Bug 938562 – sys-apps/systemd[bpf] needs kernel configs that in turn need dev-util/pahole at buildtime

• Product: Gentoo Linux
• Status: RESOLVED CANTFIX

[Description Nils Freydank 2024-08-27 17:19:54 UTC]

Hi,

recently USE=bpf was added to systemd which in turn need CONFIG_BPF_LSM and CONFIG_DEBUG_INFO_BTF.

If the latter is enabled, the kernel needs pahole at build-time (for other kernel configs enabled on the way).

I’m unsure how to track this properly, as users can use plenty different kernels - maybe add a postinst warning for the systemd package?

Best regards,
Nils

Reproducible: Always

[Comment 1 Sam James 2024-08-27 17:25:02 UTC]

gentoo-kernel[debug] handles this for you. I'm not sure what else we could do though, because the same thing applies to e.g. cpio, and then people have to install it manually.

i.e. If you want Portage to handle your kernels, let it?

[Comment 2 Sam James 2024-08-27 17:25:48 UTC]

FWIW, the kernel help text mentions pahole too: https://cateee.net/lkddb/web-lkddb/DEBUG_INFO_BTF.html

[Comment 3 Mike Gilbert 2024-08-27 17:33:55 UTC]

So what happens if you run systemd with USE=bpf enables, and the kernel is missing those options?

[Comment 4 Mike Gilbert 2024-08-27 17:41:46 UTC]

The systemd README file documents this requirement.

This feature seems like it will be seldom used, so I don't really feel like we need to advertise the kernel requirements. People can read the documentation.

Maybe mention the README file in the USE flag description?

[Comment 5 Sam James 2024-08-27 19:13:55 UTC]

(In reply to Mike Gilbert from comment #3)
> So what happens if you run systemd with USE=bpf enables, and the kernel is
> missing those options?

See https://github.com/systemd/systemd/issues/32968. But the ebuild *already* checks for these config options, it's just that OP wants us to mention pahole.

[Comment 6 Mike Gilbert 2024-08-27 19:36:21 UTC]

Ah I see. I don't think it makes sense for the systemd ebuild to document tools required by the kernel build system.

[Comment 7 Nils Freydank 2024-09-05 20:00:30 UTC]

(In reply to Sam James from comment #5)
> [...] it's just that OP wants us to
> mention pahole.
Excactly.

(In reply to Mike Gilbert from comment #6)
> Ah I see. I don't think it makes sense for the systemd ebuild to document
> tools required by the kernel build system.
I still disagree as I see it's as an unusual feature that is necessary for a certain USE flag of systemd (only?) and is slightly annoying when you stumble upon it. No show-stopper, but your kernel does not compile which is highly unusual and needs manual intervention and inspection.

Anyways, you're the maintainer, you decide ;)

I'll close this as resolved-cantfix (for the record, none of the resolved flags really fits well here in my opinion).