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[2.7] bpo-34603, ctypes/libffi_msvc: Fix returning structs from functions (GH-9258) (GH-9425)
Co-authored-by: Vladimir Matveev <v2matveev@outlook.com>
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lines changed

‎Lib/ctypes/test/test_win32.py

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@@ -52,6 +52,24 @@ def test_noargs(self):
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# This is a special case on win32 x64
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windll.user32.GetDesktopWindow()
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@unittest.skipUnless(sys.platform == "win32", 'Windows-specific test')
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class ReturnStructSizesTestCase(unittest.TestCase):
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def test_sizes(self):
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dll = CDLL(_ctypes_test.__file__)
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for i in range(1, 11):
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fields = [ ("f%d" % f, c_char) for f in range(1, i + 1)]
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class S(Structure):
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_fields_ = fields
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f = getattr(dll, "TestSize%d" % i)
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f.restype = S
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res = f()
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for i, f in enumerate(fields):
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value = getattr(res, f[0])
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expected = chr(ord('a') + i)
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self.assertEquals(value, expected)
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@unittest.skipUnless(sys.platform == "win32", 'Windows-specific test')
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class TestWintypes(unittest.TestCase):
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def test_HWND(self):

‎Misc/NEWS.d/next/Windows/2018-09-13-08-29-04.bpo-34603.2AB7sc.rst

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@@ -0,0 +1 @@
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Fix returning structs from functions produced by MSVC

‎Modules/_ctypes/_ctypes_test.c

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@@ -655,6 +655,200 @@ EXPORT(void) TwoOutArgs(int a, int *pi, int b, int *pj)
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*pj += b;
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}
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#ifdef MS_WIN32
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typedef struct {
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char f1;
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} Size1;
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typedef struct {
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char f1;
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char f2;
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} Size2;
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typedef struct {
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char f1;
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char f2;
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char f3;
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} Size3;
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typedef struct {
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char f1;
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char f2;
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char f3;
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char f4;
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} Size4;
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typedef struct {
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char f1;
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char f2;
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char f3;
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char f4;
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char f5;
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} Size5;
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typedef struct {
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char f1;
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char f2;
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char f3;
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char f4;
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char f5;
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char f6;
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} Size6;
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typedef struct {
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char f1;
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char f2;
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char f3;
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char f4;
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char f5;
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char f6;
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char f7;
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} Size7;
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typedef struct {
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char f1;
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char f2;
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char f3;
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char f4;
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char f5;
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char f6;
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char f7;
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char f8;
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} Size8;
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typedef struct {
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char f1;
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char f2;
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char f3;
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char f4;
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char f5;
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char f6;
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char f7;
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char f8;
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char f9;
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} Size9;
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typedef struct {
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char f1;
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char f2;
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char f3;
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char f4;
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char f5;
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char f6;
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char f7;
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char f8;
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char f9;
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char f10;
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} Size10;
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EXPORT(Size1) TestSize1() {
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Size1 f;
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f.f1 = 'a';
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return f;
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}
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EXPORT(Size2) TestSize2() {
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Size2 f;
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f.f1 = 'a';
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f.f2 = 'b';
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return f;
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}
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EXPORT(Size3) TestSize3() {
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Size3 f;
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f.f1 = 'a';
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f.f2 = 'b';
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f.f3 = 'c';
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return f;
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}
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EXPORT(Size4) TestSize4() {
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Size4 f;
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f.f1 = 'a';
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f.f2 = 'b';
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f.f3 = 'c';
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f.f4 = 'd';
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return f;
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}
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EXPORT(Size5) TestSize5() {
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Size5 f;
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f.f1 = 'a';
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f.f2 = 'b';
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f.f3 = 'c';
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f.f4 = 'd';
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f.f5 = 'e';
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return f;
783+
}
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EXPORT(Size6) TestSize6() {
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Size6 f;
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f.f1 = 'a';
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f.f2 = 'b';
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f.f3 = 'c';
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f.f4 = 'd';
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f.f5 = 'e';
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f.f6 = 'f';
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return f;
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}
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EXPORT(Size7) TestSize7() {
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Size7 f;
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f.f1 = 'a';
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f.f2 = 'b';
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f.f3 = 'c';
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f.f4 = 'd';
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f.f5 = 'e';
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f.f6 = 'f';
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f.f7 = 'g';
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return f;
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}
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EXPORT(Size8) TestSize8() {
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Size8 f;
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f.f1 = 'a';
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f.f2 = 'b';
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f.f3 = 'c';
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f.f4 = 'd';
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f.f5 = 'e';
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f.f6 = 'f';
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f.f7 = 'g';
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f.f8 = 'h';
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return f;
819+
}
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EXPORT(Size9) TestSize9() {
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Size9 f;
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f.f1 = 'a';
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f.f2 = 'b';
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f.f3 = 'c';
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f.f4 = 'd';
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f.f5 = 'e';
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f.f6 = 'f';
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f.f7 = 'g';
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f.f8 = 'h';
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f.f9 = 'i';
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return f;
833+
}
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EXPORT(Size10) TestSize10() {
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Size10 f;
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f.f1 = 'a';
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f.f2 = 'b';
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f.f3 = 'c';
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f.f4 = 'd';
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f.f5 = 'e';
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f.f6 = 'f';
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f.f7 = 'g';
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f.f8 = 'h';
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f.f9 = 'i';
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f.f10 = 'j';
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return f;
848+
}
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#endif
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#ifdef MS_WIN32
659853
EXPORT(S2H) __stdcall s_ret_2h_func(S2H inp) { return ret_2h_func(inp); }
660854
EXPORT(S8I) __stdcall s_ret_8i_func(S8I inp) { return ret_8i_func(inp); }

