1 // layout.h -- lay out output file sections for gold -*- C++ -*-
3 // Copyright 2006, 2007 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.
31 #include "workqueue.h"
34 #include "stringpool.h"
39 class General_options;
42 class Output_section_data;
44 class Output_section_headers;
47 class Output_data_dynamic;
51 // This task function handles mapping the input sections to output
52 // sections and laying them out in memory.
54 class Layout_task_runner : public Task_function_runner
57 // OPTIONS is the command line options, INPUT_OBJECTS is the list of
58 // input objects, SYMTAB is the symbol table, LAYOUT is the layout
60 Layout_task_runner(const General_options& options,
61 const Input_objects* input_objects,
64 : options_(options), input_objects_(input_objects), symtab_(symtab),
73 Layout_task_runner(const Layout_task_runner&);
74 Layout_task_runner& operator=(const Layout_task_runner&);
76 const General_options& options_;
77 const Input_objects* input_objects_;
78 Symbol_table* symtab_;
82 // This class handles the details of laying out input sections.
87 Layout(const General_options& options);
89 // Given an input section SHNDX, named NAME, with data in SHDR, from
90 // the object file OBJECT, return the output section where this
91 // input section should go. RELOC_SHNDX is the index of a
92 // relocation section which applies to this section, or 0 if none,
93 // or -1U if more than one. RELOC_TYPE is the type of the
94 // relocation section if there is one. Set *OFFSET to the offset
95 // within the output section.
96 template<int size, bool big_endian>
98 layout(Sized_relobj<size, big_endian> *object, unsigned int shndx,
99 const char* name, const elfcpp::Shdr<size, big_endian>& shdr,
100 unsigned int reloc_shndx, unsigned int reloc_type, off_t* offset);
102 // Like layout, only for exception frame sections. OBJECT is an
103 // object file. SYMBOLS is the contents of the symbol table
104 // section, with size SYMBOLS_SIZE. SYMBOL_NAMES is the contents of
105 // the symbol name section, with size SYMBOL_NAMES_SIZE. SHNDX is a
106 // .eh_frame section in OBJECT. SHDR is the section header.
107 // RELOC_SHNDX is the index of a relocation section which applies to
108 // this section, or 0 if none, or -1U if more than one. RELOC_TYPE
109 // is the type of the relocation section if there is one. This
110 // returns the output section, and sets *OFFSET to the offset.
111 template<int size, bool big_endian>
113 layout_eh_frame(Sized_relobj<size, big_endian>* object,
114 const unsigned char* symbols,
116 const unsigned char* symbol_names,
117 off_t symbol_names_size,
119 const elfcpp::Shdr<size, big_endian>& shdr,
120 unsigned int reloc_shndx, unsigned int reloc_type,
123 // Handle a GNU stack note. This is called once per input object
124 // file. SEEN_GNU_STACK is true if the object file has a
125 // .note.GNU-stack section. GNU_STACK_FLAGS is the section flags
126 // from that section if there was one.
128 layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags);
130 // Add an Output_section_data to the layout. This is used for
131 // special sections like the GOT section.
133 add_output_section_data(const char* name, elfcpp::Elf_Word type,
134 elfcpp::Elf_Xword flags,
135 Output_section_data*);
137 // Create dynamic sections if necessary.
139 create_initial_dynamic_sections(const Input_objects*, Symbol_table*);
141 // Define __start and __stop symbols for output sections.
143 define_section_symbols(Symbol_table*, const Target*);
145 // Return the Stringpool used for symbol names.
148 { return &this->sympool_; }
150 // Return the Stringpool used for dynamic symbol names and dynamic
154 { return &this->dynpool_; }
156 // Return whether a section is a .gnu.linkonce section, given the
159 is_linkonce(const char* name)
160 { return strncmp(name, ".gnu.linkonce", sizeof(".gnu.linkonce") - 1) == 0; }
162 // Record the signature of a comdat section, and return whether to
163 // include it in the link. The GROUP parameter is true for a
164 // section group signature, false for a signature derived from a
165 // .gnu.linkonce section.
