Further refactoring, move ImageInfo into Disassembler/DisassemblerWin32X86.

courgette/disassembler_win32_x86.cc

 // Copyright (c) 2011 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_x86.h"
 
 #include <algorithm>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 
 #include "courgette/assembly_program.h"
 #include "courgette/courgette.h"
 #include "courgette/encoded_program.h"
-#include "courgette/image_info.h"
 
 // COURGETTE_HISTOGRAM_TARGETS prints out a histogram of how frequently
 // different target addresses are referenced.  Purely for debugging.
 #define COURGETTE_HISTOGRAM_TARGETS 0
 
 namespace courgette {
 
-DisassemblerWin32X86::DisassemblerWin32X86(PEInfo* pe_info)
-  : pe_info_(pe_info),
-    incomplete_disassembly_(false) {
+DisassemblerWin32X86::DisassemblerWin32X86(const void* start, size_t length)
+  : Disassembler(start, length),
+    incomplete_disassembly_(false),
+    is_PE32_plus_(false),
+    optional_header_(NULL),
+    size_of_optional_header_(0),
+    offset_of_data_directories_(0),
+    machine_type_(0),
+    number_of_sections_(0),
+    sections_(NULL),
+    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) {
+}
+
+// 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 DisassemblerWin32X86::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.
+  uint32 offset = ReadU32(start(),
+                          kOffsetOfFileAddressOfNewExeHeader);
+
+  const uint8* const pe_header = OffsetToPointer(offset);
+  const size_t kMinPEHeaderSize = 4 /*signature*/ + kSizeOfCoffHeader;
+  if (pe_header <= start() ||
+      pe_header >= end() - kMinPEHeaderSize)
+    return Bad("Bad offset to PE header");
+
+  if (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* 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* 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 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 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);
+  return Good();
 }
 
 bool DisassemblerWin32X86::Disassemble(AssemblyProgram* target) {
-  if (!pe_info().ok())
+  if (!ok())
     return false;
 
-  target->set_image_base(pe_info().image_base());
+  target->set_image_base(image_base());
 
   if (!ParseAbs32Relocs())
     return false;
 
   ParseRel32RelocsFromSections();
 
   if (!ParseFile(target))
     return false;
 
   target->DefaultAssignIndexes();
 
   return true;
 }
 
-static uint32 Read32LittleEndian(const void* address) {
-  return *reinterpret_cast<const uint32*>(address);
+////////////////////////////////////////////////////////////////////////////////
+
+bool DisassemblerWin32X86::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* relocs_start = RVAToPointer(base_relocation_table_.address_);
+  const uint8* 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* block = relocs_start;
+
+  // Walk the variable sized blocks.
+  while (block + 8 < relocs_end) {
+    RVA page_rva = ReadU32(block, 0);
+    uint32 size = ReadU32(block, 4);
+    if (size < 8 ||        // Size includes header ...
+        size % 4  !=  0)   // ... and is word aligned.
+      return Bad("unreasonable relocs block");
+
+    const uint8* 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* p = block + 8;  p < end_entries;  p += 2) {
+      uint16 entry = ReadU16(p, 0);
+      int type = entry >> 12;
+      int offset = entry & 0xFFF;
+
+      RVA rva = page_rva + offset;
+      if (type == 3) {         // IMAGE_REL_BASED_HIGHLOW
+        relocs->push_back(rva);
+      } else if (type == 0) {  // IMAGE_REL_BASED_ABSOLUTE
+        // Ignore, used as padding.
+      } else {
+        // Does not occur in Windows x86 executables.
+        return Bad("unknown type of reloc");
+      }
+    }
+
+    block += size;
+  }
+
+  std::sort(relocs->begin(), relocs->end());
+
+  return true;
+}
+
+const Section* DisassemblerWin32X86::RVAToSection(RVA rva) const {
+  for (int i = 0; i < number_of_sections_; i++) {
+    const Section* section = &sections_[i];
+    uint32 offset = rva - section->virtual_address;
+    if (offset < section->virtual_size) {
+      return section;
+    }
+  }
+  return NULL;
+}
+
+int DisassemblerWin32X86::RVAToFileOffset(RVA rva) const {
+  const Section* section = RVAToSection(rva);
+  if (section) {
+    uint32 offset = rva - section->virtual_address;
+    if (offset < section->size_of_raw_data) {
+      return section->file_offset_of_raw_data + offset;
+    } else {
+      return kNoOffset;  // In section but not in file (e.g. uninit data).
+    }
+  }
+
+  // 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 rva;
+
+  NOTREACHED();
+  return kNoOffset;
+}
+
+const uint8* DisassemblerWin32X86::RVAToPointer(RVA rva) const {
+  int file_offset = RVAToFileOffset(rva);
+  if (file_offset == kNoOffset)
+    return NULL;
+  else
+    return OffsetToPointer(file_offset);
+}
+
+std::string DisassemblerWin32X86::SectionName(const Section* section) {
+  if (section == NULL)
+    return "<none>";
+  char name[9];
+  memcpy(name, section->name, 8);
+  name[8] = '\0';  // Ensure termination.
+  return name;
+}
+
+CheckBool DisassemblerWin32X86::ParseFile(AssemblyProgram* program) {
+  bool ok = true;
+  // Walk all the bytes in the file, whether or not in a section.
+  uint32 file_offset = 0;
+  while (ok && file_offset < length()) {
+    const Section* section = FindNextSection(file_offset);
+    if (section == NULL) {
+      // 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) {
+      uint32 section_start_offset = section->file_offset_of_raw_data;
+      ok = ParseNonSectionFileRegion(file_offset, section_start_offset,
+                                     program);
+      file_offset = section_start_offset;
+    }
+    if (ok) {
+      uint32 end = file_offset + section->size_of_raw_data;
+      ok = ParseFileRegion(section, file_offset, end, program);
+      file_offset = end;
+    }
+  }
+
+#if COURGETTE_HISTOGRAM_TARGETS
+  HistogramTargets("abs32 relocs", abs32_target_rvas_);
+  HistogramTargets("rel32 relocs", rel32_target_rvas_);
+#endif
+
+  return ok;
 }
 
