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   // Layout an input reloc section when doing a relocatable link.  The
 104   // section is RELOC_SHNDX in OBJECT, with data in SHDR.
 105   // DATA_SECTION is the reloc section to which it refers.  RR is the
 106   // relocatable information.
 107   template<int size, bool big_endian>
 108   Output_section*
 109   layout_reloc(Sized_relobj<size, big_endian>* object,
 110                unsigned int reloc_shndx,
 111                const elfcpp::Shdr<size, big_endian>& shdr,
 112                Output_section* data_section,
 113                Relocatable_relocs* rr);
 114
 115   // Layout a group section when doing a relocatable link.
 116   template<int size, bool big_endian>
 117   void
 118   layout_group(Symbol_table* symtab,
 119                Sized_relobj<size, big_endian>* object,
 120                unsigned int group_shndx,
 121                const char* group_section_name,
 122                const char* signature,
 123                const elfcpp::Shdr<size, big_endian>& shdr,
 124                const elfcpp::Elf_Word* contents);
 125
 126   // Like layout, only for exception frame sections.  OBJECT is an
 127   // object file.  SYMBOLS is the contents of the symbol table
 128   // section, with size SYMBOLS_SIZE.  SYMBOL_NAMES is the contents of
 129   // the symbol name section, with size SYMBOL_NAMES_SIZE.  SHNDX is a
 130   // .eh_frame section in OBJECT.  SHDR is the section header.
 131   // RELOC_SHNDX is the index of a relocation section which applies to
 132   // this section, or 0 if none, or -1U if more than one.  RELOC_TYPE
 133   // is the type of the relocation section if there is one.  This
 134   // returns the output section, and sets *OFFSET to the offset.
 135   template<int size, bool big_endian>
 136   Output_section*
 137   layout_eh_frame(Sized_relobj<size, big_endian>* object,
 138                   const unsigned char* symbols,
 139                   off_t symbols_size,
 140                   const unsigned char* symbol_names,
 141                   off_t symbol_names_size,
 142                   unsigned int shndx,
 143                   const elfcpp::Shdr<size, big_endian>& shdr,
 144                   unsigned int reloc_shndx, unsigned int reloc_type,
 145                   off_t* offset);
 146
 147   // Handle a GNU stack note.  This is called once per input object
 148   // file.  SEEN_GNU_STACK is true if the object file has a
 149   // .note.GNU-stack section.  GNU_STACK_FLAGS is the section flags
 150   // from that section if there was one.
 151   void
 152   layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags);
 153
 154   // Add an Output_section_data to the layout.  This is used for
 155   // special sections like the GOT section.
 156   void
 157   add_output_section_data(const char* name, elfcpp::Elf_Word type,
 158                           elfcpp::Elf_Xword flags,
 159                           Output_section_data*);
 160
 161   // Create dynamic sections if necessary.
 162   void
 163   create_initial_dynamic_sections(Symbol_table*);
 164
 165   // Define __start and __stop symbols for output sections.
 166   void
 167   define_section_symbols(Symbol_table*);
 168
 169   // Define symbols from any linker script.
 170   void
 171   define_script_symbols(Symbol_table* symtab)
 172   { this->script_options_->add_symbols_to_table(symtab); }
 173
 174   // Return the Stringpool used for symbol names.
 175   const Stringpool*
 176   sympool() const
 177   { return &this->sympool_; }
 178
 179   // Return the Stringpool used for dynamic symbol names and dynamic
 180   // tags.
 181   const Stringpool*
 182   dynpool() const
 183   { return &this->dynpool_; }
 184
 185   // Return whether a section is a .gnu.linkonce section, given the
 186   // section name.
 187   static inline bool
 188   is_linkonce(const char* name)
 189   { return strncmp(name, ".gnu.linkonce", sizeof(".gnu.linkonce") - 1) == 0; }
 190
 191   // Record the signature of a comdat section, and return whether to
 192   // include it in the link.  The GROUP parameter is true for a
 193   // section group signature, false for a signature derived from a
 194   // .gnu.linkonce section.
 195   bool
 196   add_comdat(const char*, bool group);
 197
 198   // Finalize the layout after all the input sections have been added.
 199   off_t
 200   finalize(const Input_objects*, Symbol_table*, const Task*);
 201
 202   // Return whether any sections require postprocessing.