167 add_comdat(const char*, bool group);
169 // Finalize the layout after all the input sections have been added.
171 finalize(const Input_objects*, Symbol_table*);
173 // Return the size of the output file.
175 output_file_size() const
176 { return this->output_file_size_; }
178 // Return the TLS segment. This will return NULL if there isn't
182 { return this->tls_segment_; }
184 // Return the normal symbol table.
186 symtab_section() const
188 gold_assert(this->symtab_section_ != NULL);
189 return this->symtab_section_;
192 // Return the dynamic symbol table.
194 dynsym_section() const
196 gold_assert(this->dynsym_section_ != NULL);
197 return this->dynsym_section_;
200 // Return the dynamic tags.
203 { return this->dynamic_data_; }
205 // Write out the output sections.
207 write_output_sections(Output_file* of) const;
209 // Write out data not associated with an input file or the symbol
212 write_data(const Symbol_table*, Output_file*) const;
214 // Write out output sections which can not be written until all the
215 // input sections are complete.
217 write_sections_after_input_sections(Output_file* of);
219 // Return an output section named NAME, or NULL if there is none.
221 find_output_section(const char* name) const;
223 // Return an output segment of type TYPE, with segment flags SET set
224 // and segment flags CLEAR clear. Return NULL if there is none.
226 find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
227 elfcpp::Elf_Word clear) const;
229 // Set a flag to indicate that an object file uses the static TLS model.
232 { this->has_static_tls_ = true; }
234 // Return true if any object file uses the static TLS model.
236 has_static_tls() const
237 { return this->has_static_tls_; }
239 // Dump statistical information to stderr.
243 // The list of segments.
245 typedef std::vector<Output_segment*> Segment_list;
247 // The list of sections not attached to a segment.
249 typedef std::vector<Output_section*> Section_list;
251 // The list of information to write out which is not attached to
252 // either a section or a segment.
253 typedef std::vector<Output_data*> Data_list;
256 Layout(const Layout&);
257 Layout& operator=(const Layout&);
259 // Mapping from .gnu.linkonce section names to output section names.
260 struct Linkonce_mapping
267 static const Linkonce_mapping linkonce_mapping[];
268 static const int linkonce_mapping_count;
270 // Create a .note section for gold.
274 // Record whether the stack must be executable.
276 create_executable_stack_info(const Target*);
278 // Find the first read-only PT_LOAD segment, creating one if
281 find_first_load_seg();
283 // Count the local symbols in the regular symbol table and the dynamic
284 // symbol table, and build the respective string pools.
286 count_local_symbols(const Input_objects*);
288 // Create the output sections for the symbol table.
290 create_symtab_sections(const Input_objects*, Symbol_table*, off_t*);
292 // Create the .shstrtab section.
296 // Create the section header table.
298 create_shdrs(off_t*);
300 // Create the dynamic symbol table.
302 create_dynamic_symtab(const Input_objects*, const Target*,
303 Symbol_table*, Output_section** pdynstr,
304 unsigned int* plocal_dynamic_count,
305 std::vector<Symbol*>* pdynamic_symbols,
308 // Assign offsets to each local portion of the dynamic symbol table.
310 assign_local_dynsym_offsets(const Input_objects*);
312 // Finish the .dynamic section and PT_DYNAMIC segment.
314 finish_dynamic_section(const Input_objects*, const Symbol_table*);
316 // Create the .interp section and PT_INTERP segment.
318 create_interp(const Target* target);
320 // Create the version sections.
322 create_version_sections(const Versions*,
324 unsigned int local_symcount,
325 const std::vector<Symbol*>& dynamic_symbols,
326 const Output_section* dynstr);
328 template<int size, bool big_endian>
330 sized_create_version_sections(const Versions* versions,
332 unsigned int local_symcount,
333 const std::vector<Symbol*>& dynamic_symbols,
334 const Output_section* dynstr
337 // Return whether to include this section in the link.
