text: // Copyright 2013 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #include "courgette/disassembler_win32_x64.h"
  
  #include <stddef.h>
  #include <stdint.h>
  
  #include <algorithm>
  
  #include "base/logging.h"
  #include "base/numerics/safe_conversions.h"
  #include "courgette/assembly_program.h"
  #include "courgette/courgette.h"
  
  #if COURGETTE_HISTOGRAM_TARGETS
  #include <iostream>
  #endif
  
  namespace courgette {
  
  DisassemblerWin32X64::DisassemblerWin32X64(const void* start, size_t length)
      : Disassembler(start, length),
        incomplete_disassembly_(false),
        is_PE32_plus_(false),
        optional_header_(nullptr),
        size_of_optional_header_(0),
        offset_of_data_directories_(0),
        machine_type_(0),
        number_of_sections_(0),
        sections_(nullptr),
        has_text_section_(false),
        size_of_code_(0),
        size_of_initialized_data_(0),
        size_of_uninitialized_data_(0),
        base_of_code_(0),
        base_of_data_(0),
        image_base_(0),
        size_of_image_(0),
        number_of_data_directories_(0) {
  }
  
  RVA DisassemblerWin32X64::FileOffsetToRVA(FileOffset file_offset) const {
    for (int i = 0; i < number_of_sections_; ++i) {
      const Section* section = &sections_[i];
      if (file_offset >= section->file_offset_of_raw_data) {
        FileOffset offset_in_section =
            file_offset - section->file_offset_of_raw_data;
        if (offset_in_section < section->size_of_raw_data)
          return static_cast<RVA>(section->virtual_address + offset_in_section);
      }
    }
  
    NOTREACHED();
    return kNoRVA;
  }
  
  FileOffset DisassemblerWin32X64::RVAToFileOffset(RVA rva) const {
    const Section* section = RVAToSection(rva);
    if (section != nullptr) {
      FileOffset offset_in_section = rva - section->virtual_address;
      // Need this extra check, since an |rva| may be valid for a section, but is
      // non-existent in an image (e.g. uninit data).
      if (offset_in_section >= section->size_of_raw_data)
        return kNoFileOffset;
  
      return static_cast<FileOffset>(section->file_offset_of_raw_data +
                                     offset_in_section);
    }
  
    // Small RVA values point into the file header in the loaded image.
    // RVA 0 is the module load address which Windows uses as the module handle.
    // RVA 2 sometimes occurs, I'm not sure what it is, but it would map into the
    // DOS header.
    if (rva == 0 || rva == 2)
      return static_cast<FileOffset>(rva);
  
    NOTREACHED();
    return kNoFileOffset;
  }
  
  RVA DisassemblerWin32X64::PointerToTargetRVA(const uint8_t* p) const {
    return Address64ToRVA(Read64LittleEndian(p));
  }
  
  // ParseHeader attempts to match up the buffer with the Windows data
  // structures that exist within a Windows 'Portable Executable' format file.
  // Returns 'true' if the buffer matches, and 'false' if the data looks
  // suspicious.  Rather than try to 'map' the buffer to the numerous windows
  // structures, we extract the information we need into the courgette::PEInfo
  // structure.
  //
  bool DisassemblerWin32X64::ParseHeader() {
    if (length() < kOffsetOfFileAddressOfNewExeHeader + 4 /*size*/)
      return Bad("Too small");
  
    // Have 'MZ' magic for a DOS header?
    if (start()[0] != 'M' || start()[1] != 'Z')
      return Bad("Not MZ");
  
    // offset from DOS header to PE header is stored in DOS header.
    FileOffset file_offset = static_cast<FileOffset>(
        ReadU32(start(), kOffsetOfFileAddressOfNewExeHeader));
  
    if (file_offset >= length())
      return Bad("Bad offset to PE header");
  
    const uint8_t* const pe_header = FileOffsetToPointer(file_offset);
    const size_t kMinPEHeaderSize = 4 /*signature*/ + kSizeOfCoffHeader;
    if (pe_header <= start() ||
        pe_header >= end() - kMinPEHeaderSize)
      return Bad("Bad file offset to PE header");
  
    if (file_offset % 8 != 0)
      return Bad("Misaligned PE header");
  
