diff --git a/lld/CMakeLists.txt b/lld/CMakeLists.txt
--- a/lld/CMakeLists.txt
+++ b/lld/CMakeLists.txt
@@ -194,5 +194,6 @@
 add_subdirectory(docs)
 add_subdirectory(COFF)
 add_subdirectory(ELF)
+add_subdirectory(MachO)
 add_subdirectory(MinGW)
 add_subdirectory(wasm)
diff --git a/lld/MachO/Arch/X86_64.cpp b/lld/MachO/Arch/X86_64.cpp
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Arch/X86_64.cpp
@@ -0,0 +1,60 @@
+//===- X86_64.cpp ---------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "Target.h"
+#include "lld/Common/ErrorHandler.h"
+#include "llvm/BinaryFormat/MachO.h"
+#include "llvm/Support/Endian.h"
+
+using namespace llvm::MachO;
+using namespace llvm::support::endian;
+using namespace lld;
+using namespace lld::macho;
+
+namespace {
+
+struct X86_64 : TargetInfo {
+  X86_64();
+  uint64_t getImplicitAddend(const uint8_t *loc, uint8_t type) const override;
+  void relocateOne(uint8_t *loc, uint8_t type, uint64_t val) const override;
+};
+
+X86_64::X86_64() {
+  cpuType = CPU_TYPE_X86_64;
+  cpuSubtype = CPU_SUBTYPE_X86_64_ALL;
+}
+
+uint64_t X86_64::getImplicitAddend(const uint8_t *loc, uint8_t type) const {
+  switch (type) {
+  case X86_64_RELOC_SIGNED:
+    return read32le(loc);
+  default:
+    error("TODO: Unhandled relocation type " + std::to_string(type));
+    return 0;
+  }
+}
+
+void X86_64::relocateOne(uint8_t *loc, uint8_t type, uint64_t val) const {
+  switch (type) {
+  case X86_64_RELOC_SIGNED:
+    // This type is only used for pc-relative relocations, so offset by 4 since
+    // the RIP has advanced by 4 at this point.
+    write32le(loc, val - 4);
+    break;
+  default:
+    llvm_unreachable(
+        "getImplicitAddend should have flagged all unhandled relocation types");
+  }
+}
+
+} // namespace
+
+TargetInfo *macho::createX86_64TargetInfo() {
+  static X86_64 t;
+  return &t;
+}
diff --git a/lld/MachO/CMakeLists.txt b/lld/MachO/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/lld/MachO/CMakeLists.txt
@@ -0,0 +1,34 @@
+set(LLVM_TARGET_DEFINITIONS Options.td)
+tablegen(LLVM Options.inc -gen-opt-parser-defs)
+add_public_tablegen_target(MachOOptionsTableGen)
+
+add_lld_library(lldMachO2
+  Arch/X86_64.cpp
+  Driver.cpp
+  InputFiles.cpp
+  InputSection.cpp
+  OutputSegment.cpp
+  SymbolTable.cpp
+  Symbols.cpp
+  Target.cpp
+  Writer.cpp
+
+  LINK_COMPONENTS
+  ${LLVM_TARGETS_TO_BUILD}
+  BinaryFormat
+  Core
+  DebugInfoDWARF
+  LTO
+  MC
+  Object
+  Option
+  Support
+
+  LINK_LIBS
+  lldCommon
+  ${LLVM_PTHREAD_LIB}
+
+  DEPENDS
+  MachOOptionsTableGen
+  ${tablegen_deps}
+  )
diff --git a/lld/MachO/Config.h b/lld/MachO/Config.h
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Config.h
@@ -0,0 +1,29 @@
+//===- Config.h -------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_CONFIG_H
+#define LLD_MACHO_CONFIG_H
+
+#include "llvm/ADT/StringRef.h"
+
+namespace lld {
+namespace macho {
+
+class Symbol;
+
+struct Configuration {
+  llvm::StringRef outputFile;
+  Symbol *entry;
+};
+
+extern Configuration *config;
+
+} // namespace macho
+} // namespace lld
+
+#endif
diff --git a/lld/MachO/Driver.h b/lld/MachO/Driver.h
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Driver.h
@@ -0,0 +1,35 @@
+//===- Driver.h -------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_DRIVER_H
+#define LLD_MACHO_DRIVER_H
+
+#include "lld/Common/LLVM.h"
+#include "llvm/Option/OptTable.h"
+
+namespace lld {
+namespace macho {
+
+class MachOOptTable : public llvm::opt::OptTable {
+public:
+  MachOOptTable();
+  llvm::opt::InputArgList parse(ArrayRef<const char *> argv);
+};
+
+// Create enum with OPT_xxx values for each option in Options.td
+enum {
+  OPT_INVALID = 0,
+#define OPTION(_1, _2, ID, _4, _5, _6, _7, _8, _9, _10, _11, _12) OPT_##ID,
+#include "Options.inc"
+#undef OPTION
+};
+
+} // namespace macho
+} // namespace lld
+
+#endif
diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Driver.cpp
@@ -0,0 +1,150 @@
+//===- Driver.cpp ---------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "Driver.h"
+#include "Config.h"
+#include "InputFiles.h"
+#include "OutputSegment.h"
+#include "SymbolTable.h"
+#include "Symbols.h"
+#include "Target.h"
+#include "Writer.h"
+
+#include "lld/Common/Args.h"
+#include "lld/Common/Driver.h"
+#include "lld/Common/ErrorHandler.h"
+#include "lld/Common/LLVM.h"
+#include "lld/Common/Memory.h"
+#include "lld/Common/Version.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/BinaryFormat/MachO.h"
+#include "llvm/BinaryFormat/Magic.h"
+#include "llvm/Option/ArgList.h"
+#include "llvm/Option/Option.h"
+#include "llvm/Support/MemoryBuffer.h"
+
+using namespace llvm;
+using namespace llvm::MachO;
+using namespace llvm::sys;
+using namespace lld;
+using namespace lld::macho;
+
+Configuration *lld::macho::config;
+
+// Create prefix string literals used in Options.td
+#define PREFIX(NAME, VALUE) const char *NAME[] = VALUE;
+#include "Options.inc"
+#undef PREFIX
+
+// Create table mapping all options defined in Options.td
+static const opt::OptTable::Info optInfo[] = {
+#define OPTION(X1, X2, ID, KIND, GROUP, ALIAS, X7, X8, X9, X10, X11, X12)      \
+  {X1, X2, X10,         X11,         OPT_##ID, opt::Option::KIND##Class,       \
+   X9, X8, OPT_##GROUP, OPT_##ALIAS, X7,       X12},
+#include "Options.inc"
+#undef OPTION
+};
+
+MachOOptTable::MachOOptTable() : OptTable(optInfo) {}
+
+opt::InputArgList MachOOptTable::parse(ArrayRef<const char *> argv) {
+  // Make InputArgList from string vectors.
+  unsigned missingIndex;
+  unsigned missingCount;
+  SmallVector<const char *, 256> vec(argv.data(), argv.data() + argv.size());
+
+  opt::InputArgList args = ParseArgs(vec, missingIndex, missingCount);
+
+  if (missingCount)
+    error(Twine(args.getArgString(missingIndex)) + ": missing argument");
+
+  for (opt::Arg *arg : args.filtered(OPT_UNKNOWN))
+    error("unknown argument: " + arg->getSpelling());
+  return args;
+}
+
+static TargetInfo *createTargetInfo(opt::InputArgList &args) {
+  StringRef s = args.getLastArgValue(OPT_arch, "x86_64");
+  if (s != "x86_64")
+    error("missing or unsupported -arch " + s);
+  return createX86_64TargetInfo();
+}
+
+static void addFile(StringRef path) {
+  Optional<MemoryBufferRef> buffer = readFile(path);
+  if (!buffer)
+    return;
+  MemoryBufferRef mbref = *buffer;
+
+  switch (identify_magic(mbref.getBuffer())) {
+  case file_magic::macho_object:
+    inputFiles.push_back(make<ObjFile>(mbref));
+    break;
+  default:
+    error(path + ": unhandled file type");
+  }
+}
+
+bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
+                 raw_ostream &stdoutOS, raw_ostream &stderrOS) {
+  lld::stdoutOS = &stdoutOS;
+  lld::stderrOS = &stderrOS;
+
+  MachOOptTable parser;
+  opt::InputArgList args = parser.parse(argsArr.slice(1));
+
+  if (args.hasArg(OPT_v)) {
+    message(getLLDVersion());
+    freeArena();
+    return !errorCount();
+  }
+
+  config = make<Configuration>();
+  symtab = make<SymbolTable>();
+  target = createTargetInfo(args);
+
+  config->entry = symtab->addUndefined(args.getLastArgValue(OPT_e, "_main"));
+  config->outputFile = args.getLastArgValue(OPT_o, "a.out");
+
+  getOrCreateOutputSegment("__TEXT", VM_PROT_READ | VM_PROT_EXECUTE);
+  getOrCreateOutputSegment("__DATA", VM_PROT_READ | VM_PROT_WRITE);
+
+  for (opt::Arg *arg : args) {
+    switch (arg->getOption().getID()) {
+    case OPT_INPUT:
+      addFile(arg->getValue());
+      break;
+    }
+  }
+
+  if (!isa<Defined>(config->entry)) {
+    error("undefined symbol: " + config->entry->getName());
+    return false;
+  }
+
+  // Initialize InputSections.
+  for (InputFile *file : inputFiles)
+    for (InputSection *sec : file->sections)
+      inputSections.push_back(sec);
+
+  // Add input sections to output segments.
+  for (InputSection *isec : inputSections) {
+    OutputSegment *os =
+        getOrCreateOutputSegment(isec->segname, VM_PROT_READ | VM_PROT_WRITE);
+    os->sections[isec->name].push_back(isec);
+  }
+
+  // Write to an output file.
+  writeResult();
+
+  if (canExitEarly)
+    exitLld(errorCount() ? 1 : 0);
+
+  freeArena();
+  return !errorCount();
+}
diff --git a/lld/MachO/InputFiles.h b/lld/MachO/InputFiles.h
new file mode 100644
--- /dev/null
+++ b/lld/MachO/InputFiles.h
@@ -0,0 +1,70 @@
+//===- InputFiles.h ---------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_INPUT_FILES_H
+#define LLD_MACHO_INPUT_FILES_H
+
+#include "lld/Common/LLVM.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/BinaryFormat/MachO.h"
+#include "llvm/Object/Archive.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include <vector>
+
+namespace lld {
+namespace macho {
+
+class InputSection;
+class Symbol;
+struct Reloc;
+
+class InputFile {
+public:
+  enum Kind {
+    ObjKind,
+  };
+
+  virtual ~InputFile() = default;
+
+  Kind kind() const { return fileKind; }
+  StringRef getName() const { return mb.getBufferIdentifier(); }
+
+  MemoryBufferRef mb;
+  std::vector<Symbol *> symbols;
+  std::vector<InputSection *> sections;
+  StringRef dylibName;
+
+protected:
+  InputFile(Kind kind, MemoryBufferRef mb) : mb(mb), fileKind(kind) {}
+
+  std::vector<InputSection *> parseSections(ArrayRef<llvm::MachO::section_64>);
+
+  void parseRelocations(const llvm::MachO::section_64 &,
+                        std::vector<Reloc> &relocs);
+
+private:
+  const Kind fileKind;
+};
+
+// .o file
+class ObjFile : public InputFile {
+public:
+  explicit ObjFile(MemoryBufferRef mb);
+  static bool classof(const InputFile *f) { return f->kind() == ObjKind; }
+};
+
+extern std::vector<InputFile *> inputFiles;
+
+llvm::Optional<MemoryBufferRef> readFile(StringRef path);
+
+} // namespace macho
+
+std::string toString(const macho::InputFile *file);
+} // namespace lld
+
+#endif
diff --git a/lld/MachO/InputFiles.cpp b/lld/MachO/InputFiles.cpp
new file mode 100644
--- /dev/null
+++ b/lld/MachO/InputFiles.cpp
@@ -0,0 +1,204 @@
+//===- InputFiles.cpp -----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains functions to parse Mach-O object files. In this comment,
+// we describe the Mach-O file structure and how we parse it.
+//
+// Mach-O is not very different from ELF or COFF. The notion of symbols,
+// sections and relocations exists in Mach-O as it does in ELF and COFF.
+//
+// Perhaps the notion that is new to those who know ELF/COFF is "subsections".
+// In ELF/COFF, sections are an atomic unit of data copied from input files to
+// output files. When we merge or garbage-collect sections, we treat each
+// section as an atomic unit. In Mach-O, that's not the case. Sections can
+// consist of multiple subsections, and subsections are a unit of merging and
+// garbage-collecting. Therefore, Mach-O's subsections are more similar to
+// ELF/COFF's sections than Mach-O's sections are.
+//
+// A section can have multiple symbols. A symbol that does not have the
+// N_ALT_ENTRY attribute indicates a beginning of a subsection. Therefore, by
+// definition, a symbol is always present at the beginning of each subsection. A
+// symbol with N_ALT_ENTRY attribute does not start a new subsection and can
+// point to a middle of a subsection.
+//
+// The notion of subsections also affects how relocations are represented in
+// Mach-O. All references within a section need to be explicitly represented as
+// relocations if they refer to different subsections, because we obviously need
+// to fix up addresses if subsections are laid out in an output file differently
+// than they were in object files. To represent that, Mach-O relocations can
+// refer to an unnamed location via its address. Scattered relocations (those
+// with the R_SCATTERED bit set) always refer to unnamed locations.
+// Non-scattered relocations refer to an unnamed location if r_extern is not set
+// and r_symbolnum is zero.
+//
+// Without the above differences, I think you can use your knowledge about ELF
+// and COFF for Mach-O.
+//
+//===----------------------------------------------------------------------===//
+
+#include "InputFiles.h"
+#include "InputSection.h"
+#include "OutputSegment.h"
+#include "SymbolTable.h"
+#include "Symbols.h"
+#include "Target.h"
+
+#include "lld/Common/ErrorHandler.h"
+#include "lld/Common/Memory.h"
+#include "llvm/BinaryFormat/MachO.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/MemoryBuffer.h"
+
+using namespace llvm;
+using namespace llvm::MachO;
+using namespace llvm::support::endian;
+using namespace lld;
+using namespace lld::macho;
+
+std::vector<InputFile *> macho::inputFiles;
+
+// Open a given file path and return it as a memory-mapped file.
