Update kstack switch.

kernel/src/arch/mipsel/boot/context.S

@@ -6,6 +6,7 @@
 .section .text.context
 .globl switch_context
 .extern _root_page_table_ptr
+.extern _cur_kstack_ptr
 
 switch_context:
 	// save from's registers
@@ -25,6 +26,7 @@ switch_context:
 	// sw ra, 12*4(sp)
 	// sw sp, 13*4(sp)
 
+	// save page table address
 	la s0, _root_page_table_ptr
 	lw AT, 0(s0)
 	sw AT, 4(sp)
@@ -34,6 +36,11 @@ switch_context:
 	lw AT, 4(sp)
 	sw AT, 0(s0)
 
+	// restore kstack ptr
+	// la s0, _cur_kstack_ptr
+	// addi s1, sp, 4 * 14
+	// sw s1, 0(s0)
+
 	lw ra, 0(sp)
 	lw s0, 2*4(sp)
 	lw s1, 3*4(sp)

kernel/src/arch/mipsel/boot/trap.S

@@ -147,6 +147,13 @@ trap_return:
 	lw fp, 156(sp)
 	lw ra, 160(sp)
 
+	// save kernel stack
+	la k0, _cur_kstack_ptr
+	addiu k1, sp, 168
+	sw k1, 0(k0)
+	nop
+
+	// restore stack
 	lw sp, 152(sp)
 
 	eret

kernel/src/arch/mipsel/context.rs

@@ -149,10 +149,6 @@ pub struct Context {
     sp: usize,
 }
 
-extern "C" {
-    fn _cur_kstack_ptr();
-}
-
 impl Context {
     /// Switch to another kernel thread.
     ///
@@ -165,9 +161,7 @@ impl Context {
             fn switch_context(src: *mut Context, dst: *mut Context);
         }
 
-        unsafe {
-            *(_cur_kstack_ptr as *mut usize) = target.sp;
-        }
+        info!("Switch to {:x}", target.sp);
 
         switch_context(self as *mut Context, target as *mut Context);
     }