eh_personality.cc

// -*- C++ -*- The GNU C++ exception personality routine.
// Copyright (C) 2001-2018 Free Software Foundation, Inc.
//
// This file is part of GCC.
//
// GCC is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3, or (at your option)
// any later version.
//
// GCC is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

#include <bits/c++config.h>
#include <cstdlib>
#include <bits/exception_defines.h>
#include <cxxabi.h>
#include "unwind-cxx.h"


using namespace __cxxabiv1;

#include "unwind-pe.h"


struct lsda_header_info
{
  _Unwind_Ptr Start;
  _Unwind_Ptr LPStart;
  _Unwind_Ptr ttype_base;
  const unsigned char *TType;
  const unsigned char *action_table;
  unsigned char ttype_encoding;
  unsigned char call_site_encoding;
};

static const unsigned char *
parse_lsda_header (_Unwind_Context *context, const unsigned char *p,
		   lsda_header_info *info)
{
  _uleb128_t tmp;
  unsigned char lpstart_encoding;

  info->Start = (context ? _Unwind_GetRegionStart (context) : 0);

  // Find @LPStart, the base to which landing pad offsets are relative.
  lpstart_encoding = *p++;
  if (lpstart_encoding != DW_EH_PE_omit)
    p = read_encoded_value (context, lpstart_encoding, p, &info->LPStart);
  else
    info->LPStart = info->Start;

  // Find @TType, the base of the handler and exception spec type data.
  info->ttype_encoding = *p++;
  if (info->ttype_encoding != DW_EH_PE_omit)
    {
#if _GLIBCXX_OVERRIDE_TTYPE_ENCODING
      /* Older ARM EABI toolchains set this value incorrectly, so use a
	 hardcoded OS-specific format.  */
      info->ttype_encoding = _GLIBCXX_OVERRIDE_TTYPE_ENCODING;
#endif
      p = read_uleb128 (p, &tmp);
      info->TType = p + tmp;
    }
  else
    info->TType = 0;

  // The encoding and length of the call-site table; the action table
  // immediately follows.
  info->call_site_encoding = *p++;
  p = read_uleb128 (p, &tmp);
  info->action_table = p + tmp;

  return p;
}

// Return an element from a type table.

static const std::type_info *
get_ttype_entry (lsda_header_info *info, _uleb128_t i)
{
  _Unwind_Ptr ptr;

  i *= size_of_encoded_value (info->ttype_encoding);
  read_encoded_value_with_base (info->ttype_encoding, info->ttype_base,
				info->TType - i, &ptr);

  return reinterpret_cast<const std::type_info *>(ptr);
}

#ifdef __ARM_EABI_UNWINDER__

// The ABI provides a routine for matching exception object types.
typedef _Unwind_Control_Block _throw_typet;
#define get_adjusted_ptr(catch_type, throw_type, thrown_ptr_p) \
  (__cxa_type_match (throw_type, catch_type, false, thrown_ptr_p) \
   != ctm_failed)

// Return true if THROW_TYPE matches one if the filter types.

static bool
check_exception_spec(lsda_header_info* info, _throw_typet* throw_type,
		     void* thrown_ptr, _sleb128_t filter_value)
{
  const _uleb128_t* e = ((const _uleb128_t*) info->TType)
			  - filter_value - 1;

  while (1)
    {
      const std::type_info* catch_type;
      _uleb128_t tmp;

      tmp = *e;
      
      // Zero signals the end of the list.  If we've not found
      // a match by now, then we've failed the specification.
      if (tmp == 0)
        return false;

      tmp = _Unwind_decode_typeinfo_ptr(info->ttype_base, (_Unwind_Word) e);

      // Match a ttype entry.
      catch_type = reinterpret_cast<const std::type_info*>(tmp);

      // ??? There is currently no way to ask the RTTI code about the
      // relationship between two types without reference to a specific
      // object.  There should be; then we wouldn't need to mess with
      // thrown_ptr here.
      if (get_adjusted_ptr(catch_type, throw_type, &thrown_ptr))
	return true;

      // Advance to the next entry.
      e++;
    }
}


// Save stage1 handler information in the exception object

static inline void
save_caught_exception(struct _Unwind_Exception* ue_header,
		      struct _Unwind_Context* context,
		      void* thrown_ptr,
		      int handler_switch_value,
		      const unsigned char* language_specific_data,
		      _Unwind_Ptr landing_pad,
		      const unsigned char* action_record
			__attribute__((__unused__)))
{
    ue_header->barrier_cache.sp = _Unwind_GetGR(context, UNWIND_STACK_REG);
    ue_header->barrier_cache.bitpattern[0] = (_uw) thrown_ptr;
    ue_header->barrier_cache.bitpattern[1]
      = (_uw) handler_switch_value;
    ue_header->barrier_cache.bitpattern[2]
      = (_uw) language_specific_data;
    ue_header->barrier_cache.bitpattern[3] = (_uw) landing_pad;
}


// Restore the catch handler data saved during phase1.

static inline void
restore_caught_exception(struct _Unwind_Exception* ue_header,
			 int& handler_switch_value,
			 const unsigned char*& language_specific_data,
			 _Unwind_Ptr& landing_pad)
{
  handler_switch_value = (int) ue_header->barrier_cache.bitpattern[1];
  language_specific_data =
    (const unsigned char*) ue_header->barrier_cache.bitpattern[2];
  landing_pad = (_Unwind_Ptr) ue_header->barrier_cache.bitpattern[3];
}

#define CONTINUE_UNWINDING \
  do								\
    {								\
      if (__gnu_unwind_frame(ue_header, context) != _URC_OK)	\
	return _URC_FAILURE;					\
      return _URC_CONTINUE_UNWIND;				\
    }								\
  while (0)

// Return true if the filter spec is empty, ie throw().

static bool
empty_exception_spec (lsda_header_info *info, _Unwind_Sword filter_value)
{
  const _Unwind_Word* e = ((const _Unwind_Word*) info->TType)
			  - filter_value - 1;

  return *e == 0;
}

#else
typedef const std::type_info _throw_typet;


// Given the thrown type THROW_TYPE, pointer to a variable containing a
// pointer to the exception object THROWN_PTR_P and a type CATCH_TYPE to
// compare against, return whether or not there is a match and if so,
// update *THROWN_PTR_P.

static bool
get_adjusted_ptr (const std::type_info *catch_type,
		  const std::type_info *throw_type,
		  void **thrown_ptr_p)
{
  void *thrown_ptr = *thrown_ptr_p;

  // Pointer types need to adjust the actual pointer, not
  // the pointer to pointer that is the exception object.
  // This also has the effect of passing pointer types
  // "by value" through the __cxa_begin_catch return value.
  if (throw_type->__is_pointer_p ())
    thrown_ptr = *(void **) thrown_ptr;

  if (catch_type->__do_catch (throw_type, &thrown_ptr, 1))
    {
      *thrown_ptr_p = thrown_ptr;
      return true;
    }

  return false;
}

// Return true if THROW_TYPE matches one if the filter types.

static bool
check_exception_spec(lsda_header_info* info, _throw_typet* throw_type,
		      void* thrown_ptr, _sleb128_t filter_value)
{
  const unsigned char *e = info->TType - filter_value - 1;

  while (1)
    {
      const std::type_info *catch_type;
      _uleb128_t tmp;

      e = read_uleb128 (e, &tmp);

      // Zero signals the end of the list.  If we've not found
      // a match by now, then we've failed the specification.
      if (tmp == 0)
        return false;

      // Match a ttype entry.
      catch_type = get_ttype_entry (info, tmp);

      // ??? There is currently no way to ask the RTTI code about the
      // relationship between two types without reference to a specific
      // object.  There should be; then we wouldn't need to mess with
      // thrown_ptr here.
      if (get_adjusted_ptr (catch_type, throw_type, &thrown_ptr))
	return true;
    }
}


// Save stage1 handler information in the exception object

static inline void
save_caught_exception(struct _Unwind_Exception* ue_header,
		      struct _Unwind_Context* context
			__attribute__((__unused__)),
		      void* thrown_ptr,
		      int handler_switch_value,
		      const unsigned char* language_specific_data,
		      _Unwind_Ptr landing_pad __attribute__((__unused__)),
		      const unsigned char* action_record)
{
  __cxa_exception* xh = __get_exception_header_from_ue(ue_header);

  xh->handlerSwitchValue = handler_switch_value;
  xh->actionRecord = action_record;
  xh->languageSpecificData = language_specific_data;
  xh->adjustedPtr = thrown_ptr;

