Bug report

Bug description:

Dear,

I'm wrapping a C-library with the ctypes module on Darwin (ARM64). I have a function that simply initializes a C-struct and returns the struct by value. The C-struct contains one simple C-array type. When using ArrayTypes in Python, it seems the struct is not returned properly.

On Windows and Linux platforms the same code does work as expected.

The strange thing is that if I lay out the struct explicitly with singular types in Python (as I expect the layout of the struct is the same), it does work as expected on all tried platforms.

To reproduce, I first create a simple .c file with the struct and the initializing function. In Python, I give code that I use to compile (with gcc), and then three different ways to wrap the struct and function in Python using ctypes. I believe the three ways should be equivalent (and they are on Windows and Linux), but not on Darwin (ARM64).

I saved this file asctypesexample.c

structexample{doublecoords[3];};structexampleset_defaults(){structexampleex;ex.coords[0]=1.0;ex.coords[1]=2.0;ex.coords[2]=3.0;returnex;}

I saved this file asreproduce.py

importosimportsubprocessimportctypesdefcompile():"""Compile the c file using gcc."""subprocess.call(["gcc","-c","-Wall","-Werror","-fpic","ctypesexample.c"])subprocess.call(["gcc","-shared","-o","libctypesexample","ctypesexample.o"])assertos.path.isfile('libctypesexample')# Three ways to wrap the struct:classExample1(ctypes.Structure):_fields_= [            ('coords',ctypes.c_double*3)               ]classCoordType(ctypes.Array):_type_=ctypes.c_double_length_=3classExample2(ctypes.Structure):_fields_= [('coords',CoordType)]classExample3(ctypes.Structure):_fields_= [            ('x',ctypes.c_double),            ('y',ctypes.c_double),            ('z',ctypes.c_double)               ]defrun():# Load the shared libraryso_location=os.path.abspath("libctypesexample")_lib=ctypes.cdll.LoadLibrary(so_location)_lib.set_defaults.restype=Example1o=_lib.set_defaults()print(f"Example1: ({o.coords[0]},{o.coords[1]},{o.coords[2]})")_lib.set_defaults.restype=Example2o=_lib.set_defaults()print(f"Example2: ({o.coords[0]},{o.coords[1]},{o.coords[2]})")_lib.set_defaults.restype=Example3o=_lib.set_defaults()print(f"Example3: ({o.x},{o.y},{o.z})")if__name__=="__main__":ifnotos.path.isfile('libctypesexample'):compile()run()

I tried this code on Linux (debian) -- both in Docker and WSL. And this works perfectly. Equivalent code in Windows is also working fine. In the past, I have run similar code as above on many different versions of Python (3.5-3.11) on both platforms for years (and still) without problems. For example on WSL with the following platform info

uname_result(system='Linux', release='5.15.90.1-microsoft-standard-WSL2', version='#1 SMP Fri Jan 27 02:56:13 UTC 2023', machine='x86_64')

and Python:

Python 3.10.6 (main, Mar 10 2023, 10:55:28) [GCC 11.3.0] on linux

I get this correct output:

Example1: (1.0, 2.0, 3.0)Example2: (1.0, 2.0, 3.0)Example3: (1.0, 2.0, 3.0)

While onDarwin (ARM) with the following platform info:

system='Darwin', release='22.1.0', version='Darwin Kernel Version 22.1.0: Sun Oct 9 20:14:30 PDT 2022; root:xnu-8792.41.9~2/RELEASE_ARM64_T8103', machine='arm64')

and Python

Python 3.11.4 (main, Jun 12 2023, 11:39:45) [Clang 14.0.3 (clang-1403.0.22.14.1)] on darwin

I get the following output:

Example1: (3.025693809e-314, 3.0256938013e-314, 2.1481083817e-314)Example2: (3.025693809e-314, 3.0256938013e-314, 2.1481083817e-314)Example3: (1.0, 2.0, 3.0)

In summary, the struct doesn't seem to be properly returned as value using array types, though with a literal listing of the types, it seems there is no problem. So there is a workaround, but as we're using ctypes for automatic wrapping through reflection and the code works properly on Windows and Linux, it would be quite some work to implement the workaround.

I hope my bug report finds you without any errors, and many thanks for giving the opportunity to report.

Best regards

CPython versions tested on:

3.10, 3.11

Operating systems tested on:

Linux, macOS, Windows

Linked PRs

• gh-110190: Fix ctypes structs with array on Arm #112604
• [3.11] gh-110190: Fix ctypes structs with array on Arm (#112604) #112766
• [3.12] gh-110190: Fix ctypes structs with array on Arm (#112604) #112767
• gh-110190: Temporarily skip new test introduced in gh-112604 on PPC64LE #112818
• [3.12] gh-110190: Temporarily skip new test introduced in gh-112604 on PPC64LE (GH-112818) #112829
• [3.11] gh-110190: Temporarily skip new test introduced in gh-112604 on PPC64LE (GH-112818) #112830
• gh-110190: Fix ctypes structs with array on PPCLE64 #112959
• [3.11] gh-110190: Fix ctypes structs with array on PPCLE64 (GH-112959) #113167
• [3.12] gh-110190: Fix ctypes structs with array on PPCLE64 (GH-112959) #113170
• gh-110190: Fix ctypes structs with array on Windows ARM64 #114753
• [3.11] gh-110190: Fix ctypes structs with array on Windows ARM64 (GH-114753) #114774
• [3.12] gh-110190: Fix ctypes structs with array on Windows ARM64 (GH-114753) #114775
• gh-110190: Fix ctypes structs with array on SPARC #118233