From a6f51542941e072d942fc8df7353bd10097974ea Mon Sep 17 00:00:00 2001 From: John Baldwin Date: Mon, 14 Aug 2023 13:38:42 -0700 Subject: [PATCH] fbsd-nat: Defer any ineligible events reported by wait. If wait_1 finds an event for a thread or process that does not match the set of threads and processes previously resumed, defer the event. If the event is for a specific thread, suspend the thread and continue the associated process before waiting for another event. One specific example of such an event is if a thread is created while another thread in the same process hits a breakpoint. If the second thread's event is reported first, the target resume method does not yet "know" about the new thread and will not suspend it via PT_SUSPEND. When wait is called, it will probably return the event from the first thread before the result of the step from second thread. This is the case reported in PR 21497. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=21497 --- gdb/fbsd-nat.c | 35 ++++++++++++++++++++++++++++++++++- 1 file changed, 34 insertions(+), 1 deletion(-) diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c index f9d8632c0ef..15da555ec3e 100644 --- a/gdb/fbsd-nat.c +++ b/gdb/fbsd-nat.c @@ -1486,7 +1486,40 @@ fbsd_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus, if (is_async_p ()) async_file_flush (); - ptid_t wptid = wait_1 (ptid, ourstatus, target_options); + ptid_t wptid; + while (1) + { + wptid = wait_1 (ptid, ourstatus, target_options); + + /* If no event was found, just return. */ + if (ourstatus->kind () == TARGET_WAITKIND_IGNORE + || ourstatus->kind () == TARGET_WAITKIND_NO_RESUMED) + break; + + /* If an event is reported for a thread or process while + stepping some other thread, suspend the thread reporting the + event and defer the event until it can be reported to the + core. */ + if (!wptid.matches (m_resume_ptid)) + { + add_pending_event (wptid, *ourstatus); + fbsd_nat_debug_printf ("deferring event [%s], [%s]", + target_pid_to_str (wptid).c_str (), + ourstatus->to_string ().c_str ()); + if (wptid.pid () == m_resume_ptid.pid ()) + { + fbsd_nat_debug_printf ("suspending thread [%s]", + target_pid_to_str (wptid).c_str ()); + if (ptrace (PT_SUSPEND, wptid.lwp (), NULL, 0) == -1) + perror_with_name (("ptrace (PT_SUSPEND)")); + if (ptrace (PT_CONTINUE, wptid.pid (), (caddr_t) 1, 0) == -1) + perror_with_name (("ptrace (PT_CONTINUE)")); + } + continue; + } + + break; + } /* If we are in async mode and found an event, there may still be another event pending. Trigger the event pipe so that that the -- 2.30.2