1 // layout.cc -- lay out output file sections for gold
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.
30 #include "parameters.h"
35 #include "compressed_output.h"
41 // Layout_task_runner methods.
43 // Lay out the sections. This is called after all the input objects
47 Layout_task_runner::run(Workqueue* workqueue, const Task* task)
49 off_t file_size = this->layout_->finalize(this->input_objects_,
53 // Now we know the final size of the output file and we know where
54 // each piece of information goes.
55 Output_file* of = new Output_file(this->options_,
56 this->input_objects_->target());
59 // Queue up the final set of tasks.
60 gold::queue_final_tasks(this->options_, this->input_objects_,
61 this->symtab_, this->layout_, workqueue, of);
66 Layout::Layout(const General_options& options)
67 : options_(options), namepool_(), sympool_(), dynpool_(), signatures_(),
68 section_name_map_(), segment_list_(), section_list_(),
69 unattached_section_list_(), special_output_list_(),
70 section_headers_(NULL), tls_segment_(NULL), symtab_section_(NULL),
71 dynsym_section_(NULL), dynamic_section_(NULL), dynamic_data_(NULL),
72 eh_frame_section_(NULL), output_file_size_(-1),
73 input_requires_executable_stack_(false),
74 input_with_gnu_stack_note_(false),
75 input_without_gnu_stack_note_(false),
76 has_static_tls_(false),
77 any_postprocessing_sections_(false)
79 // Make space for more than enough segments for a typical file.
80 // This is just for efficiency--it's OK if we wind up needing more.
81 this->segment_list_.reserve(12);
83 // We expect two unattached Output_data objects: the file header and
84 // the segment headers.
85 this->special_output_list_.reserve(2);
88 // Hash a key we use to look up an output section mapping.
91 Layout::Hash_key::operator()(const Layout::Key& k) const
93 return k.first + k.second.first + k.second.second;
96 // Return whether PREFIX is a prefix of STR.
99 is_prefix_of(const char* prefix, const char* str)
101 return strncmp(prefix, str, strlen(prefix)) == 0;
104 // Returns whether the given section is in the list of
105 // debug-sections-used-by-some-version-of-gdb. Currently,
106 // we've checked versions of gdb up to and including 6.7.1.
108 static const char* gdb_sections[] =
110 // ".debug_aranges", // not used by gdb as of 6.7.1
116 // ".debug_pubnames", // not used by gdb as of 6.7.1
122 is_gdb_debug_section(const char* str)
124 // We can do this faster: binary search or a hashtable. But why bother?
125 for (size_t i = 0; i < sizeof(gdb_sections)/sizeof(*gdb_sections); ++i)
126 if (strcmp(str, gdb_sections[i]) == 0)
131 // Whether to include this section in the link.
133 template<int size, bool big_endian>
135 Layout::include_section(Sized_relobj<size, big_endian>*, const char* name,
136 const elfcpp::Shdr<size, big_endian>& shdr)
138 // Some section types are never linked. Some are only linked when
139 // doing a relocateable link.
140 switch (shdr.get_sh_type())
142 case elfcpp::SHT_NULL:
143 case elfcpp::SHT_SYMTAB:
144 case elfcpp::SHT_DYNSYM:
145 case elfcpp::SHT_STRTAB:
146 case elfcpp::SHT_HASH:
147 case elfcpp::SHT_DYNAMIC:
148 case elfcpp::SHT_SYMTAB_SHNDX:
151 case elfcpp::SHT_RELA:
152 case elfcpp::SHT_REL:
153 case elfcpp::SHT_GROUP:
154 return parameters->output_is_object();
156 case elfcpp::SHT_PROGBITS:
157 if (parameters->strip_debug()
158 && (shdr.get_sh_flags() & elfcpp::SHF_ALLOC) == 0)
160 // Debugging sections can only be recognized by name.
161 if (is_prefix_of(".debug", name)
162 || is_prefix_of(".gnu.linkonce.wi.", name)
163 || is_prefix_of(".line", name)
164 || is_prefix_of(".stab", name))
167 if (parameters->strip_debug_gdb()
168 && (shdr.get_sh_flags() & elfcpp::SHF_ALLOC) == 0)
170 // Debugging sections can only be recognized by name.
171 if (is_prefix_of(".debug", name)
172 && !is_gdb_debug_section(name))
182 // Return an output section named NAME, or NULL if there is none.
185 Layout::find_output_section(const char* name) const
187 for (Section_name_map::const_iterator p = this->section_name_map_.begin();
188 p != this->section_name_map_.end();
190 if (strcmp(p->second->name(), name) == 0)
195 // Return an output segment of type TYPE, with segment flags SET set
196 // and segment flags CLEAR clear. Return NULL if there is none.
199 Layout::find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
200 elfcpp::Elf_Word clear) const
202 for (Segment_list::const_iterator p = this->segment_list_.begin();
203 p != this->segment_list_.end();
205 if (static_cast<elfcpp::PT>((*p)->type()) == type
206 && ((*p)->flags() & set) == set
207 && ((*p)->flags() & clear) == 0)
212 // Return the output section to use for section NAME with type TYPE
213 // and section flags FLAGS.
216 Layout::get_output_section(const char* name, Stringpool::Key name_key,
217 elfcpp::Elf_Word type, elfcpp::Elf_Xword flags)
219 // We should ignore some flags.
220 flags &= ~ (elfcpp::SHF_INFO_LINK
221 | elfcpp::SHF_LINK_ORDER
224 | elfcpp::SHF_STRINGS);
226 const Key key(name_key, std::make_pair(type, flags));
227 const std::pair<Key, Output_section*> v(key, NULL);
228 std::pair<Section_name_map::iterator, bool> ins(
229 this->section_name_map_.insert(v));
232 return ins.first->second;
235 // This is the first time we've seen this name/type/flags
237 Output_section* os = this->make_output_section(name, type, flags);
238 ins.first->second = os;
243 // Return the output section to use for input section SHNDX, with name
244 // NAME, with header HEADER, from object OBJECT. RELOC_SHNDX is the
245 // index of a relocation section which applies to this section, or 0
246 // if none, or -1U if more than one. RELOC_TYPE is the type of the
247 // relocation section if there is one. Set *OFF to the offset of this
248 // input section without the output section. Return NULL if the
249 // section should be discarded. Set *OFF to -1 if the section
250 // contents should not be written directly to the output file, but
251 // will instead receive special handling.
253 template<int size, bool big_endian>
255 Layout::layout(Sized_relobj<size, big_endian>* object, unsigned int shndx,
256 const char* name, const elfcpp::Shdr<size, big_endian>& shdr,
257 unsigned int reloc_shndx, unsigned int, off_t* off)
259 if (!this->include_section(object, name, shdr))
262 // If we are not doing a relocateable link, choose the name to use
263 // for the output section.
264 size_t len = strlen(name);
265 if (!parameters->output_is_object())
266 name = Layout::output_section_name(name, &len);
268 // FIXME: Handle SHF_OS_NONCONFORMING here.
270 // Canonicalize the section name.
271 Stringpool::Key name_key;
272 name = this->namepool_.add_with_length(name, len, true, &name_key);
274 // Find the output section. The output section is selected based on
275 // the section name, type, and flags.
276 Output_section* os = this->get_output_section(name, name_key,
278 shdr.get_sh_flags());
280 // FIXME: Handle SHF_LINK_ORDER somewhere.
282 *off = os->add_input_section(object, shndx, name, shdr, reloc_shndx);
287 // Special GNU handling of sections name .eh_frame. They will
288 // normally hold exception frame data as defined by the C++ ABI
289 // (http://codesourcery.com/cxx-abi/).
