[PATCH v4 4/6] perf annotate-data: Bound the member nesting recursion

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

Members are added recursively, and a broken DIE can make a member's
type point back at one of its own ancestors, recursing until the stack
is gone; nothing usable comes out of nesting members 32 deep anyway, so
stop there, marking the member as truncated and giving up on member
types that don't resolve.

The check is where the children of an aggregate would be expanded, so
only struct/union members are marked as truncated.

Assisted-by: LLM
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/annotate-data.c | 20 ++++++++++++++++++--
 tools/perf/util/annotate-data.h |  3 +++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index bc9698abc6a9e055..39e0b125a6cc1eca 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -222,6 +222,12 @@ static bool data_type_less(struct rb_node *node_a, const struct rb_node *node_b)
 	return strcmp(a->self.type_name, b->self.type_name) < 0;
 }
 
+/*
+ * A broken type can point back at one of its own ancestors: bound the
+ * nesting so it doesn't recurse until the stack is gone.
+ */
+#define MAX_MEMBER_DEPTH 32
+
 /* Recursively add new members for struct/union */
 static int __add_member_cb(Dwarf_Die *die, void *arg)
 {
@@ -236,6 +242,9 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
 	if (dwarf_tag(die) != DW_TAG_member)
 		return DIE_FIND_CB_SIBLING;
 
+	if (die_get_real_type(die, &die_mem) == NULL)
+		return DIE_FIND_CB_SIBLING;
+
 	member = zalloc(sizeof(*member));
 	if (member == NULL)
 		return DIE_FIND_CB_END;
@@ -248,8 +257,6 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
 	if (die_get_typename(die, &sb) < 0)
 		strbuf_add(&sb, "(unknown type)", 14);
 
-	die_get_real_type(die, &die_mem);
-
 	if (dwarf_aggregate_size(&die_mem, &size) < 0 || size == 0) {
 		if (dwarf_tag(&die_mem) == DW_TAG_array_type) { /* flex-array? */
 			die_get_real_type(&die_mem, &die_mem);
@@ -299,6 +306,7 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
 	}
 	member->size = size;
 	member->offset = loc + parent->offset;
+	member->depth = parent->depth + 1;
 	INIT_LIST_HEAD(&member->children);
 
 	list_for_each_entry_reverse(prev, &parent->children, node) {
@@ -313,6 +321,14 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
 		member->is_union = true;
 		/* fall through */
 	case DW_TAG_structure_type:
+		/* Only aggregates have children to expand, so only they get truncated. */
+		if (member->depth >= MAX_MEMBER_DEPTH) {
+			/* Reported by the JSON exporter so consumers can tell a truncated tree. */
+			member->truncated = true;
+			pr_debug_dtp("member nesting limit reached at %s\n",
+				     member->type_name ?: "(unknown type)");
+			break;
+		}
 		die_find_child(&die_mem, __add_member_cb, member, &die_mem);
 		break;
 	default:
diff --git a/tools/perf/util/annotate-data.h b/tools/perf/util/annotate-data.h
index 14b8113521a927cf..ca0abfb2a036d229 100644
--- a/tools/perf/util/annotate-data.h
+++ b/tools/perf/util/annotate-data.h
@@ -61,6 +61,9 @@ struct annotated_member {
 	int size;
 	bool is_union;
 	bool is_flex_array;
+	unsigned int depth;
+	/* Children not expanded because the nesting limit was reached */
+	bool truncated;
 };
 
 /**
-- 
2.53.0