HPPA_FRAME_SIZE
tf->tf_sp = stack += HPPA_FRAME_SIZE;
sp += HPPA_FRAME_SIZE;
*(register_t*)(sp - HPPA_FRAME_SIZE) = 0;
*(register_t*)(sp) = (sp - HPPA_FRAME_SIZE);
sp += HPPA_FRAME_SIZE + 16*4; /* frame + callee-saved registers */
ldo HPPA_FRAME_SIZE(sp), sp !\
ldo -HPPA_FRAME_SIZE(sp), sp !\