Index: compiler-rt/cmake/Modules/AllSupportedArchDefs.cmake
===================================================================
--- compiler-rt/cmake/Modules/AllSupportedArchDefs.cmake
+++ compiler-rt/cmake/Modules/AllSupportedArchDefs.cmake
@@ -82,3 +82,7 @@
 if (UNIX)
 set(ALL_ORC_SUPPORTED_ARCH ${X86_64} ${ARM64} ${ARM32})
 endif()
+
+if (WIN32)
+  set(ALL_ORC_SUPPORTED_ARCH ${X86_64})
+endif()
Index: compiler-rt/lib/orc/CMakeLists.txt
===================================================================
--- compiler-rt/lib/orc/CMakeLists.txt
+++ compiler-rt/lib/orc/CMakeLists.txt
@@ -1,14 +1,21 @@
 # Build for all components of the ORC runtime support library.
 
-# ORC runtime library implementation files.
-set(ORC_SOURCES
+# ORC runtime library common implementation files.
+set(ORC_COMMON_SOURCES
   debug.cpp
   extensible_rtti.cpp
   log_error_to_stderr.cpp
+  run_program_wrapper.cpp
+  dlfcn_wrapper.cpp
+  )
+
+# ORC runtime library implementation files for all ORC architectures.s
+set(ALL_ORC_SOURCES
+  ${ORC_COMMON_SOURCES}
+  coff_platform.cpp
+  elfnix_platform.cpp
   macho_ehframe_registration.cpp
   macho_platform.cpp
-  elfnix_platform.cpp
-  run_program_wrapper.cpp
   dlfcn_wrapper.cpp
   )
 
@@ -17,30 +24,37 @@
   macho_tlv.x86-64.S
   macho_tlv.arm64.S
   elfnix_tls.x86-64.S
-)
+  elfnix_tls.aarch64.S
+  )
 
-set(ORC_IMPL_HEADERS
-# Implementation headers will go here.
+# Common implementation headers will go here.
+set(ORC_COMMON_IMPL_HEADERS
   adt.h
-  c_api.h
   common.h
   compiler.h
   endianness.h
   error.h
   executor_address.h
   extensible_rtti.h
-  macho_platform.h
   simple_packed_serialization.h
   stl_extras.h
   wrapper_function_utils.h
-)
+  )
+
+# Implementation headers for all ORC architectures.  
+set(ALL_ORC_IMPL_HEADERS
+  ${ORC_COMMON_IMPL_HEADERS}
+  macho_platform.h
+  coff_platform.h
+  elfnix_platform.h
+  )
 
 # Create list of all source files for
 # consumption by tests.
 set(ORC_ALL_SOURCE_FILES
-  ${ORC_SOURCES}
+  ${ALL_ORC_SOURCES}
   ${ALL_ORC_ASM_SOURCES}
-  ${ORC_IMPL_HEADERS}
+  ${ALL_ORC_IMPL_HEADERS}
   )
 
 list(REMOVE_DUPLICATES ORC_ALL_SOURCE_FILES)
@@ -74,6 +88,17 @@
     macho_tlv.x86-64.S
     macho_tlv.arm64.S
     )
+  
+  set(ORC_IMPL_HEADERS
+    ${ORC_COMMON_IMPL_HEADERS}
+    macho_platform.h
+    )
+
+  set(ORC_SOURCES
+    ${ORC_COMMON_SOURCES}
+    macho_ehframe_registration.cpp
+    macho_platform.cpp
+    )
 
   add_compiler_rt_object_libraries(RTOrc
     OS ${ORC_SUPPORTED_OS}
@@ -93,10 +118,36 @@
     LINK_LIBS ${ORC_LINK_LIBS}
     PARENT_TARGET orc)
 else() # not Apple
-  add_asm_sources(ORC_ASM_SOURCES 
-    elfnix_tls.x86-64.S
-    elfnix_tls.aarch64.S
-    )
+  if (WIN32)
+    set(ORC_BUILD_TYPE STATIC)
+
+    set(ORC_IMPL_HEADERS
+      ${ORC_COMMON_IMPL_HEADERS}
+      coff_platform.h
+      )
+
+    set(ORC_SOURCES
+      ${ORC_COMMON_SOURCES}
+      coff_platform.cpp
+      )
+  else()
+    set(ORC_BUILD_TYPE STATIC)
+
+    set(ORC_IMPL_HEADERS
+      ${ORC_COMMON_IMPL_HEADERS}
+      elfnix_platform.h
+      )
+    
+    set(ORC_SOURCES
+      ${ORC_COMMON_SOURCES}
+      elfnix_platform.cpp
+      )
+
+    add_asm_sources(ORC_ASM_SOURCES 
+      elfnix_tls.x86-64.S
+      elfnix_tls.aarch64.S
+      )
+  endif()
 
   foreach(arch ${ORC_SUPPORTED_ARCH})
     if(NOT CAN_TARGET_${arch})
@@ -112,13 +163,13 @@
 
     # Common ORC archive for instrumented binaries.
     add_compiler_rt_runtime(clang_rt.orc
-     STATIC
-     ARCHS ${arch}
-     CFLAGS ${ORC_CFLAGS}
-     LINK_FLAGS ${ORC_LINK_FLAGS}
-     LINK_LIBS ${ORC_LINK_LIBS}
-     OBJECT_LIBS ${ORC_COMMON_RUNTIME_OBJECT_LIBS} RTOrc
-     PARENT_TARGET orc)
+      ${ORC_BUILD_TYPE}
+      ARCHS ${arch}
+      CFLAGS ${ORC_CFLAGS}
+      LINK_FLAGS ${ORC_LINK_FLAGS}
+      LINK_LIBS ${ORC_LINK_LIBS}
+      OBJECT_LIBS ${ORC_COMMON_RUNTIME_OBJECT_LIBS} RTOrc
+      PARENT_TARGET orc)
   endforeach()
 endif() # not Apple
 
Index: compiler-rt/lib/orc/adt.h
===================================================================
--- compiler-rt/lib/orc/adt.h
+++ compiler-rt/lib/orc/adt.h
@@ -87,21 +87,44 @@
   constexpr bool empty() const noexcept { return Size == 0; }
 
   friend bool operator==(const string_view &LHS, const string_view &RHS) {
-    if (LHS.Size != RHS.Size)
-      return false;
-    if (LHS.Data == RHS.Data)
-      return true;
-    for (size_t I = 0; I != LHS.Size; ++I)
-      if (LHS.Data[I] != RHS.Data[I])
-        return false;
-    return true;
+    return LHS._compare(RHS, std::min(LHS.Size, RHS.Size)) == 0;
   }
 
   friend bool operator!=(const string_view &LHS, const string_view &RHS) {
     return !(LHS == RHS);
   }
 
