uninitialized variables [Was: svn commit: r365445 - head/sys/cam/mmc]

[Andriy Gapon]

On 09/09/2020 08:49, Andriy Gapon wrote:
> On 08/09/2020 15:48, Mark Johnston wrote:
>> I observed the same thing recently as well: the compiler catches
>> uninitialized variables only in simple cases.  In my case, any uses of
>> goto within the function seemed to silence the warning, even if they
>> appeared after the uninitialized reference.
> 
> I am running a kernel build now with this addition (for clang):
> CWARNEXTRA+=   -Wconditional-uninitialized -Wno-error-conditional-uninitialized
> 
> It produces a ton of warnings.
> Some of them are probably false positives, but some look quite reasonable.
> 
> E.g.:
> sys/cam/cam_periph.c:314:19: warning: variable 'p_drv' may be uninitialized when
> used here [-Wconditional-uninitialized]
>                 TAILQ_REMOVE(&(*p_drv)->units, periph, unit_links);
> 
> Indeed, there is a conditional 'goto failure' before a first assignment to p_drv
> and the line is after the label.  So, maybe the situation is impossible, but it
> is reasonable to warn about it.
> 
> But the number of false positives (and "possible but impossible" situations) is
> too overwhelming.

But but:
/usr/devel/git//sys/cam/mmc/mmc_da.c:1824:6: warning: variable 'part_index' may
be uninitialized when used here [-Wconditional-uninitialized]
        if (part_index != softc->part_curr) {
            ^~~~~~~~~~
/usr/devel/git//sys/cam/mmc/mmc_da.c:1800:16: note: initialize the variable
'part_index' to silence this warning
        int part_index;
                      ^
                       = 0
1 warning generated.

There are useful true positives as well.

-- 
Andriy Gapon