Small Fix && cargo fmt

os/src/lang_items.rs

@@ -1,16 +1,23 @@
-use core::panic::PanicInfo;
-use core::arch::asm;
 use crate::sbi::shutdown;
 use crate::task::current_kstack_top;
+use core::arch::asm;
+use core::panic::PanicInfo;
 
 #[panic_handler]
 fn panic(info: &PanicInfo) -> ! {
     if let Some(location) = info.location() {
-        println!("[kernel] Panicked at {}:{} {}", location.file(), location.line(), info.message().unwrap());
+        println!(
+            "[kernel] Panicked at {}:{} {}",
+            location.file(),
+            location.line(),
+            info.message().unwrap()
+        );
     } else {
         println!("[kernel] Panicked: {}", info.message().unwrap());
     }
-    unsafe { backtrace(); }
+    unsafe {
+        backtrace();
+    }
     shutdown()
 }
 
@@ -20,9 +27,11 @@ unsafe fn backtrace() {
     asm!("mv {}, s0", out(reg) fp);
     println!("---START BACKTRACE---");
     for i in 0..10 {
-        if fp == stop { break; }
-        println!("#{}:ra={:#x}", i, *((fp-8) as *const usize));
-        fp = *((fp-16) as *const usize);
+        if fp == stop {
+            break;
+        }
+        println!("#{}:ra={:#x}", i, *((fp - 8) as *const usize));
+        fp = *((fp - 16) as *const usize);
     }
     println!("---END   BACKTRACE---");
 }