Throwing exceptions from XS code

Hi,

I'm writing XS bindings for JavaScriptCore (WebKit's JavaScript
engine) and a lot of the functions in the API throw an exception. The
exception it self is a JavaScript variable (kind of like an SV* for
Perl).

At first I though of rethrowing that variable wrapped as an SV but I
don't know how to do this. I read somewhere that Perl_croak_sv can do
that but I get a runtime because the symbol is undefined:

            /*  undefined symbol: Perl_croak_sv */
            SV *err;
            err = jsc_perl_js_value_to_sv(ctx, exception);
            Perl_croak_sv(aTHX_ err);

For now I reverted at returning the error as a JSON string and to use
croak but I'm leaking the string with the message since I can't free
it after croak():

            char *error;
            error = jsc_perl_js_value_to_json(ctx, exception);
            croak("%s", error);/* How can we throw an SV ? */
            free(error);/* FIXME is this free called ? */

Is it possible to throw an blessed exception from XS code? If so how
can I achieve this? Otherwise, how can I propagate an error as a
string and free the string?

-- 
Emmanuel Rodriguez