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# Copyright (C) 2021-2025 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/>.
# Defines a base class, which can be sub-classed, in order to run
# memory leak tests on some aspects of GDB's Python API. See the
# comments on the gdb_leak_detector class for more details.
import os
import tracemalloc
import gdb
# This class must be sub-classed to create a memory leak test. The
# sub-classes __init__ method should call the parent classes __init__
# method, and the sub-class should override allocate() and
# deallocate(). See the comments on the various methods below for
# more details of required arguments and expected usage.
class gdb_leak_detector:
# Class initialisation. FILENAME is the file in which the
# sub-class is defined, usually passed as just '__file__'. This
# is used when looking for memory allocations; only allocations in
# FILENAME are considered.
def __init__(self, filename):
self.filters = [tracemalloc.Filter(True, "*" + os.path.basename(filename))]
# Internal helper function to actually run the test. Calls the
# allocate() method to allocate an object from GDB's Python API.
# When CLEAR is True the object will then be deallocated by
# calling deallocate(), otherwise, deallocate() is not called.
#
# Finally, this function checks for any memory allocatios
# originating from 'self.filename' that have not been freed, and
# returns the total (in bytes) of the memory that has been
# allocated, but not freed.
def _do_test(self, clear):
# Start tracing, and take a snapshot of the current allocations.
tracemalloc.start()
snapshot1 = tracemalloc.take_snapshot()
# Generate the GDB Python API object by calling the allocate
# method.
self.allocate()
# Possibly clear the reference to the allocated object.
if clear:
self.deallocate()
# 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(self.filters)
snapshot2 = snapshot2.filter_traces(self.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 allocated things.
total = 0
for stat in stats:
total += stat.size_diff
return total
# Run the memory leak test. Prints 'PASS' if successful,
# otherwise, raises an exception (of type GdbError).
def run(self):
# 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.
self._do_test(True)
# Now run the test twice, the first time we clear our global reference
# to the allocated 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 = self._do_test(True)
bytes_without_clear = self._do_test(False)
# If there are any allocations left over when we cleared the reference
# (and expected deallocation) then this indicates a leak.
if bytes_with_clear > 0:
raise gdb.GdbError("memory leak when object reference was released")
# If there are no allocations showing when we hold onto a reference,
# then this likely indicates that the testing infrastructure is broken,
# and we're no longer spotting the allocations at all.
if bytes_without_clear == 0:
raise gdb.GdbError("object is unexpectedly not showing as allocated")
# Print a PASS message that the TCL script can see.
print("PASS")
# Sub-classes must override this method. Allocate an object (or
# multiple objects) from GDB's Python API. Store references to
# these objects within SELF.
def allocate(self):
raise NotImplementedError("allocate() not implemented")
# Sub-classes must override this method. Deallocate the object(s)
# allocated by the allocate() method. All that is required is for
# the references created in allocate() to be set to None.
def deallocate(self):
raise NotImplementedError("allocate() not implemented")
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