Crash with TraceClassLoading

[Jeremy Manson]

Now that 9 is underway, presumably we can start feeding back fixes again.

This one's a bit obscure.  TraceClassLoading expects there to be a (Java)
caller when you load a class with the bootstrap class loader.  However,
there are ways of loading a class that don't involve having a Java caller.
 For example, you can do so from a JVMTI hook.  A reproduction is attached,
and here's a patch:

diff --git a/src/share/vm/classfile/classFileParser.cpp
b/src/share/vm/classfile/classFileParser.cpp
--- a/src/share/vm/classfile/classFileParser.cpp
+++ b/src/share/vm/classfile/classFileParser.cpp
@@ -4098,8 +4098,12 @@
         tty->print("[Loaded %s from %s]\n", this_klass->external_name(),
                    cfs->source());
       } else if (class_loader.is_null()) {
-        if (THREAD->is_Java_thread()) {
-          Klass* caller =
((JavaThread*)THREAD)->security_get_caller_class(1);
+        Klass* caller =
+            THREAD->is_Java_thread()
+                ? ((JavaThread*)THREAD)->security_get_caller_class(1)
+                : NULL;
+        // caller can be NULL, for example, during a JVMTI VM_Init hook
+        if (caller != NULL) {
           tty->print("[Loaded %s by instance of %s]\n",
                      this_klass->external_name(),
                      InstanceKlass::cast(caller)->external_name());

Jeremy
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