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

[Yafang Shao <laoar.shao@gmail.com>]

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

Assisted-by: Comagic:DeepSeek-V4-Flash
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 scripts/package/kernel.spec | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/package/kernel.spec b/scripts/package/kernel.spec
index c732415662ef..abc73de019e0 100644
--- a/scripts/package/kernel.spec
+++ b/scripts/package/kernel.spec
@@ -67,7 +67,7 @@ This package provides debug information for the kernel image and modules from th
 %undefine _unique_debug_srcs
 %undefine _debugsource_packages
 %undefine _debuginfo_subpackages
-%global _find_debuginfo_opts -r
+%global _find_debuginfo_opts -r --keep-section .BTF
 %global _missing_build_ids_terminate_build 1
 %global _no_recompute_build_ids 1
 %{debug_package}
-- 
2.52.0