Patchwork [RFC] Don't show "display"s twice in MI

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Submitter Tom Tromey
Date March 12, 2019, 7:03 p.m.
Message ID <20190312190320.19645-1-tromey@adacore.com>
Download mbox | patch
Permalink /patch/31831/
State New
Headers show

Comments

Tom Tromey - March 12, 2019, 7:03 p.m.
If you run "gdb -i=mi2" and set a "display", then when "next"ing the
displays will be shown twice:

    ~"1: x = 23\n"
    ~"7\t  printf(\"%d\\n\", x);\n"
    ~"1: x = 23\n"
    *stopped,reason="end-stepping-range",frame={addr="0x0000000000400565",func="main",args=[],file="q.c",fullname="/tmp/q.c",line="7"},thread-id="1",stopped-threads="all",core="1"

The immediate cause of this is this code in mi_on_normal_stop_1:

      print_stop_event (mi_uiout);

      console_interp = interp_lookup (current_ui, INTERP_CONSOLE);
      if (should_print_stop_to_console (console_interp, tp))
	print_stop_event (mi->cli_uiout);

... which obviously prints the stop twice.

However, I think the first call to print_stop_event is intended just
to emit the MI *stopped notification, which explains why the source
line does not show up two times.

This patch fixes the bug by changing print_stop_event to only call
do_displays for non-MI-like ui-outs.

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-03-12  Tom Tromey  <tromey@adacore.com>

	* infrun.c (print_stop_event): Don't call do_displays for MI-like
	ui-outs.

gdb/testsuite/ChangeLog
2019-03-12  Tom Tromey  <tromey@adacore.com>

	* gdb.mi/mi2-cli-display.c: New file.
	* gdb.mi/mi2-cli-display.exp: New file.
---
 gdb/ChangeLog                            |  5 ++
 gdb/infrun.c                             |  3 +-
 gdb/testsuite/ChangeLog                  |  5 ++
 gdb/testsuite/gdb.mi/mi2-cli-display.c   | 30 ++++++++++++
 gdb/testsuite/gdb.mi/mi2-cli-display.exp | 62 ++++++++++++++++++++++++
 5 files changed, 104 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.mi/mi2-cli-display.c
 create mode 100644 gdb/testsuite/gdb.mi/mi2-cli-display.exp
Simon Marchi - March 12, 2019, 9:26 p.m.
On 2019-03-12 15:03, Tom Tromey wrote:
> If you run "gdb -i=mi2" and set a "display", then when "next"ing the
> displays will be shown twice:
> 
>     ~"1: x = 23\n"
>     ~"7\t  printf(\"%d\\n\", x);\n"
>     ~"1: x = 23\n"
> 
> *stopped,reason="end-stepping-range",frame={addr="0x0000000000400565",func="main",args=[],file="q.c",fullname="/tmp/q.c",line="7"},thread-id="1",stopped-threads="all",core="1"
> 
> The immediate cause of this is this code in mi_on_normal_stop_1:
> 
>       print_stop_event (mi_uiout);
> 
>       console_interp = interp_lookup (current_ui, INTERP_CONSOLE);
>       if (should_print_stop_to_console (console_interp, tp))
> 	print_stop_event (mi->cli_uiout);
> 
> ... which obviously prints the stop twice.
> 
> However, I think the first call to print_stop_event is intended just
> to emit the MI *stopped notification, which explains why the source
> line does not show up two times.
> 
> This patch fixes the bug by changing print_stop_event to only call
> do_displays for non-MI-like ui-outs.

FWIW, this is fine with me.  Maybe just format the C file of the test 
case according to GNU style.

