[Crash-utility] question about phys_base

[Wen Congyang]

At 02/29/2012 09:04 AM, HATAYAMA Daisuke Wrote:
> From: Dave Anderson <anderson at redhat.com>
> Subject: Re: [Crash-utility] question about phys_base
> Date: Tue, 28 Feb 2012 09:44:09 -0500 (EST)
> 
>>
>>
>> ----- Original Message -----
>>> At 02/28/2012 04:52 PM, HATAYAMA Daisuke Wrote:
>>
>>>>>> In general, such characteristic should not be used. You should prepare
>>>>>> a solid interface. Even if using them, it should be limited to as
>>>>>> workaround to avoid some issue.
>>>>>>
>>>>>> Why not use qemu's CPU state? Include it as note information with good
>>>>>> name, and we can use it to distinguish which. Like:
>>>>>>
>>>>>> $ readelf -n vmcore
>>>>>>
>>>>>> Notes at offset 0x000001c8 with length 0x00000838:
>>>>>>   Owner         Data size       Description
>>>>>>   CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>>>>>>   CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>>>>>>   QEMU          0x00000557      Unknown note type: (0x00000000)
>>>>>>
>>>>>> Or QEMUCPUState is better?
>>>>>
>>>>> Good idea. I will try it, and hope gdb can also work.
>>>>>
>>>>
>>>> Tools basically ignore unknown notes. Looking into gdb, it appears to
>>>> ignore unknown information.
>>>>
>>>> static bfd_boolean
>>>> elfcore_grok_note (bfd *abfd, Elf_Internal_Note *note)
>>>> {
>>>>   const struct elf_backend_data *bed = get_elf_backend_data (abfd);
>>>>
>>>>   switch (note->type)
>>>>     {
>>>>     default:
>>>>       return TRUE;
>>>> <cut>
>>>>
>>>> You might need to add new command to output contents of new note if
>>>> it's necessary.
>>>
>>> My goal is:
>>> 1. gdb uses NT_PRSTATUS, and can work well
>>> 2. crash uses unknown notes, and can get phys_base from it.
>>>
>>> Another question:
>>>
>>> What is QEMUCPUState? I donot find its definition?
>>
>> It's just the note's name character string.  Either "QEMU", "QEMUCPUState",
>> or whatever unique character string you prefer would suffice.
>>
>>> What note->type shoule be for "QEMU"? If we choose an unused value, the
>>> value may be used in the future.
>>
>> Why not do the same thing as the "VMCOREINFO" note, and leave it
>> as an "illegal/unknown" type of 0::
>>
>>   $ cat /usr/include/elf.h
>>   ... [ cut ] ...
>>
>>   /* Legal values for note segment descriptor types for core files. */
>>
>>   #define NT_PRSTATUS     1               /* Contains copy of prstatus struct */
>>   #define NT_FPREGSET     2               /* Contains copy of fpregset struct */
>>   #define NT_PRPSINFO     3               /* Contains copy of prpsinfo struct */
>>   ...
>>   $
>>
>>   $ readelf -a vmcore
>>   ... [ cut ] ...
>>
>>   Notes at offset 0x00000190 with length 0x00000f1c:
>>     Owner         Data size       Description
>>     CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>>     CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>>     CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>>     CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>>     CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>>     CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>>     CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>>     CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>>     VMCOREINFO            0x000003e4      Unknown note type: (0x00000000)
>>   $
>>
> 
> It looks OK to me for now.
> 
> But rigorously, it might be better to give it a name QEMU and then
> prepare variety of information such as NT_CPUSTATE and others to be
> needed later.

I see. I think we should decide what information should be stored in QEMUCPUState.
The CPUState in qemu cannot be used directly, because it may be changed in the furture.
I think all CPU register should be stored in QEMUCPUState. Do we need other information?

Thanks
Wen Congyang

> 
> Thanks.
> HATAYAMA, Daisuke
> 
>