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[/] [open8_urisc/] [trunk/] [gnu/] [binutils/] [gold/] [gc.h] - Blame information for rev 158

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// gc.h -- garbage collection of unused sections
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// Copyright 2009, 2010 Free Software Foundation, Inc.
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// Written by Sriraman Tallam <tmsriram@google.com>.
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// This file is part of gold.
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// This program is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 3 of the License, or
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// (at your option) any later version.
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
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// MA 02110-1301, USA.
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#ifndef GOLD_GC_H
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#define GOLD_GC_H
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#include <queue>
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#include <vector>
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#include "elfcpp.h"
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#include "symtab.h"
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#include "object.h"
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#include "icf.h"
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namespace gold
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{
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class Object;
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template<int size, bool big_endian>
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class Sized_relobj_file;
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template<int sh_type, int size, bool big_endian>
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class Reloc_types;
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class Output_section;
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class General_options;
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class Layout;
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class Garbage_collection
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{
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 public:
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  typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
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  typedef std::map<Section_id, Sections_reachable> Section_ref;
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  typedef std::queue<Section_id> Worklist_type;
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  // This maps the name of the section which can be represented as a C
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  // identifier (cident) to the list of sections that have that name.
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  // Different object files can have cident sections with the same name.
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  typedef std::map<std::string, Sections_reachable> Cident_section_map;
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  Garbage_collection()
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  : is_worklist_ready_(false)
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  { }
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  // Accessor methods for the private members.
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  Sections_reachable&
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  referenced_list()
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  { return referenced_list_; }
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  Section_ref&
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  section_reloc_map()
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  { return this->section_reloc_map_; }
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  Worklist_type&
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  worklist()
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  { return this->work_list_; }
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  bool
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  is_worklist_ready()
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  { return this->is_worklist_ready_; }
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  void
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  worklist_ready()
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  { this->is_worklist_ready_ = true; }
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87
  void
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  do_transitive_closure();
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90
  bool
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  is_section_garbage(Object* obj, unsigned int shndx)
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  { return (this->referenced_list().find(Section_id(obj, shndx))
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            == this->referenced_list().end()); }
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95
  Cident_section_map*
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  cident_sections()
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  { return &cident_sections_; }
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99
  void
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  add_cident_section(std::string section_name,
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                     Section_id secn)
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  { this->cident_sections_[section_name].insert(secn); }
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104
  // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
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  // DST_SHNDX-th section of DST_OBJECT.
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  void
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  add_reference(Object* src_object, unsigned int src_shndx,
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                Object* dst_object, unsigned int dst_shndx)
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  {
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    Section_id src_id(src_object, src_shndx);
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    Section_id dst_id(dst_object, dst_shndx);
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    Section_ref::iterator p = this->section_reloc_map_.find(src_id);
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    if (p == this->section_reloc_map_.end())
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      this->section_reloc_map_[src_id].insert(dst_id);
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    else
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      p->second.insert(dst_id);
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  }
118
 
119
 private:
120
 
121
  Worklist_type work_list_;
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  bool is_worklist_ready_;
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  Section_ref section_reloc_map_;
124
  Sections_reachable referenced_list_;
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  Cident_section_map cident_sections_;
126
};
127
 
128
// Data to pass between successive invocations of do_layout
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// in object.cc while garbage collecting.  This data structure
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// 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;
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  // 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 =
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        &symtab->icf()->reloc_info_list()[src_id];
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      secvec = &reloc_info->section_info;
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      symvec = &reloc_info->symbol_info;
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      addendvec = &reloc_info->addend_info;
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      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,
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                                                          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

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