[ORC] Introduce RedirectionManager interface and implementation using JITLink.

[sunho]

Summary

This patch introduces RedirectionManager and RedirectableSymbolManager interfaces which abstracts the redirection of call to certain symbols. It also adds JITLink implmenetation of such interface along with testcases covering basic use cases.

[lhames]

llvm/include/llvm/ExecutionEngine/Orc/JITLinkRedirectableSymbolManager.h

60

Can we remove the JD argument here? The ResourceTracker argument to createRedirectableSymbols tells us the target JITDylib already, and this would allow us to have one global JITLinkRediretableSymbolManager, rather than one per JITDylib.

101–102

Why a separate StringSaver here, rather than using the SymbolStringPool?

llvm/include/llvm/ExecutionEngine/Orc/RedirectionManager.h

33–35

I think this should be non-virtual for now. We can make it virtual later if we find a use-case where optimizing the single-symbol case is important.

55

Similarly here.

[sunho]

llvm/include/llvm/ExecutionEngine/Orc/JITLinkRedirectableSymbolManager.h

60

We need this JD since we are going to generate a stub pool inside this JD. Alternative is manage stub pool per JD within single manager, how does this sound to you?

101–102

We need to get actual string from SymbolStringPtr. Is there a way to do this?

llvm/include/llvm/ExecutionEngine/Orc/RedirectionManager.h

33–35

👍

[sunho]

llvm/include/llvm/ExecutionEngine/Orc/JITLinkRedirectableSymbolManager.h

101–102

Oh actually this was needed since JITLink isn't based on SymbolStringPtr yet. We still need to save the string cause JITLink assumes all the StringRefs are properly owned by external object like symbol string table.

[lhames]

llvm/include/llvm/ExecutionEngine/Orc/JITLinkRedirectableSymbolManager.h

60

You can get the target JITDylib from the tracker, so the aim should be to have one manager for all JITDylibs. In this case the createRedirectableSymbols method should probably be changed to a set of functions:

virtual Error createRedirectableSymbols(ResourceTrackerSP RT, const SymbolAddrMap &InitialDests) = 0;

Error createRedirectableSymbol(JITDylib &JD, const SymbolAddrMap &InitialDests) {
  return createRedirectableSymbol(JD.getDefaultResourceTracker(), InitialDests);
}

Error createRedirectableSymbol(
    ResourceTracker RT, SymbolStringPtr Symbol, ExecutorSymbolDef InitialDest) {
  return createRedirectableSymbols(std::move(RT), {{Symbol, InitialDest}});
}

Error createRedirectableSymbol(
    JITDylib &JD, SymbolStringPtr Symbol, ExecutorSymbolDef InitialDest) {
  return createRedirectableSymbol(JD.getDefaultResourceTracker(), std::move(Symbol), InitialDest);
}

101–102

You can get a StringRef for a SymbolStringPtr using the dereference operator, and that should be safe to use in a LinkGraph.

[sunho]

