Index: lld/wasm/OutputSections.h
===================================================================
--- lld/wasm/OutputSections.h
+++ lld/wasm/OutputSections.h
@@ -85,26 +85,6 @@
   raw_string_ostream BodyOutputStream;
 };
 
-// Some synthetic sections (e.g. "name" and "linking") have subsections.
-// Just like the synthetic sections themselves these need to be created before
-// they can be written out (since they are preceded by their length). This
-// class is used to create subsections and then write them into the stream
-// of the parent section.
-class SubSection : public SyntheticSection {
-public:
-  explicit SubSection(uint32_t Type) : SyntheticSection(Type) {}
-
-  std::string getSectionName() const;
-
-  void writeStr(StringRef Str, StringRef Msg);
-  void writeUleb128(uint32_t Number, StringRef Msg);
-
-  void writeToStream(raw_ostream &OS) {
-    OS.write(Header.data(), Header.size());
-    OS.write(Body.data(), Body.size());
-  }
-};
-
 class CodeSection : public OutputSection {
 public:
   explicit CodeSection(ArrayRef<InputFunction *> Functions);
Index: lld/wasm/OutputSections.cpp
===================================================================
--- lld/wasm/OutputSections.cpp
+++ lld/wasm/OutputSections.cpp
@@ -66,18 +66,6 @@
   return sectionTypeToString(Type);
 }
 
-std::string SubSection::getSectionName() const {
-  return std::string("subsection <type=") + std::to_string(Type) + ">";
-}
-
-void SubSection::writeStr(StringRef Str, StringRef Msg) {
-  lld::wasm::writeStr(BodyOutputStream, Str, Msg);
-}
-
-void SubSection::writeUleb128(uint32_t Number, StringRef Msg) {
-  lld::wasm::writeUleb128(BodyOutputStream, Number, Msg);
-}
-
 void OutputSection::createHeader(size_t BodySize) {
   raw_string_ostream OS(Header);
   debugWrite(OS.tell(), "section type [" + Twine(getSectionName()) + "]");
Index: lld/wasm/Writer.cpp
===================================================================
--- lld/wasm/Writer.cpp
+++ lld/wasm/Writer.cpp
@@ -385,6 +385,36 @@
   return Flags;
 }
 
+// Some synthetic sections (e.g. "name" and "linking") have subsections.
+// Just like the synthetic sections themselves these need to be created before
+// they can be written out (since they are preceded by their length). This
+// class is used to create subsections and then write them into the stream
+// of the parent section.
+class SubSection {
+public:
+  explicit SubSection(uint32_t Type) : Type(Type) {}
+
+  void writeStr(StringRef Str, StringRef Msg) {
+    lld::wasm::writeStr(OS, Str, Msg);
+  }
+
+  void writeUleb128(uint32_t Num, StringRef Msg) {
+    lld::wasm::writeUleb128(OS, Num, Msg);
+  }
+
+  void writeTo(raw_ostream &To) {
+    OS.flush();
+    lld::wasm::writeUleb128(To, Type, "subsection type");
+    lld::wasm::writeUleb128(To, Body.size(), "subsection size");
+    To.write(Body.data(), Body.size());
+  }
+
+private:
+  uint32_t Type;
+  std::string Body;
+  raw_string_ostream OS{Body};
+};
+
 // Create the custom "linking" section containing linker metadata.
 // This is only created when relocatable output is requested.
 void Writer::createLinkingSection() {
@@ -394,8 +424,7 @@
 
   SubSection DataSizeSubSection(WASM_DATA_SIZE);
   DataSizeSubSection.writeUleb128(DataSize, "data size");
-  DataSizeSubSection.finalizeContents();
-  DataSizeSubSection.writeToStream(OS);
+  DataSizeSubSection.writeTo(OS);
 
   if (!Config->Relocatable)
     return;
@@ -430,8 +459,7 @@
       }
     }
 
-    Sub.finalizeContents();
-    Sub.writeToStream(OS);
+    Sub.writeTo(OS);
   }
 
   if (Segments.size()) {
@@ -442,8 +470,7 @@
       Sub.writeUleb128(S->Alignment, "alignment");
       Sub.writeUleb128(0, "flags");
     }
-    Sub.finalizeContents();
-    Sub.writeToStream(OS);
+    Sub.writeTo(OS);
   }
 
   if (!InitFunctions.empty()) {
@@ -453,8 +480,7 @@
       Sub.writeUleb128(F.Priority, "priority");
       Sub.writeUleb128(F.Sym->getOutputSymbolIndex(), "function index");
     }
-    Sub.finalizeContents();
-    Sub.writeToStream(OS);
+    Sub.writeTo(OS);
   }
 
   struct ComdatEntry { unsigned Kind; uint32_t Index; };
@@ -491,8 +517,7 @@
         Sub.writeUleb128(Entry.Index, "entry index");
       }
     }
-    Sub.finalizeContents();
-    Sub.writeToStream(OS);
+    Sub.writeTo(OS);
   }
 }
 
@@ -527,8 +552,7 @@
     }
   }
 
-  Sub.finalizeContents();
-  Sub.writeToStream(Section->getStream());
+  Sub.writeTo(Section->getStream());
 }
 
 void Writer::writeHeader() {