Handle backspace for k210/qemu platform && Add lots of user tests.

user/src/bin/exit.rs

@@ -0,0 +1,29 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+use user_lib::{fork, yield_, waitpid, exit, wait};
+
+const MAGIC: i32 = -0x10384;
+
+#[no_mangle]
+pub fn main() -> i32 {
+    println!("I am the parent. Forking the child...");
+    let pid = fork();
+    if pid == 0 {
+        println!("I am the child.");
+        for _ in 0..7 { yield_(); }
+        exit(MAGIC);
+    } else {
+        println!("I am parent, fork a child pid {}", pid);
+    }
+    println!("I am the parent, waiting now..");
+    let mut xstate: i32 = 0;
+    assert!(waitpid(pid as usize, &mut xstate) == pid && xstate == MAGIC);
+    assert!(waitpid(pid as usize, &mut xstate) < 0 && wait(&mut xstate) <= 0);
+    println!("waitpid {} ok.", pid);
+    println!("exit pass.");
+    0
+}
+