291 template<int size, bool big_endian>
293 Layout::layout_eh_frame(Sized_relobj<size, big_endian>* object,
294 const unsigned char* symbols,
296 const unsigned char* symbol_names,
297 off_t symbol_names_size,
299 const elfcpp::Shdr<size, big_endian>& shdr,
300 unsigned int reloc_shndx, unsigned int reloc_type,
303 gold_assert(shdr.get_sh_type() == elfcpp::SHT_PROGBITS);
304 gold_assert(shdr.get_sh_flags() == elfcpp::SHF_ALLOC);
306 Stringpool::Key name_key;
307 const char* name = this->namepool_.add(".eh_frame", false, &name_key);
309 Output_section* os = this->get_output_section(name, name_key,
310 elfcpp::SHT_PROGBITS,
313 if (this->eh_frame_section_ == NULL)
315 this->eh_frame_section_ = os;
316 this->eh_frame_data_ = new Eh_frame();
317 os->add_output_section_data(this->eh_frame_data_);
319 if (this->options_.create_eh_frame_hdr())
321 Stringpool::Key hdr_name_key;
322 const char* hdr_name = this->namepool_.add(".eh_frame_hdr",
325 Output_section* hdr_os =
326 this->get_output_section(hdr_name, hdr_name_key,
327 elfcpp::SHT_PROGBITS,
330 Eh_frame_hdr* hdr_posd = new Eh_frame_hdr(os, this->eh_frame_data_);
331 hdr_os->add_output_section_data(hdr_posd);
333 hdr_os->set_after_input_sections();
335 Output_segment* hdr_oseg =
336 new Output_segment(elfcpp::PT_GNU_EH_FRAME, elfcpp::PF_R);
337 this->segment_list_.push_back(hdr_oseg);
338 hdr_oseg->add_output_section(hdr_os, elfcpp::PF_R);
340 this->eh_frame_data_->set_eh_frame_hdr(hdr_posd);
344 gold_assert(this->eh_frame_section_ == os);
346 if (this->eh_frame_data_->add_ehframe_input_section(object,
357 // We couldn't handle this .eh_frame section for some reason.
358 // Add it as a normal section.
359 *off = os->add_input_section(object, shndx, name, shdr, reloc_shndx);
365 // Add POSD to an output section using NAME, TYPE, and FLAGS.
368 Layout::add_output_section_data(const char* name, elfcpp::Elf_Word type,
369 elfcpp::Elf_Xword flags,
370 Output_section_data* posd)
372 // Canonicalize the name.
373 Stringpool::Key name_key;
374 name = this->namepool_.add(name, true, &name_key);
376 Output_section* os = this->get_output_section(name, name_key, type, flags);
377 os->add_output_section_data(posd);
380 // Map section flags to segment flags.
383 Layout::section_flags_to_segment(elfcpp::Elf_Xword flags)
385 elfcpp::Elf_Word ret = elfcpp::PF_R;
386 if ((flags & elfcpp::SHF_WRITE) != 0)
388 if ((flags & elfcpp::SHF_EXECINSTR) != 0)
393 // Sometimes we compress sections. This is typically done for
394 // sections that are not part of normal program execution (such as
395 // .debug_* sections), and where the readers of these sections know
396 // how to deal with compressed sections. (To make it easier for them,
397 // we will rename the ouput section in such cases from .foo to
398 // .foo.zlib.nnnn, where nnnn is the uncompressed size.) This routine
399 // doesn't say for certain whether we'll compress -- it depends on
400 // commandline options as well -- just whether this section is a
401 // candidate for compression.
404 is_compressible_debug_section(const char* secname)
406 return (strncmp(secname, ".debug", sizeof(".debug") - 1) == 0);
409 // Make a new Output_section, and attach it to segments as
413 Layout::make_output_section(const char* name, elfcpp::Elf_Word type,
414 elfcpp::Elf_Xword flags)
417 if ((flags & elfcpp::SHF_ALLOC) == 0
418 && this->options_.compress_debug_sections()
419 && is_compressible_debug_section(name))
420 os = new Output_compressed_section(&this->options_, name, type, flags);
422 os = new Output_section(name, type, flags);
424 this->section_list_.push_back(os);
426 if ((flags & elfcpp::SHF_ALLOC) == 0)
427 this->unattached_section_list_.push_back(os);
430 // This output section goes into a PT_LOAD segment.
432 elfcpp::Elf_Word seg_flags = Layout::section_flags_to_segment(flags);
434 // The only thing we really care about for PT_LOAD segments is
435 // whether or not they are writable, so that is how we search
436 // for them. People who need segments sorted on some other
437 // basis will have to wait until we implement a mechanism for
438 // them to describe the segments they want.
440 Segment_list::const_iterator p;
441 for (p = this->segment_list_.begin();
442 p != this->segment_list_.end();
445 if ((*p)->type() == elfcpp::PT_LOAD
446 && ((*p)->flags() & elfcpp::PF_W) == (seg_flags & elfcpp::PF_W))
448 (*p)->add_output_section(os, seg_flags);
453 if (p == this->segment_list_.end())
455 Output_segment* oseg = new Output_segment(elfcpp::PT_LOAD,
457 this->segment_list_.push_back(oseg);
458 oseg->add_output_section(os, seg_flags);
461 // If we see a loadable SHT_NOTE section, we create a PT_NOTE
463 if (type == elfcpp::SHT_NOTE)
465 // See if we already have an equivalent PT_NOTE segment.
466 for (p = this->segment_list_.begin();
467 p != segment_list_.end();
470 if ((*p)->type() == elfcpp::PT_NOTE
471 && (((*p)->flags() & elfcpp::PF_W)
472 == (seg_flags & elfcpp::PF_W)))
474 (*p)->add_output_section(os, seg_flags);
479 if (p == this->segment_list_.end())
481 Output_segment* oseg = new Output_segment(elfcpp::PT_NOTE,
483 this->segment_list_.push_back(oseg);
484 oseg->add_output_section(os, seg_flags);
488 // If we see a loadable SHF_TLS section, we create a PT_TLS
489 // segment. There can only be one such segment.
490 if ((flags & elfcpp::SHF_TLS) != 0)
492 if (this->tls_segment_ == NULL)
494 this->tls_segment_ = new Output_segment(elfcpp::PT_TLS,
496 this->segment_list_.push_back(this->tls_segment_);
498 this->tls_segment_->add_output_section(os, seg_flags);
505 // Handle the .note.GNU-stack section at layout time. SEEN_GNU_STACK
506 // is whether we saw a .note.GNU-stack section in the object file.
507 // GNU_STACK_FLAGS is the section flags. The flags give the
508 // protection required for stack memory. We record this in an
509 // executable as a PT_GNU_STACK segment. If an object file does not
510 // have a .note.GNU-stack segment, we must assume that it is an old
511 // object. On some targets that will force an executable stack.
514 Layout::layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags)
517 this->input_without_gnu_stack_note_ = true;
520 this->input_with_gnu_stack_note_ = true;
521 if ((gnu_stack_flags & elfcpp::SHF_EXECINSTR) != 0)
522 this->input_requires_executable_stack_ = true;
526 // Create the dynamic sections which are needed before we read the
530 Layout::create_initial_dynamic_sections(const Input_objects* input_objects,
531 Symbol_table* symtab)
533 if (parameters->doing_static_link())
536 const char* dynamic_name = this->namepool_.add(".dynamic", false, NULL);
537 this->dynamic_section_ = this->make_output_section(dynamic_name,
540 | elfcpp::SHF_WRITE));
542 symtab->define_in_output_data(input_objects->target(), "_DYNAMIC", NULL,
543 this->dynamic_section_, 0, 0,
544 elfcpp::STT_OBJECT, elfcpp::STB_LOCAL,
545 elfcpp::STV_HIDDEN, 0, false, false);
547 this->dynamic_data_ = new Output_data_dynamic(&this->dynpool_);
549 this->dynamic_section_->add_output_section_data(this->dynamic_data_);
552 // For each output section whose name can be represented as C symbol,
553 // define __start and __stop symbols for the section. This is a GNU
557 Layout::define_section_symbols(Symbol_table* symtab, const Target* target)
559 for (Section_list::const_iterator p = this->section_list_.begin();
560 p != this->section_list_.end();
563 const char* const name = (*p)->name();
564 if (name[strspn(name,
566 "ABCDEFGHIJKLMNOPWRSTUVWXYZ"
567 "abcdefghijklmnopqrstuvwxyz"
571 const std::string name_string(name);
572 const std::string start_name("__start_" + name_string);
573 const std::string stop_name("__stop_" + name_string);
575 symtab->define_in_output_data(target,
585 false, // offset_is_from_end
586 false); // only_if_ref
588 symtab->define_in_output_data(target,
598 true, // offset_is_from_end
599 false); // only_if_ref
604 // Find the first read-only PT_LOAD segment, creating one if
608 Layout::find_first_load_seg()
610 for (Segment_list::const_iterator p = this->segment_list_.begin();
611 p != this->segment_list_.end();
614 if ((*p)->type() == elfcpp::PT_LOAD
615 && ((*p)->flags() & elfcpp::PF_R) != 0
616 && ((*p)->flags() & elfcpp::PF_W) == 0)
620 Output_segment* load_seg = new Output_segment(elfcpp::PT_LOAD, elfcpp::PF_R);
621 this->segment_list_.push_back(load_seg);
625 // Finalize the layout. When this is called, we have created all the
626 // output sections and all the output segments which are based on
627 // input sections. We have several things to do, and we have to do
628 // them in the right order, so that we get the right results correctly
631 // 1) Finalize the list of output segments and create the segment
634 // 2) Finalize the dynamic symbol table and associated sections.
