Add support for SEH unwinding on Windows.

Summary:
I've tested this implementation on x86-64 to ensure that it works. All
`libc++abi` tests pass, as do all `libc++` exception-related tests. ARM
still remains to be implemented (@compnerd?).

Special thanks to KJK::Hyperion for his excellent series of articles on
how EH works on x86-64 Windows. (Seriously, check it out. It's awesome.)

I'm actually not sure if this should go in as is. I particularly don't
like that I duplicated the UnwindCursor class for this special case.

Reviewers: mstorsjo, rnk, compnerd, smeenai, javed.absar

Subscribers: mgorny, kristof.beyls, christof, chrib, cfe-commits, compnerd, llvm-commits

Differential Revision: https://reviews.llvm.org/D50564

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@341125 91177308-0d34-0410-b5e6-96231b3b80d8

9 files changed, 1091 insertions, 11 deletions

diff --git a/include/__libunwind_config.h b/include/__libunwind_config.h
index 5464e36..0704946 100644
--- a/include/__libunwind_config.h
+++ b/include/__libunwind_config.h
@@ -34,7 +34,11 @@
 #  define _LIBUNWIND_TARGET_X86_64 1
 #  if defined(_WIN64)
 #    define _LIBUNWIND_CONTEXT_SIZE 54
-#    define _LIBUNWIND_CURSOR_SIZE 66
+#    ifdef __SEH__
+#      define _LIBUNWIND_CURSOR_SIZE 204
+#    else
+#      define _LIBUNWIND_CURSOR_SIZE 66
+#    endif
 #  else
 #    define _LIBUNWIND_CONTEXT_SIZE 21
 #    define _LIBUNWIND_CURSOR_SIZE 33
@@ -57,7 +61,10 @@
 #  define _LIBUNWIND_HIGHEST_DWARF_REGISTER _LIBUNWIND_HIGHEST_DWARF_REGISTER_ARM64
 # elif defined(__arm__)
 #  define _LIBUNWIND_TARGET_ARM 1
-#  if defined(__ARM_WMMX)
+#  if defined(__SEH__)
+#    define _LIBUNWIND_CONTEXT_SIZE 42
+#    define _LIBUNWIND_CURSOR_SIZE 85
+#  elif defined(__ARM_WMMX)
 #    define _LIBUNWIND_CONTEXT_SIZE 61
 #    define _LIBUNWIND_CURSOR_SIZE 68
 #  else
diff --git a/include/unwind.h b/include/unwind.h
index 05f5a16..ae8ae5d 100644
--- a/include/unwind.h
+++ b/include/unwind.h
@@ -19,8 +19,9 @@
 #include <stdint.h>
 #include <stddef.h>
 
-#if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
+#if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__) && defined(_WIN32)
 #include <windows.h>
+#include <ntverp.h>
 #endif
 
 #if defined(__APPLE__)
@@ -378,12 +379,19 @@ extern void *__deregister_frame_info_bases(const void *fde)
     LIBUNWIND_UNAVAIL;
 
 #if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
+#ifndef _WIN32
+typedef struct _EXCEPTION_RECORD EXCEPTION_RECORD;
+typedef struct _CONTEXT CONTEXT;
+typedef struct _DISPATCHER_CONTEXT DISPATCHER_CONTEXT;
+#elif !defined(__MINGW32__) && VER_PRODUCTBUILD < 8000
+typedef struct _DISPATCHER_CONTEXT DISPATCHER_CONTEXT;
+#endif
 // This is the common wrapper for GCC-style personality functions with SEH.
-extern EXCEPTION_DISPOSITION _GCC_specific_handler(PEXCEPTION_RECORD exc,
-                                                   PVOID frame,
-                                                   PCONTEXT ctx,
-                                                   PDISPATCHER_CONTEXT disp,
-                                                   _Unwind_Personality_Fn pers);
+extern EXCEPTION_DISPOSITION _GCC_specific_handler(EXCEPTION_RECORD *exc,
+                                                   void *frame,
+                                                   CONTEXT *ctx,
+                                                   DISPATCHER_CONTEXT *disp,
+                                                   __personality_routine pers);
 #endif
 
 #ifdef __cplusplus
diff --git a/src/AddressSpace.hpp b/src/AddressSpace.hpp
index e3a7e40..32e66bb 100644
--- a/src/AddressSpace.hpp
+++ b/src/AddressSpace.hpp
@@ -155,7 +155,7 @@ namespace libunwind {
 struct UnwindInfoSections {
 #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) || defined(_LIBUNWIND_SUPPORT_DWARF_INDEX) ||       \
     defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
-  // No dso_base for ARM EHABI.
+  // No dso_base for SEH or ARM EHABI.
   uintptr_t       dso_base;
 #endif
 #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
@@ -454,6 +454,10 @@ inline bool LocalAddressSpace::findUnwindSections(pint_t targetAddr,
     }
   }
   return false;
+#elif defined(_LIBUNWIND_SUPPORT_SEH_UNWIND) && defined(_WIN32)
+  // Don't even bother, since Windows has functions that do all this stuff
+  // for us.
+  return true;
 #elif defined(_LIBUNWIND_ARM_EHABI) && defined(__BIONIC__) &&                  \
     (__ANDROID_API__ < 21)
   int length = 0;
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 484d00d..8731ed7 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -2,7 +2,8 @@
 
 set(LIBUNWIND_CXX_SOURCES
     libunwind.cpp
-    Unwind-EHABI.cpp)
+    Unwind-EHABI.cpp
+    Unwind-seh.cpp)
 append_if(LIBUNWIND_CXX_SOURCES APPLE Unwind_AppleExtras.cpp)
 
