ctypes: structure with bitfields as argument

[arigo]

BPO	16576
Nosy	@arigo, @theller, @vsajip, @amauryfa, @abalkin, @alex, @meadori
PRs	bpo-22273: Update ctypes to correctly handle arrays in small structur… #15839 bpo-16576: Add checks for bitfields passed by value to functions. #17097 [3.8] bpo-16576: Add checks for bitfields passed by value to functions. (GH-17097) #17223 [3.7] bpo-16576: Add checks for bitfields passed by value to functions. (GH-17097) #17224
Files	test185_lib.tgz test186_lib.tgz issue16576.docfix.1.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2012-11-29.04:53:32.056>
labels = ['ctypes', '3.7', '3.8', '3.9', 'type-crash']
title = 'ctypes: structure with bitfields as argument'
updated_at = <Date 2020-01-12.07:46:05.510>
user = 'https://github.com/arigo'

bugs.python.org fields:

activity = <Date 2020-01-12.07:46:05.510>
actor = 'vinay.sajip'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['ctypes']
creation = <Date 2012-11-29.04:53:32.056>
creator = 'arigo'
dependencies = []
files = ['28156', '28157', '29326']
hgrepos = []
issue_num = 16576
keywords = ['patch']
message_count = 10.0
messages = ['176629', '176631', '183595', '183665', '183816', '183818', '356447', '356869', '357224', '359835']
nosy_count = 10.0
nosy_names = ['arigo', 'theller', 'vinay.sajip', 'amaury.forgeotdarc', 'belopolsky', 'Arfrever', 'alex', 'eli.bendersky', 'meador.inge', 'python-dev']
pr_nums = ['15839', '17097', '17223', '17224']
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue16576'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[arigo]

ctypes pretends to support passing arguments to C functions that are structures containing bitfields, or at least does not explicitly forbid it. But doing so results in misbehavior or segfaults in libffi itself. Indeed, libffi has no support for this, and ctypes just describes a field like "int x:1;" as "int x;". The attached example segfaults on Linux x86-64.

[arigo]

The same misbehavior occurs if the structures are packed ("_pack_ = 1"). Attached in test186_lib.tgz.

[elibendersky]

I propose to start with the attached documentation fix (generated vs. 3.2 but should be applied to all active branches).

A code fix has to be discussed more thoroughly because in theory some code running only on x86-32 can rely on it and will break.

[elibendersky]

The patch addresses bpo-16575 as well

[python-dev]

New changeset 0acd9408b6f1 by Eli Bendersky in branch '3.2':
Add warning in ctypes documentation for bpo-16575 and bpo-16576
http://hg.python.org/cpython/rev/0acd9408b6f1

New changeset bfc159f8e4b4 by Eli Bendersky in branch '3.3':
Add warning in ctypes documentation for bpo-16575 and bpo-16576
http://hg.python.org/cpython/rev/bfc159f8e4b4

New changeset 502624235c7b by Eli Bendersky in branch 'default':
Add warning in ctypes documentation for bpo-16575 and bpo-16576
http://hg.python.org/cpython/rev/502624235c7b

[python-dev]

New changeset eece32440a52 by Eli Bendersky in branch '2.7':
Add warning in ctypes documentation for bpo-16575 and bpo-16576
http://hg.python.org/cpython/rev/eece32440a52

[vsajip]

New changeset 1062715 by Vinay Sajip in branch 'master':
bpo-16576: Add checks for bitfields passed by value to functions. (GH-17097)
1062715

[vsajip]

New changeset bef2815 by Vinay Sajip (Miss Islington (bot)) in branch '3.8':
bpo-16576: Add checks for bitfields passed by value to functions. (GH-17097) (GH-17223)
bef2815

[vsajip]

New changeset 91c15a5 by Vinay Sajip (Miss Islington (bot)) in branch '3.7':
[3.7] bpo-16576: Add checks for bitfields passed by value to functions. (GH-17097) (GH-17224)
91c15a5