diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c index 0659c28ea9c..c8de41dd009 100644 --- a/gdb/python/py-inferior.c +++ b/gdb/python/py-inferior.c @@ -864,12 +864,20 @@ static void infpy_dealloc (PyObject *obj) { inferior_object *inf_obj = (inferior_object *) obj; - struct inferior *inf = inf_obj->inferior; - if (! inf) - return; + /* The inferior itself holds a reference to this Python object, which + will keep the reference count of this object above zero until GDB + deletes the inferior and py_free_inferior is called. + + Once py_free_inferior has been called then the link between this + Python object and the inferior is set to nullptr, and then the + reference count on this Python object is decremented. + + The result of all this is that the link between this Python object and + the inferior should always have been set to nullptr before this + function is called. */ + gdb_assert (inf_obj->inferior == nullptr); - set_inferior_data (inf, infpy_inf_data_key, NULL); Py_TYPE (obj)->tp_free (obj); } diff --git a/gdb/testsuite/gdb.python/py-inferior-leak.c b/gdb/testsuite/gdb.python/py-inferior-leak.c new file mode 100644 index 00000000000..bfe52c018d4 --- /dev/null +++ b/gdb/testsuite/gdb.python/py-inferior-leak.c @@ -0,0 +1,22 @@ +/* This testcase is part of GDB, the GNU debugger. + + Copyright 2021 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 . */ + +int +main (void) +{ + return 0; +} diff --git a/gdb/testsuite/gdb.python/py-inferior-leak.exp b/gdb/testsuite/gdb.python/py-inferior-leak.exp new file mode 100644 index 00000000000..9cd1ebf2433 --- /dev/null +++ b/gdb/testsuite/gdb.python/py-inferior-leak.exp @@ -0,0 +1,33 @@ +# Copyright (C) 2021 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 . + +# This file is part of the GDB testsuite. It checks for memory leaks +# associated with allocating and deallocation gdb.Inferior objects. + +load_lib gdb-python.exp + +standard_testfile + +clean_restart + +# Skip all tests if Python scripting is not enabled. +if { [skip_python_tests] } { continue } + +set pyfile [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py] + +# Source the Python script, this runs the test (which is written +# completely in Python), and either prints PASS, or throws an +# exception. +gdb_test "source ${pyfile}" "PASS" "source python script" diff --git a/gdb/testsuite/gdb.python/py-inferior-leak.py b/gdb/testsuite/gdb.python/py-inferior-leak.py new file mode 100644 index 00000000000..914fb3ecc08 --- /dev/null +++ b/gdb/testsuite/gdb.python/py-inferior-leak.py @@ -0,0 +1,109 @@ +# Copyright (C) 2021 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 . + +import tracemalloc +import gdb +import re + +# A global variable in which we store a reference to the gdb.Inferior +# object sent to us in the new_inferior event. +inf = None + +# Register the new_inferior event handler. +def new_inferior_handler(event): + global inf + inf = event.inferior + + +gdb.events.new_inferior.connect(new_inferior_handler) + +# A global filters list, we only care about memory allocations +# originating from this script. +filters = [tracemalloc.Filter(True, "*py-inferior-leak.py")] + +# Add a new inferior, and return the number of the new inferior. +def add_inferior(): + output = gdb.execute("add-inferior", False, True) + m = re.search(r"Added inferior (\d+)", output) + if m: + num = int(m.group(1)) + else: + raise RuntimeError("no match") + return num + + +# Run the test. When CLEAR is True we clear the global INF variable +# before comparing the before and after memory allocation traces. +# When CLEAR is False we leave INF set to reference the gdb.Inferior +# object, thus preventing the gdb.Inferior from being deallocated. +def test(clear): + global filters, inf + + # Start tracing, and take a snapshot of the current allocations. + tracemalloc.start() + snapshot1 = tracemalloc.take_snapshot() + + # Create an inferior, this triggers the new_inferior event, which + # in turn holds a reference to the new gdb.Inferior object in the + # global INF variable. + num = add_inferior() + gdb.execute("remove-inferiors %s" % num) + + # Possibly clear the global INF variable. + if clear: + inf = None + + # Now grab a second snapshot of memory allocations, and stop + # tracing memory allocations. + snapshot2 = tracemalloc.take_snapshot() + tracemalloc.stop() + + # Filter the snapshots; we only care about allocations originating + # from this file. + snapshot1 = snapshot1.filter_traces(filters) + snapshot2 = snapshot2.filter_traces(filters) + + # Compare the snapshots, this leaves only things that were + # allocated, but not deallocated since the first snapshot. + stats = snapshot2.compare_to(snapshot1, "traceback") + + # Total up all the deallocated things. + total = 0 + for stat in stats: + total += stat.size_diff + return total + + +# The first time we run this some global state will be allocated which +# shows up as memory that is allocated, but not released. So, run the +# test once and discard the result. +test(True) + +# Now run the test twice, the first time we clear our global reference +# to the gdb.Inferior object, which should allow Python to deallocate +# the object. The second time we hold onto the global reference, +# preventing Python from performing the deallocation. +bytes_with_clear = test(True) +bytes_without_clear = test(False) + +# The bug that used to exist in GDB was that even when we released the +# global reference the gdb.Inferior object would not be deallocated. +if bytes_with_clear > 0: + raise gdb.GdbError("memory leak when gdb.Inferior should be released") +if bytes_without_clear == 0: + raise gdb.GdbError("gdb.Inferior object is no longer allocated") + +# Print a PASS message that the test script can see. +print("PASS")