Access IMPL_LOOKUP without Unsafe

TrustedLookupAccessor.java

import java.lang.foreign.*;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;

public final class TrustedLookupAccessor {
    private TrustedLookupAccessor() {
    }

    private static final MethodHandles.Lookup INSTANCE = null;

    static {
        try {
            SequenceLayout VL_JNIInvokeInterface = MemoryLayout.sequenceLayout(8, ValueLayout.ADDRESS);
            AddressLayout VL_P_JNIInvokeInterface = ValueLayout.ADDRESS.withTargetLayout(VL_JNIInvokeInterface);
            AddressLayout VL_PP_JNIInvokeInterface = ValueLayout.ADDRESS.withTargetLayout(VL_P_JNIInvokeInterface);

            SequenceLayout VL_JNINativeInterface = MemoryLayout.sequenceLayout(233, ValueLayout.ADDRESS);
            AddressLayout VL_P_JNINativeInterface = ValueLayout.ADDRESS.withTargetLayout(VL_JNINativeInterface);
            AddressLayout VL_PP_JNINativeInterface = ValueLayout.ADDRESS.withTargetLayout(VL_P_JNINativeInterface);

            MemoryLayout VL_JVALUE = MemoryLayout.unionLayout(
                    ValueLayout.JAVA_BOOLEAN.withName("z"),
                    ValueLayout.JAVA_BYTE.withName("b"),
                    ValueLayout.JAVA_CHAR.withName("c"),
                    ValueLayout.JAVA_SHORT.withName("s"),
                    ValueLayout.JAVA_INT.withName("i"),
                    ValueLayout.JAVA_LONG.withName("j"),
                    ValueLayout.JAVA_FLOAT.withName("f"),
                    ValueLayout.JAVA_DOUBLE.withName("d"),
                    ValueLayout.ADDRESS.withName("l")
            );

            Linker LINKER = Linker.nativeLinker();

            try (Arena ARENA = Arena.ofConfined()) {
                MethodHandle JNI_GetCreatedJavaVMs = LINKER.downcallHandle(
                        SymbolLookup.libraryLookup(System.mapLibraryName("jvm"), ARENA).find("JNI_GetCreatedJavaVMs").orElseThrow(
                                () -> new IllegalStateException("JNI_GetCreatedJavaVMs must exist.")
                        ), FunctionDescriptor.of(ValueLayout.JAVA_INT, ValueLayout.ADDRESS, ValueLayout.JAVA_INT, ValueLayout.ADDRESS)
                );

                MemorySegment pVM = ARENA.allocate(VL_PP_JNIInvokeInterface);
                MemorySegment nVMs = ARENA.allocate(ValueLayout.JAVA_INT);
                int ec = (int) JNI_GetCreatedJavaVMs.invokeExact(pVM, 1, nVMs);
                if (ec != 0) {
                    throw new IllegalStateException("JNI_GetCreatedJavaVMs returned error code " + ec);
                }
                if (nVMs.get(ValueLayout.JAVA_INT, 0) != 1) {
                    throw new IllegalStateException("There must be one VM.");
                }

                MethodHandle GetEnv = LINKER.downcallHandle(
                        pVM.get(VL_PP_JNIInvokeInterface, 0)
                                .get(VL_P_JNIInvokeInterface, 0)
                                .getAtIndex(ValueLayout.ADDRESS, 6),
                        FunctionDescriptor.of(ValueLayout.JAVA_INT, VL_PP_JNIInvokeInterface, VL_PP_JNINativeInterface, ValueLayout.JAVA_INT)
                );

                MemorySegment ppEnv = ARENA.allocate(VL_PP_JNINativeInterface);
                ec = (int) GetEnv.invokeExact(pVM, ppEnv, 0x00010008);
                if (ec != 0) {
                    throw new IllegalStateException("GetEnv returned error code " + ec);
                }

                MemorySegment pEnv = ppEnv.get(VL_PP_JNINativeInterface, 0);
                MemorySegment pJNINativeInterface = pEnv.get(VL_P_JNINativeInterface, 0);
                MethodHandle FindClass = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 6),
                        FunctionDescriptor.of(ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);
                MethodHandle NewGlobalRef = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 21),
                        FunctionDescriptor.of(ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);
                MethodHandle GetMethodID = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 33),
                        FunctionDescriptor.of(ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);
                MethodHandle DeleteGlobalRef = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 22),
                        FunctionDescriptor.ofVoid(ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);
                MethodHandle CallObjectMethodA = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 36),
                        FunctionDescriptor.of(ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);
                MethodHandle GetStaticMethodID = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 113),
                        FunctionDescriptor.of(ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);
                MethodHandle CallStaticObjectMethodA = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 116),
                        FunctionDescriptor.of(ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);
                MethodHandle CallStaticVoidMethodA = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 143),
                        FunctionDescriptor.ofVoid(ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);
                MethodHandle GetStaticFieldID = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 144),
                        FunctionDescriptor.of(ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);
                MethodHandle GetStaticObjectField = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 145),
                        FunctionDescriptor.of(ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);
                MethodHandle NewStringUTF = LINKER.downcallHandle(
                        pJNINativeInterface.getAtIndex(ValueLayout.ADDRESS, 167),
                        FunctionDescriptor.of(ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)
                ).bindTo(pEnv);

