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 // A pointer to the PT_GNU_RELRO segment if there is one.
640 Output_segment
* relro_segment_
;
641 // The SHT_SYMTAB output section.
642 Output_section
* symtab_section_
;
643 // The SHT_SYMTAB_SHNDX for the regular symbol table if there is one.
644 Output_symtab_xindex
* symtab_xindex_
;
645 // The SHT_DYNSYM output section if there is one.
646 Output_section
* dynsym_section_
;
647 // The SHT_SYMTAB_SHNDX for the dynamic symbol table if there is one.
648 Output_symtab_xindex
* dynsym_xindex_
;
649 // The SHT_DYNAMIC output section if there is one.
650 Output_section
* dynamic_section_
;
651 // The dynamic data which goes into dynamic_section_.
652 Output_data_dynamic
* dynamic_data_
;
653 // The exception frame output section if there is one.
654 Output_section
* eh_frame_section_
;
655 // The exception frame data for eh_frame_section_.
656 Eh_frame
* eh_frame_data_
;
657 // Whether we have added eh_frame_data_ to the .eh_frame section.
658 bool added_eh_frame_data_
;
659 // The exception frame header output section if there is one.
660 Output_section
* eh_frame_hdr_section_
;
661 // The space for the build ID checksum if there is one.
662 Output_section_data
* build_id_note_
;
663 // A list of group sections and their signatures.
664 Group_signatures group_signatures_
;
665 // The size of the output file.
666 off_t output_file_size_
;
667 // Whether we have seen an object file marked to require an
669 bool input_requires_executable_stack_
;
670 // Whether we have seen at least one object file with an executable
672 bool input_with_gnu_stack_note_
;
673 // Whether we have seen at least one object file without an
674 // executable stack marker.
675 bool input_without_gnu_stack_note_
;
676 // Whether we have seen an object file that uses the static TLS model.
677 bool has_static_tls_
;
678 // Whether any sections require postprocessing.
679 bool any_postprocessing_sections_
;
682 // This task handles writing out data in output sections which is not
683 // part of an input section, or which requires special handling. When
684 // this is done, it unblocks both output_sections_blocker and
687 class Write_sections_task
: public Task
690 Write_sections_task(const Layout
* layout
, Output_file
* of
,
691 Task_token
* output_sections_blocker
,
692 Task_token
* final_blocker
)
693 : layout_(layout
), of_(of
),
694 output_sections_blocker_(output_sections_blocker
),
695 final_blocker_(final_blocker
)
698 // The standard Task methods.
711 { return "Write_sections_task"; }
714 class Write_sections_locker
;
716 const Layout
* layout_
;
718 Task_token
* output_sections_blocker_
;
719 Task_token
* final_blocker_
;
722 // This task handles writing out data which is not part of a section
725 class Write_data_task
: public Task
728 Write_data_task(const Layout
* layout
, const Symbol_table
* symtab
,
729 Output_file
* of
, Task_token
* final_blocker
)
730 : layout_(layout
), symtab_(symtab
), of_(of
), final_blocker_(final_blocker
)
733 // The standard Task methods.
746 { return "Write_data_task"; }
749 const Layout
* layout_
;
750 const Symbol_table
* symtab_
;
752 Task_token
* final_blocker_
;
755 // This task handles writing out the global symbols.
757 class Write_symbols_task
: public Task
760 Write_symbols_task(const Layout
* layout
, const Symbol_table
* symtab
,
761 const Input_objects
* input_objects
,
762 const Stringpool
* sympool
, const Stringpool
* dynpool
,
763 Output_file
* of
, Task_token
* final_blocker
)
764 : layout_(layout
), symtab_(symtab
), input_objects_(input_objects
),
765 sympool_(sympool
), dynpool_(dynpool
), of_(of
),
766 final_blocker_(final_blocker
)
769 // The standard Task methods.
782 { return "Write_symbols_task"; }
785 const Layout
* layout_
;
786 const Symbol_table
* symtab_
;
787 const Input_objects
* input_objects_
;
788 const Stringpool
* sympool_
;
789 const Stringpool
* dynpool_
;
791 Task_token
* final_blocker_
;
794 // This task handles writing out data in output sections which can't
795 // be written out until all the input sections have been handled.
796 // This is for sections whose contents is based on the contents of
797 // other output sections.
799 class Write_after_input_sections_task
: public Task
802 Write_after_input_sections_task(Layout
* layout
, Output_file
* of
,
803 Task_token
* input_sections_blocker
,
804 Task_token
* final_blocker
)
805 : layout_(layout
), of_(of
),
806 input_sections_blocker_(input_sections_blocker
),
807 final_blocker_(final_blocker
)
810 // The standard Task methods.
823 { return "Write_after_input_sections_task"; }
828 Task_token
* input_sections_blocker_
;
829 Task_token
* final_blocker_
;
832 // This task function handles closing the file.
834 class Close_task_runner
: public Task_function_runner
837 Close_task_runner(const General_options
* options
, const Layout
* layout
,
839 : options_(options
), layout_(layout
), of_(of
)
842 // Run the operation.
844 run(Workqueue
*, const Task
*);
847 const General_options
* options_
;
848 const Layout
* layout_
;
852 // A small helper function to align an address.
855 align_address(uint64_t address
, uint64_t addralign
)
858 address
= (address
+ addralign
- 1) &~ (addralign
- 1);
862 } // End namespace gold.
864 #endif // !defined(GOLD_LAYOUT_H)