feat(core): check for sys.modules and main globals reallocations

Rewrite the static comparison in `utils.unimport_end()` in C.

[no changelog]

core/embed/upymod/modtrezorutils/modtrezorutils.c

@@ -302,6 +302,27 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_0(mod_trezorutils_enable_oom_dump_obj,
                                  mod_trezorutils_enable_oom_dump);
 #endif  // MICROPY_OOM_CALLBACK
 
+/// if __debug__:
+///     def check_reallocs() -> None:
+///         """
+///         Assert that `sys.modules` and `main`'s globals are never
+///         reallocated.
+///         """
+STATIC mp_obj_t mod_trezorutils_check_reallocs(void) {
+  mp_obj_dict_t *modules = &MP_STATE_VM(mp_loaded_modules_dict);
+  if (modules->map.alloc > MICROPY_LOADED_MODULES_DICT_SIZE) {
+    mp_raise_msg(&mp_type_AssertionError, "sys.modules dict is reallocated");
+  }
+  mp_obj_t main = mp_obj_dict_get(modules, MP_OBJ_NEW_QSTR(MP_QSTR_main));
+  size_t main_map_alloc = mp_obj_module_get_globals(main)->map.alloc;
+  if (main_map_alloc > MICROPY_MAIN_DICT_SIZE) {
+    mp_raise_msg(&mp_type_AssertionError, "main globals dict is reallocated");
+  }
+  return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_0(mod_trezorutils_check_reallocs_obj,
+                                 mod_trezorutils_check_reallocs);
+
 #endif  // !PYOPT
 
 /// def reboot_to_bootloader(
@@ -520,6 +541,8 @@ STATIC const mp_rom_map_elem_t mp_module_trezorutils_globals_table[] = {
     {MP_ROM_QSTR(MP_QSTR_enable_oom_dump),
      MP_ROM_PTR(&mod_trezorutils_enable_oom_dump_obj)},
 #endif
+    {MP_ROM_QSTR(MP_QSTR_check_reallocs),
+     MP_ROM_PTR(&mod_trezorutils_check_reallocs_obj)},
 #endif
     {MP_ROM_QSTR(MP_QSTR_sd_hotswap_enabled),
      MP_ROM_PTR(&mod_trezorutils_sd_hotswap_enabled_obj)},

core/mocks/generated/trezorutils.pyi

@@ -104,6 +104,12 @@ if __debug__:
         """
         Dump GC info in case of an OOM.
         """
+if __debug__:
+    def check_reallocs() -> None:
+        """
+        Assert that `sys.modules` and `main`'s globals are never
+        reallocated.
+        """
 
 
 # upymod/modtrezorutils/modtrezorutils.c

core/src/trezor/utils.py

@@ -37,7 +37,7 @@ from trezorutils import (  # noqa: F401
 from typing import TYPE_CHECKING
 
 if __debug__:
-    from trezorutils import LOG_STACK_USAGE
+    from trezorutils import LOG_STACK_USAGE, check_reallocs
 
     if LOG_STACK_USAGE:
         from trezorutils import estimate_unused_stack, zero_unused_stack  # noqa: F401
@@ -67,10 +67,9 @@ def unimport_begin() -> set[str]:
 
 
 def unimport_end(mods: set[str], collect: bool = True) -> None:
-    # static check that the size of sys.modules never grows above value of
-    # MICROPY_LOADED_MODULES_DICT_SIZE, so that the sys.modules dict is never
-    # reallocated at run-time
-    assert len(sys.modules) <= 160, "Please bump preallocated size in mpconfigport.h"
+    if __debug__:
+        # Assert that `sys.modules` and `__main__` dict are never reallocated at run-time
+        check_reallocs()
 
     for mod in sys.modules:  # pylint: disable=consider-using-dict-items
         if mod not in mods: