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

  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(-)
  

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
  

On 2023-03-22 15:46, Andrew Burgess wrote:
> Pedro Alves <pedro@palves.net> writes:

>> @@ -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.
> 

You're right.  I removed the comment.  Tweaking the comment would just end
up with the comment duplicating what the code is doing in words.

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

Thanks!