test: add a test for libctf bug 30264

If present, this bug breaks offsetof (and anything else requiring
reliable offset info, like, oh, say, *any access*) to fields of
unnamed structs/unions at nonzero offsets within their containing
struct/union.

(We just check offsetof, because it's simpler than doing full access
checks.  We check only the in-kernel CTF, because the D language does
not support unnamed struct/union fields at all.)

Signed-off-by: Nick Alcock <nick.alcock@oracle.com>
Reviewed-by: Kris Van Hees <kris.van.hees@oracle.com>

test/unittest/types/tst.nested-unnamed-structs.d

@@ -0,0 +1,32 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Licensed under the Universal Permissive License v 1.0 as shown at
+ * http://oss.oracle.com/licenses/upl.
+ */
+
+/*
+ * ASSERTION:
+ *	Check for the absence of a libctf bug breaking offsets of
+ *	members of nested unnamed structs in the kernel.
+ *	See https://sourceware.org/bugzilla/show_bug.cgi?id=30264
+ *
+ */
+
+#pragma D option quiet
+
+BEGIN {
+	printf("offset is %i\n", offsetof(struct rds`rds_message, atomic));
+}
+
+BEGIN
+/ offsetof(struct rds`rds_message, atomic) == 0 /
+{
+	exit(1);
+}
+
+BEGIN
+/ offsetof(struct rds`rds_message, atomic) != 0 /
+{
+	exit(0);
+}

test/unittest/types/tst.nested-unnamed-structs.x

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+if ! $(grep -q '^rds ' /proc/modules); then
+    exit 1
+fi
+
+exit 0