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)
49 off_t file_size = this->layout_->finalize(this->input_objects_,
52 // Now we know the final size of the output file and we know where
53 // each piece of information goes.
54 Output_file* of = new Output_file(this->options_,
55 this->input_objects_->target());
58 // Queue up the final set of tasks.
59 gold::queue_final_tasks(this->options_, this->input_objects_,
60 this->symtab_, this->layout_, workqueue, of);
65 Layout::Layout(const General_options& options)
66 : options_(options), namepool_(), sympool_(), dynpool_(), signatures_(),
67 section_name_map_(), segment_list_(), section_list_(),
68 unattached_section_list_(), special_output_list_(),
69 section_headers_(NULL), tls_segment_(NULL), symtab_section_(NULL),
70 dynsym_section_(NULL), dynamic_section_(NULL), dynamic_data_(NULL),
71 eh_frame_section_(NULL), output_file_size_(-1),
72 input_requires_executable_stack_(false),
73 input_with_gnu_stack_note_(false),
74 input_without_gnu_stack_note_(false)
76 // Make space for more than enough segments for a typical file.
77 // This is just for efficiency--it's OK if we wind up needing more.
78 this->segment_list_.reserve(12);
80 // We expect two unattached Output_data objects: the file header and
81 // the segment headers.
82 this->special_output_list_.reserve(2);
85 // Hash a key we use to look up an output section mapping.
88 Layout::Hash_key::operator()(const Layout::Key& k) const
90 return k.first + k.second.first + k.second.second;
93 // Return whether PREFIX is a prefix of STR.
96 is_prefix_of(const char* prefix, const char* str)
98 return strncmp(prefix, str, strlen(prefix)) == 0;
101 // Returns whether the given section is in the list of
102 // debug-sections-used-by-some-version-of-gdb. Currently,
103 // we've checked versions of gdb up to and including 6.7.1.
105 static const char* gdb_sections[] =
107 // ".debug_aranges", // not used by gdb as of 6.7.1
113 // ".debug_pubnames", // not used by gdb as of 6.7.1
119 is_gdb_debug_section(const char* str)
121 // We can do this faster: binary search or a hashtable. But why bother?
122 for (size_t i = 0; i < sizeof(gdb_sections)/sizeof(*gdb_sections); ++i)
123 if (strcmp(str, gdb_sections[i]) == 0)
128 // Whether to include this section in the link.
130 template<int size, bool big_endian>
132 Layout::include_section(Sized_relobj<size, big_endian>*, const char* name,
133 const elfcpp::Shdr<size, big_endian>& shdr)
135 // Some section types are never linked. Some are only linked when
136 // doing a relocateable link.
137 switch (shdr.get_sh_type())
139 case elfcpp::SHT_NULL:
140 case elfcpp::SHT_SYMTAB:
141 case elfcpp::SHT_DYNSYM:
142 case elfcpp::SHT_STRTAB:
143 case elfcpp::SHT_HASH:
144 case elfcpp::SHT_DYNAMIC:
145 case elfcpp::SHT_SYMTAB_SHNDX:
148 case elfcpp::SHT_RELA:
149 case elfcpp::SHT_REL:
150 case elfcpp::SHT_GROUP:
151 return parameters->output_is_object();
153 case elfcpp::SHT_PROGBITS:
154 if (parameters->strip_debug()
155 && (shdr.get_sh_flags() & elfcpp::SHF_ALLOC) == 0)
157 // Debugging sections can only be recognized by name.
158 if (is_prefix_of(".debug", name)
159 || is_prefix_of(".gnu.linkonce.wi.", name)
160 || is_prefix_of(".line", name)
161 || is_prefix_of(".stab", name))
164 if (parameters->strip_debug_gdb()
165 && (shdr.get_sh_flags() & elfcpp::SHF_ALLOC) == 0)
167 // Debugging sections can only be recognized by name.
168 if (is_prefix_of(".debug", name)
169 && !is_gdb_debug_section(name))
179 // Return an output section named NAME, or NULL if there is none.
182 Layout::find_output_section(const char* name) const
184 for (Section_name_map::const_iterator p = this->section_name_map_.begin();
185 p != this->section_name_map_.end();
187 if (strcmp(p->second->name(), name) == 0)
192 // Return an output segment of type TYPE, with segment flags SET set
193 // and segment flags CLEAR clear. Return NULL if there is none.
196 Layout::find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
197 elfcpp::Elf_Word clear) const
199 for (Segment_list::const_iterator p = this->segment_list_.begin();
200 p != this->segment_list_.end();
202 if (static_cast<elfcpp::PT>((*p)->type()) == type
203 && ((*p)->flags() & set) == set
204 && ((*p)->flags() & clear) == 0)
209 // Return the output section to use for section NAME with type TYPE
210 // and section flags FLAGS.
213 Layout::get_output_section(const char* name, Stringpool::Key name_key,
214 elfcpp::Elf_Word type, elfcpp::Elf_Xword flags)
216 // We should ignore some flags.
217 flags &= ~ (elfcpp::SHF_INFO_LINK
218 | elfcpp::SHF_LINK_ORDER
221 | elfcpp::SHF_STRINGS);
223 const Key key(name_key, std::make_pair(type, flags));
224 const std::pair<Key, Output_section*> v(key, NULL);
225 std::pair<Section_name_map::iterator, bool> ins(
226 this->section_name_map_.insert(v));
229 return ins.first->second;
232 // This is the first time we've seen this name/type/flags
234 Output_section* os = this->make_output_section(name, type, flags);
235 ins.first->second = os;
240 // Return the output section to use for input section SHNDX, with name
241 // NAME, with header HEADER, from object OBJECT. RELOC_SHNDX is the
242 // index of a relocation section which applies to this section, or 0
243 // if none, or -1U if more than one. RELOC_TYPE is the type of the
244 // relocation section if there is one. Set *OFF to the offset of this
245 // input section without the output section. Return NULL if the
246 // section should be discarded. Set *OFF to -1 if the section
247 // contents should not be written directly to the output file, but
248 // will instead receive special handling.
250 template<int size, bool big_endian>
252 Layout::layout(Sized_relobj<size, big_endian>* object, unsigned int shndx,
253 const char* name, const elfcpp::Shdr<size, big_endian>& shdr,
254 unsigned int reloc_shndx, unsigned int, off_t* off)
256 if (!this->include_section(object, name, shdr))
259 // If we are not doing a relocateable link, choose the name to use
260 // for the output section.
261 size_t len = strlen(name);
262 if (!parameters->output_is_object())
263 name = Layout::output_section_name(name, &len);
265 // FIXME: Handle SHF_OS_NONCONFORMING here.
267 // Canonicalize the section name.
268 Stringpool::Key name_key;
269 name = this->namepool_.add_prefix(name, len, &name_key);
271 // Find the output section. The output section is selected based on
272 // the section name, type, and flags.
273 Output_section* os = this->get_output_section(name, name_key,
275 shdr.get_sh_flags());
277 // FIXME: Handle SHF_LINK_ORDER somewhere.
279 *off = os->add_input_section(object, shndx, name, shdr, reloc_shndx);
284 // Special GNU handling of sections name .eh_frame. They will
285 // normally hold exception frame data as defined by the C++ ABI
286 // (http://codesourcery.com/cxx-abi/).
