Index: clang/tools/driver/cc1as_main.cpp
===================================================================
--- clang/tools/driver/cc1as_main.cpp
+++ clang/tools/driver/cc1as_main.cpp
@@ -29,6 +29,7 @@
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCParser/MCAsmParser.h"
 #include "llvm/MC/MCParser/MCTargetAsmParser.h"
 #include "llvm/MC/MCRegisterInfo.h"
@@ -426,11 +427,12 @@
     MCTargetOptions MCOptions;
     std::unique_ptr<MCAsmBackend> MAB(
         TheTarget->createMCAsmBackend(*STI, *MRI, MCOptions));
+    std::unique_ptr<MCObjectWriter> OW = MAB->createObjectWriter(*Out);
 
     Triple T(Opts.Triple);
     Str.reset(TheTarget->createMCObjectStreamer(
-        T, Ctx, std::move(MAB), *Out, std::move(CE), *STI, Opts.RelaxAll,
-        Opts.IncrementalLinkerCompatible,
+        T, Ctx, std::move(MAB), std::move(OW), std::move(CE), *STI,
+        Opts.RelaxAll, Opts.IncrementalLinkerCompatible,
         /*DWARFMustBeAtTheEnd*/ true));
     Str.get()->InitSections(Opts.NoExecStack);
   }
Index: llvm/include/llvm/MC/MCELFStreamer.h
===================================================================
--- llvm/include/llvm/MC/MCELFStreamer.h
+++ llvm/include/llvm/MC/MCELFStreamer.h
@@ -24,7 +24,8 @@
 class MCELFStreamer : public MCObjectStreamer {
 public:
   MCELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-                raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> Emitter);
+                std::unique_ptr<MCObjectWriter> OW,
+                std::unique_ptr<MCCodeEmitter> Emitter);
 
   ~MCELFStreamer() override = default;
 
@@ -93,7 +94,7 @@
 
 MCELFStreamer *createARMELFStreamer(MCContext &Context,
                                     std::unique_ptr<MCAsmBackend> TAB,
-                                    raw_pwrite_stream &OS,
+                                    std::unique_ptr<MCObjectWriter> OW,
                                     std::unique_ptr<MCCodeEmitter> Emitter,
                                     bool RelaxAll, bool IsThumb);
 
Index: llvm/include/llvm/MC/MCObjectStreamer.h
===================================================================
--- llvm/include/llvm/MC/MCObjectStreamer.h
+++ llvm/include/llvm/MC/MCObjectStreamer.h
@@ -48,7 +48,7 @@
 
 protected:
   MCObjectStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-                   raw_pwrite_stream &OS,
+                   std::unique_ptr<MCObjectWriter> OW,
                    std::unique_ptr<MCCodeEmitter> Emitter);
   ~MCObjectStreamer();
 
Index: llvm/include/llvm/MC/MCWasmStreamer.h
===================================================================
--- llvm/include/llvm/MC/MCWasmStreamer.h
+++ llvm/include/llvm/MC/MCWasmStreamer.h
@@ -15,6 +15,7 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/MC/MCDirectives.h"
 #include "llvm/MC/MCObjectStreamer.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/SectionKind.h"
 #include "llvm/Support/DataTypes.h"
 
@@ -27,8 +28,10 @@
 class MCWasmStreamer : public MCObjectStreamer {
 public:
   MCWasmStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-                 raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> Emitter)
-      : MCObjectStreamer(Context, std::move(TAB), OS, std::move(Emitter)),
+                 std::unique_ptr<MCObjectWriter> OW,
+                 std::unique_ptr<MCCodeEmitter> Emitter)
+      : MCObjectStreamer(Context, std::move(TAB), std::move(OW),
+                         std::move(Emitter)),
         SeenIdent(false) {}
 
   ~MCWasmStreamer() override;
Index: llvm/include/llvm/MC/MCWinCOFFStreamer.h
===================================================================
--- llvm/include/llvm/MC/MCWinCOFFStreamer.h
+++ llvm/include/llvm/MC/MCWinCOFFStreamer.h
@@ -28,7 +28,8 @@
 class MCWinCOFFStreamer : public MCObjectStreamer {
 public:
   MCWinCOFFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
-                    std::unique_ptr<MCCodeEmitter> CE, raw_pwrite_stream &OS);
+                    std::unique_ptr<MCCodeEmitter> CE,
+                    std::unique_ptr<MCObjectWriter> OW);
 
   /// state management
   void reset() override {
Index: llvm/include/llvm/Support/TargetRegistry.h
===================================================================
--- llvm/include/llvm/Support/TargetRegistry.h
+++ llvm/include/llvm/Support/TargetRegistry.h
@@ -46,6 +46,7 @@
 class MCInstPrinter;
 class MCInstrAnalysis;
 class MCInstrInfo;
+class MCObjectWriter;
 class MCRegisterInfo;
 class MCRelocationInfo;
 class MCStreamer;
@@ -86,18 +87,18 @@
 
 MCStreamer *createELFStreamer(MCContext &Ctx,
                               std::unique_ptr<MCAsmBackend> &&TAB,
-                              raw_pwrite_stream &OS,
+                              std::unique_ptr<MCObjectWriter> &&OW,
                               std::unique_ptr<MCCodeEmitter> &&CE,
                               bool RelaxAll);
 MCStreamer *createMachOStreamer(MCContext &Ctx,
                                 std::unique_ptr<MCAsmBackend> &&TAB,
-                                raw_pwrite_stream &OS,
+                                std::unique_ptr<MCObjectWriter> &&OW,
                                 std::unique_ptr<MCCodeEmitter> &&CE,
                                 bool RelaxAll, bool DWARFMustBeAtTheEnd,
                                 bool LabelSections = false);
 MCStreamer *createWasmStreamer(MCContext &Ctx,
                                std::unique_ptr<MCAsmBackend> &&TAB,
-                               raw_pwrite_stream &OS,
+                               std::unique_ptr<MCObjectWriter> &&OW,
                                std::unique_ptr<MCCodeEmitter> &&CE,
                                bool RelaxAll);
 
