Add m00054.vtc: panic when calling sub from a wrong vcl

VMODs must not use SUB references across VCLs. This test checks for a
panic if they do.

bin/varnishtest/tests/m00054.vtc

+varnishtest "VCL_SUB wrong vmod behavior"
+
+varnish v1 -arg "-p feature=+no_coredump" -vcl {
+	import debug;
+
+	backend dummy None;
+
+	sub foo {
+		set resp.http.it = "works";
+	}
+
+	sub vcl_init {
+		debug.bad_memory(foo);
+	}
+} -start
+
+varnish v1 -vcl {
+	import debug;
+	backend dummy None;
+
+	sub vcl_recv {
+		debug.call(debug.total_recall());
+	}
+
+}
+
+client c1 {
+	txreq -url "/foo"
+	expect_close
+} -run
+
+varnish v1 -wait-stopped
+varnish v1 -cliexpect "Assert error in VPI_Call_Check" "panic.show"
+varnish v1 -cliok "panic.clear"
+varnish v1 -expect MGT.child_panic == 1
+varnish v1 -expectexit 0x40

vmod/vmod_debug.c

@@ -1309,3 +1309,25 @@ xyzzy_check_call(VRT_CTX, VCL_SUB sub)
 {
 	return (VRT_check_call(ctx, sub));
 }
+
+/* the next two are to test WRONG vmod behavior:
+ * holding a VCL_SUB reference across vcls
+ */
+
+static VCL_SUB wrong = NULL;
+
+VCL_VOID v_matchproto_(td_xyzzy_bad_memory)
+xyzzy_bad_memory(VRT_CTX, VCL_SUB sub)
+{
+	(void) ctx;
+
+	wrong = sub;
+}
+
+VCL_SUB v_matchproto_(td_xyzzy_total_recall)
+xyzzy_total_recall(VRT_CTX)
+{
+	(void) ctx;
+
+	return (wrong);
+}

vmod/vmod_debug.vcc

@@ -332,3 +332,11 @@ string saying why not.
 $Function VOID call(SUB)
 
 Call a sub
+
+$Function VOID bad_memory(SUB)
+
+To test *WRONG* behavior
+
+$Function SUB total_recall()
+
+To test *WRONG* behavior