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

libkvm code janitoring

- make WARNS=6 clean for archs w/o strict alignment requirments
- add const, ANSIfy, remove unused vars, cast types for comparison
- thanks to differing definitions of VM_MIN_ADDRESS across our archs, we
need to trick the compiler to not complain about signedness. We could
either fix VM_MIN_ADDRESS to always be a simple integer or make the
check conditional on $ARCH.

Closes PRs: kern/42386, kern/83364
Reviewed by: bde

Add support for PowerPC kernel core files. This commit only adds
support for virtual core files (aka minidumps). physical core
files are not supported.

The implementation is cross-tool ready and can be used in a non-
powerpc hosted debugger to analyze PowerPC core files. It also
accepts core files that still have the dump header, as can be
the case within Juniper where TFTP-based kernel core files are
supported and savecore is not used to "extract" the core file
from some dump device.

Obtained from: Juniper Networks, Inc.

Support crash dumps > 4GB in size on 32 bit platforms. _kvm_kvatop()
returned an lseek offset in a "u_long *" value, which can't express >4GB
offsets on 32 bit machines (eg: PAE). Change to "off_t *" for all.

Support ELF crashdumps on i386 and amd64.

Support PAE crashdumps on i386. This is done by auto-detecting the
presence of the IdlePDPT which means that PAE is active.

I used Marcel's _kvm_pa2off strategy and ELF header reader for ELF support
on amd64. Paul Saab ported the amd64 changes to i386 and we implemented
the PAE support from there.

Note that gdb6 in the src tree uses whatever libkvm supports. If you want
to debug an old crash dump, you might want to keep an old libkvm.so handy
and use LD_PRELOAD or the like. This does not detect the old raw dump
format.

Approved by: re

Stub out _kvm_mdopen, we don't the same constants as NetBSD

Add a PowerPC machdep for kvm.

Obtained from: NetBSD (rev 1.4, pre-UVM)