+  friend bool operator<(const string_view &LHS, const string_view &RHS) {
+    return LHS._compare(RHS, std::min(LHS.Size, RHS.Size)) < 0;
+  }
+
+  friend bool operator<=(const string_view &LHS, const string_view &RHS) {
+    return LHS._compare(RHS, std::min(LHS.Size, RHS.Size)) <= 0;
+  }
+
+  friend bool operator>(const string_view &LHS, const string_view &RHS) {
+    return LHS._compare(RHS, std::min(LHS.Size, RHS.Size)) > 0;
+  }
+
+  friend bool operator>=(const string_view &LHS, const string_view &RHS) {
+    return LHS._compare(RHS, std::min(LHS.Size, RHS.Size)) >= 0;
+  }
+
 private:
+  int _compare(const string_view &Other, size_type N) const {
+    const char *Str1 = Data;
+    const char *Str2 = Other.Data;
+    while (N--) {
+      auto U1 = static_cast<unsigned char>(*Str1++);
+      auto U2 = static_cast<unsigned char>(*Str2++);
+      if (U1 != U2)
+        return U1 - U2;
+      if (U1 == '\0')
+        return 0;
+    }
+    return 0;
+  }
+
   const char *Data = nullptr;
   size_type Size = 0;
 };
Index: compiler-rt/lib/orc/coff_platform.h
===================================================================
--- /dev/null
+++ compiler-rt/lib/orc/coff_platform.h
@@ -0,0 +1,39 @@
+//===- cofff_platform.h ------------------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// ORC Runtime support for dynamic loading features on COFF-based platforms.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef ORC_RT_COFF_PLATFORM_H
+#define ORC_RT_COFF_PLATFORM_H
+
+#include "common.h"
+#include "executor_address.h"
+
+// dlfcn functions.
+ORC_RT_INTERFACE const char *__orc_rt_coff_jit_dlerror();
+ORC_RT_INTERFACE void *__orc_rt_coff_jit_dlopen(const char *path, int mode);
+ORC_RT_INTERFACE int __orc_rt_coff_jit_dlclose(void *header);
+ORC_RT_INTERFACE void *__orc_rt_coff_jit_dlsym(void *header,
+                                               const char *symbol);
+
+namespace __orc_rt {
+namespace coff {
+
+enum dlopen_mode : int {
+  ORC_RT_RTLD_LAZY = 0x1,
+  ORC_RT_RTLD_NOW = 0x2,
+  ORC_RT_RTLD_LOCAL = 0x4,
+  ORC_RT_RTLD_GLOBAL = 0x8
+};
+
+} // end namespace coff
+} // end namespace __orc_rt
+
+#endif
\ No newline at end of file
Index: compiler-rt/lib/orc/coff_platform.cpp
===================================================================
--- /dev/null
+++ compiler-rt/lib/orc/coff_platform.cpp
@@ -0,0 +1,721 @@
+//===- coff_platform.cpp --------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains code required to load the rest of the COFF runtime.
+//
+//===----------------------------------------------------------------------===//
+
+#define NOMINMAX
+#include <Windows.h>
+
+#include "coff_platform.h"
+
+#include "debug.h"
+#include "error.h"
+#include "wrapper_function_utils.h"
+
+#include <array>
+#include <list>
+#include <map>
+#include <mutex>
+#include <sstream>
+#include <vector>
+
+#define DEBUG_TYPE "coff_platform"
+
+using namespace __orc_rt;
+
+namespace __orc_rt {
+
+using COFFJITDylibDepInfo = std::vector<ExecutorAddr>;
+using COFFJITDylibDepInfoMap =
+    std::unordered_map<ExecutorAddr, COFFJITDylibDepInfo>;
+
+using SPSCOFFObjectSectionsMap =
+    SPSSequence<SPSTuple<SPSString, SPSExecutorAddrRange>>;
+
+using SPSCOFFJITDylibDepInfo = SPSSequence<SPSExecutorAddr>;
+
+using SPSCOFFJITDylibDepInfoMap =
+    SPSSequence<SPSTuple<SPSExecutorAddr, SPSCOFFJITDylibDepInfo>>;
+
+} // namespace __orc_rt
+
+ORC_RT_JIT_DISPATCH_TAG(__orc_rt_coff_symbol_lookup_tag)
+ORC_RT_JIT_DISPATCH_TAG(__orc_rt_coff_push_initializers_tag)
+
+namespace {
+class COFFPlatformRuntimeState {
+private:
+  // Ctor/dtor section.
+  // Manage lists of *tor functions sorted by the last character of subsection
+  // name.
+  struct XtorSection {
+    void Register(char SubsectionChar, span<void (*)(void)> Xtors) {
+      Subsections[SubsectionChar - 'A'].push_back(Xtors);
+      SubsectionsNew[SubsectionChar - 'A'].push_back(Xtors);
+    }
+
+    void RegisterNoRun(char SubsectionChar, span<void (*)(void)> Xtors) {
+      Subsections[SubsectionChar - 'A'].push_back(Xtors);
+    }
+
+    void Reset() { SubsectionsNew = Subsections; }
+
+    void RunAllNewAndFlush();
+
+  private:
+    std::array<std::list<span<void (*)(void)>>, 26> Subsections;
+    std::array<std::list<span<void (*)(void)>>, 26> SubsectionsNew;
+  };
+
+  struct JITDylibState {
+    std::string Name;
+    void *Header = nullptr;
+    size_t LinkedAgainstRefCount = 0;
+    size_t DlRefCount = 0;
+    std::vector<JITDylibState *> Deps;
+    XtorSection CInitSection;    // XIA~XIZ
+    XtorSection CXXInitSection;  // XCA~XCZ
+    XtorSection CPreTermSection; // XPA~XPZ
+    XtorSection CTermSection;    // XTA~XTZ
+
+    bool referenced() const {
+      return LinkedAgainstRefCount != 0 || DlRefCount != 0;
+    }
+  };
+
+public:
+  static void initialize();
+  static COFFPlatformRuntimeState &get();
+  static void destroy();
+
+  COFFPlatformRuntimeState() = default;
+
+  // Delete copy and move constructors.
+  COFFPlatformRuntimeState(const COFFPlatformRuntimeState &) = delete;
+  COFFPlatformRuntimeState &
+  operator=(const COFFPlatformRuntimeState &) = delete;
+  COFFPlatformRuntimeState(COFFPlatformRuntimeState &&) = delete;
+  COFFPlatformRuntimeState &operator=(COFFPlatformRuntimeState &&) = delete;
+
+  const char *dlerror();
+  void *dlopen(string_view Name, int Mode);
+  int dlclose(void *Header);
+  void *dlsym(void *Header, string_view Symbol);
+
+  Error registerJITDylib(std::string Name, void *Header);
+  Error deregisterJITDylib(void *Header);
+
+  Error registerObjectSections(
+      ExecutorAddr HeaderAddr,
+      std::vector<std::pair<string_view, ExecutorAddrRange>> Secs,
+      bool RunInitializers);
+  Error deregisterObjectSections(
+      ExecutorAddr HeaderAddr,
+      std::vector<std::pair<string_view, ExecutorAddrRange>> Secs);
+
+  void *findJITDylibBaseByPC(uint64_t PC);
+
+private:
+  Error registerBlockRange(ExecutorAddr HeaderAddr, ExecutorAddrRange Range);
+  Error deregisterBlockRange(ExecutorAddr HeaderAddr, ExecutorAddrRange Range);
+
+  Error registerSEHFrames(ExecutorAddr HeaderAddr,
+                          ExecutorAddrRange SEHFrameRange);
+  Error deregisterSEHFrames(ExecutorAddr HeaderAddr,
+                            ExecutorAddrRange SEHFrameRange);
+
+  Expected<void *> dlopenImpl(string_view Path, int Mode);
+  Error dlopenFull(JITDylibState &JDS);
+  Error dlopenInitialize(JITDylibState &JDS, COFFJITDylibDepInfoMap &DepInfo);
+
+  Error dlcloseImpl(void *DSOHandle);
+  Error dlcloseDeinitialize(JITDylibState &JDS);
+
+  JITDylibState *getJITDylibStateByHeader(void *DSOHandle);
+  JITDylibState *getJITDylibStateByName(string_view Path);
+  Expected<ExecutorAddr> lookupSymbolInJITDylib(void *DSOHandle,
+                                                string_view Symbol);
+
+  static COFFPlatformRuntimeState *CPS;
+
+  std::recursive_mutex JDStatesMutex;
+  std::map<void *, JITDylibState> JDStates;
+  struct BlockRange {
+    void *Header;
+    size_t Size;
+  };
+  std::map<void *, BlockRange> BlockRanges;
+  std::unordered_map<string_view, void *> JDNameToHeader;
+  std::string DLFcnError;
+};
+
+} // namespace
+
+COFFPlatformRuntimeState *COFFPlatformRuntimeState::CPS = nullptr;
+
+COFFPlatformRuntimeState::JITDylibState *
+COFFPlatformRuntimeState::getJITDylibStateByHeader(void *Header) {
+  auto I = JDStates.find(Header);
+  if (I == JDStates.end())
+    return nullptr;
+  return &I->second;
+}
+
+COFFPlatformRuntimeState::JITDylibState *
+COFFPlatformRuntimeState::getJITDylibStateByName(string_view Name) {
+  // FIXME: Avoid creating string copy here.
+  auto I = JDNameToHeader.find(std::string(Name.data(), Name.size()));
+  if (I == JDNameToHeader.end())
+    return nullptr;
+  void *H = I->second;
+  auto J = JDStates.find(H);
+  assert(J != JDStates.end() &&
+         "JITDylib has name map entry but no header map entry");
+  return &J->second;
+}
+
+Error COFFPlatformRuntimeState::registerJITDylib(std::string Name,
+                                                 void *Header) {
+  ORC_RT_DEBUG({
+    printdbg("Registering JITDylib %s: Header = %p\n", Name.c_str(), Header);
+  });
+  std::lock_guard<std::recursive_mutex> Lock(JDStatesMutex);
+  if (JDStates.count(Header)) {
+    std::ostringstream ErrStream;
+    ErrStream << "Duplicate JITDylib registration for header " << Header
+              << " (name = " << Name << ")";
+    return make_error<StringError>(ErrStream.str());
+  }
+  if (JDNameToHeader.count(Name)) {
+    std::ostringstream ErrStream;
+    ErrStream << "Duplicate JITDylib registration for header " << Header
+              << " (header = " << Header << ")";
+    return make_error<StringError>(ErrStream.str());
+  }
+
+  auto &JDS = JDStates[Header];
+  JDS.Name = std::move(Name);
+  JDS.Header = Header;
+  JDNameToHeader[JDS.Name] = Header;
+  return Error::success();
+}
+
+Error COFFPlatformRuntimeState::deregisterJITDylib(void *Header) {
+  std::lock_guard<std::recursive_mutex> Lock(JDStatesMutex);
+  auto I = JDStates.find(Header);
+  if (I == JDStates.end()) {
+    std::ostringstream ErrStream;
+    ErrStream << "Attempted to deregister unrecognized header " << Header;
+    return make_error<StringError>(ErrStream.str());
+  }
+
+  // Remove std::string construction once we can use C++20.
+  auto J = JDNameToHeader.find(
+      std::string(I->second.Name.data(), I->second.Name.size()));
+  assert(J != JDNameToHeader.end() &&
+         "Missing JDNameToHeader entry for JITDylib");
+
+  ORC_RT_DEBUG({
+    printdbg("Deregistering JITDylib %s: Header = %p\n", I->second.Name.c_str(),
+             Header);
+  });
+
+  JDNameToHeader.erase(J);
+  JDStates.erase(I);
+  return Error::success();
+}
+
+void COFFPlatformRuntimeState::XtorSection::RunAllNewAndFlush() {
+  for (auto &Subsection : SubsectionsNew) {
+    for (auto &XtorGroup : Subsection)
+      for (auto &Xtor : XtorGroup)
+        if (Xtor)
+          Xtor();
+    Subsection.clear();
+  }
+}
+
+const char *COFFPlatformRuntimeState::dlerror() { return DLFcnError.c_str(); }
+
+void *COFFPlatformRuntimeState::dlopen(string_view Path, int Mode) {
+  ORC_RT_DEBUG({
+    std::string S(Path.data(), Path.size());
+    printdbg("COFFPlatform::dlopen(\"%s\")\n", S.c_str());
+  });
+  std::lock_guard<std::recursive_mutex> Lock(JDStatesMutex);
+  if (auto H = dlopenImpl(Path, Mode))
+    return *H;
+  else {
+    // FIXME: Make dlerror thread safe.
+    DLFcnError = toString(H.takeError());
+    return nullptr;
+  }
+}
+
+int COFFPlatformRuntimeState::dlclose(void *DSOHandle) {
+  ORC_RT_DEBUG({
+    auto *JDS = getJITDylibStateByHeader(DSOHandle);
+    std::string DylibName;
+    if (JDS) {
+      std::string S;
+      printdbg("COFFPlatform::dlclose(%p) (%s)\n", DSOHandle, S.c_str());
+    } else
+      printdbg("COFFPlatform::dlclose(%p) (%s)\n", DSOHandle, "invalid handle");
+  });
+  std::lock_guard<std::recursive_mutex> Lock(JDStatesMutex);
+  if (auto Err = dlcloseImpl(DSOHandle)) {
+    // FIXME: Make dlerror thread safe.
+    DLFcnError = toString(std::move(Err));
+    return -1;
+  }
+  return 0;
+}
+
+void *COFFPlatformRuntimeState::dlsym(void *Header, string_view Symbol) {
+  auto Addr = lookupSymbolInJITDylib(Header, Symbol);
+  if (!Addr) {
+    return 0;
+  }
+
+  return Addr->toPtr<void *>();
+}
+
+Expected<void *> COFFPlatformRuntimeState::dlopenImpl(string_view Path,
+                                                      int Mode) {
+  // Try to find JITDylib state by name.
+  auto *JDS = getJITDylibStateByName(Path);
+
+  if (!JDS)
+    return make_error<StringError>("No registered JTIDylib for path " +
+                                   std::string(Path.data(), Path.size()));
+
+  if (auto Err = dlopenFull(*JDS))
+    return std::move(Err);
+
+  // Bump the ref-count on this dylib.
+  ++JDS->DlRefCount;
+
+  // Return the header address.
+  return JDS->Header;
+}
+
+Error COFFPlatformRuntimeState::dlopenFull(JITDylibState &JDS) {
+  // Call back to the JIT to push the initializers.
+  Expected<COFFJITDylibDepInfoMap> DepInfoMap((COFFJITDylibDepInfoMap()));
+  if (auto Err = WrapperFunction<SPSExpected<SPSCOFFJITDylibDepInfoMap>(
+          SPSExecutorAddr)>::call(&__orc_rt_coff_push_initializers_tag,
+                                  DepInfoMap,
+                                  ExecutorAddr::fromPtr(JDS.Header)))
+    return Err;
+  if (!DepInfoMap)
+    return DepInfoMap.takeError();
+
+  if (auto Err = dlopenInitialize(JDS, *DepInfoMap))
+    return Err;
+
+  if (!DepInfoMap->empty()) {
+    ORC_RT_DEBUG({
+      printdbg("Unrecognized dep-info key headers in dlopen of %s\n",
+               JDS.Name.c_str());
+    });
+    std::ostringstream ErrStream;
+    ErrStream << "Encountered unrecognized dep-info key headers "
+                 "while processing dlopen of "
+              << JDS.Name;
+    return make_error<StringError>(ErrStream.str());
+  }
+
+  return Error::success();
+}
+
+Error COFFPlatformRuntimeState::dlopenInitialize(
+    JITDylibState &JDS, COFFJITDylibDepInfoMap &DepInfo) {
+  ORC_RT_DEBUG({
+    printdbg("COFFPlatformRuntimeState::dlopenInitialize(\"%s\")\n",
+             JDS.Name.c_str());
+  });
+
+  // Skip visited dependency.
+  auto I = DepInfo.find(ExecutorAddr::fromPtr(JDS.Header));
+  if (I == DepInfo.end())
+    return Error::success();
+
+  auto DI = std::move(I->second);
+  DepInfo.erase(I);
+
+  // Run initializers of dependencies in proper order by depth-first traversal
+  // of dependency graph.
+  std::vector<JITDylibState *> OldDeps;
+  std::swap(JDS.Deps, OldDeps);
+  JDS.Deps.reserve(DI.size());
+  for (auto DepHeaderAddr : DI) {
+    auto *DepJDS = getJITDylibStateByHeader(DepHeaderAddr.toPtr<void *>());
+    if (!DepJDS) {
+      std::ostringstream ErrStream;
+      ErrStream << "Encountered unrecognized dep header "
