Index: include/llvm/Support/raw_os_ostream.h
===================================================================
--- include/llvm/Support/raw_os_ostream.h
+++ include/llvm/Support/raw_os_ostream.h
@@ -27,6 +27,12 @@
   /// write_impl - See raw_ostream::write_impl.
   void write_impl(const char *Ptr, size_t Size) override;
 
+  /// Implement optional seek support.
+  bool supportsSeeking() override { return true; }
+
+  /// Implement optional seek support.
+  uint64_t seek(uint64_t off) override;
+
   /// current_pos - Return the current position within the stream, not
   /// counting the bytes currently in the buffer.
   uint64_t current_pos() const override;
Index: include/llvm/Support/raw_ostream.h
===================================================================
--- include/llvm/Support/raw_ostream.h
+++ include/llvm/Support/raw_ostream.h
@@ -95,6 +95,12 @@
 
   virtual ~raw_ostream();
 
+  /// Seek support is optional.
+  virtual bool supportsSeeking() { return false; }
+
+  /// Optional seek support. Defaults to not changing the file position.
+  virtual uint64_t seek(uint64_t off) { return current_pos(); };
+
   /// tell - Return the current offset with the file.
   uint64_t tell() const { return current_pos() + GetNumBytesInBuffer(); }
 
@@ -426,11 +432,11 @@
   /// fsync.
   void close();
 
-  bool supportsSeeking() { return SupportsSeeking; }
+  bool supportsSeeking() override { return SupportsSeeking; }
 
   /// Flushes the stream and repositions the underlying file descriptor position
   /// to the offset specified from the beginning of the file.
-  uint64_t seek(uint64_t off);
+  uint64_t seek(uint64_t off) override;
 
   raw_ostream &changeColor(enum Colors colors, bool bold=false,
                            bool bg=false) override;
Index: lib/Support/raw_os_ostream.cpp
===================================================================
--- lib/Support/raw_os_ostream.cpp
+++ lib/Support/raw_os_ostream.cpp
@@ -26,4 +26,9 @@
   OS.write(Ptr, Size);
 }
 
+uint64_t raw_os_ostream::seek(uint64_t off) { 
+  OS.seekp(off); 
+  return current_pos();
+};
+
 uint64_t raw_os_ostream::current_pos() const { return OS.tellp(); }