[ORC][ORC-RT] Reapply "Introduce ELF/*nix Platform and runtime..." with fixes.

This reapplies e256445bfff, which was reverted in 45ac5f54418 due to bot errors
(e.g. https://lab.llvm.org/buildbot/#/builders/112/builds/8599). The issue that
caused the bot failure was fixed in 2e6a4fce356.

4 files changed, 804 insertions, 20 deletions

diff --git a/llvm/lib/ExecutionEngine/Orc/CMakeLists.txt b/llvm/lib/ExecutionEngine/Orc/CMakeLists.txt
index fb69781..59f6946 100644
--- a/llvm/lib/ExecutionEngine/Orc/CMakeLists.txt
+++ b/llvm/lib/ExecutionEngine/Orc/CMakeLists.txt
@@ -19,6 +19,7 @@ add_llvm_component_library(LLVMOrcJIT
   LookupAndRecordAddrs.cpp
   LLJIT.cpp
   MachOPlatform.cpp
+  ELFNixPlatform.cpp
   Mangling.cpp
   ObjectLinkingLayer.cpp
   ObjectTransformLayer.cpp
diff --git a/llvm/lib/ExecutionEngine/Orc/ELFNixPlatform.cpp b/llvm/lib/ExecutionEngine/Orc/ELFNixPlatform.cpp
new file mode 100644
index 0000000..ff8f0e9
--- /dev/null
+++ b/llvm/lib/ExecutionEngine/Orc/ELFNixPlatform.cpp
@@ -0,0 +1,762 @@
+//===------ ELFNixPlatform.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/ELFNixPlatform.h"
+
+#include "llvm/BinaryFormat/ELF.h"
+#include "llvm/ExecutionEngine/JITLink/ELF_x86_64.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 DSOHandleMaterializationUnit : public MaterializationUnit {
+public:
+  DSOHandleMaterializationUnit(ELFNixPlatform &ENP,
+                               const SymbolStringPtr &DSOHandleSymbol)
+      : MaterializationUnit(createDSOHandleSectionSymbols(ENP, DSOHandleSymbol),
+                            DSOHandleSymbol),
+        ENP(ENP) {}
+
+  StringRef getName() const override { return "DSOHandleMU"; }
+
+  void materialize(std::unique_ptr<MaterializationResponsibility> R) override {
+    unsigned PointerSize;
+    support::endianness Endianness;
+    jitlink::Edge::Kind EdgeKind;
+    const auto &TT =
+        ENP.getExecutionSession().getExecutorProcessControl().getTargetTriple();
+
+    switch (TT.getArch()) {
+    case Triple::x86_64:
+      PointerSize = 8;
+      Endianness = support::endianness::little;
+      EdgeKind = jitlink::x86_64::Pointer64;
+      break;
+    default:
+      llvm_unreachable("Unrecognized architecture");
+    }
+
+    // void *__dso_handle = &__dso_handle;
+    auto G = std::make_unique<jitlink::LinkGraph>(
+        "<DSOHandleMU>", TT, PointerSize, Endianness,
+        jitlink::getGenericEdgeKindName);
+    auto &DSOHandleSection =
+        G->createSection(".data.__dso_handle", sys::Memory::MF_READ);
+    auto &DSOHandleBlock = G->createContentBlock(
+        DSOHandleSection, getDSOHandleContent(PointerSize), 0, 8, 0);
+    auto &DSOHandleSymbol = G->addDefinedSymbol(
+        DSOHandleBlock, 0, *R->getInitializerSymbol(), DSOHandleBlock.getSize(),
+        jitlink::Linkage::Strong, jitlink::Scope::Default, false, true);
+    DSOHandleBlock.addEdge(EdgeKind, 0, DSOHandleSymbol, 0);
+
+    ENP.getObjectLinkingLayer().emit(std::move(R), std::move(G));
+  }
+
+  void discard(const JITDylib &JD, const SymbolStringPtr &Sym) override {}
+
+private:
+  static SymbolFlagsMap
+  createDSOHandleSectionSymbols(ELFNixPlatform &ENP,
+                                const SymbolStringPtr &DSOHandleSymbol) {
+    SymbolFlagsMap SymbolFlags;
+    SymbolFlags[DSOHandleSymbol] = JITSymbolFlags::Exported;
+    return SymbolFlags;
+  }
+