+                << DepHeaderAddr.toPtr<void *>() << " while initializing "
+                << JDS.Name;
+      return make_error<StringError>(ErrStream.str());
+    }
+    ++DepJDS->LinkedAgainstRefCount;
+    if (auto Err = dlopenInitialize(*DepJDS, DepInfo))
+      return Err;
+  }
+
+  // Run static initializers.
+  JDS.CInitSection.RunAllNewAndFlush();
+  JDS.CXXInitSection.RunAllNewAndFlush();
+
+  // Decrement old deps.
+  for (auto *DepJDS : OldDeps) {
+    --DepJDS->LinkedAgainstRefCount;
+    if (!DepJDS->referenced())
+      if (auto Err = dlcloseDeinitialize(*DepJDS))
+        return Err;
+  }
+
+  return Error::success();
+}
+
+Error COFFPlatformRuntimeState::dlcloseImpl(void *DSOHandle) {
+  // Try to find JITDylib state by header.
+  auto *JDS = getJITDylibStateByHeader(DSOHandle);
+
+  if (!JDS) {
+    std::ostringstream ErrStream;
+    ErrStream << "No registered JITDylib for " << DSOHandle;
+    return make_error<StringError>(ErrStream.str());
+  }
+
+  // Bump the ref-count.
+  --JDS->DlRefCount;
+
+  if (!JDS->referenced())
+    return dlcloseDeinitialize(*JDS);
+
+  return Error::success();
+}
+
+Error COFFPlatformRuntimeState::dlcloseDeinitialize(JITDylibState &JDS) {
+  ORC_RT_DEBUG({
+    printdbg("COFFPlatformRuntimeState::dlcloseDeinitialize(\"%s\")\n",
+             JDS.Name.c_str());
+  });
+
+  // FIXME: call atexits.
+
+  // Run static terminators.
+  JDS.CPreTermSection.RunAllNewAndFlush();
+  JDS.CTermSection.RunAllNewAndFlush();
+
+  // Queue all xtors as new again.
+  JDS.CInitSection.Reset();
+  JDS.CXXInitSection.Reset();
+  JDS.CPreTermSection.Reset();
+  JDS.CTermSection.Reset();
+
+  // Deinitialize any dependencies.
+  for (auto *DepJDS : JDS.Deps) {
+    --DepJDS->LinkedAgainstRefCount;
+    if (!DepJDS->referenced())
+      if (auto Err = dlcloseDeinitialize(*DepJDS))
+        return Err;
+  }
+
+  return Error::success();
+}
+
+Expected<ExecutorAddr>
+COFFPlatformRuntimeState::lookupSymbolInJITDylib(void *header,
+                                                 string_view Sym) {
+  Expected<ExecutorAddr> Result((ExecutorAddr()));
+  if (auto Err = WrapperFunction<SPSExpected<SPSExecutorAddr>(
+          SPSExecutorAddr, SPSString)>::call(&__orc_rt_coff_symbol_lookup_tag,
+                                             Result,
+                                             ExecutorAddr::fromPtr(header),
+                                             Sym))
+    return std::move(Err);
+  return Result;
+}
+
+Error COFFPlatformRuntimeState::registerObjectSections(
+    ExecutorAddr HeaderAddr,
+    std::vector<std::pair<string_view, ExecutorAddrRange>> Secs,
+    bool RunInitializers) {
+  std::lock_guard<std::recursive_mutex> Lock(JDStatesMutex);
+  auto I = JDStates.find(HeaderAddr.toPtr<void *>());
+  if (I == JDStates.end()) {
+    std::ostringstream ErrStream;
+    ErrStream << "Attempted to register unrecognized header "
+              << HeaderAddr.getValue();
+    return make_error<StringError>(ErrStream.str());
+  }
+  auto &JDState = I->second;
+  for (auto &KV : Secs) {
+    if (auto Err = registerBlockRange(HeaderAddr, KV.second))
+      return Err;
+    if (KV.first.empty())
+      continue;
+    char LastChar = KV.first.data()[KV.first.size() - 1];
+    if (KV.first == ".pdata") {
+      if (auto Err = registerSEHFrames(HeaderAddr, KV.second))
+        return Err;
+    } else if (KV.first >= ".CRT$XIA" && KV.first <= ".CRT$XIZ") {
+      if (RunInitializers)
+        JDState.CInitSection.Register(LastChar,
+                                      KV.second.toSpan<void (*)(void)>());
+      else
+        JDState.CInitSection.RegisterNoRun(LastChar,
+                                           KV.second.toSpan<void (*)(void)>());
+    } else if (KV.first >= ".CRT$XCA" && KV.first <= ".CRT$XCZ") {
+      if (RunInitializers)
+        JDState.CXXInitSection.Register(LastChar,
+                                        KV.second.toSpan<void (*)(void)>());
+      else
+        JDState.CXXInitSection.RegisterNoRun(
+            LastChar, KV.second.toSpan<void (*)(void)>());
+    } else if (KV.first >= ".CRT$XPA" && KV.first <= ".CRT$XPZ")
+      JDState.CPreTermSection.Register(LastChar,
+                                       KV.second.toSpan<void (*)(void)>());
+    else if (KV.first >= ".CRT$XTA" && KV.first <= ".CRT$XTZ")
+      JDState.CTermSection.Register(LastChar,
+                                    KV.second.toSpan<void (*)(void)>());
+  }
+  return Error::success();
+}
+
+Error COFFPlatformRuntimeState::deregisterObjectSections(
+    ExecutorAddr HeaderAddr,
+    std::vector<std::pair<string_view, ExecutorAddrRange>> Secs) {
+  std::lock_guard<std::recursive_mutex> Lock(JDStatesMutex);
+  auto I = JDStates.find(HeaderAddr.toPtr<void *>());
+  if (I == JDStates.end()) {
+    std::ostringstream ErrStream;
+    ErrStream << "Attempted to register unrecognized header "
+              << HeaderAddr.getValue();
+    return make_error<StringError>(ErrStream.str());
+  }
+  auto &JDState = I->second;
+  for (auto &KV : Secs) {
+    if (auto Err = deregisterBlockRange(HeaderAddr, KV.second))
+      return Err;
+    if (KV.first == ".pdata")
+      if (auto Err = deregisterSEHFrames(HeaderAddr, KV.second))
+        return Err;
+  }
+  return Error::success();
+}
+
+Error COFFPlatformRuntimeState::registerSEHFrames(
+    ExecutorAddr HeaderAddr, ExecutorAddrRange SEHFrameRange) {
+  int N = (SEHFrameRange.End.getValue() - SEHFrameRange.Start.getValue()) /
+          sizeof(RUNTIME_FUNCTION);
+  auto Func = SEHFrameRange.Start.toPtr<PRUNTIME_FUNCTION>();
+  if (!RtlAddFunctionTable(Func, N,
+                           static_cast<DWORD64>(HeaderAddr.getValue())))
+    return make_error<StringError>("Failed to register SEH frames");
+  return Error::success();
+}
+
+Error COFFPlatformRuntimeState::deregisterSEHFrames(
+    ExecutorAddr HeaderAddr, ExecutorAddrRange SEHFrameRange) {
+  if (!RtlDeleteFunctionTable(SEHFrameRange.Start.toPtr<PRUNTIME_FUNCTION>()))
+    return make_error<StringError>("Failed to deregister SEH frames");
+  return Error::success();
+}
+
+Error COFFPlatformRuntimeState::registerBlockRange(ExecutorAddr HeaderAddr,
+                                                   ExecutorAddrRange Range) {
+  assert(!this->BlockRanges.count(Range.Start.toPtr<void *>()) &&
+         "Block range address already registered");
+  BlockRange B = {HeaderAddr.toPtr<void *>(), Range.size().getValue()};
+  this->BlockRanges.emplace(Range.Start.toPtr<void *>(), B);
+  return Error::success();
+}
+
+Error COFFPlatformRuntimeState::deregisterBlockRange(ExecutorAddr HeaderAddr,
+                                                     ExecutorAddrRange Range) {
+  assert(this->BlockRanges.count(Range.Start.toPtr<void *>()) &&
+         "Block range address not registered");
+  this->BlockRanges.erase(Range.Start.toPtr<void *>());
+  return Error::success();
+}
+
+void COFFPlatformRuntimeState::initialize() {
+  assert(!CPS && "COFFPlatformRuntimeState should be null");
+  CPS = new COFFPlatformRuntimeState();
+}
+
+COFFPlatformRuntimeState &COFFPlatformRuntimeState::get() {
+  assert(CPS && "COFFPlatformRuntimeState not initialized");
+  return *CPS;
+}
+
+void COFFPlatformRuntimeState::destroy() {
+  assert(CPS && "COFFPlatformRuntimeState not initialized");
+  delete CPS;
+}
+
+void *COFFPlatformRuntimeState::findJITDylibBaseByPC(uint64_t PC) {
+  std::lock_guard<std::recursive_mutex> Lock(JDStatesMutex);
+  auto It = BlockRanges.upper_bound(reinterpret_cast<void *>(PC));
+  if (It == BlockRanges.begin())
+    return nullptr;
+  --It;
+  auto &Range = It->second;
+  if (PC >= reinterpret_cast<uint64_t>(It->first) + Range.Size)
+    return nullptr;
+  return Range.Header;
+}
+
+ORC_RT_INTERFACE __orc_rt_CWrapperFunctionResult
+__orc_rt_coff_platform_bootstrap(char *ArgData, size_t ArgSize) {
+  COFFPlatformRuntimeState::initialize();
+  return WrapperFunctionResult().release();
+}
+
+ORC_RT_INTERFACE __orc_rt_CWrapperFunctionResult
+__orc_rt_coff_platform_shutdown(char *ArgData, size_t ArgSize) {
+  COFFPlatformRuntimeState::destroy();
+  return WrapperFunctionResult().release();
+}
+
+ORC_RT_INTERFACE __orc_rt_CWrapperFunctionResult
+__orc_rt_coff_register_jitdylib(char *ArgData, size_t ArgSize) {
+  return WrapperFunction<SPSError(SPSString, SPSExecutorAddr)>::handle(
+             ArgData, ArgSize,
+             [](std::string &Name, ExecutorAddr HeaderAddr) {
+               return COFFPlatformRuntimeState::get().registerJITDylib(
+                   std::move(Name), HeaderAddr.toPtr<void *>());
+             })
+      .release();
+}
+
+ORC_RT_INTERFACE __orc_rt_CWrapperFunctionResult
+__orc_rt_coff_deregister_jitdylib(char *ArgData, size_t ArgSize) {
+  return WrapperFunction<SPSError(SPSExecutorAddr)>::handle(
+             ArgData, ArgSize,
+             [](ExecutorAddr HeaderAddr) {
+               return COFFPlatformRuntimeState::get().deregisterJITDylib(
+                   HeaderAddr.toPtr<void *>());
+             })
+      .release();
+}
+
+ORC_RT_INTERFACE __orc_rt_CWrapperFunctionResult
+__orc_rt_coff_register_object_sections(char *ArgData, size_t ArgSize) {
+  return WrapperFunction<SPSError(SPSExecutorAddr, SPSCOFFObjectSectionsMap,
+                                  bool)>::
+      handle(ArgData, ArgSize,
+             [](ExecutorAddr HeaderAddr,
+                std::vector<std::pair<string_view, ExecutorAddrRange>> &Secs,
+                bool RunInitializers) {
+               return COFFPlatformRuntimeState::get().registerObjectSections(
+                   HeaderAddr, std::move(Secs), RunInitializers);
+             })
+          .release();
+}
+
+ORC_RT_INTERFACE __orc_rt_CWrapperFunctionResult
+__orc_rt_coff_deregister_object_sections(char *ArgData, size_t ArgSize) {
+  return WrapperFunction<SPSError(SPSExecutorAddr, SPSCOFFObjectSectionsMap)>::
+      handle(ArgData, ArgSize,
+             [](ExecutorAddr HeaderAddr,
+                std::vector<std::pair<string_view, ExecutorAddrRange>> &Secs) {
+               return COFFPlatformRuntimeState::get().deregisterObjectSections(
+                   HeaderAddr, std::move(Secs));
+             })
+          .release();
+}
+//------------------------------------------------------------------------------
+//                        JIT'd dlfcn alternatives.
+//------------------------------------------------------------------------------
+
+const char *__orc_rt_coff_jit_dlerror() {
+  return COFFPlatformRuntimeState::get().dlerror();
+}
+
+void *__orc_rt_coff_jit_dlopen(const char *path, int mode) {
+  return COFFPlatformRuntimeState::get().dlopen(path, mode);
+}
+
+int __orc_rt_coff_jit_dlclose(void *header) {
+  return COFFPlatformRuntimeState::get().dlclose(header);
+}
+
+void *__orc_rt_coff_jit_dlsym(void *header, const char *symbol) {
+  return COFFPlatformRuntimeState::get().dlsym(header, symbol);
+}
+
+//------------------------------------------------------------------------------
+//                        COFF SEH exception support
+//------------------------------------------------------------------------------
+
+struct ThrowInfo {
+  uint32_t attributes;
+  void *data;
+};
+
+ORC_RT_INTERFACE void __stdcall __orc_rt_coff_cxx_throw_exception(
+    void *pExceptionObject, ThrowInfo *pThrowInfo) {
+  constexpr uint32_t EH_EXCEPTION_NUMBER = 'msc' | 0xE0000000;
+  constexpr uint32_t EH_MAGIC_NUMBER1 = 0x19930520;
+  auto BaseAddr = COFFPlatformRuntimeState::get().findJITDylibBaseByPC(
+      reinterpret_cast<uint64_t>(pThrowInfo));
+  if (!BaseAddr) {
+    // This is not from JIT'd region.
+    // FIXME: Use the default implementation like below when alias api is
+    // capable. _CxxThrowException(pExceptionObject, pThrowInfo);
+    fprintf(stderr, "Throwing exception from compiled callback into JIT'd "
+                    "exception handler not supported yet.\n");
+    abort();
+    return;
+  }
+  const ULONG_PTR parameters[] = {
+      EH_MAGIC_NUMBER1,
+      reinterpret_cast<ULONG_PTR>(pExceptionObject),
+      reinterpret_cast<ULONG_PTR>(pThrowInfo),
+      reinterpret_cast<ULONG_PTR>(BaseAddr),
+  };
+  RaiseException(EH_EXCEPTION_NUMBER, EXCEPTION_NONCONTINUABLE,
+                 _countof(parameters), parameters);
+}
+
+//------------------------------------------------------------------------------
+//                             COFF Run Program
+//------------------------------------------------------------------------------
+
+ORC_RT_INTERFACE int64_t __orc_rt_coff_run_program(const char *JITDylibName,
+                                                   const char *EntrySymbolName,
+                                                   int argc, char *argv[]) {
+  using MainTy = int (*)(int, char *[]);
+
+  void *H =
+      __orc_rt_coff_jit_dlopen(JITDylibName, __orc_rt::coff::ORC_RT_RTLD_LAZY);
+  if (!H) {
+    __orc_rt_log_error(__orc_rt_coff_jit_dlerror());
+    return -1;
+  }
+
+  auto *Main =
+      reinterpret_cast<MainTy>(__orc_rt_coff_jit_dlsym(H, EntrySymbolName));
+
+  if (!Main) {
+    __orc_rt_log_error(__orc_rt_coff_jit_dlerror());
+    return -1;
+  }
+
+  int Result = Main(argc, argv);
+
+  if (__orc_rt_coff_jit_dlclose(H) == -1)
+    __orc_rt_log_error(__orc_rt_coff_jit_dlerror());
+
+  return Result;
+}
Index: compiler-rt/lib/orc/common.h
===================================================================
--- compiler-rt/lib/orc/common.h
+++ compiler-rt/lib/orc/common.h
@@ -34,14 +34,14 @@
 /// This is declared for use by the runtime, but should be implemented in the
 /// executor or provided by a definition added to the JIT before the runtime
 /// is loaded.
-extern "C" __orc_rt_Opaque __orc_rt_jit_dispatch_ctx ORC_RT_WEAK_IMPORT;
+ORC_RT_IMPORT __orc_rt_Opaque __orc_rt_jit_dispatch_ctx ORC_RT_WEAK_IMPORT;
 
