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

[Thomas Stuefe]

On Thu, 21 Dec 2023 09:37:55 GMT, Suchismith Roy <sroy at openjdk.org> wrote:

> > > > 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 ?

Rather, this is a question you have to ask your collegues at IBM that develop the AIX libc.

Since AIX libc is not open source, we cannot look for ourselves, nor can Joachim (her works at SAP).

> 
> > > > 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 ?

Someone must implement LoadLibrary. Try looking for places where dlopen() is called.

> 
> > > 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-1865977132