[WebAssembly] Add skeleton MC support for the Wasm container format

[sunfish]

Summary

As we discussed at the LLVM developer meeting, here's the first patch adding the first level of infrastructure for writing Wasm container files via MC. It's quite incomplete, as I've pulled out most of the actual encoding functionality in order to keep the patch size manageable.

[sunfish]

ping

[sunfish]

• rebase on trunk
• instead of converting WebAssembly from ELF to Wasm binary format, add Wasm as an option, leaving ELF enabled and the default. This allows existing ELF-based use cases to continue working for now.

[pcc]

Just a couple of drive by comments.

lib/MC/WasmObjectWriter.cpp

115

It looks like this code was just copied from the ELF object writer. Do you need section symbol support in the wasm object format? Section symbols cause bugs such as http://lists.llvm.org/pipermail/llvm-dev/2016-March/097064.html so you might want to consider not supporting them.

131

Same here: is symbol versioning a necessary feature of the wasm object format?

[sunfish]

• remove section symbols
• misc. cleanups

[sunfish]

lib/MC/WasmObjectWriter.cpp

115

Ah, thanks for pointing that out about section symbols. I think you're right that we don't need section symbols, at least for now, so it seems safe to omit them.

131

Symbol versioning is desirable functionality. We don't have to do it like ELF does, but that seemed like a reasonable place to start. Are you aware of similar bugs involving ELF symbol versioning?

[pcc]

lib/MC/WasmObjectWriter.cpp

131

Not specifically bugs of that kind, but bear in mind that symbol versioning as implemented in ELF is rather complex and requires co-operation from the linker and the dynamic loader, so I'd imagine that an implementation that uses .symver would require spec changes, and if you're going to make a spec change you might want to consider a simpler design first.

For example, you might consider just having version numbers rather than names, and letting the versions be symbol attributes rather than being represented using aliases.

[sunfish]

Your suggestion to move symbol versioning out of the symbol names makes sense. I've removed those parts of the patch now.

Also, this rebases the patch on trunk.

[sunfish]

ping

[sunfish]

ping

[rnk]

This doesn't have any tests. Is this enough to get llvm-mc to make an object file, or does it need more work?

[sunfish]

All the code for actually writing any bytes has been factored out into followup patches -- WasmObjectWriter::writeObject and WasmObjectWriter::writeHeader are empty -- so there's nothing to test yet.

[rnk]

In in favor of landing this. I think with one more +1 you'll be good to go.

lib/MC/MCWasmStreamer.cpp

189

We should sink all of these calls to unreachable into MCStreamer, and tweak the message to be something like:

this directive only supported on COFF targets

lib/MC/WasmObjectWriter.cpp

80

seems unused

[sunfish]

ping

[t.p.northover]

Some minor comments, but I couldn't see anything immediately wrong with these patches. It's a bit difficult to see the wood for the trees though, with some bits being implemented, some semi-stubs and some complete assertion failures.

include/llvm/MC/MCSectionWasm.h

28–29

Stale comment.

lib/MC/MCWasmStreamer.cpp

86

I have a strong suspicion that only MachO has indirect symbols. Certainly when I put an llvm_unreachable in the ELF equivalent of this block nothing broke.

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp

101–102

Is this really necessary? It's basically exactly what the for loop is doing below.

116

llvm::alignTo does this.

[sunfish]

Address review comments.

[sunfish]

lib/MC/MCWasmStreamer.cpp

86

Sounds good. I removed the indirect symbols code and added a similar assert.

lib/MC/WasmObjectWriter.cpp

80

removed

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp

101–102

removed

116

Updated to use alignTo.

[sunfish]

In D26722#672525, @t.p.northover wrote:

Some minor comments, but I couldn't see anything immediately wrong with these patches. It's a bit difficult to see the wood for the trees though, with some bits being implemented, some semi-stubs and some complete assertion failures.

Thanks for taking a look! I am hoping to fill in all of the pieces in a series of incremental patches on top of this one. This patch is the base that everything else will build on, so it seemed to make sense to do this first. But I'd be happy to take a different approach if it'd help.

[sunfish]

Friendly ping :-).

[t.p.northover]

Sorry about the delay. I think this looks good now, so go for it!

include/llvm/CodeGen/TargetLoweringObjectFileImpl.h

MCSection *getStaticCtorSection(unsigned Priority,
                                   const MCSymbol *KeySym) const override;
   MCSection *getStaticDtorSection(unsigned Priority,
                                   const MCSymbol *KeySym) const override;
 
   void emitLinkerFlagsForGlobal(raw_ostream &OS,
                                 const GlobalValue *GV) const override;
 };
 
+class TargetLoweringObjectFileWasm : public TargetLoweringObjectFile {
+public:
+  TargetLoweringObjectFileWasm() {}
+
+  ~TargetLoweringObjectFileWasm() override {}
+
+  MCSection *getExplicitSectionGlobal(const GlobalObject *GO, SectionKind Kind,
+                                      const TargetMachine &TM) const override;
+
+  MCSection *SelectSectionForGlobal(const GlobalObject *GO, SectionKind Kind,
+                                    const TargetMachine &TM) const override;
+
+  bool shouldPutJumpTableInFunctionSection(bool UsesLabelDifference,
+                                           const Function &F) const override;
+
+  void InitializeWasm();
+
+  const MCExpr *lowerRelativeReference(const GlobalValue *LHS,
+                                       const GlobalValue *RHS,
+                                       const TargetMachine &TM) const override;
+};
+
 } // end namespace llvm
 
 #endif

include/llvm/MC/MCAsmInfoWasm.h

+//===-- llvm/MC/MCAsmInfoWasm.h - Wasm Asm info -----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCASMINFOWASM_H
+#define LLVM_MC_MCASMINFOWASM_H
+
+#include "llvm/MC/MCAsmInfo.h"
+
+namespace llvm {
+class MCAsmInfoWasm : public MCAsmInfo {
+  virtual void anchor();
+
+protected:
+  MCAsmInfoWasm();
+};
+}
+
+#endif

include/llvm/MC/MCContext.h

 #include <vector> // FIXME: Shouldn't be needed.
 
 namespace llvm {
   class MCAsmInfo;
   class MCExpr;
   class MCSection;
   class MCSymbol;
   class MCSymbolELF;
+  class MCSymbolWasm;
   class MCLabel;
   struct MCDwarfFile;
   class MCDwarfLoc;
   class MCObjectFileInfo;
   class MCRegisterInfo;
   class MCLineSection;
   class SMLoc;
   class MCSectionMachO;
   class MCSectionELF;
   class MCSectionCOFF;
+  class MCSectionWasm;
   class CodeViewContext;
 
   /// Context object for machine code objects.  This class owns all of the
   /// sections that it creates.
   ///
   class MCContext {
     MCContext(const MCContext &) = delete;
     MCContext &operator=(const MCContext &) = delete;
private:
     ///
     /// We use a bump pointer allocator to avoid the need to track all allocated
     /// objects.
     BumpPtrAllocator Allocator;
 
     SpecificBumpPtrAllocator<MCSectionCOFF> COFFAllocator;
     SpecificBumpPtrAllocator<MCSectionELF> ELFAllocator;
     SpecificBumpPtrAllocator<MCSectionMachO> MachOAllocator;
+    SpecificBumpPtrAllocator<MCSectionWasm> WasmAllocator;
 
     /// Bindings of names to symbols.
     SymbolTable Symbols;
 
     /// Sections can have a corresponding symbol. This maps one to the
     /// other.
     DenseMap<const MCSection *, MCSymbol *> SectionSymbols;
 
struct COFFSectionKey {
         if (GroupName != Other.GroupName)
           return GroupName < Other.GroupName;
         if (SelectionKey != Other.SelectionKey)
           return SelectionKey < Other.SelectionKey;
         return UniqueID < Other.UniqueID;
       }
     };
 
+    struct WasmSectionKey {
+      std::string SectionName;
+      StringRef GroupName;
+      unsigned UniqueID;
+      WasmSectionKey(StringRef SectionName, StringRef GroupName,
+                     unsigned UniqueID)
+          : SectionName(SectionName), GroupName(GroupName), UniqueID(UniqueID) {
+      }
+      bool operator<(const WasmSectionKey &Other) const {
+        if (SectionName != Other.SectionName)
+          return SectionName < Other.SectionName;
+        if (GroupName != Other.GroupName)
+          return GroupName < Other.GroupName;
+        return UniqueID < Other.UniqueID;
+      }
+    };
+
     StringMap<MCSectionMachO *> MachOUniquingMap;
     std::map<ELFSectionKey, MCSectionELF *> ELFUniquingMap;
     std::map<COFFSectionKey, MCSectionCOFF *> COFFUniquingMap;
-    StringMap<bool> ELFRelSecNames;
+    std::map<WasmSectionKey, MCSectionWasm *> WasmUniquingMap;
+    StringMap<bool> RelSecNames;
 
     SpecificBumpPtrAllocator<MCSubtargetInfo> MCSubtargetAllocator;
 
     /// Do automatic reset in destructor
     bool AutoReset;
 
     bool HadError;
 
public:
     /// Gets or creates a section equivalent to Sec that is associated with the
     /// section containing KeySym. For example, to create a debug info section
     /// associated with an inline function, pass the normal debug info section
     /// as Sec and the function symbol as KeySym.
     MCSectionCOFF *
     getAssociativeCOFFSection(MCSectionCOFF *Sec, const MCSymbol *KeySym,
                               unsigned UniqueID = GenericSectionID);
 
+    MCSectionWasm *getWasmSection(const Twine &Section, unsigned Type,
+                                  unsigned Flags) {
+      return getWasmSection(Section, Type, Flags, nullptr);
+    }
+
+    MCSectionWasm *getWasmSection(const Twine &Section, unsigned Type,
+                                  unsigned Flags, const char *BeginSymName) {
+      return getWasmSection(Section, Type, Flags, "", BeginSymName);
+    }
+
+    MCSectionWasm *getWasmSection(const Twine &Section, unsigned Type,
+                                  unsigned Flags, const Twine &Group) {
+      return getWasmSection(Section, Type, Flags, Group, nullptr);
+    }
+
+    MCSectionWasm *getWasmSection(const Twine &Section, unsigned Type,
+                                  unsigned Flags, const Twine &Group,
+                                  const char *BeginSymName) {
+      return getWasmSection(Section, Type, Flags, Group, ~0, BeginSymName);
+    }
+
+    MCSectionWasm *getWasmSection(const Twine &Section, unsigned Type,
+                                  unsigned Flags, const Twine &Group,
+                                  unsigned UniqueID) {
+      return getWasmSection(Section, Type, Flags, Group, UniqueID, nullptr);
+    }
+
+    MCSectionWasm *getWasmSection(const Twine &Section, unsigned Type,
+                                  unsigned Flags, const Twine &Group,
+                                  unsigned UniqueID, const char *BeginSymName);
+
+    MCSectionWasm *getWasmSection(const Twine &Section, unsigned Type,
+                                  unsigned Flags, const MCSymbolWasm *Group,
+                                  unsigned UniqueID, const char *BeginSymName);
+
+    /// Get a section with the provided group identifier. This section is
+    /// named by concatenating \p Prefix with '.' then \p Suffix. The \p Type
+    /// describes the type of the section and \p Flags are used to further
+    /// configure this named section.
+    MCSectionWasm *getWasmNamedSection(const Twine &Prefix, const Twine &Suffix,
+                                       unsigned Type, unsigned Flags);
+
+    MCSectionWasm *createWasmRelSection(const Twine &Name, unsigned Type,
+                                        unsigned Flags,
+                                        const MCSymbolWasm *Group);
+
+    void renameWasmSection(MCSectionWasm *Section, StringRef Name);
+
     // Create and save a copy of STI and return a reference to the copy.
     MCSubtargetInfo &getSubtargetCopy(const MCSubtargetInfo &STI);
 
