bpf: bpftool support for dumping data/bss/rodata sections

Add the ability to bpftool to handle BTF Var and DataSec kinds
in order to dump them out of btf_dumper_type(). The value has a
single object with the section name, which itself holds an array
of variables it dumps. A single variable is an object by itself
printed along with its name. From there further type information
is dumped along with corresponding value information.

Example output from .rodata:

  # ./bpftool m d i 150
  [{
          "value": {
              ".rodata": [{
                      "load_static_data.bar": 18446744073709551615
                  },{
                      "num2": 24
                  },{
                      "num5": 43947
                  },{
                      "num6": 171
                  },{
                      "str0": [97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,0,0,0,0,0,0
                      ]
                  },{
                      "struct0": {
                          "a": 42,
                          "b": 4278120431,
                          "c": 1229782938247303441
                      }
                  },{
                      "struct2": {
                          "a": 0,
                          "b": 0,
                          "c": 0
                      }
                  }
              ]
          }
      }
  ]

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index e0c650d91784..e96903078991 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -153,11 +153,13 @@ static int do_dump_btf(const struct btf_dumper *d,
 	/* start of key-value pair */
 	jsonw_start_object(d->jw);
 
-	jsonw_name(d->jw, "key");
+	if (map_info->btf_key_type_id) {
+		jsonw_name(d->jw, "key");
 
-	ret = btf_dumper_type(d, map_info->btf_key_type_id, key);
-	if (ret)
-		goto err_end_obj;
+		ret = btf_dumper_type(d, map_info->btf_key_type_id, key);
+		if (ret)
+			goto err_end_obj;
+	}
 
 	if (!map_is_per_cpu(map_info->type)) {
 		jsonw_name(d->jw, "value");