  // ??? Completely unknown what this field is supposed to be for.
  // ??? Need to cache TType encoding base for call_unexpected.
  xh->catchTemp = landing_pad;
}


// Restore the catch handler information saved during phase1.

static inline void
restore_caught_exception(struct _Unwind_Exception* ue_header,
			 int& handler_switch_value,
			 const unsigned char*& language_specific_data,
			 _Unwind_Ptr& landing_pad)
{
  __cxa_exception* xh = __get_exception_header_from_ue(ue_header);
  handler_switch_value = xh->handlerSwitchValue;
  language_specific_data = xh->languageSpecificData;
  landing_pad = (_Unwind_Ptr) xh->catchTemp;
}

#define CONTINUE_UNWINDING return _URC_CONTINUE_UNWIND

// Return true if the filter spec is empty, ie throw().

static bool
empty_exception_spec (lsda_header_info *info, _Unwind_Sword filter_value)
{
  const unsigned char *e = info->TType - filter_value - 1;
  _uleb128_t tmp;

  e = read_uleb128 (e, &tmp);
  return tmp == 0;
}

#endif // !__ARM_EABI_UNWINDER__

namespace __cxxabiv1
{

// Using a different personality function name causes link failures
// when trying to mix code using different exception handling models.
#ifdef __USING_SJLJ_EXCEPTIONS__
#define PERSONALITY_FUNCTION	__gxx_personality_sj0
#define __builtin_eh_return_data_regno(x) x
#elif defined(__SEH__)
#define PERSONALITY_FUNCTION	__gxx_personality_imp
#else
#define PERSONALITY_FUNCTION	__gxx_personality_v0
#endif

#if defined (__SEH__) && !defined (__USING_SJLJ_EXCEPTIONS__)
static
#else
extern "C"
#endif
_Unwind_Reason_Code
#ifdef __ARM_EABI_UNWINDER__
PERSONALITY_FUNCTION (_Unwind_State state,
		      struct _Unwind_Exception* ue_header,
		      struct _Unwind_Context* context)
#else
PERSONALITY_FUNCTION (int version,
		      _Unwind_Action actions,
		      _Unwind_Exception_Class exception_class,
		      struct _Unwind_Exception *ue_header,
		      struct _Unwind_Context *context)
#endif
{
  enum found_handler_type
  {
    found_nothing,
    found_terminate,
    found_cleanup,
    found_handler
  } found_type;

  lsda_header_info info;
  const unsigned char *language_specific_data;
  const unsigned char *action_record;
  const unsigned char *p;
  _Unwind_Ptr landing_pad, ip;
  int handler_switch_value;
  void* thrown_ptr = 0;
  bool foreign_exception;
  int ip_before_insn = 0;

#ifdef __ARM_EABI_UNWINDER__
  _Unwind_Action actions;

  switch (state & _US_ACTION_MASK)
    {
    case _US_VIRTUAL_UNWIND_FRAME:
      // If the unwind state pattern is
      // _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND
      // then we don't need to search for any handler as it is not a real
      // exception. Just unwind the stack.
      if (state & _US_FORCE_UNWIND)
	CONTINUE_UNWINDING;
      actions = _UA_SEARCH_PHASE;
      break;

    case _US_UNWIND_FRAME_STARTING:
      actions = _UA_CLEANUP_PHASE;
      if (!(state & _US_FORCE_UNWIND)
	  && ue_header->barrier_cache.sp == _Unwind_GetGR(context,
							  UNWIND_STACK_REG))
	actions |= _UA_HANDLER_FRAME;
      break;

    case _US_UNWIND_FRAME_RESUME:
      CONTINUE_UNWINDING;
      break;

    default:
      std::abort();
    }
  actions |= state & _US_FORCE_UNWIND;

  // We don't know which runtime we're working with, so can't check this.
  // However the ABI routines hide this from us, and we don't actually need
  // to know.
  foreign_exception = false;

  // The dwarf unwinder assumes the context structure holds things like the
  // function and LSDA pointers.  The ARM implementation caches these in
  // the exception header (UCB).  To avoid rewriting everything we make a
  // virtual scratch register point at the UCB.
  ip = (_Unwind_Ptr) ue_header;
  _Unwind_SetGR(context, UNWIND_POINTER_REG, ip);
#else
  __cxa_exception* xh = __get_exception_header_from_ue(ue_header);

