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gh-152433: Windows: fix ctypes error in UWP build #154700

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gh-152433: Windows: fix ctypes error in UWP build #154700

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7 changes: 7 additions & 0 deletions Modules/_ctypes/malloc_closure.c
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Original file line number Diff line number Diff line change
Expand Up @@ -68,10 +68,17 @@ static void more_core(void)

/* allocate a memory block */
#ifdef MS_WIN32
#ifdef MS_WINDOWS_DESKTOP
item = (ITEM *)VirtualAlloc(NULL,
count * sizeof(ITEM),
MEM_COMMIT,
PAGE_EXECUTE_READWRITE);
#else
item = (ITEM*)VirtualAllocFromApp(NULL,
count * sizeof(ITEM),
MEM_COMMIT | MEM_RESERVE,
PAGE_READWRITE);

@zooba zooba Sep 7, 2026

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If this works without EXECUTE, then do we need EXECUTE in the alternative VirtualAlloc call?

@thexai thexai Sep 11, 2026

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More work is needed for ctypes to have full functionality in UWP.

The EXECUTE flag is required, but in UWP, it is not allowed alongside READWRITE. This PR addresses some of the issues that recently arose after adding this code:

cpython/Modules/_ctypes/_ctypes.c

Lines 6390 to 6397 in e5d4fa2

_ctypes_mod_exec(PyObject *mod)
{
// See https://github.com/python/cpython/issues/128485
// This allocates some memory and then frees it to ensure that the
// the dlmalloc allocator initializes itself to avoid data races
// in free-threading.
void *codeloc = NULL;
void *ptr = Py_ffi_closure_alloc(sizeof(void *), &codeloc);

This causes errors immediately upon ctypes initialization (because reserves memory with execute permission).

But executing code in memory remains necessary for full ctypes functionality.

Let's say this PR only enables "limited" ctypes functionality on UWP but causes no harm on Windows Desktop.

#endif
if (item == NULL)
return;
#else
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