The patch for Issue #21881 causes CPython test_tcl to crash on AIX.

$ ./python -m test -v test_tcl
== CPython 3.5.0a0 (default:d1f89eb9ea1e+, Jul 10 2014, 10:21:22) [GCC 4.8.1]
==   AIX-1-00F84C0C4C00-powerpc-32bit big-endian
==   hash algorithm: siphash24 32bit
==   /home/dje/src/cpython/build/test_python_27984522
Testing with flags: sys.flags(debug=0, inspect=0, interactive=0, optimize=0, dont_write_bytecode=0, no_user_site=0, no_site=0, ignore_environment=0, verbose=0, bytes_warning=0, quiet=0, hash_randomization=1, isolated=0)
[1/1] test_tcl
patchlevel = 8.4.7
testCall (test.test_tcl.TclTest) ... ok
testCallException (test.test_tcl.TclTest) ... ok
testCallException2 (test.test_tcl.TclTest) ... ok
testEval (test.test_tcl.TclTest) ... ok
testEvalException (test.test_tcl.TclTest) ... ok
testEvalException2 (test.test_tcl.TclTest) ... ok
testEvalFile (test.test_tcl.TclTest) ... ok
testEvalFileException (test.test_tcl.TclTest) ... ok
testGetVar (test.test_tcl.TclTest) ... ok
testGetVarArray (test.test_tcl.TclTest) ... ok
testGetVarArrayException (test.test_tcl.TclTest) ... ok
testGetVarException (test.test_tcl.TclTest) ... ok
testLoadWithUNC (test.test_tcl.TclTest) ... skipped 'Requires Windows'
testPackageRequireException (test.test_tcl.TclTest) ... ok
testSetVar (test.test_tcl.TclTest) ... ok
testSetVarArray (test.test_tcl.TclTest) ... ok
testUnsetVar (test.test_tcl.TclTest) ... ok
testUnsetVarArray (test.test_tcl.TclTest) ... ok
testUnsetVarException (test.test_tcl.TclTest) ... ok
test_eval_null_in_result (test.test_tcl.TclTest) ... ok
test_evalfile_null_in_result (test.test_tcl.TclTest) ... ok
test_exprboolean (test.test_tcl.TclTest) ... ok
test_exprdouble (test.test_tcl.TclTest) ... ok
test_exprlong (test.test_tcl.TclTest) ... ok
test_exprstring (test.test_tcl.TclTest) ... ok
test_getboolean (test.test_tcl.TclTest) ... ok
test_getdouble (test.test_tcl.TclTest) ... ok
test_getint (test.test_tcl.TclTest) ... ok
test_passing_values (test.test_tcl.TclTest) ... ok
test_split (test.test_tcl.TclTest) ... ok
test_splitlist (test.test_tcl.TclTest) ... ok
test_user_command (test.test_tcl.TclTest) ... Assertion failed: __EX, file  Objects/methodobject.c, line 94
Fatal Python error: Aborted

Current thread 0x00000001 (most recent call first):
  File "/home/dje/src/cpython/Lib/test/test_tcl.py", line 426 in check
  File "/home/dje/src/cpython/Lib/test/test_tcl.py", line 458 in test_user_command
  File "/home/dje/src/cpython/Lib/unittest/case.py", line 577 in run
  File "/home/dje/src/cpython/Lib/unittest/case.py", line 625 in __call__
  File "/home/dje/src/cpython/Lib/unittest/suite.py", line 125 in run
  File "/home/dje/src/cpython/Lib/unittest/suite.py", line 87 in __call__
  File "/home/dje/src/cpython/Lib/unittest/suite.py", line 125 in run
  File "/home/dje/src/cpython/Lib/unittest/suite.py", line 87 in __call__
  File "/home/dje/src/cpython/Lib/unittest/runner.py", line 168 in run
  File "/home/dje/src/cpython/Lib/test/support/__init__.py", line 1724 in _run_suite
  File "/home/dje/src/cpython/Lib/test/support/__init__.py", line 1758 in run_unittest
  File "/home/dje/src/cpython/Lib/test/test_tcl.py", line 601 in test_main
  File "/home/dje/src/cpython/Lib/test/regrtest.py", line 1278 in runtest_inner
  File "/home/dje/src/cpython/Lib/test/regrtest.py", line 978 in runtest
  File "/home/dje/src/cpython/Lib/test/regrtest.py", line 763 in main
  File "/home/dje/src/cpython/Lib/test/regrtest.py", line 1562 in main_in_temp_cwd
  File "/home/dje/src/cpython/Lib/test/__main__.py", line 3 in <module>
  File "/home/dje/src/cpython/Lib/runpy.py", line 85 in _run_code
  File "/home/dje/src/cpython/Lib/runpy.py", line 170 in _run_module_as_main
IOT/Abort trap (core dumped)

Is it crashes when comment out "check((), '')"? Is it crashes when comment out two previous checks (for inf and -inf)?

