--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/MC/WasmObjectWriter.cpp	Fri Oct 27 17:07:41 2017 +0900
@@ -0,0 +1,1340 @@
+//===- 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/BinaryFormat/Wasm.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/Casting.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/LEB128.h"
+#include "llvm/Support/StringSaver.h"
+#include <vector>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "mc"
+
+namespace {
+
+// For patching purposes, we need to remember where each section starts, both
+// for patching up the section size field, and for patching up references to
+// locations within the section.
+struct SectionBookkeeping {
+  // Where the size of the section is written.
+  uint64_t SizeOffset;
+  // Where the contents of the section starts (after the header).
+  uint64_t ContentsOffset;
+};
+
+// The signature of a wasm function, in a struct capable of being used as a
+// DenseMap key.
+struct WasmFunctionType {
+  // Support empty and tombstone instances, needed by DenseMap.
+  enum { Plain, Empty, Tombstone } State;
+
+  // The return types of the function.
+  SmallVector<wasm::ValType, 1> Returns;
+
+  // The parameter types of the function.
+  SmallVector<wasm::ValType, 4> Params;
+
+  WasmFunctionType() : State(Plain) {}
+
+  bool operator==(const WasmFunctionType &Other) const {
+    return State == Other.State && Returns == Other.Returns &&
+           Params == Other.Params;
+  }
+};
+
+// Traits for using WasmFunctionType in a DenseMap.
+struct WasmFunctionTypeDenseMapInfo {
+  static WasmFunctionType getEmptyKey() {
+    WasmFunctionType FuncTy;
+    FuncTy.State = WasmFunctionType::Empty;
+    return FuncTy;
+  }
+  static WasmFunctionType getTombstoneKey() {
+    WasmFunctionType FuncTy;
+    FuncTy.State = WasmFunctionType::Tombstone;
+    return FuncTy;
+  }
+  static unsigned getHashValue(const WasmFunctionType &FuncTy) {
+    uintptr_t Value = FuncTy.State;
+    for (wasm::ValType Ret : FuncTy.Returns)
+      Value += DenseMapInfo<int32_t>::getHashValue(int32_t(Ret));
+    for (wasm::ValType Param : FuncTy.Params)
+      Value += DenseMapInfo<int32_t>::getHashValue(int32_t(Param));
+    return Value;
+  }
+  static bool isEqual(const WasmFunctionType &LHS,
+                      const WasmFunctionType &RHS) {
+    return LHS == RHS;
+  }
+};
+
+// A wasm data segment.  A wasm binary contains only a single data section
+// but that can contain many segments, each with their own virtual location
+// in memory.  Each MCSection data created by llvm is modeled as its own
+// wasm data segment.
+struct WasmDataSegment {
+  MCSectionWasm *Section;
+  StringRef Name;
+  uint32_t Offset;
+  uint32_t Alignment;
+  uint32_t Flags;
+  SmallVector<char, 4> Data;
+};
+
+// A wasm import to be written into the import section.
+struct WasmImport {
+  StringRef ModuleName;
+  StringRef FieldName;
+  unsigned Kind;
+  int32_t Type;
+};
+
+// A wasm function to be written into the function section.
+struct WasmFunction {
+  int32_t Type;
+  const MCSymbolWasm *Sym;
+};
+
+// A wasm export to be written into the export section.
+struct WasmExport {
+  StringRef FieldName;
+  unsigned Kind;
+  uint32_t Index;
+};
+
+// A wasm global to be written into the global section.
+struct WasmGlobal {
+  wasm::ValType Type;
+  bool IsMutable;
+  bool HasImport;
+  uint64_t InitialValue;
+  uint32_t ImportIndex;
+};
+
+// Information about a single relocation.
+struct WasmRelocationEntry {
+  uint64_t Offset;                  // Where is the relocation.
+  const MCSymbolWasm *Symbol;       // The symbol to relocate with.
+  int64_t Addend;                   // A value to add to the symbol.
+  unsigned Type;                    // The type of the relocation.
+  const MCSectionWasm *FixupSection;// The section the relocation is targeting.
+
+  WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol,
+                      int64_t Addend, unsigned Type,
+                      const MCSectionWasm *FixupSection)
+      : Offset(Offset), Symbol(Symbol), Addend(Addend), Type(Type),
+        FixupSection(FixupSection) {}
+
+  bool hasAddend() const {
+    switch (Type) {
+    case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
+    case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
+    case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
+      return true;
+    default:
+      return false;
+    }
+  }
+
+  void print(raw_ostream &Out) const {
+    Out << "Off=" << Offset << ", Sym=" << *Symbol << ", Addend=" << Addend
+        << ", Type=" << Type
+        << ", FixupSection=" << FixupSection->getSectionName();
+  }
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
+#endif
+};
+
+#if !defined(NDEBUG)
+raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) {
+  Rel.print(OS);
+  return OS;
+}
+#endif
+
+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;
+
+  // Relocations for fixing up references in the code section.
+  std::vector<WasmRelocationEntry> CodeRelocations;
+
+  // Relocations for fixing up references in the data section.
+  std::vector<WasmRelocationEntry> DataRelocations;
+
+  // Index values to use for fixing up call_indirect type indices.
+  // Maps function symbols to the index of the type of the function
+  DenseMap<const MCSymbolWasm *, uint32_t> TypeIndices;
+  // Maps function symbols to the table element index space. Used
+  // for TABLE_INDEX relocation types (i.e. address taken functions).
+  DenseMap<const MCSymbolWasm *, uint32_t> IndirectSymbolIndices;
+  // Maps function/global symbols to the function/global index space.
+  DenseMap<const MCSymbolWasm *, uint32_t> SymbolIndices;
+
+  DenseMap<WasmFunctionType, int32_t, WasmFunctionTypeDenseMapInfo>
+      FunctionTypeIndices;
+  SmallVector<WasmFunctionType, 4> FunctionTypes;
+  SmallVector<WasmGlobal, 4> Globals;
+  unsigned NumGlobalImports = 0;
+
+  // TargetObjectWriter wrappers.
