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 const elfcpp::Elf_Word* contents);
130 // Like layout, only for exception frame sections. OBJECT is an
131 // object file. SYMBOLS is the contents of the symbol table
132 // section, with size SYMBOLS_SIZE. SYMBOL_NAMES is the contents of
133 // the symbol name section, with size SYMBOL_NAMES_SIZE. SHNDX is a
134 // .eh_frame section in OBJECT. SHDR is the section header.
135 // RELOC_SHNDX is the index of a relocation section which applies to
136 // this section, or 0 if none, or -1U if more than one. RELOC_TYPE
137 // is the type of the relocation section if there is one. This
138 // returns the output section, and sets *OFFSET to the offset.
139 template<int size, bool big_endian>
141 layout_eh_frame(Sized_relobj<size, big_endian>* object,
142 const unsigned char* symbols,
144 const unsigned char* symbol_names,
145 off_t symbol_names_size,
147 const elfcpp::Shdr<size, big_endian>& shdr,
148 unsigned int reloc_shndx, unsigned int reloc_type,
151 // Handle a GNU stack note. This is called once per input object
152 // file. SEEN_GNU_STACK is true if the object file has a
153 // .note.GNU-stack section. GNU_STACK_FLAGS is the section flags
154 // from that section if there was one.
156 layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags);
158 // Add an Output_section_data to the layout. This is used for
159 // special sections like the GOT section.
161 add_output_section_data(const char* name, elfcpp::Elf_Word type,
162 elfcpp::Elf_Xword flags,
163 Output_section_data*);
165 // Create dynamic sections if necessary.
167 create_initial_dynamic_sections(Symbol_table*);
169 // Define __start and __stop symbols for output sections.
171 define_section_symbols(Symbol_table*);
173 // Create sections for linker scripts.
175 create_script_sections()
176 { this->script_options_->create_script_sections(this); }
178 // Define symbols from any linker script.
180 define_script_symbols(Symbol_table* symtab)
181 { this->script_options_->add_symbols_to_table(symtab); }
183 // Define symbols for group signatures.
185 define_group_signatures(Symbol_table*);
187 // Return the Stringpool used for symbol names.
190 { return &this->sympool_; }
192 // Return the Stringpool used for dynamic symbol names and dynamic
196 { return &this->dynpool_; }
198 // Return the symtab_xindex section used to hold large section
199 // indexes for the normal symbol table.
200 Output_symtab_xindex*
201 symtab_xindex() const
202 { return this->symtab_xindex_; }
204 // Return the dynsym_xindex section used to hold large section
205 // indexes for the dynamic symbol table.
206 Output_symtab_xindex*
207 dynsym_xindex() const
208 { return this->dynsym_xindex_; }
210 // Return whether a section is a .gnu.linkonce section, given the
213 is_linkonce(const char* name)
214 { return strncmp(name, ".gnu.linkonce", sizeof(".gnu.linkonce") - 1) == 0; }
216 // Return true if a section is a debugging section.
218 is_debug_info_section(const char* name)
220 // Debugging sections can only be recognized by name.
221 return (strncmp(name, ".debug", sizeof(".debug") - 1) == 0
222 || strncmp(name, ".gnu.linkonce.wi.",
223 sizeof(".gnu.linkonce.wi.") - 1) == 0
224 || strncmp(name, ".line", sizeof(".line") - 1) == 0
225 || strncmp(name, ".stab", sizeof(".stab") - 1) == 0);
228 // Record the signature of a comdat section, and return whether to
229 // include it in the link. The GROUP parameter is true for a
230 // section group signature, false for a signature derived from a
231 // .gnu.linkonce section.
233 add_comdat(Relobj*, unsigned int, const std::string&, bool group);
235 // Find the given comdat signature, and return the object and section
236 // index of the kept group.
238 find_kept_object(const std::string&, unsigned int*) const;
240 // Finalize the layout after all the input sections have been added.
242 finalize(const Input_objects*, Symbol_table*, Target*, const Task*);
244 // Return whether any sections require postprocessing.
246 any_postprocessing_sections() const
247 { return this->any_postprocessing_sections_; }
249 // Return the size of the output file.
251 output_file_size() const
252 { return this->output_file_size_; }
254 // Return the TLS segment. This will return NULL if there isn't
258 { return this->tls_segment_; }
260 // Return the normal symbol table.
262 symtab_section() const
264 gold_assert(this->symtab_section_ != NULL);
265 return this->symtab_section_;
268 // Return the dynamic symbol table.
270 dynsym_section() const
272 gold_assert(this->dynsym_section_ != NULL);
273 return this->dynsym_section_;
276 // Return the dynamic tags.
279 { return this->dynamic_data_; }
281 // Write out the output sections.
