//===------ MachOPlatform.cpp - Utilities for executing MachO in Orc ------===//
//
// 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 "llvm/ExecutionEngine/Orc/MachOPlatform.h"

#include "llvm/BinaryFormat/MachO.h"
#include "llvm/ExecutionEngine/JITLink/EHFrameSupport.h"
#include "llvm/ExecutionEngine/JITLink/MachO.h"
#include "llvm/ExecutionEngine/JITLink/aarch64.h"
#include "llvm/ExecutionEngine/JITLink/x86_64.h"
#include "llvm/ExecutionEngine/Orc/ExecutionUtils.h"
#include "llvm/ExecutionEngine/Orc/MachOBuilder.h"
#include "llvm/ExecutionEngine/Orc/Shared/OrcRTBridge.h"
#include "llvm/Support/Debug.h"
#include <optional>

#define DEBUG_TYPE "orc"

using namespace llvm;
using namespace llvm::orc;
using namespace llvm::orc::shared;

namespace llvm {
namespace orc {
namespace shared {

using SPSMachOJITDylibDepInfo = SPSTuple<bool, SPSSequence<SPSExecutorAddr>>;
using SPSMachOJITDylibDepInfoMap =
    SPSSequence<SPSTuple<SPSExecutorAddr, SPSMachOJITDylibDepInfo>>;

class SPSMachOExecutorSymbolFlags;

template <>
class SPSSerializationTraits<SPSMachOJITDylibDepInfo,
                             MachOPlatform::MachOJITDylibDepInfo> {
public:
  static size_t size(const MachOPlatform::MachOJITDylibDepInfo &DDI) {
    return SPSMachOJITDylibDepInfo::AsArgList::size(DDI.Sealed, DDI.DepHeaders);
  }

  static bool serialize(SPSOutputBuffer &OB,
                        const MachOPlatform::MachOJITDylibDepInfo &DDI) {
    return SPSMachOJITDylibDepInfo::AsArgList::serialize(OB, DDI.Sealed,
                                                         DDI.DepHeaders);
  }

  static bool deserialize(SPSInputBuffer &IB,
                          MachOPlatform::MachOJITDylibDepInfo &DDI) {
    return SPSMachOJITDylibDepInfo::AsArgList::deserialize(IB, DDI.Sealed,
                                                           DDI.DepHeaders);
  }
};

template <>
class SPSSerializationTraits<SPSMachOExecutorSymbolFlags,
                             MachOPlatform::MachOExecutorSymbolFlags> {
private:
  using UT = std::underlying_type_t<MachOPlatform::MachOExecutorSymbolFlags>;

public:
  static size_t size(const MachOPlatform::MachOExecutorSymbolFlags &SF) {
    return sizeof(UT);
  }

  static bool serialize(SPSOutputBuffer &OB,
                        const MachOPlatform::MachOExecutorSymbolFlags &SF) {
    return SPSArgList<UT>::serialize(OB, static_cast<UT>(SF));
  }

  static bool deserialize(SPSInputBuffer &IB,
                          MachOPlatform::MachOExecutorSymbolFlags &SF) {
    UT Tmp;
    if (!SPSArgList<UT>::deserialize(IB, Tmp))
      return false;
    SF = static_cast<MachOPlatform::MachOExecutorSymbolFlags>(Tmp);
    return true;
  }
};

} // namespace shared
} // namespace orc
} // namespace llvm

namespace {

using SPSRegisterSymbolsArgs =
    SPSArgList<SPSExecutorAddr,
               SPSSequence<SPSTuple<SPSExecutorAddr, SPSExecutorAddr,
                                    SPSMachOExecutorSymbolFlags>>>;

std::unique_ptr<jitlink::LinkGraph> createPlatformGraph(MachOPlatform &MOP,
                                                        std::string Name) {
  auto &ES = MOP.getExecutionSession();
  return std::make_unique<jitlink::LinkGraph>(
      std::move(Name), ES.getSymbolStringPool(), ES.getTargetTriple(),
      SubtargetFeatures(), jitlink::getGenericEdgeKindName);
}

// Creates a Bootstrap-Complete LinkGraph to run deferred actions.
class MachOPlatformCompleteBootstrapMaterializationUnit
    : public MaterializationUnit {
public:
  using SymbolTableVector =
      SmallVector<std::tuple<ExecutorAddr, ExecutorAddr,
                             MachOPlatform::MachOExecutorSymbolFlags>>;

  MachOPlatformCompleteBootstrapMaterializationUnit(
      MachOPlatform &MOP, StringRef PlatformJDName,
      SymbolStringPtr CompleteBootstrapSymbol, SymbolTableVector SymTab,
      shared::AllocActions DeferredAAs, ExecutorAddr MachOHeaderAddr,
      ExecutorAddr PlatformBootstrap, ExecutorAddr PlatformShutdown,
      ExecutorAddr RegisterJITDylib, ExecutorAddr DeregisterJITDylib,
      ExecutorAddr RegisterObjectSymbolTable,
      ExecutorAddr DeregisterObjectSymbolTable)
      : MaterializationUnit(
            {{{CompleteBootstrapSymbol, JITSymbolFlags::None}}, nullptr}),
        MOP(MOP), PlatformJDName(PlatformJDName),
        CompleteBootstrapSymbol(std::move(CompleteBootstrapSymbol)),
        SymTab(std::move(SymTab)), DeferredAAs(std::move(DeferredAAs)),
        MachOHeaderAddr(MachOHeaderAddr), PlatformBootstrap(PlatformBootstrap),
        PlatformShutdown(PlatformShutdown), RegisterJITDylib(RegisterJITDylib),
        DeregisterJITDylib(DeregisterJITDylib),
        RegisterObjectSymbolTable(RegisterObjectSymbolTable),
        DeregisterObjectSymbolTable(DeregisterObjectSymbolTable) {}

  StringRef getName() const override {
    return "MachOPlatformCompleteBootstrap";
  }

  void materialize(std::unique_ptr<MaterializationResponsibility> R) override {
    using namespace jitlink;
    auto G = createPlatformGraph(MOP, "<OrcRTCompleteBootstrap>");
    auto &PlaceholderSection =
        G->createSection("__orc_rt_cplt_bs", MemProt::Read);
    auto &PlaceholderBlock =
        G->createZeroFillBlock(PlaceholderSection, 1, ExecutorAddr(), 1, 0);
    G->addDefinedSymbol(PlaceholderBlock, 0, *CompleteBootstrapSymbol, 1,
                        Linkage::Strong, Scope::Hidden, false, true);

    // Reserve space for the stolen actions, plus two extras.
    G->allocActions().reserve(DeferredAAs.size() + 3);

    // 1. Bootstrap the platform support code.
    G->allocActions().push_back(
        {cantFail(WrapperFunctionCall::Create<SPSArgList<>>(PlatformBootstrap)),
         cantFail(
             WrapperFunctionCall::Create<SPSArgList<>>(PlatformShutdown))});

    // 2. Register the platform JITDylib.
    G->allocActions().push_back(
        {cantFail(WrapperFunctionCall::Create<
                  SPSArgList<SPSString, SPSExecutorAddr>>(
             RegisterJITDylib, PlatformJDName, MachOHeaderAddr)),
         cantFail(WrapperFunctionCall::Create<SPSArgList<SPSExecutorAddr>>(
             DeregisterJITDylib, MachOHeaderAddr))});

    // 3. Register deferred symbols.
    G->allocActions().push_back(
        {cantFail(WrapperFunctionCall::Create<SPSRegisterSymbolsArgs>(
             RegisterObjectSymbolTable, MachOHeaderAddr, SymTab)),
         cantFail(WrapperFunctionCall::Create<SPSRegisterSymbolsArgs>(
             DeregisterObjectSymbolTable, MachOHeaderAddr, SymTab))});

    // 4. Add the deferred actions to the graph.
    std::move(DeferredAAs.begin(), DeferredAAs.end(),
              std::back_inserter(G->allocActions()));

    MOP.getObjectLinkingLayer().emit(std::move(R), std::move(G));
  }

  void discard(const JITDylib &JD, const SymbolStringPtr &Sym) override {}

private:
  MachOPlatform &MOP;
  StringRef PlatformJDName;
  SymbolStringPtr CompleteBootstrapSymbol;
  SymbolTableVector SymTab;
  shared::AllocActions DeferredAAs;
  ExecutorAddr MachOHeaderAddr;
  ExecutorAddr PlatformBootstrap;
  ExecutorAddr PlatformShutdown;
  ExecutorAddr RegisterJITDylib;
  ExecutorAddr DeregisterJITDylib;
  ExecutorAddr RegisterObjectSymbolTable;
  ExecutorAddr DeregisterObjectSymbolTable;
};

static StringRef ObjCRuntimeObjectSectionsData[] = {
    MachOObjCCatListSectionName,   MachOObjCCatList2SectionName,
    MachOObjCClassListSectionName, MachOObjCClassRefsSectionName,
    MachOObjCConstSectionName,     MachOObjCDataSectionName,
    MachOObjCProtoListSectionName, MachOObjCProtoRefsSectionName,
    MachOObjCNLCatListSectionName, MachOObjCNLClassListSectionName,
    MachOObjCSelRefsSectionName};

static StringRef ObjCRuntimeObjectSectionsText[] = {
    MachOObjCClassNameSectionName, MachOObjCMethNameSectionName,
    MachOObjCMethTypeSectionName,  MachOSwift5TypesSectionName,
    MachOSwift5TypeRefSectionName, MachOSwift5FieldMetadataSectionName,
    MachOSwift5EntrySectionName,   MachOSwift5ProtoSectionName,
    MachOSwift5ProtosSectionName};

static StringRef ObjCRuntimeObjectSectionName =
    "__llvm_jitlink_ObjCRuntimeRegistrationObject";

static StringRef ObjCImageInfoSymbolName =
    "__llvm_jitlink_macho_objc_imageinfo";

struct ObjCImageInfoFlags {
  uint16_t SwiftABIVersion;
  uint16_t SwiftVersion;
  bool HasCategoryClassProperties;
  bool HasSignedObjCClassROs;