     /// @}
 
     /// \name Dwarf Management
     /// @{
 

include/llvm/MC/MCObjectFileInfo.h

protected:
   MCSection *COFFDebugTypesSection;
 
   /// Extra TLS Variable Data section.
   ///
   /// If the target needs to put additional information for a TLS variable,
   /// it'll go here.
   MCSection *TLSExtraDataSection;
 
-  /// Section directive for Thread Local data. ELF, MachO and COFF.
+  /// Section directive for Thread Local data. ELF, MachO, COFF, and Wasm.
   MCSection *TLSDataSection; // Defaults to ".tdata".
 
   /// Section directive for Thread Local uninitialized data.
   ///
   /// Null if this target doesn't support a BSS section. ELF and MachO only.
   MCSection *TLSBSSSection; // Defaults to ".tbss".
 
   /// StackMap section.
public:
   MCSection *getPDataSection() const { return PDataSection; }
   MCSection *getXDataSection() const { return XDataSection; }
   MCSection *getSXDataSection() const { return SXDataSection; }
 
   MCSection *getEHFrameSection() {
     return EHFrameSection;
   }
 
-  enum Environment { IsMachO, IsELF, IsCOFF };
+  enum Environment { IsMachO, IsELF, IsCOFF, IsWasm };
   Environment getObjectFileType() const { return Env; }
 
   bool isPositionIndependent() const { return PositionIndependent; }
 
 private:
   Environment Env;
   bool PositionIndependent;
   CodeModel::Model CMModel;
   MCContext *Ctx;
   Triple TT;
 
   void initMachOMCObjectFileInfo(const Triple &T);
   void initELFMCObjectFileInfo(const Triple &T);
   void initCOFFMCObjectFileInfo(const Triple &T);
+  void initWasmMCObjectFileInfo(const Triple &T);
 
 public:
   const Triple &getTargetTriple() const { return TT; }
 };
 
 } // end namespace llvm
 
 #endif

include/llvm/MC/MCSection.h

 template <> struct ilist_alloc_traits<MCFragment> {
   static void deleteNode(MCFragment *V);
 };
 
 /// Instances of this class represent a uniqued identifier for a section in the
 /// current translation unit.  The MCContext class uniques and creates these.
 class MCSection {
 public:
-  enum SectionVariant { SV_COFF = 0, SV_ELF, SV_MachO };
+  enum SectionVariant { SV_COFF = 0, SV_ELF, SV_MachO, SV_Wasm };
 
   /// \brief Express the state of bundle locked groups while emitting code.
   enum BundleLockStateType {
     NotBundleLocked,
     BundleLocked,
     BundleLockedAlignToEnd
   };
 

include/llvm/MC/MCSectionWasm.h

+//===- MCSectionWasm.h - Wasm Machine Code Sections -------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the MCSectionWasm class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCSECTIONWASM_H
+#define LLVM_MC_MCSECTIONWASM_H
+
+#include "llvm/ADT/Twine.h"
+#include "llvm/MC/MCSection.h"
+#include "llvm/MC/MCSymbolWasm.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace llvm {
+
+class MCSymbol;
+
+/// This represents a section on linux, lots of unix variants and some bare
+/// metal systems.
+class MCSectionWasm final : public MCSection {
+  /// This is the name of the section.  The referenced memory is owned by
+  /// TargetLoweringObjectFileWasm's WasmUniqueMap.
+  StringRef SectionName;
+
+  /// This is the sh_type field of a section, drawn from the enums below.
+  unsigned Type;
+
+  /// This is the sh_flags field of a section, drawn from the enums below.
+  unsigned Flags;
+
+  unsigned UniqueID;
+
+  const MCSymbolWasm *Group;
+
+private:
+  friend class MCContext;
+  MCSectionWasm(StringRef Section, unsigned type, unsigned flags, SectionKind K,
+                const MCSymbolWasm *group, unsigned UniqueID, MCSymbol *Begin)
+      : MCSection(SV_Wasm, K, Begin), SectionName(Section), Type(type),
+        Flags(flags), UniqueID(UniqueID), Group(group) {
+  }
+
+  void setSectionName(StringRef Name) { SectionName = Name; }
+
+public:
+  ~MCSectionWasm();
+
+  /// Decides whether a '.section' directive should be printed before the
+  /// section name
+  bool ShouldOmitSectionDirective(StringRef Name, const MCAsmInfo &MAI) const;
+
+  StringRef getSectionName() const { return SectionName; }
+  unsigned getType() const { return Type; }
+  unsigned getFlags() const { return Flags; }
+  void setFlags(unsigned F) { Flags = F; }
+  const MCSymbolWasm *getGroup() const { return Group; }
+
+  void PrintSwitchToSection(const MCAsmInfo &MAI, raw_ostream &OS,
+                            const MCExpr *Subsection) const override;
+  bool UseCodeAlign() const override;
+  bool isVirtualSection() const override;
+
+  bool isUnique() const { return UniqueID != ~0U; }
+  unsigned getUniqueID() const { return UniqueID; }
+
+  static bool classof(const MCSection *S) { return S->getVariant() == SV_Wasm; }
+};
+
+} // end namespace llvm
+
+#endif

include/llvm/MC/MCStreamer.h

 class MCContext;
 class MCExpr;
 class MCInst;
 class MCInstPrinter;
 class MCSection;
 class MCStreamer;
 class MCSymbolELF;
 class MCSymbolRefExpr;
+class MCSymbolWasm;
 class MCSubtargetInfo;
 class StringRef;
 class Twine;
 class raw_ostream;
 class formatted_raw_ostream;
 class AssemblerConstantPools;
 
 typedef std::pair<MCSection *, const MCExpr *> MCSectionSubPair;

include/llvm/MC/MCSymbol.h

 protected:
   /// The kind of the symbol.  If it is any value other than unset then this
   /// class is actually one of the appropriate subclasses of MCSymbol.
   enum SymbolKind {
     SymbolKindUnset,
     SymbolKindCOFF,
     SymbolKindELF,
     SymbolKindMachO,
+    SymbolKindWasm,
   };
 
   /// A symbol can contain an Offset, or Value, or be Common, but never more
   /// than one of these.
   enum Contents : uint8_t {
     SymContentsUnset,
     SymContentsOffset,
     SymContentsVariable,
protected:
   /// This symbol is visible outside this translation unit.
   mutable unsigned IsExternal : 1;
 
   /// This symbol is private extern.
   mutable unsigned IsPrivateExtern : 1;
 
   /// LLVM RTTI discriminator. This is actually a SymbolKind enumerator, but is
   /// unsigned to avoid sign extension and achieve better bitpacking with MSVC.
-  unsigned Kind : 2;
+  unsigned Kind : 3;
 
   /// True if we have created a relocation that uses this symbol.
   mutable unsigned IsUsedInReloc : 1;
 
   /// This is actually a Contents enumerator, but is unsigned to avoid sign
   /// extension and achieve better bitpacking with MSVC.
   unsigned SymbolContents : 2;
 
public:
   void setUndefined() { FragmentAndHasName.setPointer(nullptr); }
 
   bool isELF() const { return Kind == SymbolKindELF; }
 
   bool isCOFF() const { return Kind == SymbolKindCOFF; }
 
   bool isMachO() const { return Kind == SymbolKindMachO; }
 
+  bool isWasm() const { return Kind == SymbolKindWasm; }
+
   /// @}
   /// \name Variable Symbols
   /// @{
 
   /// isVariable - Check if this is a variable symbol.
   bool isVariable() const {
     return SymbolContents == SymContentsVariable;
   }

include/llvm/MC/MCSymbolWasm.h

+//===- MCSymbolWasm.h -  ----------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_MC_MCSYMBOLWASM_H
+#define LLVM_MC_MCSYMBOLWASM_H
+
+#include "llvm/MC/MCSymbol.h"
+
+namespace llvm {
+class MCSymbolWasm : public MCSymbol {
+public:
+  MCSymbolWasm(const StringMapEntry<bool> *Name, bool isTemporary)
+      : MCSymbol(SymbolKindWasm, Name, isTemporary) {}
+
+  static bool classof(const MCSymbol *S) { return S->isWasm(); }
+};
+}
+
+#endif

include/llvm/MC/MCWasmObjectWriter.h

+//===-- llvm/MC/MCWasmObjectWriter.h - Wasm Object Writer -------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCWASMOBJECTWRITER_H
+#define LLVM_MC_MCWASMOBJECTWRITER_H
+
+#include "llvm/ADT/Triple.h"
+#include "llvm/MC/MCValue.h"
+#include "llvm/Support/DataTypes.h"
+#include "llvm/Support/raw_ostream.h"
+#include <vector>
+
+namespace llvm {
+class MCAssembler;
+class MCContext;
+class MCFixup;
+class MCFragment;
+class MCObjectWriter;
+class MCSymbol;
+class MCSymbolWasm;
+class MCValue;
+class raw_pwrite_stream;
+
+struct WasmRelocationEntry {
+  uint64_t Offset;            // Where is the relocation.
+  const MCSymbolWasm *Symbol; // The symbol to relocate with.
+  unsigned Type;              // The type of the relocation.
+
+  WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol,
+                      unsigned Type)
+      : Offset(Offset), Symbol(Symbol), Type(Type) {}
+
+  void print(raw_ostream &Out) const {
+    Out << "Off=" << Offset << ", Sym=" << Symbol << ", Type=" << Type;
+  }
+  void dump() const { print(errs()); }
+};
+
+class MCWasmObjectTargetWriter {
+  const unsigned Is64Bit : 1;
+
+protected:
+  explicit MCWasmObjectTargetWriter(bool Is64Bit_);
+
+public:
+  virtual ~MCWasmObjectTargetWriter() {}
+
+  virtual unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
+                                const MCFixup &Fixup, bool IsPCRel) const = 0;
+
+  virtual bool needsRelocateWithSymbol(const MCSymbol &Sym,
+                                       unsigned Type) const;
+
+  virtual void sortRelocs(const MCAssembler &Asm,
+                          std::vector<WasmRelocationEntry> &Relocs);
+
+  /// \name Accessors
+  /// @{
+  bool is64Bit() const { return Is64Bit; }
+  /// @}
+};
+
+/// \brief Construct a new Wasm writer instance.
+///
+/// \param MOTW - The target specific Wasm writer subclass.
+/// \param OS - The stream to write to.
+/// \returns The constructed object writer.
+MCObjectWriter *createWasmObjectWriter(MCWasmObjectTargetWriter *MOTW,
+                                       raw_pwrite_stream &OS);
+} // End llvm namespace
+
+#endif

