emerge -pvu world
These are the packages that would be merged, in order:
Calculating world dependencies... done!
[blocks B ] sys-apps/pam-login (is blocking sys-apps/shadow-4.0.15)
[ebuild U ] sys-apps/shadow-4.0.15 [4.0.7-r4] USE="nls pam -nousuid -skey" 1,264 kB