  static constexpr uint32_t SIGNED_CLASS_RO = (1 << 4);
  static constexpr uint32_t HAS_CATEGORY_CLASS_PROPERTIES = (1 << 6);

  explicit ObjCImageInfoFlags(uint32_t RawFlags) {
    HasSignedObjCClassROs = RawFlags & SIGNED_CLASS_RO;
    HasCategoryClassProperties = RawFlags & HAS_CATEGORY_CLASS_PROPERTIES;
    SwiftABIVersion = (RawFlags >> 8) & 0xFF;
    SwiftVersion = (RawFlags >> 16) & 0xFFFF;
  }

  uint32_t rawFlags() const {
    uint32_t Result = 0;
    if (HasCategoryClassProperties)
      Result |= HAS_CATEGORY_CLASS_PROPERTIES;
    if (HasSignedObjCClassROs)
      Result |= SIGNED_CLASS_RO;
    Result |= (SwiftABIVersion << 8);
    Result |= (SwiftVersion << 16);
    return Result;
  }
};
} // end anonymous namespace

namespace llvm {
namespace orc {

std::optional<MachOPlatform::HeaderOptions::BuildVersionOpts>
MachOPlatform::HeaderOptions::BuildVersionOpts::fromTriple(const Triple &TT,
                                                           uint32_t MinOS,
                                                           uint32_t SDK) {

  uint32_t Platform;
  switch (TT.getOS()) {
  case Triple::IOS:
    Platform = TT.isSimulatorEnvironment() ? MachO::PLATFORM_IOSSIMULATOR
                                           : MachO::PLATFORM_IOS;
    break;
  case Triple::MacOSX:
    Platform = MachO::PLATFORM_MACOS;
    break;
  case Triple::TvOS:
    Platform = TT.isSimulatorEnvironment() ? MachO::PLATFORM_TVOSSIMULATOR
                                           : MachO::PLATFORM_TVOS;
    break;
  case Triple::WatchOS:
    Platform = TT.isSimulatorEnvironment() ? MachO::PLATFORM_WATCHOSSIMULATOR
                                           : MachO::PLATFORM_WATCHOS;
    break;
  case Triple::XROS:
    Platform = TT.isSimulatorEnvironment() ? MachO::PLATFORM_XROS_SIMULATOR
                                           : MachO::PLATFORM_XROS;
    break;
  default:
    return std::nullopt;
  }

  return MachOPlatform::HeaderOptions::BuildVersionOpts{Platform, MinOS, SDK};
}

Expected<std::unique_ptr<MachOPlatform>>
MachOPlatform::Create(ObjectLinkingLayer &ObjLinkingLayer, JITDylib &PlatformJD,
                      std::unique_ptr<DefinitionGenerator> OrcRuntime,
                      HeaderOptionsBuilder BuildHeaderOpts,
                      HeaderOptions PlatformJDOpts,
                      MachOHeaderMUBuilder BuildMachOHeaderMU,
                      std::optional<SymbolAliasMap> RuntimeAliases) {

  auto &ES = ObjLinkingLayer.getExecutionSession();

  // If the target is not supported then bail out immediately.
  if (!supportedTarget(ES.getTargetTriple()))
    return make_error<StringError>("Unsupported MachOPlatform triple: " +
                                       ES.getTargetTriple().str(),
                                   inconvertibleErrorCode());

  // Create default aliases if the caller didn't supply any.
  if (!RuntimeAliases)
    RuntimeAliases = standardPlatformAliases(ES);

  // Define the aliases.
  if (auto Err = PlatformJD.define(symbolAliases(std::move(*RuntimeAliases))))
    return std::move(Err);

  {
    // Add JIT dispatch reexports from bootstrap JITDylib.
    if (auto Err = PlatformJD.define(reexports(
            ES.getBootstrapJITDylib(),
            {{ES.intern("___orc_rt_jit_dispatch"),
              {ES.intern(rt::DispatchName),
               JITSymbolFlags::Exported | JITSymbolFlags::Callable}},
             {ES.intern("___orc_rt_jit_dispatch_ctx"),
              {ES.intern(rt::DispatchCtxName), JITSymbolFlags::Exported}}})))
      return Err;
  }

  // Create the instance.
  Error Err = Error::success();
  auto P = std::unique_ptr<MachOPlatform>(
      new MachOPlatform(ObjLinkingLayer, PlatformJD, std::move(OrcRuntime),
                        std::move(BuildHeaderOpts), std::move(PlatformJDOpts),
                        std::move(BuildMachOHeaderMU), Err));
  if (Err)
    return std::move(Err);
  return std::move(P);
}

Expected<std::unique_ptr<MachOPlatform>> MachOPlatform::Create(
    ObjectLinkingLayer &ObjLinkingLayer, JITDylib &PlatformJD,
    const char *OrcRuntimePath, HeaderOptionsBuilder BuildHeaderOpts,
    HeaderOptions PlatformJDOpts, MachOHeaderMUBuilder BuildMachOHeaderMU,
    std::optional<SymbolAliasMap> RuntimeAliases) {

  // Create a generator for the ORC runtime archive.
  auto OrcRuntimeArchiveGenerator =
      StaticLibraryDefinitionGenerator::Load(ObjLinkingLayer, OrcRuntimePath);
  if (!OrcRuntimeArchiveGenerator)
    return OrcRuntimeArchiveGenerator.takeError();

  return Create(ObjLinkingLayer, PlatformJD,
                std::move(*OrcRuntimeArchiveGenerator),
                std::move(BuildHeaderOpts), std::move(PlatformJDOpts),
                std::move(BuildMachOHeaderMU), std::move(RuntimeAliases));
}

Error MachOPlatform::setupJITDylib(JITDylib &JD) {
  return setupJITDylib(JD, BuildHeaderOpts(JD));
}

Error MachOPlatform::setupJITDylib(JITDylib &JD, HeaderOptions Opts) {
  if (auto Err = JD.define(BuildMachOHeaderMU(*this, std::move(Opts))))
    return Err;

  return ES.lookup({&JD}, MachOHeaderStartSymbol).takeError();
}

Error MachOPlatform::teardownJITDylib(JITDylib &JD) {
  std::lock_guard<std::mutex> Lock(PlatformMutex);
  auto I = JITDylibToHeaderAddr.find(&JD);
  if (I != JITDylibToHeaderAddr.end()) {
    assert(HeaderAddrToJITDylib.count(I->second) &&
           "HeaderAddrToJITDylib missing entry");
    HeaderAddrToJITDylib.erase(I->second);
    JITDylibToHeaderAddr.erase(I);
  }
  JITDylibToPThreadKey.erase(&JD);
  return Error::success();
}

Error MachOPlatform::notifyAdding(ResourceTracker &RT,
                                  const MaterializationUnit &MU) {
  auto &JD = RT.getJITDylib();
  const auto &InitSym = MU.getInitializerSymbol();
  if (!InitSym)
    return Error::success();

  RegisteredInitSymbols[&JD].add(InitSym,
                                 SymbolLookupFlags::WeaklyReferencedSymbol);
  LLVM_DEBUG({
    dbgs() << "MachOPlatform: Registered init symbol " << *InitSym << " for MU "
           << MU.getName() << "\n";
  });
  return Error::success();
}

Error MachOPlatform::notifyRemoving(ResourceTracker &RT) {
  llvm_unreachable("Not supported yet");
}

static void addAliases(ExecutionSession &ES, SymbolAliasMap &Aliases,
                       ArrayRef<std::pair<const char *, const char *>> AL) {
  for (auto &KV : AL) {
    auto AliasName = ES.intern(KV.first);
    assert(!Aliases.count(AliasName) && "Duplicate symbol name in alias map");
    Aliases[std::move(AliasName)] = {ES.intern(KV.second),
                                     JITSymbolFlags::Exported};
  }
}

SymbolAliasMap MachOPlatform::standardPlatformAliases(ExecutionSession &ES) {
  SymbolAliasMap Aliases;
  addAliases(ES, Aliases, requiredCXXAliases());
  addAliases(ES, Aliases, standardRuntimeUtilityAliases());
  addAliases(ES, Aliases, standardLazyCompilationAliases());
  return Aliases;
}

ArrayRef<std::pair<const char *, const char *>>
MachOPlatform::requiredCXXAliases() {
  static const std::pair<const char *, const char *> RequiredCXXAliases[] = {
      {"___cxa_atexit", "___orc_rt_macho_cxa_atexit"}};

  return ArrayRef<std::pair<const char *, const char *>>(RequiredCXXAliases);
}

ArrayRef<std::pair<const char *, const char *>>
MachOPlatform::standardRuntimeUtilityAliases() {
  static const std::pair<const char *, const char *>
      StandardRuntimeUtilityAliases[] = {
          {"___orc_rt_run_program", "___orc_rt_macho_run_program"},
          {"___orc_rt_jit_dlerror", "___orc_rt_macho_jit_dlerror"},
          {"___orc_rt_jit_dlopen", "___orc_rt_macho_jit_dlopen"},
          {"___orc_rt_jit_dlupdate", "___orc_rt_macho_jit_dlupdate"},
          {"___orc_rt_jit_dlclose", "___orc_rt_macho_jit_dlclose"},
          {"___orc_rt_jit_dlsym", "___orc_rt_macho_jit_dlsym"},
          {"___orc_rt_log_error", "___orc_rt_log_error_to_stderr"}};

  return ArrayRef<std::pair<const char *, const char *>>(
      StandardRuntimeUtilityAliases);
}

ArrayRef<std::pair<const char *, const char *>>
MachOPlatform::standardLazyCompilationAliases() {
  static const std::pair<const char *, const char *>
      StandardLazyCompilationAliases[] = {
          {"__orc_rt_reenter", "__orc_rt_sysv_reenter"},
          {"__orc_rt_resolve_tag", "___orc_rt_resolve_tag"}};

  return ArrayRef<std::pair<const char *, const char *>>(
      StandardLazyCompilationAliases);
}

