MachOPlatform.cpp

//===------ 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/x86_64.h"
#include "llvm/ExecutionEngine/Orc/DebugUtils.h"
#include "llvm/ExecutionEngine/Orc/ExecutionUtils.h"
#include "llvm/Support/BinaryByteStream.h"
#include "llvm/Support/Debug.h"

#define DEBUG_TYPE "orc"

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

namespace {

class MachOHeaderMaterializationUnit : public MaterializationUnit {
public:
  MachOHeaderMaterializationUnit(MachOPlatform &MOP,
                                 const SymbolStringPtr &HeaderStartSymbol)
      : MaterializationUnit(createHeaderSymbols(MOP, HeaderStartSymbol),
                            HeaderStartSymbol),
        MOP(MOP) {}

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

  void materialize(std::unique_ptr<MaterializationResponsibility> R) override {
    unsigned PointerSize;
    support::endianness Endianness;

    switch (MOP.getExecutorProcessControl().getTargetTriple().getArch()) {
    case Triple::aarch64:
    case Triple::x86_64:
      PointerSize = 8;
      Endianness = support::endianness::little;
      break;
    default:
      llvm_unreachable("Unrecognized architecture");
    }

    auto G = std::make_unique<jitlink::LinkGraph>(
        "<MachOHeaderMU>", MOP.getExecutorProcessControl().getTargetTriple(),
        PointerSize, Endianness, jitlink::getGenericEdgeKindName);
    auto &HeaderSection = G->createSection("__header", sys::Memory::MF_READ);
    auto &HeaderBlock = createHeaderBlock(*G, HeaderSection);

    // Init symbol is header-start symbol.
    G->addDefinedSymbol(HeaderBlock, 0, *R->getInitializerSymbol(),
                        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);

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

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

private:
  struct HeaderSymbol {
    const char *Name;
    uint64_t Offset;
  };

  static constexpr HeaderSymbol AdditionalHeaderSymbols[] = {
      {"___mh_executable_header", 0}};

  static jitlink::Block &createHeaderBlock(jitlink::LinkGraph &G,
                                           jitlink::Section &HeaderSection) {
    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("Unrecognized architecture");
    }
    Hdr.filetype = MachO::MH_DYLIB; // Custom file type?
    Hdr.ncmds = 0;
    Hdr.sizeofcmds = 0;
    Hdr.flags = 0;
    Hdr.reserved = 0;

    if (G.getEndianness() != support::endian::system_endianness())
      MachO::swapStruct(Hdr);

    auto HeaderContent = G.allocateString(
        StringRef(reinterpret_cast<const char *>(&Hdr), sizeof(Hdr)));

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

  static SymbolFlagsMap
  createHeaderSymbols(MachOPlatform &MOP,
                      const SymbolStringPtr &HeaderStartSymbol) {
    SymbolFlagsMap HeaderSymbolFlags;

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

    return HeaderSymbolFlags;
  }

  MachOPlatform &MOP;
};

constexpr MachOHeaderMaterializationUnit::HeaderSymbol
    MachOHeaderMaterializationUnit::AdditionalHeaderSymbols[];

StringRef EHFrameSectionName = "__TEXT,__eh_frame";
StringRef ModInitFuncSectionName = "__DATA,__mod_init_func";

StringRef InitSectionNames[] = {ModInitFuncSectionName};

} // end anonymous namespace

namespace llvm {
namespace orc {

Expected<std::unique_ptr<MachOPlatform>>
MachOPlatform::Create(ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
                      ExecutorProcessControl &EPC, JITDylib &PlatformJD,
                      const char *OrcRuntimePath,
                      Optional<SymbolAliasMap> RuntimeAliases) {

  // If the target is not supported then bail out immediately.
  if (!supportedTarget(EPC.getTargetTriple()))
    return make_error<StringError>("Unsupported MachOPlatform triple: " +
                                       EPC.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 function support symbols.
  if (auto Err = PlatformJD.define(absoluteSymbols(
          {{ES.intern("___orc_rt_jit_dispatch"),
            {EPC.getJITDispatchInfo().JITDispatchFunctionAddress.getValue(),
             JITSymbolFlags::Exported}},
           {ES.intern("___orc_rt_jit_dispatch_ctx"),
            {EPC.getJITDispatchInfo().JITDispatchContextAddress.getValue(),
             JITSymbolFlags::Exported}}})))
    return std::move(Err);

