amd64 pcpu: fix clobbers, suppress warnings, and clean up

These changes mostly apply to the !__SEG_GS section, which is no longer
the normal compilation path. They're made to be consistent with cha

amd64 pcpu: fix clobbers, suppress warnings, and clean up

These changes mostly apply to the !__SEG_GS section, which is no longer
the normal compilation path. They're made to be consistent with changes
to i386.

- Add missing cc clobber to __PCPU_ADD (which is currently unused).
- Allow the compiler the opportunity to marginally improve code
generation from __PCPU_PTR by letting it figure out how to do the add
(also removing the addition fixes a missing cc clobber).
- Quiet gcc -Warray-bounds by using constant operands instead of bogus
memory references.
- Remove the struct __s __s temporaries, just cast through the type.

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D45827

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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

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amd64: -m32 support for machine/pcpu_aux.h

Install the i386 pcpu_aux.h under /usr/include/i386 on amd64 and include
when targeting i386.

This is a kernel-only header that is required by procstat's

amd64: -m32 support for machine/pcpu_aux.h

Install the i386 pcpu_aux.h under /usr/include/i386 on amd64 and include
when targeting i386.

This is a kernel-only header that is required by procstat's ZFS support.

Reviewed by: jhb, imp

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amd64: move pcb out of kstack to struct thread.

This saves 320 bytes of the precious stack space.

The only negative aspect of the change I can think of is that the
struct thread increased by 320 by

amd64: move pcb out of kstack to struct thread.

This saves 320 bytes of the precious stack space.

The only negative aspect of the change I can think of is that the
struct thread increased by 320 bytes obviously, and that 320 bytes are
not swapped out anymore. I believe the freed stack space is much more
important than that. Also, current struct thread size is 1392 bytes
on amd64, so UMA will allocate two thread structures per (4KB) slab,
which leaves a space for pcb without increasing zone memory use.

Reviewed by: alc, markj
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Differential revision: https://reviews.freebsd.org/D22138

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Merge ^/head r351317 through r351731.

Centralize __pcpu definitions.

Many extern struct pcpu <something>__pcpu declarations were
copied/pasted in sources. The issue is that the definition is MD, but
it cannot be provided by machine/pcp

Centralize __pcpu definitions.

Many extern struct pcpu <something>__pcpu declarations were
copied/pasted in sources. The issue is that the definition is MD, but
it cannot be provided by machine/pcpu.h due to actual struct pcpu
defined in sys/pcpu.h later than the inclusion of machine/pcpu.h.
This forced the copying when other code needed direct access to
__pcpu. There is no way around it, due to machine/pcpu.h supplying
part of struct pcpu fields.

To work around the problem, add a new machine/pcpu_aux.h header, which
should fill any needed MD definitions after struct pcpu definition is
completed. This allows to remove copies of __pcpu spread around the
source. Also on x86 it makes it possible to remove work arounds like
OFFSETOF_CURTHREAD or clang specific warnings supressions.

Reported and tested by: lwhsu, bcran
Reviewed by: imp, markj (previous version)
Discussed with: jhb
Sponsored by: The FreeBSD Foundation
Differential revision: https://reviews.freebsd.org/D21418

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