linux-kernel - Re: [ANNOUNCE] Merkey's Kernel Debugger

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Date:	Tue, 5 Aug 2008 11:10:49 -0600 (MDT)
From:	jmerkey@...fmountaingroup.com
To:	"Paul Mundt" <lethal@...ux-sh.org>, jmerkey@...fmountaingroup.com,
	"Nick Piggin" <nickpiggin@...oo.com.au>,
	"Geert Uytterhoeven" <geert@...ux-m68k.org>,
	"Stefan Richter" <stefanr@...6.in-berlin.de>,
	"Josh Boyer" <jwboyer@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [ANNOUNCE] Merkey's Kernel Debugger


> That's great, except kgdb has existed in the kernel for various
> architectures well before that as well. ppc32's stub dates back to 1998,
> sh had it since 2001, mips around the same time, etc, etc. While the
> current rework and tidying of the stubs is something new, kgdb itself is
> not.
>
>> > But the ideal outcome would be if you could contribute patches to
>> > kgdb to the point where it is as good as mdb. It is already in the
>> > tree and supported by a handful of architectures... any chance of
>> > that? (I don't know kernel debugger code, so I ask as an interested
>> > user)
>>
>> I plan to work on kdb and yes, there is a version of this that runs
>> as an alternate debugger of kdb - you can even switch back and forth
>> between them - but that misses the point as well.
>>
> kgdb and kdb are totally different things, kgdb is what is generally
> available and worth improving in-kernel.
>
> While it's certainly good to have options, having multiple in-kernel
> debuggers is not going to help matters for the vast majority of users. I
> agree with Nick, it would be nice to see what we have in-kernel being
> extended and worked on by more people, especially those with a background
> in these things.


Not your call to make.  Kernel Debuggers are very personal choices and
its pure arrogance to assume any of us can make a choice for someone else
with tools.  My tastes in debuggers is like my tastes in food, or women,
or what kin of toothbrush I like to use.

>
> On the other hand, it seems like there's sufficient interest in your
> project out-of-tree, so there's not really much point in merging it if
> you're content with the interface as it exists today and it continues to
> work for your users.
>
> One of the things we can do however is try to provide cleaner
> abstractions for the various debuggers to tie in to, so we don't end up
> with each debugger piling on its own set of ifdefs in all of the same
> places (int3 handling comes to mind, which you could already do more
> cleanly through the die chain today). Perhaps it would be more useful to
> see what sort of hooks mdb wants in the architecture and core code, how
> those overlap with kgdb, and how we might extend kgdb in areas where mdb
> is more feature complete.
>


This is a great suggestion.  mdb already uses an alternate debugger
interface with the hooks into traps_XX.c and reboot_XX.c.   I still would
like to see it in kernel.  but an alternate debugger interface as you
point
out is almost a necessity at this point.  there's a good example in
mdb.c and mdb-list.c.


Jeff

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