kldxref: Reduce divergence between per-architecture files

Note that relbase is always 0 for DSOs so its omission for __KLD_SHARED
architectures was not a bug in practice.

Whilst here, also parenthesise the dest offset for where to avoid
transiently creating an out-of-bounds pointer, which is UB (though even
on CHERI architectures, where capability bounds compression can result
in that creating invalid capabilities that will trap on dereference,
optimisation will reassociate to the correct form in practice and thus
work just fine).

kldxref: Make use of libelf to be a portable cross tool

This allows kldxref to operate on kernel objects from any
architecture, not just the native architecture. In particular, this
will permit generating linker.hints files as part of a cross-arch
release build.

- elf.c is a new file that includes various wrappers around libelf
including routines to read ELF data structures such as program and
section headers and ELF relocations into the "generic" forms
described in <gelf.h>. This file also provides routines for
converting a linker set into an array of addresses (GElf_Addr)
as well as reading architecture-specific mod_* structures and
converting them into "generic" Gmod_* forms where pointers are
replaced with addresses.

- The various architecture-specific reloc handlers now use GElf_*
types for most values (including GElf_Rel and GElf_Rela for
relocation structures) and use routines from <sys/endian.h> to read
and write target values. A new linker set matches reloc handlers
to specific ELF (class, encoding, machine) tuples.

- The bits of kldxref.c that write out linker.hints now use the
encoding (ELFDATA2[LM]SB) of the first file encountered in a
directory to set the endianness of the output file. Input files
with a different architecture in the same directory are skipped with
a warning. In addition, the initial version record for the file
must be deferred until the first record is finished since the
architecture of the output file is not known until then.

- Various places that used 'sizeof(void *)' throughout now use
'elf_pointer_size()' to determine the size of a pointer in the
target architecture.

Tested by: amd64 binary on both amd64 and i386 /boot/kernel
Reviewed by: imp
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D42966

Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

Remove unneeded reference to link.h (sys/link_elf.h).

MFC after: 2 weeks

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Create the altix project branch. The altix project will add support
for the SGI Altix 350 to FreeBSD/ia64. The hardware used for porting
is a two-module system, consisting of a base compute module and a
CPU expansion module. SGI's NUMAFlex architecture can be an excellent
platform to test CPU affinity and NUMA-aware features in FreeBSD.

- Import the HEAD csup code which is the basis for the cvsmode work.

Make our ELF64 type definitions match standards. In particular this
means:
o Remove Elf64_Quarter,
o Redefine Elf64_Half to be 16-bit,
o Redefine Elf64_Word to be 32-bit,
o Add Elf64_Xword and Elf64_Sxword for 64-bit entities,
o Use Elf_Size in MI code to abstract the difference between
Elf32_Word and Elf64_Word.
o Add Elf_Ssize as the signed counterpart of Elf_Size.

MFC after: 2 weeks

Explicitly pass in the relocation base and data offset into ef_reloc()
rather than relying on a trick that happens to work for the current
relocation schemes. Also add some comments and improve variable
naming.

Add MD relocation support for amd64 and i386 platforms. The no-op
relocation is not sufficient for ELF relocatable object format
modules, since accessing the module metadata involves following
pointers between different ELF sections.

This allows kldxref to correctly build linker.hints on the amd64
platform.