 /// For dispatching calls to the JIT object.
 ///
 /// This is declared for use by the runtime, but should be implemented in the
 /// executor or provided by a definition added to the JIT before the runtime
 /// is loaded.
-extern "C" __orc_rt_CWrapperFunctionResult
+ORC_RT_IMPORT __orc_rt_CWrapperFunctionResult
 __orc_rt_jit_dispatch(__orc_rt_Opaque *DispatchCtx, const void *FnTag,
                       const char *Data, size_t Size) ORC_RT_WEAK_IMPORT;
 
Index: compiler-rt/lib/orc/compiler.h
===================================================================
--- compiler-rt/lib/orc/compiler.h
+++ compiler-rt/lib/orc/compiler.h
@@ -15,8 +15,15 @@
 #ifndef ORC_RT_COMPILER_H
 #define ORC_RT_COMPILER_H
 
+#if defined(_WIN32)
+#define ORC_RT_INTERFACE extern "C"
+#define ORC_RT_HIDDEN
+#define ORC_RT_IMPORT extern "C" __declspec(dllimport)
+#else
 #define ORC_RT_INTERFACE extern "C" __attribute__((visibility("default")))
 #define ORC_RT_HIDDEN __attribute__((visibility("hidden")))
+#define ORC_RT_IMPORT extern "C"
+#endif
 
 #ifndef __has_builtin
 # define __has_builtin(x) 0
@@ -56,8 +63,10 @@
 #define ORC_RT_UNLIKELY(EXPR) (EXPR)
 #endif
 
-#ifdef __APPLE__
+#if defined(__APPLE__)
 #define ORC_RT_WEAK_IMPORT __attribute__((weak_import))
+#elif defined(_WIN32)
+#define ORC_RT_WEAK_IMPORT
 #else
 #define ORC_RT_WEAK_IMPORT __attribute__((weak))
 #endif
Index: compiler-rt/lib/orc/error.h
===================================================================
--- compiler-rt/lib/orc/error.h
+++ compiler-rt/lib/orc/error.h
@@ -113,9 +113,7 @@
 
   bool isChecked() const { return ErrPtr & 0x1; }
 
-  void setChecked(bool Checked) {
-    ErrPtr = (reinterpret_cast<uintptr_t>(ErrPtr) & ~uintptr_t(1)) | Checked;
-  }
+  void setChecked(bool Checked) { ErrPtr = (ErrPtr & ~uintptr_t(1)) | Checked; }
 
   template <typename ErrT = ErrorInfoBase> std::unique_ptr<ErrT> takePayload() {
     static_assert(std::is_base_of<ErrorInfoBase, ErrT>::value,
Index: compiler-rt/test/orc/TestCases/Windows/lit.local.cfg.py
===================================================================
--- /dev/null
+++ compiler-rt/test/orc/TestCases/Windows/lit.local.cfg.py
@@ -0,0 +1,2 @@
+if config.root.host_os != 'Windows':
+  config.unsupported = True
Index: compiler-rt/test/orc/TestCases/Windows/x86-64/hello-world.c
===================================================================
--- /dev/null
+++ compiler-rt/test/orc/TestCases/Windows/x86-64/hello-world.c
@@ -0,0 +1,10 @@
+// RUN: %clang -c -o %t %s
+// RUN: %llvm_jitlink %t 2>&1 | FileCheck %s
+// CHECK: Hello, world!
+
+#include <stdio.h>
+int main(int argc, char *argv[]) {
+  printf("Hello, world!\n");
+  fflush(stdout);
+  return 0;
+}
Index: compiler-rt/test/orc/TestCases/Windows/x86-64/hello-world.cpp
===================================================================
--- /dev/null
+++ compiler-rt/test/orc/TestCases/Windows/x86-64/hello-world.cpp
@@ -0,0 +1,9 @@
+// RUN: %clangxx -c -o %t %s
+// RUN: %llvm_jitlink %t 2>&1 | FileCheck %s
+// CHECK: Hello, world!
+
+#include <iostream>
+int main(int argc, char *argv[]) {
+  std::cout << "Hello, world!" << std::endl;
+  return 0;
+}
Index: compiler-rt/test/orc/TestCases/Windows/x86-64/lit.local.cfg.py
===================================================================
--- /dev/null
+++ compiler-rt/test/orc/TestCases/Windows/x86-64/lit.local.cfg.py
@@ -0,0 +1,5 @@
+if config.root.host_arch not in ['AMD64','x86_64']:
+  config.unsupported = True
+
+if config.target_arch not in ['AMD64','x86_64']:
+  config.unsupported = True
Index: compiler-rt/test/orc/TestCases/Windows/x86-64/sehframe-handling.cpp
===================================================================
--- /dev/null
+++ compiler-rt/test/orc/TestCases/Windows/x86-64/sehframe-handling.cpp
@@ -0,0 +1,15 @@
+// RUN: %clangxx -c -o %t %s
+// RUN: %llvm_jitlink %t
+
+extern "C" __declspec(dllimport) void llvm_jitlink_setTestResultOverride(
+    long Value);
+
+int main(int argc, char *argv[]) {
+  llvm_jitlink_setTestResultOverride(1);
+  try {
+    throw 0;
+  } catch (int X) {
+    llvm_jitlink_setTestResultOverride(X);
+  }
+  return 0;
+}
Index: compiler-rt/test/orc/TestCases/Windows/x86-64/static-initializer.cpp
===================================================================
--- /dev/null
+++ compiler-rt/test/orc/TestCases/Windows/x86-64/static-initializer.cpp
@@ -0,0 +1,18 @@
+// RUN: %clangxx -c -o %t %s
+// RUN: %llvm_jitlink %t
+
+extern "C" __declspec(dllimport) void llvm_jitlink_setTestResultOverride(
+    long Value);
+
+static int init() { return -1; }
+
+static int init2() { return 1; }
+
+static int a = init();
+static int b = 0;
+static int c = init2();
+
+int main(int argc, char *argv[]) {
+  llvm_jitlink_setTestResultOverride(a + b + c);
+  return 0;
+}
Index: compiler-rt/test/orc/lit.cfg.py
===================================================================
--- compiler-rt/test/orc/lit.cfg.py
+++ compiler-rt/test/orc/lit.cfg.py
@@ -29,8 +29,12 @@
 config.substitutions.append(
     ('%clangxx ',
      build_invocation(config.cxx_mode_flags + [config.target_cflags])))
-config.substitutions.append(
-    ('%llvm_jitlink', (llvm_jitlink + ' -orc-runtime=' + orc_rt_path)))
+if config.host_os == 'Windows':
+  config.substitutions.append(
+      ('%llvm_jitlink', (llvm_jitlink + ' -orc-runtime=' + orc_rt_path + ' -no-process-syms=true -slab-allocate=64MB')))
+else:
+  config.substitutions.append(
+      ('%llvm_jitlink', (llvm_jitlink + ' -orc-runtime=' + orc_rt_path)))
 config.substitutions.append(
     ('%lli_orc_jitlink', (lli + ' -jit-kind=orc -jit-linker=jitlink -orc-runtime=' + orc_rt_path)))
 
@@ -40,5 +44,5 @@
 # Exclude Inputs directories.
 config.excludes = ['Inputs']
 
