message: Check for usize to i64 overflows
diff: @@ -176,12 +176,18 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  if let Some(handle) = this.machine.file_handler.handles.get_mut(&fd) {
  // We want to read at most `count` bytes
  let mut bytes = vec![0; count as usize];
  - let result = handle.file.read(&mut bytes).map(|c| c as i64);
  + let result = handle.file.read(&mut bytes);
  +
  + if let Ok(c) = result {
  + // Check that we read less than `i64::MAX` bytes.
  + if c > (i64::max_value() as usize) {
  + throw_unsup_format!("Number of read bytes {} is larger than the maximum value", c);
  + }
  // If reading to `bytes` did not fail, we write those bytes to the buffer.
  - if result.is_ok() {
  - this.memory.write_bytes(buf, bytes)?;
  + this.memory.write_bytes(buf, bytes)?
  }
  - this.try_unwrap_io_result(result)
  +
  + this.try_unwrap_io_result(result.map(|c| c as i64))
  } else {
  this.handle_not_found()
  }
  @@ -207,8 +213,16 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  if let Some(handle) = this.machine.file_handler.handles.get_mut(&fd) {
  let bytes = this.memory.read_bytes(buf, Size::from_bytes(count))?;
  - let result = handle.file.write(&bytes).map(|c| c as i64);
  - this.try_unwrap_io_result(result)
  + let result = handle.file.write(&bytes);
  +
  + if let Ok(c) = result {
  + // Check that we wrote less than `i64::MAX` bytes.
  + if c > (i64::max_value() as usize) {
  + throw_unsup_format!("Number of written bytes {} is larger than the maximum value", c);
  + }
  + }
  +
  + this.try_unwrap_io_result(result.map(|c| c as i64))
  } else {
  this.handle_not_found()
  }
  