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   // Dump statistical information to stderr.
 245   void
 246   print_stats() const;
 247
 248   // The list of segments.
 249
 250   typedef std::vector<Output_segment*> Segment_list;
 251
 252   // The list of sections not attached to a segment.
 253
 254   typedef std::vector<Output_section*> Section_list;
 255
 256   // The list of information to write out which is not attached to
 257   // either a section or a segment.
 258   typedef std::vector<Output_data*> Data_list;
 259
 260  private:
 261   Layout(const Layout&);
 262   Layout& operator=(const Layout&);
 263
 264   // Mapping from .gnu.linkonce section names to output section names.
 265   struct Linkonce_mapping
 266   {
 267     const char* from;
 268     int fromlen;
 269     const char* to;
 270     int tolen;
 271   };
 272   static const Linkonce_mapping linkonce_mapping[];
 273   static const int linkonce_mapping_count;
 274
 275   // Create a .note section for gold.
 276   void
 277   create_gold_note();
 278
 279   // Record whether the stack must be executable.
 280   void
 281   create_executable_stack_info(const Target*);
 282
 283   // Find the first read-only PT_LOAD segment, creating one if
 284   // necessary.
 285   Output_segment*
 286   find_first_load_seg();
 287
 288   // Count the local symbols in the regular symbol table and the dynamic
 289   // symbol table, and build the respective string pools.
 290   void
 291   count_local_symbols(const Task*, const Input_objects*);
 292
 293   // Create the output sections for the symbol table.
 294   void
 295   create_symtab_sections(const Input_objects*, Symbol_table*, off_t*);
 296
 297   // Create the .shstrtab section.
 298   Output_section*
 299   create_shstrtab();
 300
 301   // Create the section header table.
 302   void
 303   create_shdrs(off_t*);
 304
 305   // Create the dynamic symbol table.
 306   void
 307   create_dynamic_symtab(const Input_objects*, const Target*,
 308                         Symbol_table*, Output_section** pdynstr,
 309                         unsigned int* plocal_dynamic_count,
 310                         std::vector<Symbol*>* pdynamic_symbols,
 311                         Versions* versions);
 312
 313   // Assign offsets to each local portion of the dynamic symbol table.
 314   void
 315   assign_local_dynsym_offsets(const Input_objects*);
 316
 317   // Finish the .dynamic section and PT_DYNAMIC segment.
 318   void
 319   finish_dynamic_section(const Input_objects*, const Symbol_table*);
 320
 321   // Create the .interp section and PT_INTERP segment.
 322   void
 323   create_interp(const Target* target);
 324
 325   // Create the version sections.
 326   void
 327   create_version_sections(const Versions*,
 328                           const Symbol_table*,
 329                           unsigned int local_symcount,
 330                           const std::vector<Symbol*>& dynamic_symbols,
 331                           const Output_section* dynstr);
 332
 333   template<int size, bool big_endian>
 334   void
 335   sized_create_version_sections(const Versions* versions,
 336                                 const Symbol_table*,
 337                                 unsigned int local_symcount,
 338                                 const std::vector<Symbol*>& dynamic_symbols,
 339                                 const Output_section* dynstr
 340                                 ACCEPT_SIZE_ENDIAN);
 341
 342   // Return whether to include this section in the link.
 343   template<int size, bool big_endian>
 344   bool
 345   include_section(Sized_relobj<size, big_endian>* object, const char* name,
 346                   const elfcpp::Shdr<size, big_endian>&);
 347
 348   // Return the output section name to use given an input section
 349   // name.  Set *PLEN to the length of the name.  *PLEN must be
 350   // initialized to the length of NAME.
 351   static const char*
 352   output_section_name(const char* name, size_t* plen);
 353
 354   // Return the output section name to use for a linkonce section
 355   // name.  PLEN is as for output_section_name.
 356   static const char*
 357   linkonce_output_name(const char* name, size_t* plen);
 358
 359   // Return the output section for NAME, TYPE and FLAGS.
 360   Output_section*
 361   get_output_section(const char* name, Stringpool::Key name_key,
 362                      elfcpp::Elf_Word type, elfcpp::Elf_Xword flags);
 363
 364   // Create a new Output_section.
 365   Output_section*
 366   make_output_section(const char* name, elfcpp::Elf_Word type,
 367                       elfcpp::Elf_Xword flags);
 368
 369   // Set the final file offsets of all the segments.
 370   off_t
 371   set_segment_offsets(const Target*, Output_segment*, unsigned int* pshndx);
 372
 373   // Set the final file offsets of all the sections not associated
 374   // with a segment.  We set section offsets in three passes: the
 375   // first handles all allocated sections, the second sections that
 376   // require postprocessing, and the last the late-bound STRTAB
 377   // sections (probably only shstrtab, which is the one we care about
 378   // because it holds section names).
