Re: about kdb for Xen

Re: about kdb for Xen

[Mukesh Rathor]

You cannot continue execution when system crashed. The only thing to do is 
reboot. So go is disabled, as sometimes accidentally one might type that while 
debugging.

There is some work to get gdb to debug xen, but I'm not sure what state it's in.

To assist in debugging via kdb, use gdb on xen-syms file. Then use gdb to find 
  matching line numbers in C file. Look at gdb manual how to do that.

Thanks,
Mukesh


gjk.liu@gmail.com wrote:
> Hi Mukesh,
>    
>      Why system often show"cmd not available in fatal/crashed state .....", after
> enter "go" in kdb for Xen. I have just cloned the codes from the branch.
> 
> btw:  Is there any other debug method for xen itself? for example, using gdb at 
> source code level like linux or freebsd. I think it will be more convenient than kdb.
> You know, there are too many optimazation on code after compiled by gcc.
> 
>    Cheers:)
> 
>     Liu Jian 
> 

Re: about kdb for Xen

[Mukesh Rathor]

Liu Jian wrote:
> On Fri, Mar 27, 2009 at 10:50 AM, Mukesh Rathor
> <mukesh.rathor@oracle.com> wrote:
>> I think I'm not following you. If you enter go first time, the system is
>> crashing. You are hitting an assert (BUG()) in the hypervisor. The
>> victim is accpting input as you are able to type the second "go" when
>> it's says cmd not avail in crash state.
>>
>> After the crash, you can use dr, f, dw, etc... all those commands but
>> not the "go" cmd.
>>
> 
> Yes, "df, f, dw" works well. But the second "go" not and it show as following:
> 
> [1]xkdb> go
> cmd not available in fatal/crashed state......
> 
> Of course, now target victim cannot accept any input.

You are saying you don't get kdb prompt back now?

> 
>> 1. what version of xen are you using?
> 
> All the code is cloned from your branch as following:
> 
> [root@localhost ~]hg clone http://xenbits.xensource.com/ext/debuggers.hg
> 
> In the compile process as following, It show the version is "3.4-unstable"
> 
>> 2. Are you compiling hyp with -DEBUG?
> 
> I just compile xen by:
> 
> [root@localhost xen>make kdb=y
> 
> Do you mean I need other parameters?

The problem is debug is turned on. kdb is not currently supported with
debug on, as I had said before. Do > make kdb=y debug=n
I also suggest frame_pointer=y to get reliable stacks.

Mukesh

Re: about kdb for Xen

[Mukesh Rathor]

Liu Jian wrote:
>> The problem is debug is turned on. kdb is not currently supported with
>> debug on, as I had said before. Do > make kdb=y debug=n
>> I also suggest frame_pointer=y to get reliable stacks.
>>
> 
> after add "debug=n", it works well. Thanks lots!
> 
> btw: what is the function about "frame_pointer=y"?

you'll get reliable stack as the compiler will dedicate a register for stack 
usage.


Mukesh