Index: include/llvm/BinaryFormat/Wasm.h
===================================================================
--- include/llvm/BinaryFormat/Wasm.h
+++ include/llvm/BinaryFormat/Wasm.h
@@ -94,7 +94,7 @@
 };
 
 struct WasmDataSegment {
-  uint32_t Index;
+  uint32_t MemoryIndex;
   WasmInitExpr Offset;
   ArrayRef<uint8_t> Content;
 };
Index: include/llvm/Object/Wasm.h
===================================================================
--- include/llvm/Object/Wasm.h
+++ include/llvm/Object/Wasm.h
@@ -69,8 +69,7 @@
 #endif
 };
 
-class WasmSection {
-public:
+struct WasmSection {
   WasmSection() = default;
 
   uint32_t Type = 0; // Section type (See below)
@@ -80,6 +79,11 @@
   std::vector<wasm::WasmRelocation> Relocations; // Relocations for this section
 };
 
+struct WasmSegment {
+  uint32_t SectionOffset;
+  wasm::WasmDataSegment Data;
+};
+
 class WasmObjectFile : public ObjectFile {
 
 public:
@@ -110,7 +114,7 @@
     return ElemSegments;
   }
 
-  const std::vector<wasm::WasmDataSegment>& dataSegments() const {
+  const std::vector<WasmSegment>& dataSegments() const {
     return DataSegments;
   }
 
@@ -210,7 +214,7 @@
   std::vector<wasm::WasmImport> Imports;
   std::vector<wasm::WasmExport> Exports;
   std::vector<wasm::WasmElemSegment> ElemSegments;
-  std::vector<wasm::WasmDataSegment> DataSegments;
+  std::vector<WasmSegment> DataSegments;
   std::vector<wasm::WasmFunction> Functions;
   std::vector<WasmSymbol> Symbols;
   ArrayRef<uint8_t> CodeSection;
Index: include/llvm/ObjectYAML/WasmYAML.h
===================================================================
--- include/llvm/ObjectYAML/WasmYAML.h
+++ include/llvm/ObjectYAML/WasmYAML.h
@@ -98,7 +98,8 @@
 };
 
 struct DataSegment {
-  uint32_t Index;
+  uint32_t MemoryIndex;
+  uint32_t SectionOffset;
   wasm::WasmInitExpr Offset;
   yaml::BinaryRef Content;
 };
Index: lib/MC/WasmObjectWriter.cpp
===================================================================
--- lib/MC/WasmObjectWriter.cpp
+++ lib/MC/WasmObjectWriter.cpp
@@ -1182,6 +1182,7 @@
 
       DataSection.setSectionOffset(DataBytes.size());
 
+      uint64_t OldSize = DataBytes.size();
       for (const MCFragment &Frag : DataSection) {
         if (Frag.hasInstructions())
           report_fatal_error("only data supported in data sections");
@@ -1196,15 +1197,21 @@
                                              DataBytes.size() +
                                                  Align->getMaxBytesToEmit());
           DataBytes.resize(Size, Value);
+          DEBUG(dbgs() << "Data: " << DataBytes.size() << " added alignment\n");
         } else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) {
-          DataBytes.insert(DataBytes.end(), Fill->getSize(), Fill->getValue());
+          if (Fill->getSize()) {
+            DataBytes.insert(DataBytes.end(), Fill->getSize(), Fill->getValue());
+            DEBUG(dbgs() << "Data: " << DataBytes.size() << " added fill: " << Fill->getSize() << "\n");
+          }
         } else {
           const auto &DataFrag = cast<MCDataFragment>(Frag);
           const SmallVectorImpl<char> &Contents = DataFrag.getContents();
 
           DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
+          DEBUG(dbgs() << "Data: " << DataBytes.size() << " added bytes: " << Contents.size() << "\n");
         }
       }
+      DEBUG(dbgs() << "Added Data: " << WS.getName() << ": " << DataBytes.size() - OldSize << "\n");
 
       // For each global, prepare a corresponding wasm global holding its
       // address.  For externals these will also be named exports.
Index: lib/Object/WasmObjectFile.cpp
===================================================================
--- lib/Object/WasmObjectFile.cpp
+++ lib/Object/WasmObjectFile.cpp
@@ -675,15 +675,17 @@
 }
 
