Am Mittwoch, dem 06.12.2023 um 15:21 +0100 schrieb Jakub Jelinek:
> On Wed, Dec 06, 2023 at 02:34:10PM +0100, Martin Uecker wrote:
> > > Further I think
> > > "size less than or equal to the size requested"
> > > is quite ambiguous in the calloc case, isn't the size requested in the
> > > calloc case actually nmemb * size rather than just size?
> >
> > This is unclear but it can be understood this way.
> > This was also Joseph's point.
> >
> > I am happy to submit a patch that changes the code so
> > that the swapped arguments to calloc do not cause a warning
> > anymore.
>
> That would be my preference because then the allocation size is
> correct and it is purely a style warning.
> It doesn't follow how the warning is described:
> "Warn about calls to allocation functions decorated with attribute
> @code{alloc_size} that specify insufficient size for the target type of
> the pointer the result is assigned to"
> when the size is certainly sufficient.
The C standard defines the semantics of to allocate space
of 'nmemb' objects of size 'size', so I would say
the warning and its description are correct because
if you call calloc with '1' as size argument but
the object size is larger then you specify an
insufficient size for the object given the semantical
description of calloc in the standard.
If this does not affect alignment, then this should
not matter, but it is still not really correct.
>
> But wonder what others think about it.
>
> BTW, shouldn't the warning be for C++ as well? Sure, I know,
> people use operator new more often, but still, the <cstdlib>
> allocators are used in there as well.
We should, but it I am not familiar with the C++ FE.
>
> We have the -Wmemset-transposed-args warning, couldn't we
> have a similar one for calloc, and perhaps do it solely in
> the case where one uses sizeof of the type used in the cast
> pointer?
> So warn for
> (struct S *) calloc (sizeof (struct S), 1)
> or
> (struct S *) calloc (sizeof (struct S), n)
> but not for
> (struct S *) calloc (4, 15)
> or
> (struct S *) calloc (sizeof (struct T), 1)
> or similar? Of course check for compatible types of TYPE_MAIN_VARIANTs.
>
> Jakub
Yes, although in contrast to -Wmeset-transposed-args
this would be considered a "style" option which then
nobody would activate. And if we put it into -Wextra
then we have the same situation as today.
Martin
