Re: [PATCH bpf-next v4 2/3] bpftool: conditionally append / to the progtype

On Thu, Oct 21, 2021 at 12:55 PM Quentin Monnet [off-list ref] wrote:

2021-10-21 09:56 UTC-0700 ~ Stanislav Fomichev [off-list ref]

quoted

Otherwise, attaching with bpftool doesn't work with strict section names.

Also, switch to libbpf strict mode to use the latest conventions
(note, I don't think we have any cli api guarantees?).

Cc: Quentin Monnet <redacted>
Signed-off-by: Stanislav Fomichev <redacted>
---
 tools/bpf/bpftool/main.c | 4 ++++
 tools/bpf/bpftool/prog.c | 9 +++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 02eaaf065f65..8223bac1e401 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c

@@ -409,6 +409,10 @@ int main(int argc, char **argv)
      block_mount = false;
      bin_name = argv[0];

+     ret = libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
+     if (ret)
+             p_err("failed to enable libbpf strict mode: %d", ret);
+
      hash_init(prog_table.table);
      hash_init(map_table.table);
      hash_init(link_table.table);

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index 277d51c4c5d9..b04990588ccf 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c

@@ -1420,8 +1420,13 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
                      err = get_prog_type_by_name(type, &common_prog_type,
                                                  &expected_attach_type);
                      free(type);
-                     if (err < 0)
-                             goto err_free_reuse_maps;

Thanks a lot for the change! Can you please test it for e.g. an XDP
program? You should see that "bpftool prog load prog.o <path> type xdp"
prints a debug message from libbpf about the first attempt (above)
failing, before the second attempt (below) succeeds.

We need to get rid of this message. I think it should be easy, because
we explicitly "ask" for that message in get_prog_type_by_name(), in the
same file, if it fails to load in the first place.

Could you please update get_prog_type_by_name() to take an additional
switch as an argument, to tell if the debug-info should be retrieved
(then first attempt here would skip it, second would keep it)?
An alternative could be to move all the '/' and retries handling to that
function, and I think it would end up in bpftool keeping support for the
legacy object files with the former convention - but that would somewhat
defeat the objectives of the strict mode, so maybe not the best option.

How about we call libbpf_prog_type_by_name with the provided argv
first and then, if it doesn't work, we fallback to appending '\' and
using get_prog_type_by_name ?

quoted

+                     if (err < 0) {

We could run the second attempt only on libbpf returning -ESRCH, maybe?

Not sure it matters here, why not always retry on error?

quoted

+                             err = get_prog_type_by_name(*argv, &common_prog_type,
+                                                         &expected_attach_type);
+                             if (err < 0)
+
+                                     goto err_free_reuse_maps;
+                     }

                      NEXT_ARG();
              } else if (is_prefix(*argv, "map")) {