diff --git a/src/kxos-frame/src/lib.rs b/src/kxos-frame/src/lib.rs
index add3fa94..b4ba69ca 100644
--- a/src/kxos-frame/src/lib.rs
+++ b/src/kxos-frame/src/lib.rs
@@ -15,14 +15,14 @@ pub mod config;
 pub mod cpu;
 pub mod device;
 mod error;
+pub mod log;
 pub mod prelude;
+pub mod sync;
 pub mod task;
 pub mod timer;
 pub mod user;
 mod util;
-pub mod log;
 pub mod vm;
-pub mod sync;
 
 pub use self::error::Error;
 use alloc::sync::Arc;
diff --git a/src/kxos-frame/src/log.rs b/src/kxos-frame/src/log.rs
index a54045c3..82c3e4cc 100644
--- a/src/kxos-frame/src/log.rs
+++ b/src/kxos-frame/src/log.rs
@@ -59,4 +59,4 @@ macro_rules! error {
         $crate::log_print!($($arg)*);
         $crate::log_print!("\n");
     };
-}
\ No newline at end of file
+}
diff --git a/src/kxos-frame/src/sync/mod.rs b/src/kxos-frame/src/sync/mod.rs
index a9887a14..751ffd84 100644
--- a/src/kxos-frame/src/sync/mod.rs
+++ b/src/kxos-frame/src/sync/mod.rs
@@ -2,4 +2,4 @@ mod spin;
 mod wait;
 
 pub use self::spin::{SpinLock, SpinLockGuard};
-pub use self::wait::{WaitQueue};
\ No newline at end of file
+pub use self::wait::WaitQueue;
diff --git a/src/kxos-frame/src/sync/spin.rs b/src/kxos-frame/src/sync/spin.rs
index 8968a4cf..1b92ff1a 100644
--- a/src/kxos-frame/src/sync/spin.rs
+++ b/src/kxos-frame/src/sync/spin.rs
@@ -2,7 +2,7 @@ use core::ops::{Deref, DerefMut};
 
 /// A spin lock.
 pub struct SpinLock<T: ?Sized> {
-   val: T, 
+    val: T,
 }
 
 impl<T> SpinLock<T> {
@@ -11,8 +11,8 @@ impl<T> SpinLock<T> {
         todo!()
     }
 
-    /// Acquire the spin lock. 
-    /// 
+    /// Acquire the spin lock.
+    ///
     /// This method runs in a busy loop until the lock can be acquired.
     /// After acquiring the spin lock, all interrupts are disabled.
     pub fn lock<'a>(&self) -> SpinLockGuard<'a, T> {
@@ -25,7 +25,7 @@ unsafe impl<T: ?Sized + Send> Sync for SpinLock<T> {}
 
 /// The guard of a spin lock.
 pub struct SpinLockGuard<'a, T: ?Sized + 'a> {
-    lock: &'a SpinLock<T>
+    lock: &'a SpinLock<T>,
 }
 
 impl<'a, T> Deref for SpinLockGuard<'a, T> {
@@ -36,7 +36,7 @@ impl<'a, T> Deref for SpinLockGuard<'a, T> {
     }
 }
 
-impl <'a, T> DerefMut for SpinLockGuard<'a, T> {
+impl<'a, T> DerefMut for SpinLockGuard<'a, T> {
     fn deref_mut(&mut self) -> &mut Self::Target {
         todo!()
     }
@@ -44,4 +44,4 @@ impl <'a, T> DerefMut for SpinLockGuard<'a, T> {
 
 impl<'a, T: ?Sized> !Send for SpinLockGuard<'a, T> {}
 
-unsafe impl<T: ?Sized + Sync> Sync for SpinLockGuard<'_, T> {}
\ No newline at end of file
+unsafe impl<T: ?Sized + Sync> Sync for SpinLockGuard<'_, T> {}
diff --git a/src/kxos-std/src/lib.rs b/src/kxos-std/src/lib.rs
index 7c9c9e11..065a8732 100644
--- a/src/kxos-std/src/lib.rs
+++ b/src/kxos-std/src/lib.rs
@@ -23,6 +23,6 @@ pub fn run_first_process() {
     Process::spawn_from_elf(elf_file_content);
 }
 
