"Andrii Nakryiko" <andrii.nakryiko@...> writes:

On Sun, Feb 28, 2021 at 12:37 PM <bg.salunke09@...> wrote:

[Edited Message Follows]

Hi,

I'm looking into BTF and it's use case. Based on the document I understood to run BPF programs across different kernel versions, it needs to build with libbpf which depends on the BTF information.
Now to enable/to have BTF information on any Kernel, the kernel needs to be re-build with "" flag.

I can see the BTF support in Linux introduced from kernel version 5.1.0 (https://www.kernel.org/doc/html/v5.1/bpf/btf.html?highlight=btf)
however I can still see the BTF information(/sys/kernel/btf/vmlinux) on my 4.18.0-193.28.1.el8_2.x86_64 kernel.

I'm little confused here how old kernel can generate BTF info if the was support added recently.

Can I get information about oldest linux kernel version that can support BTF?

/sys/kernel/btf/vmlinux appeared in 5.4 kernel (upstream version). If
you see it on 4.18, that means someone backported the changes.

Yeah, that looks like a RHEL/CentOS kernel version number, which means
the 4.18 bit is mostly fiction at this point (at least as far as BPF is
concerned). IIRC we backported up to upstream kernel 5.4 for RHEL 8.2,
which seems to be what you're running (from the el8_2 bit of the
version), and I guess that fits with the availability of
/sys/kernel/btf/vmlinux

-Toke