Adapt JDK-8345687: Improve the implementation of SegmentFactories::allocateSegment

Author: mur47x111

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/Target_jdk_internal_misc_VM.java

@@ -35,6 +35,7 @@
 import com.oracle.svm.core.annotate.RecomputeFieldValue.Kind;
 import com.oracle.svm.core.annotate.Substitute;
 import com.oracle.svm.core.annotate.TargetClass;
+import com.oracle.svm.core.annotate.TargetElement;
 import com.oracle.svm.core.snippets.KnownIntrinsics;
 
 import jdk.internal.misc.Unsafe;
@@ -68,7 +69,12 @@ public static ClassLoader latestUserDefinedLoader0() {
     @Alias @InjectAccessors(DirectMemoryAccessors.class) //
     private static long directMemory;
     @Alias @InjectAccessors(PageAlignDirectMemoryAccessors.class) //
-    private static boolean pageAlignDirectMemory;
+    @TargetElement(onlyWith = JDKLatest.class) //
+    private static Boolean pageAlignDirectMemory;
+
+    @Alias @InjectAccessors(PageAlignDirectMemoryJDK21Accessors.class) //
+    @TargetElement(name = "pageAlignDirectMemory", onlyWith = JDK21OrEarlier.class) //
+    private static boolean pageAlignDirectMemoryJDK21;
 }
 
 final class DirectMemoryAccessors {
@@ -125,7 +131,7 @@ final class PageAlignDirectMemoryAccessors {
     private static boolean initialized;
     private static boolean pageAlignDirectMemory;
 
-    static boolean getPageAlignDirectMemory() {
+    static Boolean getPageAlignDirectMemory() {
         if (!initialized) {
             initialize();
         }
@@ -140,3 +146,9 @@ private static void initialize() {
         initialized = true;
     }
 }
+
+final class PageAlignDirectMemoryJDK21Accessors {
+    static boolean getPageAlignDirectMemory() {
+        return PageAlignDirectMemoryAccessors.getPageAlignDirectMemory();
+    }
+}