Why Mac Mountain Lion cannot use gdb to analzy kernel core dump??

Question

I'm trying to use gdb debug  a Core Dump after a Kernel Panic which I collected from two Macs,but when i use list command below i get some errs:
then get "can't find symblos for ****

Answer 1

Hi Linc Davis:
  thanks for your replay!
  And could you tell me which "debug kernel available" shall i need to run,because i have seached all of Apple Developer site but found nothing useful infomation to be set?!
  Below are the steps how i get  Mac Mountain Lion(10.8.3 Build:12D78) kernel core dump from Apple Developer site:
1、Configuring the Server:
1)Creating the core dump directory:
   server$ sudo mkdir /PanicDumps
   Password:********
   server$ sudo chown root:wheel /PanicDumps
   server$ sudo chmod 1777 /PanicDumps
2)Activating the core dump server
   server$ sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.kdumpd.plist
   Password:********
3)Verifying the core dump server is active
   server$ sudo launchctl list | grep kdump
   Password:********
    - 0     com.apple.kdumpd
2、Configuring a Client
  client$ sudo nvram boot-args="debug=0xd44 _panicd_ip=10.***.***.***" （10.***.***.***
  Password: ********
when i got client pc core dump,and use gdb analyze it ,i got some errs,eg,
/Volumes/KernelDebugKit?kgmacros:342:Error in sourced command file:
cannot access memory at address 0xffffff8000200004