-if config.host_os not in ['Darwin', 'FreeBSD', 'Linux']:
+if config.host_os not in ['Darwin', 'FreeBSD', 'Linux', 'Windows']:
   config.unsupported = True
Index: llvm/include/llvm/ExecutionEngine/Orc/COFFPlatform.h
===================================================================
--- /dev/null
+++ llvm/include/llvm/ExecutionEngine/Orc/COFFPlatform.h
@@ -0,0 +1,198 @@
+//===--- COFFPlatform.h -- Utilities for executing COFF in Orc --*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Utilities for executing JIT'd COFF in Orc.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_EXECUTIONENGINE_ORC_COFFPLATFORM_H
+#define LLVM_EXECUTIONENGINE_ORC_COFFPLATFORM_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ExecutionEngine/Orc/Core.h"
+#include "llvm/ExecutionEngine/Orc/ExecutorProcessControl.h"
+#include "llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h"
+#include "llvm/ExecutionEngine/Orc/Shared/ExecutorAddress.h"
+
+#include <future>
+#include <memory>
+#include <thread>
+#include <vector>
+
+namespace llvm {
+namespace orc {
+
+/// Mediates between COFF initialization and ExecutionSession state.
+class COFFPlatform : public Platform {
+public:
+  /// Try to create a COFFPlatform instance, adding the ORC runtime to the
+  /// given JITDylib.
+  static Expected<std::unique_ptr<COFFPlatform>>
+  Create(ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
+         JITDylib &PlatformJD, const char *OrcRuntimePath,
+         std::vector<std::string> &ImportedLibraries,
+         Optional<SymbolAliasMap> RuntimeAliases = None);
+
+  Error bootstrap(JITDylib &PlatformJD);
+
+  ExecutionSession &getExecutionSession() const { return ES; }
+  ObjectLinkingLayer &getObjectLinkingLayer() const { return ObjLinkingLayer; }
+
+  Error setupJITDylib(JITDylib &JD) override;
+  Error teardownJITDylib(JITDylib &JD) override;
+  Error notifyAdding(ResourceTracker &RT,
+                     const MaterializationUnit &MU) override;
+  Error notifyRemoving(ResourceTracker &RT) override;
+
+  /// Returns an AliasMap containing the default aliases for the MachOPlatform.
+  /// This can be modified by clients when constructing the platform to add
+  /// or remove aliases.
+  static SymbolAliasMap standardPlatformAliases(ExecutionSession &ES);
+
+  /// Returns the array of required CXX aliases.
+  static ArrayRef<std::pair<const char *, const char *>> requiredCXXAliases();
+
+  /// Returns the array of standard runtime utility aliases for MachO.
+  static ArrayRef<std::pair<const char *, const char *>>
+  standardRuntimeUtilityAliases();
+
+  static bool isInitializerSection(StringRef Name) {
+    return Name.startswith(".CRT");
+  }
+
+  static StringRef getSEHFrameSectionName() { return ".pdata"; }
+
+private:
+  using COFFJITDylibDepInfo = std::vector<ExecutorAddr>;
+  using COFFJITDylibDepInfoMap =
+      std::vector<std::pair<ExecutorAddr, COFFJITDylibDepInfo>>;
+  using COFFObjectSectionsMap =
+      SmallVector<std::pair<std::string, ExecutorAddrRange>>;
+  using PushInitializersSendResultFn =
+      unique_function<void(Expected<COFFJITDylibDepInfoMap>)>;
+  using SendSymbolAddressFn = unique_function<void(Expected<ExecutorAddr>)>;
+  using JITDylibDepMap = DenseMap<JITDylib *, SmallVector<JITDylib *>>;
+
+  // The COFFPlatformPlugin scans/modifies LinkGraphs to support MachO
+  // platform features including initializers, exceptions, and language
+  // runtime registration.
+  class COFFPlatformPlugin : public ObjectLinkingLayer::Plugin {
+  public:
+    COFFPlatformPlugin(COFFPlatform &CP) : CP(CP) {}
+
+    void modifyPassConfig(MaterializationResponsibility &MR,
+                          jitlink::LinkGraph &G,
+                          jitlink::PassConfiguration &Config) override;
+
+    SyntheticSymbolDependenciesMap
+    getSyntheticSymbolDependencies(MaterializationResponsibility &MR) override;
+
+    // FIXME: We should be tentatively tracking scraped sections and discarding
+    // if the MR fails.
+    Error notifyFailed(MaterializationResponsibility &MR) override {
+      return Error::success();
+    }
+
+    Error notifyRemovingResources(ResourceKey K) override {
+      return Error::success();
+    }
+
+    void notifyTransferringResources(ResourceKey DstKey,
+                                     ResourceKey SrcKey) override {}
+
+  private:
+    using InitSymbolDepMap =
+        DenseMap<MaterializationResponsibility *, JITLinkSymbolSet>;
+
+    Error associateJITDylibHeaderSymbol(jitlink::LinkGraph &G,
+                                        MaterializationResponsibility &MR,
+                                        bool Bootstrap);
+
+    Error preserveInitializerSections(jitlink::LinkGraph &G,
+                                      MaterializationResponsibility &MR);
+    Error registerObjectPlatformSections(jitlink::LinkGraph &G, JITDylib &JD);
+    Error registerObjectPlatformSectionsInBootstrap(jitlink::LinkGraph &G,
+                                                    JITDylib &JD);
+
+    std::mutex PluginMutex;
+    COFFPlatform &CP;
+    InitSymbolDepMap InitSymbolDeps;
+  };
+
+  struct JDBootstrapState {
+    JITDylib *JD = nullptr;
+    std::string JDName;
+    ExecutorAddr HeaderAddr;
+    std::list<COFFObjectSectionsMap> ObjectSectionsMaps;
+    SmallVector<std::pair<std::string, ExecutorAddr>> Initializers;
+  };
+
+  static bool supportedTarget(const Triple &TT);
+
+  COFFPlatform(ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
+               JITDylib &PlatformJD,
+               std::unique_ptr<DefinitionGenerator> OrcRuntimeGenerator,
+               Error &Err);
+
+  // Associate MachOPlatform JIT-side runtime support functions with handlers.
+  Error associateRuntimeSupportFunctions(JITDylib &PlatformJD);
+
+  // Records the addresses of runtime symbols used by the platform.
+  Error bootstrapCOFFRuntime(JITDylib &PlatformJD);
+
+  // Run a specific void function if it exists.
+  Error runSymbolIfExists(JITDylib &PlatformJD, StringRef SymbolName);
+
+  // Run collected initializers in boostrap stage.
+  Error runBootstrapInitializers(JDBootstrapState &BState);
+  Error runBootstrapSubsectionInitializers(JDBootstrapState &BState,
+                                           StringRef Start, StringRef End);
+
+  // Build dependency graph of a JITDylib
+  Expected<JITDylibDepMap> buildJDDepMap(JITDylib &JD);
+
+  // Implements rt_pushInitializers by making repeat async lookups for
+  // initializer symbols (each lookup may spawn more initializer symbols if
+  // it pulls in new materializers, e.g. from objects in a static library).
+  void pushInitializersLoop(PushInitializersSendResultFn SendResult,
+                            JITDylibSP JD, JITDylibDepMap &JDDepMap);
+
+  void rt_pushInitializers(PushInitializersSendResultFn SendResult,
+                           ExecutorAddr JDHeaderAddr);
+
+  void rt_lookupSymbol(SendSymbolAddressFn SendResult, ExecutorAddr Handle,
+                       StringRef SymbolName);
+
+  ExecutionSession &ES;
+  ObjectLinkingLayer &ObjLinkingLayer;
+
+  SymbolStringPtr COFFHeaderStartSymbol;
+
+  // State of bootstrap in progress
+  std::map<JITDylib *, JDBootstrapState> JDBootstrapStates;
+  std::atomic<bool> Bootstraping;
+
+  ExecutorAddr orc_rt_coff_platform_bootstrap;
+  ExecutorAddr orc_rt_coff_platform_shutdown;
+  ExecutorAddr orc_rt_coff_register_object_sections;
+  ExecutorAddr orc_rt_coff_deregister_object_sections;
+  ExecutorAddr orc_rt_coff_register_jitdylib;
+  ExecutorAddr orc_rt_coff_deregister_jitdylib;
+
+  DenseMap<JITDylib *, ExecutorAddr> JITDylibToHeaderAddr;
+  DenseMap<ExecutorAddr, JITDylib *> HeaderAddrToJITDylib;
+
+  DenseMap<JITDylib *, SymbolLookupSet> RegisteredInitSymbols;
+
+  std::mutex PlatformMutex;
+};
+
+} // end namespace orc
+} // end namespace llvm
+
+#endif // LLVM_EXECUTIONENGINE_ORC_COFFPLATFORM_H
Index: llvm/include/llvm/ExecutionEngine/Orc/TargetProcess/TargetExecutionUtils.h
===================================================================
--- llvm/include/llvm/ExecutionEngine/Orc/TargetProcess/TargetExecutionUtils.h
+++ llvm/include/llvm/ExecutionEngine/Orc/TargetProcess/TargetExecutionUtils.h
@@ -32,6 +32,9 @@
 int runAsMain(int (*Main)(int, char *[]), ArrayRef<std::string> Args,
               Optional<StringRef> ProgramName = None);
 
+int runAsVoidFunction(int (*Func)(void));
+int runAsIntFunction(int (*Func)(int), int Arg);
+
 } // end namespace orc
 } // end namespace llvm
 
Index: llvm/lib/ExecutionEngine/Orc/CMakeLists.txt
===================================================================
--- llvm/lib/ExecutionEngine/Orc/CMakeLists.txt
+++ llvm/lib/ExecutionEngine/Orc/CMakeLists.txt
@@ -4,6 +4,7 @@
 