    // The 'PE' header is an IMAGE_NT_HEADERS structure as defined in WINNT.H.
    // See http://msdn.microsoft.com/en-us/library/ms680336(VS.85).aspx
    //
    // The first field of the IMAGE_NT_HEADERS is the signature.
    if (!(pe_header[0] == 'P' &&
          pe_header[1] == 'E' &&
          pe_header[2] == 0 &&
          pe_header[3] == 0))
      return Bad("no PE signature");
  
    // The second field of the IMAGE_NT_HEADERS is the COFF header.
    // The COFF header is also called an IMAGE_FILE_HEADER
    //   http://msdn.microsoft.com/en-us/library/ms680313(VS.85).aspx
    const uint8_t* const coff_header = pe_header + 4;
    machine_type_       = ReadU16(coff_header, 0);
    number_of_sections_ = ReadU16(coff_header, 2);
    size_of_optional_header_ = ReadU16(coff_header, 16);
  
    // The rest of the IMAGE_NT_HEADERS is the IMAGE_OPTIONAL_HEADER(32|64)
    const uint8_t* const optional_header = coff_header + kSizeOfCoffHeader;
    optional_header_ = optional_header;
  
    if (optional_header + size_of_optional_header_ >= end())
      return Bad("optional header past end of file");
  
    // Check we can read the magic.
    if (size_of_optional_header_ < 2)
      return Bad("optional header no magic");
  
    uint16_t magic = ReadU16(optional_header, 0);
  
    if (magic == kImageNtOptionalHdr32Magic) {
      is_PE32_plus_ = false;
      offset_of_data_directories_ =
        kOffsetOfDataDirectoryFromImageOptionalHeader32;
    } else if (magic == kImageNtOptionalHdr64Magic) {
      is_PE32_plus_ = true;
      offset_of_data_directories_ =
        kOffsetOfDataDirectoryFromImageOptionalHeader64;
    } else {
      return Bad("unrecognized magic");
    }
  
    // Check that we can read the rest of the the fixed fields.  Data directories
    // directly follow the fixed fields of the IMAGE_OPTIONAL_HEADER.
    if (size_of_optional_header_ < offset_of_data_directories_)
      return Bad("optional header too short");
  
    // The optional header is either an IMAGE_OPTIONAL_HEADER32 or
    // IMAGE_OPTIONAL_HEADER64
    // http://msdn.microsoft.com/en-us/library/ms680339(VS.85).aspx
    //
    // Copy the fields we care about.
    size_of_code_               = ReadU32(optional_header, 4);
    size_of_initialized_data_   = ReadU32(optional_header, 8);
    size_of_uninitialized_data_ = ReadU32(optional_header, 12);
    base_of_code_               = ReadU32(optional_header, 20);
    if (is_PE32_plus_) {
      base_of_data_ = 0;
      image_base_  = ReadU64(optional_header, 24);
    } else {
      base_of_data_ = ReadU32(optional_header, 24);
      image_base_   = ReadU32(optional_header, 28);
    }
    size_of_image_ = ReadU32(optional_header, 56);
    number_of_data_directories_ =
      ReadU32(optional_header, (is_PE32_plus_ ? 108 : 92));
  
    if (size_of_code_ >= length() ||
        size_of_initialized_data_ >= length() ||
        size_of_code_ + size_of_initialized_data_ >= length()) {
      // This validation fires on some perfectly fine executables.
      //  return Bad("code or initialized data too big");
    }
  
    // TODO(sra): we can probably get rid of most of the data directories.
    bool b = true;
    // 'b &= ...' could be short circuit 'b = b && ...' but it is not necessary
    // for correctness and it compiles smaller this way.
    b &= ReadDataDirectory(0, &export_table_);
    b &= ReadDataDirectory(1, &import_table_);
    b &= ReadDataDirectory(2, &resource_table_);
    b &= ReadDataDirectory(3, &exception_table_);
    b &= ReadDataDirectory(5, &base_relocation_table_);
    b &= ReadDataDirectory(11, &bound_import_table_);
    b &= ReadDataDirectory(12, &import_address_table_);
    b &= ReadDataDirectory(13, &delay_import_descriptor_);
    b &= ReadDataDirectory(14, &clr_runtime_header_);
    if (!b) {
      return Bad("malformed data directory");
    }
  
