[PATCH 05/31] Support clone events in the remote protocol

Pedro Alves
2022-12-12T20:31:47Z

The previous patch taught GDB about a new
TARGET_WAITKIND_THREAD_CLONED event kind, and made the Linux target
report clone events.

A following patch will teach Linux GDBserver to do the same thing.

But before we get there, we need to teach the remote protocol about
TARGET_WAITKIND_THREAD_CLONED. That's what this patch does. Clone is
very similar to vfork and fork, and the new stop reply is likewise
handled similarly. The stub reports "T05clone:...".

GDBserver core is taught to handle TARGET_WAITKIND_THREAD_CLONED and
forward it to GDB in this patch, but no backend actually emits it yet.
That will be done in a following patch.

Documentation for this new remote protocol feature is included in a
documentation patch later in the series.

Change-Id: If271f20320d864f074d8ac0d531cc1a323da847f
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=19675
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27830
---
gdb/remote.c | 99 ++++++++++++++++++++++++++-------------
gdbserver/remote-utils.cc | 26 ++++++++--
gdbserver/server.cc | 3 +-
3 files changed, 91 insertions(+), 37 deletions(-)

diff --git a/gdb/remote.c b/gdb/remote.c
index 53c4f19c5a4..a7430eb79dd 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -672,6 +672,7 @@ class remote_target : public process_stratum_target
const struct btrace_config *btrace_conf (const struct btrace_target_info *) override;
bool augmented_libraries_svr4_read () override;
void follow_fork (inferior *, ptid_t, target_waitkind, bool, bool) override;
+ void follow_clone (ptid_t child_ptid) override;
void follow_exec (inferior *, ptid_t, const char *) override;
int insert_fork_catchpoint (int) override;
int remove_fork_catchpoint (int) override;
@@ -765,7 +766,7 @@ class remote_target : public process_stratum_target

void remote_btrace_maybe_reopen ();

- void remove_new_fork_children (threads_listing_context *context);
+ void remove_new_children (threads_listing_context *context);
void kill_new_fork_children (inferior *inf);
void discard_pending_stop_replies (struct inferior *inf);
int stop_reply_queue_length ();
@@ -2579,9 +2580,10 @@ remote_target::remote_add_thread (ptid_t ptid, bool running, bool executing,
else
thread = add_thread (this, ptid);

- /* We start by assuming threads are resumed. That state then gets updated
- when we process a matching stop reply. */
- get_remote_thread_info (thread)->set_resumed ();
+ /* We start by assuming threads are resumed. That state then gets
+ updated when we process a matching stop reply. */
+ if (executing)
+ get_remote_thread_info (thread)->set_resumed ();

set_executing (this, ptid, executing);
set_running (this, ptid, running);
@@ -3983,10 +3985,11 @@ remote_target::update_thread_list ()
}
}

- /* Remove any unreported fork child threads from CONTEXT so
- that we don't interfere with follow fork, which is where
- creation of such threads is handled. */
- remove_new_fork_children (&context);
+ /* Remove any unreported fork/vfork/clone child threads from
+ CONTEXT so that we don't interfere with follow
+ fork/vfork/clone, which is where creation of such threads is
+ handled. */
+ remove_new_children (&context);

/* And now add threads we don't know about yet to our list. */
for (thread_item &item : context.items)
@@ -4940,6 +4943,8 @@ remote_target::start_remote_1 (int from_tty, int extended_p)
}
else
switch_to_thread (find_thread_ptid (this, curr_thread));
+
+ get_remote_thread_info (inferior_thread ())->set_resumed ();
}

/* init_wait_for_inferior should be called before get_offsets in order
@@ -5893,16 +5898,25 @@ is_fork_status (target_waitkind kind)
|| kind == TARGET_WAITKIND_VFORKED);
}