288 template<int size, bool big_endian>
290 Layout::layout_eh_frame(Sized_relobj<size, big_endian>* object,
291 const unsigned char* symbols,
293 const unsigned char* symbol_names,
294 off_t symbol_names_size,
296 const elfcpp::Shdr<size, big_endian>& shdr,
297 unsigned int reloc_shndx, unsigned int reloc_type,
300 gold_assert(shdr.get_sh_type() == elfcpp::SHT_PROGBITS);
301 gold_assert(shdr.get_sh_flags() == elfcpp::SHF_ALLOC);
303 Stringpool::Key name_key;
304 const char* name = this->namepool_.add(".eh_frame", false, &name_key);
306 Output_section* os = this->get_output_section(name, name_key,
307 elfcpp::SHT_PROGBITS,
310 if (this->eh_frame_section_ == NULL)
312 this->eh_frame_section_ = os;
313 this->eh_frame_data_ = new Eh_frame();
314 os->add_output_section_data(this->eh_frame_data_);
316 if (this->options_.create_eh_frame_hdr())
318 Stringpool::Key hdr_name_key;
319 const char* hdr_name = this->namepool_.add(".eh_frame_hdr",
322 Output_section* hdr_os =
323 this->get_output_section(hdr_name, hdr_name_key,
324 elfcpp::SHT_PROGBITS,
327 Eh_frame_hdr* hdr_posd = new Eh_frame_hdr(os, this->eh_frame_data_);
328 hdr_os->add_output_section_data(hdr_posd);
330 hdr_os->set_after_input_sections();
332 Output_segment* hdr_oseg =
333 new Output_segment(elfcpp::PT_GNU_EH_FRAME, elfcpp::PF_R);
334 this->segment_list_.push_back(hdr_oseg);
335 hdr_oseg->add_output_section(hdr_os, elfcpp::PF_R);
337 this->eh_frame_data_->set_eh_frame_hdr(hdr_posd);
341 gold_assert(this->eh_frame_section_ == os);
343 if (this->eh_frame_data_->add_ehframe_input_section(object,
354 // We couldn't handle this .eh_frame section for some reason.
355 // Add it as a normal section.
356 *off = os->add_input_section(object, shndx, name, shdr, reloc_shndx);
362 // Add POSD to an output section using NAME, TYPE, and FLAGS.
365 Layout::add_output_section_data(const char* name, elfcpp::Elf_Word type,
366 elfcpp::Elf_Xword flags,
367 Output_section_data* posd)
369 // Canonicalize the name.
370 Stringpool::Key name_key;
371 name = this->namepool_.add(name, true, &name_key);
373 Output_section* os = this->get_output_section(name, name_key, type, flags);
374 os->add_output_section_data(posd);
377 // Map section flags to segment flags.
380 Layout::section_flags_to_segment(elfcpp::Elf_Xword flags)
382 elfcpp::Elf_Word ret = elfcpp::PF_R;
383 if ((flags & elfcpp::SHF_WRITE) != 0)
385 if ((flags & elfcpp::SHF_EXECINSTR) != 0)
390 // Sometimes we compress sections. This is typically done for
391 // sections that are not part of normal program execution (such as
392 // .debug_* sections), and where the readers of these sections know
393 // how to deal with compressed sections. (To make it easier for them,
394 // we will rename the ouput section in such cases from .foo to
395 // .foo.zlib.nnnn, where nnnn is the uncompressed size.) This routine
396 // doesn't say for certain whether we'll compress -- it depends on
397 // commandline options as well -- just whether this section is a
398 // candidate for compression.
401 is_compressible_debug_section(const char* secname)
403 return (strncmp(secname, ".debug", sizeof(".debug") - 1) == 0);
406 // Make a new Output_section, and attach it to segments as
410 Layout::make_output_section(const char* name, elfcpp::Elf_Word type,
411 elfcpp::Elf_Xword flags)
414 if ((flags & elfcpp::SHF_ALLOC) == 0
415 && this->options_.compress_debug_sections()
416 && is_compressible_debug_section(name))
417 os = new Output_compressed_section(&this->options_, name, type, flags);
419 os = new Output_section(name, type, flags);
421 this->section_list_.push_back(os);
423 if ((flags & elfcpp::SHF_ALLOC) == 0)
424 this->unattached_section_list_.push_back(os);
427 // This output section goes into a PT_LOAD segment.
429 elfcpp::Elf_Word seg_flags = Layout::section_flags_to_segment(flags);
431 // The only thing we really care about for PT_LOAD segments is
432 // whether or not they are writable, so that is how we search
433 // for them. People who need segments sorted on some other
434 // basis will have to wait until we implement a mechanism for
435 // them to describe the segments they want.
437 Segment_list::const_iterator p;
438 for (p = this->segment_list_.begin();
439 p != this->segment_list_.end();
442 if ((*p)->type() == elfcpp::PT_LOAD
443 && ((*p)->flags() & elfcpp::PF_W) == (seg_flags & elfcpp::PF_W))
445 (*p)->add_output_section(os, seg_flags);
450 if (p == this->segment_list_.end())
452 Output_segment* oseg = new Output_segment(elfcpp::PT_LOAD,
454 this->segment_list_.push_back(oseg);
455 oseg->add_output_section(os, seg_flags);
458 // If we see a loadable SHT_NOTE section, we create a PT_NOTE
460 if (type == elfcpp::SHT_NOTE)
462 // See if we already have an equivalent PT_NOTE segment.
463 for (p = this->segment_list_.begin();
464 p != segment_list_.end();
467 if ((*p)->type() == elfcpp::PT_NOTE
468 && (((*p)->flags() & elfcpp::PF_W)
469 == (seg_flags & elfcpp::PF_W)))
471 (*p)->add_output_section(os, seg_flags);
476 if (p == this->segment_list_.end())
478 Output_segment* oseg = new Output_segment(elfcpp::PT_NOTE,
480 this->segment_list_.push_back(oseg);
481 oseg->add_output_section(os, seg_flags);
485 // If we see a loadable SHF_TLS section, we create a PT_TLS
486 // segment. There can only be one such segment.
487 if ((flags & elfcpp::SHF_TLS) != 0)
489 if (this->tls_segment_ == NULL)
491 this->tls_segment_ = new Output_segment(elfcpp::PT_TLS,
493 this->segment_list_.push_back(this->tls_segment_);
495 this->tls_segment_->add_output_section(os, seg_flags);
502 // Handle the .note.GNU-stack section at layout time. SEEN_GNU_STACK
503 // is whether we saw a .note.GNU-stack section in the object file.
504 // GNU_STACK_FLAGS is the section flags. The flags give the
505 // protection required for stack memory. We record this in an
506 // executable as a PT_GNU_STACK segment. If an object file does not
507 // have a .note.GNU-stack segment, we must assume that it is an old
508 // object. On some targets that will force an executable stack.
511 Layout::layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags)
514 this->input_without_gnu_stack_note_ = true;
517 this->input_with_gnu_stack_note_ = true;
518 if ((gnu_stack_flags & elfcpp::SHF_EXECINSTR) != 0)
519 this->input_requires_executable_stack_ = true;
523 // Create the dynamic sections which are needed before we read the
527 Layout::create_initial_dynamic_sections(const Input_objects* input_objects,
528 Symbol_table* symtab)
530 if (parameters->doing_static_link())
533 const char* dynamic_name = this->namepool_.add(".dynamic", false, NULL);
534 this->dynamic_section_ = this->make_output_section(dynamic_name,
537 | elfcpp::SHF_WRITE));
539 symtab->define_in_output_data(input_objects->target(), "_DYNAMIC", NULL,
540 this->dynamic_section_, 0, 0,
541 elfcpp::STT_OBJECT, elfcpp::STB_LOCAL,
542 elfcpp::STV_HIDDEN, 0, false, false);
544 this->dynamic_data_ = new Output_data_dynamic(&this->dynpool_);
546 this->dynamic_section_->add_output_section_data(this->dynamic_data_);
549 // For each output section whose name can be represented as C symbol,
550 // define __start and __stop symbols for the section. This is a GNU
554 Layout::define_section_symbols(Symbol_table* symtab, const Target* target)
556 for (Section_list::const_iterator p = this->section_list_.begin();
557 p != this->section_list_.end();
560 const char* const name = (*p)->name();
561 if (name[strspn(name,
563 "ABCDEFGHIJKLMNOPWRSTUVWXYZ"
564 "abcdefghijklmnopqrstuvwxyz"
568 const std::string name_string(name);
569 const std::string start_name("__start_" + name_string);
570 const std::string stop_name("__stop_" + name_string);
572 symtab->define_in_output_data(target,
582 false, // offset_is_from_end
583 false); // only_if_ref
585 symtab->define_in_output_data(target,
595 true, // offset_is_from_end
596 false); // only_if_ref
601 // Find the first read-only PT_LOAD segment, creating one if
605 Layout::find_first_load_seg()
607 for (Segment_list::const_iterator p = this->segment_list_.begin();
608 p != this->segment_list_.end();
611 if ((*p)->type() == elfcpp::PT_LOAD
612 && ((*p)->flags() & elfcpp::PF_R) != 0
613 && ((*p)->flags() & elfcpp::PF_W) == 0)
617 Output_segment* load_seg = new Output_segment(elfcpp::PT_LOAD, elfcpp::PF_R);
618 this->segment_list_.push_back(load_seg);
622 // Finalize the layout. When this is called, we have created all the
623 // output sections and all the output segments which are based on
624 // input sections. We have several things to do, and we have to do
625 // them in the right order, so that we get the right results correctly
628 // 1) Finalize the list of output segments and create the segment
631 // 2) Finalize the dynamic symbol table and associated sections.
