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#include "qv4exception_p.h"

#include <unwind.h>
#include <cxxabi.h>
#include <bits/atomic_word.h>
#include <typeinfo>
#include <exception>

/*
 * This is a little bit hacky as it relies on the fact that exceptions are
 * reference counted in libstdc++ and that affects the layout of the standardized
 * cxa_exception, making it bigger. LLVM's libcxxabi stores the reference count
 * differently, so this here is entirely GNU libstdc++ specific.
 *
 * Eliminating this dependency is doable but requires replacing the use of C++ exceptions
 * with foreign exceptions (a different exception class) and then using __cxa_get_globals
 * to get hold of the exception inside the catch (...). AFAICS that would be portable.
 */

namespace {

// 2.1.1 from http://mentorembedded.github.io/cxx-abi/abi-eh.html
struct cxa_exception {
    std::type_info *typeInfo;
    void (*exceptionDestructor)(void*);
    std::unexpected_handler unexpectedHandler;
    std::terminate_handler terminateHandler;
    cxa_exception *nextException;
    int handlerCount;
#ifdef __ARM_EABI_UNWINDER__
    cxa_exception *nextPropagatingException;
    int propagationCount;
#else
    int handlerSwitchValue;
    const char *actionRecord;
    const char *languageSpecificData;
    void *catchTemp;
    void *adjustedPtr;
#endif
    _Unwind_Exception unwindHeader;
};

// This is what libstdc++ actually allocates
struct gcc_refcounted_compatible_exception {
    _Atomic_word refCount;
    cxa_exception x;
};

}

static void exception_cleanup(_Unwind_Reason_Code, _Unwind_Exception *ex)
{
    gcc_refcounted_compatible_exception *exception = reinterpret_cast<gcc_refcounted_compatible_exception *>(ex + 1) - 1;
    if (!--exception->refCount) {
        if (exception->x.exceptionDestructor)
            exception->x.exceptionDestructor(ex + 1);
        abi::__cxa_free_exception(ex + 1);
    }
}

static void exception_destructor(void *ex)
{
    reinterpret_cast<QV4::Exception *>(ex)->~Exception();
}

QT_BEGIN_NAMESPACE

using namespace QV4;

void Exception::throwInternal(ExecutionContext *throwingContext, const Value &exceptionValue)
{
    void *rawException = abi::__cxa_allocate_exception(sizeof(QV4::Exception));
    gcc_refcounted_compatible_exception *refCountedException = reinterpret_cast<gcc_refcounted_compatible_exception *>(rawException) - 1;
    cxa_exception *exception = &refCountedException->x;

    (void)new (rawException) Exception(throwingContext, exceptionValue);

    refCountedException->refCount = 1;
    exception->typeInfo = const_cast<std::type_info*>(&typeid(Exception));
    exception->exceptionDestructor = &exception_destructor;
    exception->unexpectedHandler = std::unexpected;
    exception->terminateHandler = std::terminate;
    exception->unwindHeader.exception_cleanup = &exception_cleanup;
#ifdef __ARM_EABI_UNWINDER__
    exception->unwindHeader.exception_class[0] = 'G';
    exception->unwindHeader.exception_class[1] = 'N';
    exception->unwindHeader.exception_class[2] = 'U';
    exception->unwindHeader.exception_class[3] = 'C';
    exception->unwindHeader.exception_class[4] = 'C';
    exception->unwindHeader.exception_class[5] = '+';
    exception->unwindHeader.exception_class[6] = '+';
    exception->unwindHeader.exception_class[7] = 0;
#else
    exception->unwindHeader.exception_class = 0x474e5543432b2b00; // GNUCC++0
#endif

    _Unwind_RaiseException(&exception->unwindHeader);
    abi::__cxa_begin_catch(rawException);
    std::terminate();
}

QT_END_NAMESPACE