+  bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
+  unsigned getRelocType(const MCValue &Target, const MCFixup &Fixup) const {
+    return TargetObjectWriter->getRelocType(Target, Fixup);
+  }
+
+  void startSection(SectionBookkeeping &Section, unsigned SectionId,
+                    const char *Name = nullptr);
+  void endSection(SectionBookkeeping &Section);
+
+public:
+  WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
+                   raw_pwrite_stream &OS)
+      : MCObjectWriter(OS, /*IsLittleEndian=*/true),
+        TargetObjectWriter(std::move(MOTW)) {}
+
+private:
+  ~WasmObjectWriter() override;
+
+  void reset() override {
+    CodeRelocations.clear();
+    DataRelocations.clear();
+    TypeIndices.clear();
+    SymbolIndices.clear();
+    IndirectSymbolIndices.clear();
+    FunctionTypeIndices.clear();
+    FunctionTypes.clear();
+    Globals.clear();
+    MCObjectWriter::reset();
+    NumGlobalImports = 0;
+  }
+
+  void writeHeader(const MCAssembler &Asm);
+
+  void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
+                        const MCFragment *Fragment, const MCFixup &Fixup,
+                        MCValue Target, uint64_t &FixedValue) override;
+
+  void executePostLayoutBinding(MCAssembler &Asm,
+                                const MCAsmLayout &Layout) override;
+
+  void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
+
+  void writeString(const StringRef Str) {
+    encodeULEB128(Str.size(), getStream());
+    writeBytes(Str);
+  }
+
+  void writeValueType(wasm::ValType Ty) {
+    encodeSLEB128(int32_t(Ty), getStream());
+  }
+
+  void writeTypeSection(ArrayRef<WasmFunctionType> FunctionTypes);
+  void writeImportSection(ArrayRef<WasmImport> Imports);
+  void writeFunctionSection(ArrayRef<WasmFunction> Functions);
+  void writeTableSection(uint32_t NumElements);
+  void writeMemorySection(uint32_t DataSize);
+  void writeGlobalSection();
+  void writeExportSection(ArrayRef<WasmExport> Exports);
+  void writeElemSection(ArrayRef<uint32_t> TableElems);
+  void writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
+                        ArrayRef<WasmFunction> Functions);
+  void writeDataSection(ArrayRef<WasmDataSegment> Segments);
+  void writeNameSection(ArrayRef<WasmFunction> Functions,
+                        ArrayRef<WasmImport> Imports,
+                        uint32_t NumFuncImports);
+  void writeCodeRelocSection();
+  void writeDataRelocSection();
+  void writeLinkingMetaDataSection(
+      ArrayRef<WasmDataSegment> Segments, uint32_t DataSize,
+      SmallVector<std::pair<StringRef, uint32_t>, 4> SymbolFlags,
+      bool HasStackPointer, uint32_t StackPointerGlobal);
+
+  uint32_t getProvisionalValue(const WasmRelocationEntry &RelEntry);
+  void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,
+                        uint64_t ContentsOffset);
+
+  void writeRelocations(ArrayRef<WasmRelocationEntry> Relocations);
+  uint32_t getRelocationIndexValue(const WasmRelocationEntry &RelEntry);
+  uint32_t getFunctionType(const MCSymbolWasm& Symbol);
+  uint32_t registerFunctionType(const MCSymbolWasm& Symbol);
+};
+
+} // end anonymous namespace
+
+WasmObjectWriter::~WasmObjectWriter() {}
+
+// Write out a section header and a patchable section size field.
+void WasmObjectWriter::startSection(SectionBookkeeping &Section,
+                                    unsigned SectionId,
+                                    const char *Name) {
+  assert((Name != nullptr) == (SectionId == wasm::WASM_SEC_CUSTOM) &&
+         "Only custom sections can have names");
+
+  DEBUG(dbgs() << "startSection " << SectionId << ": " << Name << "\n");
+  encodeULEB128(SectionId, getStream());
+
+  Section.SizeOffset = getStream().tell();
+
+  // The section size. We don't know the size yet, so reserve enough space
+  // for any 32-bit value; we'll patch it later.
+  encodeULEB128(UINT32_MAX, getStream());
+
+  // The position where the section starts, for measuring its size.
+  Section.ContentsOffset = getStream().tell();
+
+  // Custom sections in wasm also have a string identifier.
+  if (SectionId == wasm::WASM_SEC_CUSTOM) {
+    assert(Name);
+    writeString(StringRef(Name));
+  }
+}
+
+// Now that the section is complete and we know how big it is, patch up the
+// section size field at the start of the section.
+void WasmObjectWriter::endSection(SectionBookkeeping &Section) {
+  uint64_t Size = getStream().tell() - Section.ContentsOffset;
+  if (uint32_t(Size) != Size)
+    report_fatal_error("section size does not fit in a uint32_t");
+
+  DEBUG(dbgs() << "endSection size=" << Size << "\n");
+
+  // Write the final section size to the payload_len field, which follows
+  // the section id byte.
+  uint8_t Buffer[16];
+  unsigned SizeLen = encodeULEB128(Size, Buffer, 5);
+  assert(SizeLen == 5);
+  getStream().pwrite((char *)Buffer, SizeLen, Section.SizeOffset);
+}
+
+// Emit the Wasm header.
