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				commit f169cfdc08761a3d9fcd587ad8661102672403ec
				Author: John Baldwin <jhb@FreeBSD.org>
				Date: Tue Oct 24 21:06:00 2017 -0700

				Workaround a FreeBSD ptrace() bug with clearing thread events.

				When multiple threads within a process wish to report STOPPED events
				from wait(), the kernel picks one thread event as the thread event to
				report. The chosen thread event is retrieved via PT_LWPINFO by
				passing the process ID as the request pid. If multiple events are
				pending, then the subsequent wait() after resuming a process will
				report another STOPPED event after resuming the process to handle the
				next thread event and so on.

				A single thread event is cleared as a side effect of resuming the
				process with PT_CONTINUE, PT_STEP, etc. In older kernels, however,
				the request pid was used to select which thread's event was cleared
				rather than always clearing the event that was just reported. To
				avoid clearing the event of the wrong LWP, always pass the process ID
				instead of an LWP ID to PT_CONTINUE or PT_SYSCALL.

				In the case of stepping, the process ID cannot be used with PT_STEP
				since it would step the thread that reported an event which may not be
				the thread indicated by PTID. For stepping, use PT_SETSTEP to enable
				stepping on the desired thread before resuming the process via
				PT_CONTINUE instead of using PT_STEP.

				This manifested as a failure in the
				gdb.threads/continue-pending-status.exp test. Specifically, if thread
				2 reported a breakpoint and the test thus switched to thread 3 before
				continuing, thread 3's event (if any) was discarded and thread 2's
				breakpoint remained pending and was reported a second time as a
				duplicate event. As a result, the PC was decremented twice for the
				same breakpoint resulting in an illegal instruction fault on x86.

				gdb/ChangeLog:

				* fbsd-nat.c (fbsd_resume): Use PT_SETSTEP for stepping and a
				wildcard process pid for super_resume for kernels with a
				specific bug.

				diff --git gdb/fbsd-nat.c gdb/fbsd-nat.c
				index b352418813..3a216abf18 100644
				--- gdb/fbsd-nat.c
				+++ gdb/fbsd-nat.c
				@@ -1143,6 +1143,38 @@ fbsd_resume (struct target_ops *ops,
				}
				ptid = inferior_ptid;
				}
				+
				+#if __FreeBSD_version < 1200052
				+ /* When multiple threads within a process wish to report STOPPED
				+ events from wait(), the kernel picks one thread event as the
				+ thread event to report. The chosen thread event is retrieved via
				+ PT_LWPINFO by passing the process ID as the request pid. If
				+ multiple events are pending, then the subsequent wait() after
				+ resuming a process will report another STOPPED event after
				+ resuming the process to handle the next thread event and so on.
				+
				+ A single thread event is cleared as a side effect of resuming the
				+ process with PT_CONTINUE, PT_STEP, etc. In older kernels,
				+ however, the request pid was used to select which thread's event
				+ was cleared rather than always clearing the event that was just
				+ reported. To avoid clearing the event of the wrong LWP, always
				+ pass the process ID instead of an LWP ID to PT_CONTINUE or
				+ PT_SYSCALL.
				+
				+ In the case of stepping, the process ID cannot be used with
				+ PT_STEP since it would step the thread that reported an event
				+ which may not be the thread indicated by PTID. For stepping, use
				+ PT_SETSTEP to enable stepping on the desired thread before
				+ resuming the process via PT_CONTINUE instead of using
				+ PT_STEP. */
				+ if (step)
				+ {
				+ if (ptrace (PT_SETSTEP, get_ptrace_pid (ptid), NULL, 0) == -1)
				+ perror_with_name (("ptrace"));
				+ step = 0;
				+ }
				+ ptid = ptid_t (ptid.pid ());
				+#endif
				super_resume (ops, ptid, step, signo);
				}