-/* Return THREAD's pending status if it is a pending fork parent, else
- return nullptr. */
+/* Return a reference to the field where a pending child status, if
+ there's one, is recorded. If there's no child event pending, the
+ returned waitstatus has TARGET_WAITKIND_IGNORE kind. */
+
+static const target_waitstatus &
+thread_pending_status (struct thread_info *thread)
+{
+ return (thread->has_pending_waitstatus ()
+ ? thread->pending_waitstatus ()
+ : thread->pending_follow);
+}
+
+/* Return THREAD's pending status if it is a pending fork/vfork (but
+ not clone) parent, else return nullptr. */

static const target_waitstatus *
thread_pending_fork_status (struct thread_info *thread)
{
- const target_waitstatus &ws
- = (thread->has_pending_waitstatus ()
- ? thread->pending_waitstatus ()
- : thread->pending_follow);
+ const target_waitstatus &ws = thread_pending_status (thread);

if (!is_fork_status (ws.kind ()))
return nullptr;
@@ -5910,6 +5924,20 @@ thread_pending_fork_status (struct thread_info *thread)
return &ws;
}

+/* Return THREAD's pending status if is is a pending fork/vfork/clone
+ event, else return nullptr. */
+
+static const target_waitstatus *
+thread_pending_child_status (thread_info *thread)
+{
+ const target_waitstatus &ws = thread_pending_status (thread);
+
+ if (!is_new_child_status (ws.kind ()))
+ return nullptr;
+
+ return &ws;
+}
+
/* Detach the specified process. */

void
@@ -6075,6 +6103,12 @@ remote_target::follow_fork (inferior *child_inf, ptid_t child_ptid,
}
}

+void
+remote_target::follow_clone (ptid_t child_ptid)
+{
+ remote_add_thread (child_ptid, false, false, false);
+}
+
/* Target follow-exec function for remote targets. Save EXECD_PATHNAME
in the program space of the new inferior. */

@@ -6807,10 +6841,10 @@ remote_target::commit_resumed ()
if (priv->get_resume_state () == resume_state::RESUMED_PENDING_VCONT)
any_pending_vcont_resume = true;

- /* If a thread is the parent of an unfollowed fork, then we
- can't do a global wildcard, as that would resume the fork
- child. */
- if (thread_pending_fork_status (tp) != nullptr)
+ /* If a thread is the parent of an unfollowed fork/vfork/clone,
+ then we can't do a global wildcard, as that would resume the
+ pending child. */
+ if (thread_pending_child_status (tp) != nullptr)
may_global_wildcard_vcont = false;
}

@@ -7276,22 +7310,22 @@ struct notif_client notif_client_stop =
REMOTE_NOTIF_STOP,
};

-/* If CONTEXT contains any fork child threads that have not been
- reported yet, remove them from the CONTEXT list. If such a
- thread exists it is because we are stopped at a fork catchpoint
- and have not yet called follow_fork, which will set up the
- host-side data structures for the new process. */
+/* If CONTEXT contains any fork/vfork/clone child threads that have
+ not been reported yet, remove them from the CONTEXT list. If such
+ a thread exists it is because we are stopped at a fork/vfork/clone
+ catchpoint and have not yet called follow_fork/follow_clone, which
+ will set up the host-side data structures for the new child. */

void
-remote_target::remove_new_fork_children (threads_listing_context *context)
+remote_target::remove_new_children (threads_listing_context *context)
{
struct notif_client *notif = &notif_client_stop;

- /* For any threads stopped at a fork event, remove the corresponding
- fork child threads from the CONTEXT list. */
+ /* For any threads stopped at a (v)fork/clone event, remove the
+ corresponding child threads from the CONTEXT list. */
for (thread_info *thread : all_non_exited_threads (this))
{
- const target_waitstatus *ws = thread_pending_fork_status (thread);
+ const target_waitstatus *ws = thread_pending_child_status (thread);

if (ws == nullptr)
continue;
@@ -7299,13 +7333,12 @@ remote_target::remove_new_fork_children (threads_listing_context *context)
context->remove_thread (ws->child_ptid ());
}

