target = PTRDIFF(pc, script->main, jsbytecode);
target = PTRDIFF(pc, script->code, jsbytecode);
js_GetSrcNote(JSScript *script, jsbytecode *pc){    jssrcnote *sn;    ptrdiff_t offset, target;    target = PTRDIFF(pc, script->main, jsbytecode);    if ((uintN)target >= script->length)        return NULL;    offset = 0;    for (sn = SCRIPT_NOTES(script); !SN_IS_TERMINATOR(sn); sn = SN_NEXT(sn)) {        offset += SN_DELTA(sn);        if (offset == target && SN_IS_GETTABLE(sn))            return sn;    }    return NULL;}