Chapter2: Clear .bss inside application.

user/src/lib.rs

@@ -11,6 +11,7 @@ mod lang_items;
 #[no_mangle]
 #[link_section = ".text.entry"]
 pub extern "C" fn _start() -> ! {
+    clear_bss();
     syscall::sys_exit(main());
     panic!("unreachable after sys_exit!");
 }
@@ -21,3 +22,12 @@ fn main() -> i32 {
     panic!("Cannot find main!");
 }
 
+fn clear_bss() {
+    extern "C" {
+        fn start_bss();
+        fn end_bss();
+    }
+    (start_bss as usize..end_bss as usize).for_each(|addr| {
+        unsafe { (addr as *mut u8).write_volatile(0); }
+    });
+}