gold/layout.h

   1 // layout.h -- lay out output file sections for gold  -*- C++ -*-
   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 #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 "script.h"
  32 #include "workqueue.h"
  33 #include "object.h"
  34 #include "dynobj.h"
  35 #include "stringpool.h"
  36
  37 namespace gold
  38 {
  39
  40 class General_options;
  41 class Input_objects;
  42 class Symbol_table;
  43 class Output_section_data;
  44 class Output_section;
  45 class Output_section_headers;
  46 class Output_segment;
  47 class Output_data;
  48 class Output_data_dynamic;
  49 class Eh_frame;
  50 class Target;
  51
  52 // This task function handles mapping the input sections to output
  53 // sections and laying them out in memory.
  54
  55 class Layout_task_runner : public Task_function_runner
  56 {
  57  public:
  58   // OPTIONS is the command line options, INPUT_OBJECTS is the list of
  59   // input objects, SYMTAB is the symbol table, LAYOUT is the layout
  60   // object.
  61   Layout_task_runner(const General_options& options,
  62                      const Input_objects* input_objects,
  63                      Symbol_table* symtab,
  64                      Layout* layout)
  65     : options_(options), input_objects_(input_objects), symtab_(symtab),
  66       layout_(layout)
  67   { }
  68
  69   // Run the operation.
  70   void
  71   run(Workqueue*, const Task*);
  72
  73  private:
  74   Layout_task_runner(const Layout_task_runner&);
  75   Layout_task_runner& operator=(const Layout_task_runner&);
  76
  77   const General_options& options_;
  78   const Input_objects* input_objects_;
  79   Symbol_table* symtab_;
  80   Layout* layout_;
  81 };
  82
  83 // This class handles the details of laying out input sections.
  84
  85 class Layout
  86 {
  87  public:
  88   Layout(const General_options& options, Script_options*);
  89
  90   // Given an input section SHNDX, named NAME, with data in SHDR, from
  91   // the object file OBJECT, return the output section where this
  92   // input section should go.  RELOC_SHNDX is the index of a
  93   // relocation section which applies to this section, or 0 if none,
  94   // or -1U if more than one.  RELOC_TYPE is the type of the
  95   // relocation section if there is one.  Set *OFFSET to the offset
  96   // within the output section.
  97   template<int size, bool big_endian>
  98   Output_section*
  99   layout(Sized_relobj<size, big_endian> *object, unsigned int shndx,
 100          const char* name, const elfcpp::Shdr<size, big_endian>& shdr,
 101          unsigned int reloc_shndx, unsigned int reloc_type, off_t* offset);
 102
 103   // Like layout, only for exception frame sections.  OBJECT is an
 104   // object file.  SYMBOLS is the contents of the symbol table
 105   // section, with size SYMBOLS_SIZE.  SYMBOL_NAMES is the contents of
 106   // the symbol name section, with size SYMBOL_NAMES_SIZE.  SHNDX is a
 107   // .eh_frame section in OBJECT.  SHDR is the section header.
 108   // RELOC_SHNDX is the index of a relocation section which applies to
 109   // this section, or 0 if none, or -1U if more than one.  RELOC_TYPE
 110   // is the type of the relocation section if there is one.  This
 111   // returns the output section, and sets *OFFSET to the offset.
 112   template<int size, bool big_endian>
 113   Output_section*
 114   layout_eh_frame(Sized_relobj<size, big_endian>* object,
 115                   const unsigned char* symbols,
 116                   off_t symbols_size,
 117                   const unsigned char* symbol_names,
 118                   off_t symbol_names_size,
 119                   unsigned int shndx,
 120                   const elfcpp::Shdr<size, big_endian>& shdr,
 121                   unsigned int reloc_shndx, unsigned int reloc_type,
 122                   off_t* offset);
 123
 124   // Handle a GNU stack note.  This is called once per input object
 125   // file.  SEEN_GNU_STACK is true if the object file has a
 126   // .note.GNU-stack section.  GNU_STACK_FLAGS is the section flags
 127   // from that section if there was one.
 128   void
 129   layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags);
 130
 131   // Add an Output_section_data to the layout.  This is used for
 132   // special sections like the GOT section.
 133   void
 134   add_output_section_data(const char* name, elfcpp::Elf_Word type,
 135                           elfcpp::Elf_Xword flags,
 136                           Output_section_data*);
 137
 138   // Create dynamic sections if necessary.
 139   void
 140   create_initial_dynamic_sections(Symbol_table*);
 141
 142   // Define __start and __stop symbols for output sections.
 143   void
 144   define_section_symbols(Symbol_table*);
 145
 146   // Define symbols from any linker script.
