RFR: 8369393: NMT: poison the canaries of malloc header under ASAN build [v22]

[Afshin Zafari]

On Wed, 19 Nov 2025 09:39:57 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

>> NMT can detect malloc'd memory corruption using canary tests at header and footer of every memory region. This can only be done at free time of the memory where NMT checks the canaries and report error if they are not as expected.
>> In this PR, the canary parts also are poisoned using ASAN API to get notified whenever a read/write op is done. on the canary parts. `_size` member of the malloc header is also poisoned, since it is used for finding the footer address.
>
> Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review comments applied

Local ASAN build tests passed. Let's wait for GHA tests for non-ASAN builds.

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PR Comment: https://git.openjdk.org/jdk/pull/27685#issuecomment-3551764716