MachOPlatform::HeaderOptions MachOPlatform::defaultHeaderOpts(JITDylib &JD) {
  return {};
}

bool MachOPlatform::supportedTarget(const Triple &TT) {
  switch (TT.getArch()) {
  case Triple::aarch64:
  case Triple::x86_64:
    return true;
  default:
    return false;
  }
}

jitlink::Edge::Kind MachOPlatform::getPointerEdgeKind(jitlink::LinkGraph &G) {
  switch (G.getTargetTriple().getArch()) {
  case Triple::aarch64:
    return jitlink::aarch64::Pointer64;
  case Triple::x86_64:
    return jitlink::x86_64::Pointer64;
  default:
    llvm_unreachable("Unsupported architecture");
  }
}

MachOPlatform::MachOExecutorSymbolFlags
MachOPlatform::flagsForSymbol(jitlink::Symbol &Sym) {
  MachOPlatform::MachOExecutorSymbolFlags Flags{};
  if (Sym.getLinkage() == jitlink::Linkage::Weak)
    Flags |= MachOExecutorSymbolFlags::Weak;

  if (Sym.isCallable())
    Flags |= MachOExecutorSymbolFlags::Callable;

  return Flags;
}

MachOPlatform::MachOPlatform(
    ObjectLinkingLayer &ObjLinkingLayer, JITDylib &PlatformJD,
    std::unique_ptr<DefinitionGenerator> OrcRuntimeGenerator,
    HeaderOptionsBuilder BuildHeaderOpts, HeaderOptions PlatformJDOpts,
    MachOHeaderMUBuilder BuildMachOHeaderMU, Error &Err)
    : ES(ObjLinkingLayer.getExecutionSession()), PlatformJD(PlatformJD),
      ObjLinkingLayer(ObjLinkingLayer),
      BuildHeaderOpts(std::move(BuildHeaderOpts)),
      BuildMachOHeaderMU(std::move(BuildMachOHeaderMU)) {
  ErrorAsOutParameter _(Err);
  ObjLinkingLayer.addPlugin(std::make_unique<MachOPlatformPlugin>(*this));
  PlatformJD.addGenerator(std::move(OrcRuntimeGenerator));

  {
    // Check for force-eh-frame
    std::optional<bool> ForceEHFrames;
    if ((Err = ES.getBootstrapMapValue<bool, bool>("darwin-use-ehframes-only",
                                                   ForceEHFrames)))
      return;
    this->ForceEHFrames = ForceEHFrames.value_or(false);
  }

  BootstrapInfo BI;
  Bootstrap = &BI;

  // Bootstrap process -- here be phase-ordering dragons.
  //
  // The MachOPlatform class uses allocation actions to register metadata
  // sections with the ORC runtime, however the runtime contains metadata
  // registration functions that have their own metadata that they need to
  // register (e.g. the frame-info registration functions have frame-info).
  // We can't use an ordinary lookup to find these registration functions
  // because their address is needed during the link of the containing graph
  // itself (to build the allocation actions that will call the registration
  // functions). Further complicating the situation (a) the graph containing
  // the registration functions is allowed to depend on other graphs (e.g. the
  // graph containing the ORC runtime RTTI support) so we need to handle an
  // unknown set of dependencies during bootstrap, and (b) these graphs may
  // be linked concurrently if the user has installed a concurrent dispatcher.
  //
  // We satisfy these constraints by implementing a bootstrap phase during which
  // allocation actions generated by MachOPlatform are appended to a list of
  // deferred allocation actions, rather than to the graphs themselves. At the
  // end of the bootstrap process the deferred actions are attached to a final
  // "complete-bootstrap" graph that causes them to be run.
  //
  // The bootstrap steps are as follows:
  //
  // 1. Request the graph containing the mach header. This graph is guaranteed
  //    not to have any metadata so the fact that the registration functions
  //    are not available yet is not a problem.
  //
  // 2. Look up the registration functions and discard the results. This will
  //    trigger linking of the graph containing these functions, and
  //    consequently any graphs that it depends on. We do not use the lookup
  //    result to find the addresses of the functions requested (as described
  //    above the lookup will return too late for that), instead we capture the
  //    addresses in a post-allocation pass injected by the platform runtime
  //    during bootstrap only.
  //
  // 3. During bootstrap the MachOPlatformPlugin keeps a count of the number of
  //    graphs being linked (potentially concurrently), and we block until all
  //    of these graphs have completed linking. This is to avoid a race on the
  //    deferred-actions vector: the lookup for the runtime registration
  //    functions may return while some functions (those that are being
  //    incidentally linked in, but aren't reachable via the runtime functions)
  //    are still being linked, and we need to capture any allocation actions
  //    for this incidental code before we proceed.
  //
  // 4. Once all active links are complete we transfer the deferred actions to
  //    a newly added CompleteBootstrap graph and then request a symbol from
  //    the CompleteBootstrap graph to trigger materialization. This will cause
  //    all deferred actions to be run, and once this lookup returns we can
  //    proceed.
  //
  // 5. Finally, we associate runtime support methods in MachOPlatform with
  //    the corresponding jit-dispatch tag variables in the ORC runtime to make
  //    the support methods callable. The bootstrap is now complete.

  // Step (1) Add header materialization unit and request.
  if ((Err = PlatformJD.define(
           this->BuildMachOHeaderMU(*this, std::move(PlatformJDOpts)))))
    return;
  if ((Err = ES.lookup(&PlatformJD, MachOHeaderStartSymbol).takeError()))
    return;

  // Step (2) Request runtime registration functions to trigger
  // materialization..
  if ((Err = ES.lookup(makeJITDylibSearchOrder(&PlatformJD),
                       SymbolLookupSet(
                           {PlatformBootstrap.Name, PlatformShutdown.Name,
                            RegisterJITDylib.Name, DeregisterJITDylib.Name,
                            RegisterObjectSymbolTable.Name,
                            DeregisterObjectSymbolTable.Name,
                            RegisterObjectPlatformSections.Name,
                            DeregisterObjectPlatformSections.Name,
                            CreatePThreadKey.Name}))
                 .takeError()))
    return;

  // Step (3) Wait for any incidental linker work to complete.
  {
    std::unique_lock<std::mutex> Lock(PlatformMutex);
    BI.CV.wait(Lock, [&]() { return BI.ActiveGraphs == 0; });
    Bootstrap = nullptr;
  }

  // Step (4) Add complete-bootstrap materialization unit and request.
  auto BootstrapCompleteSymbol = ES.intern("__orc_rt_macho_complete_bootstrap");
  if ((Err = PlatformJD.define(
           std::make_unique<MachOPlatformCompleteBootstrapMaterializationUnit>(
               *this, PlatformJD.getName(), BootstrapCompleteSymbol,
               std::move(BI.SymTab), std::move(BI.DeferredAAs),
               BI.MachOHeaderAddr, PlatformBootstrap.Addr,
               PlatformShutdown.Addr, RegisterJITDylib.Addr,
               DeregisterJITDylib.Addr, RegisterObjectSymbolTable.Addr,
               DeregisterObjectSymbolTable.Addr))))
    return;
  if ((Err = ES.lookup(makeJITDylibSearchOrder(
                           &PlatformJD, JITDylibLookupFlags::MatchAllSymbols),
                       std::move(BootstrapCompleteSymbol))
                 .takeError()))
    return;

  // (5) Associate runtime support functions.
  // TODO: Consider moving this above (4) to make runtime support functions
  //       available to the bootstrap completion graph. We'd just need to be
  //       sure that the runtime support functions are fully usable before any
  //       bootstrap completion actions use them (e.g. the ORC runtime
  //       macho_platform object would have to have been created and
  //       initialized).
  if ((Err = associateRuntimeSupportFunctions()))
    return;
}

Error MachOPlatform::associateRuntimeSupportFunctions() {
  ExecutionSession::JITDispatchHandlerAssociationMap WFs;

  using PushInitializersSPSSig =
      SPSExpected<SPSMachOJITDylibDepInfoMap>(SPSExecutorAddr);
  WFs[ES.intern("___orc_rt_macho_push_initializers_tag")] =
      ES.wrapAsyncWithSPS<PushInitializersSPSSig>(
          this, &MachOPlatform::rt_pushInitializers);

  using PushSymbolsSPSSig =
      SPSError(SPSExecutorAddr, SPSSequence<SPSTuple<SPSString, bool>>);
  WFs[ES.intern("___orc_rt_macho_push_symbols_tag")] =
      ES.wrapAsyncWithSPS<PushSymbolsSPSSig>(this,
                                             &MachOPlatform::rt_pushSymbols);

  return ES.registerJITDispatchHandlers(PlatformJD, std::move(WFs));
}

void MachOPlatform::pushInitializersLoop(
    PushInitializersSendResultFn SendResult, JITDylibSP JD) {
  DenseMap<JITDylib *, SymbolLookupSet> NewInitSymbols;
  DenseMap<JITDylib *, SmallVector<JITDylib *>> JDDepMap;
  SmallVector<JITDylib *, 16> Worklist({JD.get()});

  ES.runSessionLocked([&]() {
    while (!Worklist.empty()) {
      // FIXME: Check for defunct dylibs.

      auto DepJD = Worklist.back();
      Worklist.pop_back();

      // If we've already visited this JITDylib on this iteration then continue.
      auto [It, Inserted] = JDDepMap.try_emplace(DepJD);
      if (!Inserted)
        continue;

      // Add dep info.
      auto &DM = It->second;
      DepJD->withLinkOrderDo([&](const JITDylibSearchOrder &O) {
        for (auto &KV : O) {
          if (KV.first == DepJD)
            continue;
          DM.push_back(KV.first);
          Worklist.push_back(KV.first);
        }
      });

      // Add any registered init symbols.
      auto RISItr = RegisteredInitSymbols.find(DepJD);
      if (RISItr != RegisteredInitSymbols.end()) {
        NewInitSymbols[DepJD] = std::move(RISItr->second);
        RegisteredInitSymbols.erase(RISItr);
      }
    }
  });

  // If there are no further init symbols to look up then send the link order
  // (as a list of header addresses) to the caller.
  if (NewInitSymbols.empty()) {

