12.0-CURRENT #54 r318674 can't enter single user mode

[bob prohaska]

While building world and kernel on RPI2  12.0-CURRENT #54 r318674 reported
"one error" and gradually became completely unresponsive. After power-cycling 
things looked normal until 

WARNING: / was not properly dismounted
warning: no time-of-day clock registered, system time will not be set accurately
random: unblocking device.
arc4random: no preloaded entropy cache
arc4random: no preloaded entropy cache
arc4random: no preloaded entropy cache
pid 27 (sh), uid 0: exited on signal 12
May 28 14:29:07 init: /bin/sh on /etc/rc terminated abnormally, going to single user mode
Enter full pathname of shell or RETURN for /bin/sh: 
pid 28 (sh), uid 0: exited on signal 12
May 28 14:29:10 init: single user shell terminated, restarting
Enter full pathname of shell or RETURN for /bin/sh: 

I've tried the escape, tilda, control-b sequence, it's echoed but
the debugger does not take over the console.

The machine had been running stably under fairly high load for
several days compiling www/epiphany. During the world
build epiphany was run  and it started segfaulting after
a couple of minutes. Shortly after that the world build stopped.
I was unable to see the error message, unfortunately.

Thanks for reading, and any thoughts.

bob prohaska