localhost chris # emerge tomcat
Calculating dependencies... done!
>>> starting parallel fetching

>>> Emerging (1 of 48) dev-java/jss-3.4-r1 to /
 * jss-3.4-src.tar.gz MD5 ;-) ...                                         [ ok ]
 * jss-3.4-src.tar.gz RMD160 ;-) ...                                      [ ok ]
 * jss-3.4-src.tar.gz SHA1 ;-) ...                                        [ ok ]
 * jss-3.4-src.tar.gz SHA256 ;-) ...                                      [ ok ]
 * jss-3.4-src.tar.gz size ;-) ...                                        [ ok ]
 * checking ebuild checksums ;-) ...                                      [ ok ]
 * checking auxfile checksums ;-) ...                                     [ ok ]
 * checking miscfile checksums ;-) ...                                    [ ok ]
 * checking jss-3.4-src.tar.gz ;-) ...                                    [ ok ]
 * 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: dev-java/jss-3.4-r1 failed.
Call stack:
  ebuild.sh, line 1584:   Called dyn_setup
  ebuild.sh, line 665:   Called pkg_setup
  ebuild.sh, line 1261:   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.

!!! When you file a bug report, please include the following information:
GENTOO_VM=blackdown-jdk-1.4.2  CLASSPATH="" JAVA_HOME="/opt/blackdown-jdk-1.4.2.03"
JAVACFLAGS="-source 1.4 -target 1.4" COMPILER=""
and of course, the output of emerge --info