MFC 290728:
Export various helper variables describing the layout and size of
certain kernel structures for use by debuggers. This mostly aids
in examining cores from a kernel without debug symbols as a debugger
can infer these values if debug symbols are available.

One set of variables describes the layout of 'struct linker_file' to
walk the list of loaded kernel modules.

A second set of variables describes the layout of 'struct proc' and
'struct thread' to walk the list of processes in the kernel and the
threads in each process.

The 'pcb_size' variable is used to index into the stoppcbs[] array.

The 'vm_maxuser_address' is used to distinguish kernel virtual addresses
from user addresses. This doesn't have to be perfect, and
'vm_maxuser_address' is a cheap and simple way to differentiate kernel
pointers from simple values like TIDs and PIDs.

While here, annotate the fields in struct pcb used by kgdb on amd64
and i386 to note that their ABI should be preserved. Annotations for
other platforms will be added in the future.

MFC r279361, r279395, r279396:

Allow the kern.osrelease and kern.osreldate sysctl values to be set in a
jail's creation parameters. This allows the kernel version to be reliably
spoofed within the jail whether examined directly with sysctl or
indirectly with the uname -r and -K options.

Export the new osreldate and osrelease jail parms in jail_get(2).

Fix line wrap.

MFC r263710, r273377, r273378, r273423 and r273455:

- De-vnet hash sizes and hash masks.
- Fix multiple issues related to arguments passed to SYSCTL macros.

Sponsored by: Mellanox Technologies

Partial MFC of r267961, r267973, r267985, r267992, r267993 and r268005:
Backport some macro definitions to make backporting code from FreeBSD
current easier.

MFC r258819,258928:

Add new sysctl, kern.supported_archs, containing the list of FreeBSD
MACHINE_ARCH values whose binaries this kernel can run. This patch provides
a feature requested for implementing pkgng ABI identifiers in a robust
way.

The list is designed to indicate whether, say, an i386 package can be run on
the current system. If kern.supported_abis contains "i386", then the answer
is yes. Otherwise, the answer is no.

At the moment, this only supports MACHINE_ARCH and MACHINE_ARCH32. As we
gain support for more interesting combinations, this needs to become more
flexible, possibily through the sysent framework, along with the
hw.machine_arch emulation immediately preceding this code in kern_mib.c.

Reviewed by: imp

MFC r279361, r279395, r279396:

Allow the kern.osrelease and kern.osreldate sysctl values to be set in a
jail's creation parameters. This allows the kernel version to be reliably
spoofed within the jail whether examined directly with sysctl or
indirectly with the uname -r and -K options.

Export the new osreldate and osrelease jail parms in jail_get(2).

Fix line wrap.

MFC r263710, r273377, r273378, r273423 and r273455:

- De-vnet hash sizes and hash masks.
- Fix multiple issues related to arguments passed to SYSCTL macros.

Sponsored by: Mellanox Technologies

Partial MFC of r267961, r267973, r267985, r267992, r267993 and r268005:
Backport some macro definitions to make backporting code from FreeBSD
current easier.

MFC r258819,258928:

Add new sysctl, kern.supported_archs, containing the list of FreeBSD
MACHINE_ARCH values whose binaries this kernel can run. This patch provides
a feature requested for implementing pkgng ABI identifiers in a robust
way.

The list is designed to indicate whether, say, an i386 package can be run on
the current system. If kern.supported_abis contains "i386", then the answer
is yes. Otherwise, the answer is no.

At the moment, this only supports MACHINE_ARCH and MACHINE_ARCH32. As we
gain support for more interesting combinations, this needs to become more
flexible, possibily through the sysent framework, along with the
hw.machine_arch emulation immediately preceding this code in kern_mib.c.

Reviewed by: imp