From d600f36bc453c7547822e675ad62b7af6325f149 Mon Sep 17 00:00:00 2001
From: Floris Bos <bos@je-eigen-domein.nl>
Date: Sun, 20 Nov 2022 14:46:58 +0100
Subject: [PATCH] Advanced settings FAT modification: add GPT partition support

---
 src/devicewrapper.cpp      | 17 +++++++++++++++++
 src/devicewrapperstructs.h | 34 ++++++++++++++++++++++++++++++++--
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/src/devicewrapper.cpp b/src/devicewrapper.cpp
index 988b6b9..9a39454 100644
--- a/src/devicewrapper.cpp
+++ b/src/devicewrapper.cpp
@@ -161,6 +161,23 @@ DeviceWrapperFatPartition *DeviceWrapper::fatPartition(int nr)
     if (nr > 4 || nr < 1)
         throw std::runtime_error("Only basic partitions 1-4 supported");
 
+    /* GPT table handling */
+    struct gpt_header gpt;
+    struct gpt_partition gptpart;
+    pread((char *) &gpt, sizeof(gpt), 512);
+
+    if (!strcmp("EFI PART", gpt.Signature) && gpt.MyLBA == 1)
+    {
+        qDebug() << "Using GPT partition table";
+        if (nr > gpt.NumberOfPartitionEntries)
+            throw std::runtime_error("Partition does not exist");
+
+        pread((char *) &gptpart, sizeof(gptpart), gpt.PartitionEntryLBA*512 + gpt.SizeOfPartitionEntry*(nr-1));
+
+        return new DeviceWrapperFatPartition(this, gptpart.StartingLBA*512, (gptpart.EndingLBA-gptpart.StartingLBA+1)*512, this);
+    }
+
+    /* MBR table handling */
     struct mbr_table mbr;
     pread((char *) &mbr, sizeof(mbr), 0);
 
diff --git a/src/devicewrapperstructs.h b/src/devicewrapperstructs.h
index 4a8cb76..6f57b73 100644
--- a/src/devicewrapperstructs.h
+++ b/src/devicewrapperstructs.h
@@ -17,8 +17,8 @@ struct mbr_partition_entry {
     char begin_hsc[3];
     unsigned char id;
     char end_hsc[3];
-    unsigned int starting_sector;
-    unsigned int nr_of_sectors;
+    uint32_t starting_sector;
+    uint32_t nr_of_sectors;
 };
 
 struct mbr_table {
@@ -29,6 +29,36 @@ struct mbr_table {
     unsigned char signature[2];
 };
 
+/* GUID on-disk structures
+ * https://www.intel.com/content/dam/www/public/us/en/zip/efi-110.zip (p. 369)
+ */
+
+struct gpt_header {
+    char     Signature[8];
+    uint32_t Revision;
+    uint32_t HeaderSize;
+    uint32_t HeaderCRC32;
+    uint32_t Reserved;
+    uint64_t MyLBA;
+    uint64_t AlternateLBA;
+    uint64_t FirstUsableLBA;
+    uint64_t LastUsableLBA;
+    unsigned char DiskGUID[16];
+    uint64_t PartitionEntryLBA;
+    uint32_t NumberOfPartitionEntries;
+    uint32_t SizeOfPartitionEntry;
+    uint32_t PartitionEntryArrayCRC32;
+    char     Reserved2[420]; /* Assuming 512 byte sectors */
+};
+
+struct gpt_partition {
+    unsigned char PartitionTypeGuid[16];
+    unsigned char UniquePartitionGuid[16];
+    uint64_t StartingLBA;
+    uint64_t EndingLBA;
+    uint64_t Attributes;
+    char     PartitionName[72];
+};
 
 /* File Allocation Table
  * https://academy.cba.mit.edu/classes/networking_communications/SD/FAT.pdf