    // To make the list intelligible to the runtime we need to convert all
    // JITDylib pointers to their header addresses. Only include JITDylibs
    // that appear in the JITDylibToHeaderAddr map (i.e. those that have been
    // through setupJITDylib) -- bare JITDylibs aren't managed by the platform.
    DenseMap<JITDylib *, ExecutorAddr> HeaderAddrs;
    HeaderAddrs.reserve(JDDepMap.size());
    {
      std::lock_guard<std::mutex> Lock(PlatformMutex);
      for (auto &KV : JDDepMap) {
        auto I = JITDylibToHeaderAddr.find(KV.first);
        if (I != JITDylibToHeaderAddr.end())
          HeaderAddrs[KV.first] = I->second;
      }
    }

    // Build the dep info map to return.
    MachOJITDylibDepInfoMap DIM;
    DIM.reserve(JDDepMap.size());
    for (auto &KV : JDDepMap) {
      auto HI = HeaderAddrs.find(KV.first);
      // Skip unmanaged JITDylibs.
      if (HI == HeaderAddrs.end())
        continue;
      auto H = HI->second;
      MachOJITDylibDepInfo DepInfo;
      for (auto &Dep : KV.second) {
        auto HJ = HeaderAddrs.find(Dep);
        if (HJ != HeaderAddrs.end())
          DepInfo.DepHeaders.push_back(HJ->second);
      }
      DIM.push_back(std::make_pair(H, std::move(DepInfo)));
    }
    SendResult(DIM);
    return;
  }

  // Otherwise issue a lookup and re-run this phase when it completes.
  lookupInitSymbolsAsync(
      [this, SendResult = std::move(SendResult), JD](Error Err) mutable {
        if (Err)
          SendResult(std::move(Err));
        else
          pushInitializersLoop(std::move(SendResult), JD);
      },
      ES, std::move(NewInitSymbols));
}

void MachOPlatform::rt_pushInitializers(PushInitializersSendResultFn SendResult,
                                        ExecutorAddr JDHeaderAddr) {
  JITDylibSP JD;
  {
    std::lock_guard<std::mutex> Lock(PlatformMutex);
    auto I = HeaderAddrToJITDylib.find(JDHeaderAddr);
    if (I != HeaderAddrToJITDylib.end())
      JD = I->second;
  }

  LLVM_DEBUG({
    dbgs() << "MachOPlatform::rt_pushInitializers(" << JDHeaderAddr << ") ";
    if (JD)
      dbgs() << "pushing initializers for " << JD->getName() << "\n";
    else
      dbgs() << "No JITDylib for header address.\n";
  });

  if (!JD) {
    SendResult(make_error<StringError>("No JITDylib with header addr " +
                                           formatv("{0:x}", JDHeaderAddr),
                                       inconvertibleErrorCode()));
    return;
  }

  pushInitializersLoop(std::move(SendResult), JD);
}

void MachOPlatform::rt_pushSymbols(
    PushSymbolsInSendResultFn SendResult, ExecutorAddr Handle,
    const std::vector<std::pair<StringRef, bool>> &SymbolNames) {

  JITDylib *JD = nullptr;

  {
    std::lock_guard<std::mutex> Lock(PlatformMutex);
    auto I = HeaderAddrToJITDylib.find(Handle);
    if (I != HeaderAddrToJITDylib.end())
      JD = I->second;
  }
  LLVM_DEBUG({
    dbgs() << "MachOPlatform::rt_pushSymbols(";
    if (JD)
      dbgs() << "\"" << JD->getName() << "\", [ ";
    else
      dbgs() << "<invalid handle " << Handle << ">, [ ";
    for (auto &Name : SymbolNames)
      dbgs() << "\"" << Name.first << "\" ";
    dbgs() << "])\n";
  });

  if (!JD) {
    SendResult(make_error<StringError>("No JITDylib associated with handle " +
                                           formatv("{0:x}", Handle),
                                       inconvertibleErrorCode()));
    return;
  }

  SymbolLookupSet LS;
  for (auto &[Name, Required] : SymbolNames)
    LS.add(ES.intern(Name), Required
                                ? SymbolLookupFlags::RequiredSymbol
                                : SymbolLookupFlags::WeaklyReferencedSymbol);

  ES.lookup(
      LookupKind::DLSym, {{JD, JITDylibLookupFlags::MatchExportedSymbolsOnly}},
      std::move(LS), SymbolState::Ready,
      [SendResult = std::move(SendResult)](Expected<SymbolMap> Result) mutable {
        SendResult(Result.takeError());
      },
      NoDependenciesToRegister);
}

Expected<uint64_t> MachOPlatform::createPThreadKey() {
  if (!CreatePThreadKey.Addr)
    return make_error<StringError>(
        "Attempting to create pthread key in target, but runtime support has "
        "not been loaded yet",
        inconvertibleErrorCode());

  Expected<uint64_t> Result(0);
  if (auto Err = ES.callSPSWrapper<SPSExpected<uint64_t>(void)>(
          CreatePThreadKey.Addr, Result))
    return std::move(Err);
  return Result;
}

void MachOPlatform::MachOPlatformPlugin::modifyPassConfig(
    MaterializationResponsibility &MR, jitlink::LinkGraph &LG,
    jitlink::PassConfiguration &Config) {

  using namespace jitlink;

  bool InBootstrapPhase = false;

  ExecutorAddr HeaderAddr;
  {
    std::lock_guard<std::mutex> Lock(MP.PlatformMutex);
    if (LLVM_UNLIKELY(&MR.getTargetJITDylib() == &MP.PlatformJD)) {
      if (MP.Bootstrap) {
        InBootstrapPhase = true;
        ++MP.Bootstrap->ActiveGraphs;
      }
    }

    // Get the dso-base address if available.
    auto I = MP.JITDylibToHeaderAddr.find(&MR.getTargetJITDylib());
    if (I != MP.JITDylibToHeaderAddr.end())
      HeaderAddr = I->second;
  }

  // If we're forcing eh-frame use then discard the compact-unwind section
  // immediately to prevent FDEs from being stripped.
  if (MP.ForceEHFrames)
    if (auto *CUSec = LG.findSectionByName(MachOCompactUnwindSectionName))
      LG.removeSection(*CUSec);

  // Point the libunwind dso-base absolute symbol at the header for the
  // JITDylib. This will prevent us from synthesizing a new header for
  // every object.
  if (HeaderAddr)
    LG.addAbsoluteSymbol("__jitlink$libunwind_dso_base", HeaderAddr, 0,
                         Linkage::Strong, Scope::Local, true);

  // If we're in the bootstrap phase then increment the active graphs.
  if (LLVM_UNLIKELY(InBootstrapPhase))
    Config.PostAllocationPasses.push_back([this](LinkGraph &G) {
      return bootstrapPipelineRecordRuntimeFunctions(G);
    });

  // --- Handle Initializers ---
  if (auto InitSymbol = MR.getInitializerSymbol()) {

    // If the initializer symbol is the MachOHeader start symbol then just
    // register it and then bail out -- the header materialization unit
    // definitely doesn't need any other passes.
    if (InitSymbol == MP.MachOHeaderStartSymbol && !InBootstrapPhase) {
      Config.PostAllocationPasses.push_back([this, &MR](LinkGraph &G) {
        return associateJITDylibHeaderSymbol(G, MR);
      });
      return;
    }

    // If the object contains an init symbol other than the header start symbol
    // then add passes to preserve, process and register the init
    // sections/symbols.
    Config.PrePrunePasses.push_back([this, &MR](LinkGraph &G) {
      if (auto Err = preserveImportantSections(G, MR))
        return Err;
      return processObjCImageInfo(G, MR);
    });
    Config.PostPrunePasses.push_back(
        [this](LinkGraph &G) { return createObjCRuntimeObject(G); });
    Config.PostAllocationPasses.push_back(
        [this, &MR](LinkGraph &G) { return populateObjCRuntimeObject(G, MR); });
  }

  // Insert TLV lowering at the start of the PostPrunePasses, since we want
  // it to run before GOT/PLT lowering.
  Config.PostPrunePasses.insert(
      Config.PostPrunePasses.begin(),
      [this, &JD = MR.getTargetJITDylib()](LinkGraph &G) {
        return fixTLVSectionsAndEdges(G, JD);
      });

  // Add symbol table prepare and register passes: These will add strings for
  // all symbols to the c-strings section, and build a symbol table registration
  // call.
  auto JITSymTabInfo = std::make_shared<JITSymTabVector>();
  Config.PostPrunePasses.push_back([this, JITSymTabInfo](LinkGraph &G) {
    return prepareSymbolTableRegistration(G, *JITSymTabInfo);
  });
  Config.PostFixupPasses.push_back([this, &MR, JITSymTabInfo,
                                    InBootstrapPhase](LinkGraph &G) {
    return addSymbolTableRegistration(G, MR, *JITSymTabInfo, InBootstrapPhase);
  });

  // Add a pass to register the final addresses of any special sections in the
  // object with the runtime.
  Config.PostAllocationPasses.push_back([this, &JD = MR.getTargetJITDylib(),
                                         HeaderAddr,
                                         InBootstrapPhase](LinkGraph &G) {
    return registerObjectPlatformSections(G, JD, HeaderAddr, InBootstrapPhase);
  });

  // If we're in the bootstrap phase then steal allocation actions and then
  // decrement the active graphs.
  if (InBootstrapPhase)
    Config.PostFixupPasses.push_back(
        [this](LinkGraph &G) { return bootstrapPipelineEnd(G); });
}

