bpo-38304: Add PyConfig.struct_size (GH-16451) (GH-16453)

Add a new struct_size field to PyPreConfig and PyConfig structures to
allow to modify these structures in the future without breaking the
backward compatibility.

* Replace private _config_version field with public struct_size field
  in PyPreConfig and PyConfig.
* Public PyPreConfig_InitIsolatedConfig() and
  PyPreConfig_InitPythonConfig()
  return type becomes PyStatus, instead of void.
* Internal _PyConfig_InitCompatConfig(),
  _PyPreConfig_InitCompatConfig(), _PyPreConfig_InitFromConfig(),
  _PyPreConfig_InitFromPreConfig() return type becomes PyStatus,
  instead of void.
* Remove _Py_CONFIG_VERSION
* Update the Initialization Configuration documentation.

(cherry picked from commit 441b10cf2855955c86565f8d59e72c2efc0f0a57)

13 files changed, 350 insertions, 60 deletions

diff --git a/Doc/c-api/init_config.rst b/Doc/c-api/init_config.rst
index 0c3c725..58e4174 100644
--- a/Doc/c-api/init_config.rst
+++ b/Doc/c-api/init_config.rst
@@ -194,18 +194,25 @@ PyPreConfig
    * Configure the LC_CTYPE locale
    * Set the UTF-8 mode
 
+   The :c:member:`struct_size` field must be explicitly initialized to
+   ``sizeof(PyPreConfig)``.
+
    Function to initialize a preconfiguration:
 
-   .. c:function:: void PyPreConfig_InitIsolatedConfig(PyPreConfig *preconfig)
+   .. c:function:: PyStatus PyPreConfig_InitIsolatedConfig(PyPreConfig *preconfig)
 
       Initialize the preconfiguration with :ref:`Python Configuration
       <init-python-config>`.
 
-   .. c:function:: void PyPreConfig_InitPythonConfig(PyPreConfig *preconfig)
+   .. c:function:: PyStatus PyPreConfig_InitPythonConfig(PyPreConfig *preconfig)
 
       Initialize the preconfiguration with :ref:`Isolated Configuration
       <init-isolated-conf>`.
 
+   The caller of these functions is responsible to handle exceptions (error or
+   exit) using :c:func:`PyStatus_Exception` and
+   :c:func:`Py_ExitStatusException`.
+
    Structure fields:
 
    .. c:member:: int allocator
@@ -267,6 +274,13 @@ PyPreConfig
       same way the regular Python parses command line arguments: see
       :ref:`Command Line Arguments <using-on-cmdline>`.
 
+   .. c:member:: size_t struct_size
+
+      Size of the structure in bytes: must be initialized to
+      ``sizeof(PyPreConfig)``.
+
+      Field used for API and ABI compatibility.
+
    .. c:member:: int use_environment
 
       See :c:member:`PyConfig.use_environment`.
@@ -316,12 +330,18 @@ the preinitialization.
 
 Example using the preinitialization to enable the UTF-8 Mode::
 
+    PyStatus status;
     PyPreConfig preconfig;
-    PyPreConfig_InitPythonConfig(&preconfig);
+    preconfig.struct_size = sizeof(PyPreConfig);
+
+    status = PyPreConfig_InitPythonConfig(&preconfig);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
 
     preconfig.utf8_mode = 1;
 
-    PyStatus status = Py_PreInitialize(&preconfig);
+    status = Py_PreInitialize(&preconfig);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
     }
@@ -340,6 +360,9 @@ PyConfig
 
    Structure containing most parameters to configure Python.
 
+   The :c:member:`struct_size` field must be explicitly initialized to
+   ``sizeof(PyConfig)``.
+
    Structure methods:
 
    .. c:function:: PyStatus PyConfig_InitPythonConfig(PyConfig *config)
@@ -656,6 +679,13 @@ PyConfig
       Encoding and encoding errors of :data:`sys.stdin`, :data:`sys.stdout` and
       :data:`sys.stderr`.
 
