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 "gc.h"
  45 #include "icf.h"
  46 #include "incremental.h"
  47
  48 namespace gold
  49 {
  50
  51 const char* program_name;
  52
  53 void
  54 gold_exit(bool status)
  55 {
  56   if (parameters != NULL
  57       && parameters->options_valid()
  58       && parameters->options().has_plugins())
  59     parameters->options().plugins()->cleanup();
  60   if (!status && parameters != NULL && parameters->options_valid())
  61     unlink_if_ordinary(parameters->options().output_file_name());
  62   exit(status ? EXIT_SUCCESS : EXIT_FAILURE);
  63 }
  64
  65 void
  66 gold_nomem()
  67 {
  68   // We are out of memory, so try hard to print a reasonable message.
  69   // Note that we don't try to translate this message, since the
  70   // translation process itself will require memory.
  71
  72   // LEN only exists to avoid a pointless warning when write is
  73   // declared with warn_use_result, as when compiling with
  74   // -D_USE_FORTIFY on GNU/Linux.  Casting to void does not appear to
  75   // work, at least not with gcc 4.3.0.
  76
  77   ssize_t len = write(2, program_name, strlen(program_name));
  78   if (len >= 0)
  79     {
  80       const char* const s = ": out of memory\n";
  81       len = write(2, s, strlen(s));
  82     }
  83   gold_exit(false);
  84 }
  85
  86 // Handle an unreachable case.
  87
  88 void
  89 do_gold_unreachable(const char* filename, int lineno, const char* function)
  90 {
  91   fprintf(stderr, _("%s: internal error in %s, at %s:%d\n"),
  92           program_name, function, filename, lineno);
  93   gold_exit(false);
  94 }
  95
  96 // This class arranges to run the functions done in the middle of the
  97 // link.  It is just a closure.
  98
  99 class Middle_runner : public Task_function_runner
 100 {
 101  public:
 102   Middle_runner(const General_options& options,
 103                 const Input_objects* input_objects,
 104                 Symbol_table* symtab,
 105                 Layout* layout, Mapfile* mapfile)
 106     : options_(options), input_objects_(input_objects), symtab_(symtab),
 107       layout_(layout), mapfile_(mapfile)
 108   { }
 109
 110   void
 111   run(Workqueue*, const Task*);
 112
 113  private:
 114   const General_options& options_;
 115   const Input_objects* input_objects_;
 116   Symbol_table* symtab_;
 117   Layout* layout_;
 118   Mapfile* mapfile_;
 119 };
 120
 121 void
 122 Middle_runner::run(Workqueue* workqueue, const Task* task)
 123 {
 124   queue_middle_tasks(this->options_, task, this->input_objects_, this->symtab_,
 125                      this->layout_, workqueue, this->mapfile_);
 126 }
 127
 128 // This class arranges the tasks to process the relocs for garbage collection.
 129
 130 class Gc_runner : public Task_function_runner
 131 {
 132   public:
 133    Gc_runner(const General_options& options,
 134              const Input_objects* input_objects,
 135              Symbol_table* symtab,
 136              Layout* layout, Mapfile* mapfile)
 137     : options_(options), input_objects_(input_objects), symtab_(symtab),
 138       layout_(layout), mapfile_(mapfile)
 139    { }
 140
 141   void
 142   run(Workqueue*, const Task*);
 143
 144  private:
 145   const General_options& options_;
 146   const Input_objects* input_objects_;
 147   Symbol_table* symtab_;
 148   Layout* layout_;
 149   Mapfile* mapfile_;
 150 };
 151
 152 void
 153 Gc_runner::run(Workqueue* workqueue, const Task* task)
 154 {
 155   queue_middle_gc_tasks(this->options_, task, this->input_objects_,
 156                         this->symtab_, this->layout_, workqueue,
 157                         this->mapfile_);
 158 }
 159
 160 // Queue up the initial set of tasks for this link job.
 161
 162 void
 163 queue_initial_tasks(const General_options& options,
 164                     Dirsearch& search_path,
 165                     const Command_line& cmdline,
 166                     Workqueue* workqueue, Input_objects* input_objects,
 167                     Symbol_table* symtab, Layout* layout, Mapfile* mapfile)
 168 {
 169   if (cmdline.begin() == cmdline.end())
 170     {
 171       if (options.printed_version())
 172         gold_exit(true);
 173       gold_fatal(_("no input files"));
 174     }
 175
 176   int thread_count = options.thread_count_initial();
 177   if (thread_count == 0)
 178     thread_count = cmdline.number_of_input_files();
 179   workqueue->set_thread_count(thread_count);
 180
 181   if (cmdline.options().incremental())
 182     {
 183       Incremental_checker incremental_checker(
 184           parameters->options().output_file_name(),
 185           layout->incremental_inputs());
 186       if (incremental_checker.can_incrementally_link_output_file())
 187         {
 188           // TODO: remove when incremental linking implemented.