Error MachOPlatform::MachOPlatformPlugin::
    bootstrapPipelineRecordRuntimeFunctions(jitlink::LinkGraph &G) {
  // Record bootstrap function names.
  std::pair<StringRef, ExecutorAddr *> RuntimeSymbols[] = {
      {*MP.MachOHeaderStartSymbol, &MP.Bootstrap->MachOHeaderAddr},
      {*MP.PlatformBootstrap.Name, &MP.PlatformBootstrap.Addr},
      {*MP.PlatformShutdown.Name, &MP.PlatformShutdown.Addr},
      {*MP.RegisterJITDylib.Name, &MP.RegisterJITDylib.Addr},
      {*MP.DeregisterJITDylib.Name, &MP.DeregisterJITDylib.Addr},
      {*MP.RegisterObjectSymbolTable.Name, &MP.RegisterObjectSymbolTable.Addr},
      {*MP.DeregisterObjectSymbolTable.Name,
       &MP.DeregisterObjectSymbolTable.Addr},
      {*MP.RegisterObjectPlatformSections.Name,
       &MP.RegisterObjectPlatformSections.Addr},
      {*MP.DeregisterObjectPlatformSections.Name,
       &MP.DeregisterObjectPlatformSections.Addr},
      {*MP.CreatePThreadKey.Name, &MP.CreatePThreadKey.Addr},
      {*MP.RegisterObjCRuntimeObject.Name, &MP.RegisterObjCRuntimeObject.Addr},
      {*MP.DeregisterObjCRuntimeObject.Name,
       &MP.DeregisterObjCRuntimeObject.Addr}};

  bool RegisterMachOHeader = false;

  for (auto *Sym : G.defined_symbols()) {
    for (auto &RTSym : RuntimeSymbols) {
      if (Sym->hasName() && *Sym->getName() == RTSym.first) {
        if (*RTSym.second)
          return make_error<StringError>(
              "Duplicate " + RTSym.first +
                  " detected during MachOPlatform bootstrap",
              inconvertibleErrorCode());

        if (Sym->getName() == MP.MachOHeaderStartSymbol)
          RegisterMachOHeader = true;

        *RTSym.second = Sym->getAddress();
      }
    }
  }

  if (RegisterMachOHeader) {
    // If this graph defines the macho header symbol then create the internal
    // mapping between it and PlatformJD.
    std::lock_guard<std::mutex> Lock(MP.PlatformMutex);
    MP.JITDylibToHeaderAddr[&MP.PlatformJD] = MP.Bootstrap->MachOHeaderAddr;
    MP.HeaderAddrToJITDylib[MP.Bootstrap->MachOHeaderAddr] = &MP.PlatformJD;
  }

  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::bootstrapPipelineEnd(
    jitlink::LinkGraph &G) {
  std::lock_guard<std::mutex> Lock(MP.PlatformMutex);

  --MP.Bootstrap->ActiveGraphs;
  // Notify Bootstrap->CV while holding the mutex because the mutex is
  // also keeping Bootstrap->CV alive.
  if (MP.Bootstrap->ActiveGraphs == 0)
    MP.Bootstrap->CV.notify_all();
  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::associateJITDylibHeaderSymbol(
    jitlink::LinkGraph &G, MaterializationResponsibility &MR) {
  auto I = llvm::find_if(G.defined_symbols(), [this](jitlink::Symbol *Sym) {
    return Sym->getName() == MP.MachOHeaderStartSymbol;
  });
  assert(I != G.defined_symbols().end() && "Missing MachO header start symbol");

  auto &JD = MR.getTargetJITDylib();
  std::lock_guard<std::mutex> Lock(MP.PlatformMutex);
  auto HeaderAddr = (*I)->getAddress();
  MP.JITDylibToHeaderAddr[&JD] = HeaderAddr;
  MP.HeaderAddrToJITDylib[HeaderAddr] = &JD;
  // We can unconditionally add these actions to the Graph because this pass
  // isn't used during bootstrap.
  G.allocActions().push_back(
      {cantFail(
           WrapperFunctionCall::Create<SPSArgList<SPSString, SPSExecutorAddr>>(
               MP.RegisterJITDylib.Addr, JD.getName(), HeaderAddr)),
       cantFail(WrapperFunctionCall::Create<SPSArgList<SPSExecutorAddr>>(
           MP.DeregisterJITDylib.Addr, HeaderAddr))});
  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::preserveImportantSections(
    jitlink::LinkGraph &G, MaterializationResponsibility &MR) {
  // __objc_imageinfo is "important": we want to preserve it and record its
  // address in the first graph that it appears in, then verify and discard it
  // in all subsequent graphs. In this pass we preserve unconditionally -- we'll
  // manually throw it away in the processObjCImageInfo pass.
  if (auto *ObjCImageInfoSec =
          G.findSectionByName(MachOObjCImageInfoSectionName)) {
    if (ObjCImageInfoSec->blocks_size() != 1)
      return make_error<StringError>(
          "In " + G.getName() +
              "__DATA,__objc_imageinfo contains multiple blocks",
          inconvertibleErrorCode());
    G.addAnonymousSymbol(**ObjCImageInfoSec->blocks().begin(), 0, 0, false,
                         true);

    for (auto *B : ObjCImageInfoSec->blocks())
      if (!B->edges_empty())
        return make_error<StringError>("In " + G.getName() + ", " +
                                           MachOObjCImageInfoSectionName +
                                           " contains references to symbols",
                                       inconvertibleErrorCode());
  }

  // Init sections are important: We need to preserve them and so that their
  // addresses can be captured and reported to the ORC runtime in
  // registerObjectPlatformSections.
  if (const auto &InitSymName = MR.getInitializerSymbol()) {

    jitlink::Symbol *InitSym = nullptr;
    for (auto &InitSectionName : MachOInitSectionNames) {
      // Skip ObjCImageInfo -- this shouldn't have any dependencies, and we may
      // remove it later.
      if (InitSectionName == MachOObjCImageInfoSectionName)
        continue;

      // Skip non-init sections.
      auto *InitSection = G.findSectionByName(InitSectionName);
      if (!InitSection || InitSection->empty())
        continue;

      // Create the init symbol if it has not been created already and attach it
      // to the first block.
      if (!InitSym) {
        auto &B = **InitSection->blocks().begin();
        InitSym = &G.addDefinedSymbol(
            B, 0, *InitSymName, B.getSize(), jitlink::Linkage::Strong,
            jitlink::Scope::SideEffectsOnly, false, true);
      }

      // Add keep-alive edges to anonymous symbols in all other init blocks.
      for (auto *B : InitSection->blocks()) {
        if (B == &InitSym->getBlock())
          continue;

        auto &S = G.addAnonymousSymbol(*B, 0, B->getSize(), false, true);
        InitSym->getBlock().addEdge(jitlink::Edge::KeepAlive, 0, S, 0);
      }
    }
  }

  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::processObjCImageInfo(
    jitlink::LinkGraph &G, MaterializationResponsibility &MR) {

  // If there's an ObjC imagine info then either
  //   (1) It's the first __objc_imageinfo we've seen in this JITDylib. In
  //       this case we name and record it.
  // OR
  //   (2) We already have a recorded __objc_imageinfo for this JITDylib,
  //       in which case we just verify it.
  auto *ObjCImageInfo = G.findSectionByName(MachOObjCImageInfoSectionName);
  if (!ObjCImageInfo)
    return Error::success();

  auto ObjCImageInfoBlocks = ObjCImageInfo->blocks();

  // Check that the section is not empty if present.
  if (ObjCImageInfoBlocks.empty())
    return make_error<StringError>("Empty " + MachOObjCImageInfoSectionName +
                                       " section in " + G.getName(),
                                   inconvertibleErrorCode());

  // Check that there's only one block in the section.
  if (std::next(ObjCImageInfoBlocks.begin()) != ObjCImageInfoBlocks.end())
    return make_error<StringError>("Multiple blocks in " +
                                       MachOObjCImageInfoSectionName +
                                       " section in " + G.getName(),
                                   inconvertibleErrorCode());

  // Check that the __objc_imageinfo section is unreferenced.
  // FIXME: We could optimize this check if Symbols had a ref-count.
  for (auto &Sec : G.sections()) {
    if (&Sec != ObjCImageInfo)
      for (auto *B : Sec.blocks())
        for (auto &E : B->edges())
          if (E.getTarget().isDefined() &&
              &E.getTarget().getSection() == ObjCImageInfo)
            return make_error<StringError>(MachOObjCImageInfoSectionName +
                                               " is referenced within file " +
                                               G.getName(),
                                           inconvertibleErrorCode());
  }

  auto &ObjCImageInfoBlock = **ObjCImageInfoBlocks.begin();
  auto *ObjCImageInfoData = ObjCImageInfoBlock.getContent().data();
  auto Version = support::endian::read32(ObjCImageInfoData, G.getEndianness());
  auto Flags =
      support::endian::read32(ObjCImageInfoData + 4, G.getEndianness());

  // Lock the mutex while we verify / update the ObjCImageInfos map.
  std::lock_guard<std::mutex> Lock(PluginMutex);

  auto ObjCImageInfoItr = ObjCImageInfos.find(&MR.getTargetJITDylib());
  if (ObjCImageInfoItr != ObjCImageInfos.end()) {
    // We've already registered an __objc_imageinfo section. Verify the
    // content of this new section matches, then delete it.
    if (ObjCImageInfoItr->second.Version != Version)
      return make_error<StringError>(
          "ObjC version in " + G.getName() +
              " does not match first registered version",
          inconvertibleErrorCode());
    if (ObjCImageInfoItr->second.Flags != Flags)
      if (Error E = mergeImageInfoFlags(G, MR, ObjCImageInfoItr->second, Flags))
        return E;

    // __objc_imageinfo is valid. Delete the block.
    while (ObjCImageInfo->symbols_size() != 0)
      G.removeDefinedSymbol(**ObjCImageInfo->symbols().begin());
    G.removeBlock(ObjCImageInfoBlock);
  } else {
    LLVM_DEBUG({
      dbgs() << "MachOPlatform: Registered __objc_imageinfo for "
             << MR.getTargetJITDylib().getName() << " in " << G.getName()
             << "; flags = " << formatv("{0:x4}", Flags) << "\n";
    });
    // We haven't registered an __objc_imageinfo section yet. Register and
    // move on. The section should already be marked no-dead-strip.
    G.addDefinedSymbol(ObjCImageInfoBlock, 0, ObjCImageInfoSymbolName,
                       ObjCImageInfoBlock.getSize(), jitlink::Linkage::Strong,
                       jitlink::Scope::Hidden, false, true);
    if (auto Err = MR.defineMaterializing(
            {{MR.getExecutionSession().intern(ObjCImageInfoSymbolName),
              JITSymbolFlags()}}))
      return Err;
    ObjCImageInfos[&MR.getTargetJITDylib()] = {Version, Flags, false};
  }

  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::mergeImageInfoFlags(
    jitlink::LinkGraph &G, MaterializationResponsibility &MR,
    ObjCImageInfo &Info, uint32_t NewFlags) {
  if (Info.Flags == NewFlags)
    return Error::success();

