[sklogic]

Usually it is implemented by reshuffling stack frame + jumping to the call destination. See how it is done in .NET, for example.

Do not confuse tail recursion, which is the least interesting narrow case of a tail call, with tail calls in general.

[ectoplasm]

Why can't you modify a JVM to do this? I don't get it.

[sklogic]

Of course you can (but you have to add another instruction or an instruction prefix). But Oracle won't ever do it.