9 speed chain ring

I am looking to move from 8 speed to 9 speed. My rear derailleur is nearly dead, and rather than buy an 8 speed I will upgrade the whole drivetrain to 9 speed.
Are the actual chain-rings 8/9 speed specific? Or will any chainring work?
Same question for cranks. Will any cranks work or do I need specific 9 speed cranks?
I am pretty sure that I currently have a 9 speed front chain-wheels and/or cranks. The crank has the shimano 'mega 9'sticker on it. But they work fine with my 8 speed setup.
Would be great if I can still use the same crank and chain-rings. The chain-rings are brand new.
Thanks for any comments.