Re: [Qemu-devel] [PATCH 2/3] qobject: assume base of a qobject is at offset 0

[Paolo Bonzini <pbonzini@redhat.com>]

On 21/03/2018 17:11, Marc-André Lureau wrote:
> Hi
> 
> On Wed, Mar 21, 2018 at 5:00 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> On 21/03/2018 16:55, Marc-André Lureau wrote:
>>> That would work with an anonymous union though:
>>>
>>> struct QObject {
>>>     union {
>>>         QType type;
>>>         QType base;
>>>     };
>>>     size_t refcnt;
>>> };
>>>
>>> If it's acceptable, I think I'll take this approach.
>>
>> You don't need QEMU_GENERIC at all then, don't you?
> 
> Ah ah, that's what I thought too, but the type of QObject * &x->base
> isn't QObject * :)
> 
> I don't think we can fool it there (without loosing some type safety)

Hmm, perhaps by making it "struct {} base"?

Or even:

struct QObjectCommon {
    QType type;
    size_t refcnt;
}

struct QObject {
    QObjectCommon base;
}

struct QString {
    QObjectCommon base;
    ...
}

Paolo