    // Sections follow the optional header.
    sections_ =
        reinterpret_cast<const Section*>(optional_header +
                                         size_of_optional_header_);
    size_t detected_length = 0;
  
    for (int i = 0; i < number_of_sections_; ++i) {
      const Section* section = &sections_[i];
  
      // TODO(sra): consider using the 'characteristics' field of the section
      // header to see if the section contains instructions.
      if (memcmp(section->name, ".text", 6) == 0)
        has_text_section_ = true;
  
      uint32_t section_end =
          section->file_offset_of_raw_data + section->size_of_raw_data;
      if (section_end > detected_length)
        detected_length = section_end;
    }
  
    // Pretend our in-memory copy is only as long as our detected length.
    ReduceLength(detected_length);
  
    if (is_32bit()) {
      return Bad("32 bit executables are not supported by this disassembler");
    }
  
    if (!has_text_section()) {
      return Bad("Resource-only executables are not yet supported");
    }
  
    return Good();
  }
  
  bool DisassemblerWin32X64::Disassemble(AssemblyProgram* target) {
    if (!ok())
      return false;
  
    target->set_image_base(image_base());
  
    if (!ParseAbs32Relocs())
      return false;
  
    ParseRel32RelocsFromSections();
  
    PrecomputeLabels(target);
    RemoveUnusedRel32Locations(target);
  
    if (!ParseFile(target))
      return false;
  
    target->DefaultAssignIndexes();
  
    return true;
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  
  bool DisassemblerWin32X64::ParseRelocs(std::vector<RVA> *relocs) {
    relocs->clear();
  
    size_t relocs_size = base_relocation_table_.size_;
    if (relocs_size == 0)
      return true;
  
    // The format of the base relocation table is a sequence of variable sized
    // IMAGE_BASE_RELOCATION blocks.  Search for
    //   "The format of the base relocation data is somewhat quirky"
    // at http://msdn.microsoft.com/en-us/library/ms809762.aspx
  
    const uint8_t* relocs_start = RVAToPointer(base_relocation_table_.address_);
    const uint8_t* relocs_end = relocs_start + relocs_size;
  
    // Make sure entire base relocation table is within the buffer.
    if (relocs_start < start() ||
        relocs_start >= end() ||
        relocs_end <= start() ||
        relocs_end > end()) {
      return Bad(".relocs outside image");
    }
  
    const uint8_t* block = relocs_start;
  
    // Walk the variable sized blocks.
    while (block + 8 < relocs_end) {
      RVA page_rva = ReadU32(block, 0);
      uint32_t size = ReadU32(block, 4);
      if (size < 8 ||        // Size includes header ...
          size % 4  !=  0)   // ... and is word aligned.
        return Bad("unreasonable relocs block");
  
      const uint8_t* end_entries = block + size;
  
      if (end_entries <= block ||
          end_entries <= start() ||
          end_entries > end())
        return Bad(".relocs block outside image");
  
      // Walk through the two-byte entries.
      for (const uint8_t* p = block + 8; p < end_entries; p += 2) {
        uint16_t entry = ReadU16(p, 0);
        int type = entry >> 12;
        int offset = entry & 0xFFF;
  
        RVA rva = page_rva + offset;
        // TODO(sebmarchand): Skip the relocs that live outside of the image. See
        //   the version of this function in disassembler_win32_x86.cc.
        if (type == 10) {  // IMAGE_REL_BASED_DIR64
          relocs->push_back(rva);
        } else if (type == 0) {  // IMAGE_REL_BASED_ABSOLUTE
          // Ignore, used as padding.
        } else {
          // Does not occur in Windows x64 executables.
          return Bad("unknown type of reloc");
        }
      }
  
      block += size;
    }
  
    std::sort(relocs->begin(), relocs->end());
    DCHECK(relocs->empty() || relocs->back() != kUnassignedRVA);
  
    return true;
  }
  
  const Section* DisassemblerWin32X64::RVAToSection(RVA rva) const {
    for (int i = 0; i < number_of_sections_; ++i) {
      const Section* section = &sections_[i];
      if (rva >= section->virtual_address) {
        FileOffset offset_in_section = rva - section->virtual_address;
        if (offset_in_section < section->virtual_size)
          return section;
      }
    }
    return nullptr;
  }
  