 bool DisassemblerWin32X86::ParseAbs32Relocs() {
   abs32_locations_.clear();
-  if (!pe_info().ParseRelocs(&abs32_locations_))
+  if (!ParseRelocs(&abs32_locations_))
     return false;
 
   std::sort(abs32_locations_.begin(), abs32_locations_.end());
 
 #if COURGETTE_HISTOGRAM_TARGETS
   for (size_t i = 0;  i < abs32_locations_.size(); ++i) {
     RVA rva = abs32_locations_[i];
     // The 4 bytes at the relocation are a reference to some address.
-    uint32 target_address = Read32LittleEndian(pe_info().RVAToPointer(rva));
-    ++abs32_target_rvas_[target_address - pe_info().image_base()];
+    uint32 target_address = Read32LittleEndian(RVAToPointer(rva));
+    ++abs32_target_rvas_[target_address - image_base()];
   }
 #endif
   return true;
 }
 
 void DisassemblerWin32X86::ParseRel32RelocsFromSections() {
   uint32 file_offset = 0;
-  while (file_offset < pe_info().length()) {
-    const Section* section = pe_info().FindNextSection(file_offset);
+  while (file_offset < length()) {
+    const Section* section = FindNextSection(file_offset);
     if (section == NULL)
       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());
 
 #if COURGETTE_HISTOGRAM_TARGETS
@@ skipping 22 matching lines @@
 }
 
 void DisassemblerWin32X86::ParseRel32RelocsFromSection(const Section* section) {
   // TODO(sra): use characteristic.
   bool isCode = strcmp(section->name, ".text") == 0;
   if (!isCode)
     return;
 
   uint32 start_file_offset = section->file_offset_of_raw_data;
   uint32 end_file_offset = start_file_offset + section->size_of_raw_data;
-  RVA relocs_start_rva = pe_info().base_relocation_table().address_;
+  RVA relocs_start_rva = base_relocation_table().address_;
 
-  const uint8* start_pointer = pe_info().FileOffsetToPointer(start_file_offset);
-  const uint8* end_pointer = pe_info().FileOffsetToPointer(end_file_offset);
+  const uint8* start_pointer = OffsetToPointer(start_file_offset);
+  const uint8* end_pointer = OffsetToPointer(end_file_offset);
 
-  RVA start_rva = pe_info().FileOffsetToRVA(start_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* const adjust_pointer_to_rva = start_pointer - start_rva;
 
   std::vector<RVA>::iterator abs32_pos = abs32_locations_.begin();
 
   // Find the rel32 relocations.
   const uint8* 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 relocs_size = pe_info().base_relocation_table().size_;
+      uint32 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;
 
     // Heuristic discovery of rel32 locations in instruction stream: are the
@@ skipping 25 matching lines @@
           // 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;
         }
       }
 
       RVA target_rva = rel32_rva + 4 + Read32LittleEndian(rel32);
       // To be valid, rel32 target must be within image, and within this
       // section.
-      if (pe_info().IsValidRVA(target_rva) &&
+      if (IsValidRVA(target_rva) &&
           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 += 4;
         continue;
       }
     }
     p += 1;
   }
 }
 
