[PATCH] Make 'import gdb.events' work

[PATCH] Make 'import gdb.events' work

[Tom Tromey]

Pierre-Marie noticed that, while gdb.events is a Python module, it
can't be imported.  This patch changes how this module is created, so
that it can be imported, while also ensuring that the module is always
visible, just as it was in the past.

This new approach required one non-obvious change -- when running
gdb.base/warning.exp, where --data-directory is intentionally not
found, the event registries can now be nullptr.  Consequently, this
patch probably also requires

    https://sourceware.org/pipermail/gdb-patches/2022-June/189796.html

Note that this patch obsoletes

    https://sourceware.org/pipermail/gdb-patches/2022-June/189797.html
---
 gdb/python/lib/gdb/__init__.py         |  5 +++++
 gdb/python/py-evtregistry.c            |  4 +++-
 gdb/python/py-evts.c                   | 28 ++++++++++++--------------
 gdb/python/python-internal.h           |  4 ++--
 gdb/python/python.c                    | 16 +++++++++++----
 gdb/testsuite/gdb.python/py-events.exp |  2 ++
 6 files changed, 37 insertions(+), 22 deletions(-)

diff --git a/gdb/python/lib/gdb/__init__.py b/gdb/python/lib/gdb/__init__.py
index a52f6b46413..17ee6a19e14 100644
--- a/gdb/python/lib/gdb/__init__.py
+++ b/gdb/python/lib/gdb/__init__.py
@@ -27,6 +27,11 @@ else:
 
 from _gdb import *
 
+# Historically, gdb.events was always available, so ensure it's
+# still available without an explicit import.
+import _gdbevents as events
+sys.modules['gdb.events'] = events
+
 
 class _GdbFile(object):
     # These two are needed in Python 3
diff --git a/gdb/python/py-evtregistry.c b/gdb/python/py-evtregistry.c
index ef96c483f47..f3a7f0ca244 100644
--- a/gdb/python/py-evtregistry.c
+++ b/gdb/python/py-evtregistry.c
@@ -118,7 +118,9 @@ gdbpy_initialize_eventregistry (void)
 bool
 evregpy_no_listeners_p (eventregistry_object *registry)
 {
-  return PyList_Size (registry->callbacks) == 0;
+  /* REGISTRY can be nullptr if gdb failed to find the data directory
+     at startup.  */
+  return registry == nullptr || PyList_Size (registry->callbacks) == 0;
 }
 
 static PyMethodDef eventregistry_object_methods[] =
diff --git a/gdb/python/py-evts.c b/gdb/python/py-evts.c
index 23a5d75ae21..ca9326a1469 100644
--- a/gdb/python/py-evts.c
+++ b/gdb/python/py-evts.c
@@ -23,7 +23,7 @@
 static struct PyModuleDef EventModuleDef =
 {
   PyModuleDef_HEAD_INIT,
-  "gdb.events",
+  "_gdbevents",
   NULL,
   -1,
   NULL,
@@ -33,7 +33,8 @@ static struct PyModuleDef EventModuleDef =
   NULL
 };
 
-/* Initialize python events.  */
+/* Helper function to add a single event registry to the events
+   module.  */
 
 static int CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION
 add_new_registry (eventregistry_object **registryp, const char *name)
@@ -48,24 +49,21 @@ add_new_registry (eventregistry_object **registryp, const char *name)
 				 (PyObject *)(*registryp));
 }
 
-int
-gdbpy_initialize_py_events (void)
+/* Create and populate the _gdbevents module.  Note that this is
+   always created, see the base gdb __init__.py.  */
+
+PyMODINIT_FUNC
+gdbpy_events_mod_func ()
 {
   gdb_py_events.module = PyModule_Create (&EventModuleDef);
+  if (gdb_py_events.module == nullptr)
+    return nullptr;
 
-  if (!gdb_py_events.module)
-    return -1;
-
-#define GDB_PY_DEFINE_EVENT(name)				\
+#define GDB_PY_DEFINE_EVENT(name)					\
   if (add_new_registry (&gdb_py_events.name, #name) < 0)	\
-    return -1;
+    return nullptr;
 #include "py-all-events.def"
 #undef GDB_PY_DEFINE_EVENT
 
-  if (gdb_pymodule_addobject (gdb_module,
-			      "events",
-			      (PyObject *) gdb_py_events.module) < 0)
-    return -1;
-
-  return 0;
+  return gdb_py_events.module;
 }
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index 217bc15bb28..2883bb1bb8d 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -521,8 +521,6 @@ int gdbpy_initialize_eventregistry (void)
   CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
 int gdbpy_initialize_event (void)
   CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
-int gdbpy_initialize_py_events (void)
-  CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
 int gdbpy_initialize_arch (void)
   CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
 int gdbpy_initialize_registers ()
@@ -541,6 +539,8 @@ int gdbpy_initialize_micommands (void)
   CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
 void gdbpy_finalize_micommands ();
 
