diff --git a/os/src/loader.rs b/os/src/loader.rs
deleted file mode 100644
index bfdc3970..00000000
--- a/os/src/loader.rs
+++ /dev/null
@@ -1,62 +0,0 @@
-use alloc::vec::Vec;
-use lazy_static::*;
-
-pub fn get_num_app() -> usize {
-    extern "C" { fn _num_app(); }
-    unsafe { (_num_app as usize as *const usize).read_volatile() }
-}
-
-pub fn get_app_data(app_id: usize) -> &'static [u8] {
-    extern "C" { fn _num_app(); }
-    let num_app_ptr = _num_app as usize as *const usize;
-    let num_app = get_num_app();
-    let app_start = unsafe {
-        core::slice::from_raw_parts(num_app_ptr.add(1), num_app + 1)
-    };
-    assert!(app_id < num_app);
-    unsafe {
-        core::slice::from_raw_parts(
-            app_start[app_id] as *const u8,
-            app_start[app_id + 1] - app_start[app_id]
-        )
-    }
-}
-
-lazy_static! {
-    static ref APP_NAMES: Vec<&'static str> = {
-        let num_app = get_num_app();
-        extern "C" { fn _app_names(); }
-        let mut start = _app_names as usize as *const u8;
-        let mut v = Vec::new();
-        unsafe {
-            for _ in 0..num_app {
-                let mut end = start;
-                while end.read_volatile() != '\0' as u8 {
-                    end = end.add(1);
-                }
-                let slice = core::slice::from_raw_parts(start, end as usize - start as usize);
-                let str = core::str::from_utf8(slice).unwrap();
-                v.push(str);
-                start = end.add(1);
-            }
-        }
-        v
-    };
-}
-
-
-#[allow(unused)]
-pub fn get_app_data_by_name(name: &str) -> Option<&'static [u8]> {
-    let num_app = get_num_app();
-    (0..num_app)
-        .find(|&i| APP_NAMES[i] == name)
-        .map(|i| get_app_data(i))
-}
-
-pub fn list_apps() {
-    println!("/**** APPS ****");
-    for app in APP_NAMES.iter() {
-        println!("{}", app);
-    }
-    println!("**************/");
-}
\ No newline at end of file
diff --git a/user/src/bin/cat.rs b/user/src/bin/cat.rs
index 988164d3..21de94f0 100644
--- a/user/src/bin/cat.rs
+++ b/user/src/bin/cat.rs
@@ -11,7 +11,6 @@ use user_lib::{
     close,
     read,
 };
-use alloc::string::String;
 
 #[no_mangle]
 pub fn main(argc: usize, argv: &[&str]) -> i32 {
@@ -21,14 +20,12 @@ pub fn main(argc: usize, argv: &[&str]) -> i32 {
         panic!("Error occured when opening file");
     }
     let fd = fd as usize;
-    let mut buf = [0u8; 16];
-    let mut s = String::new();
+    let mut buf = [0u8; 256];
     loop {
         let size = read(fd, &mut buf) as usize;
         if size == 0 { break; }
-        s.push_str(core::str::from_utf8(&buf[..size]).unwrap());
+        println!("{}", core::str::from_utf8(&buf[..size]).unwrap());
     }
-    println!("{}", s);
     close(fd);
     0
-}
\ No newline at end of file
+}
diff --git a/user/src/bin/huge_write.rs b/user/src/bin/huge_write.rs
index f9dafa17..b00ca17b 100644
--- a/user/src/bin/huge_write.rs
+++ b/user/src/bin/huge_write.rs
@@ -18,7 +18,7 @@ pub fn main() -> i32 {
     for i in 0..buffer.len() {
         buffer[i] = i as u8;
     }
-    let f = open("testf", OpenFlags::CREATE | OpenFlags::WRONLY);
+    let f = open("testf\0", OpenFlags::CREATE | OpenFlags::WRONLY);
     if f < 0 {
         panic!("Open test file failed!");
     }
@@ -33,4 +33,4 @@ pub fn main() -> i32 {
     let speed_kbs = size_mb * 1000000 / time_ms;
     println!("{}MiB written, time cost = {}ms, write speed = {}KiB/s", size_mb, time_ms, speed_kbs);
     0
-}
\ No newline at end of file
+}