Process and product to fix concrete slab surface issues prior to framing over them?
First off you mentioned hollow underneath, was the base compacted prior to the pour, if not the whole slab is in question as the base has settled underneath the poured concrete so putting paint on a pig is a waste of money.

But to answer your question directly - clean everything you can then use "ProBond" or another Concrete bonding promoter. If you do not use a bonding promoter it has a higher chance of separating from the base. 

Then use self-leveling floor resurfacer to finish the floor. 
If you are doing the whole floor and it is a large area you may want to consider talking to your local ready-mix company as they do provide mixes for self leveling of floors. It is used in apartment buildings and other large multi storied structures it is called "gypcrete" and may be your best best dollar for dollar. Oh, the results will be great.