That's one of the functions provided by the vDSO, so userspace code can call it without a context switch: http://man7.org/linux/man-pages/man7/vdso.7.html http:

That's one of the functions provided by the vDSO, so userspace code can call it without a context switch: http://man7.org/linux/man-pages/man7/vdso.7.html http://man7.org/linux/man-pages/man7/vdso.7.html