Drop materializeAllPermanently.
[oota-llvm.git] / tools / lli / lli.cpp
index 23025b4931245ac890459c52d78143022f03664d..9f714060c17a5b36aec8fad810d04d789626d69a 100644 (file)
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/LLVMContext.h"
-#include "llvm/Module.h"
-#include "llvm/Type.h"
+#include "llvm/IR/LLVMContext.h"
+#include "OrcLazyJIT.h"
+#include "RemoteMemoryManager.h"
+#include "RemoteTarget.h"
+#include "RemoteTargetExternal.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/Bitcode/ReaderWriter.h"
 #include "llvm/CodeGen/LinkAllCodegenComponents.h"
 #include "llvm/ExecutionEngine/GenericValue.h"
 #include "llvm/ExecutionEngine/Interpreter.h"
-#include "llvm/ExecutionEngine/JIT.h"
 #include "llvm/ExecutionEngine/JITEventListener.h"
-#include "llvm/ExecutionEngine/JITMemoryManager.h"
 #include "llvm/ExecutionEngine/MCJIT.h"
+#include "llvm/ExecutionEngine/ObjectCache.h"
+#include "llvm/ExecutionEngine/OrcMCJITReplacement.h"
+#include "llvm/ExecutionEngine/SectionMemoryManager.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/TypeBuilder.h"
+#include "llvm/IRReader/IRReader.h"
+#include "llvm/Object/Archive.h"
+#include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/CommandLine.h"
-#include "llvm/Support/IRReader.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/DynamicLibrary.h"
+#include "llvm/Support/Format.h"
 #include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/Memory.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/PluginLoader.h"
 #include "llvm/Support/PrettyStackTrace.h"
-#include "llvm/Support/raw_ostream.h"
 #include "llvm/Support/Process.h"
+#include "llvm/Support/Program.h"
 #include "llvm/Support/Signals.h"
+#include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetSelect.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Instrumentation.h"
 #include <cerrno>
 
 #ifdef __CYGWIN__
 
 using namespace llvm;
 
+#define DEBUG_TYPE "lli"
+
 namespace {
+
+  enum class JITKind { MCJIT, OrcMCJITReplacement, OrcLazy };
+
   cl::opt<std::string>
   InputFile(cl::desc("<input bitcode>"), cl::Positional, cl::init("-"));
 
@@ -57,10 +80,38 @@ namespace {
                                  cl::desc("Force interpretation: disable JIT"),
                                  cl::init(false));
 
-  cl::opt<bool> UseMCJIT(
-    "use-mcjit", cl::desc("Enable use of the MC-based JIT (if available)"),
+  cl::opt<JITKind> UseJITKind("jit-kind",
+                              cl::desc("Choose underlying JIT kind."),
+                              cl::init(JITKind::MCJIT),
+                              cl::values(
+                                clEnumValN(JITKind::MCJIT, "mcjit",
+                                           "MCJIT"),
+                                clEnumValN(JITKind::OrcMCJITReplacement,
+                                           "orc-mcjit",
+                                           "Orc-based MCJIT replacement"),
+                                clEnumValN(JITKind::OrcLazy,
+                                           "orc-lazy",
+                                           "Orc-based lazy JIT."),
+                                clEnumValEnd));
+
+  // The MCJIT supports building for a target address space separate from
+  // the JIT compilation process. Use a forked process and a copying
+  // memory manager with IPC to execute using this functionality.
+  cl::opt<bool> RemoteMCJIT("remote-mcjit",
+    cl::desc("Execute MCJIT'ed code in a separate process."),
     cl::init(false));
 
