- Copy stable/9 to releng/9.2 as part of the 9.2-RELEASE cycle.

[FreeBSD/releng/9.2.git] / contrib / libcxxrt / exception.cc

/* 
 * Copyright 2010-2011 PathScale, Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <stdlib.h>
#include <dlfcn.h>
#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <pthread.h>
#include "typeinfo.h"
#include "dwarf_eh.h"
#include "atomic.h"
#include "cxxabi.h"

#pragma weak pthread_key_create
#pragma weak pthread_setspecific
#pragma weak pthread_getspecific
#pragma weak pthread_once
#ifdef LIBCXXRT_WEAK_LOCKS
#pragma weak pthread_mutex_lock
#define pthread_mutex_lock(mtx) do {\
        if (pthread_mutex_lock) pthread_mutex_lock(mtx);\
        } while(0)
#pragma weak pthread_mutex_unlock
#define pthread_mutex_unlock(mtx) do {\
        if (pthread_mutex_unlock) pthread_mutex_unlock(mtx);\
        } while(0)
#pragma weak pthread_cond_signal
#define pthread_cond_signal(cv) do {\
        if (pthread_cond_signal) pthread_cond_signal(cv);\
        } while(0)
#pragma weak pthread_cond_wait
#define pthread_cond_wait(cv, mtx) do {\
        if (pthread_cond_wait) pthread_cond_wait(cv, mtx);\
        } while(0)
#endif

using namespace ABI_NAMESPACE;

/**
 * Saves the result of the landing pad that we have found.  For ARM, this is
 * stored in the generic unwind structure, while on other platforms it is
 * stored in the C++ exception.
 */
static void saveLandingPad(struct _Unwind_Context *context,
                           struct _Unwind_Exception *ucb,
                           struct __cxa_exception *ex,
                           int selector,
                           dw_eh_ptr_t landingPad)
{
#ifdef __arm__
        // On ARM, we store the saved exception in the generic part of the structure
        ucb->barrier_cache.sp = _Unwind_GetGR(context, 13);
        ucb->barrier_cache.bitpattern[1] = (uint32_t)selector;
        ucb->barrier_cache.bitpattern[3] = (uint32_t)landingPad;
#endif
        // Cache the results for the phase 2 unwind, if we found a handler
        // and this is not a foreign exception.  
        if (ex)
        {
                ex->handlerSwitchValue = selector;
                ex->catchTemp = landingPad;
        }
}

/**
 * Loads the saved landing pad.  Returns 1 on success, 0 on failure.
 */
static int loadLandingPad(struct _Unwind_Context *context,
                          struct _Unwind_Exception *ucb,
                          struct __cxa_exception *ex,
                          unsigned long *selector,
                          dw_eh_ptr_t *landingPad)
{
#ifdef __arm__
        *selector = ucb->barrier_cache.bitpattern[1];
        *landingPad = (dw_eh_ptr_t)ucb->barrier_cache.bitpattern[3];
        return 1;
#else
        if (ex)
        {
                *selector = ex->handlerSwitchValue;
                *landingPad = (dw_eh_ptr_t)ex->catchTemp;
                return 0;
        }
        return 0;
#endif
}

static inline _Unwind_Reason_Code continueUnwinding(struct _Unwind_Exception *ex,
                                                    struct _Unwind_Context *context)
{
#ifdef __arm__
        if (__gnu_unwind_frame(ex, context) != _URC_OK) { return _URC_FAILURE; }
#endif
        return _URC_CONTINUE_UNWIND;
}


extern "C" void __cxa_free_exception(void *thrown_exception);
extern "C" void __cxa_free_dependent_exception(void *thrown_exception);
extern "C" void* __dynamic_cast(const void *sub,
                                const __class_type_info *src,
                                const __class_type_info *dst,
                                ptrdiff_t src2dst_offset);

/**
 * The type of a handler that has been found.
 */
typedef enum
{
        /** No handler. */
        handler_none,
        /**
         * A cleanup - the exception will propagate through this frame, but code
         * must be run when this happens.
         */
        handler_cleanup,
        /**
         * A catch statement.  The exception will not propagate past this frame
         * (without an explicit rethrow).
         */
        handler_catch
} handler_type;

/**
 * Per-thread info required by the runtime.  We store a single structure
 * pointer in thread-local storage, because this tends to be a scarce resource
 * and it's impolite to steal all of it and not leave any for the rest of the
 * program.
 *
 * Instances of this structure are allocated lazily - at most one per thread -
 * and are destroyed on thread termination.
 */
struct __cxa_thread_info
{
        /** The termination handler for this thread. */
        terminate_handler terminateHandler;
        /** The unexpected exception handler for this thread. */
        unexpected_handler unexpectedHandler;
        /**
         * The number of emergency buffers held by this thread.  This is 0 in
         * normal operation - the emergency buffers are only used when malloc()
         * fails to return memory for allocating an exception.  Threads are not
         * permitted to hold more than 4 emergency buffers (as per recommendation
         * in ABI spec [3.3.1]).
         */
        int emergencyBuffersHeld;
        /**
         * The exception currently running in a cleanup.
         */
        _Unwind_Exception *currentCleanup;
        /**
         * Our state with respect to foreign exceptions.  Usually none, set to
         * caught if we have just caught an exception and rethrown if we are
         * rethrowing it.
         */
        enum 
        {
                none,
                caught,
                rethrown
        } foreign_exception_state;
        /**
         * The public part of this structure, accessible from outside of this
         * module.
         */
        __cxa_eh_globals globals;
};
/**
 * Dependent exception.  This 
 */
struct __cxa_dependent_exception
{
#if __LP64__
        void *primaryException;
#endif
        std::type_info *exceptionType;
        void (*exceptionDestructor) (void *); 
        unexpected_handler unexpectedHandler;
        terminate_handler terminateHandler;
        __cxa_exception *nextException;
        int handlerCount;
#ifdef __arm__
        _Unwind_Exception *nextCleanup;
        int cleanupCount;
#endif
        int handlerSwitchValue;
        const char *actionRecord;
        const char *languageSpecificData;
        void *catchTemp;
        void *adjustedPtr;
#if !__LP64__
        void *primaryException;
#endif
        _Unwind_Exception unwindHeader;
};


namespace std
{
        void unexpected();
        class exception
        {
                public:
                        virtual ~exception() throw();
                        virtual const char* what() const throw();
        };

