Index: llvm/trunk/include/llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h
===================================================================
--- llvm/trunk/include/llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h
+++ llvm/trunk/include/llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h
@@ -25,6 +25,9 @@
 namespace msf {
 class MSFBuilder;
 }
+namespace object {
+struct coff_section;
+}
 namespace pdb {
 class DbiStream;
 struct DbiStreamHeader;
@@ -44,6 +47,7 @@
   void setPdbDllRbld(uint16_t R);
   void setFlags(uint16_t F);
   void setMachineType(PDB_Machine M);
+  void setSectionMap(ArrayRef<SecMapEntry> SecMap);
 
   // Add given bytes as a new stream.
   Error addDbgStream(pdb::DbgHeaderType Type, ArrayRef<uint8_t> Data);
@@ -60,6 +64,10 @@
   Error commit(const msf::MSFLayout &Layout,
                const msf::WritableStream &Buffer);
 
+  // A helper function to create a Section Map from a COFF section header.
+  static std::vector<SecMapEntry>
+  createSectionMap(ArrayRef<llvm::object::coff_section> SecHdrs);
+
 private:
   struct DebugStream {
     ArrayRef<uint8_t> Data;
@@ -68,6 +76,7 @@
 
   Error finalize();
   uint32_t calculateModiSubstreamSize() const;
+  uint32_t calculateSectionMapStreamSize() const;
   uint32_t calculateFileInfoSubstreamSize() const;
   uint32_t calculateNamesBufferSize() const;
   uint32_t calculateDbgStreamsSize() const;
@@ -102,6 +111,7 @@
   msf::WritableStreamRef NamesBuffer;
   msf::MutableByteStream ModInfoBuffer;
   msf::MutableByteStream FileInfoBuffer;
+  ArrayRef<SecMapEntry> SectionMap;
   llvm::SmallVector<DebugStream, (int)DbgHeaderType::Max> DbgStreams;
 };
 }
Index: llvm/trunk/lib/DebugInfo/PDB/Raw/DbiStreamBuilder.cpp
===================================================================
--- llvm/trunk/lib/DebugInfo/PDB/Raw/DbiStreamBuilder.cpp
+++ llvm/trunk/lib/DebugInfo/PDB/Raw/DbiStreamBuilder.cpp
@@ -15,6 +15,8 @@
 #include "llvm/DebugInfo/MSF/StreamWriter.h"
 #include "llvm/DebugInfo/PDB/Raw/DbiStream.h"
 #include "llvm/DebugInfo/PDB/Raw/RawError.h"
+#include "llvm/Object/COFF.h"
+#include "llvm/Support/COFF.h"
 
 using namespace llvm;
 using namespace llvm::codeview;
@@ -44,6 +46,10 @@
 
 void DbiStreamBuilder::setMachineType(PDB_Machine M) { MachineType = M; }
 
+void DbiStreamBuilder::setSectionMap(ArrayRef<SecMapEntry> SecMap) {
+  SectionMap = SecMap;
+}
+
 Error DbiStreamBuilder::addDbgStream(pdb::DbgHeaderType Type,
                                      ArrayRef<uint8_t> Data) {
   if (DbgStreams[(int)Type].StreamNumber)
@@ -61,7 +67,8 @@
 uint32_t DbiStreamBuilder::calculateSerializedLength() const {
   // For now we only support serializing the header.
   return sizeof(DbiStreamHeader) + calculateFileInfoSubstreamSize() +
-         calculateModiSubstreamSize() + calculateDbgStreamsSize();
+         calculateModiSubstreamSize() + calculateSectionMapStreamSize() +
+         calculateDbgStreamsSize();
 }
 
 Error DbiStreamBuilder::addModuleInfo(StringRef ObjFile, StringRef Module) {
@@ -99,6 +106,12 @@
   return Size;
 }
 
