message: Correct fcntl behavior
diff: @@ -9,7 +9,6 @@ use crate::*;
  pub struct FileHandle {
  file: File,
  - flag: i32,
  }
  pub struct FileHandler {
  @@ -79,13 +78,14 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  }
  let o_cloexec = this.eval_libc_i32("O_CLOEXEC")?;
  if flag & o_cloexec != 0 {
  - // This flag is a noop for now because `std` already sets it.
  + // We do not need to do anything for this flag because `std` already sets it.
  + // (Technically we do not support *not* setting this flag, but we ignore that.)
  mirror |= o_cloexec;
  }
  // If `flag` is not equal to `mirror`, there is an unsupported option enabled in `flag`,
  // then we throw an error.
  if flag != mirror {
  - throw_unsup_format!("unsupported flags {:#x}", flag);
  + throw_unsup_format!("unsupported flags {:#x}", flag & !mirror);
  }
  let path_bytes = this
  @@ -97,7 +97,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  let fd = options.open(path).map(|file| {
  let mut fh = &mut this.machine.file_handler;
  fh.low += 1;
  - fh.handles.insert(fh.low, FileHandle { file, flag });
  + fh.handles.insert(fh.low, FileHandle { file });
  fh.low
  });
  @@ -108,7 +108,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  &mut self,
  fd_op: OpTy<'tcx, Tag>,
  cmd_op: OpTy<'tcx, Tag>,
  - _arg_op: Option<OpTy<'tcx, Tag>>,
  + _arg1_op: Option<OpTy<'tcx, Tag>>,
  ) -> InterpResult<'tcx, i32> {
  let this = self.eval_context_mut();
  @@ -120,7 +120,12 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  let cmd = this.read_scalar(cmd_op)?.to_i32()?;
  // We only support getting the flags for a descriptor
  if cmd == this.eval_libc_i32("F_GETFD")? {
  - this.get_handle_and(fd, |handle| Ok(handle.flag))
  + // Currently this is the only flag that `F_GETFD` returns. It is OK to just return the
  + // `FD_CLOEXEC` value without checking if the flag is set for the file because `std`
  + // always sets this flag when opening a file. However we still need to check that the
  + // file itself is open.
  + this.get_handle_and(fd, |_| Ok(0))?;
  + this.eval_libc_i32("FD_CLOEXEC")
  } else {
  throw_unsup_format!("The {:#x} command is not supported for `fcntl`)", cmd);
  }
  