+   .. c:member:: size_t struct_size
+
+      Size of the structure in bytes: must be initialized to
+      ``sizeof(PyConfig)``.
+
+      Field used for API and ABI compatibility.
+
    .. c:member:: int tracemalloc
 
       If non-zero, call :func:`tracemalloc.start` at startup.
@@ -718,6 +748,7 @@ Example setting the program name::
     {
         PyStatus status;
         PyConfig config;
+        config.struct_size = sizeof(PyConfig);
 
         status = PyConfig_InitPythonConfig(&config);
         if (PyStatus_Exception(status)) {
@@ -750,6 +781,7 @@ configuration, and then override some parameters::
     {
         PyStatus status;
         PyConfig config;
+        config.struct_size = sizeof(PyConfig);
 
         status = PyConfig_InitPythonConfig(&config);
         if (PyStatus_Exception(status)) {
@@ -835,8 +867,9 @@ Example of customized Python always running in isolated mode::
 
     int main(int argc, char **argv)
     {
-        PyConfig config;
         PyStatus status;
+        PyConfig config;
+        config.struct_size = sizeof(PyConfig);
 
         status = PyConfig_InitPythonConfig(&config);
         if (PyStatus_Exception(status)) {
@@ -1028,6 +1061,7 @@ phases::
     {
         PyStatus status;
         PyConfig config;
+        config.struct_size = sizeof(PyConfig);
 
         status = PyConfig_InitPythonConfig(&config);
         if (PyStatus_Exception(status)) {
diff --git a/Include/cpython/initconfig.h b/Include/cpython/initconfig.h
index 047f511..d5effb8 100644
--- a/Include/cpython/initconfig.h
+++ b/Include/cpython/initconfig.h
@@ -45,8 +45,10 @@ PyAPI_FUNC(PyStatus) PyWideStringList_Insert(PyWideStringList *list,
 /* --- PyPreConfig ----------------------------------------------- */
 
 typedef struct {
-    int _config_version;  /* Internal configuration version,
-                             used for ABI compatibility */
+    /* Size of the structure in bytes: must be initialized to
+       sizeof(PyPreConfig). Field used for API and ABI compatibility. */
+    size_t struct_size;
+
     int _config_init;     /* _PyConfigInitEnum value */
 
     /* Parse Py_PreInitializeFromBytesArgs() arguments?
@@ -122,15 +124,17 @@ typedef struct {
     int allocator;
 } PyPreConfig;
 
-PyAPI_FUNC(void) PyPreConfig_InitPythonConfig(PyPreConfig *config);
-PyAPI_FUNC(void) PyPreConfig_InitIsolatedConfig(PyPreConfig *config);
+PyAPI_FUNC(PyStatus) PyPreConfig_InitPythonConfig(PyPreConfig *config);
+PyAPI_FUNC(PyStatus) PyPreConfig_InitIsolatedConfig(PyPreConfig *config);
 
 
 /* --- PyConfig ---------------------------------------------- */
 
 typedef struct {
-    int _config_version;  /* Internal configuration version,
-                             used for ABI compatibility */
+    /* Size of the structure in bytes: must be initialized to
+       sizeof(PyConfig). Field used for API and ABI compatibility. */
+    size_t struct_size;
+
     int _config_init;     /* _PyConfigInitEnum value */
 
     int isolated;         /* Isolated mode? see PyPreConfig.isolated */
@@ -403,7 +407,6 @@ typedef struct {
 
     /* If equal to 0, stop Python initialization before the "main" phase */
     int _init_main;
-
 } PyConfig;
 
 PyAPI_FUNC(PyStatus) PyConfig_InitPythonConfig(PyConfig *config);
diff --git a/Include/internal/pycore_initconfig.h b/Include/internal/pycore_initconfig.h
index a7c1994..dcdb616 100644
--- a/Include/internal/pycore_initconfig.h
+++ b/Include/internal/pycore_initconfig.h
@@ -40,6 +40,8 @@ extern "C" {
     (err._type == _PyStatus_TYPE_EXIT)
 #define _PyStatus_EXCEPTION(err) \
     (err._type != _PyStatus_TYPE_OK)
+#define _PyStatus_UPDATE_FUNC(err) \
+    do { err.func = _PyStatus_GET_FUNC(); } while (0)
 
