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Re: [libvirt] using clang



On Tue, Apr 27, 2010 at 07:05:44PM +0200, Jim Meyering wrote:
> Some people have expressed an interest in setting up
> a libvirt autobuilder using clang.  If you do that, be aware that
> you'll see an ugly looking NULL-deref problem when using the clang
> that comes with F12 or F13, but if you're using a new enough version
> (rawhide), it's gone.  The offending code is in qemu_monitor.c around
> line 377 and involves the CMSG_* macros:
> 
>     365	 memset(&msg, 0, sizeof(msg));
>     366
>     367	iov[0].iov_base = (void *)data;
>     368	iov[0].iov_len = len;
>     369
>     370	msg.msg_iov = iov;
>     371	msg.msg_iovlen = 1;
>     372
>     373	msg.msg_control = control;
>     374	msg.msg_controllen = sizeof(control);
>     375
>     376	cmsg = CMSG_FIRSTHDR(&msg)((size_t) (&msg)->msg_controllen >= sizeof (struct cmsghdr
>     ) ? (struct cmsghdr *) (&msg)->msg_control : (struct cmsghdr *) 0);
> 
> *** 2 Null pointer value stored to 'cmsg'
> 
>     377	cmsg->cmsg_len = CMSG_LEN(sizeof(int))((((sizeof (struct cmsghdr)) + sizeof (size_t) - 1) & (size_t) ~(sizeof (size_t) - 1)) + (sizeof(int)));
> 
> *** 3 Dereference of null pointer
> 
> Presuming this code is actually exercised, it's obviously
> not dereferencing NULL, so it would be a false positive.
> I looked at a few usage examples and it seems like glibc's
> own tests do allocate more storage.  If this code is *not*
> currently being used, we should model it after the glibc test code.

Yes, this code is used for network interface hotplug & works 
correctly in our testing.

Daniel
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