338 template<int size, bool big_endian>
340 include_section(Sized_relobj<size, big_endian>* object, const char* name,
341 const elfcpp::Shdr<size, big_endian>&);
343 // Return the output section name to use given an input section
344 // name. Set *PLEN to the length of the name. *PLEN must be
345 // initialized to the length of NAME.
347 output_section_name(const char* name, size_t* plen);
349 // Return the output section name to use for a linkonce section
350 // name. PLEN is as for output_section_name.
352 linkonce_output_name(const char* name, size_t* plen);
354 // Return the output section for NAME, TYPE and FLAGS.
356 get_output_section(const char* name, Stringpool::Key name_key,
357 elfcpp::Elf_Word type, elfcpp::Elf_Xword flags);
359 // Create a new Output_section.
361 make_output_section(const char* name, elfcpp::Elf_Word type,
362 elfcpp::Elf_Xword flags);
364 // Set the final file offsets of all the segments.
366 set_segment_offsets(const Target*, Output_segment*, unsigned int* pshndx);
368 // Set the final file offsets of all the sections not associated
369 // with a segment. We set section offsets in three passes: the
370 // first handles all allocated sections, the second sections that
371 // can be handled after input-sections are processed, and the last
372 // the late-bound STRTAB sections (probably only shstrtab, which is
373 // the one we care about because it holds section names).
374 enum Section_offset_pass
376 BEFORE_INPUT_SECTIONS_PASS,
377 AFTER_INPUT_SECTIONS_PASS,
378 STRTAB_AFTER_INPUT_SECTIONS_PASS
381 set_section_offsets(off_t, Section_offset_pass pass);
383 // Set the final section indexes of all the sections not associated
384 // with a segment. Returns the next unused index.
386 set_section_indexes(unsigned int pshndx);
388 // Return whether SEG1 comes before SEG2 in the output file.
390 segment_precedes(const Output_segment* seg1, const Output_segment* seg2);
392 // Map from section flags to segment flags.
393 static elfcpp::Elf_Word
394 section_flags_to_segment(elfcpp::Elf_Xword flags);
396 // A mapping used for group signatures.
397 typedef Unordered_map<std::string, bool> Signatures;
399 // Mapping from input section name/type/flags to output section. We
400 // use canonicalized strings here.
402 typedef std::pair<Stringpool::Key,
403 std::pair<elfcpp::Elf_Word, elfcpp::Elf_Xword> > Key;
408 operator()(const Key& k) const;
411 typedef Unordered_map<Key, Output_section*, Hash_key> Section_name_map;
413 // A comparison class for segments.
415 struct Compare_segments
418 operator()(const Output_segment* seg1, const Output_segment* seg2)
419 { return Layout::segment_precedes(seg1, seg2); }
422 // A reference to the options on the command line.
423 const General_options& options_;
424 // The output section names.
425 Stringpool namepool_;
426 // The output symbol names.
428 // The dynamic strings, if needed.
430 // The list of group sections and linkonce sections which we have seen.
431 Signatures signatures_;
432 // The mapping from input section name/type/flags to output sections.
433 Section_name_map section_name_map_;
434 // The list of output segments.
435 Segment_list segment_list_;
436 // The list of output sections.
437 Section_list section_list_;
438 // The list of output sections which are not attached to any output
440 Section_list unattached_section_list_;
441 // The list of unattached Output_data objects which require special
442 // handling because they are not Output_sections.
443 Data_list special_output_list_;
444 // The section headers.
445 Output_section_headers* section_headers_;
446 // A pointer to the PT_TLS segment if there is one.
447 Output_segment* tls_segment_;
448 // The SHT_SYMTAB output section.
449 Output_section* symtab_section_;
450 // The SHT_DYNSYM output section if there is one.
451 Output_section* dynsym_section_;
452 // The SHT_DYNAMIC output section if there is one.
453 Output_section* dynamic_section_;
454 // The dynamic data which goes into dynamic_section_.
