sparc64 traps during probe (r293243)

I recently updated a sparc64 V120 from r291993
to r293243, and it now traps during the
autoconfiguration phase of the kernel boot:

Hit [Enter] to boot immediately, or any other key for command prompt.
Booting [/boot/kernel/kernel]...
jumping to kernel entry at 0xc00b0000.
GDB: no debug ports present
KDB: debugger backends: ddb
KDB: current backend: ddb
Copyright (c) 1992-2016 The FreeBSD Project.
Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
	The Regents of the University of California. All rights reserved.
FreeBSD is a registered trademark of The FreeBSD Foundation.
FreeBSD 11.0-CURRENT #4 r293243M: Thu Jan  7 13:50:04 EST 2016
     lidl_at_ton.pix.net:/usr/obj/usr/src/sys/GENERIC sparc64
gcc version 4.2.1 20070831 patched [FreeBSD]
WARNING: WITNESS option enabled, expect reduced performance.
VT: init without driver.
real memory  = 2147483648 (2048 MB)
avail memory = 2063785984 (1968 MB)
cpu0: Sun Microsystems UltraSparc-IIe Processor (648.00 MHz CPU)

[...]

da0 at sym0 bus 0 scbus2 target 0 lun 0
da0: <FUJITSU MAP3367NC 5605> Fixed Direct Access SCSI-3 device
da0: Serial Number UPL3P310365J
da0: 80.000MB/s transfers (40.000MHz, offset 31, 16bit)
da0: Command Queueing enabled
da0: 34732MB (71132959 512 byte sectors)
cd0 at ata2 bus 0 scbus0 target 0 lun 0
cd0: <TEAC DV-28E-B 1.2B> Removable CD-ROM SCSI device
cd0: 33.300MB/s transfers (UDMA2, ATAPI 12bytes, PIO 65534bytes)
cd0: 393MB (201600 2048 byte sectors)
da1 at sym0 bus 0 scbus2 target 1 lun 0
da1: <FUJITSU MAP3367NC 5605> Fixed Direct Access SCSI-3 device
da1: Serial Number UPL3P3506STC
da1: 80.000MB/s transfers (40.000MHz, offset 31, 16bit)
da1: Command Queueing enabled
da1: 34732MB (71132959 512 byte sectors)
WARNING: WITNESS option enabled, expect reduced performance.
Trying to mount root from zfs:sys/ROOT/default []...
GEOM_MIRROR: Device mirror/gswap launched (2/2).
[ thread pid 1 tid 100002 ]
Stopped at      tl0_utrap+0x20: ldx             [%l0 + %l1], %l0
db> bt
Tracing pid 1 tid 100002 td 0xfffff800016164d0
KDB: reentering
KDB: stack backtrace:
kdb_reenter() at kdb_reenter+0x5c
trap() at trap+0x2fc
-- data access exception sfar=0xfffffcf821ca0218 sfsr=0x41029 
%o7=0xc06165e8 --
sched_clock() at sched_clock+0x94
statclock_cnt() at statclock_cnt+0x1c0
handleevents() at handleevents+0x138
timercb() at timercb+0x410
tick_intr() at tick_intr+0x220
-- interrupt level=0xe pil=0 %o7=0xc09c6c20 --
-- kernel stack fault %o7=0xc00b1288 --
db_read_bytes() at db_read_bytes+0x44
KDB: reentering
KDB: stack backtrace:
kdb_reenter() at kdb_reenter+0x5c
trap() at trap+0x2fc
-- kernel stack fault %o7=0xc011f8f0 --
db_read_bytes() at db_read_bytes+0x44
KDB: reentering
KDB: stack backtrace:
kdb_reenter() at kdb_reenter+0x5c
trap() at trap+0x2fc

And then the stack backtrace just keeps repeating.

-Kurt