RFR: JDK-8320005 : Allow loading of shared objects with .a extension on AIX [v7]

[Suchismith Roy]

On Wed, 20 Dec 2023 11:16:03 GMT, Suchismith Roy <sroy at openjdk.org> wrote:

>> J2SE agent does not start and throws error when it tries to find the shared library ibm_16_am.
>> After searching for ibm_16_am.so ,the jvm agent throws and error as dll_load fails.It fails to identify the shared library ibm_16_am.a shared archive file on AIX.
>> Hence we are providing a function which will additionally search for .a file on AIX ,when the search for .so file fails.
>
> Suchismith Roy has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Spaces fix

> > > What happens if we accidentally attempt to load a "real" static library, which is also named *.a? Would dlopen() then crash? What would happen?
> 
> > I don't think the problem is with *.a . They would load as the default behaviour of the dlopen. It is only when the dlopen fails for *.so , we give another chance to check for .a file with the same name.
> 
> No, what I meant, and what must be clarified before going forward with this solution, is the following:
> 
> * is _every_ `*.a` object on AIX loadable with `dlopen`, and will the result be the same as when loading a `*.so` object
> * or, if we present arbitrary `*.a` files to dlopen, is there a chance for dlopen to crash or misbehave.
> 
> Reason is that I was under the impression that *.a libraries are static libraries and cannot be loaded dynamically. This is what you now try to do.
> If we cannot safely answer this question, I would opt for a more narrow solution by hard-wiring known alternative names. So, do the second *.a attempt only for your `ibm_16_am.a` which you know works. That could also be done in a reasonably maintainable manner.
> 
In AIX, both static and dynamic libraries have *.a extension. And AIX also supports *.so files.Bascially shared objects in AIX have both *.a and *.so extension.  Hence we need to implement this logic.
If we try loading a static archive specifically ,how the dlopen would behave , that is something probably @JoKern65  can answer ? 


> > > Does this really have to be handled in the OpenJDK? What does J9 on AIX do? Could this be done in a simpler way outside OpenJDK, e.g. by providing an *.so variant of the library in question? Where does this library come from?
> 
> > I am not sure how J9 handles this. I would have to consult .
> 
> J9 is Open Source, can't you just look? :)

I did try comparing the file structures, and i do not see a similar file structure over there. 
I am unable to find the jvmTiAgent code and also os_aix file. So i am not sure which functions over there are doing the same functionality. You have any suggestion on how i can check and correlate ?  
> 
> > However as per current observation, this issue does not show up on Semuru. This issue is only happening on Adoptium. The team that release these file has always released *.a files which work fine for Semuru.
> 
> I don't know what Semuru is. What is the context, is that a different VM? Also OpenJDK? J9 derived? 


Semuru is J9 derived.

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PR Comment: https://git.openjdk.org/jdk/pull/16604#issuecomment-1865945011