You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: qemu.rs
    path of file: ./repos/nearcore/runtime/runtime-params-estimator/src
    
    the code of the file until where you have to start completion: //! QEMU instrumentation code to g
    
fn hypercall(index: u32) -> u64 {
    unsafe {
        let fd = std::os::fd::BorrowedFd::borrow_raw((CATCH_BASE + index).try_into().unwrap());
        let mut buffer: [u8; 8] = [0xff; 8];
        let Err(result) = rustix::io::read(&fd, &mut buffer) else {
            panic!("this read call should have returned an error");
        };
        assert_eq!(result.raw_os_error(), rustix::io::Errno::BADF.raw_os_error());
        let buffer = u64::from_ne_bytes(buffer);
        assert!(
            buffer != 0xffff_ffff_ffff_ffff,
            "this mode must run under qemu with the counter_plugin"
        );
        buffer
    }
}