455 Output_data_dynamic* dynamic_data_;
456 // The exception frame output section if there is one.
457 Output_section* eh_frame_section_;
458 // The exception frame data for eh_frame_section_.
459 Eh_frame* eh_frame_data_;
460 // The exception frame header output section if there is one.
461 Output_section* eh_frame_hdr_section_;
462 // The size of the output file.
463 off_t output_file_size_;
464 // Whether we have seen an object file marked to require an
466 bool input_requires_executable_stack_;
467 // Whether we have seen at least one object file with an executable
469 bool input_with_gnu_stack_note_;
470 // Whether we have seen at least one object file without an
471 // executable stack marker.
472 bool input_without_gnu_stack_note_;
473 // Whether we have seen an object file that uses the static TLS model.
474 bool has_static_tls_;
477 // This task handles writing out data in output sections which is not
478 // part of an input section, or which requires special handling. When
479 // this is done, it unblocks both output_sections_blocker and
482 class Write_sections_task : public Task
485 Write_sections_task(const Layout* layout, Output_file* of,
486 Task_token* output_sections_blocker,
487 Task_token* final_blocker)
488 : layout_(layout), of_(of),
489 output_sections_blocker_(output_sections_blocker),
490 final_blocker_(final_blocker)
493 // The standard Task methods.
496 is_runnable(Workqueue*);
506 { return "Write_sections_task"; }
509 class Write_sections_locker;
511 const Layout* layout_;
513 Task_token* output_sections_blocker_;
514 Task_token* final_blocker_;
517 // This task handles writing out data which is not part of a section
520 class Write_data_task : public Task
523 Write_data_task(const Layout* layout, const Symbol_table* symtab,
524 Output_file* of, Task_token* final_blocker)
525 : layout_(layout), symtab_(symtab), of_(of), final_blocker_(final_blocker)
528 // The standard Task methods.
531 is_runnable(Workqueue*);
541 { return "Write_data_task"; }
544 const Layout* layout_;
545 const Symbol_table* symtab_;
547 Task_token* final_blocker_;
550 // This task handles writing out the global symbols.
552 class Write_symbols_task : public Task
555 Write_symbols_task(const Symbol_table* symtab,
556 const Input_objects* input_objects,
557 const Stringpool* sympool, const Stringpool* dynpool,
558 Output_file* of, Task_token* final_blocker)
559 : symtab_(symtab), input_objects_(input_objects), sympool_(sympool),
560 dynpool_(dynpool), of_(of), final_blocker_(final_blocker)
563 // The standard Task methods.
566 is_runnable(Workqueue*);
576 { return "Write_symbols_task"; }
579 const Symbol_table* symtab_;
580 const Input_objects* input_objects_;
581 const Stringpool* sympool_;
582 const Stringpool* dynpool_;
584 Task_token* final_blocker_;
587 // This task handles writing out data in output sections which can't
588 // be written out until all the input sections have been handled.
589 // This is for sections whose contents is based on the contents of
590 // other output sections.
592 class Write_after_input_sections_task : public Task
595 Write_after_input_sections_task(Layout* layout, Output_file* of,
596 Task_token* input_sections_blocker,
597 Task_token* final_blocker)
598 : layout_(layout), of_(of),
599 input_sections_blocker_(input_sections_blocker),
600 final_blocker_(final_blocker)
603 // The standard Task methods.
606 is_runnable(Workqueue*);
616 { return "Write_after_input_sections_task"; }
619 class Write_sections_locker;
623 Task_token* input_sections_blocker_;
624 Task_token* final_blocker_;
627 // This task function handles closing the file.
629 class Close_task_runner : public Task_function_runner
632 Close_task_runner(Output_file* of)
636 // Run the operation.
644 // A small helper function to align an address.
647 align_address(uint64_t address, uint64_t addralign)
650 address = (address + addralign - 1) &~ (addralign - 1);
654 } // End namespace gold.
656 #endif // !defined(GOLD_LAYOUT_H)