+Optional<MemoryBufferRef> macho::readFile(StringRef path) {
+  // Open a file.
+  auto mbOrErr = MemoryBuffer::getFile(path);
+  if (auto ec = mbOrErr.getError()) {
+    error("cannot open " + path + ": " + ec.message());
+    return None;
+  }
+
+  std::unique_ptr<MemoryBuffer> &mb = *mbOrErr;
+  MemoryBufferRef mbref = mb->getMemBufferRef();
+  make<std::unique_ptr<MemoryBuffer>>(std::move(mb)); // take mb ownership
+  return mbref;
+}
+
+static const load_command *findCommand(const mach_header_64 *hdr,
+                                       uint32_t type) {
+  const uint8_t *p =
+      reinterpret_cast<const uint8_t *>(hdr) + sizeof(mach_header_64);
+
+  for (uint32_t i = 0, n = hdr->ncmds; i < n; ++i) {
+    auto *cmd = reinterpret_cast<const load_command *>(p);
+    if (cmd->cmd == type)
+      return cmd;
+    p += cmd->cmdsize;
+  }
+  return nullptr;
+}
+
+std::vector<InputSection *>
+InputFile::parseSections(ArrayRef<section_64> sections) {
+  std::vector<InputSection *> ret;
+  ret.reserve(sections.size());
+
+  auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
+
+  for (const section_64 &sec : sections) {
+    InputSection *isec = make<InputSection>();
+    isec->file = this;
+    isec->name = StringRef(sec.sectname, strnlen(sec.sectname, 16));
+    isec->segname = StringRef(sec.segname, strnlen(sec.segname, 16));
+    isec->data = {buf + sec.offset, sec.size};
+    if (sec.align >= 32)
+      error("alignment " + std::to_string(sec.align) + " of section " +
+            isec->name + " is too large");
+    else
+      isec->align = 1 << sec.align;
+    isec->flags = sec.flags;
+    ret.push_back(isec);
+  }
+
+  return ret;
+}
+
+void InputFile::parseRelocations(const section_64 &sec,
+                                 std::vector<Reloc> &relocs) {
+  auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
+  ArrayRef<any_relocation_info> relInfos(
+      reinterpret_cast<const any_relocation_info *>(buf + sec.reloff),
+      sec.nreloc);
+
+  for (const any_relocation_info &anyRel : relInfos) {
+    Reloc r;
+    if (anyRel.r_word0 & R_SCATTERED) {
+      error("TODO: Scattered relocations not supported");
+    } else {
+      auto rel = reinterpret_cast<const relocation_info &>(anyRel);
+      r.type = rel.r_type;
+      r.offset = rel.r_address;
+      r.addend = target->getImplicitAddend(buf + sec.offset + r.offset, r.type);
+      if (rel.r_extern)
+        r.target = symbols[rel.r_symbolnum];
+      else {
+        error("TODO: Non-extern relocations are not supported");
+        continue;
+      }
+    }
+    relocs.push_back(r);
+  }
+}
+
+ObjFile::ObjFile(MemoryBufferRef mb) : InputFile(ObjKind, mb) {
+  auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
+  auto *hdr = reinterpret_cast<const mach_header_64 *>(mb.getBufferStart());
+  ArrayRef<section_64> objSections;
+
+  if (const load_command *cmd = findCommand(hdr, LC_SEGMENT_64)) {
+    auto *c = reinterpret_cast<const segment_command_64 *>(cmd);
+    objSections = ArrayRef<section_64>{
+        reinterpret_cast<const section_64 *>(c + 1), c->nsects};
+    sections = parseSections(objSections);
+  }
+
+  if (const load_command *cmd = findCommand(hdr, LC_SYMTAB)) {
+    auto *c = reinterpret_cast<const symtab_command *>(cmd);
+    const char *strtab = reinterpret_cast<const char *>(buf) + c->stroff;
+    ArrayRef<const nlist_64> nList(
+        reinterpret_cast<const nlist_64 *>(buf + c->symoff), c->nsyms);
+
+    symbols.reserve(c->nsyms);
+
+    for (const nlist_64 &sym : nList) {
+      StringRef name = strtab + sym.n_strx;
+
+      // Undefined symbol
+      if (!sym.n_sect) {
+        error("TODO: Support undefined symbols");
+        continue;
+      }
+
+      InputSection *isec = sections[sym.n_sect - 1];
+      const section_64 &objSec = objSections[sym.n_sect - 1];
+      uint64_t value = sym.n_value - objSec.addr;
+
+      // Global defined symbol
+      if (sym.n_type & N_EXT) {
+        symbols.push_back(symtab->addDefined(name, isec, value));
+        continue;
+      }
+
+      // Local defined symbol
+      symbols.push_back(make<Defined>(name, isec, value));
+    }
+  }
+
+  // The relocations may refer to the symbols, so we parse them after we have
+  // the symbols loaded.
+  if (!sections.empty()) {
+    auto it = sections.begin();
+    for (const section_64 &sec : objSections) {
+      parseRelocations(sec, (*it)->relocs);
+      ++it;
+    }
+  }
+}
+
+// Returns "<internal>" or "baz.o".
