CNI with interpreted and BC ABI compiled code

Thu Oct 12 22:25:00 GMT 2006

Robert Schuster wrote:
> Hi all
> due to my porting work on GCJ I was confronted with CNI for some time and as
> some of you know. I like CNI very much ... so much that I dont wan't to use JNI
> any more for all of my own projects. :)
>> There is however a caveat: With the neat CNI in place the GIJ runtime will not
> be able to make use of BC ABI compiled classes any longer. This limitation
> bothers me since the time I was first introduced to it last year when I worked
> on the 'lazy linker' issue.
>> Last week I woke up early with my mind being busy thinking about the reasons for
> the limitation and how one could fix it. It quickly turned out that I need more
> information about the reasons for the CNI issue.
>> I can't promise that I will be able to fix the issue soon but at least I can
> gather all the information for it and put it into GCC's Wiki so I (or someone
> else) can use that as a reference later.
>> So could any of you describe why CNI is not usable by interpreted and BC-ABI
> compiled code?
>> And a few questions:
> When trying to load a CNI SO in the runtime with System.loadLibrary() I get an
> error about missing symbols. These symbols are all the things I used at the C++
> level but which belong to the Java implementation. Why Java 'symbols' are
> nowhere available for the linker is clear to me: They only exist as bytecode.
>> Can the following be a feasible solution for the above mentioned problem?
> When a CNI SO is loaded and a symbol cannot be found, the runtime inspects the
> symbol name, calculates the class/field/method which is requested. If it exists
> a suitable accessor is created. Finally a symbol is dynamically created (is that
> possible?) which points at the accessor.
>> The accessor for an interpreted Java method would be a libffi function call. For
> a field it may be possible to use its address.
>> If symbols cannot be created dynamically is it possible to modify the places
> where the symbol in question is used to point at another location?
>> Thanks for your explanations.
>
I think the short answer is CNI only works with C++ ABI compiled code. 
As I recall, APH has plans to rectify this limitation.
David Daney.