perf expr: Force encapsulation on expr_id_data

This patch resolves some undefined behavior where variables in
expr_id_data were accessed (for debugging) without being defined. To
better enforce the tagged union behavior, the struct is moved into
expr.c and accessors provided. Tag values (kinds) are explicitly
identified.

Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-By: Kajol Jain<kjain@linux.ibm.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20200826153055.2067780-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 59 insertions, 9 deletions

diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
index 53482ef53c41..a850fd0be3ee 100644
--- a/tools/perf/util/expr.c
+++ b/tools/perf/util/expr.c
@@ -17,6 +17,29 @@
 extern int expr_debug;
 #endif
 
+struct expr_id_data {
+	union {
+		double val;
+		struct {
+			double val;
+			const char *metric_name;
+			const char *metric_expr;
+		} ref;
+		struct expr_id	*parent;
+	};
+
+	enum {
+		/* Holding a double value. */
+		EXPR_ID_DATA__VALUE,
+		/* Reference to another metric. */
+		EXPR_ID_DATA__REF,
+		/* A reference but the value has been computed. */
+		EXPR_ID_DATA__REF_VALUE,
+		/* A parent is remembered for the recursion check. */
+		EXPR_ID_DATA__PARENT,
+	} kind;
+};
+
 static size_t key_hash(const void *key, void *ctx __maybe_unused)
 {
 	const char *str = (const char *)key;
@@ -48,6 +71,7 @@ int expr__add_id(struct expr_parse_ctx *ctx, const char *id)
 		return -ENOMEM;
 
 	data_ptr->parent = ctx->parent;
+	data_ptr->kind = EXPR_ID_DATA__PARENT;
 
 	ret = hashmap__set(&ctx->ids, id, data_ptr,
 			   (const void **)&old_key, (void **)&old_data);
@@ -69,7 +93,7 @@ int expr__add_id_val(struct expr_parse_ctx *ctx, const char *id, double val)
 	if (!data_ptr)
 		return -ENOMEM;
 	data_ptr->val = val;
-	data_ptr->is_ref = false;
+	data_ptr->kind = EXPR_ID_DATA__VALUE;
 
 	ret = hashmap__set(&ctx->ids, id, data_ptr,
 			   (const void **)&old_key, (void **)&old_data);
@@ -114,8 +138,7 @@ int expr__add_ref(struct expr_parse_ctx *ctx, struct metric_ref *ref)
 	 */
 	data_ptr->ref.metric_name = ref->metric_name;
 	data_ptr->ref.metric_expr = ref->metric_expr;
-	data_ptr->ref.counted = false;
-	data_ptr->is_ref = true;
+	data_ptr->kind = EXPR_ID_DATA__REF;
 
 	ret = hashmap__set(&ctx->ids, name, data_ptr,
 			   (const void **)&old_key, (void **)&old_data);
@@ -148,17 +171,30 @@ int expr__resolve_id(struct expr_parse_ctx *ctx, const char *id,
 
 	data = *datap;
 
-	pr_debug2("lookup: is_ref %d, counted %d, val %f: %s\n",
-		  data->is_ref, data->ref.counted, data->val, id);
-
-	if (data->is_ref && !data->ref.counted) {
-		data->ref.counted = true;
+	switch (data->kind) {
+	case EXPR_ID_DATA__VALUE:
+		pr_debug2("lookup(%s): val %f\n", id, data->val);
+		break;
+	case EXPR_ID_DATA__PARENT:
+		pr_debug2("lookup(%s): parent %s\n", id, data->parent->id);
+		break;
+	case EXPR_ID_DATA__REF:
+		pr_debug2("lookup(%s): ref metric name %s\n", id,
+			data->ref.metric_name);
 		pr_debug("processing metric: %s ENTRY\n", id);
-		if (expr__parse(&data->val, ctx, data->ref.metric_expr, 1)) {
+		data->kind = EXPR_ID_DATA__REF_VALUE;
+		if (expr__parse(&data->ref.val, ctx, data->ref.metric_expr, 1)) {
 			pr_debug("%s failed to count\n", id);
 			return -1;
 		}
 		pr_debug("processing metric: %s EXIT: %f\n", id, data->val);
+		break;
+	case EXPR_ID_DATA__REF_VALUE:
+		pr_debug2("lookup(%s): ref val %f metric name %s\n", id,
+			data->ref.val, data->ref.metric_name);
+		break;
+	default:
+		assert(0);  /* Unreachable. */
 	}
 
 	return 0;
@@ -241,3 +277,17 @@ int expr__find_other(const char *expr, const char *one,
 
 	return ret;
 }
+
+double expr_id_data__value(const struct expr_id_data *data)
+{
+	if (data->kind == EXPR_ID_DATA__VALUE)
+		return data->val;
+	assert(data->kind == EXPR_ID_DATA__REF_VALUE);
+	return data->ref.val;
+}
+
+struct expr_id *expr_id_data__parent(struct expr_id_data *data)
+{
+	assert(data->kind == EXPR_ID_DATA__PARENT);
+	return data->parent;
+}