// layout.cc -- lay out output file sections for gold // Copyright 2006, 2007, 2008 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 #include #include #include "libiberty.h" #include "md5.h" #include "sha1.h" #include "parameters.h" #include "options.h" #include "script.h" #include "script-sections.h" #include "output.h" #include "symtab.h" #include "dynobj.h" #include "ehframe.h" #include "compressed_output.h" #include "reloc.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, const Task* task) { off_t file_size = this->layout_->finalize(this->input_objects_, this->symtab_, this->target_, task); // 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(parameters->options().output_file_name()); if (this->options_.oformat_enum() != General_options::OBJECT_FORMAT_ELF) of->set_is_temporary(); 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, Script_options* script_options) : options_(options), script_options_(script_options), namepool_(), sympool_(), dynpool_(), signatures_(), section_name_map_(), segment_list_(), section_list_(), unattached_section_list_(), sections_are_attached_(false), special_output_list_(), section_headers_(NULL), tls_segment_(NULL), symtab_section_(NULL), symtab_xindex_(NULL), dynsym_section_(NULL), dynsym_xindex_(NULL), dynamic_section_(NULL), dynamic_data_(NULL), eh_frame_section_(NULL), eh_frame_data_(NULL), added_eh_frame_data_(false), eh_frame_hdr_section_(NULL), build_id_note_(NULL), group_signatures_(), output_file_size_(-1), input_requires_executable_stack_(false), input_with_gnu_stack_note_(false), input_without_gnu_stack_note_(false), has_static_tls_(false), any_postprocessing_sections_(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 two unattached Output_data objects: the file header and // the segment headers. this->special_output_list_.reserve(2); } // 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) { 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: // If we are emitting relocations these should be handled // elsewhere. gold_assert(!parameters->options().relocatable() && !parameters->options().emit_relocs()); return false; case elfcpp::SHT_PROGBITS: if (parameters->options().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->options().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_list::const_iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) if (strcmp((*p)->name(), name) == 0) return *p; 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. NAME must be canonicalized in the string // pool, and NAME_KEY is the key. Output_section* Layout::get_output_section(const char* name, Stringpool::Key name_key, elfcpp::Elf_Word type, elfcpp::Elf_Xword flags) { elfcpp::Elf_Xword lookup_flags = flags; // Ignoring SHF_WRITE and SHF_EXECINSTR here means that we combine // read-write with read-only sections. Some other ELF linkers do // not do this. FIXME: Perhaps there should be an option // controlling this. lookup_flags &= ~(elfcpp::SHF_WRITE | elfcpp::SHF_EXECINSTR); const Key key(name_key, std::make_pair(type, lookup_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. For compatibility with the GNU linker, we // combine sections with contents and zero flags with sections // with non-zero flags. This is a workaround for cases where // assembler code forgets to set section flags. FIXME: Perhaps // there should be an option to control this. Output_section* os = NULL; if (type == elfcpp::SHT_PROGBITS) { if (flags == 0) { Output_section* same_name = this->find_output_section(name); if (same_name != NULL && same_name->type() == elfcpp::SHT_PROGBITS && (same_name->flags() & elfcpp::SHF_TLS) == 0) os = same_name; } else if ((flags & elfcpp::SHF_TLS) == 0) { elfcpp::Elf_Xword zero_flags = 0; const Key zero_key(name_key, std::make_pair(type, zero_flags)); Section_name_map::iterator p = this->section_name_map_.find(zero_key); if (p != this->section_name_map_.end()) os = p->second; } } if (os == NULL) os = this->make_output_section(name, type, flags); ins.first->second = os; return os; } } // Pick the output section to use for section NAME, in input file // RELOBJ, with type TYPE and flags FLAGS. RELOBJ may be NULL for a // linker created section. IS_INPUT_SECTION is true if we are // choosing an output section for an input section found in a input // file. This will return NULL if the input section should be // discarded. Output_section* Layout::choose_output_section(const Relobj* relobj, const char* name, elfcpp::Elf_Word type, elfcpp::Elf_Xword flags, bool is_input_section) { // We should not see any input sections after we have attached // sections to segments. gold_assert(!is_input_section || !this->sections_are_attached_); // Some flags in the input section should not be automatically // copied to the output section. flags &= ~ (elfcpp::SHF_INFO_LINK | elfcpp::SHF_LINK_ORDER | elfcpp::SHF_GROUP | elfcpp::SHF_MERGE | elfcpp::SHF_STRINGS); if (this->script_options_->saw_sections_clause()) { // We are using a SECTIONS clause, so the output section is // chosen based only on the name. Script_sections* ss = this->script_options_->script_sections(); const char* file_name = relobj == NULL ? NULL : relobj->name().c_str(); Output_section** output_section_slot; name = ss->output_section_name(file_name, name, &output_section_slot); if (name == NULL) { // The SECTIONS clause says to discard this input section. return NULL; } // If this is an orphan section--one not mentioned in the linker // script--then OUTPUT_SECTION_SLOT will be NULL, and we do the // default processing below. if (output_section_slot != NULL) { if (*output_section_slot != NULL) return *output_section_slot; // We don't put sections found in the linker script into // SECTION_NAME_MAP_. That keeps us from getting confused // if an orphan section is mapped to a section with the same // name as one in the linker script. name = this->namepool_.add(name, false, NULL); Output_section* os = this->make_output_section(name, type, flags); os->set_found_in_sections_clause(); *output_section_slot = os; return os; } } // FIXME: Handle SHF_OS_NONCONFORMING somewhere. // Turn NAME from the name of the input section into the name of the // output section. size_t len = strlen(name); if (is_input_section && !parameters->options().relocatable()) name = Layout::output_section_name(name, &len); Stringpool::Key name_key; name = this->namepool_.add_with_length(name, len, true, &name_key); // Find or make the output section. The output section is selected // based on the section name, type, and flags. return this->get_output_section(name, name_key, type, flags); } // 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; Output_section* os; // In a relocatable link a grouped section must not be combined with // any other sections. if (parameters->options().relocatable() && (shdr.get_sh_flags() & elfcpp::SHF_GROUP) != 0) { name = this->namepool_.add(name, true, NULL); os = this->make_output_section(name, shdr.get_sh_type(), shdr.get_sh_flags()); } else { os = this->choose_output_section(object, name, shdr.get_sh_type(), shdr.get_sh_flags(), true); if (os == NULL) return NULL; } // By default the GNU linker sorts input sections whose names match // .ctor.