Add rust user program to test efault

rust/src/bin/fault.rs

@@ -0,0 +1,12 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate rcore_user;
+
+// IMPORTANT: Must define main() like this
+#[no_mangle]
+pub fn main() {
+    println!("Faulting sys_exec");
+    rcore_user::syscall::sys_exec(0 as *const u8, 0 as *const *const u8, 0 as *const *const u8);
+}