user_backtrace
user_backtrace(frame, l, type);
user_backtrace(frame, l, type);
user_backtrace(frame, l, -1);
static void user_backtrace(struct trapframe *, struct lwp *, int);
user_backtrace(frame, l, type);
user_backtrace(frame, l, type);
user_backtrace(frame, l, type);
user_backtrace(frame, l, type);