- /* Check for any pending fork events (not reported or processed yet)
- in process PID and remove those fork child threads from the
- CONTEXT list as well. */
+ /* Check for any pending (v)fork/clone events (not reported or
+ processed yet) in process PID and remove those child threads from
+ the CONTEXT list as well. */
remote_notif_get_pending_events (notif);
for (auto &event : get_remote_state ()->stop_reply_queue)
- if (event->ws.kind () == TARGET_WAITKIND_FORKED
- || event->ws.kind () == TARGET_WAITKIND_VFORKED)
+ if (is_new_child_status (event->ws.kind ()))
context->remove_thread (event->ws.child_ptid ());
else if (event->ws.kind () == TARGET_WAITKIND_THREAD_EXITED)
context->remove_thread (event->ptid);
@@ -7634,6 +7667,8 @@ Packet: '%s'\n"),
event->ws.set_forked (read_ptid (++p1, &p));
else if (strprefix (p, p1, "vfork"))
event->ws.set_vforked (read_ptid (++p1, &p));
+ else if (strprefix (p, p1, "clone"))
+ event->ws.set_thread_cloned (read_ptid (++p1, &p));
else if (strprefix (p, p1, "vforkdone"))
{
event->ws.set_vfork_done ();
diff --git a/gdbserver/remote-utils.cc b/gdbserver/remote-utils.cc
index 2ddb275bd15..6a673cb1ca8 100644
--- a/gdbserver/remote-utils.cc
+++ b/gdbserver/remote-utils.cc
@@ -1062,6 +1062,7 @@ prepare_resume_reply (char *buf, ptid_t ptid, const target_waitstatus &status)
case TARGET_WAITKIND_FORKED:
case TARGET_WAITKIND_VFORKED:
case TARGET_WAITKIND_VFORK_DONE:
+ case TARGET_WAITKIND_THREAD_CLONED:
case TARGET_WAITKIND_EXECD:
case TARGET_WAITKIND_THREAD_CREATED:
case TARGET_WAITKIND_SYSCALL_ENTRY:
@@ -1071,13 +1072,30 @@ prepare_resume_reply (char *buf, ptid_t ptid, const target_waitstatus &status)
struct regcache *regcache;
char *buf_start = buf;

- if ((status.kind () == TARGET_WAITKIND_FORKED && cs.report_fork_events)
+ if ((status.kind () == TARGET_WAITKIND_FORKED
+ && cs.report_fork_events)
|| (status.kind () == TARGET_WAITKIND_VFORKED
- && cs.report_vfork_events))
+ && cs.report_vfork_events)
+ || status.kind () == TARGET_WAITKIND_THREAD_CLONED)
{
enum gdb_signal signal = GDB_SIGNAL_TRAP;
- const char *event = (status.kind () == TARGET_WAITKIND_FORKED
- ? "fork" : "vfork");
+
+ auto kind_remote_str = [] (target_waitkind kind)
+ {
+ switch (kind)
+ {
+ case TARGET_WAITKIND_FORKED:
+ return "fork";
+ case TARGET_WAITKIND_VFORKED:
+ return "vfork";
+ case TARGET_WAITKIND_THREAD_CLONED:
+ return "clone";
+ default:
+ gdb_assert_not_reached ("unhandled kind");
+ }
+ };
+
+ const char *event = kind_remote_str (status.kind ());

sprintf (buf, "T%02x%s:", signal, event);
buf += strlen (buf);
diff --git a/gdbserver/server.cc b/gdbserver/server.cc
index aaef38e0062..56b7f97a388 100644
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -236,7 +236,8 @@ in_queued_stop_replies_ptid (struct notif_event *event, ptid_t filter_ptid)

/* Don't resume fork children that GDB does not know about yet. */
if ((vstop_event->status.kind () == TARGET_WAITKIND_FORKED
- || vstop_event->status.kind () == TARGET_WAITKIND_VFORKED)
+ || vstop_event->status.kind () == TARGET_WAITKIND_VFORKED
+ || vstop_event->status.kind () == TARGET_WAITKIND_THREAD_CLONED)
&& vstop_event->status.child_ptid ().matches (filter_ptid))
return true;

--
2.36.0