The necessary code is required in MapsBuilder::buildBuffer to successfully create run construct() on a pid: maps[maps.length - 1] = 0; Without that line the following error is thrown java.lang.RuntimeException: missing NUL at frysk.sys.proc.MapsBuilder.construct(TestRunner) at frysk.sys.proc.MapsBuilder.construct(TestRunner) at frysk.rt.TestStackBacktrace.testBacktrace(TestRunner) at frysk.junit.Runner.<init>(TestRunner) at TestRunner.main(TestRunner)