perf probe: Add union member access support

Union members can be accessed with '.' or '->' like data structure
member access

Signed-off-by: Hyunchul Lee <hyc.lee@gmail.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/CANFS6baeuSBxPGQ8SUZWZErJ2bWs-Nojg+FSo138E1QK8bJJig@mail.gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-finder.c

@@ -525,8 +525,10 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
 			return -ENOENT;
 		}
 		/* Verify it is a data structure  */
-		if (dwarf_tag(&type) != DW_TAG_structure_type) {
-			pr_warning("%s is not a data structure.\n", varname);
+		tag = dwarf_tag(&type);
+		if (tag != DW_TAG_structure_type && tag != DW_TAG_union_type) {
+			pr_warning("%s is not a data structure nor an union.\n",
+				   varname);
 			return -EINVAL;
 		}
 
@@ -539,8 +541,9 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
 			*ref_ptr = ref;
 	} else {
 		/* Verify it is a data structure  */
-		if (tag != DW_TAG_structure_type) {
-			pr_warning("%s is not a data structure.\n", varname);
+		if (tag != DW_TAG_structure_type && tag != DW_TAG_union_type) {
+			pr_warning("%s is not a data structure nor an union.\n",
+				   varname);
 			return -EINVAL;
 		}
 		if (field->name[0] == '[') {
@@ -567,10 +570,15 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
 	}
 
 	/* Get the offset of the field */
-	ret = die_get_data_member_location(die_mem, &offs);
-	if (ret < 0) {
-		pr_warning("Failed to get the offset of %s.\n", field->name);
-		return ret;
+	if (tag == DW_TAG_union_type) {
+		offs = 0;
+	} else {
+		ret = die_get_data_member_location(die_mem, &offs);
+		if (ret < 0) {
+			pr_warning("Failed to get the offset of %s.\n",
+				   field->name);
+			return ret;
+		}
 	}
 	ref->offset += (long)offs;