// layout.cc -- lay out output file sections for gold // Copyright 2006, 2007 Free Software Foundation, Inc. // Written by Ian Lance Taylor . // This file is part of gold. // This program is free software; you can redistribute it and/or modify // it under the terms of the GNU General Public License as published by // the Free Software Foundation; either version 3 of the License, or // (at your option) any later version. // This program is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // You should have received a copy of the GNU General Public License // along with this program; if not, write to the Free Software // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, // MA 02110-1301, USA. #include "gold.h" #include #include #include #include #include "parameters.h" #include "output.h" #include "symtab.h" #include "dynobj.h" #include "ehframe.h" #include "layout.h" namespace gold { // Layout_task_runner methods. // Lay out the sections. This is called after all the input objects // have been read. void Layout_task_runner::run(Workqueue* workqueue) { off_t file_size = this->layout_->finalize(this->input_objects_, this->symtab_); // Now we know the final size of the output file and we know where // each piece of information goes. Output_file* of = new Output_file(this->options_, this->input_objects_->target()); of->open(file_size); // Queue up the final set of tasks. gold::queue_final_tasks(this->options_, this->input_objects_, this->symtab_, this->layout_, workqueue, of); } // Layout methods. Layout::Layout(const General_options& options) : options_(options), namepool_(), sympool_(), dynpool_(), signatures_(), section_name_map_(), segment_list_(), section_list_(), unattached_section_list_(), special_output_list_(), tls_segment_(NULL), symtab_section_(NULL), dynsym_section_(NULL), dynamic_section_(NULL), dynamic_data_(NULL), eh_frame_section_(NULL), output_file_size_(-1), input_requires_executable_stack_(false), input_with_gnu_stack_note_(false), input_without_gnu_stack_note_(false) { // Make space for more than enough segments for a typical file. // This is just for efficiency--it's OK if we wind up needing more. this->segment_list_.reserve(12); // We expect three unattached Output_data objects: the file header, // the segment headers, and the section headers. this->special_output_list_.reserve(3); } // Hash a key we use to look up an output section mapping. size_t Layout::Hash_key::operator()(const Layout::Key& k) const { return k.first + k.second.first + k.second.second; } // Return whether PREFIX is a prefix of STR. static inline bool is_prefix_of(const char* prefix, const char* str) { return strncmp(prefix, str, strlen(prefix)) == 0; } // Returns whether the given section is in the list of // debug-sections-used-by-some-version-of-gdb. Currently, // we've checked versions of gdb up to and including 6.7.1. static const char* gdb_sections[] = { ".debug_abbrev", // ".debug_aranges", // not used by gdb as of 6.7.1 ".debug_frame", ".debug_info", ".debug_line", ".debug_loc", ".debug_macinfo", // ".debug_pubnames", // not used by gdb as of 6.7.1 ".debug_ranges", ".debug_str", }; static inline bool is_gdb_debug_section(const char* str) { // We can do this faster: binary search or a hashtable. But why bother? for (size_t i = 0; i < sizeof(gdb_sections)/sizeof(*gdb_sections); ++i) if (strcmp(str, gdb_sections[i]) == 0) return true; return false; } // Whether to include this section in the link. template bool Layout::include_section(Sized_relobj*, const char* name, const elfcpp::Shdr& shdr) { // Some section types are never linked. Some are only linked when // doing a relocateable link. switch (shdr.get_sh_type()) { case elfcpp::SHT_NULL: case elfcpp::SHT_SYMTAB: case elfcpp::SHT_DYNSYM: case elfcpp::SHT_STRTAB: case elfcpp::SHT_HASH: case elfcpp::SHT_DYNAMIC: case elfcpp::SHT_SYMTAB_SHNDX: return false; case elfcpp::SHT_RELA: case elfcpp::SHT_REL: case elfcpp::SHT_GROUP: return parameters->output_is_object(); case elfcpp::SHT_PROGBITS: if (parameters->strip_debug() && (shdr.get_sh_flags() & elfcpp::SHF_ALLOC) == 0) { // Debugging sections can only be recognized by name. if (is_prefix_of(".debug", name) || is_prefix_of(".gnu.linkonce.wi.", name) || is_prefix_of(".line", name) || is_prefix_of(".stab", name)) return false; } if (parameters->strip_debug_gdb() && (shdr.get_sh_flags() & elfcpp::SHF_ALLOC) == 0) { // Debugging sections can only be recognized by name. if (is_prefix_of(".debug", name) && !is_gdb_debug_section(name)) return false; } return true; default: return true; } } // Return an output section named NAME, or NULL if there is none. Output_section* Layout::find_output_section(const char* name) const { for (Section_name_map::const_iterator p = this->section_name_map_.begin(); p != this->section_name_map_.end(); ++p) if (strcmp(p->second->name(), name) == 0) return p->second; return NULL; } // Return an output segment of type TYPE, with segment flags SET set // and segment flags CLEAR clear. Return NULL if there is none. Output_segment* Layout::find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set, elfcpp::Elf_Word clear) const { for (Segment_list::const_iterator p = this->segment_list_.begin(); p != this->segment_list_.end(); ++p) if (static_cast((*p)->type()) == type && ((*p)->flags() & set) == set && ((*p)->flags() & clear) == 0) return *p; return NULL; } // Return the output section to use for section NAME with type TYPE // and section flags FLAGS. Output_section* Layout::get_output_section(const char* name, Stringpool::Key name_key, elfcpp::Elf_Word type, elfcpp::Elf_Xword flags) { // We should ignore some flags. flags &= ~ (elfcpp::SHF_INFO_LINK | elfcpp::SHF_LINK_ORDER | elfcpp::SHF_GROUP | elfcpp::SHF_MERGE | elfcpp::SHF_STRINGS); const Key key(name_key, std::make_pair(type, flags)); const std::pair v(key, NULL); std::pair ins( this->section_name_map_.insert(v)); if (!ins.second) return ins.first->second; else { // This is the first time we've seen this name/type/flags // combination. Output_section* os = this->make_output_section(name, type, flags); ins.first->second = os; return os; } } // Return the output section to use for input section SHNDX, with name // NAME, with header HEADER, from object OBJECT. RELOC_SHNDX is the // index of a relocation section which applies to this section, or 0 // if none, or -1U if more than one. RELOC_TYPE is the type of the // relocation section if there is one. Set *OFF to the offset of this // input section without the output section. Return NULL if the // section should be discarded. Set *OFF to -1 if the section // contents should not be written directly to the output file, but // will instead receive special handling. template Output_section* Layout::layout(Sized_relobj* object, unsigned int shndx, const char* name, const elfcpp::Shdr& shdr, unsigned int reloc_shndx, unsigned int, off_t* off) { if (!this->include_section(object, name, shdr)) return NULL; // If we are not doing a relocateable link, choose the name to use // for the output section. size_t len = strlen(name); if (!parameters->output_is_object()) name = Layout::output_section_name(name, &len); // FIXME: Handle SHF_OS_NONCONFORMING here. // Canonicalize the section name. Stringpool::Key name_key; name = this->namepool_.add_prefix(name, len, &name_key); // Find the output section. The output section is selected based on // the section name, type, and flags. Output_section* os = this->get_output_section(name, name_key, shdr.get_sh_type(), shdr.get_sh_flags()); // FIXME: Handle SHF_LINK_ORDER somewhere. *off = os->add_input_section(object, shndx, name, shdr, reloc_shndx); return os; } // Special GNU handling of sections name .eh_frame. They will // normally hold exception frame data as defined by the C++ ABI // (http://codesourcery.com/cxx-abi/). template Output_section* Layout::layout_eh_frame(Sized_relobj* object, const unsigned char* symbols, off_t symbols_size, const unsigned char* symbol_names, off_t symbol_names_size, unsigned int shndx, const elfcpp::Shdr& shdr, unsigned int reloc_shndx, unsigned int reloc_type, off_t* off) { gold_assert(shdr.get_sh_type() == elfcpp::SHT_PROGBITS); gold_assert(shdr.get_sh_flags() == elfcpp::SHF_ALLOC); Stringpool::Key name_key; const char* name = this->namepool_.add(".eh_frame", false, &name_key); Output_section* os = this->get_output_section(name, name_key, elfcpp::SHT_PROGBITS, elfcpp::SHF_ALLOC); if (this->eh_frame_section_ == NULL) { this->eh_frame_section_ = os; this->eh_frame_data_ = new Eh_frame(); os->add_output_section_data(this->eh_frame_data_); if (this->options_.create_eh_frame_hdr()) { Stringpool::Key hdr_name_key; const char* hdr_name = this->namepool_.add(".eh_frame_hdr", false, &hdr_name_key); Output_section* hdr_os = this->get_output_section(hdr_name, hdr_name_key, elfcpp::SHT_PROGBITS, elfcpp::SHF_ALLOC); Eh_frame_hdr* hdr_posd = new Eh_frame_hdr(os, this->eh_frame_data_); hdr_os->add_output_section_data(hdr_posd); hdr_os->set_after_input_sections(); Output_segment* hdr_oseg = new Output_segment(elfcpp::PT_GNU_EH_FRAME, elfcpp::PF_R); this->segment_list_.push_back(hdr_oseg); hdr_oseg->add_output_section(hdr_os, elfcpp::PF_R); this->eh_frame_data_->set_eh_frame_hdr(hdr_posd); } } gold_assert(this->eh_frame_section_ == os); if (this->eh_frame_data_->add_ehframe_input_section(object, symbols, symbols_size, symbol_names, symbol_names_size, shndx, reloc_shndx, reloc_type)) *off = -1; else { // We couldn't handle this .eh_frame section for some reason. // Add it as a normal section. *off = os->add_input_section(object, shndx, name, shdr, reloc_shndx); } return os; } // Add POSD to an output section using NAME, TYPE, and FLAGS. void Layout::add_output_section_data(const char* name, elfcpp::Elf_Word type, elfcpp::Elf_Xword flags, Output_section_data* posd) { // Canonicalize the name. Stringpool::Key name_key; name = this->namepool_.add(name, true, &name_key); Output_section* os = this->get_output_section(name, name_key, type, flags); os->add_output_section_data(posd); } // Map section flags to segment flags. elfcpp::Elf_Word Layout::section_flags_to_segment(elfcpp::Elf_Xword flags) { elfcpp::Elf_Word ret = elfcpp::PF_R; if ((flags & elfcpp::SHF_WRITE) != 0) ret |= elfcpp::PF_W; if ((flags & elfcpp::SHF_EXECINSTR) != 0) ret |= elfcpp::PF_X; return ret; } // Make a new Output_section, and attach it to segments as // appropriate. Output_section* Layout::make_output_section(const char* name, elfcpp::Elf_Word type, elfcpp::Elf_Xword flags) { Output_section* os = new Output_section(name, type, flags); this->section_list_.push_back(os); if ((flags & elfcpp::SHF_ALLOC) == 0) this->unattached_section_list_.push_back(os); else { // This output section goes into a PT_LOAD segment. elfcpp::Elf_Word seg_flags = Layout::section_flags_to_segment(flags); // The only thing we really care about for PT_LOAD segments is // whether or not they are writable, so that is how we search // for them. People who need segments sorted on some other // basis will have to wait until we implement a mechanism for // them to describe the segments they want. Segment_list::const_iterator p; for (p = this->segment_list_.begin(); p != this->segment_list_.end(); ++p) { if ((*p)->type() == elfcpp::PT_LOAD && ((*p)->flags() & elfcpp::PF_W) == (seg_flags & elfcpp::PF_W)) { (*p)->add_output_section(os, seg_flags); break; } } if (p == this->segment_list_.end()) { Output_segment* oseg = new Output_segment(elfcpp::PT_LOAD, seg_flags); this->segment_list_.push_back(oseg); oseg->add_output_section(os, seg_flags); } // If we see a loadable SHT_NOTE section, we create a PT_NOTE // segment. if (type == elfcpp::SHT_NOTE) { // See if we already have an equivalent PT_NOTE segment. for (p = this->segment_list_.begin(); p != segment_list_.end(); ++p) { if ((*p)->type() == elfcpp::PT_NOTE && (((*p)->flags() & elfcpp::PF_W) == (seg_flags & elfcpp::PF_W))) { (*p)->add_output_section(os, seg_flags); break; } } if (p == this->segment_list_.end()) { Output_segment* oseg = new Output_segment(elfcpp::PT_NOTE, seg_flags); this->segment_list_.push_back(oseg); oseg->add_output_section(os, seg_flags); } } // If we see a loadable SHF_TLS section, we create a PT_TLS // segment. There can only be one such segment. if ((flags & elfcpp::SHF_TLS) != 0) { if (this->tls_segment_ == NULL) { this->tls_segment_ = new Output_segment(elfcpp::PT_TLS, seg_flags); this->segment_list_.push_back(this->tls_segment_); } this->tls_segment_->add_output_section(os, seg_flags); } } return os; } // Handle the .note.GNU-stack section at layout time. SEEN_GNU_STACK // is whether we saw a .note.GNU-stack section in the object file. // GNU_STACK_FLAGS is the section flags. The flags give the // protection required for stack memory. We record this in an // executable as a PT_GNU_STACK segment. If an object file does not // have a .note.GNU-stack segment, we must assume that it is an old // object. On some targets that will force an executable stack. void Layout::layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags) { if (!seen_gnu_stack) this->input_without_gnu_stack_note_ = true; else { this->input_with_gnu_stack_note_ = true; if ((gnu_stack_flags & elfcpp::SHF_EXECINSTR) != 0) this->input_requires_executable_stack_ = true; } } // Create the dynamic sections which are needed before we read the // relocs. void Layout::create_initial_dynamic_sections(const Input_objects* input_objects, Symbol_table* symtab) { if (parameters->doing_static_link()) return; const char* dynamic_name = this->namepool_.add(".dynamic", false, NULL); this->dynamic_section_ = this->make_output_section(dynamic_name, elfcpp::SHT_DYNAMIC, (elfcpp::SHF_ALLOC | elfcpp::SHF_WRITE)); symtab->define_in_output_data(input_objects->target(), "_DYNAMIC", NULL, this->dynamic_section_, 0, 0, elfcpp::STT_OBJECT, elfcpp::STB_LOCAL, elfcpp::STV_HIDDEN, 0, false, false); this->dynamic_data_ = new Output_data_dynamic(&this->dynpool_); this->dynamic_section_->add_output_section_data(this->dynamic_data_); } // For each output section whose name can be represented as C symbol, // define __start and __stop symbols for the section. This is a GNU // extension. void