If I comment out all three tests, it runs.

--- a/Lib/test/test_tcl.py      Thu Jul 10 01:17:11 2014 -0400
+++ b/Lib/test/test_tcl.py      Sat Jul 12 16:59:33 2014 -0700
@@ -455,9 +455,9 @@
         check(float('inf'), 'Inf', eq=float_eq)
         check(-float('inf'), '-Inf', eq=float_eq)
         # XXX NaN representation can be not parsable by float()
-        check((), '')
-        check((1, (2,), (3, 4), '5 6', ()), '1 2 {3 4} {5 6} {}')
-        check([1, [2,], [3, 4], '5 6', []], '1 2 {3 4} {5 6} {}')
+        #check((), '')
+        #check((1, (2,), (3, 4), '5 6', ()), '1 2 {3 4} {5 6} {}')
+        #check([1, [2,], [3, 4], '5 6', []], '1 2 {3 4} {5 6} {}')
 
     def test_splitlist(self):
         splitlist = self.interp.tk.splitlist

Is following test passed?

        check((1,), '1')

Is CPython crashes when change signature of testfunc?

--- a/Lib/test/test_tcl.py      Sat Jul 12 18:26:03 2014 +0300
+++ b/Lib/test/test_tcl.py      Sun Jul 13 19:21:55 2014 +0300
@@ -416,7 +416,7 @@
 
     def test_user_command(self):
         result = None
-        def testfunc(arg):
+        def testfunc(arg=None, *args):
             nonlocal result
             result = arg
             return arg

> Is following test passed?

>         check((1,), '1')

That test succeeds.

> Is CPython crashes when change signature of testfunc?

--- a/Lib/test/test_tcl.py      Sat Jul 12 18:26:03 2014 +0300
+++ b/Lib/test/test_tcl.py      Sun Jul 13 19:21:55 2014 +0300
@@ -416,7 +416,7 @@
 
     def test_user_command(self):
         result = None
-        def testfunc(arg):
+        def testfunc(arg=None, *args):
             nonlocal result
             result = arg
             return arg

This change does not have any effect on the original failure. The assertion failure and crash continues to occur.

#5  0x1019bb90 in PyCFunction_Call (func=0x30533b5c, arg=0x305d8ab4, kw=0x0)
    at Objects/methodobject.c:94
#6  0x1012534c in call_function (pp_stack=0x2ff16144, oparg=2)
    at Python/ceval.c:4269

94                  CHECK_RESULT(res);

(gdb) print res
$9 = (PyObject *) 0x0
(gdb) print meth
$10 = (PyCFunction) @0x20380888: 0xd8dd57dc <Tkapp_Call>
(gdb) print self
$11 = (PyObject *) 0x305d44d8

May be this patch will help.

No difference with the patch. The problem is not a a malloc() failure.

New changeset 7de64def6565 by Serhiy Storchaka in branch '2.7':
Issue #21951: Temporary skip crashing test_user_command on AIX.
http://hg.python.org/cpython/rev/7de64def6565

New changeset 31f4cb1fede9 by Serhiy Storchaka in branch '3.4':
Issue #21951: Temporary skip crashing test_user_command on AIX.
http://hg.python.org/cpython/rev/31f4cb1fede9

New changeset de32cd419174 by Serhiy Storchaka in branch 'default':
Issue #21951: Temporary skip crashing test_user_command on AIX.
http://hg.python.org/cpython/rev/de32cd419174

Link to log with a crash:

http://buildbot.python.org/all/builders/PPC64%20AIX%203.x/builds/2442/steps/test/logs/stdio

The failing assertion means that the method raised an exception and returned a result, or failed but didn't raised an exception. According to the gdb trace, the function failed (res is NULL). You can display the current exception in gdb using: "print PyErr_Occurred()" (NULL if there is no exception).

Please run test_tcl on AIX with attached test_tkinter.patch applied.

As far as I remember, both res and PyErr_Occurred() were NULL.

