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Xcode Development Tools

A small collection of scripts I have developed to make working with Xcode easier.

copy_dylibs.py

copy_dylibs.py is used to detect and copy local library dependencies into your app bundle.

A local dependency is a dynamic library that you will have built yourself or installed using a package management tool like homebrew or MacPorts. They won't exist on the end-user system and therefore your app won't run on their system if you have used them (there is also a good chance they won't run on your system either until they are copied into the app bundle and code-signed).

Any library dependency that resides outside of /System or /usr/lib is deemed a local library dependency.

The script works by examining the main executable and looking for local library dependencies and then copying them into the app bundle Frameworks folder. Any local library dependencies copied are themselves examined to see if they use any other local library dependencies, ad infinitum.

When a local library dependency is copied into the app bundle, its "install name" is adjusted in both the executable/dynamic library that references it and within the library dependency itself. The script changes the "install name" to use @rpath instead of an absolute path.

Xcode will provide all the information the script needs, via environment variables, however additional local library dependencies can be specifed on the command line. This is useful for libraries that are loaded via dlopen() and therefore cannot be detected by the script.

Notes on fat binary dependencies

copy_dylibs.py will fail on fat binary dependencies that have not had their install name fixed when they were created.

Here's an example:

An external build system was used to create two libraries for use with the iOS Simulator, one arm64 and the other x86_64. These were building into different output directories:

extlib/arm64/libfoo.dylib
extlib/x86_64/libfoo.dylib

and lipo was used to create the fat binary:

$ lipo -create -output extlib/fat/libfoo.dylib extlib/arm64/libfoo.dylib extlib/x86_64/libfoo.dylib

When you examine this library you will see that the original install names are preserved in the fat binary:

$ otool -L extlib/fat/libfoo.dylib

extlib/fat/libfoo.dylib (architecture x86_64):
	extlib/x64_64/libfoo.dylib (compatibility version 0.0.0, current version 0.0.0)
	...
	system libraries
	...
extlib/fat/libfoo.dylib (architecture arm64):
	extlib/arm64/libfoo.dylib (compatibility version 0.0.0, current version 0.0.0)
	...
	system libraries
    ...

This will confuse copy_dylibs.py and it will end-up copying in one of the thin libraries into the Xcode build directory, overwriting the fat binary because it has the same name.

The way to fix this is to use install_name_tool after lipo:

install_name_tool -id extlib/fat/libfoo.dylib extlib/fat/libfoo.dylib

Configuring

In order to configure copy_dylibs.py into your Xcode project:

  • Add this repo as a submodule in a directory of your choosing, for example External, using git submodule add https://github.com/trojanfoe/xcodedevtools External/xcodedevtools.
  • Select the project settings of the App Target and in the Build Phases tab press the + top-left above Target Dependencies and select New Run Script Phase. Rename the script to Copy Dylibs.
  • In the new Run Script section put python $PROJECT_DIR/External/xcodedevtools/copy_dylibs.py in the top textbox, depending on where you added the submodule.
  • You should move Copy Dylibs so it runs after Link Binary With Libraries and before Copy Bundle Resources to avoid warning messages like changes being made to the file will invalidate the code signature in ....

Code Signing

The script will code sign all .dylib files that it copies into the app bundle.

Previously I was relying on adding --deep to the Other Code Signing Flags, however I have noticed that has no effect when running an app on an iOS device and the embedded frameworks remain unsigned. The --deep flag does work when running on the iOS Simulator or running a native macOS app, however to cover all cases I have put code signing back into the script.

bump_buildnum.py

bump_buildnum.py is used to manage build number versioning of your app bundle.

It works by maintaining a .ver file in the source tree that is incremented whenever a source file change is detected during a build. The updated build number is then written into the Info.plist file to allow for automatic versioning. Only the build version is incremented, and the main version needs to be incremented manually, based on feature updates that only you know about.

It is configured in a similar way to copy_dylibs.py.

I don't use it any longer so don't have much more to say about it, however if you find it useful let me know and I'll put more effort into documenting it.