 189           printf("Incremental linking might be possible "
 190               "(not implemented yet)\n");
 191         }
 192       // TODO: If we decide on an incremental build, fewer tasks
 193       // should be scheduled.
 194     }
 195
 196   // Read the input files.  We have to add the symbols to the symbol
 197   // table in order.  We do this by creating a separate blocker for
 198   // each input file.  We associate the blocker with the following
 199   // input file, to give us a convenient place to delete it.
 200   Task_token* this_blocker = NULL;
 201   for (Command_line::const_iterator p = cmdline.begin();
 202        p != cmdline.end();
 203        ++p)
 204     {
 205       Task_token* next_blocker = new Task_token(true);
 206       next_blocker->add_blocker();
 207       workqueue->queue(new Read_symbols(input_objects, symtab, layout,
 208                                         &search_path, 0, mapfile, &*p, NULL,
 209                                         this_blocker, next_blocker));
 210       this_blocker = next_blocker;
 211     }
 212
 213   if (options.has_plugins())
 214     {
 215       Task_token* next_blocker = new Task_token(true);
 216       next_blocker->add_blocker();
 217       workqueue->queue(new Plugin_hook(options, input_objects, symtab, layout,
 218                                        &search_path, mapfile, this_blocker,
 219                                        next_blocker));
 220       this_blocker = next_blocker;
 221     }
 222
 223   if (parameters->options().relocatable()
 224       && (parameters->options().gc_sections()
 225           || parameters->options().icf_enabled()))
 226     gold_error(_("cannot mix -r with --gc-sections or --icf"));
 227
 228   if (parameters->options().gc_sections()
 229       || parameters->options().icf_enabled())
 230     {
 231       workqueue->queue(new Task_function(new Gc_runner(options,
 232                                                        input_objects,
 233                                                        symtab,
 234                                                        layout,
 235                                                        mapfile),
 236                                          this_blocker,
 237                                          "Task_function Gc_runner"));
 238     }
 239   else
 240     {
 241       workqueue->queue(new Task_function(new Middle_runner(options,
 242                                                            input_objects,
 243                                                            symtab,
 244                                                            layout,
 245                                                            mapfile),
 246                                          this_blocker,
 247                                          "Task_function Middle_runner"));
 248     }
 249 }
 250
 251 // Queue up a set of tasks to be done before queueing the middle set
 252 // of tasks.  This is only necessary when garbage collection
 253 // (--gc-sections) of unused sections is desired.  The relocs are read
 254 // and processed here early to determine the garbage sections before the
 255 // relocs can be scanned in later tasks.
 256
 257 void
 258 queue_middle_gc_tasks(const General_options& options,
 259                       const Task* ,
 260                       const Input_objects* input_objects,
 261                       Symbol_table* symtab,
 262                       Layout* layout,
 263                       Workqueue* workqueue,
 264                       Mapfile* mapfile)
 265 {
 266   // Read_relocs for all the objects must be done and processed to find
 267   // unused sections before any scanning of the relocs can take place.
 268   Task_token* blocker = new Task_token(true);
 269   Task_token* symtab_lock = new Task_token(false);
 270   for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 271        p != input_objects->relobj_end();
 272        ++p)
 273     {
 274       // We can read and process the relocations in any order.
 275       blocker->add_blocker();
 276       workqueue->queue(new Read_relocs(options, symtab, layout, *p,
 277                                        symtab_lock, blocker));
 278     }
 279
 280   Task_token* this_blocker = new Task_token(true);
 281   workqueue->queue(new Task_function(new Middle_runner(options,
 282                                                        input_objects,
 283                                                        symtab,
 284                                                        layout,
 285                                                        mapfile),
 286                                      this_blocker,
 287                                      "Task_function Middle_runner"));
 288 }
 289
 290 // Queue up the middle set of tasks.  These are the tasks which run
 291 // after all the input objects have been found and all the symbols
 292 // have been read, but before we lay out the output file.
