path: root/src/common/dwarf/dwarf2reader.cc

// Copyright (c) 2010 Google Inc. All Rights Reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// CFI reader author: Jim Blandy <jimb@mozilla.com> <jimb@red-bean.com>

// Implementation of dwarf2reader::LineInfo, dwarf2reader::CompilationUnit,
// and dwarf2reader::CallFrameInfo. See dwarf2reader.h for details.

#include "common/dwarf/dwarf2reader.h"

#include <stdint.h>
#include <stdio.h>
#include <string.h>

#include <map>
#include <memory>
#include <stack>
#include <string>
#include <utility>

#include <sys/stat.h>

#include "common/dwarf/bytereader-inl.h"
#include "common/dwarf/bytereader.h"
#include "common/dwarf/line_state_machine.h"
#include "common/using_std_string.h"
#include "google_breakpad/common/breakpad_types.h"

namespace dwarf2reader {

const SectionMap::const_iterator GetSectionByName(const SectionMap&
                                                  sections, const char *name) {
  assert(name[0] == '.');
  auto iter = sections.find(name);
  if (iter != sections.end())
    return iter;
  std::string macho_name("__");
  macho_name += name + 1;
  iter = sections.find(macho_name);
  return iter;
}

CompilationUnit::CompilationUnit(const string& path,
                                 const SectionMap& sections, uint64_t offset,
                                 ByteReader* reader, Dwarf2Handler* handler)
    : path_(path), offset_from_section_start_(offset), reader_(reader),
      sections_(sections), handler_(handler), abbrevs_(),
      string_buffer_(NULL), string_buffer_length_(0),
      line_string_buffer_(NULL), line_string_buffer_length_(0),
      str_offsets_buffer_(NULL), str_offsets_buffer_length_(0),
      addr_buffer_(NULL), addr_buffer_length_(0),
      is_split_dwarf_(false), dwo_id_(0), dwo_name_(),
      skeleton_dwo_id_(0), ranges_base_(0), addr_base_(0),
      have_checked_for_dwp_(false), dwp_path_(),
      dwp_byte_reader_(), dwp_reader_() {}

// Initialize a compilation unit from a .dwo or .dwp file.
// In this case, we need the .debug_addr section from the
// executable file that contains the corresponding skeleton
// compilation unit.  We also inherit the Dwarf2Handler from
// the executable file, and call it as if we were still
// processing the original compilation unit.

void CompilationUnit::SetSplitDwarf(const uint8_t* addr_buffer,
                                    uint64_t addr_buffer_length,
                                    uint64_t addr_base,
                                    uint64_t ranges_base,
                                    uint64_t dwo_id) {
  is_split_dwarf_ = true;
  addr_buffer_ = addr_buffer;
  addr_buffer_length_ = addr_buffer_length;
  addr_base_ = addr_base;
  ranges_base_ = ranges_base;
  skeleton_dwo_id_ = dwo_id;
}

// Read a DWARF2/3 abbreviation section.
// Each abbrev consists of a abbreviation number, a tag, a byte
// specifying whether the tag has children, and a list of
// attribute/form pairs.
// The list of forms is terminated by a 0 for the attribute, and a
// zero for the form.  The entire abbreviation section is terminated
// by a zero for the code.

void CompilationUnit::ReadAbbrevs() {
  if (abbrevs_)
    return;

  // First get the debug_abbrev section.
  SectionMap::const_iterator iter =
      GetSectionByName(sections_, ".debug_abbrev");
  assert(iter != sections_.end());

  abbrevs_ = new std::vector<Abbrev>;
  abbrevs_->resize(1);

  // The only way to check whether we are reading over the end of the
  // buffer would be to first compute the size of the leb128 data by
  // reading it, then go back and read it again.
  const uint8_t* abbrev_start = iter->second.first +
                                      header_.abbrev_offset;
  const uint8_t* abbrevptr = abbrev_start;
#ifndef NDEBUG
  const uint64_t abbrev_length = iter->second.second - header_.abbrev_offset;
#endif

  while (1) {
    CompilationUnit::Abbrev abbrev;
    size_t len;
    const uint64_t number = reader_->ReadUnsignedLEB128(abbrevptr, &len);

    if (number == 0)
      break;
    abbrev.number = number;
    abbrevptr += len;

    assert(abbrevptr < abbrev_start + abbrev_length);
    const uint64_t tag = reader_->ReadUnsignedLEB128(abbrevptr, &len);
    abbrevptr += len;
    abbrev.tag = static_cast<enum DwarfTag>(tag);

    assert(abbrevptr < abbrev_start + abbrev_length);
    abbrev.has_children = reader_->ReadOneByte(abbrevptr);
    abbrevptr += 1;

    assert(abbrevptr < abbrev_start + abbrev_length);

    while (1) {
      const uint64_t nametemp = reader_->ReadUnsignedLEB128(abbrevptr, &len);
      abbrevptr += len;

      assert(abbrevptr < abbrev_start + abbrev_length);
      const uint64_t formtemp = reader_->ReadUnsignedLEB128(abbrevptr, &len);
      abbrevptr += len;
      if (nametemp == 0 && formtemp == 0)
        break;

      const enum DwarfAttribute name =
        static_cast<enum DwarfAttribute>(nametemp);
      const enum DwarfForm form = static_cast<enum DwarfForm>(formtemp);
      abbrev.attributes.push_back(std::make_pair(name, form));
    }
    assert(abbrev.number == abbrevs_->size());
    abbrevs_->push_back(abbrev);
  }
}

// Skips a single DIE's attributes.
const uint8_t* CompilationUnit::SkipDIE(const uint8_t* start,
                                        const Abbrev& abbrev) {
  for (AttributeList::const_iterator i = abbrev.attributes.begin();
       i != abbrev.attributes.end();
       i++)  {
    start = SkipAttribute(start, i->second);
  }
  return start;
}

// Skips a single attribute form's data.
const uint8_t* CompilationUnit::SkipAttribute(const uint8_t* start,
                                              enum DwarfForm form) {
  size_t len;

  switch (form) {
    case DW_FORM_indirect:
      form = static_cast<enum DwarfForm>(reader_->ReadUnsignedLEB128(start,
                                                                     &len));
      start += len;
      return SkipAttribute(start, form);

    case DW_FORM_flag_present:
      return start;
    case DW_FORM_addrx1:
    case DW_FORM_data1:
    case DW_FORM_flag:
    case DW_FORM_ref1:
    case DW_FORM_strx1:
      return start + 1;
    case DW_FORM_addrx2:
    case DW_FORM_ref2:
    case DW_FORM_data2:
    case DW_FORM_strx2:
      return start + 2;
    case DW_FORM_addrx3:
    case DW_FORM_strx3:
      return start + 3;
    case DW_FORM_addrx4:
    case DW_FORM_ref4:
    case DW_FORM_data4:
    case DW_FORM_strx4:
      return start + 4;
    case DW_FORM_ref8:
    case DW_FORM_data8:
    case DW_FORM_ref_sig8:
      return start + 8;
    case DW_FORM_string:
      return start + strlen(reinterpret_cast<const char*>(start)) + 1;
    case DW_FORM_udata:
    case DW_FORM_ref_udata:
    case DW_FORM_strx:
    case DW_FORM_GNU_str_index:
    case DW_FORM_GNU_addr_index:
    case DW_FORM_addrx:
      reader_->ReadUnsignedLEB128(start, &len);
      return start + len;

    case DW_FORM_sdata:
      reader_->ReadSignedLEB128(start, &len);
      return start + len;
    case DW_FORM_addr:
      return start + reader_->AddressSize();
    case DW_FORM_ref_addr:
      // DWARF2 and 3/4 differ on whether ref_addr is address size or
      // offset size.
      assert(header_.version >= 2);
      if (header_.version == 2) {
        return start + reader_->AddressSize();
      } else if (header_.version >= 3) {
        return start + reader_->OffsetSize();
      }
      break;

    case DW_FORM_block1:
      return start + 1 + reader_->ReadOneByte(start);
    case DW_FORM_block2:
      return start + 2 + reader_->ReadTwoBytes(start);
    case DW_FORM_block4:
      return start + 4 + reader_->ReadFourBytes(start);
    case DW_FORM_block:
    case DW_FORM_exprloc: {
      uint64_t size = reader_->ReadUnsignedLEB128(start, &len);
      return start + size + len;
    }
    case DW_FORM_strp:
    case DW_FORM_line_strp:
    case DW_FORM_strp_sup:
    case DW_FORM_sec_offset:
      return start + reader_->OffsetSize();
  }
  fprintf(stderr,"Unhandled form type");
  return NULL;
}

// Read the abbreviation offset from a compilation unit header.
size_t CompilationUnit::ReadAbbrevOffset(const uint8_t* headerptr) {
  assert(headerptr + reader_->OffsetSize() < buffer_ + buffer_length_);
  header_.abbrev_offset = reader_->ReadOffset(headerptr);
  return reader_->OffsetSize();
}

// Read the address size from a compilation unit header.
size_t CompilationUnit::ReadAddressSize(const uint8_t* headerptr) {
  // Compare against less than or equal because this may be the last
  // section in the file.
  assert(headerptr + 1 <= buffer_ + buffer_length_);
  header_.address_size = reader_->ReadOneByte(headerptr);
  reader_->SetAddressSize(header_.address_size);
  return 1;
}

// Read the DWO id from a split or skeleton compilation unit header.
size_t CompilationUnit::ReadDwoId(const uint8_t* headerptr) {
  assert(headerptr + 8 <= buffer_ + buffer_length_);
  dwo_id_ = reader_->ReadEightBytes(headerptr);
  return 8;
}

// Read the type signature from a type or split type compilation unit header.
size_t CompilationUnit::ReadTypeSignature(const uint8_t* headerptr) {
  assert(headerptr + 8 <= buffer_ + buffer_length_);
  type_signature_ = reader_->ReadEightBytes(headerptr);
  return 8;
}

// Read the DWO id from a split or skeleton compilation unit header.
size_t CompilationUnit::ReadTypeOffset(const uint8_t* headerptr) {
  assert(headerptr + reader_->OffsetSize() < buffer_ + buffer_length_);
  type_offset_ = reader_->ReadOffset(headerptr);
  return reader_->OffsetSize();
}


// Read a DWARF header.  The header is variable length in DWARF3 and DWARF4
// (and DWARF2 as extended by most compilers), and consists of an length
// field, a version number, the offset in the .debug_abbrev section for our
// abbrevs, and an address size. DWARF5 adds a unit_type to distinguish
// between partial-, full-, skeleton-, split-, and type- compilation units.
void CompilationUnit::ReadHeader() {
  const uint8_t* headerptr = buffer_;
  size_t initial_length_size;

  assert(headerptr + 4 < buffer_ + buffer_length_);
  const uint64_t initial_length
    = reader_->ReadInitialLength(headerptr, &initial_length_size);
  headerptr += initial_length_size;
  header_.length = initial_length;

  assert(headerptr + 2 < buffer_ + buffer_length_);
  header_.version = reader_->ReadTwoBytes(headerptr);
  headerptr += 2;

  if (header_.version <= 4) {
    // Older versions of dwarf have a relatively simple structure.
    headerptr += ReadAbbrevOffset(headerptr);
    headerptr += ReadAddressSize(headerptr);
  } else {
    // DWARF5 adds a unit_type field, and various fields based on unit_type.
    assert(headerptr + 1 < buffer_ + buffer_length_);
    uint8_t unit_type = reader_->ReadOneByte(headerptr);
    headerptr += 1;
    headerptr += ReadAddressSize(headerptr);
    headerptr += ReadAbbrevOffset(headerptr);
    switch (unit_type) {
      case DW_UT_compile:
      case DW_UT_partial:
        // nothing else to read
        break;
      case DW_UT_skeleton:
      case DW_UT_split_compile:
        headerptr += ReadDwoId(headerptr);
        break;
      case DW_UT_type:
      case DW_UT_split_type:
        headerptr += ReadTypeSignature(headerptr);
        headerptr += ReadTypeOffset(headerptr);
        break;
      default:
        fprintf(stderr, "Unhandled compilation unit type 0x%x", unit_type);
        break;
    }
  }
  after_header_ = headerptr;

  // This check ensures that we don't have to do checking during the
  // reading of DIEs. header_.length does not include the size of the
  // initial length.
  assert(buffer_ + initial_length_size + header_.length <=
        buffer_ + buffer_length_);
}

uint64_t CompilationUnit::Start() {
  // First get the debug_info section.
  SectionMap::const_iterator iter =
      GetSectionByName(sections_, ".debug_info");
  assert(iter != sections_.end());

  // Set up our buffer
  buffer_ = iter->second.first + offset_from_section_start_;
  buffer_length_ = iter->second.second - offset_from_section_start_;

  // Read the header
  ReadHeader();

  // Figure out the real length from the end of the initial length to
  // the end of the compilation unit, since that is the value we
  // return.
  uint64_t ourlength = header_.length;
  if (reader_->OffsetSize() == 8)
    ourlength += 12;
  else
    ourlength += 4;

  // See if the user wants this compilation unit, and if not, just return.
  if (!handler_->StartCompilationUnit(offset_from_section_start_,
                                      reader_->AddressSize(),
                                      reader_->OffsetSize(),
                                      header_.length,
                                      header_.version))
    return ourlength;

  // Otherwise, continue by reading our abbreviation entries.
  ReadAbbrevs();

  // Set the string section if we have one.
  iter = GetSectionByName(sections_, ".debug_str");
  if (iter != sections_.end()) {
    string_buffer_ = iter->second.first;
    string_buffer_length_ = iter->second.second;
  }

  // Set the line string section if we have one.
  iter = GetSectionByName(sections_, ".debug_line_str");
  if (iter != sections_.end()) {
    line_string_buffer_ = iter->second.first;
    line_string_buffer_length_ = iter->second.second;
  }

  // Set the string offsets section if we have one.
  iter = GetSectionByName(sections_, ".debug_str_offsets");
  if (iter != sections_.end()) {
    str_offsets_buffer_ = iter->second.first;
    str_offsets_buffer_length_ = iter->second.second;
  }

  // Set the address section if we have one.
  iter = GetSectionByName(sections_, ".debug_addr");
  if (iter != sections_.end()) {
    addr_buffer_ = iter->second.first;
    addr_buffer_length_ = iter->second.second;
  }

