diff --git a/ch2/user/src/lib.rs b/ch2/user/src/lib.rs
index 081d219..e859d12 100644
--- a/ch2/user/src/lib.rs
+++ b/ch2/user/src/lib.rs
@@ -2,6 +2,7 @@
 #![feature(linkage)]  // 开启弱链接特性
 #![feature(panic_info_message)]
 
+pub mod syscall;
 pub mod user_lang_items;
 pub use user_lang_items::*;
 
diff --git a/ch2/user/src/syscall.rs b/ch2/user/src/syscall.rs
new file mode 100644
index 0000000..1604d1b
--- /dev/null
+++ b/ch2/user/src/syscall.rs
@@ -0,0 +1,30 @@
+use core::arch::asm;
+
+const SYSCALL_WRITE: usize = 64;
+const SYSCALL_EXIT: usize = 93;
+
+
+fn syscall(id: usize, args: [usize; 3]) -> isize {
+    let mut ret: isize;
+    unsafe {
+        // a0寄存器同时作为输入参数和输出参数, {in_var} => {out_var}
+        asm!(
+        "ecall",
+        inlateout("x10") args[0] => ret,
+        in("x11") args[1],
+        in("x12") args[2],
+        in("x17") id
+        );
+    }
+    ret
+}
+
+
+pub fn sys_write(fd: usize, buffer: &[u8]) -> isize {
+    syscall(SYSCALL_WRITE, [fd, buffer.as_ptr() as usize, buffer.len()])
+}
+
+pub fn sys_exit(exit_code: i32) -> isize {
+    syscall(SYSCALL_EXIT, [exit_code as usize, 0, 0])
+}
+