diff --git a/os/src/syscall/process.rs b/os/src/syscall/process.rs
index 9e83ffe8..d919006f 100644
--- a/os/src/syscall/process.rs
+++ b/os/src/syscall/process.rs
@@ -4,7 +4,7 @@ use crate::task::{
     run_next_task
 };
 
-pub fn sys_exit(xstate: i32) -> ! {
+pub fn sys_exit(exit_code: i32) -> ! {
     println!("[kernel] Application exited with code {}", xstate);
     mark_current_exited();
     run_next_task();
diff --git a/user/src/bin/00write_a.rs b/user/src/bin/00write_a.rs
index f7ada612..979ec0bc 100644
--- a/user/src/bin/00write_a.rs
+++ b/user/src/bin/00write_a.rs
@@ -4,7 +4,7 @@
 #[macro_use]
 extern crate user_lib;
 
-use user_lib::sys_yield;
+use user_lib::yield_;
 
 const WIDTH: usize = 10;
 const HEIGHT: usize = 5;
@@ -14,7 +14,7 @@ fn main() -> i32 {
     for i in 0..HEIGHT {
         for _ in 0..WIDTH { print!("A"); }
         println!(" [{}/{}]", i + 1, HEIGHT);
-        sys_yield();
+        yield_();
     }
     println!("Test write_a OK!");
     0
diff --git a/user/src/bin/01write_b.rs b/user/src/bin/01write_b.rs
index e16b79da..7691b315 100644
--- a/user/src/bin/01write_b.rs
+++ b/user/src/bin/01write_b.rs
@@ -4,7 +4,7 @@
 #[macro_use]
 extern crate user_lib;
 
-use user_lib::sys_yield;
+use user_lib::yield_;
 
 const WIDTH: usize = 10;
 const HEIGHT: usize = 2;
@@ -14,7 +14,7 @@ fn main() -> i32 {
     for i in 0..HEIGHT {
         for _ in 0..WIDTH { print!("B"); }
         println!(" [{}/{}]", i + 1, HEIGHT);
-        sys_yield();
+        yield_();
     }
     println!("Test write_b OK!");
     0
diff --git a/user/src/bin/02write_c.rs b/user/src/bin/02write_c.rs
index 771f6447..6f342d12 100644
--- a/user/src/bin/02write_c.rs
+++ b/user/src/bin/02write_c.rs
@@ -4,7 +4,7 @@
 #[macro_use]
 extern crate user_lib;
 
-use user_lib::sys_yield;
+use user_lib::yield_;
 
 const WIDTH: usize = 10;
 const HEIGHT: usize = 3;
@@ -14,7 +14,7 @@ fn main() -> i32 {
     for i in 0..HEIGHT {
         for _ in 0..WIDTH { print!("C"); }
         println!(" [{}/{}]", i + 1, HEIGHT);
-        sys_yield();
+        yield_();
     }
     println!("Test write_c OK!");
     0
diff --git a/user/src/console.rs b/user/src/console.rs
index a826b8fe..ac801174 100644
--- a/user/src/console.rs
+++ b/user/src/console.rs
@@ -1,11 +1,13 @@
 use core::fmt::{self, Write};
-use crate::syscall::{STDOUT, sys_write};
+use super::write;
 
 struct Stdout;
 
+const STDOUT: usize = 1;
+
 impl Write for Stdout {
     fn write_str(&mut self, s: &str) -> fmt::Result {
-        sys_write(STDOUT, s.as_bytes());
+        write(STDOUT, s.as_bytes());
         Ok(())
     }
 }
diff --git a/user/src/lib.rs b/user/src/lib.rs
index fdcb6d56..d14e3d89 100644
--- a/user/src/lib.rs
+++ b/user/src/lib.rs
@@ -12,7 +12,7 @@ mod lang_items;
 #[link_section = ".text.entry"]
 pub extern "C" fn _start() -> ! {
     clear_bss();
-    syscall::sys_exit(main());
+    exit(main());
     panic!("unreachable after sys_exit!");
 }
 
@@ -32,4 +32,8 @@ fn clear_bss() {
     });
 }
 
-pub use syscall::*;
\ No newline at end of file
+use syscall::*;
+
+pub fn write(fd: usize, buf: &[u8]) -> isize { sys_write(fd, buf) }
+pub fn exit(exit_code: i32) -> isize { sys_exit(exit_code) }
+pub fn yield_() -> isize { sys_yield() }
\ No newline at end of file
diff --git a/user/src/syscall.rs b/user/src/syscall.rs
index 8e4ff50b..1b23a48a 100644
--- a/user/src/syscall.rs
+++ b/user/src/syscall.rs
@@ -1,5 +1,3 @@
-pub const STDOUT: usize = 1;
-
 const SYSCALL_WRITE: usize = 64;
 const SYSCALL_EXIT: usize = 93;
 const SYSCALL_YIELD: usize = 124;
@@ -22,8 +20,8 @@ pub fn sys_write(fd: usize, buffer: &[u8]) -> isize {
     syscall(SYSCALL_WRITE, [fd, buffer.as_ptr() as usize, buffer.len()])
 }
 
-pub fn sys_exit(xstate: i32) -> isize {
-    syscall(SYSCALL_EXIT, [xstate as usize, 0, 0])
+pub fn sys_exit(exit_code: i32) -> isize {
+    syscall(SYSCALL_EXIT, [exit_code as usize, 0, 0])
 }
 
 pub fn sys_yield() -> isize {