+  ArrayRef<char> getDSOHandleContent(size_t PointerSize) {
+    static const char Content[8] = {0};
+    assert(PointerSize <= sizeof Content);
+    return {Content, PointerSize};
+  }
+
+  ELFNixPlatform &ENP;
+};
+
+StringRef EHFrameSectionName = ".eh_frame";
+StringRef InitArrayFuncSectionName = ".init_array";
+
+StringRef ThreadBSSSectionName = ".tbss";
+StringRef ThreadDataSectionName = ".tdata";
+
+StringRef InitSectionNames[] = {InitArrayFuncSectionName};
+
+} // end anonymous namespace
+
+namespace llvm {
+namespace orc {
+
+Expected<std::unique_ptr<ELFNixPlatform>>
+ELFNixPlatform::Create(ExecutionSession &ES,
+                       ObjectLinkingLayer &ObjLinkingLayer,
+                       JITDylib &PlatformJD, const char *OrcRuntimePath,
+                       Optional<SymbolAliasMap> RuntimeAliases) {
+
+  auto &EPC = ES.getExecutorProcessControl();
+
+  // If the target is not supported then bail out immediately.
+  if (!supportedTarget(EPC.getTargetTriple()))
+    return make_error<StringError>("Unsupported ELFNixPlatform 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<ELFNixPlatform>(
+      new ELFNixPlatform(ES, ObjLinkingLayer, PlatformJD,
+                         std::move(*OrcRuntimeArchiveGenerator), Err));
+  if (Err)
+    return std::move(Err);
+  return std::move(P);
+}
+
+Error ELFNixPlatform::setupJITDylib(JITDylib &JD) {
+  return JD.define(
+      std::make_unique<DSOHandleMaterializationUnit>(*this, DSOHandleSymbol));
+  return Error::success();
+}
+
+Error ELFNixPlatform::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() << "ELFNixPlatform: Registered init symbol " << *InitSym
+           << " for MU " << MU.getName() << "\n";
+  });
+  return Error::success();
+}
+
+Error ELFNixPlatform::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 ELFNixPlatform::standardPlatformAliases(ExecutionSession &ES) {
+  SymbolAliasMap Aliases;
+  addAliases(ES, Aliases, requiredCXXAliases());
+  addAliases(ES, Aliases, standardRuntimeUtilityAliases());
+  return Aliases;
+}
+
+ArrayRef<std::pair<const char *, const char *>>
+ELFNixPlatform::requiredCXXAliases() {
+  static const std::pair<const char *, const char *> RequiredCXXAliases[] = {
+      {"__cxa_atexit", "__orc_rt_elfnix_cxa_atexit"}};
+
+  return ArrayRef<std::pair<const char *, const char *>>(RequiredCXXAliases);
+}
+
+ArrayRef<std::pair<const char *, const char *>>
+ELFNixPlatform::standardRuntimeUtilityAliases() {
+  static const std::pair<const char *, const char *>
+      StandardRuntimeUtilityAliases[] = {
+          {"__orc_rt_run_program", "__orc_rt_elfnix_run_program"},
+          {"__orc_rt_log_error", "__orc_rt_log_error_to_stderr"}};
+
+  return ArrayRef<std::pair<const char *, const char *>>(
+      StandardRuntimeUtilityAliases);
+}
+
+bool ELFNixPlatform::isInitializerSection(StringRef SecName) {
+  for (auto &Name : InitSectionNames) {
+    if (Name.equals(SecName))
+      return true;
+  }
+  return false;
+}
+
+bool ELFNixPlatform::supportedTarget(const Triple &TT) {
+  switch (TT.getArch()) {
+  case Triple::x86_64:
+    return true;
+  default:
+    return false;
+  }
+}
+
+ELFNixPlatform::ELFNixPlatform(
+    ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
+    JITDylib &PlatformJD,
+    std::unique_ptr<DefinitionGenerator> OrcRuntimeGenerator, Error &Err)
+    : ES(ES), ObjLinkingLayer(ObjLinkingLayer),