  RVA DisassemblerWin32X64::Address64ToRVA(uint64_t address) const {
    if (address < image_base() || address >= image_base() + size_of_image_)
      return kNoRVA;
    return base::checked_cast<RVA>(address - image_base());
  }
  
  std::string DisassemblerWin32X64::SectionName(const Section* section) {
    if (section == nullptr)
      return "<none>";
    char name[9];
    memcpy(name, section->name, 8);
    name[8] = '\0';  // Ensure termination.
    return name;
  }
  
  RvaVisitor* DisassemblerWin32X64::CreateAbs32TargetRvaVisitor() {
    return new RvaVisitor_Abs32(abs32_locations_, *this);
  }
  
  RvaVisitor* DisassemblerWin32X64::CreateRel32TargetRvaVisitor() {
    return new RvaVisitor_Rel32(rel32_locations_, *this);
  }
  
  void DisassemblerWin32X64::RemoveUnusedRel32Locations(
      AssemblyProgram* program) {
    auto cond = [this, program](RVA rva) -> bool {
      // + 4 since offset is relative to start of next instruction.
      RVA target_rva = rva + 4 + Read32LittleEndian(RVAToPointer(rva));
      return program->FindRel32Label(target_rva) == nullptr;
    };
    rel32_locations_.erase(
        std::remove_if(rel32_locations_.begin(), rel32_locations_.end(), cond),
        rel32_locations_.end());
  }
  
  CheckBool DisassemblerWin32X64::ParseFile(AssemblyProgram* program) {
    // Walk all the bytes in the file, whether or not in a section.
    FileOffset file_offset = 0;
    while (file_offset < length()) {
      const Section* section = FindNextSection(file_offset);
      if (section == nullptr) {
        // No more sections. There should not be extra stuff following last
        // section.
        //   ParseNonSectionFileRegion(file_offset, pe_info().length(), program);
        break;
      }
      if (file_offset < section->file_offset_of_raw_data) {
        FileOffset section_start_offset = section->file_offset_of_raw_data;
        if (!ParseNonSectionFileRegion(file_offset, section_start_offset,
                                       program)) {
          return false;
        }
  
        file_offset = section_start_offset;
      }
      FileOffset end = file_offset + section->size_of_raw_data;
      if (!ParseFileRegion(section, file_offset, end, program))
        return false;
      file_offset = end;
    }
  
  #if COURGETTE_HISTOGRAM_TARGETS
    HistogramTargets("abs32 relocs", abs32_target_rvas_);
    HistogramTargets("rel32 relocs", rel32_target_rvas_);
  #endif
  
    return true;
  }
  
  bool DisassemblerWin32X64::ParseAbs32Relocs() {
    abs32_locations_.clear();
    if (!ParseRelocs(&abs32_locations_))
      return false;
  
  #if COURGETTE_HISTOGRAM_TARGETS
    for (size_t i = 0; i < abs32_locations_.size(); ++i) {
      RVA rva = abs32_locations_[i];
      // The 8 bytes at the relocation are a reference to some address.
      ++abs32_target_rvas_[PointerToTargetRVA(RVAToPointer(rva))];
    }
  #endif
    return true;
  }
  
  void DisassemblerWin32X64::ParseRel32RelocsFromSections() {
    FileOffset file_offset = 0;
    while (file_offset < length()) {
      const Section* section = FindNextSection(file_offset);
      if (section == nullptr)
        break;
      if (file_offset < section->file_offset_of_raw_data)
        file_offset = section->file_offset_of_raw_data;
      ParseRel32RelocsFromSection(section);
      file_offset += section->size_of_raw_data;
    }
    std::sort(rel32_locations_.begin(), rel32_locations_.end());
    DCHECK(rel32_locations_.empty() ||
           rel32_locations_.back() != kUnassignedRVA);
  
