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