636 // 3) Determine the final file offset of all the output segments.
638 // 4) Determine the final file offset of all the SHF_ALLOC output
641 // 5) Create the symbol table sections and the section name table
644 // 6) Finalize the symbol table: set symbol values to their final
645 // value and make a final determination of which symbols are going
646 // into the output symbol table.
648 // 7) Create the section table header.
650 // 8) Determine the final file offset of all the output sections which
651 // are not SHF_ALLOC, including the section table header.
653 // 9) Finalize the ELF file header.
655 // This function returns the size of the output file.
658 Layout::finalize(const Input_objects* input_objects, Symbol_table* symtab,
661 Target* const target = input_objects->target();
663 target->finalize_sections(this);
665 this->count_local_symbols(task, input_objects);
667 this->create_gold_note();
668 this->create_executable_stack_info(target);
670 Output_segment* phdr_seg = NULL;
671 if (!parameters->doing_static_link())
673 // There was a dynamic object in the link. We need to create
674 // some information for the dynamic linker.
676 // Create the PT_PHDR segment which will hold the program
678 phdr_seg = new Output_segment(elfcpp::PT_PHDR, elfcpp::PF_R);
679 this->segment_list_.push_back(phdr_seg);
681 // Create the dynamic symbol table, including the hash table.
682 Output_section* dynstr;
683 std::vector<Symbol*> dynamic_symbols;
684 unsigned int local_dynamic_count;
686 this->create_dynamic_symtab(input_objects, target, symtab, &dynstr,
687 &local_dynamic_count, &dynamic_symbols,
690 // Create the .interp section to hold the name of the
691 // interpreter, and put it in a PT_INTERP segment.
692 if (!parameters->output_is_shared())
693 this->create_interp(target);
695 // Finish the .dynamic section to hold the dynamic data, and put
696 // it in a PT_DYNAMIC segment.
697 this->finish_dynamic_section(input_objects, symtab);
699 // We should have added everything we need to the dynamic string
701 this->dynpool_.set_string_offsets();
703 // Create the version sections. We can't do this until the
704 // dynamic string table is complete.
705 this->create_version_sections(&versions, symtab, local_dynamic_count,
706 dynamic_symbols, dynstr);
709 // FIXME: Handle PT_GNU_STACK.
711 Output_segment* load_seg = this->find_first_load_seg();
713 // Lay out the segment headers.
714 Output_segment_headers* segment_headers;
715 segment_headers = new Output_segment_headers(this->segment_list_);
716 load_seg->add_initial_output_data(segment_headers);
717 this->special_output_list_.push_back(segment_headers);
718 if (phdr_seg != NULL)
719 phdr_seg->add_initial_output_data(segment_headers);
721 // Lay out the file header.
722 Output_file_header* file_header;
723 file_header = new Output_file_header(target, symtab, segment_headers);
724 load_seg->add_initial_output_data(file_header);
725 this->special_output_list_.push_back(file_header);
727 // We set the output section indexes in set_segment_offsets and
728 // set_section_indexes.
729 unsigned int shndx = 1;
731 // Set the file offsets of all the segments, and all the sections
733 off_t off = this->set_segment_offsets(target, load_seg, &shndx);
735 // Set the file offsets of all the non-data sections we've seen so
736 // far which don't have to wait for the input sections. We need
737 // this in order to finalize local symbols in non-allocated
739 off = this->set_section_offsets(off, BEFORE_INPUT_SECTIONS_PASS);
741 // Create the symbol table sections.
742 this->create_symtab_sections(input_objects, symtab, &off);
743 if (!parameters->doing_static_link())
744 this->assign_local_dynsym_offsets(input_objects);
746 // Create the .shstrtab section.
747 Output_section* shstrtab_section = this->create_shstrtab();
749 // Set the file offsets of the rest of the non-data sections which
750 // don't have to wait for the input sections.
751 off = this->set_section_offsets(off, BEFORE_INPUT_SECTIONS_PASS);
753 // Now that all sections have been created, set the section indexes.
754 shndx = this->set_section_indexes(shndx);
756 // Create the section table header.
757 this->create_shdrs(&off);
759 // If there are no sections which require postprocessing, we can
760 // handle the section names now, and avoid a resize later.
761 if (!this->any_postprocessing_sections_)
762 off = this->set_section_offsets(off,
763 STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS);
765 file_header->set_section_info(this->section_headers_, shstrtab_section);
767 // Now we know exactly where everything goes in the output file
768 // (except for non-allocated sections which require postprocessing).
769 Output_data::layout_complete();
771 this->output_file_size_ = off;
776 // Create a .note section for an executable or shared library. This
777 // records the version of gold used to create the binary.
780 Layout::create_gold_note()
782 if (parameters->output_is_object())
785 // Authorities all agree that the values in a .note field should
786 // be aligned on 4-byte boundaries for 32-bit binaries. However,
787 // they differ on what the alignment is for 64-bit binaries.
788 // The GABI says unambiguously they take 8-byte alignment:
789 // http://sco.com/developers/gabi/latest/ch5.pheader.html#note_section
790 // Other documentation says alignment should always be 4 bytes:
791 // http://www.netbsd.org/docs/kernel/elf-notes.html#note-format
792 // GNU ld and GNU readelf both support the latter (at least as of
793 // version 2.16.91), and glibc always generates the latter for
794 // .note.ABI-tag (as of version 1.6), so that's the one we go with
796 #ifdef GABI_FORMAT_FOR_DOTNOTE_SECTION // This is not defined by default.
797 const int size = parameters->get_size();
802 // The contents of the .note section.
803 const char* name = "GNU";
804 std::string desc(std::string("gold ") + gold::get_version_string());
805 size_t namesz = strlen(name) + 1;
806 size_t aligned_namesz = align_address(namesz, size / 8);
807 size_t descsz = desc.length() + 1;
808 size_t aligned_descsz = align_address(descsz, size / 8);
809 const int note_type = 4;
811 size_t notesz = 3 * (size / 8) + aligned_namesz + aligned_descsz;
813 unsigned char buffer[128];
814 gold_assert(sizeof buffer >= notesz);
815 memset(buffer, 0, notesz);
817 bool is_big_endian = parameters->is_big_endian();
823 elfcpp::Swap<32, false>::writeval(buffer, namesz);
824 elfcpp::Swap<32, false>::writeval(buffer + 4, descsz);
825 elfcpp::Swap<32, false>::writeval(buffer + 8, note_type);
829 elfcpp::Swap<32, true>::writeval(buffer, namesz);
830 elfcpp::Swap<32, true>::writeval(buffer + 4, descsz);
831 elfcpp::Swap<32, true>::writeval(buffer + 8, note_type);
838 elfcpp::Swap<64, false>::writeval(buffer, namesz);
839 elfcpp::Swap<64, false>::writeval(buffer + 8, descsz);
840 elfcpp::Swap<64, false>::writeval(buffer + 16, note_type);
844 elfcpp::Swap<64, true>::writeval(buffer, namesz);
845 elfcpp::Swap<64, true>::writeval(buffer + 8, descsz);
846 elfcpp::Swap<64, true>::writeval(buffer + 16, note_type);
852 memcpy(buffer + 3 * (size / 8), name, namesz);
853 memcpy(buffer + 3 * (size / 8) + aligned_namesz, desc.data(), descsz);
855 const char* note_name = this->namepool_.add(".note", false, NULL);
856 Output_section* os = this->make_output_section(note_name,
859 Output_section_data* posd = new Output_data_const(buffer, notesz,
861 os->add_output_section_data(posd);
864 // Record whether the stack should be executable. This can be set
865 // from the command line using the -z execstack or -z noexecstack
866 // options. Otherwise, if any input file has a .note.GNU-stack
867 // section with the SHF_EXECINSTR flag set, the stack should be
868 // executable. Otherwise, if at least one input file a
869 // .note.GNU-stack section, and some input file has no .note.GNU-stack
870 // section, we use the target default for whether the stack should be
871 // executable. Otherwise, we don't generate a stack note. When
872 // generating a object file, we create a .note.GNU-stack section with
873 // the appropriate marking. When generating an executable or shared
874 // library, we create a PT_GNU_STACK segment.