include/llvm/MC/MCWasmStreamer.h

+//===- MCWasmStreamer.h - MCStreamer Wasm Object File Interface -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCWASMSTREAMER_H
+#define LLVM_MC_MCWASMSTREAMER_H
+
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/MC/MCDirectives.h"
+#include "llvm/MC/MCObjectStreamer.h"
+#include "llvm/MC/SectionKind.h"
+#include "llvm/Support/DataTypes.h"
+
+namespace llvm {
+class MCAsmBackend;
+class MCAssembler;
+class MCCodeEmitter;
+class MCExpr;
+class MCInst;
+class raw_ostream;
+
+class MCWasmStreamer : public MCObjectStreamer {
+public:
+  MCWasmStreamer(MCContext &Context, MCAsmBackend &TAB, raw_pwrite_stream &OS,
+                 MCCodeEmitter *Emitter)
+      : MCObjectStreamer(Context, TAB, OS, Emitter), SeenIdent(false) {}
+
+  ~MCWasmStreamer() override;
+
+  /// state management
+  void reset() override {
+    SeenIdent = false;
+    MCObjectStreamer::reset();
+  }
+
+  /// \name MCStreamer Interface
+  /// @{
+
+  void ChangeSection(MCSection *Section, const MCExpr *Subsection) override;
+  void EmitAssemblerFlag(MCAssemblerFlag Flag) override;
+  void EmitThumbFunc(MCSymbol *Func) override;
+  void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) override;
+  bool EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
+  void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) override;
+  void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
+                        unsigned ByteAlignment) override;
+  void BeginCOFFSymbolDef(const MCSymbol *Symbol) override;
+  void EmitCOFFSymbolStorageClass(int StorageClass) override;
+  void EmitCOFFSymbolType(int Type) override;
+  void EndCOFFSymbolDef() override;
+
+  void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
+                             unsigned ByteAlignment) override;
+
+  void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
+                    uint64_t Size = 0, unsigned ByteAlignment = 0) override;
+  void EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol, uint64_t Size,
+                      unsigned ByteAlignment = 0) override;
+  void EmitValueImpl(const MCExpr *Value, unsigned Size,
+                     SMLoc Loc = SMLoc()) override;
+
+  void EmitFileDirective(StringRef Filename) override;
+
+  void EmitIdent(StringRef IdentString) override;
+
+  void EmitValueToAlignment(unsigned, int64_t, unsigned, unsigned) override;
+
+  void FinishImpl() override;
+
+private:
+  void EmitInstToFragment(const MCInst &Inst, const MCSubtargetInfo &) override;
+  void EmitInstToData(const MCInst &Inst, const MCSubtargetInfo &) override;
+
+  /// \brief Merge the content of the fragment \p EF into the fragment \p DF.
+  void mergeFragment(MCDataFragment *, MCDataFragment *);
+
+  bool SeenIdent;
+};
+
+} // end namespace llvm
+
+#endif

include/llvm/Support/TargetRegistry.h

 /// Takes ownership of \p TAB and \p CE.
 MCStreamer *createELFStreamer(MCContext &Ctx, MCAsmBackend &TAB,
                               raw_pwrite_stream &OS, MCCodeEmitter *CE,
                               bool RelaxAll);
 MCStreamer *createMachOStreamer(MCContext &Ctx, MCAsmBackend &TAB,
                                 raw_pwrite_stream &OS, MCCodeEmitter *CE,
                                 bool RelaxAll, bool DWARFMustBeAtTheEnd,
                                 bool LabelSections = false);
+MCStreamer *createWasmStreamer(MCContext &Ctx, MCAsmBackend &TAB,
+                               raw_pwrite_stream &OS, MCCodeEmitter *CE,
+                               bool RelaxAll);
 
 MCRelocationInfo *createMCRelocationInfo(const Triple &TT, MCContext &Ctx);
 
 MCSymbolizer *createMCSymbolizer(const Triple &TT, LLVMOpInfoCallback GetOpInfo,
                                  LLVMSymbolLookupCallback SymbolLookUp,
                                  void *DisInfo, MCContext *Ctx,
                                  std::unique_ptr<MCRelocationInfo> &&RelInfo);
 
typedef MCStreamer *(*MachOStreamerCtorTy)(MCContext &Ctx, MCAsmBackend &TAB,
                                              MCCodeEmitter *Emitter,
                                              bool RelaxAll,
                                              bool DWARFMustBeAtTheEnd);
   typedef MCStreamer *(*COFFStreamerCtorTy)(MCContext &Ctx, MCAsmBackend &TAB,
                                             raw_pwrite_stream &OS,
                                             MCCodeEmitter *Emitter,
                                             bool RelaxAll,
                                             bool IncrementalLinkerCompatible);
+  typedef MCStreamer *(*WasmStreamerCtorTy)(const Triple &T, MCContext &Ctx,
+                                            MCAsmBackend &TAB,
+                                            raw_pwrite_stream &OS,
+                                            MCCodeEmitter *Emitter,
+                                            bool RelaxAll);
   typedef MCTargetStreamer *(*NullTargetStreamerCtorTy)(MCStreamer &S);
   typedef MCTargetStreamer *(*AsmTargetStreamerCtorTy)(
       MCStreamer &S, formatted_raw_ostream &OS, MCInstPrinter *InstPrint,
       bool IsVerboseAsm);
   typedef MCTargetStreamer *(*ObjectTargetStreamerCtorTy)(
       MCStreamer &S, const MCSubtargetInfo &STI);
   typedef MCRelocationInfo *(*MCRelocationInfoCtorTy)(const Triple &TT,
                                                       MCContext &Ctx);
private:
   /// MCCodeEmitterCtorFn - Construction function for this target's
   /// CodeEmitter, if registered.
   MCCodeEmitterCtorTy MCCodeEmitterCtorFn;
 
   // Construction functions for the various object formats, if registered.
   COFFStreamerCtorTy COFFStreamerCtorFn;
   MachOStreamerCtorTy MachOStreamerCtorFn;
   ELFStreamerCtorTy ELFStreamerCtorFn;
+  WasmStreamerCtorTy WasmStreamerCtorFn;
 
   /// Construction function for this target's null TargetStreamer, if
   /// registered (default = nullptr).
   NullTargetStreamerCtorTy NullTargetStreamerCtorFn;
 
   /// Construction function for this target's asm TargetStreamer, if
   /// registered (default = nullptr).
   AsmTargetStreamerCtorTy AsmTargetStreamerCtorFn;
 
   /// Construction function for this target's obj TargetStreamer, if
   /// registered (default = nullptr).
   ObjectTargetStreamerCtorTy ObjectTargetStreamerCtorFn;
 
   /// MCRelocationInfoCtorFn - Construction function for this target's
   /// MCRelocationInfo, if registered (default = llvm::createMCRelocationInfo)
   MCRelocationInfoCtorTy MCRelocationInfoCtorFn;
 
   /// MCSymbolizerCtorFn - Construction function for this target's
   /// MCSymbolizer, if registered (default = llvm::createMCSymbolizer)
   MCSymbolizerCtorTy MCSymbolizerCtorFn;
 
 public:
   Target()
       : COFFStreamerCtorFn(nullptr), MachOStreamerCtorFn(nullptr),
-        ELFStreamerCtorFn(nullptr), NullTargetStreamerCtorFn(nullptr),
+        ELFStreamerCtorFn(nullptr), WasmStreamerCtorFn(nullptr),
+        NullTargetStreamerCtorFn(nullptr),
         AsmTargetStreamerCtorFn(nullptr), ObjectTargetStreamerCtorFn(nullptr),
         MCRelocationInfoCtorFn(nullptr), MCSymbolizerCtorFn(nullptr) {}
 
   /// @name Target Information
   /// @{
 
   // getNext - Return the next registered target.
   const Target *getNext() const { return Next; }
case Triple::MachO:
                                 DWARFMustBeAtTheEnd);
       break;
     case Triple::ELF:
       if (ELFStreamerCtorFn)
         S = ELFStreamerCtorFn(T, Ctx, TAB, OS, Emitter, RelaxAll);
       else
         S = createELFStreamer(Ctx, TAB, OS, Emitter, RelaxAll);
       break;
+    case Triple::Wasm:
+      if (WasmStreamerCtorFn)
+        S = WasmStreamerCtorFn(T, Ctx, TAB, OS, Emitter, RelaxAll);
+      else
+        S = createWasmStreamer(Ctx, TAB, OS, Emitter, RelaxAll);
+      break;
     }
     if (ObjectTargetStreamerCtorFn)
       ObjectTargetStreamerCtorFn(*S, STI);
     return S;
   }
 
   MCStreamer *createAsmStreamer(MCContext &Ctx,
                                 std::unique_ptr<formatted_raw_ostream> OS,
struct TargetRegistry {
   static void RegisterMachOStreamer(Target &T, Target::MachOStreamerCtorTy Fn) {
     T.MachOStreamerCtorFn = Fn;
   }
 
   static void RegisterELFStreamer(Target &T, Target::ELFStreamerCtorTy Fn) {
     T.ELFStreamerCtorFn = Fn;
   }
 