 set(LIBUNWIND_C_SOURCES
diff --git a/src/Unwind-seh.cpp b/src/Unwind-seh.cpp
new file mode 100644
index 0000000..aaf2e98
--- /dev/null
+++ b/src/Unwind-seh.cpp
@@ -0,0 +1,468 @@
+//===--------------------------- Unwind-seh.cpp ---------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  Implements SEH-based Itanium C++ exceptions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "config.h"
+
+#if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
+
+#include <unwind.h>
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdlib.h>
+
+#include <windef.h>
+#include <excpt.h>
+#include <winnt.h>
+#include <ntstatus.h>
+
+#include "libunwind_ext.h"
+#include "UnwindCursor.hpp"
+
+using namespace libunwind;
+
+#define STATUS_USER_DEFINED (1u << 29)
+
+#define STATUS_GCC_MAGIC  (('G' << 16) | ('C' << 8) | 'C')
+
+#define MAKE_CUSTOM_STATUS(s, c) \
+  ((NTSTATUS)(((s) << 30) | STATUS_USER_DEFINED | (c)))
+#define MAKE_GCC_EXCEPTION(c) \
+  MAKE_CUSTOM_STATUS(STATUS_SEVERITY_SUCCESS, STATUS_GCC_MAGIC | ((c) << 24))
+
+/// SEH exception raised by libunwind when the program calls
+/// \c _Unwind_RaiseException.
+#define STATUS_GCC_THROW MAKE_GCC_EXCEPTION(0) // 0x20474343
+/// SEH exception raised by libunwind to initiate phase 2 of exception
+/// handling.
+#define STATUS_GCC_UNWIND MAKE_GCC_EXCEPTION(1) // 0x21474343
+
+/// Class of foreign exceptions based on unrecognized SEH exceptions.
+static const uint64_t kSEHExceptionClass = 0x434C4E4753454800; // CLNGSEH\0
+
+/// Exception cleanup routine used by \c _GCC_specific_handler to
+/// free foreign exceptions.
+static void seh_exc_cleanup(_Unwind_Reason_Code urc, _Unwind_Exception *exc) {
+  if (exc->exception_class != kSEHExceptionClass)
+    _LIBUNWIND_ABORT("SEH cleanup called on non-SEH exception");
+  free(exc);
+}
+
+static int _unw_init_seh(unw_cursor_t *cursor, CONTEXT *ctx);
+static DISPATCHER_CONTEXT *_unw_seh_get_disp_ctx(unw_cursor_t *cursor);
+static void _unw_seh_set_disp_ctx(unw_cursor_t *cursor, DISPATCHER_CONTEXT *disp);
+
+/// Common implementation of SEH-style handler functions used by Itanium-
+/// style frames.  Depending on how and why it was called, it may do one of:
+///  a) Delegate to the given Itanium-style personality function; or
+///  b) Initiate a collided unwind to halt unwinding.
+_LIBUNWIND_EXPORT EXCEPTION_DISPOSITION
+_GCC_specific_handler(PEXCEPTION_RECORD ms_exc, PVOID frame, PCONTEXT ms_ctx,
+                      DISPATCHER_CONTEXT *disp, __personality_routine pers) {
+  unw_context_t uc;
+  unw_cursor_t cursor;
+  _Unwind_Exception *exc;
+  _Unwind_Action action;
+  struct _Unwind_Context *ctx = nullptr;
+  _Unwind_Reason_Code urc;
+  uintptr_t retval, target;
+  bool ours = false;
+
+  _LIBUNWIND_TRACE_UNWINDING("_GCC_specific_handler(%#010x(%x), %p)", ms_exc->ExceptionCode, ms_exc->ExceptionFlags, frame);
+  if (ms_exc->ExceptionCode == STATUS_GCC_UNWIND) {
+    if (IS_TARGET_UNWIND(ms_exc->ExceptionFlags)) {
+      // Set up the upper return value (the lower one and the target PC
+      // were set in the call to RtlUnwindEx()) for the landing pad.
+#ifdef __x86_64__
+      disp->ContextRecord->Rdx = ms_exc->ExceptionInformation[3];
+#elif defined(__arm__)
+      disp->ContextRecord->R1 = ms_exc->ExceptionInformation[3];
+#endif
+    }
+    // This is the collided unwind to the landing pad. Nothing to do.
+    return ExceptionContinueSearch;
+  }
+
+  if (ms_exc->ExceptionCode == STATUS_GCC_THROW) {
+    // This is (probably) a libunwind-controlled exception/unwind. Recover the
+    // parameters which we set below, and pass them to the personality function.
+    ours = true;
+    exc = (_Unwind_Exception *)ms_exc->ExceptionInformation[0];
+    if (!IS_UNWINDING(ms_exc->ExceptionFlags) && ms_exc->NumberParameters > 1) {
+      ctx = (struct _Unwind_Context *)ms_exc->ExceptionInformation[1];
+      action = (_Unwind_Action)ms_exc->ExceptionInformation[2];
+    }
+  } else {
+    // Foreign exception.
+    exc = (_Unwind_Exception *)malloc(sizeof(_Unwind_Exception));
+    exc->exception_class = kSEHExceptionClass;
+    exc->exception_cleanup = seh_exc_cleanup;
+    memset(exc->private_, 0, sizeof(exc->private_));
+  }
+  if (!ctx) {
+    _unw_init_seh(&cursor, disp->ContextRecord);
+    _unw_seh_set_disp_ctx(&cursor, disp);
+    unw_set_reg(&cursor, UNW_REG_IP, disp->ControlPc-1);
+    ctx = (struct _Unwind_Context *)&cursor;
+
+    if (!IS_UNWINDING(ms_exc->ExceptionFlags)) {
+      if (ours && ms_exc->NumberParameters > 1)
+        action =  (_Unwind_Action)(_UA_CLEANUP_PHASE | _UA_FORCE_UNWIND);
+      else
+        action = _UA_SEARCH_PHASE;
+    } else {
+      if (ours && ms_exc->ExceptionInformation[1] == (ULONG_PTR)frame)
+        action = (_Unwind_Action)(_UA_CLEANUP_PHASE | _UA_HANDLER_FRAME);
+      else
+        action = _UA_CLEANUP_PHASE;
+    }
+  }
+
+  _LIBUNWIND_TRACE_UNWINDING("_GCC_specific_handler() calling personality function %p(1, %d, %llx, %p, %p)", pers, action, exc->exception_class, exc, ctx);
+  urc = pers(1, action, exc->exception_class, exc, ctx);
+  _LIBUNWIND_TRACE_UNWINDING("_GCC_specific_handler() personality returned %d", urc);
+  switch (urc) {
+  case _URC_CONTINUE_UNWIND:
+    // If we're in phase 2, and the personality routine said to continue
+    // at the target frame, we're in real trouble.
+    if (action & _UA_HANDLER_FRAME)
+      _LIBUNWIND_ABORT("Personality continued unwind at the target frame!");
+    return ExceptionContinueSearch;
+  case _URC_HANDLER_FOUND:
+    // If we were called by __libunwind_seh_personality(), indicate that
+    // a handler was found; otherwise, initiate phase 2 by unwinding.
+    if (ours && ms_exc->NumberParameters > 1)
+      return 4 /* ExecptionExecuteHandler in mingw */;
+    // This should never happen in phase 2.
+    if (IS_UNWINDING(ms_exc->ExceptionFlags))
+      _LIBUNWIND_ABORT("Personality indicated exception handler in phase 2!");
+    exc->private_[1] = (ULONG_PTR)frame;
+    if (ours) {
+      ms_exc->NumberParameters = 4;
+      ms_exc->ExceptionInformation[1] = (ULONG_PTR)frame;
+    }
+    // FIXME: Indicate target frame in foreign case!
+    // phase 2: the clean up phase
+    RtlUnwindEx(frame, (PVOID)disp->ControlPc, ms_exc, exc, ms_ctx, disp->HistoryTable);
+    _LIBUNWIND_ABORT("RtlUnwindEx() failed");
+  case _URC_INSTALL_CONTEXT: {
+    // If we were called by __libunwind_seh_personality(), indicate that
+    // a handler was found; otherwise, it's time to initiate a collided
+    // unwind to the target.
+    if (ours && !IS_UNWINDING(ms_exc->ExceptionFlags) && ms_exc->NumberParameters > 1)
+      return 4 /* ExecptionExecuteHandler in mingw */;
+    // This should never happen in phase 1.
+    if (!IS_UNWINDING(ms_exc->ExceptionFlags))
