[PATCH] Fix 8.2 regression in gdb.python/py-evthreads.exp w/ gdbserver (PR gdb/23379)

[PATCH] Fix 8.2 regression in gdb.python/py-evthreads.exp w/ gdbserver (PR gdb/23379)

[Pedro Alves]

This commit fixes a 8.1->8.2 regression exposed by
gdb.python/py-evthreads.exp when testing with
--target_board=native-gdbserver.

gdb.log shows:

  src/gdb/thread.c:93: internal-error: thread_info* inferior_thread(): Assertion `tp' failed.
  A problem internal to GDB has been detected,
  further debugging may prove unreliable.
  Quit this debugging session? (y or n) FAIL: gdb.python/py-evthreads.exp: run to breakpoint 1 (GDB internal error)

A backtrace shows (frames #2 and #10 highlighted) that the assertion
fails when GDB is setting up the connection to the remote target, in
non-stop mode:

  #0  0x0000000000622ff0 in internal_error(char const*, int, char const*, ...) (file=0xc1ad98 "src/gdb/thread.c", line=93, fmt=0xc1ad20 "%s: Assertion `%s' failed.") at src/gdb/common/errors.c:54
  #1  0x000000000089567e in inferior_thread() () at src/gdb/thread.c:93
= #2  0x00000000004da91d in get_event_thread() () at src/gdb/python/py-threadevent.c:38
  #3  0x00000000004da9b7 in create_thread_event_object(_typeobject*, _object*) (py_type=0x11574c0 <continue_event_object_type>, thread=0x0)
      at src/gdb/python/py-threadevent.c:60
  #4  0x00000000004bf6fe in create_continue_event_object() () at src/gdb/python/py-continueevent.c:27
  #5  0x00000000004bf738 in emit_continue_event(ptid_t) (ptid=...) at src/gdb/python/py-continueevent.c:40
  #6  0x00000000004c7d47 in python_on_resume(ptid_t) (ptid=...) at src/gdb/python/py-inferior.c:108
  #7  0x0000000000485bfb in std::_Function_handler<void (ptid_t), void (*)(ptid_t)>::_M_invoke(std::_Any_data const&, ptid_t&&) (__functor=..., __args#0=...) at /usr/include/c++/7/bits/std_function.h:316
  #8  0x000000000089b416 in std::function<void (ptid_t)>::operator()(ptid_t) const (this=0x12aa600, __args#0=...)
      at /usr/include/c++/7/bits/std_function.h:706
  #9  0x000000000089aa0e in gdb::observers::observable<ptid_t>::notify(ptid_t) const (this=0x118a7a0 <gdb::observers::target_resumed>, args#0=...)
      at src/gdb/common/observable.h:106
= #10 0x0000000000896fbe in set_running(ptid_t, int) (ptid=..., running=1) at src/gdb/thread.c:880
  #11 0x00000000007f750f in remote_target::remote_add_thread(ptid_t, bool, bool) (this=0x12c5440, ptid=..., running=true, executing=true) at src/gdb/remote.c:2434
  #12 0x00000000007f779d in remote_target::remote_notice_new_inferior(ptid_t, int) (this=0x12c5440, currthread=..., executing=1)
      at src/gdb/remote.c:2515
  #13 0x00000000007f9c44 in remote_target::update_thread_list() (this=0x12c5440) at src/gdb/remote.c:3831
  #14 0x00000000007fb922 in remote_target::start_remote(int, int) (this=0x12c5440, from_tty=0, extended_p=0)
      at src/gdb/remote.c:4655
  #15 0x00000000007fd102 in remote_target::open_1(char const*, int, int) (name=0x1a4f45e "localhost:2346", from_tty=0, extended_p=0)
      at src/gdb/remote.c:5638
  #16 0x00000000007fbec1 in remote_target::open(char const*, int) (name=0x1a4f45e "localhost:2346", from_tty=0)
      at src/gdb/remote.c:4862

So on frame #10, we're marking a newly-discovered thread as running,
and that causes the Python API to emit a gdb.ContinueEvent.
gdb.ContinueEvent is a gdb.ThreadEvent, and as such includes the event
thread as the "inferior_thread" attribute.  The problem is that when
we get to frame #3/#4, we lost all references to the thread that is
being marked as running.  create_continue_event_object assumes that it
is the current thread, which is not true in this case.

Fix this by passing down the right thread in
create_continue_event_object.  Also remove
create_thread_event_object's default argument and have the only other
caller left pass down the right thread explicitly too.

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <palves@redhat.com>

	PR gdb/23379
	* python/py-continueevent.c: Include "gdbthread.h".
	(create_continue_event_object): Add intro comment.  Add 'ptid'
	parameter.  Use it to find thread to pass to
	create_thread_event_object.
	(emit_continue_event): Pass PTID down to
	create_continue_event_object.
	* python/py-event.h (py_get_event_thread): Declare.
	(create_thread_event_object): Remove default from 'thread'
	parameter.
	* python/py-stopevent.c (create_stop_event_object): Use
	py_get_event_thread.
	* python/py-threadevent.c (get_event_thread): Rename to ...
	(py_get_event_thread): ... this, and make extern.
	(create_thread_event_object): Assert that THREAD isn't null.
	Don't find the event thread here.
---
 gdb/python/py-continueevent.c | 31 ++++++++++++++++++++++++++++---
 gdb/python/py-event.h         | 12 +++++++++++-
 gdb/python/py-stopevent.c     |  2 +-
 gdb/python/py-threadevent.c   | 22 +++++-----------------
 4 files changed, 45 insertions(+), 22 deletions(-)

diff --git a/gdb/python/py-continueevent.c b/gdb/python/py-continueevent.c
index e5e922f0155..08d7da3cf2f 100644
--- a/gdb/python/py-continueevent.c
+++ b/gdb/python/py-continueevent.c
@@ -20,11 +20,36 @@
 #include "defs.h"
 #include "py-event.h"
 #include "py-ref.h"
+#include "gdbthread.h"
+
+/* Create a gdb.ContinueEvent event.  gdb.ContinueEvent is-a
+   gdb.ThreadEvent, and thread events can either be thread specific or
+   process wide.  If gdb is running in non-stop mode then the event is
+   thread specific (in which case the PTID thread is included in the
+   event), otherwise it is process wide (in which case PTID is
+   ignored).  In either case a borrowed reference is returned.  */
 
 static gdbpy_ref<>
-create_continue_event_object (void)
+create_continue_event_object (ptid_t ptid)
 {
-  return create_thread_event_object (&continue_event_object_type);
+  PyObject *py_thr = nullptr;
+
+  if (non_stop)
+    {
+      thread_info *thr = find_thread_ptid (ptid);
+      if (thr != nullptr)
+	py_thr = (PyObject *) thread_to_thread_object (thr);
+    }
+  else
+    py_thr = Py_None;
+
+  if (py_thr == nullptr)
+    {
+      PyErr_SetString (PyExc_RuntimeError, _("Could not find event thread"));
+      return nullptr;
+    }
+
+  return create_thread_event_object (&continue_event_object_type, py_thr);
 }
 
 /* Callback function which notifies observers when a continue event occurs.
@@ -37,7 +62,7 @@ emit_continue_event (ptid_t ptid)
   if (evregpy_no_listeners_p (gdb_py_events.cont))
     return 0;
 
-  gdbpy_ref<> event (create_continue_event_object ());
+  gdbpy_ref<> event (create_continue_event_object (ptid));
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.cont);
   return -1;
diff --git a/gdb/python/py-event.h b/gdb/python/py-event.h
index 22bab108ed1..7a9a51ddb1c 100644
--- a/gdb/python/py-event.h
+++ b/gdb/python/py-event.h
@@ -63,8 +63,18 @@ extern int evpy_emit_event (PyObject *event,
                             eventregistry_object *registry);
 
 extern gdbpy_ref<> create_event_object (PyTypeObject *py_type);
+
+/* thread events can either be thread specific or process wide.  If gdb is
+   running in non-stop mode then the event is thread specific, otherwise
+   it is process wide.
+   This function returns the currently stopped thread in non-stop mode and
+   Py_None otherwise.  In each case it returns a borrowed reference.  */
+extern PyObject *py_get_event_thread ()
+  CPYCHECKER_RETURNS_BORROWED_REF;
+
 extern gdbpy_ref<> create_thread_event_object (PyTypeObject *py_type,
-					       PyObject *thread = nullptr);
+					       PyObject *thread);
+
 extern int emit_new_objfile_event (struct objfile *objfile);
 extern int emit_clear_objfiles_event (void);
 
diff --git a/gdb/python/py-stopevent.c b/gdb/python/py-stopevent.c
index 884e6e3ef8f..33b65f99b80 100644
--- a/gdb/python/py-stopevent.c
+++ b/gdb/python/py-stopevent.c
@@ -23,7 +23,7 @@
 gdbpy_ref<>
 create_stop_event_object (PyTypeObject *py_type)
 {
-  return create_thread_event_object (py_type);
+  return create_thread_event_object (py_type, py_get_event_thread ());
 }
 
 /* Callback observers when a stop event occurs.  This function will create a
diff --git a/gdb/python/py-threadevent.c b/gdb/python/py-threadevent.c
index d6aa9467b9a..1a115bad801 100644
--- a/gdb/python/py-threadevent.c
+++ b/gdb/python/py-threadevent.c
@@ -20,17 +20,10 @@
 #include "infrun.h"
 #include "gdbthread.h"
 
