Arch Linux

Sacharon

Member

Registered: 2025-02-23

Posts: 1

kernel PKGBUILD trouble - BTF .elf section missing

Hey all,

I am encountering an issue when trying to crosscompile a kernel as a package for a different slower system.
System specs for the build system is a VMware virtual machine, 12cpus, 48GB RAM assigned. I did a fresh arch install for this kernel build as I had the same issue on my test VM before and wanted to try clean.
Running kernel is 6.13.5-arch1.
Previous installed build packages are base-devel, devtools, git, llvm. pahole reports v1.29, but I also tried a rollback to v1.23. libelf from pacman is 0.192. All system packages are uptodate with Syu at present time.

I cloned the linux repo, edited the pkgbuild with vim, removed the two htmldocs entries in build and pkgname. I changed in the prepare the "make olddefconfig" to "make menuconfig" and added a "make prepare" after.
In my /etc/makepkg.conf march and mtune are set to broadwell (tried also with default values), and makeflags activated and set to -j12.
In the menuconfig, some options were changed regarding target architecture (core2) and some legacy device driver stacks (mainly amateurradio and similar items) removed.
If I run the makepkg -C -s --skippgpchecks, at some point, I will end up with

libbpf: failed to find '.BTF' ELF section in vmlinux
FAILED: load BTF from vmlinux: No data available

If I go in the extracted src/linux-6.13.5/testing/selftests/bpf/ and run a make, I end up with the same errors.
Funnily, when I pull a clean kernel tarball, load the same modified .config into that and make it, it compiles without errors, so the error seems to be somewhere either in the PKGBUILD or the arch patches. I tried also deactivating the complete kernel debug btf output and the bpf subsystem in the general section to no avail.

These are the used files:
PKGBUILD
.config

Can anyone try to crosscheck if this config / PKGBUILD compiles smoothly on their system, or tell me what I am doing wrong?
Thanks!

EDIT:
I tried what @altoid suggested here, but to no avail.

Last edited by Sacharon (2025-03-01 12:07:43)

Unmoon

Member

Registered: 2025-04-05

Posts: 2

Re: kernel PKGBUILD trouble - BTF .elf section missing

Had the same issue and found the solution on Chinese side of internet:
You need to enable

CONFIG_DEBUG_INFO_BTF
CONFIG_DEBUG_INFO_BTF_MODULES

I had toggled off CONFIG_DEBUG_KERNEL which toggles also those two. Not sure this is really intended to fail the build, but there you go. Could not find a way to disable the build of bpftool in config.

ReDress

Member

From: Nairobi

Registered: 2024-11-30

Posts: 239

Re: kernel PKGBUILD trouble - BTF .elf section missing

If I go in the extracted src/linux-6.13.5/testing/selftests/bpf/ and run a make, I end up with the same errors.

Probably also worth noting that BTF and Berkerly Packet Filter(bpf) are probably different things.