Update

llvm/include/llvm/ExecutionEngine/Orc/JITLinkRedirectableSymbolManager.h

+//===- JITLinkRedirectableSymbolManager.h - JITLink redirection --*- C++
+//-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Redirectable Symbol Manager implementation using JITLink
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_EXECUTIONENGINE_ORC_JITLINKREDIRECABLEMANAGER_H
+#define LLVM_EXECUTIONENGINE_ORC_JITLINKREDIRECABLEMANAGER_H
+
+#include "llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h"
+#include "llvm/ExecutionEngine/Orc/RedirectionManager.h"
+#include "llvm/Support/StringSaver.h"
+
+namespace llvm {
+namespace orc {
+
+class JITLinkRedirectableSymbolManager : public RedirectableSymbolManager,
+                                         public ResourceManager {
+public:
+  /// Create redirection manager that uses JITLink based implementaion.
+  static Expected<std::unique_ptr<RedirectableSymbolManager>>
+  Create(ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
+         JITDylib &JD) {
+    Error Err = Error::success();
+    auto RM = std::unique_ptr<RedirectableSymbolManager>(
+        new JITLinkRedirectableSymbolManager(ES, ObjLinkingLayer, JD, Err));
+    if (Err)
+      return Err;
+    return std::move(RM);
+  }
+
+  Error createRedirectableSymbols(ResourceTrackerSP RT,
+                                  const SymbolAddrMap &InitialDests) override;
+
+  Error redirect(JITDylib &TargetJD, const SymbolAddrMap &NewDests) override;
+
+  Error handleRemoveResources(JITDylib &TargetJD, ResourceKey K) override;
+
+  void handleTransferResources(JITDylib &TargetJD, ResourceKey DstK,
+                               ResourceKey SrcK) override;
+
+private:
+  using StubHandle = unsigned;
+  constexpr static unsigned StubBlockSize = 256;
+  constexpr static StringRef JumpStubPrefix = "$__IND_JUMP_STUBS";
+  constexpr static StringRef StubPtrPrefix = "$IND_JUMP_PTR_";
+  constexpr static StringRef JumpStubTableName = "$IND_JUMP_";
+  constexpr static StringRef StubPtrTableName = "$__IND_JUMP_PTRS";
+
+  JITLinkRedirectableSymbolManager(ExecutionSession &ES,
+                                   ObjectLinkingLayer &ObjLinkingLayer,
+                                   JITDylib &JD, Error &Err)
+      : ES(ES), ObjLinkingLayer(ObjLinkingLayer), JD(JD),
+        AnonymousPtrCreator(
+            jitlink::getAnonymousPointerCreator(ES.getTargetTriple())),
+        PtrJumpStubCreator(
+            jitlink::getPointerJumpStubCreator(ES.getTargetTriple())) {
+    if (!AnonymousPtrCreator || !PtrJumpStubCreator)
+      Err = make_error<StringError>("Architecture not supported",
+                                    inconvertibleErrorCode());
+    if (Err)
+      return;
+    ES.registerResourceManager(*this);
+  }
+
+  ~JITLinkRedirectableSymbolManager() { ES.deregisterResourceManager(*this); }
+
+  StringRef JumpStubSymbolName(unsigned I) {
+    return *ES.intern((JumpStubPrefix + Twine(I)).str());
+  }
+
+  StringRef StubPtrSymbolName(unsigned I) {
+    return *ES.intern((StubPtrPrefix + Twine(I)).str());
+  }
+
+  unsigned GetNumAvailableStubs() const { return AvailableStubs.size(); }
+
+  Error redirectInner(JITDylib &TargetJD, const SymbolAddrMap &NewDests);
+  Error grow(unsigned Need);
+
+  ExecutionSession &ES;
+  ObjectLinkingLayer &ObjLinkingLayer;
+  JITDylib &JD;
+  jitlink::AnonymousPointerCreator AnonymousPtrCreator;
+  jitlink::PointerJumpStubCreator PtrJumpStubCreator;
+
+  std::vector<StubHandle> AvailableStubs;
+  using SymbolToStubMap = DenseMap<SymbolStringPtr, StubHandle>;
+  DenseMap<JITDylib *, SymbolToStubMap> SymbolToStubs;
+  std::vector<ExecutorSymbolDef> JumpStubs;
+  std::vector<ExecutorSymbolDef> StubPointers;
+  DenseMap<ResourceKey, std::vector<SymbolStringPtr>> TrackedResources;
+
+  std::mutex Mutex;
+};
+
+} // namespace orc
+} // namespace llvm
+
+#endif

