fixup error handling

crates/nit/src/main.rs

@@ -9,7 +9,7 @@ use system::dmesg;
 fn main() {
     if let Err(e) = init() {
         dmesg(format!("Error: {e}"));
-        let mut opt = Some(&e as &dyn std::error::Error);
+        let mut opt = std::error::Error::source(&e);
         while let Some(current_source) = opt {
             dmesg(format!("Caused by: {current_source}"));
             opt = current_source.source();
@@ -28,7 +28,7 @@ fn init() -> Result<()> {
     if let Err(errors) = system::mount_default_targets() {
         for error in errors {
             dmesg(format!("Error while mounting: {error}"));
-            let mut opt = Some(&error as &dyn std::error::Error);
+            let mut opt = std::error::Error::source(&error);
             while let Some(current_source) = opt {
                 dmesg(format!("Caused by: {current_source}"));
                 opt = current_source.source();
@@ -65,7 +65,7 @@ fn init() -> Result<()> {
             */
         }
         config::Mode::Exec => {
-            dmesg("pivoting to {command}");
+            dmesg(format!("pivoting to {command}"));
             system::syscall::execv(command, &[])?;
         }
     }

crates/nit/src/system/syscall.rs

@@ -200,12 +200,18 @@ pub fn execv(command: impl AsRef<Path>, args: &[&str]) -> Result<()> {
         .context(format_args!("bad command: {}", command.display()))?;
     let mut args_cstr = vec![];
     for arg in args {
-        let cur_arg_cstr = CString::new(arg.as_bytes()).context(format_args!("bad arg: {arg}"));
+        let cur_arg_cstr = CString::new(arg.as_bytes()).context(format_args!("bad arg: {arg}"))?;
         args_cstr.push(cur_arg_cstr);
     }
 
+    // NOTE: The last arg must be a null pointer. We construct a CString from the raw pointer.
+    args_cstr.push(unsafe { CString::from_raw(std::ptr::null_mut()) });
+
     if unsafe { libc::execv(command_cstr.as_ptr().cast(), args_cstr.as_ptr().cast()) } == -1 {
-        return ctx_os_error(format_args!("error calling exec()"));
+        return ctx_os_error(format_args!(
+            "error calling exec({command}, {args:?})",
+            command = command.display()
+        ));
     }
 
     Ok(())