Am Montag, dem 28.07.2025 um 16:01 -0700 schrieb Bill Wendling:
> On Mon, Jul 28, 2025 at 2:39 PM Martin Uecker <ma.uec...@gmail.com> wrote:
> > Yes, forwards declarations are this simplest solution.
> >
> Forward declarations work until you get something complex. For
> example, if we want to support substructure fields in the attribute,
> you'd have to replicate the whole substructure's declaration in the
> forward decl. That becomes unwieldy when the substructure is very big:
>
> struct foo {
> char *buf __counted_by_expr(struct bar { ... } sub; sub.a.b);
> struct bar {
> int x, y;
> struct baz {
> int b;
> /* 20 other elements */
> } a;
> unsigned b1 : 1;
> unsigned b2 : 4;
> unsigned : 8;
> unsigned b3 : 2;
> /* and on and on... */
> } sub;
> };
You could write it like this:
struct bar {
int x, y;
struct baz {
int b;
/* 20 other elements */
} a;
unsigned b1 : 1;
unsigned b2 : 4;
unsigned : 8;
unsigned b3 : 2;
/* and on and on... */
};
struct foo {
char *buf __counted_by_expr(struct bar sub; sub.a.b);
struct bar sub;
};
Martin
>
> However, with delayed parsing, we wouldn't have to worry about forward
> declaring all of 'struct bar'
>
> -bw
>
> > Another idea I mentioned before is to let __self.N have type
> > int, and then emit an error later if it has a type that
> > would change the type / meaning of the immediate
> > parent expression.
> >
> > This would allow all of the following:
> >
> > struct foo {
> > char * __counted_by_expr(__self.N) buf;
> > int N;
> > };
> > struct foo {
> > char * __counted_by_expr(__self.N + 1L) buf;
> > long N;
> > };
> > struct foo {
> > char * __counted_by_expr(__self.N * 2) buf;
> > int N;
> > };
> > struct foo {
> > char * __counted_by_expr(__self.N + 2) buf;
> > char N;
> > };
> > struct foo {
> > char * __counted_by_expr(__self.N + .M) buf;
> > int N; int M;
> > };
> > struct foo {
> > char * __counted_by_expr((int)__self.N) buf;
> > double N;
> > };
> > struct foo {
> > char * __counted_by_expr(3 * sizeof(__self.buf2)) buf;
> > char buf2[5];
> > };
> > struct foo {
> > char * __counted_by_expr(((struct bar *)__self.x)->z) buf;
> > struct bar *x;
> > };
> >
> >
> > It would *not* allow:
> >
> > struct foo {
> > char * __counted_by_expr(__self.N + 1) buf;
> > long N;
> > };
> > struct foo {
> > char * __counted_by_expr(__self.x->z) buf;
> > struct foo *x;
> > };
> >
> >
> > But in this case you would get an explicit error:
> >
> > xyz:13.4: Type of `__self.N' needs to be known. Did you forget to
> > add a cast `(long)__self.N'?
> >
> >
> >
> > Martin
> >
> >
> >
> >
> >
> >