‎Modules/_ctypes/callproc.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -747,9 +747,9 @@ ffi_type *_ctypes_get_ffi_type(PyObject *obj)
747747
It returns small structures in registers
748748
*/
749749
if (dict->ffi_type_pointer.type == FFI_TYPE_STRUCT) {
750-
if (dict->ffi_type_pointer.size <= 4)
750+
if (can_return_struct_as_int(dict->ffi_type_pointer.size))
751751
return &ffi_type_sint32;
752-
else if (dict->ffi_type_pointer.size <= 8)
752+
else if (can_return_struct_as_sint64 (dict->ffi_type_pointer.size))
753753
return &ffi_type_sint64;
754754
}
755755
#endif

‎Modules/_ctypes/libffi_msvc/ffi.c

Lines changed: 17 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -126,6 +126,21 @@ void ffi_prep_args(char *stack, extended_cif *ecif)
126126
return;
127127
}
128128

129+
/*
130+
Per: https://msdn.microsoft.com/en-us/library/7572ztz4.aspx
131+
To be returned by value in RAX, user-defined types must have a length
132+
of 1, 2, 4, 8, 16, 32, or 64 bits
133+
*/
134+
int can_return_struct_as_int(size_t s)
135+
{
136+
return s == 1 || s == 2 || s == 4;
137+
}
138+
139+
int can_return_struct_as_sint64(size_t s)
140+
{
141+
return s == 8;
142+
}
143+
129144
/* Perform machine dependent cif processing */
130145
ffi_status ffi_prep_cif_machdep(ffi_cif *cif)
131146
{
@@ -144,9 +159,9 @@ ffi_status ffi_prep_cif_machdep(ffi_cif *cif)
144159
/* MSVC returns small structures in registers. Put in cif->flags
145160
the value FFI_TYPE_STRUCT only if the structure is big enough;
146161
otherwise, put the 4- or 8-bytes integer type. */
147-
if (cif->rtype->size <= 4)
162+
if (can_return_struct_as_int(cif->rtype->size))
148163
cif->flags = FFI_TYPE_INT;
149-
else if (cif->rtype->size <= 8)
164+
else if (can_return_struct_as_sint64(cif->rtype->size))
150165
cif->flags = FFI_TYPE_SINT64;
151166
else
152167
cif->flags = FFI_TYPE_STRUCT;

‎Modules/_ctypes/libffi_msvc/ffi.h

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@@ -136,6 +136,9 @@ typedef struct _ffi_type
136136
/*@null@*/ struct _ffi_type **elements;
137137
} ffi_type;
138138

139+
int can_return_struct_as_int(size_t);
140+
int can_return_struct_as_sint64(size_t);
141+
139142
/* These are defined in types.c */
140143
extern ffi_type ffi_type_void;
141144
extern ffi_type ffi_type_uint8;

‎Modules/_ctypes/libffi_msvc/prep_cif.c

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -117,7 +117,8 @@ ffi_status ffi_prep_cif(/*@out@*/ /*@partial@*/ ffi_cif *cif,
117117
/* Make space for the return structure pointer */
118118
if (cif->rtype->type == FFI_TYPE_STRUCT
119119
#ifdef _WIN32
120-
&& (cif->rtype->size > 8) /* MSVC returns small structs in registers */
120+
&& !can_return_struct_as_int(cif->rtype->size) /* MSVC returns small structs in registers */
121+
&& !can_return_struct_as_sint64(cif->rtype->size)
121122
#endif
122123
#ifdef SPARC
123124
&& (cif->abi != FFI_V9 || cif->rtype->size > 32)
@@ -146,7 +147,9 @@ ffi_status ffi_prep_cif(/*@out@*/ /*@partial@*/ ffi_cif *cif,
146147
bytes += sizeof(void*);
147148
else
148149
#elif defined (_WIN64)
149-
if ((*ptr)->type == FFI_TYPE_STRUCT && ((*ptr)->size > 8))
150+
if ((*ptr)->type == FFI_TYPE_STRUCT &&
151+
!can_return_struct_as_int((*ptr)->size) &&
152+
!can_return_struct_as_sint64((*ptr)->size))
150153
bytes += sizeof(void*);
151154
else
152155
#endif

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