---
 dwarf_loader.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++--
 dwarves.h      |  33 +++++++++++++-
 pahole.c       |   8 ++++
 3 files changed, 153 insertions(+), 4 deletions(-)

diff --git a/dwarf_loader.c b/dwarf_loader.c
index 1b07a62..5b2bebb 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c

@@ -1206,6 +1206,88 @@ static struct tag *die__create_new_tag(Dwarf_Die *die, struct cu *cu)
 	return tag;
 }
 
+static struct btf_type_tag_ptr_type *die__create_new_btf_type_tag_ptr_type(Dwarf_Die *die, struct cu *cu)
+{
+	struct btf_type_tag_ptr_type *tag;
+
+	tag  = tag__alloc_with_spec(cu, sizeof(struct btf_type_tag_ptr_type));
+	if (tag == NULL)
+		return NULL;
+
+	tag__init(&tag->tag, cu, die);
+	tag->tag.has_btf_type_tag = true;
+	INIT_LIST_HEAD(&tag->tags);
+	return tag;
+}
+
+static struct btf_type_tag_type *die__create_new_btf_type_tag_type(Dwarf_Die *die, struct cu *cu,
+								   struct conf_load *conf)
+{
+	struct btf_type_tag_type *tag;
+
+	tag  = tag__alloc_with_spec(cu, sizeof(struct btf_type_tag_type));
+	if (tag == NULL)
+		return NULL;
+
+	tag__init(&tag->tag, cu, die);
+	tag->value = attr_string(die, DW_AT_const_value, conf);
+	return tag;
+}
+
+static struct tag *die__create_new_pointer_tag(Dwarf_Die *die, struct cu *cu,
+					       struct conf_load *conf)
+{
+	struct btf_type_tag_ptr_type *tag = NULL;
+	struct btf_type_tag_type *annot;
+	Dwarf_Die *cdie, child;
+	const char *name;
+	uint32_t id;
+
+	/* If no child tags or skipping btf_type_tag encoding, just create a new tag
+	 * and return
+	 */
+	if (!dwarf_haschildren(die) || dwarf_child(die, &child) != 0 ||
+	    conf->skip_encoding_btf_type_tag)
+		return tag__new(die, cu);
+
+	/* Otherwise, check DW_TAG_LLVM_annotation child tags */
+	cdie = &child;
+	do {
+		if (dwarf_tag(cdie) == DW_TAG_LLVM_annotation) {
+			/* Only check btf_type_tag annotations */
+			name = attr_string(cdie, DW_AT_name, conf);
+			if (strcmp(name, "btf_type_tag") != 0)
+				continue;
+
+			if (tag == NULL) {
+				/* Create a btf_type_tag_ptr type. */
+				tag = die__create_new_btf_type_tag_ptr_type(die, cu);
+				if (!tag)
+					return NULL;
+			}
+
+			/* Create a btf_type_tag type for this annotation. */
+			annot = die__create_new_btf_type_tag_type(cdie, cu, conf);
+			if (annot == NULL)
+				return NULL;
+
+			if (cu__table_add_tag(cu, &annot->tag, &id) < 0)
+				return NULL;
+
+			struct dwarf_tag *dtag = annot->tag.priv;
+			dtag->small_id = id;
+			cu__hash(cu, &annot->tag);
+
+			/* For a list of DW_TAG_LLVM_annotation like tag1 -> tag2 -> tag3,
+			 * the tag->tags contains tag3 -> tag2 -> tag1.
+			 */
+			list_add(&annot->node, &tag->tags);
+		}
+	} while (dwarf_siblingof(cdie, cdie) == 0);
+
+	return tag ? &tag->tag : tag__new(die, cu);
+}
+
 static struct tag *die__create_new_ptr_to_member_type(Dwarf_Die *die,
 						      struct cu *cu)
 {

@@ -1903,12 +1985,13 @@ static struct tag *__die__process_tag(Dwarf_Die *die, struct cu *cu,
 	case DW_TAG_const_type:
 	case DW_TAG_imported_declaration:
 	case DW_TAG_imported_module:
-	case DW_TAG_pointer_type:
 	case DW_TAG_reference_type:
 	case DW_TAG_restrict_type:
 	case DW_TAG_unspecified_type:
 	case DW_TAG_volatile_type:
 		tag = die__create_new_tag(die, cu);		break;
+	case DW_TAG_pointer_type:
+		tag = die__create_new_pointer_tag(die, cu, conf);	break;
 	case DW_TAG_ptr_to_member_type:
 		tag = die__create_new_ptr_to_member_type(die, cu); break;
 	case DW_TAG_enumeration_type:

@@ -2192,6 +2275,26 @@ static void lexblock__recode_dwarf_types(struct lexblock *tag, struct cu *cu)
 	}
 }
 
