Check the Backup GPT table if the Primary GPT table is invalid. Renamed "Secondary GPT" to "Backup GPT" as per: UEFI Specification (Version 2.3.1, Errata A)

Signed-off-by: Steve Rae srae@broadcom.com ---

Changes in v3: - renamed: "Secondary GPT" to "Backup GPT"

Changes in v2: - changed wording: "Alternate" to "Secondary"

disk/part_efi.c | 22 +++++++++++++++++++--- doc/README.gpt | 14 +++++++------- 2 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/disk/part_efi.c b/disk/part_efi.c index 216a292..c74b7b9 100644 --- a/disk/part_efi.c +++ b/disk/part_efi.c @@ -93,7 +93,15 @@ void print_part_efi(block_dev_desc_t * dev_desc) if (is_gpt_valid(dev_desc, GPT_PRIMARY_PARTITION_TABLE_LBA, gpt_head, &gpt_pte) != 1) { printf("%s: *** ERROR: Invalid GPT ***\n", __func__); - return; + if (is_gpt_valid(dev_desc, (dev_desc->lba - 1), + gpt_head, &gpt_pte) != 1) { + printf("%s: *** ERROR: Invalid Backup GPT ***\n", + __func__); + return; + } else { + printf("%s: *** Using Backup GPT ***\n", + __func__); + } }

debug("%s: gpt-entry at %p\n", __func__, gpt_pte); @@ -142,7 +150,15 @@ int get_partition_info_efi(block_dev_desc_t * dev_desc, int part, if (is_gpt_valid(dev_desc, GPT_PRIMARY_PARTITION_TABLE_LBA, gpt_head, &gpt_pte) != 1) { printf("%s: *** ERROR: Invalid GPT ***\n", __func__); - return -1; + if (is_gpt_valid(dev_desc, (dev_desc->lba - 1), + gpt_head, &gpt_pte) != 1) { + printf("%s: *** ERROR: Invalid Backup GPT ***\n", + __func__); + return -1; + } else { + printf("%s: *** Using Backup GPT ***\n", + __func__); + } }

if (part > le32_to_cpu(gpt_head->num_partition_entries) || @@ -252,7 +268,7 @@ int write_gpt_table(block_dev_desc_t *dev_desc, != pte_blk_cnt) goto err;

- /* recalculate the values for the Second GPT Header */ + /* recalculate the values for the Backup GPT Header */ val = le64_to_cpu(gpt_h->my_lba); gpt_h->my_lba = gpt_h->alternate_lba; gpt_h->alternate_lba = cpu_to_le64(val); diff --git a/doc/README.gpt b/doc/README.gpt index f822894..ec0156d 100644 --- a/doc/README.gpt +++ b/doc/README.gpt @@ -66,14 +66,14 @@ GPT brief explanation: |Partition n | | | ---------------------------------------------------------- - LBA -34 |Entry 1|Entry 2| Entry 3| Entry 4| Secondary - -------------------------------------------------- (bkp) - LBA -33 |Entries 5 - 128 | GPT + LBA -34 |Entry 1|Entry 2| Entry 3| Entry 4| Backup + -------------------------------------------------- GPT + LBA -33 |Entries 5 - 128 | | | | | LBA -2 | | -------------------------------------------------- - LBA -1 |Secondary GPT Header | + LBA -1 |Backup GPT Header | ----------------------------------------------------------

For a legacy reasons, GPT's LBA 0 sector has a MBR structure. It is called @@ -86,7 +86,7 @@ It is possible to define 128 linearly placed partition entries. "LBA -1" means the last addressable block (in the mmc subsystem: "dev_desc->lba - 1")

-Primary/Secondary GPT header: +Primary/Backup GPT header: ---------------------------- Offset Size Description

@@ -115,7 +115,7 @@ IMPORTANT:

GPT headers and partition entries are protected by CRC32 (the POSIX CRC32).

-Primary GPT header and Secondary GPT header have swapped values of "Current LBA" +Primary GPT header and Backup GPT header have swapped values of "Current LBA" and "Backup LBA" and therefore different CRC32 check-sum.

CRC32 for GPT headers (field "CRC of header") are calculated up till @@ -125,7 +125,7 @@ CRC32 for partition entries (field "CRC32 of partition array") is calculated for the whole array entry ( Number_of_partition_entries * sizeof(partition_entry_size (usually 128)))

-Observe, how Secondary GPT is placed in the memory. It is NOT a mirror reflect +Observe, how Backup GPT is placed in the memory. It is NOT a mirror reflect of the Primary.

Partition Entry Format: