Index: lld/trunk/wasm/OutputSections.h
===================================================================
--- lld/trunk/wasm/OutputSections.h
+++ lld/trunk/wasm/OutputSections.h
@@ -40,7 +40,7 @@
   void createHeader(size_t BodySize);
   virtual size_t getSize() const = 0;
   virtual void writeTo(uint8_t *Buf) = 0;
-  virtual void finalizeContents() {}
+  virtual void finalizeContents() = 0;
   virtual uint32_t numRelocations() const { return 0; }
   virtual void writeRelocations(raw_ostream &OS) const {}
 
@@ -69,7 +69,10 @@
 
   size_t getSize() const override { return Header.size() + Body.size(); }
 
+  virtual void writeBody() {}
+
   void finalizeContents() override {
+    writeBody();
     BodyOutputStream.flush();
     createHeader(Body.size());
   }
@@ -84,11 +87,14 @@
 
 class CodeSection : public OutputSection {
 public:
-  explicit CodeSection(ArrayRef<InputFunction *> Functions);
-  size_t getSize() const override { return Header.size() + BodySize; }
+  explicit CodeSection(ArrayRef<InputFunction *> Functions)
+      : OutputSection(llvm::wasm::WASM_SEC_CODE), Functions(Functions) {}
+
+  size_t getSize() const override { assert(BodySize); return Header.size() + BodySize; }
   void writeTo(uint8_t *Buf) override;
   uint32_t numRelocations() const override;
   void writeRelocations(raw_ostream &OS) const override;
+  void finalizeContents() override;
 
 protected:
   ArrayRef<InputFunction *> Functions;
@@ -98,11 +104,14 @@
 
 class DataSection : public OutputSection {
 public:
-  explicit DataSection(ArrayRef<OutputSegment *> Segments);
+  explicit DataSection(ArrayRef<OutputSegment *> Segments)
+      : OutputSection(llvm::wasm::WASM_SEC_DATA), Segments(Segments) {}
+
   size_t getSize() const override { return Header.size() + BodySize; }
   void writeTo(uint8_t *Buf) override;
   uint32_t numRelocations() const override;
   void writeRelocations(raw_ostream &OS) const override;
+  void finalizeContents() override;
 
 protected:
   ArrayRef<OutputSegment *> Segments;
@@ -119,20 +128,36 @@
 // separately and are instead synthesized by the linker.
 class CustomSection : public OutputSection {
 public:
-  CustomSection(std::string Name, ArrayRef<InputSection *> InputSections);
+  CustomSection(std::string Name, ArrayRef<InputSection *> InputSections)
+      : OutputSection(llvm::wasm::WASM_SEC_CUSTOM, Name),
+        InputSections(InputSections) {}
   size_t getSize() const override {
     return Header.size() + NameData.size() + PayloadSize;
   }
   void writeTo(uint8_t *Buf) override;
   uint32_t numRelocations() const override;
   void writeRelocations(raw_ostream &OS) const override;
+  void finalizeContents() override;
 
 protected:
-  size_t PayloadSize;
+  size_t PayloadSize = 0;
   ArrayRef<InputSection *> InputSections;
   std::string NameData;
 };
 
+class RelocSection : public SyntheticSection {
+public:
+  RelocSection(StringRef Name, OutputSection *Sec, uint32_t SectionIndex)
+      : SyntheticSection(llvm::wasm::WASM_SEC_CUSTOM, Name), Sec(Sec),
+        SectionIndex(SectionIndex) {}
+  void writeBody() override;
+
+protected:
+  OutputSection* Sec;
+  uint32_t SectionIndex;
+};
+
+
 } // namespace wasm
 } // namespace lld
 
Index: lld/trunk/wasm/OutputSections.cpp
===================================================================
--- lld/trunk/wasm/OutputSections.cpp
+++ lld/trunk/wasm/OutputSections.cpp
@@ -79,10 +79,7 @@
       " total=" + Twine(getSize()));
 }
 
-CodeSection::CodeSection(ArrayRef<InputFunction *> Functions)
-    : OutputSection(WASM_SEC_CODE), Functions(Functions) {
-  assert(Functions.size() > 0);
-
+void CodeSection::finalizeContents() {
   raw_string_ostream OS(CodeSectionHeader);
   writeUleb128(OS, Functions.size(), "function count");
   OS.flush();
@@ -128,8 +125,7 @@
     C->writeRelocations(OS);
 }
 
-DataSection::DataSection(ArrayRef<OutputSegment *> Segments)
-    : OutputSection(WASM_SEC_DATA), Segments(Segments) {
+void DataSection::finalizeContents() {
   raw_string_ostream OS(DataSectionHeader);
 
   writeUleb128(OS, Segments.size(), "data segment count");
@@ -202,10 +198,7 @@
       C->writeRelocations(OS);
 }
 
-CustomSection::CustomSection(std::string Name,
-                             ArrayRef<InputSection *> InputSections)
-    : OutputSection(WASM_SEC_CUSTOM, Name), PayloadSize(0),
-      InputSections(InputSections) {
+void CustomSection::finalizeContents() {
   raw_string_ostream OS(NameData);
   encodeULEB128(Name.size(), OS);
   OS << Name;
@@ -248,3 +241,9 @@
   for (const InputSection *S : InputSections)
     S->writeRelocations(OS);
 }
+
+void RelocSection::writeBody() {
+  writeUleb128(BodyOutputStream, SectionIndex, "reloc section");
+  writeUleb128(BodyOutputStream, Sec->numRelocations(), "reloc count");
+  Sec->writeRelocations(BodyOutputStream);
+}
Index: lld/trunk/wasm/Writer.cpp
===================================================================
--- lld/trunk/wasm/Writer.cpp
+++ lld/trunk/wasm/Writer.cpp
@@ -469,11 +469,7 @@
       llvm_unreachable(
           "relocations only supported for code, data, or custom sections");
 
-    SyntheticSection *Section = createSyntheticSection(WASM_SEC_CUSTOM, Name);
-    raw_ostream &OS = Section->getStream();
-    writeUleb128(OS, I, "reloc section");
-    writeUleb128(OS, Count, "reloc count");
-    OSec->writeRelocations(OS);
+    OutputSections.push_back(make<RelocSection>(Name, OSec, I));
   }
 }