On Thu, Sep 23, 2021 at 12:33:58PM +0100, Lorenz Bauer wrote:

Some questions:
* How can this handle kernels that don't have built-in BTF? Not a
problem for myself, but some people have to deal with BTF-less distro
kernels by using pahole to generate external BTF from debug symbols.
Can we accommodate that?

I think so, but it probably should be done as a generic feature:
"populate kernel BTF".
When kernel wasn't compiled with BTF there could be a way to
populate it with such. Just like we do sys_bpf(BTF_LOAD)
for program's BTF we can allow populating vmlinux BTF this way.
Unlike builtin BTF it wouldn't be trusted for certain verifier assumptions,
but better than nothing and more convenient than specifying BTF file
on a side for every bpf prog load with traditional libbpf style.