gold/merge.cc

   1 // merge.cc -- handle section merging for gold
   2
   3 // Copyright 2006, 2007, 2008, 2010 Free Software Foundation, Inc.
   4 // Written by Ian Lance Taylor <iant@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 #include "gold.h"
  24
  25 #include <cstdlib>
  26 #include <algorithm>
  27
  28 #include "merge.h"
  29 #include "compressed_output.h"
  30
  31 namespace gold
  32 {
  33
  34 // Class Object_merge_map.
  35
  36 // Destructor.
  37
  38 Object_merge_map::~Object_merge_map()
  39 {
  40   for (Section_merge_maps::iterator p = this->section_merge_maps_.begin();
  41        p != this->section_merge_maps_.end();
  42        ++p)
  43     delete p->second;
  44 }
  45
  46 // Get the Input_merge_map to use for an input section, or NULL.
  47
  48 Object_merge_map::Input_merge_map*
  49 Object_merge_map::get_input_merge_map(unsigned int shndx)
  50 {
  51   gold_assert(shndx != -1U);
  52   if (shndx == this->first_shnum_)
  53     return &this->first_map_;
  54   if (shndx == this->second_shnum_)
  55     return &this->second_map_;
  56   Section_merge_maps::const_iterator p = this->section_merge_maps_.find(shndx);
  57   if (p != this->section_merge_maps_.end())
  58     return p->second;
  59   return NULL;
  60 }
  61
  62 // Get or create the Input_merge_map to use for an input section.
  63
  64 Object_merge_map::Input_merge_map*
  65 Object_merge_map::get_or_make_input_merge_map(const Merge_map* merge_map,
  66                                               unsigned int shndx)
  67 {
  68   Input_merge_map* map = this->get_input_merge_map(shndx);
  69   if (map != NULL)
  70     {
  71       // For a given input section in a given object, every mapping
  72       // must be done with the same Merge_map.
  73       gold_assert(map->merge_map == merge_map);
  74       return map;
  75     }
  76
  77   // We need to create a new entry.
  78   if (this->first_shnum_ == -1U)
  79     {
  80       this->first_shnum_ = shndx;
  81       this->first_map_.merge_map = merge_map;
  82       return &this->first_map_;
  83     }
  84   if (this->second_shnum_ == -1U)
  85     {
  86       this->second_shnum_ = shndx;
  87       this->second_map_.merge_map = merge_map;
  88       return &this->second_map_;
  89     }
  90
  91   Input_merge_map* new_map = new Input_merge_map;
  92   new_map->merge_map = merge_map;
  93   this->section_merge_maps_[shndx] = new_map;
  94   return new_map;
  95 }
  96
  97 // Add a mapping.
  98
  99 void
 100 Object_merge_map::add_mapping(const Merge_map* merge_map, unsigned int shndx,
 101                               section_offset_type input_offset,
 102                               section_size_type length,
 103                               section_offset_type output_offset)
 104 {
 105   Input_merge_map* map = this->get_or_make_input_merge_map(merge_map, shndx);
 106
 107   // Try to merge the new entry in the last one we saw.
 108   if (!map->entries.empty())
 109     {
 110       Input_merge_entry& entry(map->entries.back());
 111
 112       // Use section_size_type to avoid signed/unsigned warnings.
 113       section_size_type input_offset_u = input_offset;
 114       section_size_type output_offset_u = output_offset;
 115
 116       // If this entry is not in order, we need to sort the vector
 117       // before looking anything up.
 118       if (input_offset_u < entry.input_offset + entry.length)
 119         {
 120           gold_assert(input_offset < entry.input_offset);
 121           gold_assert(input_offset_u + length
 122                       <= static_cast<section_size_type>(entry.input_offset));
 123           map->sorted = false;
 124         }
 125       else if (entry.input_offset + entry.length == input_offset_u
 126                && (output_offset == -1
 127                    ? entry.output_offset == -1
 128                    : entry.output_offset + entry.length == output_offset_u))
 129         {
 130           entry.length += length;
 131           return;
 132         }
 133     }
 134
 135   Input_merge_entry entry;
 136   entry.input_offset = input_offset;
 137   entry.length = length;
 138   entry.output_offset = output_offset;
 139   map->entries.push_back(entry);
 140 }
 141
 142 // Get the output offset for an input address.
