[gentoo-embedded] facilities for creating /proc /dev /sys directories?

[Kfir Lavi]

Hi,
I would like to create those directories when the target system finished the
emerge.
The easiest is to do:
mkdir -p $target_dir/{proc,dev,sys}
inside a script.
Is there any mechanism that I can use to automate  this without running my
own script?

Thanks,
Kfir