core: Record if a CU has a DW_TAG_unspecified_type

So that the BTF encoder can turn such functions into returning void
instead, as BTF doesn't have a representation for such tags.

First noticed with Linux circa v6.1 built with GNU AS 2.39.50, git
HEAD at the time building a .S file where the entry_ibpb assembly
"function" was encoded as DWARF with DW_TAG_unspecified_type as its
return type.

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

2 files changed, 14 insertions, 1 deletions

diff --git a/dwarf_loader.c b/dwarf_loader.c
index 28a912ec..03ac8718 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -2006,10 +2006,12 @@ static struct tag *__die__process_tag(Dwarf_Die *die, struct cu *cu,
 	case DW_TAG_imported_module:
 	case DW_TAG_reference_type:
 	case DW_TAG_restrict_type:
-	case DW_TAG_unspecified_type:
 	case DW_TAG_volatile_type:
 	case DW_TAG_atomic_type:
 		tag = die__create_new_tag(die, cu);		break;
+	case DW_TAG_unspecified_type:
+		cu->unspecified_type.tag =
+			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:
@@ -2077,6 +2079,8 @@ static int die__process_unit(Dwarf_Die *die, struct cu *cu, struct conf_load *co
 		cu__hash(cu, tag);
 		struct dwarf_tag *dtag = tag->priv;
 		dtag->small_id = id;
+		if (tag->tag == DW_TAG_unspecified_type)
+			cu->unspecified_type.type = id;
 	} while (dwarf_siblingof(die, die) == 0);
 
 	return 0;
@@ -2512,6 +2516,7 @@ static int cu__recode_dwarf_types_table(struct cu *cu,
 			if (tag__recode_dwarf_type(tag, cu))
 				return -1;
 	}
+
 	return 0;
 }
 
diff --git a/dwarves.h b/dwarves.h
index 9aaf87f2..f8b15002 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -230,6 +230,10 @@ struct debug_fmt_ops {
 	bool		   has_alignment_info;
 };
 
+/*
+ * unspecified_type: If this CU has a DW_TAG_unspecified_type, as BTF doesn't have a representation for this
+ * 		     and thus we need to check functions returning this to convert it to void.
+ */
 struct cu {
 	struct list_head node;
 	struct list_head tags;
@@ -238,6 +242,10 @@ struct cu {
 	struct ptr_table functions_table;
 	struct ptr_table tags_table;
 	struct rb_root	 functions;
+	struct {
+		struct tag	 *tag;
+		uint32_t	 type;
+	} unspecified_type;
 	char		 *name;
 	char		 *filename;
 	void 		 *priv;