vmx_lab 0.1.1

vt-x
Documentation 
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//! Functions to read time stamp counters on x86.
use core::arch::asm;

use crate::x86::arch::_rdtsc;

/// Read the time stamp counter.
///
/// The RDTSC instruction is not a serializing instruction.
/// It does not necessarily wait until all previous instructions
/// have been executed before reading the counter. Similarly,
/// subsequent instructions may begin execution before the
/// read operation is performed. If software requires RDTSC to be
/// executed only after all previous instructions have completed locally,
/// it can either use RDTSCP or execute the sequence LFENCE;RDTSC.
///
/// # Safety
/// * Causes a GP fault if the TSD flag in register CR4 is set and the CPL
///   is greater than 0.
pub unsafe fn rdtsc() -> u64 {
    (unsafe { _rdtsc() }) as u64
}

/// Read the time stamp counter.
///
/// The RDTSCP instruction waits until all previous instructions have been
/// executed before reading the counter. However, subsequent instructions may
/// begin execution before the read operation is performed.
///
/// Volatile is used here because the function may be used to act as an
/// instruction barrier.
///
/// # Returns
/// - The current time stamp counter value of the CPU as a `u64`.
/// - The contents of `IA32_TSC_AUX` on that particular core. This is an OS
///   defined value. For example, Linux writes `numa_id << 12 | core_id` into
///   it. See also [`crate::rdpid`].
///
/// # Note
/// One can use `core::arch::x86_64::__rdtscp` from the Rust core library as
/// well. We don't rely on it because it only returns the time-stamp counter of
/// rdtscp and not the contents of `IA32_TSC_AUX`.
///
/// # Safety
/// * Causes a GP fault if the TSD flag in register CR4 is set and the CPL is
///   greater than 0.
pub fn rdtscp() -> (u64, u32) {
    let eax: u32;
    let ecx: u32;
    let edx: u32;
    unsafe {asm!(
      "rdtscp",
      lateout("eax") eax,
      lateout("ecx") ecx,
      lateout("edx") edx,
      options(nomem, nostack)
    );}

    let counter: u64 = (edx as u64) << 32 | eax as u64;
    (counter, ecx)
}