gold/layout.h

   1 // layout.h -- lay out output file sections for gold  -*- C++ -*-
   2
   3 // Copyright 2006, 2007 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 #ifndef GOLD_LAYOUT_H
  24 #define GOLD_LAYOUT_H
  25
  26 #include <list>
  27 #include <string>
  28 #include <utility>
  29 #include <vector>
  30
  31 #include "workqueue.h"
  32 #include "object.h"
  33 #include "dynobj.h"
  34 #include "stringpool.h"
  35
  36 namespace gold
  37 {
  38
  39 class General_options;
  40 class Input_objects;
  41 class Symbol_table;
  42 class Output_section_data;
  43 class Output_section;
  44 class Output_section_headers;
  45 class Output_segment;
  46 class Output_data;
  47 class Output_data_dynamic;
  48 class Eh_frame;
  49 class Target;
  50
  51 // This task function handles mapping the input sections to output
  52 // sections and laying them out in memory.
  53
  54 class Layout_task_runner : public Task_function_runner
  55 {
  56  public:
  57   // OPTIONS is the command line options, INPUT_OBJECTS is the list of
  58   // input objects, SYMTAB is the symbol table, LAYOUT is the layout
  59   // object.
  60   Layout_task_runner(const General_options& options,
  61                      const Input_objects* input_objects,
  62                      Symbol_table* symtab,
  63                      Layout* layout)
  64     : options_(options), input_objects_(input_objects), symtab_(symtab),
  65       layout_(layout)
  66   { }
  67
  68   // Run the operation.
  69   void
  70   run(Workqueue*, const Task*);
  71
  72  private:
  73   Layout_task_runner(const Layout_task_runner&);
  74   Layout_task_runner& operator=(const Layout_task_runner&);
  75
  76   const General_options& options_;
  77   const Input_objects* input_objects_;
  78   Symbol_table* symtab_;
  79   Layout* layout_;
  80 };
  81
  82 // This class handles the details of laying out input sections.
  83
  84 class Layout
  85 {
  86  public:
  87   Layout(const General_options& options);
  88
  89   // Given an input section SHNDX, named NAME, with data in SHDR, from
  90   // the object file OBJECT, return the output section where this
  91   // input section should go.  RELOC_SHNDX is the index of a
  92   // relocation section which applies to this section, or 0 if none,
  93   // or -1U if more than one.  RELOC_TYPE is the type of the
  94   // relocation section if there is one.  Set *OFFSET to the offset
  95   // within the output section.
  96   template<int size, bool big_endian>
  97   Output_section*
  98   layout(Sized_relobj<size, big_endian> *object, unsigned int shndx,
  99          const char* name, const elfcpp::Shdr<size, big_endian>& shdr,
 100          unsigned int reloc_shndx, unsigned int reloc_type, off_t* offset);
 101
 102   // Like layout, only for exception frame sections.  OBJECT is an
 103   // object file.  SYMBOLS is the contents of the symbol table
 104   // section, with size SYMBOLS_SIZE.  SYMBOL_NAMES is the contents of
 105   // the symbol name section, with size SYMBOL_NAMES_SIZE.  SHNDX is a
 106   // .eh_frame section in OBJECT.  SHDR is the section header.
 107   // RELOC_SHNDX is the index of a relocation section which applies to
 108   // this section, or 0 if none, or -1U if more than one.  RELOC_TYPE
 109   // is the type of the relocation section if there is one.  This
 110   // returns the output section, and sets *OFFSET to the offset.
 111   template<int size, bool big_endian>
 112   Output_section*
 113   layout_eh_frame(Sized_relobj<size, big_endian>* object,
 114                   const unsigned char* symbols,
 115                   off_t symbols_size,
 116                   const unsigned char* symbol_names,
 117                   off_t symbol_names_size,
 118                   unsigned int shndx,
 119                   const elfcpp::Shdr<size, big_endian>& shdr,
 120                   unsigned int reloc_shndx, unsigned int reloc_type,
 121                   off_t* offset);
 122
 123   // Handle a GNU stack note.  This is called once per input object
 124   // file.  SEEN_GNU_STACK is true if the object file has a
 125   // .note.GNU-stack section.  GNU_STACK_FLAGS is the section flags
 126   // from that section if there was one.
 127   void
 128   layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags);
 129
 130   // Add an Output_section_data to the layout.  This is used for
 131   // special sections like the GOT section.