 147   void
 148   define_script_symbols(Symbol_table* symtab)
 149   { this->script_options_->add_symbols_to_table(symtab); }
 150
 151   // Return the Stringpool used for symbol names.
 152   const Stringpool*
 153   sympool() const
 154   { return &this->sympool_; }
 155
 156   // Return the Stringpool used for dynamic symbol names and dynamic
 157   // tags.
 158   const Stringpool*
 159   dynpool() const
 160   { return &this->dynpool_; }
 161
 162   // Return whether a section is a .gnu.linkonce section, given the
 163   // section name.
 164   static inline bool
 165   is_linkonce(const char* name)
 166   { return strncmp(name, ".gnu.linkonce", sizeof(".gnu.linkonce") - 1) == 0; }
 167
 168   // Record the signature of a comdat section, and return whether to
 169   // include it in the link.  The GROUP parameter is true for a
 170   // section group signature, false for a signature derived from a
 171   // .gnu.linkonce section.
 172   bool
 173   add_comdat(const char*, bool group);
 174
 175   // Finalize the layout after all the input sections have been added.
 176   off_t
 177   finalize(const Input_objects*, Symbol_table*, const Task*);
 178
 179   // Return whether any sections require postprocessing.
 180   bool
 181   any_postprocessing_sections() const
 182   { return this->any_postprocessing_sections_; }
 183
 184   // Return the size of the output file.
 185   off_t
 186   output_file_size() const
 187   { return this->output_file_size_; }
 188
 189   // Return the TLS segment.  This will return NULL if there isn't
 190   // one.
 191   Output_segment*
 192   tls_segment() const
 193   { return this->tls_segment_; }
 194
 195   // Return the normal symbol table.
 196   Output_section*
 197   symtab_section() const
 198   {
 199     gold_assert(this->symtab_section_ != NULL);
 200     return this->symtab_section_;
 201   }
 202
 203   // Return the dynamic symbol table.
 204   Output_section*
 205   dynsym_section() const
 206   {
 207     gold_assert(this->dynsym_section_ != NULL);
 208     return this->dynsym_section_;
 209   }
 210
 211   // Return the dynamic tags.
 212   Output_data_dynamic*
 213   dynamic_data() const
 214   { return this->dynamic_data_; }
 215
 216   // Write out the output sections.
 217   void
 218   write_output_sections(Output_file* of) const;
 219
 220   // Write out data not associated with an input file or the symbol
 221   // table.
 222   void
 223   write_data(const Symbol_table*, Output_file*) const;
 224
 225   // Write out output sections which can not be written until all the
 226   // input sections are complete.
 227   void
 228   write_sections_after_input_sections(Output_file* of);
 229
 230   // Return an output section named NAME, or NULL if there is none.
 231   Output_section*
 232   find_output_section(const char* name) const;
 233
 234   // Return an output segment of type TYPE, with segment flags SET set
 235   // and segment flags CLEAR clear.  Return NULL if there is none.
 236   Output_segment*
 237   find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
 238                       elfcpp::Elf_Word clear) const;
 239
 240   // Return the number of segments we expect to produce.
 241   size_t
 242   expected_segment_count() const;
 243
 244   // Set a flag to indicate that an object file uses the static TLS model.
 245   void
 246   set_has_static_tls()
 247   { this->has_static_tls_ = true; }
 248
 249   // Return true if any object file uses the static TLS model.
 250   bool
 251   has_static_tls() const
 252   { return this->has_static_tls_; }
 253
 254   // Return the options which may be set by a linker script.
 255   Script_options*
 256   script_options()
 257   { return this->script_options_; }
 258
 259   const Script_options*
 260   script_options() const
 261   { return this->script_options_; }
 262
 263   // Dump statistical information to stderr.
 264   void
 265   print_stats() const;
 266
 267   // A list of segments.
 268
 269   typedef std::vector<Output_segment*> Segment_list;
 270
 271   // A list of sections.
 272
 273   typedef std::vector<Output_section*> Section_list;
 274
 275   // The list of information to write out which is not attached to
 276   // either a section or a segment.
 277   typedef std::vector<Output_data*> Data_list;
 278
 279   // Store the allocated sections into the section list.  This is used
 280   // by the linker script code.
 281   void
 282   get_allocated_sections(Section_list*) const;
 283
 284   // Make a segment.  This is used by the linker script code.
 285   Output_segment*
 286   make_output_segment(elfcpp::Elf_Word type, elfcpp::Elf_Word flags);
 287
 288   // Return the number of segments.
 289   size_t
 290   segment_count() const
 291   { return this->segment_list_.size(); }
 292
 293   // Map from section flags to segment flags.
