RFR: 8284331: Add sanity check for signal handler modification warning.

[Kevin Walls]

On Fri, 29 Apr 2022 03:15:09 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> How does this relate the failure in JDK-8285647? Is this just meant to detect that failure, but a proper fix is still needed for it?

..it's not directly related - I had this test addition in progress already, as an addition to JDK-8283337 which fixes the modification handler being broken by a previous change (the warning was firing all the time, after JDK-8279124 and before JDK-8283337).  So we should have a sanity check (this PR) which fails if the warning starts firing unnecessarily.

Logged JDK-8285792 to signal that we need some more cleanup here, including the news that I think JDK-8285647 shows that we don't consistently ignore the crash_handler.

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PR: https://git.openjdk.java.net/jdk/pull/8106