 add_llvm_component_library(LLVMOrcJIT
   COFFVCRuntimeSupport.cpp
+  COFFPlatform.cpp
   CompileOnDemandLayer.cpp
   CompileUtils.cpp
   Core.cpp
Index: llvm/lib/ExecutionEngine/Orc/COFFPlatform.cpp
===================================================================
--- /dev/null
+++ llvm/lib/ExecutionEngine/Orc/COFFPlatform.cpp
@@ -0,0 +1,796 @@
+//===------- COFFPlatform.cpp - Utilities for executing COFF 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/COFFPlatform.h"
+#include "llvm/ExecutionEngine/Orc/DebugUtils.h"
+#include "llvm/ExecutionEngine/Orc/ExecutionUtils.h"
+#include "llvm/ExecutionEngine/Orc/LookupAndRecordAddrs.h"
+
+#include "llvm/Object/COFF.h"
+
+#include "llvm/ExecutionEngine/Orc/EPCDynamicLibrarySearchGenerator.h"
+
+#include "llvm/ExecutionEngine/JITLink/x86_64.h"
+
+#define DEBUG_TYPE "orc"
+
+using namespace llvm;
+using namespace llvm::orc;
+using namespace llvm::orc::shared;
+
+namespace llvm {
+namespace orc {
+namespace shared {
+
+using SPSCOFFJITDylibDepInfo = SPSSequence<SPSExecutorAddr>;
+using SPSCOFFJITDylibDepInfoMap =
+    SPSSequence<SPSTuple<SPSExecutorAddr, SPSCOFFJITDylibDepInfo>>;
+using SPSCOFFObjectSectionsMap =
+    SPSSequence<SPSTuple<SPSString, SPSExecutorAddrRange>>;
+using SPSCOFFRegisterObjectSectionsArgs =
+    SPSArgList<SPSExecutorAddr, SPSCOFFObjectSectionsMap, bool>;
+using SPSCOFFDeregisterObjectSectionsArgs =
+    SPSArgList<SPSExecutorAddr, SPSCOFFObjectSectionsMap>;
+
+} // namespace shared
+} // namespace orc
+} // namespace llvm
+namespace {
+
+class COFFHeaderMaterializationUnit : public MaterializationUnit {
+public:
+  COFFHeaderMaterializationUnit(COFFPlatform &CP,
+                                const SymbolStringPtr &HeaderStartSymbol)
+      : MaterializationUnit(createHeaderInterface(CP, HeaderStartSymbol)),
+        CP(CP) {}
+
+  StringRef getName() const override { return "COFFHeaderMU"; }
+
+  void materialize(std::unique_ptr<MaterializationResponsibility> R) override {
+    unsigned PointerSize;
+    support::endianness Endianness;
+    const auto &TT =
+        CP.getExecutionSession().getExecutorProcessControl().getTargetTriple();
+
+    switch (TT.getArch()) {
+    case Triple::x86_64:
+      PointerSize = 8;
+      Endianness = support::endianness::little;
+      break;
+    default:
+      llvm_unreachable("Unrecognized architecture");
+    }
+
+    auto G = std::make_unique<jitlink::LinkGraph>(
+        "<COFFHeaderMU>", TT, PointerSize, Endianness,
+        jitlink::getGenericEdgeKindName);
+    auto &HeaderSection = G->createSection("__header", jitlink::MemProt::Read);
+    auto &HeaderBlock = createHeaderBlock(*G, HeaderSection);
+
+    // Init symbol is __ImageBase symbol.
+    auto &ImageBaseSymbol = G->addDefinedSymbol(
+        HeaderBlock, 0, *R->getInitializerSymbol(), HeaderBlock.getSize(),
+        jitlink::Linkage::Strong, jitlink::Scope::Default, false, true);
+
+    addImageBaseRelocationEdge(HeaderBlock, ImageBaseSymbol);
+
+    CP.getObjectLinkingLayer().emit(std::move(R), std::move(G));
+  }
+
+  void discard(const JITDylib &JD, const SymbolStringPtr &Sym) override {}
+
+private:
+  struct HeaderSymbol {
+    const char *Name;
+    uint64_t Offset;
+  };
+
+  struct NTHeader {
+    support::ulittle32_t PEMagic;
+    object::coff_file_header FileHeader;
+    struct PEHeader {
+      object::pe32plus_header Header;
+      object::data_directory DataDirectory[COFF::NUM_DATA_DIRECTORIES + 1];
+    } OptionalHeader;
+  };
+
+  struct HeaderBlockContent {
+    object::dos_header DOSHeader;
+    NTHeader NTHeader;
+  };
+
+  static jitlink::Block &createHeaderBlock(jitlink::LinkGraph &G,
+                                           jitlink::Section &HeaderSection) {
+    HeaderBlockContent Hdr = {};
+
+    // Set up magic
+    Hdr.DOSHeader.Magic[0] = 'M';
+    Hdr.DOSHeader.Magic[1] = 'Z';
+    Hdr.DOSHeader.AddressOfNewExeHeader =
+        offsetof(HeaderBlockContent, NTHeader);
+    uint32_t PEMagic = *reinterpret_cast<const uint32_t *>(COFF::PEMagic);
+    Hdr.NTHeader.PEMagic = PEMagic;
+    Hdr.NTHeader.OptionalHeader.Header.Magic = COFF::PE32Header::PE32_PLUS;
+
+    switch (G.getTargetTriple().getArch()) {
+    case Triple::x86_64:
+      Hdr.NTHeader.FileHeader.Machine = COFF::IMAGE_FILE_MACHINE_AMD64;
+      break;
+    default:
+      llvm_unreachable("Unrecognized architecture");
+    }
+
+    auto HeaderContent = G.allocateString(
+        StringRef(reinterpret_cast<const char *>(&Hdr), sizeof(Hdr)));
+
+    return G.createContentBlock(HeaderSection, HeaderContent, ExecutorAddr(), 8,
+                                0);
+  }
+
+  static void addImageBaseRelocationEdge(jitlink::Block &B,
+                                         jitlink::Symbol &ImageBase) {
+    auto ImageBaseOffset = offsetof(HeaderBlockContent, NTHeader) +
+                           offsetof(NTHeader, OptionalHeader) +
+                           offsetof(object::pe32plus_header, ImageBase);
+    B.addEdge(jitlink::x86_64::Pointer64, ImageBaseOffset, ImageBase, 0);
+  }
+
+  static MaterializationUnit::Interface
+  createHeaderInterface(COFFPlatform &MOP,
+                        const SymbolStringPtr &HeaderStartSymbol) {
+    SymbolFlagsMap HeaderSymbolFlags;
+
+    HeaderSymbolFlags[HeaderStartSymbol] = JITSymbolFlags::Exported;
+
+    return MaterializationUnit::Interface(std::move(HeaderSymbolFlags),
+                                          HeaderStartSymbol);
+  }
+
+  COFFPlatform &CP;
+};
+
+} // end anonymous namespace
+
+namespace llvm {
+namespace orc {
+
+Expected<std::unique_ptr<COFFPlatform>>
+COFFPlatform::Create(ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
+                     JITDylib &PlatformJD, const char *OrcRuntimePath,
+                     std::vector<std::string> &ImportedLibraries,
+                     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 COFFPlatform 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().JITDispatchFunction.getValue(),
+             JITSymbolFlags::Exported}},
+           {ES.intern("__orc_rt_jit_dispatch_ctx"),
+            {EPC.getJITDispatchInfo().JITDispatchContext.getValue(),
+             JITSymbolFlags::Exported}}})))
+    return std::move(Err);
+
+  // Create a generator for the ORC runtime archive.
+  auto OrcRuntimeArchiveGenerator =
+      StaticLibraryDefinitionGenerator::Load(ObjLinkingLayer, OrcRuntimePath);
+  if (!OrcRuntimeArchiveGenerator)
+    return OrcRuntimeArchiveGenerator.takeError();
+
+  ImportedLibraries.clear();
+  for (auto Lib : (*OrcRuntimeArchiveGenerator)->getImportedDynamicLibraries())
+    ImportedLibraries.push_back(Lib);
+
+  // Create the instance.
+  Error Err = Error::success();
+  auto P = std::unique_ptr<COFFPlatform>(
+      new COFFPlatform(ES, ObjLinkingLayer, PlatformJD,
+                       std::move(*OrcRuntimeArchiveGenerator), Err));
+  if (Err)
+    return std::move(Err);
+  return std::move(P);
+}
+
+Error COFFPlatform::setupJITDylib(JITDylib &JD) {
+  if (auto Err = JD.define(std::make_unique<COFFHeaderMaterializationUnit>(
+          *this, COFFHeaderStartSymbol)))
+    return Err;
+
+  return ES.lookup({&JD}, COFFHeaderStartSymbol).takeError();
+}
+
+Error COFFPlatform::teardownJITDylib(JITDylib &JD) {
+  std::lock_guard<std::mutex> Lock(PlatformMutex);
+  auto I = JITDylibToHeaderAddr.find(&JD);
+  if (I != JITDylibToHeaderAddr.end()) {
+    assert(HeaderAddrToJITDylib.count(I->second) &&
+           "HeaderAddrToJITDylib missing entry");
+    HeaderAddrToJITDylib.erase(I->second);
+    JITDylibToHeaderAddr.erase(I);
+  }
+  return Error::success();
+}
+
+Error COFFPlatform::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() << "COFFPlatform: Registered init symbol " << *InitSym << " for MU "
+           << MU.getName() << "\n";
+  });
+  return Error::success();
+}
+
+Error COFFPlatform::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 COFFPlatform::standardPlatformAliases(ExecutionSession &ES) {
+  SymbolAliasMap Aliases;
+  addAliases(ES, Aliases, requiredCXXAliases());
+  addAliases(ES, Aliases, standardRuntimeUtilityAliases());
+  return Aliases;
+}
+
+ArrayRef<std::pair<const char *, const char *>>
+COFFPlatform::requiredCXXAliases() {
+  static const std::pair<const char *, const char *> RequiredCXXAliases[] = {
+      {"_CxxThrowException", "__orc_rt_coff_cxx_throw_exception"},
+  };
+
+  return ArrayRef<std::pair<const char *, const char *>>(RequiredCXXAliases);
+}
+
+ArrayRef<std::pair<const char *, const char *>>
+COFFPlatform::standardRuntimeUtilityAliases() {
+  static const std::pair<const char *, const char *>
+      StandardRuntimeUtilityAliases[] = {
+          {"__orc_rt_run_program", "__orc_rt_coff_run_program"},
+          {"__orc_rt_jit_dlerror", "__orc_rt_coff_jit_dlerror"},
+          {"__orc_rt_jit_dlopen", "__orc_rt_coff_jit_dlopen"},
+          {"__orc_rt_jit_dlclose", "__orc_rt_coff_jit_dlclose"},
+          {"__orc_rt_jit_dlsym", "__orc_rt_coff_jit_dlsym"},
+          {"__orc_rt_log_error", "__orc_rt_log_error_to_stderr"}};
+
+  return ArrayRef<std::pair<const char *, const char *>>(
+      StandardRuntimeUtilityAliases);
+}
+
+bool COFFPlatform::supportedTarget(const Triple &TT) {
+  switch (TT.getArch()) {
+  case Triple::x86_64:
+    return true;
+  default:
+    return false;
+  }
+}
+
+COFFPlatform::COFFPlatform(
+    ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
+    JITDylib &PlatformJD,
+    std::unique_ptr<DefinitionGenerator> OrcRuntimeGenerator, Error &Err)
+    : ES(ES), ObjLinkingLayer(ObjLinkingLayer),
+      COFFHeaderStartSymbol(ES.intern("__ImageBase")) {
+  ErrorAsOutParameter _(&Err);
+
+  Bootstraping.store(true);
+  ObjLinkingLayer.addPlugin(std::make_unique<COFFPlatformPlugin>(*this));
+
+  // 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;
+  }
+
+  PlatformJD.addGenerator(std::move(OrcRuntimeGenerator));
+}
+
+Error COFFPlatform::bootstrap(JITDylib &PlatformJD) {
+  // Associate wrapper function tags with JIT-side function implementations.
+  if (auto Err = associateRuntimeSupportFunctions(PlatformJD)) {
+    return Err;
+  }
+
+  // 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 Err = bootstrapCOFFRuntime(PlatformJD)) {
+    return Err;
+  }
+
+  Bootstraping.store(false);
+  JDBootstrapStates.clear();
+
+  return Error::success();
+}
+
+Expected<COFFPlatform::JITDylibDepMap>
+COFFPlatform::buildJDDepMap(JITDylib &JD) {
+  return ES.runSessionLocked([&]() -> Expected<JITDylibDepMap> {
+    JITDylibDepMap JDDepMap;
+
+    SmallVector<JITDylib *, 16> Worklist({&JD});
+    while (!Worklist.empty()) {
+      auto CurJD = Worklist.back();
+      Worklist.pop_back();
+      {
+        std::lock_guard<std::mutex> Lock(PlatformMutex);
+        if (!JITDylibToHeaderAddr.count(CurJD))
+          return make_error<StringError>(
+              "JITDylib unregistered to COFFPlatform detected in LinkOrder",
+              inconvertibleErrorCode());
+      }
+
+      auto &DM = JDDepMap[CurJD];
+      CurJD->withLinkOrderDo([&](const JITDylibSearchOrder &O) {
+        DM.reserve(O.size());
+        for (auto &KV : O) {
+          if (KV.first == CurJD)
+            continue;
+          DM.push_back(KV.first);
+          // Push unvisited entry.
+          if (!JDDepMap.count(KV.first)) {
+            Worklist.push_back(KV.first);
+            JDDepMap[KV.first] = {};
+          }
+        }
+      });
+    }
+    return std::move(JDDepMap);
+  });
+}
+
+void COFFPlatform::pushInitializersLoop(PushInitializersSendResultFn SendResult,
+                                        JITDylibSP JD,
+                                        JITDylibDepMap &JDDepMap) {
+  SmallVector<JITDylib *, 16> Worklist({JD.get()});
+  DenseSet<JITDylib *> Visited({JD.get()});
+  DenseMap<JITDylib *, SymbolLookupSet> NewInitSymbols;
+  ES.runSessionLocked([&]() {
+    while (!Worklist.empty()) {
+      auto CurJD = Worklist.back();
+      Worklist.pop_back();
+
+      auto RISItr = RegisteredInitSymbols.find(CurJD);
+      if (RISItr != RegisteredInitSymbols.end()) {
+        NewInitSymbols[CurJD] = std::move(RISItr->second);
+        RegisteredInitSymbols.erase(RISItr);
+      }
+
+      for (auto DepJD : JDDepMap[CurJD])
+        if (!Visited.count(DepJD)) {
+          Worklist.push_back(DepJD);
+          Visited.insert(CurJD);
+        }
+    }
+
+  });
+
+  // If there are no further init symbols to look up then send the link order
+  // (as a list of header addresses) to the caller.
+  if (NewInitSymbols.empty()) {
+    // Build the dep info map to return.
+    COFFJITDylibDepInfoMap DIM;
+    DIM.reserve(JDDepMap.size());
+    for (auto &KV : JDDepMap) {
+      COFFJITDylibDepInfo DepInfo;
+      DepInfo.reserve(KV.second.size());
+      for (auto &Dep : KV.second) {
+        std::lock_guard<std::mutex> Lock(PlatformMutex);