283 write_output_sections(Output_file* of) const;
285 // Write out data not associated with an input file or the symbol
288 write_data(const Symbol_table*, Output_file*) const;
290 // Write out output sections which can not be written until all the
291 // input sections are complete.
293 write_sections_after_input_sections(Output_file* of);
295 // Return an output section named NAME, or NULL if there is none.
297 find_output_section(const char* name) const;
299 // Return an output segment of type TYPE, with segment flags SET set
300 // and segment flags CLEAR clear. Return NULL if there is none.
302 find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
303 elfcpp::Elf_Word clear) const;
305 // Return the number of segments we expect to produce.
307 expected_segment_count() const;
309 // Set a flag to indicate that an object file uses the static TLS model.
312 { this->has_static_tls_ = true; }
314 // Return true if any object file uses the static TLS model.
316 has_static_tls() const
317 { return this->has_static_tls_; }
319 // Return the options which may be set by a linker script.
322 { return this->script_options_; }
324 const Script_options*
325 script_options() const
326 { return this->script_options_; }
328 // Compute and write out the build ID if needed.
330 write_build_id(Output_file*) const;
332 // Rewrite output file in binary format.
334 write_binary(Output_file* in) const;
336 // Dump statistical information to stderr.
340 // A list of segments.
342 typedef std::vector<Output_segment*> Segment_list;
344 // A list of sections.
346 typedef std::vector<Output_section*> Section_list;
348 // The list of information to write out which is not attached to
349 // either a section or a segment.
350 typedef std::vector<Output_data*> Data_list;
352 // Store the allocated sections into the section list. This is used
353 // by the linker script code.
355 get_allocated_sections(Section_list*) const;
357 // Make a section for a linker script to hold data.
359 make_output_section_for_script(const char* name);
361 // Make a segment. This is used by the linker script code.
363 make_output_segment(elfcpp::Elf_Word type, elfcpp::Elf_Word flags);
365 // Return the number of segments.
367 segment_count() const
368 { return this->segment_list_.size(); }
370 // Map from section flags to segment flags.
371 static elfcpp::Elf_Word
372 section_flags_to_segment(elfcpp::Elf_Xword flags);
374 // Attach sections to segments.
376 attach_sections_to_segments();
379 Layout(const Layout&);
380 Layout& operator=(const Layout&);
382 // Mapping from .gnu.linkonce section names to output section names.
383 struct Linkonce_mapping
390 static const Linkonce_mapping linkonce_mapping[];
391 static const int linkonce_mapping_count;
393 // During a relocatable link, a list of group sections and
395 struct Group_signature
397 // The group section.
398 Output_section* section;
400 const char* signature;
403 : section(NULL), signature(NULL)
406 Group_signature(Output_section* sectiona, const char* signaturea)
407 : section(sectiona), signature(signaturea)
410 typedef std::vector<Group_signature> Group_signatures;
412 // Create a .note section, filling in the header.
414 create_note(const char* name, int note_type, size_t descsz,
415 bool allocate, size_t* trailing_padding);
417 // Create a .note section for gold.
421 // Record whether the stack must be executable.
423 create_executable_stack_info(const Target*);
425 // Create a build ID note if needed.
429 // Find the first read-only PT_LOAD segment, creating one if
432 find_first_load_seg();
434 // Count the local symbols in the regular symbol table and the dynamic
435 // symbol table, and build the respective string pools.
437 count_local_symbols(const Task*, const Input_objects*);
439 // Create the output sections for the symbol table.
441 create_symtab_sections(const Input_objects*, Symbol_table*,
442 unsigned int, off_t*);
444 // Create the .shstrtab section.
448 // Create the section header table.
450 create_shdrs(const Output_section* shstrtab_section, off_t*);
452 // Create the dynamic symbol table.
454 create_dynamic_symtab(const Input_objects*, Symbol_table*,
455 Output_section** pdynstr,
456 unsigned int* plocal_dynamic_count,
457 std::vector<Symbol*>* pdynamic_symbols,
460 // Assign offsets to each local portion of the dynamic symbol table.
462 assign_local_dynsym_offsets(const Input_objects*);
464 // Finish the .dynamic section and PT_DYNAMIC segment.
466 finish_dynamic_section(const Input_objects*, const Symbol_table*);
468 // Create the .interp section and PT_INTERP segment.
470 create_interp(const Target* target);
472 // Create the version sections.
474 create_version_sections(const Versions*,
476 unsigned int local_symcount,
477 const std::vector<Symbol*>& dynamic_symbols,
478 const Output_section* dynstr);
480 template<int size, bool big_endian>
482 sized_create_version_sections(const Versions* versions,
484 unsigned int local_symcount,
485 const std::vector<Symbol*>& dynamic_symbols,
486 const Output_section* dynstr);
488 // Return whether to include this section in the link.