+std::string lld::toString(const InputFile *file) {
+  return file ? std::string(file->getName()) : "<internal>";
+}
diff --git a/lld/MachO/InputSection.h b/lld/MachO/InputSection.h
new file mode 100644
--- /dev/null
+++ b/lld/MachO/InputSection.h
@@ -0,0 +1,52 @@
+//===- InputSection.h -------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_INPUT_SECTION_H
+#define LLD_MACHO_INPUT_SECTION_H
+
+#include "lld/Common/LLVM.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/PointerUnion.h"
+#include "llvm/BinaryFormat/MachO.h"
+
+namespace lld {
+namespace macho {
+
+class InputFile;
+class InputSection;
+class Symbol;
+
+struct Reloc {
+  uint8_t type;
+  uint32_t addend;
+  uint32_t offset;
+  llvm::PointerUnion<Symbol *, InputSection *> target;
+};
+
+class InputSection {
+public:
+  void writeTo(uint8_t *buf);
+
+  InputFile *file = nullptr;
+  StringRef name;
+  StringRef segname;
+
+  ArrayRef<uint8_t> data;
+  uint64_t addr = 0;
+  uint32_t align = 1;
+  uint32_t flags = 0;
+
+  std::vector<Reloc> relocs;
+};
+
+extern std::vector<InputSection *> inputSections;
+
+} // namespace macho
+} // namespace lld
+
+#endif
diff --git a/lld/MachO/InputSection.cpp b/lld/MachO/InputSection.cpp
new file mode 100644
--- /dev/null
+++ b/lld/MachO/InputSection.cpp
@@ -0,0 +1,39 @@
+//===- InputSection.cpp ---------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "InputSection.h"
+#include "Symbols.h"
+#include "Target.h"
+#include "lld/Common/Memory.h"
+#include "llvm/Support/Endian.h"
+
+using namespace llvm::MachO;
+using namespace llvm::support;
+using namespace lld;
+using namespace lld::macho;
+
+std::vector<InputSection *> macho::inputSections;
+
+void InputSection::writeTo(uint8_t *buf) {
+  memcpy(buf, data.data(), data.size());
+
+  for (Reloc &r : relocs) {
+    uint64_t va = 0;
+    if (auto *s = r.target.dyn_cast<Symbol *>())
+      va = s->getVA();
+    else if (auto *isec = r.target.dyn_cast<InputSection *>())
+      va = isec->addr;
+    else
+      llvm_unreachable("Unknown relocation target");
+
+    uint64_t val = va + r.addend;
+    if (1) // TODO: handle non-pcrel relocations
+      val -= addr - ImageBase + r.offset;
+    target->relocateOne(buf + r.offset, r.type, val);
+  }
+}
diff --git a/lld/MachO/Options.td b/lld/MachO/Options.td
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Options.td
@@ -0,0 +1,18 @@
+include "llvm/Option/OptParser.td"
+
+def arch: Separate<["-"], "arch">, MetaVarName<"<arch-name>">,
+  HelpText<"Architecture to link">;
+
+def e: Separate<["-"], "e">, HelpText<"Name of entry point symbol">;
+
+def o: Separate<["-"], "o">, MetaVarName<"<path>">,
+  HelpText<"Path to file to write output">;
+
+def v: Flag<["-"], "v">, HelpText<"Display the version number and exit">;
+
+// Ignored options
+def: Flag<["-"], "demangle">;
+def: Flag<["-"], "dynamic">;
+def: Flag<["-"], "no_deduplicate">;
+def: Separate<["-"], "lto_library">;
+def: Separate<["-"], "macosx_version_min">;
diff --git a/lld/MachO/OutputSegment.h b/lld/MachO/OutputSegment.h
new file mode 100644
--- /dev/null
+++ b/lld/MachO/OutputSegment.h
@@ -0,0 +1,34 @@
+//===- OutputSegment.h ------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_OUTPUT_SEGMENT_H
+#define LLD_MACHO_OUTPUT_SEGMENT_H
+
+#include "lld/Common/LLVM.h"
+#include "llvm/ADT/MapVector.h"
+
+namespace lld {
+namespace macho {
+
+class InputSection;
+
+class OutputSegment {
+public:
+  StringRef name;
+  uint32_t perms;
+  llvm::MapVector<StringRef, std::vector<InputSection *>> sections;
+};
+
+extern std::vector<OutputSegment *> outputSegments;
+
+OutputSegment *getOrCreateOutputSegment(StringRef name, uint32_t perms);
+
+} // namespace macho
+} // namespace lld
+
+#endif
diff --git a/lld/MachO/OutputSegment.cpp b/lld/MachO/OutputSegment.cpp
new file mode 100644
--- /dev/null
+++ b/lld/MachO/OutputSegment.cpp
@@ -0,0 +1,30 @@
+//===- OutputSegment.cpp --------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "OutputSegment.h"
+#include "lld/Common/Memory.h"
+
+using namespace llvm;
+using namespace lld;
+using namespace lld::macho;
+
+std::vector<OutputSegment *> macho::outputSegments;
+
+OutputSegment *macho::getOrCreateOutputSegment(StringRef name, uint32_t perms) {
+  for (OutputSegment *os : outputSegments)
+    if (os->name == name)
+      // TODO: assert that os->perms == perms, once we figure out what to do
+      // about default-created segments.
+      return os;
+
+  auto *os = make<OutputSegment>();
+  os->name = name;
+  os->perms = perms;
+  outputSegments.push_back(os);
+  return os;
+}
diff --git a/lld/MachO/SymbolTable.h b/lld/MachO/SymbolTable.h
new file mode 100644
--- /dev/null
+++ b/lld/MachO/SymbolTable.h
@@ -0,0 +1,44 @@
+//===- SymbolTable.h --------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_SYMBOL_TABLE_H
+#define LLD_MACHO_SYMBOL_TABLE_H
+
+#include "lld/Common/LLVM.h"
+#include "llvm/ADT/CachedHashString.h"
+#include "llvm/Object/Archive.h"
+
+namespace lld {
+namespace macho {
+
+class InputFile;
+class InputSection;
+class ArchiveFile;
+class Symbol;
+
+class SymbolTable {
+public:
+  Symbol *addDefined(StringRef name, InputSection *isec, uint32_t value);
+
+  Symbol *addUndefined(StringRef name);
+
+  ArrayRef<Symbol *> getSymbols() const { return symVector; }
+  Symbol *find(StringRef name);
+
+private:
+  std::pair<Symbol *, bool> insert(StringRef name);
+  llvm::DenseMap<llvm::CachedHashStringRef, int> symMap;
+  std::vector<Symbol *> symVector;
+};
+
+extern SymbolTable *symtab;
+
+} // namespace macho
+} // namespace lld
+
+#endif
diff --git a/lld/MachO/SymbolTable.cpp b/lld/MachO/SymbolTable.cpp
new file mode 100644
--- /dev/null
+++ b/lld/MachO/SymbolTable.cpp
@@ -0,0 +1,62 @@
+//===- SymbolTable.cpp ----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "SymbolTable.h"
+#include "InputFiles.h"
+#include "Symbols.h"
+#include "lld/Common/ErrorHandler.h"
+#include "lld/Common/Memory.h"
+
+using namespace llvm;
+using namespace lld;
+using namespace lld::macho;
+
+Symbol *SymbolTable::find(StringRef name) {
+  auto it = symMap.find(llvm::CachedHashStringRef(name));
+  if (it == symMap.end())
+    return nullptr;
+  return symVector[it->second];
+}
+
+std::pair<Symbol *, bool> SymbolTable::insert(StringRef name) {
+  auto p = symMap.insert({CachedHashStringRef(name), (int)symVector.size()});
+
+  // Name already present in the symbol table.
+  if (!p.second)
+    return {symVector[p.first->second], false};
+
+  // Name is a new symbol.
