[PATCH 2/4] perf dwarf-aux: Add die_has_flex_array() helper

[Namhyung Kim <namhyung@kernel.org>]

The die_has_flex_array() returns true when the given type is a struct
and contains an array at the end of the struct.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/dwarf-aux.c | 57 +++++++++++++++++++++++++++++++++++++
 tools/perf/util/dwarf-aux.h |  3 ++
 2 files changed, 60 insertions(+)

diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index d7160f87ac7d7ab3..98d018798fa750ae 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -2180,3 +2180,60 @@ Dwarf_Die *die_deref_ptr_type(Dwarf_Die *ptr_die, int offset,
 
 	return die_get_member_type(&type_die, offset, die_mem);
 }
+
+static bool __die_find_last_member(Dwarf_Die *parent_die, Dwarf_Die *die_mem)
+{
+	Dwarf_Die tmp_die;
+	bool found = false;
+
+	if (dwarf_child(parent_die, &tmp_die))
+		return false;
+
+	do {
+		if (dwarf_tag(&tmp_die) == DW_TAG_member) {
+			memcpy(die_mem, &tmp_die, sizeof(tmp_die));
+			found = true;
+		}
+	} while (dwarf_siblingof(&tmp_die, &tmp_die) == 0);
+
+	return found;
+}
+
+/**
+ * die_has_flex_array - Check if the given type has a flex-array at the end
+ * @parent_die: a pointer to type DIE
+ *
+ * This function returns %true iff @parent_die is a struct type and has an
+ * array at the end.  Note that the flex-array has no element, it should have
+ * no size and the parent size doesn't include the flex-array.  So it should
+ * locate at the offset of the parent size.
+ *
+ * For simplicity, it assumes the parent size of aligned with the flex-array.
+ */
+bool die_has_flex_array(Dwarf_Die *parent_die)
+{
+	Dwarf_Die die_mem, type_die;
+	Dwarf_Word size, loc;
+
+	if (dwarf_tag(parent_die) != DW_TAG_structure_type)
+		return false;
+
+	if (dwarf_aggregate_size(parent_die, &size) < 0)
+		return false;
+
+	/* get the member field at the end of the struct */
+	if (!__die_find_last_member(parent_die, &die_mem))
+		return false;
+
+	/* get the type of the member */
+	if (die_get_real_type(&die_mem, &type_die) == NULL)
+		return false;
+
+	if (dwarf_tag(&type_die) == DW_TAG_array_type)
+		return die_get_data_member_location(&die_mem, &loc) == 0 && loc == size;
+
+	if (dwarf_tag(&type_die) == DW_TAG_structure_type)
+		return die_has_flex_array(&type_die);
+
+	return false;
+}
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index 161f0bf980b6ee6a..9b662db710220522 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -189,4 +189,7 @@ void die_collect_global_vars(Dwarf_Die *cu_die, struct die_var_type **var_types)
 /* Get the frame base information from CFA */
 int die_get_cfa(Dwarf *dwarf, u64 pc, int *preg, int *poffset);
 
+/* Check whether given type has a flex array */
+bool die_has_flex_array(Dwarf_Die *parent_die);
+
 #endif /* _DWARF_AUX_H */
-- 
2.55.0.1032.g73a4cd73de-goog