Index: lld/trunk/wasm/OutputSections.h
===================================================================
--- lld/trunk/wasm/OutputSections.h
+++ lld/trunk/wasm/OutputSections.h
@@ -60,7 +60,7 @@
   SyntheticSection(uint32_t Type, std::string Name = "")
       : OutputSection(Type, Name), BodyOutputStream(Body) {
     if (!Name.empty())
-      writeStr(BodyOutputStream, Name);
+      writeStr(BodyOutputStream, Name, "section name");
   }
 
   void writeTo(uint8_t *Buf) override {
@@ -96,8 +96,8 @@
 
   std::string getSectionName() const;
   void writeToStream(raw_ostream &OS) {
-    writeBytes(OS, Header.data(), Header.size());
-    writeBytes(OS, Body.data(), Body.size());
+    OS.write(Header.data(), Header.size());
+    OS.write(Body.data(), Body.size());
   }
 };
 
Index: lld/trunk/wasm/OutputSections.cpp
===================================================================
--- lld/trunk/wasm/OutputSections.cpp
+++ lld/trunk/wasm/OutputSections.cpp
@@ -15,6 +15,7 @@
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Threads.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/Support/LEB128.h"
 
 #define DEBUG_TYPE "lld"
 
@@ -72,7 +73,7 @@
 void OutputSection::createHeader(size_t BodySize) {
   raw_string_ostream OS(Header);
   debugWrite(OS.tell(), "section type [" + Twine(getSectionName()) + "]");
-  writeUleb128(OS, Type, nullptr);
+  encodeULEB128(Type, OS);
   writeUleb128(OS, BodySize, "section size");
   OS.flush();
   log("createHeader: " + toString(*this) + " body=" + Twine(BodySize) +
Index: lld/trunk/wasm/WriterUtils.h
===================================================================
--- lld/trunk/wasm/WriterUtils.h
+++ lld/trunk/wasm/WriterUtils.h
@@ -10,6 +10,7 @@
 #ifndef LLD_WASM_WRITERUTILS_H
 #define LLD_WASM_WRITERUTILS_H
 
+#include "lld/Common/LLVM.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Object/Wasm.h"
 #include "llvm/Support/raw_ostream.h"
@@ -36,23 +37,21 @@
   uint32_t Value;
 };
 
-void debugWrite(uint64_t Offset, llvm::Twine Msg);
+void debugWrite(uint64_t Offset, const Twine &Msg);
 
-void writeUleb128(raw_ostream &OS, uint32_t Number, const char *Msg);
+void writeUleb128(raw_ostream &OS, uint32_t Number, StringRef Msg);
 
-void writeSleb128(raw_ostream &OS, int32_t Number, const char *Msg);
+void writeSleb128(raw_ostream &OS, int32_t Number, StringRef Msg);
 
-void writeBytes(raw_ostream &OS, const char *Bytes, size_t count,
-                const char *Msg = nullptr);
+void writeBytes(raw_ostream &OS, const char *Bytes, size_t count, StringRef Msg);
 
-void writeStr(raw_ostream &OS, const llvm::StringRef String,
-              const char *Msg = nullptr);
+void writeStr(raw_ostream &OS, StringRef String, StringRef Msg);
 
-void writeU8(raw_ostream &OS, uint8_t byte, const char *Msg);
+void writeU8(raw_ostream &OS, uint8_t byte, StringRef Msg);
 
-void writeU32(raw_ostream &OS, uint32_t Number, const char *Msg);
+void writeU32(raw_ostream &OS, uint32_t Number, StringRef Msg);
 
-void writeValueType(raw_ostream &OS, int32_t Type, const char *Msg);
+void writeValueType(raw_ostream &OS, int32_t Type, StringRef Msg);
 
 void writeSig(raw_ostream &OS, const llvm::wasm::WasmSignature &Sig);
 
Index: lld/trunk/wasm/WriterUtils.cpp
===================================================================
--- lld/trunk/wasm/WriterUtils.cpp
+++ lld/trunk/wasm/WriterUtils.cpp
@@ -13,7 +13,6 @@
 