 Error WasmObjectFile::parseDataSection(const uint8_t *Ptr, const uint8_t *End) {
+  const uint8_t *Start = Ptr;
   uint32_t Count = readVaruint32(Ptr);
   DataSegments.reserve(Count);
   while (Count--) {
-    wasm::WasmDataSegment Segment;
-    Segment.Index = readVaruint32(Ptr);
-    if (Error Err = readInitExpr(Segment.Offset, Ptr))
+    WasmSegment Segment;
+    Segment.Data.MemoryIndex = readVaruint32(Ptr);
+    if (Error Err = readInitExpr(Segment.Data.Offset, Ptr))
       return Err;
     uint32_t Size = readVaruint32(Ptr);
-    Segment.Content = ArrayRef<uint8_t>(Ptr, Size);
+    Segment.Data.Content = ArrayRef<uint8_t>(Ptr, Size);
+    Segment.SectionOffset = Ptr - Start;
     Ptr += Size;
     DataSegments.push_back(Segment);
   }
Index: lib/ObjectYAML/WasmYAML.cpp
===================================================================
--- lib/ObjectYAML/WasmYAML.cpp
+++ lib/ObjectYAML/WasmYAML.cpp
@@ -345,7 +345,8 @@
 
 void MappingTraits<WasmYAML::DataSegment>::mapping(
     IO &IO, WasmYAML::DataSegment &Segment) {
-  IO.mapRequired("Index", Segment.Index);
+  IO.mapOptional("SectionOffset", Segment.SectionOffset);
+  IO.mapRequired("MemoryIndex", Segment.MemoryIndex);
   IO.mapRequired("Offset", Segment.Offset);
   IO.mapRequired("Content", Segment.Content);
 }
Index: test/MC/WebAssembly/external-data.ll
===================================================================
--- test/MC/WebAssembly/external-data.ll
+++ test/MC/WebAssembly/external-data.ll
@@ -13,7 +13,8 @@
 ; CHECK:         Index:           0
 ; CHECK:         Offset:          0x0000000E
 ; CHECK:     Segments:
-; CHECK:       - Index:           0
+; CHECK:       - SectionOffset:   6
+; CHECK:         MemoryIndex:     0
 ; CHECK:         Offset:
 ; CHECK:           Opcode:          I32_CONST
 ; CHECK:           Value:           0
Index: test/MC/WebAssembly/unnamed-data.ll
===================================================================
--- test/MC/WebAssembly/unnamed-data.ll
+++ test/MC/WebAssembly/unnamed-data.ll
@@ -46,7 +46,8 @@
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:         Offset:          0x0000001E
 ; CHECK-NEXT:     Segments:        
-; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:       - SectionOffset:   6
+; CHECK-NEXT:         MemoryIndex:     0
 ; CHECK-NEXT:         Offset:          
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           0
Index: test/ObjectYAML/wasm/data_section.yaml
===================================================================
--- test/ObjectYAML/wasm/data_section.yaml
+++ test/ObjectYAML/wasm/data_section.yaml
@@ -8,7 +8,7 @@
       - Initial:         0x00000003
   - Type:            DATA
     Segments:
-      - Index:           0
+      - MemoryIndex:      0
         Offset:
           Opcode:          I32_CONST
           Value:           4
@@ -38,7 +38,8 @@
 # CHECK-NEXT:        Offset:          0x00000006
 # CHECK-NEXT:        Addend:          -6
 # CHECK-NEXT:     Segments:
-# CHECK-NEXT:       - Index:           0
+# CHECK-NEXT:       - SectionOffset:   6
+# CHECK-NEXT:         MemoryIndex:     0
 # CHECK-NEXT:         Offset:
 # CHECK-NEXT:           Opcode:          I32_CONST
 # CHECK-NEXT:           Value:           4
Index: tools/obj2yaml/wasm2yaml.cpp
===================================================================
--- tools/obj2yaml/wasm2yaml.cpp
+++ tools/obj2yaml/wasm2yaml.cpp
@@ -236,9 +236,10 @@
       auto DataSec = make_unique<WasmYAML::DataSection>();
       for (auto &Segment : Obj.dataSegments()) {
         WasmYAML::DataSegment Seg;
-        Seg.Index = Segment.Index;
-        Seg.Offset = Segment.Offset;
-        Seg.Content = yaml::BinaryRef(Segment.Content);
+        Seg.SectionOffset = Segment.SectionOffset;
+        Seg.MemoryIndex = Segment.Data.MemoryIndex;
+        Seg.Offset = Segment.Data.Offset;
+        Seg.Content = yaml::BinaryRef(Segment.Data.Content);
         DataSec->Segments.push_back(Seg);
       }
       S = std::move(DataSec);
Index: tools/yaml2obj/yaml2wasm.cpp
===================================================================
--- tools/yaml2obj/yaml2wasm.cpp
+++ tools/yaml2obj/yaml2wasm.cpp
@@ -338,7 +338,7 @@
                                     WasmYAML::DataSection &Section) {
   encodeULEB128(Section.Segments.size(), OS);
   for (auto &Segment : Section.Segments) {
-    encodeULEB128(Segment.Index, OS);
+    encodeULEB128(Segment.MemoryIndex, OS);
     writeInitExpr(Segment.Offset, OS);
     encodeULEB128(Segment.Content.binary_size(), OS);
     Segment.Content.writeAsBinary(OS);