message: Handle `read`s on STDIN
diff: @@ -67,7 +67,18 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  let buf = this.read_scalar(buf)?.not_undef()?;
  let count = this.read_scalar(count)?.to_machine_usize(this)?;
  let result = if fd == 0 {
  - throw_unsup_format!("reading from stdin is not implemented")
  + use std::io::{self, Read};
  +
  + let mut buffer = String::new();
  + let res = io::stdin().read_to_string(&mut buffer);
  +
  + match res {
  + Ok(bytes) => {
  + this.memory.write_bytes(buf, buffer.bytes())?;
  + i64::try_from(bytes).unwrap()
  + },
  + Err(_) => -1,
  + }
  } else if fd == 1 || fd == 2 {
  throw_unsup_format!("cannot read from stdout/stderr")
  } else {
  