@@ -160,22 +161,22 @@
   using ELFStreamerCtorTy =
       MCStreamer *(*)(const Triple &T, MCContext &Ctx,
                       std::unique_ptr<MCAsmBackend> &&TAB,
-                      raw_pwrite_stream &OS,
+                      std::unique_ptr<MCObjectWriter> &&OW,
                       std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll);
   using MachOStreamerCtorTy =
       MCStreamer *(*)(MCContext &Ctx, std::unique_ptr<MCAsmBackend> &&TAB,
-                      raw_pwrite_stream &OS,
+                      std::unique_ptr<MCObjectWriter> &&OW,
                       std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll,
                       bool DWARFMustBeAtTheEnd);
   using COFFStreamerCtorTy =
       MCStreamer *(*)(MCContext &Ctx, std::unique_ptr<MCAsmBackend> &&TAB,
-                      raw_pwrite_stream &OS,
+                      std::unique_ptr<MCObjectWriter> &&OW,
                       std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll,
                       bool IncrementalLinkerCompatible);
   using WasmStreamerCtorTy =
       MCStreamer *(*)(const Triple &T, MCContext &Ctx,
                       std::unique_ptr<MCAsmBackend> &&TAB,
-                      raw_pwrite_stream &OS,
+                      std::unique_ptr<MCObjectWriter> &&OW,
                       std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll);
   using NullTargetStreamerCtorTy = MCTargetStreamer *(*)(MCStreamer &S);
   using AsmTargetStreamerCtorTy = MCTargetStreamer *(*)(
@@ -463,7 +464,7 @@
   /// \param RelaxAll Relax all fixups?
   MCStreamer *createMCObjectStreamer(const Triple &T, MCContext &Ctx,
                                      std::unique_ptr<MCAsmBackend> &&TAB,
-                                     raw_pwrite_stream &OS,
+                                     std::unique_ptr<MCObjectWriter> &&OW,
                                      std::unique_ptr<MCCodeEmitter> &&Emitter,
                                      const MCSubtargetInfo &STI, bool RelaxAll,
                                      bool IncrementalLinkerCompatible,
@@ -474,32 +475,35 @@
       llvm_unreachable("Unknown object format");
     case Triple::COFF:
       assert(T.isOSWindows() && "only Windows COFF is supported");
-      S = COFFStreamerCtorFn(Ctx, std::move(TAB), OS, std::move(Emitter),
-                             RelaxAll, IncrementalLinkerCompatible);
+      S = COFFStreamerCtorFn(Ctx, std::move(TAB), std::move(OW),
+                             std::move(Emitter), RelaxAll,
+                             IncrementalLinkerCompatible);
       break;
     case Triple::MachO:
       if (MachOStreamerCtorFn)
-        S = MachOStreamerCtorFn(Ctx, std::move(TAB), OS, std::move(Emitter),
-                                RelaxAll, DWARFMustBeAtTheEnd);
+        S = MachOStreamerCtorFn(Ctx, std::move(TAB), std::move(OW),
+                                std::move(Emitter), RelaxAll,
+                                DWARFMustBeAtTheEnd);
       else
-        S = createMachOStreamer(Ctx, std::move(TAB), OS, std::move(Emitter),
-                                RelaxAll, DWARFMustBeAtTheEnd);
+        S = createMachOStreamer(Ctx, std::move(TAB), std::move(OW),
+                                std::move(Emitter), RelaxAll,
+                                DWARFMustBeAtTheEnd);
       break;
     case Triple::ELF:
       if (ELFStreamerCtorFn)
-        S = ELFStreamerCtorFn(T, Ctx, std::move(TAB), OS, std::move(Emitter),
-                              RelaxAll);
+        S = ELFStreamerCtorFn(T, Ctx, std::move(TAB), std::move(OW),
+                              std::move(Emitter), RelaxAll);
       else
-        S = createELFStreamer(Ctx, std::move(TAB), OS, std::move(Emitter),
-                              RelaxAll);
+        S = createELFStreamer(Ctx, std::move(TAB), std::move(OW),
+                              std::move(Emitter), RelaxAll);
       break;
     case Triple::Wasm:
       if (WasmStreamerCtorFn)
-        S = WasmStreamerCtorFn(T, Ctx, std::move(TAB), OS, std::move(Emitter),
-                               RelaxAll);
+        S = WasmStreamerCtorFn(T, Ctx, std::move(TAB), std::move(OW),
+                               std::move(Emitter), RelaxAll);
       else
-        S = createWasmStreamer(Ctx, std::move(TAB), OS, std::move(Emitter),
-                               RelaxAll);
+        S = createWasmStreamer(Ctx, std::move(TAB), std::move(OW),
+                               std::move(Emitter), RelaxAll);
       break;
     }
     if (ObjectTargetStreamerCtorFn)
Index: llvm/lib/CodeGen/LLVMTargetMachine.cpp
===================================================================
--- llvm/lib/CodeGen/LLVMTargetMachine.cpp
+++ llvm/lib/CodeGen/LLVMTargetMachine.cpp
@@ -23,6 +23,7 @@
 #include "llvm/MC/MCCodeEmitter.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/Support/CommandLine.h"
@@ -166,8 +167,9 @@
 
     Triple T(getTargetTriple().str());
     AsmStreamer.reset(getTarget().createMCObjectStreamer(
-        T, Context, std::unique_ptr<MCAsmBackend>(MAB), Out,
-        std::unique_ptr<MCCodeEmitter>(MCE), STI, Options.MCOptions.MCRelaxAll,
+        T, Context, std::unique_ptr<MCAsmBackend>(MAB),
+        MAB->createObjectWriter(Out), std::unique_ptr<MCCodeEmitter>(MCE), STI,
+        Options.MCOptions.MCRelaxAll,
         Options.MCOptions.MCIncrementalLinkerCompatible,
         /*DWARFMustBeAtTheEnd*/ true));
     break;
@@ -241,7 +243,7 @@
 
   const Triple &T = getTargetTriple();
   std::unique_ptr<MCStreamer> AsmStreamer(getTarget().createMCObjectStreamer(
-      T, *Ctx, std::unique_ptr<MCAsmBackend>(MAB), Out,
+      T, *Ctx, std::unique_ptr<MCAsmBackend>(MAB), MAB->createObjectWriter(Out),
       std::unique_ptr<MCCodeEmitter>(MCE), STI, Options.MCOptions.MCRelaxAll,
       Options.MCOptions.MCIncrementalLinkerCompatible,
       /*DWARFMustBeAtTheEnd*/ true));
Index: llvm/lib/MC/MCELFStreamer.cpp
===================================================================
--- llvm/lib/MC/MCELFStreamer.cpp
+++ llvm/lib/MC/MCELFStreamer.cpp
@@ -41,9 +41,10 @@
 
 MCELFStreamer::MCELFStreamer(MCContext &Context,
                              std::unique_ptr<MCAsmBackend> TAB,
-                             raw_pwrite_stream &OS,
+                             std::unique_ptr<MCObjectWriter> OW,
                              std::unique_ptr<MCCodeEmitter> Emitter)
-    : MCObjectStreamer(Context, std::move(TAB), OS, std::move(Emitter)) {}
+    : MCObjectStreamer(Context, std::move(TAB), std::move(OW),
+                       std::move(Emitter)) {}
 
 bool MCELFStreamer::isBundleLocked() const {
   return getCurrentSectionOnly()->isBundleLocked();
@@ -647,11 +648,11 @@
 
 MCStreamer *llvm::createELFStreamer(MCContext &Context,
                                     std::unique_ptr<MCAsmBackend> &&MAB,
-                                    raw_pwrite_stream &OS,
+                                    std::unique_ptr<MCObjectWriter> &&OW,
                                     std::unique_ptr<MCCodeEmitter> &&CE,
                                     bool RelaxAll) {
   MCELFStreamer *S =
-      new MCELFStreamer(Context, std::move(MAB), OS, std::move(CE));
+      new MCELFStreamer(Context, std::move(MAB), std::move(OW), std::move(CE));
   if (RelaxAll)
     S->getAssembler().setRelaxAll(true);
   return S;
Index: llvm/lib/MC/MCMachOStreamer.cpp
===================================================================
--- llvm/lib/MC/MCMachOStreamer.cpp
+++ llvm/lib/MC/MCMachOStreamer.cpp
@@ -24,6 +24,7 @@
 #include "llvm/MC/MCLinkerOptimizationHint.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCObjectStreamer.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCSectionMachO.h"
 #include "llvm/MC/MCStreamer.h"
@@ -63,9 +64,11 @@
 
 public:
   MCMachOStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
-                  raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> Emitter,
+                  std::unique_ptr<MCObjectWriter> OW,
+                  std::unique_ptr<MCCodeEmitter> Emitter,
                   bool DWARFMustBeAtTheEnd, bool label)
-      : MCObjectStreamer(Context, std::move(MAB), OS, std::move(Emitter)),
+      : MCObjectStreamer(Context, std::move(MAB), std::move(OW),
+                         std::move(Emitter)),
         LabelSections(label), DWARFMustBeAtTheEnd(DWARFMustBeAtTheEnd),
         CreatedADWARFSection(false) {}
 
