Thursday, December 31, 2020

Mac meets Arm64

Looking for sponsorship

Apple now ships Macs which are running on an arm64 variant machine with the latest version of MacOS, Big Sur M1. We are getting requests for PyPy to support this new architecture. Here is our position on this topic (or at least mine, Armin Rigo's), and how you can help.

Porting PyPy is harder than just re-running the compiler, because PyPy contains a few big architecture-dependent "details", like the JIT compiler and the foreign function interfaces (CFFI and ctypes).

Fixing the JIT compiler should not be too much work: we already support arm64, just the Linux one. But Apple made various details different (like the calling conventions). A few other parts need to be fixed too, notably CFFI and ctypes, again because of the calling conventions.

Fixing that would be a reasonable amount of work. I would do it myself for a small amount of money. However, the story doesn't finish here. Obviously, the start of the story would be to get ssh access to a Big Sur M1 machine. (If at this point you're thinking "sure, I can give you ssh access for three months", then please read on.) The next part of the story is that we need a machine available long term. It can be either a machine provided and maintained by a third party, or alternatively a pot of money big enough to support the acquision of a machine and ongoing work of one of us.

If we go with the provided-machine solution: What we need isn't a lot of resources. Our CI requires maybe 10 GB of disk space, and a few hours of CPU per run. It should fit into 8 GB of RAM. We normally do a run every night but we can certainly lower the frequency a bit if that would help. However, we'd ideally like some kind of assurance that you are invested into maintaining the machine for the next 3-5 years (I guess, see below). We had far too many machines that disappeared after a few months.

If we go with the money-supported solution: it's likely that after 3-5 years the whole Mac base will have switched to arm64, we'll drop x86-64 support for Mac, and we'll be back to the situation of the past where there was only one kind of Mac machine to care about. In the meantime, we are looking at 3-5 years of lightweight extra maintenance. We have someone that has said he would do it, but not for free.

If either of these two solutions occurs, we'll still have, I quote, "probably some changes in distutils-type stuff to make python happy", and then some packaging/deployment changes to support the "universal2" architecture, i.e. including both versions inside a single executable (which will not be just an extra switch to clang, because the two versions need a different JIT backend and so must be translated separately).

So, now all the factors are on the table. We won't do the minimal "just the JIT compiler fixes" if we don't have a plan that goes farther. Either we get sufficient money, and maybe support, and then we can do it quickly; or PyPy will just remain not natively available on M1 hardware for the next 3-5 years. We are looking forward to supporting M1, and view resources contributed by the community as a vote of confidence in assuring the future of PyPy on this hardware. Contact us:, or our private mailing list

Thanks for reading!

Armin Rigo