+void WasmObjectWriter::writeHeader(const MCAssembler &Asm) {
+  writeBytes(StringRef(wasm::WasmMagic, sizeof(wasm::WasmMagic)));
+  writeLE32(wasm::WasmVersion);
+}
+
+void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
+                                                const MCAsmLayout &Layout) {
+}
+
+void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
+                                        const MCAsmLayout &Layout,
+                                        const MCFragment *Fragment,
+                                        const MCFixup &Fixup, MCValue Target,
+                                        uint64_t &FixedValue) {
+  MCAsmBackend &Backend = Asm.getBackend();
+  bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
+                 MCFixupKindInfo::FKF_IsPCRel;
+  const auto &FixupSection = cast<MCSectionWasm>(*Fragment->getParent());
+  uint64_t C = Target.getConstant();
+  uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
+  MCContext &Ctx = Asm.getContext();
+
+  if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
+    assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
+           "Should not have constructed this");
+
+    // Let A, B and C being the components of Target and R be the location of
+    // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
+    // If it is pcrel, we want to compute (A - B + C - R).
+
+    // In general, Wasm has no relocations for -B. It can only represent (A + C)
+    // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
+    // replace B to implement it: (A - R - K + C)
+    if (IsPCRel) {
+      Ctx.reportError(
+          Fixup.getLoc(),
+          "No relocation available to represent this relative expression");
+      return;
+    }
+
+    const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol());
+
+    if (SymB.isUndefined()) {
+      Ctx.reportError(Fixup.getLoc(),
+                      Twine("symbol '") + SymB.getName() +
+                          "' can not be undefined in a subtraction expression");
+      return;
+    }
+
+    assert(!SymB.isAbsolute() && "Should have been folded");
+    const MCSection &SecB = SymB.getSection();
+    if (&SecB != &FixupSection) {
+      Ctx.reportError(Fixup.getLoc(),
+                      "Cannot represent a difference across sections");
+      return;
+    }
+
+    uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
+    uint64_t K = SymBOffset - FixupOffset;
+    IsPCRel = true;
+    C -= K;
+  }
+
+  // We either rejected the fixup or folded B into C at this point.
+  const MCSymbolRefExpr *RefA = Target.getSymA();
+  const auto *SymA = RefA ? cast<MCSymbolWasm>(&RefA->getSymbol()) : nullptr;
+
+  if (SymA && SymA->isVariable()) {
+    const MCExpr *Expr = SymA->getVariableValue();
+    const auto *Inner = cast<MCSymbolRefExpr>(Expr);
+    if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
+      llvm_unreachable("weakref used in reloc not yet implemented");
+  }
+
+  // Put any constant offset in an addend. Offsets can be negative, and
+  // LLVM expects wrapping, in contrast to wasm's immediates which can't
+  // be negative and don't wrap.
+  FixedValue = 0;
+
+  if (SymA)
+    SymA->setUsedInReloc();
+
+  assert(!IsPCRel);
+  assert(SymA);
+
+  unsigned Type = getRelocType(Target, Fixup);
+
+  WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection);
+  DEBUG(dbgs() << "WasmReloc: " << Rec << "\n");
+
+  if (FixupSection.isWasmData())
+    DataRelocations.push_back(Rec);
+  else if (FixupSection.getKind().isText())
+    CodeRelocations.push_back(Rec);
+  else if (!FixupSection.getKind().isMetadata())
+    // TODO(sbc): Add support for debug sections.
+    llvm_unreachable("unexpected section type");
+}
+
+// Write X as an (unsigned) LEB value at offset Offset in Stream, padded
+// to allow patching.
+static void
+WritePatchableLEB(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) {
+  uint8_t Buffer[5];
+  unsigned SizeLen = encodeULEB128(X, Buffer, 5);
+  assert(SizeLen == 5);
+  Stream.pwrite((char *)Buffer, SizeLen, Offset);
+}
+
+// Write X as an signed LEB value at offset Offset in Stream, padded
+// to allow patching.
+static void
+WritePatchableSLEB(raw_pwrite_stream &Stream, int32_t X, uint64_t Offset) {
+  uint8_t Buffer[5];
+  unsigned SizeLen = encodeSLEB128(X, Buffer, 5);
+  assert(SizeLen == 5);
+  Stream.pwrite((char *)Buffer, SizeLen, Offset);
+}
+
+// Write X as a plain integer value at offset Offset in Stream.
+static void WriteI32(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) {
+  uint8_t Buffer[4];
+  support::endian::write32le(Buffer, X);
+  Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset);
+}
+
+static const MCSymbolWasm* ResolveSymbol(const MCSymbolWasm& Symbol) {
+  if (Symbol.isVariable()) {
+    const MCExpr *Expr = Symbol.getVariableValue();
+    auto *Inner = cast<MCSymbolRefExpr>(Expr);
+    return cast<MCSymbolWasm>(&Inner->getSymbol());
+  }
+  return &Symbol;
+}
+
+// Compute a value to write into the code at the location covered
+// by RelEntry. This value isn't used by the static linker, since
+// we have addends; it just serves to make the code more readable
+// and to make standalone wasm modules directly usable.
+uint32_t
+WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry) {
+  const MCSymbolWasm *Sym = ResolveSymbol(*RelEntry.Symbol);
+
+  // For undefined symbols, use a hopefully invalid value.
+  if (!Sym->isDefined(/*SetUsed=*/false))
+    return UINT32_MAX;
+
+  uint32_t GlobalIndex = SymbolIndices[Sym];
+  const WasmGlobal& Global = Globals[GlobalIndex - NumGlobalImports];
+  uint64_t Address = Global.InitialValue + RelEntry.Addend;
+
+  // Ignore overflow. LLVM allows address arithmetic to silently wrap.
+  uint32_t Value = Address;
+
+  return Value;
+}
+
+static void addData(SmallVectorImpl<char> &DataBytes,
+                    MCSectionWasm &DataSection) {
+  DEBUG(errs() << "addData: " << DataSection.getSectionName() << "\n");
+
+  DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlignment()));
+
+  size_t LastFragmentSize = 0;
+  for (const MCFragment &Frag : DataSection) {
+    if (Frag.hasInstructions())
+      report_fatal_error("only data supported in data sections");
+
+    if (auto *Align = dyn_cast<MCAlignFragment>(&Frag)) {
+      if (Align->getValueSize() != 1)
+        report_fatal_error("only byte values supported for alignment");
+      // If nops are requested, use zeros, as this is the data section.
