Re: [PATCH v2] gdb/mi: consistently notify user when GDB/MI client uses -thread-select

[Andrew Burgess <aburgess@redhat.com>]

Jan Vrany <jan.vrany@labware.com> writes:

> Changes since v1:
>
> * all improvements and tests by Andrew - thanks a lot!
> * merged mi_command::invoke() and mi_command::do_invoke() into
> single method (mi_command::invoke()). See the commit message
> for rationale.
>
> -- >8 --
> GDB notifies users about user selected thread changes somewhat
> inconsistently as mentioned on gdb-patches mailing list here:
>
>   https://sourceware.org/pipermail/gdb-patches/2022-February/185989.html
>
> Consider GDB debugging a multi-threaded inferior with both CLI and GDB/MI
> interfaces connected to separate terminals.
>
> Assuming inferior is stopped and thread 1 is selected, when a thread
> 2 is selected using '-thread-select 2' command on GDB/MI terminal:
>
>     -thread-select 2
>     ^done,new-thread-id="2",frame={level="0",addr="0x00005555555551cd",func="child_sub_function",args=[],file="/home/jv/Projects/gdb/users_jv_patches/gdb/testsuite/gdb.mi/user-selected-context-sync.c",fullname="/home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c",line="30",arch="i386:x86-64"}
>     (gdb)
>
> and on CLI terminal we get the notification (as expected):
>
>     [Switching to thread 2 (Thread 0x7ffff7daa640 (LWP 389659))]
>     #0  child_sub_function () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30
>     30        volatile int dummy = 0;
>
> However, now that thread 2 is selected, if thread 1 is selected
> using 'thread-select --thread 1 1' command on GDB/MI terminal
> terminal:
>
>    -thread-select --thread 1 1
>    ^done,new-thread-id="1",frame={level="0",addr="0x0000555555555294",func="main",args=[],file="/home/jv/Projects/gdb/users_jv_patches/gdb/testsuite/gdb.mi/user-selected-context-sync.c",fullname="/home/jv/Projects/gdb/users_jv_patches/gdb/testsuite/gdb.mi/user-selected-context-sync.c",line="66",arch="i386:x86-64"}
>    (gdb)
>
> but no notification is printed on CLI terminal, despite the fact
> that user selected thread has changed.
>
> The problem is that when `-thread-select --thread 1 1` is executed
> then thread is switched to thread 1 before mi_cmd_thread_select () is
> called, therefore the condition "inferior_ptid != previous_ptid"
> there does not hold.
>
> To address this problem, we have to move notification logic up to
> mi_cmd_execute () where --thread option is processed and notify
> user selected contents observers there if context changes.
>
> However, this in itself breaks GDB/MI because it would cause context
> notification to be sent on MI channel. This is because by the time
> we notify, MI notification suppression is already restored (done in
> mi_command::invoke(). Therefore we had to lift notification suppression
> logic also up to mi_cmd_execute (). This change in made distinction
> between mi_command::invoke() and mi_command::do_invoke() unnecessary
> as all mi_command::invoke() did (after the change) was to call
> do_invoke(). So this patches removes do_invoke() and moves the command
> execution logic directly to invoke().
>
> With this change, all gdb.mi tests pass, tested on x86_64-linux.
>
> Co-authored-by: Andrew Burgess <aburgess@redhat.com>
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=20631
> ---
>  gdb/mi/mi-cmd-stack.c                         | 12 +---
>  gdb/mi/mi-cmds.c                              | 18 +-----
>  gdb/mi/mi-cmds.h                              | 17 ++----
>  gdb/mi/mi-main.c                              | 51 +++++++++++++---
>  gdb/python/py-micmd.c                         |  5 +-
>  gdb/stack.c                                   |  8 ---
>  gdb/stack.h                                   |  6 --
>  .../gdb.mi/user-selected-context-sync.exp     | 58 +++++++++++++++++--
>  8 files changed, 106 insertions(+), 69 deletions(-)

Thanks this looks great.  Please go ahead and push this.

