Suspicion of regression in uninitialized value detection

[David Brown]

On 06/12/2011 16:27, Robert Dewar wrote:
> On 12/6/2011 10:18 AM, David Brown wrote:
>
>> Unfortunately, there are no such tools available that compare with gcc
>> and its warnings.
>
> It's surprising this is true of C, it's certainly not true of Ada,
> where CodePeer can do a much better job than GNAT+gcc together on
> this kind of issue.
>

I can't answer of Ada - while learning Ada is on my "things to do" list, 
it has never made it to the top :-(

And there are large, expensive commercial tools that can do better (in 
some ways at least) than gcc - but nothing open source.

>> Every time I have looked at this, I have always come back to gcc as the
>> best free general-purpose tool for static analysis. I also think it has
>> the best starting point for such tools - after all, gcc does a great
>> deal of analysis on the code already, much of which would need
>> duplicating in a lint program. I don't see any fundamental reason why a
>> linter could do any better than gcc for such warnings.
>
> Well I am not sure what you mean by a linter or lint program, but
> obviously it is possible for a static analysis program to do far
> better than the compiler, since it can do inter-unit analysis
> that is out of reach of the compiler.
>

The compiler can also do inter-unit analysis - that is part of LTO.

I can't say whether gcc does a lot of inter-unit analysis and warnings 
at the moment - I haven't tried LTO much as yet.  But I have little 
doubt that this is something that gcc will be able to do more as LTO 
matures.

The other recent new feature to gcc that opens potential for better 
static analysis is plugins.

Of course, much of this depends on the directions the gcc developers 
want to go, and what they want to spend time and effort on.  When I say 
I don't see why gcc can't do static analysis as well as any lint program 
could, I mean I don't think there are any insurmountable technical 
barriers - not that I think it is the best use of gcc development resources.

It's worth noting that perhaps the most active open-source general 
purpose C static analysis project is the "Clang Static Analyzer" - part 
of the LLVM compiler suite.

>> Don't get me wrong here - I understand that making accurate
>> uninitialised warnings is a hard problem, especially while producing
>> optimal code, and that it is not likely to be a high priority for the
>> gcc developers. But I don't think I am alone in saying it is a feature
>> that gcc users appreciate, that we prefer not to see regressions in such
>> features, and that we would be very happy to see even more accurate
>> warnings.
>
> One feature in GNAT that is really valuable for addressing uninitialized
> variables is the option to set all otherwise uninitialized variables to
> a constant value that can be changed at bind time, or even at run time
> with an environment variable. Then you run with different values, and if
> you get a different behavior, you know you have an uninit variable.
>
> Of course good compiler warnings, and warnings from a tool like codepeer
> are very valuable in smoking out as many cases prior to testing as
> possible.
>>
>> mvh.,
>>
>> David
>
>