 203   bool
 204   any_postprocessing_sections() const
 205   { return this->any_postprocessing_sections_; }
 206
 207   // Return the size of the output file.
 208   off_t
 209   output_file_size() const
 210   { return this->output_file_size_; }
 211
 212   // Return the TLS segment.  This will return NULL if there isn't
 213   // one.
 214   Output_segment*
 215   tls_segment() const
 216   { return this->tls_segment_; }
 217
 218   // Return the normal symbol table.
 219   Output_section*
 220   symtab_section() const
 221   {
 222     gold_assert(this->symtab_section_ != NULL);
 223     return this->symtab_section_;
 224   }
 225
 226   // Return the dynamic symbol table.
 227   Output_section*
 228   dynsym_section() const
 229   {
 230     gold_assert(this->dynsym_section_ != NULL);
 231     return this->dynsym_section_;
 232   }
 233
 234   // Return the dynamic tags.
 235   Output_data_dynamic*
 236   dynamic_data() const
 237   { return this->dynamic_data_; }
 238
 239   // Write out the output sections.
 240   void
 241   write_output_sections(Output_file* of) const;
 242
 243   // Write out data not associated with an input file or the symbol
 244   // table.
 245   void
 246   write_data(const Symbol_table*, Output_file*) const;
 247
 248   // Write out output sections which can not be written until all the
 249   // input sections are complete.
 250   void
 251   write_sections_after_input_sections(Output_file* of);
 252
 253   // Return an output section named NAME, or NULL if there is none.
 254   Output_section*
 255   find_output_section(const char* name) const;
 256
 257   // Return an output segment of type TYPE, with segment flags SET set
 258   // and segment flags CLEAR clear.  Return NULL if there is none.
 259   Output_segment*
 260   find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
 261                       elfcpp::Elf_Word clear) const;
 262
 263   // Return the number of segments we expect to produce.
 264   size_t
 265   expected_segment_count() const;
 266
 267   // Set a flag to indicate that an object file uses the static TLS model.
 268   void
 269   set_has_static_tls()
 270   { this->has_static_tls_ = true; }
 271
 272   // Return true if any object file uses the static TLS model.
 273   bool
 274   has_static_tls() const
 275   { return this->has_static_tls_; }
 276
 277   // Return the options which may be set by a linker script.
 278   Script_options*
 279   script_options()
 280   { return this->script_options_; }
 281
 282   const Script_options*
 283   script_options() const
 284   { return this->script_options_; }
 285
 286   // Dump statistical information to stderr.
 287   void
 288   print_stats() const;
 289
 290   // A list of segments.
 291
 292   typedef std::vector<Output_segment*> Segment_list;
 293
 294   // A list of sections.
 295
 296   typedef std::vector<Output_section*> Section_list;
 297
 298   // The list of information to write out which is not attached to
 299   // either a section or a segment.
 300   typedef std::vector<Output_data*> Data_list;
 301
 302   // Store the allocated sections into the section list.  This is used
 303   // by the linker script code.
 304   void
 305   get_allocated_sections(Section_list*) const;
 306
 307   // Make a segment.  This is used by the linker script code.
 308   Output_segment*
 309   make_output_segment(elfcpp::Elf_Word type, elfcpp::Elf_Word flags);
 310
 311   // Return the number of segments.
 312   size_t
 313   segment_count() const
 314   { return this->segment_list_.size(); }
 315
 316   // Map from section flags to segment flags.
 317   static elfcpp::Elf_Word
 318   section_flags_to_segment(elfcpp::Elf_Xword flags);
 319
 320  private:
 321   Layout(const Layout&);
 322   Layout& operator=(const Layout&);
 323
 324   // Mapping from .gnu.linkonce section names to output section names.
 325   struct Linkonce_mapping
 326   {
 327     const char* from;
 328     int fromlen;
 329     const char* to;
 330     int tolen;
 331   };
 332   static const Linkonce_mapping linkonce_mapping[];
 333   static const int linkonce_mapping_count;
 334
 335   // Create a .note section for gold.
 336   void
 337   create_gold_note();
 338
 339   // Record whether the stack must be executable.
 340   void
 341   create_executable_stack_info(const Target*);
 342
 343   // Find the first read-only PT_LOAD segment, creating one if
 344   // necessary.
 345   Output_segment*
 346   find_first_load_seg();
 347
 348   // Count the local symbols in the regular symbol table and the dynamic
 349   // symbol table, and build the respective string pools.