+uint32_t DbiStreamBuilder::calculateSectionMapStreamSize() const {
+  if (SectionMap.empty())
+    return 0;
+  return sizeof(SecMapHeader) + sizeof(SecMapEntry) * SectionMap.size();
+}
+
 uint32_t DbiStreamBuilder::calculateFileInfoSubstreamSize() const {
   uint32_t Size = 0;
   Size += sizeof(ulittle16_t);                         // NumModules
@@ -237,7 +250,7 @@
   H->ModiSubstreamSize = ModInfoBuffer.getLength();
   H->OptionalDbgHdrSize = DbgStreams.size() * sizeof(uint16_t);
   H->SecContrSubstreamSize = 0;
-  H->SectionMapSize = 0;
+  H->SectionMapSize = calculateSectionMapStreamSize();
   H->TypeServerSize = 0;
   H->SymRecordStreamIndex = kInvalidStreamIndex;
   H->PublicSymbolStreamIndex = kInvalidStreamIndex;
@@ -255,6 +268,65 @@
   return Error::success();
 }
 
+static uint16_t toSecMapFlags(uint32_t Flags) {
+  uint16_t Ret = 0;
+  if (Flags & COFF::IMAGE_SCN_MEM_READ)
+    Ret |= static_cast<uint16_t>(OMFSegDescFlags::Read);
+  if (Flags & COFF::IMAGE_SCN_MEM_WRITE)
+    Ret |= static_cast<uint16_t>(OMFSegDescFlags::Write);
+  if (Flags & COFF::IMAGE_SCN_MEM_EXECUTE)
+    Ret |= static_cast<uint16_t>(OMFSegDescFlags::Execute);
+  if (Flags & COFF::IMAGE_SCN_MEM_EXECUTE)
+    Ret |= static_cast<uint16_t>(OMFSegDescFlags::Execute);
+  if (!(Flags & COFF::IMAGE_SCN_MEM_16BIT))
+    Ret |= static_cast<uint16_t>(OMFSegDescFlags::AddressIs32Bit);
+
+  // This seems always 1.
+  Ret |= static_cast<uint16_t>(OMFSegDescFlags::IsSelector);
+
+  return Ret;
+}
+
+// A utility function to create a Section Map for a given list of COFF sections.
+//
+// A Section Map seem to be a copy of a COFF section list in other format.
+// I don't know why a PDB file contains both a COFF section header and
+// a Section Map, but it seems it must be present in a PDB.
+std::vector<SecMapEntry> DbiStreamBuilder::createSectionMap(
+    ArrayRef<llvm::object::coff_section> SecHdrs) {
+  std::vector<SecMapEntry> Ret;
+  int Idx = 0;
+
+  auto Add = [&]() -> SecMapEntry & {
+    Ret.emplace_back();
+    auto &Entry = Ret.back();
+    memset(&Entry, 0, sizeof(Entry));
+
+    Entry.Frame = Idx + 1;
+
+    // We don't know the meaning of these fields yet.
+    Entry.SecName = UINT16_MAX;
+    Entry.ClassName = UINT16_MAX;
+
+    return Entry;
+  };
+
+  for (auto &Hdr : SecHdrs) {
+    auto &Entry = Add();
+    Entry.Flags = toSecMapFlags(Hdr.Characteristics);
+    Entry.SecByteLength = Hdr.VirtualSize;
+    ++Idx;
+  }
+
+  // The last entry is for absolute symbols.
+  auto &Entry = Add();
+  Entry.Flags = static_cast<uint16_t>(OMFSegDescFlags::AddressIs32Bit) |
+                static_cast<uint16_t>(OMFSegDescFlags::IsAbsoluteAddress);
+  Entry.SecByteLength = UINT32_MAX;
+
+  return Ret;
+}
+
 Expected<std::unique_ptr<DbiStream>>
 DbiStreamBuilder::build(PDBFile &File, const msf::WritableStream &Buffer) {
   if (!VerHeader.hasValue())
@@ -290,8 +362,19 @@
 
   if (auto EC = Writer.writeStreamRef(ModInfoBuffer))
     return EC;
+
+  if (!SectionMap.empty()) {
+    ulittle16_t Size = static_cast<ulittle16_t>(SectionMap.size());
+    SecMapHeader SMHeader = {Size, Size};
+    if (auto EC = Writer.writeObject(SMHeader))
+      return EC;
+    if (auto EC = Writer.writeArray(SectionMap))
+      return EC;
+  }
+
   if (auto EC = Writer.writeStreamRef(FileInfoBuffer))
     return EC;
+
   for (auto &Stream : DbgStreams)
     if (auto EC = Writer.writeInteger(Stream.StreamNumber))
       return EC;