  #if COURGETTE_HISTOGRAM_TARGETS
    VLOG(1) << "abs32_locations_ " << abs32_locations_.size()
            << "\nrel32_locations_ " << rel32_locations_.size()
            << "\nabs32_target_rvas_ " << abs32_target_rvas_.size()
            << "\nrel32_target_rvas_ " << rel32_target_rvas_.size();
  
    int common = 0;
    std::map<RVA, int>::iterator abs32_iter = abs32_target_rvas_.begin();
    std::map<RVA, int>::iterator rel32_iter = rel32_target_rvas_.begin();
    while (abs32_iter != abs32_target_rvas_.end() &&
           rel32_iter != rel32_target_rvas_.end()) {
      if (abs32_iter->first < rel32_iter->first) {
        ++abs32_iter;
      } else if (rel32_iter->first < abs32_iter->first) {
        ++rel32_iter;
      } else {
        ++common;
        ++abs32_iter;
        ++rel32_iter;
      }
    }
    VLOG(1) << "common " << common;
  #endif
  }
  
  void DisassemblerWin32X64::ParseRel32RelocsFromSection(const Section* section) {
    // TODO(sra): use characteristic.
    bool isCode = strcmp(section->name, ".text") == 0;
    if (!isCode)
      return;
  
    FileOffset start_file_offset = section->file_offset_of_raw_data;
    FileOffset end_file_offset = start_file_offset + section->size_of_raw_data;
    RVA relocs_start_rva = base_relocation_table().address_;
  
    const uint8_t* start_pointer = FileOffsetToPointer(start_file_offset);
    const uint8_t* end_pointer = FileOffsetToPointer(end_file_offset);
  
    RVA start_rva = FileOffsetToRVA(start_file_offset);
    RVA end_rva = start_rva + section->virtual_size;
  
    // Quick way to convert from Pointer to RVA within a single Section is to
    // subtract |pointer_to_rva|.
    const uint8_t* const adjust_pointer_to_rva = start_pointer - start_rva;
  
    std::vector<RVA>::iterator abs32_pos = abs32_locations_.begin();
  
    // Find the rel32 relocations.
    const uint8_t* p = start_pointer;
    while (p < end_pointer) {
      RVA current_rva = static_cast<RVA>(p - adjust_pointer_to_rva);
      if (current_rva == relocs_start_rva) {
        uint32_t relocs_size = base_relocation_table().size_;
        if (relocs_size) {
          p += relocs_size;
          continue;
        }
      }
  
      // Heuristic discovery of rel32 locations in instruction stream: are the
      // next few bytes the start of an instruction containing a rel32
      // addressing mode?
      const uint8_t* rel32 = nullptr;
      bool is_rip_relative = false;
  
      if (p + 5 <= end_pointer) {
        if (*p == 0xE8 || *p == 0xE9)  // jmp rel32 and call rel32
          rel32 = p + 1;
      }
      if (p + 6 <= end_pointer) {
        if (*p == 0x0F && (*(p + 1) & 0xF0) == 0x80) {  // Jcc long form
          if (p[1] != 0x8A && p[1] != 0x8B)  // JPE/JPO unlikely
            rel32 = p + 2;
        } else if (*p == 0xFF && (*(p + 1) == 0x15 || *(p + 1) == 0x25)) {
          // rip relative call/jmp
          rel32 = p + 2;
          is_rip_relative = true;
        }
      }
      if (p + 7 <= end_pointer) {
        if ((*p & 0xFB) == 0x48 && *(p + 1) == 0x8D &&
            (*(p + 2) & 0xC7) == 0x05) {
          // rip relative lea
          rel32 = p + 3;
          is_rip_relative = true;
        } else if ((*p & 0xFB) == 0x48 && *(p + 1) == 0x8B &&
                   (*(p + 2) & 0xC7) == 0x05) {
          // rip relative mov
          rel32 = p + 3;
          is_rip_relative = true;
        }
      }
  
      if (rel32) {
        RVA rel32_rva = static_cast<RVA>(rel32 - adjust_pointer_to_rva);
  
        // Is there an abs32 reloc overlapping the candidate?
        while (abs32_pos != abs32_locations_.end() && *abs32_pos < rel32_rva - 3)
          ++abs32_pos;
        // Now: (*abs32_pos > rel32_rva - 4) i.e. the lowest addressed 4-byte
        // region that could overlap rel32_rva.
        if (abs32_pos != abs32_locations_.end()) {
          if (*abs32_pos < rel32_rva + 4) {
            // Beginning of abs32 reloc is before end of rel32 reloc so they
            // overlap. Skip four bytes past the abs32 reloc.
            p += (*abs32_pos + 4) - current_rva;
            continue;
          }
        }
  
