ObjectLinkingLayer.cpp

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//===------- ObjectLinkingLayer.cpp - JITLink backed ORC ObjectLayer ------===//
//
// 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/ObjectLinkingLayer.h"
#include "llvm/ExecutionEngine/JITLink/EHFrameSupport.h"
#include "llvm/ExecutionEngine/JITLink/aarch32.h"
#include "llvm/ExecutionEngine/Orc/DebugObjectManagerPlugin.h"
#include "llvm/ExecutionEngine/Orc/DebugUtils.h"
#include "llvm/ExecutionEngine/Orc/ObjectFileInterface.h"
#include "llvm/ExecutionEngine/Orc/Shared/ObjectFormats.h"
#include "llvm/Support/MemoryBuffer.h"
#include <string>
#include <vector>
 
#define DEBUG_TYPE "orc"
 
using namespace llvm;
using namespace llvm::jitlink;
using namespace llvm::orc;
 
namespace {
 
bool hasInitializerSection(jitlink::LinkGraph &G) {
  bool IsMachO = G.getTargetTriple().isOSBinFormatMachO();
  bool IsElf = G.getTargetTriple().isOSBinFormatELF();
  if (!IsMachO && !IsElf)
    return false;
 
  for (auto &Sec : G.sections()) {
    if (IsMachO && isMachOInitializerSection(Sec.getName()))
      return true;
    if (IsElf && isELFInitializerSection(Sec.getName()))
      return true;
  }
 
  return false;
}
 
ExecutorAddr getJITSymbolPtrForSymbol(Symbol &Sym, const Triple &TT) {
  switch (TT.getArch()) {
  case Triple::arm:
  case Triple::armeb:
  case Triple::thumb:
  case Triple::thumbeb:
    if (hasTargetFlags(Sym, aarch32::ThumbSymbol)) {
      // Set LSB to indicate thumb target
      assert(Sym.isCallable() && "Only callable symbols can have thumb flag");
      assert((Sym.getAddress().getValue() & 0x01) == 0 && "LSB is clear");
      return Sym.getAddress() + 0x01;
    }
    return Sym.getAddress();
  default:
    return Sym.getAddress();
  }
}
 
JITSymbolFlags getJITSymbolFlagsForSymbol(Symbol &Sym) {
  JITSymbolFlags Flags;
 
  if (Sym.getLinkage() == Linkage::Weak)
    Flags |= JITSymbolFlags::Weak;
 
  if (Sym.getScope() == Scope::Default)
    Flags |= JITSymbolFlags::Exported;
 
  if (Sym.isCallable())
    Flags |= JITSymbolFlags::Callable;
 
  return Flags;
}
 
class LinkGraphMaterializationUnit : public MaterializationUnit {
public:
  static std::unique_ptr<LinkGraphMaterializationUnit>
  Create(ObjectLinkingLayer &ObjLinkingLayer, std::unique_ptr<LinkGraph> G) {
    auto LGI = scanLinkGraph(ObjLinkingLayer.getExecutionSession(), *G);
    return std::unique_ptr<LinkGraphMaterializationUnit>(
        new LinkGraphMaterializationUnit(ObjLinkingLayer, std::move(G),
                                         std::move(LGI)));
  }
 
  StringRef getName() const override { return G->getName(); }
  void materialize(std::unique_ptr<MaterializationResponsibility> MR) override {
    ObjLinkingLayer.emit(std::move(MR), std::move(G));
  }
 
private:
  static Interface scanLinkGraph(ExecutionSession &ES, LinkGraph &G) {
 
    Interface LGI;
 
    auto AddSymbol = [&](Symbol *Sym) {
      // Skip local symbols.
      if (Sym->getScope() == Scope::Local)
        return;
      assert(Sym->hasName() && "Anonymous non-local symbol?");
 
      LGI.SymbolFlags[ES.intern(Sym->getName())] =
          getJITSymbolFlagsForSymbol(*Sym);
    };
 
    for (auto *Sym : G.defined_symbols())
      AddSymbol(Sym);
    for (auto *Sym : G.absolute_symbols())
      AddSymbol(Sym);
 
    if (hasInitializerSection(G))
      LGI.InitSymbol = makeInitSymbol(ES, G);
 
    return LGI;
  }
 
  static SymbolStringPtr makeInitSymbol(ExecutionSession &ES, LinkGraph &G) {
    std::string InitSymString;
    raw_string_ostream(InitSymString)
        << "$." << G.getName() << ".__inits" << Counter++;
    return ES.intern(InitSymString);
  }
 
