[COFF, ARM64] Add support for Windows ARM64 COFF format

[mgrang]

Summary

This is the llvm part of the initial implementation to support Windows ARM64 COFF format.
I will gradually add more functionality in subsequent patches.

[mgrang]

Here is the clang part of this patch: https://reviews.llvm.org/D34706

[compnerd]

Please add a check for the incremental link compatible flag.

[ruiu]

lib/Target/AArch64/AArch64MCInstLower.cpp

168

Remove else as the last if ends with return.

lib/Target/AArch64/AArch64MCInstLower.h

46

Fix indentation

lib/Target/AArch64/AArch64TargetMachine.cpp

170

Ditto

lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFObjectWriter.cpp

50–51

For now, remove switch and default.

[mgrang]

Comments addressed.

[ruiu]

I'm no expert of this code, but as Saleem has already LGTMed, I think you can go ahead to submit.

lib/Object/COFFObjectFile.cpp

1221

Sort alphabetically.

lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFStreamer.cpp

23

Is this the correct indentation? Please use clang-format-diff on your patch so that we don't need to worry about formatting.

lib/Object/COFFObjectFile.cpp

case COFF::IMAGE_FILE_MACHINE_ARMNT:
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM_MOV32T);
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM_BRANCH20T);
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM_BRANCH24T);
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM_BLX23T);
     default:
       Res = "Unknown";
     }
     break;
+  case COFF::IMAGE_FILE_MACHINE_ARM64:
+    switch (Reloc->Type) {
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_ABSOLUTE);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_ADDR32);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_ADDR32NB);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_BRANCH26);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_PAGEBASE_REL21);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_REL21);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_PAGEOFFSET_12A);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_PAGEOFFSET_12L);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_SECREL);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_SECREL_LOW12A);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_SECREL_HIGH12A);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_SECREL_LOW12L);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_TOKEN);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_SECTION);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_ADDR64);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_BRANCH19);
+    LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_BRANCH14);
+    default:
+      Res = "Unknown";
+    }
+    break;
   case COFF::IMAGE_FILE_MACHINE_I386:
     switch (Reloc->Type) {
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_I386_ABSOLUTE);
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_I386_DIR16);
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_I386_REL16);
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_I386_DIR32);
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_I386_DIR32NB);
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_I386_SEG12);

lib/Target/AArch64/AArch64MCInstLower.h

public:
 
   bool lowerOperand(const MachineOperand &MO, MCOperand &MCOp) const;
   void Lower(const MachineInstr *MI, MCInst &OutMI) const;
 
   MCOperand lowerSymbolOperandDarwin(const MachineOperand &MO,
                                      MCSymbol *Sym) const;
   MCOperand lowerSymbolOperandELF(const MachineOperand &MO,
                                   MCSymbol *Sym) const;
+  MCOperand lowerSymbolOperandCOFF(const MachineOperand &MO,
+                                  MCSymbol *Sym) const;
   MCOperand LowerSymbolOperand(const MachineOperand &MO, MCSymbol *Sym) const;
 
   MCSymbol *GetGlobalAddressSymbol(const MachineOperand &MO) const;
   MCSymbol *GetExternalSymbolSymbol(const MachineOperand &MO) const;
 };
 }
 
 #endif

lib/Target/AArch64/AArch64MCInstLower.cpp

MCOperand AArch64MCInstLower::lowerSymbolOperandELF(const MachineOperand &MO,
 
   AArch64MCExpr::VariantKind RefKind;
   RefKind = static_cast<AArch64MCExpr::VariantKind>(RefFlags);
   Expr = AArch64MCExpr::create(Expr, RefKind, Ctx);
 