  // Now that we have our abbreviations, start processing DIE's.
  ProcessDIEs();

  // If this is a skeleton compilation unit generated with split DWARF,
  // and the client needs the full debug info, we need to find the full
  // compilation unit in a .dwo or .dwp file.
  if (!is_split_dwarf_
      && dwo_name_ != NULL
      && handler_->NeedSplitDebugInfo())
    ProcessSplitDwarf();

  return ourlength;
}

void CompilationUnit::ProcessFormStringIndex(
    uint64_t dieoffset, enum DwarfAttribute attr, enum DwarfForm form,
    uint64_t str_index) {
  const uint8_t* offset_ptr =
      str_offsets_buffer_ + str_index * reader_->OffsetSize();
  const uint64_t offset = reader_->ReadOffset(offset_ptr);
  if (offset >= string_buffer_length_) {
    return;
  }

  const char* str = reinterpret_cast<const char*>(string_buffer_) + offset;
  ProcessAttributeString(dieoffset, attr, form, str);
}

// If one really wanted, you could merge SkipAttribute and
// ProcessAttribute
// This is all boring data manipulation and calling of the handler.
const uint8_t* CompilationUnit::ProcessAttribute(
    uint64_t dieoffset, const uint8_t* start, enum DwarfAttribute attr,
    enum DwarfForm form) {
  size_t len;

  switch (form) {
    // DW_FORM_indirect is never used because it is such a space
    // waster.
    case DW_FORM_indirect:
      form = static_cast<enum DwarfForm>(reader_->ReadUnsignedLEB128(start,
                                                                     &len));
      start += len;
      return ProcessAttribute(dieoffset, start, attr, form);

    case DW_FORM_flag_present:
      ProcessAttributeUnsigned(dieoffset, attr, form, 1);
      return start;
    case DW_FORM_data1:
    case DW_FORM_flag:
      ProcessAttributeUnsigned(dieoffset, attr, form,
                               reader_->ReadOneByte(start));
      return start + 1;
    case DW_FORM_data2:
      ProcessAttributeUnsigned(dieoffset, attr, form,
                               reader_->ReadTwoBytes(start));
      return start + 2;
    case DW_FORM_data4:
      ProcessAttributeUnsigned(dieoffset, attr, form,
                               reader_->ReadFourBytes(start));
      return start + 4;
    case DW_FORM_data8:
      ProcessAttributeUnsigned(dieoffset, attr, form,
                               reader_->ReadEightBytes(start));
      return start + 8;
    case DW_FORM_string: {
      const char* str = reinterpret_cast<const char*>(start);
      ProcessAttributeString(dieoffset, attr, form, str);
      return start + strlen(str) + 1;
    }
    case DW_FORM_udata:
      ProcessAttributeUnsigned(dieoffset, attr, form,
                               reader_->ReadUnsignedLEB128(start, &len));
      return start + len;

    case DW_FORM_sdata:
      ProcessAttributeSigned(dieoffset, attr, form,
                             reader_->ReadSignedLEB128(start, &len));
      return start + len;
    case DW_FORM_addr:
      ProcessAttributeUnsigned(dieoffset, attr, form,
                               reader_->ReadAddress(start));
      return start + reader_->AddressSize();
    case DW_FORM_sec_offset:
      ProcessAttributeUnsigned(dieoffset, attr, form,
                               reader_->ReadOffset(start));
      return start + reader_->OffsetSize();

    case DW_FORM_ref1:
      handler_->ProcessAttributeReference(dieoffset, attr, form,
                                          reader_->ReadOneByte(start)
                                          + offset_from_section_start_);
      return start + 1;
    case DW_FORM_ref2:
      handler_->ProcessAttributeReference(dieoffset, attr, form,
                                          reader_->ReadTwoBytes(start)
                                          + offset_from_section_start_);
      return start + 2;
    case DW_FORM_ref4:
      handler_->ProcessAttributeReference(dieoffset, attr, form,
                                          reader_->ReadFourBytes(start)
                                          + offset_from_section_start_);
      return start + 4;
    case DW_FORM_ref8:
      handler_->ProcessAttributeReference(dieoffset, attr, form,
                                          reader_->ReadEightBytes(start)
                                          + offset_from_section_start_);
      return start + 8;
    case DW_FORM_ref_udata:
      handler_->ProcessAttributeReference(dieoffset, attr, form,
                                          reader_->ReadUnsignedLEB128(start,
                                                                      &len)
                                          + offset_from_section_start_);
      return start + len;
    case DW_FORM_ref_addr:
      // DWARF2 and 3/4 differ on whether ref_addr is address size or
      // offset size.
      assert(header_.version >= 2);
      if (header_.version == 2) {
        handler_->ProcessAttributeReference(dieoffset, attr, form,
                                            reader_->ReadAddress(start));
        return start + reader_->AddressSize();
      } else if (header_.version >= 3) {
        handler_->ProcessAttributeReference(dieoffset, attr, form,
                                            reader_->ReadOffset(start));
        return start + reader_->OffsetSize();
      }
      break;
    case DW_FORM_ref_sig8:
      handler_->ProcessAttributeSignature(dieoffset, attr, form,
                                          reader_->ReadEightBytes(start));
      return start + 8;

    case DW_FORM_block1: {
      uint64_t datalen = reader_->ReadOneByte(start);
      handler_->ProcessAttributeBuffer(dieoffset, attr, form, start + 1,
                                       datalen);
      return start + 1 + datalen;
    }
    case DW_FORM_block2: {
      uint64_t datalen = reader_->ReadTwoBytes(start);
      handler_->ProcessAttributeBuffer(dieoffset, attr, form, start + 2,
                                       datalen);
      return start + 2 + datalen;
    }
    case DW_FORM_block4: {
      uint64_t datalen = reader_->ReadFourBytes(start);
      handler_->ProcessAttributeBuffer(dieoffset, attr, form, start + 4,
                                       datalen);
      return start + 4 + datalen;
    }
    case DW_FORM_block:
    case DW_FORM_exprloc: {
      uint64_t datalen = reader_->ReadUnsignedLEB128(start, &len);
      handler_->ProcessAttributeBuffer(dieoffset, attr, form, start + len,
                                       datalen);
      return start + datalen + len;
    }
    case DW_FORM_strp: {
      assert(string_buffer_ != NULL);

      const uint64_t offset = reader_->ReadOffset(start);
      assert(string_buffer_ + offset < string_buffer_ + string_buffer_length_);

      const char* str = reinterpret_cast<const char*>(string_buffer_ + offset);
      ProcessAttributeString(dieoffset, attr, form, str);
      return start + reader_->OffsetSize();
    }
    case DW_FORM_line_strp: {
      assert(line_string_buffer_ != NULL);

      const uint64_t offset = reader_->ReadOffset(start);
      assert(line_string_buffer_ + offset <
             line_string_buffer_ + line_string_buffer_length_);

      const char* str =
          reinterpret_cast<const char*>(line_string_buffer_ + offset);
      ProcessAttributeString(dieoffset, attr, form, str);
      return start + reader_->OffsetSize();
    }
    case DW_FORM_strp_sup:
      // No support currently for suplementary object files.
      fprintf(stderr, "Unhandled form type: DW_FORM_strp_sup\n");
      return start + 4;

    case DW_FORM_strx:
    case DW_FORM_GNU_str_index: {
      uint64_t str_index = reader_->ReadUnsignedLEB128(start, &len);
      ProcessFormStringIndex(dieoffset, attr, form, str_index);
      return start + len;
    }
    case DW_FORM_strx1: {
      uint64_t str_index = reader_->ReadOneByte(start);
      ProcessFormStringIndex(dieoffset, attr, form, str_index);
      return start + 1;
    }
    case DW_FORM_strx2: {
      uint64_t str_index = reader_->ReadTwoBytes(start);
      ProcessFormStringIndex(dieoffset, attr, form, str_index);
      return start + 2;
    }
    case DW_FORM_strx3: {
      uint64_t str_index = reader_->ReadThreeBytes(start);
      ProcessFormStringIndex(dieoffset, attr, form, str_index);
      return start + 3;
    }
    case DW_FORM_strx4: {
      uint64_t str_index = reader_->ReadFourBytes(start);
      ProcessFormStringIndex(dieoffset, attr, form, str_index);
      return start + 4;
    }

    case DW_FORM_addrx:
    case DW_FORM_GNU_addr_index:
      ProcessAttributeAddrIndex(
          dieoffset, attr, form, reader_->ReadUnsignedLEB128(start, &len));
      return start + len;
    case DW_FORM_addrx1:
      ProcessAttributeAddrIndex(
          dieoffset, attr, form, reader_->ReadOneByte(start));
      return start + 1;
    case DW_FORM_addrx2:
      ProcessAttributeAddrIndex(
          dieoffset, attr, form, reader_->ReadTwoBytes(start));
      return start + 2;
    case DW_FORM_addrx3:
      ProcessAttributeAddrIndex(
          dieoffset, attr, form, reader_->ReadThreeBytes(start));
      return start + 3;
    case DW_FORM_addrx4:
      ProcessAttributeAddrIndex(
          dieoffset, attr, form, reader_->ReadFourBytes(start));
      return start + 4;
  }
  fprintf(stderr, "Unhandled form type\n");
  return NULL;
}

const uint8_t* CompilationUnit::ProcessDIE(uint64_t dieoffset,
                                           const uint8_t* start,
                                           const Abbrev& abbrev) {
  for (AttributeList::const_iterator i = abbrev.attributes.begin();
       i != abbrev.attributes.end();
       i++)  {
    start = ProcessAttribute(dieoffset, start, i->first, i->second);
  }

  // If this is a compilation unit in a split DWARF object, verify that
  // the dwo_id matches. If it does not match, we will ignore this
  // compilation unit.
  if (abbrev.tag == DW_TAG_compile_unit
      && is_split_dwarf_
      && dwo_id_ != skeleton_dwo_id_) {
    return NULL;
  }

  return start;
}

void CompilationUnit::ProcessDIEs() {
  const uint8_t* dieptr = after_header_;
  size_t len;

  // lengthstart is the place the length field is based on.
  // It is the point in the header after the initial length field
  const uint8_t* lengthstart = buffer_;

  // In 64 bit dwarf, the initial length is 12 bytes, because of the
  // 0xffffffff at the start.
  if (reader_->OffsetSize() == 8)
    lengthstart += 12;
  else
    lengthstart += 4;

  std::stack<uint64_t> die_stack;
  
  while (dieptr < (lengthstart + header_.length)) {
    // We give the user the absolute offset from the beginning of
    // debug_info, since they need it to deal with ref_addr forms.
    uint64_t absolute_offset = (dieptr - buffer_) + offset_from_section_start_;

    uint64_t abbrev_num = reader_->ReadUnsignedLEB128(dieptr, &len);

    dieptr += len;

    // Abbrev == 0 represents the end of a list of children, or padding
    // at the end of the compilation unit.
    if (abbrev_num == 0) {
      if (die_stack.size() == 0)
        // If it is padding, then we are done with the compilation unit's DIEs.
        return;
      const uint64_t offset = die_stack.top();
      die_stack.pop();
      handler_->EndDIE(offset);
      continue;
    }

    const Abbrev& abbrev = abbrevs_->at(static_cast<size_t>(abbrev_num));
    const enum DwarfTag tag = abbrev.tag;
    if (!handler_->StartDIE(absolute_offset, tag)) {
      dieptr = SkipDIE(dieptr, abbrev);
    } else {
      dieptr = ProcessDIE(absolute_offset, dieptr, abbrev);
    }

    if (abbrev.has_children) {
      die_stack.push(absolute_offset);
    } else {
      handler_->EndDIE(absolute_offset);
    }
  }
}

// Check for a valid ELF file and return the Address size.
// Returns 0 if not a valid ELF file.
inline int GetElfWidth(const ElfReader& elf) {
  if (elf.IsElf32File())
    return 4;
  if (elf.IsElf64File())
    return 8;
  return 0;
}

void CompilationUnit::ProcessSplitDwarf() {
  struct stat statbuf;
  if (!have_checked_for_dwp_) {
    // Look for a .dwp file in the same directory as the executable.
    have_checked_for_dwp_ = true;
    string dwp_suffix(".dwp");
    dwp_path_ = path_ + dwp_suffix;
    if (stat(dwp_path_.c_str(), &statbuf) != 0) {
      // Fall back to a split .debug file in the same directory.
      string debug_suffix(".debug");
      dwp_path_ = path_;
      size_t found = path_.rfind(debug_suffix);
      if (found + debug_suffix.length() == path_.length())
        dwp_path_ = dwp_path_.replace(found, debug_suffix.length(), dwp_suffix);
    }
    if (stat(dwp_path_.c_str(), &statbuf) == 0) {
      ElfReader* elf = new ElfReader(dwp_path_);
      int width = GetElfWidth(*elf);
      if (width != 0) {
        dwp_byte_reader_.reset(new ByteReader(reader_->GetEndianness()));
        dwp_byte_reader_->SetAddressSize(width);
        dwp_reader_.reset(new DwpReader(*dwp_byte_reader_, elf));
        dwp_reader_->Initialize();
      } else {
        delete elf;
      }
    }
  }
  bool found_in_dwp = false;
  if (dwp_reader_) {
    // If we have a .dwp file, read the debug sections for the requested CU.
    SectionMap sections;
    dwp_reader_->ReadDebugSectionsForCU(dwo_id_, &sections);
    if (!sections.empty()) {
      found_in_dwp = true;
      CompilationUnit dwp_comp_unit(dwp_path_, sections, 0,
                                    dwp_byte_reader_.get(), handler_);
      dwp_comp_unit.SetSplitDwarf(addr_buffer_, addr_buffer_length_, addr_base_,
                                  ranges_base_, dwo_id_);
      dwp_comp_unit.Start();
    }
  }
  if (!found_in_dwp) {
    // If no .dwp file, try to open the .dwo file.
    if (stat(dwo_name_, &statbuf) == 0) {
      ElfReader elf(dwo_name_);
      int width = GetElfWidth(elf);
      if (width != 0) {
        ByteReader reader(ENDIANNESS_LITTLE);
        reader.SetAddressSize(width);
        SectionMap sections;
        ReadDebugSectionsFromDwo(&elf, &sections);
        CompilationUnit dwo_comp_unit(dwo_name_, sections, 0, &reader,
                                      handler_);
        dwo_comp_unit.SetSplitDwarf(addr_buffer_, addr_buffer_length_,
                                    addr_base_, ranges_base_, dwo_id_);
        dwo_comp_unit.Start();
      }
    }
  }
}

void CompilationUnit::ReadDebugSectionsFromDwo(ElfReader* elf_reader,
                                               SectionMap* sections) {
  static const char* const section_names[] = {
    ".debug_abbrev",
    ".debug_info",
    ".debug_str_offsets",
    ".debug_str"
  };
  for (unsigned int i = 0u;
       i < sizeof(section_names)/sizeof(*(section_names)); ++i) {
    string base_name = section_names[i];
    string dwo_name = base_name + ".dwo";
    size_t section_size;
    const char* section_data = elf_reader->GetSectionByName(dwo_name,
                                                            &section_size);
    if (section_data != NULL)
      sections->insert(std::make_pair(
          base_name, std::make_pair(
             reinterpret_cast<const uint8_t*>(section_data),
             section_size)));
  }
}