877 Layout::create_executable_stack_info(const Target* target)
879 bool is_stack_executable;
880 if (this->options_.is_execstack_set())
881 is_stack_executable = this->options_.is_stack_executable();
882 else if (!this->input_with_gnu_stack_note_)
886 if (this->input_requires_executable_stack_)
887 is_stack_executable = true;
888 else if (this->input_without_gnu_stack_note_)
889 is_stack_executable = target->is_default_stack_executable();
891 is_stack_executable = false;
894 if (parameters->output_is_object())
896 const char* name = this->namepool_.add(".note.GNU-stack", false, NULL);
897 elfcpp::Elf_Xword flags = 0;
898 if (is_stack_executable)
899 flags |= elfcpp::SHF_EXECINSTR;
900 this->make_output_section(name, elfcpp::SHT_PROGBITS, flags);
904 int flags = elfcpp::PF_R | elfcpp::PF_W;
905 if (is_stack_executable)
906 flags |= elfcpp::PF_X;
907 Output_segment* oseg = new Output_segment(elfcpp::PT_GNU_STACK, flags);
908 this->segment_list_.push_back(oseg);
912 // Return whether SEG1 should be before SEG2 in the output file. This
913 // is based entirely on the segment type and flags. When this is
914 // called the segment addresses has normally not yet been set.
917 Layout::segment_precedes(const Output_segment* seg1,
918 const Output_segment* seg2)
920 elfcpp::Elf_Word type1 = seg1->type();
921 elfcpp::Elf_Word type2 = seg2->type();
923 // The single PT_PHDR segment is required to precede any loadable
924 // segment. We simply make it always first.
925 if (type1 == elfcpp::PT_PHDR)
927 gold_assert(type2 != elfcpp::PT_PHDR);
930 if (type2 == elfcpp::PT_PHDR)
933 // The single PT_INTERP segment is required to precede any loadable
934 // segment. We simply make it always second.
935 if (type1 == elfcpp::PT_INTERP)
937 gold_assert(type2 != elfcpp::PT_INTERP);
940 if (type2 == elfcpp::PT_INTERP)
943 // We then put PT_LOAD segments before any other segments.
944 if (type1 == elfcpp::PT_LOAD && type2 != elfcpp::PT_LOAD)
946 if (type2 == elfcpp::PT_LOAD && type1 != elfcpp::PT_LOAD)
949 // We put the PT_TLS segment last, because that is where the dynamic
950 // linker expects to find it (this is just for efficiency; other
951 // positions would also work correctly).
952 if (type1 == elfcpp::PT_TLS && type2 != elfcpp::PT_TLS)
954 if (type2 == elfcpp::PT_TLS && type1 != elfcpp::PT_TLS)
957 const elfcpp::Elf_Word flags1 = seg1->flags();
958 const elfcpp::Elf_Word flags2 = seg2->flags();
960 // The order of non-PT_LOAD segments is unimportant. We simply sort
961 // by the numeric segment type and flags values. There should not
962 // be more than one segment with the same type and flags.
963 if (type1 != elfcpp::PT_LOAD)
966 return type1 < type2;
967 gold_assert(flags1 != flags2);
968 return flags1 < flags2;
971 // We sort PT_LOAD segments based on the flags. Readonly segments
972 // come before writable segments. Then executable segments come
973 // before non-executable segments. Then the unlikely case of a
974 // non-readable segment comes before the normal case of a readable
975 // segment. If there are multiple segments with the same type and
976 // flags, we require that the address be set, and we sort by
977 // virtual address and then physical address.
978 if ((flags1 & elfcpp::PF_W) != (flags2 & elfcpp::PF_W))
979 return (flags1 & elfcpp::PF_W) == 0;
980 if ((flags1 & elfcpp::PF_X) != (flags2 & elfcpp::PF_X))
981 return (flags1 & elfcpp::PF_X) != 0;
982 if ((flags1 & elfcpp::PF_R) != (flags2 & elfcpp::PF_R))
983 return (flags1 & elfcpp::PF_R) == 0;
985 uint64_t vaddr1 = seg1->vaddr();
986 uint64_t vaddr2 = seg2->vaddr();
987 if (vaddr1 != vaddr2)
988 return vaddr1 < vaddr2;
990 uint64_t paddr1 = seg1->paddr();
991 uint64_t paddr2 = seg2->paddr();
992 gold_assert(paddr1 != paddr2);
993 return paddr1 < paddr2;
996 // Set the file offsets of all the segments, and all the sections they
997 // contain. They have all been created. LOAD_SEG must be be laid out
998 // first. Return the offset of the data to follow.
1001 Layout::set_segment_offsets(const Target* target, Output_segment* load_seg,
1002 unsigned int *pshndx)
1004 // Sort them into the final order.
1005 std::sort(this->segment_list_.begin(), this->segment_list_.end(),
1006 Layout::Compare_segments());
1008 // Find the PT_LOAD segments, and set their addresses and offsets
1009 // and their section's addresses and offsets.
1011 if (parameters->output_is_shared())
1013 else if (options_.user_set_text_segment_address())
1014 addr = options_.text_segment_address();
1016 addr = target->default_text_segment_address();
1018 bool was_readonly = false;
1019 for (Segment_list::iterator p = this->segment_list_.begin();
1020 p != this->segment_list_.end();
1023 if ((*p)->type() == elfcpp::PT_LOAD)
1025 if (load_seg != NULL && load_seg != *p)
1029 // If the last segment was readonly, and this one is not,
1030 // then skip the address forward one page, maintaining the
1031 // same position within the page. This lets us store both
1032 // segments overlapping on a single page in the file, but
1033 // the loader will put them on different pages in memory.
1035 uint64_t orig_addr = addr;
1036 uint64_t orig_off = off;
1038 uint64_t aligned_addr = addr;
1039 uint64_t abi_pagesize = target->abi_pagesize();
1041 // FIXME: This should depend on the -n and -N options.
1042 (*p)->set_minimum_addralign(target->common_pagesize());
1044 if (was_readonly && ((*p)->flags() & elfcpp::PF_W) != 0)
1046 uint64_t align = (*p)->addralign();
1048 addr = align_address(addr, align);
1049 aligned_addr = addr;
1050 if ((addr & (abi_pagesize - 1)) != 0)
1051 addr = addr + abi_pagesize;
1054 unsigned int shndx_hold = *pshndx;
1055 off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1));
1056 uint64_t new_addr = (*p)->set_section_addresses(addr, &off, pshndx);
1058 // Now that we know the size of this segment, we may be able
1059 // to save a page in memory, at the cost of wasting some
1060 // file space, by instead aligning to the start of a new
1061 // page. Here we use the real machine page size rather than
1062 // the ABI mandated page size.
1064 if (aligned_addr != addr)
1066 uint64_t common_pagesize = target->common_pagesize();
1067 uint64_t first_off = (common_pagesize
1069 & (common_pagesize - 1)));
1070 uint64_t last_off = new_addr & (common_pagesize - 1);
1073 && ((aligned_addr & ~ (common_pagesize - 1))
1074 != (new_addr & ~ (common_pagesize - 1)))
1075 && first_off + last_off <= common_pagesize)
1077 *pshndx = shndx_hold;
1078 addr = align_address(aligned_addr, common_pagesize);
1079 off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1));
1080 new_addr = (*p)->set_section_addresses(addr, &off, pshndx);
1086 if (((*p)->flags() & elfcpp::PF_W) == 0)
1087 was_readonly = true;
1091 // Handle the non-PT_LOAD segments, setting their offsets from their
1092 // section's offsets.
1093 for (Segment_list::iterator p = this->segment_list_.begin();
1094 p != this->segment_list_.end();
1097 if ((*p)->type() != elfcpp::PT_LOAD)
1101 // Set the TLS offsets for each section in the PT_TLS segment.
1102 if (this->tls_segment_ != NULL)
1103 this->tls_segment_->set_tls_offsets();
1108 // Set the file offset of all the sections not associated with a
1112 Layout::set_section_offsets(off_t off, Layout::Section_offset_pass pass)
1114 for (Section_list::iterator p = this->unattached_section_list_.begin();
1115 p != this->unattached_section_list_.end();
1118 // The symtab section is handled in create_symtab_sections.
