Support unattached threads in VMError.shouldNotReachHere().

Author: christianhaeubl

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/VMErrorSubstitutions.java

@@ -27,17 +27,21 @@
 import static com.oracle.svm.core.heap.RestrictHeapAccess.Access.NO_ALLOCATION;
 
 import org.graalvm.compiler.nodes.UnreachableNode;
+import org.graalvm.nativeimage.CurrentIsolate;
 import org.graalvm.nativeimage.ImageSingletons;
+import org.graalvm.nativeimage.Isolate;
 import org.graalvm.nativeimage.LogHandler;
 import org.graalvm.nativeimage.Platforms;
 import org.graalvm.nativeimage.c.function.CodePointer;
 import org.graalvm.nativeimage.impl.InternalPlatform;
 
 import com.oracle.svm.core.NeverInline;
 import com.oracle.svm.core.SubstrateDiagnostics;
+import com.oracle.svm.core.SubstrateOptions;
 import com.oracle.svm.core.Uninterruptible;
 import com.oracle.svm.core.annotate.Substitute;
 import com.oracle.svm.core.annotate.TargetClass;
+import com.oracle.svm.core.c.function.CEntryPointActions;
 import com.oracle.svm.core.heap.RestrictHeapAccess;
 import com.oracle.svm.core.log.Log;
 import com.oracle.svm.core.snippets.KnownIntrinsics;
@@ -135,6 +139,10 @@ public class VMErrorSubstitutions {
     static RuntimeException shouldNotReachHere(CodePointer callerIP, String msg, Throwable ex) {
         ThreadStackPrinter.printBacktrace();
 
+        if (SubstrateOptions.SpawnIsolates.getValue() && CurrentIsolate.getCurrentThread().isNull()) {
+            CEntryPointActions.enterAttachThreadFromCrashHandler((Isolate) KnownIntrinsics.heapBase());
+        }
+
         SafepointBehavior.preventSafepoints();
         StackOverflowCheck.singleton().disableStackOverflowChecksForFatalError();