py/objexcept: Add uncatchable SystemAbort exception.

laurensvalk · laurensvalk · commit f4b08ea435d8 · 2022-11-17T11:22:17.000+01:00
This adds an exception type that forces MicroPython to exit even if the
user MicroPython script catches all exceptions.

This exception can be raised by C code to force MicroPython to exit for
safety reasons, such as very low battery or very high temperatures.
diff --git a/py/mpconfig.h b/py/mpconfig.h
@@ -658,6 +658,12 @@
 #define MICROPY_KBD_EXCEPTION (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_EXTRA_FEATURES)
 #endif
 
+// Whether to provide the SystemAbort exception, used to exit MicroPython
+// even if user code catches all exceptions.
+#ifndef MICROPY_ENABLE_SYSTEM_ABORT
+#define MICROPY_ENABLE_SYSTEM_ABORT (0)
+#endif
+
 // Prefer to raise KeyboardInterrupt asynchronously (from signal or interrupt
 // handler) - if supported by a particular port.
 #ifndef MICROPY_ASYNC_KBD_INTR
diff --git a/py/obj.h b/py/obj.h
@@ -860,6 +860,9 @@ extern const mp_obj_type_t mp_type_UnicodeError;
 extern const mp_obj_type_t mp_type_ValueError;
 extern const mp_obj_type_t mp_type_ViperTypeError;
 extern const mp_obj_type_t mp_type_ZeroDivisionError;
+#if MICROPY_ENABLE_SYSTEM_ABORT
+extern const mp_obj_type_t mp_type_SystemAbort;
+#endif
 
 // Constant objects, globally accessible: None, False, True
 // These should always be accessed via the below macros.
diff --git a/py/objexcept.c b/py/objexcept.c
@@ -376,6 +376,12 @@ MP_DEFINE_EXCEPTION(Exception, BaseException)
     MP_DEFINE_EXCEPTION(ResourceWarning, Warning)
     */
 
+#if MICROPY_ENABLE_SYSTEM_ABORT
+// Exception that can't be raised or caught by user code, not even with a
+// bare except. Can be used to force MicroPython to exit from C code.
+MP_DEFINE_EXCEPTION(SystemAbort, BaseException)
+#endif
+
 // *FORMAT-ON*
 
 mp_obj_t mp_obj_new_exception(const mp_obj_type_t *exc_type) {
diff --git a/py/vm.c b/py/vm.c
@@ -1441,8 +1441,12 @@ unwind_jump:;
                 POP_EXC_BLOCK();
             }
 
-            if (exc_sp >= exc_stack) {
-                // catch exception and pass to byte code
+            if (exc_sp >= exc_stack
+            #if MICROPY_ENABLE_SYSTEM_ABORT
+            && !mp_obj_exception_match(MP_OBJ_FROM_PTR(nlr.ret_val), MP_OBJ_FROM_PTR(&mp_type_SystemAbort))
+            #endif
+            ) {
+                // catch exception (but not SystemAbort) and pass to byte code
                 code_state->ip = exc_sp->handler;
                 mp_obj_t *sp = MP_TAGPTR_PTR(exc_sp->val_sp);
                 // save this exception in the stack so it can be used in a reraise, if needed
