The ffi_prep_args function in libffi_msvc/ffi.c needs the attached patch to handle 64-bit parameters with the correct padding.Without this patch, garbage may appear in the top part of 64-bit arguments as the values are not zeroed out by the memcpy.I'm not 100% sure who 'owns' this file - is there an upstream project that should get the patch rather than Python? If not, I see no reason not to check this in now, even though it doesn't seem to repro with the VC10 builds.

Nosying the other Windows guys - seems like the ctypes nosy list is inactive, and this only affects MSVC.

This patch also resolves this test issue:[ 68/390/2] test_ttk_textonlytest test_ttk_textonly crashed -- Traceback (most recent call last):  File "D:\...\lib\test\regrtest.py", line 1280, in runtest_inner    test_runner()  File "D:\...\lib\test\test_ttk_textonly.py", line 14, in test_main    *runtktests.get_tests(gui=False, packages=['test_ttk']))  File "D:\...\lib\tkinter\test\runtktests.py", line 65, in get_tests    for module in get_tests_modules(gui=gui, packages=packages):  File "D:\...\lib\tkinter\test\runtktests.py", line 50, in get_tests_modules    "tkinter.test")  File "D:\...\lib\importlib\__init__.py", line 109, in import_module    return _bootstrap._gcd_import(name[level:], package, level)  File "<frozen importlib._bootstrap>", line 2208, in _gcd_import  File "<frozen importlib._bootstrap>", line 2191, in _find_and_load  File "<frozen importlib._bootstrap>", line 2180, in _find_and_load_unlocked  File "<frozen importlib._bootstrap>", line 1149, in _load_unlocked  File "<frozen importlib._bootstrap>", line 1420, in exec_module  File "<frozen importlib._bootstrap>", line 321, in _call_with_frames_removed  File "D:\...\lib\tkinter\test\test_ttk\test_extensions.py", line 8, in <module>    requires('gui')  File "D:\...\lib\test\support\__init__.py", line 492, in requires    if resource == 'gui' and not _is_gui_available():  File "D:\...\lib\test\support\__init__.py", line 436, in _is_gui_available    raise ctypes.WinError()OSError: [WinError 0] The operation completed successfully.I'm not entirely sure when/if I should just commit the fix without any reviews, but this issue needs to be fixed, so eventually I'll probably just do it :)

I don't know near enough to comment on this one.  If you feel confident in it, I'd say go ahead.

Likewise.

New changeset4c81b1846e14 by Steve Dower in branch 'default':Issue#22733: MSVC ffi_prep_args doesn't handle 64-bit arguments properlyhttps://hg.python.org/cpython/rev/4c81b1846e14

New changeset24f4569a1308 by Steve Dower in branch 'default':Issue#22733: Added NEWS itemhttps://hg.python.org/cpython/rev/24f4569a1308

Maybe worth backporting to 3.3 and up? Especially if#20160 is to be backported as they seem to be related.