6714758: hotspot: provide an entry point to the BootStrap Class loader[dholmes,acorn]

Adds JVM_FindClassFromBootLoader entry point, for jdk's use

Reviewed-by: dholmes, acorn

hotspot/src/share/vm/prims/jvm.cpp

@@ -624,6 +624,30 @@ JVM_ENTRY(void, JVM_ResolveClass(JNIEnv* env, jclass cls))
   if (PrintJVMWarnings) warning("JVM_ResolveClass not implemented");
 JVM_END
 
+// Rationale behind JVM_FindClassFromBootLoader
+// a> JVM_FindClassFromClassLoader was never exported in the export tables.
+// b> because of (a) java.dll has a direct dependecy on the  unexported
+//    private symbol "_JVM_FindClassFromClassLoader@20".
+// c> the launcher cannot use the private symbol as it dynamically opens
+//    the entry point, so if something changes, the launcher will fail
+//    unexpectedly at runtime, it is safest for the launcher to dlopen a
+//    stable exported interface.
+// d> re-exporting JVM_FindClassFromClassLoader as public, will cause its
+//    signature to change from _JVM_FindClassFromClassLoader@20 to
+//    JVM_FindClassFromClassLoader and will not be backward compatible
+//    with older JDKs.
+// Thus a public/stable exported entry point is the right solution,
+// public here means public in linker semantics, and is exported only
+// to the JDK, and is not intended to be a public API.
+
+JVM_ENTRY(jclass, JVM_FindClassFromBootLoader(JNIEnv* env,
+                                              const char* name,
+                                              jboolean throwError))
+  JVMWrapper3("JVM_FindClassFromBootLoader %s throw %s", name,
+              throwError ? "error" : "exception");
+  return JVM_FindClassFromClassLoader(env, name, JNI_FALSE,
+                                      (jobject)NULL, throwError);
+JVM_END
 
 JVM_ENTRY(jclass, JVM_FindClassFromClassLoader(JNIEnv* env, const char* name,
                                                jboolean init, jobject loader,