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

[Marc-André Lureau]

Hi

On Wed, Mar 21, 2018 at 5:23 PM, Paolo Bonzini <address@hidden> wrote:
> On 21/03/2018 17:11, Marc-André Lureau wrote:
>> Hi
>>
>> On Wed, Mar 21, 2018 at 5:00 PM, Paolo Bonzini <address@hidden> 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;
>     ...
> }

I fail to see what that solves. You are moving the problem to
QObjectCommon: we would have to replace all QObject * user to take
QObjectCommon *, and then we wouldn't solve the problem for
QObjectCommon.



-- 
Marc-André Lureau