bpftool: Dump more info about DATASEC members

Dump succinct information for each member of DATASEC: its kinds and name. This
is extremely helpful to see at a quick glance what is inside each DATASEC of
a given BTF. Without this, one has to jump around BTF data to just find out
the name of a VAR or FUNC. DATASEC's var_secinfo member is special in that
regard because it doesn't itself contain the name of the member, delegating
that to the referenced VAR and FUNC kinds. Other kinds, like
STRUCT/UNION/FUNC/ENUM, encode member names directly and thus are clearly
identifiable in BTF dump.

The new output looks like this:

[35] DATASEC '.bss' size=0 vlen=6
        type_id=8 offset=0 size=4 (VAR 'input_bss1')
        type_id=13 offset=0 size=4 (VAR 'input_bss_weak')
        type_id=16 offset=0 size=4 (VAR 'output_bss1')
        type_id=17 offset=0 size=4 (VAR 'output_data1')
        type_id=18 offset=0 size=4 (VAR 'output_rodata1')
        type_id=20 offset=0 size=8 (VAR 'output_sink1')
[36] DATASEC '.data' size=0 vlen=2
        type_id=9 offset=0 size=4 (VAR 'input_data1')
        type_id=14 offset=0 size=4 (VAR 'input_data_weak')
[37] DATASEC '.kconfig' size=0 vlen=2
        type_id=25 offset=0 size=4 (VAR 'LINUX_KERNEL_VERSION')
        type_id=28 offset=0 size=1 (VAR 'CONFIG_BPF_SYSCALL')
[38] DATASEC '.ksyms' size=0 vlen=1
        type_id=30 offset=0 size=1 (VAR 'bpf_link_fops')
[39] DATASEC '.rodata' size=0 vlen=2
        type_id=12 offset=0 size=4 (VAR 'input_rodata1')
        type_id=15 offset=0 size=4 (VAR 'input_rodata_weak')
[40] DATASEC 'license' size=0 vlen=1
        type_id=24 offset=0 size=4 (VAR 'LICENSE')

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210423181348.1801389-3-andrii@kernel.org

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 001749a..385d5c9 100644 (file)
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -100,26 +100,28 @@ static const char *btf_str(const struct btf *btf, __u32 off)
        return btf__name_by_offset(btf, off) ? : "(invalid)";
 }
 
+static int btf_kind_safe(int kind)
+{
+       return kind <= BTF_KIND_MAX ? kind : BTF_KIND_UNKN;
+}
+
 static int dump_btf_type(const struct btf *btf, __u32 id,
                         const struct btf_type *t)
 {
        json_writer_t *w = json_wtr;
-       int kind, safe_kind;
-
-       kind = BTF_INFO_KIND(t->info);
-       safe_kind = kind <= BTF_KIND_MAX ? kind : BTF_KIND_UNKN;
+       int kind = btf_kind(t);
 
        if (json_output) {
                jsonw_start_object(w);
                jsonw_uint_field(w, "id", id);
-               jsonw_string_field(w, "kind", btf_kind_str[safe_kind]);
+               jsonw_string_field(w, "kind", btf_kind_str[btf_kind_safe(kind)]);
                jsonw_string_field(w, "name", btf_str(btf, t->name_off));
        } else {
-               printf("[%u] %s '%s'", id, btf_kind_str[safe_kind],
+               printf("[%u] %s '%s'", id, btf_kind_str[btf_kind_safe(kind)],
                       btf_str(btf, t->name_off));
        }
 
-       switch (BTF_INFO_KIND(t->info)) {
+       switch (kind) {
        case BTF_KIND_INT: {
                __u32 v = *(__u32 *)(t + 1);
                const char *enc;
@@ -302,7 +304,8 @@ static int dump_btf_type(const struct btf *btf, __u32 id,
                break;
        }
        case BTF_KIND_DATASEC: {
-               const struct btf_var_secinfo *v = (const void *)(t+1);
+               const struct btf_var_secinfo *v = (const void *)(t + 1);
+               const struct btf_type *vt;
                __u16 vlen = BTF_INFO_VLEN(t->info);
                int i;
 
@@ -324,6 +327,13 @@ static int dump_btf_type(const struct btf *btf, __u32 id,
                        } else {
                                printf("\n\ttype_id=%u offset=%u size=%u",
                                       v->type, v->offset, v->size);
+
+                               if (v->type <= btf__get_nr_types(btf)) {
+                                       vt = btf__type_by_id(btf, v->type);
+                                       printf(" (%s '%s')",
+                                              btf_kind_str[btf_kind_safe(btf_kind(vt))],
+                                              btf_str(btf, vt->name_off));
+                               }
                        }
                }
                if (json_output)