633 // 3) Determine the final file offset of all the output segments.
635 // 4) Determine the final file offset of all the SHF_ALLOC output
638 // 5) Create the symbol table sections and the section name table
641 // 6) Finalize the symbol table: set symbol values to their final
642 // value and make a final determination of which symbols are going
643 // into the output symbol table.
645 // 7) Create the section table header.
647 // 8) Determine the final file offset of all the output sections which
648 // are not SHF_ALLOC, including the section table header.
650 // 9) Finalize the ELF file header.
652 // This function returns the size of the output file.
655 Layout::finalize(const Input_objects* input_objects, Symbol_table* symtab)
657 Target* const target = input_objects->target();
659 target->finalize_sections(this);
661 this->count_local_symbols(input_objects);
663 this->create_gold_note();
664 this->create_executable_stack_info(target);
666 Output_segment* phdr_seg = NULL;
667 if (!parameters->doing_static_link())
669 // There was a dynamic object in the link. We need to create
670 // some information for the dynamic linker.
672 // Create the PT_PHDR segment which will hold the program
674 phdr_seg = new Output_segment(elfcpp::PT_PHDR, elfcpp::PF_R);
675 this->segment_list_.push_back(phdr_seg);
677 // Create the dynamic symbol table, including the hash table.
678 Output_section* dynstr;
679 std::vector<Symbol*> dynamic_symbols;
680 unsigned int local_dynamic_count;
682 this->create_dynamic_symtab(input_objects, target, symtab, &dynstr,
683 &local_dynamic_count, &dynamic_symbols,
686 // Create the .interp section to hold the name of the
687 // interpreter, and put it in a PT_INTERP segment.
688 if (!parameters->output_is_shared())
689 this->create_interp(target);
691 // Finish the .dynamic section to hold the dynamic data, and put
692 // it in a PT_DYNAMIC segment.
693 this->finish_dynamic_section(input_objects, symtab);
695 // We should have added everything we need to the dynamic string
697 this->dynpool_.set_string_offsets();
699 // Create the version sections. We can't do this until the
700 // dynamic string table is complete.
701 this->create_version_sections(&versions, symtab, local_dynamic_count,
702 dynamic_symbols, dynstr);
705 // FIXME: Handle PT_GNU_STACK.
707 Output_segment* load_seg = this->find_first_load_seg();
709 // Lay out the segment headers.
710 Output_segment_headers* segment_headers;
711 segment_headers = new Output_segment_headers(this->segment_list_);
712 load_seg->add_initial_output_data(segment_headers);
713 this->special_output_list_.push_back(segment_headers);
714 if (phdr_seg != NULL)
715 phdr_seg->add_initial_output_data(segment_headers);
717 // Lay out the file header.
718 Output_file_header* file_header;
719 file_header = new Output_file_header(target, symtab, segment_headers);
720 load_seg->add_initial_output_data(file_header);
721 this->special_output_list_.push_back(file_header);
723 // We set the output section indexes in set_segment_offsets and
724 // set_section_indexes.
725 unsigned int shndx = 1;
727 // Set the file offsets of all the segments, and all the sections
729 off_t off = this->set_segment_offsets(target, load_seg, &shndx);
731 // Create the symbol table sections.
732 this->create_symtab_sections(input_objects, symtab, &off);
733 if (!parameters->doing_static_link())
734 this->assign_local_dynsym_offsets(input_objects);
736 // Create the .shstrtab section.
737 Output_section* shstrtab_section = this->create_shstrtab();
739 // Set the file offsets of all the non-data sections which don't
740 // have to wait for the input sections.
741 off = this->set_section_offsets(off, BEFORE_INPUT_SECTIONS_PASS);
743 // Now that all sections have been created, set the section indexes.
744 shndx = this->set_section_indexes(shndx);
746 // Create the section table header.
747 this->create_shdrs(&off);
749 file_header->set_section_info(this->section_headers_, shstrtab_section);
751 // Now we know exactly where everything goes in the output file
752 // (except for non-allocated sections which require postprocessing).
753 Output_data::layout_complete();
755 this->output_file_size_ = off;
760 // Create a .note section for an executable or shared library. This
761 // records the version of gold used to create the binary.
764 Layout::create_gold_note()
766 if (parameters->output_is_object())
769 // Authorities all agree that the values in a .note field should
770 // be aligned on 4-byte boundaries for 32-bit binaries. However,
771 // they differ on what the alignment is for 64-bit binaries.
772 // The GABI says unambiguously they take 8-byte alignment:
773 // http://sco.com/developers/gabi/latest/ch5.pheader.html#note_section
774 // Other documentation says alignment should always be 4 bytes:
775 // http://www.netbsd.org/docs/kernel/elf-notes.html#note-format
776 // GNU ld and GNU readelf both support the latter (at least as of
777 // version 2.16.91), and glibc always generates the latter for
778 // .note.ABI-tag (as of version 1.6), so that's the one we go with
780 #ifdef GABI_FORMAT_FOR_DOTNOTE_SECTION // This is not defined by default.
781 const int size = parameters->get_size();
786 // The contents of the .note section.
787 const char* name = "GNU";
788 std::string desc(std::string("gold ") + gold::get_version_string());
789 size_t namesz = strlen(name) + 1;
790 size_t aligned_namesz = align_address(namesz, size / 8);
791 size_t descsz = desc.length() + 1;
792 size_t aligned_descsz = align_address(descsz, size / 8);
793 const int note_type = 4;
795 size_t notesz = 3 * (size / 8) + aligned_namesz + aligned_descsz;
797 unsigned char buffer[128];
798 gold_assert(sizeof buffer >= notesz);
799 memset(buffer, 0, notesz);
801 bool is_big_endian = parameters->is_big_endian();
807 elfcpp::Swap<32, false>::writeval(buffer, namesz);
808 elfcpp::Swap<32, false>::writeval(buffer + 4, descsz);
809 elfcpp::Swap<32, false>::writeval(buffer + 8, note_type);
813 elfcpp::Swap<32, true>::writeval(buffer, namesz);
814 elfcpp::Swap<32, true>::writeval(buffer + 4, descsz);
815 elfcpp::Swap<32, true>::writeval(buffer + 8, note_type);
822 elfcpp::Swap<64, false>::writeval(buffer, namesz);
823 elfcpp::Swap<64, false>::writeval(buffer + 8, descsz);
824 elfcpp::Swap<64, false>::writeval(buffer + 16, note_type);
828 elfcpp::Swap<64, true>::writeval(buffer, namesz);
829 elfcpp::Swap<64, true>::writeval(buffer + 8, descsz);
830 elfcpp::Swap<64, true>::writeval(buffer + 16, note_type);
836 memcpy(buffer + 3 * (size / 8), name, namesz);
837 memcpy(buffer + 3 * (size / 8) + aligned_namesz, desc.data(), descsz);
839 const char* note_name = this->namepool_.add(".note", false, NULL);
840 Output_section* os = this->make_output_section(note_name,
843 Output_section_data* posd = new Output_data_const(buffer, notesz,
845 os->add_output_section_data(posd);
848 // Record whether the stack should be executable. This can be set
849 // from the command line using the -z execstack or -z noexecstack
850 // options. Otherwise, if any input file has a .note.GNU-stack
851 // section with the SHF_EXECINSTR flag set, the stack should be
852 // executable. Otherwise, if at least one input file a
853 // .note.GNU-stack section, and some input file has no .note.GNU-stack
854 // section, we use the target default for whether the stack should be
855 // executable. Otherwise, we don't generate a stack note. When
856 // generating a object file, we create a .note.GNU-stack section with
857 // the appropriate marking. When generating an executable or shared
858 // library, we create a PT_GNU_STACK segment.
