Re: Couldn't `function(arg[static 3])` imply nonnull and array size in C?

[Martin Uecker <uecker at eecs dot berkeley dot edu>]

Am Mon, 04 May 2015 18:28:49 +0200
schrieb Manuel LÃpez-IbÃÃez <lopezibanez@gmail.com>:

> On 04/05/15 07:40, Martin Uecker wrote:
> >
> > BTW: Why is 'nonnull' a function attribute and not something
> > which can be attached to pointer types?
> 
> I think this is something wanted for a long time:
> 
> https://gcc.gnu.org/ml/gcc/2006-04/msg00550.html
> 
> but nobody has implemented it yet. Perhaps there was some technical hurdle in 
> the past, probably long gone.
> 
> Clang has implemented this variation already sometime ago:
> 
> http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20140203/098497.html
> 
> so there is a precedent.

Interestingly, this leads to an incompatibility between gcc and
clang. Consider this:

void foo(__attribute__((nonnull)) int *a)
{
}

void bar(__attribute__((nonnull)) int (*a)(int*))
{
        (*a)(0);
}

void test(void)
{
        foo(0);
        bar(0);
}

clang warns when calling 'foo' and 'bar' with 0 argument.
gcc ignores nonnull on the argument of foo and warns about
calling *a.

Martin