 293
 294 void
 295 queue_middle_tasks(const General_options& options,
 296                    const Task* task,
 297                    const Input_objects* input_objects,
 298                    Symbol_table* symtab,
 299                    Layout* layout,
 300                    Workqueue* workqueue,
 301                    Mapfile* mapfile)
 302 {
 303   // Add any symbols named with -u options to the symbol table.
 304   symtab->add_undefined_symbols_from_command_line();
 305
 306   // If garbage collection was chosen, relocs have been read and processed
 307   // at this point by pre_middle_tasks.  Layout can then be done for all
 308   // objects.
 309   if (parameters->options().gc_sections())
 310     {
 311       // Find the start symbol if any.
 312       Symbol* start_sym;
 313       if (parameters->options().entry())
 314         start_sym = symtab->lookup(parameters->options().entry());
 315       else
 316         start_sym = symtab->lookup("_start");
 317       if (start_sym !=NULL)
 318         {
 319           bool is_ordinary;
 320           unsigned int shndx = start_sym->shndx(&is_ordinary);
 321           if (is_ordinary)
 322             {
 323               symtab->gc()->worklist().push(
 324                 Section_id(start_sym->object(), shndx));
 325             }
 326         }
 327       // Symbols named with -u should not be considered garbage.
 328       symtab->gc_mark_undef_symbols();
 329       gold_assert(symtab->gc() != NULL);
 330       // Do a transitive closure on all references to determine the worklist.
 331       symtab->gc()->do_transitive_closure();
 332     }
 333
 334   // If identical code folding (--icf) is chosen it makes sense to do it
 335   // only after garbage collection (--gc-sections) as we do not want to
 336   // be folding sections that will be garbage.
 337   if (parameters->options().icf_enabled())
 338     {
 339       symtab->icf()->find_identical_sections(input_objects, symtab);
 340     }
 341
 342   // Call Object::layout for the second time to determine the
 343   // output_sections for all referenced input sections.  When
 344   // --gc-sections or --icf is turned on, Object::layout is
 345   // called twice.  It is called the first time when the
 346   // symbols are added.
 347   if (parameters->options().gc_sections()
 348       || parameters->options().icf_enabled())
 349     {
 350       for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 351            p != input_objects->relobj_end();
 352            ++p)
 353         {
 354           (*p)->layout(symtab, layout, NULL);
 355         }
 356     }
 357
 358   // Layout deferred objects due to plugins.
 359   if (parameters->options().has_plugins())
 360     {
 361       Plugin_manager* plugins = parameters->options().plugins();
 362       gold_assert(plugins != NULL);
 363       plugins->layout_deferred_objects();
 364     }
 365
 366   if (parameters->options().gc_sections()
 367       || parameters->options().icf_enabled())
 368     {
 369       for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 370            p != input_objects->relobj_end();
 371            ++p)
 372         {
 373           // Update the value of output_section stored in rd.
 374           Read_relocs_data *rd = (*p)->get_relocs_data();
 375           for (Read_relocs_data::Relocs_list::iterator q = rd->relocs.begin();
 376                q != rd->relocs.end();
 377                ++q)
 378             {
 379               q->output_section = (*p)->output_section(q->data_shndx);
 380               q->needs_special_offset_handling =
 381                       (*p)->is_output_section_offset_invalid(q->data_shndx);
 382             }
 383         }
 384     }
 385
 386   // We have to support the case of not seeing any input objects, and
 387   // generate an empty file.  Existing builds depend on being able to
 388   // pass an empty archive to the linker and get an empty object file
 389   // out.  In order to do this we need to use a default target.
 390   if (input_objects->number_of_input_objects() == 0)
 391     parameters_force_valid_target();
 392
 393   int thread_count = options.thread_count_middle();
 394   if (thread_count == 0)
 395     thread_count = std::max(2, input_objects->number_of_input_objects());
 396   workqueue->set_thread_count(thread_count);
 397
 398   // Now we have seen all the input files.
 399   const bool doing_static_link = (!input_objects->any_dynamic()
 400                                   && !parameters->options().shared());
 401   set_parameters_doing_static_link(doing_static_link);
 402   if (!doing_static_link && options.is_static())
 403     {
 404       // We print out just the first .so we see; there may be others.
