RFR: JDK-8263557: Possible NULL dereference in Arena::destruct_contents()

[Kim Barrett]

On Sun, 14 Mar 2021 06:07:00 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> Trivial.
> 
> Sonarcloud reports a possible access to a NULL C++ object in Arena::destruct_contents():
> 
> _first->chop();
> 
> I have found no code path where this could happen but _first could conceivably be NULL after a call to Arena::reset(). Lets fix that.
> 
> GA test error on windows seems unrelated.

Arena::move_contents leaves _first == nullptr. ~Arena calls destruct_contents. Calling ~Arena on a moved-from arena would hit this. So change looks good, though I'm not so sure about "trivial".

I'm not sure why we don't hit this.  C2 (in Matcher::match) calls move_contents, but I couldn't figure out what it did with the old (moved-from) arena after that.

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Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2994