 294   static elfcpp::Elf_Word
 295   section_flags_to_segment(elfcpp::Elf_Xword flags);
 296
 297  private:
 298   Layout(const Layout&);
 299   Layout& operator=(const Layout&);
 300
 301   // Mapping from .gnu.linkonce section names to output section names.
 302   struct Linkonce_mapping
 303   {
 304     const char* from;
 305     int fromlen;
 306     const char* to;
 307     int tolen;
 308   };
 309   static const Linkonce_mapping linkonce_mapping[];
 310   static const int linkonce_mapping_count;
 311
 312   // Create a .note section for gold.
 313   void
 314   create_gold_note();
 315
 316   // Record whether the stack must be executable.
 317   void
 318   create_executable_stack_info(const Target*);
 319
 320   // Find the first read-only PT_LOAD segment, creating one if
 321   // necessary.
 322   Output_segment*
 323   find_first_load_seg();
 324
 325   // Count the local symbols in the regular symbol table and the dynamic
 326   // symbol table, and build the respective string pools.
 327   void
 328   count_local_symbols(const Task*, const Input_objects*);
 329
 330   // Create the output sections for the symbol table.
 331   void
 332   create_symtab_sections(const Input_objects*, Symbol_table*, off_t*);
 333
 334   // Create the .shstrtab section.
 335   Output_section*
 336   create_shstrtab();
 337
 338   // Create the section header table.
 339   void
 340   create_shdrs(off_t*);
 341
 342   // Create the dynamic symbol table.
 343   void
 344   create_dynamic_symtab(const Input_objects*, Symbol_table*,
 345                         Output_section** pdynstr,
 346                         unsigned int* plocal_dynamic_count,
 347                         std::vector<Symbol*>* pdynamic_symbols,
 348                         Versions* versions);
 349
 350   // Assign offsets to each local portion of the dynamic symbol table.
 351   void
 352   assign_local_dynsym_offsets(const Input_objects*);
 353
 354   // Finish the .dynamic section and PT_DYNAMIC segment.
 355   void
 356   finish_dynamic_section(const Input_objects*, const Symbol_table*);
 357
 358   // Create the .interp section and PT_INTERP segment.
 359   void
 360   create_interp(const Target* target);
 361
 362   // Create the version sections.
 363   void
 364   create_version_sections(const Versions*,
 365                           const Symbol_table*,
 366                           unsigned int local_symcount,
 367                           const std::vector<Symbol*>& dynamic_symbols,
 368                           const Output_section* dynstr);
 369
 370   template<int size, bool big_endian>
 371   void
 372   sized_create_version_sections(const Versions* versions,
 373                                 const Symbol_table*,
 374                                 unsigned int local_symcount,
 375                                 const std::vector<Symbol*>& dynamic_symbols,
 376                                 const Output_section* dynstr
 377                                 ACCEPT_SIZE_ENDIAN);
 378
 379   // Return whether to include this section in the link.
 380   template<int size, bool big_endian>
 381   bool
 382   include_section(Sized_relobj<size, big_endian>* object, const char* name,
 383                   const elfcpp::Shdr<size, big_endian>&);
 384
 385   // Return the output section name to use given an input section
 386   // name.  Set *PLEN to the length of the name.  *PLEN must be
 387   // initialized to the length of NAME.
 388   static const char*
 389   output_section_name(const char* name, size_t* plen);
 390
 391   // Return the output section name to use for a linkonce section
 392   // name.  PLEN is as for output_section_name.
 393   static const char*
 394   linkonce_output_name(const char* name, size_t* plen);
 395
 396   // Return the output section for NAME, TYPE and FLAGS.
 397   Output_section*
 398   get_output_section(const char* name, Stringpool::Key name_key,
 399                      elfcpp::Elf_Word type, elfcpp::Elf_Xword flags);
 400
 401   // Choose the output section for NAME in RELOBJ.
 402   Output_section*
 403   choose_output_section(const Relobj* relobj, const char* name,
 404                         elfcpp::Elf_Word type, elfcpp::Elf_Xword flags,
 405                         bool adjust_name);
 406
 407   // Create a new Output_section.
 408   Output_section*
 409   make_output_section(const char* name, elfcpp::Elf_Word type,
 410                       elfcpp::Elf_Xword flags);
 411
 412   // Set the final file offsets of all the segments.
 413   off_t
 414   set_segment_offsets(const Target*, Output_segment*, unsigned int* pshndx);
 415
 416   // Set the final file offsets of all the sections not associated
 417   // with a segment.  We set section offsets in three passes: the
 418   // first handles all allocated sections, the second sections that
 419   // require postprocessing, and the last the late-bound STRTAB
 420   // sections (probably only shstrtab, which is the one we care about
 421   // because it holds section names).
