Re: question: python gc doesn't collect buffer allocated by read_memory()

Tom Tromey
2012-03-28T17:37:58Z

>>>>> ">" == HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com> writes:

>> I suspect another objects allocated remain while not collected.

Thanks, you are correct.

I used valgrind --tool=massif to find the problem.

TRY_CATCH clears the cleanup chain, so making a cleanup in a TRY_CATCH
and then trying to run or discard it outside the TRY_CATCH will not
work; instead it leaks the cleanup.

I am checking in the appended patch. It fixes both leaks. Verified
with massif.

Tom

2012-03-28 Tom Tromey <tromey@redhat.com>

* python/py-inferior.c (infpy_read_memory): Remove cleanups and
explicitly free 'buffer' on exit paths. Decref 'membuf_object'
before returning.

diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c
index 339a221..06d3272 100644
--- a/gdb/python/py-inferior.c
+++ b/gdb/python/py-inferior.c
@@ -405,8 +405,7 @@ infpy_read_memory (PyObject *self, PyObject *args, PyObject *kw)
CORE_ADDR addr, length;
void *buffer = NULL;
membuf_object *membuf_obj;
- PyObject *addr_obj, *length_obj;
- struct cleanup *cleanups;
+ PyObject *addr_obj, *length_obj, *result;
volatile struct gdb_exception except;
static char *keywords[] = { "address", "length", NULL };

@@ -414,8 +413,6 @@ infpy_read_memory (PyObject *self, PyObject *args, PyObject *kw)
&addr_obj, &length_obj))
return NULL;

- cleanups = make_cleanup (null_cleanup, NULL);
-
TRY_CATCH (except, RETURN_MASK_ALL)
{
if (!get_addr_from_python (addr_obj, &addr)
@@ -426,39 +423,38 @@ infpy_read_memory (PyObject *self, PyObject *args, PyObject *kw)
}

buffer = xmalloc (length);
- make_cleanup (xfree, buffer);

read_memory (addr, buffer, length);
}
if (except.reason < 0)
{
- do_cleanups (cleanups);
+ xfree (buffer);
GDB_PY_HANDLE_EXCEPTION (except);
}

if (error)
{
- do_cleanups (cleanups);
+ xfree (buffer);
return NULL;
}

membuf_obj = PyObject_New (membuf_object, &membuf_object_type);
if (membuf_obj == NULL)
{
+ xfree (buffer);
PyErr_SetString (PyExc_MemoryError,
_("Could not allocate memory buffer object."));
- do_cleanups (cleanups);
return NULL;
}

- discard_cleanups (cleanups);
-
membuf_obj->buffer = buffer;
membuf_obj->addr = addr;
membuf_obj->length = length;

- return PyBuffer_FromReadWriteObject ((PyObject *) membuf_obj, 0,
- Py_END_OF_BUFFER);
+ result = PyBuffer_FromReadWriteObject ((PyObject *) membuf_obj, 0,
+ Py_END_OF_BUFFER);
+ Py_DECREF (membuf_obj);
+ return result;
}

/* Implementation of gdb.write_memory (address, buffer [, length]).