RFR: 8287812: Cleanup JDWP agent GetEnv initialization [v2]

[Chris Plummer]

On Fri, 9 Dec 2022 03:00:36 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

> Should we consider filing a CSR as potentially there is a minimal compatibility risk?

It don't think it should be necessary. I don't believe there are any known compatibility issues here. Although we switched from requesting `JVMTI_VERSION_1` to requesting the current compile time `JVMTI_VERSION`, it's always been a requirement of the `compatible_versions()` check that the compile time and runtime major versions match up. What has changed somewhat is that the micro versions must also match up, but I don't think we bother with minor or micro versions anymore.

There is one downside of requesting `JVMTI_VERSION` instead of `JVMTI_VERSION_1` that I'm now realizing. If you do try to drop a newer debug agent into an older jdk release, GetEnv() will fail. That's ok, but if we allowed it to succeed by fetching `JVMTI_VERSION_1`, then instead the `compatible_versions()` check would fail, which would give you a more meaningful error message. In other words, rather than a "GetEnv() failed" message you would get a "incompatible version" error message.

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PR: https://git.openjdk.org/jdk/pull/11602