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From: Frank Mori Hess (fmhess_at_[hidden])
Date: 2008-04-20 10:08:31
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On Tuesday 15 April 2008 13:19, Sebastian Redl wrote:
> I can use current_exception() to get the currently handled exception.
> However, calling it again will yield a null pointer. That's because I
> can't abuse handlerCount properly.
>
> The exception_ptr works so far that it lets the exception escape the
> catch.
>
> I can use rethrow_exception() to rethrow the exception. However, when I
> catch it again, it won't escape the catch. I.e.
Here's a partial proof-of-concept implementation of exception_ptr for
Linux, tested on gcc 4.1.2. The unwind-cxx.h file is just a copy from the
gcc source: gcc-4.1.1/libstdc++-v3/libsupc++/unwind-cxx.h. The test
program demonstrates that you can rethrow more than once. There is no
implementation for copy_exception() yet. If you call current_exception
multiple times for one exception, it will probably crash. That should be
fixable by adding a global/singleton map which would let you find if
another exception_ptr already owns a particular exception object.
- --
Frank
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Content-Type: text/x-c++src; charset="iso-8859-1";
name="exception_ptr_test.cpp"
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Content-Disposition: attachment;
filename="exception_ptr_test.cpp"
#include <boost/shared_ptr.hpp>
#include <stdexcept>
#include <iostream>
#include "unwind-cxx.h"
using namespace __cxxabiv1;
void
__cxxabiv1::__terminate (std::terminate_handler handler)
{
try {
handler ();
std::abort ();
} catch (...) {
std::abort ();
}
}
typedef boost::shared_ptr<__cxa_exception> exception_ptr;
namespace detail
{
void fake_cleanup(_Unwind_Reason_Code code, struct _Unwind_Exception *exc)
{
std::cerr << __PRETTY_FUNCTION__ << std::endl;
__cxa_exception *header =3D __get_exception_header_from_ue (exc);
// If we haven't been caught by a foreign handler, then this is
// some sort of unwind error. In that case just die immediately.
// _Unwind_DeleteException in the HP-UX IA64 libunwind library
// returns _URC_NO_REASON and not _URC_FOREIGN_EXCEPTION_CAUGHT
// like the GCC _Unwind_DeleteException function does.
if (code !=3D _URC_FOREIGN_EXCEPTION_CAUGHT && code !=3D _URC_NO_REASON)
__terminate (header->terminateHandler);
}
=09
void exception_ptr_deleter(__cxa_exception *header)
{
if (header->exceptionDestructor)
header->exceptionDestructor(header + 1);
__cxa_free_exception (header + 1);
}
}
exception_ptr current_exception()
{
__cxa_eh_globals *globals =3D __cxa_get_globals();
__cxa_exception *header =3D globals->caughtExceptions;
exception_ptr current(header, &detail::exception_ptr_deleter);
header->unwindHeader.exception_cleanup =3D &detail::fake_cleanup;
return current;
}
void rethrow_exception(exception_ptr ep)
{
#ifdef _GLIBCXX_SJLJ_EXCEPTIONS
_Unwind_SjLj_RaiseException (&ep->unwindHeader);
#else
_Unwind_RaiseException (&ep->unwindHeader);
#endif
// Some sort of unwinding error. Note that terminate is a handler.
__cxa_begin_catch (&ep->unwindHeader);
std::terminate ();
}
class test_exception: public std::runtime_error
{
public:
test_exception(const char *what_string): runtime_error(what_string)
{}
test_exception(const std::string &what_string): runtime_error(what_string)
{}
~test_exception() throw()
{
std::cerr << __PRETTY_FUNCTION__ << std::endl;
}
};
int main()
{
{
exception_ptr ep;
try
{
throw test_exception("this is my test exception");
}
catch(...)
{
std::cerr << "caught error, getting exception_ptr." << std::endl;
ep =3D current_exception();
}
try
{
rethrow_exception(ep);
}
catch(test_exception &err)
{
std::cerr << "caught test exception: " << err.what() << std::endl;
}
try
{
rethrow_exception(ep);
}
catch(test_exception &err)
{
std::cerr << "caught test exception again: " << err.what() << std::endl;
}
std::cerr << "exception_ptr going out of scope" << std::endl;
}
return 0;
}
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Content-Type: text/x-c++hdr;
charset="iso-8859-1";
name="unwind-cxx.h"
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filename="unwind-cxx.h"
// -*- C++ -*- Exception handling and frame unwind runtime interface routin=
es.
