FreeBSD 11 sparc64 instability

[David Cross]

After upgrading to FreeBSD 11 on some of my sparc64 machines (Sun Ultra
10), I noticed some truly disturbing behavior.

1) ipfw won't work, at all.

kldload ipfw
ipfw add 100 allow all from any to any

ipfw -a list

you will get errors about invalid arguments.

*HOWEVER* if you use the ipfw that was from a 10.x install (10.3 in my
case), it works perfectly.  ???

2) fsck will destroy your filesystems
clean filesystem, "fsck -t ufs /dev/foo"  you will see more errors than you
knew were possible.

*HOWEVER* if you take a version of fsck from 10.x (again, 10.3 in my case)
***AND*** libufs.so from that (LD_LIBRARY_PATH), everything is fine

I suspected this may have been because I did a 11 buildworld on a 10.3
machine and "something leaked" with respect to headers, so I id a fresh
buildworld, and when that too didn't fix it, I grabbed install images and
used binaries and reproduced both of these errors.

What is going on here?