Initial commit of support for moving main partition table to arbitrary

location on disk (within limits based on existing partitions).

NEWS

@@ -1,6 +1,16 @@
-1.0.2 (?/??/2016):
+1.0.2 (?/??/2017):
 ------------------
 
+- Added new option: 'j' on the experts' menu in gdisk;
+  '-j/--move-main-table={sector}' in sgdisk. This option enables relocating
+  the main partition table from sector 2 (the default location) to somewhere
+  else on the disk. The main reason I know of to do this is if the disk is
+  to be used with a system-on-chip (SoC) computer, some of which require the
+  boot loader to be located at sector 2. If you pass this option the default
+  value of 2, it has the effect of reducing the padding placed between the
+  main partition table and the first usable sector value created by the
+  Linux fdisk tool.
+
 - Updated man pages with new recommendations for ESP and BIOS Boot Partition
   sizes.
 

gdisk.8

@@ -466,6 +466,14 @@ boot.
 Show detailed partition information. This option is identical to the 'i'
 option on the main menu.
 
+.TP
+.B j
+Adjust the location of the main partition table. This value is normally 2,
+but it may need to be increased in some cases, such as when a
+system\-on\-chip (SoC) is hard\-coded to read boot code from sector 2. I
+recommend against adjusting this value unless doing so is absolutely
+necessary.
+
 .TP 
 .B l
 Change the sector alignment value. Disks with more logical sectors per

gpt.cc

@@ -276,6 +276,23 @@ int GPTData::Verify(void) {
            << "The 'e' option on the experts' menu may fix this problem.\n";
    } // if
 
+   // Check the main and backup partition tables for overlap with things
+   if (mainHeader.partitionEntriesLBA + GetTableSizeInSectors() > mainHeader.firstUsableLBA) {
+       problems++;
+       cout << "\nProblem: Main partition table extends past the first usable LBA.\n"
+            << "Using 'j' on the experts' menu may enable fixing this problem.\n";
+   } // if
+   if (mainHeader.partitionEntriesLBA < 2) {
+       problems++;
+       cout << "\nProblem: Main partition table appears impossibly early on the disk.\n"
+            << "Using 'j' on the experts' menu may enable fixing this problem.\n";
+   } // if
+   if (secondHeader.partitionEntriesLBA + GetTableSizeInSectors() > secondHeader.currentLBA) {
+       problems++;
+       cout << "\nProblem: The backup partition table overlaps the backup header.\n"
+            << "Using 'e' on the experts' menu may fix this problem.\n";
+   } // if
+
    if ((mainHeader.lastUsableLBA >= diskSize) || (mainHeader.lastUsableLBA > mainHeader.backupLBA)) {
       problems++;
       cout << "\nProblem: GPT claims the disk is larger than it is! (Claimed last usable\n"
@@ -552,8 +569,8 @@ void GPTData::RebuildMainHeader(void) {
    mainHeader.firstUsableLBA = secondHeader.firstUsableLBA;
    mainHeader.lastUsableLBA = secondHeader.lastUsableLBA;
    mainHeader.diskGUID = secondHeader.diskGUID;
-   mainHeader.partitionEntriesLBA = UINT64_C(2);
    mainHeader.numParts = secondHeader.numParts;
+   mainHeader.partitionEntriesLBA = secondHeader.firstUsableLBA - GetTableSizeInSectors();
    mainHeader.sizeOfPartitionEntries = secondHeader.sizeOfPartitionEntries;
    mainHeader.partitionEntriesCRC = secondHeader.partitionEntriesCRC;
    memcpy(mainHeader.reserved2, secondHeader.reserved2, sizeof(mainHeader.reserved2));
@@ -658,7 +675,7 @@ int GPTData::FindInsanePartitions(void) {
          } // if
          if (partitions[i].GetLastLBA() >= diskSize) {
             problems++;
-         cout << "\nProblem: partition " << i + 1 << " is too big for the disk.\n";
+            cout << "\nProblem: partition " << i + 1 << " is too big for the disk.\n";
          } // if
       } // if
    } // for
@@ -1441,6 +1458,8 @@ void GPTData::DisplayGPTData(void) {
    cout << "Logical sector size: " << blockSize << " bytes\n";
    cout << "Disk identifier (GUID): " << mainHeader.diskGUID << "\n";
    cout << "Partition table holds up to " << numParts << " entries\n";
+   cout << "Main partition table begins at sector " << mainHeader.partitionEntriesLBA
+        << " and ends at sector " << mainHeader.partitionEntriesLBA + GetTableSizeInSectors() - 1 << "\n";
    cout << "First usable sector is " << mainHeader.firstUsableLBA
         << ", last usable sector is " << mainHeader.lastUsableLBA << "\n";
    totalFree = FindFreeBlocks(&i, &temp);
@@ -1732,7 +1751,7 @@ int GPTData::SetGPTSize(uint32_t numEntries, int fillGPTSectors) {
             partitions = newParts;
          } // if/else existing partitions
          numParts = numEntries;
-         mainHeader.firstUsableLBA = ((numEntries * GPT_SIZE) / blockSize) + (((numEntries * GPT_SIZE) % blockSize) != 0) + 2 ;
+         mainHeader.firstUsableLBA = GetTableSizeInSectors() + mainHeader.partitionEntriesLBA;
          secondHeader.firstUsableLBA = mainHeader.firstUsableLBA;
          MoveSecondHeaderToEnd();
          if (diskSize > 0)
@@ -1747,6 +1766,23 @@ int GPTData::SetGPTSize(uint32_t numEntries, int fillGPTSectors) {
    return (allOK);
 } // GPTData::SetGPTSize()
 