Layout::define_section_symbols(Symbol_table* symtab, const Target* target) { for (Section_list::const_iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { const char* const name = (*p)->name(); if (name[strspn(name, ("0123456789" "ABCDEFGHIJKLMNOPWRSTUVWXYZ" "abcdefghijklmnopqrstuvwxyz" "_"))] == '\0') { const std::string name_string(name); const std::string start_name("__start_" + name_string); const std::string stop_name("__stop_" + name_string); symtab->define_in_output_data(target, start_name.c_str(), NULL, // version *p, 0, // value 0, // symsize elfcpp::STT_NOTYPE, elfcpp::STB_GLOBAL, elfcpp::STV_DEFAULT, 0, // nonvis false, // offset_is_from_end false); // only_if_ref symtab->define_in_output_data(target, stop_name.c_str(), NULL, // version *p, 0, // value 0, // symsize elfcpp::STT_NOTYPE, elfcpp::STB_GLOBAL, elfcpp::STV_DEFAULT, 0, // nonvis true, // offset_is_from_end false); // only_if_ref } } } // Find the first read-only PT_LOAD segment, creating one if // necessary. Output_segment* Layout::find_first_load_seg() { for (Segment_list::const_iterator p = this->segment_list_.begin(); p != this->segment_list_.end(); ++p) { if ((*p)->type() == elfcpp::PT_LOAD && ((*p)->flags() & elfcpp::PF_R) != 0 && ((*p)->flags() & elfcpp::PF_W) == 0) return *p; } Output_segment* load_seg = new Output_segment(elfcpp::PT_LOAD, elfcpp::PF_R); this->segment_list_.push_back(load_seg); return load_seg; } // Finalize the layout. When this is called, we have created all the // output sections and all the output segments which are based on // input sections. We have several things to do, and we have to do // them in the right order, so that we get the right results correctly // and efficiently. // 1) Finalize the list of output segments and create the segment // table header. // 2) Finalize the dynamic symbol table and associated sections. // 3) Determine the final file offset of all the output segments. // 4) Determine the final file offset of all the SHF_ALLOC output // sections. // 5) Create the symbol table sections and the section name table // section. // 6) Finalize the symbol table: set symbol values to their final // value and make a final determination of which symbols are going // into the output symbol table. // 7) Create the section table header. // 8) Determine the final file offset of all the output sections which // are not SHF_ALLOC, including the section table header. // 9) Finalize the ELF file header. // This function returns the size of the output file. off_t Layout::finalize(const Input_objects* input_objects, Symbol_table* symtab) { Target* const target = input_objects->target(); target->finalize_sections(this); this->create_gold_note(); this->create_executable_stack_info(target); Output_segment* phdr_seg = NULL; if (!parameters->doing_static_link()) { // There was a dynamic object in the link. We need to create // some information for the dynamic linker. // Create the PT_PHDR segment which will hold the program // headers. phdr_seg = new Output_segment(elfcpp::PT_PHDR, elfcpp::PF_R); this->segment_list_.push_back(phdr_seg); // Create the dynamic symbol table, including the hash table. Output_section* dynstr; std::vector dynamic_symbols; unsigned int local_dynamic_count; Versions versions; this->create_dynamic_symtab(target, symtab, &dynstr, &local_dynamic_count, &dynamic_symbols, &versions); // Create the .interp section to hold the name of the // interpreter, and put it in a PT_INTERP segment. if (!parameters->output_is_shared()) this->create_interp(target); // Finish the .dynamic section to hold the dynamic data, and put // it in a PT_DYNAMIC segment. this->finish_dynamic_section(input_objects, symtab); // We should have added everything we need to the dynamic string // table. this->dynpool_.set_string_offsets(); // Create the version sections. We can't do this until the // dynamic string table is complete. this->create_version_sections(&versions, symtab, local_dynamic_count, dynamic_symbols, dynstr); } // FIXME: Handle PT_GNU_STACK. Output_segment* load_seg = this->find_first_load_seg(); // Lay out the segment headers. Output_segment_headers* segment_headers; segment_headers = new Output_segment_headers(this->segment_list_); load_seg->add_initial_output_data(segment_headers); this->special_output_list_.push_back(segment_headers); if (phdr_seg != NULL) phdr_seg->add_initial_output_data(segment_headers); // Lay out the file header. Output_file_header* file_header; file_header = new Output_file_header(target, symtab, segment_headers); load_seg->add_initial_output_data(file_header); this->special_output_list_.push_back(file_header); // We set the output section indexes in set_segment_offsets and // set_section_offsets. unsigned int shndx = 1; // Set the file offsets of all the segments, and all the sections // they contain. off_t off = this->set_segment_offsets(target, load_seg, &shndx); // Set the file offsets of all the data sections not associated with // segments. This makes sure that debug sections have their offsets // before symbols are finalized. off = this->set_section_offsets(off, true); // Create the symbol table sections. this->create_symtab_sections(input_objects, symtab, &off); // Create the .shstrtab section. Output_section* shstrtab_section = this->create_shstrtab(); // Set the file offsets of all the non-data sections not associated with // segments. off = this->set_section_offsets(off, false); // Now that all sections have been created, set the section indexes. shndx = this->set_section_indexes(shndx); // Create the section table header. Output_section_headers* oshdrs = this->create_shdrs(&off); file_header->set_section_info(oshdrs, shstrtab_section); // Now we know exactly where everything goes in the output file. Output_data::layout_complete(); this->output_file_size_ = off; return off; } // Create a .note section for an executable or shared library. This // records the version of gold used to create the binary. void Layout::create_gold_note() { if (parameters->output_is_object()) return; // Authorities all agree that the values in a .note field should // be aligned on 4-byte boundaries for 32-bit binaries. However, // they differ on what the alignment is for 64-bit binaries. // The GABI says unambiguously they take 8-byte alignment: // http://sco.com/developers/gabi/latest/ch5.pheader.html#note_section // Other documentation says alignment should always be 4 bytes: // http://www.netbsd.org/docs/kernel/elf-notes.html#note-format // GNU ld and GNU readelf both support the latter (at least as of // version 2.16.91), and glibc always generates the latter for // .note.ABI-tag (as of version 1.6), so that's the one we go with // here. #ifdef GABI_FORMAT_FOR_DOTNOTE_SECTION // This is not defined by default. const int size = parameters->get_size(); #else const int size = 32; #endif // The contents of the .note section. const char* name = "GNU"; std::string desc(std::string("gold ") + gold::get_version_string()); size_t namesz = strlen(name) + 1; size_t aligned_namesz = align_address(namesz, size / 8); size_t descsz = desc.length() + 1; size_t aligned_descsz = align_address(descsz, size / 8); const int note_type = 4; size_t notesz = 3 * (size / 8) + aligned_namesz + aligned_descsz; unsigned char buffer[128]; gold_assert(sizeof buffer >= notesz); memset(buffer, 0, notesz); bool is_big_endian = parameters->is_big_endian(); if (size == 32) { if (!is_big_endian) { elfcpp::Swap<32, false>::writeval(buffer, namesz); elfcpp::Swap<32, false>::writeval(buffer + 4, descsz); elfcpp::Swap<32, false>::writeval(buffer + 8, note_type); } else { elfcpp::Swap<32, true>::writeval(buffer, namesz); elfcpp::Swap<32, true>::writeval(buffer + 4, descsz); elfcpp::Swap<32, true>::writeval(buffer + 8, note_type); } } else if (size == 64) { if (!is_big_endian) { elfcpp::Swap<64, false>::writeval(buffer, namesz); elfcpp::Swap<64, false>::writeval(buffer + 8, descsz); elfcpp::Swap<64, false>::writeval(buffer + 16, note_type); } else { elfcpp::Swap<64, true>::writeval(buffer, namesz); elfcpp::Swap<64, true>::writeval(buffer + 8, descsz); elfcpp::Swap<64, true>::writeval(buffer + 16, note_type); } } else gold_unreachable(); memcpy(buffer + 3 * (size / 8), name, namesz); memcpy(buffer + 3 * (size / 8) + aligned_namesz, desc.data(), descsz); const char* note_name = this->namepool_.add(".note", false, NULL); Output_section* os = this->make_output_section(note_name, elfcpp::SHT_NOTE, 0); Output_section_data* posd = new Output_data_const(buffer, notesz, size / 8); os->add_output_section_data(posd); } // Record whether the stack should be executable. This can be set // from the command line using the -z execstack or -z noexecstack // options. Otherwise, if any input file has a .note.GNU-stack // section with the SHF_EXECINSTR flag set, the stack should be // executable. Otherwise, if at least one input file a // .note.GNU-stack section, and some input file has no .note.GNU-stack // section, we use the target default for whether the stack should be // executable. Otherwise, we don't generate a stack note. When // generating a object file, we create a .note.GNU-stack section with // the appropriate marking. When generating an executable or shared // library, we create a PT_GNU_STACK segment. void Layout::create_executable_stack_info(const Target* target) { bool is_stack_executable; if (this->options_.is_execstack_set()) is_stack_executable = this->options_.is_stack_executable(); else if (!this->input_with_gnu_stack_note_) return; else { if (this->input_requires_executable_stack_) is_stack_executable = true; else if (this->input_without_gnu_stack_note_) is_stack_executable = target->is_default_stack_executable(); else is_stack_executable = false; } if (parameters->output_is_object()) { const char* name = this->namepool_.add(".note.GNU-stack", false, NULL); elfcpp::Elf_Xword flags = 0; if (is_stack_executable) flags |= elfcpp::SHF_EXECINSTR; this->make_output_section(name, elfcpp::SHT_PROGBITS, flags); } else { int flags = elfcpp::PF_R | elfcpp::PF_W; if (is_stack_executable) flags |= elfcpp::PF_X; Output_segment* oseg = new Output_segment(elfcpp::PT_GNU_STACK, flags); this->segment_list_.push_back(oseg); } } // Return whether SEG1 should be before SEG2 in the output file. This // is based entirely on the segment type and flags. When this is // called the segment addresses has normally not yet been set. bool Layout::segment_precedes(const Output_segment* seg1, const Output_segment* seg2) { elfcpp::Elf_Word type1 = seg1->type(); elfcpp::Elf_Word type2 = seg2->type(); // The single PT_PHDR segment is required to precede any loadable // segment. We simply make it always first. if (type1 == elfcpp::PT_PHDR) { gold_assert(type2 != elfcpp::PT_PHDR); return true; } if (type2 == elfcpp::PT_PHDR) return false; // The single PT_INTERP segment is required to precede any loadable // segment. We simply make it always second. if (type1 == elfcpp::PT_INTERP) { gold_assert(type2 != elfcpp::PT_INTERP); return true; } if (type2 == elfcpp::PT_INTERP) return false; // We then put PT_LOAD segments before any other segments. if (type1 == elfcpp::PT_LOAD && type2 != elfcpp::PT_LOAD) return true; if (type2 == elfcpp::PT_LOAD && type1 != elfcpp::PT_LOAD) return false; // We put the PT_TLS segment last, because that is where the dynamic // linker expects to find it (this is just for efficiency; other // positions would also work correctly). if (type1 == elfcpp::PT_TLS && type2 != elfcpp::PT_TLS) return false; if (type2 == elfcpp::PT_TLS && type1 != elfcpp::PT_TLS) return true; const elfcpp::Elf_Word flags1 = seg1->flags(); const elfcpp::Elf_Word flags2 = seg2->flags(); // The order of non-PT_LOAD segments is unimportant. We simply sort // by the numeric segment type and flags values. There should not // be more than one segment with the same type and flags. if (type1 != elfcpp::PT_LOAD) { if (type1 != type2) return type1 < type2; gold_assert(flags1 != flags2); return flags1 < flags2; } // We sort PT_LOAD segments based on the flags. Readonly segments // come before writable segments. Then executable segments come // before non-executable segments. Then the unlikely case of a // non-readable segment comes before the normal case of a readable // segment. If there are multiple segments with the same type and // flags, we require that the address be set, and we sort by // virtual address and then physical address. if ((flags1 & elfcpp::PF_W) != (flags2 & elfcpp::PF_W)) return (flags1 & elfcpp::PF_W) == 0; if ((flags1 & elfcpp::PF_X) != (flags2 & elfcpp::PF_X)) return (flags1 & elfcpp::PF_X) != 0; if ((flags1 & elfcpp::PF_R) != (flags2 & elfcpp::PF_R)) return (flags1 & elfcpp::PF_R) == 0; uint64_t vaddr1 = seg1->vaddr(); uint64_t vaddr2 = seg2->vaddr(); if (vaddr1 != vaddr2) return vaddr1 < vaddr2; uint64_t paddr1 = seg1->paddr(); uint64_t paddr2 = seg2->paddr(); gold_assert(paddr1 != paddr2); return paddr1 < paddr2; } // Set the file offsets of all the segments, and all the sections they // contain. They have all been created. LOAD_SEG must be be laid out // first. Return the offset of the data to follow. off_t Layout::set_segment_offsets(const Target* target, Output_segment* load_seg, unsigned int *pshndx) { // Sort them into the final order. std::sort(this->segment_list_.begin(), this->segment_list_.end(), Layout::Compare_segments()); // Find the PT_LOAD segments, and set their addresses and offsets // and their section's addresses and offsets. uint64_t addr; if (options_.user_set_text_segment_address()) addr = options_.text_segment_address(); else addr = target->default_text_segment_address(); off_t off = 0; bool was_readonly = false; for (Segment_list::iterator p = this->segment_list_.begin(); p != this->segment_list_.end(); ++p) { if ((*p)->type() == elfcpp::PT_LOAD) { if (load_seg != NULL && load_seg != *p) gold_unreachable(); load_seg = NULL; // If the last segment was readonly, and this one is not, // then skip the address forward one page, maintaining the // same position within the page. This lets us store both // segments overlapping on a single page in the file, but // the loader will put them on different pages in memory. uint64_t orig_addr = addr; uint64_t orig_off = off; uint64_t