Thanks,
Andrew

>
> diff --git a/gdb/mi/mi-cmd-stack.c b/gdb/mi/mi-cmd-stack.c
> index 1be8aa81c3d..e894411765a 100644
> --- a/gdb/mi/mi-cmd-stack.c
> +++ b/gdb/mi/mi-cmd-stack.c
> @@ -757,17 +757,7 @@ mi_cmd_stack_select_frame (const char *command, char **argv, int argc)
>  {
>    if (argc == 0 || argc > 1)
>      error (_("-stack-select-frame: Usage: FRAME_SPEC"));
> -
> -  ptid_t previous_ptid = inferior_ptid;
> -
> -  select_frame_for_mi (parse_frame_specification (argv[0]));
> -
> -  /* Notify if the thread has effectively changed.  */
> -  if (inferior_ptid != previous_ptid)
> -    {
> -      gdb::observers::user_selected_context_changed.notify
> -	(USER_SELECTED_THREAD | USER_SELECTED_FRAME);
> -    }
> +  select_frame (parse_frame_specification (argv[0]));
>  }
>  
>  void
> diff --git a/gdb/mi/mi-cmds.c b/gdb/mi/mi-cmds.c
> index 38fbe0d8a32..60fec0a0b85 100644
> --- a/gdb/mi/mi-cmds.c
> +++ b/gdb/mi/mi-cmds.c
> @@ -45,11 +45,9 @@ struct mi_command_mi : public mi_command
>      gdb_assert (func != nullptr);
>    }
>  
> -protected:
> -
>    /* Called when this MI command has been invoked, calls m_argv_function
>       with arguments contained within PARSE.  */
> -  void do_invoke (struct mi_parse *parse) const override
> +  void invoke (struct mi_parse *parse) const override
>    {
>      mi_parse_argv (parse->args, parse);
>  
> @@ -83,13 +81,11 @@ struct mi_command_cli : public mi_command
>        m_args_p (args_p)
>    { /* Nothing.  */ }
>  
> -protected:
> -
>    /* Called when this MI command has been invoked, calls the m_cli_name
>       CLI function.  In m_args_p is true then the argument string from
>       within PARSE is passed through to the CLI function, otherwise nullptr
>       is passed through to the CLI function as its argument string.  */
> -  void do_invoke (struct mi_parse *parse) const override
> +  void invoke (struct mi_parse *parse) const override
>    {
>      const char *args = m_args_p ? parse->args : nullptr;
>      mi_execute_cli_command (m_cli_name, m_args_p, args);
> @@ -173,16 +169,6 @@ mi_command::mi_command (const char *name, int *suppress_notification)
>  
>  /* See mi-cmds.h.  */
>  
> -void
> -mi_command::invoke (struct mi_parse *parse) const
> -{
> -  gdb::optional<scoped_restore_tmpl<int>> restore
> -    = do_suppress_notification ();
> -  this->do_invoke (parse);
> -}
> -
> -/* See mi-cmds.h.  */
> -
>  gdb::optional<scoped_restore_tmpl<int>>
>  mi_command::do_suppress_notification () const
>  {
> diff --git a/gdb/mi/mi-cmds.h b/gdb/mi/mi-cmds.h
> index 47b90a26064..05b702f83ec 100644
> --- a/gdb/mi/mi-cmds.h
> +++ b/gdb/mi/mi-cmds.h
> @@ -160,9 +160,10 @@ struct mi_command
>    const char *name () const
>    { return m_name; }
>  
> -  /* Execute the MI command.  Can throw an exception if something goes
> -     wrong.  */
> -  void invoke (struct mi_parse *parse) const;
> +  /* Execute the MI command.  this needs to be overridden in each
> +     base class.  PARSE is the parsed command line from the user.
> +     Can throw an exception if something goes wrong.  */
> +  virtual void invoke (struct mi_parse *parse) const = 0;
>  
>    /* Return whether this command preserves user selected context (thread
>       and frame).  */
> @@ -175,14 +176,6 @@ struct mi_command
>      return m_suppress_notification != &mi_suppress_notification.user_selected_context;
>    }
>  
> -protected:
> -
> -  /* The core of command invocation, this needs to be overridden in each
> -     base class.  PARSE is the parsed command line from the user.  */
> -  virtual void do_invoke (struct mi_parse *parse) const = 0;
> -
> -private:
> -
>    /* If this command was created with a suppress notifications pointer,
>       then this function will set the suppress flag and return a
>       gdb::optional with its value set to an object that will restore the
> @@ -192,6 +185,8 @@ struct mi_command
>       then this function returns an empty gdb::optional.  */
>    gdb::optional<scoped_restore_tmpl<int>> do_suppress_notification () const;
>  
> +private:
> +
>    /* The name of the command.  */
>    const char *m_name;
>  
> diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
> index 73380f5e668..abd033b22ae 100644
> --- a/gdb/mi/mi-main.c
> +++ b/gdb/mi/mi-main.c
> @@ -556,19 +556,10 @@ mi_cmd_thread_select (const char *command, char **argv, int argc)
>    if (thr == NULL)
>      error (_("Thread ID %d not known."), num);
>  
> -  ptid_t previous_ptid = inferior_ptid;
> -
>    thread_select (argv[0], thr);
>  
>    print_selected_thread_frame (current_uiout,
>  			       USER_SELECTED_THREAD | USER_SELECTED_FRAME);
> -
> -  /* Notify if the thread has effectively changed.  */
> -  if (inferior_ptid != previous_ptid)
> -    {
> -      gdb::observers::user_selected_context_changed.notify
> -	(USER_SELECTED_THREAD | USER_SELECTED_FRAME);
> -    }
>  }
>  
>  void
> @@ -1975,6 +1966,37 @@ mi_execute_command (const char *cmd, int from_tty)
>      }
>  }
>  
> +/* Captures the current user selected context state, that is the current
> +   thread and frame.  Later we can then check if the user selected context
> +   has changed at all.  */
> +
> +struct user_selected_context
> +{
> +  /* Constructor.  */
> +  user_selected_context ()
> +    : m_previous_ptid (inferior_ptid),
> +      m_previous_frame (deprecated_safe_get_selected_frame ())
> +  { /* Nothing.  */ }
> +
> +  /* Return true if the user selected context has changed since this object
> +     was created.  */
> +  bool has_changed () const
> +  {
> +    return ((m_previous_ptid != null_ptid
> +	     && inferior_ptid != null_ptid
> +	     && m_previous_ptid != inferior_ptid)
> +	    || m_previous_frame != deprecated_safe_get_selected_frame ());
> +  }
> +private:
> +  /* The previously selected thread.  This might be null_ptid if there was
> +     no previously selected thread.  */
> +  ptid_t m_previous_ptid;
> +
> +  /* The previously selected frame.  This might be nullptr if there was no
> +     previously selected frame.  */
> +  frame_info *m_previous_frame;
> +};
> +
>  static void
>  mi_cmd_execute (struct mi_parse *parse)
>  {
> @@ -2015,6 +2037,8 @@ mi_cmd_execute (struct mi_parse *parse)
>        set_current_program_space (inf->pspace);
>      }
>  
> +  user_selected_context current_user_selected_context;
> +
>    gdb::optional<scoped_restore_current_thread> thread_saver;
>    if (parse->thread != -1)
>      {
> @@ -2060,7 +2084,16 @@ mi_cmd_execute (struct mi_parse *parse)
>    current_context = parse;
>  
>    gdb_assert (parse->cmd != nullptr);
> +
> +  gdb::optional<scoped_restore_tmpl<int>> restore_suppress_notification
> +    = parse->cmd->do_suppress_notification ();
> +
>    parse->cmd->invoke (parse);
> +
> +  if (!parse->cmd->preserve_user_selected_context ()
> +      && current_user_selected_context.has_changed ())
> +    gdb::observers::user_selected_context_changed.notify
> +      (USER_SELECTED_THREAD | USER_SELECTED_FRAME);
>  }
>  
>  /* See mi-main.h.  */
> diff --git a/gdb/python/py-micmd.c b/gdb/python/py-micmd.c
> index 4665fcc75c7..399e89b0298 100644
> --- a/gdb/python/py-micmd.c
> +++ b/gdb/python/py-micmd.c
> @@ -134,9 +134,8 @@ struct mi_command_py : public mi_command
>      m_pyobj = new_pyobj;
>    }
>  
> -protected:
>    /* Called when the MI command is invoked.  */
> -  virtual void do_invoke(struct mi_parse *parse) const override;
> +  virtual void invoke(struct mi_parse *parse) const override;
>  
>  private:
>    /* The Python object representing this MI command.  */
> @@ -311,7 +310,7 @@ serialize_mi_result (PyObject *result)
>     command line arguments from the user.  */
>  
>  void
> -mi_command_py::do_invoke (struct mi_parse *parse) const
> +mi_command_py::invoke (struct mi_parse *parse) const
>  {
>    PYMICMD_SCOPED_DEBUG_ENTER_EXIT;
>  
> diff --git a/gdb/stack.c b/gdb/stack.c
> index 8855ed8fe70..10da88b88e5 100644
> --- a/gdb/stack.c
> +++ b/gdb/stack.c
> @@ -1841,14 +1841,6 @@ select_frame_command_core (struct frame_info *fi, bool ignored)
>      gdb::observers::user_selected_context_changed.notify (USER_SELECTED_FRAME);
>  }
>  
> -/* See stack.h.  */
> -
> -void
> -select_frame_for_mi (struct frame_info *fi)
> -{
> -  select_frame_command_core (fi, false /* Ignored.  */);