 /* --- PyWideStringList ------------------------------------------------ */
 
@@ -118,11 +120,11 @@ extern PyStatus _PyPreCmdline_Read(_PyPreCmdline *cmdline,
 
 /* --- PyPreConfig ----------------------------------------------- */
 
-PyAPI_FUNC(void) _PyPreConfig_InitCompatConfig(PyPreConfig *preconfig);
-extern void _PyPreConfig_InitFromConfig(
+PyAPI_FUNC(PyStatus) _PyPreConfig_InitCompatConfig(PyPreConfig *preconfig);
+extern PyStatus _PyPreConfig_InitFromConfig(
     PyPreConfig *preconfig,
     const PyConfig *config);
-extern void _PyPreConfig_InitFromPreConfig(
+extern PyStatus _PyPreConfig_InitFromPreConfig(
     PyPreConfig *preconfig,
     const PyPreConfig *config2);
 extern PyObject* _PyPreConfig_AsDict(const PyPreConfig *preconfig);
@@ -135,8 +137,6 @@ extern PyStatus _PyPreConfig_Write(const PyPreConfig *preconfig);
 
 /* --- PyConfig ---------------------------------------------- */
 
-#define _Py_CONFIG_VERSION 1
-
 typedef enum {
     /* Py_Initialize() API: backward compatibility with Python 3.6 and 3.7 */
     _PyConfig_INIT_COMPAT = 1,
@@ -144,7 +144,7 @@ typedef enum {
     _PyConfig_INIT_ISOLATED = 3
 } _PyConfigInitEnum;
 
-PyAPI_FUNC(void) _PyConfig_InitCompatConfig(PyConfig *config);
+PyAPI_FUNC(PyStatus) _PyConfig_InitCompatConfig(PyConfig *config);
 extern PyStatus _PyConfig_Copy(
     PyConfig *config,
     const PyConfig *config2);
diff --git a/Misc/NEWS.d/next/C API/2019-09-28-03-43-27.bpo-38304.RqHAwd.rst b/Misc/NEWS.d/next/C API/2019-09-28-03-43-27.bpo-38304.RqHAwd.rst
new file mode 100644
index 0000000..b797933
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2019-09-28-03-43-27.bpo-38304.RqHAwd.rst
@@ -0,0 +1,3 @@
+Add a new ``struct_size`` field to :c:type:`PyPreConfig` and :c:type:`PyConfig`
+structures to allow to modify these structures in the future without breaking
+the backward compatibility.
diff --git a/Modules/main.c b/Modules/main.c
index b8a1c9b..13936ad 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -53,13 +53,20 @@ pymain_init(const _PyArgv *args)
 #endif
 
     PyPreConfig preconfig;
-    PyPreConfig_InitPythonConfig(&preconfig);
+    preconfig.struct_size = sizeof(PyPreConfig);
+
+    status = PyPreConfig_InitPythonConfig(&preconfig);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
+
     status = _Py_PreInitializeFromPyArgv(&preconfig, args);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
 
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
     status = PyConfig_InitPythonConfig(&config);
     if (_PyStatus_EXCEPTION(status)) {
         goto done;
diff --git a/Programs/_freeze_importlib.c b/Programs/_freeze_importlib.c
index 74735f2..7c494c2 100644
--- a/Programs/_freeze_importlib.c
+++ b/Programs/_freeze_importlib.c
@@ -78,6 +78,7 @@ main(int argc, char *argv[])
 
     PyStatus status;
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
 
     status = PyConfig_InitIsolatedConfig(&config);
     if (PyStatus_Exception(status)) {
diff --git a/Programs/_testembed.c b/Programs/_testembed.c
index 83c266b..a375945 100644
--- a/Programs/_testembed.c
+++ b/Programs/_testembed.c
@@ -385,7 +385,12 @@ static int check_init_compat_config(int preinit)
 
     if (preinit) {
         PyPreConfig preconfig;
-        _PyPreConfig_InitCompatConfig(&preconfig);
+        preconfig.struct_size = sizeof(PyPreConfig);
+
+        status = _PyPreConfig_InitCompatConfig(&preconfig);
+        if (PyStatus_Exception(status)) {
+            Py_ExitStatusException(status);
+        }
 
         status = Py_PreInitialize(&preconfig);
         if (PyStatus_Exception(status)) {
@@ -394,7 +399,13 @@ static int check_init_compat_config(int preinit)
     }
 
     PyConfig config;
-    _PyConfig_InitCompatConfig(&config);
+    config.struct_size = sizeof(PyConfig);
+
+    status = _PyConfig_InitCompatConfig(&config);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
+
     config_set_program_name(&config);
     init_from_config_clear(&config);
 
@@ -470,7 +481,12 @@ static int test_init_from_config(void)
     PyStatus status;
 
