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Date: Thu, 04 Mar 2004 14:02:54 -0800
From: George Anzinger <george@mvista.com>
Organization: MontaVista Software
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To: "Amit S. Kale" <amitkale@emsyssoft.com>
CC: Tom Rini <trini@kernel.crashing.org>, Pavel Machek <pavel@ucw.cz>,
       Kernel Mailing List <linux-kernel@vger.kernel.org>,
       kgdb-bugreport@lists.sourceforge.net
Subject: Re: [Kgdb-bugreport] [PATCH] Kill kgdb_serial
References: <20040302213901.GF20227@smtp.west.cox.net> <20040303160409.GT20227@smtp.west.cox.net> <40467999.8000106@mvista.com> <200403041031.00316.amitkale@emsyssoft.com>
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Amit S. Kale wrote:
> On Thursday 04 Mar 2004 6:04 am, George Anzinger wrote:
> 
>>Tom Rini wrote:
>>
>>>On Wed, Mar 03, 2004 at 04:51:06PM +0100, Pavel Machek wrote:
>>>
>>>>Hi!
>>>>
>>>>
>>>>>>>More precisely:
>>>>>>>http://lkml.org/lkml/2004/2/11/224
>>>>>>
>>>>>>Well, that just says Andrew does not care too much. I think that
>>>>>>having both serial and ethernet support *is* good idea after all... I
>>>>>>have few machines here, some of them do not have serial, and some of
>>>>>>them do not have supported ethernet. It would be nice to use same
>>>>>>kernel on all of them. Also distribution wants to have "debugging
>>>>>>kernel", but does _not_ want to have 10 of them.
>>>>>
>>>>>But unless I'm missing something, supporting eth or 8250 at all times
>>>>>doesn't work right now anyhow, as eth if available will always take
>>>>>over.
>>>>
>>>>Well, that can be fixed. [Probably if kgdbeth= is not passed, ethernet
>>>>interface should not take over. So user selects which one should be
>>>>used by either passing kgdbeth or kgdb8250. That means that 8250
>>>>should not be initialized until user passes kgdb8250=... not sure how
>>>>you'll like that].
>>>
>>>At this point, I'm going to give up on killing kgdb_serial, and pass
>>>along some comments from David Woodhouse on IRC as well (I was talking
>>>about this issue, and the init/main.c change):
>>>(Tartarus == me, dwmw2 == David Woodhouse)
>>>
>>><Tartarus> dwmw2, the problem is how do you deal with all of the
>>>possibilities of i/o (8250, kgdboe, or other serial) and do you allow
>>>for passing 'gdb' on the command line to result in kgdb not being dropped
>>>into?  You can always break in later on of course
>>><dwmw2> parse command line early for 'gdb=' argument specifying which
>>>i/o device to use. init kgdb core early. init each i/o device as early
>>>as possible for that i/o device. Start the selected i/o device as soon
>>>as it becomes available.
>>><dwmw2> just like console could, if we looked for console= a little bit
>>>earlier. (forget all the earlyconsole shite, it's not necessary)
>>><dwmw2> Tartarrus, do the __early_setup() thing to replace __setup() for
>>>selected args. We can use that for console= too.
>>><dwmw2> since 'console=' on the command line _already_ remembers its
>>>arguments, and starts to use the offending device as soon as it gets
>>>registered with register_console().
>>><Tartarus> dwmw2, __early_setup() ?
>>><dwmw2> See __setup("gdb=", gdb_setup_func);
>>><dwmw2> Replace with __early_setup(...)
>>><Tartarus> where is __early_setup ?
>>><dwmw2> before we normally parse the command line
>>><dwmw2> in my head
>>>
>>>So perhaps someone can take these ideas and fix both problems... :)
>>>(I've got some other stuff I need to work on today).
>>
>>Well, __early_setup could mean the fist setup call and if so that would be
>>what we do in -mm.  It is done by putting the code in the first module ld
>>sees, not nice, but it works.
> 
> 
> I would prefer something that modifies start_kernel itself, rather than 
> depending on ld. It will split start_kernel command line parsing into early 
> parse and late parse, but that's the price we have to pay to do special 
> parsing of kgdb arguments.

There was some talk along these lines at one point, I don't think anything came 
of it.  We would like it to be the very first, not just one of the first.

I think modifying the kernel to support this for kgdb is more like the tail 
wagging the dog :)


-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml

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