linux-vdso.so is mostly about sharing a data page so syscalls can be optimised away. It's not for all the kernel API entry points (and it's userland specific so

linux-vdso.so is mostly about sharing a data page so syscalls can be optimised away. It's not for all the kernel API entry points (and it's userland specific so the VDSO varies with the libc version according to which features it optimises in this way). For the specific example above gettimeofday() - each process can read the clock value straight out of the shared VVARS page mapped into its space, no expensive context switch.