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.
32 #include "workqueue.h"
35 #include "stringpool.h"
40 class General_options;
43 class Output_section_data;
45 class Output_section_headers;
48 class Output_data_dynamic;
49 class Output_symtab_xindex;
53 // This task function handles mapping the input sections to output
54 // sections and laying them out in memory.
56 class Layout_task_runner : public Task_function_runner
59 // OPTIONS is the command line options, INPUT_OBJECTS is the list of
60 // input objects, SYMTAB is the symbol table, LAYOUT is the layout
62 Layout_task_runner(const General_options& options,
63 const Input_objects* input_objects,
67 : options_(options), input_objects_(input_objects), symtab_(symtab),
68 target_(target), layout_(layout)
73 run(Workqueue*, const Task*);
76 Layout_task_runner(const Layout_task_runner&);
77 Layout_task_runner& operator=(const Layout_task_runner&);
79 const General_options& options_;
80 const Input_objects* input_objects_;
81 Symbol_table* symtab_;
86 // This class handles the details of laying out input sections.
91 Layout(const General_options& options, Script_options*);
93 // Given an input section SHNDX, named NAME, with data in SHDR, from
94 // the object file OBJECT, return the output section where this
95 // input section should go. RELOC_SHNDX is the index of a
96 // relocation section which applies to this section, or 0 if none,
97 // or -1U if more than one. RELOC_TYPE is the type of the
98 // relocation section if there is one. Set *OFFSET to the offset
99 // within the output section.
100 template<int size, bool big_endian>
102 layout(Sized_relobj<size, big_endian> *object, unsigned int shndx,
103 const char* name, const elfcpp::Shdr<size, big_endian>& shdr,
104 unsigned int reloc_shndx, unsigned int reloc_type, off_t* offset);
106 // Layout an input reloc section when doing a relocatable link. The
107 // section is RELOC_SHNDX in OBJECT, with data in SHDR.
108 // DATA_SECTION is the reloc section to which it refers. RR is the
109 // relocatable information.
110 template<int size, bool big_endian>
112 layout_reloc(Sized_relobj<size, big_endian>* object,
113 unsigned int reloc_shndx,
114 const elfcpp::Shdr<size, big_endian>& shdr,
115 Output_section* data_section,
116 Relocatable_relocs* rr);
118 // Layout a group section when doing a relocatable link.
119 template<int size, bool big_endian>
121 layout_group(Symbol_table* symtab,
122 Sized_relobj<size, big_endian>* object,
123 unsigned int group_shndx,
124 const char* group_section_name,
125 const char* signature,
126 const elfcpp::Shdr<size, big_endian>& shdr,
127 const elfcpp::Elf_Word* contents);
129 // Like layout, only for exception frame sections. OBJECT is an
130 // object file. SYMBOLS is the contents of the symbol table
131 // section, with size SYMBOLS_SIZE. SYMBOL_NAMES is the contents of
132 // the symbol name section, with size SYMBOL_NAMES_SIZE. SHNDX is a
133 // .eh_frame section in OBJECT. SHDR is the section header.
134 // RELOC_SHNDX is the index of a relocation section which applies to
135 // this section, or 0 if none, or -1U if more than one. RELOC_TYPE
136 // is the type of the relocation section if there is one. This
137 // returns the output section, and sets *OFFSET to the offset.
138 template<int size, bool big_endian>
140 layout_eh_frame(Sized_relobj<size, big_endian>* object,
141 const unsigned char* symbols,
143 const unsigned char* symbol_names,
144 off_t symbol_names_size,
146 const elfcpp::Shdr<size, big_endian>& shdr,
147 unsigned int reloc_shndx, unsigned int reloc_type,
150 // Handle a GNU stack note. This is called once per input object
151 // file. SEEN_GNU_STACK is true if the object file has a
152 // .note.GNU-stack section. GNU_STACK_FLAGS is the section flags
153 // from that section if there was one.
155 layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags);
157 // Add an Output_section_data to the layout. This is used for
158 // special sections like the GOT section.
160 add_output_section_data(const char* name, elfcpp::Elf_Word type,
161 elfcpp::Elf_Xword flags,
162 Output_section_data*);
164 // Create dynamic sections if necessary.