861 Layout::create_executable_stack_info(const Target* target)
863 bool is_stack_executable;
864 if (this->options_.is_execstack_set())
865 is_stack_executable = this->options_.is_stack_executable();
866 else if (!this->input_with_gnu_stack_note_)
870 if (this->input_requires_executable_stack_)
871 is_stack_executable = true;
872 else if (this->input_without_gnu_stack_note_)
873 is_stack_executable = target->is_default_stack_executable();
875 is_stack_executable = false;
878 if (parameters->output_is_object())
880 const char* name = this->namepool_.add(".note.GNU-stack", false, NULL);
881 elfcpp::Elf_Xword flags = 0;
882 if (is_stack_executable)
883 flags |= elfcpp::SHF_EXECINSTR;
884 this->make_output_section(name, elfcpp::SHT_PROGBITS, flags);
888 int flags = elfcpp::PF_R | elfcpp::PF_W;
889 if (is_stack_executable)
890 flags |= elfcpp::PF_X;
891 Output_segment* oseg = new Output_segment(elfcpp::PT_GNU_STACK, flags);
892 this->segment_list_.push_back(oseg);
896 // Return whether SEG1 should be before SEG2 in the output file. This
897 // is based entirely on the segment type and flags. When this is
898 // called the segment addresses has normally not yet been set.
901 Layout::segment_precedes(const Output_segment* seg1,
902 const Output_segment* seg2)
904 elfcpp::Elf_Word type1 = seg1->type();
905 elfcpp::Elf_Word type2 = seg2->type();
907 // The single PT_PHDR segment is required to precede any loadable
908 // segment. We simply make it always first.
909 if (type1 == elfcpp::PT_PHDR)
911 gold_assert(type2 != elfcpp::PT_PHDR);
914 if (type2 == elfcpp::PT_PHDR)
917 // The single PT_INTERP segment is required to precede any loadable
918 // segment. We simply make it always second.
919 if (type1 == elfcpp::PT_INTERP)
921 gold_assert(type2 != elfcpp::PT_INTERP);
924 if (type2 == elfcpp::PT_INTERP)
927 // We then put PT_LOAD segments before any other segments.
928 if (type1 == elfcpp::PT_LOAD && type2 != elfcpp::PT_LOAD)
930 if (type2 == elfcpp::PT_LOAD && type1 != elfcpp::PT_LOAD)
933 // We put the PT_TLS segment last, because that is where the dynamic
934 // linker expects to find it (this is just for efficiency; other
935 // positions would also work correctly).
936 if (type1 == elfcpp::PT_TLS && type2 != elfcpp::PT_TLS)
938 if (type2 == elfcpp::PT_TLS && type1 != elfcpp::PT_TLS)
941 const elfcpp::Elf_Word flags1 = seg1->flags();
942 const elfcpp::Elf_Word flags2 = seg2->flags();
944 // The order of non-PT_LOAD segments is unimportant. We simply sort
945 // by the numeric segment type and flags values. There should not
946 // be more than one segment with the same type and flags.
947 if (type1 != elfcpp::PT_LOAD)
950 return type1 < type2;
951 gold_assert(flags1 != flags2);
952 return flags1 < flags2;
955 // We sort PT_LOAD segments based on the flags. Readonly segments
956 // come before writable segments. Then executable segments come
957 // before non-executable segments. Then the unlikely case of a
958 // non-readable segment comes before the normal case of a readable
959 // segment. If there are multiple segments with the same type and
960 // flags, we require that the address be set, and we sort by
961 // virtual address and then physical address.
962 if ((flags1 & elfcpp::PF_W) != (flags2 & elfcpp::PF_W))
963 return (flags1 & elfcpp::PF_W) == 0;
964 if ((flags1 & elfcpp::PF_X) != (flags2 & elfcpp::PF_X))
965 return (flags1 & elfcpp::PF_X) != 0;
966 if ((flags1 & elfcpp::PF_R) != (flags2 & elfcpp::PF_R))
967 return (flags1 & elfcpp::PF_R) == 0;
969 uint64_t vaddr1 = seg1->vaddr();
970 uint64_t vaddr2 = seg2->vaddr();
971 if (vaddr1 != vaddr2)
972 return vaddr1 < vaddr2;
974 uint64_t paddr1 = seg1->paddr();
975 uint64_t paddr2 = seg2->paddr();
976 gold_assert(paddr1 != paddr2);
977 return paddr1 < paddr2;
980 // Set the file offsets of all the segments, and all the sections they
981 // contain. They have all been created. LOAD_SEG must be be laid out
982 // first. Return the offset of the data to follow.
985 Layout::set_segment_offsets(const Target* target, Output_segment* load_seg,
986 unsigned int *pshndx)
988 // Sort them into the final order.
989 std::sort(this->segment_list_.begin(), this->segment_list_.end(),
990 Layout::Compare_segments());
992 // Find the PT_LOAD segments, and set their addresses and offsets
993 // and their section's addresses and offsets.
995 if (parameters->output_is_shared())
997 else if (options_.user_set_text_segment_address())
998 addr = options_.text_segment_address();
1000 addr = target->default_text_segment_address();
1002 bool was_readonly = false;
1003 for (Segment_list::iterator p = this->segment_list_.begin();
1004 p != this->segment_list_.end();
1007 if ((*p)->type() == elfcpp::PT_LOAD)
1009 if (load_seg != NULL && load_seg != *p)
1013 // If the last segment was readonly, and this one is not,
1014 // then skip the address forward one page, maintaining the
1015 // same position within the page. This lets us store both
1016 // segments overlapping on a single page in the file, but
1017 // the loader will put them on different pages in memory.
1019 uint64_t orig_addr = addr;
1020 uint64_t orig_off = off;
1022 uint64_t aligned_addr = addr;
1023 uint64_t abi_pagesize = target->abi_pagesize();
1025 // FIXME: This should depend on the -n and -N options.
1026 (*p)->set_minimum_addralign(target->common_pagesize());
1028 if (was_readonly && ((*p)->flags() & elfcpp::PF_W) != 0)
1030 uint64_t align = (*p)->addralign();
1032 addr = align_address(addr, align);
1033 aligned_addr = addr;
1034 if ((addr & (abi_pagesize - 1)) != 0)
1035 addr = addr + abi_pagesize;
1038 unsigned int shndx_hold = *pshndx;
1039 off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1));
1040 uint64_t new_addr = (*p)->set_section_addresses(addr, &off, pshndx);
1042 // Now that we know the size of this segment, we may be able
1043 // to save a page in memory, at the cost of wasting some
1044 // file space, by instead aligning to the start of a new
1045 // page. Here we use the real machine page size rather than
1046 // the ABI mandated page size.
1048 if (aligned_addr != addr)
1050 uint64_t common_pagesize = target->common_pagesize();
1051 uint64_t first_off = (common_pagesize
1053 & (common_pagesize - 1)));
1054 uint64_t last_off = new_addr & (common_pagesize - 1);
1057 && ((aligned_addr & ~ (common_pagesize - 1))
1058 != (new_addr & ~ (common_pagesize - 1)))
1059 && first_off + last_off <= common_pagesize)
1061 *pshndx = shndx_hold;
1062 addr = align_address(aligned_addr, common_pagesize);
1063 off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1));
1064 new_addr = (*p)->set_section_addresses(addr, &off, pshndx);
1070 if (((*p)->flags() & elfcpp::PF_W) == 0)
1071 was_readonly = true;
1075 // Handle the non-PT_LOAD segments, setting their offsets from their
1076 // section's offsets.
1077 for (Segment_list::iterator p = this->segment_list_.begin();
1078 p != this->segment_list_.end();
1081 if ((*p)->type() != elfcpp::PT_LOAD)
1085 // Set the TLS offsets for each section in the PT_TLS segment.
1086 if (this->tls_segment_ != NULL)
1087 this->tls_segment_->set_tls_offsets();
1092 // Set the file offset of all the sections not associated with a
1096 Layout::set_section_offsets(off_t off, Layout::Section_offset_pass pass)
1098 for (Section_list::iterator p = this->unattached_section_list_.begin();
1099 p != this->unattached_section_list_.end();
1102 // The symtab section is handled in create_symtab_sections.
