gold/merge.cc

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