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docs: Raise minimum pahole version to 1.26 for KF_IMPLICIT_ARGS kfuncs

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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 (e.g. scx_bpf_create_dsq, scx_bpf_kick_cpu).

The root cause: scripts/Makefile.btf passes --btf_features=decl_tag_kfuncs
to pahole only when pahole >= 1.26.  Without that flag, pahole emits no
DECL_TAG BTF entries for __bpf_kfunc-annotated functions.  As a result,
resolve_btfids/main.c::collect_kfuncs() finds no bpf_kfunc DECL_TAGs,
short-circuits at line 1002, and btf2btf() never creates the _impl
variants or strips the implicit 'aux' argument from the visible proto.
The vmlinux BTF retains the 3-param prototype while BPF programs declare
the 2-param version, triggering the mismatch.

Raise the minimum version in the requirements table from 1.22 to 1.26
and add a note explaining the failure mode, so users understand why
their BPF programs fail on distributions shipping pahole v1.25 (e.g.
Ubuntu 24.04 LTS).

Suggested-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: zhidao su <suzhidao@xiaomi.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
zhidao su 2026-03-25 02:47:18 +08:00 committed by Tejun Heo
parent 4624211bc6
commit 9edd04c418
1 changed files with 6 additions and 1 deletions
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7
Documentation/process/changes.rst
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@ -38,7 +38,7 @@ bash 4.2 bash --version
binutils 2.30 ld -v binutils 2.30 ld -v
flex 2.5.35 flex --version flex 2.5.35 flex --version
bison 2.0 bison --version bison 2.0 bison --version
pahole 1.22 pahole --version pahole 1.26 pahole --version
util-linux 2.10o mount --version util-linux 2.10o mount --version
kmod 13 depmod -V kmod 13 depmod -V
e2fsprogs 1.41.4 e2fsck -V e2fsprogs 1.41.4 e2fsck -V
@ -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 generates BTF (BPF Type Format) from DWARF in vmlinux, a bit later from kernel
modules as well. This requires pahole v1.22 or later. 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 It is found in the 'dwarves' or 'pahole' distro packages or from
https://fedorapeople.org/~acme/dwarves/. https://fedorapeople.org/~acme/dwarves/.