Kernel cannot dump now.

os/src/trap/mod.rs

@@ -44,11 +44,11 @@ pub fn trap_handler(cx: &mut TrapContext) -> &mut TrapContext {
         }
         Trap::Exception(Exception::StoreFault) |
         Trap::Exception(Exception::StorePageFault) => {
-            println!("[kernel] PageFault in application, bad addr = {:#x}, bad instruction = {:#x}, core dumped.", stval, cx.sepc);
+            println!("[kernel] PageFault in application, bad addr = {:#x}, bad instruction = {:#x}, kernel killed it.", stval, cx.sepc);
             exit_current_and_run_next();
         }
         Trap::Exception(Exception::IllegalInstruction) => {
-            println!("[kernel] IllegalInstruction in application, core dumped.");
+            println!("[kernel] IllegalInstruction in application, kernel killed it.");
             exit_current_and_run_next();
         }
         Trap::Interrupt(Interrupt::SupervisorTimer) => {