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From: Markus Armbruster <armbru@redhat.com>
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Date: Tue, 24 Apr 2018 17:24:56 +0200
In-Reply-To: <CAFEAcA-ynm85eJ9Q7F8mtYNNiUBY+BQQcCdEg_eAdfmVTD4GRw@mail.gmail.com>
	(Peter Maydell's message of "Tue, 24 Apr 2018 13:34:27 +0100")
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Subject: Re: [Qemu-devel] [PATCH v6 1/5] qobject: ensure base is at offset 0
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>, =?utf-8?Q?Marc-Andr=C3=A9?= Lureau <marcandre.lureau@gmail.com>, QEMU <qemu-devel@nongnu.org>

Peter Maydell <peter.maydell@linaro.org> writes:

> On 24 April 2018 at 13:18, Markus Armbruster <armbru@redhat.com> wrote:
>> We define hundreds of QOM types without ever bothering to check the
>> super type comes first.  We don't even bother to clearly document it has
>> to come first.
>
> If you don't put the super type first then the first time you
> do MyParent *p =3D MY_PARENT(me); then the QOM cast will assert
> on you, so you'll figure it out pretty quickly...

Same for QObject & friends, where qobject_to() asserts.

Marc-Andr=C3=A9's argument for adding more checks was the possibility of
someone doing MyParent *p =3D (MyParent *)me without running into
MY_PARENT(me).