+      DSOHandleSymbol(ES.intern("__dso_handle")) {
+  ErrorAsOutParameter _(&Err);
+
+  ObjLinkingLayer.addPlugin(std::make_unique<ELFNixPlatformPlugin>(*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(
+      DSOHandleSymbol, 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 = bootstrapELFNixRuntime(PlatformJD)) {
+    Err = std::move(E2);
+    return;
+  }
+}
+
+Error ELFNixPlatform::associateRuntimeSupportFunctions(JITDylib &PlatformJD) {
+  ExecutionSession::JITDispatchHandlerAssociationMap WFs;
+
+  using GetInitializersSPSSig =
+      SPSExpected<SPSELFNixJITDylibInitializerSequence>(SPSString);
+  WFs[ES.intern("__orc_rt_elfnix_get_initializers_tag")] =
+      ES.wrapAsyncWithSPS<GetInitializersSPSSig>(
+          this, &ELFNixPlatform::rt_getInitializers);
+
+  using GetDeinitializersSPSSig =
+      SPSExpected<SPSELFJITDylibDeinitializerSequence>(SPSExecutorAddress);
+  WFs[ES.intern("__orc_rt_elfnix_get_deinitializers_tag")] =
+      ES.wrapAsyncWithSPS<GetDeinitializersSPSSig>(
+          this, &ELFNixPlatform::rt_getDeinitializers);
+
+  using LookupSymbolSPSSig =
+      SPSExpected<SPSExecutorAddress>(SPSExecutorAddress, SPSString);
+  WFs[ES.intern("__orc_rt_elfnix_symbol_lookup_tag")] =
+      ES.wrapAsyncWithSPS<LookupSymbolSPSSig>(this,
+                                              &ELFNixPlatform::rt_lookupSymbol);
+
+  return ES.registerJITDispatchHandlers(PlatformJD, std::move(WFs));
+}
+
+void ELFNixPlatform::getInitializersBuildSequencePhase(
+    SendInitializerSequenceFn SendResult, JITDylib &JD,
+    std::vector<JITDylibSP> DFSLinkOrder) {
+  ELFNixJITDylibInitializerSequence FullInitSeq;
+  {
+    std::lock_guard<std::mutex> Lock(PlatformMutex);
+    for (auto &InitJD : reverse(DFSLinkOrder)) {
+      LLVM_DEBUG({
+        dbgs() << "ELFNixPlatform: 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 ELFNixPlatform::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 ELFNixPlatform::rt_getInitializers(SendInitializerSequenceFn SendResult,
+                                        StringRef JDName) {
+  LLVM_DEBUG({
+    dbgs() << "ELFNixPlatform::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 ELFNixPlatform::rt_getDeinitializers(
+    SendDeinitializerSequenceFn SendResult, ExecutorAddress Handle) {
+  LLVM_DEBUG({
+    dbgs() << "ELFNixPlatform::rt_getDeinitializers(\""
+           << formatv("{0:x}", Handle.getValue()) << "\")\n";
+  });
+
+  JITDylib *JD = nullptr;
+
+  {
+    std::lock_guard<std::mutex> Lock(PlatformMutex);
+    auto I = HandleAddrToJITDylib.find(Handle.getValue());
+    if (I != HandleAddrToJITDylib.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(ELFNixJITDylibDeinitializerSequence());
+}
+
+void ELFNixPlatform::rt_lookupSymbol(SendSymbolAddressFn SendResult,
+                                     ExecutorAddress Handle,
+                                     StringRef SymbolName) {
+  LLVM_DEBUG({
+    dbgs() << "ELFNixPlatform::rt_lookupSymbol(\""
+           << formatv("{0:x}", Handle.getValue()) << "\")\n";
+  });
+
+  JITDylib *JD = nullptr;
+
+  {
+    std::lock_guard<std::mutex> Lock(PlatformMutex);
+    auto I = HandleAddrToJITDylib.find(Handle.getValue());
+    if (I != HandleAddrToJITDylib.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;
+  }
+
+  // Use functor class to work around XL build compiler issue on AIX.
