make installworld broke / how to recover

Hello,

When trying to upgrade from 11-stable to 12-current, make installworld broke. The OS is mainly on a ssd, there is zfs installed (usr/src is on zfs). Is there a guide somewhere that shows how to recover from this situation? both 11.1 and 12-current kernels are bootable. I can just blat the system and install from scratch but that would mean i've not learned how to fix it. I have subsequently tried make buildworld again but it bais out with this error:

#####

objcopy --only-keep-debug xinstall.full install.debug
objcopy --strip-debug --add-gnu-debuglink=install.debug  xinstall.full xinstall
sh /storage/usr/src/tools/install.sh  -s -o root -g wheel -m 555   xinstall /obj/storage/usr/src/amd64.amd64/tmp/legacy/usr/bin/install
sh /storage/usr/src/tools/install.sh  -o root -g wheel -m 444  install.debug /obj/storage/usr/src/amd64.amd64/tmp/legacy/usr/lib/debug/usr/bin/install.debug
install: install.debug: Inappropriate file type or format
*** Error code 71

Stop.
make[3]: stopped in /storage/usr/src/usr.bin/xinstall
*** Error code 1

Stop.
make[2]: stopped in /storage/usr/src
*** Error code 1

Stop.
make[1]: stopped in /storage/usr/src
*** Error code 1

Stop.
make: stopped in /storage/usr/src

#####

thanks,

-- 
  John
  tech-lists_at_zyxst.net