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

Jan Vrany via Gdb-patches
2022-03-16T15:09:45Z

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(-)

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