[PATCH 4/4] perf annotate-data: Adjust type offset for flex-array

[Namhyung Kim <namhyung@kernel.org>]

The flex array members are located beyond the original type size.  Also
it needs to adjust the offset in an array to find a corresponding
element using module operation.  Note that we focus on access to type and
field, so array index is not important.

Make sure to find a field name for flex arrays.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/annotate-data.c | 73 ++++++++++++++++++++++++++++++---
 1 file changed, 67 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index ad043403ced58d98..0789a8cbea7c0355 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -332,19 +332,40 @@ static void delete_members(struct annotated_member *member)
 }
 
 static int fill_member_name(char *buf, size_t sz, struct annotated_member *m,
-			    int offset, bool first)
+			    int offset, bool first, bool has_flex_array)
 {
 	struct annotated_member *child;
+	bool found = false;
+	int len;
 
 	if (list_empty(&m->children))
 		return 0;
 
 	list_for_each_entry(child, &m->children, node) {
-		int len;
-
 		if (offset < child->offset || offset >= child->offset + child->size)
 			continue;
 
+		found = true;
+		break;
+	}
+
+	if (!found && has_flex_array) {
+		/*
+		 * It may have an intermediate struct that has another struct that
+		 * contains a flex array.  In that case, the outer struct itself is
+		 * has no array and the size is less than the offset so the above
+		 * logic won't find the outer struct at the offset.  Let's use the
+		 * last struct if it couldn't find a member for the flex array.
+		 */
+		child = list_last_entry(&m->children, struct annotated_member, node);
+
+		if (!strstr(child->type_name, "struct "))
+			return 0;
+
+		found = true;
+	}
+
+	if (found) {
 		/* It can have anonymous struct/union members */
 		if (child->var_name) {
 			len = scnprintf(buf, sz, "%s%s",
@@ -354,15 +375,37 @@ static int fill_member_name(char *buf, size_t sz, struct annotated_member *m,
 			len = 0;
 		}
 
-		return fill_member_name(buf + len, sz - len, child, offset, first) + len;
+		return fill_member_name(buf + len, sz - len, child, offset, first,
+					has_flex_array) + len;
 	}
+
 	return 0;
 }
 
 int annotated_data_type__get_member_name(struct annotated_data_type *adt,
 					 char *buf, size_t sz, int member_offset)
 {
-	return fill_member_name(buf, sz, &adt->self, member_offset, /*first=*/true);
+	return fill_member_name(buf, sz, &adt->self, member_offset, /*first=*/true,
+				adt->flex_array);
+}
+
+static struct annotated_member *find_flex_array(struct annotated_member *m, int offset)
+{
+	struct annotated_member *child;
+
+	if (list_empty(&m->children))
+		return NULL;
+
+	child = list_last_entry(&m->children, struct annotated_member, node);
+	if (offset == child->offset && strstr(child->type_name, "[]"))
+		return child;
+
+	return find_flex_array(child, offset);
+}
+
+static struct annotated_member *get_flex_array_member(struct annotated_data_type *adt)
+{
+	return find_flex_array(&adt->self, adt->self.size);
 }
 
 static struct annotated_data_type *dso__findnew_data_type(struct dso *dso,
@@ -1743,6 +1786,7 @@ struct annotated_data_type *find_data_type(struct data_loc_info *dloc)
 {
 	struct dso *dso = map__dso(dloc->ms->map);
 	Dwarf_Die type_die;
+	struct annotated_data_type *result;
 
 	/*
 	 * The type offset is the same as instruction offset by default.
@@ -1755,7 +1799,24 @@ struct annotated_data_type *find_data_type(struct data_loc_info *dloc)
 	if (find_data_type_die(dloc, &type_die) < 0)
 		return NULL;
 
-	return dso__findnew_data_type(dso, &type_die);
+	result = dso__findnew_data_type(dso, &type_die);
+	if (result == NULL)
+		return NULL;
+
+	if (result->flex_array && dloc->type_offset > result->self.size) {
+		struct annotated_member *flex_array = get_flex_array_member(result);
+		if (flex_array) {
+			int offset = dloc->type_offset;
+
+			/* adjust offset in the flex array */
+			offset -= result->self.size;
+			offset %= flex_array->size;
+			offset += result->self.size;
+
+			dloc->type_offset = offset;
+		}
+	}
+	return result;
 }
 
 static size_t data_type_hash(long key, void *ctx __maybe_unused)
-- 
2.55.0.1032.g73a4cd73de-goog