 143
 144 bool
 145 Object_merge_map::get_output_offset(const Merge_map* merge_map,
 146                                     unsigned int shndx,
 147                                     section_offset_type input_offset,
 148                                     section_offset_type *output_offset)
 149 {
 150   Input_merge_map* map = this->get_input_merge_map(shndx);
 151   if (map == NULL
 152       || (merge_map != NULL && map->merge_map != merge_map))
 153     return false;
 154
 155   if (!map->sorted)
 156     {
 157       std::sort(map->entries.begin(), map->entries.end(),
 158                 Input_merge_compare());
 159       map->sorted = true;
 160     }
 161
 162   Input_merge_entry entry;
 163   entry.input_offset = input_offset;
 164   std::vector<Input_merge_entry>::const_iterator p =
 165     std::lower_bound(map->entries.begin(), map->entries.end(),
 166                      entry, Input_merge_compare());
 167   if (p == map->entries.end() || p->input_offset > input_offset)
 168     {
 169       if (p == map->entries.begin())
 170         return false;
 171       --p;
 172       gold_assert(p->input_offset <= input_offset);
 173     }
 174
 175   if (input_offset - p->input_offset
 176       >= static_cast<section_offset_type>(p->length))
 177     return false;
 178
 179   *output_offset = p->output_offset;
 180   if (*output_offset != -1)
 181     *output_offset += (input_offset - p->input_offset);
 182   return true;
 183 }
 184
 185 // Return whether this is the merge map for section SHNDX.
 186
 187 inline bool
 188 Object_merge_map::is_merge_section_for(const Merge_map* merge_map,
 189                                        unsigned int shndx)
 190 {
 191   Input_merge_map* map = this->get_input_merge_map(shndx);
 192   return map != NULL && map->merge_map == merge_map;
 193 }
 194
 195 // Initialize a mapping from input offsets to output addresses.
 196
 197 template<int size>
 198 void
 199 Object_merge_map::initialize_input_to_output_map(
 200     unsigned int shndx,
 201     typename elfcpp::Elf_types<size>::Elf_Addr starting_address,
 202     Unordered_map<section_offset_type,
 203                   typename elfcpp::Elf_types<size>::Elf_Addr>* initialize_map)
 204 {
 205   Input_merge_map* map = this->get_input_merge_map(shndx);
 206   gold_assert(map != NULL);
 207
 208   gold_assert(initialize_map->empty());
 209   // We know how many entries we are going to add.
 210   // reserve_unordered_map takes an expected count of buckets, not a
 211   // count of elements, so double it to try to reduce collisions.
 212   reserve_unordered_map(initialize_map, map->entries.size() * 2);
 213
 214   for (Input_merge_map::Entries::const_iterator p = map->entries.begin();
 215        p != map->entries.end();
 216        ++p)
 217     {
 218       section_offset_type output_offset = p->output_offset;
 219       if (output_offset != -1)
 220         output_offset += starting_address;
 221       else
 222         {
 223           // If we see a relocation against an address we have chosen
 224           // to discard, we relocate to zero.  FIXME: We could also
 225           // issue a warning in this case; that would require
 226           // reporting this somehow and checking it in the routines in
 227           // reloc.h.
 228           output_offset = 0;
 229         }
 230       initialize_map->insert(std::make_pair(p->input_offset, output_offset));
 231     }
 232 }
 233
 234 // Class Merge_map.
 235
 236 // Add a mapping for the bytes from OFFSET to OFFSET + LENGTH in input
 237 // section SHNDX in object OBJECT to an OUTPUT_OFFSET in merged data
 238 // in an output section.