-/* thread events can either be thread specific or process wide.  If gdb is
-   running in non-stop mode then the event is thread specific, otherwise
-   it is process wide.
-   This function returns the currently stopped thread in non-stop mode and
-   Py_None otherwise.  In each case it returns a borrowed reference.  */
+/* See py-event.h.  */
 
-static PyObject *get_event_thread (void)
-  CPYCHECKER_RETURNS_BORROWED_REF;
-
-static PyObject *
-get_event_thread (void)
+PyObject *
+py_get_event_thread ()
 {
   PyObject *thread;
 
@@ -51,17 +44,12 @@ get_event_thread (void)
 gdbpy_ref<>
 create_thread_event_object (PyTypeObject *py_type, PyObject *thread)
 {
+  gdb_assert (thread != NULL);
+
   gdbpy_ref<> thread_event_obj (create_event_object (py_type));
   if (thread_event_obj == NULL)
     return NULL;
 
-  if (thread == NULL)
-    {
-      thread = get_event_thread ();
-      if (!thread)
-	return NULL;
-    }
-
   if (evpy_add_attribute (thread_event_obj.get (),
                           "inferior_thread",
                           thread) < 0)
-- 
2.14.4

Re: [PATCH] Fix 8.2 regression in gdb.python/py-evthreads.exp w/ gdbserver (PR gdb/23379)

[Simon Marchi]

On 2018-08-24 01:46 PM, Pedro Alves wrote:
> This commit fixes a 8.1->8.2 regression exposed by
> gdb.python/py-evthreads.exp when testing with
> --target_board=native-gdbserver.
> 
> gdb.log shows:
> 
>   src/gdb/thread.c:93: internal-error: thread_info* inferior_thread(): Assertion `tp' failed.
>   A problem internal to GDB has been detected,
>   further debugging may prove unreliable.
>   Quit this debugging session? (y or n) FAIL: gdb.python/py-evthreads.exp: run to breakpoint 1 (GDB internal error)
> 
> A backtrace shows (frames #2 and #10 highlighted) that the assertion
> fails when GDB is setting up the connection to the remote target, in
> non-stop mode:
> 
>   #0  0x0000000000622ff0 in internal_error(char const*, int, char const*, ...) (file=0xc1ad98 "src/gdb/thread.c", line=93, fmt=0xc1ad20 "%s: Assertion `%s' failed.") at src/gdb/common/errors.c:54
>   #1  0x000000000089567e in inferior_thread() () at src/gdb/thread.c:93
> = #2  0x00000000004da91d in get_event_thread() () at src/gdb/python/py-threadevent.c:38
>   #3  0x00000000004da9b7 in create_thread_event_object(_typeobject*, _object*) (py_type=0x11574c0 <continue_event_object_type>, thread=0x0)
>       at src/gdb/python/py-threadevent.c:60
>   #4  0x00000000004bf6fe in create_continue_event_object() () at src/gdb/python/py-continueevent.c:27
>   #5  0x00000000004bf738 in emit_continue_event(ptid_t) (ptid=...) at src/gdb/python/py-continueevent.c:40
>   #6  0x00000000004c7d47 in python_on_resume(ptid_t) (ptid=...) at src/gdb/python/py-inferior.c:108
>   #7  0x0000000000485bfb in std::_Function_handler<void (ptid_t), void (*)(ptid_t)>::_M_invoke(std::_Any_data const&, ptid_t&&) (__functor=..., __args#0=...) at /usr/include/c++/7/bits/std_function.h:316
>   #8  0x000000000089b416 in std::function<void (ptid_t)>::operator()(ptid_t) const (this=0x12aa600, __args#0=...)
>       at /usr/include/c++/7/bits/std_function.h:706
>   #9  0x000000000089aa0e in gdb::observers::observable<ptid_t>::notify(ptid_t) const (this=0x118a7a0 <gdb::observers::target_resumed>, args#0=...)
>       at src/gdb/common/observable.h:106
> = #10 0x0000000000896fbe in set_running(ptid_t, int) (ptid=..., running=1) at src/gdb/thread.c:880
>   #11 0x00000000007f750f in remote_target::remote_add_thread(ptid_t, bool, bool) (this=0x12c5440, ptid=..., running=true, executing=true) at src/gdb/remote.c:2434
>   #12 0x00000000007f779d in remote_target::remote_notice_new_inferior(ptid_t, int) (this=0x12c5440, currthread=..., executing=1)
>       at src/gdb/remote.c:2515
>   #13 0x00000000007f9c44 in remote_target::update_thread_list() (this=0x12c5440) at src/gdb/remote.c:3831
>   #14 0x00000000007fb922 in remote_target::start_remote(int, int) (this=0x12c5440, from_tty=0, extended_p=0)
>       at src/gdb/remote.c:4655
>   #15 0x00000000007fd102 in remote_target::open_1(char const*, int, int) (name=0x1a4f45e "localhost:2346", from_tty=0, extended_p=0)
>       at src/gdb/remote.c:5638
>   #16 0x00000000007fbec1 in remote_target::open(char const*, int) (name=0x1a4f45e "localhost:2346", from_tty=0)
>       at src/gdb/remote.c:4862
> 
> So on frame #10, we're marking a newly-discovered thread as running,
> and that causes the Python API to emit a gdb.ContinueEvent.
> gdb.ContinueEvent is a gdb.ThreadEvent, and as such includes the event
> thread as the "inferior_thread" attribute.  The problem is that when
> we get to frame #3/#4, we lost all references to the thread that is
> being marked as running.  create_continue_event_object assumes that it
> is the current thread, which is not true in this case.
> 
> Fix this by passing down the right thread in
> create_continue_event_object.  Also remove
> create_thread_event_object's default argument and have the only other
> caller left pass down the right thread explicitly too.
> 
> gdb/ChangeLog:
> yyyy-mm-dd  Pedro Alves  <palves@redhat.com>
> 
> 	PR gdb/23379
> 	* python/py-continueevent.c: Include "gdbthread.h".
> 	(create_continue_event_object): Add intro comment.  Add 'ptid'
> 	parameter.  Use it to find thread to pass to
> 	create_thread_event_object.
> 	(emit_continue_event): Pass PTID down to
> 	create_continue_event_object.
> 	* python/py-event.h (py_get_event_thread): Declare.
> 	(create_thread_event_object): Remove default from 'thread'
> 	parameter.
> 	* python/py-stopevent.c (create_stop_event_object): Use
> 	py_get_event_thread.
> 	* python/py-threadevent.c (get_event_thread): Rename to ...
> 	(py_get_event_thread): ... this, and make extern.
> 	(create_thread_event_object): Assert that THREAD isn't null.
> 	Don't find the event thread here.
> ---
>  gdb/python/py-continueevent.c | 31 ++++++++++++++++++++++++++++---
>  gdb/python/py-event.h         | 12 +++++++++++-
>  gdb/python/py-stopevent.c     |  2 +-
>  gdb/python/py-threadevent.c   | 22 +++++-----------------
>  4 files changed, 45 insertions(+), 22 deletions(-)
> 
> diff --git a/gdb/python/py-continueevent.c b/gdb/python/py-continueevent.c
> index e5e922f0155..08d7da3cf2f 100644
> --- a/gdb/python/py-continueevent.c
> +++ b/gdb/python/py-continueevent.c
> @@ -20,11 +20,36 @@
>  #include "defs.h"
>  #include "py-event.h"
>  #include "py-ref.h"
> +#include "gdbthread.h"
> +
> +/* Create a gdb.ContinueEvent event.  gdb.ContinueEvent is-a
> +   gdb.ThreadEvent, and thread events can either be thread specific or
> +   process wide.  If gdb is running in non-stop mode then the event is
> +   thread specific (in which case the PTID thread is included in the
> +   event), otherwise it is process wide (in which case PTID is
> +   ignored).  In either case a borrowed reference is returned.  */

I think the last sentence is wrong.  If we are returning a gdbpy_ref, doesn't
mean we are returning an owning reference?  From what I understand, a borrowed
reference would be a naked pointer that you don't need to decref.

py_get_event_thread, from which this seems to have been copied from, does indeed
return a borrowed reference.

So it should say "a new reference is returned".

Ref: https://docs.python.org/3.7/c-api/intro.html, ctrl-f "borrow".

>  static gdbpy_ref<>
> -create_continue_event_object (void)
> +create_continue_event_object (ptid_t ptid)
>  {
> -  return create_thread_event_object (&continue_event_object_type);
> +  PyObject *py_thr = nullptr;
> +
> +  if (non_stop)
> +    {
> +      thread_info *thr = find_thread_ptid (ptid);
> +      if (thr != nullptr)
> +	py_thr = (PyObject *) thread_to_thread_object (thr);
> +    }
> +  else
> +    py_thr = Py_None;
> +
> +  if (py_thr == nullptr)
> +    {
> +      PyErr_SetString (PyExc_RuntimeError, _("Could not find event thread"));
> +      return nullptr;
> +    }
> +
> +  return create_thread_event_object (&continue_event_object_type, py_thr);

This and py_get_thread_event look very similar, could we use py_get_thread_event
from here?  See the patch at the end of the message.

