2002 95 is billowing white smoke and now power!

My son has a 2002 saab 95 linear that basically stopped running today while driving on the highway. He found that the power was getting less and less and then saw in the rear view mirror that i was billowing white smoke. He pulled over and checked the oil and there was none on the stick, he had topped it off that morning. He didn't see any other engine lights at all but the oil light, at that time. He put more oil in the engine, but at that point it still felt like it was in limp home mode and couldn't get much in the way of RPM's ether. There isn't oil or coolant mixing and there isn't any sign of oil leaking.
Is this a turbo problem and if so, why would this stop the engine from running at smooth. He said it was bucking and felt like it had a trans problem as well.

Any ideas on this, I appreciate your time,
thanks!