Fetching buffer arguments from user space.

os/src/trap/context.rs

@@ -5,17 +5,34 @@ pub struct TrapContext {
     pub x: [usize; 32],
     pub sstatus: Sstatus,
     pub sepc: usize,
+    pub kernel_satp: usize,
+    pub kernel_sp: usize,
+    pub trap_handler: usize,
 }
 
 impl TrapContext {
     pub fn set_sp(&mut self, sp: usize) { self.x[2] = sp; }
-    pub fn app_init_context(entry: usize, sp: usize) -> Self {
+    pub fn app_init_context(
+        entry: usize,
+        sp: usize,
+        kernel_satp: usize,
+        kernel_sp: usize,
+        trap_handler: usize,
+    ) -> Self {
         let mut sstatus = sstatus::read();
         sstatus.set_spp(SPP::User);
+        let mut temp_sstatus: usize;
+        unsafe {
+            llvm_asm!("csrr $0, sstatus" : "=r"(temp_sstatus) ::: "volatile");
+        }
+        println!("sstatus={:#x}", temp_sstatus);
         let mut cx = Self {
             x: [0; 32],
             sstatus,
             sepc: entry,
+            kernel_satp,
+            kernel_sp,
+            trap_handler,
         };
         cx.set_sp(sp);
         cx