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ctypes mishandles void return type #91353

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hoodmane mannequin opened this issue Apr 2, 2022 · 3 comments
Closed

ctypes mishandles void return type #91353

hoodmane mannequin opened this issue Apr 2, 2022 · 3 comments
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3.11 only security fixes tests Tests in the Lib/test dir topic-ctypes type-bug An unexpected behavior, bug, or error

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@hoodmane
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hoodmane mannequin commented Apr 2, 2022

BPO 47197
Nosy @amauryfa, @abalkin, @tiran, @meadori, @hoodmane, @hoodmane
PRs
  • gh-91353: Fix void return type handling in ctypes (GH-32246) #32246
    		•

    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 2022-04-02.01:14:09.315>
labels = ['ctypes', 'type-bug', 'tests', '3.11']
title = 'ctypes mishandles `void` return type'
updated_at = <Date 2022-04-03.21:02:00.133>
user = 'https://github.com/hoodmane'

    bugs.python.org fields:

    activity = <Date 2022-04-03.21:02:00.133>
actor = 'christian.heimes'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Tests', 'ctypes']
creation = <Date 2022-04-02.01:14:09.315>
creator = 'hoodchatham'
dependencies = []
files = []
hgrepos = []
issue_num = 47197
keywords = ['patch']
message_count = 1.0
messages = ['416526']
nosy_count = 6.0
nosy_names = ['amaury.forgeotdarc', 'belopolsky', 'christian.heimes', 'meador.inge', 'hoodmane', 'hoodchatham']
pr_nums = ['32246']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue47197'
versions = ['Python 3.11']
    @hoodmane
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    hoodmane mannequin commented Apr 2, 2022

    On wasm targets, test_code fails. It's because of a bad function pointer cast. The problematic code is as follows:

    import ctypes

py = ctypes.pythonapi
freefunc = ctypes.CFUNCTYPE(None, ctypes.c_voidp)

RequestCodeExtraIndex = py._PyEval_RequestCodeExtraIndex
RequestCodeExtraIndex.argtypes = (freefunc,)
RequestCodeExtraIndex.restype = ctypes.c_ssize_t

SetExtra = py._PyCode_SetExtra
SetExtra.argtypes = (ctypes.py_object, ctypes.c_ssize_t, ctypes.c_voidp)
SetExtra.restype = ctypes.c_int

LAST_FREED = None
def myfree(ptr):
    global LAST_FREED
    LAST_FREED = ptr

FREE_FUNC = freefunc(myfree)
FREE_INDEX = RequestCodeExtraIndex(FREE_FUNC)


# Verify that the provided free function gets invoked
# when the code object is cleaned up.
f = eval('lambda:42')

SetExtra(f.__code__, FREE_INDEX, ctypes.c_voidp(100))
del f # crashes!!

    The problem: freefunc = ctypes.CFUNCTYPE(None, ctypes.c_voidp) declares a function with signature int f(void*). However, the definition of freefunc is void f(void*). These function signatures do not agree, and trying to make the call crashes.

    Due to a bug(?) ctypes can produce closures that have void return type but it can't produce simple functions with void return type.

    Closures code: checks if restype == Py_None and if so gives the callback a void return type
    https://github.com/python/cpython/blob/main/Modules/_ctypes/callbacks.c#L381

    Direct call code: calls _ctypes_get_ffi_type which never returns ffi_type_void:

    cpython/Modules/_ctypes/callproc.c

    Line 1212 in b183f48

    rtype = _ctypes_get_ffi_type(restype);

    @hoodmane hoodmane mannequin added topic-ctypes labels Apr 2, 2022
    @tiran tiran added tests Tests in the Lib/test dir 3.11 only security fixes type-bug An unexpected behavior, bug, or error labels Apr 3, 2022
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
    tiran pushed a commit that referenced this issue Apr 14, 2022
    @hoodmane
    gh-91353: Fix void return type handling in ctypes (GH-32246)
    1b035d9
    @corona10
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    I think that we can close this issue. Please feel free to reopen this issue if needed.

    @tiran
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    tiran commented Jul 12, 2022

    Yeah, the issue is fixed in 3.11 and main branches.

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