update ch4:add some exception support in trap_handler function, add two *_fault.rs apps

user/src/bin/04load_fault.rs

@@ -0,0 +1,18 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+
+use core::ptr::{read_volatile,null_mut};
+
+#[no_mangle]
+fn main() -> i32 {
+    println!("\nload_fault APP running...\n");
+    println!("Into Test load_fault, we will insert an invalid load operation...");
+    println!("Kernel should kill this application!");
+    unsafe {
+        let _i=read_volatile(null_mut::<u8>());
+    }
+    0
+}

user/src/bin/05store_fault.rs

@@ -0,0 +1,18 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+
+use core::ptr::null_mut;
+
+#[no_mangle]
+fn main() -> i32 {
+    println!("\nstore_fault APP running...\n");
+    println!("Into Test store_fault, we will insert an invalid store operation...");
+    println!("Kernel should kill this application!");
+    unsafe {
+       null_mut::<u8>().write_volatile(1);
+    }
+    0
+}