  ObjCImageInfoFlags Old(Info.Flags);
  ObjCImageInfoFlags New(NewFlags);

  // Check for incompatible flags.
  if (Old.SwiftABIVersion && New.SwiftABIVersion &&
      Old.SwiftABIVersion != New.SwiftABIVersion)
    return make_error<StringError>("Swift ABI version in " + G.getName() +
                                       " does not match first registered flags",
                                   inconvertibleErrorCode());

  // HasCategoryClassProperties and HasSignedObjCClassROs can be disabled before
  // they are registered, if necessary, but once they are in use must be
  // supported by subsequent objects.
  if (Info.Finalized && Old.HasCategoryClassProperties &&
      !New.HasCategoryClassProperties)
    return make_error<StringError>("ObjC category class property support in " +
                                       G.getName() +
                                       " does not match first registered flags",
                                   inconvertibleErrorCode());
  if (Info.Finalized && Old.HasSignedObjCClassROs && !New.HasSignedObjCClassROs)
    return make_error<StringError>("ObjC class_ro_t pointer signing in " +
                                       G.getName() +
                                       " does not match first registered flags",
                                   inconvertibleErrorCode());

  // If we cannot change the flags, ignore any remaining differences. Adding
  // Swift or changing its version are unlikely to cause problems in practice.
  if (Info.Finalized)
    return Error::success();

  // Use the minimum Swift version.
  if (Old.SwiftVersion && New.SwiftVersion)
    New.SwiftVersion = std::min(Old.SwiftVersion, New.SwiftVersion);
  else if (Old.SwiftVersion)
    New.SwiftVersion = Old.SwiftVersion;
  // Add a Swift ABI version if it was pure objc before.
  if (!New.SwiftABIVersion)
    New.SwiftABIVersion = Old.SwiftABIVersion;
  // Disable class properties if any object does not support it.
  if (Old.HasCategoryClassProperties != New.HasCategoryClassProperties)
    New.HasCategoryClassProperties = false;
  // Disable signed class ro data if any object does not support it.
  if (Old.HasSignedObjCClassROs != New.HasSignedObjCClassROs)
    New.HasSignedObjCClassROs = false;

  LLVM_DEBUG({
    dbgs() << "MachOPlatform: Merging __objc_imageinfo flags for "
           << MR.getTargetJITDylib().getName() << " (was "
           << formatv("{0:x4}", Old.rawFlags()) << ")"
           << " with " << G.getName() << " (" << formatv("{0:x4}", NewFlags)
           << ")"
           << " -> " << formatv("{0:x4}", New.rawFlags()) << "\n";
  });

  Info.Flags = New.rawFlags();
  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::fixTLVSectionsAndEdges(
    jitlink::LinkGraph &G, JITDylib &JD) {
  auto TLVBootStrapSymbolName = G.intern("__tlv_bootstrap");
  // Rename external references to __tlv_bootstrap to ___orc_rt_tlv_get_addr.
  for (auto *Sym : G.external_symbols())
    if (Sym->getName() == TLVBootStrapSymbolName) {
      auto TLSGetADDR =
          MP.getExecutionSession().intern("___orc_rt_macho_tlv_get_addr");
      Sym->setName(std::move(TLSGetADDR));
      break;
    }

  // Store key in __thread_vars struct fields.
  if (auto *ThreadDataSec = G.findSectionByName(MachOThreadVarsSectionName)) {
    std::optional<uint64_t> Key;
    {
      std::lock_guard<std::mutex> Lock(MP.PlatformMutex);
      auto I = MP.JITDylibToPThreadKey.find(&JD);
      if (I != MP.JITDylibToPThreadKey.end())
        Key = I->second;
    }

    if (!Key) {
      if (auto KeyOrErr = MP.createPThreadKey())
        Key = *KeyOrErr;
      else
        return KeyOrErr.takeError();
    }

    uint64_t PlatformKeyBits =
        support::endian::byte_swap(*Key, G.getEndianness());

    for (auto *B : ThreadDataSec->blocks()) {
      if (B->getSize() != 3 * G.getPointerSize())
        return make_error<StringError>("__thread_vars block at " +
                                           formatv("{0:x}", B->getAddress()) +
                                           " has unexpected size",
                                       inconvertibleErrorCode());

      auto NewBlockContent = G.allocateBuffer(B->getSize());
      llvm::copy(B->getContent(), NewBlockContent.data());
      memcpy(NewBlockContent.data() + G.getPointerSize(), &PlatformKeyBits,
             G.getPointerSize());
      B->setContent(NewBlockContent);
    }
  }

  // Transform any TLV edges into GOT edges.
  for (auto *B : G.blocks())
    for (auto &E : B->edges())
      if (E.getKind() ==
          jitlink::x86_64::RequestTLVPAndTransformToPCRel32TLVPLoadREXRelaxable)
        E.setKind(jitlink::x86_64::
                      RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable);

  return Error::success();
}

std::optional<MachOPlatform::MachOPlatformPlugin::UnwindSections>
MachOPlatform::MachOPlatformPlugin::findUnwindSectionInfo(
    jitlink::LinkGraph &G) {
  using namespace jitlink;

  UnwindSections US;

  // ScanSection records a section range and adds any executable blocks that
  // that section points to to the CodeBlocks vector.
  SmallVector<Block *> CodeBlocks;
  auto ScanUnwindInfoSection = [&](Section &Sec, ExecutorAddrRange &SecRange,
                                   auto AddCodeBlocks) {
    if (Sec.blocks().empty())
      return;
    SecRange = (*Sec.blocks().begin())->getRange();
    for (auto *B : Sec.blocks()) {
      auto R = B->getRange();
      SecRange.Start = std::min(SecRange.Start, R.Start);
      SecRange.End = std::max(SecRange.End, R.End);
      AddCodeBlocks(*B);
    }
  };

  if (Section *EHFrameSec = G.findSectionByName(MachOEHFrameSectionName)) {
    ScanUnwindInfoSection(*EHFrameSec, US.DwarfSection, [&](Block &B) {
      if (auto *Fn = jitlink::EHFrameCFIBlockInspector::FromEdgeScan(B)
                         .getPCBeginEdge())
        if (Fn->getTarget().isDefined())
          CodeBlocks.push_back(&Fn->getTarget().getBlock());
    });
  }

  if (Section *CUInfoSec = G.findSectionByName(MachOUnwindInfoSectionName)) {
    ScanUnwindInfoSection(
        *CUInfoSec, US.CompactUnwindSection, [&](Block &B) {
          for (auto &E : B.edges()) {
            assert(E.getTarget().isDefined() &&
                   "unwind-info record edge has external target");
            assert(E.getKind() == Edge::KeepAlive &&
                   "unwind-info record has unexpected edge kind");
            CodeBlocks.push_back(&E.getTarget().getBlock());
          }
        });
  }

  // If we didn't find any pointed-to code-blocks then there's no need to
  // register any info.
  if (CodeBlocks.empty())
    return std::nullopt;

  // We have info to register. Sort the code blocks into address order and
  // build a list of contiguous address ranges covering them all.
  llvm::sort(CodeBlocks, [](const Block *LHS, const Block *RHS) {
    return LHS->getAddress() < RHS->getAddress();
  });
  for (auto *B : CodeBlocks) {
    if (US.CodeRanges.empty() || US.CodeRanges.back().End != B->getAddress())
      US.CodeRanges.push_back(B->getRange());
    else
      US.CodeRanges.back().End = B->getRange().End;
  }

  LLVM_DEBUG({
    dbgs() << "MachOPlatform identified unwind info in " << G.getName() << ":\n"
           << "  DWARF: ";
    if (US.DwarfSection.Start)
      dbgs() << US.DwarfSection << "\n";
    else
      dbgs() << "none\n";
    dbgs() << "  Compact-unwind: ";
    if (US.CompactUnwindSection.Start)
      dbgs() << US.CompactUnwindSection << "\n";
    else
      dbgs() << "none\n"
             << "for code ranges:\n";
    for (auto &CR : US.CodeRanges)
      dbgs() << "  " << CR << "\n";
    if (US.CodeRanges.size() >= G.sections_size())
      dbgs() << "WARNING: High number of discontiguous code ranges! "
                "Padding may be interfering with coalescing.\n";
  });

  return US;
}

Error MachOPlatform::MachOPlatformPlugin::registerObjectPlatformSections(
    jitlink::LinkGraph &G, JITDylib &JD, ExecutorAddr HeaderAddr,
    bool InBootstrapPhase) {

  // Get a pointer to the thread data section if there is one. It will be used
  // below.
  jitlink::Section *ThreadDataSection =
      G.findSectionByName(MachOThreadDataSectionName);

  // Handle thread BSS section if there is one.
  if (auto *ThreadBSSSection = G.findSectionByName(MachOThreadBSSSectionName)) {
    // If there's already a thread data section in this graph then merge the
    // thread BSS section content into it, otherwise just treat the thread
    // BSS section as the thread data section.
    if (ThreadDataSection)
      G.mergeSections(*ThreadDataSection, *ThreadBSSSection);
    else
      ThreadDataSection = ThreadBSSSection;
  }

  SmallVector<std::pair<StringRef, ExecutorAddrRange>, 8> MachOPlatformSecs;

  // Collect data sections to register.
  StringRef DataSections[] = {MachODataDataSectionName,
                              MachODataCommonSectionName,
                              MachOEHFrameSectionName};
  for (auto &SecName : DataSections) {
    if (auto *Sec = G.findSectionByName(SecName)) {
      jitlink::SectionRange R(*Sec);
      if (!R.empty())
        MachOPlatformSecs.push_back({SecName, R.getRange()});
    }
  }

  // Having merged thread BSS (if present) and thread data (if present),
  // record the resulting section range.
  if (ThreadDataSection) {
    jitlink::SectionRange R(*ThreadDataSection);
    if (!R.empty())
      MachOPlatformSecs.push_back({MachOThreadDataSectionName, R.getRange()});
  }

