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List:       openjdk-serviceability-dev
Subject:    JVM crashes when adding more than 2 methods to java.lang.Object
From:       tom.rodriguez () oracle ! com (Tom Rodriguez)
Date:       2010-05-21 23:15:18
Message-ID: 0F1066F2-3FCE-40A9-9785-6E8E9509D21B () oracle ! com
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On May 21, 2010, at 1:11 PM, Daniel D. Daugherty wrote:

> Sorry that I'm really late to this e-mail thread. We don't support
> using the RedefineClasses() API to add a public method. This testing
> assertion is verified by an internal test (redefclass020) and I just
> verified that the test does pass.
> 
> In Guillaume's scenarios, the Object.class bits are being replaced at
> ClassFileLoadHook time or by providing the modified Object class using
> the -Xbootclasspath/p parameter. (That info was provided in another
> e-mail.) In neither of those cases is the RedefineClasses() API being
> called so the error check I mention above isn't being made.
> 
> It more be worth adding a sanity check of some sort to the early
> bring up/boot strapping logic to verify that the Object class that
> we're about to load has the expected number of virtual methods. This
> will allow us to get a cleaner error message for now.

There are existing asserts and I think they should just be converted to exceptions.  \
We could also consider making the base table size into a flag so it could be \
increased.

tom

> 
> Dan
> 
> 
> On 4/28/2010 12:09 PM, Tom Rodriguez wrote:
> > I didn't think we supporting redefining Object and adding public methods after \
> > JVM bootstrap.  Adding methods to classes which are already loaded with \
> > subclasses means that you have to generate new vtables for all subclasses and as \
> > far as I know we don't do that.  You might get more answer over on \
> > serviceability-dev. 
> > tom
> > 
> > On Apr 24, 2010, at 1:30 PM, Guillaume Pothier wrote:
> > 
> > 
> > > Hi,
> > > First of all I hope it is appropriate to ask this kind of question in
> > > this list, otherwise what would be the correct forum?
> > > Here is my problem: I'm adding public, non-native methods to the
> > > Object class through instrumentation, and it seems that adding more
> > > than 2 such methods causes the JVM to crash. I get different kinds of
> > > crashes depending on the number of methods I add. With 3 and 4 methods
> > > I get a SIGSEGV; with more methods I get an NPE during VM
> > > initialization (in String.charAt). For testing purposes, all added
> > > methods take no arguments and return void, and have an empty body
> > > (only the RETURN bytecode).
> > > Is that expected behavior? Is there something I can do about it?
> > > Kind regards,
> > > Guillaume Pothier
> > > PhD student, University of Chile
> > > 
> > 
> > 
> > 
> 


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