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

Andrew Burgess via Gdb-patches
2023-03-22T15:46:31Z

Pedro Alves <pedro@palves.net> writes:

> 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 feels like that comment is now out of date. We surely aren't
assuming anything anymore, rather marking the thread as resumed when its
executing.

Otherwise, this commit looks good.

Reviewed-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew

> + 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