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Re: [PATCH 2/3] kgdb, mips: add arch support for the kernel's kgdb core

To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Subject: Re: [PATCH 2/3] kgdb, mips: add arch support for the kernel's kgdb core
From: Jason Wessel <jason.wessel@windriver.com>
Date: Mon, 28 Jul 2008 13:50:55 -0500
Cc: linux-kernel@vger.kernel.org, ralf@linux-mips.org, linux-mips@linux-mips.org
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Atsushi Nemoto wrote:
> On Fri, 25 Jul 2008 23:52:33 +0900 (JST), Atsushi Nemoto 
> <anemo@mba.ocn.ne.jp> wrote:
>>> It seem ok to me to try it.  Here is version 3 of the patch, which I was 
>>> going to send to Ralf.
>> Thanks, it works for me with serial_txx9 kgdboc module.
> 
> BTW, is FRAME_POINTER mandatory for kgdb?  I agree that FRAME_POINTER
> (ie. -fno-omit-frame-pointer -fno-optimize-sibling-calls) helps source
> level debugging, but I think transparency is more important.
> 
> Now kgdboc can be loaded/activated at run-time, so I want to enable
> CONFIG_KGDB usually.  But CONFIG_FRAME_POINTER introduces runtime
> overhead on overall kernel, which is too bad (at least on MIPS).
> 
> Also, selecting FRAME_POINTER (which is not selectable on MIPS)
> unconditionally looks somewhat inconsistent.
> 
> So ... Is this patch reasonable?
> 

Sure the patch is reasonable for MIPS, but I think it is worth going a
step further.

There is no technical reason that frame pointers are required for KGDB
in the present mainline sources.  This does allow for further
traceability but it is certainly not a requirement for the use of kgdb.
If all you want to do is look at frame 0 and inspect memory or set a
breakpoint and look at some structures kgdb will certainly serve your
purpose.

I'll consider this a defect to the kgdb core and update the
documentation to reflect that it is advised to use frame pointers, but
not a requirement.

Jason.



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