How do functions like alloca allocate memory from the stack?

One thing that scares me a little is whether there are younger developers, say, 25-40, who can and want to pick up the mantle of Windows internals gurus.

I mean, Chen has decades of winternals in his head. Microsoft has been gutting their staff for years now. When the Petzold/Chen generation hang up their spurs, does Microsoft still have a critical mass of people who understand Windows from the metal up?