  LinkGraphMaterializationUnit(ObjectLinkingLayer &ObjLinkingLayer,
                               std::unique_ptr<LinkGraph> G, Interface LGI)
      : MaterializationUnit(std::move(LGI)), ObjLinkingLayer(ObjLinkingLayer),
        G(std::move(G)) {}
 
  void discard(const JITDylib &JD, const SymbolStringPtr &Name) override {
    for (auto *Sym : G->defined_symbols())
      if (Sym->getName() == *Name) {
        assert(Sym->getLinkage() == Linkage::Weak &&
               "Discarding non-weak definition");
        G->makeExternal(*Sym);
        break;
      }
  }
 
  ObjectLinkingLayer &ObjLinkingLayer;
  std::unique_ptr<LinkGraph> G;
  static std::atomic<uint64_t> Counter;
};
 
std::atomic<uint64_t> LinkGraphMaterializationUnit::Counter{0};
 
} // end anonymous namespace
 
namespace llvm {
namespace orc {
 
class ObjectLinkingLayerJITLinkContext final : public JITLinkContext {
public:
  ObjectLinkingLayerJITLinkContext(
      ObjectLinkingLayer &Layer,
      std::unique_ptr<MaterializationResponsibility> MR,
      std::unique_ptr<MemoryBuffer> ObjBuffer)
      : JITLinkContext(&MR->getTargetJITDylib()), Layer(Layer),
        MR(std::move(MR)), ObjBuffer(std::move(ObjBuffer)) {
    std::lock_guard<std::mutex> Lock(Layer.LayerMutex);
    Plugins = Layer.Plugins;
  }
 
  ~ObjectLinkingLayerJITLinkContext() {
    // If there is an object buffer return function then use it to
    // return ownership of the buffer.
    if (Layer.ReturnObjectBuffer && ObjBuffer)
      Layer.ReturnObjectBuffer(std::move(ObjBuffer));
  }
 
  JITLinkMemoryManager &getMemoryManager() override { return Layer.MemMgr; }
 
  void notifyMaterializing(LinkGraph &G) {
    for (auto &P : Plugins)
      P->notifyMaterializing(*MR, G, *this,
                             ObjBuffer ? ObjBuffer->getMemBufferRef()
                             : MemoryBufferRef());
  }
 
  void notifyFailed(Error Err) override {
    for (auto &P : Plugins)
      Err = joinErrors(std::move(Err), P->notifyFailed(*MR));
    Layer.getExecutionSession().reportError(std::move(Err));
    MR->failMaterialization();
  }
 
  void lookup(const LookupMap &Symbols,
              std::unique_ptr<JITLinkAsyncLookupContinuation> LC) override {
 
    JITDylibSearchOrder LinkOrder;
    MR->getTargetJITDylib().withLinkOrderDo(
        [&](const JITDylibSearchOrder &LO) { LinkOrder = LO; });
 
    auto &ES = Layer.getExecutionSession();
 
    SymbolLookupSet LookupSet;
    for (auto &KV : Symbols) {
      orc::SymbolLookupFlags LookupFlags;
      switch (KV.second) {
      case jitlink::SymbolLookupFlags::RequiredSymbol:
        LookupFlags = orc::SymbolLookupFlags::RequiredSymbol;
        break;
      case jitlink::SymbolLookupFlags::WeaklyReferencedSymbol:
        LookupFlags = orc::SymbolLookupFlags::WeaklyReferencedSymbol;
        break;
      }
      LookupSet.add(ES.intern(KV.first), LookupFlags);
    }
 
    // OnResolve -- De-intern the symbols and pass the result to the linker.
    auto OnResolve = [LookupContinuation =
                          std::move(LC)](Expected<SymbolMap> Result) mutable {
      if (!Result)
        LookupContinuation->run(Result.takeError());
      else {
        AsyncLookupResult LR;
        for (auto &KV : *Result)
          LR[*KV.first] = KV.second;
        LookupContinuation->run(std::move(LR));
      }
    };
 
    ES.lookup(LookupKind::Static, LinkOrder, std::move(LookupSet),
              SymbolState::Resolved, std::move(OnResolve),
              [this](const SymbolDependenceMap &Deps) {
                // Translate LookupDeps map to SymbolSourceJD.
                for (auto &[DepJD, Deps] : Deps)
                  for (auto &DepSym : Deps)
                    SymbolSourceJDs[NonOwningSymbolStringPtr(DepSym)] = DepJD;
              });
  }
 