@@ -462,12 +465,12 @@
 
 MCStreamer *llvm::createMachOStreamer(MCContext &Context,
                                       std::unique_ptr<MCAsmBackend> &&MAB,
-                                      raw_pwrite_stream &OS,
+                                      std::unique_ptr<MCObjectWriter> &&OW,
                                       std::unique_ptr<MCCodeEmitter> &&CE,
                                       bool RelaxAll, bool DWARFMustBeAtTheEnd,
                                       bool LabelSections) {
   MCMachOStreamer *S =
-      new MCMachOStreamer(Context, std::move(MAB), OS, std::move(CE),
+      new MCMachOStreamer(Context, std::move(MAB), std::move(OW), std::move(CE),
                           DWARFMustBeAtTheEnd, LabelSections);
   const Triple &Target = Context.getObjectFileInfo()->getTargetTriple();
   S->EmitVersionForTarget(Target);
Index: llvm/lib/MC/MCObjectStreamer.cpp
===================================================================
--- llvm/lib/MC/MCObjectStreamer.cpp
+++ llvm/lib/MC/MCObjectStreamer.cpp
@@ -25,12 +25,11 @@
 
 MCObjectStreamer::MCObjectStreamer(MCContext &Context,
                                    std::unique_ptr<MCAsmBackend> TAB,
-                                   raw_pwrite_stream &OS,
+                                   std::unique_ptr<MCObjectWriter> OW,
                                    std::unique_ptr<MCCodeEmitter> Emitter)
     : MCStreamer(Context),
-      Assembler(llvm::make_unique<MCAssembler>(Context, std::move(TAB),
-                                               std::move(Emitter),
-                                               TAB->createObjectWriter(OS))),
+      Assembler(llvm::make_unique<MCAssembler>(
+          Context, std::move(TAB), std::move(Emitter), std::move(OW))),
       EmitEHFrame(true), EmitDebugFrame(false) {}
 
 MCObjectStreamer::~MCObjectStreamer() {}
Index: llvm/lib/MC/MCWasmStreamer.cpp
===================================================================
--- llvm/lib/MC/MCWasmStreamer.cpp
+++ llvm/lib/MC/MCWasmStreamer.cpp
@@ -198,11 +198,11 @@
 
 MCStreamer *llvm::createWasmStreamer(MCContext &Context,
                                      std::unique_ptr<MCAsmBackend> &&MAB,
-                                     raw_pwrite_stream &OS,
+                                     std::unique_ptr<MCObjectWriter> &&OW,
                                      std::unique_ptr<MCCodeEmitter> &&CE,
                                      bool RelaxAll) {
   MCWasmStreamer *S =
-      new MCWasmStreamer(Context, std::move(MAB), OS, std::move(CE));
+      new MCWasmStreamer(Context, std::move(MAB), std::move(OW), std::move(CE));
   if (RelaxAll)
     S->getAssembler().setRelaxAll(true);
   return S;
Index: llvm/lib/MC/MCWinCOFFStreamer.cpp
===================================================================
--- llvm/lib/MC/MCWinCOFFStreamer.cpp
+++ llvm/lib/MC/MCWinCOFFStreamer.cpp
@@ -25,6 +25,7 @@
 #include "llvm/MC/MCFragment.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCObjectStreamer.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCSymbolCOFF.h"
 #include "llvm/MC/MCWinCOFFStreamer.h"
@@ -44,8 +45,8 @@
 MCWinCOFFStreamer::MCWinCOFFStreamer(MCContext &Context,
                                      std::unique_ptr<MCAsmBackend> MAB,
                                      std::unique_ptr<MCCodeEmitter> CE,
-                                     raw_pwrite_stream &OS)
-    : MCObjectStreamer(Context, std::move(MAB), OS, std::move(CE)),
+                                     std::unique_ptr<MCObjectWriter> OW)
+    : MCObjectStreamer(Context, std::move(MAB), std::move(OW), std::move(CE)),
       CurSymbol(nullptr) {}
 
 void MCWinCOFFStreamer::EmitInstToData(const MCInst &Inst,
Index: llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.h
===================================================================
--- llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.h
+++ llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.h
@@ -20,7 +20,7 @@
 
 MCELFStreamer *createAArch64ELFStreamer(MCContext &Context,
                                         std::unique_ptr<MCAsmBackend> TAB,
-                                        raw_pwrite_stream &OS,
+                                        std::unique_ptr<MCObjectWriter> OW,
                                         std::unique_ptr<MCCodeEmitter> Emitter,
                                         bool RelaxAll);
 }
Index: llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
===================================================================
--- llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
+++ llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
@@ -27,6 +27,7 @@
 #include "llvm/MC/MCELFStreamer.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
@@ -87,9 +88,10 @@
   friend class AArch64TargetELFStreamer;
 
   AArch64ELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-                     raw_pwrite_stream &OS,
+                     std::unique_ptr<MCObjectWriter> OW,
                      std::unique_ptr<MCCodeEmitter> Emitter)
-      : MCELFStreamer(Context, std::move(TAB), OS, std::move(Emitter)),
+      : MCELFStreamer(Context, std::move(TAB), std::move(OW),
+                      std::move(Emitter)),
         MappingSymbolCounter(0), LastEMS(EMS_None) {}
 
   void ChangeSection(MCSection *Section, const MCExpr *Subsection) override {
@@ -209,11 +211,11 @@
 
 MCELFStreamer *createAArch64ELFStreamer(MCContext &Context,
                                         std::unique_ptr<MCAsmBackend> TAB,
-                                        raw_pwrite_stream &OS,
+                                        std::unique_ptr<MCObjectWriter> OW,
                                         std::unique_ptr<MCCodeEmitter> Emitter,
                                         bool RelaxAll) {
-  AArch64ELFStreamer *S =
-      new AArch64ELFStreamer(Context, std::move(TAB), OS, std::move(Emitter));
+  AArch64ELFStreamer *S = new AArch64ELFStreamer(
+      Context, std::move(TAB), std::move(OW), std::move(Emitter));
   if (RelaxAll)
     S->getAssembler().setRelaxAll(true);
   return S;
Index: llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp
===================================================================
--- llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp
+++ llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp
@@ -20,6 +20,7 @@
 #include "llvm/MC/MCCodeEmitter.h"
 #include "llvm/MC/MCInstrAnalysis.h"
 #include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
@@ -103,30 +104,30 @@
 
 static MCStreamer *createELFStreamer(const Triple &T, MCContext &Ctx,
                                      std::unique_ptr<MCAsmBackend> &&TAB,
-                                     raw_pwrite_stream &OS,
+                                     std::unique_ptr<MCObjectWriter> &&OW,
                                      std::unique_ptr<MCCodeEmitter> &&Emitter,
                                      bool RelaxAll) {
-  return createAArch64ELFStreamer(Ctx, std::move(TAB), OS, std::move(Emitter),
-                                  RelaxAll);
+  return createAArch64ELFStreamer(Ctx, std::move(TAB), std::move(OW),
+                                  std::move(Emitter), RelaxAll);
 }
 