*, .dtor.*, .init_array.*, or .fini_array.*. The sections // are sorted by name. This is used to implement constructor // priority ordering. We are compatible. if (!this->script_options_->saw_sections_clause() && (is_prefix_of(".ctors.", name) || is_prefix_of(".dtors.", name) || is_prefix_of(".init_array.", name) || is_prefix_of(".fini_array.", name))) os->set_must_sort_attached_input_sections(); // FIXME: Handle SHF_LINK_ORDER somewhere. *off = os->add_input_section(object, shndx, name, shdr, reloc_shndx, this->script_options_->saw_sections_clause()); return os; } // Handle a relocation section when doing a relocatable link. template Output_section* Layout::layout_reloc(Sized_relobj* object, unsigned int, const elfcpp::Shdr& shdr, Output_section* data_section, Relocatable_relocs* rr) { gold_assert(parameters->options().relocatable() || parameters->options().emit_relocs()); int sh_type = shdr.get_sh_type(); std::string name; if (sh_type == elfcpp::SHT_REL) name = ".rel"; else if (sh_type == elfcpp::SHT_RELA) name = ".rela"; else gold_unreachable(); name += data_section->name(); Output_section* os = this->choose_output_section(object, name.c_str(), sh_type, shdr.get_sh_flags(), false); os->set_should_link_to_symtab(); os->set_info_section(data_section); Output_section_data* posd; if (sh_type == elfcpp::SHT_REL) { os->set_entsize(elfcpp::Elf_sizes::rel_size); posd = new Output_relocatable_relocs(rr); } else if (sh_type == elfcpp::SHT_RELA) { os->set_entsize(elfcpp::Elf_sizes::rela_size); posd = new Output_relocatable_relocs(rr); } else gold_unreachable(); os->add_output_section_data(posd); rr->set_output_data(posd); return os; } // Handle a group section when doing a relocatable link. template void Layout::layout_group(Symbol_table* symtab, Sized_relobj* object, unsigned int, const char* group_section_name, const char* signature, const elfcpp::Shdr& shdr, const elfcpp::Elf_Word* contents) { gold_assert(parameters->options().relocatable()); gold_assert(shdr.get_sh_type() == elfcpp::SHT_GROUP); group_section_name = this->namepool_.add(group_section_name, true, NULL); Output_section* os = this->make_output_section(group_section_name, elfcpp::SHT_GROUP, shdr.get_sh_flags()); // We need to find a symbol with the signature in the symbol table. // If we don't find one now, we need to look again later. Symbol* sym = symtab->lookup(signature, NULL); if (sym != NULL) os->set_info_symndx(sym); else { // We will wind up using a symbol whose name is the signature. // So just put the signature in the symbol name pool to save it. signature = symtab->canonicalize_name(signature); this->group_signatures_.push_back(Group_signature(os, signature)); } os->set_should_link_to_symtab(); os->set_entsize(4); section_size_type entry_count = convert_to_section_size_type(shdr.get_sh_size() / 4); Output_section_data* posd = new Output_data_group(object, entry_count, contents); os->add_output_section_data(posd); } // 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) != 0); const char* const name = ".eh_frame"; Output_section* os = this->choose_output_section(object, name, elfcpp::SHT_PROGBITS, elfcpp::SHF_ALLOC, false); if (os == NULL) return NULL; if (this->eh_frame_section_ == NULL) { this->eh_frame_section_ = os; this->eh_frame_data_ = new Eh_frame(); if (this->options_.eh_frame_hdr()) { Output_section* hdr_os = this->choose_output_section(NULL, ".eh_frame_hdr", elfcpp::SHT_PROGBITS, elfcpp::SHF_ALLOC, false); if (hdr_os != NULL) { 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(); if (!this->script_options_->saw_phdrs_clause()) { Output_segment* hdr_oseg; hdr_oseg = this->make_output_segment(elfcpp::PT_GNU_EH_FRAME, elfcpp::PF_R); 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)) { os->update_flags_for_input_section(shdr.get_sh_flags()); // We found a .eh_frame section we are going to optimize, so now // we can add the set of optimized sections to the output // section. We need to postpone adding this until we've found a // section we can optimize so that the .eh_frame section in // crtbegin.o winds up at the start of the output section. if (!this->added_eh_frame_data_) { os->add_output_section_data(this->eh_frame_data_); this->added_eh_frame_data_ = true; } *off = -1; } else { // We couldn't handle this .eh_frame section for some reason. // Add it as a normal section. bool saw_sections_clause = this->script_options_->saw_sections_clause(); *off = os->add_input_section(object, shndx, name, shdr, reloc_shndx, saw_sections_clause); } 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) { Output_section* os = this->choose_output_section(NULL, name, type, flags, false); if (os != NULL) 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; } // Sometimes we compress sections. This is typically done for // sections that are not part of normal program execution (such as // .debug_* sections), and where the readers of these sections know // how to deal with compressed sections. (To make it easier for them, // we will rename the ouput section in such cases from .foo to // .foo.zlib.nnnn, where nnnn is the uncompressed size.) This routine // doesn't say for certain whether we'll compress -- it depends on // commandline options as well -- just whether this section is a // candidate for compression. static bool is_compressible_debug_section(const char* secname) { return (strncmp(secname, ".debug", sizeof(".debug") - 1) == 0); } // 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; if ((flags & elfcpp::SHF_ALLOC) == 0 && strcmp(this->options_.compress_debug_sections(), "none") != 0 && is_compressible_debug_section(name)) os = new Output_compressed_section(&this->options_, name, type, flags); else os = new Output_section(name, type, flags); this->section_list_.push_back(os); // The GNU linker by default sorts some sections by priority, so we // do the same. We need to know that this might happen before we // attach any input sections. if (!this->script_options_->saw_sections_clause() && (strcmp(name, ".ctors") == 0 || strcmp(name, ".dtors") == 0 || strcmp(name, ".init_array") == 0 || strcmp(name, ".fini_array") == 0)) os->set_may_sort_attached_input_sections(); // If we have already attached the sections to segments, then we // need to attach this one now. This happens for sections created // directly by the linker. if (this->sections_are_attached_) this->attach_section_to_segment(os); return os; } // Attach output sections to segments. This is called after we have // seen all the input sections. void Layout::attach_sections_to_segments() { for (Section_list::iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) this->attach_section_to_segment(*p); this->sections_are_attached_ = true; } // Attach an output section to a segment. void Layout::attach_section_to_segment(Output_section* os) { if ((os->flags() & elfcpp::SHF_ALLOC) == 0) this->unattached_section_list_.push_back(os); else this->attach_allocated_section_to_segment(os); } // Attach an allocated output section to a segment. void Layout::attach_allocated_section_to_segment(Output_section* os) { elfcpp::Elf_Xword flags = os->flags(); gold_assert((flags & elfcpp::SHF_ALLOC) != 0); if (parameters->options().relocatable()) return; // If we have a SECTIONS clause, we can't handle the attachment to // segments until after we've seen all the sections. if (this->script_options_->saw_sections_clause()) return; gold_assert(!this->script_options_->saw_phdrs_clause()); // This output section goes into a PT_LOAD segment. elfcpp::Elf_Word seg_flags = Layout::section_flags_to_segment(flags); // In general 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 use a linker script. 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)) { // If -Tbss was specified, we need to separate the data // and BSS segments. if (this->options_.user_set_Tbss()) { if ((os->type() == elfcpp::SHT_NOBITS) == (*p)->has_any_data_sections()) continue; } (*p)->add_output_section(os, seg_flags); break; } } if (p == this->segment_list_.end()) { Output_segment* oseg = this->make_output_segment(elfcpp::PT_LOAD, seg_flags); oseg->add_output_section(os, seg_flags); } // If we see a loadable SHT_NOTE section, we create a PT_NOTE // segment. if (os->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 = this->make_output_segment(elfcpp::PT_NOTE, seg_flags); 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_ = this->make_output_segment(elfcpp::PT_TLS, seg_flags); this->tls_segment_->add_output_section(os, seg_flags); } } // Make an output section for a script. Output_section* Layout::make_output_section_for_script(const char* name) { name = this->namepool_.add(name, false, NULL); Output_section* os = this->make_output_section(name, elfcpp::SHT_PROGBITS, elfcpp::SHF_ALLOC); os->set_found_in_sections_clause(); return os; } // Return the number of segments we expect to see. size_t Layout::expected_segment_count() const { size_t ret = this->segment_list_.size(); // If we didn't see a SECTIONS clause in a linker script, we should // already have the complete list of segments. Otherwise we ask the // SECTIONS clause how many segments it expects, and add in the ones // we already have (PT_GNU_STACK, PT_GNU_EH_FRAME, etc.) if (!this->script_options_->saw_sections_clause()) return ret; else { const Script_sections* ss = this->script_options_->script_sections(); return ret + ss->expected_segment_count(this); } } // 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(Symbol_table* symtab) { if (parameters->doing_static_link()) return; this->dynamic_section_ = this->choose_output_section(NULL, ".dynamic", elfcpp::SHT_DYNAMIC, (elfcpp::SHF_ALLOC | elfcpp::SHF_WRITE), false); symtab->define_in_output_data("_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) { 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(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 true); // only_if_ref symtab->define_in_output_data(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 true); // only_if_ref } } } // Define symbols for group signatures. void Layout::define_group_signatures(Symbol_table* symtab) { for (Group_signatures::iterator p = this->group_signatures_.begin(); p != this->group_signatures_.end(); ++p) { Symbol* sym = symtab->lookup(p->signature, NULL); if (sym != NULL) p->section->set_info_symndx(sym); else { // Force the name of the group section to the group // signature, and use the group's section symbol as the // signature symbol. if (strcmp(p->section->name(), p->signature) != 0) { const char* name = this->namepool_.add(p->signature, true, NULL); p->section->set_name(name); } p->section->set_needs_symtab_index(); p->section->set_info_section_symndx(p->section); } } this->group_signatures_.clear(); } // 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; } gold_assert(!this->script_options_->saw_phdrs_clause()); Output_segment* load_seg = this->make_output_segment(elfcpp::PT_LOAD, elfcpp::PF_R); 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* target, const Task* task) { target->finalize_sections(this); this->count_local_symbols(task, input_objects); this->create_gold_note(); this->create_executable_stack_info(target); this->create_build_id(); Output_segment* phdr_seg = NULL; if (!parameters->options().relocatable() && !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. if (!this->script_options_->saw_phdrs_clause()) phdr_seg = this->make_output_segment(elfcpp::PT_PHDR, elfcpp::PF_R); // Create the dynamic symbol table, including the hash table. Output_section* dynstr; std::vector dynamic_symbols; unsigned int local_dynamic_count; Versions versions(*this->script_options()->version_script_info(), &this->dynpool_); this->create_dynamic_symtab(input_objects, 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->options().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); } // If there is a SECTIONS clause, put all the input sections into // the required order. Output_segment* load_seg; if (this->script_options_->saw_sections_clause()) load_seg = this->set_section_addresses_from_script(symtab); else if (parameters->options().relocatable()) load_seg = NULL; else load_seg = this->find_first_load_seg(); if (this->options_.oformat_enum() != General_options::OBJECT_FORMAT_ELF) load_seg = NULL; gold_assert(phdr_seg == NULL || load_seg != NULL); // Lay out the segment headers. Output_segment_headers* segment_headers; if (parameters->options().relocatable()) segment_headers = NULL; else { segment_headers = new Output_segment_headers(this->segment_list_); if (load_seg != NULL) load_seg->add_initial_output_data(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, this->options_.entry()); if (load_seg != NULL) load_seg->add_initial_output_data(file_header); this->special_output_list_.push_back(file_header); if (segment_headers != NULL) this->special_output_list_.push_back(segment_headers); if (this->script_options_->saw_phdrs_clause() && !parameters->options().relocatable()) { // Support use of FILEHDRS and PHDRS attachments in a PHDRS // clause in a linker script. Script_sections* ss = this->script_options_->script_sections(); ss->put_headers_in_phdrs(file_header, segment_headers); } // We set the output section indexes in set_segment_offsets and // set_section_indexes. unsigned int shndx = 1; // Set the file offsets of all the segments, and all the sections // they contain. off_t off; if (!parameters->options().relocatable()) off = this->set_segment_offsets(target, load_seg, &shndx); else