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/EndianStream.h"
-#include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/LEB128.h"
 
 #define DEBUG_TYPE "lld"
@@ -39,49 +38,43 @@
 
 namespace lld {
 
-void wasm::debugWrite(uint64_t Offset, Twine Msg) {
-  DEBUG(dbgs() << format("  | %08" PRIx64 ": ", Offset) << Msg << "\n");
+void wasm::debugWrite(uint64_t Offset, const Twine &Msg) {
+  DEBUG(dbgs() << format("  | %08lld: ", Offset) << Msg << "\n");
 }
 
-void wasm::writeUleb128(raw_ostream &OS, uint32_t Number, const char *Msg) {
-  if (Msg)
-    debugWrite(OS.tell(), Msg + formatv(" [{0:x}]", Number));
+void wasm::writeUleb128(raw_ostream &OS, uint32_t Number, StringRef Msg) {
+  debugWrite(OS.tell(), Msg + "[" + utohexstr(Number) + "]");
   encodeULEB128(Number, OS);
 }
 
-void wasm::writeSleb128(raw_ostream &OS, int32_t Number, const char *Msg) {
-  if (Msg)
-    debugWrite(OS.tell(), Msg + formatv(" [{0:x}]", Number));
+void wasm::writeSleb128(raw_ostream &OS, int32_t Number, StringRef Msg) {
+  debugWrite(OS.tell(), Msg + "[" + utohexstr(Number) + "]");
   encodeSLEB128(Number, OS);
 }
 
 void wasm::writeBytes(raw_ostream &OS, const char *Bytes, size_t Count,
-                      const char *Msg) {
-  if (Msg)
-    debugWrite(OS.tell(), Msg + formatv(" [data[{0}]]", Count));
+                      StringRef Msg) {
+  debugWrite(OS.tell(), Msg + " [data[" + Twine(Count) + "]]");
   OS.write(Bytes, Count);
 }
 
-void wasm::writeStr(raw_ostream &OS, const StringRef String, const char *Msg) {
-  if (Msg)
-    debugWrite(OS.tell(),
-               Msg + formatv(" [str[{0}]: {1}]", String.size(), String));
-  writeUleb128(OS, String.size(), nullptr);
-  writeBytes(OS, String.data(), String.size());
+void wasm::writeStr(raw_ostream &OS, StringRef String, StringRef Msg) {
+  debugWrite(OS.tell(),
+             Msg + " [str[" + Twine(String.size()) + "]: " + String + "]");
+  encodeULEB128(String.size(), OS);
+  OS.write(String.data(), String.size());
 }
 
-void wasm::writeU8(raw_ostream &OS, uint8_t byte, const char *Msg) {
-  OS << byte;
-}
+void wasm::writeU8(raw_ostream &OS, uint8_t byte, StringRef Msg) { OS << byte; }
 
-void wasm::writeU32(raw_ostream &OS, uint32_t Number, const char *Msg) {
-  debugWrite(OS.tell(), Msg + formatv("[{0:x}]", Number));
+void wasm::writeU32(raw_ostream &OS, uint32_t Number, StringRef Msg) {
+  debugWrite(OS.tell(), Msg + "[" + utohexstr(Number) + "]");
   support::endian::Writer<support::little>(OS).write(Number);
 }
 
-void wasm::writeValueType(raw_ostream &OS, int32_t Type, const char *Msg) {
-  debugWrite(OS.tell(), Msg + formatv("[type: {0}]", valueTypeToString(Type)));
-  writeSleb128(OS, Type, nullptr);
+void wasm::writeValueType(raw_ostream &OS, int32_t Type, StringRef Msg) {
+  debugWrite(OS.tell(), Msg + "[type: " + valueTypeToString(Type) + "]");
+  encodeSLEB128(Type, OS);
 }
 
 void wasm::writeSig(raw_ostream &OS, const WasmSignature &Sig) {