[$] Compile-time stack validation

An occasionally heard horror story about the kernel development communityconcerns developers who are told that, in order to get their code upstream,they must first invest considerable effort into fixing a relatedsubsystem. As with many such stories, this is not an experience manykernel developers have had, but there is also agrain of truth behind it. The ongoing live-patching effort, and the extrawork that has been required to push that work forward, is a case in point.