These aren't in an extern (C); won't they mark *all* of stdioo as `nothrow` and `@nogc` for platforms with `GENERIC_IO`? The unittests seem to be passing, but do you know if this code is covered by any of our releases?

I think you want something more limited, like:
```D
else version (GENERIC_IO)
{
  nothrow
  @nogc
  {
     ...
  }
}
```
?