void
registCallback(cb)
    SV* cb;
    PROTOTYPE: $
    PPCODE:
        if (callback_ref == (SV*)NULL) {
            callback_ref = newSVsv((SV*)cb);
        } else {
            SvSetSV(callback_ref, cb);
        }

##</code><code>##

Bizarre copy of CODE in entersub  (#1)
    (P) Perl detected an attempt to copy an internal value that is not
    copyable.