OS X tool for dumping and reconstructing the IOKit classes hierarchy. iokit-dumper directly generates DOT files (see here, which can then be processed with dot tool.

Keep in mind this tool is in its early release, so stuff may happen. Also, careful when playing with the code, since a wrong read in the kernel will cause a kernel panic.
Remember to always slide kernel addresses before reading from them.

You need to have dot installed. If not, do:

brew install graphviz

Then test with:

dot -v

Now you can generate DOT files with iokit-dumper!

Firstly, disable SIP if your system has it present/enabled. If you are on 10.11.1, check out my SIP bypass via a kernel-exploit here.
Otherwise, just reboot into Recovery Mode and run csrutil disable from the Terminal.
Once SIP is disabled, do:

sudo ./iokit-dumper [-o] [-a kernel/[kext_bundle_id]] [-p output_path]

Options:

• -o : Override. This is a boolean value. Include the -o argument if you want to override the output file content. If you omit the -o argument, the newly generated graph will be appended to the end of the file.
• -a : Address. String value. Can either be the kernel string or any KEXT bundle ID.
• -p : Path. String value. The output file path on disk.

So, sample usage:

sudo ./iokit-dumper -o -a com.apple.driver.AppleHDA -p /Users/$USER/Desktop/test.dot

This will write the com.apple.driver.AppleHDA KEXT hierarchy to /Users/$USER/Desktop/test.dot, overwriting the file's content. Then do:

dot -Tpdf test.dot -o test.pdf

To process the test.dot file and generate a visual graph in PDF format.

DOT graphs are a bit hard on the eye, and tend to take a lot of space horizontally. To improve visual layout, add these properties at the start of the DOT file (just after the Digraph declaration, and before the hierarchy):

nodesep=[int];  // amount of space between nodes
ranksep=[int];  // amount of space between ranks (increses vertical space)

You can just learn to use DOT and add pretty much everything you want to your graph. Future updates will support more graph customization.

iokit-dumper reconstructs the whole IOKit hierarchy of the kernel or a KEXT. This is possible via special objects stored in kernel memory, known as gMetaClasses. These objects are instances of the OSMetaClass class, which basically provides informations about another class.
These objects contain interesting informations, such as the class name, the class size, a pointer to the parent class' gMetaClass, etc..
Once we find these objects in memory, we can climb up the hierarchy and reconstruct it.

The code is iOS-friendly, not meaning it works as-it-is on iOS, but that the algorithm can be reapplied in iOS. This is possible since iokit-dumper does not rely on symbols (which could be used on OS X to hasten the process), which are not present in iOS (the prelinked-kernel is stripped).

The steps to make it work on iOS would roughly be:

• Finding a way to read from kernel memory. (On OS X we can read kernel memory directly from the kernel mach port, obtained via processor_set_tasks workaround, or via /dev/kmem. These methods are obviously unavailable in iOS)
• Obtaining the kernel slide. We cannot read from kernel addresses without first sliding the addresses. (On OS X we call kas_info as root to get the kernel slide)
• Changing the parsing part. Look for KEXTs in the __PRELINK_TEXT segment of the kernel. (iOS stores all KEXTs inside the prelinked-kernel, hence they are not floating around in the file system)