How do I use the osx-64 version of a package on osx-arm64?

[mahesh-panchal]

A colleague of mine has a conda environment file like:

name: hmmcleaner
channels:
  - conda-forge
  - bioconda
dependencies:
  - chrisjackson-pellicle::hmmcleaner

where hmmcleaner has builds for linux-64 and osx-64. We've both tried on our Macs to create this environment, but we get:

% pixi init --import conda_env.yml -p osx-arm64 -p osx-64 -p linux-64
✔ Created /Users/myuser/Downloads/test_hmmcleaner/pixi.toml
% pixi install
Error: 
  x failed to solve the conda requirements of 'default' 'osx-arm64'
  `-> Cannot solve the request because of: No candidates were found for hmmcleaner *.

I was under the impression that it would automatically install the osx-64 build version and use Rosetta with it. What did I misunderstand?

[baszalmstra]

If you dont add osx-arm64 as a platform but do add osx-64, pixi will fall back to osx-64 on osx-arm64 machines.

[mahesh-panchal]

Thank you. I guess that means even if a package does have an osx-arm64 build if I want to put it in an environment with a tool that only has as an osx-64, I can only specify the osx-64 platform?

[baszalmstra]

Yes, because arm64 and x86_64 binaries might not be ABI compatible.

[mahesh-panchal]

What's ABI?
Ah, https://en.wikipedia.org/wiki/Application_binary_interface?

[baszalmstra]

Its a long story but in a nutshell:

Its the "Application Binary Interface". Binaries (shared libraries and executables) can call into other binaries. But it requires that the interface that a binary provides matches the one that is expected by the caller. If that is not the case you can get all sorts of corruptions.

Compiling the same source for different architectures most likely leads to differences in this interface. So mixing binaries build for different architectures will fail.

But Im also pretty sure that its not possible simply because the binaries target different architecture specific instruction sets. I dont think Rosetta (the emulator to run x86 binaries on arm64) would work in a mixed architecture environment..