; CLOCK64 · native TSC full · FULL BGF
; LINEAR BGS->BGF->SDF · atoms EZZIE PHI THERMO on BGF · free rides · no duo
; out: rax = 64-bit TSC · then live resolve low |1 in eax sense kept separate
; rdx clobbered by rdtsc then rebuilt
        rdtsc
        shl     rdx, 32
        or      rax, rdx
        ret