Copyright update for binutils
[external/binutils.git] / gold / gc.h
1 // gc.h -- garbage collection of unused sections
2
3 // Copyright (C) 2009-2016 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 <vector>
27
28 #include "elfcpp.h"
29 #include "symtab.h"
30 #include "object.h"
31 #include "icf.h"
32
33 namespace gold
34 {
35
36 class Object;
37
38 template<int size, bool big_endian>
39 class Sized_relobj_file;
40
41 template<int sh_type, int size, bool big_endian>
42 struct Reloc_types;
43
44 class Output_section;
45 class General_options;
46 class Layout;
47
48 class Garbage_collection
49 {
50  public:
51
52   typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
53   typedef std::map<Section_id, Sections_reachable> Section_ref;
54   typedef std::vector<Section_id> Worklist_type;
55   // This maps the name of the section which can be represented as a C
56   // identifier (cident) to the list of sections that have that name.
57   // Different object files can have cident sections with the same name.
58   typedef std::map<std::string, Sections_reachable> Cident_section_map;
59
60   Garbage_collection()
61   : is_worklist_ready_(false)
62   { }
63
64   // Accessor methods for the private members.
65
66   Sections_reachable&
67   referenced_list()
68   { return referenced_list_; }
69
70   Section_ref&
71   section_reloc_map()
72   { return this->section_reloc_map_; }
73
74   Worklist_type&
75   worklist()
76   { return this->work_list_; }
77
78   bool
79   is_worklist_ready()
80   { return this->is_worklist_ready_; }
81
82   void
83   worklist_ready()
84   { this->is_worklist_ready_ = true; }
85
86   void
87   do_transitive_closure();
88
89   bool
90   is_section_garbage(Relobj* obj, unsigned int shndx)
91   { return (this->referenced_list().find(Section_id(obj, shndx))
92             == this->referenced_list().end()); }
93
94   Cident_section_map*
95   cident_sections()
96   { return &cident_sections_; }
97
98   void
99   add_cident_section(std::string section_name,
100                      Section_id secn)
101   { this->cident_sections_[section_name].insert(secn); }
102
103   // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
104   // DST_SHNDX-th section of DST_OBJECT.
105   void
106   add_reference(Relobj* src_object, unsigned int src_shndx,
107                 Relobj* dst_object, unsigned int dst_shndx)
108   {
109     Section_id src_id(src_object, src_shndx);
110     Section_id dst_id(dst_object, dst_shndx);
111     Sections_reachable& reachable = this->section_reloc_map_[src_id];
112     reachable.insert(dst_id);
113   }
114
115  private:
116
117   Worklist_type work_list_;
118   bool is_worklist_ready_;
119   Section_ref section_reloc_map_;
120   Sections_reachable referenced_list_;
121   Cident_section_map cident_sections_;
122 };
123
124 // Data to pass between successive invocations of do_layout
125 // in object.cc while garbage collecting.  This data structure
126 // is filled by using the data from Read_symbols_data.
127
128 struct Symbols_data
129 {
130   // Section headers.
131   unsigned char* section_headers_data;
132   // Section names.
133   unsigned char* section_names_data;
134   // Size of section name data in bytes.
135   section_size_type section_names_size;
136   // Symbol data.
137   unsigned char* symbols_data;
138   // Size of symbol data in bytes.
139   section_size_type symbols_size;
140   // Offset of external symbols within symbol data.  This structure
141   // sometimes contains only external symbols, in which case this will
142   // be zero.  Sometimes it contains all symbols.
143   section_offset_type external_symbols_offset;
144   // Symbol names.
145   unsigned char* symbol_names_data;
146   // Size of symbol name data in bytes.
147   section_size_type symbol_names_size;
148 };
149
150 // Relocations of type SHT_REL store the addend value in their bytes.
151 // This function returns the size of the embedded addend which is
152 // nothing but the size of the relocation.
153
154 template<typename Classify_reloc>
155 inline unsigned int
156 get_embedded_addend_size(int sh_type, int r_type, Relobj* obj)
157 {
158   if (sh_type != elfcpp::SHT_REL)
159     return 0;
160   Classify_reloc classify_reloc;
161   return classify_reloc.get_size_for_reloc(r_type, obj);
162 }
163
164 // This function implements the generic part of reloc
165 // processing to map a section to all the sections it
166 // references through relocs.  It is called only during
167 // garbage collection (--gc-sections) and identical code
168 // folding (--icf).
