Fix register naming in backtrace

Signed-off-by: Harry Chen <i@harrychen.xyz>

kernel/src/arch/mipsel/context.rs

@@ -156,14 +156,13 @@ impl Context {
     /// Push all callee-saved registers at the current kernel stack.
     /// Store current sp, switch to target.
     /// Pop all callee-saved registers, then return to the target.
-    #[naked]
-    #[inline(never)]
-    pub unsafe extern fn switch(&mut self, _target: &mut Self) {
-        extern {
-            fn switch_context(src : &mut Context, dst : &mut Context);
+    #[inline(always)]
+    pub unsafe fn switch(&mut self, target: &mut Self) {
+        extern "C" {
+            fn switch_context(src: *mut Context, dst: *mut Context);
         }
 
-        switch_context(self, _target);
+        switch_context(self as *mut Context, target as *mut Context);
     }
 
     /// Constructs a null Context for the current running thread.

kernel/src/backtrace.rs

@@ -25,7 +25,7 @@ pub fn fp() -> usize {
     #[cfg(any(target_arch = "mips"))]
     unsafe {
         // fp = $30
-        asm!("ori $0, $$$30, 0" : "=r"(ptr));
+        asm!("ori $0, $$30, 0" : "=r"(ptr));
     }
 
     ptr
@@ -51,7 +51,7 @@ pub fn lr() -> usize {
 
     #[cfg(target_arch = "mips")]
     unsafe {
-        asm!("ori $0, $$$31, 0" : "=r"(ptr));
+        asm!("ori $0, $$31, 0" : "=r"(ptr));
     }
 
     ptr