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

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?

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.