[PATCH 2/6] Add returns_zero_on_success/failure attributes

[Peter Zijlstra]

On Mon, Nov 15, 2021 at 12:33:16PM +0530, Prathamesh Kulkarni wrote:
> On Sun, 14 Nov 2021 at 02:07, David Malcolm via Gcc-patches

> > +/* Handle "returns_zero_on_failure" and "returns_zero_on_success" attributes;
> > +   arguments as in struct attribute_spec.handler.  */
> > +
> > +static tree
> > +handle_returns_zero_on_attributes (tree *node, tree name, tree, int,
> > +                                  bool *no_add_attrs)
> > +{
> > +  if (!INTEGRAL_TYPE_P (TREE_TYPE (*node)))
> > +    {
> > +      error ("%qE attribute on a function not returning an integral type",
> > +            name);
> > +      *no_add_attrs = true;
> > +    }
> > +  return NULL_TREE;
> Hi David,
> Just curious if a warning should be emitted if the function is marked
> with the attribute but it's return value isn't actually 0 ?
> 
> There are other constants like -1 or 1 that are often used to indicate
> error, so maybe tweak the attribute to
> take the integer as an argument ?
> Sth like returns_int_on_success(cst) / returns_int_on_failure(cst) ?
> 
> Also, would it make sense to extend it for pointers too for returning
> NULL on success / failure ?

Please also consider that in Linux we use the 'last' page for error code
returns. That is, a function returning a pointer could return '(void
*)-EFAULT' also see linux/err.h