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