LWPINS

features = cpuid_leaf(0x80000001, 0)[2]
if not features >> 15 & 1:
    fault(UD)                    # CPUID: no LWP
if not xcr0 >> 62 & 1:           # LWP's state not enabled by the
    fault(UD)                    # OS
a = lwp_cbaddr
cf = 0
if a:                            # running: a record of event 255
    opts = load(a, 32)
    t = ptsc() if opts >> 30 & 1 else 0
    r = 255 | (lwp_cfg >> 32 & 0xFF) << 8  # CoreId
    r |= (imm & 0xFFFF) << 16    # imm's low 16 bits, src2 (Data1),
    r |= src2 << 32 | this_rip << 64  # this instruction's address,
    r |= src1 << 128 | t << 192  # src1 (Data2), the time stamp
    size = load(a + 4, 32) & 0xFFFFFFF
    size -= size % 32
    h = lwp_head
    store(load(a + 8, 64) + h, 256, r)  # at BufferBase + head
    nh = (h + 32) % size
    if nh == load(a + 64, 32):   # BufferTailOffset: full
        missed = load(a + 24, 64)
        store(a + 24, 64, missed + 1)
        if opts >> 29 & 1:       # continuous mode: on over the
            lwp_head = nh        # oldest record
        else:                    # synchronized: the next record
            cf = 1               # goes over this one
    else:
        lwp_head = nh
# with LWP off it only clears CF. Past the LWPCB's threshold, with
# its interrupts on, LWP interrupts the program, later. XED lists
# src1 as written: the APM has LWPINS only read it