From mboxrd@z Thu Jan  1 00:00:00 1970
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From: Oleg Nesterov <oleg@redhat.com>
To: elfutils-devel@lists.fedorahosted.org
Subject: Re: [PATCH] Add --core-pattern option to eu-stack
Date: Wed, 26 Nov 2014 21:08:22 +0100
Message-ID: <20141126200822.GB19810@redhat.com>
In-Reply-To: 20141126143239.GA16611@host2.jankratochvil.net

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On 11/26, Jan Kratochvil wrote:
>
> On Thu, 30 Oct 2014 22:55:41 +0100, Mark Wielaard wrote:
> > On Thu, 2014-10-09 at 23:25 +0200, Jan Kratochvil wrote:
> > > +      if (opt_core_pattern =3D=3D true && show_one_tid =3D=3D false)
> > > +	argp_error (state,
> > > +		    N_("--core-pattern requires -1"));
> >
> > Why this restriction?
>
> I was blindly following Oleg's note which was not so obvious to me, thoug=
h:
>
> On Wed, 03 Sep 2014 16:26:41 +0200, Oleg Nesterov wrote:
> # Obviously, this way you can only inspect the thread which dumps the cor=
e.
>
> Therefore I have now tried to remove this limitation of
>   -1                         Show the backtrace of only one thread
>
> But I have found the other threads end up with:
> 	wait4(13902, [{WIFSIGNALED(s) && WTERMSIG(s) =3D=3D SIGSEGV && WCOREDUMP=
(s)}], __WALL, NULL) =3D 13902
>
> Therefore they are dead at the core_pattern time, they cannot be ptraced =
and
> therefore they cannot be unwound.

Yes. I guess PTRACE_ATTACH should work but it is pointless, this
thread can't report an event and other ptrace requests won't work.

In fact I think PTRACE_ATTACH should fail in this case...

Oleg.


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