Is the strict aliasing rule incorrectly specified?

Question

As previously established, a union of the form

union some_union {
    type_a member_a;
    type_b member_b;
    ...
};

with n memb

Answer 1

The C11 standard (§6.5.2.3.9 EXAMPLE 3) has following example:

The following is not a valid fragment (because the union type is not visible within function f):

 struct t1 { int m; };
 struct t2 { int m; };
 int f(struct t1 *p1, struct t2 *p2)
 {
       if (p1->m < 0)
               p2->m = -p2->m;
       return p1->m;
 }
 int g()
 {
       union {
               struct t1 s1;
               struct t2 s2;
       } u;
       /* ... */
       return f(&u.s1, &u.s2);
 }

But I can't find more clarification on this.