 132   void
 133   add_output_section_data(const char* name, elfcpp::Elf_Word type,
 134                           elfcpp::Elf_Xword flags,
 135                           Output_section_data*);
 136
 137   // Create dynamic sections if necessary.
 138   void
 139   create_initial_dynamic_sections(const Input_objects*, Symbol_table*);
 140
 141   // Define __start and __stop symbols for output sections.
 142   void
 143   define_section_symbols(Symbol_table*, const Target*);
 144
 145   // Return the Stringpool used for symbol names.
 146   const Stringpool*
 147   sympool() const
 148   { return &this->sympool_; }
 149
 150   // Return the Stringpool used for dynamic symbol names and dynamic
 151   // tags.
 152   const Stringpool*
 153   dynpool() const
 154   { return &this->dynpool_; }
 155
 156   // Return whether a section is a .gnu.linkonce section, given the
 157   // section name.
 158   static inline bool
 159   is_linkonce(const char* name)
 160   { return strncmp(name, ".gnu.linkonce", sizeof(".gnu.linkonce") - 1) == 0; }
 161
 162   // Record the signature of a comdat section, and return whether to
 163   // include it in the link.  The GROUP parameter is true for a
 164   // section group signature, false for a signature derived from a
 165   // .gnu.linkonce section.
 166   bool
 167   add_comdat(const char*, bool group);
 168
 169   // Finalize the layout after all the input sections have been added.
 170   off_t
 171   finalize(const Input_objects*, Symbol_table*, const Task*);
 172
 173   // Return whether any sections require postprocessing.
 174   bool
 175   any_postprocessing_sections() const
 176   { return this->any_postprocessing_sections_; }
 177
 178   // Return the size of the output file.
 179   off_t
 180   output_file_size() const
 181   { return this->output_file_size_; }
 182
 183   // Return the TLS segment.  This will return NULL if there isn't
 184   // one.
 185   Output_segment*
 186   tls_segment() const
 187   { return this->tls_segment_; }
 188
 189   // Return the normal symbol table.
 190   Output_section*
 191   symtab_section() const
 192   {
 193     gold_assert(this->symtab_section_ != NULL);
 194     return this->symtab_section_;
 195   }
 196
 197   // Return the dynamic symbol table.
 198   Output_section*
 199   dynsym_section() const
 200   {
 201     gold_assert(this->dynsym_section_ != NULL);
 202     return this->dynsym_section_;
 203   }
 204
 205   // Return the dynamic tags.
 206   Output_data_dynamic*
 207   dynamic_data() const
 208   { return this->dynamic_data_; }
 209
 210   // Write out the output sections.
 211   void
 212   write_output_sections(Output_file* of) const;
 213
 214   // Write out data not associated with an input file or the symbol
 215   // table.
 216   void
 217   write_data(const Symbol_table*, Output_file*) const;
 218
 219   // Write out output sections which can not be written until all the
 220   // input sections are complete.
 221   void
 222   write_sections_after_input_sections(Output_file* of);
 223
 224   // Return an output section named NAME, or NULL if there is none.
 225   Output_section*
 226   find_output_section(const char* name) const;
 227
 228   // Return an output segment of type TYPE, with segment flags SET set
 229   // and segment flags CLEAR clear.  Return NULL if there is none.
 230   Output_segment*
 231   find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
 232                       elfcpp::Elf_Word clear) const;
 233
 234   // Set a flag to indicate that an object file uses the static TLS model.
 235   void
 236   set_has_static_tls()
 237   { this->has_static_tls_ = true; }
 238
 239   // Return true if any object file uses the static TLS model.
 240   bool
 241   has_static_tls() const
 242   { return this->has_static_tls_; }
 243
 244   // Set the name of the entry symbol.  This is used by linker scripts
 245   // which look like regular objects.
 246   void
 247   set_entry(const char* entry)
 248   { this->entry_ = entry; }
 249
 250   // Dump statistical information to stderr.
 251   void
 252   print_stats() const;
 253
 254   // The list of segments.
 255
 256   typedef std::vector<Output_segment*> Segment_list;
 257
 258   // The list of sections not attached to a segment.
 259
 260   typedef std::vector<Output_section*> Section_list;
 261
 262   // The list of information to write out which is not attached to
 263   // either a section or a segment.
 264   typedef std::vector<Output_data*> Data_list;
 265
 266  private:
 267   Layout(const Layout&);
 268   Layout& operator=(const Layout&);
 269
 270   // Mapping from .gnu.linkonce section names to output section names.
