RFR: 8316694: Implement relocation of nmethod within CodeCache [v48]

[Vladimir Kozlov]

On Fri, 3 Oct 2025 19:52:49 GMT, Chad Rakoczy <duke at openjdk.org> wrote:

>> This PR introduces a new function to replace nmethods, addressing [JDK-8316694](https://bugs.openjdk.org/browse/JDK-8316694). It enables the creation of new nmethods from existing ones, allowing method relocation in the code heap and supporting [JDK-8328186](https://bugs.openjdk.org/browse/JDK-8328186).
>> 
>> When an nmethod is replaced, a deep copy is performed. The corresponding Java method is updated to reference the new nmethod, while the old one is marked as unused. The garbage collector handles final cleanup and deallocation.
>> 
>> This does not modify existing code paths and therefore does not benefit much from existing tests. New tests were created to test the new functionality
>> 
>> Additional Testing:
>> - [x] Linux x64 fastdebug tier 1/2/3/4
>> - [x] Linux aarch64 fastdebug tier 1/2/3/4
>
> Chad Rakoczy has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 114 commits:
> 
>  - Merge remote-tracking branch 'origin/master' into JDK-8316694-Final
>  - Fix race when not installed nmethod is deoptimized
>  - Fix NMethodRelocationTest.java logging race
>  - Merge remote-tracking branch 'origin/master' into JDK-8316694-Final
>  - Refactor JVMTI test
>  - Merge remote-tracking branch 'origin/master' into JDK-8316694-Final
>  - Fix WB_RelocateNMethodFromAddr to not use stale nmethod pointer
>  - Merge remote-tracking branch 'origin/master' into JDK-8316694-Final
>  - Lock nmethod::relocate behind experimental flag
>  - Use CompiledICLocker instead of CompiledIC_lock
>  - ... and 104 more: https://git.openjdk.org/jdk/compare/012e079d...104661c6

Re-approved.

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Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23573#pullrequestreview-3301222369