 350   void
 351   count_local_symbols(const Task*, const Input_objects*);
 352
 353   // Create the output sections for the symbol table.
 354   void
 355   create_symtab_sections(const Input_objects*, Symbol_table*, off_t*);
 356
 357   // Create the .shstrtab section.
 358   Output_section*
 359   create_shstrtab();
 360
 361   // Create the section header table.
 362   void
 363   create_shdrs(off_t*);
 364
 365   // Create the dynamic symbol table.
 366   void
 367   create_dynamic_symtab(const Input_objects*, Symbol_table*,
 368                         Output_section** pdynstr,
 369                         unsigned int* plocal_dynamic_count,
 370                         std::vector<Symbol*>* pdynamic_symbols,
 371                         Versions* versions);
 372
 373   // Assign offsets to each local portion of the dynamic symbol table.
 374   void
 375   assign_local_dynsym_offsets(const Input_objects*);
 376
 377   // Finish the .dynamic section and PT_DYNAMIC segment.
 378   void
 379   finish_dynamic_section(const Input_objects*, const Symbol_table*);
 380
 381   // Create the .interp section and PT_INTERP segment.
 382   void
 383   create_interp(const Target* target);
 384
 385   // Create the version sections.
 386   void
 387   create_version_sections(const Versions*,
 388                           const Symbol_table*,
 389                           unsigned int local_symcount,
 390                           const std::vector<Symbol*>& dynamic_symbols,
 391                           const Output_section* dynstr);
 392
 393   template<int size, bool big_endian>
 394   void
 395   sized_create_version_sections(const Versions* versions,
 396                                 const Symbol_table*,
 397                                 unsigned int local_symcount,
 398                                 const std::vector<Symbol*>& dynamic_symbols,
 399                                 const Output_section* dynstr
 400                                 ACCEPT_SIZE_ENDIAN);
 401
 402   // Return whether to include this section in the link.
 403   template<int size, bool big_endian>
 404   bool
 405   include_section(Sized_relobj<size, big_endian>* object, const char* name,
 406                   const elfcpp::Shdr<size, big_endian>&);
 407
 408   // Return the output section name to use given an input section
 409   // name.  Set *PLEN to the length of the name.  *PLEN must be
 410   // initialized to the length of NAME.
 411   static const char*
 412   output_section_name(const char* name, size_t* plen);
 413
 414   // Return the output section name to use for a linkonce section
 415   // name.  PLEN is as for output_section_name.
 416   static const char*
 417   linkonce_output_name(const char* name, size_t* plen);
 418
 419   // Return the output section for NAME, TYPE and FLAGS.
 420   Output_section*
 421   get_output_section(const char* name, Stringpool::Key name_key,
 422                      elfcpp::Elf_Word type, elfcpp::Elf_Xword flags);
 423
 424   // Choose the output section for NAME in RELOBJ.
 425   Output_section*
 426   choose_output_section(const Relobj* relobj, const char* name,
 427                         elfcpp::Elf_Word type, elfcpp::Elf_Xword flags,
 428                         bool adjust_name);
 429
 430   // Create a new Output_section.
 431   Output_section*
 432   make_output_section(const char* name, elfcpp::Elf_Word type,
 433                       elfcpp::Elf_Xword flags);
 434
 435   // Set the final file offsets of all the segments.
 436   off_t
 437   set_segment_offsets(const Target*, Output_segment*, unsigned int* pshndx);
 438
 439   // Set the file offsets of the sections when doing a relocatable
 440   // link.
 441   off_t
 442   set_relocatable_section_offsets(Output_data*, unsigned int* pshndx);
 443
 444   // Set the final file offsets of all the sections not associated
 445   // with a segment.  We set section offsets in three passes: the
 446   // first handles all allocated sections, the second sections that
 447   // require postprocessing, and the last the late-bound STRTAB
 448   // sections (probably only shstrtab, which is the one we care about
 449   // because it holds section names).
 450   enum Section_offset_pass
 451   {
 452     BEFORE_INPUT_SECTIONS_PASS,
 453     POSTPROCESSING_SECTIONS_PASS,
 454     STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS
 455   };
 456   off_t
 457   set_section_offsets(off_t, Section_offset_pass pass);
 458
 459   // Set the final section indexes of all the sections not associated
 460   // with a segment.  Returns the next unused index.