>  }
>  
>  /* Callback function which notifies observers when a continue event occurs.
> @@ -37,7 +62,7 @@ emit_continue_event (ptid_t ptid)
>    if (evregpy_no_listeners_p (gdb_py_events.cont))
>      return 0;
>  
> -  gdbpy_ref<> event (create_continue_event_object ());
> +  gdbpy_ref<> event (create_continue_event_object (ptid));
>    if (event != NULL)
>      return evpy_emit_event (event.get (), gdb_py_events.cont);
>    return -1;
> diff --git a/gdb/python/py-event.h b/gdb/python/py-event.h
> index 22bab108ed1..7a9a51ddb1c 100644
> --- a/gdb/python/py-event.h
> +++ b/gdb/python/py-event.h
> @@ -63,8 +63,18 @@ extern int evpy_emit_event (PyObject *event,
>                              eventregistry_object *registry);
>  
>  extern gdbpy_ref<> create_event_object (PyTypeObject *py_type);
> +
> +/* thread events can either be thread specific or process wide.  If gdb is
> +   running in non-stop mode then the event is thread specific, otherwise
> +   it is process wide.
> +   This function returns the currently stopped thread in non-stop mode and
> +   Py_None otherwise.  In each case it returns a borrowed reference.  */
> +extern PyObject *py_get_event_thread ()
> +  CPYCHECKER_RETURNS_BORROWED_REF;
> +
>  extern gdbpy_ref<> create_thread_event_object (PyTypeObject *py_type,
> -					       PyObject *thread = nullptr);
> +					       PyObject *thread);
> +
>  extern int emit_new_objfile_event (struct objfile *objfile);
>  extern int emit_clear_objfiles_event (void);
>  
> diff --git a/gdb/python/py-stopevent.c b/gdb/python/py-stopevent.c
> index 884e6e3ef8f..33b65f99b80 100644
> --- a/gdb/python/py-stopevent.c
> +++ b/gdb/python/py-stopevent.c
> @@ -23,7 +23,7 @@
>  gdbpy_ref<>
>  create_stop_event_object (PyTypeObject *py_type)
>  {
> -  return create_thread_event_object (py_type);
> +  return create_thread_event_object (py_type, py_get_event_thread ());
>  }
>  
>  /* Callback observers when a stop event occurs.  This function will create a
> diff --git a/gdb/python/py-threadevent.c b/gdb/python/py-threadevent.c
> index d6aa9467b9a..1a115bad801 100644
> --- a/gdb/python/py-threadevent.c
> +++ b/gdb/python/py-threadevent.c
> @@ -20,17 +20,10 @@
>  #include "infrun.h"
>  #include "gdbthread.h"
>  
> -/* thread events can either be thread specific or process wide.  If gdb is
> -   running in non-stop mode then the event is thread specific, otherwise
> -   it is process wide.
> -   This function returns the currently stopped thread in non-stop mode and
> -   Py_None otherwise.  In each case it returns a borrowed reference.  */
> +/* See py-event.h.  */
>  
> -static PyObject *get_event_thread (void)
> -  CPYCHECKER_RETURNS_BORROWED_REF;
> -
> -static PyObject *
> -get_event_thread (void)
> +PyObject *
> +py_get_event_thread ()
>  {
>    PyObject *thread;
>  
> @@ -51,17 +44,12 @@ get_event_thread (void)
>  gdbpy_ref<>
>  create_thread_event_object (PyTypeObject *py_type, PyObject *thread)
>  {
> +  gdb_assert (thread != NULL);
> +
>    gdbpy_ref<> thread_event_obj (create_event_object (py_type));

You mentioned at some point that you preferred

  gdbpy_ref<> thread_event_obj = create_event_object (py_type);

over

  gdbpy_ref<> thread_event_obj (create_event_object (py_type));

(which I agree with).

>    if (thread_event_obj == NULL)
>      return NULL;
>  
> -  if (thread == NULL)
> -    {
> -      thread = get_event_thread ();
> -      if (!thread)
> -	return NULL;
> -    }
> -
>    if (evpy_add_attribute (thread_event_obj.get (),
>                            "inferior_thread",
>                            thread) < 0)
> 

Proposed changes:

From 6b789cb151b5160fca3e3c90d47fb921e3d7697e Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@ericsson.com>
Date: Fri, 24 Aug 2018 14:26:23 -0400
Subject: [PATCH] Use py_get_event_thread in create_continue_event_object

---
 gdb/python/py-continueevent.c | 18 +++---------------
 gdb/python/py-event.h         |  2 +-
 gdb/python/py-stopevent.c     |  3 ++-
 gdb/python/py-threadevent.c   | 16 ++++++++++------
 4 files changed, 16 insertions(+), 23 deletions(-)

diff --git a/gdb/python/py-continueevent.c b/gdb/python/py-continueevent.c
index 08d7da3..c011b71 100644
--- a/gdb/python/py-continueevent.c
+++ b/gdb/python/py-continueevent.c
@@ -32,22 +32,10 @@
 static gdbpy_ref<>
 create_continue_event_object (ptid_t ptid)
 {
-  PyObject *py_thr = nullptr;
-
-  if (non_stop)
-    {
-      thread_info *thr = find_thread_ptid (ptid);
-      if (thr != nullptr)
-	py_thr = (PyObject *) thread_to_thread_object (thr);
-    }
-  else
-    py_thr = Py_None;
+  PyObject *py_thr = py_get_event_thread (ptid);

   if (py_thr == nullptr)
-    {
-      PyErr_SetString (PyExc_RuntimeError, _("Could not find event thread"));
-      return nullptr;
-    }
+    return nullptr;

   return create_thread_event_object (&continue_event_object_type, py_thr);
 }
@@ -62,7 +50,7 @@ emit_continue_event (ptid_t ptid)
   if (evregpy_no_listeners_p (gdb_py_events.cont))
     return 0;

-  gdbpy_ref<> event (create_continue_event_object (ptid));
+  gdbpy_ref<> event = create_continue_event_object (ptid);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.cont);
   return -1;
diff --git a/gdb/python/py-event.h b/gdb/python/py-event.h
index 7a9a51d..56003e8 100644
--- a/gdb/python/py-event.h
+++ b/gdb/python/py-event.h
@@ -69,7 +69,7 @@ extern gdbpy_ref<> create_event_object (PyTypeObject *py_type);
    it is process wide.
    This function returns the currently stopped thread in non-stop mode and
    Py_None otherwise.  In each case it returns a borrowed reference.  */
-extern PyObject *py_get_event_thread ()
+extern PyObject *py_get_event_thread (ptid_t ptid)
   CPYCHECKER_RETURNS_BORROWED_REF;

 extern gdbpy_ref<> create_thread_event_object (PyTypeObject *py_type,
diff --git a/gdb/python/py-stopevent.c b/gdb/python/py-stopevent.c
index 33b65f9..f6bd207 100644
--- a/gdb/python/py-stopevent.c
+++ b/gdb/python/py-stopevent.c
@@ -23,7 +23,8 @@
 gdbpy_ref<>
 create_stop_event_object (PyTypeObject *py_type)
 {
-  return create_thread_event_object (py_type, py_get_event_thread ());
+  return create_thread_event_object (py_type,
+				     py_get_event_thread (inferior_ptid));
 }

 /* Callback observers when a stop event occurs.  This function will create a
diff --git a/gdb/python/py-threadevent.c b/gdb/python/py-threadevent.c
index 1a115ba..1bc2fb0 100644
--- a/gdb/python/py-threadevent.c
+++ b/gdb/python/py-threadevent.c
@@ -23,22 +23,26 @@
 /* See py-event.h.  */

 PyObject *
-py_get_event_thread ()
+py_get_event_thread (ptid_t ptid)
 {
-  PyObject *thread;
+  PyObject *pythread;

   if (non_stop)
-    thread = (PyObject *) thread_to_thread_object (inferior_thread ());
+    {
+      thread_info *thread = find_thread_ptid (ptid);
+      if (thread != nullptr)
+	pythread = (PyObject *) thread_to_thread_object (thread);
+    }
   else
-    thread = Py_None;
+    pythread = Py_None;

-  if (!thread)
+  if (!pythread)
     {
       PyErr_SetString (PyExc_RuntimeError, "Could not find event thread");
       return NULL;
     }

-  return thread;
+  return pythread;
 }

 gdbpy_ref<>
-- 
2.7.4

[PATCH v2] Fix 8.2 regression in gdb.python/py-evthreads.exp w/ gdbserver (PR gdb/23379)

[Pedro Alves]

On 08/24/2018 07:52 PM, Simon Marchi wrote:
> On 2018-08-24 01:46 PM, Pedro Alves wrote:

> I think the last sentence is wrong.  If we are returning a gdbpy_ref, doesn't
> mean we are returning an owning reference?  From what I understand, a borrowed
> reference would be a naked pointer that you don't need to decref.
> 
> py_get_event_thread, from which this seems to have been copied from, does indeed
> return a borrowed reference.
> 
> So it should say "a new reference is returned".
> 
> Ref: https://docs.python.org/3.7/c-api/intro.html, ctrl-f "borrow".

Whoops, yes, blind copy&paste.  Fixed.

> This and py_get_thread_event look very similar, could we use py_get_thread_event
> from here?  See the patch at the end of the message.

I like it!

> 
>>  }
>>  
>>  /* Callback function which notifies observers when a continue event occurs.
>> @@ -37,7 +62,7 @@ emit_continue_event (ptid_t ptid)
>>    if (evregpy_no_listeners_p (gdb_py_events.cont))
>>      return 0;
>>  
>> -  gdbpy_ref<> event (create_continue_event_object ());
>> +  gdbpy_ref<> event (create_continue_event_object (ptid));

*see below*

>> @@ -51,17 +44,12 @@ get_event_thread (void)
>>  gdbpy_ref<>
>>  create_thread_event_object (PyTypeObject *py_type, PyObject *thread)
>>  {
>> +  gdb_assert (thread != NULL);
>> +
>>    gdbpy_ref<> thread_event_obj (create_event_object (py_type));
> 
> You mentioned at some point that you preferred
> 
>   gdbpy_ref<> thread_event_obj = create_event_object (py_type);
> 
> over
> 
>   gdbpy_ref<> thread_event_obj (create_event_object (py_type));
> 
> (which I agree with).