+// Change the start sector for the main partition table.
+// Returns 1 on success, 0 on failure
+int GPTData::MoveMainTable(uint64_t pteSector) {
+    uint64_t pteSize = GetTableSizeInSectors();
+    int retval = 1;
+
+    if ((pteSector >= 2) && ((pteSector + pteSize) <= FindFirstUsedLBA())) {
+       mainHeader.partitionEntriesLBA = pteSector;
+       mainHeader.firstUsableLBA = pteSector + pteSize;
+       RebuildSecondHeader();
+    } else {
+       cerr << "Unable to set the main partition table's location to " << pteSector << "!\n";
+       retval = 0;
+    } // if/else
+    return retval;
+} // GPTData::MoveMainTable()
+
 // Blank the partition array
 void GPTData::BlankPartitions(void) {
    uint32_t i;
@@ -2121,6 +2157,20 @@ uint64_t GPTData::FindFirstAvailable(uint64_t start) {
    return (first);
 } // GPTData::FindFirstAvailable()
 
+// Returns the LBA of the start of the first partition on the disk (by
+// sector number), or 0 if there are no partitions defined.
+uint64_t GPTData::FindFirstUsedLBA(void) {
+    uint32_t i;
+    uint64_t firstFound = UINT64_MAX;
+
+    for (i = 0; i < numParts; i++) {
+        if ((partitions[i].IsUsed()) && (partitions[i].GetFirstLBA() < firstFound)) {
+            firstFound = partitions[i].GetFirstLBA();
+        } // if
+    } // for
+    return firstFound;
+} // GPTData::FindFirstUsedLBA()
+
 // Finds the first available sector in the largest block of unallocated
 // space on the disk. Returns 0 if there are no available blocks left
 uint64_t GPTData::FindFirstInLargest(void) {

gpt.h

@@ -140,6 +140,7 @@ public:
 
    // Adjust GPT structures WITHOUT user interaction...
    int SetGPTSize(uint32_t numEntries, int fillGPTSectors = 1);
+   int MoveMainTable(uint64_t pteSector);
    void BlankPartitions(void);
    int DeletePartition(uint32_t partNum);
    uint32_t CreatePartition(uint32_t partNum, uint64_t startSector, uint64_t endSector);
@@ -162,6 +163,8 @@ public:
    int GetPartRange(uint32_t* low, uint32_t* high);
    int FindFirstFreePart(void);
    uint32_t GetNumParts(void) {return mainHeader.numParts;}
+   uint64_t GetTableSizeInSectors(void) {return (((numParts * GPT_SIZE) / blockSize) +
+                                                 (((numParts * GPT_SIZE) % blockSize) != 0)); }
    uint64_t GetMainHeaderLBA(void) {return mainHeader.currentLBA;}
    uint64_t GetSecondHeaderLBA(void) {return secondHeader.currentLBA;}
    uint64_t GetMainPartsLBA(void) {return mainHeader.partitionEntriesLBA;}
@@ -176,6 +179,7 @@ public:
 
