runtime/irq: use assembly for naked IRQ handler

and solves the bug introduced due to stack unwinding...

src/runtime/src/irq.rs

@@ -18,14 +18,36 @@ static CORE1_RESTART: AtomicBool = AtomicBool::new(false);
 #[no_mangle]
 #[naked]
 pub unsafe extern "C" fn IRQ() {
+    asm!(
+        // setup SP, depending on CPU 0 or 1
+        "mrc p15, #0, r0, c0, c0, #5",
+        "movw r1, :lower16:__stack0_start",
+        "movt r1, :upper16:__stack0_start",
+        "tst r0, #3",
+        "movwne r1, :lower16:__stack1_start",
+        "movtne r1, :upper16:__stack1_start",
+        "mov sp, r1",
+        "bl __IRQ",
+        options(noreturn)
+    );
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn __IRQ() {
     if MPIDR.read().cpu_id() == 1 {
         let mpcore = mpcore::RegisterBlock::mpcore();
         let mut gic = gic::InterruptController::gic(mpcore);
         let id = gic.get_interrupt_id();
         if id.0 == 0 {
             gic.end_interrupt(id);
+            // save the SP and set it back after exiting IRQ
+            // exception unwinding expect to unwind from this function, as this is not the entrance
+            // function, maybe to IRQ which cannot further unwind...
+            // if we set the SP to __stack1_start, interesting exceptions would be triggered when
+            // we try to unwind the stack...
+            let v = SP.read();
             asm::exit_irq();
-            SP.write(&mut __stack1_start as *mut _ as u32);
+            SP.write(v);
             asm::enable_irq();
             CORE1_RESTART.store(false, Ordering::Relaxed);
             notify_spin_lock();

src/runtime/src/main.rs

@@ -7,6 +7,7 @@
 #![feature(const_btree_new)]
 #![feature(const_in_array_repeat_expressions)]
 #![feature(naked_functions)]
+#![feature(asm)]
 
 extern crate alloc;