Gentry, a linebacker, was the Pack's leader in special teams tackles and ranked second in special teams snaps in 2011. Purvis saw action in 11 games last season at fullback and on special teams, hauling in two touchdown receptions in just 11 plays versus Georgia Tech.
"These two young men have worked hard on and off the field," said O'Brien. "We look forward to their continued contributions to our team in 2012."
Both played mainly on special teams as redshirt sophomores in 2011, seeing action from scrimmage for seven and 12 snaps respectively.
Coleman graduated last Saturday and would be eligible to play immediately.
Quarterback Brian Taylor, a true freshman last season, has decided to remain at NC State, but will no longer play football.