Re: [RFC hid v1 01/10] bpftool: generate json output of skeletons

[Andrii Nakryiko]

On Thu, Dec 1, 2022 at 6:23 AM Benjamin Tissoires
<benjamin.tissoires@xxxxxxxxxx> wrote:
>
> On Thu, Dec 1, 2022 at 12:06 AM Andrii Nakryiko
> <andrii.nakryiko@xxxxxxxxx> wrote:
> >
> > On Thu, Nov 24, 2022 at 7:16 AM Benjamin Tissoires
> > <benjamin.tissoires@xxxxxxxxxx> wrote:
> > >
> > > So we can then build light skeletons with loaders in any language.
> > >
> >
> > It would be useful to include an example generated JSON. Other than
> > that the overall idea makes sense. Kind of machine-friendly "BPF
> > object schema" to allow automation.
> >
>
> Great :)
> I'll add the generated example in v2 then.
>
> However, I have problems figuring out how I can hit the
> "codegen_datasecs()" path. I think that's the only code path I am not
> duplicating from the do_skeleton() function, but I don't know what
> kind of .bpf.c program will trigger that part.
>

You'll hit this whenever you have global variables in your .bpf.c
code. It's very important part, so let's make sure it is covered. Try
using both `const volatile` read-only variables (they will end up in
.rodata datasec) and global non-read-only variables (they will go into
.data, if initialized to non-zero defaults, or .bss if
zero-initialized).

> Also, should I add some tests for it in tools/testing/selftests/bpf?

Yes, it probably makes sense to check expected JSON output is
generated for a few example BPF object files.

>
> Cheers,
> Benjamin
>
> > > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
> > > ---
> > >  tools/bpf/bpftool/gen.c | 95 +++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 95 insertions(+)
> > >
> > > diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> > > index cf8b4e525c88..818a5209b3ac 100644
> > > --- a/tools/bpf/bpftool/gen.c
> > > +++ b/tools/bpf/bpftool/gen.c
> > > @@ -904,6 +904,96 @@ codegen_progs_skeleton(struct bpf_object *obj, size_t prog_cnt, bool populate_li
> > >         }
> > >  }
> > >
> > > +static int gen_json(struct bpf_object *obj, const char *obj_name, size_t file_sz, uint8_t *obj_data)
> > > +{
> > > +       struct bpf_program *prog;
> > > +       struct bpf_map *map;
> > > +       char ident[256];
> > > +
> > > +       jsonw_start_object(json_wtr);   /* root object */
> > > +
> > > +       jsonw_string_field(json_wtr, "name", obj_name);
> > > +
> > > +       jsonw_bool_field(json_wtr, "use_loader", use_loader);
> > > +
> > > +       /* print all maps */
> > > +       jsonw_name(json_wtr, "maps");
> > > +       jsonw_start_array(json_wtr);
> > > +       bpf_object__for_each_map(map, obj) {
> > > +               if (!get_map_ident(map, ident, sizeof(ident))) {
> > > +                       p_err("ignoring unrecognized internal map '%s'...",
> > > +                             bpf_map__name(map));
> > > +                       continue;
> > > +               }
> > > +
> > > +               jsonw_start_object(json_wtr);   /* map object */
> > > +               jsonw_string_field(json_wtr, "ident", ident);
> > > +               jsonw_string_field(json_wtr, "name", bpf_map__name(map));
> > > +
> > > +               /* print mmap data value */
> > > +               if (is_internal_mmapable_map(map, ident, sizeof(ident))) {
> > > +                       const void *mmap_data = NULL;
> > > +                       size_t mmap_size = 0;
> > > +
> > > +                       mmap_data = bpf_map__initial_value(map, &mmap_size);
> > > +
> > > +                       jsonw_uint_field(json_wtr, "size", mmap_size);
> > > +                       jsonw_uint_field(json_wtr, "mmap_sz", bpf_map_mmap_sz(map));
> > > +                       jsonw_name(json_wtr, "data");
> > > +                       print_hex_data_json((uint8_t *)mmap_data, mmap_size);
> > > +
> > > +               }
> > > +               jsonw_end_object(json_wtr);     /* map object */
> > > +       }
> > > +       jsonw_end_array(json_wtr);
> > > +
> > > +       /* print all progs */
> > > +       jsonw_name(json_wtr, "progs");
> > > +       jsonw_start_array(json_wtr);
> > > +       bpf_object__for_each_program(prog, obj) {
> > > +               jsonw_start_object(json_wtr);   /* prog object */
> > > +               jsonw_string_field(json_wtr, "name", bpf_program__name(prog));
> > > +               jsonw_string_field(json_wtr, "sec", bpf_program__section_name(prog));
> > > +               jsonw_end_object(json_wtr);     /* prog object */
> > > +       }
> > > +       jsonw_end_array(json_wtr);
> > > +
> > > +       /* print object data */
> > > +       if (use_loader) {
> > > +               DECLARE_LIBBPF_OPTS(gen_loader_opts, opts);
> > > +               int err = 0;
> > > +
> > > +               err = bpf_object__gen_loader(obj, &opts);
> > > +               if (err)
> > > +                       return err;
> > > +
> > > +               err = bpf_object__load(obj);
> > > +               if (err) {
> > > +                       p_err("failed to load object file");
> > > +                       return err;
> > > +               }
> > > +               /* If there was no error during load then gen_loader_opts
> > > +                * are populated with the loader program.
> > > +                */
> > > +
> > > +               jsonw_uint_field(json_wtr, "data_sz", opts.data_sz);
> > > +               jsonw_name(json_wtr, "data");
> > > +               print_hex_data_json((uint8_t *)opts.data, opts.data_sz);
> > > +
> > > +               jsonw_uint_field(json_wtr, "insns_sz", opts.insns_sz);
> > > +               jsonw_name(json_wtr, "insns");
> > > +               print_hex_data_json((uint8_t *)opts.insns, opts.insns_sz);
> > > +
> > > +       } else {
> > > +               jsonw_name(json_wtr, "data");
> > > +               print_hex_data_json(obj_data, file_sz);
> > > +       }
> > > +
> > > +       jsonw_end_object(json_wtr);     /* root object */
> > > +
> > > +       return 0;
> > > +}
> > > +
> > >  static int do_skeleton(int argc, char **argv)
> > >  {
> > >         char header_guard[MAX_OBJ_NAME_LEN + sizeof("__SKEL_H__")];
> > > @@ -986,6 +1076,11 @@ static int do_skeleton(int argc, char **argv)
> > >                 goto out;
> > >         }
> > >
> > > +       if (json_output) {
> > > +               err = gen_json(obj, obj_name, file_sz, (uint8_t *)obj_data);
> > > +               goto out;
> > > +       }
> > > +
> > >         bpf_object__for_each_map(map, obj) {
> > >                 if (!get_map_ident(map, ident, sizeof(ident))) {
> > >                         p_err("ignoring unrecognized internal map '%s'...",
> > > --
> > > 2.38.1
> > >
> >
>