 239
 240 void
 241 Merge_map::add_mapping(Relobj* object, unsigned int shndx,
 242                        section_offset_type offset, section_size_type length,
 243                        section_offset_type output_offset)
 244 {
 245   Object_merge_map* object_merge_map = object->merge_map();
 246   if (object_merge_map == NULL)
 247     {
 248       object_merge_map = new Object_merge_map();
 249       object->set_merge_map(object_merge_map);
 250     }
 251
 252   object_merge_map->add_mapping(this, shndx, offset, length, output_offset);
 253 }
 254
 255 // Return the output offset for an input address.  The input address
 256 // is at offset OFFSET in section SHNDX in OBJECT.  This sets
 257 // *OUTPUT_OFFSET to the offset in the merged data in the output
 258 // section.  This returns true if the mapping is known, false
 259 // otherwise.
 260
 261 bool
 262 Merge_map::get_output_offset(const Relobj* object, unsigned int shndx,
 263                              section_offset_type offset,
 264                              section_offset_type* output_offset) const
 265 {
 266   Object_merge_map* object_merge_map = object->merge_map();
 267   if (object_merge_map == NULL)
 268     return false;
 269   return object_merge_map->get_output_offset(this, shndx, offset,
 270                                              output_offset);
 271 }
 272
 273 // Return whether this is the merge section for SHNDX in OBJECT.
 274
 275 bool
 276 Merge_map::is_merge_section_for(const Relobj* object, unsigned int shndx) const
 277 {
 278   Object_merge_map* object_merge_map = object->merge_map();
 279   if (object_merge_map == NULL)
 280     return false;
 281   return object_merge_map->is_merge_section_for(this, shndx);
 282 }
 283
 284 // Class Output_merge_base.
 285
 286 // Return the output offset for an input offset.  The input address is
 287 // at offset OFFSET in section SHNDX in OBJECT.  If we know the
 288 // offset, set *POUTPUT and return true.  Otherwise return false.
 289
 290 bool
 291 Output_merge_base::do_output_offset(const Relobj* object,
 292                                     unsigned int shndx,
 293                                     section_offset_type offset,
 294                                     section_offset_type* poutput) const
 295 {
 296   return this->merge_map_.get_output_offset(object, shndx, offset, poutput);
 297 }
 298
 299 // Return whether this is the merge section for SHNDX in OBJECT.
 300
 301 bool
 302 Output_merge_base::do_is_merge_section_for(const Relobj* object,
 303                                            unsigned int shndx) const
 304 {
 305   return this->merge_map_.is_merge_section_for(object, shndx);
 306 }
 307
 308 // Record a merged input section for script processing.
 309
 310 void
 311 Output_merge_base::record_input_section(Relobj* relobj, unsigned int shndx)
 312 {
 313   gold_assert(this->keeps_input_sections_ && relobj != NULL);
 314   // If this is the first input section, record it.  We need do this because
 315   // this->input_sections_ is unordered.
 316   if (this->first_relobj_ == NULL)
 317     {
 318       this->first_relobj_ = relobj;
 319       this->first_shndx_ = shndx;
 320     }
 321
 322   std::pair<Input_sections::iterator, bool> result =
 323     this->input_sections_.insert(Section_id(relobj, shndx));
 324   // We should insert a merge section once only.
 325   gold_assert(result.second);
 326 }
 327
 328 // Class Output_merge_data.
 329
 330 // Compute the hash code for a fixed-size constant.
 331
 332 size_t
 333 Output_merge_data::Merge_data_hash::operator()(Merge_data_key k) const
 334 {
 335   const unsigned char* p = this->pomd_->constant(k);
 336   section_size_type entsize =
 337     convert_to_section_size_type(this->pomd_->entsize());
 338
 339   // Fowler/Noll/Vo (FNV) hash (type FNV-1a).
 340   if (sizeof(size_t) == 8)
 341     {
 342       size_t result = static_cast<size_t>(14695981039346656037ULL);
 343       for (section_size_type i = 0; i < entsize; ++i)
 344         {
 345           result &= (size_t) *p++;
 346           result *= 1099511628211ULL;
 347         }
 348       return result;
 349     }
 350   else
 351     {
 352       size_t result = 2166136261UL;
 353       for (section_size_type i = 0; i < entsize; ++i)
 354         {
 355           result ^= (size_t) *p++;
 356           result *= 16777619UL;
 357         }
 358       return result;
 359     }
 360 }
 361
 362 // Return whether one hash table key equals another.