+      _LIBUNWIND_ABORT("Personality installed context during phase 1!");
+    exc->private_[2] = disp->TargetIp;
+#ifdef __x86_64__
+    unw_get_reg(&cursor, UNW_X86_64_RAX, &retval);
+    unw_get_reg(&cursor, UNW_X86_64_RDX, &exc->private_[3]);
+#elif defined(__arm__)
+    unw_get_reg(&cursor, UNW_ARM_R0, &retval);
+    unw_get_reg(&cursor, UNW_ARM_R1, &exc->private_[3]);
+#endif
+    unw_get_reg(&cursor, UNW_REG_IP, &target);
+    ms_exc->ExceptionCode = STATUS_GCC_UNWIND;
+    ms_exc->ExceptionInformation[2] = disp->TargetIp;
+    ms_exc->ExceptionInformation[3] = exc->private_[3];
+    // Give NTRTL some scratch space to keep track of the collided unwind.
+    // Don't use the one that was passed in; we don't want to overwrite the
+    // context in the DISPATCHER_CONTEXT.
+    CONTEXT new_ctx;
+    RtlUnwindEx(frame, (PVOID)target, ms_exc, (PVOID)retval, &new_ctx, disp->HistoryTable);
+    _LIBUNWIND_ABORT("RtlUnwindEx() failed");
+  }
+  // Anything else indicates a serious problem.
+  default: return ExceptionContinueExecution;
+  }
+}
+
+/// Personality function returned by \c unw_get_proc_info() in SEH contexts.
+/// This is a wrapper that calls the real SEH handler function, which in
+/// turn (at least, for Itanium-style frames) calls the real Itanium
+/// personality function (see \c _GCC_specific_handler()).
+extern "C" _Unwind_Reason_Code
+__libunwind_seh_personality(int version, _Unwind_Action state,
+                            uint64_t klass, _Unwind_Exception *exc,
+                            struct _Unwind_Context *context) {
+  EXCEPTION_RECORD ms_exc;
+  bool phase2 = (state & (_UA_SEARCH_PHASE|_UA_CLEANUP_PHASE)) == _UA_CLEANUP_PHASE;
+  ms_exc.ExceptionCode = STATUS_GCC_THROW;
+  ms_exc.ExceptionFlags = 0;
+  ms_exc.NumberParameters = 3;
+  ms_exc.ExceptionInformation[0] = (ULONG_PTR)exc;
+  ms_exc.ExceptionInformation[1] = (ULONG_PTR)context;
+  ms_exc.ExceptionInformation[2] = state;
+  DISPATCHER_CONTEXT *disp_ctx = _unw_seh_get_disp_ctx((unw_cursor_t *)context);
+  EXCEPTION_DISPOSITION ms_act = disp_ctx->LanguageHandler(&ms_exc,
+                                                           (PVOID)disp_ctx->EstablisherFrame,
+                                                           disp_ctx->ContextRecord,
+                                                           disp_ctx);
+  switch (ms_act) {
+  case ExceptionContinueSearch: return _URC_CONTINUE_UNWIND;
+  case 4 /*ExceptionExecuteHandler*/:
+    return phase2 ? _URC_INSTALL_CONTEXT : _URC_HANDLER_FOUND;
+  default:
+    return phase2 ? _URC_FATAL_PHASE2_ERROR : _URC_FATAL_PHASE1_ERROR;
+  }
+}
+
+static _Unwind_Reason_Code
+unwind_phase2_forced(unw_context_t *uc,
+                     _Unwind_Exception *exception_object,
+                     _Unwind_Stop_Fn stop, void *stop_parameter) {
+  unw_cursor_t cursor2;
+  unw_init_local(&cursor2, uc);
+
+  // Walk each frame until we reach where search phase said to stop
+  while (unw_step(&cursor2) > 0) {
+
+    // Update info about this frame.
+    unw_proc_info_t frameInfo;
+    if (unw_get_proc_info(&cursor2, &frameInfo) != UNW_ESUCCESS) {
+      _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): unw_step "
+                                 "failed => _URC_END_OF_STACK",
+                                 (void *)exception_object);
+      return _URC_FATAL_PHASE2_ERROR;
+    }
+
+    // When tracing, print state information.
+    if (_LIBUNWIND_TRACING_UNWINDING) {
+      char functionBuf[512];
+      const char *functionName = functionBuf;
+      unw_word_t offset;
+      if ((unw_get_proc_name(&cursor2, functionBuf, sizeof(functionBuf),
+                             &offset) != UNW_ESUCCESS) ||
+          (frameInfo.start_ip + offset > frameInfo.end_ip))
+        functionName = ".anonymous.";
+      _LIBUNWIND_TRACE_UNWINDING(
+          "unwind_phase2_forced(ex_ojb=%p): start_ip=0x%" PRIx64
+          ", func=%s, lsda=0x%" PRIx64 ", personality=0x%" PRIx64,
+          (void *)exception_object, frameInfo.start_ip, functionName,
+          frameInfo.lsda, frameInfo.handler);
+    }
+
+    // Call stop function at each frame.
+    _Unwind_Action action =
+        (_Unwind_Action)(_UA_FORCE_UNWIND | _UA_CLEANUP_PHASE);
+    _Unwind_Reason_Code stopResult =
+        (*stop)(1, action, exception_object->exception_class, exception_object,
+                (struct _Unwind_Context *)(&cursor2), stop_parameter);
+    _LIBUNWIND_TRACE_UNWINDING(
+        "unwind_phase2_forced(ex_ojb=%p): stop function returned %d",
+        (void *)exception_object, stopResult);
+    if (stopResult != _URC_NO_REASON) {
+      _LIBUNWIND_TRACE_UNWINDING(
+          "unwind_phase2_forced(ex_ojb=%p): stopped by stop function",
+          (void *)exception_object);
+      return _URC_FATAL_PHASE2_ERROR;
+    }
+
+    // If there is a personality routine, tell it we are unwinding.
+    if (frameInfo.handler != 0) {
+      __personality_routine p =
+          (__personality_routine)(intptr_t)(frameInfo.handler);
+      _LIBUNWIND_TRACE_UNWINDING(
+          "unwind_phase2_forced(ex_ojb=%p): calling personality function %p",
+          (void *)exception_object, (void *)(uintptr_t)p);
+      _Unwind_Reason_Code personalityResult =
+          (*p)(1, action, exception_object->exception_class, exception_object,
+               (struct _Unwind_Context *)(&cursor2));
+      switch (personalityResult) {
+      case _URC_CONTINUE_UNWIND:
+        _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): "
+                                   "personality returned "
+                                   "_URC_CONTINUE_UNWIND",
+                                   (void *)exception_object);
+        // Destructors called, continue unwinding
+        break;
+      case _URC_INSTALL_CONTEXT:
+        _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): "
+                                   "personality returned "
+                                   "_URC_INSTALL_CONTEXT",
+                                   (void *)exception_object);
+        // We may get control back if landing pad calls _Unwind_Resume().
+        unw_resume(&cursor2);
+        break;
+      default:
+        // Personality routine returned an unknown result code.
+        _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): "
+                                   "personality returned %d, "
+                                   "_URC_FATAL_PHASE2_ERROR",
+                                   (void *)exception_object, personalityResult);
+        return _URC_FATAL_PHASE2_ERROR;
+      }
+    }
+  }
+
+  // Call stop function one last time and tell it we've reached the end
+  // of the stack.
+  _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): calling stop "
+                             "function with _UA_END_OF_STACK",