                MemorySegment lookupJClass = (MemorySegment) FindClass.invokeExact(ARENA.allocateFrom("java/lang/invoke/MethodHandles$Lookup"));
                MemorySegment lookupJClassRef = (MemorySegment) NewGlobalRef.invokeExact(lookupJClass);
                MemorySegment lookupJFieldID = (MemorySegment) GetStaticFieldID.invokeExact(
                        lookupJClassRef, ARENA.allocateFrom("IMPL_LOOKUP"), ARENA.allocateFrom("Ljava/lang/invoke/MethodHandles$Lookup;")
                );
                MemorySegment lookupJObject = (MemorySegment) GetStaticObjectField.invokeExact(lookupJClassRef, lookupJFieldID);
                MemorySegment lookupJObjectRef = (MemorySegment) NewGlobalRef.invokeExact(lookupJObject);

                MemorySegment threadJClass = (MemorySegment) FindClass.invokeExact(ARENA.allocateFrom("java/lang/Thread"));
                MemorySegment threadJClassRef = (MemorySegment) NewGlobalRef.invokeExact(threadJClass);
                MemorySegment getCurrentThreadJMethodID = (MemorySegment) GetStaticMethodID.invokeExact(
                        threadJClassRef, ARENA.allocateFrom("currentThread"), ARENA.allocateFrom("()Ljava/lang/Thread;")
                );
                MemorySegment threadJObject = (MemorySegment) CallStaticObjectMethodA.invokeExact(threadJClassRef, getCurrentThreadJMethodID, MemorySegment.NULL);
                MemorySegment threadJObjectRef = (MemorySegment) NewGlobalRef.invokeExact(threadJObject);

                MemorySegment getContextClassLoaderJMethodID = (MemorySegment) GetMethodID.invokeExact(
                        threadJClassRef, ARENA.allocateFrom("getContextClassLoader"), ARENA.allocateFrom("()Ljava/lang/ClassLoader;")
                );
                MemorySegment classLoaderJObject = (MemorySegment) CallObjectMethodA.invokeExact(
                        threadJObjectRef, getContextClassLoaderJMethodID, MemorySegment.NULL
                );
                MemorySegment classLoaderJObjectRef = (MemorySegment) NewGlobalRef.invokeExact(classLoaderJObject);

                MemorySegment classJClass = (MemorySegment) FindClass.invokeExact(ARENA.allocateFrom("java/lang/Class"));
                MemorySegment classJClassRef = (MemorySegment) NewGlobalRef.invokeExact(classJClass);
                MemorySegment forNameJMethodID = (MemorySegment) GetStaticMethodID.invokeExact(
                        classJClassRef, ARENA.allocateFrom("forName"), ARENA.allocateFrom("(Ljava/lang/String;ZLjava/lang/ClassLoader;)Ljava/lang/Class;")
                );

                MemorySegment targetJClassArguments = ARENA.allocate(VL_JVALUE, 3);
                MemorySegment targetJClassArgument0 = ARENA.allocateFrom(TrustedLookupAccessor.class.getName());
                MemorySegment targetJClassArgument0PlatformString = (MemorySegment) NewStringUTF.invokeExact(targetJClassArgument0);
                MemorySegment targetJClassArgument0Ref = (MemorySegment) NewGlobalRef.invokeExact(targetJClassArgument0PlatformString);
                targetJClassArguments.set(ValueLayout.JAVA_LONG, 0, targetJClassArgument0Ref.address());
                targetJClassArguments.set(ValueLayout.JAVA_BOOLEAN, VL_JVALUE.byteSize(), true);
                targetJClassArguments.set(ValueLayout.JAVA_LONG, VL_JVALUE.byteSize() * 2, classLoaderJObjectRef.address());

                MemorySegment targetJClass = (MemorySegment) CallStaticObjectMethodA.invokeExact(
                        classJClassRef, forNameJMethodID, targetJClassArguments
                );
                MemorySegment targetJClassRef = (MemorySegment) NewGlobalRef.invokeExact(targetJClass);
                MemorySegment targetJMethodID = (MemorySegment) GetStaticMethodID.invokeExact(
                        targetJClassRef, ARENA.allocateFrom("callback"), ARENA.allocateFrom("(Ljava/lang/invoke/MethodHandles$Lookup;)V")
                );
                MemorySegment targetJClassArguments2 = ARENA.allocate(VL_JVALUE, 1);
                targetJClassArguments2.set(ValueLayout.JAVA_LONG, 0, lookupJObjectRef.address());
                CallStaticVoidMethodA.invokeExact(targetJClassRef, targetJMethodID, targetJClassArguments2);

                DeleteGlobalRef.invoke(lookupJClassRef);
                DeleteGlobalRef.invoke(lookupJObjectRef);
                DeleteGlobalRef.invoke(threadJClassRef);
                DeleteGlobalRef.invoke(threadJObjectRef);
                DeleteGlobalRef.invoke(classLoaderJObjectRef);
                DeleteGlobalRef.invoke(classJClassRef);
                DeleteGlobalRef.invoke(targetJClassArgument0Ref);
                DeleteGlobalRef.invoke(targetJClassRef);
            }
        } catch (Throwable t) {
            throw new ExceptionInInitializerError(t);
        }
    }

    private static void callback(MethodHandles.Lookup lookup) throws Throwable {
        lookup.findStaticSetter(
                TrustedLookupAccessor.class,
                "INSTANCE",
                MethodHandles.Lookup.class
        ).invokeExact(lookup);
    }
}

found a cleaner version here https://gist.github.com/XiaoPangxie732/fac9f360ed8e7bed9fb45d306d704233
unfortunately it uses stinky reflection

For Java 23+:

• allocateUtf8String has been renamed into allocateFrom
• allocateArray has been renamed into allocate