Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Make this file more C++ friendly.

Add thr_kill2 syscall which sends a signal to a thread in another process.

Submitted by: Tijl Coosemans tijl at ulyssis dot org
Approved by: re (kensmith)

- Remove unused variable from create_thread().
- Move kern_thr_*() prototype to <sys/syscallsubr.h> where all the other
kern_*() prototypes live.

Merge posix4/* into normal kernel hierarchy.

Reviewed by: glanced at by jhb
Approved by: silence on -arch@ and -standards@

Add compatible code to let 32bit libthr work on 64bit kernel.

Replace system call thr_getscheduler, thr_setscheduler, thr_setschedparam
with rtprio_thread, while rtprio system call is for process only, the new
system call rtprio_thread is responsible for LWP.

Add syscalls thr_setscheduler, thr_getscheduler, and thr_setschedparam,
these syscalls are designed to set thread's scheduling parameters and
policy, because each syscall contains a size parameter, it is possible
to support future scheduling option, e.g SCHED_SPORADIC, this option
needs other fields in structure sched_param, current they are not
avaiblable.

Add POSIX scheduler parameters support to thr_new syscall, this permits
privileged process to create realtime thread.

Implement thr_set_name to set a name for thread.

Reviewed by: julian

Add new syscall thr_new to create thread in atomic, it will
inherit signal mask from parent thread, setup TLS and stack, and
user entry address.
Also support POSIX thread's PTHREAD_SCOPE_PROCESS and PTHREAD_SCOPE_SYSTEM,
sysctl is also provided to control the scheduler scope.

/* -> /*- for license, minor formatting changes

Close a race between a thread exiting and the freeing of it's stack.
After some discussion the best option seems to be to signal the thread's
death from within the kernel. This requires that thr_exit() take an
argument.

Discussed with: davidxu, deischen, marcel
MFC after: 3 days

Change the thread ID (thr_id_t) used for 1:1 threading from being a
pointer to the corresponding struct thread to the thread ID (lwpid_t)
assigned to that thread. The primary reason for this change is that
libthr now internally uses the same ID as the debugger and the kernel
when referencing to a kernel thread. This allows us to implement the
support for debugging without additional translations and/or mappings.

To preserve the ABI, the 1:1 threading syscalls, including the umtx
locking API have not been changed to work on a lwpid_t. Instead the
1:1 threading syscalls operate on long and the umtx locking API has
not been changed except for the contested bit. Previously this was
the least significant bit. Now it's the most significant bit. Since
the contested bit should not be tested by userland, this change is
not expected to be visible. Just to be sure, UMTX_CONTESTED has been
removed from <sys/umtx.h>.

Reviewed by: mtm@
ABI preservation tested on: i386, ia64

Separate thread synchronization from signals in libthr. Instead
use msleep() and wakeup_one().

Discussed with: jhb, peter, tjr

- Add two files to support the thr threading interface.
- sys/thr.h contains the user space visible api that is intended only for
use in threading library packages.
- kern/kern_thr.c contains thr system calls and other thr specific code.