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Date:   Fri, 7 Dec 2018 21:42:46 +0300
From:   "Dmitry V. Levin" <ldv@altlinux.org>
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Breno Leitao <leitao@debian.org>,
        Andy Lutomirski <luto@kernel.org>,
        Eugene Syromyatnikov <esyr@redhat.com>,
        Elvira Khabirova <lineprinter@altlinux.org>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] powerpc/ptrace: replace ptrace_report_syscall() with
 a tracehook call
Message-ID: <20181207184246.GA31278@altlinux.org>
References: <20181116121701.14359da0@akathisia>
 <87ftw12nyn.fsf@concordia.ellerman.id.au>
 <20181119210139.GA8360@altlinux.org>
 <87efbe166y.fsf@concordia.ellerman.id.au>
 <20181203031823.GE11573@altlinux.org>
 <20181207011946.GA18558@altlinux.org>
 <87y391k2tq.fsf@concordia.ellerman.id.au>
 <20181207154255.GA28964@altlinux.org>
 <20181207163410.GA19110@redhat.com>
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On Fri, Dec 07, 2018 at 05:34:10PM +0100, Oleg Nesterov wrote:
> On 12/07, Dmitry V. Levin wrote:
> > On Fri, Dec 07, 2018 at 10:12:49PM +1100, Michael Ellerman wrote:
> >
> > > > Sorry, this patch does not work, please ignore it.
> > >
> > > Hmm OK. Why exactly?
> >
> > Unfortunately, I have no idea why it doesn't work.
> > All I can say is it breaks strace because the kernel no longer sends
> > syscall entry stops.
>=20
> May be because TIF_SYSCALL_EMU/etc is a bit number, not a mask? IOW, rath=
er
> than
>=20
> 	whatever & TIF_XXX
>=20
> you should do
>=20
> 	whatever & _TIF_XXX
>=20
> intstead?

Thanks Oleg, this was exactly the reason why it didn't work.
That kind of things happens when you let userspace people hack you kernel. =
:)


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