  // Interface version check.
  if (version != 1)
    return _URC_FATAL_PHASE1_ERROR;
  foreign_exception = !__is_gxx_exception_class(exception_class);
#endif

  // Shortcut for phase 2 found handler for domestic exception.
  if (actions == (_UA_CLEANUP_PHASE | _UA_HANDLER_FRAME)
      && !foreign_exception)
    {
      restore_caught_exception(ue_header, handler_switch_value,
			       language_specific_data, landing_pad);
      found_type = (landing_pad == 0 ? found_terminate : found_handler);
      goto install_context;
    }

  language_specific_data = (const unsigned char *)
    _Unwind_GetLanguageSpecificData (context);

  // If no LSDA, then there are no handlers or cleanups.
  if (! language_specific_data)
    CONTINUE_UNWINDING;

  // Parse the LSDA header.
  p = parse_lsda_header (context, language_specific_data, &info);
  info.ttype_base = base_of_encoded_value (info.ttype_encoding, context);
#ifdef _GLIBCXX_HAVE_GETIPINFO
  ip = _Unwind_GetIPInfo (context, &ip_before_insn);
#else
  ip = _Unwind_GetIP (context);
#endif
  if (! ip_before_insn)
    --ip;
  landing_pad = 0;
  action_record = 0;
  handler_switch_value = 0;

#ifdef __USING_SJLJ_EXCEPTIONS__
  // The given "IP" is an index into the call-site table, with two
  // exceptions -- -1 means no-action, and 0 means terminate.  But
  // since we're using uleb128 values, we've not got random access
  // to the array.
  if ((int) ip < 0)
    return _URC_CONTINUE_UNWIND;
  else if (ip == 0)
    {
      // Fall through to set found_terminate.
    }
  else
    {
      _uleb128_t cs_lp, cs_action;
      do
	{
	  p = read_uleb128 (p, &cs_lp);
	  p = read_uleb128 (p, &cs_action);
	}
      while (--ip);

      // Can never have null landing pad for sjlj -- that would have
      // been indicated by a -1 call site index.
      landing_pad = cs_lp + 1;
      if (cs_action)
	action_record = info.action_table + cs_action - 1;
      goto found_something;
    }
#else
  // Search the call-site table for the action associated with this IP.
  while (p < info.action_table)
    {
      _Unwind_Ptr cs_start, cs_len, cs_lp;
      _uleb128_t cs_action;

      // Note that all call-site encodings are "absolute" displacements.
      p = read_encoded_value (0, info.call_site_encoding, p, &cs_start);
      p = read_encoded_value (0, info.call_site_encoding, p, &cs_len);
      p = read_encoded_value (0, info.call_site_encoding, p, &cs_lp);
      p = read_uleb128 (p, &cs_action);

      // The table is sorted, so if we've passed the ip, stop.
      if (ip < info.Start + cs_start)
	p = info.action_table;
      else if (ip < info.Start + cs_start + cs_len)
	{
	  if (cs_lp)
	    landing_pad = info.LPStart + cs_lp;
	  if (cs_action)
	    action_record = info.action_table + cs_action - 1;
	  goto found_something;
	}
    }
#endif // __USING_SJLJ_EXCEPTIONS__

  // If ip is not present in the table, call terminate.  This is for
  // a destructor inside a cleanup, or a library routine the compiler
  // was not expecting to throw.
  found_type = found_terminate;
  goto do_something;

 found_something:
  if (landing_pad == 0)
    {
      // If ip is present, and has a null landing pad, there are
      // no cleanups or handlers to be run.
      found_type = found_nothing;
    }
  else if (action_record == 0)
    {
      // If ip is present, has a non-null landing pad, and a null
      // action table offset, then there are only cleanups present.
      // Cleanups use a zero switch value, as set above.
      found_type = found_cleanup;
    }
  else
    {
      // Otherwise we have a catch handler or exception specification.

