gold/merge.cc

   1 // merge.cc -- handle section merging for gold
   2
   3 // Copyright (C) 2006-2024 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 const Object_merge_map::Input_merge_map*
  49 Object_merge_map::get_input_merge_map(unsigned int shndx) const
  50 {
  51   gold_assert(shndx != -1U);
  52   const Section_merge_maps &maps = this->section_merge_maps_;
  53   for (Section_merge_maps::const_iterator i = maps.begin(), e = maps.end();
  54        i != e; ++i)
  55     {
  56       if (i->first == shndx)
  57         return i->second;
  58     }
  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(
  66     const Output_section_data* output_data, unsigned int shndx) {
  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->output_data == output_data);
  73       return map;
  74     }
  75
  76   Input_merge_map* new_map = new Input_merge_map;
  77   new_map->output_data = output_data;
  78   Section_merge_maps &maps = this->section_merge_maps_;
  79   maps.push_back(std::make_pair(shndx, new_map));
  80   return new_map;
  81 }
  82
  83 // Add a mapping.
  84
  85 void
  86 Object_merge_map::add_mapping(const Output_section_data* output_data,
  87                               unsigned int shndx,
  88                               section_offset_type input_offset,
  89                               section_size_type length,
  90                               section_offset_type output_offset)
  91 {
  92   Input_merge_map* map = this->get_or_make_input_merge_map(output_data, shndx);
  93   map->add_mapping(input_offset, length, output_offset);
  94 }
  95
  96 void
  97 Object_merge_map::Input_merge_map::add_mapping(
  98     section_offset_type input_offset, section_size_type length,
  99     section_offset_type output_offset) {
 100   // Try to merge the new entry in the last one we saw.
 101   if (!this->entries.empty())
 102     {
 103       Input_merge_entry& entry(this->entries.back());
 104
 105       // Use section_size_type to avoid signed/unsigned warnings.
 106       section_size_type input_offset_u = input_offset;
 107       section_size_type output_offset_u = output_offset;
 108
 109       // If this entry is not in order, we need to sort the vector
 110       // before looking anything up.
 111       if (input_offset_u < entry.input_offset + entry.length)
 112         {
 113           gold_assert(input_offset < entry.input_offset);
 114           gold_assert(input_offset_u + length
 115                       <= static_cast<section_size_type>(entry.input_offset));
 116           this->sorted = false;
 117         }
 118       else if (entry.input_offset + entry.length == input_offset_u
 119                && (output_offset == -1
 120                    ? entry.output_offset == -1
 121                    : entry.output_offset + entry.length == output_offset_u))
 122         {
 123           entry.length += length;
 124           return;
 125         }
 126     }
 127
 128   Input_merge_entry entry;
 129   entry.input_offset = input_offset;
 130   entry.length = length;
 131   entry.output_offset = output_offset;
 132   this->entries.push_back(entry);
 133 }
 134
 135 // Get the output offset for an input address.
 136
 137 bool
 138 Object_merge_map::get_output_offset(unsigned int shndx,
 139                                     section_offset_type input_offset,
 140                                     section_offset_type* output_offset)
 141 {
 142   Input_merge_map* map = this->get_input_merge_map(shndx);
 143   if (map == NULL)
 144     return false;
 145
 146   if (!map->sorted)
 147     {
 148       std::sort(map->entries.begin(), map->entries.end(),
 149                 Input_merge_compare());
 150       map->sorted = true;
 151     }
 152
 153   Input_merge_entry entry;
 154   entry.input_offset = input_offset;
 155   std::vector<Input_merge_entry>::const_iterator p =
 156     std::upper_bound(map->entries.begin(), map->entries.end(),
 157                      entry, Input_merge_compare());
 158   if (p == map->entries.begin())
 159     return false;
 160   --p;
 161   gold_assert(p->input_offset <= input_offset);
 162
 163   if (input_offset - p->input_offset
 164       >= static_cast<section_offset_type>(p->length))
 165     return false;
 166
 167   *output_offset = p->output_offset;
 168   if (*output_offset != -1)
 169     *output_offset += (input_offset - p->input_offset);
 170   return true;
 171 }
 172
 173 // Return whether this is the merge map for section SHNDX.
 174
 175 const Output_section_data*
 176 Object_merge_map::find_merge_section(unsigned int shndx) const {
 177   const Object_merge_map::Input_merge_map* map =
 178     this->get_input_merge_map(shndx);
 179   if (map == NULL)
 180     return NULL;
 181   return map->output_data;
 182 }
 183
 184 // Initialize a mapping from input offsets to output addresses.