+  static void RegisterWasmStreamer(Target &T, Target::WasmStreamerCtorTy Fn) {
+    T.WasmStreamerCtorFn = Fn;
+  }
+
   static void RegisterNullTargetStreamer(Target &T,
                                          Target::NullTargetStreamerCtorTy Fn) {
     T.NullTargetStreamerCtorFn = Fn;
   }
 
   static void RegisterAsmTargetStreamer(Target &T,
                                         Target::AsmTargetStreamerCtorTy Fn) {
     T.AsmTargetStreamerCtorFn = Fn;

lib/CodeGen/TargetLoweringObjectFileImpl.cpp

 #include "llvm/IR/Mangler.h"
 #include "llvm/IR/Module.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCSectionCOFF.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCSectionMachO.h"
+#include "llvm/MC/MCSectionWasm.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbolELF.h"
+#include "llvm/MC/MCSymbolWasm.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/COFF.h"
 #include "llvm/Support/Dwarf.h"
 #include "llvm/Support/ELF.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetLowering.h"
void TargetLoweringObjectFileCOFF::emitLinkerFlagsForGlobal(
 
   if (!GV->getValueType()->isFunctionTy()) {
     if (TT.isKnownWindowsMSVCEnvironment())
       OS << ",DATA";
     else
       OS << ",data";
   }
 }
+
+//===----------------------------------------------------------------------===//
+//                                  Wasm
+//===----------------------------------------------------------------------===//
+
+MCSection *TargetLoweringObjectFileWasm::getExplicitSectionGlobal(
+    const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
+  llvm_unreachable("getExplicitSectionGlobal not yet implemented");
+  return nullptr;
+}
+
+MCSection *TargetLoweringObjectFileWasm::SelectSectionForGlobal(
+    const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
+  if (Kind.isText())
+    return TextSection;
+  assert(!Kind.isMetadata() && "metadata sections not yet implemented");
+  return DataSection;
+}
+
+bool TargetLoweringObjectFileWasm::shouldPutJumpTableInFunctionSection(
+    bool UsesLabelDifference, const Function &F) const {
+  // We can always create relative relocations, so use another section
+  // that can be marked non-executable.
+  return false;
+}
+
+const MCExpr *TargetLoweringObjectFileWasm::lowerRelativeReference(
+    const GlobalValue *LHS, const GlobalValue *RHS,
+    const TargetMachine &TM) const {
+  // We may only use a PLT-relative relocation to refer to unnamed_addr
+  // functions.
+  if (!LHS->hasGlobalUnnamedAddr() || !LHS->getValueType()->isFunctionTy())
+    return nullptr;
+
+  // Basic sanity checks.
+  if (LHS->getType()->getPointerAddressSpace() != 0 ||
+      RHS->getType()->getPointerAddressSpace() != 0 || LHS->isThreadLocal() ||
+      RHS->isThreadLocal())
+    return nullptr;
+
+  return MCBinaryExpr::createSub(
+      MCSymbolRefExpr::create(TM.getSymbol(LHS), MCSymbolRefExpr::VK_None,
+                              getContext()),
+      MCSymbolRefExpr::create(TM.getSymbol(RHS), getContext()), getContext());
+}
+
+void
+TargetLoweringObjectFileWasm::InitializeWasm() {
+  // TODO: Initialize StaticCtorSection and StaticDtorSection.
+}

lib/MC/CMakeLists.txt

 add_llvm_library(LLVMMC
   ConstantPools.cpp
   ELFObjectWriter.cpp
   MCAsmBackend.cpp
   MCAsmInfo.cpp
   MCAsmInfoCOFF.cpp
   MCAsmInfoDarwin.cpp
   MCAsmInfoELF.cpp
+  MCAsmInfoWasm.cpp
   MCAsmStreamer.cpp
   MCAssembler.cpp
   MCCodeEmitter.cpp
   MCCodeView.cpp
   MCContext.cpp
   MCDwarf.cpp
   MCELFObjectTargetWriter.cpp
   MCELFStreamer.cpp
add_llvm_library(LLVMMC
   MCObjectStreamer.cpp
   MCObjectWriter.cpp
   MCRegisterInfo.cpp
   MCSchedule.cpp
   MCSection.cpp
   MCSectionCOFF.cpp
   MCSectionELF.cpp
   MCSectionMachO.cpp
+  MCSectionWasm.cpp
   MCStreamer.cpp
   MCSubtargetInfo.cpp
   MCSymbol.cpp
   MCSymbolELF.cpp
   MCTargetOptions.cpp
   MCValue.cpp
+  MCWasmObjectTargetWriter.cpp
+  MCWasmStreamer.cpp
   MCWin64EH.cpp
   MCWinEH.cpp
   MachObjectWriter.cpp
   StringTableBuilder.cpp
   SubtargetFeature.cpp
+  WasmObjectWriter.cpp
   WinCOFFObjectWriter.cpp
   WinCOFFStreamer.cpp
 
   ADDITIONAL_HEADER_DIRS
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/MC
   )
 
 add_subdirectory(MCParser)
 add_subdirectory(MCDisassembler)

lib/MC/MCAsmInfoWasm.cpp

+//===-- MCAsmInfoWasm.cpp - Wasm asm properties -----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines target asm properties related what form asm statements
+// should take in general on Wasm-based targets
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCAsmInfoWasm.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCSectionWasm.h"
+using namespace llvm;
+
+void MCAsmInfoWasm::anchor() { }
+
+MCAsmInfoWasm::MCAsmInfoWasm() {
+  HasIdentDirective = true;
+  WeakRefDirective = "\t.weak\t";
+  PrivateGlobalPrefix = ".L";
+  PrivateLabelPrefix = ".L";
+}

lib/MC/MCContext.cpp

 #include "llvm/MC/MCCodeView.h"
 #include "llvm/MC/MCDwarf.h"
 #include "llvm/MC/MCLabel.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSectionCOFF.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCSectionMachO.h"
+#include "llvm/MC/MCSectionWasm.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbolCOFF.h"
 #include "llvm/MC/MCSymbolELF.h"
 #include "llvm/MC/MCSymbolMachO.h"
+#include "llvm/MC/MCSymbolWasm.h"
 #include "llvm/Support/COFF.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ELF.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/SourceMgr.h"
 
MCSymbol *MCContext::createSymbolImpl(const StringMapEntry<bool> *Name,
   if (MOFI) {
     switch (MOFI->getObjectFileType()) {
     case MCObjectFileInfo::IsCOFF:
       return new (Name, *this) MCSymbolCOFF(Name, IsTemporary);
     case MCObjectFileInfo::IsELF:
       return new (Name, *this) MCSymbolELF(Name, IsTemporary);
     case MCObjectFileInfo::IsMachO:
       return new (Name, *this) MCSymbolMachO(Name, IsTemporary);
+    case MCObjectFileInfo::IsWasm:
+      return new (Name, *this) MCSymbolWasm(Name, IsTemporary);
     }
   }
   return new (Name, *this) MCSymbol(MCSymbol::SymbolKindUnset, Name,
                                     IsTemporary);
 }
 
 MCSymbol *MCContext::createSymbol(StringRef Name, bool AlwaysAddSuffix,
                                   bool CanBeUnnamed) {

 
 MCSectionELF *MCContext::createELFRelSection(const Twine &Name, unsigned Type,
                                              unsigned Flags, unsigned EntrySize,
                                              const MCSymbolELF *Group,
                                              const MCSectionELF *Associated) {
   StringMap<bool>::iterator I;
   bool Inserted;
   std::tie(I, Inserted) =
-      ELFRelSecNames.insert(std::make_pair(Name.str(), true));
+      RelSecNames.insert(std::make_pair(Name.str(), true));
 
   return new (ELFAllocator.Allocate())
       MCSectionELF(I->getKey(), Type, Flags, SectionKind::getReadOnly(),
                    EntrySize, Group, true, nullptr, Associated);
 }
 
 MCSectionELF *MCContext::getELFNamedSection(const Twine &Prefix,
                                             const Twine &Suffix, unsigned Type,
return getCOFFSection(Sec->getSectionName(), Characteristics,
                           Sec->getKind(), KeySym->getName(),
                           COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE, UniqueID);
   }
 
   return getCOFFSection(Sec->getSectionName(), Characteristics, Sec->getKind(),
                         "", 0, UniqueID);
 }
 
+void MCContext::renameWasmSection(MCSectionWasm *Section, StringRef Name) {
+  StringRef GroupName;
+  assert(!Section->getGroup() && "not yet implemented");
+
+  unsigned UniqueID = Section->getUniqueID();
+  WasmUniquingMap.erase(
+      WasmSectionKey{Section->getSectionName(), GroupName, UniqueID});
+  auto I = WasmUniquingMap.insert(std::make_pair(
+                                     WasmSectionKey{Name, GroupName, UniqueID},
+                                     Section))
+               .first;
+  StringRef CachedName = I->first.SectionName;
+  const_cast<MCSectionWasm *>(Section)->setSectionName(CachedName);
+}
+
+MCSectionWasm *MCContext::createWasmRelSection(const Twine &Name, unsigned Type,
+                                               unsigned Flags,
+                                               const MCSymbolWasm *Group) {
+  StringMap<bool>::iterator I;
+  bool Inserted;
+  std::tie(I, Inserted) =
+      RelSecNames.insert(std::make_pair(Name.str(), true));
+
+  return new (WasmAllocator.Allocate())
+      MCSectionWasm(I->getKey(), Type, Flags, SectionKind::getReadOnly(),
+                    Group, ~0, nullptr);
+}
+
+MCSectionWasm *MCContext::getWasmNamedSection(const Twine &Prefix,
+                                              const Twine &Suffix, unsigned Type,
+                                              unsigned Flags) {
+  return getWasmSection(Prefix + "." + Suffix, Type, Flags, Suffix);
+}
+
+MCSectionWasm *MCContext::getWasmSection(const Twine &Section, unsigned Type,
+                                         unsigned Flags,
+                                         const Twine &Group, unsigned UniqueID,
+                                         const char *BeginSymName) {
+  MCSymbolWasm *GroupSym = nullptr;
+  if (!Group.isTriviallyEmpty() && !Group.str().empty())
+    GroupSym = cast<MCSymbolWasm>(getOrCreateSymbol(Group));
+
+  return getWasmSection(Section, Type, Flags, GroupSym, UniqueID, BeginSymName);
+}
+
+MCSectionWasm *MCContext::getWasmSection(const Twine &Section, unsigned Type,
+                                         unsigned Flags,
+                                         const MCSymbolWasm *GroupSym,
+                                         unsigned UniqueID,
+                                         const char *BeginSymName) {
+  StringRef Group = "";
+  if (GroupSym)
+    Group = GroupSym->getName();
+  // Do the lookup, if we have a hit, return it.
+  auto IterBool = WasmUniquingMap.insert(
+      std::make_pair(WasmSectionKey{Section.str(), Group, UniqueID}, nullptr));
+  auto &Entry = *IterBool.first;
+  if (!IterBool.second)
+    return Entry.second;
+
+  StringRef CachedName = Entry.first.SectionName;
+
+  SectionKind Kind = SectionKind::getText();
+
+  MCSymbol *Begin = nullptr;
+  if (BeginSymName)
+    Begin = createTempSymbol(BeginSymName, false);
+
+  MCSectionWasm *Result = new (WasmAllocator.Allocate())
+      MCSectionWasm(CachedName, Type, Flags, Kind, GroupSym, UniqueID, Begin);
+  Entry.second = Result;
+  return Result;
+}
+
 MCSubtargetInfo &MCContext::getSubtargetCopy(const MCSubtargetInfo &STI) {
   return *new (MCSubtargetAllocator.Allocate()) MCSubtargetInfo(STI);
 }
 
