RFR: 8369393: NMT: poison the malloc header and footer under ASAN build [v2]

[Afshin Zafari]

On Wed, 3 Dec 2025 14:45:35 GMT, Paul Hübner <phubner at openjdk.org> wrote:

>> I prefer `mark_block_as_alive()` with no assertion on being already `dead`. `revive()` with assertion that it has to be `dead` already. Thoughts?
>
> Works for me. But I see no assertion in the current code that asserts it has to be dead.

The asserts in revive() are removed in this PR at this [commit](https://github.com/openjdk/jdk/pull/28503/commits/4ebd70290f148e4613506605eadd05bc480a7d5f#diff-ea9fba8b125ca1dea6607148566da0913ff8f4eafbee79cb9a5a3b56801d3947:~:text=MallocHeader%3A%3Arevive()%20%7B-,assert(_canary%20%3D%3D%20_header_canary_dead_mark%2C%20%22must%20be%20dead%22)%3B,(assert(_alt_canary%20%3D%3D%20_header_alt_canary_dead_mark%2C%20%22must%20be%20dead%22))%3B,-_canary%20%3D%20_header_canary_live_mark%3B).

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PR Review Comment: https://git.openjdk.org/jdk/pull/28503#discussion_r2585863405