hwo to compile a generic kernel

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as per the instructions given here
http://www.gentoo.org/doc/en/handbook/handbook-ppc.xml?part=1&chap=7

and here
http://linuxfromscratch.org/pipermail/lfs-support/2005-February/026055.html
I concluded that when linux is being installed on a system for the
first time then a generic cd is used to installed which does a
[b]devfs[/b] and probes the hardware for the first time
for installation then mounts the initrd
+ if [ "$CHECK_TYPE" = "try_mount" ]; then
+ mount -n -t iso9660 ${cdrom_device} $TMP_MOUNT

and

+ mount -n -o ro -t iso9660 $LFS_CDROM_DEVICE $TMP_MOUNT
+ cd $TMP_MOUNT
+ pivot_root . mnt

and pivot root mounts the root file system and linuxrc script then
continues with installation