 static MCStreamer *createMachOStreamer(MCContext &Ctx,
                                        std::unique_ptr<MCAsmBackend> &&TAB,
-                                       raw_pwrite_stream &OS,
+                                       std::unique_ptr<MCObjectWriter> &&OW,
                                        std::unique_ptr<MCCodeEmitter> &&Emitter,
                                        bool RelaxAll,
                                        bool DWARFMustBeAtTheEnd) {
-  return createMachOStreamer(Ctx, std::move(TAB), OS, std::move(Emitter),
-                             RelaxAll, DWARFMustBeAtTheEnd,
+  return createMachOStreamer(Ctx, std::move(TAB), std::move(OW),
+                             std::move(Emitter), RelaxAll, DWARFMustBeAtTheEnd,
                              /*LabelSections*/ true);
 }
 
 static MCStreamer *
 createWinCOFFStreamer(MCContext &Ctx, std::unique_ptr<MCAsmBackend> &&TAB,
-                      raw_pwrite_stream &OS,
+                      std::unique_ptr<MCObjectWriter> &&OW,
                       std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll,
                       bool IncrementalLinkerCompatible) {
-  return createAArch64WinCOFFStreamer(Ctx, std::move(TAB), OS,
+  return createAArch64WinCOFFStreamer(Ctx, std::move(TAB), std::move(OW),
                                       std::move(Emitter), RelaxAll,
                                       IncrementalLinkerCompatible);
 }
Index: llvm/lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFStreamer.h
===================================================================
--- llvm/lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFStreamer.h
+++ llvm/lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFStreamer.h
@@ -35,7 +35,7 @@
 
 MCWinCOFFStreamer *createAArch64WinCOFFStreamer(
     MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-    raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> Emitter,
+    std::unique_ptr<MCObjectWriter> OW, std::unique_ptr<MCCodeEmitter> Emitter,
     bool RelaxAll, bool IncrementalLinkerCompatible);
 } // end llvm namespace
 
Index: llvm/lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFStreamer.cpp
===================================================================
--- llvm/lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFStreamer.cpp
+++ llvm/lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFStreamer.cpp
@@ -10,6 +10,7 @@
 #include "AArch64WinCOFFStreamer.h"
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCObjectWriter.h"
 
 using namespace llvm;
 
@@ -21,8 +22,8 @@
 
   AArch64WinCOFFStreamer(MCContext &C, std::unique_ptr<MCAsmBackend> AB,
                          std::unique_ptr<MCCodeEmitter> CE,
-                         raw_pwrite_stream &OS)
-      : MCWinCOFFStreamer(C, std::move(AB), std::move(CE), OS) {}
+                         std::unique_ptr<MCObjectWriter> OW)
+      : MCWinCOFFStreamer(C, std::move(AB), std::move(CE), std::move(OW)) {}
 
   void FinishImpl() override;
 };
@@ -37,10 +38,10 @@
 namespace llvm {
 MCWinCOFFStreamer *createAArch64WinCOFFStreamer(
     MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
-    raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> Emitter,
+    std::unique_ptr<MCObjectWriter> OW, std::unique_ptr<MCCodeEmitter> Emitter,
     bool RelaxAll, bool IncrementalLinkerCompatible) {
   auto *S = new AArch64WinCOFFStreamer(Context, std::move(MAB),
-                                       std::move(Emitter), OS);
+                                       std::move(Emitter), std::move(OW));
   S->getAssembler().setIncrementalLinkerCompatible(IncrementalLinkerCompatible);
   return S;
 }
Index: llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFStreamer.h
===================================================================
--- llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFStreamer.h
+++ llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFStreamer.h
@@ -23,17 +23,9 @@
 class MCContext;
 class MCSubtargetInfo;
 
-class AMDGPUELFStreamer : public MCELFStreamer {
-public:
-  AMDGPUELFStreamer(const Triple &T, MCContext &Context,
-                    std::unique_ptr<MCAsmBackend> MAB, raw_pwrite_stream &OS,
-                    std::unique_ptr<MCCodeEmitter> Emitter)
-      : MCELFStreamer(Context, std::move(MAB), OS, std::move(Emitter)) {}
-};
-
 MCELFStreamer *createAMDGPUELFStreamer(const Triple &T, MCContext &Context,
                                        std::unique_ptr<MCAsmBackend> MAB,
-                                       raw_pwrite_stream &OS,
+                                       std::unique_ptr<MCObjectWriter> OW,
                                        std::unique_ptr<MCCodeEmitter> Emitter,
                                        bool RelaxAll);
 } // namespace llvm.
Index: llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFStreamer.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFStreamer.cpp
+++ llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFStreamer.cpp
@@ -12,13 +12,28 @@
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCObjectWriter.h"
 
 using namespace llvm;
 
+namespace {
+
+class AMDGPUELFStreamer : public MCELFStreamer {
+public:
+  AMDGPUELFStreamer(const Triple &T, MCContext &Context,
+                    std::unique_ptr<MCAsmBackend> MAB,
+                    std::unique_ptr<MCObjectWriter> OW,
+                    std::unique_ptr<MCCodeEmitter> Emitter)
+      : MCELFStreamer(Context, std::move(MAB), std::move(OW),
+                      std::move(Emitter)) {}
+};
+
+}
+
 MCELFStreamer *llvm::createAMDGPUELFStreamer(
     const Triple &T, MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
-    raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> Emitter,
+    std::unique_ptr<MCObjectWriter> OW, std::unique_ptr<MCCodeEmitter> Emitter,
     bool RelaxAll) {
-  return new AMDGPUELFStreamer(T, Context, std::move(MAB), OS,
+  return new AMDGPUELFStreamer(T, Context, std::move(MAB), std::move(OW),
                                std::move(Emitter));
 }
Index: llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUMCTargetDesc.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUMCTargetDesc.cpp
+++ llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUMCTargetDesc.cpp
@@ -22,6 +22,7 @@
 #include "llvm/MC/MCCodeEmitter.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
@@ -81,10 +82,10 @@
 
 static MCStreamer *createMCStreamer(const Triple &T, MCContext &Context,
                                     std::unique_ptr<MCAsmBackend> &&MAB,
-                                    raw_pwrite_stream &OS,
+                                    std::unique_ptr<MCObjectWriter> &&OW,
                                     std::unique_ptr<MCCodeEmitter> &&Emitter,
                                     bool RelaxAll) {
-  return createAMDGPUELFStreamer(T, Context, std::move(MAB), OS,
+  return createAMDGPUELFStreamer(T, Context, std::move(MAB), std::move(OW),
                                  std::move(Emitter), RelaxAll);
 }
 
Index: llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
===================================================================
--- llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
+++ llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
@@ -33,6 +33,7 @@
 #include "llvm/MC/MCFragment.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCInstPrinter.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCSectionELF.h"
@@ -441,9 +442,9 @@
   friend class ARMTargetELFStreamer;
 
   ARMELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-                 raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> Emitter,
+                 std::unique_ptr<MCObjectWriter> OW, std::unique_ptr<MCCodeEmitter> Emitter,
                  bool IsThumb)
-      : MCELFStreamer(Context, std::move(TAB), OS, std::move(Emitter)),
+      : MCELFStreamer(Context, std::move(TAB), std::move(OW), std::move(Emitter)),
         IsThumb(IsThumb) {
     EHReset();
   }
@@ -1494,10 +1495,10 @@
 
