RFR: 8352251: Implement Cooperative JFR Sampling [v16]

[Martin Doerr]

On Mon, 5 May 2025 17:31:37 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

> Are we not using _last_java_FP on all platforms?

The field `_last_Java_fp` is only needed on platforms which don't have a Back Chain.

> Implementation seems to be in the correct direction, but its missing locations in TemplateInterpreterGenerator and TemplateTable.

Yeah, I'll look into them later when the first part is correct.

> Also, i do not see any pre-emptive move of the fp, which is required for fetching a correct (non-racy) CPU context.

Isn't this problem already solved by using the `_last_sender_Java_fp`? Why do we need both, the frame pop before the safepoint check and the _last_sender_Java_fp trick?

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PR Comment: https://git.openjdk.org/jdk/pull/24296#issuecomment-2852162604