m1n1 VS pdp7-unix

One of the coolest things (IMO) about the entire Asahi effort, and why I'm not at all surprised that they surpassed Apple, was the dedicated effort to build bespoke developer-friendly Python tooling early in the reverse engineering process.

https://asahilinux.org/2021/08/progress-report-august-2021/

> Since the hypervisor is built on m1n1, it works together with Python code running on a separate host machine. Effectively, the Python host can “puppeteer” the M1 and its guest OS remotely. The hypervisor itself is partially written in Python! This allows us to have a very fast test cycle, and we can even update parts of the hypervisor itself live during guest execution, without a reboot.

> We then started building a Python implementation of this RPC protocol and marshaling system. This implementation serves a triple purpose: it allows us to parse the DCP logs from the hypervisor to understand what macOS does, it allows us to build a prototype DCP driver entirely in Python, and it will in the future be used to automatically generate marshaling code for the Linux kernel DCP driver.

Code here: https://github.com/AsahiLinux/m1n1/blob/main/proxyclient/m1n...

If you watch any of Asahi Lina's streams from the time before they had working drivers, she's able to weave together complex bitflag-manipulating pipelines at the speed of thought with self-documenting code, all in Python running on the host machine, all while joking with viewers via her adorable avatar. I've never seen anything like it before. The whole workflow is a tremendous and unprecedented accomplishment by the entire Asahi team.

I wrote a m1n1 experiment to test IRQ delivery in EL1 and noticed something was weird. I already knew about that IRQ control register (3 masks IRQs entirely and is the default, that whole thing took like a day or two back when I first added M1 Pro/Max support), so I tried other values and 2 fixed it.

They have not dropped hardly any official documentation on iBoot. The best safe documentation is in: https://github.com/AsahiLinux/m1n1/ There's a lot of tainted docs out there because the source to iBoot was illegally leaked a while back, but marcan is known for being a bit of a hardass when it comes to legal reverse engineering (thankfully).

No its uefi boot manager “https://github.com/AsahiLinux/m1n1 “

What makes you say there isn't community participation? The repo for m1n1, at least, has 42 contributors according to Github[1]. There's plenty more reporting bugs and such, and their IRC channel seems relatively active.

1: https://github.com/AsahiLinux/m1n1

I can confirm that’s pretty much exactly what happens. I did some digging with the help of m1n1 a while back, and essentially yeah, this is almost exactly what it does. The only difference is that, rather than tracking which cores are running emulated code, the scheduler keeps track of which processes are running in emulation mode, and prior to returning to userland after a context switch, the kernel sets control register bits for features like TSO (which is what I was interested in looking into at the time; I believe that specifically is controlled somewhere in the actlr_el1 register). Although only the P-cores actually implement the necessary x86 emulation behavior, the scheduler of course wants to ensure that a process is not pinned to any one core, and that native and emulated processes alike can preempt and interleave with each other on the P-cores just as they would if there were no emulation.

That shim/stub is m1n1. It is the bootloader for Asahi Linux, but also makes it possible to talk to the hardware over USB as just described by Lina. marcan even implemented a small hypervisor in m1n1, so it can be used to run MacOS and trace how MacOS is accessing the hardware.

Windows 11 ARM dualboot will come to M1 macs in the near future. See m1n1 for progress.

TIL there is a version of UNIX for PDP-7, and PDP-7 did not have MMU, therefore UNIX by definition do not require MMU, and that version of UNIX had been archeologied in a runnable form on GitHub[1]

1: https://github.com/DoctorWkt/pdp7-unix

I've never heard of a copy being used outside of the original authors' site. However, it can be built from source code and run on a PDP-7 emulator. https://github.com/DoctorWkt/pdp7-unix.

Well first of all I was wrong -- the PDP7 did have syscalls, I'm just bad at reading PDP7 assembly and missed the dispatcher. Curiously, it looks like the sequence is entirely different, although there could be some magic that makes the order different than it appears at first glance.

https://github.com/DoctorWkt/pdp7-unix/blob/master/src/sys/s...

It's all just guessing, but I figure the explanation is much simpler -- for PDP11 UNIX, they just kept using the same syscalls up till V7 / 2BSD, and there should have been a sort of "rolling release" binary compatibility. For the VAX, the first port (32v) probably just retained the original numbering since there was no reason to deviate from it, which colored 3BSD and 4BSD, hence {Net,Free,Open}BSD and Darwin and friends.

Worth pointing out that several versions of Linux have rather different syscall tables. 32 bit ARM and x86 are more-or-less matches, with ARM differing on a few early syscalls, while 64 bit ARM and amd64 differing quite dramatically. The old ABI for 32bit MIPS also matches, but both the n32 and n64 ABIs use slightly variant syscall tables. PowerPC 32/64 bit is also a close match, although it has some impedance (I think it matches closer to AIX by design)

At the end of the day, I think the similarity is mostly a mixture of coincidence, system developers being influenced by their bootstrap system's syscall tables, and no real reason to change them up. No reason to not change them, either, since it's pretty trivial to use different dispatch tables for different types of processes, like how the BSD's handle other-OS compat.