+        DepInfo.push_back(JITDylibToHeaderAddr[Dep]);
+      }
+      {
+        std::lock_guard<std::mutex> Lock(PlatformMutex);
+        auto H = JITDylibToHeaderAddr[KV.first];
+        DIM.push_back(std::make_pair(H, std::move(DepInfo)));
+      }
+    }
+    SendResult(DIM);
+    return;
+  }
+
+  // Otherwise issue a lookup and re-run this phase when it completes.
+  lookupInitSymbolsAsync(
+      [this, SendResult = std::move(SendResult), &JD,
+       JDDepMap = std::move(JDDepMap)](Error Err) mutable {
+        if (Err)
+          SendResult(std::move(Err));
+        else
+          pushInitializersLoop(std::move(SendResult), JD, JDDepMap);
+      },
+      ES, std::move(NewInitSymbols));
+}
+
+void COFFPlatform::rt_pushInitializers(PushInitializersSendResultFn SendResult,
+                                       ExecutorAddr JDHeaderAddr) {
+  JITDylibSP JD;
+  {
+    std::lock_guard<std::mutex> Lock(PlatformMutex);
+    auto I = HeaderAddrToJITDylib.find(JDHeaderAddr);
+    if (I != HeaderAddrToJITDylib.end())
+      JD = I->second;
+  }
+
+  LLVM_DEBUG({
+    dbgs() << "COFFPlatform::rt_pushInitializers(" << JDHeaderAddr << ") ";
+    if (JD)
+      dbgs() << "pushing initializers for " << JD->getName() << "\n";
+    else
+      dbgs() << "No JITDylib for header address.\n";
+  });
+
+  if (!JD) {
+    SendResult(
+        make_error<StringError>("No JITDylib with header addr " +
+                                    formatv("{0:x}", JDHeaderAddr.getValue()),
+                                inconvertibleErrorCode()));
+    return;
+  }
+
+  auto JDDepMap = buildJDDepMap(*JD);
+  if (!JDDepMap) {
+    SendResult(JDDepMap.takeError());
+    return;
+  }
+
+  pushInitializersLoop(std::move(SendResult), JD, *JDDepMap);
+}
+
+void COFFPlatform::rt_lookupSymbol(SendSymbolAddressFn SendResult,
+                                   ExecutorAddr Handle, StringRef SymbolName) {
+  LLVM_DEBUG({
+    dbgs() << "COFFPlatform::rt_lookupSymbol(\""
+           << formatv("{0:x}", Handle.getValue()) << "\")\n";
+  });
+
+  JITDylib *JD = nullptr;
+
+  {
+    std::lock_guard<std::mutex> Lock(PlatformMutex);
+    auto I = HeaderAddrToJITDylib.find(Handle);
+    if (I != HeaderAddrToJITDylib.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(ExecutorAddr(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 COFFPlatform::associateRuntimeSupportFunctions(JITDylib &PlatformJD) {
+  ExecutionSession::JITDispatchHandlerAssociationMap WFs;
+
+  using LookupSymbolSPSSig =
+      SPSExpected<SPSExecutorAddr>(SPSExecutorAddr, SPSString);
+  WFs[ES.intern("__orc_rt_coff_symbol_lookup_tag")] =
+      ES.wrapAsyncWithSPS<LookupSymbolSPSSig>(this,
+                                              &COFFPlatform::rt_lookupSymbol);
+  using PushInitializersSPSSig =
+      SPSExpected<SPSCOFFJITDylibDepInfoMap>(SPSExecutorAddr);
+  WFs[ES.intern("__orc_rt_coff_push_initializers_tag")] =
+      ES.wrapAsyncWithSPS<PushInitializersSPSSig>(
+          this, &COFFPlatform::rt_pushInitializers);
+
+  return ES.registerJITDispatchHandlers(PlatformJD, std::move(WFs));
+}
+
+Error COFFPlatform::runBootstrapInitializers(JDBootstrapState &BState) {
+  llvm::sort(BState.Initializers);
+  if (auto Err =
+          runBootstrapSubsectionInitializers(BState, ".CRT$XIA", ".CRT$XIZ"))
+    return Err;
+
+  if (auto Err = runSymbolIfExists(*BState.JD, "__run_after_c_init"))
+    return Err;
+
+  if (auto Err =
+          runBootstrapSubsectionInitializers(BState, ".CRT$XCA", ".CRT$XCZ"))
+    return Err;
+  return Error::success();
+}
+
+Error COFFPlatform::runBootstrapSubsectionInitializers(JDBootstrapState &BState,
+                                                       StringRef Start,
+                                                       StringRef End) {
+  for (auto &Initializer : BState.Initializers)
+    if (Initializer.first >= Start && Initializer.first <= End &&
+        Initializer.second) {
+      auto Res =
+          ES.getExecutorProcessControl().runAsVoidFunction(Initializer.second);
+      if (!Res)
+        return Res.takeError();
+    }
+  return Error::success();
+}
+
+Error COFFPlatform::bootstrapCOFFRuntime(JITDylib &PlatformJD) {
+  // Lookup of runtime symbols causes the collection of initializers if
+  // it's static linking setting.
+  if (auto Err = lookupAndRecordAddrs(
+          ES, LookupKind::Static, makeJITDylibSearchOrder(&PlatformJD),
+          {
+              {ES.intern("__orc_rt_coff_platform_bootstrap"),
+               &orc_rt_coff_platform_bootstrap},
+              {ES.intern("__orc_rt_coff_platform_shutdown"),
+               &orc_rt_coff_platform_shutdown},
+              {ES.intern("__orc_rt_coff_register_jitdylib"),
+               &orc_rt_coff_register_jitdylib},
+              {ES.intern("__orc_rt_coff_deregister_jitdylib"),
+               &orc_rt_coff_deregister_jitdylib},
+              {ES.intern("__orc_rt_coff_register_object_sections"),
+               &orc_rt_coff_register_object_sections},
+              {ES.intern("__orc_rt_coff_deregister_object_sections"),
+               &orc_rt_coff_deregister_object_sections},
+          }))
+    return Err;
+
+  // Run static initializers collected in bootstrap stage.
+  for (auto KV : JDBootstrapStates) {
+    auto &JDBState = KV.second;
+    if (auto Err = runBootstrapInitializers(JDBState))
+      return Err;
+  }
+
+  // Call bootstrap functions
+  if (auto Err = ES.callSPSWrapper<void()>(orc_rt_coff_platform_bootstrap))
+    return Err;
+
+  // Do the pending jitdylib registration actions that we couldn't do
+  // because orc runtime was not linked fully.
+  for (auto KV : JDBootstrapStates) {
+    auto &JDBState = KV.second;
+    if (auto Err = ES.callSPSWrapper<void(SPSString, SPSExecutorAddr)>(
+            orc_rt_coff_register_jitdylib, JDBState.JDName,
+            JDBState.HeaderAddr))
+      return Err;
+
+    for (auto &ObjSectionMap : JDBState.ObjectSectionsMaps)
+      if (auto Err = ES.callSPSWrapper<void(SPSExecutorAddr,
+                                            SPSCOFFObjectSectionsMap, bool)>(
+              orc_rt_coff_register_object_sections, JDBState.HeaderAddr,
+              ObjSectionMap, false))
+        return Err;
+  }
+
+  return Error::success();
+}
+
+Error COFFPlatform::runSymbolIfExists(JITDylib &PlatformJD,
+                                      StringRef SymbolName) {
+  ExecutorAddr jit_function;
+  auto AfterCLookupErr = lookupAndRecordAddrs(
+      ES, LookupKind::Static, makeJITDylibSearchOrder(&PlatformJD),
+      {{ES.intern(SymbolName), &jit_function}});
+  if (!AfterCLookupErr) {
+    auto Res = ES.getExecutorProcessControl().runAsVoidFunction(jit_function);
+    if (!Res)
+      return Res.takeError();
+    return Error::success();
+  }
+  if (!AfterCLookupErr.isA<SymbolsNotFound>())
+    return AfterCLookupErr;
+  consumeError(std::move(AfterCLookupErr));
+  return Error::success();
+}
+
+void COFFPlatform::COFFPlatformPlugin::modifyPassConfig(
+    MaterializationResponsibility &MR, jitlink::LinkGraph &LG,
+    jitlink::PassConfiguration &Config) {
+  auto IsBootstraping = CP.Bootstraping.load();
+
+  if (auto InitSymbol = MR.getInitializerSymbol()) {
+    if (InitSymbol == CP.COFFHeaderStartSymbol) {
+      Config.PostAllocationPasses.push_back(
+          [this, &MR, IsBootstraping](jitlink::LinkGraph &G) {
+            return associateJITDylibHeaderSymbol(G, MR, IsBootstraping);
+          });
+      return;
+    }
+    Config.PrePrunePasses.push_back([this, &MR](jitlink::LinkGraph &G) {
+      return preserveInitializerSections(G, MR);
+    });
+  }
+
+  if (!IsBootstraping)
+    Config.PostFixupPasses.push_back(
+        [this, &JD = MR.getTargetJITDylib()](jitlink::LinkGraph &G) {
+          return registerObjectPlatformSections(G, JD);
+        });
+  else
+    Config.PostFixupPasses.push_back(
+        [this, &JD = MR.getTargetJITDylib()](jitlink::LinkGraph &G) {
+          return registerObjectPlatformSectionsInBootstrap(G, JD);
+        });
+}
+
+ObjectLinkingLayer::Plugin::SyntheticSymbolDependenciesMap
+COFFPlatform::COFFPlatformPlugin::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();
+}
+
+Error COFFPlatform::COFFPlatformPlugin::associateJITDylibHeaderSymbol(
+    jitlink::LinkGraph &G, MaterializationResponsibility &MR,
+    bool IsBootstraping) {
+  auto I = llvm::find_if(G.defined_symbols(), [this](jitlink::Symbol *Sym) {
+    return Sym->getName() == *CP.COFFHeaderStartSymbol;
+  });
+  assert(I != G.defined_symbols().end() && "Missing COFF header start symbol");
+
+  auto &JD = MR.getTargetJITDylib();
+  std::lock_guard<std::mutex> Lock(CP.PlatformMutex);
+  auto HeaderAddr = (*I)->getAddress();
+  CP.JITDylibToHeaderAddr[&JD] = HeaderAddr;
+  CP.HeaderAddrToJITDylib[HeaderAddr] = &JD;
+  if (!IsBootstraping) {
+    G.allocActions().push_back(
+        {cantFail(WrapperFunctionCall::Create<
+                  SPSArgList<SPSString, SPSExecutorAddr>>(
+             CP.orc_rt_coff_register_jitdylib, JD.getName(), HeaderAddr)),
+         cantFail(WrapperFunctionCall::Create<SPSArgList<SPSExecutorAddr>>(
+             CP.orc_rt_coff_deregister_jitdylib, HeaderAddr))});
+  } else {
+    G.allocActions().push_back(
+        {{},
+         cantFail(WrapperFunctionCall::Create<SPSArgList<SPSExecutorAddr>>(
+             CP.orc_rt_coff_deregister_jitdylib, HeaderAddr))});
+    JDBootstrapState BState;
+    BState.JD = &JD;
+    BState.JDName = JD.getName();
+    BState.HeaderAddr = HeaderAddr;
+    CP.JDBootstrapStates.emplace(&JD, BState);
+  }
+
+  return Error::success();
+}
+
+Error COFFPlatform::COFFPlatformPlugin::registerObjectPlatformSections(
+    jitlink::LinkGraph &G, JITDylib &JD) {
+  COFFObjectSectionsMap ObjSecs;
+  auto HeaderAddr = CP.JITDylibToHeaderAddr[&JD];
+  for (auto &S : G.sections()) {
+    jitlink::SectionRange Range(S);
+    if (Range.getSize())
+      ObjSecs.push_back(std::make_pair(S.getName().str(), Range.getRange()));
+  }
+
+  G.allocActions().push_back(
+      {cantFail(WrapperFunctionCall::Create<SPSCOFFRegisterObjectSectionsArgs>(
+           CP.orc_rt_coff_register_object_sections, HeaderAddr, ObjSecs, true)),
+       cantFail(
+           WrapperFunctionCall::Create<SPSCOFFDeregisterObjectSectionsArgs>(
+               CP.orc_rt_coff_deregister_object_sections, HeaderAddr,
+               ObjSecs))});
+
+  return Error::success();
+}
+
+Error COFFPlatform::COFFPlatformPlugin::preserveInitializerSections(
+    jitlink::LinkGraph &G, MaterializationResponsibility &MR) {
+  JITLinkSymbolSet InitSectionSymbols;
+  for (auto &Sec : G.sections())
+    if (COFFPlatform::isInitializerSection(Sec.getName()))
+      for (auto *B : Sec.blocks())
+        if (!B->edges_empty())
+          InitSectionSymbols.insert(
+              &G.addAnonymousSymbol(*B, 0, 0, false, true));
+
+  std::lock_guard<std::mutex> Lock(PluginMutex);
+  InitSymbolDeps[&MR] = InitSectionSymbols;
+  return Error::success();
+}
+
+Error COFFPlatform::COFFPlatformPlugin::
+    registerObjectPlatformSectionsInBootstrap(jitlink::LinkGraph &G,
+                                              JITDylib &JD) {
+  std::lock_guard<std::mutex> Lock(CP.PlatformMutex);
+  auto HeaderAddr = CP.JITDylibToHeaderAddr[&JD];
+  COFFObjectSectionsMap ObjSecs;
+  for (auto &S : G.sections()) {
+    jitlink::SectionRange Range(S);
+    if (Range.getSize())
+      ObjSecs.push_back(std::make_pair(S.getName().str(), Range.getRange()));
+  }
+
+  G.allocActions().push_back(
+      {{},
+       cantFail(
+           WrapperFunctionCall::Create<SPSCOFFDeregisterObjectSectionsArgs>(
+               CP.orc_rt_coff_deregister_object_sections, HeaderAddr,
+               ObjSecs))});
+
+  auto &BState = CP.JDBootstrapStates[&JD];
+  BState.ObjectSectionsMaps.push_back(std::move(ObjSecs));
+
+  // Collect static initializers
+  for (auto &S : G.sections())
+    if (COFFPlatform::isInitializerSection(S.getName()))
+      for (auto *B : S.blocks()) {
+        if (B->edges_empty())
+          continue;
+        for (auto &E : B->edges())
+          BState.Initializers.push_back(std::make_pair(
+              S.getName().str(),
+              ExecutorAddr(E.getTarget().getAddress() + E.getAddend())));
+      }
+
+  return Error::success();
+}
+
+} // End namespace orc.
+} // End namespace llvm.
Index: llvm/lib/ExecutionEngine/Orc/ExecutorProcessControl.cpp
===================================================================
--- llvm/lib/ExecutionEngine/Orc/ExecutorProcessControl.cpp
+++ llvm/lib/ExecutionEngine/Orc/ExecutorProcessControl.cpp
@@ -124,13 +124,13 @@
 Expected<int32_t>
 SelfExecutorProcessControl::runAsVoidFunction(ExecutorAddr VoidFnAddr) {
   using VoidTy = int (*)();
-  return VoidFnAddr.toPtr<VoidTy>()();
+  return orc::runAsVoidFunction(VoidFnAddr.toPtr<VoidTy>());
 }
 
