RFR: 8362566: Use -Xlog:aot+map to print contents of existing AOT cache

[María Arias de Reyna]

On Mon, 28 Jul 2025 16:56:32 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> Implement `-Xlog:aot+map` in the production run:
> 
> 
> $ java -cp HelloWorld.jar -XX:AOTCache=HelloWorld.aot \
>     -Xlog:aot+map=file=aot.map:none:filesize=0 \
>     HelloWorld
> 
> 
> I moved the old logging code from archiveBuilder.cpp into a new fille, aotMapLogger.cpp. I did the following to print the map in the production run:
> 
> 1. When dumping the AOT cache, `ArchiveBuilder` maintains a list of all the metaspace objects in the archive. However, there's no such list when we are loading from the AOT cache. Therefore, I added a new `RuntimeGatherArchivedMetaspaceObjs` class to discover all the metaspace objects that are stored in the AOT cache.
> 2. A significant rewrite is needed for printing the oops (see comments around `FakeOop`) because we only have an image of the oops in the AOT cache and these aren't real heap objects.

Tested locally and working fine:


0x00000008004c2128: @@ ConstantPool      528 java.lang.System$In
{constant pool}
 - flags: 0x6 on_stack
 - holder: 0x00000008000da9c8
 - cache: 0x0000000800313528
 - resolved_references: 0x0000000000000000
 - reference_map: 0x0000000000000000
 - resolved_klasses: 0x00000008003134e8
 - cp length: 57
 -   1 :  : klass_index=2 name_and_type_index=3
 -   2 :  : 'java/io/FileInputStream' {0x00000008000daf48}
 -   3 :  : name_index=5 signature_index=6
 -   4 :  : 'java/io/FileInputStream'
 -   5 :  : '<init>'
 -   6 :  : '(Ljava/io/FileDescriptor;)V'
 -   7 :  : klass_index=8 name_and_type_index=9
[...]

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

PR Comment: https://git.openjdk.org/jdk/pull/26514#issuecomment-3131536644