> [...] they usually run their experiments on top of an operating system that was never built for the job. They open up macOS or Linux, patch the kernel by hand, and hope the modifications hold. The approach is unstable, hard to reproduce, and on Apple’s platforms, slated for deprecation.
I'd also like to hear more about why that's a problem, not because I disagree, but because I don't know jack about this and it's fascinating. However, I could imagine at least a couple of advantages to this approach.
* It's not a general purpose OS. It doesn't have to support 10,000,000 different accessories, just enough to get the kernel booted so researchers can interact with the hardware.
* You don't have to deal with general purpose constraints here. Who needs something like a fair scheduler when the goal is to give researchers direct access to the hardware for minutes at a time?
* If broad hardware support and universal use case support aren't goals, you can write something vastly simpler that basically loads a program and turns it loose on the underlying bare metal. I imagine that'd make repeatability vastly easier, with no "oops, an Ethernet packet came in so I need to service that mid-test" interrupt{,ion}s.
Those would seem like good reasons to make a minimal kernel that doesn't get between the researchers and their work.
it's hard for me to justify the tremendous effort of implementing the OS from scratch, instead of adding the functionality that you need to for example linux or xv6.
> (it) exposes primitives that let a single experiment switch privilege levels at runtime while executing the same instructions in the same address space.
why not just create a linux kernel driver that exposes svc/eret functionality via MMIO?