[PATCH v3] kbuild: rpm-pkg: Preserve .BTF section in kernel modules during debuginfo stripping

[PATCH v3] kbuild: rpm-pkg: Preserve .BTF section in kernel modules during debuginfo stripping

[Yafang Shao]

After switching to the kernel's default package scripts for our local
kernel RPM builds, we noticed that module BTF entries were missing:

  $ ls /sys/kernel/btf/
  vmlinux    <<<< only vmlinux, no module BTF

Root cause: find-debuginfo.sh (from the debugedit package) prefers
eu-strip over strip when elfutils is installed, which is the common
case on RHEL 9. eu-strip removes non-allocated ELF sections, including
the .BTF section that contains BPF Type Format information for kernel
modules. Without .BTF, BPF tools (bpftool, bcc, bpftrace) cannot resolve
kernel types at runtime, and /sys/kernel/btf/<module> entries are not
created when modules are loaded.

Fix by passing --keep-section .BTF via _find_debuginfo_opts, which adds
-K .BTF to the eu-strip/strip command, preserving the .BTF section while
allowing normal debuginfo extraction to proceed.

After this change, all module BTF files are properly generated:

  $ ls /sys/kernel/btf/
  aesni_intel         drm                 i2c_i801            mfd_core
  ahci                drm_client_lib      i2c_mux             net_failover
  backlight           drm_kms_helper      i2c_smbus           pcspkr
  ccp                 drm_shmem_helper    input_leds          qemu_fw_cfg
  dm_log              failover            intel_rapl_common   sch_fq_codel
  dm_mirror           fat                 intel_rapl_msr      serio_raw
  dm_mod              fuse                irqbypass           sunrpc
  dm_region_hash      gf128mul            iTCO_wdt            vfat
  virtio_balloon      virtio_console      virtio_dma_buf      virtio_gpu
  virtio_net          virtio_rng          virtio_blk          vmlinux
  xfs

Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 scripts/package/kernel.spec | 10 ++++++++++
 1 file changed, 10 insertions(+)

v2->v3: use %{__find_debuginfo} (Nathan)
v1->v2: check if find-debuginfo.sh supports --keep-section (sashiko-bot)

diff --git a/scripts/package/kernel.spec b/scripts/package/kernel.spec
index c732415662ef..1032f337a71c 100644
--- a/scripts/package/kernel.spec
+++ b/scripts/package/kernel.spec
@@ -67,7 +67,17 @@ This package provides debug information for the kernel image and modules from th
 %undefine _unique_debug_srcs
 %undefine _debugsource_packages
 %undefine _debuginfo_subpackages
+
+# Preserve .BTF section in kernel modules during debuginfo stripping
+# find-debuginfo.sh (from debugedit) uses eu-strip which removes
+# non-allocated ELF sections like .BTF by default.
+%global with_keep_section %(%{__find_debuginfo} --help 2>&1 | grep -c keep-section)
+%if %{with_keep_section}
+%global _find_debuginfo_opts -r --keep-section .BTF
+%else
 %global _find_debuginfo_opts -r
+%endif
+
 %global _missing_build_ids_terminate_build 1
 %global _no_recompute_build_ids 1
 %{debug_package}
-- 
2.52.0

Re: [PATCH v3] kbuild: rpm-pkg: Preserve .BTF section in kernel modules during debuginfo stripping

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The patch preserves the `.BTF` section during debuginfo stripping but fails to also preserve the `.BTF.base` section, causing module BTF validation to fail.
--

--- Patch [1]: [PATCH v3] kbuild: rpm-pkg: Preserve .BTF section in kernel modules during debuginfo stripping ---
commit cd09ed46074d0224c00066939452278fca769e51
Author: Yafang Shao <laoar.shao@gmail.com>
kbuild: rpm-pkg: Preserve .BTF section in kernel modules during debuginfo stripping

This commit updates the RPM build scripts to pass --keep-section .BTF to
find-debuginfo.sh. This prevents eu-strip from dropping the .BTF section
from kernel modules during debuginfo extraction.