        // + 4 since offset is relative to start of next instruction.
        RVA target_rva = rel32_rva + 4 + Read32LittleEndian(rel32);
        // To be valid, rel32 target must be within image, and within this
        // section.
        if (target_rva < size_of_image_ &&  // Subsumes rva != kUnassignedRVA.
            (is_rip_relative ||
             (start_rva <= target_rva && target_rva < end_rva))) {
          rel32_locations_.push_back(rel32_rva);
  #if COURGETTE_HISTOGRAM_TARGETS
          ++rel32_target_rvas_[target_rva];
  #endif
          p = rel32 + 4;
          continue;
        }
      }
      p += 1;
    }
  }
  
  CheckBool DisassemblerWin32X64::ParseNonSectionFileRegion(
      FileOffset start_file_offset,
      FileOffset end_file_offset,
      AssemblyProgram* program) {
    if (incomplete_disassembly_)
      return true;
  
    if (end_file_offset > start_file_offset) {
      if (!program->EmitBytesInstruction(FileOffsetToPointer(start_file_offset),
                                         end_file_offset - start_file_offset)) {
        return false;
      }
    }
  
    return true;
  }
  
  CheckBool DisassemblerWin32X64::ParseFileRegion(const Section* section,
                                                  FileOffset start_file_offset,
                                                  FileOffset end_file_offset,
                                                  AssemblyProgram* program) {
    RVA relocs_start_rva = base_relocation_table().address_;
  
    const uint8_t* start_pointer = FileOffsetToPointer(start_file_offset);
    const uint8_t* end_pointer = FileOffsetToPointer(end_file_offset);
  
    RVA start_rva = FileOffsetToRVA(start_file_offset);
    RVA end_rva = start_rva + section->virtual_size;
  
    // Quick way to convert from Pointer to RVA within a single Section is to
    // subtract 'pointer_to_rva'.
    const uint8_t* const adjust_pointer_to_rva = start_pointer - start_rva;
  
    std::vector<RVA>::iterator rel32_pos = rel32_locations_.begin();
    std::vector<RVA>::iterator abs32_pos = abs32_locations_.begin();
  
    if (!program->EmitOriginInstruction(start_rva))
      return false;
  
    const uint8_t* p = start_pointer;
  
    while (p < end_pointer) {
      RVA current_rva = static_cast<RVA>(p - adjust_pointer_to_rva);
  
      // The base relocation table is usually in the .relocs section, but it could
      // actually be anywhere.  Make sure we skip it because we will regenerate it
      // during assembly.
      if (current_rva == relocs_start_rva) {
        if (!program->EmitPeRelocsInstruction())
          return false;
        uint32_t relocs_size = base_relocation_table().size_;
        if (relocs_size) {
          p += relocs_size;
          continue;
        }
      }
  
      while (abs32_pos != abs32_locations_.end() && *abs32_pos < current_rva)
        ++abs32_pos;
  
      if (abs32_pos != abs32_locations_.end() && *abs32_pos == current_rva) {
        RVA target_rva = PointerToTargetRVA(p);
        DCHECK_NE(kNoRVA, target_rva);
        // TODO(sra): target could be Label+offset.  It is not clear how to guess
        // which it might be.  We assume offset==0.
        Label* label = program->FindAbs32Label(target_rva);
        DCHECK(label);
        if (!program->EmitAbs64(label))
          return false;
        p += 8;
        continue;
      }
  
      while (rel32_pos != rel32_locations_.end() && *rel32_pos < current_rva)
        ++rel32_pos;
  
      if (rel32_pos != rel32_locations_.end() && *rel32_pos == current_rva) {
        // + 4 since offset is relative to start of next instruction.
        RVA target_rva = current_rva + 4 + Read32LittleEndian(p);
        Label* label = program->FindRel32Label(target_rva);
        DCHECK(label);
        if (!program->EmitRel32(label))
          return false;
        p += 4;
        continue;
      }
  
