RFR: 8331942: On Linux aarch64, CDS archives should be using 64K alignment by default

[Andrew Haley]

On Wed, 8 May 2024 15:14:16 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> On Linux aarch64, a JVM may encounter three different page sizes: 4K, 64K, and (when run on Mac M1 hardware) 16K.
> 
> Since forgetting to specify `--enable-compatible-cds-alignment` is a common error that is only noticed when running the produced JVM on hardware with different page size, we propose to enable that option by default on Linux aarch64. The cost is a moderate increase in CDS archive size (about 300K).
> 
> I tested this patch on:
> - x64 Linux
> - x64 Linux, crossbuilding to aarch64
> - building natively on aarch64 Linux

This is obviously correct. Otherwise, the CDS archive will only work if the JDK happens to have been built on a machine with greater or equal page size.

Does the default `compatible-cds-alignment=false` make any sense anywhere on other platforms, though? We might simply make compatibility the default.

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Marked as reviewed by aph (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/19142#pullrequestreview-2046199994