It seems the s390x failure on bionic is fixed by the patch(es) for bug 1895132. I'm not 100% sure why it is returning the normal ENOSYS for invalid syscalls except while running under systemd-nspawn, but it might be due to the different syscall entry path taken when _TIF_TRACE is set, and that does get set if _TIF_SECCOMP is set.
In any case, I'll send the kernel patches to the ML.
It seems the s390x failure on bionic is fixed by the patch(es) for bug 1895132. I'm not 100% sure why it is returning the normal ENOSYS for invalid syscalls except while running under systemd-nspawn, but it might be due to the different syscall entry path taken when _TIF_TRACE is set, and that does get set if _TIF_SECCOMP is set.
In any case, I'll send the kernel patches to the ML.