1 // layout.h -- lay out output file sections for gold -*- C++ -*-
3 // Copyright 2006, 2007, 2008 Free Software Foundation, Inc.
4 // Written by Ian Lance Taylor <iant@google.com>.
6 // This file is part of gold.
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.
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.
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.
33 #include "workqueue.h"
36 #include "stringpool.h"
41 class General_options;
44 class Output_section_data;
46 class Output_section_headers;
49 class Output_data_dynamic;
50 class Output_symtab_xindex;
54 // This task function handles mapping the input sections to output
55 // sections and laying them out in memory.
57 class Layout_task_runner : public Task_function_runner
60 // OPTIONS is the command line options, INPUT_OBJECTS is the list of
61 // input objects, SYMTAB is the symbol table, LAYOUT is the layout
63 Layout_task_runner(const General_options& options,
64 const Input_objects* input_objects,
68 : options_(options), input_objects_(input_objects), symtab_(symtab),
69 target_(target), layout_(layout)
74 run(Workqueue*, const Task*);
77 Layout_task_runner(const Layout_task_runner&);
78 Layout_task_runner& operator=(const Layout_task_runner&);
80 const General_options& options_;
81 const Input_objects* input_objects_;
82 Symbol_table* symtab_;
87 // This class handles the details of laying out input sections.
92 Layout(const General_options& options, Script_options*);
94 // Given an input section SHNDX, named NAME, with data in SHDR, from
95 // the object file OBJECT, return the output section where this
96 // input section should go. RELOC_SHNDX is the index of a
97 // relocation section which applies to this section, or 0 if none,
98 // or -1U if more than one. RELOC_TYPE is the type of the
99 // relocation section if there is one. Set *OFFSET to the offset
100 // within the output section.
101 template<int size, bool big_endian>
103 layout(Sized_relobj<size, big_endian> *object, unsigned int shndx,
104 const char* name, const elfcpp::Shdr<size, big_endian>& shdr,
105 unsigned int reloc_shndx, unsigned int reloc_type, off_t* offset);
107 // Layout an input reloc section when doing a relocatable link. The
108 // section is RELOC_SHNDX in OBJECT, with data in SHDR.
109 // DATA_SECTION is the reloc section to which it refers. RR is the
110 // relocatable information.
111 template<int size, bool big_endian>
113 layout_reloc(Sized_relobj<size, big_endian>* object,
114 unsigned int reloc_shndx,
115 const elfcpp::Shdr<size, big_endian>& shdr,
116 Output_section* data_section,
117 Relocatable_relocs* rr);
119 // Layout a group section when doing a relocatable link.
120 template<int size, bool big_endian>
122 layout_group(Symbol_table* symtab,
123 Sized_relobj<size, big_endian>* object,
124 unsigned int group_shndx,
125 const char* group_section_name,
126 const char* signature,
127 const elfcpp::Shdr<size, big_endian>& shdr,
128 elfcpp::Elf_Word flags,
129 std::vector<unsigned int>* shndxes);
131 // Like layout, only for exception frame sections. OBJECT is an
132 // object file. SYMBOLS is the contents of the symbol table
133 // section, with size SYMBOLS_SIZE. SYMBOL_NAMES is the contents of
134 // the symbol name section, with size SYMBOL_NAMES_SIZE. SHNDX is a
135 // .eh_frame section in OBJECT. SHDR is the section header.
136 // RELOC_SHNDX is the index of a relocation section which applies to
137 // this section, or 0 if none, or -1U if more than one. RELOC_TYPE
138 // is the type of the relocation section if there is one. This
139 // returns the output section, and sets *OFFSET to the offset.
140 template<int size, bool big_endian>
142 layout_eh_frame(Sized_relobj<size, big_endian>* object,
143 const unsigned char* symbols,
145 const unsigned char* symbol_names,
146 off_t symbol_names_size,
148 const elfcpp::Shdr<size, big_endian>& shdr,
149 unsigned int reloc_shndx, unsigned int reloc_type,
152 // Handle a GNU stack note. This is called once per input object
153 // file. SEEN_GNU_STACK is true if the object file has a
154 // .note.GNU-stack section. GNU_STACK_FLAGS is the section flags
155 // from that section if there was one.
157 layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags);
159 // Add an Output_section_data to the layout. This is used for
160 // special sections like the GOT section.
