Recently pseudo-device ptm appeared uncommented in GENERIC.
What is it?
It is broken (on i386). It causes reproducible panics.
If I open more than ~16 pseudoterminals via screen or xterm
kernel panics like this:

panic: kernel debugging assertion "(fdp->fd_lomap[off] & (1
<< (fd & NDENTRYMASK))) != 0" failed:
file
"/var/worksrc/netbsd-current/src/sys/kern/kern_descrip.c",
line 190
stopped in pid 345.1 (screen-4.0.1) at
netbsd:breakpoint+0x4: popl %ebp

Also MP kernel built with LOCKDEBUG stops on uniprocessor
i386 at startup:

simplelock: uninitialized lock
lock: 0xc0730a6c, currently at:
../../../../kern_descrip.c:1028
on CPU 0
cwdshare ...
fork1 ...
kthread_create1 ...
deferred_crypto_thread ...
kthread_run_deferred_queue ...
main ...
Stopped in pid 0.1 (swapper) at netbsd:breakpoint+0x4:
leave

The latter works fine if continued.