diff --git a/Cargo.lock b/Cargo.lock
index ba5ffbdf87..f5b6528f7a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -128,6 +128,7 @@ dependencies = [
  "axlog",
  "axruntime",
  "axstd",
+ "axtask",
  "memory_addr",
 ]
 
diff --git a/modules/axhal/linker.lds.S b/modules/axhal/linker.lds.S
index 73b7a7884d..ea5213735f 100644
--- a/modules/axhal/linker.lds.S
+++ b/modules/axhal/linker.lds.S
@@ -29,6 +29,11 @@ SECTIONS
         _sdata = .;
         *(.data.boot_page_table)
         . = ALIGN(4K);
+
+        __start_ax_task_ext = .;
+        *(ax_task_ext)
+        __stop_ax_task_ext = .;
+
         *(.data .data.*)
         *(.sdata .sdata.*)
         *(.got .got.*)
@@ -53,13 +58,9 @@ SECTIONS
         _percpu_load_start = .;
         *(.percpu .percpu.*)
         _percpu_load_end = .;
-        . = ALIGN(64);
-        _percpu_size_aligned = .;
-
-        . = _percpu_load_start + _percpu_size_aligned * %SMP%;
+        . = _percpu_load_start + ALIGN(64) * %SMP%;
     }
     . = _percpu_start + SIZEOF(.percpu);
-    _percpu_end = .;
 
     . = ALIGN(4K);
     _edata = .;
diff --git a/modules/axhal/src/arch/x86_64/context.rs b/modules/axhal/src/arch/x86_64/context.rs
index e4bc073229..b3c31727f1 100644
--- a/modules/axhal/src/arch/x86_64/context.rs
+++ b/modules/axhal/src/arch/x86_64/context.rs
@@ -1,7 +1,7 @@
 use core::{arch::asm, fmt};
 use memory_addr::VirtAddr;
 
-#[cfg(feature = "irq")]
+#[cfg(all(feature = "irq", feature = "uspace"))]
 use x86_64::registers::rflags::RFlags;
 
 #[cfg(feature = "uspace")]
diff --git a/modules/axtask/src/api.rs b/modules/axtask/src/api.rs
index 8e75f270ea..9196fabf30 100644
--- a/modules/axtask/src/api.rs
+++ b/modules/axtask/src/api.rs
@@ -7,6 +7,8 @@ pub(crate) use crate::run_queue::{AxRunQueue, RUN_QUEUE};
 #[doc(cfg(feature = "multitask"))]
 pub use crate::task::{CurrentTask, TaskId, TaskInner};
 #[doc(cfg(feature = "multitask"))]
+pub use crate::task_ext::{TaskExtMut, TaskExtRef};
+#[doc(cfg(feature = "multitask"))]
 pub use crate::wait_queue::WaitQueue;
 
 /// The reference type of a task.
diff --git a/modules/axtask/src/lib.rs b/modules/axtask/src/lib.rs
index b02a1ea1f2..475b3232b1 100644
--- a/modules/axtask/src/lib.rs
+++ b/modules/axtask/src/lib.rs
@@ -28,6 +28,7 @@
 #![cfg_attr(not(test), no_std)]
 #![feature(doc_cfg)]
 #![feature(doc_auto_cfg)]
+#![feature(linkage)]
 
 #[cfg(test)]
 mod tests;
@@ -40,6 +41,7 @@ cfg_if::cfg_if! {
 
         mod run_queue;
         mod task;
+        mod task_ext;
         mod api;
         mod wait_queue;
 
diff --git a/modules/axtask/src/run_queue.rs b/modules/axtask/src/run_queue.rs
index 9c31f4384c..ee7abb49cb 100644
--- a/modules/axtask/src/run_queue.rs
+++ b/modules/axtask/src/run_queue.rs
@@ -214,6 +214,7 @@ fn gc_entry() {
 }
 
 pub(crate) fn init() {
+    // Put the subsequent execution into the `main` task.
     const IDLE_TASK_STACK_SIZE: usize = 4096;
     let idle_task = TaskInner::new(|| crate::run_idle(), "idle".into(), IDLE_TASK_STACK_SIZE);
     IDLE_TASK.with_current(|i| i.init_by(idle_task.clone()));
@@ -226,6 +227,7 @@ pub(crate) fn init() {
 }
 
 pub(crate) fn init_secondary() {
+    // Put the subsequent execution into the `idle` task.
     let idle_task = TaskInner::new_init("idle".into());
     idle_task.set_state(TaskState::Running);
     IDLE_TASK.with_current(|i| i.init_by(idle_task.clone()));
diff --git a/modules/axtask/src/task.rs b/modules/axtask/src/task.rs
index 7db9d78b61..6833672054 100644
--- a/modules/axtask/src/task.rs
+++ b/modules/axtask/src/task.rs
@@ -12,6 +12,7 @@ use axhal::tls::TlsArea;
 use axhal::arch::TaskContext;
 use memory_addr::{align_up_4k, VirtAddr};
 
