#define offsetof(s, m)   (size_t)&(((s *)0)->m)

typedef struct mv_s  mv_t;
 
struct mv_s {
      mv_t *t;
      char *name;
      int age;
};
 
//something else
mv_t *mv, *mvt, *mvtt;
mv->t = ....;
mv->name = ...;
mv->age = ...;
 
mvtt = mv->t;
mvt = (mv_t *) ((u_char *) mvtt - offsetof(mv_t, t))
 
//now, mvt == mv
printf("%d\n", mvt->age);