emerge cryptsetup
emerge sys-kernel/genkernel
emerge sys-kernel/gentoo-sources
wget http://dev.gentoo.org/~prometheanfire/dist/kernel-patches/linux-3.5.0-gfp-vmalloc.patch -O - | patch -p1 -d /usr/src/linux
wget http://dev.gentoo.org/~ryao/dist/linux-3.5.0-zfs.patch -O - | patch -p1 -d /usr/src/linux
wget http://dev.gentoo.org/~prometheanfire/dist/kernel-patches/linux-3.5.0-zfs-builtin.patch -O - | patch -p1 -d /usr/src/linux

cd /usr/src/linux
zcat /proc/config.gz > .config
make oldconfig