Fix ehframe header handling for shared libraries.

[deliverable/binutils-gdb.git] / gold / layout.cc

// layout.cc -- lay out output file sections for gold

// Copyright 2006, 2007 Free Software Foundation, Inc.
// Written by Ian Lance Taylor <iant@google.com>.

// 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 <cstring>
#include <algorithm>
#include <iostream>
#include <utility>

#include "parameters.h"
#include "output.h"
#include "symtab.h"
#include "dynobj.h"
#include "ehframe.h"
#include "compressed_output.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_(),
    section_headers_(NULL), 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 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<int size, bool big_endian>
bool
Layout::include_section(Sized_relobj<size, big_endian>*, const char* name,
                        const elfcpp::Shdr<size, big_endian>& 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<elfcpp::PT>((*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<Key, Output_section*> v(key, NULL);
  std::pair<Section_name_map::iterator, bool> 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<int size, bool big_endian>
Output_section*
Layout::layout(Sized_relobj<size, big_endian>* object, unsigned int shndx,
               const char* name, const elfcpp::Shdr<size, big_endian>& 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<int size, bool big_endian>
Output_section*
Layout::layout_eh_frame(Sized_relobj<size, big_endian>* 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<size, big_endian>& 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;
}

// 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
      && this->options_.compress_debug_sections()
      && 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);

  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->count_local_symbols(input_objects);

  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<Symbol*> dynamic_symbols;
      unsigned int local_dynamic_count;
      Versions versions;
      this->create_dynamic_symtab(input_objects, 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_indexes.
  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);

  // Create the symbol table sections.
  this->create_symtab_sections(input_objects, symtab, &off);
  if (!parameters->doing_static_link())
    this->assign_local_dynsym_offsets(input_objects);

  // Create the .shstrtab section.
  Output_section* shstrtab_section = this->create_shstrtab();

  // Set the file offsets of all 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.
  shndx = this->set_section_indexes(shndx);

  // Create the section table header.
  this->create_shdrs(&off);

  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 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 (parameters->output_is_shared())
    addr = 0;
  else 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();
    }

  // 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 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 (pass == BEFORE_INPUT_SECTIONS_PASS
          && (*p)->requires_postprocessing())
        (*p)->create_postprocessing_buffer();

      if (pass == BEFORE_INPUT_SECTIONS_PASS
          && (*p)->after_input_sections())
        continue;
      else if (pass == AFTER_INPUT_SECTIONS_PASS
               && (!(*p)->after_input_sections()
                   || (*p)->type() == elfcpp::SHT_STRTAB))
        continue;
      else if (pass == STRTAB_AFTER_INPUT_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_INPUT_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)
    {
      (*p)->set_out_shndx(shndx);
      ++shndx;
    }
  return shndx;
}

// 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 Input_objects* input_objects)
{
  for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
       p != input_objects->relobj_end();
       ++p)
    {
      Task_lock_obj<Object> tlo(**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.

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)
    {
      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<off_t>(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_fixed_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_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(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_and_file_offset(0, off);
  off += oshdrs->data_size();
  *poff = off;
  this->section_headers_ = oshdrs;
}

// Create the dynamic symbol table.

void
Layout::create_dynamic_symtab(const Input_objects* input_objects,
                              const Target* target, Symbol_table* symtab,
                              Output_section **pdynstr,
                              unsigned int* plocal_dynamic_count,
                              std::vector<Symbol*>* 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;

  // 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_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);

  // 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);
}

// 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<Symbol*>& 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<int size, bool big_endian>
void
Layout::sized_create_version_sections(
    const Versions* versions,
    const Symbol_table* symtab,
    unsigned int local_symcount,
    const std::vector<Symbol*>& 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<Signatures::iterator, bool> 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)
{
  // 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.
  off_t off = this->output_file_size_;
  off = this->set_section_offsets(off, AFTER_INPUT_SECTIONS_PASS);

  // Now that we've finalized the names, we can finalize the shstrab.
  off = this->set_section_offsets(off, STRTAB_AFTER_INPUT_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);
    }

  for (Section_list::const_iterator p = this->unattached_section_list_.begin();
       p != this->unattached_section_list_.end();
       ++p)
    {
      if ((*p)->after_input_sections())
        (*p)->write(of);
    }

  this->section_headers_->write(of);
}

// 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");
}

// 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.