162 add_output_section_data(const char* name, elfcpp::Elf_Word type,
163 elfcpp::Elf_Xword flags,
164 Output_section_data*);
166 // Create dynamic sections if necessary.
168 create_initial_dynamic_sections(Symbol_table*);
170 // Define __start and __stop symbols for output sections.
172 define_section_symbols(Symbol_table*);
174 // Create sections for linker scripts.
176 create_script_sections()
177 { this->script_options_->create_script_sections(this); }
179 // Define symbols from any linker script.
181 define_script_symbols(Symbol_table* symtab)
182 { this->script_options_->add_symbols_to_table(symtab); }
184 // Define symbols for group signatures.
186 define_group_signatures(Symbol_table*);
188 // Return the Stringpool used for symbol names.
191 { return &this->sympool_; }
193 // Return the Stringpool used for dynamic symbol names and dynamic
197 { return &this->dynpool_; }
199 // Return the symtab_xindex section used to hold large section
200 // indexes for the normal symbol table.
201 Output_symtab_xindex*
202 symtab_xindex() const
203 { return this->symtab_xindex_; }
205 // Return the dynsym_xindex section used to hold large section
206 // indexes for the dynamic symbol table.
207 Output_symtab_xindex*
208 dynsym_xindex() const
209 { return this->dynsym_xindex_; }
211 // Return whether a section is a .gnu.linkonce section, given the
214 is_linkonce(const char* name)
215 { return strncmp(name, ".gnu.linkonce", sizeof(".gnu.linkonce") - 1) == 0; }
217 // Return true if a section is a debugging section.
219 is_debug_info_section(const char* name)
221 // Debugging sections can only be recognized by name.
222 return (strncmp(name, ".debug", sizeof(".debug") - 1) == 0
223 || strncmp(name, ".gnu.linkonce.wi.",
224 sizeof(".gnu.linkonce.wi.") - 1) == 0
225 || strncmp(name, ".line", sizeof(".line") - 1) == 0
226 || strncmp(name, ".stab", sizeof(".stab") - 1) == 0);
229 // Record the signature of a comdat section, and return whether to
230 // include it in the link. The GROUP parameter is true for a
231 // section group signature, false for a signature derived from a
232 // .gnu.linkonce section.
234 add_comdat(Relobj*, unsigned int, const std::string&, bool group);
236 // Find the given comdat signature, and return the object and section
237 // index of the kept group.
239 find_kept_object(const std::string&, unsigned int*) const;
241 // Finalize the layout after all the input sections have been added.
243 finalize(const Input_objects*, Symbol_table*, Target*, const Task*);
245 // Return whether any sections require postprocessing.
247 any_postprocessing_sections() const
248 { return this->any_postprocessing_sections_; }
250 // Return the size of the output file.
252 output_file_size() const
253 { return this->output_file_size_; }
255 // Return the TLS segment. This will return NULL if there isn't
259 { return this->tls_segment_; }
261 // Return the normal symbol table.
263 symtab_section() const
265 gold_assert(this->symtab_section_ != NULL);
266 return this->symtab_section_;
269 // Return the dynamic symbol table.
271 dynsym_section() const
273 gold_assert(this->dynsym_section_ != NULL);
274 return this->dynsym_section_;
277 // Return the dynamic tags.
280 { return this->dynamic_data_; }
282 // Write out the output sections.
284 write_output_sections(Output_file* of) const;
286 // Write out data not associated with an input file or the symbol
289 write_data(const Symbol_table*, Output_file*) const;
291 // Write out output sections which can not be written until all the
292 // input sections are complete.
294 write_sections_after_input_sections(Output_file* of);
296 // Return an output section named NAME, or NULL if there is none.
298 find_output_section(const char* name) const;
300 // Return an output segment of type TYPE, with segment flags SET set
301 // and segment flags CLEAR clear. Return NULL if there is none.
303 find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
304 elfcpp::Elf_Word clear) const;
306 // Return the number of segments we expect to produce.
308 expected_segment_count() const;
310 // Set a flag to indicate that an object file uses the static TLS model.
313 { this->has_static_tls_ = true; }
315 // Return true if any object file uses the static TLS model.
317 has_static_tls() const
318 { return this->has_static_tls_; }
320 // Return the options which may be set by a linker script.
323 { return this->script_options_; }
325 const Script_options*
326 script_options() const
327 { return this->script_options_; }
329 // Compute and write out the build ID if needed.
