RFR: 8333658: NMT: Use an allocator with 4-byte pointers to save memory in NativeCallStackStorage [v34]

[Sonia Zaldana Calles]

On Tue, 25 Jun 2024 17:57:36 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> Thank you for the in-depth reviewing of this change.
>
>> Hi @jdksjolen, I'm seeing some build failures after this PR got integrated. I filed [JDK-8335108](https://bugs.openjdk.org/browse/JDK-8335108) for reference.
> 
> Hi Sonia, thanks for contacting me. It seems like this is a C++20 issue, but Hotspot only supports up to C++14. Here's a Godbolt for reproducing the issue, change the `-std=c++14` to `-std=c++20` to see the issue: https://godbolt.org/z/eK5GaTceY
> 
> That ought to mean that I don't have to back out this PR and re-introduce it with the bug fixed, but I still think that we should fix the bug because we do want to get to C++20 some day :-).
> 
> There's something weird with the fact that you get builds with C++20 support enabled, not sure what your configure options are.

Hi @jdksjolen, thanks for looking into it! 

> Hi Sonia, thanks for contacting me. It seems like this is a C++20 issue, but Hotspot only supports up to C++14. Here's a Godbolt for reproducing the issue, change the `-std=c++14` to `-std=c++20` to see the issue: https://godbolt.org/z/eK5GaTceY
> 
> That ought to mean that I don't have to back out this PR and re-introduce it with the bug fixed, but I still think that we should fix the bug because we do want to get to C++20 some day :-).

Makes sense. I'll submit a follow-up PR to fix this. 

> There's something weird with the fact that you get builds with C++20 support enabled, not sure what your configure options are.

I'm not sure. I don't have any special configure options. I came across this error after a plain ```bash configure``` but I guess my installed g++ version is 14.1.1.

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PR Comment: https://git.openjdk.org/jdk/pull/18979#issuecomment-2189747196