 MCELFStreamer *createARMELFStreamer(MCContext &Context,
                                     std::unique_ptr<MCAsmBackend> TAB,
-                                    raw_pwrite_stream &OS,
+                                    std::unique_ptr<MCObjectWriter> OW,
                                     std::unique_ptr<MCCodeEmitter> Emitter,
                                     bool RelaxAll, bool IsThumb) {
-  ARMELFStreamer *S = new ARMELFStreamer(Context, std::move(TAB), OS,
+  ARMELFStreamer *S = new ARMELFStreamer(Context, std::move(TAB), std::move(OW),
                                          std::move(Emitter), IsThumb);
   // FIXME: This should eventually end up somewhere else where more
   // intelligent flag decisions can be made. For now we are just maintaining
Index: llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.h
===================================================================
--- llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.h
+++ llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.h
@@ -81,7 +81,7 @@
 // object file.
 MCStreamer *createARMWinCOFFStreamer(MCContext &Context,
                                      std::unique_ptr<MCAsmBackend> &&MAB,
-                                     raw_pwrite_stream &OS,
+                                     std::unique_ptr<MCObjectWriter> &&OW,
                                      std::unique_ptr<MCCodeEmitter> &&Emitter,
                                      bool RelaxAll,
                                      bool IncrementalLinkerCompatible);
Index: llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
===================================================================
--- llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
+++ llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
@@ -21,6 +21,7 @@
 #include "llvm/MC/MCELFStreamer.h"
 #include "llvm/MC/MCInstrAnalysis.h"
 #include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
@@ -205,21 +206,21 @@
 
 static MCStreamer *createELFStreamer(const Triple &T, MCContext &Ctx,
                                      std::unique_ptr<MCAsmBackend> &&MAB,
-                                     raw_pwrite_stream &OS,
+                                     std::unique_ptr<MCObjectWriter> &&OW,
                                      std::unique_ptr<MCCodeEmitter> &&Emitter,
                                      bool RelaxAll) {
   return createARMELFStreamer(
-      Ctx, std::move(MAB), OS, std::move(Emitter), false,
+      Ctx, std::move(MAB), std::move(OW), std::move(Emitter), false,
       (T.getArch() == Triple::thumb || T.getArch() == Triple::thumbeb));
 }
 
 static MCStreamer *
 createARMMachOStreamer(MCContext &Ctx, std::unique_ptr<MCAsmBackend> &&MAB,
-                       raw_pwrite_stream &OS,
+                       std::unique_ptr<MCObjectWriter> &&OW,
                        std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll,
                        bool DWARFMustBeAtTheEnd) {
-  return createMachOStreamer(Ctx, std::move(MAB), OS, std::move(Emitter), false,
-                             DWARFMustBeAtTheEnd);
+  return createMachOStreamer(Ctx, std::move(MAB), std::move(OW),
+                             std::move(Emitter), false, DWARFMustBeAtTheEnd);
 }
 
 static MCInstPrinter *createARMMCInstPrinter(const Triple &T,
Index: llvm/lib/Target/ARM/MCTargetDesc/ARMWinCOFFStreamer.cpp
===================================================================
--- llvm/lib/Target/ARM/MCTargetDesc/ARMWinCOFFStreamer.cpp
+++ llvm/lib/Target/ARM/MCTargetDesc/ARMWinCOFFStreamer.cpp
@@ -10,6 +10,7 @@
 #include "ARMMCTargetDesc.h"
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCWinCOFFStreamer.h"
 
 using namespace llvm;
@@ -18,8 +19,9 @@
 class ARMWinCOFFStreamer : public MCWinCOFFStreamer {
 public:
   ARMWinCOFFStreamer(MCContext &C, std::unique_ptr<MCAsmBackend> AB,
-                     std::unique_ptr<MCCodeEmitter> CE, raw_pwrite_stream &OS)
-      : MCWinCOFFStreamer(C, std::move(AB), std::move(CE), OS) {}
+                     std::unique_ptr<MCCodeEmitter> CE,
+                     std::unique_ptr<MCObjectWriter> OW)
+      : MCWinCOFFStreamer(C, std::move(AB), std::move(CE), std::move(OW)) {}
 
   void EmitAssemblerFlag(MCAssemblerFlag Flag) override;
   void EmitThumbFunc(MCSymbol *Symbol) override;
@@ -48,10 +50,11 @@
 
 MCStreamer *llvm::createARMWinCOFFStreamer(
     MCContext &Context, std::unique_ptr<MCAsmBackend> &&MAB,
-    raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> &&Emitter,
-    bool RelaxAll, bool IncrementalLinkerCompatible) {
-  auto *S =
-      new ARMWinCOFFStreamer(Context, std::move(MAB), std::move(Emitter), OS);
+    std::unique_ptr<MCObjectWriter> &&OW,
+    std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll,
+    bool IncrementalLinkerCompatible) {
+  auto *S = new ARMWinCOFFStreamer(Context, std::move(MAB), std::move(Emitter),
+                                   std::move(OW));
   S->getAssembler().setIncrementalLinkerCompatible(IncrementalLinkerCompatible);
   return S;
 }
Index: llvm/lib/Target/AVR/MCTargetDesc/AVRMCELFStreamer.h
===================================================================
--- llvm/lib/Target/AVR/MCTargetDesc/AVRMCELFStreamer.h
+++ llvm/lib/Target/AVR/MCTargetDesc/AVRMCELFStreamer.h
@@ -16,6 +16,7 @@
 #include "llvm/MC/MCCodeEmitter.h"
 #include "llvm/MC/MCELFStreamer.h"
 #include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 
 namespace llvm {
 
@@ -27,16 +28,18 @@
 
 public:
   AVRMCELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-                   raw_pwrite_stream &OS,
+                   std::unique_ptr<MCObjectWriter> OW,
                    std::unique_ptr<MCCodeEmitter> Emitter)
-      : MCELFStreamer(Context, std::move(TAB), OS, std::move(Emitter)),
+      : MCELFStreamer(Context, std::move(TAB), std::move(OW),
+                      std::move(Emitter)),
         MCII(createAVRMCInstrInfo()) {}
 
   AVRMCELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-                   raw_pwrite_stream &OS,
+                   std::unique_ptr<MCObjectWriter> OW,
                    std::unique_ptr<MCCodeEmitter> Emitter,
                    MCAssembler *Assembler)
-      : MCELFStreamer(Context, std::move(TAB), OS, std::move(Emitter)),
+      : MCELFStreamer(Context, std::move(TAB), std::move(OW),
+                      std::move(Emitter)),
         MCII(createAVRMCInstrInfo()) {}
 
   void EmitValueForModiferKind(
@@ -46,7 +49,7 @@
 
 MCStreamer *createAVRELFStreamer(Triple const &TT, MCContext &Context,
                                  std::unique_ptr<MCAsmBackend> MAB,
-                                 raw_pwrite_stream &OS,
+                                 std::unique_ptr<MCObjectWriter> OW,
                                  std::unique_ptr<MCCodeEmitter> CE);
 
 } // end namespace llvm
Index: llvm/lib/Target/AVR/MCTargetDesc/AVRMCELFStreamer.cpp
===================================================================
--- llvm/lib/Target/AVR/MCTargetDesc/AVRMCELFStreamer.cpp
+++ llvm/lib/Target/AVR/MCTargetDesc/AVRMCELFStreamer.cpp
@@ -17,6 +17,7 @@
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCSymbol.h"
+#include "llvm/MC/MCObjectWriter.h"
 
 using namespace llvm;
 
