IF it was your "Principal Residence" during that time, you report the sale in the 'Sale of Home' section.
You will have "Nonqualified Use". The essentially means will still pay some tax because it is prorated based on the time it was your Principal Residence (the prorated portion for the time you owned it before it became your Principal Residence will be taxable).
Be aware that IF this cabin was your Principal Residence during that time, that means your current home was NOT your Principal Residence, so you will again have "Nonqualified Use". That means whenever you sell your current home the 121 Exclusion will be prorated and part of the sale will be taxable.