     PyPreConfig preconfig;
-    _PyPreConfig_InitCompatConfig(&preconfig);
+    preconfig.struct_size = sizeof(PyPreConfig);
+
+    status = _PyPreConfig_InitCompatConfig(&preconfig);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
 
     putenv("PYTHONMALLOC=malloc_debug");
     preconfig.allocator = PYMEM_ALLOCATOR_MALLOC;
@@ -485,7 +501,12 @@ static int test_init_from_config(void)
     }
 
     PyConfig config;
-    _PyConfig_InitCompatConfig(&config);
+    config.struct_size = sizeof(PyConfig);
+
+    status = _PyConfig_InitCompatConfig(&config);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
     config.install_signal_handlers = 0;
 
     /* FIXME: test use_environment */
@@ -617,6 +638,8 @@ static int check_init_parse_argv(int parse_argv)
     PyStatus status;
 
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
@@ -702,6 +725,8 @@ static int test_init_python_env(void)
     set_all_env_vars();
 
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
@@ -755,6 +780,8 @@ static int test_init_isolated_flag(void)
 
     /* Test PyConfig.isolated=1 */
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
@@ -779,7 +806,13 @@ static int test_preinit_isolated1(void)
     PyStatus status;
 
     PyPreConfig preconfig;
-    _PyPreConfig_InitCompatConfig(&preconfig);
+    preconfig.struct_size = sizeof(PyPreConfig);
+
+    status = _PyPreConfig_InitCompatConfig(&preconfig);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
+
     preconfig.isolated = 1;
 
     status = Py_PreInitialize(&preconfig);
@@ -788,7 +821,12 @@ static int test_preinit_isolated1(void)
     }
 
     PyConfig config;
-    _PyConfig_InitCompatConfig(&config);
+    config.struct_size = sizeof(PyConfig);
+
+    status = _PyConfig_InitCompatConfig(&config);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
     config_set_program_name(&config);
     set_all_env_vars();
     init_from_config_clear(&config);
@@ -805,7 +843,13 @@ static int test_preinit_isolated2(void)
     PyStatus status;
 
     PyPreConfig preconfig;
-    _PyPreConfig_InitCompatConfig(&preconfig);
+    preconfig.struct_size = sizeof(PyPreConfig);
+
+    status = _PyPreConfig_InitCompatConfig(&preconfig);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
+
     preconfig.isolated = 0;
 
     status = Py_PreInitialize(&preconfig);
@@ -815,7 +859,11 @@ static int test_preinit_isolated2(void)
 
     /* Test PyConfig.isolated=1 */
     PyConfig config;
-    _PyConfig_InitCompatConfig(&config);
+    config.struct_size = sizeof(PyConfig);
+    status = _PyConfig_InitCompatConfig(&config);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
 
     Py_IsolatedFlag = 0;
     config.isolated = 1;
@@ -835,7 +883,12 @@ static int test_preinit_dont_parse_argv(void)
     PyStatus status;
 
     PyPreConfig preconfig;
-    PyPreConfig_InitIsolatedConfig(&preconfig);
+    preconfig.struct_size = sizeof(PyPreConfig);
+
+    status = PyPreConfig_InitIsolatedConfig(&preconfig);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
 
     preconfig.isolated = 0;
 
@@ -852,6 +905,7 @@ static int test_preinit_dont_parse_argv(void)
     }
 
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
 
     status = PyConfig_InitIsolatedConfig(&config);
     if (PyStatus_Exception(status)) {
@@ -877,6 +931,7 @@ static int test_preinit_parse_argv(void)
 {
     PyStatus status;
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
 
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
@@ -934,7 +989,12 @@ static int check_preinit_isolated_config(int preinit)
 
     if (preinit) {
         PyPreConfig preconfig;
-        PyPreConfig_InitIsolatedConfig(&preconfig);
+        preconfig.struct_size = sizeof(PyPreConfig);
+
+        status = PyPreConfig_InitIsolatedConfig(&preconfig);
+        if (PyStatus_Exception(status)) {
+            Py_ExitStatusException(status);
+        }
 
         status = Py_PreInitialize(&preconfig);
         if (PyStatus_Exception(status)) {
@@ -947,6 +1007,8 @@ static int check_preinit_isolated_config(int preinit)
     }
 
