Re: [PATCH] docs: Document pahole v1.26 requirement for KF_IMPLICIT_ARGS kfuncs

[Jonathan Corbet <corbet@lwn.net>]

zhidao su <soolaugust@gmail.com> writes:

> Since Linux 7.0, kfuncs annotated with KF_IMPLICIT_ARGS require pahole
> v1.26 or later. Without it, such kfuncs have incorrect BTF prototypes in
> vmlinux, causing BPF programs to fail with 'func_proto incompatible with
> vmlinux' error.
>
> This affects all sched_ext kfuncs (e.g. scx_bpf_create_dsq,
> scx_bpf_dispatch) and other KF_IMPLICIT_ARGS kfuncs across the kernel.
> Ubuntu 24.04 LTS ships pahole v1.25 by default, causing 23/30 sched_ext
> selftests to fail on affected systems.
>
> Document this requirement in Documentation/process/changes.rst so users
> understand the failure mode and can upgrade pahole appropriately.
>
> Signed-off-by: zhidao su <suzhidao@xiaomi.com>
> ---
>  Documentation/process/changes.rst | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst
> index 6b373e193548..141a4576c24d 100644
> --- a/Documentation/process/changes.rst
> +++ b/Documentation/process/changes.rst
> @@ -145,6 +145,11 @@ Since Linux 5.2, if CONFIG_DEBUG_INFO_BTF is selected, the build system
>  generates BTF (BPF Type Format) from DWARF in vmlinux, a bit later from kernel
>  modules as well.  This requires pahole v1.22 or later.
>  
> +Since Linux 7.0, kfuncs annotated with KF_IMPLICIT_ARGS require pahole v1.26
> +or later.  Without it, such kfuncs will have incorrect BTF prototypes in
> +vmlinux, causing BPF programs to fail to load with a "func_proto incompatible
> +with vmlinux" error.  Many sched_ext kfuncs are affected.

This seems like reasonable information, but is there a reason to not
just raise the minimum pahole version to 1.26 and be done with it?

Thanks,

jon