Simon
Pedro Alves - March 13, 2019, 3:04 p.m.
On 03/12/2019 07:03 PM, Tom Tromey wrote:
> If you run "gdb -i=mi2" and set a "display", then when "next"ing the
> displays will be shown twice:
> 
>     ~"1: x = 23\n"
>     ~"7\t  printf(\"%d\\n\", x);\n"
>     ~"1: x = 23\n"
>     *stopped,reason="end-stepping-range",frame={addr="0x0000000000400565",func="main",args=[],file="q.c",fullname="/tmp/q.c",line="7"},thread-id="1",stopped-threads="all",core="1"
> 
> The immediate cause of this is this code in mi_on_normal_stop_1:
> 
>       print_stop_event (mi_uiout);
> 
>       console_interp = interp_lookup (current_ui, INTERP_CONSOLE);
>       if (should_print_stop_to_console (console_interp, tp))
> 	print_stop_event (mi->cli_uiout);
> 
> ... which obviously prints the stop twice.
> 
> However, I think the first call to print_stop_event is intended just
> to emit the MI *stopped notification, which explains why the source
> line does not show up two times.
> 
> This patch fixes the bug by changing print_stop_event to only call
> do_displays for non-MI-like ui-outs.

Yeah, this was previously discussed here:

  https://sourceware.org/ml/gdb/2018-06/msg00006.html

See my comment there:

> Fixing this probably needs to take in consideration whether
> we print the displays on the CLI uiout even if the stop
> isn't printed there according to should_print_stop_to_console.
> I.e., what makes more sense for a user that enabled some display,
> but then stepped with the frontend's "step" buttons instead of
> typing "next" or "step".  Probably we shouldn't print the
> displays in that case, just to keep things simple, respecting
> should_print_stop_to_console, but not 100% sure.

So your patch makes GDB not do the displays in the
-exec-step/-exec-next case, which is the solution I was
leaning to above too, even though I'm not 100% sure about it.
I think that change should be covered by the testcase too, though.
I.e., check that displays aren't printed in the -exec-step/-exec-next
cases (they are without your patch), and that they are in the
-exec-continue case (I believe they are with your patch).

> 
> Tested on x86-64 Fedora 29.
> 
> gdb/ChangeLog
> 2019-03-12  Tom Tromey  <tromey@adacore.com>
> 
> 	* infrun.c (print_stop_event): Don't call do_displays for MI-like
> 	ui-outs.
> 
> gdb/testsuite/ChangeLog
> 2019-03-12  Tom Tromey  <tromey@adacore.com>
> 
> 	* gdb.mi/mi2-cli-display.c: New file.
> 	* gdb.mi/mi2-cli-display.exp: New file.
> ---
>  gdb/ChangeLog                            |  5 ++
>  gdb/infrun.c                             |  3 +-
>  gdb/testsuite/ChangeLog                  |  5 ++
>  gdb/testsuite/gdb.mi/mi2-cli-display.c   | 30 ++++++++++++
>  gdb/testsuite/gdb.mi/mi2-cli-display.exp | 62 ++++++++++++++++++++++++
>  5 files changed, 104 insertions(+), 1 deletion(-)
>  create mode 100644 gdb/testsuite/gdb.mi/mi2-cli-display.c
>  create mode 100644 gdb/testsuite/gdb.mi/mi2-cli-display.exp
> 
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 33e5d434b35..9261588db32 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -7867,7 +7867,8 @@ print_stop_event (struct ui_out *uiout)
>      print_stop_location (&last);
>  
>      /* Display the auto-display expressions.  */
> -    do_displays ();
> +    if (!uiout->is_mi_like_p ())
> +      do_displays ();
>    }
>  
>    tp = inferior_thread ();
> diff --git a/gdb/testsuite/gdb.mi/mi2-cli-display.c b/gdb/testsuite/gdb.mi/mi2-cli-display.c
> new file mode 100644
> index 00000000000..813fda47cfc
> --- /dev/null
> +++ b/gdb/testsuite/gdb.mi/mi2-cli-display.c
> @@ -0,0 +1,30 @@
> +/* Copyright 2019 Free Software Foundation, Inc.
> +
> +   This file is part of GDB.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +int do_tests (int x)

Like break after return type?

> +{
> +  ++x;
> +  ++x;
> +  ++x;
> +  ++x;
> +  return x;
> +}
> +
> +int main (void)

Ditto.