+  class RtLookupNotifyComplete {
+  public:
+    RtLookupNotifyComplete(SendSymbolAddressFn &&SendResult)
+        : SendResult(std::move(SendResult)) {}
+    void operator()(Expected<SymbolMap> Result) {
+      if (Result) {
+        assert(Result->size() == 1 && "Unexpected result map count");
+        SendResult(ExecutorAddress(Result->begin()->second.getAddress()));
+      } else {
+        SendResult(Result.takeError());
+      }
+    }
+
+  private:
+    SendSymbolAddressFn SendResult;
+  };
+
+  ES.lookup(
+      LookupKind::DLSym, {{JD, JITDylibLookupFlags::MatchExportedSymbolsOnly}},
+      SymbolLookupSet(ES.intern(SymbolName)), SymbolState::Ready,
+      RtLookupNotifyComplete(std::move(SendResult)), NoDependenciesToRegister);
+}
+
+Error ELFNixPlatform::bootstrapELFNixRuntime(JITDylib &PlatformJD) {
+
+  std::pair<const char *, ExecutorAddress *> Symbols[] = {
+      {"__orc_rt_elfnix_platform_bootstrap", &orc_rt_elfnix_platform_bootstrap},
+      {"__orc_rt_elfnix_platform_shutdown", &orc_rt_elfnix_platform_shutdown},
+      {"__orc_rt_elfnix_register_object_sections",
+       &orc_rt_elfnix_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 = ES.callSPSWrapper<void()>(
+          orc_rt_elfnix_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<ELFPerObjectSectionsToRegister> 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 ELFNixPlatform::registerInitInfo(
+    JITDylib &JD, ArrayRef<jitlink::Section *> InitSections) {
+
+  std::unique_lock<std::mutex> Lock(PlatformMutex);
+
+  ELFNixJITDylibInitializers *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, DSOHandleSymbol).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 ELFNixPlatform::registerPerObjectSections(
+    const ELFPerObjectSectionsToRegister &POSR) {
+
+  if (!orc_rt_elfnix_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 = ES.callSPSWrapper<shared::SPSError(
+                     SPSELFPerObjectSectionsToRegister)>(
+          orc_rt_elfnix_register_object_sections.getValue(), ErrResult, POSR))
+    return Err;
+  return ErrResult;
+}
+
+void ELFNixPlatform::ELFNixPlatformPlugin::modifyPassConfig(
+    MaterializationResponsibility &MR, jitlink::LinkGraph &LG,
+    jitlink::PassConfiguration &Config) {
+
+  // If the initializer symbol is the __dso_handle symbol then just add
+  // the DSO handle support passes.
+  if (MR.getInitializerSymbol() == MP.DSOHandleSymbol) {
+    addDSOHandleSupportPasses(MR, Config);
+    // The DSOHandle 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 and TLV support.
+  addEHAndTLVSupportPasses(MR, Config);
+}
+
+ObjectLinkingLayer::Plugin::SyntheticSymbolDependenciesMap
+ELFNixPlatform::ELFNixPlatformPlugin::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 ELFNixPlatform::ELFNixPlatformPlugin::addInitializerSupportPasses(
+    MaterializationResponsibility &MR, jitlink::PassConfiguration &Config) {
+
+  /// Preserve init sections.
+  Config.PrePrunePasses.push_back([this, &MR](jitlink::LinkGraph &G) -> Error {
+    if (auto Err = preserveInitSections(G, MR))
+      return Err;
+    return Error::success();
+  });
+
+  Config.PostFixupPasses.push_back(
+      [this, &JD = MR.getTargetJITDylib()](jitlink::LinkGraph &G) {
+        return registerInitSections(G, JD);
+      });
+}
+
+void ELFNixPlatform::ELFNixPlatformPlugin::addDSOHandleSupportPasses(
+    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.DSOHandleSymbol;
+    });
+    assert(I != G.defined_symbols().end() && "Missing DSO handle symbol");
+    {
+      std::lock_guard<std::mutex> Lock(MP.PlatformMutex);
+      JITTargetAddress HandleAddr = (*I)->getAddress();
+      MP.HandleAddrToJITDylib[HandleAddr] = &JD;
+      assert(!MP.InitSeqs.count(&JD) && "InitSeq entry for JD already exists");
+      MP.InitSeqs.insert(
+          std::make_pair(&JD, ELFNixJITDylibInitializers(
+                                  JD.getName(), ExecutorAddress(HandleAddr))));
+    }
+    return Error::success();
+  });
+}
+
+void ELFNixPlatform::ELFNixPlatformPlugin::addEHAndTLVSupportPasses(
+    MaterializationResponsibility &MR, jitlink::PassConfiguration &Config) {
+
+  // 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()](jitlink::LinkGraph &G) {
+        return fixTLVSectionsAndEdges(G, JD);
+      });
+
+  // Add a pass to register the final addresses of the eh-frame and TLV sections
+  // with the runtime.
