currentClassLoader problem

[Andrew Haley]

David Holmes writes:
 > I'm having a lot of trouble trying to understand what needs to be done to
 > correctly set up class loaders in Classpath.
 > 
 > Present point of confusion is SecurityManager.currentClassLoader and its
 > helper VMSecurityManager.currentClassLoader.
 > 
 > The docs for SecurityManager.currentClassLoader states that it returns:
 > 
 >    ClassLoader of the first non-system class on the execution
 >    stack. A non-system class is one whose ClassLoader is not equal to
 >    address@hidden ClassLoader#getSystemClassLoader()} or its ancestors.
 > 
 > and it simply returns VMSecurityManager.currentClassLoader() *but* the docs
 > for VMSecurityManager.currentClassLoader state that it returns:
 > 
 >      This is the first non-null class loader
 >    * on the stack, if one exists, stopping either at the end of the stack
 >    * or the first instance of a PrivilegedAction. In other words, this call
 >    * automatically unwinds past all classes loaded by the bootstrap loader,
 >    * where getClassLoader() returns null, to get to the user class that
 >    * really invoked the call that needs a classloader.
 > 
 > These two descriptions do not match, so the delegation from SecurityManager
 > to VMSecurityManager is incorrect as the latter would return the
 > system/application classloader, while the former should not return that.
 > There seems to be confusion between the bootstrap loader (which is often
 > null) and the system/application loader (as returned by
 > getSystemClassLoader()) which is never null.

What we do at the moment is wrong.  I've needed to make quite a few
changes, and I'm sorry that I haven't folded them back into the main
sources.

Andrew.


Index: java/lang/ClassLoader.java
===================================================================
RCS file: /cvs/gcc/gcc/libjava/java/lang/ClassLoader.java,v
retrieving revision 1.31
diff -c -2 -p -r1.31 ClassLoader.java
*** java/lang/ClassLoader.java  9 Oct 2003 16:24:55 -0000       1.31
--- java/lang/ClassLoader.java  15 Mar 2004 09:54:49 -0000
*************** public abstract class ClassLoader
*** 729,733 ****
        {
        Class c = VMSecurityManager.getClassContext()[1];
!       ClassLoader cl = c.getClassLoader();
        if (cl != null && cl != systemClassLoader)
          sm.checkPermission(new RuntimePermission("getClassLoader"));
--- 742,746 ----
        {
        Class c = VMSecurityManager.getClassContext()[1];
!       ClassLoader cl = getClassLoader0(c);
        if (cl != null && cl != systemClassLoader)
          sm.checkPermission(new RuntimePermission("getClassLoader"));
*************** public abstract class ClassLoader
*** 950,952 ****
--- 963,967 ----
      return false;
    }
+ 
+     static private final native ClassLoader getClassLoader0(Class c);
  }
Index: java/lang/natClassLoader.cc
===================================================================
RCS file: /cvs/gcc/gcc/libjava/java/lang/natClassLoader.cc,v
retrieving revision 1.63
diff -c -2 -p -r1.63 natClassLoader.cc
*** java/lang/natClassLoader.cc 9 Jan 2004 17:10:43 -0000       1.63
--- java/lang/natClassLoader.cc 15 Mar 2004 09:54:56 -0000
*************** java::lang::VMClassLoader::loadClass(jst
*** 147,150 ****
--- 147,158 ----
  }
  
+ // Return the true ClassLoader for a class, without doing security checks
+ ::java::lang::ClassLoader *
+ ::java::lang::ClassLoader::getClassLoader0 (::java::lang::Class *c)
+ {
+   return c->loader;
+ }
+ 
+ 
  void
  _Jv_WaitForState (jclass klass, int state)
Index: java/lang/VMSecurityManager.java
===================================================================
RCS file: /cvs/gcc/gcc/libjava/java/lang/VMSecurityManager.java,v
retrieving revision 1.2
diff -c -2 -p -r1.2 VMSecurityManager.java
*** java/lang/VMSecurityManager.java    5 Dec 2002 00:49:29 -0000       1.2
--- java/lang/VMSecurityManager.java    15 Mar 2004 09:54:54 -0000
*************** class VMSecurityManager
*** 55,63 ****
      // FIXME this implementation is a bit wrong too -- the docs say we
      // must also consider ancestors of the system class loader.
      Class[] classStack = getClassContext ();
      for (int i = 0; i < classStack.length; i++)
        {
        ClassLoader loader = classStack[i].getClassLoader();
!       if (loader != null)
          return loader;
        }
--- 55,64 ----
      // FIXME this implementation is a bit wrong too -- the docs say we
      // must also consider ancestors of the system class loader.
+     ClassLoader systemClassLoader = VMClassLoader.getSystemClassLoader();
      Class[] classStack = getClassContext ();
      for (int i = 0; i < classStack.length; i++)
        {
        ClassLoader loader = classStack[i].getClassLoader();
!       if (loader != null && loader != systemClassLoader)
          return loader;
        }