1119 if (*p == this->symtab_section_)
1122 // If we've already set the data size, don't set it again.
1123 if ((*p)->is_offset_valid() && (*p)->is_data_size_valid())
1126 if (pass == BEFORE_INPUT_SECTIONS_PASS
1127 && (*p)->requires_postprocessing())
1129 (*p)->create_postprocessing_buffer();
1130 this->any_postprocessing_sections_ = true;
1133 if (pass == BEFORE_INPUT_SECTIONS_PASS
1134 && (*p)->after_input_sections())
1136 else if (pass == POSTPROCESSING_SECTIONS_PASS
1137 && (!(*p)->after_input_sections()
1138 || (*p)->type() == elfcpp::SHT_STRTAB))
1140 else if (pass == STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS
1141 && (!(*p)->after_input_sections()
1142 || (*p)->type() != elfcpp::SHT_STRTAB))
1145 off = align_address(off, (*p)->addralign());
1146 (*p)->set_file_offset(off);
1147 (*p)->finalize_data_size();
1148 off += (*p)->data_size();
1150 // At this point the name must be set.
1151 if (pass != STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS)
1152 this->namepool_.add((*p)->name(), false, NULL);
1157 // Set the section indexes of all the sections not associated with a
1161 Layout::set_section_indexes(unsigned int shndx)
1163 for (Section_list::iterator p = this->unattached_section_list_.begin();
1164 p != this->unattached_section_list_.end();
1167 (*p)->set_out_shndx(shndx);
1173 // Count the local symbols in the regular symbol table and the dynamic
1174 // symbol table, and build the respective string pools.
1177 Layout::count_local_symbols(const Task* task,
1178 const Input_objects* input_objects)
1180 // First, figure out an upper bound on the number of symbols we'll
1181 // be inserting into each pool. This helps us create the pools with
1182 // the right size, to avoid unnecessary hashtable resizing.
1183 unsigned int symbol_count = 0;
1184 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
1185 p != input_objects->relobj_end();
1187 symbol_count += (*p)->local_symbol_count();
1189 // Go from "upper bound" to "estimate." We overcount for two
1190 // reasons: we double-count symbols that occur in more than one
1191 // object file, and we count symbols that are dropped from the
1192 // output. Add it all together and assume we overcount by 100%.
1195 // We assume all symbols will go into both the sympool and dynpool.
1196 this->sympool_.reserve(symbol_count);
1197 this->dynpool_.reserve(symbol_count);
1199 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
1200 p != input_objects->relobj_end();
1203 Task_lock_obj<Object> tlo(task, *p);
1204 (*p)->count_local_symbols(&this->sympool_, &this->dynpool_);
1208 // Create the symbol table sections. Here we also set the final
1209 // values of the symbols. At this point all the loadable sections are
1213 Layout::create_symtab_sections(const Input_objects* input_objects,
1214 Symbol_table* symtab,
1219 if (parameters->get_size() == 32)
1221 symsize = elfcpp::Elf_sizes<32>::sym_size;
1224 else if (parameters->get_size() == 64)
1226 symsize = elfcpp::Elf_sizes<64>::sym_size;
1233 off = align_address(off, align);
1234 off_t startoff = off;
1236 // Save space for the dummy symbol at the start of the section. We
1237 // never bother to write this out--it will just be left as zero.
1239 unsigned int local_symbol_index = 1;
1241 // Add STT_SECTION symbols for each Output section which needs one.
1242 for (Section_list::iterator p = this->section_list_.begin();
1243 p != this->section_list_.end();
1246 if (!(*p)->needs_symtab_index())
1247 (*p)->set_symtab_index(-1U);
1250 (*p)->set_symtab_index(local_symbol_index);
1251 ++local_symbol_index;
1256 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
1257 p != input_objects->relobj_end();
1260 unsigned int index = (*p)->finalize_local_symbols(local_symbol_index,
1262 off += (index - local_symbol_index) * symsize;
1263 local_symbol_index = index;
1266 unsigned int local_symcount = local_symbol_index;
1267 gold_assert(local_symcount * symsize == off - startoff);
1270 size_t dyn_global_index;
1272 if (this->dynsym_section_ == NULL)
1275 dyn_global_index = 0;
1280 dyn_global_index = this->dynsym_section_->info();
1281 off_t locsize = dyn_global_index * this->dynsym_section_->entsize();
1282 dynoff = this->dynsym_section_->offset() + locsize;
1283 dyncount = (this->dynsym_section_->data_size() - locsize) / symsize;
1284 gold_assert(static_cast<off_t>(dyncount * symsize)
1285 == this->dynsym_section_->data_size() - locsize);
1288 off = symtab->finalize(local_symcount, off, dynoff, dyn_global_index,
1289 dyncount, &this->sympool_);
1291 if (!parameters->strip_all())
1293 this->sympool_.set_string_offsets();
1295 const char* symtab_name = this->namepool_.add(".symtab", false, NULL);
1296 Output_section* osymtab = this->make_output_section(symtab_name,
1299 this->symtab_section_ = osymtab;
1301 Output_section_data* pos = new Output_data_fixed_space(off - startoff,
1303 osymtab->add_output_section_data(pos);
1305 const char* strtab_name = this->namepool_.add(".strtab", false, NULL);
1306 Output_section* ostrtab = this->make_output_section(strtab_name,
1310 Output_section_data* pstr = new Output_data_strtab(&this->sympool_);
1311 ostrtab->add_output_section_data(pstr);
1313 osymtab->set_file_offset(startoff);
1314 osymtab->finalize_data_size();
1315 osymtab->set_link_section(ostrtab);
1316 osymtab->set_info(local_symcount);
1317 osymtab->set_entsize(symsize);
1323 // Create the .shstrtab section, which holds the names of the
1324 // sections. At the time this is called, we have created all the
1325 // output sections except .shstrtab itself.
1328 Layout::create_shstrtab()
1330 // FIXME: We don't need to create a .shstrtab section if we are
1331 // stripping everything.
1333 const char* name = this->namepool_.add(".shstrtab", false, NULL);
1335 Output_section* os = this->make_output_section(name, elfcpp::SHT_STRTAB, 0);
1337 // We can't write out this section until we've set all the section
1338 // names, and we don't set the names of compressed output sections
1339 // until relocations are complete.
1340 os->set_after_input_sections();
1342 Output_section_data* posd = new Output_data_strtab(&this->namepool_);
1343 os->add_output_section_data(posd);
1348 // Create the section headers. SIZE is 32 or 64. OFF is the file
1352 Layout::create_shdrs(off_t* poff)
1354 Output_section_headers* oshdrs;
1355 oshdrs = new Output_section_headers(this,
1356 &this->segment_list_,
1357 &this->unattached_section_list_,
1359 off_t off = align_address(*poff, oshdrs->addralign());
1360 oshdrs->set_address_and_file_offset(0, off);
1361 off += oshdrs->data_size();
1363 this->section_headers_ = oshdrs;
1366 // Create the dynamic symbol table.
1369 Layout::create_dynamic_symtab(const Input_objects* input_objects,
1370 const Target* target, Symbol_table* symtab,
1371 Output_section **pdynstr,
1372 unsigned int* plocal_dynamic_count,
1373 std::vector<Symbol*>* pdynamic_symbols,
1374 Versions* pversions)
1376 // Count all the symbols in the dynamic symbol table, and set the
1377 // dynamic symbol indexes.
1379 // Skip symbol 0, which is always all zeroes.
1380 unsigned int index = 1;
1382 // Add STT_SECTION symbols for each Output section which needs one.
1383 for (Section_list::iterator p = this->section_list_.begin();
1384 p != this->section_list_.end();
1387 if (!(*p)->needs_dynsym_index())
1388 (*p)->set_dynsym_index(-1U);
1391 (*p)->set_dynsym_index(index);
1396 // Count the local symbols that need to go in the dynamic symbol table,
1397 // and set the dynamic symbol indexes.
1398 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
1399 p != input_objects->relobj_end();
1402 unsigned int new_index = (*p)->set_local_dynsym_indexes(index);
1406 unsigned int local_symcount = index;
1407 *plocal_dynamic_count = local_symcount;
1409 // FIXME: We have to tell set_dynsym_indexes whether the
1410 // -E/--export-dynamic option was used.