  Error notifyResolved(LinkGraph &G) override {
    auto &ES = Layer.getExecutionSession();
 
    SymbolFlagsMap ExtraSymbolsToClaim;
    bool AutoClaim = Layer.AutoClaimObjectSymbols;
 
    SymbolMap InternedResult;
    for (auto *Sym : G.defined_symbols())
      if (Sym->hasName() && Sym->getScope() != Scope::Local) {
        auto InternedName = ES.intern(Sym->getName());
        auto Ptr = getJITSymbolPtrForSymbol(*Sym, G.getTargetTriple());
        auto Flags = getJITSymbolFlagsForSymbol(*Sym);
        InternedResult[InternedName] = {Ptr, Flags};
        if (AutoClaim && !MR->getSymbols().count(InternedName)) {
          assert(!ExtraSymbolsToClaim.count(InternedName) &&
                 "Duplicate symbol to claim?");
          ExtraSymbolsToClaim[InternedName] = Flags;
        }
      }
 
    for (auto *Sym : G.absolute_symbols())
      if (Sym->hasName() && Sym->getScope() != Scope::Local) {
        auto InternedName = ES.intern(Sym->getName());
        auto Ptr = getJITSymbolPtrForSymbol(*Sym, G.getTargetTriple());
        auto Flags = getJITSymbolFlagsForSymbol(*Sym);
        InternedResult[InternedName] = {Ptr, Flags};
        if (AutoClaim && !MR->getSymbols().count(InternedName)) {
          assert(!ExtraSymbolsToClaim.count(InternedName) &&
                 "Duplicate symbol to claim?");
          ExtraSymbolsToClaim[InternedName] = Flags;
        }
      }
 
    if (!ExtraSymbolsToClaim.empty())
      if (auto Err = MR->defineMaterializing(ExtraSymbolsToClaim))
        return Err;
 
    {
 
      // Check that InternedResult matches up with MR->getSymbols(), overriding
      // flags if requested.
      // This guards against faulty transformations / compilers / object caches.
 
      // First check that there aren't any missing symbols.
      size_t NumMaterializationSideEffectsOnlySymbols = 0;
      SymbolNameVector ExtraSymbols;
      SymbolNameVector MissingSymbols;
      for (auto &KV : MR->getSymbols()) {
 
        auto I = InternedResult.find(KV.first);
 
        // If this is a materialization-side-effects only symbol then bump
        // the counter and make sure it's *not* defined, otherwise make
        // sure that it is defined.
        if (KV.second.hasMaterializationSideEffectsOnly()) {
          ++NumMaterializationSideEffectsOnlySymbols;
          if (I != InternedResult.end())
            ExtraSymbols.push_back(KV.first);
          continue;
        } else if (I == InternedResult.end())
          MissingSymbols.push_back(KV.first);
        else if (Layer.OverrideObjectFlags)
          I->second.setFlags(KV.second);
      }
 
      // If there were missing symbols then report the error.
      if (!MissingSymbols.empty())
        return make_error<MissingSymbolDefinitions>(
            Layer.getExecutionSession().getSymbolStringPool(), G.getName(),
            std::move(MissingSymbols));
 
      // If there are more definitions than expected, add them to the
      // ExtraSymbols vector.
      if (InternedResult.size() >
          MR->getSymbols().size() - NumMaterializationSideEffectsOnlySymbols) {
        for (auto &KV : InternedResult)
          if (!MR->getSymbols().count(KV.first))
            ExtraSymbols.push_back(KV.first);
      }
 
      // If there were extra definitions then report the error.
      if (!ExtraSymbols.empty())
        return make_error<UnexpectedSymbolDefinitions>(
            Layer.getExecutionSession().getSymbolStringPool(), G.getName(),
            std::move(ExtraSymbols));
    }
 
    if (auto Err = MR->notifyResolved(InternedResult))
      return Err;
 
    notifyLoaded();
    return Error::success();
  }
 
  void notifyFinalized(JITLinkMemoryManager::FinalizedAlloc A) override {
    if (auto Err = notifyEmitted(std::move(A))) {
      Layer.getExecutionSession().reportError(std::move(Err));
      MR->failMaterialization();
      return;
    }
    if (auto Err = MR->notifyEmitted(SymbolDepGroups)) {
      Layer.getExecutionSession().reportError(std::move(Err));
      MR->failMaterialization();
    }
  }
 