}

/**
 * Class of exceptions to distinguish between this and other exception types.
 *
 * The first four characters are the vendor ID.  Currently, we use GNUC,
 * because we aim for ABI-compatibility with the GNU implementation, and
 * various checks may test for equality of the class, which is incorrect.
 */
static const uint64_t exception_class =
        EXCEPTION_CLASS('G', 'N', 'U', 'C', 'C', '+', '+', '\0');
/**
 * Class used for dependent exceptions.  
 */
static const uint64_t dependent_exception_class =
        EXCEPTION_CLASS('G', 'N', 'U', 'C', 'C', '+', '+', '\x01');
/**
 * The low four bytes of the exception class, indicating that we conform to the
 * Itanium C++ ABI.  This is currently unused, but should be used in the future
 * if we change our exception class, to allow this library and libsupc++ to be
 * linked to the same executable and both to interoperate.
 */
static const uint32_t abi_exception_class = 
        GENERIC_EXCEPTION_CLASS('C', '+', '+', '\0');

static bool isCXXException(uint64_t cls)
{
        return (cls == exception_class) || (cls == dependent_exception_class);
}

static bool isDependentException(uint64_t cls)
{
        return cls == dependent_exception_class;
}

static __cxa_exception *exceptionFromPointer(void *ex)
{
        return (__cxa_exception*)((char*)ex -
                        offsetof(struct __cxa_exception, unwindHeader));
}
static __cxa_exception *realExceptionFromException(__cxa_exception *ex)
{
        if (!isDependentException(ex->unwindHeader.exception_class)) { return ex; }
        return ((__cxa_exception*)(((__cxa_dependent_exception*)ex)->primaryException))-1;
}


namespace std
{
        // Forward declaration of standard library terminate() function used to
        // abort execution.
        void terminate(void);
}

using namespace ABI_NAMESPACE;



/** The global termination handler. */
static terminate_handler terminateHandler = abort;
/** The global unexpected exception handler. */
static unexpected_handler unexpectedHandler = std::terminate;

/** Key used for thread-local data. */
static pthread_key_t eh_key;


/**
 * Cleanup function, allowing foreign exception handlers to correctly destroy
 * this exception if they catch it.
 */
static void exception_cleanup(_Unwind_Reason_Code reason, 
                              struct _Unwind_Exception *ex)
{
        __cxa_free_exception((void*)ex);
}
static void dependent_exception_cleanup(_Unwind_Reason_Code reason, 
                              struct _Unwind_Exception *ex)
{

        __cxa_free_dependent_exception((void*)ex);
}

/**
 * Recursively walk a list of exceptions and delete them all in post-order.
 */
static void free_exception_list(__cxa_exception *ex)
{
        if (0 != ex->nextException)
        {
                free_exception_list(ex->nextException);
        }
        // __cxa_free_exception() expects to be passed the thrown object, which
        // immediately follows the exception, not the exception itself
        __cxa_free_exception(ex+1);
}

/**
 * Cleanup function called when a thread exists to make certain that all of the
 * per-thread data is deleted.
 */
static void thread_cleanup(void* thread_info)
{
        __cxa_thread_info *info = (__cxa_thread_info*)thread_info;
        if (info->globals.caughtExceptions)
        {
                // If this is a foreign exception, ask it to clean itself up.
                if (info->foreign_exception_state != __cxa_thread_info::none)
                {
                        _Unwind_Exception *e = (_Unwind_Exception*)info->globals.caughtExceptions;
                        e->exception_cleanup(_URC_FOREIGN_EXCEPTION_CAUGHT, e);
                }
                else
                {
                        free_exception_list(info->globals.caughtExceptions);
                }
        }
        free(thread_info);
}


/**
 * Once control used to protect the key creation.
 */
static pthread_once_t once_control = PTHREAD_ONCE_INIT;

/**
 * We may not be linked against a full pthread implementation.  If we're not,
 * then we need to fake the thread-local storage by storing 'thread-local'
 * things in a global.
 */
static bool fakeTLS;
/**
 * Thread-local storage for a single-threaded program.
 */
static __cxa_thread_info singleThreadInfo;
/**
 * Initialise eh_key.
 */
static void init_key(void)
{
        if ((0 == pthread_key_create) ||
            (0 == pthread_setspecific) ||
            (0 == pthread_getspecific))
        {
                fakeTLS = true;
                return;
        }
        pthread_key_create(&eh_key, thread_cleanup);
        pthread_setspecific(eh_key, (void*)0x42);
        fakeTLS = (pthread_getspecific(eh_key) != (void*)0x42);
        pthread_setspecific(eh_key, 0);
}

/**
 * Returns the thread info structure, creating it if it is not already created.
 */
static __cxa_thread_info *thread_info()
{
        if ((0 == pthread_once) || pthread_once(&once_control, init_key))
        {
                fakeTLS = true;
        }
        if (fakeTLS) { return &singleThreadInfo; }
        __cxa_thread_info *info = (__cxa_thread_info*)pthread_getspecific(eh_key);
        if (0 == info)
        {
                info = (__cxa_thread_info*)calloc(1, sizeof(__cxa_thread_info));
                pthread_setspecific(eh_key, info);
        }
        return info;
}
/**
 * Fast version of thread_info().  May fail if thread_info() is not called on
 * this thread at least once already.
 */
static __cxa_thread_info *thread_info_fast()
{
        if (fakeTLS) { return &singleThreadInfo; }
        return (__cxa_thread_info*)pthread_getspecific(eh_key);
}
/**
 * ABI function returning the __cxa_eh_globals structure.
 */
extern "C" __cxa_eh_globals *ABI_NAMESPACE::__cxa_get_globals(void)
{
        return &(thread_info()->globals);
}
/**
 * Version of __cxa_get_globals() assuming that __cxa_get_globals() has already
 * been called at least once by this thread.
 */
extern "C" __cxa_eh_globals *ABI_NAMESPACE::__cxa_get_globals_fast(void)
{
        return &(thread_info_fast()->globals);
}

