Re: Use of initialized variable in strtod.c

[Joel Sherrill <joel dot sherrill at oarcorp dot com>]

Sorry to keep replying to myself. More below.

On 3/15/2017 3:03 PM, Joel Sherrill wrote:
> On 3/15/2017 2:54 PM, Joel Sherrill wrote:
> > On 3/15/2017 2:31 PM, Jeffrey Walton wrote:
> > > > Does Coverity have a way in which in the code it can be marked as OK?  (I'd
> > > > expect some '#pragma CoverityIgnore(bits)' or the like ought to be
> > > > available.)
> > >
> > > Yes. You have to provide a modeling file. Also see the Coverity Scan
> > > FAQ entry "what is a model" at https://scan.coverity.com/faq.
> >
> > A model is for odd cases like where you have your
> > own memory allocators or synchronization primitives.
> >
> > I think this is a case for what they call annotations.
> > I have never written one of these but I think we would
> > have to add a comment something like this ahead of the
> > call:
> >
> > /* coverity[uninit_use_in_call] */
>
> Adding this does result in silencing Coverity on this issue.
> It doesn't change the fact that the uninitialized bits
> variable is used on the RHS of ULtod() though. :(

But this in __call_atexit.c is definitely correct. It is
treating free() as a weak symbol and the only way to
silence Coverity is to add an annotation.

136      /* Don't dynamically free the atexit array if free is not
137         available.  */
   	
CID 175323 (#1 of 1): Function address comparison (BAD_COMPARE)
func_conv: This implicit conversion to a function pointer is suspicious: free.
   	Did you intend to call free?
138      if (!free)
139        break;
 
> > I will try adding that notation but we clearly need
> > some guidelines as a project.

Agreed. There appear to be cases where annotation is the
only solution. Is adding annotation acceptable?

If a solution other than annotation exists, is that
the preferred option?

> > > Other projects use them, like Python. See, for example,
> > > https://docs.python.org/devguide/coverity.html.
> > >
> > > > I agree with trying to get rid of the message, but it is worth
> > > > bloat to do it?  (It will add instructions to either initialize bits to 0 or
> > > > add the else.)
> > >
> > > If I am parsing things correctly, it seems like the bloat is going the
> > > other way: if the code is not needed, then remove it. It will avoid
> > > findings like these, and speed up the compile.
> > >
> > > > I would rather mark something in the code as a false
> > > > positive than add code because the tool is not smart enough to know--so we
> > > > might differ in philosophy there.
> > >
> > > Perhaps a better strategy would be to initialize all variables, and
> > > then allow the optimizer to remove the unneeded writes. It will ensure
> > > a program is in a good state, and avoid findings like these.
> >
> > I'm a middle of the road guy. I add initialization in cases
> > where there are paths where it is used and doesn't otherwise
> > get set. I wouldn't automatically initialize everything.
> >
> > In this case, "bits" is actually used on the RHS multiple
> > times in ULtod() so it bothers me that it has an undefined
> > value. That means the output of ULtod() is undefined in
> > this case.
> >
> > > Another strategy is to do nothing. In this case, the same findings
> > > will waste multiple developer's time, and generate additional mailing
> > > list messages.
> >
> > Agreed.
> >
> > > I like dark and silent cockpits, so I don't want tools generating
> > > findings, and I don't want mailing list messages. I would squash it
> > > once and for all and avoid all future problems. But that's just me,
> > > and I understand the Newlib project may have a different outlook on
> > > things.
> >
> > +1
> >
> > There are still 60 others issues. We should do our best to squash
> > them permanently. IMO marking them with Coverity specific annotation
> > just means that another static analyzer may find the same issue
> > in the future. The annotation won't help.
> >
> > > Jeff
> > --joel

--
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill@OARcorp.com        On-Line Applications Research
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