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 Target;
  49
  50 // This task function handles mapping the input sections to output
  51 // sections and laying them out in memory.
  52
  53 class Layout_task_runner : public Task_function_runner
  54 {
  55  public:
  56   // OPTIONS is the command line options, INPUT_OBJECTS is the list of
  57   // input objects, SYMTAB is the symbol table, LAYOUT is the layout
  58   // object.
  59   Layout_task_runner(const General_options& options,
  60                      const Input_objects* input_objects,
  61                      Symbol_table* symtab,
  62                      Layout* layout)
  63     : options_(options), input_objects_(input_objects), symtab_(symtab),
  64       layout_(layout)
  65   { }
  66
  67   // Run the operation.
  68   void
  69   run(Workqueue*);
  70
  71  private:
  72   Layout_task_runner(const Layout_task_runner&);
  73   Layout_task_runner& operator=(const Layout_task_runner&);
  74
  75   const General_options& options_;
  76   const Input_objects* input_objects_;
  77   Symbol_table* symtab_;
  78   Layout* layout_;
  79 };
  80
  81 // This class handles the details of laying out input sections.
  82
  83 class Layout
  84 {
  85  public:
  86   Layout(const General_options& options);
  87
  88   // Given an input section SHNDX, named NAME, with data in SHDR, from
  89   // the object file OBJECT, return the output section where this
  90   // input section should go.  Set *OFFSET to the offset within the
  91   // output section.
  92   template<int size, bool big_endian>
  93   Output_section*
  94   layout(Relobj *object, unsigned int shndx, const char* name,
  95          const elfcpp::Shdr<size, big_endian>& shdr, off_t* offset);
  96
  97   // Handle a GNU stack note.  This is called once per input object
  98   // file.  SEEN_GNU_STACK is true if the object file has a
  99   // .note.GNU-stack section.  GNU_STACK_FLAGS is the section flags
 100   // from that section if there was one.
 101   void
 102   layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags);
 103
 104   // Add an Output_section_data to the layout.  This is used for
 105   // special sections like the GOT section.
 106   void
 107   add_output_section_data(const char* name, elfcpp::Elf_Word type,
 108                           elfcpp::Elf_Xword flags,
 109                           Output_section_data*);
 110
 111   // Create dynamic sections if necessary.
 112   void
 113   create_initial_dynamic_sections(const Input_objects*, Symbol_table*);
 114
 115   // Define __start and __stop symbols for output sections.
 116   void
 117   define_section_symbols(Symbol_table*, const Target*);
 118
 119   // Return the Stringpool used for symbol names.
 120   const Stringpool*
 121   sympool() const
 122   { return &this->sympool_; }
 123
 124   // Return the Stringpool used for dynamic symbol names and dynamic
 125   // tags.
 126   const Stringpool*
 127   dynpool() const
 128   { return &this->dynpool_; }
 129
 130   // Return whether a section is a .gnu.linkonce section, given the
 131   // section name.
 132   static inline bool
 133   is_linkonce(const char* name)
 134   { return strncmp(name, ".gnu.linkonce", sizeof(".gnu.linkonce") - 1) == 0; }
 135
 136   // Record the signature of a comdat section, and return whether to
 137   // include it in the link.  The GROUP parameter is true for a
 138   // section group signature, false for a signature derived from a
 139   // .gnu.linkonce section.
 140   bool
 141   add_comdat(const char*, bool group);
 142
 143   // Finalize the layout after all the input sections have been added.
 144   off_t
 145   finalize(const Input_objects*, Symbol_table*);
 146
 147   // Return the size of the output file.
 148   off_t
 149   output_file_size() const
 150   { return this->output_file_size_; }
 151
 152   // Return the TLS segment.  This will return NULL if there isn't
 153   // one.
 154   Output_segment*
 155   tls_segment() const
 156   { return this->tls_segment_; }
 157
 158   // Return the normal symbol table.
 159   Output_section*
 160   symtab_section() const
 161   {
 162     gold_assert(this->symtab_section_ != NULL);
 163     return this->symtab_section_;
 164   }
 165
 166   // Return the dynamic symbol table.
 167   Output_section*
 168   dynsym_section() const
 169   {
 170     gold_assert(this->dynsym_section_ != NULL);
 171     return this->dynsym_section_;
 172   }
 173
 174   // Return the dynamic tags.
 175   Output_data_dynamic*
 176   dynamic_data() const
 177   { return this->dynamic_data_; }
 178
 179   // Write out data not associated with an input file or the symbol
 180   // table.
 181   void
 182   write_data(const Symbol_table*, Output_file*) const;
 183
 184   // Return an output section named NAME, or NULL if there is none.
 185   Output_section*
 186   find_output_section(const char* name) const;
 187
 188   // Return an output segment of type TYPE, with segment flags SET set
 189   // and segment flags CLEAR clear.  Return NULL if there is none.
 190   Output_segment*
 191   find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
 192                       elfcpp::Elf_Word clear) const;
 193
 194   // The list of segments.
