RFR: Restore Method pointer for every AOTCodeEntry

[Ashutosh Mehra]

On Thu, 7 Aug 2025 18:16:55 GMT, Ashutosh Mehra <asmehra at openjdk.org> wrote:

> There was a recent commit [0] that included code to invalidate preload entry when invalidating a normal `AOTCodeEntry`. This is done by reaching out to the preload entry through the normal `AOTCodeEntry::_method`:
> 
> https://github.com/openjdk/leyden/blob/7b7648a4c9f67be509c6fccbcbc0502648388fdc/src/hotspot/share/code/aotCodeCache.cpp#L1056-L1070
> 
> But unfortunately `AOTCodeEntry::_method` is restored only for the entries marked for preload:
> https://github.com/openjdk/leyden/blob/7b7648a4c9f67be509c6fccbcbc0502648388fdc/src/hotspot/share/code/aotCodeCache.cpp#L1938-L1939
> 
> This PR fixes this bug by restoring `AOTCodeEntry::_method` for all AOTCodeEntry-s. This is achieved by using AOTCache's pointer bitmap to track `AOTCodeEntry::_method`. It removes the need to store method offset separately in the AOTCodeEntry.
> It also fixes a couple of related bugs:
> 1. In `AOTCodeCache::finish_write()` it is possible that the AOTCodeEntry array is not properly aligned.
> 2. When invalidating a preload entry, it is possible that the entry has not been loaded. This triggers the assert that expects an entry to be invalidated is always loaded.
> 
> [0] https://github.com/openjdk/leyden/commit/392fbbb1859cd71521cb915b601a65cf59ba495b

Pushed a commit to store offset of AOTCodeEntry array separately in the header.

-------------

PR Comment: https://git.openjdk.org/leyden/pull/90#issuecomment-3166528597