RFR: 8348426: Generate binary file for -XX:AOTMode=record -XX:AOTConfiguration=file [v8]

[Ashutosh Mehra]

On Tue, 25 Feb 2025 01:11:25 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Currently, with `java -XX:AOTMode=record -XX:AOTConfiguration=file ...`, a text file is written. The file contains the names of loaded classes, indices of resolved constant pools entries, etc, that are easily represented in text.
>> 
>> With the upcoming 2nd JEP of the Leyden project, [JDK-8325147](https://bugs.openjdk.org/browse/JDK-8325147) (Ahead-of-Time Method Profiling), the AOT config file needs to record complex data structures that are difficult to represent in text (we would need code for serializing hierarchical data structures to/from text). Also, a next step after [JDK-8325147](https://bugs.openjdk.org/browse/JDK-8325147) would be to support hidden classes that have no predictable names. Representing such classes with textual names would become another challenge.
>> 
>> To prepare for  [JDK-8325147](https://bugs.openjdk.org/browse/JDK-8325147), this PR writes the AOT configuration file in a **binary format** (essentially the same format as a CDS archive file). This allows arbitrary data associated with the cached classes to be processed and stored using the existing `MetaspaceClosure` API (which can recursively copy C++ objects). Such a change in the file format is allowed by [JEP 483](https://openjdk.org/jeps/483):
>> 
>>> the format of the configuration and cache files is not specified and is subject to change without notice.
>> 
>> **Notes for reviewers:**
>> 
>> - Although the new config file format is essentially the same as a CDS "static" archive, for sanity, we use a different magic number so that the config file cannot be accidentally used as a CDS archive. See new tests inside AOTFlags.java.
>> - After this PR, the CDS "static" archive can be dumped in three modes: "classic", "preimage", and "final". See new comments in cdsConfig.hpp.
>> - The main starting point of this PR is `CDSConfig::check_aot_flags()` - it checks the existence of `-XX:AOTConfiguration` and `-XX:AOTMode` to configure the JVM to dump the CDS "preimage" or "final" archives as necessary.
>> - Most of the other changes are checks for `CDSConfig::is_dumping_preimage_static_archive()` and `CDSConfig::is_dumping_final_static_archive()` to handle subtlle differences between the different dumping modes.
>> - I also updated the UL messages to use the new JEP 483 terminology ("AOT cache", "AOT configuration file",  etc) when JEP 483 options are specified.
>> 
>> **Misc Note**
>> - The changes in [CDS.java and RunTests.gmk](https://github.com/iklam/jdk/commit/0e77a35c25a968c7d931931bc108ccb...
>
> Ioi Lam has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 15 commits:
> 
>  - all tests in runtime/cds/appcds/aotClassLinking should be excluded for hotspot_appcds_dynamic testing
>  - @ashu-mehra comment - simplified _archived_cpp_vtptrs; also fixed old comments near by
>  - Merge branch 'master' into 8348426-binary-aot-config-file
>  - Merge branch 'master' into 8348426-binary-aot-config-file
>  - @ashu-mehra comments
>  - @calvinccheung comments
>  - Improved JTREG_AOT_JDK=true so we do not need to add test code into the JDK itself
>  - Improve error message when AOTMode=create has an incompatible classpath
>  - Fixed test cases @vnkozlov
>  - Update "make test JTREG_AOT_JDK=true ..." to work with binary AOT configuration
>  - ... and 5 more: https://git.openjdk.org/jdk/compare/990d40e9...1ec67c11

src/hotspot/share/cds/cppVtables.cpp line 322:

> 320:   assert(MetaspaceShared::is_in_shared_metaspace(m), "must be");
> 321:   return vtable_of(m) == _index[Method_Kind]->cloned_vtable() ||
> 322:          vtable_of(m) == _archived_cpp_vtptrs[Method_Kind];

I am not sure if this needs any fixing. If `m` is in the archive (as the above assert says), then its vtable should always be `_index[Method_Kind]->cloned_vtable()`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23484#discussion_r1968979794