2025/5/14 05:19, "Alexei Starovoitov" <alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Mon, May 12, 2025 at 8:59 PM Jiayuan Chen <jiayuan.chen@xxxxxxxxx> wrote:
>
> >
> > This patch exposes the btf_custom_path feature to bpftool, allowing users
> >
> > to specify a custom BTF file when loading BPF programs using prog load or
> >
> > prog loadall commands. This feature is already supported by libbpf, and
> >
> > this patch makes it accessible through the bpftool command-line interface.
> >
> > Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
> >
> > ---
> >
> > tools/bpf/bpftool/prog.c | 11 ++++++++++-
> >
> > 1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> >
> > index f010295350be..63f84e765b34 100644
> >
> > --- a/tools/bpf/bpftool/prog.c
> >
> > +++ b/tools/bpf/bpftool/prog.c
> >
> > @@ -1681,8 +1681,17 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
> >
> > } else if (is_prefix(*argv, "autoattach")) {
> >
> > auto_attach = true;
> >
> > NEXT_ARG();
> >
> > + } else if (is_prefix(*argv, "custom_btf")) {
> >
> > + NEXT_ARG();
> >
> > +
> >
> > + if (!REQ_ARGS(1))
> >
> > + goto err_free_reuse_maps;
> >
> > +
> >
> > + open_opts.btf_custom_path = GET_ARG();
> >
>
> I don't see a use case yet.
>
> What exactly is the scenario where it's useful ?
>
This patch just exposes the btf_custom_path feature of libbpf to bpftool.
The argument 'btf_custom_path' in libbpf is used for those kernes that
don't have CONFIG_DEBUG_INFO_BTF enabled but still want to perform CO-RE
relocations. Specifically for older kernels, separate BTF files are already
provided: https://github.com/aquasecurity/btfhub-archive/.
If we want load prog using bpftool on those systems, we have to hack
btf__load_vmlinux_btf() before or write custom loader with libbpf and specify
'btf_custom_path'.
I also found a the similar topic:
https://lore.kernel.org/bpf/20220215225856.671072-1-mauricio@xxxxxxxxxx/
Additionally, pwru supports "--kernel-btf" which serves the same purpose as
this patch.
Therefore, using an external BTF file is a common practice.