 363
 364 bool
 365 Output_merge_data::Merge_data_eq::operator()(Merge_data_key k1,
 366                                              Merge_data_key k2) const
 367 {
 368   const unsigned char* p1 = this->pomd_->constant(k1);
 369   const unsigned char* p2 = this->pomd_->constant(k2);
 370   return memcmp(p1, p2, this->pomd_->entsize()) == 0;
 371 }
 372
 373 // Add a constant to the end of the section contents.
 374
 375 void
 376 Output_merge_data::add_constant(const unsigned char* p)
 377 {
 378   section_size_type entsize = convert_to_section_size_type(this->entsize());
 379   section_size_type addralign =
 380     convert_to_section_size_type(this->addralign());
 381   section_size_type addsize = std::max(entsize, addralign);
 382   if (this->len_ + addsize > this->alc_)
 383     {
 384       if (this->alc_ == 0)
 385         this->alc_ = 128 * addsize;
 386       else
 387         this->alc_ *= 2;
 388       this->p_ = static_cast<unsigned char*>(realloc(this->p_, this->alc_));
 389       if (this->p_ == NULL)
 390         gold_nomem();
 391     }
 392
 393   memcpy(this->p_ + this->len_, p, entsize);
 394   if (addsize > entsize)
 395     memset(this->p_ + this->len_ + entsize, 0, addsize - entsize);
 396   this->len_ += addsize;
 397 }
 398
 399 // Add the input section SHNDX in OBJECT to a merged output section
 400 // which holds fixed length constants.  Return whether we were able to
 401 // handle the section; if not, it will be linked as usual without
 402 // constant merging.
 403
 404 bool
 405 Output_merge_data::do_add_input_section(Relobj* object, unsigned int shndx)
 406 {
 407   section_size_type len;
 408   section_size_type uncompressed_size = 0;
 409   unsigned char* uncompressed_data = NULL;
 410   const unsigned char* p = object->section_contents(shndx, &len, false);
 411
 412   if (object->section_is_compressed(shndx, &uncompressed_size))
 413     {
 414       uncompressed_data = new unsigned char[uncompressed_size];
 415       if (!decompress_input_section(p, len, uncompressed_data,
 416                                     uncompressed_size))
 417         object->error(_("could not decompress section %s"),
 418                       object->section_name(shndx).c_str());
 419       p = uncompressed_data;
 420       len = uncompressed_size;
 421     }
 422
 423   section_size_type entsize = convert_to_section_size_type(this->entsize());
 424
 425   if (len % entsize != 0)
 426     {
 427       if (uncompressed_data != NULL)
 428         delete[] uncompressed_data;
 429       return false;
 430     }
 431
 432   this->input_count_ += len / entsize;
 433
 434   for (section_size_type i = 0; i < len; i += entsize, p += entsize)
 435     {
 436       // Add the constant to the section contents.  If we find that it
 437       // is already in the hash table, we will remove it again.
 438       Merge_data_key k = this->len_;
 439       this->add_constant(p);
 440
 441       std::pair<Merge_data_hashtable::iterator, bool> ins =
 442         this->hashtable_.insert(k);
 443
 444       if (!ins.second)
 445         {
 446           // Key was already present.  Remove the copy we just added.
 447           this->len_ -= entsize;
 448           k = *ins.first;
 449         }
 450
 451       // Record the offset of this constant in the output section.
 452       this->add_mapping(object, shndx, i, entsize, k);
 453     }
 454
 455   // For script processing, we keep the input sections.
 456   if (this->keeps_input_sections())
 457     record_input_section(object, shndx);
 458
 459   if (uncompressed_data != NULL)
 460     delete[] uncompressed_data;
 461
 462   return true;
 463 }
 464
 465 // Set the final data size in a merged output section with fixed size
 466 // constants.
 467
 468 void
 469 Output_merge_data::set_final_data_size()
 470 {
 471   // Release the memory we don't need.
