GPT fdisk (aka gdisk) and FixParts

by Roderick W. Smith, rodsmith@rodsbooks.com

******************************** IMPORTANT ********************************
Most versions of Windows cannot boot from a GPT disk on BIOS-based
computers, and most varieties prior to Vista cannot read GPT disks. GPT
fdisk is a partition editor for GPT disks, and it will *AUTOMATICALLY
CONVERT* MBR disks to GPT form. Therefore, you should **NOT** use GPT fdisk
on a Windows system unless you fully understand what you're doing! If you
accidentally use GPT fdisk on your boot disk, or perhaps even on a data
disk, you may find recovery to be very difficult! This caveat does not
apply to FixParts, though; that tool works only on MBR disks.
***************************************************************************

Read the main README file for general information on the program, and read
the gdisk.html or fixparts.html documents (the Linux man pages converted to
HTML format) for detailed use information. My GPT fdisk Web page,
http://www.rodsbooks.com/gdisk/, provides a more tutorial introduction to
the software. I originally wrote GPT fdisk on Linux, and some Linux- and
Unix-centric language remains in the documentation.

Windows Use Notes
-----------------

The Windows version of GPT fdisk was added with version 0.6.2 of the
package. The Windows binary package includes the gdisk.exe interactive
text-mode program file but no equivalent to the sgdisk program that's
available with Linux, FreeBSD, and OS X builds. In theory, an sgdisk.exe
for Windows could be built if the popt library were installed. I've not
attempted to do this myself, though. If you care to try, check
http://gnuwin32.sourceforge.net/packages/popt.htm for information on popt
for Windows.

The FixParts program (fixparts.txt) is new with GPT fdisk 0.7.0. As
described in the main README file, this program fixes certain partition
table problems that can be created by buggy partitioning software. Windows
seems to be unfazed by most such problems, but I've not done an extensive
survey of Windows partitioning tools on this score.

To install the programs, copy the gdisk.exe and fixparts.exe program files
to any directory on your path, such as C:\Windows. Alternatively, you can
change to the program's directory or type its complete path whenever you
use it.

To use the programs, first launch a Command Prompt as the Administrator. To
do this, locate the Command Prompt program icon, right-click it, and select
"Run as Administrator." If you use a non-Administrator Command Prompt, you
won't be able to edit hard disk partition tables, although you will be able
to edit raw disk image files.

The program requires a hard disk identifier as an option. You can specify
this in either of two forms. The first way is as a number followed by a
colon, as in:

gdisk 0:

Disks are numbered starting from 0, so the preceding command launches gdisk
on the first disk. The second way to specify a disk device is via a
harder-to-remember name:

gdisk \\.\physicaldrive0

This command is equivalent to the earlier one -- it edits the partition
table on the first physical disk. Change the number at the end of the
device name to change the disk edited.

If you pass the "-l" option to gdisk.exe in addition to the disk
identifier, the program displays the current partition table information
and then exits. This use entails no risk to MBR disks, since the program
never writes data back to the disk when used in this way.

As noted above, editing the first disk with GPT fdisk is usually a Bad
Idea. An exception would be if your system uses an Extensible Firmware
Interface (EFI) and already boots from a GPT disk. It's safer to edit
non-boot disks, which usually have numbers of 1 and above, but only if you
run a version of Windows with GPT support. For more information on Windows'
support of GPT, see Microsoft's Web page on the topic:

http://www.microsoft.com/whdc/device/storage/GPT_FAQ.mspx

The GUIDs generated by gdisk to uniquely identify disks and partitions
aren't "proper" GUIDs; they're purely random numbers. In practice, this has
caused me no problems; however, it's conceivable that some disk utility
will complain. The Unix versions of GPT fdisk generate proper GUIDs, as of
version 0.6.3. Note that this limitation applies ONLY to the unique GUIDs
for disks and partitions, not to the GUIDs used to identify partition type
codes; those are standardized and are handled correctly by all versions of
GPT fdisk.

The Windows binaries I've compiled do not support Unicode UTF-16LE GPT
partition names. This feature was added to version 0.7.1 of the software
for Linux, FreeBSD, and OS X, and with changes to some #ifndef lines in the
source files, it can be compiled for Windows; however, it seems to do
little good in Windows because of Command Prompt window and/or ICU library
limitations. Thus, I've omitted this support in the interests of
simplifying the binary distribution, since including it would mean
distributing the ICU libraries.

Source Code and Compilation Issues
----------------------------------

I have successfully compiled GPT fdisk using three different Windows
compilers:

- MinGW (http://www.mingw.org), and in particular its Linux-hosted
  cross-compiler -- Under Fedora Linux, the Makefile.mingw file enables
  compilation of the software via MinGW. (Type "make -f Makefile.mingw" to
  compile the software.) If you try to compile using another compiler or
  even using MinGW under Windows or another Linux variety, you may need to
  adjust the Makefile.mingw options.

- Microsoft Visual C++ 2008 Express
  (http://www.microsoft.com/express/Windows/) -- This compiler requires a
  third-party stdint.h file (I used the one from
  http://msinttypes.googlecode.com/svn/trunk/stdint.h), but it otherwise
  works fine. A project is easily created by adding all the *.h files and
  all the *.cc files except diskio-unix.cc, sgdisk.cc, and whichever
  program file you intend to NOT build (gdisk.cc or fixparts.cc).

- Microsoft Visual C++ 2010 Express -- This compiler works much like the
  2008 version, although I didn't need to add a third-party stdint.h file.

The MinGW compiler produces much larger executables than do the MS
compilers. The resulting binaries seem to work equally well, but my testing
has been minimal.

I've also attempted to compile the code with OpenWatcom 1.8, but this
attempt failed, mostly because the compiler can't yet handle iostream
output on standard C++ strings. OpenWatcom also seems to have incorrectly
set the value of UINT32_MAX as if uint32_t values were 64-bit integers.
This alone won't cause the compile to fail, but it would create bugs.

If you modify GPT fdisk to get it to compile under another compiler, I
welcome submission of patches.