> diff --git a/scripts/package/kernel.spec b/scripts/package/kernel.spec
> index c732415662ef2..1032f337a71cd 100644
> --- a/scripts/package/kernel.spec
> +++ b/scripts/package/kernel.spec

[ ... ]

> @@ -67,7 +67,17 @@ This package provides debug information for the kernel image and modules from th
>  %undefine _unique_debug_srcs
>  %undefine _debugsource_packages
>  %undefine _debuginfo_subpackages
> +
> +# Preserve .BTF section in kernel modules during debuginfo stripping
> +# find-debuginfo.sh (from debugedit) uses eu-strip which removes
> +# non-allocated ELF sections like .BTF by default.
> +%global with_keep_section %(%{__find_debuginfo} --help 2>&1 | grep -c keep-section)
> +%if %{with_keep_section}
> +%global _find_debuginfo_opts -r --keep-section .BTF

[Severity: High]
Does this also need to preserve the .BTF.base section?

When modules are built with BTF distillation (which is standard on recent
kernels), both .BTF and .BTF.base sections are generated. If .BTF.base is
stripped, btf_parse_module() in kernel/bpf/btf.c falls back to using the
vmlinux_btf. 

This fallback causes type ID mismatches during btf_check_all_metas() because
the module's .BTF was built with distilled IDs, ultimately resulting in the
module's BTF being rejected entirely.

Could we add --keep-section .BTF.base here as well to ensure distilled BTF
validation succeeds?

> +%else
>  %global _find_debuginfo_opts -r
> +%endif
> +
>  %global _missing_build_ids_terminate_build 1
>  %global _no_recompute_build_ids 1
>  %{debug_package}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260726025242.42245-1-laoar.shao@gmail.com?part=1

Re: [PATCH v3] kbuild: rpm-pkg: Preserve .BTF section in kernel modules during debuginfo stripping

[Yafang Shao]

On Sun, Jul 26, 2026 at 11:03 AM <sashiko-bot@kernel.org> wrote:
>
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] The patch preserves the `.BTF` section during debuginfo stripping but fails to also preserve the `.BTF.base` section, causing module BTF validation to fail.
> --
>
> --- Patch [1]: [PATCH v3] kbuild: rpm-pkg: Preserve .BTF section in kernel modules during debuginfo stripping ---
> commit cd09ed46074d0224c00066939452278fca769e51
> Author: Yafang Shao <laoar.shao@gmail.com>
> kbuild: rpm-pkg: Preserve .BTF section in kernel modules during debuginfo stripping
>
> This commit updates the RPM build scripts to pass --keep-section .BTF to
> find-debuginfo.sh. This prevents eu-strip from dropping the .BTF section
> from kernel modules during debuginfo extraction.
>
> > diff --git a/scripts/package/kernel.spec b/scripts/package/kernel.spec
> > index c732415662ef2..1032f337a71cd 100644
> > --- a/scripts/package/kernel.spec
> > +++ b/scripts/package/kernel.spec
>
> [ ... ]
>
> > @@ -67,7 +67,17 @@ This package provides debug information for the kernel image and modules from th
> >  %undefine _unique_debug_srcs
> >  %undefine _debugsource_packages
> >  %undefine _debuginfo_subpackages
> > +
> > +# Preserve .BTF section in kernel modules during debuginfo stripping
> > +# find-debuginfo.sh (from debugedit) uses eu-strip which removes
> > +# non-allocated ELF sections like .BTF by default.
> > +%global with_keep_section %(%{__find_debuginfo} --help 2>&1 | grep -c keep-section)
> > +%if %{with_keep_section}
> > +%global _find_debuginfo_opts -r --keep-section .BTF
>
> [Severity: High]
> Does this also need to preserve the .BTF.base section?
>
> When modules are built with BTF distillation (which is standard on recent
> kernels), both .BTF and .BTF.base sections are generated. If .BTF.base is
> stripped, btf_parse_module() in kernel/bpf/btf.c falls back to using the
> vmlinux_btf.
>
> This fallback causes type ID mismatches during btf_check_all_metas() because
> the module's .BTF was built with distilled IDs, ultimately resulting in the
> module's BTF being rejected entirely.
>
> Could we add --keep-section .BTF.base here as well to ensure distilled BTF
> validation succeeds?

You're right. .BTF.base should also be preserved. I'll update it.

-- 
Regards
Yafang