 //===----------------------------------------------------------------------===//
 // Dwarf Management
 //===----------------------------------------------------------------------===//
 

lib/MC/MCObjectFileInfo.cpp

 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCSectionCOFF.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCSectionMachO.h"
+#include "llvm/MC/MCSectionWasm.h"
 #include "llvm/Support/COFF.h"
 
 using namespace llvm;
 
 static bool useCompactUnwind(const Triple &T) {
   // Only on darwin.
   if (!T.isOSDarwin())
     return false;
TLSDataSection = Ctx->getCOFFSection(
       SectionKind::getData());
 
   StackMapSection = Ctx->getCOFFSection(".llvm_stackmaps",
                                         COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                                             COFF::IMAGE_SCN_MEM_READ,
                                         SectionKind::getReadOnly());
 }
 
+void MCObjectFileInfo::initWasmMCObjectFileInfo(const Triple &T) {
+  // TODO: Set the section types and flags.
+  TextSection = Ctx->getWasmSection("", 0, 0);
+  DataSection = Ctx->getWasmSection("", 0, 0);
+
+  // TODO: Set the section types and flags.
+  DwarfLineSection = Ctx->getWasmSection(".debug_line", 0, 0);
+  DwarfStrSection = Ctx->getWasmSection(".debug_str", 0, 0);
+  DwarfLocSection = Ctx->getWasmSection(".debug_loc", 0, 0);
+  DwarfAbbrevSection = Ctx->getWasmSection(".debug_abbrev", 0, 0, "section_abbrev");
+  DwarfARangesSection = Ctx->getWasmSection(".debug_aranges", 0, 0);
+  DwarfRangesSection = Ctx->getWasmSection(".debug_ranges", 0, 0, "debug_range");
+  DwarfMacinfoSection = Ctx->getWasmSection(".debug_macinfo", 0, 0, "debug_macinfo");
+  DwarfAddrSection = Ctx->getWasmSection(".debug_addr", 0, 0);
+  DwarfCUIndexSection = Ctx->getWasmSection(".debug_cu_index", 0, 0);
+  DwarfTUIndexSection = Ctx->getWasmSection(".debug_tu_index", 0, 0);
+  DwarfInfoSection = Ctx->getWasmSection(".debug_info", 0, 0, "section_info");
+  DwarfFrameSection = Ctx->getWasmSection(".debug_frame", 0, 0);
+  DwarfPubNamesSection = Ctx->getWasmSection(".debug_pubnames", 0, 0);
+  DwarfPubTypesSection = Ctx->getWasmSection(".debug_pubtypes", 0, 0);
+
+  // TODO: Define more sections.
+}
+
 void MCObjectFileInfo::InitMCObjectFileInfo(const Triple &TheTriple, bool PIC,
                                             CodeModel::Model cm,
                                             MCContext &ctx) {
   PositionIndependent = PIC;
   CMModel = cm;
   Ctx = &ctx;
 
   // Common.
case Triple::COFF:
 
     Env = IsCOFF;
     initCOFFMCObjectFileInfo(TT);
     break;
   case Triple::ELF:
     Env = IsELF;
     initELFMCObjectFileInfo(TT);
     break;
+  case Triple::Wasm:
+    Env = IsWasm;
+    initWasmMCObjectFileInfo(TT);
+    break;
   case Triple::UnknownObjectFormat:
     report_fatal_error("Cannot initialize MC for unknown object file format.");
     break;
   }
 }
 
 MCSection *MCObjectFileInfo::getDwarfTypesSection(uint64_t Hash) const {
   return Ctx->getELFSection(".debug_types", ELF::SHT_PROGBITS, ELF::SHF_GROUP,
                             0, utostr(Hash));
 }

lib/MC/MCParser/AsmParser.cpp

case MCObjectFileInfo::IsCOFF:
     break;
   case MCObjectFileInfo::IsMachO:
     PlatformParser.reset(createDarwinAsmParser());
     IsDarwin = true;
     break;
   case MCObjectFileInfo::IsELF:
     PlatformParser.reset(createELFAsmParser());
     break;
+  case MCObjectFileInfo::IsWasm:
+    llvm_unreachable("Wasm parsing not supported yet");
+    break;
   }
 
   PlatformParser->Initialize(*this);
   initializeDirectiveKindMap();
 
   NumOfMacroInstantiations = 0;
 }
 

lib/MC/MCSectionWasm.cpp

+//===- lib/MC/MCSectionWasm.cpp - Wasm Code Section Representation --------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCSectionWasm.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCSymbol.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+MCSectionWasm::~MCSectionWasm() {} // anchor.
+
+// Decides whether a '.section' directive
+// should be printed before the section name.
+bool MCSectionWasm::ShouldOmitSectionDirective(StringRef Name,
+                                               const MCAsmInfo &MAI) const {
+  return MAI.shouldOmitSectionDirective(Name);
+}
+
+static void printName(raw_ostream &OS, StringRef Name) {
+  if (Name.find_first_not_of("0123456789_."
+                             "abcdefghijklmnopqrstuvwxyz"
+                             "ABCDEFGHIJKLMNOPQRSTUVWXYZ") == Name.npos) {
+    OS << Name;
+    return;
+  }
+  OS << '"';
+  for (const char *B = Name.begin(), *E = Name.end(); B < E; ++B) {
+    if (*B == '"') // Unquoted "
+      OS << "\\\"";
+    else if (*B != '\\') // Neither " or backslash
+      OS << *B;
+    else if (B + 1 == E) // Trailing backslash
+      OS << "\\\\";
+    else {
+      OS << B[0] << B[1]; // Quoted character
+      ++B;
+    }
+  }
+  OS << '"';
+}
+
+void MCSectionWasm::PrintSwitchToSection(const MCAsmInfo &MAI, raw_ostream &OS,
+                                         const MCExpr *Subsection) const {
+
+  if (ShouldOmitSectionDirective(SectionName, MAI)) {
+    OS << '\t' << getSectionName();
+    if (Subsection) {
+      OS << '\t';
+      Subsection->print(OS, &MAI);
+    }
+    OS << '\n';
+    return;
+  }
+
+  OS << "\t.section\t";
+  printName(OS, getSectionName());
+  OS << ",\"";
+
+  // TODO: Print section flags.
+
+  OS << '"';
+
+  OS << ',';
+
+  // If comment string is '@', e.g. as on ARM - use '%' instead
+  if (MAI.getCommentString()[0] == '@')
+    OS << '%';
+  else
+    OS << '@';
+
+  // TODO: Print section type.
+
+  if (isUnique())
+    OS << ",unique," << UniqueID;
+
+  OS << '\n';
+
+  if (Subsection) {
+    OS << "\t.subsection\t";
+    Subsection->print(OS, &MAI);
+    OS << '\n';
+  }
+}
+
+bool MCSectionWasm::UseCodeAlign() const { return false; }
+
+bool MCSectionWasm::isVirtualSection() const { return false; }

lib/MC/MCWasmObjectTargetWriter.cpp

+//===-- MCWasmObjectTargetWriter.cpp - Wasm Target Writer Subclass --------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCValue.h"
+#include "llvm/MC/MCWasmObjectWriter.h"
+
+using namespace llvm;
+
+MCWasmObjectTargetWriter::MCWasmObjectTargetWriter(bool Is64Bit_)
+    : Is64Bit(Is64Bit_) {}
+
+bool MCWasmObjectTargetWriter::needsRelocateWithSymbol(const MCSymbol &Sym,
+                                                       unsigned Type) const {
+  return false;
+}
+
+void MCWasmObjectTargetWriter::sortRelocs(
+    const MCAssembler &Asm, std::vector<WasmRelocationEntry> &Relocs) {
+}