aligned_addr = addr; uint64_t abi_pagesize = target->abi_pagesize(); // FIXME: This should depend on the -n and -N options. (*p)->set_minimum_addralign(target->common_pagesize()); if (was_readonly && ((*p)->flags() & elfcpp::PF_W) != 0) { uint64_t align = (*p)->addralign(); addr = align_address(addr, align); aligned_addr = addr; if ((addr & (abi_pagesize - 1)) != 0) addr = addr + abi_pagesize; } unsigned int shndx_hold = *pshndx; off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1)); uint64_t new_addr = (*p)->set_section_addresses(addr, &off, pshndx); // Now that we know the size of this segment, we may be able // to save a page in memory, at the cost of wasting some // file space, by instead aligning to the start of a new // page. Here we use the real machine page size rather than // the ABI mandated page size. if (aligned_addr != addr) { uint64_t common_pagesize = target->common_pagesize(); uint64_t first_off = (common_pagesize - (aligned_addr & (common_pagesize - 1))); uint64_t last_off = new_addr & (common_pagesize - 1); if (first_off > 0 && last_off > 0 && ((aligned_addr & ~ (common_pagesize - 1)) != (new_addr & ~ (common_pagesize - 1))) && first_off + last_off <= common_pagesize) { *pshndx = shndx_hold; addr = align_address(aligned_addr, common_pagesize); off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1)); new_addr = (*p)->set_section_addresses(addr, &off, pshndx); } } addr = new_addr; if (((*p)->flags() & elfcpp::PF_W) == 0) was_readonly = true; } } // Handle the non-PT_LOAD segments, setting their offsets from their // section's offsets. for (Segment_list::iterator p = this->segment_list_.begin(); p != this->segment_list_.end(); ++p) { if ((*p)->type() != elfcpp::PT_LOAD) (*p)->set_offset(); } return off; } // Set the file offset of all the sections not associated with a // segment. off_t Layout::set_section_offsets(off_t off, bool do_bits_sections) { for (Section_list::iterator p = this->unattached_section_list_.begin(); p != this->unattached_section_list_.end(); ++p) { bool is_bits_section = ((*p)->type() == elfcpp::SHT_PROGBITS || (*p)->type() == elfcpp::SHT_NOBITS); if (is_bits_section != do_bits_sections) continue; if ((*p)->offset() != -1) continue; off = align_address(off, (*p)->addralign()); (*p)->set_address(0, off); off += (*p)->data_size(); } return off; } // Set the section indexes of all the sections not associated with a // segment. unsigned int Layout::set_section_indexes(unsigned int shndx) { for (Section_list::iterator p = this->unattached_section_list_.begin(); p != this->unattached_section_list_.end(); ++p) { (*p)->set_out_shndx(shndx); ++shndx; } return shndx; } // Create the symbol table sections. Here we also set the final // values of the symbols. At this point all the loadable sections are // fully laid out. void Layout::create_symtab_sections(const Input_objects* input_objects, Symbol_table* symtab, off_t* poff) { int symsize; unsigned int align; if (parameters->get_size() == 32) { symsize = elfcpp::Elf_sizes<32>::sym_size; align = 4; } else if (parameters->get_size() == 64) { symsize = elfcpp::Elf_sizes<64>::sym_size; align = 8; } else gold_unreachable(); off_t off = *poff; off = align_address(off, align); off_t startoff = off; // Save space for the dummy symbol at the start of the section. We // never bother to write this out--it will just be left as zero. off += symsize; unsigned int local_symbol_index = 1; // Add STT_SECTION symbols for each Output section which needs one. for (Section_list::iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { if (!(*p)->needs_symtab_index()) (*p)->set_symtab_index(-1U); else { (*p)->set_symtab_index(local_symbol_index); ++local_symbol_index; off += symsize; } } for (Input_objects::Relobj_iterator p = input_objects->relobj_begin(); p != input_objects->relobj_end(); ++p) { Task_lock_obj tlo(**p); unsigned int index = (*p)->finalize_local_symbols(local_symbol_index, off, &this->sympool_); off += (index - local_symbol_index) * symsize; local_symbol_index = index; } unsigned int local_symcount = local_symbol_index; gold_assert(local_symcount * symsize == off - startoff); off_t dynoff; size_t dyn_global_index; size_t dyncount; if (this->dynsym_section_ == NULL) { dynoff = 0; dyn_global_index = 0; dyncount = 0; } else { dyn_global_index = this->dynsym_section_->info(); off_t locsize = dyn_global_index * this->dynsym_section_->entsize(); dynoff = this->dynsym_section_->offset() + locsize; dyncount = (this->dynsym_section_->data_size() - locsize) / symsize; gold_assert(static_cast(dyncount * symsize) == this->dynsym_section_->data_size() - locsize); } off = symtab->finalize(local_symcount, off, dynoff, dyn_global_index, dyncount, &this->sympool_); if (!parameters->strip_all()) { this->sympool_.set_string_offsets(); const char* symtab_name = this->namepool_.add(".symtab", false, NULL); Output_section* osymtab = this->make_output_section(symtab_name, elfcpp::SHT_SYMTAB, 0); this->symtab_section_ = osymtab; Output_section_data* pos = new Output_data_space(off - startoff, align); osymtab->add_output_section_data(pos); const char* strtab_name = this->namepool_.add(".strtab", false, NULL); Output_section* ostrtab = this->make_output_section(strtab_name, elfcpp::SHT_STRTAB, 0); Output_section_data* pstr = new Output_data_strtab(&this->sympool_); ostrtab->add_output_section_data(pstr); osymtab->set_address(0, startoff); osymtab->set_link_section(ostrtab); osymtab->set_info(local_symcount); osymtab->set_entsize(symsize); *poff = off; } } // Create the .shstrtab section, which holds the names of the // sections. At the time this is called, we have created all the // output sections except .shstrtab itself. Output_section* Layout::create_shstrtab() { // FIXME: We don't need to create a .shstrtab section if we are // stripping everything. const char* name = this->namepool_.add(".shstrtab", false, NULL); this->namepool_.set_string_offsets(); Output_section* os = this->make_output_section(name, elfcpp::SHT_STRTAB, 0); Output_section_data* posd = new Output_data_strtab(&this->namepool_); os->add_output_section_data(posd); return os; } // Create the section headers. SIZE is 32 or 64. OFF is the file // offset. Output_section_headers* Layout::create_shdrs(off_t* poff) { Output_section_headers* oshdrs; oshdrs = new Output_section_headers(this, &this->segment_list_, &this->unattached_section_list_, &this->namepool_); off_t off = align_address(*poff, oshdrs->addralign()); oshdrs->set_address(0, off); off += oshdrs->data_size(); *poff = off; this->special_output_list_.push_back(oshdrs); return oshdrs; } // Create the dynamic symbol table. void Layout::create_dynamic_symtab(const Target* target, Symbol_table* symtab, Output_section **pdynstr, unsigned int* plocal_dynamic_count, std::vector* pdynamic_symbols, Versions* pversions) { // Count all the symbols in the dynamic symbol table, and set the // dynamic symbol indexes. // Skip symbol 0, which is always all zeroes. unsigned int index = 1; // Add STT_SECTION symbols for each Output section which needs one. for (Section_list::iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { if (!