489 template<int size, bool big_endian>
491 include_section(Sized_relobj<size, big_endian>* object, const char* name,
492 const elfcpp::Shdr<size, big_endian>&);
494 // Return the output section name to use given an input section
495 // name. Set *PLEN to the length of the name. *PLEN must be
496 // initialized to the length of NAME.
498 output_section_name(const char* name, size_t* plen);
500 // Return the output section name to use for a linkonce section
501 // name. PLEN is as for output_section_name.
503 linkonce_output_name(const char* name, size_t* plen);
505 // Return the number of allocated output sections.
507 allocated_output_section_count() const;
509 // Return the output section for NAME, TYPE and FLAGS.
511 get_output_section(const char* name, Stringpool::Key name_key,
512 elfcpp::Elf_Word type, elfcpp::Elf_Xword flags);
514 // Choose the output section for NAME in RELOBJ.
516 choose_output_section(const Relobj* relobj, const char* name,
517 elfcpp::Elf_Word type, elfcpp::Elf_Xword flags,
518 bool is_input_section);
520 // Create a new Output_section.
522 make_output_section(const char* name, elfcpp::Elf_Word type,
523 elfcpp::Elf_Xword flags);
525 // Attach a section to a segment.
527 attach_section_to_segment(Output_section*);
529 // Attach an allocated section to a segment.
531 attach_allocated_section_to_segment(Output_section*);
533 // Set the final file offsets of all the segments.
535 set_segment_offsets(const Target*, Output_segment*, unsigned int* pshndx);
537 // Set the file offsets of the sections when doing a relocatable
540 set_relocatable_section_offsets(Output_data*, unsigned int* pshndx);
542 // Set the final file offsets of all the sections not associated
543 // with a segment. We set section offsets in three passes: the
544 // first handles all allocated sections, the second sections that
545 // require postprocessing, and the last the late-bound STRTAB
546 // sections (probably only shstrtab, which is the one we care about
547 // because it holds section names).
548 enum Section_offset_pass
550 BEFORE_INPUT_SECTIONS_PASS,
551 POSTPROCESSING_SECTIONS_PASS,
552 STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS
555 set_section_offsets(off_t, Section_offset_pass pass);
557 // Set the final section indexes of all the sections not associated
558 // with a segment. Returns the next unused index.
560 set_section_indexes(unsigned int pshndx);
562 // Set the section addresses when using a script.
564 set_section_addresses_from_script(Symbol_table*);
566 // Return whether SEG1 comes before SEG2 in the output file.
568 segment_precedes(const Output_segment* seg1, const Output_segment* seg2);
570 // A mapping used for group signatures.
574 : object_(NULL), shndx_(0), group_(false)
576 Kept_section(Relobj* object, unsigned int shndx, bool group)
577 : object_(object), shndx_(shndx), group_(group)
583 typedef Unordered_map<std::string, Kept_section> Signatures;
585 // Mapping from input section name/type/flags to output section. We
586 // use canonicalized strings here.
588 typedef std::pair<Stringpool::Key,
589 std::pair<elfcpp::Elf_Word, elfcpp::Elf_Xword> > Key;
594 operator()(const Key& k) const;
597 typedef Unordered_map<Key, Output_section*, Hash_key> Section_name_map;
599 // A comparison class for segments.
601 struct Compare_segments
604 operator()(const Output_segment* seg1, const Output_segment* seg2)
605 { return Layout::segment_precedes(seg1, seg2); }
608 // A reference to the options on the command line.
609 const General_options& options_;
610 // Information set by scripts or by command line options.
611 Script_options* script_options_;
612 // The output section names.
613 Stringpool namepool_;
614 // The output symbol names.
616 // The dynamic strings, if needed.
618 // The list of group sections and linkonce sections which we have seen.
619 Signatures signatures_;
620 // The mapping from input section name/type/flags to output sections.
621 Section_name_map section_name_map_;
622 // The list of output segments.
623 Segment_list segment_list_;
624 // The list of output sections.
625 Section_list section_list_;
626 // The list of output sections which are not attached to any output
628 Section_list unattached_section_list_;
629 // Whether we have attached the sections to the segments.
630 bool sections_are_attached_;
631 // The list of unattached Output_data objects which require special
632 // handling because they are not Output_sections.
633 Data_list special_output_list_;
634 // The section headers.
635 Output_section_headers* section_headers_;
636 // A pointer to the PT_TLS segment if there is one.
637 Output_segment* tls_segment_;
638 // The SHT_SYMTAB output section.
639 Output_section* symtab_section_;
640 // The SHT_SYMTAB_SHNDX for the regular symbol table if there is one.
641 Output_symtab_xindex* symtab_xindex_;
642 // The SHT_DYNSYM output section if there is one.