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

  // Create the instance.
  Error Err = Error::success();
  auto P = std::unique_ptr<MachOPlatform>(
      new MachOPlatform(ES, ObjLinkingLayer, EPC, PlatformJD,
                        std::move(*OrcRuntimeArchiveGenerator), Err));
  if (Err)
    return std::move(Err);
  return std::move(P);
}

Error MachOPlatform::setupJITDylib(JITDylib &JD) {
  return JD.define(std::make_unique<MachOHeaderMaterializationUnit>(
      *this, MachOHeaderStartSymbol));
}

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());
  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_log_error", "___orc_rt_log_error_to_stderr"}};

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

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

MachOPlatform::MachOPlatform(
    ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
    ExecutorProcessControl &EPC, JITDylib &PlatformJD,
    std::unique_ptr<DefinitionGenerator> OrcRuntimeGenerator, Error &Err)
    : ES(ES), ObjLinkingLayer(ObjLinkingLayer), EPC(EPC),
      MachOHeaderStartSymbol(ES.intern("___dso_handle")) {
  ErrorAsOutParameter _(&Err);

  ObjLinkingLayer.addPlugin(std::make_unique<MachOPlatformPlugin>(*this));

  PlatformJD.addGenerator(std::move(OrcRuntimeGenerator));

  // PlatformJD hasn't been 'set-up' by the platform yet (since we're creating
  // the platform now), so set it up.
  if (auto E2 = setupJITDylib(PlatformJD)) {
    Err = std::move(E2);
    return;
  }

  RegisteredInitSymbols[&PlatformJD].add(
      MachOHeaderStartSymbol, SymbolLookupFlags::WeaklyReferencedSymbol);

  // Associate wrapper function tags with JIT-side function implementations.
  if (auto E2 = associateRuntimeSupportFunctions(PlatformJD)) {
    Err = std::move(E2);
    return;
  }

  // Lookup addresses of runtime functions callable by the platform,
  // call the platform bootstrap function to initialize the platform-state
  // object in the executor.
  if (auto E2 = bootstrapMachORuntime(PlatformJD)) {
    Err = std::move(E2);
    return;
  }
}

Error MachOPlatform::associateRuntimeSupportFunctions(JITDylib &PlatformJD) {
  ExecutorProcessControl::WrapperFunctionAssociationMap WFs;

  using GetInitializersSPSSig =
      SPSExpected<SPSMachOJITDylibInitializerSequence>(SPSString);
  WFs[ES.intern("___orc_rt_macho_get_initializers_tag")] =
      EPC.wrapAsyncWithSPS<GetInitializersSPSSig>(
          this, &MachOPlatform::rt_getInitializers);

  using GetDeinitializersSPSSig =
      SPSExpected<SPSMachOJITDylibDeinitializerSequence>(SPSExecutorAddress);
  WFs[ES.intern("___orc_rt_macho_get_deinitializers_tag")] =
      EPC.wrapAsyncWithSPS<GetDeinitializersSPSSig>(
          this, &MachOPlatform::rt_getDeinitializers);

  using LookupSymbolSPSSig =
      SPSExpected<SPSExecutorAddress>(SPSExecutorAddress, SPSString);
  WFs[ES.intern("___orc_rt_macho_symbol_lookup_tag")] =
      EPC.wrapAsyncWithSPS<LookupSymbolSPSSig>(this,
                                               &MachOPlatform::rt_lookupSymbol);

  return EPC.associateJITSideWrapperFunctions(PlatformJD, std::move(WFs));
}

void MachOPlatform::getInitializersBuildSequencePhase(
    SendInitializerSequenceFn SendResult, JITDylib &JD,
    std::vector<JITDylibSP> DFSLinkOrder) {
  MachOJITDylibInitializerSequence FullInitSeq;
  {
    std::lock_guard<std::mutex> Lock(PlatformMutex);
    for (auto &InitJD : reverse(DFSLinkOrder)) {
      LLVM_DEBUG({
        dbgs() << "MachOPlatform: Appending inits for \"" << InitJD->getName()
               << "\" to sequence\n";
      });
      auto ISItr = InitSeqs.find(InitJD.get());
      if (ISItr != InitSeqs.end()) {
        FullInitSeq.emplace_back(std::move(ISItr->second));
        InitSeqs.erase(ISItr);
      }
    }
  }

