Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- There's no need to wrap kdb_active and kdb_trap() in #ifdef KDB as
they're always available.
- Remove unused variable. [1]
- Add a missing const.
- Sort includes.

Submitted by: Christoph Mallon [1]

Use the PROM provided SUNW,set-trap-table to take over the trap
table. This is required in order to set obp-control-relinquished
within the PROM, allowing to safely read the OFW translations node.
Without this, f.e. a `ofwdump -ap` triggers a fatal reset error or
worse things on machines based on USIII and beyond.
In theory this should allow to remove touching %tba in cpu_setregs(),
in practice we seem to currently face a chicken and egg problem when
doing so however.

Correct typos (s/OFERFLOW/OVERFLOW/).

Reviewed by: jhb

Allow fast instruction and data access mmu miss traps to be handled by
user trap handlers.

Greatly improve readability of trap() by using a table to convert between
trap types and signals to send. Rearrange KASSERTs to better handle faults
early before curthread is setup, or in the case that it gets corrupted or
set to 0.

Add a panic stack, which is used as a known good stack when there is
something wrong with the kernel stack.
Add code to check the kernel stack pointer in various important places
and try hard not to go down in flames if its wrong.

Rename and renumber trap types to comply with the user trap types as
specified by the sparc abi. We use numerically higher values for all
internal kernel types.
Remove soft trap types which need to be exposed to userland. They will
move to utrap.h.

Add support for physical address hardware watchpoints.

Wrap hardware trap types in ifdef _kernel.

Change tf_arg to uintptr_t from void * to reflect the fact that
non-pointer values may be passed in it. Add appropriate casts.

The interrupt type is now passed in tf_arg instead tf_type.

Add a system call trap type and syscall() call request handler.
Also add support for hardware watch point traps.

Submitted by: tmm

Add trap types for interrupts. Ad definitions to get the interrupt level
from the trap type.

The author isn't a [UC] Regents. Correct the copyright language.

Flesh out the sparc64 port considerably. This contains:
- mostly complete kernel pmap support, and tested but currently turned
off userland pmap support
- low level assembly language trap, context switching and support code
- fully implemented atomic.h and supporting cpufunc.h
- some support for kernel debugging with ddb
- various header tweaks and filling out of machine dependent structures