systemd: Detect ELF ABI version for bpf build on powerpc64

[OPNA2608]

With the BPF feature enabled, SystemD assumes that ELFv2 ABI will be used on 64-bit POWER:

https://github.com/systemd/systemd/blob/879ed340a1e80ab64890f8f473df406fd0c80b76/meson.build#L1731

On ELFv1, this causes a compilation failure. Patch this so it no longer means ELFv2. The check for this is usually defined(_CALL_ELF) && _CALL_ELF == 2, so setting the define to 1 should do the trick.

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • powerpc64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and others READMEs.

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[arianvp]

This feels like this should be a patch to systemd's meson.build instead? Why don't we send them a PR with these changes?

We can make sure they get backported 257. That's not an issue.

[OPNA2608]

That'll need abit more work then, because _CALL_ELF=2 by itself isn't wrong… depending on the ABI that the compiler is built to (be able to) target. Can try.

[arianvp]

Just to explain: Our philosophy is to only accept patches that are required to make systemd work with the nix package manager and the nix store. This way we keep our maintenance burden low. If this is fixing a bug in systemd then I would highly prefer you either open an issue or a pull request there.

[OPNA2608]

Makes sense!

Will convert this to a draft for now, just so I don't forget about this matter.

Why don't we send them a PR with these changes?

Moved the decision of what ABI version to use into the Meson code, and submitted it upstream: systemd/systemd#38307

[flokli]

@OPNA2608 the upstream PR already landed, I asked about it being backported to 257.x in systemd/systemd#38307 (comment).

In the meantime, can you update this PR to be a lib.optionals fetchpatch'ed https://github.com/systemd/systemd/commit/b676aeaee18044f51f9644d8e5ae4e7497581a44.patch, including a link to systemd/systemd#38307 (comment) in a comment above.

Considering the upstream PR is already merged, the URL won't disappear, and if it stays conditionalized on the platform it could go to master directly, without a staging round.

[OPNA2608]

Done, though I opted to use systemd/systemd@f950919 instead, which is the commit that's actually in the upstream repository now.

[flokli]

I assume you're building natively?

I tried pkgsCross.ppc64-elfv1.systemdMinimal, but it fails with ncurses and kexec-tools…

[OPNA2608]

I assume you're building natively?

I'm building natively yeah.

I tried pkgsCross.ppc64-elfv1.systemdMinimal

systemdMinimal doesn't enable withLibBPF, so it won't actually test what the patch is doing.

it fails with ncurses and kexec-tools…

You can give this branch a try if you want, but I haven't checked if there are any cross-specific issues anywhere: https://github.com/OPNA2608/nixpkgs/tree/wip/ppc64-elfv1.

Fixes for these packages are submitted to Nixpkgs in #427495 and #422007 respectively. You can find some more submitted ones by searching is:open is:pr author:OPNA2608 powerpc64. I think there should be enough submitted already that you're able to build up to systemd if you apply the PRs locally, and maybe cherry-pick some things that already landed in staging.

[flokli]

I tried pkgsCross.ppc64-elfv1.systemdMinimal

systemdMinimal doesn't enable withLibBPF, so it won't actually test what the patch is doing.

Yeah, this was more of a "I don't even get past systemdMinimal".

it fails with ncurses and kexec-tools…

You can give this branch a try if you want, but I haven't checked if there are any cross-specific issues anywhere: https://github.com/OPNA2608/nixpkgs/tree/wip/ppc64-elfv1.

Fixes for these packages are submitted to Nixpkgs in #427495 and #422007 respectively. You can find some more submitted ones by searching is:open is:pr author:OPNA2608 powerpc64. I think there should be enough submitted already that you're able to build up to systemd if you apply the PRs locally, and maybe cherry-pick some things that already landed in staging.

I'll try to chery-pick things together later, thanks!

[flokli]

With da9a49a, then #427495 and #422007, and this one cherry-picked on top, I was able to successfully compile all the way up to nix-build -A pkgsCross.ppc64-elfv{1,2}.systemd (from aarch64-linux), but building pkgsCross.ppc64-elfv{1,2}.systemd itself still fails:

• /nix/store/ydlsm7hkpy09xz36npqkw1np8cjz4a2x-systemd-powerpc64-unknown-linux-gnuabielfv1-257.6.drv: https://dpaste.com/CZF48RW5G
• /nix/store/a1s1c433ly3zbbwv3cbr2w6jgw1afkwa-systemd-powerpc64-unknown-linux-gnuabielfv2-257.6.drv: https://dpaste.com/FWB6BX3D4

       > meson.build:1114:28: ERROR: Command `/nix/store/2z38g8x06c0sliq48ajpq7z1d9pa6q97-powerpc64-unknown-linux-gnuabielfv2-clang-wrapper-19.1.7/bin/powerpc64-unknown-linux-gnuabielfv2-clang --version` failed with status 1.

[OPNA2608]

[...]clang --version` failed with status 1

Can you give the errors that running this command interactively is causing? I imagine this is likely Clang not recognising the explicit ABI part of the target triplet and erroring out when it tries to interpret the value as something different. Try applying #297425 if that's the case.

[flokli]

[...]clang --version` failed with status 1

Can you give the errors that running this command interactively is causing? I imagine this is likely Clang not recognising the explicit ABI part of the target triplet and erroring out when it tries to interpret the value as something different. Try applying #297425 if that's the case.

Yup:

❯ /nix/store/2z38g8x06c0sliq48ajpq7z1d9pa6q97-powerpc64-unknown-linux-gnuabielfv2-clang-wrapper-19.1.7/bin/powerpc64-unknown-linux-gnuabielfv2-clang --version
clang: error: version 'abielfv2' in target triple 'powerpc64-unknown-linux-gnuabielfv2' is invalid
clang version 19.1.7
Target: powerpc64-unknown-linux-gnuabielfv2
Thread model: posix
InstalledDir: /nix/store/zxyvh8psxzbidvskh8cqn8dvxagz1lkl-clang-19.1.7/bin

… and cherry-picking #297425 fixes that, thanks!

[flokli]

With all these other PRs, now both pkgsCross.ppc64-elfv{1,2}.systemd succeeds in building. Thanks!