  SendResult(std::move(FullInitSeq));
}

void MachOPlatform::getInitializersLookupPhase(
    SendInitializerSequenceFn SendResult, JITDylib &JD) {

  auto DFSLinkOrder = JD.getDFSLinkOrder();
  DenseMap<JITDylib *, SymbolLookupSet> NewInitSymbols;
  ES.runSessionLocked([&]() {
    for (auto &InitJD : DFSLinkOrder) {
      auto RISItr = RegisteredInitSymbols.find(InitJD.get());
      if (RISItr != RegisteredInitSymbols.end()) {
        NewInitSymbols[InitJD.get()] = std::move(RISItr->second);
        RegisteredInitSymbols.erase(RISItr);
      }
    }
  });

  // If there are no further init symbols to look up then move on to the next
  // phase.
  if (NewInitSymbols.empty()) {
    getInitializersBuildSequencePhase(std::move(SendResult), JD,
                                      std::move(DFSLinkOrder));
    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
          getInitializersLookupPhase(std::move(SendResult), JD);
      },
      ES, std::move(NewInitSymbols));
}

void MachOPlatform::rt_getInitializers(SendInitializerSequenceFn SendResult,
                                       StringRef JDName) {
  LLVM_DEBUG({
    dbgs() << "MachOPlatform::rt_getInitializers(\"" << JDName << "\")\n";
  });

  JITDylib *JD = ES.getJITDylibByName(JDName);
  if (!JD) {
    LLVM_DEBUG({
      dbgs() << "  No such JITDylib \"" << JDName << "\". Sending error.\n";
    });
    SendResult(make_error<StringError>("No JITDylib named " + JDName,
                                       inconvertibleErrorCode()));
    return;
  }

  getInitializersLookupPhase(std::move(SendResult), *JD);
}

void MachOPlatform::rt_getDeinitializers(SendDeinitializerSequenceFn SendResult,
                                         ExecutorAddress Handle) {
  LLVM_DEBUG({
    dbgs() << "MachOPlatform::rt_getDeinitializers(\""
           << formatv("{0:x}", Handle.getValue()) << "\")\n";
  });

  JITDylib *JD = nullptr;

  {
    std::lock_guard<std::mutex> Lock(PlatformMutex);
    auto I = HeaderAddrToJITDylib.find(Handle.getValue());
    if (I != HeaderAddrToJITDylib.end())
      JD = I->second;
  }

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

  SendResult(MachOJITDylibDeinitializerSequence());
}

void MachOPlatform::rt_lookupSymbol(SendSymbolAddressFn SendResult,
                                    ExecutorAddress Handle,
                                    StringRef SymbolName) {
  LLVM_DEBUG({
    dbgs() << "MachOPlatform::rt_lookupSymbol(\""
           << formatv("{0:x}", Handle.getValue()) << "\")\n";
  });

  JITDylib *JD = nullptr;

  {
    std::lock_guard<std::mutex> Lock(PlatformMutex);
    auto I = HeaderAddrToJITDylib.find(Handle.getValue());
    if (I != HeaderAddrToJITDylib.end())
      JD = I->second;
  }

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

  // FIXME: Proper mangling.
  auto MangledName = ("_" + SymbolName).str();
  ES.lookup(
      LookupKind::DLSym, {{JD, JITDylibLookupFlags::MatchExportedSymbolsOnly}},
      SymbolLookupSet(ES.intern(MangledName)), SymbolState::Ready,
      [SendResult = std::move(SendResult)](Expected<SymbolMap> Result) mutable {
        if (Result) {
          assert(Result->size() == 1 && "Unexpected result map count");
          SendResult(ExecutorAddress(Result->begin()->second.getAddress()));
        } else
          SendResult(Result.takeError());
      },
      NoDependenciesToRegister);
}

Error MachOPlatform::bootstrapMachORuntime(JITDylib &PlatformJD) {

  std::pair<const char *, ExecutorAddress *> Symbols[] = {
      {"___orc_rt_macho_platform_bootstrap", &orc_rt_macho_platform_bootstrap},
      {"___orc_rt_macho_platform_shutdown", &orc_rt_macho_platform_shutdown},
      {"___orc_rt_macho_register_object_sections",
       &orc_rt_macho_register_object_sections}};

  SymbolLookupSet RuntimeSymbols;
  std::vector<std::pair<SymbolStringPtr, ExecutorAddress *>> AddrsToRecord;
  for (const auto &KV : Symbols) {
    auto Name = ES.intern(KV.first);
    RuntimeSymbols.add(Name);
    AddrsToRecord.push_back({std::move(Name), KV.second});
  }

  auto RuntimeSymbolAddrs = ES.lookup(
      {{&PlatformJD, JITDylibLookupFlags::MatchAllSymbols}}, RuntimeSymbols);
  if (!RuntimeSymbolAddrs)
    return RuntimeSymbolAddrs.takeError();

  for (const auto &KV : AddrsToRecord) {
    auto &Name = KV.first;
    assert(RuntimeSymbolAddrs->count(Name) && "Missing runtime symbol?");
    KV.second->setValue((*RuntimeSymbolAddrs)[Name].getAddress());
  }

  if (auto Err =
          EPC.runSPSWrapper<void()>(orc_rt_macho_platform_bootstrap.getValue()))
    return Err;