+PyMODINIT_FUNC gdbpy_events_mod_func ();
+
 /* A wrapper for PyErr_Fetch that handles reference counting for the
    caller.  */
 class gdbpy_err_fetch
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 9bef2252e88..d67fcc60df3 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -2000,11 +2000,20 @@ do_start_initialization ()
      remain alive for the duration of the program's execution, so
      it is not freed after this call.  */
   Py_SetProgramName (progname_copy);
-
-  /* Define _gdb as a built-in module.  */
-  PyImport_AppendInittab ("_gdb", init__gdb_module);
 #endif
 
+  /* Define all internal modules.  These are all imported (and thus
+     created) during initialization.  */
+  struct _inittab mods[3] =
+  {
+    { "_gdb", init__gdb_module },
+    { "_gdbevents", gdbpy_events_mod_func },
+    { nullptr, nullptr }
+  };
+
+  if (PyImport_ExtendInittab (mods) < 0)
+    return false;
+
   Py_Initialize ();
 #if PY_VERSION_HEX < 0x03090000
   /* PyEval_InitThreads became deprecated in Python 3.9 and will
@@ -2071,7 +2080,6 @@ do_start_initialization ()
       || gdbpy_initialize_thread () < 0
       || gdbpy_initialize_inferior () < 0
       || gdbpy_initialize_eventregistry () < 0
-      || gdbpy_initialize_py_events () < 0
       || gdbpy_initialize_event () < 0
       || gdbpy_initialize_arch () < 0
       || gdbpy_initialize_registers () < 0
diff --git a/gdb/testsuite/gdb.python/py-events.exp b/gdb/testsuite/gdb.python/py-events.exp
index 2fdd2160a44..4feeb029951 100644
--- a/gdb/testsuite/gdb.python/py-events.exp
+++ b/gdb/testsuite/gdb.python/py-events.exp
@@ -42,6 +42,8 @@ clean_restart ${testfile}
 
 if { [skip_python_tests] } { continue }
 
+gdb_test_no_output "python import gdb.events"
+
 set pyfile [gdb_remote_download host ${srcdir}/${subdir}/py-events.py]
 gdb_test_no_output "source ${pyfile}" "load python file"
 
-- 
2.34.1

Re: [PATCH] Make 'import gdb.events' work

[Tom Tromey]

>>>>> "Tom" == Tom Tromey via Gdb-patches <gdb-patches@sourceware.org> writes:

Tom> Pierre-Marie noticed that, while gdb.events is a Python module, it
Tom> can't be imported.  This patch changes how this module is created, so
Tom> that it can be imported, while also ensuring that the module is always
Tom> visible, just as it was in the past.

I'm checking this in.

Tom

Re: [PATCH] Make 'import gdb.events' work

[Kevin Buettner]

On Tue,  7 Jun 2022 07:20:25 -0600
Tom Tromey via Gdb-patches <gdb-patches@sourceware.org> wrote:

> +  /* Define all internal modules.  These are all imported (and thus
> +     created) during initialization.  */
> +  struct _inittab mods[3] =
> +  {
> +    { "_gdb", init__gdb_module },
> +    { "_gdbevents", gdbpy_events_mod_func },
> +    { nullptr, nullptr }
> +  };

Something I just noticed while looking at a conflict while rebasing
my Python 3.11 deprecation patch:

Is there any reason not to do...

  struct _inittab mods[] =
  ...

instead?

Since I've had to move this hunk of code, I've made the above tweak in
my (soon to come) v3 Python 3.11 deprecation patch.

Kevin

Re: [PATCH] Make 'import gdb.events' work

[Tom Tromey]

>>>>> "Kevin" == Kevin Buettner <kevinb@redhat.com> writes:

>> +  /* Define all internal modules.  These are all imported (and thus
>> +     created) during initialization.  */
>> +  struct _inittab mods[3] =
>> +  {
>> +    { "_gdb", init__gdb_module },
>> +    { "_gdbevents", gdbpy_events_mod_func },
>> +    { nullptr, nullptr }
>> +  };

Kevin> Something I just noticed while looking at a conflict while rebasing
Kevin> my Python 3.11 deprecation patch:

Kevin> Is there any reason not to do...

Kevin>   struct _inittab mods[] =
Kevin>   ...

Kevin> instead?

Not that I can think of, and I don't recall writing it this way :)
It seems better to remove the '3' TBH.

Tom