Integrated: JDK-8320890: [AIX] Find a better way to mimic dl handle equality

[Joachim Kern]

On Fri, 1 Dec 2023 11:33:46 GMT, Joachim Kern <jkern at openjdk.org> wrote:

> On AIX, repeated calls to dlopen referring to the same shared library may result in different, unique dl handles to be returned from libc. In that it differs from typical libc implementations that cache dl handles.
> 
> This causes problems in the JVM with code that assumes equality of handles. One such problem is in the JVMTI agent handler. That problem was fixed with a local fix to said handler ([JDK-8315706](https://bugs.openjdk.org/browse/JDK-8315706)). However, this fix causes follow-up problems since it assumes that the file name passed to `os::dll_load()` is the file that has been opened. It prevents efficient, os_aix.cpp-local workarounds for other AIX issues like the *.so/*.a duality. See [JDK-8320005](https://bugs.openjdk.org/browse/JDK-8320005). As such, it is a hack that causes other, more uglier hacks to follow (see discussion of https://github.com/openjdk/jdk/pull/16604).
> 
> We propose a different, cleaner way of handling this:
> 
> - Handle this entirely inside the AIX versions of os::dll_load and os::dll_unload.
> - Cache dl handles; repeated opening of a library should return the cached handle.
> - Increase handle-local ref counter on open, Decrease it on close
> - Make sure calls to os::dll_load are matched to os::dll_unload (See [JDK-8320830](https://bugs.openjdk.org/browse/JDK-8320830)).
> 
> This way we mimic dl handle equality as it is implemented on other platforms, and this works for all callers of os::dll_load.

This pull request has now been integrated.

Changeset: b8ae4a8c
Author:    Joachim Kern <jkern at openjdk.org>
Committer: Martin Doerr <mdoerr at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/b8ae4a8c0985d1763ac48ba78943d8b992d7be77
Stats:     446 lines in 12 files changed: 332 ins; 108 del; 6 mod

8320890: [AIX] Find a better way to mimic dl handle equality

Reviewed-by: stuefe, mdoerr

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PR: https://git.openjdk.org/jdk/pull/16920