ctypes on Windows: error calling C function that returns a struct containing 3 bools

[mattneri]

BPO	34603
Nosy	@amauryfa, @abalkin, @vstinner, @meadori, @serhiy-storchaka, @miss-islington, @vladima
PRs	bpo-34603: Fix returning structs from functions #9258 [3.7] bpo-34603, ctypes/libffi_msvc: Fix returning structs from functions (GH-9258) #9340 [3.6] bpo-34603, ctypes/libffi_msvc: Fix returning structs from functions (GH-9258) #9341 [2.7] bpo-34603, ctypes/libffi_msvc: Fix returning structs from functions (GH-9258) #9342 [2.7] bpo-34603, ctypes/libffi_msvc: Fix returning structs from functions (GH-9258) #9425 Use assertEqual() instead of assertEquals(). #9721 [3.7] Use assertEqual() instead of assertEquals(). (GH-9721) #9725 [3.6] Use assertEqual() instead of assertEquals(). (GH-9721) (GH-9725) #9727
Files	MarshallingTest.zip

^{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 = <Date 2018-09-19.20:49:26.494>
created_at = <Date 2018-09-07.11:15:17.826>
labels = ['ctypes', 'type-bug', '3.7']
title = 'ctypes on Windows: error calling C function that returns a struct containing 3 bools'
updated_at = <Date 2018-10-05.19:11:26.672>
user = 'https://bugs.python.org/mattneri'

bugs.python.org fields:

activity = <Date 2018-10-05.19:11:26.672>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2018-09-19.20:49:26.494>
closer = 'vstinner'
components = ['ctypes']
creation = <Date 2018-09-07.11:15:17.826>
creator = 'mattneri'
dependencies = []
files = ['47789']
hgrepos = []
issue_num = 34603
keywords = ['patch']
message_count = 11.0
messages = ['324732', '325207', '325471', '325472', '325473', '325800', '325801', '327159', '327161', '327170', '327175']
nosy_count = 8.0
nosy_names = ['amaury.forgeotdarc', 'belopolsky', 'vstinner', 'meador.inge', 'serhiy.storchaka', 'miss-islington', 'v2m', 'mattneri']
pr_nums = ['9258', '9340', '9341', '9342', '9425', '9721', '9725', '9727']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34603'
versions = ['Python 3.4', 'Python 3.5', 'Python 3.6', 'Python 3.7']

[mattneri]

Marshalling the following C structure with ctypes in Windows (compiled with VS2015) is not working correctly.
As you can see, in the simple demo program I attached, the integer I pass as a parameter gets somehow corrupted. I use cdecl calling convention.

The corruption happens only if the returned structure contains 3 booleans, if I add a fourth bool to the structure than I get expected results.

In linux (compiling with Gcc) the same code (with 3 booleans) work as expected.

typedef uint64_t CustomHandle;

typedef struct
{
bool first;
bool second;
bool third;
} Flags;

CustomHandle GetHandle();
Flags GetFlags(CustomHandle handle);

As already mention I attached all the files to reproduce the issue with the related cmake file

[vladima]

I think the problem is that FFI layer assumes that MSVC compiler will try to pass any structure less than 8 bytes in registers whereis it is not always true:
To be returned by value in RAX, user-defined types must have a length of 1, 2, 4, 8, 16, 32, or 64 bits (from https://msdn.microsoft.com/en-us/library/7572ztz4.aspx).
I have a fix, now adding tests.

[vstinner]

New changeset 7843cae by Victor Stinner (Vladimir Matveev) in branch 'master':
bpo-34603, ctypes/libffi_msvc: Fix returning structs from functions (GH-9258)
7843cae

[miss-islington]

New changeset e3f6aa7 by Miss Islington (bot) in branch '3.7':
bpo-34603, ctypes/libffi_msvc: Fix returning structs from functions (GH-9258)
e3f6aa7

[miss-islington]

New changeset e536320 by Miss Islington (bot) in branch '3.6':
bpo-34603, ctypes/libffi_msvc: Fix returning structs from functions (GH-9258)
e536320

[vstinner]

New changeset b63a16f by Victor Stinner (Vladimir Matveev) in branch '2.7':
[2.7] bpo-34603, ctypes/libffi_msvc: Fix returning structs from functions (GH-9258) (GH-9425)
b63a16f

[vstinner]

Thanks MatteoL for the bug report, it has been fixed in 2.7, 3.6, 3.7 and master. Thanks Vladimir Matveev for the fix!

[serhiy-storchaka]

assertEquals() is deprecated, use assertEqual() instead.

[serhiy-storchaka]

New changeset 4642d5f by Serhiy Storchaka in branch 'master':
Use assertEqual() instead of assertEquals(). (GH-9721)
4642d5f

[serhiy-storchaka]

New changeset 6bffe50 by Serhiy Storchaka in branch '3.7':
Use assertEqual() instead of assertEquals(). (GH-9721) (GH-9725)
6bffe50