RefCell->UPSafeCell && TaskCx->TCB

os/Makefile

@@ -29,7 +29,14 @@ OBJCOPY := rust-objcopy --binary-architecture=riscv64
 # Disassembly
 DISASM ?= -x
 
-build: env $(KERNEL_BIN)
+build: env switch-check $(KERNEL_BIN)
+
+switch-check:
+ifeq ($(BOARD), qemu)
+	(which last-qemu) || (rm last-k210 -f && touch last-qemu && make clean)
+else ifeq ($(BOARD), k210)
+	(which last-k210) || (rm last-qemu -f && touch last-k210 && make clean)
+endif
 
 env:
 	(rustup target list | grep "riscv64gc-unknown-none-elf (installed)") || rustup target add $(TARGET)
@@ -85,4 +92,4 @@ debug: build
 		tmux split-window -h "riscv64-unknown-elf-gdb -ex 'file $(KERNEL_ELF)' -ex 'set arch riscv:rv64' -ex 'target remote localhost:1234'" && \
 		tmux -2 attach-session -d
 
-.PHONY: build env kernel clean disasm disasm-vim run-inner
+.PHONY: build env kernel clean disasm disasm-vim run-inner switch-check

os/src/main.rs

@@ -3,7 +3,6 @@
 #![feature(global_asm)]
 #![feature(llvm_asm)]
 #![feature(panic_info_message)]
-#![feature(const_in_array_repeat_expressions)]
 #![feature(alloc_error_handler)]
 
 extern crate alloc;
@@ -21,6 +20,7 @@ mod loader;
 mod config;
 mod task;
 mod timer;
+mod sync;
 mod mm;
 
 global_asm!(include_str!("entry.asm"));
@@ -31,9 +31,12 @@ 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/context.rs

@@ -3,13 +3,22 @@ use crate::trap::trap_return;
 #[repr(C)]
 pub struct TaskContext {
     ra: usize,
+    sp: usize,
     s: [usize; 12],
 }
 
 impl TaskContext {
-    pub fn goto_trap_return() -> Self {
+    pub fn zero_init() -> Self {
+        Self {
+            ra: 0,
+            sp: 0,
+            s: [0; 12],
+        }
+    }
+    pub fn goto_trap_return(kstack_ptr: usize) -> Self {
         Self {
             ra: trap_return as usize,
+            sp: kstack_ptr,
             s: [0; 12],
         }
     }

os/src/task/mod.rs

@@ -4,7 +4,7 @@ mod task;
 
 use crate::loader::{get_num_app, get_app_data};
 use crate::trap::TrapContext;
-use core::cell::RefCell;
+use crate::sync::UPSafeCell;
 use lazy_static::*;
 use switch::__switch;
 use task::{TaskControlBlock, TaskStatus};
@@ -14,7 +14,7 @@ pub use context::TaskContext;
 
 pub struct TaskManager {
     num_app: usize,
-    inner: RefCell<TaskManagerInner>,
+    inner: UPSafeCell<TaskManagerInner>,
 }
 
 struct TaskManagerInner {
@@ -22,8 +22,6 @@ struct TaskManagerInner {
     current_task: usize,
 }
 
-unsafe impl Sync for TaskManager {}
-
 lazy_static! {
     pub static ref TASK_MANAGER: TaskManager = {
         println!("init TASK_MANAGER");
@@ -38,41 +36,41 @@ 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 _unused: usize = 0;
+        let next_task = &mut self.inner.upsafe_access().tasks[0];
+        next_task.task_status = TaskStatus::Running;
+        let next_task_cx_ptr = &next_task.task_cx as *const TaskContext;
+        drop(next_task);
+        let mut _unused = TaskContext::zero_init();
         unsafe {
             __switch(
-                &_unused as *const _,
-                next_task_cx_ptr2,
+                &mut _unused as *mut _,
+                next_task_cx_ptr,
             );
         }
     }
 
     fn mark_current_suspended(&self) {
-        let mut inner = self.inner.borrow_mut();
-        let current = inner.current_task;
-        inner.tasks[current].task_status = TaskStatus::Ready;
+        let inner = self.inner.upsafe_access();
+        inner.tasks[inner.current_task].task_status = TaskStatus::Ready;
     }
 
     fn mark_current_exited(&self) {
-        let mut inner = self.inner.borrow_mut();
-        let current = inner.current_task;
-        inner.tasks[current].task_status = TaskStatus::Exited;
+        let inner = self.inner.upsafe_access();
+        inner.tasks[inner.current_task].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)
@@ -82,30 +80,28 @@ impl TaskManager {
     }
 
     fn get_current_token(&self) -> usize {
-        let inner = self.inner.borrow();
-        let current = inner.current_task;
-        inner.tasks[current].get_user_token()
+        let inner = self.inner.upsafe_access();
+        inner.tasks[inner.current_task].get_user_token()
     }
 
     fn get_current_trap_cx(&self) -> &mut TrapContext {
-        let inner = self.inner.borrow();
-        let current = inner.current_task;
-        inner.tasks[current].get_trap_cx()
+        let inner = self.inner.upsafe_access();
+        inner.tasks[inner.current_task].get_trap_cx()
     }
 
