RFR: 8017234: Hotspot should stop using mapfiles [v5]

[Mikael Vidstedt]

On Thu, 22 Feb 2024 16:15:23 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 incrementally with one additional commit since the last revision:
> 
>   Use #pragma instead of HIDDEN define

Not a review but I did want to mention that I proved to myself that your addition of `.hidden` for the assembly file symbols is the right thing to do. In particular, when we compile the .cpp files with the `-fvisibility=hidden` flag that's exactly what g++ does in the background.

Just a thought: Perhaps worth introducing some kind of macro that captures defining a symbol in assembly code (something that does `.globl` + `.hidden` on Linux and `.private_extern` on `__APPLE__`?

Also, separate from this change: perhaps worth turning on whitespace checking (no tabs) for .S files?

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PR Comment: https://git.openjdk.org/jdk/pull/17955#issuecomment-1960276436