off = this->set_relocatable_section_offsets(file_header, &shndx); // Set the file offsets of all the non-data sections we've seen so // far which don't have to wait for the input sections. We need // this in order to finalize local symbols in non-allocated // sections. off = this->set_section_offsets(off, BEFORE_INPUT_SECTIONS_PASS); // Set the section indexes of all unallocated sections seen so far, // in case any of them are somehow referenced by a symbol. shndx = this->set_section_indexes(shndx); // Create the symbol table sections. this->create_symtab_sections(input_objects, symtab, shndx, &off); if (!parameters->doing_static_link()) this->assign_local_dynsym_offsets(input_objects); // Process any symbol assignments from a linker script. This must // be called after the symbol table has been finalized. this->script_options_->finalize_symbols(symtab, this); // Create the .shstrtab section. Output_section* shstrtab_section = this->create_shstrtab(); // Set the file offsets of the rest of the non-data sections which // don't have to wait for the input sections. off = this->set_section_offsets(off, BEFORE_INPUT_SECTIONS_PASS); // Now that all sections have been created, set the section indexes // for any sections which haven't been done yet. shndx = this->set_section_indexes(shndx); // Create the section table header. this->create_shdrs(shstrtab_section, &off); // If there are no sections which require postprocessing, we can // handle the section names now, and avoid a resize later. if (!this->any_postprocessing_sections_) off = this->set_section_offsets(off, STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS); file_header->set_section_info(this->section_headers_, shstrtab_section); // Now we know exactly where everything goes in the output file // (except for non-allocated sections which require postprocessing). Output_data::layout_complete(); this->output_file_size_ = off; return off; } // Create a note header following the format defined in the ELF ABI. // NAME is the name, NOTE_TYPE is the type, DESCSZ is the size of the // descriptor. ALLOCATE is true if the section should be allocated in // memory. This returns the new note section. It sets // *TRAILING_PADDING to the number of trailing zero bytes required. Output_section* Layout::create_note(const char* name, int note_type, size_t descsz, bool allocate, size_t* trailing_padding) { // 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->target().get_size(); #else const int size = 32; #endif // The contents of the .note section. size_t namesz = strlen(name) + 1; size_t aligned_namesz = align_address(namesz, size / 8); size_t aligned_descsz = align_address(descsz, size / 8); size_t notehdrsz = 3 * (size / 8) + aligned_namesz; unsigned char* buffer = new unsigned char[notehdrsz]; memset(buffer, 0, notehdrsz); bool is_big_endian = parameters->target().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); const char* note_name = this->namepool_.add(".note", false, NULL); elfcpp::Elf_Xword flags = 0; if (allocate) flags = elfcpp::SHF_ALLOC; Output_section* os = this->make_output_section(note_name, elfcpp::SHT_NOTE, flags); Output_section_data* posd = new Output_data_const_buffer(buffer, notehdrsz, size / 8); os->add_output_section_data(posd); *trailing_padding = aligned_descsz - descsz; return os; } // For an executable or shared library, create a note to record the // version of gold used to create the binary. void Layout::create_gold_note() { if (parameters->options().relocatable()) return; std::string desc = std::string("gold ") + gold::get_version_string(); size_t trailing_padding; Output_section *os = this->create_note("GNU", elfcpp::NT_GNU_GOLD_VERSION, desc.size(), false, &trailing_padding); Output_section_data* posd = new Output_data_const(desc, 4); os->add_output_section_data(posd); if (trailing_padding > 0) { posd = new Output_data_fixed_space(trailing_padding, 0); 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->options().relocatable()) { 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 { if (this->script_options_->saw_phdrs_clause()) return; int flags = elfcpp::PF_R | elfcpp::PF_W; if (is_stack_executable) flags |= elfcpp::PF_X; this->make_output_segment(elfcpp::PT_GNU_STACK, flags); } } // If --build-id was used, set up the build ID note. void Layout::create_build_id() { if (!parameters->options().user_set_build_id()) return; const char* style = parameters->options().build_id(); if (strcmp(style, "none") == 0) return; // Set DESCSZ to the size of the note descriptor. When possible, // set DESC to the note descriptor contents. size_t descsz; std::string desc; if (strcmp(style, "md5") == 0) descsz = 128 / 8; else if (strcmp(style, "sha1") == 0) descsz = 160 / 8; else if (strcmp(style, "uuid") == 0) { const size_t uuidsz = 128 / 8; char buffer[uuidsz]; memset(buffer, 0, uuidsz); int descriptor = ::open("/dev/urandom", O_RDONLY); if (descriptor < 0) gold_error(_("--build-id=uuid failed: could not open /dev/urandom: %s"), strerror(errno)); else { ssize_t got = ::read(descriptor, buffer, uuidsz); ::close(descriptor); if (got < 0) gold_error(_("/dev/urandom: read failed: %s"), strerror(errno)); else if (static_cast(got) != uuidsz) gold_error(_("/dev/urandom: expected %zu bytes, got %zd bytes"), uuidsz, got); } desc.assign(buffer, uuidsz); descsz = uuidsz; } else if (strncmp(style, "0x", 2) == 0) { hex_init(); const char* p = style + 2; while (*p != '\0') { if (hex_p(p[0]) && hex_p(p[1])) { char c = (hex_value(p[0]) << 4) | hex_value(p[1]); desc += c; p += 2; } else if (*p == '-' || *p == ':') ++p; else gold_fatal(_("--build-id argument '%s' not a valid hex number"), style); } descsz = desc.size(); } else gold_fatal(_("unrecognized --build-id argument '%s'"), style); // Create the note. size_t trailing_padding; Output_section* os = this->create_note("GNU", elfcpp::NT_GNU_BUILD_ID, descsz, true, &trailing_padding); if (!desc.empty()) { // We know the value already, so we fill it in now. gold_assert(desc.size() == descsz); Output_section_data* posd = new Output_data_const(desc, 4); os->add_output_section_data(posd); if (trailing_padding != 0) { posd = new Output_data_fixed_space(trailing_padding, 0); os->add_output_section_data(posd); } } else { // We need to compute a checksum after we have completed the // link. gold_assert(trailing_padding == 0); this->build_id_note_ = new Output_data_fixed_space(descsz, 4); os->add_output_section_data(this->build_id_note_); os->set_after_input_sections(); } } // 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; } // If the addresses are set already, sort by load address. if (seg1->are_addresses_set()) { if (!seg2->are_addresses_set()) return true; unsigned int section_count1 = seg1->output_section_count(); unsigned int section_count2 = seg2->output_section_count(); if (section_count1 == 0 && section_count2 > 0) return true; if (section_count1 > 0 && section_count2 == 0) return false; uint64_t paddr1 = seg1->first_section_load_address(); uint64_t paddr2 = seg2->first_section_load_address(); if (paddr1 != paddr2) return paddr1 < paddr2; } else if (seg2->are_addresses_set()) return false; // We sort PT_LOAD segments based on the flags. Readonly segments // come before writable segments. Then writable segments with data // come before writable segments without data. 