 185
 186 template<int size>
 187 void
 188 Object_merge_map::initialize_input_to_output_map(
 189     unsigned int shndx,
 190     typename elfcpp::Elf_types<size>::Elf_Addr starting_address,
 191     Unordered_map<section_offset_type,
 192                   typename elfcpp::Elf_types<size>::Elf_Addr>* initialize_map)
 193 {
 194   Input_merge_map* map = this->get_input_merge_map(shndx);
 195   gold_assert(map != NULL);
 196
 197   gold_assert(initialize_map->empty());
 198   // We know how many entries we are going to add.
 199   // reserve_unordered_map takes an expected count of buckets, not a
 200   // count of elements, so double it to try to reduce collisions.
 201   reserve_unordered_map(initialize_map, map->entries.size() * 2);
 202
 203   for (Input_merge_map::Entries::const_iterator p = map->entries.begin();
 204        p != map->entries.end();
 205        ++p)
 206     {
 207       section_offset_type output_offset = p->output_offset;
 208       if (output_offset != -1)
 209         output_offset += starting_address;
 210       else
 211         {
 212           // If we see a relocation against an address we have chosen
 213           // to discard, we relocate to zero.  FIXME: We could also
 214           // issue a warning in this case; that would require
 215           // reporting this somehow and checking it in the routines in
 216           // reloc.h.
 217           output_offset = 0;
 218         }
 219       initialize_map->insert(std::make_pair(p->input_offset, output_offset));
 220     }
 221 }
 222
 223 // Class Output_merge_base.
 224
 225 // Return the output offset for an input offset.  The input address is
 226 // at offset OFFSET in section SHNDX in OBJECT.  If we know the
 227 // offset, set *POUTPUT and return true.  Otherwise return false.
 228
 229 bool
 230 Output_merge_base::do_output_offset(const Relobj* object,
 231                                     unsigned int shndx,
 232                                     section_offset_type offset,
 233                                     section_offset_type* poutput) const
 234 {
 235   return object->merge_output_offset(shndx, offset, poutput);
 236 }
 237
 238 // Record a merged input section for script processing.
 239
 240 void
 241 Output_merge_base::record_input_section(Relobj* relobj, unsigned int shndx)
 242 {
 243   gold_assert(this->keeps_input_sections_ && relobj != NULL);
 244   // If this is the first input section, record it.  We need do this because
 245   // this->input_sections_ is unordered.
 246   if (this->first_relobj_ == NULL)
 247     {
 248       this->first_relobj_ = relobj;
 249       this->first_shndx_ = shndx;
 250     }
 251
 252   std::pair<Input_sections::iterator, bool> result =
 253     this->input_sections_.insert(Section_id(relobj, shndx));
 254   // We should insert a merge section once only.
 255   gold_assert(result.second);
 256 }
 257
 258 // Class Output_merge_data.
 259
 260 // Compute the hash code for a fixed-size constant.
 261
 262 size_t
 263 Output_merge_data::Merge_data_hash::operator()(Merge_data_key k) const
 264 {
 265   const unsigned char* p = this->pomd_->constant(k);
 266   section_size_type entsize =
 267     convert_to_section_size_type(this->pomd_->entsize());
 268
 269   // Fowler/Noll/Vo (FNV) hash (type FNV-1a).
 270   if (sizeof(size_t) == 8)
 271     {
 272       size_t result = static_cast<size_t>(14695981039346656037ULL);
 273       for (section_size_type i = 0; i < entsize; ++i)
 274         {
 275           result &= (size_t) *p++;
 276           result *= 1099511628211ULL;
 277         }
 278       return result;
 279     }
 280   else
 281     {
 282       size_t result = 2166136261UL;
 283       for (section_size_type i = 0; i < entsize; ++i)
 284         {
 285           result ^= (size_t) *p++;
 286           result *= 16777619UL;
 287         }
 288       return result;
 289     }
 290 }
 291
 292 // Return whether one hash table key equals another.
 293
 294 bool
 295 Output_merge_data::Merge_data_eq::operator()(Merge_data_key k1,
 296                                              Merge_data_key k2) const
 297 {
 298   const unsigned char* p1 = this->pomd_->constant(k1);
 299   const unsigned char* p2 = this->pomd_->constant(k2);
 300   return memcmp(p1, p2, this->pomd_->entsize()) == 0;
 301 }
 302
 303 // Add a constant to the end of the section contents.