@@ -43,9 +44,10 @@
 namespace llvm {
 MCStreamer *createAVRELFStreamer(Triple const &TT, MCContext &Context,
                                  std::unique_ptr<MCAsmBackend> MAB,
-                                 raw_pwrite_stream &OS,
+                                 std::unique_ptr<MCObjectWriter> OW,
                                  std::unique_ptr<MCCodeEmitter> CE) {
-  return new AVRMCELFStreamer(Context, std::move(MAB), OS, std::move(CE));
+  return new AVRMCELFStreamer(Context, std::move(MAB), std::move(OW),
+                              std::move(CE));
 }
 
 } // end namespace llvm
Index: llvm/lib/Target/AVR/MCTargetDesc/AVRMCTargetDesc.cpp
===================================================================
--- llvm/lib/Target/AVR/MCTargetDesc/AVRMCTargetDesc.cpp
+++ llvm/lib/Target/AVR/MCTargetDesc/AVRMCTargetDesc.cpp
@@ -70,11 +70,11 @@
 
 static MCStreamer *createMCStreamer(const Triple &T, MCContext &Context,
                                     std::unique_ptr<MCAsmBackend> &&MAB,
-                                    raw_pwrite_stream &OS,
+                                    std::unique_ptr<MCObjectWriter> &&OW,
                                     std::unique_ptr<MCCodeEmitter> &&Emitter,
                                     bool RelaxAll) {
-  return createELFStreamer(Context, std::move(MAB), OS,
-      std::move(Emitter), RelaxAll);
+  return createELFStreamer(Context, std::move(MAB), std::move(OW),
+                           std::move(Emitter), RelaxAll);
 }
 
 static MCTargetStreamer *
Index: llvm/lib/Target/BPF/MCTargetDesc/BPFMCTargetDesc.cpp
===================================================================
--- llvm/lib/Target/BPF/MCTargetDesc/BPFMCTargetDesc.cpp
+++ llvm/lib/Target/BPF/MCTargetDesc/BPFMCTargetDesc.cpp
@@ -52,10 +52,10 @@
 
 static MCStreamer *createBPFMCStreamer(const Triple &T, MCContext &Ctx,
                                        std::unique_ptr<MCAsmBackend> &&MAB,
-                                       raw_pwrite_stream &OS,
+                                       std::unique_ptr<MCObjectWriter> &&OW,
                                        std::unique_ptr<MCCodeEmitter> &&Emitter,
                                        bool RelaxAll) {
-  return createELFStreamer(Ctx, std::move(MAB), OS, std::move(Emitter),
+  return createELFStreamer(Ctx, std::move(MAB), std::move(OW), std::move(Emitter),
                            RelaxAll);
 }
 
Index: llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCELFStreamer.h
===================================================================
--- llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCELFStreamer.h
+++ llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCELFStreamer.h
@@ -23,11 +23,11 @@
 
 public:
   HexagonMCELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-                       raw_pwrite_stream &OS,
+                       std::unique_ptr<MCObjectWriter> OW,
                        std::unique_ptr<MCCodeEmitter> Emitter);
 
   HexagonMCELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-                       raw_pwrite_stream &OS,
+                       std::unique_ptr<MCObjectWriter> OW,
                        std::unique_ptr<MCCodeEmitter> Emitter,
                        MCAssembler *Assembler);
 
@@ -43,7 +43,7 @@
 
 MCStreamer *createHexagonELFStreamer(Triple const &TT, MCContext &Context,
                                      std::unique_ptr<MCAsmBackend> MAB,
-                                     raw_pwrite_stream &OS,
+                                     std::unique_ptr<MCObjectWriter> OW,
                                      std::unique_ptr<MCCodeEmitter> CE);
 
 } // end namespace llvm
Index: llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCELFStreamer.cpp
===================================================================
--- llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCELFStreamer.cpp
+++ llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCELFStreamer.cpp
@@ -25,6 +25,7 @@
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCObjectStreamer.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCStreamer.h"
@@ -47,15 +48,15 @@
 
 HexagonMCELFStreamer::HexagonMCELFStreamer(
     MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-    raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> Emitter)
-    : MCELFStreamer(Context, std::move(TAB), OS, std::move(Emitter)),
+    std::unique_ptr<MCObjectWriter> OW, std::unique_ptr<MCCodeEmitter> Emitter)
+    : MCELFStreamer(Context, std::move(TAB), std::move(OW), std::move(Emitter)),
       MCII(createHexagonMCInstrInfo()) {}
 
 HexagonMCELFStreamer::HexagonMCELFStreamer(
     MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-    raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> Emitter,
+    std::unique_ptr<MCObjectWriter> OW, std::unique_ptr<MCCodeEmitter> Emitter,
     MCAssembler *Assembler)
-    : MCELFStreamer(Context, std::move(TAB), OS, std::move(Emitter)),
+    : MCELFStreamer(Context, std::move(TAB), std::move(OW), std::move(Emitter)),
       MCII(createHexagonMCInstrInfo()) {}
 
 void HexagonMCELFStreamer::EmitInstruction(const MCInst &MCB,
@@ -151,9 +152,10 @@
 namespace llvm {
 MCStreamer *createHexagonELFStreamer(Triple const &TT, MCContext &Context,
                                      std::unique_ptr<MCAsmBackend> MAB,
-                                     raw_pwrite_stream &OS,
+                                     std::unique_ptr<MCObjectWriter> OW,
                                      std::unique_ptr<MCCodeEmitter> CE) {
-  return new HexagonMCELFStreamer(Context, std::move(MAB), OS, std::move(CE));
+  return new HexagonMCELFStreamer(Context, std::move(MAB), std::move(OW),
+                                  std::move(CE));
   }
 
 } // end namespace llvm
Index: llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCTargetDesc.cpp
===================================================================
--- llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCTargetDesc.cpp
+++ llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCTargetDesc.cpp
@@ -29,6 +29,7 @@
 #include "llvm/MC/MCELFStreamer.h"
 #include "llvm/MC/MCInstrAnalysis.h"
 #include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
@@ -248,10 +249,10 @@
 
 static MCStreamer *createMCStreamer(Triple const &T, MCContext &Context,
                                     std::unique_ptr<MCAsmBackend> &&MAB,
-                                    raw_pwrite_stream &OS,
+                                    std::unique_ptr<MCObjectWriter> &&OW,
                                     std::unique_ptr<MCCodeEmitter> &&Emitter,
                                     bool RelaxAll) {
-  return createHexagonELFStreamer(T, Context, std::move(MAB), OS,
+  return createHexagonELFStreamer(T, Context, std::move(MAB), std::move(OW),
                                   std::move(Emitter));
 }
 
Index: llvm/lib/Target/Lanai/MCTargetDesc/LanaiMCTargetDesc.cpp
===================================================================
--- llvm/lib/Target/Lanai/MCTargetDesc/LanaiMCTargetDesc.cpp
+++ llvm/lib/Target/Lanai/MCTargetDesc/LanaiMCTargetDesc.cpp
@@ -61,14 +61,14 @@
 
 static MCStreamer *createMCStreamer(const Triple &T, MCContext &Context,
                                     std::unique_ptr<MCAsmBackend> &&MAB,
-                                    raw_pwrite_stream &OS,
+                                    std::unique_ptr<MCObjectWriter> &&OW,
                                     std::unique_ptr<MCCodeEmitter> &&Emitter,
                                     bool RelaxAll) {
   if (!T.isOSBinFormatELF())
     llvm_unreachable("OS not supported");
 