 472   this->p_ = static_cast<unsigned char*>(realloc(this->p_, this->len_));
 473   // An Output_merge_data object may be empty and realloc is allowed
 474   // to return a NULL pointer in this case.  An Output_merge_data is empty
 475   // if all its input sections have sizes that are not multiples of entsize.
 476   gold_assert(this->p_ != NULL || this->len_ == 0);
 477   this->set_data_size(this->len_);
 478 }
 479
 480 // Write the data of a merged output section with fixed size constants
 481 // to the file.
 482
 483 void
 484 Output_merge_data::do_write(Output_file* of)
 485 {
 486   of->write(this->offset(), this->p_, this->len_);
 487 }
 488
 489 // Write the data to a buffer.
 490
 491 void
 492 Output_merge_data::do_write_to_buffer(unsigned char* buffer)
 493 {
 494   memcpy(buffer, this->p_, this->len_);
 495 }
 496
 497 // Print merge stats to stderr.
 498
 499 void
 500 Output_merge_data::do_print_merge_stats(const char* section_name)
 501 {
 502   fprintf(stderr,
 503           _("%s: %s merged constants size: %lu; input: %zu; output: %zu\n"),
 504           program_name, section_name,
 505           static_cast<unsigned long>(this->entsize()),
 506           this->input_count_, this->hashtable_.size());
 507 }
 508
 509 // Class Output_merge_string.
 510
 511 // Add an input section to a merged string section.
 512
 513 template<typename Char_type>
 514 bool
 515 Output_merge_string<Char_type>::do_add_input_section(Relobj* object,
 516                                                      unsigned int shndx)
 517 {
 518   section_size_type len;
 519   section_size_type uncompressed_size = 0;
 520   unsigned char* uncompressed_data = NULL;
 521   const unsigned char* pdata = object->section_contents(shndx, &len, false);
 522
 523   if (object->section_is_compressed(shndx, &uncompressed_size))
 524     {
 525       uncompressed_data = new unsigned char[uncompressed_size];
 526       if (!decompress_input_section(pdata, len, uncompressed_data,
 527                                     uncompressed_size))
 528         object->error(_("could not decompress section %s"),
 529                       object->section_name(shndx).c_str());
 530       pdata = uncompressed_data;
 531       len = uncompressed_size;
 532     }
 533
 534   const Char_type* p = reinterpret_cast<const Char_type*>(pdata);
 535   const Char_type* pend = p + len / sizeof(Char_type);
 536
 537   if (len % sizeof(Char_type) != 0)
 538     {
 539       object->error(_("mergeable string section length not multiple of "
 540                       "character size"));
 541       if (uncompressed_data != NULL)
 542         delete[] uncompressed_data;
 543       return false;
 544     }
 545
 546   size_t count = 0;
 547
 548   // The index I is in bytes, not characters.
 549   section_size_type i = 0;
 550   while (i < len)
 551     {
 552       const Char_type* pl;
 553       for (pl = p; *pl != 0; ++pl)
 554         {
 555           if (pl >= pend)
 556             {
 557               gold_warning(_("%s: last entry in mergeable string section '%s' "
 558                              "not null terminated"),
 559                            object->name().c_str(),
 560                            object->section_name(shndx).c_str());
 561               break;
 562             }
 563         }
 564
 565       Stringpool::Key key;
 566       const Char_type* str = this->stringpool_.add_with_length(p, pl - p, true,
 567                                                                &key);
 568
 569       section_size_type bytelen_with_null = ((pl - p) + 1) * sizeof(Char_type);
 570       this->merged_strings_.push_back(Merged_string(object, shndx, i, str,
 571                                                     bytelen_with_null, key));
 572
 573       p = pl + 1;
 574       i += bytelen_with_null;
 575       ++count;
 576     }
 577
 578   this->input_count_ += count;
 579
 580   // For script processing, we keep the input sections.