 304
 305 void
 306 Output_merge_data::add_constant(const unsigned char* p)
 307 {
 308   section_size_type entsize = convert_to_section_size_type(this->entsize());
 309   section_size_type addralign =
 310     convert_to_section_size_type(this->addralign());
 311   section_size_type addsize = std::max(entsize, addralign);
 312   if (this->len_ + addsize > this->alc_)
 313     {
 314       if (this->alc_ == 0)
 315         this->alc_ = 128 * addsize;
 316       else
 317         this->alc_ *= 2;
 318       this->p_ = static_cast<unsigned char*>(realloc(this->p_, this->alc_));
 319       if (this->p_ == NULL)
 320         gold_nomem();
 321     }
 322
 323   memcpy(this->p_ + this->len_, p, entsize);
 324   if (addsize > entsize)
 325     memset(this->p_ + this->len_ + entsize, 0, addsize - entsize);
 326   this->len_ += addsize;
 327 }
 328
 329 // Add the input section SHNDX in OBJECT to a merged output section
 330 // which holds fixed length constants.  Return whether we were able to
 331 // handle the section; if not, it will be linked as usual without
 332 // constant merging.
 333
 334 bool
 335 Output_merge_data::do_add_input_section(Relobj* object, unsigned int shndx)
 336 {
 337   section_size_type len;
 338   bool is_new;
 339   const unsigned char* p = object->decompressed_section_contents(shndx, &len,
 340                                                                  &is_new);
 341
 342   section_size_type entsize = convert_to_section_size_type(this->entsize());
 343
 344   if (len % entsize != 0)
 345     {
 346       if (is_new)
 347         delete[] p;
 348       return false;
 349     }
 350
 351   this->input_count_ += len / entsize;
 352
 353   Object_merge_map* merge_map = object->get_or_create_merge_map();
 354   Object_merge_map::Input_merge_map* input_merge_map =
 355     merge_map->get_or_make_input_merge_map(this, shndx);
 356
 357   for (section_size_type i = 0; i < len; i += entsize, p += entsize)
 358     {
 359       // Add the constant to the section contents.  If we find that it
 360       // is already in the hash table, we will remove it again.
 361       Merge_data_key k = this->len_;
 362       this->add_constant(p);
 363
 364       std::pair<Merge_data_hashtable::iterator, bool> ins =
 365         this->hashtable_.insert(k);
 366
 367       if (!ins.second)
 368         {
 369           // Key was already present.  Remove the copy we just added.
 370           this->len_ -= entsize;
 371           k = *ins.first;
 372         }
 373
 374       // Record the offset of this constant in the output section.
 375       input_merge_map->add_mapping(i, entsize, k);
 376     }
 377
 378   // For script processing, we keep the input sections.
 379   if (this->keeps_input_sections())
 380     record_input_section(object, shndx);
 381
 382   if (is_new)
 383     delete[] p;
 384
 385   return true;
 386 }
 387
 388 // Set the final data size in a merged output section with fixed size
 389 // constants.
 390
 391 void
 392 Output_merge_data::set_final_data_size()
 393 {
 394   // Release the memory we don't need.
 395   this->p_ = static_cast<unsigned char*>(realloc(this->p_, this->len_));
 396   // An Output_merge_data object may be empty and realloc is allowed
 397   // to return a NULL pointer in this case.  An Output_merge_data is empty
 398   // if all its input sections have sizes that are not multiples of entsize.
 399   gold_assert(this->p_ != NULL || this->len_ == 0);
 400   this->set_data_size(this->len_);
 401 }
 402
 403 // Write the data of a merged output section with fixed size constants
 404 // to the file.
 405
 406 void
 407 Output_merge_data::do_write(Output_file* of)
 408 {
 409   of->write(this->offset(), this->p_, this->len_);
 410 }
 411
 412 // Write the data to a buffer.
 413
 414 void
 415 Output_merge_data::do_write_to_buffer(unsigned char* buffer)
 416 {
 417   memcpy(buffer, this->p_, this->len_);
 418 }
 419
 420 // Print merge stats to stderr.
 421
 422 void
 423 Output_merge_data::do_print_merge_stats(const char* section_name)
 424 {
 425   fprintf(stderr,
 426           _("%s: %s merged constants size: %lu; input: %zu; output: %zu\n"),
 427           program_name, section_name,
 428           static_cast<unsigned long>(this->entsize()),
 429           this->input_count_, this->hashtable_.size());
 430 }
 431
 432 // Class Output_merge_string.