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_W) != 0 && seg1->has_any_data_sections() != seg2->has_any_data_sections()) return seg1->has_any_data_sections(); 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; // We shouldn't get here--we shouldn't create segments which we // can't distinguish. gold_unreachable(); } // 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 (this->options_.user_set_Ttext()) addr = this->options_.Ttext(); else if (parameters->options().shared()) addr = 0; else addr = target->default_text_segment_address(); off_t off = 0; // If LOAD_SEG is NULL, then the file header and segment headers // will not be loadable. But they still need to be at offset 0 in // the file. Set their offsets now. if (load_seg == NULL) { for (Data_list::iterator p = this->special_output_list_.begin(); p != this->special_output_list_.end(); ++p) { off = align_address(off, (*p)->addralign()); (*p)->set_address_and_file_offset(0, off); off += (*p)->data_size(); } } 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; bool are_addresses_set = (*p)->are_addresses_set(); if (are_addresses_set) { // When it comes to setting file offsets, we care about // the physical address. addr = (*p)->paddr(); } else if (this->options_.user_set_Tdata() && ((*p)->flags() & elfcpp::PF_W) != 0 && (!this->options_.user_set_Tbss() || (*p)->has_any_data_sections())) { addr = this->options_.Tdata(); are_addresses_set = true; } else if (this->options_.user_set_Tbss() && ((*p)->flags() & elfcpp::PF_W) != 0 && !(*p)->has_any_data_sections()) { addr = this->options_.Tbss(); are_addresses_set = true; } uint64_t orig_addr = addr; uint64_t orig_off = off; uint64_t aligned_addr = 0; uint64_t abi_pagesize = target->abi_pagesize(); // FIXME: This should depend on the -n and -N options. (*p)->set_minimum_p_align(target->common_pagesize()); if (are_addresses_set) { // Adjust the file offset to the same address modulo the // page size. uint64_t unsigned_off = off; uint64_t aligned_off = ((unsigned_off & ~(abi_pagesize - 1)) | (addr & (abi_pagesize - 1))); if (aligned_off < unsigned_off) aligned_off += abi_pagesize; off = aligned_off; } else { // 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. addr = align_address(addr, (*p)->maximum_alignment()); aligned_addr = addr; if (was_readonly && ((*p)->flags() & elfcpp::PF_W) != 0) { if ((addr & (abi_pagesize - 1)) != 0) addr = addr + abi_pagesize; } off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1)); } unsigned int shndx_hold = *pshndx; uint64_t new_addr = (*p)->set_section_addresses(this, false, 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 (!are_addresses_set && 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); addr = align_address(addr, (*p)->maximum_alignment()); off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1)); new_addr = (*p)->set_section_addresses(this, true, 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(); } // Set the TLS offsets for each section in the PT_TLS segment. if (this->tls_segment_ != NULL) this->tls_segment_->set_tls_offsets(); return off; } // Set the offsets of all the allocated sections when doing a // relocatable link. This does the same jobs as set_segment_offsets, // only for a relocatable link. off_t Layout::set_relocatable_section_offsets(Output_data* file_header, unsigned int *pshndx) { off_t off = 0; file_header->set_address_and_file_offset(0, 0); off += file_header->data_size(); for (Section_list::iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { // We skip unallocated sections here, except that group sections // have to come first. if (((*p)->flags() & elfcpp::SHF_ALLOC) == 0 && (*p)->type() != elfcpp::SHT_GROUP) continue; off = align_address(off, (*p)->addralign()); // The linker script might have set the address. if (!(*p)->is_address_valid()) (*p)->set_address(0); (*p)->set_file_offset(off); (*p)->finalize_data_size(); off += (*p)->data_size(); (*p)->set_out_shndx(*pshndx); ++*pshndx; } return off; } // Set the file offset of all the sections not associated with a // segment. off_t Layout::set_section_offsets(off_t off, Layout::Section_offset_pass pass) { for (Section_list::iterator p = this->unattached_section_list_.begin(); p != this->unattached_section_list_.end(); ++p) { // The symtab section is handled in create_symtab_sections. if (*p == this->symtab_section_) continue; // If we've already set the data size, don't set it again. if ((*p)->is_offset_valid() && (*p)->is_data_size_valid()) continue; if (pass == BEFORE_INPUT_SECTIONS_PASS && (*p)->requires_postprocessing()) { (*p)->create_postprocessing_buffer(); this->any_postprocessing_sections_ = true; } if (pass == BEFORE_INPUT_SECTIONS_PASS && (*p)->after_input_sections()) continue; else if (pass == POSTPROCESSING_SECTIONS_PASS && (!(*p)->after_input_sections() || (*p)->type() == elfcpp::SHT_STRTAB)) continue; else if (pass == STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS && (!(*p)->after_input_sections() || (*p)->type() != elfcpp::SHT_STRTAB)) continue; off = align_address(off, (*p)->addralign()); (*p)->set_file_offset(off); (*p)->finalize_data_size(); off += (*p)->data_size(); // At this point the name must be set. if (pass != STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS) this->namepool_.add((*p)->name(), false, NULL); } 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) { if (!(*p)->has_out_shndx()) { (*p)->set_out_shndx(shndx); ++shndx; } } return shndx; } // Set the section addresses according to the linker script. This is // only called when we see a SECTIONS clause. This returns the // program segment which should hold the file header and segment // headers, if any. It will return NULL if they should not be in a // segment. Output_segment* Layout::set_section_addresses_from_script(Symbol_table* symtab) { Script_sections* ss = this->script_options_->script_sections(); gold_assert(ss->saw_sections_clause()); // Place each orphaned output section in the script. for (Section_list::iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { if (!