gold/gold.cc

   1 // gold.cc -- main linker functions
   2
   3 // Copyright 2006, 2007, 2008, 2009 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 #include "gold.h"
  24
  25 #include <cstdlib>
  26 #include <cstdio>
  27 #include <cstring>
  28 #include <unistd.h>
  29 #include <algorithm>
  30 #include "libiberty.h"
  31
  32 #include "options.h"
  33 #include "debug.h"
  34 #include "workqueue.h"
  35 #include "dirsearch.h"
  36 #include "readsyms.h"
  37 #include "symtab.h"
  38 #include "common.h"
  39 #include "object.h"
  40 #include "layout.h"
  41 #include "reloc.h"
  42 #include "defstd.h"
  43 #include "plugin.h"
  44 #include "icf.h"
  45 #include "incremental.h"
  46
  47 namespace gold
  48 {
  49
  50 const char* program_name;
  51
  52 void
  53 gold_exit(bool status)
  54 {
  55   if (parameters != NULL
  56       && parameters->options_valid()
  57       && parameters->options().has_plugins())
  58     parameters->options().plugins()->cleanup();
  59   if (!status && parameters != NULL && parameters->options_valid())
  60     unlink_if_ordinary(parameters->options().output_file_name());
  61   exit(status ? EXIT_SUCCESS : EXIT_FAILURE);
  62 }
  63
  64 void
  65 gold_nomem()
  66 {
  67   // We are out of memory, so try hard to print a reasonable message.
  68   // Note that we don't try to translate this message, since the
  69   // translation process itself will require memory.
  70
  71   // LEN only exists to avoid a pointless warning when write is
  72   // declared with warn_use_result, as when compiling with
  73   // -D_USE_FORTIFY on GNU/Linux.  Casting to void does not appear to
  74   // work, at least not with gcc 4.3.0.
  75
  76   ssize_t len = write(2, program_name, strlen(program_name));
  77   if (len >= 0)
  78     {
  79       const char* const s = ": out of memory\n";
  80       len = write(2, s, strlen(s));
  81     }
  82   gold_exit(false);
  83 }
  84
  85 // Handle an unreachable case.
  86
  87 void
  88 do_gold_unreachable(const char* filename, int lineno, const char* function)
  89 {
  90   fprintf(stderr, _("%s: internal error in %s, at %s:%d\n"),
  91           program_name, function, filename, lineno);
  92   gold_exit(false);
  93 }
  94
  95 // This class arranges to run the functions done in the middle of the
  96 // link.  It is just a closure.
  97
  98 class Middle_runner : public Task_function_runner
  99 {
 100  public:
 101   Middle_runner(const General_options& options,
 102                 const Input_objects* input_objects,
 103                 Symbol_table* symtab,
 104                 Layout* layout, Mapfile* mapfile)
 105     : options_(options), input_objects_(input_objects), symtab_(symtab),
 106       layout_(layout), mapfile_(mapfile)
 107   { }
 108
 109   void
 110   run(Workqueue*, const Task*);
 111
 112  private:
 113   const General_options& options_;
 114   const Input_objects* input_objects_;
 115   Symbol_table* symtab_;
 116   Layout* layout_;
 117   Mapfile* mapfile_;
 118 };
 119
 120 void
 121 Middle_runner::run(Workqueue* workqueue, const Task* task)
 122 {
 123   queue_middle_tasks(this->options_, task, this->input_objects_, this->symtab_,
 124                      this->layout_, workqueue, this->mapfile_);
 125 }
 126
 127 // This class arranges the tasks to process the relocs for garbage collection.
 128
 129 class Gc_runner : public Task_function_runner
 130 {
 131   public:
 132    Gc_runner(const General_options& options,
 133              const Input_objects* input_objects,
 134              Symbol_table* symtab,
 135              Layout* layout, Mapfile* mapfile)
 136     : options_(options), input_objects_(input_objects), symtab_(symtab),
 137       layout_(layout), mapfile_(mapfile)
 138    { }
 139
 140   void
 141   run(Workqueue*, const Task*);
 142
 143  private:
 144   const General_options& options_;
 145   const Input_objects* input_objects_;
 146   Symbol_table* symtab_;
 147   Layout* layout_;
 148   Mapfile* mapfile_;
 149 };
 150
 151 void
 152 Gc_runner::run(Workqueue* workqueue, const Task* task)
 153 {
 154   queue_middle_gc_tasks(this->options_, task, this->input_objects_,
 155                         this->symtab_, this->layout_, workqueue,
 156                         this->mapfile_);
 157 }
 158
 159 // Queue up the initial set of tasks for this link job.