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitIsolatedConfig(&config);
     if (PyStatus_Exception(status)) {
         PyConfig_Clear(&config);
@@ -996,7 +1058,12 @@ static int check_init_python_config(int preinit)
 
     if (preinit) {
         PyPreConfig preconfig;
-        PyPreConfig_InitPythonConfig(&preconfig);
+        preconfig.struct_size = sizeof(PyPreConfig);
+
+        status = PyPreConfig_InitPythonConfig(&preconfig);
+        if (PyStatus_Exception(status)) {
+            Py_ExitStatusException(status);
+        }
 
         status = Py_PreInitialize(&preconfig);
         if (PyStatus_Exception(status)) {
@@ -1005,6 +1072,8 @@ static int check_init_python_config(int preinit)
     }
 
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
@@ -1035,7 +1104,13 @@ static int test_init_dont_configure_locale(void)
     PyStatus status;
 
     PyPreConfig preconfig;
-    PyPreConfig_InitPythonConfig(&preconfig);
+    preconfig.struct_size = sizeof(PyPreConfig);
+
+    status = PyPreConfig_InitPythonConfig(&preconfig);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
+
     preconfig.configure_locale = 0;
     preconfig.coerce_c_locale = 1;
     preconfig.coerce_c_locale_warn = 1;
@@ -1046,6 +1121,8 @@ static int test_init_dont_configure_locale(void)
     }
 
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
@@ -1063,6 +1140,8 @@ static int test_init_dev_mode(void)
 {
     PyStatus status;
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
@@ -1286,6 +1365,8 @@ static int run_audit_run_test(int argc, wchar_t **argv, void *test)
 {
     PyStatus status;
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
@@ -1334,6 +1415,8 @@ static int test_init_read_set(void)
 {
     PyStatus status;
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
@@ -1382,6 +1465,8 @@ static int test_init_sys_add(void)
     PySys_AddWarnOption(L"ignore:::sysadd_warnoption");
 
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     PyStatus status;
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
@@ -1450,7 +1535,12 @@ static int test_init_setpath_config(void)
 {
     PyStatus status;
     PyPreConfig preconfig;
-    PyPreConfig_InitPythonConfig(&preconfig);
+    preconfig.struct_size = sizeof(PyPreConfig);
+
+    status = PyPreConfig_InitPythonConfig(&preconfig);
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
 
     /* Explicitly preinitializes with Python preconfiguration to avoid
       Py_SetPath() implicit preinitialization with compat preconfiguration. */
@@ -1474,6 +1564,7 @@ static int test_init_setpath_config(void)
     putenv("TESTPATH=");
 
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
 
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
@@ -1531,6 +1622,8 @@ static int test_init_run_main(void)
 {
     PyStatus status;
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
@@ -1546,6 +1639,7 @@ static int test_init_main(void)
 {
     PyStatus status;
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
 
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
@@ -1577,6 +1671,7 @@ static int test_run_main(void)
 {
     PyStatus status;
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
 
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
diff --git a/Python/frozenmain.c b/Python/frozenmain.c
index c56938a..76309e9 100644
--- a/Python/frozenmain.c
+++ b/Python/frozenmain.c
@@ -40,6 +40,7 @@ Py_FrozenMain(int argc, char **argv)
     }
 
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
     status = PyConfig_InitPythonConfig(&config);
     if (PyStatus_Exception(status)) {
         PyConfig_Clear(&config);
diff --git a/Python/initconfig.c b/Python/initconfig.c
index a527271..dbc9de5 100644
--- a/Python/initconfig.c
+++ b/Python/initconfig.c
@@ -528,6 +528,18 @@ Py_GetArgcArgv(int *argc, wchar_t ***argv)
      ? _PyStatus_ERR("cannot decode " NAME) \
      : _PyStatus_NO_MEMORY())
 
+
+static PyStatus
+config_check_struct_size(const PyConfig *config)
+{
+    if (config->struct_size != sizeof(PyConfig)) {
+        return _PyStatus_ERR("unsupported PyConfig structure size "
+                             "(Python version mismatch?)");
+    }
+    return _PyStatus_OK();
+}
+
+
 /* Free memory allocated in config, but don't clear all attributes */
 void
 PyConfig_Clear(PyConfig *config)
@@ -568,12 +580,19 @@ PyConfig_Clear(PyConfig *config)
 }
 
 
-void
+PyStatus
 _PyConfig_InitCompatConfig(PyConfig *config)
 {
+    size_t struct_size = config->struct_size;
     memset(config, 0, sizeof(*config));
+    config->struct_size = struct_size;
+
+    PyStatus status = config_check_struct_size(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyStatus_UPDATE_FUNC(status);
+        return status;
+    }
 