   return MCOperand::createExpr(Expr);
 }
 
+MCOperand AArch64MCInstLower::lowerSymbolOperandCOFF(const MachineOperand &MO,
+                                                     MCSymbol *Sym) const {
+  MCSymbolRefExpr::VariantKind RefKind = MCSymbolRefExpr::VK_None;
+  const MCExpr *Expr = MCSymbolRefExpr::create(Sym, RefKind, Ctx);
+  if (!MO.isJTI() && MO.getOffset())
+    Expr = MCBinaryExpr::createAdd(
+        Expr, MCConstantExpr::create(MO.getOffset(), Ctx), Ctx);
+  return MCOperand::createExpr(Expr);
+}
+
 MCOperand AArch64MCInstLower::LowerSymbolOperand(const MachineOperand &MO,
                                                  MCSymbol *Sym) const {
   if (Printer.TM.getTargetTriple().isOSDarwin())
     return lowerSymbolOperandDarwin(MO, Sym);
+  else if (Printer.TM.getTargetTriple().isOSBinFormatCOFF())
+    return lowerSymbolOperandCOFF(MO, Sym);
 
   assert(Printer.TM.getTargetTriple().isOSBinFormatELF() &&
-         "Expect Darwin or ELF target");
+         "Expect Darwin, ELF or COFF target");
   return lowerSymbolOperandELF(MO, Sym);
 }
 
 bool AArch64MCInstLower::lowerOperand(const MachineOperand &MO,
                                       MCOperand &MCOp) const {
   switch (MO.getType()) {
   default:
     llvm_unreachable("unknown operand type");

lib/Target/AArch64/AArch64TargetMachine.cpp

 }
 
 //===----------------------------------------------------------------------===//
 // AArch64 Lowering public interface.
 //===----------------------------------------------------------------------===//
 static std::unique_ptr<TargetLoweringObjectFile> createTLOF(const Triple &TT) {
   if (TT.isOSBinFormatMachO())
     return llvm::make_unique<AArch64_MachoTargetObjectFile>();
+  else if (TT.isOSBinFormatCOFF())
+    return llvm::make_unique<AArch64_COFFTargetObjectFile>();
 
   return llvm::make_unique<AArch64_ELFTargetObjectFile>();
 }
 
 // Helper function to build a DataLayout string
 static std::string computeDataLayout(const Triple &TT,
                                      const MCTargetOptions &Options,
                                      bool LittleEndian) {
   if (Options.getABIName() == "ilp32")
     return "e-m:e-p:32:32-i8:8-i16:16-i64:64-S128";
   if (TT.isOSBinFormatMachO())
     return "e-m:o-i64:64-i128:128-n32:64-S128";
+  if (TT.isOSBinFormatCOFF())
+    return "e-m:w-i64:64-i128:128-n32:64-S128";
   if (LittleEndian)
     return "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128";
   return "E-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128";
 }
 
 static Reloc::Model getEffectiveRelocModel(const Triple &TT,
                                            Optional<Reloc::Model> RM) {
   // AArch64 Darwin is always PIC.

lib/Target/AArch64/AArch64TargetObjectFile.h

const MCExpr *getIndirectSymViaGOTPCRel(const MCSymbol *Sym,
                                           const MCValue &MV, int64_t Offset,
                                           MachineModuleInfo *MMI,
                                           MCStreamer &Streamer) const override;
 
   void getNameWithPrefix(SmallVectorImpl<char> &OutName, const GlobalValue *GV,
                          const TargetMachine &TM) const override;
 };
 
+/// This implementation is used for AArch64 COFF targets.
+class AArch64_COFFTargetObjectFile : public TargetLoweringObjectFileCOFF {};
+
 } // end namespace llvm
 
 #endif

lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp

void ELFAArch64AsmBackend::processFixupValue(const MCAssembler &Asm,
   // section isn't 0x1000-aligned, we therefore need to delegate this decision
   // to the linker -- a relocation!
   if ((uint32_t)Fixup.getKind() == AArch64::fixup_aarch64_pcrel_adrp_imm21)
     IsResolved = false;
 }
 