DwpReader::DwpReader(const ByteReader& byte_reader, ElfReader* elf_reader)
    : elf_reader_(elf_reader), byte_reader_(byte_reader),
      cu_index_(NULL), cu_index_size_(0), string_buffer_(NULL),
      string_buffer_size_(0), version_(0), ncolumns_(0), nunits_(0),
      nslots_(0), phash_(NULL), pindex_(NULL), shndx_pool_(NULL),
      offset_table_(NULL), size_table_(NULL), abbrev_data_(NULL),
      abbrev_size_(0), info_data_(NULL), info_size_(0),
      str_offsets_data_(NULL), str_offsets_size_(0) {}

DwpReader::~DwpReader() {
  if (elf_reader_) delete elf_reader_;
}

void DwpReader::Initialize() {
  cu_index_ = elf_reader_->GetSectionByName(".debug_cu_index",
                                            &cu_index_size_);
  if (cu_index_ == NULL) {
    return;
  }
  // The .debug_str.dwo section is shared by all CUs in the file.
  string_buffer_ = elf_reader_->GetSectionByName(".debug_str.dwo",
                                                 &string_buffer_size_);

  version_ = byte_reader_.ReadFourBytes(
      reinterpret_cast<const uint8_t*>(cu_index_));

  if (version_ == 1) {
    nslots_ = byte_reader_.ReadFourBytes(
        reinterpret_cast<const uint8_t*>(cu_index_)
        + 3 * sizeof(uint32_t));
    phash_ = cu_index_ + 4 * sizeof(uint32_t);
    pindex_ = phash_ + nslots_ * sizeof(uint64_t);
    shndx_pool_ = pindex_ + nslots_ * sizeof(uint32_t);
    if (shndx_pool_ >= cu_index_ + cu_index_size_) {
      version_ = 0;
    }
  } else if (version_ == 2) {
    ncolumns_ = byte_reader_.ReadFourBytes(
        reinterpret_cast<const uint8_t*>(cu_index_) + sizeof(uint32_t));
    nunits_ = byte_reader_.ReadFourBytes(
        reinterpret_cast<const uint8_t*>(cu_index_) + 2 * sizeof(uint32_t));
    nslots_ = byte_reader_.ReadFourBytes(
        reinterpret_cast<const uint8_t*>(cu_index_) + 3 * sizeof(uint32_t));
    phash_ = cu_index_ + 4 * sizeof(uint32_t);
    pindex_ = phash_ + nslots_ * sizeof(uint64_t);
    offset_table_ = pindex_ + nslots_ * sizeof(uint32_t);
    size_table_ = offset_table_ + ncolumns_ * (nunits_ + 1) * sizeof(uint32_t);
    abbrev_data_ = elf_reader_->GetSectionByName(".debug_abbrev.dwo",
                                                 &abbrev_size_);
    info_data_ = elf_reader_->GetSectionByName(".debug_info.dwo", &info_size_);
    str_offsets_data_ = elf_reader_->GetSectionByName(".debug_str_offsets.dwo",
                                                      &str_offsets_size_);
    if (size_table_ >= cu_index_ + cu_index_size_) {
      version_ = 0;
    }
  }
}

void DwpReader::ReadDebugSectionsForCU(uint64_t dwo_id,
                                       SectionMap* sections) {
  if (version_ == 1) {
    int slot = LookupCU(dwo_id);
    if (slot == -1) {
      return;
    }

    // The index table points to the section index pool, where we
    // can read a list of section indexes for the debug sections
    // for the CU whose dwo_id we are looking for.
    int index = byte_reader_.ReadFourBytes(
        reinterpret_cast<const uint8_t*>(pindex_)
        + slot * sizeof(uint32_t));
    const char* shndx_list = shndx_pool_ + index * sizeof(uint32_t);
    for (;;) {
      if (shndx_list >= cu_index_ + cu_index_size_) {
        version_ = 0;
        return;
      }
      unsigned int shndx = byte_reader_.ReadFourBytes(
          reinterpret_cast<const uint8_t*>(shndx_list));
      shndx_list += sizeof(uint32_t);
      if (shndx == 0)
        break;
      const char* section_name = elf_reader_->GetSectionName(shndx);
      size_t section_size;
      const char* section_data;
      // We're only interested in these four debug sections.
      // The section names in the .dwo file end with ".dwo", but we
      // add them to the sections table with their normal names.
      if (!strncmp(section_name, ".debug_abbrev", strlen(".debug_abbrev"))) {
        section_data = elf_reader_->GetSectionByIndex(shndx, &section_size);
        sections->insert(std::make_pair(
            ".debug_abbrev",
            std::make_pair(reinterpret_cast<const uint8_t*> (section_data),
                                                              section_size)));
      } else if (!strncmp(section_name, ".debug_info", strlen(".debug_info"))) {
        section_data = elf_reader_->GetSectionByIndex(shndx, &section_size);
        sections->insert(std::make_pair(
            ".debug_info",
            std::make_pair(reinterpret_cast<const uint8_t*> (section_data),
                           section_size)));
      } else if (!strncmp(section_name, ".debug_str_offsets",
                          strlen(".debug_str_offsets"))) {
        section_data = elf_reader_->GetSectionByIndex(shndx, &section_size);
        sections->insert(std::make_pair(
            ".debug_str_offsets",
            std::make_pair(reinterpret_cast<const uint8_t*> (section_data),
                           section_size)));
      }
    }
    sections->insert(std::make_pair(
        ".debug_str",
        std::make_pair(reinterpret_cast<const uint8_t*> (string_buffer_),
                       string_buffer_size_)));
  } else if (version_ == 2) {
    uint32_t index = LookupCUv2(dwo_id);
    if (index == 0) {
      return;
    }

    // The index points to a row in each of the section offsets table
    // and the section size table, where we can read the offsets and sizes
    // of the contributions to each debug section from the CU whose dwo_id
    // we are looking for. Row 0 of the section offsets table has the
    // section ids for each column of the table. The size table begins
    // with row 1.
    const char* id_row = offset_table_;
    const char* offset_row = offset_table_
                             + index * ncolumns_ * sizeof(uint32_t);
    const char* size_row =
        size_table_ + (index - 1) * ncolumns_ * sizeof(uint32_t);
    if (size_row + ncolumns_ * sizeof(uint32_t) > cu_index_ + cu_index_size_) {
      version_ = 0;
      return;
    }
    for (unsigned int col = 0u; col < ncolumns_; ++col) {
      uint32_t section_id =
          byte_reader_.ReadFourBytes(reinterpret_cast<const uint8_t*>(id_row)
                                     + col * sizeof(uint32_t));
      uint32_t offset = byte_reader_.ReadFourBytes(
          reinterpret_cast<const uint8_t*>(offset_row)
          + col * sizeof(uint32_t));
      uint32_t size = byte_reader_.ReadFourBytes(
          reinterpret_cast<const uint8_t*>(size_row) + col * sizeof(uint32_t));
      if (section_id == DW_SECT_ABBREV) {
        sections->insert(std::make_pair(
            ".debug_abbrev",
            std::make_pair(reinterpret_cast<const uint8_t*> (abbrev_data_)
                           + offset, size)));
      } else if (section_id == DW_SECT_INFO) {
        sections->insert(std::make_pair(
            ".debug_info",
            std::make_pair(reinterpret_cast<const uint8_t*> (info_data_)
                           + offset, size)));
      } else if (section_id == DW_SECT_STR_OFFSETS) {
        sections->insert(std::make_pair(
            ".debug_str_offsets",
            std::make_pair(reinterpret_cast<const uint8_t*> (str_offsets_data_)
                           + offset, size)));
      }
    }
    sections->insert(std::make_pair(
        ".debug_str",
        std::make_pair(reinterpret_cast<const uint8_t*> (string_buffer_),
                       string_buffer_size_)));
  }
}

int DwpReader::LookupCU(uint64_t dwo_id) {
  uint32_t slot = static_cast<uint32_t>(dwo_id) & (nslots_ - 1);
  uint64_t probe = byte_reader_.ReadEightBytes(
      reinterpret_cast<const uint8_t*>(phash_) + slot * sizeof(uint64_t));
  if (probe != 0 && probe != dwo_id) {
    uint32_t secondary_hash =
        (static_cast<uint32_t>(dwo_id >> 32) & (nslots_ - 1)) | 1;
    do {
      slot = (slot + secondary_hash) & (nslots_ - 1);
      probe = byte_reader_.ReadEightBytes(
          reinterpret_cast<const uint8_t*>(phash_) + slot * sizeof(uint64_t));
    } while (probe != 0 && probe != dwo_id);
  }
  if (probe == 0)
    return -1;
  return slot;
}

uint32_t DwpReader::LookupCUv2(uint64_t dwo_id) {
  uint32_t slot = static_cast<uint32_t>(dwo_id) & (nslots_ - 1);
  uint64_t probe = byte_reader_.ReadEightBytes(
      reinterpret_cast<const uint8_t*>(phash_) + slot * sizeof(uint64_t));
  uint32_t index = byte_reader_.ReadFourBytes(
      reinterpret_cast<const uint8_t*>(pindex_) + slot * sizeof(uint32_t));
  if (index != 0 && probe != dwo_id) {
    uint32_t secondary_hash =
        (static_cast<uint32_t>(dwo_id >> 32) & (nslots_ - 1)) | 1;
    do {
      slot = (slot + secondary_hash) & (nslots_ - 1);
      probe = byte_reader_.ReadEightBytes(
          reinterpret_cast<const uint8_t*>(phash_) + slot * sizeof(uint64_t));
      index = byte_reader_.ReadFourBytes(
          reinterpret_cast<const uint8_t*>(pindex_) + slot * sizeof(uint32_t));
    } while (index != 0 && probe != dwo_id);
  }
  return index;
}

LineInfo::LineInfo(const uint8_t* buffer, uint64_t buffer_length,
                   ByteReader* reader, const uint8_t* string_buffer,
                   size_t string_buffer_length,
                   const uint8_t* line_string_buffer,
                   size_t line_string_buffer_length, LineInfoHandler* handler):
    handler_(handler), reader_(reader), buffer_(buffer),
    string_buffer_(string_buffer),
    line_string_buffer_(line_string_buffer) {
#ifndef NDEBUG
  buffer_length_ = buffer_length;
  string_buffer_length_ = string_buffer_length;
  line_string_buffer_length_ = line_string_buffer_length;
#endif
  header_.std_opcode_lengths = NULL;
}

uint64_t LineInfo::Start() {
  ReadHeader();
  ReadLines();
  return after_header_ - buffer_;
}

void LineInfo::ReadTypesAndForms(const uint8_t** lineptr,
                                 uint32_t* content_types,
                                 uint32_t* content_forms,
                                 uint32_t max_types,
                                 uint32_t* format_count) {
  size_t len;

  uint32_t count = reader_->ReadUnsignedLEB128(*lineptr, &len);
  *lineptr += len;
  if (count < 1 || count > max_types) {
    return;
  }
  for (uint32_t col = 0; col < count; ++col) {
    content_types[col] = reader_->ReadUnsignedLEB128(*lineptr, &len);
    *lineptr += len;
    content_forms[col] = reader_->ReadUnsignedLEB128(*lineptr, &len);
    *lineptr += len;
  }
  *format_count = count;
}

const char* LineInfo::ReadStringForm(uint32_t form, const uint8_t** lineptr) {
  const char* name = nullptr;
  if (form == DW_FORM_string) {
    name = reinterpret_cast<const char*>(*lineptr);
    *lineptr += strlen(name) + 1;
    return name;
  } else if (form == DW_FORM_strp) {
    uint64_t offset = reader_->ReadOffset(*lineptr);
    assert(offset < string_buffer_length_);
    *lineptr += reader_->OffsetSize();
    if (string_buffer_ != nullptr) {
      name = reinterpret_cast<const char*>(string_buffer_) + offset;
      return name;
    }
  } else if (form == DW_FORM_line_strp) {
    uint64_t offset = reader_->ReadOffset(*lineptr);
    assert(offset < line_string_buffer_length_);
    *lineptr += reader_->OffsetSize();
    if (line_string_buffer_ != nullptr) {
      name = reinterpret_cast<const char*>(line_string_buffer_) + offset;
      return name;
    }
  }
  // Shouldn't be called with a non-string-form, and
  // if there is a string form but no string buffer,
  // that is a problem too.
  assert(0);
  return nullptr;
}

uint64_t LineInfo::ReadUnsignedData(uint32_t form, const uint8_t** lineptr) {
  size_t len;
  uint64_t value;

  switch (form) {
    case DW_FORM_data1:
      value = reader_->ReadOneByte(*lineptr);
      *lineptr += 1;
      return value;
    case DW_FORM_data2:
      value = reader_->ReadTwoBytes(*lineptr);
      *lineptr += 2;
      return value;
    case DW_FORM_data4:
      value = reader_->ReadFourBytes(*lineptr);
      *lineptr += 4;
      return value;
    case DW_FORM_data8:
      value = reader_->ReadEightBytes(*lineptr);
      *lineptr += 8;
      return value;
    case DW_FORM_udata:
      value = reader_->ReadUnsignedLEB128(*lineptr, &len);
      *lineptr += len;
      return value;
    default:
      fprintf(stderr, "Unrecognized data form.");
      return 0;
  }
}

void LineInfo::ReadFileRow(const uint8_t** lineptr,
                           const uint32_t* content_types,
                           const uint32_t* content_forms, uint32_t row,
                           uint32_t format_count) {
  const char* filename = nullptr;
  uint64_t dirindex = 0;
  uint64_t mod_time = 0;
  uint64_t filelength = 0;

  for (uint32_t col = 0; col < format_count; ++col) {
    switch (content_types[col]) {
      case DW_LNCT_path:
        filename = ReadStringForm(content_forms[col], lineptr);
        break;
      case DW_LNCT_directory_index:
        dirindex = ReadUnsignedData(content_forms[col], lineptr);
        break;
      case DW_LNCT_timestamp:
        mod_time = ReadUnsignedData(content_forms[col], lineptr);
        break;
      case DW_LNCT_size:
        filelength = ReadUnsignedData(content_forms[col], lineptr);
        break;
      case DW_LNCT_MD5:
        // MD5 entries help a debugger sort different versions of files with
        // the same name.  It is always paired with a DW_FORM_data16 and is
        // unused in this case.
        lineptr += 16;
        break;
      default:
        fprintf(stderr, "Unrecognized form in line table header. %d\n",
                content_types[col]);
        assert(false);
        break;
    }
  }
  assert(filename != nullptr);
  handler_->DefineFile(filename, row, dirindex, mod_time, filelength);
}

