[U-Boot-Users] need for explaination

Hi All, I like to clarify one doubt ,when i try to boot my kernel using ramdisk image via bootm command .I have back traced the cmd_bootm.c(Version u_boot-1.1.6 in the common directory) our code flow hangs at the following function:

(*kernel) (kbd, initrd_start, initrd_end, cmd_start, cmd_end);

it's calling function pointer .It hangs at this call can any one help me out where is the exact definition of this function call so that i can proceed further.I think it should be in the u-boot side.It will be of great help if any one reply me ASAP in this regard. Regards Ramesh.K.V