Awesome

dynadump

Yet another Objective-C class-dump CLI tool

Why?

For fun. I got burnt out on the complexity of dsdump trying to grab all of Apple's dyld/objc4 opensource code and compiling it. This attempts to class-dump ObjC code via mostly public or unlikely to change private APIs

Features

  dynadump (built: May 30 2024, 00:59:46) - yet another class-dump done via dlopen & exception catching

	Parameters:
	list                list all the dylibs in the dyld shared cache (dsc)
	list  $DYLIB        list all the objc classes in a dylib $DYLIB
	dump  $DYLIB        dump all the ObjC classes found in a dylib on disk
	dump  $DYLIB $CLASS dump a specific ObjC class found in dylib $DYLIB
	sig   $SIGSTR       prints the demangled objc signature
	sign  $DYLIB        attempts to sign a dylib in place
	list  $DYLIB $CLASS Same cmd as above (convenience for listing then dumping)

	Environment Variables:
	NOCOLOR - Forces no color, color will be on by default unless piped
	COLOR   - Forces color, regardless of stdout destination
	VERBOSE - Verbose output
	NOEXC   - Don't use an exception handler (on in x86_64)
	DEBUG   - Used internally to hunt down f ups

The following example looks for any images in the dsc with Shaz, which can display a numerical number to print for listing or dumping. You can dump every ObjC class in the module or just a specific class. Use the VERBOSE flag to provide more detail, like load addresses or offsets. <img width="1402" alt="screenshot" src="https://github.com/DerekSelander/dynadump/assets/1037191/7d18a258-fb6f-4044-bc67-cafbad641d55">

If the color hurts the eyes, a NOCOLOR environment variable can calm it down.

Neat/bad design choices

Since this loads an image through dlopen, one has to be careful to prevent the image constructors from doing something bad, like crashing the program (I am looking at you, /S*/L*/PrivateFrameworks/SpringBoard.framework). To get around this, exception handlers are created on all callouts to load addresses. So when an image loads, an exception (a breakpoint) is hit and the exception handler steps over the code. This will prevent all constructors from executing for good or for bad. If you see something not working try using the NOEXC=1 to prevent exception handlers from being setup

The other shitty consequence of this design is that dlopen really is limited to dylibs and not standalone executables. In addition, a platform could be for iOS while being opened for Mac Catalyst. To deal with this, after dlopen fails for the first time, dynadump will copy the image of interest and patch the needed commands needed to be able to dlopen. This gets more fun when dealing with things like LC_RPATH.

Caveats

Due to the different platforms and the architectures that can be run, you will need to use arch -arm64 or arch -arm64e depending on the desired images to inspect. Apple will use arm64e on their stuff, while 3rd party code will be in arm64 (at the time of writing). You also need to be aware of any images that are Mac Catalyst builds as they're viewed as a different platform and will import different libraries when loaded. As a result, there's a Xcode scheme to build a Catalyst versino of dynadump

Here's an example of looking at Amazon Prime which appears to be ported from the iPad version.