Programming

Right, exactly. If you're using C in this day and age, that means you want to be one step above assembly language. Saying C should attempt to emulate a particular specific architecture -- for operations as basic as signed integer add and subtract -- if you're on some weird other architecture, is counter to the whole point. From the point of view of the standard, the behavior is "undefined," but from the point of view of the programmer it's very defined; it means whatever those operations are in reality on my current architecture.

That example of the NULL pointer use in the kernel was pretty fascinating. I'd say that's another exact example of the same thing: Russ Cox apparently wants the behavior to be "defined" by the standard, but that's just not how C works or should work. The behavior is defined; the behavior is whatever the processor does when you read memory from address 0. Trying to say it should be something else just means you're wanting to use a language other than C -- which again is fine, but for writing a kernel, I think you're going to have a hard time saying that the language need to introduce an extra layer of semantics between the code author and the CPU.