static int find_valid_gpt(struct rt_mmcsd_card *card, gpt_header **gpt,
              gpt_entry **ptes)
{
    int good_pgpt = 0, good_agpt = 0, good_pmbr = 0;
    gpt_header *pgpt = RT_NULL, *agpt = RT_NULL;
    gpt_entry *pptes = RT_NULL, *aptes = RT_NULL;
    legacy_mbr *legacymbr;
    size_t total_sectors = last_lba(card) + 1;
    size_t lastlba;
    int status = 0;
    if (!ptes)
    {
        return 0;
    }
    lastlba = last_lba(card);
    if (!force_gpt)
    {
        /* This will be added to the EFI Spec. per Intel after v1.02. */
        legacymbr = rt_malloc(512);
        if (!legacymbr)
        {
            goto fail;
        }
        status = read_lba(card, 0, (uint8_t *)legacymbr, 1);
        if (status)
        {
            LOG_I("status:%d", status);
            goto fail;
        }
        good_pmbr = is_pmbr_valid(legacymbr, total_sectors);
        rt_free(legacymbr);
        if (!good_pmbr)
        {
            goto fail;
        }
        rt_kprintf("Device has a %s MBR\n",
             good_pmbr == GPT_MBR_PROTECTIVE ?
                        "protective" : "hybrid");
    }
    good_pgpt = is_gpt_valid(card, GPT_PRIMARY_PARTITION_TABLE_LBA,
                 &pgpt, &pptes);
    if (good_pgpt)
    {
        good_agpt = is_gpt_valid(card, (pgpt->alternate_lba), &agpt, &aptes);
        if (!good_agpt && force_gpt)
        {
             good_agpt = is_gpt_valid(card, lastlba, &agpt, &aptes);
        }
        /* The obviously unsuccessful case */
        if (!good_pgpt && !good_agpt)
        {
            goto fail;
        }
        compare_gpts(pgpt, agpt, lastlba);
        /* The good cases */
        if (good_pgpt)
        {
            *gpt  = pgpt;
            *ptes = pptes;
            rt_free(agpt);
            rt_free(aptes);
            if (!good_agpt)
            {
                LOG_D("Alternate GPT is invalid, using primary GPT.");
            }
            return 1;
        }
        else if (good_agpt)
        {
            *gpt  = agpt;
            *ptes = aptes;
            rt_free(pgpt);
            rt_free(pptes);
            LOG_D("Primary GPT is invalid, using alternate GPT.");
                return 1;
        }
    }
 fail:
        rt_free(pgpt);
        rt_free(agpt);
        rt_free(pptes);
        rt_free(aptes);
        *gpt = RT_NULL;
        *ptes = RT_NULL;
        return 0;
}