-    config->_config_version = _Py_CONFIG_VERSION;
     config->_config_init = (int)_PyConfig_INIT_COMPAT;
     config->isolated = -1;
     config->use_environment = -1;
@@ -603,13 +622,17 @@ _PyConfig_InitCompatConfig(PyConfig *config)
 #ifdef MS_WINDOWS
     config->legacy_windows_stdio = -1;
 #endif
+    return _PyStatus_OK();
 }
 
 
-static void
+static PyStatus
 config_init_defaults(PyConfig *config)
 {
-    _PyConfig_InitCompatConfig(config);
+    PyStatus status = _PyConfig_InitCompatConfig(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
 
     config->isolated = 0;
     config->use_environment = 1;
@@ -628,13 +651,18 @@ config_init_defaults(PyConfig *config)
 #ifdef MS_WINDOWS
     config->legacy_windows_stdio = 0;
 #endif
+    return _PyStatus_OK();
 }
 
 
 PyStatus
 PyConfig_InitPythonConfig(PyConfig *config)
 {
-    config_init_defaults(config);
+    PyStatus status = config_init_defaults(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyStatus_UPDATE_FUNC(status);
+        return status;
+    }
 
     config->_config_init = (int)_PyConfig_INIT_PYTHON;
     config->configure_c_stdio = 1;
@@ -647,7 +675,11 @@ PyConfig_InitPythonConfig(PyConfig *config)
 PyStatus
 PyConfig_InitIsolatedConfig(PyConfig *config)
 {
-    config_init_defaults(config);
+    PyStatus status = config_init_defaults(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyStatus_UPDATE_FUNC(status);
+        return status;
+    }
 
     config->_config_init = (int)_PyConfig_INIT_ISOLATED;
     config->isolated = 1;
@@ -742,6 +774,19 @@ PyStatus
 _PyConfig_Copy(PyConfig *config, const PyConfig *config2)
 {
     PyStatus status;
+
+    status = config_check_struct_size(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyStatus_UPDATE_FUNC(status);
+        return status;
+    }
+
+    status = config_check_struct_size(config2);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyStatus_UPDATE_FUNC(status);
+        return status;
+    }
+
     PyConfig_Clear(config);
 
 #define COPY_ATTR(ATTR) config->ATTR = config2->ATTR
@@ -2199,7 +2244,12 @@ core_read_precmdline(PyConfig *config, _PyPreCmdline *precmdline)
     }
 
     PyPreConfig preconfig;
-    _PyPreConfig_InitFromPreConfig(&preconfig, &_PyRuntime.preconfig);
+    preconfig.struct_size = sizeof(PyPreConfig);
+
+    status = _PyPreConfig_InitFromPreConfig(&preconfig, &_PyRuntime.preconfig);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
 
     _PyPreConfig_GetConfig(&preconfig, config);
 
@@ -2338,6 +2388,12 @@ PyConfig_Read(PyConfig *config)
     PyStatus status;
     PyWideStringList orig_argv = PyWideStringList_INIT;
 
+    status = config_check_struct_size(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyStatus_UPDATE_FUNC(status);
+        return status;
+    }
+
     status = _Py_PreInitializeFromConfig(config, NULL);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
diff --git a/Python/pathconfig.c b/Python/pathconfig.c
index d5b8b1a..41ef7d2 100644
--- a/Python/pathconfig.c
+++ b/Python/pathconfig.c
@@ -434,7 +434,12 @@ pathconfig_global_read(_PyPathConfig *pathconfig)
 {
     PyStatus status;
     PyConfig config;
-    _PyConfig_InitCompatConfig(&config);
+    config.struct_size = sizeof(PyConfig);
+
+    status = _PyConfig_InitCompatConfig(&config);
+    if (_PyStatus_EXCEPTION(status)) {
+        goto done;
+    }
 
     /* Call _PyConfig_InitPathConfig() */
     status = PyConfig_Read(&config);
diff --git a/Python/preconfig.c b/Python/preconfig.c
index 8be6533..d18b01d 100644
--- a/Python/preconfig.c
+++ b/Python/preconfig.c
@@ -269,12 +269,30 @@ _PyPreCmdline_Read(_PyPreCmdline *cmdline, const PyPreConfig *preconfig)
 /* --- PyPreConfig ----------------------------------------------- */
 
