Re: What do you use for kernel debugging?

On 9/29/14, 8:31 AM, José Pérez Arauzo wrote:
> Hi Garrett,
>
> On Sun, 28 Sep 2014 13:38:24 -0700, Garrett Cooper wrote
>> On Sep 28, 2014, at 0:34, José Pérez Arauzo <fbl_at_aoek.com> wrote:
>>
>>> Hello,
>>> I am trying to track down a (deadlock?) issue in CURRENT via DDB. The
> kernel does
>>> not complete hw probes on my Acer V5.
>>>
>>> I get stuck on apic_isr looping which leads nowhere.
>>>
>>> So I thought maybe things improve if I debug from another machine.
>>>
>>>
>>> What do you use for kernel debugging? According to the handbook kgdb over
> serial
>>> is a good option, do you agree? I'm on a netbook with no ethernet and no
> option
>>> for firewire: can I have a USB / nullmodem setup to work?
>>>
>>> I have no old-style uarts hardware anymore, as the handbook suggests...
>>>
>>> Any idea is welcome before I buy extra hw. I have a USB to serial showing
> up as
>>> /dev/cuaU0, do I need to grab another one and a nullmodem cable or there
> are better
>>> alternatives? Thank you.
>> There was some discussion recently about this on an internal list.
>> Unfortunately no, there isn’t a usable way, but there were some
>> interesting viable methods that came up (which haven’t been
>> implemented): ethernet/sound/xHCI.
>>
>> Your best bet, as others have noted, is to use boot -d, use WITNESS
>> to spot locking issues, dtrace to isolate which section of code
>> there are problems, and finally use one of the DEBUG options noted
>> in /sys/conf/NOTES and /sys/<your-architecture>/conf/NOTES .
>>
>> Hope that helps!
> Well, it's not so encouraging but I'll work on it.
>
> Do you mean that we can get rid of chapter 10.5 of the handbook (On-Line
> Kernel Debugging Using Remote GDB)?
no it works when you have the hardware. but modern laptops have so 
little hardware..
we really will have to define an API/ABI to add to teh current 
ethernet driver API so that we can do network based debugging.
it's getting harder and harder to find alternatives. (though debugging 
a VM works well).

> Just to have it clear, when people develop or fix drivers in FreeBSD
> their only option is to use the above mentioned tools, as they have no
> access to a live, on-line kernel debugger?? It's disappointing, to say
> the least!
>
> I hope Dcons + 1394 works where it's applicable.
>
> BR,
>
> --
> José Pérez Arauzo
>
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