FYI: Going from head -r313864 to -r313999 I had to rebuild virtualbox-ose-additions 5.1.14

For amd64 I run FreeBSD under VirtualBox on macOS. So I use
emulators/virtualbox-ose-additions in the FreeBSD instance.

I've been using virtualbox-ose-additions-5.1.14 for some time
under -r313864 (and some prior versions), no problems, no
need to rebuild virtualbox-ose-additions-5.1.14 along the way
to -r313864.

On updating to -r313999 the boot got the following shortly
before it would have given the login prompt normally. . .

> # kgdb kernel.debug /var/crash/vmcore.0
> GNU gdb 6.1.1 [FreeBSD]
> Copyright 2004 Free Software Foundation, Inc.
> GDB is free software, covered by the GNU General Public License, and you are
> welcome to change it and/or distribute copies of it under certain conditions.
> Type "show copying" to see the conditions.
> There is absolutely no warranty for GDB.  Type "show warranty" for details.
> This GDB was configured as "amd64-marcel-freebsd"...
> 
> Unread portion of the kernel message buffer:
> <118>Starting vboxservice.
> <118>VBoxService 5.1.14 r112924 (verbosity: 0) freebsd.amd64 (Jan 20 2017 18:37:45) release log
> <118>00:00:00.000120 main     Log opened 2017-02-20T22:38:46.348080000Z
> <118>00:00:00.000162 main     OS Product: FreeBSD
> <118>00:00:00.000171 main     OS Release: 12.0-CURRENT
> <118>00:00:00.000180 main     OS Version: FreeBSD 12.0-CURRENT  r313999M
> <118>00:00:00.000192 main     Executable: /usr/local/sbin/VBoxService
> <118>00:00:00.000194 main     Process ID: 609
> <118>00:00:00.000196 main     Package type: BSD_64BITS_GENERIC (OSE)
> 
> 
> Fatal trap 12: page fault while in kernel mode
> cpuid = 2; apic id = 02
> fault virtual address   = 0xd6
> fault code              = supervisor read data, page not present
> instruction pointer     = 0x20:0xffffffff80d4ebaf
> stack pointer           = 0x28:0xfffffe0122e2bef0
> frame pointer           = 0x28:0xfffffe0122e2bf00
> code segment            = base 0x0, limit 0xfffff, type 0x1b
>                        = DPL 0, pres 1, long 1, def32 0, gran 1
> processor eflags        = interrupt enabled, resume, IOPL = 0
> current process         = 609 (VBoxService)
> 
> Reading symbols from /boot/kernel/zfs.ko...Reading symbols from /usr/lib/debug//boot/kernel/zfs.ko.debug...done.
> done.
> Loaded symbols for /boot/kernel/zfs.ko
> Reading symbols from /boot/kernel/opensolaris.ko...Reading symbols from /usr/lib/debug//boot/kernel/opensolaris.ko.debug...done.
> done.
> Loaded symbols for /boot/kernel/opensolaris.ko
> Reading symbols from /boot/modules/vboxguest.ko...done.
> Loaded symbols for /boot/modules/vboxguest.ko
> #0  doadump (textdump=0) at pcpu.h:232
> 232             __asm("movq %%gs:%1,%0" : "=r" (td)
> (kgdb) bt
> #0  doadump (textdump=0) at pcpu.h:232
> #1  0xffffffff8039dd0b in db_dump (dummy=<value optimized out>, dummy2=<value optimized out>, dummy3=<value optimized out>, dummy4=<value optimized out>) at /usr/src/sys/ddb/db_command.c:546
> #2  0xffffffff8039db0f in db_command (cmd_table=<value optimized out>) at /usr/src/sys/ddb/db_command.c:453
> #3  0xffffffff8039d884 in db_command_loop () at /usr/src/sys/ddb/db_command.c:506
> #4  0xffffffff803a0814 in db_trap (type=<value optimized out>, code=<value optimized out>) at /usr/src/sys/ddb/db_main.c:254