+      uint8_t Value = Align->hasEmitNops() ? 0 : Align->getValue();
+      uint64_t Size = std::min<uint64_t>(alignTo(DataBytes.size(),
+                                                 Align->getAlignment()),
+                                         DataBytes.size() +
+                                             Align->getMaxBytesToEmit());
+      DataBytes.resize(Size, Value);
+    } else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) {
+      DataBytes.insert(DataBytes.end(), Fill->getSize(), Fill->getValue());
+    } else {
+      const auto &DataFrag = cast<MCDataFragment>(Frag);
+      const SmallVectorImpl<char> &Contents = DataFrag.getContents();
+
+      DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
+      LastFragmentSize = Contents.size();
+    }
+  }
+
+  // Don't allow empty segments, or segments that end with zero-sized
+  // fragment, otherwise the linker cannot map symbols to a unique
+  // data segment.  This can be triggered by zero-sized structs
+  // See: test/MC/WebAssembly/bss.ll
+  if (LastFragmentSize == 0)
+    DataBytes.resize(DataBytes.size() + 1);
+  DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n");
+}
+
+uint32_t WasmObjectWriter::getRelocationIndexValue(
+    const WasmRelocationEntry &RelEntry) {
+  switch (RelEntry.Type) {
+  case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
+  case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32:
+    if (!IndirectSymbolIndices.count(RelEntry.Symbol))
+      report_fatal_error("symbol not found table index space: " +
+                         RelEntry.Symbol->getName());
+    return IndirectSymbolIndices[RelEntry.Symbol];
+  case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
+  case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
+  case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
+  case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
+  case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
+    if (!SymbolIndices.count(RelEntry.Symbol))
+      report_fatal_error("symbol not found function/global index space: " +
+                         RelEntry.Symbol->getName());
+    return SymbolIndices[RelEntry.Symbol];
+  case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
+    if (!TypeIndices.count(RelEntry.Symbol))
+      report_fatal_error("symbol not found in type index space: " +
+                         RelEntry.Symbol->getName());
+    return TypeIndices[RelEntry.Symbol];
+  default:
+    llvm_unreachable("invalid relocation type");
+  }
+}
+
+// Apply the portions of the relocation records that we can handle ourselves
+// directly.
+void WasmObjectWriter::applyRelocations(
+    ArrayRef<WasmRelocationEntry> Relocations, uint64_t ContentsOffset) {
+  raw_pwrite_stream &Stream = getStream();
+  for (const WasmRelocationEntry &RelEntry : Relocations) {
+    uint64_t Offset = ContentsOffset +
+                      RelEntry.FixupSection->getSectionOffset() +
+                      RelEntry.Offset;
+
+    DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n");
+    switch (RelEntry.Type) {
+    case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
+    case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
+    case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
+    case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB: {
+      uint32_t Index = getRelocationIndexValue(RelEntry);
+      WritePatchableSLEB(Stream, Index, Offset);
+      break;
+    }
+    case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32: {
+      uint32_t Index = getRelocationIndexValue(RelEntry);
+      WriteI32(Stream, Index, Offset);
+      break;
+    }
+    case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB: {
+      uint32_t Value = getProvisionalValue(RelEntry);
+      WritePatchableSLEB(Stream, Value, Offset);
+      break;
+    }
+    case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB: {
+      uint32_t Value = getProvisionalValue(RelEntry);
+      WritePatchableLEB(Stream, Value, Offset);
+      break;
+    }
+    case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32: {
+      uint32_t Value = getProvisionalValue(RelEntry);
+      WriteI32(Stream, Value, Offset);
+      break;
+    }
+    default:
+      llvm_unreachable("invalid relocation type");
+    }
+  }
+}
+
+// Write out the portions of the relocation records that the linker will
+// need to handle.
+void WasmObjectWriter::writeRelocations(
+    ArrayRef<WasmRelocationEntry> Relocations) {
+  raw_pwrite_stream &Stream = getStream();
+  for (const WasmRelocationEntry& RelEntry : Relocations) {
+
+    uint64_t Offset = RelEntry.Offset +
+                      RelEntry.FixupSection->getSectionOffset();
+    uint32_t Index = getRelocationIndexValue(RelEntry);
+
+    encodeULEB128(RelEntry.Type, Stream);
+    encodeULEB128(Offset, Stream);
+    encodeULEB128(Index, Stream);
+    if (RelEntry.hasAddend())
+      encodeSLEB128(RelEntry.Addend, Stream);
+  }
+}
+
+void WasmObjectWriter::writeTypeSection(
+    ArrayRef<WasmFunctionType> FunctionTypes) {
+  if (FunctionTypes.empty())
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_TYPE);
+
+  encodeULEB128(FunctionTypes.size(), getStream());
+
+  for (const WasmFunctionType &FuncTy : FunctionTypes) {
+    encodeSLEB128(wasm::WASM_TYPE_FUNC, getStream());
+    encodeULEB128(FuncTy.Params.size(), getStream());
+    for (wasm::ValType Ty : FuncTy.Params)
+      writeValueType(Ty);
+    encodeULEB128(FuncTy.Returns.size(), getStream());
+    for (wasm::ValType Ty : FuncTy.Returns)
+      writeValueType(Ty);
+  }
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeImportSection(ArrayRef<WasmImport> Imports) {
+  if (Imports.empty())
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_IMPORT);
+
+  encodeULEB128(Imports.size(), getStream());
+  for (const WasmImport &Import : Imports) {
+    writeString(Import.ModuleName);
+    writeString(Import.FieldName);
+
+    encodeULEB128(Import.Kind, getStream());
+
+    switch (Import.Kind) {
+    case wasm::WASM_EXTERNAL_FUNCTION:
+      encodeULEB128(Import.Type, getStream());
+      break;
+    case wasm::WASM_EXTERNAL_GLOBAL:
+      encodeSLEB128(int32_t(Import.Type), getStream());
+      encodeULEB128(0, getStream()); // mutability
+      break;
+    default:
+      llvm_unreachable("unsupported import kind");
+    }
+  }
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeFunctionSection(ArrayRef<WasmFunction> Functions) {
+  if (Functions.empty())
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_FUNCTION);
+
+  encodeULEB128(Functions.size(), getStream());
+  for (const WasmFunction &Func : Functions)
+    encodeULEB128(Func.Type, getStream());
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeTableSection(uint32_t NumElements) {
+  // For now, always emit the table section, since indirect calls are not
+  // valid without it. In the future, we could perhaps be more clever and omit
+  // it if there are no indirect calls.
