RFR: 8377339: Implement AOTCacheAccess::get_archived_object using heap roots [v2]

[Dan Heidinga]

On Mon, 9 Feb 2026 17:49:40 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> The API `oop AOTCacheAccess::get_archived_object(int)` is used by the AOT compiler to access heap objects in the AOT cache.
>> 
>>  Because the objects can move in the production run, there's currently a complicated way to keep them alive using OopHandles.
>> 
>> https://github.com/openjdk/leyden/blob/6ce1832147ef3f01602b8fac02160038422a77bf/src/hotspot/share/cds/heapShared.cpp#L545-L610
>> 
>> However, we already have a mechanism for this: `oop HeapShared::get_root(int index, ...)`
>> 
>> So we just need to make sure that all oops needed by the AOT compiler are all stored as heap roots.
>> 
>> This PR is intended to provide an acceptable solution in the short run to be used by the initial AOT compiler integration into the mainline.
>> 
>> The AOT compiler only needs the following objects
>> 
>> - a few common exception objects
>> - class loaders
>> - class mirrors
>> - interned strings
>> - method handles
>> 
>> Most of these objects are in the roots already. We just need to add interned strings and method handles into the heap roots.
>> 
>> (In the future, we should move the AOT compilation before we dump the heap. This way we know exactly what oops should be stored into the heap roots.)
>> 
>> Notes to reviewers
>> - `HeapShared::archived_object_cache()` can now survive GCs that might happen during AOT compilation. I added a new function `HeapShared::archived_object_cache_hash()` with comments about how it uses `oop::identity_hash()`.
>> - This code is added to make sure interned strings and method handles are roots
>> 
>>   if (AOTCodeCache::is_dumping_code() &&
>>                (java_lang_invoke_MethodHandle::is_instance(obj) || is_interned_string(obj))) {
>>       // Needed by AOT compiler.
>>       append_root(obj);
>>     }
>> 
>> - Also some clean up that's not necessary but nice to have:
>>   - I removed the `DumpedInternedStrings` and replaced it with much simpler code.
>
> Ioi Lam has updated the pull request incrementally with four additional commits since the last revision:
> 
>  - @DanHeidinga review comment
>  - @DanHeidinga review comment
>  - @DanHeidinga review comment
>  - fixed typo

Minor comments, overall looks good

src/hotspot/share/cds/heapShared.cpp line 256:

> 254: //   copying the objects into the cache. This will allow the hashcode to be
> 255: //   dynamically and randomly computed in each production, which generally
> 256: //   desirable for security reasons.

Suggestion:

//   desirable to make the hashcodes more random between runs.

src/hotspot/share/cds/heapShared.cpp line 2468:

> 2466: 
> 2467:   ResourceMark rm;
> 2468:   int len;

Suggestion:

  int len = 0;

Nitpick: default values make the code easier to reason about.

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

PR Review: https://git.openjdk.org/leyden/pull/108#pullrequestreview-3765087080
PR Review Comment: https://git.openjdk.org/leyden/pull/108#discussion_r2775979090
PR Review Comment: https://git.openjdk.org/leyden/pull/108#discussion_r2775995306