I guess you may have wanted to quote the other hunk above,
since I didn't touch that line.

Yeah, I definitely prefer copy-init when possible.  In this
case I'd prefer doing that as a separate patch though, because
that's not something that the regression fix is adding, and
also grepping around I see there's a lot of similar instances
that can all get the same treatment.  I'll post a patch
for that as follow up.

> Proposed changes:
> 

Here's the two patches combined.  Should I merge it?

From aa0125e4c1fe4021aa4087cec5324ecc829c7fc3 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Fri, 24 Aug 2018 20:03:57 +0100
Subject: [PATCH] Fix 8.2 regression in gdb.python/py-evthreads.exp w/
 gdbserver (PR gdb/23379)

This commit fixes a 8.1->8.2 regression exposed by
gdb.python/py-evthreads.exp when testing with
--target_board=native-gdbserver.

gdb.log shows:

  src/gdb/thread.c:93: internal-error: thread_info* inferior_thread(): Assertion `tp' failed.
  A problem internal to GDB has been detected,
  further debugging may prove unreliable.
  Quit this debugging session? (y or n) FAIL: gdb.python/py-evthreads.exp: run to breakpoint 1 (GDB internal error)

A backtrace shows (frames #2 and #10 highlighted) that the assertion
fails when GDB is setting up the connection to the remote target, in
non-stop mode:

  #0  0x0000000000622ff0 in internal_error(char const*, int, char const*, ...) (file=0xc1ad98 "src/gdb/thread.c", line=93, fmt=0xc1ad20 "%s: Assertion `%s' failed.") at src/gdb/common/errors.c:54
  #1  0x000000000089567e in inferior_thread() () at src/gdb/thread.c:93
= #2  0x00000000004da91d in get_event_thread() () at src/gdb/python/py-threadevent.c:38
  #3  0x00000000004da9b7 in create_thread_event_object(_typeobject*, _object*) (py_type=0x11574c0 <continue_event_object_type>, thread=0x0)
      at src/gdb/python/py-threadevent.c:60
  #4  0x00000000004bf6fe in create_continue_event_object() () at src/gdb/python/py-continueevent.c:27
  #5  0x00000000004bf738 in emit_continue_event(ptid_t) (ptid=...) at src/gdb/python/py-continueevent.c:40
  #6  0x00000000004c7d47 in python_on_resume(ptid_t) (ptid=...) at src/gdb/python/py-inferior.c:108
  #7  0x0000000000485bfb in std::_Function_handler<void (ptid_t), void (*)(ptid_t)>::_M_invoke(std::_Any_data const&, ptid_t&&) (__functor=..., __args#0=...) at /usr/include/c++/7/bits/std_function.h:316
  #8  0x000000000089b416 in std::function<void (ptid_t)>::operator()(ptid_t) const (this=0x12aa600, __args#0=...)
      at /usr/include/c++/7/bits/std_function.h:706
  #9  0x000000000089aa0e in gdb::observers::observable<ptid_t>::notify(ptid_t) const (this=0x118a7a0 <gdb::observers::target_resumed>, args#0=...)
      at src/gdb/common/observable.h:106
= #10 0x0000000000896fbe in set_running(ptid_t, int) (ptid=..., running=1) at src/gdb/thread.c:880
  #11 0x00000000007f750f in remote_target::remote_add_thread(ptid_t, bool, bool) (this=0x12c5440, ptid=..., running=true, executing=true) at src/gdb/remote.c:2434
  #12 0x00000000007f779d in remote_target::remote_notice_new_inferior(ptid_t, int) (this=0x12c5440, currthread=..., executing=1)
      at src/gdb/remote.c:2515
  #13 0x00000000007f9c44 in remote_target::update_thread_list() (this=0x12c5440) at src/gdb/remote.c:3831
  #14 0x00000000007fb922 in remote_target::start_remote(int, int) (this=0x12c5440, from_tty=0, extended_p=0)
      at src/gdb/remote.c:4655
  #15 0x00000000007fd102 in remote_target::open_1(char const*, int, int) (name=0x1a4f45e "localhost:2346", from_tty=0, extended_p=0)
      at src/gdb/remote.c:5638
  #16 0x00000000007fbec1 in remote_target::open(char const*, int) (name=0x1a4f45e "localhost:2346", from_tty=0)
      at src/gdb/remote.c:4862

So on frame #10, we're marking a newly-discovered thread as running,
and that causes the Python API to emit a gdb.ContinueEvent.
gdb.ContinueEvent is a gdb.ThreadEvent, and as such includes the event
thread as the "inferior_thread" attribute.  The problem is that when
we get to frame #3/#4, we lost all references to the thread that is
being marked as running.  create_continue_event_object assumes that it
is the current thread, which is not true in this case.

Fix this by passing down the right thread in
create_continue_event_object.  Also remove
create_thread_event_object's default argument and have the only other
caller left pass down the right thread explicitly too.

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <palves@redhat.com>
	    Simon Marchi  <simon.marchi@ericsson.com>

	PR gdb/23379
	* python/py-continueevent.c: Include "gdbthread.h".
	(create_continue_event_object): Add intro comment.  Add 'ptid'
	parameter.  Use it to find thread to pass to
	create_thread_event_object.
	(emit_continue_event): Pass PTID down to
	create_continue_event_object.
	* python/py-event.h (py_get_event_thread): Declare.
	(create_thread_event_object): Remove default from 'thread'
	parameter.
	* python/py-stopevent.c (create_stop_event_object): Use
	py_get_event_thread.
	* python/py-threadevent.c (get_event_thread): Rename to ...
	(py_get_event_thread): ... this, make extern, add 'ptid' parameter
	and use it to find the thread.
	(create_thread_event_object): Assert that THREAD isn't null.
	Don't find the event thread here.
---
 gdb/python/py-continueevent.c | 19 ++++++++++++++++---
 gdb/python/py-event.h         | 12 +++++++++++-
 gdb/python/py-stopevent.c     |  3 ++-
 gdb/python/py-threadevent.c   | 36 ++++++++++++++----------------------
 4 files changed, 43 insertions(+), 27 deletions(-)

diff --git a/gdb/python/py-continueevent.c b/gdb/python/py-continueevent.c
index e5e922f0155..b047a83522b 100644
--- a/gdb/python/py-continueevent.c
+++ b/gdb/python/py-continueevent.c
@@ -20,11 +20,24 @@
 #include "defs.h"
 #include "py-event.h"
 #include "py-ref.h"
+#include "gdbthread.h"
+
+/* Create a gdb.ContinueEvent event.  gdb.ContinueEvent is-a
+   gdb.ThreadEvent, and thread events can either be thread specific or
+   process wide.  If gdb is running in non-stop mode then the event is
+   thread specific (in which case the PTID thread is included in the
+   event), otherwise it is process wide (in which case PTID is
+   ignored).  In either case a new reference is returned.  */
 
 static gdbpy_ref<>
-create_continue_event_object (void)
+create_continue_event_object (ptid_t ptid)
 {
-  return create_thread_event_object (&continue_event_object_type);
+  PyObject *py_thr = py_get_event_thread (ptid);
+
+  if (py_thr == nullptr)
+    return nullptr;
+
+  return create_thread_event_object (&continue_event_object_type, py_thr);
 }
 
 /* Callback function which notifies observers when a continue event occurs.
@@ -37,7 +50,7 @@ emit_continue_event (ptid_t ptid)
   if (evregpy_no_listeners_p (gdb_py_events.cont))
     return 0;
 
-  gdbpy_ref<> event (create_continue_event_object ());
+  gdbpy_ref<> event (create_continue_event_object (ptid));
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.cont);
   return -1;
diff --git a/gdb/python/py-event.h b/gdb/python/py-event.h
index 22bab108ed1..56003e8785f 100644
--- a/gdb/python/py-event.h
+++ b/gdb/python/py-event.h
@@ -63,8 +63,18 @@ extern int evpy_emit_event (PyObject *event,
                             eventregistry_object *registry);
 
 extern gdbpy_ref<> create_event_object (PyTypeObject *py_type);
+
+/* thread events can either be thread specific or process wide.  If gdb is
+   running in non-stop mode then the event is thread specific, otherwise
+   it is process wide.
+   This function returns the currently stopped thread in non-stop mode and
+   Py_None otherwise.  In each case it returns a borrowed reference.  */
+extern PyObject *py_get_event_thread (ptid_t ptid)
+  CPYCHECKER_RETURNS_BORROWED_REF;
+
 extern gdbpy_ref<> create_thread_event_object (PyTypeObject *py_type,
-					       PyObject *thread = nullptr);
+					       PyObject *thread);
+
 extern int emit_new_objfile_event (struct objfile *objfile);
 extern int emit_clear_objfiles_event (void);
 
diff --git a/gdb/python/py-stopevent.c b/gdb/python/py-stopevent.c
index 884e6e3ef8f..f6bd207f3b8 100644
--- a/gdb/python/py-stopevent.c
+++ b/gdb/python/py-stopevent.c
@@ -23,7 +23,8 @@
 gdbpy_ref<>
 create_stop_event_object (PyTypeObject *py_type)
 {
-  return create_thread_event_object (py_type);
+  return create_thread_event_object (py_type,
+				     py_get_event_thread (inferior_ptid));
 }
 