 422   enum Section_offset_pass
 423   {
 424     BEFORE_INPUT_SECTIONS_PASS,
 425     POSTPROCESSING_SECTIONS_PASS,
 426     STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS
 427   };
 428   off_t
 429   set_section_offsets(off_t, Section_offset_pass pass);
 430
 431   // Set the final section indexes of all the sections not associated
 432   // with a segment.  Returns the next unused index.
 433   unsigned int
 434   set_section_indexes(unsigned int pshndx);
 435
 436   // Set the section addresses when using a script.
 437   Output_segment*
 438   set_section_addresses_from_script(Symbol_table*);
 439
 440   // Return whether SEG1 comes before SEG2 in the output file.
 441   static bool
 442   segment_precedes(const Output_segment* seg1, const Output_segment* seg2);
 443
 444   // A mapping used for group signatures.
 445   typedef Unordered_map<std::string, bool> Signatures;
 446
 447   // Mapping from input section name/type/flags to output section.  We
 448   // use canonicalized strings here.
 449
 450   typedef std::pair<Stringpool::Key,
 451                     std::pair<elfcpp::Elf_Word, elfcpp::Elf_Xword> > Key;
 452
 453   struct Hash_key
 454   {
 455     size_t
 456     operator()(const Key& k) const;
 457   };
 458
 459   typedef Unordered_map<Key, Output_section*, Hash_key> Section_name_map;
 460
 461   // A comparison class for segments.
 462
 463   struct Compare_segments
 464   {
 465     bool
 466     operator()(const Output_segment* seg1, const Output_segment* seg2)
 467     { return Layout::segment_precedes(seg1, seg2); }
 468   };
 469
 470   // A reference to the options on the command line.
 471   const General_options& options_;
 472   // Information set by scripts or by command line options.
 473   Script_options* script_options_;
 474   // The output section names.
 475   Stringpool namepool_;
 476   // The output symbol names.
 477   Stringpool sympool_;
 478   // The dynamic strings, if needed.
 479   Stringpool dynpool_;
 480   // The list of group sections and linkonce sections which we have seen.
 481   Signatures signatures_;
 482   // The mapping from input section name/type/flags to output sections.
 483   Section_name_map section_name_map_;
 484   // The list of output segments.
 485   Segment_list segment_list_;
 486   // The list of output sections.
 487   Section_list section_list_;
 488   // The list of output sections which are not attached to any output
 489   // segment.
 490   Section_list unattached_section_list_;
 491   // The list of unattached Output_data objects which require special
 492   // handling because they are not Output_sections.
 493   Data_list special_output_list_;
 494   // The section headers.
 495   Output_section_headers* section_headers_;
 496   // A pointer to the PT_TLS segment if there is one.
 497   Output_segment* tls_segment_;
 498   // The SHT_SYMTAB output section.
 499   Output_section* symtab_section_;
 500   // The SHT_DYNSYM output section if there is one.
 501   Output_section* dynsym_section_;
 502   // The SHT_DYNAMIC output section if there is one.
 503   Output_section* dynamic_section_;
 504   // The dynamic data which goes into dynamic_section_.
 505   Output_data_dynamic* dynamic_data_;
 506   // The exception frame output section if there is one.
 507   Output_section* eh_frame_section_;
 508   // The exception frame data for eh_frame_section_.
 509   Eh_frame* eh_frame_data_;
 510   // The exception frame header output section if there is one.
 511   Output_section* eh_frame_hdr_section_;
 512   // The size of the output file.
 513   off_t output_file_size_;
 514   // Whether we have seen an object file marked to require an
 515   // executable stack.
 516   bool input_requires_executable_stack_;
 517   // Whether we have seen at least one object file with an executable
 518   // stack marker.
 519   bool input_with_gnu_stack_note_;
 520   // Whether we have seen at least one object file without an
 521   // executable stack marker.
 522   bool input_without_gnu_stack_note_;
 523   // Whether we have seen an object file that uses the static TLS model.
 524   bool has_static_tls_;
 525   // Whether any sections require postprocessing.
 526   bool any_postprocessing_sections_;
 527 };
 528
 529 // This task handles writing out data in output sections which is not
 530 // part of an input section, or which requires special handling.  When
 531 // this is done, it unblocks both output_sections_blocker and
 532 // final_blocker.
