list: don't multiple-evaluate arguments to tlist_top and tlist_tail

ccan/list/list.h

@@ -279,8 +279,15 @@ static inline void list_del_from(struct list_head *h, struct list_node *n)
  *	struct child *first;
  *	first = list_top(&parent->children, struct child, list);
  */
-#define list_top(h, type, member) \
-	(list_empty(h) ? NULL : list_entry((h)->n.next, type, member))
+#define list_top(h, type, member)					\
+	((type *)list_top_((h), container_off((h)->n.next, type, member)))
+
+static inline const void *list_top_(const struct list_head *h, size_t off)
+{
+	if (list_empty(h))
+		return NULL;
+	return (const char *)h->n.next - off;
+}
 
 /**
  * list_tail - get the last entry in a list
@@ -295,11 +302,18 @@ static inline void list_del_from(struct list_head *h, struct list_node *n)
  *	last = list_tail(&parent->children, struct child, list);
  */
 #define list_tail(h, type, member) \
-	(list_empty(h) ? NULL : list_entry((h)->n.prev, type, member))
+	((type *)list_tail_((h), container_off((h)->n.next, type, member)))
+
+static inline const void *list_tail_(const struct list_head *h, size_t off)
+{
+	if (list_empty(h))
+		return NULL;
+	return (const char *)h->n.prev - off;
+}
 
 /**
  * list_for_each - iterate through a list.
- * @h: the list_head
+ * @h: the list_head (warning: evaluated multiple times!)
  * @i: the structure containing the list_node
  * @member: the list_node member of the structure
  *

