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Date: Fri, 23 Nov 2012 17:25:17 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1.3 1/2] qom: dynamic_cast of NULL is
 always NULL
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To: =?ISO-8859-15?Q?Andreas_F=E4rber?= <afaerber@suse.de>
Cc: aliguori@us.ibm.com, lcapitulino@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com

Il 23/11/2012 17:16, Andreas F=E4rber ha scritto:
>> > @@ -430,7 +430,7 @@ Object *object_dynamic_cast_assert(Object *obj, =
const char *typename)
>> > =20
>> >      inst =3D object_dynamic_cast(obj, typename);
>> > =20
>> > -    if (!inst) {
>> > +    if (!inst && obj) {
>> >          fprintf(stderr, "Object %p is not an instance of type %s\n"=
,
>> >                  obj, typename);
>> >          abort();
> This is followed by return inst;
>=20
> Since this function clearly has assert in the name I don't think this i=
s
> right. I would expect %p to print 0x0 and the function to abort.

I think it's okay to segfault in this case.

Otherwise you need to replace this simple cast+check pair:

    SCSIDevice *s =3D SCSI_DEVICE(some->long.expressio[n]);
    if (!s) {
        return;
    }

with something that is more complex:

    DeviceState *d =3D some->long.expressio[n];
    SCSIDevice *s;

    if (!d) {
        return;
    }
    s =3D SCSI_DEVICE(d);

Paolo