+use crate::task_ext::AxTaskExt;
 use crate::{AxRunQueue, AxTask, AxTaskRef, WaitQueue};
 
 /// A unique identifier for a thread.
@@ -52,6 +53,7 @@ pub struct TaskInner {
 
     kstack: Option<TaskStack>,
     ctx: UnsafeCell<TaskContext>,
+    task_ext: AxTaskExt,
 
     #[cfg(feature = "tls")]
     tls: TlsArea,
@@ -109,6 +111,19 @@ impl TaskInner {
             .wait_until(|| self.state() == TaskState::Exited);
         Some(self.exit_code.load(Ordering::Acquire))
     }
+
+    /// Returns the pointer to the user-defined task extended data.
+    ///
+    /// # Safety
+    ///
+    /// The caller should not access the pointer directly, use [`TaskExtRef::task_ext`]
+    /// or [`TaskExtMut::task_ext_mut`] instead.
+    ///
+    /// [`TaskExtRef::task_ext`]: crate::task_ext::TaskExtRef::task_ext
+    /// [`TaskExtMut::task_ext_mut`]: crate::task_ext::TaskExtMut::task_ext_mut
+    pub unsafe fn task_ext_ptr(&self) -> *mut u8 {
+        self.task_ext.as_ptr()
+    }
 }
 