(*p)->found_in_sections_clause()) ss->place_orphan(*p); } return this->script_options_->set_section_addresses(symtab, this); } // Count the local symbols in the regular symbol table and the dynamic // symbol table, and build the respective string pools. void Layout::count_local_symbols(const Task* task, const Input_objects* input_objects) { // First, figure out an upper bound on the number of symbols we'll // be inserting into each pool. This helps us create the pools with // the right size, to avoid unnecessary hashtable resizing. unsigned int symbol_count = 0; for (Input_objects::Relobj_iterator p = input_objects->relobj_begin(); p != input_objects->relobj_end(); ++p) symbol_count += (*p)->local_symbol_count(); // Go from "upper bound" to "estimate." We overcount for two // reasons: we double-count symbols that occur in more than one // object file, and we count symbols that are dropped from the // output. Add it all together and assume we overcount by 100%. symbol_count /= 2; // We assume all symbols will go into both the sympool and dynpool. this->sympool_.reserve(symbol_count); this->dynpool_.reserve(symbol_count); for (Input_objects::Relobj_iterator p = input_objects->relobj_begin(); p != input_objects->relobj_end(); ++p) { Task_lock_obj tlo(task, *p); (*p)->count_local_symbols(&this->sympool_, &this->dynpool_); } } // 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. SHNUM is the number of sections so far. void Layout::create_symtab_sections(const Input_objects* input_objects, Symbol_table* symtab, unsigned int shnum, off_t* poff) { int symsize; unsigned int align; if (parameters->target().get_size() == 32) { symsize = elfcpp::Elf_sizes<32>::sym_size; align = 4; } else if (parameters->target().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) { unsigned int index = (*p)->finalize_local_symbols(local_symbol_index, off); 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(off, dynoff, dyn_global_index, dyncount, &this->sympool_, &local_symcount); if (!parameters->options().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_fixed_space(off - startoff, align); osymtab->add_output_section_data(pos); // We generate a .symtab_shndx section if we have more than // SHN_LORESERVE sections. Technically it is possible that we // don't need one, because it is possible that there are no // symbols in any of sections with indexes larger than // SHN_LORESERVE. That is probably unusual, though, and it is // easier to always create one than to compute section indexes // twice (once here, once when writing out the symbols). if (shnum >= elfcpp::SHN_LORESERVE) { const char* symtab_xindex_name = this->namepool_.add(".symtab_shndx", false, NULL); Output_section* osymtab_xindex = this->make_output_section(symtab_xindex_name, elfcpp::SHT_SYMTAB_SHNDX, 0); size_t symcount = (off - startoff) / symsize; this->symtab_xindex_ = new Output_symtab_xindex(symcount); osymtab_xindex->add_output_section_data(this->symtab_xindex_); osymtab_xindex->set_link_section(osymtab); osymtab_xindex->set_addralign(4); osymtab_xindex->set_entsize(4); osymtab_xindex->set_after_input_sections(); // This tells the driver code to wait until the symbol table // has written out before writing out the postprocessing // sections, including the .symtab_shndx section. this->any_postprocessing_sections_ = true; } 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_file_offset(startoff); osymtab->finalize_data_size(); 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); Output_section* os = this->make_output_section(name, elfcpp::SHT_STRTAB, 0); // We can't write out this section until we've set all the section // names, and we don't set the names of compressed output sections // until relocations are complete. os->set_after_input_sections(); 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. void Layout::create_shdrs(const Output_section* shstrtab_section, off_t* poff) { Output_section_headers* oshdrs; oshdrs = new Output_section_headers(this, &this->segment_list_, &this->section_list_, &this->unattached_section_list_, &this->namepool_, shstrtab_section); off_t off = align_address(*poff, oshdrs->addralign()); oshdrs->set_address_and_file_offset(0, off); off += oshdrs->data_size(); *poff = off; this->section_headers_ = oshdrs; } // Count the allocated sections. size_t Layout::allocated_output_section_count() const { size_t section_count = 0; for (Segment_list::const_iterator p = this->segment_list_.begin(); p != this->segment_list_.end(); ++p) section_count += (*p)->output_section_count(); return section_count; } // Create the dynamic symbol table. void Layout::create_dynamic_symtab(const Input_objects* input_objects, 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; } } // Count the local symbols that need to go in the dynamic symbol table, // and set the dynamic symbol indexes. for (Input_objects::Relobj_iterator p = input_objects->relobj_begin(); p != input_objects->relobj_end(); ++p) { unsigned int new_index = (*p)->set_local_dynsym_indexes(index); index = new_index; } unsigned int local_symcount = index; *plocal_dynamic_count = local_symcount; index = symtab->set_dynsym_indexes(index, pdynamic_symbols, &this->dynpool_, pversions); int symsize; unsigned int align; const int size = parameters->target().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. Output_section* dynsym = this->choose_output_section(NULL, ".dynsym", elfcpp::SHT_DYNSYM, elfcpp::SHF_ALLOC, false); Output_section_data* odata = new Output_data_fixed_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); // If there are more than SHN_LORESERVE allocated sections, we // create a .dynsym_shndx section. It is possible that we don't // need one, because it is possible that there are no dynamic // symbols in any of the sections with indexes larger than // SHN_LORESERVE. This is probably unusual, though, and at this // time we don't know the actual section indexes so it is // inconvenient to check. if (this->allocated_output_section_count() >= elfcpp::SHN_LORESERVE) { Output_section* dynsym_xindex = this->choose_output_section(NULL, ".dynsym_shndx", elfcpp::SHT_SYMTAB_SHNDX, elfcpp::SHF_ALLOC, false); this->dynsym_xindex_ = new Output_symtab_xindex(index); dynsym_xindex->add_output_section_data(this->dynsym_xindex_); dynsym_xindex->set_link_section(dynsym); dynsym_xindex->set_addralign(4); dynsym_xindex->set_entsize(4); dynsym_xindex->set_after_input_sections(); // This tells the driver code to wait until the symbol table has // written out before writing out the postprocessing sections, // including the .dynsym_shndx section. this->any_postprocessing_sections_ = true; } // Create the dynamic string table section. Output_section* dynstr = this->choose_output_section(NULL, ".dynstr", elfcpp::SHT_STRTAB, elfcpp::SHF_ALLOC, false); 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. if (strcmp(parameters->options().hash_style(), "sysv") == 0 || strcmp(parameters->options().hash_style(), "both") == 0) { unsigned char* phash; unsigned int hashlen; Dynobj::create_elf_hash_table(*pdynamic_symbols, local_symcount, &phash, &hashlen); Output_section* hashsec = this->choose_output_section(NULL, ".hash", elfcpp::SHT_HASH, elfcpp::SHF_ALLOC, false); 