    // Find information about free space
    uint64_t FindFirstAvailable(uint64_t start = 0);
+   uint64_t FindFirstUsedLBA(void);
    uint64_t FindFirstInLargest(void);
    uint64_t FindLastAvailable();
    uint64_t FindLastInFree(uint64_t start);

gptcl.cc

@@ -64,7 +64,7 @@ int GPTDataCL::DoOptions(int argc, char* argv[]) {
    GPTData secondDevice;
    int opt, numOptions = 0, saveData = 0, neverSaveData = 0;
    int partNum = 0, newPartNum = -1, saveNonGPT = 1, retval = 0, pretend = 0;
-   uint64_t low, high, startSector, endSector, sSize;
+   uint64_t low, high, startSector, endSector, sSize, mainTableLBA;
    uint64_t temp; // temporary variable; free to use in any case
    char *device;
    string cmd, typeGUID, name;
@@ -88,6 +88,7 @@ int GPTDataCL::DoOptions(int argc, char* argv[]) {
       {"randomize-guids", 'G', POPT_ARG_NONE, NULL, 'G', "randomize disk and partition GUIDs", ""},
       {"hybrid", 'h', POPT_ARG_STRING, &hybrids, 'h', "create hybrid MBR", "partnum[:partnum...]"},
       {"info", 'i', POPT_ARG_INT, &infoPartNum, 'i', "show detailed information on partition", "partnum"},
+      {"move-main-table", 'j', POPT_ARG_INT, &mainTableLBA, 'j', "adjust the location of the main partition table", "sector"},
       {"load-backup", 'l', POPT_ARG_STRING, &backupFile, 'l', "load GPT backup from file", "file"},
       {"list-types", 'L', POPT_ARG_NONE, NULL, 'L', "list known partition types", ""},
       {"gpttombr", 'm', POPT_ARG_STRING, &mbrParts, 'm', "convert GPT to MBR", "partnum[:partnum...]"},
@@ -262,6 +263,14 @@ int GPTDataCL::DoOptions(int argc, char* argv[]) {
                case 'i':
                   ShowPartDetails(infoPartNum - 1);
                   break;
+               case 'j':
+                   if (MoveMainTable(mainTableLBA)) {
+                       JustLooking(0);
+                       saveData = 1;
+                   } else {
+                       neverSaveData = 1;
+                   } // if/else
+                   break;
                case 'l':
                   LoadBackupFile(backupFile, saveData, neverSaveData);
                   free(backupFile);

gpttext.cc

@@ -132,7 +132,7 @@ int GPTDataTextUI::XFormDisklabel(void) {
       numDone = GPTData::XFormDisklabel(partNum);
 
    return numDone;
-} // GPTData::XFormDisklabel(void)
+} // GPTDataTextUI::XFormDisklabel(void)
 
 
 /*********************************************************************
@@ -179,6 +179,24 @@ void GPTDataTextUI::ResizePartitionTable(void) {
    SetGPTSize(newSize);
 } // GPTDataTextUI::ResizePartitionTable()
 
