[PATCH] gdb: fix target_ops reference count for some cases
Andrew Burgess
aburgess@redhat.com
Thu Sep 22 17:24:07 GMT 2022
Simon Marchi <simark@simark.ca> writes:
>> 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.
I suspect the comment you quote is just out of date.
switch_to_program_space_and_thread can end up calling
switch_to_inferior_no_thread if there are no running threads in the
program space being switched too. But, even if switch_to_thread does
end up being called we:
- set the program space,
- set the inferior,
- set the current thread,
- reinit the frame cache,
By comparison, switch_to_inferior_no_thread does:
- sets the program space,
- sets the inferior,
- sets the current thread (to nullptr this time though),
- reinits the frame cache,
As you can see they do the same set of things, all of which I think
should be reverted once we leave the scope, hence
scoped_restore_current_pspace_and_thread seems like the way to go.
>
>> 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.
OK.
Thanks,
Andrew
>
> Simon
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