Add user program initproc/user_shell, allow user programs allocate data on heap.

user/src/bin/user_shell.rs

@@ -0,0 +1,61 @@
+#![no_std]
+#![no_main]
+
+extern crate alloc;
+
+#[macro_use]
+extern crate user_lib;
+
+const LF: u8 = 0x0au8;
+const CR: u8 = 0x0du8;
+const DL: u8 = 0x7fu8;
+const BS: u8 = 0x08u8;
+
+use alloc::string::String;
+use user_lib::{fork, exec, wait};
+use user_lib::console::getchar;
+
+#[no_mangle]
+pub fn main() -> i32 {
+    println!("Rust user shell");
+    let mut line: String = String::new();
+    print!(">> ");
+    loop {
+        let c = getchar();
+        match c {
+            LF | CR => {
+                println!("");
+                if !line.is_empty() {
+                    line.push('\0');
+                    let pid = fork();
+                    if pid == 0 {
+                        // child process
+                        if exec(line.as_str()) == -1 {
+                            println!("Command not found!");
+                            return 0;
+                        }
+                        unreachable!();
+                    } else {
+                        let mut xstate: i32 = 0;
+                        wait(&mut xstate);
+                        println!("Shell: Process {} exited with code {}", pid, xstate);
+                    }
+                    line.clear();
+                }
+                print!(">> ");
+            }
+            DL => {
+                if !line.is_empty() {
+                    print!("{}", BS as char);
+                    print!(" ");
+                    print!("{}", BS as char);
+                    line.pop();
+                }
+            }
+            _ => {
+                print!("{}", c as char);
+                line.push(c as char);
+            }
+        }
+    }
+}