debug linux kernel hangs

Hi all:
My platform is MPC8247, u-boot verison is 1.1.1 and linux kernel version is 2.4.22
in the serial console I load the linux kernel and want to boot it under u-boot:

=> setenv ethaddr 00:01:02:03:04:05
=> setenv ipaddr 192.168.0.33
=> setenv serverip 192.168.0.222
=> tftp 0x100000 uImage
Using FCC1 ETHERNET device
TFTP from server 192.168.0.222; our IP address is 192.168.0.33 Filename 'uImage'.
Load address: 0x100000
Loading: #################################################################

         #################################################################
         #####################################

done
Bytes transferred = 853098 (d046a hex)
=> bootm 0x100000
## Booting image at 00100000 ...

   Image Name:   Linux Kernel Image
   Image Type:   PowerPC Linux Kernel Image (gzip compressed)
   Data Size:    853034 Bytes = 833 kB

Load Address: 00000000
Entry Point: 00000000
Verifying Checksum ... OK
Uncompressing Kernel Image ... OK

but after print the "Uncompressing Kernel Image ... OK" msg, the kernel hangs.
I use the same u-boot.h file under linux kernel and u-boot, and sure the bd_info in them are same. IMMR address also are same at 0xf0000000.

My bdi2000 run and print below:
++++++++++++++++++++++++++++++++++
8272>i

    Target CPU        : MPC8280/8220/5200 (Zeppo)
    Target state      : debug mode
    Debug entry cause : COP freeze (startup)
    Current PC        : 0xfff00100
    Current CR        : 0x00000000
    Current MSR       : 0x00001042
    Current LR        : 0x00000000
8272>g
8272>h
    Target CPU        : MPC8280/8220/5200 (Zeppo)
    Target state      : debug mode
    Debug entry cause : COP halt
    Current PC        : 0x07fe94c8
    Current CR        : 0x84002024
    Current MSR       : 0x0000b002
    Current LR        : 0x07fda464

8272>bi 0xc01554c8 (which is the start_kernel_address)
Breakpoint identification is 1
8272>g
- TARGET: stopped
8272>i

    Target CPU        : MPC8280/8220/5200 (Zeppo)
    Target state      : debug mode
    Debug entry cause : <reserved 0>
    Current PC        : 0x001cbde4
    Current CR        : 0x24008084
    Current MSR       : 0x00003002
    Current LR        : 0x00000028

+++++++++++++++++++++++++++++++++++++++++++

Why the Current PC can not get the start_kernel address? How can i to debug the linux kernel? Any hits will be very appreciated!

BRG
Alexander

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