-  return createELFStreamer(Context, std::move(MAB), OS, std::move(Emitter),
-                           RelaxAll);
+  return createELFStreamer(Context, std::move(MAB), std::move(OW),
+                           std::move(Emitter), RelaxAll);
 }
 
 static MCInstPrinter *createLanaiMCInstPrinter(const Triple & /*T*/,
Index: llvm/lib/Target/Mips/MCTargetDesc/MipsELFStreamer.h
===================================================================
--- llvm/lib/Target/Mips/MCTargetDesc/MipsELFStreamer.h
+++ llvm/lib/Target/Mips/MCTargetDesc/MipsELFStreamer.h
@@ -34,7 +34,7 @@
 
 public:
   MipsELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
-                  raw_pwrite_stream &OS,
+                  std::unique_ptr<MCObjectWriter> OW,
                   std::unique_ptr<MCCodeEmitter> Emitter);
 
   /// Overriding this function allows us to add arbitrary behaviour before the
@@ -67,7 +67,7 @@
 
 MCELFStreamer *createMipsELFStreamer(MCContext &Context,
                                      std::unique_ptr<MCAsmBackend> MAB,
-                                     raw_pwrite_stream &OS,
+                                     std::unique_ptr<MCObjectWriter> OW,
                                      std::unique_ptr<MCCodeEmitter> Emitter,
                                      bool RelaxAll);
 } // end namespace llvm
Index: llvm/lib/Target/Mips/MCTargetDesc/MipsELFStreamer.cpp
===================================================================
--- llvm/lib/Target/Mips/MCTargetDesc/MipsELFStreamer.cpp
+++ llvm/lib/Target/Mips/MCTargetDesc/MipsELFStreamer.cpp
@@ -16,6 +16,7 @@
 #include "llvm/MC/MCCodeEmitter.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCSymbolELF.h"
 #include "llvm/Support/Casting.h"
 
@@ -23,9 +24,10 @@
 
 MipsELFStreamer::MipsELFStreamer(MCContext &Context,
                                  std::unique_ptr<MCAsmBackend> MAB,
-                                 raw_pwrite_stream &OS,
+                                 std::unique_ptr<MCObjectWriter> OW,
                                  std::unique_ptr<MCCodeEmitter> Emitter)
-    : MCELFStreamer(Context, std::move(MAB), OS, std::move(Emitter)) {
+    : MCELFStreamer(Context, std::move(MAB), std::move(OW),
+                    std::move(Emitter)) {
   RegInfoRecord = new MipsRegInfoRecord(this, Context);
   MipsOptionRecords.push_back(
       std::unique_ptr<MipsRegInfoRecord>(RegInfoRecord));
@@ -91,7 +93,8 @@
 
 MCELFStreamer *llvm::createMipsELFStreamer(
     MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
-    raw_pwrite_stream &OS, std::unique_ptr<MCCodeEmitter> Emitter,
+    std::unique_ptr<MCObjectWriter> OW, std::unique_ptr<MCCodeEmitter> Emitter,
     bool RelaxAll) {
-  return new MipsELFStreamer(Context, std::move(MAB), OS, std::move(Emitter));
+  return new MipsELFStreamer(Context, std::move(MAB), std::move(OW),
+                             std::move(Emitter));
 }
Index: llvm/lib/Target/Mips/MCTargetDesc/MipsMCNaCl.h
===================================================================
--- llvm/lib/Target/Mips/MCTargetDesc/MipsMCNaCl.h
+++ llvm/lib/Target/Mips/MCTargetDesc/MipsMCNaCl.h
@@ -24,7 +24,7 @@
 // This function creates an MCELFStreamer for Mips NaCl.
 MCELFStreamer *createMipsNaClELFStreamer(MCContext &Context,
                                          std::unique_ptr<MCAsmBackend> TAB,
-                                         raw_pwrite_stream &OS,
+                                         std::unique_ptr<MCObjectWriter> OW,
                                          std::unique_ptr<MCCodeEmitter> Emitter,
                                          bool RelaxAll);
 }
Index: llvm/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
===================================================================
--- llvm/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
+++ llvm/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
@@ -23,6 +23,7 @@
 #include "llvm/MC/MCELFStreamer.h"
 #include "llvm/MC/MCInstrAnalysis.h"
 #include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCSymbol.h"
@@ -93,15 +94,15 @@
 
 static MCStreamer *createMCStreamer(const Triple &T, MCContext &Context,
                                     std::unique_ptr<MCAsmBackend> &&MAB,
-                                    raw_pwrite_stream &OS,
+                                    std::unique_ptr<MCObjectWriter> &&OW,
                                     std::unique_ptr<MCCodeEmitter> &&Emitter,
                                     bool RelaxAll) {
   MCStreamer *S;
   if (!T.isOSNaCl())
-    S = createMipsELFStreamer(Context, std::move(MAB), OS, std::move(Emitter),
-                              RelaxAll);
+    S = createMipsELFStreamer(Context, std::move(MAB), std::move(OW),
+                              std::move(Emitter), RelaxAll);
   else
-    S = createMipsNaClELFStreamer(Context, std::move(MAB), OS,
+    S = createMipsNaClELFStreamer(Context, std::move(MAB), std::move(OW),
                                   std::move(Emitter), RelaxAll);
   return S;
 }
Index: llvm/lib/Target/Mips/MCTargetDesc/MipsNaClELFStreamer.cpp
===================================================================
--- llvm/lib/Target/Mips/MCTargetDesc/MipsNaClELFStreamer.cpp
+++ llvm/lib/Target/Mips/MCTargetDesc/MipsNaClELFStreamer.cpp
@@ -25,6 +25,7 @@
 #include "llvm/MC/MCCodeEmitter.h"
 #include "llvm/MC/MCELFStreamer.h"
 #include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/Support/ErrorHandling.h"
 #include <cassert>
 
@@ -43,9 +44,10 @@
 class MipsNaClELFStreamer : public MipsELFStreamer {
 public:
   MipsNaClELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
-                      raw_pwrite_stream &OS,
+                      std::unique_ptr<MCObjectWriter> OW,
                       std::unique_ptr<MCCodeEmitter> Emitter)
-      : MipsELFStreamer(Context, std::move(TAB), OS, std::move(Emitter)) {}
+      : MipsELFStreamer(Context, std::move(TAB), std::move(OW),
+                        std::move(Emitter)) {}
 
   ~MipsNaClELFStreamer() override = default;
 
@@ -260,11 +262,11 @@
 
 MCELFStreamer *createMipsNaClELFStreamer(MCContext &Context,
                                          std::unique_ptr<MCAsmBackend> TAB,
-                                         raw_pwrite_stream &OS,
+                                         std::unique_ptr<MCObjectWriter> OW,
                                          std::unique_ptr<MCCodeEmitter> Emitter,
                                          bool RelaxAll) {
-  MipsNaClELFStreamer *S =
-      new MipsNaClELFStreamer(Context, std::move(TAB), OS, std::move(Emitter));
+  MipsNaClELFStreamer *S = new MipsNaClELFStreamer(
+      Context, std::move(TAB), std::move(OW), std::move(Emitter));
   if (RelaxAll)
     S->getAssembler().setRelaxAll(true);
 