-fn read_elf_content<'a>() -> &'a [u8]{
-    todo!()
-}
\ No newline at end of file
+fn read_elf_content() -> &'static [u8] {
+    include_bytes!("../../kxos-user/hello_world/hello_world")
+}
diff --git a/src/kxos-std/src/memory/elf.rs b/src/kxos-std/src/memory/elf.rs
index a6700e90..a817f176 100644
--- a/src/kxos-std/src/memory/elf.rs
+++ b/src/kxos-std/src/memory/elf.rs
@@ -2,7 +2,7 @@ use core::ops::Range;
 
 use alloc::vec::Vec;
 use kxos_frame::{
-    vm::{Vaddr, VmIo, VmPerm, VmSpace, VmFrameVec, VmAllocOptions},
+    vm::{Vaddr, VmAllocOptions, VmFrameVec, VmIo, VmPerm, VmSpace},
     Error,
 };
 use xmas_elf::{
diff --git a/src/kxos-std/src/process/fifo_scheduler.rs b/src/kxos-std/src/process/fifo_scheduler.rs
index e03227af..5ab36106 100644
--- a/src/kxos-std/src/process/fifo_scheduler.rs
+++ b/src/kxos-std/src/process/fifo_scheduler.rs
@@ -1,6 +1,6 @@
 use alloc::{boxed::Box, collections::VecDeque, sync::Arc};
-use kxos_frame::task::{set_scheduler, Scheduler, Task};
 use kxos_frame::sync::SpinLock;
+use kxos_frame::task::{set_scheduler, Scheduler, Task};
 
 pub const TASK_INIT_CAPABILITY: usize = 16;
 
diff --git a/src/kxos-std/src/process/mod.rs b/src/kxos-std/src/process/mod.rs
index 0ab02964..27410c2a 100644
--- a/src/kxos-std/src/process/mod.rs
+++ b/src/kxos-std/src/process/mod.rs
@@ -19,7 +19,7 @@ pub struct Process {
     task: Arc<Task>,
     exit_code: i32,
     // user_space: Option<Arc<UserSpace>>,
-    // TODO: childs, parent, files, 
+    // TODO: childs, parent, files,
 }
 
 impl Process {
@@ -27,7 +27,11 @@ impl Process {
         let pid = new_pid();
         let task = spawn_user_task_from_elf(elf_file_content);
         let exit_code = 0;
-        Self { pid, task, exit_code }
+        Self {
+            pid,
+            task,
+            exit_code,
+        }
     }
 }
 
diff --git a/src/kxos-std/src/process/task.rs b/src/kxos-std/src/process/task.rs
index a4aae7aa..f0b17079 100644
--- a/src/kxos-std/src/process/task.rs
+++ b/src/kxos-std/src/process/task.rs
@@ -1,5 +1,10 @@
 use alloc::sync::Arc;
-use kxos_frame::{cpu::CpuContext, task::Task, user::{UserSpace, UserEvent}, vm::VmSpace};
+use kxos_frame::{
+    cpu::CpuContext,
+    task::Task,
+    user::{UserEvent, UserSpace},
+    vm::VmSpace,
+};
 
 use crate::{memory::load_elf_to_vm_space, syscall::syscall_handler};
 
@@ -22,7 +27,10 @@ pub fn spawn_user_task_from_elf(elf_file_content: &[u8]) -> Arc<Task> {
         loop {
             let user_event = user_mode.execute();
             let context = user_mode.context_mut();
-            handle_user_event(user_event, context);
+            if let HandlerResult::Exit = handle_user_event(user_event, context) {
+                // FIXME: How to set task status? How to set exit code of process?
+                break;
+            }
         }
     }
 
@@ -30,10 +38,15 @@ pub fn spawn_user_task_from_elf(elf_file_content: &[u8]) -> Arc<Task> {
     Task::spawn(user_task_entry, None::<u8>, Some(user_space)).expect("spawn user task failed.")
 }
 
-fn handle_user_event(user_event: UserEvent, context: &mut CpuContext) {
+fn handle_user_event(user_event: UserEvent, context: &mut CpuContext) -> HandlerResult {
     match user_event {
         UserEvent::Syscall => syscall_handler(context),
         UserEvent::Fault => todo!(),
         UserEvent::Exception => todo!(),
     }
-}
\ No newline at end of file
+}
+
+pub enum HandlerResult {
+    Exit,
+    Continue,
+}
diff --git a/src/kxos-std/src/syscall/mod.rs b/src/kxos-std/src/syscall/mod.rs
index 75a8480e..40491efd 100644
--- a/src/kxos-std/src/syscall/mod.rs
+++ b/src/kxos-std/src/syscall/mod.rs
@@ -1,11 +1,13 @@
 use alloc::vec;
 use alloc::{sync::Arc, vec::Vec};
-use kxos_frame::Error;
 use kxos_frame::cpu::CpuContext;
+use kxos_frame::Error;
 use kxos_frame::{task::Task, user::UserSpace, vm::VmIo};
 
 use kxos_frame::info;
 
