vDSO interception

The signature for the vDSO callback in the API has the following arguments:

• 1 long for the syscall number
• 1 generic pointer to the vDSO function originally called

and returns a generic pointer to the user-defined handler function. The original function may be returned directly, or passed to the handler, or even discarded.

The vDSO callback is then called by the rewriter while rewriting the vDSO segment.