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_TABLE);
+
+  encodeULEB128(1, getStream());                       // The number of tables.
+                                                       // Fixed to 1 for now.
+  encodeSLEB128(wasm::WASM_TYPE_ANYFUNC, getStream()); // Type of table
+  encodeULEB128(0, getStream());                       // flags
+  encodeULEB128(NumElements, getStream());             // initial
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeMemorySection(uint32_t DataSize) {
+  // For now, always emit the memory section, since loads and stores are not
+  // valid without it. In the future, we could perhaps be more clever and omit
+  // it if there are no loads or stores.
+  SectionBookkeeping Section;
+  uint32_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize;
+
+  startSection(Section, wasm::WASM_SEC_MEMORY);
+  encodeULEB128(1, getStream()); // number of memory spaces
+
+  encodeULEB128(0, getStream()); // flags
+  encodeULEB128(NumPages, getStream()); // initial
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeGlobalSection() {
+  if (Globals.empty())
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_GLOBAL);
+
+  encodeULEB128(Globals.size(), getStream());
+  for (const WasmGlobal &Global : Globals) {
+    writeValueType(Global.Type);
+    write8(Global.IsMutable);
+
+    if (Global.HasImport) {
+      assert(Global.InitialValue == 0);
+      write8(wasm::WASM_OPCODE_GET_GLOBAL);
+      encodeULEB128(Global.ImportIndex, getStream());
+    } else {
+      assert(Global.ImportIndex == 0);
+      write8(wasm::WASM_OPCODE_I32_CONST);
+      encodeSLEB128(Global.InitialValue, getStream()); // offset
+    }
+    write8(wasm::WASM_OPCODE_END);
+  }
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeExportSection(ArrayRef<WasmExport> Exports) {
+  if (Exports.empty())
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_EXPORT);
+
+  encodeULEB128(Exports.size(), getStream());
+  for (const WasmExport &Export : Exports) {
+    writeString(Export.FieldName);
+    encodeSLEB128(Export.Kind, getStream());
+    encodeULEB128(Export.Index, getStream());
+  }
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeElemSection(ArrayRef<uint32_t> TableElems) {
+  if (TableElems.empty())
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_ELEM);
+
+  encodeULEB128(1, getStream()); // number of "segments"
+  encodeULEB128(0, getStream()); // the table index
+
+  // init expr for starting offset
+  write8(wasm::WASM_OPCODE_I32_CONST);
+  encodeSLEB128(0, getStream());
+  write8(wasm::WASM_OPCODE_END);
+
+  encodeULEB128(TableElems.size(), getStream());
+  for (uint32_t Elem : TableElems)
+    encodeULEB128(Elem, getStream());
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
+                                        const MCAsmLayout &Layout,
+                                        ArrayRef<WasmFunction> Functions) {
+  if (Functions.empty())
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_CODE);
+
+  encodeULEB128(Functions.size(), getStream());
+
+  for (const WasmFunction &Func : Functions) {
+    auto &FuncSection = static_cast<MCSectionWasm &>(Func.Sym->getSection());
+
+    int64_t Size = 0;
+    if (!Func.Sym->getSize()->evaluateAsAbsolute(Size, Layout))
+      report_fatal_error(".size expression must be evaluatable");
+
+    encodeULEB128(Size, getStream());
+    FuncSection.setSectionOffset(getStream().tell() - Section.ContentsOffset);
+    Asm.writeSectionData(&FuncSection, Layout);
+  }
+
+  // Apply fixups.
+  applyRelocations(CodeRelocations, Section.ContentsOffset);
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeDataSection(ArrayRef<WasmDataSegment> Segments) {
+  if (Segments.empty())
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_DATA);
+
+  encodeULEB128(Segments.size(), getStream()); // count
+
+  for (const WasmDataSegment & Segment : Segments) {
+    encodeULEB128(0, getStream()); // memory index
+    write8(wasm::WASM_OPCODE_I32_CONST);
+    encodeSLEB128(Segment.Offset, getStream()); // offset
+    write8(wasm::WASM_OPCODE_END);
+    encodeULEB128(Segment.Data.size(), getStream()); // size
+    Segment.Section->setSectionOffset(getStream().tell() - Section.ContentsOffset);
+    writeBytes(Segment.Data); // data
+  }
+
+  // Apply fixups.
+  applyRelocations(DataRelocations, Section.ContentsOffset);
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeNameSection(
+    ArrayRef<WasmFunction> Functions,
+    ArrayRef<WasmImport> Imports,
+    unsigned NumFuncImports) {
+  uint32_t TotalFunctions = NumFuncImports + Functions.size();
+  if (TotalFunctions == 0)
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_CUSTOM, "name");
+  SectionBookkeeping SubSection;
+  startSection(SubSection, wasm::WASM_NAMES_FUNCTION);
+
+  encodeULEB128(TotalFunctions, getStream());
+  uint32_t Index = 0;
+  for (const WasmImport &Import : Imports) {
+    if (Import.Kind == wasm::WASM_EXTERNAL_FUNCTION) {
+      encodeULEB128(Index, getStream());
+      writeString(Import.FieldName);
+      ++Index;
+    }
+  }
+  for (const WasmFunction &Func : Functions) {
+    encodeULEB128(Index, getStream());
+    writeString(Func.Sym->getName());
+    ++Index;
+  }
+
+  endSection(SubSection);
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeCodeRelocSection() {
+  // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
+  // for descriptions of the reloc sections.