643 Output_section* dynsym_section_;
644 // The SHT_SYMTAB_SHNDX for the dynamic symbol table if there is one.
645 Output_symtab_xindex* dynsym_xindex_;
646 // The SHT_DYNAMIC output section if there is one.
647 Output_section* dynamic_section_;
648 // The dynamic data which goes into dynamic_section_.
649 Output_data_dynamic* dynamic_data_;
650 // The exception frame output section if there is one.
651 Output_section* eh_frame_section_;
652 // The exception frame data for eh_frame_section_.
653 Eh_frame* eh_frame_data_;
654 // Whether we have added eh_frame_data_ to the .eh_frame section.
655 bool added_eh_frame_data_;
656 // The exception frame header output section if there is one.
657 Output_section* eh_frame_hdr_section_;
658 // The space for the build ID checksum if there is one.
659 Output_section_data* build_id_note_;
660 // A list of group sections and their signatures.
661 Group_signatures group_signatures_;
662 // The size of the output file.
663 off_t output_file_size_;
664 // Whether we have seen an object file marked to require an
666 bool input_requires_executable_stack_;
667 // Whether we have seen at least one object file with an executable
669 bool input_with_gnu_stack_note_;
670 // Whether we have seen at least one object file without an
671 // executable stack marker.
672 bool input_without_gnu_stack_note_;
673 // Whether we have seen an object file that uses the static TLS model.
674 bool has_static_tls_;
675 // Whether any sections require postprocessing.
676 bool any_postprocessing_sections_;
679 // This task handles writing out data in output sections which is not
680 // part of an input section, or which requires special handling. When
681 // this is done, it unblocks both output_sections_blocker and
684 class Write_sections_task : public Task
687 Write_sections_task(const Layout* layout, Output_file* of,
688 Task_token* output_sections_blocker,
689 Task_token* final_blocker)
690 : layout_(layout), of_(of),
691 output_sections_blocker_(output_sections_blocker),
692 final_blocker_(final_blocker)
695 // The standard Task methods.
708 { return "Write_sections_task"; }
711 class Write_sections_locker;
713 const Layout* layout_;
715 Task_token* output_sections_blocker_;
716 Task_token* final_blocker_;
719 // This task handles writing out data which is not part of a section
722 class Write_data_task : public Task
725 Write_data_task(const Layout* layout, const Symbol_table* symtab,
726 Output_file* of, Task_token* final_blocker)
727 : layout_(layout), symtab_(symtab), of_(of), final_blocker_(final_blocker)
730 // The standard Task methods.
743 { return "Write_data_task"; }
746 const Layout* layout_;
747 const Symbol_table* symtab_;
749 Task_token* final_blocker_;
752 // This task handles writing out the global symbols.
754 class Write_symbols_task : public Task
757 Write_symbols_task(const Layout* layout, const Symbol_table* symtab,
758 const Input_objects* input_objects,
759 const Stringpool* sympool, const Stringpool* dynpool,
760 Output_file* of, Task_token* final_blocker)
761 : layout_(layout), symtab_(symtab), input_objects_(input_objects),
762 sympool_(sympool), dynpool_(dynpool), of_(of),
763 final_blocker_(final_blocker)
766 // The standard Task methods.
779 { return "Write_symbols_task"; }
782 const Layout* layout_;
783 const Symbol_table* symtab_;
784 const Input_objects* input_objects_;
785 const Stringpool* sympool_;
786 const Stringpool* dynpool_;
788 Task_token* final_blocker_;
791 // This task handles writing out data in output sections which can't
792 // be written out until all the input sections have been handled.
793 // This is for sections whose contents is based on the contents of
794 // other output sections.
796 class Write_after_input_sections_task : public Task
799 Write_after_input_sections_task(Layout* layout, Output_file* of,
800 Task_token* input_sections_blocker,
801 Task_token* final_blocker)
802 : layout_(layout), of_(of),
803 input_sections_blocker_(input_sections_blocker),
804 final_blocker_(final_blocker)
807 // The standard Task methods.
820 { return "Write_after_input_sections_task"; }
825 Task_token* input_sections_blocker_;
826 Task_token* final_blocker_;
829 // This task function handles closing the file.
831 class Close_task_runner : public Task_function_runner
834 Close_task_runner(const General_options* options, const Layout* layout,
836 : options_(options), layout_(layout), of_(of)
839 // Run the operation.
841 run(Workqueue*, const Task*);
844 const General_options* options_;
845 const Layout* layout_;
849 // A small helper function to align an address.
852 align_address(uint64_t address, uint64_t addralign)
855 address = (address + addralign - 1) &~ (addralign - 1);
859 } // End namespace gold.
861 #endif // !defined(GOLD_LAYOUT_H)