When the failing test is re-enabled, the _tkinter patch produces the following output:

test_user_command (test.test_tcl.TclTest) ... Assertion failed: __EX, file  /home/dje/src/cpython/Modules/_tkinter.c, line 1277
Fatal Python error: Aborted

Current thread 0x00000001 (most recent call first):
  File "/home/dje/src/cpython/Lib/test/test_tcl.py", line 435 in check
  File "/home/dje/src/cpython/Lib/test/test_tcl.py", line 468 in test_user_command
  File "/home/dje/src/cpython/Lib/unittest/case.py", line 577 in run
  File "/home/dje/src/cpython/Lib/unittest/case.py", line 625 in __call__
  File "/home/dje/src/cpython/Lib/unittest/suite.py", line 125 in run
  File "/home/dje/src/cpython/Lib/unittest/suite.py", line 87 in __call__
  File "/home/dje/src/cpython/Lib/unittest/suite.py", line 125 in run
  File "/home/dje/src/cpython/Lib/unittest/suite.py", line 87 in __call__
  File "/home/dje/src/cpython/Lib/unittest/runner.py", line 168 in run
  File "/home/dje/src/cpython/Lib/test/support/__init__.py", line 1750 in _run_suite
  File "/home/dje/src/cpython/Lib/test/support/__init__.py", line 1784 in run_unittest
  File "/home/dje/src/cpython/Lib/test/test_tcl.py", line 615 in test_main
  File "/home/dje/src/cpython/Lib/test/regrtest.py", line 1280 in runtest_inner
  File "/home/dje/src/cpython/Lib/test/regrtest.py", line 978 in runtest
  File "/home/dje/src/cpython/Lib/test/regrtest.py", line 763 in main
  File "/home/dje/src/cpython/Lib/test/regrtest.py", line 1564 in main_in_temp_cwd
  File "/home/dje/src/cpython/Lib/test/__main__.py", line 3 in <module>
  File "/home/dje/src/cpython/Lib/runpy.py", line 85 in _run_code
  File "/home/dje/src/cpython/Lib/runpy.py", line 170 in _run_module_as_main
IOT/Abort trap (core dumped)

New changeset 9ab404cdcaa1 by Victor Stinner in branch 'default':
Issue #21951: Fix AsObj() of the _tkinter module: raise MemoryError on memory
http://hg.python.org/cpython/rev/9ab404cdcaa1

> When the failing test is re-enabled, the _tkinter patch produces the following output:

Thanks. I found and fixed a bug in AsObj() for tuple and list. It looks like ckalloc(size) returns NULL if size is 0. Please update Python, compile and run test_tcl to see if you get a MemoryError exception instead of a crash.

I just created the issue #22336 which may fix this issue if my analysis was correct. It uses PyMem_Malloc(size) which has a well-defined behaviour when size is 0.

$ ./python -m test -v test_tcl
== CPython 3.5.0a0 (default:9ab404cdcaa1+, Sep 4 2014, 10:06:33) [GCC 4.8.1]
==   AIX-1-00F84C0C4C00-powerpc-32bit big-endian
==   hash algorithm: siphash24 32bit
==   /home/dje/src/cpython/build/test_python_48694044
Testing with flags: sys.flags(debug=0, inspect=0, interactive=0, optimize=0, dont_write_bytecode=0, no_user_site=0, no_site=0, ignore_environment=0, verbose=0, bytes_warning=0, quiet=0, hash_randomization=1, isolated=0)
[1/1] test_tcl
patchlevel = 8.4.7
testCall (test.test_tcl.TclTest) ... ok
testCallException (test.test_tcl.TclTest) ... ok
testCallException2 (test.test_tcl.TclTest) ... ok
testEval (test.test_tcl.TclTest) ... ok
testEvalException (test.test_tcl.TclTest) ... ok
testEvalException2 (test.test_tcl.TclTest) ... ok
testEvalFile (test.test_tcl.TclTest) ... ok
testEvalFileException (test.test_tcl.TclTest) ... ok
testGetVar (test.test_tcl.TclTest) ... ok
testGetVarArray (test.test_tcl.TclTest) ... ok
testGetVarArrayException (test.test_tcl.TclTest) ... ok
testGetVarException (test.test_tcl.TclTest) ... ok
testLoadWithUNC (test.test_tcl.TclTest) ... skipped 'Requires Windows'
testPackageRequireException (test.test_tcl.TclTest) ... ok
testSetVar (test.test_tcl.TclTest) ... ok
testSetVarArray (test.test_tcl.TclTest) ... ok
testUnsetVar (test.test_tcl.TclTest) ... ok
testUnsetVarArray (test.test_tcl.TclTest) ... ok
testUnsetVarException (test.test_tcl.TclTest) ... ok
test_eval_null_in_result (test.test_tcl.TclTest) ... ok
test_evalfile_null_in_result (test.test_tcl.TclTest) ... ok
test_exprboolean (test.test_tcl.TclTest) ... ok
test_exprdouble (test.test_tcl.TclTest) ... ok
test_exprlong (test.test_tcl.TclTest) ... ok
test_exprstring (test.test_tcl.TclTest) ... ok
test_getboolean (test.test_tcl.TclTest) ... ok
test_getdouble (test.test_tcl.TclTest) ... ok
test_getint (test.test_tcl.TclTest) ... ok
test_passing_values (test.test_tcl.TclTest) ... ok
test_split (test.test_tcl.TclTest) ... ok
test_splitlist (test.test_tcl.TclTest) ... ok
test_user_command (test.test_tcl.TclTest) ... ERROR
testFlattenLen (test.test_tcl.TkinterTest) ... ok
test_huge_string_builtins (test.test_tcl.BigmemTclTest) ... skipped 'needs UINT_MAX < SIZE_MAX'
test_huge_string_call (test.test_tcl.BigmemTclTest) ... skipped 'needs UINT_MAX < SIZE_MAX'