// Copyright (C) 2001 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 2, 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.
//
// You should have received a copy of the GNU General Public License
// along with GCC; see the file COPYING. If not, write to
// the Free Software Foundation, 51 Franklin Street, Fifth Floor,
// Boston, MA 02110-1301, USA.
// As a special exception, you may use this file as part of a free software
// library without restriction. Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compi=
le
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License. This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.
// This is derived from the C++ ABI for IA-64. Where we diverge
// for cross-architecture compatibility are noted with "@@@".
#ifndef _UNWIND_CXX_H
#define _UNWIND_CXX_H 1
// Level 2: C++ ABI
#include <typeinfo>
#include <exception>
#include <cstddef>
#include "unwind.h"
#pragma GCC visibility push(default)
namespace __cxxabiv1
{
// A C++ exception object consists of a header, which is a wrapper around
// an unwind object header with additional C++ specific information,
// followed by the exception object itself.
struct __cxa_exception
{=20
// Manage the exception object itself.
std::type_info *exceptionType;
void (*exceptionDestructor)(void *);=20
// The C++ standard has entertaining rules wrt calling set_terminate
// and set_unexpected in the middle of the exception cleanup process.
std::unexpected_handler unexpectedHandler;
std::terminate_handler terminateHandler;
// The caught exception stack threads through here.
__cxa_exception *nextException;
// How many nested handlers have caught this exception. A negated
// value is a signal that this object has been rethrown.
int handlerCount;
#ifdef __ARM_EABI_UNWINDER__
// Stack of exceptions in cleanups.
__cxa_exception* nextPropagatingException;
// The nuber of active cleanup handlers for this exception.
int propagationCount;
#else
// Cache parsed handler data from the personality routine Phase 1
// for Phase 2 and __cxa_call_unexpected.
int handlerSwitchValue;
const unsigned char *actionRecord;
const unsigned char *languageSpecificData;
_Unwind_Ptr catchTemp;
void *adjustedPtr;
#endif
// The generic exception header. Must be last.
_Unwind_Exception unwindHeader;
};
// Each thread in a C++ program has access to a __cxa_eh_globals object.
struct __cxa_eh_globals
{
__cxa_exception *caughtExceptions;
unsigned int uncaughtExceptions;
#ifdef __ARM_EABI_UNWINDER__
__cxa_exception* propagatingExceptions;
#endif
};
// The __cxa_eh_globals for the current thread can be obtained by using
// either of the following functions. The "fast" version assumes at least
// one prior call of __cxa_get_globals has been made from the current
// thread, so no initialization is necessary.
extern "C" __cxa_eh_globals *__cxa_get_globals () throw();
extern "C" __cxa_eh_globals *__cxa_get_globals_fast () throw();
// Allocate memory for the exception plus the thown object.
extern "C" void *__cxa_allocate_exception(std::size_t thrown_size) throw();
// Free the space allocated for the exception.
extern "C" void __cxa_free_exception(void *thrown_exception) throw();
// Throw the exception.
extern "C" void __cxa_throw (void *thrown_exception,
std::type_info *tinfo,
void (*dest) (void *))
__attribute__((noreturn));
// Used to implement exception handlers.
extern "C" void *__cxa_get_exception_ptr (void *) throw();
extern "C" void *__cxa_begin_catch (void *) throw();
extern "C" void __cxa_end_catch ();
extern "C" void __cxa_rethrow () __attribute__((noreturn));
// These facilitate code generation for recurring situations.
extern "C" void __cxa_bad_cast ();
extern "C" void __cxa_bad_typeid ();
// @@@ These are not directly specified by the IA-64 C++ ABI.