llvm/include/llvm/ExecutionEngine/Orc/RedirectionManager.h

+//===- RedirectionManager.h - Redirection manager interface -----*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Redirection manager interface that redirects a call to symbol to another.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ExecutionEngine/Orc/Core.h"
+
+namespace llvm {
+namespace orc {
+
+/// Base class for performing redirection of call to symbol to another symbol in
+/// runtime.
+class RedirectionManager {
+public:
+  /// Symbol name to symbol definition map.
+  using SymbolAddrMap = DenseMap<SymbolStringPtr, ExecutorSymbolDef>;
+
+  virtual ~RedirectionManager() = default;
+  /// Change the redirection destination of given symbols to new destination
+  /// symbols.
+  virtual Error redirect(JITDylib &JD, const SymbolAddrMap &NewDests) = 0;
+
+  /// Change the redirection destination of given symbol to new destination
+  /// symbol.
+  virtual Error redirect(JITDylib &JD, SymbolStringPtr Symbol,
+                         ExecutorSymbolDef NewDest) {
+    return redirect(JD, {{Symbol, NewDest}});
+  }
+
+private:
+  virtual void anchor();
+};
+
+/// Base class for managing redirectable symbols in which a call
+/// gets redirected to another symbol in runtime.
+class RedirectableSymbolManager : public RedirectionManager {
+public:
+  /// Symbol name to symbol definition map.
+  using SymbolAddrMap = DenseMap<SymbolStringPtr, ExecutorSymbolDef>;
+
+  /// Create redirectable symbols with given symbol names and initial
+  /// desitnation symbols.
+  virtual Error
+  createRedirectableSymbols(ResourceTrackerSP RT,
+                            const SymbolAddrMap &InitialDests) = 0;
+
+  /// Create a single redirectable symbol with given symbol name and initial
+  /// desitnation symbol.
+  Error createRedirectableSymbol(ResourceTrackerSP RT, SymbolStringPtr Symbol,
+                                 ExecutorSymbolDef InitialDest) {
+    return createRedirectableSymbols(RT, {{Symbol, InitialDest}});
+  }
+
+  /// Create redirectable symbols with given symbol names and initial
+  /// desitnation symbols.
+  Error createRedirectableSymbols(JITDylib &JD,
+                                  const SymbolAddrMap &InitialDests) {
+    return createRedirectableSymbols(JD.getDefaultResourceTracker(),
+                                     InitialDests);
+  }
+
+  /// Create a single redirectable symbol with given symbol name and initial
+  /// desitnation symbol.
+  Error createRedirectableSymbol(JITDylib &JD, SymbolStringPtr Symbol,
+                                 ExecutorSymbolDef InitialDest) {
+    return createRedirectableSymbols(JD, {{Symbol, InitialDest}});
+  }
+};
+
+} // namespace orc
+} // namespace llvm

llvm/lib/ExecutionEngine/Orc/CMakeLists.txt

add_llvm_component_library(LLVMOrcJIT
   OrcV2CBindings.cpp
   RTDyldObjectLinkingLayer.cpp
   SimpleRemoteEPC.cpp
   Speculation.cpp
   SpeculateAnalyses.cpp
   ExecutorProcessControl.cpp
   TaskDispatch.cpp
   ThreadSafeModule.cpp
+  RedirectionManager.cpp
+  JITLinkRedirectableSymbolManager.cpp
   ADDITIONAL_HEADER_DIRS
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/ExecutionEngine/Orc
 
