安装arm_linux的build_toolchain时遇到

安装arm_linux的build_toolchain时遇到shell的问题

我的所有安装文件放在usr/src/armlinux但是安装时出现如下错误
You haven't changed KERNEL to point at a valid kernel tree

查看build_toolchain有如下内容，哪位能百忙中解释下啊，多谢！
#!/bin/sh -e
PREFIX=~/arm-linux
KERNEL=/home/rmk/v2.5/linux-rpc/
#HOST=sparc-linux
HOST=
mkdir -p $PREFIX
if [ "$KERNEL" = "" -o ! -f "$KERNEL/Documentation/arm/README" ]; then
  echo "You haven't changed KERNEL to point at a valid kernel tree"
  exit 1
fi

怎么这里的人气不旺啊：）

很明显：
[code:1]You haven't changed KERNEL to point at a valid kernel tree[/code:1]