+
+  if (CodeRelocations.empty())
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_CUSTOM, "reloc.CODE");
+
+  encodeULEB128(wasm::WASM_SEC_CODE, getStream());
+  encodeULEB128(CodeRelocations.size(), getStream());
+
+  writeRelocations(CodeRelocations);
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeDataRelocSection() {
+  // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
+  // for descriptions of the reloc sections.
+
+  if (DataRelocations.empty())
+    return;
+
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_CUSTOM, "reloc.DATA");
+
+  encodeULEB128(wasm::WASM_SEC_DATA, getStream());
+  encodeULEB128(DataRelocations.size(), getStream());
+
+  writeRelocations(DataRelocations);
+
+  endSection(Section);
+}
+
+void WasmObjectWriter::writeLinkingMetaDataSection(
+    ArrayRef<WasmDataSegment> Segments, uint32_t DataSize,
+    SmallVector<std::pair<StringRef, uint32_t>, 4> SymbolFlags,
+    bool HasStackPointer, uint32_t StackPointerGlobal) {
+  SectionBookkeeping Section;
+  startSection(Section, wasm::WASM_SEC_CUSTOM, "linking");
+  SectionBookkeeping SubSection;
+
+  if (HasStackPointer) {
+    startSection(SubSection, wasm::WASM_STACK_POINTER);
+    encodeULEB128(StackPointerGlobal, getStream()); // id
+    endSection(SubSection);
+  }
+
+  if (SymbolFlags.size() != 0) {
+    startSection(SubSection, wasm::WASM_SYMBOL_INFO);
+    encodeULEB128(SymbolFlags.size(), getStream());
+    for (auto Pair: SymbolFlags) {
+      writeString(Pair.first);
+      encodeULEB128(Pair.second, getStream());
+    }
+    endSection(SubSection);
+  }
+
+  if (DataSize > 0) {
+    startSection(SubSection, wasm::WASM_DATA_SIZE);
+    encodeULEB128(DataSize, getStream());
+    endSection(SubSection);
+  }
+
+  if (Segments.size()) {
+    startSection(SubSection, wasm::WASM_SEGMENT_INFO);
+    encodeULEB128(Segments.size(), getStream());
+    for (const WasmDataSegment &Segment : Segments) {
+      writeString(Segment.Name);
+      encodeULEB128(Segment.Alignment, getStream());
+      encodeULEB128(Segment.Flags, getStream());
+    }
+    endSection(SubSection);
+  }
+
+  endSection(Section);
+}
+
+uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm& Symbol) {
+  assert(Symbol.isFunction());
+  assert(TypeIndices.count(&Symbol));
+  return TypeIndices[&Symbol];
+}
+
+uint32_t WasmObjectWriter::registerFunctionType(const MCSymbolWasm& Symbol) {
+  assert(Symbol.isFunction());
+
+  WasmFunctionType F;
+  const MCSymbolWasm* ResolvedSym = ResolveSymbol(Symbol);
+  F.Returns = ResolvedSym->getReturns();
+  F.Params = ResolvedSym->getParams();
+
+  auto Pair =
+      FunctionTypeIndices.insert(std::make_pair(F, FunctionTypes.size()));
+  if (Pair.second)
+    FunctionTypes.push_back(F);
+  TypeIndices[&Symbol] = Pair.first->second;
+
+  DEBUG(dbgs() << "registerFunctionType: " << Symbol << " new:" << Pair.second << "\n");
+  DEBUG(dbgs() << "  -> type index: " << Pair.first->second << "\n");
+  return Pair.first->second;
+}
+
+void WasmObjectWriter::writeObject(MCAssembler &Asm,
+                                   const MCAsmLayout &Layout) {
+  DEBUG(dbgs() << "WasmObjectWriter::writeObject\n");
+  MCContext &Ctx = Asm.getContext();
+  wasm::ValType PtrType = is64Bit() ? wasm::ValType::I64 : wasm::ValType::I32;
+
+  // Collect information from the available symbols.
+  SmallVector<WasmFunction, 4> Functions;
+  SmallVector<uint32_t, 4> TableElems;
+  SmallVector<WasmImport, 4> Imports;
+  SmallVector<WasmExport, 4> Exports;
+  SmallVector<std::pair<StringRef, uint32_t>, 4> SymbolFlags;
+  SmallPtrSet<const MCSymbolWasm *, 4> IsAddressTaken;
+  unsigned NumFuncImports = 0;
+  SmallVector<WasmDataSegment, 4> DataSegments;
+  uint32_t StackPointerGlobal = 0;
+  uint32_t DataSize = 0;
+  bool HasStackPointer = false;
+
+  // Populate the IsAddressTaken set.
+  for (const WasmRelocationEntry &RelEntry : CodeRelocations) {
+    switch (RelEntry.Type) {
+    case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
+    case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
+      IsAddressTaken.insert(RelEntry.Symbol);
+      break;
+    default:
+      break;
+    }
+  }
+  for (const WasmRelocationEntry &RelEntry : DataRelocations) {
+    switch (RelEntry.Type) {
+    case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32:
+    case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
+      IsAddressTaken.insert(RelEntry.Symbol);
+      break;
+    default:
+      break;
+    }
+  }
+
+  // Populate FunctionTypeIndices and Imports.
+  for (const MCSymbol &S : Asm.symbols()) {
+    const auto &WS = static_cast<const MCSymbolWasm &>(S);
+
+    if (WS.isTemporary())
+      continue;
+
+    if (WS.isFunction())
+      registerFunctionType(WS);
+
+    // If the symbol is not defined in this translation unit, import it.