/**
 * An emergency allocation reserved for when malloc fails.  This is treated as
 * 16 buffers of 1KB each.
 */
static char emergency_buffer[16384];
/**
 * Flag indicating whether each buffer is allocated.
 */
static bool buffer_allocated[16];
/**
 * Lock used to protect emergency allocation.
 */
static pthread_mutex_t emergency_malloc_lock = PTHREAD_MUTEX_INITIALIZER;
/**
 * Condition variable used to wait when two threads are both trying to use the
 * emergency malloc() buffer at once.
 */
static pthread_cond_t emergency_malloc_wait = PTHREAD_COND_INITIALIZER;

/**
 * Allocates size bytes from the emergency allocation mechanism, if possible.
 * This function will fail if size is over 1KB or if this thread already has 4
 * emergency buffers.  If all emergency buffers are allocated, it will sleep
 * until one becomes available.
 */
static char *emergency_malloc(size_t size)
{
        if (size > 1024) { return 0; }

        __cxa_thread_info *info = thread_info();
        // Only 4 emergency buffers allowed per thread!
        if (info->emergencyBuffersHeld > 3) { return 0; }

        pthread_mutex_lock(&emergency_malloc_lock);
        int buffer = -1;
        while (buffer < 0)
        {
                // While we were sleeping on the lock, another thread might have free'd
                // enough memory for us to use, so try the allocation again - no point
                // using the emergency buffer if there is some real memory that we can
                // use...
                void *m = calloc(1, size);
                if (0 != m)
                {
                        pthread_mutex_unlock(&emergency_malloc_lock);
                        return (char*)m;
                }
                for (int i=0 ; i<16 ; i++)
                {
                        if (!buffer_allocated[i])
                        {
                                buffer = i;
                                buffer_allocated[i] = true;
                                break;
                        }
                }
                // If there still isn't a buffer available, then sleep on the condition
                // variable.  This will be signalled when another thread releases one
                // of the emergency buffers.
                if (buffer < 0)
                {
                        pthread_cond_wait(&emergency_malloc_wait, &emergency_malloc_lock);
                }
        }
        pthread_mutex_unlock(&emergency_malloc_lock);
        info->emergencyBuffersHeld++;
        return emergency_buffer + (1024 * buffer);
}

/**
 * Frees a buffer returned by emergency_malloc().
 *
 * Note: Neither this nor emergency_malloc() is particularly efficient.  This
 * should not matter, because neither will be called in normal operation - they
 * are only used when the program runs out of memory, which should not happen
 * often.
 */
static void emergency_malloc_free(char *ptr)
{
        int buffer = -1;
        // Find the buffer corresponding to this pointer.
        for (int i=0 ; i<16 ; i++)
        {
                if (ptr == (void*)(emergency_buffer + (1024 * i)))
                {
                        buffer = i;
                        break;
                }
        }
        assert(buffer > 0 &&
               "Trying to free something that is not an emergency buffer!");
        // emergency_malloc() is expected to return 0-initialized data.  We don't
        // zero the buffer when allocating it, because the static buffers will
        // begin life containing 0 values.
        memset((void*)ptr, 0, 1024);
        // Signal the condition variable to wake up any threads that are blocking
        // waiting for some space in the emergency buffer
        pthread_mutex_lock(&emergency_malloc_lock);
        // In theory, we don't need to do this with the lock held.  In practice,
        // our array of bools will probably be updated using 32-bit or 64-bit
        // memory operations, so this update may clobber adjacent values.
        buffer_allocated[buffer] = false;
        pthread_cond_signal(&emergency_malloc_wait);
        pthread_mutex_unlock(&emergency_malloc_lock);
}

static char *alloc_or_die(size_t size)
{
        char *buffer = (char*)calloc(1, size);

        // If calloc() doesn't want to give us any memory, try using an emergency
        // buffer.
        if (0 == buffer)
        {
                buffer = emergency_malloc(size);
                // This is only reached if the allocation is greater than 1KB, and
                // anyone throwing objects that big really should know better.  
                if (0 == buffer)
                {
                        fprintf(stderr, "Out of memory attempting to allocate exception\n");
                        std::terminate();
                }
        }
        return buffer;
}
static void free_exception(char *e)
{
        // If this allocation is within the address range of the emergency buffer,
        // don't call free() because it was not allocated with malloc()
        if ((e > emergency_buffer) &&
            (e < (emergency_buffer + sizeof(emergency_buffer))))
        {
                emergency_malloc_free(e);
        }
        else
        {
                free(e);
        }
}

/**
 * Allocates an exception structure.  Returns a pointer to the space that can
 * be used to store an object of thrown_size bytes.  This function will use an
 * emergency buffer if malloc() fails, and may block if there are no such
 * buffers available.
 */
extern "C" void *__cxa_allocate_exception(size_t thrown_size)
{
        size_t size = thrown_size + sizeof(__cxa_exception);
        char *buffer = alloc_or_die(size);
        return buffer+sizeof(__cxa_exception);
}

extern "C" void *__cxa_allocate_dependent_exception(void)
{
        size_t size = sizeof(__cxa_dependent_exception);
        char *buffer = alloc_or_die(size);
        return buffer+sizeof(__cxa_dependent_exception);
}

