picolibc: init at 1.8.9

[RossSmyth]

Things done

Added Picolibc with configuration options.

Closes #368022

• 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/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 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.

Also tested:

• nix-build -A pkgsCross.arm-embedded.picolibc
• nix-build -A pkgsLLVM.picolibc
  - nix-build -A pkgsCross.arm-embedded.pkgsLLVM.picolibc (unsure if this is the right incantation?)

TODO (future PRs):

• Get tests running under emulated embedded arm (I have it building, but it overflows the "flash")
• Get this hooked up so it can be used as a libc

---

Add a 👍 reaction to pull requests you find important.

[RossSmyth]

I put the meson options because they are pretty important to be able to fiddle with for embedded devs, so this makes them easier to do so.

[RossSmyth]

• nix-build -A pkgsCross.arm-embedded.pkgsLLVM.picolibc (unsure if this is the right incantation?)

Or at least it did...running it at home the stdenv fails to build :/

[RossSmyth]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 395318

---

x86_64-linux

✅ 2 packages built:

• picolibc
• picolibc.dev

[ghost]

Something more in passthru.tests would be nice. Maybe build GNU hello against picolibc and show that it works. Otherwise looks fine to me.

[kuruczgy]

I like the idea, would be cool if picolibc could be used just like any other libc in nixpkgs (with isNone platforms)

Get this hooked up so it can be used as a libc

FYI you will probably run into libc++ (or probably libstdc++ too, I only tried llvm) expecting features that picolibc cannot provide (e.g. a clock).

You might find it useful to look at my PR attempting to address this, and the discussions there: #352629

(Unfortunately I don't have the time to work on it right now, feel free to cannibalize parts of it if they are useful and you are working on a more comprehensive solution.)

[RossSmyth]

Is there an equivalent to hello for embedded environments? Because it doesn't build with pkgsCross.arm-embedded.hello. I tried to do it for just the x86 linux and haven't been able to figure out how to wire it up yet.

[ghost]

If its useful then tests will happen.

[Ericson2314]

We can rig this up, but I can't help with that until after Nix 2.28 for Nixpkgs 25.05 is good to go.