1103 if (*p == this->symtab_section_)
1106 if (pass == BEFORE_INPUT_SECTIONS_PASS
1107 && (*p)->requires_postprocessing())
1108 (*p)->create_postprocessing_buffer();
1110 if (pass == BEFORE_INPUT_SECTIONS_PASS
1111 && (*p)->after_input_sections())
1113 else if (pass == AFTER_INPUT_SECTIONS_PASS
1114 && (!(*p)->after_input_sections()
1115 || (*p)->type() == elfcpp::SHT_STRTAB))
1117 else if (pass == STRTAB_AFTER_INPUT_SECTIONS_PASS
1118 && (!(*p)->after_input_sections()
1119 || (*p)->type() != elfcpp::SHT_STRTAB))
1122 off = align_address(off, (*p)->addralign());
1123 (*p)->set_file_offset(off);
1124 (*p)->finalize_data_size();
1125 off += (*p)->data_size();
1127 // At this point the name must be set.
1128 if (pass != STRTAB_AFTER_INPUT_SECTIONS_PASS)
1129 this->namepool_.add((*p)->name(), false, NULL);
1134 // Set the section indexes of all the sections not associated with a
1138 Layout::set_section_indexes(unsigned int shndx)
1140 for (Section_list::iterator p = this->unattached_section_list_.begin();
1141 p != this->unattached_section_list_.end();
1144 (*p)->set_out_shndx(shndx);
1150 // Count the local symbols in the regular symbol table and the dynamic
1151 // symbol table, and build the respective string pools.
1154 Layout::count_local_symbols(const Input_objects* input_objects)
1156 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
1157 p != input_objects->relobj_end();
1160 Task_lock_obj<Object> tlo(**p);
1161 (*p)->count_local_symbols(&this->sympool_, &this->dynpool_);
1165 // Create the symbol table sections. Here we also set the final
1166 // values of the symbols. At this point all the loadable sections are
1170 Layout::create_symtab_sections(const Input_objects* input_objects,
1171 Symbol_table* symtab,
1176 if (parameters->get_size() == 32)
1178 symsize = elfcpp::Elf_sizes<32>::sym_size;
1181 else if (parameters->get_size() == 64)
1183 symsize = elfcpp::Elf_sizes<64>::sym_size;
1190 off = align_address(off, align);
1191 off_t startoff = off;
1193 // Save space for the dummy symbol at the start of the section. We
1194 // never bother to write this out--it will just be left as zero.
1196 unsigned int local_symbol_index = 1;
1198 // Add STT_SECTION symbols for each Output section which needs one.
1199 for (Section_list::iterator p = this->section_list_.begin();
1200 p != this->section_list_.end();
1203 if (!(*p)->needs_symtab_index())
1204 (*p)->set_symtab_index(-1U);
1207 (*p)->set_symtab_index(local_symbol_index);
1208 ++local_symbol_index;
1213 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
1214 p != input_objects->relobj_end();
1217 unsigned int index = (*p)->finalize_local_symbols(local_symbol_index,
1219 off += (index - local_symbol_index) * symsize;
1220 local_symbol_index = index;
1223 unsigned int local_symcount = local_symbol_index;
1224 gold_assert(local_symcount * symsize == off - startoff);
1227 size_t dyn_global_index;
1229 if (this->dynsym_section_ == NULL)
1232 dyn_global_index = 0;
1237 dyn_global_index = this->dynsym_section_->info();
1238 off_t locsize = dyn_global_index * this->dynsym_section_->entsize();
1239 dynoff = this->dynsym_section_->offset() + locsize;
1240 dyncount = (this->dynsym_section_->data_size() - locsize) / symsize;
1241 gold_assert(static_cast<off_t>(dyncount * symsize)
1242 == this->dynsym_section_->data_size() - locsize);
1245 off = symtab->finalize(local_symcount, off, dynoff, dyn_global_index,
1246 dyncount, &this->sympool_);
1248 if (!parameters->strip_all())
1250 this->sympool_.set_string_offsets();
1252 const char* symtab_name = this->namepool_.add(".symtab", false, NULL);
1253 Output_section* osymtab = this->make_output_section(symtab_name,
1256 this->symtab_section_ = osymtab;
1258 Output_section_data* pos = new Output_data_fixed_space(off - startoff,
1260 osymtab->add_output_section_data(pos);
1262 const char* strtab_name = this->namepool_.add(".strtab", false, NULL);
1263 Output_section* ostrtab = this->make_output_section(strtab_name,
1267 Output_section_data* pstr = new Output_data_strtab(&this->sympool_);
1268 ostrtab->add_output_section_data(pstr);
1270 osymtab->set_file_offset(startoff);
1271 osymtab->finalize_data_size();
1272 osymtab->set_link_section(ostrtab);
1273 osymtab->set_info(local_symcount);
1274 osymtab->set_entsize(symsize);
1280 // Create the .shstrtab section, which holds the names of the
1281 // sections. At the time this is called, we have created all the
1282 // output sections except .shstrtab itself.
1285 Layout::create_shstrtab()
1287 // FIXME: We don't need to create a .shstrtab section if we are
1288 // stripping everything.
1290 const char* name = this->namepool_.add(".shstrtab", false, NULL);
1292 Output_section* os = this->make_output_section(name, elfcpp::SHT_STRTAB, 0);
1294 // We can't write out this section until we've set all the section
1295 // names, and we don't set the names of compressed output sections
1296 // until relocations are complete.
1297 os->set_after_input_sections();
1299 Output_section_data* posd = new Output_data_strtab(&this->namepool_);
1300 os->add_output_section_data(posd);
1305 // Create the section headers. SIZE is 32 or 64. OFF is the file
1309 Layout::create_shdrs(off_t* poff)
1311 Output_section_headers* oshdrs;
1312 oshdrs = new Output_section_headers(this,
1313 &this->segment_list_,
1314 &this->unattached_section_list_,
1316 off_t off = align_address(*poff, oshdrs->addralign());
1317 oshdrs->set_address_and_file_offset(0, off);
1318 off += oshdrs->data_size();
1320 this->section_headers_ = oshdrs;
1323 // Create the dynamic symbol table.
1326 Layout::create_dynamic_symtab(const Input_objects* input_objects,
1327 const Target* target, Symbol_table* symtab,
1328 Output_section **pdynstr,
1329 unsigned int* plocal_dynamic_count,
1330 std::vector<Symbol*>* pdynamic_symbols,
1331 Versions* pversions)
1333 // Count all the symbols in the dynamic symbol table, and set the
1334 // dynamic symbol indexes.
1336 // Skip symbol 0, which is always all zeroes.
1337 unsigned int index = 1;
1339 // Add STT_SECTION symbols for each Output section which needs one.
1340 for (Section_list::iterator p = this->section_list_.begin();
1341 p != this->section_list_.end();
1344 if (!(*p)->needs_dynsym_index())
1345 (*p)->set_dynsym_index(-1U);
1348 (*p)->set_dynsym_index(index);
1353 // Count the local symbols that need to go in the dynamic symbol table,
1354 // and set the dynamic symbol indexes.
1355 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
1356 p != input_objects->relobj_end();
1359 unsigned int new_index = (*p)->set_local_dynsym_indexes(index);
1363 unsigned int local_symcount = index;
1364 *plocal_dynamic_count = local_symcount;
1366 // FIXME: We have to tell set_dynsym_indexes whether the
1367 // -E/--export-dynamic option was used.
1368 index = symtab->set_dynsym_indexes(target, index, pdynamic_symbols,
1369 &this->dynpool_, pversions);
1373 const int size = parameters->get_size();
1376 symsize = elfcpp::Elf_sizes<32>::sym_size;
1379 else if (size == 64)
1381 symsize = elfcpp::Elf_sizes<64>::sym_size;
1387 // Create the dynamic symbol table section.
1389 const char* dynsym_name = this->namepool_.add(".dynsym", false, NULL);
1390 Output_section* dynsym = this->make_output_section(dynsym_name,
1394 Output_section_data* odata = new Output_data_fixed_space(index * symsize,
1396 dynsym->add_output_section_data(odata);
1398 dynsym->set_info(local_symcount);
1399 dynsym->set_entsize(symsize);
1400 dynsym->set_addralign(align);
1402 this->dynsym_section_ = dynsym;
1404 Output_data_dynamic* const odyn = this->dynamic_data_;
1405 odyn->add_section_address(elfcpp::DT_SYMTAB, dynsym);
1406 odyn->add_constant(elfcpp::DT_SYMENT, symsize);
1408 // Create the dynamic string table section.
