kernel: Sync ldscript files wrt gnu.attributes and .note.GNU-stack

Bring the keeping of .gnu.attributes to all architectures. Also discard
.note.GNU-stack on all archtiectures. Plus delete obsolete comment that
was removed from i386 in 2010.

Sponsored by: Netflix
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D44069

Import the kernel parts of bhyve/arm64

To support virtual machines on arm64 add the vmm code. This is based on
earlier work by Mihai Carabas and Alexandru Elisei at University
Politehnica of Bucharest, with further work by myself and Mark Johnston.

All AArch64 CPUs should work, however only the GICv3 interrupt
controller is supported. There is initial support to allow the GICv2
to be supported in the future. Only pure Armv8.0 virtualisation is
supported, the Virtualization Host Extensions are not currently used.

With a separate userspace patch and U-Boot port FreeBSD guests are able
to boot to multiuser mode, and the hypervisor can be tested with the
kvm unit tests. Linux partially boots, but hangs before entering
userspace. Other operating systems are untested.

Sponsored by: Arm Ltd
Sponsored by: Innovate UK
Sponsored by: The FreeBSD Foundation
Sponsored by: University Politehnica of Bucharest
Differential Revision: https://reviews.freebsd.org/D37428

sys: Remove $FreeBSD$: one-line .c comment pattern

Remove /^/[*/]\s*\$FreeBSD\$.*\n/

arm64: add read_frequently, read_mostluy and exclusive_cache_line to linker script

Reviewed by: andrew
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D31643

More the arm64 early page tables and stack to .bss

This removes 806k from the kernel ELF file that is only needed while
the kernel is running, not in the static file.

Sponsored by: Innovate UK

Eliminate the generated ldscript for arm and arm64, and strip $a/$d marker
symbols from the linked kernel.

The main thrust of this change is to generate a kernel that has the arm
"marker" symbols stripped. Marker symbols start with $a, $d, $t or $x, and
are emitted by the compiler to tell other toolchain components about the
locations of data embedded in the instruction stream (literal-pool
stuff). They are used for generating mixed-endian binaries (which we don't
support). The linked kernel has approximately 21,000 such symbols in it,
wasting space (500K in kernel.full, 190K in the final linked kernel), and
sometimes obscuring function names in stack tracebacks.

This change also simplifies the way the kernel is linked. Instead of using
sed to generate two different ldscript files to generate both an elf kernel
and a binary (elf headers stripped) kernel, we now use a single ldscript
that refers to a "text_start" symbol, and we provide the value for that
symbol using --defsym on the linker command line.

Expose the kernel's build-ID through sysctl

After our migration (of certain architectures) to lld the kernel is built
with a unique build-ID. Make it available via a sysctl and uname(1) to
allow the user to identify their running kernel.

Submitted by: Ali Mashtizadeh <ali_mashtizadeh.com>
MFC after: 2 weeks
Relnotes: Yes
Event: Waterloo Hackathon 2019
Differential Revision: https://reviews.freebsd.org/D20326

Explicitly include all .rodata.* sections in the kernel .rodata. This
helps link the kernel with lld as it will then put all these into a single
.rodata section.

MFC after: 1 week
Sponsored by: ABT Systems Ltd

remove CONSTRUCTORS from kernel linker scripts

The linker script CONSTRUCTORS keyword is only meaningful "when linking
object file formats which do not support arbitrary sections, such as
ECOFF and XCOFF"[1] and is ignored for other object file formats.

LLVM's lld does not yet accept (and ignore) CONSTRUCTORS, so just remove
CONSTRUCTORS from the linker scripts as it has no effect.

[1] https://sourceware.org/binutils/docs/ld/Output-Section-Keywords.html

Reviewed by: kib
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D7343

Bring in the start of the arm64 kernel.

This is only the minimum set of files needed to boot in qemu. As such it is
missing a few things.

The bus_dma code is currently only stub functions with a full implementation
from the development tree to follow.

The gic driver has been copied as the interrupt framework is different. It
is expected the two drivers will be merged by the arm intrng project,
however this will need to be imported into the tree and support for arm64
would need to be added.

This includes code developed by myself, SemiHalf, Ed Maste, and Robin
Randhawa from ARM. This has been funded by the FreeBSD Foundation, with
early development by myself in my spare time with assistance from Robin.

Differential Revision: https://reviews.freebsd.org/D2199
Reviewed by: emaste, imp
Relnotes: yes
Sponsored by: The FreeBSD Foundation