   DEPENDS
   intrinsics_gen
 
   LINK_LIBS
   ${LLVM_PTHREAD_LIB}

llvm/lib/ExecutionEngine/Orc/JITLinkRedirectableSymbolManager.cpp

+//===-- JITLinkRedirectableSymbolManager.cpp - JITLink redirection 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/JITLinkRedirectableSymbolManager.h"
+#include "llvm/ExecutionEngine/Orc/Core.h"
+
+#define DEBUG_TYPE "orc"
+
+using namespace llvm;
+using namespace llvm::orc;
+
+Error JITLinkRedirectableSymbolManager::createRedirectableSymbols(
+    ResourceTrackerSP RT, const SymbolAddrMap &InitialDests) {
+  std::unique_lock<std::mutex> Lock(Mutex);
+  if (GetNumAvailableStubs() < InitialDests.size())
+    if (auto Err = grow(InitialDests.size() - GetNumAvailableStubs()))
+      return Err;
+
+  JITDylib &TargetJD = RT->getJITDylib();
+  SymbolMap NewSymbolDefs;
+  std::vector<SymbolStringPtr> Symbols;
+  for (auto &[K, V] : InitialDests) {
+    StubHandle StubID = AvailableStubs.back();
+    if (SymbolToStubs[&TargetJD].count(K))
+      return make_error<StringError>(
+          "Tried to create duplicate redirectable symbols",
+          inconvertibleErrorCode());
+    SymbolToStubs[&TargetJD][K] = StubID;
+    NewSymbolDefs[K] = JumpStubs[StubID];
+    Symbols.push_back(K);
+    AvailableStubs.pop_back();
+  }
+
+  if (auto Err = TargetJD.define(absoluteSymbols(NewSymbolDefs), RT))
+    return Err;
+
+  if (auto Err = redirectInner(TargetJD, InitialDests))
+    return Err;
+
+  auto Err = RT->withResourceKeyDo([&](ResourceKey Key) {
+    TrackedResources[Key].insert(TrackedResources[Key].end(), Symbols.begin(),
+                                 Symbols.end());
+  });
+  if (Err)
+    return Err;
+
+  return Error::success();
+}
+
+Error JITLinkRedirectableSymbolManager::redirect(
+    JITDylib &TargetJD, const SymbolAddrMap &NewDests) {
+  std::unique_lock<std::mutex> Lock(Mutex);
+  return redirectInner(TargetJD, NewDests);
+}
+
+Error JITLinkRedirectableSymbolManager::redirectInner(
+    JITDylib &TargetJD, const SymbolAddrMap &NewDests) {
+  std::vector<std::pair<ExecutorAddr, ExecutorAddr>> PtrWrites;
+  for (auto &[K, V] : NewDests) {
+    if (!SymbolToStubs[&TargetJD].count(K))
+      return make_error<StringError>(
+          "Tried to redirect non-existent redirectalbe symbol",
+          inconvertibleErrorCode());
+    StubHandle StubID = SymbolToStubs[&TargetJD].at(K);
+    PtrWrites.push_back({StubPointers[StubID].getAddress(), V.getAddress()});
+  }
+
+  if (ES.getTargetTriple().isArch64Bit()) {
+    std::vector<tpctypes::UInt64Write> NativeWrites;
+    for (auto &[Ptr, Target] : PtrWrites)
+      NativeWrites.push_back(tpctypes::UInt64Write(Ptr, Target.getValue()));
+    if (auto Err =
+            ES.getExecutorProcessControl().getMemoryAccess().writeUInt64s(
+                NativeWrites))
+      return Err;
+  } else {
+    assert(DL.getPointerSize() == 4 && "Unsupported pointer size");
+    std::vector<tpctypes::UInt32Write> NativeWrites;
+    for (auto &[Ptr, Target] : PtrWrites)
+      NativeWrites.push_back(tpctypes::UInt32Write(Ptr, Target.getValue()));
+    if (auto Err =
+            ES.getExecutorProcessControl().getMemoryAccess().writeUInt32s(
+                NativeWrites))