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); } if (strcmp(parameters->options().hash_style(), "gnu") == 0 || strcmp(parameters->options().hash_style(), "both") == 0) { unsigned char* phash; unsigned int hashlen; Dynobj::create_gnu_hash_table(*pdynamic_symbols, local_symcount, &phash, &hashlen); Output_section* hashsec = this->choose_output_section(NULL, ".gnu.hash", elfcpp::SHT_GNU_HASH, elfcpp::SHF_ALLOC, false); 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_GNU_HASH, hashsec); } } // Assign offsets to each local portion of the dynamic symbol table. void Layout::assign_local_dynsym_offsets(const Input_objects* input_objects) { Output_section* dynsym = this->dynsym_section_; gold_assert(dynsym != NULL); off_t off = dynsym->offset(); // Skip the dummy symbol at the start of the section. off += dynsym->entsize(); for (Input_objects::Relobj_iterator p = input_objects->relobj_begin(); p != input_objects->relobj_end(); ++p) { unsigned int count = (*p)->set_local_dynsym_offset(off); off += count * dynsym->entsize(); } } // 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; switch (parameters->size_and_endianness()) { #ifdef HAVE_TARGET_32_LITTLE case Parameters::TARGET_32_LITTLE: this->sized_create_version_sections<32, false>(versions, symtab, local_symcount, dynamic_symbols, dynstr); break; #endif #ifdef HAVE_TARGET_32_BIG case Parameters::TARGET_32_BIG: this->sized_create_version_sections<32, true>(versions, symtab, local_symcount, dynamic_symbols, dynstr); break; #endif #ifdef HAVE_TARGET_64_LITTLE case Parameters::TARGET_64_LITTLE: this->sized_create_version_sections<64, false>(versions, symtab, local_symcount, dynamic_symbols, dynstr); break; #endif #ifdef HAVE_TARGET_64_BIG case Parameters::TARGET_64_BIG: this->sized_create_version_sections<64, true>(versions, symtab, local_symcount, dynamic_symbols, dynstr); break; #endif default: 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) { Output_section* vsec = this->choose_output_section(NULL, ".gnu.version", elfcpp::SHT_GNU_versym, elfcpp::SHF_ALLOC, false); unsigned char* vbuf; unsigned int vsize; versions->symbol_section_contents(symtab, &this->dynpool_, local_symcount, dynamic_symbols, &vbuf, &vsize); 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()) { Output_section* vdsec; vdsec= this->choose_output_section(NULL, ".gnu.version_d", elfcpp::SHT_GNU_verdef, elfcpp::SHF_ALLOC, false); unsigned char* vdbuf; unsigned int vdsize; unsigned int vdentries; versions->def_section_contents(&this->dynpool_, &vdbuf, &vdsize, &vdentries); 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()) { Output_section* vnsec; vnsec = this->choose_output_section(NULL, ".gnu.version_r", elfcpp::SHT_GNU_verneed, elfcpp::SHF_ALLOC, false); unsigned char* vnbuf; unsigned int vnsize; unsigned int vnentries; versions->need_section_contents(&this->dynpool_, &vnbuf, &vnsize, &vnentries); 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); Output_section* osec = this->choose_output_section(NULL, ".interp", elfcpp::SHT_PROGBITS, elfcpp::SHF_ALLOC, false); osec->add_output_section_data(odata); if (!this->script_options_->saw_phdrs_clause()) { Output_segment* oseg = this->make_output_segment(elfcpp::PT_INTERP, elfcpp::PF_R); 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) { if (!this->script_options_->saw_phdrs_clause()) { Output_segment* oseg = this->make_output_segment(elfcpp::PT_DYNAMIC, (elfcpp::PF_R | elfcpp::PF_W)); 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()); } if (parameters->options().shared()) { const char* soname = this->options_.soname(); if (soname != NULL) odyn->add_string(elfcpp::DT_SONAME, 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); if (parameters->options().enable_new_dtags()) odyn->add_string(elfcpp::DT_RUNPATH, rpath_val); } // Look for text segments that have dynamic relocations. bool have_textrel = false; if (!this->script_options_->saw_sections_clause()) { 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; } } } else { // We don't know the section -> segment mapping, so we are // conservative and just look for readonly sections with // relocations. If those sections wind up in writable segments, // then we have created an unnecessary DT_TEXTREL entry. for (Section_list::const_iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { if (((*p)->flags() & elfcpp::SHF_ALLOC) != 0 && ((*p)->flags() & elfcpp::SHF_WRITE) == 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) { // Add a DT_TEXTREL for compatibility with older loaders. odyn->add_constant(elfcpp::DT_TEXTREL, 0); flags |= elfcpp::DF_TEXTREL; } if (parameters->options().shared() && this->has_static_tls()) flags |= elfcpp::DF_STATIC_TLS; odyn->add_constant(elfcpp::DT_FLAGS, flags); flags = 0; if (parameters->options().initfirst()) flags |= elfcpp::DF_1_INITFIRST; if (parameters->options().interpose()) flags |= elfcpp::DF_1_INTERPOSE; if (parameters->options().loadfltr()) flags |= elfcpp::DF_1_LOADFLTR; if (parameters->options().nodefaultlib()) flags |= elfcpp::DF_1_NODEFLIB; if (parameters->options().nodelete()) flags |= elfcpp::DF_1_NODELETE; if (parameters->options().nodlopen()) flags |= elfcpp::DF_1_NOOPEN; if (parameters->options().nodump()) flags |= elfcpp::DF_1_NODUMP; if (!parameters->options().shared()) flags &= ~(elfcpp::DF_1_INITFIRST | elfcpp::DF_1_NODELETE | elfcpp::DF_1_NOOPEN); if (flags) odyn->add_constant(elfcpp::DT_FLAGS_1, 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; } } // Store the allocated sections into the section list. void Layout::get_allocated_sections(Section_list* section_list) const { for (Section_list::const_iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) if (((*p)->flags() & elfcpp::SHF_ALLOC) != 0) section_list->push_back(*p); } // Create an output segment. Output_segment* Layout::make_output_segment(elfcpp::Elf_Word type, elfcpp::Elf_Word flags) { gold_assert(!parameters->options().relocatable()); Output_segment* oseg = new Output_segment(type, flags); this->segment_list_.push_back(oseg); return oseg; } // 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->options().