(*p)->needs_dynsym_index()) (*p)->set_dynsym_index(-1U); else { (*p)->set_dynsym_index(index); ++index; } } // FIXME: Some targets apparently require local symbols in the // dynamic symbol table. Here is where we will have to count them, // and set the dynamic symbol indexes, and add the names to // this->dynpool_. unsigned int local_symcount = index; *plocal_dynamic_count = local_symcount; // FIXME: We have to tell set_dynsym_indexes whether the // -E/--export-dynamic option was used. index = symtab->set_dynsym_indexes(target, index, pdynamic_symbols, &this->dynpool_, pversions); int symsize; unsigned int align; const int size = parameters->get_size(); if (size == 32) { symsize = elfcpp::Elf_sizes<32>::sym_size; align = 4; } else if (size == 64) { symsize = elfcpp::Elf_sizes<64>::sym_size; align = 8; } else gold_unreachable(); // Create the dynamic symbol table section. const char* dynsym_name = this->namepool_.add(".dynsym", false, NULL); Output_section* dynsym = this->make_output_section(dynsym_name, elfcpp::SHT_DYNSYM, elfcpp::SHF_ALLOC); Output_section_data* odata = new Output_data_space(index * symsize, align); dynsym->add_output_section_data(odata); dynsym->set_info(local_symcount); dynsym->set_entsize(symsize); dynsym->set_addralign(align); this->dynsym_section_ = dynsym; Output_data_dynamic* const odyn = this->dynamic_data_; odyn->add_section_address(elfcpp::DT_SYMTAB, dynsym); odyn->add_constant(elfcpp::DT_SYMENT, symsize); // Create the dynamic string table section. const char* dynstr_name = this->namepool_.add(".dynstr", false, NULL); Output_section* dynstr = this->make_output_section(dynstr_name, elfcpp::SHT_STRTAB, elfcpp::SHF_ALLOC); Output_section_data* strdata = new Output_data_strtab(&this->dynpool_); dynstr->add_output_section_data(strdata); dynsym->set_link_section(dynstr); this->dynamic_section_->set_link_section(dynstr); odyn->add_section_address(elfcpp::DT_STRTAB, dynstr); odyn->add_section_size(elfcpp::DT_STRSZ, dynstr); *pdynstr = dynstr; // Create the hash tables. // FIXME: We need an option to create a GNU hash table. unsigned char* phash; unsigned int hashlen; Dynobj::create_elf_hash_table(*pdynamic_symbols, local_symcount, &phash, &hashlen); const char* hash_name = this->namepool_.add(".hash", false, NULL); Output_section* hashsec = this->make_output_section(hash_name, elfcpp::SHT_HASH, elfcpp::SHF_ALLOC); Output_section_data* hashdata = new Output_data_const_buffer(phash, hashlen, align); hashsec->add_output_section_data(hashdata); hashsec->set_link_section(dynsym); hashsec->set_entsize(4); odyn->add_section_address(elfcpp::DT_HASH, hashsec); } // Create the version sections. void Layout::create_version_sections(const Versions* versions, const Symbol_table* symtab, unsigned int local_symcount, const std::vector& dynamic_symbols, const Output_section* dynstr) { if (!versions->any_defs() && !versions->any_needs()) return; if (parameters->get_size() == 32) { if (parameters->is_big_endian()) { #ifdef HAVE_TARGET_32_BIG this->sized_create_version_sections SELECT_SIZE_ENDIAN_NAME(32, true)( versions, symtab, local_symcount, dynamic_symbols, dynstr SELECT_SIZE_ENDIAN(32, true)); #else gold_unreachable(); #endif } else { #ifdef HAVE_TARGET_32_LITTLE this->sized_create_version_sections SELECT_SIZE_ENDIAN_NAME(32, false)( versions, symtab, local_symcount, dynamic_symbols, dynstr SELECT_SIZE_ENDIAN(32, false)); #else gold_unreachable(); #endif } } else if (parameters->get_size() == 64) { if (parameters->is_big_endian()) { #ifdef HAVE_TARGET_64_BIG this->sized_create_version_sections SELECT_SIZE_ENDIAN_NAME(64, true)( versions, symtab, local_symcount, dynamic_symbols, dynstr SELECT_SIZE_ENDIAN(64, true)); #else gold_unreachable(); #endif } else { #ifdef HAVE_TARGET_64_LITTLE this->sized_create_version_sections SELECT_SIZE_ENDIAN_NAME(64, false)( versions, symtab, local_symcount, dynamic_symbols, dynstr SELECT_SIZE_ENDIAN(64, false)); #else gold_unreachable(); #endif } } else gold_unreachable(); } // Create the version sections, sized version. template void Layout::sized_create_version_sections( const Versions* versions, const Symbol_table* symtab, unsigned int local_symcount, const std::vector& dynamic_symbols, const Output_section* dynstr ACCEPT_SIZE_ENDIAN) { const char* vname = this->namepool_.add(".gnu.version", false, NULL); Output_section* vsec = this->make_output_section(vname, elfcpp::SHT_GNU_versym, elfcpp::SHF_ALLOC); unsigned char* vbuf; unsigned int vsize; versions->symbol_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)( symtab, &this->dynpool_, local_symcount, dynamic_symbols, &vbuf, &vsize SELECT_SIZE_ENDIAN(size, big_endian)); Output_section_data* vdata = new Output_data_const_buffer(vbuf, vsize, 2); vsec->add_output_section_data(vdata); vsec->set_entsize(2); vsec->set_link_section(this->dynsym_section_); Output_data_dynamic* const odyn = this->dynamic_data_; odyn->add_section_address(elfcpp::DT_VERSYM, vsec); if (versions->any_defs()) { const char* vdname = this->namepool_.add(".gnu.version_d", false, NULL); Output_section *vdsec; vdsec = this->make_output_section(vdname, elfcpp::SHT_GNU_verdef, elfcpp::SHF_ALLOC); unsigned char* vdbuf; unsigned int vdsize; unsigned int vdentries; versions->def_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)( &this->dynpool_, &vdbuf, &vdsize, &vdentries SELECT_SIZE_ENDIAN(size, big_endian)); Output_section_data* vddata = new Output_data_const_buffer(vdbuf, vdsize, 4); vdsec->add_output_section_data(vddata); vdsec->set_link_section(dynstr); vdsec->set_info(vdentries); odyn->add_section_address(elfcpp::DT_VERDEF, vdsec); odyn->add_constant(elfcpp::DT_VERDEFNUM, vdentries); } if (versions->any_needs()) { const char* vnname = this->namepool_.add(".gnu.version_r", false, NULL); Output_section* vnsec; vnsec = this->make_output_section(vnname, elfcpp::SHT_GNU_verneed, elfcpp::SHF_ALLOC); unsigned char* vnbuf; unsigned int vnsize; unsigned int vnentries; versions->need_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian) (&this->dynpool_, &vnbuf, &vnsize, &vnentries SELECT_SIZE_ENDIAN(size, big_endian)); Output_section_data* vndata = new Output_data_const_buffer(vnbuf, vnsize, 4); vnsec->add_output_section_data(vndata); vnsec->set_link_section(dynstr); vnsec->set_info(vnentries); odyn->add_section_address(elfcpp::DT_VERNEED, vnsec); odyn->add_constant(elfcpp::DT_VERNEEDNUM, vnentries); } } // Create the .interp section and PT_INTERP segment. void Layout::create_interp(const Target* target) { const char* interp = this->options_.dynamic_linker(); if (interp == NULL) { interp = target->dynamic_linker(); gold_assert(interp != NULL); } size_t len = strlen(interp) + 1; Output_section_data* odata = new Output_data_const(interp, len, 1); const char* interp_name = this->namepool_.add(".interp", false, NULL); Output_section* osec = this->make_output_section(interp_name, elfcpp::SHT_PROGBITS, elfcpp::SHF_ALLOC); osec->add_output_section_data(odata); Output_segment* oseg = new Output_segment(elfcpp::PT_INTERP, elfcpp::PF_R); this->segment_list_.push_back(oseg); oseg->add_initial_output_section(osec, elfcpp::PF_R); } // Finish