I'm not aware of a generalized safe subset of C. There are lots of compiler extensions and model annotations that offer security improvements, but very few will

I'm not aware of a generalized safe subset of C. There are lots of compiler extensions and model annotations that offer security improvements, but very few will claim to offer spatial and temporary memory safety in the way that safe programming languages can. There are lots of specification driven C applications, which rely on (1) the specification being bug free, (2) the application of the specification being bug free, and (3) the model or proof assistant for the specification being sound and bug free. Getting all three of those is historically very difficult.