[PATCH 18/31] Implement GDB_THREAD_OPTION_EXIT support for Linux GDBserver

Pedro Alves
2022-12-12T20:33:28Z

This implements support for the new GDB_THREAD_OPTION_EXIT thread
option for Linux GDBserver.

Change-Id: I96b719fdf7fee94709e98bb3a90751d8134f3a38
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27338
---
gdbserver/linux-low.cc | 38 +++++++++++++++++++++++++-------------
gdbserver/linux-low.h | 9 +++++----
2 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
index 8c0d3103398..ebc3bf34127 100644
--- a/gdbserver/linux-low.cc
+++ b/gdbserver/linux-low.cc
@@ -144,6 +144,18 @@ is_leader (thread_info *thread)
return ptid.pid () == ptid.lwp ();
}

+/* Return true if we should report thread exit events to GDB, for
+ THR. */
+
+static bool
+report_exit_events_for (thread_info *thr)
+{
+ client_state &cs = get_client_state ();
+
+ return (cs.report_thread_events
+ || (thr->thread_options & GDB_THREAD_OPTION_EXIT) != 0);
+}
+
/* LWP accessors. */

/* See nat/linux-nat.h. */
@@ -2230,7 +2242,6 @@ linux_low_ptrace_options (int attached)
void
linux_process_target::filter_event (int lwpid, int wstat)
{
- client_state &cs = get_client_state ();
struct lwp_info *child;
struct thread_info *thread;
int have_stop_pc = 0;
@@ -2317,7 +2328,7 @@ linux_process_target::filter_event (int lwpid, int wstat)
/* If this is not the leader LWP, then the exit signal was not
the end of the debugged application and should be ignored,
unless GDB wants to hear about thread exits. */
- if (cs.report_thread_events || is_leader (thread))
+ if (report_exit_events_for (thread) || is_leader (thread))
{
/* Since events are serialized to GDB core, and we can't
report this one right now. Leave the status pending for
@@ -2879,13 +2890,20 @@ ptid_t
linux_process_target::filter_exit_event (lwp_info *event_child,
target_waitstatus *ourstatus)
{
- client_state &cs = get_client_state ();
struct thread_info *thread = get_lwp_thread (event_child);
ptid_t ptid = ptid_of (thread);

+ /* Note we must filter TARGET_WAITKIND_SIGNALLED as well, otherwise
+ if a non-leader thread exits with a signal, we'd report it to the
+ core which would interpret it as the whole-process exiting.
+ There is no TARGET_WAITKIND_THREAD_SIGNALLED event kind. */
+ if (ourstatus->kind () != TARGET_WAITKIND_EXITED
+ && ourstatus->kind () != TARGET_WAITKIND_SIGNALLED)
+ return ptid;
+
if (!is_leader (thread))
{
- if (cs.report_thread_events)
+ if (report_exit_events_for (thread))
ourstatus->set_thread_exited (0);
else
ourstatus->set_ignore ();
@@ -3028,10 +3046,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
WTERMSIG (w));
}

- if (ourstatus->kind () == TARGET_WAITKIND_EXITED)
- return filter_exit_event (event_child, ourstatus);
-
- return ptid_of (current_thread);
+ return filter_exit_event (event_child, ourstatus);
}

/* If step-over executes a breakpoint instruction, in the case of a
@@ -3600,10 +3615,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
target_pid_to_str (ptid_of (current_thread)).c_str (),
ourstatus->to_string ().c_str ());

- if (ourstatus->kind () == TARGET_WAITKIND_EXITED)
- return filter_exit_event (event_child, ourstatus);
-
- return ptid_of (current_thread);
+ return filter_exit_event (event_child, ourstatus);
}

/* Get rid of any pending event in the pipe. */
@@ -5909,7 +5921,7 @@ linux_process_target::supports_vfork_events ()
gdb_thread_options
linux_process_target::supported_thread_options ()
{
- return GDB_THREAD_OPTION_CLONE;
+ return GDB_THREAD_OPTION_CLONE | GDB_THREAD_OPTION_EXIT;
}

/* Check if exec events are supported. */
diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
index c9f9db71e09..1c1754d2b59 100644
--- a/gdbserver/linux-low.h
+++ b/gdbserver/linux-low.h
@@ -575,10 +575,11 @@ class linux_process_target : public process_stratum_target
exited. */
void check_zombie_leaders ();

- /* Convenience function that is called when the kernel reports an exit
- event. This decides whether to report the event to GDB as a
- process exit event, a thread exit event, or to suppress the
- event. */
+ /* Convenience function that is called when we're about to return an
+ event to the core. If the event is an exit or signalled event,
+ then this decides whether to report it as process-wide event, as
+ a thread exit event, or to suppress it. All other event kinds
+ are passed through unmodified. */
ptid_t filter_exit_event (lwp_info *event_child,
target_waitstatus *ourstatus);

--
2.36.0