> +{
> +  return do_tests (23);
> +}
> diff --git a/gdb/testsuite/gdb.mi/mi2-cli-display.exp b/gdb/testsuite/gdb.mi/mi2-cli-display.exp
> new file mode 100644
> index 00000000000..b11306a51cd
> --- /dev/null
> +++ b/gdb/testsuite/gdb.mi/mi2-cli-display.exp
> @@ -0,0 +1,62 @@
> +# Copyright 2019 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +# Ensure that CLI "display"s aren't double-emitted in MI mode.
> +
> +load_lib mi-support.exp
> +set MIFLAGS "-i=mi2"
> +
> +if {[mi_gdb_start]} {
> +    continue
> +}
> +
> +standard_testfile
> +
> +if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
> +    untested "failed to compile"
> +    return -1
> +}
> +
> +mi_delete_breakpoints
> +mi_gdb_reinitialize_dir $srcdir/$subdir
> +mi_gdb_load ${binfile}
> +
> +mi_runto do_tests
> +
> +mi_gdb_test "display x" \
> +    "&\"display x\\\\n\"\r\n~\"1: x = 23\\\\n\"\r\n\\^done" \
> +    "display x"
> +
> +mi_send_resuming_command "interpreter-exec console next" next
> +
> +# Now check for the display and the source line.  Note we don't check
> +# the source line too closely, since it's not really important here.
> +gdb_expect {
> +    -re "~\"1: x = 24\\\\n\"\r\n~\"\[0-9\]+.*\\\\n\"\r\n~\"1: x = 24\\\\n\"\r\n" {
> +	# This case is the bug: the display is shown twice.
> +	fail "check display and source line"
> +    }
> +    -re "~\"\[0-9\]+.*\\\\n\"\r\n~\"1: x = 24\\\\n\"\r\n" {
> +	pass "check display and source line"

Hard to tell, but just to double-check -- is the pass regex a
subset of the fail regex case above?  I'm just wondering whether
this could issue a false pass if expect consumes just the right amount
of the bad case's output.  A comment indicating otherwise here would
be good, IMO.

> +    }
> +    -re ".*\r\n$mi_gdb_prompt$" {
> +	fail "check display and source line"
> +    }
> +    timeout {
> +	fail "check display and source line"

Add " (timeout)" ?

> +    }
> +}
> +
> +mi_expect_stop end-stepping-range {.*} {.*} {.*} {.*} {.*} "stop for next"
> 

Thanks,
Pedro Alves
Tom Tromey - March 13, 2019, 3:17 p.m.
>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:

>> Probably we shouldn't print the displays in that case, just to keep
>> things simple, respecting should_print_stop_to_console, but not 100%
>> sure.

Pedro> So your patch makes GDB not do the displays in the
Pedro> -exec-step/-exec-next case, which is the solution I was
Pedro> leaning to above too, even though I'm not 100% sure about it.

I'm not 100% sure either.

We could have a more complicated patch that arranges for do_displays to
be called just once, no matter what decision is made.  Maybe this would
be better?

I originally thought it was somewhat odd to deal with displays in an MI
stepping situation -- MI clients presumably would use varobj.  But,
really the scenario is that the MI client provides a console, the user
types "display ...", and then debugs some more.  I suppose the way that
the "next" is done wouldn't matter to the user?

Tom
Pedro Alves - March 13, 2019, 3:50 p.m.
On 03/13/2019 03:17 PM, Tom Tromey wrote:
>>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:
> 
>>> Probably we shouldn't print the displays in that case, just to keep
>>> things simple, respecting should_print_stop_to_console, but not 100%
>>> sure.
> 
> Pedro> So your patch makes GDB not do the displays in the
> Pedro> -exec-step/-exec-next case, which is the solution I was
> Pedro> leaning to above too, even though I'm not 100% sure about it.
> 
> I'm not 100% sure either.
> 
> We could have a more complicated patch that arranges for do_displays to
> be called just once, no matter what decision is made.  Maybe this would
> be better?

Maybe we could simply move the do_display call elsewhere?

> I originally thought it was somewhat odd to deal with displays in an MI
> stepping situation -- MI clients presumably would use varobj.  

Yeah, that's not the way to look at it, IMO.  

> But, really the scenario is that the MI client provides a console, the user
> types "display ...", and then debugs some more.  I suppose the way that
> the "next" is done wouldn't matter to the user?

Yeah.  Thinking a bit more, I think I'd be surprised if my console-created "display"
wasn't redisplayed in the console regardless of whether I pressed a "next" button,
or typed "next" in the console.  Kind of the mirror view of creating a
"watch expression" thingy in Eclipse (or whatever), which is implemented with
varobjs, and then that widget not updating with "next" in the console.

