typedef struct s_st { int a; int *b; } st;
typedef union  s_ut { int a; st s; st *t; int **c; } ut;

st gst;
ut *gu;

int f (int ia[], st s1, ut *u1) st gst; ut *gu; { } 

void model (int ia[]) st gst; ut *gu; { modifies ia[6]; }

void modst (st s1) { modifies *s1.b; }

void modu (ut *u)  { modifies *u; }