diff --git a/Include/cpython/unicodeobject.h b/Include/cpython/unicodeobject.h
index e8b04d158b0805..136f5d5c5f8425 100644
--- a/Include/cpython/unicodeobject.h
+++ b/Include/cpython/unicodeobject.h
@@ -99,6 +99,11 @@ typedef struct {
PyObject_HEAD
Py_ssize_t length; /* Number of code points in the string */
Py_hash_t hash; /* Hash value; -1 if not set */
+#ifdef Py_GIL_DISABLED
+ /* Ensure 4 byte alignment for PyUnicode_DATA(), see gh-63736 on m68k.
+ In the non-free-threaded build, we'll use explicit padding instead */
+ _Py_ALIGN_AS(4)
+#endif
struct {
/* If interned is non-zero, the two references from the
dictionary to this object are *not* counted in ob_refcnt.
@@ -109,7 +114,12 @@ typedef struct {
3: Interned, Immortal, and Static
This categorization allows the runtime to determine the right
cleanup mechanism at runtime shutdown. */
- uint16_t interned;
+#ifdef Py_GIL_DISABLED
+ // Needs to be accessed atomically, so can't be a bit field.
+ unsigned char interned;
+#else
+ unsigned int interned:2;
+#endif
/* Character size:
- PyUnicode_1BYTE_KIND (1):
@@ -132,23 +142,23 @@ typedef struct {
* all characters are in the range U+0000-U+10FFFF
* at least one character is in the range U+10000-U+10FFFF
*/
- unsigned short kind:3;
+ unsigned int kind:3;
/* Compact is with respect to the allocation scheme. Compact unicode
objects only require one memory block while non-compact objects use
one block for the PyUnicodeObject struct and another for its data
buffer. */
- unsigned short compact:1;
+ unsigned int compact:1;
/* The string only contains characters in the range U+0000-U+007F (ASCII)
and the kind is PyUnicode_1BYTE_KIND. If ascii is set and compact is
set, use the PyASCIIObject structure. */
- unsigned short ascii:1;
+ unsigned int ascii:1;
/* The object is statically allocated. */
- unsigned short statically_allocated:1;
+ unsigned int statically_allocated:1;
+#ifndef Py_GIL_DISABLED
/* Padding to ensure that PyUnicode_DATA() is always aligned to
- 4 bytes (see issue #19537 on m68k) and we use unsigned short to avoid
- the extra four bytes on 32-bit Windows. This is restricted features
- for specific compilers including GCC, MSVC, Clang and IBM's XL compiler. */
- unsigned short :10;
+ 4 bytes (see issue gh-63736 on m68k) */
+ unsigned int :24;
+#endif
} state;
} PyASCIIObject;
@@ -198,7 +208,7 @@ typedef struct {
/* Use only if you know it's a string */
static inline unsigned int PyUnicode_CHECK_INTERNED(PyObject *op) {
#ifdef Py_GIL_DISABLED
- return _Py_atomic_load_uint16_relaxed(&_PyASCIIObject_CAST(op)->state.interned);
+ return _Py_atomic_load_uint8_relaxed(&_PyASCIIObject_CAST(op)->state.interned);
#else
return _PyASCIIObject_CAST(op)->state.interned;
#endif
diff --git a/Include/pymacro.h b/Include/pymacro.h
index a82f347866e8d0..218987a80b0d91 100644
--- a/Include/pymacro.h
+++ b/Include/pymacro.h
@@ -23,6 +23,47 @@
# define static_assert _Static_assert
#endif
+
+// _Py_ALIGN_AS: this compiler's spelling of `alignas` keyword,
+// We currently use alignas for free-threaded builds only; additional compat
+// checking would be great before we add it to the default build.
+// Standards/compiler support:
+// - `alignas` is a keyword in C23 and C++11.
