walkcontext
(void) walkcontext(&uc, (int (*)())fmd_trace_frame, trp);
extern int walkcontext(const ucontext_t *, int (*)(uintptr_t, int, void *),
return (walkcontext(&u, display_stack_info, (void*)(intptr_t)dofd));
(void) walkcontext(&u, callback, &bt);