%sr is the symbolic name for a register. If I had to guess I would say that the actual name might be something like "Status Register" or "System Register" The GNU documentation may or may not speak to your question. My experience has been that GNU documentation is generally voluminous and poorly indexed for the neophyte. It is always a worthwhile effort to try to track things like this down. As you gain more experience with it, it does become easier. As far as the particular processor you are using you need to find a document on the Freescale site that is titled something like "Hardware Manual" or "Instruction Set Reference"

I charge at least $150.00/hr to do this stuff by the way.

Good Luck.