RFR: 8352251: Implement JEP 518: JFR Cooperative Sampling [v23]

[Markus Grönlund]

On Thu, 15 May 2025 22:28:04 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> The intent is to maintain the logical (Java and JVM) view that we have not popped the frame yet, which is why we still save the ljf to the original frame, just as before. Anything working with ljf, such as InterpreterRuntime::at_unwind(), should function as before. 
>> 
>> All tiers 1-6 pass, but I can double check all the JVMTI tests specifically, as they are as you say, tricky.
>
> The description might not be detailed enough: we are updating one of the physical registers in a staged leave, but this is only visible to anyone directly inspecting the CPU context, such as a cpu sampler.  Anything logical, working in the JVM, especially ljfs, will work just as before.

The JVMTI things should have already been done before we start to manipulate the rbp, just like before.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24296#discussion_r2092048878