+  Symbol *sym = reinterpret_cast<Symbol *>(make<SymbolUnion>());
+  symVector.push_back(sym);
+  return {sym, true};
+}
+
+Symbol *SymbolTable::addDefined(StringRef name, InputSection *isec,
+                                uint32_t value) {
+  Symbol *s;
+  bool wasInserted;
+  std::tie(s, wasInserted) = insert(name);
+
+  if (!wasInserted && isa<Defined>(s))
+    error("duplicate symbol: " + name);
+
+  replaceSymbol<Defined>(s, name, isec, value);
+  return s;
+}
+
+Symbol *SymbolTable::addUndefined(StringRef name) {
+  Symbol *s;
+  bool wasInserted;
+  std::tie(s, wasInserted) = insert(name);
+
+  if (wasInserted)
+    replaceSymbol<Undefined>(s, name);
+  return s;
+}
+
+SymbolTable *macho::symtab;
diff --git a/lld/MachO/Symbols.h b/lld/MachO/Symbols.h
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Symbols.h
@@ -0,0 +1,100 @@
+//===- Symbols.h ------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_SYMBOLS_H
+#define LLD_MACHO_SYMBOLS_H
+
+#include "InputSection.h"
+#include "Target.h"
+#include "lld/Common/Strings.h"
+#include "llvm/Object/Archive.h"
+
+namespace lld {
+namespace macho {
+
+class InputSection;
+class InputFile;
+class ArchiveFile;
+
+struct StringRefZ {
+  StringRefZ(const char *s) : data(s), size(-1) {}
+  StringRefZ(StringRef s) : data(s.data()), size(s.size()) {}
+
+  const char *data;
+  const uint32_t size;
+};
+
+class Symbol {
+public:
+  enum Kind {
+    DefinedKind,
+    UndefinedKind,
+  };
+
+  Kind kind() const { return static_cast<Kind>(symbolKind); }
+
+  StringRef getName() const { return {name.data, name.size}; }
+
+  uint64_t getVA() const;
+
+  InputFile *file;
+
+protected:
+  Symbol(Kind k, InputFile *file, StringRefZ name)
+      : file(file), symbolKind(k), name(name) {}
+
+  Kind symbolKind;
+  StringRefZ name;
+};
+
+class Defined : public Symbol {
+public:
+  Defined(StringRefZ name, InputSection *isec, uint32_t value)
+      : Symbol(DefinedKind, nullptr, name), isec(isec), value(value) {}
+
+  InputSection *isec;
+  uint32_t value;
+
+  static bool classof(const Symbol *s) { return s->kind() == DefinedKind; }
+};
+
+class Undefined : public Symbol {
+public:
+  Undefined(StringRefZ name) : Symbol(UndefinedKind, nullptr, name) {}
+
+  static bool classof(const Symbol *s) { return s->kind() == UndefinedKind; }
+};
+
+inline uint64_t Symbol::getVA() const {
+  if (auto *d = dyn_cast<Defined>(this))
+    return d->isec->addr + d->value - ImageBase;
+  return 0;
+}
+
+union SymbolUnion {
+  alignas(Defined) char a[sizeof(Defined)];
+  alignas(Undefined) char b[sizeof(Undefined)];
+};
+
+template <typename T, typename... ArgT>
+void replaceSymbol(Symbol *s, ArgT &&... arg) {
+  static_assert(sizeof(T) <= sizeof(SymbolUnion), "SymbolUnion too small");
+  static_assert(alignof(T) <= alignof(SymbolUnion),
+                "SymbolUnion not aligned enough");
+  assert(static_cast<Symbol *>(static_cast<T *>(nullptr)) == nullptr &&
+         "Not a Symbol");
+
+  new (s) T(std::forward<ArgT>(arg)...);
+}
+
+} // namespace macho
+
+std::string toString(const macho::Symbol &);
+} // namespace lld
+
+#endif
diff --git a/lld/MachO/Symbols.cpp b/lld/MachO/Symbols.cpp
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Symbols.cpp
@@ -0,0 +1,23 @@
+//===- Symbols.cpp --------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "Symbols.h"
+#include "InputFiles.h"
+#include "lld/Common/ErrorHandler.h"
+#include "lld/Common/Strings.h"
+
+using namespace llvm;
+using namespace lld;
+using namespace lld::macho;
+
+// Returns a symbol for an error message.
+std::string lld::toString(const Symbol &sym) {
+  if (Optional<std::string> s = demangleItanium(sym.getName()))
+    return *s;
+  return std::string(sym.getName());
+}
diff --git a/lld/MachO/Target.h b/lld/MachO/Target.h
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Target.h
@@ -0,0 +1,41 @@
+//===- Target.h -------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_TARGET_H
+#define LLD_MACHO_TARGET_H
+
+#include <cstdint>
+
+namespace lld {
+namespace macho {
+
+enum {
+  PageSize = 4096,
+  ImageBase = 4096,
+  MaxAlignmentPowerOf2 = 32,
+};
+
+class TargetInfo {
+public:
+  virtual ~TargetInfo() = default;
+  virtual uint64_t getImplicitAddend(const uint8_t *loc,
+                                     uint8_t type) const = 0;
+  virtual void relocateOne(uint8_t *loc, uint8_t type, uint64_t val) const = 0;
+
+  uint32_t cpuType;
+  uint32_t cpuSubtype;
+};
+
+TargetInfo *createX86_64TargetInfo();
+
+extern TargetInfo *target;
+
+} // namespace macho
+} // namespace lld
+
+#endif
diff --git a/lld/MachO/Target.cpp b/lld/MachO/Target.cpp
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Target.cpp
@@ -0,0 +1,14 @@
+//===- Target.cpp ---------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "Target.h"
+
+using namespace lld;
+using namespace lld::macho;
+
+TargetInfo *macho::target = nullptr;
diff --git a/lld/MachO/Writer.h b/lld/MachO/Writer.h
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Writer.h
@@ -0,0 +1,20 @@
+//===- Writer.h -------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_WRITER_H
+#define LLD_MACHO_WRITER_H
+
+namespace lld {
+namespace macho {
+
+void writeResult();
+
+} // namespace macho
+} // namespace lld
+
+#endif
diff --git a/lld/MachO/Writer.cpp b/lld/MachO/Writer.cpp
new file mode 100644
--- /dev/null
+++ b/lld/MachO/Writer.cpp
@@ -0,0 +1,359 @@
+//===- Writer.cpp ---------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "Writer.h"
+#include "Config.h"
+#include "InputFiles.h"
+#include "InputSection.h"
+#include "OutputSegment.h"
+#include "SymbolTable.h"
+#include "Symbols.h"
+#include "Target.h"
+
+#include "lld/Common/ErrorHandler.h"
+#include "lld/Common/Memory.h"
+#include "llvm/BinaryFormat/MachO.h"
+#include "llvm/Support/LEB128.h"
+#include "llvm/Support/MathExtras.h"
+
+using namespace llvm;
+using namespace llvm::MachO;
+using namespace llvm::support;
+using namespace lld;
+using namespace lld::macho;
+
+namespace {
+class LCLinkEdit;
+class LCDyldInfo;
+class LCSymtab;
+
+class LoadCommand {
+public:
+  virtual ~LoadCommand() = default;
+  virtual uint32_t getSize() const = 0;
+  virtual void writeTo(uint8_t *buf) const = 0;
+};
+
+class Writer {
+public:
+  Writer() : buffer(errorHandler().outputBuffer) {}
+
+  void createLoadCommands();
+  void assignAddresses();
+
+  void openFile();
+  void writeHeader();
+  void writeSections();
+
+  void run();
+
+  std::vector<LoadCommand *> loadCommands;
+  std::unique_ptr<FileOutputBuffer> &buffer;
