Implementation Questions

[tsujp]

Would you prefer such a thread be an Issue or an email-chain instead? I figured a Discussion for others' discovery. I have a few questions popping up as I examine the source more thoroughly and I wanted to get some queries answered.

On line 23 of the current Makefile I see xcrun clang $(OSAX_PATH)/loader.m -shared -O2 -mmacosx-version-min=10.13 -arch x86_64 -o $(OSAX_PATH)/loader -framework Foundation which is compiling loader.m into a dynamic library named loader.

On line 26 of the current Makefile I see xxd -i -a $(OSAX_PATH)/loader $(OSAX_PATH)/loader_bin.c which hexdumps the contents (so effectively "it") of shared library loader into loader_bin.c which is then compiled later on the Makefile.

Is it done this way because macOS doesn't support static linking against the C runtime (when I tried I get -lcrt0.o errors) and so there's no other way to get the loader statically linked to loader_bin? That's what I gather from this where you're instead straight dumping the object code into loader_bin.c before it's compiled resulting in a statically linked library; but I wanted to ask to be sure!

[koekeishiya]

Discussions are fine for this purpose.

So the way this works is that I compile the source for the scripting-addition separately; there are 3 such binary files that are built so far.
After they are built, I use xxd to do a dump of the file into C arrays, that include the actual bytes of the files. These dump files are then built into yabai alongside the regular source. When you run yabai install-sa this binary data (for each file/array) is written out to disk at the appropriate location. This is just a way for me to avoid having to ship 4 separate binaries to the user that they then have to place correctly on their system; it's basically just a way to implement a primitive installer -- it has nothing to do with linking really. See #1287 for potential future changes.

The loader you reference is the entry point of the scripting-addition infrastructure that macOS supports. This is an old artifact that yabai only uses on High Sierra, Mojave, and Catalina. It is still included for backwards compatibility.

The mach_loader is the new version of loader that no longer relies on the scripting-addition infrastructure, but it is simply an executable that performs injection of a shared library, into Dock.app.

The payload file is the shared library containing the code that we actually want to inject into the Dock process, and this is where the extended functionality is implemented.