      if (incomplete_disassembly_) {
        if ((abs32_pos == abs32_locations_.end() || end_rva <= *abs32_pos) &&
            (rel32_pos == rel32_locations_.end() || end_rva <= *rel32_pos) &&
            (end_rva <= relocs_start_rva || current_rva >= relocs_start_rva)) {
          // No more relocs in this section, don't bother encoding bytes.
          break;
        }
      }
  
      if (!program->EmitByteInstruction(*p))
        return false;
      p += 1;
    }
  
    return true;
  }
  
  #if COURGETTE_HISTOGRAM_TARGETS
  // Histogram is printed to std::cout.  It is purely for debugging the algorithm
  // and is only enabled manually in 'exploration' builds.  I don't want to add
  // command-line configuration for this feature because this code has to be
  // small, which means compiled-out.
  void DisassemblerWin32X64::HistogramTargets(const char* kind,
                                              const std::map<RVA, int>& map) {
    int total = 0;
    std::map<int, std::vector<RVA> > h;
    for (std::map<RVA, int>::const_iterator p = map.begin();
         p != map.end();
         ++p) {
      h[p->second].push_back(p->first);
      total += p->second;
    }
  
    std::cout << total << " " << kind << " to "
              << map.size() << " unique targets" << std::endl;
  
    std::cout << "indegree: #targets-with-indegree (example)" << std::endl;
    const int kFirstN = 15;
    bool someSkipped = false;
    int index = 0;
    for (std::map<int, std::vector<RVA> >::reverse_iterator p = h.rbegin();
         p != h.rend();
         ++p) {
      ++index;
      if (index <= kFirstN || p->first <= 3) {
        if (someSkipped) {
          std::cout << "..." << std::endl;
        }
        size_t count = p->second.size();
        std::cout << std::dec << p->first << ": " << count;
        if (count <= 2) {
          for (size_t i = 0; i < count; ++i)
            std::cout << "  " << DescribeRVA(p->second[i]);
        }
        std::cout << std::endl;
        someSkipped = false;
      } else {
        someSkipped = true;
      }
    }
  }
  #endif  // COURGETTE_HISTOGRAM_TARGETS
  
  // DescribeRVA is for debugging only.  I would put it under #ifdef DEBUG except
  // that during development I'm finding I need to call it when compiled in
  // Release mode.  Hence:
  // TODO(sra): make this compile only for debug mode.
  std::string DisassemblerWin32X64::DescribeRVA(RVA rva) const {
    const Section* section = RVAToSection(rva);
    std::ostringstream s;
    s << std::hex << rva;
    if (section) {
      s << " (";
      s << SectionName(section) << "+"
        << std::hex << (rva - section->virtual_address)
        << ")";
    }
    return s.str();
  }
  
  const Section* DisassemblerWin32X64::FindNextSection(
      FileOffset file_offset) const {
    const Section* best = 0;
    for (int i = 0; i < number_of_sections_; ++i) {
      const Section* section = &sections_[i];
      if (section->size_of_raw_data > 0) {  // i.e. has data in file.
        if (file_offset <= section->file_offset_of_raw_data) {
          if (best == 0 ||
              section->file_offset_of_raw_data < best->file_offset_of_raw_data) {
            best = section;
          }
        }
      }
    }
    return best;
  }
  
  bool DisassemblerWin32X64::ReadDataDirectory(
      int index,
      ImageDataDirectory* directory) {
  
    if (index < number_of_data_directories_) {
      FileOffset file_offset = index * 8 + offset_of_data_directories_;
      if (file_offset >= size_of_optional_header_)
        return Bad("number of data directories inconsistent");
      const uint8_t* data_directory = optional_header_ + file_offset;
      if (data_directory < start() ||
          data_directory + 8 >= end())
        return Bad("data directory outside image");
      RVA rva = ReadU32(data_directory, 0);
      size_t size  = ReadU32(data_directory, 4);
      if (size > size_of_image_)
        return Bad("data directory size too big");
  
      // TODO(sra): validate RVA.
      directory->address_ = rva;
      directory->size_ = static_cast<uint32_t>(size);
      return true;
    } else {
      directory->address_ = 0;
      directory->size_ = 0;
      return true;
    }
  }
  
  }  // namespace courgette
  