166 create_initial_dynamic_sections(Symbol_table*);
168 // Define __start and __stop symbols for output sections.
170 define_section_symbols(Symbol_table*);
172 // Create sections for linker scripts.
174 create_script_sections()
175 { this->script_options_->create_script_sections(this); }
177 // Define symbols from any linker script.
179 define_script_symbols(Symbol_table* symtab)
180 { this->script_options_->add_symbols_to_table(symtab); }
182 // Define symbols for group signatures.
184 define_group_signatures(Symbol_table*);
186 // Return the Stringpool used for symbol names.
189 { return &this->sympool_; }
191 // Return the Stringpool used for dynamic symbol names and dynamic
195 { return &this->dynpool_; }
197 // Return the symtab_xindex section used to hold large section
198 // indexes for the normal symbol table.
199 Output_symtab_xindex*
200 symtab_xindex() const
201 { return this->symtab_xindex_; }
203 // Return the dynsym_xindex section used to hold large section
204 // indexes for the dynamic symbol table.
205 Output_symtab_xindex*
206 dynsym_xindex() const
207 { return this->dynsym_xindex_; }
209 // Return whether a section is a .gnu.linkonce section, given the
212 is_linkonce(const char* name)
213 { return strncmp(name, ".gnu.linkonce", sizeof(".gnu.linkonce") - 1) == 0; }
215 // Record the signature of a comdat section, and return whether to
216 // include it in the link. The GROUP parameter is true for a
217 // section group signature, false for a signature derived from a
218 // .gnu.linkonce section.
220 add_comdat(const char*, bool group);
222 // Finalize the layout after all the input sections have been added.
224 finalize(const Input_objects*, Symbol_table*, Target*, const Task*);
226 // Return whether any sections require postprocessing.
228 any_postprocessing_sections() const
229 { return this->any_postprocessing_sections_; }
231 // Return the size of the output file.
233 output_file_size() const
234 { return this->output_file_size_; }
236 // Return the TLS segment. This will return NULL if there isn't
240 { return this->tls_segment_; }
242 // Return the normal symbol table.
244 symtab_section() const
246 gold_assert(this->symtab_section_ != NULL);
247 return this->symtab_section_;
250 // Return the dynamic symbol table.
252 dynsym_section() const
254 gold_assert(this->dynsym_section_ != NULL);
255 return this->dynsym_section_;
258 // Return the dynamic tags.
261 { return this->dynamic_data_; }
263 // Write out the output sections.
265 write_output_sections(Output_file* of) const;
267 // Write out data not associated with an input file or the symbol
270 write_data(const Symbol_table*, Output_file*) const;
272 // Write out output sections which can not be written until all the
273 // input sections are complete.
275 write_sections_after_input_sections(Output_file* of);
277 // Return an output section named NAME, or NULL if there is none.
279 find_output_section(const char* name) const;
281 // Return an output segment of type TYPE, with segment flags SET set
282 // and segment flags CLEAR clear. Return NULL if there is none.
284 find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
285 elfcpp::Elf_Word clear) const;
287 // Return the number of segments we expect to produce.
289 expected_segment_count() const;
291 // Set a flag to indicate that an object file uses the static TLS model.
294 { this->has_static_tls_ = true; }
296 // Return true if any object file uses the static TLS model.
298 has_static_tls() const
299 { return this->has_static_tls_; }
301 // Return the options which may be set by a linker script.
304 { return this->script_options_; }
306 const Script_options*
307 script_options() const
308 { return this->script_options_; }
310 // Compute and write out the build ID if needed.
312 write_build_id(Output_file*) const;
314 // Rewrite output file in binary format.
316 write_binary(Output_file* in) const;
318 // Dump statistical information to stderr.
322 // A list of segments.
324 typedef std::vector<Output_segment*> Segment_list;
326 // A list of sections.
328 typedef std::vector<Output_section*> Section_list;
330 // The list of information to write out which is not attached to
331 // either a section or a segment.
332 typedef std::vector<Output_data*> Data_list;
334 // Store the allocated sections into the section list. This is used
335 // by the linker script code.