/**
 * __cxa_free_exception() is called when an exception was thrown in between
 * calling __cxa_allocate_exception() and actually throwing the exception.
 * This happens when the object's copy constructor throws an exception.
 *
 * In this implementation, it is also called by __cxa_end_catch() and during
 * thread cleanup.
 */
extern "C" void __cxa_free_exception(void *thrown_exception)
{
        __cxa_exception *ex = ((__cxa_exception*)thrown_exception) - 1;
        // Free the object that was thrown, calling its destructor
        if (0 != ex->exceptionDestructor)
        {
                try
                {
                        ex->exceptionDestructor(thrown_exception);
                }
                catch(...)
                {
                        // FIXME: Check that this is really what the spec says to do.
                        std::terminate();
                }
        }

        free_exception((char*)ex);
}

static void releaseException(__cxa_exception *exception)
{
        if (isDependentException(exception->unwindHeader.exception_class))
        {
                __cxa_free_dependent_exception(exception+1);
                return;
        }
        if (__sync_sub_and_fetch(&exception->referenceCount, 1) == 0)
        {
                // __cxa_free_exception() expects to be passed the thrown object,
                // which immediately follows the exception, not the exception
                // itself
                __cxa_free_exception(exception+1);
        }
}

void __cxa_free_dependent_exception(void *thrown_exception)
{
        __cxa_dependent_exception *ex = ((__cxa_dependent_exception*)thrown_exception) - 1;
        assert(isDependentException(ex->unwindHeader.exception_class));
        if (ex->primaryException)
        {
                releaseException(realExceptionFromException((__cxa_exception*)ex));
        }
        free_exception((char*)ex);
}

/**
 * Callback function used with _Unwind_Backtrace().
 *
 * Prints a stack trace.  Used only for debugging help.
 *
 * Note: As of FreeBSD 8.1, dladd() still doesn't work properly, so this only
 * correctly prints function names from public, relocatable, symbols.
 */
static _Unwind_Reason_Code trace(struct _Unwind_Context *context, void *c)
{
        Dl_info myinfo;
        int mylookup =
                dladdr((void*)(uintptr_t)__cxa_current_exception_type, &myinfo);
        void *ip = (void*)_Unwind_GetIP(context);
        Dl_info info;
        if (dladdr(ip, &info) != 0)
        {
                if (mylookup == 0 || strcmp(info.dli_fname, myinfo.dli_fname) != 0)
                {
                        printf("%p:%s() in %s\n", ip, info.dli_sname, info.dli_fname);
                }
        }
        return _URC_CONTINUE_UNWIND;
}

/**
 * Report a failure that occurred when attempting to throw an exception.
 *
 * If the failure happened by falling off the end of the stack without finding
 * a handler, prints a back trace before aborting.
 */
static void report_failure(_Unwind_Reason_Code err, __cxa_exception *thrown_exception)
{
        switch (err)
        {
                default: break;
                case _URC_FATAL_PHASE1_ERROR:
                        fprintf(stderr, "Fatal error during phase 1 unwinding\n");
                        break;
#ifndef __arm__
                case _URC_FATAL_PHASE2_ERROR:
                        fprintf(stderr, "Fatal error during phase 2 unwinding\n");
                        break;
#endif
                case _URC_END_OF_STACK:
                        fprintf(stderr, "Terminating due to uncaught exception %p", 
                                        (void*)thrown_exception);
                        thrown_exception = realExceptionFromException(thrown_exception);
                        static const __class_type_info *e_ti =
                                static_cast<const __class_type_info*>(&typeid(std::exception));
                        const __class_type_info *throw_ti =
                                dynamic_cast<const __class_type_info*>(thrown_exception->exceptionType);
                        if (throw_ti)
                        {
                                std::exception *e =
                                        (std::exception*)e_ti->cast_to((void*)(thrown_exception+1),
                                                        throw_ti);
                                if (e)
                                {
                                        fprintf(stderr, " '%s'", e->what());
                                }
                        }

                        size_t bufferSize = 128;
                        char *demangled = (char*)malloc(bufferSize);
                        const char *mangled = thrown_exception->exceptionType->name();
                        int status;
                        demangled = __cxa_demangle(mangled, demangled, &bufferSize, &status);
                        fprintf(stderr, " of type %s\n", 
                                status == 0 ? (const char*)demangled : mangled);
                        if (status == 0) { free(demangled); }
                        // Print a back trace if no handler is found.
                        // TODO: Make this optional
                        _Unwind_Backtrace(trace, 0);
                        break;
        }
        std::terminate();
}

static void throw_exception(__cxa_exception *ex)
{
        __cxa_thread_info *info = thread_info();
        ex->unexpectedHandler = info->unexpectedHandler;
        if (0 == ex->unexpectedHandler)
        {
                ex->unexpectedHandler = unexpectedHandler;
        }
        ex->terminateHandler  = info->terminateHandler;
        if (0 == ex->terminateHandler)
        {
                ex->terminateHandler = terminateHandler;
        }
        info->globals.uncaughtExceptions++;

        _Unwind_Reason_Code err = _Unwind_RaiseException(&ex->unwindHeader);
        // The _Unwind_RaiseException() function should not return, it should
        // unwind the stack past this function.  If it does return, then something
        // has gone wrong.
        report_failure(err, ex);
}


/**
 * ABI function for throwing an exception.  Takes the object to be thrown (the
 * pointer returned by __cxa_allocate_exception()), the type info for the
 * pointee, and the destructor (if there is one) as arguments.
 */
extern "C" void __cxa_throw(void *thrown_exception,
                            std::type_info *tinfo,
                            void(*dest)(void*))
{
        __cxa_exception *ex = ((__cxa_exception*)thrown_exception) - 1;

        ex->referenceCount = 1;
        ex->exceptionType = tinfo;
        
        ex->exceptionDestructor = dest;
        
        ex->unwindHeader.exception_class = exception_class;
        ex->unwindHeader.exception_cleanup = exception_cleanup;

        throw_exception(ex);
}

extern "C" void __cxa_rethrow_primary_exception(void* thrown_exception)
{
        if (NULL == thrown_exception) { return; }