Thanks,
Pedro Alves
André Pönitz - March 13, 2019, 6:43 p.m.
On Wed, Mar 13, 2019 at 09:17:48AM -0600, Tom Tromey wrote:
> >>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:
> 
> >> Probably we shouldn't print the displays in that case, just to keep
> >> things simple, respecting should_print_stop_to_console, but not 100%
> >> sure.
> 
> Pedro> So your patch makes GDB not do the displays in the
> Pedro> -exec-step/-exec-next case, which is the solution I was
> Pedro> leaning to above too, even though I'm not 100% sure about it.
> 
> I'm not 100% sure either.
> 
> We could have a more complicated patch that arranges for do_displays to
> be called just once, no matter what decision is made.  Maybe this would
> be better?
> 
> I originally thought it was somewhat odd to deal with displays in an MI
> stepping situation -- MI clients presumably would use varobj. 

That's possibly a bit too general: As counterexample, I'd call Qt Creator
an "MI client" but it doesn't use varobj.

On the other hand, I would not use "display" in that setup either (there's a
separate window to evaluate expression that gets updated after each stop)
so any number of copies of the value in the output is fine in that
situation.

> But, really the scenario is that the MI client provides a console, the
> user types "display ...", and then debugs some more.  I suppose the way
> that the "next" is done wouldn't matter to the user?

Probably not, indeed.

Andre'

Patch

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 33e5d434b35..9261588db32 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -7867,7 +7867,8 @@  print_stop_event (struct ui_out *uiout)
     print_stop_location (&last);
 
     /* Display the auto-display expressions.  */
-    do_displays ();
+    if (!uiout->is_mi_like_p ())
+      do_displays ();
   }
 
   tp = inferior_thread ();
diff --git a/gdb/testsuite/gdb.mi/mi2-cli-display.c b/gdb/testsuite/gdb.mi/mi2-cli-display.c
new file mode 100644
index 00000000000..813fda47cfc
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi2-cli-display.c
@@ -0,0 +1,30 @@ 
+/* Copyright 2019 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int do_tests (int x)
+{
+  ++x;
+  ++x;
+  ++x;
+  ++x;
+  return x;
+}
+
+int main (void)
+{
+  return do_tests (23);
+}
diff --git a/gdb/testsuite/gdb.mi/mi2-cli-display.exp b/gdb/testsuite/gdb.mi/mi2-cli-display.exp
new file mode 100644
index 00000000000..b11306a51cd
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi2-cli-display.exp
@@ -0,0 +1,62 @@ 
+# Copyright 2019 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Ensure that CLI "display"s aren't double-emitted in MI mode.
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi2"
+
+if {[mi_gdb_start]} {
+    continue
+}
+
+standard_testfile
+
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
+    untested "failed to compile"
+    return -1
+}
+
+mi_delete_breakpoints
+mi_gdb_reinitialize_dir $srcdir/$subdir
+mi_gdb_load ${binfile}
+
+mi_runto do_tests
+
+mi_gdb_test "display x" \
+    "&\"display x\\\\n\"\r\n~\"1: x = 23\\\\n\"\r\n\\^done" \
+    "display x"
+
+mi_send_resuming_command "interpreter-exec console next" next
+
+# Now check for the display and the source line.  Note we don't check
+# the source line too closely, since it's not really important here.
+gdb_expect {
+    -re "~\"1: x = 24\\\\n\"\r\n~\"\[0-9\]+.*\\\\n\"\r\n~\"1: x = 24\\\\n\"\r\n" {
+	# This case is the bug: the display is shown twice.
+	fail "check display and source line"
+    }
+    -re "~\"\[0-9\]+.*\\\\n\"\r\n~\"1: x = 24\\\\n\"\r\n" {
+	pass "check display and source line"
+    }
+    -re ".*\r\n$mi_gdb_prompt$" {
+	fail "check display and source line"
+    }
+    timeout {
+	fail "check display and source line"
+    }
+}
+
+mi_expect_stop end-stepping-range {.*} {.*} {.*} {.*} {.*} "stop for next"