kernel #defines to figure out where the stack is located. This stops
libc_r from exploding when the kernel is compiled with a different
KVM size. IMHO this is all kinda bogus, it would be better to just
check %esp and work from that.
be malloc()ed, but they are now allocated using mmap(), just as the
default-size stacks are. A separate cache of stacks is kept for
non-default-size stacks.
Collaboration with: deischen