XPath to get attribute names in Oracle

I have an XML file, for example:

<a b="123" c="456"/>

and I want to get all attribute names and values using xpath from Oracle SQL. Executing

select extractvalue(value(p), 'text()')
  from xmltable('/*/@*' passing xmltype('<a b="123" c="456"/>')) p;

I get only ["123","456"], but I want to get ["b", "c"] too. How can I do this?