Re: [Aegisvm-devel] patch to jni.c

[Philip F. <pw...@us...>]

Hi Gildas,

I have just finished the implementation of the jni functions for method
calling.  I ended up doing things differently than what you suggested
in your patch:

1/ The non-virtual method invocation functions you suggested is 
   simply a macro-based factoring of the stub code.  I filled in
   the actual implementation and didn't use macros.
2/ The virtual method invocation functions are actually much more
   subtle than your implementation.  It involves instance/interface
   method dispatching logic.  So I ended up doing things my own way.
3/ I really appreciate your factoring of common code in CallMethodA
   and CallMethodV.  You basically did two things:
   a/ You introduced an extra argument obj to reuse the static method
      invocation code for instance method invocation.  I adopted the
      idea in my code.
   b/ You make CallMethodV delegate its method invocation task to
      CallMethodA.  You achieve this by converting the input va_list
      into an array of jvalue.  This is real nice, with only one
      catch.  Since you allocate the array from the stack frame of
      the caller, if the caller perform multiple jni calls, then
      all these intermediate arrays will be accumulated in the 
      caller's frame without deallocation.  One apparent fix would
      be to use the arena check-pointing mechanism to deallocate the
      intermediate array when the invocation returns.  However, the
      catch is, in the mean time, JNI may have already allocated
      some local references from the caller frame, and simple
      rewinding based on check-pointing will corrupt the local
      reference registry.  The cleanest way to implement this
      is to allocate the intermediate arrays in the callee's stack
      frame.  I am too eager to release soon, and so I'll leave the
      code unfactored for now, and will return to this issue later.
      If you have a good way of fixing it, please do let me know.

Again, thanks for your contribution. :-)

Philip
--
Philip W. L. Fong            pw...@us...
The Aegis VM Project         http://aegisvm.sourceforge.net

The Aegis VM Project is an on-going effort to implement a lightweight,
secure JVM.  It will eventually feature a modular architecture, Proof
Linking, that supports pluggable verification modules.