// Handles re-checking the exception specification if unexpectedHandler
// throws, and if bad_exception needs to be thrown. Called from the
// compiler.
extern "C" void __cxa_call_unexpected (void *) __attribute__((noreturn));
extern "C" void __cxa_call_terminate (void*) __attribute__((noreturn));
#ifdef __ARM_EABI_UNWINDER__
// Arm EABI specified routines.
typedef enum {
ctm_failed =3D 0,
ctm_succeeded =3D 1,
ctm_succeeded_with_ptr_to_base =3D 2
} __cxa_type_match_result;
extern "C" bool __cxa_type_match(_Unwind_Exception*, const std::type_info*,
bool, void**);
extern "C" void __cxa_begin_cleanup (_Unwind_Exception*);
extern "C" void __cxa_end_cleanup (void);
#endif
// Invokes given handler, dying appropriately if the user handler was
// so inconsiderate as to return.
extern void __terminate(std::terminate_handler) __attribute__((noreturn));
extern void __unexpected(std::unexpected_handler) __attribute__((noreturn));
// The current installed user handlers.
extern std::terminate_handler __terminate_handler;
extern std::unexpected_handler __unexpected_handler;
// These are explicitly GNU C++ specific.
// Acquire the C++ exception header from the C++ object.
static inline __cxa_exception *
__get_exception_header_from_obj (void *ptr)
{
return reinterpret_cast<__cxa_exception *>(ptr) - 1;
}
// Acquire the C++ exception header from the generic exception header.
static inline __cxa_exception *
__get_exception_header_from_ue (_Unwind_Exception *exc)
{
return reinterpret_cast<__cxa_exception *>(exc + 1) - 1;
}
#ifdef __ARM_EABI_UNWINDER__
static inline bool
__is_gxx_exception_class(_Unwind_Exception_Class c)
{
// TODO: Take advantage of the fact that c will always be word aligned.
return c[0] =3D=3D 'G'
&& c[1] =3D=3D 'N'
&& c[2] =3D=3D 'U'
&& c[3] =3D=3D 'C'
&& c[4] =3D=3D 'C'
&& c[5] =3D=3D '+'
&& c[6] =3D=3D '+'
&& c[7] =3D=3D '\0';
}
static inline void
__GXX_INIT_EXCEPTION_CLASS(_Unwind_Exception_Class c)
{
c[0] =3D 'G';
c[1] =3D 'N';
c[2] =3D 'U';
c[3] =3D 'C';
c[4] =3D 'C';
c[5] =3D '+';
c[6] =3D '+';
c[7] =3D '\0';
}
static inline void*
__gxx_caught_object(_Unwind_Exception* eo)
{
return (void*)eo->barrier_cache.bitpattern[0];
}
#else // !__ARM_EABI_UNWINDER__
// This is the exception class we report -- "GNUCC++\0".
const _Unwind_Exception_Class __gxx_exception_class
=3D ((((((((_Unwind_Exception_Class) 'G'=20
<< 8 | (_Unwind_Exception_Class) 'N')
<< 8 | (_Unwind_Exception_Class) 'U')
<< 8 | (_Unwind_Exception_Class) 'C')
<< 8 | (_Unwind_Exception_Class) 'C')
<< 8 | (_Unwind_Exception_Class) '+')
<< 8 | (_Unwind_Exception_Class) '+')
<< 8 | (_Unwind_Exception_Class) '\0');
static inline bool
__is_gxx_exception_class(_Unwind_Exception_Class c)
{
return c =3D=3D __gxx_exception_class;
}
#define __GXX_INIT_EXCEPTION_CLASS(c) c =3D __gxx_exception_class
// GNU C++ personality routine, Version 0.
extern "C" _Unwind_Reason_Code __gxx_personality_v0
(int, _Unwind_Action, _Unwind_Exception_Class,
struct _Unwind_Exception *, struct _Unwind_Context *);
// GNU C++ sjlj personality routine, Version 0.
extern "C" _Unwind_Reason_Code __gxx_personality_sj0
(int, _Unwind_Action, _Unwind_Exception_Class,
struct _Unwind_Exception *, struct _Unwind_Context *);
static inline void*
__gxx_caught_object(_Unwind_Exception* eo)
{
__cxa_exception* header =3D __get_exception_header_from_ue (eo);
return header->adjustedPtr;
}
#endif // !__ARM_EABI_UNWINDER__
} /* namespace __cxxabiv1 */
#pragma GCC visibility pop
#endif // _UNWIND_CXX_H
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