 160
 161 void
 162 queue_initial_tasks(const General_options& options,
 163                     Dirsearch& search_path,
 164                     const Command_line& cmdline,
 165                     Workqueue* workqueue, Input_objects* input_objects,
 166                     Symbol_table* symtab, Layout* layout, Mapfile* mapfile)
 167 {
 168   if (cmdline.begin() == cmdline.end())
 169     {
 170       if (options.printed_version())
 171         gold_exit(true);
 172       gold_fatal(_("no input files"));
 173     }
 174
 175   int thread_count = options.thread_count_initial();
 176   if (thread_count == 0)
 177     thread_count = cmdline.number_of_input_files();
 178   workqueue->set_thread_count(thread_count);
 179
 180   if (cmdline.options().incremental())
 181     {
 182       Incremental_checker incremental_checker(
 183           parameters->options().output_file_name());
 184       if (incremental_checker.can_incrementally_link_output_file())
 185         {
 186           // TODO: remove when incremental linking implemented.
 187           printf("Incremental linking might be possible "
 188               "(not implemented yet)\n");
 189         }
 190       // TODO: If we decide on an incremental build, fewer tasks
 191       // should be scheduled.
 192     }
 193
 194   // Read the input files.  We have to add the symbols to the symbol
 195   // table in order.  We do this by creating a separate blocker for
 196   // each input file.  We associate the blocker with the following
 197   // input file, to give us a convenient place to delete it.
 198   Task_token* this_blocker = NULL;
 199   for (Command_line::const_iterator p = cmdline.begin();
 200        p != cmdline.end();
 201        ++p)
 202     {
 203       Task_token* next_blocker = new Task_token(true);
 204       next_blocker->add_blocker();
 205       workqueue->queue(new Read_symbols(input_objects, symtab, layout,
 206                                         &search_path, 0, mapfile, &*p, NULL,
 207                                         this_blocker, next_blocker));
 208       this_blocker = next_blocker;
 209     }
 210
 211   if (options.has_plugins())
 212     {
 213       Task_token* next_blocker = new Task_token(true);
 214       next_blocker->add_blocker();
 215       workqueue->queue(new Plugin_hook(options, input_objects, symtab, layout,
 216                                        &search_path, mapfile, this_blocker,
 217                                        next_blocker));
 218       this_blocker = next_blocker;
 219     }
 220
 221   if (parameters->options().relocatable()
 222       && (parameters->options().gc_sections() || parameters->options().icf()))
 223     gold_error(_("cannot mix -r with --gc-sections or --icf"));
 224
 225   if (parameters->options().gc_sections() || parameters->options().icf())
 226     {
 227       workqueue->queue(new Task_function(new Gc_runner(options,
 228                                                        input_objects,
 229                                                        symtab,
 230                                                        layout,
 231                                                        mapfile),
 232                                          this_blocker,
 233                                          "Task_function Gc_runner"));
 234     }
 235   else
 236     {
 237       workqueue->queue(new Task_function(new Middle_runner(options,
 238                                                            input_objects,
 239                                                            symtab,
 240                                                            layout,
 241                                                            mapfile),
 242                                          this_blocker,
 243                                          "Task_function Middle_runner"));
 244     }
 245 }
 246
 247 // Queue up a set of tasks to be done before queueing the middle set
 248 // of tasks.  This is only necessary when garbage collection
 249 // (--gc-sections) of unused sections is desired.  The relocs are read
 250 // and processed here early to determine the garbage sections before the
 251 // relocs can be scanned in later tasks.
 252
 253 void
 254 queue_middle_gc_tasks(const General_options& options,
 255                       const Task* ,
 256                       const Input_objects* input_objects,
 257                       Symbol_table* symtab,
 258                       Layout* layout,
 259                       Workqueue* workqueue,
 260                       Mapfile* mapfile)
 261 {
 262   // Read_relocs for all the objects must be done and processed to find
 263   // unused sections before any scanning of the relocs can take place.
 264   Task_token* blocker = new Task_token(true);
 265   Task_token* symtab_lock = new Task_token(false);
 266   for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 267        p != input_objects->relobj_end();
 268        ++p)
 269     {
 270       // We can read and process the relocations in any order.