+  // Manually specify the child process for remote execution. This overrides
+  // the simulated remote execution that allocates address space for child
+  // execution. The child process will be executed and will communicate with
+  // lli via stdin/stdout pipes.
+  cl::opt<std::string>
+  ChildExecPath("mcjit-remote-process",
+                cl::desc("Specify the filename of the process to launch "
+                         "for remote MCJIT execution.  If none is specified,"
+                         "\n\tremote execution will be simulated in-process."),
+                cl::value_desc("filename"), cl::init(""));
+
   // Determine optimization level.
   cl::opt<char>
   OptLevel("O",
@@ -95,12 +146,38 @@ namespace {
                      "of the executable"),
             cl::value_desc("function"),
             cl::init("main"));
-  
+
+  cl::list<std::string>
+  ExtraModules("extra-module",
+         cl::desc("Extra modules to be loaded"),
+         cl::value_desc("input bitcode"));
+
+  cl::list<std::string>
+  ExtraObjects("extra-object",
+         cl::desc("Extra object files to be loaded"),
+         cl::value_desc("input object"));
+
+  cl::list<std::string>
+  ExtraArchives("extra-archive",
+         cl::desc("Extra archive files to be loaded"),
+         cl::value_desc("input archive"));
+
+  cl::opt<bool>
+  EnableCacheManager("enable-cache-manager",
+        cl::desc("Use cache manager to save/load mdoules"),
+        cl::init(false));
+
+  cl::opt<std::string>
+  ObjectCacheDir("object-cache-dir",
+                  cl::desc("Directory to store cached object files "
+                           "(must be user writable)"),
+                  cl::init(""));
+
   cl::opt<std::string>
   FakeArgv0("fake-argv0",
             cl::desc("Override the 'argv[0]' value passed into the executing"
                      " program"), cl::value_desc("executable"));
-  
+
   cl::opt<bool>
   DisableCoreFiles("disable-core-files", cl::Hidden,
                    cl::desc("Disable emission of core files if possible"));
@@ -141,25 +218,173 @@ namespace {
                                 "Large code model"),
                      clEnumValEnd));
 
+  cl::opt<bool>
+  GenerateSoftFloatCalls("soft-float",
+    cl::desc("Generate software floating point library calls"),
+    cl::init(false));
+
+  cl::opt<llvm::FloatABI::ABIType>
+  FloatABIForCalls("float-abi",
+                   cl::desc("Choose float ABI type"),
+                   cl::init(FloatABI::Default),
+                   cl::values(
+                     clEnumValN(FloatABI::Default, "default",
+                                "Target default float ABI type"),
+                     clEnumValN(FloatABI::Soft, "soft",
+                                "Soft float ABI (implied by -soft-float)"),
+                     clEnumValN(FloatABI::Hard, "hard",
+                                "Hard float ABI (uses FP registers)"),
+                     clEnumValEnd));
 }
 
-static ExecutionEngine *EE = 0;
+//===----------------------------------------------------------------------===//
+// Object cache
+//
+// This object cache implementation writes cached objects to disk to the
+// directory specified by CacheDir, using a filename provided in the module
+// descriptor. The cache tries to load a saved object using that path if the
+// file exists. CacheDir defaults to "", in which case objects are cached
+// alongside their originating bitcodes.
+//
+class LLIObjectCache : public ObjectCache {
+public:
+  LLIObjectCache(const std::string& CacheDir) : CacheDir(CacheDir) {
+    // Add trailing '/' to cache dir if necessary.
+    if (!this->CacheDir.empty() &&
+        this->CacheDir[this->CacheDir.size() - 1] != '/')
+      this->CacheDir += '/';
+  }
+  ~LLIObjectCache() override {}
+
+  void notifyObjectCompiled(const Module *M, MemoryBufferRef Obj) override {
+    const std::string ModuleID = M->getModuleIdentifier();
+    std::string CacheName;
+    if (!getCacheFilename(ModuleID, CacheName))
+      return;
+    if (!CacheDir.empty()) { // Create user-defined cache dir.
+      SmallString<128> dir(sys::path::parent_path(CacheName));
+      sys::fs::create_directories(Twine(dir));
+    }
+    std::error_code EC;
+    raw_fd_ostream outfile(CacheName, EC, sys::fs::F_None);
+    outfile.write(Obj.getBufferStart(), Obj.getBufferSize());
+    outfile.close();
+  }
+
+  std::unique_ptr<MemoryBuffer> getObject(const Module* M) override {
+    const std::string ModuleID = M->getModuleIdentifier();
+    std::string CacheName;
+    if (!getCacheFilename(ModuleID, CacheName))
+      return nullptr;
+    // Load the object from the cache filename
+    ErrorOr<std::unique_ptr<MemoryBuffer>> IRObjectBuffer =
+        MemoryBuffer::getFile(CacheName.c_str(), -1, false);
+    // If the file isn't there, that's OK.
+    if (!IRObjectBuffer)
+      return nullptr;
+    // MCJIT will want to write into this buffer, and we don't want that
+    // because the file has probably just been mmapped.  Instead we make
+    // a copy.  The filed-based buffer will be released when it goes
+    // out of scope.
+    return MemoryBuffer::getMemBufferCopy(IRObjectBuffer.get()->getBuffer());
+  }
+
+private:
+  std::string CacheDir;
+
+  bool getCacheFilename(const std::string &ModID, std::string &CacheName) {
+    std::string Prefix("file:");
+    size_t PrefixLength = Prefix.length();
+    if (ModID.substr(0, PrefixLength) != Prefix)
+      return false;
+        std::string CacheSubdir = ModID.substr(PrefixLength);
+#if defined(_WIN32)
+        // Transform "X:\foo" => "/X\foo" for convenience.
+        if (isalpha(CacheSubdir[0]) && CacheSubdir[1] == ':') {
+          CacheSubdir[1] = CacheSubdir[0];
+          CacheSubdir[0] = '/';
+        }
+#endif
+    CacheName = CacheDir + CacheSubdir;
+    size_t pos = CacheName.rfind('.');
+    CacheName.replace(pos, CacheName.length() - pos, ".o");
+    return true;
+  }
+};
+
+static ExecutionEngine *EE = nullptr;
+static LLIObjectCache *CacheManager = nullptr;
 
