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 (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 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, this RFE 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:

> the format of the configuration and cache files is not specified and is subject to change without notice.