337 get_allocated_sections(Section_list*) const;
339 // Make a section for a linker script to hold data.
341 make_output_section_for_script(const char* name);
343 // Make a segment. This is used by the linker script code.
345 make_output_segment(elfcpp::Elf_Word type, elfcpp::Elf_Word flags);
347 // Return the number of segments.
349 segment_count() const
350 { return this->segment_list_.size(); }
352 // Map from section flags to segment flags.
353 static elfcpp::Elf_Word
354 section_flags_to_segment(elfcpp::Elf_Xword flags);
356 // Attach sections to segments.
358 attach_sections_to_segments();
361 Layout(const Layout&);
362 Layout& operator=(const Layout&);
364 // Mapping from .gnu.linkonce section names to output section names.
365 struct Linkonce_mapping
372 static const Linkonce_mapping linkonce_mapping[];
373 static const int linkonce_mapping_count;
375 // During a relocatable link, a list of group sections and
377 struct Group_signature
379 // The group section.
380 Output_section* section;
382 const char* signature;
385 : section(NULL), signature(NULL)
388 Group_signature(Output_section* sectiona, const char* signaturea)
389 : section(sectiona), signature(signaturea)
392 typedef std::vector<Group_signature> Group_signatures;
394 // Create a .note section, filling in the header.
396 create_note(const char* name, int note_type, size_t descsz,
397 bool allocate, size_t* trailing_padding);
399 // Create a .note section for gold.
403 // Record whether the stack must be executable.
405 create_executable_stack_info(const Target*);
407 // Create a build ID note if needed.
411 // Find the first read-only PT_LOAD segment, creating one if
414 find_first_load_seg();
416 // Count the local symbols in the regular symbol table and the dynamic
417 // symbol table, and build the respective string pools.
419 count_local_symbols(const Task*, const Input_objects*);
421 // Create the output sections for the symbol table.
423 create_symtab_sections(const Input_objects*, Symbol_table*,
424 unsigned int, off_t*);
426 // Create the .shstrtab section.
430 // Create the section header table.
432 create_shdrs(const Output_section* shstrtab_section, off_t*);
434 // Create the dynamic symbol table.
436 create_dynamic_symtab(const Input_objects*, Symbol_table*,
437 Output_section** pdynstr,
438 unsigned int* plocal_dynamic_count,
439 std::vector<Symbol*>* pdynamic_symbols,
442 // Assign offsets to each local portion of the dynamic symbol table.
444 assign_local_dynsym_offsets(const Input_objects*);
446 // Finish the .dynamic section and PT_DYNAMIC segment.
448 finish_dynamic_section(const Input_objects*, const Symbol_table*);
450 // Create the .interp section and PT_INTERP segment.
452 create_interp(const Target* target);
454 // Create the version sections.
456 create_version_sections(const Versions*,
458 unsigned int local_symcount,
459 const std::vector<Symbol*>& dynamic_symbols,
460 const Output_section* dynstr);
462 template<int size, bool big_endian>
464 sized_create_version_sections(const Versions* versions,
466 unsigned int local_symcount,
467 const std::vector<Symbol*>& dynamic_symbols,
468 const Output_section* dynstr);
470 // Return whether to include this section in the link.
471 template<int size, bool big_endian>
473 include_section(Sized_relobj<size, big_endian>* object, const char* name,
474 const elfcpp::Shdr<size, big_endian>&);
476 // Return the output section name to use given an input section
477 // name. Set *PLEN to the length of the name. *PLEN must be
478 // initialized to the length of NAME.
480 output_section_name(const char* name, size_t* plen);
482 // Return the output section name to use for a linkonce section
483 // name. PLEN is as for output_section_name.
485 linkonce_output_name(const char* name, size_t* plen);
487 // Return the number of allocated output sections.
489 allocated_output_section_count() const;
491 // Return the output section for NAME, TYPE and FLAGS.
493 get_output_section(const char* name, Stringpool::Key name_key,
494 elfcpp::Elf_Word type, elfcpp::Elf_Xword flags);
496 // Choose the output section for NAME in RELOBJ.