1410 const char* dynstr_name = this->namepool_.add(".dynstr", false, NULL);
1411 Output_section* dynstr = this->make_output_section(dynstr_name,
1415 Output_section_data* strdata = new Output_data_strtab(&this->dynpool_);
1416 dynstr->add_output_section_data(strdata);
1418 dynsym->set_link_section(dynstr);
1419 this->dynamic_section_->set_link_section(dynstr);
1421 odyn->add_section_address(elfcpp::DT_STRTAB, dynstr);
1422 odyn->add_section_size(elfcpp::DT_STRSZ, dynstr);
1426 // Create the hash tables.
1428 // FIXME: We need an option to create a GNU hash table.
1430 unsigned char* phash;
1431 unsigned int hashlen;
1432 Dynobj::create_elf_hash_table(*pdynamic_symbols, local_symcount,
1435 const char* hash_name = this->namepool_.add(".hash", false, NULL);
1436 Output_section* hashsec = this->make_output_section(hash_name,
1440 Output_section_data* hashdata = new Output_data_const_buffer(phash,
1443 hashsec->add_output_section_data(hashdata);
1445 hashsec->set_link_section(dynsym);
1446 hashsec->set_entsize(4);
1448 odyn->add_section_address(elfcpp::DT_HASH, hashsec);
1451 // Assign offsets to each local portion of the dynamic symbol table.
1454 Layout::assign_local_dynsym_offsets(const Input_objects* input_objects)
1456 Output_section* dynsym = this->dynsym_section_;
1457 gold_assert(dynsym != NULL);
1459 off_t off = dynsym->offset();
1461 // Skip the dummy symbol at the start of the section.
1462 off += dynsym->entsize();
1464 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
1465 p != input_objects->relobj_end();
1468 unsigned int count = (*p)->set_local_dynsym_offset(off);
1469 off += count * dynsym->entsize();
1473 // Create the version sections.
1476 Layout::create_version_sections(const Versions* versions,
1477 const Symbol_table* symtab,
1478 unsigned int local_symcount,
1479 const std::vector<Symbol*>& dynamic_symbols,
1480 const Output_section* dynstr)
1482 if (!versions->any_defs() && !versions->any_needs())
1485 if (parameters->get_size() == 32)
1487 if (parameters->is_big_endian())
1489 #ifdef HAVE_TARGET_32_BIG
1490 this->sized_create_version_sections
1491 SELECT_SIZE_ENDIAN_NAME(32, true)(
1492 versions, symtab, local_symcount, dynamic_symbols, dynstr
1493 SELECT_SIZE_ENDIAN(32, true));
1500 #ifdef HAVE_TARGET_32_LITTLE
1501 this->sized_create_version_sections
1502 SELECT_SIZE_ENDIAN_NAME(32, false)(
1503 versions, symtab, local_symcount, dynamic_symbols, dynstr
1504 SELECT_SIZE_ENDIAN(32, false));
1510 else if (parameters->get_size() == 64)
1512 if (parameters->is_big_endian())
1514 #ifdef HAVE_TARGET_64_BIG
1515 this->sized_create_version_sections
1516 SELECT_SIZE_ENDIAN_NAME(64, true)(
1517 versions, symtab, local_symcount, dynamic_symbols, dynstr
1518 SELECT_SIZE_ENDIAN(64, true));
1525 #ifdef HAVE_TARGET_64_LITTLE
1526 this->sized_create_version_sections
1527 SELECT_SIZE_ENDIAN_NAME(64, false)(
1528 versions, symtab, local_symcount, dynamic_symbols, dynstr
1529 SELECT_SIZE_ENDIAN(64, false));
1539 // Create the version sections, sized version.
1541 template<int size, bool big_endian>
1543 Layout::sized_create_version_sections(
1544 const Versions* versions,
1545 const Symbol_table* symtab,
1546 unsigned int local_symcount,
1547 const std::vector<Symbol*>& dynamic_symbols,
1548 const Output_section* dynstr
1551 const char* vname = this->namepool_.add(".gnu.version", false, NULL);
1552 Output_section* vsec = this->make_output_section(vname,
1553 elfcpp::SHT_GNU_versym,
1556 unsigned char* vbuf;
1558 versions->symbol_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)(
1559 symtab, &this->dynpool_, local_symcount, dynamic_symbols, &vbuf, &vsize
1560 SELECT_SIZE_ENDIAN(size, big_endian));
1562 Output_section_data* vdata = new Output_data_const_buffer(vbuf, vsize, 2);
1564 vsec->add_output_section_data(vdata);
1565 vsec->set_entsize(2);
1566 vsec->set_link_section(this->dynsym_section_);
1568 Output_data_dynamic* const odyn = this->dynamic_data_;
1569 odyn->add_section_address(elfcpp::DT_VERSYM, vsec);
1571 if (versions->any_defs())
1573 const char* vdname = this->namepool_.add(".gnu.version_d", false, NULL);
1574 Output_section *vdsec;
1575 vdsec = this->make_output_section(vdname, elfcpp::SHT_GNU_verdef,
1578 unsigned char* vdbuf;
1579 unsigned int vdsize;
1580 unsigned int vdentries;
1581 versions->def_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)(
1582 &this->dynpool_, &vdbuf, &vdsize, &vdentries
1583 SELECT_SIZE_ENDIAN(size, big_endian));
1585 Output_section_data* vddata = new Output_data_const_buffer(vdbuf,
1589 vdsec->add_output_section_data(vddata);
1590 vdsec->set_link_section(dynstr);
1591 vdsec->set_info(vdentries);
1593 odyn->add_section_address(elfcpp::DT_VERDEF, vdsec);
1594 odyn->add_constant(elfcpp::DT_VERDEFNUM, vdentries);
1597 if (versions->any_needs())
1599 const char* vnname = this->namepool_.add(".gnu.version_r", false, NULL);
1600 Output_section* vnsec;
1601 vnsec = this->make_output_section(vnname, elfcpp::SHT_GNU_verneed,
1604 unsigned char* vnbuf;
1605 unsigned int vnsize;
1606 unsigned int vnentries;
1607 versions->need_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)
1608 (&this->dynpool_, &vnbuf, &vnsize, &vnentries
1609 SELECT_SIZE_ENDIAN(size, big_endian));
1611 Output_section_data* vndata = new Output_data_const_buffer(vnbuf,
1615 vnsec->add_output_section_data(vndata);
1616 vnsec->set_link_section(dynstr);
1617 vnsec->set_info(vnentries);
1619 odyn->add_section_address(elfcpp::DT_VERNEED, vnsec);
1620 odyn->add_constant(elfcpp::DT_VERNEEDNUM, vnentries);
1624 // Create the .interp section and PT_INTERP segment.
1627 Layout::create_interp(const Target* target)
1629 const char* interp = this->options_.dynamic_linker();
1632 interp = target->dynamic_linker();
1633 gold_assert(interp != NULL);
1636 size_t len = strlen(interp) + 1;
1638 Output_section_data* odata = new Output_data_const(interp, len, 1);
1640 const char* interp_name = this->namepool_.add(".interp", false, NULL);
1641 Output_section* osec = this->make_output_section(interp_name,
1642 elfcpp::SHT_PROGBITS,
1644 osec->add_output_section_data(odata);
1646 Output_segment* oseg = new Output_segment(elfcpp::PT_INTERP, elfcpp::PF_R);
1647 this->segment_list_.push_back(oseg);
1648 oseg->add_initial_output_section(osec, elfcpp::PF_R);
1651 // Finish the .dynamic section and PT_DYNAMIC segment.
1654 Layout::finish_dynamic_section(const Input_objects* input_objects,
1655 const Symbol_table* symtab)
1657 Output_segment* oseg = new Output_segment(elfcpp::PT_DYNAMIC,
1658 elfcpp::PF_R | elfcpp::PF_W);
1659 this->segment_list_.push_back(oseg);
1660 oseg->add_initial_output_section(this->dynamic_section_,
1661 elfcpp::PF_R | elfcpp::PF_W);
1663 Output_data_dynamic* const odyn = this->dynamic_data_;
1665 for (Input_objects::Dynobj_iterator p = input_objects->dynobj_begin();
1666 p != input_objects->dynobj_end();
1669 // FIXME: Handle --as-needed.
