2 files changed, 33 insertions, 1 deletions
diff --git a/src/wasm-binary.h b/src/wasm-binary.h
index 50b78fbae..1f6222cba 100644
--- a/src/wasm-binary.h
+++ b/src/wasm-binary.h
@@ -322,7 +322,8 @@ enum Section {
   Start = 8,
   Element = 9,
   Code = 10,
-  Data = 11
+  Data = 11,
+  DataCount = 12,
 };
 
 enum SegmentFlag {
@@ -891,6 +892,7 @@ public:
   void writeFunctions();
   void writeGlobals();
   void writeExports();
+  void writeDataCount();
   void writeDataSegments();
 
   std::unordered_map<Name, Index> mappedFunctions; // name of the Function => index. first imports, then internals
@@ -1083,8 +1085,14 @@ public:
   std::map<Index, Name> mappedGlobals; // index of the Global => name. first imported globals, then internal globals
 
   Name getGlobalName(Index index);
+  void validateBinary(); // validations that cannot be performed on the Module
   void processFunctions();
+
+  size_t dataCount = 0;
+  bool hasDataCount = false;
+
   void readDataSegments();
+  void readDataCount();
 
   std::map<Index, std::vector<Index>> functionTable;
 
diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index b351a46e5..f3642203d 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -58,6 +58,7 @@ void WasmBinaryWriter::write() {
   writeExports();
   writeStart();
   writeTableElements();
+  writeDataCount();
   writeFunctions();
   writeDataSegments();
   if (debugInfo) writeNames();
@@ -312,6 +313,15 @@ void WasmBinaryWriter::writeExports() {
   finishSection(start);
 }
 
+void WasmBinaryWriter::writeDataCount() {
+  if (!wasm->features.hasBulkMemory() || !wasm->memory.segments.size()) {
+    return;
+  }
+  auto start = startSection(BinaryConsts::Section::DataCount);
+  o << U32LEB(wasm->memory.segments.size());
+  finishSection(start);
+}
+
 void WasmBinaryWriter::writeDataSegments() {
   if (wasm->memory.segments.size() == 0) return;
   if (wasm->memory.segments.size() > WebLimitations::MaxDataSegments) {
@@ -657,6 +667,7 @@ void WasmBinaryBuilder::read() {
         break;
       }
       case BinaryConsts::Section::Data: readDataSegments(); break;
+      case BinaryConsts::Section::DataCount: readDataCount(); break;
       case BinaryConsts::Section::Table: readFunctionTableDeclaration(); break;
       default: {
         readUserSection(payloadLen);
@@ -673,6 +684,7 @@ void WasmBinaryBuilder::read() {
     }
   }
 
+  validateBinary();
   processFunctions();
 }
 
@@ -1457,6 +1469,12 @@ Name WasmBinaryBuilder::getGlobalName(Index index) {
   return mappedGlobals[index];
 }
 
+void WasmBinaryBuilder::validateBinary() {
+  if (hasDataCount && wasm.memory.segments.size() != dataCount) {
+    throwError("Number of segments does not agree with DataCount section");
+  }
+}
+
 void WasmBinaryBuilder::processFunctions() {
   for (auto* func : functions) {
     wasm.addFunction(func);
@@ -1504,6 +1522,12 @@ void WasmBinaryBuilder::processFunctions() {
   wasm.updateMaps();
 }
 
+void WasmBinaryBuilder::readDataCount() {
+  if (debug) std::cerr << "== readDataCount" << std::endl;
+  hasDataCount = true;
+  dataCount = getU32LEB();
+}
+
 void WasmBinaryBuilder::readDataSegments() {
   if (debug) std::cerr << "== readDataSegments" << std::endl;
   auto num = getU32LEB();