ccan/list/test/run-single-eval.c

+/* Make sure macros only evaluate their args once. */
+#include <ccan/list/list.h>
+#include <ccan/tap/tap.h>
+#include <ccan/list/list.c>
+
+struct parent {
+	const char *name;
+	struct list_head children;
+	unsigned int num_children;
+	int eval_count;
+};
+
+struct child {
+	const char *name;
+	struct list_node list;
+};
+
+static LIST_HEAD(static_list);
+
+#define ref(obj, counter) ((counter)++, (obj))
+
+int main(int argc, char *argv[])
+{
+	struct parent parent;
+	struct child c1, c2, c3, *c, *n;
+	unsigned int i;
+	unsigned int static_count = 0, parent_count = 0, list_count = 0,
+		node_count = 0;
+	struct list_head list = LIST_HEAD_INIT(list);
+
+	plan_tests(74);
+	/* Test LIST_HEAD, LIST_HEAD_INIT, list_empty and check_list */
+	ok1(list_empty(ref(&static_list, static_count)));
+	ok1(static_count == 1);
+	ok1(list_check(ref(&static_list, static_count), NULL));
+	ok1(static_count == 2);
+	ok1(list_empty(ref(&list, list_count)));
+	ok1(list_count == 1);
+	ok1(list_check(ref(&list, list_count), NULL));
+	ok1(list_count == 2);
+
+	parent.num_children = 0;
+	list_head_init(ref(&parent.children, parent_count));
+	ok1(parent_count == 1);
+	/* Test list_head_init */
+	ok1(list_empty(ref(&parent.children, parent_count)));
+	ok1(parent_count == 2);
+	ok1(list_check(ref(&parent.children, parent_count), NULL));
+	ok1(parent_count == 3);
+
+	c2.name = "c2";
+	list_add(ref(&parent.children, parent_count), &c2.list);
+	ok1(parent_count == 4);
+	/* Test list_add and !list_empty. */
+	ok1(!list_empty(ref(&parent.children, parent_count)));
+	ok1(parent_count == 5);
+	ok1(c2.list.next == &parent.children.n);
+	ok1(c2.list.prev == &parent.children.n);
+	ok1(parent.children.n.next == &c2.list);
+	ok1(parent.children.n.prev == &c2.list);
+	/* Test list_check */
+	ok1(list_check(ref(&parent.children, parent_count), NULL));
+	ok1(parent_count == 6);
+
+	c1.name = "c1";
+	list_add(ref(&parent.children, parent_count), &c1.list);
+	ok1(parent_count == 7);
+	/* Test list_add and !list_empty. */
+	ok1(!list_empty(ref(&parent.children, parent_count)));
+	ok1(parent_count == 8);
+	ok1(c2.list.next == &parent.children.n);
+	ok1(c2.list.prev == &c1.list);
+	ok1(parent.children.n.next == &c1.list);
+	ok1(parent.children.n.prev == &c2.list);
+	ok1(c1.list.next == &c2.list);
+	ok1(c1.list.prev == &parent.children.n);
+	/* Test list_check */
+	ok1(list_check(ref(&parent.children, parent_count), NULL));
+	ok1(parent_count == 9);
+
+	c3.name = "c3";
+	list_add_tail(ref(&parent.children, parent_count), &c3.list);
+	ok1(parent_count == 10);
+	/* Test list_add_tail and !list_empty. */
+	ok1(!list_empty(ref(&parent.children, parent_count)));
+	ok1(parent_count == 11);
+	ok1(parent.children.n.next == &c1.list);
+	ok1(parent.children.n.prev == &c3.list);
+	ok1(c1.list.next == &c2.list);
+	ok1(c1.list.prev == &parent.children.n);
+	ok1(c2.list.next == &c3.list);
+	ok1(c2.list.prev == &c1.list);
+	ok1(c3.list.next == &parent.children.n);
+	ok1(c3.list.prev == &c2.list);
+	/* Test list_check */
+	ok1(list_check(ref(&parent.children, parent_count), NULL));
+	ok1(parent_count == 12);
+
+	/* Test list_check_node */
+	ok1(list_check_node(&c1.list, NULL));
+	ok1(list_check_node(&c2.list, NULL));
+	ok1(list_check_node(&c3.list, NULL));
+
+	/* Test list_top */
+	ok1(list_top(ref(&parent.children, parent_count), struct child, list) == &c1);
+	ok1(parent_count == 13);
+
+	/* Test list_tail */
+	ok1(list_tail(ref(&parent.children, parent_count), struct child, list) == &c3);
+	ok1(parent_count == 14);
+
+	/* Test list_for_each. */
+	i = 0;
+	list_for_each(&parent.children, c, list) {
+		switch (i++) {
+		case 0:
+			ok1(c == &c1);
+			break;
+		case 1:
+			ok1(c == &c2);
+			break;
+		case 2:
+			ok1(c == &c3);
+			break;
+		}
+		if (i > 2)
+			break;
+	}
+	ok1(i == 3);
+
+	/* Test list_for_each_safe, list_del and list_del_from. */
+	i = 0;
+	list_for_each_safe(&parent.children, c, n, list) {
+		switch (i++) {
+		case 0:
+			ok1(c == &c1);
+			list_del(ref(&c->list, node_count));
+			ok1(node_count == 1);
+			break;
+		case 1:
+			ok1(c == &c2);
+			list_del_from(ref(&parent.children, parent_count),
+				      ref(&c->list, node_count));
+			ok1(node_count == 2);
+			break;
+		case 2:
+			ok1(c == &c3);
+			list_del_from(ref(&parent.children, parent_count),
+				      ref(&c->list, node_count));
+			ok1(node_count == 3);
+			break;
+		}
+		ok1(list_check(ref(&parent.children, parent_count), NULL));
+		if (i > 2)
+			break;
+	}
+	ok1(i == 3);
+	ok1(parent_count == 19);
+	ok1(list_empty(ref(&parent.children, parent_count)));
+	ok1(parent_count == 20);
+
+	/* Test list_top/list_tail on empty list. */
+	ok1(list_top(ref(&parent.children, parent_count), struct child, list) == NULL);
+	ok1(parent_count == 21);
+	ok1(list_tail(ref(&parent.children, parent_count), struct child, list) == NULL);
+	ok1(parent_count == 22);
+	return exit_status();
+}