linux-kernel - Re: [PATCH 03/10] ptrace: implement PTRACE

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Date:	Thu, 26 May 2011 12:11:02 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Pedro Alves <pedro@...esourcery.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	jan.kratochvil@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	indan@....nu, bdonlan@...il.com
Subject: Re: [PATCH 03/10] ptrace: implement PTRACE_SEIZE

Hello, Pedro.

On Thu, May 26, 2011 at 11:01:42AM +0100, Pedro Alves wrote:
> SYSGOOD makes sense, it just enables a means to distinguish syscall
> SIGTRAPs from regular SIGTRAPs -- it doesn't cause child stops itself.
> TRACE_EXEC, I'm not so sure.  (and it appears to have been proposed
> on the premise that SEIZE would still report the SIGTRAP).
> Why would that make sense, and not TRACE_FORK, for example?  I can imagine
> a tracer only caring for syscall entry/exit, and not needing a special
> event on exec.  IMO, any kind of event that forces a child stop that
> would't happen if the child wasn't traced should have to be enabled
> explicitly.

The problem with exec is that very weird things happen during exec.
Tasks change their ids, tracees get silently pruned and so on, so
there might not be a transparent way for a ptracer to deal with it.
It needs to be notified and handle the situation whether it wants or
not.

What I was saying was there won't be SIGTRAP.  In general, we're
trying to move away from kernel implicitly sending actual signals.  If
we enable it by default, it will be a proper ptrace trap.

Thanks.

-- 
tejun
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