// The header for a debug_line section is mildly complicated, because
// the line info is very tightly encoded.
void LineInfo::ReadHeader() {
  const uint8_t* lineptr = buffer_;
  size_t initial_length_size;

  const uint64_t initial_length
    = reader_->ReadInitialLength(lineptr, &initial_length_size);

  lineptr += initial_length_size;
  header_.total_length = initial_length;
  assert(buffer_ + initial_length_size + header_.total_length <=
        buffer_ + buffer_length_);


  header_.version = reader_->ReadTwoBytes(lineptr);
  lineptr += 2;

  if (header_.version >= 5) {
    uint8_t address_size = reader_->ReadOneByte(lineptr);
    reader_->SetAddressSize(address_size);
    lineptr += 1;
    uint8_t segment_selector_size = reader_->ReadOneByte(lineptr);
    if (segment_selector_size != 0) {
      fprintf(stderr,"No support for segmented memory.");
    }
    lineptr += 1;
  } else {
    // Address size *must* be set by CU ahead of time.
    assert(reader_->AddressSize() != 0);
  }

  header_.prologue_length = reader_->ReadOffset(lineptr);
  lineptr += reader_->OffsetSize();

  header_.min_insn_length = reader_->ReadOneByte(lineptr);
  lineptr += 1;

  if (header_.version >= 4) {
    __attribute__((unused)) uint8_t max_ops_per_insn =
        reader_->ReadOneByte(lineptr);
    ++lineptr;
    assert(max_ops_per_insn == 1);
  }

  header_.default_is_stmt = reader_->ReadOneByte(lineptr);
  lineptr += 1;

  header_.line_base = *reinterpret_cast<const int8_t*>(lineptr);
  lineptr += 1;

  header_.line_range = reader_->ReadOneByte(lineptr);
  lineptr += 1;

  header_.opcode_base = reader_->ReadOneByte(lineptr);
  lineptr += 1;

  header_.std_opcode_lengths = new std::vector<unsigned char>;
  header_.std_opcode_lengths->resize(header_.opcode_base + 1);
  (*header_.std_opcode_lengths)[0] = 0;
  for (int i = 1; i < header_.opcode_base; i++) {
    (*header_.std_opcode_lengths)[i] = reader_->ReadOneByte(lineptr);
    lineptr += 1;
  }

  if (header_.version <= 4) {
    // Directory zero is assumed to be the compilation directory and special
    // cased where used. It is not actually stored in the dwarf data. But an
    // empty entry here avoids off-by-one errors elsewhere in the code.
    handler_->DefineDir("", 0);
    // It is legal for the directory entry table to be empty.
    if (*lineptr) {
      uint32_t dirindex = 1;
      while (*lineptr) {
        const char* dirname = reinterpret_cast<const char*>(lineptr);
        handler_->DefineDir(dirname, dirindex);
        lineptr += strlen(dirname) + 1;
        dirindex++;
      }
    }
    lineptr++;
    // It is also legal for the file entry table to be empty.

    // Similarly for file zero.
    handler_->DefineFile("", 0, 0, 0, 0);
    if (*lineptr) {
      uint32_t fileindex = 1;
      size_t len;
      while (*lineptr) {
        const char* filename = ReadStringForm(DW_FORM_string, &lineptr);

        uint64_t dirindex = reader_->ReadUnsignedLEB128(lineptr, &len);
        lineptr += len;

        uint64_t mod_time = reader_->ReadUnsignedLEB128(lineptr, &len);
        lineptr += len;

        uint64_t filelength = reader_->ReadUnsignedLEB128(lineptr, &len);
        lineptr += len;
        handler_->DefineFile(filename, fileindex,
                             static_cast<uint32_t>(dirindex), mod_time,
                             filelength);
        fileindex++;
      }
    }
    lineptr++;
  } else {
    // Read the DWARF-5 directory table.

    // Dwarf5 supports five different types and forms per directory- and
    // file-table entry. Theoretically, there could be duplicate entries
    // in this table, but that would be quite unusual.
    static const uint32_t kMaxTypesAndForms = 5;
    uint32_t content_types[kMaxTypesAndForms];
    uint32_t content_forms[kMaxTypesAndForms];
    uint32_t format_count;
    size_t len;

    ReadTypesAndForms(&lineptr, content_types, content_forms, kMaxTypesAndForms,
                      &format_count);
    uint32_t entry_count = reader_->ReadUnsignedLEB128(lineptr, &len);
    lineptr += len;
    for (uint32_t row = 0; row < entry_count; ++row) {
      const char* dirname = nullptr;
      for (uint32_t col = 0; col < format_count; ++col) {
        // The path is the only relevant content type for this implementation.
        if (content_types[col] == DW_LNCT_path) {
          dirname = ReadStringForm(content_forms[col], &lineptr);
        }
      }
      handler_->DefineDir(dirname, row);
    }

    // Read the DWARF-5 filename table.
    ReadTypesAndForms(&lineptr, content_types, content_forms, kMaxTypesAndForms,
                      &format_count);
    entry_count = reader_->ReadUnsignedLEB128(lineptr, &len);
    lineptr += len;

    for (uint32_t row = 0; row < entry_count; ++row) {
      ReadFileRow(&lineptr, content_types, content_forms, row, format_count);
    }
  }
  after_header_ = lineptr;
}

/* static */
bool LineInfo::ProcessOneOpcode(ByteReader* reader,
                                LineInfoHandler* handler,
                                const struct LineInfoHeader& header,
                                const uint8_t* start,
                                struct LineStateMachine* lsm,
                                size_t* len,
                                uintptr pc,
                                bool* lsm_passes_pc) {
  size_t oplen = 0;
  size_t templen;
  uint8_t opcode = reader->ReadOneByte(start);
  oplen++;
  start++;

  // If the opcode is great than the opcode_base, it is a special
  // opcode. Most line programs consist mainly of special opcodes.
  if (opcode >= header.opcode_base) {
    opcode -= header.opcode_base;
    const int64_t advance_address = (opcode / header.line_range)
                                  * header.min_insn_length;
    const int32_t advance_line = (opcode % header.line_range)
                               + header.line_base;

    // Check if the lsm passes "pc". If so, mark it as passed.
    if (lsm_passes_pc &&
        lsm->address <= pc && pc < lsm->address + advance_address) {
      *lsm_passes_pc = true;
    }

    lsm->address += advance_address;
    lsm->line_num += advance_line;
    lsm->basic_block = true;
    *len = oplen;
    return true;
  }

  // Otherwise, we have the regular opcodes
  switch (opcode) {
    case DW_LNS_copy: {
      lsm->basic_block = false;
      *len = oplen;
      return true;
    }

    case DW_LNS_advance_pc: {
      uint64_t advance_address = reader->ReadUnsignedLEB128(start, &templen);
      oplen += templen;

      // Check if the lsm passes "pc". If so, mark it as passed.
      if (lsm_passes_pc && lsm->address <= pc &&
          pc < lsm->address + header.min_insn_length * advance_address) {
        *lsm_passes_pc = true;
      }

      lsm->address += header.min_insn_length * advance_address;
    }
      break;
    case DW_LNS_advance_line: {
      const int64_t advance_line = reader->ReadSignedLEB128(start, &templen);
      oplen += templen;
      lsm->line_num += static_cast<int32_t>(advance_line);

      // With gcc 4.2.1, we can get the line_no here for the first time
      // since DW_LNS_advance_line is called after DW_LNE_set_address is
      // called. So we check if the lsm passes "pc" here, not in
      // DW_LNE_set_address.
      if (lsm_passes_pc && lsm->address == pc) {
        *lsm_passes_pc = true;
      }
    }
      break;
    case DW_LNS_set_file: {
      const uint64_t fileno = reader->ReadUnsignedLEB128(start, &templen);
      oplen += templen;
      lsm->file_num = static_cast<uint32_t>(fileno);
    }
      break;
    case DW_LNS_set_column: {
      const uint64_t colno = reader->ReadUnsignedLEB128(start, &templen);
      oplen += templen;
      lsm->column_num = static_cast<uint32_t>(colno);
    }
      break;
    case DW_LNS_negate_stmt: {
      lsm->is_stmt = !lsm->is_stmt;
    }
      break;
    case DW_LNS_set_basic_block: {
      lsm->basic_block = true;
    }
      break;
    case DW_LNS_fixed_advance_pc: {
      const uint16_t advance_address = reader->ReadTwoBytes(start);
      oplen += 2;

      // Check if the lsm passes "pc". If so, mark it as passed.
      if (lsm_passes_pc &&
          lsm->address <= pc && pc < lsm->address + advance_address) {
        *lsm_passes_pc = true;
      }

      lsm->address += advance_address;
    }
      break;
    case DW_LNS_const_add_pc: {
      const int64_t advance_address = header.min_insn_length
                                    * ((255 - header.opcode_base)
                                       / header.line_range);

      // Check if the lsm passes "pc". If so, mark it as passed.
      if (lsm_passes_pc &&
          lsm->address <= pc && pc < lsm->address + advance_address) {
        *lsm_passes_pc = true;
      }

      lsm->address += advance_address;
    }
      break;
    case DW_LNS_extended_op: {
      const uint64_t extended_op_len = reader->ReadUnsignedLEB128(start,
                                                                &templen);
      start += templen;
      oplen += templen + extended_op_len;

      const uint64_t extended_op = reader->ReadOneByte(start);
      start++;

      switch (extended_op) {
        case DW_LNE_end_sequence: {
          lsm->end_sequence = true;
          *len = oplen;
          return true;
        }
          break;
        case DW_LNE_set_address: {
          // With gcc 4.2.1, we cannot tell the line_no here since
          // DW_LNE_set_address is called before DW_LNS_advance_line is
          // called.  So we do not check if the lsm passes "pc" here.  See
          // also the comment in DW_LNS_advance_line.
          uint64_t address = reader->ReadAddress(start);
          lsm->address = address;
        }
          break;
        case DW_LNE_define_file: {
          const char* filename = reinterpret_cast<const char*>(start);

          templen = strlen(filename) + 1;
          start += templen;

          uint64_t dirindex = reader->ReadUnsignedLEB128(start, &templen);
          oplen += templen;

          const uint64_t mod_time = reader->ReadUnsignedLEB128(start,
                                                             &templen);
          oplen += templen;

          const uint64_t filelength = reader->ReadUnsignedLEB128(start,
                                                               &templen);
          oplen += templen;

          if (handler) {
            handler->DefineFile(filename, -1, static_cast<uint32_t>(dirindex), 
                                mod_time, filelength);
          }
        }
          break;
      }
    }
      break;

    default: {
      // Ignore unknown opcode  silently
      if (header.std_opcode_lengths) {
        for (int i = 0; i < (*header.std_opcode_lengths)[opcode]; i++) {
          reader->ReadUnsignedLEB128(start, &templen);
          start += templen;
          oplen += templen;
        }
      }
    }
      break;
  }
  *len = oplen;
  return false;
}

void LineInfo::ReadLines() {
  struct LineStateMachine lsm;

  // lengthstart is the place the length field is based on.
  // It is the point in the header after the initial length field
  const uint8_t* lengthstart = buffer_;

  // In 64 bit dwarf, the initial length is 12 bytes, because of the
  // 0xffffffff at the start.
  if (reader_->OffsetSize() == 8)
    lengthstart += 12;
  else
    lengthstart += 4;

  const uint8_t* lineptr = after_header_;
  lsm.Reset(header_.default_is_stmt);

