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