mount /dev/sda3 /mnt/gentoo
mount /dev/sda1 /mnt/gentoo/boot
cp /etc/resolv.conf /mnt/gentoo/etc/resolv.conf
mount -t proc none /mnt/gentoo/proc
mount -o bind /dev /mnt/gentoo/dev
chroot /mnt/gentoo /bin/bash
env-update
source /etc/profile
export PS1="(chroot) $PS1"
cd /usr/src/linux
make menuconfig

make && make modules_install
cp arch/x86/boot/bzImage /boot/bzImage
cp .config /boot/config

emerge grub
grub
root (hd0,0) # should return file system type
setup (hd0)  # should tell you that it embedded stage 1.5
quit