  // The LineInfoHandler interface expects each line's length along
  // with its address, but DWARF only provides addresses (sans
  // length), and an end-of-sequence address; one infers the length
  // from the next address. So we report a line only when we get the
  // next line's address, or the end-of-sequence address.
  bool have_pending_line = false;
  uint64_t pending_address = 0;
  uint32_t pending_file_num = 0, pending_line_num = 0, pending_column_num = 0;

  while (lineptr < lengthstart + header_.total_length) {
    size_t oplength;
    bool add_row = ProcessOneOpcode(reader_, handler_, header_,
                                    lineptr, &lsm, &oplength, (uintptr)-1,
                                    NULL);
    if (add_row) {
      if (have_pending_line)
        handler_->AddLine(pending_address, lsm.address - pending_address,
                          pending_file_num, pending_line_num,
                          pending_column_num);
      if (lsm.end_sequence) {
        lsm.Reset(header_.default_is_stmt);      
        have_pending_line = false;
      } else {
        pending_address = lsm.address;
        pending_file_num = lsm.file_num;
        pending_line_num = lsm.line_num;
        pending_column_num = lsm.column_num;
        have_pending_line = true;
      }
    }
    lineptr += oplength;
  }

  after_header_ = lengthstart + header_.total_length;
}

RangeListReader::RangeListReader(const uint8_t* buffer, uint64_t size,
                                 ByteReader* reader)
    : buffer_(buffer), size_(size), reader_(reader) { }

bool RangeListReader::ReadRangeList(uint64_t offset,
                                    RangeListHandler* handler) {
  const uint64_t max_address =
    (reader_->AddressSize() == 4) ? 0xffffffffUL
                                  : 0xffffffffffffffffULL;
  const uint64_t entry_size = reader_->AddressSize() * 2;
  bool list_end = false;

  do {
    if (offset > size_ - entry_size) {
      return false; // Invalid range detected
    }

    uint64_t start_address = reader_->ReadAddress(buffer_ + offset);
    uint64_t end_address =
      reader_->ReadAddress(buffer_ + offset + reader_->AddressSize());

    if (start_address == max_address) { // Base address selection
      handler->SetBaseAddress(end_address);
    } else if (start_address == 0 && end_address == 0) { // End-of-list
      handler->Finish();
      list_end = true;
    } else { // Add a range entry
      handler->AddRange(start_address, end_address);
    }

    offset += entry_size;
  } while (!list_end);

  return true;
}

// A DWARF rule for recovering the address or value of a register, or
// computing the canonical frame address. There is one subclass of this for
// each '*Rule' member function in CallFrameInfo::Handler.
//
// It's annoying that we have to handle Rules using pointers (because
// the concrete instances can have an arbitrary size). They're small,
// so it would be much nicer if we could just handle them by value
// instead of fretting about ownership and destruction.
//
// It seems like all these could simply be instances of std::tr1::bind,
// except that we need instances to be EqualityComparable, too.
//
// This could logically be nested within State, but then the qualified names
// get horrendous.
class CallFrameInfo::Rule {
 public:
  virtual ~Rule() { }

  // Tell HANDLER that, at ADDRESS in the program, REG can be recovered using
  // this rule. If REG is kCFARegister, then this rule describes how to compute
  // the canonical frame address. Return what the HANDLER member function
  // returned.
  virtual bool Handle(Handler* handler,
                      uint64_t address, int reg) const = 0;

  // Equality on rules. We use these to decide which rules we need
  // to report after a DW_CFA_restore_state instruction.
  virtual bool operator==(const Rule& rhs) const = 0;

  bool operator!=(const Rule& rhs) const { return ! (*this == rhs); }

  // Return a pointer to a copy of this rule.
  virtual Rule* Copy() const = 0;

  // If this is a base+offset rule, change its base register to REG.
  // Otherwise, do nothing. (Ugly, but required for DW_CFA_def_cfa_register.)
  virtual void SetBaseRegister(unsigned reg) { }

  // If this is a base+offset rule, change its offset to OFFSET. Otherwise,
  // do nothing. (Ugly, but required for DW_CFA_def_cfa_offset.)
  virtual void SetOffset(long long offset) { }
};

// Rule: the value the register had in the caller cannot be recovered.
class CallFrameInfo::UndefinedRule: public CallFrameInfo::Rule {
 public:
  UndefinedRule() { }
  ~UndefinedRule() { }
  bool Handle(Handler* handler, uint64_t address, int reg) const {
    return handler->UndefinedRule(address, reg);
  }
  bool operator==(const Rule& rhs) const {
    // dynamic_cast is allowed by the Google C++ Style Guide, if the use has
    // been carefully considered; cheap RTTI-like workarounds are forbidden.
    const UndefinedRule* our_rhs = dynamic_cast<const UndefinedRule*>(&rhs);
    return (our_rhs != NULL);
  }
  Rule* Copy() const { return new UndefinedRule(*this); }
};

// Rule: the register's value is the same as that it had in the caller.
class CallFrameInfo::SameValueRule: public CallFrameInfo::Rule {
 public:
  SameValueRule() { }
  ~SameValueRule() { }
  bool Handle(Handler* handler, uint64_t address, int reg) const {
    return handler->SameValueRule(address, reg);
  }
  bool operator==(const Rule& rhs) const {
    // dynamic_cast is allowed by the Google C++ Style Guide, if the use has
    // been carefully considered; cheap RTTI-like workarounds are forbidden.
    const SameValueRule* our_rhs = dynamic_cast<const SameValueRule*>(&rhs);
    return (our_rhs != NULL);
  }
  Rule* Copy() const { return new SameValueRule(*this); }
};

// Rule: the register is saved at OFFSET from BASE_REGISTER.  BASE_REGISTER
// may be CallFrameInfo::Handler::kCFARegister.
class CallFrameInfo::OffsetRule: public CallFrameInfo::Rule {
 public:
  OffsetRule(int base_register, long offset)
      : base_register_(base_register), offset_(offset) { }
  ~OffsetRule() { }
  bool Handle(Handler* handler, uint64_t address, int reg) const {
    return handler->OffsetRule(address, reg, base_register_, offset_);
  }
  bool operator==(const Rule& rhs) const {
    // dynamic_cast is allowed by the Google C++ Style Guide, if the use has
    // been carefully considered; cheap RTTI-like workarounds are forbidden.
    const OffsetRule* our_rhs = dynamic_cast<const OffsetRule*>(&rhs);
    return (our_rhs &&
            base_register_ == our_rhs->base_register_ &&
            offset_ == our_rhs->offset_);
  }
  Rule* Copy() const { return new OffsetRule(*this); }
  // We don't actually need SetBaseRegister or SetOffset here, since they
  // are only ever applied to CFA rules, for DW_CFA_def_cfa_offset, and it
  // doesn't make sense to use OffsetRule for computing the CFA: it
  // computes the address at which a register is saved, not a value.
 private:
  int base_register_;
  long offset_;
};

// Rule: the value the register had in the caller is the value of
// BASE_REGISTER plus offset. BASE_REGISTER may be
// CallFrameInfo::Handler::kCFARegister.
class CallFrameInfo::ValOffsetRule: public CallFrameInfo::Rule {
 public:
  ValOffsetRule(int base_register, long offset)
      : base_register_(base_register), offset_(offset) { }
  ~ValOffsetRule() { }
  bool Handle(Handler* handler, uint64_t address, int reg) const {
    return handler->ValOffsetRule(address, reg, base_register_, offset_);
  }
  bool operator==(const Rule& rhs) const {
    // dynamic_cast is allowed by the Google C++ Style Guide, if the use has
    // been carefully considered; cheap RTTI-like workarounds are forbidden.
    const ValOffsetRule* our_rhs = dynamic_cast<const ValOffsetRule*>(&rhs);
    return (our_rhs &&
            base_register_ == our_rhs->base_register_ &&
            offset_ == our_rhs->offset_);
  }
  Rule* Copy() const { return new ValOffsetRule(*this); }
  void SetBaseRegister(unsigned reg) { base_register_ = reg; }
  void SetOffset(long long offset) { offset_ = offset; }
 private:
  int base_register_;
  long offset_;
};

// Rule: the register has been saved in another register REGISTER_NUMBER_.
class CallFrameInfo::RegisterRule: public CallFrameInfo::Rule {
 public:
  explicit RegisterRule(int register_number)
      : register_number_(register_number) { }
  ~RegisterRule() { }
  bool Handle(Handler* handler, uint64_t address, int reg) const {
    return handler->RegisterRule(address, reg, register_number_);
  }
  bool operator==(const Rule& rhs) const {
    // dynamic_cast is allowed by the Google C++ Style Guide, if the use has
    // been carefully considered; cheap RTTI-like workarounds are forbidden.
    const RegisterRule* our_rhs = dynamic_cast<const RegisterRule*>(&rhs);
    return (our_rhs && register_number_ == our_rhs->register_number_);
  }
  Rule* Copy() const { return new RegisterRule(*this); }
 private:
  int register_number_;
};

// Rule: EXPRESSION evaluates to the address at which the register is saved.
class CallFrameInfo::ExpressionRule: public CallFrameInfo::Rule {
 public:
  explicit ExpressionRule(const string& expression)
      : expression_(expression) { }
  ~ExpressionRule() { }
  bool Handle(Handler* handler, uint64_t address, int reg) const {
    return handler->ExpressionRule(address, reg, expression_);
  }
  bool operator==(const Rule& rhs) const {
    // dynamic_cast is allowed by the Google C++ Style Guide, if the use has
    // been carefully considered; cheap RTTI-like workarounds are forbidden.
    const ExpressionRule* our_rhs = dynamic_cast<const ExpressionRule*>(&rhs);
    return (our_rhs && expression_ == our_rhs->expression_);
  }
  Rule* Copy() const { return new ExpressionRule(*this); }
 private:
  string expression_;
};

// Rule: EXPRESSION evaluates to the address at which the register is saved.
class CallFrameInfo::ValExpressionRule: public CallFrameInfo::Rule {
 public:
  explicit ValExpressionRule(const string& expression)
      : expression_(expression) { }
  ~ValExpressionRule() { }
  bool Handle(Handler* handler, uint64_t address, int reg) const {
    return handler->ValExpressionRule(address, reg, expression_);
  }
  bool operator==(const Rule& rhs) const {
    // dynamic_cast is allowed by the Google C++ Style Guide, if the use has
    // been carefully considered; cheap RTTI-like workarounds are forbidden.
    const ValExpressionRule* our_rhs =
        dynamic_cast<const ValExpressionRule*>(&rhs);
    return (our_rhs && expression_ == our_rhs->expression_);
  }
  Rule* Copy() const { return new ValExpressionRule(*this); }
 private:
  string expression_;
};

// A map from register numbers to rules.
class CallFrameInfo::RuleMap {
 public:
  RuleMap() : cfa_rule_(NULL) { }
  RuleMap(const RuleMap& rhs) : cfa_rule_(NULL) { *this = rhs; }
  ~RuleMap() { Clear(); }

  RuleMap& operator=(const RuleMap& rhs);

  // Set the rule for computing the CFA to RULE. Take ownership of RULE.
  void SetCFARule(Rule* rule) { delete cfa_rule_; cfa_rule_ = rule; }

  // Return the current CFA rule. Unlike RegisterRule, this RuleMap retains
  // ownership of the rule. We use this for DW_CFA_def_cfa_offset and
  // DW_CFA_def_cfa_register, and for detecting references to the CFA before
  // a rule for it has been established.
  Rule* CFARule() const { return cfa_rule_; }

  // Return the rule for REG, or NULL if there is none. The caller takes
  // ownership of the result.
  Rule* RegisterRule(int reg) const;

  // Set the rule for computing REG to RULE. Take ownership of RULE.
  void SetRegisterRule(int reg, Rule* rule);

  // Make all the appropriate calls to HANDLER as if we were changing from
  // this RuleMap to NEW_RULES at ADDRESS. We use this to implement
  // DW_CFA_restore_state, where lots of rules can change simultaneously.
  // Return true if all handlers returned true; otherwise, return false.
  bool HandleTransitionTo(Handler* handler, uint64_t address,
                          const RuleMap& new_rules) const;

 private:
  // A map from register numbers to Rules.
  typedef std::map<int, Rule*> RuleByNumber;

  // Remove all register rules and clear cfa_rule_.
  void Clear();

  // The rule for computing the canonical frame address. This RuleMap owns
  // this rule.
  Rule* cfa_rule_;

  // A map from register numbers to postfix expressions to recover
  // their values. This RuleMap owns the Rules the map refers to.
  RuleByNumber registers_;
};

CallFrameInfo::RuleMap& CallFrameInfo::RuleMap::operator=(const RuleMap& rhs) {
  Clear();
  // Since each map owns the rules it refers to, assignment must copy them.
  if (rhs.cfa_rule_) cfa_rule_ = rhs.cfa_rule_->Copy();
  for (RuleByNumber::const_iterator it = rhs.registers_.begin();
       it != rhs.registers_.end(); it++)
    registers_[it->first] = it->second->Copy();
  return *this;
}

CallFrameInfo::Rule* CallFrameInfo::RuleMap::RegisterRule(int reg) const {
  assert(reg != Handler::kCFARegister);
  RuleByNumber::const_iterator it = registers_.find(reg);
  if (it != registers_.end())
    return it->second->Copy();
  else
    return NULL;
}

void CallFrameInfo::RuleMap::SetRegisterRule(int reg, Rule* rule) {
  assert(reg != Handler::kCFARegister);
  assert(rule);
  Rule** slot = &registers_[reg];
  delete *slot;
  *slot = rule;
}

bool CallFrameInfo::RuleMap::HandleTransitionTo(
    Handler* handler,
    uint64_t address,
    const RuleMap& new_rules) const {
  // Transition from cfa_rule_ to new_rules.cfa_rule_.
  if (cfa_rule_ && new_rules.cfa_rule_) {
    if (*cfa_rule_ != *new_rules.cfa_rule_ &&
        !new_rules.cfa_rule_->Handle(handler, address,
                                     Handler::kCFARegister))
      return false;
  } else if (cfa_rule_) {
    // this RuleMap has a CFA rule but new_rules doesn't.
    // CallFrameInfo::Handler has no way to handle this --- and shouldn't;
    // it's garbage input. The instruction interpreter should have
    // detected this and warned, so take no action here.
  } else if (new_rules.cfa_rule_) {
    // This shouldn't be possible: NEW_RULES is some prior state, and
    // there's no way to remove entries.
    assert(0);
  } else {
    // Both CFA rules are empty.  No action needed.
  }

