Debug box: Do not reboot by default

The `debug_halt_error` handler should not implicitly infer a reboot of
the system.

The debug box handler can reboot, if it thinks it's necessary. The newly
introduced vIRQ_SystemReset API can be used for this purpose.

By default, the debug handler will go back to `debug_halt_error`. Since
it has been called twice, this function will eventually halt forever
(hence implementing a proper halt, as expected by the API name).

Author: AlessandroA

core/debug/src/debug.c

@@ -156,20 +156,10 @@ void debug_fault(THaltError reason, uint32_t lr, uint32_t sp)
     DEBUG_PRINT_END();
 }
 
-static void __debug_reboot(void)
-{
-    UVISOR_SVC(UVISOR_SVC_ID_DEBUG_REBOOT, "");
-}
-
-/* This function must be called as an SVCall handler.
- * All debug handlers that are required to reboot upon exit should use the
- * __debug_reboot function as return value, which triggers the SVCall. This note
- * applies to uVisor internally, as the actual debug box does not need to care
- * about this. */
+/* FIXME: The halt will be replaced with a proper return code. An ACL will be
+ *        created to allow single boxes to reset the device. */
 void debug_reboot(void)
 {
-    /* FIXME: The halt will be replaced with a proper return code. An ACL will
-     *        be created to allow single boxes to reset the device. */
     if (!g_debug_box.initialized || g_active_box != g_debug_box.box_id) {
         HALT_ERROR(NOT_ALLOWED, "This function can only be called from the context of an initialized debug box.\n\r");
     }
@@ -180,8 +170,7 @@ void debug_reboot(void)
 }
 
 /* FIXME: Currently it is not possible to return to a regular execution flow
- *        after the execution of the debug box handler. It is possible to
- *        reboot, though. */
+ *        after the execution of the debug box handler. */
 static void debug_deprivilege_and_return(void * debug_handler, void * return_handler,
                                          uint32_t a0, uint32_t a1, uint32_t a2, uint32_t a3)
 {
@@ -239,8 +228,9 @@ void debug_halt_error(THaltError reason)
 
         /* The following arguments are passed to the destination function:
          *   1. reason
-         * Upon return from the debug handler, the system will reboot. */
-        debug_deprivilege_and_return(g_debug_box.driver->halt_error, __debug_reboot, reason, 0, 0, 0);
+         * Upon return from the debug handler, this function will be called
+         * again, causing the final halt. */
+        debug_deprivilege_and_return(g_debug_box.driver->halt_error, debug_halt_error, reason, 0, 0, 0);
     }
 }