RFR: 8345826: Do not automatically resolve jdk.internal.vm.ci when libgraal is used [v6]

[Alan Bateman]

On Sun, 18 May 2025 19:14:06 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> The `EnableJVMCI` flag currently serves 2 purposes:
>> * Guards VM code ([example](https://github.com/openjdk/jdk/blob/b1e778d9d2ad13ee5f1ed629a8805008580f86c0/src/hotspot/share/runtime/sharedRuntime.cpp#L652)).
>> * [Adds](https://github.com/openjdk/jdk/blob/b1e778d9d2ad13ee5f1ed629a8805008580f86c0/src/hotspot/share/runtime/arguments.cpp#L1804) `jdk.internal.vm.ci` to the root module set.
>> 
>> This PR changes nothing about the first point.
>> 
>> On the second point, to use the `jdk.internal.vm.ci` module when libgraal is enabled, `-XX:+EnableJVMCI` must be explicitly specified to the launcher (as opposed to being true as a result of [`-XX:+UseJVMCICompiler`](https://github.com/openjdk/jdk/blob/76570c627db527f856f2394fb9ead02939eca621/src/hotspot/share/jvmci/jvmci_globals.cpp#L88) or [`-XX:+EnableJVMCIProduct`](https://github.com/openjdk/jdk/blob/76570c627db527f856f2394fb9ead02939eca621/src/hotspot/share/jvmci/jvmci_globals.cpp#L64)). Alternatively, `--add-modules=jdk.internal.vm.ci` can be specified - it has the same semantics as `-XX:+EnableJVMCI`.
>> If libgraal is not enabled, +EnableJVMCI will continue to add `jdk.internal.vm.ci` to the root module set.
>> 
>> The primary motivation is to make use of libgraal compatible with `-XX:+AOTClassLinking`. This flag relies on the root module set archive created in a training run. If the root module set is different in the production run, the AOTClassLinking [optimizations](https://bugs.openjdk.org/browse/JDK-8342279) are disabled. As `jdk.internal.vm.ci` is not resolved in the training run, it must not be resolved in production run. As such, `-XX:+EnableJVMCI` must not cause resolution of `jdk.internal.vm.ci`, otherwise libgraal will not have the startup advantages of AOTClassLinking.
>> 
>> Graal adaption PR: https://github.com/oracle/graal/pull/11212
>
> Doug Simon has updated the pull request incrementally with one additional commit since the last revision:
> 
>   load the JVMCI module if +EnableJVMCI is set in the jimage

src/hotspot/share/jvmci/jvmciRuntime.hpp line 38:

> 36: #endif // INCLUDE_G1GC
> 37: 
> 38: #define JVMCI_NOT_ENABLED_ERROR_MESSAGE "JVMCI is not enabled. Must specify '--add-modules=jdk.internal.vm.ci' or '-XX:+EnableJVMCI' to the java launcher."

It's the exception message for an InternalError so maybe this is okay but in general I don't think you want to be asking users to have to name a JDK internal module.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25240#discussion_r2095016026