lib/MC/MCWasmStreamer.cpp

+//===- lib/MC/MCWasmStreamer.cpp - Wasm Object Output ---------------------===//
+//
+//                     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 Wasm .o object files.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCWasmStreamer.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCAsmLayout.h"
+#include "llvm/MC/MCAssembler.h"
+#include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCObjectStreamer.h"
+#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/MC/MCSection.h"
+#include "llvm/MC/MCSectionWasm.h"
+#include "llvm/MC/MCSymbol.h"
+#include "llvm/MC/MCSymbolWasm.h"
+#include "llvm/MC/MCValue.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/TargetRegistry.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+MCWasmStreamer::~MCWasmStreamer() {}
+
+void MCWasmStreamer::mergeFragment(MCDataFragment *DF, MCDataFragment *EF) {
+  flushPendingLabels(DF, DF->getContents().size());
+
+  for (unsigned i = 0, e = EF->getFixups().size(); i != e; ++i) {
+    EF->getFixups()[i].setOffset(EF->getFixups()[i].getOffset() +
+                                 DF->getContents().size());
+    DF->getFixups().push_back(EF->getFixups()[i]);
+  }
+  DF->setHasInstructions(true);
+  DF->getContents().append(EF->getContents().begin(), EF->getContents().end());
+}
+
+void MCWasmStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
+  // Let the target do whatever target specific stuff it needs to do.
+  getAssembler().getBackend().handleAssemblerFlag(Flag);
+
+  // Do any generic stuff we need to do.
+  llvm_unreachable("invalid assembler flag!");
+}
+
+void MCWasmStreamer::ChangeSection(MCSection *Section,
+                                   const MCExpr *Subsection) {
+  MCAssembler &Asm = getAssembler();
+  auto *SectionWasm = static_cast<const MCSectionWasm *>(Section);
+  const MCSymbol *Grp = SectionWasm->getGroup();
+  if (Grp)
+    Asm.registerSymbol(*Grp);
+
+  this->MCObjectStreamer::ChangeSection(Section, Subsection);
+}
+
+void MCWasmStreamer::EmitWeakReference(MCSymbol *Alias,
+                                       const MCSymbol *Symbol) {
+  getAssembler().registerSymbol(*Symbol);
+  const MCExpr *Value = MCSymbolRefExpr::create(
+      Symbol, MCSymbolRefExpr::VK_WEAKREF, getContext());
+  Alias->setVariableValue(Value);
+}
+
+bool MCWasmStreamer::EmitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
+  auto *Symbol = cast<MCSymbolWasm>(S);
+  // Indirect symbols are handled differently, to match how 'as' handles
+  // them. This makes writing matching .o files easier.
+  if (Attribute == MCSA_IndirectSymbol) {
+    // Note that we intentionally cannot use the symbol data here; this is
+    // important for matching the string table that 'as' generates.
+    IndirectSymbolData ISD;
+    ISD.Symbol = Symbol;
+    ISD.Section = getCurrentSectionOnly();
+    getAssembler().getIndirectSymbols().push_back(ISD);
+    return true;
+  }
+
+  // Adding a symbol attribute always introduces the symbol, note that an
+  // important side effect of calling registerSymbol here is to register
+  // the symbol with the assembler.
+  getAssembler().registerSymbol(*Symbol);
+
+  // TODO: Set the symbol binding, type, etc.
+
+  return true;
+}
+
+void MCWasmStreamer::EmitCommonSymbol(MCSymbol *S, uint64_t Size,
+                                      unsigned ByteAlignment) {
+  llvm_unreachable("Common symbols are not yet implemented for Wasm");
+}
+
+void MCWasmStreamer::EmitLocalCommonSymbol(MCSymbol *S, uint64_t Size,
+                                           unsigned ByteAlignment) {
+  llvm_unreachable("Local common symbols are not yet implemented for Wasm");
+}
+
+void MCWasmStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
+                                   SMLoc Loc) {
+  MCObjectStreamer::EmitValueImpl(Value, Size, Loc);
+}
+
+void MCWasmStreamer::EmitValueToAlignment(unsigned ByteAlignment, int64_t Value,
+                                          unsigned ValueSize,
+                                          unsigned MaxBytesToEmit) {
+  MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value, ValueSize,
+                                         MaxBytesToEmit);
+}
+
+// Add a symbol for the file name of this module. They start after the
+// null symbol and don't count as normal symbol, i.e. a non-STT_FILE symbol
+// with the same name may appear.
+void MCWasmStreamer::EmitFileDirective(StringRef Filename) {
+  getAssembler().addFileName(Filename);
+}
+
+void MCWasmStreamer::EmitIdent(StringRef IdentString) {
+  llvm_unreachable("Ident sections not yet implemented for wasm");
+}
+
+void MCWasmStreamer::EmitInstToFragment(const MCInst &Inst,
+                                        const MCSubtargetInfo &STI) {
+  this->MCObjectStreamer::EmitInstToFragment(Inst, STI);
+}
+
+void MCWasmStreamer::EmitInstToData(const MCInst &Inst,
+                                    const MCSubtargetInfo &STI) {
+  MCAssembler &Assembler = getAssembler();
+  SmallVector<MCFixup, 4> Fixups;
+  SmallString<256> Code;
+  raw_svector_ostream VecOS(Code);
+  Assembler.getEmitter().encodeInstruction(Inst, VecOS, Fixups, STI);
+
+  // Append the encoded instruction to the current data fragment (or create a
+  // new such fragment if the current fragment is not a data fragment).
+  MCDataFragment *DF = getOrCreateDataFragment();
+
+  // Add the fixups and data.
+  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
+    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
+    DF->getFixups().push_back(Fixups[i]);
+  }
+  DF->setHasInstructions(true);
+  DF->getContents().append(Code.begin(), Code.end());
+}
+
+void MCWasmStreamer::FinishImpl() {
+  EmitFrames(nullptr);
+
+  this->MCObjectStreamer::FinishImpl();
+}
+
+MCStreamer *llvm::createWasmStreamer(MCContext &Context, MCAsmBackend &MAB,
+                                     raw_pwrite_stream &OS, MCCodeEmitter *CE,
+                                     bool RelaxAll) {
+  MCWasmStreamer *S = new MCWasmStreamer(Context, MAB, OS, CE);
+  if (RelaxAll)
+    S->getAssembler().setRelaxAll(true);
+  return S;
+}
+
+void MCWasmStreamer::EmitThumbFunc(MCSymbol *Func) {
+  llvm_unreachable("Generic Wasm doesn't support this directive");
+}
+
+void MCWasmStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
+  llvm_unreachable("Wasm doesn't support this directive");
+}
+
+void MCWasmStreamer::BeginCOFFSymbolDef(const MCSymbol *Symbol) {
+  llvm_unreachable("Wasm doesn't support this directive");
+}
+
+void MCWasmStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
+  llvm_unreachable("Wasm doesn't support this directive");
+}
+
+void MCWasmStreamer::EmitCOFFSymbolType(int Type) {
+  llvm_unreachable("Wasm doesn't support this directive");
+}
+
+void MCWasmStreamer::EndCOFFSymbolDef() {
+  llvm_unreachable("Wasm doesn't support this directive");
+}
+
+void MCWasmStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
+                                  uint64_t Size, unsigned ByteAlignment) {
+  llvm_unreachable("Wasm doesn't support this directive");
+}
+
+void MCWasmStreamer::EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
+                                    uint64_t Size, unsigned ByteAlignment) {
+  llvm_unreachable("Wasm doesn't support this directive");
+}

lib/MC/WasmObjectWriter.cpp

+//===- lib/MC/WasmObjectWriter.cpp - Wasm File Writer ---------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements Wasm object file writer information.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCAsmLayout.h"
+#include "llvm/MC/MCAssembler.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCFixupKindInfo.h"
+#include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/MC/MCSectionWasm.h"
+#include "llvm/MC/MCSymbolWasm.h"
+#include "llvm/MC/MCValue.h"
+#include "llvm/MC/MCWasmObjectWriter.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/StringSaver.h"
+#include <vector>
+
+using namespace llvm;
+
+#undef DEBUG_TYPE
+#define DEBUG_TYPE "reloc-info"
+
+namespace {
+typedef DenseMap<const MCSectionWasm *, uint32_t> SectionIndexMapTy;
+
+class WasmObjectWriter : public MCObjectWriter {
+  /// Helper struct for containing some precomputed information on symbols.
+  struct WasmSymbolData {
+    const MCSymbolWasm *Symbol;
+    StringRef Name;
+
+    // Support lexicographic sorting.
+    bool operator<(const WasmSymbolData &RHS) const { return Name < RHS.Name; }
+  };
+
+  /// The target specific Wasm writer instance.
+  std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter;
+
+  DenseMap<const MCSymbolWasm *, const MCSymbolWasm *> Renames;
+
+  /// @}
+  /// @name Symbol Table Data
+  /// @{
+
+  BumpPtrAllocator Alloc;
+  StringSaver VersionSymSaver{Alloc};
+
+  /// @}
+
+  // TargetObjectWriter wrappers.
+  bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
+  unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
+                        const MCFixup &Fixup, bool IsPCRel) const {
+    return TargetObjectWriter->getRelocType(Ctx, Target, Fixup, IsPCRel);
+  }
+
+public:
+  WasmObjectWriter(MCWasmObjectTargetWriter *MOTW, raw_pwrite_stream &OS)
+      : MCObjectWriter(OS, /*IsLittleEndian=*/true), TargetObjectWriter(MOTW) {}
+
+  void reset() override {
+    Renames.clear();
+    MCObjectWriter::reset();
+  }
+
+  ~WasmObjectWriter() override;
+
+  void writeHeader(const MCAssembler &Asm);
+
+  // Fixup offset and size of each section
+  typedef std::map<const MCSectionWasm *, std::pair<uint64_t, uint64_t>>
+      SectionSizesTy;
+
+  void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
+                        const MCFragment *Fragment, const MCFixup &Fixup,
+                        MCValue Target, bool &IsPCRel,
+                        uint64_t &FixedValue) override;
+
+  void executePostLayoutBinding(MCAssembler &Asm,
+                                const MCAsmLayout &Layout) override;
+
+  void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
+};
+} // end anonymous namespace
+
+WasmObjectWriter::~WasmObjectWriter() {}
+
+// Emit the Wasm header.
+void WasmObjectWriter::writeHeader(const MCAssembler &Asm) {
+  // TODO: write the magic cookie and the version.
+}
+
+void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
+                                                const MCAsmLayout &Layout) {
+  // The presence of symbol versions causes undefined symbols and
+  // versions declared with @@@ to be renamed.
+  for (const MCSymbol &A : Asm.symbols()) {
+    const auto &Alias = cast<MCSymbolWasm>(A);
+    // Not an alias.
+    if (!Alias.isVariable())
+      continue;
+    auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
+    if (!Ref)
+      continue;
+    const auto &Symbol = cast<MCSymbolWasm>(Ref->getSymbol());
+
+    StringRef AliasName = Alias.getName();
+    size_t Pos = AliasName.find('@');
+    if (Pos == StringRef::npos)
+      continue;
+
+    // Aliases defined with .symvar copy the binding from the symbol they alias.
+    // This is the first place we are able to copy this information.
+    StringRef Rest = AliasName.substr(Pos);
+    if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
+      continue;
+
+    // FIXME: produce a better error message.
+    if (Symbol.isUndefined() && Rest.startswith("@@") &&
+        !Rest.startswith("@@@"))
+      report_fatal_error("A @@ version cannot be undefined");
+
+    Renames.insert(std::make_pair(&Symbol, &Alias));
+  }
+}
+
+void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
+                                        const MCAsmLayout &Layout,
+                                        const MCFragment *Fragment,
+                                        const MCFixup &Fixup, MCValue Target,
+                                        bool &IsPCRel, uint64_t &FixedValue) {
+  // TODO: Implement
+}
+
+void WasmObjectWriter::writeObject(MCAssembler &Asm,
+                                   const MCAsmLayout &Layout) {
+  // Write out the Wasm header.
+  writeHeader(Asm);
+
+  // TODO: Write the contents.
+}
+
+MCObjectWriter *llvm::createWasmObjectWriter(MCWasmObjectTargetWriter *MOTW,
+                                             raw_pwrite_stream &OS) {
+  return new WasmObjectWriter(MOTW, OS);
+}

lib/Target/ARM/AsmParser/ARMAsmParser.cpp

bool ARMAsmParser::parsePrefix(ARMMCExpr::VariantKind &RefKind) {
   if (getLexer().isNot(AsmToken::Identifier)) {
     Error(Parser.getTok().getLoc(), "expected prefix identifier in operand");
     return true;
   }
 
   enum {
     COFF = (1 << MCObjectFileInfo::IsCOFF),
     ELF = (1 << MCObjectFileInfo::IsELF),
-    MACHO = (1 << MCObjectFileInfo::IsMachO)
+    MACHO = (1 << MCObjectFileInfo::IsMachO),
+    WASM = (1 << MCObjectFileInfo::IsWasm),
   };
   static const struct PrefixEntry {
     const char *Spelling;
     ARMMCExpr::VariantKind VariantKind;
     uint8_t SupportedFormats;
   } PrefixEntries[] = {
     { "lower16", ARMMCExpr::VK_ARM_LO16, COFF | ELF | MACHO },
     { "upper16", ARMMCExpr::VK_ARM_HI16, COFF | ELF | MACHO },
case MCObjectFileInfo::IsMachO:
     CurrentFormat = MACHO;
     break;
   case MCObjectFileInfo::IsELF:
     CurrentFormat = ELF;
     break;
   case MCObjectFileInfo::IsCOFF:
     CurrentFormat = COFF;
     break;
+  case MCObjectFileInfo::IsWasm:
+    CurrentFormat = WASM;
+    break;
   }
 
   if (~Prefix->SupportedFormats & CurrentFormat) {
     Error(Parser.getTok().getLoc(),
           "cannot represent relocation in the current file format");
     return true;
   }
 

lib/Target/WebAssembly/MCTargetDesc/CMakeLists.txt

 add_llvm_library(LLVMWebAssemblyDesc
   WebAssemblyAsmBackend.cpp
   WebAssemblyELFObjectWriter.cpp
   WebAssemblyMCAsmInfo.cpp
   WebAssemblyMCCodeEmitter.cpp
   WebAssemblyMCTargetDesc.cpp
   WebAssemblyTargetStreamer.cpp
+  WebAssemblyWasmObjectWriter.cpp
 )