+                             (void *)exception_object);
+  _Unwind_Action lastAction =
+      (_Unwind_Action)(_UA_FORCE_UNWIND | _UA_CLEANUP_PHASE | _UA_END_OF_STACK);
+  (*stop)(1, lastAction, exception_object->exception_class, exception_object,
+          (struct _Unwind_Context *)(&cursor2), stop_parameter);
+
+  // Clean up phase did not resume at the frame that the search phase said it
+  // would.
+  return _URC_FATAL_PHASE2_ERROR;
+}
+
+/// Called by \c __cxa_throw().  Only returns if there is a fatal error.
+_LIBUNWIND_EXPORT _Unwind_Reason_Code
+_Unwind_RaiseException(_Unwind_Exception *exception_object) {
+  _LIBUNWIND_TRACE_API("_Unwind_RaiseException(ex_obj=%p)",
+                       (void *)exception_object);
+
+  // Mark that this is a non-forced unwind, so _Unwind_Resume()
+  // can do the right thing.
+  memset(exception_object->private_, 0, sizeof(exception_object->private_));
+
+  // phase 1: the search phase
+  // We'll let the system do that for us.
+  RaiseException(STATUS_GCC_THROW, 0, 1, (ULONG_PTR *)&exception_object);
+
+  // If we get here, either something went horribly wrong or we reached the
+  // top of the stack. Either way, let libc++abi call std::terminate().
+  return _URC_END_OF_STACK;
+}
+
+/// When \c _Unwind_RaiseException() is in phase2, it hands control
+/// to the personality function at each frame.  The personality
+/// may force a jump to a landing pad in that function; the landing
+/// pad code may then call \c _Unwind_Resume() to continue with the
+/// unwinding.  Note: the call to \c _Unwind_Resume() is from compiler
+/// geneated user code.  All other \c _Unwind_* routines are called
+/// by the C++ runtime \c __cxa_* routines.
+///
+/// Note: re-throwing an exception (as opposed to continuing the unwind)
+/// is implemented by having the code call \c __cxa_rethrow() which
+/// in turn calls \c _Unwind_Resume_or_Rethrow().
+_LIBUNWIND_EXPORT void
+_Unwind_Resume(_Unwind_Exception *exception_object) {
+  _LIBUNWIND_TRACE_API("_Unwind_Resume(ex_obj=%p)", (void *)exception_object);
+
+  if (exception_object->private_[0] != 0) {
+    unw_context_t uc;
+
+    unw_getcontext(&uc);
+    unwind_phase2_forced(&uc, exception_object,
+                         (_Unwind_Stop_Fn) exception_object->private_[0],
+                         (void *)exception_object->private_[4]);
+  } else {
+    // Recover the parameters for the unwind from the exception object
+    // so we can start unwinding again.
+    EXCEPTION_RECORD ms_exc;
+    CONTEXT ms_ctx;
+    UNWIND_HISTORY_TABLE hist;
+
+    ms_exc.ExceptionCode = STATUS_GCC_THROW;
+    ms_exc.ExceptionFlags = EXCEPTION_NONCONTINUABLE;
+    ms_exc.NumberParameters = 4;
+    ms_exc.ExceptionInformation[0] = (ULONG_PTR)exception_object;
+    ms_exc.ExceptionInformation[1] = exception_object->private_[1];
+    ms_exc.ExceptionInformation[2] = exception_object->private_[2];
+    ms_exc.ExceptionInformation[3] = exception_object->private_[3];
+    RtlUnwindEx((PVOID)exception_object->private_[1],
+                (PVOID)exception_object->private_[2], &ms_exc,
+                exception_object, &ms_ctx, &hist);
+  }
+
+  // Clients assume _Unwind_Resume() does not return, so all we can do is abort.
+  _LIBUNWIND_ABORT("_Unwind_Resume() can't return");
+}
+
+/// Not used by C++.
+/// Unwinds stack, calling "stop" function at each frame.
+/// Could be used to implement \c longjmp().
+_LIBUNWIND_EXPORT _Unwind_Reason_Code
+_Unwind_ForcedUnwind(_Unwind_Exception *exception_object,
+                     _Unwind_Stop_Fn stop, void *stop_parameter) {
+  _LIBUNWIND_TRACE_API("_Unwind_ForcedUnwind(ex_obj=%p, stop=%p)",
+                       (void *)exception_object, (void *)(uintptr_t)stop);
+  unw_context_t uc;
+  unw_getcontext(&uc);
+
+  // Mark that this is a forced unwind, so _Unwind_Resume() can do
+  // the right thing.
+  exception_object->private_[0] = (uintptr_t) stop;
+  exception_object->private_[4] = (uintptr_t) stop_parameter;
+
+  // do it
+  return unwind_phase2_forced(&uc, exception_object, stop, stop_parameter);
+}
+
+/// Called by personality handler during phase 2 to get LSDA for current frame.
+_LIBUNWIND_EXPORT uintptr_t
+_Unwind_GetLanguageSpecificData(struct _Unwind_Context *context) {
+  uintptr_t result = (uintptr_t)_unw_seh_get_disp_ctx((unw_cursor_t *)context)->HandlerData;
+  _LIBUNWIND_TRACE_API(
+      "_Unwind_GetLanguageSpecificData(context=%p) => 0x%" PRIxPTR,
+      (void *)context, result);
+  return result;
+}
+
+/// Called by personality handler during phase 2 to find the start of the
+/// function.
+_LIBUNWIND_EXPORT uintptr_t
+_Unwind_GetRegionStart(struct _Unwind_Context *context) {
+  DISPATCHER_CONTEXT *disp = _unw_seh_get_disp_ctx((unw_cursor_t *)context);
+  uintptr_t result = (uintptr_t)disp->FunctionEntry->BeginAddress + disp->ImageBase;
+  _LIBUNWIND_TRACE_API("_Unwind_GetRegionStart(context=%p) => 0x%" PRIxPTR,
+                       (void *)context, result);
+  return result;
+}
+
+static int
+_unw_init_seh(unw_cursor_t *cursor, CONTEXT *context) {
+#ifdef _LIBUNWIND_TARGET_X86_64
+  new ((void *)cursor) UnwindCursor<LocalAddressSpace, Registers_x86_64>(
+      context, LocalAddressSpace::sThisAddressSpace);
+  auto *co = reinterpret_cast<AbstractUnwindCursor *>(cursor);
+  co->setInfoBasedOnIPRegister();
+  return UNW_ESUCCESS;
+#elif defined(_LIBUNWIND_TARGET_ARM)
+  new ((void *)cursor) UnwindCursor<LocalAddressSpace, Registers_arm>(
+      context, LocalAddressSpace::sThisAddressSpace);
+  auto *co = reinterpret_cast<AbstractUnwindCursor *>(cursor);
+  co->setInfoBasedOnIPRegister();
+  return UNW_ESUCCESS;
+#else
+  return UNW_EINVAL;
+#endif
+}
+
+static DISPATCHER_CONTEXT *
+_unw_seh_get_disp_ctx(unw_cursor_t *cursor) {
+#ifdef _LIBUNWIND_TARGET_X86_64
+  return reinterpret_cast<UnwindCursor<LocalAddressSpace, Registers_x86_64> *>(cursor)->getDispatcherContext();
+#elif defined(_LIBUNWIND_TARGET_ARM)
+  return reinterpret_cast<UnwindCursor<LocalAddressSpace, Registers_arm> *>(cursor)->getDispatcherContext();
+#else
+  return nullptr;
+#endif
+}
+
+static void
+_unw_seh_set_disp_ctx(unw_cursor_t *cursor, DISPATCHER_CONTEXT *disp) {
+#ifdef _LIBUNWIND_TARGET_X86_64
+  reinterpret_cast<UnwindCursor<LocalAddressSpace, Registers_x86_64> *>(cursor)->setDispatcherContext(disp);
+#elif defined(_LIBUNWIND_TARGET_ARM)
+  reinterpret_cast<UnwindCursor<LocalAddressSpace, Registers_arm> *>(cursor)->setDispatcherContext(disp);
+#endif
+}
+
+#endif // defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
diff --git a/src/UnwindCursor.hpp b/src/UnwindCursor.hpp
index 0be4cd9..7c1506a 100644
--- a/src/UnwindCursor.hpp
+++ b/src/UnwindCursor.hpp
@@ -18,10 +18,51 @@
 #include <stdlib.h>
 #include <unwind.h>
 
+#ifdef _WIN32
+  #include <windows.h>
+  #include <ntverp.h>
+#endif
 #ifdef __APPLE__
   #include <mach-o/dyld.h>
 #endif
 
+#if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
+// Provide a definition for the DISPATCHER_CONTEXT struct for old (Win7 and
+// earlier) SDKs.
+// MinGW-w64 has always provided this struct.
+  #if defined(_WIN32) && defined(_LIBUNWIND_TARGET_X86_64) && \
+      !defined(__MINGW32__) && VER_PRODUCTBUILD < 8000
+struct _DISPATCHER_CONTEXT {
+  ULONG64 ControlPc;
+  ULONG64 ImageBase;
+  PRUNTIME_FUNCTION FunctionEntry;
+  ULONG64 EstablisherFrame;
+  ULONG64 TargetIp;
+  PCONTEXT ContextRecord;
+  PEXCEPTION_ROUTINE LanguageHandler;
+  PVOID HandlerData;
+  PUNWIND_HISTORY_TABLE HistoryTable;
+  ULONG ScopeIndex;
+  ULONG Fill0;
+};
+  #endif
+
+struct UNWIND_INFO {
+  uint8_t Version : 3;
+  uint8_t Flags : 5;
+  uint8_t SizeOfProlog;
+  uint8_t CountOfCodes;
+  uint8_t FrameRegister : 4;
+  uint8_t FrameOffset : 4;
+  uint16_t UnwindCodes[2];
+};
+
+extern "C" _Unwind_Reason_Code __libunwind_seh_personality(
+    int, _Unwind_Action, uint64_t, _Unwind_Exception *,
+    struct _Unwind_Context *);
+
+#endif
+
 #include "config.h"
 
