Help with adding a native method

Tom Rodriguez tom.rodriguez at
Wed Mar 21 10:48:41 PDT 2012

One issue is you've duplicated a signature with a different name which may cause unexpected problems:

    do_signature(compareAndSwapObject_signature,  "(Ljava/lang/Object;JLjava/lang/Object;Ljava/lang/Object;)Z")          \

+   do_signature(myCompareAndSwapObject_signature,  "(Ljava/lang/Object;JLjava/lang/Object;Ljava/lang/Object;)Z")          \

There's a mapping between Symbol* and enumeration values and duplicating Symbols will break that though I'm not sure what exactly will go wrong.

Additionally I think you need to register your new method using a separate RegisterMethods call.  Otherwise your JVM won't be able to bootstrap when run with a JDK that is missing the Unsafe method.  I suspect that's what's happening here.  Errors during bootstrap lead to mysterious failures.


On Mar 21, 2012, at 8:18 AM, Ilya Mirsky wrote:

> Hi,
> Following my post from a week ago, I'm trying to add a native method to the unsafe class.
> For a start I'm trying to duplicate an existing method (CompareAndSwap).
> I added the new method, and registered it in the unsafe.cpp file and in vmSymbols.hpp (a patch is attached).
> When I'm compiling the jdk I get the following error from test_gamma:
> cd linux_i486_compiler2/product && ./test_gamma
> java full version "1.6.0_22-b22"
> Using java runtime at: /usr/lib/jvm/java-6-openjdk/jre
> Error occurred during initialization of VM
> java.lang.NullPointerException
> 	at java.util.Hashtable.put(
> 	at java.lang.System.initProperties(Native Method)
> 	at java.lang.System.initializeSystemClass(
> What am I doing wrong?
> Any help will be highly appreciated
> ---
> Best Regards,
> Ilya Mirsky
> <jdk7u2.patch>

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