 /* Callback observers when a stop event occurs.  This function will create a
diff --git a/gdb/python/py-threadevent.c b/gdb/python/py-threadevent.c
index d6aa9467b9a..1bc2fb06d54 100644
--- a/gdb/python/py-threadevent.c
+++ b/gdb/python/py-threadevent.c
@@ -20,48 +20,40 @@
 #include "infrun.h"
 #include "gdbthread.h"
 
-/* thread events can either be thread specific or process wide.  If gdb is
-   running in non-stop mode then the event is thread specific, otherwise
-   it is process wide.
-   This function returns the currently stopped thread in non-stop mode and
-   Py_None otherwise.  In each case it returns a borrowed reference.  */
+/* See py-event.h.  */
 
-static PyObject *get_event_thread (void)
-  CPYCHECKER_RETURNS_BORROWED_REF;
-
-static PyObject *
-get_event_thread (void)
+PyObject *
+py_get_event_thread (ptid_t ptid)
 {
-  PyObject *thread;
+  PyObject *pythread;
 
   if (non_stop)
-    thread = (PyObject *) thread_to_thread_object (inferior_thread ());
+    {
+      thread_info *thread = find_thread_ptid (ptid);
+      if (thread != nullptr)
+	pythread = (PyObject *) thread_to_thread_object (thread);
+    }
   else
-    thread = Py_None;
+    pythread = Py_None;
 
-  if (!thread)
+  if (!pythread)
     {
       PyErr_SetString (PyExc_RuntimeError, "Could not find event thread");
       return NULL;
     }
 
-  return thread;
+  return pythread;
 }
 
 gdbpy_ref<>
 create_thread_event_object (PyTypeObject *py_type, PyObject *thread)
 {
+  gdb_assert (thread != NULL);
+
   gdbpy_ref<> thread_event_obj (create_event_object (py_type));
   if (thread_event_obj == NULL)
     return NULL;
 
-  if (thread == NULL)
-    {
-      thread = get_event_thread ();
-      if (!thread)
-	return NULL;
-    }
-
   if (evpy_add_attribute (thread_event_obj.get (),
                           "inferior_thread",
                           thread) < 0)
-- 
2.14.4

Re: [PATCH v2] Fix 8.2 regression in gdb.python/py-evthreads.exp w/ gdbserver (PR gdb/23379)

[Pedro Alves]

On 08/24/2018 08:44 PM, Pedro Alves wrote:

> 
> Yeah, I definitely prefer copy-init when possible.  In this
> case I'd prefer doing that as a separate patch though, because
> that's not something that the regression fix is adding, and
> also grepping around I see there's a lot of similar instances
> that can all get the same treatment.  I'll post a patch
> for that as follow up.
Here's what I mean.

From bc3b8da0180c6ef782d3e38109b6bcb49b3664e1 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Fri, 24 Aug 2018 20:09:19 +0100
Subject: [PATCH] use copy-init more

---
 gdb/python/py-bpevent.c         |  2 +-
 gdb/python/py-continueevent.c   |  2 +-
 gdb/python/py-exitedevent.c     |  8 ++++----
 gdb/python/py-inferior.c        |  8 ++++----
 gdb/python/py-infevents.c       | 22 +++++++++++-----------
 gdb/python/py-newobjfileevent.c | 24 ++++++++++--------------
 gdb/python/py-signalevent.c     |  5 ++---
 gdb/python/py-threadevent.c     |  2 +-
 8 files changed, 34 insertions(+), 39 deletions(-)

diff --git a/gdb/python/py-bpevent.c b/gdb/python/py-bpevent.c
index 03863e4c9a2..f6f3c4c2378 100644
--- a/gdb/python/py-bpevent.c
+++ b/gdb/python/py-bpevent.c
@@ -28,7 +28,7 @@ gdbpy_ref<>
 create_breakpoint_event_object (PyObject *breakpoint_list, PyObject *first_bp)
 {
   gdbpy_ref<> breakpoint_event_obj
-    (create_stop_event_object (&breakpoint_event_object_type));
+    = create_stop_event_object (&breakpoint_event_object_type);
 
   if (breakpoint_event_obj == NULL)
     return NULL;
diff --git a/gdb/python/py-continueevent.c b/gdb/python/py-continueevent.c
index b047a83522b..759b4831366 100644
--- a/gdb/python/py-continueevent.c
+++ b/gdb/python/py-continueevent.c
@@ -50,7 +50,7 @@ emit_continue_event (ptid_t ptid)
   if (evregpy_no_listeners_p (gdb_py_events.cont))
     return 0;
 
-  gdbpy_ref<> event (create_continue_event_object (ptid));
+  gdbpy_ref<> event = create_continue_event_object (ptid);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.cont);
   return -1;
diff --git a/gdb/python/py-exitedevent.c b/gdb/python/py-exitedevent.c
index 6a7c9f51fa1..22c095c7c79 100644
--- a/gdb/python/py-exitedevent.c
+++ b/gdb/python/py-exitedevent.c
@@ -20,10 +20,10 @@
 #include "defs.h"
 #include "py-event.h"
 
-static PyObject *
+static gdbpy_ref<>
 create_exited_event_object (const LONGEST *exit_code, struct inferior *inf)
 {
-  gdbpy_ref<> exited_event (create_event_object (&exited_event_object_type));
+  gdbpy_ref<> exited_event = create_event_object (&exited_event_object_type);
 
   if (exited_event == NULL)
     return NULL;
@@ -45,7 +45,7 @@ create_exited_event_object (const LONGEST *exit_code, struct inferior *inf)
 					     (PyObject *) inf_obj.get ()) < 0)
     return NULL;
 
-  return exited_event.release ();
+  return exited_event;
 }
 
 /* Callback that is used when an exit event occurs.  This function
@@ -57,7 +57,7 @@ emit_exited_event (const LONGEST *exit_code, struct inferior *inf)
   if (evregpy_no_listeners_p (gdb_py_events.exited))
     return 0;
 
-  gdbpy_ref<> event (create_exited_event_object (exit_code, inf));
+  gdbpy_ref<> event = create_exited_event_object (exit_code, inf);
 
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.exited);
diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c
index 9f09ae93756..1cf37296973 100644
--- a/gdb/python/py-inferior.c
+++ b/gdb/python/py-inferior.c
@@ -256,7 +256,7 @@ python_new_inferior (struct inferior *inf)
       return;
     }
 
-  gdbpy_ref<> event (create_event_object (&new_inferior_event_object_type));
+  gdbpy_ref<> event = create_event_object (&new_inferior_event_object_type);
   if (event == NULL
       || evpy_add_attribute (event.get (), "inferior",
 			     (PyObject *) inf_obj.get ()) < 0
@@ -284,7 +284,7 @@ python_inferior_deleted (struct inferior *inf)
       return;
     }
 
-  gdbpy_ref<> event (create_event_object (&inferior_deleted_event_object_type));
+  gdbpy_ref<> event = create_event_object (&inferior_deleted_event_object_type);
   if (event == NULL
       || evpy_add_attribute (event.get (), "inferior",
 			     (PyObject *) inf_obj.get ()) < 0
@@ -353,8 +353,8 @@ add_thread_object (struct thread_info *tp)
   if (evregpy_no_listeners_p (gdb_py_events.new_thread))
     return;
 
-  gdbpy_ref<> event (create_thread_event_object (&new_thread_event_object_type,
-						 (PyObject *) thread_obj));
+  gdbpy_ref<> event = create_thread_event_object (&new_thread_event_object_type,
+						  (PyObject *) thread_obj);
   if (event == NULL
       || evpy_emit_event (event.get (), gdb_py_events.new_thread) < 0)
     gdbpy_print_stack ();
diff --git a/gdb/python/py-infevents.c b/gdb/python/py-infevents.c
index 2bd0bc7f2c4..0df7d96df30 100644
--- a/gdb/python/py-infevents.c
+++ b/gdb/python/py-infevents.c
@@ -24,7 +24,7 @@
 /* Construct either a gdb.InferiorCallPreEvent or a
    gdb.InferiorCallPostEvent. */
 
-static PyObject *
+static gdbpy_ref<>
 create_inferior_call_event_object (inferior_call_kind flag, ptid_t ptid,
 				   CORE_ADDR addr)
 {
@@ -56,17 +56,17 @@ create_inferior_call_event_object (inferior_call_kind flag, ptid_t ptid,
   if (evpy_add_attribute (event.get (), "address", addr_obj.get ()) < 0)
     return NULL;
 
-  return event.release ();
+  return event;
 }
 
 /* Construct a gdb.RegisterChangedEvent containing the affected
    register number. */
 
-static PyObject *
+static gdbpy_ref<>
 create_register_changed_event_object (struct frame_info *frame, 
 				      int regnum)
 {
-  gdbpy_ref<> event (create_event_object (&register_changed_event_object_type));
+  gdbpy_ref<> event = create_event_object (&register_changed_event_object_type);
   if (event == NULL)
     return NULL;
 
@@ -84,16 +84,16 @@ create_register_changed_event_object (struct frame_info *frame,
   if (evpy_add_attribute (event.get (), "regnum", regnum_obj.get ()) < 0)
     return NULL;
 
-  return event.release ();
+  return event;
 }
 
 /* Construct a gdb.MemoryChangedEvent describing the extent of the
    affected memory. */
 