 // private methods
@@ -132,6 +147,7 @@ impl TaskInner {
             wait_for_exit: WaitQueue::new(),
             kstack: None,
             ctx: UnsafeCell::new(TaskContext::new()),
+            task_ext: AxTaskExt::alloc(),
             #[cfg(feature = "tls")]
             tls: TlsArea::alloc(),
         }
diff --git a/modules/axtask/src/task_ext.rs b/modules/axtask/src/task_ext.rs
new file mode 100644
index 0000000000..47d9ead2e9
--- /dev/null
+++ b/modules/axtask/src/task_ext.rs
@@ -0,0 +1,108 @@
+//! User-defined task extended data.
+
+extern "C" {
+    fn __start_ax_task_ext();
+    fn __stop_ax_task_ext();
+}
+
+#[no_mangle]
+#[linkage = "weak"]
+#[link_section = "ax_task_ext"]
+static __AX_TASK_EXT: () = ();
+
+pub(crate) struct AxTaskExt {
+    ptr: *mut u8,
+}
+
+impl AxTaskExt {
+    fn size() -> usize {
+        __stop_ax_task_ext as usize - __start_ax_task_ext as usize
+    }
+
+    pub(crate) fn as_ptr(&self) -> *mut u8 {
+        self.ptr
+    }
+
+    pub(crate) fn alloc() -> Self {
+        let size = Self::size();
+        let ptr = if size == 0 {
+            core::ptr::null_mut()
+        } else {
+            let layout = core::alloc::Layout::from_size_align(size, 0x10).unwrap();
+            let dst = unsafe { alloc::alloc::alloc(layout) };
+            let src = &__AX_TASK_EXT as *const _ as *const u8;
+            unsafe { core::ptr::copy_nonoverlapping(src, dst, size) };
+            dst
+        };
+        Self { ptr }
+    }
+}
+
+impl Drop for AxTaskExt {
+    fn drop(&mut self) {
+        if !self.ptr.is_null() {
+            let layout = core::alloc::Layout::from_size_align(Self::size(), 0x10).unwrap();
+            unsafe { alloc::alloc::dealloc(self.ptr, layout) };
+        }
+    }
+}
+
+/// A trait to convert [`TaskInner::task_ext_ptr`] to the reference of the
+/// concrete type.
+///
+/// [`TaskInner::task_ext_ptr`]: crate::TaskInner::task_ext_ptr
+pub trait TaskExtRef<T: Sized> {
+    /// Get a reference to the task extended data.
+    fn task_ext(&self) -> &T;
+}
+
+/// A trait to convert [`TaskInner::task_ext_ptr`] to the mutable reference of
+/// the concrete type.
+///
+/// [`TaskInner::task_ext_ptr`]: crate::TaskInner::task_ext_ptr
+pub trait TaskExtMut<T: Sized> {
+    /// Get a mutable reference to the task extended data.
+    fn task_ext_mut(&mut self) -> &mut T;
+}
+
+/// Define the task extended data.
+///
+/// It automatically implements [`TaskExtRef`] and [`TaskExtMut`] for
+/// [`TaskInner`].
+///
+/// # Example
+///
+/// ```no_run
+/// use axtask::{def_task_ext, TaskExtRef};
+///
+/// pub struct TaskExtImpl {
+///    proc_id: usize,
+/// }
+///
+/// def_task_ext!(TaskExtImpl, TaskExtImpl { proc_id: 0 });
+///
+/// let task = axtask::spawn(|| {});
+/// assert_eq!(task.task_ext().proc_id, 0);
+/// ```
+///
+/// [`TaskInner`]: crate::TaskInner
+#[macro_export]
+macro_rules! def_task_ext {
+    ($task_ext_struct:ty, $default:expr) => {
+        #[no_mangle]
+        #[link_section = "ax_task_ext"]
+        static __AX_TASK_EXT: $task_ext_struct = $default;
+
+        impl $crate::TaskExtRef<$task_ext_struct> for $crate::TaskInner {
+            fn task_ext(&self) -> &$task_ext_struct {
+                unsafe { &*(self.task_ext_ptr() as *const $task_ext_struct) }
+            }
+        }
+
+        impl $crate::TaskExtMut<$task_ext_struct> for $crate::TaskInner {
+            fn task_ext_mut(&mut self) -> &mut $task_ext_struct {
+                unsafe { &mut *(self.task_ext_ptr() as *mut $task_ext_struct) }
+            }
+        }
+    };
+}
diff --git a/variants/monolithic/Cargo.toml b/variants/monolithic/Cargo.toml
index 7644e1e22a..ae79bbc73d 100644
--- a/variants/monolithic/Cargo.toml
+++ b/variants/monolithic/Cargo.toml
@@ -8,5 +8,6 @@ axstd = { path = "../../ulib/axstd", features = ["paging"] }
 axhal = { path = "../../modules/axhal", features = ["uspace"] }
 axlog = { path = "../../modules/axlog" }
 axconfig = { path = "../../modules/axconfig" }
-axruntime = { path = "../../modules/axruntime" }
+axtask = { path = "../../modules/axtask" }
+axruntime = { path = "../../modules/axruntime", features = ["multitask"] }
 memory_addr = { path = "../../crates/memory_addr" }
diff --git a/variants/monolithic/src/main.rs b/variants/monolithic/src/main.rs
index 8f19dc714e..fd35a66c80 100644
--- a/variants/monolithic/src/main.rs
+++ b/variants/monolithic/src/main.rs
@@ -6,12 +6,15 @@ extern crate axlog;
 extern crate alloc;
 extern crate axstd;
 
+mod task;
+
 use memory_addr::VirtAddr;
 
 use axhal::arch::UspaceContext;
 use axhal::mem::virt_to_phys;
 use axhal::paging::MappingFlags;
 use axruntime::KERNEL_PAGE_TABLE;
+use axtask::TaskExtRef;
 
 const USER_STACK_SIZE: usize = 4096;
 
@@ -73,6 +76,12 @@ fn run_apps() -> ! {
     .unwrap();
 
     let ctx = UspaceContext::new(entry_vaddr.into(), ustack_top, 2333);
+    let pid = axtask::current().task_ext().proc_id;
+    let parent = axtask::current().task_ext().parent;
+    warn!("pid = {}", pid);
+    warn!("parent = {}", parent);
+    assert_eq!(pid, 233);
+    assert_eq!(parent, 456);
 
     info!(
         "Enter user space: entry={:#x}, ustack={:#x}, kstack={:#x}",
diff --git a/variants/monolithic/src/task.rs b/variants/monolithic/src/task.rs
new file mode 100644
index 0000000000..f737425f98
--- /dev/null
+++ b/variants/monolithic/src/task.rs
@@ -0,0 +1,15 @@
+pub struct TaskExt {
+    pub proc_id: usize,
+    pub parent: usize,
+}
+
+impl TaskExt {
+    pub const fn default() -> Self {
+        Self {
+            proc_id: 233,
+            parent: 456,
+        }
+    }
+}
+
+axtask::def_task_ext!(TaskExt, TaskExt::default());