  // Traverse the two maps in order by register number, and report
  // whatever differences we find.
  RuleByNumber::const_iterator old_it = registers_.begin();
  RuleByNumber::const_iterator new_it = new_rules.registers_.begin();
  while (old_it != registers_.end() && new_it != new_rules.registers_.end()) {
    if (old_it->first < new_it->first) {
      // This RuleMap has an entry for old_it->first, but NEW_RULES
      // doesn't.
      //
      // This isn't really the right thing to do, but since CFI generally
      // only mentions callee-saves registers, and GCC's convention for
      // callee-saves registers is that they are unchanged, it's a good
      // approximation.
      if (!handler->SameValueRule(address, old_it->first))
        return false;
      old_it++;
    } else if (old_it->first > new_it->first) {
      // NEW_RULES has entry for new_it->first, but this RuleMap
      // doesn't. This shouldn't be possible: NEW_RULES is some prior
      // state, and there's no way to remove entries.
      assert(0);
    } else {
      // Both maps have an entry for this register. Report the new
      // rule if it is different.
      if (*old_it->second != *new_it->second &&
          !new_it->second->Handle(handler, address, new_it->first))
        return false;
      new_it++, old_it++;
    }
  }
  // Finish off entries from this RuleMap with no counterparts in new_rules.
  while (old_it != registers_.end()) {
    if (!handler->SameValueRule(address, old_it->first))
      return false;
    old_it++;
  }
  // Since we only make transitions from a rule set to some previously
  // saved rule set, and we can only add rules to the map, NEW_RULES
  // must have fewer rules than *this.
  assert(new_it == new_rules.registers_.end());

  return true;
}

// Remove all register rules and clear cfa_rule_.
void CallFrameInfo::RuleMap::Clear() {
  delete cfa_rule_;
  cfa_rule_ = NULL;
  for (RuleByNumber::iterator it = registers_.begin();
       it != registers_.end(); it++)
    delete it->second;
  registers_.clear();
}

// The state of the call frame information interpreter as it processes
// instructions from a CIE and FDE.
class CallFrameInfo::State {
 public:
  // Create a call frame information interpreter state with the given
  // reporter, reader, handler, and initial call frame info address.
  State(ByteReader* reader, Handler* handler, Reporter* reporter,
        uint64_t address)
      : reader_(reader), handler_(handler), reporter_(reporter),
        address_(address), entry_(NULL), cursor_(NULL) { }

  // Interpret instructions from CIE, save the resulting rule set for
  // DW_CFA_restore instructions, and return true. On error, report
  // the problem to reporter_ and return false.
  bool InterpretCIE(const CIE& cie);

  // Interpret instructions from FDE, and return true. On error,
  // report the problem to reporter_ and return false.
  bool InterpretFDE(const FDE& fde);

 private:  
  // The operands of a CFI instruction, for ParseOperands.
  struct Operands {
    unsigned register_number;  // A register number.
    uint64_t offset;             // An offset or address.
    long signed_offset;        // A signed offset.
    string expression;         // A DWARF expression.
  };

  // Parse CFI instruction operands from STATE's instruction stream as
  // described by FORMAT. On success, populate OPERANDS with the
  // results, and return true. On failure, report the problem and
  // return false.
  //
  // Each character of FORMAT should be one of the following:
  //
  //   'r'  unsigned LEB128 register number (OPERANDS->register_number)
  //   'o'  unsigned LEB128 offset          (OPERANDS->offset)
  //   's'  signed LEB128 offset            (OPERANDS->signed_offset)
  //   'a'  machine-size address            (OPERANDS->offset)
  //        (If the CIE has a 'z' augmentation string, 'a' uses the
  //        encoding specified by the 'R' argument.)
  //   '1'  a one-byte offset               (OPERANDS->offset)
  //   '2'  a two-byte offset               (OPERANDS->offset)
  //   '4'  a four-byte offset              (OPERANDS->offset)
  //   '8'  an eight-byte offset            (OPERANDS->offset)
  //   'e'  a DW_FORM_block holding a       (OPERANDS->expression)
  //        DWARF expression
  bool ParseOperands(const char* format, Operands* operands);

  // Interpret one CFI instruction from STATE's instruction stream, update
  // STATE, report any rule changes to handler_, and return true. On
  // failure, report the problem and return false.
  bool DoInstruction();

  // The following Do* member functions are subroutines of DoInstruction,
  // factoring out the actual work of operations that have several
  // different encodings.

  // Set the CFA rule to be the value of BASE_REGISTER plus OFFSET, and
  // return true. On failure, report and return false. (Used for
  // DW_CFA_def_cfa and DW_CFA_def_cfa_sf.)
  bool DoDefCFA(unsigned base_register, long offset);

  // Change the offset of the CFA rule to OFFSET, and return true. On
  // failure, report and return false. (Subroutine for
  // DW_CFA_def_cfa_offset and DW_CFA_def_cfa_offset_sf.)
  bool DoDefCFAOffset(long offset);

  // Specify that REG can be recovered using RULE, and return true. On
  // failure, report and return false.
  bool DoRule(unsigned reg, Rule* rule);

  // Specify that REG can be found at OFFSET from the CFA, and return true.
  // On failure, report and return false. (Subroutine for DW_CFA_offset,
  // DW_CFA_offset_extended, and DW_CFA_offset_extended_sf.)
  bool DoOffset(unsigned reg, long offset);

  // Specify that the caller's value for REG is the CFA plus OFFSET,
  // and return true. On failure, report and return false. (Subroutine
  // for DW_CFA_val_offset and DW_CFA_val_offset_sf.)
  bool DoValOffset(unsigned reg, long offset);

  // Restore REG to the rule established in the CIE, and return true. On
  // failure, report and return false. (Subroutine for DW_CFA_restore and
  // DW_CFA_restore_extended.)
  bool DoRestore(unsigned reg);

  // Return the section offset of the instruction at cursor. For use
  // in error messages.
  uint64_t CursorOffset() { return entry_->offset + (cursor_ - entry_->start); }

  // Report that entry_ is incomplete, and return false. For brevity.
  bool ReportIncomplete() {
    reporter_->Incomplete(entry_->offset, entry_->kind);
    return false;
  }

  // For reading multi-byte values with the appropriate endianness.
  ByteReader* reader_;

  // The handler to which we should report the data we find.
  Handler* handler_;

  // For reporting problems in the info we're parsing.
  Reporter* reporter_;

  // The code address to which the next instruction in the stream applies.
  uint64_t address_;

  // The entry whose instructions we are currently processing. This is
  // first a CIE, and then an FDE.
  const Entry* entry_;

  // The next instruction to process.
  const uint8_t* cursor_;

  // The current set of rules.
  RuleMap rules_;

  // The set of rules established by the CIE, used by DW_CFA_restore
  // and DW_CFA_restore_extended. We set this after interpreting the
  // CIE's instructions.
  RuleMap cie_rules_;

  // A stack of saved states, for DW_CFA_remember_state and
  // DW_CFA_restore_state.
  std::stack<RuleMap> saved_rules_;
};

bool CallFrameInfo::State::InterpretCIE(const CIE& cie) {
  entry_ = &cie;
  cursor_ = entry_->instructions;
  while (cursor_ < entry_->end)
    if (!DoInstruction())
      return false;
  // Note the rules established by the CIE, for use by DW_CFA_restore
  // and DW_CFA_restore_extended.
  cie_rules_ = rules_;
  return true;
}

bool CallFrameInfo::State::InterpretFDE(const FDE& fde) {
  entry_ = &fde;
  cursor_ = entry_->instructions;
  while (cursor_ < entry_->end)
    if (!DoInstruction())
      return false;
  return true;
}

bool CallFrameInfo::State::ParseOperands(const char* format,
                                         Operands* operands) {
  size_t len;
  const char* operand;

  for (operand = format; *operand; operand++) {
    size_t bytes_left = entry_->end - cursor_;
    switch (*operand) {
      case 'r':
        operands->register_number = reader_->ReadUnsignedLEB128(cursor_, &len);
        if (len > bytes_left) return ReportIncomplete();
        cursor_ += len;
        break;

      case 'o':
        operands->offset = reader_->ReadUnsignedLEB128(cursor_, &len);
        if (len > bytes_left) return ReportIncomplete();
        cursor_ += len;
        break;

      case 's':
        operands->signed_offset = reader_->ReadSignedLEB128(cursor_, &len);
        if (len > bytes_left) return ReportIncomplete();
        cursor_ += len;
        break;

      case 'a':
        operands->offset =
          reader_->ReadEncodedPointer(cursor_, entry_->cie->pointer_encoding,
                                      &len);
        if (len > bytes_left) return ReportIncomplete();
        cursor_ += len;
        break;

      case '1':
        if (1 > bytes_left) return ReportIncomplete();
        operands->offset = static_cast<unsigned char>(*cursor_++);
        break;

      case '2':
        if (2 > bytes_left) return ReportIncomplete();
        operands->offset = reader_->ReadTwoBytes(cursor_);
        cursor_ += 2;
        break;

      case '4':
        if (4 > bytes_left) return ReportIncomplete();
        operands->offset = reader_->ReadFourBytes(cursor_);
        cursor_ += 4;
        break;

      case '8':
        if (8 > bytes_left) return ReportIncomplete();
        operands->offset = reader_->ReadEightBytes(cursor_);
        cursor_ += 8;
        break;

      case 'e': {
        size_t expression_length = reader_->ReadUnsignedLEB128(cursor_, &len);
        if (len > bytes_left || expression_length > bytes_left - len)
          return ReportIncomplete();
        cursor_ += len;
        operands->expression = string(reinterpret_cast<const char*>(cursor_),
                                      expression_length);
        cursor_ += expression_length;
        break;
      }

      default:
          assert(0);
    }
  }

  return true;
}

bool CallFrameInfo::State::DoInstruction() {
  CIE* cie = entry_->cie;
  Operands ops;

  // Our entry's kind should have been set by now.
  assert(entry_->kind != kUnknown);

  // We shouldn't have been invoked unless there were more
  // instructions to parse.
  assert(cursor_ < entry_->end);

  unsigned opcode = *cursor_++;
  if ((opcode & 0xc0) != 0) {
    switch (opcode & 0xc0) {
      // Advance the address.
      case DW_CFA_advance_loc: {
        size_t code_offset = opcode & 0x3f;
        address_ += code_offset * cie->code_alignment_factor;
        break;
      }

      // Find a register at an offset from the CFA.
      case DW_CFA_offset:
        if (!ParseOperands("o", &ops) ||
            !DoOffset(opcode & 0x3f, ops.offset * cie->data_alignment_factor))
          return false;
        break;

      // Restore the rule established for a register by the CIE.
      case DW_CFA_restore:
        if (!DoRestore(opcode & 0x3f)) return false;
        break;

      // The 'if' above should have excluded this possibility.
      default:
        assert(0);
    }

    // Return here, so the big switch below won't be indented.
    return true;
  }

  switch (opcode) {
    // Set the address.
    case DW_CFA_set_loc:
      if (!ParseOperands("a", &ops)) return false;
      address_ = ops.offset;
      break;

    // Advance the address.
    case DW_CFA_advance_loc1:
      if (!ParseOperands("1", &ops)) return false;
      address_ += ops.offset * cie->code_alignment_factor;
      break;
      
    // Advance the address.
    case DW_CFA_advance_loc2:
      if (!ParseOperands("2", &ops)) return false;
      address_ += ops.offset * cie->code_alignment_factor;
      break;
      
    // Advance the address.
    case DW_CFA_advance_loc4:
      if (!ParseOperands("4", &ops)) return false;
      address_ += ops.offset * cie->code_alignment_factor;
      break;
      
    // Advance the address.
    case DW_CFA_MIPS_advance_loc8:
      if (!ParseOperands("8", &ops)) return false;
      address_ += ops.offset * cie->code_alignment_factor;
      break;

    // Compute the CFA by adding an offset to a register.
    case DW_CFA_def_cfa:
      if (!ParseOperands("ro", &ops) ||
          !DoDefCFA(ops.register_number, ops.offset))
        return false;
      break;

    // Compute the CFA by adding an offset to a register.
    case DW_CFA_def_cfa_sf:
      if (!ParseOperands("rs", &ops) ||
          !DoDefCFA(ops.register_number,
                    ops.signed_offset * cie->data_alignment_factor))
        return false;
      break;

    // Change the base register used to compute the CFA.
    case DW_CFA_def_cfa_register: {
      if (!ParseOperands("r", &ops)) return false;
      Rule* cfa_rule = rules_.CFARule();
      if (!cfa_rule) {
        if (!DoDefCFA(ops.register_number, ops.offset)) {
          reporter_->NoCFARule(entry_->offset, entry_->kind, CursorOffset());
          return false;
        }
      } else {
        cfa_rule->SetBaseRegister(ops.register_number);
        if (!cfa_rule->Handle(handler_, address_,
                              Handler::kCFARegister))
        return false;
      }
      break;
    }

    // Change the offset used to compute the CFA.
    case DW_CFA_def_cfa_offset:
      if (!ParseOperands("o", &ops) ||
          !DoDefCFAOffset(ops.offset))
        return false;
      break;

    // Change the offset used to compute the CFA.
    case DW_CFA_def_cfa_offset_sf:
      if (!ParseOperands("s", &ops) ||
          !DoDefCFAOffset(ops.signed_offset * cie->data_alignment_factor))
        return false;
      break;

    // Specify an expression whose value is the CFA.
    case DW_CFA_def_cfa_expression: {
      if (!ParseOperands("e", &ops))
        return false;
      Rule* rule = new ValExpressionRule(ops.expression);
      rules_.SetCFARule(rule);
      if (!rule->Handle(handler_, address_,
                        Handler::kCFARegister))
        return false;
      break;
    }

    // The register's value cannot be recovered.
    case DW_CFA_undefined: {
      if (!ParseOperands("r", &ops) ||
          !DoRule(ops.register_number, new UndefinedRule()))
        return false;
      break;
    }

    // The register's value is unchanged from its value in the caller.
    case DW_CFA_same_value: {
      if (!ParseOperands("r", &ops) ||
          !DoRule(ops.register_number, new SameValueRule()))
        return false;
      break;
    }

    // Find a register at an offset from the CFA.
    case DW_CFA_offset_extended:
      if (!ParseOperands("ro", &ops) ||
          !DoOffset(ops.register_number,
                    ops.offset * cie->data_alignment_factor))
        return false;
      break;

    // The register is saved at an offset from the CFA.
    case DW_CFA_offset_extended_sf:
      if (!ParseOperands("rs", &ops) ||
          !DoOffset(ops.register_number,
                    ops.signed_offset * cie->data_alignment_factor))
        return false;
      break;

    // The register is saved at an offset from the CFA.
    case DW_CFA_GNU_negative_offset_extended:
      if (!ParseOperands("ro", &ops) ||
          !DoOffset(ops.register_number,
                    -ops.offset * cie->data_alignment_factor))
        return false;
      break;

    // The register's value is the sum of the CFA plus an offset.
    case DW_CFA_val_offset:
      if (!ParseOperands("ro", &ops) ||
          !DoValOffset(ops.register_number,
                       ops.offset * cie->data_alignment_factor))
        return false;
      break;