+  Config.PostFixupPasses.push_back([this](jitlink::LinkGraph &G) -> Error {
+    ELFPerObjectSectionsToRegister POSR;
+
+    if (auto *EHFrameSection = G.findSectionByName(EHFrameSectionName)) {
+      jitlink::SectionRange R(*EHFrameSection);
+      if (!R.empty())
+        POSR.EHFrameSection = {ExecutorAddress(R.getStart()),
+                               ExecutorAddress(R.getEnd())};
+    }
+
+    // Get a pointer to the thread data section if there is one. It will be used
+    // below.
+    jitlink::Section *ThreadDataSection =
+        G.findSectionByName(ThreadDataSectionName);
+
+    // Handle thread BSS section if there is one.
+    if (auto *ThreadBSSSection = G.findSectionByName(ThreadBSSSectionName)) {
+      // 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;
+    }
+
+    // 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())
+        POSR.ThreadDataSection = {ExecutorAddress(R.getStart()),
+                                  ExecutorAddress(R.getEnd())};
+    }
+
+    if (POSR.EHFrameSection.StartAddress ||
+        POSR.ThreadDataSection.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 ELFNixPlatform::ELFNixPlatformPlugin::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 ELFNixPlatform::ELFNixPlatformPlugin::registerInitSections(
+    jitlink::LinkGraph &G, JITDylib &JD) {
+
+  SmallVector<jitlink::Section *> InitSections;
+
+  LLVM_DEBUG({ dbgs() << "ELFNixPlatform::registerInitSections\n"; });
+
+  for (auto InitSectionName : InitSectionNames) {
+    if (auto *Sec = G.findSectionByName(InitSectionName)) {
+      InitSections.push_back(Sec);
+    }
+  }
+
+  // Dump the scraped inits.
+  LLVM_DEBUG({
+    dbgs() << "ELFNixPlatform: 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);
+}
+
+Error ELFNixPlatform::ELFNixPlatformPlugin::fixTLVSectionsAndEdges(
+    jitlink::LinkGraph &G, JITDylib &JD) {
+
+  // TODO implement TLV support
+
+  return Error::success();
+}
+
+} // End namespace orc.
+} // End namespace llvm.