+// - `_Alignas` is a keyword in C11
+// - GCC & clang has __attribute__((aligned))
+// (use that for older standards in pedantic mode)
+// - MSVC has __declspec(align)
+// - `_Alignas` is common C compiler extension
+// Older compilers may name it differently; to allow compilation on such
+// unsupported platforms, we don't redefine _Py_ALIGN_AS if it's already
+// defined. Note that defining it wrong (including defining it to nothing) will
+// cause ABI incompatibilities.
+#ifdef Py_GIL_DISABLED
+# ifndef _Py_ALIGN_AS
+# ifdef __cplusplus
+# if __cplusplus >= 201103L
+# define _Py_ALIGN_AS(V) alignas(V)
+# elif defined(__GNUC__) || defined(__clang__)
+# define _Py_ALIGN_AS(V) __attribute__((aligned(V)))
+# elif defined(_MSC_VER)
+# define _Py_ALIGN_AS(V) __declspec(align(V))
+# else
+# define _Py_ALIGN_AS(V) alignas(V)
+# endif
+# elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L
+# define _Py_ALIGN_AS(V) alignas(V)
+# elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
+# define _Py_ALIGN_AS(V) _Alignas(V)
+# elif (defined(__GNUC__) || defined(__clang__))
+# define _Py_ALIGN_AS(V) __attribute__((aligned(V)))
+# elif defined(_MSC_VER)
+# define _Py_ALIGN_AS(V) __declspec(align(V))
+# else
+# define _Py_ALIGN_AS(V) _Alignas(V)
+# endif
+# endif
+#endif
+
/* Minimum value between x and y */
#define Py_MIN(x, y) (((x) > (y)) ? (y) : (x))
diff --git a/Misc/NEWS.d/next/C_API/2025-04-28-15-36-01.gh-issue-128972.8bZMIm.rst b/Misc/NEWS.d/next/C_API/2025-04-28-15-36-01.gh-issue-128972.8bZMIm.rst
new file mode 100644
index 00000000000000..4b6a6e3606ff16
--- /dev/null
+++ b/Misc/NEWS.d/next/C_API/2025-04-28-15-36-01.gh-issue-128972.8bZMIm.rst
@@ -0,0 +1,3 @@
+For non-free-threaded builds, the memory layout of :c:struct:`PyASCIIObject`
+is reverted to match Python 3.13. (Note that the structure is not part of
+stable ABI and so its memory layout is *guaranteed* to remain stable.)
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 462323a828ef49..eb3e1c48fd4050 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -15918,7 +15918,7 @@ immortalize_interned(PyObject *s)
_Py_DecRefTotal(_PyThreadState_GET());
}
#endif
- FT_ATOMIC_STORE_UINT16_RELAXED(_PyUnicode_STATE(s).interned, SSTATE_INTERNED_IMMORTAL);
+ FT_ATOMIC_STORE_UINT8_RELAXED(_PyUnicode_STATE(s).interned, SSTATE_INTERNED_IMMORTAL);
_Py_SetImmortal(s);
}
@@ -16036,7 +16036,7 @@ intern_common(PyInterpreterState *interp, PyObject *s /* stolen */,
Py_DECREF(s);
Py_DECREF(s);
}
- FT_ATOMIC_STORE_UINT16_RELAXED(_PyUnicode_STATE(s).interned, SSTATE_INTERNED_MORTAL);
+ FT_ATOMIC_STORE_UINT8_RELAXED(_PyUnicode_STATE(s).interned, SSTATE_INTERNED_MORTAL);
/* INTERNED_MORTAL -> INTERNED_IMMORTAL (if needed) */
@@ -16172,7 +16172,7 @@ _PyUnicode_ClearInterned(PyInterpreterState *interp)
Py_UNREACHABLE();
}
if (!shared) {
- FT_ATOMIC_STORE_UINT16_RELAXED(_PyUnicode_STATE(s).interned, SSTATE_NOT_INTERNED);
+ FT_ATOMIC_STORE_UINT8_RELAXED(_PyUnicode_STATE(s).interned, SSTATE_NOT_INTERNED);
}
}
#ifdef INTERNED_STATS
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