stack_frame_user
struct stack_frame_user sf;
OFFSET(__SFUSER_BACKCHAIN, stack_frame_user, back_chain);
DEFINE(STACK_FRAME_USER_OVERHEAD, sizeof(struct stack_frame_user));
struct stack_frame_user __user *sf;
struct stack_frame_user frame;
copy_stack_frame(const struct stack_frame_user __user *fp,
struct stack_frame_user *frame)