 #include "AddressSpace.hpp"
@@ -412,6 +453,472 @@ public:
 #endif
 };
 
+#if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND) && defined(_WIN32)
+
+/// \c UnwindCursor contains all state (including all register values) during
+/// an unwind.  This is normally stack-allocated inside a unw_cursor_t.
+template <typename A, typename R>
+class UnwindCursor : public AbstractUnwindCursor {
+  typedef typename A::pint_t pint_t;
+public:
+                      UnwindCursor(unw_context_t *context, A &as);
+                      UnwindCursor(CONTEXT *context, A &as);
+                      UnwindCursor(A &as, void *threadArg);
+  virtual             ~UnwindCursor() {}
+  virtual bool        validReg(int);
+  virtual unw_word_t  getReg(int);
+  virtual void        setReg(int, unw_word_t);
+  virtual bool        validFloatReg(int);
+  virtual unw_fpreg_t getFloatReg(int);
+  virtual void        setFloatReg(int, unw_fpreg_t);
+  virtual int         step();
+  virtual void        getInfo(unw_proc_info_t *);
+  virtual void        jumpto();
+  virtual bool        isSignalFrame();
+  virtual bool        getFunctionName(char *buf, size_t len, unw_word_t *off);
+  virtual void        setInfoBasedOnIPRegister(bool isReturnAddress = false);
+  virtual const char *getRegisterName(int num);
+#ifdef __arm__
+  virtual void        saveVFPAsX();
+#endif
+
+  DISPATCHER_CONTEXT *getDispatcherContext() { return &_dispContext; }
+  void setDispatcherContext(DISPATCHER_CONTEXT *disp) { _dispContext = *disp; }
+
+private:
+
+  pint_t getLastPC() const { return _dispContext.ControlPc; }
+  void setLastPC(pint_t pc) { _dispContext.ControlPc = pc; }
+  RUNTIME_FUNCTION *lookUpSEHUnwindInfo(pint_t pc, pint_t *base) {
+    _dispContext.FunctionEntry = RtlLookupFunctionEntry(pc,
+                                                        &_dispContext.ImageBase,
+                                                        _dispContext.HistoryTable);
+    *base = _dispContext.ImageBase;
+    return _dispContext.FunctionEntry;
+  }
+  bool getInfoFromSEH(pint_t pc);
+  int stepWithSEHData() {
+    _dispContext.LanguageHandler = RtlVirtualUnwind(UNW_FLAG_UHANDLER,
+                                                    _dispContext.ImageBase,
+                                                    _dispContext.ControlPc,
+                                                    _dispContext.FunctionEntry,
+                                                    _dispContext.ContextRecord,
+                                                    &_dispContext.HandlerData,
+                                                    &_dispContext.EstablisherFrame,
+                                                    NULL);
+    // Update some fields of the unwind info now, since we have them.
+    _info.lsda = reinterpret_cast<unw_word_t>(_dispContext.HandlerData);
+    if (_dispContext.LanguageHandler) {
+      _info.handler = reinterpret_cast<unw_word_t>(__libunwind_seh_personality);
+    } else
+      _info.handler = 0;
+    return UNW_STEP_SUCCESS;
+  }
+
+  A                   &_addressSpace;
+  unw_proc_info_t      _info;
+  DISPATCHER_CONTEXT   _dispContext;
+  CONTEXT              _msContext;
+  UNWIND_HISTORY_TABLE _histTable;
+  bool                 _unwindInfoMissing;
+};
+
+
+template <typename A, typename R>
+UnwindCursor<A, R>::UnwindCursor(unw_context_t *context, A &as)
+    : _addressSpace(as), _unwindInfoMissing(false) {
+  static_assert((check_fit<UnwindCursor<A, R>, unw_cursor_t>::does_fit),
+                "UnwindCursor<> does not fit in unw_cursor_t");
+  memset(&_info, 0, sizeof(_info));
+  memset(&_histTable, 0, sizeof(_histTable));
+  _dispContext.ContextRecord = &_msContext;
+  _dispContext.HistoryTable = &_histTable;
+  // Initialize MS context from ours.
+  R r(context);
+  _msContext.ContextFlags = CONTEXT_CONTROL|CONTEXT_INTEGER|CONTEXT_FLOATING_POINT;
+#if defined(_LIBUNWIND_TARGET_X86_64)
+  _msContext.Rax = r.getRegister(UNW_X86_64_RAX);
+  _msContext.Rcx = r.getRegister(UNW_X86_64_RCX);
+  _msContext.Rdx = r.getRegister(UNW_X86_64_RDX);
+  _msContext.Rbx = r.getRegister(UNW_X86_64_RBX);
+  _msContext.Rsp = r.getRegister(UNW_X86_64_RSP);
+  _msContext.Rbp = r.getRegister(UNW_X86_64_RBP);
+  _msContext.Rsi = r.getRegister(UNW_X86_64_RSI);
+  _msContext.Rdi = r.getRegister(UNW_X86_64_RDI);
+  _msContext.R8 = r.getRegister(UNW_X86_64_R8);
+  _msContext.R9 = r.getRegister(UNW_X86_64_R9);
+  _msContext.R10 = r.getRegister(UNW_X86_64_R10);
+  _msContext.R11 = r.getRegister(UNW_X86_64_R11);
+  _msContext.R12 = r.getRegister(UNW_X86_64_R12);
+  _msContext.R13 = r.getRegister(UNW_X86_64_R13);
+  _msContext.R14 = r.getRegister(UNW_X86_64_R14);
+  _msContext.R15 = r.getRegister(UNW_X86_64_R15);
+  _msContext.Rip = r.getRegister(UNW_REG_IP);
+  union {
+    v128 v;
+    M128A m;
+  } t;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM0);
+  _msContext.Xmm0 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM1);
+  _msContext.Xmm1 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM2);
+  _msContext.Xmm2 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM3);
+  _msContext.Xmm3 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM4);
+  _msContext.Xmm4 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM5);
+  _msContext.Xmm5 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM6);
+  _msContext.Xmm6 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM7);
+  _msContext.Xmm7 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM8);
+  _msContext.Xmm8 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM9);
+  _msContext.Xmm9 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM10);
+  _msContext.Xmm10 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM11);
+  _msContext.Xmm11 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM12);
+  _msContext.Xmm12 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM13);
+  _msContext.Xmm13 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM14);
+  _msContext.Xmm14 = t.m;
+  t.v = r.getVectorRegister(UNW_X86_64_XMM15);
+  _msContext.Xmm15 = t.m;
+#elif defined(_LIBUNWIND_TARGET_ARM)
+  _msContext.R0 = r.getRegister(UNW_ARM_R0);
+  _msContext.R1 = r.getRegister(UNW_ARM_R1);
+  _msContext.R2 = r.getRegister(UNW_ARM_R2);
+  _msContext.R3 = r.getRegister(UNW_ARM_R3);
+  _msContext.R4 = r.getRegister(UNW_ARM_R4);
+  _msContext.R5 = r.getRegister(UNW_ARM_R5);
+  _msContext.R6 = r.getRegister(UNW_ARM_R6);
+  _msContext.R7 = r.getRegister(UNW_ARM_R7);
+  _msContext.R8 = r.getRegister(UNW_ARM_R8);
+  _msContext.R9 = r.getRegister(UNW_ARM_R9);
+  _msContext.R10 = r.getRegister(UNW_ARM_R10);
+  _msContext.R11 = r.getRegister(UNW_ARM_R11);
+  _msContext.R12 = r.getRegister(UNW_ARM_R12);
+  _msContext.Sp = r.getRegister(UNW_ARM_SP);
+  _msContext.Lr = r.getRegister(UNW_ARM_LR);
+  _msContext.Pc = r.getRegister(UNW_ARM_PC);
+  for (int r = UNW_ARM_D0; r <= UNW_ARM_D31; ++r) {
+    union {
+      uint64_t w;
+      double d;
+    } d;
+    d.d = r.getFloatRegister(r);
+    _msContext.D[r - UNW_ARM_D0] = d.w;
+  }
+#endif
+}
+
+template <typename A, typename R>
+UnwindCursor<A, R>::UnwindCursor(CONTEXT *context, A &as)
+    : _addressSpace(as), _unwindInfoMissing(false) {
+  static_assert((check_fit<UnwindCursor<A, R>, unw_cursor_t>::does_fit),
+                "UnwindCursor<> does not fit in unw_cursor_t");
+  memset(&_info, 0, sizeof(_info));
+  memset(&_histTable, 0, sizeof(_histTable));
+  _dispContext.ContextRecord = &_msContext;
+  _dispContext.HistoryTable = &_histTable;
+  _msContext = *context;
+}
+
+
+template <typename A, typename R>
+bool UnwindCursor<A, R>::validReg(int regNum) {
+  if (regNum == UNW_REG_IP || regNum == UNW_REG_SP) return true;
+#if defined(_LIBUNWIND_TARGET_X86_64)
+  if (regNum >= UNW_X86_64_RAX && regNum <= UNW_X86_64_R15) return true;
+#elif defined(_LIBUNWIND_TARGET_ARM)
+  if (regNum >= UNW_ARM_R0 && regNum <= UNW_ARM_R15) return true;
+#endif
+  return false;
+}
+
+template <typename A, typename R>
+unw_word_t UnwindCursor<A, R>::getReg(int regNum) {
+  switch (regNum) {
+#if defined(_LIBUNWIND_TARGET_X86_64)
+  case UNW_REG_IP: return _msContext.Rip;
+  case UNW_X86_64_RAX: return _msContext.Rax;
+  case UNW_X86_64_RDX: return _msContext.Rdx;
+  case UNW_X86_64_RCX: return _msContext.Rcx;
+  case UNW_X86_64_RBX: return _msContext.Rbx;
+  case UNW_REG_SP:
+  case UNW_X86_64_RSP: return _msContext.Rsp;
+  case UNW_X86_64_RBP: return _msContext.Rbp;
+  case UNW_X86_64_RSI: return _msContext.Rsi;
+  case UNW_X86_64_RDI: return _msContext.Rdi;
+  case UNW_X86_64_R8: return _msContext.R8;
+  case UNW_X86_64_R9: return _msContext.R9;
+  case UNW_X86_64_R10: return _msContext.R10;
+  case UNW_X86_64_R11: return _msContext.R11;
+  case UNW_X86_64_R12: return _msContext.R12;
+  case UNW_X86_64_R13: return _msContext.R13;
+  case UNW_X86_64_R14: return _msContext.R14;
