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