the .dynamic section and PT_DYNAMIC segment. void Layout::finish_dynamic_section(const Input_objects* input_objects, const Symbol_table* symtab) { Output_segment* oseg = new Output_segment(elfcpp::PT_DYNAMIC, elfcpp::PF_R | elfcpp::PF_W); this->segment_list_.push_back(oseg); oseg->add_initial_output_section(this->dynamic_section_, elfcpp::PF_R | elfcpp::PF_W); Output_data_dynamic* const odyn = this->dynamic_data_; for (Input_objects::Dynobj_iterator p = input_objects->dynobj_begin(); p != input_objects->dynobj_end(); ++p) { // FIXME: Handle --as-needed. odyn->add_string(elfcpp::DT_NEEDED, (*p)->soname()); } // FIXME: Support --init and --fini. Symbol* sym = symtab->lookup("_init"); if (sym != NULL && sym->is_defined() && !sym->is_from_dynobj()) odyn->add_symbol(elfcpp::DT_INIT, sym); sym = symtab->lookup("_fini"); if (sym != NULL && sym->is_defined() && !sym->is_from_dynobj()) odyn->add_symbol(elfcpp::DT_FINI, sym); // FIXME: Support DT_INIT_ARRAY and DT_FINI_ARRAY. // Add a DT_RPATH entry if needed. const General_options::Dir_list& rpath(this->options_.rpath()); if (!rpath.empty()) { std::string rpath_val; for (General_options::Dir_list::const_iterator p = rpath.begin(); p != rpath.end(); ++p) { if (rpath_val.empty()) rpath_val = p->name(); else { // Eliminate duplicates. General_options::Dir_list::const_iterator q; for (q = rpath.begin(); q != p; ++q) if (q->name() == p->name()) break; if (q == p) { rpath_val += ':'; rpath_val += p->name(); } } } odyn->add_string(elfcpp::DT_RPATH, rpath_val); } // Look for text segments that have dynamic relocations. bool have_textrel = false; for (Segment_list::const_iterator p = this->segment_list_.begin(); p != this->segment_list_.end(); ++p) { if (((*p)->flags() & elfcpp::PF_W) == 0 && (*p)->dynamic_reloc_count() > 0) { have_textrel = true; break; } } // Add a DT_FLAGS entry. We add it even if no flags are set so that // post-link tools can easily modify these flags if desired. unsigned int flags = 0; if (have_textrel) flags |= elfcpp::DF_TEXTREL; odyn->add_constant(elfcpp::DT_FLAGS, flags); } // The mapping of .gnu.linkonce section names to real section names. #define MAPPING_INIT(f, t) { f, sizeof(f) - 1, t, sizeof(t) - 1 } const Layout::Linkonce_mapping Layout::linkonce_mapping[] = { MAPPING_INIT("d.rel.ro", ".data.rel.ro"), // Must be before "d". MAPPING_INIT("t", ".text"), MAPPING_INIT("r", ".rodata"), MAPPING_INIT("d", ".data"), MAPPING_INIT("b", ".bss"), MAPPING_INIT("s", ".sdata"), MAPPING_INIT("sb", ".sbss"), MAPPING_INIT("s2", ".sdata2"), MAPPING_INIT("sb2", ".sbss2"), MAPPING_INIT("wi", ".debug_info"), MAPPING_INIT("td", ".tdata"), MAPPING_INIT("tb", ".tbss"), MAPPING_INIT("lr", ".lrodata"), MAPPING_INIT("l", ".ldata"), MAPPING_INIT("lb", ".lbss"), }; #undef MAPPING_INIT const int Layout::linkonce_mapping_count = sizeof(Layout::linkonce_mapping) / sizeof(Layout::linkonce_mapping[0]); // Return the name of the output section to use for a .gnu.linkonce // section. This is based on the default ELF linker script of the old // GNU linker. For example, we map a name like ".gnu.linkonce.t.foo" // to ".text". Set *PLEN to the length of the name. *PLEN is // initialized to the length of NAME. const char* Layout::linkonce_output_name(const char* name, size_t *plen) { const char* s = name + sizeof(".gnu.linkonce") - 1; if (*s != '.') return name; ++s; const Linkonce_mapping* plm = linkonce_mapping; for (int i = 0; i < linkonce_mapping_count; ++i, ++plm) { if (strncmp(s, plm->from, plm->fromlen) == 0 && s[plm->fromlen] == '.') { *plen = plm->tolen; return plm->to; } } return name; } // Choose the output section name to use given an input section name. // Set *PLEN to the length of the name. *PLEN is initialized to the // length of NAME. const char* Layout::output_section_name(const char* name, size_t* plen) { if (Layout::is_linkonce(name)) { // .gnu.linkonce sections are laid out as though they were named // for the sections are placed into. return Layout::linkonce_output_name(name, plen); } // gcc 4.3 generates the following sorts of section names when it // needs a section name specific to a function: // .text.FN // .rodata.FN // .sdata2.FN // .data.FN // .data.rel.FN // .data.rel.local.FN // .data.rel.ro.FN // .data.rel.ro.local.FN // .sdata.FN // .bss.FN // .sbss.FN // .tdata.FN // .tbss.FN // The GNU linker maps all of those to the part before the .FN, // except that .data.rel.local.FN is mapped to .data, and // .data.rel.ro.local.FN is mapped to .data.rel.ro. The sections // beginning with .data.rel.ro.local are grouped together. // For an anonymous namespace, the string FN can contain a '.'. // Also of interest: .rodata.strN.N, .rodata.cstN, both of which the // GNU linker maps to .rodata. // The .data.rel.ro sections enable a security feature triggered by // the -z relro option. Section which need to be relocated at // program startup time but which may be readonly after startup are // grouped into .data.rel.ro. They are then put into a PT_GNU_RELRO // segment. The dynamic linker will make that segment writable, // perform relocations, and then make it read-only. FIXME: We do // not yet implement this optimization. // It is hard to handle this in a principled way. // These are the rules we follow: // If the section name has no initial '.', or no dot other than an // initial '.', we use the name unchanged (i.e., "mysection" and // ".text" are unchanged). // If the name starts with ".data.rel.ro" we use ".data.rel.ro". // Otherwise, we drop the second '.' and everything that comes after // it (i.e., ".text.XXX" becomes ".text"). const char* s = name; if (*s != '.') return name; ++s; const char* sdot = strchr(s, '.'); if (sdot == NULL) return name; const char* const data_rel_ro = ".data.rel.ro"; if (strncmp(name, data_rel_ro, strlen(data_rel_ro)) == 0) { *plen = strlen(data_rel_ro); return data_rel_ro; } *plen = sdot - name; return name; } // Record the signature of a comdat section, and return whether to // include it in the link. If GROUP is true, this is a regular // section group. If GROUP is false, this is a group signature // derived from the name of a linkonce section. We want linkonce // signatures and group signatures to block each other, but we don't // want a linkonce signature to block another linkonce signature. bool Layout::add_comdat(const char* signature, bool group) { std::string sig(signature); std::pair ins( this->signatures_.insert(std::make_pair(sig, group))); if (ins.second) { // This is the first time we've seen this signature. return true; } if (ins.first->second) { // We've already seen a real section group with this signature. return false; } else if (group) { // This is a real section group, and we've already seen a // linkonce section with this signature. Record that we've seen // a section group, and don't include this section group. ins.first->second = true; return false; } else { // We've already seen a linkonce section and this is a linkonce // section. These don't block each other--this may be the same // symbol name with different section types. return true; } } // Write out the Output_sections. Most won't have anything to write, // since most of the data will come from input sections which are // handled elsewhere. But some Output_sections do have Output_data. void Layout::write_output_sections(Output_file* of) const { for (Section_list::const_iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { if (!