498 choose_output_section(const Relobj* relobj, const char* name,
499 elfcpp::Elf_Word type, elfcpp::Elf_Xword flags,
500 bool is_input_section);
502 // Create a new Output_section.
504 make_output_section(const char* name, elfcpp::Elf_Word type,
505 elfcpp::Elf_Xword flags);
507 // Attach a section to a segment.
509 attach_section_to_segment(Output_section*);
511 // Attach an allocated section to a segment.
513 attach_allocated_section_to_segment(Output_section*);
515 // Set the final file offsets of all the segments.
517 set_segment_offsets(const Target*, Output_segment*, unsigned int* pshndx);
519 // Set the file offsets of the sections when doing a relocatable
522 set_relocatable_section_offsets(Output_data*, unsigned int* pshndx);
524 // Set the final file offsets of all the sections not associated
525 // with a segment. We set section offsets in three passes: the
526 // first handles all allocated sections, the second sections that
527 // require postprocessing, and the last the late-bound STRTAB
528 // sections (probably only shstrtab, which is the one we care about
529 // because it holds section names).
530 enum Section_offset_pass
532 BEFORE_INPUT_SECTIONS_PASS,
533 POSTPROCESSING_SECTIONS_PASS,
534 STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS
537 set_section_offsets(off_t, Section_offset_pass pass);
539 // Set the final section indexes of all the sections not associated
540 // with a segment. Returns the next unused index.
542 set_section_indexes(unsigned int pshndx);
544 // Set the section addresses when using a script.
546 set_section_addresses_from_script(Symbol_table*);
548 // Return whether SEG1 comes before SEG2 in the output file.
550 segment_precedes(const Output_segment* seg1, const Output_segment* seg2);
552 // A mapping used for group signatures.
553 typedef Unordered_map<std::string, bool> Signatures;
555 // Mapping from input section name/type/flags to output section. We
556 // use canonicalized strings here.
558 typedef std::pair<Stringpool::Key,
559 std::pair<elfcpp::Elf_Word, elfcpp::Elf_Xword> > Key;
564 operator()(const Key& k) const;
567 typedef Unordered_map<Key, Output_section*, Hash_key> Section_name_map;
569 // A comparison class for segments.
571 struct Compare_segments
574 operator()(const Output_segment* seg1, const Output_segment* seg2)
575 { return Layout::segment_precedes(seg1, seg2); }
578 // A reference to the options on the command line.
579 const General_options& options_;
580 // Information set by scripts or by command line options.
581 Script_options* script_options_;
582 // The output section names.
583 Stringpool namepool_;
584 // The output symbol names.
586 // The dynamic strings, if needed.
588 // The list of group sections and linkonce sections which we have seen.
589 Signatures signatures_;
590 // The mapping from input section name/type/flags to output sections.
591 Section_name_map section_name_map_;
592 // The list of output segments.
593 Segment_list segment_list_;
594 // The list of output sections.
595 Section_list section_list_;
596 // The list of output sections which are not attached to any output
598 Section_list unattached_section_list_;
599 // Whether we have attached the sections to the segments.
600 bool sections_are_attached_;
601 // The list of unattached Output_data objects which require special
602 // handling because they are not Output_sections.
603 Data_list special_output_list_;
604 // The section headers.
605 Output_section_headers* section_headers_;
606 // A pointer to the PT_TLS segment if there is one.
607 Output_segment* tls_segment_;
608 // The SHT_SYMTAB output section.
609 Output_section* symtab_section_;
610 // The SHT_SYMTAB_SHNDX for the regular symbol table if there is one.
611 Output_symtab_xindex* symtab_xindex_;
612 // The SHT_DYNSYM output section if there is one.
613 Output_section* dynsym_section_;
614 // The SHT_SYMTAB_SHNDX for the dynamic symbol table if there is one.
615 Output_symtab_xindex* dynsym_xindex_;
616 // The SHT_DYNAMIC output section if there is one.
617 Output_section* dynamic_section_;
618 // The dynamic data which goes into dynamic_section_.
619 Output_data_dynamic* dynamic_data_;
620 // The exception frame output section if there is one.
621 Output_section* eh_frame_section_;
622 // The exception frame data for eh_frame_section_.
