Include java_lang_Class_getClassFileVersion0 native for jdk20+

[pshipton]

Follow on to #21787

Fixes #21942

Failed tests are passing with this change.
https://openj9-jenkins.osuosl.org/view/Test/job/Grinder/4459

[pshipton]

jenkins compile amac jdk25

[keithc-ca]

getClassFileVersion0() is defined for Java 20+: the boundary for this change should be updated.

[pshipton]

getClassFileVersion0() is defined for Java 20+: the boundary for this change should be updated.

I think that's only for Valhalla.

[keithc-ca]

Class.java currently says:

/*[IF JAVA_SPEC_VERSION >= 20]*/
	/*[IF (JAVA_SPEC_VERSION < 25) & !INLINE-TYPES]*/
	private
	/*[ENDIF] (JAVA_SPEC_VERSION < 25) & !INLINE-TYPES */
	int getClassFileVersion() { ... }
	private native int getClassFileVersion0();
/*[ENDIF] JAVA_SPEC_VERSION >= 20 */

This and the native code should agree. If it's only truly needed for Java 25+, then the Java code should be:

/*[IF JAVA_SPEC_VERSION >= 25]*/
	int getClassFileVersion() { ... }
	private native int getClassFileVersion0();
/*[ENDIF] JAVA_SPEC_VERSION >= 25 */

[keithc-ca]

See also https://github.com/ibmruntimes/openj9-openjdk-jdk20/blob/openj9/src/java.base/share/classes/java/lang/Class.java#L4691.

[pshipton]

Ya, I updated it. It didn't make sense to have a private method that nobody seems to call and wouldn't work anyway.

[keithc-ca]

It is used via reflection: see https://github.com/ibmruntimes/openj9-openjdk-jdk20/blob/openj9/test/hotspot/jtreg/runtime/ClassFile/ClassFileVersionTest.java#L66.

[pshipton]

We don't run that test, so I guess we don't need it.

[pshipton]

The only "hotspot" tests run on OpenJ9 are serviceability tests.

[pshipton]

I suppose some app might be using reflection, so I'd better keep it.

[pshipton]

I suppose some app might be using reflection, so I'd better keep it.

Hmm, although if this was true, somebody would have complained that it didn't work. I'll keep it as-is unless you think we need to support it in 21.

[keithc-ca]

The only "hotspot" tests run on OpenJ9 are serviceability tests.

I think it's easy enough to keep it for Java 20+ that we should do that. We don't need to make trouble for the unknown reflective users and it might be helpful to enable more openjdk tests.

[pshipton]

Ok, updated the natives to be included from 20.

[keithc-ca]

Please update the commit message and the description here to reflect that this applies to jdk20+.

[pshipton]

Updated.

[keithc-ca]

Jenkins compile zlinux jdk17,jdk21