  LinkGraphPassFunction getMarkLivePass(const Triple &TT) const override {
    return [this](LinkGraph &G) { return markResponsibilitySymbolsLive(G); };
  }
 
  Error modifyPassConfig(LinkGraph &LG, PassConfiguration &Config) override {
    // Add passes to mark duplicate defs as should-discard, and to walk the
    // link graph to build the symbol dependence graph.
    Config.PrePrunePasses.push_back([this](LinkGraph &G) {
      return claimOrExternalizeWeakAndCommonSymbols(G);
    });
 
    for (auto &P : Plugins)
      P->modifyPassConfig(*MR, LG, Config);
 
    Config.PreFixupPasses.push_back(
        [this](LinkGraph &G) { return registerDependencies(G); });
 
    return Error::success();
  }
 
  void notifyLoaded() {
    for (auto &P : Plugins)
      P->notifyLoaded(*MR);
  }
 
  Error notifyEmitted(jitlink::JITLinkMemoryManager::FinalizedAlloc FA) {
    Error Err = Error::success();
    for (auto &P : Plugins)
      Err = joinErrors(std::move(Err), P->notifyEmitted(*MR));
 
    if (Err) {
      if (FA)
        Err =
            joinErrors(std::move(Err), Layer.MemMgr.deallocate(std::move(FA)));
      return Err;
    }
 
    if (FA)
      return Layer.recordFinalizedAlloc(*MR, std::move(FA));
 
    return Error::success();
  }
 
private:
  // Symbol name dependencies:
  // Internal: Defined in this graph.
  // External: Defined externally.
  struct BlockSymbolDependencies {
    SymbolNameSet Internal, External;
  };
 
  // Lazily populated map of blocks to BlockSymbolDependencies values.
  class BlockDependenciesMap {
  public:
    BlockDependenciesMap(ExecutionSession &ES,
                         DenseMap<const Block *, DenseSet<Block *>> BlockDeps)
        : ES(ES), BlockDeps(std::move(BlockDeps)) {}
 
    const BlockSymbolDependencies &operator[](const Block &B) {
      // Check the cache first.
      auto I = BlockTransitiveDepsCache.find(&B);
      if (I != BlockTransitiveDepsCache.end())
        return I->second;
 
      // No value. Populate the cache.
      BlockSymbolDependencies BTDCacheVal;
      auto BDI = BlockDeps.find(&B);
      assert(BDI != BlockDeps.end() && "No block dependencies");
 
      for (auto *BDep : BDI->second) {
        auto &BID = getBlockImmediateDeps(*BDep);
        for (auto &ExternalDep : BID.External)
          BTDCacheVal.External.insert(ExternalDep);
        for (auto &InternalDep : BID.Internal)
          BTDCacheVal.Internal.insert(InternalDep);
      }
 
      return BlockTransitiveDepsCache
          .insert(std::make_pair(&B, std::move(BTDCacheVal)))
          .first->second;
    }
 
    SymbolStringPtr &getInternedName(Symbol &Sym) {
      auto I = NameCache.find(&Sym);
      if (I != NameCache.end())
        return I->second;
 
      return NameCache.insert(std::make_pair(&Sym, ES.intern(Sym.getName())))
          .first->second;
    }
 
  private:
    BlockSymbolDependencies &getBlockImmediateDeps(Block &B) {
      // Check the cache first.
      auto I = BlockImmediateDepsCache.find(&B);
      if (I != BlockImmediateDepsCache.end())
        return I->second;
 
      BlockSymbolDependencies BIDCacheVal;
      for (auto &E : B.edges()) {
        auto &Tgt = E.getTarget();
        if (Tgt.getScope() != Scope::Local) {
          if (Tgt.isExternal()) {
            if (Tgt.getAddress() || !Tgt.isWeaklyReferenced())
              BIDCacheVal.External.insert(getInternedName(Tgt));
          } else
            BIDCacheVal.Internal.insert(getInternedName(Tgt));
        }
      }
 
      return BlockImmediateDepsCache
          .insert(std::make_pair(&B, std::move(BIDCacheVal)))
          .first->second;
    }
 
