where is GHC.Prim.sym defined?

[Paul L]

I'm trying to parse Core file generated by -fext-core, here is a snippet I got:

 %cast (base:GHCziSTRef.STRef @ ghczmprim:GHCziPrim.RealWorld
                     @ ((base:GHCziIOziBuffer.Buffer
base:GHCziWord.Word8)) rbd1ep)
              ((ghczmprim:GHCziPrim.sym
                base:GHCziIORef.NTCoZCIORef
                ((base:GHCziIOziBuffer.Buffer base:GHCziWord.Word8))))

But I can't seem to find GHC.Prim.sym defined anywhere in the ghc-prim
package, any hints?

-- 
Regards,
Paul Liu