  // FIXME: Ordering is fuzzy here. We're probably best off saying
  // "behavior is undefined if code that uses the runtime is added before
  // the platform constructor returns", then move all this to the constructor.
  RuntimeBootstrapped = true;
  std::vector<MachOPerObjectSectionsToRegister> DeferredPOSRs;
  {
    std::lock_guard<std::mutex> Lock(PlatformMutex);
    DeferredPOSRs = std::move(BootstrapPOSRs);
  }

  for (auto &D : DeferredPOSRs)
    if (auto Err = registerPerObjectSections(D))
      return Err;

  return Error::success();
}

Error MachOPlatform::registerInitInfo(
    JITDylib &JD, ArrayRef<jitlink::Section *> InitSections) {

  std::unique_lock<std::mutex> Lock(PlatformMutex);

  MachOJITDylibInitializers *InitSeq = nullptr;
  {
    auto I = InitSeqs.find(&JD);
    if (I == InitSeqs.end()) {
      // If there's no init sequence entry yet then we need to look up the
      // header symbol to force creation of one.
      Lock.unlock();

      auto SearchOrder =
          JD.withLinkOrderDo([](const JITDylibSearchOrder &SO) { return SO; });
      if (auto Err = ES.lookup(SearchOrder, MachOHeaderStartSymbol).takeError())
        return Err;

      Lock.lock();
      I = InitSeqs.find(&JD);
      assert(I != InitSeqs.end() &&
             "Entry missing after header symbol lookup?");
    }
    InitSeq = &I->second;
  }

  for (auto *Sec : InitSections) {
    // FIXME: Avoid copy here.
    jitlink::SectionRange R(*Sec);
    InitSeq->InitSections[Sec->getName()].push_back(
        {ExecutorAddress(R.getStart()), ExecutorAddress(R.getEnd())});
  }

  return Error::success();
}

Error MachOPlatform::registerPerObjectSections(
    const MachOPerObjectSectionsToRegister &POSR) {

  if (!orc_rt_macho_register_object_sections)
    return make_error<StringError>("Attempting to register per-object "
                                   "sections, but runtime support has not "
                                   "been loaded yet",
                                   inconvertibleErrorCode());

  Error ErrResult = Error::success();
  if (auto Err = EPC.runSPSWrapper<shared::SPSError(
                     SPSMachOPerObjectSectionsToRegister)>(
          orc_rt_macho_register_object_sections.getValue(), ErrResult, POSR))
    return Err;
  return ErrResult;
}

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

  // If the initializer symbol is the MachOHeader start symbol then just add
  // the macho header support passes.
  if (MR.getInitializerSymbol() == MP.MachOHeaderStartSymbol) {
    addMachOHeaderSupportPasses(MR, Config);
    // The header materialization unit doesn't require any other support, so we
    // can bail out early.
    return;
  }

  // If the object contains initializers then add passes to record them.
  if (MR.getInitializerSymbol())
    addInitializerSupportPasses(MR, Config);

  // Add passes for eh-frame support.
  addEHSupportPasses(MR, Config);
}

ObjectLinkingLayer::Plugin::SyntheticSymbolDependenciesMap
MachOPlatform::MachOPlatformPlugin::getSyntheticSymbolDependencies(
    MaterializationResponsibility &MR) {
  std::lock_guard<std::mutex> Lock(PluginMutex);
  auto I = InitSymbolDeps.find(&MR);
  if (I != InitSymbolDeps.end()) {
    SyntheticSymbolDependenciesMap Result;
    Result[MR.getInitializerSymbol()] = std::move(I->second);
    InitSymbolDeps.erase(&MR);
    return Result;
  }
  return SyntheticSymbolDependenciesMap();
}

void MachOPlatform::MachOPlatformPlugin::addInitializerSupportPasses(
    MaterializationResponsibility &MR, jitlink::PassConfiguration &Config) {

  /// Preserve init sections.
  Config.PrePrunePasses.push_back([this, &MR](jitlink::LinkGraph &G) {
    return preserveInitSections(G, MR);
  });