-static PyObject *
+static gdbpy_ref<>
 create_memory_changed_event_object (CORE_ADDR addr, ssize_t len)
 {
-  gdbpy_ref<> event (create_event_object (&memory_changed_event_object_type));
+  gdbpy_ref<> event = create_event_object (&memory_changed_event_object_type);
 
   if (event == NULL)
     return NULL;
@@ -112,7 +112,7 @@ create_memory_changed_event_object (CORE_ADDR addr, ssize_t len)
   if (evpy_add_attribute (event.get (), "length", len_obj.get ()) < 0)
     return NULL;
 
-  return event.release ();
+  return event;
 }
 
 /* Callback function which notifies observers when an event occurs which
@@ -127,7 +127,7 @@ emit_inferior_call_event (inferior_call_kind flag, ptid_t thread,
   if (evregpy_no_listeners_p (gdb_py_events.inferior_call))
     return 0;
 
-  gdbpy_ref<> event (create_inferior_call_event_object (flag, thread, addr));
+  gdbpy_ref<> event = create_inferior_call_event_object (flag, thread, addr);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.inferior_call);
   return -1;
@@ -142,7 +142,7 @@ emit_memory_changed_event (CORE_ADDR addr, ssize_t len)
   if (evregpy_no_listeners_p (gdb_py_events.memory_changed))
     return 0;
 
-  gdbpy_ref<> event (create_memory_changed_event_object (addr, len));
+  gdbpy_ref<> event = create_memory_changed_event_object (addr, len);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.memory_changed);
   return -1;
@@ -157,7 +157,7 @@ emit_register_changed_event (struct frame_info* frame, int regnum)
   if (evregpy_no_listeners_p (gdb_py_events.register_changed))
     return 0;
 
-  gdbpy_ref<> event (create_register_changed_event_object (frame, regnum));
+  gdbpy_ref<> event = create_register_changed_event_object (frame, regnum);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.register_changed);
   return -1;
diff --git a/gdb/python/py-newobjfileevent.c b/gdb/python/py-newobjfileevent.c
index 86de9ac10ad..a9341a3be18 100644
--- a/gdb/python/py-newobjfileevent.c
+++ b/gdb/python/py-newobjfileevent.c
@@ -20,25 +20,23 @@
 #include "defs.h"
 #include "py-event.h"
 
-static PyObject *
+static gdbpy_ref<>
 create_new_objfile_event_object (struct objfile *objfile)
 {
-  PyObject *py_objfile;
-
   gdbpy_ref<> objfile_event
-    (create_event_object (&new_objfile_event_object_type));
+    = create_event_object (&new_objfile_event_object_type);
   if (objfile_event == NULL)
     return NULL;
 
   /* Note that objfile_to_objfile_object returns a borrowed reference,
      so we don't need a decref here.  */
-  py_objfile = objfile_to_objfile_object (objfile);
+  PyObject *py_objfile = objfile_to_objfile_object (objfile);
   if (!py_objfile || evpy_add_attribute (objfile_event.get (),
                                          "new_objfile",
                                          py_objfile) < 0)
     return NULL;
 
-  return objfile_event.release ();
+  return objfile_event;
 }
 
 /* Callback function which notifies observers when a new objfile event occurs.
@@ -51,7 +49,7 @@ emit_new_objfile_event (struct objfile *objfile)
   if (evregpy_no_listeners_p (gdb_py_events.new_objfile))
     return 0;
 
-  gdbpy_ref<> event (create_new_objfile_event_object (objfile));
+  gdbpy_ref<> event = create_new_objfile_event_object (objfile);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.new_objfile);
   return -1;
@@ -60,25 +58,23 @@ emit_new_objfile_event (struct objfile *objfile)
 \f
 /* Subroutine of emit_clear_objfiles_event to simplify it.  */
 
-static PyObject *
+static gdbpy_ref<>
 create_clear_objfiles_event_object (void)
 {
-  PyObject *py_progspace;
-
   gdbpy_ref<> objfile_event
-    (create_event_object (&clear_objfiles_event_object_type));
+    = create_event_object (&clear_objfiles_event_object_type);
   if (objfile_event == NULL)
     return NULL;
 
   /* Note that pspace_to_pspace_object returns a borrowed reference,
      so we don't need a decref here.  */
-  py_progspace = pspace_to_pspace_object (current_program_space);
+  PyObject *py_progspace = pspace_to_pspace_object (current_program_space);
   if (!py_progspace || evpy_add_attribute (objfile_event.get (),
 					   "progspace",
 					   py_progspace) < 0)
     return NULL;
 
-  return objfile_event.release ();
+  return objfile_event;
 }
 
 /* Callback function which notifies observers when the "clear objfiles"
@@ -92,7 +88,7 @@ emit_clear_objfiles_event (void)
   if (evregpy_no_listeners_p (gdb_py_events.clear_objfiles))
     return 0;
 
-  gdbpy_ref<> event (create_clear_objfiles_event_object ());
+  gdbpy_ref<> event = create_clear_objfiles_event_object ();
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.clear_objfiles);
   return -1;
diff --git a/gdb/python/py-signalevent.c b/gdb/python/py-signalevent.c
index d88aaeaedea..a2e7519460c 100644
--- a/gdb/python/py-signalevent.c
+++ b/gdb/python/py-signalevent.c
@@ -23,14 +23,13 @@
 gdbpy_ref<>
 create_signal_event_object (enum gdb_signal stop_signal)
 {
-  const char *signal_name;
   gdbpy_ref<> signal_event_obj
-    (create_stop_event_object (&signal_event_object_type));
+    = create_stop_event_object (&signal_event_object_type);
 
   if (signal_event_obj == NULL)
     return NULL;
 
-  signal_name = gdb_signal_to_name (stop_signal);
+  const char *signal_name = gdb_signal_to_name (stop_signal);
 
   gdbpy_ref<> signal_name_obj (PyString_FromString (signal_name));
   if (signal_name_obj == NULL)
diff --git a/gdb/python/py-threadevent.c b/gdb/python/py-threadevent.c
index 1bc2fb06d54..a78f0a38310 100644
--- a/gdb/python/py-threadevent.c
+++ b/gdb/python/py-threadevent.c
@@ -50,7 +50,7 @@ create_thread_event_object (PyTypeObject *py_type, PyObject *thread)
 {
   gdb_assert (thread != NULL);
 
-  gdbpy_ref<> thread_event_obj (create_event_object (py_type));
+  gdbpy_ref<> thread_event_obj = create_event_object (py_type);
   if (thread_event_obj == NULL)
     return NULL;
 
-- 
2.14.4

Re: [PATCH v2] Fix 8.2 regression in gdb.python/py-evthreads.exp w/ gdbserver (PR gdb/23379)

[Simon Marchi]

On 2018-08-24 15:44, Pedro Alves wrote:
> Here's the two patches combined.  Should I merge it?

LGTM, thanks!

Simon

Re: [PATCH v2] Fix 8.2 regression in gdb.python/py-evthreads.exp w/ gdbserver (PR gdb/23379)

[Simon Marchi]

On 2018-08-24 15:47, Pedro Alves wrote:
> On 08/24/2018 08:44 PM, Pedro Alves wrote:
> 
>> 
>> Yeah, I definitely prefer copy-init when possible.  In this
>> case I'd prefer doing that as a separate patch though, because
>> that's not something that the regression fix is adding, and
>> also grepping around I see there's a lot of similar instances
>> that can all get the same treatment.  I'll post a patch
>> for that as follow up.
> Here's what I mean.

Indeed, in the previous patch I just meant you could change the line you 
were touching (and indeed quoted the wrong hunk), but this more 
far-reaching cleanup is great too.  I wouldn't put this one in the 8.2 
branch though, since it doesn't actually fix anything.

Simon

[pushed] gdb/python: Use copy-initialization more when possible

[Pedro Alves]

On 08/24/2018 09:06 PM, Simon Marchi wrote:
> On 2018-08-24 15:47, Pedro Alves wrote:
>> On 08/24/2018 08:44 PM, Pedro Alves wrote:
>>
>>>
>>> Yeah, I definitely prefer copy-init when possible.  In this
>>> case I'd prefer doing that as a separate patch though, because
>>> that's not something that the regression fix is adding, and
>>> also grepping around I see there's a lot of similar instances
>>> that can all get the same treatment.  I'll post a patch
>>> for that as follow up.
>> Here's what I mean.
> 
> Indeed, in the previous patch I just meant you could change the line you were touching (and indeed quoted the wrong hunk), but this more far-reaching cleanup is great too.  I wouldn't put this one in the 8.2 branch though, since it doesn't actually fix anything.

Agreed.  I've merged this to master now.

