RefCell->UPSafeCell

os/src/loader.rs

@@ -3,11 +3,13 @@ use crate::task::TaskContext;
 use crate::config::*;
 
 #[repr(align(4096))]
+#[derive(Copy, Clone)]
 struct KernelStack {
     data: [u8; KERNEL_STACK_SIZE],
 }
 
 #[repr(align(4096))]
+#[derive(Copy, Clone)]
 struct UserStack {
     data: [u8; USER_STACK_SIZE],
 }

os/src/main.rs

@@ -3,7 +3,6 @@
 #![feature(global_asm)]
 #![feature(llvm_asm)]
 #![feature(panic_info_message)]
-#![feature(const_in_array_repeat_expressions)]
 
 #[macro_use]
 mod console;
@@ -15,6 +14,7 @@ mod loader;
 mod config;
 mod task;
 mod timer;
+mod sync;
 
 global_asm!(include_str!("entry.asm"));
 global_asm!(include_str!("link_app.S"));
@@ -24,9 +24,12 @@ fn clear_bss() {
         fn sbss();
         fn ebss();
     }
-    (sbss as usize..ebss as usize).for_each(|a| {
-        unsafe { (a as *mut u8).write_volatile(0) }
-    });
+    unsafe {
+        core::slice::from_raw_parts_mut(
+            sbss as usize as *mut u8, 
+            ebss as usize - sbss as usize,
+        ).fill(0);
+    }
 }
 
 #[no_mangle]

os/src/sync/mod.rs

@@ -0,0 +1,3 @@
+mod up;
+
+pub use up::UPSafeCell;

os/src/sync/up.rs

@@ -0,0 +1,27 @@
+/// Wrap a static data structure inside it so that we are 
+/// able to access it without any `unsafe`.
+///
+/// We should only use it in uniprocessor.
+///
+/// In order to get mutable reference of inner data, call 
+/// `upsafe_access`. 
+pub struct UPSafeCell<T> {
+    /// inner data
+    data: T,
+}
+
+unsafe impl<T> Sync for UPSafeCell<T> {}
+
+impl<T> UPSafeCell<T> {
+    /// User is responsible to guarantee that inner struct is only used in
+    /// uniprocessor.
+    pub unsafe fn new(value: T) -> Self {
+        Self { data: value, }
+    }
+    /// Mention that user should hold exactly one &mut T at a time. 
+    pub fn upsafe_access(&self) -> &mut T {
+        unsafe {
+            &mut *(&self.data as *const _ as usize as *mut T)
+        }
+    }
+}

os/src/task/mod.rs

@@ -4,16 +4,16 @@ mod task;
 
 use crate::config::MAX_APP_NUM;
 use crate::loader::{get_num_app, init_app_cx};
-use core::cell::RefCell;
 use lazy_static::*;
 use switch::__switch;
 use task::{TaskControlBlock, TaskStatus};
+use crate::sync::UPSafeCell;
 
 pub use context::TaskContext;
 
 pub struct TaskManager {
     num_app: usize,
-    inner: RefCell<TaskManagerInner>,
+    inner: UPSafeCell<TaskManagerInner>,
 }
 
 struct TaskManagerInner {
@@ -21,8 +21,6 @@ struct TaskManagerInner {
     current_task: usize,
 }
 
-unsafe impl Sync for TaskManager {}
-
 lazy_static! {
     pub static ref TASK_MANAGER: TaskManager = {
         let num_app = get_num_app();
@@ -36,18 +34,19 @@ lazy_static! {
         }
         TaskManager {
             num_app,
-            inner: RefCell::new(TaskManagerInner {
+            inner: unsafe { UPSafeCell::new(TaskManagerInner {
                 tasks,
                 current_task: 0,
-            }),
+            })},
         }
     };
 }
 
 impl TaskManager {
     fn run_first_task(&self) {
-        self.inner.borrow_mut().tasks[0].task_status = TaskStatus::Running;
-        let next_task_cx_ptr2 = self.inner.borrow().tasks[0].get_task_cx_ptr2();
+        let task0 = &mut self.inner.upsafe_access().tasks[0];
+        task0.task_status = TaskStatus::Running;
+        let next_task_cx_ptr2 = task0.get_task_cx_ptr2();
         let _unused: usize = 0;
         unsafe {
             __switch(
@@ -58,19 +57,19 @@ impl TaskManager {
     }
 
     fn mark_current_suspended(&self) {
-        let mut inner = self.inner.borrow_mut();
+        let mut inner = self.inner.upsafe_access();
         let current = inner.current_task;
         inner.tasks[current].task_status = TaskStatus::Ready;
     }
 
     fn mark_current_exited(&self) {
-        let mut inner = self.inner.borrow_mut();
+        let mut inner = self.inner.upsafe_access();
         let current = inner.current_task;
         inner.tasks[current].task_status = TaskStatus::Exited;
     }
 
     fn find_next_task(&self) -> Option<usize> {
-        let inner = self.inner.borrow();
+        let inner = self.inner.upsafe_access();
         let current = inner.current_task;
         (current + 1..current + self.num_app + 1)
             .map(|id| id % self.num_app)
@@ -81,7 +80,7 @@ impl TaskManager {
 
     fn run_next_task(&self) {
         if let Some(next) = self.find_next_task() {
-            let mut inner = self.inner.borrow_mut();
+            let mut inner = self.inner.upsafe_access();
             let current = inner.current_task;
             inner.tasks[next].task_status = TaskStatus::Running;
             inner.current_task = next;

os/src/task/task.rs

@@ -1,3 +1,4 @@
+#[derive(Copy, Clone)]
 pub struct TaskControlBlock {
     pub task_cx_ptr: usize,
     pub task_status: TaskStatus,