I work in a company that has a old codebse in c with tons of realtime intime stuff that is acessed via a shared memory from the realtime to the non realtime system. Tons of strucs get copied around then typecast to other structs and global variables all over the place. You never know where a variable is written to and where it is also acessed from or if it is just a copy. No assembly but still super obscure.

With embedded stuff its still done like that. And if you go from the arduino functionss to writing the registers directly its a hell of a lot faster.