Index: wasm/InputChunks.h
===================================================================
--- wasm/InputChunks.h
+++ wasm/InputChunks.h
@@ -24,6 +24,7 @@
 #include "Config.h"
 #include "InputFiles.h"
 #include "lld/Common/ErrorHandler.h"
+#include "lld/Common/Strings.h"
 #include "llvm/Object/Wasm.h"
 
 using llvm::object::WasmSegment;
@@ -151,17 +152,16 @@
 
 class SyntheticFunction : public InputFunction {
 public:
-  SyntheticFunction(const WasmSignature &S, ArrayRef<uint8_t> Body,
-                    StringRef Name)
-      : InputFunction(S, nullptr, nullptr), Name(Name), Body(Body) {}
+  SyntheticFunction(const WasmSignature &S, std::string Body, StringRef Name)
+      : InputFunction(S, nullptr, nullptr), Name(Name), Body(std::move(Body)) {}
 
   StringRef getName() const override { return Name; }
 
 protected:
-  ArrayRef<uint8_t> data() const override { return Body; }
+  ArrayRef<uint8_t> data() const override { return toArrayRef(Body); }
 
   StringRef Name;
-  ArrayRef<uint8_t> Body;
+  std::string Body;
 };
 
 } // namespace wasm
Index: wasm/Writer.cpp
===================================================================
--- wasm/Writer.cpp
+++ wasm/Writer.cpp
@@ -17,7 +17,6 @@
 #include "WriterUtils.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Memory.h"
-#include "lld/Common/Strings.h"
 #include "lld/Common/Threads.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/BinaryFormat/Wasm.h"
@@ -137,7 +136,6 @@
   std::vector<OutputSection *> OutputSections;
 
   std::unique_ptr<FileOutputBuffer> Buffer;
-  std::string CtorFunctionBody;
 
   std::vector<OutputSegment *> Segments;
   llvm::SmallDenseMap<StringRef, OutputSegment *> SegmentMap;
@@ -859,27 +857,28 @@
   uint32_t FunctionIndex = NumImportedFunctions + InputFunctions.size();
   WasmSym::CallCtors->setOutputIndex(FunctionIndex);
 
-  // First write the body bytes to a string.
   std::string FunctionBody;
   {
-    raw_string_ostream OS(FunctionBody);
+    // First write the body's contents to a string.
+    SmallString<256> BodyContent;
+    raw_svector_ostream OS(BodyContent);
     writeUleb128(OS, 0, "num locals");
-    for (const WasmInitEntry &F : InitFunctions) {
+    for (const WasmInitEntry& F : InitFunctions) {
       writeU8(OS, OPCODE_CALL, "CALL");
       writeUleb128(OS, F.Sym->getOutputIndex(), "function index");
     }
     writeU8(OS, OPCODE_END, "END");
-  }
 
-  // Once we know the size of the body we can create the final function body
-  raw_string_ostream OS(CtorFunctionBody);
-  writeUleb128(OS, FunctionBody.size(), "function size");
-  OS.flush();
-  CtorFunctionBody += FunctionBody;
+    // Once we know the size of the body we can create the final function body
+    raw_string_ostream OS2(FunctionBody);
+    writeUleb128(OS2, BodyContent.size(), "function size");
+    OS2 << BodyContent;
+    OS2.flush();
+  }
 
   const WasmSignature *Sig = WasmSym::CallCtors->getFunctionType();
   SyntheticFunction *F = make<SyntheticFunction>(
-      *Sig, toArrayRef(CtorFunctionBody), WasmSym::CallCtors->getName());
+      *Sig, std::move(FunctionBody), WasmSym::CallCtors->getName());
 
   F->setOutputIndex(FunctionIndex);
   F->Live = true;
@@ -891,11 +890,15 @@
 // This is then used either when creating the output linking section or to
 // synthesize the "__wasm_call_ctors" function.
 void Writer::calculateInitFunctions() {
+  WasmSignature VoidSignature = {{}, WASM_TYPE_NORESULT};
+
   for (ObjFile *File : Symtab->ObjectFiles) {
     const WasmLinkingData &L = File->getWasmObj()->linkingData();
-    for (const WasmInitFunc &F : L.InitFunctions)
-      InitFunctions.emplace_back(
-          WasmInitEntry{File->getFunctionSymbol(F.Symbol), F.Priority});
+    for (const WasmInitFunc &F : L.InitFunctions) {
+      FunctionSymbol *Sym = File->getFunctionSymbol(F.Symbol);
+      assert(*Sym->getFunctionType() == VoidSignature);
+      InitFunctions.emplace_back(WasmInitEntry{Sym, F.Priority});
+    }
   }
 
   // Sort in order of priority (lowest first) so that they are called