im just putting this here cause i sometimes forget this.

these steps allow you to fully chroot to an existing drive from a livecd

# fdisk -l /dev/sda
Password:

Disk /dev/sda: 80.0 GB, 80026361856 bytes
255 heads, 63 sectors/track, 9729 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x0006bcbb

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          13      104391   83  Linux
/dev/sda2              14         268     2048287+  82  Linux swap / Solaris
/dev/sda3             269        9729    75995482+  83  Linux

# mount /dev/sda3 /mnt/gentoo
# mount -t proc none /mnt/gentoo/proc
# mount -o bind /dev /mnt/gentoo/dev
# chroot /mnt/gentoo /bin/bash
# env-update
# source /etc/profile

now from the prompt you can repair your drive with no issue.