 static void do_shutdown() {
   // Cygwin-1.5 invokes DLL's dtors before atexit handler.
 #ifndef DO_NOTHING_ATEXIT
   delete EE;
+  if (CacheManager)
+    delete CacheManager;
   llvm_shutdown();
 #endif
 }
 
+// On Mingw and Cygwin, an external symbol named '__main' is called from the
+// generated 'main' function to allow static intialization.  To avoid linking
+// problems with remote targets (because lli's remote target support does not
+// currently handle external linking) we add a secondary module which defines
+// an empty '__main' function.
+static void addCygMingExtraModule(ExecutionEngine *EE,
+                                  LLVMContext &Context,
+                                  StringRef TargetTripleStr) {
+  IRBuilder<> Builder(Context);
+  Triple TargetTriple(TargetTripleStr);
+
+  // Create a new module.
+  std::unique_ptr<Module> M = make_unique<Module>("CygMingHelper", Context);
+  M->setTargetTriple(TargetTripleStr);
+
+  // Create an empty function named "__main".
+  Function *Result;
+  if (TargetTriple.isArch64Bit()) {
+    Result = Function::Create(
+      TypeBuilder<int64_t(void), false>::get(Context),
+      GlobalValue::ExternalLinkage, "__main", M.get());
+  } else {
+    Result = Function::Create(
+      TypeBuilder<int32_t(void), false>::get(Context),
+      GlobalValue::ExternalLinkage, "__main", M.get());
+  }
+  BasicBlock *BB = BasicBlock::Create(Context, "__main", Result);
+  Builder.SetInsertPoint(BB);
+  Value *ReturnVal;
+  if (TargetTriple.isArch64Bit())
+    ReturnVal = ConstantInt::get(Context, APInt(64, 0));
+  else
+    ReturnVal = ConstantInt::get(Context, APInt(32, 0));
+  Builder.CreateRet(ReturnVal);
+
+  // Add this new module to the ExecutionEngine.
+  EE->addModule(std::move(M));
+}
+
+CodeGenOpt::Level getOptLevel() {
+  switch (OptLevel) {
+  default:
+    errs() << "lli: Invalid optimization level.\n";
+    exit(1);
+  case '0': return CodeGenOpt::None;
+  case '1': return CodeGenOpt::Less;
+  case ' ':
+  case '2': return CodeGenOpt::Default;
+  case '3': return CodeGenOpt::Aggressive;
+  }
+  llvm_unreachable("Unrecognized opt level.");
+}
+
 //===----------------------------------------------------------------------===//
 // main Driver function
 //
 int main(int argc, char **argv, char * const *envp) {
   sys::PrintStackTraceOnErrorSignal();
   PrettyStackTraceProgram X(argc, argv);
-  
+
   LLVMContext &Context = getGlobalContext();
   atexit(do_shutdown);  // Call llvm_shutdown() on exit.
 
@@ -167,6 +392,7 @@ int main(int argc, char **argv, char * const *envp) {
   // usable by the JIT.
   InitializeNativeTarget();
   InitializeNativeTargetAsmPrinter();
+  InitializeNativeTargetAsmParser();
 
   cl::ParseCommandLineOptions(argc, argv,
                               "llvm interpreter & dynamic compiler\n");
@@ -174,58 +400,76 @@ int main(int argc, char **argv, char * const *envp) {
   // If the user doesn't want core files, disable them.
   if (DisableCoreFiles)
     sys::Process::PreventCoreFiles();
-  
+
   // Load the bitcode...
   SMDiagnostic Err;
-  Module *Mod = ParseIRFile(InputFile, Err, Context);
+  std::unique_ptr<Module> Owner = parseIRFile(InputFile, Err, Context);
+  Module *Mod = Owner.get();
   if (!Mod) {
     Err.print(argv[0], errs());
     return 1;
   }
 