+  uint64_t fileSize = 0;
+  uint64_t sizeofCmds = 0;
+  LCLinkEdit *linkEditSeg = nullptr;
+  LCDyldInfo *dyldInfoSeg = nullptr;
+  LCSymtab *symtabSeg = nullptr;
+};
+
+class LCPagezero : public LoadCommand {
+public:
+  uint32_t getSize() const override { return sizeof(segment_command_64); }
+
+  void writeTo(uint8_t *buf) const override {
+    auto *c = reinterpret_cast<segment_command_64 *>(buf);
+    c->cmd = LC_SEGMENT_64;
+    c->cmdsize = getSize();
+    strcpy(c->segname, "__PAGEZERO");
+    c->vmsize = PageSize;
+  }
+};
+
+class LCLinkEdit : public LoadCommand {
+public:
+  uint32_t getSize() const override { return sizeof(segment_command_64); }
+
+  void writeTo(uint8_t *buf) const override {
+    auto *c = reinterpret_cast<segment_command_64 *>(buf);
+    c->cmd = LC_SEGMENT_64;
+    c->cmdsize = getSize();
+    strcpy(c->segname, "__LINKEDIT");
+    c->fileoff = fileOff;
+    c->filesize = contents.size();
+    c->maxprot = VM_PROT_READ | VM_PROT_WRITE;
+    c->initprot = VM_PROT_READ;
+  }
+
+  uint64_t getOffset() const { return fileOff + contents.size(); }
+
+  uint64_t fileOff = 0;
+  SmallVector<char, 128> contents;
+};
+
+class LCDyldInfo : public LoadCommand {
+public:
+  uint32_t getSize() const override { return sizeof(dyld_info_command); }
+
+  void writeTo(uint8_t *buf) const override {
+    auto *c = reinterpret_cast<dyld_info_command *>(buf);
+    c->cmd = LC_DYLD_INFO_ONLY;
+    c->cmdsize = getSize();
+    c->export_off = exportOff;
+    c->export_size = exportSize;
+  }
+
+  uint64_t exportOff = 0;
+  uint64_t exportSize = 0;
+};
+
+class LCDysymtab : public LoadCommand {
+public:
+  uint32_t getSize() const override { return sizeof(dysymtab_command); }
+
+  void writeTo(uint8_t *buf) const override {
+    auto *c = reinterpret_cast<dysymtab_command *>(buf);
+    c->cmd = LC_DYSYMTAB;
+    c->cmdsize = getSize();
+  }
+};
+
+class LCSegment : public LoadCommand {
+public:
+  LCSegment(StringRef name, OutputSegment *seg) : name(name), seg(seg) {}
+
+  uint32_t getSize() const override {
+    return sizeof(segment_command_64) +
+           seg->sections.size() * sizeof(section_64);
+  }
+
+  void writeTo(uint8_t *buf) const override {
+    auto *c = reinterpret_cast<segment_command_64 *>(buf);
+    buf += sizeof(segment_command_64);
+
+    c->cmd = LC_SEGMENT_64;
+    c->cmdsize = getSize();
+    memcpy(c->segname, name.data(), name.size());
+
+    InputSection *firstSec = seg->sections.front().second[0];
+    InputSection *lastSec = seg->sections.back().second.back();
+
+    // dyld3's MachOLoaded::getSlide() assumes that the __TEXT segment starts
+    // from the beginning of the file (i.e. the header).
+    // TODO: replace this logic by creating a synthetic __TEXT,__mach_header
+    // section instead.
+    c->fileoff = name == "__TEXT" ? 0 : firstSec->addr - ImageBase;
+    c->vmaddr = c->fileoff + ImageBase;
+    c->vmsize = c->filesize = lastSec->addr + lastSec->data.size() - c->vmaddr;
+    c->maxprot = VM_PROT_READ | VM_PROT_WRITE | VM_PROT_EXECUTE;
+    c->initprot = seg->perms;
+    c->nsects = seg->sections.size();
+
+    for (auto &p : seg->sections) {
+      StringRef s = p.first;
+      std::vector<InputSection *> &sections = p.second;
+
+      auto *sectHdr = reinterpret_cast<section_64 *>(buf);
+      buf += sizeof(section_64);
+
+      memcpy(sectHdr->sectname, s.data(), s.size());
+      memcpy(sectHdr->segname, name.data(), name.size());
+
+      sectHdr->addr = sections[0]->addr;
+      sectHdr->offset = sections[0]->addr - ImageBase;
+      sectHdr->align = sections[0]->align;
+      uint32_t maxAlign = 0;
+      for (const InputSection *section : sections)
+        maxAlign = std::max(maxAlign, section->align);
+      sectHdr->align = Log2_32(maxAlign);
+      sectHdr->flags = sections[0]->flags;
+      sectHdr->size = sections.back()->addr + sections.back()->data.size() -
+                      sections[0]->addr;
+    }
+  }
+
+private:
+  StringRef name;
+  OutputSegment *seg;
+};
+
+class LCMain : public LoadCommand {
+  uint32_t getSize() const override { return sizeof(entry_point_command); }
+
+  void writeTo(uint8_t *buf) const override {
+    auto *c = reinterpret_cast<entry_point_command *>(buf);
+    c->cmd = LC_MAIN;
+    c->cmdsize = getSize();
+    c->entryoff = config->entry->getVA();
+    c->stacksize = 0;
+  }
+};
+
+class LCSymtab : public LoadCommand {
+public:
+  uint32_t getSize() const override { return sizeof(symtab_command); }
+
+  void writeTo(uint8_t *buf) const override {
+    auto *c = reinterpret_cast<symtab_command *>(buf);
+    c->cmd = LC_SYMTAB;
+    c->cmdsize = getSize();
+  }
+};
+
+class LCLoadDylib : public LoadCommand {
+public:
+  LCLoadDylib(StringRef path) : path(path) {}
+
+  uint32_t getSize() const override {
+    return alignTo(sizeof(dylib_command) + path.size() + 1, 8);
+  }
+
+  void writeTo(uint8_t *buf) const override {
+    auto *c = reinterpret_cast<dylib_command *>(buf);
+    buf += sizeof(dylib_command);
+
+    c->cmd = LC_LOAD_DYLIB;
+    c->cmdsize = getSize();
+    c->dylib.name = sizeof(dylib_command);
+
+    memcpy(buf, path.data(), path.size());
+    buf[path.size()] = '\0';
+  }
+
+private:
+  StringRef path;
+};
+
+class LCLoadDylinker : public LoadCommand {
+public:
+  uint32_t getSize() const override {
+    return alignTo(sizeof(dylinker_command) + path.size() + 1, 8);
+  }
+
+  void writeTo(uint8_t *buf) const override {
+    auto *c = reinterpret_cast<dylinker_command *>(buf);
+    buf += sizeof(dylinker_command);
+
+    c->cmd = LC_LOAD_DYLINKER;
+    c->cmdsize = getSize();
+    c->name = sizeof(dylinker_command);
+
+    memcpy(buf, path.data(), path.size());
+    buf[path.size()] = '\0';
+  }
+
+private:
+  // Recent versions of Darwin won't run any binary that has dyld at a
+  // different location.
+  const StringRef path = "/usr/lib/dyld";
+};
+} // namespace
+
+void Writer::createLoadCommands() {
+  linkEditSeg = make<LCLinkEdit>();
+  dyldInfoSeg = make<LCDyldInfo>();
+  symtabSeg = make<LCSymtab>();
+
+  loadCommands.push_back(linkEditSeg);
+  loadCommands.push_back(dyldInfoSeg);
+  loadCommands.push_back(symtabSeg);
+  loadCommands.push_back(make<LCPagezero>());
+  loadCommands.push_back(make<LCLoadDylinker>());
+  loadCommands.push_back(make<LCDysymtab>());
+  loadCommands.push_back(make<LCMain>());
+  // TODO: dyld requires libSystem to be loaded. libSystem is a universal
+  // binary and we don't have support for that yet, so mock it out here.
