diff --git a/Cargo.lock b/Cargo.lock
index 35614fa766..1a65381e18 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -123,12 +123,15 @@ dependencies = [
 name = "arceos-monolithic"
 version = "0.1.0"
 dependencies = [
+ "arceos_posix_api",
  "axconfig",
+ "axerrno",
  "axhal",
  "axlog",
  "axruntime",
  "axstd",
  "axtask",
+ "crate_interface",
  "memory_addr",
 ]
 
diff --git a/modules/axhal/src/arch/x86_64/context.rs b/modules/axhal/src/arch/x86_64/context.rs
index bad85de9c2..b40f4c1ad6 100644
--- a/modules/axhal/src/arch/x86_64/context.rs
+++ b/modules/axhal/src/arch/x86_64/context.rs
@@ -40,6 +40,36 @@ pub struct TrapFrame {
 }
 
 impl TrapFrame {
+    /// Gets the 0th syscall argument.
+    pub const fn arg0(&self) -> usize {
+        self.rdi as _
+    }
+
+    /// Gets the 1st syscall argument.
+    pub const fn arg1(&self) -> usize {
+        self.rsi as _
+    }
+
+    /// Gets the 2nd syscall argument.
+    pub const fn arg2(&self) -> usize {
+        self.rdx as _
+    }
+
+    /// Gets the 3rd syscall argument.
+    pub const fn arg3(&self) -> usize {
+        self.r10 as _
+    }
+
+    /// Gets the 4th syscall argument.
+    pub const fn arg4(&self) -> usize {
+        self.r8 as _
+    }
+
+    /// Gets the 5th syscall argument.
+    pub const fn arg5(&self) -> usize {
+        self.r9 as _
+    }
+
     /// Whether the trap is from userspace.
     pub const fn is_user(&self) -> bool {
         self.cs & 0b11 == 3
diff --git a/modules/axhal/src/arch/x86_64/syscall.rs b/modules/axhal/src/arch/x86_64/syscall.rs
index fb57432362..8d6a774812 100644
--- a/modules/axhal/src/arch/x86_64/syscall.rs
+++ b/modules/axhal/src/arch/x86_64/syscall.rs
@@ -16,10 +16,7 @@ core::arch::global_asm!(
 
 #[no_mangle]
 pub(super) fn x86_syscall_handler(tf: &mut TrapFrame) {
-    info!(
-        "syscall @ {:#x}: {} [{}, {}, {}, {}]",
-        tf.rip, tf.rax, tf.rdi, tf.rsi, tf.rdx, tf.rdx,
-    );
+    tf.rax = crate::trap::handle_syscall(tf.rax as usize, tf) as u64;
 }
 
 /// Initializes syscall support and setups the syscall handler.
diff --git a/modules/axhal/src/trap.rs b/modules/axhal/src/trap.rs
index 5fc9f76dcc..14f4dcfb5c 100644
--- a/modules/axhal/src/trap.rs
+++ b/modules/axhal/src/trap.rs
@@ -2,6 +2,16 @@
 
 use crate_interface::{call_interface, def_interface};
 
+use crate::arch::TrapFrame;
+
+/// Syscall handler interface.
+#[def_interface]
+pub trait SyscallHandler {
+    /// Handles a system call with the given number, arguments are stored in
+    /// [`TrapFrame`].
+    fn handle_syscall(syscall_num: usize, tf: &TrapFrame) -> isize;
+}
+
 /// Trap handler interface.
 ///
 /// This trait is defined with the [`#[def_interface]`][1] attribute. Users
@@ -21,3 +31,9 @@ pub trait TrapHandler {
 pub(crate) fn handle_irq_extern(irq_num: usize) {
     call_interface!(TrapHandler::handle_irq, irq_num);
 }
+
+/// Call the external syscall handler.
+#[allow(dead_code)]
+pub(crate) fn handle_syscall(syscall_num: usize, tf: &TrapFrame) -> isize {
+    call_interface!(SyscallHandler::handle_syscall, syscall_num, tf)
+}
diff --git a/variants/monolithic/Cargo.toml b/variants/monolithic/Cargo.toml
index ae79bbc73d..acb02ab10a 100644
--- a/variants/monolithic/Cargo.toml
+++ b/variants/monolithic/Cargo.toml
@@ -5,9 +5,14 @@ edition = "2021"
 
