Panic after updating from source

[Janos Dohanics]

Hello Experts,

After updating my FreeBSD 12 workhorse panics on boot.

I have updated /usr/src, then

make buildworld
make buildkernel KERNCONF=MYKERNEL
make installkernel KERNCONF=MYKERNEL

but after rebooting, kernel panic.

Unfortunately, 'boot kernel.old' does not boot either.

This system has a single zpool on a 3-way mirror. I have installed an
additional hard drive and on that drive installed 12.2-STABLE.

Fortunately, I have been able to import the old zpool 'zroot' of the
3-way mirror:

# zpool status
  pool: buffrescue
 state: ONLINE
  scan: none requested
config:

	NAME        STATE     READ WRITE CKSUM
	buffrescue  ONLINE       0     0     0
	  ada3p3    ONLINE       0     0     0

errors: No known data errors

  pool: zroot
 state: ONLINE
status: Some supported features are not enabled on the pool. The pool can
	still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
	the pool may no longer be accessible by software that does not support
	the features. See zpool-features(7) for details.
  scan: scrub repaired 0 in 0 days 00:36:07 with 0 errors on Wed Sep 18 12:25:53 2019
config:

	NAME        STATE     READ WRITE CKSUM
	zroot       ONLINE       0     0     0
	  mirror-0  ONLINE       0     0     0
	    ada0p3  ONLINE       0     0     0
	    ada1p3  ONLINE       0     0     0
	    ada2p3  ONLINE       0     0     0

Also:

# gpart status
  Name  Status  Components
ada0p1      OK  ada0
ada0p2      OK  ada0
ada0p3      OK  ada0
ada1p1      OK  ada1
ada1p2      OK  ada1
ada1p3      OK  ada1
ada2p1      OK  ada2
ada2p2      OK  ada2
ada2p3      OK  ada2
ada3p1      OK  ada3
ada3p2      OK  ada3
ada3p3      OK  ada3

My question is: Is there any way to repair the kernel on the drives of
the 3-way mirror?

Please advise...

-- 
Janos Dohanics