[lworld] RFR: 8366093: [lworld] Add preview mode to C++ classloader [v2]

[Roger Riggs]

On Tue, 14 Oct 2025 12:34:14 GMT, David Beaumont <duke at openjdk.org> wrote:

>> C++ changes for supporting preview mode when preview mode resources (with new location flags) are available.
>> 
>> At the moment, this code will operate on non-preview jimage files (1.0) and act as if no preview resources are available by virtue of the default value for missing attributes being zero (which matches location flags for "normal" entries).
>
> David Beaumont has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Reorganising to catch preview-only cases

Still looks good. One question.

src/hotspot/share/classfile/classLoader.cpp line 1522:

> 1520:   if (jimage_exists()) {
> 1521:     jimage_init(enable_preview);
> 1522:   }

This silently ignores enable_preview if there there is no open image. 
Is it only the exploded build that will not have an open image?
Should there be an assert on the false branch of  `jimage_exists`?

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Marked as reviewed by rriggs (Committer).

PR Review: https://git.openjdk.org/valhalla/pull/1618#pullrequestreview-3362126080
PR Review Comment: https://git.openjdk.org/valhalla/pull/1618#discussion_r2449299184