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

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

[zhidao su]

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.
+
 It is found in the 'dwarves' or 'pahole' distro packages or from
 https://fedorapeople.org/~acme/dwarves/.
 
-- 
2.43.0

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

[Jonathan Corbet]

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

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

[Alexei Starovoitov]

On Mon, Mar 23, 2026 at 11:22 PM zhidao su <soolaugust@gmail.com> wrote:
>
> 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.

I don't think that's true.
At least when implicit args were designed the goal was to avoid
pahole dependencies.

Please share exact steps to reproduce.

Updating doc is definitely not an answer.

pw-bot: cr