        __cxa_exception *original = exceptionFromPointer(thrown_exception);
        __cxa_dependent_exception *ex = ((__cxa_dependent_exception*)__cxa_allocate_dependent_exception())-1;

        ex->primaryException = thrown_exception;
        __cxa_increment_exception_refcount(thrown_exception);

        ex->exceptionType = original->exceptionType;
        ex->unwindHeader.exception_class = dependent_exception_class;
        ex->unwindHeader.exception_cleanup = dependent_exception_cleanup;

        throw_exception((__cxa_exception*)ex);
}

extern "C" void *__cxa_current_primary_exception(void)
{
        __cxa_eh_globals* globals = __cxa_get_globals();
        __cxa_exception *ex = globals->caughtExceptions;

        if (0 == ex) { return NULL; }
        ex = realExceptionFromException(ex);
        __sync_fetch_and_add(&ex->referenceCount, 1);
        return ex + 1;
}

extern "C" void __cxa_increment_exception_refcount(void* thrown_exception)
{
        if (NULL == thrown_exception) { return; }
        __cxa_exception *ex = ((__cxa_exception*)thrown_exception) - 1;
        if (isDependentException(ex->unwindHeader.exception_class)) { return; }
        __sync_fetch_and_add(&ex->referenceCount, 1);
}
extern "C" void __cxa_decrement_exception_refcount(void* thrown_exception)
{
        if (NULL == thrown_exception) { return; }
        __cxa_exception *ex = ((__cxa_exception*)thrown_exception) - 1;
        releaseException(ex);
}

/**
 * ABI function.  Rethrows the current exception.  Does not remove the
 * exception from the stack or decrement its handler count - the compiler is
 * expected to set the landing pad for this function to the end of the catch
 * block, and then call _Unwind_Resume() to continue unwinding once
 * __cxa_end_catch() has been called and any cleanup code has been run.
 */
extern "C" void __cxa_rethrow()
{
        __cxa_thread_info *ti = thread_info();
        __cxa_eh_globals *globals = &ti->globals;
        // Note: We don't remove this from the caught list here, because
        // __cxa_end_catch will be called when we unwind out of the try block.  We
        // could probably make this faster by providing an alternative rethrow
        // function and ensuring that all cleanup code is run before calling it, so
        // we can skip the top stack frame when unwinding.
        __cxa_exception *ex = globals->caughtExceptions;

        if (0 == ex)
        {
                fprintf(stderr,
                        "Attempting to rethrow an exception that doesn't exist!\n");
                std::terminate();
        }

        if (ti->foreign_exception_state != __cxa_thread_info::none)
        {
                ti->foreign_exception_state = __cxa_thread_info::rethrown;
                _Unwind_Exception *e = (_Unwind_Exception*)ex;
                _Unwind_Reason_Code err = _Unwind_Resume_or_Rethrow(e);
                report_failure(err, ex);
                return;
        }

        assert(ex->handlerCount > 0 && "Rethrowing uncaught exception!");

        // ex->handlerCount will be decremented in __cxa_end_catch in enclosing
        // catch block
        
        // Make handler count negative. This will tell __cxa_end_catch that
        // exception was rethrown and exception object should not be destroyed
        // when handler count become zero
        ex->handlerCount = -ex->handlerCount;

        // Continue unwinding the stack with this exception.  This should unwind to
        // the place in the caller where __cxa_end_catch() is called.  The caller
        // will then run cleanup code and bounce the exception back with
        // _Unwind_Resume().
        _Unwind_Reason_Code err = _Unwind_Resume_or_Rethrow(&ex->unwindHeader);
        report_failure(err, ex);
}

/**
 * Returns the type_info object corresponding to the filter.
 */
static std::type_info *get_type_info_entry(_Unwind_Context *context,
                                           dwarf_eh_lsda *lsda,
                                           int filter)
{
        // Get the address of the record in the table.
        dw_eh_ptr_t record = lsda->type_table - 
                dwarf_size_of_fixed_size_field(lsda->type_table_encoding)*filter;
        //record -= 4;
        dw_eh_ptr_t start = record;
        // Read the value, but it's probably an indirect reference...
        int64_t offset = read_value(lsda->type_table_encoding, &record);

        // (If the entry is 0, don't try to dereference it.  That would be bad.)
        if (offset == 0) { return 0; }

        // ...so we need to resolve it
        return (std::type_info*)resolve_indirect_value(context,
                        lsda->type_table_encoding, offset, start);
}



/**
 * Checks the type signature found in a handler against the type of the thrown
 * object.  If ex is 0 then it is assumed to be a foreign exception and only
 * matches cleanups.
 */
static bool check_type_signature(__cxa_exception *ex,
                                 const std::type_info *type,
                                 void *&adjustedPtr)
{
        void *exception_ptr = (void*)(ex+1);
        const std::type_info *ex_type = ex ? ex->exceptionType : 0;

        bool is_ptr = ex ? ex_type->__is_pointer_p() : false;
        if (is_ptr)
        {
                exception_ptr = *(void**)exception_ptr;
        }
        // Always match a catchall, even with a foreign exception
        //
        // Note: A 0 here is a catchall, not a cleanup, so we return true to
        // indicate that we found a catch.
        if (0 == type)
        {
                if (ex)
                {
                        adjustedPtr = exception_ptr;
                }
                return true;
        }

        if (0 == ex) { return false; }

        // If the types are the same, no casting is needed.
        if (*type == *ex_type)
        {
                adjustedPtr = exception_ptr;
                return true;
        }


        if (type->__do_catch(ex_type, &exception_ptr, 1))
        {
                adjustedPtr = exception_ptr;
                return true;
        }