 271       blocker->add_blocker();
 272       workqueue->queue(new Read_relocs(options, symtab, layout, *p,
 273                                        symtab_lock, blocker));
 274     }
 275
 276   Task_token* this_blocker = new Task_token(true);
 277   workqueue->queue(new Task_function(new Middle_runner(options,
 278                                                        input_objects,
 279                                                        symtab,
 280                                                        layout,
 281                                                        mapfile),
 282                                      this_blocker,
 283                                      "Task_function Middle_runner"));
 284 }
 285
 286 // Queue up the middle set of tasks.  These are the tasks which run
 287 // after all the input objects have been found and all the symbols
 288 // have been read, but before we lay out the output file.
 289
 290 void
 291 queue_middle_tasks(const General_options& options,
 292                    const Task* task,
 293                    const Input_objects* input_objects,
 294                    Symbol_table* symtab,
 295                    Layout* layout,
 296                    Workqueue* workqueue,
 297                    Mapfile* mapfile)
 298 {
 299   // Add any symbols named with -u options to the symbol table.
 300   symtab->add_undefined_symbols_from_command_line();
 301
 302   // If garbage collection was chosen, relocs have been read and processed
 303   // at this point by pre_middle_tasks.  Layout can then be done for all
 304   // objects.
 305   if (parameters->options().gc_sections())
 306     {
 307       // Find the start symbol if any.
 308       Symbol* start_sym;
 309       if (parameters->options().entry())
 310         start_sym = symtab->lookup(parameters->options().entry());
 311       else
 312         start_sym = symtab->lookup("_start");
 313       if (start_sym !=NULL)
 314         {
 315           bool is_ordinary;
 316           unsigned int shndx = start_sym->shndx(&is_ordinary);
 317           if (is_ordinary)
 318             {
 319               symtab->gc()->worklist().push(
 320                 Section_id(start_sym->object(), shndx));
 321             }
 322         }
 323       // Symbols named with -u should not be considered garbage.
 324       symtab->gc_mark_undef_symbols();
 325       gold_assert(symtab->gc() != NULL);
 326       // Do a transitive closure on all references to determine the worklist.
 327       symtab->gc()->do_transitive_closure();
 328     }
 329
 330   // If identical code folding (--icf) is chosen it makes sense to do it
 331   // only after garbage collection (--gc-sections) as we do not want to
 332   // be folding sections that will be garbage.
 333   if (parameters->options().icf())
 334     {
 335       symtab->icf()->find_identical_sections(input_objects, symtab);
 336     }
 337
 338   // Call Object::layout for the second time to determine the
 339   // output_sections for all referenced input sections.  When
 340   // --gc-sections or --icf is turned on, Object::layout is
 341   // called twice.  It is called the first time when the
 342   // symbols are added.
 343   if (parameters->options().gc_sections() || parameters->options().icf())
 344     {
 345       for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 346            p != input_objects->relobj_end();
 347            ++p)
 348         {
 349           (*p)->layout(symtab, layout, NULL);
 350         }
 351     }
 352
 353   // Layout deferred objects due to plugins.
 354   if (parameters->options().has_plugins())
 355     {
 356       Plugin_manager* plugins = parameters->options().plugins();
 357       gold_assert(plugins != NULL);
 358       plugins->layout_deferred_objects();
 359     }
 360
 361   if (parameters->options().gc_sections() || parameters->options().icf())
 362     {
 363       for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 364            p != input_objects->relobj_end();
 365            ++p)
 366         {
 367           // Update the value of output_section stored in rd.
 368           Read_relocs_data *rd = (*p)->get_relocs_data();
 369           for (Read_relocs_data::Relocs_list::iterator q = rd->relocs.begin();
 370                q != rd->relocs.end();
 371                ++q)
 372             {
 373               q->output_section = (*p)->output_section(q->data_shndx);
 374               q->needs_special_offset_handling =
 375                       (*p)->is_output_section_offset_invalid(q->data_shndx);
 376             }
 377         }
 378     }
 379
 380   // We have to support the case of not seeing any input objects, and
 381   // generate an empty file.  Existing builds depend on being able to
 382   // pass an empty archive to the linker and get an empty object file
 383   // out.  In order to do this we need to use a default target.
 384   if (input_objects->number_of_input_objects() == 0)
 385     parameters_force_valid_target();
 386
 387   int thread_count = options.thread_count_middle();
 388   if (thread_count == 0)
 389     thread_count = std::max(2, input_objects->number_of_input_objects());
 390   workqueue->set_thread_count(thread_count);
 391
 392   // Now we have seen all the input files.