1670 odyn->add_string(elfcpp::DT_NEEDED, (*p)->soname());
1673 // FIXME: Support --init and --fini.
1674 Symbol* sym = symtab->lookup("_init");
1675 if (sym != NULL && sym->is_defined() && !sym->is_from_dynobj())
1676 odyn->add_symbol(elfcpp::DT_INIT, sym);
1678 sym = symtab->lookup("_fini");
1679 if (sym != NULL && sym->is_defined() && !sym->is_from_dynobj())
1680 odyn->add_symbol(elfcpp::DT_FINI, sym);
1682 // FIXME: Support DT_INIT_ARRAY and DT_FINI_ARRAY.
1684 // Add a DT_RPATH entry if needed.
1685 const General_options::Dir_list& rpath(this->options_.rpath());
1688 std::string rpath_val;
1689 for (General_options::Dir_list::const_iterator p = rpath.begin();
1693 if (rpath_val.empty())
1694 rpath_val = p->name();
1697 // Eliminate duplicates.
1698 General_options::Dir_list::const_iterator q;
1699 for (q = rpath.begin(); q != p; ++q)
1700 if (q->name() == p->name())
1705 rpath_val += p->name();
1710 odyn->add_string(elfcpp::DT_RPATH, rpath_val);
1713 // Look for text segments that have dynamic relocations.
1714 bool have_textrel = false;
1715 for (Segment_list::const_iterator p = this->segment_list_.begin();
1716 p != this->segment_list_.end();
1719 if (((*p)->flags() & elfcpp::PF_W) == 0
1720 && (*p)->dynamic_reloc_count() > 0)
1722 have_textrel = true;
1727 // Add a DT_FLAGS entry. We add it even if no flags are set so that
1728 // post-link tools can easily modify these flags if desired.
1729 unsigned int flags = 0;
1732 // Add a DT_TEXTREL for compatibility with older loaders.
1733 odyn->add_constant(elfcpp::DT_TEXTREL, 0);
1734 flags |= elfcpp::DF_TEXTREL;
1736 odyn->add_constant(elfcpp::DT_FLAGS, flags);
1739 // The mapping of .gnu.linkonce section names to real section names.
1741 #define MAPPING_INIT(f, t) { f, sizeof(f) - 1, t, sizeof(t) - 1 }
1742 const Layout::Linkonce_mapping Layout::linkonce_mapping[] =
1744 MAPPING_INIT("d.rel.ro", ".data.rel.ro"), // Must be before "d".
1745 MAPPING_INIT("t", ".text"),
1746 MAPPING_INIT("r", ".rodata"),
1747 MAPPING_INIT("d", ".data"),
1748 MAPPING_INIT("b", ".bss"),
1749 MAPPING_INIT("s", ".sdata"),
1750 MAPPING_INIT("sb", ".sbss"),
1751 MAPPING_INIT("s2", ".sdata2"),
1752 MAPPING_INIT("sb2", ".sbss2"),
1753 MAPPING_INIT("wi", ".debug_info"),
1754 MAPPING_INIT("td", ".tdata"),
1755 MAPPING_INIT("tb", ".tbss"),
1756 MAPPING_INIT("lr", ".lrodata"),
1757 MAPPING_INIT("l", ".ldata"),
1758 MAPPING_INIT("lb", ".lbss"),
1762 const int Layout::linkonce_mapping_count =
1763 sizeof(Layout::linkonce_mapping) / sizeof(Layout::linkonce_mapping[0]);
1765 // Return the name of the output section to use for a .gnu.linkonce
1766 // section. This is based on the default ELF linker script of the old
1767 // GNU linker. For example, we map a name like ".gnu.linkonce.t.foo"
1768 // to ".text". Set *PLEN to the length of the name. *PLEN is
1769 // initialized to the length of NAME.
1772 Layout::linkonce_output_name(const char* name, size_t *plen)
1774 const char* s = name + sizeof(".gnu.linkonce") - 1;
1778 const Linkonce_mapping* plm = linkonce_mapping;
1779 for (int i = 0; i < linkonce_mapping_count; ++i, ++plm)
1781 if (strncmp(s, plm->from, plm->fromlen) == 0 && s[plm->fromlen] == '.')
1790 // Choose the output section name to use given an input section name.
1791 // Set *PLEN to the length of the name. *PLEN is initialized to the
1795 Layout::output_section_name(const char* name, size_t* plen)
1797 if (Layout::is_linkonce(name))
1799 // .gnu.linkonce sections are laid out as though they were named
1800 // for the sections are placed into.
1801 return Layout::linkonce_output_name(name, plen);
1804 // gcc 4.3 generates the following sorts of section names when it
1805 // needs a section name specific to a function:
1811 // .data.rel.local.FN
1813 // .data.rel.ro.local.FN
1820 // The GNU linker maps all of those to the part before the .FN,
1821 // except that .data.rel.local.FN is mapped to .data, and
1822 // .data.rel.ro.local.FN is mapped to .data.rel.ro. The sections
1823 // beginning with .data.rel.ro.local are grouped together.
1825 // For an anonymous namespace, the string FN can contain a '.'.
1827 // Also of interest: .rodata.strN.N, .rodata.cstN, both of which the
1828 // GNU linker maps to .rodata.
1830 // The .data.rel.ro sections enable a security feature triggered by
1831 // the -z relro option. Section which need to be relocated at
1832 // program startup time but which may be readonly after startup are
1833 // grouped into .data.rel.ro. They are then put into a PT_GNU_RELRO
1834 // segment. The dynamic linker will make that segment writable,
1835 // perform relocations, and then make it read-only. FIXME: We do
1836 // not yet implement this optimization.
1838 // It is hard to handle this in a principled way.
1840 // These are the rules we follow:
1842 // If the section name has no initial '.', or no dot other than an
1843 // initial '.', we use the name unchanged (i.e., "mysection" and
1844 // ".text" are unchanged).
1846 // If the name starts with ".data.rel.ro" we use ".data.rel.ro".
1848 // Otherwise, we drop the second '.' and everything that comes after
1849 // it (i.e., ".text.XXX" becomes ".text").
1851 const char* s = name;
1855 const char* sdot = strchr(s, '.');
1859 const char* const data_rel_ro = ".data.rel.ro";
1860 if (strncmp(name, data_rel_ro, strlen(data_rel_ro)) == 0)
1862 *plen = strlen(data_rel_ro);
1866 *plen = sdot - name;
1870 // Record the signature of a comdat section, and return whether to
1871 // include it in the link. If GROUP is true, this is a regular
1872 // section group. If GROUP is false, this is a group signature
1873 // derived from the name of a linkonce section. We want linkonce
1874 // signatures and group signatures to block each other, but we don't
1875 // want a linkonce signature to block another linkonce signature.
1878 Layout::add_comdat(const char* signature, bool group)
1880 std::string sig(signature);
1881 std::pair<Signatures::iterator, bool> ins(
1882 this->signatures_.insert(std::make_pair(sig, group)));
1886 // This is the first time we've seen this signature.
1890 if (ins.first->second)
1892 // We've already seen a real section group with this signature.
1897 // This is a real section group, and we've already seen a
1898 // linkonce section with this signature. Record that we've seen
1899 // a section group, and don't include this section group.
1900 ins.first->second = true;
1905 // We've already seen a linkonce section and this is a linkonce
1906 // section. These don't block each other--this may be the same
1907 // symbol name with different section types.
1912 // Write out the Output_sections. Most won't have anything to write,
1913 // since most of the data will come from input sections which are
1914 // handled elsewhere. But some Output_sections do have Output_data.
1917 Layout::write_output_sections(Output_file* of) const
1919 for (Section_list::const_iterator p = this->section_list_.begin();
1920 p != this->section_list_.end();
1923 if (!(*p)->after_input_sections())
1928 // Write out data not associated with a section or the symbol table.