 405       gold_assert(input_objects->dynobj_begin() != input_objects->dynobj_end());
 406       gold_error(_("cannot mix -static with dynamic object %s"),
 407                  (*input_objects->dynobj_begin())->name().c_str());
 408     }
 409   if (!doing_static_link && parameters->options().relocatable())
 410     gold_fatal(_("cannot mix -r with dynamic object %s"),
 411                (*input_objects->dynobj_begin())->name().c_str());
 412   if (!doing_static_link
 413       && options.oformat_enum() != General_options::OBJECT_FORMAT_ELF)
 414     gold_fatal(_("cannot use non-ELF output format with dynamic object %s"),
 415                (*input_objects->dynobj_begin())->name().c_str());
 416
 417   if (parameters->options().relocatable())
 418     {
 419       Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 420       if (p != input_objects->relobj_end())
 421         {
 422           bool uses_split_stack = (*p)->uses_split_stack();
 423           for (++p; p != input_objects->relobj_end(); ++p)
 424             {
 425               if ((*p)->uses_split_stack() != uses_split_stack)
 426                 gold_fatal(_("cannot mix split-stack '%s' and "
 427                              "non-split-stack '%s' when using -r"),
 428                            (*input_objects->relobj_begin())->name().c_str(),
 429                            (*p)->name().c_str());
 430             }
 431         }
 432     }
 433
 434   if (is_debugging_enabled(DEBUG_SCRIPT))
 435     layout->script_options()->print(stderr);
 436
 437   // For each dynamic object, record whether we've seen all the
 438   // dynamic objects that it depends upon.
 439   input_objects->check_dynamic_dependencies();
 440
 441   // See if any of the input definitions violate the One Definition Rule.
 442   // TODO: if this is too slow, do this as a task, rather than inline.
 443   symtab->detect_odr_violations(task, options.output_file_name());
 444
 445   // Create any automatic note sections.
 446   layout->create_notes();
 447
 448   // Create any output sections required by any linker script.
 449   layout->create_script_sections();
 450
 451   // Define some sections and symbols needed for a dynamic link.  This
 452   // handles some cases we want to see before we read the relocs.
 453   layout->create_initial_dynamic_sections(symtab);
 454
 455   // Define symbols from any linker scripts.
 456   layout->define_script_symbols(symtab);
 457
 458   // Attach sections to segments.
 459   layout->attach_sections_to_segments();
 460
 461   if (!parameters->options().relocatable())
 462     {
 463       // Predefine standard symbols.
 464       define_standard_symbols(symtab, layout);
 465
 466       // Define __start and __stop symbols for output sections where
 467       // appropriate.
 468       layout->define_section_symbols(symtab);
 469     }
 470
 471   // Make sure we have symbols for any required group signatures.
 472   layout->define_group_signatures(symtab);
 473
 474   Task_token* blocker = new Task_token(true);
 475   Task_token* symtab_lock = new Task_token(false);
 476
 477   // If doing garbage collection, the relocations have already been read.
 478   // Otherwise, read and scan the relocations.
 479   if (parameters->options().gc_sections()
 480       || parameters->options().icf_enabled())
 481     {
 482       for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 483            p != input_objects->relobj_end();
 484            ++p)
 485         {
 486           blocker->add_blocker();
 487           workqueue->queue(new Scan_relocs(options, symtab, layout, *p,
 488                            (*p)->get_relocs_data(),symtab_lock, blocker));
 489         }
 490     }
 491   else
 492     {
 493       // Read the relocations of the input files.  We do this to find
 494       // which symbols are used by relocations which require a GOT and/or
 495       // a PLT entry, or a COPY reloc.  When we implement garbage
 496       // collection we will do it here by reading the relocations in a
 497       // breadth first search by references.
 498       //
 499       // We could also read the relocations during the first pass, and
 500       // mark symbols at that time.  That is how the old GNU linker works.
 501       // Doing that is more complex, since we may later decide to discard
 502       // some of the sections, and thus change our minds about the types
 503       // of references made to the symbols.
 504       for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 505            p != input_objects->relobj_end();
 506            ++p)
 507         {
 508           // We can read and process the relocations in any order.  But we
 509           // only want one task to write to the symbol table at a time.
 510           // So we queue up a task for each object to read the
 511           // relocations.  That task will in turn queue a task to wait
 512           // until it can write to the symbol table.
 513           blocker->add_blocker();
 514           workqueue->queue(new Read_relocs(options, symtab, layout, *p,
 515                    symtab_lock, blocker));
 516         }
 517     }
 518
 519   // Allocate common symbols.  This requires write access to the
 520   // symbol table, but is independent of the relocation processing.