  Config.PostFixupPasses.push_back(
      [this, &JD = MR.getTargetJITDylib()](jitlink::LinkGraph &G) {
        return registerInitSections(G, JD);
      });
}

void MachOPlatform::MachOPlatformPlugin::addMachOHeaderSupportPasses(
    MaterializationResponsibility &MR, jitlink::PassConfiguration &Config) {

  Config.PostAllocationPasses.push_back([this, &JD = MR.getTargetJITDylib()](
                                            jitlink::LinkGraph &G) -> Error {
    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");
    {
      std::lock_guard<std::mutex> Lock(MP.PlatformMutex);
      JITTargetAddress HeaderAddr = (*I)->getAddress();
      MP.HeaderAddrToJITDylib[HeaderAddr] = &JD;
      assert(!MP.InitSeqs.count(&JD) && "InitSeq entry for JD already exists");
      MP.InitSeqs.insert(
          std::make_pair(&JD, MachOJITDylibInitializers(
                                  JD.getName(), ExecutorAddress(HeaderAddr))));
    }
    return Error::success();
  });
}

void MachOPlatform::MachOPlatformPlugin::addEHSupportPasses(
    MaterializationResponsibility &MR, jitlink::PassConfiguration &Config) {

  // Add a pass to register the final addresses of the eh-frame sections
  // with the runtime.
  Config.PostFixupPasses.push_back([this](jitlink::LinkGraph &G) -> Error {
    MachOPerObjectSectionsToRegister POSR;

    if (auto *EHFrameSection = G.findSectionByName(EHFrameSectionName)) {
      jitlink::SectionRange R(*EHFrameSection);
      if (!R.empty())
        POSR.EHFrameSection = {ExecutorAddress(R.getStart()),
                               ExecutorAddress(R.getEnd())};
    }

    if (POSR.EHFrameSection.StartAddress) {

      // If we're still bootstrapping the runtime then just record this
      // frame for now.
      if (!MP.RuntimeBootstrapped) {
        std::lock_guard<std::mutex> Lock(MP.PlatformMutex);
        MP.BootstrapPOSRs.push_back(POSR);
        return Error::success();
      }

      // Otherwise register it immediately.
      if (auto Err = MP.registerPerObjectSections(POSR))
        return Err;
    }

    return Error::success();
  });
}

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

  JITLinkSymbolSet InitSectionSymbols;
  for (auto &InitSectionName : InitSectionNames) {
    // Skip non-init sections.
    auto *InitSection = G.findSectionByName(InitSectionName);
    if (!InitSection)
      continue;

    // Make a pass over live symbols in the section: those blocks are already
    // preserved.
    DenseSet<jitlink::Block *> AlreadyLiveBlocks;
    for (auto &Sym : InitSection->symbols()) {
      auto &B = Sym->getBlock();
      if (Sym->isLive() && Sym->getOffset() == 0 &&
          Sym->getSize() == B.getSize() && !AlreadyLiveBlocks.count(&B)) {
        InitSectionSymbols.insert(Sym);
        AlreadyLiveBlocks.insert(&B);
      }
    }

    // Add anonymous symbols to preserve any not-already-preserved blocks.
    for (auto *B : InitSection->blocks())
      if (!AlreadyLiveBlocks.count(B))
        InitSectionSymbols.insert(
            &G.addAnonymousSymbol(*B, 0, B->getSize(), false, true));
  }

  if (!InitSectionSymbols.empty()) {
    std::lock_guard<std::mutex> Lock(PluginMutex);
    InitSymbolDeps[&MR] = std::move(InitSectionSymbols);
  }

  return Error::success();
}

Error MachOPlatform::MachOPlatformPlugin::registerInitSections(
    jitlink::LinkGraph &G, JITDylib &JD) {

  SmallVector<jitlink::Section *> InitSections;

  for (auto InitSectionName : InitSectionNames)
    if (auto *Sec = G.findSectionByName(InitSectionName))
      InitSections.push_back(Sec);

  // Dump the scraped inits.
  LLVM_DEBUG({
    dbgs() << "MachOPlatform: Scraped " << G.getName() << " init sections:\n";
    for (auto *Sec : InitSections) {
      jitlink::SectionRange R(*Sec);
      dbgs() << "  " << Sec->getName() << ": "
             << formatv("[ {0:x} -- {1:x} ]", R.getStart(), R.getEnd()) << "\n";
    }
  });

  return MP.registerInitInfo(JD, InitSections);
}

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