1931 Layout::write_data(const Symbol_table* symtab, Output_file* of) const
1933 if (!parameters->strip_all())
1935 const Output_section* symtab_section = this->symtab_section_;
1936 for (Section_list::const_iterator p = this->section_list_.begin();
1937 p != this->section_list_.end();
1940 if ((*p)->needs_symtab_index())
1942 gold_assert(symtab_section != NULL);
1943 unsigned int index = (*p)->symtab_index();
1944 gold_assert(index > 0 && index != -1U);
1945 off_t off = (symtab_section->offset()
1946 + index * symtab_section->entsize());
1947 symtab->write_section_symbol(*p, of, off);
1952 const Output_section* dynsym_section = this->dynsym_section_;
1953 for (Section_list::const_iterator p = this->section_list_.begin();
1954 p != this->section_list_.end();
1957 if ((*p)->needs_dynsym_index())
1959 gold_assert(dynsym_section != NULL);
1960 unsigned int index = (*p)->dynsym_index();
1961 gold_assert(index > 0 && index != -1U);
1962 off_t off = (dynsym_section->offset()
1963 + index * dynsym_section->entsize());
1964 symtab->write_section_symbol(*p, of, off);
1968 // Write out the Output_data which are not in an Output_section.
1969 for (Data_list::const_iterator p = this->special_output_list_.begin();
1970 p != this->special_output_list_.end();
1975 // Write out the Output_sections which can only be written after the
1976 // input sections are complete.
1979 Layout::write_sections_after_input_sections(Output_file* of)
1981 // Determine the final section offsets, and thus the final output
1982 // file size. Note we finalize the .shstrab last, to allow the
1983 // after_input_section sections to modify their section-names before
1985 off_t off = this->output_file_size_;
1986 off = this->set_section_offsets(off, AFTER_INPUT_SECTIONS_PASS);
1988 // Now that we've finalized the names, we can finalize the shstrab.
1989 off = this->set_section_offsets(off, STRTAB_AFTER_INPUT_SECTIONS_PASS);
1991 if (off > this->output_file_size_)
1994 this->output_file_size_ = off;
1997 for (Section_list::const_iterator p = this->section_list_.begin();
1998 p != this->section_list_.end();
2001 if ((*p)->after_input_sections())
2005 for (Section_list::const_iterator p = this->unattached_section_list_.begin();
2006 p != this->unattached_section_list_.end();
2009 if ((*p)->after_input_sections())
2013 this->section_headers_->write(of);
2016 // Print statistical information to stderr. This is used for --stats.
2019 Layout::print_stats() const
2021 this->namepool_.print_stats("section name pool");
2022 this->sympool_.print_stats("output symbol name pool");
2023 this->dynpool_.print_stats("dynamic name pool");
2026 // Write_sections_task methods.
2028 // We can always run this task.
2030 Task::Is_runnable_type
2031 Write_sections_task::is_runnable(Workqueue*)
2036 // We need to unlock both OUTPUT_SECTIONS_BLOCKER and FINAL_BLOCKER
2039 class Write_sections_task::Write_sections_locker : public Task_locker
2042 Write_sections_locker(Task_token& output_sections_blocker,
2043 Task_token& final_blocker,
2044 Workqueue* workqueue)
2045 : output_sections_block_(output_sections_blocker, workqueue),
2046 final_block_(final_blocker, workqueue)
2050 Task_block_token output_sections_block_;
2051 Task_block_token final_block_;
2055 Write_sections_task::locks(Workqueue* workqueue)
2057 return new Write_sections_locker(*this->output_sections_blocker_,
2058 *this->final_blocker_,
2062 // Run the task--write out the data.
2065 Write_sections_task::run(Workqueue*)
2067 this->layout_->write_output_sections(this->of_);
2070 // Write_data_task methods.
2072 // We can always run this task.
2074 Task::Is_runnable_type
2075 Write_data_task::is_runnable(Workqueue*)
2080 // We need to unlock FINAL_BLOCKER when finished.
2083 Write_data_task::locks(Workqueue* workqueue)
2085 return new Task_locker_block(*this->final_blocker_, workqueue);
2088 // Run the task--write out the data.
2091 Write_data_task::run(Workqueue*)
2093 this->layout_->write_data(this->symtab_, this->of_);
2096 // Write_symbols_task methods.
2098 // We can always run this task.
2100 Task::Is_runnable_type
2101 Write_symbols_task::is_runnable(Workqueue*)
2106 // We need to unlock FINAL_BLOCKER when finished.
2109 Write_symbols_task::locks(Workqueue* workqueue)
2111 return new Task_locker_block(*this->final_blocker_, workqueue);
2114 // Run the task--write out the symbols.
2117 Write_symbols_task::run(Workqueue*)
2119 this->symtab_->write_globals(this->input_objects_, this->sympool_,
2120 this->dynpool_, this->of_);
2123 // Write_after_input_sections_task methods.
2125 // We can only run this task after the input sections have completed.
2127 Task::Is_runnable_type
2128 Write_after_input_sections_task::is_runnable(Workqueue*)
2130 if (this->input_sections_blocker_->is_blocked())
2135 // We need to unlock FINAL_BLOCKER when finished.
2138 Write_after_input_sections_task::locks(Workqueue* workqueue)
2140 return new Task_locker_block(*this->final_blocker_, workqueue);
2146 Write_after_input_sections_task::run(Workqueue*)
2148 this->layout_->write_sections_after_input_sections(this->of_);
2151 // Close_task_runner methods.
2153 // Run the task--close the file.
2156 Close_task_runner::run(Workqueue*)
2161 // Instantiate the templates we need. We could use the configure
2162 // script to restrict this to only the ones for implemented targets.
2164 #ifdef HAVE_TARGET_32_LITTLE
2167 Layout::layout<32, false>(Sized_relobj<32, false>* object, unsigned int shndx,
2169 const elfcpp::Shdr<32, false>& shdr,
2170 unsigned int, unsigned int, off_t*);
2173 #ifdef HAVE_TARGET_32_BIG
2176 Layout::layout<32, true>(Sized_relobj<32, true>* object, unsigned int shndx,
2178 const elfcpp::Shdr<32, true>& shdr,
2179 unsigned int, unsigned int, off_t*);
2182 #ifdef HAVE_TARGET_64_LITTLE
2185 Layout::layout<64, false>(Sized_relobj<64, false>* object, unsigned int shndx,
2187 const elfcpp::Shdr<64, false>& shdr,
2188 unsigned int, unsigned int, off_t*);
2191 #ifdef HAVE_TARGET_64_BIG
2194 Layout::layout<64, true>(Sized_relobj<64, true>* object, unsigned int shndx,
2196 const elfcpp::Shdr<64, true>& shdr,
2197 unsigned int, unsigned int, off_t*);
2200 #ifdef HAVE_TARGET_32_LITTLE
2203 Layout::layout_eh_frame<32, false>(Sized_relobj<32, false>* object,
2204 const unsigned char* symbols,
2206 const unsigned char* symbol_names,
2207 off_t symbol_names_size,
2209 const elfcpp::Shdr<32, false>& shdr,
2210 unsigned int reloc_shndx,
2211 unsigned int reloc_type,
2215 #ifdef HAVE_TARGET_32_BIG
2218 Layout::layout_eh_frame<32, true>(Sized_relobj<32, true>* object,
2219 const unsigned char* symbols,
2221 const unsigned char* symbol_names,
2222 off_t symbol_names_size,
2224 const elfcpp::Shdr<32, true>& shdr,
2225 unsigned int reloc_shndx,
2226 unsigned int reloc_type,
2230 #ifdef HAVE_TARGET_64_LITTLE
2233 Layout::layout_eh_frame<64, false>(Sized_relobj<64, false>* object,
2234 const unsigned char* symbols,
2236 const unsigned char* symbol_names,
2237 off_t symbol_names_size,
2239 const elfcpp::Shdr<64, false>& shdr,
2240 unsigned int reloc_shndx,
2241 unsigned int reloc_type,
2245 #ifdef HAVE_TARGET_64_BIG
2248 Layout::layout_eh_frame<64, true>(Sized_relobj<64, true>* object,
2249 const unsigned char* symbols,
2251 const unsigned char* symbol_names,
2252 off_t symbol_names_size,
2254 const elfcpp::Shdr<64, true>& shdr,
2255 unsigned int reloc_shndx,
2256 unsigned int reloc_type,
2260 } // End namespace gold.