[Orc] Allow LLJITBuilder's CreateObjectLinkingLayer to return errors

[sgraenitz]

Summary

It can be useful for an ObjectLinkingLayerCreator to allow callee errors to get propagated to the builder. Specifically, this is the case when the ObjectLayer uses the EHFrameRegistrationPlugin, because it requires a TPCEHFrameRegistrar and instantiation for it may fail (e.g. if the required registration symbols are missing in the target process).

[lhames]

llvm/examples/OrcV2Examples/LLJITWithCustomObjectLinkingLayer/LLJITWithCustomObjectLinkingLayer.cpp

48 ↗

(On Diff #316658)

Rather than pass an Error by reference here, could you change ObjectLinkingLayerCreator's signature to return an Expected<std::unique_ptr<ObjectLayer>> ?

[sgraenitz]

llvm/examples/OrcV2Examples/LLJITWithCustomObjectLinkingLayer/LLJITWithCustomObjectLinkingLayer.cpp

48 ↗

(On Diff #316658)

Yes good point. I will make an update.

[sgraenitz]

Drop the Error output parameter and return an Expected instead

[lhames]

Great. Thanks very much Stefan!

llvm/examples/OrcV2Examples/LLJITWithGDBRegistrationListener/LLJITWithGDBRegistrationListener.cpp

auto J =
 
                       // Register the event listener.
                       ObjLinkingLayer->registerJITEventListener(
                           *JITEventListener::createGDBRegistrationListener());
 
                       // Make sure the debug info sections aren't stripped.
                       ObjLinkingLayer->setProcessAllSections(true);
 
-                      return ObjLinkingLayer;
+                      return std::move(ObjLinkingLayer);
                     })
                     .create());
 
   // Make sure that our process symbols are visible to JIT'd code.
   {
     MangleAndInterner Mangle(J->getExecutionSession(), J->getDataLayout());
     J->getMainJITDylib().addGenerator(
         ExitOnErr(orc::DynamicLibrarySearchGenerator::GetForCurrentProcess(

llvm/examples/OrcV2Examples/LLJITWithObjectLinkingLayerPlugin/LLJITWithObjectLinkingLayerPlugin.cpp

auto J = ExitOnErr(
           .setJITTargetMachineBuilder(std::move(JTMB))
           .setObjectLinkingLayerCreator(
               [&](ExecutionSession &ES, const Triple &TT) {
                 // Create ObjectLinkingLayer.
                 auto ObjLinkingLayer = std::make_unique<ObjectLinkingLayer>(
                     ES, std::make_unique<jitlink::InProcessMemoryManager>());
                 // Add an instance of our plugin.
                 ObjLinkingLayer->addPlugin(std::make_unique<MyPlugin>());
-                return ObjLinkingLayer;
+                return std::move(ObjLinkingLayer);
               })
           .create());
 
   auto M = ExitOnErr(parseExampleModule(TestMod, "test-module"));
 
   ExitOnErr(J->addIRModule(std::move(M)));
 
   // Look up the JIT'd function, cast it to a function pointer, then call it.

llvm/include/llvm/ExecutionEngine/Orc/LLJIT.h

public:
   std::string mangle(StringRef UnmangledName) const;
 
   /// Returns an interned, linker-mangled version of UnmangledName.
   SymbolStringPtr mangleAndIntern(StringRef UnmangledName) const {
     return ES->intern(mangle(UnmangledName));
   }
 
 protected:
-  static std::unique_ptr<ObjectLayer>
+  static Expected<std::unique_ptr<ObjectLayer>>
   createObjectLinkingLayer(LLJITBuilderState &S, ExecutionSession &ES);
 
   static Expected<std::unique_ptr<IRCompileLayer::IRCompiler>>
   createCompileFunction(LLJITBuilderState &S, JITTargetMachineBuilder JTMB);
 
