catch a small overflow in malloc-standard

test/malloc/malloc-standard-alignment.c

@@ -0,0 +1,42 @@
+/* exercise a bug found in malloc-standard when alignment
+ * values are out of whack and cause a small overflow into
+ * actual user data.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+
+#define ok(p) ((void*)p > (void*)0x1000)
+#define x \
+	do { \
+		printf("%i: phead = %p, phead->link @ %p = %p %s\n", \
+			__LINE__, phead, \
+			ok(phead) ? &phead->link : 0, \
+			ok(phead) ? phead->link : 0, \
+			ok(phead) ? phead->link == 0 ? "" : "!!!!!!!!!!!" : ""); \
+		if (phead->link != NULL) exit(1); \
+	} while (0);
+
+struct llist_s {
+	void *data;
+	struct llist_s *link;
+} *phead;
+
+int main()
+{
+	char *line, *reg;
+
+	setbuf(stdout, NULL);
+	setbuf(stderr, NULL);
+
+	phead = malloc(sizeof(*phead));
+	phead->link = NULL;
+
+x	line = malloc(80);
+x	line = realloc(line, 2);
+x	reg = malloc(32);
+x	free(line);
+
+x	return 0;
+}