genkernel --menuconfig
Gentoo Linux Genkernel 3.4.6
Usage:
        genkernel [options] all

Some useful options:
        --menuconfig            Run menuconfig after oldconfig
        --no-clean              Do not run make clean before compilation
        --no-mrproper           Do not run make mrproper before compilation,
                                this is implied by --no-clean.

For a detailed list of supported options and flags; issue:
        genkernel --help