169
170 template<int size, bool big_endian, typename Target_type, int sh_type,
171          typename Scan, typename Classify_reloc>
172 inline void
173 gc_process_relocs(
174     Symbol_table* symtab,
175     Layout*,
176     Target_type* target,
177     Sized_relobj_file<size, big_endian>* src_obj,
178     unsigned int src_indx,
179     const unsigned char* prelocs,
180     size_t reloc_count,
181     Output_section*,
182     bool,
183     size_t local_count,
184     const unsigned char* plocal_syms)
185 {
186   Scan scan;
187
188   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
189   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
190   const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
191
192   Icf::Sections_reachable_info* secvec = NULL;
193   Icf::Symbol_info* symvec = NULL;
194   Icf::Addend_info* addendvec = NULL;
195   Icf::Offset_info* offsetvec = NULL;
196   Icf::Reloc_addend_size_info* reloc_addend_size_vec = NULL;
197   bool is_icf_tracked = false;
198   const char* cident_section_name = NULL;
199
200   std::string src_section_name = (parameters->options().icf_enabled()
201                                   ? src_obj->section_name(src_indx)
202                                   : "");
203
204   bool check_section_for_function_pointers = false;
205
206   if (parameters->options().icf_enabled()
207       && is_section_foldable_candidate(src_section_name.c_str()))
208     {
209       is_icf_tracked = true;
210       Section_id src_id(src_obj, src_indx);
211       Icf::Reloc_info* reloc_info =
212         &symtab->icf()->reloc_info_list()[src_id];
213       secvec = &reloc_info->section_info;
214       symvec = &reloc_info->symbol_info;
215       addendvec = &reloc_info->addend_info;
216       offsetvec = &reloc_info->offset_info;
217       reloc_addend_size_vec = &reloc_info->reloc_addend_size_info;
218     }
219
220   check_section_for_function_pointers =
221     symtab->icf()->check_section_for_function_pointers(src_section_name,
222                                                        target);
223
224   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
225     {
226       Reltype reloc(prelocs);
227       typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
228       unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
229       unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
230       typename elfcpp::Elf_types<size>::Elf_Swxword addend =
231       Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);
232       Relobj* dst_obj;
233       unsigned int dst_indx;
234       typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
235       Address dst_off;
236
237       if (r_sym < local_count)
238         {
239           gold_assert(plocal_syms != NULL);
240           typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
241                                                       + r_sym * sym_size);
242           dst_indx = lsym.get_st_shndx();
243           bool is_ordinary;
244           dst_indx = src_obj->adjust_sym_shndx(r_sym, dst_indx, &is_ordinary);
245           dst_obj = src_obj;
246           dst_off = lsym.get_st_value() + addend;
247
248           if (is_icf_tracked)
249             {
250               Address symvalue = dst_off - addend;
251               if (is_ordinary) 
252                 (*secvec).push_back(Section_id(src_obj, dst_indx));
253               else
254                 (*secvec).push_back(Section_id(NULL, 0));
255               (*symvec).push_back(NULL);
256               (*addendvec).push_back(std::make_pair(
257                                         static_cast<long long>(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 || dst_indx == 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               && !gsym->object()->is_dynamic())
294             {
295               dst_obj = static_cast<Relobj*>(gsym->object());
296               dst_indx = gsym->shndx(&is_ordinary);
297             }
298           dst_off = static_cast<const Sized_symbol<size>*>(gsym)->value();
299           dst_off += addend;
300
301           // When doing safe folding, check to see if this relocation is that
302           // of a function pointer being taken.
303           if (gsym->source() == Symbol::FROM_OBJECT
304               && check_section_for_function_pointers
305               && dst_obj != NULL
306               && (!is_ordinary
307                   || scan.global_reloc_may_be_function_pointer(
308                        symtab, NULL, NULL, src_obj, src_indx, NULL, reloc,
309                        r_type, gsym)))
310             symtab->icf()->set_section_has_function_pointers(dst_obj, dst_indx);
311
312           // If the symbol name matches '__start_XXX' then the section with
313           // the C identifier like name 'XXX' should not be garbage collected.
314           // A similar treatment to symbols with the name '__stop_XXX'.
315           if (is_prefix_of(cident_section_start_prefix, gsym->name()))
316             {
317               cident_section_name = (gsym->name() 
318                                      + strlen(cident_section_start_prefix));
319             }
320           else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))
321             {
322               cident_section_name = (gsym->name() 
323                                      + strlen(cident_section_stop_prefix));
324             }
325           if (is_icf_tracked)
326             {
327               Address symvalue = dst_off - addend;
328               if (is_ordinary && dst_obj != NULL)
329                 (*secvec).push_back(Section_id(dst_obj, dst_indx));
330               else
331                 (*secvec).push_back(Section_id(NULL, 0));
332               (*symvec).push_back(gsym);
333               (*addendvec).push_back(std::make_pair(
334                                         static_cast<long long>(symvalue),
335                                         static_cast<long long>(addend)));
336               uint64_t reloc_offset =
337                 convert_to_section_size_type(reloc.get_r_offset());
338               (*offsetvec).push_back(reloc_offset);
339               (*reloc_addend_size_vec).push_back(
340                 get_embedded_addend_size<Classify_reloc>(sh_type, r_type,
341                                                          src_obj));
342             }
343
344           if (dst_obj == NULL)
345             continue;
346           if (!is_ordinary)
347             continue;
348         }
349       if (parameters->options().gc_sections())
350         {
351           symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx);
352           parameters->sized_target<size, big_endian>()
353             ->gc_add_reference(symtab, src_obj, src_indx, dst_obj, dst_indx,
354                                dst_off);
355           if (cident_section_name != NULL)
356             {
357               Garbage_collection::Cident_section_map::iterator ele =
358                 symtab->gc()->cident_sections()->find(std::string(cident_section_name));
359               if (ele == symtab->gc()->cident_sections()->end())
360                 continue;
361               Section_id src_id(src_obj, src_indx);
362               Garbage_collection::Sections_reachable&
363                 v(symtab->gc()->section_reloc_map()[src_id]);
364               Garbage_collection::Sections_reachable& cident_secn(ele->second);
365               for (Garbage_collection::Sections_reachable::iterator it_v
366                      = cident_secn.begin();
367                    it_v != cident_secn.end();
368                    ++it_v)
369                 {
370                   v.insert(*it_v);
371                 }
372             }
373         }
374     }
375   return;
376 }
377
378 } // End of namespace gold.
379
380 #endif