 521   if (parameters->options().define_common())
 522     {
 523       blocker->add_blocker();
 524       workqueue->queue(new Allocate_commons_task(symtab, layout, mapfile,
 525                                                  symtab_lock, blocker));
 526     }
 527
 528   // When all those tasks are complete, we can start laying out the
 529   // output file.
 530   // TODO(csilvers): figure out a more principled way to get the target
 531   Target* target = const_cast<Target*>(&parameters->target());
 532   workqueue->queue(new Task_function(new Layout_task_runner(options,
 533                                                             input_objects,
 534                                                             symtab,
 535                                                             target,
 536                                                             layout,
 537                                                             mapfile),
 538                                      blocker,
 539                                      "Task_function Layout_task_runner"));
 540 }
 541
 542 // Queue up the final set of tasks.  This is called at the end of
 543 // Layout_task.
 544
 545 void
 546 queue_final_tasks(const General_options& options,
 547                   const Input_objects* input_objects,
 548                   const Symbol_table* symtab,
 549                   Layout* layout,
 550                   Workqueue* workqueue,
 551                   Output_file* of)
 552 {
 553   int thread_count = options.thread_count_final();
 554   if (thread_count == 0)
 555     thread_count = std::max(2, input_objects->number_of_input_objects());
 556   workqueue->set_thread_count(thread_count);
 557
 558   bool any_postprocessing_sections = layout->any_postprocessing_sections();
 559
 560   // Use a blocker to wait until all the input sections have been
 561   // written out.
 562   Task_token* input_sections_blocker = NULL;
 563   if (!any_postprocessing_sections)
 564     input_sections_blocker = new Task_token(true);
 565
 566   // Use a blocker to block any objects which have to wait for the
 567   // output sections to complete before they can apply relocations.
 568   Task_token* output_sections_blocker = new Task_token(true);
 569
 570   // Use a blocker to block the final cleanup task.
 571   Task_token* final_blocker = new Task_token(true);
 572
 573   // Queue a task to write out the symbol table.
 574   final_blocker->add_blocker();
 575   workqueue->queue(new Write_symbols_task(layout,
 576                                           symtab,
 577                                           input_objects,
 578                                           layout->sympool(),
 579                                           layout->dynpool(),
 580                                           of,
 581                                           final_blocker));
 582
 583   // Queue a task to write out the output sections.
 584   output_sections_blocker->add_blocker();
 585   final_blocker->add_blocker();
 586   workqueue->queue(new Write_sections_task(layout, of, output_sections_blocker,
 587                                            final_blocker));
 588
 589   // Queue a task to write out everything else.
 590   final_blocker->add_blocker();
 591   workqueue->queue(new Write_data_task(layout, symtab, of, final_blocker));
 592
 593   // Queue a task for each input object to relocate the sections and
 594   // write out the local symbols.
 595   for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
 596        p != input_objects->relobj_end();
 597        ++p)
 598     {
 599       if (input_sections_blocker != NULL)
 600         input_sections_blocker->add_blocker();
 601       final_blocker->add_blocker();
 602       workqueue->queue(new Relocate_task(options, symtab, layout, *p, of,
 603                                          input_sections_blocker,
 604                                          output_sections_blocker,
 605                                          final_blocker));
 606     }
 607
 608   // Queue a task to write out the output sections which depend on
 609   // input sections.  If there are any sections which require
 610   // postprocessing, then we need to do this last, since it may resize
 611   // the output file.
 612   if (!any_postprocessing_sections)
 613     {
 614       final_blocker->add_blocker();
 615       Task* t = new Write_after_input_sections_task(layout, of,
 616                                                     input_sections_blocker,
 617                                                     final_blocker);
 618       workqueue->queue(t);
 619     }
 620   else
 621     {
 622       Task_token *new_final_blocker = new Task_token(true);
 623       new_final_blocker->add_blocker();
 624       Task* t = new Write_after_input_sections_task(layout, of,
 625                                                     final_blocker,
 626                                                     new_final_blocker);
 627       workqueue->queue(t);
 628       final_blocker = new_final_blocker;
 629     }
 630
 631   // Queue a task to close the output file.  This will be blocked by
 632   // FINAL_BLOCKER.
 633   workqueue->queue(new Task_function(new Close_task_runner(&options, layout,
 634                                                            of),
 635                                      final_blocker,
 636                                      "Task_function Close_task_runner"));
 637 }
 638
 639 } // End namespace gold.