 433
 434 // Add an input section to a merged string section.
 435
 436 template<typename Char_type>
 437 bool
 438 Output_merge_string<Char_type>::do_add_input_section(Relobj* object,
 439                                                      unsigned int shndx)
 440 {
 441   section_size_type sec_len;
 442   bool is_new;
 443   uint64_t addralign = this->addralign();
 444   const unsigned char* pdata = object->decompressed_section_contents(shndx,
 445                                                                      &sec_len,
 446                                                                      &is_new,
 447                                                                      &addralign);
 448
 449   const Char_type* p = reinterpret_cast<const Char_type*>(pdata);
 450   const Char_type* pend = p + sec_len / sizeof(Char_type);
 451   const Char_type* pend0 = pend;
 452
 453   if (sec_len % sizeof(Char_type) != 0)
 454     {
 455       object->error(_("mergeable string section length not multiple of "
 456                       "character size"));
 457       if (is_new)
 458         delete[] pdata;
 459       return false;
 460     }
 461
 462   if (pend[-1] != 0)
 463     {
 464       gold_warning(_("%s: last entry in mergeable string section '%s' "
 465                      "not null terminated"),
 466                    object->name().c_str(),
 467                    object->section_name(shndx).c_str());
 468       // Find the end of the last NULL-terminated string in the buffer.
 469       while (pend0 > p && pend0[-1] != 0)
 470         --pend0;
 471     }
 472
 473   Merged_strings_list* merged_strings_list =
 474       new Merged_strings_list(object, shndx);
 475   this->merged_strings_lists_.push_back(merged_strings_list);
 476   Merged_strings& merged_strings = merged_strings_list->merged_strings;
 477
 478   // Count the number of non-null strings in the section and size the list.
 479   size_t count = 0;
 480   const Char_type* pt = p;
 481   while (pt < pend0)
 482     {
 483       size_t len = string_length(pt);
 484       if (len != 0)
 485         ++count;
 486       pt += len + 1;
 487     }
 488   if (pend0 < pend)
 489     ++count;
 490   merged_strings.reserve(count + 1);
 491
 492   // The index I is in bytes, not characters.
 493   section_size_type i = 0;
 494
 495   // We assume here that the beginning of the section is correctly
 496   // aligned, so each string within the section must retain the same
 497   // modulo.
 498   uintptr_t init_align_modulo = (reinterpret_cast<uintptr_t>(pdata)
 499                                  & (addralign - 1));
 500   bool has_misaligned_strings = false;
 501
 502   while (p < pend)
 503     {
 504       size_t len = p < pend0 ? string_length(p) : pend - p;
 505
 506       // Within merge input section each string must be aligned.
 507       if (len != 0
 508           && ((reinterpret_cast<uintptr_t>(p) & (addralign - 1))
 509               != init_align_modulo))
 510           has_misaligned_strings = true;
 511
 512       Stringpool::Key key;
 513       this->stringpool_.add_with_length(p, len, true, &key);
 514
 515       merged_strings.push_back(Merged_string(i, key));
 516       p += len + 1;
 517       i += (len + 1) * sizeof(Char_type);
 518     }
 519
 520   // Record the last offset in the input section so that we can
 521   // compute the length of the last string.
 522   merged_strings.push_back(Merged_string(i, 0));
 523
 524   this->input_count_ += count;
 525   this->input_size_ += i;
 526
 527   if (has_misaligned_strings)
 528     gold_warning(_("%s: section %s contains incorrectly aligned strings;"
 529                    " the alignment of those strings won't be preserved"),
 530                  object->name().c_str(),
 531                  object->section_name(shndx).c_str());
 532
 533   // For script processing, we keep the input sections.
 534   if (this->keeps_input_sections())
 535     record_input_section(object, shndx);
 536
 537   if (is_new)
 538     delete[] pdata;
 539
 540   return true;
 541 }
 542
 543 // Finalize the mappings from the input sections to the output
 544 // section, and return the final data size.