======================================================================
ERROR: test_user_command (test.test_tcl.TclTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/dje/src/cpython/Lib/test/test_tcl.py", line 468, in test_user_command
    check((), '')
  File "/home/dje/src/cpython/Lib/test/test_tcl.py", line 435, in check
    r = self.interp.call('testfunc', value)
MemoryError

----------------------------------------------------------------------
Ran 35 tests in 0.133s

FAILED (errors=1, skipped=3)
test test_tcl failed
1 test failed:
    test_tcl

Thanks David! Your ouput confirms my analysis. asobj_empty_sequence.patch should fix the test on AIX.

I read Tcl source code, Tcl_NewListObj() doesn't use the second parameter if the first parameter (length) is zero.

The patch can be simpler. And there is yet one similar bug, for unicode strings.

As Victor noted on IRC, ckalloc() panics and doesn't returns NULL in case of error. We should use attemptckalloc() instead.

I'm not sure that tkinter_ckallock.patch is correct. Extract of attemptckalloc() manual page:
"If the allocation fails, these functions will return NULL. Note that on some platforms, but not all, attempting to allocate a zero-sized block of memory will also cause these functions to return NULL."

http://linux.die.net/man/3/attemptckalloc

It looks like you are fixing two different issues in the same patch: fix AIX and enhance handling of memory allocation failure.

Can you please split your patch in two parts? For AIX, adding these two lines for list/tuple should be enough:

if (size == 0)
    return Tcl_NewListObj(0, NULL);

"I'm not sure that tkinter_ckallock.patch is correct."

Oh, when I read my message, I realized that I was not explicit enough. It looks like attemptckalloc() can be called with 0 at some places with  tkinter_ckallock.patch. But I didn't check carefully, the patch is maybe correct.

New changeset ee969a717cb5 by Serhiy Storchaka in branch '2.7':
Issue #21951: Use attemptckalloc() instead of ckalloc() in Tkinter.
http://hg.python.org/cpython/rev/ee969a717cb5

New changeset 1223c882253f by Serhiy Storchaka in branch '3.4':
Issue #21951: Use attemptckalloc() instead of ckalloc() in Tkinter.
http://hg.python.org/cpython/rev/1223c882253f

New changeset 499b60b7d067 by Serhiy Storchaka in branch 'default':
Issue #21951: Use attemptckalloc() instead of ckalloc() in Tkinter.
http://hg.python.org/cpython/rev/499b60b7d067

New changeset d6c7ab5a2065 by Serhiy Storchaka in branch '2.7':
Issue #21951: Fixed a crash in Tkinter on AIX when called Tcl command with
http://hg.python.org/cpython/rev/d6c7ab5a2065

New changeset 6a96c28f9474 by Serhiy Storchaka in branch '3.4':
Issue #21951: Fixed a crash in Tkinter on AIX when called Tcl command with
http://hg.python.org/cpython/rev/6a96c28f9474

New changeset 7b7bae546959 by Serhiy Storchaka in branch 'default':
Issue #21951: Fixed a crash in Tkinter on AIX when called Tcl command with
http://hg.python.org/cpython/rev/7b7bae546959

Committed these two changes as separate patches.

> Committed these two changes as separate patches.

Thanks, it's clearer like that.

test_tcl now pass on AIX:
http://buildbot.python.org/all/builders/PPC64%20AIX%203.x/builds/2592/steps/test/logs/stdio

Thanks Serhiy for the fix.

Thank you Victor for great investigation of this issue.