sys: Remove ancient SCCS tags.

Remove ancient SCCS tags from the tree, automated scripting, with two
minor fixup to keep things compiling. All the common forms in the tree
were removed with a perl script.

Sponsored by: Netflix

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

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

Rework how shared page related data is stored

Store the shared page address in struct vmspace.
Also instead of storing absolute addresses of various shared page
segments save their offsets with respect to the shared page address.
This will be more useful when the shared page address is randomized.

Approved by: mw(mentor)
Sponsored by: Stormshield
Obtained from: Semihalf
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D35393

Introduce the PROC_SIGCODE() macro

Use a getter macro instead of fetching the sigcode address directly
from a sysent of a given process. It assumes that the sigcode is stored
in the shared page, which is true in all cases, except for a.out
binaries. This will be later useful when the shared page address
randomization is introduced.
No functional change intended.

Approved by: mw(mentor)
Sponsored by: Stormshield
Obtained from: Semihalf
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D35392

amd64: Add static asssert for context size

Add a static assert for the siginfo_t, mcontext_t and ucontext_t
sizes. These are de-facto ABI options and cannot change size ever.

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D34212

Unstaticize {get,set}_fpcontext() on amd64

This will be used to fix Linux signal delivery.

Discussed With: kib
Sponsored By: EPSRC

amd64 get_mcontext(): third argument to get_fpcontext() is a pointer

Use NULL instead of raw 0

Sponsored by: The FreeBSD Foundation
MFC after: 3 days

amd64 sendsig: fix context corruption

Drop fpstate only after copying out xfpustate from the thread usermode
save area. Otherwise a context switch between get_fpcontext(), which now
returns the pointer directly into user save area, and copyout, would
cause reinit of the save area, loosing user registers.

Reported, reviewed, and tested by: markj
Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Differential revision: https://reviews.freebsd.org/D32159

amd64: consistently use uprintf() to report weird situations in sigreturn

Reviewed by: jhb
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D31954

amd64: eliminate td_md.md_fpu_scratch

For signal send, copyout from the user FPU save area directly.

For sigreturn, we are in sleepable context and can do temporal
allocation of the transient save area. We cannot copying from userspace
directly to user save area because XSAVE state needs to be validated,
also partial copyins can corrupt it.

Requested by: jhb
Reviewed by: jhb, markj
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D31954

amd64: stop using top of the thread' kernel stack for FPU user save area

Instead do one more allocation at the thread creation time. This frees
a lot of space on the stack.

Also do not use alloca() for temporal storage in signal delivery sendsig()
function and signal return syscall sys_sigreturn(). This saves equal
amount of space, again by the cost of one more allocation at the thread
creation time.

A useful experiment now would be to reduce KSTACK_PAGES.

Reviewed by: jhb, markj
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D31954

exec_machdep.c: some style, use ANSI C definition for sys_sigreturn()

Reviewed by: jhb, markj
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D31954

amd64: move signal handling and register structures manipulations into exec_machdep.c

from machdep.c which is too large pile of unrelated things.
Some ptrace functions are moved from machdep.c to ptrace_machdep.c.

Now machdep.c contains code mostly related to the low level initialization
and regular low level operation of the architecture, while signal MD code
and registers handling is placed in exec_machdep.c.

Reviewed by: jhb, markj
Discussed with: jrtc27
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D31954