linux-kernel - Re: [PATCH 04/11] ptrace: implement PTRACE

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Date:	Thu, 12 May 2011 19:06:17 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	jan.kratochvil@...hat.com, vda.linux@...glemail.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu
Subject: Re: [PATCH 04/11] ptrace: implement PTRACE_INTERRUPT

On 05/11, Tejun Heo wrote:
>
> On Tue, May 10, 2011 at 08:08:11PM +0200, Oleg Nesterov wrote:
> >
> > Hmm. Suddenly I got lost. Perhaps instead JOBCTL_TRAP_INTERRUPT should
> > be cleared on any trap too, like SEIZE.
>
> I don't think that's a good idea especially because there are
> functionality differences among different traps.  ie. group stop and
> interrupt traps support re-trapping on job control events while other
> traps don't, so there will be cases where the debugger wants to put
> tracee specifically into INTERRUPT trap.  It's just cleaner to use and
> say that if you ask for INTERRUPT, you get an INTERRUPT.

Hmm. This is not clear to me... OK, I'll read other emails first.

> > Another special (and nasty!) case is PTRACE_TRACEME. I do not know
> > how often it is used, but probabaly it is important enough. At least,
> > iirc, it is used by strace. Probably we need PTRACE_SEIZEME as well.
>
> I don't agree.  PTRACE_TRACEME predates PTRACE_ATTACH and is
> completely redundant.  If you can make the child do PTRACE_TRACEME,
> you might as well just make it do pause() and PTRACE_SEIZE yourself,
> so unless there's something PTRACE_SEIZE can't do, I don't think I'll
> be adding SEIZEME.

Heh. I think that you are very right technically and I thought the
same. That is why I never mentioned PTRACE_TRACEME before. In fact
I never understood why PTRACE_TRACEME exists.

However. Perhaps this is wrong from the practical pov. SEIZEME can
simplify the conversion of the existing code. People are lazy, but
we need the users of PTRACE_SEIZE.

Anyway. SEIZEME is absolutely trivial. We can add it at any moment,
right now this is almost offtopic.

Oleg.

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