RFR: 8329706: Implement -XX:+AOTClassLinking [v12]

[Calvin Cheung]

On Mon, 23 Sep 2024 17:07:56 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> This is the 3rd PR for [JEP 483: Ahead-of-Time Class Loading & Linking](https://bugs.openjdk.org/browse/JDK-8315737).
>> 
>> **Overview**
>> 
>> - A new `-XX:+AOTClassLinking` flag is added. See [JEP 498](https://bugs.openjdk.org/browse/JDK-8315737) and the [CSR](https://bugs.openjdk.org/browse/JDK-8339506) for a discussion of this command-line option, its default value, and its impact on compatibility.
>> - When this flag is enabled during the creation of an AOT cache (aka CDS archive), an `AOTLinkedClassTable` is added to the cache to include all classes that are AOT-linked. For this PR, only classes for the boot/platform/application loaders are eligible. The main logic is in `aotClassLinker.cpp`.
>> - When an AOT archive is loaded in a production run, all classes in the `AOTLinkedClassTable` are loaded into their respective class loaders at the earliest opportunity. The main logic is in `aotLinkedClassBulkLoader.cpp`.
>>   - The boot classes are loaded as part of `vmClasses::resolve_all()`
>>   - The platform/application classes are loaded after the module graph is restored (see changes in `threads.cpp`).
>> - Since all classes in a `AOTLinkedClassTable` are loaded before any user-code is executed, we can resolve constant pool entries that refer to these classes during AOT cache creation. See changes in `AOTConstantPoolResolver::is_class_resolution_deterministic()`.
>> 
>> **All-or-nothing Loading**
>> 
>> - Because AOT-linked classes can refer to each other, using direct C++ pointers, all AOT-linked classes must be loaded together. Otherwise we will have dangling C++ pointers in the class metadata structures. 
>> - During a production run, we check during VM start-up for incompatible VM options that would prevent some of the AOT-linked classes from being loaded. For example:
>>   - If the VM is started with an JVMTI agent that has ClassFileLoadHook capabilities, it could replace some of the AOT-linked classes with alternative versions.
>>   - If the VM is started with certain module options, such as `--patch-module` or `--module`, some AOT-linked classes may be replaced with patched versions, or may become invisible and cannot be loaded into the JVM.
>> - When incompatible VM options are detected, the JVM will refuse to load an AOT cache that has AOT-linked classes. See `FileMapInfo::validate_aot_class_linking()`.
>>   - For simplfication, `FileMapInfo::validate_aot_class_linking()` requires `CDSConfig::is_using_full_module_graph()` to be true. This means that the exa...
>
> 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:
> 
>  - Merge branch 'jep-483-step-02-8338018-rename-class-prelinker-to-aot-cp-resolver' into jep-483-step-03-8329706-implement-xx-aot-class-linking
>  - @dholmes-ora comments
>  - @dholmes-ora comments
>  - Fixed ZERO build
>  - minor comment fix
>  - @ashu-mehra comment: move code outside of call_initPhase2(); also renamed BOOT/BOOT2 to BOOT1/BOOT2 and refactored code related to AOTLinkedClassCategory
>  - @ashu-mehra reviews
>  - @ashu-mehra comments
>  - @adinn comments
>  - @dholmes-ora comments: logging indents
>  - ... and 5 more: https://git.openjdk.org/jdk/compare/49dbfa6a...6029b35f

Spotted a few nits.

src/hotspot/share/cds/metaspaceShared.cpp line 1536:

> 1534:   if (lsh.is_enabled()) {
> 1535:     lsh.print("Using AOT-linked classes: %s (static archive: %s aot-linked classes",
> 1536:               CDSConfig::is_using_aot_linked_classes() ? "true" : "false",

Suggestion:
    `BOOL_TO_STR(CDSConfig::is_using_aot_linked_classes()),`

test/hotspot/jtreg/runtime/cds/appcds/jvmti/ClassFileLoadHookTest.java line 100:

> 98:         TestCommon.checkExec(out);
> 99: 
> 100:         // JEP 483: if dumped with -XX:+AOTClassLinking, cannot use archive when CFLH

Suggestion:
    `..., cannot use archive when CFLH is enabled`

test/lib/jdk/test/lib/cds/CDSAppTester.java line 50:

> 48:     public CDSAppTester(String name) {
> 49:         if (CDSTestUtils.DYNAMIC_DUMP) {
> 50:             throw new jtreg.SkippedException("Tests based on CDSAppTester should be excluded when -Dtest.dynamic.cds.archive is specified");

You could omit the `jtreg.` in the above throw statement.

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

PR Review: https://git.openjdk.org/jdk/pull/20843#pullrequestreview-2322962760
PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1771865540
PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1771878531
PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1771871838