fix(idt): panic in impl fmt::Debug for EntryOptions

Author: mkroening

src/structures/idt.rs

@@ -1002,8 +1002,8 @@ impl EntryOptions {
         self
     }
 
-    fn stack_index(&self) -> u16 {
-        self.bits.get_bits(0..3) - 1
+    fn stack_index(&self) -> Option<u16> {
+        self.bits.get_bits(0..3).checked_sub(1)
     }
 }
 
@@ -1720,6 +1720,11 @@ mod test {
         }
     }
 
+    #[test]
+    fn idt_fmt_debug() {
+        dbg!(InterruptDescriptorTable::new());
+    }
+
     #[test]
     fn entry_derive_test() {
         fn foo(_: impl Copy + PartialEq + fmt::Debug) {}