331 write_build_id(Output_file*) const;
333 // Rewrite output file in binary format.
335 write_binary(Output_file* in) const;
337 // Dump statistical information to stderr.
341 // A list of segments.
343 typedef std::vector<Output_segment*> Segment_list;
345 // A list of sections.
347 typedef std::vector<Output_section*> Section_list;
349 // The list of information to write out which is not attached to
350 // either a section or a segment.
351 typedef std::vector<Output_data*> Data_list;
353 // Store the allocated sections into the section list. This is used
354 // by the linker script code.
356 get_allocated_sections(Section_list*) const;
358 // Make a section for a linker script to hold data.
360 make_output_section_for_script(const char* name);
362 // Make a segment. This is used by the linker script code.
364 make_output_segment(elfcpp::Elf_Word type, elfcpp::Elf_Word flags);
366 // Return the number of segments.
368 segment_count() const
369 { return this->segment_list_.size(); }
371 // Map from section flags to segment flags.
372 static elfcpp::Elf_Word
373 section_flags_to_segment(elfcpp::Elf_Xword flags);
375 // Attach sections to segments.
377 attach_sections_to_segments();
380 Layout(const Layout&);
381 Layout& operator=(const Layout&);
383 // Mapping from .gnu.linkonce section names to output section names.
384 struct Linkonce_mapping
391 static const Linkonce_mapping linkonce_mapping[];
392 static const int linkonce_mapping_count;
394 // During a relocatable link, a list of group sections and
396 struct Group_signature
398 // The group section.
399 Output_section* section;
401 const char* signature;
404 : section(NULL), signature(NULL)
407 Group_signature(Output_section* sectiona, const char* signaturea)
408 : section(sectiona), signature(signaturea)
411 typedef std::vector<Group_signature> Group_signatures;
413 // Create a .note section, filling in the header.
415 create_note(const char* name, int note_type, size_t descsz,
416 bool allocate, size_t* trailing_padding);
418 // Create a .note section for gold.
422 // Record whether the stack must be executable.
424 create_executable_stack_info(const Target*);
426 // Create a build ID note if needed.
430 // Find the first read-only PT_LOAD segment, creating one if
433 find_first_load_seg();
435 // Count the local symbols in the regular symbol table and the dynamic
436 // symbol table, and build the respective string pools.
438 count_local_symbols(const Task*, const Input_objects*);
440 // Create the output sections for the symbol table.
442 create_symtab_sections(const Input_objects*, Symbol_table*,
443 unsigned int, off_t*);
445 // Create the .shstrtab section.
449 // Create the section header table.
451 create_shdrs(const Output_section* shstrtab_section, off_t*);
453 // Create the dynamic symbol table.
455 create_dynamic_symtab(const Input_objects*, Symbol_table*,
456 Output_section** pdynstr,
457 unsigned int* plocal_dynamic_count,
458 std::vector<Symbol*>* pdynamic_symbols,
461 // Assign offsets to each local portion of the dynamic symbol table.
463 assign_local_dynsym_offsets(const Input_objects*);
465 // Finish the .dynamic section and PT_DYNAMIC segment.
467 finish_dynamic_section(const Input_objects*, const Symbol_table*);
469 // Create the .interp section and PT_INTERP segment.
471 create_interp(const Target* target);
473 // Create the version sections.
475 create_version_sections(const Versions*,
477 unsigned int local_symcount,
478 const std::vector<Symbol*>& dynamic_symbols,
479 const Output_section* dynstr);
481 template<int size, bool big_endian>
483 sized_create_version_sections(const Versions* versions,
485 unsigned int local_symcount,
486 const std::vector<Symbol*>& dynamic_symbols,
487 const Output_section* dynstr);
489 // Return whether to include this section in the link.
490 template<int size, bool big_endian>
492 include_section(Sized_relobj<size, big_endian>* object, const char* name,
493 const elfcpp::Shdr<size, big_endian>&);
495 // Return the output section name to use given an input section
496 // name. Set *PLEN to the length of the name. *PLEN must be
497 // initialized to the length of NAME.
499 output_section_name(const char* name, size_t* plen);
501 // Return the output section name to use for a linkonce section
502 // name. PLEN is as for output_section_name.
504 linkonce_output_name(const char* name, size_t* plen);
506 // Return the number of allocated output sections.
508 allocated_output_section_count() const;
510 // Return the output section for NAME, TYPE and FLAGS.
