Building a kernel extension for macOS using bazel

[YungRaj]

Hey all,

Is there a way to build kernel extensions for macOS using bazel?

I want to port https://github.com/YungRaj/MacRootKit to bazel so that I don't have to deal with the stress that comes with using another build system such as cmake. Any ideas?

I know that genrule()'s could probably work in building the .kext artifact but I think the major challenge is getting the Xcode frameworks and tooling to play nicely and ensuring that all the relevant compiler and linker flags (which I use here https://github.com/YungRaj/MacRootKit/blob/main/make_kext.mk) are included.

Thanks

[brentleyjones]

I haven't used it personally, but the macos_kernel_extension rule exists.

[keith]

oop thanks, I totally missed this an recommended OP file an issue

[YungRaj]

Okay, great. Thanks! I'll give a try and report back.

It looks like the first thing I noticed is that I cannot specify the target architecture for the kext that I want to build.

Currently, MacRootKit supports arm64 and x86_64. Is that supported?

And maybe, using a special rule like macos_kernel_extension() is not necessarily needed? Would it work if I port all the existing linker and compiler flags that I used via Makefile and create the BUILD target that way? Does this cause issues with Xcode's tools playing nicely?

Thanks!

[YungRaj]

Generally speaking I don't need to worry about code signing my kext, so that was why I was brainstorming a path forward without using the rule. I guess since all the code signing parameters to the macos_kernel_extension() are optional it's not a big blocker. Thanks so much for the help! I'll report back when I get something working.

[keith]

probably easier to strip the codesigning from the final binary

[YungRaj]

I have the kernel extension's code built using bazel. For some reason the cc_library() static library that I have as a dependency to macos_kernel_extension() doesn't link in the dependency that contains all the kext's code. I should be able to figure this out and once I do, I'll test the final kext artifact on baremetal and in a virtual machine.

[keith]

i don't know how kernel extensions work but maybe you need alwayslink=True on the cc_library to make sure the contents are loaded?

[YungRaj]

that worked. I still need to finish up certain rules, but I'm pretty sure the rest of the porting to bazel should work fine. thanks for all the help!