pmap fault during buildworld on rpi2

[bob prohaska]

FWIW, all the pmap faults observed when top has been running list
ld as one of the active processes at the time of the panic.

There seem to be problems with ld on arm, might the two be
related?

What records I have are in http://www.zefox.net/~fbsd/rpi2/crashes/
The first example is in 
http://www.zefox.net/~fbsd/rpi2/crashes/crash_9_22_17/top

If there are tests that can be usefully performed (and simply
described!) I'd be pleased to try them. From cleandir to crash
seems to take about 36 hours on an rpi2.

Thanks for reading,

bob prohaska