    ExecutionSession &ES;
    DenseMap<const Block *, DenseSet<Block *>> BlockDeps;
    DenseMap<const Symbol *, SymbolStringPtr> NameCache;
    DenseMap<const Block *, BlockSymbolDependencies> BlockImmediateDepsCache;
    DenseMap<const Block *, BlockSymbolDependencies> BlockTransitiveDepsCache;
  };
 
  Error claimOrExternalizeWeakAndCommonSymbols(LinkGraph &G) {
    auto &ES = Layer.getExecutionSession();
 
    SymbolFlagsMap NewSymbolsToClaim;
    std::vector<std::pair<SymbolStringPtr, Symbol *>> NameToSym;
 
    auto ProcessSymbol = [&](Symbol *Sym) {
      if (Sym->hasName() && Sym->getLinkage() == Linkage::Weak &&
          Sym->getScope() != Scope::Local) {
        auto Name = ES.intern(Sym->getName());
        if (!MR->getSymbols().count(ES.intern(Sym->getName()))) {
          NewSymbolsToClaim[Name] =
              getJITSymbolFlagsForSymbol(*Sym) | JITSymbolFlags::Weak;
          NameToSym.push_back(std::make_pair(std::move(Name), Sym));
        }
      }
    };
 
    for (auto *Sym : G.defined_symbols())
      ProcessSymbol(Sym);
    for (auto *Sym : G.absolute_symbols())
      ProcessSymbol(Sym);
 
    // Attempt to claim all weak defs that we're not already responsible for.
    // This may fail if the resource tracker has become defunct, but should
    // always succeed otherwise.
    if (auto Err = MR->defineMaterializing(std::move(NewSymbolsToClaim)))
      return Err;
 
    // Walk the list of symbols that we just tried to claim. Symbols that we're
    // responsible for are marked live. Symbols that we're not responsible for
    // are turned into external references.
    for (auto &KV : NameToSym) {
      if (MR->getSymbols().count(KV.first))
        KV.second->setLive(true);
      else
        G.makeExternal(*KV.second);
    }
 
    return Error::success();
  }
 
  Error markResponsibilitySymbolsLive(LinkGraph &G) const {
    auto &ES = Layer.getExecutionSession();
    for (auto *Sym : G.defined_symbols())
      if (Sym->hasName() && MR->getSymbols().count(ES.intern(Sym->getName())))
        Sym->setLive(true);
    return Error::success();
  }
 
  Error registerDependencies(LinkGraph &G) {
    auto &TargetJD = MR->getTargetJITDylib();
    auto &ES = TargetJD.getExecutionSession();
    auto BlockDeps = computeBlockNonLocalDeps(G);
 
    DenseSet<Block *> BlockDepsProcessed;
    DenseMap<Block *, SymbolDependenceGroup> DepGroupForBlock;
 
    // Compute dependencies for symbols defined in the JITLink graph.
    for (auto *Sym : G.defined_symbols()) {
 
      // Skip local symbols.
      if (Sym->getScope() == Scope::Local)
        continue;
      assert(Sym->hasName() &&
             "Defined non-local jitlink::Symbol should have a name");
 
      auto &BDeps = BlockDeps[Sym->getBlock()];
 
      // Skip symbols in blocks that don't depend on anything.
      if (BDeps.Internal.empty() && BDeps.External.empty())
        continue;
 
      SymbolDependenceGroup &SDG = DepGroupForBlock[&Sym->getBlock()];
      SDG.Symbols.insert(ES.intern(Sym->getName()));
 
      if (!BlockDepsProcessed.count(&Sym->getBlock())) {
        BlockDepsProcessed.insert(&Sym->getBlock());
 
        if (!BDeps.Internal.empty())
          SDG.Dependencies[&TargetJD] = BDeps.Internal;
        for (auto &Dep : BDeps.External) {
          auto DepSrcItr = SymbolSourceJDs.find(NonOwningSymbolStringPtr(Dep));
          if (DepSrcItr != SymbolSourceJDs.end())
            SDG.Dependencies[DepSrcItr->second].insert(Dep);
        }
      }
    }
 
    SymbolDependenceGroup SynthSDG;
 
    for (auto &P : Plugins) {
      auto SynthDeps = P->getSyntheticSymbolDependencies(*MR);
      if (SynthDeps.empty())
        continue;
 
