[FFI/Jtreg_JDK21] IndexOutOfBoundsException detected in TestClassLoaderFindNative.java

[ChengJin01]

The test suite ended up with the following error:

test TestClassLoaderFindNative.testVariableSymbolLookup(): failure
java.lang.IndexOutOfBoundsException: Out of bound access on segment MemorySegment{ heapBase: Optional.empty address:139995130122248 limit: 0 }; new offset = 0; new length = 4
        at java.base/jdk.internal.foreign.AbstractMemorySegmentImpl.outOfBoundException(AbstractMemorySegmentImpl.java:426)
        at java.base/jdk.internal.foreign.AbstractMemorySegmentImpl.apply(AbstractMemorySegmentImpl.java:407)
        at java.base/jdk.internal.foreign.AbstractMemorySegmentImpl.apply(AbstractMemorySegmentImpl.java:69)
        at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:98)
        at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:124)
        at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:448)
        at java.base/jdk.internal.foreign.AbstractMemorySegmentImpl.checkBounds(AbstractMemorySegmentImpl.java:396)
        at java.base/jdk.internal.foreign.AbstractMemorySegmentImpl.checkAccess(AbstractMemorySegmentImpl.java:356)
        at java.base/java.lang.invoke.VarHandleSegmentAsInts.checkAddress(VarHandleSegmentAsInts.java:81)
        at java.base/java.lang.invoke.VarHandleSegmentAsInts.get(VarHandleSegmentAsInts.java:108)
        at java.base/java.lang.foreign.MemorySegment.get(MemorySegment.java:1517)
        at TestClassLoaderFindNative.testVariableSymbolLookup(TestClassLoaderFindNative.java:75)

FYI: @tajila, @pshipton

[ChengJin01]

Looking at the test code at https://github.com/ibmruntimes/openj9-openjdk-jdk21/blob/0bf8e32b3c5e101ce38ef51a5fa795ea1d28f5f6/test/jdk/java/foreign/TestClassLoaderFindNative.java#L62

    public void testVariableSymbolLookup() {
        MemorySegment segment = SymbolLookup.loaderLookup().find("c").get(); <--------
        /* The variable is 'int c;', so JAVA_INT is a better choice than JAVA_BYTE.
         * See libLookupTest.c.
         */
        assertEquals(segment.get(ValueLayout.JAVA_INT, 0), 42);
    }

It turns out SymbolLookup.loaderLookup().find("c").get() returns a zero-sized segment for ADDRESS as specified in OpenJDK at https://github.com/ibmruntimes/openj9-openjdk-jdk21/blob/8fdc0f13b1557ace8be6a63c1f1c429e3b5bac54/src/java.base/share/classes/java/lang/foreign/SymbolLookup.java#L129:

    /**
     * Returns the address of the symbol with the given name.
     * @param name the symbol name.
     * @return a zero-length memory segment whose address indicates the address of the symbol, if found. <-----------
     */
    Optional<MemorySegment> find(String name); 

in which case we have to restore the previous fix for reinterpret() the size as mentioned at ibmruntimes/openj9-openjdk-jdk21#3 (comment) to ensure the value can be accessed correctly.

[ChengJin01]

Close the issue as resolved at ibmruntimes/openj9-openjdk-jdk21#11.