Add arch::cpu::halt(). Halt when panic.

kernel/src/arch/riscv32/cpu.rs

@@ -28,4 +28,9 @@ pub unsafe fn start_others(hart_mask: usize) {
             write_volatile(&mut STARTED[cpu_id], true);
         }
     }
+}
+
+pub fn halt() {
+    use super::riscv::asm::wfi;
+    unsafe { wfi() }
 }

kernel/src/arch/x86_64/cpu.rs

@@ -24,4 +24,9 @@ pub fn send_ipi(cpu_id: usize) {
 pub fn init() {
     let mut lapic = unsafe { XApic::new(0xffffff00_fee00000) };
     lapic.cpu_init();
+}
+
+pub fn halt() {
+    use x86_64::instructions::hlt;
+    hlt();
 }

kernel/src/lang.rs

@@ -1,4 +1,4 @@
-// Rust language features implementions
+// Rust language features implementations
 
 use core::panic::PanicInfo;
 use core::alloc::Layout;
@@ -13,7 +13,8 @@ pub fn panic(info: &PanicInfo) -> ! {
     let location = info.location().unwrap();
     let message = info.message().unwrap();
     error!("\n\nPANIC in {} at line {}\n    {}", location.file(), location.line(), message);
-    loop { }
+    use arch::cpu::halt;
+    loop { halt() }
 }
 
 #[lang = "oom"]