 581   if (this->keeps_input_sections())
 582     record_input_section(object, shndx);
 583
 584   if (uncompressed_data != NULL)
 585     delete[] uncompressed_data;
 586
 587   return true;
 588 }
 589
 590 // Finalize the mappings from the input sections to the output
 591 // section, and return the final data size.
 592
 593 template<typename Char_type>
 594 section_size_type
 595 Output_merge_string<Char_type>::finalize_merged_data()
 596 {
 597   this->stringpool_.set_string_offsets();
 598
 599   for (typename Merged_strings::const_iterator p =
 600          this->merged_strings_.begin();
 601        p != this->merged_strings_.end();
 602        ++p)
 603     {
 604       section_offset_type offset =
 605         this->stringpool_.get_offset_from_key(p->stringpool_key);
 606       this->add_mapping(p->object, p->shndx, p->offset, p->length, offset);
 607     }
 608
 609   // Save some memory.  This also ensures that this function will work
 610   // if called twice, as may happen if Layout::set_segment_offsets
 611   // finds a better alignment.
 612   this->merged_strings_.clear();
 613
 614   return this->stringpool_.get_strtab_size();
 615 }
 616
 617 template<typename Char_type>
 618 void
 619 Output_merge_string<Char_type>::set_final_data_size()
 620 {
 621   const off_t final_data_size = this->finalize_merged_data();
 622   this->set_data_size(final_data_size);
 623 }
 624
 625 // Write out a merged string section.
 626
 627 template<typename Char_type>
 628 void
 629 Output_merge_string<Char_type>::do_write(Output_file* of)
 630 {
 631   this->stringpool_.write(of, this->offset());
 632 }
 633
 634 // Write a merged string section to a buffer.
 635
 636 template<typename Char_type>
 637 void
 638 Output_merge_string<Char_type>::do_write_to_buffer(unsigned char* buffer)
 639 {
 640   this->stringpool_.write_to_buffer(buffer, this->data_size());
 641 }
 642
 643 // Return the name of the types of string to use with
 644 // do_print_merge_stats.
 645
 646 template<typename Char_type>
 647 const char*
 648 Output_merge_string<Char_type>::string_name()
 649 {
 650   gold_unreachable();
 651   return NULL;
 652 }
 653
 654 template<>
 655 const char*
 656 Output_merge_string<char>::string_name()
 657 {
 658   return "strings";
 659 }
 660
 661 template<>
 662 const char*
 663 Output_merge_string<uint16_t>::string_name()
 664 {
 665   return "16-bit strings";
 666 }
 667
 668 template<>
 669 const char*
 670 Output_merge_string<uint32_t>::string_name()
 671 {
 672   return "32-bit strings";
 673 }
 674
 675 // Print merge stats to stderr.
 676
 677 template<typename Char_type>
 678 void
 679 Output_merge_string<Char_type>::do_print_merge_stats(const char* section_name)
 680 {
 681   char buf[200];
 682   snprintf(buf, sizeof buf, "%s merged %s", section_name, this->string_name());
 683   fprintf(stderr, _("%s: %s input: %zu\n"),
 684           program_name, buf, this->input_count_);
 685   this->stringpool_.print_stats(buf);
 686 }
 687
 688 // Instantiate the templates we need.
 689
 690 template
 691 class Output_merge_string<char>;
 692
 693 template
 694 class Output_merge_string<uint16_t>;
 695
 696 template
 697 class Output_merge_string<uint32_t>;
 698
 699 #if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
 700 template
 701 void
 702 Object_merge_map::initialize_input_to_output_map<32>(
 703     unsigned int shndx,
 704     elfcpp::Elf_types<32>::Elf_Addr starting_address,
 705     Unordered_map<section_offset_type, elfcpp::Elf_types<32>::Elf_Addr>*);
 706 #endif
 707
 708 #if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
 709 template
 710 void
 711 Object_merge_map::initialize_input_to_output_map<64>(
 712     unsigned int shndx,
 713     elfcpp::Elf_types<64>::Elf_Addr starting_address,
 714     Unordered_map<section_offset_type, elfcpp::Elf_types<64>::Elf_Addr>*);
 715 #endif
 716
 717 } // End namespace gold.