     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;
-            let current_task_cx_ptr2 = inner.tasks[current].get_task_cx_ptr2();
-            let next_task_cx_ptr2 = inner.tasks[next].get_task_cx_ptr2();
-            core::mem::drop(inner);
+            let current_task_cx_ptr = &mut inner.tasks[current].task_cx as *mut TaskContext;
+            let next_task_cx_ptr = &inner.tasks[next].task_cx as *const TaskContext;
+            drop(inner);
             unsafe {
                 __switch(
-                    current_task_cx_ptr2,
-                    next_task_cx_ptr2,
+                    current_task_cx_ptr,
+                    next_task_cx_ptr,
                 );
             }
         } else {

os/src/task/switch.S

@@ -1,37 +1,34 @@
 .altmacro
 .macro SAVE_SN n
-    sd s\n, (\n+1)*8(sp)
+    sd s\n, (\n+2)*8(a0)
 .endm
 .macro LOAD_SN n
-    ld s\n, (\n+1)*8(sp)
+    ld s\n, (\n+2)*8(a1)
 .endm
     .section .text
     .globl __switch
 __switch:
     # __switch(
-    #     current_task_cx_ptr2: &*const TaskContext,
-    #     next_task_cx_ptr2: &*const TaskContext
+    #     current_task_cx_ptr: *mut TaskContext,
+    #     next_task_cx_ptr: *const TaskContext
     # )
-    # push TaskContext to current sp and save its address to where a0 points to
-    addi sp, sp, -13*8
-    sd sp, 0(a0)
-    # fill TaskContext with ra & s0-s11
-    sd ra, 0(sp)
+    # save kernel stack of current task
+    sd sp, 8(a0)
+    # save ra & s0~s11 of current execution
+    sd ra, 0(a0)
     .set n, 0
     .rept 12
         SAVE_SN %n
         .set n, n + 1
     .endr
-    # ready for loading TaskContext a1 points to
-    ld sp, 0(a1)
-    # load registers in the TaskContext
-    ld ra, 0(sp)
+    # restore ra & s0~s11 of next execution
+    ld ra, 0(a1)
     .set n, 0
     .rept 12
         LOAD_SN %n
         .set n, n + 1
     .endr
-    # pop TaskContext
-    addi sp, sp, 13*8
+    # restore kernel stack of next task
+    ld sp, 8(a1)
     ret
 

os/src/task/switch.rs

@@ -1,8 +1,10 @@
 global_asm!(include_str!("switch.S"));
 
+use super::TaskContext;
+
 extern "C" {
     pub fn __switch(
-        current_task_cx_ptr2: *const usize,
-        next_task_cx_ptr2: *const usize
+        current_task_cx_ptr: *mut TaskContext,
+        next_task_cx_ptr: *const TaskContext
     );
 }

os/src/task/task.rs

@@ -4,17 +4,14 @@ use crate::config::{TRAP_CONTEXT, kernel_stack_position};
 use super::TaskContext;
 
 pub struct TaskControlBlock {
-    pub task_cx_ptr: usize,
     pub task_status: TaskStatus,
+    pub task_cx: TaskContext,
     pub memory_set: MemorySet,
     pub trap_cx_ppn: PhysPageNum,
     pub base_size: usize,
 }
 
 impl TaskControlBlock {
-    pub fn get_task_cx_ptr2(&self) -> *const usize {
-        &self.task_cx_ptr as *const usize
-    }
     pub fn get_trap_cx(&self) -> &'static mut TrapContext {
         self.trap_cx_ppn.get_mut()
     }
@@ -38,11 +35,9 @@ impl TaskControlBlock {
                 kernel_stack_top.into(),
                 MapPermission::R | MapPermission::W,
             );
-        let task_cx_ptr = (kernel_stack_top - core::mem::size_of::<TaskContext>()) as *mut TaskContext;
-        unsafe { *task_cx_ptr = TaskContext::goto_trap_return(); }
         let task_control_block = Self {
-            task_cx_ptr: task_cx_ptr as usize,
             task_status,
+            task_cx: TaskContext::goto_trap_return(kernel_stack_top),
             memory_set,
             trap_cx_ppn,
             base_size: user_sp,