GDT_CACHE_SG_LST
GDT_CACHE_SG_LST + i * GDT_SG_SZ +
sc->sc_cmd + GDT_CMD_UNION + GDT_CACHE_SG_LST +
roundup(GDT_CMD_UNION + GDT_CACHE_SG_LST + sg_canz * GDT_SG_SZ,