From d98fc15be2b8dd5699c1852db7d9d979231123dc Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Fri, 24 Aug 2018 20:09:19 +0100
Subject: [PATCH] gdb/python: Use copy-initialization more when possible

gdb/ChangeLog:
2018-08-24  Pedro Alves  <palves@redhat.com>

	* python/py-bpevent.c (create_breakpoint_event_object): Use
	copy-initialization.
	* python/py-continueevent.c (emit_continue_event): Use
	copy-initialization.
	* python/py-exitedevent.c (create_exited_event_object): Return a
	gdbpy_ref<>.
	(emit_exited_event): Use copy-initialization.
	* python/py-inferior.c (python_new_inferior)
	(python_inferior_deleted, add_thread_object): Use
	copy-initialization.
	* python/py-infevents.c (create_inferior_call_event_object)
	(create_register_changed_event_object)
	(create_memory_changed_event_object): Return a gdbpy_ref<>.
	(emit_inferior_call_event, emit_memory_changed_event)
	(emit_register_changed_event): Use copy-initialization.
	* python/py-newobjfileevent.c (create_new_objfile_event_object):
	Return a gdbpy_ref<>.
	(emit_new_objfile_event): Use copy-initialization.
	(create_clear_objfiles_event_object): Return a gdbpy_ref<>.
	(emit_clear_objfiles_event): Use copy-initialization.
	* python/py-signalevent.c (create_signal_event_object): Use
	copy-initialization.
	* python/py-threadevent.c (create_thread_event_object): Use
	copy-initialization.
---
 gdb/ChangeLog                   | 27 +++++++++++++++++++++++++++
 gdb/python/py-bpevent.c         |  2 +-
 gdb/python/py-continueevent.c   |  2 +-
 gdb/python/py-exitedevent.c     |  8 ++++----
 gdb/python/py-inferior.c        |  8 ++++----
 gdb/python/py-infevents.c       | 22 +++++++++++-----------
 gdb/python/py-newobjfileevent.c | 24 ++++++++++--------------
 gdb/python/py-signalevent.c     |  5 ++---
 gdb/python/py-threadevent.c     |  2 +-
 9 files changed, 61 insertions(+), 39 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index e1bdd392b1b..12dda6c541d 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,30 @@
+2018-08-24  Pedro Alves  <palves@redhat.com>
+
+	* python/py-bpevent.c (create_breakpoint_event_object): Use
+	copy-initialization.
+	* python/py-continueevent.c (emit_continue_event): Use
+	copy-initialization.
+	* python/py-exitedevent.c (create_exited_event_object): Return a
+	gdbpy_ref<>.
+	(emit_exited_event): Use copy-initialization.
+	* python/py-inferior.c (python_new_inferior)
+	(python_inferior_deleted, add_thread_object): Use
+	copy-initialization.
+	* python/py-infevents.c (create_inferior_call_event_object)
+	(create_register_changed_event_object)
+	(create_memory_changed_event_object): Return a gdbpy_ref<>.
+	(emit_inferior_call_event, emit_memory_changed_event)
+	(emit_register_changed_event): Use copy-initialization.
+	* python/py-newobjfileevent.c (create_new_objfile_event_object):
+	Return a gdbpy_ref<>.
+	(emit_new_objfile_event): Use copy-initialization.
+	(create_clear_objfiles_event_object): Return a gdbpy_ref<>.
+	(emit_clear_objfiles_event): Use copy-initialization.
+	* python/py-signalevent.c (create_signal_event_object): Use
+	copy-initialization.
+	* python/py-threadevent.c (create_thread_event_object): Use
+	copy-initialization.
+
 2018-08-24  Pedro Alves  <palves@redhat.com>
 	    Simon Marchi  <simon.marchi@ericsson.com>
 
diff --git a/gdb/python/py-bpevent.c b/gdb/python/py-bpevent.c
index 03863e4c9a2..f6f3c4c2378 100644
--- a/gdb/python/py-bpevent.c
+++ b/gdb/python/py-bpevent.c
@@ -28,7 +28,7 @@ gdbpy_ref<>
 create_breakpoint_event_object (PyObject *breakpoint_list, PyObject *first_bp)
 {
   gdbpy_ref<> breakpoint_event_obj
-    (create_stop_event_object (&breakpoint_event_object_type));
+    = create_stop_event_object (&breakpoint_event_object_type);
 
   if (breakpoint_event_obj == NULL)
     return NULL;
diff --git a/gdb/python/py-continueevent.c b/gdb/python/py-continueevent.c
index b047a83522b..759b4831366 100644
--- a/gdb/python/py-continueevent.c
+++ b/gdb/python/py-continueevent.c
@@ -50,7 +50,7 @@ emit_continue_event (ptid_t ptid)
   if (evregpy_no_listeners_p (gdb_py_events.cont))
     return 0;
 
-  gdbpy_ref<> event (create_continue_event_object (ptid));
+  gdbpy_ref<> event = create_continue_event_object (ptid);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.cont);
   return -1;
diff --git a/gdb/python/py-exitedevent.c b/gdb/python/py-exitedevent.c
index 6a7c9f51fa1..22c095c7c79 100644
--- a/gdb/python/py-exitedevent.c
+++ b/gdb/python/py-exitedevent.c
@@ -20,10 +20,10 @@
 #include "defs.h"
 #include "py-event.h"
 
-static PyObject *
+static gdbpy_ref<>
 create_exited_event_object (const LONGEST *exit_code, struct inferior *inf)
 {
-  gdbpy_ref<> exited_event (create_event_object (&exited_event_object_type));
+  gdbpy_ref<> exited_event = create_event_object (&exited_event_object_type);
 
   if (exited_event == NULL)
     return NULL;
@@ -45,7 +45,7 @@ create_exited_event_object (const LONGEST *exit_code, struct inferior *inf)
 					     (PyObject *) inf_obj.get ()) < 0)
     return NULL;
 
-  return exited_event.release ();
+  return exited_event;
 }
 
 /* Callback that is used when an exit event occurs.  This function
@@ -57,7 +57,7 @@ emit_exited_event (const LONGEST *exit_code, struct inferior *inf)
   if (evregpy_no_listeners_p (gdb_py_events.exited))
     return 0;
 
-  gdbpy_ref<> event (create_exited_event_object (exit_code, inf));
+  gdbpy_ref<> event = create_exited_event_object (exit_code, inf);
 
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.exited);
diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c
index 9f09ae93756..1cf37296973 100644
--- a/gdb/python/py-inferior.c
+++ b/gdb/python/py-inferior.c
@@ -256,7 +256,7 @@ python_new_inferior (struct inferior *inf)
       return;
     }
 
-  gdbpy_ref<> event (create_event_object (&new_inferior_event_object_type));
+  gdbpy_ref<> event = create_event_object (&new_inferior_event_object_type);
   if (event == NULL
       || evpy_add_attribute (event.get (), "inferior",
 			     (PyObject *) inf_obj.get ()) < 0
@@ -284,7 +284,7 @@ python_inferior_deleted (struct inferior *inf)
       return;
     }
 
-  gdbpy_ref<> event (create_event_object (&inferior_deleted_event_object_type));
+  gdbpy_ref<> event = create_event_object (&inferior_deleted_event_object_type);
   if (event == NULL
       || evpy_add_attribute (event.get (), "inferior",
 			     (PyObject *) inf_obj.get ()) < 0
@@ -353,8 +353,8 @@ add_thread_object (struct thread_info *tp)
   if (evregpy_no_listeners_p (gdb_py_events.new_thread))
     return;
 
-  gdbpy_ref<> event (create_thread_event_object (&new_thread_event_object_type,
-						 (PyObject *) thread_obj));
+  gdbpy_ref<> event = create_thread_event_object (&new_thread_event_object_type,
+						  (PyObject *) thread_obj);
   if (event == NULL
       || evpy_emit_event (event.get (), gdb_py_events.new_thread) < 0)
     gdbpy_print_stack ();
diff --git a/gdb/python/py-infevents.c b/gdb/python/py-infevents.c
index 2bd0bc7f2c4..0df7d96df30 100644
--- a/gdb/python/py-infevents.c
+++ b/gdb/python/py-infevents.c
@@ -24,7 +24,7 @@
 /* Construct either a gdb.InferiorCallPreEvent or a
    gdb.InferiorCallPostEvent. */
 
-static PyObject *
+static gdbpy_ref<>
 create_inferior_call_event_object (inferior_call_kind flag, ptid_t ptid,
 				   CORE_ADDR addr)
 {
@@ -56,17 +56,17 @@ create_inferior_call_event_object (inferior_call_kind flag, ptid_t ptid,
   if (evpy_add_attribute (event.get (), "address", addr_obj.get ()) < 0)
     return NULL;
 
-  return event.release ();
+  return event;
 }
 
 /* Construct a gdb.RegisterChangedEvent containing the affected
    register number. */
 
-static PyObject *
+static gdbpy_ref<>
 create_register_changed_event_object (struct frame_info *frame, 
 				      int regnum)
 {
-  gdbpy_ref<> event (create_event_object (&register_changed_event_object_type));
+  gdbpy_ref<> event = create_event_object (&register_changed_event_object_type);
   if (event == NULL)
     return NULL;
 
@@ -84,16 +84,16 @@ create_register_changed_event_object (struct frame_info *frame,
   if (evpy_add_attribute (event.get (), "regnum", regnum_obj.get ()) < 0)
     return NULL;
 
-  return event.release ();
+  return event;
 }
 
 /* Construct a gdb.MemoryChangedEvent describing the extent of the
    affected memory. */
 
-static PyObject *
+static gdbpy_ref<>
 create_memory_changed_event_object (CORE_ADDR addr, ssize_t len)
 {
-  gdbpy_ref<> event (create_event_object (&memory_changed_event_object_type));
+  gdbpy_ref<> event = create_event_object (&memory_changed_event_object_type);
 
   if (event == NULL)
     return NULL;
@@ -112,7 +112,7 @@ create_memory_changed_event_object (CORE_ADDR addr, ssize_t len)
   if (evpy_add_attribute (event.get (), "length", len_obj.get ()) < 0)
     return NULL;
 
-  return event.release ();
+  return event;
 }
 
 /* Callback function which notifies observers when an event occurs which
@@ -127,7 +127,7 @@ emit_inferior_call_event (inferior_call_kind flag, ptid_t thread,
   if (evregpy_no_listeners_p (gdb_py_events.inferior_call))
     return 0;
 