        return false;
}
/**
 * Checks whether the exception matches the type specifiers in this action
 * record.  If the exception only matches cleanups, then this returns false.
 * If it matches a catch (including a catchall) then it returns true.
 *
 * The selector argument is used to return the selector that is passed in the
 * second exception register when installing the context.
 */
static handler_type check_action_record(_Unwind_Context *context,
                                        dwarf_eh_lsda *lsda,
                                        dw_eh_ptr_t action_record,
                                        __cxa_exception *ex,
                                        unsigned long *selector,
                                        void *&adjustedPtr)
{
        if (!action_record) { return handler_cleanup; }
        handler_type found = handler_none;
        while (action_record)
        {
                int filter = read_sleb128(&action_record);
                dw_eh_ptr_t action_record_offset_base = action_record;
                int displacement = read_sleb128(&action_record);
                action_record = displacement ? 
                        action_record_offset_base + displacement : 0;
                // We only check handler types for C++ exceptions - foreign exceptions
                // are only allowed for cleanups and catchalls.
                if (filter > 0)
                {
                        std::type_info *handler_type = get_type_info_entry(context, lsda, filter);
                        if (check_type_signature(ex, handler_type, adjustedPtr))
                        {
                                *selector = filter;
                                return handler_catch;
                        }
                }
                else if (filter < 0 && 0 != ex)
                {
                        bool matched = false;
                        *selector = filter;
#ifdef __arm__
                        filter++;
                        std::type_info *handler_type = get_type_info_entry(context, lsda, filter--);
                        while (handler_type)
                        {
                                if (check_type_signature(ex, handler_type, adjustedPtr))
                                {
                                        matched = true;
                                        break;
                                }
                                handler_type = get_type_info_entry(context, lsda, filter--);
                        }
#else
                        unsigned char *type_index = ((unsigned char*)lsda->type_table - filter - 1);
                        while (*type_index)
                        {
                                std::type_info *handler_type = get_type_info_entry(context, lsda, *(type_index++));
                                // If the exception spec matches a permitted throw type for
                                // this function, don't report a handler - we are allowed to
                                // propagate this exception out.
                                if (check_type_signature(ex, handler_type, adjustedPtr))
                                {
                                        matched = true;
                                        break;
                                }
                        }
#endif
                        if (matched) { continue; }
                        // If we don't find an allowed exception spec, we need to install
                        // the context for this action.  The landing pad will then call the
                        // unexpected exception function.  Treat this as a catch
                        return handler_catch;
                }
                else if (filter == 0)
                {
                        *selector = filter;
                        found = handler_cleanup;
                }
        }
        return found;
}

static void pushCleanupException(_Unwind_Exception *exceptionObject,
                                 __cxa_exception *ex)
{
#ifdef __arm__
        __cxa_thread_info *info = thread_info_fast();
        if (ex)
        {
                ex->cleanupCount++;
                if (ex->cleanupCount > 1)
                {
                        assert(exceptionObject == info->currentCleanup);
                        return;
                }
                ex->nextCleanup = info->currentCleanup;
        }
        info->currentCleanup = exceptionObject;
#endif
}

/**
 * The exception personality function.  This is referenced in the unwinding
 * DWARF metadata and is called by the unwind library for each C++ stack frame
 * containing catch or cleanup code.
 */
extern "C"
BEGIN_PERSONALITY_FUNCTION(__gxx_personality_v0)
        // This personality function is for version 1 of the ABI.  If you use it
        // with a future version of the ABI, it won't know what to do, so it
        // reports a fatal error and give up before it breaks anything.
        if (1 != version)
        {
                return _URC_FATAL_PHASE1_ERROR;
        }
        __cxa_exception *ex = 0;
        __cxa_exception *realEx = 0;

        // If this exception is throw by something else then we can't make any
        // assumptions about its layout beyond the fields declared in
        // _Unwind_Exception.
        bool foreignException = !isCXXException(exceptionClass);

        // If this isn't a foreign exception, then we have a C++ exception structure
        if (!foreignException)
        {
                ex = exceptionFromPointer(exceptionObject);
                realEx = realExceptionFromException(ex);
        }

        unsigned char *lsda_addr =
                (unsigned char*)_Unwind_GetLanguageSpecificData(context);

        // No LSDA implies no landing pads - try the next frame
        if (0 == lsda_addr) { return continueUnwinding(exceptionObject, context); }

        // These two variables define how the exception will be handled.
        dwarf_eh_action action = {0};
        unsigned long selector = 0;
        
        // During the search phase, we do a complete lookup.  If we return
        // _URC_HANDLER_FOUND, then the phase 2 unwind will call this function with
        // a _UA_HANDLER_FRAME action, telling us to install the handler frame.  If
        // we return _URC_CONTINUE_UNWIND, we may be called again later with a
        // _UA_CLEANUP_PHASE action for this frame.
        //
        // The point of the two-stage unwind allows us to entirely avoid any stack
        // unwinding if there is no handler.  If there are just cleanups found,
        // then we can just panic call an abort function.
        //
        // Matching a handler is much more expensive than matching a cleanup,
        // because we don't need to bother doing type comparisons (or looking at
        // the type table at all) for a cleanup.  This means that there is no need
        // to cache the result of finding a cleanup, because it's (quite) quick to
        // look it up again from the action table.
        if (actions & _UA_SEARCH_PHASE)
        {
                struct dwarf_eh_lsda lsda = parse_lsda(context, lsda_addr);

                if (!dwarf_eh_find_callsite(context, &lsda, &action))
                {
                        // EH range not found. This happens if exception is thrown and not
                        // caught inside a cleanup (destructor).  We should call
                        // terminate() in this case.  The catchTemp (landing pad) field of
                        // exception object will contain null when personality function is
                        // called with _UA_HANDLER_FRAME action for phase 2 unwinding.  
                        return _URC_HANDLER_FOUND;
                }

                handler_type found_handler = check_action_record(context, &lsda,
                                action.action_record, realEx, &selector, ex->adjustedPtr);
                // If there's no action record, we've only found a cleanup, so keep
                // searching for something real
                if (found_handler == handler_catch)
                {
                        // Cache the results for the phase 2 unwind, if we found a handler
                        // and this is not a foreign exception.
                        if (ex)
                        {
                                saveLandingPad(context, exceptionObject, ex, selector, action.landing_pad);
                                ex->languageSpecificData = (const char*)lsda_addr;
                                ex->actionRecord = (const char*)action.action_record;
                                // ex->adjustedPtr is set when finding the action record.
                        }
                        return _URC_HANDLER_FOUND;
                }
                return continueUnwinding(exceptionObject, context);
        }


