtab, src_obj, src_indx,
357                                dst_obj, dst_indx, dst_off);
358           if (cident_section_name != NULL)
359             {
360               Garbage_collection::Cident_section_map::iterator ele =
361                 symtab->gc()->cident_sections()->find(std::string(cident_section_name));
362               if (ele == symtab->gc()->cident_sections()->end())
363                 continue;
364               Section_id src_id(src_obj, src_indx);
365               Garbage_collection::Sections_reachable&
366                 v(symtab->gc()->section_reloc_map()[src_id]);
367               Garbage_collection::Sections_reachable& cident_secn(ele->second);
368               for (Garbage_collection::Sections_reachable::iterator it_v
369                      = cident_secn.begin();
370                    it_v != cident_secn.end();
371                    ++it_v)
372                 {
373                   v.insert(*it_v);
374                 }
375             }
376         }
377     }
378   return;
379 }
380
381 } // End of namespace gold.
382
383 #endif