 }
 
+namespace {
+class COFFAArch64AsmBackend : public AArch64AsmBackend {
+public:
+  COFFAArch64AsmBackend(const Target &T, const Triple &TheTriple)
+      : AArch64AsmBackend(T, /*IsLittleEndian*/true) {}
+
+  MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const override {
+    return createAArch64WinCOFFObjectWriter(OS);
+  }
+};
+}
+
 MCAsmBackend *llvm::createAArch64leAsmBackend(const Target &T,
                                               const MCRegisterInfo &MRI,
                                               const Triple &TheTriple,
                                               StringRef CPU,
                                               const MCTargetOptions &Options) {
   if (TheTriple.isOSBinFormatMachO())
     return new DarwinAArch64AsmBackend(T, MRI);
 
-  assert(TheTriple.isOSBinFormatELF() && "Expect either MachO or ELF target");
+  if (TheTriple.isOSBinFormatCOFF())
+    return new COFFAArch64AsmBackend(T, TheTriple);
+
+  assert(TheTriple.isOSBinFormatELF() &&
+         "Expect either MachO, ELF or COFF target");
+
   uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TheTriple.getOS());
   bool IsILP32 = Options.getABIName() == "ilp32";
   return new ELFAArch64AsmBackend(T, OSABI, /*IsLittleEndian=*/true, IsILP32);
 }
 
 MCAsmBackend *llvm::createAArch64beAsmBackend(const Target &T,
                                               const MCRegisterInfo &MRI,
                                               const Triple &TheTriple,
                                               StringRef CPU,
                                               const MCTargetOptions &Options) {
   assert(TheTriple.isOSBinFormatELF() &&
          "Big endian is only supported for ELF targets!");
   uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TheTriple.getOS());
   bool IsILP32 = Options.getABIName() == "ilp32";
   return new ELFAArch64AsmBackend(T, OSABI, /*IsLittleEndian=*/false, IsILP32);
 }

lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp

 //===- lib/MC/AArch64ELFStreamer.cpp - ELF Object Output for AArch64 ------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file assembles .s files and emits AArch64 ELF .o object files. Different
 // from generic ELF streamer in emitting mapping symbols ($x and $d) to delimit
 // regions of data and code.
 //
 //===----------------------------------------------------------------------===//
 
 #include "AArch64TargetStreamer.h"
+#include "AArch64WinCOFFStreamer.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCCodeEmitter.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCELFStreamer.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCSymbolELF.h"
+#include "llvm/MC/MCWinCOFFStreamer.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/FormattedStream.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
 
 namespace {
 
MCELFStreamer *createAArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB,
   return S;
 }
 
 MCTargetStreamer *
 createAArch64ObjectTargetStreamer(MCStreamer &S, const MCSubtargetInfo &STI) {
   const Triple &TT = STI.getTargetTriple();
   if (TT.isOSBinFormatELF())
     return new AArch64TargetELFStreamer(S);
+  if (TT.isOSBinFormatCOFF())
+    return new AArch64TargetWinCOFFStreamer(S);
   return nullptr;
 }
 
 } // end namespace llvm

lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.h

 // This file contains the declaration of the AArch64MCAsmInfo class.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIB_TARGET_AARCH64_MCTARGETDESC_AARCH64MCASMINFO_H
 #define LLVM_LIB_TARGET_AARCH64_MCTARGETDESC_AARCH64MCASMINFO_H
 
 #include "llvm/MC/MCAsmInfoDarwin.h"
+#include "llvm/MC/MCAsmInfoCOFF.h"
 #include "llvm/MC/MCAsmInfoELF.h"
 
 namespace llvm {
 class MCStreamer;
 class Target;
 class Triple;
 
 struct AArch64MCAsmInfoDarwin : public MCAsmInfoDarwin {
   explicit AArch64MCAsmInfoDarwin();
   const MCExpr *
   getExprForPersonalitySymbol(const MCSymbol *Sym, unsigned Encoding,
                               MCStreamer &Streamer) const override;
 };
 
 struct AArch64MCAsmInfoELF : public MCAsmInfoELF {
   explicit AArch64MCAsmInfoELF(const Triple &T);
 };
 
+struct AArch64MCAsmInfoCOFF : public MCAsmInfoCOFF {
+  explicit AArch64MCAsmInfoCOFF();
+};
+
 } // namespace llvm
 
