linux-kernel - Re: [RFC] Proposal for ptrace improvements

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Message-ID: <20110304170737.GA26904@redhat.com>
Date:	Fri, 4 Mar 2011 18:07:37 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jan Kratochvil <jan.kratochvil@...hat.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Tejun Heo <tj@...nel.org>, Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [RFC] Proposal for ptrace improvements

On 03/04, Jan Kratochvil wrote:
>
> On Tue, 01 Mar 2011 23:14:14 +0100, Denys Vlasenko wrote:
> > On Tue, Mar 1, 2011 at 8:06 PM, Jan Kratochvil <jan.kratochvil@...hat.com> wrote:
> > > Currently it is already a problem that apps did not / do not expect the first
> > > waitpid after PTRACE_ATTACH may not be SIGSTOP.
> >
> > That's exactly why we want to add a better alternative, which doesn't
> > insert that blasted SIGSTOP.
>
> But it insteads blasted SIGTRAP (or some other signal) instead.

I don't really understand your concerns... If you modify gdb to use
PTRACE_SEIZE you can forget about the current problems with the first
signal.

Currently gdb has to take care, but mostly because it should "dismiss"
the real signal sent by attach.

> It would be best if such PTRACE_SEIZE (similar to PTRACE_INTERRUPT) would
> guarantee the first waitpid afterwards returns the artificial signal from
> PTRACE_SEIZE.

Again, I don't think this really matters.

Suppose that the tracee reports, say, a signal after PTRACE_SEIZE/INTERRUPT.
And this is possible anyway if the debugger races with kill(). Why this
is bad?

Oleg.

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