Fix MIPS registers access in backtrace.rs.

kernel/src/arch/mipsel/context.rs

@@ -156,8 +156,7 @@ 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)]
+    #[inline(always)]
     pub unsafe extern fn switch(&mut self, _target: &mut Self) {
         extern {
             fn switch_context(src : &mut Context, dst : &mut Context);

kernel/src/backtrace.rs

@@ -24,8 +24,8 @@ pub fn fp() -> usize {
     }
     #[cfg(any(target_arch = "mips"))]
     unsafe {
-        // fp = $30
-        asm!("ori $0, $$$30, 0" : "=r"(ptr));
+        // fp = s8 = $30
+        asm!("ori $0, $$$1, 0" : "=r"(ptr): "i"(30));
     }
 
     ptr
@@ -51,7 +51,7 @@ pub fn lr() -> usize {
 
     #[cfg(target_arch = "mips")]
     unsafe {
-        asm!("ori $0, $$$31, 0" : "=r"(ptr));
+        asm!("ori $0, $$$1, 0" : "=r"(ptr) : "i"(31));
     }
 
     ptr