+  case UNW_X86_64_R15: return _msContext.R15;
+#elif defined(_LIBUNWIND_TARGET_ARM)
+  case UNW_ARM_R0: return _msContext.R0;
+  case UNW_ARM_R1: return _msContext.R1;
+  case UNW_ARM_R2: return _msContext.R2;
+  case UNW_ARM_R3: return _msContext.R3;
+  case UNW_ARM_R4: return _msContext.R4;
+  case UNW_ARM_R5: return _msContext.R5;
+  case UNW_ARM_R6: return _msContext.R6;
+  case UNW_ARM_R7: return _msContext.R7;
+  case UNW_ARM_R8: return _msContext.R8;
+  case UNW_ARM_R9: return _msContext.R9;
+  case UNW_ARM_R10: return _msContext.R10;
+  case UNW_ARM_R11: return _msContext.R11;
+  case UNW_ARM_R12: return _msContext.R12;
+  case UNW_REG_SP:
+  case UNW_ARM_SP: return _msContext.Sp;
+  case UNW_ARM_LR: return _msContext.Lr;
+  case UNW_REG_IP:
+  case UNW_ARM_PC: return _msContext.Pc;
+#endif
+  }
+  _LIBUNWIND_ABORT("unsupported register");
+}
+
+template <typename A, typename R>
+void UnwindCursor<A, R>::setReg(int regNum, unw_word_t value) {
+  switch (regNum) {
+#if defined(_LIBUNWIND_TARGET_X86_64)
+  case UNW_REG_IP: _msContext.Rip = value; break;
+  case UNW_X86_64_RAX: _msContext.Rax = value; break;
+  case UNW_X86_64_RDX: _msContext.Rdx = value; break;
+  case UNW_X86_64_RCX: _msContext.Rcx = value; break;
+  case UNW_X86_64_RBX: _msContext.Rbx = value; break;
+  case UNW_REG_SP:
+  case UNW_X86_64_RSP: _msContext.Rsp = value; break;
+  case UNW_X86_64_RBP: _msContext.Rbp = value; break;
+  case UNW_X86_64_RSI: _msContext.Rsi = value; break;
+  case UNW_X86_64_RDI: _msContext.Rdi = value; break;
+  case UNW_X86_64_R8: _msContext.R8 = value; break;
+  case UNW_X86_64_R9: _msContext.R9 = value; break;
+  case UNW_X86_64_R10: _msContext.R10 = value; break;
+  case UNW_X86_64_R11: _msContext.R11 = value; break;
+  case UNW_X86_64_R12: _msContext.R12 = value; break;
+  case UNW_X86_64_R13: _msContext.R13 = value; break;
+  case UNW_X86_64_R14: _msContext.R14 = value; break;
+  case UNW_X86_64_R15: _msContext.R15 = value; break;
+#elif defined(_LIBUNWIND_TARGET_ARM)
+  case UNW_ARM_R0: _msContext.R0 = value; break;
+  case UNW_ARM_R1: _msContext.R1 = value; break;
+  case UNW_ARM_R2: _msContext.R2 = value; break;
+  case UNW_ARM_R3: _msContext.R3 = value; break;
+  case UNW_ARM_R4: _msContext.R4 = value; break;
+  case UNW_ARM_R5: _msContext.R5 = value; break;
+  case UNW_ARM_R6: _msContext.R6 = value; break;
+  case UNW_ARM_R7: _msContext.R7 = value; break;
+  case UNW_ARM_R8: _msContext.R8 = value; break;
+  case UNW_ARM_R9: _msContext.R9 = value; break;
+  case UNW_ARM_R10: _msContext.R10 = value; break;
+  case UNW_ARM_R11: _msContext.R11 = value; break;
+  case UNW_ARM_R12: _msContext.R12 = value; break;
+  case UNW_REG_SP:
+  case UNW_ARM_SP: _msContext.Sp = value; break;
+  case UNW_ARM_LR: _msContext.Lr = value; break;
+  case UNW_REG_IP:
+  case UNW_ARM_PC: _msContext.Pc = value; break;
+#endif
+  default:
+    _LIBUNWIND_ABORT("unsupported register");
+  }
+}
+
+template <typename A, typename R>
+bool UnwindCursor<A, R>::validFloatReg(int regNum) {
+#if defined(_LIBUNWIND_TARGET_ARM)
+  if (regNum >= UNW_ARM_S0 && regNum <= UNW_ARM_S31) return true;
+  if (regNum >= UNW_ARM_D0 && regNum <= UNW_ARM_D31) return true;
+#endif
+  return false;
+}
+
+template <typename A, typename R>
+unw_fpreg_t UnwindCursor<A, R>::getFloatReg(int regNum) {
+#if defined(_LIBUNWIND_TARGET_ARM)
+  if (regNum >= UNW_ARM_S0 && regNum <= UNW_ARM_S31) {
+    union {
+      uint32_t w;
+      float f;
+    } d;
+    d.w = _msContext.S[regNum - UNW_ARM_S0];
+    return d.f;
+  }
+  if (regNum >= UNW_ARM_D0 && regNum <= UNW_ARM_D31) {
+    union {
+      uint64_t w;
+      double d;
+    } d;
+    d.w = _msContext.D[regNum - UNW_ARM_D0];
+    return d.d;
+  }
+  _LIBUNWIND_ABORT("unsupported float register");
+#else
+  _LIBUNWIND_ABORT("float registers unimplemented");
+#endif
+}
+
+template <typename A, typename R>
+void UnwindCursor<A, R>::setFloatReg(int regNum, unw_fpreg_t value) {
+#if defined(_LIBUNWIND_TARGET_ARM)
+  if (regNum >= UNW_ARM_S0 && regNum <= UNW_ARM_S31) {
+    union {
+      uint32_t w;
+      float f;
+    } d;
+    d.f = value;
+    _msContext.S[regNum - UNW_ARM_S0] = d.w;
+  }
+  if (regNum >= UNW_ARM_D0 && regNum <= UNW_ARM_D31) {
+    union {
+      uint64_t w;
+      double d;
+    } d;
+    d.d = value;
+    _msContext.D[regNum - UNW_ARM_D0] = d.w;
+  }
+  _LIBUNWIND_ABORT("unsupported float register");
+#else
+  _LIBUNWIND_ABORT("float registers unimplemented");
+#endif
+}
+
+template <typename A, typename R> void UnwindCursor<A, R>::jumpto() {
+  RtlRestoreContext(&_msContext, nullptr);
+}
+
+#ifdef __arm__
+template <typename A, typename R> void UnwindCursor<A, R>::saveVFPAsX() {}
+#endif
+
+template <typename A, typename R>
+const char *UnwindCursor<A, R>::getRegisterName(int regNum) {
+  switch (regNum) {
+#if defined(_LIBUNWIND_TARGET_X86_64)
+  case UNW_REG_IP: return "rip";
+  case UNW_X86_64_RAX: return "rax";
+  case UNW_X86_64_RDX: return "rdx";
+  case UNW_X86_64_RCX: return "rcx";
+  case UNW_X86_64_RBX: return "rbx";
+  case UNW_REG_SP:
+  case UNW_X86_64_RSP: return "rsp";
+  case UNW_X86_64_RBP: return "rbp";
+  case UNW_X86_64_RSI: return "rsi";
+  case UNW_X86_64_RDI: return "rdi";
+  case UNW_X86_64_R8: return "r8";
+  case UNW_X86_64_R9: return "r9";
+  case UNW_X86_64_R10: return "r10";
+  case UNW_X86_64_R11: return "r11";
+  case UNW_X86_64_R12: return "r12";
+  case UNW_X86_64_R13: return "r13";
+  case UNW_X86_64_R14: return "r14";
+  case UNW_X86_64_R15: return "r15";
+#elif defined(_LIBUNWIND_TARGET_ARM)
+  case UNW_ARM_R0: return "r0";
+  case UNW_ARM_R1: return "r1";
+  case UNW_ARM_R2: return "r2";
+  case UNW_ARM_R3: return "r3";
+  case UNW_ARM_R4: return "r4";
+  case UNW_ARM_R5: return "r5";
+  case UNW_ARM_R6: return "r6";
+  case UNW_ARM_R7: return "r7";
+  case UNW_ARM_R8: return "r8";
+  case UNW_ARM_R9: return "r9";
+  case UNW_ARM_R10: return "r10";
+  case UNW_ARM_R11: return "r11";
+  case UNW_ARM_R12: return "r12";
+  case UNW_REG_SP:
+  case UNW_ARM_SP: return "sp";
+  case UNW_ARM_LR: return "lr";
+  case UNW_REG_IP:
+  case UNW_ARM_PC: return "pc";
+  case UNW_ARM_S0: return "s0";
+  case UNW_ARM_S1: return "s1";
+  case UNW_ARM_S2: return "s2";
+  case UNW_ARM_S3: return "s3";
+  case UNW_ARM_S4: return "s4";
+  case UNW_ARM_S5: return "s5";
+  case UNW_ARM_S6: return "s6";
+  case UNW_ARM_S7: return "s7";
+  case UNW_ARM_S8: return "s8";
+  case UNW_ARM_S9: return "s9";
+  case UNW_ARM_S10: return "s10";
+  case UNW_ARM_S11: return "s11";
+  case UNW_ARM_S12: return "s12";
+  case UNW_ARM_S13: return "s13";
+  case UNW_ARM_S14: return "s14";
+  case UNW_ARM_S15: return "s15";
+  case UNW_ARM_S16: return "s16";
+  case UNW_ARM_S17: return "s17";
+  case UNW_ARM_S18: return "s18";
+  case UNW_ARM_S19: return "s19";
+  case UNW_ARM_S20: return "s20";
+  case UNW_ARM_S21: return "s21";
+  case UNW_ARM_S22: return "s22";
+  case UNW_ARM_S23: return "s23";
+  case UNW_ARM_S24: return "s24";
+  case UNW_ARM_S25: return "s25";
+  case UNW_ARM_S26: return "s26";
+  case UNW_ARM_S27: return "s27";
+  case UNW_ARM_S28: return "s28";
+  case UNW_ARM_S29: return "s29";
+  case UNW_ARM_S30: return "s30";
+  case UNW_ARM_S31: return "s31";
+  case UNW_ARM_D0: return "d0";
+  case UNW_ARM_D1: return "d1";
+  case UNW_ARM_D2: return "d2";
+  case UNW_ARM_D3: return "d3";
+  case UNW_ARM_D4: return "d4";
+  case UNW_ARM_D5: return "d5";
+  case UNW_ARM_D6: return "d6";
+  case UNW_ARM_D7: return "d7";
+  case UNW_ARM_D8: return "d8";
+  case UNW_ARM_D9: return "d9";
+  case UNW_ARM_D10: return "d10";
+  case UNW_ARM_D11: return "d11";
+  case UNW_ARM_D12: return "d12";
+  case UNW_ARM_D13: return "d13";
+  case UNW_ARM_D14: return "d14";
+  case UNW_ARM_D15: return "d15";
+  case UNW_ARM_D16: return "d16";
+  case UNW_ARM_D17: return "d17";
+  case UNW_ARM_D18: return "d18";
+  case UNW_ARM_D19: return "d19";
+  case UNW_ARM_D20: return "d20";
+  case UNW_ARM_D21: return "d21";
+  case UNW_ARM_D22: return "d22";
+  case UNW_ARM_D23: return "d23";
+  case UNW_ARM_D24: return "d24";
+  case UNW_ARM_D25: return "d25";
+  case UNW_ARM_D26: return "d26";
+  case UNW_ARM_D27: return "d27";
+  case UNW_ARM_D28: return "d28";
+  case UNW_ARM_D29: return "d29";
+  case UNW_ARM_D30: return "d30";
+  case UNW_ARM_D31: return "d31";
+#endif
+  default:
+    _LIBUNWIND_ABORT("unsupported register");
+  }
+}
+
+template <typename A, typename R> bool UnwindCursor<A, R>::isSignalFrame() {
+  return false;
+}
+
+#else  // !defined(_LIBUNWIND_SUPPORT_SEH_UNWIND) || !defined(_WIN32)
+
 /// UnwindCursor contains all state (including all register values) during
 /// an unwind.  This is normally stack allocated inside a unw_cursor_t.
 template <typename A, typename R>
@@ -651,6 +1158,20 @@ private:
 #endif
 #endif // defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
 