 271   struct Linkonce_mapping
 272   {
 273     const char* from;
 274     int fromlen;
 275     const char* to;
 276     int tolen;
 277   };
 278   static const Linkonce_mapping linkonce_mapping[];
 279   static const int linkonce_mapping_count;
 280
 281   // Create a .note section for gold.
 282   void
 283   create_gold_note();
 284
 285   // Record whether the stack must be executable.
 286   void
 287   create_executable_stack_info(const Target*);
 288
 289   // Find the first read-only PT_LOAD segment, creating one if
 290   // necessary.
 291   Output_segment*
 292   find_first_load_seg();
 293
 294   // Count the local symbols in the regular symbol table and the dynamic
 295   // symbol table, and build the respective string pools.
 296   void
 297   count_local_symbols(const Task*, const Input_objects*);
 298
 299   // Create the output sections for the symbol table.
 300   void
 301   create_symtab_sections(const Input_objects*, Symbol_table*, off_t*);
 302
 303   // Create the .shstrtab section.
 304   Output_section*
 305   create_shstrtab();
 306
 307   // Create the section header table.
 308   void
 309   create_shdrs(off_t*);
 310
 311   // Create the dynamic symbol table.
 312   void
 313   create_dynamic_symtab(const Input_objects*, const Target*,
 314                         Symbol_table*, Output_section** pdynstr,
 315                         unsigned int* plocal_dynamic_count,
 316                         std::vector<Symbol*>* pdynamic_symbols,
 317                         Versions* versions);
 318
 319   // Assign offsets to each local portion of the dynamic symbol table.
 320   void
 321   assign_local_dynsym_offsets(const Input_objects*);
 322
 323   // Finish the .dynamic section and PT_DYNAMIC segment.
 324   void
 325   finish_dynamic_section(const Input_objects*, const Symbol_table*);
 326
 327   // Create the .interp section and PT_INTERP segment.
 328   void
 329   create_interp(const Target* target);
 330
 331   // Create the version sections.
 332   void
 333   create_version_sections(const Versions*,
 334                           const Symbol_table*,
 335                           unsigned int local_symcount,
 336                           const std::vector<Symbol*>& dynamic_symbols,
 337                           const Output_section* dynstr);
 338
 339   template<int size, bool big_endian>
 340   void
 341   sized_create_version_sections(const Versions* versions,
 342                                 const Symbol_table*,
 343                                 unsigned int local_symcount,
 344                                 const std::vector<Symbol*>& dynamic_symbols,
 345                                 const Output_section* dynstr
 346                                 ACCEPT_SIZE_ENDIAN);
 347
 348   // Return whether to include this section in the link.
 349   template<int size, bool big_endian>
 350   bool
 351   include_section(Sized_relobj<size, big_endian>* object, const char* name,
 352                   const elfcpp::Shdr<size, big_endian>&);
 353
 354   // Return the output section name to use given an input section
 355   // name.  Set *PLEN to the length of the name.  *PLEN must be
 356   // initialized to the length of NAME.
 357   static const char*
 358   output_section_name(const char* name, size_t* plen);
 359
 360   // Return the output section name to use for a linkonce section
 361   // name.  PLEN is as for output_section_name.
 362   static const char*
 363   linkonce_output_name(const char* name, size_t* plen);
 364
 365   // Return the output section for NAME, TYPE and FLAGS.
 366   Output_section*
 367   get_output_section(const char* name, Stringpool::Key name_key,
 368                      elfcpp::Elf_Word type, elfcpp::Elf_Xword flags);
 369
 370   // Create a new Output_section.
 371   Output_section*
 372   make_output_section(const char* name, elfcpp::Elf_Word type,
 373                       elfcpp::Elf_Xword flags);
 374
 375   // Set the final file offsets of all the segments.
 376   off_t
 377   set_segment_offsets(const Target*, Output_segment*, unsigned int* pshndx);
 378
 379   // Set the final file offsets of all the sections not associated
 380   // with a segment.  We set section offsets in three passes: the
 381   // first handles all allocated sections, the second sections that
 382   // require postprocessing, and the last the late-bound STRTAB
 383   // sections (probably only shstrtab, which is the one we care about
 384   // because it holds section names).
 385   enum Section_offset_pass
 386   {
 387     BEFORE_INPUT_SECTIONS_PASS,
 388     POSTPROCESSING_SECTIONS_PASS,
 389     STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS
 390   };
 391   off_t
 392   set_section_offsets(off_t, Section_offset_pass pass);
 393
 394   // Set the final section indexes of all the sections not associated
 395   // with a segment.  Returns the next unused index.