+      return Err;
+  }
+  return Error::success();
+}
+
+Error JITLinkRedirectableSymbolManager::grow(unsigned Need) {
+  unsigned OldSize = JumpStubs.size();
+  unsigned NumNewStubs = alignTo(Need, StubBlockSize);
+  unsigned NewSize = OldSize + NumNewStubs;
+
+  JumpStubs.resize(NewSize);
+  StubPointers.resize(NewSize);
+  AvailableStubs.reserve(NewSize);
+
+  SymbolLookupSet LookupSymbols;
+  DenseMap<SymbolStringPtr, ExecutorSymbolDef *> NewDefsMap;
+
+  Triple TT = ES.getTargetTriple();
+  auto G = std::make_unique<jitlink::LinkGraph>(
+      "<INDIRECT STUBS>", TT, TT.isArch64Bit() ? 8 : 4,
+      TT.isLittleEndian() ? support::little : support::big,
+      jitlink::getGenericEdgeKindName);
+  auto &PointerSection =
+      G->createSection(StubPtrTableName, MemProt::Write | MemProt::Read);
+  auto &StubsSection =
+      G->createSection(JumpStubTableName, MemProt::Exec | MemProt::Read);
+
+  for (size_t I = OldSize; I < NewSize; I++) {
+    auto Pointer = AnonymousPtrCreator(*G, PointerSection, nullptr, 0);
+    if (auto Err = Pointer.takeError())
+      return Err;
+
+    StringRef PtrSymName = StubPtrSymbolName(I);
+    Pointer->setName(PtrSymName);
+    Pointer->setScope(jitlink::Scope::Default);
+    LookupSymbols.add(ES.intern(PtrSymName));
+    NewDefsMap[ES.intern(PtrSymName)] = &StubPointers[I];
+
+    auto Stub = PtrJumpStubCreator(*G, StubsSection, *Pointer);
+    if (auto Err = Stub.takeError())
+      return Err;
+
+    StringRef JumpStubSymName = JumpStubSymbolName(I);
+    Stub->setName(JumpStubSymName);
+    Stub->setScope(jitlink::Scope::Default);
+    LookupSymbols.add(ES.intern(JumpStubSymName));
+    NewDefsMap[ES.intern(JumpStubSymName)] = &JumpStubs[I];
+  }
+
+  if (auto Err = ObjLinkingLayer.add(JD, std::move(G)))
+    return Err;
+
+  auto LookupResult = ES.lookup(makeJITDylibSearchOrder(&JD), LookupSymbols);
+  if (auto Err = LookupResult.takeError())
+    return Err;
+
+  for (auto &[K, V] : *LookupResult)
+    *NewDefsMap.at(K) = V;
+
+  for (size_t I = OldSize; I < NewSize; I++)
+    AvailableStubs.push_back(I);
+
+  return Error::success();
+}
+
+Error JITLinkRedirectableSymbolManager::handleRemoveResources(
+    JITDylib &TargetJD, ResourceKey K) {
+  std::unique_lock<std::mutex> Lock(Mutex);
+  for (auto &Symbol : TrackedResources[K]) {
+    if (!SymbolToStubs[&TargetJD].count(Symbol))
+      return make_error<StringError>(
+          "Tried to remove non-existent redirectable symbol",
+          inconvertibleErrorCode());
+    AvailableStubs.push_back(SymbolToStubs[&TargetJD].at(Symbol));
+    SymbolToStubs[&TargetJD].erase(Symbol);
+    if (SymbolToStubs[&TargetJD].empty())
+      SymbolToStubs.erase(&TargetJD);
+  }
+  TrackedResources.erase(K);
+
+  return Error::success();
+}
+
+void JITLinkRedirectableSymbolManager::handleTransferResources(
+    JITDylib &TargetJD, ResourceKey DstK, ResourceKey SrcK) {
+  std::unique_lock<std::mutex> Lock(Mutex);
+  TrackedResources[DstK].insert(TrackedResources[DstK].end(),
+                                TrackedResources[SrcK].begin(),
+                                TrackedResources[SrcK].end());
+  TrackedResources.erase(SrcK);
+}

