diff --git a/kernel/src/services.rs b/kernel/src/services.rs
index f6d59946e..547ef0608 100644
--- a/kernel/src/services.rs
+++ b/kernel/src/services.rs
@@ -265,6 +265,9 @@ impl Process {
         self.state = ProcessState::Free;
         Ok(())
     }
+
+    /// Reveal state for debugging outside the crate.
+    pub fn state(&self) -> ProcessState { self.state }
 }
 
 #[cfg(not(baremetal))]
@@ -679,6 +682,12 @@ impl SystemServices {
                     );
                 }
                 CallbackType::Swap(args) => {
+                    #[cfg(feature = "debug-swap")]
+                    {
+                        let pid = crate::arch::process::current_pid();
+                        let hardware_pid = (riscv::register::satp::read().bits() >> 22) & ((1 << 9) - 1);
+                        println!("bef invoke PROCESS_TABLE.current: {}, hw_pid: {}", pid.get(), hardware_pid);
+                    }
                     arch::syscall::invoke(
                         arch_process.current_thread_mut(),
                         pid.get() == 1,