 396   unsigned int
 397   set_section_indexes(unsigned int pshndx);
 398
 399   // Return whether SEG1 comes before SEG2 in the output file.
 400   static bool
 401   segment_precedes(const Output_segment* seg1, const Output_segment* seg2);
 402
 403   // Map from section flags to segment flags.
 404   static elfcpp::Elf_Word
 405   section_flags_to_segment(elfcpp::Elf_Xword flags);
 406
 407   // A mapping used for group signatures.
 408   typedef Unordered_map<std::string, bool> Signatures;
 409
 410   // Mapping from input section name/type/flags to output section.  We
 411   // use canonicalized strings here.
 412
 413   typedef std::pair<Stringpool::Key,
 414                     std::pair<elfcpp::Elf_Word, elfcpp::Elf_Xword> > Key;
 415
 416   struct Hash_key
 417   {
 418     size_t
 419     operator()(const Key& k) const;
 420   };
 421
 422   typedef Unordered_map<Key, Output_section*, Hash_key> Section_name_map;
 423
 424   // A comparison class for segments.
 425
 426   struct Compare_segments
 427   {
 428     bool
 429     operator()(const Output_segment* seg1, const Output_segment* seg2)
 430     { return Layout::segment_precedes(seg1, seg2); }
 431   };
 432
 433   // A reference to the options on the command line.
 434   const General_options& options_;
 435   // The name of the entry symbol.  This is from the command line, or
 436   // from a linker script, or is NULL.
 437   const char* entry_;
 438   // The output section names.
 439   Stringpool namepool_;
 440   // The output symbol names.
 441   Stringpool sympool_;
 442   // The dynamic strings, if needed.
 443   Stringpool dynpool_;
 444   // The list of group sections and linkonce sections which we have seen.
 445   Signatures signatures_;
 446   // The mapping from input section name/type/flags to output sections.
 447   Section_name_map section_name_map_;
 448   // The list of output segments.
 449   Segment_list segment_list_;
 450   // The list of output sections.
 451   Section_list section_list_;
 452   // The list of output sections which are not attached to any output
 453   // segment.
 454   Section_list unattached_section_list_;
 455   // The list of unattached Output_data objects which require special
 456   // handling because they are not Output_sections.
 457   Data_list special_output_list_;
 458   // The section headers.
 459   Output_section_headers* section_headers_;
 460   // A pointer to the PT_TLS segment if there is one.
 461   Output_segment* tls_segment_;
 462   // The SHT_SYMTAB output section.
 463   Output_section* symtab_section_;
 464   // The SHT_DYNSYM output section if there is one.
 465   Output_section* dynsym_section_;
 466   // The SHT_DYNAMIC output section if there is one.
 467   Output_section* dynamic_section_;
 468   // The dynamic data which goes into dynamic_section_.
 469   Output_data_dynamic* dynamic_data_;
 470   // The exception frame output section if there is one.
 471   Output_section* eh_frame_section_;
 472   // The exception frame data for eh_frame_section_.
 473   Eh_frame* eh_frame_data_;
 474   // The exception frame header output section if there is one.
 475   Output_section* eh_frame_hdr_section_;
 476   // The size of the output file.
 477   off_t output_file_size_;
 478   // Whether we have seen an object file marked to require an
 479   // executable stack.
 480   bool input_requires_executable_stack_;
 481   // Whether we have seen at least one object file with an executable
 482   // stack marker.
 483   bool input_with_gnu_stack_note_;
 484   // Whether we have seen at least one object file without an
 485   // executable stack marker.
 486   bool input_without_gnu_stack_note_;
 487   // Whether we have seen an object file that uses the static TLS model.
 488   bool has_static_tls_;
 489   // Whether any sections require postprocessing.
 490   bool any_postprocessing_sections_;
 491 };
 492
 493 // This task handles writing out data in output sections which is not
 494 // part of an input section, or which requires special handling.  When
 495 // this is done, it unblocks both output_sections_blocker and
 496 // final_blocker.
 497
 498 class Write_sections_task : public Task
 499 {
 500  public:
 501   Write_sections_task(const Layout* layout, Output_file* of,
 502                       Task_token* output_sections_blocker,
 503                       Task_token* final_blocker)
 504     : layout_(layout), of_(of),
 505       output_sections_blocker_(output_sections_blocker),
 506       final_blocker_(final_blocker)
 507   { }
 508
 509   // The standard Task methods.
 510
 511   Task_token*
 512   is_runnable();
 513
 514   void
 515   locks(Task_locker*);
 516
 517   void
 518   run(Workqueue*);
 519
 520   std::string
 521   get_name() const
 522   { return "Write_sections_task"; }
 523
 524  private:
 525   class Write_sections_locker;
 526
 527   const Layout* layout_;
 528   Output_file* of_;
 529   Task_token* output_sections_blocker_;
 530   Task_token* final_blocker_;
 531 };
 532
 533 // This task handles writing out data which is not part of a section
 534 // or segment.
 535
 536 class Write_data_task : public Task
 537 {
 538  public:
 539   Write_data_task(const Layout* layout, const Symbol_table* symtab,
 540                   Output_file* of, Task_token* final_blocker)
 541     : layout_(layout), symtab_(symtab), of_(of), final_blocker_(final_blocker)
 542   { }
 543
 544   // The standard Task methods.
 545
 546   Task_token*
 547   is_runnable();
 548
 549   void
 550   locks(Task_locker*);
 551
 552   void
 553   run(Workqueue*);
 554
 555   std::string
 556   get_name() const
 557   { return "Write_data_task"; }
 558
 559  private:
 560   const Layout* layout_;
 561   const Symbol_table* symtab_;
 562   Output_file* of_;
 563   Task_token* final_blocker_;
 564 };
 565
 566 // This task handles writing out the global symbols.
 567
 568 class Write_symbols_task : public Task
 569 {
 570  public:
 571   Write_symbols_task(const Symbol_table* symtab,
 572                      const Input_objects* input_objects,
 573                      const Stringpool* sympool, const Stringpool* dynpool,
 574                      Output_file* of, Task_token* final_blocker)
 575     : symtab_(symtab), input_objects_(input_objects), sympool_(sympool),
 576       dynpool_(dynpool), of_(of), final_blocker_(final_blocker)
 577   { }
 578
 579   // The standard Task methods.
 580
 581   Task_token*
 582   is_runnable();
 583
 584   void
 585   locks(Task_locker*);
 586
 587   void
 588   run(Workqueue*);
 589
 590   std::string
 591   get_name() const
 592   { return "Write_symbols_task"; }
 593
 594  private:
 595   const Symbol_table* symtab_;
 596   const Input_objects* input_objects_;
 597   const Stringpool* sympool_;
 598   const Stringpool* dynpool_;
 599   Output_file* of_;
 600   Task_token* final_blocker_;
 601 };
 602
 603 // This task handles writing out data in output sections which can't
 604 // be written out until all the input sections have been handled.
 605 // This is for sections whose contents is based on the contents of
 606 // other output sections.
 607
 608 class Write_after_input_sections_task : public Task
 609 {
 610  public:
 611   Write_after_input_sections_task(Layout* layout, Output_file* of,
 612                                   Task_token* input_sections_blocker,
 613                                   Task_token* final_blocker)
 614     : layout_(layout), of_(of),
 615       input_sections_blocker_(input_sections_blocker),
 616       final_blocker_(final_blocker)
 617   { }
 618
 619   // The standard Task methods.
 620
 621   Task_token*
 622   is_runnable();
 623
 624   void
 625   locks(Task_locker*);
 626
 627   void
 628   run(Workqueue*);
 629
 630   std::string
 631   get_name() const
 632   { return "Write_after_input_sections_task"; }
 633
 634  private:
 635   Layout* layout_;
 636   Output_file* of_;
 637   Task_token* input_sections_blocker_;
 638   Task_token* final_blocker_;
 639 };
 640
 641 // This task function handles closing the file.
 642
 643 class Close_task_runner : public Task_function_runner
 644 {
 645  public:
 646   Close_task_runner(Output_file* of)
 647     : of_(of)
 648   { }
 649
 650   // Run the operation.
 651   void
 652   run(Workqueue*, const Task*);
 653
 654  private:
 655   Output_file* of_;
 656 };
 657
 658 // A small helper function to align an address.
 659
 660 inline uint64_t
 661 align_address(uint64_t address, uint64_t addralign)
 662 {
 663   if (addralign != 0)
 664     address = (address + addralign - 1) &~ (addralign - 1);
 665   return address;
 666 }
 667
 668 } // End namespace gold.
 669
 670 #endif // !defined(GOLD_LAYOUT_H)