+// Move the main partition table (to enable some SoC boot loaders to place
+// code at sector 2, for instance).
+void GPTDataTextUI::MoveMainTable(void) {
+    uint64_t newStart, pteSize = GetTableSizeInSectors();
+    uint64_t maxValue = FindFirstUsedLBA() - pteSize;
+    ostringstream prompt;
+
+    cout << "Currently, main partition table begins at sector " << mainHeader.partitionEntriesLBA
+         << " and ends at sector " << mainHeader.partitionEntriesLBA + pteSize - 1 << "\n";
+    prompt << "Enter new starting location (2 to " << maxValue << "; default is 2; 1 to abort): ";
+    newStart = GetNumber(1, maxValue, 2, prompt.str());
+    if (newStart != 1) {
+        GPTData::MoveMainTable(newStart);
+    } else {
+        cout << "Aborting change!\n";
+    } // if
+} // GPTDataTextUI::MoveMainTable()
+
 // Interactively create a partition
 void GPTDataTextUI::CreatePartition(void) {
    uint64_t firstBlock, firstInLargest, lastBlock, sector, origSector;
@@ -811,6 +829,9 @@ void GPTDataTextUI::ExpertsMenu(string filename) {
          case 'i': case 'I':
             ShowDetails();
             break;
+         case 'j': case 'J':
+             MoveMainTable();
+             break;
          case 'l': case 'L':
             prompt.seekp(0);
             prompt << "Enter the sector alignment value (1-" << MAX_ALIGNMENT << ", default = "
@@ -878,9 +899,11 @@ void GPTDataTextUI::ShowExpertCommands(void) {
    cout << "c\tchange partition GUID\n";
    cout << "d\tdisplay the sector alignment value\n";
    cout << "e\trelocate backup data structures to the end of the disk\n";
+   cout << "f\trandomize disk and partition unique GUIDs\n";
    cout << "g\tchange disk GUID\n";
    cout << "h\trecompute CHS values in protective/hybrid MBR\n";
    cout << "i\tshow detailed information on a partition\n";
+   cout << "j\tmove the main partition table\n";
    cout << "l\tset the sector alignment value\n";
    cout << "m\treturn to main menu\n";
    cout << "n\tcreate a new protective MBR\n";

gpttext.h

@@ -42,6 +42,7 @@ class GPTDataTextUI : public GPTData {
       // Request information from the user (& possibly do something with it)
       uint32_t GetPartNum(void);
       void ResizePartitionTable(void);
+      void MoveMainTable(void);
       void CreatePartition(void);
       void DeletePartition(void);
       void ChangePartType(void);

sgdisk.8

@@ -280,6 +280,14 @@ unique GUID and the translation of \fBsgdisk\fR's
 internal partition type code to a plain type name. The \fI\-i\fR option
 displays this information for a single partition.
 
+.TP
+.B \-j, \-\-adjust\-main\-table=sector
+Adjust the location of the main partition table. This value is normally 2,
+but it may need to be increased in some cases, such as when a
+system\-on\-chip (SoC) is hard\-coded to read boot code from sector 2. I
+recommend against adjusting this value unless doing so is absolutely
+necessary.
+
 .TP 
 .B \-l, \-\-load\-backup=file
 Load partition data from a backup file. This option is the reverse of the

support.cc

@@ -67,8 +67,8 @@ string ReadString(void) {
 // If user provides no input, def (default value) is returned.
 // (If def is outside of the low-high range, an explicit response
 // is required.)
-int GetNumber(int low, int high, int def, const string & prompt) {
-   int response, num;
+uint64_t GetNumber(uint64_t low, uint64_t high, uint64_t def, const string & prompt) {
+   uint64_t response, num;
    char line[255];
 
    if (low != high) { // bother only if low and high differ...
@@ -77,7 +77,7 @@ int GetNumber(int low, int high, int def, const string & prompt) {
          cin.getline(line, 255);
          if (!cin.good())
             exit(5);
-         num = sscanf(line, "%d", &response);
+         num = sscanf(line, "%ld", &response);
          if (num == 1) { // user provided a response
             if ((response < low) || (response > high))
                cout << "Value out of range\n";

support.h

@@ -72,7 +72,7 @@
 using namespace std;
 
 string ReadString(void);
-int GetNumber(int low, int high, int def, const string & prompt);
+uint64_t GetNumber(uint64_t low, uint64_t high, uint64_t def, const string & prompt);
 char GetYN(void);
 uint64_t GetSectorNum(uint64_t low, uint64_t high, uint64_t def, uint64_t sSize, const std::string& prompt);
 uint64_t IeeeToInt(string IeeeValue, uint64_t sSize, uint64_t low, uint64_t high, uint64_t def = 0);