btf_loader: Initial support for BTF_KIND_DECL_TAGtmp.masternext

For now for just the first one found for a given tag (function,
class_member, etc).

Pretty print it initially just on functions, with it we can test the
kfunc decl tags:

  $ pfunct --prototypes -F btf vmlinux.btf.decl_tag,decl_tag_kfuncs | grep ^bpf_kfunc | head
  bpf_kfunc void cubictcp_init(struct sock * sk);
  bpf_kfunc void cubictcp_cwnd_event(struct sock * sk, enum tcp_ca_event event);
  bpf_kfunc void cubictcp_cong_avoid(struct sock * sk, u32 ack, u32 acked);
  bpf_kfunc u32 cubictcp_recalc_ssthresh(struct sock * sk);
  bpf_kfunc void cubictcp_state(struct sock * sk, u8 new_state);
  bpf_kfunc void cubictcp_acked(struct sock * sk, const struct ack_sample  * sample);
  bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css * it, struct cgroup_subsys_state * start, unsigned int flags);
  bpf_kfunc struct cgroup_subsys_state * bpf_iter_css_next(struct bpf_iter_css * it);
  bpf_kfunc void bpf_iter_css_destroy(struct bpf_iter_css * it);
  bpf_kfunc s64 bpf_map_sum_elem_count(const struct bpf_map  * map);
  $ pfunct --prototypes -F btf vmlinux.btf.decl_tag,decl_tag_kfuncs | grep ^bpf_kfunc | wc -l
  116
  $

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

4 files changed, 36 insertions, 0 deletions

diff --git a/btf_loader.c b/btf_loader.c
index 57d6d007..e0d029a1 100644
--- a/btf_loader.c
+++ b/btf_loader.c
@@ -454,6 +454,34 @@ static int create_new_tag(struct cu *cu, int type, const struct btf_type *tp, ui
 	return 0;
 }
 
+static int process_decl_tag(struct cu *cu, const struct btf_type *tp)
+{
+	struct tag *tag = cu__type(cu, tp->type);
+
+	if (tag == NULL)
+		tag = cu__function(cu, tp->type);
+
+	if (tag == NULL)
+		tag = cu__tag(cu, tp->type);
+
+	if (tag == NULL) {
+		printf("WARNING: BTF_KIND_DECL_TAG for unknown BTF id %d\n", tp->type);
+		return 0;
+	}
+
+	const char *attribute = cu__btf_str(cu, tp->name_off);
+
+	if (tag->attribute != NULL) {
+		char bf[128];
+		printf("WARNING: still unsuported BTF_KIND_DECL_TAG(%s) for %s already with attribute (%s), ignoring\n",
+		       attribute, tag__name(tag, cu, bf, sizeof(bf), NULL), tag->attribute);
+	} else {
+		tag->attribute = attribute;
+	}
+
+	return 0;
+}
+
 static int btf__load_types(struct btf *btf, struct cu *cu)
 {
 	uint32_t type_index;
@@ -522,6 +550,9 @@ static int btf__load_types(struct btf *btf, struct cu *cu)
 		case BTF_KIND_FLOAT:
 			err = create_new_float_type(cu, type_ptr, type_index);
 			break;
+		case BTF_KIND_DECL_TAG:
+			err = process_decl_tag(cu, type_ptr);
+			break;
 		default:
 			fprintf(stderr, "BTF: idx: %d, Unknown kind %d\n", type_index, type);
 			fflush(stderr);
diff --git a/dwarf_loader.c b/dwarf_loader.c
index b15cf543..f59477b4 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -498,6 +498,7 @@ static void tag__init(struct tag *tag, struct cu *cu, Dwarf_Die *die)
 
 	dtag->abstract_origin = attr_type(die, DW_AT_abstract_origin);
 	tag->recursivity_level = 0;
+	tag->attribute = NULL;
 
 	if (cu->extra_dbg_info) {
 		pthread_mutex_lock(&libdw__lock);
diff --git a/dwarves.h b/dwarves.h
index 7d566b60..f5ae79ff 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -493,6 +493,7 @@ struct tag {
 	bool		 top_level;
 	bool		 has_btf_type_tag;
 	uint16_t	 recursivity_level;
+	const char	 *attribute;
 	void		 *priv;
 };
 
diff --git a/dwarves_fprintf.c b/dwarves_fprintf.c
index f3bf96f5..54d2fc23 100644
--- a/dwarves_fprintf.c
+++ b/dwarves_fprintf.c
@@ -1406,6 +1406,9 @@ static size_t function__fprintf(const struct tag *tag, const struct cu *cu,
 	size_t printed = 0;
 	bool inlined = !conf->strip_inline && function__declared_inline(func);
 
+	if (tag->attribute)
+		printed += fprintf(fp, "%s ", tag->attribute);
+
 	if (func->virtuality == DW_VIRTUALITY_virtual ||
 	    func->virtuality == DW_VIRTUALITY_pure_virtual)
 		printed += fprintf(fp, "virtual ");