Add first user program hello_world.rs

user/src/lib.rs

@@ -0,0 +1,23 @@
+#![no_std]
+#![feature(llvm_asm)]
+#![feature(linkage)]
+#![feature(panic_info_message)]
+
+#[macro_use]
+pub mod console;
+mod syscall;
+mod lang_items;
+
+#[no_mangle]
+#[link_section = ".text.entry"]
+pub extern "C" fn _start() -> ! {
+    main();
+    loop {}
+}
+
+#[linkage = "weak"]
+#[no_mangle]
+fn main() -> i32 {
+    panic!("Cannot find main!");
+}
+