add usr app: sig_ctrlc for sig testing

user/src/bin/sig_ctrlc.rs

@@ -0,0 +1,42 @@
+#![no_std]
+#![no_main]
+
+extern crate alloc;
+
+#[macro_use]
+extern crate user_lib;
+use user_lib::*;
+use user_lib::console::getchar;
+
+const LF: u8 = 0x0au8;
+const CR: u8 = 0x0du8;
+
+fn func() {
+    println!("signal_handler: caught signal SIGINT， and exit(1)");
+    exit(1);
+}
+
+#[no_mangle]
+pub fn main() -> i32 {
+    println!("sig_ctrlc starting....  Press 'ctrl-c' or 'ENTER'  will quit.");
+
+    let mut new = SignalAction::default();
+    let old = SignalAction::default();
+    new.handler = func as usize;
+
+    println!("sig_ctrlc: sigaction");
+    if sigaction(SIGINT, &new, &old) < 0 {
+        panic!("Sigaction failed!");
+    }
+    println!("sig_ctrlc: getchar....");
+    loop {
+        let c = getchar();
+
+        println!("Got Char  {}", c);
+        if c == LF || c==CR  {
+            return 0;
+        }
+    }
+    println!("sig_ctrlc: Done");
+    0
+}