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp

 ///
 //===----------------------------------------------------------------------===//
 
 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCDirectives.h"
 #include "llvm/MC/MCELFObjectWriter.h"
+#include "llvm/MC/MCWasmObjectWriter.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCFixupKindInfo.h"
 #include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 namespace {
+class WebAssemblyAsmBackendELF final : public MCAsmBackend {
+  bool Is64Bit;
+
+public:
+  explicit WebAssemblyAsmBackendELF(bool Is64Bit)
+      : MCAsmBackend(), Is64Bit(Is64Bit) {}
+  ~WebAssemblyAsmBackendELF() override {}
+
+  void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
+                  uint64_t Value, bool IsPCRel) const override;
+
+  MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const override;
+
+  // No instruction requires relaxation
+  bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
+                            const MCRelaxableFragment *DF,
+                            const MCAsmLayout &Layout) const override {
+    return false;
+  }
+
+  unsigned getNumFixupKinds() const override {
+    // We currently just use the generic fixups in MCFixup.h and don't have any
+    // target-specific fixups.
+    return 0;
+  }
+
+  bool mayNeedRelaxation(const MCInst &Inst) const override { return false; }
+
+  void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
+                        MCInst &Res) const override {}
+
+  bool writeNopData(uint64_t Count, MCObjectWriter *OW) const override;
+};
+
 class WebAssemblyAsmBackend final : public MCAsmBackend {
   bool Is64Bit;
 
 public:
   explicit WebAssemblyAsmBackend(bool Is64Bit)
       : MCAsmBackend(), Is64Bit(Is64Bit) {}
   ~WebAssemblyAsmBackend() override {}
 
public:
   bool mayNeedRelaxation(const MCInst &Inst) const override { return false; }
 
   void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
                         MCInst &Res) const override {}
 
   bool writeNopData(uint64_t Count, MCObjectWriter *OW) const override;
 };
 
+bool WebAssemblyAsmBackendELF::writeNopData(uint64_t Count,
+                                            MCObjectWriter *OW) const {
+  if (Count == 0)
+    return true;
+
+  for (uint64_t i = 0; i < Count; ++i)
+    OW->write8(WebAssembly::Nop);
+
+  return true;
+}
+
+void WebAssemblyAsmBackendELF::applyFixup(const MCFixup &Fixup, char *Data,
+                                          unsigned DataSize, uint64_t Value,
+                                          bool IsPCRel) const {
+  const MCFixupKindInfo &Info = getFixupKindInfo(Fixup.getKind());
+  assert(Info.Flags == 0 && "WebAssembly does not use MCFixupKindInfo flags");
+
+  unsigned NumBytes = (Info.TargetSize + 7) / 8;
+  if (Value == 0)
+    return; // Doesn't change encoding.
+
+  // Shift the value into position.
+  Value <<= Info.TargetOffset;
+
+  unsigned Offset = Fixup.getOffset();
+  assert(Offset + NumBytes <= DataSize && "Invalid fixup offset!");
+
+  // For each byte of the fragment that the fixup touches, mask in the
+  // bits from the fixup value.
+  for (unsigned i = 0; i != NumBytes; ++i)
+    Data[Offset + i] |= uint8_t((Value >> (i * 8)) & 0xff);
+}
+
+MCObjectWriter *
+WebAssemblyAsmBackendELF::createObjectWriter(raw_pwrite_stream &OS) const {
+  return createWebAssemblyELFObjectWriter(OS, Is64Bit, 0);
+}
+
 bool WebAssemblyAsmBackend::writeNopData(uint64_t Count,
                                          MCObjectWriter *OW) const {
   if (Count == 0)
     return true;
 
   for (uint64_t i = 0; i < Count; ++i)
     OW->write8(WebAssembly::Nop);
 
void WebAssemblyAsmBackend::applyFixup(const MCFixup &Fixup, char *Data,
   // For each byte of the fragment that the fixup touches, mask in the
   // bits from the fixup value.
   for (unsigned i = 0; i != NumBytes; ++i)
     Data[Offset + i] |= uint8_t((Value >> (i * 8)) & 0xff);
 }
 
 MCObjectWriter *
 WebAssemblyAsmBackend::createObjectWriter(raw_pwrite_stream &OS) const {
-  return createWebAssemblyELFObjectWriter(OS, Is64Bit, 0);
+  return createWebAssemblyWasmObjectWriter(OS, Is64Bit);
 }
 } // end anonymous namespace
 
 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) {
+  if (TT.isOSBinFormatELF())
+    return new WebAssemblyAsmBackendELF(TT.isArch64Bit());
   return new WebAssemblyAsmBackend(TT.isArch64Bit());
 }

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCAsmInfo.h

 /// \brief This file contains the declaration of the WebAssemblyMCAsmInfo class.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIB_TARGET_WEBASSEMBLY_MCTARGETDESC_WEBASSEMBLYMCASMINFO_H
 #define LLVM_LIB_TARGET_WEBASSEMBLY_MCTARGETDESC_WEBASSEMBLYMCASMINFO_H
 
 #include "llvm/MC/MCAsmInfoELF.h"
+#include "llvm/MC/MCAsmInfoWasm.h"
 
 namespace llvm {
 
 class Triple;
 
-class WebAssemblyMCAsmInfo final : public MCAsmInfoELF {
+class WebAssemblyMCAsmInfoELF final : public MCAsmInfoELF {
+public:
+  explicit WebAssemblyMCAsmInfoELF(const Triple &T);
+  ~WebAssemblyMCAsmInfoELF() override;
+};
+
+class WebAssemblyMCAsmInfo final : public MCAsmInfoWasm {
 public:
   explicit WebAssemblyMCAsmInfo(const Triple &T);
   ~WebAssemblyMCAsmInfo() override;
 };
 
 } // end namespace llvm
 
 #endif

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCAsmInfo.cpp

 //===----------------------------------------------------------------------===//
 
 #include "WebAssemblyMCAsmInfo.h"
 #include "llvm/ADT/Triple.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "wasm-mc-asm-info"
 
-WebAssemblyMCAsmInfo::~WebAssemblyMCAsmInfo() {}
+WebAssemblyMCAsmInfoELF::~WebAssemblyMCAsmInfoELF() {}
 
-WebAssemblyMCAsmInfo::WebAssemblyMCAsmInfo(const Triple &T) {
+WebAssemblyMCAsmInfoELF::WebAssemblyMCAsmInfoELF(const Triple &T) {
   PointerSize = CalleeSaveStackSlotSize = T.isArch64Bit() ? 8 : 4;
 
   // TODO: What should MaxInstLength be?
 
   UseDataRegionDirectives = true;
 
   // Use .skip instead of .zero because .zero is confusing when used with two
   // arguments (it doesn't actually zero things out).
WebAssemblyMCAsmInfoELF::WebAssemblyMCAsmInfoELF(const Triple &T) {
   // For now, WebAssembly does not support exceptions.
   ExceptionsType = ExceptionHandling::None;
 
   // TODO: UseIntegratedAssembler?
 
   // WebAssembly's stack is never executable.
   UsesNonexecutableStackSection = false;
 }
+
+WebAssemblyMCAsmInfo::~WebAssemblyMCAsmInfo() {}
+
+WebAssemblyMCAsmInfo::WebAssemblyMCAsmInfo(const Triple &T) {
+  PointerSize = CalleeSaveStackSlotSize = T.isArch64Bit() ? 8 : 4;
+
+  // TODO: What should MaxInstLength be?
+
+  UseDataRegionDirectives = true;
+
+  // Use .skip instead of .zero because .zero is confusing when used with two
+  // arguments (it doesn't actually zero things out).
+  ZeroDirective = "\t.skip\t";
+
+  Data8bitsDirective = "\t.int8\t";
+  Data16bitsDirective = "\t.int16\t";
+  Data32bitsDirective = "\t.int32\t";
+  Data64bitsDirective = "\t.int64\t";
+
+  AlignmentIsInBytes = false;
+  COMMDirectiveAlignmentIsInBytes = false;
+  LCOMMDirectiveAlignmentType = LCOMM::Log2Alignment;
+
+  SupportsDebugInformation = true;
+
+  // For now, WebAssembly does not support exceptions.
+  ExceptionsType = ExceptionHandling::None;
+
+  // TODO: UseIntegratedAssembler?
+}

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h

 
 MCCodeEmitter *createWebAssemblyMCCodeEmitter(const MCInstrInfo &MCII);
 
 MCAsmBackend *createWebAssemblyAsmBackend(const Triple &TT);
 
 MCObjectWriter *createWebAssemblyELFObjectWriter(raw_pwrite_stream &OS,
                                                  bool Is64Bit, uint8_t OSABI);
 
+MCObjectWriter *createWebAssemblyWasmObjectWriter(raw_pwrite_stream &OS,
+                                                  bool Is64Bit);
+
 namespace WebAssembly {
 enum OperandType {
   /// Basic block label in a branch construct.
   OPERAND_BASIC_BLOCK = MCOI::OPERAND_FIRST_TARGET,
   /// Local index.
   OPERAND_LOCAL,
   /// 32-bit integer immediates.
   OPERAND_I32IMM,

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.cpp

 #define GET_SUBTARGETINFO_MC_DESC
 #include "WebAssemblyGenSubtargetInfo.inc"
 
 #define GET_REGINFO_MC_DESC
 #include "WebAssemblyGenRegisterInfo.inc"
 
 static MCAsmInfo *createMCAsmInfo(const MCRegisterInfo & /*MRI*/,
                                   const Triple &TT) {
+  if (TT.isOSBinFormatELF())
+    return new WebAssemblyMCAsmInfoELF(TT);
   return new WebAssemblyMCAsmInfo(TT);
 }
 
 static void adjustCodeGenOpts(const Triple & /*TT*/, Reloc::Model /*RM*/,
                               CodeModel::Model &CM) {
   CodeModel::Model M = (CM == CodeModel::Default || CM == CodeModel::JITDefault)
                            ? CodeModel::Large
                            : CM;

