Do not write to the user address directly, use suword().

Extend struct sysvec with new method sv_schedtail, which is used for an
explicit process at fork trampoline path instead of eventhadler(schedtail)
invocation for each child process.

Remove eventhandler(schedtail) code and change linux ABI to use newly added
sysvec method.

While here replace explicit comparing of module sysentvec structure with the
newly created process sysentvec to detect the linux ABI.

MFC r219421:
Remove bogus since r219405 check of the Linux ABI.

Sort include files in the alphabetical order.

Reorganize syscall entry and leave handling.
Implement ptrace_lwpinfo pl_flags PL_FLAG_SCE, PL_FLAG_SCX and
PL_FLAG_EXEC.

The i386, amd64, sparc64, sun4v, powerpc and ia64 syscall()s are
changed to use syscallenter()/syscallret(). MIPS and arm are not
converted and use the mostly unchanged syscall() implementation.

MFC r208514:
Change ia64' struct syscall_args definition so that args is a pointer to
the arguments array instead of array itself.

MFC r208566:
Allow to use syscallname(9) outside subr_trap.c.

MFC r209258 (by rpaulo):
Make DTrace syscall provider work again by including opt_kdtrace.h here.

MFC r209313:
Only enable kdtrace hook in the LINT on the architectures that implement it.

MFC r209697:
Obey sv_syscallnames bounds in syscallname().

NOTE: The KBI of the struct sysentvec is changed, new required members
sv_set_syscall_retval, sv_fetch_syscall_args and sv_syscallnames are
added. The sv_prepsyscall field is now ignored. Third-party modules
using the struct sysentvec must be modified and recompiled, we believe
that only ABI emulators are affected. No such out-of-tree modules are
known. In-tree modules that are affected by the change were converted
to depend on exact version of the kernel, see r214421.

Add macro DECLARE_MODULE_TIED to denote a module as requiring the
kernel of exactly the same __FreeBSD_version as the headers module was
compiled against.

Mark our in-tree ABI emulators with DECLARE_MODULE_TIED. The modules
use kernel interfaces that the Release Engineering Team feel are not
stable enough to guarantee they will not change during the life cycle
of a STABLE branch. In particular, the layout of struct sysentvec is
declared to be not part of the STABLE KBI.

Use kern_sigprocmask() instead of direct manipulation of td_sigmask to
reschedule newly blocked signals.

MFC r198590:
Trapsignal() calls kern_sigprocmask() when delivering catched signal
with proc lock held.

MFC r198670:
For trapsignal() and postsig(), kern_sigprocmask() is called with
both process lock and curproc->p_sigacts->ps_mtx locked. Prevent lock
recursion on ps_mtx in reschedule_signals().

  Fix handling of .note.ABI-tag section for GNU systems [1].
  Handle GNU/Linux according to LSB Core Specification 4.0,
  Chapter 11. Object Format, 11.8. ABI note tag.

  Also check the first word of desc, not only name, according to
  glibc abi-tags specification to distinguish between Linux and
  kFreeBSD.

  Add explicit handling for Debian GNU/kFreeBSD, which runs
  on our kernels as well [2].

  In {amd64,i386}/trap.c, when checking osrel of the current process,
  also check the ABI to not change the signal behaviour for Linux
  binary processes, now that we save an osrel version for all three
  from the lists above in struct proc [2].

  These changes make it possible to run FreeBSD, Debian GNU/kFreeBSD
  and Linux binaries on the same machine again for at least i386 and
  amd64, and no longer break kFreeBSD which was detected as GNU(/Linux).

PR:		kern/135468
Submitted by:	dchagin [1] (initial patch)
Suggested by:	kib [2]
Tested by:	Petr Salinger (Petr.Salinger seznam.cz) for kFreeBSD
Reviewed by:	kib
Approved by:	re (kensmith)

to 2.4.0, as it has appeared in the 2.4.0-rc7 first time.
Being exported, AT_CLKTCK is returned by sysconf(_SC_CLK_TCK),
glibc falls back to the hard-coded CLK_TCK value when aux entry
is not present.

Glibc versions prior to 2.2.1 always use hard-coded CLK_TCK value.

For older applications/libc's which depends on hard-coded CLK_TCK
value user should set compat.linux.osrelease less than 2.4.0.

Approved by:	kib (mentor)

The frequency of the statistics clock is given by stathz.
Use stathz if it is available, otherwise use hz.

Pointed out by:	bde

Approved by:	kib (mentor)

OSD-based jail extensions.  This allows the Linux MIB to accessed via
jail_set and jail_get, and serves as a demonstration of adding jail support
to a module.

Reviewed by:	dchagin, kib
Approved by:	bz (mentor)