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fix backup GPT partition entries offset to respect UEFI minimum array size #128

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fix backup GPT partition entries offset to respect UEFI minimum array size #128

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8 changes: 7 additions & 1 deletion src/gpt.js
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,11 @@ const PART_ATT_UNBOOTABLE_VAL = 1n << PART_ATT_UNBOOTABLE_BIT;
const MAX_PRIORITY = 3n;
const MAX_RETRY_COUNT = 7n;

// GPT images only contain the primary table. When we create the backup in asAlternate(),
// we must reserve at least 16,384 bytes for the partition entry array per UEFI spec.
// https://uefi.org/specs/UEFI/2.10/05_GUID_Partition_Table_Format.html#gpt-overview
const MIN_PARTITION_ARRAY_SIZE = 16384;

const logger = createLogger("gpt");


Expand Down Expand Up @@ -187,7 +192,8 @@ export class GPT {
const alternate = this.#header.$clone();
alternate.currentLba = this.#header.alternateLba;
alternate.alternateLba = this.#header.currentLba;
alternate.partEntriesStartLba = this.#header.alternateLba - BigInt(this.partEntriesSectors);
const partArraySize = Math.max(this.numPartEntries * this.partEntrySize, MIN_PARTITION_ARRAY_SIZE);
alternate.partEntriesStartLba = this.#header.alternateLba - BigInt(Math.ceil(partArraySize / this.sectorSize));

const gpt = new GPT(this.sectorSize);
gpt.#header = alternate;
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