Calling clock_gettime() in libc will call the newer syscall (assuming __TIME_BITS=64 is set). But Linux has kept backwards compat, old programs can still call the old syscall.

If you wrote your seccomp rule for your program before clock_gettime64 existed, it'd break when glibc switched. I guess that implies each language stdlib should have their own seccomp etc wrappers.

For landlock, the equivalent is that glibc reads various files in /etc varying per libc version or system settings, so landlock rules need to account for that.