-  gdbpy_ref<> event (create_inferior_call_event_object (flag, thread, addr));
+  gdbpy_ref<> event = create_inferior_call_event_object (flag, thread, addr);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.inferior_call);
   return -1;
@@ -142,7 +142,7 @@ emit_memory_changed_event (CORE_ADDR addr, ssize_t len)
   if (evregpy_no_listeners_p (gdb_py_events.memory_changed))
     return 0;
 
-  gdbpy_ref<> event (create_memory_changed_event_object (addr, len));
+  gdbpy_ref<> event = create_memory_changed_event_object (addr, len);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.memory_changed);
   return -1;
@@ -157,7 +157,7 @@ emit_register_changed_event (struct frame_info* frame, int regnum)
   if (evregpy_no_listeners_p (gdb_py_events.register_changed))
     return 0;
 
-  gdbpy_ref<> event (create_register_changed_event_object (frame, regnum));
+  gdbpy_ref<> event = create_register_changed_event_object (frame, regnum);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.register_changed);
   return -1;
diff --git a/gdb/python/py-newobjfileevent.c b/gdb/python/py-newobjfileevent.c
index 86de9ac10ad..a9341a3be18 100644
--- a/gdb/python/py-newobjfileevent.c
+++ b/gdb/python/py-newobjfileevent.c
@@ -20,25 +20,23 @@
 #include "defs.h"
 #include "py-event.h"
 
-static PyObject *
+static gdbpy_ref<>
 create_new_objfile_event_object (struct objfile *objfile)
 {
-  PyObject *py_objfile;
-
   gdbpy_ref<> objfile_event
-    (create_event_object (&new_objfile_event_object_type));
+    = create_event_object (&new_objfile_event_object_type);
   if (objfile_event == NULL)
     return NULL;
 
   /* Note that objfile_to_objfile_object returns a borrowed reference,
      so we don't need a decref here.  */
-  py_objfile = objfile_to_objfile_object (objfile);
+  PyObject *py_objfile = objfile_to_objfile_object (objfile);
   if (!py_objfile || evpy_add_attribute (objfile_event.get (),
                                          "new_objfile",
                                          py_objfile) < 0)
     return NULL;
 
-  return objfile_event.release ();
+  return objfile_event;
 }
 
 /* Callback function which notifies observers when a new objfile event occurs.
@@ -51,7 +49,7 @@ emit_new_objfile_event (struct objfile *objfile)
   if (evregpy_no_listeners_p (gdb_py_events.new_objfile))
     return 0;
 
-  gdbpy_ref<> event (create_new_objfile_event_object (objfile));
+  gdbpy_ref<> event = create_new_objfile_event_object (objfile);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.new_objfile);
   return -1;
@@ -60,25 +58,23 @@ emit_new_objfile_event (struct objfile *objfile)
 \f
 /* Subroutine of emit_clear_objfiles_event to simplify it.  */
 
-static PyObject *
+static gdbpy_ref<>
 create_clear_objfiles_event_object (void)
 {
-  PyObject *py_progspace;
-
   gdbpy_ref<> objfile_event
-    (create_event_object (&clear_objfiles_event_object_type));
+    = create_event_object (&clear_objfiles_event_object_type);
   if (objfile_event == NULL)
     return NULL;
 
   /* Note that pspace_to_pspace_object returns a borrowed reference,
      so we don't need a decref here.  */
-  py_progspace = pspace_to_pspace_object (current_program_space);
+  PyObject *py_progspace = pspace_to_pspace_object (current_program_space);
   if (!py_progspace || evpy_add_attribute (objfile_event.get (),
 					   "progspace",
 					   py_progspace) < 0)
     return NULL;
 
-  return objfile_event.release ();
+  return objfile_event;
 }
 
 /* Callback function which notifies observers when the "clear objfiles"
@@ -92,7 +88,7 @@ emit_clear_objfiles_event (void)
   if (evregpy_no_listeners_p (gdb_py_events.clear_objfiles))
     return 0;
 
-  gdbpy_ref<> event (create_clear_objfiles_event_object ());
+  gdbpy_ref<> event = create_clear_objfiles_event_object ();
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.clear_objfiles);
   return -1;
diff --git a/gdb/python/py-signalevent.c b/gdb/python/py-signalevent.c
index d88aaeaedea..a2e7519460c 100644
--- a/gdb/python/py-signalevent.c
+++ b/gdb/python/py-signalevent.c
@@ -23,14 +23,13 @@
 gdbpy_ref<>
 create_signal_event_object (enum gdb_signal stop_signal)
 {
-  const char *signal_name;
   gdbpy_ref<> signal_event_obj
-    (create_stop_event_object (&signal_event_object_type));
+    = create_stop_event_object (&signal_event_object_type);
 
   if (signal_event_obj == NULL)
     return NULL;
 
-  signal_name = gdb_signal_to_name (stop_signal);
+  const char *signal_name = gdb_signal_to_name (stop_signal);
 
   gdbpy_ref<> signal_name_obj (PyString_FromString (signal_name));
   if (signal_name_obj == NULL)
diff --git a/gdb/python/py-threadevent.c b/gdb/python/py-threadevent.c
index 1bc2fb06d54..a78f0a38310 100644
--- a/gdb/python/py-threadevent.c
+++ b/gdb/python/py-threadevent.c
@@ -50,7 +50,7 @@ create_thread_event_object (PyTypeObject *py_type, PyObject *thread)
 {
   gdb_assert (thread != NULL);
 
-  gdbpy_ref<> thread_event_obj (create_event_object (py_type));
+  gdbpy_ref<> thread_event_obj = create_event_object (py_type);
   if (thread_event_obj == NULL)
     return NULL;
 
-- 
2.14.4

Re: [PATCH v2] Fix 8.2 regression in gdb.python/py-evthreads.exp w/ gdbserver (PR gdb/23379)

[Tom Tromey]

>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:

Pedro> 	* python/py-threadevent.c (get_event_thread): Rename to ...
Pedro> 	(py_get_event_thread): ... this, make extern, add 'ptid' parameter

I get this warning now:

../../binutils-gdb/gdb/python/py-threadevent.c: In function ‘PyObject* py_get_event_thread(ptid_t)’:
../../binutils-gdb/gdb/python/py-threadevent.c:39:3: warning: ‘pythread’ may be used uninitialized in this function [-Wmaybe-uninitialized]

... which seems legitimate to me:

  PyObject *pythread;

  if (non_stop)
    {
      thread_info *thread = find_thread_ptid (ptid);
      if (thread != nullptr)
	pythread = (PyObject *) thread_to_thread_object (thread);
// ... else pythread is uninitialized ...
    }

pythread should be set to nullptr where I stuck the comment (or
initialized to nullptr).

Tom

Re: [PATCH v2] Fix 8.2 regression in gdb.python/py-evthreads.exp w/ gdbserver (PR gdb/23379)

[Simon Marchi]

On 2018-08-25 10:52 a.m., Tom Tromey wrote:
>>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:
> 
> Pedro> 	* python/py-threadevent.c (get_event_thread): Rename to ...
> Pedro> 	(py_get_event_thread): ... this, make extern, add 'ptid' parameter
> 
> I get this warning now:
> 
> ../../binutils-gdb/gdb/python/py-threadevent.c: In function ‘PyObject* py_get_event_thread(ptid_t)’:
> ../../binutils-gdb/gdb/python/py-threadevent.c:39:3: warning: ‘pythread’ may be used uninitialized in this function [-Wmaybe-uninitialized]
> 
> ... which seems legitimate to me:
> 
>   PyObject *pythread;
> 
>   if (non_stop)
>     {
>       thread_info *thread = find_thread_ptid (ptid);
>       if (thread != nullptr)
> 	pythread = (PyObject *) thread_to_thread_object (thread);
> // ... else pythread is uninitialized ...
>     }
> 
> pythread should be set to nullptr where I stuck the comment (or
> initialized to nullptr).
> 
> Tom
> 

Huh indeed, thanks for pointing it out.  I wonder why I don't get the warning with my gcc 8.2.0...

I pushed this patch to master and the 8.2 branch.

From bbbbbceebc342d583057a11d88bae85f451cd904 Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@polymtl.ca>
Date: Sat, 25 Aug 2018 11:52:24 -0400
Subject: [PATCH] Initialize variable in py_get_event_thread

The pythread variable could be used without being initialized, fix it by
initializing it to nullptr.

gdb/ChangeLog:

	* python/py-threadevent.c (py_get_event_thread): Initialize
	pythread.
---
 gdb/ChangeLog               | 5 +++++
 gdb/python/py-threadevent.c | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 12dda6c541d9..9e3d6bc27acd 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-08-25  Simon Marchi  <simon.marchi@polymtl.ca>
+
+	* python/py-threadevent.c (py_get_event_thread): Initialize
+	pythread.
+
 2018-08-24  Pedro Alves  <palves@redhat.com>

 	* python/py-bpevent.c (create_breakpoint_event_object): Use
diff --git a/gdb/python/py-threadevent.c b/gdb/python/py-threadevent.c
index a78f0a38310c..4f822b4ae09c 100644
--- a/gdb/python/py-threadevent.c
+++ b/gdb/python/py-threadevent.c
@@ -25,7 +25,7 @@
 PyObject *
 py_get_event_thread (ptid_t ptid)
 {
-  PyObject *pythread;
+  PyObject *pythread = nullptr;

   if (non_stop)
     {
@@ -36,7 +36,7 @@ py_get_event_thread (ptid_t ptid)
   else
     pythread = Py_None;

-  if (!pythread)
+  if (pythread == nullptr)
     {
       PyErr_SetString (PyExc_RuntimeError, "Could not find event thread");
       return NULL;
-- 
2.18.0