kaiser@localhost ~ $ sudo emerge -av ati-drivers

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild     U ] x11-drivers/ati-drivers-8.37.6-r90 [8.34.8-r90] USE="acpi distribution qt3" 0 kB [1]

Total: 1 package (1 upgrade), Size of downloads: 0 kB
Portage overlays:
 [1] /usr/portage/local/layman/sabayon
 [2] /usr/portage/local/layman/einit

Would you like to merge these packages? [Yes/No] Yes
>>> Verifying ebuild Manifests...

>>> Emerging (1 of 1) x11-drivers/ati-drivers-8.37.6-r90 to /
 * ati-driver-installer-8.37.6-x86.x86_64.run RMD160 ;-) ...              [ ok ]
 * ati-driver-installer-8.37.6-x86.x86_64.run SHA1 ;-) ...                [ ok ]
 * ati-driver-installer-8.37.6-x86.x86_64.run SHA256 ;-) ...              [ ok ]
 * ati-driver-installer-8.37.6-x86.x86_64.run size ;-) ...                [ ok ]
 * checking ebuild checksums ;-) ...                                      [ ok ]
 * checking auxfile checksums ;-) ...                                     [ ok ]
 * checking miscfile checksums ;-) ...                                    [ ok ]
 * checking ati-driver-installer-8.37.6-x86.x86_64.run ;-) ...            [ ok ]
 * Determining the location of the kernel source code
 * Unable to find kernel sources at /usr/src/linux
 * This package requires Linux sources.
 * Please make sure that /usr/src/linux points at your running kernel,
 * (or the kernel you wish to build against).
 * Alternatively, set the KERNEL_DIR environment variable to the kernel sources location

!!! ERROR: x11-drivers/ati-drivers-8.37.6-r90 failed.
Call stack:
  ebuild.sh, line 1637:   Called dyn_setup
  ebuild.sh, line 704:   Called qa_call 'pkg_setup'
  ebuild.sh, line 44:   Called pkg_setup
  ati-drivers-8.37.6-r90.ebuild, line 61:   Called linux-mod_pkg_setup
  linux-mod.eclass, line 464:   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.
!!! A complete build log is located at '/var/tmp/portage/x11-drivers/ati-drivers-8.37.6-r90/temp/build.log'.

!!! This ebuild is from an overlay: '/usr/portage/local/layman/sabayon'