623 Eh_frame* eh_frame_data_;
624 // Whether we have added eh_frame_data_ to the .eh_frame section.
625 bool added_eh_frame_data_;
626 // The exception frame header output section if there is one.
627 Output_section* eh_frame_hdr_section_;
628 // The space for the build ID checksum if there is one.
629 Output_section_data* build_id_note_;
630 // A list of group sections and their signatures.
631 Group_signatures group_signatures_;
632 // The size of the output file.
633 off_t output_file_size_;
634 // Whether we have seen an object file marked to require an
636 bool input_requires_executable_stack_;
637 // Whether we have seen at least one object file with an executable
639 bool input_with_gnu_stack_note_;
640 // Whether we have seen at least one object file without an
641 // executable stack marker.
642 bool input_without_gnu_stack_note_;
643 // Whether we have seen an object file that uses the static TLS model.
644 bool has_static_tls_;
645 // Whether any sections require postprocessing.
646 bool any_postprocessing_sections_;
649 // This task handles writing out data in output sections which is not
650 // part of an input section, or which requires special handling. When
651 // this is done, it unblocks both output_sections_blocker and
654 class Write_sections_task : public Task
657 Write_sections_task(const Layout* layout, Output_file* of,
658 Task_token* output_sections_blocker,
659 Task_token* final_blocker)
660 : layout_(layout), of_(of),
661 output_sections_blocker_(output_sections_blocker),
662 final_blocker_(final_blocker)
665 // The standard Task methods.
678 { return "Write_sections_task"; }
681 class Write_sections_locker;
683 const Layout* layout_;
685 Task_token* output_sections_blocker_;
686 Task_token* final_blocker_;
689 // This task handles writing out data which is not part of a section
692 class Write_data_task : public Task
695 Write_data_task(const Layout* layout, const Symbol_table* symtab,
696 Output_file* of, Task_token* final_blocker)
697 : layout_(layout), symtab_(symtab), of_(of), final_blocker_(final_blocker)
700 // The standard Task methods.
713 { return "Write_data_task"; }
716 const Layout* layout_;
717 const Symbol_table* symtab_;
719 Task_token* final_blocker_;
722 // This task handles writing out the global symbols.
724 class Write_symbols_task : public Task
727 Write_symbols_task(const Layout* layout, const Symbol_table* symtab,
728 const Input_objects* input_objects,
729 const Stringpool* sympool, const Stringpool* dynpool,
730 Output_file* of, Task_token* final_blocker)
731 : layout_(layout), symtab_(symtab), input_objects_(input_objects),
732 sympool_(sympool), dynpool_(dynpool), of_(of),
733 final_blocker_(final_blocker)
736 // The standard Task methods.
749 { return "Write_symbols_task"; }
752 const Layout* layout_;
753 const Symbol_table* symtab_;
754 const Input_objects* input_objects_;
755 const Stringpool* sympool_;
756 const Stringpool* dynpool_;
758 Task_token* final_blocker_;
761 // This task handles writing out data in output sections which can't
762 // be written out until all the input sections have been handled.
763 // This is for sections whose contents is based on the contents of
764 // other output sections.
766 class Write_after_input_sections_task : public Task
769 Write_after_input_sections_task(Layout* layout, Output_file* of,
770 Task_token* input_sections_blocker,
771 Task_token* final_blocker)
772 : layout_(layout), of_(of),
773 input_sections_blocker_(input_sections_blocker),
774 final_blocker_(final_blocker)
777 // The standard Task methods.
790 { return "Write_after_input_sections_task"; }
795 Task_token* input_sections_blocker_;
796 Task_token* final_blocker_;
799 // This task function handles closing the file.
801 class Close_task_runner : public Task_function_runner
804 Close_task_runner(const General_options* options, const Layout* layout,
806 : options_(options), layout_(layout), of_(of)
809 // Run the operation.
811 run(Workqueue*, const Task*);
814 const General_options* options_;
815 const Layout* layout_;
819 // A small helper function to align an address.
822 align_address(uint64_t address, uint64_t addralign)
825 address = (address + addralign - 1) &~ (addralign - 1);
829 } // End namespace gold.
831 #endif // !defined(GOLD_LAYOUT_H)