[ELDK] how to compile linux kernel in eldk-5.0?

[wolfking]

Hi, everybody:
  I'm compiling linux kernel for powerpc in eldk-5.0, the following is the steps I took:
  1. download the denx linux kernel: "git clone git://git.denx.de/linux-2.6-denx.git linux-2.6-denx"
  2. run the environment shell to construct the compile environment. "source ./environment-setup-powerpc-linux"
  3. according to the FAQ about eldk-5.0, I modified some Makefile under the kernel tree, change 
      the -Os to -O2. I am not sure whether it is right to do this, can anyone tell me how to modify the compile flags?
  4. start the compile:
      a. make mrproper
      b. make ARCH=powerpc CROSS_COMPILE=powerpc-linux- 86xx/mpc8641_hpcn_defconfig
      c. make ARCH=powerpc CROSS_COMPILE=powerpc-linux- uImage
  At the end of the compilation, one error is presented:
 
  HOSTCC  arch/powerpc/boot/hack-coff
  HOSTCC  arch/powerpc/boot/mktree
  WRAP    arch/powerpc/boot/uImage
"mkimage" command not found - U-Boot images will not be built
make[1]: *** [arch/powerpc/boot/uImage] Error 1
make: *** [uImage] Error 2
 
   It seems that something is wrong with U-boot, but this process is about kernel, why does it report error about U-boot?
   Thanks!