 #endif

lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp

AArch64MCAsmInfoELF::AArch64MCAsmInfoELF(const Triple &T) {
 
   // Exceptions handling
   ExceptionsType = ExceptionHandling::DwarfCFI;
 
   UseIntegratedAssembler = true;
 
   HasIdentDirective = true;
 }
+
+AArch64MCAsmInfoCOFF::AArch64MCAsmInfoCOFF() {
+  CommentString = ";";
+}

lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.h

MCObjectWriter *createAArch64ELFObjectWriter(raw_pwrite_stream &OS,
                                              uint8_t OSABI,
                                              bool IsLittleEndian,
                                              bool IsILP32);
 
 MCObjectWriter *createAArch64MachObjectWriter(raw_pwrite_stream &OS,
                                               uint32_t CPUType,
                                               uint32_t CPUSubtype);
 
+MCObjectWriter *createAArch64WinCOFFObjectWriter(raw_pwrite_stream &OS);
+
 MCTargetStreamer *createAArch64AsmTargetStreamer(MCStreamer &S,
                                                  formatted_raw_ostream &OS,
                                                  MCInstPrinter *InstPrint,
                                                  bool isVerboseAsm);
 
 MCTargetStreamer *createAArch64ObjectTargetStreamer(MCStreamer &S,
                                                     const MCSubtargetInfo &STI);
 

lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp

 //===-- AArch64MCTargetDesc.cpp - AArch64 Target Descriptions ---*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file provides AArch64 specific target descriptions.
 //
 //===----------------------------------------------------------------------===//
 
 #include "AArch64MCTargetDesc.h"
 #include "AArch64ELFStreamer.h"
 #include "AArch64MCAsmInfo.h"
+#include "AArch64WinCOFFStreamer.h"
 #include "InstPrinter/AArch64InstPrinter.h"
 #include "llvm/MC/MCInstrAnalysis.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/TargetRegistry.h"
static MCRegisterInfo *createAArch64MCRegisterInfo(const Triple &Triple) {
   return X;
 }
 
 static MCAsmInfo *createAArch64MCAsmInfo(const MCRegisterInfo &MRI,
                                          const Triple &TheTriple) {
   MCAsmInfo *MAI;
   if (TheTriple.isOSBinFormatMachO())
     MAI = new AArch64MCAsmInfoDarwin();
+  else if (TheTriple.isOSBinFormatCOFF())
+    MAI = new AArch64MCAsmInfoCOFF();
   else {
-    assert(TheTriple.isOSBinFormatELF() && "Only expect Darwin or ELF");
+    assert(TheTriple.isOSBinFormatELF() && "Only expect Darwin, ELF or COFF");
     MAI = new AArch64MCAsmInfoELF(TheTriple);
   }
 
   // Initial state of the frame pointer is SP.
   unsigned Reg = MRI.getDwarfRegNum(AArch64::SP, true);
   MCCFIInstruction Inst = MCCFIInstruction::createDefCfa(nullptr, Reg, 0);
   MAI->addInitialFrameState(Inst);
 
   return MAI;
 }
 
 static void adjustCodeGenOpts(const Triple &TT, Reloc::Model RM,
                               CodeModel::Model &CM) {
-  assert((TT.isOSBinFormatELF() || TT.isOSBinFormatMachO()) &&
-         "Only expect Darwin and ELF targets");
+  assert((TT.isOSBinFormatELF() || TT.isOSBinFormatMachO() ||
+          TT.isOSBinFormatCOFF()) &&
+         "Only expect Darwin, ELF and COFF targets");
 
   if (CM == CodeModel::Default)
     CM = CodeModel::Small;
   // The default MCJIT memory managers make no guarantees about where they can
   // find an executable page; JITed code needs to be able to refer to globals
   // no matter how far away they are.
   else if (CM == CodeModel::JITDefault)
     CM = CodeModel::Large;
static MCStreamer *createMachOStreamer(MCContext &Ctx, MCAsmBackend &TAB,
                                        raw_pwrite_stream &OS,
                                        MCCodeEmitter *Emitter, bool RelaxAll,
                                        bool DWARFMustBeAtTheEnd) {
   return createMachOStreamer(Ctx, TAB, OS, Emitter, RelaxAll,
                              DWARFMustBeAtTheEnd,
                              /*LabelSections*/ true);
 }
 
