[issue23815] Segmentation fault when create _tkinter objects

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

After looking closer I found that making PyType_FromSpec() not inheriting 
tp_new for static types whose base class is 'object' is not an option, because 
this breaks examples in the documentation, and likely break some third-party 
code. Opened new issue26979 for documenting the catch.

Thank you for your review Terry.

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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue23815] Segmentation fault when create _tkinter objects

[Roundup Robot]

Roundup Robot added the comment:

New changeset cd25508c62fc by Serhiy Storchaka in branch '3.5':
Issue #23815: Fixed crashes related to directly created instances of types in
https://hg.python.org/cpython/rev/cd25508c62fc

New changeset 1c6326e81c33 by Serhiy Storchaka in branch 'default':
Issue #23815: Fixed crashes related to directly created instances of types in
https://hg.python.org/cpython/rev/1c6326e81c33

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[issue23815] Segmentation fault when create _tkinter objects

[Terry J. Reedy]

Terry J. Reedy added the comment:

I noticed that you reported the crash and asked for a fix or reversion on 
#15721 6 months ago, with no response.  Hence, lets not wait longer.

Looking again, I see that there were 3 rounds of patches in 2012/2013.  If you 
want to follow up, I suggest closing that issue and open a fresh issue with 
with alternatives and your recommendation.

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[issue23815] Segmentation fault when create _tkinter objects

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

I called the fix a workaround because other solution may be to make 
PyType_FromSpec() not setting tp_new in such cases. I expect that this is 
common mistake when convert a static class to a heap class with 
PyType_FromSpec(). At least we should add warnings in C API documentation and 
PEP 384. Or change the behavior of PyType_FromSpec() if it is appropriate. But 
this is different issue. If PyType_FromSpec() will be changed, proposed fix can 
be reverted.

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[issue23815] Segmentation fault when create _tkinter objects

[Terry J. Reedy]

Terry J. Reedy added the comment:

The news part of the patch did not apply  -- best not to include such in posted 
patches.

After recompiliing 3.5 on Windows 10, the two tkinter test cases give the 3.3 
TypeErrors instead of crashing.  test_tcl also runs.  curses does not run on 
Windows.

I do not know enough internals to really understand #15721 or why you call the 
fix a workaround, but I do understand 'exception' (OK) versus 'crash' 
(forbidden).  Unless you think restoring the previous situation (tp_new = NUll) 
can cause a worse problem, I would apply this soon, within a week, so not 
forgotten before the June update releases.  The tcl test addition is correct.  
The fix can be improved later if you think of something better.

I initially wondered why _tkinter has classes that cannot be instantiated (from 
Python).  Then I discovered that this is normal, and that the exception is 
standard.

>>> type(iter([]))()
Traceback (most recent call last):
  File "", line 1, in 
TypeError: cannot create 'list_iterator' instances

Is list_iterator.tp_new NULL?  Or does it raise instead of crash by other means?

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[issue23815] Segmentation fault when create _tkinter objects

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

There is special exception -- tp_new is not inherited for static types whose 
base class is 'object' (see a comment in inherit_special() in 
Objects/typeobject.c#4569 for explanation). After converting them to heap types 
they became inherit tp_new from object.

Proposed patch adds workarounds for types in _tkinter and curses.panel modules.

--
assignee:  -> serhiy.storchaka
keywords: +patch
stage:  -> patch review
versions:  -Python 3.4
Added file: http://bugs.python.org/file42775/tp_new_workaround.patch

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[issue23815] Segmentation fault when create _tkinter objects

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

PyType_Ready() is called inside PyType_FromSpec().

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[issue23815] Segmentation fault when create _tkinter objects

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc added the comment:

Probably a PyType_Ready() missing.

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[issue23815] Segmentation fault when create _tkinter objects

[Terry J. Reedy]

Terry J. Reedy added the comment:

With 3.4.3, I get the equivalent on Windows (a 'python has stopped working' 
box).

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[issue23815] Segmentation fault when create _tkinter objects

[Serhiy Storchaka]

New submission from Serhiy Storchaka:

In 2.7 and 3.3:

 import _tkinter
 _tkinter.Tcl_Obj()
Traceback (most recent call last):
  File stdin, line 1, in module
TypeError: cannot create '_tkinter.Tcl_Obj' instances
 _tkinter.TkttType()
Traceback (most recent call last):
  File stdin, line 1, in module
TypeError: cannot create 'tktimertoken' instances

In 3.4+:

 import _tkinter
 _tkinter.Tcl_Obj()
Segmentation fault (core dumped)

And the same for _tkinter.TkttType.

Looks as this is a result of issue15721.

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components: Extension Modules, Tkinter
messages: 239636
nosy: Robin.Schreiber, amaury.forgeotdarc, asvetlov, loewis, ned.deily, pitrou, 
serhiy.storchaka
priority: normal
severity: normal
status: open
title: Segmentation fault when create _tkinter objects
type: crash
versions: Python 3.4, Python 3.5

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