Index: llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.h
===================================================================
--- llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.h
+++ llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.h
@@ -96,7 +96,7 @@
 /// Takes ownership of \p AB and \p CE.
 MCStreamer *createX86WinCOFFStreamer(MCContext &C,
                                      std::unique_ptr<MCAsmBackend> &&AB,
-                                     raw_pwrite_stream &OS,
+                                     std::unique_ptr<MCObjectWriter> &&OW,
                                      std::unique_ptr<MCCodeEmitter> &&CE,
                                      bool RelaxAll,
                                      bool IncrementalLinkerCompatible);
Index: llvm/lib/Target/X86/MCTargetDesc/X86WinCOFFStreamer.cpp
===================================================================
--- llvm/lib/Target/X86/MCTargetDesc/X86WinCOFFStreamer.cpp
+++ llvm/lib/Target/X86/MCTargetDesc/X86WinCOFFStreamer.cpp
@@ -11,6 +11,7 @@
 #include "X86TargetStreamer.h"
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCWin64EH.h"
 #include "llvm/MC/MCWinCOFFStreamer.h"
 
@@ -21,8 +22,9 @@
   Win64EH::UnwindEmitter EHStreamer;
 public:
   X86WinCOFFStreamer(MCContext &C, std::unique_ptr<MCAsmBackend> AB,
-                     std::unique_ptr<MCCodeEmitter> CE, raw_pwrite_stream &OS)
-      : MCWinCOFFStreamer(C, std::move(AB), std::move(CE), OS) {}
+                     std::unique_ptr<MCCodeEmitter> CE,
+                     std::unique_ptr<MCObjectWriter> OW)
+      : MCWinCOFFStreamer(C, std::move(AB), std::move(CE), std::move(OW)) {}
 
   void EmitWinEHHandlerData(SMLoc Loc) override;
   void EmitWindowsUnwindTables() override;
@@ -60,12 +62,12 @@
 
 MCStreamer *llvm::createX86WinCOFFStreamer(MCContext &C,
                                            std::unique_ptr<MCAsmBackend> &&AB,
-                                           raw_pwrite_stream &OS,
+                                           std::unique_ptr<MCObjectWriter> &&OW,
                                            std::unique_ptr<MCCodeEmitter> &&CE,
                                            bool RelaxAll,
                                            bool IncrementalLinkerCompatible) {
   X86WinCOFFStreamer *S =
-      new X86WinCOFFStreamer(C, std::move(AB), std::move(CE), OS);
+      new X86WinCOFFStreamer(C, std::move(AB), std::move(CE), std::move(OW));
   S->getAssembler().setRelaxAll(RelaxAll);
   S->getAssembler().setIncrementalLinkerCompatible(IncrementalLinkerCompatible);
   return S;
Index: llvm/tools/dsymutil/DwarfLinker.cpp
===================================================================
--- llvm/tools/dsymutil/DwarfLinker.cpp
+++ llvm/tools/dsymutil/DwarfLinker.cpp
@@ -52,6 +52,7 @@
 #include "llvm/MC/MCDwarf.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCStreamer.h"
@@ -882,9 +883,9 @@
 
   MCTargetOptions MCOptions = InitMCTargetOptionsFromFlags();
   MS = TheTarget->createMCObjectStreamer(
-      TheTriple, *MC, std::unique_ptr<MCAsmBackend>(MAB), OutFile,
-      std::unique_ptr<MCCodeEmitter>(MCE), *MSTI, MCOptions.MCRelaxAll,
-      MCOptions.MCIncrementalLinkerCompatible,
+      TheTriple, *MC, std::unique_ptr<MCAsmBackend>(MAB),
+      MAB->createObjectWriter(OutFile), std::unique_ptr<MCCodeEmitter>(MCE),
+      *MSTI, MCOptions.MCRelaxAll, MCOptions.MCIncrementalLinkerCompatible,
       /*DWARFMustBeAtTheEnd*/ false);
   if (!MS)
     return error("no object streamer for target " + TripleName, Context);
Index: llvm/tools/llvm-dwp/llvm-dwp.cpp
===================================================================
--- llvm/tools/llvm-dwp/llvm-dwp.cpp
+++ llvm/tools/llvm-dwp/llvm-dwp.cpp
@@ -24,6 +24,7 @@
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCTargetOptionsCommandFlags.inc"
@@ -701,9 +702,9 @@
 
   MCTargetOptions MCOptions = InitMCTargetOptionsFromFlags();
   std::unique_ptr<MCStreamer> MS(TheTarget->createMCObjectStreamer(
-      TheTriple, MC, std::unique_ptr<MCAsmBackend>(MAB), OutFile,
-      std::unique_ptr<MCCodeEmitter>(MCE), *MSTI, MCOptions.MCRelaxAll,
-      MCOptions.MCIncrementalLinkerCompatible,
+      TheTriple, MC, std::unique_ptr<MCAsmBackend>(MAB),
+      MAB->createObjectWriter(OutFile), std::unique_ptr<MCCodeEmitter>(MCE),
+      *MSTI, MCOptions.MCRelaxAll, MCOptions.MCIncrementalLinkerCompatible,
       /*DWARFMustBeAtTheEnd*/ false));
   if (!MS)
     return error("no object streamer for target " + TripleName, Context);
Index: llvm/tools/llvm-mc/llvm-mc.cpp
===================================================================
--- llvm/tools/llvm-mc/llvm-mc.cpp
+++ llvm/tools/llvm-mc/llvm-mc.cpp
@@ -20,6 +20,7 @@
 #include "llvm/MC/MCInstPrinter.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCParser/AsmLexer.h"
 #include "llvm/MC/MCParser/MCTargetAsmParser.h"
 #include "llvm/MC/MCRegisterInfo.h"
@@ -467,9 +468,9 @@
     MCCodeEmitter *CE = TheTarget->createMCCodeEmitter(*MCII, *MRI, Ctx);
     MCAsmBackend *MAB = TheTarget->createMCAsmBackend(*STI, *MRI, MCOptions);
     Str.reset(TheTarget->createMCObjectStreamer(
-        TheTriple, Ctx, std::unique_ptr<MCAsmBackend>(MAB), *OS,
-        std::unique_ptr<MCCodeEmitter>(CE), *STI, MCOptions.MCRelaxAll,
-        MCOptions.MCIncrementalLinkerCompatible,
+        TheTriple, Ctx, std::unique_ptr<MCAsmBackend>(MAB),
+        MAB->createObjectWriter(*OS), std::unique_ptr<MCCodeEmitter>(CE), *STI,
+        MCOptions.MCRelaxAll, MCOptions.MCIncrementalLinkerCompatible,
         /*DWARFMustBeAtTheEnd*/ false));
     if (NoExecStack)
       Str->InitSections(true);
Index: llvm/unittests/DebugInfo/DWARF/DwarfGenerator.cpp
===================================================================
--- llvm/unittests/DebugInfo/DWARF/DwarfGenerator.cpp
+++ llvm/unittests/DebugInfo/DWARF/DwarfGenerator.cpp
@@ -22,6 +22,7 @@
 #include "llvm/MC/MCDwarf.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
@@ -400,9 +401,9 @@
   Stream = make_unique<raw_svector_ostream>(FileBytes);
 
   MS = TheTarget->createMCObjectStreamer(
-      TheTriple, *MC, std::unique_ptr<MCAsmBackend>(MAB), *Stream,
-      std::unique_ptr<MCCodeEmitter>(MCE), *MSTI, MCOptions.MCRelaxAll,
-      MCOptions.MCIncrementalLinkerCompatible,
+      TheTriple, *MC, std::unique_ptr<MCAsmBackend>(MAB),
+      MAB->createObjectWriter(*Stream), std::unique_ptr<MCCodeEmitter>(MCE),
+      *MSTI, MCOptions.MCRelaxAll, MCOptions.MCIncrementalLinkerCompatible,
       /*DWARFMustBeAtTheEnd*/ false);
   if (!MS)
     return make_error<StringError>("no object streamer for target " +