   /// Create an LLJIT instance with a single compile thread.
   LLJIT(LLJITBuilderState &S, Error &Err);
 
private:
   LLLazyJIT(LLLazyJITBuilderState &S, Error &Err);
 
   std::unique_ptr<LazyCallThroughManager> LCTMgr;
   std::unique_ptr<CompileOnDemandLayer> CODLayer;
 };
 
 class LLJITBuilderState {
 public:
-  using ObjectLinkingLayerCreator = std::function<std::unique_ptr<ObjectLayer>(
-      ExecutionSession &, const Triple &TT)>;
+  using ObjectLinkingLayerCreator =
+      std::function<Expected<std::unique_ptr<ObjectLayer>>(ExecutionSession &,
+                                                           const Triple &)>;
 
   using CompileFunctionCreator =
       std::function<Expected<std::unique_ptr<IRCompileLayer::IRCompiler>>(
           JITTargetMachineBuilder JTMB)>;
 
   using PlatformSetupFunction = std::function<Error(LLJIT &J)>;
 
   std::unique_ptr<ExecutionSession> ES;

llvm/lib/ExecutionEngine/Orc/LLJIT.cpp

Error LLJITBuilderState::prepareForConstruction() {
   if (!CreateObjectLinkingLayer) {
     auto &TT = JTMB->getTargetTriple();
     if (TT.isOSBinFormatMachO() &&
         (TT.getArch() == Triple::aarch64 || TT.getArch() == Triple::x86_64)) {
 
       JTMB->setRelocationModel(Reloc::PIC_);
       JTMB->setCodeModel(CodeModel::Small);
       CreateObjectLinkingLayer =
-          [TPC = this->TPC](ExecutionSession &ES,
-                            const Triple &) -> std::unique_ptr<ObjectLayer> {
+          [TPC = this->TPC](
+              ExecutionSession &ES,
+              const Triple &) -> Expected<std::unique_ptr<ObjectLayer>> {
         std::unique_ptr<ObjectLinkingLayer> ObjLinkingLayer;
         if (TPC)
           ObjLinkingLayer =
               std::make_unique<ObjectLinkingLayer>(ES, TPC->getMemMgr());
         else
           ObjLinkingLayer = std::make_unique<ObjectLinkingLayer>(
               ES, std::make_unique<jitlink::InProcessMemoryManager>());
         ObjLinkingLayer->addPlugin(std::make_unique<EHFrameRegistrationPlugin>(

 }
 
 Expected<JITEvaluatedSymbol> LLJIT::lookupLinkerMangled(JITDylib &JD,
                                                         SymbolStringPtr Name) {
   return ES->lookup(
       makeJITDylibSearchOrder(&JD, JITDylibLookupFlags::MatchAllSymbols), Name);
 }
 
-std::unique_ptr<ObjectLayer>
+Expected<std::unique_ptr<ObjectLayer>>
 LLJIT::createObjectLinkingLayer(LLJITBuilderState &S, ExecutionSession &ES) {
 
   // If the config state provided an ObjectLinkingLayer factory then use it.
   if (S.CreateObjectLinkingLayer)
     return S.CreateObjectLinkingLayer(ES, S.JTMB->getTargetTriple());
 
   // Otherwise default to creating an RTDyldObjectLinkingLayer that constructs
   // a new SectionMemoryManager for each object.
LLJIT::createCompileFunction(LLJITBuilderState &S,
   if (!TM)
     return TM.takeError();
 
   return std::make_unique<TMOwningSimpleCompiler>(std::move(*TM));
 }
 
 LLJIT::LLJIT(LLJITBuilderState &S, Error &Err)
     : ES(S.ES ? std::move(S.ES) : std::make_unique<ExecutionSession>()), Main(),
-      DL(""), TT(S.JTMB->getTargetTriple()),
-      ObjLinkingLayer(createObjectLinkingLayer(S, *ES)) {
+      DL(""), TT(S.JTMB->getTargetTriple()) {
 
   ErrorAsOutParameter _(&Err);
 
   if (auto MainOrErr = this->ES->createJITDylib("main"))
     Main = &*MainOrErr;
   else {
     Err = MainOrErr.takeError();
     return;
   }
 
   if (S.DL)
     DL = std::move(*S.DL);
   else if (auto DLOrErr = S.JTMB->getDefaultDataLayoutForTarget())
     DL = std::move(*DLOrErr);
   else {
     Err = DLOrErr.takeError();
     return;
   }
 
+  auto ObjLayer = createObjectLinkingLayer(S, *ES);
+  if (!ObjLayer) {
+    Err = ObjLayer.takeError();
+    return;
+  }
+  ObjLinkingLayer = std::move(*ObjLayer);
   ObjTransformLayer =
       std::make_unique<ObjectTransformLayer>(*ES, *ObjLinkingLayer);
 
   {
     auto CompileFunction = createCompileFunction(S, std::move(*S.JTMB));
     if (!CompileFunction) {
       Err = CompileFunction.takeError();
       return;