1411 index = symtab->set_dynsym_indexes(target, index, pdynamic_symbols,
1412 &this->dynpool_, pversions);
1416 const int size = parameters->get_size();
1419 symsize = elfcpp::Elf_sizes<32>::sym_size;
1422 else if (size == 64)
1424 symsize = elfcpp::Elf_sizes<64>::sym_size;
1430 // Create the dynamic symbol table section.
1432 const char* dynsym_name = this->namepool_.add(".dynsym", false, NULL);
1433 Output_section* dynsym = this->make_output_section(dynsym_name,
1437 Output_section_data* odata = new Output_data_fixed_space(index * symsize,
1439 dynsym->add_output_section_data(odata);
1441 dynsym->set_info(local_symcount);
1442 dynsym->set_entsize(symsize);
1443 dynsym->set_addralign(align);
1445 this->dynsym_section_ = dynsym;
1447 Output_data_dynamic* const odyn = this->dynamic_data_;
1448 odyn->add_section_address(elfcpp::DT_SYMTAB, dynsym);
1449 odyn->add_constant(elfcpp::DT_SYMENT, symsize);
1451 // Create the dynamic string table section.
1453 const char* dynstr_name = this->namepool_.add(".dynstr", false, NULL);
1454 Output_section* dynstr = this->make_output_section(dynstr_name,
1458 Output_section_data* strdata = new Output_data_strtab(&this->dynpool_);
1459 dynstr->add_output_section_data(strdata);
1461 dynsym->set_link_section(dynstr);
1462 this->dynamic_section_->set_link_section(dynstr);
1464 odyn->add_section_address(elfcpp::DT_STRTAB, dynstr);
1465 odyn->add_section_size(elfcpp::DT_STRSZ, dynstr);
1469 // Create the hash tables.
1471 // FIXME: We need an option to create a GNU hash table.
1473 unsigned char* phash;
1474 unsigned int hashlen;
1475 Dynobj::create_elf_hash_table(*pdynamic_symbols, local_symcount,
1478 const char* hash_name = this->namepool_.add(".hash", false, NULL);
1479 Output_section* hashsec = this->make_output_section(hash_name,
1483 Output_section_data* hashdata = new Output_data_const_buffer(phash,
1486 hashsec->add_output_section_data(hashdata);
1488 hashsec->set_link_section(dynsym);
1489 hashsec->set_entsize(4);
1491 odyn->add_section_address(elfcpp::DT_HASH, hashsec);
1494 // Assign offsets to each local portion of the dynamic symbol table.
1497 Layout::assign_local_dynsym_offsets(const Input_objects* input_objects)
1499 Output_section* dynsym = this->dynsym_section_;
1500 gold_assert(dynsym != NULL);
1502 off_t off = dynsym->offset();
1504 // Skip the dummy symbol at the start of the section.
1505 off += dynsym->entsize();
1507 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
1508 p != input_objects->relobj_end();
1511 unsigned int count = (*p)->set_local_dynsym_offset(off);
1512 off += count * dynsym->entsize();
1516 // Create the version sections.
1519 Layout::create_version_sections(const Versions* versions,
1520 const Symbol_table* symtab,
1521 unsigned int local_symcount,
1522 const std::vector<Symbol*>& dynamic_symbols,
1523 const Output_section* dynstr)
1525 if (!versions->any_defs() && !versions->any_needs())
1528 if (parameters->get_size() == 32)
1530 if (parameters->is_big_endian())
1532 #ifdef HAVE_TARGET_32_BIG
1533 this->sized_create_version_sections
1534 SELECT_SIZE_ENDIAN_NAME(32, true)(
1535 versions, symtab, local_symcount, dynamic_symbols, dynstr
1536 SELECT_SIZE_ENDIAN(32, true));
1543 #ifdef HAVE_TARGET_32_LITTLE
1544 this->sized_create_version_sections
1545 SELECT_SIZE_ENDIAN_NAME(32, false)(
1546 versions, symtab, local_symcount, dynamic_symbols, dynstr
1547 SELECT_SIZE_ENDIAN(32, false));
1553 else if (parameters->get_size() == 64)
1555 if (parameters->is_big_endian())
1557 #ifdef HAVE_TARGET_64_BIG
1558 this->sized_create_version_sections
1559 SELECT_SIZE_ENDIAN_NAME(64, true)(
1560 versions, symtab, local_symcount, dynamic_symbols, dynstr
1561 SELECT_SIZE_ENDIAN(64, true));
1568 #ifdef HAVE_TARGET_64_LITTLE
1569 this->sized_create_version_sections
1570 SELECT_SIZE_ENDIAN_NAME(64, false)(
1571 versions, symtab, local_symcount, dynamic_symbols, dynstr
1572 SELECT_SIZE_ENDIAN(64, false));
1582 // Create the version sections, sized version.
1584 template<int size, bool big_endian>
1586 Layout::sized_create_version_sections(
1587 const Versions* versions,
1588 const Symbol_table* symtab,
1589 unsigned int local_symcount,
1590 const std::vector<Symbol*>& dynamic_symbols,
1591 const Output_section* dynstr
1594 const char* vname = this->namepool_.add(".gnu.version", false, NULL);
1595 Output_section* vsec = this->make_output_section(vname,
1596 elfcpp::SHT_GNU_versym,
1599 unsigned char* vbuf;
1601 versions->symbol_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)(
1602 symtab, &this->dynpool_, local_symcount, dynamic_symbols, &vbuf, &vsize
1603 SELECT_SIZE_ENDIAN(size, big_endian));
1605 Output_section_data* vdata = new Output_data_const_buffer(vbuf, vsize, 2);
1607 vsec->add_output_section_data(vdata);
1608 vsec->set_entsize(2);
1609 vsec->set_link_section(this->dynsym_section_);
1611 Output_data_dynamic* const odyn = this->dynamic_data_;
1612 odyn->add_section_address(elfcpp::DT_VERSYM, vsec);
1614 if (versions->any_defs())
1616 const char* vdname = this->namepool_.add(".gnu.version_d", false, NULL);
1617 Output_section *vdsec;
1618 vdsec = this->make_output_section(vdname, elfcpp::SHT_GNU_verdef,
1621 unsigned char* vdbuf;
1622 unsigned int vdsize;
1623 unsigned int vdentries;
1624 versions->def_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)(
1625 &this->dynpool_, &vdbuf, &vdsize, &vdentries
1626 SELECT_SIZE_ENDIAN(size, big_endian));
1628 Output_section_data* vddata = new Output_data_const_buffer(vdbuf,
1632 vdsec->add_output_section_data(vddata);
1633 vdsec->set_link_section(dynstr);
1634 vdsec->set_info(vdentries);
1636 odyn->add_section_address(elfcpp::DT_VERDEF, vdsec);
1637 odyn->add_constant(elfcpp::DT_VERDEFNUM, vdentries);
1640 if (versions->any_needs())
1642 const char* vnname = this->namepool_.add(".gnu.version_r", false, NULL);
1643 Output_section* vnsec;
1644 vnsec = this->make_output_section(vnname, elfcpp::SHT_GNU_verneed,
1647 unsigned char* vnbuf;
1648 unsigned int vnsize;
1649 unsigned int vnentries;
1650 versions->need_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)
1651 (&this->dynpool_, &vnbuf, &vnsize, &vnentries
1652 SELECT_SIZE_ENDIAN(size, big_endian));
1654 Output_section_data* vndata = new Output_data_const_buffer(vnbuf,
1658 vnsec->add_output_section_data(vndata);
1659 vnsec->set_link_section(dynstr);
1660 vnsec->set_info(vnentries);
1662 odyn->add_section_address(elfcpp::DT_VERNEED, vnsec);
1663 odyn->add_constant(elfcpp::DT_VERNEEDNUM, vnentries);
1667 // Create the .interp section and PT_INTERP segment.
1670 Layout::create_interp(const Target* target)
1672 const char* interp = this->options_.dynamic_linker();
1675 interp = target->dynamic_linker();
1676 gold_assert(interp != NULL);
1679 size_t len = strlen(interp) + 1;
1681 Output_section_data* odata = new Output_data_const(interp, len, 1);
1683 const char* interp_name = this->namepool_.add(".interp", false, NULL);
1684 Output_section* osec = this->make_output_section(interp_name,
1685 elfcpp::SHT_PROGBITS,
1687 osec->add_output_section_data(odata);
1689 Output_segment* oseg = new Output_segment(elfcpp::PT_INTERP, elfcpp::PF_R);
1690 this->segment_list_.push_back(oseg);
1691 oseg->add_initial_output_section(osec, elfcpp::PF_R);
1694 // Finish the .dynamic section and PT_DYNAMIC segment.