        // If this is a foreign exception, we didn't have anywhere to cache the
        // lookup stuff, so we need to do it again.  If this is either a forced
        // unwind, a foreign exception, or a cleanup, then we just install the
        // context for a cleanup.
        if (!(actions & _UA_HANDLER_FRAME))
        {
                // cleanup
                struct dwarf_eh_lsda lsda = parse_lsda(context, lsda_addr);
                dwarf_eh_find_callsite(context, &lsda, &action);
                if (0 == action.landing_pad) { return continueUnwinding(exceptionObject, context); }
                handler_type found_handler = check_action_record(context, &lsda,
                                action.action_record, realEx, &selector, ex->adjustedPtr);
                // Ignore handlers this time.
                if (found_handler != handler_cleanup) { return continueUnwinding(exceptionObject, context); }
                pushCleanupException(exceptionObject, ex);
        }
        else if (foreignException)
        {
                struct dwarf_eh_lsda lsda = parse_lsda(context, lsda_addr);
                dwarf_eh_find_callsite(context, &lsda, &action);
                check_action_record(context, &lsda, action.action_record, realEx,
                                &selector, ex->adjustedPtr);
        }
        else if (ex->catchTemp == 0)
        {
                // Uncaught exception in cleanup, calling terminate
                std::terminate();
        }
        else
        {
                // Restore the saved info if we saved some last time.
                loadLandingPad(context, exceptionObject, ex, &selector, &action.landing_pad);
                ex->catchTemp = 0;
                ex->handlerSwitchValue = 0;
        }


        _Unwind_SetIP(context, (unsigned long)action.landing_pad);
        _Unwind_SetGR(context, __builtin_eh_return_data_regno(0),
                      (unsigned long)exceptionObject);
        _Unwind_SetGR(context, __builtin_eh_return_data_regno(1), selector);

        return _URC_INSTALL_CONTEXT;
}

/**
 * ABI function called when entering a catch statement.  The argument is the
 * pointer passed out of the personality function.  This is always the start of
 * the _Unwind_Exception object.  The return value for this function is the
 * pointer to the caught exception, which is either the adjusted pointer (for
 * C++ exceptions) of the unadjusted pointer (for foreign exceptions).
 */
#if __GNUC__ > 3 && __GNUC_MINOR__ > 2
extern "C" void *__cxa_begin_catch(void *e) throw()
#else
extern "C" void *__cxa_begin_catch(void *e)
#endif
{
        // We can't call the fast version here, because if the first exception that
        // we see is a foreign exception then we won't have called it yet.
        __cxa_thread_info *ti = thread_info();
        __cxa_eh_globals *globals = &ti->globals;
        globals->uncaughtExceptions--;
        _Unwind_Exception *exceptionObject = (_Unwind_Exception*)e;

        if (isCXXException(exceptionObject->exception_class))
        {
                __cxa_exception *ex =  exceptionFromPointer(exceptionObject);

                if (ex->handlerCount == 0)
                {
                        // Add this to the front of the list of exceptions being handled
                        // and increment its handler count so that it won't be deleted
                        // prematurely.
                        ex->nextException = globals->caughtExceptions;
                        globals->caughtExceptions = ex;
                }

                if (ex->handlerCount < 0)
                {
                        // Rethrown exception is catched before end of catch block.
                        // Clear the rethrow flag (make value positive) - we are allowed
                        // to delete this exception at the end of the catch block, as long
                        // as it isn't thrown again later.
                        
                        // Code pattern:
                        //
                        // try {
                        //     throw x;
                        // }
                        // catch() {
                        //     try {
                        //         throw;
                        //     }
                        //     catch() {
                        //         __cxa_begin_catch() <- we are here
                        //     }
                        // }
                        ex->handlerCount = -ex->handlerCount + 1;
                }
                else
                {
                        ex->handlerCount++;
                }
                ti->foreign_exception_state = __cxa_thread_info::none;
                
                return ex->adjustedPtr;
        }
        else
        {
                // If this is a foreign exception, then we need to be able to
                // store it.  We can't chain foreign exceptions, so we give up
                // if there are already some outstanding ones.
                if (globals->caughtExceptions != 0)
                {
                        std::terminate();
                }
                globals->caughtExceptions = (__cxa_exception*)exceptionObject;
                ti->foreign_exception_state = __cxa_thread_info::caught;
        }
        // exceptionObject is the pointer to the _Unwind_Exception within the
        // __cxa_exception.  The throw object is after this
        return ((char*)exceptionObject + sizeof(_Unwind_Exception));
}



/**
 * ABI function called when exiting a catch block.  This will free the current
 * exception if it is no longer referenced in other catch blocks.
 */
extern "C" void __cxa_end_catch()
{
        // We can call the fast version here because the slow version is called in
        // __cxa_throw(), which must have been called before we end a catch block
        __cxa_thread_info *ti = thread_info_fast();
        __cxa_eh_globals *globals = &ti->globals;
        __cxa_exception *ex = globals->caughtExceptions;

        assert(0 != ex && "Ending catch when no exception is on the stack!");
        
        if (ti->foreign_exception_state != __cxa_thread_info::none)
        {
                globals->caughtExceptions = 0;
                if (ti->foreign_exception_state != __cxa_thread_info::rethrown)
                {
                        _Unwind_Exception *e = (_Unwind_Exception*)ti->globals.caughtExceptions;
                        e->exception_cleanup(_URC_FOREIGN_EXCEPTION_CAUGHT, e);
                }
                ti->foreign_exception_state = __cxa_thread_info::none;
                return;
        }

        bool deleteException = true;

        if (ex->handlerCount < 0)
        {
                // exception was rethrown. Exception should not be deleted even if
                // handlerCount become zero.
                // Code pattern:
                // try {
                //     throw x;
                // }
                // catch() {
                //     {
                //         throw;
                //     }
                //     cleanup {
                //         __cxa_end_catch();   <- we are here
                //     }
                // }
                //
                
                ex->handlerCount++;
                deleteException = false;
        }
        else
        {
                ex->handlerCount--;
        }

        if (ex->handlerCount == 0)
        {
                globals->caughtExceptions = ex->nextException;
                if (deleteException)
                {
                        releaseException(ex);
                }
        }
}