 
-void
+static PyStatus
+preconfig_check_struct_size(PyPreConfig *config)
+{
+    if (config->struct_size != sizeof(PyPreConfig)) {
+        return _PyStatus_ERR("unsupported PyPreConfig structure size "
+                             "(Python version mismatch?)");
+    }
+    return _PyStatus_OK();
+}
+
+
+PyStatus
 _PyPreConfig_InitCompatConfig(PyPreConfig *config)
 {
+    size_t struct_size = config->struct_size;
     memset(config, 0, sizeof(*config));
+    config->struct_size = struct_size;
+
+    PyStatus status = preconfig_check_struct_size(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyStatus_UPDATE_FUNC(status);
+        return status;
+    }
 
-    config->_config_version = _Py_CONFIG_VERSION;
     config->_config_init = (int)_PyConfig_INIT_COMPAT;
     config->parse_argv = 0;
     config->isolated = -1;
@@ -295,13 +313,18 @@ _PyPreConfig_InitCompatConfig(PyPreConfig *config)
 #ifdef MS_WINDOWS
     config->legacy_windows_fs_encoding = -1;
 #endif
+    return _PyStatus_OK();
 }
 
 
-void
+PyStatus
 PyPreConfig_InitPythonConfig(PyPreConfig *config)
 {
-    _PyPreConfig_InitCompatConfig(config);
+    PyStatus status = _PyPreConfig_InitCompatConfig(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyStatus_UPDATE_FUNC(status);
+        return status;
+    }
 
     config->_config_init = (int)_PyConfig_INIT_PYTHON;
     config->isolated = 0;
@@ -316,13 +339,18 @@ PyPreConfig_InitPythonConfig(PyPreConfig *config)
 #ifdef MS_WINDOWS
     config->legacy_windows_fs_encoding = 0;
 #endif
+    return _PyStatus_OK();
 }
 
 
-void
+PyStatus
 PyPreConfig_InitIsolatedConfig(PyPreConfig *config)
 {
-    _PyPreConfig_InitCompatConfig(config);
+    PyStatus status = _PyPreConfig_InitCompatConfig(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyStatus_UPDATE_FUNC(status);
+        return status;
+    }
 
     config->_config_init = (int)_PyConfig_INIT_ISOLATED;
     config->configure_locale = 0;
@@ -333,41 +361,55 @@ PyPreConfig_InitIsolatedConfig(PyPreConfig *config)
 #ifdef MS_WINDOWS
     config->legacy_windows_fs_encoding = 0;
 #endif
+    return _PyStatus_OK();
 }
 
 
-void
+PyStatus
 _PyPreConfig_InitFromPreConfig(PyPreConfig *config,
                                const PyPreConfig *config2)
 {
-    PyPreConfig_InitPythonConfig(config);
+    PyStatus status = PyPreConfig_InitPythonConfig(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
+
     preconfig_copy(config, config2);
+    return _PyStatus_OK();
 }
 
 
-void
+PyStatus
 _PyPreConfig_InitFromConfig(PyPreConfig *preconfig, const PyConfig *config)
 {
+    PyStatus status;
     _PyConfigInitEnum config_init = (_PyConfigInitEnum)config->_config_init;
     switch (config_init) {
     case _PyConfig_INIT_PYTHON:
-        PyPreConfig_InitPythonConfig(preconfig);
+        status = PyPreConfig_InitPythonConfig(preconfig);
         break;
     case _PyConfig_INIT_ISOLATED:
-        PyPreConfig_InitIsolatedConfig(preconfig);
+        status = PyPreConfig_InitIsolatedConfig(preconfig);
         break;
     case _PyConfig_INIT_COMPAT:
     default:
-        _PyPreConfig_InitCompatConfig(preconfig);
+        status = _PyPreConfig_InitCompatConfig(preconfig);
     }
+
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
+
     _PyPreConfig_GetConfig(preconfig, config);
+    return _PyStatus_OK();
 }
 
 
 static void
 preconfig_copy(PyPreConfig *config, const PyPreConfig *config2)
 {
-    assert(config2->_config_version == _Py_CONFIG_VERSION);
+    assert(config->struct_size == sizeof(PyPreConfig));
+
 #define COPY_ATTR(ATTR) config->ATTR = config2->ATTR
 
     COPY_ATTR(_config_init);
@@ -787,6 +829,12 @@ _PyPreConfig_Read(PyPreConfig *config, const _PyArgv *args)
         return status;
     }
 
