tool: fix cpu error message

Signed-off-by: Ivan Velickovic <[email protected]>

Author: Ivan-Velickovic

tool/microkit/src/sdf.rs

@@ -556,7 +556,7 @@ impl ProtectionDomain {
                 node,
                 format!(
                     "cpu core must be less than {}, got {}",
-                    config.num_cores, cpu
+                    config.num_cores, cpu.0
                 ),
             ));
         }

tool/microkit/tests/sdf/pd_invalid_cpu.system

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+ Copyright 2025, UNSW
+
+ SPDX-License-Identifier: BSD-2-Clause
+-->
+<system>
+    <protection_domain name="test" cpu="10">
+        <program_image path="test" />
+    </protection_domain>
+</system>

tool/microkit/tests/test.rs

@@ -525,6 +525,15 @@ mod protection_domain {
             "Error: size must be > 0 on element 'ioport':",
         )
     }
+
+    #[test]
+    fn test_invalid_cpu() {
+        check_error(
+            &DEFAULT_AARCH64_KERNEL_CONFIG,
+            "pd_invalid_cpu.system",
+            "Error: cpu core must be less than 1, got 10 on element 'protection_domain':",
+        )
+    }
 }
 
 #[cfg(test)]