 393   const bool doing_static_link = (!input_objects->any_dynamic()
 394                                   && !parameters->options().shared());
 395   set_parameters_doing_static_link(doing_static_link);
 396   if (!doing_static_link && options.is_static())
 397     {
 398       // We print out just the first .so we see; there may be others.
 399       gold_assert(input_objects->dynobj_begin() != input_objects->dynobj_end());
 400       gold_error(_("cannot mix -static with dynamic object %s"),
 401                  (*input_objects->dynobj_begin())->name().c_str());
 402     }
 403   if (!doing_static_link && parameters->options().relocatable())
 404     gold_fatal(_("cannot mix -r with dynamic object %s"),
 405                (*input_objects->dynobj_begin())->name().c_str());
 406   if (!doing_static_link
 407       && options.oformat_enum() != General_options::OBJECT_FORMAT_ELF)
 408     gold_fatal(_("cannot use non-ELF output format with dynamic object %s"),
 409                (*input_objects->dynobj_begin())->name().c_str());
 410
 411   if (is_debugging_enabled(DEBUG_SCRIPT))
 412     layout->script_options()->print(stderr);
 413
 414   // For each dynamic object, record whether we've seen all the
 415   // dynamic objects that it depends upon.
 416   input_objects->check_dynamic_dependencies();
 417
 418   // See if any of the input definitions violate the One Definition Rule.
 419   // TODO: if this is too slow, do this as a task, rather than inline.
 420   symtab->detect_odr_violations(task, options.output_file_name());
 421
 422   // Create any automatic note sections.
 423   layout->create_notes();
 424
 425   // Create any output sections required by any linker script.
 426   layout->create_script_sections();
 427
 428   // Define some sections and symbols needed for a dynamic link.  This
 429   // handles some cases we want to see before we read the relocs.
 430   layout->create_initial_dynamic_sections(symtab);
 431
 432   // Define symbols from any linker scripts.
 433   layout->define_script_symbols(symtab);
 434
 435   // Attach sections to segments.
 436   layout->attach_sections_to_segments();
 437
 438   if (!parameters->options().relocatable())
 439     {
 440       // Predefine standard symbols.
 441       define_standard_symbols(symtab, layout);
 442
 443       // Define __start and __stop symbols for output sections where
 444       // appropriate.
 445       layout->define_section_symbols(symtab);
 446     }
 447
 448   // Make sure we have symbols for any required group signatures.
 449   layout->define_group_signatures(symtab);
 450
 451   Task_token* blocker = new Task_token(true);
 452   Task_token* symtab_lock = new Task_token(false);
 453
 454   // If doing garbage collection, the relocations have already been read.
 455   // Otherwise, read and scan the relocations.
 456   if (parameters->options().gc_sections() || parameters->options().icf())
 457     {
 458       for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 459            p != input_objects->relobj_end();
 460            ++p)
 461         {
 462           blocker->add_blocker();
 463           workqueue->queue(new Scan_relocs(options, symtab, layout, *p,
 464                            (*p)->get_relocs_data(),symtab_lock, blocker));
 465         }
 466     }
 467   else
 468     {
 469       // Read the relocations of the input files.  We do this to find
 470       // which symbols are used by relocations which require a GOT and/or
 471       // a PLT entry, or a COPY reloc.  When we implement garbage
 472       // collection we will do it here by reading the relocations in a
 473       // breadth first search by references.
 474       //
 475       // We could also read the relocations during the first pass, and
 476       // mark symbols at that time.  That is how the old GNU linker works.
 477       // Doing that is more complex, since we may later decide to discard
 478       // some of the sections, and thus change our minds about the types
 479       // of references made to the symbols.
 480       for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 481            p != input_objects->relobj_end();
 482            ++p)
 483         {
 484           // We can read and process the relocations in any order.  But we
 485           // only want one task to write to the symbol table at a time.
 486           // So we queue up a task for each object to read the
 487           // relocations.  That task will in turn queue a task to wait
 488           // until it can write to the symbol table.
 489           blocker->add_blocker();
 490           workqueue->queue(new Read_relocs(options, symtab, layout, *p,
 491                    symtab_lock, blocker));
 492         }
 493     }
 494
 495   // Allocate common symbols.  This requires write access to the
 496   // symbol table, but is independent of the relocation processing.
 497   if (parameters->options().define_common())
 498     {
 499       blocker->add_blocker();
 500       workqueue->queue(new Allocate_commons_task(symtab, layout, mapfile,
 501                                                  symtab_lock, blocker));
 502     }
 503
 504   // When all those tasks are complete, we can start laying out the
 505   // output file.
 506   // TODO(csilvers): figure out a more principled way to get the target
 507   Target* target = const_cast<Target*>(&parameters->target());
 508   workqueue->queue(new Task_function(new Layout_task_runner(options,
 509                                                             input_objects,
 510                                                             symtab,
 511                                                             target,
 512                                                             layout,
 513                                                             mapfile),
 514                                      blocker,
 515                                      "Task_function Layout_task_runner"));
 516 }
 517
 518 // Queue up the final set of tasks.  This is called at the end of
 519 // Layout_task.
 520
 521 void
 522 queue_final_tasks(const General_options& options,
 523                   const Input_objects* input_objects,
 524                   const Symbol_table* symtab,
 525                   Layout* layout,
 526                   Workqueue* workqueue,
 527                   Output_file* of)
 528 {
 529   int thread_count = options.thread_count_final();
 530   if (thread_count == 0)
 531     thread_count = std::max(2, input_objects->number_of_input_objects());
 532   workqueue->set_thread_count(thread_count);
 533
 534   bool any_postprocessing_sections = layout->any_postprocessing_sections();
 535
 536   // Use a blocker to wait until all the input sections have been
 537   // written out.
 538   Task_token* input_sections_blocker = NULL;
 539   if (!any_postprocessing_sections)
 540     input_sections_blocker = new Task_token(true);
 541
 542   // Use a blocker to block any objects which have to wait for the
 543   // output sections to complete before they can apply relocations.
 544   Task_token* output_sections_blocker = new Task_token(true);
 545
 546   // Use a blocker to block the final cleanup task.
 547   Task_token* final_blocker = new Task_token(true);
 548
 549   // Queue a task to write out the symbol table.
 550   final_blocker->add_blocker();
 551   workqueue->queue(new Write_symbols_task(layout,
 552                                           symtab,
 553                                           input_objects,
 554                                           layout->sympool(),
 555                                           layout->dynpool(),
 556                                           of,
 557                                           final_blocker));
 558
 559   // Queue a task to write out the output sections.
 560   output_sections_blocker->add_blocker();
 561   final_blocker->add_blocker();
 562   workqueue->queue(new Write_sections_task(layout, of, output_sections_blocker,
 563                                            final_blocker));
 564
 565   // Queue a task to write out everything else.
 566   final_blocker->add_blocker();
 567   workqueue->queue(new Write_data_task(layout, symtab, of, final_blocker));
 568
 569   // Queue a task for each input object to relocate the sections and
 570   // write out the local symbols.
 571   for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 572        p != input_objects->relobj_end();
 573        ++p)
 574     {
 575       if (input_sections_blocker != NULL)
 576         input_sections_blocker->add_blocker();
 577       final_blocker->add_blocker();
 578       workqueue->queue(new Relocate_task(options, symtab, layout, *p, of,
 579                                          input_sections_blocker,
 580                                          output_sections_blocker,
 581                                          final_blocker));
 582     }
 583
 584   // Queue a task to write out the output sections which depend on
 585   // input sections.  If there are any sections which require
 586   // postprocessing, then we need to do this last, since it may resize
 587   // the output file.
 588   if (!any_postprocessing_sections)
 589     {
 590       final_blocker->add_blocker();
 591       Task* t = new Write_after_input_sections_task(layout, of,
 592                                                     input_sections_blocker,
 593                                                     final_blocker);
 594       workqueue->queue(t);
 595     }
 596   else
 597     {
 598       Task_token *new_final_blocker = new Task_token(true);
 599       new_final_blocker->add_blocker();
 600       Task* t = new Write_after_input_sections_task(layout, of,
 601                                                     final_blocker,
 602                                                     new_final_blocker);
 603       workqueue->queue(t);
 604       final_blocker = new_final_blocker;
 605     }
 606
 607   // Queue a task to close the output file.  This will be blocked by
 608   // FINAL_BLOCKER.
 609   workqueue->queue(new Task_function(new Close_task_runner(&options, layout,
 610                                                            of),
 611                                      final_blocker,
 612                                      "Task_function Close_task_runner"));
 613 }
 614
 615 } // End namespace gold.