strace.open does probe does not fire

[Wolfram Gettert <Wolfram.Gettert@mixed-mode.de>]

Hi,
I am executing the following script:

----

probe begin
{
  printf("Start probing syscall.open\n")
}

probe syscall.open
{
  printf ("%s(%d) open(%s)\n", execname(), pid(), argstr)
}

probe timer.s(10)
{
  exit ()
}

probe end
{
  printf("Stop probing syscall.open\n")
}

----


I get the "Start probing syscall.open" and the "Stop probing syscall.open" message. I am executing "cat /dev/null" calls in a shell to be sure there is an open call. But the syscall.open probe does not fire.

I am using Ubuntu 18.04.2 LTS with Systemtap translator/driver (version 4.0/0.170, non-git sources).

I know that this script already worked for me on older versions. Is there anything what has changed?
Does anyone has an idea why it should not work?

Wolfram