RFR: 8369642: [ubsan] nmethod::nmethod null pointer passed as argument 2 to memcpy [v2]

[Vladimir Kozlov]

On Tue, 14 Oct 2025 22:33:40 GMT, Chad Rakoczy <duke at openjdk.org> wrote:

>> [JDK-8316694](https://bugs.openjdk.org/browse/JDK-8316694) introduced a counter so that the nmethod immutable data can be shared between relocated nmethods to eliminate an unnecessary copy. The counter is aligned in memory so that must be taken into account when calculating the amount of memory used by the counter
>
> Chad Rakoczy has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add reference counter offset

My testing passed.

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Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27778#pullrequestreview-3351187097