> #5  0xffffffff80a9c0c3 in kdb_trap (type=<value optimized out>, code=<value optimized out>, tf=<value optimized out>) at /usr/src/sys/kern/subr_kdb.c:654
> #6  0xffffffff80ed25d2 in trap_fatal (frame=0xfffffe0122e2be30, eva=214) at /usr/src/sys/amd64/amd64/trap.c:796
> #7  0xffffffff80ed27dc in trap_pfault (frame=0xfffffe0122e2be30, usermode=0) at /usr/src/sys/amd64/amd64/trap.c:658
> #8  0xffffffff80ed1e90 in trap (frame=0xfffffe0122e2be30) at /usr/src/sys/amd64/amd64/trap.c:421
> #9  0xffffffff80eb6be1 in calltrap () at /usr/src/sys/amd64/amd64/exception.S:236
> #10 0xffffffff80d4ebaf in _vm_map_lock (map=0x1, file=0x0, line=0) at /usr/src/sys/vm/vm_map.c:501
> #11 0xffffffff80d51ea2 in vm_map_wire (map=<value optimized out>, start=4534272, end=4538368, flags=1) at /usr/src/sys/vm/vm_map.c:2534
> #12 0xffffffff8265291c in rtR0MemObjNativeLockInMap () from /boot/modules/vboxguest.ko
> #13 0xffffffff82652881 in rtR0MemObjNativeLockUser () from /boot/modules/vboxguest.ko
> #14 0xffffffff8264ec01 in RTR0MemObjLockUserTag () from /boot/modules/vboxguest.ko
> #15 0xffffffff82624afd in vbglR0HGCMInternalPreprocessCall () from /boot/modules/vboxguest.ko
> #16 0xffffffff8262411a in VbglR0HGCMInternalCall () from /boot/modules/vboxguest.ko
> #17 0xffffffff8261ec4f in vgdrvIoCtl_HGCMCall () from /boot/modules/vboxguest.ko
> #18 0xffffffff8261d221 in VGDrvCommonIoCtl () from /boot/modules/vboxguest.ko
> #19 0xffffffff8262327d in vgdrvFreeBSDIOCtl () from /boot/modules/vboxguest.ko
> #20 0xffffffff8092976e in devfs_ioctl (ap=<value optimized out>) at /usr/src/sys/fs/devfs/devfs_vnops.c:805
> #21 0xffffffff8103ef58 in VOP_IOCTL_APV (vop=<value optimized out>, a=<value optimized out>) at vnode_if.c:1067
> #22 0xffffffff80b29431 in vn_ioctl (fp=0xfffff80006d37730, com=<value optimized out>, data=0xfffffe0122e2c870, active_cred=0xfffff80006495a00, td=<value optimized out>) at vnode_if.h:448
> #23 0xffffffff80929d5f in devfs_ioctl_f (fp=<value optimized out>, com=<value optimized out>, data=<value optimized out>, cred=<value optimized out>, td=0xfffff8001504e000) at /usr/src/sys/fs/devfs/devfs_vnops.c:763
> #24 0xffffffff80ab8bf0 in kern_ioctl (td=<value optimized out>, fd=3, com=<value optimized out>, data=0xfffffe0122e2c870 "\031\002R\031P") at file.h:322
> #25 0xffffffff80ab88bf in sys_ioctl (td=<value optimized out>, uap=0xfffffe0122e2ca30) at /usr/src/sys/kern/sys_generic.c:743
> #26 0xffffffff80ed2e27 in amd64_syscall (td=0xfffff8001504e000, traced=0) at subr_syscall.c:135
> #27 0xffffffff80eb6ecb in Xfast_syscall () at /usr/src/sys/amd64/amd64/exception.S:396
> #28 0x0000000800c5317a in ?? ()
> Previous frame inner to this frame (corrupt stack?)
> Current language:  auto; currently minimal


Booting using kernel.old and rebuilding virtualbox-ose-additions-5.1.14
got my boot context back to working when I again booted with kernel
(-r31399) instead of kernel.old (-r313864).

Mateusz Guzik has said: "I think this is r313992" for what
made such rebuilding required. I have not done a bisection
to find just where the rebuild became required. So this is
not confirmed.

There may be other things around that would need rebuilding.

There were no UPDATING notes and uname -apKU continued to
list the same thing (varying the replacement for ??? below):

# uname -apKU
FreeBSD FreeBSDx64 12.0-CURRENT FreeBSD 12.0-CURRENT  r313???M  amd64 amd64 1200021 1200021


===
Mark Millard
markmi at dsl-only.net