[译]C++异常的幕后18：获取正确的栈帧

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void __cxa_throw(void* thrown_exception,

                 std::type_info *tinfo,

                 void (*dest)(void*))

{

    __cxa_exception *header = ((__cxa_exception *) thrown_exception - 1);

    // We need to save the type info in the exception header _Unwind_ will

    // receive, otherwise we won't be able to know it when unwinding

    header->exceptionType = tinfo;

    _Unwind_RaiseException(&header->unwindHeader);

}

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// Get the type of the exception we can handle

const void* catch_type_info = lsda.types_table_start[ -1 * type_index ];

const std::type_info *catch_ti = (const std::type_info *) catch_type_info;

// Get the type of the original exception being thrown

__cxa_exception* exception_header = (__cxa_exception*)(unwind_exception+1) - 1;

std::type_info *org_ex_type = exception_header->exceptionType;

printf("%s thrown, catch handles %s\n",

            org_ex_type->name(),

            catch_ti->name());

// Check if the exception being thrown is of the same type

// than the exception we can handle

if (org_ex_type->name() != catch_ti->name())

    continue;

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_Unwind_Reason_Code __gxx_personality_v0 (...)

{

    printf("Personality function, searching for handler\n");

    // ...

    foreach (call site entry in lsda)

    {

        if (call site entry.not_good()) continue;

        // We found a landing pad for this exception; resume execution

        // If we are on search phase, tell _Unwind_ we can handle this one

        if (actions & _UA_SEARCH_PHASE) return _URC_HANDLER_FOUND;

        // If we are not on search phase then we are on _UA_CLEANUP_PHASE

        /* set everything so the landing pad can run */

        return _URC_INSTALL_CONTEXT;

    }

    return _URC_CONTINUE_UNWIND;

}

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void catchit() {

    try {

        try_but_dont_catch();

    } catch(Fake_Exception&) {

        printf("Caught a Fake_Exception!\n");

    } catch(Exception&) {

        printf("Caught an Exception!\n");

    }

    printf("catchit handled the exception\n");

}