 379   enum Section_offset_pass
 380   {
 381     BEFORE_INPUT_SECTIONS_PASS,
 382     POSTPROCESSING_SECTIONS_PASS,
 383     STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS
 384   };
 385   off_t
 386   set_section_offsets(off_t, Section_offset_pass pass);
 387
 388   // Set the final section indexes of all the sections not associated
 389   // with a segment.  Returns the next unused index.
 390   unsigned int
 391   set_section_indexes(unsigned int pshndx);
 392
 393   // Return whether SEG1 comes before SEG2 in the output file.
 394   static bool
 395   segment_precedes(const Output_segment* seg1, const Output_segment* seg2);
 396
 397   // Map from section flags to segment flags.
 398   static elfcpp::Elf_Word
 399   section_flags_to_segment(elfcpp::Elf_Xword flags);
 400
 401   // A mapping used for group signatures.
 402   typedef Unordered_map<std::string, bool> Signatures;
 403
 404   // Mapping from input section name/type/flags to output section.  We
 405   // use canonicalized strings here.
 406
 407   typedef std::pair<Stringpool::Key,
 408                     std::pair<elfcpp::Elf_Word, elfcpp::Elf_Xword> > Key;
 409
 410   struct Hash_key
 411   {
 412     size_t
 413     operator()(const Key& k) const;
 414   };
 415
 416   typedef Unordered_map<Key, Output_section*, Hash_key> Section_name_map;
 417
 418   // A comparison class for segments.
 419
 420   struct Compare_segments
 421   {
 422     bool
 423     operator()(const Output_segment* seg1, const Output_segment* seg2)
 424     { return Layout::segment_precedes(seg1, seg2); }
 425   };
 426
 427   // A reference to the options on the command line.
 428   const General_options& options_;
 429   // The output section names.
 430   Stringpool namepool_;
 431   // The output symbol names.
 432   Stringpool sympool_;
 433   // The dynamic strings, if needed.
 434   Stringpool dynpool_;
 435   // The list of group sections and linkonce sections which we have seen.
 436   Signatures signatures_;
 437   // The mapping from input section name/type/flags to output sections.
 438   Section_name_map section_name_map_;
 439   // The list of output segments.
 440   Segment_list segment_list_;
 441   // The list of output sections.
 442   Section_list section_list_;
 443   // The list of output sections which are not attached to any output
 444   // segment.
 445   Section_list unattached_section_list_;
 446   // The list of unattached Output_data objects which require special
 447   // handling because they are not Output_sections.
 448   Data_list special_output_list_;
 449   // The section headers.
 450   Output_section_headers* section_headers_;
 451   // A pointer to the PT_TLS segment if there is one.
 452   Output_segment* tls_segment_;
 453   // The SHT_SYMTAB output section.
 454   Output_section* symtab_section_;
 455   // The SHT_DYNSYM output section if there is one.
 456   Output_section* dynsym_section_;
 457   // The SHT_DYNAMIC output section if there is one.
 458   Output_section* dynamic_section_;
 459   // The dynamic data which goes into dynamic_section_.
 460   Output_data_dynamic* dynamic_data_;
 461   // The exception frame output section if there is one.
 462   Output_section* eh_frame_section_;
 463   // The exception frame data for eh_frame_section_.
 464   Eh_frame* eh_frame_data_;
 465   // The exception frame header output section if there is one.
 466   Output_section* eh_frame_hdr_section_;
 467   // The size of the output file.
 468   off_t output_file_size_;
 469   // Whether we have seen an object file marked to require an
 470   // executable stack.
 471   bool input_requires_executable_stack_;
 472   // Whether we have seen at least one object file with an executable
 473   // stack marker.
 474   bool input_with_gnu_stack_note_;
 475   // Whether we have seen at least one object file without an
 476   // executable stack marker.
 477   bool input_without_gnu_stack_note_;
 478   // Whether we have seen an object file that uses the static TLS model.
 479   bool has_static_tls_;
 480   // Whether any sections require postprocessing.
 481   bool any_postprocessing_sections_;
 482 };
 483
 484 // This task handles writing out data in output sections which is not
 485 // part of an input section, or which requires special handling.  When
 486 // this is done, it unblocks both output_sections_blocker and
 487 // final_blocker.