      DenseSet<Block *> BlockVisited;
      for (auto &[Name, DepSyms] : SynthDeps) {
        SynthSDG.Symbols.insert(Name);
        for (auto *Sym : DepSyms) {
          if (Sym->getScope() == Scope::Local) {
            auto &BDeps = BlockDeps[Sym->getBlock()];
            for (auto &S : BDeps.Internal)
              SynthSDG.Dependencies[&TargetJD].insert(S);
            for (auto &S : BDeps.External) {
              auto DepSrcItr =
                  SymbolSourceJDs.find(NonOwningSymbolStringPtr(S));
              if (DepSrcItr != SymbolSourceJDs.end())
                SynthSDG.Dependencies[DepSrcItr->second].insert(S);
            }
          } else {
            auto SymName = ES.intern(Sym->getName());
            if (Sym->isExternal()) {
              assert(SymbolSourceJDs.count(NonOwningSymbolStringPtr(SymName)) &&
                     "External symbol source entry missing");
              SynthSDG
                  .Dependencies[SymbolSourceJDs[NonOwningSymbolStringPtr(
                      SymName)]]
                  .insert(SymName);
            } else
              SynthSDG.Dependencies[&TargetJD].insert(SymName);
          }
        }
      }
    }
 
    // Transfer SDGs to SymbolDepGroups.
    DepGroupForBlock.reserve(DepGroupForBlock.size() + 1);
    for (auto &[B, SDG] : DepGroupForBlock) {
      assert(!SDG.Symbols.empty() && "SymbolDependenceGroup covers no symbols");
      if (!SDG.Dependencies.empty())
        SymbolDepGroups.push_back(std::move(SDG));
    }
    if (!SynthSDG.Symbols.empty() && !SynthSDG.Dependencies.empty())
      SymbolDepGroups.push_back(std::move(SynthSDG));
 
    return Error::success();
  }
 
  BlockDependenciesMap computeBlockNonLocalDeps(LinkGraph &G) {
    // First calculate the reachable-via-non-local-symbol blocks for each block.
    struct BlockInfo {
      DenseSet<Block *> Dependencies;
      DenseSet<Block *> Dependants;
      bool DependenciesChanged = true;
    };
    DenseMap<Block *, BlockInfo> BlockInfos;
    SmallVector<Block *> WorkList;
 
    // Pre-allocate map entries. This prevents any iterator/reference
    // invalidation in the next loop.
    for (auto *B : G.blocks())
      (void)BlockInfos[B];
 
    // Build initial worklist, record block dependencies/dependants and
    // non-local symbol dependencies.
    for (auto *B : G.blocks()) {
      auto &BI = BlockInfos[B];
      for (auto &E : B->edges()) {
        if (E.getTarget().getScope() == Scope::Local &&
            !E.getTarget().isAbsolute()) {
          auto &TgtB = E.getTarget().getBlock();
          if (&TgtB != B) {
            BI.Dependencies.insert(&TgtB);
            BlockInfos[&TgtB].Dependants.insert(B);
          }
        }
      }
    }
 
    // Add blocks with both dependants and dependencies to the worklist to
    // propagate dependencies to dependants.
    for (auto &[B, BI] : BlockInfos) {
      if (!BI.Dependants.empty() && !BI.Dependencies.empty())
        WorkList.push_back(B);
    }
 
    // Propagate block-level dependencies through the block-dependence graph.
    while (!WorkList.empty()) {
      auto *B = WorkList.pop_back_val();
 
      auto &BI = BlockInfos[B];
      assert(BI.DependenciesChanged &&
             "Block in worklist has unchanged dependencies");
      BI.DependenciesChanged = false;
      for (auto *Dependant : BI.Dependants) {
        auto &DependantBI = BlockInfos[Dependant];
        for (auto *Dependency : BI.Dependencies) {
          if (Dependant != Dependency &&
              DependantBI.Dependencies.insert(Dependency).second)
            if (!DependantBI.DependenciesChanged) {
              DependantBI.DependenciesChanged = true;
              WorkList.push_back(Dependant);
            }
        }
      }
    }
 
    DenseMap<const Block *, DenseSet<Block *>> BlockDeps;
    for (auto &KV : BlockInfos)
      BlockDeps[KV.first] = std::move(KV.second.Dependencies);
 
    return BlockDependenciesMap(Layer.getExecutionSession(),
                                std::move(BlockDeps));
  }
 
  ObjectLinkingLayer &Layer;
  std::vector<std::shared_ptr<ObjectLinkingLayer::Plugin>> Plugins;
  std::unique_ptr<MaterializationResponsibility> MR;
  std::unique_ptr<MemoryBuffer> ObjBuffer;
  DenseMap<Block *, SymbolNameSet> ExternalBlockDeps;
  DenseMap<Block *, SymbolNameSet> InternalBlockDeps;
  DenseMap<NonOwningSymbolStringPtr, JITDylib *> SymbolSourceJDs;
  std::vector<SymbolDependenceGroup> SymbolDepGroups;
};
 
ObjectLinkingLayer::Plugin::~Plugin() = default;
 
char ObjectLinkingLayer::ID;
 
using BaseT = RTTIExtends<ObjectLinkingLayer, ObjectLayer>;
 
ObjectLinkingLayer::ObjectLinkingLayer(ExecutionSession &ES)
    : BaseT(ES), MemMgr(ES.getExecutorProcessControl().getMemMgr()) {
  ES.registerResourceManager(*this);
}
 
ObjectLinkingLayer::ObjectLinkingLayer(ExecutionSession &ES,
                                       JITLinkMemoryManager &MemMgr)
    : BaseT(ES), MemMgr(MemMgr) {
  ES.registerResourceManager(*this);
}
 
ObjectLinkingLayer::ObjectLinkingLayer(
    ExecutionSession &ES, std::unique_ptr<JITLinkMemoryManager> MemMgr)
    : BaseT(ES), MemMgr(*MemMgr), MemMgrOwnership(std::move(MemMgr)) {
  ES.registerResourceManager(*this);
}
 
ObjectLinkingLayer::~ObjectLinkingLayer() {
  assert(Allocs.empty() && "Layer destroyed with resources still attached");
  getExecutionSession().deregisterResourceManager(*this);
}
 
Error ObjectLinkingLayer::add(ResourceTrackerSP RT,
                              std::unique_ptr<LinkGraph> G) {
  auto &JD = RT->getJITDylib();
  return JD.define(LinkGraphMaterializationUnit::Create(*this, std::move(G)),
                   std::move(RT));
}
 
void ObjectLinkingLayer::emit(std::unique_ptr<MaterializationResponsibility> R,
                              std::unique_ptr<MemoryBuffer> O) {
  assert(O && "Object must not be null");
  MemoryBufferRef ObjBuffer = O->getMemBufferRef();
 
  auto Ctx = std::make_unique<ObjectLinkingLayerJITLinkContext>(
      *this, std::move(R), std::move(O));
  if (auto G = createLinkGraphFromObject(ObjBuffer)) {
    Ctx->notifyMaterializing(**G);
    link(std::move(*G), std::move(Ctx));
  } else {
    Ctx->notifyFailed(G.takeError());
  }
}
 
void ObjectLinkingLayer::emit(std::unique_ptr<MaterializationResponsibility> R,
                              std::unique_ptr<LinkGraph> G) {
  auto Ctx = std::make_unique<ObjectLinkingLayerJITLinkContext>(
      *this, std::move(R), nullptr);
  Ctx->notifyMaterializing(*G);
  link(std::move(G), std::move(Ctx));
}
 
Error ObjectLinkingLayer::recordFinalizedAlloc(
    MaterializationResponsibility &MR, FinalizedAlloc FA) {
  auto Err = MR.withResourceKeyDo(
      [&](ResourceKey K) { Allocs[K].push_back(std::move(FA)); });
 
  if (Err)
    Err = joinErrors(std::move(Err), MemMgr.deallocate(std::move(FA)));
 
  return Err;
}
 
Error ObjectLinkingLayer::handleRemoveResources(JITDylib &JD, ResourceKey K) {
 
  {
    Error Err = Error::success();
    for (auto &P : Plugins)
      Err = joinErrors(std::move(Err), P->notifyRemovingResources(JD, K));
    if (Err)
      return Err;
  }
 
  std::vector<FinalizedAlloc> AllocsToRemove;
  getExecutionSession().runSessionLocked([&] {
    auto I = Allocs.find(K);
    if (I != Allocs.end()) {
      std::swap(AllocsToRemove, I->second);
      Allocs.erase(I);
    }
  });
 
  if (AllocsToRemove.empty())
    return Error::success();
 
  return MemMgr.deallocate(std::move(AllocsToRemove));
}
 
void ObjectLinkingLayer::handleTransferResources(JITDylib &JD,
                                                 ResourceKey DstKey,
                                                 ResourceKey SrcKey) {
  auto I = Allocs.find(SrcKey);
  if (I != Allocs.end()) {
    auto &SrcAllocs = I->second;
    auto &DstAllocs = Allocs[DstKey];
    DstAllocs.reserve(DstAllocs.size() + SrcAllocs.size());
    for (auto &Alloc : SrcAllocs)
      DstAllocs.push_back(std::move(Alloc));
 