      _sleb128_t ar_filter, ar_disp;
      const std::type_info* catch_type;
      _throw_typet* throw_type;
      bool saw_cleanup = false;
      bool saw_handler = false;

#ifdef __ARM_EABI_UNWINDER__
      // ??? How does this work - more importantly, how does it interact with
      // dependent exceptions?
      throw_type = ue_header;
      if (actions & _UA_FORCE_UNWIND)
	{
	  __GXX_INIT_FORCED_UNWIND_CLASS(ue_header->exception_class);
	}
      else if (!foreign_exception)
	thrown_ptr = __get_object_from_ue (ue_header);
#else
#if __cpp_rtti
      // During forced unwinding, match a magic exception type.
      if (actions & _UA_FORCE_UNWIND)
	{
	  throw_type = &typeid(abi::__forced_unwind);
	}
      // With a foreign exception class, there's no exception type.
      // ??? What to do about GNU Java and GNU Ada exceptions?
      else if (foreign_exception)
	{
	  throw_type = &typeid(abi::__foreign_exception);
	}
      else
#endif
        {
          thrown_ptr = __get_object_from_ue (ue_header);
          throw_type = __get_exception_header_from_obj
            (thrown_ptr)->exceptionType;
        }
#endif

      while (1)
	{
	  p = action_record;
	  p = read_sleb128 (p, &ar_filter);
	  read_sleb128 (p, &ar_disp);

	  if (ar_filter == 0)
	    {
	      // Zero filter values are cleanups.
	      saw_cleanup = true;
	    }
	  else if (ar_filter > 0)
	    {
	      // Positive filter values are handlers.
	      catch_type = get_ttype_entry (&info, ar_filter);

	      // Null catch type is a catch-all handler; we can catch foreign
	      // exceptions with this.  Otherwise we must match types.
	      if (! catch_type
		  || (throw_type
		      && get_adjusted_ptr (catch_type, throw_type,
					   &thrown_ptr)))
		{
		  saw_handler = true;
		  break;
		}
	    }
	  else
	    {
	      // Negative filter values are exception specifications.
	      // ??? How do foreign exceptions fit in?  As far as I can
	      // see we can't match because there's no __cxa_exception
	      // object to stuff bits in for __cxa_call_unexpected to use.
	      // Allow them iff the exception spec is non-empty.  I.e.
	      // a throw() specification results in __unexpected.
	      if ((throw_type
		   && !(actions & _UA_FORCE_UNWIND)
		   && !foreign_exception)
		  ? ! check_exception_spec (&info, throw_type, thrown_ptr,
					    ar_filter)
		  : empty_exception_spec (&info, ar_filter))
		{
		  saw_handler = true;
		  break;
		}
	    }

	  if (ar_disp == 0)
	    break;
	  action_record = p + ar_disp;
	}

      if (saw_handler)
	{
	  handler_switch_value = ar_filter;
	  found_type = found_handler;
	}
      else
	found_type = (saw_cleanup ? found_cleanup : found_nothing);
    }

 do_something:
   if (found_type == found_nothing)
     CONTINUE_UNWINDING;

  if (actions & _UA_SEARCH_PHASE)
    {
      if (found_type == found_cleanup)
	CONTINUE_UNWINDING;

      // For domestic exceptions, we cache data from phase 1 for phase 2.
      if (!foreign_exception)
        {
	  save_caught_exception(ue_header, context, thrown_ptr,
				handler_switch_value, language_specific_data,
				landing_pad, action_record);
	}
      return _URC_HANDLER_FOUND;
    }

 install_context:
  
  // We can't use any of the cxa routines with foreign exceptions,
  // because they all expect ue_header to be a struct __cxa_exception.
  // So in that case, call terminate or unexpected directly.
  if ((actions & _UA_FORCE_UNWIND)
      || foreign_exception)
    {
      if (found_type == found_terminate)
	std::terminate ();
      else if (handler_switch_value < 0)
	{
	  __try 
	    { std::unexpected (); } 
	  __catch(...) 
	    { std::terminate (); }
	}
    }
  else
    {
      if (found_type == found_terminate)
	__cxa_call_terminate(ue_header);

      // Cache the TType base value for __cxa_call_unexpected, as we won't
      // have an _Unwind_Context then.
      if (handler_switch_value < 0)
	{
	  parse_lsda_header (context, language_specific_data, &info);
	  info.ttype_base = base_of_encoded_value (info.ttype_encoding,
						   context);

#ifdef __ARM_EABI_UNWINDER__
	  const _Unwind_Word* e;
	  _Unwind_Word n;
	  
	  e = ((const _Unwind_Word*) info.TType) - handler_switch_value - 1;
	  // Count the number of rtti objects.
	  n = 0;
	  while (e[n] != 0)
	    n++;