1697 Layout::finish_dynamic_section(const Input_objects* input_objects,
1698 const Symbol_table* symtab)
1700 Output_segment* oseg = new Output_segment(elfcpp::PT_DYNAMIC,
1701 elfcpp::PF_R | elfcpp::PF_W);
1702 this->segment_list_.push_back(oseg);
1703 oseg->add_initial_output_section(this->dynamic_section_,
1704 elfcpp::PF_R | elfcpp::PF_W);
1706 Output_data_dynamic* const odyn = this->dynamic_data_;
1708 for (Input_objects::Dynobj_iterator p = input_objects->dynobj_begin();
1709 p != input_objects->dynobj_end();
1712 // FIXME: Handle --as-needed.
1713 odyn->add_string(elfcpp::DT_NEEDED, (*p)->soname());
1716 if (parameters->output_is_shared())
1718 const char* soname = this->options_.soname();
1720 odyn->add_string(elfcpp::DT_SONAME, soname);
1723 // FIXME: Support --init and --fini.
1724 Symbol* sym = symtab->lookup("_init");
1725 if (sym != NULL && sym->is_defined() && !sym->is_from_dynobj())
1726 odyn->add_symbol(elfcpp::DT_INIT, sym);
1728 sym = symtab->lookup("_fini");
1729 if (sym != NULL && sym->is_defined() && !sym->is_from_dynobj())
1730 odyn->add_symbol(elfcpp::DT_FINI, sym);
1732 // FIXME: Support DT_INIT_ARRAY and DT_FINI_ARRAY.
1734 // Add a DT_RPATH entry if needed.
1735 const General_options::Dir_list& rpath(this->options_.rpath());
1738 std::string rpath_val;
1739 for (General_options::Dir_list::const_iterator p = rpath.begin();
1743 if (rpath_val.empty())
1744 rpath_val = p->name();
1747 // Eliminate duplicates.
1748 General_options::Dir_list::const_iterator q;
1749 for (q = rpath.begin(); q != p; ++q)
1750 if (q->name() == p->name())
1755 rpath_val += p->name();
1760 odyn->add_string(elfcpp::DT_RPATH, rpath_val);
1763 // Look for text segments that have dynamic relocations.
1764 bool have_textrel = false;
1765 for (Segment_list::const_iterator p = this->segment_list_.begin();
1766 p != this->segment_list_.end();
1769 if (((*p)->flags() & elfcpp::PF_W) == 0
1770 && (*p)->dynamic_reloc_count() > 0)
1772 have_textrel = true;
1777 // Add a DT_FLAGS entry. We add it even if no flags are set so that
1778 // post-link tools can easily modify these flags if desired.
1779 unsigned int flags = 0;
1782 // Add a DT_TEXTREL for compatibility with older loaders.
1783 odyn->add_constant(elfcpp::DT_TEXTREL, 0);
1784 flags |= elfcpp::DF_TEXTREL;
1786 if (parameters->output_is_shared() && this->has_static_tls())
1787 flags |= elfcpp::DF_STATIC_TLS;
1788 odyn->add_constant(elfcpp::DT_FLAGS, flags);
1791 // The mapping of .gnu.linkonce section names to real section names.
1793 #define MAPPING_INIT(f, t) { f, sizeof(f) - 1, t, sizeof(t) - 1 }
1794 const Layout::Linkonce_mapping Layout::linkonce_mapping[] =
1796 MAPPING_INIT("d.rel.ro", ".data.rel.ro"), // Must be before "d".
1797 MAPPING_INIT("t", ".text"),
1798 MAPPING_INIT("r", ".rodata"),
1799 MAPPING_INIT("d", ".data"),
1800 MAPPING_INIT("b", ".bss"),
1801 MAPPING_INIT("s", ".sdata"),
1802 MAPPING_INIT("sb", ".sbss"),
1803 MAPPING_INIT("s2", ".sdata2"),
1804 MAPPING_INIT("sb2", ".sbss2"),
1805 MAPPING_INIT("wi", ".debug_info"),
1806 MAPPING_INIT("td", ".tdata"),
1807 MAPPING_INIT("tb", ".tbss"),
1808 MAPPING_INIT("lr", ".lrodata"),
1809 MAPPING_INIT("l", ".ldata"),
1810 MAPPING_INIT("lb", ".lbss"),
1814 const int Layout::linkonce_mapping_count =
1815 sizeof(Layout::linkonce_mapping) / sizeof(Layout::linkonce_mapping[0]);
1817 // Return the name of the output section to use for a .gnu.linkonce
1818 // section. This is based on the default ELF linker script of the old
1819 // GNU linker. For example, we map a name like ".gnu.linkonce.t.foo"
1820 // to ".text". Set *PLEN to the length of the name. *PLEN is
1821 // initialized to the length of NAME.
1824 Layout::linkonce_output_name(const char* name, size_t *plen)
1826 const char* s = name + sizeof(".gnu.linkonce") - 1;
1830 const Linkonce_mapping* plm = linkonce_mapping;
1831 for (int i = 0; i < linkonce_mapping_count; ++i, ++plm)
1833 if (strncmp(s, plm->from, plm->fromlen) == 0 && s[plm->fromlen] == '.')
1842 // Choose the output section name to use given an input section name.
1843 // Set *PLEN to the length of the name. *PLEN is initialized to the
1847 Layout::output_section_name(const char* name, size_t* plen)
1849 if (Layout::is_linkonce(name))
1851 // .gnu.linkonce sections are laid out as though they were named
1852 // for the sections are placed into.
1853 return Layout::linkonce_output_name(name, plen);
1856 // gcc 4.3 generates the following sorts of section names when it
1857 // needs a section name specific to a function:
1863 // .data.rel.local.FN
1865 // .data.rel.ro.local.FN
1872 // The GNU linker maps all of those to the part before the .FN,
1873 // except that .data.rel.local.FN is mapped to .data, and
1874 // .data.rel.ro.local.FN is mapped to .data.rel.ro. The sections
1875 // beginning with .data.rel.ro.local are grouped together.
1877 // For an anonymous namespace, the string FN can contain a '.'.
1879 // Also of interest: .rodata.strN.N, .rodata.cstN, both of which the
1880 // GNU linker maps to .rodata.
1882 // The .data.rel.ro sections enable a security feature triggered by
1883 // the -z relro option. Section which need to be relocated at
1884 // program startup time but which may be readonly after startup are
1885 // grouped into .data.rel.ro. They are then put into a PT_GNU_RELRO
1886 // segment. The dynamic linker will make that segment writable,
1887 // perform relocations, and then make it read-only. FIXME: We do
1888 // not yet implement this optimization.
1890 // It is hard to handle this in a principled way.
1892 // These are the rules we follow:
1894 // If the section name has no initial '.', or no dot other than an
1895 // initial '.', we use the name unchanged (i.e., "mysection" and
1896 // ".text" are unchanged).
1898 // If the name starts with ".data.rel.ro" we use ".data.rel.ro".
1900 // Otherwise, we drop the second '.' and everything that comes after
1901 // it (i.e., ".text.XXX" becomes ".text").
1903 const char* s = name;
1907 const char* sdot = strchr(s, '.');
1911 const char* const data_rel_ro = ".data.rel.ro";
1912 if (strncmp(name, data_rel_ro, strlen(data_rel_ro)) == 0)
1914 *plen = strlen(data_rel_ro);
1918 *plen = sdot - name;
1922 // Record the signature of a comdat section, and return whether to
1923 // include it in the link. If GROUP is true, this is a regular
1924 // section group. If GROUP is false, this is a group signature
1925 // derived from the name of a linkonce section. We want linkonce
1926 // signatures and group signatures to block each other, but we don't
1927 // want a linkonce signature to block another linkonce signature.
1930 Layout::add_comdat(const char* signature, bool group)
1932 std::string sig(signature);
1933 std::pair<Signatures::iterator, bool> ins(
1934 this->signatures_.insert(std::make_pair(sig, group)));
1938 // This is the first time we've seen this signature.
1942 if (ins.first->second)
1944 // We've already seen a real section group with this signature.
1949 // This is a real section group, and we've already seen a
1950 // linkonce section with this signature. Record that we've seen
1951 // a section group, and don't include this section group.