    // Erase SrcKey entry using value rather than iterator I: I may have been
    // invalidated when we looked up DstKey.
    Allocs.erase(SrcKey);
  }
 
  for (auto &P : Plugins)
    P->notifyTransferringResources(JD, DstKey, SrcKey);
}
 
EHFrameRegistrationPlugin::EHFrameRegistrationPlugin(
    ExecutionSession &ES, std::unique_ptr<EHFrameRegistrar> Registrar)
    : ES(ES), Registrar(std::move(Registrar)) {}
 
void EHFrameRegistrationPlugin::modifyPassConfig(
    MaterializationResponsibility &MR, LinkGraph &G,
    PassConfiguration &PassConfig) {
 
  PassConfig.PostFixupPasses.push_back(createEHFrameRecorderPass(
      G.getTargetTriple(), [this, &MR](ExecutorAddr Addr, size_t Size) {
        if (Addr) {
          std::lock_guard<std::mutex> Lock(EHFramePluginMutex);
          assert(!InProcessLinks.count(&MR) &&
                 "Link for MR already being tracked?");
          InProcessLinks[&MR] = {Addr, Size};
        }
      }));
}
 
Error EHFrameRegistrationPlugin::notifyEmitted(
    MaterializationResponsibility &MR) {
 
  ExecutorAddrRange EmittedRange;
  {
    std::lock_guard<std::mutex> Lock(EHFramePluginMutex);
 
    auto EHFrameRangeItr = InProcessLinks.find(&MR);
    if (EHFrameRangeItr == InProcessLinks.end())
      return Error::success();
 
    EmittedRange = EHFrameRangeItr->second;
    assert(EmittedRange.Start && "eh-frame addr to register can not be null");
    InProcessLinks.erase(EHFrameRangeItr);
  }
 
  if (auto Err = MR.withResourceKeyDo(
          [&](ResourceKey K) { EHFrameRanges[K].push_back(EmittedRange); }))
    return Err;
 
  return Registrar->registerEHFrames(EmittedRange);
}
 
Error EHFrameRegistrationPlugin::notifyFailed(
    MaterializationResponsibility &MR) {
  std::lock_guard<std::mutex> Lock(EHFramePluginMutex);
  InProcessLinks.erase(&MR);
  return Error::success();
}
 
Error EHFrameRegistrationPlugin::notifyRemovingResources(JITDylib &JD,
                                                         ResourceKey K) {
  std::vector<ExecutorAddrRange> RangesToRemove;
 
  ES.runSessionLocked([&] {
    auto I = EHFrameRanges.find(K);
    if (I != EHFrameRanges.end()) {
      RangesToRemove = std::move(I->second);
      EHFrameRanges.erase(I);
    }
  });
 
  Error Err = Error::success();
  while (!RangesToRemove.empty()) {
    auto RangeToRemove = RangesToRemove.back();
    RangesToRemove.pop_back();
    assert(RangeToRemove.Start && "Untracked eh-frame range must not be null");
    Err = joinErrors(std::move(Err),
                     Registrar->deregisterEHFrames(RangeToRemove));
  }
 
  return Err;
}
 
void EHFrameRegistrationPlugin::notifyTransferringResources(
    JITDylib &JD, ResourceKey DstKey, ResourceKey SrcKey) {
  auto SI = EHFrameRanges.find(SrcKey);
  if (SI == EHFrameRanges.end())
    return;
 
  auto DI = EHFrameRanges.find(DstKey);
  if (DI != EHFrameRanges.end()) {
    auto &SrcRanges = SI->second;
    auto &DstRanges = DI->second;
    DstRanges.reserve(DstRanges.size() + SrcRanges.size());
    for (auto &SrcRange : SrcRanges)
      DstRanges.push_back(std::move(SrcRange));
    EHFrameRanges.erase(SI);
  } else {
    // We need to move SrcKey's ranges over without invalidating the SI
    // iterator.
    auto Tmp = std::move(SI->second);
    EHFrameRanges.erase(SI);
    EHFrameRanges[DstKey] = std::move(Tmp);
  }
}
 
} // End namespace orc.
} // End namespace llvm.