[jdk18] RFR: 8273108: RunThese24H crashes with SEGV in markWord::displaced_mark_helper() after JDK-8268276

[Kevin Rushforth]

On Fri, 10 Dec 2021 00:17:36 GMT, Scott Gibbons <duke at openjdk.java.net> wrote:

> The base64 decoder overwrites memory past the end of its output buffer in certain cases. It will not overwrite if the encoded string length is < 64 bytes. It also will not overwrite if the encoded string length mod 64 is >= 16. So the case where it will overwrite is when the input string length (the encoded byte length) mod 64 is less than 16.
> 
> I also added a test case to detect this overrun.

@asgibbons I see that [JDK-8275427](https://bugs.openjdk.java.net/browse/JDK-8275427) is closed as a duplicate. Normally, duplicates are not listed in the commit message of a fix.

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PR: https://git.openjdk.java.net/jdk18/pull/4