+use crate::process::task::HandlerResult;
+
 const SYS_WRITE: u64 = 64;
 const SYS_EXIT: u64 = 93;
 
@@ -14,6 +16,11 @@ pub struct SyscallFrame {
     args: [u64; 6],
 }
 
+pub enum SyscallResult {
+    Exit(i32),
+    Return(i32),
+}
+
 impl SyscallFrame {
     fn new_from_context(context: &CpuContext) -> Self {
         let syscall_number = context.gp_regs.rax;
@@ -25,20 +32,27 @@ impl SyscallFrame {
         args[4] = context.gp_regs.r8;
         args[5] = context.gp_regs.r9;
         Self {
-            syscall_number, args,
+            syscall_number,
+            args,
         }
     }
 }
 
-pub fn syscall_handler(context: &mut CpuContext) {
+pub fn syscall_handler(context: &mut CpuContext) -> HandlerResult {
     let syscall_frame = SyscallFrame::new_from_context(context);
     let syscall_return = syscall_dispatch(syscall_frame.syscall_number, syscall_frame.args);
 
-    // FIXME: set return value?
-    context.gp_regs.rax = syscall_return as u64;
+    match syscall_return {
+        SyscallResult::Return(return_value) => {
+            // FIXME: set return value?
+            context.gp_regs.rax = return_value as u64;
+            HandlerResult::Continue
+        }
+        SyscallResult::Exit(exit_code) => HandlerResult::Exit,
+    }
 }
 
-pub fn syscall_dispatch(syscall_number: u64, args: [u64; 6]) -> isize {
+pub fn syscall_dispatch(syscall_number: u64, args: [u64; 6]) -> SyscallResult {
     match syscall_number {
         SYS_WRITE => sys_write(args[0], args[1], args[2]),
         SYS_EXIT => sys_exit(args[0] as _),
@@ -46,27 +60,26 @@ pub fn syscall_dispatch(syscall_number: u64, args: [u64; 6]) -> isize {
     }
 }
 
-pub fn sys_write(fd: u64, user_buf_ptr: u64, user_buf_len: u64) -> isize {
+pub fn sys_write(fd: u64, user_buf_ptr: u64, user_buf_len: u64) -> SyscallResult {
     // only suppprt STDOUT now.
     const STDOUT: u64 = 1;
     if fd == STDOUT {
         let task = Task::current();
         let user_space = task.user_space().expect("No user space attached");
-        let user_buffer = copy_bytes_from_user(user_space, user_buf_ptr as usize, user_buf_len as usize)
-            .expect("read user buffer failed");
+        let user_buffer =
+            copy_bytes_from_user(user_space, user_buf_ptr as usize, user_buf_len as usize)
+                .expect("read user buffer failed");
         let content = alloc::str::from_utf8(user_buffer.as_slice()).expect("Invalid content");
         // TODO: print content
         info!("Message from user mode: {}", content);
-        0
+        SyscallResult::Return(0)
     } else {
         panic!("Unsupported fd number {}", fd);
     }
 }
 
-pub fn sys_exit(exit_code: i32) -> isize {
-    // let current = Task::current();
-    // current.exit(exit_code);
-    todo!()
+pub fn sys_exit(exit_code: i32) -> SyscallResult {
+    SyscallResult::Exit(exit_code)
 }
 
 fn copy_bytes_from_user(
diff --git a/src/kxos-user/hello_world/Makefile b/src/kxos-user/hello_world/Makefile
new file mode 100644
index 00000000..2e439425
--- /dev/null
+++ b/src/kxos-user/hello_world/Makefile
@@ -0,0 +1,9 @@
+.PHONY: build clean run
+build: hello_world.s
+	@nasm -f elf64 hello_world.s -o hello_world.o
+	@ld hello_world.o -o hello_world
+	@rm hello_world.o
+clean:
+	@rm hello_world
+run: build
+	@./hello_world
diff --git a/src/kxos-user/hello_world/hello_world.s b/src/kxos-user/hello_world/hello_world.s
new file mode 100644
index 00000000..c55da226
--- /dev/null
+++ b/src/kxos-user/hello_world/hello_world.s
@@ -0,0 +1,18 @@
+global _start
+
+section .text
+
+_start:
+  mov rax, 1        ; syswrite
+  mov rdi, 1        ; fd
+  mov rsi, msg      ; "Hello, world!\n",
+  mov rdx, msglen   ; sizeof("Hello, world!\n")
+  syscall           
+
+  mov rax, 60       ; sys_exit
+  mov rdi, 0        ; exit_code
+  syscall           
+
+section .rodata
+  msg: db "Hello, world!", 10
+  msglen: equ $ - msg
\ No newline at end of file