+  if (UseJITKind == JITKind::OrcLazy)
+    return runOrcLazyJIT(std::move(Owner), argc, argv);
+
+  if (EnableCacheManager) {
+    std::string CacheName("file:");
+    CacheName.append(InputFile);
+    Mod->setModuleIdentifier(CacheName);
+  }
+
   // If not jitting lazily, load the whole bitcode file eagerly too.
-  std::string ErrorMsg;
   if (NoLazyCompilation) {
-    if (Mod->MaterializeAllPermanently(&ErrorMsg)) {
+    if (std::error_code EC = Mod->materializeAll()) {
       errs() << argv[0] << ": bitcode didn't read correctly.\n";
-      errs() << "Reason: " << ErrorMsg << "\n";
+      errs() << "Reason: " << EC.message() << "\n";
       exit(1);
     }
   }
 
-  EngineBuilder builder(Mod);
+  std::string ErrorMsg;
+  EngineBuilder builder(std::move(Owner));
   builder.setMArch(MArch);
   builder.setMCPU(MCPU);
   builder.setMAttrs(MAttrs);
   builder.setRelocationModel(RelocModel);
   builder.setCodeModel(CMModel);
   builder.setErrorStr(&ErrorMsg);
-  builder.setJITMemoryManager(ForceInterpreter ? 0 :
-                              JITMemoryManager::CreateDefaultMemManager());
   builder.setEngineKind(ForceInterpreter
                         ? EngineKind::Interpreter
                         : EngineKind::JIT);
+  builder.setUseOrcMCJITReplacement(UseJITKind == JITKind::OrcMCJITReplacement);
 
   // If we are supposed to override the target triple, do so now.
   if (!TargetTriple.empty())
     Mod->setTargetTriple(Triple::normalize(TargetTriple));
 
-  // Enable MCJIT, if desired.
-  if (UseMCJIT)
-    builder.setUseMCJIT(true);
-
-  CodeGenOpt::Level OLvl = CodeGenOpt::Default;
-  switch (OptLevel) {
-  default:
-    errs() << argv[0] << ": invalid optimization level.\n";
-    return 1;
-  case ' ': break;
-  case '0': OLvl = CodeGenOpt::None; break;
-  case '1': OLvl = CodeGenOpt::Less; break;
-  case '2': OLvl = CodeGenOpt::Default; break;
-  case '3': OLvl = CodeGenOpt::Aggressive; break;
+  // Enable MCJIT if desired.
+  RTDyldMemoryManager *RTDyldMM = nullptr;
+  if (!ForceInterpreter) {
+    if (RemoteMCJIT)
+      RTDyldMM = new RemoteMemoryManager();
+    else
+      RTDyldMM = new SectionMemoryManager();
+
+    // Deliberately construct a temp std::unique_ptr to pass in. Do not null out
+    // RTDyldMM: We still use it below, even though we don't own it.
+    builder.setMCJITMemoryManager(
+      std::unique_ptr<RTDyldMemoryManager>(RTDyldMM));
+  } else if (RemoteMCJIT) {
+    errs() << "error: Remote process execution does not work with the "
+              "interpreter.\n";
+    exit(1);
   }
-  builder.setOptLevel(OLvl);
+
+  builder.setOptLevel(getOptLevel());
+
+  TargetOptions Options;
+  if (FloatABIForCalls != FloatABI::Default)
+    Options.FloatABIType = FloatABIForCalls;
+
+  builder.setTargetOptions(Options);
 
   EE = builder.create();
   if (!EE) {
@@ -236,14 +480,82 @@ int main(int argc, char **argv, char * const *envp) {
     exit(1);
   }
 