 Expected<int32_t>
 SelfExecutorProcessControl::runAsIntFunction(ExecutorAddr IntFnAddr, int Arg) {
   using IntTy = int (*)(int);
-  return IntFnAddr.toPtr<IntTy>()(Arg);
+  return orc::runAsIntFunction(IntFnAddr.toPtr<IntTy>(), Arg);
 }
 
 void SelfExecutorProcessControl::callWrapperAsync(ExecutorAddr WrapperFnAddr,
Index: llvm/lib/ExecutionEngine/Orc/ObjectFileInterface.cpp
===================================================================
--- llvm/lib/ExecutionEngine/Orc/ObjectFileInterface.cpp
+++ llvm/lib/ExecutionEngine/Orc/ObjectFileInterface.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ExecutionEngine/Orc/ObjectFileInterface.h"
+#include "llvm/ExecutionEngine/Orc/COFFPlatform.h"
 #include "llvm/ExecutionEngine/Orc/ELFNixPlatform.h"
 #include "llvm/ExecutionEngine/Orc/MachOPlatform.h"
 #include "llvm/Object/COFF.h"
@@ -214,7 +215,15 @@
     I.SymbolFlags[ES.intern(*Name)] = std::move(*SymFlags);
   }
 
-  // FIXME: handle init symbols
+  SymbolStringPtr InitSymbol;
+  for (auto &Sec : Obj.sections()) {
+    if (auto SecName = Sec.getName()) {
+      if (COFFPlatform::isInitializerSection(*SecName)) {
+        addInitSymbol(I, ES, Obj.getFileName());
+        break;
+      }
+    }
+  }
 
   return I;
 }
Index: llvm/lib/ExecutionEngine/Orc/TargetProcess/TargetExecutionUtils.cpp
===================================================================
--- llvm/lib/ExecutionEngine/Orc/TargetProcess/TargetExecutionUtils.cpp
+++ llvm/lib/ExecutionEngine/Orc/TargetProcess/TargetExecutionUtils.cpp
@@ -39,5 +39,9 @@
   return Main(Args.size() + !!ProgramName, ArgV.data());
 }
 
+int runAsVoidFunction(int (*Func)(void)) { return Func(); }
+
+int runAsIntFunction(int (*Func)(int), int Arg) { return Func(Arg); }
+
 } // End namespace orc.
 } // End namespace llvm.
Index: llvm/tools/llvm-jitlink/llvm-jitlink.h
===================================================================
--- llvm/tools/llvm-jitlink/llvm-jitlink.h
+++ llvm/tools/llvm-jitlink/llvm-jitlink.h
@@ -53,9 +53,16 @@
     StringMap<MemoryRegionInfo> GOTEntryInfos;
   };
 
+  using DynLibJDMap = std::map<std::string, orc::JITDylib *>;
+  using KnownDynLibPathMap = std::map<std::string, std::string>;
   using SymbolInfoMap = StringMap<MemoryRegionInfo>;
   using FileInfoMap = StringMap<FileInfo>;
 
+  Expected<orc::JITDylib *> getOrLoadDynamicLibrary(StringRef LibName,
+                                                    StringRef LibPath);
+  Error loadAndLinkDynamicLibrary(orc::JITDylib &JD, StringRef LibName,
+                                  StringRef LibPath);
+
   Expected<FileInfo &> findFileInfo(StringRef FileName);
   Expected<MemoryRegionInfo &> findSectionInfo(StringRef FileName,
                                                StringRef SectionName);
@@ -68,6 +75,9 @@
   Expected<MemoryRegionInfo &> findSymbolInfo(StringRef SymbolName,
                                               Twine ErrorMsgStem);
 
+  DynLibJDMap DynLibJDs;
+  KnownDynLibPathMap KnownDynLibPaths;
+
   SymbolInfoMap SymbolInfos;
   FileInfoMap FileInfos;
   uint64_t SizeBeforePruning = 0;
Index: llvm/tools/llvm-jitlink/llvm-jitlink.cpp
===================================================================
--- llvm/tools/llvm-jitlink/llvm-jitlink.cpp
+++ llvm/tools/llvm-jitlink/llvm-jitlink.cpp
@@ -15,6 +15,8 @@
 #include "llvm-jitlink.h"
 
 #include "llvm/BinaryFormat/Magic.h"
+#include "llvm/ExecutionEngine/Orc/COFFPlatform.h"
+#include "llvm/ExecutionEngine/Orc/COFFVCRuntimeSupport.h"
 #include "llvm/ExecutionEngine/Orc/DebugObjectManagerPlugin.h"
 #include "llvm/ExecutionEngine/Orc/DebuggerSupportPlugin.h"
 #include "llvm/ExecutionEngine/Orc/ELFNixPlatform.h"
@@ -809,10 +811,8 @@
   LLVM_DEBUG(dbgs() << "Loading dylibs...\n");
   for (const auto &Dylib : Dylibs) {
     LLVM_DEBUG(dbgs() << "  " << Dylib << "\n");
-    auto G = orc::EPCDynamicLibrarySearchGenerator::Load(S.ES, Dylib.c_str());
-    if (!G)
-      return G.takeError();
-    S.MainJD->addGenerator(std::move(*G));
+    if (auto Err = S.loadAndLinkDynamicLibrary(*S.MainJD, Dylib, Dylib))
+      return Err;
   }
 
   return Error::success();
@@ -1066,8 +1066,22 @@
 
   if (!NoProcessSymbols)
     ExitOnErr(loadProcessSymbols(*this));
+  else
+    ExitOnErr(MainJD->define(absoluteSymbols(
+        {{ES.intern("llvm_jitlink_setTestResultOverride"),
+          {pointerToJITTargetAddress(llvm_jitlink_setTestResultOverride),
+           JITSymbolFlags::Exported}}})));
+
   ExitOnErr(loadDylibs(*this));
 
+  auto LoadDLLFile = [&](StringRef DLLName) -> Error {
+    if (!DLLName.endswith_insensitive(".dll"))
+      return make_error<StringError>("DLLName not ending with .dll",
+                                     inconvertibleErrorCode());
+    return loadAndLinkDynamicLibrary(*MainJD, DLLName.drop_back(strlen(".dll")),
+                                     DLLName);
+  };
+
   auto &TT = ES.getExecutorProcessControl().getTargetTriple();
 
   if (DebuggerSupport && TT.isOSBinFormatMachO())
@@ -1091,6 +1105,49 @@
       Err = P.takeError();
       return;
     }
+  } else if (TT.isOSBinFormatCOFF() && !OrcRuntime.empty()) {
+    auto LoadDynLibrary = [&](JITDylib &JD, StringRef DLLName) -> Error {
+      return LoadDLLFile(DLLName);
+    };
+    auto VCRT = COFFVCRuntimeBootstrapper::Create(ES, ObjLayer,
+                                                  std::move(LoadDynLibrary));
+    if (!VCRT) {
+      Err = VCRT.takeError();
+      return;
+    }
+
+    std::vector<std::string> ImportedLibraries;
+    if (auto P = COFFPlatform::Create(ES, ObjLayer, *MainJD, OrcRuntime.c_str(),
+                                      ImportedLibraries)) {
+      // Set platform early to register jitdylib of dynamic libraries.
+      auto &CP = **P;
+      ES.setPlatform(std::move(*P));
+
+      for (auto DLLName : ImportedLibraries)
+        if (auto E2 = LoadDLLFile(DLLName)) {
+          Err = std::move(E2);
+          return;
+        }
+
+      if (auto E2 = (*VCRT)->loadStaticVCRuntime(*MainJD)) {
+        Err = std::move(E2);
+        return;
+      }
+
+      if (auto E2 = (*VCRT)->initializeStaticVCRuntime(*MainJD)) {
+        Err = std::move(E2);
+        return;
+      }
+
+      if (auto E2 = CP.bootstrap(*MainJD)) {
+        Err = std::move(E2);
+        return;
+      }
+
+    } else {
+      Err = P.takeError();
+      return;
+    }
   } else if (TT.isOSBinFormatELF()) {
     if (!NoExec)
       ObjLayer.addPlugin(std::make_unique<EHFrameRegistrationPlugin>(
@@ -1190,6 +1247,47 @@
     PassConfig.PostPrunePasses.push_back(addSelfRelocations);
 }
 
+Expected<JITDylib *> Session::getOrLoadDynamicLibrary(StringRef LibName,
+                                                      StringRef LibPath) {
+  auto It = DynLibJDs.find(LibName.str());
+  if (It != DynLibJDs.end()) {
+    LLVM_DEBUG({
+      if (LibPath != KnownDynLibPaths[LibName.str()])
+        dbgs() << "Warning: dynamic library from " << LibPath
+               << " is ignored.\n";
+    });
+    return It->second;
+  }
+  auto G = EPCDynamicLibrarySearchGenerator::Load(ES, LibPath.data());
+  if (!G)
+    return G.takeError();
+  auto JD = ES.createJITDylib(LibName.str());
+  if (!JD)
+    return JD.takeError();
+
+  JD->addGenerator(std::move(*G));
+  DynLibJDs.emplace(LibName.str(), &*JD);
+  KnownDynLibPaths.emplace(LibName.str(), LibPath.str());
+  LLVM_DEBUG({
+    dbgs() << "Loaded dynamic library " << LibPath.data() << " for " << LibName
+           << "\n";
+  });
+  return &*JD;
+}
+
+Error Session::loadAndLinkDynamicLibrary(JITDylib &JD, StringRef LibName,
+                                         StringRef LibPath) {
+  auto DL = getOrLoadDynamicLibrary(LibName, LibPath);
+  if (!DL)
+    return DL.takeError();
+  JD.addToLinkOrder(**DL);
+  LLVM_DEBUG({
+    dbgs() << "Linking dynamic library " << LibName << " to " << JD.getName()
+           << "\n";
+  });
+  return Error::success();
+}
+
 Expected<Session::FileInfo &> Session::findFileInfo(StringRef FileName) {
   auto FileInfoItr = FileInfos.find(FileName);
   if (FileInfoItr == FileInfos.end())
@@ -1761,18 +1859,9 @@
         case file_magic::pecoff_executable:
         case file_magic::elf_shared_object:
         case file_magic::macho_dynamically_linked_shared_lib: {
-          // TODO: On first reference to LibPath this should create a JITDylib
-          // with a generator and add it to JD's links-against list. Subsquent
-          // references should use the JITDylib created on the first
-          // reference.
-          auto G = EPCDynamicLibrarySearchGenerator::Load(S.ES, LibPath.data());
-          if (!G)
-            return G.takeError();
-          LLVM_DEBUG({
-            dbgs() << "Adding generator for dynamic library " << LibPath.data()
-                   << " to " << JD.getName() << "\n";
-          });
-          JD.addGenerator(std::move(*G));
+          if (auto Err =
+                  S.loadAndLinkDynamicLibrary(JD, LL.LibName, LibPath.data()))
+            return Err;
           break;
         }
         case file_magic::archive: