Building module for a 2.6 kernel
make[1]: Entering directory `/usr/src/openswan-2.4.12'
make[2]: Entering directory `/usr/src/openswan-2.4.12'
make[2]: `/usr/src/openswan-2.4.12/modobj26/Makefile' is up to date.
make[2]: Leaving directory `/usr/src/openswan-2.4.12'
make -C /usr/src/linux-source-2.6.18  BUILDDIR=/usr/src/openswan-2.4.12/modobj26
make[2]: Entering directory `/usr/src/linux-source-2.6.18'

  ERROR: Kernel configuration is invalid.
         include/linux/autoconf.h or include/config/auto.conf are missing.
         Run 'make oldconfig && make prepare' on kernel src to fix it.


  WARNING: Symbol version dump /usr/src/linux-source-2.6.18/Module.symvers
           is missing; modules will have no dependencies and modversions.

  CC [M]  /usr/src/openswan-2.4.12/modobj26/ipsec_init.o
make[2]: Leaving directory `/usr/src/linux-source-2.6.18'
make[1]: Leaving directory `/usr/src/openswan-2.4.12'