(*p)->after_input_sections()) (*p)->write(of); } } // Write out data not associated with a section or the symbol table. void Layout::write_data(const Symbol_table* symtab, Output_file* of) const { if (!parameters->strip_all()) { const Output_section* symtab_section = this->symtab_section_; for (Section_list::const_iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { if ((*p)->needs_symtab_index()) { gold_assert(symtab_section != NULL); unsigned int index = (*p)->symtab_index(); gold_assert(index > 0 && index != -1U); off_t off = (symtab_section->offset() + index * symtab_section->entsize()); symtab->write_section_symbol(*p, of, off); } } } const Output_section* dynsym_section = this->dynsym_section_; for (Section_list::const_iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { if ((*p)->needs_dynsym_index()) { gold_assert(dynsym_section != NULL); unsigned int index = (*p)->dynsym_index(); gold_assert(index > 0 && index != -1U); off_t off = (dynsym_section->offset() + index * dynsym_section->entsize()); symtab->write_section_symbol(*p, of, off); } } // Write out the Output_data which are not in an Output_section. for (Data_list::const_iterator p = this->special_output_list_.begin(); p != this->special_output_list_.end(); ++p) (*p)->write(of); } // Write out the Output_sections which can only be written after the // input sections are complete. void Layout::write_sections_after_input_sections(Output_file* of) const { for (Section_list::const_iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { if ((*p)->after_input_sections()) (*p)->write(of); } } // Write_sections_task methods. // We can always run this task. Task::Is_runnable_type Write_sections_task::is_runnable(Workqueue*) { return IS_RUNNABLE; } // We need to unlock both OUTPUT_SECTIONS_BLOCKER and FINAL_BLOCKER // when finished. class Write_sections_task::Write_sections_locker : public Task_locker { public: Write_sections_locker(Task_token& output_sections_blocker, Task_token& final_blocker, Workqueue* workqueue) : output_sections_block_(output_sections_blocker, workqueue), final_block_(final_blocker, workqueue) { } private: Task_block_token output_sections_block_; Task_block_token final_block_; }; Task_locker* Write_sections_task::locks(Workqueue* workqueue) { return new Write_sections_locker(*this->output_sections_blocker_, *this->final_blocker_, workqueue); } // Run the task--write out the data. void Write_sections_task::run(Workqueue*) { this->layout_->write_output_sections(this->of_); } // Write_data_task methods. // We can always run this task. Task::Is_runnable_type Write_data_task::is_runnable(Workqueue*) { return IS_RUNNABLE; } // We need to unlock FINAL_BLOCKER when finished. Task_locker* Write_data_task::locks(Workqueue* workqueue) { return new Task_locker_block(*this->final_blocker_, workqueue); } // Run the task--write out the data. void Write_data_task::run(Workqueue*) { this->layout_->write_data(this->symtab_, this->of_); } // Write_symbols_task methods. // We can always run this task. Task::Is_runnable_type Write_symbols_task::is_runnable(Workqueue*) { return IS_RUNNABLE; } // We need to unlock FINAL_BLOCKER when finished. Task_locker* Write_symbols_task::locks(Workqueue* workqueue) { return new Task_locker_block(*this->final_blocker_, workqueue); } // Run the task--write out the symbols. void Write_symbols_task::run(Workqueue*) { this->symtab_->write_globals(this->input_objects_, this->sympool_, this->dynpool_, this->of_); } // Write_after_input_sections_task methods. // We can only run this task after the input sections have completed. Task::Is_runnable_type Write_after_input_sections_task::is_runnable(Workqueue*) { if (this->input_sections_blocker_->is_blocked()) return IS_BLOCKED; return IS_RUNNABLE; } // We need to unlock FINAL_BLOCKER when finished. Task_locker* Write_after_input_sections_task::locks(Workqueue* workqueue) { return new Task_locker_block(*this->final_blocker_, workqueue); } // Run the task. void Write_after_input_sections_task::run(Workqueue*) { this->layout_->write_sections_after_input_sections(this->of_); } // Close_task_runner methods. // Run the task--close the file. void Close_task_runner::run(Workqueue*) { this->of_->close(); } // Instantiate the templates we need. We could use the configure // script to restrict this to only the ones for implemented targets. #ifdef HAVE_TARGET_32_LITTLE template Output_section* Layout::layout<32, false>(Sized_relobj<32, false>* object, unsigned int shndx, const char* name, const elfcpp::Shdr<32, false>& shdr, unsigned int, unsigned int, off_t*); #endif #ifdef HAVE_TARGET_32_BIG template Output_section* Layout::layout<32, true>(Sized_relobj<32, true>* object, unsigned int shndx, const char* name, const elfcpp::Shdr<32, true>& shdr, unsigned int, unsigned int, off_t*); #endif #ifdef HAVE_TARGET_64_LITTLE template Output_section* Layout::layout<64, false>(Sized_relobj<64, false>* object, unsigned int shndx, const char* name, const elfcpp::Shdr<64, false>& shdr, unsigned int, unsigned int, off_t*); #endif #ifdef HAVE_TARGET_64_BIG template Output_section* Layout::layout<64, true>(Sized_relobj<64, true>* object, unsigned int shndx, const char* name, const elfcpp::Shdr<64, true>& shdr, unsigned int, unsigned int, off_t*); #endif #ifdef HAVE_TARGET_32_LITTLE template Output_section* Layout::layout_eh_frame<32, false>(Sized_relobj<32, false>* object, const unsigned char* symbols, off_t symbols_size, const unsigned char* symbol_names, off_t symbol_names_size, unsigned int shndx, const elfcpp::Shdr<32, false>& shdr, unsigned int reloc_shndx, unsigned int reloc_type, off_t* off); #endif #ifdef HAVE_TARGET_32_BIG template Output_section* Layout::layout_eh_frame<32, true>(Sized_relobj<32, true>* object, const unsigned char* symbols, off_t symbols_size, const unsigned char* symbol_names, off_t symbol_names_size, unsigned int shndx, const elfcpp::Shdr<32, true>& shdr, unsigned int reloc_shndx, unsigned int reloc_type, off_t* off); #endif #ifdef HAVE_TARGET_64_LITTLE template Output_section* Layout::layout_eh_frame<64, false>(Sized_relobj<64, false>* object, const unsigned char* symbols, off_t symbols_size, const unsigned char* symbol_names, off_t symbol_names_size, unsigned int shndx, const elfcpp::Shdr<64, false>& shdr, unsigned int reloc_shndx, unsigned int reloc_type, off_t* off); #endif #ifdef HAVE_TARGET_64_BIG template Output_section* Layout::layout_eh_frame<64, true>(Sized_relobj<64, true>* object, const unsigned char* symbols, off_t symbols_size, const unsigned char* symbol_names, off_t symbol_names_size, unsigned int shndx, const elfcpp::Shdr<64, true>& shdr, unsigned int reloc_shndx, unsigned int reloc_type, off_t* off); #endif } // End namespace gold.