	  // Count.
	  ue_header->barrier_cache.bitpattern[1] = n;
	  // Base
	  ue_header->barrier_cache.bitpattern[2] = info.ttype_base;
	  // Stride.
	  ue_header->barrier_cache.bitpattern[3] = 4;
	  // List head.
	  ue_header->barrier_cache.bitpattern[4] = (_Unwind_Word) e;
#else
	  xh->catchTemp = base_of_encoded_value (info.ttype_encoding, context);
#endif
	}
    }

  /* For targets with pointers smaller than the word size, we must extend the
     pointer, and this extension is target dependent.  */
  _Unwind_SetGR (context, __builtin_eh_return_data_regno (0),
		 __builtin_extend_pointer (ue_header));
  _Unwind_SetGR (context, __builtin_eh_return_data_regno (1),
		 handler_switch_value);
  _Unwind_SetIP (context, landing_pad);
#ifdef __ARM_EABI_UNWINDER__
  if (found_type == found_cleanup)
    __cxa_begin_cleanup(ue_header);
#endif
  return _URC_INSTALL_CONTEXT;
}

/* The ARM EABI implementation of __cxa_call_unexpected is in a
   different file so that the personality routine (PR) can be used
   standalone.  The generic routine shared datastructures with the PR
   so it is most convenient to implement it here.  */
#ifndef __ARM_EABI_UNWINDER__
extern "C" void
__cxa_call_unexpected (void *exc_obj_in)
{
  _Unwind_Exception *exc_obj
    = reinterpret_cast <_Unwind_Exception *>(exc_obj_in);

  __cxa_begin_catch (exc_obj);

  // This function is a handler for our exception argument.  If we exit
  // by throwing a different exception, we'll need the original cleaned up.
  struct end_catch_protect
  {
    end_catch_protect() { }
    ~end_catch_protect() { __cxa_end_catch(); }
  } end_catch_protect_obj;

  lsda_header_info info;
  __cxa_exception *xh = __get_exception_header_from_ue (exc_obj);
  const unsigned char *xh_lsda;
  _Unwind_Sword xh_switch_value;
  std::terminate_handler xh_terminate_handler;

  // If the unexpectedHandler rethrows the exception (e.g. to categorize it),
  // it will clobber data about the current handler.  So copy the data out now.
  xh_lsda = xh->languageSpecificData;
  xh_switch_value = xh->handlerSwitchValue;
  xh_terminate_handler = xh->terminateHandler;
  info.ttype_base = (_Unwind_Ptr) xh->catchTemp;

  __try 
    { __unexpected (xh->unexpectedHandler); } 
  __catch(...) 
    {
      // Get the exception thrown from unexpected.

      __cxa_eh_globals *globals = __cxa_get_globals_fast ();
      __cxa_exception *new_xh = globals->caughtExceptions;
      void *new_ptr = __get_object_from_ambiguous_exception (new_xh);

      // We don't quite have enough stuff cached; re-parse the LSDA.
      parse_lsda_header (0, xh_lsda, &info);

      // If this new exception meets the exception spec, allow it.
      if (check_exception_spec (&info, __get_exception_header_from_obj
                                  (new_ptr)->exceptionType,
				new_ptr, xh_switch_value))
	{ __throw_exception_again; }

      // If the exception spec allows std::bad_exception, throw that.
      // We don't have a thrown object to compare against, but since
      // bad_exception doesn't have virtual bases, that's OK; just pass 0.
#if __cpp_exceptions && __cpp_rtti
      const std::type_info &bad_exc = typeid (std::bad_exception);
      if (check_exception_spec (&info, &bad_exc, 0, xh_switch_value))
	throw std::bad_exception();
#endif   

      // Otherwise, die.
      __terminate (xh_terminate_handler);
    }
}
#endif

#if defined (__SEH__) && !defined (__USING_SJLJ_EXCEPTIONS__)
extern "C"
EXCEPTION_DISPOSITION
__gxx_personality_seh0 (PEXCEPTION_RECORD ms_exc, void *this_frame,
			PCONTEXT ms_orig_context, PDISPATCHER_CONTEXT ms_disp)
{
  return _GCC_specific_handler (ms_exc, this_frame, ms_orig_context,
				ms_disp, __gxx_personality_imp);
}
#endif /* SEH */

} // namespace __cxxabiv1