+static MCStreamer *createWinCOFFStreamer(MCContext &Ctx, MCAsmBackend &TAB,
+                                         raw_pwrite_stream &OS,
+                                         MCCodeEmitter *Emitter, bool RelaxAll,
+                                         bool IncrementalLinkerCompatible) {
+  return createAArch64WinCOFFStreamer(Ctx, TAB, OS, Emitter, RelaxAll,
+                                      IncrementalLinkerCompatible);
+}
+
 static MCInstrAnalysis *createAArch64InstrAnalysis(const MCInstrInfo *Info) {
   return new MCInstrAnalysis(Info);
 }
 
 // Force static initialization.
 extern "C" void LLVMInitializeAArch64TargetMC() {
   for (Target *T : {&getTheAArch64leTarget(), &getTheAArch64beTarget(),
                     &getTheARM64Target()}) {
for (Target *T : {&getTheAArch64leTarget(), &getTheAArch64beTarget(),
     TargetRegistry::RegisterMCInstrAnalysis(*T, createAArch64InstrAnalysis);
 
     // Register the MC Code Emitter
     TargetRegistry::RegisterMCCodeEmitter(*T, createAArch64MCCodeEmitter);
 
     // Register the obj streamers.
     TargetRegistry::RegisterELFStreamer(*T, createELFStreamer);
     TargetRegistry::RegisterMachOStreamer(*T, createMachOStreamer);
+    TargetRegistry::RegisterCOFFStreamer(*T, createWinCOFFStreamer);
 
     // Register the obj target streamer.
     TargetRegistry::RegisterObjectTargetStreamer(
         *T, createAArch64ObjectTargetStreamer);
 
     // Register the asm streamer.
     TargetRegistry::RegisterAsmTargetStreamer(*T,
                                               createAArch64AsmTargetStreamer);

lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFObjectWriter.cpp

+//= AArch64WinCOFFObjectWriter.cpp - AArch64 Windows COFF Object Writer C++ =//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===---------------------------------------------------------------------===//
+
+#include "MCTargetDesc/AArch64FixupKinds.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/BinaryFormat/COFF.h"
+#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCFixup.h"
+#include "llvm/MC/MCFixupKindInfo.h"
+#include "llvm/MC/MCValue.h"
+#include "llvm/MC/MCWinCOFFObjectWriter.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+#include <cassert>
+
+using namespace llvm;
+
+namespace {
+
+class AArch64WinCOFFObjectWriter : public MCWinCOFFObjectTargetWriter {
+public:
+  AArch64WinCOFFObjectWriter()
+    : MCWinCOFFObjectTargetWriter(COFF::IMAGE_FILE_MACHINE_ARM64) {
+  }
+
+  ~AArch64WinCOFFObjectWriter() override = default;
+
+  unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
+                        const MCFixup &Fixup, bool IsCrossSection,
+                        const MCAsmBackend &MAB) const override;
+
+   bool recordRelocation(const MCFixup &) const override;
+};
+
+} // end anonymous namespace
+
+unsigned
+AArch64WinCOFFObjectWriter::getRelocType(MCContext &Ctx,
+                                         const MCValue &Target,
+                                         const MCFixup &Fixup,
+                                         bool IsCrossSection,
+                                         const MCAsmBackend &MAB) const {
+  switch (static_cast<unsigned>(Fixup.getKind())) {
+    default: {
+      const MCFixupKindInfo &Info = MAB.getFixupKindInfo(Fixup.getKind());
+      report_fatal_error(Twine("unsupported relocation type: ") + Info.Name);
+    }
+  }
+}
+
+bool AArch64WinCOFFObjectWriter::recordRelocation(const MCFixup &Fixup) const {
+  return true;
+}
+
+namespace llvm {
+
+MCObjectWriter *createAArch64WinCOFFObjectWriter(raw_pwrite_stream &OS) {
+  MCWinCOFFObjectTargetWriter *MOTW = new AArch64WinCOFFObjectWriter();
+  return createWinCOFFObjectWriter(MOTW, OS);
+}
+
+} // end namespace llvm

lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFStreamer.h

+//===-- AArch64WinCOFFStreamer.h - WinCOFF Streamer for AArch64 -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements WinCOFF streamer information for the AArch64 backend.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_AARCH64_MCTARGETDESC_AARCH64WINCOFFSTREAMER_H
+#define LLVM_LIB_TARGET_AARCH64_MCTARGETDESC_AARCH64WINCOFFSTREAMER_H
+
+#include "AArch64TargetStreamer.h"
+#include "llvm/MC/MCWinCOFFStreamer.h"
+
+namespace {
+class AArch64WinCOFFStreamer;
+
+class AArch64TargetWinCOFFStreamer : public llvm::AArch64TargetStreamer {
+private:
+  AArch64WinCOFFStreamer &getStreamer();
+
+public:
+  AArch64TargetWinCOFFStreamer(llvm::MCStreamer &S)
+    : AArch64TargetStreamer(S) {}
+};
+
+} // end anonymous namespace
+
+namespace llvm {
+
+MCWinCOFFStreamer
+*createAArch64WinCOFFStreamer(MCContext &Context, MCAsmBackend &TAB,
+                              raw_pwrite_stream &OS,
+                              MCCodeEmitter *Emitter, bool RelaxAll,
+                              bool IncrementalLinkerCompatible);
+} // end llvm namespace
+
+#endif

lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFStreamer.cpp

+//===-- AArch64WinCOFFStreamer.cpp - ARM Target WinCOFF Streamer ----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AArch64WinCOFFStreamer.h"
+
+using namespace llvm;
+
+namespace {
+
+class AArch64WinCOFFStreamer : public MCWinCOFFStreamer {
+public:
+  friend class AArch64TargetWinCOFFStreamer;
+
+  AArch64WinCOFFStreamer(MCContext &C, MCAsmBackend &AB, MCCodeEmitter &CE,
+                        raw_pwrite_stream &OS)
+      : MCWinCOFFStreamer(C, AB, CE, OS) {}
+};
+} // end anonymous namespace
+
+namespace llvm {
+MCWinCOFFStreamer
+*createAArch64WinCOFFStreamer(MCContext &Context, MCAsmBackend &MAB,
+                              raw_pwrite_stream &OS,
+                              MCCodeEmitter *Emitter, bool RelaxAll,
+                              bool IncrementalLinkerCompatible) {
+  auto *S = new AArch64WinCOFFStreamer(Context, MAB, *Emitter, OS);
+  S->getAssembler().setIncrementalLinkerCompatible(IncrementalLinkerCompatible);
+  return S;
+}
+
+} // end llvm namespace

lib/Target/AArch64/MCTargetDesc/CMakeLists.txt

 add_llvm_library(LLVMAArch64Desc
   AArch64AsmBackend.cpp
   AArch64ELFObjectWriter.cpp
   AArch64ELFStreamer.cpp
   AArch64MCAsmInfo.cpp
   AArch64MCCodeEmitter.cpp
   AArch64MCExpr.cpp
   AArch64MCTargetDesc.cpp
   AArch64MachObjectWriter.cpp
   AArch64TargetStreamer.cpp
+  AArch64WinCOFFObjectWriter.cpp
+  AArch64WinCOFFStreamer.cpp
 )
 add_dependencies(LLVMAArch64Desc AArch64CommonTableGen)
 
 # Hack: we need to include 'main' target directory to grab private headers
 include_directories(${CMAKE_CURRENT_SOURCE_DIR}/.. ${CMAKE_CURRENT_BINARY_DIR}/..)

test/MC/AArch64/coff-basic.ll

+; RUN: llc -mtriple aarch64-windows < %s | FileCheck %s
+
+define i32 @foo() {
+entry:
+  ret i32 1
+}
+
+; CHECK: .globl foo