512 get_output_section(const char* name, Stringpool::Key name_key,
513 elfcpp::Elf_Word type, elfcpp::Elf_Xword flags);
515 // Choose the output section for NAME in RELOBJ.
517 choose_output_section(const Relobj* relobj, const char* name,
518 elfcpp::Elf_Word type, elfcpp::Elf_Xword flags,
519 bool is_input_section);
521 // Create a new Output_section.
523 make_output_section(const char* name, elfcpp::Elf_Word type,
524 elfcpp::Elf_Xword flags);
526 // Attach a section to a segment.
528 attach_section_to_segment(Output_section*);
530 // Attach an allocated section to a segment.
532 attach_allocated_section_to_segment(Output_section*);
534 // Set the final file offsets of all the segments.
536 set_segment_offsets(const Target*, Output_segment*, unsigned int* pshndx);
538 // Set the file offsets of the sections when doing a relocatable
541 set_relocatable_section_offsets(Output_data*, unsigned int* pshndx);
543 // Set the final file offsets of all the sections not associated
544 // with a segment. We set section offsets in three passes: the
545 // first handles all allocated sections, the second sections that
546 // require postprocessing, and the last the late-bound STRTAB
547 // sections (probably only shstrtab, which is the one we care about
548 // because it holds section names).
549 enum Section_offset_pass
551 BEFORE_INPUT_SECTIONS_PASS,
552 POSTPROCESSING_SECTIONS_PASS,
553 STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS
556 set_section_offsets(off_t, Section_offset_pass pass);
558 // Set the final section indexes of all the sections not associated
559 // with a segment. Returns the next unused index.
561 set_section_indexes(unsigned int pshndx);
563 // Set the section addresses when using a script.
565 set_section_addresses_from_script(Symbol_table*);
567 // Return whether SEG1 comes before SEG2 in the output file.
569 segment_precedes(const Output_segment* seg1, const Output_segment* seg2);
571 // A mapping used for group signatures.
575 : object_(NULL), shndx_(0), group_(false)
577 Kept_section(Relobj* object, unsigned int shndx, bool group)
578 : object_(object), shndx_(shndx), group_(group)
584 typedef Unordered_map<std::string, Kept_section> Signatures;
586 // Mapping from input section name/type/flags to output section. We
587 // use canonicalized strings here.
589 typedef std::pair<Stringpool::Key,
590 std::pair<elfcpp::Elf_Word, elfcpp::Elf_Xword> > Key;
595 operator()(const Key& k) const;
598 typedef Unordered_map<Key, Output_section*, Hash_key> Section_name_map;
600 // A comparison class for segments.
602 struct Compare_segments
605 operator()(const Output_segment* seg1, const Output_segment* seg2)
606 { return Layout::segment_precedes(seg1, seg2); }
609 // A reference to the options on the command line.
610 const General_options& options_;
611 // Information set by scripts or by command line options.
612 Script_options* script_options_;
613 // The output section names.
614 Stringpool namepool_;
615 // The output symbol names.
617 // The dynamic strings, if needed.
619 // The list of group sections and linkonce sections which we have seen.
620 Signatures signatures_;
621 // The mapping from input section name/type/flags to output sections.
622 Section_name_map section_name_map_;
623 // The list of output segments.
624 Segment_list segment_list_;
625 // The list of output sections.
626 Section_list section_list_;
627 // The list of output sections which are not attached to any output
629 Section_list unattached_section_list_;
630 // Whether we have attached the sections to the segments.
631 bool sections_are_attached_;
632 // The list of unattached Output_data objects which require special
633 // handling because they are not Output_sections.
634 Data_list special_output_list_;
635 // The section headers.
636 Output_section_headers* section_headers_;
637 // A pointer to the PT_TLS segment if there is one.
638 Output_segment* tls_segment_;
639 // The SHT_SYMTAB output section.
640 Output_section* symtab_section_;
641 // The SHT_SYMTAB_SHNDX for the regular symbol table if there is one.
642 Output_symtab_xindex* symtab_xindex_;
643 // The SHT_DYNSYM output section if there is one.
644 Output_section* dynsym_section_;
645 // The SHT_SYMTAB_SHNDX for the dynamic symbol table if there is one.
646 Output_symtab_xindex* dynsym_xindex_;
647 // The SHT_DYNAMIC output section if there is one.
648 Output_section* dynamic_section_;
649 // The dynamic data which goes into dynamic_section_.
650 Output_data_dynamic* dynamic_data_;
651 // The exception frame output section if there is one.
652 Output_section* eh_frame_section_;
653 // The exception frame data for eh_frame_section_.
654 Eh_frame* eh_frame_data_;
655 // Whether we have added eh_frame_data_ to the .eh_frame section.
656 bool added_eh_frame_data_;
657 // The exception frame header output section if there is one.
658 Output_section* eh_frame_hdr_section_;
659 // The space for the build ID checksum if there is one.
660 Output_section_data* build_id_note_;
661 // A list of group sections and their signatures.
662 Group_signatures group_signatures_;
663 // The size of the output file.
664 off_t output_file_size_;
665 // Whether we have seen an object file marked to require an
667 bool input_requires_executable_stack_;
668 // Whether we have seen at least one object file with an executable
670 bool input_with_gnu_stack_note_;
671 // Whether we have seen at least one object file without an
672 // executable stack marker.
673 bool input_without_gnu_stack_note_;
674 // Whether we have seen an object file that uses the static TLS model.
675 bool has_static_tls_;
676 // Whether any sections require postprocessing.
677 bool any_postprocessing_sections_;
680 // This task handles writing out data in output sections which is not
681 // part of an input section, or which requires special handling. When
682 // this is done, it unblocks both output_sections_blocker and
685 class Write_sections_task : public Task
688 Write_sections_task(const Layout* layout, Output_file* of,
689 Task_token* output_sections_blocker,
690 Task_token* final_blocker)
691 : layout_(layout), of_(of),
692 output_sections_blocker_(output_sections_blocker),
693 final_blocker_(final_blocker)
696 // The standard Task methods.
709 { return "Write_sections_task"; }
712 class Write_sections_locker;
714 const Layout* layout_;
716 Task_token* output_sections_blocker_;
717 Task_token* final_blocker_;
720 // This task handles writing out data which is not part of a section
723 class Write_data_task : public Task
726 Write_data_task(const Layout* layout, const Symbol_table* symtab,
727 Output_file* of, Task_token* final_blocker)
728 : layout_(layout), symtab_(symtab), of_(of), final_blocker_(final_blocker)
731 // The standard Task methods.
744 { return "Write_data_task"; }
747 const Layout* layout_;
748 const Symbol_table* symtab_;
750 Task_token* final_blocker_;
753 // This task handles writing out the global symbols.
755 class Write_symbols_task : public Task
758 Write_symbols_task(const Layout* layout, const Symbol_table* symtab,
759 const Input_objects* input_objects,
760 const Stringpool* sympool, const Stringpool* dynpool,
761 Output_file* of, Task_token* final_blocker)
762 : layout_(layout), symtab_(symtab), input_objects_(input_objects),
763 sympool_(sympool), dynpool_(dynpool), of_(of),
764 final_blocker_(final_blocker)
767 // The standard Task methods.
780 { return "Write_symbols_task"; }
783 const Layout* layout_;
784 const Symbol_table* symtab_;
785 const Input_objects* input_objects_;
786 const Stringpool* sympool_;
787 const Stringpool* dynpool_;
789 Task_token* final_blocker_;
792 // This task handles writing out data in output sections which can't
793 // be written out until all the input sections have been handled.
794 // This is for sections whose contents is based on the contents of
795 // other output sections.
797 class Write_after_input_sections_task : public Task
800 Write_after_input_sections_task(Layout* layout, Output_file* of,
801 Task_token* input_sections_blocker,
802 Task_token* final_blocker)
803 : layout_(layout), of_(of),
804 input_sections_blocker_(input_sections_blocker),
805 final_blocker_(final_blocker)
808 // The standard Task methods.
821 { return "Write_after_input_sections_task"; }
826 Task_token* input_sections_blocker_;
827 Task_token* final_blocker_;
830 // This task function handles closing the file.
832 class Close_task_runner : public Task_function_runner
835 Close_task_runner(const General_options* options, const Layout* layout,
837 : options_(options), layout_(layout), of_(of)
840 // Run the operation.
842 run(Workqueue*, const Task*);
845 const General_options* options_;
846 const Layout* layout_;
850 // A small helper function to align an address.
853 align_address(uint64_t address, uint64_t addralign)
856 address = (address + addralign - 1) &~ (addralign - 1);
860 } // End namespace gold.
862 #endif // !defined(GOLD_LAYOUT_H)