+#if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
+  // For runtime environments using SEH unwind data without Windows runtime
+  // support.
+  pint_t getLastPC() const { /* FIXME: Implement */ return 0; }
+  void setLastPC(pint_t pc) { /* FIXME: Implement */ }
+  RUNTIME_FUNCTION *lookUpSEHUnwindInfo(pint_t pc, pint_t *base) {
+    /* FIXME: Implement */
+    *base = 0;
+    return nullptr;
+  }
+  bool getInfoFromSEH(pint_t pc);
+  int stepWithSEHData() { /* FIXME: Implement */ return 0; }
+#endif // defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
+
 
   A               &_addressSpace;
   R                _registers;
@@ -727,6 +1248,8 @@ template <typename A, typename R> bool UnwindCursor<A, R>::isSignalFrame() {
   return _isSignalFrame;
 }
 
+#endif // defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
+
 #if defined(_LIBUNWIND_ARM_EHABI)
 struct EHABIIndexEntry {
   uint32_t functionOffset;
@@ -1261,6 +1784,55 @@ bool UnwindCursor<A, R>::getInfoFromCompactEncodingSection(pint_t pc,
 #endif // defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
 
 
+#if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
+template <typename A, typename R>
+bool UnwindCursor<A, R>::getInfoFromSEH(pint_t pc) {
+  pint_t base;
+  RUNTIME_FUNCTION *unwindEntry = lookUpSEHUnwindInfo(pc, &base);
+  if (!unwindEntry) {
+    _LIBUNWIND_DEBUG_LOG("\tpc not in table, pc=0x%llX", (uint64_t) pc);
+    return false;
+  }
+  _info.gp = 0;
+  _info.flags = 0;
+  _info.format = 0;
+  _info.unwind_info_size = sizeof(RUNTIME_FUNCTION);
+  _info.unwind_info = reinterpret_cast<unw_word_t>(unwindEntry);
+  _info.extra = base;
+  _info.start_ip = base + unwindEntry->BeginAddress;
+#ifdef _LIBUNWIND_TARGET_X86_64
+  _info.end_ip = base + unwindEntry->EndAddress;
+  // Only fill in the handler and LSDA if they're stale.
+  if (pc != getLastPC()) {
+    UNWIND_INFO *xdata = reinterpret_cast<UNWIND_INFO *>(base + unwindEntry->UnwindData);
+    if (xdata->Flags & (UNW_FLAG_EHANDLER|UNW_FLAG_UHANDLER)) {
+      // The personality is given in the UNWIND_INFO itself. The LSDA immediately
+      // follows the UNWIND_INFO. (This follows how both Clang and MSVC emit
+      // these structures.)
+      // N.B. UNWIND_INFO structs are DWORD-aligned.
+      uint32_t lastcode = (xdata->CountOfCodes + 1) & ~1;
+      const uint32_t *handler = reinterpret_cast<uint32_t *>(&xdata->UnwindCodes[lastcode]);
+      _info.lsda = reinterpret_cast<unw_word_t>(handler+1);
+      if (*handler) {
+        _info.handler = reinterpret_cast<unw_word_t>(__libunwind_seh_personality);
+      } else
+        _info.handler = 0;
+    } else {
+      _info.lsda = 0;
+      _info.handler = 0;
+    }
+  }
+#elif defined(_LIBUNWIND_TARGET_ARM)
+  _info.end_ip = _info.start_ip + unwindEntry->FunctionLength;
+  _info.lsda = 0; // FIXME
+  _info.handler = 0; // FIXME
+#endif
+  setLastPC(pc);
+  return true;
+}
+#endif
+
+
 template <typename A, typename R>
 void UnwindCursor<A, R>::setInfoBasedOnIPRegister(bool isReturnAddress) {
   pint_t pc = (pint_t)this->getReg(UNW_REG_IP);
@@ -1304,6 +1876,12 @@ void UnwindCursor<A, R>::setInfoBasedOnIPRegister(bool isReturnAddress) {
     }
 #endif // defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
 
+#if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
+    // If there is SEH unwind info, look there next.
+    if (this->getInfoFromSEH(pc))
+      return;
+#endif
+
 #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
     // If there is dwarf unwind info, look there next.
     if (sects.dwarf_section != 0) {
@@ -1396,12 +1974,15 @@ int UnwindCursor<A, R>::step() {
   int result;
 #if defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
   result = this->stepWithCompactEncoding();
+#elif defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
+  result = this->stepWithSEHData();
 #elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
   result = this->stepWithDwarfFDE();
 #elif defined(_LIBUNWIND_ARM_EHABI)
   result = this->stepWithEHABI();
 #else
   #error Need _LIBUNWIND_SUPPORT_COMPACT_UNWIND or \
+              _LIBUNWIND_SUPPORT_SEH_UNWIND or \
               _LIBUNWIND_SUPPORT_DWARF_UNWIND or \
               _LIBUNWIND_ARM_EHABI
 #endif
diff --git a/src/UnwindLevel1-gcc-ext.c b/src/UnwindLevel1-gcc-ext.c
index 38f141e..1c66265 100644
--- a/src/UnwindLevel1-gcc-ext.c
+++ b/src/UnwindLevel1-gcc-ext.c
@@ -25,6 +25,10 @@
 
 #if defined(_LIBUNWIND_BUILD_ZERO_COST_APIS)
 
+#if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
+#define private_1 private_[0]
+#endif
+
 ///  Called by __cxa_rethrow().
 _LIBUNWIND_EXPORT _Unwind_Reason_Code
 _Unwind_Resume_or_Rethrow(_Unwind_Exception *exception_object) {
diff --git a/src/UnwindLevel1.c b/src/UnwindLevel1.c
index 04d62b8..0a04438 100644
--- a/src/UnwindLevel1.c
+++ b/src/UnwindLevel1.c
@@ -32,6 +32,8 @@
 
 #if !defined(_LIBUNWIND_ARM_EHABI) && !defined(__USING_SJLJ_EXCEPTIONS__)
 
+#ifndef _LIBUNWIND_SUPPORT_SEH_UNWIND
+
 static _Unwind_Reason_Code
 unwind_phase1(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *exception_object) {
   unw_init_local(cursor, uc);
@@ -449,6 +451,7 @@ _Unwind_GetRegionStart(struct _Unwind_Context *context) {
   return result;
 }
 
+#endif // !_LIBUNWIND_SUPPORT_SEH_UNWIND
 
 /// Called by personality handler during phase 2 if a foreign exception
 // is caught.
diff --git a/src/config.h b/src/config.h
index 1a7a306..fc7fd64 100644
--- a/src/config.h
+++ b/src/config.h
@@ -38,7 +38,11 @@
     #define _LIBUNWIND_SUPPORT_DWARF_UNWIND   1
   #endif
 #elif defined(_WIN32)
-  #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
+  #ifdef __SEH__
+    #define _LIBUNWIND_SUPPORT_SEH_UNWIND 1
+  #else
+    #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
+  #endif
 #else
   #if defined(__ARM_DWARF_EH__) || !defined(__arm__)
     #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1