  // If any platform sections were found then add an allocation action to call
  // the registration function.
  StringRef PlatformSections[] = {MachOModInitFuncSectionName,
                                  ObjCRuntimeObjectSectionName};

  for (auto &SecName : PlatformSections) {
    auto *Sec = G.findSectionByName(SecName);
    if (!Sec)
      continue;
    jitlink::SectionRange R(*Sec);
    if (R.empty())
      continue;

    MachOPlatformSecs.push_back({SecName, R.getRange()});
  }

  std::optional<std::tuple<SmallVector<ExecutorAddrRange>, ExecutorAddrRange,
                           ExecutorAddrRange>>
      UnwindInfo;
  if (auto UI = findUnwindSectionInfo(G))
    UnwindInfo = std::make_tuple(std::move(UI->CodeRanges), UI->DwarfSection,
                                 UI->CompactUnwindSection);

  if (!MachOPlatformSecs.empty() || UnwindInfo) {
    // Dump the scraped inits.
    LLVM_DEBUG({
      dbgs() << "MachOPlatform: Scraped " << G.getName() << " init sections:\n";
      for (auto &KV : MachOPlatformSecs)
        dbgs() << "  " << KV.first << ": " << KV.second << "\n";
    });

    assert(HeaderAddr && "Null header registered for JD");
    using SPSRegisterObjectPlatformSectionsArgs = SPSArgList<
        SPSExecutorAddr,
        SPSOptional<SPSTuple<SPSSequence<SPSExecutorAddrRange>,
                             SPSExecutorAddrRange, SPSExecutorAddrRange>>,
        SPSSequence<SPSTuple<SPSString, SPSExecutorAddrRange>>>;

    AllocActionCallPair AllocActions = {
        cantFail(
            WrapperFunctionCall::Create<SPSRegisterObjectPlatformSectionsArgs>(
                MP.RegisterObjectPlatformSections.Addr, HeaderAddr, UnwindInfo,
                MachOPlatformSecs)),
        cantFail(
            WrapperFunctionCall::Create<SPSRegisterObjectPlatformSectionsArgs>(
                MP.DeregisterObjectPlatformSections.Addr, HeaderAddr,
                UnwindInfo, MachOPlatformSecs))};

    if (LLVM_LIKELY(!InBootstrapPhase))
      G.allocActions().push_back(std::move(AllocActions));
    else {
      std::lock_guard<std::mutex> Lock(MP.PlatformMutex);
      MP.Bootstrap->DeferredAAs.push_back(std::move(AllocActions));
    }
  }

  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::createObjCRuntimeObject(
    jitlink::LinkGraph &G) {

  bool NeedTextSegment = false;
  size_t NumRuntimeSections = 0;

  for (auto ObjCRuntimeSectionName : ObjCRuntimeObjectSectionsData)
    if (G.findSectionByName(ObjCRuntimeSectionName))
      ++NumRuntimeSections;

  for (auto ObjCRuntimeSectionName : ObjCRuntimeObjectSectionsText) {
    if (G.findSectionByName(ObjCRuntimeSectionName)) {
      ++NumRuntimeSections;
      NeedTextSegment = true;
    }
  }

  // Early out for no runtime sections.
  if (NumRuntimeSections == 0)
    return Error::success();

  // If there were any runtime sections then we need to add an __objc_imageinfo
  // section.
  ++NumRuntimeSections;

  size_t MachOSize = sizeof(MachO::mach_header_64) +
                     (NeedTextSegment + 1) * sizeof(MachO::segment_command_64) +
                     NumRuntimeSections * sizeof(MachO::section_64);

  auto &Sec = G.createSection(ObjCRuntimeObjectSectionName,
                              MemProt::Read | MemProt::Write);
  G.createMutableContentBlock(Sec, MachOSize, ExecutorAddr(), 16, 0, true);

  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::populateObjCRuntimeObject(
    jitlink::LinkGraph &G, MaterializationResponsibility &MR) {

  auto *ObjCRuntimeObjectSec =
      G.findSectionByName(ObjCRuntimeObjectSectionName);

  if (!ObjCRuntimeObjectSec)
    return Error::success();

  switch (G.getTargetTriple().getArch()) {
  case Triple::aarch64:
  case Triple::x86_64:
    // Supported.
    break;
  default:
    return make_error<StringError>("Unrecognized MachO arch in triple " +
                                       G.getTargetTriple().str(),
                                   inconvertibleErrorCode());
  }

  auto &SecBlock = **ObjCRuntimeObjectSec->blocks().begin();

  struct SecDesc {
    MachO::section_64 Sec;
    unique_function<void(size_t RecordOffset)> AddFixups;
  };

  std::vector<SecDesc> TextSections, DataSections;
  auto AddSection = [&](SecDesc &SD, jitlink::Section &GraphSec) {
    jitlink::SectionRange SR(GraphSec);
    StringRef FQName = GraphSec.getName();
    memset(&SD.Sec, 0, sizeof(MachO::section_64));
    memcpy(SD.Sec.sectname, FQName.drop_front(7).data(), FQName.size() - 7);
    memcpy(SD.Sec.segname, FQName.data(), 6);
    SD.Sec.addr = SR.getStart() - SecBlock.getAddress();
    SD.Sec.size = SR.getSize();
    SD.Sec.flags = MachO::S_REGULAR;
  };

  // Add the __objc_imageinfo section.
  {
    DataSections.push_back({});
    auto &SD = DataSections.back();
    memset(&SD.Sec, 0, sizeof(SD.Sec));
    memcpy(SD.Sec.sectname, "__objc_imageinfo", 16);
    strcpy(SD.Sec.segname, "__DATA");
    SD.Sec.size = 8;
    jitlink::Symbol *ObjCImageInfoSym = nullptr;
    SD.AddFixups = [&, ObjCImageInfoSym](size_t RecordOffset) mutable {
      auto PointerEdge = getPointerEdgeKind(G);

      // Look for an existing __objc_imageinfo symbol.
      if (!ObjCImageInfoSym) {
        auto Name = G.intern(ObjCImageInfoSymbolName);
        ObjCImageInfoSym = G.findExternalSymbolByName(Name);
        if (!ObjCImageInfoSym)
          ObjCImageInfoSym = G.findAbsoluteSymbolByName(Name);
        if (!ObjCImageInfoSym) {
          ObjCImageInfoSym = G.findDefinedSymbolByName(Name);
          if (ObjCImageInfoSym) {
            std::optional<uint32_t> Flags;
            {
              std::lock_guard<std::mutex> Lock(PluginMutex);
              auto It = ObjCImageInfos.find(&MR.getTargetJITDylib());
              if (It != ObjCImageInfos.end()) {
                It->second.Finalized = true;
                Flags = It->second.Flags;
              }
            }

            if (Flags) {
              // We own the definition of __objc_image_info; write the final
              // merged flags value.
              auto Content = ObjCImageInfoSym->getBlock().getMutableContent(G);
              assert(
                  Content.size() == 8 &&
                  "__objc_image_info size should have been verified already");
              support::endian::write32(&Content[4], *Flags, G.getEndianness());
            }
          }
        }
        if (!ObjCImageInfoSym)
          ObjCImageInfoSym = &G.addExternalSymbol(std::move(Name), 8, false);
      }

      SecBlock.addEdge(PointerEdge,
                       RecordOffset + ((char *)&SD.Sec.addr - (char *)&SD.Sec),
                       *ObjCImageInfoSym, -SecBlock.getAddress().getValue());
    };
  }

  for (auto ObjCRuntimeSectionName : ObjCRuntimeObjectSectionsData) {
    if (auto *GraphSec = G.findSectionByName(ObjCRuntimeSectionName)) {
      DataSections.push_back({});
      AddSection(DataSections.back(), *GraphSec);
    }
  }

  for (auto ObjCRuntimeSectionName : ObjCRuntimeObjectSectionsText) {
    if (auto *GraphSec = G.findSectionByName(ObjCRuntimeSectionName)) {
      TextSections.push_back({});
      AddSection(TextSections.back(), *GraphSec);
    }
  }

  assert(ObjCRuntimeObjectSec->blocks_size() == 1 &&
         "Unexpected number of blocks in runtime sections object");

  // Build the header struct up-front. This also gives us a chance to check
  // that the triple is supported, which we'll assume below.
  MachO::mach_header_64 Hdr;
  Hdr.magic = MachO::MH_MAGIC_64;
  switch (G.getTargetTriple().getArch()) {
  case Triple::aarch64:
    Hdr.cputype = MachO::CPU_TYPE_ARM64;
    Hdr.cpusubtype = MachO::CPU_SUBTYPE_ARM64_ALL;
    break;
  case Triple::x86_64:
    Hdr.cputype = MachO::CPU_TYPE_X86_64;
    Hdr.cpusubtype = MachO::CPU_SUBTYPE_X86_64_ALL;
    break;
  default:
    llvm_unreachable("Unsupported architecture");
  }

  Hdr.filetype = MachO::MH_DYLIB;
  Hdr.ncmds = 1 + !TextSections.empty();
  Hdr.sizeofcmds =
      Hdr.ncmds * sizeof(MachO::segment_command_64) +
      (TextSections.size() + DataSections.size()) * sizeof(MachO::section_64);
  Hdr.flags = 0;
  Hdr.reserved = 0;

  auto SecContent = SecBlock.getAlreadyMutableContent();
  char *P = SecContent.data();
  auto WriteMachOStruct = [&](auto S) {
    if (G.getEndianness() != llvm::endianness::native)
      MachO::swapStruct(S);
    memcpy(P, &S, sizeof(S));
    P += sizeof(S);
  };

  auto WriteSegment = [&](StringRef Name, std::vector<SecDesc> &Secs) {
    MachO::segment_command_64 SegLC;
    memset(&SegLC, 0, sizeof(SegLC));
    memcpy(SegLC.segname, Name.data(), Name.size());
    SegLC.cmd = MachO::LC_SEGMENT_64;
    SegLC.cmdsize = sizeof(MachO::segment_command_64) +
                    Secs.size() * sizeof(MachO::section_64);
    SegLC.nsects = Secs.size();
    WriteMachOStruct(SegLC);
    for (auto &SD : Secs) {
      if (SD.AddFixups)
        SD.AddFixups(P - SecContent.data());
      WriteMachOStruct(SD.Sec);
    }
  };

