Next steps for BPF support in the GNU toolchain

Summary

By Jonathan CorbetOctober 6, 2025 Cauldron Support for BPF in the kernel has been tied to the LLVM toolchain since the advent of extended BPF. There has been a growing effort to add BPF support to the GNU toolchain as well, though. At the 2025 GNU Tools Cauldron, the developers involved got together with representatives of the kernel community to talk about the state of that work and what needs to happen next. Integrating BTF and CTF The BPF type format (BTF) represents the types of kernel data structures and functions; it is used to enable BPF programs to run on multiple kernels, and by the verifier to ensure program correctness, among other uses. It is derived from the Compact C Type Format (CTF), which is a more general-purpose format that makes debugging information available for compiled programs. Nick Alcock gave a high-speed presentation of his work to reunify those two formats. The libctf library, which works with CTF, is now able to both produce and consume BTF, he began. It can also work with an under-development "CTFv4" format that adds support for some of the trickier cases. This work is being tied into the kernel build, which would allow the creation of BTF directly when building the kernel, rather than as a separate step using the pahole utility as is done now. There are a couple of enhancements that are needed before BTF can completely replace CTF beyond the kernel, though. A string header field is needed to be able to separate the BTF from each translation unit when the results are all combined. Some sort of agreement on a format for referring to structure members in archives (holding BTF data for multiple translation units) is required for compaction purposes. To be able to use this format in user space, there has to be a representation for floating-point data — a feature the kernel has never needed. With those in place, the extra capabilities provided by CTF would only be needed to represent huge structures (rather larger than would ever make sense...