RFR: JDK-8275320: NMT should perform buffer overrun checks [v3]

[Thomas Stuefe]

On Thu, 18 Nov 2021 17:33:50 GMT, Volker Simonis <simonis at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Feedback Volker
>
> Looks good to me know except for Zhengyu question.

Hi @simonis, @zhengyu123,

I somehow messed up and force-pushed. This is what happened since the last review:

- https://github.com/openjdk/jdk/pull/5952/commits/2247b5e6f6d6aff2c54fe51f1e064876bba43963 : increases the footer canary to two bytes.
- https://github.com/openjdk/jdk/pull/5952/commits/188f0ea36a12d20be960ec98eb303669c6fcd714 : extended the gtests, mainly to test realloc more thoroughly.
    - Added one death test to show that realloc also does heap corruption checks on the old block. 
    - Another test - not a death test but a regular test - just to test that realloc works. This was in reaction to the bug Zhengyu found, but I never got it to fire. After analysing I believe the bug was benign. Still, good to have this test.
 - https://github.com/openjdk/jdk/pull/5952/commits/ea6fe31c08af1a7073e3d14a37a572beb43a027c : This one actually fixes the bug Zhengyu found. I kept the fix simple stupid and refrained from cleaning up too much. I just removed two methods which were not needed anymore.
 - https://github.com/openjdk/jdk/pull/5952/commits/3d2a5d00b7dac5411f3c1956a4b5c8b6e1a76a66 : Last one fixes the last typos Volker found.

Thanks again, guys, for your reviews. I plan to give this another round in our test systems before pushing.

Cheers, Thomas

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PR: https://git.openjdk.java.net/jdk/pull/5952