Add test early_exit

user/src/bin/early_exit.rs

@@ -0,0 +1,22 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+extern crate alloc;
+
+use user_lib::{thread_create, exit};
+use alloc::vec::Vec;
+
+pub fn thread_a() -> ! {
+    for i in 0..1000 { print!("{}", i); }
+    exit(1)
+}
+
+#[no_mangle]
+pub fn main() -> i32 {
+    thread_create(thread_a as usize, 0);
+    println!("main thread exited.");
+    exit(0)
+}
+