Barebones rust example working in user space.

Requires manually copying the executable over to the image.

rust/usr/testbed/src/main.rs

@@ -0,0 +1,10 @@
+#![no_std]
+#![no_main]
+
+use mammoth::debug;
+
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+    debug("Test!");
+    panic!()
+}