-CheckBool DisassemblerWin32X86::ParseFile(AssemblyProgram* program) {
-  bool ok = true;
-  // Walk all the bytes in the file, whether or not in a section.
-  uint32 file_offset = 0;
-  while (ok && file_offset < pe_info().length()) {
-    const Section* section = pe_info().FindNextSection(file_offset);
-    if (section == NULL) {
-      // 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) {
-      uint32 section_start_offset = section->file_offset_of_raw_data;
-      ok = ParseNonSectionFileRegion(file_offset, section_start_offset,
-                                     program);
-      file_offset = section_start_offset;
-    }
-    if (ok) {
-      uint32 end = file_offset + section->size_of_raw_data;
-      ok = ParseFileRegion(section, file_offset, end, program);
-      file_offset = end;
-    }
-  }
-
-#if COURGETTE_HISTOGRAM_TARGETS
-  HistogramTargets("abs32 relocs", abs32_target_rvas_);
-  HistogramTargets("rel32 relocs", rel32_target_rvas_);
-#endif
-
-  return ok;
-}
-
 CheckBool DisassemblerWin32X86::ParseNonSectionFileRegion(
     uint32 start_file_offset,
     uint32 end_file_offset,
     AssemblyProgram* program) {
   if (incomplete_disassembly_)
     return true;
 
-  const uint8* start = pe_info().FileOffsetToPointer(start_file_offset);
-  const uint8* end = pe_info().FileOffsetToPointer(end_file_offset);
+  const uint8* start = OffsetToPointer(start_file_offset);
+  const uint8* end = OffsetToPointer(end_file_offset);
 
   const uint8* p = start;
 
   bool ok = true;
   while (p < end && ok) {
     ok = program->EmitByteInstruction(*p);
     ++p;
   }
 
   return ok;
 }
 
 CheckBool DisassemblerWin32X86::ParseFileRegion(
     const Section* section,
     uint32 start_file_offset, uint32 end_file_offset,
     AssemblyProgram* program) {
-  RVA relocs_start_rva = pe_info().base_relocation_table().address_;
+  RVA relocs_start_rva = base_relocation_table().address_;
 
-  const uint8* start_pointer = pe_info().FileOffsetToPointer(start_file_offset);
-  const uint8* end_pointer = pe_info().FileOffsetToPointer(end_file_offset);
+  const uint8* start_pointer = OffsetToPointer(start_file_offset);
+  const uint8* end_pointer = OffsetToPointer(end_file_offset);
 
-  RVA start_rva = pe_info().FileOffsetToRVA(start_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* 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();
 
   bool ok = program->EmitOriginInstruction(start_rva);
 
   const uint8* p = start_pointer;
 
   while (ok && 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) {
       ok = program->EmitMakeRelocsInstruction();
       if (!ok)
         break;
-      uint32 relocs_size = pe_info().base_relocation_table().size_;
+      uint32 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) {
       uint32 target_address = Read32LittleEndian(p);
-      RVA target_rva = target_address - pe_info().image_base();
+      RVA target_rva = target_address - image_base();
       // TODO(sra): target could be Label+offset.  It is not clear how to guess
       // which it might be.  We assume offset==0.
       ok = program->EmitAbs32(program->FindOrMakeAbs32Label(target_rva));
       if (!ok)
         break;
       p += 4;
       continue;
     }
 
     while (rel32_pos != rel32_locations_.end() && *rel32_pos < current_rva)
@@ skipping 50 matching lines @@
        ++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 << "  " << pe_info().DescribeRVA(p->second[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 DisassemblerWin32X86::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* DisassemblerWin32X86::FindNextSection(uint32 fileOffset) 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 (fileOffset <= 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;
+}
+
+RVA DisassemblerWin32X86::FileOffsetToRVA(uint32 file_offset) const {
+  for (int i = 0; i < number_of_sections_; i++) {
+    const Section* section = &sections_[i];
+    uint32 offset = file_offset - section->file_offset_of_raw_data;
+    if (offset < section->size_of_raw_data) {
+      return section->virtual_address + offset;
+    }
+  }
+  return 0;
+}
+
+bool DisassemblerWin32X86::ReadDataDirectory(
+    int index,
+    ImageDataDirectory* directory) {
+
+  if (index < number_of_data_directories_) {
+    size_t offset = index * 8 + offset_of_data_directories_;
+    if (offset >= size_of_optional_header_)
+      return Bad("number of data directories inconsistent");
+    const uint8* data_directory = optional_header_ + 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>(size);
+    return true;
+  } else {
+    directory->address_ = 0;
+    directory->size_ = 0;
+    return true;
+  }
+}
+
 }  // namespace courgette