RFR: 8017234: Hotspot should stop using mapfiles [v7]

[Daniel Jeliński]

On Mon, 26 Feb 2024 16:18:14 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> **Summary:** Finally get rid of the mapfiles in Hotspot, and replace it with compiler options and `JNIEXPORT` on all platforms.
>> 
>> The bug that this PR solves, [JDK-8017234](https://bugs.openjdk.org/browse/JDK-8017234), was created in 2013. Even back then the use of mapfiles in Hotspot was dated, so this is really good riddance with old rubbish.
>> 
>> This code touches on central but not well understood parts of the Hotspot dynamic library, which has contributed to why this bug has stayed unresolved for so long. I will need to explain this fix in more detail than usually necessary. (Please bare with me if this gets long.) I also anticipate that not all solutions that I've picked will be accepted, and we'll have to discuss how to proceed. I think it is better to have actual concrete code to discuss around, rather than starting by an abstract discussion. To keep this description short, I will post the discussion as a comment to the PR.
>> 
>> I have run this PR through tier 1-3 in our CI system. I have also carefully checked how the resulting dynamic library differs with this patch (not much; see discussion below). For build system changes, this is often the most relevant metric.
>
> Magnus Ihse Bursie has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:
> 
>  - Merge branch 'master' into hotspot-symbols-proper
>  - Revert "Use #pragma instead of HIDDEN define"
>    
>    This reverts commit 00e40a7f6e4cdef6592d72b3d08063cdcc41532a.
>  - Use #pragma instead of HIDDEN define
>  - Rename the version script to version-script.txt
>  - Restore linker script to linux/gcc builds
>  - Rename the Windows export file to .def
>  - Remove unused symbol _Copy_conjoint_bytes on linux/arm32
>  - 8017234: Hotspot should stop using mapfiles

This is on GCC 9.4.0, Ubuntu 20.04.
I wonder if the reference to a temporary was intentional... but I guess that's a subject for another PR.

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PR Comment: https://git.openjdk.org/jdk/pull/17955#issuecomment-1964619969