 [dependencies]
 axstd = { path = "../../ulib/axstd", features = ["paging"] }
+arceos_posix_api = { path = "../../api/arceos_posix_api" }
+
 axhal = { path = "../../modules/axhal", features = ["uspace"] }
 axlog = { path = "../../modules/axlog" }
 axconfig = { path = "../../modules/axconfig" }
 axtask = { path = "../../modules/axtask" }
 axruntime = { path = "../../modules/axruntime", features = ["multitask"] }
+
+axerrno = { path = "../../crates/axerrno" }
 memory_addr = { path = "../../crates/memory_addr" }
+crate_interface = { path = "../../crates/crate_interface" }
diff --git a/variants/monolithic/src/main.rs b/variants/monolithic/src/main.rs
index e06a472156..fb0a2dd9e7 100644
--- a/variants/monolithic/src/main.rs
+++ b/variants/monolithic/src/main.rs
@@ -6,11 +6,12 @@ extern crate axlog;
 extern crate alloc;
 extern crate axstd;
 
+mod syscall;
 mod task;
 
 use memory_addr::{PhysAddr, VirtAddr};
 
-use axhal::arch::{TrapFrame, UspaceContext};
+use axhal::arch::UspaceContext;
 use axhal::mem::virt_to_phys;
 use axhal::paging::MappingFlags;
 use axruntime::KERNEL_PAGE_TABLE;
@@ -24,14 +25,14 @@ fn app_main(arg0: usize) {
         core::arch::asm!(
             "2:",
             "int3",
+            "mov rax, r12",
             "syscall",
-            "add rax, 1",
+            "add r12, 1",
             "jmp 2b",
-            in("rax") arg0,
+            in("r12") arg0,
             in("rdi") 2,
             in("rsi") 3,
             in("rdx") 3,
-            in("rcx") 3,
             options(nostack, nomem)
         )
     }
@@ -59,15 +60,6 @@ fn spawn_user_task(page_table_root: PhysAddr, uctx: UspaceContext) -> AxTaskRef
     axtask::spawn_task(task)
 }
 
-fn sys_clone(tf: &TrapFrame, newsp: usize) -> usize {
-    let page_table_root = axtask::current().task_ext().page_table_root;
-    let mut uctx = UspaceContext::from(tf);
-    uctx.set_sp(newsp);
-    uctx.set_ret_reg(0);
-    let new_task = spawn_user_task(page_table_root, uctx);
-    new_task.id().as_u64() as usize
-}
-
 fn run_apps() -> ! {
     let entry = VirtAddr::from(app_main as usize);
     let entry_paddr_align = virt_to_phys(entry.align_down_4k());
@@ -98,7 +90,7 @@ fn run_apps() -> ! {
         ustack_vaddr,
         ustack_paddr,
         4096,
-        MappingFlags::READ | MappingFlags::EXECUTE | MappingFlags::USER,
+        MappingFlags::READ | MappingFlags::WRITE | MappingFlags::USER,
         false,
     )
     .unwrap();
diff --git a/variants/monolithic/src/syscall.rs b/variants/monolithic/src/syscall.rs
new file mode 100644
index 0000000000..c4be646990
--- /dev/null
+++ b/variants/monolithic/src/syscall.rs
@@ -0,0 +1,44 @@
+#![allow(dead_code)]
+
+use arceos_posix_api as api;
+use axerrno::LinuxError;
+use axhal::arch::{TrapFrame, UspaceContext};
+use axhal::trap::SyscallHandler;
+use axtask::TaskExtRef;
+
+const SYS_READ: usize = 0;
+const SYS_WRITE: usize = 1;
+const SYS_SCHED_YIELD: usize = 24;
+const SYS_GETPID: usize = 39;
+const SYS_CLONE: usize = 56;
+const SYS_FORK: usize = 57;
+const SYS_EXECVE: usize = 59;
+const SYS_EXIT: usize = 60;
+
+fn sys_clone(tf: &TrapFrame, newsp: usize) -> usize {
+    let page_table_root = axtask::current().task_ext().page_table_root;
+    let mut uctx = UspaceContext::from(tf);
+    uctx.set_sp(newsp);
+    uctx.set_ret_reg(0);
+    let new_task = super::spawn_user_task(page_table_root, uctx);
+    new_task.id().as_u64() as usize
+}
+
+struct SyscallHandlerImpl;
+
+#[crate_interface::impl_interface]
+impl SyscallHandler for SyscallHandlerImpl {
+    fn handle_syscall(syscall_num: usize, tf: &TrapFrame) -> isize {
+        let ret = match syscall_num {
+            SYS_READ => api::sys_read(tf.arg0() as _, tf.arg1() as _, tf.arg2() as _),
+            SYS_WRITE => api::sys_write(tf.arg0() as _, tf.arg1() as _, tf.arg2() as _),
+            SYS_SCHED_YIELD => api::sys_sched_yield() as isize,
+            SYS_GETPID => api::sys_getpid() as isize,
+            _ => {
+                warn!("Unimplemented syscall: {}", syscall_num);
+                -LinuxError::ENOSYS.code() as _
+            }
+        };
+        ret
+    }
+}