Index: llvm/trunk/include/llvm/DebugInfo/PDB/Native/DbiStreamBuilder.h
===================================================================
--- llvm/trunk/include/llvm/DebugInfo/PDB/Native/DbiStreamBuilder.h
+++ llvm/trunk/include/llvm/DebugInfo/PDB/Native/DbiStreamBuilder.h
@@ -82,6 +82,7 @@
 
   Error finalize();
   uint32_t calculateModiSubstreamSize() const;
+  uint32_t calculateNamesOffset() const;
   uint32_t calculateSectionContribsStreamSize() const;
   uint32_t calculateSectionMapStreamSize() const;
   uint32_t calculateFileInfoSubstreamSize() const;
Index: llvm/trunk/lib/DebugInfo/PDB/Native/DbiStreamBuilder.cpp
===================================================================
--- llvm/trunk/lib/DebugInfo/PDB/Native/DbiStreamBuilder.cpp
+++ llvm/trunk/lib/DebugInfo/PDB/Native/DbiStreamBuilder.cpp
@@ -129,16 +129,21 @@
   return sizeof(SecMapHeader) + sizeof(SecMapEntry) * SectionMap.size();
 }
 
-uint32_t DbiStreamBuilder::calculateFileInfoSubstreamSize() const {
-  uint32_t Size = 0;
-  Size += sizeof(ulittle16_t);                         // NumModules
-  Size += sizeof(ulittle16_t);                         // NumSourceFiles
-  Size += ModiList.size() * sizeof(ulittle16_t);       // ModIndices
-  Size += ModiList.size() * sizeof(ulittle16_t);       // ModFileCounts
+uint32_t DbiStreamBuilder::calculateNamesOffset() const {
+  uint32_t Offset = 0;
+  Offset += sizeof(ulittle16_t);                         // NumModules
+  Offset += sizeof(ulittle16_t);                         // NumSourceFiles
+  Offset += ModiList.size() * sizeof(ulittle16_t);       // ModIndices
+  Offset += ModiList.size() * sizeof(ulittle16_t);       // ModFileCounts
   uint32_t NumFileInfos = 0;
   for (const auto &M : ModiList)
     NumFileInfos += M->source_files().size();
-  Size += NumFileInfos * sizeof(ulittle32_t); // FileNameOffsets
+  Offset += NumFileInfos * sizeof(ulittle32_t); // FileNameOffsets
+  return Offset;
+}
+
+uint32_t DbiStreamBuilder::calculateFileInfoSubstreamSize() const {
+  uint32_t Size = calculateNamesOffset();
   Size += calculateNamesBufferSize();
   return alignTo(Size, sizeof(uint32_t));
 }
@@ -157,9 +162,8 @@
 
 Error DbiStreamBuilder::generateFileInfoSubstream() {
   uint32_t Size = calculateFileInfoSubstreamSize();
-  uint32_t NameSize = calculateNamesBufferSize();
   auto Data = Allocator.Allocate<uint8_t>(Size);
-  uint32_t NamesOffset = Size - NameSize;
+  uint32_t NamesOffset = calculateNamesOffset();
 
   FileInfoBuffer = MutableBinaryByteStream(MutableArrayRef<uint8_t>(Data, Size),
                                            llvm::support::little);
@@ -207,6 +211,9 @@
     }
   }
 
+  if (auto EC = NameBufferWriter.padToAlignment(sizeof(uint32_t)))
+    return EC;
+
   if (NameBufferWriter.bytesRemaining() > 0)
     return make_error<RawError>(raw_error_code::invalid_format,
                                 "The names buffer contained unexpected data.");
Index: llvm/trunk/test/DebugInfo/PDB/Inputs/source-names-1.yaml
===================================================================
--- llvm/trunk/test/DebugInfo/PDB/Inputs/source-names-1.yaml
+++ llvm/trunk/test/DebugInfo/PDB/Inputs/source-names-1.yaml
@@ -0,0 +1,8 @@
+---
+DbiStream:
+  Modules:
+    - Module:          'C:\src\test.obj'
+      ObjFile:         'C:\src\test.obj'
+      SourceFiles:
+        - 'C:\src\test.c'
+...
Index: llvm/trunk/test/DebugInfo/PDB/Inputs/source-names-2.yaml
===================================================================
--- llvm/trunk/test/DebugInfo/PDB/Inputs/source-names-2.yaml
+++ llvm/trunk/test/DebugInfo/PDB/Inputs/source-names-2.yaml
@@ -0,0 +1,8 @@
+---
+DbiStream:
+  Modules:
+    - Module:          'C:\src\test.obj'
+      ObjFile:         'C:\src\test.obj'
+      SourceFiles:
+        - 'C:\src\test.cc'
+...
Index: llvm/trunk/test/DebugInfo/PDB/pdbdump-source-names.test
===================================================================
--- llvm/trunk/test/DebugInfo/PDB/pdbdump-source-names.test
+++ llvm/trunk/test/DebugInfo/PDB/pdbdump-source-names.test
@@ -0,0 +1,20 @@
+# Test that we can write source file names to PDBs and read them back.
+# Because the subsection the file names are stored in is 4-byte
+# aligned, there is a possibility of misaligning the file names. This
+# will cause them to be read back empty or truncated.  To guard
+# against this, we test with two different lengths of file name data
+# that differ by one byte, so that at least one of those will only
+# pass if alignment is implemented correctly.
+
+RUN: llvm-pdbdump yaml2pdb -pdb=%T/source-names-1.pdb %p/Inputs/source-names-1.yaml
+RUN: llvm-pdbdump pdb2yaml -dbi-module-source-info %T/source-names-1.pdb \
+RUN:     | FileCheck -check-prefix=CHECK1 %s
+RUN: llvm-pdbdump yaml2pdb -pdb=%T/source-names-2.pdb %p/Inputs/source-names-2.yaml
+RUN: llvm-pdbdump pdb2yaml -dbi-module-source-info %T/source-names-2.pdb \
+RUN:     | FileCheck -check-prefix=CHECK2 %s
+
+CHECK1: SourceFiles:
+CHECK1: 'C:\src\test.c'
+
+CHECK2: SourceFiles:
+CHECK2: 'C:\src\test.cc'