  WriteMachOStruct(Hdr);
  if (!TextSections.empty())
    WriteSegment("__TEXT", TextSections);
  if (!DataSections.empty())
    WriteSegment("__DATA", DataSections);

  assert(P == SecContent.end() && "Underflow writing ObjC runtime object");
  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::prepareSymbolTableRegistration(
    jitlink::LinkGraph &G, JITSymTabVector &JITSymTabInfo) {

  auto *CStringSec = G.findSectionByName(MachOCStringSectionName);
  if (!CStringSec)
    CStringSec = &G.createSection(MachOCStringSectionName,
                                  MemProt::Read | MemProt::Exec);

  // Make a map of existing strings so that we can re-use them:
  DenseMap<StringRef, jitlink::Symbol *> ExistingStrings;
  for (auto *Sym : CStringSec->symbols()) {

    // The LinkGraph builder should have created single strings blocks, and all
    // plugins should have maintained this invariant.
    auto Content = Sym->getBlock().getContent();
    ExistingStrings.insert(
        std::make_pair(StringRef(Content.data(), Content.size()), Sym));
  }

  // Add all symbol names to the string section, and record the symbols for
  // those names.
  {
    SmallVector<jitlink::Symbol *> SymsToProcess;
    llvm::append_range(SymsToProcess, G.defined_symbols());
    llvm::append_range(SymsToProcess, G.absolute_symbols());

    for (auto *Sym : SymsToProcess) {
      if (!Sym->hasName())
        continue;

      auto I = ExistingStrings.find(*Sym->getName());
      if (I == ExistingStrings.end()) {
        auto &NameBlock = G.createMutableContentBlock(
            *CStringSec, G.allocateCString(*Sym->getName()),
            orc::ExecutorAddr(), 1, 0);
        auto &SymbolNameSym = G.addAnonymousSymbol(
            NameBlock, 0, NameBlock.getSize(), false, true);
        JITSymTabInfo.push_back({Sym, &SymbolNameSym});
      } else
        JITSymTabInfo.push_back({Sym, I->second});
    }
  }

  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::addSymbolTableRegistration(
    jitlink::LinkGraph &G, MaterializationResponsibility &MR,
    JITSymTabVector &JITSymTabInfo, bool InBootstrapPhase) {

  ExecutorAddr HeaderAddr;
  {
    std::lock_guard<std::mutex> Lock(MP.PlatformMutex);
    auto I = MP.JITDylibToHeaderAddr.find(&MR.getTargetJITDylib());
    assert(I != MP.JITDylibToHeaderAddr.end() && "No header registered for JD");
    assert(I->second && "Null header registered for JD");
    HeaderAddr = I->second;
  }

  if (LLVM_UNLIKELY(InBootstrapPhase)) {
    // If we're in the bootstrap phase then just record these symbols in the
    // bootstrap object and then bail out -- registration will be attached to
    // the bootstrap graph.
    std::lock_guard<std::mutex> Lock(MP.PlatformMutex);
    auto &SymTab = MP.Bootstrap->SymTab;
    for (auto &[OriginalSymbol, NameSym] : JITSymTabInfo)
      SymTab.push_back({NameSym->getAddress(), OriginalSymbol->getAddress(),
                        flagsForSymbol(*OriginalSymbol)});
    return Error::success();
  }

  SymbolTableVector SymTab;
  for (auto &[OriginalSymbol, NameSym] : JITSymTabInfo)
    SymTab.push_back({NameSym->getAddress(), OriginalSymbol->getAddress(),
                      flagsForSymbol(*OriginalSymbol)});

  G.allocActions().push_back(
      {cantFail(WrapperFunctionCall::Create<SPSRegisterSymbolsArgs>(
           MP.RegisterObjectSymbolTable.Addr, HeaderAddr, SymTab)),
       cantFail(WrapperFunctionCall::Create<SPSRegisterSymbolsArgs>(
           MP.DeregisterObjectSymbolTable.Addr, HeaderAddr, SymTab))});

  return Error::success();
}

template <typename MachOTraits>
jitlink::Block &createHeaderBlock(MachOPlatform &MOP,
                                  const MachOPlatform::HeaderOptions &Opts,
                                  JITDylib &JD, jitlink::LinkGraph &G,
                                  jitlink::Section &HeaderSection) {
  auto HdrInfo =
      getMachOHeaderInfoFromTriple(MOP.getExecutionSession().getTargetTriple());
  MachOBuilder<MachOTraits> B(HdrInfo.PageSize);

  B.Header.filetype = MachO::MH_DYLIB;
  B.Header.cputype = HdrInfo.CPUType;
  B.Header.cpusubtype = HdrInfo.CPUSubType;

  if (Opts.IDDylib)
    B.template addLoadCommand<MachO::LC_ID_DYLIB>(
        Opts.IDDylib->Name, Opts.IDDylib->Timestamp,
        Opts.IDDylib->CurrentVersion, Opts.IDDylib->CompatibilityVersion);
  else
    B.template addLoadCommand<MachO::LC_ID_DYLIB>(JD.getName(), 0, 0, 0);

  if (Opts.UUID)
    B.template addLoadCommand<MachO::LC_UUID>(*Opts.UUID);

  for (auto &BV : Opts.BuildVersions)
    B.template addLoadCommand<MachO::LC_BUILD_VERSION>(
        BV.Platform, BV.MinOS, BV.SDK, static_cast<uint32_t>(0));

  if (Opts.TargetTriple)
    B.template addLoadCommand<MachO::LC_TARGET_TRIPLE>(*Opts.TargetTriple);

  using LoadKind = MachOPlatform::HeaderOptions::LoadDylibCmd::LoadKind;
  for (auto &LD : Opts.LoadDylibs) {
    switch (LD.K) {
    case LoadKind::Default:
      B.template addLoadCommand<MachO::LC_LOAD_DYLIB>(
          LD.D.Name, LD.D.Timestamp, LD.D.CurrentVersion,
          LD.D.CompatibilityVersion);
      break;
    case LoadKind::Weak:
      B.template addLoadCommand<MachO::LC_LOAD_WEAK_DYLIB>(
          LD.D.Name, LD.D.Timestamp, LD.D.CurrentVersion,
          LD.D.CompatibilityVersion);
      break;
    }
  }
  for (auto &P : Opts.RPaths)
    B.template addLoadCommand<MachO::LC_RPATH>(P);

  auto HeaderContent = G.allocateBuffer(B.layout());
  B.write(HeaderContent);

  return G.createContentBlock(HeaderSection, HeaderContent, ExecutorAddr(), 8,
                              0);
}

SimpleMachOHeaderMU::SimpleMachOHeaderMU(MachOPlatform &MOP,
                                         SymbolStringPtr HeaderStartSymbol,
                                         MachOPlatform::HeaderOptions Opts)
    : MaterializationUnit(
          createHeaderInterface(MOP, std::move(HeaderStartSymbol))),
      MOP(MOP), Opts(std::move(Opts)) {}

void SimpleMachOHeaderMU::materialize(
    std::unique_ptr<MaterializationResponsibility> R) {
  auto G = createPlatformGraph(MOP, "<MachOHeaderMU>");
  addMachOHeader(R->getTargetJITDylib(), *G, R->getInitializerSymbol());
  MOP.getObjectLinkingLayer().emit(std::move(R), std::move(G));
}

void SimpleMachOHeaderMU::discard(const JITDylib &JD,
                                  const SymbolStringPtr &Sym) {}

void SimpleMachOHeaderMU::addMachOHeader(
    JITDylib &JD, jitlink::LinkGraph &G,
    const SymbolStringPtr &InitializerSymbol) {
  auto &HeaderSection = G.createSection("__header", MemProt::Read);
  auto &HeaderBlock = createHeaderBlock(JD, G, HeaderSection);

  // Init symbol is header-start symbol.
  G.addDefinedSymbol(HeaderBlock, 0, *InitializerSymbol, HeaderBlock.getSize(),
                     jitlink::Linkage::Strong, jitlink::Scope::Default, false,
                     true);
  for (auto &HS : AdditionalHeaderSymbols)
    G.addDefinedSymbol(HeaderBlock, HS.Offset, HS.Name, HeaderBlock.getSize(),
                       jitlink::Linkage::Strong, jitlink::Scope::Default, false,
                       true);
}

jitlink::Block &
SimpleMachOHeaderMU::createHeaderBlock(JITDylib &JD, jitlink::LinkGraph &G,
                                       jitlink::Section &HeaderSection) {
  switch (MOP.getExecutionSession().getTargetTriple().getArch()) {
  case Triple::aarch64:
  case Triple::x86_64:
    return ::createHeaderBlock<MachO64LE>(MOP, Opts, JD, G, HeaderSection);
  default:
    llvm_unreachable("Unsupported architecture");
  }
}

MaterializationUnit::Interface SimpleMachOHeaderMU::createHeaderInterface(
    MachOPlatform &MOP, const SymbolStringPtr &HeaderStartSymbol) {
  SymbolFlagsMap HeaderSymbolFlags;

  HeaderSymbolFlags[HeaderStartSymbol] = JITSymbolFlags::Exported;
  for (auto &HS : AdditionalHeaderSymbols)
    HeaderSymbolFlags[MOP.getExecutionSession().intern(HS.Name)] =
        JITSymbolFlags::Exported;

  return MaterializationUnit::Interface(std::move(HeaderSymbolFlags),
                                        HeaderStartSymbol);
}

MachOHeaderInfo getMachOHeaderInfoFromTriple(const Triple &TT) {
  switch (TT.getArch()) {
  case Triple::aarch64:
    return {/* PageSize   = */ 16 * 1024,
            /* CPUType    = */ MachO::CPU_TYPE_ARM64,
            /* CPUSubType = */ MachO::CPU_SUBTYPE_ARM64_ALL};
  case Triple::x86_64:
    return {/* PageSize   = */ 4 * 1024,
            /* CPUType    = */ MachO::CPU_TYPE_X86_64,
            /* CPUSubType = */ MachO::CPU_SUBTYPE_X86_64_ALL};
  default:
    llvm_unreachable("Unrecognized architecture");
  }
}

} // End namespace orc.
} // End namespace llvm.