[libvirt] [PATCH] qemu: avoid dereference of null pointer

[Alex Jia]

On 08/05/2011 03:47 AM, Eric Blake wrote:
> On 08/04/2011 11:14 AM, Alex Jia wrote:
>>> Also, how does checking for a non-zero union value prevent a null
>>> dereference?
>>>
>> To be honest, I'm not sure this, however, it's okay for ccc-analyzer if
>> I add these judgements,
>
> Is ccc-analyzer different from clang?  If so, how can I set it up, to 
> reproduce the problem you saw?
It may be different, I will tidy up a docs or resource and then sending 
to you.

Regards,
Alex
>
> I previously saw a false positive in one of these functions 
> (qemudDomainGetMemoryParameters) when using Coverity, but that was 
> fixed by commit f768b4c3, but Coverity was silent for the other 4 
> functions you touched.  I'm now trying to do a clang run to see if 
> that differs from Coverity.  The Coverity false positive was that our 
> logic confused the static analyzers:
>
> type var; // uninit
> if (flags & _CONFIG)
>   var = something
> if (flags & _LIVE)
>   do something else
> if (flags & _CONFIG)
>   use var
>
> this pattern was enough to make the analyzers think that var could be 
> used uninitialized, or initialized to NULL, in a setting where it must 
> not be NULL; but once you see that it is merely a case of the analyzer 
> getting it wrong (var is _only_ used under the same conditions where 
> it was previously assigned earlier on), the solution is to add 
> sa_assert() hints to the analyzers.
>
> NACK to this patch; we need to get to the real root of why the 
> analyzers are complaining, and fix the real bug if there is one (but I 
> didn't see one in my manual inspection), or more likely add 
> sa_assert() hints to silence the analyzer.
>