/**
 * ABI function.  Returns the type of the current exception.
 */
extern "C" std::type_info *__cxa_current_exception_type()
{
        __cxa_eh_globals *globals = __cxa_get_globals();
        __cxa_exception *ex = globals->caughtExceptions;
        return ex ? ex->exceptionType : 0;
}

/**
 * ABI function, called when an exception specification is violated.
 *
 * This function does not return.
 */
extern "C" void __cxa_call_unexpected(void*exception) 
{
        _Unwind_Exception *exceptionObject = (_Unwind_Exception*)exception;
        if (exceptionObject->exception_class == exception_class)
        {
                __cxa_exception *ex =  exceptionFromPointer(exceptionObject);
                if (ex->unexpectedHandler)
                {
                        ex->unexpectedHandler();
                        // Should not be reached.  
                        abort();
                }
        }
        std::unexpected();
        // Should not be reached.  
        abort();
}

/**
 * ABI function, returns the adjusted pointer to the exception object.
 */
extern "C" void *__cxa_get_exception_ptr(void *exceptionObject)
{
        return exceptionFromPointer(exceptionObject)->adjustedPtr;
}

/**
 * As an extension, we provide the ability for the unexpected and terminate
 * handlers to be thread-local.  We default to the standards-compliant
 * behaviour where they are global.
 */
static bool thread_local_handlers = false;


namespace pathscale
{
        /**
         * Sets whether unexpected and terminate handlers should be thread-local.
         */
        void set_use_thread_local_handlers(bool flag) throw()
        {
                thread_local_handlers = flag;
        }
        /**
         * Sets a thread-local unexpected handler.  
         */
        unexpected_handler set_unexpected(unexpected_handler f) throw()
        {
                static __cxa_thread_info *info = thread_info();
                unexpected_handler old = info->unexpectedHandler;
                info->unexpectedHandler = f;
                return old;
        }
        /**
         * Sets a thread-local terminate handler.  
         */
        terminate_handler set_terminate(terminate_handler f) throw()
        {
                static __cxa_thread_info *info = thread_info();
                terminate_handler old = info->terminateHandler;
                info->terminateHandler = f;
                return old;
        }
}

namespace std
{
        /**
         * Sets the function that will be called when an exception specification is
         * violated.
         */
        unexpected_handler set_unexpected(unexpected_handler f) throw()
        {
                if (thread_local_handlers) { return pathscale::set_unexpected(f); }

                return ATOMIC_SWAP(&unexpectedHandler, f);
        }
        /**
         * Sets the function that is called to terminate the program.
         */
        terminate_handler set_terminate(terminate_handler f) throw()
        {
                if (thread_local_handlers) { return pathscale::set_terminate(f); }

                return ATOMIC_SWAP(&terminateHandler, f);
        }
        /**
         * Terminates the program, calling a custom terminate implementation if
         * required.
         */
        void terminate()
        {
                static __cxa_thread_info *info = thread_info();
                if (0 != info && 0 != info->terminateHandler)
                {
                        info->terminateHandler();
                        // Should not be reached - a terminate handler is not expected to
                        // return.
                        abort();
                }
                terminateHandler();
        }
        /**
         * Called when an unexpected exception is encountered (i.e. an exception
         * violates an exception specification).  This calls abort() unless a
         * custom handler has been set..
         */
        void unexpected()
        {
                static __cxa_thread_info *info = thread_info();
                if (0 != info && 0 != info->unexpectedHandler)
                {
                        info->unexpectedHandler();
                        // Should not be reached - a terminate handler is not expected to
                        // return.
                        abort();
                }
                unexpectedHandler();
        }
        /**
         * Returns whether there are any exceptions currently being thrown that
         * have not been caught.  This can occur inside a nested catch statement.
         */
        bool uncaught_exception() throw()
        {
                __cxa_thread_info *info = thread_info();
                return info->globals.uncaughtExceptions != 0;
        }
        /**
         * Returns the current unexpected handler.
         */
        unexpected_handler get_unexpected() throw()
        {
                __cxa_thread_info *info = thread_info();
                if (info->unexpectedHandler)
                {
                        return info->unexpectedHandler;
                }
                return ATOMIC_LOAD(&unexpectedHandler);
        }
        /**
         * Returns the current terminate handler.
         */
        terminate_handler get_terminate() throw()
        {
                __cxa_thread_info *info = thread_info();
                if (info->terminateHandler)
                {
                        return info->terminateHandler;
                }
                return ATOMIC_LOAD(&terminateHandler);
        }
}
#ifdef __arm__
extern "C" _Unwind_Exception *__cxa_get_cleanup(void)
{
        __cxa_thread_info *info = thread_info_fast();
        _Unwind_Exception *exceptionObject = info->currentCleanup;
        if (isCXXException(exceptionObject->exception_class))
        {
                __cxa_exception *ex =  exceptionFromPointer(exceptionObject);
                ex->cleanupCount--;
                if (ex->cleanupCount == 0)
                {
                        info->currentCleanup = ex->nextCleanup;
                        ex->nextCleanup = 0;
                }
        }
        else
        {
                info->currentCleanup = 0;
        }
        return exceptionObject;
}

asm (
".pushsection .text.__cxa_end_cleanup    \n"
".global __cxa_end_cleanup               \n"
".type __cxa_end_cleanup, \"function\"   \n"
"__cxa_end_cleanup:                      \n"
"       push {r1, r2, r3, r4}                \n"
"       bl __cxa_get_cleanup                 \n"
"       push {r1, r2, r3, r4}                \n"
"       b _Unwind_Resume                     \n"
"       bl abort                             \n"
".popsection                             \n"
);
#endif