+    status = preconfig_check_struct_size(config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyStatus_UPDATE_FUNC(status);
+        return status;
+    }
+
     preconfig_get_global_vars(config);
 
     /* Copy LC_CTYPE locale, since it's modified later */
@@ -801,7 +849,12 @@ _PyPreConfig_Read(PyPreConfig *config, const _PyArgv *args)
 
     /* Save the config to be able to restore it if encodings change */
     PyPreConfig save_config;
-    _PyPreConfig_InitFromPreConfig(&save_config, config);
+    save_config.struct_size = sizeof(PyPreConfig);
+
+    status = _PyPreConfig_InitFromPreConfig(&save_config, config);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
 
     /* Set LC_CTYPE to the user preferred locale */
     if (config->configure_locale) {
@@ -923,7 +976,12 @@ PyStatus
 _PyPreConfig_Write(const PyPreConfig *src_config)
 {
     PyPreConfig config;
-    _PyPreConfig_InitFromPreConfig(&config, src_config);
+    config.struct_size = sizeof(PyPreConfig);
+
+    PyStatus status = _PyPreConfig_InitFromPreConfig(&config, src_config);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
 
     if (_PyRuntime.core_initialized) {
         /* bpo-34008: Calling this functions after Py_Initialize() ignores
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 42a062e..c154d06 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -731,7 +731,12 @@ _Py_PreInitializeFromPyArgv(const PyPreConfig *src_config, const _PyArgv *args)
     runtime->preinitializing = 1;
 
     PyPreConfig config;
-    _PyPreConfig_InitFromPreConfig(&config, src_config);
+    config.struct_size = sizeof(PyPreConfig);
+
+    status = _PyPreConfig_InitFromPreConfig(&config, src_config);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
 
     status = _PyPreConfig_Read(&config, args);
     if (_PyStatus_EXCEPTION(status)) {
@@ -790,7 +795,12 @@ _Py_PreInitializeFromConfig(const PyConfig *config,
     }
 
     PyPreConfig preconfig;
-    _PyPreConfig_InitFromConfig(&preconfig, config);
+    preconfig.struct_size = sizeof(PyPreConfig);
+
+    status = _PyPreConfig_InitFromConfig(&preconfig, config);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
 
     if (!config->parse_argv) {
         return Py_PreInitialize(&preconfig);
@@ -838,7 +848,12 @@ pyinit_core(_PyRuntimeState *runtime,
     }
 
     PyConfig config;
-    _PyConfig_InitCompatConfig(&config);
+    config.struct_size = sizeof(PyConfig);
+
+    status = _PyConfig_InitCompatConfig(&config);
+    if (_PyStatus_EXCEPTION(status)) {
+        goto done;
+    }
 
     status = _PyConfig_Copy(&config, src_config);
     if (_PyStatus_EXCEPTION(status)) {
@@ -1061,7 +1076,13 @@ Py_InitializeEx(int install_sigs)
     }
 
     PyConfig config;
-    _PyConfig_InitCompatConfig(&config);
+    config.struct_size = sizeof(PyConfig);
+
+    status = _PyConfig_InitCompatConfig(&config);
+    if (_PyStatus_EXCEPTION(status)) {
+        Py_ExitStatusException(status);
+    }
+
     config.install_signal_handlers = install_sigs;
 
     status = Py_InitializeFromConfig(&config);
diff --git a/Python/pystate.c b/Python/pystate.c
index f2924a8..f0662fa 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -60,7 +60,12 @@ _PyRuntimeState_Init_impl(_PyRuntimeState *runtime)
 
     _PyGC_Initialize(&runtime->gc);
     _PyEval_Initialize(&runtime->ceval);
-    PyPreConfig_InitPythonConfig(&runtime->preconfig);
+
+    runtime->preconfig.struct_size = sizeof(PyPreConfig);
+    PyStatus status = PyPreConfig_InitPythonConfig(&runtime->preconfig);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
 
     runtime->gilstate.check_enabled = 1;
 
@@ -205,6 +210,7 @@ PyInterpreterState_New(void)
     interp->id_refcount = -1;
     interp->check_interval = 100;
 
+    interp->config.struct_size = sizeof(PyConfig);
     PyStatus status = PyConfig_InitPythonConfig(&interp->config);
     if (_PyStatus_EXCEPTION(status)) {
         /* Don't report status to caller: PyConfig_InitPythonConfig()