llvm/lib/ExecutionEngine/Orc/RedirectionManager.cpp

+//===---- RedirectionManager.cpp - Redirection manager interface 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/RedirectionManager.h"
+
+#define DEBUG_TYPE "orc"
+
+using namespace llvm;
+using namespace llvm::orc;
+
+void RedirectionManager::anchor() {}

llvm/unittests/ExecutionEngine/Orc/CMakeLists.txt

add_llvm_unittest(OrcJITTests
   RTDyldObjectLinkingLayerTest.cpp
   SharedMemoryMapperTest.cpp
   SimpleExecutorMemoryManagerTest.cpp
   SimplePackedSerializationTest.cpp
   SymbolStringPoolTest.cpp
   TaskDispatchTest.cpp
   ThreadSafeModuleTest.cpp
   WrapperFunctionUtilsTest.cpp
+  JITLinkRedirectionManagerTest.cpp
   )
 
 target_link_libraries(OrcJITTests PRIVATE
                         LLVMTestingSupport
                         ${ORC_JIT_TEST_LIBS})
 
 set_property(TARGET OrcJITTests PROPERTY FOLDER "Tests/UnitTests/ExecutionTests")
 
 export_executable_symbols(OrcJITTests)

llvm/unittests/ExecutionEngine/Orc/JITLinkRedirectionManagerTest.cpp

+#include "OrcTestCommon.h"
+#include "llvm/ExecutionEngine/JITLink/JITLinkMemoryManager.h"
+#include "llvm/ExecutionEngine/Orc/ExecutorProcessControl.h"
+#include "llvm/ExecutionEngine/Orc/JITLinkRedirectableSymbolManager.h"
+#include "llvm/ExecutionEngine/Orc/JITTargetMachineBuilder.h"
+#include "llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h"
+#include "llvm/ExecutionEngine/Orc/Shared/ExecutorAddress.h"
+#include "llvm/Testing/Support/Error.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace llvm::orc;
+using namespace llvm::jitlink;
+
+static int initialTarget() { return 42; }
+static int middleTarget() { return 13; }
+static int finalTarget() { return 53; }
+
+class JITLinkRedirectionManagerTest : public testing::Test {
+public:
+  ~JITLinkRedirectionManagerTest() {
+    if (ES)
+      if (auto Err = ES->endSession())
+        ES->reportError(std::move(Err));
+  }
+
+protected:
+  void SetUp() override {
+    auto JTMB = JITTargetMachineBuilder::detectHost();
+    // Bail out if we can not detect the host.
+    if (!JTMB) {
+      consumeError(JTMB.takeError());
+      GTEST_SKIP();
+    }
+
+    ES = std::make_unique<ExecutionSession>(
+        std::make_unique<UnsupportedExecutorProcessControl>(
+            nullptr, nullptr, JTMB->getTargetTriple().getTriple()));
+    JD = &ES->createBareJITDylib("main");
+    ObjLinkingLayer = std::make_unique<ObjectLinkingLayer>(
+        *ES, std::make_unique<InProcessMemoryManager>(4096));
+    DL = std::make_unique<DataLayout>(
+        cantFail(JTMB->getDefaultDataLayoutForTarget()));
+  }
+  JITDylib *JD{nullptr};
+  std::unique_ptr<ExecutionSession> ES;
+  std::unique_ptr<ObjectLinkingLayer> ObjLinkingLayer;
+  std::unique_ptr<DataLayout> DL;
+};
+
+TEST_F(JITLinkRedirectionManagerTest, BasicRedirectionOperation) {
+  auto RM =
+      JITLinkRedirectableSymbolManager::Create(*ES, *ObjLinkingLayer, *JD);
+  // Bail out if we can not create
+  if (!RM) {
+    consumeError(RM.takeError());
+    GTEST_SKIP();
+  }
+
+  auto DefineTarget = [&](StringRef TargetName, ExecutorAddr Addr) {
+    SymbolStringPtr Target = ES->intern(TargetName);
+    cantFail(JD->define(std::make_unique<SimpleMaterializationUnit>(
+        SymbolFlagsMap({{Target, JITSymbolFlags::Exported}}),
+        [&](std::unique_ptr<MaterializationResponsibility> R) -> void {
+          // No dependencies registered, can't fail.
+          cantFail(
+              R->notifyResolved({{Target, {Addr, JITSymbolFlags::Exported}}}));
+          cantFail(R->notifyEmitted());
+        })));
+    return cantFail(ES->lookup({JD}, TargetName));
+  };
+
+  auto InitialTarget =
+      DefineTarget("InitialTarget", ExecutorAddr::fromPtr(&initialTarget));
+  auto MiddleTarget =
+      DefineTarget("MiddleTarget", ExecutorAddr::fromPtr(&middleTarget));
+  auto FinalTarget =
+      DefineTarget("FinalTarget", ExecutorAddr::fromPtr(&finalTarget));
+
+  auto RedirectableSymbol = ES->intern("RedirectableTarget");
+  EXPECT_THAT_ERROR((*RM)->createRedirectableSymbols(
+                        *JD, {{RedirectableSymbol, InitialTarget}}),
+                    Succeeded());
+  auto RTDef = cantFail(ES->lookup({JD}, RedirectableSymbol));
+
+  auto RTPtr = RTDef.getAddress().toPtr<int (*)()>();
+  auto Result = RTPtr();
+  EXPECT_EQ(Result, 42) << "Failed to call initial target";
+
+  EXPECT_THAT_ERROR((*RM)->redirect(*JD, {{RedirectableSymbol, MiddleTarget}}),
+                    Succeeded());
+  Result = RTPtr();
+  EXPECT_EQ(Result, 13) << "Failed to call middle redirected target";
+
+  EXPECT_THAT_ERROR((*RM)->redirect(*JD, {{RedirectableSymbol, FinalTarget}}),
+                    Succeeded());
+  Result = RTPtr();
+  EXPECT_EQ(Result, 53) << "Failed to call redirected target";
+}