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Date: Thu, 13 Dec 2018 14:24:52 +1100
From: David Gibson <david@gibson.dropbear.id.au>
Message-ID: <20181213032452.GA25689@umbus.fritz.box>
References: <20180830143348.10595-1-marcandre.lureau@redhat.com>
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In-Reply-To: <20180830143348.10595-1-marcandre.lureau@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] seccomp: check TSYNC host capability
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To: =?iso-8859-1?Q?Marc-Andr=E9?= Lureau <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org, otubo@redhat.com


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On Thu, Aug 30, 2018 at 04:33:48PM +0200, Marc-Andr=E9 Lureau wrote:
> Remove -sandbox option if the host is not capable of TSYNC, since the
> sandbox will fail at setup time otherwise. This will help libvirt, for
> ex, to figure out if -sandbox will work.
>=20
> Signed-off-by: Marc-Andr=E9 Lureau <marcandre.lureau@redhat.com>

This seems to have introduced a regression, which I found when
preparing a ppc pull request.  Specifically when running with RHEL7 on
a POWER host, using "-sandbox off" which one of my tests did, causes a
cryptic error followed by a SEGV:

$ ./ppc64-softmmu/qemu-system-ppc64 -sandbox off
qemu-system-ppc64: -sandbox off: There is no option group 'sandbox'
Segmentation fault
$ ./x86_64-softmmu/qemu-system-x86_64 -sandbox off
qemu-system-x86_64: -sandbox off: There is no option group 'sandbox'
Segmentation fault

I think the problem is that while this wrapped one use of the sandbox
option group to produce a sensible error, it didn't do the same for
another call to qemu_opts_parse_noisily():

(gdb) bt
#0  0x00000000105b36d8 in opts_parse (list=3D0x0, params=3D0x3ffffffffab5 "=
off", permit_abbrev=3Dtrue, defaults=3Dfalse, errp=3D0x3ffffffff080)
    at util/qemu-option.c:829
#1  0x00000000105b3b74 in qemu_opts_parse_noisily (list=3D<optimized out>, =
params=3D<optimized out>, permit_abbrev=3D<optimized out>) at util/qemu-opt=
ion.c:890
#2  0x0000000010024964 in main (argc=3D<optimized out>, argv=3D<optimized o=
ut>, envp=3D<optimized out>) at vl.c:3589

I'm guessing RHEL7 triggers it because that has a version of
libseccomp that doesn't support the feature needed to complete
registration (maybe on ppc host only; I haven't had a chance to try on
an x86 RHEL7 host).

--=20
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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