mkgpt: create GPT disk images from partition images

A simple tool for creating disk images with a GPT header and including the contents of provided partition images.

How to build

Just say make followed by sudo make install and you'll most likely be happy. If you want a compact, statically-linked executable instead, install the musl toolchain of your choice (even the musl-gcc wrapper works) and say make static (or CC=whatever make static) followed by sudo make install instead.

How to use

Program options

• -o <output_file> specify output filename
• --sector-size <size> size of a sector (defaults to 512)
• --minimum-image-size <size> minimum size of the image in sectors (defaults to 2048)
• --disk-guid <guid> GUID of the entire disk (see GUID format below, defaults to random)
• --part <file> <options> begin a partition entry containing the specified image as its data and options as below

Partition options

• --name <name> set the name of the entry in the GPT
• --type <type> set the type of the entry, either a GUID, numeric MBR-style partition ID, or one of the known partition types
• --uuid <guid> specify the UUID of the partition in the GPT (defaults to a random UUID)

Known partition types

• EFI system partition: system
• BIOS boot partition: bios
• FAT types: fat12, fat16, fat16b, fat32, fat16x, fat32x, fat16+, fat32+
• NTFS types: ntfs
• Linux types: linux, swap

GUID format

GUIDs/UUIDs should be in the canonical representation as per https://en.wikipedia.org/wiki/Universally_unique_identifier#Format without any surrounding braces. An example is: 123E4567-E89B-12D3-A456-426655440000 Optionally, the string random can be used to generate a random GUID.

Why fork?

• the original build process seemed bloated for a tool this simple
• no way to create swap partitions (borked GUID parsing)
• some overly specific code (Linux, Windoze) without a strong need for it
• some strange code (static info in oversized, dynamically populated array?)
• some rather broken code (required calls in asserts, misaligned pointers, memory leaks)

References

Not enough people seem to know about these things, so here you go:

• https://www.drdobbs.com/the-new-c-x-macros/184401387
• https://www.embedded.com/reduce-c-language-coding-errors-with-x-macros-part-1/
• https://www.embedded.com/reduce-c-language-coding-errors-with-x-macros-part-2/
• https://www.embedded.com/reduce-c-language-coding-errors-with-x-macros-part-3/
• http://www.catb.org/esr/structure-packing/
• https://nullprogram.com/blog/2016/11/22/

Here's some background on the whole GPT mess:

• https://en.wikipedia.org/wiki/GUID_Partition_Table
• https://en.wikipedia.org/wiki/BIOS_boot_partition (I misunderstood this at first, read if you come from MBR)
• Apple's Secrets of the GPT has some useful background (once you ignore the Apple-rific stuff)
• https://thestarman.pcministry.com/asm/mbr/GPT.htm (points out disagreements between Windoze protective MBRs and the UEFI specification)

Want to scare yourself?

• https://uefi.org/sites/default/files/resources/UEFI_Spec_2_8_final.pdf (enjoy 2,500 pages of dread)

Similar tool with JSON input?

• https://gitlab.com/bztsrc/bootboot/tree/master/mkbootimg