dyld-shared-cache-extractor

As of macOS Big Sur, instead of shipping the system libraries with macOS, Apple ships a generated cache of all built in dynamic libraries and excludes the originals. This tool allows you to extract these libraries from the cache for reverse engineering.

Usage

Extract the default shared cache to /tmp/libraries:

dyld-shared-cache-extractor \
   /System/Volumes/Preboot/Cryptexes/OS/System/Library/dyld/dyld_shared_cache_arm64e \
   /tmp/libraries

If this fails it could be because the shared cache format has changed, and the version you're trying to extract isn't supported by the version of Xcode you have selected globally (which you can view with xcode-select -p and xcodebuild -version). In this case you might have to download a newer version of Xcode (potentially a beta version if you're trying to extract the cache from a beta OS version) and override the Xcode version when running dyld-shared-cache-extractor:

DEVELOPER_DIR=/Applications/Xcode-beta.app \
   dyld-shared-cache-extractor \
   /System/Volumes/Preboot/Cryptexes/OS/System/Library/dyld/dyld_shared_cache_arm64e \
   /tmp/libraries

If you want to prefer the system installation of dsc_extractor.bundle instead of Xcode's version, you can pass it manually on the command line:

dyld-shared-cache-extractor \
   /System/Volumes/Preboot/Cryptexes/OS/System/Library/dyld/dyld_shared_cache_arm64e \
   /tmp/libraries \
   /usr/lib/dsc_extractor.bundle

On macOS versions before Ventura the shared cache was in a different location, you can extract on older macOS versions with:

dyld-shared-cache-extractor \
   /System/Library/dyld/dyld_shared_cache_arm64e \
   /tmp/libraries

Installation

Homebrew:

brew install keith/formulae/dyld-shared-cache-extractor

Manually:

cmake -B build
cmake --build build
cmake --install build

More details

There are a few different ways you can interact with these shared caches.

Depending on what you're doing inspecting them in Hopper is the easiest option
For a bit more functionality you can build the dyld_shared_cache_util target from the latest dyld source dump, but this requires some modifications

The problem with the 2 options above is that they can lag behind format changes in the shared cache. This tool loads the private dsc_extractor.bundle from Xcode, meaning it should always be able to extract the shared cache files even from beta OS versions (potentially using a beta Xcode version).

This logic is based on the function at the bottom of dyld3/shared-cache/dsc_extractor.cpp from the dyld source dump.

License

ink-splatters/dyld-shared-cache-extractor

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