2 files changed, 31 insertions, 12 deletions
diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index 0b4a3d2f4..5399be0b7 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -6984,6 +6984,9 @@ bool WasmBinaryBuilder::maybeVisitStringNew(Expression*& out, uint32_t code) {
   Expression* start = nullptr;
   Expression* end = nullptr;
   if (code == BinaryConsts::StringNewWTF8) {
+    if (getInt8() != 0) {
+      throwError("Unexpected nonzero memory index");
+    }
     auto policy = getU32LEB();
     switch (policy) {
       case BinaryConsts::StringPolicy::UTF8:
@@ -7000,6 +7003,9 @@ bool WasmBinaryBuilder::maybeVisitStringNew(Expression*& out, uint32_t code) {
     }
     length = popNonVoidExpression();
   } else if (code == BinaryConsts::StringNewWTF16) {
+    if (getInt8() != 0) {
+      throwError("Unexpected nonzero memory index");
+    }
     op = StringNewWTF16;
     length = popNonVoidExpression();
   } else if (code == BinaryConsts::StringNewWTF8Array) {
@@ -7080,6 +7086,9 @@ bool WasmBinaryBuilder::maybeVisitStringEncode(Expression*& out,
   Expression* start = nullptr;
   // TODO: share this code with string.measure?
   if (code == BinaryConsts::StringEncodeWTF8) {
+    if (getInt8() != 0) {
+      throwError("Unexpected nonzero memory index");
+    }
     auto policy = getU32LEB();
     switch (policy) {
       case BinaryConsts::StringPolicy::UTF8:
@@ -7092,6 +7101,9 @@ bool WasmBinaryBuilder::maybeVisitStringEncode(Expression*& out,
         throwError("bad policy for string.encode");
     }
   } else if (code == BinaryConsts::StringEncodeWTF16) {
+    if (getInt8() != 0) {
+      throwError("Unexpected nonzero memory index");
+    }
     op = StringEncodeWTF16;
   } else if (code == BinaryConsts::StringEncodeWTF8Array) {
     auto policy = getU32LEB();
diff --git a/src/wasm/wasm-stack.cpp b/src/wasm/wasm-stack.cpp
index 95da14c72..83586f559 100644
--- a/src/wasm/wasm-stack.cpp
+++ b/src/wasm/wasm-stack.cpp
@@ -2176,19 +2176,23 @@ void BinaryInstWriter::visitStringNew(StringNew* curr) {
   o << int8_t(BinaryConsts::GCPrefix);
   switch (curr->op) {
     case StringNewUTF8:
-      o << int8_t(BinaryConsts::StringNewWTF8)
-        << U32LEB(BinaryConsts::StringPolicy::UTF8);
+      o << int8_t(BinaryConsts::StringNewWTF8);
+      o << int8_t(0); // Memory index.
+      o << U32LEB(BinaryConsts::StringPolicy::UTF8);
       break;
     case StringNewWTF8:
-      o << int8_t(BinaryConsts::StringNewWTF8)
-        << U32LEB(BinaryConsts::StringPolicy::WTF8);
+      o << int8_t(BinaryConsts::StringNewWTF8);
+      o << int8_t(0); // Memory index.
+      o << U32LEB(BinaryConsts::StringPolicy::WTF8);
       break;
     case StringNewReplace:
-      o << int8_t(BinaryConsts::StringNewWTF8)
-        << U32LEB(BinaryConsts::StringPolicy::Replace);
+      o << int8_t(BinaryConsts::StringNewWTF8);
+      o << int8_t(0); // Memory index.
+      o << U32LEB(BinaryConsts::StringPolicy::Replace);
       break;
     case StringNewWTF16:
       o << int8_t(BinaryConsts::StringNewWTF16);
+      o << int8_t(0); // Memory index.
       break;
     case StringNewUTF8Array:
       o << int8_t(BinaryConsts::StringNewWTF8Array)
@@ -2244,19 +2248,22 @@ void BinaryInstWriter::visitStringEncode(StringEncode* curr) {
   o << int8_t(BinaryConsts::GCPrefix);
   switch (curr->op) {
     case StringEncodeUTF8:
-      o << int8_t(BinaryConsts::StringEncodeWTF8)
-        << U32LEB(BinaryConsts::StringPolicy::UTF8);
+      o << int8_t(BinaryConsts::StringEncodeWTF8);
+      o << int8_t(0); // Memory index.
+      o << U32LEB(BinaryConsts::StringPolicy::UTF8);
       break;
     case StringEncodeWTF8:
-      o << int8_t(BinaryConsts::StringEncodeWTF8)
-        << U32LEB(BinaryConsts::StringPolicy::WTF8);
+      o << int8_t(BinaryConsts::StringEncodeWTF8);
+      o << int8_t(0); // Memory index.
+      o << U32LEB(BinaryConsts::StringPolicy::WTF8);
       break;
     case StringEncodeWTF16:
       o << int8_t(BinaryConsts::StringEncodeWTF16);
+      o << int8_t(0); // Memory index.
       break;
     case StringEncodeUTF8Array:
-      o << int8_t(BinaryConsts::StringEncodeWTF8Array)
-        << U32LEB(BinaryConsts::StringPolicy::UTF8);
+      o << int8_t(BinaryConsts::StringEncodeWTF8Array);
+      o << U32LEB(BinaryConsts::StringPolicy::UTF8);
       break;
     case StringEncodeWTF8Array:
       o << int8_t(BinaryConsts::StringEncodeWTF8Array)