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

[Suchismith Roy]

On Thu, 21 Dec 2023 10:01:04 GMT, Thomas Stuefe <stuefe 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 ? 
>> 
>> 
>>> > > 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.
>
>> > > > 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 ...

Hi @tstuefe 
Any further clarifications ,required for this change ?

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PR Comment: https://git.openjdk.org/jdk/pull/16604#issuecomment-1905320564