sys: Remove $FreeBSD$: two-line .h pattern

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

Make UMA and malloc(9) return non-executable memory in most cases.

Most kernel memory that is allocated after boot does not need to be
executable. There are a few exceptions. For example, kernel modules
do need executable memory, but they don't use UMA or malloc(9). The
BPF JIT compiler also needs executable memory and did use malloc(9)
until r317072.

(Note that a side effect of r316767 was that the "small allocation"
path in UMA on amd64 already returned non-executable memory. This
meant that some calls to malloc(9) or the UMA zone(9) allocator could
return executable memory, while others could return non-executable
memory. This change makes the behavior consistent.)

This change makes malloc(9) return non-executable memory unless the new
M_EXEC flag is specified. After this change, the UMA zone(9) allocator
will always return non-executable memory, and a KASSERT will catch
attempts to use the M_EXEC flag to allocate executable memory using
uma_zalloc() or its variants.

Allocations that do need executable memory have various choices. They
may use the M_EXEC flag to malloc(9), or they may use a different VM
interfact to obtain executable pages.

Now that malloc(9) again allows executable allocations, this change also
reverts most of r317072.

PR: 228927
Reviewed by: alc, kib, markj, jhb (previous version)
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D15691

sys: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 3-Clause license.

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.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

Use kmem_malloc() instead of malloc(9) for the native amd64 filter.

r316767 broke the BPF JIT compiler for amd64 because malloc()'d space is no
longer executable.

Discussed with: kib, alc

Move declarations for a machine-dependent function to the header file.

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

- Allocate scratch memory on stack instead of pre-allocating it with
the filter as we do from bpf_filter()[1].
- Revert experimental use of contigmalloc(9)/contigfree(9). It has no
performance benefit over malloc(9)/free(9)[2].

Requested by: rwatson[1]
Pointed out by: rwatson, jhb, alc[2]

- Change internal function bpf_jit_compile() to return allocated size of
the generated binary and remove page size limitation for userland.
- Use contigmalloc(9)/contigfree(9) instead of malloc(9)/free(9) to make
sure the generated binary aligns properly and make it physically contiguous.

- Make BPF JIT compiler working again in userland. We are limiting size of
generated native binary to page size for now.
- Update copyright date and fix some style nits.

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

Fix a typo in copyrights.

Embed scratch memory in the filter structure.

MFC after: 3 days

- Make these files compilable on user land.
- Update copyrights and fix style(9).

Add BPF Just-In-Time compiler support for ng_bpf(4).

The sysctl is changed from net.bpf.jitter.enable to net.bpf_jitter.enable
and this controls both bpf(4) and ng_bpf(4) now.

Add experimental BPF Just-In-Time compiler for amd64 and i386.

Use the following kernel configuration option to enable:

options BPF_JITTER

If you want to use bpf_filter() instead (e. g., debugging), do:

sysctl net.bpf.jitter.enable=0

to turn it off.

Currently BIOCSETWF and bpf_mtap2() are unsupported, and bpf_mtap() is
partially supported because 1) no need, 2) avoid expensive m_copydata(9).

Obtained from: WinPcap 3.1 (for i386)