_REG_SP
gr[_REG_SP] = (__greg_t)sp;
sp = (unsigned int *)gr[_REG_SP];
gr[_REG_SP] = (__greg_t)sfp;
gr[_REG_SP] = r->r_sp;
r->r_sp = gr[_REG_SP];
gr[_REG_SP] = tf->tf_usr_sp;
tf->tf_usr_sp = gr[_REG_SP];