 }
 
 static MCSubtargetInfo *createMCSubtargetInfo(const Triple &TT, StringRef CPU,
                                               StringRef FS) {
   return createWebAssemblyMCSubtargetInfoImpl(TT, CPU, FS);
 }
 
 static MCTargetStreamer *
-createObjectTargetStreamer(MCStreamer &S, const MCSubtargetInfo & /*STI*/) {
-  return new WebAssemblyTargetELFStreamer(S);
+createObjectTargetStreamer(MCStreamer &S, const MCSubtargetInfo &STI) {
+  const Triple &TT = STI.getTargetTriple();
+  if (TT.isOSBinFormatELF())
+    new WebAssemblyTargetELFStreamer(S);
+
+  return new WebAssemblyTargetWasmStreamer(S);
 }
 
 static MCTargetStreamer *createAsmTargetStreamer(MCStreamer &S,
                                                  formatted_raw_ostream &OS,
                                                  MCInstPrinter * /*InstPrint*/,
                                                  bool /*isVerboseAsm*/) {
   return new WebAssemblyTargetAsmStreamer(S, OS);
 }

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h

 #define LLVM_LIB_TARGET_WEBASSEMBLY_MCTARGETDESC_WEBASSEMBLYTARGETSTREAMER_H
 
 #include "llvm/CodeGen/MachineValueType.h"
 #include "llvm/MC/MCStreamer.h"
 
 namespace llvm {
 
 class MCELFStreamer;
+class MCWasmStreamer;
 
 /// WebAssembly-specific streamer interface, to implement support
 /// WebAssembly-specific assembly directives.
 class WebAssemblyTargetStreamer : public MCTargetStreamer {
 public:
   explicit WebAssemblyTargetStreamer(MCStreamer &S);
 
   /// .param
public:
   void emitEndFunc() override;
   void emitIndirectFunctionType(StringRef name,
                                 SmallVectorImpl<MVT> &Params,
                                 SmallVectorImpl<MVT> &Results) override;
   void emitIndIdx(const MCExpr *Value) override;
   void emitGlobalImport(StringRef name) override;
 };
 
+/// This part is for Wasm object output
+class WebAssemblyTargetWasmStreamer final : public WebAssemblyTargetStreamer {
+public:
+  explicit WebAssemblyTargetWasmStreamer(MCStreamer &S);
+
+  void emitParam(ArrayRef<MVT> Types) override;
+  void emitResult(ArrayRef<MVT> Types) override;
+  void emitLocal(ArrayRef<MVT> Types) override;
+  void emitEndFunc() override;
+  void emitIndirectFunctionType(StringRef name,
+                                SmallVectorImpl<MVT> &Params,
+                                SmallVectorImpl<MVT> &Results) override;
+  void emitIndIdx(const MCExpr *Value) override;
+  void emitGlobalImport(StringRef name) override;
+};
+
 } // end namespace llvm
 
 #endif

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp

 ///
 //===----------------------------------------------------------------------===//
 
 #include "WebAssemblyTargetStreamer.h"
 #include "InstPrinter/WebAssemblyInstPrinter.h"
 #include "WebAssemblyMCTargetDesc.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCSectionELF.h"
+#include "llvm/MC/MCSectionWasm.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCSymbolELF.h"
-#include "llvm/Support/ELF.h"
+#include "llvm/MC/MCSymbolWasm.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FormattedStream.h"
 using namespace llvm;
 
 WebAssemblyTargetStreamer::WebAssemblyTargetStreamer(MCStreamer &S)
     : MCTargetStreamer(S) {}
 
 WebAssemblyTargetAsmStreamer::WebAssemblyTargetAsmStreamer(
     MCStreamer &S, formatted_raw_ostream &OS)
     : WebAssemblyTargetStreamer(S), OS(OS) {}
 
 WebAssemblyTargetELFStreamer::WebAssemblyTargetELFStreamer(MCStreamer &S)
     : WebAssemblyTargetStreamer(S) {}
 
+WebAssemblyTargetWasmStreamer::WebAssemblyTargetWasmStreamer(MCStreamer &S)
+    : WebAssemblyTargetStreamer(S) {}
+
 static void PrintTypes(formatted_raw_ostream &OS, ArrayRef<MVT> Types) {
   bool First = true;
   for (MVT Type : Types) {
     if (First)
       First = false;
     else
       OS << ", ";
     OS << WebAssembly::TypeToString(Type);

 
 void WebAssemblyTargetELFStreamer::emitIndirectFunctionType(
     StringRef name, SmallVectorImpl<MVT> &Params, SmallVectorImpl<MVT> &Results) {
   // Nothing to emit here. TODO: Re-design how linking works and re-evaluate
   // whether it's necessary for .o files to declare indirect function types.
 }
 
 void WebAssemblyTargetELFStreamer::emitGlobalImport(StringRef name) {
-}
+}
+
+void WebAssemblyTargetWasmStreamer::emitParam(ArrayRef<MVT> Types) {
+  // Nothing to emit; params are declared as part of the function signature.
+}
+
+void WebAssemblyTargetWasmStreamer::emitResult(ArrayRef<MVT> Types) {
+  // Nothing to emit; results are declared as part of the function signature.
+}
+
+void WebAssemblyTargetWasmStreamer::emitLocal(ArrayRef<MVT> Types) {
+  Streamer.EmitULEB128IntValue(Types.size());
+  for (MVT Type : Types)
+    Streamer.EmitIntValue(int64_t(WebAssembly::toValType(Type)), 1);
+}
+
+void WebAssemblyTargetWasmStreamer::emitEndFunc() {
+  Streamer.EmitIntValue(WebAssembly::End, 1);
+}
+
+void WebAssemblyTargetWasmStreamer::emitIndIdx(const MCExpr *Value) {
+  llvm_unreachable(".indidx encoding not yet implemented");
+}
+
+void WebAssemblyTargetWasmStreamer::emitIndirectFunctionType(
+    StringRef name, SmallVectorImpl<MVT> &Params, SmallVectorImpl<MVT> &Results) {
+  // Nothing to emit here. TODO: Re-design how linking works and re-evaluate
+  // whether it's necessary for .o files to declare indirect function types.
+}
+
+void WebAssemblyTargetWasmStreamer::emitGlobalImport(StringRef name) {
+}

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp

+//===-- WebAssemblyWasmObjectWriter.cpp - WebAssembly Wasm Writer ---------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief This file handles Wasm-specific object emission, converting LLVM's
+/// internal fixups into the appropriate relocations.
+///
+//===----------------------------------------------------------------------===//
+
+#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
+#include "llvm/MC/MCFixup.h"
+#include "llvm/MC/MCWasmObjectWriter.h"
+#include "llvm/Support/ErrorHandling.h"
+using namespace llvm;
+
+namespace {
+class WebAssemblyWasmObjectWriter final : public MCWasmObjectTargetWriter {
+public:
+  explicit WebAssemblyWasmObjectWriter(bool Is64Bit);
+
+protected:
+  unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
+                        const MCFixup &Fixup, bool IsPCRel) const override;
+};
+} // end anonymous namespace
+
+WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit)
+    : MCWasmObjectTargetWriter(Is64Bit) {}
+
+unsigned WebAssemblyWasmObjectWriter::getRelocType(MCContext &Ctx,
+                                                   const MCValue &Target,
+                                                   const MCFixup &Fixup,
+                                                   bool IsPCRel) const {
+  llvm_unreachable("Relocations not yet implemented");
+  return 0;
+}
+
+MCObjectWriter *llvm::createWebAssemblyWasmObjectWriter(raw_pwrite_stream &OS,
+                                                        bool Is64Bit) {
+  MCWasmObjectTargetWriter *MOTW = new WebAssemblyWasmObjectWriter(Is64Bit);
+  return createWasmObjectWriter(MOTW, OS);
+}

lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp

WebAssemblyTargetMachine::WebAssemblyTargetMachine(
     const Target &T, const Triple &TT, StringRef CPU, StringRef FS,
     const TargetOptions &Options, Optional<Reloc::Model> RM,
     CodeModel::Model CM, CodeGenOpt::Level OL)
     : LLVMTargetMachine(T,
                         TT.isArch64Bit() ? "e-m:e-p:64:64-i64:64-n32:64-S128"
                                          : "e-m:e-p:32:32-i64:64-n32:64-S128",
                         TT, CPU, FS, Options, getEffectiveRelocModel(RM),
                         CM, OL),
-      TLOF(make_unique<WebAssemblyTargetObjectFile>()) {
+      TLOF(TT.isOSBinFormatELF() ?
+              static_cast<TargetLoweringObjectFile*>(
+                  new WebAssemblyTargetObjectFileELF()) :
+              static_cast<TargetLoweringObjectFile*>(
+                  new WebAssemblyTargetObjectFile())) {
   // WebAssembly type-checks instructions, but a noreturn function with a return
   // type that doesn't match the context will cause a check failure. So we lower
   // LLVM 'unreachable' to ISD::TRAP and then lower that to WebAssembly's
   // 'unreachable' instructions which is meant for that case.
   this->Options.TrapUnreachable = true;
 
   initAsmInfo();
 

lib/Target/WebAssembly/WebAssemblyTargetObjectFile.h

 
 #ifndef LLVM_LIB_TARGET_WEBASSEMBLY_WEBASSEMBLYTARGETOBJECTFILE_H
 #define LLVM_LIB_TARGET_WEBASSEMBLY_WEBASSEMBLYTARGETOBJECTFILE_H
 
 #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
 
 namespace llvm {
 
-class WebAssemblyTargetObjectFile final : public TargetLoweringObjectFileELF {
+class WebAssemblyTargetObjectFileELF final
+    : public TargetLoweringObjectFileELF {
+public:
+  void Initialize(MCContext &Ctx, const TargetMachine &TM) override;
+};
+
+class WebAssemblyTargetObjectFile final : public TargetLoweringObjectFileWasm {
 public:
   void Initialize(MCContext &Ctx, const TargetMachine &TM) override;
 };
 
 } // end namespace llvm
 
 #endif

lib/Target/WebAssembly/WebAssemblyTargetObjectFile.cpp

 /// of TargetLoweringObjectFile.
 ///
 //===----------------------------------------------------------------------===//
 
 #include "WebAssemblyTargetObjectFile.h"
 #include "WebAssemblyTargetMachine.h"
 using namespace llvm;
 
-void WebAssemblyTargetObjectFile::Initialize(MCContext &Ctx,
+void WebAssemblyTargetObjectFileELF::Initialize(MCContext &Ctx,
                                                 const TargetMachine &TM) {
   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
   InitializeELF(TM.Options.UseInitArray);
 }
+
+void WebAssemblyTargetObjectFile::Initialize(MCContext &Ctx,
+                                             const TargetMachine &TM) {
+  TargetLoweringObjectFileWasm::Initialize(Ctx, TM);
+  InitializeWasm();
+}