+    if (!WS.isDefined(/*SetUsed=*/false)) {
+      WasmImport Import;
+      Import.ModuleName = WS.getModuleName();
+      Import.FieldName = WS.getName();
+
+      if (WS.isFunction()) {
+        Import.Kind = wasm::WASM_EXTERNAL_FUNCTION;
+        Import.Type = getFunctionType(WS);
+        SymbolIndices[&WS] = NumFuncImports;
+        ++NumFuncImports;
+      } else {
+        Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
+        Import.Type = int32_t(PtrType);
+        SymbolIndices[&WS] = NumGlobalImports;
+        ++NumGlobalImports;
+      }
+
+      Imports.push_back(Import);
+    }
+  }
+
+  // In the special .global_variables section, we've encoded global
+  // variables used by the function. Translate them into the Globals
+  // list.
+  MCSectionWasm *GlobalVars =
+      Ctx.getWasmSection(".global_variables", SectionKind::getMetadata());
+  if (!GlobalVars->getFragmentList().empty()) {
+    if (GlobalVars->getFragmentList().size() != 1)
+      report_fatal_error("only one .global_variables fragment supported");
+    const MCFragment &Frag = *GlobalVars->begin();
+    if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
+      report_fatal_error("only data supported in .global_variables");
+    const auto &DataFrag = cast<MCDataFragment>(Frag);
+    if (!DataFrag.getFixups().empty())
+      report_fatal_error("fixups not supported in .global_variables");
+    const SmallVectorImpl<char> &Contents = DataFrag.getContents();
+    for (const uint8_t *p = (const uint8_t *)Contents.data(),
+                     *end = (const uint8_t *)Contents.data() + Contents.size();
+         p != end; ) {
+      WasmGlobal G;
+      if (end - p < 3)
+        report_fatal_error("truncated global variable encoding");
+      G.Type = wasm::ValType(int8_t(*p++));
+      G.IsMutable = bool(*p++);
+      G.HasImport = bool(*p++);
+      if (G.HasImport) {
+        G.InitialValue = 0;
+
+        WasmImport Import;
+        Import.ModuleName = (const char *)p;
+        const uint8_t *nul = (const uint8_t *)memchr(p, '\0', end - p);
+        if (!nul)
+          report_fatal_error("global module name must be nul-terminated");
+        p = nul + 1;
+        nul = (const uint8_t *)memchr(p, '\0', end - p);
+        if (!nul)
+          report_fatal_error("global base name must be nul-terminated");
+        Import.FieldName = (const char *)p;
+        p = nul + 1;
+
+        Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
+        Import.Type = int32_t(G.Type);
+
+        G.ImportIndex = NumGlobalImports;
+        ++NumGlobalImports;
+
+        Imports.push_back(Import);
+      } else {
+        unsigned n;
+        G.InitialValue = decodeSLEB128(p, &n);
+        G.ImportIndex = 0;
+        if ((ptrdiff_t)n > end - p)
+          report_fatal_error("global initial value must be valid SLEB128");
+        p += n;
+      }
+      Globals.push_back(G);
+    }
+  }
+
+  // In the special .stack_pointer section, we've encoded the stack pointer
+  // index.
+  MCSectionWasm *StackPtr =
+      Ctx.getWasmSection(".stack_pointer", SectionKind::getMetadata());
+  if (!StackPtr->getFragmentList().empty()) {
+    if (StackPtr->getFragmentList().size() != 1)
+      report_fatal_error("only one .stack_pointer fragment supported");
+    const MCFragment &Frag = *StackPtr->begin();
+    if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
+      report_fatal_error("only data supported in .stack_pointer");
+    const auto &DataFrag = cast<MCDataFragment>(Frag);
+    if (!DataFrag.getFixups().empty())
+      report_fatal_error("fixups not supported in .stack_pointer");
+    const SmallVectorImpl<char> &Contents = DataFrag.getContents();
+    if (Contents.size() != 4)
+      report_fatal_error("only one entry supported in .stack_pointer");
+    HasStackPointer = true;
+    StackPointerGlobal = NumGlobalImports + *(const int32_t *)Contents.data();
+  }
+
+  for (MCSection &Sec : Asm) {
+    auto &Section = static_cast<MCSectionWasm &>(Sec);
+    if (!Section.isWasmData())
+      continue;
+
+    DataSize = alignTo(DataSize, Section.getAlignment());
+    DataSegments.emplace_back();
+    WasmDataSegment &Segment = DataSegments.back();
+    Segment.Name = Section.getSectionName();
+    Segment.Offset = DataSize;
+    Segment.Section = &Section;
+    addData(Segment.Data, Section);
+    Segment.Alignment = Section.getAlignment();
+    Segment.Flags = 0;
+    DataSize += Segment.Data.size();
+    Section.setMemoryOffset(Segment.Offset);
+  }
+
+  // Handle regular defined and undefined symbols.
+  for (const MCSymbol &S : Asm.symbols()) {
+    // Ignore unnamed temporary symbols, which aren't ever exported, imported,
+    // or used in relocations.
+    if (S.isTemporary() && S.getName().empty())
+      continue;
+
+    const auto &WS = static_cast<const MCSymbolWasm &>(S);
+    DEBUG(dbgs() << "MCSymbol: '" << S << "'"
+                 << " isDefined=" << S.isDefined() << " isExternal="
+                 << S.isExternal() << " isTemporary=" << S.isTemporary()
+                 << " isFunction=" << WS.isFunction()
+                 << " isWeak=" << WS.isWeak()
+                 << " isVariable=" << WS.isVariable() << "\n");
+
+    if (WS.isWeak())
+      SymbolFlags.emplace_back(WS.getName(), wasm::WASM_SYMBOL_BINDING_WEAK);
+
+    if (WS.isVariable())
+      continue;
+
+    unsigned Index;
+
+    if (WS.isFunction()) {
+      if (WS.isDefined(/*SetUsed=*/false)) {
+        if (WS.getOffset() != 0)
+          report_fatal_error(
+              "function sections must contain one function each");
+
+        if (WS.getSize() == 0)
+          report_fatal_error(
+              "function symbols must have a size set with .size");
+
+        // A definition. Take the next available index.
