linux-kernel - Re: [RFC] semantics of singlestepping vs. tracer exiting

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Message-ID: <20120904165823.GA11332@redhat.com>
Date:	Tue, 4 Sep 2012 18:58:23 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org
Subject: Re: [RFC] semantics of singlestepping vs. tracer exiting

On 09/04, Al Viro wrote:
>
> On Tue, Sep 04, 2012 at 05:39:38PM +0200, Oleg Nesterov wrote:
>
> > > BTW, speaking of alpha, what about PTRACE_SINGLESTEP when the task is stopped
> > > on syscall entry/exit after previous PTRACE_SYSCALL, BTW?  Looks like it will
> > > be like PTRACE_CONT until we hit the first signal, at which point it converts
> > > to singlesteping mode; unless I'm seriously misreading that code, we rely
> > > on ptrace_set_bpt() done shortly after returning from get_signal_to_deliver()
> > > if we found that we'd been singlestepping.  Fine, but in this case we
> > > had been resumed *not* in get_signal_to_deliver()...
> >
> > Again, "single_stepping |= ptrace_cancel_bpt()" after get_signal_to_deliver()
> > should work I think... Not sure.
>
> Umm...  What would get us anywhere near get_signal_to_deliver() in this
> case?

Yes, I misread this code...

> so we happily proceed
> to run the process until a signal arrives, same as we would with PTRACE_CONT.
> What am I missing here?

Looks like, you are right.

Oleg.

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