vmlinux-btf

OpenWrt package that generates a detached BTF (vmlinux) file from kernel headers and .config, enabling CO-RE (Compile Once – Run Everywhere) eBPF programs on OpenWrt without rebuilding or replacing the running kernel.

Overview

Official OpenWrt release kernels typically omit CONFIG_DEBUG_INFO_BTF=y. Without kernel BTF, modern eBPF tools that rely on CO-RE (such as libbpf-based loaders) cannot resolve kernel type layouts.

Rather than recompiling the entire kernel tree, this package compiles lightweight stub sources (src/shadow_btf_*.c) against the prepared target kernel headers ($(LINUX_DIR)) using the target configuration and toolchain. pahole then extracts the detached BTF blob from the linked object.

Requirements

• OpenWrt buildroot or SDK environment.
• Host pahole >= 1.22 (from the dwarves package).

Building

In OpenWrt SDK

git clone https://github.com/QiuSimons/vmlinux-btf.git package/vmlinux-btf
make package/vmlinux-btf/compile V=s

In OpenWrt Buildroot

Select vmlinux-btf under Kernel in make menuconfig, then build:

make package/vmlinux-btf/compile V=s

Installed Files

• /usr/lib/debug/boot/vmlinux: Detached BTF file.
• /usr/lib/debug/boot/vmlinux-<release>: Symlink targeting vmlinux (linked to uname -r on target installation).

Standard loaders such as libbpf look for BTF at /usr/lib/debug/boot/vmlinux-$(uname -r) and /usr/lib/debug/boot/vmlinux by default.

License

GPL-3.0-or-later