+static void dwarf_cu__recode_btf_type_tag_ptr(struct btf_type_tag_ptr_type *tag,
+					      uint32_t pointee_type)
+{
+	struct btf_type_tag_type *annot;
+	struct dwarf_tag *annot_dtag;
+	struct tag *prev_tag;
+
+	/* If tag->tags contains tag3 -> tag2 -> tag1, the final type chain
+	 * looks like:
+	 *   pointer -> tag3 -> tag2 -> tag1 -> pointee
+	 */
+	prev_tag = &tag->tag;
+	list_for_each_entry(annot, &tag->tags, node) {
+		annot_dtag = annot->tag.priv;
+		prev_tag->type = annot_dtag->small_id;
+		prev_tag = &annot->tag;
+	}
+	prev_tag->type = pointee_type;
+}
+
 static int tag__recode_dwarf_type(struct tag *tag, struct cu *cu)
 {
 	struct dwarf_tag *dtag = tag->priv;

@@ -2301,7 +2404,10 @@ static int tag__recode_dwarf_type(struct tag *tag, struct cu *cu)
 	}
 
 	if (dtag->type.off == 0) {
-		tag->type = 0; /* void */
+		if (tag->tag != DW_TAG_pointer_type || !tag->has_btf_type_tag)
+			tag->type = 0; /* void */
+		else
+			dwarf_cu__recode_btf_type_tag_ptr(tag__btf_type_tag_ptr(tag), 0);
 		return 0;
 	}
 

@@ -2313,7 +2419,11 @@ check_type:
 		return 0;
 	}
 out:
-	tag->type = dtype->small_id;
+	if (tag->tag != DW_TAG_pointer_type || !tag->has_btf_type_tag)
+		tag->type = dtype->small_id;
+	else
+		dwarf_cu__recode_btf_type_tag_ptr(tag__btf_type_tag_ptr(tag), dtype->small_id);
+
 	return 0;
 }
 

diff --git a/dwarves.h b/dwarves.h
index 0d3e204..4425d3c 100644
--- a/dwarves.h
+++ b/dwarves.h

@@ -63,6 +63,7 @@ struct conf_load {
 	bool			ptr_table_stats;
 	bool			skip_encoding_btf_decl_tag;
 	bool			skip_missing;
+	bool			skip_encoding_btf_type_tag;
 	uint8_t			hashtable_bits;
 	uint8_t			max_hashtable_bits;
 	uint16_t		kabi_prefix_len;

@@ -413,6 +414,7 @@ struct tag {
 	uint16_t	 tag;
 	bool		 visited;
 	bool		 top_level;
+	bool		 has_btf_type_tag;
 	uint16_t	 recursivity_level;
 	void		 *priv;
 };

@@ -533,7 +535,8 @@ static inline int tag__is_tag_type(const struct tag *tag)
 	       tag->tag == DW_TAG_restrict_type ||
 	       tag->tag == DW_TAG_subroutine_type ||
 	       tag->tag == DW_TAG_unspecified_type ||
-	       tag->tag == DW_TAG_volatile_type;
+	       tag->tag == DW_TAG_volatile_type ||
+	       tag->tag == DW_TAG_LLVM_annotation;
 }
 
 static inline const char *tag__decl_file(const struct tag *tag,

@@ -606,6 +609,34 @@ struct llvm_annotation {
 	struct list_head	node;
 };
 
+/** struct btf_type_tag_type - representing a btf_type_tag annotation
+ *
+ * @tag   - DW_TAG_LLVM_annotation tag
+ * @value - btf_type_tag value string
+ * @node  - list_head node
+ */
+struct btf_type_tag_type {
+	struct tag		tag;
+	const char		*value;
+	struct list_head	node;
+};
+
+/** The struct btf_type_tag_ptr_type - type containing both pointer type and
+ *  its btf_type_tag annotations
+ *
+ * @tag  - pointer type tag
+ * @tags - btf_type_tag annotations for the pointer type
+ */
+struct btf_type_tag_ptr_type {
+	struct tag		tag;
+	struct list_head 	tags;
+};
+
+static inline struct btf_type_tag_ptr_type *tag__btf_type_tag_ptr(struct tag *tag)
+{
+	return (struct btf_type_tag_ptr_type *)tag;
+}
+
 /** struct namespace - base class for enums, structs, unions, typedefs, etc
  *
  * @tags - class_member, enumerators, etc

diff --git a/pahole.c b/pahole.c
index 5fc1cca..f3a51cb 100644
--- a/pahole.c
+++ b/pahole.c

@@ -1126,6 +1126,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 #define ARGP_devel_stats	   330
 #define ARGP_skip_encoding_btf_decl_tag 331
 #define ARGP_skip_missing          332
+#define ARGP_skip_encoding_btf_type_tag 333
 
 static const struct argp_option pahole__options[] = {
 	{

@@ -1506,6 +1507,11 @@ static const struct argp_option pahole__options[] = {
 		.key  = ARGP_skip_missing,
 		.doc = "skip missing types passed to -C rather than stop",
 	},
+	{
+		.name = "skip_encoding_btf_type_tag",
+		.key  = ARGP_skip_encoding_btf_type_tag,
+		.doc  = "Do not encode TAGs in BTF."
+	},
 	{
 		.name = NULL,
 	}

@@ -1658,6 +1664,8 @@ static error_t pahole__options_parser(int key, char *arg,
 		conf_load.skip_encoding_btf_decl_tag = true;	break;
 	case ARGP_skip_missing:
 		conf_load.skip_missing = true;          break;
+	case ARGP_skip_encoding_btf_type_tag:
+		conf_load.skip_encoding_btf_type_tag = true;	break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}

-- 
2.30.2