[PATCH] gdb: fix target_ops reference count for some cases

[Simon Marchi]

> diff --git a/gdb/inferior.c b/gdb/inferior.c
> index 7eb2bd97907..0c0b4b78ff5 100644
> --- a/gdb/inferior.c
> +++ b/gdb/inferior.c
> @@ -70,6 +70,16 @@ inferior::~inferior ()
>  {
>    inferior *inf = this;
>  
> +  /* Before the inferior is deleted, all target_ops should be popped from
> +     the target stack, this leaves just the dummy_target behind.  If this
> +     is not done, then any target left in the target stack will be left
> +     with an artificially high reference count.  As the dummy_target is
> +     still on the target stack then we are about to loose a reference to
loose -> lose?

> @@ -191,6 +201,26 @@ delete_inferior (struct inferior *inf)
>  
>    gdb::observers::inferior_removed.notify (inf);
>  
> +  {
> +    /* Limit the change of inferior to an inner scope so that the original
> +       inferior and program space will have been restored by the time that
> +       we delete the inferior INF and (possibly) its related  program

two spaces between related and program.

> +       space.  */
> +    scoped_restore_current_pspace_and_thread restore_pspace_and_thread;

Just wondering, why do we need to restore explicitly the current
pspace, instead of using just scoped_restore_current_thread?

scoped_restore_current_pspace_and_thread's doc says:

/* Save/restore the current program space, thread, inferior and frame.
   Use this when you need to call
   switch_to_program_space_and_thread.  */

... but you are not using switch_to_program_space_and_thread here.
Maybe it's ok and I just don't understand.  Same in
~scoped_mock_context.

> diff --git a/gdb/testsuite/gdb.python/py-connection-removed.exp b/gdb/testsuite/gdb.python/py-connection-removed.exp
> new file mode 100644
> index 00000000000..1b139cedc0d
> --- /dev/null
> +++ b/gdb/testsuite/gdb.python/py-connection-removed.exp
> @@ -0,0 +1,92 @@
> +# Copyright (C) 2022 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/>.
> +
> +# Check that the gdb.connect_removed event triggers when we expect it
> +# too.

too -> to

> +#
> +# Checking this event has wider implications that simply some corner

simply -> imply?  Or I don't get what you mean.

> +# of the Python API working or not.  The connection_removed event
> +# triggers when the reference count of a process_stratum_target
> +# reaches zero.  If these events stop triggering when expected then
> +# GDB might be getting the reference counting on target_ops objects
> +# wrong.
> +
> +load_lib gdb-python.exp
> +
> +standard_testfile py-connection.c
> +
> +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
> +    return -1
> +}
> +
> +# Skip all tests if Python scripting is not enabled.
> +if { [skip_python_tests] } { continue }
> +
> +if ![runto_main] then {
> +    return 0
> +}
> +
> +# Register a callback that will trigger when a connection is removed
> +# (deleted) within GDB.
> +gdb_test_multiline "Add connection_removed event" \
> +    "python" "" \
> +    "def connection_removed_handler(event):" "" \
> +    "   num = event.connection.num" "" \
> +    "   type = event.connection.type" "" \
> +    "   print(f'Connection {num} ({type}) removed')" "" \

I think unfortunately need to support Python versions that don't know
about f-strings.

Simon