> -}
> -
>  /* The core of all the "frame" sub-commands.  Select frame FI, and if this
>     means we change frame send out a change notification (otherwise, just
>     reprint the current frame summary).   */
> diff --git a/gdb/stack.h b/gdb/stack.h
> index c49d2e2cbef..f78aedf1c85 100644
> --- a/gdb/stack.h
> +++ b/gdb/stack.h
> @@ -20,12 +20,6 @@
>  #ifndef STACK_H
>  #define STACK_H
>  
> -/* Access method used by the MI -stack-select-frame command to switch to
> -   frame FI.  This differs from SELECT_FRAME in that the observers for a
> -   user selected context change will be triggered.  */
> -
> -void select_frame_for_mi (struct frame_info *fi);
> -
>  gdb::unique_xmalloc_ptr<char> find_frame_funname (struct frame_info *frame,
>  						  enum language *funlang,
>  						  struct symbol **funcp);
> diff --git a/gdb/testsuite/gdb.mi/user-selected-context-sync.exp b/gdb/testsuite/gdb.mi/user-selected-context-sync.exp
> index 3b4ff0bf2e4..9444ca5acf4 100644
> --- a/gdb/testsuite/gdb.mi/user-selected-context-sync.exp
> +++ b/gdb/testsuite/gdb.mi/user-selected-context-sync.exp
> @@ -916,7 +916,7 @@ proc_with_prefix test_mi_thread_select { mode } {
>  	}
>      }
>  
> -    with_test_prefix "thread 1.2 with --thread" {
> +    with_test_prefix "thread 1.2 with --thread 2" {
>  	# Test selecting a thread from MI with a --thread option.  This test
>  	# verifies that even if the thread GDB would switch to is the same as
>  	# the thread specified with --thread, an event is still sent to CLI.
> @@ -930,10 +930,28 @@ proc_with_prefix test_mi_thread_select { mode } {
>  	}
>  
>  	with_spawn_id $gdb_main_spawn_id {
> -	    # This doesn't work as of now, no event is sent on CLI.  It is
> -	    # commented out so we don't have to wait for the timeout every time.
> -	    # match_re_or_ensure_no_output "$cli_re\r\n" "-thread-select, event on cli"
> -	    kfail "gdb/20631" "thread-select, event on cli"
> +	    match_re_or_ensure_no_output "$cli_re\r\n" "-thread-select, event on cli"
> +	}
> +    }
> +
> +    with_test_prefix "thread 1.2 with --thread 3" {
> +	# Test selecting a thread from MI with a --thread option.
> +	# This test verifies that when different thread numbers are
> +	# passed to the --thread option and the underlying
> +	# -thread-select command, the correct thread is selected.
> +	# In this case this is thread 1.2
> +
> +	reset_selection "1.1"
> +
> +	set mi_re [make_mi_re $mode 2 0 response]
> +	set cli_re [make_cli_re $mode -1 1.2 0]
> +
> +	with_spawn_id $mi_spawn_id {
> +	    mi_gdb_test "-thread-select --thread 3 2" $mi_re "-thread-select"
> +	}
> +
> +	with_spawn_id $gdb_main_spawn_id {
> +	    match_re_or_ensure_no_output "$cli_re\r\n" "-thread-select, event on cli"
>  	}
>      }
>  
> @@ -974,6 +992,36 @@ proc_with_prefix test_mi_stack_select_frame { mode } {
>  	with_spawn_id $gdb_main_spawn_id {
>  	    match_re_or_ensure_no_output $cli_re "-stack-select-frame again, event on CLI"
>  	}
> +
> +	# Now use the '-stack-select-frame' command with the --frame
> +	# option, this verifies that even when the frame GDB would
> +	# swith to is the same as the frame specified with --frame, an
> +	# event is still sent to the CLI.
> +
> +	set cli_re [make_cli_re $mode -1 -1 0]
> +
> +	with_spawn_id $mi_spawn_id {
> +	    mi_gdb_test "-stack-select-frame --thread 2 --frame 0 0" $mi_re
> +	}
> +
> +	with_spawn_id $gdb_main_spawn_id {
> +	    match_re_or_ensure_no_output "$cli_re\r\n" "-stack-select-frame with --frame 0, event on CLI"
> +	}
> +
> +	# Now use the '-stack-select-frame' command with the --frame
> +	# option, this verifies that the correct event is sent to the
> +	# CLI when the frame specified with --frame is different to
> +	# the actual frame selected.
> +
> +	set cli_re [make_cli_re $mode -1 -1 1]
> +
> +	with_spawn_id $mi_spawn_id {
> +	    mi_gdb_test "-stack-select-frame --thread 2 --frame 2 1" $mi_re
> +	}
> +
> +	with_spawn_id $gdb_main_spawn_id {
> +	    match_re_or_ensure_no_output "$cli_re\r\n" "-stack-select-frame with --frame 2, event on CLI"
> +	}
>      }
>  
>      with_test_prefix "thread 1.3" {
> -- 
> 2.35.1