* Use continuation->backing_store to determine if we return for the first
time from getcontext(). This avoids having to depend on non-POSIX semantics
of the Linux implementation.
* Avoid using __libc_ia64_register_backing_store_base by hardcoding the base
of the backing store. The kernel is changed to put the backing store at
this address. It's not entirely clean, but I want to avoid adding all sorts
of variables in our libc for this for now.
* Fix a genuine bug in the ia64 case: the ia64-specific fields are not
initialized. On FreeBSD this means they have garbage (= 0xd0). Call
memset() after allocation to make sure the contregs structure is properly
cleared. Since this may affect other architectures, this patch will be
ia64 only.
Submitted by: marcel