-  EE->RegisterJITEventListener(createOProfileJITEventListener());
+  if (EnableCacheManager) {
+    CacheManager = new LLIObjectCache(ObjectCacheDir);
+    EE->setObjectCache(CacheManager);
+  }
+
+  // Load any additional modules specified on the command line.
+  for (unsigned i = 0, e = ExtraModules.size(); i != e; ++i) {
+    std::unique_ptr<Module> XMod = parseIRFile(ExtraModules[i], Err, Context);
+    if (!XMod) {
+      Err.print(argv[0], errs());
+      return 1;
+    }
+    if (EnableCacheManager) {
+      std::string CacheName("file:");
+      CacheName.append(ExtraModules[i]);
+      XMod->setModuleIdentifier(CacheName);
+    }
+    EE->addModule(std::move(XMod));
+  }
+
+  for (unsigned i = 0, e = ExtraObjects.size(); i != e; ++i) {
+    ErrorOr<object::OwningBinary<object::ObjectFile>> Obj =
+        object::ObjectFile::createObjectFile(ExtraObjects[i]);
+    if (!Obj) {
+      Err.print(argv[0], errs());
+      return 1;
+    }
+    object::OwningBinary<object::ObjectFile> &O = Obj.get();
+    EE->addObjectFile(std::move(O));
+  }
+
+  for (unsigned i = 0, e = ExtraArchives.size(); i != e; ++i) {
+    ErrorOr<std::unique_ptr<MemoryBuffer>> ArBufOrErr =
+        MemoryBuffer::getFileOrSTDIN(ExtraArchives[i]);
+    if (!ArBufOrErr) {
+      Err.print(argv[0], errs());
+      return 1;
+    }
+    std::unique_ptr<MemoryBuffer> &ArBuf = ArBufOrErr.get();
+
+    ErrorOr<std::unique_ptr<object::Archive>> ArOrErr =
+        object::Archive::create(ArBuf->getMemBufferRef());
+    if (std::error_code EC = ArOrErr.getError()) {
+      errs() << EC.message();
+      return 1;
+    }
+    std::unique_ptr<object::Archive> &Ar = ArOrErr.get();
+
+    object::OwningBinary<object::Archive> OB(std::move(Ar), std::move(ArBuf));
+
+    EE->addArchive(std::move(OB));
+  }
 
+  // If the target is Cygwin/MingW and we are generating remote code, we
+  // need an extra module to help out with linking.
+  if (RemoteMCJIT && Triple(Mod->getTargetTriple()).isOSCygMing()) {
+    addCygMingExtraModule(EE, Context, Mod->getTargetTriple());
+  }
+
+  // The following functions have no effect if their respective profiling
+  // support wasn't enabled in the build configuration.
+  EE->RegisterJITEventListener(
+                JITEventListener::createOProfileJITEventListener());
+  EE->RegisterJITEventListener(
+                JITEventListener::createIntelJITEventListener());
+
+  if (!NoLazyCompilation && RemoteMCJIT) {
+    errs() << "warning: remote mcjit does not support lazy compilation\n";
+    NoLazyCompilation = true;
+  }
   EE->DisableLazyCompilation(NoLazyCompilation);
 
   // If the user specifically requested an argv[0] to pass into the program,
   // do it now.
   if (!FakeArgv0.empty()) {
-    InputFile = FakeArgv0;
+    InputFile = static_cast<std::string>(FakeArgv0);
   } else {
     // Otherwise, if there is a .bc suffix on the executable strip it off, it
     // might confuse the program.
@@ -265,44 +577,118 @@ int main(int argc, char **argv, char * const *envp) {
     return -1;
   }
 
-  // If the program doesn't explicitly call exit, we will need the Exit 
-  // function later on to make an explicit call, so get the function now. 
-  Constant *Exit = Mod->getOrInsertFunction("exit", Type::getVoidTy(Context),
-                                                    Type::getInt32Ty(Context),
-                                                    NULL);
-  
   // Reset errno to zero on entry to main.
   errno = 0;
-  // Run static constructors.
-  EE->runStaticConstructorsDestructors(false);
 
-  if (NoLazyCompilation) {
-    for (Module::iterator I = Mod->begin(), E = Mod->end(); I != E; ++I) {
-      Function *Fn = &*I;
-      if (Fn != EntryFn && !Fn->isDeclaration())
-        EE->getPointerToFunction(Fn);
-    }
-  }
+  int Result;
+
+  if (!RemoteMCJIT) {
+    // If the program doesn't explicitly call exit, we will need the Exit
+    // function later on to make an explicit call, so get the function now.
+    Constant *Exit = Mod->getOrInsertFunction("exit", Type::getVoidTy(Context),
+                                                      Type::getInt32Ty(Context),
+                                                      nullptr);
 