    // The register's value is the sum of the CFA plus an offset.
    case DW_CFA_val_offset_sf:
      if (!ParseOperands("rs", &ops) ||
          !DoValOffset(ops.register_number,
                       ops.signed_offset * cie->data_alignment_factor))
        return false;
      break;

    // The register has been saved in another register.
    case DW_CFA_register: {
      if (!ParseOperands("ro", &ops) ||
          !DoRule(ops.register_number, new RegisterRule(ops.offset)))
        return false;
      break;
    }

    // An expression yields the address at which the register is saved.
    case DW_CFA_expression: {
      if (!ParseOperands("re", &ops) ||
          !DoRule(ops.register_number, new ExpressionRule(ops.expression)))
        return false;
      break;
    }

    // An expression yields the caller's value for the register.
    case DW_CFA_val_expression: {
      if (!ParseOperands("re", &ops) ||
          !DoRule(ops.register_number, new ValExpressionRule(ops.expression)))
        return false;
      break;
    }

    // Restore the rule established for a register by the CIE.
    case DW_CFA_restore_extended:
      if (!ParseOperands("r", &ops) ||
          !DoRestore( ops.register_number))
        return false;
      break;

    // Save the current set of rules on a stack.
    case DW_CFA_remember_state:
      saved_rules_.push(rules_);
      break;

    // Pop the current set of rules off the stack.
    case DW_CFA_restore_state: {
      if (saved_rules_.empty()) {
        reporter_->EmptyStateStack(entry_->offset, entry_->kind,
                                   CursorOffset());
        return false;
      }
      const RuleMap& new_rules = saved_rules_.top();
      if (rules_.CFARule() && !new_rules.CFARule()) {
        reporter_->ClearingCFARule(entry_->offset, entry_->kind,
                                   CursorOffset());
        return false;
      }
      rules_.HandleTransitionTo(handler_, address_, new_rules);
      rules_ = new_rules;
      saved_rules_.pop();
      break;
    }

    // No operation.  (Padding instruction.)
    case DW_CFA_nop:
      break;

    // A SPARC register window save: Registers 8 through 15 (%o0-%o7)
    // are saved in registers 24 through 31 (%i0-%i7), and registers
    // 16 through 31 (%l0-%l7 and %i0-%i7) are saved at CFA offsets
    // (0-15 * the register size). The register numbers must be
    // hard-coded. A GNU extension, and not a pretty one.
    case DW_CFA_GNU_window_save: {
      // Save %o0-%o7 in %i0-%i7.
      for (int i = 8; i < 16; i++)
        if (!DoRule(i, new RegisterRule(i + 16)))
          return false;
      // Save %l0-%l7 and %i0-%i7 at the CFA.
      for (int i = 16; i < 32; i++)
        // Assume that the byte reader's address size is the same as
        // the architecture's register size. !@#%*^ hilarious.
        if (!DoRule(i, new OffsetRule(Handler::kCFARegister,
                                      (i - 16) * reader_->AddressSize())))
          return false;
      break;
    }

    // I'm not sure what this is. GDB doesn't use it for unwinding.
    case DW_CFA_GNU_args_size:
      if (!ParseOperands("o", &ops)) return false;
      break;

    // An opcode we don't recognize.
    default: {
      reporter_->BadInstruction(entry_->offset, entry_->kind, CursorOffset());
      return false;
    }
  }

  return true;
}

bool CallFrameInfo::State::DoDefCFA(unsigned base_register, long offset) {
  Rule* rule = new ValOffsetRule(base_register, offset);
  rules_.SetCFARule(rule);
  return rule->Handle(handler_, address_,
                      Handler::kCFARegister);
}

bool CallFrameInfo::State::DoDefCFAOffset(long offset) {
  Rule* cfa_rule = rules_.CFARule();
  if (!cfa_rule) {
    reporter_->NoCFARule(entry_->offset, entry_->kind, CursorOffset());
    return false;
  }
  cfa_rule->SetOffset(offset);
  return cfa_rule->Handle(handler_, address_,
                          Handler::kCFARegister);
}

bool CallFrameInfo::State::DoRule(unsigned reg, Rule* rule) {
  rules_.SetRegisterRule(reg, rule);
  return rule->Handle(handler_, address_, reg);
}

bool CallFrameInfo::State::DoOffset(unsigned reg, long offset) {
  if (!rules_.CFARule()) {
    reporter_->NoCFARule(entry_->offset, entry_->kind, CursorOffset());
    return false;
  }
  return DoRule(reg,
                new OffsetRule(Handler::kCFARegister, offset));
}

bool CallFrameInfo::State::DoValOffset(unsigned reg, long offset) {
  if (!rules_.CFARule()) {
    reporter_->NoCFARule(entry_->offset, entry_->kind, CursorOffset());
    return false;
  }
  return DoRule(reg,
                new ValOffsetRule(Handler::kCFARegister, offset));
}

bool CallFrameInfo::State::DoRestore(unsigned reg) {
  // DW_CFA_restore and DW_CFA_restore_extended don't make sense in a CIE.
  if (entry_->kind == kCIE) {
    reporter_->RestoreInCIE(entry_->offset, CursorOffset());
    return false;
  }
  Rule* rule = cie_rules_.RegisterRule(reg);
  if (!rule) {
    // This isn't really the right thing to do, but since CFI generally
    // only mentions callee-saves registers, and GCC's convention for
    // callee-saves registers is that they are unchanged, it's a good
    // approximation.
    rule = new SameValueRule();
  }
  return DoRule(reg, rule);
}

bool CallFrameInfo::ReadEntryPrologue(const uint8_t* cursor, Entry* entry) {
  const uint8_t* buffer_end = buffer_ + buffer_length_;

  // Initialize enough of ENTRY for use in error reporting.
  entry->offset = cursor - buffer_;
  entry->start = cursor;
  entry->kind = kUnknown;
  entry->end = NULL;

  // Read the initial length. This sets reader_'s offset size.
  size_t length_size;
  uint64_t length = reader_->ReadInitialLength(cursor, &length_size);
  if (length_size > size_t(buffer_end - cursor))
    return ReportIncomplete(entry);
  cursor += length_size;

  // In a .eh_frame section, a length of zero marks the end of the series
  // of entries.
  if (length == 0 && eh_frame_) {
    entry->kind = kTerminator;
    entry->end = cursor;
    return true;
  }

  // Validate the length.
  if (length > size_t(buffer_end - cursor))
    return ReportIncomplete(entry);
 
  // The length is the number of bytes after the initial length field;
  // we have that position handy at this point, so compute the end
  // now. (If we're parsing 64-bit-offset DWARF on a 32-bit machine,
  // and the length didn't fit in a size_t, we would have rejected it
  // above.)
  entry->end = cursor + length;

  // Parse the next field: either the offset of a CIE or a CIE id.
  size_t offset_size = reader_->OffsetSize();
  if (offset_size > size_t(entry->end - cursor)) return ReportIncomplete(entry);
  entry->id = reader_->ReadOffset(cursor);

  // Don't advance cursor past id field yet; in .eh_frame data we need
  // the id's position to compute the section offset of an FDE's CIE.

  // Now we can decide what kind of entry this is.
  if (eh_frame_) {
    // In .eh_frame data, an ID of zero marks the entry as a CIE, and
    // anything else is an offset from the id field of the FDE to the start
    // of the CIE.
    if (entry->id == 0) {
      entry->kind = kCIE;
    } else {
      entry->kind = kFDE;
      // Turn the offset from the id into an offset from the buffer's start.
      entry->id = (cursor - buffer_) - entry->id;
    }
  } else {
    // In DWARF CFI data, an ID of ~0 (of the appropriate width, given the
    // offset size for the entry) marks the entry as a CIE, and anything
    // else is the offset of the CIE from the beginning of the section.
    if (offset_size == 4)
      entry->kind = (entry->id == 0xffffffff) ? kCIE : kFDE;
    else {
      assert(offset_size == 8);
      entry->kind = (entry->id == 0xffffffffffffffffULL) ? kCIE : kFDE;
    }
  }

  // Now advance cursor past the id.
   cursor += offset_size;
 
  // The fields specific to this kind of entry start here.
  entry->fields = cursor;

  entry->cie = NULL;

  return true;
}

bool CallFrameInfo::ReadCIEFields(CIE* cie) {
  const uint8_t* cursor = cie->fields;
  size_t len;

  assert(cie->kind == kCIE);

  // Prepare for early exit.
  cie->version = 0;
  cie->augmentation.clear();
  cie->code_alignment_factor = 0;
  cie->data_alignment_factor = 0;
  cie->return_address_register = 0;
  cie->has_z_augmentation = false;
  cie->pointer_encoding = DW_EH_PE_absptr;
  cie->instructions = 0;

  // Parse the version number.
  if (cie->end - cursor < 1)
    return ReportIncomplete(cie);
  cie->version = reader_->ReadOneByte(cursor);
  cursor++;

  // If we don't recognize the version, we can't parse any more fields of the
  // CIE. For DWARF CFI, we handle versions 1 through 4 (there was never a
  // version 2 of CFI data). For .eh_frame, we handle versions 1 and 4 as well;
  // the difference between those versions seems to be the same as for
  // .debug_frame.
  if (cie->version < 1 || cie->version > 4) {
    reporter_->UnrecognizedVersion(cie->offset, cie->version);
    return false;
  }

  const uint8_t* augmentation_start = cursor;
  const uint8_t* augmentation_end =
      reinterpret_cast<const uint8_t*>(memchr(augmentation_start, '\0',
                                               cie->end - augmentation_start));
  if (! augmentation_end) return ReportIncomplete(cie);
  cursor = augmentation_end;
  cie->augmentation = string(reinterpret_cast<const char*>(augmentation_start),
                             cursor - augmentation_start);
  // Skip the terminating '\0'.
  cursor++;

  // Is this CFI augmented?
  if (!cie->augmentation.empty()) {
    // Is it an augmentation we recognize?
    if (cie->augmentation[0] == DW_Z_augmentation_start) {
      // Linux C++ ABI 'z' augmentation, used for exception handling data.
      cie->has_z_augmentation = true;
    } else {
      // Not an augmentation we recognize. Augmentations can have arbitrary
      // effects on the form of rest of the content, so we have to give up.
      reporter_->UnrecognizedAugmentation(cie->offset, cie->augmentation);
      return false;
    }
  }

  if (cie->version >= 4) {
    cie->address_size = *cursor++;
    if (cie->address_size != 8 && cie->address_size != 4) {
      reporter_->UnexpectedAddressSize(cie->offset, cie->address_size);
      return false;
    }

    cie->segment_size = *cursor++;
    if (cie->segment_size != 0) {
      reporter_->UnexpectedSegmentSize(cie->offset, cie->segment_size);
      return false;
    }
  }

  // Parse the code alignment factor.
  cie->code_alignment_factor = reader_->ReadUnsignedLEB128(cursor, &len);
  if (size_t(cie->end - cursor) < len) return ReportIncomplete(cie);
  cursor += len;

  // Parse the data alignment factor.
  cie->data_alignment_factor = reader_->ReadSignedLEB128(cursor, &len);
  if (size_t(cie->end - cursor) < len) return ReportIncomplete(cie);
  cursor += len;

  // Parse the return address register. This is a ubyte in version 1, and
  // a ULEB128 in version 3.
  if (cie->version == 1) {
    if (cursor >= cie->end) return ReportIncomplete(cie);
    cie->return_address_register = uint8_t(*cursor++);
  } else {
    cie->return_address_register = reader_->ReadUnsignedLEB128(cursor, &len);
    if (size_t(cie->end - cursor) < len) return ReportIncomplete(cie);
    cursor += len;
  }

  // If we have a 'z' augmentation string, find the augmentation data and
  // use the augmentation string to parse it.
  if (cie->has_z_augmentation) {
    uint64_t data_size = reader_->ReadUnsignedLEB128(cursor, &len);
    if (size_t(cie->end - cursor) < len + data_size)
      return ReportIncomplete(cie);
    cursor += len;
    const uint8_t* data = cursor;
    cursor += data_size;
    const uint8_t* data_end = cursor;

    cie->has_z_lsda = false;
    cie->has_z_personality = false;
    cie->has_z_signal_frame = false;

    // Walk the augmentation string, and extract values from the
    // augmentation data as the string directs.
    for (size_t i = 1; i < cie->augmentation.size(); i++) {
      switch (cie->augmentation[i]) {
        case DW_Z_has_LSDA:
          // The CIE's augmentation data holds the language-specific data
          // area pointer's encoding, and the FDE's augmentation data holds
          // the pointer itself.
          cie->has_z_lsda = true;
          // Fetch the LSDA encoding from the augmentation data.
          if (data >= data_end) return ReportIncomplete(cie);
          cie->lsda_encoding = DwarfPointerEncoding(*data++);
          if (!reader_->ValidEncoding(cie->lsda_encoding)) {
            reporter_->InvalidPointerEncoding(cie->offset, cie->lsda_encoding);
            return false;
          }
          // Don't check if the encoding is usable here --- we haven't
          // read the FDE's fields yet, so we're not prepared for
          // DW_EH_PE_funcrel, although that's a fine encoding for the
          // LSDA to use, since it appears in the FDE.
          break;

        case DW_Z_has_personality_routine:
          // The CIE's augmentation data holds the personality routine
          // pointer's encoding, followed by the pointer itself.
          cie->has_z_personality = true;
          // Fetch the personality routine pointer's encoding from the
          // augmentation data.
          if (data >= data_end) return ReportIncomplete(cie);
          cie->personality_encoding = DwarfPointerEncoding(*data++);
          if (!reader_->ValidEncoding(cie->personality_encoding)) {
            reporter_->InvalidPointerEncoding(cie->offset,
                                              cie->personality_encoding);
            return false;
          }
          if (!reader_->UsableEncoding(cie->personality_encoding)) {
            reporter_->UnusablePointerEncoding(cie->offset,
                                               cie->personality_encoding);
            return false;
          }
          // Fetch the personality routine's pointer itself from the data.
          cie->personality_address =
            reader_->ReadEncodedPointer(data, cie->personality_encoding,
                                        &len);
          if (len > size_t(data_end - data))
            return ReportIncomplete(cie);
          data += len;
          break;

        case DW_Z_has_FDE_address_encoding:
          // The CIE's augmentation data holds the pointer encoding to use
          // for addresses in the FDE.
          if (data >= data_end) return ReportIncomplete(cie);
          cie->pointer_encoding = DwarfPointerEncoding(*data++);
          if (!reader_->ValidEncoding(cie->pointer_encoding)) {
            reporter_->InvalidPointerEncoding(cie->offset,
                                              cie->pointer_encoding);
            return false;
          }
          if (!reader_->UsableEncoding(cie->pointer_encoding)) {
            reporter_->UnusablePointerEncoding(cie->offset,
                                               cie->pointer_encoding);
            return false;
          }
          break;

        case DW_Z_is_signal_trampoline:
          // Frames using this CIE are signal delivery frames.
          cie->has_z_signal_frame = true;
          break;

        default:
          // An augmentation we don't recognize.
          reporter_->UnrecognizedAugmentation(cie->offset, cie->augmentation);
          return false;
      }
    }
  }