1952 ins.first->second = true;
1957 // We've already seen a linkonce section and this is a linkonce
1958 // section. These don't block each other--this may be the same
1959 // symbol name with different section types.
1964 // Write out the Output_sections. Most won't have anything to write,
1965 // since most of the data will come from input sections which are
1966 // handled elsewhere. But some Output_sections do have Output_data.
1969 Layout::write_output_sections(Output_file* of) const
1971 for (Section_list::const_iterator p = this->section_list_.begin();
1972 p != this->section_list_.end();
1975 if (!(*p)->after_input_sections())
1980 // Write out data not associated with a section or the symbol table.
1983 Layout::write_data(const Symbol_table* symtab, Output_file* of) const
1985 if (!parameters->strip_all())
1987 const Output_section* symtab_section = this->symtab_section_;
1988 for (Section_list::const_iterator p = this->section_list_.begin();
1989 p != this->section_list_.end();
1992 if ((*p)->needs_symtab_index())
1994 gold_assert(symtab_section != NULL);
1995 unsigned int index = (*p)->symtab_index();
1996 gold_assert(index > 0 && index != -1U);
1997 off_t off = (symtab_section->offset()
1998 + index * symtab_section->entsize());
1999 symtab->write_section_symbol(*p, of, off);
2004 const Output_section* dynsym_section = this->dynsym_section_;
2005 for (Section_list::const_iterator p = this->section_list_.begin();
2006 p != this->section_list_.end();
2009 if ((*p)->needs_dynsym_index())
2011 gold_assert(dynsym_section != NULL);
2012 unsigned int index = (*p)->dynsym_index();
2013 gold_assert(index > 0 && index != -1U);
2014 off_t off = (dynsym_section->offset()
2015 + index * dynsym_section->entsize());
2016 symtab->write_section_symbol(*p, of, off);
2020 // Write out the Output_data which are not in an Output_section.
2021 for (Data_list::const_iterator p = this->special_output_list_.begin();
2022 p != this->special_output_list_.end();
2027 // Write out the Output_sections which can only be written after the
2028 // input sections are complete.
2031 Layout::write_sections_after_input_sections(Output_file* of)
2033 // Determine the final section offsets, and thus the final output
2034 // file size. Note we finalize the .shstrab last, to allow the
2035 // after_input_section sections to modify their section-names before
2037 if (this->any_postprocessing_sections_)
2039 off_t off = this->output_file_size_;
2040 off = this->set_section_offsets(off, POSTPROCESSING_SECTIONS_PASS);
2042 // Now that we've finalized the names, we can finalize the shstrab.
2044 this->set_section_offsets(off,
2045 STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS);
2047 if (off > this->output_file_size_)
2050 this->output_file_size_ = off;
2054 for (Section_list::const_iterator p = this->section_list_.begin();
2055 p != this->section_list_.end();
2058 if ((*p)->after_input_sections())
2062 this->section_headers_->write(of);
2065 // Print statistical information to stderr. This is used for --stats.
2068 Layout::print_stats() const
2070 this->namepool_.print_stats("section name pool");
2071 this->sympool_.print_stats("output symbol name pool");
2072 this->dynpool_.print_stats("dynamic name pool");
2074 for (Section_list::const_iterator p = this->section_list_.begin();
2075 p != this->section_list_.end();
2077 (*p)->print_merge_stats();
2080 // Write_sections_task methods.
2082 // We can always run this task.
2085 Write_sections_task::is_runnable()
2090 // We need to unlock both OUTPUT_SECTIONS_BLOCKER and FINAL_BLOCKER
2094 Write_sections_task::locks(Task_locker* tl)
2096 tl->add(this, this->output_sections_blocker_);
2097 tl->add(this, this->final_blocker_);
2100 // Run the task--write out the data.
2103 Write_sections_task::run(Workqueue*)
2105 this->layout_->write_output_sections(this->of_);
2108 // Write_data_task methods.
2110 // We can always run this task.
2113 Write_data_task::is_runnable()
2118 // We need to unlock FINAL_BLOCKER when finished.
2121 Write_data_task::locks(Task_locker* tl)
2123 tl->add(this, this->final_blocker_);
2126 // Run the task--write out the data.
2129 Write_data_task::run(Workqueue*)
2131 this->layout_->write_data(this->symtab_, this->of_);
2134 // Write_symbols_task methods.
2136 // We can always run this task.
2139 Write_symbols_task::is_runnable()
2144 // We need to unlock FINAL_BLOCKER when finished.
2147 Write_symbols_task::locks(Task_locker* tl)
2149 tl->add(this, this->final_blocker_);
2152 // Run the task--write out the symbols.
2155 Write_symbols_task::run(Workqueue*)
2157 this->symtab_->write_globals(this->input_objects_, this->sympool_,
2158 this->dynpool_, this->of_);
2161 // Write_after_input_sections_task methods.
2163 // We can only run this task after the input sections have completed.
2166 Write_after_input_sections_task::is_runnable()
2168 if (this->input_sections_blocker_->is_blocked())
2169 return this->input_sections_blocker_;
2173 // We need to unlock FINAL_BLOCKER when finished.
2176 Write_after_input_sections_task::locks(Task_locker* tl)
2178 tl->add(this, this->final_blocker_);
2184 Write_after_input_sections_task::run(Workqueue*)
2186 this->layout_->write_sections_after_input_sections(this->of_);
2189 // Close_task_runner methods.
2191 // Run the task--close the file.
2194 Close_task_runner::run(Workqueue*, const Task*)
2199 // Instantiate the templates we need. We could use the configure
2200 // script to restrict this to only the ones for implemented targets.
2202 #ifdef HAVE_TARGET_32_LITTLE
2205 Layout::layout<32, false>(Sized_relobj<32, false>* object, unsigned int shndx,
2207 const elfcpp::Shdr<32, false>& shdr,
2208 unsigned int, unsigned int, off_t*);
2211 #ifdef HAVE_TARGET_32_BIG
2214 Layout::layout<32, true>(Sized_relobj<32, true>* object, unsigned int shndx,
2216 const elfcpp::Shdr<32, true>& shdr,
2217 unsigned int, unsigned int, off_t*);
2220 #ifdef HAVE_TARGET_64_LITTLE
2223 Layout::layout<64, false>(Sized_relobj<64, false>* object, unsigned int shndx,
2225 const elfcpp::Shdr<64, false>& shdr,
2226 unsigned int, unsigned int, off_t*);
2229 #ifdef HAVE_TARGET_64_BIG
2232 Layout::layout<64, true>(Sized_relobj<64, true>* object, unsigned int shndx,
2234 const elfcpp::Shdr<64, true>& shdr,
2235 unsigned int, unsigned int, off_t*);
2238 #ifdef HAVE_TARGET_32_LITTLE
2241 Layout::layout_eh_frame<32, false>(Sized_relobj<32, false>* object,
2242 const unsigned char* symbols,
2244 const unsigned char* symbol_names,
2245 off_t symbol_names_size,
2247 const elfcpp::Shdr<32, false>& shdr,
2248 unsigned int reloc_shndx,
2249 unsigned int reloc_type,
2253 #ifdef HAVE_TARGET_32_BIG
2256 Layout::layout_eh_frame<32, true>(Sized_relobj<32, true>* object,
2257 const unsigned char* symbols,
2259 const unsigned char* symbol_names,
2260 off_t symbol_names_size,
2262 const elfcpp::Shdr<32, true>& shdr,
2263 unsigned int reloc_shndx,
2264 unsigned int reloc_type,
2268 #ifdef HAVE_TARGET_64_LITTLE
2271 Layout::layout_eh_frame<64, false>(Sized_relobj<64, false>* object,
2272 const unsigned char* symbols,
2274 const unsigned char* symbol_names,
2275 off_t symbol_names_size,
2277 const elfcpp::Shdr<64, false>& shdr,
2278 unsigned int reloc_shndx,
2279 unsigned int reloc_type,
2283 #ifdef HAVE_TARGET_64_BIG
2286 Layout::layout_eh_frame<64, true>(Sized_relobj<64, true>* object,
2287 const unsigned char* symbols,
2289 const unsigned char* symbol_names,
2290 off_t symbol_names_size,
2292 const elfcpp::Shdr<64, true>& shdr,
2293 unsigned int reloc_shndx,
2294 unsigned int reloc_type,
2298 } // End namespace gold.