 195
 196   typedef std::vector<Output_segment*> Segment_list;
 197
 198   // The list of sections not attached to a segment.
 199
 200   typedef std::vector<Output_section*> Section_list;
 201
 202   // The list of information to write out which is not attached to
 203   // either a section or a segment.
 204   typedef std::vector<Output_data*> Data_list;
 205
 206  private:
 207   Layout(const Layout&);
 208   Layout& operator=(const Layout&);
 209
 210   // Mapping from .gnu.linkonce section names to output section names.
 211   struct Linkonce_mapping
 212   {
 213     const char* from;
 214     int fromlen;
 215     const char* to;
 216     int tolen;
 217   };
 218   static const Linkonce_mapping linkonce_mapping[];
 219   static const int linkonce_mapping_count;
 220
 221   // Handle an exception frame section.
 222   template<int size, bool big_endian>
 223   void
 224   layout_eh_frame(Relobj*, unsigned int, const char*,
 225                   const elfcpp::Shdr<size, big_endian>&,
 226                   Output_section*, off_t*);
 227
 228   // Create a .note section for gold.
 229   void
 230   create_gold_note();
 231
 232   // Record whether the stack must be executable.
 233   void
 234   create_executable_stack_info(const Target*);
 235
 236   // Find the first read-only PT_LOAD segment, creating one if
 237   // necessary.
 238   Output_segment*
 239   find_first_load_seg();
 240
 241   // Create the output sections for the symbol table.
 242   void
 243   create_symtab_sections(const Input_objects*, Symbol_table*, off_t*);
 244
 245   // Create the .shstrtab section.
 246   Output_section*
 247   create_shstrtab();
 248
 249   // Create the section header table.
 250   Output_section_headers*
 251   create_shdrs(off_t*);
 252
 253   // Create the dynamic symbol table.
 254   void
 255   create_dynamic_symtab(const Target*, Symbol_table*, Output_section** pdynstr,
 256                         unsigned int* plocal_dynamic_count,
 257                         std::vector<Symbol*>* pdynamic_symbols,
 258                         Versions* versions);
 259
 260   // Finish the .dynamic section and PT_DYNAMIC segment.
 261   void
 262   finish_dynamic_section(const Input_objects*, const Symbol_table*);
 263
 264   // Create the .interp section and PT_INTERP segment.
 265   void
 266   create_interp(const Target* target);
 267
 268   // Create the version sections.
 269   void
 270   create_version_sections(const Versions*,
 271                           const Symbol_table*,
 272                           unsigned int local_symcount,
 273                           const std::vector<Symbol*>& dynamic_symbols,
 274                           const Output_section* dynstr);
 275
 276   template<int size, bool big_endian>
 277   void
 278   sized_create_version_sections(const Versions* versions,
 279                                 const Symbol_table*,
 280                                 unsigned int local_symcount,
 281                                 const std::vector<Symbol*>& dynamic_symbols,
 282                                 const Output_section* dynstr
 283                                 ACCEPT_SIZE_ENDIAN);
 284
 285   // Return whether to include this section in the link.
 286   template<int size, bool big_endian>
 287   bool
 288   include_section(Object* object, const char* name,
 289                   const elfcpp::Shdr<size, big_endian>&);
 290
 291   // Return the output section name to use given an input section
 292   // name.  Set *PLEN to the length of the name.  *PLEN must be
 293   // initialized to the length of NAME.
 294   static const char*
 295   output_section_name(const char* name, size_t* plen);
 296
 297   // Return the output section name to use for a linkonce section
 298   // name.  PLEN is as for output_section_name.
 299   static const char*
 300   linkonce_output_name(const char* name, size_t* plen);
 301
 302   // Return the output section for NAME, TYPE and FLAGS.
 303   Output_section*
 304   get_output_section(const char* name, Stringpool::Key name_key,
 305                      elfcpp::Elf_Word type, elfcpp::Elf_Xword flags);
 306
 307   // Create a new Output_section.
 308   Output_section*
 309   make_output_section(const char* name, elfcpp::Elf_Word type,
 310                       elfcpp::Elf_Xword flags);
 311
 312   // Set the final file offsets of all the segments.
 313   off_t
 314   set_segment_offsets(const Target*, Output_segment*, unsigned int* pshndx);
 315
 316   // Set the final file offsets and section indexes of all the
 317   // sections not associated with a segment.
 318   off_t
 319   set_section_offsets(off_t, unsigned int *pshndx, bool do_bits_sections);
 320
 321   // Return whether SEG1 comes before SEG2 in the output file.
 322   static bool
 323   segment_precedes(const Output_segment* seg1, const Output_segment* seg2);
 324
 325   // Map from section flags to segment flags.
 326   static elfcpp::Elf_Word
 327   section_flags_to_segment(elfcpp::Elf_Xword flags);
 328
 329   // A mapping used for group signatures.
 330   typedef Unordered_map<std::string, bool> Signatures;
 331
 332   // Mapping from input section name/type/flags to output section.  We
 333   // use canonicalized strings here.