+        Index = NumFuncImports + Functions.size();
+
+        // Prepare the function.
+        WasmFunction Func;
+        Func.Type = getFunctionType(WS);
+        Func.Sym = &WS;
+        SymbolIndices[&WS] = Index;
+        Functions.push_back(Func);
+      } else {
+        // An import; the index was assigned above.
+        Index = SymbolIndices.find(&WS)->second;
+      }
+
+      DEBUG(dbgs() << "  -> function index: " << Index << "\n");
+
+      // If needed, prepare the function to be called indirectly.
+      if (IsAddressTaken.count(&WS) != 0) {
+        IndirectSymbolIndices[&WS] = TableElems.size();
+        DEBUG(dbgs() << "  -> adding to table: " << TableElems.size() << "\n");
+        TableElems.push_back(Index);
+      }
+    } else {
+      if (WS.isTemporary() && !WS.getSize())
+        continue;
+
+      if (!WS.isDefined(/*SetUsed=*/false))
+        continue;
+
+      if (!WS.getSize())
+        report_fatal_error("data symbols must have a size set with .size: " +
+                           WS.getName());
+
+      int64_t Size = 0;
+      if (!WS.getSize()->evaluateAsAbsolute(Size, Layout))
+        report_fatal_error(".size expression must be evaluatable");
+
+      // For each global, prepare a corresponding wasm global holding its
+      // address.  For externals these will also be named exports.
+      Index = NumGlobalImports + Globals.size();
+      auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
+
+      WasmGlobal Global;
+      Global.Type = PtrType;
+      Global.IsMutable = false;
+      Global.HasImport = false;
+      Global.InitialValue = DataSection.getMemoryOffset() + Layout.getSymbolOffset(WS);
+      Global.ImportIndex = 0;
+      SymbolIndices[&WS] = Index;
+      DEBUG(dbgs() << "  -> global index: " << Index << "\n");
+      Globals.push_back(Global);
+    }
+
+    // If the symbol is visible outside this translation unit, export it.
+    if (WS.isDefined(/*SetUsed=*/false)) {
+      WasmExport Export;
+      Export.FieldName = WS.getName();
+      Export.Index = Index;
+      if (WS.isFunction())
+        Export.Kind = wasm::WASM_EXTERNAL_FUNCTION;
+      else
+        Export.Kind = wasm::WASM_EXTERNAL_GLOBAL;
+      DEBUG(dbgs() << "  -> export " << Exports.size() << "\n");
+      Exports.push_back(Export);
+      if (!WS.isExternal())
+        SymbolFlags.emplace_back(WS.getName(), wasm::WASM_SYMBOL_BINDING_LOCAL);
+    }
+  }
+
+  // Handle weak aliases. We need to process these in a separate pass because
+  // we need to have processed the target of the alias before the alias itself
+  // and the symbols are not necessarily ordered in this way.
+  for (const MCSymbol &S : Asm.symbols()) {
+    if (!S.isVariable())
+      continue;
+
+    assert(S.isDefined(/*SetUsed=*/false));
+
+    // Find the target symbol of this weak alias and export that index
+    const auto &WS = static_cast<const MCSymbolWasm &>(S);
+    const MCSymbolWasm *ResolvedSym = ResolveSymbol(WS);
+    DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *ResolvedSym << "'\n");
+    assert(SymbolIndices.count(ResolvedSym) > 0);
+    uint32_t Index = SymbolIndices.find(ResolvedSym)->second;
+    DEBUG(dbgs() << "  -> index:" << Index << "\n");
+
+    SymbolIndices[&WS] = Index;
+    WasmExport Export;
+    Export.FieldName = WS.getName();
+    Export.Index = Index;
+    if (WS.isFunction())
+      Export.Kind = wasm::WASM_EXTERNAL_FUNCTION;
+    else
+      Export.Kind = wasm::WASM_EXTERNAL_GLOBAL;
+    DEBUG(dbgs() << "  -> export " << Exports.size() << "\n");
+    Exports.push_back(Export);
+
+    if (!WS.isExternal())
+      SymbolFlags.emplace_back(WS.getName(), wasm::WASM_SYMBOL_BINDING_LOCAL);
+  }
+
+  // Add types for indirect function calls.
+  for (const WasmRelocationEntry &Fixup : CodeRelocations) {
+    if (Fixup.Type != wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB)
+      continue;
+
+    registerFunctionType(*Fixup.Symbol);
+  }
+
+  // Write out the Wasm header.
+  writeHeader(Asm);
+
+  writeTypeSection(FunctionTypes);
+  writeImportSection(Imports);
+  writeFunctionSection(Functions);
+  writeTableSection(TableElems.size());
+  writeMemorySection(DataSize);
+  writeGlobalSection();
+  writeExportSection(Exports);
+  // TODO: Start Section
+  writeElemSection(TableElems);
+  writeCodeSection(Asm, Layout, Functions);
+  writeDataSection(DataSegments);
+  writeNameSection(Functions, Imports, NumFuncImports);
+  writeCodeRelocSection();
+  writeDataRelocSection();
+  writeLinkingMetaDataSection(DataSegments, DataSize, SymbolFlags,
+                              HasStackPointer, StackPointerGlobal);
+
+  // TODO: Translate the .comment section to the output.
+  // TODO: Translate debug sections to the output.
+}
+
+std::unique_ptr<MCObjectWriter>
+llvm::createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
+                             raw_pwrite_stream &OS) {
+  // FIXME: Can't use make_unique<WasmObjectWriter>(...) as WasmObjectWriter's
+  //        destructor is private. Is that necessary?
+  return std::unique_ptr<MCObjectWriter>(
+      new WasmObjectWriter(std::move(MOTW), OS));
+}