treewide: freebsd13 -> freebsd

[Ericson2314]

Description of changes

@rhelmot and @artemist think this is correct. @alyssais was once quite convinced it was not correct. I have no idea, but we should decide soon so we can all be happy for 24.05.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

---

Add a 👍 reaction to pull requests you find important.

[rhelmot]

Some references in favor of dropping the version number

https://wiki.freebsd.org/BinaryCompatibility
https://wiki.freebsd.org/KernelModulePackages (just the first paragraph)
https://wiki.freebsd.org/AddingSyscalls (edited to add this; this actually discusses some limited applications where forward compat is policy)
#254801 (comment)

tl;dr FreeBSD provides syscall abi backwards compatibility. We can convert that to forwards compatibility by running our buildbots on the oldest supported (wrt nixpkgs) version of FreeBSD. This can be further converted to forwards compatibility for everyone once the jail code is merged, nix can simply be configured to build in a jail claiming to be the lowest supported version.

[Aleksanaa]

tl;dr FreeBSD provides syscall abi backwards compatibility. We can convert that to forwards compatibility by running our buildbots on the oldest supported (wrt nixpkgs) version of FreeBSD. This can be further converted to forwards compatibility for everyone once the NixOS/nix#9968 is merged, nix can simply be configured to build in a jail claiming to be the lowest supported version.

Thanks for pointing it out! When NixBSD chose to use freebsd (instead of netbsd), and removed the version number from the code (similar to this PR), I once doubted the correctness of what they did.

[artemist]

The decision to use FreeBSD and to remove the version number were very practical.

Removing the version number removes a lot of manual work adding new platforms, and it's not even that useful: if you're worried about forward compatibility than a binary built for 13.2-RELEASE isn't guaranteed to run on 13.0-RELEASE.

NetBSD can't easily support sandboxed builders, so if we wanted pure native builds we'd have to figure out how to do something weird (maybe boot a vm for each derivation off virtio-9p of that's possible?). FreeBSD makes this relatively easy with jails.

[Ericson2314]

So the ABI can grow but not changing in a breaking away from 13.0 -> 13.2 and also from 13.03 -> 14? Are the ABI guarantees more or less the same regardless of whether it a difference in the major or minor number?

[alyssais]

Makes sense to me.

[Ericson2314]

@alyssais that's an approval, with the indentation fixed?