 334
 335   typedef std::pair<Stringpool::Key,
 336                     std::pair<elfcpp::Elf_Word, elfcpp::Elf_Xword> > Key;
 337
 338   struct Hash_key
 339   {
 340     size_t
 341     operator()(const Key& k) const;
 342   };
 343
 344   typedef Unordered_map<Key, Output_section*, Hash_key> Section_name_map;
 345
 346   // A comparison class for segments.
 347
 348   struct Compare_segments
 349   {
 350     bool
 351     operator()(const Output_segment* seg1, const Output_segment* seg2)
 352     { return Layout::segment_precedes(seg1, seg2); }
 353   };
 354
 355   // A reference to the options on the command line.
 356   const General_options& options_;
 357   // The output section names.
 358   Stringpool namepool_;
 359   // The output symbol names.
 360   Stringpool sympool_;
 361   // The dynamic strings, if needed.
 362   Stringpool dynpool_;
 363   // The list of group sections and linkonce sections which we have seen.
 364   Signatures signatures_;
 365   // The mapping from input section name/type/flags to output sections.
 366   Section_name_map section_name_map_;
 367   // The list of output segments.
 368   Segment_list segment_list_;
 369   // The list of output sections.
 370   Section_list section_list_;
 371   // The list of output sections which are not attached to any output
 372   // segment.
 373   Section_list unattached_section_list_;
 374   // The list of unattached Output_data objects which require special
 375   // handling because they are not Output_sections.
 376   Data_list special_output_list_;
 377   // A pointer to the PT_TLS segment if there is one.
 378   Output_segment* tls_segment_;
 379   // The SHT_SYMTAB output section.
 380   Output_section* symtab_section_;
 381   // The SHT_DYNSYM output section if there is one.
 382   Output_section* dynsym_section_;
 383   // The SHT_DYNAMIC output section if there is one.
 384   Output_section* dynamic_section_;
 385   // The dynamic data which goes into dynamic_section_.
 386   Output_data_dynamic* dynamic_data_;
 387   // The exception frame section.
 388   Output_section* eh_frame_section_;
 389   // The size of the output file.
 390   off_t output_file_size_;
 391   // Whether we have seen an object file marked to require an
 392   // executable stack.
 393   bool input_requires_executable_stack_;
 394   // Whether we have seen at least one object file with an executable
 395   // stack marker.
 396   bool input_with_gnu_stack_note_;
 397   // Whether we have seen at least one object file without an
 398   // executable stack marker.
 399   bool input_without_gnu_stack_note_;
 400 };
 401
 402 // This task handles writing out data which is not part of a section
 403 // or segment.
 404
 405 class Write_data_task : public Task
 406 {
 407  public:
 408   Write_data_task(const Layout* layout, const Symbol_table* symtab,
 409                   Output_file* of, Task_token* final_blocker)
 410     : layout_(layout), symtab_(symtab), of_(of), final_blocker_(final_blocker)
 411   { }
 412
 413   // The standard Task methods.
 414
 415   Is_runnable_type
 416   is_runnable(Workqueue*);
 417
 418   Task_locker*
 419   locks(Workqueue*);
 420
 421   void
 422   run(Workqueue*);
 423
 424  private:
 425   const Layout* layout_;
 426   const Symbol_table* symtab_;
 427   Output_file* of_;
 428   Task_token* final_blocker_;
 429 };
 430
 431 // This task handles writing out the global symbols.
 432
 433 class Write_symbols_task : public Task
 434 {
 435  public:
 436   Write_symbols_task(const Symbol_table* symtab, const Target* target,
 437                      const Stringpool* sympool, const Stringpool* dynpool,
 438                      Output_file* of, Task_token* final_blocker)
 439     : symtab_(symtab), target_(target), sympool_(sympool), dynpool_(dynpool),
 440       of_(of), final_blocker_(final_blocker)
 441   { }
 442
 443   // The standard Task methods.
 444
 445   Is_runnable_type
 446   is_runnable(Workqueue*);
 447
 448   Task_locker*
 449   locks(Workqueue*);
 450
 451   void
 452   run(Workqueue*);
 453
 454  private:
 455   const Symbol_table* symtab_;
 456   const Target* target_;
 457   const Stringpool* sympool_;
 458   const Stringpool* dynpool_;
 459   Output_file* of_;
 460   Task_token* final_blocker_;
 461 };
 462
 463 // This task function handles closing the file.
 464
 465 class Close_task_runner : public Task_function_runner
 466 {
 467  public:
 468   Close_task_runner(Output_file* of)
 469     : of_(of)
 470   { }
 471
 472   // Run the operation.
 473   void
 474   run(Workqueue*);
 475
 476  private:
 477   Output_file* of_;
 478 };
 479
 480 // A small helper function to align an address.
 481
 482 inline uint64_t
 483 align_address(uint64_t address, uint64_t addralign)
 484 {
 485   if (addralign != 0)
 486     address = (address + addralign - 1) &~ (addralign - 1);
 487   return address;
 488 }
 489
 490 } // End namespace gold.
 491
 492 #endif // !defined(GOLD_LAYOUT_H)