boot2 / loader can not check superblock checksum and refuse to boot, but fsck_ffs doesn't see problems

[Harry Schmalzbauer]

Am 01.11.2018 um 13:17 schrieb Lev Serebryakov:
>   I have NanoBSD image built from head/r339933, which passes all checks
> on other system: "fsck_ffs" passes, it could be mounted without
> problems, everything could be read.
>
>   But when I try to boot from it, boot2 (or loader?) complains about
> failed superblock checksum several times (for each copy?), like this:
>
> Superblock check-hash failed: recorded check-hash 0xcfa0ae67 != computed
> check-hash 0x21993fb
>
>   ALL these messages contains SAME "recorded" and "compuded" hashes, so
> it doesn't look like corrupted flash.
>
>   Looks like boot2/loader wrongly calculate hash...

I think I've had the same / a similar problem some dozend moons ago, 
which I could track down to a 'newfs' induced problem.  'newfs'ing the 
same partition [/md(4) deivce  without partitions in my case] multiple 
times (4 times) triggered that problem, as far as I remember.
Can't find any notices :-( And haven't investigated further :-(
Maybe it's worth checking if your problem is also related to the number 
of newfs runs – unfortunately I can't remember if it really was boot2 
where my – at least very similar – error came from. Other symptoms match 
– no problem by fsck_ffs(8) found.

-harry