baremetal aarch64: error on unexpected interrupt

baremetal/lib/aarch64.S

@@ -21,12 +21,10 @@ mystart:
 
 LKMC_VECTOR_TABLE
 
-/* Default trap handler that does nothing.
+/* Default trap handler. */
- *
- * Weak means that if any other file defines it as a non-weak global,
- * that one will take precedence.
- *
- * We need this one to not get undefined references.
- */
 LKMC_WEAK(lkmc_vector_trap_handler)
-    ret
+    ldr x0, =lkmc_vector_trap_handler_error
+    bl puts
+    bl lkmc_assert_fail
+lkmc_vector_trap_handler_error:
+    .asciz "error: unexpected interrupt"

lkmc.h

@@ -22,6 +22,10 @@ bool lkmc_vector_equal(size_t n, double *v1, double *v2, double max_err);
     .global name; \
     name:
 
+/* Weak means that if any other file defines it as a non-weak global,
+ * that one will take precedence:
+ * https://stackoverflow.com/questions/274753/how-to-make-weak-linking-work-with-gcc/54601464#54601464
+ */
 #define LKMC_WEAK(name) \
     .weak name; \
     name: