GraalVM-built native image does not support Unsafe.staticFieldOffset() method

[rpuch]

Describe the issue

Unsafe.staticFieldOffset() causes an exception when invoked inside a native image:

Exception in thread "main" com.oracle.svm.core.jdk.UnsupportedFeatureError: Unsupported method of Unsafe
	at com.oracle.svm.core.util.VMError.unsupportedFeature(VMError.java:86)
	at jdk.internal.misc.Unsafe.staticFieldOffset(Unsafe.java:230)
	at sun.misc.Unsafe.staticFieldOffset(Unsafe.java:662)
	at Test.main(Test.java:9)

Steps to reproduce the issue

1. Save the following program to Test.java:

import sun.misc.Unsafe;
import java.lang.reflect.*;

public class Test {
    public static void main(String[] args) throws Exception {
        Field unsafeField = Unsafe.class.getDeclaredField("theUnsafe");
        unsafeField.setAccessible(true);
        Unsafe unsafe = (Unsafe) unsafeField.get(null);
        long offset = unsafe.staticFieldOffset(unsafeField);
        System.out.println(offset);
    }
}

2. Run javac Test.java
3. Run java Test to verify that it works (it does)
4. Run native-image --no-server --no-fallback Test app
5. Run ./app

Describe GraalVM and your environment:

I tried both the latest released version (20.1)

openjdk version "11.0.7" 2020-04-14
OpenJDK Runtime Environment GraalVM CE 20.1.0 (build 11.0.7+10-jvmci-20.1-b02)
OpenJDK 64-Bit Server VM GraalVM CE 20.1.0 (build 11.0.7+10-jvmci-20.1-b02, mixed mode, sharing)

and the latest snapshot version (20.2):

openjdk version "11.0.7" 2020-04-14
OpenJDK Runtime Environment GraalVM CE 20.2.0-dev (build 11.0.7+10-jvmci-20.2-b02)
OpenJDK 64-Bit Server VM GraalVM CE 20.2.0-dev (build 11.0.7+10-jvmci-20.2-b02, mixed mode, sharing)

JDK version is 11

OS is Ubuntu Linux 16.04, kernel version 4.15.0-107-generic

Architecture is Amd64.

[rpuch]

Actually, I'm not sure whether it is a bug or not. If it is 'just not implemented yet', are there any plans to support this feature? If I just do something wrong, please let me know.

Unsafe.staticFieldOffset() is used by Netty, for instance: https://github.com/netty/netty/blob/4.1/common/src/main/java/io/netty/util/internal/PlatformDependent0.java

[rpuch]

When I add

[
{
  "name":"sun.misc.Unsafe",
  "fields":[{"name":"theUnsafe", "allowUnsafeAccess" : true}]
}
]

to reflect-config.json in an attempt to let native-image know that Unsafe access is needed to the field, I get the following error during native-image invocation:

Fatal error:jdk.vm.ci.common.JVMCIError: should not reach here: Unsafe access of static fields is not supported.
	at jdk.internal.vm.ci/jdk.vm.ci.common.JVMCIError.shouldNotReachHere(JVMCIError.java:48)
	at com.oracle.graal.pointsto.meta.AnalysisField.registerAsUnsafeAccessed(AnalysisField.java:267)
	at com.oracle.graal.pointsto.meta.AnalysisField.registerAsUnsafeAccessed(AnalysisField.java:261)
	at com.oracle.svm.hosted.FeatureImpl$BeforeAnalysisAccessImpl.registerAsUnsafeAccessed(FeatureImpl.java:327)

So it looks like Unsafe field offsets are not supported in native mode on purpose. Still, it's interesting to know why and whether this will change in the future.

[cstancu]

Fixed by 46cd5c7.

[rpuch]

@cstancu The commit you mentioned 46cd5c7 was made on July, 17, so it seems that the issue should be fixed in the nightly builds for a looong time. But it is still present in the nightly build I downloaded today.

I've put together a demo project: https://github.com/rpuch/native-unsafe-static-field-offset

GraalVM's java identifies itself as follows:

openjdk version "11.0.8" 2020-07-14
OpenJDK Runtime Environment GraalVM CE 20.3.0-dev (build 11.0.8+10-jvmci-20.3-b01)
OpenJDK 64-Bit Server VM GraalVM CE 20.3.0-dev (build 11.0.8+10-jvmci-20.3-b01, mixed mode, sharing)

I did not find a way to reopen the issue. Could please anyone do it?

[HeikoBornholdt]

The issue persists in current GraalVM versions as well:

openjdk 11.0.10 2021-01-19
OpenJDK Runtime Environment GraalVM CE 21.0.0 (build 11.0.10+8-jvmci-21.0-b06)
OpenJDK 64-Bit Server VM GraalVM CE 21.0.0 (build 11.0.10+8-jvmci-21.0-b06, mixed mode, sharing)

[cstancu]

You are right, that commit only updated the internal mechanism to properly support Unsafe.staticFieldOffset(). The missing substitutions have been added in f97bdb5.

[makingthematrix]

@cstancu : Hey, thanks for the fix! :) It looks like this fix is also important for making Scala 3 work with GraalVM native image. Currently, with GraalVM 21.1.0, I'm getting this error:

[INFO] [SUB] Exception in thread "main" scala.runtime.LazyVals$$anon$1
[INFO] [SUB] 	at scala.runtime.LazyVals$.$init$$$anonfun$3(LazyVals.scala:18)
[INFO] [SUB] 	at scala.Option.getOrElse(Option.scala:201)
[INFO] [SUB] 	at scala.runtime.LazyVals$.<clinit>(LazyVals.scala:19)
[INFO] [SUB] 	at com.oracle.svm.core.classinitialization.ClassInitializationInfo.invokeClassInitializer(ClassInitializationInfo.java:375)
[INFO] [SUB] 	at com.oracle.svm.core.classinitialization.ClassInitializationInfo.initialize(ClassInitializationInfo.java:295)
[INFO] [SUB] 	at calculator.Main.<clinit>(Main.scala:16)
[INFO] [SUB] 	at com.oracle.svm.core.classinitialization.ClassInitializationInfo.invokeClassInitializer(ClassInitializationInfo.java:375)
[INFO] [SUB] 	at com.oracle.svm.core.classinitialization.ClassInitializationInfo.initialize(ClassInitializationInfo.java:295)

where the code in the class LazyVals depends on sun.misc.Unsafe. (https://github.com/lampepfl/dotty/blob/master/library/src/scala/runtime/LazyVals.scala)

Do you maybe have an idea when this fix will land in production?

[kpodsiad]

@makingthematrix I had the very same error (Scala 3, GraalVM CE 21.1.0) but I managed to run native image successfully. Are you sure that you passed reflect-config.json to the native-image command?

[makingthematrix]

@makingthematrix I had the very same error (Scala 3, GraalVM CE 21.1.0) but I managed to run native image successfully. Are you sure that you passed reflect-config.json to the native-image command?

I'm sure I don't do that :) why? and how?

[kpodsiad]

I'm terrible at writing explanations so see this and this2 in order to find answers how & why ;)
Hope these links will help you.