int mkjmp(jmp_buf env, void(*func)(void *), void *arg, void *sp, size_t size)
Creates and stores a calling environment with a user-provided stack suitable for use by longjmp().
int sigmkjmp(sigjmp_buf env, int savemask, void(*func)(void *), void *arg, void *sp, size_t size)
Creates and stores a calling environment with a user-provided stack suitable for use by siglongjmp().