+  loadCommands.push_back(make<LCLoadDylib>("/usr/lib/libSystem.B.dylib"));
+
+  for (OutputSegment *seg : outputSegments)
+    if (!seg->sections.empty())
+      loadCommands.push_back(make<LCSegment>(seg->name, seg));
+}
+
+void Writer::assignAddresses() {
+  uint64_t addr = ImageBase + sizeof(mach_header_64);
+
+  uint64_t size = 0;
+  for (LoadCommand *lc : loadCommands)
+    size += lc->getSize();
+  sizeofCmds = size;
+  addr += size;
+
+  for (OutputSegment *seg : outputSegments) {
+    addr = alignTo(addr, PageSize);
+
+    for (auto &p : seg->sections) {
+      ArrayRef<InputSection *> sections = p.second;
+      for (InputSection *isec : sections) {
+        addr = alignTo(addr, isec->align);
+        isec->addr = addr;
+        addr += isec->data.size();
+      }
+    }
+  }
+
+  linkEditSeg->fileOff = addr - ImageBase;
+}
+
+void Writer::openFile() {
+  Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
+      FileOutputBuffer::create(config->outputFile, fileSize,
+                               FileOutputBuffer::F_executable);
+
+  if (!bufferOrErr)
+    error("failed to open " + config->outputFile + ": " +
+          llvm::toString(bufferOrErr.takeError()));
+  else
+    buffer = std::move(*bufferOrErr);
+}
+
+void Writer::writeHeader() {
+  auto *hdr = reinterpret_cast<mach_header_64 *>(buffer->getBufferStart());
+  hdr->magic = MH_MAGIC_64;
+  hdr->cputype = CPU_TYPE_X86_64;
+  hdr->cpusubtype = CPU_SUBTYPE_X86_64_ALL | CPU_SUBTYPE_LIB64;
+  hdr->filetype = MH_EXECUTE;
+  hdr->ncmds = loadCommands.size();
+  hdr->sizeofcmds = sizeofCmds;
+  hdr->flags = MH_NOUNDEFS | MH_DYLDLINK | MH_TWOLEVEL;
+
+  uint8_t *p = reinterpret_cast<uint8_t *>(hdr + 1);
+  for (LoadCommand *lc : loadCommands) {
+    lc->writeTo(p);
+    p += lc->getSize();
+  }
+}
+
+void Writer::writeSections() {
+  uint8_t *buf = buffer->getBufferStart();
+
+  for (OutputSegment *seg : outputSegments)
+    for (auto &sect : seg->sections)
+      for (InputSection *isec : sect.second)
+        isec->writeTo(buf + isec->addr - ImageBase);
+
+  memcpy(buf + linkEditSeg->fileOff, linkEditSeg->contents.data(),
+         linkEditSeg->contents.size());
+}
+
+void Writer::run() {
+  createLoadCommands();
+  assignAddresses();
+  fileSize = linkEditSeg->fileOff + linkEditSeg->contents.size();
+
+  openFile();
+  if (errorCount())
+    return;
+
+  writeHeader();
+  writeSections();
+
+  if (auto e = buffer->commit())
+    error("failed to write to the output file: " + toString(std::move(e)));
+}
+
+void macho::writeResult() { Writer().run(); }
diff --git a/lld/include/lld/Common/Driver.h b/lld/include/lld/Common/Driver.h
--- a/lld/include/lld/Common/Driver.h
+++ b/lld/include/lld/Common/Driver.h
@@ -33,6 +33,11 @@
           llvm::raw_ostream &stdoutOS, llvm::raw_ostream &stderrOS);
 }
 
+namespace macho {
+bool link(llvm::ArrayRef<const char *> args, bool canExitEarly,
+          llvm::raw_ostream &stdoutOS, llvm::raw_ostream &stderrOS);
+}
+
 namespace wasm {
 bool link(llvm::ArrayRef<const char *> args, bool canExitEarly,
           llvm::raw_ostream &stdoutOS, llvm::raw_ostream &stderrOS);
diff --git a/lld/test/MachO/alignment-too-large.yaml b/lld/test/MachO/alignment-too-large.yaml
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/alignment-too-large.yaml
@@ -0,0 +1,58 @@
+# RUN: yaml2obj %s -o %t.o
+# RUN: not lld -flavor darwinnew -o %t %t.o 2>&1 | FileCheck %s
+#
+# CHECK: alignment 32 of section __text is too large
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x01000007
+  cpusubtype:      0x00000003
+  filetype:        0x00000001
+  ncmds:           4
+  sizeofcmds:      280
+  flags:           0x00000000
+  reserved:        0x00000000
+LoadCommands:
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         152
+    segname:         ''
+    vmaddr:          0
+    vmsize:          8
+    fileoff:         312
+    filesize:        8
+    maxprot:         7
+    initprot:        7
+    nsects:          1
+    flags:           0
+    Sections:
+      - sectname:        __text
+        segname:         __TEXT
+        addr:            0x0000000000000000
+        size:            8
+        offset:          0x00000138
+        align:           32
+        reloff:          0x00000000
+        nreloc:          0
+        flags:           0x80000400
+        reserved1:       0x00000000
+        reserved2:       0x00000000
+        reserved3:       0x00000000
+        content:         48C7C000000000C3
+  - cmd:             LC_SYMTAB
+    cmdsize:         24
+    symoff:          320
+    nsyms:           1
+    stroff:          336
+    strsize:         8
+LinkEditData:
+  NameList:
+    - n_strx:          1
+      n_type:          0x0F
+      n_sect:          1
+      n_desc:          0
+      n_value:         0
+  StringTable:
+    - ''
+    - _main
+    - ''
+...
diff --git a/lld/test/MachO/arch.s b/lld/test/MachO/arch.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/arch.s
@@ -0,0 +1,11 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-darwin %s -o %t.o
+# RUN: lld -flavor darwinnew -arch x86_64 -o /dev/null %t.o
+# RUN: not lld -flavor darwinnew -arch i386 -o /dev/null %t.o 2>&1 | FileCheck %s
+# CHECK: missing or unsupported -arch i386
+
+.text
+.global _main
+_main:
+  mov $0, %rax
+  ret
diff --git a/lld/test/MachO/duplicate-symbol.s b/lld/test/MachO/duplicate-symbol.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/duplicate-symbol.s
@@ -0,0 +1,12 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t-dup.o
+# RUN: not lld -flavor darwinnew -o /dev/null %t-dup.o %t.o 2>&1 | FileCheck %s
+
+# CHECK: duplicate symbol: _main
+
+.text
+.global _main
+_main:
+  mov $0, %rax
+  ret
diff --git a/lld/test/MachO/entry-symbol.s b/lld/test/MachO/entry-symbol.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/entry-symbol.s
@@ -0,0 +1,13 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+# RUN: lld -flavor darwinnew -o /dev/null %t.o -e _not_main
+# RUN: not lld -flavor darwinnew -o /dev/null %t.o -e _missing 2>&1 | FileCheck %s
+# RUN: not lld -flavor darwinnew -o /dev/null %t.o 2>&1 | FileCheck %s --check-prefix=DEFAULT_ENTRY
+
+# CHECK: undefined symbol: _missing
+# DEFAULT_ENTRY: undefined symbol: _main
+
+.text
+.global _not_main
+_not_main:
+  ret
diff --git a/lld/test/MachO/invalid-executable.s b/lld/test/MachO/invalid-executable.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/invalid-executable.s
@@ -0,0 +1,11 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-darwin %s -o %t.o
+# RUN: lld -flavor darwinnew -o %t %t.o
+# RUN: not lld -flavor darwinnew -o /dev/null %t 2>&1 | FileCheck %s
+# CHECK: unhandled file type
+
+.text
+.global _main
+_main:
+  mov $0, %rax
+  ret
diff --git a/lld/test/MachO/load-commands.s b/lld/test/MachO/load-commands.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/load-commands.s
@@ -0,0 +1,17 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+# RUN: lld -flavor darwinnew -o %t %t.o
+# RUN: obj2yaml %t | FileCheck %s
+
+# Check for the presence of a couple of load commands that are essential for
+# a working binary.
+
+# CHECK-DAG: cmd:             LC_DYLD_INFO_ONLY
+# CHECK-DAG: cmd:             LC_SYMTAB
+# CHECK-DAG: cmd:             LC_DYSYMTAB
+
+.text
+.global _main
+_main:
+  mov $0, %rax
+  ret
diff --git a/lld/test/MachO/no-such-file.s b/lld/test/MachO/no-such-file.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/no-such-file.s
@@ -0,0 +1,4 @@
+# REQUIRES: x86
+# RUN: not lld -flavor darwinnew -o /dev/null %t-no-such-file.o 2>&1 | FileCheck %s
+
+# CHECK: cannot open {{.*}}no-such-file.o
diff --git a/lld/test/MachO/relocations.s b/lld/test/MachO/relocations.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/relocations.s
@@ -0,0 +1,21 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+# RUN: lld -flavor darwinnew -o %t %t.o
+# RUN: llvm-objdump -d %t | FileCheck %s
+
+# CHECK: leaq 17(%rip), %rsi
+
+.section __TEXT,__text
+.globl _main
+_main:
+  movl $0x2000004, %eax # write() syscall
+  mov $1, %rdi # stdout
+  leaq str(%rip), %rsi
+  mov $13, %rdx # length of str
+  syscall
+  mov $0, %rax
+  ret
+
+.section __TEXT,__cstring
+str:
+  .asciz "Hello world!\n"
diff --git a/lld/test/MachO/section-headers.s b/lld/test/MachO/section-headers.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/section-headers.s
@@ -0,0 +1,46 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+# RUN: lld -flavor darwinnew -o %t %t.o
+# RUN: llvm-readobj --section-headers %t | FileCheck %s
+
+# CHECK:      Name: __text
+# CHECK-NEXT: Segment: __TEXT
+# CHECK-NOT:  }
+# CHECK:      Alignment: 1
+# CHECK-NOT:  }
+# CHECK:      Type: Regular (0x0)
+# CHECK-NEXT: Attributes [ (0x800004)
+# CHECK-NEXT:   PureInstructions (0x800000)
+# CHECK-NEXT:   SomeInstructions (0x4)
+# CHECK-NEXT: ]
+
+# CHECK:      Name: __cstring
+# CHECK-NEXT: Segment: __TEXT
+# CHECK-NOT:  }
+# CHECK:      Alignment: 2
+# CHECK-NOT:  }
+# CHECK:      Type: CStringLiterals (0x2)
+# CHECK-NEXT: Attributes [ (0x0)
+# CHECK-NEXT: ]
+
+# CHECK:      Name: maxlen_16ch_name
+# CHECK-NEXT: Segment: __TEXT
+# CHECK-NOT:  }
+# CHECK:      Alignment: 3
+# CHECK-NOT:  }
+# CHECK:      Type: Regular (0x0)
+
+.text
+.align 1
+.global _main
+_main:
+  mov $0, %rax
+  ret
+
+.section __TEXT,__cstring
+.align 2
+str:
+  .asciz "Hello world!\n"
+
+.section __TEXT,maxlen_16ch_name
+.align 3
diff --git a/lld/test/MachO/segments.s b/lld/test/MachO/segments.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/segments.s
@@ -0,0 +1,20 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+# RUN: lld -flavor darwinnew -o %t %t.o
+# RUN: llvm-readobj --macho-segment %t | FileCheck %s
+
+# These segments must always be present.
+# CHECK-DAG: Name: __PAGEZERO
+# CHECK-DAG: Name: __LINKEDIT
+# CHECK-DAG: Name: __TEXT
+
+# Check that we handle max-length names correctly.
+# CHECK-DAG: Name: maxlen_16ch_name
+
+.text
+.global _main
+_main:
+  mov $0, %rax
+  ret
+
+.section maxlen_16ch_name,foo
diff --git a/lld/test/MachO/silent-ignore.test b/lld/test/MachO/silent-ignore.test
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/silent-ignore.test
@@ -0,0 +1,8 @@
+RUN: lld -flavor darwinnew -v \
+RUN:   -demangle \
+RUN:   -dynamic \
+RUN:   -no_deduplicate \
+RUN:   -lto_library /lib/foo \
+RUN:   -macosx_version_min 0
+RUN: not lld -flavor darwinnew -v --not-an-ignored-argument 2>&1 | FileCheck %s
+CHECK: unknown argument: --not-an-ignored-argument
diff --git a/lld/test/MachO/text-segment.s b/lld/test/MachO/text-segment.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/text-segment.s
@@ -0,0 +1,15 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+# RUN: lld -flavor darwinnew -o %t %t.o
+# RUN: llvm-readobj --macho-segment %t | FileCheck %s
+
+# CHECK: Name: __TEXT
+# CHECK-NOT: }
+# dyld3 assumes that the __TEXT segment starts from the file header
+# CHECK:       fileoff: 0
+
+.text
+.global _main
+_main:
+  mov $0, %rax
+  ret
diff --git a/lld/tools/lld/CMakeLists.txt b/lld/tools/lld/CMakeLists.txt
--- a/lld/tools/lld/CMakeLists.txt
+++ b/lld/tools/lld/CMakeLists.txt
@@ -12,6 +12,7 @@
   lldCOFF
   lldDriver
   lldELF
+  lldMachO2
   lldMinGW
   lldWasm
   )
diff --git a/lld/tools/lld/lld.cpp b/lld/tools/lld/lld.cpp
--- a/lld/tools/lld/lld.cpp
+++ b/lld/tools/lld/lld.cpp
@@ -44,10 +44,11 @@
 
 enum Flavor {
   Invalid,
-  Gnu,     // -flavor gnu
-  WinLink, // -flavor link
-  Darwin,  // -flavor darwin
-  Wasm,    // -flavor wasm
+  Gnu,       // -flavor gnu
+  WinLink,   // -flavor link
+  Darwin,    // -flavor darwin
+  DarwinNew, // -flavor darwinnew
+  Wasm,      // -flavor wasm
 };
 
 LLVM_ATTRIBUTE_NORETURN static void die(const Twine &s) {
@@ -61,6 +62,7 @@
       .CasesLower("wasm", "ld-wasm", Wasm)
       .CaseLower("link", WinLink)
       .CasesLower("ld64", "ld64.lld", "darwin", Darwin)
+      .CaseLower("darwinnew", DarwinNew)
       .Default(Invalid);
 }
 
@@ -156,6 +158,8 @@
     return !coff::link(args, canExitEarly(), llvm::outs(), llvm::errs());
   case Darwin:
     return !mach_o::link(args, canExitEarly(), llvm::outs(), llvm::errs());
+  case DarwinNew:
+    return !macho::link(args, canExitEarly(), llvm::outs(), llvm::errs());
   case Wasm:
     return !wasm::link(args, canExitEarly(), llvm::outs(), llvm::errs());
   default: