--- gdb/fbsd-nat.c.orig 2016-03-14 00:00:11.831889802 +0100 +++ gdb/fbsd-nat.c 2016-03-14 00:04:35.906871361 +0100 @@ -471,6 +471,14 @@ ptid_get_tid (ptid)); if (ptid_lwp_p (ptid)) { +#ifndef PT_LWP_EVENTS + /* When LWP events are not supported, a new thread might already be + running that has not yet reported an event when GDB wishes to + only run a single thread. Force an update of the thread list + to ensure that any such threads are suspended before the process + is resumed. */ + fbsd_add_threads (ptid_get_pid (ptid)); +#endif /* If ptid is a specific LWP, suspend all other LWPs in the process. */ iterate_over_threads (resume_one_thread_cb, &ptid); }