Merge branch 'vendor/GCC44'
[dragonfly.git] / contrib / binutils-2.22 / gold / gc.h
1 // gc.h -- garbage collection of unused sections
2
3 // Copyright 2009, 2010 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 class 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   Object* dst_obj;
191   unsigned int dst_indx;
192   Scan scan;
193
194   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
195   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
196   const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
197
198   Icf::Sections_reachable_info* secvec = NULL;
199   Icf::Symbol_info* symvec = NULL;
200   Icf::Addend_info* addendvec = NULL;
201   Icf::Offset_info* offsetvec = NULL;
202   Icf::Reloc_addend_size_info* reloc_addend_size_vec = NULL;
203   bool is_icf_tracked = false;
204   const char* cident_section_name = NULL;
205
206   std::string src_section_name = (parameters->options().icf_enabled()
207                                   ? src_obj->section_name(src_indx)
208                                   : "");
209
210   bool check_section_for_function_pointers = false;
211
212   if (parameters->options().icf_enabled()
213       && is_section_foldable_candidate(src_section_name.c_str()))
214     {
215       is_icf_tracked = true;
216       Section_id src_id(src_obj, src_indx);
217       Icf::Reloc_info* reloc_info =
218         &symtab->icf()->reloc_info_list()[src_id];
219       secvec = &reloc_info->section_info;
220       symvec = &reloc_info->symbol_info;
221       addendvec = &reloc_info->addend_info;
222       offsetvec = &reloc_info->offset_info;
223       reloc_addend_size_vec = &reloc_info->reloc_addend_size_info;
224     }
225
226   check_section_for_function_pointers =
227     symtab->icf()->check_section_for_function_pointers(src_section_name,
228                                                        target);
229
230   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
231     {
232       Reltype reloc(prelocs);
233       typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
234       unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
235       unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
236       typename elfcpp::Elf_types<size>::Elf_Swxword addend =
237       Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);
238
239       if (r_sym < local_count)
240         {
241           gold_assert(plocal_syms != NULL);
242           typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
243                                                       + r_sym * sym_size);
244           unsigned int shndx = lsym.get_st_shndx();
245           bool is_ordinary;
246           shndx = src_obj->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
247           dst_obj = src_obj;
248           dst_indx = shndx;
249           if (is_icf_tracked)
250             {
251               if (is_ordinary) 
252                 (*secvec).push_back(Section_id(dst_obj, dst_indx));
253               else
254                 (*secvec).push_back(Section_id(NULL, 0));
255               (*symvec).push_back(NULL);
256               long long symvalue = static_cast<long long>(lsym.get_st_value());
257               (*addendvec).push_back(std::make_pair(symvalue,
258                                               static_cast<long long>(addend)));
259               uint64_t reloc_offset =
260                 convert_to_section_size_type(reloc.get_r_offset());
261               (*offsetvec).push_back(reloc_offset);
262               (*reloc_addend_size_vec).push_back(
263                 get_embedded_addend_size<Classify_reloc>(sh_type, r_type,
264                                                          src_obj));
265             }
266
267           // When doing safe folding, check to see if this relocation is that
268           // of a function pointer being taken.
269           if (is_ordinary
270               && check_section_for_function_pointers
271               && lsym.get_st_type() != elfcpp::STT_OBJECT
272               && scan.local_reloc_may_be_function_pointer(symtab, NULL, NULL,
273                                                           src_obj, src_indx,
274                                                           NULL, reloc, r_type,
275                                                           lsym))
276             symtab->icf()->set_section_has_function_pointers(
277               src_obj, lsym.get_st_shndx());
278
279           if (!is_ordinary || shndx == src_indx)
280             continue;
281         }
282       else
283         {
284           Symbol* gsym = src_obj->global_symbol(r_sym);
285           gold_assert(gsym != NULL);
286           if (gsym->is_forwarder())
287             gsym = symtab->resolve_forwards(gsym);
288
289           dst_obj = NULL;
290           dst_indx = 0;
291           bool is_ordinary = false;
292           if (gsym->source() == Symbol::FROM_OBJECT)
293             {
294               dst_obj = gsym->object();
295               dst_indx = gsym->shndx(&is_ordinary);
296             }
297
298           // When doing safe folding, check to see if this relocation is that
299           // of a function pointer being taken.
300           if (gsym->source() == Symbol::FROM_OBJECT
301               && check_section_for_function_pointers
302               && gsym->type() != elfcpp::STT_OBJECT
303               && (!is_ordinary
304                   || scan.global_reloc_may_be_function_pointer(
305                        symtab, NULL, NULL, src_obj, src_indx, NULL, reloc,
306                        r_type, gsym)))
307             symtab->icf()->set_section_has_function_pointers(dst_obj, dst_indx);
308
309           // If the symbol name matches '__start_XXX' then the section with
310           // the C identifier like name 'XXX' should not be garbage collected.
311           // A similar treatment to symbols with the name '__stop_XXX'.
312           if (is_prefix_of(cident_section_start_prefix, gsym->name()))
313             {
314               cident_section_name = (gsym->name() 
315                                      + strlen(cident_section_start_prefix));
316             }
317           else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))
318             {
319               cident_section_name = (gsym->name() 
320                                      + strlen(cident_section_stop_prefix));
321             }
322           if (is_icf_tracked)
323             {
324               if (is_ordinary && gsym->source() == Symbol::FROM_OBJECT)
325                 (*secvec).push_back(Section_id(dst_obj, dst_indx));
326               else
327                 (*secvec).push_back(Section_id(NULL, 0));
328               (*symvec).push_back(gsym);
329               Sized_symbol<size>* sized_gsym =
330                         static_cast<Sized_symbol<size>* >(gsym);
331               long long symvalue =
332                         static_cast<long long>(sized_gsym->value());
333               (*addendvec).push_back(std::make_pair(symvalue,
334                                         static_cast<long long>(addend)));
335               uint64_t reloc_offset =
336                 convert_to_section_size_type(reloc.get_r_offset());
337               (*offsetvec).push_back(reloc_offset);
338               (*reloc_addend_size_vec).push_back(
339                 get_embedded_addend_size<Classify_reloc>(sh_type, r_type,
340                                                          src_obj));
341             }
342
343           if (gsym->source() != Symbol::FROM_OBJECT)
344             continue;
345           if (!is_ordinary)
346             continue;
347         }
348       if (parameters->options().gc_sections())
349         {
350           symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx);
351           if (cident_section_name != NULL)
352             {
353               Garbage_collection::Cident_section_map::iterator ele =
354                 symtab->gc()->cident_sections()->find(std::string(cident_section_name));
355               if (ele == symtab->gc()->cident_sections()->end())
356                 continue;
357               Section_id src_id(src_obj, src_indx);
358               Garbage_collection::Sections_reachable&
359                 v(symtab->gc()->section_reloc_map()[src_id]);
360               Garbage_collection::Sections_reachable& cident_secn(ele->second);
361               for (Garbage_collection::Sections_reachable::iterator it_v
362                      = cident_secn.begin();
363                    it_v != cident_secn.end();
364                    ++it_v)
365                 {
366                   v.insert(*it_v);
367                 }
368             }
369         }
370     }
371   return;
372 }
373
374 } // End of namespace gold.
375
376 #endif