Re: [PATCH bpf-next 2/3] libbpf: Add support for program extensions

On 1/20/20 2:51 PM, Andrii Nakryiko wrote:

On Fri, Jan 17, 2020 at 4:47 PM Alexei Starovoitov [off-list ref] wrote:

quoted

Add minimal support for program extensions. bpf_object_open_opts() needs to be
called with attach_prog_fd = target_prog_fd and BPF program extension needs to
have in .c file section definition like SEC("replace/func_to_be_replaced").
libbpf will search for "func_to_be_replaced" in the target_prog_fd's BTF and
will pass it in attach_btf_id to the kernel. This approach works for tests, but
more compex use case may need to request function name (and attach_btf_id that
kernel sees) to be more dynamic. Such API will be added in future patches.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
  tools/include/uapi/linux/bpf.h |  1 +
  tools/lib/bpf/bpf.c            |  3 ++-
  tools/lib/bpf/libbpf.c         | 14 +++++++++++---
  tools/lib/bpf/libbpf.h         |  2 ++
  tools/lib/bpf/libbpf.map       |  2 ++
  tools/lib/bpf/libbpf_probes.c  |  1 +
  6 files changed, 19 insertions(+), 4 deletions(-)

[...]

quoted

  enum bpf_attach_type
  bpf_program__get_expected_attach_type(struct bpf_program *prog)

@@ -6265,6 +6269,10 @@ static const struct bpf_sec_def section_defs[] = {
                 .expected_attach_type = BPF_TRACE_FEXIT,
                 .is_attach_btf = true,
                 .attach_fn = attach_trace),
+       SEC_DEF("replace/", EXT,

how about freplace/, similar to fentry/fexit?

I think it's uglier, but fine.

quoted

+               .expected_attach_type = 0,

no need, it will be zero, if not specified here

fixed.