 545
 546 template<typename Char_type>
 547 section_size_type
 548 Output_merge_string<Char_type>::finalize_merged_data()
 549 {
 550   this->stringpool_.set_string_offsets();
 551
 552   for (typename Merged_strings_lists::const_iterator l =
 553          this->merged_strings_lists_.begin();
 554        l != this->merged_strings_lists_.end();
 555        ++l)
 556     {
 557       section_offset_type last_input_offset = 0;
 558       section_offset_type last_output_offset = 0;
 559       Relobj *object = (*l)->object;
 560       Object_merge_map* merge_map = object->get_or_create_merge_map();
 561       Object_merge_map::Input_merge_map* input_merge_map =
 562         merge_map->get_or_make_input_merge_map(this, (*l)->shndx);
 563
 564       for (typename Merged_strings::const_iterator p =
 565              (*l)->merged_strings.begin();
 566            p != (*l)->merged_strings.end();
 567            ++p)
 568         {
 569           section_size_type length = p->offset - last_input_offset;
 570           if (length > 0)
 571             input_merge_map->add_mapping(last_input_offset, length,
 572                                          last_output_offset);
 573           last_input_offset = p->offset;
 574           if (p->stringpool_key != 0)
 575             last_output_offset =
 576                 this->stringpool_.get_offset_from_key(p->stringpool_key);
 577         }
 578       delete *l;
 579     }
 580
 581   // Save some memory.  This also ensures that this function will work
 582   // if called twice, as may happen if Layout::set_segment_offsets
 583   // finds a better alignment.
 584   this->merged_strings_lists_.clear();
 585
 586   return this->stringpool_.get_strtab_size();
 587 }
 588
 589 template<typename Char_type>
 590 void
 591 Output_merge_string<Char_type>::set_final_data_size()
 592 {
 593   const off_t final_data_size = this->finalize_merged_data();
 594   this->set_data_size(final_data_size);
 595 }
 596
 597 // Write out a merged string section.
 598
 599 template<typename Char_type>
 600 void
 601 Output_merge_string<Char_type>::do_write(Output_file* of)
 602 {
 603   this->stringpool_.write(of, this->offset());
 604 }
 605
 606 // Write a merged string section to a buffer.
 607
 608 template<typename Char_type>
 609 void
 610 Output_merge_string<Char_type>::do_write_to_buffer(unsigned char* buffer)
 611 {
 612   this->stringpool_.write_to_buffer(buffer, this->data_size());
 613 }
 614
 615 // Return the name of the types of string to use with
 616 // do_print_merge_stats.
 617
 618 template<typename Char_type>
 619 const char*
 620 Output_merge_string<Char_type>::string_name()
 621 {
 622   gold_unreachable();
 623   return NULL;
 624 }
 625
 626 template<>
 627 const char*
 628 Output_merge_string<char>::string_name()
 629 {
 630   return "strings";
 631 }
 632
 633 template<>
 634 const char*
 635 Output_merge_string<uint16_t>::string_name()
 636 {
 637   return "16-bit strings";
 638 }
 639
 640 template<>
 641 const char*
 642 Output_merge_string<uint32_t>::string_name()
 643 {
 644   return "32-bit strings";
 645 }
 646
 647 // Print merge stats to stderr.
 648
 649 template<typename Char_type>
 650 void
 651 Output_merge_string<Char_type>::do_print_merge_stats(const char* section_name)
 652 {
 653   char buf[200];
 654   snprintf(buf, sizeof buf, "%s merged %s", section_name, this->string_name());
 655   fprintf(stderr, _("%s: %s input bytes: %zu\n"),
 656           program_name, buf, this->input_size_);
 657   fprintf(stderr, _("%s: %s input strings: %zu\n"),
 658           program_name, buf, this->input_count_);
 659   this->stringpool_.print_stats(buf);
 660 }
 661
 662 // Instantiate the templates we need.
 663
 664 template
 665 class Output_merge_string<char>;
 666
 667 template
 668 class Output_merge_string<char16_t>;
 669
 670 template
 671 class Output_merge_string<char32_t>;
 672
 673 #if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
 674 template
 675 void
 676 Object_merge_map::initialize_input_to_output_map<32>(
 677     unsigned int shndx,
 678     elfcpp::Elf_types<32>::Elf_Addr starting_address,
 679     Unordered_map<section_offset_type, elfcpp::Elf_types<32>::Elf_Addr>*);
 680 #endif
 681
 682 #if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
 683 template
 684 void
 685 Object_merge_map::initialize_input_to_output_map<64>(
 686     unsigned int shndx,
 687     elfcpp::Elf_types<64>::Elf_Addr starting_address,
 688     Unordered_map<section_offset_type, elfcpp::Elf_types<64>::Elf_Addr>*);
 689 #endif
 690
 691 } // End namespace gold.