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From: Eric Blake <eblake@redhat.com>
To: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: qemu-devel <qemu-devel@nongnu.org>,
	"P. Berrange, Daniel" <berrange@redhat.com>,
	"Armbruster, Markus" <armbru@redhat.com>,
	"Bonzini, Paolo" <pbonzini@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v2 2/3] qobject: introduce QObjectCommon
Date: Wed, 28 Mar 2018 08:55:51 -0500	[thread overview]
Message-ID: <ac132600-ac94-c9b7-b280-f2ff2ebebf74@redhat.com> (raw)
In-Reply-To: <CAMxuvayFZiYwf99mbMVFVwFZR2Bnqfv4rYS1O2SpDT1mhFtAEg@mail.gmail.com>

On 03/28/2018 08:48 AM, Marc-André Lureau wrote:

>>> +#define QOBJECT(x) \
>>> +   container_of(&(x)->base, QObject, base)
>>
>>
>> If I understand correctly, this still causes clang complaints when called as
>> QOBJECT(NULL).  As long as we are touching this, should we improve this
>> macro to be friendly to NULL conversion?
> 
> I don't see much need for allowing NULL (literally) to be passed to
> QOBJECT(). If it's a null pointer, as long as it has the right type,
> it should be fine, shouldn't it?

Not with clang ubsan (okay, the failure is at runtime, not compile time):

https://lists.gnu.org/archive/html/qemu-devel/2018-03/msg05143.html
https://lists.gnu.org/archive/html/qemu-devel/2018-03/msg05148.html

Even when the offset is 0, the mere fact that you are computing an 
offset relative to a NULL pointer is undefined behavior.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

  reply	other threads:[~2018-03-28 13:56 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-28 13:07 [Qemu-devel] [PATCH v2 0/3] RFC: simplify qobject refcount Marc-André Lureau
2018-03-28 13:07 ` [Qemu-devel] [PATCH v2 1/3] qobject: ensure base is at offset 0 Marc-André Lureau
2018-03-28 13:07 ` [Qemu-devel] [PATCH v2 2/3] qobject: introduce QObjectCommon Marc-André Lureau
2018-03-28 13:45   ` Eric Blake
2018-03-28 13:48     ` Marc-André Lureau
2018-03-28 13:55       ` Eric Blake [this message]
2018-03-28 14:11         ` Paolo Bonzini
2018-03-28 14:19           ` Marc-André Lureau
2018-03-28 13:07 ` [Qemu-devel] [PATCH v2 3/3] qobject: replace qobject_incref/QINCREF qobject_decref/QDECREF Marc-André Lureau

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