localhost ~ # emerge xorg-x11   
Calculating dependencies... done!
>>> Emerging (1 of 5) media-video/nvidia-kernel-1.0.6629-r6 to /
>>> checking ebuild checksums ;-)
>>> checking auxfile checksums ;-)
>>> checking miscfile checksums ;-)
>>> checking NVIDIA-Linux-x86-1.0-6629-pkg1.run ;-)
 * Determining the location of the kernel source code
 * Found kernel source directory:
 *     /usr/src/linux
 * Could not find a usable .config in the kernel source directory.
 * Please ensure that /usr/src/linux points to a configured set of Linux sources.
 * If you are using KBUILD_OUTPUT, please set the environment var so that
 * it points to the necessary object directory so that it might find .config.

!!! ERROR: media-video/nvidia-kernel-1.0.6629-r6 failed.
Call stack:
  ebuild.sh, line 1555:   Called dyn_setup
  ebuild.sh, line 668:   Called pkg_setup
  nvidia-kernel-1.0.6629-r6.ebuild, line 62:   Called linux-mod_pkg_setup
  linux-mod.eclass, line 419:   Called linux-info_pkg_setup
  linux-info.eclass, line 554:   Called die

!!! Unable to calculate Linux Kernel version
!!! If you need support, post the topmost build error, and the call stack if relevant.