diff --git a/llvm/lib/ExecutionEngine/Orc/Mangling.cpp b/llvm/lib/ExecutionEngine/Orc/Mangling.cpp
index b71ae13..7b21e6a 100644
--- a/llvm/lib/ExecutionEngine/Orc/Mangling.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/Mangling.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ExecutionEngine/Orc/Mangling.h"
+#include "llvm/ExecutionEngine/Orc/ELFNixPlatform.h"
 #include "llvm/ExecutionEngine/Orc/MachOPlatform.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Mangler.h"
@@ -84,6 +85,23 @@ void IRSymbolMapper::add(ExecutionSession &ES, const ManglingOptions &MO,
   }
 }
 
+static SymbolStringPtr addInitSymbol(SymbolFlagsMap &SymbolFlags,
+                                     ExecutionSession &ES,
+                                     StringRef ObjFileName) {
+  SymbolStringPtr InitSymbol;
+  size_t Counter = 0;
+
+  do {
+    std::string InitSymString;
+    raw_string_ostream(InitSymString)
+      << "$." << ObjFileName << ".__inits." << Counter++;
+    InitSymbol = ES.intern(InitSymString);
+  } while (SymbolFlags.count(InitSymbol));
+
+  SymbolFlags[InitSymbol] = JITSymbolFlags::MaterializationSideEffectsOnly;
+  return InitSymbol;
+}
+
 static Expected<std::pair<SymbolFlagsMap, SymbolStringPtr>>
 getMachOObjectFileSymbolInfo(ExecutionSession &ES,
                              const object::MachOObjectFile &Obj) {
@@ -126,30 +144,16 @@ getMachOObjectFileSymbolInfo(ExecutionSession &ES,
   }
 
   SymbolStringPtr InitSymbol;
-  size_t Counter = 0;
-  auto AddInitSymbol = [&]() {
-    while (true) {
-      std::string InitSymString;
-      raw_string_ostream(InitSymString)
-          << "$." << Obj.getFileName() << ".__inits." << Counter++;
-      InitSymbol = ES.intern(InitSymString);
-      if (SymbolFlags.count(InitSymbol))
-        continue;
-      SymbolFlags[InitSymbol] = JITSymbolFlags::MaterializationSideEffectsOnly;
-      return;
-    }
-  };
-
   for (auto &Sec : Obj.sections()) {
     auto SecType = Obj.getSectionType(Sec);
     if ((SecType & MachO::SECTION_TYPE) == MachO::S_MOD_INIT_FUNC_POINTERS) {
-      AddInitSymbol();
+      InitSymbol = addInitSymbol(SymbolFlags, ES, Obj.getFileName());
       break;
     }
     auto SegName = Obj.getSectionFinalSegmentName(Sec.getRawDataRefImpl());
     auto SecName = cantFail(Obj.getSectionName(Sec.getRawDataRefImpl()));
     if (MachOPlatform::isInitializerSection(SegName, SecName)) {
-      AddInitSymbol();
+      InitSymbol = addInitSymbol(SymbolFlags, ES, Obj.getFileName());
       break;
     }
   }
@@ -197,7 +201,17 @@ getELFObjectFileSymbolInfo(ExecutionSession &ES,
     SymbolFlags[InternedName] = std::move(*SymFlags);
   }
 
-  return std::make_pair(std::move(SymbolFlags), nullptr);
+  SymbolStringPtr InitSymbol;
+  for (auto &Sec : Obj.sections()) {
+    if (auto SecName = Sec.getName()) {
+      if (ELFNixPlatform::isInitializerSection(*SecName)) {
+        InitSymbol = addInitSymbol(SymbolFlags, ES, Obj.getFileName());
+        break;
+      }
+    }
+  }
+
+  return std::make_pair(std::move(SymbolFlags), InitSymbol);
 }
 
 Expected<std::pair<SymbolFlagsMap, SymbolStringPtr>>
diff --git a/llvm/lib/ExecutionEngine/Orc/ObjectLinkingLayer.cpp b/llvm/lib/ExecutionEngine/Orc/ObjectLinkingLayer.cpp
index fd26008..3c22c93 100644
--- a/llvm/lib/ExecutionEngine/Orc/ObjectLinkingLayer.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/ObjectLinkingLayer.cpp
@@ -64,9 +64,9 @@ private:
       LGI.SymbolFlags[ES.intern(Sym->getName())] = Flags;
     }
 
-    if (G.getTargetTriple().isOSBinFormatMachO())
-      if (hasMachOInitSection(G))
-        LGI.InitSymbol = makeInitSymbol(ES, G);
+    if ((G.getTargetTriple().isOSBinFormatMachO() && hasMachOInitSection(G)) ||
+        (G.getTargetTriple().isOSBinFormatELF() && hasELFInitSection(G)))
+      LGI.InitSymbol = makeInitSymbol(ES, G);
 
     return LGI;
   }
@@ -82,6 +82,13 @@ private:
     return false;
   }
 
+  static bool hasELFInitSection(LinkGraph &G) {
+    for (auto &Sec : G.sections())
+      if (Sec.getName() == ".init_array")
+        return true;
+    return false;
+  }
+
   static SymbolStringPtr makeInitSymbol(ExecutionSession &ES, LinkGraph &G) {
     std::string InitSymString;
     raw_string_ostream(InitSymString)