  // The CIE's instructions start here.
  cie->instructions = cursor;

  return true;
}

bool CallFrameInfo::ReadFDEFields(FDE* fde) {
  const uint8_t* cursor = fde->fields;
  size_t size;

  fde->address = reader_->ReadEncodedPointer(cursor, fde->cie->pointer_encoding,
                                             &size);
  if (size > size_t(fde->end - cursor))
    return ReportIncomplete(fde);
  cursor += size;
  reader_->SetFunctionBase(fde->address);

  // For the length, we strip off the upper nybble of the encoding used for
  // the starting address.
  DwarfPointerEncoding length_encoding =
    DwarfPointerEncoding(fde->cie->pointer_encoding & 0x0f);
  fde->size = reader_->ReadEncodedPointer(cursor, length_encoding, &size);
  if (size > size_t(fde->end - cursor))
    return ReportIncomplete(fde);
  cursor += size;

  // If the CIE has a 'z' augmentation string, then augmentation data
  // appears here.
  if (fde->cie->has_z_augmentation) {
    uint64_t data_size = reader_->ReadUnsignedLEB128(cursor, &size);
    if (size_t(fde->end - cursor) < size + data_size)
      return ReportIncomplete(fde);
    cursor += size;
    
    // In the abstract, we should walk the augmentation string, and extract
    // items from the FDE's augmentation data as we encounter augmentation
    // string characters that specify their presence: the ordering of items
    // in the augmentation string determines the arrangement of values in
    // the augmentation data.
    //
    // In practice, there's only ever one value in FDE augmentation data
    // that we support --- the LSDA pointer --- and we have to bail if we
    // see any unrecognized augmentation string characters. So if there is
    // anything here at all, we know what it is, and where it starts.
    if (fde->cie->has_z_lsda) {
      // Check whether the LSDA's pointer encoding is usable now: only once
      // we've parsed the FDE's starting address do we call reader_->
      // SetFunctionBase, so that the DW_EH_PE_funcrel encoding becomes
      // usable.
      if (!reader_->UsableEncoding(fde->cie->lsda_encoding)) {
        reporter_->UnusablePointerEncoding(fde->cie->offset,
                                           fde->cie->lsda_encoding);
        return false;
      }

      fde->lsda_address =
        reader_->ReadEncodedPointer(cursor, fde->cie->lsda_encoding, &size);
      if (size > data_size)
        return ReportIncomplete(fde);
      // Ideally, we would also complain here if there were unconsumed
      // augmentation data.
    }

    cursor += data_size;
  }

  // The FDE's instructions start after those.
  fde->instructions = cursor;

  return true;
}
  
bool CallFrameInfo::Start() {
  const uint8_t* buffer_end = buffer_ + buffer_length_;
  const uint8_t* cursor;
  bool all_ok = true;
  const uint8_t* entry_end;
  bool ok;

  // Traverse all the entries in buffer_, skipping CIEs and offering
  // FDEs to the handler.
  for (cursor = buffer_; cursor < buffer_end;
       cursor = entry_end, all_ok = all_ok && ok) {
    FDE fde;

    // Make it easy to skip this entry with 'continue': assume that
    // things are not okay until we've checked all the data, and
    // prepare the address of the next entry.
    ok = false;

    // Read the entry's prologue.
    if (!ReadEntryPrologue(cursor, &fde)) {
      if (!fde.end) {
        // If we couldn't even figure out this entry's extent, then we
        // must stop processing entries altogether.
        all_ok = false;
        break;
      }
      entry_end = fde.end;
      continue;
    }

    // The next iteration picks up after this entry.
    entry_end = fde.end;

    // Did we see an .eh_frame terminating mark?
    if (fde.kind == kTerminator) {
      // If there appears to be more data left in the section after the
      // terminating mark, warn the user. But this is just a warning;
      // we leave all_ok true.
      if (fde.end < buffer_end) reporter_->EarlyEHTerminator(fde.offset);
      break;
    }

    // In this loop, we skip CIEs. We only parse them fully when we
    // parse an FDE that refers to them. This limits our memory
    // consumption (beyond the buffer itself) to that needed to
    // process the largest single entry.
    if (fde.kind != kFDE) {
      ok = true;
      continue;
    }

    // Validate the CIE pointer.
    if (fde.id > buffer_length_) {
      reporter_->CIEPointerOutOfRange(fde.offset, fde.id);
      continue;
    }
      
    CIE cie;

    // Parse this FDE's CIE header.
    if (!ReadEntryPrologue(buffer_ + fde.id, &cie))
      continue;
    // This had better be an actual CIE.
    if (cie.kind != kCIE) {
      reporter_->BadCIEId(fde.offset, fde.id);
      continue;
    }
    if (!ReadCIEFields(&cie))
      continue;

    // TODO(nbilling): This could lead to strange behavior if a single buffer
    // contained a mixture of DWARF versions as well as address sizes. Not
    // sure if it's worth handling such a case.

    // DWARF4 CIE specifies address_size, so use it for this call frame.
    if (cie.version >= 4) {
      reader_->SetAddressSize(cie.address_size);
    }

    // We now have the values that govern both the CIE and the FDE.
    cie.cie = &cie;
    fde.cie = &cie;

    // Parse the FDE's header.
    if (!ReadFDEFields(&fde))
      continue;

    // Call Entry to ask the consumer if they're interested.
    if (!handler_->Entry(fde.offset, fde.address, fde.size,
                         cie.version, cie.augmentation,
                         cie.return_address_register)) {
      // The handler isn't interested in this entry. That's not an error.
      ok = true;
      continue;
    }
                         
    if (cie.has_z_augmentation) {
      // Report the personality routine address, if we have one.
      if (cie.has_z_personality) {
        if (!handler_
            ->PersonalityRoutine(cie.personality_address,
                                 IsIndirectEncoding(cie.personality_encoding)))
          continue;
      }

      // Report the language-specific data area address, if we have one.
      if (cie.has_z_lsda) {
        if (!handler_
            ->LanguageSpecificDataArea(fde.lsda_address,
                                       IsIndirectEncoding(cie.lsda_encoding)))
          continue;
      }

      // If this is a signal-handling frame, report that.
      if (cie.has_z_signal_frame) {
        if (!handler_->SignalHandler())
          continue;
      }
    }

    // Interpret the CIE's instructions, and then the FDE's instructions.
    State state(reader_, handler_, reporter_, fde.address);
    ok = state.InterpretCIE(cie) && state.InterpretFDE(fde);

    // Tell the ByteReader that the function start address from the
    // FDE header is no longer valid.
    reader_->ClearFunctionBase();

    // Report the end of the entry.
    handler_->End();
  }

  return all_ok;
}

const char* CallFrameInfo::KindName(EntryKind kind) {
  if (kind == CallFrameInfo::kUnknown)
    return "entry";
  else if (kind == CallFrameInfo::kCIE)
    return "common information entry";
  else if (kind == CallFrameInfo::kFDE)
    return "frame description entry";
  else {
    assert (kind == CallFrameInfo::kTerminator);
    return ".eh_frame sequence terminator";
  }
}

bool CallFrameInfo::ReportIncomplete(Entry* entry) {
  reporter_->Incomplete(entry->offset, entry->kind);
  return false;
}

void CallFrameInfo::Reporter::Incomplete(uint64_t offset,
                                         CallFrameInfo::EntryKind kind) {
  fprintf(stderr,
          "%s: CFI %s at offset 0x%" PRIx64 " in '%s': entry ends early\n",
          filename_.c_str(), CallFrameInfo::KindName(kind), offset,
          section_.c_str());
}

void CallFrameInfo::Reporter::EarlyEHTerminator(uint64_t offset) {
  fprintf(stderr,
          "%s: CFI at offset 0x%" PRIx64 " in '%s': saw end-of-data marker"
          " before end of section contents\n",
          filename_.c_str(), offset, section_.c_str());
}

void CallFrameInfo::Reporter::CIEPointerOutOfRange(uint64_t offset,
                                                   uint64_t cie_offset) {
  fprintf(stderr,
          "%s: CFI frame description entry at offset 0x%" PRIx64 " in '%s':"
          " CIE pointer is out of range: 0x%" PRIx64 "\n",
          filename_.c_str(), offset, section_.c_str(), cie_offset);
}

void CallFrameInfo::Reporter::BadCIEId(uint64_t offset, uint64_t cie_offset) {
  fprintf(stderr,
          "%s: CFI frame description entry at offset 0x%" PRIx64 " in '%s':"
          " CIE pointer does not point to a CIE: 0x%" PRIx64 "\n",
          filename_.c_str(), offset, section_.c_str(), cie_offset);
}

void CallFrameInfo::Reporter::UnexpectedAddressSize(uint64_t offset,
                                                    uint8_t address_size) {
  fprintf(stderr,
          "%s: CFI frame description entry at offset 0x%" PRIx64 " in '%s':"
          " CIE specifies unexpected address size: %d\n",
          filename_.c_str(), offset, section_.c_str(), address_size);
}

void CallFrameInfo::Reporter::UnexpectedSegmentSize(uint64_t offset,
                                                    uint8_t segment_size) {
  fprintf(stderr,
          "%s: CFI frame description entry at offset 0x%" PRIx64 " in '%s':"
          " CIE specifies unexpected segment size: %d\n",
          filename_.c_str(), offset, section_.c_str(), segment_size);
}

void CallFrameInfo::Reporter::UnrecognizedVersion(uint64_t offset, int version) {
  fprintf(stderr,
          "%s: CFI frame description entry at offset 0x%" PRIx64 " in '%s':"
          " CIE specifies unrecognized version: %d\n",
          filename_.c_str(), offset, section_.c_str(), version);
}

void CallFrameInfo::Reporter::UnrecognizedAugmentation(uint64_t offset,
                                                       const string& aug) {
  fprintf(stderr,
          "%s: CFI frame description entry at offset 0x%" PRIx64 " in '%s':"
          " CIE specifies unrecognized augmentation: '%s'\n",
          filename_.c_str(), offset, section_.c_str(), aug.c_str());
}

void CallFrameInfo::Reporter::InvalidPointerEncoding(uint64_t offset,
                                                     uint8_t encoding) {
  fprintf(stderr,
          "%s: CFI common information entry at offset 0x%" PRIx64 " in '%s':"
          " 'z' augmentation specifies invalid pointer encoding: 0x%02x\n",
          filename_.c_str(), offset, section_.c_str(), encoding);
}

void CallFrameInfo::Reporter::UnusablePointerEncoding(uint64_t offset,
                                                      uint8_t encoding) {
  fprintf(stderr,
          "%s: CFI common information entry at offset 0x%" PRIx64 " in '%s':"
          " 'z' augmentation specifies a pointer encoding for which"
          " we have no base address: 0x%02x\n",
          filename_.c_str(), offset, section_.c_str(), encoding);
}

void CallFrameInfo::Reporter::RestoreInCIE(uint64_t offset, uint64_t insn_offset) {
  fprintf(stderr,
          "%s: CFI common information entry at offset 0x%" PRIx64 " in '%s':"
          " the DW_CFA_restore instruction at offset 0x%" PRIx64
          " cannot be used in a common information entry\n",
          filename_.c_str(), offset, section_.c_str(), insn_offset);
}

void CallFrameInfo::Reporter::BadInstruction(uint64_t offset,
                                             CallFrameInfo::EntryKind kind,
                                             uint64_t insn_offset) {
  fprintf(stderr,
          "%s: CFI %s at offset 0x%" PRIx64 " in section '%s':"
          " the instruction at offset 0x%" PRIx64 " is unrecognized\n",
          filename_.c_str(), CallFrameInfo::KindName(kind),
          offset, section_.c_str(), insn_offset);
}

void CallFrameInfo::Reporter::NoCFARule(uint64_t offset,
                                        CallFrameInfo::EntryKind kind,
                                        uint64_t insn_offset) {
  fprintf(stderr,
          "%s: CFI %s at offset 0x%" PRIx64 " in section '%s':"
          " the instruction at offset 0x%" PRIx64 " assumes that a CFA rule has"
          " been set, but none has been set\n",
          filename_.c_str(), CallFrameInfo::KindName(kind), offset,
          section_.c_str(), insn_offset);
}

void CallFrameInfo::Reporter::EmptyStateStack(uint64_t offset,
                                              CallFrameInfo::EntryKind kind,
                                              uint64_t insn_offset) {
  fprintf(stderr,
          "%s: CFI %s at offset 0x%" PRIx64 " in section '%s':"
          " the DW_CFA_restore_state instruction at offset 0x%" PRIx64
          " should pop a saved state from the stack, but the stack is empty\n",
          filename_.c_str(), CallFrameInfo::KindName(kind), offset,
          section_.c_str(), insn_offset);
}

void CallFrameInfo::Reporter::ClearingCFARule(uint64_t offset,
                                              CallFrameInfo::EntryKind kind,
                                              uint64_t insn_offset) {
  fprintf(stderr,
          "%s: CFI %s at offset 0x%" PRIx64 " in section '%s':"
          " the DW_CFA_restore_state instruction at offset 0x%" PRIx64
          " would clear the CFA rule in effect\n",
          filename_.c_str(), CallFrameInfo::KindName(kind), offset,
          section_.c_str(), insn_offset);
}

}  // namespace dwarf2reader