When installing udev on a new installation, you have to set RC_DEVICE_TARBALL="no" in /etc/conf.d/rc, else you won't be able to boot.
or you'll have to start udevd manually directly after you emerge it.
Mayb you could put making the tarball in the installation script ?
Steps to Reproduce:
1. Install clean Gentoo
2. emerge udev
the system wouldnt boot...
RC_DEVICE_TARBALL="no" in /etc/conf.d/rc
or: make the tarball in the installation of udev
you need to provide more information about your problem
When udev is emerged after a clean install, the device tarball isn't made, so when you reboot at that moment, the system wont start due to the missing of that tarball.
Solution: set RC_DEVICE_TARBALL to no, or include the creation of this tarball in the emerge of udev.
its a default ~x86 system.
ive added some sanity checks to the bootup process
however, the udev tarball should have been created by the baselayout ebuild when you emerged it