 533
 534 class Write_sections_task : public Task
 535 {
 536  public:
 537   Write_sections_task(const Layout* layout, Output_file* of,
 538                       Task_token* output_sections_blocker,
 539                       Task_token* final_blocker)
 540     : layout_(layout), of_(of),
 541       output_sections_blocker_(output_sections_blocker),
 542       final_blocker_(final_blocker)
 543   { }
 544
 545   // The standard Task methods.
 546
 547   Task_token*
 548   is_runnable();
 549
 550   void
 551   locks(Task_locker*);
 552
 553   void
 554   run(Workqueue*);
 555
 556   std::string
 557   get_name() const
 558   { return "Write_sections_task"; }
 559
 560  private:
 561   class Write_sections_locker;
 562
 563   const Layout* layout_;
 564   Output_file* of_;
 565   Task_token* output_sections_blocker_;
 566   Task_token* final_blocker_;
 567 };
 568
 569 // This task handles writing out data which is not part of a section
 570 // or segment.
 571
 572 class Write_data_task : public Task
 573 {
 574  public:
 575   Write_data_task(const Layout* layout, const Symbol_table* symtab,
 576                   Output_file* of, Task_token* final_blocker)
 577     : layout_(layout), symtab_(symtab), of_(of), final_blocker_(final_blocker)
 578   { }
 579
 580   // The standard Task methods.
 581
 582   Task_token*
 583   is_runnable();
 584
 585   void
 586   locks(Task_locker*);
 587
 588   void
 589   run(Workqueue*);
 590
 591   std::string
 592   get_name() const
 593   { return "Write_data_task"; }
 594
 595  private:
 596   const Layout* layout_;
 597   const Symbol_table* symtab_;
 598   Output_file* of_;
 599   Task_token* final_blocker_;
 600 };
 601
 602 // This task handles writing out the global symbols.
 603
 604 class Write_symbols_task : public Task
 605 {
 606  public:
 607   Write_symbols_task(const Symbol_table* symtab,
 608                      const Input_objects* input_objects,
 609                      const Stringpool* sympool, const Stringpool* dynpool,
 610                      Output_file* of, Task_token* final_blocker)
 611     : symtab_(symtab), input_objects_(input_objects), sympool_(sympool),
 612       dynpool_(dynpool), of_(of), final_blocker_(final_blocker)
 613   { }
 614
 615   // The standard Task methods.
 616
 617   Task_token*
 618   is_runnable();
 619
 620   void
 621   locks(Task_locker*);
 622
 623   void
 624   run(Workqueue*);
 625
 626   std::string
 627   get_name() const
 628   { return "Write_symbols_task"; }
 629
 630  private:
 631   const Symbol_table* symtab_;
 632   const Input_objects* input_objects_;
 633   const Stringpool* sympool_;
 634   const Stringpool* dynpool_;
 635   Output_file* of_;
 636   Task_token* final_blocker_;
 637 };
 638
 639 // This task handles writing out data in output sections which can't
 640 // be written out until all the input sections have been handled.
 641 // This is for sections whose contents is based on the contents of
 642 // other output sections.
 643
 644 class Write_after_input_sections_task : public Task
 645 {
 646  public:
 647   Write_after_input_sections_task(Layout* layout, Output_file* of,
 648                                   Task_token* input_sections_blocker,
 649                                   Task_token* final_blocker)
 650     : layout_(layout), of_(of),
 651       input_sections_blocker_(input_sections_blocker),
 652       final_blocker_(final_blocker)
 653   { }
 654
 655   // The standard Task methods.
 656
 657   Task_token*
 658   is_runnable();
 659
 660   void
 661   locks(Task_locker*);
 662
 663   void
 664   run(Workqueue*);
 665
 666   std::string
 667   get_name() const
 668   { return "Write_after_input_sections_task"; }
 669
 670  private:
 671   Layout* layout_;
 672   Output_file* of_;
 673   Task_token* input_sections_blocker_;
 674   Task_token* final_blocker_;
 675 };
 676
 677 // This task function handles closing the file.
 678
 679 class Close_task_runner : public Task_function_runner
 680 {
 681  public:
 682   Close_task_runner(Output_file* of)
 683     : of_(of)
 684   { }
 685
 686   // Run the operation.
 687   void
 688   run(Workqueue*, const Task*);
 689
 690  private:
 691   Output_file* of_;
 692 };
 693
 694 // A small helper function to align an address.
 695
 696 inline uint64_t
 697 align_address(uint64_t address, uint64_t addralign)
 698 {
 699   if (addralign != 0)
 700     address = (address + addralign - 1) &~ (addralign - 1);
 701   return address;
 702 }
 703
 704 } // End namespace gold.
 705
 706 #endif // !defined(GOLD_LAYOUT_H)