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, this->symtab_xindex_, 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, this->dynsym_xindex_, 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) { // Determine the final section offsets, and thus the final output // file size. Note we finalize the .shstrab last, to allow the // after_input_section sections to modify their section-names before // writing. if (this->any_postprocessing_sections_) { off_t off = this->output_file_size_; off = this->set_section_offsets(off, POSTPROCESSING_SECTIONS_PASS); // Now that we've finalized the names, we can finalize the shstrab. off = this->set_section_offsets(off, STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS); if (off > this->output_file_size_) { of->resize(off); this->output_file_size_ = off; } } for (Section_list::const_iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) { if ((*p)->after_input_sections()) (*p)->write(of); } this->section_headers_->write(of); } // If the build ID requires computing a checksum, do so here, and // write it out. We compute a checksum over the entire file because // that is simplest. void Layout::write_build_id(Output_file* of) const { if (this->build_id_note_ == NULL) return; const unsigned char* iv = of->get_input_view(0, this->output_file_size_); unsigned char* ov = of->get_output_view(this->build_id_note_->offset(), this->build_id_note_->data_size()); const char* style = parameters->options().build_id(); if (strcmp(style, "sha1") == 0) { sha1_ctx ctx; sha1_init_ctx(&ctx); sha1_process_bytes(iv, this->output_file_size_, &ctx); sha1_finish_ctx(&ctx, ov); } else if (strcmp(style, "md5") == 0) { md5_ctx ctx; md5_init_ctx(&ctx); md5_process_bytes(iv, this->output_file_size_, &ctx); md5_finish_ctx(&ctx, ov); } else gold_unreachable(); of->write_output_view(this->build_id_note_->offset(), this->build_id_note_->data_size(), ov); of->free_input_view(0, this->output_file_size_, iv); } // Write out a binary file. This is called after the link is // complete. IN is the temporary output file we used to generate the // ELF code. We simply walk through the segments, read them from // their file offset in IN, and write them to their load address in // the output file. FIXME: with a bit more work, we could support // S-records and/or Intel hex format here. void Layout::write_binary(Output_file* in) const { gold_assert(this->options_.oformat_enum() == General_options::OBJECT_FORMAT_BINARY); // Get the size of the binary file. uint64_t max_load_address = 0; for (Segment_list::const_iterator p = this->segment_list_.begin(); p != this->segment_list_.end(); ++p) { if ((*p)->type() == elfcpp::PT_LOAD && (*p)->filesz() > 0) { uint64_t max_paddr = (*p)->paddr() + (*p)->filesz(); if (max_paddr > max_load_address) max_load_address = max_paddr; } } Output_file out(parameters->options().output_file_name()); out.open(max_load_address); for (Segment_list::const_iterator p = this->segment_list_.begin(); p != this->segment_list_.end(); ++p) { if ((*p)->type() == elfcpp::PT_LOAD && (*p)->filesz() > 0) { const unsigned char* vin = in->get_input_view((*p)->offset(), (*p)->filesz()); unsigned char* vout = out.get_output_view((*p)->paddr(), (*p)->filesz()); memcpy(vout, vin, (*p)->filesz()); out.write_output_view((*p)->paddr(), (*p)->filesz(), vout); in->free_input_view((*p)->offset(), (*p)->filesz(), vin); } } out.close(); } // Print statistical information to stderr. This is used for --stats. void Layout::print_stats() const { this->namepool_.print_stats("section name pool"); this->sympool_.print_stats("output symbol name pool"); this->dynpool_.print_stats("dynamic name pool"); for (Section_list::const_iterator p = this->section_list_.begin(); p != this->section_list_.end(); ++p) (*p)->print_merge_stats(); } // Write_sections_task methods. // We can always run this task. Task_token* Write_sections_task::is_runnable() { return NULL; } // We need to unlock both OUTPUT_SECTIONS_BLOCKER and FINAL_BLOCKER // when finished. void Write_sections_task::locks(Task_locker* tl) { tl->add(this, this->output_sections_blocker_); tl->add(this, this->final_blocker_); } // 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_token* Write_data_task::is_runnable() { return NULL; } // We need to unlock FINAL_BLOCKER when finished. void Write_data_task::locks(Task_locker* tl) { tl->add(this, this->final_blocker_); } // 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_token* Write_symbols_task::is_runnable() { return NULL; } // We need to unlock FINAL_BLOCKER when finished. void Write_symbols_task::locks(Task_locker* tl) { tl->add(this, this->final_blocker_); } // 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->layout_->symtab_xindex(), this->layout_->dynsym_xindex(), this->of_); } // Write_after_input_sections_task methods. // We can only run this task after the input sections have completed. Task_token* Write_after_input_sections_task::is_runnable() { if (this->input_sections_blocker_->is_blocked()) return this->input_sections_blocker_; return NULL; } // We need to unlock FINAL_BLOCKER when finished. void Write_after_input_sections_task::locks(Task_locker* tl) { tl->add(this, this->final_blocker_); } // 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*, const Task*) { // If we need to compute a checksum for the BUILD if, we do so here. this->layout_->write_build_id(this->of_); // If we've been asked to create a binary file, we do so here. if (this->options_->oformat_enum() != General_options::OBJECT_FORMAT_ELF) this->layout_->write_binary(this->of_); 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_reloc<32, false>(Sized_relobj<32, false>* object, unsigned int reloc_shndx, const elfcpp::Shdr<32, false>& shdr, Output_section* data_section, Relocatable_relocs* rr); #endif #ifdef HAVE_TARGET_32_BIG template Output_section* Layout::layout_reloc<32, true>(Sized_relobj<32, true>* object, unsigned int reloc_shndx, const elfcpp::Shdr<32, true>& shdr, Output_section* data_section, Relocatable_relocs* rr); #endif #ifdef HAVE_TARGET_64_LITTLE template Output_section* Layout::layout_reloc<64, false>(Sized_relobj<64, false>* object, unsigned int reloc_shndx, const elfcpp::Shdr<64, false>& shdr, Output_section* data_section, Relocatable_relocs* rr); #endif #ifdef HAVE_TARGET_64_BIG template Output_section* Layout::layout_reloc<64, true>(Sized_relobj<64, true>* object, unsigned int reloc_shndx, const elfcpp::Shdr<64, true>& shdr, Output_section* data_section, Relocatable_relocs* rr); #endif #ifdef HAVE_TARGET_32_LITTLE template void Layout::layout_group<32, false>(Symbol_table* symtab, Sized_relobj<32, false>* object, unsigned int, const char* group_section_name, const char* signature, const elfcpp::Shdr<32, false>& shdr, const elfcpp::Elf_Word* contents); #endif #ifdef HAVE_TARGET_32_BIG template void Layout::layout_group<32, true>(Symbol_table* symtab, Sized_relobj<32, true>* object, unsigned int, const char* group_section_name, const char* signature, const elfcpp::Shdr<32, true>& shdr, const elfcpp::Elf_Word* contents); #endif #ifdef HAVE_TARGET_64_LITTLE template void Layout::layout_group<64, false>(Symbol_table* symtab, Sized_relobj<64, false>* object, unsigned int, const char* group_section_name, const char* signature, const elfcpp::Shdr<64, false>& shdr, const elfcpp::Elf_Word* contents); #endif #ifdef HAVE_TARGET_64_BIG template void Layout::layout_group<64, true>(Symbol_table* symtab, Sized_relobj<64, true>* object, unsigned int, const char* group_section_name, const char* signature, const elfcpp::Shdr<64, true>& shdr, const elfcpp::Elf_Word* contents); #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.