 461   unsigned int
 462   set_section_indexes(unsigned int pshndx);
 463
 464   // Set the section addresses when using a script.
 465   Output_segment*
 466   set_section_addresses_from_script(Symbol_table*);
 467
 468   // Return whether SEG1 comes before SEG2 in the output file.
 469   static bool
 470   segment_precedes(const Output_segment* seg1, const Output_segment* seg2);
 471
 472   // A mapping used for group signatures.
 473   typedef Unordered_map<std::string, bool> Signatures;
 474
 475   // Mapping from input section name/type/flags to output section.  We
 476   // use canonicalized strings here.
 477
 478   typedef std::pair<Stringpool::Key,
 479                     std::pair<elfcpp::Elf_Word, elfcpp::Elf_Xword> > Key;
 480
 481   struct Hash_key
 482   {
 483     size_t
 484     operator()(const Key& k) const;
 485   };
 486
 487   typedef Unordered_map<Key, Output_section*, Hash_key> Section_name_map;
 488
 489   // A comparison class for segments.
 490
 491   struct Compare_segments
 492   {
 493     bool
 494     operator()(const Output_segment* seg1, const Output_segment* seg2)
 495     { return Layout::segment_precedes(seg1, seg2); }
 496   };
 497
 498   // A reference to the options on the command line.
 499   const General_options& options_;
 500   // Information set by scripts or by command line options.
 501   Script_options* script_options_;
 502   // The output section names.
 503   Stringpool namepool_;
 504   // The output symbol names.
 505   Stringpool sympool_;
 506   // The dynamic strings, if needed.
 507   Stringpool dynpool_;
 508   // The list of group sections and linkonce sections which we have seen.
 509   Signatures signatures_;
 510   // The mapping from input section name/type/flags to output sections.
 511   Section_name_map section_name_map_;
 512   // The list of output segments.
 513   Segment_list segment_list_;
 514   // The list of output sections.
 515   Section_list section_list_;
 516   // The list of output sections which are not attached to any output
 517   // segment.
 518   Section_list unattached_section_list_;
 519   // The list of unattached Output_data objects which require special
 520   // handling because they are not Output_sections.
 521   Data_list special_output_list_;
 522   // The section headers.
 523   Output_section_headers* section_headers_;
 524   // A pointer to the PT_TLS segment if there is one.
 525   Output_segment* tls_segment_;
 526   // The SHT_SYMTAB output section.
 527   Output_section* symtab_section_;
 528   // The SHT_DYNSYM output section if there is one.
 529   Output_section* dynsym_section_;
 530   // The SHT_DYNAMIC output section if there is one.
 531   Output_section* dynamic_section_;
 532   // The dynamic data which goes into dynamic_section_.
 533   Output_data_dynamic* dynamic_data_;
 534   // The exception frame output section if there is one.
 535   Output_section* eh_frame_section_;
 536   // The exception frame data for eh_frame_section_.
 537   Eh_frame* eh_frame_data_;
 538   // The exception frame header output section if there is one.
 539   Output_section* eh_frame_hdr_section_;
 540   // The size of the output file.
 541   off_t output_file_size_;
 542   // Whether we have seen an object file marked to require an
 543   // executable stack.
 544   bool input_requires_executable_stack_;
 545   // Whether we have seen at least one object file with an executable
 546   // stack marker.
 547   bool input_with_gnu_stack_note_;
 548   // Whether we have seen at least one object file without an
 549   // executable stack marker.
 550   bool input_without_gnu_stack_note_;
 551   // Whether we have seen an object file that uses the static TLS model.
 552   bool has_static_tls_;
 553   // Whether any sections require postprocessing.
 554   bool any_postprocessing_sections_;
 555 };
 556
 557 // This task handles writing out data in output sections which is not
 558 // part of an input section, or which requires special handling.  When
 559 // this is done, it unblocks both output_sections_blocker and
 560 // final_blocker.
 561
 562 class Write_sections_task : public Task
 563 {
 564  public:
 565   Write_sections_task(const Layout* layout, Output_file* of,
 566                       Task_token* output_sections_blocker,
 567                       Task_token* final_blocker)
 568     : layout_(layout), of_(of),
 569       output_sections_blocker_(output_sections_blocker),
 570       final_blocker_(final_blocker)
 571   { }
 572
 573   // The standard Task methods.