-  // Run main.
-  int Result = EE->runFunctionAsMain(EntryFn, InputArgv, envp);
-
-  // Run static destructors.
-  EE->runStaticConstructorsDestructors(true);
-  
-  // If the program didn't call exit explicitly, we should call it now. 
-  // This ensures that any atexit handlers get called correctly.
-  if (Function *ExitF = dyn_cast<Function>(Exit)) {
-    std::vector<GenericValue> Args;
-    GenericValue ResultGV;
-    ResultGV.IntVal = APInt(32, Result);
-    Args.push_back(ResultGV);
-    EE->runFunction(ExitF, Args);
-    errs() << "ERROR: exit(" << Result << ") returned!\n";
-    abort();
+    // Run static constructors.
+    if (!ForceInterpreter) {
+      // Give MCJIT a chance to apply relocations and set page permissions.
+      EE->finalizeObject();
+    }
+    EE->runStaticConstructorsDestructors(false);
+
+    // Trigger compilation separately so code regions that need to be
+    // invalidated will be known.
+    (void)EE->getPointerToFunction(EntryFn);
+    // Clear instruction cache before code will be executed.
+    if (RTDyldMM)
+      static_cast<SectionMemoryManager*>(RTDyldMM)->invalidateInstructionCache();
+
+    // Run main.
+    Result = EE->runFunctionAsMain(EntryFn, InputArgv, envp);
+
+    // Run static destructors.
+    EE->runStaticConstructorsDestructors(true);
+
+    // If the program didn't call exit explicitly, we should call it now.
+    // This ensures that any atexit handlers get called correctly.
+    if (Function *ExitF = dyn_cast<Function>(Exit)) {
+      std::vector<GenericValue> Args;
+      GenericValue ResultGV;
+      ResultGV.IntVal = APInt(32, Result);
+      Args.push_back(ResultGV);
+      EE->runFunction(ExitF, Args);
+      errs() << "ERROR: exit(" << Result << ") returned!\n";
+      abort();
+    } else {
+      errs() << "ERROR: exit defined with wrong prototype!\n";
+      abort();
+    }
   } else {
-    errs() << "ERROR: exit defined with wrong prototype!\n";
-    abort();
+    // else == "if (RemoteMCJIT)"
+
+    // Remote target MCJIT doesn't (yet) support static constructors. No reason
+    // it couldn't. This is a limitation of the LLI implemantation, not the
+    // MCJIT itself. FIXME.
+    //
+    RemoteMemoryManager *MM = static_cast<RemoteMemoryManager*>(RTDyldMM);
+    // Everything is prepared now, so lay out our program for the target
+    // address space, assign the section addresses to resolve any relocations,
+    // and send it to the target.
+
+    std::unique_ptr<RemoteTarget> Target;
+    if (!ChildExecPath.empty()) { // Remote execution on a child process
+#ifndef LLVM_ON_UNIX
+      // FIXME: Remove this pointless fallback mode which causes tests to "pass"
+      // on platforms where they should XFAIL.
+      errs() << "Warning: host does not support external remote targets.\n"
+             << "  Defaulting to simulated remote execution\n";
+      Target.reset(new RemoteTarget);
+#else
+      if (!sys::fs::can_execute(ChildExecPath)) {
+        errs() << "Unable to find usable child executable: '" << ChildExecPath
+               << "'\n";
+        return -1;
+      }
+      Target.reset(new RemoteTargetExternal(ChildExecPath));
+#endif
+    } else {
+      // No child process name provided, use simulated remote execution.
+      Target.reset(new RemoteTarget);
+    }
+
+    // Give the memory manager a pointer to our remote target interface object.
+    MM->setRemoteTarget(Target.get());
+
+    // Create the remote target.
+    if (!Target->create()) {
+      errs() << "ERROR: " << Target->getErrorMsg() << "\n";
+      return EXIT_FAILURE;
+    }
+
+    // Since we're executing in a (at least simulated) remote address space,
+    // we can't use the ExecutionEngine::runFunctionAsMain(). We have to
+    // grab the function address directly here and tell the remote target
+    // to execute the function.
+    //
+    // Our memory manager will map generated code into the remote address
+    // space as it is loaded and copy the bits over during the finalizeMemory
+    // operation.
+    //
+    // FIXME: argv and envp handling.
+    uint64_t Entry = EE->getFunctionAddress(EntryFn->getName().str());
+
+    DEBUG(dbgs() << "Executing '" << EntryFn->getName() << "' at 0x"
+                 << format("%llx", Entry) << "\n");
+
+    if (!Target->executeCode(Entry, Result))
+      errs() << "ERROR: " << Target->getErrorMsg() << "\n";
+
+    // Like static constructors, the remote target MCJIT support doesn't handle
+    // this yet. It could. FIXME.
+
+    // Stop the remote target
+    Target->stop();
   }
+
+  return Result;
 }