RFC: Stack saving/tracing functionality.

[Bakul Shah]

> ... but it would be neat if it could also save/print userland stacks
> so that we could get tracebacks from abort()'ing userland programs.

Along these lines; wouldn't it be neat if there was a sysctl
to leave a segfaulted or aborted process around so that you
can attach a debugger to it and find out what went wrong (and
may be even correct it!)?  Debugging a live process (even if
fatally injured) yields more clues as you can poke around at
its I/O connections, its caller process etc.  A separate
program can be used to create a coredump if you really wish
to preseve the dead body for later autopsy.