On Sun, Oct 14, 2012 at 08:24:03PM +0100, Al Viro wrote:

Russell, could you recall what those had been about?  I'm not sure if that
had been oopsable that far back (again, oops scenario is userland stack
page getting swapped out before we get to start_thread(), leading to
direct read from an absent page in start_thread() by plain ldr, without
anything in exception table about that insn), but it looks very odd
regardless of that problem.

BTW, arm64 has copied that logics, so it also seems to be unsafe and very
odd - there we definitely have only ELF to cope with.  arm64 folks Cc'd...