Processors and Environments

Hi all, trust all is well!

I want to ask you're help with something. Have been googling around for a related set of problems, but can't seem to find a solution for the problem. I don't know if this is the correct place to post this, if not, kindly provide me a location where I can.

I'm in the process of developing a small OS. While doing the programming tasks have been progressing quite nicely, I'm having a problem with doing the cross-platform stuff inside Bazel.

The idea I have is, that the OS can be compiled for a specific device, say, the Pixel phone. The device has a very specific set of features, such as an ARM processor, it's 64-bit, and the CPU also has bi-endian.

No the problem comes in when specifying the toolchains. I understand that I can specify constraints for all things (CPU Architecture, CPU Sub-Architecture, Bit Size, Endianess). It's just the explosion of variations that comes with it. For the CPU architecture, you have possibly x86 and ARM, and then for the sub-architectures you have on the x86 side Sandy Bridge, Knights Landing, etc.

Bit sizes and endianess aside, there's also different "environments", like the firmware (UEFI, BIOS, etc.), kernel-mode code, driver code, user-mode code, etc.

So basically, is there a way to use the `platforms` workspace for this, can it be cleanly mapped? I know I will have to define a few constraints for the extra features.

Also, how would I manage the various combinations of these items, like UEFI on x86 Sandy Bridge, and U-Boot on ARM Corext-A53 for example? I've been looking at possible ways of doing inheritance inside Starlark for the C++ toolchain rules, but can't seem to find a nice solution, always ending up with a lot of duplication.