 488
 489 class Write_sections_task : public Task
 490 {
 491  public:
 492   Write_sections_task(const Layout* layout, Output_file* of,
 493                       Task_token* output_sections_blocker,
 494                       Task_token* final_blocker)
 495     : layout_(layout), of_(of),
 496       output_sections_blocker_(output_sections_blocker),
 497       final_blocker_(final_blocker)
 498   { }
 499
 500   // The standard Task methods.
 501
 502   Task_token*
 503   is_runnable();
 504
 505   void
 506   locks(Task_locker*);
 507
 508   void
 509   run(Workqueue*);
 510
 511   std::string
 512   get_name() const
 513   { return "Write_sections_task"; }
 514
 515  private:
 516   class Write_sections_locker;
 517
 518   const Layout* layout_;
 519   Output_file* of_;
 520   Task_token* output_sections_blocker_;
 521   Task_token* final_blocker_;
 522 };
 523
 524 // This task handles writing out data which is not part of a section
 525 // or segment.
 526
 527 class Write_data_task : public Task
 528 {
 529  public:
 530   Write_data_task(const Layout* layout, const Symbol_table* symtab,
 531                   Output_file* of, Task_token* final_blocker)
 532     : layout_(layout), symtab_(symtab), of_(of), final_blocker_(final_blocker)
 533   { }
 534
 535   // The standard Task methods.
 536
 537   Task_token*
 538   is_runnable();
 539
 540   void
 541   locks(Task_locker*);
 542
 543   void
 544   run(Workqueue*);
 545
 546   std::string
 547   get_name() const
 548   { return "Write_data_task"; }
 549
 550  private:
 551   const Layout* layout_;
 552   const Symbol_table* symtab_;
 553   Output_file* of_;
 554   Task_token* final_blocker_;
 555 };
 556
 557 // This task handles writing out the global symbols.
 558
 559 class Write_symbols_task : public Task
 560 {
 561  public:
 562   Write_symbols_task(const Symbol_table* symtab,
 563                      const Input_objects* input_objects,
 564                      const Stringpool* sympool, const Stringpool* dynpool,
 565                      Output_file* of, Task_token* final_blocker)
 566     : symtab_(symtab), input_objects_(input_objects), sympool_(sympool),
 567       dynpool_(dynpool), of_(of), final_blocker_(final_blocker)
 568   { }
 569
 570   // The standard Task methods.
 571
 572   Task_token*
 573   is_runnable();
 574
 575   void
 576   locks(Task_locker*);
 577
 578   void
 579   run(Workqueue*);
 580
 581   std::string
 582   get_name() const
 583   { return "Write_symbols_task"; }
 584
 585  private:
 586   const Symbol_table* symtab_;
 587   const Input_objects* input_objects_;
 588   const Stringpool* sympool_;
 589   const Stringpool* dynpool_;
 590   Output_file* of_;
 591   Task_token* final_blocker_;
 592 };
 593
 594 // This task handles writing out data in output sections which can't
 595 // be written out until all the input sections have been handled.
 596 // This is for sections whose contents is based on the contents of
 597 // other output sections.
 598
 599 class Write_after_input_sections_task : public Task
 600 {
 601  public:
 602   Write_after_input_sections_task(Layout* layout, Output_file* of,
 603                                   Task_token* input_sections_blocker,
 604                                   Task_token* final_blocker)
 605     : layout_(layout), of_(of),
 606       input_sections_blocker_(input_sections_blocker),
 607       final_blocker_(final_blocker)
 608   { }
 609
 610   // The standard Task methods.
 611
 612   Task_token*
 613   is_runnable();
 614
 615   void
 616   locks(Task_locker*);
 617
 618   void
 619   run(Workqueue*);
 620
 621   std::string
 622   get_name() const
 623   { return "Write_after_input_sections_task"; }
 624
 625  private:
 626   Layout* layout_;
 627   Output_file* of_;
 628   Task_token* input_sections_blocker_;
 629   Task_token* final_blocker_;
 630 };
 631
 632 // This task function handles closing the file.
 633
 634 class Close_task_runner : public Task_function_runner
 635 {
 636  public:
 637   Close_task_runner(Output_file* of)
 638     : of_(of)
 639   { }
 640
 641   // Run the operation.
 642   void
 643   run(Workqueue*, const Task*);
 644
 645  private:
 646   Output_file* of_;
 647 };
 648
 649 // A small helper function to align an address.
 650
 651 inline uint64_t
 652 align_address(uint64_t address, uint64_t addralign)
 653 {
 654   if (addralign != 0)
 655     address = (address + addralign - 1) &~ (addralign - 1);
 656   return address;
 657 }
 658
 659 } // End namespace gold.
 660
 661 #endif // !defined(GOLD_LAYOUT_H)