[PATCH dwarves v2 2/2] btf_encoder: generate BTF_KIND_DECL_TAGs for typedef btf_decl_tag attributes

[Yonghong Song <yhs@xxxxxx>]

Emit BTF BTF_KIND_DECL_TAGs for btf_decl_tag attributes attached to
typedef declarations. The following is a simple example:
  $ cat t.c
    #define __tag1 __attribute__((btf_decl_tag("tag1")))
    #define __tag2 __attribute__((btf_decl_tag("tag2")))
    typedef struct { int a; int b; } __t __tag1 __tag2;
    __t g;
  $ clang -O2 -g -c t.c
  $ pahole -JV t.o
    btf_encoder__new: 't.o' doesn't have '.data..percpu' section
    Found 0 per-CPU variables!
    File t.o:
    [1] TYPEDEF __t type_id=2
    [2] STRUCT (anon) size=8
            a type_id=3 bits_offset=0
            b type_id=3 bits_offset=32
    [3] INT int size=4 nr_bits=32 encoding=SIGNED
    [4] DECL_TAG tag1 type_id=1 component_idx=-1
    [5] DECL_TAG tag2 type_id=1 component_idx=-1

Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
 btf_encoder.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index 40f6aa3..117656e 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -1438,9 +1438,21 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu)
 
 	cu__for_each_type(cu, core_id, pos) {
 		struct namespace *ns;
+		const char *tag_name;
 
-		if (pos->tag != DW_TAG_structure_type && pos->tag != DW_TAG_union_type)
+		switch (pos->tag) {
+		case DW_TAG_structure_type:
+			tag_name = "struct";
+			break;
+		case DW_TAG_union_type:
+			tag_name = "union";
+			break;
+		case DW_TAG_typedef:
+			tag_name = "typedef";
+			break;
+		default:
 			continue;
+		}
 
 		btf_type_id = type_id_off + core_id;
 		ns = tag__namespace(pos);
@@ -1448,8 +1460,7 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu)
 			tag_type_id = btf_encoder__add_decl_tag(encoder, annot->value, btf_type_id, annot->component_idx);
 			if (tag_type_id < 0) {
 				fprintf(stderr, "error: failed to encode tag '%s' to %s '%s' with component_idx %d\n",
-					annot->value, pos->tag == DW_TAG_structure_type ? "struct" : "union",
-					namespace__name(ns), annot->component_idx);
+					annot->value, tag_name, namespace__name(ns), annot->component_idx);
 				goto out;
 			}
 		}
-- 
2.30.2