 574
 575   Task_token*
 576   is_runnable();
 577
 578   void
 579   locks(Task_locker*);
 580
 581   void
 582   run(Workqueue*);
 583
 584   std::string
 585   get_name() const
 586   { return "Write_sections_task"; }
 587
 588  private:
 589   class Write_sections_locker;
 590
 591   const Layout* layout_;
 592   Output_file* of_;
 593   Task_token* output_sections_blocker_;
 594   Task_token* final_blocker_;
 595 };
 596
 597 // This task handles writing out data which is not part of a section
 598 // or segment.
 599
 600 class Write_data_task : public Task
 601 {
 602  public:
 603   Write_data_task(const Layout* layout, const Symbol_table* symtab,
 604                   Output_file* of, Task_token* final_blocker)
 605     : layout_(layout), symtab_(symtab), of_(of), final_blocker_(final_blocker)
 606   { }
 607
 608   // The standard Task methods.
 609
 610   Task_token*
 611   is_runnable();
 612
 613   void
 614   locks(Task_locker*);
 615
 616   void
 617   run(Workqueue*);
 618
 619   std::string
 620   get_name() const
 621   { return "Write_data_task"; }
 622
 623  private:
 624   const Layout* layout_;
 625   const Symbol_table* symtab_;
 626   Output_file* of_;
 627   Task_token* final_blocker_;
 628 };
 629
 630 // This task handles writing out the global symbols.
 631
 632 class Write_symbols_task : public Task
 633 {
 634  public:
 635   Write_symbols_task(const Symbol_table* symtab,
 636                      const Input_objects* input_objects,
 637                      const Stringpool* sympool, const Stringpool* dynpool,
 638                      Output_file* of, Task_token* final_blocker)
 639     : symtab_(symtab), input_objects_(input_objects), sympool_(sympool),
 640       dynpool_(dynpool), of_(of), final_blocker_(final_blocker)
 641   { }
 642
 643   // The standard Task methods.
 644
 645   Task_token*
 646   is_runnable();
 647
 648   void
 649   locks(Task_locker*);
 650
 651   void
 652   run(Workqueue*);
 653
 654   std::string
 655   get_name() const
 656   { return "Write_symbols_task"; }
 657
 658  private:
 659   const Symbol_table* symtab_;
 660   const Input_objects* input_objects_;
 661   const Stringpool* sympool_;
 662   const Stringpool* dynpool_;
 663   Output_file* of_;
 664   Task_token* final_blocker_;
 665 };
 666
 667 // This task handles writing out data in output sections which can't
 668 // be written out until all the input sections have been handled.
 669 // This is for sections whose contents is based on the contents of
 670 // other output sections.
 671
 672 class Write_after_input_sections_task : public Task
 673 {
 674  public:
 675   Write_after_input_sections_task(Layout* layout, Output_file* of,
 676                                   Task_token* input_sections_blocker,
 677                                   Task_token* final_blocker)
 678     : layout_(layout), of_(of),
 679       input_sections_blocker_(input_sections_blocker),
 680       final_blocker_(final_blocker)
 681   { }
 682
 683   // The standard Task methods.
 684
 685   Task_token*
 686   is_runnable();
 687
 688   void
 689   locks(Task_locker*);
 690
 691   void
 692   run(Workqueue*);
 693
 694   std::string
 695   get_name() const
 696   { return "Write_after_input_sections_task"; }
 697
 698  private:
 699   Layout* layout_;
 700   Output_file* of_;
 701   Task_token* input_sections_blocker_;
 702   Task_token* final_blocker_;
 703 };
 704
 705 // This task function handles closing the file.
 706
 707 class Close_task_runner : public Task_function_runner
 708 {
 709  public:
 710   Close_task_runner(Output_file* of)
 711     : of_(of)
 712   { }
 713
 714   // Run the operation.
 715   void
 716   run(Workqueue*, const Task*);
 717
 718  private:
 719   Output_file* of_;
 720 };
 721
 722 // A small helper function to align an address.
 723
 724 inline uint64_t
 725 align_address(uint64_t address, uint64_t addralign)
 726 {
 727   if (addralign != 0)
 728     address = (address + addralign - 1) &~ (addralign - 1);
 729   return address;
 730 }
 731
 732 } // End namespace gold.
 733
 734 #endif // !defined(GOLD_LAYOUT_H)