linux-kernel - Re: [RFC] [PATCH] In-kernel gdbstub based on utrace Infrastructure.

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Message-ID: <20091201170954.GA4699@elte.hu>
Date:	Tue, 1 Dec 2009 18:09:54 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	utrace-devel <utrace-devel@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [RFC] [PATCH] In-kernel gdbstub based on utrace Infrastructure.


* Frank Ch. Eigler <fche@...hat.com> wrote:

> Hi -
> 
> On Tue, Dec 01, 2009 at 05:11:32PM +0100, Ingo Molnar wrote:
>
> > Those facilities are not overlapping with kgdb though so my point 
> > doesnt apply to them. An in-kernel gdb server sure overlaps/extends 
> > kgdb though.
> 
> Only in name.  One is highly invasive, for debugging the kernel across 
> serial consoles.  The other is highly noninvasive, for debugging user 
> processes across normal userspace channels.  They both happen to talk 
> to gdb, but that's the end of the natural "overlap".
> 
> Even if kgdb was extended to be able to manage userspace, and if gdb 
> itself was extended to be able to use that same single channel, this 
> would still not duplicate the use scenario for an ordinary user 
> debugging his own processes.
> 
> (Plus, in the future where at least gdb is applied toward kernel+user 
> debugging, it is unlikely to be the case that this would need to be 
> done *over a single channel*.  A separate channel for kernel and 
> separate channels for userspace programs are no less likely.)

Well nothing that you mention here changes our obvious suggestion that 
an in-kernel gdb stub should obviously either be a kgdb extension, or a 
replacement of it. We dont want to separate facilities for the same 
conceptual thing: examining application state (be that in user-space and 
kernel-space).

> > Btw., perf does meet that definition: it functionally replaces all 
> > facilities that it overlaps/extends - such as Oprofile. [...]
> 
> (And they currently separately coexist.)

You didnt get my point apparently. Keeping the overlapped facility for 
compatibility (and general user inertia) is fine. Creating a new 
facility that doesnt do everything that the existing facility does, and 
not integrating it either, is not fine.

Which was both Peter's and my point really.

	Ingo
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