Access before exec in sh

Makefile

@@ -70,6 +70,9 @@ ifeq ($(arch), $(filter $(arch), x86_64 aarch64))
 	@mv tmp/bin/busybox $(busybox)
 	@rm -rf tmp && rm busybox.tar.xz
 endif
+ifeq ($(arch), riscv64)
+	@wget https://github.com/rcore-os/busybox-riscv-prebuilts/raw/master/busybox-1.30.1-riscv64/busybox -O $(busybox)
+endif
 
 busybox: $(busybox)
 

rust/src/bin/sh.rs

@@ -10,7 +10,7 @@ use alloc::vec::Vec;
 use core::ptr;
 
 use rcore_user::io::get_line;
-use rcore_user::syscall::{sys_exec, sys_vfork, sys_wait};
+use rcore_user::syscall::{sys_exec, sys_vfork, sys_wait, sys_getcwd, sys_chdir, sys_access};
 
 // IMPORTANT: Must define main() like this
 #[no_mangle]
@@ -19,10 +19,12 @@ pub fn main() -> i32 {
     let mut history = Vec::new();
 
     loop {
-        print!(">> ");
+        print!("{}> ", sys_getcwd());
         let cmd = get_line(&mut history);
         // split cmd, make argc & argv
+        // to-do: handle quotes
         let cmd = cmd.replace(' ', "\0") + "\0";
+        let cmds: Vec<&str> = cmd.split('\0').collect();
         let mut ptrs: Vec<usize> = cmd
             .split('\0')
             .filter(|s| !s.is_empty())
@@ -31,20 +33,33 @@ pub fn main() -> i32 {
         if ptrs.is_empty() {
             continue;
         }
-        ptrs.push(0); // indicate the end of argv
-
-        let pid = sys_vfork();
-        assert!(pid >= 0);
-        if pid == 0 {
-            return sys_exec(
-                ptrs[0] as *const u8,
-                ptrs.as_ptr() as *const *const u8,
-                ptr::null(),
-            );
+
+        if cmds.len() == 3 {
+            // handle cd
+            if cmds[0] == "cd" {
+                sys_chdir(cmds[1]);
+                continue;
+            }
+        }
+
+        if sys_access(cmds[0]) == 0 {
+            ptrs.push(0); // indicate the end of argv
+
+            let pid = sys_vfork();
+            assert!(pid >= 0);
+            if pid == 0 {
+                return sys_exec(
+                    ptrs[0] as *const u8,
+                    ptrs.as_ptr() as *const *const u8,
+                    ptr::null(),
+                );
+            } else {
+                let mut code: i32 = 0;
+                sys_wait(pid as usize, &mut code);
+                println!("\n[Process exited with code {}]", code);
+            }
         } else {
-            let mut code: i32 = 0;
-            sys_wait(pid as usize, &mut code);
-            println!("\n[Process exited with code {}]", code);
+            println!("\n[Command {} not found]", cmds[0]);
         }
     }
 }

rust/src/syscall.rs

@@ -1,4 +1,5 @@
 use crate::ALLOCATOR;
+use alloc::string::String;
 
 #[inline(always)]
 fn sys_call(syscall_id: SyscallId, arg0: usize, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) -> i32 {
@@ -111,6 +112,25 @@ pub fn sys_getpid() -> i32 {
     sys_call(SyscallId::GetPid, 0, 0, 0, 0, 0, 0)
 }
 
+/// Get the current working directory
+pub fn sys_getcwd() -> String {
+    let buffer = [0u8; 256];
+    sys_call(SyscallId::GetCwd, buffer.as_ptr() as usize, 256, 0, 0, 0, 0);
+    String::from_utf8(buffer.to_vec()).unwrap()
+}
+
+/// Change the current working directory
+pub fn sys_chdir(path: &str) {
+    let path = String::from(path) + "\0";
+    sys_call(SyscallId::Chdir, path.as_bytes().as_ptr() as usize, 0, 0, 0, 0, 0);
+}
+
+/// Check file accessibility
+pub fn sys_access(path: &str) -> i32 {
+    let path = String::from(path) + "\0";
+    sys_call(SyscallId::FAccessAt, -100isize as usize, path.as_bytes().as_ptr() as usize, 0, 0, 0, 0)
+}
+
 #[repr(C)]
 #[derive(Debug, Copy, Clone)]
 pub struct TimeSpec {
@@ -171,11 +191,13 @@ enum SyscallId {
     Kill = 62,
     Fsync = 74,
     GetCwd = 79,
+    Chdir = 80,
     GetTime = 96,
     SetPriority = 141,
     ArchPrctl = 158,
     GetDirEntry64 = 217,
     Openat = 257,
+    FAccessAt = 269,
     Dup3 = 292,
     // custom
     MapPciDevice = 999,
@@ -187,14 +209,12 @@ enum SyscallId {
 enum SyscallId {
     Read = 63,
     Write = 64,
-    Openat = 56,
     Close = 57,
     Fstat = 80,
     Seek = 62,
     Mmap = 222,
     Munmap = 215,
     Yield = 124,
-    Dup3 = 24,
     Sleep = 101,
     GetPid = 172,
     Clone = 220,
@@ -203,11 +223,15 @@ enum SyscallId {
     Wait = 260,
     Kill = 129,
     Fsync = 82,
-    GetDirEntry64 = 61,
     GetCwd = 17,
+    Chdir = 49,
     GetTime = 169,
     SetPriority = 140,
     ArchPrctl = -4,
+    GetDirEntry64 = 61,
+    Openat = 56,
+    Dup3 = 24,
+    FAccessAt = 269,
     // custom
     MapPciDevice = 999,
     GetPaddr = 998,